Performance of a Zerovalent Iron Reactive Barrier for the Treatment of Arsenic in Groundwater: Part 2. Geochemical Modeling and Solid Phase Studies

EPA Science Inventory

Arsenic uptake processes were evaluated in a zerovalent iron reactive barrier installed at a lead smelting facility using geochemical modeling, solid-phase analysis, and X-ray absorption spectroscopy techniques. Aqueous speciation of arsenic plays a key role in directing arsenic...

Changes in iron, sulfur, and arsenic speciation associated with bacterial sulfate reduction in ferrihydrite-rich systems.

PubMed

Saalfield, Samantha L; Bostick, Benjamin C

2009-12-01

Biologically mediated redox processes have been shown to affect the mobility of iron oxide-bound arsenic in reducing aquifers. This work investigates how dissimilatory sulfate reduction and secondary iron reduction affect sulfur, iron, and arsenic speciation. Incubation experiments were conducted with As(III/V)-bearing ferrihydrite in carbonate-buffered artificial groundwater enriched with lactate (10 mM) and sulfate (0.08-10 mM) and inoculated with Desulfovibrio vulgaris (ATCC 7757, formerly D. desulfuricans), which reduces sulfate but not iron or arsenic. Sulfidization of ferrihydrite led to formation of magnetite, elemental sulfur, and trace iron sulfides. Observed reaction rates imply that the majority of sulfide is recycled to sulfate, promoting microbial sulfate reduction in low-sulfate systems. Despite dramatic changes in Fe and S speciation, and minimal formation of Fe or As sulfides, most As remained in the solid phase. Arsenic was not solubilized in As(V)-loaded incubations, which experienced slow As reduction by sulfide, whereas As(III)-loaded incubations showed limited and transient As release associated with iron remineralization. This suggests that As(III) production is critical to As release under reducing conditions, with sulfate reduction alone unlikely to release As. These data also suggest that bacterial reduction of As(V) is necessary for As sequestration in sulfides, even where sulfate reduction is active.

Chemistry of Marine Ligands and Siderophores

PubMed Central

Vraspir, Julia M.; Butler, Alison

2011-01-01

Marine microorganisms are presented with unique challenges to obtain essential metal ions required to survive and thrive in the ocean. The production of organic ligands to complex transition metal ions is one strategy to both facilitate uptake of specific metals, such as iron, and to mitigate the potential toxic effects of other metal ions, such as copper. A number of important trace metal ions are complexed by organic ligands in seawater, including iron, cobalt, nickel, copper, zinc, and cadmium, thus defining the speciation of these metal ions in the ocean. In the case of iron, siderophores have been identified and structurally characterized. Siderophores are low molecular weight iron-binding ligands produced by marine bacteria. Although progress has been made toward the identity of in situ iron-binding ligands, few compounds have been identified that coordinate the other trace metals. Deciphering the chemical structures and production stimuli of naturally produced organic ligands and the organisms they come from is fundamental to understanding metal speciation and bioavailability. The current evidence for marine ligands, with an emphasis on siderophores, and discussion of the importance and implications of metal-binding ligands in controlling metal speciation and cycling within the world’s oceans are presented. PMID:21141029

Iron Speciation and Mixing in Single Aerosol Particles from the Asian Continental Outflow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moffet, Ryan C.; Furutani, Hiroshi; Rodel, Tobias

2012-04-04

Bioavailable iron from atmospheric aerosol is an essential nutrient that can control oceanic productivity, thereby impacting the global carbon budget and climate. Particles collected on Okinawa Island during an atmospheric pollution transport event from China were analyzed using complementary single particle techniques to determine the iron source and speciation. Comparing the spatial distribution of iron within ambient particles and standard Asian mineral dust, it was determined that field-collected atmospheric Fe-containing particles have numerous sources, including anthropogenic sources such as coal combustion. Fe-containing particles were found to be internally mixed with secondary species such as sulfate, soot, and organic carbon. Themore » mass weighted average Fe(II) fraction (defined as Fe(II)/[Fe(II)+Fe(III)]) was determined to be 0.33 {+-} 0.08. Within the experimental uncertainty, this value lies close to the range of 0.26-0.30 determined for representative Asian mineral dust. Previous studies have indicated that the solubility of iron from combustion is much higher than that from mineral dust. Therefore, chemical and/or physical differences other than oxidation state may help explain the higher solubility of iron in atmospheric particles.« less

Voltammetric determination of arsenic in high iron and manganese groundwaters.

PubMed

Gibbon-Walsh, Kristoff; Salaün, Pascal; Uroic, M Kalle; Feldmann, Joerg; McArthur, John M; van den Berg, Constant M G

2011-09-15

Determination of the speciation of arsenic in groundwaters, using cathodic stripping voltammetry (CSV), is severely hampered by high levels of iron and manganese. Experiments showed that the interference is eliminated by addition of EDTA, making it possible to determine the arsenic speciation on-site by CSV. This work presents the CSV method to determine As(III) in high-iron or -manganese groundwaters in the field with only minor sample treatment. The method was field-tested in West-Bengal (India) on a series of groundwater samples. Total arsenic was subsequently determined after acidification to pH 1 by anodic stripping voltammetry (ASV). Comparative measurements by ICP-MS as reference method for total As, and by HPLC for its speciation, were used to corroborate the field data in stored samples. Most of the arsenic (78±0.02%) was found to occur as inorganic As(III) in the freshly collected waters, in accordance with previous studies. The data shows that the modified on-site CSV method for As(III) is a good measure of water contamination with As. The EDTA was also found to be effective in stabilising the arsenic speciation for longterm sample storage at room temperature. Without sample preservation, in water exposed to air and sunlight, the As(III) was found to become oxidised to As(V), and Fe(II) oxidised to Fe(III), removing the As(V) by adsorption on precipitating Fe(III)-hydroxides within a few hours. Copyright © 2011 Elsevier B.V. All rights reserved.

Photochemical changes in cyanide speciation in drainage from a precious metal ore heap

USGS Publications Warehouse

Johnson, C.A.; Leinz, R.W.; Grimes, D.J.; Rye, R.O.

2002-01-01

In drainage from an inactive ore heap at a former gold mine, the speciation of cyanide and the concentrations of several metals were found to follow diurnal cycles. Concentrations of the hexacyanoferrate complex, iron, manganese, and ammonium were higher at night than during the day, whereas weak-acid-dissociable cyanide, silver, gold, copper, nitrite, and pH displayed the reverse behavior. The changes in cyanide speciation, iron, and trace metals can be explained by photodissociation of iron and cobalt cyanocomplexes as the solutions emerged from the heap into sunlight-exposed channels. At midday, environmentally significant concentrations of free cyanide were produced in a matter of minutes, causing trace copper, silver, and gold to be mobilized as cyanocomplexes from solids. Whether rapid photodissociation is a general phenomenon common to other sites will be important to determine in reaching a general understanding of the environmental risks posed by routine or accidental water discharges from precious metal mining facilities.

Speciation and Health Risks of Atmospheric Nanoparticulates

NASA Astrophysics Data System (ADS)

Nguyen, Kennedy

Exposure to air pollution causes several adverse health effects such as asthma, respiratory disease, cardiovascular disease, cancer, and premature death; and the San Joaquin Valley is one of the most heavily polluted regions in the US. The mountains that surround the valley allow air pollution, including particulate matter, to remain stagnant, prolonging the exposure of valley populations to it. The primary sources of particulate matter for this region are aluminosilicate dust from agricultural activities, and soot emissions from diesel trucks and vehicular traffic. A substantial fraction of emitted material is nanoparticulate matter (<100 nm), which contains trace iron and polycyclic aromatic hydrocarbons that can traverse into human organs via the lungs, initiate inflammation, and lead to disease. The traditional approach of reducing the total mass of emitted material is beginning to reach its limit of effectiveness for mitigating the negative health impacts of particulate matter. There is a need for chemical speciation of particulate matter that will allow the identification of the chemical and physical properties of particulates by source, the creation of well-controlled proxy particles with those properties for testing in cell culture studies, and correlation of particulate properties and sources with their negative health impacts. These results can help identify the sources of air pollution to prioritize for mitigation for the greatest health benefit. In addition, further chemical speciation can help monitor the results of such mitigation efforts. Here, natural particulate matter samples from Merced and Fresno, two cities in the San Joaquin Valley, were analyzed. Ultrafine particles present were 40 to 50 nm in diameter and mostly composed of aluminum, silicon, oxygen, and iron hydroxide. XAS data confirmed the presence of the aluminosilicate as smectite clay and the iron hydroxide as ferrihydrite. Furthermore, a chemical speciation study investigated industrial emissions of air particulate matter. Samples were analyzed using electron microscopy for elemental composition and size distribution, and found to contain fine metal particulates (lead and iron) that can lead to lung inflammation. From characterization data, in order to create a simplified proxy particle system for cell culture studies, amorphous silica particles were synthesized using a modified Stober Synthesis and coated with iron hydroxide. A range of iron hydroxide concentrations (0.06 to 1.63 mmol of iron per gram of silica) were used to test the effect of iron contamination on THP-1 cells, and higher concentrations of iron with silica (0.43 and 1.63 mmol of iron per gram of silica) were found to increase production of pro-inflammatory mediators compared to silica alone. Iron alone did not induce an effect relative to the control, demonstrating a synergistic effect when iron is combined with silica at low doses. It was found that crystalline silica was more toxic than amorphous silica (70% vs 80% respectively at 100 mug/ml). In addition, mesoporous silica was found to be more toxic than solid silica (73% vs 82% respectively at 100 mug/ml), likely due to a higher surface area (60.2 m2/g for mesoporous external surface area without internal pores vs 1.72 m 2/g for solid 2 mum silica and 54.5 m2/g for 50 nm silica) and increased particle loading at the same dose. Finally, a preliminary investigation of Printex 90 as a proxy material for soot, with and without the addition of iron and quinones, was conducted.

Solubility of iron from combustion source particles in acidic media linked to iron speciation.

PubMed

Fu, Hongbo; Lin, Jun; Shang, Guangfeng; Dong, Wenbo; Grassian, Vichi H; Carmichael, Gregory R; Li, Yan; Chen, Jianmin

2012-10-16

In this study, iron solubility from six combustion source particles was investigated in acidic media. For comparison, a Chinese loess (CL) dust was also included. The solubility experiments confirmed that iron solubility was highly variable and dependent on particle sources. Under dark and light conditions, the combustion source particles dissolved faster and to a greater extent relative to CL. Oil fly ash (FA) yielded the highest soluble iron as compared to the other samples. Total iron solubility fractions measured in the dark after 12 h ranged between 2.9 and 74.1% of the initial iron content for the combustion-derived particles (Oil FA > biomass burning particles (BP) > coal FA). Ferrous iron represented the dominant soluble form of Fe in the suspensions of straw BP and corn BP, while total dissolved Fe presented mainly as ferric iron in the cases of oil FA, coal FA, and CL. Mössbauer measurements and TEM analysis revealed that Fe in oil FA was commonly presented as nanosized Fe(3)O(4) aggregates and Fe/S-rich particles. Highly labile source of Fe in corn BP could be originated from amorphous Fe form mixed internally with K-rich particles. However, Fe in coal FA was dominated by the more insoluble forms of both Fe-bearing aluminosilicate glass and Fe oxides. The data presented herein showed that iron speciation varies by source and is an important factor controlling iron solubility from these anthropogenic emissions in acidic solutions, suggesting that the variability of iron solubility from combustion-derived particles is related to the inherent character and origin of the aerosols themselves. Such information can be useful in improving our understanding on iron solubility from combustion aerosols when they undergo acidic processing during atmospheric transport.

Effect of Mineralogy on Dissolution and Speciation of Iron Containing Mineral Oxides in Atmospheric Aerosol Dust

NASA Astrophysics Data System (ADS)

Hettiarachchi, E.; Rubasinghege, G. R. S.; Reynolds, R. L.; Goldstein, H. L.; Moskowitz, B. M.

2017-12-01

Iron is one of the important trace elements for the life. Though it is the fourth most abundant element in the terrestrial crust, given higher pH ( 8.5) in the ocean, the direct dissolution of iron from the Earth crust is limited. Despite this limitation, ocean contains about 2 nM of dissolved iron that is 20-fold greater. Therefore, it is hypothesized most iron comes to the ocean via atmosphere, and dissolution occurs in the acidic atmospheric environments. The current work focuses on the effect of minerology on atmospheric processing of Fe-containing mineral dust using four authentic dust samples, collected from different parts of the world, along with three model systems, hematite (α-Fe2O3), magnetite (Fe3O4) and ilmenite (FeTiO3). Here, spectroscopic methods are combined with batch reactor studies to investigate total iron dissolution and speciation, with a specific focus on source material i.e. particle size, mineralogy, and environmental conditions, i.e. pH, temperature and solar flux. Our data suggests that the presence of Ti metal enhances the dissolution of iron regardless the total %Fe in the mineral. The surface area normalized total iron dissolution in ilmenite, under the dark conditions, in the presence of nitric acid (HNO3) is 3-fold higher than that of hematite. In authentic samples, similar effects were observed for samples containing %Ti. Further, 74% of the dissolved iron in ilmenite remained as Fe(II), bioavailable iron, whereas it was only 60% for magnetite and 8% for hematite. In this study, these results were used to interpret similar trends observed for authentic dust samples with high magnetite content. Thus, the findings of the current study highlight important, yet unconsidered, factors in the atmospheric processing of iron-containing mineral dust aerosol.

The Iron Metallome in Eukaryotic Organisms

PubMed Central

Dlouhy, Adrienne C.; Outten, Caryn E.

2013-01-01

This chapter is focused on the iron metallome in eukaryotes at the cellular and subcellular level, including properties, utilization in metalloproteins, trafficking, storage, and regulation of these processes. Studies in the model eukaryote Saccharomyces cerevisiae and mammalian cells will be highlighted. The discussion of iron properties will center on the speciation and localization of intracellular iron as well as the cellular and molecular mechanisms for coping with both low iron bioavailability and iron toxicity. The section on iron metalloproteins will emphasize heme, iron-sulfur cluster, and non-heme iron centers, particularly their cellular roles and mechanisms of assembly. The section on iron uptake, trafficking, and storage will compare methods used by yeast and mammalian cells to import iron, how this iron is brought into various organelles, and types of iron storage proteins. Regulation of these processes will be compared between yeast and mammalian cells at the transcriptional, post-transcriptional, and post-translational levels. PMID:23595675

VARIATION OF ELEMENT SPECIATION IN COAL COMBUSTION AEROSOLS WITH PARTICLE SIZE

EPA Science Inventory

The speciation of sulfur, iron and key trace elements (Cr, As, Se, Zn) in combustion ash aerosols has been examined as a function of size from experimental combustion units burning Utah and Illinois bituminous coals. Although predominantly present as sulfate, sulfur was also pre...

THE DISTRIBUTION, SOLID-PHASE SPECIATION, AND DESORPTION/DISSOLUTION OF AS IN IRON-BASED DRINKING WATER TREATMENT MEDIA 1

EPA Science Inventory

Arsenic concentrations (Total Recoverable As by EPA Method 3051, soluble, Toxicity Characteristic Leaching Procedure extractable) and solid-phase speciation (by X-ray Absorption Near-Edge Spectroscopy-XANES) were assessed as a function of depth through Fe-media beds for two comme...

THE DISTRIBUTION, SOLID-PHASE SPECIATION, AND DESORPTION/DISSOLUTION OF AS IN IRON-BASED TREATMENT MEDIA

EPA Science Inventory

Arsenic concentrations (Total Recoverable As by EPA Method 3051) and solid-phase speciation (by X-ray Absorption Near-Edge Spectroscopy-XANES) were assessed as a function of depth through Fe-media beds for two commercially available products from pilot-scale field tests. These re...

THE DISTRIBUTION, SOLID-PHASE SPECIATION, AND DESORPTION/DISSOLUTION OF AS IN IRON-BASED DRINKING WATER TREATMENT MEDIA - JOURNAL

EPA Science Inventory

Arsenic concentrations (Total Recoverable As by EPA Method 3051, soluble, Toxicity Characteristic Leaching Procedure extractable) and solid-phase speciation (by X-ray Absorption Near-Edge Spectroscopy-XANES) were assessed as a function of depth through Fe-media beds for two comme...

THE DISTRIBUTION AND SOLID-PHASE SPECIATION OF AS IN IRON-BASED TREATMENT MEDIA

EPA Science Inventory

Arsenic concentrations (Total Recoverable As by EPA Method 3051) and solid-phase speciation (by X-ray Absorption Near-Edge Spectroscopy-XANES) were assessed as a function of depth through Fe-media beds for two commercially available products from pilot-scale field tests. These r...

Photometric flow analysis system for biomedical investigations of iron/transferrin speciation in human serum.

PubMed

Strzelak, Kamil; Rybkowska, Natalia; Wiśniewska, Agnieszka; Koncki, Robert

2017-12-01

The Multicommutated Flow Analysis (MCFA) system for the estimation of clinical iron parameters: Serum Iron (SI), Unsaturated Iron Binding Capacity (UIBC) and Total Iron Binding Capacity (TIBC) has been proposed. The developed MCFA system based on simple photometric detection of iron with chromogenic agent (ferrozine) enables a speciation of transferrin (determination of free and Fe-bound protein) in human serum. The construction of manifold was adapted to the requirements of measurements under changing conditions. In the course of studies, a different effect of proteins on SI and UIBC determination has been proven. That was in turn the reason to perform two kinds of calibration methods. For measurements in acidic medium for SI/holotransferrin determination, the calibration curve method was applied, characterized by limit of determination and limit of quantitation on the level of 3.4 μmol L -1 and 9.1 μmol L -1 , respectively. The determination method for UIBC parameter (related to apotransferrin level) in physiological medium of pH 7.4 forced the use of standard addition method due to the strong influence of proteins on obtaining analytical signals. These two different methodologies, performed in the presented system, enabled the estimation of all three clinical iron/transferrin parameters in human serum samples. TIBC corresponding to total transferrin level was calculated as a sum of SI and UIBC. Copyright © 2017 Elsevier B.V. All rights reserved.

Sulfur-binding in recent environments: II. Speciation of sulfur and iron and implications for the occurrence of organo-sulfur compounds

NASA Astrophysics Data System (ADS)

Hartgers, Walter A.; Lòpez, Jordi F.; Sinninghe Damsté, Jaap S.; Reiss, Christine; Maxwell, James R.; Grimalt, Joan O.

1997-11-01

Speciation of iron and sulfur species was determined for two recent sediments (La Trinitat and Lake Cisó) which were deposited in environments with a high biological productivity and sulfate-reducing activity. In sediments from calcite ponds of La Trinitat an excess of reactive iron species (iron monosulfides, iron hydroxides) results in a depletion of reactive sulfur which is accompanied by a virtual absence of organo-sulfur compounds, both in low (LMW) and high molecular-weight (HMW) fractions. Small amounts of phytanyl and highly branched isoprenoid (HBI) thiophenes in the extract demonstrate that these molecules exhibit a higher reactivity towards reduced sulfur species as compared to detrital iron. Euxinic sediments from Lake Cisó are characterised by an excess of reduced sulfur species which can rapidly trap reactive iron. High concentrations of H 2S results in the formation of organo-sulfur compounds which were encountered in both LMW and HMW fractions. The major part of the organic sulfur is bound to the carbohydrate portion of woody tissues, whose presence was revealed by a specific alkylthiophene distribution in the flash pyrolysate and by Li/EtNH 2 desulfurisation of the kerogen which resulted in the solubilisation of the sulfur-enriched hemicellulose fraction. Relatively high amounts of sulfurised C 25 HBI compounds in the sediment extract of Lake Cisó reflect the incorporation of sulfur into algal derived organic matter upon early diagenesis. The combined approach of the speciation of iron and sulfur species and the molecular analysis of sedimentary fractions demonstrates that abiotic sulfur binding to organic matter occurs at the earliest stages of diagenesis under specific depositional conditions (anoxic, stratified water column) in which an excess of reduced sulfur species relative to the amount of reactive iron is a controlling factor.

A Novel Permeable Reactive Barrier (PRB) for Simultaneous and Rapid Removal of Heavy Metal and Organic Matter - A Systematic Chemical Speciation Approach on Sustainable Technique for Pallikarani Marshland Remediation

NASA Astrophysics Data System (ADS)

Selvaraj, A.; Nambi, I. M.

2014-12-01

In this study, an innovative technique of ZVI mediated 'coupling of Fenton like oxidation of phenol and Cr(VI) reduction technique' was attempted. The hypothesis is that Fe3+ generated from Cr(VI) reduction process acts as electron acceptor and catalyst for Fenton's Phenol oxidation process. The Fe2+ formed from Fenton reactions can be reused for Cr(VI) reduction. Thus iron can be made to recycle between two reactions, changing back and forth between Fe2+ and Fe3+ forms, makes treatment sustainable.(Fig 1) This approach advances current Fenton like oxidation process by (i)single system removal of heavy metal and organic matter (ii)recycling of iron species; hence no additional iron required (iii)more contaminant removal to ZVI ratio (iv)eliminating sludge related issues. Preliminary batch studies were conducted at different modes i) concurrent removal ii) sequential removal. The sequential removal was found better for in-situ PRB applications. PRB was designed based on kinetic rate slope and half-life time, obtained from primary column study. This PRB has two segments (i)ZVI segment[Cr(VI)] (ii)iron species segment[phenol]. This makes treatment sustainable by (i) having no iron ions in outlet stream (ii)meeting hypothesis and elongates the life span of PRB. Sequential removal of contaminates were tested in pilot scale PRB(Fig 2) and its life span was calculated based on the exhaustion of filling material. Aqueous, sand and iron aliquots were collected at various segments of PRB and analyzed for precipitation and chemical speciation thoroughly (UV spectrometer, XRD, FTIR, electron microscope). Chemical speciation profile eliminates the uncertainties over in-situ PRB's long term performance. Based on the pilot scale PRB study, 'field level PRB wall construction' was suggested to remove heavy metal and organic compounds from Pallikaranai marshland(Fig 3)., which is contaminated with leachate coming from nearby Perungudi dumpsite. This research provides (i)deeper insight into the environmental friendly, accelerated, sustainable technique for combined removal of organic matter and heavy metal (ii)evaluation of the novel technique in PRB, which resulted in PRB's increased life span (iii)designing of PRB to remediate the marshland and its ecosystem, thus save the habitats related to it.

Evidence for ferritin as dominant iron-bearing species in the rhizobacterium Azospirillum brasilense Sp7 provided by low-temperature/in-field Mössbauer spectroscopy.

PubMed

Kovács, Krisztina; Kamnev, Alexander A; Pechoušek, Jiří; Tugarova, Anna V; Kuzmann, Ernő; Machala, Libor; Zbořil, Radek; Homonnay, Zoltán; Lázár, Károly

2016-02-01

For the ubiquitous diazotrophic rhizobacterium Azospirillum brasilense, which has been attracting the attention of researchers worldwide for the last 35 years owing to its significant agrobiotechnological and phytostimulating potential, the data on iron acquisition and its chemical speciation in cells are scarce. In this work, for the first time for azospirilla, low-temperature (at 80 K, 5 K, as well as at 2 K without and with an external magnetic field of 5 T) transmission Mössbauer spectroscopic studies were performed for lyophilised biomass of A. brasilense (wild-type strain Sp7 grown with (57)Fe(III) nitrilotriacetate complex as the sole source of iron) to enable quantitative chemical speciation analysis of the intracellular iron. In the Mössbauer spectrum at 80 K, a broadened quadrupole doublet of high-spin iron(III) was observed with a few percent of a high-spin iron(II) contribution. In the spectrum measured at 5 K, a dominant magnetically split component appeared with the parameters typical of ferritin species from other bacteria, together with a quadrupole doublet of a superparamagnetic iron(III) component and a similarly small contribution from the high-spin iron(II) component. The Mössbauer spectra recorded at 2 K (with or without a 5 T external field) confirmed the assignment of ferritin species. About 20% of total Fe in the dry cells of A. brasilense strain Sp7 were present in iron(III) forms superparamagnetic at both 5 and 2 K, i.e. either different from ferritin cores or as ferritin components with very small particle sizes.

Iron Mineralogy and Speciation in Clay-Sized Fractions of Chinese Desert Sediments

NASA Astrophysics Data System (ADS)

Lu, Wanyi; Zhao, Wancang; Balsam, William; Lu, Huayu; Liu, Pan; Lu, Zunli; Ji, Junfeng

2017-12-01

Iron released from Asian desert dust may be an important source of bioavailable iron for the North Pacific Ocean and thereby may stimulate primary productivity. However, the Fe species of the fine dusts from this source region are poorly characterized. Here we investigate iron species and mineralogy in the clay-sized fractions (<2 μm), the size fraction most prone to long-distance transport as dust. Samples were analyzed by sequential chemical extraction, X-ray diffraction, and diffuse reflectance spectrometry. Our results show that Fe dissolved from easily reducible iron phases (ferrihydrite and lepidocrocite) and reducible iron oxides (dominated by goethite) are 0.81 wt % and 2.39 wt %, respectively, and Fe dissolved from phyllosilicates extracted by boiling HCl (dominated by chlorite) is 3.15 wt %. Dusts originating from deserts in northwestern China, particularly the Taklimakan desert, are relatively enriched in easily reducible Fe phases, probably due to abundant Fe contained in fresh weathering products resulting from the rapid erosion associated with active uplift of mountains to the west. Data about Fe speciation and mineralogy in Asian dust sources will be useful for improving the quantification of soluble Fe supplied to the oceans, especially in dust models.

Composition, speciation and distribution of iron minerals in Imperata cylindrica.

PubMed

Amils, Ricardo; de la Fuente, Vicenta; Rodríguez, Nuria; Zuluaga, Javier; Menéndez, Nieves; Tornero, Jesús

2007-05-01

A comparative study of the roots, rhizomes and leaves of an iron hyperaccumulator plant, Imperata cylindrica, isolated from the banks of an extreme acidic environment, using complementary techniques: Mösbauer spectroscopy (MS), X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled to energy-dispersive X-ray microanalysis (EDAX) and transmission electron microscopy (TEM), has shown that two main biominerals, jarosite and ferrihydrate-ferritin, accumulate in the different tissues. Jarosite accumulates mainly in roots and rhizomes, while ferritin has been detected in all the structures. A model of iron management in I. cylindrica is presented.

Influence of a soil enzyme on iron-cyanide complex speciation and mineral adsorption.

PubMed

Zimmerman, Andrew R; Kang, Dong-Hee; Ahn, Mi-Youn; Hyun, Seunghun; Banks, M Katherine

2008-01-01

Cyanide is commonly found as ferrocyanide [Fe(II)(CN)(6)](-4) and in the more mobile form, ferricyanide [Fe(III)(CN)(6)](-3) in contaminated soils and sediments. Although soil minerals may influence ferrocyanide speciation, and thus mobility, the possible influence of soil enzymes has not been examined. In a series of experiments conducted under a range of soil-like conditions, laccase, a phenoloxidase enzyme derived from the fungi Trametes versicolor, was found to exert a large influence on iron-cyanide speciation and mobility. In the presence of laccase, up to 93% of ferrocyanide (36-362ppm) was oxidized to ferricyanide within 4h. No significant effect of pH (3.6 and 6.2) or initial ferrocyanide concentration on the extent or rate of oxidation was found and ferrocyanide oxidation did not occur in the absence of laccase. Relative to iron-cyanide-mineral systems without laccase, ferrocyanide adsorption to aluminum hydroxide and montmorillonite decreased in the presence of laccase and was similar to or somewhat greater than that of ferricyanide without laccase. Laccase-catalyzed conversion of ferrocyanide to ferricyanide was extensive though up to 33% of the enzyme was mineral-bound. These results demonstrate that soil enzymes can play a major role in ferrocyanide speciation and mobility. Biotic soil components must be considered as highly effective oxidation catalysts that may alter the mobility of metals and metal complexes in soil. Immobilized enzymes should also be considered for use in soil metal remediation efforts.

A model of Fe speciation and biogeochemistry at the Tropical Eastern North Atlantic Time-Series Observatory site

NASA Astrophysics Data System (ADS)

Ye, Y.; Völker, C.; Wolf-Gladrow, D. A.

2009-10-01

A one-dimensional model of Fe speciation and biogeochemistry, coupled with the General Ocean Turbulence Model (GOTM) and a NPZD-type ecosystem model, is applied for the Tropical Eastern North Atlantic Time-Series Observatory (TENATSO) site. Among diverse processes affecting Fe speciation, this study is focusing on investigating the role of dust particles in removing dissolved iron (DFe) by a more complex description of particle aggregation and sinking, and explaining the abundance of organic Fe-binding ligands by modelling their origin and fate. The vertical distribution of different particle classes in the model shows high sensitivity to changing aggregation rates. Using the aggregation rates from the sensitivity study in this work, modelled particle fluxes are close to observations, with dust particles dominating near the surface and aggregates deeper in the water column. POC export at 1000 m is a little higher than regional sediment trap measurements, suggesting further improvement of modelling particle aggregation, sinking or remineralisation. Modelled strong ligands have a high abundance near the surface and decline rapidly below the deep chlorophyll maximum, showing qualitative similarity to observations. Without production of strong ligands, phytoplankton concentration falls to 0 within the first 2 years in the model integration, caused by strong Fe-limitation. A nudging of total weak ligands towards a constant value is required for reproducing the observed nutrient-like profiles, assuming a decay time of 7 years for weak ligands. This indicates that weak ligands have a longer decay time and therefore cannot be modelled adequately in a one-dimensional model. The modelled DFe profile is strongly influenced by particle concentration and vertical distribution, because the most important removal of DFe in deeper waters is colloid formation and aggregation. Redissolution of particulate iron is required to reproduce an observed DFe profile at TENATSO site. Assuming colloidal iron is mainly composed of inorganic colloids, the modelled colloidal to soluble iron ratio is lower that observations, indicating the importance of organic colloids.

Microanalysis of iron oxidation state in iron oxides using X Ray Absorption Near Edge Structure (XANES)

NASA Technical Reports Server (NTRS)

Sutton, S. R.; Delaney, J.; Bajt, S.; Rivers, M. L.; Smith, J. V.

1993-01-01

An exploratory application of x ray absorption near edge structure (XANES) analysis using the synchrotron x ray microprobe was undertaken to obtain Fe XANES spectra on individual sub-millimeter grains in conventional polished sections. The experiments concentrated on determinations of Fe valence in a suite of iron oxide minerals for which independent estimates of the iron speciation could be made by electron microprobe analysis and x ray diffraction.

Revision of iron(III)-citrate speciation in aqueous solution. Voltammetric and spectrophotometric studies.

PubMed

Vukosav, Petra; Mlakar, Marina; Tomišić, Vladislav

2012-10-01

A detailed study of iron (III)-citrate speciation in aqueous solution (θ=25°C, I(c)=0.7 mol L(-1)) was carried out by voltammetric and UV-vis spectrophotometric measurements and the obtained data were used for reconciled characterization of iron (III)-citrate complexes. Four different redox processes were registered in the voltammograms: at 0.1 V (pH=5.5) which corresponded to the reduction of iron(III)-monocitrate species (Fe:cit=1:1), at about -0.1 V (pH=5.5) that was related to the reduction of FeL(2)(5-), FeL(2)H(4-) and FeL(2)H(2)(3-) complexes, at -0.28 V (pH=5.5) which corresponded to the reduction of polynuclear iron(III)-citrate complex(es), and at -0.4V (pH=7.5) which was probably a consequence of Fe(cit)(2)(OH)(x) species reduction. Reversible redox process at -0.1 V allowed for the determination of iron(III)-citrate species and their stability constants by analyzing E(p) vs. pH and E(p) vs. [L(4-)] dependence. The UV-vis spectra recorded at varied pH revealed four different spectrally active species: FeLH (logβ=25.69), FeL(2)H(2)(3-) (log β=48.06), FeL(2)H(4-) (log β=44.60), and FeL(2)(5-) (log β=38.85). The stability constants obtained by spectrophotometry were in agreement with those determined electrochemically. The UV-vis spectra recorded at various citrate concentrations (pH=2.0) supported the results of spectrophotometric-potentiometric titration. Copyright © 2012 Elsevier B.V. All rights reserved.

Speciation in the Fe(III)-Cl(I)-H2O System at 298.15 K, 313.15 K, and 333.15 K (25 °C, 40 °C, and 60 °C)

NASA Astrophysics Data System (ADS)

Jamett, Nathalie E.; Hernández, Pía C.; Casas, Jesús M.; Taboada, María E.

2018-02-01

This article presents the results on speciation of ferric iron generated by the dissolution of chemical reagent hydromolysite (ferric chloride hexahydrate, FeCl3:6H2O) in water at 298.15 K, 313.15 K, and 333.15 K (25 °C, 40 °C, and 60 °C). Experiments were performed with a thermoregulated system up to the equilibrium point, as manifested by solution pH. Solution samples were analyzed in terms of concentration, pH, and electrical conductivity. Measurements of density and refractive index were obtained at different temperatures and iron concentrations. A decrease of pH was observed with the increase in the amount of dissolved iron, indicating that ferric chloride is a strong electrolyte that reacts readily with water. Experimental results were modeled using the hydrogeochemical code PHREEQC in order to obtain solution speciation. Cations and neutral and anion complexes were simultaneously present in the system at the studied conditions according to model simulations, where dominant species included Cl-, FeCl2+, FeCl2 +, FeOHCl 2 0 , and H+. A decrease in the concentration of Cl- and Fe3+ ions took place with increasing temperature due to the association of Fe-Cl species. Standard equilibrium constants for the formation of FeOHCl 2 0 obtained in this study were log Kf0 = -0.8 ± 0.01 at 298.15 K (25 °C), -0.94 ± 0.02 at 313.15 K (40 °C), and -1.03 ± 0.01 at 333.15 K (60 °C).

Iron overload diseases: the chemical speciation of non-heme iron deposits in iron loaded mammalian tissues

NASA Astrophysics Data System (ADS)

St. Pierre, T. G.; Chua-Anusorn, W.; Webb, J.; Macey, D. J.

2000-07-01

57Fe Mössbauer spectra of iron overloaded human spleen, rat spleen and rat liver tissue samples at 78 K were found to consist of a quadrupole doublet (major component) with magnetic sextet (minor component with fractional spectral area F s). The distributions of F s for spleen tissue from two different clinically identifiable groups (n = 7 and n = 12) of thalassemic patients were found to be significantly different. The value of F s for dietary-iron loaded rat liver was found to rise significantly with age/duration (up to 24 months) of iron loading.

Impact on the Fe redox cycling of organic ligands released by Synechococcus PCC 7002, under different iron fertilization scenarios. Modeling approach

NASA Astrophysics Data System (ADS)

Samperio-Ramos, Guillermo; González-Dávila, Melchor; Santana-Casiano, J. Magdalena

2018-06-01

The kinetics of Fe redox transformations are of crucial importance in determining the bioavailability of iron, due to inorganic Fe(II) and Fe weakly organic complexes being the most easily assimilated species by phytoplankton. The role played by the natural organic ligands excreted by the cyanobacteria Synecococcus PCC 7002 on the iron redox chemistry was studied at different stages of growth, considering changes in the organic exudation of the cyanobacteria, associated with growth under two different scenarios of iron availability. The oxidation/reduction processes of iron were studied at nanomolar levels and under different physicochemical conditions of pH (7.2- 8.2), temperature (5- 35 °C) and salinity (10- 37). The presence of natural organic exudates of Synechococcus affected the redox behavior of iron. A pH-dependent and photo-induced Fe(III) reduction process was detected in the presence of exudates produced under Fe-Low conditions. Photolytic reactions also modified the reactivity of those exudates with respect to Fe(II), increasing its lifetime in seawater. Without light mediated processes, organic ligands excreted under iron deficient conditions intensified the Fe(II) oxidation at pH < 7.5. The organic exudates released under High-Fe conditions retarded the Fe(II) oxidation rate, as a function of DOC produced. The changes in the apparent oxidation rate were fitted to polynomial functions for both of the Fe-scenarios considered. A kinetic modeling approach to describe the speciation and the contribution of individual Fe(II) species to the overall oxidation rate was applied, considering the experimental data and delimiting the equilibrium and redox constants between iron and the major ligands present in solution. Two organic type ligands for the exudates of Synechococcus PCC 7002, with different iron-chelation properties were included in the model. The Fe(II) speciation was radically affected when organic ligands were considered. The individual contributions to the overall Fe(II) oxidation rate demonstrated that these organic ligands played a key role in the oxidation process, although their contributions were dependent on the prescribed iron conditions. The study, therefore, suggests that the variability in the composition and nature of organic exudates released, due to iron availability conditions, might determine the redox behaviour of iron in seawater.

Assessing the Selectivity of Extractant Solutions for Recovering Labile Arsenic Associated with Iron (Hydr)oxides and Sulfides in Sediments

EPA Science Inventory

Sequential extractions can provide analytical constraints on the identification of mineral phases that control arsenic speciation in sediments. Model solids were used in this study to evaluate different solutions designed to extract arsenic from relatively labile solid phases. ...

CD SPECIATION ASSOCIATED WITH IRON OXIDES AND BIOSOLIDS

EPA Science Inventory

The environmental impact and potential hazards of metals in biosolids to plants, animals and the human food chain have been studied for decades. From this body of work, it has been concluded the addition of biosolids to the soil alters the chemical phases in the soil system beyon...

Preparation of trout liver microsomes for iron speciation in P-450 enzymes by AE-FPLC with ICP-(ORS)MS detection.

PubMed

Rodríguez-Cea, Andrés; de la Campa, María Rosario Fernández; Sanz-Medel, Alfredo

2005-01-01

Cytochromes P-450 are members of a superfamily of hemoproteins involved in the oxidative metabolism of various physiological and xenobiotic compounds in eukaryotes and prokaryotes. The multiplicity of this group of enzymes has been widely studied by chromatographic techniques, mainly high-performance liquid chromatography (HPLC). Because these enzymes are membrane-bound proteins, sample preparation for chromatographic separation of P-450 enzymes requires a solubilization step. The sample-preparation procedures are critical, because detergents affect not only the efficiency of protein solubilization but also their further chromatographic resolution. Trout liver microsomes have been taken here as a model sample to investigate iron speciation in cytochrome P-450. Trouts were treated intraperitoneally with beta-naphthoflavone, a potent inducer of some P-450 enzymes, and a microsomal suspension containing 7.4+/-0.1 nmol mL(-1) P-450 enzymes was obtained by ultracentrifugation. Lubrol PX was selected as detergent for solubilization, resulting in about 90% solubilization recovery. The solubilized cytochromes P-450 were further separated by AE-FPLC, with UV detection, or coupled to ICP-MS with an octapole reaction system, ICP-(ORS)MS (monitoring Fe signals at masses 54, 56, and 57). A sampling procedure and chromatographic conditions are developed and were successfully applied to iron speciation in trout liver P-450 enzymes. ICP-(ORS)MS detection of P-450 enzymes is Fe-specific and so will give accurate information on the prosthetic group of the protein, which can constitute an advantageous alternative to classical methods for detection of these hemoproteins.

Water management impacts on arsenic speciation and iron-reducing bacteria in contrasting rice-rhizosphere compartments.

PubMed

Somenahally, Anil C; Hollister, Emily B; Yan, Wengui; Gentry, Terry J; Loeppert, Richard H

2011-10-01

Rice cultivated on arsenic (As) contaminated-soils will accumulate variable grain-As concentrations, as impacted by varietal differences, soil variables, and crop management. A field-scale experiment was conducted to study the impact of intermittent and continuous flooding on As speciation and microbial populations in rice rhizosphere compartments of soils that were either historically amended with As pesticide or unamended with As. Rhizosphere-soil, root-plaque, pore-water and grain As were quantified and speciated, and microbial populations in rhizosphere soil and root-plaque were characterized. Total-As concentrations in rhizosphere and grain were significantly lower in intermittently flooded compared to the continuously flooded plots (86% lower in pore-water, 55% lower in root-plaque and 41% lower in grain samples). iAs(V), iAs(III), and DMAs(V) were the predominant As species detected in rhizosphere-soil and root-plaque, pore-water and grain samples, respectively. Relative proportions of Archaea and iron-reducing bacteria (FeRB) were higher in rhizosphere soil compared to root-plaque. In rhizosphere soil, the relative abundance of FeRB was lower in intermittently flooded compared to continuously flooded plots, but there were no differences between root-plaque samples. This study has demonstrated that reductions in dissolved As concentrations in the rhizosphere and subsequent decreases in grain-As concentration can be attained through water management.

Interactions between microbial iron reduction and metal geochemistry: effect of redox cycling on transition metal speciation in iron bearing sediments.

PubMed

Cooper, D Craig; Picardal, Flynn F; Coby, Aaron J

2006-03-15

Microbial iron reduction is an important biogeochemical process that can affect metal geochemistry in sediments through direct and indirect mechanisms. With respectto Fe(III) (hydr)oxides bearing sorbed divalent metals, recent reports have indicated that (1) microbial reduction of goethite/ferrihydrite mixtures preferentially removes ferrihydrite, (2) this process can incorporate previously sorbed Zn(II) into an authigenic crystalline phase that is insoluble in 0.5 M HCl, (3) this new phase is probably goethite, and (4) the presence of nonreducible minerals can inhibit this transformation. This study demonstrates that a range of sorbed transition metals can be selectively sequestered into a 0.5 M HCl insoluble phase and that the process can be stimulated through sequential steps of microbial iron reduction and air oxidation. Microbial reduction experiments with divalent Cd, Co, Mn, Ni, Pb, and Zn indicate that all metals save Mn experienced some sequestration, with the degree of metal incorporation into the 0.5 M HCl insoluble phase correlating positively with crystalline ionic radius at coordination number = 6. Redox cycling experiments with Zn adsorbed to synthetic goethite/ferrihydrite or iron-bearing natural sediments indicate that redox cycling from iron reducing to iron oxidizing conditions sequesters more Zn within authigenic minerals than microbial iron reduction alone. In addition, the process is more effective in goethite/ferrihydrite mixtures than in iron-bearing natural sediments. Microbial reduction alone resulted in a -3x increase in 0.5 M HCl insoluble Zn and increased aqueous Zn (Zn-aq) in goethite/ferrihydrite, but did not significantly affect Zn speciation in natural sediments. Redox cycling enhanced the Zn sequestration by approximately 12% in both goethite/ferrihydrite and natural sediments and reduced Zn-aq to levels equal to the uninoculated control in goethite/ferrihydrite and less than the uninoculated control in natural sediments. These data suggest that in situ redox cycling may serve as an effective method for

Effect of iron oxide reductive dissolution on the transformation and immobilization of arsenic in soils: New insights from X-ray photoelectron and X-ray absorption spectroscopy.

PubMed

Fan, Jian-Xin; Wang, Yu-Jun; Liu, Cun; Wang, Li-Hua; Yang, Ke; Zhou, Dong-Mei; Li, Wei; Sparks, Donald L

2014-08-30

The geochemical behavior and speciation of arsenic (As) in paddy soils is strongly controlled by soil redox conditions and the sequestration by soil iron oxyhydroxides. Hence, the effects of iron oxide reductive dissolution on the adsorption, transformation and precipitation of As(III) and As(V) in soils were investigated using batch experiments and synchrotron based techniques to gain a deeper understanding at both macroscopic and microscopic scales. The results of batch sorption experiments revealed that the sorption capacity of As(V) on anoxic soil was much higher than that on control soil. Synchrotron based X-ray fluorescence (μ-XRF) mapping studies indicated that As was heterogeneously distributed and was mainly associated with iron in the soil. X-ray absorption near edge structure (XANES), micro-X-ray absorption near edge structure (μ-XANES) and X-ray photoelectron spectroscopy (XPS) analyses revealed that the primary speciation of As in the soil is As(V). These results further suggested that, when As(V) was introduced into the anoxic soil, the rapid coprecipitation of As(V) with ferric/ferrous ion prevented its reduction to As(III), and was the main mechanism controlling the immobilization of As. This research could improve the current understanding of soil As chemistry in paddy and wetland soils. Copyright © 2014 Elsevier B.V. All rights reserved.

The analysis of forms of sulfur in ancient sediments and sedimentary rocks: comments and cautions

USGS Publications Warehouse

Rice, C.A.; Tuttle, M.L.; Reynolds, R.L.

1993-01-01

Assumptions commonly made during analysis of the amount of monosulfides [acid-volatile sulfides (AVS)] and disulfides in modern sediments, may not be valid for ancient sedimentary rocks. It is known that ferric iron can oxidize H2S during AVS analysis unless a reducing agent such as stannous chloride is added to the treatment. In addition, some monosulfides such as greigite and pyrrhotite require heat during the AVS analysis in order to dissolve completely. However, the use of heat and/or stannous chloride in the AVS treatment may partially dissolve disulfides and it is generally recommended that stannous chloride not be used in the AVS treatment for modern sediments. Most of the monosulfides are assumed to be recovered as AVS without the addition of stannous chloride. This study investigates the recovery of monosulfides during sulfur speciation analysis with application to ancient sedimentary rocks. Sulfur in samples containing naturally occurring greigite and mackinawite or pyrite was measured using variations of a common sulfur-speciation scheme. The sulfur-speciation scheme analyzes for monosulfide sulfur, disulfide sulfur, elemental sulfur, inorganic sulfate and organically bound sulfur. The effects of heat, stannous chloride and ferric iron on the amounts of acid-volatile sulfide and disulfide recovered during treatment for AVS were investigated. Isotopic compositions of the recovered sulfur species along with yields from an extended sulfur-speciation scheme were used to quantify the effects. Hot 6 N HCl AVS treatment recovers > 60% of the monosulfides as AVS in samples containing pure greigite and mackinawite. The remaining monosulfide sulfur is recovered in a subsequent elemental sulfur extraction. Hot 6 N HCl plus stannous chloride recovers 100% of the monosulfides as AVS. The addition of ferric iron to pure greigite and mackinawite samples during AVS treatment without stannous chloride decreased the amount of monosulfides recovered as AVS and, if present in great enough concentration, oxidized some of the AVS to a form not recovered in later treatments. The hot stannous chloride AVS treatments dissolve <5% of well-crystallized pyrite in this study. The amount of pyrite dissolved depends on grain size and crystallinity. Greigite in ancient sedimentary rocks was quantitatively recovered as AVS only with hot 6 N HCl plus stannous chloride. Hot 6 N HCl AVS treatment of these rocks did not detect any monosulfides in most samples. A subsequent elemental sulfur extraction did not completely recover the oxidized monosulfides. Therefore, the use of stannous chloride plus heat is recommended in the AVS treatment of ancient sedimentary rocks if monosulfides are present and of interest. All assumptions about the amount of monosulfides and disulfides recovered with the sulfur-speciation scheme used should be verified by extended sulfur-speciation and/or isotopic analysis of the species recovered. ?? 1993.

Mercury speciation and mobilization in a wastewater-contaminated groundwater plume

USGS Publications Warehouse

Lamborg, Carl H.; Kent, Doug B.; Swarr, Gretchen J.; Munson, Kathleen M.; Kading, Tristan; O'Connor, Alison E.; Fairchild, Gillian M.; LeBlanc, Denis R.; Wiatrowski, Heather A.

2013-01-01

We measured the concentration and speciation of mercury (Hg) in groundwater down-gradient from the site of wastewater infiltration beds operated by the Massachusetts Military Reservation, western Cape Cod, Massachusetts. Total mercury concentrations in oxic, mildly acidic, uncontaminated groundwater are 0.5–1 pM, and aquifer sediments have 0.5–1 ppb mercury. The plume of impacted groundwater created by the wastewater disposal is still evident, although inputs ceased in 1995, as indicated by anoxia extending at least 3 km down-gradient from the disposal site. Solutes indicative of a progression of anaerobic metabolisms are observed vertically and horizontally within the plume, with elevated nitrate concentrations and nitrate reduction surrounding a region with elevated iron concentrations indicating iron reduction. Mercury concentrations up to 800 pM were observed in shallow groundwater directly under the former infiltration beds, but concentrations decreased with depth and with distance down-gradient. Mercury speciation showed significant connections to the redox and metabolic state of the groundwater, with relatively little methylated Hg within the iron reducing sector of the plume, and dominance of this form within the higher nitrate/ammonium zone. Furthermore, substantial reduction of Hg(II) to Hg0 within the core of the anoxic zone was observed when iron reduction was evident. These trends not only provide insight into the biogeochemical factors controlling the interplay of Hg species in natural waters, but also support hypotheses that anoxia and eutrophication in groundwater facilitate the mobilization of natural and anthropogenic Hg from watersheds/aquifers, which can be transported down-gradient to freshwaters and the coastal zone.

Mercury transformation and speciation in flue gases from anthropogenic emission sources: a critical review

NASA Astrophysics Data System (ADS)

Zhang, Lei; Wang, Shuxiao; Wu, Qingru; Wang, Fengyang; Lin, Che-Jen; Zhang, Leiming; Hui, Mulin; Yang, Mei; Su, Haitao; Hao, Jiming

2016-02-01

Mercury transformation mechanisms and speciation profiles are reviewed for mercury formed in and released from flue gases of coal-fired boilers, non-ferrous metal smelters, cement plants, iron and steel plants, waste incinerators, biomass burning and so on. Mercury in coal, ores, and other raw materials is released to flue gases in the form of Hg0 during combustion or smelting in boilers, kilns or furnaces. Decreasing temperature from over 800 °C to below 300 °C in flue gases leaving boilers, kilns or furnaces promotes homogeneous and heterogeneous oxidation of Hg0 to gaseous divalent mercury (Hg2+), with a portion of Hg2+ adsorbed onto fly ash to form particulate-bound mercury (Hgp). Halogen is the primary oxidizer for Hg0 in flue gases, and active components (e.g., TiO2, Fe2O3, etc.) on fly ash promote heterogeneous oxidation and adsorption processes. In addition to mercury removal, mercury transformation also occurs when passing through air pollution control devices (APCDs), affecting the mercury speciation in flue gases. In coal-fired power plants, selective catalytic reduction (SCR) system promotes mercury oxidation by 34-85 %, electrostatic precipitator (ESP) and fabric filter (FF) remove over 99 % of Hgp, and wet flue gas desulfurization system (WFGD) captures 60-95 % of Hg2+. In non-ferrous metal smelters, most Hg0 is converted to Hg2+ and removed in acid plants (APs). For cement clinker production, mercury cycling and operational conditions promote heterogeneous mercury oxidation and adsorption. The mercury speciation profiles in flue gases emitted to the atmosphere are determined by transformation mechanisms and mercury removal efficiencies by various APCDs. For all the sectors reviewed in this study, Hgp accounts for less than 5 % in flue gases. In China, mercury emission has a higher Hg0 fraction (66-82 % of total mercury) in flue gases from coal combustion, in contrast to a greater Hg2+ fraction (29-90 %) from non-ferrous metal smelting, cement and iron and/or steel production. The higher Hg2+ fractions shown here than previous estimates may imply stronger local environmental impacts than previously thought, caused by mercury emissions in East Asia. Future research should focus on determining mercury speciation in flue gases from iron and steel plants, waste incineration and biomass burning, and on elucidating the mechanisms of mercury oxidation and adsorption in flue gases.

Mercury transformation and speciation in flue gases from anthropogenic emission sources: a critical review

NASA Astrophysics Data System (ADS)

Zhang, L.; Wang, S. X.; Wu, Q. R.; Wang, F. Y.; Lin, C.-J.; Zhang, L. M.; Hui, M. L.; Hao, J. M.

2015-11-01

Mercury transformation mechanisms and speciation profiles are reviewed for mercury formed in and released from flue gases of coal-fired boilers, non-ferrous metal smelters, cement plants, iron and steel plants, municipal solid waste incinerators, and biomass burning. Mercury in coal, ores and other raw materials is released to flue gases in the form of Hg0 during combustion or smelting in boilers, kilns or furnaces. Decreasing temperature from over 800 °C to below 300 °C in flue gases leaving boilers, kilns or furnaces promotes homogeneous and heterogeneous oxidation of gaseous elemental mercury (Hg0) to gaseous divalent mercury (Hg2+), with a portion of Hg2+ adsorbed onto fly ash to form particulate-bound mercury (Hgp). Halogen is the primary oxidizer for Hg0 in flue gases, and active components (e.g.,TiO2, Fe2O3, etc.) on fly ash promote heterogeneous oxidation and adsorption processes. In addition to mercury removal, mercury transformation also occurs when passing through air pollution control devices (APCDs), affecting the mercury speciation in flue gases. In coal-fired power plants, selective catalytic reduction (SCR) system promotes mercury oxidation by 34-85 %, electrostatic precipitator (ESP) and fabric filter (FF) remove over 99 % of Hgp, and wet flue gas desulfurization system (WFGD) captures 60-95 % of Hg2+. In non-ferrous metal smelters, most Hg0 is converted to Hg2+ and removed in acid plants (APs). For cement clinker production, mercury cycling and operational conditions promote heterogeneous mercury oxidation and adsorption. The mercury speciation profiles in flue gases emitted to the atmosphere are determined by transformation mechanisms and mercury removal efficiencies by various APCDs. For all the sectors reviewed in this study, Hgp accounts for less than 5 % in flue gases. In China, mercury emission has a higher fraction (66-82 % of total mercury) in flue gases from coal combustion, in contrast to a greater Hg2+ fraction (29-90 %) from non-ferrous metal smelting, cement and iron/steel production. The higher Hg2+ fractions shown here than previous estimates may imply stronger local environmental impacts than previously thought, caused by mercury emissions in East Asia. Future research should focus on determining mercury speciation in flue gases from iron and steel plants, waste incineration and biomass burning, and on elucidating the mechanisms of mercury oxidation and adsorption in flue gases.

Iron speciation in peats: Chemical and spectroscopic evidence for the co-occurrence of ferric and ferrous iron in organic complexes and mineral precipitates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhattacharyya, Amrita; Schmidt, Michael P.; Stavitski, Eli

The speciation of iron (Fe) in organic matter (OM)-rich environments under in situ variable redox conditions is largely unresolved. Peatlands provide a natural setting to study Fe–OM interactions. Utilizing chemical, spectroscopic and theoretical modeling approaches, we report the chemical forms, oxidation states and local coordination environment of naturally occurring Fe in the vertically redox-stratified Manning peatlands of western New York. In addition, we report dominant carbon, sulfur and nitrogen species that can potentially stabilize the various Fe species present in these peatlands. Our results provide clear direct and indirect evidence for the co-occurrence of ferrous (Fe 2+) and ferric (Femore » 3+) iron species in peats under both oxic and anoxic conditions. Iron is mostly present within the operationally defined organic and amorphous (i.e., short range ordered, SRO) fractions; ferric iron primarily as magnetically isolated paramagnetic Fe 3+ in Fe(III)-organic complexes, but also in mineral forms such as ferrihydrite; ferrous iron in tetrahedral coordination in Fe(II)-organic complexes with minor contribution from pyrite. All of the Fe species identified stabilize Fe(III) and/or Fe(II) in anoxic and oxic peats. Fundamental differences are also observed in the relative proportion of C, S and N functionalities of OM in oxic and anoxic peats. Aromatic C=C, ester, phenol and anomeric C (R-O-C-O-R), as well as thiol, sulfide and heterocyclic N functionalities are more prevalent in anoxic peats. Collectively, our experimental evidence suggests iron forms coordination complexes with O-, S- and N-containing functional groups of OM. We posit the co-occurrence of organic and mineral forms of Fe(II) and Fe(III) in both oxic and anoxic peat layers results from dynamic complexation and hydrolysis-precipitation reactions that occur under variable redox conditions. In conclusion, our findings aid in understanding the crucial role OM plays in determining Fe species in soils and sediments.« less

Iron speciation in peats: Chemical and spectroscopic evidence for the co-occurrence of ferric and ferrous iron in organic complexes and mineral precipitates

DOE PAGES

Bhattacharyya, Amrita; Schmidt, Michael P.; Stavitski, Eli; ...

2017-10-31

The speciation of iron (Fe) in organic matter (OM)-rich environments under in situ variable redox conditions is largely unresolved. Peatlands provide a natural setting to study Fe–OM interactions. Utilizing chemical, spectroscopic and theoretical modeling approaches, we report the chemical forms, oxidation states and local coordination environment of naturally occurring Fe in the vertically redox-stratified Manning peatlands of western New York. In addition, we report dominant carbon, sulfur and nitrogen species that can potentially stabilize the various Fe species present in these peatlands. Our results provide clear direct and indirect evidence for the co-occurrence of ferrous (Fe 2+) and ferric (Femore » 3+) iron species in peats under both oxic and anoxic conditions. Iron is mostly present within the operationally defined organic and amorphous (i.e., short range ordered, SRO) fractions; ferric iron primarily as magnetically isolated paramagnetic Fe 3+ in Fe(III)-organic complexes, but also in mineral forms such as ferrihydrite; ferrous iron in tetrahedral coordination in Fe(II)-organic complexes with minor contribution from pyrite. All of the Fe species identified stabilize Fe(III) and/or Fe(II) in anoxic and oxic peats. Fundamental differences are also observed in the relative proportion of C, S and N functionalities of OM in oxic and anoxic peats. Aromatic C=C, ester, phenol and anomeric C (R-O-C-O-R), as well as thiol, sulfide and heterocyclic N functionalities are more prevalent in anoxic peats. Collectively, our experimental evidence suggests iron forms coordination complexes with O-, S- and N-containing functional groups of OM. We posit the co-occurrence of organic and mineral forms of Fe(II) and Fe(III) in both oxic and anoxic peat layers results from dynamic complexation and hydrolysis-precipitation reactions that occur under variable redox conditions. In conclusion, our findings aid in understanding the crucial role OM plays in determining Fe species in soils and sediments.« less

Arsenite and Ferrous Iron Oxidation Linked to Chemolithotrophic Denitrification for the Immobilization of Arsenic in Anoxic Environments

PubMed Central

Sun, Wenjie; Sierra-Alvarez, Reyes; Milner, Lily; Oremland, Ron; Field, Jim A.

2014-01-01

The objective of this study was to explore a bioremediation strategy based on injecting NO3− to support the anoxic oxidation of ferrous iron (Fe(II)) and arsenite (As(III)) in the subsurface as a means to immobilize As in the form of arsenate (As(V)) adsorbed onto biogenic ferric (Fe(III)) (hydr)oxides. Continuous flow sand filled columns were used to simulate a natural anaerobic groundwater and sediment system with co-occurring As(III) and Fe(II) in the presence (SF1) or absence (SF2) of nitrate, respectively. During operation for 250 days, the average influent arsenic concentration of 567 µg l−1 was reduced to 10.6 (±9.6) µg l−1 in the effluent of column SF1. The cumulative removal of Fe(II) and As(III) in SF1 was 6.5–10-fold higher than that in SF2. Extraction and measurement of the mass of iron and arsenic immobilized on the sand packing of the columns was close to the iron and arsenic removed from the aqueous phase during column operation. The dominant speciation of the immobilized iron and arsenic was Fe(III) and As(V) in SF1, compared with Fe(II) and As(III) in SF2. The speciation was confirmed by XRD and XPS. The results indicate that microbial oxidation of As(III) and Fe(II) linked to denitrification resulted in the enhanced immobilization of aqueous arsenic in anaerobic environments by forming Fe(III) (hydr)oxides coated sands with adsorbed As(V). PMID:19764221

Migration and speciation of heavy metal in salinized mine tailings affected by iron mining.

PubMed

Zhang, Xu; Yang, Huanhuan; Cui, Zhaojie

2017-10-01

The negative effects of heavy metals have aroused much attention due to their high toxicity to human beings. Migration and transformation trend of heavy metals have a close relationship with soil safety. Researching on migration and transformation of heavy metals in tailings can provide a reliable basis for pollution management and ecosystem restoration. Heavy metal speciation plays an important role in risk assessment. We chose Anshan tailings for our study, including field investigations and laboratory research. Four typical heavy metal elements of mine tailings {Fe (373.89 g/kg), Mn (2,303.80 mg/kg), Pb (40.99 mg/kg) and Cr (199.92 mg/kg)} were studied via Tessier test in vertical and horizontal direction. The main speciation of heavy metals in Anshan tailings was the residual. However, heavy metals have a strong ability for migration and transformation in vertical and horizontal directions. Its tendency to change from stable to unstable speciation results in increasing bioavailability and potential bioavailability. Fe, Mn, Pb and Cr showed different ability in the migration and transformation process (Mn > Pb > Fe > Cr) depending on the characteristics of heavy metals and physicochemical properties of the environment.

Redox speciation of dissolved iron in the northeastern atlantic ocean.

NASA Astrophysics Data System (ADS)

Ussher, S. J.; Achterberg, E. P.; Worsfold, P. J.

2003-04-01

Dissolved iron (<0.2 micron) and iron(II) (<0.2 micron) distributions were determined during the Iron from Below and Iron from Above research cruises in the North Eastern Atlantic Ocean. The cruises were part of the EU Ironages project. Iron(II) was measured on-board ship using an iron(II) specific, automated flow injection analyser with luminol chemiluminescence detection [1]. Total dissolved iron (DFe) was determined in a land-based laboratory, using the same FI technique but with prior reduction of iron(III) to iron(II) [2]. The limits of detection for the methods were 5 -15 pM and 35 pM respectively, the analysis time was 8 - 10 minutes per sample (minimum of 3 replicates). The Iron from Below expedition took place over the European Continental Shelf, 200 km South West of Brittany (France) in March 2002. A transect between 47.61°N, 4.24°W and 46.00°N, 8.01°W was completed. Over the transect, the depth increased from 100 m to 5000 m. Iron(II) concentrations ranged between 10 and 100 pM and DFe between 0.2 and 1 nM, with the higher concentrations (Fe(II) ca. > 50 pM and DFe ca. > 0.8 nM) generally found in the shallow shelf waters. These observations imply that benthic inputs and sediment resuspension may form important inputs of dissolved iron and iron(II) in the shelf waters. Iron speciation measurements were also made for underway surface and shallow cast samples during the Iron from Above cruise October 2002. Fe(II) and DFe concentrations were typically 5 to 50 pM and 0.2 to 0.6 nM, respectively. Sampling was carried out within a grid in the Canary Basin around 5 degrees W of the Canary Islands, an area assumed to be strongly influenced by the Saharan dust plume. Observed Fe(II) concentrations are compared and ratioed to the DFe concentrations, and indicate that iron(II) forms an important fraction (between 5 and 15%) of the total dissolved iron concentration in the study areas. Data plots for surface samples are presented with the corresponding physical oceanographic and solar irradiance data. The concentrations of Fe(II) observed during our studies exceed the values predicted from thermodynamic equilibrium modelling. This indicates that there is a steady supply of Fe(II) (possibly from photoreduction and/or biological origins) and/or Fe(II) is prevented from oxidation through stabilisation mechanisms (possibly by organic ligands). [1] A. R. Bowie, E. P. Achterberg, P. N. Sedwick, S. Ussher, P. J. Worsfold, Environ. Sci. Technol., 36, (2002) 4600. [2] A. R. Bowie, E. P. Achterberg, R. F. C. Mantoura, P. J. Worsfold, Anal. Chim. Acta, 377, (1998) 113.

Alginate-Iron Speciation and Its Effect on In Vitro Cellular Iron Metabolism

PubMed Central

Horniblow, Richard D.; Dowle, Miriam; Iqbal, Tariq H.; Latunde-Dada, Gladys O.; Palmer, Richard E.

2015-01-01

Alginates are a class of biopolymers with known iron binding properties which are routinely used in the fabrication of iron-oxide nanoparticles. In addition, alginates have been implicated in influencing human iron absorption. However, the synthesis of iron oxide nanoparticles employs non-physiological pH conditions and whether nanoparticle formation in vivo is responsible for influencing cellular iron metabolism is unclear. Thus the aims of this study were to determine how alginate and iron interact at gastric-comparable pH conditions and how this influences iron metabolism. Employing a range of spectroscopic techniques under physiological conditions alginate-iron complexation was confirmed and, in conjunction with aberration corrected scanning transmission electron microscopy, nanoparticles were observed. The results infer a nucleation-type model of iron binding whereby alginate is templating the condensation of iron-hydroxide complexes to form iron oxide centred nanoparticles. The interaction of alginate and iron at a cellular level was found to decrease cellular iron acquisition by 37% (p < 0.05) and in combination with confocal microscopy the alginate inhibits cellular iron transport through extracellular iron chelation with the resulting complexes not internalised. These results infer alginate as being useful in the chelation of excess iron, especially in the context of inflammatory bowel disease and colorectal cancer where excess unabsorbed luminal iron is thought to be a driver of disease. PMID:26378798

Arsenite and ferrous iron oxidation linked to chemolithotrophic denitrification for the immobilization of arsenic in anoxic environments

USGS Publications Warehouse

Sun, W.; Sierra-Alvarez, R.; Milner, L.; Oremland, R.; Field, J.A.

2009-01-01

The objective of this study was to explore a bioremediation strategy based on injecting NO3- to support the anoxic oxidation of ferrous iron (Fe(II)) and arsenite (As(III)) in the subsurface as a means to immobilize As in the form of arsenate (As(V)) adsorbed onto biogenic ferric (Fe(III)) (hydr)oxides. Continuous flows and filled columns were used to simulate a natural anaerobic groundwater and sediment system with co-occurring As(III) and Fe(II) in the presence (column SF1) or absence (column SF2) of nitrate, respectively. During operation for 250 days, the average influent arsenic concentration of 567 ??g L-1 was reduced to 10.6 (??9.6) ??g L-1 in the effluent of column SF1. The cumulative removal of Fe(II) and As(III) in SF1 was 6.5 to 10-fold higher than that in SF2. Extraction and measurement of the mass of iron and arsenic immobilized on the sand packing of the columns were close to the iron and arsenic removed from the aqueous phase during column operation. The dominant speciation of the immobilized iron and arsenic was Fe(III) and As(V) in SF1, compared with Fe(II) and As(III) in SF2. The speciation was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicate that microbial oxidation of As(III) and Fe(II) linked to denitrification resulted in the enhanced immobilization of aqueous arsenic in anaerobic environments by forming Fe(III) (hydr)oxide coated sands with adsorbed As(V). ?? 2009 American Chemical Society.

Synchrotron speciation data for zero-valent iron nanoparticles

EPA Pesticide Factsheets

This data set encompasses a complete analysis of synchrotron speciation data for 5 iron nanoparticle samples (P1, P2, P3, S1, S2, and metallic iron) to include linear combination fitting results (Table 6 and Figure 9) and ab-initio extended x-ray absorption fine structure spectroscopy fitting (Figure 10 and Table 7).Table 6: Linear combination fitting of the XAS data for the 5 commercial nZVI/ZVI products tested. Species proportions are presented as percentages. Goodness of fit is indicated by the chi^2 value.Figure 9: Normalised Fe K-edge k3-weighted EXAFS of the 5 commercial nZVI/ZVIproducts tested. Dotted lines show the best 4-component linear combination fit ofreference spectra.Figure 10: Fourier transformed radial distribution functions (RDFs) of the five samplesand an iron metal foil. The black lines in Fig. 10 represent the sample data and the reddotted curves represent the non-linear fitting results of the EXAFS data.Table 7: Coordination parameters of Fe in the samples.This dataset is associated with the following publication:Chekli, L., B. Bayatsarmadi, R. Sekine, B. Sarkar, A. Maoz Shen, K. Scheckel , W. Skinner, R. Naidu, H. Shon, E. Lombi, and E. Donner. Analytical Characterisation of Nanoscale Zero-Valent Iron: A Methodological Review. Richard P. Baldwin ANALYTICA CHIMICA ACTA. Elsevier Science Ltd, New York, NY, USA, 903: 13-35, (2016).

Effect of Transport and Aging Processes on Metal Speciation in Iron Oxyhydroxide Aggregates, Tar Creek Superfund Site, Oklahoma

NASA Astrophysics Data System (ADS)

Estes, E. R.; Schaider, L. A.; Shine, J. P.; Brabander, D. J.

2010-12-01

Following the cessation of mining activity in the late 20th century, Tar Creek Superfund Site was left highly contaminated by Pb, Zn, and Cd. Tar Creek, which flows through the site and into the Neosho River, has been studied extensively because of its potential to transport metals from the mining site to downstream communities. Previous research identified aggregated iron oxyhydroxide material, which forms when mine seepage mixes with Tar Creek surface water, as a major transport vector of metals. Frequent flooding in Tar Creek deposits aggregates on downstream floodplains, where wetting and drying processes alter the speciation of iron and other metals. This study seeks to better quantify those changes and to determine how transport and aging affects the human and ecological health risk. Sequential extractions of aggregate samples collected from the creek demonstrate that Fe is present in both amorphous (10-35% of Fe extracted) and more crystalline (8-23% of Fe extracted) phases. Substantial portions of heavy metals sorb to amorphous iron oxyhydroxide phases (accounting for 10-30% of Pb and Zn extracted) but are not associated with more crystalline iron oxide phases (representing only 1% or less of the Pb and Zn extracted). Samples have a high organic matter content (18-25% mass loss on ignition), but only Fe was significantly extracted by the oxidizing step targeting organic matter (1-2% of Pb and Zn extracted, but 10-26% of Fe extracted). The majority of metals were extracted by the soluble or residual steps. If metals and organic matter inhibit transformation of amorphous iron oxyhydroxide material to nano and crystalline iron oxides, then a steady-state volume of amorphous iron oxyhydroxide material with a high total sorption capacity may exist within Tar Creek, enhancing the metal flux accommodated by this transport mechanism. Once transported downstream and deposited on floodplains, however, it is hypothesized that repeated changes in soil matrix composition and thermodynamic conditions could facilitate a transformation to more crystalline iron phases and increase metal bioavailability. While preliminary data from in-creek aggregates show no clear trend in mineralogical composition with downstream transport, only the furthest downstream samples have 2-line ferrihydrite in amounts detectable by XRD.

Characterisation of zinc in slags originated from a contaminated sediment by coupling /μ-PIXE, /μ-RBS, /μ-EXAFS and powder EXAFS spectroscopy

NASA Astrophysics Data System (ADS)

Isaure, M. P.; Laboudigue, A.; Manceau, A.; Sarret, G.; Tiffreau, C.; Trocellier, P.

2001-07-01

Depositing dredged sediments on soils is usual but it is a hazardous practice for the local environment when these sediments are polluted by heavy metals. This chemical hazard can be assessed by determining the speciation of metals. In this study, slags highly polluted with Zn and originated from a contaminated dredged sediment were investigated. Zn speciation was studied by laterally resolved techniques such as μ-particle induced X-ray emission (μ-PIXE), μ-Rutherford backscattering spectrometry (μ-RBS), μ-extended X-ray absorption fine structure (μ-EXAFS), and bulk analyses such as powder EXAFS spectroscopy. μ-PIXE and μ-RBS results showed that high concentrations of Zn were associated with S in localised areas at the surface of the slags while moderate amounts of Zn were mainly associated with Fe in the matrix. EXAFS results allowed to identify ZnS and Zn sorbed on ferrihydrite (5Fe 2O 3·9H 2O), proxy for iron oxy-hydroxides, as the main Zn-bearing phases. The occurrence of this Zn-iron oxy-hydroxide is interpreted as a mobilisation of Zn released from ZnS oxidation.

Degassing of reduced carbon from planetary basalts.

PubMed

Wetzel, Diane T; Rutherford, Malcolm J; Jacobsen, Steven D; Hauri, Erik H; Saal, Alberto E

2013-05-14

Degassing of planetary interiors through surface volcanism plays an important role in the evolution of planetary bodies and atmospheres. On Earth, carbon dioxide and water are the primary volatile species in magmas. However, little is known about the speciation and degassing of carbon in magmas formed on other planets (i.e., Moon, Mars, Mercury), where the mantle oxidation state [oxygen fugacity (fO2)] is different from that of the Earth. Using experiments on a lunar basalt composition, we confirm that carbon dissolves as carbonate at an fO2 higher than -0.55 relative to the iron wustite oxygen buffer (IW-0.55), whereas at a lower fO2, we discover that carbon is present mainly as iron pentacarbonyl and in smaller amounts as methane in the melt. The transition of carbon speciation in mantle-derived melts at fO2 less than IW-0.55 is associated with a decrease in carbon solubility by a factor of 2. Thus, the fO2 controls carbon speciation and solubility in mantle-derived melts even more than previous data indicate, and the degassing of reduced carbon from Fe-rich basalts on planetary bodies would produce methane-bearing, CO-rich early atmospheres with a strong greenhouse potential.

Molecular Speciation of Trace Metal Organic Complexes in the Pacific Ocean

NASA Astrophysics Data System (ADS)

Repeta, D.; Boiteau, R. M.; Bundy, R. M.; Babcock-Adams, L.

2017-12-01

Microbial production across approximately one third of the surface ocean is limited by extraordinarily low (picomolar) concentrations of dissolved iron, essentially all of which is complexed to strong organic ligands of unknown composition. Other biologically important trace metals (cobalt, copper, zinc, nickel) are also complexed to strong organic ligands, which again have not been extensively characterized. Nevertheless, organic ligands exert a strong influence on metal bioavailability and toxicity. For example, amendment experiments using commercially available siderophores, organic compounds synthesized by microbes to facilitate iron uptake, show these ligands can both facilitate or impede iron uptake depending on the siderophore composition and available uptake pathways. Over the past few years we have developed analytical techniques using high pressure liquid chromatography interfaced with inductively coupled plasma and electrospray ionization mass spectrometry to identify and quantify trace metal organic complexes in laboratory cultures of marine microbes and in seawater. We found siderophores to be widely distributed in the ocean, particularly in regions characterized by low iron concentrations. We also find chemically distinct complexes of copper, zinc, colbalt and nickel that we have yet to fully characterize. We will discuss some of our recent work on trace metal organic speciation in seawater and laboratory cultures, and outline future efforts to better understand the microbial cycling of trace metal organic complexes in the sea.

Biogeochemical controls on mercury methylation in the Allequash Creek wetland.

PubMed

Creswell, Joel E; Shafer, Martin M; Babiarz, Christopher L; Tan, Sue-Zanne; Musinsky, Abbey L; Schott, Trevor H; Roden, Eric E; Armstrong, David E

2017-06-01

We measured mercury methylation potentials and a suite of related biogeochemical parameters in sediment cores and porewater from two geochemically distinct sites in the Allequash Creek wetland, northern Wisconsin, USA. We found a high degree of spatial variability in the methylation rate potentials but no significant differences between the two sites. We identified the primary geochemical factors controlling net methylmercury production at this site to be acid-volatile sulfide, dissolved organic carbon, total dissolved iron, and porewater iron(II). Season and demethylation rates also appear to regulate net methylmercury production. Our equilibrium speciation modeling demonstrated that sulfide likely regulated methylation rates by controlling the speciation of inorganic mercury and therefore its bioavailability to methylating bacteria. We found that no individual geochemical parameter could explain a significant amount of the observed variability in mercury methylation rates, but we found significant multivariate relationships, supporting the widely held understanding that net methylmercury production is balance of several simultaneously occurring processes.

Organic iron (III) complexing ligands during an iron enrichment experiment in the western subarctic North Pacific

NASA Astrophysics Data System (ADS)

Kondo, Yoshiko; Takeda, Shigenobu; Nishioka, Jun; Obata, Hajime; Furuya, Ken; Johnson, William Keith; Wong, C. S.

2008-06-01

Complexation of iron (III) with natural organic ligands was investigated during a mesoscale iron enrichment experiment in the western subarctic North Pacific (SEEDS II). After the iron infusions, ligand concentrations increased rapidly with subsequent decreases. While the increases of ligands might have been partly influenced by amorphous iron colloids formation (12-29%), most in-situ increases were attributable to the <200 kDa fraction. Dilution of the fertilized patch may have contributed to the rapid decreases of the ligands. During the bloom decline, ligand concentration increased again, and the high concentrations persisted for 10 days. The conditional stability constant was not different between inside and outside of the fertilized patch. These results suggest that the chemical speciation of the released iron was strongly affected by formation of the ligands; the production of ligands observed during the bloom decline will strongly impact the iron cycle and bioavailability in the surface water.

Atmospheric Processing and Iron Mobilization of Ilmenite: Iron-Containing Ternary Oxide in Mineral Dust Aerosol.

PubMed

Hettiarachchi, Eshani; Hurab, Omar; Rubasinghege, Gayan

2018-02-08

Over the last several decades, iron has been identified as a limiting nutrient in about half of the world's oceans. Its most significant source is identified as deposited iron-containing mineral dust that has been processed during atmospheric transportation. The current work focuses on chemical and photochemical processing of iron-containing mineral dust particles in the presence of nitric acid, and an organic pollutant dimethyl sulfide under atmospherically relevant conditions. More importantly, ilmenite (FeTiO 3 ) is evaluated as a proxy for the iron-containing mineral dust. The presence of titanium in its lattice structure provides higher complexity to mimic mineral dust, yet it is simple enough to study reaction pathways and mechanisms. Here, spectroscopic methods are combined with dissolution measurements to investigate atmospheric processing of iron in mineral dust, with specific focus on particle mineralogy, particle size, and their environmental conditions (i.e., pH and solar flux). Our results indicate that the presence of titanium elemental composition enhances iron dissolution from mineral dust, at least by 2-fold comparison with its nontitanium-containing counterparts. The extent of iron dissolution and speciation is further influenced by the above factors. Thus, our work highlights these important, yet unconsidered, factors in the atmospheric processing of iron-containing mineral dust aerosol.

The role of iron-sulfides on cycling of organic carbon in the St Lawrence River system: Evidence of sulfur-promoted carbon sequestration?

NASA Astrophysics Data System (ADS)

Balind, K.; Barber, A.; Gélinas, Y.

2017-12-01

The biogeochemical cycle of sulfur is intimately linked with that of carbon, as well as with that of iron through the formation of iron-sulfur complexes. Iron-sulfide minerals such as mackinawite (FeS) and greigite (Fe3S4) form below the oxic/anoxic redox boundary in marine and lacustrine sediments and soils. Reactive iron species, abundant in surface sediments, can undergo reductive dissolution leading to the formation of soluble Fe(II) which can then precipitate in the form of iron sulfur species. While sedimentary iron-oxides have been thoroughly explored in terms of their ability to sorb and sequester organic carbon (OC) (Lalonde et al.; 2012), the role of FeS in the long-term preservation of OC remains undefined. In this study, we present depth profiles for carbon, iron, and sulfur in the aqueous-phase, along with data from sequential extractions of sulfur speciation in the solid-phase collected from sediment cores from the St Lawrence River and estuarine system, demonstrating the transition from fresh to saltwater sediments. Additionally, we present synthetic iron sulfur sorption experiments using both model and natural organic molecules in order to assess the importance of FeS in sedimentary carbon storage.

Degassing of reduced carbon from planetary basalts

PubMed Central

Wetzel, Diane T.; Rutherford, Malcolm J.; Jacobsen, Steven D.; Hauri, Erik H.; Saal, Alberto E.

2013-01-01

Degassing of planetary interiors through surface volcanism plays an important role in the evolution of planetary bodies and atmospheres. On Earth, carbon dioxide and water are the primary volatile species in magmas. However, little is known about the speciation and degassing of carbon in magmas formed on other planets (i.e., Moon, Mars, Mercury), where the mantle oxidation state [oxygen fugacity (fO2)] is different from that of the Earth. Using experiments on a lunar basalt composition, we confirm that carbon dissolves as carbonate at an fO2 higher than -0.55 relative to the iron wustite oxygen buffer (IW-0.55), whereas at a lower fO2, we discover that carbon is present mainly as iron pentacarbonyl and in smaller amounts as methane in the melt. The transition of carbon speciation in mantle-derived melts at fO2 less than IW-0.55 is associated with a decrease in carbon solubility by a factor of 2. Thus, the fO2 controls carbon speciation and solubility in mantle-derived melts even more than previous data indicate, and the degassing of reduced carbon from Fe-rich basalts on planetary bodies would produce methane-bearing, CO-rich early atmospheres with a strong greenhouse potential. PMID:23569260

Microbial Sulfate Reduction Enhances Arsenic Mobility Downstream of Zerovalent-Iron-Based Permeable Reactive Barrier.

PubMed

Kumar, Naresh; Couture, Raoul-Marie; Millot, Romain; Battaglia-Brunet, Fabienne; Rose, Jérôme

2016-07-19

We assessed the potential of zerovalent-iron- (Fe(0)) based permeable reactive barrier (PRB) systems for arsenic (As) remediation in the presence or absence of microbial sulfate reduction. We conducted long-term (200 day) flow-through column experiments to investigate the mechanisms of As transformation and mobility in aquifer sediment (in particular, the PRB downstream linkage). Changes in As speciation in the aqueous phase were monitored continuously. Speciation in the solid phase was determined at the end of the experiment using X-ray absorption near-edge structure (XANES) spectroscopy analysis. We identified thio-As species in solution and AsS in solid phase, which suggests that the As(V) was reduced to As(III) and precipitated as AsS under sulfate-reducing conditions and remained as As(V) under abiotic conditions, even with low redox potential and high Fe(II) content (4.5 mM). Our results suggest that the microbial sulfate reduction plays a key role in the mobilization of As from Fe-rich aquifer sediment under anoxic conditions. Furthermore, they illustrate that the upstream-downstream linkage of PRB affects the speciation and mobility of As in downstream aquifer sediment, where up to 47% of total As initially present in the sediment was leached out in the form of mobile thio-As species.

Emission characteristics and chemical components of size-segregated particulate matter in iron and steel industry

NASA Astrophysics Data System (ADS)

Jia, Jia; Cheng, Shuiyuan; Yao, Sen; Xu, Tiebing; Zhang, Tingting; Ma, Yuetao; Wang, Hongliang; Duan, Wenjiao

2018-06-01

As one of the highest energy consumption and pollution industries, the iron and steel industry is regarded as a most important source of particulate matter emission. In this study, chemical components of size-segregated particulate matters (PM) emitted from different manufacturing units in iron and steel industry were sampled by a comprehensive sampling system. Results showed that the average particle mass concentration was highest in sintering process, followed by puddling, steelmaking and then rolling processes. PM samples were divided into eight size fractions for testing the chemical components, SO42- and NH4+ distributed more into fine particles while most of the Ca2+ was concentrated in coarse particles, the size distribution of mineral elements depended on the raw materials applied. Moreover, local database with PM chemical source profiles of iron and steel industry were built and applied in CMAQ modeling for simulating SO42- and NO3- concentration, results showed that the accuracy of model simulation improved with local chemical source profiles compared to the SPECIATE database. The results gained from this study are expected to be helpful to understand the components of PM in iron and steel industry and contribute to the source apportionment researches.

Influence of silicon treatment on antimony uptake and translocation in rice genotypes with different radial oxygen loss.

PubMed

Zhang, Liping; Yang, Qianqian; Wang, Shiliang; Li, Wanting; Jiang, Shaoqing; Liu, Yan

2017-10-01

Antimony (Sb) pollution in soil may have a negative impact on the health of people consuming rice. This study investigated the effect of silicon (Si) application on rice biomass, iron plaque formation, and Sb uptake and speciation in rice plants with different radial oxygen loss (ROL) using pot experiments. The results demonstrated that Si addition increased the biomass of straw and grain, but had no obvious impact on the root biomass. Indica genotypes with higher ROL underwent greater iron plaque formation and exhibited more Sb sequestration in iron plaque. Silicon treatments increased iron levels in iron plaque from the different genotypes but decreased the total Sb concentration in root, straw, husk, and grain. In addition, Si treatment reduced the inorganic Sb concentrations but slightly increased the trimethylantimony (TMSb) concentrations in rice straw. Moreover, rice straw from hybrid genotypes accumulated higher concentrations of TMSb and inorganic Sb than that from indica genotypes. The conclusions from this study indicate that Sb contamination in rice can be efficiently reduced by applying Si treatment and selecting genotypes with high ROL. Copyright © 2017 Elsevier Inc. All rights reserved.

Iron Speciation in Minerals and Melts at High Pressure: Implications for the Redox Evolution of the Early Mantle

NASA Astrophysics Data System (ADS)

Armstrong, K.; Frost, D. J.; McCammon, C. A.; Rubie, D. C.; Boffa Ballaran, T.; Miyajima, N.

2016-12-01

During the differentiation of the early Earth, the silicates of the mantle must have been in equilibrium with core-forming metal iron, as indicated by the depletion of siderophile elements from the mantle. Studies of ancient rocks suggest that by at least 3.9 Ga, the upper mantle was 4-5 log units more oxidized than metal saturation implies (Delano 2001). The process(es) by which the mantle was oxidized is unclear, but has implications for the timing of accretion, differentiation, and volatile delivery to the early Earth, as well as evolution of the early atmosphere. One plausible oxidation mechanism is suggested by the tendency of high-pressure silicate minerals to favor Fe3+ over Fe2+ in their structures, even at metal saturation. This preference in the lower mantle mineral bridgmanite has been proposed to drive the disproportionation reaction of FeO to form Fe­2O3 and iron metal (Frost and McCammon 2008). We have performed experiments at the Ru-RuO2 fO2 buffer which show that silicate melts may mirror this behavior and Fe3+ may be stabilized with pressure for a constant fO2; by 21 GPa, the previously observed trend of Fe3+ decreasing with pressure (O'Neill, 2006) reverses and ferric iron content had increased. If this is also the case at lower oxygen fugacities, FeO disproportionation may have occurred at the base of an early magma ocean, establishing a redox gradient similar to what is presumed for the mantle today. Here we report results of further multianvil and diamond anvil cell experiments exploring the plausibility of FeO disproportionation driving mantle oxidation. Experiments investigating Fe speciation in high pressure melts at variable fO2 will be discussed along with results of diamond anvil cell experiments investigating ferric iron content of lower mantle minerals at metal saturation.

Chromium in urban sediment particulates: an integrated micro-chemical and XANES study

NASA Astrophysics Data System (ADS)

Taylor, Kevin; Byrne, Patrick; Hudson-Edwards, Karen

2015-04-01

Chromium is generally common within the urban sediment cascade as a result of abundant industrial and transport-related sources. The risks that Cr-bearing particles pose to ecosystems and humans depend on the solid phase chemical speciation of Cr in the particles. In this study, we use bulk chemical digests, sequential chemical extraction analysis, electron microscopy, electron microprobe and microfocus XANES analysis to describe the solid-phase speciation of Cr in urban particulate matter from both aquatic sediment and road dust sediment (RDS) in Manchester, UK. Cr-bearing grains within RDS are predominantly iron oxide grains, commonly of goethite or haematite mineralogy, but Cr-bearing silicate glass grains are also present. Iron oxide glass grains most likely have sorbed Cr, and derive from the rusting of Cr-steel particles from vehicles. Electron microprobe analysis indicates concentrations of Cr up to 3200 μg/g in these grains, and XANES analysis indicates that Cr(III) is the dominant oxidation state, with some trace amounts of Cr(VI). Cr-bearing grains within aquatic sediments are dominated by alumino-silicate glass grains derived from industrial waste. These grains contain Cr-rich areas with up to 19% Cr2O3 and XANES analysis indicates that Cr is present as Cr(III). The dominance of Cr(III) in these urban particulate grains suggests limited bioavailability or toxicity. However, the presence within two markedly different grain types (iron oxides and silicate glasses) indicates that the long-term geochemical behaviour and environmental risk of RDS and the aquatic sediments studied are likely to be quite different. These findings highlight the importance of understanding sources of metal contaminants in urban environments and the geochemical processes that affect their transfer through the urban sediment cascade and the wider river basin.

Storm water runoff measurements of copper from a naturally patinated roof and from a parking space. Aspects on environmental fate and chemical speciation.

PubMed

Odnevall Wallinder, I; Hedberg, Y; Dromberg, P

2009-12-01

Release of copper from a naturally aged copper roof on a shopping centre building in a suburban site of Stockholm has been measured during different rain events after its interaction with the internal drainage system and storm drains made of cast iron and concrete. Concentrations of copper removed by means of urban storm water from a nearby parking space have been determined for comparison. Predictions and measurements of the chemical speciation of released copper are discussed compared to the total concentration, and to threshold values for freshwater and drinking water. The results clearly illustrate that the major part of the released copper from the roof is readily retained already during transport through the internal drainage system of the building, a pathway that also changes the chemical speciation of released copper and its bioavailable fraction. Most copper, not retained by cast iron and concrete surfaces, was strongly complexed to organic matter. The median concentration of free cupric ions and weak copper complexes was less than, or within the range of reported no effect concentrations, NOECs, of copper in surface waters. The parking space contributed with significantly higher and time-dependent concentrations of total copper compared to measured concentrations of copper from the roof after the interaction with the drainage system. Most copper in the surface runoff water was strongly complexed with organic matter, hence reducing the bioavailable fraction significantly to concentrations within the NOEC range. Dilution with other sources of urban storm water will reduce the released concentration of copper even further. The results illustrate that already the internal drainage system and the storm drains made of cast iron and concrete act as efficient sinks for released copper which means that any installation of additional infiltration devices is redundant.

Speciation of strontium-90 in NIST natural matrix standard reference materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, J.W.L.; Inn, K.G.W.; Garcia, M.E.

1995-12-31

A sequential leaching, radiochemical separating, and low-level beta-particle counting procedure was designed to study the speciation of radionuclides in natural matrix standard reference materials, SRMs 4350B (Columbia River Sediment) and 4353 (Rocky Flats Soil-1). Strontium-90 is the first radionuclide studied because of the difficulty experienced with this nuclide in natural-matrix SRMs. The nine-step procedure extracted {sup 90}Sr from the following fractions: water solubles, exchangeables, carbonates, reducibles, organics, iron and manganese oxides, acid leachables, micas, and silicates. The majority of {sup 90}Sr in the soil samples was found in the exchangeable fraction. By contrast, the {sup 90}Sr in the sediment ismore » more evenly distributed among the various leached fractions. Information on the leach distribution of radionuclides in environmental SRMs, based on the procedure described, should lead to more cost-effective restoration strategies and more confidence in risk assessments of human health hazards.« less

Linear Combination Fitting (LCF)-XANES analysis of As speciation in selected mine-impacted materials

EPA Pesticide Factsheets

This table provides sample identification labels and classification of sample type (tailings, calcinated, grey slime). For each sample, total arsenic and iron concentrations determined by acid digestion and ICP analysis are provided along with arsenic in-vitro bioaccessibility (As IVBA) values to estimate arsenic risk. Lastly, the table provides linear combination fitting results from synchrotron XANES analysis showing the distribution of arsenic speciation phases present in each sample along with fitting error (R-factor).This dataset is associated with the following publication:Ollson, C., E. Smith, K. Scheckel, A. Betts, and A. Juhasz. Assessment of arsenic speciation and bioaccessibility in mine-impacted materials. Diana Aga, Wonyong Choi, Andrew Daugulis, Gianluca Li Puma, Gerasimos Lyberatos, and Joo Hwa Tay JOURNAL OF HAZARDOUS MATERIALS. Elsevier Science Ltd, New York, NY, USA, 313: 130-137, (2016).

ARSENIC PARTITIONING TO IRON OXIDES AND SULFIDES: LOCAL ENVIRONMENT AND OXIDATION STATE

EPA Science Inventory

his document summarizes research activities conducted at the Advanced Photon Source at Argonne National Laboratory, Argonne, IL during FY2003. The analytical data collected using X-ray absorption spectroscopy was used to evaluated the chemical speciation of arsenic associated wi...

When soils become sediments: Large-scale storage of soils in sandpits and lakes and the impact of reduction kinetics on heavy metals and arsenic release to groundwater.

PubMed

Vink, Jos P M; van Zomeren, Andre; Dijkstra, Joris J; Comans, Rob N J

2017-08-01

Simulating the storage of aerobic soils under water, the chemical speciation of heavy metals and arsenic was studied over a long-term reduction period. Time-dynamic and redox-discrete measurements in reactors were used to study geochemical changes. Large kinetic differences in the net-complexation quantities of heavy metals with sulfides was observed, and elevated pore water concentrations remained for a prolonged period (>1 year) specifically for As, B, Ba, Co, Mo, and Ni. Arsenic is associated to the iron phases as a co-precipitate or sorbed fraction to Fe-(hydr)oxides, and it is being released into solution as a consequence of the reduction of iron. The composition of dissolved organic matter (DOM) in reducing pore water was monitored, and relative contributions of fulvic, humic and hydrophylic compounds were measured via analytical batch procedures. Quantitative and qualitative shifts in organic compounds occur during reduction; DOM increased up to a factor 10, while fulvic acids become dominant over humic acids which disappear altogether as reduction progresses. Both the hydrophobic and hydrophilic fractions increase and may even become the dominant fraction. Reactive amorphous and crystalline iron phases, as well as dissolved FeII/FeIII speciation, were measured and used as input for the geochemical model to improve predictions for risk assessment to suboxic and anaerobic environments. The release of arsenic is related to readily reducible iron fractions that may be identified by 1 mM CaCl 2 extraction procedure. Including DOM concentration shifts and compositional changes during reduction significantly improved model simulations, enabling the prediction of peak concentrations and identification of soils with increased emission risk. Practical methods are suggested to facilitate the practice of environmentally acceptable soil storage under water. Copyright © 2017 Elsevier Ltd. All rights reserved.

Enhanced ferrihydrite dissolution by a unicellular, planktonic cyanobacterium: a biological contribution to particulate iron bioavailability.

PubMed

Kranzler, Chana; Kessler, Nivi; Keren, Nir; Shaked, Yeala

2016-12-01

Iron (Fe) bioavailability, as determined by its sources, sinks, solubility and speciation, places severe environmental constraints on microorganisms in aquatic environments. Cyanobacteria are a widespread group of aquatic, photosynthetic microorganisms with especially high iron requirements. While iron exists predominantly in particulate form, little is known about its bioavailability to cyanobacteria. Some cyanobacteria secrete iron solubilizing ligands called siderophores, yet many environmentally relevant strains do not have this ability. This work explores the bioavailability of amorphous synthetic Fe-oxides (ferrihydrite) to the non-siderophore producing, unicellular cyanobacterium, Synechocystis sp PCC 6803. Iron uptake assays with 55 ferrihydrite established dissolution as a critical prerequisite for iron transport. Dissolution assays with the iron binding ligand, desferrioxamine B, demonstrated that Synechocystis 6803 enhances ferrihydrite dissolution, exerting siderophore-independent biological influence on ferrihydrite bioavailability. Dissolution mechanisms were studied using a range of experimental conditions; both cell-particle physical proximity and cellular electron flow were shown to be important determinants of bio-dissolution by Synechocystis 6803. Finally, the effects of ferrihydrite stability on bio-dissolution rates and cell physiology were measured, integrating biological and chemical aspects of ferrihydrite bioavailability. Collectively, these findings demonstrate that Synechocystis 6803 actively dissolves ferrihydrite, highlighting a significant biological component to mineral phase iron bioavailability in aquatic environments. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

Iron isotope biogeochemistry of Neoproterozoic marine shales

NASA Astrophysics Data System (ADS)

Kunzmann, Marcus; Gibson, Timothy M.; Halverson, Galen P.; Hodgskiss, Malcolm S. W.; Bui, Thi Hao; Carozza, David A.; Sperling, Erik A.; Poirier, André; Cox, Grant M.; Wing, Boswell A.

2017-07-01

Iron isotopes have been widely applied to investigate the redox evolution of Earth's surface environments. However, it is still unclear whether iron cycling in the water column or during diagenesis represents the major control on the iron isotope composition of sediments and sedimentary rocks. Interpretation of isotopic data in terms of oceanic redox conditions is only possible if water column processes dominate the isotopic composition, whereas redox interpretations are less straightforward if diagenetic iron cycling controls the isotopic composition. In the latter scenario, iron isotope data is more directly related to microbial processes such as dissimilatory iron reduction. Here we present bulk rock iron isotope data from late Proterozoic marine shales from Svalbard, northwestern Canada, and Siberia, to better understand the controls on iron isotope fractionation in late Proterozoic marine environments. Bulk shales span a δ 56Fe range from -0.45 ‰ to +1.04 ‰ . Although δ 56Fe values show significant variation within individual stratigraphic units, their mean value is closer to that of bulk crust and hydrothermal iron in samples post-dating the ca. 717-660 Ma Sturtian glaciation compared to older samples. After correcting for the highly reactive iron content in our samples based on iron speciation data, more than 90% of the calculated δ 56Fe compositions of highly reactive iron falls in the range from ca. -0.8 ‰ to +3 ‰ . An isotope mass-balance model indicates that diagenetic iron cycling can only change the isotopic composition of highly reactive iron by < 1 ‰ , suggesting that water column processes, namely the degree of oxidation of the ferrous seawater iron reservoir, control the isotopic composition of highly reactive iron. Considering a long-term decrease in the isotopic composition of the iron source to the dissolved seawater Fe(II) reservoir to be unlikely, we offer two possible explanations for the Neoproterozoic δ 56Fe trend. First, a decreasing supply of Fe(II) to the ferrous seawater iron reservoir could have caused the reservoir to decrease in size, allowing a higher degree of partial oxidation, irrespective of increasing environmental oxygen levels. Alternatively, increasing oxygen levels would have led to a higher proportion of Fe(II) being oxidized, without decreasing the initial size of the ferrous seawater iron pool. We consider the latter explanation as the most likely. According to this hypothesis, the δ 56Fe record reflects the redox evolution of Earth's surface environments. δ 56Fe values in pre-Sturtian samples significantly heavier than bulk crust and hydrothermal iron imply partial oxidation of a ferrous seawater iron reservoir. In contrast, mean δ 56Fe values closer to that of hydrothermal iron in post-Sturtian shales reflects oxidation of a larger proportion of the ferrous seawater iron reservoir, and by inference, higher environmental oxygen levels. Nevertheless, significant iron isotopic variation in post-Sturtian shales suggest redox heterogeneity and possibly a dominantly anoxic deep ocean, consistent with results from recent studies using iron speciation and redox sensitive trace metals. However, the interpretation of generally increasing environmental oxygen levels after the Sturtian glaciation highlights the need to better understand the sensitivity of different redox proxies to incremental changes in oxygen levels to enable us to reconcile results from different paleoredox proxies.

The Speciation of Sulfur in an Ocean on Europa

NASA Technical Reports Server (NTRS)

Zolotov, M. Yu.; Shock, E. L.

2002-01-01

Stability of native sulfur, iron sulfides, and aqueous sulfur compounds is evaluated at assumed P-T conditions of the Europa's ocean floor. Pyrite, gypsum, and ferric hydroxides can coexist in contact with sulfate-rich oceanic water. Additional information is contained in the original extended abstract.

Increased iron bioavailability from lactic-fermented vegetables is likely an effect of promoting the formation of ferric iron (Fe(3+)).

PubMed

Scheers, Nathalie; Rossander-Hulthen, Lena; Torsdottir, Inga; Sandberg, Ann-Sofie

2016-02-01

Lactic fermentation of foods increases the availability of iron as shown in a number of studies throughout the years. Several explanations have been provided such as decreased content of inhibitory phytate, increased solubility of iron, and increased content of lactic acid in the fermented product. However, to our knowledge, there are no data to support that the bioavailability of iron is affected by lactic fermentation. The objective of the present study was to investigate whether the bioavailability of iron from a vegetable mix was affected by lactic fermentation and to propose a mechanism for such an event, by conducting human and cell (Caco-2, HepG2) studies and iron speciation measurements (voltammetry). We also investigated whether the absorption of zinc was affected by the lactic fermentation. In human subjects, we observed that lactic-fermented vegetables served with both a high-phytate and low-phytate meal increased the absorption of iron, but not zinc. In vitro digested fermented vegetables were able to provoke a greater hepcidin response per ng Fe than fresh vegetables, indicating that Fe in the fermented mixes was more bioavailable, independent on the soluble Fe content. We measured that hydrated Fe(3+) species were increased after the lactic fermentation, while there was no significant change in hydrated Fe(2+). Furthermore, lactate addition to Caco-2 cells did not affect ferritin formation in response to Fe nor did lactate affect the hepcidin response in the Caco-2/HepG2 cell system. The mechanism for the increased bioavailability of iron from lactic-fermented vegetables is likely an effect of the increase in ferric iron (Fe(3+)) species caused by the lactic fermentation. No effect on zinc bioavailability was observed.

Coal fly ash as a source of iron in atmospheric dust.

PubMed

Chen, Haihan; Laskin, Alexander; Baltrusaitis, Jonas; Gorski, Christopher A; Scherer, Michelle M; Grassian, Vicki H

2012-02-21

Anthropogenic coal fly ash (FA) aerosol may represent a significant source of bioavailable iron in the open ocean. Few measurements have been made that compare the solubility of atmospheric iron from anthropogenic aerosols and other sources. We report here an investigation of iron dissolution for three FA samples in acidic aqueous solutions and compare the solubilities with that of Arizona test dust (AZTD), a reference material for mineral dust. The effects of pH, simulated cloud processing, and solar radiation on iron solubility have been explored. Similar to previously reported results on mineral dust, iron in aluminosilicate phases provides the predominant component of dissolved iron. Iron solubility of FA is substantially higher than of the crystalline minerals comprising AZTD. Simulated atmospheric processing elevates iron solubility due to significant changes in the morphology of aluminosilicate glass, a dominant material in FA particles. Iron is continuously released into the aqueous solution as FA particles break up into smaller fragments. These results suggest that the assessment of dissolved atmospheric iron deposition fluxes and their effect on the biogeochemistry at the ocean surface should be constrained by the source, environmental pH, iron speciation, and solar radiation.

[Iron from soil to plant products].

PubMed

Briat, Jean-François

2005-11-01

As an essential mineral, iron plays an important role in fundamental biological processes such as photosynthesis, respiration, nitrogen fixation and assimilation, and DNA synthesis. Iron is also a co-factor of many enzymes involved in the synthesis of plant hormones. The latter are involved in many pathways controling plant development or adaptative responses to environmental conditions. Iron reactivity with oxygen leads to its insolubility (responsible for deficiency) and potential toxicity, and complicates iron use by aerobic organisms. If plants lacked an active root system with which to acquire iron from the soil, most would experience iron deficiency and show physiological changes. In contrast, an excess of soluble iron, which can occur in flooded acidic soils, can lead to ferrous iron toxicity due to iron reactivity with reduced forms of oxygen and subsequent free radical production. An optimal iron concentration is thus required for a plant to grow and develop normally. This concentration depends on multiple regulatory mechanisms controlling iron uptake from soil by the roots, as well as iron transport and distribution to the various plant organs. Optimized seed iron content is a major biotechnological challenge identified by the World Health Organization, and it is therefore crucial to understand the underlying mechanisms. Iron delivery to seeds is tightly controlled, and depends on the nature of iron speciation in specific chelates, and their transport.

Assessment of bioavailability of iron delivered to marine phytoplankton in different mineralogical forms

NASA Astrophysics Data System (ADS)

Ammar, Rawaa; Delmelle, Pierre; Journet, Emilie

2017-04-01

Iron (Fe) is an essential element in cellular biochemical processes and its availability in the surface ocean limits phytoplankton-mediated fixation of C, i.e. the biological pump. In vast regions of the open ocean, atmospheric deposition of Fe-bearing continental dust and volcanic ash to the surface ocean acts as an important source of bioavailable Fe to phytoplankton. The capacity of dust and ash to alleviate Fe limitation is usually discussed in terms of Fe solubility, which has been shown to be controlled by speciation/mineralogy. However, little information exists on the relationship between Fe bioavailability and Fe speciation/mineralogy in dust and ash. In this study, Fe-bearing materials of known mineralogy, including three volcanic ash samples from different eruptions (Eyjafjallajökull 2010, Chaitén 2008 and Tungurahua 2012), two continental dust specimens (Douz and Banizoumbou) and three Fe-bearing minerals (illite/smectite, ferrihydrite, and goethite) were added to Fe-stressed cultures of Dunaliella tertiolecta, a marine algae commonly found in high-nutrient, low chlorophyll waters. Photosynthetic activity, chlorophyll content and cell population growth were measured at regular intervals during 168 h after Fe addition. Our results indicate that all the tested Fe-bearing materials induced a similar biological response; and were able to alleviate Fe stress in D. tertiolecta within 2 h from the beginning of the experiment and to induce cell growth up to 168 h. This unexpected finding contrasts with the traditional view that Fe speciation/mineralogy in dust and ash plays a key role in governing Fe bioavailability to phytoplankton. Supplementary measurements on the fractional solubility of Fe in dust and ash will be presented.

Aluminum and Fenton reaction: how can the reaction be modulated by speciation? A computational study using citrate as a test case.

PubMed

Mujika, Jon I; Dalla Torre, Gabriele; Lopez, Xabier

2018-06-13

The pro-oxidant ability of aluminum is behind many of the potential toxic effects of this exogenous element in the human organism. Although the overall process is still far from being understood at the molecular level, the well known ability of aluminum to promote the Fenton reaction is mediated through the formation of stable aluminum-superoxide radical complexes. However, the properties of metal complexes are highly influenced by the speciation of the metal. In this paper, we investigate the effect that speciation could have on the pro-oxidant activity of aluminum. We choose citrate as a test case, because it is the main low-molecular-mass chelator of aluminum in blood serum, forming very stable aluminum-citrate complexes. The influence of citrate in the interaction of aluminum with the superoxide radical is investigated, determining how the formation of aluminum-citrate complexes affects the promotion of the Fenton reaction. The results indicate that citrate increases the stability of the aluminum-superoxide complexes through the formation of ternary compounds, and that the Fenton reaction is even more favorable when aluminum is chelated to citrate. Nevertheless, our results demonstrate that overall, citrate may prevent the pro-oxidant activity of aluminum: on one hand, in an excess of citrate, the formation of 1 : 2 aluminum-citrate complexes is expected. On the other hand, the chelation of iron by citrate makes the reduction of iron thermodynamically unfavorable. In summary, the results suggest that citrate can have both a promotion and protective role, depending on subtle factors, such as initial concentration, non-equilibrium behavior and the exchange rate of ligands in the first shell of the metals.

Sulfur and iron speciation in gas-rich impact-melt glasses from basaltic shergottites determined by microXANES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sutton, S.R.; Rao, M.N.; Nyquist, L.E.

2008-04-28

Sulfur and iron K XANES measurements were made on GRIM glasses from EET 79001. Iron is in the ferrous state. Sulfur speciation is predominately sulfide coordination but is Fe coordinated in Lith B and, most likely, Ca coordinated in Lith A. Sulfur is abundantly present as sulfate near Martian surface based on chemical and mineralogical investigations on soils and rocks in Viking, Pathfinder and MER missions. Jarosite is identified by Moessbauer studies on rocks at Meridian and Gusev, whereas MgSO{sub 4} is deduced from MgO-SO{sub 3} correlations in Pathfinder MER and Viking soils. Other sulfate minerals such as gypsum andmore » alunogen/S-rich aluminosilicates and halides are detected only in martian meteorites such as shergottites and nakhlites using SEM/FE-SEM and EMPA techniques. Because sulfur has the capacity to occur in multiple valence states, determination of sulfur speciation (sulfide/sulfate) in secondary mineral assemblages in soils and rocks near Mars surface may help us understand whether the fluid-rock interactions occurred under oxidizing or reducing conditions. On Earth, volcanic rocks contain measurable quantities of sulfur present as both sulfide and sulfate. Carroll and Rutherford showed that oxidized forms of sulfur may comprise a significant fraction of total dissolved sulfur, if the oxidation state is higher than {approx}2 log fO{sub 2} units relative to the QFM buffer. Terrestrial samples containing sulfates up to {approx}25% in fresh basalts from the Galapagos Rift on one hand and high sulfide contents present in oceanic basalts on the other indicate that the relative abundance of sulfide and sulfate varies depending on the oxygen fugacity of the system. Basaltic shergottites (bulk) such as Shergotty, EET79001 and Zagami usually contain small amounts of sulfur ({approx}0.5%) as pyrrhotite. But, in isolated glass pockets containing secondary salts (known as GRIM glasses) in these meteorites, sulfur is present in high abundance ({approx}1-12%). To determine sulfur speciation (sulfide, sulfate or elemental sulfur) in these glasses, Gooding et al. and Burgess et al. carried out vacuum pyrolysis experiments on these GRIM glasses (also called Lith C) using quadrupole mass-spectrometric methods. They found that the evolved S-bearing gases from these samples consisted of both SO{sub 2} (from sulfate) and H{sub 2}S (from sulfide) in varying proportions. However, as mass-spectrometric studies do not provide details about spatial association of these S-species in these samples, we have studied the spatial distribution of sulfides and sulfates in GRIM glasses using sulfur K micro-XANES techniques in the present study. The microscale speciation of S may have important implications for the Rb-Sr isotope systematics of EET79001 Lith C glasses. In reference to oxidative weathering of surface basalts on Mars yielding secondary iron sulfates, Solberg and Burns examined a GRIM glass in EET79001 by Moessbauer spectroscopic techniques and showed that the percentage of Fe{sup 3+} in Lith C is <2%. They suggested that the Lith C contains very little Fe{sup 3+} despite the occurrence of oxidized sulfate in them, indicating that the conditions leading to the formation of these glasses were insufficiently oxidizing to produce Fe{sup 3+} from Fe{sup 2+} in these glasses. To understand the implications of these observations for the formation of the GRIM glasses, we determined the oxidation state of Fe in the GRIM glasses using Fe K micro-XANES techniques. The S and Fe K micro-XANES measurements were performed on thin sections from EET79001: 506 from Lith A and 507 from Lith B.« less

Sequestration of arsenic in ombrotrophic peatlands

NASA Astrophysics Data System (ADS)

Rothwell, James; Hudson-Edwards, Karen; Taylor, Kevin; Polya, David; Evans, Martin; Allott, Tim

2014-05-01

Peatlands can be important stores of arsenic but we are lacking spectroscopic evidence of the sequestration pathways of this toxic metalloid in peatland environments. This study reports on the solid-phase speciation of anthropogenically-derived arsenic in atmospherically contaminated peat from the Peak District National Park (UK). Surface and sub-surface peat samples were analysed by synchrotron X-ray absorption spectroscopy on B18 beamline at Diamond Light Source (UK). The results suggest that there are contrasting arsenic sequestration mechanisms in the peat. The bulk arsenic speciation results, in combination with strong arsenic-iron correlations at the surface, suggest that iron (hydr)oxides are key phases for the immobilisation of arsenic at the peat surface. In contrast, the deeper peat samples are dominated by arsenic sulphides (arsenopyrite, realgar and orpiment). Given that these peats receive inputs solely from the atmosphere, the presence of these sulphide phases suggests an in-situ authigenic formation. Redox oscillations in the peat due to a fluctuating water table and an abundant store of legacy sulphur from historic acid rain inputs may favour the precipitation of arsenic sequestering sulphides in sub-surface horizons. Oxidation-induced loss of these arsenic sequestering sulphur species by water table drawdown has important implications for the mobility of arsenic and the quality of waters draining peatlands.

Updated atmospheric speciated mercury emissions from iron and steel production in China during 2000-2015

NASA Astrophysics Data System (ADS)

Wu, Qingru; Gao, Wei; Wang, Shuxiao; Hao, Jiming

2017-09-01

Iron and steel production (ISP) is one of the significant atmospheric Hg emission sources in China. Atmospheric mercury (Hg) emissions from ISP during 2000-2015 were estimated by using a technology-based emission factor method. To support the application of this method, databases of Hg concentrations in raw materials, technology development trends, and Hg removal efficiencies of air pollution control devices (APCDs) were constructed through national sampling and literature review. Hg input to ISP increased from 21.6 t in 2000 to 94.5 t in 2015. In the various types of raw materials, coking coal and iron concentrates contributed 35-46 and 25-32 % of the total Hg input. Atmospheric Hg emissions from ISP increased from 11.5 t in 2000 to 32.7 t in 2015 with a peak of 35.6 t in 2013. Pollution control promoted the increase in average Hg removal efficiency, from 47 % in 2000 to 65 % in 2015. During the study period, sinter/pellet plants and blast furnaces were the largest two emission processes. However, emissions from roasting plants and coke ovens cannot be ignored, which accounted for 22-34 % of ISP's emissions. Overall, Hg speciation shifted from 50/44/6 (gaseous elemental Hg (Hg0)/gaseous oxidized Hg (HgII)/particulate-bound Hg (Hgp)) in 2000 to 40/59/1 in 2015, which indicated a higher proportion of Hg deposition around the emission points. Future emissions of ISP were expected to decrease based on the comprehensive consideration crude-steel production, steel scrap utilization, energy saving, and pollution control measures.

Surficial weathering of iron sulfide mine tailings under semi-arid climate.

PubMed

Hayes, Sarah M; Root, Robert A; Perdrial, Nicolas; Maier, Raina; Chorover, Jon

2014-09-15

Mine wastes introduce anthropogenic weathering profiles to the critical zone that often remain unvegetated for decades after mining cessation. As such, they are vulnerable to wind and water dispersion of particulate matter to adjacent ecosystems and residential communities. In sulfide-rich ore tailings, propagation to depth of the oxidative weathering front controls the depth-variation in speciation of major and trace elements. Despite the prevalence of surficial mine waste deposits in arid regions of the globe, few prior studies have been conducted to resolve the near-surface profile of sulfide ore tailings weathered under semi-arid climate. We investigated relations between gossan oxidative reaction-front propagation and the molecular speciation of iron and sulfur in tailings subjected to weathering under semi-arid climate at an EPA Superfund Site in semi-arid central Arizona (USA). Here we report a multi-method data set combining wet chemical and synchrotron-based X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES) methods to resolve the tight coupling of iron (Fe) and sulfur (S) geochemical changes in the top 2 m of tailings. Despite nearly invariant Fe and S concentration with depth (130-140 and 100-120 g kg -1 , respectively), a sharp redox gradient and distinct morphological change was observed within the top 0.5 m, associated with a progressive oxidative alteration of ferrous sulfides to (oxyhydr)oxides and (hydroxy)sulfates. Transformation is nearly complete in surficial samples. Trends in molecular-scale alteration were co-located with a decrease in pH from 7.3 to 2.3, and shifts in Fe and S lability as measured via chemical extraction. Initial weathering products, ferrihydrite and gypsum, transform to schwertmannite, then jarosite-group minerals with an accompanying decrease in pH. Interestingly, thermodynamically stable phases such as goethite and hematite were not detected in any samples, but ferrihydrite was observed even in the lowest pH samples, indicating its metastable persistence in these semiarid tailings. The resulting sharp geochemical speciation gradients in close proximity to the tailings surface have important implications for plant colonization, as well as mobility and bioavailability of co-associated toxic metal(loid)s.

Surficial weathering of iron sulfide mine tailings under semi-arid climate

PubMed Central

Hayes, Sarah M.; Root, Robert A.; Perdrial, Nicolas; Maier, Raina; Chorover, Jon

2014-01-01

Mine wastes introduce anthropogenic weathering profiles to the critical zone that often remain unvegetated for decades after mining cessation. As such, they are vulnerable to wind and water dispersion of particulate matter to adjacent ecosystems and residential communities. In sulfide-rich ore tailings, propagation to depth of the oxidative weathering front controls the depth-variation in speciation of major and trace elements. Despite the prevalence of surficial mine waste deposits in arid regions of the globe, few prior studies have been conducted to resolve the near-surface profile of sulfide ore tailings weathered under semi-arid climate. We investigated relations between gossan oxidative reaction-front propagation and the molecular speciation of iron and sulfur in tailings subjected to weathering under semi-arid climate at an EPA Superfund Site in semi-arid central Arizona (USA). Here we report a multi-method data set combining wet chemical and synchrotron-based X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES) methods to resolve the tight coupling of iron (Fe) and sulfur (S) geochemical changes in the top 2 m of tailings. Despite nearly invariant Fe and S concentration with depth (130–140 and 100–120 g kg−1, respectively), a sharp redox gradient and distinct morphological change was observed within the top 0.5 m, associated with a progressive oxidative alteration of ferrous sulfides to (oxyhydr)oxides and (hydroxy)sulfates. Transformation is nearly complete in surficial samples. Trends in molecular-scale alteration were co-located with a decrease in pH from 7.3 to 2.3, and shifts in Fe and S lability as measured via chemical extraction. Initial weathering products, ferrihydrite and gypsum, transform to schwertmannite, then jarosite-group minerals with an accompanying decrease in pH. Interestingly, thermodynamically stable phases such as goethite and hematite were not detected in any samples, but ferrihydrite was observed even in the lowest pH samples, indicating its metastable persistence in these semiarid tailings. The resulting sharp geochemical speciation gradients in close proximity to the tailings surface have important implications for plant colonization, as well as mobility and bioavailability of co-associated toxic metal(loid)s. PMID:25197102

Surficial weathering of iron sulfide mine tailings under semi-arid climate

NASA Astrophysics Data System (ADS)

Hayes, Sarah M.; Root, Robert A.; Perdrial, Nicolas; Maier, Raina M.; Chorover, Jon

2014-09-01

Mine wastes introduce anthropogenic weathering profiles to the critical zone that often remain unvegetated for decades after mining cessation. As such, they are vulnerable to wind and water dispersion of particulate matter to adjacent ecosystems and residential communities. In sulfide-rich ore tailings, propagation to depth of the oxidative weathering front controls the depth-variation in speciation of major and trace elements. Despite the prevalence of surficial mine waste deposits in arid regions of the globe, few prior studies have been conducted to resolve the near-surface profile of sulfide ore tailings weathered under semi-arid climate. We investigated relations between gossan oxidative reaction-front propagation and the molecular speciation of iron and sulfur in tailings subjected to weathering in a semi-arid climate at an EPA Superfund Site in central Arizona (USA). Here we report a multi-method data set combining wet chemical and synchrotron-based X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES) methods to resolve the tight coupling of iron (Fe) and sulfur (S) geochemical changes in the top 2 m of tailings. Despite nearly invariant Fe and S concentration with depth (130-140 and 100-120 g kg-1, respectively), a sharp redox gradient and distinct morphological change was observed within the top 0.5 m, associated with a progressive oxidative alteration of ferrous sulfides to (oxyhydr)oxides and (hydroxy)sulfates. Transformation is nearly complete in surficial samples. Trends in molecular-scale alteration were co-located with a decrease in pH from 7.3 to 2.3, and shifts in Fe and S lability as measured via chemical extraction. Initial weathering products, ferrihydrite and gypsum, transform to schwertmannite, then jarosite-group minerals with an accompanying decrease in pH. Interestingly, thermodynamically stable phases such as goethite and hematite were not detected in any samples, but ferrihydrite was observed even in samples with the lowest pH, indicating its metastable persistence in these semiarid tailings. The resulting sharp geochemical speciation gradients in close proximity to the tailings surface have important implications for plant colonization, as well as mobility and bioavailability of co-associated toxic metal(loid)s.

Key Roles of Size and Crystallinity of Nanosized Iron Hydr(oxides) Stabilized by Humic Substances in Iron Bioavailability to Plants.

PubMed

Kulikova, Natalia A; Polyakov, Alexander Yu; Lebedev, Vasily A; Abroskin, Dmitry P; Volkov, Dmitry S; Pankratov, Denis A; Klein, Olga I; Senik, Svetlana V; Sorkina, Tatiana A; Garshev, Alexey V; Veligzhanin, Alexey A; Garcia Mina, Jose M; Perminova, Irina V

2017-12-27

Availability of Fe in soil to plants is closely related to the presence of humic substances (HS). Still, the systematic data on applicability of iron-based nanomaterials stabilized with HS as a source for plant nutrition are missing. The goal of our study was to establish a connection between properties of iron-based materials stabilized by HS and their bioavailability to plants. We have prepared two samples of leonardite HS-stabilized iron-based materials with substantially different properties using the reported protocols and studied their physical chemical state in relation to iron uptake and other biological effects. We used Mössbauer spectroscopy, XRD, SAXS, and TEM to conclude on iron speciation, size, and crystallinity. One material (Fe-HA) consisted of polynuclear iron(III) (hydr)oxide complexes, so-called ferric polymers, distributed in HS matrix. These complexes are composed of predominantly amorphous small-size components (<5 nm) with inclusions of larger crystalline particles (the mean size of (11 ± 4) nm). The other material was composed of well-crystalline feroxyhyte (δ'-FeOOH) NPs with mean transverse sizes of (35 ± 20) nm stabilized by small amounts of HS. Bioavailability studies were conducted on wheat plants under conditions of iron deficiency. The uptake studies have shown that small and amorphous ferric polymers were readily translocated into the leaves on the level of Fe-EDTA, whereas relatively large and crystalline feroxyhyte NPs were mostly sorbed on the roots. The obtained data are consistent with the size exclusion limits of cell wall pores (5-20 nm). Both samples demonstrated distinct beneficial effects with respect to photosynthetic activity and lipid biosynthesis. The obtained results might be of use for production of iron-based nanomaterials stabilized by HS with the tailored iron availability to plants. They can be applied as the only source for iron nutrition as well as in combination with the other elements, for example, for industrial production of "nanofortified" macrofertilizers (NPK).

Iron Drinking Water Pipe Corrosion Products: Concentrators of Toxic Metals

DTIC Science & Technology

2013-01-01

health risk. In addition Pb corrosion products may be sinks for other metals such as chromium (Cr), copper (Cu), manganese (Mn), and zinc (Zn). These...Vanadium K-Edge X-ray Absorption Near-Edge Structure Interpretation: Application to the Speciation of Vanadium in Oxide Phases from Steel Slag ’, Journal

Thermodynamic Characterization of Iron Oxide-Aqueous Fe(2+) Redox Couples.

PubMed

Gorski, Christopher A; Edwards, Rebecca; Sander, Michael; Hofstetter, Thomas B; Stewart, Sydney M

2016-08-16

Iron is present in virtually all terrestrial and aquatic environments, where it participates in redox reactions with surrounding metals, organic compounds, contaminants, and microorganisms. The rates and extent of these redox reactions strongly depend on the speciation of the Fe2+ and Fe3+ phases, although the underlying reasons remain unclear. In particular, numerous studies have observed that Fe2+ associated with iron oxide surfaces (i.e., oxide-associated Fe2+) often reduces oxidized contaminants much faster than aqueous Fe2+ alone. Here, we tested two hypotheses related to this observation by determining if solutions containing two commonly studied iron oxides—hematite and goethite—and aqueous Fe2+ reached thermodynamic equilibrium over the course of a day. We measured reduction potential (EH) values in solutions containing these oxides at different pH values and aqueous Fe2+ concentrations using mediated potentiometry. This analysis yielded standard reduction potential (EH0) values of 768 ± 1 mV for the aqueous Fe2+–goethite redox couple and 769 ± 2 mV for the aqueous Fe2+–hematite redox couple. These values were in excellent agreement with those calculated from existing thermodynamic data, and the data could be explained by the presence of an iron oxide lowering EH values of aqueous Fe3+/Fe2+ redox couples.

Speciation and distribution of arsenic and localization of nutrients in rice grains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lombi, E.; Scheckel, K.G.; Pallon, J.

2012-09-05

Arsenic (As) contamination of rice grains and the generally low concentration of micronutrients in rice have been recognized as a major concern for human health. Here, we investigated the speciation and localization of As and the distribution of (micro)nutrients in rice grains because these are key factors controlling bioavailability of nutrients and contaminants. Bulk total and speciation analyses using high-pressure liquid chromatography (HPLC)-inductively coupled plasma mass spectrometry (ICP-MS) and X-ray absorption near-edge spectroscopy (XANES) was complemented by spatially resolved microspectroscopic techniques ({mu}-XANES, {mu}-X-ray fluorescence ({mu}-XRF) and particle induced X-ray emission (PIXE)) to investigate both speciation and distribution of As andmore » localization of nutrients in situ. The distribution of As and micronutrients varied between the various parts of the grains (husk, bran and endosperm) and was characterized by element-specific distribution patterns. The speciation of As in bran and endosperm was dominated by As(III)-thiol complexes. The results indicate that the translocation from the maternal to filial tissues may be a bottleneck for As accumulation in the grain. Strong similarities between the distribution of iron (Fe), manganese (Mn) and phosphorus (P) and between zinc (Zn) and sulphur (S) may be indicative of complexation mechanisms in rice grains.« less

Immobilization of selenate by iron in aqueous solution under anoxic conditions and the influence of uranyl

NASA Astrophysics Data System (ADS)

Puranen, Anders; Jonsson, Mats; Dähn, Rainer; Cui, Daqing

2009-08-01

In proposed high level radioactive waste repositories a large part of the spent nuclear fuel (SNF) canisters are commonly composed of iron. Selenium is present in spent nuclear fuel as a long lived fission product. This study investigates the influence of iron on the uptake of dissolved selenium in the form of selenate and the effect of the presence of dissolved uranyl on the above interaction of selenate. The iron oxide, and selenium speciation on the surfaces was investigated by Raman spectroscopy. X-ray Absorption Spectroscopy was used to determine the oxidation state of the selenium and uranium on the surfaces. Under the simulated groundwater conditions (10 mM NaCl, 2 mM NaHCO 3, <0.1 ppm O 2) the immobilized selenate was found to be reduced to oxidation states close to zero or lower and uranyl was found to be largely reduced to U(IV). The near simultaneous reduction of uranyl was found to greatly enhance the rate of selenate reduction. These findings suggest that the presence of uranyl being reduced by an iron surface could substantially enhance the rate of reduction of selenate under anoxic conditions relevant for a repository.

Leaching of Arsenic from Granular Ferric Hydroxide Residuals under Mature Landfill Conditions

PubMed Central

Ghosh, Amlan; Mukiibi, Muhammed; Sáez, A. Eduardo; Ela, Wendell P.

2008-01-01

Most arsenic bearing solid residuals (ABSR) from water treatment will be disposed in non-hazardous landfills. The lack of an appropriate leaching test to predict arsenic mobilization from ABSR creates a need to evaluate the magnitude and mechanisms of arsenic release under landfill conditions. This work studies the leaching of arsenic and iron from a common ABSR, granular ferric hydroxide, in a laboratory-scale column that simulates the biological and physicochemical conditions of a mature, mixed solid waste landfill. The column operated for approximately 900 days and the mode of transport as well as chemical speciation of iron and arsenic changed with column age. Both iron and arsenic were readily mobilized under the anaerobic, reducing conditions. During the early stages of operation, most arsenic and iron leaching (80% and 65%, respectively) was associated with suspended particulate matter and iron was lost proportionately faster than arsenic. In later stages, while the rate of iron leaching declined, the arsenic leaching rate increased greater than 7-fold. The final phase was characterized by dissolved species leaching. Future work on the development of standard batch leaching tests should take into account the dominant mobilization mechanisms identified in this work: solid associated transport, reductive sorbent dissolution, and microbially mediated arsenic reduction. PMID:17051802

Leaching of arsenic from granular ferric hydroxide residuals under mature landfill conditions.

PubMed

Ghosh, Amlan; Mukiibi, Muhammed; Sáez, A Eduardo; Ela, Wendell P

2006-10-01

Most arsenic bearing solid residuals (ABSR) from water treatment will be disposed in nonhazardous landfills. The lack of an appropriate leaching test to predict arsenic mobilization from ABSR creates a need to evaluate the magnitude and mechanisms of arsenic release under landfill conditions. This work studies the leaching of arsenic and iron from a common ABSR, granular ferric hydroxide, in a laboratory-scale column that simulates the biological and physicochemical conditions of a mature, mixed solid waste landfill. The column operated for approximately 900 days and the mode of transport as well as chemical speciation of iron and arsenic changed with column age. Both iron and arsenic were readily mobilized under the anaerobic, reducing conditions. During the early stages of operation, most arsenic and iron leaching (80% and 65%, respectively) was associated with suspended particulate matter, and iron was lost proportionately faster than arsenic. In later stages, while the rate of iron leaching declined, the arsenic leaching rate increased greater than 7-fold. The final phase was characterized by dissolved species leaching. Future work on the development of standard batch leaching tests should take into account the dominant mobilization mechanisms identified in this work: solid associated transport, reductive sorbent dissolution, and microbially mediated arsenic reduction.

Iron solubility related to particle sulfur content in source emission and ambient fine particles.

PubMed

Oakes, M; Ingall, E D; Lai, B; Shafer, M M; Hays, M D; Liu, Z G; Russell, A G; Weber, R J

2012-06-19

The chemical factors influencing iron solubility (soluble iron/total iron) were investigated in source emission (e.g., biomass burning, coal fly ash, mineral dust, and mobile exhaust) and ambient (Atlanta, GA) fine particles (PM2.5). Chemical properties (speciation and mixing state) of iron-containing particles were characterized using X-ray absorption near edge structure (XANES) spectroscopy and micro-X-ray fluorescence measurements. Bulk iron solubility (soluble iron/total iron) of the samples was quantified by leaching experiments. Major differences were observed in iron solubility in source emission samples, ranging from low solubility (<1%, mineral dust and coal fly ash) up to 75% (mobile exhaust and biomass burning emissions). Differences in iron solubility did not correspond to silicon content or Fe(II) content. However, source emission and ambient samples with high iron solubility corresponded to the sulfur content observed in single particles. A similar correspondence between bulk iron solubility and bulk sulfate content in a series of Atlanta PM2.5 fine particle samples (N = 358) further supported this trend. In addition, results of linear combination fitting experiments show the presence of iron sulfates in several high iron solubility source emission and ambient PM2.5 samples. These results suggest that the sulfate content (related to the presence of iron sulfates and/or acid-processing mechanisms by H(2)SO(4)) of iron-containing particles is an important proxy for iron solubility.

Sulfidization of Organic Freshwater Flocs from a Minerotrophic Peatland: Speciation Changes of Iron, Sulfur, and Arsenic.

PubMed

ThomasArrigo, Laurel K; Mikutta, Christian; Lohmayer, Regina; Planer-Friedrich, Britta; Kretzschmar, Ruben

2016-04-05

Iron-rich organic flocs are frequently observed in surface waters of wetlands and show a high affinity for trace metal(loid)s. Under low-flow stream conditions, flocs may settle, become buried, and eventually be subjected to reducing conditions facilitating trace metal(loid) release. In this study, we reacted freshwater flocs (704-1280 mg As/kg) from a minerotrophic peatland (Gola di Lago, Switzerland) with sulfide (5.2 mM, S(-II)spike/Fe = 0.75-1.62 mol/mol) at neutral pH and studied the speciation changes of Fe, S, and As at 25 ± 1 °C over 1 week through a combination of synchrotron X-ray techniques and wet-chemical analyses. Sulfidization of floc ferrihydrite and nanocrystalline lepidocrocite caused the rapid formation of mackinawite (52-81% of Fesolid at day 7) as well as solid-phase associated S(0) and polysulfides. Ferrihydrite was preferentially reduced over lepidocrocite, although neoformation of lepidocrocite from ferrihydrite could not be excluded. Sulfide-reacted flocs contained primarily arsenate (47-72%) which preferentially adsorbed to Fe(III)-(oxyhydr)oxides, despite abundant mackinawite precipitation. At higher S(-II)spike/Fe molar ratios (≥1.0), the formation of an orpiment-like phase accounted for up to 35% of solid-phase As. Despite Fe and As sulfide precipitation and the presence of residual Fe(III)-(oxyhydr)oxides, mobilization of As was recorded in all samples (Asaq = 0.45-7.0 μM at 7 days). Aqueous As speciation analyses documented the formation of thioarsenates contributing up to 33% of Asaq. Our findings show that freshwater flocs from the Gola di Lago peatland may become a source of As under sulfate-reducing conditions and emphasize the pivotal role Fe-rich organic freshwater flocs play in trace metal(loid) cycling in S-rich wetlands characterized by oscillating redox conditions.

IroN, a Novel Outer Membrane Siderophore Receptor Characteristic of Salmonella enterica

PubMed Central

Bäumler, Andreas J.; Norris, Tracy L.; Lasco, Todd; Voigt, Wolfgang; Reissbrodt, Rolf; Rabsch, Wolfgang; Heffron, Fred

1998-01-01

Speciation in enterobacteria involved horizontal gene transfer. Therefore, analysis of genes acquired by horizontal transfer that are present in one species but not its close relatives is expected to give insights into how new bacterial species were formed. In this study we characterize iroN, a gene located downstream of the iroBC operon in the iroA locus of Salmonella enterica serotype Typhi. Like iroBC, the iroN gene is present in all phylogenetic lineages of S. enterica but is absent from closely related species such as Salmonella bongori or Escherichia coli. Comparison of the deduced amino acid sequence of iroN with other proteins suggested that this gene encodes an outer membrane siderophore receptor protein. Mutational analysis in S. enterica and expression in E. coli identified a 78-kDa outer membrane protein as the iroN gene product. When introduced into an E. coli fepA cir fiu aroB mutant on a cosmid, iroN mediated utilization of structurally related catecholate siderophores, including N-(2,3-dihydroxybenzoyl)-l-serine, myxochelin A, benzaldehyde-2,3-dihydroxybenzhydrazone, 2-N,6-N-bis(2,3-dihydroxybenzoyl)-l-lysine, 2-N,6-N-bis(2,3-dihydroxybenzoyl)-l-lysine amide, and enterochelin. These results suggest that the iroA locus functions in iron acquisition in S. enterica. PMID:9515912

Iron persistence in a distal hydrothermal plume supported by dissolved-particulate exchange

NASA Astrophysics Data System (ADS)

Fitzsimmons, Jessica N.; John, Seth G.; Marsay, Christopher M.; Hoffman, Colleen L.; Nicholas, Sarah L.; Toner, Brandy M.; German, Christopher R.; Sherrell, Robert M.

2017-02-01

Hydrothermally sourced dissolved metals have been recorded in all ocean basins. In the oceans' largest known hydrothermal plume, extending westwards across the Pacific from the Southern East Pacific Rise, dissolved iron and manganese were shown by the GEOTRACES program to be transported halfway across the Pacific. Here, we report that particulate iron and manganese in the same plume also exceed background concentrations, even 4,000 km from the vent source. Both dissolved and particulate iron deepen by more than 350 m relative to 3He--a non-reactive tracer of hydrothermal input--crossing isopycnals. Manganese shows no similar descent. Individual plume particle analyses indicate that particulate iron occurs within low-density organic matrices, consistent with its slow sinking rate of 5-10 m yr-1. Chemical speciation and isotopic composition analyses reveal that particulate iron consists of Fe(III) oxyhydroxides, whereas dissolved iron consists of nanoparticulate Fe(III) oxyhydroxides and an organically complexed iron phase. The descent of plume-dissolved iron is best explained by reversible exchange onto slowly sinking particles, probably mediated by organic compounds binding iron. We suggest that in ocean regimes with high particulate iron loadings, dissolved iron fluxes may depend on the balance between stabilization in the dissolved phase and the reversibility of exchange onto sinking particles.

High-Iron Biosolids Compost-Induced Changes in Lead and Arsenic Speciation and Bioaccessibility in Co-contaminated Soils

EPA Science Inventory

The safety of urban farming has been questioned due to the potential for contamination in urban soils. A laboratory incubation, a field trial, and a second laboratory incubation were conducted to test the ability of high-Fe biosolids–based composts to reduce the bioaccessibil...

Speciation And Distribution Of Vanadium In Drinking Water Iron Pipe Corrosion By-Products

EPA Science Inventory

Vanadium (V) when ingested from drinking water in high concentrations (> 15 µg L^-1) is a potential health risk and is on track to becoming a regulated contaminant. High concentrations of V have been documented in lead corrosion by-products as Pb₅(V⁵⁺

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Euan; Kempson, Ivan; Juhasz, Albert L.

The consumption of arsenic (As) contaminated rice is an important exposure route for humans in countries where rice cultivation employs As contaminated irrigation water. Arsenic toxicity and mobility are a function of its chemical-speciation. The distribution and identification of As in the rice plant are hence necessary to determine the uptake, transformation and potential risk posed by As contaminated rice. In this study we report on the distribution and chemical-speciation of As in rice (Oryza sativa Quest) by X-ray fluorescence (XRF) and X-ray absorption near edge structure (XANES) measurements of rice plants grown in As contaminated paddy water. Investigations ofmore » {mu}XRF images from rice tissues found that As was present in all rice tissues, and its presence correlated with the presence of iron at the root surface and copper in the rice leaf. X-ray absorption near edge structure analysis of rice tissues identified that inorganic As was the predominant form of As in all rice tissues studied, and that arsenite became increasingly dominant in the aerial portion of the rice plant.« less

Iron chelates: a challenge to chemists and Mössbauer spectroscopists

NASA Astrophysics Data System (ADS)

Homonnay, Z.; Szilágyi, P. Á.; Vértes, A.; Kuzmann, E.; Sharma, V. K.; Molnár, G.; Bousseksou, A.; Grenèche, J.-M.; Brausam, A.; Meier, R.; van Eldik, R.

2008-02-01

The speciation of iron in aqueous solutions containing Fe3 + and selected chelates such as EDTA, EDDA, CDTA and HEDTA has been studied using transmission 57Fe Mössbauer spectrometry in frozen solutions. The protonation of various complexes as well as binuclear complex formation could be detected as a function of pH. Autoreduction of Fe3 + to Fe2 + was observed in several cases. Reaction with hydrogen peroxide proved to be rather different for the four ligands, while the dihapto complex [XFe( η 2-O2)]3 - had surprisingly identical Mössbauer parameters for X = EDTA, CDTA or HEDTA. Paramagnetic spin relaxation observed in the Mössbauer spectra was found to be strongly influenced by the identity of the chelating ligand, despite the basically spin-spin origin of the phenomenon.

Effect of nanoscale zero-valent iron and magnetite (Fe3O4) on the fate of metals during anaerobic digestion of sludge.

PubMed

Suanon, Fidèle; Sun, Qian; Mama, Daouda; Li, Jiangwei; Dimon, Biaou; Yu, Chang-Ping

2016-01-01

Anaerobic digestion (AD) is one of the most widely used processes to stabilize waste sewage sludge and produce biogas renewable energy. In this study, two different iron nanoparticles [nanoscale zero-valent iron (nZVI) and magnetite (Fe3O4)] were used in the mesophilic AD processes (37 ± 1 °C) to improve biogas production. In addition, changes of heavy metal (Cd, Co, Cu, Zn, Ni and Cr) speciation during AD of sludge with and without iron nanoparticles have been investigated. Concentrations of metals in the initial sludge were as follows: 63.1, 73.4, 1102.2, 2060.3, 483.9 and 604.1 mg kg(-1) (dry sludge basis) for Cd, Co, Cu, Zn, Ni and Cr, respectively. Sequential fractionation showed that metals were predominantly bonded to organic matter and carbonates in the initial sludge. Compared with AD without iron nanoparticles, the application of iron nanoparticles (at dose of 0.5% in this study) showed positive impact not only on biogas production, but also on improvement of metals stabilization in the digestate. Metals were found concentrated in Fe-Mn bound and residual fractions and little was accumulated in the liquid digestate and most mobile fractions of solid digestate (water soluble, exchangeable and carbonates bound). Therefore, iron nanoparticles when properly used, could improve not only biogas yield, but also regulate and control the mobilization of metals during AD process. However, our study also observed that iron nanoparticles could promote the immobilization of phosphorus within the sludge during AD, and more research is needed to fully address the mechanism behind this phenomenon and the impact on future phosphorus reuse. Copyright © 2015 Elsevier Ltd. All rights reserved.

Controls on the Fate and Speciation of Np(V) During Iron (Oxyhydr)oxide Crystallization.

PubMed

Bots, Pieter; Shaw, Samuel; Law, Gareth T W; Marshall, Timothy A; Mosselmans, J Frederick W; Morris, Katherine

2016-04-05

The speciation and fate of neptunium as Np(V)O2(+) during the crystallization of ferrihydrite to hematite and goethite was explored in a range of systems. Adsorption of NpO2(+) to iron(III) (oxyhydr)oxide phases was reversible and, for ferrihydrite, occurred through the formation of mononuclear bidentate surface complexes. By contrast, chemical extractions and X-ray absorption spectroscopy (XAS) analyses showed the incorporation of Np(V) into the structure of hematite during its crystallization from ferrihydrite (pH 10.5). This occurred through direct replacement of octahedrally coordinated Fe(III) by Np(V) in neptunate-like coordination. Subsequent analyses on mixed goethite and hematite crystallization products (pH 9.5 and 11) showed that Np(V) was incorporated during crystallization. Conversely, there was limited evidence for Np(V) incorporation during goethite crystallization at the extreme pH of 13.3. This is likely due to the formation of a Np(V) hydroxide precipitate preventing incorporation into the goethite particles. Overall these data highlight the complex behavior of Np(V) during the crystallization of iron(III) (oxyhydr)oxides, and demonstrate clear evidence for neptunium incorporation into environmentally important mineral phases. This extends our knowledge of the range of geochemical conditions under which there is potential for long-term immobilization of radiotoxic Np in natural and engineered environments.

Variability of the health effects of crystalline silica: Fe speciation in industrial quartz reagents and suspended dusts—insights from XAS spectroscopy

NASA Astrophysics Data System (ADS)

Di Benedetto, Francesco; D'Acapito, Francesco; Capacci, Fabio; Fornaciai, Gabriele; Innocenti, Massimo; Montegrossi, Giordano; Oberhauser, Werner; Pardi, Luca A.; Romanelli, Maurizio

2014-03-01

We investigated the speciation of Fe in bulk and in suspended respirable quartz dusts coming from ceramic and iron-casting industrial processes via X-ray absorption spectroscopy, with the aim of contributing to a better understanding of the variability of crystalline silica toxicity. Four different bulk industrial quartz powders, nominally pure quartz samples with Fe contents below 200 ppm, and three respirable dusts filters were selected. Fe speciation was determined in all samples through a coupled study of the X-ray absorption near-edge structure and extended X-ray absorption fine structure regions, operating at the Fe-K edge. Fe speciation revealed common features at the beginning of the different production processes, whereas significant differences were observed on both respirable dusts and bulk dusts exiting from the production process. Namely, a common pollution of the raw quartz dusts by elemental Fe was evidenced and attributed to residuals of the industrial production of quartz materials. Moreover, the respirable samples indicated that reactivity occurs after the suspension of the powders in air. The gravitational selection during the particle suspension consistently allowed us to clearly discriminate between suspended and bulk dusts. On the basis of the obtained results, we provide an apparent spectroscopic discrimination between the raw materials used in the considered industrial processes, and those that are effectively inhaled by workers. In particular, an amorphous FeIII oxide, with an unsaturated coordination sphere, can be related to silica reactivity (and health consequences).

Size-separated particle fractions of stainless steel welding fume particles - A multi-analytical characterization focusing on surface oxide speciation and release of hexavalent chromium.

PubMed

Mei, N; Belleville, L; Cha, Y; Olofsson, U; Odnevall Wallinder, I; Persson, K-A; Hedberg, Y S

2018-01-15

Welding fume of stainless steels is potentially health hazardous. The aim of this study was to investigate the manganese (Mn) and chromium (Cr) speciation of welding fume particles and their extent of metal release relevant for an inhalation scenario, as a function of particle size, welding method (manual metal arc welding, metal arc welding using an active shielding gas), different electrodes (solid wires and flux-cored wires) and shielding gases, and base alloy (austenitic AISI 304L and duplex stainless steel LDX2101). Metal release investigations were performed in phosphate buffered saline (PBS), pH 7.3, 37°, 24h. The particles were characterized by means of microscopic, spectroscopic, and electroanalytical methods. Cr was predominantly released from particles of the welding fume when exposed in PBS [3-96% of the total amount of Cr, of which up to 70% as Cr(VI)], followed by Mn, nickel, and iron. Duplex stainless steel welded with a flux-cored wire generated a welding fume that released most Cr(VI). Nano-sized particles released a significantly higher amount of nickel compared with micron-sized particle fractions. The welding fume did not contain any solitary known chromate compounds, but multi-elemental highly oxidized oxide(s) (iron, Cr, and Mn, possibly bismuth and silicon). Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Following iron speciation in the early stages of magnetite magnetosome biomineralization

DOE PAGES

Firlar, Emre; Perez-Gonzalez, Teresa; Olszewska, Agata; ...

2016-02-26

Understanding magnetosome magnetite biomineralization is of fundamental interest to devising the strategies for bioinspired synthesis of magnetic materials at the nanoscale. Thus, we investigated the early stages of magnetosome formation in this work and correlated the size and emergent crystallinity of magnetosome nanoparticles with the changes in chemical environment of iron and oxygen by utilizing advanced analytical electron microscopy techniques. We observed that magnetosomes in the early stages of biomineralization with the sizes of 5–10 nm were amorphous, with a majority of iron present as Fe 3+, indicative of ferric hydroxide. The magnetosomes with intermediate sizes showed partially crystalline structuremore » with a majority of iron present as Fe 3+ and trace amounts of Fe 2+. The fully maturated magnetosomes were indexed to magnetite. Furthermore, our approach provides spatially resolved structural and chemical information of individual magnetosomes with different particle sizes, attributed to magnetosomes at different stages of biomineralization.« less

ARSENIC SPECIATION, SEASONAL TRANSFORMATIONS, AND CO-DISTRIBUTION WITH IRON IN A MINE WASTE-INFLUENCED PALUSTRINE EMERGENT WETLAND. (R825399)

EPA Science Inventory

Arsenic is commonly associated with mined ores and thus may be detrimental to naturally occurring wetlands that reside in mine waste-impacted regions. Understanding the relationship between Fe and As in both the aqueous and solid phase is critical for assessing the risk As impose...

Schwertmannite stability in acidified coastal environments

NASA Astrophysics Data System (ADS)

Collins, Richard N.; Jones, Adele M.; Waite, T. David

2010-01-01

A combination of analytical and field measurements has been used to probe the speciation and cycling of iron in coastal lowland acid sulfate soils. Iron K-edge EXAFS spectroscopy demonstrated that schwertmannite dominated (43-77%) secondary iron mineralization throughout the oxidized and acidified soil profile, while pyrite and illite were the major iron-bearing minerals in the reduced potential acid sulfate soil layers. Analyses of contemporary precipitates from shallow acid sulfate soil groundwaters indicated that 2-line ferrihydrite, in addition to schwertmannite, is presently controlling secondary Fe(III) mineralization. Although aqueous pH values and concentrations of Fe(II) were seasonally high, no evidence was obtained for the Fe(II)-catalyzed crystallization of either mineral to goethite. The results of this study indicate that: (a) schwertmannite is likely to persist in coastal lowland acid sulfate soils on a much longer time-scale than predicted by laboratory experiments; (b) this mineral is less reactive in these types of soils due to surface-site coverage by components such as silicate and possibly, to a lesser extent, natural organic matter and phosphate and; (c) active water table management to promote oxic/anoxic cycles around the Fe(II)-Fe(III) redox couple, or reflooding of these soils, will be ineffective in promoting the Fe(II)-catalyzed transformation of either schwertmannite or 2-line ferrihydrite to crystalline iron oxyhydroxides.

Can sediments at hydrocarbon seep sites represent a source for marine bioavailable iron? — A case study from the South China Sea

NASA Astrophysics Data System (ADS)

Li, N.; Feng, D.; Chen, D.

2017-12-01

Niu Li1, Dong Feng1,2, and Duofu Chen2,31CAS Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China. 2Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China. 3Hadal Science and Technology Research Center, College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China. Iron is an essential micronutrient and commonly considered to be one of the key-limiting factors for biological productivity in many ocean regions. Seafloor Fe supply should be most efficient in suboxic conditions. Recent studies shown that widely spread anoxic environments can develop in hydrocarbon seep sediment and local bottom water, owing to the occurrence of aerobic and/or anaerobic methane oxidation. Under this condition, the iron in sediment can be reduced to dissolved Fe2+ in the ocean. However, questions remain about whether the hydrocarbon seep sediment can represent a source for bioavailable iron to the ocean, and the control factor for the transformation of iron in the sediment remains largely unexplored. For a number of hydrocarbon seeps from the northern and southern South China Sea, the iron speciation, pyrite sulfur isotope, and iron isotope, as well as the major and trace elements are used to constrain the intensity of cold seep, and its impact on transformation of iron in sediment. Samples from both areas show sediment iron lost during the high methane flux conditions, owing to the suboxic conditions cause by aerobic methane oxidation. On the other hand, high sediment iron content accompanied by high sulfur content can be seen during the conditions of high methane flux without the occurrence of aerobic methane oxidation, which is possible ascribed to the anaerobic methane oxidation and the release of iron through seep activity. This study reveals the transformation of iron in the sediment is closely related to the methane flux and the hydrocarbon seep sediment can represent a source for bioavailable iron to the ocean. Acknowledgments: Funding was provided by the NSF of China (Grants: 41422602 and 41373085).

Manganese and iron geochemistry in sediments underlying the redox-stratified Fayetteville Green Lake

NASA Astrophysics Data System (ADS)

Herndon, Elizabeth M.; Havig, Jeff R.; Singer, David M.; McCormick, Michael L.; Kump, Lee R.

2018-06-01

Manganese and iron are redox-sensitive elements that yield clues about biogeochemistry and redox conditions both in modern environments and in the geologic past. Here, we investigated Mn and Fe-bearing minerals preserved in basin sediments underlying Fayetteville Green Lake, a redox-stratified lake that serves as a geochemical analogue for Paleoproterozoic oceans. Synchrotron-source microprobe techniques (μXRF, μXANES, and μXRD) and bulk geochemical analyses were used to examine the microscale distribution and speciation of Mn, Fe, and S as a function of depth in the top 48 cm of anoxic lake sediments. Manganese was primarily associated with calcite grains as a manganese-rich carbonate that precipitated in the chemocline of the water column and settled through the euxinic basin to collect in lake sediments. Iron was preserved in framboidal iron sulfides that precipitated in euxinic bottom waters and underwent transformation to pyrite and marcasite in the sediments. Previous studies attribute the formation of manganese-rich carbonates to the diagenetic alteration of manganese oxides deposited in basins underlying oxygenated water. Our study challenges this paradigm by providing evidence that Mn-bearing carbonates form in the water column and accumulate in sediments below anoxic waters. Consequently, manganoan carbonates preserved in the rock record do not necessarily denote the presence of oxygenated bottom waters in ocean basins.

An improved leaping detector for flow analysis applied to iron speciation in drugs

PubMed Central

Santos, Sérgio R. B.; Araújo, Mário C. U.; Honorato, Ricardo S.; Zagatto, Elias A. G.; Lima, José F. C.; Lapa, Rui A. S.

2000-01-01

A low inner volume (ca. 64 ml) probe was built up in an injector-commutator in order to behave as a photometric leaping detector in flow analysis. It comprises a bicolour light-emitting diode (BLED), as a source of pulsed radiation in the red and green visible region, and two phototransistors as transducers. Sample injection, detector relocation, analytical signal recording, data treatment and definition of the spectral working range were computer-controlled. The feasibility of the system was initially demonstrated in the flow-injection speciation of iron, and the overall standard deviation of results was estimated as ± 1.6 and ± 1.4% for 1.6–4.0 mg l−1 Fe(II) or total iron after eightfold processing of synthetic samples. The system was further applied to drug analysis: the mean deviations of results for typical samples were estimated as ± 5.2 and ± 3.3%, and the relative standard deviation as ± 1.6 and ± 1.3% for Fe(II) and total iron, respectively. Results were compared with those obtained by a conventional spectrophotometric procedure and no statistic differences at the 95% confidence level were found. In relation to an earlier system with multi-site detection, the proposed system is more stable, presenting low drift with a relative standard deviation of 0.026% and 0.039% for measurements (n=120 during 4 h of observation) with green and red emission. It is also faster with a sampling rate of 133 h−1 and carryover problems are not found. The possibility of compensating the Schlieren noise by dual-wavelength spectrophotometry is discussed. PMID:18924860

The global record of local iron geochemical data from Proterozoic through Paleozoic basins

NASA Astrophysics Data System (ADS)

Sperling, E. A.; Wolock, C.; Johnston, D. T.; Knoll, A. H.

2013-12-01

Iron-based redox proxies represent one of the most mature tools available to sedimentary geochemists. These techniques, which benefit from decades of refinement, are based on the fact that rocks deposited under anoxic conditions tend to be enriched in highly-reactive iron. However, there are myriad local controls on the development of anoxia, and no local section is an exemplar for the global ocean. The global signal must thus be determined using techniques like those developed to solve an analogous problem in paleobiology: the inference of global diversity patterns through time from faunas seen in local stratigraphic sections. Here we analyze a dataset of over 4000 iron speciation measurements (including over 600 de novo analyses) to better understand redox changes from the Proterozoic through the Paleozoic Era. Preliminary database analyses yield interesting observations. We find that although anoxic water columns in the middle Proterozoic were dominantly ferruginous, there was a statistical tendency towards euxinia not seen in early Neoproterozoic or Ediacaran data. Also, we find that in the Neoproterozoic oceans, oxic depositional environments-the likely home for early animals-have exceptionally low pyrite contents, and by inference low levels of porewater sulfide. This runs contrary to notions of sulfide stress on early metazoans. Finally, the current database of iron speciation data does not support an Ediacaran or Cambrian oxygenation event. This conclusion is of course only as sharp as the ability of the Fe-proxy database to track dissolved oxygen and does not rule out the possibility of a small-magnitude change in oxygen. It does suggest, however, that if changing pO2 facilitated animal diversification it did so by a limited rise past critical ecological thresholds, such as seen in the modern Oxygen Minimum Zones benthos. Oxygen increase to modern levels thus becomes a Paleozoic problem, and one in need of better sampling if a database approach is to be employed.

Theoretical speciation of ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid (o,p-EDDHA) in agronomic conditions.

PubMed

Yunta, Felipe; García-Marco, Sonia; Lucena, Juan J

2003-08-27

The presence of ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid (o,p-EDDHA) as the second largest component in commercial EDDHA iron chelates has recently been demonstrated. Here is reported the speciation of o,p-EDDHA by the application of a novel methodology through the determination of the complexing capacity, protonation, and Ca(2+), Mg(2+), Cu(2+), and Fe(3+) stability constants. The pM values and species distribution in solution, hydroponic, and soil conditions were obtained. Due to the para position of one phenol group in o,p-EDDHA, the protonation constants and Ca and Mg stability constants have different values from those of o,o-EDDHA and p,p-EDDHA regioisomers. o,p-EDDHA/Fe(3+) stability constants are higher than those of EDTA/Fe(3+) but lower than those of o,o-EDDHA/Fe(3+). The sequence obtained for pFe is o,o-EDDHA/Fe(3+) >/= o,p-EDDHA/Fe(3+) > EDTA/Fe(3+). o,p-EDDHA/Fe(3+) can be used as an iron chelate in hydroponic conditions. Also, it can be used in soils with limited Cu availability.

Sulfur and Iron Speciation in Gas-rich Impact-melt Glasses from Basaltic Shergottites Determined by Microxanes

NASA Technical Reports Server (NTRS)

Sutton, S. R.; Rao, M. N.; Nyquist, L. E.

2008-01-01

Sulfur is abundantly present as sulfate near Martian surface based on chemical and mineralogical investigations on soils and rocks in Viking, Pathfinder and MER missions. Jarosite is identified by Mossbauer studies on rocks at Meridian and Gusev, whereas MgSO4 is deduced from MgO - SO3 correlations in Pathfinder MER and Viking soils. Other sulfate minerals such as gypsum and alunogen/ S-rich aluminosilicates and halides are detected only in martian meteorites such as shergottites and nakhlites using SEM/FE-SEM and EMPA techniques. Because sulfur has the capacity to occur in multiple valence states, determination of sulfur speciation (sulfide/ sulfate) in secondary mineral assemblages in soils and rocks near Mars surface may help us understand whether the fluid-rock interactions occurred under oxidizing or reducing conditions. To understand the implications of these observations for the formation of the Gas-rich Impact-melt (GRIM) glasses, we determined the oxidation state of Fe in the GRIM glasses using Fe K micro-XANES techniques.

Chemistry of volcanic soils used for agriculture in Brava Island (Cape Verde)

NASA Astrophysics Data System (ADS)

Prudêncio, Maria Isabel; Marques, Rosa; Waerenborgh, João Carlos; José Vieira, Bruno; Dias, Maria Isabel; Rocha, Fernando

2017-04-01

Brava is a small volcanic island located on the south-western part of the Cape Verde archipelago. It is characterized by an irregular plateau between 300 and 976 m above sea level, which is bounded by steep coastal cliffs and cut by fluvial incision in a generally radial drainage pattern. The major volcano-stratigraphic units of the island are: Lower Unit, Middle Unit, Upper Unit, and Sediments. Although Brava is one of the islands with more frequent rainy periods in Cape Verde, the climate is essentially semi-arid, which associated with the rough topography leads to incipient soils. Detailed Fe speciation and chemical composition studies of Cape Verde soils have shown that oxidation is a major weathering mechanism, and high contents of trace elements may occur originated from imbalance of elements in the volcanic parent materials, which can be a threat to the environmental health. The soils mostly used for agriculture in Brava Island are those developed on phonolitic pyroclasts on the plateau and also on sediments. In this work the whole sample (< 2 mm) and the clay-sized fraction (< 2 µm) of these soils were analysed by Mössbauer spectroscopy and neutron activation analysis, aiming to characterize the iron speciation and to determine the concentration and distribution of 30 chemical elements in Brava soils. Mössbauer spectroscopy shows that Fe is more oxidyzed in topsoils developed on sediments (84-87%) than in soils developed on pyroclasts (71-79%). In the clay sized-fraction of all the studied soils only Fe(III) was detected. Iron oxides clearly distinguish the soils derived from the two types of parent materials, hematite being the only Fe oxide present in soils developed on sediments, while maghemite is more abundant in soils developed on pyroclasts. Iron and chromium are depleted in this fine fraction suggesting their occurrence as iron oxides and ferromagnesian minerals present in coarser particles. Among the chemical elements studied, antimony was found to be particularly concentrated in the clay-sized fraction (up to 28 mg/kg) in soils located in the northern part of the island. The existence of significant Sb amounts in the fine particles may contribute to its accumulation in plants both by absorption or by dust deposition onto the plant leaves.

High methylmercury production under ferruginous conditions in sediments impacted by sewage treatment plant discharges.

PubMed

Bravo, Andrea G; Bouchet, Sylvain; Guédron, Stéphane; Amouroux, David; Dominik, Janusz; Zopfi, Jakob

2015-09-01

Sewage treatment plants (STPs) are important point sources of mercury (Hg) to the environment. STPs are also significant sources of iron when hydrated ferric oxide (HFO) is used as a dephosphatation agent during water purification. In this study, we combined geochemical and microbiological characterization with Hg speciation and sediment amendments to evaluate the impact of STP's effluents on monomethylmercury (MMHg) production. The highest in-situ Hg methylation was found close to the discharge pipe in subsurface sediments enriched with Hg, organic matter, and iron. There, ferruginous conditions were prevailing with high concentrations of dissolved Fe(2+) and virtually no free sulfide in the porewater. Sediment incubations demonstrated that the high MMHg production close to the discharge was controlled by low demethylation yields. Inhibition of dissimilatory sulfate reduction with molybdate led to increased iron reduction rates and Hg-methylation, suggesting that sulfate-reducing bacteria (SRB) may not have been the main Hg methylators under these conditions. However, Hg methylation in sediments amended with amorphous Fe(III)-oxides was only slightly higher than control conditions. Thus, in addition to iron-reducing bacteria, other non-SRB most likely contributed to Hg methylation. Overall, this study highlights that sediments impacted by STP discharges can become local hot-spots for Hg methylation due to the combined inputs of i) Hg, ii) organic matter, which fuels bacterial activities and iii) iron, which keeps porewater sulfide concentration low and hence Hg bioavailable. Copyright © 2015 Elsevier Ltd. All rights reserved.

Oxidation States of Grim Glasses in EET79001 Based on Vanadium Valence

NASA Technical Reports Server (NTRS)

Sutton, S. R.; Rao, M. N.; Nyquist, L. E.

2010-01-01

Gas-rich impact-melt (GRIM) glasses in SNC meteorites are very rich in Martian atmospheric noble gases and sulfur suggesting a possible occurrence of regolith-derived secondary mineral assemblages in these samples. Previously, we have studied two GRIM glasses, 506 and 507, from EET79001 Lith A and Lith B, respectively, for elemental abundances and spatial distribution of sulfur using EMPA (WDS) and FE-SEM (EDS) techniques and for sulfur-speciation using K-edge XANES techniques. These elemental and FE-SEM micro-graph data at several locations in the GRIM glasses from Shergotty (DBS), Zagami 994 and EET79001, Lith B showed that FeO and SO3 are positively correlated (SO3 represents a mixture of sulfide and sulfate). FE-SEM (EDS) study revealed that the sulfur-rich pockets in these glasses contain numerous micron-sized iron-sulfide (Fe-S) globules sequestered throughout the volume. However, in some areas (though less frequently), we detected significant Fe-S-O signals suggesting the occurrence of iron sulfate. These GRIM glasses were studied by K-edge microXANES techniques for sulfur speciation in association with iron in sulfur-rich areas. In both samples, we found the sulfur speciation dominated by sulfide with minor oxidized sulfur mixed in with various proportions. The abundance of oxidized sulfur was greater in 506 than in 507. Based on these results, we hypothesize that sulfur initially existed as sulfate in the glass precursor materials and, on shock-impact melting of the precursor materials producing these glasses, the oxidized sulfur was reduced to predominately sulfide. In order to further test this hypothesis, we have used microXANES to measure the valence states of vanadium in GRIM glasses from Lith A and Lith B to complement and compare with previous analogous measurements on Lith C (note: 506 and 507 contain the largest amounts of martian atmospheric gases but the gas-contents in Lith C measured by are unknown). Vanadium is ideal for addressing this re-dox issue because it has multiple valence states and is a well-studied element. Ferrous-dominated iron valences determined by microXANES on the Lith A and Lith B glasses provide little redox sensitivity. Vanadium valence measurements for impact glass in Lith C at three different locations yielded valence values of 3.1, 3.2 and 3.4 with inferred fO2 values of IW-0.7, IW-0.1 and IW+0.7, respectively. This range of oxygen-fugacity values is understandable because the glasses are shock-molten impact glasses which are heterogeneous in nature. Oxygen fugacity values obtained from the analysis of Fe-Ti oxides and Eu partitioning in pyroxenes from EET79001 Lith A and Lith B (host lithologies) were in the range of IW+0.3 to IW+1.9 suggesting that V in the Lith C impact glass was reduced in the impact process. Here, we examine whether the 506 from Lith A and 507 from Lith B GRIM glasses yield similar or different fO2 values from those of Lith C using the vanadium K-edge microXANES technique.

Derivation of Pitzer Interaction Parameters for an Aqueous Species Pair of Sodium and Iron(II)-Citrate Complex

NASA Astrophysics Data System (ADS)

Jang, J. H.; Nemer, M.

2015-12-01

The U.S. DOE Waste Isolation Pilot Plant (WIPP) is a deep underground repository for the permanent disposal of transuranic (TRU) radioactive waste. The WIPP is located in the Permian Delaware Basin near Carlsbad, New Mexico, U.S.A. The TRU waste includes, but is not limited to, iron-based alloys and the complexing agent, citric acid. Iron is also present from the steel used in the waste containers. The objective of this analysis is to derive the Pitzer activity coefficients for the pair of Na+ and FeCit- complex to expand current WIPP thermodynamic database. An aqueous model for the dissolution of Fe(OH)2(s) in a Na3Cit solution was fitted to the experimentally measured solubility data. The aqueous model consists of several chemical reactions and related Pitzer interaction parameters. Specifically, Pitzer interaction parameters for the Na+ and FeCit- pair (β(0), β(1), and Cφ) plus the stability constant for species of FeCit- were fitted to the experimental data. Anoxic gloveboxes were used to keep the oxygen level low (<1 ppm) throughout the experiments due to redox sensitivity. EQ3NR, a computer program for geochemical aqueous speciation-solubility calculations, packaged in EQ3/6 v.8.0a, calculates the aqueous speciation and saturation index using an aqueous model addressed in EQ3/6's database. The saturation index indicates how far the system is from equilibrium with respect to the solid of interest. Thus, the smaller the sum of squared saturation indices that the aqueous model calculates for the given number of experiments, the more closely the model attributes equilibrium to each individual experiment with respect to the solid of interest. The calculation of aqueous speciation and saturation indices was repeated by adjusting stability constant of FeCit-, β(0), β(1), and Cφ in the database until the values are found that make the sum of squared saturation indices the smallest for the given number of experiments. Results will be presented at the time of conference.

Nickel speciation in several serpentine (ultramafic) topsoils via bulk synchrotron-based techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siebecker, Matthew G.; Chaney, Rufus L.; Sparks, Donald L.

2017-07-01

Serpentine soils have elevated concentrations of trace metals including nickel, cobalt, and chromium compared to non-serpentine soils. Identifying the nickel bearing minerals allows for prediction of potential mobility of nickel. Synchrotron-based techniques can identify the solid-phase chemical forms of nickel with minimal sample treatment. Element concentrations are known to vary among soil particle sizes in serpentine soils. Sonication is a useful method to physically disperse sand, silt and clay particles in soils. Synchrotron-based techniques and sonication were employed to identify nickel species in discrete particle size fractions in several serpentine (ultramafic) topsoils to better understand solid-phase nickel geochemistry. Nickel commonlymore » resided in primary serpentine parent material such as layered-phyllosilicate and chain-inosilicate minerals and was associated with iron oxides. In the clay fractions, nickel was associated with iron oxides and primary serpentine minerals, such as lizardite. Linear combination fitting (LCF) was used to characterize nickel species. Total metal concentration did not correlate with nickel speciation and is not an indicator of the major nickel species in the soil. Differences in soil texture were related to different nickel speciation for several particle size fractionated samples. A discussion on LCF illustrates the importance of choosing standards based not only on statistical methods such as Target Transformation but also on sample mineralogy and particle size. Results from the F-test (Hamilton test), which is an underutilized tool in the literature for LCF in soils, highlight its usefulness to determine the appropriate number of standards to for LCF. EXAFS shell fitting illustrates that destructive interference commonly found for light and heavy elements in layered double hydroxides and in phyllosilicates also can occur in inosilicate minerals, causing similar structural features and leading to false positive results in LCF.« less

Mössbauer investigations to characterize Fe lattice sites in sheet silicates and Peru Basin deep-sea sediments

NASA Astrophysics Data System (ADS)

Lougear, André; König, Iris; Trautwein, Alfred X.; Suess, Erwin

A procedure to classify different Fe lattice sites, i.e., OH-group geometries, in the clay mineral content of deep-sea sediments was developed using Mössbauer spectroscopy at low temperature (77 K). This speciation is of interest with regard to the redox behavior, reactivity and color of marine sediments, since substantial iron redox transitions (associated with sediment color change) have been documented for the structural sheet silicate iron. Lattice site classification was achieved for the Fe(II) fraction, all of which is structural clay Fe(II) in the sediments under investigation. Whereas the major part of the Fe(III) is structural clay iron as well, there is a small Fe(III) fraction in oxide minerals. Therefore, further elaboration of the procedure would be required to also achieve lattice site classification for the Fe(III) fraction. Analysis of the Mössbauer spectra is based on computer fits, the input parameters of which were derived from a separate study of Fe(II)-rich pure chlorites. The procedure of classification is qualified to investigate, e.g., in laboratory experiments, the site-specific reaction rates and the effects on sediment color of iron redox transitions in the sheet silicate content of sediments. The new skills were successfully applied in environmental impact studies on the mining of polymetallic nodules from the Peru Basin deep-sea floor.

Ascorbate Efflux as a New Strategy for Iron Reduction and Transport in Plants*

PubMed Central

Grillet, Louis; Ouerdane, Laurent; Flis, Paulina; Hoang, Minh Thi Thanh; Isaure, Marie-Pierre; Lobinski, Ryszard; Curie, Catherine; Mari, Stéphane

2014-01-01

Iron (Fe) is essential for virtually all living organisms. The identification of the chemical forms of iron (the speciation) circulating in and between cells is crucial to further understand the mechanisms of iron delivery to its final targets. Here we analyzed how iron is transported to the seeds by the chemical identification of iron complexes that are delivered to embryos, followed by the biochemical characterization of the transport of these complexes by the embryo, using the pea (Pisum sativum) as a model species. We have found that iron circulates as ferric complexes with citrate and malate (Fe(III)3Cit2Mal2, Fe(III)3Cit3Mal1, Fe(III)Cit2). Because dicotyledonous plants only transport ferrous iron, we checked whether embryos were capable of reducing iron of these complexes. Indeed, embryos did express a constitutively high ferric reduction activity. Surprisingly, iron(III) reduction is not catalyzed by the expected membrane-bound ferric reductase. Instead, embryos efflux high amounts of ascorbate that chemically reduce iron(III) from citrate-malate complexes. In vitro transport experiments on isolated embryos using radiolabeled 55Fe demonstrated that this ascorbate-mediated reduction is an obligatory step for the uptake of iron(II). Moreover, the ascorbate efflux activity was also measured in Arabidopsis embryos, suggesting that this new iron transport system may be generic to dicotyledonous plants. Finally, in embryos of the ascorbate-deficient mutants vtc2-4, vtc5-1, and vtc5-2, the reducing activity and the iron concentration were reduced significantly. Taken together, our results identified a new iron transport mechanism in plants that could play a major role to control iron loading in seeds. PMID:24347170

Ascorbate efflux as a new strategy for iron reduction and transport in plants.

PubMed

Grillet, Louis; Ouerdane, Laurent; Flis, Paulina; Hoang, Minh Thi Thanh; Isaure, Marie-Pierre; Lobinski, Ryszard; Curie, Catherine; Mari, Stéphane

2014-01-31

Iron (Fe) is essential for virtually all living organisms. The identification of the chemical forms of iron (the speciation) circulating in and between cells is crucial to further understand the mechanisms of iron delivery to its final targets. Here we analyzed how iron is transported to the seeds by the chemical identification of iron complexes that are delivered to embryos, followed by the biochemical characterization of the transport of these complexes by the embryo, using the pea (Pisum sativum) as a model species. We have found that iron circulates as ferric complexes with citrate and malate (Fe(III)3Cit2Mal2, Fe(III)3Cit3Mal1, Fe(III)Cit2). Because dicotyledonous plants only transport ferrous iron, we checked whether embryos were capable of reducing iron of these complexes. Indeed, embryos did express a constitutively high ferric reduction activity. Surprisingly, iron(III) reduction is not catalyzed by the expected membrane-bound ferric reductase. Instead, embryos efflux high amounts of ascorbate that chemically reduce iron(III) from citrate-malate complexes. In vitro transport experiments on isolated embryos using radiolabeled (55)Fe demonstrated that this ascorbate-mediated reduction is an obligatory step for the uptake of iron(II). Moreover, the ascorbate efflux activity was also measured in Arabidopsis embryos, suggesting that this new iron transport system may be generic to dicotyledonous plants. Finally, in embryos of the ascorbate-deficient mutants vtc2-4, vtc5-1, and vtc5-2, the reducing activity and the iron concentration were reduced significantly. Taken together, our results identified a new iron transport mechanism in plants that could play a major role to control iron loading in seeds.

The impact of particle size, relative humidity, and sulfur dioxide on iron solubility in simulated atmospheric marine aerosols.

PubMed

Cartledge, Benton T; Marcotte, Aurelie R; Herckes, Pierre; Anbar, Ariel D; Majestic, Brian J

2015-06-16

Iron is a limiting nutrient in about half of the world's oceans, and its most significant source is atmospheric deposition. To understand the pathways of iron solubilization during atmospheric transport, we exposed size segregated simulated marine aerosols to 5 ppm sulfur dioxide at arid (23 ± 1% relative humidity, RH) and marine (98 ± 1% RH) conditions. Relative iron solubility increased as the particle size decreased for goethite and hematite, while for magnetite, the relative solubility was similar for all of the fine size fractions (2.5-0.25 μm) investigated but higher than the coarse size fraction (10-2.5 μm). Goethite and hematite showed increased solubility at arid RH, but no difference (p > 0.05) was observed between the two humidity levels for magnetite. There was no correlation between iron solubility and exposure to SO2 in any mineral for any size fraction. X-ray absorption near edge structure (XANES) measurements showed no change in iron speciation [Fe(II) and Fe(III)] in any minerals following SO2 exposure. SEM-EDS measurements of SO2-exposed goethite revealed small amounts of sulfur uptake on the samples; however, the incorporated sulfur did not affect iron solubility. Our results show that although sulfur is incorporated into particles via gas-phase processes, changes in iron solubility also depend on other species in the aerosol.

Real-time redox speciation of iron in estuarine and coastal surface waters.

PubMed

Huang, Yongming; Yuan, Dongxing; Zhu, Yong; Feng, Sichao

2015-03-17

An automated, shipboard-use system was developed for real-time speciation of iron in coastal surface waters. It comprised a towed Fish underway sampler and a modified reverse flow injection analysis system with a liquid waveguide capillary flow cell-spectrophotometric detection device. The detection was based on the reaction between ferrozine and Fe(II). The detection limits of 0.3 and 0.7 nM were achieved for Fe(II) and Fe(II+III), together with their respective dynamic linear ranges of 0.5-250 and 0.9-250 nM. The system was successfully deployed and run consecutively for about 1 week during a cruise in August 2009 to the East China Sea off the Changjiang Estuary. The distribution of operationally defined field dissolvable Fe(II) and Fe(II+III) (expressed as Fea(II) and Fea(II+III)) in these areas was obtained, which showed that both Fea(II) and Fea(II+III) concentrations decreased with salinity when there were relatively high Fea(II) concentrations (up to about 120 nM) near shore. A distinct distribution of Fea(II) to Fea(II+III) ratios was also revealed, with a ratio of 0.58 in the water off Changjiang Estuary and 0.19 in the open ocean.

Removal of phosphate from aqueous solutions and sewage using natural and surface modified coir pith.

PubMed

Krishnan, K Anoop; Haridas, Ajit

2008-04-01

Iron impregnated coir pith (CP-Fe-I) can be effectively used for the removal of phosphate from aqueous streams and sewage. Iron impregnation on natural coir pith was carried out by drop by drop addition method. The effect of various factors such as pH, initial concentration of phosphate, contact time and adsorbent dose on phosphate adsorption was studied by batch technique. The pH at 3.0 favored the maximum adsorption of phosphate from aqueous solutions. The effect of pH on phosphate adsorption was explained by pH(zpc), phosphate speciation in solution and affinity of anions towards the adsorbent sites. A comparative study of the adsorption of phosphate using CP-Fe-I and CP (coir pith) was made and results show that the former one is five to six times more effective than the latter. Kinetic studies revealed that the adsorption process followed a pseudo-second order kinetic model. Adsorption followed Langmuir isotherm model. Column studies were conducted to examine the utility of the investigated adsorbent for the removal of phosphate from continuously flowing aqueous solutions.

Speciation of phosphorus in the continental shelf sediments in the Eastern Arabian Sea

NASA Astrophysics Data System (ADS)

Acharya, Shiba Shankar; Panigrahi, Mruganka Kumar; Kurian, John; Gupta, Anil Kumar; Tripathy, Subhasish

2016-03-01

The distributions of various forms of phosphorus (P) and their relation with sediment geochemistry in two core sediments near Karwar and Mangalore offshore have been studied through the modified SEDEX procedure (Ruttenberg et al., 2009) and bulk chemical analysis. The present study provides the first quantitative analysis of complete phosphorus speciation in the core sediments of the Eastern Arabian shelf. The chemical index of alteration (CIA), chemical Index of Weathering (CIW) and Al-Ti-Zr ternary diagram suggest low to moderate source area weathering of granodioritic to tonalitic source rock composition, despite the intense orographic rainfall in the source area. Due to the presence of same source rock and identical oxic depositional environment, the studied sediments show the same range of variation of total phosphorus (24 to 83 μmol/g) with a down-depth depleting trend. Organic bound P and detrital P are the two major chemical forms followed by iron-bound P, exchangeable/loosely bound P and authigenic P. The authigenic P content in the sediments near Mangalore coast varies linearly with calcium (r=0.88) unlike that of Karwar coast. The different reactive-phosphorus pools exhibit identical depleting trend with depth. This indicates that the phosphorus released from the organic matter and Fe bound fractions are prevented from precipitating as authigenic phosphates in the deeper parts of the sediment column. The low concentration of total P, dominance of detrital non-reactive fraction of P and inhibition of formation of authigenic phosphate result in the absence of active phosphatization in the Eastern Arabian Shelf in the studied region. High sedimentation rate (35-58 cm/kyr) and absence of winnowing effect appear to be the dominant factor controlling the P-speciation in the studied sediments.

Accumulation of Fe oxyhydroxides in the Peruvian oxygen deficient zone implies non-oxygen dependent Fe oxidation

DOE PAGES

Heller, Maija I.; Lam, Phoebe J.; Moffett, James W.; ...

2017-05-19

Oxygen minimum zones (OMZs) have been proposed to be an important source of dissolved iron (Fe) into the interior ocean. However, previous studies in OMZs have shown a sharp decrease in total dissolved Fe (dFe) and/or dissolved Fe(II) (dFe(II)) concentrations at the shelf-break, despite constant temperature, salinity and continued lack of oxygen across the shelf-break. The loss of both total dFe and dFe(II) suggests a conversion of the dFe to particulate form, but studies that have coupled the reduction-oxidation (redox) speciation of both dissolved and particulate phases have not previously been done. Here in this work, we have measured themore » redox speciation and concentrations of both dissolved and particulate forms of Fe in samples collected during the U.S. GEOTRACES Eastern tropical Pacific Zonal Transect (EPZT) cruise in 2013 (GP16). This complete data set allows us to assess possible mechanisms for loss of dFe. We observed an offshore loss of dFe(II) within the oxygen deficient zone (ODZ), where dissolved oxygen is undetectable, accompanied by an increase in total particulate Fe (pFe). Total pFe concentrations were highest in the upper ODZ. X-ray absorption spectroscopy revealed that the pFe maximum was primarily in the Fe(III) form as Fe(III) oxyhydroxides. The remarkable similarity in the distributions of total particulate iron and nitrite suggests a role for nitrite in the oxidation of dFe(II) to pFe(III). Lastly, we present a conceptual model for the rapid redox cycling of Fe that occurs in ODZs, despite the absence of oxygen.« less

Accumulation of Fe oxyhydroxides in the Peruvian oxygen deficient zone implies non-oxygen dependent Fe oxidation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heller, Maija I.; Lam, Phoebe J.; Moffett, James W.

Oxygen minimum zones (OMZs) have been proposed to be an important source of dissolved iron (Fe) into the interior ocean. However, previous studies in OMZs have shown a sharp decrease in total dissolved Fe (dFe) and/or dissolved Fe(II) (dFe(II)) concentrations at the shelf-break, despite constant temperature, salinity and continued lack of oxygen across the shelf-break. The loss of both total dFe and dFe(II) suggests a conversion of the dFe to particulate form, but studies that have coupled the reduction-oxidation (redox) speciation of both dissolved and particulate phases have not previously been done. Here in this work, we have measured themore » redox speciation and concentrations of both dissolved and particulate forms of Fe in samples collected during the U.S. GEOTRACES Eastern tropical Pacific Zonal Transect (EPZT) cruise in 2013 (GP16). This complete data set allows us to assess possible mechanisms for loss of dFe. We observed an offshore loss of dFe(II) within the oxygen deficient zone (ODZ), where dissolved oxygen is undetectable, accompanied by an increase in total particulate Fe (pFe). Total pFe concentrations were highest in the upper ODZ. X-ray absorption spectroscopy revealed that the pFe maximum was primarily in the Fe(III) form as Fe(III) oxyhydroxides. The remarkable similarity in the distributions of total particulate iron and nitrite suggests a role for nitrite in the oxidation of dFe(II) to pFe(III). Lastly, we present a conceptual model for the rapid redox cycling of Fe that occurs in ODZs, despite the absence of oxygen.« less

Accumulation of Fe oxyhydroxides in the Peruvian oxygen deficient zone implies non-oxygen dependent Fe oxidation

NASA Astrophysics Data System (ADS)

Heller, Maija I.; Lam, Phoebe J.; Moffett, James W.; Till, Claire P.; Lee, Jong-Mi; Toner, Brandy M.; Marcus, Matthew A.

2017-08-01

Oxygen minimum zones (OMZs) have been proposed to be an important source of dissolved iron (Fe) into the interior ocean. However, previous studies in OMZs have shown a sharp decrease in total dissolved Fe (dFe) and/or dissolved Fe(II) (dFe(II)) concentrations at the shelf-break, despite constant temperature, salinity and continued lack of oxygen across the shelf-break. The loss of both total dFe and dFe(II) suggests a conversion of the dFe to particulate form, but studies that have coupled the reduction-oxidation (redox) speciation of both dissolved and particulate phases have not previously been done. Here we have measured the redox speciation and concentrations of both dissolved and particulate forms of Fe in samples collected during the U.S. GEOTRACES Eastern tropical Pacific Zonal Transect (EPZT) cruise in 2013 (GP16). This complete data set allows us to assess possible mechanisms for loss of dFe. We observed an offshore loss of dFe(II) within the oxygen deficient zone (ODZ), where dissolved oxygen is undetectable, accompanied by an increase in total particulate Fe (pFe). Total pFe concentrations were highest in the upper ODZ. X-ray absorption spectroscopy revealed that the pFe maximum was primarily in the Fe(III) form as Fe(III) oxyhydroxides. The remarkable similarity in the distributions of total particulate iron and nitrite suggests a role for nitrite in the oxidation of dFe(II) to pFe(III). We present a conceptual model for the rapid redox cycling of Fe that occurs in ODZs, despite the absence of oxygen.

Bioaccessibility, release kinetics, and molecular speciation of arsenic and lead in geo-dusts from the Iron King Mine Federal Superfund site in Humboldt, Arizona.

PubMed

Menka, Nazune; Root, Rob; Chorover, Jon

2014-01-01

Mine tailings contain multiple toxic metal(loid)s that pose a threat to human health via inhalation and ingestion. The goals of this research include understanding the speciation and molecular environment of these toxic metal(loid)s (arsenic and lead) as well as the impacts particle size and residence time have on their bioaccessibilty in simulated gastric and lung fluid. Additionally, future work will include smaller size fractions (PM10 and PM2.5) of surface mine tailings, with the goal of increasing our understanding of multi-metal release from contaminated geo-dusts in simulated bio-fluids. This research is important to environmental human health risk assessment as it increases the accuracy of exposure estimations to toxic metal(loid)s.

Predicting toxic effects of copper on aquatic biota in mineralized areas by using the Biotic Ligand Model

USGS Publications Warehouse

Smith, Kathleen S.; Ranville, James F.; Adams, M.; Choate, LaDonna M.; Church, Stan E.; Fey, David L.; Wanty, Richard B.; Crock, James G.

2006-01-01

The chemical speciation of metals influences their biological effects. The Biotic Ligand Model (BLM) is a computational approach to predict chemical speciation and acute toxicological effects of metals on aquatic biota. Recently, the U.S. Environmental Protection Agency incorporated the BLM into their regulatory water-quality criteria for copper. Results from three different laboratory copper toxicity tests were compared with BLM predictions for simulated test-waters. This was done to evaluate the ability of the BLM to accurately predict the effects of hardness and concentrations of dissolved organic carbon (DOC) and iron on aquatic toxicity. In addition, we evaluated whether the BLM and the three toxicity tests provide consistent results. Comparison of BLM predictions with two types of Ceriodaphnia dubia toxicity tests shows that there is fairly good agreement between predicted LC50 values computed by the BLM and LC50 values determined from the two toxicity tests. Specifically, the effect of increasing calcium concentration (and hardness) on copper toxicity appears to be minimal. Also, there is fairly good agreement between the BLM and the two toxicity tests for test solutions containing elevated DOC, for which the LC50 is 3-to-5 times greater (less toxic) than the LC50 for the lower-DOC test water. This illustrates the protective effects of DOC on copper toxicity and demonstrates the ability of the BLM to predict these protective effects. In contrast, for test solutions with added iron there is a decrease in LC50 values (increase in toxicity) in results from the two C. dubia toxicity tests, and the agreement between BLM LC50 predictions and results from these toxicity tests is poor. The inability of the BLM to account for competitive iron binding to DOC or DOC fractionation may be a significant shortcoming of the BLM for predicting site- specific water-quality criteria in streams affected by iron-rich acidic drainage in mined and mineralized areas.

Arsenic mobilization and immobilization in paddy soils

NASA Astrophysics Data System (ADS)

Kappler, A.; Hohmann, C.; Zhu, Y. G.; Morin, G.

2010-05-01

Arsenic is oftentimes of geogenic origin and in many cases bound to iron(III) minerals. Iron(III)-reducing bacteria can harvest energy by coupling the oxidation of organic or inorganic electron donors to the reduction of Fe(III). This process leads either to dissolution of Fe(III)-containing minerals and thus to a release of the arsenic into the environment or to secondary Fe-mineral formation and immobilisation of arsenic. Additionally, aerobic and anaerobic iron(II)-oxidizing bacteria have the potential to co-precipitate or sorb arsenic during iron(II) oxidation at neutral pH that is usually followed by iron(III) mineral precipitation. We are currently investigating arsenic immobilization by Fe(III)-reducing bacteria and arsenic co-precipitation and immobilization by anaerobic iron(II)-oxidizing bacteria in batch, microcosm and rice pot experiments. Co-precipitation batch experiments with pure cultures of nitrate-dependent Fe(II)-oxidizing bacteria are used to quantify the amount of arsenic that can be immobilized during microbial iron mineral precipitation, to identify the minerals formed and to analyze the arsenic binding environment in the precipitates. Microcosm and rice pot experiments are set-up with arsenic-contaminated rice paddy soil. The microorganisms (either the native microbial population or the soil amended with the nitrate-dependent iron(II)-oxidizing Acidovorax sp. strain BoFeN1) are stimulated either with iron(II), nitrate, or oxygen. Dissolved and solid-phase arsenic and iron are quantified. Iron and arsenic speciation and redox state in batch and microcosm experiments are determined by LC-ICP-MS and synchrotron-based methods (EXAFS, XANES).

Disassembling Iron Availability to Phytoplankton

PubMed Central

Shaked, Yeala; Lis, Hagar

2012-01-01

The bioavailability of iron to microorganisms and its underlying mechanisms have far reaching repercussions to many natural systems and diverse fields of research, including ocean biogeochemistry, carbon cycling and climate, harmful algal blooms, soil and plant research, bioremediation, pathogenesis, and medicine. Within the framework of ocean sciences, short supply and restricted bioavailability of Fe to phytoplankton is thought to limit primary production and curtail atmospheric CO2 drawdown in vast ocean regions. Yet a clear-cut definition of bioavailability remains elusive, with elements of iron speciation and kinetics, phytoplankton physiology, light, temperature, and microbial interactions, to name a few, all intricately intertwined into this concept. Here, in a synthesis of published and new data, we attempt to disassemble the complex concept of iron bioavailability to phytoplankton by individually exploring some of its facets. We distinguish between the fundamentals of bioavailability – the acquisition of Fe-substrate by phytoplankton – and added levels of complexity involving interactions among organisms, iron, and ecosystem processes. We first examine how phytoplankton acquire free and organically bound iron, drawing attention to the pervasiveness of the reductive uptake pathway in both prokaryotic and eukaryotic autotrophs. Turning to acquisition rates, we propose to view the availability of various Fe-substrates to phytoplankton as a spectrum rather than an absolute “all or nothing.” We then demonstrate the use of uptake rate constants to make comparisons across different studies, organisms, Fe-compounds, and environments, and for gaging the contribution of various Fe-substrates to phytoplankton growth in situ. Last, we describe the influence of aquatic microorganisms on iron chemistry and fate by way of organic complexation and bio-mediated redox transformations and examine the bioavailability of these bio-modified Fe species. PMID:22529839

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swanner, E. D.; Bayer, T.; Wu, W.

In this study, we couple iron isotope analysis to microscopic and mineralogical investigation of iron speciation during circumneutral Fe(II) oxidation and Fe(III) precipitation with photosynthetically produced oxygen. In the presence of the cyanobacterium Synechococcus PCC 7002, aqueous Fe(II) (Fe(II) aq) is oxidized and precipitated as amorphous Fe(III) oxyhydroxide minerals (iron precipitates, Fe ppt), with distinct isotopic fractionation (ε 56Fe) values determined from fitting the δ 56Fe(II) aq (1.79‰ and 2.15‰) and the δ 56Fe ppt (2.44‰ and 2.98‰) data trends from two replicate experiments. Additional Fe(II) and Fe(III) phases were detected using microscopy and chemical extractions and likely represent Fe(II)more » and Fe(III) sorbed to minerals and cells. The iron desorbed with sodium acetate (FeNaAc) yielded heavier δ 56Fe compositions than Fe(II) aq. Modeling of the fractionation during Fe(III) sorption to cells and Fe(II) sorption to Feppt, combined with equilibration of sorbed iron and with Fe(II) aq using published fractionation factors, is consistent with our resulting δ 56FeNaAc. The δ 56Fe ppt data trend is inconsistent with complete equilibrium exchange with Fe(II)aq. Because of this and our detection of microbially excreted organics (e.g., exopolysaccharides) coating Feppt in our microscopic analysis, we suggest that electron and atom exchange is partially suppressed in this system by biologically produced organics. These results indicate that cyanobacteria influence the fate and composition of iron in sunlit environments via their role in Fe(II) oxidation through O 2 production, the capacity of their cell surfaces to sorb iron, and the interaction of secreted organics with Fe(III) minerals.« less

Influence of iron redox cycling on organo-mineral associations in arctic tundra soils

NASA Astrophysics Data System (ADS)

Herndon, E.; AlBashaireh, A.; Duroe, K.; Singer, D. M.

2016-12-01

Geochemical interactions between soil organic matter and minerals influence decomposition in many environments but remain poorly understood in arctic tundra systems. In tundra soils that are periodically to persistently saturated, the accumulation of iron oxyhydroxides and organo-iron precipitates at redox interfaces may inhibit decomposition by binding organic molecules and protecting them from microbial degradation. Here, we couple synchrotron-source spectroscopic techniques with chemical sequential extractions and physical density fractionations to evaluate the spatial distribution and speciation of Fe-bearing phases and associated organic matter in organic and mineral horizons of the seasonally thawed active layer in tundra soils from northern Alaska. Mineral-associated organic matter comprised 63 ± 9% of soil organic carbon stored in the active layer of ice wedge polygons. Ferrous iron produced in anoxic mineral horizons diffused upwards and precipitated as poorly-crystalline oxyhydroxides and organic-bound Fe(III) in the organic horizons. Ferrihydrite and goethite were present as coatings on mineral grains and plant debris and in aggregates with clays and particulate organic matter. Organic matter released through acid-dissolution of iron oxides may represent a small pool of readily-degradable organic molecules temporarily stabilized by sorption to iron oxyhydroxide surfaces, while larger quantities of particulate organic carbon and humic-like substances may be physically protected from decomposition by Fe-oxide coatings and aggregation. We conclude that formation of poorly-crystalline and crystalline iron oxides at redox interfaces contributes to mineral protection of organic matter through sorption, aggregation, and co-precipitation reactions. Further study of organo-mineral associations is necessary to determine the net impact of mineral-stabilization on carbon storage in rapidly warming arctic ecosystems.

In-situ identification of iron electrocoagulation speciation and application for natural organic matter (NOM) removal.

PubMed

Dubrawski, Kristian L; Mohseni, Madjid

2013-09-15

In this work, iron speciation in electrocoagulation (EC) was studied to determine the impact of operating parameters on natural organic matter (NOM) removal from natural water. Two electrochemical EC parameters, current density (i) and charge loading rate (CLR), were investigated. Variation of these parameters led to a near unity current efficiency (φ = 0.957 ± 0.03), at any combination of i in a range of 1-25 mA/cm(2) and CLR in a range of 12-300 C/L/min. Higher i and CLR led to a higher bulk pH and limited the amount of dissolved oxygen (DO) reduced at the cathode surface due to mass transfer limitations. A low i (1 mA/cm(2)) and intermediate CLR (60 C/L/min) resulted in low bulk DO (<2.5 mg/L), where green rust (GR) was identified by in-situ Raman spectroscopy as the primary crystalline electrochemical product. Longer electrolysis times at higher i led to magnetite (Fe3O4) formation. Both higher (300 C/L/min) and lower (12 C/L/min) CLR values led to increased DO and/or increased pH, with lepidocrocite (γ-FeOOH) as the only crystalline species observed. The NOM removal of the three identified species was compared, with conditions leading to GR formation showing the greatest dissolved organic carbon removal, and highest removal of the low apparent molecular weight (<550 Da) chromophoric NOM fraction, determined by high performance size exclusion chromatography. Copyright © 2013 Elsevier Ltd. All rights reserved.

Particles, sweat, and tears: a comparative study on bioaccessibility of ferrochromium alloy and stainless steel particles, the pure metals and their metal oxides, in simulated skin and eye contact.

PubMed

Hedberg, Yolanda; Midander, Klara; Wallinder, Inger Odnevall

2010-07-01

Ferrochromium alloys are manufactured in large quantities and placed on the global market for use as master alloys (secondary raw materials), primarily for stainless steel production. Any potential human exposure to ferrochromium alloy particles is related to occupational activities during production and use, with 2 main exposure routes, dermal contact and inhalation and subsequent digestion. Alloy and reference particles exposed in vitro in synthetic biological fluids relevant for these main exposure routes have been investigated in a large research effort combining bioaccessibility; chemical speciation; and material, surface, and particle characteristics. In this paper, data for the dermal exposure route, including skin and eye contact, will be presented and discussed. Bioaccessibility data have been generated for particles of a ferrochromium alloy, stainless steel grade AISI 316L, pure Fe, pure Cr, iron(II,III)oxide, and chromium(III)oxide, upon immersion in artificial sweat (pH 6.5) and artificial tear (pH 8.0) fluids for various time periods. Measured released amounts of Fe, Cr, and Ni are presented in terms of average Fe and Cr release rates and amounts released per amount of particles loaded. The results are discussed in relation to bulk and surface composition of the particles. Additional information, essential to assess the bioavailability of Cr released, was generated by determining its chemical speciation and by providing information on its complexation and oxidation states in both media investigated. The effect of differences in experimental temperature, 30 degrees C and 37 degrees C, on the extent of metal release in artificial sweat is demonstrated. Iron was the preferentially released element in all test media and for all time periods and iron-containing particles investigated. The extent of metal release was highly pH dependent and was also dependent on the medium composition. Released amounts of Cr and Fe were very low (close to the limit of detection, <0.008% of particles released or dissolved as iron or chromium) for the alloy particles (ferrochromium alloy and stainless steel), the pure Cr particles, and the metal oxide particles. The released fraction of Cr (Cr/[Cr + Fe]) varied with the material investigated, the test medium, and the exposure time and cannot be predicted from either the bulk or the surface composition. Chromium was released as noncomplexed Cr(III) and in addition in very low concentrations (<3 microg/L). Nickel released was under the limit of detection (0.5 microg/L), except for ultrafine stainless steel particles (<10 microg/L). It is evident that media chemistry and material properties from a bulk and surface perspective, as well as other particle characteristics, and the chemical speciation of released metals have to be considered when assessing any potential hazard or risk induced by sparingly soluble metal or alloy particles. (c) 2010 SETAC.

The Importance of Kinetics and Redox in the Biogeochemical Cycling of Iron in the Surface Ocean

PubMed Central

Croot, Peter L.; Heller, Maija I.

2012-01-01

It is now well established that Iron (Fe) is a limiting element in many regions of the open ocean. Our current understanding of the key processes which control iron distribution in the open ocean have been largely based on thermodynamic measurements performed under the assumption of equilibrium conditions. Using this equilibrium approach, researchers have been able to detect and quantify organic complexing ligands in seawater and examine their role in increasing the overall solubility of iron. Our current knowledge about iron bioavailability to phytoplankton and bacteria is also based heavily on carefully controlled laboratory studies where it is assumed the chemical species are in equilibrium in line with the free ion association model and/or its successor the biotic ligand model. Similarly most field work on iron biogeochemistry generally consists of a single profile which is in essence a “snap-shot” in time of the system under investigation. However it is well known that the surface ocean is an extremely dynamic environment and it is unlikely if thermodynamic equilibrium between all the iron species present is ever truly achieved. In sunlit waters this is mostly due to the daily passage of the sun across the sky leading to photoredox processes which alter Fe speciation by cycling between redox states and between inorganic and organic species. Episodic deposition events, dry and wet, are also important perturbations to iron cycling as they bring in new iron to the system and alter the equilibrium between iron species and phases. Here we utilize new field data collected in the open ocean on the complexation kinetics of iron in the surface ocean to identify the important role of weak iron binding ligands (i.e., those that cannot maintain iron in solution indefinitely at seawater pH: αFeL < αFe′) in allowing transient increases in iron solubility in response to iron deposition events. Experiments with the thermal O2- source SOTS-1 also indicate the short term impact of this species on iron solubility also with relevance to the euphotic zone. This data highlights the roles of kinetics, redox, and weaker iron binding ligands in the biogeochemical cycling of iron in the ocean. PMID:22723797

The impact of steeping, germination and hydrothermal processing of wheat (Triticum aestivum L.) grains on phytate hydrolysis and the distribution, speciation and bio-accessibility of iron and zinc elements.

PubMed

Lemmens, Elien; De Brier, Niels; Spiers, Kathryn M; Ryan, Chris; Garrevoet, Jan; Falkenberg, Gerald; Goos, Peter; Smolders, Erik; Delcour, Jan A

2018-10-30

Chelation of iron and zinc in wheat as phytates lowers their bio-accessibility. Steeping and germination (15 °C, 120 h) lowered phytate content from 0.96% to only 0.81% of initial dry matter. A multifactorial experiment in which (steeped/germinated) wheat was subjected to different time (2-24 h), temperature (20-80 °C) and pH (2.0-8.0) conditions showed that hydrothermal processing of germinated (15 °C, 120 h) wheat at 50 °C and pH 3.8 for 24 h reduced phytate content by 95%. X-ray absorption near-edge structure imaging showed that it indeed abolished chelation of iron to phytate. It also proved that iron was oxidized during steeping, germination and hydrothermal processing. It was further shown that zinc and iron bio-accessibility were respectively 3 and 5% in wheat and 27 and 37% in hydrothermally processed wheat. Thus, hydrothermal processing of (germinated) wheat paves the way for increasing elemental bio-accessibility in whole grain-based products. Copyright © 2018 Elsevier Ltd. All rights reserved.

Glacial influence on the geochemistry of riverine iron fluxes to the Gulf of Alaska and effects of deglaciation

USGS Publications Warehouse

Schroth, A.W.; Crusius, John; Chever, F.; Bostick, B.C.; Rouxel, O.J.

2011-01-01

Riverine iron (Fe) derived from glacial weathering is a critical micronutrient source to ecosystems of the Gulf of Alaska (GoA). Here we demonstrate that the source and chemical nature of riverine Fe input to the GoA could change dramatically due to the widespread watershed deglaciation that is underway. We examine Fe size partitioning, speciation, and isotopic composition in tributaries of the Copper River which exemplify a long-term GoA watershed evolution from one strongly influenced by glacial weathering to a boreal-forested watershed. Iron fluxes from glacierized tributaries bear high suspended sediment and colloidal Fe loads of mixed valence silicate species, with low concentrations of dissolved Fe and dissolved organic carbon (DOC). Iron isotopic composition is indicative of mechanical weathering as the Fe source. Conversely, Fe fluxes from boreal-forested systems have higher dissolved Fe concentrations corresponding to higher DOC concentrations. Iron colloids and suspended sediment consist of Fe (hydr)oxides and organic complexes. These watersheds have an iron isotopic composition indicative of an internal chemical processing source. We predict that as the GoA watershed evolves due to deglaciation, so will the source, flux, and chemical nature of riverine Fe loads, which could have significant ramifications for Alaskan marine and freshwater ecosystems.

A geochemical study of the Ediacaran discoidal fossil Aspidella preserved in limestones: Implications for its taphonomy and paleoecology.

PubMed

Bykova, N; Gill, B C; Grazhdankin, D; Rogov, V; Xiao, S

2017-07-01

The Ediacara biota features the rise of macroscopic complex life immediately before the Cambrian explosion. One of the most abundant and widely distributed elements of the Ediacara biota is the discoidal fossil Aspidella, which is interpreted as a subsurface holdfast possibly anchoring a frondose epibenthic organism. It is a morphologically simple fossil preserved mainly in siliciclastic rocks, which are unsuitable for comprehensive stable isotope geochemical analyses to decipher its taphonomy and paleoecology. In this regard, three-dimensionally preserved Aspidella fossils from upper Ediacaran limestones of the Khatyspyt Formation in the Olenek Uplift of northern Siberia offer a rare opportunity to leverage geochemistry for insights into their taphonomy and paleoecology. To take advantage of this opportunity, we analyzed δ 13 C carb , δ 18 O carb , δ 13 C org , δ 34 S pyr , and iron speciation of the Khatyspyt Aspidella fossils and surrounding sediment matrix in order to investigate whether they hosted microbial symbionts, how they were fossilized, and the redox conditions of their ecological environments. Aspidella holdfasts and surrounding sediment matrix show indistinguishable δ 13 C org values, suggesting they did not host and derive significant amount of nutrients from microbial symbionts such as methanogens, methylotrophs, or sulfide-oxidizing bacteria. δ 13 C carb , δ 18 O carb , and δ 34 S pyr data, along with petrographic observations, suggest that microbial sulfate reduction facilitated the preservation of Aspidella by promoting early authigenic calcite cementation in the holdfasts before matrix cementation and sediment compaction. Iron speciation data are equivocal, largely because of the low total iron concentrations. However, consideration of published sulfur isotope and biomarker data suggests that Aspidella likely lived in non-euxinic waters. It is possible that Aspidella was an opportunistic organism, colonizing the seafloor in large numbers when paleoenvironments were favorable. This study demonstrates that geochemical data of Ediacaran fossils preserved in limestones can offer important insights into the taphonomy and paleoecology of these enigmatic organisms living on the eve of the Cambrian explosion. © 2017 John Wiley & Sons Ltd.

Geochemical Weathering Increases Lead Bioaccessibility in Semi-Arid Mine Tailings

PubMed Central

Hayes, Sarah M.; Webb, Sam M.; Bargar, John R.; O'Day, Peggy A.; Maier, Raina M.; Chorover, Jon

2012-01-01

Mine tailings can host elevated concentrations of toxic metal(loid)s that represent a significant hazard to surrounding communities and ecosystems. Eolian transport, capable of translocating small (micrometer-sized) particles, can be the dominant mechanism of toxic metal dispersion in arid or semi-arid landscapes. Human exposure to metals can then occur via direct inhalation or ingestion of particulates. The fact that measured doses of total lead (Pb) in geomedia correlate poorly with blood Pb levels highlights a need to better resolve the precise distribution of molecularly-speciated metal-bearing phases in the complex particle mixtures. Species distribution controls bioaccessibility, thereby directly impacting health risk. This study seeks to correlate Pb-containing particle size and mineral composition with lability and bioaccessibility in mine tailings subjected to weathering in a semi-arid environment. We employed X-ray absorption spectroscopy (XAS) and X-ray fluorescence (XRF), coupled with sequential chemical extractions, to study Pb speciation in tailings from the semi-arid Arizona Klondyke State Superfund Site. Representative samples ranging in pH from 2.6 to 5.4 were selected for in-depth study of Pb solid-phase speciation. The principle lead-bearing phase was plumbojarosite (PbFe6(SO4)4(OH)12), but anglesite (PbSO4) and iron oxide-sorbed Pb were also observed. Anglesite, the most bioavailable mineral species of lead identified in this study, was enriched in surficial tailings samples, where Pb concentrations in the clay size fraction were 2–3 times higher by mass relative to bulk. A mobile and bioaccessible Pb phase accumulates in surficial tailings, with a corresponding increase in risk of human exposure to atmospheric particles. PMID:22553941

Sorptive Uptake Studies of an Aryl-Arsenical with Iron Oxide Composites on an Activated Carbon Support

PubMed Central

Kwon, Jae H.; Wilson, Lee D.; Sammynaiken, Ramaswami

2014-01-01

Sorption uptake kinetics and equilibrium studies for 4-hydroxy-3-nitrobenzene arsonic acid (roxarsone) was evaluated with synthetic magnetite (Mag-P), commercial magnetite (Mag-C), magnetite 10%, 19%, and 32% composite material (CM-10, -19, -32) that contains granular activated carbon (GAC), and synthetic goethite at pH 7.00 in water at 21 °C for 24 h. GAC showed the highest sorptive removal of roxarsone and the relative uptake for each sorbent material with roxarsone are listed in descending order as follows: GAC (471 mg/g) > goethite (418 mg/g) > CM-10 (377 mg/g) CM-19 (254 mg/g) > CM-32 (227 mg/g) > Mag-P (132 mg/g) > Mag-C (29.5 mg/g). The As (V) moiety of roxarsone is adsorbed onto the surface of the iron oxide/oxyhydrate and is inferred as inner-sphere surface complexes; monodentate-mononuclear, bidentate-mononuclear, and bidentate-binuclear depending on the protolytic speciation of roxarsone. The phenyl ring of roxarsone provides the primary driving force for the sorptive interaction with the graphene surface of GAC and its composites. Thus, magnetite composites are proposed as multi-purpose adsorbents for the co-removal of inorganic and organic arsenicals due to the presence of graphenic and iron oxide active adsorption sites. PMID:28788545

Thermodynamic and Kinetic Response of Microbial Reactions to High CO2.

PubMed

Jin, Qusheng; Kirk, Matthew F

2016-01-01

Geological carbon sequestration captures CO 2 from industrial sources and stores the CO 2 in subsurface reservoirs, a viable strategy for mitigating global climate change. In assessing the environmental impact of the strategy, a key question is how microbial reactions respond to the elevated CO 2 concentration. This study uses biogeochemical modeling to explore the influence of CO 2 on the thermodynamics and kinetics of common microbial reactions in subsurface environments, including syntrophic oxidation, iron reduction, sulfate reduction, and methanogenesis. The results show that increasing CO 2 levels decreases groundwater pH and modulates chemical speciation of weak acids in groundwater, which in turn affect microbial reactions in different ways and to different extents. Specifically, a thermodynamic analysis shows that increasing CO 2 partial pressure lowers the energy available from syntrophic oxidation and acetoclastic methanogenesis, but raises the available energy of microbial iron reduction, hydrogenotrophic sulfate reduction and methanogenesis. Kinetic modeling suggests that high CO 2 has the potential of inhibiting microbial sulfate reduction while promoting iron reduction. These results are consistent with the observations of previous laboratory and field studies, and highlight the complexity in microbiological responses to elevated CO 2 abundance, and the potential power of biogeochemical modeling in evaluating and quantifying these responses.

Thermodynamic and Kinetic Response of Microbial Reactions to High CO2

PubMed Central

Jin, Qusheng; Kirk, Matthew F.

2016-01-01

Geological carbon sequestration captures CO2 from industrial sources and stores the CO2 in subsurface reservoirs, a viable strategy for mitigating global climate change. In assessing the environmental impact of the strategy, a key question is how microbial reactions respond to the elevated CO2 concentration. This study uses biogeochemical modeling to explore the influence of CO2 on the thermodynamics and kinetics of common microbial reactions in subsurface environments, including syntrophic oxidation, iron reduction, sulfate reduction, and methanogenesis. The results show that increasing CO2 levels decreases groundwater pH and modulates chemical speciation of weak acids in groundwater, which in turn affect microbial reactions in different ways and to different extents. Specifically, a thermodynamic analysis shows that increasing CO2 partial pressure lowers the energy available from syntrophic oxidation and acetoclastic methanogenesis, but raises the available energy of microbial iron reduction, hydrogenotrophic sulfate reduction and methanogenesis. Kinetic modeling suggests that high CO2 has the potential of inhibiting microbial sulfate reduction while promoting iron reduction. These results are consistent with the observations of previous laboratory and field studies, and highlight the complexity in microbiological responses to elevated CO2 abundance, and the potential power of biogeochemical modeling in evaluating and quantifying these responses. PMID:27909425

[Effect of the interaction of microorganisms and iron oxides on arsenic releasing into groundwater in Chinese Loess].

PubMed

Xie, Yun-Yun; Chen, Tian-Hu; Zhou, Yue-Fei; Xie, Qiao-Qin

2013-10-01

A large part of groundwater in the Chinese Loess Plateau area is characterized by high arsenic concentration. Anaerobic bacteria have been considered to play key roles in promoting arsenic releasing from loess to groundwater. However, this hypothesis remains unconfirmed. Based on modeling experiments, this study investigated the speciation of arsenic in loess, and then determined the release rates and quantities of arsenic with the mediation of anaerobic bacteria. The results showed that arsenic contents in loess were between 23 mg.kg-1 and 30 mg.kg-1. No obvious arsenic content difference among loess samples was observed. The ratios for specific adsorbed, iron oxides co-precipitated and silicate co-precipitated arsenic were 37.76% , 36. 15% and 25. 69% , respectively. Indigenous microorganisms, dissimilatory iron reducing bacteria (DIRB) and sulfate reducing bacteria (SRB) could all promote the release of arsenic from loess. Organic matters highly affected the release rates. More than 100 mg.L-1 sodium lactate was required for all bacterial experiments to facilitate obvious arsenic release. Considering the redox condition in loess, the contribution of SRB to arsenic release in loess area was less feasible than that of DIRB and indigenous microorganisms.

Arsenic Speciation and Extraction and the Significance of Biodegradable Acid on Arsenic Removal—An Approach for Remediation of Arsenic-Contaminated Soil

PubMed Central

Nguyen Van, Thinh; Osanai, Yasuhito; Do Nguyen, Hai; Kurosawa, Kiyoshi

2017-01-01

A series of arsenic remediation tests were conducted using a washing method with biodegradable organic acids, including oxalic, citric and ascorbic acids. Approximately 80% of the arsenic in one sample was removed under the effect of the ascorbic and oxalic acid combination, which was roughly twice higher than the effectiveness of the ascorbic and citric acid combination under the same conditions. The soils treated using biodegradable acids had low remaining concentrations of arsenic that are primarily contained in the crystalline iron oxides and organic matter fractions. The close correlation between extracted arsenic and extracted iron/aluminum suggested that arsenic was removed via the dissolution of Fe/Al oxides in soils. The fractionation of arsenic in four contaminated soils was investigated using a modified sequential extraction method. Regarding fractionation, we found that most of the soil contained high proportions of arsenic (As) in exchangeable fractions with phosphorus, amorphous oxides, and crystalline iron oxides, while a small amount of the arsenic fraction was organic matter-bound. This study indicated that biodegradable organic acids can be considered as a means for arsenic-contaminated soil remediation.

The redox state of iron in the matrix of CI, CM and metamorphosed CM chondrites by XANES spectroscopy

NASA Astrophysics Data System (ADS)

Beck, P.; De Andrade, V.; Orthous-Daunay, F.-R.; Veronesi, G.; Cotte, M.; Quirico, E.; Schmitt, B.

2012-12-01

Carbonaceous chondrites record the action of water at some point of their petrological history. These meteorites are usually connected to low albedo asteroid, which present visible/near-IR absorption explained by iron related absorption within phyllosilicates and oxides. In order to obtain quantitative insight into the mineralogy of iron-bearing phases, we have measured X-ray absorption near-edge spectroscopy at the iron K-edge of matrix from carbonaceous chondrites. This method enables to constrain the redox state and environment of iron in these meteorites. For this study, we selected seven CM chondrites and the CI Orgueil, expected to span a range of aqueous alteration degrees. Our analysis of the pre-edge features show that the redox state of Orgueil (CI) is dominated by octahedral Fe and that the Fe3+/(Fe3++Fe2+) atomic ratio is above 80%. Full-inversion of the spectra suggests that the iron budget is dominated by iron oxides, with additional contributions from phyllosilicate. In the case of the CM, the iron speciation appears different that in the case of Orgueil. Cronstedtite is identified from the inversion of the spectra, and suggested by the presence of significant amount of tetrahedral Fe3+. Within the CM chondrites, a trend of aqueous alteration appears presents, and which is roughly correlated to the scheme defined by Rubin et al. (2007). This trend is characterized by an increase in the amount of iron oxides. Two shock metamorphosed CM are present in our dataset (PCA 91008, WIS 91600). If WIS 91600 does not appear distinguishable, from the CM trend, in the case of PCA 91008, shock metamorphism did impact the pre-edge intensity and an increased amount of anhydrous silicates is found. Although the matrix was dehydrated, significant amount of Fe3+ is still present, providing a memory of the aqueous alteration.

Hydroquinone-Mediated Redox Cycling of Iron and Concomitant Oxidation of Hydroquinone in Oxic Waters under Acidic Conditions: Comparison with Iron-Natural Organic Matter Interactions.

PubMed

Jiang, Chao; Garg, Shikha; Waite, T David

2015-12-15

Interactions of 1,4-hydroquinone with soluble iron species over a pH range of 3-5 in the air-saturated and partially deoxygenated solution are examined here. Our results show that 1,4-hydroquinone reduces Fe(III) in acidic conditions, generating semiquinone radicals (Q(•-)) that can oxidize Fe(II) back to Fe(III). The oxidation rate of Fe(II) by Q(•-)increases with increase in pH due to the speciation change of Q(•-) with its deprotonated form (Q(•-)) oxidizing Fe(II) more rapidly than the protonated form (HQ(•)). Although the oxygenation of Fe(II) is negligible at pH < 5, O2 still plays an important role in iron redox transformation by rapidly oxidizing Q(•-) to form benzoquinone (Q). A kinetic model is developed to describe the transformation of quinone and iron under all experimental conditions. The results obtained here are compared with those obtained in our previous studies of iron-Suwannee River fulvic acid (SRFA) interactions in acidic solutions and support the hypothesis that hydroquinone moieties can reduce Fe(III) in natural waters. However, the semiquinone radicals generated in pure hydroquinone solution are rapidly oxidized by dioxygen, while the semiquinone radicals generated in SRFA solution are resistant to oxidation by dioxygen, with the result that steady-state semiquinone concentrations in SRFA solutions are 2-3 orders of magnitude greater than in solutions of 1,4-hydroquinone. As a result, semiquinone moieties in SRFA play a much more important role in iron redox transformations than is the case in solutions of simple quinones such as 1,4-hydroquinone. This difference in the steady-state concentration of semiquinone species has a dramatic effect on the cycling of iron between the +II and +III oxidation states, with iron turnover frequencies in solutions containing SRFA being 10-20 times higher than those observed in solutions of 1,4-hydroquinone.

Characterization of Fe-leonardite complexes as novel natural iron fertilizers.

PubMed

Kovács, Krisztina; Czech, Viktória; Fodor, Ferenc; Solti, Adam; Lucena, Juan J; Santos-Rosell, Sheila; Hernández-Apaolaza, Lourdes

2013-12-18

Water-soluble humic substances (denoted by LN) extracted at alkaline pH from leonardite are proposed to be used as complexing agents to overcome micronutrient deficiencies in plants such as iron chlorosis. LN presents oxidized functional groups that can bind Fe(2+) and Fe(3+). The knowledge of the environment of Fe in the Fe-LN complexes is a key point in the studies on their efficacy as Fe fertilizers. The aim of this work was to study the Fe(2+)/Fe(3+) species formed in Fe-LN complexes with (57)Fe Mössbauer spectroscopy under different experimental conditions in relation to the Fe-complexing capacities, chemical characteristics, and efficiency to provide iron in hydroponics. A high oxidation rate of Fe(2+) to Fe(3+) was found when samples were prepared with Fe(2+), although no well-crystalline magnetically ordered ferric oxide formation could be observed in slightly acidic or neutral media. It seems to be the case that the formation of Fe(3+)-LN compounds is favored over Fe(2+)-LN compounds, although at acidic pH no complex formation between Fe(3+) and LN occurred. The Fe(2+)/Fe(3+) speciation provided by the Mössbauer data showed that Fe(2+)-LN could be efficient in hydroponics while Fe(3+)-LN is suggested to be used more effectively under calcareous soil conditions. However, according to the biological assay, Fe(3+)-LN proved to be effective as a chlorosis corrector applied to iron-deficient cucumber in nutrient solution.

Incorporating Geochemical And Microbial Kinetics In Reactive Transport Models For Generation Of Acid Rock Drainage

NASA Astrophysics Data System (ADS)

Andre, B. J.; Rajaram, H.; Silverstein, J.

2010-12-01

Acid mine drainage, AMD, results from the oxidation of metal sulfide minerals (e.g. pyrite), producing ferrous iron and sulfuric acid. Acidophilic autotrophic bacteria such as Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans obtain energy by oxidizing ferrous iron back to ferric iron, using oxygen as the electron acceptor. Most existing models of AMD do not account for microbial kinetics or iron geochemistry rigorously. Instead they assume that oxygen limitation controls pyrite oxidation and thus focus on oxygen transport. These models have been successfully used for simulating conditions where oxygen availability is a limiting factor (e.g. source prevention by capping), but have not been shown to effectively model acid generation and effluent chemistry under a wider range of conditions. The key reactions, oxidation of pyrite and oxidation of ferrous iron, are both slow kinetic processes. Despite being extensively studied for the last thirty years, there is still not a consensus in the literature about the basic mechanisms, limiting factors or rate expressions for microbially enhanced oxidation of metal sulfides. An indirect leaching mechanism (chemical oxidation of pyrite by ferric iron to produce ferrous iron, with regeneration of ferric iron by microbial oxidation of ferrous iron) is used as the foundation of a conceptual model for microbially enhanced oxidation of pyrite. Using literature data, a rate expression for microbial consumption of ferrous iron is developed that accounts for oxygen, ferrous iron and pH limitation. Reaction rate expressions for oxidation of pyrite and chemical oxidation of ferrous iron are selected from the literature. A completely mixed stirred tank reactor (CSTR) model is implemented coupling the kinetic rate expressions, speciation calculations and flow. The model simulates generation of AMD and effluent chemistry that qualitatively agrees with column reactor and single rock experiments. A one dimensional reaction diffusion model at the scale of a single rock is developed incorporating the proposed kinetic rate expressions. Simulations of initiation, washout and AMD flows are discussed to gain a better understanding of the role of porosity, effective diffusivity and reactive surface area in generating AMD. Simulations indicate that flow boundary conditions control generation of acid rock drainage as porosity increases.

Reductive Sequestration Of Pertechnetate (99TcO4–) By Nano Zerovalent Iron (nZVI) Transformed By Abiotic Sulfide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, Dimin; Anitori, Roberto; Tebo, Bradley M.

2013-04-24

Under anoxic conditions, soluble 99TcO4– can be reduced to less soluble TcO2•nH2O, but the oxide is highly susceptible to reoxidation. Here we investigate an alternative strategy for remediation of Tc-contaminated groundwater whereby sequestration as Tc sulfide is favored by sulfidic conditions stimulated by nano zero-valent iron (nZVI). nZVI was pre-exposed to increasing concentrations of sulfide in simulated Hanford groundwater for 24 hrs to mimic the stages of aquifer sulfate reduction and onset of biotic sulfidogenesis. Solid-phase characterizations of the sulfidated nZVI confirmed the formation of nanocrystalline FeS phases, but higher S/Fe ratios (>0.112) did not result in the formation ofmore » significantly more FeS. The kinetics of Tc sequestration by these materials showed faster Tc removal rates with increasing S/Fe between S/Fe = 0–0.056, but decreasing Tc removal rates with S/Fe > 0.224. The more favorable Tc removal kinetics at low S/Fe could be due to a higher affinity of TcO4– for FeS (over iron oxides), and electron microscopy confirmed that the majority of the Tc was associated with FeS phases. The inhibition of Tc removal at high S/Fe appears to have been caused by excess HS–. X-ray absorption spectroscopy revealed that as S/Fe increased, Tc speciation shifted from TcO2•nH2O to TcS2. The most substantial change of Tc speciation occurred at low S/Fe, coinciding with the rapid increase of Tc removal rate. This agreement further confirms the importance of FeS in Tc sequestration.« less

Hybrid biosorbents for removal of pollutants and remediation

NASA Astrophysics Data System (ADS)

Burlakovs, Juris; Klavins, Maris; Robalds, Artis; Ansone, Linda

2014-05-01

For remediation of soils and purification of polluted waters, wastewaters, biosorbents might be considered as prospective groups of materials. Amongst them peat have a special role due to low cost, biodegradability, high number of functional groups, well developed surface area and combination of hydrophilic/hydrophobic structural elements. Peat as sorbent have good application potential for removal of trace metals, and we have demonstrated peat sorption capacities, sorption kinetics, thermodynamics in respect to metals with different valencies - Tl(I), Cu(II), Cr(III). However, peat sorption capacity in respect to nonmetallic (anionic species) elements is low. Also peat mechanical properties do not support application in large scale column processes thereby, to expand peat application sphere, the approach of biomass based hybrid sorbents has been elaborated. The concept "hybrid sorbent" in understanding of biosorbent means natural, biomass based modified material, covered with another sorbent material, thus combining properties of both such as sorbent functionalities, surface properties etc. As the "covering layer" both inorganic substances, mineral phases (iron oxohydroxides, oxyappatite) and organic polymers (using graft polymerization) were used. The obtained sorbents were characterised by their spectral properties, surface area and elemental composition. The obtained hybrid sorbents were tested for sorption of compounds in anionic speciation forms, for example of arsenic, antimony, tellurium and phosphorous compounds in comparison with weakly basic anionites. The highest sorption capacity was observed when peat sorbents modified with iron compounds were used. Sorption of different arsenic speciation forms onto iron-modified peat sorbents was investigated as a function of pH and temperature. It was established that sorption capacity increases with a rise in temperature as the calculation of sorption process thermodynamic parameters indicates the spontaneity of sorption process and its endothermic nature. The recycling options of obtained compounds after their saturation with metal or non-metallic species are suggested.

River-derived humic substances as iron chelators in seawater

PubMed Central

Krachler, Regina; Krachler, Rudolf F.; Wallner, Gabriele; Hann, Stephan; Laux, Monika; Cervantes Recalde, Maria F.; Jirsa, Franz; Neubauer, Elisabeth; von der Kammer, Frank; Hofmann, Thilo; Keppler, Bernhard K.

2015-01-01

The speciation of iron(III) in oxic seawater is dominated by its hydrolysis and sedimentation of insoluble iron(III)-oxyhydroxide. As a consequence, many oceanic areas have very low iron levels in surface seawater which leads to iron deficiency since phytoplankton require iron as a micronutrient in order to grow. Fortunately, iron solubility is not truly as low as Fe(III) solubility measurements in inorganic seawater would suggest, since oceanic waters contain organic molecules which tend to bind the iron and keep it in solution. Various iron-binding organic ligands which combine to stabilize dissolved iron have been detected and thoroughly investigated in recent years. However, the role of iron-binding ligands from terrestrial sources remains poorly constrained. Blackwater rivers supply large amounts of natural organic material (NOM) to the ocean. This NOM (which consists mainly of vascular plant-derived humic substances) is able to greatly enhance iron bioavailability in estuaries and coastal regions, however, breakdown processes lead to a rapid decrease of river-derived NOM concentrations with increasing distance from land. It has therefore been argued that the influence of river-derived NOM on iron biogeochemistry in offshore seawater does not seem to be significant. Here we used a standard method based on 59Fe as a radiotracer to study the solubility of Fe(III)-oxyhydroxide in seawater in the presence of riverine NOM. We aimed to address the question how effective is freshwater NOM as an iron chelator under open ocean conditions where the concentration of land-derived organic material is about 3 orders of magnitude smaller than in coastal regions, and does this iron chelating ability vary between NOM from different sources and between different size fractions of the river-borne NOM. Our results show that the investigated NOM fractions were able to substantially enhance Fe(III)-oxyhydroxide solubility in seawater at concentrations of the NOM ≥ 5 μg L− 1. Terrigenous NOM concentrations ≥ 5 μg L− 1 are in no way unusual in open ocean surface waters especially of the Arctic and the North Atlantic Oceans. River-derived humic substances could therefore play a greater role as iron carriers in the ocean than previously thought. PMID:26412934

Iron speciation of airborne subway particles by the combined use of energy dispersive electron probe X-ray microanalysis and Raman microspectrometry.

PubMed

Eom, Hyo-Jin; Jung, Hae-Jin; Sobanska, Sophie; Chung, Sang-Gwi; Son, Youn-Suk; Kim, Jo-Chun; Sunwoo, Young; Ro, Chul-Un

2013-11-05

Quantitative energy-dispersive electron probe X-ray microanalysis (ED-EPMA), known as low-Z particle EPMA, and Raman microspectrometry (RMS) were applied in combination for an analysis of the iron species in airborne PM10 particles collected in underground subway tunnels. Iron species have been reported to be a major chemical species in underground subway particles generated mainly from mechanical wear and friction processes. In particular, iron-containing particles in subway tunnels are expected to be generated with minimal outdoor influence on the particle composition. Because iron-containing particles have different toxicity and magnetic properties depending on their oxidation states, it is important to determine the iron species of underground subway particles in the context of both indoor public health and control measures. A recently developed analytical methodology, i.e., the combined use of low-Z particle EPMA and RMS, was used to identify the chemical species of the same individual subway particles on a single particle basis, and the bulk iron compositions of airborne subway particles were also analyzed by X-ray diffraction. The majority of airborne subway particles collected in the underground tunnels were found to be magnetite, hematite, and iron metal. All the particles collected in the tunnels of underground subway stations were attracted to permanent magnets due mainly to the almost ubiquitous ferrimagnetic magnetite, indicating that airborne subway particles can be removed using magnets as a control measure.

Siderophores in Cloud Waters and Potential Impact on Atmospheric Chemistry: Photoreactivity of Iron Complexes under Sun-Simulated Conditions.

PubMed

Passananti, Monica; Vinatier, Virginie; Delort, Anne-Marie; Mailhot, Gilles; Brigante, Marcello

2016-09-06

In the present work, the photoreactivity of a mixture of iron(III)–pyoverdin (Fe(III)–Pyo) complexes was investigated under simulated cloud conditions. Pyoverdins are expected to complex ferric ions naturally present in cloudwater, thus modifying their availability and photoreactivity. The spectroscopic properties and photoreactivity of Fe(III)-Pyo were investigated, with particular attention to their fate under solar irradiation, also studied through simulations. The photolysis of the Fe(III)–Pyo complex leads to the generation of Fe(II), with rates of formation (RFe(II)f) of 6.98 and 3.96 × 10–9 M s–1 at pH 4.0 and 6.0, respectively. Interestingly, acetate formation was observed during the iron-complex photolysis, suggesting that fragmentation can occur after the ligand-to-metal charge transfer (LMCT) via a complex reaction mechanism. Moreover, photogenerated Fe(II) represent an important source of hydroxyl radical via the Fenton reaction in cloudwater. This reactivity might be relevant for the estimation of the rates of formation and steady-state concentrations of the hydroxyl radical by cloud chemistry models and for organic matter speciation in the cloud aqueous phase. In fact, the conventional models, which describe the iron photoreactivity in terms of iron–aqua and oxalate complexes, are not in accordance with our results.

Identifying Marine Copper-Binding Ligands in Seawater

NASA Astrophysics Data System (ADS)

Whitby, H.; Hollibaugh, J. T.; Maldonado, M. T.; Ouchi, S.; van den Berg, S. M.

2016-02-01

Complexation reactions are important because they affect the bioavailability of trace metals such as copper and iron. For example, organic complexation can determine whether copper is a limiting or a toxic micronutrient at natural levels. Copper competes with iron for complexing ligands, and when iron is limiting, copper can also substitute for iron in some metabolic pathways. The speciation of copper can be measured using complexing capacity titrations, which provide the concentration of individual ligand classes (L1, L2 etc.) and the complex stabilities (log K). Using methods recently developed in our laboratory, we show that the ligands within these classes can be measured independently of titrations, thus confirming the titration method and simultaneously identifying the ligands within each class. Thiols were identified as the L1 ligand class and humic compounds as the weaker L2 class in samples from coastal Georgia, USA, collected monthly from April to December. Log K values of the ligand complexes were consistent with values expected for thiols and humic substances. Recent results from culture studies and from samples collected along Line P, a coastal - oceanic transect in the HNLC region of the NE subarctic Pacific, will be presented in comparison to the estuarine results. This comparison will help to broaden our perspective on copper complexation and the ligands responsible, furthering our understanding of ligand sources and life cycles.

Arsenic speciation in arsenic-rich Brazilian soils from gold mining sites under anaerobic incubation

USGS Publications Warehouse

De Mello, J. W. V.; Talbott, J.L.; Scott, J.; Roy, W.R.; Stucki, J.W.

2007-01-01

Background. Arsenic speciation in environmental samples is essential for studying toxicity, mobility and bio-transformation of As in aquatic and terrestrial environments. Although the inorganic species As(III) and As(V) have been considered dominant in soils and sediments, organisms are able to metabolize inorganic forms of arsenic into organo-arsenic compounds. Arsenosugars and methylated As compounds can be found in terrestrial organisms, but they generally occur only as minor constituents. We investigated the dynamics of arsenic species under anaerobic conditions in soils surrounding gold mining areas from Minas Gerais State, Brazil to elucidate the arsenic biogeochemical cycle and water contamination mechanisms. Methods. Surface soil samples were collected at those sites, namely Paracatu Formation, Banded Iron Formation and Riacho dos Machados Sequence, and incubated in CaCl2 2.5 mmol L-1 suspensions under anaerobic conditions for 1, 28, 56 and 112 days. After that, suspensions were centrifuged and supernatants analyzed for soluble As species by IC-ICPMS and HPLC-ICPMS. Results. Easily exchangeable As was mainly arsenite, except when reducible manganese was present. Arsenate was mainly responsible for the increase in soluble arsenic due to the reductive dissolution of either iron or manganese in samples from the Paracatu Formation and Riacho dos Machados Sequence. On the other hand, organic species of As dominated in samples from the Banded Iron Formation during anaerobic incubation. Discussion. Results are contrary to the expectation that, in anaerobic environments, As release due to the reductive dissolution of Fe is followed by As(V) reduction to As(III). The occurrence of organo-arsenic species was also found to be significant to the dynamics of soluble arsenic, mainly in soils from the Banded Iron Formation (BIF), under our experimental conditions. Conclusions. In general, As(V) and organic As were the dominant species in solution, which is surprising under anaerobic conditions in terrestrial environments. The unexpected occurrence of organic species of As was attributed to enrollment of ternary organic complexes or living organisms such as algae or cyanobacteria. Perspectives. These findings are believed to be useful for remediation strategies in mine-affected regions, as the organic As species are in general considered to be less toxic than inorganic ones and even As(V) is considered less mobile and toxic than As(III). ?? 2007 ecomed publishers (Verlagsgruppe Hu??thig Jehle Rehm GmbH).

Vivianite as an important iron phosphate precipitate in sewage treatment plants.

PubMed

Wilfert, P; Mandalidis, A; Dugulan, A I; Goubitz, K; Korving, L; Temmink, H; Witkamp, G J; Van Loosdrecht, M C M

2016-11-01

Iron is an important element for modern sewage treatment, inter alia to remove phosphorus from sewage. However, phosphorus recovery from iron phosphorus containing sewage sludge, without incineration, is not yet economical. We believe, increasing the knowledge about iron-phosphorus speciation in sewage sludge can help to identify new routes for phosphorus recovery. Surplus and digested sludge of two sewage treatment plants was investigated. The plants relied either solely on iron based phosphorus removal or on biological phosphorus removal supported by iron dosing. Mössbauer spectroscopy showed that vivianite and pyrite were the dominating iron compounds in the surplus and anaerobically digested sludge solids in both plants. Mössbauer spectroscopy and XRD suggested that vivianite bound phosphorus made up between 10 and 30% (in the plant relying mainly on biological removal) and between 40 and 50% of total phosphorus (in the plant that relies on iron based phosphorus removal). Furthermore, Mössbauer spectroscopy indicated that none of the samples contained a significant amount of Fe(III), even though aerated treatment stages existed and although besides Fe(II) also Fe(III) was dosed. We hypothesize that chemical/microbial Fe(III) reduction in the treatment lines is relatively quick and triggers vivianite formation. Once formed, vivianite may endure oxygenated treatment zones due to slow oxidation kinetics and due to oxygen diffusion limitations into sludge flocs. These results indicate that vivianite is the major iron phosphorus compound in sewage treatment plants with moderate iron dosing. We hypothesize that vivianite is dominating in most plants where iron is dosed for phosphorus removal which could offer new routes for phosphorus recovery. Copyright © 2016 Elsevier Ltd. All rights reserved.

Oxidation and deprotonation of synthetic Fe{sup II}-Fe{sup III} (oxy)hydroxycarbonate Green Rust: An X-ray photoelectron study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mullet, M.; Guillemin, Y.; Ruby, C.

X-ray photoelectron spectroscopy (XPS) was used to investigate chemical bonding and distribution of iron and oxygen species at the surface of Green Rusts (GRs). GRs with variable composition, i.e. Fe{sup II}{sub 6(1-x)}Fe{sup III}{sub 6x}O{sub 12}H{sub 2(7-3x)} CO{sub 3}.3H{sub 2}O where the Fe{sup III} molar fraction of the positively charged hydroxide sheets, x=[Fe(III)]/[Fe(total)] belongs to [1/3, 1], were synthesised under an inert atmosphere. The broadened Fe(2p{sub 3/2}) spectra were fitted using Gupta and Sen multiplets peaks and additional satellite and surface features. The [Fe(III)]/[Fe(total)] surface atomic ratios closely agree with the x ratios expected from the bulk composition, which gives amore » high degree of confidence on the validity of the proposed fitting procedure. The valence band spectra are also reported and show dependencies on iron speciation. The O(1s) spectra revealed the presence of O{sup 2-}, OH{sup -} species and adsorbed water. The hydroxyl component decreases with increasing x values, i.e. with the amount of ferric iron, while the oxide component increases. This study provides direct spectroscopic evidence of the deprotonation of hydroxyl groups that occurs simultaneously with the oxidation of ferrous iron within the GR structure. - Graphical abstract: X-ray photoelectron spectroscopy (XPS) is used to investigate chemical bonding and distribution of iron and oxygen species at the surface of Green Rust (GR) compounds. First spectroscopic evidence of the deprotonation of hydroxyls groups occurring simultaneously to the oxidation of Fe(II) into Fe(III) species is provided.« less

Solid surface photochemistry of montmorillonite: mechanisms for the arsenite oxidation under UV-A irradiation.

PubMed

Yuan, Yanan; Wang, Yajie; Ding, Wei; Li, Jinjun; Wu, Feng

2016-01-01

Transformation of inorganic arsenic species has drawn great concern in recent decades because of worldwide and speciation-dependent pollution and the hazards that they pose to the environment and to human health. As(III) photooxidation in aquatic systems has received much attention, but little is known about photochemical transformation of arsenic species on top soil. As(III) photooxidation on natural montmorillonite under UV-A radiation was investigated by using a moisture- and temperature-controlled photochemical chamber with two black-light lamps. Initial As(III) concentration, pH, layer thickness, humic acid (HA) concentration, the presence of additional iron ions, and the contribution of reactive oxygen species (ROS) were examined. The results show that pH values of the clay layers greatly influenced As(III) photooxidation on montmorillonite. As(III) photooxidation followed the Langmuir-Hinshelwood model. HA and additional iron ions greatly promoted photooxidation, but excess Fe(II) competed with As(III) for oxidation by ROS. Scavenging experiments revealed that natural montmorillonite induced the conversion of As(III) to As(V) by generating ROS (mainly HO(•) and HO2(•)/O2(•-)) and that HO(•) radical was the predominant oxidant in this system. Our work demonstrates that photooxidation on the surface of natural clay minerals in top soil can be important to As(III) transformation. This allows understanding and predicting the speciation and behavior of arsenic on the soil surface.

Do radial oxygen loss and external aeration affect iron plaque formation and arsenic accumulation and speciation in rice?

PubMed Central

Wu, Chuan; Ye, Zhihong; Li, Hui; Wu, Shengchun; Deng, Dan; Zhu, Yongguan; Wong, Minghung

2012-01-01

Hydroponic experiments were conducted to investigate the effect of radial oxygen loss (ROL) and external aeration on iron (Fe) plaque formation, and arsenic (As) accumulation and speciation in rice (Oryza sativa L.). The data showed that there were significant correlations between ROL and Fe concentrations in Fe plaque produced on different genotypes of rice. There were also significant differences in the amounts of Fe plaque formed between different genotypes in different positions of roots and under different aeration conditions (aerated, normal, and stagnant treatments). In aerated treatments, rice tended to have a higher Fe plaque formation than in a stagnant solution, with the greatest formation at the root tip decreasing with increasing distances away, in accordance with a trend of spatial ROL. Genotypes with higher rates of ROL induced higher degrees of Fe plaque formation. Plaques sequestered As on rice roots, with arsenate almost double that with arsenite, leading to decreased As accumulation in both roots and shoots. The major As species detected in roots and shoots was arsenite, ranging from 34 to 78% of the total As in the different treatments and genotypes. These results contribute to our understanding of genotypic differences in As uptake by rice and the mechanisms causing rice genotypes with higher ROL to show lower overall As accumulation. PMID:22345639

Sorption and speciation of selenium in boreal forest soil.

PubMed

Söderlund, Mervi; Virkanen, Juhani; Holgersson, Stellan; Lehto, Jukka

2016-11-01

Sorption and speciation of selenium in the initial chemical forms of selenite and selenate were investigated in batch experiments on humus and mineral soil samples taken from a 4-m deep boreal forest soil excavator pit on Olkiluoto Island, on the Baltic Sea coast in southwestern Finland. The HPLC-ICP-MS technique was used to monitor any possible transformations in the selenium liquid phase speciation and to determine the concentrations of selenite and selenate in the samples for calculation of the mass distribution coefficient, K d , for both species. Both SeO 3 2- and SeO 4 2- proved to be resistant forms in the prevailing soil conditions and no changes in selenium liquid phase speciation were seen in the sorption experiments in spite of variations in the initial selenium species, incubation time or conditions, pH, temperature or microbial activity. Selenite sorption on the mineral soil increased with time in aerobic conditions whilst the opposite trend was seen for the anaerobic soil samples. Selenite retention correlated with the contents of organic matter and weakly crystalline oxides of aluminum and iron, solution pH and the specific surface area. Selenate exhibited poorer sorption on soil than selenite and on average the K d values were 27-times lower. Mineral soil was more efficient in retaining selenite and selenate than humus, implicating the possible importance of weakly crystalline aluminum and iron oxides for the retention of oxyanions in Olkiluoto soil. Sterilization of the soil samples decreased the retention of selenite, thus implying some involvement of soil microbes in the sorption processes or a change in sample composition, but it produced no effect for selenate. There was no sorption of selenite by quartz, potassium feldspar, hornblende or muscovite. Biotite showed the best retentive properties for selenite in the model soil solution at about pH 8, followed by hematite, plagioclase and chlorite. The K d values for these minerals were 18, 14, 8 and 7 L/kg, respectively. It is proposed that selenite sorption is affected by the structural Fe(II) in biotite, which is capable of inducing the reduction of SeO 3 2- to Se(0). Selenite probably forms a surface complex with Fe(III) atoms on the surface of hematite, thus explaining its retention on this mineral. None of the minerals retained selenate to any extent. Copyright © 2016 Elsevier Ltd. All rights reserved.

Human calprotectin affects the redox speciation of iron.

PubMed

Nakashige, Toshiki G; Nolan, Elizabeth M

2017-08-16

We report that the metal-sequestering human host-defense protein calprotectin (CP, S100A8/S100A9 oligomer) affects the redox speciation of iron (Fe) in bacterial growth media and buffered aqueous solution. Under aerobic conditions and in the absence of an exogenous reducing agent, CP-Ser (S100A8(C42S)/S100A9(C3S) oligomer) depletes Fe from three different bacterial growth media preparations over a 48 h timeframe (T = 30 °C). The presence of the reducing agent β-mercaptoethanol accelerates this process and allows CP-Ser to deplete Fe over a ≈1 h timeframe. Fe-depletion assays performed with metal-binding-site variants of CP-Ser show that the hexahistidine (His 6 ) site, which coordinates Fe(ii) with high affinity, is required for Fe depletion. An analysis of Fe redox speciation in buffer containing Fe(iii) citrate performed under aerobic conditions demonstrates that CP-Ser causes a time-dependent increase in the [Fe(ii)]/[Fe(iii)] ratio. Taken together, these results indicate that the hexahistidine site of CP stabilizes Fe(ii) and thereby shifts the redox equilibrium of Fe to the reduced ferrous state under aerobic conditions. We also report that the presence of bacterial metabolites affects the Fe-depleting activity of CP-Ser. Supplementation of bacterial growth media with an Fe(iii)-scavenging siderophore (enterobactin, staphyloferrin B, or desferrioxamine B) attenuates the Fe-depleting activity of CP-Ser. This result indicates that formation of Fe(iii)-siderophore complexes blocks CP-mediated reduction of Fe(iii) and hence the ability of CP to coordinate Fe(ii). In contrast, the presence of pyocyanin (PYO), a redox-cycling phenazine produced by Pseudomonas aeruginosa that reduces Fe(iii) to Fe(ii), accelerates Fe depletion by CP-Ser under aerobic conditions. These findings indicate that the presence of microbial metabolites that contribute to metal homeostasis at the host/pathogen interface can affect the metal-sequestering function of CP.

The glacial iron cycle from source to export

NASA Astrophysics Data System (ADS)

Hawkings, J.; Wadham, J. L.; Tranter, M.; Raiswell, R.; Benning, L. G.; Statham, P. J.; Tedstone, A. J.; Nienow, P. W.; Telling, J.; Bagshaw, E.; Simmons, S. L.

2014-12-01

Nutrient availability limits primary production in large sectors of the world's oceans. Iron is the major limiting nutrient in around one third of the oceanic euphotic zone, most significantly in the Southern Ocean proximal to Antarctica. In these areas the availability of bioavailable iron can influence the amount of primary production, and thus the strength of the biological pump and associated carbon drawdown from the atmosphere. Despite experiencing widespread iron limitation, the Polar oceans are among the most productive on Earth. Due to the extreme cold, remoteness and their perceived "stasis", ice sheets have previously been though of as insignificant in global biogeochemical cycles. However, large marine algal blooms have been observed in iron-limited areas where glacial influence is large, and it is possible that these areas are stimulated by glacial bioavailable iron input. Here we discuss the importance of the Greenland and Antarctic ice sheets in the global iron cycle. Using field collected trace element data, bulk meltwater chemistry and mineralogical analysis, including photomicrographs, EELS and XANES, we present, for the first time, a conceptual model of the glacial iron cycle from source to export. Using this data we discuss the sources of iron in glacial meltwater, transportation and alteration through the glacial system, and subsequent export to downstream environments. Data collected in 2012 and 2013 from two different Greenlandic glacial catchments are shown, with the most detailed breakdown of iron speciation and concentrations in glacial areas yet reported. Furthermore, the first data from Greenlandic icebergs is presented, allowing meltwater-derived and iceberg-derived iron export to be compared, and the influence of both in marine productivity to be estimated. Using our conceptual model and flux estimates from our dataset, glacial iron delivery in both the northern and southern hemisphere is discussed. Finally, we compare our flux estimates to other major iron sources to the polar regions such as aeolian dust, and discuss potential implications of increased melting of the ice sheets on the global iron cycle in the future.

The Organic Complexation of Iron in the Marine Environment: A Review

PubMed Central

Gledhill, Martha; Buck, Kristen N.

2012-01-01

Iron (Fe) is an essential micronutrient for marine organisms, and it is now well established that low Fe availability controls phytoplankton productivity, community structure, and ecosystem functioning in vast regions of the global ocean. The biogeochemical cycle of Fe involves complex interactions between lithogenic inputs (atmospheric, continental, or hydrothermal), dissolution, precipitation, scavenging, biological uptake, remineralization, and sedimentation processes. Each of these aspects of Fe biogeochemical cycling is likely influenced by organic Fe-binding ligands, which complex more than 99% of dissolved Fe. In this review we consider recent advances in our knowledge of Fe complexation in the marine environment and their implications for the biogeochemistry of Fe in the ocean. We also highlight the importance of constraining the dissolved Fe concentration value used in interpreting voltammetric titration data for the determination of Fe speciation. Within the published Fe speciation data, there appear to be important temporal and spatial variations in Fe-binding ligand concentrations and their conditional stability constants in the marine environment. Excess ligand concentrations, particularly in the truly soluble size fraction, seem to be consistently higher in the upper water column, and especially in Fe-limited, but productive, waters. Evidence is accumulating for an association of Fe with both small, well-defined ligands, such as siderophores, as well as with larger, macromolecular complexes like humic substances, exopolymeric substances, and transparent exopolymers. The diverse size spectrum and chemical nature of Fe ligand complexes corresponds to a change in kinetic inertness which will have a consequent impact on biological availability. However, much work is still to be done in coupling voltammetry, mass spectrometry techniques, and process studies to better characterize the nature and cycling of Fe-binding ligands in the marine environment. PMID:22403574

Questa baseline and pre-mining ground-water quality investigation. 12. Geochemical and reactive-transport modeling based on tracer injection-synoptic sampling studies for the Red River, New Mexico, 2001-2002

USGS Publications Warehouse

Ball, James W.; Runkel, Robert L.; Nordstrom, D. Kirk

2005-01-01

Reactive-transport processes in the Red River, downstream from the town of Red River in north-central New Mexico, were simulated using the OTEQ reactive-transport model. The simulations were calibrated using physical and chemical data from synoptic studies conducted during low-flow conditions in August 2001 and during March/April 2002. Discharge over the 20-km reach from the town of Red River to the USGS streamflow-gaging station near the town of Questa ranged from 395 to 1,180 L/s during the 2001 tracer and from 234 to 421 L/s during the 2002 tracer. The pH of the Red River ranged from 7.4 to 8.5 during the 2001 tracer and from 7.1 to 8.7 during the 2002 tracer, and seep and tributary samples had pH values of 2.8 to 9.0 during the 2001 tracer and 3.8 to 7.2 during the 2002 tracer. Mass-loading calculations allowed identification of several specific locations where elevated concentrations of potential contaminants entered the Red River . These locations, characterized by features on the north side of the Red River that are known to be sources of low-pH water containing elevated metal and sulfate concentrations, are: the initial 2.4 km of the study reach, including Bitter Creek, the stream section from 6.2 to 7.8 km, encompassing La Bobita well and the Hansen debris fan, Sulphur Gulch, at about 10.5 km, the area near Portal Springs, from 12.2 to 12.6 km, and the largest contributors of mass loading, the 13.7 to 13.9 km stream section near Cabin Springs and the 14.7 to 17.5 km stream section from Shaft Spring to Thunder Bridge, Goathill Gulch, and Capulin Canyon. Speciation and saturation index calculations indicated that although solubility limits the concentration of aluminum above pH 5.0, at pH values above 7 and aluminum concentrations below 0.3 mg/L inorganic speciation and mineral solubility controls no longer dominate and aluminum-organic complexing may occur. The August 2001 reactive-transport simulations included dissolved iron(II) oxidation, constrained using measured concentrations of dissolved iron(II) and dissolved iron(total). Both simulations included precipitation of amorphous Al(OH)3 and hydrous ferric oxide as Fe(OH)3, and sorption of copper and zinc to the precipitated hydrous ferric oxide. Simulations revealed that hydrogen, iron, aluminum, copper, and zinc were non-conservative and that mineral precipitation can account for iron and aluminum concentrations. Copper and zinc concentrations can be accounted for by simulating their sorption to hydrous ferric oxide forming in the water column of the Red River , although hydrous manganese oxides also may be important sorption substrates.

Suspended particulate matter determines physical speciation of Fe, Mn, and trace metals in surface waters of Loire watershed.

PubMed

Baalousha, Mohamed; Stoll, Serge; Motelica-Heino, Mikaël; Guigues, Nathalie; Braibant, Gilles; Huneau, Frédéric; Le Coustumer, Philippe

2018-02-10

This study investigates the spatiotemporal variability of major and trace elements, dissolved organic carbon (DOC), total dissolved solids (TDS), and suspended particulate matter (SPM) in surface waters of several hydrosystems of the Loire River watershed in France. In particular, this study aims to delineate the impact of the abovementioned water physicochemical parameters on natural iron and manganese physical speciation (homoaggregation/heteroaggregation) among fine colloidal and dissolved (< 10 nm), colloidal (10-450 nm) and particulate (> 450 nm) phases in Loire River watershed. Results show that the chemistry of the Loire River watershed is controlled by two end members: magmatic and metamorphic petrographic context on the upper part of the watershed; and sedimentary rocks for the middle and low part of the Loire. The percentage of particulate Fe and Mn increased downstream concurrent with the increase in SPM and major cations concentration, whereas the percentage of colloidal Fe and Mn decreased downstream. Transmission electron microscopy analyses of the colloidal and particulate fractions (from the non-filtered water sample) revealed that heteroaggregation of Fe and Mn rich natural nanoparticles and natural organic matter to the particulate phase is the dominant mechanism. The heteroaggregation controls the partitioning of Fe and Mn in the different fractions, potentially due to the increase in the ionic strength, and divalent cations concentration downstream, and SPM concentration. These findings imply that SPM concentration plays an important role in controlling the fate and behavior of Fe and Mn in various sized fractions. Graphical abstract Physical speciation by heteroaggregation of (Fe-Mn) compounds: high [SPM] → [Fe-Mn] particulate faction; low {SPM] → [Fe-Mn] colloid-dissolved fraction.

Arsenic speciation and trace element analysis of the volcanic río Agrio and the geothermal waters of Copahue, Argentina.

PubMed

Farnfield, Hannah R; Marcilla, Andrea L; Ward, Neil I

2012-09-01

Surface water originating from the Copahue volcano crater-lake was analysed for total arsenic and four arsenic species: arsenite (iAs(III)), arsenate (iAs(V)), monomethylarsonic acid (MA(V)) and dimethylarsinic acid (DMA(V)) and other trace elements (Fe, Mn, V, Cr, Ni, Zn). A novel in-field technique for the preconcentration and separation of four arsenic species was, for the first time, used for the analysis of geothermal and volcanic waters. Total arsenic levels along the río Agrio ranged from <0.2-3783 μg/l As(T). The highest arsenic levels were recorded in the el Vertedero spring (3783 μg/l As(T)) on the flank of the Copahue volcano, which feeds the acidic río Agrio. Arsenite (H(3)AsO(3)) predominated along the upper río Agrio (78.9-81.2% iAs(III)) but the species distribution changed at lago Caviahue and arsenate (H(2)AsO(4)(-)) became the main species (51.4-61.4% iAs(V)) up until Salto del Agrio. The change in arsenic species is potentially a result of an increase in redox potential and the formation of iron-based precipitates. Arsenic speciation showed a statistically significant correlation with redox potential (r=0.9697, P=0.01). Both total arsenic and arsenic speciation displayed a statistically significant correlation with vanadium levels along the river (r=0.9961, P=0.01 and r=0.8488, P=0.05, respectively). This study highlights that chemical speciation analysis of volcanic waters is important in providing ideas on potential chemical toxicity. Furthermore there is a need for further work evaluating how arsenic (and other trace elements), released in volcanic and geothermal streams/vents, impacts on both biota and humans (via exposure in thermal pools or consuming commercial drinking water). Copyright © 2012 Elsevier B.V. All rights reserved.

Source tracing of fluvial suspended sediments by magnetic and geochemical particle characterization: example of the Canche watershed (Nord-Pas-de-Calais, France)

NASA Astrophysics Data System (ADS)

Patault, Edouard; Alary, Claire; Franke, Christine; Gauthier, Arnaud; Abriak, Nor-Edine

2016-04-01

In France, erosion by water run-off is estimated to 1.5 t ha-1yr-1 and can exceed 10 t ha-1yr-1 in large growing areas, such as the North of France (Nord-Pas-de-Calais). In this region, the Canche watershed (1294 km2) sustains heavy loss of fertile soils. The land use is mainly dominated by arable lands (80%) and in 2013, 104 kt of suspended sediment transited to the estuary. As demonstrated in literature, agricultural soil erosion leads to the gradual disappearance and depletion of fertile soil, which constitute a non-renewable resource at human time scale. Additionally, water erosion can significantly damage the aquatic habitat and can be responsible for the input of nutrients, bacteria, pesticides, heavy metals and radionuclides into surface waters. Conscious of these effects, many programs have emerged in the Nord-Pas-de-Calais to reduce erosion. This study presents a combination of environmental magnetic proxy parameters and geochemical analyses on sediments and suspended particulate matter. The aim is to develop effective tools to trace erosion by water run-off and quantify this process. In order to identify the respective sediment sources in the Canche watershed, sediment trap samples of suspended particulate matter were recovered at key positions along the Canche watershed. The preliminary results show that magnetic concentration (Mrs) shows typical values for the agricultural soils in the region, but these variations in magnetic concentrations and total irons concentrations are not always correlated, which may be explained by the iron speciation. In calculating the so-called S-ratio for each sample we can distinguish changes in magneto-mineralogy (and thus iron speciation) from magnetite-dominated assemblages in the mainstream Canche (naturel background signal) to high-coercivity-dominated assemblages in the tributaries, typical for soil erosion material rich in hematite/goethite. In combination with the element concentrations from ICP analyses, this proxy parameter may give valuable insight into the tracing of the suspended sediment sources. In perspective, the seasonal variability and the discharge in the Canche watershed have to be taken into account.

Speciation and reactivity of uranium products formed during in situ bioremediation in a shallow alluvial aquifer.

PubMed

Alessi, Daniel S; Lezama-Pacheco, Juan S; Janot, Noémie; Suvorova, Elena I; Cerrato, José M; Giammar, Daniel E; Davis, James A; Fox, Patricia M; Williams, Kenneth H; Long, Philip E; Handley, Kim M; Bernier-Latmani, Rizlan; Bargar, John R

2014-11-04

In this study, we report the results of in situ U(VI) bioreduction experiments at the Integrated Field Research Challenge site in Rifle, Colorado, USA. Columns filled with sediments were deployed into a groundwater well at the site and, after a period of conditioning with groundwater, were amended with a mixture of groundwater, soluble U(VI), and acetate to stimulate the growth of indigenous microorganisms. Individual reactors were collected as various redox regimes in the column sediments were achieved: (i) during iron reduction, (ii) just after the onset of sulfate reduction, and (iii) later into sulfate reduction. The speciation of U retained in the sediments was studied using X-ray absorption spectroscopy, electron microscopy, and chemical extractions. Circa 90% of the total uranium was reduced to U(IV) in each reactor. Noncrystalline U(IV) comprised about two-thirds of the U(IV) pool, across large changes in microbial community structure, redox regime, total uranium accumulation, and reaction time. A significant body of recent research has demonstrated that noncrystalline U(IV) species are more suceptible to remobilization and reoxidation than crystalline U(IV) phases such as uraninite. Our results highlight the importance of considering noncrystalline U(IV) formation across a wide range of aquifer parameters when designing in situ remediation plans.

Chemical Imaging Analysis of Environmental Particles Using the Focused Ion Beam/Scanning Electron Microscopy Technique. Microanalysis Insights into Atmospheric Chemistry of Fly Ash

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Haihan; Grassian, Vicki H.; Saraf, Laxmikant V.

2012-11-08

Airborne fly ash from coal combustion may represent a source of bioavailable iron (Fe) in the open ocean. However, few studies have been made focusing on Fe speciation and distribution in coal fly ash. In this study, chemical imaging of fly ash has been performed using a dual-beam FIB/SEM (focused ion beam/scanning electron microscope) system for a better understanding of how simulated atmospheric processing modify the morphology, chemical compositions and element distributions of individual particles. A novel approach has been applied for cross-sectioning of fly ash specimen with a FIB in order to explore element distribution within the interior ofmore » individual particles. Our results indicate that simulated atmospheric processing causes disintegration of aluminosilicate glass, a dominant material in fly ash particles. Aluminosilicate-phase Fe in the inner core of fly ash particles is more easily mobilized compared with oxide-phase Fe present as surface aggregates on fly ash spheres. Fe release behavior depends strongly on Fe speciation in aerosol particles. The approach for preparation of cross-sectioned specimen described here opens new opportunities for particle microanalysis, particular with respect to inorganic refractive materials like fly ash and mineral dust.« less

Speciation and Reactivity of Uranium Products Formed during in Situ Bioremediation in a Shallow Alluvial Aquifer

PubMed Central

2015-01-01

In this study, we report the results of in situ U(VI) bioreduction experiments at the Integrated Field Research Challenge site in Rifle, Colorado, USA. Columns filled with sediments were deployed into a groundwater well at the site and, after a period of conditioning with groundwater, were amended with a mixture of groundwater, soluble U(VI), and acetate to stimulate the growth of indigenous microorganisms. Individual reactors were collected as various redox regimes in the column sediments were achieved: (i) during iron reduction, (ii) just after the onset of sulfate reduction, and (iii) later into sulfate reduction. The speciation of U retained in the sediments was studied using X-ray absorption spectroscopy, electron microscopy, and chemical extractions. Circa 90% of the total uranium was reduced to U(IV) in each reactor. Noncrystalline U(IV) comprised about two-thirds of the U(IV) pool, across large changes in microbial community structure, redox regime, total uranium accumulation, and reaction time. A significant body of recent research has demonstrated that noncrystalline U(IV) species are more suceptible to remobilization and reoxidation than crystalline U(IV) phases such as uraninite. Our results highlight the importance of considering noncrystalline U(IV) formation across a wide range of aquifer parameters when designing in situ remediation plans. PMID:25265543

Reactivity of catecholamine-driven Fenton reaction and its relationships with iron(III) speciation.

PubMed

Melin, Victoria; Henríquez, Adolfo; Freer, Juanita; Contreras, David

2015-03-01

Fenton reaction is the main source of free radicals in biological systems. The reactivity of this reaction can be modified by several factors, among these iron ligands are important. Catecholamine (dopamine, epinephrine, and norepinephrine) are able to form Fe(III) complexes whose extension in the coordination number depends upon the pH. Fe(III)-catecholamine complexes have been related with the development of several pathologies. In this work, the ability of catecholamines to enhance the oxidative degradation of an organic substrate (veratryl alcohol, VA) through Fenton and Fenton-like reactions was studied. The initial VA degradation rate at different pH values and its relationship to the different iron species present in solution were determined. Furthermore, the oxidative degradation of VA after 24 hours of reaction and its main oxidation products were also determined. The catecholamine-driven Fenton and Fenton-like systems showed higher VA degradation compared to unmodified Fenton or Fenton-like systems, which also showed an increase in the oxidation state of the VA degradation product. All of this oxidative degradation takes place at pH values lower than 5.50, where the primarily responsible species would be the Fe(III) mono-complex. The presence of Fe(III) mono-complex is essential in the ability of catecholamines to increase the oxidative capacity of Fenton systems.

Constraints on Meteoric Smoke Composition and Meteoric Influx Using SOFIE Observations With Models

NASA Astrophysics Data System (ADS)

Hervig, Mark E.; Brooke, James S. A.; Feng, Wuhu; Bardeen, Charles G.; Plane, John M. C.

2017-12-01

The composition of meteoric smoke particles in the mesosphere is constrained using measurements from the Solar Occultation For Ice Experiment (SOFIE) in conjunction with models. Comparing the multiwavelength observations with models suggests smoke compositions of magnetite, wüstite, magnesiowüstite, or iron-rich olivine. Smoke compositions of pure pyroxene, hematite, iron-poor olivine, magnesium silicate, and silica are excluded, although this may be because these materials have weak signatures at the SOFIE wavelengths. Information concerning smoke composition allows the SOFIE extinction measurements to be converted to smoke volume density. Comparing the observed volume density with model results for varying meteoric influx (MI) provides constraints on the ablated fraction of incoming meteoric material. The results indicate a global ablated MI of 3.3 ± 1.9 t d-1, which represents only iron, magnesium, and possibly silica, given the smoke compositions indicated here. Considering the optics and iron content of individual smoke compositions gives an ablated Fe influx of 1.8 ± 0.9 t d-1. Finally, the global total meteoric influx (ablated plus surviving) is estimated to be 30 ± 18 t d-1, when considering the present results and a recent description of the speciation of meteoric material.

Bioleaching of heavy metals from sewage sludge by indigenous iron-oxidizing microorganisms using ammonium ferrous sulfate and ferrous sulfate as energy sources: a comparative study.

PubMed

Pathak, Ashish; Dastidar, M G; Sreekrishnan, T R

2009-11-15

The potential of indigenous iron-oxidizing microorganisms enriched at initial neutral pH of the sewage sludge for bioleaching of heavy metals was investigated at initial neutral pH of the sludge using ammonium ferrous sulfate (FAS) and ferrous sulfate (FS) as an energy sources in two different sets of experiments. After 16 days of bioleaching, 56% Cu, 48% Ni, 68% Zn and 42% C were removed from the sludge using ammonium ferrous sulfate as an energy source. On the other hand, 64% Cu, 58% Ni, 76% Zn and 52% Cr were removed using ferrous sulfate. Further, 32% nitrogen and 24% phosphorus were leached from the sludge using ferrous sulfate, whereas only 22% nitrogen and 17% phosphorus were removed using ammonium ferrous sulfate. The BCR sequential extraction study on speciation of metals showed that using ammonium ferrous sulfate and ferrous sulfate, all the metals remained in bioleached sludge as stable form (F4 fraction). The results of the present study indicate that the bioleached sludge would be safer for land application. Also, the fertilizing property was largely conserved in the bioleached sludge using both the substrates.

Iron mineral structure, reactivity, and isotopic composition in a South Pacific Gyre ferromanganese nodule over 4 Ma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marcus, Matthew A.; Edwards, Katrina J.; Gueguen, Bleuenn

Deep-sea ferromanganese nodules accumulate trace elements from seawater and underlying sediment porewaters during the growth of concentric mineral layers over millions of years. These trace elements have the potential to record past ocean geochemical conditions. The goal of this study was to determine whether Fe mineral alteration occurs and how the speciation of trace elements responds to alteration over ~3.7Ma of marine ferromanganese nodule (MFN) formation, a timeline constrained by estimates from 9 Be/ 10 Be concentrations in the nodule material. We determined Fe-bearing phases and Fe isotope composition in a South Pacific Gyre (SPG) nodule. Specifically, the distribution patternsmore » and speciation of trace element uptake by these Fe phases were investigated. The time interval covered by the growth of our sample of the nodule was derived from 9 Be/ 10 Be accelerator mass spectrometry (AMS). The composition and distribution of major and trace elements were mapped at various spatial scales, using micro-X-ray fluorescence (μXRF), electron microprobe analysis (EMPA), and inductively coupled plasma mass spectrometry (ICP-MS). Fe phases were characterized by micro-extended X-ray absorption fine structure (μEXAFS) spectroscopy and micro-X-ray diffraction (μXRD). Speciation of Ti and V, associated with Fe, was measured using micro-X-ray absorption near edge structure (μXANES) spectroscopy. Iron isotope composition (δ 56/54 Fe) in subsamples of 1-3mm increments along the radius of the nodule was determined with multiple-collector ICP-MS (MC-ICP-MS). The SPG nodule formed through primarily hydrogeneous inputs at a rate of 4.0±0.4mm/Ma. The nodule exhibited a high diversity of Fe mineral phases: feroxyhite (δ-FeOOH), goethite (α-FeOOH), lepidocrocite (γ-FeOOH), and poorly ordered ferrihydrite-like phases. These findings provide evidence that Fe oxyhydroxides within the nodule undergo alteration to more stable phases over millions of years. Trace Ti and V were spatially correlated with Fe and found to be adsorbed to Fe-bearing minerals. Ti/Fe and V/Fe ratios, and Ti and V speciation, did not vary along the nodule radius. The δ 56/54 Fe values, when averaged over sample increments representing 0.25-0.75Ma, were homogeneous within uncertainty along the nodule radius, at -0.12±0.07‰ (2sd, n=10). Our results indicate that the Fe isotope composition of the nodule remained constant during nodule growth and that mineral alteration did not affect the primary Fe isotope composition of the nodule. Furthermore, the average δ 56/54 Fe value of -0.12‰ we find is consistent with Fe sourced from continental eolian particles (dust). Despite mineral alteration, the trace element partitioning of Ti and V, and Fe isotope composition, do not appear to change within the sensitivity of our measurements. These findings suggest that Fe oxyhydroxides within hydrogenetic ferromanganese nodules are out of geochemical contact with seawater once they are covered by subsequent concentric mineral layers. Even though Fe-bearing minerals are altered, trace element ratios, speciation and Fe isotope composition are preserved within the nodule.« less

Iron mineral structure, reactivity, and isotopic composition in a South Pacific Gyre ferromanganese nodule over 4 Ma

DOE PAGES

Marcus, Matthew A.; Edwards, Katrina J.; Gueguen, Bleuenn; ...

2015-09-05

Deep-sea ferromanganese nodules accumulate trace elements from seawater and underlying sediment porewaters during the growth of concentric mineral layers over millions of years. These trace elements have the potential to record past ocean geochemical conditions. The goal of this study was to determine whether Fe mineral alteration occurs and how the speciation of trace elements responds to alteration over ~3.7Ma of marine ferromanganese nodule (MFN) formation, a timeline constrained by estimates from 9 Be/ 10 Be concentrations in the nodule material. We determined Fe-bearing phases and Fe isotope composition in a South Pacific Gyre (SPG) nodule. Specifically, the distribution patternsmore » and speciation of trace element uptake by these Fe phases were investigated. The time interval covered by the growth of our sample of the nodule was derived from 9 Be/ 10 Be accelerator mass spectrometry (AMS). The composition and distribution of major and trace elements were mapped at various spatial scales, using micro-X-ray fluorescence (μXRF), electron microprobe analysis (EMPA), and inductively coupled plasma mass spectrometry (ICP-MS). Fe phases were characterized by micro-extended X-ray absorption fine structure (μEXAFS) spectroscopy and micro-X-ray diffraction (μXRD). Speciation of Ti and V, associated with Fe, was measured using micro-X-ray absorption near edge structure (μXANES) spectroscopy. Iron isotope composition (δ 56/54 Fe) in subsamples of 1-3mm increments along the radius of the nodule was determined with multiple-collector ICP-MS (MC-ICP-MS). The SPG nodule formed through primarily hydrogeneous inputs at a rate of 4.0±0.4mm/Ma. The nodule exhibited a high diversity of Fe mineral phases: feroxyhite (δ-FeOOH), goethite (α-FeOOH), lepidocrocite (γ-FeOOH), and poorly ordered ferrihydrite-like phases. These findings provide evidence that Fe oxyhydroxides within the nodule undergo alteration to more stable phases over millions of years. Trace Ti and V were spatially correlated with Fe and found to be adsorbed to Fe-bearing minerals. Ti/Fe and V/Fe ratios, and Ti and V speciation, did not vary along the nodule radius. The δ 56/54 Fe values, when averaged over sample increments representing 0.25-0.75Ma, were homogeneous within uncertainty along the nodule radius, at -0.12±0.07‰ (2sd, n=10). Our results indicate that the Fe isotope composition of the nodule remained constant during nodule growth and that mineral alteration did not affect the primary Fe isotope composition of the nodule. Furthermore, the average δ 56/54 Fe value of -0.12‰ we find is consistent with Fe sourced from continental eolian particles (dust). Despite mineral alteration, the trace element partitioning of Ti and V, and Fe isotope composition, do not appear to change within the sensitivity of our measurements. These findings suggest that Fe oxyhydroxides within hydrogenetic ferromanganese nodules are out of geochemical contact with seawater once they are covered by subsequent concentric mineral layers. Even though Fe-bearing minerals are altered, trace element ratios, speciation and Fe isotope composition are preserved within the nodule.« less

Acid-Sulfate-Weathering Activity in Shergottite Sites on Mars Recorded in Grim Glasses

NASA Technical Reports Server (NTRS)

Rao, M. N.; Nyquist, L. E.; Ross, K.; Sutton, S. R.; Schwandt, C. S.

2011-01-01

Based on mass spectrometric studies of sulfur species in Shergotty and EET79001, [1] and [2] showed that sulfates and sulfides occur in different proportions in shergottites. Sulfur speciation studies in gas-rich impact-melt (GRIM) glasses in EET79001 by the XANES method [3] showed that S K-XANES spectra in GRIM glasses from Lith A indicate that S is associated with Ca and Al presumably as sulfides/sulfates whereas the XANES spectra of amorphous sulfide globules in GRIM glasses from Lith B indicate that S is associated with Fe as FeS. In these amorphous iron sulfide globules, [4] found no Ni using FE-SEM and suggested that the globules resulting from immiscible sulfide melt may not be related to the igneous iron sulfides having approximately 1-3% Ni. Furthermore, in the amorphous iron sulfides from 507 GRIM glass, [5] determined delta(sup 34)S values ranging from +3.5%o to -3.1%o using Nano-SIMS. These values plot between the delta(sup 34)S value of +5.25%o determined in the sulfate fraction in Shergotty [6] at one extreme and the value of -1.7%o obtained for igneous sulfides in EET79001 and Shergotty [7] at the other. These results suggest that the amorphous Fe-S globules likely originated by shock reduction of secondary iron sulfate phases occurring in the regolith precursor materials during impact [7]. Sulfates in the regolith materials near the basaltic shergottite sites on Mars owe their origin to surficial acid-sulfate interactions. We examine the nature of these reactions by studying the composition of the end products in altered regolith materials. For the parent material composition, we use that of the host shergottite material in which the impact glasses are situated.

Evaluating EDGARv4.tox2 speciated mercury emissions ex-post scenarios and their impacts on modelled global and regional wet deposition patterns

NASA Astrophysics Data System (ADS)

Muntean, Marilena; Janssens-Maenhout, Greet; Song, Shaojie; Giang, Amanda; Selin, Noelle E.; Zhong, Hui; Zhao, Yu; Olivier, Jos G. J.; Guizzardi, Diego; Crippa, Monica; Schaaf, Edwin; Dentener, Frank

2018-07-01

Speciated mercury gridded emissions inventories together with chemical transport models and concentration measurements are essential when investigating both the effectiveness of mitigation measures and the mercury cycle in the environment. Since different mercury species have contrasting behaviour in the atmosphere, their proportion in anthropogenic emissions could determine the spatial impacts. In this study, the time series from 1970 to 2012 of the EDGARv4.tox2 global mercury emissions inventory are described; the total global mercury emission in 2010 is 1772 tonnes. Global grid-maps with geospatial distribution of mercury emissions at a 0.1° × 0.1° resolution are provided for each year. Compared to the previous tox1 version, tox2 provides updates for more recent years and improved emissions in particular for agricultural waste burning, power generation and artisanal and small-scale gold mining (ASGM) sectors. We have also developed three retrospective emissions scenarios based on different hypotheses related to the proportion of mercury species in the total mercury emissions for each activity sector; improvements in emissions speciation are seen when using information primarily from field measurements. We evaluated them using the GEOS-Chem 3-D mercury model in order to explore the influence of speciation shifts, to reactive mercury forms in particular, on regional wet deposition patterns. The reference scenario S1 (EDGARv4.tox2_S1) uses speciation factors from the Arctic Monitoring and Assessment Programme (AMAP); scenario S2 ("EPA_power") uses factors from EPA's Information Collection Request (ICR); and scenario S3 ("Asia_filedM") factors from recent scientific publications. In the reference scenario, the sum of reactive mercury emissions (Hg-P and Hg2+) accounted for 25.3% of the total global emissions; the regions/countries that have shares of reactive mercury emissions higher than 6% in total global reactive mercury are China+ (30.9%), India+ (12.5%) and the United States (9.9%). In 2010, the variations of reactive mercury emissions amongst the different scenarios are in the range of -19.3 t/yr (China+) to 4.4 t/yr (OECD_Europe). However, at the sector level, the variation could be different, e.g., for the iron and steel industry in China reaches 15.4 t/yr. Model evaluation at the global level shows a variation of approximately ±10% in wet deposition for the three emissions scenarios. An evaluation of the impact of mercury speciation within nested grid sensitivity simulations is performed for the United States and modelled wet deposition fluxes are compared with measurements. These studies show that using the S2 and S3 emissions of reactive mercury, can improve wet deposition estimates near sources.

Route and Regulation of Zinc, Cadmium, and Iron Transport in Rice Plants (Oryza sativa L.) during Vegetative Growth and Grain Filling: Metal Transporters, Metal Speciation, Grain Cd Reduction and Zn and Fe Biofortification

PubMed Central

Yoneyama, Tadakatsu; Ishikawa, Satoru; Fujimaki, Shu

2015-01-01

Zinc (Zn) and iron (Fe) are essential but are sometimes deficient in humans, while cadmium (Cd) is toxic if it accumulates in the liver and kidneys at high levels. All three are contained in the grains of rice, a staple cereal. Zn and Fe concentrations in rice grains harvested under different levels of soil/hydroponic metals are known to change only within a small range, while Cd concentrations show greater changes. To clarify the mechanisms underlying such different metal contents, we synthesized information on the routes of metal transport and accumulation in rice plants by examining metal speciation, metal transporters, and the xylem-to-phloem transport system. At grain-filling, Zn and Cd ascending in xylem sap are transferred to the phloem by the xylem-to-phloem transport system operating at stem nodes. Grain Fe is largely derived from the leaves by remobilization. Zn and Fe concentrations in phloem-sap and grains are regulated within a small range, while Cd concentrations vary depending on xylem supply. Transgenic techniques to increase concentrations of the metal chelators (nicotianamine, 2′-deoxymugineic acid) are useful in increasing grain Zn and Fe concentrations. The elimination of OsNRAMP5 Cd-uptake transporter and the enhancement of root cell vacuolar Cd sequestration reduce uptake and root-to-shoot transport, respectively, resulting in a reduction of grain Cd accumulation. PMID:26287170

Route and Regulation of Zinc, Cadmium, and Iron Transport in Rice Plants (Oryza sativa L.) during Vegetative Growth and Grain Filling: Metal Transporters, Metal Speciation, Grain Cd Reduction and Zn and Fe Biofortification.

PubMed

Yoneyama, Tadakatsu; Ishikawa, Satoru; Fujimaki, Shu

2015-08-13

Zinc (Zn) and iron (Fe) are essential but are sometimes deficient in humans, while cadmium (Cd) is toxic if it accumulates in the liver and kidneys at high levels. All three are contained in the grains of rice, a staple cereal. Zn and Fe concentrations in rice grains harvested under different levels of soil/hydroponic metals are known to change only within a small range, while Cd concentrations show greater changes. To clarify the mechanisms underlying such different metal contents, we synthesized information on the routes of metal transport and accumulation in rice plants by examining metal speciation, metal transporters, and the xylem-to-phloem transport system. At grain-filling, Zn and Cd ascending in xylem sap are transferred to the phloem by the xylem-to-phloem transport system operating at stem nodes. Grain Fe is largely derived from the leaves by remobilization. Zn and Fe concentrations in phloem-sap and grains are regulated within a small range, while Cd concentrations vary depending on xylem supply. Transgenic techniques to increase concentrations of the metal chelators (nicotianamine, 2'-deoxymugineic acid) are useful in increasing grain Zn and Fe concentrations. The elimination of OsNRAMP5 Cd-uptake transporter and the enhancement of root cell vacuolar Cd sequestration reduce uptake and root-to-shoot transport, respectively, resulting in a reduction of grain Cd accumulation.

Source-specific speciation profiles of PM2.5 for heavy metals and their anthropogenic emissions in China.

PubMed

Liu, Yayong; Xing, Jia; Wang, Shuxiao; Fu, Xiao; Zheng, Haotian

2018-08-01

Heavy metals are concerned for its adverse effect on human health and long term burden on biogeochemical cycling in the ecosystem. In this study, a provincial-level emission inventory of 13 kinds of heavy metals including V, Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Sn, Sb, Ba and Pb from 10 anthropogenic sources was developed for China, based on the 2015 national emission inventory of primary particulate matters and source category-specific speciation profiles collected from 50 previous studies measured in China. Uncertainties associated with the speciation profiles were also evaluated. Our results suggested that total emissions of the 13 types of heavy metals in China are estimated at about 58000 ton for the year 2015. The iron production is the dominant source of heavy metal, contributing 42% of total emissions of heavy metals. The emissions of heavy metals vary significantly at regional scale, with largest amount of emissions concentrated in northern and eastern China. Particular, high emissions of Cr, Co, Ni, As and Sb (contributing 8%-18% of the national emissions) are found in Shandong where has large capacity of industrial production. Uncertainty analysis suggested that the implementation of province-specific source profiles in this study significantly reduced the emission uncertainties from (-89%, 289%) to (-99%, 91%), particularly for coal combustion. However, source profiles for industry sectors such as non-metallic mineral manufacturing are quite limited, resulting in a relative high uncertainty. The high-resolution emission inventories of heavy metals are essential not only for their distribution, deposition and transport studies, but for the design of policies to redress critical atmospheric environmental hazards at local and regional scales. Detailed investigation on source-specific profile in China are still needed to achieve more accurate estimations of heavy metals in the future. Copyright © 2018 Elsevier Ltd. All rights reserved.

Abundance and Speciation of Water and Sulfate at Gusev Crater and Meridiani Planum

NASA Technical Reports Server (NTRS)

Ming, D. W.; Clark, B. C.; Klingelhoefer, G.; Gellert, R.; Rodionov, D.; Schroeder, C.; deSouza, P.; Yen, A.

2005-01-01

A major science goal of the Mars Exploration Rover (MER) mission is to search for evidence of water activity, and direct mineralogical evidence for aqueous activity has been reported for Meridiani Planum in the form of the iron sulfate hydroxide mineral jarosite and at Gusev crater in the form of goethite. The Spirit and Opportunity rovers have each collected 110+ Moessbauer (MB) and 75+ Alpha Particle X-Ray Spectrometer (APXS) spectra from Gusev crater and Meridiani Planum [1 - 4]. In this abstract, we use mineralogical and elemental data, primarily from the Moessbauer and APXS instruments, to infer the speciation and estimate the abundance of sulfate and water (as either the H2O molecule or the hydroxyl anion) at Gusev crater and Meridiani Planum. Throughout the abstract, we adopt a format for mineral formulas that shows water explicitly rather than the usual practice of structure-based formulas (e.g., for goethite we write Fe2O3xH2O instead of FeOOH).

Concentrations and speciation of arsenic along a groundwater flow-path in the Upper Floridan aquifer, Florida, USA

NASA Astrophysics Data System (ADS)

Haque, S. E.; Johannesson, K. H.

2006-05-01

Arsenic (As) concentrations and speciation were determined in groundwaters along a flow-path in the Upper Floridan aquifer (UFA) to investigate the biogeochemical “evolution“ of As in this relatively pristine aquifer. Dissolved inorganic As species were separated in the field using anion-exchange chromatography and subsequently analyzed by inductively coupled plasma mass spectrometry. Total As concentrations are higher in the recharge area groundwaters compared to down-gradient portions of UFA. Redox conditions vary from relatively oxic to anoxic along the flow-path. Mobilization of As species in UFA groundwaters is influenced by ferric iron reduction and subsequent dissolution, sulfate reduction, and probable pyrite precipitation that are inferred from the data to occur along distinct regions of the flow-path. In general, the distribution of As species are consistent with equilibrium thermodynamics, such that arsenate dominates in more oxidizing waters near the recharge area, and arsenite predominates in the progressively reducing groundwaters beyond the recharge area.

Toxic metal(loid) speciation during weathering of iron sulfide mine tailings under semi-arid climate

PubMed Central

Root, Robert A.; Hayes, Sarah M.; Hammond, Corin M.; Maier, Raina M.; Chorover, Jon

2015-01-01

Toxic metalliferous mine-tailings pose a significant health risk to ecosystems and neighboring communities from wind and water dispersion of particulates containing high concentrations of toxic metal(loid)s (e.g., Pb, As, Zn). Tailings are particularly vulnerable to erosion before vegetative cover can be reestablished, i.e., decades or longer in semi-arid environments without intervention. Metal(loid) speciation, linked directly to bioaccessibility and lability, is controlled by mineral weathering and is a key consideration when assessing human and environmental health risks associated with mine sites. At the semi-arid Iron King Mine and Humboldt Smelter Superfund site in central Arizona, the mineral assemblage of the top 2 m of tailings has been previously characterized. A distinct redox gradient was observed in the top 0.5 m of the tailings and the mineral assemblage indicates progressive transformation of ferrous iron sulfides to ferrihydrite and gypsum, which, in turn weather to form schwertmannite and then jarosite accompanied by a progressive decrease in pH (7.3 to 2.3). Within the geochemical context of this reaction front, we examined enriched toxic metal(loid)s As, Pb, and Zn with surficial concentrations 41.1, 10.7, 39.3 mM kg-1 (3080, 2200, and 2570 mg kg-1), respectively. The highest bulk concentrations of As and Zn occur at the redox boundary representing a 1.7 and 4.2 fold enrichment relative to surficial concentrations, respectively, indicating the translocation of toxic elements from the gossan zone to either the underlying redox boundary or the surface crust. Metal speciation was also examined as a function of depth using X-ray absorption spectroscopy (XAS). The deepest sample (180 cm) contains sulfides (e.g., pyrite, arsenopyrite, galena, and sphalerite). Samples from the redox transition zone (25-54 cm) contain a mixture of sulfides, carbonates (siderite, ankerite, cerrusite, and smithsonite) and metal(loid)s sorbed to neoformed secondary Fe phases, principally ferrihydrite. In surface samples (0-35 cm), metal(loid)s are found as sorbed species or incorporated into secondary Fe hydroxysulfate phases, such as schwertmannite and jarosites. Metal-bearing efflorescent salts (e.g., ZnSO4·nH2O) were detected in the surficial sample. Taken together, these data suggest the bioaccessibility and lability of metal(loid)s are altered by mineral weathering, which results in both the downward migration of metal(loid)s to the redox boundary, as well as the precipitation of metal salts at the surface. PMID:26549929

Unraveling the complexity of iron oxides at high pressure and temperature: Synthesis of Fe 5O 6

DOE PAGES

Lavina, Barbara; Meng, Yue

2015-06-26

The iron-oxygen system is the most important reference of rocks’ redox state. Even as minor components, iron oxides can play a critical role in redox equilibria, which affect the speciation of the fluid phases chemical differentiation, melting, and physical properties. Until our recent finding of Fe 4O 5, iron oxides were assumed to comprise only the polymorphs of FeO, Fe 3O 4, and Fe 2O 3. Combining synthesis at high pressure and temperature with micro- diffraction mapping, we have identified yet another distinct iron oxide, Fe 5O 6. The new compound, which has an orthorhombic structure, was obtained in themore » pressure range from 10 to 20 GPa upon laser heating mixtures of iron and hematite at ~2000 K, and is recoverable to ambient conditions. The high-pressure orthorhombic iron oxides Fe 5O 6, Fe 4O 5, and h-Fe 3O 4 display similar iron coordination geometries and structural arrangements, and indeed exhibit coherent systematic behavior of crystallographic parameters and compressibility. Fe 5O 6, along with FeO and Fe 4O 5, is a candidate key minor phase of planetary interiors; as such, it is of major petrological and geo- chemical importance. Here, we are revealing an unforeseen complexity in the Fe-O system with four different compounds—FeO, Fe 5O 6, Fe 4O 5, and h-Fe 3O 4—in a narrow compositional range (0.75 < Fe/O < 1.0). New, finely spaced oxygen buffers at conditions of the Earth’s mantle can be defined.« less

Speciation of iron in ambient aerosol and cloudwater

NASA Astrophysics Data System (ADS)

Siefert, Ronald Lyn

1997-03-01

Atmospheric iron (Fe) is thought to play an important role in cloudwater chemistry (e.g., S(IV) oxidation, oxidant production, etc.), and is also an important source of Fe to certain regions of the world's oceans where Fe is believed to be a rate-limiting nutrient for primary productivity. This thesis focuses on understanding the chemistry, speciation and abundance of Fe in cloudwater and aerosol in the troposphere, through observations of Fe speciation in the cloudwater and aerosol samples collected over the continental United States and the Arabian Sea. Different chemical species of atmospheric Fe were measured in aerosol and cloudwater samples to help assess the role of Fe in cloudwater chemistry. Chapter 2 presents a set of experiments which used ambient aerosol samples suspended in aqueous solution and then irradiated with uv-light to simulate cloudwater conditions. These experiments found Fe to be a critical component for the production of H2O2. Chapter 3 discusses the development and application of a novel photochemical extraction method for the determination of photochemically-available Fe in ambient aerosol samples. Photochemically-available Fe ranged from <4 ng m-3 to 308 ng m-3, and accounted for 2.8% to 100% of the total Fe in aerosol samples collected in California and New York. Calculations based on the results of these experiments predicted that redox reactions of Fe in cloudwater could be an important in situ source of oxidants (ċOH, HO2ċ/O2/cdot/sb- ). Chapter 4 presents results of several field studies which measured the redox states of Fe and other transition metals (Mn, Cu and Cr) in cloudwater. These measurements were then used in thermodynamic models which predicted Fe(III) to be either as Fe(III)-hydroxy species or Fe(III)-oxalate species. However, an unidentified strong chelating ligand with Fe(III) was also suggested by the thermodynamic model results. Chapter 5 presents results of a field study conducted on the Arabian Sea. Total atmospheric labile-Fe(II) ranged between <0.09 ng m-3 to 7.5 ng m-3 during the inter-monsoon period, and was consistently below the detection limit during the southwest-monsoon period. The labile-Fe(II) measured during the inter-monsoon period was predominantly found in the fine fraction of the aerosol. Principal component analysis revealed a significant source of Fe and Mn which was not associated with the main aeolian dust component.

Peat hybrid sorbents for treatment of wastewaters and remediation of polluted environment

NASA Astrophysics Data System (ADS)

Klavins, Maris; Burlakovs, Juris; Robalds, Artis; Ansone-Bertina, Linda

2015-04-01

For remediation of soils and purification of polluted waters, wastewaters, sorbents might be considered as an prospective group of materials and amongst them peat have a special role due to low cost, biodegradability, high number of functional groups, well developed surface area and combination of hydrophilic/hydrophobic structural elements. Peat as sorbent have good application potential for removal of trace metals, and we have demonstrated peat sorption capacities, sorption kinetics, thermodynamics in respect to metals with different valencies - Tl(I), Cu(II), Cr(III). However peat sorption capacity in respect to nonmetallic (anionic species) elements is low. Also peat mechanical properties do not support application in large scale column processes. To expand peat application possibilities the approach of biomass based hybrid sorbents has been elaborated. The concept "hybrid sorbent" in our understanding means natural, biomass based sorbent modified, covered with another sorbent material, thus combining two types of sorbent properties, sorbent functionalities, surface properties etc. As the "covering layer" both inorganic substances, mineral phases (iron oxohydroxides, oxyapatite) both organic polymers (using graft polymerization) were used. The obtained sorbents were characterised by their spectral properties, surface area, elemental composition. The obtained hybrid sorbents were tested for sorption of compounds in anionic speciation forms, for example of arsenic, antimony, tellurium and phosphorous compounds in comparison with weakly basic anionites. The highest sorption capacity was observed when peat sorbents modified with iron compounds were used. Sorption of different arsenic speciation forms onto iron-modified peat sorbents was investigated as a function of pH and temperature. It was established that sorption capacity increases with a rise in temperature, and the calculation of sorption process thermodynamic parameters indicates the spontaneity of sorption process and its endothermic nature. The recycling options of obtained compounds after their saturation with metal or non-metallic species are suggested. Acknowledgement: Support from a project 2014/0009/1DP/1.1.1.2.0/13/APIA/VIAA/044

Solid-Phase Speciation of Arsenic As the Primary Control on Dissolved As Concentrations in a Glacial Aquifer System: Quantifying Speciation of Arsenic in Glacial Aquifer Solids with μXAS Mapping.

NASA Astrophysics Data System (ADS)

Nicholas, S. L.; Gowan, A. S.; Knaeble, A. R.; Erickson, M. L.; Woodruff, L. G.; Marcus, M.; Toner, B. M.

2014-12-01

Western Minnesota, USA, is a regional locus of drinking-water wells with high arsenic (As) (As>10µgL-1). Arsenic concentrations vary widely among neighboring wells with otherwise similar water chemistry [1,2]. As(III) should be the most mobile As species in Minnesota well waters (median Eh in As affected wells is -50mV). This As is geogenic, sourced from glacial deposits derived from Cretaceous sedimentary bedrock (dolostone, limestone, shale). Our hypothesis is that As speciation in the solid phase is the important factor controlling the introduction of As to groundwater—more significant in this region than absolute As concentrations or landscape variability. Our previous research used micro-X-ray absorption spectroscopy (µXAS) speciation mapping [3] on archived glacial tills (stored dry at room temperature in air). µXAS results from this material showed that As in a reduced chemical state within the till aquitard is spatially correlated with iron sulfide at the micron scale. Conversley, As in aquifer sediments was mainly oxidized As(V). At the aquifer-aquitard contact As was observed as a mixture of both reduced and oxidized forms. This suggests that the aquifer-aquitard contact is a geochemically active zone in which reduced As species present within glacial till are converted to As(V) through complex redox processes, and subsequently release into aquifer sediments. Our current research applies the same methods to describe As speciation in samples collected from fresh cores of glacial sediment and frozen under argon in the field. Preliminary results are similar to our previous work in that As is, in general, more reduced in aquitard sediments, and more oxidized at the contact and in aquifer sediments. Arsenic(III) was preserved as a minor consitutent in ambient archived cores but is a more significant constituent in fresh, anaerobically preserved cores. Results will be presented comparing anaerobic samples with ambient-air aliquots of the same sample to document changes in the relative abundance of As species depending on sample preservation. This work was supported by LBNL-ALS, ANL-APS, USGS-MNWSC, MGS, and CURA. [1]Berndt & Soule (1999) Minnesota Arsenic Research Study: Report on Geochemistry. [2] Erickson & Barnes (2005) Water Research 39 4029-4039. [3] Toner et al. (2014) Env. Chem. 11 4-9.

The effect of silicon on iron plaque formation and arsenic accumulation in rice genotypes with different radial oxygen loss (ROL).

PubMed

Wu, Chuan; Zou, Qi; Xue, Sheng-Guo; Pan, Wei-Song; Huang, Liu; Hartley, William; Mo, Jing-Yu; Wong, Ming-Hung

2016-05-01

Rice is one of the major pathways of arsenic (As) exposure in human food chain, threatening over half of the global population. Greenhouse pot experiments were conducted to examine the effects of Si application on iron (Fe) plaque formation, As uptake and rice grain As speciation in indica and hybrid rice genotypes with different radial oxygen loss (ROL) ability. The results demonstrated that Si significantly increased root and grain biomass. Indica genotypes with higher ROL induced greater Fe plaque formation, compared to hybrid genotypes and sequestered more As in Fe plaque. Silicon applications significantly increased Fe concentrations in iron plaque of different genotypes, but it decreased As concentrations in the roots, straws and husks by 28-35%, 15-35% and 32-57% respectively. In addition, it significantly reduced DMA accumulation in rice grains but not inorganic As accumulation. Rice of indica genotypes with higher ROL accumulated lower concentrations of inorganic As in grains than hybrid genotypes with lower ROL. Copyright © 2016 Elsevier Ltd. All rights reserved.

Solid phase studies and geochemical modelling of low-cost permeable reactive barriers.

PubMed

Bartzas, Georgios; Komnitsas, Kostas

2010-11-15

A continuous column experiment was carried out under dynamic flow conditions in order to study the efficiency of low-cost permeable reactive barriers (PRBs) to remove several inorganic contaminants from acidic solutions. A 50:50 w/w waste iron/sand mixture was used as candidate reactive media in order to activate precipitation and promote sorption and reduction-oxidation mechanisms. Solid phase studies of the exhausted reactive products after column shutdown, using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), confirmed that the principal Fe corrosion products identified in the reactive zone are amorphous iron (hydr)oxides (maghemite/magnetite and goethite), intermediate products (sulfate green rust), and amorphous metal sulfides such as amFeS and/or mackinawite. Geochemical modelling of the metal removal processes, including interactions between reactive media, heavy metal ions and sulfates, and interpretation of the ionic profiles was also carried out by using the speciation/mass transfer computer code PHREEQC-2 and the WATEQ4F database. Mineralogical characterization studies as well as geochemical modelling calculations also indicate that the effect of sulfate and silica sand on the efficiency of the reactive zone should be considered carefully during design and operation of low-cost field PRBs. Copyright © 2010 Elsevier B.V. All rights reserved.

Speciation and characterization of arsenic in Ketza River mine tailings using X-ray absorption spectroscopy.

PubMed

Paktunc, Dogan; Foster, Andrea; Laflamme, Gilles

2003-05-15

Ketza River mine tailings deposited underwater and those exposed near the tailings impoundment contain approximately 4 wt % As. Column-leaching tests indicated the potential for high As releases from the tailings. The tailings are composed dominantly of iron oxyhydroxides, quartz, calcite, dolomite, muscovite, ferric arsenates, and calcium-iron arsenates. Arsenopyrite and pyrite are trace constituents. Chemical compositions of iron oxyhydroxide and arsenate minerals are highly variable. The XANES spectra indicate that arsenic occurs as As(V) in tailings, but air-drying prior to analysis may have oxidized lower-valent As. The EXAFS spectra indicate As-Fe distances of 3.35-3.36 A for the exposed tailings and 3.33-3.35 A for the saturated tailings with coordination numbers of 0.96-1.11 and 0.46-0.64, respectively. The As-Ca interatomic distances ranging from 4.15 to 4.18 A and the coordination numbers of 4.12-4.58 confirm the presence of calcium-iron arsenates in the tailings. These results suggest that ferric arsenates and inner-sphere corner sharing or bidentate-binuclear attachment of arsenate tetrahedra onto iron hydroxide octahedra are the dominant form of As in the tailings. EXAFS spectra indicate that the exposed tailings are richer in arsenate minerals whereas the saturated tailings are dominated by the iron oxyhydroxides, which could help explain the greater release of As from the exposed tailings during leaching tests. It is postulated that the dissolution of ferric arsenates during flow-through experiments caused the high As releases from both types of tailings. Arsenic tied to iron oxyhydroxides as adsorbed species are considered stable; however, iron oxyhydroxides having low Fe/As molar ratios may not be as stable. Continued As releases from the tailings are likely due to dissolution of both ferric and calcium-iron arsenates and desorption of As from high-As bearing iron oxyhydroxides during aging.

Speciation and characterization of arsenic in Ketza River mine tailings using x-ray absorption spectroscopy

USGS Publications Warehouse

Paktunc, D.; Foster, A.; Laflamme, G.

2003-01-01

Ketza River mine tailings deposited underwater and those exposed near the tailings impoundment contain approximately 4 wt % As. Column-leaching tests indicated the potential for high As releases from the tailings. The tailings are composed dominantly of iron oxyhydroxides, quartz, calcite, dolomite, muscovite, ferric arsenates, and calcium-iron arsenates. Arsenopyrite and pyrite are trace constituents. Chemical compositions of iron oxyhydroxide and arsenate minerals are highly variable. The XANES spectra indicate that arsenic occurs as As(V) in tailings, but air-drying prior to analysis may have oxidized lower-valent As. The EXAFS spectra indicate As-Fe distances of 3.35-3.36 A?? for the exposed tailings and 3.33-3.35 A?? for the saturated tailings with coordination numbers of 0.96-1.11 and 0.46-0.64, respectively. The As-Ca interatomic distances ranging from 4.15 to 4.18 A?? and the coordination numbers of 4.12-4.58 confirm the presence of calcium-iron arsenates in the tailings. These results suggest that ferric arsenates and inner-sphere corner sharing or bidentatebinuclear attachment of arsenate tetrahedra onto iron hydroxide octahedra are the dominant form of As in the tailings. EXAFS spectra indicate that the exposed tailings are richer in arsenate minerals whereas the saturated tailings are dominated by the iron oxyhydroxides, which could help explain the greater release of As from the exposed tailings during leaching tests. It is postulated that the dissolution of ferric arsenates during flow-through experiments caused the high As releases from both types of tailings. Arsenic tied to iron oxyhydroxides as adsorbed species are considered stable; however, iron oxyhydroxides having low Fe/As molar ratios may not be as stable. Continued As releases from the tailings are likely due to dissolution of both ferric and calcium-iron arsenates and desorption of As from high-As bearing iron oxyhydroxides during aging.

Speciation and Localization of Arsenic in White and Brown Rice Grains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meharg, Andrew A.; Lombi, Enzo; Williams, Paul N.

2008-06-30

Synchrotron-based X-ray fluorescence (S-XRF) was utilized to locate arsenic (As) in polished (white) and unpolished (brown) rice grains from the United States, China, and Bangladesh. In white rice As was generally dispersed throughout the grain, the bulk of which constitutes the endosperm. In brown rice As was found to be preferentially localized at the surface, in the region corresponding to the pericarp and aleurone layer. Copper, iron, manganese, and zinc localization followed that of arsenic in brown rice, while the location for cadmium and nickel was distinctly different, showing relatively even distribution throughout the endosperm. The localization of As inmore » the outer grain of brown rice was confirmed by laser ablation ICP?MS. Arsenic speciation of all grains using spatially resolved X-ray absorption near edge structure (?-XANES) and bulk extraction followed by anion exchange HPLC?ICP?MS revealed the presence of mainly inorganic As and dimethylarsinic acid (DMA). However, the two techniques indicated different proportions of inorganic:organic As species. A wider survey of whole grain speciation of white (n = 39) and brown (n = 45) rice samples from numerous sources (field collected, supermarket survey, and pot trials) showed that brown rice had a higher proportion of inorganic arsenic present than white rice. Furthermore, the percentage of DMA present in the grain increased along with total grain arsenic.« less

The life cycle of iron Fe(III) oxide: impact of fungi and bacteria

NASA Astrophysics Data System (ADS)

Bonneville, Steeve

2014-05-01

Iron oxides are ubiquitous reactive constituents of soils, sediments and aquifers. They exhibit vast surface areas which bind a large array of trace metals, nutrients and organic molecules hence controlling their mobility/reactivity in the subsurface. In this context, understanding the "life cycle" of iron oxide in soils is paramount to many biogeochemical processes. Soils environments are notorious for their extreme heterogeneity and variability of chemical, physical conditions and biological agents at play. Here, we present studies investigating the role of two biological agents driving iron oxide dynamics in soils, root-associated fungi (mycorrhiza) and bacteria. Mycorrhiza filaments (hypha) grow preferentially around, and on the surface of nutrient-rich minerals, making mineral-fungi contact zones, hot-spots of chemical alteration in soils. However, because of the microscopic nature of hyphae (only ~ 5 µm wide for up to 1 mm long) and their tendency to strongly adhere to mineral surface, in situ observations of this interfacial micro-environment are scarce. In a microcosm, ectomycorrhiza (Paxillus involutus) was grown symbiotically with a pine tree (Pinus sylvestris) in the presence of freshly-cleaved biotite under humid, yet undersaturated, conditions typical of soils. Using spatially-resolved ion milling technique (FIB), transmission electron microscopy and spectroscopy (TEM/STEM-EDS), synchrotron based X-ray microscopy (STXM), we were able to quantify the speciation of Fe at the biotite-hypha interface. The results shows that substantial oxidation of biotite structural-Fe(II) into Fe(III) subdomains occurs at the contact zone between mycorrhiza and biotite. Once formed, iron(III) oxides can reductively dissolve under suboxic conditions via several abiotic and microbial pathways. In particular, they serve as terminal electron acceptors for the oxidation of organic matter by iron reducing bacteria. We aimed here to understand the role of Fe(III) mineral properties, in particular the influence of solubility, in the kinetics of microbial iron reduction. We used the facultative anaerobic gram-positive bacterium Shewanella putrefaciens as model iron reducing bacterium, with several ferrihydrite, hematite, goethite or lepidocrocite as electron acceptor, and lactate as electron donor. Maximum microbial Fe(III) reduction rates and solubility of Fe(III) phases were found to positively correlated in a Linear Free Energy Relationship suggesting a rate limitation by the electron transfer between iron reductases and a Fe(III) center, or by the subsequent desorption of Fe2+ from the iron oxide mineral surface.

Activation of Persulfate by Nanosized Zero-Valent Iron (NZVI): Mechanisms and Transformation Products of NZVI.

PubMed

Kim, Cheolyong; Ahn, Jun-Young; Kim, Tae Yoo; Shin, Won Sik; Hwang, Inseong

2018-03-20

The mechanisms involved in the activation of persulfate by nanosized zero-valent iron (NZVI) were elucidated and the NZVI transformation products identified. Two distinct reaction stages, in terms of the kinetics and radical formation mechanism, were found when phenol was oxidized by the persulfate/NZVI system. In the initial stage, lasting 10 min, Fe 0 (s) was consumed rapidly and sulfate radicals were produced through activation by aqueous Fe 2+ . The second stage was governed by Fe catalyzed activation in the presence of aqueous Fe 3+ and iron (oxyhydr)oxides in the NZVI shells. The second stage was 3 orders of magnitude slower than the initial stage. An electron balance showed that the sulfate radical yield per mole of persulfate was more than two times higher in the persulfate/NZVI system than in the persulfate/Fe 2+ system. Radicals were believed to be produced more efficiently in the persulfate/NZVI system because aqueous Fe 2+ was supplied slowly, preventing sulfate radicals being scavenged by excess aqueous Fe 2+ . In the second stage, the multilayered shell conducted electrons, and magnetite in the shell provided electrons for the activation of persulfate. Iron speciation analysis (including X-ray absorption spectroscopy) results indicated that a shrinking core/growing shell model explained NZVI transformation during the persulfate/NZVI process.

Iron speciation and dynamics during SERIES, a mesoscale iron enrichment experiment in the NE Pacific

NASA Astrophysics Data System (ADS)

Wong, C. S.; Johnson, W. K.; Sutherland, N.; Nishioka, J.; Timothy, D. A.; Robert, M.; Takeda, S.

2006-10-01

During the Sub-arctic Ecosystem Response to Iron Enrichment Study (SERIES), the addition of ferrous iron to high-nitrate low-chlorophyll (HNLC) waters near Ocean Station PAPA (OSP: 50°N, 145°W) produced a phytoplankton bloom and CO 2 drawdown, as evidenced by decreasing CO 2 fugacity ( fCO 2). We analyzed five fractions or phases of iron: soluble (<0.03 μm), dissolved (<0.22 μm), total dissolved (acidified dissolved, <0.22 μm), labile (unfiltered), and total (acidified, unfiltered). From these, we also calculated non-labile iron, colloidal iron (0.03-0.22 μm), and both labile and non-labile particulate iron (>0.22 μm). Here, we describe iron distributions and the evolution of iron phases in the upper ocean during the experiment. We also present an iron budget accounting for horizontal and vertical dilution. At the time of our first sampling eight hours after fertilization was completed, total iron reached 8.6 nmol L -1 and dissolved iron was approximately 3 nmol L -1. Early in the experiment the dissolved iron phase decreased the most rapidly and by late day 6 the integrated dissolved iron (8.6 μmol m -2) represented less than 10% of the initial addition (90-95 μmol m -2). However at this same time the total integrated iron at the centre of the patch was still 52 μmol m -2 or almost 60% of the calculated initial addition. By day 12,45% of the added iron (from both injections) could be accounted for in the patch. The half-life of total iron in the patch for the first injection was estimated to be less than 5 days if dilution is not considered, but more than 13 days if dilution is taken into account. The most notable change in iron percentages from one form to another occurred early in the first week of the experiment where the predominant phase shift was from the colloidal portion of dissolved iron to labile particulate iron that could have been biologically induced or simply aggregation of oxyhydroxides. This was immediately followed by a physical event resulting in a reduction in the non-labile particulate iron due to sinking out of the patch. The second infusion did not change the relative concentration of the various pools of iron as might be expected, but this was likely due to the fact that it was a much smaller injection than the first. The most pronounced change after the second infusion was the reduction in the labile particulate pool which coincided with one of the largest decreases in silicate observed during the entire experiment. In general the gradual decrease in the fraction of the 10 m colloidal iron as well as episodic losses of, or shifts in, integrated colloidal iron are thought to be the result of adsorption of colloidal iron to the plankton cell surfaces as well as aggregation of oxyhydroxides but could also be the result of utilization of colloidal iron by mixotrophic phytoplankton.

Sol-gel based optical sensor for determination of Fe (II): a novel probe for iron speciation.

PubMed

Samadi-Maybodi, Abdolraouf; Rezaei, Vida; Rastegarzadeh, Saadat

2015-02-05

A highly selective optical sensor for Fe (II) ions was developed based on entrapment of a sensitive reagent, 2,4,6-tri(2-pyridyl)-s-triazine (TPTZ), in a silica sol-gel thin film coated on a glass substrate. The thin films fabricated based on tetraethoxysilane (TEOS) as precursor, sol-gel pH∼3, water:alkoxyde ratio of 4:1 and TPTZ concentration of 0.112 mol L(-1). The influence of sol-gel parameters on sensing behavior of the fabricated sensor was also investigated. The fabricated sensor can be used for determination of Fe (II) ion with an outstanding high selectivity over a dynamic range of 5-115 ng mL(-1) and a detection limit of 1.68 ng mL(-1). It also showed reproducible results with relative standard deviation of 3.5% and 1.27% for 10 and 90 ng mL(-1) of Fe (II), respectively, along with a fast response time of ∼120 s. Total iron also was determined after reduction of Fe (III) to Fe (II) using ascorbic acid as reducing agent. Then, the concentration of Fe (III) was calculated by subtracting the concentration of Fe (II) from the total iron concentration. Interference studies showed a good selectivity for Fe (II) with trapping TPTZ into sol-gel matrix and appropriately adjusting the structure of doped sol-gel. The sensor was compared with other sensors and was applied to determine iron in different water samples with good results. Copyright © 2014 Elsevier B.V. All rights reserved.

Quantification of ferritin bound iron in human serum using species-specific isotope dilution mass spectrometry.

PubMed

Ren, Yao; Walczyk, Thomas

2014-09-01

Ferritin is a hollow sphere protein composed of 24 subunits that can store up to 4500 iron atoms in its inner cavity. It is mainly found in the liver and spleen but also in serum at trace levels. Serum ferritin is considered as the best single indicator in assessing body iron stores except liver or bone marrow biopsy. However, it is confounded by other disease conditions. Ferritin bound iron (FBI) and ferritin saturation have been suggested as more robust biomarkers. The current techniques for FBI determination are limited by low antibody specificity, low instrument sensitivity and possible analyte losses during sample preparation. The need for a highly sensitive and reliable method is widely recognized. Here we describe a novel technique to detect serum FBI using species-specific isotope dilution mass spectrometry (SS-IDMS). [(57)Fe]-ferritin was produced by biosynthesis and in vitro labeling with the (57)Fe spike in the form of [(57)Fe]-citrate after cell lysis and heat treatment. [(57)Fe]-ferritin for sample spiking was further purified by fast liquid protein chromatography. Serum ferritin and added [(57)Fe]-ferritin were separated from other iron species by ultrafiltration followed by isotopic analysis of FBI using negative thermal ionization mass spectrometry. Repeatability of our assay is 8% with an absolute detection limit of 18 ng FBI in the sample. As compared to other speciation techniques, SS-IDMS offers maximum control over sample losses and species conversion during analysis. The described technique may therefore serve as a reference technique for clinical applications of FBI as a new biomarker for assessing body iron status.

Stability of oxidized iron species and the redox budget of slab-derived fluids

NASA Astrophysics Data System (ADS)

Sanchez-Valle, C.; Hin, R.; Testemale, D.; Borca, C.; Grolimund, D.

2017-12-01

The high oxidation state of subduction zone magmas compared to magmas from other locations might result from the influx of oxidized fluid from the subducted oceanic plate into the mantle wedge. However, the nature of the chemical agent(s) and the mechanism responsible for the transfer of the oxidized signature from the slab to the mantle wedge remains poorly understood. In this contribution, we will discuss the oxidizing capacity of slab-derived fluids in the light of experimental results of the solubility and speciation of iron in high-pressure fluids that mimic the slab flux. Iron-bearing mineral assemblages were equilibrated with chlorinated aqueous fluids and hydrous granitic melts at different oxygen fugacities relevant for the present day crust/mantle. The concentration of iron and the distribution of stability of oxidized iron species were monitored up to 2.5 GPa and 800 °C using a combination of diamond trap experiments and XANES measurements in diamond anvil cells. The results illustrate the role of coordination chemistry involving halogen and polymerized species in the stability of oxidized iron in the fluids. The concentration of Fe3+ in the fluids progressively decreases as temperature increases, regardless of fluid composition and pressure. This implies that the fluid capacity to transport Fe3+ at high temperature may be limited, even at the redox conditions relevant for the present day crust and mantle. With the new experimental results, we place constrains on the oxidizing capacity of Fe-bearing metasomatic fluids and discuss the transfer of the oxidizing signature and the conditions for the genesis of oxidized arc magmas.

The effects of soil liming and sewage sludge application on dynamics of copper fractions and total copper concentration.

PubMed

Malinowska, Elżbieta

2016-10-01

The paper deals with effects of liming and different doses of municipal sewage sludge (5, 10, and 15 % of soil mass) on copper speciation in soil. In all samples, pH was determined together with total copper concentration, which was measured with the ICP-AES method. Concentration of copper chemical fractions was determined using the seven-step procedure of Zeien and Brümmer. In the soil treated with the highest dose of sludge (15 %), there was, compared to the control, a twofold increase in the concentration of copper and a threefold increase in the concentration of nitrogen. Copper speciation analysis showed that in the municipal sewage sludge the easily soluble and exchangeable fractions (F1 and F2) constituted only a small share of copper with the highest amount of this metal in the organic (F4) and residual (F7) fractions. In the soil, at the beginning of the experiment, the highest share was in the organic fraction (F4), the residual fraction (F7) but also in the fraction where copper is bound to amorphous iron oxides (F5). After 420 days, at the end of the experiment, the highest amount of copper was mainly in the organic fraction (F4) and in the fraction with amorphous iron oxides (F5). Due to mineralization of organic matter in the sewage sludge, copper was released into the soil with the share of the residual fraction (F7) decreasing. In this fraction, there was much more copper in limed soil than in non-limed soil.

Characterizing the production and retention of dissolved iron as Fe(II) across a natural gradient in chlorophyll concentrations in the Southern Drake Passage - Final Technical Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katherine Barbeau

2007-04-10

Recent mesoscale iron fertilization studies in the Southern Ocean (e.g. SOIREE, EisenEx, SOFeX) have demonstrated the importance of iron as a limiting factor for phytoplankton growth in these high nutrient, low-chlorophyll (HNLC) waters. Results of these experiments have demonstrated that factors which influence the biological availability of the iron supplied to phytoplankton are crucial in bloom development, longevity, and generation of carbon export flux. These findings have important implications for the future development of iron fertilization protocols to enhance carbon sequestration in high-latitude oceans. In particular, processes which lead to the mobilization and retention of iron in dissolved form inmore » the upper ocean are important in promoting continued biological availability of iron. Such processes can include photochemical redox cycling, which leads to the formation of soluble reduced iron, Fe(II), within iron-enriched waters. Creation of effective fertilization schemes will thus require more information about Fe(II) photoproduction in Southern Ocean waters as a means to retain new iron within the euphotic zone. To contribute to our knowledge base in this area, this project was funded by DOE with a goal of characterizing the production and retention of dissolved Fe as Fe(II) in an area of the southern Drake Passage near the Shackleton Transverse Ridge, a region with a strong recurrent chlorophyll gradient which is believed to be a site of natural iron enrichment in the Southern Ocean. This area was the focus of a multidisciplinary NSF/OPP-funded investigation in February 2004 (OPP02-30443, lead PI Greg Mitchell, SIO/UCSD) to determine the influence of mesoscale circulation and iron transport with regard to the observed patterns in sea surface chlorophyll in the region near the Shackleton Transverse Ridge. A number of parameters were assessed across this gradient in order to reveal interactions between plankton community structure and iron distributions. As a co-PI in the NSF/OPP-funded project, I was responsible for iron addition incubation and radiotracer experiments, and analysis of iron chemistry, including iron-organic speciation. This final technical report describes the results of my DOE funded project to analyse reduced iron species using an FeLume flow injection analysis chemiluminescence system as an extension of my work on the NSF/OPP project. On the cruise in 2004, spatial and temporal gradients in Fe(II) were determined, and on-board incubations were conducted to study Fe(II) lifetime and production. Following the cruise a further series of experiments was conducted in my laboratory to study Fe(II) lifetimes and photoproduction under conditions typical of high latitude waters. The findings of this study suggest that, in contrast to results observed during mesoscale iron addition experiments, steady-state levels of Fe(II) are likely to remain low (below detection) even within a significant gradient in dissolved Fe concentrations produced as a result of natural iron enrichment processes. Fe(II) is likely to be produced, however, as a reactive intermediate associated with photochemical reactions in surface waters. While Fe(II) lifetimes measured in the field in this study were commensurate with those determined in previously published Southern Ocean work, Fe(II) lifetimes reflective of realistic Southern Ocean environmental conditions have proven difficult to determine in a laboratory setting, due to contamination by trace levels of H2O2. Laboratory experiments demonstrated that direct ligand-to-metal charge transfer reactions of strong Fe(III)-organic complexes do appear to be a viable source of available Fe(II) in Antarctic waters, and further studies are needed to characterize the temperature dependence of this phenomenon.« less

Fe-C-S systematics in Bengal Fan sediments

NASA Astrophysics Data System (ADS)

Volvoikar, S. P.; Mazumdar, A.; Goswami, H.; Pujari, S.; Peketi, A.

2017-12-01

Global biogeochemical cycles of iron, carbon and sulfur (Fe-C-S) are interrelated. Sulfate reduction in marine sediments is the major factor controlling the cycling and burial of carbon, sulfur and iron. Organoclastic sulfate reduction and anaerobic oxidation of methane (AOM) are the two main processes responsible for sulfate reduction in marine sediments. The amount and reactivity of organic matter, iron minerals and concentrations of dissolved sulfide in pore water control the burial of iron sulfide and organic bound sulfur in marine sediments. Here we investigate the sulfidization process in a sediment core from the western part of upper Bay of Bengal fan characterized by efficient burial of organic matter with siliclastic load. A 30 m long sediment core (MD 161/29, Lat. 170 18.04' N, Long. 870 22.56' E, water depth: 2434m) was collected onboard Marion Dufresne (May, 2007) and studied for Fe-S speciation and organic matter characterization. Buffered dithionite extractable iron (FeD) varies from 0.71 to 1.43 wt % (Avg. 0.79 wt %). FeD represents Fe oxides and oxyhydroxides mainly, ferrihydrite, lepidocrocite, goethite and hematite. Acid volatile sulfur (AVS) varies from 0.0015 to 0.63 wt % (avg: 0.058 wt %), while chromium reducible sulfur (CRS) varies from 0.00047 to 0.29 wt % (avg. 0.054 wt %). Based on the vertical distribution patterns of FeD, AVS and CRS, the core is divided into three zones, the lower (3000 to 1833 cm), middle (1833 to 398 cm) and upper (398 cm to surface) zones. FeD shows higher concentration in the lower zone. FeTR (FeOx + FeD + FeCRS + FeAVS) also exhibit higher concentration in this zone, suggesting higher availability of reactive iron for iron sulfide precipitation. AVS, elemental sulfur, spikes of CRS and gradual enrichment of δ34SAVS and δ34SCRS with sharp peaks in-between is noted in the lower zone. The gradual enrichment of δ34SAVS and δ34SCRS is the outcome of late diagenetic pyritization with higher availability of sulfide (HS- and H2S) from AOM.

Iron behaving badly: inappropriate iron chelation as a major contributor to the aetiology of vascular and other progressive inflammatory and degenerative diseases

PubMed Central

Kell, Douglas B

2009-01-01

Background The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular 'reactive oxygen species' (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation. Review We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation). The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible. This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, since in some circumstances (especially the presence of poorly liganded iron) molecules that are nominally antioxidants can actually act as pro-oxidants. The reduction of redox stress thus requires suitable levels of both antioxidants and effective iron chelators. Some polyphenolic antioxidants may serve both roles. Understanding the exact speciation and liganding of iron in all its states is thus crucial to separating its various pro- and anti-inflammatory activities. Redox stress, innate immunity and pro- (and some anti-)inflammatory cytokines are linked in particular via signalling pathways involving NF-kappaB and p38, with the oxidative roles of iron here seemingly involved upstream of the IkappaB kinase (IKK) reaction. In a number of cases it is possible to identify mechanisms by which ROSs and poorly liganded iron act synergistically and autocatalytically, leading to 'runaway' reactions that are hard to control unless one tackles multiple sites of action simultaneously. Some molecules such as statins and erythropoietin, not traditionally associated with anti-inflammatory activity, do indeed have 'pleiotropic' anti-inflammatory effects that may be of benefit here. Conclusion Overall we argue, by synthesising a widely dispersed literature, that the role of poorly liganded iron has been rather underappreciated in the past, and that in combination with peroxide and superoxide its activity underpins the behaviour of a great many physiological processes that degrade over time. Understanding these requires an integrative, systems-level approach that may lead to novel therapeutic targets. PMID:19133145

Influence of uranyl speciation and iron oxides on uranium biogeochemical redox reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stewart, B.D.; Amos, R.T.; Nico, P.S.

2010-03-15

Uranium is a pollutant of concern to both human and ecosystem health. Uranium's redox state often dictates its partitioning between the aqueous- and solid-phases, and thus controls its dissolved concentration and, coupled with groundwater flow, its migration within the environment. In anaerobic environments, the more oxidized and mobile form of uranium (UO{sub 2}{sup 2+} and associated species) may be reduced, directly or indirectly, by microorganisms to U(IV) with subsequent precipitation of UO{sub 2}. However, various factors within soils and sediments may limit biological reduction of U(VI), inclusive of alterations in U(VI) speciation and competitive electron acceptors. Here we elucidate themore » impact of U(VI) speciation on the extent and rate of reduction with specific emphasis on speciation changes induced by dissolved Ca, and we examine the impact of Fe(III) (hydr)oxides (ferrihydrite, goethite and hematite) varying in free energies of formation on U reduction. The amount of uranium removed from solution during 100 h of incubation with S. putrefaciens was 77% with no Ca or ferrihydrite present but only 24% (with ferrihydrite) and 14% (no ferrihydrite) were removed for systems with 0.8 mM Ca. Imparting an important criterion on uranium reduction, goethite and hematite decrease the dissolved concentration of calcium through adsorption and thus tend to diminish the effect of calcium on uranium reduction. Dissimilatory reduction of Fe(III) and U(VI) can proceed through different enzyme pathways, even within a single organism, thus providing a potential second means by which Fe(III) bearing minerals may impact U(VI) reduction. We quantify rate coefficients for simultaneous dissimilatory reduction of Fe(III) and U(VI) in systems varying in Ca concentration (0 to 0.8 mM), and using a mathematical construct implemented with the reactive transport code MIN3P, we reveal the predominant influence of uranyl speciation, specifically the formation of uranyl-calcium-carbonato complexes, and ferrihydrite on the rate and extent of uranium reduction in complex geochemical systems.« less

Sulfur speciation in hydrous experimental glasses of varying oxidation state - Results from measured wavelength shifts of sulfur X-rays

NASA Technical Reports Server (NTRS)

Carroll, Michael R.; Rutherford, Malcolm J.

1988-01-01

The focusing geometry of an electron microprobe has been used to measure the wavelength shifts of sulfur X-rays from hydrous experimental melts synthesized at oxygen fugacities that range from near the iron-wustite buffer to the magnetite-hermatite buffer. It is found that the proportion of dissolved sulfur which is present as sulfate increases with increasing oxygen fugacity. It is noted that in natural melts that have equilibrated at or below fayalite-magnetite-quartz values of +1, sulfur is probably present mainly as S(2-).

Local vs Nonlocal States in FeTiO3 Probed with 1s2pRIXS: Implications for Photochemistry.

PubMed

Hunault, Myrtille O J Y; Khan, Wilayat; Minár, Jan; Kroll, Thomas; Sokaras, Dimosthenis; Zimmermann, Patric; Delgado-Jaime, Mario U; de Groot, Frank M F

2017-09-18

Metal-metal charge transfer (MMCT) is expected to be the main mechanism that enables the harvesting of solar light by iron-titanium oxides for photocatalysis. We have studied FeTiO 3 as a model compound for MMCT with 1s2pRIXS at the Fe K-edge. The high-energy resolution XANES enables distinguishing five pre-edge features. The three first well distinct RIXS features are assigned to electric quadrupole transitions to the localized Fe* 3d states, shifted to lower energy by the 1s core-hole. Crystal field multiplet calculations confirm the speciation of divalent iron. The contribution of electric dipole absorption due to local p-d mixing allowed by the trigonal distortion of the cation site is supported by DFT and CFM calculations. The two other nonlocal features are assigned to electric dipole transitions to excited Fe* 4p states mixed with the neighboring Ti 3d states. The comparison with DFT calculations demonstrates that MMCT in ilmenite is favored by the hybridization between the Fe 4p and delocalized Ti 3d orbitals via the O 2p orbitals.

Preserving the distribution of inorganic arsenic species in groundwater and acid mine drainage samples

USGS Publications Warehouse

Bednar, A.J.; Garbarino, J.R.; Ranville, J.F.; Wildeman, T.R.

2002-01-01

The distribution of inorganic arsenic species must be preserved in the field to eliminate changes caused by metal oxyhydroxide precipitation, photochemical oxidation, and redox reactions. Arsenic species sorb to iron and manganese oxyhydroxide precipitates, and arsenite can be oxidized to arsenate by photolytically produced free radicals in many sample matrices. Several preservatives were evaluated to minimize metal oxyhydroxide precipitation, such as inorganic acids and ethylenediaminetetraacetic acid (EDTA). EDTA was found to work best for all sample matrices tested. Storing samples in opaque polyethylene bottles eliminated the effects of photochemical reactions. The preservation technique was tested on 71 groundwater and six acid mine drainage samples. Concentrations in groundwater samples reached 720 ??g-As/L for arsenite and 1080 ??g-As/L for arsenate, and acid mine drainage samples reached 13 000 ??g-As/L for arsenite and 3700 ??g-As/L for arsenate. The arsenic species distribution in the samples ranged from 0 to 90% arsenite. The stability of the preservation technique was established by comparing laboratory arsenic speciation results for samples preserved in the field to results for subsamples speciated onsite. Statistical analyses indicated that the difference between arsenite and arsenate concentrations for samples preserved with EDTA in opaque bottles and field speciation results were analytically insignificant. The percentage change in arsenite:arsenate ratios for a preserved acid mine drainage sample and groundwater sample during a 3-month period was -5 and +3%, respectively.

Bimetallic Porous Iron (pFe) Materials for Remediation/Removal of Tc from Aqueous Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, D.

Remediation of Tc remains an unresolved challenge at SRS and other DOE sites. The objective of this project was to develop novel bimetallic porous iron (pFe) materials for Tc removal from aqueous systems. We showed that the pFe is much more effective in removing TcO 4 - (×30) and ReO 4 - (×8) from artificial groundwater than granular iron. Tc K-edge XANES spectroscopy indicated that Tc speciation on the pFe was 18% adsorbed TcO 4 -, 28% Tc(IV) in Tc dioxide and 54% Tc(IV) into the structure of Fe hydroxide. A variety of catalytic metal nanoparticles (i.e., Ni, Cu, Zn,more » Ag, Sn and Pd) were successfully deposited on the pFe using scalable chemical reduction methods. The Zn-pFe was outstanding among the six bimetallic pFe materials, with a capacity increase of >100% for TcO 4 - removal and of 50% for ReO 4 - removal, compared to the pFe. These results provide a highly applicable platform for solving critical DOE and industrial needs related to nuclear environmental stewardship and nuclear power production.« less

Iron isotope fractionation during microbially stimulated Fe(II) oxidation and Fe(III) precipitation

USGS Publications Warehouse

Balci, N.; Bullen, T.D.; Witte-Lien, K.; Shanks, Wayne C.; Motelica, M.; Mandernack, K.W.

2006-01-01

Interpretation of the origins of iron-bearing minerals preserved in modern and ancient rocks based on measured iron isotope ratios depends on our ability to distinguish between biological and non-biological iron isotope fractionation processes. In this study, we compared 56Fe/54Fe ratios of coexisting aqueous iron (Fe(II)aq, Fe(III)aq) and iron oxyhydroxide precipitates (Fe(III)ppt) resulting from the oxidation of ferrous iron under experimental conditions at low pH (<3). Experiments were carried out using both pure cultures of Acidothiobacillus ferrooxidans and sterile controls to assess possible biological overprinting of non-biological fractionation, and both SO42- and Cl- salts as Fe(II) sources to determine possible ionic/speciation effects that may be associated with oxidation/precipitation reactions. In addition, a series of ferric iron precipitation experiments were performed at pH ranging from 1.9 to 3.5 to determine if different precipitation rates cause differences in the isotopic composition of the iron oxyhydroxides. During microbially stimulated Fe(II) oxidation in both the sulfate and chloride systems, 56Fe/54Fe ratios of residual Fe(II)aq sampled in a time series evolved along an apparent Rayleigh trend characterized by a fractionation factor ??Fe(III)aq-Fe(II)aq???1.0022. This fractionation factor was significantly less than that measured in our sterile control experiments (???1.0034) and that predicted for isotopic equilibrium between Fe(II)aq and Fe(III)aq (???1.0029), and thus might be interpreted to reflect a biological isotope effect. However, in our biological experiments the measured difference in 56Fe/54Fe ratios between Fe(III)aq, isolated as a solid by the addition of NaOH to the final solution at each time point under N2-atmosphere, and Fe(II)aq was in most cases and on average close to 2.9??? (??Fe(III)aq-Fe(II)aq ???1.0029), consistent with isotopic equilibrium between Fe(II)aq and Fe(III)aq. The ferric iron precipitation experiments revealed that 56Fe/54Fe ratios of Fe(III)aq were generally equal to or greater than those of Fe(III)ppt, and isotopic fractionation between these phases decreased with increasing precipitation rate and decreasing grain size. Considered together, the data confirm that the iron isotope variations observed in our microbial experiments are primarily controlled by non-biological equilibrium and kinetic factors, a result that aids our ability to interpret present-day iron cycling processes but further complicates our ability to use iron isotopes alone to identify biological processing in the rock record. ?? 2005 Elsevier Inc. All rights reserved.

Dissolved and labile concentrations of Cd, Cu, Pb, and Zn in the South Fork Coeur d'Alene River, Idaho: Comparisons among chemical equilibrium models and implications for biotic ligand models

USGS Publications Warehouse

Balistrieri, L.S.; Blank, R.G.

2008-01-01

In order to evaluate thermodynamic speciation calculations inherent in biotic ligand models, the speciation of dissolved Cd, Cu, Pb, and Zn in aquatic systems influenced by historical mining activities is examined using equilibrium computer models and the diffusive gradients in thin films (DGT) technique. Several metal/organic-matter complexation models, including WHAM VI, NICA-Donnan, and Stockholm Humic model (SHM), are used in combination with inorganic speciation models to calculate the thermodynamic speciation of dissolved metals and concentrations of metal associated with biotic ligands (e.g., fish gills). Maximum dynamic metal concentrations, determined from total dissolved metal concentrations and thermodynamic speciation calculations, are compared with labile metal concentrations measured by DGT to assess which metal/organic-matter complexation model best describes metal speciation and, thereby, biotic ligand speciation, in the studied systems. Results indicate that the choice of model that defines metal/organic-matter interactions does not affect calculated concentrations of Cd and Zn associated with biotic ligands for geochemical conditions in the study area, whereas concentrations of Cu and Pb associated with biotic ligands depend on whether the speciation calculations use WHAM VI, NICA-Donnan, or SHM. Agreement between labile metal concentrations and dynamic metal concentrations occurs when WHAM VI is used to calculate Cu speciation and SHM is used to calculate Pb speciation. Additional work in systems that contain wide ranges in concentrations of multiple metals should incorporate analytical speciation methods, such as DGT, to constrain the speciation component of biotic ligand models. ?? 2008 Elsevier Ltd.

Assessing bioavailability levels of metals in effluent-affected rivers: effect of Fe(III) and chelating agents on the distribution of metal speciation.

PubMed

Han, Shuping; Naito, Wataru; Masunaga, Shigeki

To assess the effects of Fe(III) and anthropogenic ligands on the bioavailability of Ni, Cu, Zn, and Pb, concentrations of bioavailable metals were measured by the DGT (diffusive gradients in thin films) method in some urban rivers, and were compared with concentrations calculated by a chemical equilibrium model (WHAM 7.0). Assuming that dissolved Fe(III) (<0.45 μm membrane filtered) was in equilibrium with colloidal iron oxide, the WHAM 7.0 model estimated that bioavailable concentrations of Ni, Cu, and Zn were slightly higher than the corresponding values estimated assuming that dissolved Fe(III) was absent. In contrast, lower levels of free Pb were predicted by the WHAM 7.0 model when dissolved Fe(III) was included. Estimates showed that most of the dissolved Pb was present as colloidal iron-Pb complex. Ethylene-diamine-tetra-acetic acid (EDTA) concentrations at sampling sites were predicted from the relationship between EDTA and the calculated bioavailable concentration of Zn. When both colloidal iron and predicted EDTA concentrations were included in the WHAM 7.0 calculations, dissolved metals showed a strong tendency to form EDTA complexes, in the order Ni > Cu > Zn > Pb. With the inclusion of EDTA, bioavailable concentrations of Ni, Cu, and Zn predicted by WHAM 7.0 were different from those predicted considering only humic substances and colloidal iron.

Magnetic susceptibility of the South African Agouron scientific drillcores quantifies iron and sulfur alteration relevant to geochemical oxygenation proxies

NASA Astrophysics Data System (ADS)

Raub, T. D.; Nayak, P. M.; Tikoo, S. M.; Johnson, J. E.; Peek, S.; Fischer, W. W.; Kirschvink, J. L.

2010-12-01

Various geochemical characteristics of sedimentary iron- and sulfur-bearing minerals motivate early- to late-oxygenation hypotheses from South African and Australian scientific drillcores. Most intervals of these drillcores appear to be remagnetized (in some cases multiple times); and ~2.0 Ga magnetic sulfide crystallization is particularly pervasive in carbonaceous siltstones of the ca. 2.7-2.2 Ga Griqualand margin of Kaapvaal craton. Robust interpretation of trace element abundances suggesting “whiffs” to “pervasive” levels of late Archean oxygen depends upon systematics of presumed depositional iron speciation; so multiple iron- and sulfur-mineral-altering events affecting existing drillcore records call straightforward interpretations into question. We report ca. 10,000 magnetic susceptibility measurements and associated detailed rock-magnetic results from all lithologies of Archean basinal and slope facies in drillcores GKP and GKF and relatively younger and shallower facies in Paleoproterozoic drillcores GEC and GTF. Specific carbonaceous siltstone and carbonate intervals are less-altered as revealed by coherent and relatively low magnetic susceptibilities: geochemical and biomarker interpretations based upon data from these intervals should be preferred to those from others. Magnetic susceptibility tracks subtle facies variation in drillcore GTF diamictite and suggests highly-structured Paleoproterozoic glacioeustatic sequence architecture consistent with assignment of Makganyene glaciation and its associated geochemical signature to a ca. 2.2 Ga “Snowball Earth” ice age.

Divergence with gene flow across a speciation continuum of Heliconius butterflies.

PubMed

Supple, Megan A; Papa, Riccardo; Hines, Heather M; McMillan, W Owen; Counterman, Brian A

2015-09-24

A key to understanding the origins of species is determining the evolutionary processes that drive the patterns of genomic divergence during speciation. New genomic technologies enable the study of high-resolution genomic patterns of divergence across natural speciation continua, where taxa pairs with different levels of reproductive isolation can be used as proxies for different stages of speciation. Empirical studies of these speciation continua can provide valuable insights into how genomes diverge during speciation. We examine variation across a handful of genomic regions in parapatric and allopatric populations of Heliconius butterflies with varying levels of reproductive isolation. Genome sequences were mapped to 2.2-Mb of the H. erato genome, including 1-Mb across the red color pattern locus and multiple regions unlinked to color pattern variation. Phylogenetic analyses reveal a speciation continuum of pairs of hybridizing races and incipient species in the Heliconius erato clade. Comparisons of hybridizing pairs of divergently colored races and incipient species reveal that genomic divergence increases with ecological and reproductive isolation, not only across the locus responsible for adaptive variation in red wing coloration, but also at genomic regions unlinked to color pattern. We observe high levels of divergence between the incipient species H. erato and H. himera, suggesting that divergence may accumulate early in the speciation process. Comparisons of genomic divergence between the incipient species and allopatric races suggest that limited gene flow cannot account for the observed high levels of divergence between the incipient species. Our results provide a reconstruction of the speciation continuum across the H. erato clade and provide insights into the processes that drive genomic divergence during speciation, establishing the H. erato clade as a powerful framework for the study of speciation.

Sources and fates of heavy metals in a mining-impacted stream: Temporal variability and the role of iron oxides

PubMed Central

Schaider, Laurel A.; Senn, David B.; Estes, Emily R.; Brabander, Daniel J.; Shine, James P.

2014-01-01

Heavy metal contamination of surface waters at mining sites often involves complex interactions of multiple sources and varying biogeochemical conditions. We compared surface and subsurface metal loading from mine waste pile runoff and mine drainage discharge and characterized the influence of iron oxides on metal fate along a 0.9-km stretch of Tar Creek (Oklahoma, USA), which drains an abandoned Zn/Pb mining area. The importance of each source varied by metal: mine waste pile runoff contributed 70% of Cd, while mine drainage contributed 90% of Pb, and both sources contributed similarly to Zn loading. Subsurface inputs accounted for 40% of flow and 40-70% of metal loading along this stretch. Streambed iron oxide aggregate material contained highly elevated Zn (up to 27,000 μg g−1), Pb (up to 550 μg g−1) and Cd (up to 200 μg g−1) and was characterized as a heterogeneous mixture of iron oxides, fine-grain mine waste, and organic material. Sequential extractions confirmed preferential sequestration of Pb by iron oxides, as well as substantial concentrations of Zn and Cd in iron oxide fractions, with additional accumulation of Zn, Pb, and Cd during downstream transport. Comparisons with historical data show that while metal concentrations in mine drainage have decreased by more than an order of magnitude in recent decades, the chemical composition of mine waste pile runoff has remained relatively constant, indicating less attenuation and increased relative importance of pile runoff. These results highlight the importance of monitoring temporal changes at contaminated sites associated with evolving speciation and simultaneously addressing surface and subsurface contamination from both mine waste piles and mine drainage. PMID:24867708

Rock magnetic and geochemical evidence for authigenic magnetite formation via iron reduction in coal-bearing sediments offshore Shimokita Peninsula, Japan (IODP Site C0020)

NASA Astrophysics Data System (ADS)

Phillips, Stephen C.; Johnson, Joel E.; Clyde, William C.; Setera, Jacob B.; Maxbauer, Daniel P.; Severmann, Silke; Riedinger, Natascha

2017-06-01

Sediments recovered at Integrated Ocean Drilling Program (IODP) Site C0020, in a fore-arc basin offshore Shimokita Peninsula, Japan, include numerous coal beds (0.3-7 m thick) that are associated with a transition from a terrestrial to marine depositional environment. Within the primary coal-bearing unit (˜2 km depth below seafloor) there are sharp increases in magnetic susceptibility in close proximity to the coal beds, superimposed on a background of consistently low magnetic susceptibility throughout the remainder of the recovered stratigraphic sequence. We investigate the source of the magnetic susceptibility variability and characterize the dominant magnetic assemblage throughout the entire cored record, using isothermal remanent magnetization (IRM), thermal demagnetization, anhysteretic remanent magnetization (ARM), iron speciation, and iron isotopes. Magnetic mineral assemblages in all samples are dominated by very low-coercivity minerals with unblocking temperatures between 350 and 580°C that are interpreted to be magnetite. Samples with lower unblocking temperatures (300-400°C), higher ARM, higher-frequency dependence, and isotopically heavy δ56Fe across a range of lithologies in the coal-bearing unit (between 1925 and 1995 mbsf) indicate the presence of fine-grained authigenic magnetite. We suggest that iron-reducing bacteria facilitated the production of fine-grained magnetite within the coal-bearing unit during burial and interaction with pore waters. The coal/peat acted as a source of electron donors during burial, mediated by humic acids, to supply iron-reducing bacteria in the surrounding siliciclastic sediments. These results indicate that coal-bearing sediments may play an important role in iron cycling in subsiding peat environments and if buried deeply through time, within the subsequent deep biosphere.

Effect of sulfide on As(III) and As(V) sequestration by ferrihydrite.

PubMed

Zhao, Zhixi; Wang, Shaofeng; Jia, Yongfeng

2017-10-01

The sulfide-induced change in arsenic speciation is often coupled to iron geochemical processes, including redox reaction, adsorption/desorption and precipitation/dissolution. Knowledge about how sulfide influenced the coupled geochemistry of iron and arsenic was not explored well up to now. In this work, retention and mobilization of As(III) and As(V) on ferrihydrite in sulfide-rich environment was studied. The initial oxidation states of arsenic and the contact order of sulfide notably influenced arsenic sequestration on ferrihydrite. For As(III) systems, pre-sulfidation of As(III) decreased arsenic sequestration mostly. The arsenic adsorption capacity decreased about 50% in comparison with the system without sulfide addition. For As(V) systems, pre-sulfidation of ferrihydrite decreased 30% sequestration of arsenic on ferrihydrite. Reduction of ferrihydrite by sulfide in As(V) system was higher than that in As(III) system. Geochemical modeling calculations identified formation of thioarsenite in the pre-sulfidation of As(III) system. Formation of arsenic thioanions enhanced As solubility in the pre-sulfidation of As(III) system. The high concentration of sulfide and Fe(II) in pre-sulfidation of ferrihydrite system contributed to saturation of FeS. This supplied new solid phase to immobilize soluble arsenic in aqueous phase. X-ray absorption near edge spectroscopy (XANES) of sulfur K-edge, arsenic K-edge and iron L-edge analysis gave the consistent evidence for the sulfidation reaction of arsenic and ferrihydrite under specific geochemical settings. Copyright © 2017 Elsevier Ltd. All rights reserved.

Fe-Impregnated Mineral Colloids for Peroxide Activation: Effects of Mineral Substrate and Fe Precursor.

PubMed

Li, Yue; Machala, Libor; Yan, Weile

2016-02-02

Heterogeneous iron species at the mineral/water interface are important catalysts for the generation of reactive oxygen species at circumneutral pH. One significant pathway leading to the formation of such species arises from deposition of dissolved iron onto mineral colloids due to changes in redox conditions. This study investigates the catalytic properties of Fe impregnated on silica, alumina, and titania nanoparticles (as prototypical mineral colloids). Fe impregnation was carried out by immersing the mineral nanoparticles in dilute Fe(II) or Fe(III) solutions at pH 6 and 3, respectively, in an aerobic environment. The uptake of iron per unit surface area follows the order of nTiO2 > nAl2O3 > nSiO2 for both types of Fe precursors. Impregnation of mineral particles in Fe(II) solutions results in predominantly Fe(III) species due to efficient surface-mediated oxidation. The catalytic activity of the impregnated solids to produce hydroxyl radical (·OH) from H2O2 decomposition was evaluated using benzoic acid as a probe compound under dark conditions. Invariably, the rates of benzoic acid oxidation with different Fe-laden particles increase with the surface density of Fe until a critical density above which the catalytic activity approaches a plateau, suggesting active Fe species are formed predominantly at low surface loadings. The critical surface density of Fe varies with the mineral substrate as well as the aqueous Fe precursor. Fe impregnated on TiO2 exhibits markedly higher activity than its Al2O3 and SiO2 counterparts. The speciation of interfacial Fe is analyzed with diffuse reflectance UV-vis analysis and interpretation of the data in the context of benzoic oxidation rates suggests that the surface activity of the solids for ·OH generation correlates strongly with the isolated (i.e., mononuclear) Fe species. Therefore, iron dispersed on mineral colloids is a significant form of reactive iron surfaces in the aquatic environment.

Hydrothermal ore-forming processes in the light of studies in rock- buffered systems: I. Iron-copper-zinc-lead sulfide solubility relations

USGS Publications Warehouse

Hemley, J.J.; Cygan, G.L.; Fein, J.B.; Robinson, G.R.; d'Angelo, W. M.

1992-01-01

Experimental studies, using cold-seal and extraction vessel techniques, were conducted on Fe, Pb, Zn, and Cu sulfide solubilities in chloride soultions at temperatures from 300?? to 700??C and pressures from 0.5 to 2 kbars. The solutions were buffered in pH by quartz monzonite and the pure potassium feldspar-muscovite-quartz assemblage and in fS2-fO2 largely by the assemblage pyrite-pyrrhotite-magnetite. Solubilities increase with increasing temperature and total chloride, and decrease with increasing pressure. The effect of increasing chloride concentration on solubility reflects primarily a shift to lower pH via the silicate buffer reactions. Similarity in behaviour with respect to the temperature and pressure of Fe, Zn, and Pb sulfide solubilities points to similarity in chloride speciation, and the neutral species appear to be dominant in the high-temperature region. -from Authors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Fan; Parker, Jack C.; Watson, David B

This study investigates uranium and technetium sorption onto aluminum and iron hydroxides during titration of acidic groundwater. The contaminated groundwater exhibits oxic conditions with high concentrations of NO{sub 3}{sup -}, SO{sub 4}{sup 2-}, U, Tc, and various metal cations. More than 90% of U and Tc was removed from the aqueous phase as Al and Fe precipitated above pH 5.5, but was partially resolublized at higher pH values. An equilibrium hydrolysis and precipitation reaction model adequately described variations in aqueous concentrations of metal cations. An anion exchange reaction model was incorporated to simulate sulfate, U and Tc sorption onto variablymore » charged (pH-dependent) Al and Fe hydroxides. Modeling results indicate that competitive sorption/desorption on mixed mineral phases needs to be considered to adequately predict U and Tc mobility. The model could be useful for future studies of the speciation of U, Tc and co-existing ions during pre- and post-groundwater treatment practices.« less

Impact of phenazine-1-carboxylic acid upon iron speciation and microbial biomass in the rhizosphere of wheat

NASA Astrophysics Data System (ADS)

LeTourneau, M.; Marshall, M.; Grant, M.; Freeze, P.; Cliff, J. B.; Lai, B.; Strawn, D. G.; Thomashow, L. S.; Weller, D. M.; Harsh, J. B.

2015-12-01

Phenazine-1-carboxylic acid (PCA) is a redox-active antibiotic produced by diverse bacterial taxa, and has been shown to facilitate interactions between biofilms and iron (hydr)oxides in culture systems (Wang et al. 2011, J Bacteriol 192: 365). Because rhizobacterial biofilms are a major sink for plant-derived carbon and source for soil organic matter (SOM), and Fe (hydr)oxides have reactive surfaces that influence the stability of microbial biomass and SOM, PCA-producing rhizobacteria could influence soil carbon fluxes. Large populations of Pseudomonas fluorescens strains producing PCA in concentrations up to 1 μg/g root have been observed in the rhizosphere of non-irrigated wheat fields covering 1.56 million hectares of central Washington state. This is one of the highest concentrations ever reported for a natural antibiotic in a terrestrial ecosystem (Mavrodi et al. 2012, Appl Environ Microb 78: 804). Microscopic comparisons of PCA-producing (PCA+) and non-PCA-producing (PCA-) rhizobacterial colony morphologies, and comparisons of Fe extractions from rhizosphere soil inoculated with PCA+ and PCA- strains suggest that PCA promotes biofilm development as well as dramatic Fe transformations throughout the rhizosphere (unpublished data). In order to illustrate PCA-mediated interactions between biofilms and Fe (hydr)oxides in the rhizosphere, identify the specific Fe phases favored by PCA, and establish the ramifications for stability and distribution of microbial biomass and SOM, we have collected electron micrographs, X-ray fluorescence images, X-ray absorption near-edge spectra, and secondary-ion mass spectrometry images of wheat root sections inoculated with 15N-labelled PCA+ or PCA- rhizobacteria. These images and spectra allow us to assess the accumulation, turnover, and distribution of microbial biomass, the associations between Fe and other nutrients such as phosphorus, and the redox status and speciation of iron in the presence and absence of PCA. This information provides a starting point to model the impact of PCA upon carbon fluxes in Columbia Basin agro-ecosystems and other environments where PCA-producing bacteria are prevalent.

Chemical transformations during aging of zerovalent iron nanoparticles in the presence of common groundwater dissolved constituents.

PubMed

Reinsch, Brian C; Forsberg, Brady; Penn, R Lee; Kim, Christopher S; Lowry, Gregory V

2010-05-01

Nanoscale zerovalent iron (NZVI) that was aged in simulated groundwater was evaluated for alterations in composition and speciation over 6 months to understand the possible transformations NZVI could undergo in natural waters. NZVI was exposed to 10 mN of various common groundwater anions (Cl(-), NO(3)(-), SO(4)(2-), HPO(4)(2-), and HCO(3)(-)) or to dissolved oxygen (saturated, approximately 9 mg/L). Fresh and exposed NZVI samples, along with Fe-oxide model compounds, were then analyzed using synchrotron radiation X-ray absorption spectroscopy (XAS) to yield both relative oxidation state, using the X-ray absorption near edge structure (XANES), and quantitative speciation information regarding the types and proportions of mineral species present, from analysis of the extended X-ray absorption fine structure (EXAFS). Over 1 month of aging the dissolved anions inhibited the oxidation of the NZVI to varying degrees. Aging for 6 months, however, resulted in average oxidation states that were similar to each other regardless of the anion used, except for nitrate. Nitrate passivated the NZVI surface such that even after 6 months of aging the particles retained nearly the same mineral and Fe(0) content as fresh NZVI. Linear least-squares combination fitting (LCF) of the EXAFS spectra for 1 month-aged samples indicated that the oxidized particles remain predominantly a binary phase system containing Fe(0) and Fe(3)O(4), while the 6 month aged samples contained additional mineral phases such as vivianite (Fe(3)(PO(4))(2).8H(2)O) and iron sulfate species, possibly schwertmannite (Fe(3+)(16)O(16)(OH,SO(4))(12-13).10-12H(2)O). The presence of these additional mineral species was confirmed using synchrotron-based X-ray diffraction (XRD). NZVI exposed to water saturated with dissolved oxygen showed a rapid (<24 h) loss of Fe(0) and evolved both magnetite and maghemite (gamma-Fe(2)O(3)) within the oxide layer. These findings have implications toward the eventual fate, transport, and toxicity of NZVI used for groundwater remediation.

Microscale speciation of arsenic and iron in ferric-based sorbents subjected to simulated landfill conditions

PubMed Central

Root, Robert A.; Fathordoobadi, Sahar; Alday, Fernando; Ela, Wendell; Chorover, Jon

2013-01-01

During treatment for potable use, water utilities generate arsenic-bearing ferric wastes that are subsequently dispatched to landfills. The biogeochemical weathering of these residuals in mature landfills affects the potential mobilization of sorbed arsenic species via desorption from solids subjected to phase transformations driven by abundant organic matter and bacterial activity. Such processes are not simulated with the Toxicity Characteristic Leaching Procedure (TCLP) currently used to characterize hazard. To examine the effect of sulfate on As retention in landfill leachate, columns of As(V) loaded amorphous ferric hydroxide were reacted biotically at two leachate sulfate concentrations (0.064 mM and 2.1 mM). After 300 d, ferric sorbents were reductively dissolved. Arsenic released to porewaters was partially co-precipitated in mixed-valent secondary iron phases whose speciation was dependent on sulfate concentration. As and Fe XAS showed that, in the low sulfate column, 75–81% of As(V) was reduced to As(III), and 53–68% of the Fe(III) sorbent was transformed, dominantly to siderite and green rust. In the high sulfate column, Fe(III) solids were reduced principally to FeS(am), whereas As(V) was reduced to a polymeric sulfide with local atomic structure of realgar. Multi-energy micro-X-ray fluorescence (ME-μXRF) imaging at Fe and As K-edges showed that As formed surface complexes with ferrihydrite > siderite > green rust in the low sulfate column; while discrete realgar-like phases formed in the high sulfate systems. Results indicate that landfill sulfur chemistry exerts strong control over the potential mobilization of As from ferric sorbent residuals by controlling secondary As and Fe sulfide co-precipitate formation. PMID:24102155

Cold Temperature Effects on Speciated VOC Emissions from modern GDI Light Duty Truck

EPA Science Inventory

Although gasoline direct injection (GDI) vehicles represent nearly half of the light-duty vehicle market share, few studies have reported speciated volatile organic compounds (VOCs) in GDI vehicle exhaust emissions. In this study, speciated VOC emissions were characterized from t...

Indirect effects of climate change on zinc cycling in sediments: The role of changing water levels.

PubMed

Nedrich, Sara M; Burton, G Allen

2017-09-01

Increased variability in lake and river water levels associated with changing climate could impact the fate and effects of metals in redox-sensitive sediments through the alteration of microbial communities and of acid-base and redox chemistry. The objective of the present study was to determine the influence of water level fluctuation on metal speciation in porewater and predict environmental risk to high-carbonate systems. Using experimental microcosms with sediments collected from 4 metal-contaminated coastal freshwater wetlands in Michigan, USA, we conducted water level fluctuation experiments. Porewater and sediment metals (Ca, Cu, Fe, Mg, Mn, Ni, Zn) and important metal binding phases (iron-oxide speciation, acid-volatile sulfide) were quantified. In a short-term drying (seiche) experiment, there were decreases in all porewater metals after inundation of saturated sediments. During a drought experiment, re-inundation of oxidized sediments increased porewater Cu, Zn, Mg, Ca for most sites. Porewater Zn increased after inundation to levels exceeding the US Environmental Protection Agency threshold for chronic toxicity. These data show that the dissolution of metal carbonates and metal sulfates contributes to metal release after re-flooding and indicate that we might expect increased ecological risk to organisms present in drought-sensitive regions where altered hydroperiods are likely to increase metal bioavailability. Environ Toxicol Chem 2017;36:2456-2464. © 2017 SETAC. © 2017 SETAC.

Statistical analysis of iron geochemical data suggests limited late Proterozoic oxygenation

NASA Astrophysics Data System (ADS)

Sperling, Erik A.; Wolock, Charles J.; Morgan, Alex S.; Gill, Benjamin C.; Kunzmann, Marcus; Halverson, Galen P.; MacDonald, Francis A.; Knoll, Andrew H.; Johnston, David T.

2015-07-01

Sedimentary rocks deposited across the Proterozoic-Phanerozoic transition record extreme climate fluctuations, a potential rise in atmospheric oxygen or re-organization of the seafloor redox landscape, and the initial diversification of animals. It is widely assumed that the inferred redox change facilitated the observed trends in biodiversity. Establishing this palaeoenvironmental context, however, requires that changes in marine redox structure be tracked by means of geochemical proxies and translated into estimates of atmospheric oxygen. Iron-based proxies are among the most effective tools for tracking the redox chemistry of ancient oceans. These proxies are inherently local, but have global implications when analysed collectively and statistically. Here we analyse about 4,700 iron-speciation measurements from shales 2,300 to 360 million years old. Our statistical analyses suggest that subsurface water masses in mid-Proterozoic oceans were predominantly anoxic and ferruginous (depleted in dissolved oxygen and iron-bearing), but with a tendency towards euxinia (sulfide-bearing) that is not observed in the Neoproterozoic era. Analyses further indicate that early animals did not experience appreciable benthic sulfide stress. Finally, unlike proxies based on redox-sensitive trace-metal abundances, iron geochemical data do not show a statistically significant change in oxygen content through the Ediacaran and Cambrian periods, sharply constraining the magnitude of the end-Proterozoic oxygen increase. Indeed, this re-analysis of trace-metal data is consistent with oxygenation continuing well into the Palaeozoic era. Therefore, if changing redox conditions facilitated animal diversification, it did so through a limited rise in oxygen past critical functional and ecological thresholds, as is seen in modern oxygen minimum zone benthic animal communities.

Non-steady state diagenesis of organic and inorganic sulfur in lake sediments

NASA Astrophysics Data System (ADS)

Couture, Raoul-Marie; Fischer, Rachele; Van Cappellen, Philippe; Gobeil, Charles

2016-12-01

Sulfur controls the fate of many geochemical elements in lake sediments, including iron, phosphorus and environmentally important trace elements. We measured the speciation of pore-water and sediment-bound sulfur (aqueous sulfate and sulfides, elemental sulfur, iron monosulfide, pyrite, organic sulfur) and supporting geochemical variables (carbon, oxygen, iron) in the sediments of a perennially oxygenated and a seasonally anoxic basin of an oligotrophic lake in Québec, using a combination of pore-water analyses, sequential extractions and X-ray absorption near edge structure. A non-steady state early diagenetic model was developed and calibrated against this extensive dataset to help unravel the pathways and quantify the rates of S transformations. Results suggest that the main source of S to the sediments is the settling of organic ester-sulfate (R-O-SO3-H). Hydrolysis of these compounds provides an additional source of sulfate for anaerobic microbial oxidation of sedimentary organic matter, releasing sulfide to the pore-water. Reduced solid-bound S species accumulate as thiols (R-SH) and iron sulfides in the perennially oxygenated and seasonally anoxic basin, respectively. The model-estimated rate constant for R-SH formation is lower than previously estimated for this particular lacustrine site, but similar to that proposed for marine shelf sediments. The solid sediment S profiles, however, carry the imprint of the time-dependent sulfate input to the lake. Iron sulfide enrichments formed during past decades of elevated atmospheric SO4 deposition are presently dissolving. In the sediments of the perennially oxygenated basin this reaction hampers the build-up of Fe(III) (oxy)hydroxide near the sediment-water interface.

Self-consistent approach for neutral community models with speciation

NASA Astrophysics Data System (ADS)

Haegeman, Bart; Etienne, Rampal S.

2010-03-01

Hubbell’s neutral model provides a rich theoretical framework to study ecological communities. By incorporating both ecological and evolutionary time scales, it allows us to investigate how communities are shaped by speciation processes. The speciation model in the basic neutral model is particularly simple, describing speciation as a point-mutation event in a birth of a single individual. The stationary species abundance distribution of the basic model, which can be solved exactly, fits empirical data of distributions of species’ abundances surprisingly well. More realistic speciation models have been proposed such as the random-fission model in which new species appear by splitting up existing species. However, no analytical solution is available for these models, impeding quantitative comparison with data. Here, we present a self-consistent approximation method for neutral community models with various speciation modes, including random fission. We derive explicit formulas for the stationary species abundance distribution, which agree very well with simulations. We expect that our approximation method will be useful to study other speciation processes in neutral community models as well.

Development of a mercury speciation, fate, and biotic uptake (BIOTRANSPEC) model: Application to Lahontan Reservoir (Nevada, USA)

USGS Publications Warehouse

Gandhi, N.; Bhavsar, S.P.; Diamond, M.L.; Kuwabara, J.S.; Marvin-DiPasquale, M.; Krabbenhoft, D.P.

2007-01-01

A mathematically linked mercury transport, speciation, kinetic, and simple biotic uptake (BIOTRANSPEC) model has been developed. An extension of the metal transport and speciation (TRANSPEC) model, BIOTRANSPEC estimates the fate and biotic uptake of inorganic (Hg(II)), elemental (Hg(0)) and organic (MeHg) forms of mercury and their species in the dissolved, colloidal (e.g., dissolved organic matter [DOM]), and particulate phases of surface aquatic systems. A pseudo-steady state version of the model was used to describe mercury dynamics in Lahontan Reservoir (near Carson City, NV, USA), where internal loading of the historically deposited mercury is remobilized, thereby maintaining elevated water concentrations. The Carson River is the main source of total mercury (THg), of which more than 90% is tightly bound in a gold-silver-mercury amalgam, to the system through loadings in the spring, with negligible input from the atmospheric deposition. The speciation results suggest that aqueous species are dominated by Hg-DOM, Hg(OH)2, and HgClOH. Sediment-to-water diffusion of MeHg and Hg-DOM accounts for approximately 10% of total loadings to the water column. The water column acts as a net sink for MeHg by reducing its levels through two competitive processes: Uptake by fish, and net MeHg demethylation. Although reservoir sediments produce significant amounts of MeHg (4 g/d), its transport from sediment to water is limited (1.6 g/d), possibly because of its adsorption on metal oxides of iron and manganese at the sediment-water interface. Fish accumulate approximately 45% of the total MeHg mass in the water column, and 9% of total MeHg uptake by fish leaves the system because of fishing. Results from this new model reiterate the previous conclusion that more than 90% of THg input is retained in sediment, which perpetuates elevated water concentrations. ?? 2007 SETAC.

Micronutrient metal speciation is controlled by competitive organic chelation in grassland soils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boiteau, Rene M.; Shaw, Jared B.; Pasa-Tolic, Ljiljana

Many elements are scarcely soluble in aqueous conditions found in high pH environments, such as calcareous grassland soils, unless complexed to strong binding organic ligands. To overcome this limitation, some plants and microbes produce chelators that solubilize micronutrient metals such as Fe, Ni, Cu, and Zn from mineral phases. These complexes are taken up by organisms via specific membrane receptors, thereby differentially impacting the bioavailability of these metals to the plant and microbial community. Although the importance of these chelation strategies for individual organisms has been well established, little is known about which pathways coexist within rhizosphere microbiomes or howmore » they interact and compete for metal binding. Identifying these metallo-organic species within natural ecosystems has remained a formidable analytical challenge due to the vast diversity of compounds and poorly defined metabolic processes in complex soil matrix. Herein, we employed recently developed liquid chromatography (LC) mass spectrometry (MS) methods to characterize the speciation of water-soluble dissolved trace elements (Fe, Ni, Cu, and Zn) from Kansas Prairie soil. Both plant and fungal chelators were identified, revealing compound-specific patterns of chelation to biologically essential metals. Numerous metabolites typically implicated in plant iron acquisition and homeostasis, including mugineic acids, deoxymugineic acid, nicotianamine, and hydroxynicotianamine, dominated the speciation of divalent metals such as Ni, Cu, and Zn (2-57 pmol / g soil). In contrast, the fungal siderophore ferricrocine bound comparatively more trivalent Fe (9pmol / g soil). These results define biochemical pathways that underpin the regulation of metals in the grassland rhizosphere. They also raise new questions about the competition of these compounds for metal binding and their bioavailability to different members of the rhizosphere population. Even small structural differences result in significant differences in their environmental metal speciation, and likely impact metal uptake within the rhizosphere of calcareous soils.« less

Chromium fate in constructed wetlands treating tannery wastewaters.

PubMed

Dotro, Gabriela; Palazolo, Paul; Larsen, Daniel

2009-06-01

Nine experimental wetlands were built to determine chromium partitioning inside systems treating tannery wastewaters. Results showed 5-day biochemical oxygen demand and chromium removals of 95 to 99% and 90 to 99%, respectively. The majority of chromium was found in association with media (96 to 98%), followed by effluents (2.9 to 3.9%), and the least was found in plant parts (0.1%). Chemical speciation modeling of solutions and scanning electron microscope analysis suggest two potential chromium removal mechanisms--sorption/coprecipitation with iron hydroxides or oxyhydroxides and biomass sorption. The release of the majority of chromium in the iron- and organic-bound phases during sequential extractions supports the proposed dominant removal mechanisms. The use of a mixture of peat and gravel resulted in lower removal efficiencies and stronger partitioning in organic phases during sequential extractions. Chromium was efficiently removed by wetlands, retained through chemical and biological processes. Future research will focus on further exploring removal mechanisms and proposing management strategies for the chromium-containing wetland media.

Biological effects of four iron-containing nanoremediation materials on the green alga Chlamydomonas sp.

PubMed

Nguyen, Nhung H A; Von Moos, Nadia R; Slaveykova, Vera I; Mackenzie, Katrin; Meckenstock, Rainer U; Thűmmler, Silke; Bosch, Julian; Ševců, Alena

2018-06-15

As nanoremediation strategies for in-situ groundwater treatment extend beyond nanoiron-based applications to adsorption and oxidation, ecotoxicological evaluations of newly developed materials are required. The biological effects of four new materials with different iron (Fe) speciations ([i] FerMEG12 - pristine flake-like milled Fe(0) nanoparticles (nZVI), [ii] Carbo-Iron ® - Fe(0)-nanoclusters containing activated carbon (AC) composite, [iii] Trap-Ox® Fe-BEA35 (Fe-zeolite) - Fe-doped zeolite, and [iv] Nano-Goethite - 'pure' FeOOH) were studied using the unicellular green alga Chlamydomonas sp. as a model test system. Algal growth rate, chlorophyll fluorescence, efficiency of photosystem II, membrane integrity and reactive oxygen species (ROS) generation were assessed following exposure to 10, 50 and 500 mg L -1 of the particles for 2 h and 24 h. The particles had a concentration-, material- and time-dependent effect on Chlamydomonas sp., with increased algal growth rate after 24 h. Conversely, significant intracellular ROS levels were detected after 2 h, with much lower levels after 24 h. All Fe-nanomaterials displayed similar Z-average sizes and zeta-potentials at 2 h and 24 h. Effects on Chlamydomonas sp. decreased in the order FerMEG12 > Carbo-Iron® > Fe-zeolite > Nano-Goethite. Ecotoxicological studies were challenged due to some particle properties, i.e. dark colour, effect of constituents and a tendency to agglomerate, especially at high concentrations. All particles exhibited potential to induce significant toxicity at high concentrations (500 mg L -1 ), though such concentrations would rapidly decrease to mg or µg L -1 in aquatic environments, levels harmless to Chlamydomonas sp. The presented findings contribute to the practical usage of particle-based nanoremediation in environmental restoration. Copyright © 2018. Published by Elsevier Inc.

A comparative analysis of island floras challenges taxonomy-based biogeographical models of speciation.

PubMed

Igea, Javier; Bogarín, Diego; Papadopulos, Alexander S T; Savolainen, Vincent

2015-02-01

Speciation on islands, and particularly the divergence of species in situ, has long been debated. Here, we present one of the first, complete assessments of the geographic modes of speciation for the flora of a small oceanic island. Cocos Island (Costa Rica) is pristine; it is located 550 km off the Pacific coast of Central America. It harbors 189 native plant species, 33 of which are endemic. Using phylogenetic data from insular and mainland congeneric species, we show that all of the endemic species are derived from independent colonization events rather than in situ speciation. This is in sharp contrast to the results of a study carried out in a comparable system, Lord Howe Island (Australia), where as much as 8.2% of the plant species were the product of sympatric speciation. Differences in physiography and age between the islands may be responsible for the contrasting patterns of speciation observed. Importantly, comparing phylogenetic assessments of the modes of speciation with taxonomy-based measures shows that widely used island biogeography approaches overestimate rates of in situ speciation. © 2014 The Author(s). Evolution © 2014 The Society for the Study of Evolution.

Quantification of Cation Sorption to Engineered Barrier Materials Under Extreme Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Powell, Brian; Schlautman, Mark; Rao, Linfeng

The objective of this research is to examine mechanisms and thermodynamics of actinide sorption to engineered barrier materials (iron (oxyhydr)oxides and bentonite clay) for nuclear waste repositories under high temperature and high ionic strength conditions using a suite of macroscopic and microscopic techniques which will be coupled with interfacial reaction models. Gaining a mechanistic understanding of interfacial processes governing the sorption/sequestration of actinides at mineral-water interfaces is fundamental for the accurate prediction of actinide behavior in waste repositories. Although macroscale sorption data and various spectroscopic techniques have provided valuable information regarding speciation of actinides at solid-water interfaces, significant knowledge gapsmore » still exist with respect to sorption mechanisms and the ability to quantify sorption, particularly at high temperatures and ionic strengths. This objective is addressed through three major tasks: (1) influence of oxidation state on actinide sorption to iron oxides and clay minerals at elevated temperatures and ionic strengths; (2) calorimetric titrations of actinide-mineral suspensions; (3) evaluation of bentonite performance under repository conditions. The results of the work will include a qualitative conceptual model and a quantitative thermodynamic speciation model describing actinide partitioning to minerals and sediments, which is based upon a mechanistic understanding of specific sorption processes as determined from both micro-scale and macroscale experimental techniques. The speciation model will be a thermodynamic aqueous and surface complexation model of actinide interactions with mineral surfaces that is self-consistent with macroscopic batch sorption data, calorimetric and potentiometric titrations, X-ray absorption Spectroscopy (XAS, mainly Extended X-ray Absorption Fine Structure (EXAFS)), and electron microscopy analyses. The novelty of the proposed work lies largely in the unique system conditions which will be examined (i.e. elevated temperature and ionic strength) and the manner in which the surface complexation model will be developed in terms of specific surface species identified using XAS. These experiments will thus provide a fundamental understanding of the chemical and physical processes occurring at the solid-solution interface under expected repository conditions. Additionally, the focus on thermodynamic treatment of actinide ion interactions with minerals as proposed will provide information on the driving forces involved and contribute to the overall understanding of the high affinity many actinide ions have for oxide surfaces. The utility of this model will be demonstrated in this work through a series of advective and diffusive flow experiments.« less

Microbial Diversity and Metal Speciation Changes in Mine Tailings Following Compost-Assisted Direct Planting: A Four-Year Superfund Site Field Study

NASA Astrophysics Data System (ADS)

Maier, R. M.; Gil-Loaiza, J.; Honeker, L. K.; Hottenstein, J. D.; Valentin-Vargas, A.; Jennings, L. L.; Hammond, C.; Neilson, J. W.; Root, R. A.; Chorover, J.

2014-12-01

EPA estimates that future mine tailings remediation costs will exceed US $50 billion using present technologies based on constructing an inert or biological cap on the tailings. Both approaches require large amounts of capping materials that can be difficult and expensive to obtain especially for sites several thousand hectares in size. An alternative technology is direct planting into tailings. However, direct planting alone is not feasible for many legacy sites due to extreme acidity and high metal content which prevent plant germination and growth. Therefore the process must be "assisted" through the addition of amendments such as compost. Here we present results from the first four years of a field study at the Iron King Mine and Humboldt Smelter Superfund site demonstrating the feasibility of compost-assisted direct planting. Parameters measured during the field study included: canopy cover, pH, nutrient content, plant metal uptake, metal(loid) speciation, mineral analysis, microbiome analysis, and plant root-metal-microbe interactions. Integrated analysis of these parameters suggests that even in this "worst-case scenario" mine tailings site (pH 2.5; As and Pb each exceeding 2 g kg-1), we have created a sustainable system. In this system, phyto-catalyzed stabilization of inorganic contaminants in the root zone is driven by plant root exudates and the associated rhizosphere microbial community. The results of this research will be put into context of a larger topic- that of ecological engineering of mine tailings sites - a technique being proposed to prevent creation of acidic conditions and metal(loid) mobilization in the first place.

Microbial Diversity and Metal Speciation Changes in Mine Tailings Following Compost-Assisted Direct Planting: A Four-Year Superfund Site Field Study

NASA Astrophysics Data System (ADS)

Maier, R. M.; Gil-Loaiza, J.; Honeker, L. K.; Hottenstein, J. D.; Valentin-Vargas, A.; Jennings, L. L.; Hammond, C.; Neilson, J. W.; Root, R. A.; Chorover, J.

2015-12-01

EPA estimates that future mine tailings remediation costs will exceed US $50 billion using present technologies based on constructing an inert or biological cap on the tailings. Both approaches require large amounts of capping materials that can be difficult and expensive to obtain especially for sites several thousand hectares in size. An alternative technology is direct planting into tailings. However, direct planting alone is not feasible for many legacy sites due to extreme acidity and high metal content which prevent plant germination and growth. Therefore the process must be "assisted" through the addition of amendments such as compost. Here we present results from the first four years of a field study at the Iron King Mine and Humboldt Smelter Superfund site demonstrating the feasibility of compost-assisted direct planting. Parameters measured during the field study included: canopy cover, pH, nutrient content, plant metal uptake, metal(loid) speciation, mineral analysis, microbiome analysis, and plant root-metal-microbe interactions. Integrated analysis of these parameters suggests that even in this "worst-case scenario" mine tailings site (pH 2.5; As and Pb each exceeding 2 g kg-1), we have created a sustainable system. In this system, phyto-catalyzed stabilization of inorganic contaminants in the root zone is driven by plant root exudates and the associated rhizosphere microbial community. The results of this research will be put into context of a larger topic- that of ecological engineering of mine tailings sites - a technique being proposed to prevent creation of acidic conditions and metal(loid) mobilization in the first place.

Experimental constrain of hydrogen production during early serpentinization stages

NASA Astrophysics Data System (ADS)

Clément, M.; Munoz, M.; Vidal, O.; Parra, T.

2009-04-01

Hydrothermal alteration of mantellic peridotites and ultramafic rocks along axial valleys of low spread oceanic ridges plays a key role in different fundamental domains like, 1) energetic gaz production (H2 and hydrocarbons) representing a potential source of energy for future generations, 2) formation of organic pre-biotic molecules in potential relation with the origin of life. Moreover, such complex volcanic-related alteration processes play fundamental role in economic geology, being widely associated to important polymetallic sulphides ore deposits. Recent researches proposed an initial hydrogen production due to the integration of ferric iron in Fe,Mg-serpentine. To better understand the early stages of hydrogen production, a series of natural peridotite rocks have been experimentally exposed to hydrothermal conditions, up to 300°C, 300 bars during different time scales. Experiments have been performed in using autoclaves with a sampling gas system. A systematic mineralogical characterization of the new products was carried out using classical spectroscopic tools. In particular, we focused on the iron behaviour using a redox and structural micro-XANES investigation. Redox information has been accurately derived from the pre-peak features previously calibrated from model compounds, while structural information about short and medium range order around iron has been extracted from the XANES region of the spectra, based both on experimental standards and ab-initio theoretical calculations. Two processes of oxidation emerged. Before two month experiment duration, serpentine displays a not negligible oxidation of ferrous iron in his structure (up to 60%), while after two months, iron oxides and hydroxides appear in the system. These results seem to correspond to natural observations. The iron coordination decreases linearly with time. It means that iron also integrates the serpentine tetrahedral sites. Moreover, high resolution µ-XAS maps on experimental samples were collected on the iron K-edge (7712 eV). These maps give valuable information concerning both kinetic of mineral phases transformation and spatial speciation of iron through the altered part of the samples. Finally, these results allow us to define a non linear model of "Fe3+ in serpentine vs hydrogen production" as a function of time.

The Effect of Pressure on Iron Speciation in Silicate Melts at a Fixed Oxygen Fugacity: The Possibility of a Redox Profile Through a Terrestrial Magma Ocean

NASA Astrophysics Data System (ADS)

Armstrong, K.; Frost, D. J.; McCammon, C. A.; Rubie, D. C.; Boffa Ballaran, T.

2017-12-01

As terrestrial planets accreted, mantle silicates equilibrated with core-forming metallic iron, which would have imposed a mantle oxygen fugacity below the iron-wüstite oxygen buffer. Throughout Earth's history, however, the oxygen fugacity of at least the accessible portions of the upper mantle has been 4-5 orders of magnitude higher. The process that caused the rapid increase in the redox state of the mantle soon after core formation is unclear. Here we test the possibility that pressure stabilises ferric iron in silicate melts, as has been observed in silicate minerals. A deep magma ocean, which would have likely existed towards the end of accretion, could then develop a gradient in oxygen fugacity for a fixed ferric-ferrous ratio as a result of pressure. We have equilibrated an andesitic melt with a Ru-RuO2 buffer in a multianvil press between 5 and 24 GPa. Further experiments were performed on the same melt in equilibrium with iron metal. The recovered melts were then analysed using Mössbauer spectroscopy to determine the ferric/ferrous ratio. The results show that for the Ru-RuO2 buffer at lower pressures, the ferric iron content decreases with pressure, due to a positive volume change of the reaction FeO + 1/4O2 = FeO1.5. Ferric iron content also appears to be sensitive to water content at lower pressures. However, above 15 GPa this trend apparently reverses and the ferric iron content increases with pressure. This reversal in pressure dependence would drive the oxygen fugacity of a deep magma ocean with a fixed ferric/ferrous ratio down with increasing depth. This would create a redox gradient, where the magma ocean could potentially be in equilibrium with metallic iron at its base but more oxidised in its shallower regions. Crystallisation of this magma ocean could render an upper mantle oxygen fugacity similar to that in the Earth's accessible mantle today.

Towards a unifying, systems biology understanding of large-scale cellular death and destruction caused by poorly liganded iron: Parkinson’s, Huntington’s, Alzheimer’s, prions, bactericides, chemical toxicology and others as examples

PubMed Central

2010-01-01

Exposure to a variety of toxins and/or infectious agents leads to disease, degeneration and death, often characterised by circumstances in which cells or tissues do not merely die and cease to function but may be more or less entirely obliterated. It is then legitimate to ask the question as to whether, despite the many kinds of agent involved, there may be at least some unifying mechanisms of such cell death and destruction. I summarise the evidence that in a great many cases, one underlying mechanism, providing major stresses of this type, entails continuing and autocatalytic production (based on positive feedback mechanisms) of hydroxyl radicals via Fenton chemistry involving poorly liganded iron, leading to cell death via apoptosis (probably including via pathways induced by changes in the NF-κB system). While every pathway is in some sense connected to every other one, I highlight the literature evidence suggesting that the degenerative effects of many diseases and toxicological insults converge on iron dysregulation. This highlights specifically the role of iron metabolism, and the detailed speciation of iron, in chemical and other toxicology, and has significant implications for the use of iron chelating substances (probably in partnership with appropriate anti-oxidants) as nutritional or therapeutic agents in inhibiting both the progression of these mainly degenerative diseases and the sequelae of both chronic and acute toxin exposure. The complexity of biochemical networks, especially those involving autocatalytic behaviour and positive feedbacks, means that multiple interventions (e.g. of iron chelators plus antioxidants) are likely to prove most effective. A variety of systems biology approaches, that I summarise, can predict both the mechanisms involved in these cell death pathways and the optimal sites of action for nutritional or pharmacological interventions. PMID:20967426

Modeling Anaerobic Soil Organic Carbon Decomposition in Arctic Polygon Tundra: Insights into Soil Geochemical Influences on Carbon Mineralization: Modeling Archive

DOE Data Explorer

Zheng, Jianqiu; Thornton, Peter; Painter, Scott; Gu, Baohua; Wullschleger, Stan; Graham, David

2018-06-13

This anaerobic carbon decomposition model is developed with explicit representation of fermentation, methanogenesis and iron reduction by combining three well-known modeling approaches developed in different disciplines. A pool-based model to represent upstream carbon transformations and replenishment of DOC pool, a thermodynamically-based model to calculate rate kinetics and biomass growth for methanogenesis and Fe(III) reduction, and a humic ion-binding model for aqueous phase speciation and pH calculation are implemented into the open source geochemical model PHREEQC (V3.0). Installation of PHREEQC is required to run this model.

Ecological speciation in the tropics: insights from comparative genetic studies in Amazonia

PubMed Central

Beheregaray, Luciano B.; Cooke, Georgina M.; Chao, Ning L.; Landguth, Erin L.

2015-01-01

Evolution creates and sustains biodiversity via adaptive changes in ecologically relevant traits. Ecologically mediated selection contributes to genetic divergence both in the presence or absence of geographic isolation between populations, and is considered an important driver of speciation. Indeed, the genetics of ecological speciation is becoming increasingly studied across a variety of taxa and environments. In this paper we review the literature of ecological speciation in the tropics. We report on low research productivity in tropical ecosystems and discuss reasons accounting for the rarity of studies. We argue for research programs that simultaneously address biogeographical and taxonomic questions in the tropics, while effectively assessing relationships between reproductive isolation and ecological divergence. To contribute toward this goal, we propose a new framework for ecological speciation that integrates information from phylogenetics, phylogeography, population genomics, and simulations in evolutionary landscape genetics (ELG). We introduce components of the framework, describe ELG simulations (a largely unexplored approach in ecological speciation), and discuss design and experimental feasibility within the context of tropical research. We then use published genetic datasets from populations of five codistributed Amazonian fish species to assess the performance of the framework in studies of tropical speciation. We suggest that these approaches can assist in distinguishing the relative contribution of natural selection from biogeographic history in the origin of biodiversity, even in complex ecosystems such as Amazonia. We also discuss on how to assess ecological speciation using ELG simulations that include selection. These integrative frameworks have considerable potential to enhance conservation management in biodiversity rich ecosystems and to complement historical biogeographic and evolutionary studies of tropical biotas. PMID:25653668

Invasive species and biodiversity crises: testing the link in the late devonian.

PubMed

Stigall, Alycia L

2010-12-29

During the Late Devonian Biodiversity Crisis, the primary driver of biodiversity decline was the dramatic reduction in speciation rates, not elevated extinction rates; however, the causes of speciation decline have been previously unstudied. Speciation, the formation of new species from ancestral populations, occurs by two primary allopatric mechanisms: vicariance, where the ancestral population is passively divided into two large subpopulations that later diverge and form two daughter species, and dispersal, in which a small subset of the ancestral population actively migrates then diverges to form a new species. Studies of modern and fossil clades typically document speciation by vicariance in much higher frequencies than speciation by dispersal. To assess the mechanism behind Late Devonian speciation reduction, speciation rates were calculated within stratigraphically constrained species-level phylogenetic hypotheses for three representative clades and mode of speciation at cladogenetic events was assessed across four clades in three phyla: Arthropoda, Brachiopoda, and Mollusca. In all cases, Devonian taxa exhibited a congruent reduction in speciation rate between the Middle Devonian pre-crisis interval and the Late Devonian crisis interval. Furthermore, speciation via vicariance is almost entirely absent during the crisis interval; most episodes of speciation during this time were due to dispersal. The shutdown of speciation by vicariance during this interval was related to widespread interbasinal species invasions. The lack of Late Devonian vicariance is diametrically opposed to the pattern observed in other geologic intervals, which suggests the loss of vicariant speciation attributable to species invasions during the Late Devonian was a causal factor in the biodiversity crisis. Similarly, modern ecosystems, in which invasive species are rampant, may be expected to exhibit similar shutdown of speciation by vicariance as an outcome of the modern biodiversity crisis.

Effect of uranium(VI) speciation on simultaneous microbial reduction of uranium(VI) and iron(III).

PubMed

Stewart, Brandy D; Amos, Richard T; Fendorf, Scott

2011-01-01

Uranium is a pollutant of concern to both human and ecosystem health. Uranium's redox state often dictates whether it will reside in the aqueous or solid phase and thus plays an integral role in the mobility of uranium within the environment. In anaerobic environments, the more oxidized and mobile form of uranium (UO2(2+) and associated species) may be reduced, directly or indirectly, by microorganisms to U(IV) with subsequent precipitation of UO. However, various factors within soils and sediments, such as U(VI) speciation and the presence of competitive electron acceptors, may limit biological reduction of U(VI). Here we examine simultaneous dissimilatory reduction of Fe(III) and U(VI) in batch systems containing dissolved uranyl acetate and ferrihydrite-coated sand. Varying amounts of calcium were added to induce changes in aqueous U(VI) speciation. The amount of uranium removed from solution during 100 h of incubation with S. putrefaciens was 77% in absence of Ca or ferrihydrite, but only 24% (with ferrihydrite) and 14% (without ferrihydrite) were removed for systems with 0.8 mM Ca. Dissimilatory reduction of Fe(III) and U(VI) proceed through different enzyme pathways within one type of organism. We quantified the rate coefficients for simultaneous dissimilatory reduction of Fe(III) and U(VI) in systems varying in Ca concecentration (0-0.8 mM). The mathematical construct, implemented with the reactive transport code MIN3P, reveals predominant factors controlling rates and extent of uranium reduction in complex geochemical systems.

Speciation in birds: genes, geography, and sexual selection.

PubMed

Edwards, Scott V; Kingan, Sarah B; Calkins, Jennifer D; Balakrishnan, Christopher N; Jennings, W Bryan; Swanson, Willie J; Sorenson, Michael D

2005-05-03

Molecular studies of speciation in birds over the last three decades have been dominated by a focus on the geography, ecology, and timing of speciation, a tradition traceable to Mayr's Systematics and the Origin of Species. However, in the recent years, interest in the behavioral and molecular mechanisms of speciation in birds has increased, building in part on the older traditions and observations from domesticated species. The result is that many of the same mechanisms proffered for model lineages such as Drosophila--mechanisms such as genetic incompatibilities, reinforcement, and sexual selection--are now being seriously entertained for birds, albeit with much lower resolution. The recent completion of a draft sequence of the chicken genome, and an abundance of single-nucleotide polymorphisms on the autosomes and sex chromosomes, will dramatically accelerate research on the molecular mechanisms of avian speciation over the next few years. The challenge for ornithologists is now to inform well studied examples of speciation in nature with increased molecular resolution-to clone speciation genes if they exist--and thereby evaluate the relative roles of extrinsic, intrinsic, deterministic, and stochastic causes for avian diversification.

Acid Sulfate Alteration in Gusev Crater, Mars

NASA Technical Reports Server (NTRS)

Morris, R. V.; Ming, D. W.; Catalano, J. G.

2016-01-01

The Mars Exploration Rover (MER) Spirit landed on the Gusev Crater plains west of the Columbia Hills in January, 2004, during the Martian summer (sol 0; sol = 1 Martian day = 24 hr 40 min). Spirit explored the Columbia Hills of Gusev Crater in the vicinity of Home Plate at the onset on its second winter (sol approximately 900) until the onset of its fourth winter (sol approximately 2170). At that time, Spirit became mired in a deposit of fined-grained and sulfate-rich soil with dust-covered solar panels and unfavorable pointing of the solar arrays toward the sun. Spirit has not communicated with the Earth since sol 2210 (January, 2011). Like its twin rover Opportunity, which landed on the opposite side of Mars at Meridiani Planum, Spirit has an Alpha Particle X-Ray Spectrometer (APXS) instrument for chemical analyses and a Moessbauer spectrometer (MB) for measurement of iron redox state, mineralogical speciation, and quantitative distribution among oxidation (Fe(3+)/sigma Fe) and coordination (octahedral versus tetrahedral) states and mineralogical speciation (e.g., olivine, pyroxene, ilmenite, carbonate, and sulfate). The concentration of SO3 in Gusev rocks and soils varies from approximately 1 to approximately 34 wt%. Because the APXS instrument does not detect low atomic number elements (e.g., H and C), major-element oxide concentrations are normalized to sum to 100 wt%, i.e., contributions of H2O, CO2, NO2, etc. to the bulk composition care not considered. The majority of Gusev samples have approximately 6 plus or minus 5 wt% SO3, but there is a group of samples with high SO3 concentrations (approximately 30 wt%) and high total iron concentrations (approximately 20 wt%). There is also a group with low total Fe and SO3 concentrations that is also characterized by high SiO2 concentrations (greater than 70 wt%). The trend labeled "Basaltic Soil" is interpreted as mixtures in variable proportions between unaltered igneous material and oxidized and SO3-rich basaltic dust. The Moessbauer parameters are not definitive for mineralogical speciation (other than octahedrally-coordinated Fe(3+) but are consistent with a schwertmannite-like phase (i.e., a nanophase ferric oxide). The high oxidation state and values of Moessbauer parameters (center shift and quadrupole splitting) for the high-SO3 samples imply ferric sulfate (i.e., oxidized sulfur), although the hydration state cannot be constrained. In no case is there an excess of SO3 over available cations (i.e., no evidence for elemental sulfur), and Fe sulfide (pyrite) has been detected in only one Gusev sample. The presence of both high-SiO2 (and low total iron and SO3) and high SO3 (and high total iron as ferric sulfate) can be accommodated by a two-step geochemical model developed with the Geochemist's Workbench. (1) Step 1 is anoxic acid sulfate leaching of Martian basalt at high water-to rock ratios (greater than 70). The result is a high-SiO2 residue0, and anoxic conditions are required to solubilize Fe as Fe(2+). (2) Step 2 is the oxic precipitation of sulfate salts from the leachate. Oxic conditions are required to produce the high concentrations of ferric sulfate with minor Mg-sulfates and no detectable Fe(2+)-sulfates.

Iron and oxygen isotope fractionation during iron UV photo-oxidation: Implications for early Earth and Mars

NASA Astrophysics Data System (ADS)

Nie, Nicole X.; Dauphas, Nicolas; Greenwood, Richard C.

2017-01-01

Banded iron formations (BIFs) contain appreciable amounts of ferric iron (Fe3+). The mechanism by which ferrous iron (Fe2+) was oxidized into Fe3+ in an atmosphere that was globally anoxic is highly debated. Of the three scenarios that have been proposed to explain BIF formation, photo-oxidation by UV photons is the only one that does not involve life (the other two are oxidation by O2 produced by photosynthesis, and anoxygenic photosynthesis whereby Fe2+ is directly used as electron donor in place of water). We experimentally investigated iron and oxygen isotope fractionation imparted by iron photo-oxidation at a pH of 7.3. The iron isotope fractionation between precipitated Fe3+-bearing lepidocrocite and dissolved Fe2+ follows a Rayleigh distillation with an instantaneous 56Fe/54Fe fractionation factor of + 1.2 ‰. Such enrichment in the heavy isotopes of iron is consistent with the values measured in BIFs. We also investigated the nature of the mass-fractionation law that governs iron isotope fractionation in the photo-oxidation experiments (i.e., the slope of the δ56Fe-δ57Fe relationship). The experimental run products follow a mass-dependent law corresponding to the high-T equilibrium limit. The fact that a ∼3.8 Gyr old BIF sample (IF-G) from Isua (Greenland) falls on the same fractionation line confirms that iron photo-oxidation in the surface layers of the oceans was a viable pathway to BIF formation in the Archean, when the atmosphere was largely transparent to UV photons. Our experiments allow us to estimate the quantum yield of the photo-oxidation process (∼0.07 iron atom oxidized per photon absorbed). This yield is used to model iron oxidation on early Mars. As the photo-oxidation proceeds, the aqueous medium becomes more acidic, which slows down the reaction by changing the speciation of iron to species that are less efficient at absorbing UV-photons. Iron photo-oxidation in centimeter to meter-deep water ponds would take months to years to complete. Oxidation by O2 in acidic conditions would be slower. Iron photo-oxidation is thus likely responsible for the formation of jarosite-hematite deposits on Mars, provided that shallow standing water bodies could persist for extended periods of time. The oxygen isotopic composition of lepidocrocite precipitated from the photo-oxidation experiment was measured and it is related to the composition of water by mass-dependent fractionation. The precipitate-fluid 18O/16O isotope fractionation of ∼ + 6 ‰ is consistent with previous determinations of oxygen equilibrium fraction factors between iron oxyhydroxides and water.

Arsenic Redistribution Between Sediments and Water Near a Highly Contaminated Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keimowitz,A.; Zheng, Y.; Chillrud, S.

2005-01-01

Mechanisms controlling arsenic partitioning between sediment, groundwater, porewaters, and surface waters were investigated at the Vineland Chemical Company Superfund site in southern New Jersey. Extensive inorganic and organic arsenic contamination at this site (historical total arsenic >10 000 {micro}g L{sup -1} or >130 {micro}M in groundwater) has spread downstream to the Blackwater Branch, Maurice River, and Union Lake. Stream discharge was measured in the Blackwater Branch, and water samples and sediment cores were obtained from both the stream and the lake. Porewaters and sediments were analyzed for arsenic speciation as well as total arsenic, iron, manganese, and sulfur, and theymore » indicate that geochemical processes controlling mobility of arsenic were different in these two locations. Arsenic partitioning in the Blackwater Branch was consistent with arsenic primarily being controlled by sulfur, whereas in Union Lake, the data were consistent with arsenic being controlled largely by iron. Stream discharge and arsenic concentrations indicate that despite large-scale groundwater extraction and treatment, >99% of arsenic transport away from the site results from continued discharge of high arsenic groundwater to the stream, rather than remobilization of arsenic in stream sediments. Changing redox conditions would be expected to change arsenic retention on sediments. In sulfur-controlled stream sediments, more oxic conditions could oxidize arsenic-bearing sulfide minerals, thereby releasing arsenic to porewaters and streamwaters; in iron-controlled lake sediments, more reducing conditions could release arsenic from sediments via reductive dissolution of arsenic-bearing iron oxides.« less

Frequency-dependent selection predicts patterns of radiations and biodiversity.

PubMed

Melián, Carlos J; Alonso, David; Vázquez, Diego P; Regetz, James; Allesina, Stefano

2010-08-26

Most empirical studies support a decline in speciation rates through time, although evidence for constant speciation rates also exists. Declining rates have been explained by invoking pre-existing niches, whereas constant rates have been attributed to non-adaptive processes such as sexual selection and mutation. Trends in speciation rate and the processes underlying it remain unclear, representing a critical information gap in understanding patterns of global diversity. Here we show that the temporal trend in the speciation rate can also be explained by frequency-dependent selection. We construct a frequency-dependent and DNA sequence-based model of speciation. We compare our model to empirical diversity patterns observed for cichlid fish and Darwin's finches, two classic systems for which speciation rates and richness data exist. Negative frequency-dependent selection predicts well both the declining speciation rate found in cichlid fish and explains their species richness. For groups like the Darwin's finches, in which speciation rates are constant and diversity is lower, speciation rate is better explained by a model without frequency-dependent selection. Our analysis shows that differences in diversity may be driven by incipient species abundance with frequency-dependent selection. Our results demonstrate that genetic-distance-based speciation and frequency-dependent selection are sufficient to explain the high diversity observed in natural systems and, importantly, predict decay through time in speciation rate in the absence of pre-existing niches.

Organic Exudates Enhance Iron Bioavailability to Trichodesmium (IMS101) by Modifying Fe Speciation

NASA Astrophysics Data System (ADS)

Tohidi Farid, H.; Rose, A.; Schulz, K.

2016-02-01

Although ferrous iron (Fe (II)) is believed to be the most readily absorbed form of Fe by cells, under alkaline and oxygenated conditions typical of marine environments, the thermodynamically stable Fe(III) state dominates. In marine environments, this Fe(III) is primarily presents as organic Fe(III)L complexes whose bioavailability is highly variable. However, it has been demonstrated that some eukaryotic marine algae are able to release organic ligands into their surrounding environments that change Fe bioavailability through complexation and/or redox reactions. Nevertheless, it is unclear how Fe(II) oxidation and Fe(III) reduction rates might be modified by these exudates and how this might increase or decrease iron bioavailability to microorganisms. Here, the role of natural organic ligands excreted by the cyanobacterium Trichodesmium erythraeum on the oxidation kinetics of Fe(II) was studied using the luminol chemiluminescence technique. The oxidation kinetics of Fe(II) were examined at nanomolar Fe concentrations in presence of different concentrations of EDTA and dissolved organic carbon exuded by Trichodesmium cells. The results indicated that an increase in the concentration of exuded organic matter, and consequently L:Fe(II) ratio, resulted in decreasing rates of Fe(II) oxidation by oxygen, primarily due to formation of Fe(II) complexes. Moreover, the results demonstrated that the exudates from Trichodesmium may be able to reduce Fe(III) to the more bioavailable Fe(II) state under some circumstances. This study therefore supports the ability of microorganisms to manipulate Fe bioavailability by releasing organic compounds into the extracellular environment that retard Fe(II) oxidation rates or reducing Fe(III) species to Fe(II). It also provides new insight into the potential mechanism(s) by which Trichdesmium may acquire Fe under conditions where Fe bioavailability is otherwise limited.

Speciation And Uptake of Arsenic Accumulated By Corn Seedlings Using XAS And DRC-ICP-MS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parsons, J.G.; Martinez-Martinez, A.; Peralta-Videa, J.R.

ICP-MS was used to investigate the uptake of As(III) and As(V) from hydroponics growth media by corn seedlings. It was found that arsenic uptake by the plant roots for the arsenic(V) and arsenic(III) treatments were 95 and 112 ppm, respectively. However, in the shoots of the arsenic (V) treatments had 18 ppm whereas arsenic(III) treatments had 12 ppm. XANES studies showed that As for both treatments arsenic was present as a mixture of an As(III) sulfur complex and an As(V) oxygen complex. The XANES data was corroborated by the EXAFS studies showing the presence of both oxygen and sulfur ligandsmore » coordinated to the arsenic. Iron concentrations were found to increase by 4 fold in the As(V) contaminated growth media and 7 fold in the As(III) treatment compared to the control iron concentration of 500 ppm. Whereas, the total iron concentration in the shoots was found to decrease by approximately the same amount for both treatments from 360 ppm in the control to approximately 125 ppm in both arsenic treatments. Phosphorus concentrations were found to decrease in both the roots and shoots compared to the control plants. The total sulfur in the roots was found to increase in the arsenic(III) and arsenic(V) treatments to 560 ppm and 800 ppm, respectively, compared to the control plants 358 ppm. In addition, the total sulfur in shoots of the plants was found to remain relatively constant at approximately 1080 ppm. The potassium concentrations in the plants were found to increase in the roots and decrease in the shoots.« less

Cyanide speciation at four gold leach operations undergoing remediation

USGS Publications Warehouse

Johnson, Craig A.; Grimes, David J.; Leinz, Reinhard W.; Rye, Robert O.

2008-01-01

Analyses have been made of 81 effluents from four gold leach operations in various stages of remediation to identify the most-persistent cyanide species. Total cyanide and weak acid-dissociable (WAD) cyanide were measured using improved methods, and metals known to form stable cyanocomplexes were also measured. Typically, total cyanide greatly exceeded WAD indicating that cyanide was predominantly in strong cyanometallic complexes. Iron was generally too low to accommodate the strongly complexed cyanide as Fe(CN)63- or Fe(CN)64-, but cobalt was abundant enough to implicate Co(CN)63- or its dissociation products (Co(CN)6-x(H2O)x(3-x)-). Supporting evidence for cobalt-cyanide complexation was found in tight correlations between cobalt and cyanide in some sample suites. Also, abundant free cyanide was produced upon UV illumination. Iron and cobalt cyanocomplexes both photodissociate; however, the iron concentration was insufficient to have carried the liberated cyanide, while the cobalt concentration was sufficient. Cobalt cyanocomplexes have not previously been recognized in cyanidation wastes. Their identification at four separate operations, which had treated ores that were not especially rich in cobalt, suggests that cobalt complexation may be a common source of cyanide persistence. There is a need for more information on the importance and behavior of cobalt cyanocomplexes in ore-processing wastes at gold mines.

Cyanide speciation at four gold leach operations undergoing remediation.

PubMed

Johnson, Craig A; Grimes, David J; Leinz, Reinhard W; Rye, Robert O

2008-02-15

Analyses have been made of 81 effluents from four gold leach operations in various stages of remediation to identify the most -persistent cyanide species. Total cyanide and weak acid-dissociable (WAD) cyanide were measured using improved methods, and metals known to form stable cyanocomplexes were also measured. Typically, total cyanide greatly exceeded WAD indicating that cyanide was predominantly in strong cyanometallic complexes. Iron was generally too low to accommodate the strongly complexed cyanide as Fe(CN)6s3- or Fe(CN)6(4-), but cobalt was abundant enough to implicate Co(CN)6(3-) or its dissociation products (Co(CN)(6-x)(H2O)x((3-x)-)). Supporting evidenceforcobalt-cyanide complexationwas found in tight correlations between cobalt and cyanide in some sample suites. Also, abundant free cyanide was produced upon UV illumination. Iron and cobalt cyanocomplexes both photodissociate; however, the iron concentration was insufficient to have carried the liberated cyanide, while the cobalt concentration was sufficient. Cobalt cyanocomplexes have not previously been recognized in cyanidation wastes. Their identification atfour separate operations, which had treated ores that were not especially rich in cobalt, suggests that cobalt complexation may be a common source of cyanide persistence. There is a need for more information on the importance and behavior of cobalt cyanocomplexes in ore-processing wastes at gold mines.

Direct and indirect photodegradation of estriol in the presence of humic acid, nitrate and iron complexes in water solutions.

PubMed

Chen, Yong; Zhang, Kai; Zuo, Yuegang

2013-10-01

The photochemical behavior of a natural estrogen estriol (E3) was investigated in the presence of the natural photoreactive constituents including nitrate, iron(III), and humic acid (HA). The direct photodegradation of E3 increased with increasing incident light intensity, decreasing initial concentration of E3 and increasing pH in the range of 6.0 to 10.0. The direct photodegradation of the deprotonated speciation of E3 was much faster than that of its protonated form. The presence of NO3(-) and iron(III) promoted the photochemical loss of E3 in the aqueous solutions. The quenching experiments verified that hydroxyl radicals were predominantly responsible for the indirect photodegradation of E3. HA could act as photosensitizer, light screening agent and free radical quencher. For the first time, the enhancement or inhibition effect of HA on photodegradation was found to depend on the irradiation light intensity. HA enhanced the photodegradation of E3 under sunlight or weak irradiation of simulated sunlight. In contrast, under high irradiation light intensity, HA inhibited the photodegradation. The hydroxylation photoproducts were identified using GC-MS and the photodegradation pathway of E3 was proposed. Copyright © 2013 Elsevier B.V. All rights reserved.

Competitive and Cooperative Effects during Nickel Adsorption to Iron Oxides in the Presence of Oxalate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flynn, Elaine D.; Catalano, Jeffrey G.

Iron oxides are ubiquitous in soils and sediments and play a critical role in the geochemical distribution of trace elements and heavy metals via adsorption and coprecipitation. The presence of organic acids may potentially alter how metals associate with iron oxide minerals through a series of cooperative or competitive processes: solution complexation, ternary surface complexation, and surface site competition. The macroscopic and molecular-scale effects of these processes were investigated for Ni adsorption to hematite and goethite at pH 7 in the presence of oxalate. The addition of this organic acid suppresses Ni uptake on both minerals. Aqueous speciation suggests thatmore » this is dominantly the result of oxalate complexing and solubilizing Ni. Comparison of the Ni surface coverage to the concentration of free (uncomplexed) Ni 2+ in solution suggests that the oxalate also alters Ni adsorption affinity. EXAFS and ATR-FTIR spectroscopies indicate that these changes in binding affinity are due to the formation of Ni–oxalate ternary surface complexes. These observations demonstrate that competition between dissolved oxalate and the mineral surface for Ni overwhelms the enhancement in adsorption associated with ternary complexation. Oxalate thus largely enhances Ni mobility, thereby increasing micronutrient bioavailability and inhibiting contaminant sequestration.« less

Chemical equilibrium modeling of organic acids, pH, aluminum, and iron in Swedish surface waters.

PubMed

Sjöstedt, Carin S; Gustafsson, Jon Petter; Köhler, Stephan J

2010-11-15

A consistent chemical equilibrium model that calculates pH from charge balance constraints and aluminum and iron speciation in the presence of natural organic matter is presented. The model requires input data for total aluminum, iron, organic carbon, fluoride, sulfate, and charge balance ANC. The model is calibrated to pH measurements (n = 322) by adjusting the fraction of active organic matter only, which results in an error of pH prediction on average below 0.2 pH units. The small systematic discrepancy between the analytical results for the monomeric aluminum fractionation and the model results is corrected for separately for two different fractionation techniques (n = 499) and validated on a large number (n = 3419) of geographically widely spread samples all over Sweden. The resulting average error for inorganic monomeric aluminum is around 1 µM. In its present form the model is the first internally consistent modeling approach for Sweden and may now be used as a tool for environmental quality management. Soil gibbsite with a log *Ks of 8.29 at 25°C together with a pH dependent loading function that uses molar Al/C ratios describes the amount of aluminum in solution in the presence of organic matter if the pH is roughly above 6.0.

Experimental determination of iron isotope fractionations among Fe aq 2 + -FeSaq-Mackinawite at low temperatures: Implications for the rock record

NASA Astrophysics Data System (ADS)

Wu, Lingling; Druschel, Greg; Findlay, Alyssa; Beard, Brian L.; Johnson, Clark M.

2012-07-01

The Fe isotope fractionation factors among aqueous ferrous iron (Fe aq 2 +), aqueous FeS clusters (FeSaq), and nanoparticulate mackinawite under neutral and mildly acidic and alkaline pH conditions have been determined using the three-isotope method. Combined voltammetric analysis and geochemical modeling were used to determine the Fe speciation in the experimental systems. The equilibrium 56Fe/54Fe fractionation factor at 20 °C and pH 7 has been determined to be -0.32 ± 0.29 (2σ)‰ between Fe aq 2 + (minor FeSaq also present in the experiment) and mackinawite. This fractionation factor was essentially constant when pH was changed to 6 or 8. When equal molarity of HS- and Fe aq 2 + were added to the system, however, the isotopic fractionation at pH 7 changed to -0.64 ± 0.36 (2σ)‰, correlating with a significant increase in the proportion of FeHS+ and FeSaq. These results highlight a more important role of aqueous Fe-S speciation in the equilibrium Fe isotope fractionation factor than recognized in previous studies. The isotopic fractionation remained constant when temperature was increased from 20 °C to 35 °C for fractionation factors between Fe aq 2 + , and mackinawite and between dominantly FeHS+ and mackinawite. Synthesis experiments similar to those of Butler et al. (2005) and Guilbaud et al. (2010) at pH 4 show consistent results: over time, the aqueous Fe-mackinawite fractionation decreases but even after 38 days of aging the fractionation factor is far from the equilibrium value inferred using the three-isotope method. In contrast, at near-neutral pH the fractionation factor for the synthesis experiment reached the equilibrium value in 38 days. These differences are best explained by noting that at low pH the FeS mackinawite particles coarsen more rapidly via particle aggregation, which limits isotopic exchange, whereas at higher pH mackinawite aggregation is limited, and Fe isotope exchange occurs more rapidly, converging on the equilibrium value. These results suggest that mackinawite formed in natural environments at near-neutral or alkaline pH are unlikely to retain kinetic isotope fractionations, but are more likely to reflect equilibrium isotope compositions. This in turn has important implications for interpreting iron isotope compositions of Fe sulfides in natural systems.

Mechanisms of Arsenic Sequestration by Prosopis juliflora during the Phytostabilization of Metalliferous Mine Tailings.

PubMed

Hammond, Corin M; Root, Robert A; Maier, Raina M; Chorover, Jon

2018-02-06

Phytostabilization is a cost-effective long-term bioremediation technique for the immobilization of metalliferous mine tailings. However, the biogeochemical processes affecting metal(loid) molecular stabilization and mobility in the root zone remain poorly resolved. The roots of Prosopis juliflora grown for up to 36 months in compost-amended pyritic mine tailings from a federal Superfund site were investigated by microscale and bulk synchrotron X-ray absorption spectroscopy (XAS) and multiple energy micro-X-ray fluorescence imaging to determine iron, arsenic, and sulfur speciation, abundance, and spatial distribution. Whereas ferrihydrite-bound As(V) species predominated in the initial bulk mine tailings, the rhizosphere speciation of arsenic was distinctly different. Root-associated As(V) was immobilized on the root epidermis bound to ferric sulfate precipitates and within root vacuoles as trivalent As(III)-(SR) 3  tris-thiolate complexes. Molar Fe-to-As ratios of root epidermis tissue were two times higher than the 15% compost-amended bulk tailings growth medium. Rhizoplane-associated ferric sulfate phases that showed a high capacity to scavenge As(V) were dissimilar from the bulk-tailings mineralogy as shown by XAS and X-ray diffraction, indicating a root-surface mechanism for their formation or accumulation.

Speciation has a spatial scale that depends on levels of gene flow.

PubMed

Kisel, Yael; Barraclough, Timothy G

2010-03-01

Area is generally assumed to affect speciation rates, but work on the spatial context of speciation has focused mostly on patterns of range overlap between emerging species rather than on questions of geographical scale. A variety of geographical theories of speciation predict that the probability of speciation occurring within a given region should (1) increase with the size of the region and (2) increase as the spatial extent of intraspecific gene flow becomes smaller. Using a survey of speciation events on isolated oceanic islands for a broad range of taxa, we find evidence for both predictions. The probability of in situ speciation scales with island area in bats, carnivorous mammals, birds, flowering plants, lizards, butterflies and moths, and snails. Ferns are an exception to these findings, but they exhibit high frequencies of polyploid and hybrid speciation, which are expected to be scale independent. Furthermore, the minimum island size for speciation correlates across groups with the strength of intraspecific gene flow, as is estimated from a meta-analysis of published population genetic studies. These results indicate a general geographical model of speciation rates that are dependent on both area and gene flow. The spatial scale of population divergence is an important but neglected determinant of broad-scale diversity patterns.

Pollinator-driven ecological speciation in plants: new evidence and future perspectives

PubMed Central

Van der Niet, Timotheüs; Peakall, Rod; Johnson, Steven D.

2014-01-01

Background The hypothesis that pollinators have been important drivers of angiosperm diversity dates back to Darwin, and remains an important research topic today. Mounting evidence indicates that pollinators have the potential to drive diversification at several different stages of the evolutionary process. Microevolutionary studies have provided evidence for pollinator-mediated floral adaptation, while macroevolutionary evidence supports a general pattern of pollinator-driven diversification of angiosperms. However, the overarching issue of whether, and how, shifts in pollination system drive plant speciation represents a critical gap in knowledge. Bridging this gap is crucial to fully understand whether pollinator-driven microevolution accounts for the observed macroevolutionary patterns. Testable predictions about pollinator-driven speciation can be derived from the theory of ecological speciation, according to which adaptation (microevolution) and speciation (macroevolution) are directly linked. This theory is a particularly suitable framework for evaluating evidence for the processes underlying shifts in pollination systems and their potential consequences for the evolution of reproductive isolation and speciation. Scope This Viewpoint paper focuses on evidence for the four components of ecological speciation in the context of plant-pollinator interactions, namely (1) the role of pollinators as selective agents, (2) floral trait divergence, including the evolution of ‘pollination ecotypes‘, (3) the geographical context of selection on floral traits, and (4) the role of pollinators in the evolution of reproductive isolation. This Viewpoint also serves as the introduction to a Special Issue on Pollinator-Driven Speciation in Plants. The 13 papers in this Special Issue range from microevolutionary studies of ecotypes to macroevolutionary studies of historical ecological shifts, and span a wide range of geographical areas and plant families. These studies further illustrate innovative experimental approaches, and they employ modern tools in genetics and floral trait quantification. Future advances to the field require better quantification of selection through male fitness and pollinator isolation, for instance by exploiting next-generation sequencing technologies. By combining these new tools with strategically chosen study systems, and smart experimental design, we predict that examples of pollinator-driven speciation will be among the most widespread and compelling of all cases of ecological speciation. PMID:24418954

Transient deep-water oxygenation in the early Cambrian Nanhua Basin, South China

NASA Astrophysics Data System (ADS)

Cheng, Meng; Li, Chao; Zhou, Lian; Feng, LianJun; Algeo, Thomas J.; Zhang, FeiFei; Romaniello, Stephen; Jin, ChengSheng; Ling, HongFei; Jiang, ShaoYong

2017-08-01

Many late Neoproterozoic to early Cambrian fossils of multicellular eukaryotes, including those of benthic animals, are found preserved under anoxic and even euxinic bottom-water conditions, which is contradictory to the consensus that oxygen is essential to eukaryotes. To investigate this conundrum, we conducted an integrated study of iron speciation, redox-sensitive trace elements, and Mo isotopes (δ98Mo) on the black shale interval of the lower Cambrian Hetang Formation (∼535-521 Ma) at Lantian, South China, in which benthic sponge fossils are abundant in the lower member (LM) but absent in the upper member (UM). Iron speciation data point to uniformly anoxic-ferruginous conditions in the LM and euxinic conditions in the UM, whereas the trace-element and δ98Mo data show greater secular variation in redox conditions. The LM shows higher mean trace element concentrations (Mo: 108 ppm, U: 36 ppm, V: 791 ppm) and lower and more variable δ98Mo (+0.13 to +1.76‰) relative to the UM (Mo: 45 ppm, U: 18 ppm, V: 265 ppm, δ98Mo: +1.59 to +1.67‰), and ratios of redox-sensitive trace element concentrations to total organic carbon are significantly more variable and higher on average in the LM relative to the UM. The appearance of sponge fossils and lower δ98Mo values correlate strongly with gray (i.e., lighter-colored) layers in the LM. These patterns can best be interpreted as recording mainly euxinic conditions throughout deposition of the study units, with more intense background euxinia in the LM relative to the UM, but also with frequent transient oxygenation events in the LM that do not appear in the UM. The transient oxygenation events of the LM led to the initial colonization of the deep Nanhua Basin by sponges, and the termination of these events in the UM caused sponge faunas to disappear until a general rise in O2 levels later in the Cambrian permitted their return to deeper-water habitats. Our study also illustrates that multiple geochemical and paleobiological proxies exhibit different responses in 'poikiloredox' environments (i.e., characterized by small-scale spatial and high-frequency temporal variations), which can lead to apparent contradictions between metazoan fossil occurrences and their inferred watermass redox conditions.

A high-resolution regional emission inventory of atmospheric mercury and its comparison with multi-scale inventories: a case study of Jiangsu, China

NASA Astrophysics Data System (ADS)

Zhong, Hui; Zhao, Yu; Muntean, Marilena; Zhang, Lei; Zhang, Jie

2016-12-01

A better understanding of the discrepancies in multi-scale inventories could give an insight into their approaches and limitations as well as provide indications for further improvements; international, national, and plant-by-plant data are primarily obtained to compile those inventories. In this study we develop a high-resolution inventory of Hg emissions at 0.05° × 0.05° for Jiangsu, China, using a bottom-up approach and then compare the results with available global/national inventories. With detailed information on individual sources and the updated emission factors from field measurements applied, the annual Hg emissions of anthropogenic origin in Jiangsu in 2010 are estimated at 39 105 kg, of which 51, 47, and 2 % were Hg0, Hg2+, and Hgp, respectively. This provincial inventory is thoroughly compared to three downscaled national inventories (NJU, THU, and BNU) and two global ones (AMAP/UNEP and EDGARv4.tox2). Attributed to varied methods and data sources, clear information gaps exist in multi-scale inventories, leading to differences in the emission levels, speciation, and spatial distributions of atmospheric Hg. The total emissions in the provincial inventory are 28, 7, 19, 22, and 70 % larger than NJU, THU, BNU, AMAP/UNEP, and EDGARv4.tox2, respectively. For major sectors, including power generation, cement, iron and steel, and other coal combustion, the Hg contents (HgC) in coals/raw materials, abatement rates of air pollution control devices (APCDs) and activity levels are identified as the crucial parameters responsible for the differences in estimated emissions between inventories. Regarding speciated emissions, a larger fraction of Hg2+ is found in the provincial inventory than national and global inventories, resulting mainly from the results by the most recent domestic studies in which enhanced Hg2+ were measured for cement and iron and steel plants. Inconsistent information on large power and industrial plants is the main source of differences in spatial distribution of emissions between the provincial and other inventories, particularly in southern and northwestern Jiangsu, where intensive coal combustion and industry are located. Quantified with Monte Carlo simulation, uncertainties in the provincial inventory are smaller than those of the NJU national inventory, resulting mainly from the more accurate activity data of individual plants and the reduced uncertainties in HgC in coals/raw materials.

Uranium association with iron-bearing phases in mill tailings from Gunnar, Canada.

PubMed

Othmane, Guillaume; Allard, Thierry; Morin, Guillaume; Sélo, Madeleine; Brest, Jessica; Llorens, Isabelle; Chen, Ning; Bargar, John R; Fayek, Mostafa; Calas, Georges

2013-11-19

The speciation of uranium was studied in the mill tailings of the Gunnar uranium mine (Saskatchewan, Canada), which operated in the 1950s and 1960s. The nature, quantification, and spatial distribution of uranium-bearing phases were investigated by chemical and mineralogical analyses, fission track mapping, electron microscopy, and X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies at the U LIII-edge and Fe K-edge. In addition to uranium-containing phases from the ore, uranium is mostly associated with iron-bearing minerals in all tailing sites. XANES and EXAFS data and transmission electron microscopy analyses of the samples with the highest uranium concentrations (∼400-700 mg kg(-1) of U) demonstrate that uranium primarily occurs as monomeric uranyl ions (UO2(2+)), forming inner-sphere surface complexes bound to ferrihydrite (50-70% of the total U) and to a lesser extent to chlorite (30-40% of the total U). Thus, the stability and mobility of uranium at the Gunnar site are mainly influenced by sorption/desorption processes. In this context, acidic pH or alkaline pH with the presence of UO2(2+)- and/or Fe(3+)-complexing agents (e.g., carbonate) could potentially solubilize U in the tailings pore waters.

Effect of Humic Acid on As Redox Transformation and Kinetic Adsorption onto Iron Oxide Based Adsorbent (IBA)

PubMed Central

Fakour, Hoda; Lin, Tsair-Fuh

2014-01-01

Due to the importance of adsorption kinetics and redox transformation of arsenic (As) during the adsorption process, the present study elucidated natural organic matter (NOM) effects on As adsorption-desorption kinetics and speciation transformation. The experimental procedures were conducted by examining interactions of arsenate and arsenite with different concentrations of humic acid (HA) as a model representative of NOM, in the presence of iron oxide based adsorbent (IBA), as a model solid surface in three environmentally relevant conditions, including the simultaneous adsorption of both As and HA onto IBA, HA adsorption onto As-presorbed IBA, and As adsorption onto HA-presorbed IBA. Experimental adsorption-desorption data were all fitted by original and modified Lagergren pseudo-first and -second order adsorption kinetic models, respectively. Weber’s intraparticle diffusion was also used to gain insight into the mechanisms and rate controlling steps, which the results suggested that intraparticle diffusion of As species onto IBA is the main rate-controlling step. Different concentrations of HA mediated the redox transformation of As species, with a higher oxidation ability than reduction. The overall results indicated the significant effect of organic matter on the adsorption kinetics and redox transformation of As species, and consequently, the fate, transport and mobility of As in different environmentally relevant conditions. PMID:25325357

Speciation in fungal and oomycete plant pathogens

USDA-ARS?s Scientific Manuscript database

The process of speciation by definition involves evolution of one or more reproductive isolating mechanisms that split a single species into two that can no longer interbreed. Determination of which processes are responsible for speciation is important yet challenging. Several studies have proposed ...

A STUDY OF GAS-PHASE MERCURY SPECIATION USING DETAILED CHEMICAL KINETICS

EPA Science Inventory

Mercury (Hg) speciation in combustion-generated flue gas is modeled using a detailed chemical mechanism consisting of 60 reactions and 21 species. This speciation model accounts for chlorination and oxidation of key flue-gas components, including elemental mercury. Results indica...

Selenium Speciation and Management in Wet FGD Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Searcy, K; Richardson, M; Blythe, G

2012-02-29

This report discusses results from bench- and pilot-scale simulation tests conducted to determine the factors that impact selenium speciation and phase partitioning in wet FGD systems. The selenium chemistry in wet FGD systems is highly complex and not completely understood, thus extrapolation and scale-up of these results may be uncertain. Control of operating parameters and application of scrubber additives have successfully demonstrated the avoidance or decrease of selenite oxidation at the bench and pilot scale. Ongoing efforts to improve sample handling methods for selenium speciation measurements are also discussed. Bench-scale scrubber tests explored the impacts of oxidation air rate, tracemore » metals, scrubber additives, and natural limestone on selenium speciation in synthetic and field-generated full-scale FGD liquors. The presence and concentration of redox-active chemical species as well as the oxidation air rate contribute to the oxidation-reduction potential (ORP) conditions in FGD scrubbers. Selenite oxidation to the undesirable selenate form increases with increasing ORP conditions, and decreases with decreasing ORP conditions. Solid-phase manganese [Mn(IV)] appeared to be the significant metal impacting the oxidation of selenite to selenate. Scrubber additives were tested for their ability to inhibit selenite oxidation. Although dibasic acid and other scrubber additives showed promise in early clear liquor (sodium based and without calcium solids) bench-scale tests, these additives did not show strong inhibition of selenite oxidation in tests with higher manganese concentrations and with slurries from full-scale wet FGD systems. In bench-tests with field liquors, addition of ferric chloride at a 250:1 iron-to-selenium mass ratio sorbed all incoming selenite to the solid phase, although addition of ferric salts had no impact on native selenate that already existed in the field slurry liquor sample. As ORP increases, selenite may oxidize to selenate more rapidly than it sorbs to ferric solids. Though it was not possible to demonstrate a decrease in selenium concentrations to levels below the project'ale testing were evident at the pilot scale. Specifically, reducing oxidation air rate and ORP tends to either retain selenium as selenite in the liquor or shift selenium phase partitioning to the solid phase. Oxidation air flow rate control may be one option for managing selenium behavior in FGD scrubbers. Units that cycle load widely may find it more difficult to impact ORP conditions with oxidation air flow rate control alone. Because decreasing oxidation air rates to the reaction tank showed that all new selenium reported to the solids, the addition of ferric chloride to the pilot scrubber could not show further improvements in selenium behavior. Ferric chloride addition did shift mercury to the slurry solids, specifically to the fine particles. Several competing pathways may govern the reporting of selenium to the slurry solids: co-precipitation with gypsum into the bulk solids and sorption or co-precipitation with iron into the fine particles. Simultaneous measurement of selenium and mercury behavior suggests a holistic management strategy is best to optimize the fate of both of these elements in FGD waters. Work conducted under this project evaluated sample handling and analytical methods for selenium speciation in FGD waters. Three analytical techniques and several preservation methods were employed. Measurements of selenium speciation over time indicated that for accurate selenium speciation, it is best to conduct measurements on unpreserved, filtered samples as soon after sampling as possible. The capital and operating costs for two selenium management strategies were considered: ferric chloride addition and oxidation air flow rate control. For ferric chloride addition, as might be expected the reagent makeup costs dominate the overall costs, and range from 0.22 to 0.29 mills/kWh. For oxidation air flow rate control, a cursory comparison of capital costs and turndown capabilities for multi-stage and single-stage centrifugal blowers and several flow control methods was completed. For greenfield systems, changing the selection of blower type and flow control method may have payback periods of 4 to 5 years or more if based on energy savings alone. However, the benefits to managing redox chemistry in the scrubber could far outweigh the savings in electricity costs under some circumstances.« less

The development of exhaust speciation profiles for commercial jet engines.

DOT National Transportation Integrated Search

2007-10-01

This study reports the emissions of CO, CO2, NOx, Particulate Matter (PM) mass, : speciated PM and speciated hydrocarbons at six thrust settings: 4%, 7%, 30%, 40%, 65% : and 85%, measured from both engines on four parked 737 aircraft at the Oakland :...

Speciation by Symbiosis: the Microbiome and Behavior

PubMed Central

Shropshire, J. Dylan

2016-01-01

ABSTRACT Species are fundamental units of comparison in biology. The newly discovered importance and ubiquity of host-associated microorganisms are now stimulating work on the roles that microbes can play in animal speciation. We previously synthesized the literature and advanced concepts of speciation by symbiosis with notable attention to hybrid sterility and lethality. Here, we review recent studies and relevant data on microbes as players in host behavior and behavioral isolation, emphasizing the patterns seen in these analyses and highlighting areas worthy of additional exploration. We conclude that the role of microbial symbionts in behavior and speciation is gaining exciting traction and that the holobiont and hologenome concepts afford an evolving intellectual framework to promote research and intellectual exchange between disciplines such as behavior, microbiology, genetics, symbiosis, and speciation. Given the increasing centrality of microbiology in macroscopic life, microbial symbiosis is arguably the most neglected aspect of animal and plant speciation, and studying it should yield a better understanding of the origin of species. PMID:27034284

Speciation by Symbiosis: the Microbiome and Behavior.

PubMed

Shropshire, J Dylan; Bordenstein, Seth R

2016-03-31

Species are fundamental units of comparison in biology. The newly discovered importance and ubiquity of host-associated microorganisms are now stimulating work on the roles that microbes can play in animal speciation. We previously synthesized the literature and advanced concepts of speciation by symbiosis with notable attention to hybrid sterility and lethality. Here, we review recent studies and relevant data on microbes as players in host behavior and behavioral isolation, emphasizing the patterns seen in these analyses and highlighting areas worthy of additional exploration. We conclude that the role of microbial symbionts in behavior and speciation is gaining exciting traction and that the holobiont and hologenome concepts afford an evolving intellectual framework to promote research and intellectual exchange between disciplines such as behavior, microbiology, genetics, symbiosis, and speciation. Given the increasing centrality of microbiology in macroscopic life, microbial symbiosis is arguably the most neglected aspect of animal and plant speciation, and studying it should yield a better understanding of the origin of species. Copyright © 2016 Shropshire and Bordenstein.

X-ray Microprobe Investigations of Elemental Distributions and Concentrations at Mineral-Microbe Interfaces

NASA Astrophysics Data System (ADS)

Kemner, K. M.; Kelly, S. D.; O'Loughlin, E. J.; Lai, B.; Maser, J.; Cai, Z.; Londer, Y.; Schiffer, M.; Nealson, K.

2003-12-01

Understanding the fate of heavy-metal contaminants in the environment is of fundamental importance in the development and evaluation of effective remediation and sequestration strategies. Bacteria and the extracellular material associated with them are thought to play a key role in determining a contaminant's speciation and thus its mobility in the environment. Additionally, the metabolism and surface properties of bacteria can be quite different depending upon whether the bacteria exhibit a planktonic (free-floating) or biofilm (surface adhered) habit. The microenvironment at and adjacent to actively metabolizing cells also can be significantly different from the bulk environment. Thus, to understand the microscopic physical, geological, chemical, and biological interfaces that determine a contaminant's macroscopic fate, the spatial distribution and chemical speciation of contaminants and elements that are key to biological processes must be characterized at micron and submicron lengthscales for bacteria in both planktonic and adhered states. Hard x-ray microimaging is a powerful technique for the element-specific investigation of complex environmental samples at the needed micron and submicron resolution. An important advantage of these techniques results from the large penetration depth of hard x-rays in water. This advantage minimizes the requirements for sample preparation and allows the detailed study of hydrated samples. The objectives of the studies to be presented are (1) to determine the spatial distribution, concentration, and chemical speciation of metals at, in, and near bacteria and bacteria-geosurface interfaces, (2) to use this information to identify the metabolic processes occurring within the microbes, and (3) to identify the interactions occurring near these interfaces among the metals, mineral surfaces, and bacteria under a variety of conditions. We have used x-ray fluorescence microscopy to investigate the spatial distribution of 3d elements in Pseudomonas fluorescens cells in both planktonic and surface-adhered states. We have used x-ray fluorescence spectromicroscopy to investigate the chemical speciation and distribution of Cr that was introduced to these cells as Cr(VI). Additionally, we have used these techniques to identify the distribution of an over expressed cytochrome c7 in individual E. coli. Finally, we have used x-ray fluorescence microscopy to investigate Shewanella oneidensis MR-1 cells adhered to iron oxyhydroxide thin films. The zone plate used in these microscopy experiments produced a focused beam with a cross section (and hence spatial resolution) of 100-300 nanometers. Results from x-ray fluorescence imaging experiments indicate that the distribution of P, S, Cl, Ca, Fe, Ni, Cu, and Zn can define the location of the microbe. Additionally, quantitative elemental analysis of individual microbes identified significant changes in concentration of 3d transition elements depending on the age of the culture and the type of electron acceptor presented to the microbes. These results and a discussion of the use of this technique for identifying metabolic states of individual microbes within communities and the chemical speciation of metal contaminants at the mineral-microbe interface will be presented.

Modification of an Existing In vitro Method to Predict Relative ...

EPA Pesticide Factsheets

The soil matrix can sequester arsenic (As) and reduces its exposure by soil ingestion. In vivo dosing studies and in vitro gastrointestinal (IVG) methods have been used to predict relative bioavailable (RBA) As. Originally, the Ohio State University (OSU-IVG) method predicted RBA As for soils exclusively from mining and smelting sites with a median of 5,636 mg As kg-1. The objectives of the current study were to (i) evaluate the ability of the OSU-IVG method to predict RBA As for As contaminated soils with a wider range of As content and As contaminant sources, and (ii) evaluate a modified extraction procedure's ability to improve prediction of RBA As. In vitro bioaccessible (IVBA) by OSU-IVG and California Bioaccessibility Method (CAB) methods, RBA As, speciation, and properties of 33 As contaminated soils were determined. Total As ranged from 162 to 12,483 mg kg-1 with a median of 731 mg kg-1. RBA As ranged from 1.30 to 60.0% and OSU-IVG IVBA As ranged from 0.80 to 52.3%. Arsenic speciation was predominantly As(V) adsorbed to hydrous ferric oxide (HFO) or iron (Fe), manganese (Mn), and aluminum (Al) oxides. The OSU-IVG often extracted significantly less As in vitro than in vivo RBA As, in particularly for soils from historical gold mining. The CAB method, which is a modified OSU-IVG method extracted more As than OSU-IVG for most soils, resulting in a more accurate predictor than OSU-IVG, especially for low to moderately contaminated soils (<1,500 mg As

Rapid photooxidation of Sb(III) in the presence of different Fe(III) species

NASA Astrophysics Data System (ADS)

Kong, Linghao; He, Mengchang; Hu, Xingyun

2016-05-01

The toxicity and mobility of antimony (Sb) are strongly influenced by the redox processes associated with Sb. Dissolved iron (Fe) is widely distributed in the environment as different species and plays a significant role in Sb speciation. However, the mechanisms of Sb(III) oxidation in the presence of Fe have remained unclear because of the complexity of Fe and Sb speciation. In this study, the mechanisms of Sb(III) photooxidation in the presence of different Fe species were investigated systematically. The photooxidation of Sb(III) occurred over a wide pH range, from 1 to 10. Oxygen was not a predominant or crucial factor in the Sb(III) oxidation process. The mechanism of Sb(III) photooxidation varied depending on the Fe(III) species. In acidic solution (pH 1-3), dichloro radicals (radCl2-) and hydroxyl radicals (radOH) generated by the photocatalysis of FeCl2+ and FeOH2+ were the main oxidants for Sb(III) oxidation. Fe(III) gradually transformed into the colloid ferric hydroxide (CFH) and ferrihydrite in circumneutral and alkaline solutions (pH 4-10). Photooxidation of Sb(III) occurred through electron transfer from Sb(III) to Fe(III) along with the reduction of Fe(III) to Fe(II) through a ligand-to-metal charge-transfer (LMCT) process. The photocatalysis of different Fe(III) species may play an important role in the geochemical cycle of Sb(III) in surface soil and aquatic environments.

Surface reactions kinetics between nanocrystalline magnetite and uranyl.

PubMed

Missana, Tiziana; Maffiotte, César; García-Gutiérrez, Miguel

2003-05-01

Magnetite is the most important end member of iron corrosion products under reducing environment, which is the condition expected in a deep geological high level radioactive waste disposal. Nanocrystalline magnetite was synthesized in the laboratory and its physicochemical properties were analyzed in detail. The kinetics of the adsorption of U(VI) and the kinetics of the actinide reduction to a lower oxidation state, in presence of the oxide, were studied by means of batch sorption techniques and X-ray photoelectron spectroscopy (XPS) analysis. The results showed that the uranium sorption and reduction processes on the magnetite surface have very fast kinetics (hours), the reduction process being triggered by sorption. XPS measurements showed that the speciation of uranium at the surface does not show significant changes with time (from 1 day to 3 months), as well as the quantity of uranium detected at the surface. The surface speciation depended on the initial pH of the contact solution. Considering that the Eh of equilibrium between magnetite and the solution, under our experimental conditions, is slightly positive (50-100 mV), the uranium reduction would also be thermodynamically possible within the liquid phase. However, the kinetics of reduction in the liquid occur at a much slower rate which, in turn, has to depend on the attainment of the magnetite/solution equilibrium. The decrease of uranium in solution, observed after the uranyl adsorption stage, and particularly at acidic pH, is most probably due to the precipitation of U(IV) formed in the solution.

Phosphorus cycling in the Early Aptian

NASA Astrophysics Data System (ADS)

Oakes, R.; Dittrich, M.; Wortmann, U. G.

2012-12-01

Phosphorus is an essential nutrient for living organisms. It is vital for the formation of ATP, the energy store in cells, and is needed for DNA synthesis. Seawater phosphorus concentration therefore plays a critical role in controlling marine productivity on geological timescales. The majority of research on the P cycle focuses on modern lacustrine and marine settings. This follows the necessity to gain a further understanding on the effects of agricultural fertilisers on nutrient cycling; in particular on the mechanisms which lead to eutrophication. These studies use sequential extraction to determine the speciation of P. The results suggest that bottom sediments can act as both a source and a sink of phosphorus; the role they assume depends on range of factors including bottom water oxygen concentrations, sedimentation rate and the concentration of iron. This study applies a sequential extraction method developed in modern sediments to sediments from the Early Cretaceous, specifically the Early Aptian. During this time, globally synchronous oceanic anoxic events (OAE's) appear in the rock record. It has been suggested that these events represent an increase in marine productivity combined with bottom water anoxia. Our study investigates whether the speciation of sedimentary phosphorus can be used to reconstruct P cycling at this time. Our samples are taken from pre-, syn- and post-OAE1a but are not from the organic matter rich layers. Our results show that the original fractions of phosphorus have been altered during diagenesis with the majority of phosphorus now being preserved as either apatite (Ca-P) or phosphorus in organic matter (Porg). The dominance of Ca-P is expected as it is thought that redox-sensitive forms of P undergo 'sink switching' during diagenesis and are preserved as Ca-P. The high concentration of Porg however, differs from previous studies which generally find that Ca-P or iron (oxyhydr)oxide associated phosphorus (Fe-P) are dominant depending on deposition conditions. We find that during the anoxic event Ca-P preservation is enhanced, a trend which is not mirrored by an increase in total phosphorus concentration. This suggests that the formation of authigenic apatite via sink switching may have been enhanced during OAE1a. This agrees with the findings of a modern field and lab based study which proposes that more P is fixed than regenerated under anoxic conditions but contradicts earlier studies which suggest that more P will be refluxed from sediments under anoxic bottom-water conditions.

A complex speciation–richness relationship in a simple neutral model

PubMed Central

Desjardins-Proulx, Philippe; Gravel, Dominique

2012-01-01

Speciation is the “elephant in the room” of community ecology. As the ultimate source of biodiversity, its integration in ecology's theoretical corpus is necessary to understand community assembly. Yet, speciation is often completely ignored or stripped of its spatial dimension. Recent approaches based on network theory have allowed ecologists to effectively model complex landscapes. In this study, we use this framework to model allopatric and parapatric speciation in networks of communities. We focus on the relationship between speciation, richness, and the spatial structure of communities. We find a strong opposition between speciation and local richness, with speciation being more common in isolated communities and local richness being higher in more connected communities. Unlike previous models, we also find a transition to a positive relationship between speciation and local richness when dispersal is low and the number of communities is small. We use several measures of centrality to characterize the effect of network structure on diversity. The degree, the simplest measure of centrality, is the best predictor of local richness and speciation, although it loses some of its predictive power as connectivity grows. Our framework shows how a simple neutral model can be combined with network theory to reveal complex relationships between speciation, richness, and the spatial organization of populations. PMID:22957181

Ecological Impacts of Reverse Speciation in Threespine Stickleback.

PubMed

Rudman, Seth M; Schluter, Dolph

2016-02-22

Young species are highly prone to extinction via increased gene flow after human-caused environmental changes. This mechanism of biodiversity loss, often termed reverse speciation or introgressive extinction, is of exceptional interest because the parent species are typically highly differentiated ecologically. Reverse speciation events are potentially powerful case studies for the role of evolution in driving ecological changes, as the phenotypic shifts associated with introgressive extinction can be large and they occur over particularly short timescales. Furthermore, reverse speciation can lead to novel phenotypes, which may in turn produce novel ecological effects. Here we investigate the ecological shift associated with reverse speciation in threespine stickleback fish using a field study and a replicated experiment. We find that an instance of introgressive extinction had cascading ecological consequences that altered the abundance of both aquatic prey and the pupating aquatic insects that emerged into the terrestrial ecosystem. The community and ecosystem impacts of reverse speciation were novel, and yet they were also predictable based on ecological and morphological considerations. The study suggests that knowledge about the community ecology and changes in functional morphology of a dominant species may lead to some predictive power for the ecological effects of evolutionary change. Moreover, the rapid nature and resultant ecological impacts associated with reverse speciation demonstrates the interplay between biodiversity, evolutionary change, and ecosystem function. Copyright © 2016 Elsevier Ltd. All rights reserved.

Experimental Studies of Phase Equilibria of Meteorites and Planetary Bodies

NASA Technical Reports Server (NTRS)

Stolper, Edward M.

2005-01-01

The primary theme of this project was the application of experimental petrology and geochemistry to a variety of problems in meteoritics and planetary geology. The studies were designed to help develop constraints on the histories of primitive meteorites and their components, the environments in which they formed and evolved, and to understand quantitatively the processes involved in the evolution of igneous rocks on the earth and other planetary bodies. We undertook several projects relating to the origin of CAIs and chondrules. Systematics in the thermodynamic properties of CAI-like liquids were investigated and used to elucidate speciation of multi-valent cations and sulfide capacity of silicate melts and to constrain redox conditions and the vapor pressures of volatile species over molten chondrules. We experimentally determined vanadium speciation in meteoritic pyroxenes and in pyroxenes crystallized from CAI-like melts under very reducing conditions. We also found that bulk oxygen isotope compositions of chondrules in the moderately unequilibrated LL chondrites are related to the relative timing of plagioclase crystallization. We completed an experimental study on the vaporization of beta-SiC and SiO2 (glass or cristobalite) in reducing gases and established the conditions under which these presolar grains could have survived in the solar nebula. We expanded our technique for determining the thermodynamic properties of minerals and liquids to iron-bearing systems. We determined activity-composition relationships in Pt-Fe, Pt-Cr and Pt-Fe-Cr alloys. Results were used to determine the thermodynamic properties of chromite-picrochromite spinels including the free energy of formation of end-member FeCr2O4. We also established a new approach for evaluating Pt-Fe saturation experiments. We calculated the T-fO2 relationships in equilibrated ordinary chondrites and thereby constrained the conditions of metamorphism in their parent bodies.

Evolution of Early Paleoproterozoic Ocean Chemistry as Recorded by Black Shales

NASA Astrophysics Data System (ADS)

Scott, C.; Bekker, A.; Lyons, T. W.; Planavsky, N. J.; Wing, B. A.

2010-12-01

In recent years, Precambrian biogeochemists have focused largely on the abundance, speciation and isotopic composition of major and trace elements preserved in organic carbon-rich black shales in order to track the co-evolution of ocean chemistry and life on Earth. Despite the fact that the period from 2.5 to 2.0 Ga hosted major events in Earth’s history, such as the Great Oxidation Event (GOE), an era of global glaciations, a massive and long-lived carbon isotope excursion and the end to banded iron formation (BIF) deposition, each with the potential to directly alter global biogeochemical cycles, it is perhaps best known for its unknowns. In order to help close this gap in our understanding of the evolution of Precambrian ocean chemistry we present a detailed biogeochemical study of Paleoproterozoic black shales deposited between 2.5 and 2.0 Ga. Our study integrates Fe speciation, trace metal chemistry and C, S and N isotope analyses to provide a thorough characterization of marine biogeochemical cycles as they responded to the GOE and set the stage for the demise of BIFs at ca. 1.8 Ga. Our data reveal an ocean that was both surprising similar to, and demonstrably different from, Archean and later Proterozoic oceans. Of particular interest, we find that ferruginous and euxinic conditions co-existed during this period and that sea water trace metal inventories fluctuated dramatically in conjunction with major carbon isotope excursions. By comparing our Paleoproterozoic contribution with recent biogeochemical studies of other Precambrian black shales we can begin to track first order changes in ocean chemistry without the major time gaps that have plagued previous attempts.

Micronutrient metal speciation is driven by competitive organic chelation in grassland soils.

NASA Astrophysics Data System (ADS)

Boiteau, R.; Shaw, J. B.; Paša-Tolić, L.; Koppenaal, D.; Jansson, J.

2017-12-01

Many elements are scarcely soluble in aqueous conditions found in high pH environments, such as calcareous grassland soils, unless complexed to strong binding organic ligands. To overcome this limitation, some plants and microbes produce chelators that solubilize micronutrient metals such as Fe, Ni, Cu, and Zn from mineral phases. These complexes are taken up by organisms via specific membrane receptors, thereby differentially impacting the bioavailability of these metals to the plant and microbial community. Although the importance of these chelation strategies for individual organisms has been well established, little is known about which pathways coexist within rhizosphere microbiomes or how they interact and compete for metal binding. Identifying these metallo-organic species within natural ecosystems has remained a formidable analytical challenge due to the vast diversity of compounds and poorly defined metabolic processes in complex soil matrix. Herein, we employed recently developed liquid chromatography (LC) mass spectrometry (MS) methods to characterize the speciation of water-soluble dissolved trace elements (Fe, Ni, Cu, and Zn) from Kansas Prairie soil. Both plant and fungal chelators were identified, revealing compound-specific patterns of chelation to biologically essential metals. Numerous metabolites typically implicated in plant iron acquisition and homeostasis, including mugineic acids, deoxymugineic acid, nicotianamine, and hydroxynicotianamine, dominated the speciation of divalent metals such as Ni, Cu, and Zn (2-57 pmol / g soil). In contrast, the fungal siderophore ferricrocine bound comparatively more trivalent Fe (9pmol / g soil). These results define biochemical pathways that underpin the regulation of metals in the grassland rhizosphere. They also raise new questions about the competition of these compounds for metal binding and their bioavailability to different members of the rhizosphere population.

Distribution and speciation of trace elements in iron and manganese oxide cave deposits

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frierdich, Andrew J.; Catalano, Jeffrey G.

2012-10-24

Fe and Mn oxide minerals control the distribution and speciation of heavy metals and trace elements in soils and aquatic systems through chemical mechanisms involving adsorption, incorporation, and electron transfer. The Pautler Cave System in Southwest Illinois, an analog to other temperate carbonate-hosted karst systems, contains Fe and Mn oxide minerals that form in multiple depositional environments and have high concentrations of associated trace elements. Synchrotron-based micro-scanning X-ray fluorescence ({mu}-SXRF) shows unique spatial distributions of Fe, Mn, and trace elements in mineral samples. Profile maps of Mn oxide cave stream pebble coatings show Fe- and As-rich laminations, indicating dynamic redoxmore » conditions in the cave stream. {mu}-SXRF maps demonstrate that Ni, Cu, and Zn correlate primarily with Mn whereas As correlates with both Mn and Fe; As is more enriched in the Fe phase. Zn is concentrated in the periphery of Mn oxide stream pebble coatings, and may be an indication of recent anthropogenic surface activity. X-ray absorption fine structure spectroscopy measurements reveal that As(V) occurs as surface complexes on Mn and Fe oxides whereas Zn(II) associated with Mn oxides is adsorbed to the basal planes of phyllomanganates in a tetrahedral coordination. Co(III) and Se(IV) are also observed to be associated with Mn oxides. The observation of Fe, Mn, and trace element banding in Mn oxide cave stream pebble coatings suggests that these materials are sensitive to and document aqueous redox conditions, similar to ferromanganese nodules in soils and in marine and freshwater sediments. Furthermore, speciation and distribution measurements indicate that these minerals scavenge trace elements and limit the transport of micronutrients and contaminants in karst aquifer systems while also potentially recording changes in anthropogenic surface activity and land-use.« less

Sorption, desorption, and speciation of Cd, Ni, and Fe by four calcareous soils as affected by pH.

PubMed

Tahervand, Samaneh; Jalali, Mohsen

2016-06-01

The sorption, desorption, and speciation of cadmium (Cd), nickel (Ni), and iron (Fe) in four calcareous soils were investigated at the pH range of 2-9. The results indicated that sorption of Fe by four soils was higher than 80 % at pH 2, while in the case of Cd and Ni was less than 30 %. The most common sequence of metal sorption at pH 2-9 for four soils was in the order of Fe ≫ Ni > Cd. Cadmium and Ni sorption as a function of pH showed the predictable trend of increasing metal sorption with increase in equilibrium pH, while the Fe sorption trend was different and characterized by three phases. With regard to the order of Cd, Ni, and Fe sorption on soils, Cd and Ni showed high affinity for organic matter (OM), whereas Fe had high tendency for calcium carbonate (CaCO3). Results of metal desorption using 0.01 M NaCl demonstrated that metal sorption on soils containing high amounts of CaCO3 was less reversible in comparison to soils containing high OM. In general, Cd and Ni desorption curves were characterized by three phases; (1) the greatest desorption at pH 2, (2) the low desorption at pH 3-7, and (3) the least desorption at pH > 7. The MINTEQ speciation solubility program showed that the percentage of free metals declined markedly with increase of pH, while the percentage of carbonate and hydroxyl species increased. Furthermore, MINTEQ predicted that saturation index (SI) of metals increased with increasing pH.

Geochemistry of some rare earth elements in groundwater, Vierlingsbeek, The Netherlands.

PubMed

Janssen, René P T; Verweij, Wilko

2003-03-01

Groundwater samples were taken from seven bore holes at depths ranging from 2 to 41m nearby drinking water pumping station Vierlingsbeek, The Netherlands and analysed for Y, La, Ce, Pr, Nd, Sm and Eu. Shale-normalized patterns were generally flat and showed that the observed rare earth elements (REE) were probably of natural origin. In the shallow groundwaters the REEs were light REE (LREE) enriched, probably caused by binding of LREEs to colloids. To improve understanding of the behaviour of the REE, two approaches were used: calculations of the speciation and a statistical approach. For the speciation calculations, complexation and precipitation reactions including inorganic and dissolved organic carbon (DOC) compounds, were taken into account. The REE speciation showed REE(3+), REE(SO(4))(+), REE(CO(3))(+) and REE(DOC) being the major species. Dissolution of pure REE precipitates and REE-enriched solid phases did not account for the observed REEs in groundwater. Regulation of REE concentrations by adsorption-desorption processes to Fe(III)(OH)(3) and Al(OH)(3) minerals, which were calculated to be present in nearly all groundwaters, is a probable explanation. The statistical approach (multiple linear regression) showed that pH is by far the most significant groundwater characteristic which contributes to the variation in REE concentrations. Also DOC, SO(4), Fe and Al contributed significantly, although to a much lesser extent, to the variation in REE concentrations. This is in line with the calculated REE-species in solution and REE-adsorption to iron and aluminium (hydr)oxides. Regression equations including only pH, were derived to predict REE concentrations in groundwater. External validation showed that these regression equations were reasonably successful to predict REE concentrations of groundwater of another drinking water pumping station in quite different region of The Netherlands.

Speciation in Drosophila: from phenotypes to molecules.

PubMed

Orr, H Allen; Masly, J P; Phadnis, Nitin

2007-01-01

Study of the genetics of speciation--and especially of the genetics of intrinsic postzygotic isolation-has enjoyed remarkable progress over the last 2 decades. Indeed progress has been so rapid that one might be tempted to ask if the genetics of postzygotic isolation is now wrapped up. Here we argue that the genetics of speciation is far from complete. In particular, we review 2 topics where recent work has revealed major surprises: 1) the role of meiotic drive in hybrid sterility and 2) the role of gene transposition in speciation. These surprises, and others like them, suggest that evolutionary biologists may understand less about the genetic basis of speciation than seemed likely a few years ago.

Sulfur cycling in an iron oxide-dominated, dynamic marine depositional system: The Argentine continental margin

NASA Astrophysics Data System (ADS)

Riedinger, Natascha; Brunner, Benjamin; Krastel, Sebastian; Arnold, Gail L.; Wehrmann, Laura M.; Formolo, Michael J.; Beck, Antje; Bates, Steven M.; Henkel, Susann; Kasten, Sabine; Lyons, Timothy W.

2017-05-01

The interplay between sediment deposition patterns, organic matter type and the quantity and quality of reactive mineral phases determines the accumulation, speciation and isotope composition of pore water and solid phase sulfur constituents in marine sediments. Here, we present the sulfur geochemistry of siliciclastic sediments from two sites along the Argentine continental slope—a system characterized by dynamic deposition and reworking, which result in non-steady state conditions. The two investigated sites have different depositional histories but have in common that reactive iron phases are abundant and that organic matter is refractory—conditions that result in low organoclastic sulfate reduction rates. Deposition of reworked, isotopically light pyrite and sulfurized organic matter appear to be important contributors to the sulfur inventory, with only minor addition of pyrite from organoclastic sulfate reduction above the sulfate-methane transition (SMT). Pore-water sulfide is limited to a narrow zone at the SMT. The core of that zone is dominated by pyrite accumulation. Iron monosulfide and elemental sulfur accumulate above and below this zone. Iron monosulfide precipitation is driven by the reaction of low amounts of hydrogen sulfide with ferrous iron and is in competition with the oxidation of sulfide by iron (oxyhydr)oxides to form elemental sulfur. The intervals marked by precipitation of intermediate sulfur phases at the margin of the zone with free sulfide are bordered by two distinct peaks in total organic sulfur. Organic matter sulfurization appears to precede pyrite formation in the iron-dominated margins of the sulfide zone, potentially linked to the presence of polysulfides formed by reaction between dissolved sulfide and elemental sulfur. Thus, SMTs can be hotspots for organic matter sulfurization in sulfide-limited, reactive iron-rich marine sedimentary systems. Furthermore, existence of elemental sulfur and iron monosulfide phases meters below the SMT demonstrates that in sulfide-limited systems metastable sulfur constituents are not readily converted to pyrite but can be buried to deeper sediment depths. Our data show that in non-steady state systems, redox zones do not occur in sequence but can reappear or proceed in inverse sequence throughout the sediment column, causing similar mineral alteration processes to occur at the same time at different sediment depths.

Speciation and characterization of arsenic in gold ores and cyanidation tailings using X-ray absorption spectroscopy

USGS Publications Warehouse

Paktunc, D.; Foster, A.; Heald, S.; Laflamme, G.

2004-01-01

The knowledge of mineralogy and molecular structure of As is needed to better understand the stability of As in wastes resulting from processing of gold ores. In this study, optical microscopy, scanning electron microscopy, electron microprobe, X-ray diffraction and X-ray absorption fine structure (XAFS) spectroscopy (including both XANES and EXAFS regimes) were employed to determine the mineralogical composition and local coordination environment of As in gold ores and process tailings from bench-scale tests designed to mimic a common plant practice. Arsenic-bearing minerals identified in the ores and tailings include iron (III) oxyhydroxides, scorodite (FeAsO4??2H2O), ferric arsenates, arseniosiderite (Ca2Fe3 (AsO4)3O2??3H2O), Ca-Fe arsenates, pharmacosiderite (KFe4 (AsO4)3(OH)4??6-7H2O), jarosite (K2Fe6(SO4)4 (OH)12) and arsenopyrite (FeAsS). Iron (III) oxyhydroxides contain variable levels of As from trace to about 22 wt% and Ca up to approximately 9 wt%. Finely ground ore and tailings samples were examined by bulk XAFS and selected mineral grains were analyzed by microfocused XAFS (micro-EXAFS) spectroscopy to reconcile the ambiguities of multiple As sources in the complex bulk EXAFS spectra. XANES spectra indicated that As occurs as As5+in all the samples. Micro-EXAFS spectra of individual iron (III) oxyhydroxide grains with varying As concentrations point to inner-sphere bidentate-binuclear arsenate complexes as the predominant form of As. There are indications for the presence of a second Fe shell corresponding to bidentate-mononuclear arrangement. Iron (III) oxyhydroxides with high As concentrations corresponding to maximum adsorption densities probably occur as nanoparticles. The discovery of Ca atoms around As in iron (III) oxyhydroxides at interatomic distances of 4.14-4.17 A?? and the coordination numbers suggest the formation of arseniosiderite-like nanoclusters by coprecipitation rather than simple adsorption of Ca onto iron (III) oxyhydroxides. Correlation of Ca with As in iron (III) oxyhydroxides as determined by electron microprobe analysis supports the coprecipitate origin for the presence of Ca in iron (III) oxyhydroxides. The samples containing higher abundances of ferric arsenates released higher As concentrations during the cyanidation tests. The presence of highly soluble ferric arsenates and Ca-Fe arsenates, and relatively unstable iron (III) oxyhydroxides with Fe/As molar ratios of less than 4 in the ore and process tailings suggests that not only the tailings in the impoundment will continue to release As, but also there is the potential for mobilization of As from the natural sources such as the unmined ore. ?? 2004 Elsevier Ltd.

Speciation and characterization of arsenic in gold ores and cyanidation tailings using X-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Paktunc, Dogan; Foster, Andrea; Heald, Steve; Laflamme, Gilles

2004-03-01

The knowledge of mineralogy and molecular structure of As is needed to better understand the stability of As in wastes resulting from processing of gold ores. In this study, optical microscopy, scanning electron microscopy, electron microprobe, X-ray diffraction and X-ray absorption fine structure (XAFS) spectroscopy (including both XANES and EXAFS regimes) were employed to determine the mineralogical composition and local coordination environment of As in gold ores and process tailings from bench-scale tests designed to mimic a common plant practice. Arsenic-bearing minerals identified in the ores and tailings include iron (III) oxyhydroxides, scorodite (FeAsO 4·2H 2O), ferric arsenates, arseniosiderite (Ca 2Fe 3(AsO 4) 3O 2·3H 2O), Ca-Fe arsenates, pharmacosiderite (KFe 4(AsO 4) 3(OH) 4·6-7H 2O), jarosite (K 2Fe 6(SO 4) 4(OH) 12) and arsenopyrite (FeAsS). Iron (III) oxyhydroxides contain variable levels of As from trace to about 22 wt% and Ca up to approximately 9 wt%. Finely ground ore and tailings samples were examined by bulk XAFS and selected mineral grains were analyzed by microfocused XAFS (micro-EXAFS) spectroscopy to reconcile the ambiguities of multiple As sources in the complex bulk EXAFS spectra. XANES spectra indicated that As occurs as As 5+in all the samples. Micro-EXAFS spectra of individual iron (III) oxyhydroxide grains with varying As concentrations point to inner-sphere bidentate-binuclear arsenate complexes as the predominant form of As. There are indications for the presence of a second Fe shell corresponding to bidentate-mononuclear arrangement. Iron (III) oxyhydroxides with high As concentrations corresponding to maximum adsorption densities probably occur as nanoparticles. The discovery of Ca atoms around As in iron (III) oxyhydroxides at interatomic distances of 4.14-4.17 Å and the coordination numbers suggest the formation of arseniosiderite-like nanoclusters by coprecipitation rather than simple adsorption of Ca onto iron (III) oxyhydroxides. Correlation of Ca with As in iron (III) oxyhydroxides as determined by electron microprobe analysis supports the coprecipitate origin for the presence of Ca in iron (III) oxyhydroxides. The samples containing higher abundances of ferric arsenates released higher As concentrations during the cyanidation tests. The presence of highly soluble ferric arsenates and Ca-Fe arsenates, and relatively unstable iron (III) oxyhydroxides with Fe/As molar ratios of less than 4 in the ore and process tailings suggests that not only the tailings in the impoundment will continue to release As, but also there is the potential for mobilization of As from the natural sources such as the unmined ore.

Comment on “Isotopic fractionation between Fe(III) and Fe(II) in aqueous solutions” by Clark Johnson et al., [Earth Planet. Sci. Lett. 195 (2002) 141–153

USGS Publications Warehouse

Bullen, Thomas D.; White, Arthur F.; Childs, Cyril W.

2003-01-01

In a recent contribution [1], Johnson et al. reported the equilibrium isotope fractionation factor between dissolved Fe(II) and Fe(III) in aqueous solutions at pH=2.5 and 5.5. They suggest that because the iron isotope fractionation observed in their experiments spans virtually the entire range observed in sedimentary rocks, Fe(II)–Fe(III) aqueous speciation may play a major role in determining iron isotope variations in nature where Fe(II) and Fe(III) can become physically separated. They discounted earlier conclusions by us and others [2] ;  [3] that significant equilibrium fractionation between specific coexisting Fe(II)- or Fe(III)-aqueous complexes (e.g., between aqueous Fe(II)(OH)x(aq)and Fe(II)(aq) ion) is capable of producing iron isotope contrasts that can be preserved in nature. This is an important contribution not only because the authors recognize the importance of abiotic equilibrium iron isotope fractionation in nature in contrast to previous assertions [4], but also because it will help to focus discussion on the development and evaluation of experimental approaches that can reveal abiotic fractionation mechanisms. However, in this Comment we propose that the experiments presented in this paper cannot be interpreted as straightforwardly as Johnson et al. contend. In particular, we show that in one of their critical experiments attainment of either isotope mass balance or equilibrium was not demonstrated, and thus the results of that experiment cannot be used to calculate an Fe(II)–Fe(III) equilibrium fractionation factor.

Comparative evaluation of short-term leach tests for heavy metal release from mineral processing waste

USGS Publications Warehouse

Al-Abed, S. R.; Hageman, P.L.; Jegadeesan, G.; Madhavan, N.; Allen, D.

2006-01-01

Evaluation of metal leaching using a single leach test such as the Toxicity Characteristic Leaching Procedure (TCLP) is often questionable. The pH, redox potential (Eh), particle size and contact time are critical variables in controlling metal stability, not accounted for in the TCLP. This paper compares the leaching behavior of metals in mineral processing waste via short-term extraction tests such as TCLP, Field Leach Test (FLT) used by USGS and deionized water extraction tests. Variation in the extracted amounts was attributed to the use of different particle sizes, extraction fluid and contact time. In the controlled pH experiments, maximum metal extraction was obtained at acidic pH for cationic heavy metals such as Cu, Pb and Zn, while desorption of Se from the waste resulted in high extract concentrations in the alkaline region. Precipitation of iron, caused by a pH increase, probably resulted in co-precipitation and immobilization of Cu, Pb and Zn in the alkaline pH region. A sequential extraction procedure was performed on the original waste and the solid residue from the Eh-pH experiments to determine the chemical speciation and distribution of the heavy metals. In the as-received waste, Cu existed predominantly in water soluble or sulfidic phases, with no binding to carbonates or iron oxides. Similar characteristics were observed for Pb and Zn, while Se existed mostly associated with iron oxides or sulfides. Adsorption/co-precipitation of Cu, Se and Pb on precipitated iron hydroxides was observed in the experimental solid residues, resulting in metal immobilization above pH 7.

Role of natural nanoparticles on the speciation of Ni in andosols of la Reunion

NASA Astrophysics Data System (ADS)

Levard, Clément; Doelsch, Emmanuel; Rose, Jérôme; Masion, Armand; Basile-Doelsch, Isabelle; Proux, Olivier; Hazemann, Jean-Louis; Borschneck, Daniel; Bottero, Jean-Yves

2009-08-01

Andosols on the island of Réunion have high nickel (Ni) concentrations due to the natural pedo-geochemical background. Enhanced knowledge of Ni speciation is necessary to predict the bioavailability and potential toxicity of this element. Ni speciation in these andosols, marked by the presence of high amounts of natural aluminosilicate nanoparticles, was investigated in two complementary systems: (i) In a soil sample—densimetric fractionation was first performed in order to separate the potential bearing phases, prior to Ni speciation characterization. (ii) In a synthetic sample—Ni reactivity with synthetic aluminosilicate nanoparticle analogs were studied. In both cases, Ni speciation was determined using X-ray absorption spectroscopy (XAS). The results revealed that Ni had the same local environment in both systems (natural and synthetic systems), and Ni was chemically linked to natural short-range ordered aluminosilicates or analogs. This complex represented about 75% of the total Ni in the studied soil.

Comparative impacts of iron oxide nanoparticles and ferric ions on the growth of Citrus maxima.

PubMed

Hu, Jing; Guo, Huiyuan; Li, Junli; Gan, Qiuliang; Wang, Yunqiang; Xing, Baoshan

2017-02-01

The impacts of iron oxide nanoparticles (γ-Fe 2 O 3 NPs) and ferric ions (Fe 3+ ) on plant growth and molecular responses associated with the transformation and transport of Fe 2+ were poorly understood. This study comprehensively compared and evaluated the physiological and molecular changes of Citrus maxima plants as affected by different levels of γ-Fe 2 O 3 NPs and Fe 3+ . We found that γ-Fe 2 O 3 NPs could enter plant roots but no translocation from roots to shoots was observed. 20 mg/L γ-Fe 2 O 3 NPs had no impact on plant growth. 50 mg/L γ-Fe 2 O 3 NPs significantly enhanced chlorophyll content by 23.2% and root activity by 23.8% as compared with control. However, 100 mg/L γ-Fe 2 O 3 NPs notably increased MDA formation, decreased chlorophyll content and root activity. Although Fe 3+ ions could be used by plants and promoted the synthesis of chlorophyll, they appeared to be more toxic than γ-Fe 2 O 3 NPs, especially for 100 mg/L Fe 3+ . The impacts caused by γ-Fe 2 O 3 NPs and Fe 3+ were concentration-dependent. Physiological results showed that γ-Fe 2 O 3 NPs at proper concentrations had the potential to be an effective iron nanofertilizer for plant growth. RT-PCR analysis showed that γ-Fe 2 O 3 NPs had no impact on AHA gene expression. 50 mg/L γ-Fe 2 O 3 NPs and Fe 3+ significantly increased expression levels of FRO2 gene and correspondingly had a higher ferric reductase activity compared to both control and Fe(II)-EDTA exposure, thus promoting the iron transformation and enhancing the tolerance of plants to iron deficiency. Relative levels of Nramp3 gene expression exposed to γ-Fe 2 O 3 NPs and Fe 3+ were significantly lower than control, indicating that all γ-Fe 2 O 3 NPs and Fe 3+ treatments could supply iron to C. maxima seedlings. Overall, plants can modify the speciation and transport of γ-Fe 2 O 3 NPs or Fe 3+ for self-protection and development by activating many physiological and molecular processes. Copyright © 2016 Elsevier Ltd. All rights reserved.

Secondary sympatry caused by range expansion informs on the dynamics of microendemism in a biodiversity hotspot.

PubMed

Nattier, Romain; Grandcolas, Philippe; Elias, Marianne; Desutter-Grandcolas, Laure; Jourdan, Hervé; Couloux, Arnaud; Robillard, Tony

2012-01-01

Islands are bounded areas where high endemism is explained either by allopatric speciation through the fragmentation of the limited amount of space available, or by sympatric speciation and accumulation of daughter species. Most empirical evidence point out the dominant action of allopatric speciation. We evaluate this general view by looking at a case study where sympatric speciation is suspected. We analyse the mode, tempo and geography of speciation in Agnotecous, a cricket genus endemic to New Caledonia showing a generalized pattern of sympatry between species making sympatric speciation plausible. We obtained five mitochondrial and five nuclear markers (6.8 kb) from 37 taxa corresponding to 17 of the 21 known extant species of Agnotecous, and including several localities per species, and we conducted phylogenetic and dating analyses. Our results suggest that the diversification of Agnotecous occurred mostly through allopatric speciation in the last 10 Myr. Highly microendemic species are the most recent ones (<2 Myr) and current sympatry is due to secondary range expansion after allopatric speciation. Species distribution should then be viewed as a highly dynamic process and extreme microendemism only as a temporary situation. We discuss these results considering the influence of climatic changes combined with intricate soil diversity and mountain topography. A complex interplay between these factors could have permitted repeated speciation events and range expansion.

Selenium Metabolism in Cancer Cells: The Combined Application of XAS and XFM Techniques to the Problem of Selenium Speciation in Biological Systems

PubMed Central

Weekley, Claire M.; Aitken, Jade B.; Finney, Lydia; Vogt, Stefan; Witting, Paul K.; Harris, Hugh H.

2013-01-01

Determining the speciation of selenium in vivo is crucial to understanding the biological activity of this essential element, which is a popular dietary supplement due to its anti-cancer properties. Hyphenated techniques that combine separation and detection methods are traditionally and effectively used in selenium speciation analysis, but require extensive sample preparation that may affect speciation. Synchrotron-based X-ray absorption and fluorescence techniques offer an alternative approach to selenium speciation analysis that requires minimal sample preparation. We present a brief summary of some key HPLC-ICP-MS and ESI-MS/MS studies of the speciation of selenium in cells and rat tissues. We review the results of a top-down approach to selenium speciation in human lung cancer cells that aims to link the speciation and distribution of selenium to its biological activity using a combination of X-ray absorption spectroscopy (XAS) and X-ray fluorescence microscopy (XFM). The results of this approach highlight the distinct fates of selenomethionine, methylselenocysteine and selenite in terms of their speciation and distribution within cells: organic selenium metabolites were widely distributed throughout the cells, whereas inorganic selenium metabolites were compartmentalized and associated with copper. New data from the XFM mapping of electrophoretically-separated cell lysates show the distribution of selenium in the proteins of selenomethionine-treated cells. Future applications of this top-down approach are discussed. PMID:23698165

The effect of bonding environment on iron isotope fractionation between minerals at high temperature

NASA Astrophysics Data System (ADS)

Sossi, Paolo A.; O'Neill, Hugh St. C.

2017-01-01

Central to understanding the processes that drive stable isotope fractionation in nature is their quantification under controlled experimental conditions. The polyvalent element iron, given its abundance in terrestrial rocks, exerts controls on the structural and chemical properties of minerals and melts. The iron isotope compositions of typical high temperature minerals are, however, poorly constrained and their dependence on intensive (e.g. fO2) and extensive (e.g. compositional) variables is unknown. In this work, experiments involving a reference phase, 2 M FeCl2·4H2O(l), together with an oxide mix corresponding to the bulk composition of the chosen mineral were performed in a piston cylinder in Ag capsules. The oxide mix crystallised in situ at 1073 K and 1 GPa, in equilibrium with the iron chloride, and was held for 72 h. In order to characterise the effect of co-ordination and oxidation state on the isotope composition independently, exclusively Fe2+ minerals were substituted in: VIII-fold almandine, VI-fold ilmenite, fayalite and IV-fold chromite and hercynite. Δ57FeMin-FeCl2 increases in the order VIII < VI < IV, consistent with a decrease in the mean Fe-O bond length. Magnetite, which has mixed VI- and IV-fold co-ordination, has the heaviest Δ57Fe by virtue of 2/3 of its iron being the smaller, ferric ion. The composition of the VIFe2+-bearing minerals is similar to that of the aqueous FeCl2 fluid. To the degree that this represents the speciation of iron in fluids exsolving from magmas, the fractionation between them should be small, unless the iron is hosted in magnetite. By contrast, predominantly Fe2+-bearing mantle garnets should preserve a much lighter δ57Fe than their lower pressure spinel counterparts, a signature that may be reflected in partial melts from these lithologies. As the Fe-O bond lengths in fayalite and ilmenite are comparable, their isotope compositions overlap, suggesting that high Ti mare basalts acquired their heavy isotopic signature from ilmenite that crystallised late during lunar magma ocean solidification.

Atmospheric Processing of Volcanic Glass: Effects on Iron Solubility and Redox Speciation.

PubMed

Maters, Elena C; Delmelle, Pierre; Bonneville, Steeve

2016-05-17

Volcanic ash from explosive eruptions can provide iron (Fe) to oceanic regions where this micronutrient limits primary production. Controls on the soluble Fe fraction in ash remain poorly understood but Fe solubility is likely influenced during atmospheric transport by condensation-evaporation cycles which induce large pH fluctuations. Using glass powder as surrogate for ash, we experimentally simulate its atmospheric processing via cycles of pH 2 and 5 exposure. Glass fractional Fe solubility (maximum 0.4%) is governed by the pH 2 exposure duration rather than by the pH fluctuations, however; pH 5 exposure induces precipitation of Fe-bearing nanoparticles which (re)dissolve at pH 2. Glass leaching/dissolution release Fe(II) and Fe(III) which are differentially affected by changes in pH; the average dissolved Fe(II)/Fetot ratio is ∼0.09 at pH 2 versus ∼0.18 at pH 5. Iron release at pH 2 from glass with a relatively high bulk Fe(II)/Fetot ratio (0.5), limited aqueous Fe(II) oxidation at pH 5, and possibly glass-mediated aqueous Fe(III) reduction may render atmospherically processed ash a significant source of Fe(II) for phytoplankton. By providing new insight into the form(s) of Fe associated with ash as wet aerosol versus cloud droplet, we improve knowledge of atmospheric controls on volcanogenic Fe delivery to the ocean.

Factors influencing sorption of ciprofloxacin onto activated sludge: experimental assessment and modelling implications.

PubMed

Polesel, Fabio; Lehnberg, Kai; Dott, Wolfgang; Trapp, Stefan; Thomas, Kevin V; Plósz, Benedek Gy

2015-01-01

Many of the pharmaceuticals and personal care products occurring in municipal sewage are ionizing substances, and their partitioning behaviour is affected by ionic interactions with solid matrices. In activated sludge systems, such interactions have currently not been adequately understood and described, particularly for zwitterionic chemicals. Here we present an assessment of the effects of pH and iron salt dosing on the sorption of ciprofloxacin onto activated sludge using laboratory experiments and full-scale fate modelling. Experimental results were described with Freundlich isotherms and showed that non-linear sorption occurred under all the conditions tested. The greatest sorption potential was measured at pH=7.4, at which ciprofloxacin is speciated mostly as zwitterion. Iron salt dosing increased sorption under aerobic and, to a lesser extent, anoxic conditions, whereas no effect was registered under anaerobic conditions. The activated sludge model for xenobiotics (ASM-X) was extended with Freundlich-based sorption kinetics and used to predict the fate of ciprofloxacin in a wastewater treatment plant (WWTP). Scenario simulations, using experimental Freundlich parameters, were used to identify whether the assessed factors caused a significant increase of aqueous ciprofloxacin concentration in full-scale bioreactors. Simulation results suggest that a pH increase, rather than a reduction in iron salt dosing, could be responsible for a systematic deterioration of sorption of ciprofloxacin in the WWTP. Copyright © 2014 Elsevier Ltd. All rights reserved.

Speciation and amphotericin B sensitivity studies on blood isolates of Candida from burned patients

PubMed Central

Stieritz, Donald D.; Law, Edward J.; Holder, Ian Alan

1973-01-01

Methods of speciating Candida isolates from clinical specimens are described and the necessity of speciation is emphasized. Differences in susceptibility of C. albicans and C. tropicalis to amphotericin B were observed and the implications of this in relation to treatment with amphotericin B and the development of resistance are discussed. PMID:4578160

Bioaccessibility, bioavailability and toxicity of commercially relevant iron- and chromium-based particles: in vitro studies with an inhalation perspective.

PubMed

Hedberg, Yolanda; Gustafsson, Johanna; Karlsson, Hanna L; Möller, Lennart; Odnevall Wallinder, Inger

2010-09-03

Production of ferrochromium alloys (FeCr), master alloys for stainless steel manufacture, involves casting and crushing processes where particles inevitably become airborne and potentially inhaled. The aim of this study was to assess potential health hazards induced by inhalation of different well-characterized iron- and chromium-based particles, i.e. ferrochromium (FeCr), ferrosiliconchromium (FeSiCr), stainless steel (316L), iron (Fe), chromium (Cr), and chromium(III)oxide (Cr2O3), in different size fractions using in vitro methods. This was done by assessing the extent and speciation of released metals in synthetic biological medium and by analyzing particle reactivity and toxicity towards cultured human lung cells (A549). The amount of released metals normalized to the particle surface area increased with decreasing particle size for all alloy particles, whereas the opposite situation was valid for particles of the pure metals. These effects were evident in artificial lysosomal fluid (ALF) of pH 4.5 containing complexing agents, but not in neutral or weakly alkaline biological media. Chromium, iron and nickel were released to very low extent from all alloy particles, and from particles of Cr due to the presence of a Cr(III)-rich protective surface oxide. Released elements were neither proportional to the bulk nor to the surface composition after the investigated 168 hours of exposure. Due to a surface oxide with less protective properties, significantly more iron was released from pure iron particles compared with the alloys. Cr was predominantly released as Cr(III) from all particles investigated and was strongly complexed by organic species of ALF. Cr2O3 particles showed hemolytic activity, but none of the alloy particles did. Fine-sized particles of stainless steel caused however DNA damage, measured with the comet assay after 4 h exposure. None of the particles revealed any significant cytotoxicity in terms of cell death after 24 h exposure. It is evident that particle and alloy characteristics such as particle size and surface composition are important aspects to consider when assessing particle toxicity and metal release from alloy particles compared to pure metal particles. Generated results clearly elucidate that neither the low released concentrations of metals primarily as a result of protective and poorly soluble surface oxides, nor non-bioavailable chromium complexes, nor the particles themselves of occupational relevance induced significant acute toxic response, with exception of DNA damage from stainless steel.

Bioaccessibility, bioavailability and toxicity of commercially relevant iron- and chromium-based particles: in vitro studies with an inhalation perspective

PubMed Central

2010-01-01

Background Production of ferrochromium alloys (FeCr), master alloys for stainless steel manufacture, involves casting and crushing processes where particles inevitably become airborne and potentially inhaled. The aim of this study was to assess potential health hazards induced by inhalation of different well-characterized iron- and chromium-based particles, i.e. ferrochromium (FeCr), ferrosiliconchromium (FeSiCr), stainless steel (316L), iron (Fe), chromium (Cr), and chromium(III)oxide (Cr2O3), in different size fractions using in vitro methods. This was done by assessing the extent and speciation of released metals in synthetic biological medium and by analyzing particle reactivity and toxicity towards cultured human lung cells (A549). Results The amount of released metals normalized to the particle surface area increased with decreasing particle size for all alloy particles, whereas the opposite situation was valid for particles of the pure metals. These effects were evident in artificial lysosomal fluid (ALF) of pH 4.5 containing complexing agents, but not in neutral or weakly alkaline biological media. Chromium, iron and nickel were released to very low extent from all alloy particles, and from particles of Cr due to the presence of a Cr(III)-rich protective surface oxide. Released elements were neither proportional to the bulk nor to the surface composition after the investigated 168 hours of exposure. Due to a surface oxide with less protective properties, significantly more iron was released from pure iron particles compared with the alloys. Cr was predominantly released as Cr(III) from all particles investigated and was strongly complexed by organic species of ALF. Cr2O3 particles showed hemolytic activity, but none of the alloy particles did. Fine-sized particles of stainless steel caused however DNA damage, measured with the comet assay after 4 h exposure. None of the particles revealed any significant cytotoxicity in terms of cell death after 24 h exposure. Conclusion It is evident that particle and alloy characteristics such as particle size and surface composition are important aspects to consider when assessing particle toxicity and metal release from alloy particles compared to pure metal particles. Generated results clearly elucidate that neither the low released concentrations of metals primarily as a result of protective and poorly soluble surface oxides, nor non-bioavailable chromium complexes, nor the particles themselves of occupational relevance induced significant acute toxic response, with exception of DNA damage from stainless steel. PMID:20815895

Understanding Uranium Behavior in a Reduced Aquifer

NASA Astrophysics Data System (ADS)

Janot, N.; Lezama-Pacheco, J. S.; Williams, K. H.; Bernier-Latmani, R.; Long, P. E.; Davis, J. A.; Fox, P. M.; Yang, L.; Giammar, D.; Cerrato, J. M.; Bargar, J.

2012-12-01

Uranium contamination of groundwater is a concern at several US Department of Energy sites, such Old Rifle, CO. Uranium transport in the environment is mainly controlled by its oxidation state, since oxidized U(VI) is relatively mobile, whereas U(IV) is relatively insoluble. Bio-remediation of contaminated aquifers aims at immobilizing uranium in a reduced form. Previous laboratory and field studies have shown that adding electron donor (lactate, acetate, ethanol) to groundwater stimulates the activity of metal- and sulfate-reducing bacteria, which promotes U(VI) reduction in contaminated aquifers. However, obtaining information on chemical and physical forms of U, Fe and S species for sediments biostimulated in the field, as well as kinetic parameters such as U(VI) reduction rate, is challenging due to the low concentration of uranium in the aquifers (typically < 10 ppm) and the expense of collecting large number of cores. An in-situ technique has been developed for studying uranium, iron and sulfur reduction dynamics during such bioremediation episodes. This technique uses in-well columns to obtain direct access to chemical and physical forms of U(IV) produced in the aquifer, evolving microbial communities, and trace and major ion groundwater constituents. While several studies have explored bioreduction of uranium under sulfate-reducing conditions, less attention has been paid to the initial iron-reducing phase, noted as being of particular importance to uranium removal. The aim of this work was to assess the formation of U(IV) during the early stages of a bio-remediation experiment at the Old Rifle site, CO, from early iron-reducing conditions to the transition to sulfate-reducing conditions. Several in-well chromatographic columns packed with sediment were deployed and were sampled at different days after the start of bio-reduction. X-ray absorption spectroscopy and X-ray microscopy were used to obtain information on Fe, S and U speciation and distribution. Chemical extractions of the reduced sediments have also been performed, to determine the rate of Fe(II) and U(IV) accumulation.

SPECIATE 4.3: Addendum to SPECIATE 4.2--Speciation database development documentation

EPA Science Inventory

SPECIATE is the U.S. Environmental Protection Agency's (EPA) repository of volatile organic gas and particulate matter (PM) speciation profiles of air pollution sources. Among the many uses of speciation data, these source profiles are used to: (1) create speciated emissions inve...

SPECIATE 4.0: SPECIATION DATABASE DEVELOPMENT DOCUMENTATION--FINAL REPORT

EPA Science Inventory

SPECIATE is the U.S. EPA's repository of total organic compounds (TOC) and particulate matter (PM) speciation profiles of air pollution sources. This report documents how EPA developed the SPECIATE 4.0 database that replaces the prior version, SPECIATE 3.2. SPECIATE 4.0 includes ...

Extensive range overlap between heliconiine sister species: evidence for sympatric speciation in butterflies?

PubMed

Rosser, Neil; Kozak, Krzysztof M; Phillimore, Albert B; Mallet, James

2015-06-30

Sympatric speciation is today generally viewed as plausible, and some well-supported examples exist, but its relative contribution to biodiversity remains to be established. We here quantify geographic overlap of sister species of heliconiine butterflies, and use age-range correlations and spatial simulations of the geography of speciation to infer the frequency of sympatric speciation. We also test whether shifts in mimetic wing colour pattern, host plant use and climate niche play a role in speciation, and whether such shifts are associated with sympatry. Approximately a third of all heliconiine sister species pairs exhibit near complete range overlap, and analyses of the observed patterns of range overlap suggest that sympatric speciation contributes 32%-95% of speciation events. Müllerian mimicry colour patterns and host plant choice are highly labile traits that seem to be associated with speciation, but we find no association between shifts in these traits and range overlap. In contrast, climatic niches of sister species are more conserved. Unlike birds and mammals, sister species of heliconiines are often sympatric and our inferences using the most recent comparative methods suggest that sympatric speciation is common. However, if sister species spread rapidly into sympatry (e.g. due to their similar climatic niches), then assumptions underlying our methods would be violated. Furthermore, although we find some evidence for the role of ecology in speciation, ecological shifts did not show the associations with range overlap expected under sympatric speciation. We delimit species of heliconiines in three different ways, based on "strict and " "relaxed" biological species concepts (BSC), as well as on a surrogate for the widely-used "diagnostic" version of the phylogenetic species concept (PSC). We show that one reason why more sympatric speciation is inferred in heliconiines than in birds may be due to a different culture of species delimitation in the two groups. To establish whether heliconiines are exceptional will require biogeographic comparative studies for a wider range of animal taxa including many more invertebrates.

Tracking niche variation over millennial timescales in sympatric killer whale lineages

PubMed Central

Foote, Andrew D.; Newton, Jason; Ávila-Arcos, María C.; Kampmann, Marie-Louise; Samaniego, Jose A.; Post, Klaas; Rosing-Asvid, Aqqalu; Sinding, Mikkel-Holger S.; Gilbert, M. Thomas P.

2013-01-01

Niche variation owing to individual differences in ecology has been hypothesized to be an early stage of sympatric speciation. Yet to date, no study has tracked niche width over more than a few generations. In this study, we show the presence of isotopic niche variation over millennial timescales and investigate the evolutionary outcomes. Isotopic ratios were measured from tissue samples of sympatric killer whale Orcinus orca lineages from the North Sea, spanning over 10 000 years. Isotopic ratios spanned a range similar to the difference in isotopic values of two known prey items, herring Clupea harengus and harbour seal Phoca vitulina. Two proxies of the stage of speciation, lineage sorting of mitogenomes and genotypic clustering, were both weak to intermediate indicating that speciation has made little progress. Thus, our study confirms that even with the necessary ecological conditions, i.e. among-individual variation in ecology, it is difficult for sympatric speciation to progress in the face of gene flow. In contrast to some theoretical models, our empirical results suggest that sympatric speciation driven by among-individual differences in ecological niche is a slow process and may not reach completion. We argue that sympatric speciation is constrained in this system owing to the plastic nature of the behavioural traits under selection when hunting either mammals or fish. PMID:23945688

Tracking niche variation over millennial timescales in sympatric killer whale lineages.

PubMed

Foote, Andrew D; Newton, Jason; Ávila-Arcos, María C; Kampmann, Marie-Louise; Samaniego, Jose A; Post, Klaas; Rosing-Asvid, Aqqalu; Sinding, Mikkel-Holger S; Gilbert, M Thomas P

2013-10-07

Niche variation owing to individual differences in ecology has been hypothesized to be an early stage of sympatric speciation. Yet to date, no study has tracked niche width over more than a few generations. In this study, we show the presence of isotopic niche variation over millennial timescales and investigate the evolutionary outcomes. Isotopic ratios were measured from tissue samples of sympatric killer whale Orcinus orca lineages from the North Sea, spanning over 10 000 years. Isotopic ratios spanned a range similar to the difference in isotopic values of two known prey items, herring Clupea harengus and harbour seal Phoca vitulina. Two proxies of the stage of speciation, lineage sorting of mitogenomes and genotypic clustering, were both weak to intermediate indicating that speciation has made little progress. Thus, our study confirms that even with the necessary ecological conditions, i.e. among-individual variation in ecology, it is difficult for sympatric speciation to progress in the face of gene flow. In contrast to some theoretical models, our empirical results suggest that sympatric speciation driven by among-individual differences in ecological niche is a slow process and may not reach completion. We argue that sympatric speciation is constrained in this system owing to the plastic nature of the behavioural traits under selection when hunting either mammals or fish.

Implications of mercury speciation in thiosulfate treated plants.

PubMed

Wang, Jianxu; Feng, Xinbin; Anderson, Christopher W N; Wang, Heng; Zheng, Lirong; Hu, Tiandou

2012-05-15

Mercury uptake was induced in two cultivars of Brassica juncea under field conditions using thiosulfate. Analysis was conducted to better understand the mechanism of uptake, speciation of mercury in plants, and redistribution of mercury in the soil. Plant mercury and sulfur concentrations were increased after thiosulfate treatment, and a linear correlation between mercury and sulfur was observed. Mercury may be absorbed and transported in plants as the Hg-thiosulfate complex. The majority of mercury in treated plant tissues (two cultivars) was bound to sulfur in a form similar to β-HgS (66-94%). Remaining mercury was present in forms similar to Hg-cysteine (1-10%) and Hg-dicysteine (8-28%). The formation of β-HgS may relate to the transport and assimilation of sulfate in plant tissues. Mercury-thiosulfate complex could decompose to mercuric and sulfate ions in the presence of free protons inside the plasma membrane, while sulfide ions would be produced by the assimilation of sulfate. The concomitant presence of mercuric ions and S(2-) would precipitate β-HgS. The mercury concentration in the rhizosphere decreased in the treated relative to the nontreated soil. The iron/manganese oxide and organic-bound fractions of soil mercury were transformed to more bioavailable forms (soluble and exchangeable and specifically sorbed) and taken up by plants.

Influence of porewater sulfide on methylmercury production and partitioning in sulfate-impacted lake sediments.

PubMed

Bailey, Logan T; Mitchell, Carl P J; Engstrom, Daniel R; Berndt, Michael E; Coleman Wasik, Jill K; Johnson, Nathan W

2017-02-15

In low-sulfate and sulfate-limited freshwater sediments, sulfate loading increases the production of methylmercury (MeHg), a potent and bioaccumulative neurotoxin. Sulfate loading to anoxic sediments leads to sulfide production that can inhibit mercury methylation, but this has not been commonly observed in freshwater lakes and wetlands. In this study, sediments were collected from sulfate-impacted, neutral pH, surface water bodies located downstream from ongoing and historic mining activities to examine how chronic sulfate loading produces porewater sulfide, and influences MeHg production and transport. Sediments were collected over two years, during several seasons from lakes with a wide range of overlying water sulfate concentration. Samples were characterized for in-situ solid phase and porewater MeHg, Hg methylation potentials via incubations with enriched stable Hg isotopes, and sulfur, carbon, and iron content and speciation. Porewater sulfide reflected historic sulfur loading and was strongly related to the extractable iron content of sediment. Overall, methylation potentials were consistent with the accumulation of MeHg on the solid phase, but both methylation potentials and MeHg were significantly lower at chronically sulfate-impacted sites with a low solid-phase Fe:S ratio. At these heavily sulfate-impacted sites that also contained elevated porewater sulfide, both MeHg production and partitioning are influenced: Hg methylation potentials and sediment MeHg concentrations are lower, but occasionally porewater MeHg concentrations in sediment are elevated, particularly in the spring. The dual role of sulfide as a ligand for inorganic mercury (decreasing bioavailability) and methylmercury (increasing partitioning into porewater) means that elucidating the role of iron and sulfur loads as they define porewater sulfide is key to understanding sulfate's influence on MeHg production and partitioning in sulfate-impacted freshwater sediment. Copyright © 2016 Elsevier B.V. All rights reserved.

Low molecular weight carboxylic acids in oxidizing porphyry copper tailings.

PubMed

Dold, Bernhard; Blowes, David W; Dickhout, Ralph; Spangenberg, Jorge E; Pfeifer, Hans-Rudolf

2005-04-15

The distribution of low molecular weight carboxylic acids (LMWCA) was investigated in pore water profiles from two porphyry copper tailings impoundments in Chile (Piuquenes at La Andina and Cauquenes at El Teniente mine). The objectives of this study were (1) to determine the distribution of LMWCA, which are interpreted to be the metabolic byproducts of the autotroph microbial community in this low organic carbon system, and (2) to infer the potential role of these acids in cycling of Fe and other elements in the tailings impoundments. The speciation and mobility of iron, and potential for the release of H+ via hydrolysis of the ferric iron, are key factors in the formation of acid mine drainage in sulfidic mine wastes. In the low-pH oxidation zone of the Piuquenes tailings, Fe(III) is the dominant iron species and shows high mobility. LMWCA, which occur mainly between the oxidation front down to 300 cm below the tailings surface at both locations (e.g., max concentrations of 0.12 mmol/L formate, 0.17 mmol/L acetate, and 0.01 mmol/L pyruvate at Piuquenes and 0.14 mmol/L formate, 0.14 mmol/L acetate, and 0.006 mmol/L pyruvate at Cauquenes), are observed at the same location as high Fe concentrations (up to 71.2 mmol/L Fe(II) and 16.1 mmol/L Fe(III), respectively). In this zone, secondary Fe(III) hydroxides are depleted. Our data suggest that LMWCA may influence the mobility of iron in two ways. First, complexation of Fe(III), through formation of bidentate Fe(III)-LMWCA complexes (e.g., pyruvate, oxalate), may enhance the dissolution of Fe(III) (oxy)hydroxides or may prevent precipitation of Fe(III) (oxy)hydroxides. Soluble Fe(III) chelate complexes which may be mobilized downward and convert to Fe(II) by Fe(III) reducing bacteria. Second, monodentate LMWCA (e.g., acetate and formate) can be used by iron-reducing bacteria as electron donors (e.g., Acidophilum spp.), with ferric iron as the electron acceptor. These processes may, in part, explain the low abundances of secondary Fe(III) hydroxide precipitates below the oxidation front and the high concentrations of Fe(II) observed in the pore waters of some low-sulfide systems. The reduction of Fe(III) and the subsequent increase of iron mobility and potential acidity transfer (Fe(II) oxidation can result in the release of H+ in an oxic environment) should be taken in account in mine waste management strategies.

Demographic modelling with whole-genome data reveals parallel origin of similar Pundamilia cichlid species after hybridization.

PubMed

Meier, Joana I; Sousa, Vitor C; Marques, David A; Selz, Oliver M; Wagner, Catherine E; Excoffier, Laurent; Seehausen, Ole

2017-01-01

Modes and mechanisms of speciation are best studied in young species pairs. In older taxa, it is increasingly difficult to distinguish what happened during speciation from what happened after speciation. Lake Victoria cichlids in the genus Pundamilia encompass a complex of young species and polymorphic populations. One Pundamilia species pair, P. pundamilia and P. nyererei, is particularly well suited to study speciation because sympatric population pairs occur with different levels of phenotypic differentiation and reproductive isolation at different rocky islands within the lake. Genetic distances between allopatric island populations of the same nominal species often exceed those between the sympatric species. It thus remained unresolved whether speciation into P. nyererei and P. pundamilia occurred once, followed by geographical range expansion and interspecific gene flow in local sympatry, or if the species pair arose repeatedly by parallel speciation. Here, we use genomic data and demographic modelling to test these alternative evolutionary scenarios. We demonstrate that gene flow plays a strong role in shaping the observed patterns of genetic similarity, including both gene flow between sympatric species and gene flow between allopatric populations, as well as recent and early gene flow. The best supported model for the origin of P. pundamilia and P. nyererei population pairs at two different islands is one where speciation happened twice, whereby the second speciation event follows shortly after introgression from an allopatric P. nyererei population that arose earlier. Our findings support the hypothesis that very similar species may arise repeatedly, potentially facilitated by introgressed genetic variation. © 2016 John Wiley & Sons Ltd.

Refining the conditions for sympatric ecological speciation.

PubMed

Débarre, F

2012-12-01

Can speciation occur in a single population when different types of resources are available, in the absence of any geographical isolation, or any spatial or temporal variation in selection? The controversial topics of sympatric speciation and ecological speciation have already stimulated many theoretical studies, most of them agreeing on the fact that mechanisms generating disruptive selection, some level of assortment, and enough heterogeneity in the available resources, are critical for sympatric speciation to occur. Few studies, however, have combined the three factors and investigated their interactions. In this article, I analytically derive conditions for sympatric speciation in a general model where the distribution of resources can be uni- or bimodal, and where a parameter controls the range of resources that an individual can exploit. This approach bridges the gap between models of a unimodal continuum of resources and Levene-type models with discrete resources. I then test these conditions against simulation results from a recently published article (Thibert-Plante & Hendry, 2011, J. Evol. Biol. 24: 2186-2196) and confirm that sympatric ecological speciation is favoured when (i) selection is disruptive (i.e. individuals with an intermediate trait are at a local fitness minimum), (ii) resources are differentiated enough and (iii) mating is assortative. I also discuss the role of mating preference functions and the need (or lack thereof) for bimodality in resource distributions for diversification. © 2012 The Author. Journal of Evolutionary Biology © 2012 European Society For Evolutionary Biology.

Utilization of red mud and Pb/Zn smelter waste for the synthesis of a red mud-based cementitious material.

PubMed

Li, Yuan-Cheng; Min, Xiao-Bo; Ke, Yong; Chai, Li-Yuan; Shi, Mei-Qing; Tang, Chong-Jian; Wang, Qing-Wei; Liang, Yan-Jie; Lei, Jie; Liu, De-Gang

2018-02-15

A new method in which Pb/Zn smelter waste containing arsenic and heavy metals (arsenic sludge), red mud and lime are utilized to prepare red mud-based cementitious material (RCM) is proposed in this study. XRD, SEM, FTIR and unconfined compressive strength (UCS) tests were employed to assess the physicochemical properties of RCM. In addition, ettringite and iron oxide-containing ettringite were used to study the hydration mechanism of RCM. The results show that the UCS of the RCM (red mud+arsenic sludge+lime) was higher than that of the binder (red mud+arsenic sludge). When the mass ratio of m (binder): m (lime) was 94:6 and then maintained 28days at ambient temperature, the UCS reached 12.05MPa. The red mud has potential cementitious characteristics, and the major source of those characteristics was the aluminium oxide. In the red mud-arsenic sludge-lime system, aluminium oxide was effectively activated by lime and gypsum to form complex hydration products. Some of the aluminium in ettringite was replaced by iron to form calcium sulfoferrite hydrate. The BCR and leaching toxicity results show that the leaching concentration was strongly dependent on the chemical speciation of arsenic and the hydration products. Therefore, the investigated red mud and arsenic sludge can be successfully utilized in cement composites to create a red mud-based cementitious material. Copyright © 2017 Elsevier B.V. All rights reserved.

Influence of organic matter on arsenic removal by continuous flow electrocoagulation treatment of weakly mineralized waters.

PubMed

Pallier, Virginie; Feuillade-Cathalifaud, Geneviève; Serpaud, Bernard

2011-03-01

The aim of this study is to evaluate and understand the electrocoagulation/flocculation (ECF) process to remove arsenic from both model and natural waters with low mineral content and to compare its performances to the coagulation/flocculation (CF) process already optimized. Experiments were thus conducted with iron electrodes in the same specific treatment conditions (4≤current density (mAcm(-2))≤33) to study the influence of organic matter on arsenic removal in conditions avoiding the oxidation step usually required to improve As(III) removal. The process performance was evaluated by combining quantification of arsenic residual concentrations and speciation and dissolved organic carbon residual concentrations with zeta potential and turbidity measurements. When compared to CF, ECF presented several disadvantages: (i) lower As(V) removal yield because of the ferrous iron dissolved from the anode and the subsequent negative zeta potential of the colloidal suspension, (ii) higher residual DOC concentrations because of the fractionation of high molecular weight compounds during the treatment leading to compounds less prone to coagulate and (iii) higher residual turbidities because of the charge neutralization mechanisms involved. However, during this process, As(III) was oxidized to As(V) improving considerably its removal whatever the matrix conditions. ECF thus allowed to improve As(III) removal without applying an oxidation step that could potentially lead to the formation of toxic oxidation by-products. Copyright © 2011 Elsevier Ltd. All rights reserved.

Comparative study of adaptive radiations with an example using parasitic flatworms (Platyhelminthes): Cercomeria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brooks, D.R.; McLennan, D.A.

1993-11-01

Studies of adaptive radiations require robust phylogenies, estimates of species numbers for monophyletic groups within clades, assessments of the adaptive value of putative key innovations, and estimates of the frequency of speciation modes. Four criteria are necessary to identify an adaptive radiation within the parasitic platyhelminths: (1) a group contains significantly more species than its sister group, (2) species richness is apomorphic, (3) apomorphic traits enhance the potential for adaptively driven modes of speciation (sympatric speciation and speciation by peripheral isolation via host switching), and (4) the frequency of adaptively driven speciation modes is high within the group when comparedmore » with data from free-living groups. Only the species-rich Monogenea fulfill all four criteria. The Digenea and Eucestoda also are more species rich than their sister groups, their species richness is derived, and they possess unique characters that increase the potential for host switching to occur. However, because there is not enough information to determine whether the frequency of adaptive modes of speciation is high for those groups, we cannot yet assert that their radiations have been adaptive. 102 refs., 3 figs., 1 tab.« less

Speciation and Elemental Mapping of Metal Containing Aerosols

NASA Astrophysics Data System (ADS)

Fraund, M. W.; Moffet, R.; Harder, T.; Williams, G.; Chen-Wiegart, Y. C. K.; Laskin, A.; Gilles, M. K.; Schoonen, M. A.; Thieme, J.

2017-12-01

Transition metals play a key roles in biogeochemical processes and health effects of aerosols. The Submicron Resolution X-ray (SRX) beamline at the second National Synchrotron Light Source (NSLS-II) can be used to obtain spatially resolved elemental composition using X-ray fluorescence (XRF) as well as element specific molecular information through X-ray absorption near edge structure (XANES) spectroscopy. Here, XANES spectroscopy was used to identify the oxidation state of iron-rich particles collected from the Cape Hedo Observatory on the island of Okinawa, Japan which is subject to aerosols from both biogenic (Gobi desert) and anthropogenic sources (e.g. Beijing and Shanghai). This data was compared with standards to help classify the minerology and source of these aerosol particles with regards to their potential solubility and bioavailability. In another application of the XRF/XANES measurements from NSLS-II, Pb rich particles from Mexico City were probed for distribution and speciation of Pb. Prior study has indicated that elevated concentrations of Pb occur in an industrialized section of northern Mexico City. It has been established that Pb and Zn are internally mixed in atmospheric aerosol and that Zn primarily exists as ZnCl2 and Zn(NO3)2. Based on these observations, it is hypothesized that Pb also exists as PbCl2 and Pb(NO3)­2. In this study it is shown that X-ray absorption near edge structure (XANES) spectroscopy at the Pb L-edge supports Pb being present as PbCl2 and Pb(NO3)2. Submicron resolution X-ray fluorescence mapping is also used to provide complimentary information on the collocation of other high-Z elements.

Nickel and manganese transfer from soil to plant in lateritic mining soils from New Caledonia

NASA Astrophysics Data System (ADS)

Pouschat, P.; Rose, J.; Alliot, I.; Dominici, C.; Keller, C.; Laffont-Schwob, I.; Olivi, L.; Ambrosi, J.-P.

2009-04-01

New Caledonian ferritic soils (more than 50 % of iron) are naturally rich in metals (chromium, nickel, cobalt, and manganese), deficient in major nutrients (nitrogen, phosphorous, and potassium), and unbalanced for the calcium/magnesium ratio. Under these particular ecological conditions, New Caledonia, recognized as a hot-spot of biodiversity, is a natural laboratory to study and understand the adaptation strategies of plants to metalliferous soils, and particularly the tolerance and (hyper)accumulation of metals by plants. Moreover, understanding such mechanisms is essential to develop rehabilitation or phytoremediation techniques for polluted soils, as well as phytomining techniques. Thus, in order to understand the soil - plant relationship and metal mobility along a toposequence in a future nickel mining massif, field experiments were conducted in an isolated ultramafic massif of New Caledonia. Several plant species of two endemic and frequent plant genera were chosen: Tristaniopsis guillainii and T. calobuxus (Myrtaceae), and Phyllanthus serpentinus and P. favieri (Euphorbiaceae), because of their nickel and/or manganese accumulating or hyperaccumulating nature. Leaves, twigs, and roots of all plants were collected along the soil sequence and their associated rhizospheric and bulk soils were sampled. Next, a series of characterization techniques were adapted and then coupled to cryogenics. The combined use of those multiple techniques (cryo-microtomy, cryo-SEM, µXRF, cryo-XAS, and soil characterization) allowed to study co-location and speciation of nickel and manganese in the different plant organs and soils (rhizospheric and bulk). Bioaccumulated nickel and manganese had different distribution patterns. In leaves, Ni accumulated in non photosynthetic tissues (e.g. epidermis) whereas Mn preferentially accumulated in mesophyll whatever the plant species. Nevertheless, in spite of a different speciation in soils, nickel and manganese were both found as similar divalent organometallic complexes in the different plant parts.

The reality and importance of founder speciation in evolution.

PubMed

Templeton, Alan R

2008-05-01

A founder event occurs when a new population is established from a small number of individuals drawn from a large ancestral population. Mayr proposed that genetic drift in an isolated founder population could alter the selective forces in an epistatic system, an observation supported by recent studies. Carson argued that a period of relaxed selection could occur when a founder population is in an open ecological niche, allowing rapid population growth after the founder event. Selectable genetic variation can actually increase during this founder-flush phase due to recombination, enhanced survival of advantageous mutations, and the conversion of non-additive genetic variance into additive variance in an epistatic system, another empirically confirmed prediction. Templeton combined the theories of Mayr and Carson with population genetic models to predict the conditions under which founder events can contribute to speciation, and these predictions are strongly confirmed by the empirical literature. Much of the criticism of founder speciation is based upon equating founder speciation to an adaptive peak shift opposed by selection. However, Mayr, Carson and Templeton all modeled a positive interaction of selection and drift, and Templeton showed that founder speciation is incompatible with peak-shift conditions. Although rare, founder speciation can have a disproportionate importance in adaptive innovation and radiation, and examples are given to show that "rare" does not mean "unimportant" in evolution. Founder speciation also interacts with other speciation mechanisms such that a speciation event is not a one-dimensional process due to either selection alone or drift alone. (c) 2008 Wiley Periodicals, Inc.

In Vitro Model To Assess Arsenic Bioaccessibility and Speciation in Cooked Shrimp.

PubMed

Chi, Haifeng; Zhang, Youchi; Williams, Paul N; Lin, Shanna; Hou, Yanwei; Cai, Chao

2018-05-09

Shrimp, a popular and readily consumed seafood, contains high concentrations of arsenic. However, few studies have focused on whether arsenic in the shrimp could be transformed during the cooking process and gastrointestinal digestion. In this study, a combined in vitro model [Unified Bioaccessibility Research Group of Europe (BARGE) Method-Simulator of Human Intestinal Microbial Ecosystem (UBM-SHIME)] was used to investigate arsenic bioaccessibility and its speciation in raw and cooked shrimps. The results showed that the cooking practices had little effect on the arsenic content and speciation. Bioaccessibility of arsenic in raw shrimp was at a high level, averaging 76.9 ± 4.28 and 86.7 ± 3.74% in gastric and small intestinal phases, respectively. Arsenic speciation was stable in all of the shrimp digestions, with nontoxic arsenobetaine (AsB) being the dominated speciation. The cooking practice significantly increased the bioaccessibility of arsenate ( p < 0.05) in shrimp digests, indicating the increase of the potential health risks.

Genomic islands of divergence are not affected by geography of speciation in sunflowers.

PubMed

Renaut, S; Grassa, C J; Yeaman, S; Moyers, B T; Lai, Z; Kane, N C; Bowers, J E; Burke, J M; Rieseberg, L H

2013-01-01

Genomic studies of speciation often report the presence of highly differentiated genomic regions interspersed within a milieu of weakly diverged loci. The formation of these speciation islands is generally attributed to reduced inter-population gene flow near loci under divergent selection, but few studies have critically evaluated this hypothesis. Here, we report on transcriptome scans among four recently diverged pairs of sunflower (Helianthus) species that vary in the geographical context of speciation. We find that genetic divergence is lower in sympatric and parapatric comparisons, consistent with a role for gene flow in eroding neutral differences. However, genomic islands of divergence are numerous and small in all comparisons, and contrary to expectations, island number and size are not significantly affected by levels of interspecific gene flow. Rather, island formation is strongly associated with reduced recombination rates. Overall, our results indicate that the functional architecture of genomes plays a larger role in shaping genomic divergence than does the geography of speciation.

SPECIATE and using the Speciation Tool to prepare VOC and PM chemical speciation profiles for air quality modeling

EPA Science Inventory

This product provides training to air pollution inventory and modeling professionals to understand the US EPA's SPECIATE database base and Speciation Tool and their use to develop speciated emission inventories.

SPECIATE's VOC and PM Speciation Profiles and Their use to Prepare for Air quality Modeling (2017 EIC)

EPA Pesticide Factsheets

This training provides general concepts on chemical speciation, the SPECIATE database and browser, and how to use the Speciation Tool to create model ready speciation inputs for a photochemical air quality model.

SPECIATE 4.2: speciation Database Development Documentation

EPA Science Inventory

SPECIATE is the U.S. Environmental Protection Agency's (EPA) repository of volatile organic gas and particulate matter (PM) speciation profiles of air pollution sources. Among the many uses of speciation data, these source profiles are used to: (1) create speciated emissions inve...

Ephemeral ecological speciation and the latitudinal biodiversity gradient.

PubMed

Cutter, Asher D; Gray, Jeremy C

2016-10-01

The richness of biodiversity in the tropics compared to high-latitude parts of the world forms one of the most globally conspicuous patterns in biology, and yet few hypotheses aim to explain this phenomenon in terms of explicit microevolutionary mechanisms of speciation and extinction. We link population genetic processes of selection and adaptation to speciation and extinction by way of their interaction with environmental factors to drive global scale macroecological patterns. High-latitude regions are both cradle and grave with respect to species diversification. In particular, we point to a conceptual equivalence of "environmental harshness" and "hard selection" as eco-evolutionary drivers of local adaptation and ecological speciation. By describing how ecological speciation likely occurs more readily at high latitudes, with such nascent species especially prone to extinction by fusion, we derive the ephemeral ecological speciation hypothesis as an integrative mechanistic explanation for latitudinal gradients in species turnover and the net accumulation of biodiversity. © 2016 The Author(s). Evolution © 2016 The Society for the Study of Evolution.

Characteristics of arsenic in humic substances extracted from natural organic sediments.

PubMed

Hara, Junko; Norota, Susumu; Kawebe, Yoshishige; Sugita, Hajime; Zhang, Ming

2018-06-01

The stability and dispersion of naturally occurring As have been receiving increasing attention, because As is toxic and its contamination is a widespread problem in many countries. This study investigated As fractionation and speciation in organic sediments collected from different depositional settings to elucidate the existence of stable As in humic substances. Eleven organic sediment samples were collected from marine and terrestrial alluvial regions in Hokkaido prefecture, Japan, and the chemical fraction of As and species of humic substances were identified by sequential extraction. In addition, stable As bound in organic matter was evaluated by FT-IR spectroscopy. The As fraction mainly comprised inorganic substances, especially sulfur, iron, and manganese, and terrestrial sediments (lacustrine and inland deposits) were rich in sulfides and Fe and Al (hydr)oxides. When the residual fraction was excluded, the organic fraction of As was higher in seawater sediments than in terrestrial sediments. Among humic substances, cellulose, humic acid, and hydrophilic fulvic acid were clearly associated with As accumulation, and As speciation showed that the As was of organic origin. Cellulose, an organic compound of plant origin, was abundant in As=S and As (III)=O bonds, and As accumulation was higher in sulfur-rich peat sediments, corresponding with the physiological activities of As in plants. Hydrophilic fulvic acid and humic acid in these sediments, originating from small animals and microorganisms in addition to plants, denote higher As contents and abound in As (III, V)=C and C-H, CH 3 bonds even in sulfur-rich sediments. The methylated As bonds reflect the ecological transition of organisms.

Fate of Metals in Relation to Water and Sediment Properties in a Subtropical Lake in Central Himalaya, India.

PubMed

Inaotombi, Shaikhom; Gupta, Prem Kumar

2017-04-01

Lakes of Himalaya are one of the most fragile ecosystems on earth. Tourism and urban development in the upland region strongly affect its water resources. The high rate of sedimentation and organic matter deposition alters the ecological state of sediment bed, which indirectly influences on dynamics of metallic elements. We investigated spatial and temporal variations of water and sediment characteristic in Lake Sattal of Central Himalaya, India. Samples were collected seasonally from four sampling locations from January 2011 to December 2012. Pearson's correlation and Canonical correspondence analysis (CCAs) were applied to examine the dynamics and behaviors of heavy metals. Concentrations of elements were in the order of fluoride (Fl) > zinc (Zn) > copper (Cu) > iron (Fe) > manganese (Mn). Sand size fraction was higher in the littoral zone while clay particle was dominant in the profundal zone of the lake. Dissolved oxygen at sediment-water-interface (SWI) and water temperature were the major factors influencing the dynamics of metallic contents in the water column. Spatially, total organic matter (TOM) was higher in the deeper portion of the lake. Our study revealed that mobility of Fe is temperature-dependent, whereas speciation of Mn and Cu are primarily controlled by the suboxic condition of SWI in organic-rich site. Upland lakes are more vulnerable to anoxic condition and have severe implications on heavy metals speciation. Proper implementation of land use policies and management practices, including stormwater detention, can be integrated into resolving such problems.

Assessing the impact of preload on pyrite-rich sediment and groundwater quality.

PubMed

Karikari-Yeboah, Ohene; Addai-Mensah, Jonas

2017-02-01

Pyrite-rich sediments would, invariably, undergo redox reactions which would lead to acidic aqueous environment containing solubilized toxic metal species. When such sediments are subjected to preload, a technique employed by geotechnical engineers to improve the load-bearing capacity of highly compressible formation, transient flow of pore water, accompanied by acidity transfer, would occur as a response. Despite the concomitant environmental and socio-economic significance, to date, there has been limited interdisciplinary research on the underpinning geotechnical engineering and geo-environmental science issues for pyrite-rich sediments under preload. In this study, we investigate the effect of pyrite-rich sediment pore water transfer under preload surcharge on the receiving environment and the impact on the groundwater speciation and quality. Sediment samples were obtained at close depth intervals from boreholes established within pristine areas and those subjected to the preload application. Soil and pore water samples were subjected to solid/solution speciation, moisture contents, soil pH and the Atterberg Limits' analyses using standard analytical techniques and methods. Standpipes were also installed in the boreholes for groundwater sampling and in situ monitoring of water quality parameters. It is shown that the imposition of preload surcharge over pyritic sediment created a reducing environment rich in SO 4 2- , iron oxide minerals and organic matter. This reducing environment fostered organic carbon catabolism to generate excess pyrite and bicarbonate alkalinity, which would invariably impact adversely on soil quality and plant growth. These were accompanied by increase in pH, dissolved Al, Ca, Mg and K species beneath the surcharge.

Interaction between Digestive Strategy and Niche Specialization Predicts Speciation Rates across Herbivorous Mammals.

PubMed

Tran, Lucy A P

2016-04-01

Biotic and abiotic factors often are treated as mutually exclusive drivers of diversification processes. In this framework, ecological specialists are expected to have higher speciation rates than generalists if abiotic factors are the primary controls on species diversity but lower rates if biotic interactions are more important. Speciation rate is therefore predicted to positively correlate with ecological specialization in the purely abiotic model but negatively correlate in the biotic model. In this study, I show that the positive relationship between ecological specialization and speciation expected from the purely abiotic model is recovered only when a species-specific trait, digestive strategy, is modeled in the terrestrial, herbivorous mammals (Mammalia). This result suggests a more nuanced model in which the response of specialized lineages to abiotic factors is dependent on a biological trait. I also demonstrate that the effect of digestive strategy on the ecological specialization-speciation rate relationship is not due to a difference in either the degree of ecological specialization or the speciation rate between foregut- and hindgut-fermenting mammals. Together, these findings suggest that a biological trait, alongside historical abiotic events, played an important role in shaping mammal speciation at long temporal and large geographic scales.

Fe and S redox states during serpentinite dehydration in subduction settings

NASA Astrophysics Data System (ADS)

Merkulova, Margarita; Munoz, Manuel; Vidal, Olivier; Brunet, Fabrice

2016-04-01

Serpentinite rocks formed by hydrothermal alteration of oceanic peridotites compose ~70% of the oceanic crust (Hacker et al., 2003), which later sinks into subduction zone and experiences metamorphic reactions. Serpentinites carry ~12 wt.% H2O and thereby introduces large amount of water in the upper mantle during dehydration in subduction (Ulmer and Trommsdorff, 1995). In addition, serpentinites are known to contain such minerals as magnetite Fe3O4 and pyrite FeS2 in the amounts of ~5 wt.% (Debret et al., 2014) and 1.5 wt.% (Alt et al., 2013), respectively. During metamorphic reactions speciations of Fe and S are tended to change and affect oxygen fugacity. In turn, oxygen fugacity influences the mobility of fluid mobile elements and metals (Pokrovski and Dubrovinsky 2011). We characterized Fe and S speciation and amount of released water during serpentinite dehydration at different temperature and pressure intervals along a subduction zone. We performed three sets of experiments using piston-cylinder apparatus. Three different starting materials composed of powdered mineral mixtures were used: Fe(III)-antigorite (atg), atg + magnetite, atg + pyrite. Experimental runs were performed at 2 GPa, between 400 and 900°C. Experimental products were first characterized by X-ray diffraction and electron microprobe. Speciation of Fe and S were characterized by X-ray absorption spectroscopy (XANES) at iron and sulfur K-edges. In addition, thermodynamic modeling was applied in this work with constrained thermodynamical data for Fe-bearing antigorite. The results demonstrate the continuous dehydration of serpentinites with the main water releasing domain between 670 and 700°C, which is happening due to breakdown of antigorite. Fe K-edge XANES measurements show that the amount of ferric iron dramatically decreases between 550-650°C, leading to a release of free oxygen in the system. As a result, we show that the first fluids released from the slab dehydration most likely present highly oxidizing properties. At higher P-T conditions, higher amounts of water are released with minor oxygen release. In addition, sulfur is shown to be progressively reduced at temperature 450-500°C due to pyrite to pyrrhotite transition. The reaction of pyrite reduction was observed to happen with sequestration of Fe from silicates and a release of oxygen. Effectively, the presence of sulphides in serpentinites contribute additional oxygen to the fluid, whereas the release of S may be negligible. The detailed study of the evolution of redox conditions during serpentinite dehydration in subduction zones will help constraining, 1) the behavior and mobility, from slab to the upper mantle, of elements of economical interest, as well as 2) the global geochemical cycling of elements. References: 1. Hacker et al. (2003) J. Geophys. Res. 108, article number 2029. 2. Ulmer & Trommsdorff (1995) Science 268, 858-861. 3. Debret et al. (2014) EPSL 400, 206-218. 4. Alt et al. (2013) Lithos 178, 40-54. 5. Pokrovski & Dubrovinsky (2011) Science 331, 1052-1056.

Linking carbon and iron cycles by investigating transport, fate and mineralogy of iron-bearing colloids from peat-draining rivers - Scotland as model for high-latitude rivers

NASA Astrophysics Data System (ADS)

Wood, Deborah; Crocket, Kirsty; Brand, Tim; Stutter, Marc; Wilson, Clare; Schröder, Christian

2016-04-01

Linking carbon and iron cycles by investigating transport, fate and mineralogy of iron-bearing colloids from peat-draining rivers - Scotland as model for high-latitude rivers Wood, D.A¹, Crocket, K², Brand, T², Stutter, M³, Wilson, C¹ & Schröder, C¹ ¹Biological and Environmental Sciences, University of Stirling, Stirling, FK9 4LA ²Scottish Association for Marine Science, University of the Highlands and Islands, Dunbeg, Oban, PA37 1QA ³James Hutton Institute, Craigiebuckler, Aberdeen, AB15 8QH The biogeochemical iron cycle exerts significant control on the carbon cycle¹. Iron is a limiting nutrient in large areas of the world's oceans and its bioavailability controls CO2 uptake by marine photosynthesizing microorganisms. While atmospheric iron inputs to the open ocean have been extensively measured, global river inputs have likely been underestimated because most major world rivers exhibit extensive iron removal by flocculation and sedimentation during seawater mixing. Iron minerals and organic matter mutually stabilise each other², which results in a 'rusty carbon sink' in sediments³ on the one hand but may also enhance transport beyond the salinity gradient on the other. Humic-rich, high latitude rivers have a higher iron-carrying capacity⁴-⁶ but are underrepresented in iron flux calculations. The West Coast sea lochs in Scotland are fed by predominantly peatland drainage catchments, and the rivers entering the sea lochs carry a high load of organic matter. The short distance between many of these catchments and the coastal ocean facilitates source-to-sea research investigating transport, fate and mineralogy of iron-bearing colloids providing a good analogue for similar high latitude fjordic systems. We use SeaFAST+ICP-MS and Mössbauer spectroscopy to survey trace metal concentrations, with emphasis on iron concentrations, speciation and mineralogy, across salinity gradients. In combination with ultra-filtration techniques, this allows determination of the concentrations and chemical composition of different size fractions of iron-organic matter particles and colloids. We are developing new filtering and enrichment protocols to enable the use of Mössbauer spectroscopy in order to close a gap in the understanding of iron mineralogy in sub-micron particles. Here we will present results from a first sampling campaign in Loch Sunart and its tributaries. Acknowledgements: This is a MASTS-funded PhD project (GSS30). Preliminary work was supported by a SAGES PECRE grant to C.S., and a MASTS Visiting Fellowship award (VF41) to K.C. References: 1. Raiswell and Canfield (2012). The Iron Biogeochemical Cycle Past and Present. Geochemical Perspectives 1(1), 1-220. 2. Schröder et al. The biogeochemical iron cycle and astrobiology. Hyperfine Interactions in press. 3. Lalonde et al. (2012). Preservation of organic matter in sediments promoted by iron. Nature 483, 198-200. 4. Batchelli et al. (2010). Evidence for strong but dynamic iron-humic colloidal associations in humic-rich coastal waters. Environ. Sci. Technol., 44, 8485-8490. 5. Krachler et al. (2010). Relevance of peat-draining rivers for the riverine input of dissolved iron into the ocean. Sci. Total Environ., 408, 2402-2408. 6. Pokrovsky et al. (2014). Fate of colloids during estuarine mixing in the Arctic. Ocean Sci., 10, 107-125.

X exceptionalism in Caenorhabditis speciation.

PubMed

Cutter, Asher D

2017-11-13

Speciation genetics research in diverse organisms shows the X-chromosome to be exceptional in how it contributes to "rules" of speciation. Until recently, however, the nematode phylum has been nearly silent on this issue, despite the model organism Caenorhabditis elegans having touched most other topics in biology. Studies of speciation with Caenorhabditis accelerated with the recent discovery of species pairs showing partial interfertility. The resulting genetic analyses of reproductive isolation in nematodes demonstrate key roles for the X-chromosome in hybrid male sterility and inviability, opening up new understanding of the genetic causes of Haldane's rule, Darwin's corollary to Haldane's rule, and enabling tests of the large-X effect hypothesis. Studies to date implicate improper chromatin regulation of the X-chromosome by small RNA pathways as integral to hybrid male dysfunction. Sexual transitions in reproductive mode to self-fertilizing hermaphroditism inject distinctive molecular evolutionary features into the speciation process for some species. Caenorhabditis also provides unique opportunities for analysis in a system with XO sex determination that lacks a Y-chromosome, sex chromosome-dependent sperm competition differences and mechanisms of gametic isolation, exceptional accessibility to the development process and rapid experimental evolution. As genetic analysis of reproductive isolation matures with investigation of multiple pairs of Caenorhabditis species and new species discovery, nematodes will provide a powerful complement to more established study organisms for deciphering the genetic basis of and rules to speciation. © 2017 John Wiley & Sons Ltd.

Geochemical data for mercury, methylmercury, and other constituents in sediments from Englebright Lake, California, 2002

USGS Publications Warehouse

Alpers, Charles N.; Hunerlach, Michael P.; Marvin-DePasquale, Mark C.; Antweiler, Ronald C.; Lasorsa, Brenda K.; De Wild, John F.; Snyder, Noah P.

2006-01-01

Deep coring penetrated the full thickness of material deposited after 1940 at six locations in the reservoir; the cores reached a maximum depth of 32.8 meters below the reservoir floor. At the three deep coring sites closest to Englebright Dam, concentrations of HgT (dry basis) were consistently in the range of 100 to 500 ng/g (nanogram per gram), in sediment dominantly of silt size (median grain size of 0.004 to 0.063 mm [millimeter]). At the deep coring sites located farther upstream, the upper parts of the profile had lower concentrations of HgT, generally ranging from 2 to 100 ng/g, in sediment dominantly of sand size (median grain size from 0.063 to 2 mm). The lower part of the vertical profiles at three upstream coring sites had higher concentrations of HgT than the upper and middle parts of these profiles, and had finer median grain size. The highest median concentration of MeHg (1.1 ng/g) was in the top 2 cm (centimeter) of the shallow box cores. This vertical interval also had the highest value of the ratio of MeHg to HgT, 0.41 percent. Median concentrations of MeHg and median values of MeHg/HgT decreased systematically with depth from 0-4 to 4-8 to 8-12 cm in the shallow cores. However, similar systematic decreases were not observed at the meter scale in the deep cores of the MEM (MEthylMercury) series. The overall median of the ratio MeHg/HgT in the deep cores was 0.25 percent, not much less than the overall median value for the shallow cores (0.33 percent). Mercury-203 radiotracer divalent inorganic mercury (203Hg(II)) was used to determine microbial mercury-methylation potential rates for 11 samples collected from three reservoir locations and various depths in the sediment profile. For the five shallow mercury-methylation subsamples, ancillary geochemical parameters were assayed, including microbial sulfate reduction rates, sulfur speciation (sediment acid volatile sulfide, total reduced sulfur, and pore-water sulfate), iron speciation (sediment acid extractable iron(II), amorphous iron(III), crystalline iron(III) and pore-water iron(II)), pore-water chloride and dissolved organic carbon, and pH, oxidation-reduction potential (Eh) and whole-sediment organic content. The highest potential rates of microbial mercury methylation were measured in shallow (0 to 8 cm depth) sediments (5 to 30 nanograms of mercury per gram dry sediment per day), whereas potential rates for subsamples collected from depths greater than 500 cm were consistently below the detection limit of the radiotracer method (< 0.02 nanogram of mercury per gram dry sediment per day). Chemical analyses of trace and major elements in bed sediment are presented for 202 samples from deep cores from five locations in Englebright Lake. The mean values and standard deviations for selected trace elements were as follows (in micrograms per gram): antimony, 2.4 ? 1.6; arsenic, 69 ? 48; chromium, 134 ? 23; lead, 33 ? 25; and nickel, 87 ? 24. Concentrated samples of heavy-mineral grains, prepared using nine large-volume composite samples from

Fe behavior in iron-bearing phonolitic and pantelleritic melts and its significance for magma dynamics in the volcanic conduits

NASA Astrophysics Data System (ADS)

Borovkov, Nikita; Hess, Kai-Uwe; Fehr, Karl-Thomas; Cimarelli, Corrado; Dingwell, Donald Bruce

2014-05-01

The style of volcanic eruptions is determined entirely by dynamics of magma ascent in conduits. Physical properties of a silicate melt, particulary viscosity, are responsible for fragmentation processes, bubble growth and their ascent, which are in their turn related to explosivity of eruptions. Therefore, comprehension of the macroscopic properties of silicate melts is required for adequate conduit modelling. Considering eruptions of Mt. Vesuvius, Italy, we observe that eruption style varies from strombolian to plinean and sub-plinean which is related to the changes of melts viscosity in conduits. At Vesuvius the composition of volcanic deposits (III phase) is mainly phonolitic with 5 - 8 wt. % FeO. Fe changes the valence and coordination depending on oxidation state. The changing of iron coordination causes increasing or decreasing viscosity because of the presence of higher or lower amounts of Fe species coordinated with stronger covalence bonds. Mossbauer spectra of iron-bearing natural pantelleritic and phonolitic glasses were studied to get data on speciation and coordination state of iron. Mössbauer spectroscopy measures hyperfine interactions (isomer shift (IS)) and quadrupole splitting (QS)) at Fe atoms embedded in glass structure, which provide the amount of ferric and ferrous iron and their coordination state depending on Redox conditions. Based on these data, we have considered redox-viscosity relationships and also iron coordination effects on viscosity of both mentioned natural melt compositions. For glasses, due to short range order, the Mössbauer spectra were fitted using mathematical procedures based on functional analysis (extended Voight lineshape included in "Recoil" and "Mosslab" software). Mössbauer spectra are deconvoluted in two sites: ferrous iron (IS=0,79-1,00 mm/s; QS= 1,78-2,25 mm/s) and ferric iron (IS=0,26-0,50 mm/s; QS= 0,75-0,95 mm/s). For both sites we observe that IS and QS gradually decrease towards more oxidized conditions. From functional analysis of Mössbauer spectra this increasing is due to transformation of iron coordination: Fe2+ [5]-Fe2+ [4] and Fe3+ [5]-Fe3+ [4], depending on Redox conditions. XANES data helps us to prove coordination transformation of Fe clearly. This methods (Giuli et al., 2011) reveal that Fe3+ is always in tetrahedral coordination and Fe2+ is in the form of both [4] and [5] species. The presence of minor [5] or even [6] cannot be excluded. Combining Mössbauer and XANES methods, we can suggest that more reduced samples include more high coordinated Fe species. Under oxidized conditions Fe3+ tends to be [4] - coordinated completely and amount of Fe2+ [5] decreases. Viscosity for phonolitic and pantelleritic melts increases as well with more oxidized conditions, suggesting more polymerized structure. Under reduced conditions, low viscosity means that some higher coordinated Fe2+ and Fe3+ sites occur in structure and function as a depolymerizing factor. Therefore, in the presence of iron-bearing peralkaline melts, the prediction of an eruptive style requires knowledge of the dependence of viscosity on thermodynamic parameters as well as dependence on RedOx conditions, which are responsible for ferric and ferrous iron structural transformations.

Source apportionment of settleable particles in an impacted urban and industrialized region in Brazil.

PubMed

Santos, Jane Meri; Reis, Neyval Costa; Galvão, Elson Silva; Silveira, Alexsander; Goulart, Elisa Valentim; Lima, Ana Teresa

2017-09-01

Settleable particulate matter (SPM), especially coarser particles with diameters greater than 10 μm, has been found culprit of high deposition rates in cities affected by hinterland industrial activities. This is the case of Metropolitan Region of Vitoria (MRV), Espirito Santo, Brazil where industrial facilities are located within the urban sprawl and building constructions are intense. Frequent population complaints to the environmental protection agency (IEMA) throughout the years have triggered monitoring campaigns to determine SPM deposition rates and source apportionment. Eight different locations were monitored throughout the MRV, and SPM was quantified and chemically characterized. Sources profiles were defined either by using US EPA SPECIATE data or by experimental analysis. Atmospheric fallout in the MRV ranged between 2 and 20g/(m 2 30-day), with only one monitoring station ranging from 6-10 g/(m 2 30-day). EC, OC, Fe, Al, and Si were found the main constituents of dry deposition in the region. Source apportionment by the chemical mass balance (CMB) model determined that steel and iron ore pelletizing industries were the main contributor to one of the eight locations whereas resuspension, civil construction, and vehicular sources were also very important contributors to the other stations. Quarries and soil were also considered expressive SPM sources, but at the city periphery. CMB model could differentiate contributions from six industrial source groups: thermoelectric; iron ore, pellet, and pellet furnaces; coal coke and coke oven; sintering, blast furnace, and basic oxygen furnace; and soil, resuspension, and vehicles. However, the CMB model was unable to differentiate between iron ore and pellet stockpiles which are present in both steel and iron ore pelletizing industries. Further characterization of source and SPM might be necessary to aid local authorities in decision-making regarding these two industrial sources.

New analytic results for speciation times in neutral models.

PubMed

Gernhard, Tanja

2008-05-01

In this paper, we investigate the standard Yule model, and a recently studied model of speciation and extinction, the "critical branching process." We develop an analytic way-as opposed to the common simulation approach-for calculating the speciation times in a reconstructed phylogenetic tree. Simple expressions for the density and the moments of the speciation times are obtained. Methods for dating a speciation event become valuable, if for the reconstructed phylogenetic trees, no time scale is available. A missing time scale could be due to supertree methods, morphological data, or molecular data which violates the molecular clock. Our analytic approach is, in particular, useful for the model with extinction, since simulations of birth-death processes which are conditioned on obtaining n extant species today are quite delicate. Further, simulations are very time consuming for big n under both models.

Monte Carlo simulations of parapatric speciation

NASA Astrophysics Data System (ADS)

Schwämmle, V.; Sousa, A. O.; de Oliveira, S. M.

2006-06-01

Parapatric speciation is studied using an individual-based model with sexual reproduction. We combine the theory of mutation accumulation for biological ageing with an environmental selection pressure that varies according to the individuals geographical positions and phenotypic traits. Fluctuations and genetic diversity of large populations are crucial ingredients to model the features of evolutionary branching and are intrinsic properties of the model. Its implementation on a spatial lattice gives interesting insights into the population dynamics of speciation on a geographical landscape and the disruptive selection that leads to the divergence of phenotypes. Our results suggest that assortative mating is not an obligatory ingredient to obtain speciation in large populations at low gene flow.

Song evolution, speciation, and vocal learning in passerine birds.

PubMed

Mason, Nicholas A; Burns, Kevin J; Tobias, Joseph A; Claramunt, Santiago; Seddon, Nathalie; Derryberry, Elizabeth P

2017-03-01

Phenotypic divergence can promote reproductive isolation and speciation, suggesting a possible link between rates of phenotypic evolution and the tempo of speciation at multiple evolutionary scales. To date, most macroevolutionary studies of diversification have focused on morphological traits, whereas behavioral traits─including vocal signals─are rarely considered. Thus, although behavioral traits often mediate mate choice and gene flow, we have a limited understanding of how behavioral evolution contributes to diversification. Furthermore, the developmental mode by which behavioral traits are acquired may affect rates of behavioral evolution, although this hypothesis is seldom tested in a phylogenetic framework. Here, we examine evidence for rate shifts in vocal evolution and speciation across two major radiations of codistributed passerines: one oscine clade with learned songs (Thraupidae) and one suboscine clade with innate songs (Furnariidae). We find that evolutionary bursts in rates of speciation and song evolution are coincident in both thraupids and furnariids. Further, overall rates of vocal evolution are higher among taxa with learned rather than innate songs. Taken together, these findings suggest an association between macroevolutionary bursts in speciation and vocal evolution, and that the tempo of behavioral evolution can be influenced by variation in developmental modes among lineages. © 2016 The Author(s). Evolution © 2016 The Society for the Study of Evolution.

Kinetic model to explain the effect of ocean warming and acidification on the Fe(II) oxidation rate in oligotrophic and eutrophic natural waters

NASA Astrophysics Data System (ADS)

González-Dávila, M.; Samperio-Ramos, G.; Santana-Casiano, J. M.; Gonzallez, A. G.; Pérez-Almeida, N.

2016-12-01

The speciation of inorganic Fe(II) as a function of the pH and temperature have been modeled in order to elucidate the inorganic Fe(II) redox behavior over a wide range of scenarios of acidification and global warming of the upper ocean, as well as, changes due to natural ambient fluctuations of pH and temperature. In addition, a kinetic modeling approach has been carried out to elucidate the fractional contribution of most kinetically active Fe(II) species to the overall oxidation rate to improve our future and present knowledge with respect to redox iron chemistry in the marine systems. The kinetic model considers the interactions of Fe(II) with the major ions in seawater, including phosphate and silicate and the competition with copper with the ROS. The model has been applied to the experimental results in order to describe the effect of temperature and pH in the speciation of Fe(II) and to compute the fractional contribution of each Fe(II)-specie to the overall oxidation rate. The oxidation rates (kapp) of nanomolar levels of Fe(II) have been studied in seawater enriched with nutrients (SWEN) in air saturated conditions. The nutrient effect (nitrate, phosphate and silicate), on the oxidation of Fe(II), has been evaluated as a function of pH (7.2-8.2), temperature (5-35 ºC) and salinity (10-37.09). The oxidation of Fe(II) was faster in the presence of nutrient with the change in the Fe(II) oxidation rates (Δlogkapp) more intensive at higher temperatures over the entire pH range studied. From the model it can be observed that the inorganic speciation of Fe(II) is controlled largely by pH, either in SW or in SWEN. A greater presence of Fe-nutrient reactive species (FeH3SiO4+ and FePO4-) in SWEN at higher temperatures explained the changes in the oxidation process. The individual oxidation rates by oxygen, for the Fe(II) most kinetically active species (Fe2+, FeOH+, Fe(OH)2, FeCO3(OH)-, FeCO3, Fe(CO3)22-, FeH3SiO3+, FePO4-), were fitted as a function of the temperature.

Linking patterns and processes of species diversification in the cone flies Strobilomyia (Diptera: Anthomyiidae).

PubMed

Sachet, Jean-Marie; Roques, Alain; Després, Laurence

2006-12-01

Phytophagous insects provide useful models for the study of ecological speciation. Much attention has been paid to host shifts, whereas situations where closely related lineages of insects use the same plant during different time periods have been relatively neglected in previous studies of insect diversification. Flies of the genus Strobilomyia are major pests of conifers in Eurasia and North America. They are specialized feeders in cones and seeds of Abies (fir), Larix (larch) ,and Picea (spruce). This close association is accompanied by a large number of sympatric Strobilomyia species coexisting within each tree genus. We constructed a molecular phylogeny with a 1320 base-pair fragment of mitochondrial DNA that demonstrated contrasting patterns of speciation in larch cone flies, as opposed to spruce and fir cone flies; this despite their comparable geographic distributions and similar resource quality of the host. Species diversity is the highest on larch, and speciation is primarily driven by within-host phenological shifts, followed by allopatric speciation during geographical expansion. By contrast, fewer species exploit spruce and fir, and within-host phenological shifts did not occur. This study illustrates within-host adaptive radiation through phenological shifts, a neglected mode of sympatric speciation.

PARTICLE SPECIATION AND EMISSION PROFILES OF SMALL 2-STROKE ENGINES

EPA Science Inventory

The Human Exposure and Atmospheric Sciences Division (HEASD) conducts studies designed to acquire information from emission sources for use in source apportionment studies. The objective of this work is to characterize a complete, speciated emission profile (PM and air toxics) ...

Aging effect on Zn retention on a calcareous soil: column experiments and synchrotron X-ray micro-spectroscopic investigation.

PubMed

Sayen, Stéphanie; Guillon, Emmanuel

2014-07-15

In this study, a combination of column experiments and micro-analytical techniques exploiting synchrotron generated X-rays was used to assess the effect of aging time on Zn retention and mobility in the specific case of calcareous soils (high pH value, ≈ 8). The samples were subjected to aging for 2, 6, 17, and 63 days. Freshly added Zn mainly existed as an exchangeable form, and this metal fraction decreased over time due to Zn redistribution to stronger binding sites. Thus, after aging for 63 days, 45% of Zn is remobilized from exchangeable sites to stronger binding sites. μ-XRF maps were used to find correlations among elements in the sample, and μ-XANES spectra were recorded to precise Zn speciation. These analyses evidenced an increasing partitioning of Zn from organic matter to iron oxy(hydr)oxides over time. The occurrence of hydrozincite is evidenced in all samples. Copyright © 2014 Elsevier B.V. All rights reserved.

Effect of phosphate on U(VI) sorption to montmorillonite: Ternary complexation and precipitation barriers

NASA Astrophysics Data System (ADS)

Troyer, Lyndsay D.; Maillot, Fabien; Wang, Zheming; Wang, Zimeng; Mehta, Vrajesh S.; Giammar, Daniel E.; Catalano, Jeffrey G.

2016-02-01

Phosphate addition is a potential treatment method to lower the solubility of U(VI) in soil and groundwater systems by causing U(VI) phosphate precipitation as well as enhancing adsorption. Previous work has shown that iron oxide surfaces may facilitate the nucleation of U(VI) phosphate minerals and, that under weakly acidic conditions, phosphate also enhances U(VI) adsorption to such phases. Like iron oxides, clays are important reactive phases in the subsurface but little is known about the interaction of U(VI) and phosphate with these minerals. The effect of aqueous phosphate on U(VI) binding to Wyoming montmorillonite (SWy-2) in air-equilibrated systems was investigated. Equilibrium U(VI) uptake to montmorillonite was determined at pH 4, 6 and 8 at discrete initial phosphate concentrations between 0 and 100 μM. The observed behavior of U(VI) indicates a transition from adsorption to precipitation with increasing total uranium and phosphate concentrations at all pH values. At the highest phosphate concentration examined at each pH value, a barrier to U(VI) phosphate nucleation is observed. At lower concentrations, phosphate has no effect on macroscopic U(VI) adsorption. To assess the mechanisms of U(VI)-phosphate interactions on smectite surfaces, U(VI) speciation was investigated under selected conditions using laser-induced fluorescence spectroscopy (LIFS) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Samples above the precipitation threshold display EXAFS and LIFS spectral signatures consistent with the autunite family of U(VI) phosphate minerals. However, at lower U(VI) concentrations, changes in LIFS spectra upon phosphate addition suggest that U(VI)-phosphate ternary surface complexes form on the montmorillonite surface at pH 4 and 6 despite the lack of a macroscopic effect on adsorption. The speciation of solid-associated U(VI) below the precipitation threshold at pH 8 is dominated by U(VI)-carbonate surface complexes. This work reveals that ternary complexation may occur without a macroscopic signature, which is attributed to phosphate not appreciably binding to smectite in the absence of U(VI), with U(VI) surface complexes serving as the sole reactive surface sites for phosphate. This study shows that phosphate does not enhance U(VI) adsorption to smectite clay minerals, unlike oxide phases, and that a barrier to homogeneous nucleation of U(VI) phosphates was not affected by the presence of the smectite surface.

XAS Studies of Se Speciation in Selenite-Fed Rats

PubMed Central

Weekley, Claire M.; Aitken, Jade B.; Witting, Paul K.; Harris, Hugh H.

2014-01-01

The biological activity of selenium is dependent on its chemical form. Therefore, knowledge of Se chemistry in vivo is required for efficacious use of selenium compounds in disease prevention and treatment. Using X-ray absorption spectroscopy, Se speciation in the kidney, liver, heart, spleen, testis and red blood cells of rats fed control (~0.3 ppm Se) or selenite-supplemented (1 ppm or 5 ppm Se) diets for 3 or 6 weeks, was investigated. X-ray absorption spectroscopy revealed the presence of Se–Se and Se–C species in the kidney and liver, and Se–S species in the kidney, but not the liver. X-ray absorption near edge structure (XANES) spectra showed that there was variation in speciation in the liver and kidneys, but Se speciation was much more uniform in the remaining organs. Using principal component analysis (PCA) to interpret the Se K-edge X-ray absorption spectra, we were able to directly compare the speciation of Se in two different models of selenite metabolism – human lung cancer cells and rat tissues. The effects of Se dose, tissue type and duration of diet on selenium speciation in rat tissues were investigated, and a relationship between the duration of the diet (3 weeks versus 6 weeks) and selenium speciation was observed. PMID:25363824

Application of ESI-HRMS for molybdenum speciation in natural waters: An investigation of molybdate-halide reactions.

PubMed

Dang, Duc Huy; Evans, R Douglas

2018-03-01

High resolution electrospray ionization mass spectrometry (ESI-HRMS) was used to study the speciation of molybdate in interaction with halides (Cl, F, Br). Desolvation during electrospray ionization induced alteration of aqueous species but method optimization successfully suppressed artefact compounds. At low Mo concentrations, chloro(oxo)molybdate and fluoro(oxo)molybdate species were found and in natural samples, MoO 3 Cl was detected for the first time, to the best of our knowledge. Apparent equilibrium constants for Cl substitution on molybdate were calculated for a range of pH values from 4.5 to 8.5. A minor alteration in speciation during the gas phase (conversion of doubly charged MoO 4 2- to HMoO 4 - ) did not allow investigation of the molybdate acid-base properties; however this could be determined by speciation modeling. This study provides further evidence that ESI-HRMS is a fast and suitable tool to Deceasedassess the speciation of inorganic compounds such as Mo. Copyright © 2017 Elsevier B.V. All rights reserved.

Speciation at the Mogollon Rim in the Arizona Mountain Kingsnake (Lampropeltis pyromelana).

PubMed

Burbrink, Frank T; Yao, Helen; Ingrasci, Matthew; Bryson, Robert W; Guiher, Timothy J; Ruane, Sara

2011-09-01

Studies of speciation and taxon delimitation are usually decoupled. Combining these methods provides a stronger theoretical ground for recognizing new taxa and understanding processes of speciation. Using coalescent methods, we examine speciation, post-speciation population demographics, and taxon delimitation in the Arizona Mountain Kingsnake (Lampropeltis pyromelana), a species restricted to high elevations in southwestern United States and northern Mexico (SW). These methods provide a solid foundation for understanding how biogeographic barriers operate at the regional scale in the SW. Bayesian species delimitation methods, using three loci from samples of L. pyromelana taken throughout their range, show strong support for the existence of two species that are separated by low elevation habitats found between the Colorado Plateau/ Mogollon Rim and the Sierra Madre Occidental. Our results suggest an allopatric mode of speciation given the near absence of gene flow over time, which resulted in two lineages of unequal population sizes. Speciation likely occurred prior to the Pleistocene, during the aridification of the SW and/or the uplift of the Colorado Plateau, and while these species occupy similar high-elevation niches, they are isolated by xeric conditions found in the intervening low deserts. Furthermore, post-speciation demographics suggest that populations of both lineages were not negatively impacted by climate change throughout the Pleistocene. Finally, our results suggest that at least for this group, where divergence is old and gene flow is low, Bayesian species delimitation performs well. Copyright © 2011 Elsevier Inc. All rights reserved.

Use of Mössbauer spectroscopy to determine the effect of salinity on the speciation of triorganotins in Anacostia River sediments

NASA Astrophysics Data System (ADS)

Eng, George; Song, Xueqing; May, Leopold

2006-06-01

The speciation of several tributyltin and triphenyltin compounds under varying salinity conditions (0, 20, 40 and 60%) was studied by Mössbauer spectroscopy in both anaerobic and aerobic Anacostia River sediments. The Mössbauer spectral parameters of the spiked sediments indicated that changes in the salinity did not affect the speciation of the tin compounds in either aerobic or anaerobic sediments.

Use of Mössbauer spectroscopy to determine the effect of salinity on the speciation of triorganotins in Anacostia River sediments

NASA Astrophysics Data System (ADS)

Eng, George; Song, Xueqing; May, Leopold

The speciation of several tributyltin and triphenyltin compounds under varying salinity conditions (0, 20, 40 and 60%) was studied by Mössbauer spectroscopy in both anaerobic and aerobic Anacostia River sediments. The Mössbauer spectral parameters of the spiked sediments indicated that changes in the salinity did not affect the speciation of the tin compounds in either aerobic or anaerobic sediments.

Trace metal speciation in natural waters: Computational vs. analytical

USGS Publications Warehouse

Nordstrom, D. Kirk

1996-01-01

Improvements in the field sampling, preservation, and determination of trace metals in natural waters have made many analyses more reliable and less affected by contamination. The speciation of trace metals, however, remains controversial. Chemical model speciation calculations do not necessarily agree with voltammetric, ion exchange, potentiometric, or other analytical speciation techniques. When metal-organic complexes are important, model calculations are not usually helpful and on-site analytical separations are essential. Many analytical speciation techniques have serious interferences and only work well for a limited subset of water types and compositions. A combined approach to the evaluation of speciation could greatly reduce these uncertainties. The approach proposed would be to (1) compare and contrast different analytical techniques with each other and with computed speciation, (2) compare computed trace metal speciation with reliable measurements of solubility, potentiometry, and mean activity coefficients, and (3) compare different model calculations with each other for the same set of water analyses, especially where supplementary data on speciation already exist. A comparison and critique of analytical with chemical model speciation for a range of water samples would delineate the useful range and limitations of these different approaches to speciation. Both model calculations and analytical determinations have useful and different constraints on the range of possible speciation such that they can provide much better insight into speciation when used together. Major discrepancies in the thermodynamic databases of speciation models can be evaluated with the aid of analytical speciation, and when the thermodynamic models are highly consistent and reliable, the sources of error in the analytical speciation can be evaluated. Major thermodynamic discrepancies also can be evaluated by simulating solubility and activity coefficient data and testing various chemical models for their range of applicability. Until a comparative approach such as this is taken, trace metal speciation will remain highly uncertain and controversial.

Speciation of the trivalent f-elements Eu(III) and Cm(III) in digestive media.

PubMed

Wilke, Claudia; Barkleit, Astrid; Stumpf, Thorsten; Ikeda-Ohno, Atsushi

2017-10-01

In case radioactive materials are released into the environment, their incorporation into our digestive system would be a significant concern. Trivalent f-elements, i.e., trivalent actinides and lanthanides, could potentially represent a serious health risk due to their chemo- and radiotoxicity, nevertheless the biochemical behavior of these elements are mostly unknown even to date. This study, therefore, focuses on the chemical speciation of trivalent f-elements in the human gastrointestinal tract. To simulate the digestive system artificial digestive juices (saliva, gastric juice, pancreatic juice and bile fluid) were prepared. The chemical speciation of lanthanides (as Eu(III)) and actinides (as Cm(III)) was determined experimentally by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and the results were compared with thermodynamic modeling. The results indicate a dominant inorganic species with phosphate/carbonate in the mouth, while the aquo ion is predominantly formed with a minor contribution of the enzyme pepsin in the stomach. In the intestinal tract the most significant species are with the protein mucin. We demonstrated the first experimental results on the chemical speciation of trivalent f-elements in the digestive media by TRLFS. The results highlight a significant gap in chemical speciation between experiments and thermodynamic modeling due to the limited availability of thermodynamic stability constants particularly for organic species. Chemical speciation strongly influences the in vivo behavior of metal ions. Therefore, the results of this speciation study will help to enhance the assessment of health risks and to improve decorporation strategies after ingestion of these (radio-)toxic heavy metal ions. Copyright © 2017 Elsevier Inc. All rights reserved.

Evolution of Metallic Trace Elements in Contaminated River Sediments: Geochemical Variation Along River Linear and Vertical Profile

NASA Astrophysics Data System (ADS)

Kanbar, Hussein; Montarges-Pelletier, Emmanuelle; Mansuy-Huault, Laurence; Losson, Benoit; Manceau, Luc; Bauer, Allan; Bihannic, Isabelle; Gley, Renaud; El Samrani, Antoine; Kobaissi, Ahmad; Kazpard, Veronique; Villieras, Frédéric

2015-04-01

Metal pollution in riverine systems poses a serious threat that jeopardizes water and sediment quality, and hence river dwelling biota. Since those metallic pollutants can be transported for long distances via river flow, river management has become a great necessity, especially in times where industrial activities and global climate change are causing metal release and spreading (by flooding events). These changes are able to modify river hydrodynamics, and as a consequence natural physico-chemical status of different aquatic system compartments, which in turn alter metal mobility, availability and speciation. Vertical profiles of sediments hold the archive of what has been deposited for several tenths of years, thus they are used as a tool to study what had been deposited in rivers beds. The studied area lies in the Orne river, northeastern France. This river had been strongly modified physically and affected by steelmaking industrial activities that had boosted in the middle of the last century. This study focuses on several sites along the linear of the Orne river, as well as vertical profiles of sediments. Sediment cores were collected at sites where sedimentation is favoured, and in particular upstream two dams, built in the second half of the XXth century for industrial purposes. Sediment cores were sliced into 2-5cm layers, according to suitability, and analysed for physical and physico-chemical properties, elemental content and mineralogy. Data of the vertical profile in a sediment core is important to show the evolution of sediments as a function of depth, and hence age, in terms of nature, size and constituents. The physical properties include particle size distribution (PSD) and water content. In addition, the physico-chemical properties, such as pH and oxido-reduction potential (ORP) of interstitial water from undisturbed cores were also detected. Total elemental content of sediment and available ones of extracted interstitial waters was detected using ICP-MS and ICP-OES for trace and major elements respectively. Well crystallized minerals were detected by X-Ray Diffraction (XRD), while amorphous and poorly crystallized phases were identified with scanning and transmission electron microscope (SEM and TEM respectively), combined with Energy Dispersive X-Ray Spectroscopy (EDXS). Such microscopic techniques also provided information about metal carriers. To have an insight about the metal speciation at molecular level, X-Ray Absorption spectroscopy (XAS) was performed at Zn K-edge. The first analyses of Orne sediment cores evidenced different particle size distribution and sediment consolidation levels. Yet the cores showed that below a layer of apparently recent sediments (about 10-20 cm), lie highly contaminated ones. Zn and Pb content in deep sediment layers reach several thousands ppm, where they appeared mainly as Zn and Pb sulphides. Also, the high content of iron in deep sediments resulted in the presence of different iron phases: hematite, wuestite, magnetite, goethite, sulphides (pyrite), as well as undefined iron-silicate. In addition, interstitial waters contained high values of available metals (Zn: 500-35000 ppm, Pb: 150-5700 ppm, Cd: 1-10ppm), which might cause a greater concern than solid-bound metals, especially when river bed sediments are disturbed.

Variation of the NMVOC speciation in the solvent sector and the sensitivity of modelled tropospheric ozone

NASA Astrophysics Data System (ADS)

von Schneidemesser, E.; Coates, J.; Denier van der Gon, H. A. C.; Visschedijk, A. J. H.; Butler, T. M.

2016-06-01

Non-methane volatile organic compounds (NMVOCs) are detrimental to human health owing to the toxicity of many of the NMVOC species, as well as their role in the formation of secondary air pollutants such as tropospheric ozone (O3) and secondary organic aerosol. The speciation and amount of NMVOCs emitted into the troposphere are represented in emission inventories (EIs) for input to chemical transport models that predict air pollutant levels. Much of the information in EIs pertaining to speciation of NMVOCs is likely outdated, but before taking on the task of providing an up-to-date and highly speciated EI, a better understanding of the sensitivity of models to the change in NMVOC input would be highly beneficial. According to the EIs, the solvent sector is the most important sector for NMVOC emissions. Here, the sensitivity of modelled tropospheric O3 to NMVOC emission inventory speciation was investigated by comparing the maximum potential difference in O3 produced using a variety of reported solvent sector EI speciations in an idealized study using a box model. The sensitivity was tested using three chemical mechanisms that describe O3 production chemistry, typically employed for different types of modelling scales - point (MCM v3.2), regional (RADM2), and global (MOZART-4). In the box model simulations, a maximum difference of 15 ppbv (ca. 22% of the mean O3 mixing ratio of 69 ppbv) between the different EI speciations of the solvent sector was calculated. In comparison, for the same EI speciation, but comparing the three different mechanisms, a maximum difference of 6.7 ppbv was observed. Relationships were found between the relative contribution of NMVOC compound classes (alkanes and oxygenated species) in the speciations to the amount of Ox produced in the box model. These results indicate that modelled tropospheric O3 is sensitive to the speciation of NMVOCs as specified by emission inventories, suggesting that detailed updates to the EI speciation information would be warranted. Furthermore, modelled tropospheric O3 was also sensitive to the choice of chemical mechanism and further evaluation of both of these sensitivities in more realistic chemical-transport models is needed.

Volcanic and atmospheric controls on ash iron solubility: A review

NASA Astrophysics Data System (ADS)

Ayris, Paul; Delmelle, Pierre

2012-01-01

The ash material produced by volcanic eruptions carries important information about the underground magma eruptive conditions and subsequent modifications in the volcanic plume and during atmospheric transport. Volcanic ash is also studied because of its impacts on the environment and human health. In particular, there is a growing interest from a multidisciplinary scientific community to understand the role that ash deposition over open ocean regions may play as a source of bioavailable Fe for phytoplankton production. Similar to aeolian mineral dust, the processes that affect the mineralogy and speciation of Fe in ash may promote solubilisation of Fe in ash, and thus may increase the amount of volcanic Fe supplied to ocean surface waters. Our knowledge of these controls is still very limited, a situation which has hindered quantitative interpretation of experimental Fe release measurements. In this review, we identify the key volcanic and atmospheric controls that are likely to modulate ash Fe solubility. We also briefly discuss existing data on Fe release from ash and make some recommendations for future studies in this area.

Iron(III) solubility and speciation in aqueous solutions. experimental study and modelling: part 1. hematite solubility from 60 to 300°C in NaOH-NaCl solutions and thermodynamic properties of Fe(OH) 4 -(aq)

NASA Astrophysics Data System (ADS)

Diakonov, Igor I.; Schott, Jacques; Martin, Francois; Harrichourry, Jean-Claude; Escalier, Jocelyne

1999-08-01

The solubility of natural and synthetic hematite (α-Fe 2O 3) was measured in NaOH-NaCl solutions (0.007 ≤ m(NaOH) ≤ 2.0) between 60 and 300°C at saturated water vapour pressure and under excess oxygen. Solubility constants determined in the present study and by Yishan et al. (1986) at 300°C were combined with the thermodynamic properties of hematite (Hemingway, 1990) and water (SUPCRT92, Johnson et al., 1992) to generate within the framework of the revised Helgeson-Kirkham-Flowers (HKF) model the standard partial molal thermodynamic properties at 25°C and 1 bar, and the revised HKF equations of state parameters of Fe(OH) 4 -. The extrapolated value for the Gibbs energy of formation for Fe(OH) 4 - at 25°C is -201.97 kcal/mol. Thermodynamic calculations show that Fe(OH) 4 - exhibits a chemical behaviour different from that of Ga(OH) 4 - and Al(OH) 4 -.

Chemical fractionation of heavy metals in urban soils of Guangzhou, China.

PubMed

Lu, Ying; Zhu, Feng; Chen, Jie; Gan, Haihua; Guo, Yanbiao

2007-11-01

Knowledge of the total concentration of heavy metals is not enough to fully assess the environmental impact of urban soils. For this reason, the determination of metal speciation is important to evaluate their environment and the mobilization capacity. Sequential extraction technique proposed by the former European Community Bureau of Reference (BCR) was used to speciate Cd, Cu, Fe, Mn, Ni, Pb, and Zn in urban soils from Guangzhou into four operationally defined fractions: HOAc extractable, reducible, oxidizable, and residual. The Cu, Fe, Ni, and Zn were predominantly located in the residual fraction, Pb in the reducible fraction, and Cd and Mn within the HOAc extractable fraction. The order of Cd in each fraction was generally HOAc extractable > reducible > residual > oxidizable; Cu and Fe were residual > reducible > oxidizable > HOAc extractable; Mn was HOAc extractable > residual > reducible > oxidizable; Ni and Zn were residual > reducible > HOAc extractable > oxidizable; and Pb was reducible > residual > oxidizable > HOAc extractable. Cadmium was identified as being the most mobile of the elements, followed by Mn, Zn, Ni, Cu, Pb and Fe. Iron-Mn oxides can play an important role in binding Cd, Cu, Ni, Pb, and Zn and in decreasing their proportion associated with the residual fraction in the soils. With total concentrations of Cd, Cu, Ni, Pb, Zn, and Mn increase, these metals more easily release and may produce more negative effects on the urban environment.

End-of-life nickel-cadmium accumulators: characterization of electrode materials and industrial Black Mass.

PubMed

Hazotte, Claire; Leclerc, Nathalie; Diliberto, Sébastien; Meux, Eric; Lapicque, Francois

2015-01-01

The aim of this paper is the characterization of spent NiCd batteries and the characterization of an industrial Black Mass obtained after crushing spent NiCd batteries and physical separation in a treatment plant. The characterization was first performed with five cylindrical NiCd batteries which were manually dismantled. Their characterization includes mass balance of the components, active powders elemental analysis and phase identification by X-ray powder diffraction. Chemical speciation of the two metals was also investigated. For cadmium, speciation was previously developed on solid synthetic samples. In a spent battery, the active powders correspond to about 43% of the battery weight. The other components are the separator and polymeric pieces (5%), the support plates (25%) and the carbon steel external case (27%). The sequential procedure shows that the nickel in the positive powders from the dismantled Ni-Cd batteries is distributed between Ni0 (39.7%), Ni(OH)2 (58.5%) and NiOOH (1.8%). Cadmium in the negative powder is about 99.9% as the Cd(OH)2 form with 0.1% of metal cadmium. In the industrial Black Mass, the distribution of cadmium is the same, whereas the distribution of nickel is Ni0 (46.9%), Ni(OH)2 (43.2%) and NiOOH (9.9%). This material contains also 1.8% cobalt and approx. 1% iron.

Speciation in Metal Toxicity and Metal-Based Therapeutics

PubMed Central

Templeton, Douglas M.

2015-01-01

Metallic elements, ions and compounds produce varying degrees of toxicity in organisms with which they come into contact. Metal speciation is critical to understanding these adverse effects; the adjectives “heavy” and “toxic” are not helpful in describing the biological properties of individual elements, but detailed chemical structures are. As a broad generalization, the metallic form of an element is inert, and the ionic salts are the species that show more significant bioavailability. Yet the salts and other chelates of a metal ion can give rise to quite different toxicities, as exemplified by a range of carcinogenic potential for various nickel species. Another important distinction comes when a metallic element is organified, increasing its lipophilicity and hence its ability to penetrate the blood brain barrier, as is seen, for example, with organic mercury and tin species. Some metallic elements, such as gold and platinum, are themselves useful therapeutic agents in some forms, while other species of the same element can be toxic, thus focusing attention on species interconversions in evaluating metal-based drugs. The therapeutic use of metal-chelating agents introduces new species of the target metal in vivo, and this can affect not only its desired detoxification, but also introduce a potential for further mechanisms of toxicity. Examples of therapeutic iron chelator species are discussed in this context, as well as the more recent aspects of development of chelation therapy for uranium exposure. PMID:29056656

Visualizing speciation in artificial cichlid fish.

PubMed

Clement, Ross

2006-01-01

The Cichlid Speciation Project (CSP) is an ALife simulation system for investigating open problems in the speciation of African cichlid fish. The CSP can be used to perform a wide range of experiments that show that speciation is a natural consequence of certain biological systems. A visualization system capable of extracting the history of speciation from low-level trace data and creating a phylogenetic tree has been implemented. Unlike previous approaches, this visualization system presents a concrete trace of speciation, rather than a summary of low-level information from which the viewer can make subjective decisions on how speciation progressed. The phylogenetic trees are a more objective visualization of speciation, and enable automated collection and summarization of the results of experiments. The visualization system is used to create a phylogenetic tree from an experiment that models sympatric speciation.

Chemical Speciation and Metallomics.

PubMed

de Jesus, Jemmyson Romário; da Costa, Luana Ferreira; Lehmann, Eraldo Luiz; Galazzi, Rodrigo Moretto; Madrid, Katherine Chacón; Arruda, Marco Aurélio Zezzi

2018-01-01

Chemical speciation approaches is an inherent part of metallomics, once metals/metalloids and organic structures need to be currently evaluated for attaining metallomics studies. Then, this chapter focuses on the applications of the chemical speciation applied to the human health risk, food and human diet, drugs, forensic, nanoscience, and geological metallomics, also pointing out the advances in such area. Some aspects regarding sample preparation is commented along this chapter, and some strategies for maintaining the integrity of the metallomics information are also emphasized.

Hybrid Speciation in a Marine Mammal: The Clymene Dolphin (Stenella clymene)

PubMed Central

Amaral, Ana R.; Lovewell, Gretchen; Coelho, Maria M.; Amato, George; Rosenbaum, Howard C.

2014-01-01

Natural hybridization may result in the exchange of genetic material between divergent lineages and even the formation of new taxa. Many of the Neo-Darwinian architects argued that, particularly for animal clades, natural hybridization was maladaptive. Recent evidence, however, has falsified this hypothesis, instead indicating that this process may lead to increased biodiversity through the formation of new species. Although such cases of hybrid speciation have been described in plants, fish and insects, they are considered exceptionally rare in mammals. Here we present evidence for a marine mammal, Stenella clymene, arising through natural hybridization. We found phylogenetic discordance between mitochondrial and nuclear markers, which, coupled with a pattern of transgressive segregation seen in the morphometric variation of some characters, support a case of hybrid speciation. S. clymene is currently genetically differentiated from its putative parental species, Stenella coerueloalba and Stenella longisrostris, although low levels of introgressive hybridization may be occurring. Although non-reticulate forms of evolution, such as incomplete lineage sorting, could explain our genetic results, we consider that the genetic and morphological evidence taken together argue more convincingly towards a case of hybrid speciation. We anticipate that our study will bring attention to this important aspect of reticulate evolution in non-model mammal species. The study of speciation through hybridization is an excellent opportunity to understand the mechanisms leading to speciation in the context of gene flow. PMID:24421898

Hybrid speciation in a marine mammal: the clymene dolphin (Stenella clymene).

PubMed

Amaral, Ana R; Lovewell, Gretchen; Coelho, Maria M; Amato, George; Rosenbaum, Howard C

2014-01-01

Natural hybridization may result in the exchange of genetic material between divergent lineages and even the formation of new taxa. Many of the Neo-Darwinian architects argued that, particularly for animal clades, natural hybridization was maladaptive. Recent evidence, however, has falsified this hypothesis, instead indicating that this process may lead to increased biodiversity through the formation of new species. Although such cases of hybrid speciation have been described in plants, fish and insects, they are considered exceptionally rare in mammals. Here we present evidence for a marine mammal, Stenella clymene, arising through natural hybridization. We found phylogenetic discordance between mitochondrial and nuclear markers, which, coupled with a pattern of transgressive segregation seen in the morphometric variation of some characters, support a case of hybrid speciation. S. clymene is currently genetically differentiated from its putative parental species, Stenella coerueloalba and Stenella longisrostris, although low levels of introgressive hybridization may be occurring. Although non-reticulate forms of evolution, such as incomplete lineage sorting, could explain our genetic results, we consider that the genetic and morphological evidence taken together argue more convincingly towards a case of hybrid speciation. We anticipate that our study will bring attention to this important aspect of reticulate evolution in non-model mammal species. The study of speciation through hybridization is an excellent opportunity to understand the mechanisms leading to speciation in the context of gene flow.

Heavy metal contamination of the soils used for stocking raw materials in the former ILVA iron-steel industrial plant of Bagnoli (southern Italy).

PubMed

Adamo, P; Arienzo, M; Bianco, M R; Terribile, F; Violante, P

2002-08-05

The total contents and the chemical and mineralogical forms of the metals Fe, Al, Cu, Co, Cr, Pb, Zn, Ni and Mn in the horizons of a soil profile, representative of an area devoted to stocking raw materials in the dismantled iron-steel industrial plant of ILVA of Bagnoli (Naples), were studied by physical and chemical methods. The geological setting of the study area is the result of volcanic activity in the Phlegrean Fields, a group of polygenic volcanoes to the west of Naples, which give rise to the parent soil material. Soil morphology appeared to be strongly disturbed by the occurrence and stratification of materials used in the industrial process. Fine sediments illuviation down the profile resulted in the occurrence of silt and clay coatings. The total contents of Cu, Co, Cr, Pb, Zn and Ni, in the whole soil samples, especially in the surface layers, were above the regulatory levels (Cu 120, Co 20, Cr 150, Pb 100, Zn 150, Ni 120 mg kg(-1)) stated by the Italian Ministry of Environment for soils in public, private and residential areas, and below the levels (Cu 600, Co 250, Cr 800, Pb 1000, Zn 1500, Ni 500 mg kg(-1)) outlined for soils and subsoils of industrial and commercial areas (Gazzetta Ufficiale della Repubblica Italiana, 1999). Speciation of heavy metals and the determination of the different chemical pools in the fraction < 2 mm identified the large presence of elements trapped in the mineralogical structure of oxides and silicates and occluded in easily reducible manganese or iron oxides. A constant amount of Cu was associated with organic compounds. A significant amount of Zn (> 20%) was extracted in diluted acetic acid solution, indicating that the element was present in a more readily and potentially available form. In the clay fraction (< 2 microm) heavy metals were associated with both amorphous and crystalline iron forms. The presence of iron-rich clay coatings was evident in the illuvial pores of deeper horizons. Enrichment in Cu, Co, Cr and Zn of the coatings was observed. Possible translocation of metals down through the soil profile mainly bound to fine particles of relatively inert forms of iron is hypothesised. The dispersion in water of the clay fraction resulted in an average percentage dispersion of approximately 20% with a peak of 41.7% at 68-72 cm depth. Magnetite, goethite, hematite, calcite and quartz mixed with K-feldspars, clynopyroxenes and mica occurred in the coarse sand fractions (2-0.2 mm) of the soil samples from all the surface horizons. Talcum and goethite together with clay minerals at 1.4 nm, kaolinite and illite were found in the clays (< 2 microm).

Comparative tests of the role of dewlap size in Anolis lizard speciation

PubMed Central

Harrison, Alexis; Mahler, D. Luke; Castañeda, María del Rosario; Glor, Richard E.; Herrel, Anthony; Stuart, Yoel E.; Losos, Jonathan B.

2016-01-01

Phenotypic traits may be linked to speciation in two distinct ways: character values may influence the rate of speciation or diversification in the trait may be associated with speciation events. Traits involved in signal transmission, such as the dewlap of Anolis lizards, are often involved in the speciation process. The dewlap is an important visual signal with roles in species recognition and sexual selection, and dewlaps vary among species in relative size as well as colour and pattern. We compile a dataset of relative dewlap size digitized from photographs of 184 anole species from across the genus' geographical range. We use phylogenetic comparative methods to test two hypotheses: that larger dewlaps are associated with higher speciation rates, and that relative dewlap area diversifies according to a speciational model of evolution. We find no evidence of trait-dependent speciation, indicating that larger signals do not enhance any role the dewlap has in promoting speciation. Instead, we find a signal of mixed speciational and gradual trait evolution, with a particularly strong signal of speciational change in the dewlaps of mainland lineages. This indicates that dewlap size diversifies in association with the speciation process, suggesting that divergent selection may play a role in the macroevolution of this signalling trait. PMID:28003450

Expanding the Therapeutic Potential of the Iron Chelator Deferasirox in the Development of Aqueous Stable Ti(IV) Anticancer Complexes.

PubMed

Loza-Rosas, Sergio A; Vázquez-Salgado, Alexandra M; Rivero, Kennett I; Negrón, Lenny J; Delgado, Yamixa; Benjamín-Rivera, Josué A; Vázquez-Maldonado, Angel L; Parks, Timothy B; Munet-Colón, Charlene; Tinoco, Arthur D

2017-07-17

The recent X-ray structure of titanium(IV)-bound human serum transferrin (STf) exhibiting citrate as a synergistic anion reveals a difference in Ti(IV) coordination versus iron(III), the metal endogenously delivered by the protein to cells. This finding enriches our bioinspired drug design strategy for Ti(IV)-based anticancer therapeutics, which applies a family of Fe(III) chelators termed chemical transferrin mimetic (cTfm) ligands to inhibit Fe bioavailability in cancer cells. Deferasirox, a drug used for iron overload disease, is a cTfm ligand that models STf coordination to Fe(III), favoring Fe(III) binding versus Ti(IV). This metal affinity preference drives deferasirox to facilitate the release of cytotoxic Ti(IV) intracellularly in exchange for Fe(III). An aqueous speciation study performed by potentiometric titration from pH 4 to 8 with micromolar levels of Ti(IV) deferasirox at a 1:2 ratio reveals exclusively Ti(deferasirox) 2 in solution. The predominant complex at pH 7.4, [Ti(deferasirox) 2 ] 2- , exhibits the one of the highest aqueous stabilities observed for a potent cytotoxic Ti(IV) species, demonstrating little dissociation even after 1 month in cell culture media. UV-vis and 1 H NMR studies show that the stability is unaffected by the presence of biomolecular Ti(IV) binders such as citrate, STf, and albumin, which have been shown to induce dissociation or regulate cellular uptake and can alter the activity of other antiproliferative Ti(IV) complexes. Kinetic studies on [Ti(deferasirox) 2 ] 2- transmetalation with Fe(III) show that a labile Fe(III) source is required to induce this process. The initial step of this process occurs on the time scale of minutes, and equilibrium for the complete transmetalation is reached on a time scale of hours to a day. This work reveals a mechanism to deliver Ti(IV) compounds into cells and trigger Ti(IV) release by a labile Fe(III) species. Cellular studies including other cTfm ligands confirm the Fe(III) depletion mechanism of these compounds and show their ability to induce early and late apoptosis.

EPA’s SPECIATE 4.4 Database:Development and Uses

EPA Science Inventory

SPECIATE is the U.S. Environmental Protection Agency's (EPA)repository of volatile organic gas and particulate matter (PM) speciation profiles for air pollution sources. EPA released SPECIATE 4.4 in early 2014 and, in total, the SPECIATE 4.4 database includes 5,728 PM, VOC, total...

EPA’s SPECIATE 4.4 Database: Development and Uses

EPA Science Inventory

SPECIATE is the U.S. Environmental Protection Agency's (EPA)repository of volatile organic gas and particulate matter (PM) speciation profiles for air pollution sources. EPA released SPECIATE 4.4 in early 2014 and, in total, the SPECIATE 4.4 database includes 5,728 PM, VOC, total...

Metal Ion Speciation and Dissolved Organic Matter Composition in Soil Solutions

NASA Astrophysics Data System (ADS)

Benedetti, M. F.; Ren, Z. L.; Bravin, M.; Tella, M.; Dai, J.

2014-12-01

Knowledge of the speciation of heavy metals and the role of dissolved organic matter (DOM) in soil solution is a key to understand metal mobility and ecotoxicity. In this study, soil column-Donnan membrane technique (SC-DMT) was used to measure metal speciation of Cd, Cu, Ni, Pb, and Zn in eighteen soil solutions, covering a wide range of metal sources and concentrations. DOM composition in these soil solutions was also determined. Our results show that in soil solution Pb and Cu are dominant in complex form, whereas Cd, Ni and Zn mainly exist as free ions; for the whole range of soil solutions, only 26.2% of DOM is reactive and consists mainly of fulvic acid (FA). The metal speciation measured by SC-DMT was compared to the predicted ones obtained via the NICA-Donnan model using the measured FA concentrations. The free ion concentrations predicted by speciation modelling were in good agreement with the measurements. Diffusive gradients in thin-films gels (DGT) were also performed to quantify the labile metal species in the fluxes from solid phase to solution in fourteen soils. The concentrations of metal species detected by DGT were compared with the free ion concentrations measured by DMT and the maximum concentrations calculated based on the predicted metal speciation in SC-DMT soil solutions. It is concluded that both inorganic species and a fraction of FA bound species account for the amount of labile metals measured by DGT, consistent with the dynamic features of this technique. The comparisons between measurements using analytical techniques and mechanistic model predictions provided mutual validation in their performance. Moreover, we show that to make accurate modelling of metal speciation in soil solutions, the knowledge of DOM composition is the crucial information, especially for Cu; like in previous studies the modelling of Pb speciation is not optimal and an updated of Pb generic binding parameters is required to reduce model prediction uncertainties.

Rapid radiation in spiny lobsters (Palinurus spp) as revealed by classic and ABC methods using mtDNA and microsatellite data.

PubMed

Palero, Ferran; Lopes, Joao; Abelló, Pere; Macpherson, Enrique; Pascual, Marta; Beaumont, Mark A

2009-11-09

Molecular tools may help to uncover closely related and still diverging species from a wide variety of taxa and provide insight into the mechanisms, pace and geography of marine speciation. There is a certain controversy on the phylogeography and speciation modes of species-groups with an Eastern Atlantic-Western Indian Ocean distribution, with previous studies suggesting that older events (Miocene) and/or more recent (Pleistocene) oceanographic processes could have influenced the phylogeny of marine taxa. The spiny lobster genus Palinurus allows for testing among speciation hypotheses, since it has a particular distribution with two groups of three species each in the Northeastern Atlantic (P. elephas, P. mauritanicus and P. charlestoni) and Southeastern Atlantic and Southwestern Indian Oceans (P. gilchristi, P. delagoae and P. barbarae). In the present study, we obtain a more complete understanding of the phylogenetic relationships among these species through a combined dataset with both nuclear and mitochondrial markers, by testing alternative hypotheses on both the mutation rate and tree topology under the recently developed approximate Bayesian computation (ABC) methods. Our analyses support a North-to-South speciation pattern in Palinurus with all the South-African species forming a monophyletic clade nested within the Northern Hemisphere species. Coalescent-based ABC methods allowed us to reject the previously proposed hypothesis of a Middle Miocene speciation event related with the closure of the Tethyan Seaway. Instead, divergence times obtained for Palinurus species using the combined mtDNA-microsatellite dataset and standard mutation rates for mtDNA agree with known glaciation-related processes occurring during the last 2 my. The Palinurus speciation pattern is a typical example of a series of rapid speciation events occurring within a group, with very short branches separating different species. Our results support the hypothesis that recent climate change-related oceanographic processes have influenced the phylogeny of marine taxa, with most Palinurus species originating during the last two million years. The present study highlights the value of new coalescent-based statistical methods such as ABC for testing different speciation hypotheses using molecular data.

Impact of Fe(III)-OM complexes and Fe(III) polymerization on SOM pools reactivity under different land uses

NASA Astrophysics Data System (ADS)

Giannetta, B.; Plaza, C.; Zaccone, C.; Siebecker, M. G.; Rovira, P.; Vischetti, C.; Sparks, D. L.

2017-12-01

Soil organic matter (SOM) protection and long-term accumulation are controlled by adsorption to mineral surfaces in different ways, depending on its molecular structure and pedo-climatic conditions. Iron (Fe) oxides are known to be key regulators of the soil carbon (C) cycle, and Fe speciation in soils is highly dependent on environmental conditions and chemical interactions with SOM. However, the molecular structure and hydrolysis of Fe species formed in association with SOM is still poorly described. We hypothesize the existence of two pools of Fe which interact with SOM: mononuclear Fe(III)-SOM complexes and precipitated Fe(III) hydroxides. To verify our hypothesis, we investigated the interactions between Fe(III) and physically isolated soil fractions by means of batch experiments at pH 7. Specifically, we examined the fine silt plus clay (FSi+C) fraction, obtained by ultrasonic dispersion and wet sieving. The soil samples spanned several land uses, including coniferous forest (CFS), grassland (GS), technosols (TS) and agricultural (AS) soils. Solid phase products and supernatants were analyzed for C and Fe content. X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) analysis were also performed. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to assess the main C functional groups involved in C complexation and desorption experiments. Preliminary linear combination fitting (LCF) of Fe K-edge extended X-ray absorption fine structure (EXAFS) spectra suggested the formation of ferrihydrite-like polymeric Fe(III) oxides in reacted CFS and GS samples, with higher C and Fe concentration. Conversely, mononuclear Fe(III) OM complexes dominated the speciation for TS and AS samples, characterized by lower C and Fe concentration, inhibiting the hydrolysis and polymerization of Fe (III). This approach will help revealing the mechanisms by which SOM pools can control Fe(III) speciation, and will elucidate how both Fe(III)-OM complexes and Fe(III) polymerization can affect SOM reactivity and, consequently, its mean residence time in different ecosystems.

Specialization of Bacillus in the Geochemically Challenged Environment of Death Valley

NASA Astrophysics Data System (ADS)

Kopac, S.

2014-04-01

Death Valley is the hottest, driest place in North America, a desert with soils containing toxic elements such as boron and lead. While most organisms are unable to survive under these conditions, a diverse community of bacteria survives here. What has enabled bacteria to adapt and thrive in a plethora of extreme and stressful environments where other organisms are unable to grow? The unique environmental adaptations that distinguish ecologically distinct bacterial groups (ecotypes) remain a mystery, in contrast to many animal species (perhaps most notably Darwin's ecologically distinct finch species). We resolve the ecological factors associated with recently diverged ecotypes of the soil bacteria Bacillus subtilis and Bacillus licheniformis, isolated from the dry, geochemically challenging soils of Death Valley, CA. To investigate speciation associated with challenging environmental parameters, we sampled soil transects along a 400m stretch that parallels a decrease in salinity adjacent to a salt flat; transects also encompass gradients in soil B, Cu, Fe, NO3, and P, all of which were quantified in our soil samples. We demarcated strains using Ecotype Simulation, a sequence-based algorithm. Each ecotype's habitat associations were determined with respect to salinity, B, Cu, Fe, NO3, and P. In addition, our sample strains were tested for tolerance of copper, boron and salinity (all known to inhibit growth at high concentrations) by comparing their growth over a 20 hour period. Ecotypes differed in their habitat associations with salinity, boron, copper, iron, and other ecological factors; these environmental dimensions are likely causing speciation of B. subtilis-licheniformis ecotypes at our sample site. Strains also differed in tolerance of boron and copper, providing evidence that our sequence-based demarcations reflect real differences in metabolism. By better understanding the relationship between bacterial speciation and the environment, we can begin to predict the habitability of unexplored extreme and extra-Earth environments.

Authigenic apatite and octacalcium phosphate formation due to adsorption-precipitation switching across estuarine salinity gradients

NASA Astrophysics Data System (ADS)

Oxmann, J. F.; Schwendenmann, L.

2015-02-01

Mechanisms governing phosphorus (P) speciation in coastal sediments remain largely unknown due to the diversity of coastal environments and poor analytical specificity for P phases. We investigated P speciation across salinity gradients comprising diverse ecosystems in a P-enriched estuary. To determine P load effects on P speciation we compared the high P site with a low P site. Octacalcium phosphate (OCP), authigenic apatite (carbonate fluorapatite, CFAP) and detrital apatite (fluorapatite) were quantitated in addition to Al/Fe-bound P (Al/Fe-P) and Ca-bound P (Ca-P). Gradients in sediment pH strongly affected P fractions across ecosystems and independent of the site-specific total P status. We found a pronounced switch from adsorbed Al/Fe-P to mineral Ca-P with decreasing acidity from land to sea. This switch occurred at near-neutral sediment pH and has possibly been enhanced by redox-driven phosphate desorption from iron oxyhydroxides. The seaward decline in Al/Fe-P was counterbalanced by the precipitation of Ca-P. Correspondingly, two location-dependent accumulation mechanisms occurred at the high P site due to the switch, leading to elevated Al/Fe-P at pH < 6.6 (landward; adsorption) and elevated Ca-P at pH > 6.6 (seaward; precipitation). Enhanced Ca-P precipitation by increased P loads was also evident from disproportional accumulation of metastable Ca-P (Ca-Pmeta) at the high P site. Here, sediments contained on average 6-fold higher Ca-Pmeta levels compared with the low P site, although these sediments contained only 2-fold more total Ca-P than the low P sediments. Phosphorus species distributions indicated that these elevated Ca-Pmeta levels resulted from transformation of fertilizer-derived Al/Fe-P to OCP and CFAP in nearshore areas. Formation of CFAP as well as its precursor, OCP, results in P retention in coastal zones and can thus lead to substantial inorganic P accumulation in response to anthropogenic P input.

PM 2.5 CHEMICAL SPECIATION SAMPLER EVALUATION FIELD PROGRAM: RESULTS FROM THE FOUR CITY STUDY

EPA Science Inventory

The objective of this sampler intercomparison field study is to determine the performance characteristics for the collection of the chemical components of PM2.5 by the chemical speciation monitors developed for the national network relative to each other, to the Federal Referen...

A COMPUTATIONAL AND EXPERIMENTAL STUDY OF MERCURY SPECIATION AS FACILITATED BY THE DEACON PROCESS

EPA Science Inventory

The paper gives results of a computational and experimental study of mercury (Hg) speciation as facilitated by the Deacon process. Fly ashes that contain trace cupric or ferric oxide are effective catalysts for elemental mercury (Hg) conversion to mercuric chloride in the presenc...

US EPA's SPECIATE 4.4 Database: Development and Uses

EPA Science Inventory

SPECIATE is the U.S. Environmental Protection Agency’s (EPA) repository of volatile organic gas and particulate matter (PM) speciation profiles of air pollution sources. EPA released SPECIATE 4.4 in early 2014 and, in total, the SPECIATE 4.4 database includes 5,728 PM, volatile o...

EPA’s SPECIATE 4.4 Database: Bridging Data Sources and Data Users

EPA Science Inventory

SPECIATE is the U.S. Environmental Protection Agency's (EPA)repository of volatile organic gas and particulate matter (PM) speciation profiles for air pollution sources. EPA released SPECIATE 4.4 in early 2014 and, in total, the SPECIATE 4.4 database includes 5,728 PM, VOC, total...

Arsenic speciation in rice and risk assessment of inorganic arsenic in Taiwan population.

PubMed

Chen, Hsiu-Ling; Lee, Ching-Chang; Huang, Winn-Jung; Huang, Han-Ting; Wu, Yi-Chen; Hsu, Ya-Chen; Kao, Yi-Ting

2016-03-01

This study assessed the total arsenic content and arsenic speciation in rice to determine the health risks associated with rice consumption in various age-gender subgroups in Taiwan. The average total arsenic levels in white rice and brown rice were 116.6 ± 39.2 and 215.5 ± 63.5 ng/g weight (n = 51 and 13), respectively. The cumulative cancer risk among males was 10.4/100,000. The highest fraction of inorganic/total arsenic content in white rice ranged from 76.9 to 88.2 % and from 81.0 to 96.5 % in brown rice. The current study found different arsenic speciation of rice in southern Taiwan, where the famous blackfoot disease has been reported compared with arsenic speciation from other Taiwan areas. Therefore, rice and other grains should be further monitored in southern Taiwan to evaluate whether arsenic contamination is well controlled in this area.

Modeling Non-Steady Isotopologue and Isotopomer Speciation and Fractionation during Denitrification in Soils

NASA Astrophysics Data System (ADS)

Maggi, F.; Riley, W. J.

2009-12-01

The composition and location of 15N atoms on N2O isotopomers and isotopologues during isotope speciation has been used to characterize soil biological N cycling and N2O surface emissions. Although there exist few experimental observations, no attempt has been made to model N2O isotopomer speciation. The mathematical treatment of biological kinetic reactions in isotopic applications normally makes use of first-order and quasi steady-state complexation assumptions without taking into account changes in enzyme concentration, reaction stoichiometry, and isotopologue and isotopomer speciation. When multiatomic isotopically-labeled reactants are used in a multi-molecurar reaction, these assumptions may fail since they always lead to a constant fractionation factor and cannot describe speciation of isotopologues and isotopomers. We have developed a mathematical framework that is capable of describing isotopologue and isotopmer speciation and fractionation under the assumption of non-steady complexation during biological kinetic reactions that overcome the limitations mentioned above. This framework was applied to a case study of non-steady (variable and inverse) isotopic effects observed during N2O production and consumption in soils. Our mathematical treatment has led to generalized kinetic equations which replicate experimental observations with high accuracy and help interpret non-steady isotopic effects and isotopologue and isotopomer speciation. The kinetic equations introduced and applied here have general validity in describing isotopic effects in any biochemical reactions by considering: changing enzyme concentrations, mass and isotope conservation, and reaction stoichiometry. The equations also describe speciation of any isotopologue and isotopomer product from any isotopologue and isotopmer reactant.

New mitochondrial DNA data affirm the importance of Pleistocene speciation in North American birds.

PubMed

Johnson, Ned K; Cicero, Carla

2004-05-01

The timing of origin of modern North American bird species in relation to Pleistocene glaciations has long been the topic of significant discussion and disagreement. Recently, Klicka and Zink (1997) and Avise and Walker (1998) enlivened this debate by using calibrated molecular distance values to estimate timing of speciations. Here we use new molecular studies to test their conclusions. Molecular distance values for 39 pairs of proven sister species, 27 of which are based on new data, alter the currently perceived pattern that avian species splits occurred mainly in the Pliocene and early-mid-Pleistocene. Mitochondrial DNA divergence values for this set of taxa showed a skewed distribution pointing toward relatively young speciation times, in contrast to the pattern presented by Klicka and Zink (1997) for 35 sister plus non-sister species pairs. Our pattern was not significantly different from that of Avise and Walker (1998) for "intraspecific phylogroups," some of which are species. We conclude that the entire Pleistocene, including the last two glacial cycles (<250,000 years ago), was important in speciations of modern North American birds. A substantial number of speciations were both initiated and completed in the last 250,000 years. Simultaneously, many taxa began to diverge in the Pleistocene but their speciations are not yet complete (per Avise and Walker 1998). The suggestion that durations of speciations average two million years is probably a substantial overestimate.

Treatment of air pollution control residues with iron rich waste sulfuric acid: does it work for antimony (Sb)?

PubMed

Okkenhaug, Gudny; Breedveld, Gijs D; Kirkeng, Terje; Lægreid, Marit; Mæhlum, Trond; Mulder, Jan

2013-03-15

Antimony (Sb) in air pollution control (APC) residues from municipal solid waste incineration has gained increased focus due to strict Sb leaching limits set by the EU landfill directive. Here we study the chemical speciation and solubility of Sb at the APC treatment facility NOAH Langøya (Norway), where iron (Fe)-rich sulfuric acid (∼3.6M, 2.3% Fe(II)), a waste product from the industrial extraction of ilmenite, is used for neutralization. Antimony in water extracts of untreated APC residues occurred exclusively as pentavalent antimonate, even at low pH and Eh values. The Sb solubility increased substantially at pH<10, possibly due to the dissolution of ettringite (at alkaline pH) or calcium (Ca)-antimonate. Treated APC residues, stored anoxically in the laboratory, simulating the conditions at the NOAH Langøya landfill, gave rise to decreasing concentrations of Sb in porewater, occurring exclusively as Sb(V). Concentrations of Sb decreased from 87-918μgL(-1) (day 3) to 18-69μgL(-1) (day 600). We hypothesize that an initial sorption of Sb to Fe(II)-Fe(III) hydroxides (green rust) and eventually precipitation of Ca- and Fe-antimonates (tripuhyite; FeSbO4) occurred. We conclude that Fe-rich, sulfuric acid waste is efficient to immobilize Sb in APC residues from waste incineration. Copyright © 2013 Elsevier B.V. All rights reserved.

Structure and reactivity of oxalate surface complexes on lepidocrocite derived from infrared spectroscopy, DFT-calculations, adsorption, dissolution and photochemical experiments

NASA Astrophysics Data System (ADS)

Borowski, Susan C.; Biswakarma, Jagannath; Kang, Kyounglim; Schenkeveld, Walter D. C.; Hering, Janet G.; Kubicki, James D.; Kraemer, Stephan M.; Hug, Stephan J.

2018-04-01

Oxalate, together with other ligands, plays an important role in the dissolution of iron(hdyr)oxides and the bio-availability of iron. The formation and properties of oxalate surface complexes on lepidocrocite were studied with a combination of infrared spectroscopy (IR), density functional theory (DFT) calculations, dissolution, and photochemical experiments. IR spectra measured as a function of time, concentration, and pH (50-200 μM oxalate, pH 3-7) showed that several surface complexes are formed at different rates and in different proportions. Measured spectra could be separated into three contributions described by Gaussian line shapes, with frequencies that agreed well with the theoretical frequencies of three different surface complexes: an outer-sphere complex (OS), an inner-sphere monodentate mononuclear complex (MM), and a bidentate mononuclear complex (BM) involving one O atom from each carboxylate group. At pH 6, OS was formed at the highest rate. The contribution of BM increased with decreasing pH. In dissolution experiments, lepidocrocite was dissolved at rates proportional to the surface concentration of BM, rather than to the total adsorbed concentration. Under UV-light (365 nm), BM was photolyzed at a higher rate than MM and OS. Although the comparison of measured spectra with calculated frequencies cannot exclude additional possible structures, the combined results allowed the assignment of three main structures with different reactivities consistent with experiments. The results illustrate the importance of the surface speciation of adsorbed ligands in dissolution and photochemical reactions.

Biosorption of uranium by Pseudomonas aeruginosa strain CSU: Characterization and comparison studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, M.Z.C.; Norman, J.M.; Faison, B.D.

1996-07-20

Pseudomonas aeruginosa strain CSU, a nongenetically engineered bacterial strain known to bind dissolved hexavalent uranium (as UO{sub 2}{sup 2+} and/or its cationic hydroxo complexes) was characterized with respect to its sorptive activity. The uranium biosorption equilibrium could be described by the Langmuir isotherm. The rate of uranium adsorption increased following permeabilization of the outer and/or cytoplasmic membrane by organic solvents such as acetone. P. aeruginosa CSU biomass was significantly more sorptive toward uranium than certain novel, patented biosorbents derived from algal or fungal biomass sources. P. aeruginosa CSU biomass was also competitive with commercial cation-exchange resins, particularly in the presencemore » of dissolved transition metals. Uranium binding by P. aeruginosa CSU was clearly pH dependent. Uranium loading capacity increased with increasing pH under acidic conditions, presumably as a function of uranium speciation and due to the H{sup +} competition at some binding sites. Nevertheless, preliminary evidence suggests that this microorganism is also capable of binding anionic hexavalent uranium complexes. Ferric iron was a strong inhibitor of uranium binding to P. aeruginosa CSU biomass, and the presence of uranium also decreased the Fe{sup 3+} loading when the biomass was not saturated with Fe{sup 3+}. Thus, a two-state process in which iron and uranium are removed in consecutive steps was proposed for efficient use of the biomass as a biosorbent in uranium removal from mine wastewater, especially acidic leachates.« less

Non-enzymatic U(VI) interactions with biogenic mackinawite

NASA Astrophysics Data System (ADS)

Veeramani, H.; Qafoku, N. P.; Kukkadapu, R. K.; Murayama, M.; Hochella, M. F.

2011-12-01

Reductive immobilization of hexavalent uranium [U(VI)] by stimulation of dissimilatory metal and/or sulfate reducing bacteria (DMRB or DSRB) has been extensively researched as a remediation strategy for subsurface U(VI) contamination. These bacteria derive energy by reducing oxidized metals as terminal electron acceptors, often utilizing organic substrates as electron donors. Thus, when evaluating the potential for in-situ uranium remediation in heterogeneous subsurface media, it is important to understand how the presence of alternative electron acceptors such as Fe(III) and sulfate affect U(VI) remediation and the long term behavior and reactivity of reduced uranium. Iron, an abundant subsurface element, represents a substantial sink for electrons from DMRB, and the reduction of Fe(III) leads to the formation of dissolved Fe(II) or to reactive biogenic Fe(II)- and mixed Fe(II)/Fe(III)- mineral phases. Consequently, abiotic U(VI) reduction by reactive forms of biogenic Fe(II) minerals could be a potentially important process for uranium immobilization. In our study, the DMRB Shewanella putrefaciens CN32 was used to synthesize a biogenic Fe(II)-bearing sulfide mineral: mackinawite, that has been characterized by XRD, SEM, HRTEM and Mössbauer spectroscopy. Batch experiments involving treated biogenic mackinawite and uranium (50:1 molar ratio) were carried out at room temperature under strict anoxic conditions. Following complete removal of uranium from solution, the biogenic mackinawite was analyzed by a suite of analytical techniques including XAS, HRTEM and Mössbauer spectroscopy to determine the speciation of uranium and investigate concomitant Fe(II)-phase transformation. Determining the speciation of uranium is critical to success of a remediation strategy. The present work elucidates non-enzymatic/abiotic molecular scale redox interactions between biogenic mackinawite and uranium.

High-Iron Biosolids Compost-Induced Changes in Lead and Arsenic Speciation and Bioaccessibility in Co-contaminated Soils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, Sally L; Clausen, Ingrid; Chappell, Mark A

2012-10-23

The safety of urban farming has been questioned due to the potential for contamination in urban soils. A laboratory incubation, a field trial, and a second laboratory incubation were conducted to test the ability of high-Fe biosolids–based composts to reduce the bioaccessibility of soil Pb and As in situ. Lead and As bioaccessibility were evaluated using an in vitro assay. Changes in Pb, As, and Fe speciation were determined on select samples after the second laboratory incubation using μ–X-ray fluorescence mapping followed by μ–X-ray absorption near-edge structure (XANES). A compost with Fe added to wastewater treatment residuals (Fe WTR compost)more » added to soils at 100 g kg -1 decreased Pb bioaccessibility in both laboratory incubations. Mixed results were observed for As. Composts tested in the field trial (Fe added as Fe powder or FeCl 2) did not reduce bioaccessible Pb, and limited reductions were observed in bioaccessible As. These composts had no effect on Pb bioaccessibility during the second laboratory incubation. Bulk XANES showed association of Pb with sulfates and carbonates in the control soil. μ-XANES for three points in the Fe WTR amended soil showed Pb present as Fe-sorbed Pb (88 and 100% of two points) and pyromorphite (12 and 53% of two points). Bulk XANES of the Fe WTR compost showed 97% of total Fe present as Fe 3+. The results of this study indicate that addition of high-Fe biosolids compost is an effective means to reduce Pb accessibility only for certain types of Fe-rich materials.« less

Influence of water management on the active root-associated microbiota involved in arsenic, iron, and sulfur cycles in rice paddies.

PubMed

Zecchin, Sarah; Corsini, Anna; Martin, Maria; Cavalca, Lucia

2017-09-01

In recent years, the role of microorganisms inhabiting rice rhizosphere in promoting arsenic contamination has emerged. However, little is known concerning the species and metabolic properties involved in this phenomenon. In this study, the influence of water management on the rhizosphere microbiota in relation to arsenic dissolution in soil solution was tested. Rice plants were cultivated in macrocosms under different water regimes: continuous flooding, continuous flooding with a 2-week period drainage before flowering, and dry soil watered every 10 days. The active bacterial communities in rhizosphere soil and in rhizoplane were characterized by 16S rRNA pyrosequencing. An in-depth analysis of microbial taxa with direct or indirect effects on arsenic speciation was performed and related contribution was evaluated. Continuous flooding promoted high diversity in the rhizosphere, with the plant strongly determining species richness and evenness. On the contrary, under watering the communities were uniform, with little differences between rhizosphere soil and rhizoplane. Arsenic-releasing and arsenite-methylating bacteria were selected by continuous flooding, where they represented 8% of the total. On the contrary, bacteria decreasing arsenic solubility were more abundant under watering, with relative abundance of 10%. These values reflected arsenic concentrations in soil solution: 135 μg L -1 and negligible in continuous flooding and under watering, respectively. When short-term drainage was applied before flowering, intermediate conditions were achieved. This evidence strongly indicates an active role of the rhizosphere microbiota in driving arsenic biogeochemistry in rice paddies, influenced by water management, explaining amounts and speciation of arsenic often found in rice grains.

Bacteria and Genes Involved in Arsenic Speciation in Sediment Impacted by Long-Term Gold Mining

PubMed Central

Costa, Patrícia S.; Scholte, Larissa L. S.; Reis, Mariana P.; Chaves, Anderson V.; Oliveira, Pollyanna L.; Itabayana, Luiza B.; Suhadolnik, Maria Luiza S.; Barbosa, Francisco A. R.; Chartone-Souza, Edmar; Nascimento, Andréa M. A.

2014-01-01

The bacterial community and genes involved in geobiocycling of arsenic (As) from sediment impacted by long-term gold mining were characterized through culture-based analysis of As-transforming bacteria and metagenomic studies of the arsC, arrA, and aioA genes. Sediment was collected from the historically gold mining impacted Mina stream, located in one of the world’s largest mining regions known as the “Iron Quadrangle”. A total of 123 As-resistant bacteria were recovered from the enrichment cultures, which were phenotypically and genotypically characterized for As-transformation. A diverse As-resistant bacteria community was found through phylogenetic analyses of the 16S rRNA gene. Bacterial isolates were affiliated with Proteobacteria, Firmicutes, and Actinobacteria and were represented by 20 genera. Most were AsV-reducing (72%), whereas AsIII-oxidizing accounted for 20%. Bacteria harboring the arsC gene predominated (85%), followed by aioA (20%) and arrA (7%). Additionally, we identified two novel As-transforming genera, Thermomonas and Pannonibacter. Metagenomic analysis of arsC, aioA, and arrA sequences confirmed the presence of these genes, with arrA sequences being more closely related to uncultured organisms. Evolutionary analyses revealed high genetic similarity between some arsC and aioA sequences obtained from isolates and clone libraries, suggesting that those isolates may represent environmentally important bacteria acting in As speciation. In addition, our findings show that the diversity of arrA genes is wider than earlier described, once none arrA-OTUs were affiliated with known reference strains. Therefore, the molecular diversity of arrA genes is far from being fully explored deserving further attention. PMID:24755825

Arsenic and chromium speciation in an urban contaminated soil.

PubMed

Landrot, Gautier; Tappero, Ryan; Webb, Samuel M; Sparks, Donald L

2012-08-01

The distribution and speciation of As and Cr in a contaminated soil were studied by synchrotron-based X-ray microfluorescence (μ-XRF), microfocused X-ray absorption spectroscopy (μ-XAS), and bulk extended X-ray absorption fine structure spectroscopy (EXAFS). The soil was taken from a park in Wilmington, DE, which had been an important center for the leather tanning industry along the Atlantic seaboard of the United States, until the early 20th century. Soil concentrations of As, Cr, and Pb measured at certain locations in the park greatly exceeded the background levels of these heavy metals in the State of Delaware. Results show that Cr(III) and As(V) species are mainly present in the soil, with insignificant amounts of Cr(VI) and As(III). Micro-XRF maps show that Cr and Fe are distributed together in regions where their concentrations are diffuse, and at local spots where their concentrations are high. Iron oxides, which can reduce Cr(VI) to Cr(III), are present at some of these hot spots where Cr and Fe are highly concentrated. Arsenic is mainly associated with Al in the soil, and to a minor extent with Fe. Arsenate may be sorbed to aluminum oxides, which might have transformed after a long period of time into an As-Al precipitate phase, having a structure and chemical composition similar to mansfieldite (AlAsO(4)⋅2H(2)O). The latter hypothesis is supported by the fact that only a small amount of As present in the soil was desorbed using the characteristic toxicity leaching procedure tests. This suggests that As is immobilized in the soil. Copyright © 2012 Elsevier Ltd. All rights reserved.

A gel probe equilibrium sampler for measuring arsenic porewater profiles and sorption gradients in sediments: I. Laboratory development

USGS Publications Warehouse

Campbell, K.M.; Root, R.; O'Day, P. A.; Hering, J.G.

2008-01-01

A gel probe equilibrium sampler has been developed to study arsenic (As) geochemistry and sorption behavior in sediment porewater. The gels consist of a hydrated polyacrylamide polymer, which has a 92% water content. Two types of gels were used in this study. Undoped (clear) gels were used to measure concentrations of As and other elements in sediment porewater. The polyacrylamide gel was also doped with hydrous ferric oxide (HFO), an amorphous iron (Fe) oxyhydroxide. When deployed in the field, HFO-doped gels introduce a fresh sorbent into the subsurface thus allowing assessment of in situ sorption. In this study, clear and HFO-doped gels were tested under laboratory conditions to constrain the gel behavior prior to field deployment. Both types of gels were allowed to equilibrate with solutions of varying composition and re-equilibrated in acid for analysis. Clear gels accurately measured solution concentrations (??1%), and As was completely recovered from HFO-doped gels (??4%). Arsenic speciation was determined in clear gels through chromatographic separation of the re-equilibrated solution. For comparison to speciation in solution, mixtures of As(III) and As(V) adsorbed on HFO embedded in gel were measured in situ using X-ray absorption spectroscopy (XAS). Sorption densities for As(III) and As(V) on HFO embedded in gel were obtained from sorption isotherms at pH 7.1. When As and phosphate were simultaneously equilibrated (in up to 50-fold excess of As) with HFO-doped gels, phosphate inhibited As sorption by up to 85% and had a stronger inhibitory effect on As(V) than As(III). Natural organic matter (>200 ppm) decreased As adsorption by up to 50%, and had similar effects on As(V) and As(III). The laboratory results provide a basis for interpreting results obtained by deploying the gel probe in the field and elucidating the mechanisms controlling As partitioning between solid and dissolved phases in the environment. ?? 2008 American Chemical Society.

STUDY OF THE FUNDAMENTALS OF MERCURY SPECIATION IN COAL-FIRED BOILERS UNDER SIMULATED POST-COMBUSTION CONDITIONS

EPA Science Inventory

The report discusses a continuation of the study on mercury speciation initiated in the fiscal year 1997 (FY97). The previous study found that cupric oxide (CuO) and ferric oxide (Fe2O3) in the presence of hydrogen chloride (HCl) promote elemental mercury oxidation in simulated f...

Speciation evolution of zinc and copper during pyrolysis and hydrothermal carbonization treatments of sewage sludges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Rixiang; Zhang, Bei; Saad, Emily M.

Thermal and hydrothermal treatments are promising techniques for sewage sludge management that can potentially facilitate safe waste disposal, energy recovery, and nutrient recovery/recycling. Content and speciation of heavy metals in the treatment products affect the potential environmental risks upon sludge disposal and/or application of the treatment products. Therefore, it is important to study the speciation transformation of heavy metals and the effects of treatment conditions. By combining synchrotron X-ray spectroscopy/microscopy analysis and sequential chemical extraction, this study systematically characterized the speciation of Zn and Cu in municipal sewage sludges and their chars derived from pyrolysis (a representative thermal treatment technique)more » and hydrothermal carbonization (HTC; a representative hydrothermal treatment technique). Spectroscopy analysis revealed enhanced sulfidation of Zn and Cu by anaerobic digestion and HTC treatments, as compared to desulfidation by pyrolysis. Overall, changes in the chemical speciation and matrix properties led to reduced mobility of Zn and Cu in the treatment products. These results provide insights into the reaction mechanisms during pyrolysis and HTC treatments of sludges and can help evaluate the environmental/health risks associated with the metals in the treatment products.« less

ARSENIC SPECIATION ANALYSIS IN HUMAN SALIVA

EPA Science Inventory

Background: Determination of arsenic species in human saliva is potentially useful for biomonitoring of human exposure to arsenic and for studying arsenic metabolism. However, there is no report on the speciation analysis of arsenic in saliva. Methods: Arsenic species in saliva ...

Speciation of heavy metals in landfill leachate: a review.

PubMed

Baun, Dorthe L; Christensen, Thomas H

2004-02-01

The literature was reviewed with respect to metal speciation methods in aquatic samples specifically emphasizing speciation of heavy metals in landfill leachate. Speciation here refers to physical fractionation (particulate, colloidal, dissolved), chemical fractionation (organic complexes, inorganic complexes, free metal ions), as well as computer-based thermodynamic models. Relatively few landfill leachate samples have been speciated in detail (less than 30) representing only a few landfills (less than 15). This suggests that our knowledge about metal species in landfill leachate still is indicative. In spite of the limited database and the different definitions of the dissolved fraction (< 0.45 microm or < 0.001 microm) the studies consistently show that colloids as well as organic and inorganic complexes are important for all heavy metals in landfill leachate. The free metal ion constitutes less than 30%, typically less than 10%, of the total metal concentration. This has significant implications for sampling, since no standardized procedures exist, and for assessing the content of metals in leachate in the context of its treatment, toxicity and migration in aquifers.

Parapatric speciation in three islands: dynamics of geographical configuration of allele sharing

PubMed Central

Iwasa, Yoh

2017-01-01

We studied the time to speciation by geographical isolation for a species living on three islands connected by rare migration. We assumed that incompatibility was controlled by a number of quantitative loci and that individuals differing in loci by more than a threshold did not mix genetically with each other. For each locus, we defined the geographical configuration (GC), which specifies islands with common alleles, and traced the stochastic transitions between different GCs. From these results, we calculated the changes in genetic distances. As a single migration event provides an opportunity for transitions in multiple loci, the GCs of different loci are correlated, which can be evaluated by constructing the stochastic differential equations of the number of loci with different GCs. Our model showed that the low number of incompatibility loci facilitates parapatric speciation and that migrants arriving as a group shorten the waiting time to speciation compared with the same number of migrants arriving individually. We also discuss how speciation rate changes with geographical structure. PMID:28386439

Mobility and fractionation of Fe, Pb and Zn in river sediments from a silver and base-metals mining area: Taxco, México.

PubMed

Espinosa, E; Armienta, M A

2007-08-01

The impact of mining wastes on both the concentration and environmental mobility of Zn, Pb and Fe was studied in a shallow river. The studied tributary of the Taxco river is located south of the historical Ag, Zn, Cu and Pb mining area of Taxco, about 150 km south of México City. Methodology included total concentration determinations and sequential extraction analyses of the operational defined fractions of sediments. Results indicated that Fe, Pb and Zn concentrations are up to 5, 100 and 390 times respectively, greater than regional background concentrations. Higher contents of Pb and Zn were observed in the rainy season versus the dry season, whereas Fe was lower in the rainy season. Zinc and lead increased downflow in the dry season, and did not show any trend during the rainy season. Speciation showed that Zn was mainly linked to the carbonatic fraction (25-39%), to the hydrous Fe/Mn oxides fraction (15-25%) and to the organic matter and sulfide fraction (14-48%); lead was mainly associated to the hydrous Fe/Mn oxides (49-59%) and residual (22-39%) fractions; finally, iron was contained mainly in the residual (65-78%) and the hydrous Fe/Mn oxides fraction (15%). Mobility decreased according to the relation: Zn > Pb > Fe. Sediments were classified as strongly polluted in zinc, strongly to very strongly polluted in Pb, and moderately to strongly polluted in iron. However, a low proportion of metals in the exchangeable fractions, indicates low bioavailability. Limestone presence played a very important role on Zn and Pb fractionation and environmental mobility. Results show the importance of including geological background in river pollution studies.

Oxidation of Fe(II) in rainwater.

PubMed

Willey, J D; Whitehead, R F; Kieber, R J; Hardison, D R

2005-04-15

Photochemically produced Fe(II) is oxidized within hours under environmentally realistic conditions in rainwater. The diurnal variation between photochemical production and reoxidation of Fe(II) observed in our laboratory accurately mimics the behavior of ferrous iron observed in field studies where the highest concentrations of dissolved Fe(ll) occur in afternoon rain during the period of maximum sunlight intensity followed by gradually decreasing concentrations eventually returning to early morning pre-light values. The experimental work presented here, along with the results of kinetics studies done by others, suggests thatthe primary process responsible for the decline in photochemically produced Fe(II) concentrations is oxidation by hydrogen peroxide. This reaction is first order with respect to both the concentrations of Fe(II) and H2O2. The second-order rate constant determined for six different authentic rain samples varied over an order of magnitude and was always less than or equal to the rate constant determined for this reaction in simple acidic solutions. Oxidation of photochemically produced ferrous iron by other oxidants including molecular oxygen, ozone, hydroxyl radical, hydroperoxyl/superoxide radical, and hexavalent chromium were found to be insignificant under the conditions present in rainwater. This study shows that Fe(II) occurs as at least two different chemical species in rain; photochemically produced Fe(II) that is oxidized over time periods of hours, and a background Fe(II) that is protected against oxidation, perhaps by organic complexation, and is stable against oxidation for days. Because the rate of oxidation of photochemically produced Fe(II) does not increase with increasing rainwater pH, the speciation of this more labile form of Fe(II) is also not controlled by simple hydrolysis reactions.

Sediment phosphorus speciation and mobility under dynamic redox conditions

NASA Astrophysics Data System (ADS)

Parsons, Chris T.; Rezanezhad, Fereidoun; O'Connell, David W.; Van Cappellen, Philippe

2017-07-01

Anthropogenic nutrient enrichment has caused phosphorus (P) accumulation in many freshwater sediments, raising concerns that internal loading from legacy P may delay the recovery of aquatic ecosystems suffering from eutrophication. Benthic recycling of P strongly depends on the redox regime within surficial sediment. In many shallow environments, redox conditions tend to be highly dynamic as a result of, among others, bioturbation by macrofauna, root activity, sediment resuspension and seasonal variations in bottom-water oxygen (O2) concentrations. To gain insight into the mobility and biogeochemistry of P under fluctuating redox conditions, a suspension of sediment from a hypereutrophic freshwater marsh was exposed to alternating 7-day periods of purging with air and nitrogen gas (N2), for a total duration of 74 days, in a bioreactor system. We present comprehensive data time series of bulk aqueous- and solid-phase chemistry, solid-phase phosphorus speciation and hydrolytic enzyme activities demonstrating the mass balanced redistribution of P in sediment during redox cycling. Aqueous phosphate concentrations remained low ( ˜ 2.5 µM) under oxic conditions due to sorption to iron(III) oxyhydroxides. During anoxic periods, once nitrate was depleted, the reductive dissolution of iron(III) oxyhydroxides released P. However, only 4.5 % of the released P accumulated in solution while the rest was redistributed between the MgCl2 and NaHCO3 extractable fractions of the solid phase. Thus, under the short redox fluctuations imposed in the experiments, P remobilization to the aqueous phase remained relatively limited. Orthophosphate predominated at all times during the experiment in both the solid and aqueous phase. Combined P monoesters and diesters accounted for between 9 and 16 % of sediment particulate P. Phosphatase activities up to 2.4 mmol h-1 kg-1 indicated the potential for rapid mineralization of organic P (Po), in particular during periods of aeration when the activity of phosphomonoesterases was 37 % higher than under N2 sparging. The results emphasize that the magnitude and timing of internal P loading during periods of anoxia are dependent on both P redistribution within sediments and bottom-water nitrate concentrations.

Nanoscale zero-valent iron for metal/metalloid removal from model hydraulic fracturing wastewater.

PubMed

Sun, Yuqing; Lei, Cheng; Khan, Eakalak; Chen, Season S; Tsang, Daniel C W; Ok, Yong Sik; Lin, Daohui; Feng, Yujie; Li, Xiang-Dong

2017-06-01

Nanoscale zero-valent iron (nZVI) was tested for the removal of Cu(II), Zn(II), Cr(VI), and As(V) in model saline wastewaters from hydraulic fracturing. Increasing ionic strength (I) from 0.35 to 4.10 M (Day-1 to Day-90 wastewaters) increased Cu(II) removal (25.4-80.0%), inhibited Zn(II) removal (58.7-42.9%), slightly increased and then reduced Cr(VI) removal (65.7-44.1%), and almost unaffected As(V) removal (66.7-75.1%) by 8-h reaction with nZVI at 1-2 g L -1 . The removal kinetics conformed to pseudo-second-order model, and increasing I decreased the surface area-normalized rate coefficient (k sa ) of Cu(II) and Cr(VI), probably because agglomeration of nZVI in saline wastewaters restricted diffusion of metal(loid)s to active surface sites. Increasing I induced severe Fe dissolution from 0.37 to 0.77% in DIW to 4.87-13.0% in Day-90 wastewater; and Fe dissolution showed a significant positive correlation with Cu(II) removal. With surface stabilization by alginate and polyvinyl alcohol, the performance of entrapped nZVI in Day-90 wastewater was improved for Zn(II) and Cr(VI), and Fe dissolution was restrained (3.20-7.36%). The X-ray spectroscopic analysis and chemical speciation modelling demonstrated that the difference in removal trends from Day-1 to Day-90 wastewaters was attributed to: (i) distinctive removal mechanisms of Cu(II) and Cr(VI) (adsorption, (co-)precipitation, and reduction), compared to Zn(II) (adsorption) and As(V) (bidentate inner-sphere complexation); and (ii) changes in solution speciation (e.g., from Zn 2+ to ZnCl 3 - and ZnCl 4 2- ; from CrO 4 2- to CaCrO 4 complex). Bare nZVI was susceptible to variations in wastewater chemistry while entrapped nZVI was more stable and environmentally benign, which could be used to remove metals/metalloids before subsequent treatment for reuse/disposal. Copyright © 2017 Elsevier Ltd. All rights reserved.

Unpacking paleoenvironmental change across OAE2 using paired d34S records of pyrite and organic matter

NASA Astrophysics Data System (ADS)

Raven, M. R.; Gomes, M.; Fike, D. A.

2017-12-01

Pyrite sulfur isotopes have proven to be a powerful tool for reconstructing major changes in global redox state and the emergence of microbial metabolisms. Still, pyrite can be a challenging archive, as its formation depends on the availability of reactive iron species and can occur over multiple generations of sedimentary processes. Accordingly, pyrite δ34S records commonly have large point-to-point variability reflecting local processes. By pairing pyrite δ34S records with those of coexisting organic matter (OM), including both kerogens and extractable bitumens, we can begin to parse the various potential causes of this variability and gain greater insights into changes in the sedimentary paleoenvironment. Here, we present the first collection of records of OM δ34S for the Cretaceous, focusing on sections spanning Ocean Anoxic Event 2 (OAE2, 94 Mya), a period of globally widespread marine anoxia and carbon cycle disruption. In carbonates and shales from OAE2 in Pont d'Issole, France, pyrite and OM δ34S values vary in parallel throughout most of the section, consistent with their shared sulfide source. There are also distinct exceptions: In one interval, an excursion in pyrite δ34S is entirely absent from the organic sulfur record but associated with unusual organic sulfur redox speciation (by XAS), potentially reflecting later exposure to oxic porewaters. Across the core interval of shale deposition during OAE2, the offset between pyrite and OM δ34S values declines smoothly from +17.4 to -7.9‰, which we interpret in terms of changes in the speciation of detrital iron minerals that may have regional implications. We then compare these results with data for other well-characterized OAE2 sections, including Cismon (Italy), Tarfaya (Morocco), and the Demerara Rise (offshore Brazil), which represent environments with a variety of apparent redox states. These paired pyrite - OM δ34S profiles yield new information about how the local and global forcings associated with OAE2 impacted environmental redox states, which in turn drove major changes in microbial energy cycling and sulfur and carbon burial fluxes during this critical period of Earth history.

Something's Fishy in Paxton Lake: A Case on Speciation in Sticklebacks.

ERIC Educational Resources Information Center

Sharp, Joan

2002-01-01

Introduces a case study on speciation and evolutionary mechanisms. Teaches science process skills as well as natural selection, biological species concepts, basic genetic terminology, and classification. Includes teaching notes and classroom management strategies. (Contains 14 references.) (YDS)

Selenium speciation in acidic environmental samples: application to acid rain-soil interaction at Mount Etna volcano.

PubMed

Floor, Geerke H; Iglesías, Mònica; Román-Ross, Gabriela; Corvini, Philippe F X; Lenz, Markus

2011-09-01

Speciation plays a crucial role in elemental mobility. However, trace level selenium (Se) speciation analyses in aqueous samples from acidic environments are hampered due to adsorption of the analytes (i.e. selenate, selenite) on precipitates. Such solid phases can form during pH adaptation up till now necessary for chromatographic separation. Thermodynamic calculations in this study predicted that a pH<4 is needed to prevent precipitation of Al and Fe phases. Therefore, a speciation method with a low pH eluent that matches the natural sample pH of acid rain-soil interaction samples from Etna volcano was developed. With a mobile phase containing 20mM ammonium citrate at pH 3, selenate and selenite could be separated in different acidic media (spiked water, rain, soil leachates) in <10 min with a LOQ of 0.2 μg L(-1) using (78)Se for detection. Applying this speciation analysis to study acid rain-soil interaction using synthetic rain based on H(2)SO(4) and soil samples collected at the flanks of Etna volcano demonstrated the dominance of selenate over selenite in leachates from samples collected close to the volcanic craters. This suggests that competitive behavior with sulfate present in acid rain might be a key factor in Se mobilization. The developed speciation method can significantly contribute to understand Se cycling in acidic, Al/Fe rich environments. Copyright © 2011 Elsevier Ltd. All rights reserved.

Arsenic Speciation in Groundwater: Role of Thioanions

EPA Science Inventory

The behavior of arsenic in groundwater environments is fundamentally linked to its speciation. Understanding arsenic speciation is important because chemical speciation impacts reactivity, bioavailability, toxicity, and transport and fate processes. In aerobic environments arsen...

The shape and temporal dynamics of phylogenetic trees arising from geographic speciation.

PubMed

Pigot, Alex L; Phillimore, Albert B; Owens, Ian P F; Orme, C David L

2010-12-01

Phylogenetic trees often depart from the expectations of stochastic models, exhibiting imbalance in diversification among lineages and slowdowns in the rate of lineage accumulation through time. Such departures have led to a widespread perception that ecological differences among species or adaptation and subsequent niche filling are required to explain patterns of diversification. However, a key element missing from models of diversification is the geographical context of speciation and extinction. In this study, we develop a spatially explicit model of geographic range evolution and cladogenesis, where speciation arises via vicariance or peripatry, and explore the effects of these processes on patterns of diversification. We compare the results with those observed in 41 reconstructed avian trees. Our model shows that nonconstant rates of speciation and extinction are emergent properties of the apportioning of geographic ranges that accompanies speciation. The dynamics of diversification exhibit wide variation, depending on the mode of speciation, tendency for range expansion, and rate of range evolution. By varying these parameters, the model is able to capture many, but not all, of the features exhibited by birth-death trees and extant bird clades. Under scenarios with relatively stable geographic ranges, strong slowdowns in diversification rates are produced, with faster rates of range dynamics leading to constant or accelerating rates of apparent diversification. A peripatric model of speciation with stable ranges also generates highly unbalanced trees typical of bird phylogenies but fails to produce realistic range size distributions among the extant species. Results most similar to those of a birth-death process are reached under a peripatric speciation scenario with highly volatile range dynamics. Taken together, our results demonstrate that considering the geographical context of speciation and extinction provides a more conservative null model of diversification and offers a very different perspective on the phylogenetic patterns expected in the absence of ecology.

Ecological speciation in an island snail: evidence for the parallel evolution of a novel ecotype and maintenance by ecologically dependent postzygotic isolation.

PubMed

Stankowski, Sean

2013-05-01

Speciation is the process by which reproductive isolation evolves between populations. Two general models of speciation have been proposed: ecological speciation, where reproductive barriers evolve due to ecologically based divergent selection, and mutation-order speciation, where populations fix different mutations as they adapt to similar selection pressures. I evaluate these alternative models and determine the progress of speciation in a diverse group of land snails, genus Rhagada, inhabiting Rosemary Island. A recently derived keeled-flat morphotype occupies two isolated rocky hills, while globose-shelled snails inhabit the surrounding plains. The study of one hill reveals that they are separated by a narrow hybrid zone. As predicted by ecological speciation theory, there are local and landscape level associations between shell shape and habitat, and the morphological transition coincides with a narrow ecotone between the two distinct environments. Microsatellite DNA revealed a cline of hybrid index scores much wider than the morphological cline, further supporting the ecological maintenance of the morphotypes. The hybrid zone does not run through an area of low population density, as is expected for mutation-order hybrid zones, and there is a unimodal distribution of phenotypes at the centre, suggesting that there is little or no prezygotic isolation. Instead, these data suggest that the ecotypes are maintained by ecologically dependent postzygotic isolation (i.e. ecological selection against hybrids). Mitochondrial and Microsatellite DNA indicate that the keeled-flat form evolved recently, and without major historical disruptions to gene flow. The data also suggest that the two keeled-flat populations, inhabiting similar rocky hills, have evolved in parallel. These snails provide a complex example of ecological speciation in its early stages. © 2013 Blackwell Publishing Ltd.

Geological and climatic forces driving speciation in the continentally distributed trilling chorus frogs (Pseudacris).

PubMed

Lemmon, Emily Moriarty; Lemmon, Alan R; Cannatella, David C

2007-09-01

Tertiary geological events and Quaternary climatic fluctuations have been proposed as important factors of speciation in the North American flora and fauna. Few studies, however, have rigorously tested hypotheses regarding the specific factors driving divergence of taxa. Here, we test explicit speciation hypotheses by correlating geologic events with divergence times among species in the continentally distributed trilling chorus frogs (Pseudacris). In particular, we ask whether marine inundation of the Mississippi Embayment, uplift of the Appalachian Mountains, or modification of the ancient Teays-Mahomet River system contributed to speciation. To examine the plausibility of ancient rivers causing divergence, we tested whether modern river systems inhibit gene flow. Additionally, we compared the effects of Quaternary climatic factors (glaciation and aridification) on levels of genetic variation. Divergence time estimates using penalized likelihood and coalescent approaches indicate that the major lineages of chorus frogs diversified during the Tertiary, and also exclude Quaternary climate change as a factor in speciation of chorus frogs. We show the first evidence that inundation of the Mississippi Embayment contributed to speciation. We reject the hypotheses that Cenozoic uplift of the Appalachians and that diversion of the Teays-Mahomet River contributed to speciation in this clade. We find that by reducing gene flow, rivers have the potential to cause divergence of lineages. Finally, we demonstrate that populations in areas affected by Quaternary glaciation and aridification have reduced levels of genetic variation compared to those from more equable regions, suggesting recent colonization.

Anaerobic Digestion Alters Copper and Zinc Speciation.

PubMed

Legros, Samuel; Levard, Clément; Marcato-Romain, Claire-Emmanuelle; Guiresse, Maritxu; Doelsch, Emmanuel

2017-09-19

Anaerobic digestion is a widely used organic waste treatment process. However, little is known on how it could alter the speciation of contaminants in organic waste. This study was focused on determining the influence of anaerobic digestion on the speciation of copper and zinc, two metals that generally occur at high concentration in organic waste. Copper and zinc speciation was investigated by X-ray absorption spectroscopy in four different raw organic wastes (predigestion) and their digested counterparts (postdigestion, i.e., digestates). The results highlighted an increase in the digestates of the proportion of amorphous or nanostructured copper sulfides as well as amorphous or nanostructured zinc sulfides and zinc phosphate as compared to raw waste. We therefore suggest that the environmental fate of these elements would be different when spreading either digestates or raw waste on cropland.

Capillary electrophoresis application in metal speciation and complexation characterization

USDA-ARS?s Scientific Manuscript database

Capillary electrophoresis is amenable to the separation of metal ionic species and the characterization of metal-ligand interactions. This book chapter reviews and discusses three representative case studies in applications of CE technology in speciation and reactions of metal with organic molecules...

Bats (Chiroptera: Noctilionoidea) Challenge a Recent Origin of Extant Neotropical Diversity.

PubMed

Rojas, Danny; Warsi, Omar M; Dávalos, Liliana M

2016-05-01

The mechanisms underlying the high extant biodiversity in the Neotropics have been controversial since the 19th century. Support for the influence of period-specific changes on diversification often rests on detecting more speciation events during a particular period. The timing of speciation events may reflect the influence of incomplete taxon sampling, protracted speciation, and null processes of lineage accumulation. Here we assess the influence of these factors on the timing of speciation with new multilocus data for New World noctilionoid bats (Chiroptera: Noctilionoidea). Biogeographic analyses revealed the importance of the Neotropics in noctilionoid diversification, and the critical role of dispersal. We detected no shift in speciation rate associated with the Quaternary or pre-Quaternary periods, and instead found an increase in speciation linked to the evolution of the subfamily Stenodermatinae (∼18 Ma). Simulations modeling constant speciation and extinction rates for the phylogeny systematically showed more speciation events in the Quaternary. Since recording more divergence events in the Quaternary can result from lineage accumulation, the age of extant sister species cannot be interpreted as supporting higher speciation rates during this period. Instead, analyzing the factors that influence speciation requires modeling lineage-specific traits and environmental, spatial, and ecological drivers of speciation. © The Author(s) 2016. Published by Oxford University Press, on behalf of the Society of Systematic Biologists. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Trace elements geochemistry of fractured basement aquifer in southern Malawi: A case of Blantyre rural

NASA Astrophysics Data System (ADS)

Mapoma, Harold Wilson Tumwitike; Xie, Xianjun; Nyirenda, Mathews Tananga; Zhang, Liping; Kaonga, Chikumbusko Chiziwa; Mbewe, Rex

2017-07-01

In this study, twenty one (21) trace elements in the basement complex groundwater of Blantyre district, Malawi were analyzed. The majority of the analyzed trace elements in the water were within the standards set by World Health Organization (WHO) and Malawi Standards Board (MSB). But, iron (Fe) (BH16 and 21), manganese (Mn) (BH01) and selenium (Se) (BH02, 13, 18, 19 and 20) were higher than the WHO and MSB standards. Factor analysis (FA) revealed up to five significant factors which accounted for 87.4% of the variance. Factor 1, 2 and 3 suggest evaporite dissolution and silicate weathering processes while the fourth factor may explain carbonate dissolution and pH influence on trace element geochemistry of the studied groundwater samples. According to PHREEQC computed saturation indices, dissolution, precipitation and rock-water-interaction control the levels of trace elements in this aquifer. Elevated concentrations of Fe, Mn and Se in certain boreholes are due to the geology of the aquifer and probable redox status of groundwater. From PHREEQC speciation results, variations in trace element species were observed. Based on this study, boreholes need constant monitoring and assessment for human consumption to avoid health related issues.

Modeling the two-locus architecture of divergent pollinator adaptation: how variation in SAD paralogs affects fitness and evolutionary divergence in sexually deceptive orchids.

PubMed

Xu, Shuqing; Schlüter, Philipp M

2015-01-01

Divergent selection by pollinators can bring about strong reproductive isolation via changes at few genes of large effect. This has recently been demonstrated in sexually deceptive orchids, where studies (1) quantified the strength of reproductive isolation in the field; (2) identified genes that appear to be causal for reproductive isolation; and (3) demonstrated selection by analysis of natural variation in gene sequence and expression. In a group of closely related Ophrys orchids, specific floral scent components, namely n-alkenes, are the key floral traits that control specific pollinator attraction by chemical mimicry of insect sex pheromones. The genetic basis of species-specific differences in alkene production mainly lies in two biosynthetic genes encoding stearoyl-acyl carrier protein desaturases (SAD) that are associated with floral scent variation and reproductive isolation between closely related species, and evolve under pollinator-mediated selection. However, the implications of this genetic architecture of key floral traits on the evolutionary processes of pollinator adaptation and speciation in this plant group remain unclear. Here, we expand on these recent findings to model scenarios of adaptive evolutionary change at SAD2 and SAD5, their effects on plant fitness (i.e., offspring number), and the dynamics of speciation. Our model suggests that the two-locus architecture of reproductive isolation allows for rapid sympatric speciation by pollinator shift; however, the likelihood of such pollinator-mediated speciation is asymmetric between the two orchid species O. sphegodes and O. exaltata due to different fitness effects of their predominant SAD2 and SAD5 alleles. Our study not only provides insight into pollinator adaptation and speciation mechanisms of sexually deceptive orchids but also demonstrates the power of applying a modeling approach to the study of pollinator-driven ecological speciation.

Bioreduction of Selenium Oxyanions via the Feammox Process

NASA Astrophysics Data System (ADS)

Sherman, A.; Jaffe, P. R.

2017-12-01

Selenium (Se) is an important environmental contaminant found in both agricultural and industrial wastewater. A novel bacterium, Acidimicrobiaceae bacterium A6 (hereon referred to as A6), has been shown to oxidize ammonium through the reduction of iron oxides (termed the Feammox process) and has also been shown to reduce trace metals and radionuclides. This research aims to establish whether the Feammox process can be used to reduce Se oxyanions in wastewater, and to determine the pathway by which this reduction occurs. A novel method of Se analysis using ion chromatography (Dionex Aquion IC system, AS18 separator and guard columns, 18mM KOH eluent, 45mA) has been developed, showing clear resolution of SeO32- and SeO42- peaks and detection limits in the ppb range. Batch incubations were run using pure A6 culture to tie the reduction of Se to the activity of this bacterium. Nontronite was used as the iron source to sustain A6 activity. Unlike other iron sources, such as ferrihydrite, nontronite does not sorb Se oxyanions, and thus selenium remains bioavailable as an electron acceptor for use during the Feammox process. Concentrations of 1ppm of SeO32- and SeO42- were used, below the toxic threshold for A6, and incubations were sampled destructively over the course of 8 days. Samples were analyzed using ion chromatography and UV-Vis spectroscopy to determine bacterial activity and chemical speciation. Initial results indicate that A6 may be able to reduce 300ppb of SeO32-in 3 days, however more work is needed to further explain this result.

Feedback Interactions between Trace Metal Nutrients and Phytoplankton in the Ocean

PubMed Central

Sunda, William G.

2012-01-01

In addition to control by major nutrient elements (nitrogen, phosphorus, and silicon) the productivity and species composition of marine phytoplankton communities are also regulated by a number of trace metal nutrients (iron, zinc, cobalt, manganese, copper, and cadmium). Of these, iron is most limiting to phytoplankton growth and has the greatest effect on algal species diversity. It also plays an important role in limiting di-nitrogen (N2) fixation rates, and thus is important in controlling ocean inventories of fixed nitrogen. Because of these effects, iron is thought to play a key role in regulating biological cycles of carbon and nitrogen in the ocean, including the biological transfer of carbon to the deep sea, the so-called biological CO2 pump, which helps regulate atmospheric CO2 and CO2-linked global warming. Other trace metal nutrients (zinc, cobalt, copper, and manganese) have lesser effects on productivity; but may exert an important influence on the species composition of algal communities because of large differences in metal requirements among species. The interactions between trace metals and ocean plankton are reciprocal: not only do the metals control the plankton, but the plankton regulate the distributions, chemical speciation, and cycling of these metals through cellular uptake and recycling processes, downward flux of biogenic particles, biological release of organic chelators, and mediation of redox reactions. This two way interaction has influenced not only the biology and chemistry of the modern ocean, but has had a profound influence on biogeochemistry of the ocean and earth system as a whole, and on the evolution of marine and terrestrial biology over geologic history. PMID:22701115

Instrumentation for Aerosol and Gas Speciation

NASA Technical Reports Server (NTRS)

Coggiola, Michael J.

1998-01-01

Using support from NASA Grant No. NAG 2-963, SRI International successfully completed the project, entitled, 'Instrumentation for Aerosol and Gas Speciation.' This effort (SRI Project 7383) covered the design, fabrication, testing, and deployment of a real-time aerosol speciation instrument in NASA's DC-8 aircraft during the Spring 1996 SUbsonic aircraft: Contrail and Cloud Effects Special Study (SUCCESS) mission. This final technical report describes the pertinent details of the instrument design, its abilities, its deployment during SUCCESS and the data acquired from the mission, and the post-mission calibration, data reduction, and analysis.

[Assessment of occupational exposure of welders based on determination of fumes and their components produced during stainless steel welding].

PubMed

Stanisławska, Magdalena; Janasik, Beata; Trzcinka-Ochocka, Małgorzata

2011-01-01

Occupational exposure to welding fumes is a known health hazard. The aim of this study was to determine concentrations of welding fumes components such as: iron, manganese, nickel and chromium (including chromium speciation) to assess exposure of stainless steel welders. The survey covered 14 workers of two metallurgic plants engaged in welding stainless steel (18% Cr and 8% Ni) by different techniques: manual metal arc (MMA), metal inert gas (MIG) and tungsten inert gas (TIG). Personal air samples were collected in the welders' breathing zone over a period of about 6-7 h (dust was collected on a membrane and glass filter) to determine time weighted average (TWA) concentration of welding fumes and its components. The concentrations of welding fumes (total particulate) were determined with use of the gravimetric method. Concentrations and welding fume components, such as: iron, manganese, nickel and chromium were determined by ICP-MS technique. The total hexavalent chromium was analyzed by applying the spectrophotometry method according to NIOSH. The water-soluble chromium species were analyzed by HPLC-ICP-MS. Time weighted average concentrations of the welding fumes and its components at the worker's breathing zone were (mg/m3): dust, 0.14-10.7; iron, 0.004-2.9; manganese, 0.001-1.12; nickel, < 0.001-0.2; and chromium <0.002-0.85 (mainly Cr(III) and insoluble Cr(VI)). The maximum admissible limits for workplace pollutants (TLV-TWA) were exceeded for manganese and for insoluble chromium Cr (VI). For Cr (III) the limit was exceeded in individual cases. The assessment of the workers' occupational exposure, based on the determined time weighted average (TWA) of fumes and their components, shows that the stainless steel welders worked in conditions harmful to their health owing to the significantly exceeded maximum admissible limits for manganese and the exceeded TLV value for insoluble chromium (VI).

Effect of secondary fuels and combustor temperature on mercury speciation in pulverized fuel co-combustion: part 1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shishir P. Sable; Wiebren de Jong; Ruud Meij

2007-08-15

The present work mainly involves bench scale studies to investigate partitioning of mercury in pulverized fuel co-combustion at 1000 and 1300{sup o}C. High volatile bituminous coal is used as a reference case and chicken manure, olive residue, and B quality (demolition) wood are used as secondary fuels with 10 and 20% thermal shares. The combustion experiments are carried out in an entrained flow reactor with a fuel input of 7-8 kWth. Elemental and total gaseous mercury concentrations in the flue gas of the reactor are measured on-line, and ash is analyzed for particulate mercury along with other elemental and surfacemore » properties. Animal waste like chicken manure behaves very differently from plant waste. The higher chlorine contents of chicken manure cause higher ionic mercury concentrations whereas even with high unburnt carbon, particulate mercury reduces with increase in the chicken manure share. This might be a problem due to coarse fuel particles, low surface area, and iron contents. B-wood and olive residue cofiring reduces the emission of total gaseous mercury and increases particulate mercury capture due to unburnt carbon formed, fine particles, and iron contents of the ash. Calcium in chicken manure does not show any effect on particulate or gaseous mercury. It is probably due to a higher calcium sulfation rate in the presence of high sulfur and chlorine contents. However, in plant waste cofiring, calcium may have reacted with chlorine to reduce ionic mercury to its elemental form. According to thermodynamic predictions, almost 50% of the total ash is melted to form slag at 1300{sup o}C in cofiring because of high calcium, iron, and potassium and hence mercury and other remaining metals are concentrated in small amounts of ash and show an increase at higher temperatures. No slag formation was predicted at 1000{sup o}C. 24 refs., 8 figs., 4 tabs.« less

Primate diversification inferred from phylogenies and fossils.

PubMed

Herrera, James P

2017-12-01

Biodiversity arises from the balance between speciation and extinction. Fossils record the origins and disappearance of organisms, and the branching patterns of molecular phylogenies allow estimation of speciation and extinction rates, but the patterns of diversification are frequently incongruent between these two data sources. I tested two hypotheses about the diversification of primates based on ∼600 fossil species and 90% complete phylogenies of living species: (1) diversification rates increased through time; (2) a significant extinction event occurred in the Oligocene. Consistent with the first hypothesis, analyses of phylogenies supported increasing speciation rates and negligible extinction rates. In contrast, fossils showed that while speciation rates increased, speciation and extinction rates tended to be nearly equal, resulting in zero net diversification. Partially supporting the second hypothesis, the fossil data recorded a clear pattern of diversity decline in the Oligocene, although diversification rates were near zero. The phylogeny supported increased extinction ∼34 Ma, but also elevated extinction ∼10 Ma, coinciding with diversity declines in some fossil clades. The results demonstrated that estimates of speciation and extinction ignoring fossils are insufficient to infer diversification and information on extinct lineages should be incorporated into phylogenetic analyses. © 2017 The Author(s). Evolution © 2017 The Society for the Study of Evolution.

Bromine speciation in hydrous haplogranitic melts up to 7 GPa

NASA Astrophysics Data System (ADS)

Cochain, B.; de Grouchy, C.; Crepisson, C.; Kantor, I.; Irifune, T.; Sanloup, C.

2013-12-01

Halogens are minor volatiles in the Earth's mantle and crust, but they have significant and specific influences on magmatic and degassing processes. They also provide insights about subsurface magma movement and eruption likelihood in subduction-related volcanism. Their speciation in silicate melts affects volatile exsolution, rheology, and the thermodynamic properties of the melts but still remains relatively unknown. A few studies have explored halogen speciation at room conditions, i.e. in glasses but no firm conclusion has yet been reached. Furthermore, halogen speciation remains unexplored at high pressures and temperatures. In this work we investigate the speciation of Br in subduction-related melt (hydrous haplogranite melt) up to 1200°C and 7 GPa using X-ray absorption spectroscopy (XANES and EXAFS) at the Br K-edge. High P-T conditions were generated by the Paris-Edinburgh press. The use of nanocrystalline diamond capsules enabled us to avoid glitches in the EXAFS spectra. The results provide valuable information on Br speciation and its evolution with pressure. It gives insights into solubility mechanisms for halogens in magmas at depth and on their degassing from the melt. In addition, we were able to identify quench effects on the atomic environment of Br by comparison of high P-T in-situ spectra and ex-situ spectra recorded on quenched samples.

PILOT-SCALE STUDY OF THE EFFECT OF SELECTIVE CATALYTIC REDUCTION CATALYST ON MERCURY SPECIATION IN ILLINOIS AND POWDER RIVER BASIN COAL COMBUSTION FLUE GASES

EPA Science Inventory

A study was conducted to investigate the effect of selective catalytic reduction (SCR) catalyst on mercury (Hg) speciation in bituminous and subbituminous coal combustion flue gases. Three different Illinois Basin bituminous coals (from high to low sulfur and chlorine) and one Po...

Early events in speciation: Cryptic species of Drosophila aldrichi.

PubMed

Castro Vargas, Cynthia; Richmond, Maxi Polihronakis; Ramirez Loustalot Laclette, Mariana; Markow, Therese Ann

2017-06-01

Understanding the earliest events in speciation remains a major challenge in evolutionary biology. Thus identifying species whose populations are beginning to diverge can provide useful systems to study the process of speciation. Drosophila aldrichi , a cactophilic fruit fly species with a broad distribution in North America, has long been assumed to be a single species owing to its morphological uniformity. While previous reports either of genetic divergence or reproductive isolation among different D. aldrichi strains have hinted at the existence of cryptic species, the evolutionary relationships of this species across its range have not been thoroughly investigated. Here we show that D. aldrichi actually is paraphyletic with respect to its closest relative, Drosophila wheeleri , and that divergent D. aldrichi lineages show complete hybrid male sterility when crossed. Our data support the interpretation that there are at least two species of D. aldrichi, making these flies particularly attractive for studies of speciation in an ecological and geographical context.

EPAs SPECIATE 4.4 Database: Development and Uses

EPA Science Inventory

SPECIATE is the U.S. Environmental Protection Agency’s (EPA) repository of source category-specific particulate matter (PM), volatile organic gas, and other gas speciation profiles of air pollutant emissions. Abt Associates, Inc. developed SPECIATE 4.4 through a collaborat...

SPECIATE Version 4.4 Database Development Documentation

EPA Science Inventory

SPECIATE is the U.S. Environmental Protection Agency’s (EPA) repository of volatile organic gas and particulate matter (PM) speciation profiles of air pollution sources. Some of the many uses of these source profiles include: (1) creating speciated emissions inventories for regi...

SPECIATE - EPA'S DATABASE OF SPECIATED EMISSION PROFILES

EPA Science Inventory

SPECIATE is the U.S. Environmental Protection Agency's (EPA) repository of total organic compound (TOC) and particulate matter (PM) speciation profiles for emissions from air pollution sources. The data base has recently been updated and an associated report has recently been re...

Influence of dissolved organic matter and manganese oxides on metal speciation in soil solution: A modelling approach.

PubMed

Schneider, Arnaud R; Ponthieu, Marie; Cancès, Benjamin; Conreux, Alexandra; Morvan, Xavier; Gommeaux, Maxime; Marin, Béatrice; Benedetti, Marc F

2016-06-01

Trace element (TE) speciation modelling in soil solution is controlled by the assumptions made about the soil solution composition. To evaluate this influence, different assumptions using Visual MINTEQ were tested and compared to measurements of free TE concentrations. The soil column Donnan membrane technique (SC-DMT) was used to estimate the free TE (Cd, Cu, Ni, Pb and Zn) concentrations in six acidic soil solutions. A batch technique using DAX-8 resin was used to fractionate the dissolved organic matter (DOM) into four fractions: humic acids (HA), fulvic acids (FA), hydrophilic acids (Hy) and hydrophobic neutral organic matter (HON). To model TE speciation, particular attention was focused on the hydrous manganese oxides (HMO) and the Hy fraction, ligands not considered in most of the TE speciation modelling studies in soil solution. In this work, the model predictions of free ion activities agree with the experimental results. The knowledge of the FA fraction seems to be very useful, especially in the case of high DOM content, for more accurately representing experimental data. Finally, the role of the manganese oxides and of the Hy fraction on TE speciation was identified and, depending on the physicochemical conditions of the soil solution, should be considered in future studies. Copyright © 2016 Elsevier Ltd. All rights reserved.

The composition of coexisting jarosite-group minerals and water from the Richmond mine, Iron Mountain, California

USGS Publications Warehouse

Jamieson, Heather E.; Robinson, Clare; Alpers, Charles N.; Nordstrom, D. Kirk; Poustovetov, Alexei; Lowers, Heather A.

2005-01-01

Jarosite-group minerals accumulate in the form of stalactites and fine-grained mud on massive pyrite in the D drift of the Richmond mine, Iron Mountain, California. Water samples were collected by placing beakers under the dripping stalactites and by extracting pore water from the mud using a centrifuge. The water is rich in Fe3+ and SO4 2−, with a pH of approximately 2.1, which is significantly higher than the extremely acidic waters found elsewhere in the mine. Electron-microprobe analysis and X-ray mapping indicate that the small crystals (<10 μm in diameter) are compositionally zoned with respect to Na and K, and include hydronium jarosite corresponding to the formula (H3O)0.6K0.3Na0.1Fe3 3+(SO4)2(OH)6. The proton-microprobe analyses indicate that the jarosite-group minerals contain significant amounts of As, Pb and Zn, and minor levels of Bi, Rb, Sb, Se, Sn and Sr. Speciation modeling indicates that the drip waters are supersaturated with respect to jarosite-group minerals. The expected range in composition of jarosite-group solid-solution in equilibrium with the pore water extracted from the mud was found to be consistent with the observed range in composition.

SPECIATE--EPA'S DATABASE OF SPECIATED EMISSION PROFILES

EPA Science Inventory

SPECIATE is EPA's repository of Total Organic Compound and Particulate Matter speciated profiles for a wide variety of sources. The profiles in this system are provided for air quality dispersion modeling and as a library for source-receptor and source apportionment type models. ...

SPECIATE 4.4: The Bridge Between Emissions Characterization and Modeling

EPA Science Inventory

SPECIATE is the U.S. Environmental Protection Agency’s (EPA) repository of volatile organic gas and particulate matter (PM) speciation profiles of air pollution sources. Some of the many uses of these source profiles include: (1) creating speciated emissions inventories for...

Algae metabolism and organic carbon in sediments determining arsenic mobilisation in ground- and surface water. A field study in Doñana National Park, Spain.

PubMed

Kohfahl, Claus; Navarro, Daniel Sánchez-Rodas; Mendoza, Jorge Armando; Vadillo, Iñaki; Giménez-Forcada, Elena

2016-02-15

A study has been performed to explore the origin, spatiotemporal behaviour and mobilisation mechanism of the elevated arsenic (As) concentrations found in ground water and drinking ponds of the Doñana National Park, Southern Spain. At a larger scale, 13 piezometers and surface water samples of about 50 artificial drinking ponds and freshwater lagoons throughout the National Park were collected and analysed for major ions, metals and trace elements. At a smaller scale, 5 locations were equipped with piezometers and groundwater was sampled up to 4 times for ambient parameters, major ions, metals, trace elements and iron (Fe) speciation. As was analysed for inorganic and organic speciation. Undisturbed sediment samples were analysed for physical parameters, mineralogy, geochemistry as well as As species. Sediment analyses yielded total As between 0.1 and 18 mg/kg and are not correlated with As concentration in water. Results of the surface- and groundwater sampling revealed elevated concentration of As up to 302 μg/L within a restricted area of the National Park. Results of groundwater sampling reveals strong correlation of As with Fe(2+) pointing to As mobilisation due to reductive dissolution of hydroferric oxides (HFO) in areas of locally elevated amounts of organic matter within the sediments. High As concentrations in surface water ponds are correlated with elevated alkalinity and pH attributed to algae metabolism, leading to As desorption from HFO. The algae metabolism is responsible for the presence of methylated arsenic species in surface water, in contrast to ground water in which only inorganic As species was found. Temporal variations in surface water and groundwater are also related to changes in pH and alkalinity as a result of enhanced algae metabolism in surface water or related to changes in the redox level in the case of groundwater. Copyright © 2015 Elsevier B.V. All rights reserved.

Antipredator defenses predict diversification rates

PubMed Central

Arbuckle, Kevin; Speed, Michael P.

2015-01-01

The “escape-and-radiate” hypothesis predicts that antipredator defenses facilitate adaptive radiations by enabling escape from constraints of predation, diversified habitat use, and subsequently speciation. Animals have evolved diverse strategies to reduce the direct costs of predation, including cryptic coloration and behavior, chemical defenses, mimicry, and advertisement of unprofitability (conspicuous warning coloration). Whereas the survival consequences of these alternative defenses for individuals are well-studied, little attention has been given to the macroevolutionary consequences of alternative forms of defense. Here we show, using amphibians as the first, to our knowledge, large-scale empirical test in animals, that there are important macroevolutionary consequences of alternative defenses. However, the escape-and-radiate hypothesis does not adequately describe them, due to its exclusive focus on speciation. We examined how rates of speciation and extinction vary across defensive traits throughout amphibians. Lineages that use chemical defenses show higher rates of speciation as predicted by escape-and-radiate but also show higher rates of extinction compared with those without chemical defense. The effect of chemical defense is a net reduction in diversification compared with lineages without chemical defense. In contrast, acquisition of conspicuous coloration (often used as warning signals or in mimicry) is associated with heightened speciation rates but unchanged extinction rates. We conclude that predictions based on the escape-and-radiate hypothesis must incorporate the effect of traits on both speciation and extinction, which is rarely considered in such studies. Our results also suggest that knowledge of defensive traits could have a bearing on the predictability of extinction, perhaps especially important in globally threatened taxa such as amphibians. PMID:26483488

The importance of ligand speciation in environmental research: a case study.

PubMed

Sillanpää, M; Orama, M; Rämö, J; Oikari, A

2001-02-21

The speciations of EDTA and DTPA in process, waste and river waters are modelled and simulated, specifically to the mode of occurrence in the pulp and paper mill effluents and subsequently in receiving waters. Due to relatively short residence times in bleaching process and waste water treatment and slow exchange kinetics, it is expected that the thermodynamic equilibrium is not necessarily reached. Therefore, the initial speciation plays a key role. As such, the simulations have been extended to the process waters of the pulp and paper industry taking into account estimated average conditions. The results reveal that the main species are; Mn and Ca complexes of EDTA and DTPA in pulp mill process waters; Fe(III) and Mn complexes of EDTA and DTPA in waste waters; Fe(III) and Zn complexes of EDTA and DTPA in receiving waters. It is also shown how the increasing concentration of complexing agents effects the speciation. Alkaline earth metal chelation plays a significant role in the speciation of EDTA and DTPA when there is a noticeable molar excess of complexing agents compared with transition metals.

Speciation through the lens of biomechanics: locomotion, prey capture and reproductive isolation.

PubMed

Higham, Timothy E; Rogers, Sean M; Langerhans, R Brian; Jamniczky, Heather A; Lauder, George V; Stewart, William J; Martin, Christopher H; Reznick, David N

2016-09-14

Speciation is a multifaceted process that involves numerous aspects of the biological sciences and occurs for multiple reasons. Ecology plays a major role, including both abiotic and biotic factors. Whether populations experience similar or divergent ecological environments, they often adapt to local conditions through divergence in biomechanical traits. We investigate the role of biomechanics in speciation using fish predator-prey interactions, a primary driver of fitness for both predators and prey. We highlight specific groups of fishes, or specific species, that have been particularly valuable for understanding these dynamic interactions and offer the best opportunities for future studies that link genetic architecture to biomechanics and reproductive isolation (RI). In addition to emphasizing the key biomechanical techniques that will be instrumental, we also propose that the movement towards linking biomechanics and speciation will include (i) establishing the genetic basis of biomechanical traits, (ii) testing whether similar and divergent selection lead to biomechanical divergence, and (iii) testing whether/how biomechanical traits affect RI. Future investigations that examine speciation through the lens of biomechanics will propel our understanding of this key process. © 2016 The Author(s).

250 years of hybridization between two biennial herb species without speciation.

PubMed

Matthews, Andrew; Emelianova, Katie; Hatimy, Abubakar A; Chester, Michael; Pellicer, Jaume; Ahmad, Khawaja Shafique; Guignard, Maité S; Rouhan, Germinal; Soltis, Douglas E; Soltis, Pamela S; Leitch, Ilia J; Leitch, Andrew R; Mavrodiev, Evgeny V; Buggs, Richard J A

2015-07-17

Hybridization between plant species can generate novel morphological diversity and lead to speciation at homoploid or polyploid levels. Hybrids between biennial herbs Tragopogon pratensis and T. porrifolius have been studied in experimental and natural populations for over 250 years. Here we examine their current status in natural populations in southeast England. All hybrids found were diploid; they tended to grow taller and with more buds than their parental species; many showed partial fertility; a few showed evidence of backcrossing. However, we found no evidence to suggest that the hybrids are establishing as a new species, nor can we find literature documenting speciation of these hybrids elsewhere. This lack of speciation despite at least 250 years of hybridization contrasts with the fact that both parental species have formed new allopolyploid species through hybridization with another diploid, T. dubius. Understanding why hybrids often do not speciate, despite repeated opportunities, would enhance our understanding of both the evolutionary process and risk assessments of invasive species. Published by Oxford University Press on behalf of the Annals of Botany Company.

Complete genomes of Hairstreak butterflies, their speciation, and nucleo-mitochondrial incongruence

PubMed Central

Cong, Qian; Shen, Jinhui; Borek, Dominika; Robbins, Robert K.; Otwinowski, Zbyszek; Grishin, Nick V.

2016-01-01

Comparison of complete genomes of closely related species enables research on speciation and how phenotype is determined by genotype. Lepidoptera, an insect order of 150,000 species with diverse phenotypes, is well-suited for such comparative genomics studies if new genomes, which cover additional Lepidoptera families are acquired. We report a 729 Mbp genome assembly of the Calycopis cecrops, the first genome from the family Lycaenidae and the largest available Lepidoptera genome. As detritivore, Calycopis shows expansion in detoxification and digestion enzymes. We further obtained complete genomes of 8 Calycopis specimens: 3 C. cecrops and 5 C. isobeon, including a dry specimen stored in the museum for 30 years. The two species differ subtly in phenotype and cannot be differentiated by mitochondrial DNA. However, nuclear genomes revealed a deep split between them. Genes that can clearly separate the two species (speciation hotspots) mostly pertain to circadian clock, mating behavior, transcription regulation, development and cytoskeleton. The speciation hotspots and their function significantly overlap with those we previously found in Pterourus, suggesting common speciation mechanisms in these butterflies. PMID:27120974

A review of recent developments in the speciation and location of arsenic and selenium in rice grain

PubMed Central

Carey, Anne-Marie; Lombi, Enzo; Donner, Erica; de Jonge, Martin D.; Punshon, Tracy; Jackson, Brian P.; Guerinot, Mary Lou; Price, Adam H.; Meharg, Andrew A.

2014-01-01

Rice is a staple food yet is a significant dietary source of inorganic arsenic, a class 1, nonthreshold carcinogen. Establishing the location and speciation of arsenic within the edible rice grain is essential for understanding the risk and for developing effective strategies to reduce grain arsenic concentrations. Conversely, selenium is an essential micronutrient and up to 1 billion people worldwide are selenium-deficient. Several studies have suggested that selenium supplementation can reduce the risk of some cancers, generating substantial interest in biofortifying rice. Knowledge of selenium location and speciation is important, because the anti-cancer effects of selenium depend on its speciation. Germanic acid is an arsenite/silicic acid analogue, and location of germanium may help elucidate the mechanisms of arsenite transport into grain. This review summarises recent discoveries in the location and speciation of arsenic, germanium, and selenium in rice grain using state-of-the-art mass spectrometry and synchrotron techniques, and illustrates both the importance of high-sensitivity and high-resolution techniques and the advantages of combining techniques in an integrated quantitative and spatial approach. PMID:22159463

Complete genomes of Hairstreak butterflies, their speciation, and nucleo-mitochondrial incongruence.

PubMed

Cong, Qian; Shen, Jinhui; Borek, Dominika; Robbins, Robert K; Otwinowski, Zbyszek; Grishin, Nick V

2016-04-28

Comparison of complete genomes of closely related species enables research on speciation and how phenotype is determined by genotype. Lepidoptera, an insect order of 150,000 species with diverse phenotypes, is well-suited for such comparative genomics studies if new genomes, which cover additional Lepidoptera families are acquired. We report a 729 Mbp genome assembly of the Calycopis cecrops, the first genome from the family Lycaenidae and the largest available Lepidoptera genome. As detritivore, Calycopis shows expansion in detoxification and digestion enzymes. We further obtained complete genomes of 8 Calycopis specimens: 3 C. cecrops and 5 C. isobeon, including a dry specimen stored in the museum for 30 years. The two species differ subtly in phenotype and cannot be differentiated by mitochondrial DNA. However, nuclear genomes revealed a deep split between them. Genes that can clearly separate the two species (speciation hotspots) mostly pertain to circadian clock, mating behavior, transcription regulation, development and cytoskeleton. The speciation hotspots and their function significantly overlap with those we previously found in Pterourus, suggesting common speciation mechanisms in these butterflies.

Speciation through the lens of biomechanics: locomotion, prey capture and reproductive isolation

PubMed Central

Rogers, Sean M.; Langerhans, R. Brian; Jamniczky, Heather A.; Lauder, George V.; Stewart, William J.; Martin, Christopher H.; Reznick, David N.

2016-01-01

Speciation is a multifaceted process that involves numerous aspects of the biological sciences and occurs for multiple reasons. Ecology plays a major role, including both abiotic and biotic factors. Whether populations experience similar or divergent ecological environments, they often adapt to local conditions through divergence in biomechanical traits. We investigate the role of biomechanics in speciation using fish predator–prey interactions, a primary driver of fitness for both predators and prey. We highlight specific groups of fishes, or specific species, that have been particularly valuable for understanding these dynamic interactions and offer the best opportunities for future studies that link genetic architecture to biomechanics and reproductive isolation (RI). In addition to emphasizing the key biomechanical techniques that will be instrumental, we also propose that the movement towards linking biomechanics and speciation will include (i) establishing the genetic basis of biomechanical traits, (ii) testing whether similar and divergent selection lead to biomechanical divergence, and (iii) testing whether/how biomechanical traits affect RI. Future investigations that examine speciation through the lens of biomechanics will propel our understanding of this key process. PMID:27629033

ASSESSING SPECIATION AND RELEASE OF HEAVY METALS FROM COAL COMBUSTION PRODUCTS

EPA Science Inventory

In this study, the speciation of heavy metals such as arsenic, selenium, lead, zinc and mercury in coal combustion products (CCPs) was evaluated using sequential extraction procedures. Coal fly ash, bottom ash and flue gas desulphurization (FGD) sludge samples were used in the ex...

Examination of Arsenic Speciation in Sulfidic Solutions Using X-ray Absorption Spectroscopy

EPA Science Inventory

The chemical speciation of arsenic in sulfidic waters is complicated by the existence of thioarsenic species. The purpose of this research was to use advanced spectroscopy techniques along with speciation modeling and chromatography to elucidate the chemical speciation of As in ...

MODELING MONOMETHYLMERCURY AND TRIBUTYLTIN SPECIATION WITH EPA'S GEOCHEMICAL SPECIATION MODEL MINTEQA2

EPA Science Inventory

Given the complexity of the various, simultaneous (and competing) equilibrium reactions governing the speciation of ionic species in aquatic systems, EPA has developed and distributed the geochemical speciation model MINTEQA2 (Brown and Allison, 1987, Allison et al., 1991; Hydrog...

Carbonate-mediated Fe(II) oxidation in the air-cathode fuel cell: a kinetic model in terms of Fe(II) speciation.

PubMed

Song, Wei; Zhai, Lin-Feng; Cui, Yu-Zhi; Sun, Min; Jiang, Yuan

2013-06-06

Due to the high redox activity of Fe(II) and its abundance in natural waters, the electro-oxidation of Fe(II) can be found in many air-cathode fuel cell systems, such as acid mine drainage fuel cells and sediment microbial fuel cells. To deeply understand these iron-related systems, it is essential to elucidate the kinetics and mechanisms involved in the electro-oxidation of Fe(II). This work aims to develop a kinetic model that adequately describes the electro-oxidation process of Fe(II) in air-cathode fuel cells. The speciation of Fe(II) is incorporated into the model, and contributions of individual Fe(II) species to the overall Fe(II) oxidation rate are quantitatively evaluated. The results show that the kinetic model can accurately predict the electro-oxidation rate of Fe(II) in air-cathode fuel cells. FeCO3, Fe(OH)2, and Fe(CO3)2(2-) are the most important species determining the electro-oxidation kinetics of Fe(II). The Fe(II) oxidation rate is primarily controlled by the oxidation of FeCO3 species at low pH, whereas at high pH Fe(OH)2 and Fe(CO3)2(2-) are the dominant species. Solution pH, carbonate concentration, and solution salinity are able to influence the electro-oxidation kinetics of Fe(II) through changing both distribution and kinetic activity of Fe(II) species.

Microfluidic Experiments Studying Pore Scale Interactions of Microbes and Geochemistry

NASA Astrophysics Data System (ADS)

Chen, M.; Kocar, B. D.

2016-12-01

Understanding how physical phenomena, chemical reactions, and microbial behavior interact at the pore-scale is crucial to understanding larger scale trends in groundwater chemistry. Recent studies illustrate the utility of microfluidic devices for illuminating pore-scale physical-biogeochemical processes and their control(s) on the cycling of iron, uranium, and other important elements 1-3. These experimental systems are ideal for examining geochemical reactions mediated by microbes, which include processes governed by complex biological phenomenon (e.g. biofilm formation, etc.)4. We present results of microfluidic experiments using a model metal reducing bacteria and varying pore geometries, exploring the limitations of the microorganisms' ability to access tight pore spaces, and examining coupled biogeochemical-physical controls on the cycling of redox sensitive metals. Experimental results will provide an enhanced understanding of coupled physical-biogeochemical processes transpiring at the pore-scale, and will constrain and compliment continuum models used to predict and describe the subsurface cycling of redox-sensitive elements5. 1. Vrionis, H. A. et al. Microbiological and geochemical heterogeneity in an in situ uranium bioremediation field site. Appl. Environ. Microbiol. 71, 6308-6318 (2005). 2. Pearce, C. I. et al. Pore-scale characterization of biogeochemical controls on iron and uranium speciation under flow conditions. Environ. Sci. Technol. 46, 7992-8000 (2012). 3. Zhang, C., Liu, C. & Shi, Z. Micromodel investigation of transport effect on the kinetics of reductive dissolution of hematite. Environ. Sci. Technol. 47, 4131-4139 (2013). 4. Ginn, T. R. et al. Processes in microbial transport in the natural subsurface. Adv. Water Resour. 25, 1017-1042 (2002). 5. Scheibe, T. D. et al. Coupling a genome-scale metabolic model with a reactive transport model to describe in situ uranium bioremediation. Microb. Biotechnol. 2, 274-286 (2009).

Sulfur speciation and stable isotope trends of water-soluble sulfates in mine tailings profiles.

PubMed

Dold, Bernhard; Spangenberg, Jorge E

2005-08-01

Sulfur speciation and the sources of water-soluble sulfate in three oxidizing sulfidic mine tailings impoundments were investigated by selective dissolution and stable isotopes. The studied tailings impoundments--Piuquenes, Cauquenes, and Salvador No. 1--formed from the exploitation of the Rio Blanco/La Andina, El Teniente, and El Salvador Chilean porphyry copper deposits, which are located in Alpine, Mediterranean, and hyperarid climates, respectively. The water-soluble sulfate may originate from dissolution of primary ore sulfates (e.g., gypsum, anhydrite, jarosite) or from oxidation of sulfide minerals exposed to aerobic conditions during mining activity. With increasing aridity and decreasing pyrite content of the tailings, the sulfur speciation in the unsaturated oxidation zones showed a trend from dominantly Fe(III) oxyhydroxide fixed sulfate (e.g., jarosite and schwertmannite) in Piuquenes toward increasing presence of water-soluble sulfate at Cauquenes and Salvador No. 1. In the saturated primary zones, sulfate is predominantly present in water-soluble form (mainly as anhydrite and/or gypsum). In the unsaturated zone at Piuquenes and Cauquenes, the delta34S(SO4)values ranged from +0.5 per thousand to +2.0 per thousand and from -0.4 per thousand to +1.4 per thousand Vienna Canyon Diablo Troilite (V-CDT), respectively, indicating a major sulfate source from pyrite oxidation (delta34S(pyrite) = -1.1 per thousand and -0.9 per thousand). In the saturated zone at Piuquenes and Cauquenes, the values ranged from -0.8 per thousand to +0.3 per thousand and from +2.2 per thousand to +3.9 per thousand, respectively. At Cauquenes the 34S enrichment in the saturated zone toward depth indicates the increasing contribution of isotopically heavy dissolved sulfate from primary anhydrite (approximately +10.9 per thousand). At El Salvador No. 1, the delta34S(SO4) average value is -0.9 per thousand, suggesting dissolution of supergene sulfate minerals (jarosite, alunite, gypsum) with a delta34S approximately -0.7 per thousand as the most probable sulfate source. The gradual decrease of delta18O(SO4) values from the surface to the oxidation front in the tailings impoundments at Piuquenes (from -4.5 per thousand to -8.6 per thousand Vienna Standard Mean Ocean Water, V-SMOW) and at Cauquenes (from -1.3 per thousand to -3.5 per thousand) indicates the increasing importance of ferric iron as the main electron acceptor in the oxidation of pyrite. The different delta18O(SO4) values between the tailings impoundments studied here reflect the local climates.

Speciation genetics: current status and evolving approaches

PubMed Central

Wolf, Jochen B. W.; Lindell, Johan; Backström, Niclas

2010-01-01

The view of species as entities subjected to natural selection and amenable to change put forth by Charles Darwin and Alfred Wallace laid the conceptual foundation for understanding speciation. Initially marred by a rudimental understanding of hereditary principles, evolutionists gained appreciation of the mechanistic underpinnings of speciation following the merger of Mendelian genetic principles with Darwinian evolution. Only recently have we entered an era where deciphering the molecular basis of speciation is within reach. Much focus has been devoted to the genetic basis of intrinsic postzygotic isolation in model organisms and several hybrid incompatibility genes have been successfully identified. However, concomitant with the recent technological advancements in genome analysis and a newfound interest in the role of ecology in the differentiation process, speciation genetic research is becoming increasingly open to non-model organisms. This development will expand speciation research beyond the traditional boundaries and unveil the genetic basis of speciation from manifold perspectives and at various stages of the splitting process. This review aims at providing an extensive overview of speciation genetics. Starting from key historical developments and core concepts of speciation genetics, we focus much of our attention on evolving approaches and introduce promising methodological approaches for future research venues. PMID:20439277

Assessment of Important SPECIATE Profiles in EPA’s Emissions Modeling Platform and Current Data Gaps

EPA Science Inventory

The US Environmental Protection Agency (EPA)’s SPECIATE database contains speciation profiles for both particulate matter (PM) and volatile organic compounds (VOCs) that are key inputs for creating speciated emission inventories for air quality modeling. The objective of th...

Extraordinarily rapid speciation in a marine fish

PubMed Central

Momigliano, Paolo; Jokinen, Henri; Fraimout, Antoine; Florin, Ann-Britt; Norkko, Alf; Merilä, Juha

2017-01-01

Divergent selection may initiate ecological speciation extremely rapidly. How often and at what pace ecological speciation proceeds to yield strong reproductive isolation is more uncertain. Here, we document a case of extraordinarily rapid speciation associated with ecological selection in the postglacial Baltic Sea. European flounders (Platichthys flesus) in the Baltic exhibit two contrasting reproductive behaviors: pelagic and demersal spawning. Demersal spawning enables flounders to thrive in the low salinity of the Northern Baltic, where eggs cannot achieve neutral buoyancy. We show that demersal and pelagic flounders are a species pair arising from a recent event of speciation. Despite having a parapatric distribution with extensive overlap, the two species are reciprocally monophyletic and show strongly bimodal genotypic clustering and no evidence of contemporary migration, suggesting strong reproductive isolation. Divergence across the genome is weak but shows strong signatures of selection, a pattern suggestive of a recent ecological speciation event. We propose that spawning behavior in Baltic flounders is the trait under ecologically based selection causing reproductive isolation, directly implicating a process of ecological speciation. We evaluated different possible evolutionary scenarios under the approximate Bayesian computation framework and estimate that the speciation process started in allopatry ∼2,400 generations ago, following the colonization of the Baltic by the demersal lineage. This is faster than most known cases of ecological speciation and represents the most rapid event of speciation ever reported for any marine vertebrate. PMID:28533412

Assessing element distribution and speciation in a stream at abandoned Pb-Zn mining site by combining classical, in-situ DGT and modelling approaches.

PubMed

Omanović, Dario; Pižeta, Ivanka; Vukosav, Petra; Kovács, Elza; Frančišković-Bilinski, Stanislav; Tamás, János

2015-04-01

The distribution and speciation of elements along a stream subjected to neutralised acid mine drainage (NAMD) effluent waters (Mátra Mountain, Hungary; Toka stream) were studied by a multi-methodological approach: dissolved and particulate fractions of elements were determined by HR-ICPMS, whereas speciation was carried out by DGT, supported by speciation modelling performed by Visual MINTEQ. Before the NAMD discharge, the Toka is considered as a pristine stream, with averages of dissolved concentrations of elements lower than world averages. A considerable increase of element concentrations caused by effluent water inflow is followed by a sharp or gradual concentration decrease. A large difference between total and dissolved concentrations was found for Fe, Al, Pb, Cu, Zn and As in effluent water and at the first downstream site, with high correlation factors between elements in particulate fraction, indicating their common behaviour, governed by the formation of ferri(hydr)oxides (co)precipitates. In-situ speciation by the DGT technique revealed that Zn, Cd, Ni, Co, Mn and U were predominantly present as a labile, potentially bioavailable fraction (>90%). The formation of strong complexes with dissolved organic matter (DOM) resulted in a relatively low DGT-labile concentration of Cu (42%), while low DGT-labile concentrations of Fe (5%) and Pb (12%) were presumably caused by their existence in colloidal (particulate) fraction which is not accessible to DGT. Except for Fe and Pb, a very good agreement between DGT-labile concentrations and those predicted by the applied speciation model was obtained, with an average correlation factor of 0.96. This study showed that the in-situ DGT technique in combination with model-predicted speciation and classical analysis of samples could provide a reasonable set of data for the assessment of the water quality status (WQS), as well as for the more general study of overall behaviour of the elements in natural waters subjected to high element loads. Copyright © 2014 Elsevier B.V. All rights reserved.

Cobalt Distribution and Speciation: Effect of Aging, Intermittent Submergence, In situ Rice Roots

EPA Science Inventory

The speciation and distribution of cobalt (Co) in soils is poorly understood. This study was conducted using X-ray absorption spectroscopy (XAS) techniques to examine the influence of soluble Co(II) aging, submergence-dried cycling, and the presence of in vivo rice roots on the...

Phosphorus solubility of agricultural soils: a surface charge and phosphorus-31 NMR speciation study

USDA-ARS?s Scientific Manuscript database

We investigated ten soils from six states in United States to determine the relationship between potentiometric titration derived soil surface charge and Phosphorus-31 (P) nuclear magnetic resonance (NMR) speciation with the concentration of water-extractable P (WEP). The surface charge value at the...

METHODS INTERCOMPARISON OF SAMPLERS FOR EPA'S NATIONAL PM 2.5 CHEMICAL SPECIATION NETWORK

EPA Science Inventory

The objective of this sampler intercomparison field study is to determine the performance characteristics for the collection of the chemical components of PM2.5 by the chemical speciation monitors developed for the national PM2.5 network relative to each other, to the Federal R...

TEMPORAL VARIABILITY IN PHYSICAL SPECIATION OF METALS DURING A WINTER RAIN-ON-SNOW EVENT

EPA Science Inventory

Particulate matter in urban rivers transports a significant fraction of pollutants, changes rapidly during storm events and is difficult to characterize. In this study, the physical speciation of trace metals and organic carbon in an urban river and upstream headwaters site in To...

Application of chemometric analysis and self Organizing Map-Artificial Neural Network as source receptor modeling for metal speciation in river sediment.

PubMed

Pandey, Mayank; Pandey, Ashutosh Kumar; Mishra, Ashutosh; Tripathi, B D

2015-09-01

Present study deals with the river Ganga water quality and its impact on metal speciation in its sediments. Concentration of physico-chemical parameters was highest in summer season followed by winter and lowest in rainy season. Metal speciation study in river sediments revealed that exchangeable, reducible and oxidizable fractions were dominant in all the studied metals (Cr, Ni, Cu, Zn, Cd, Pb) except Mn and Fe. High pollution load index (1.64-3.89) recommends urgent need of mitigation measures. Self-organizing Map-Artificial Neural Network (SOM-ANN) was applied to the data set for the prediction of major point sources of pollution in the river Ganga. Copyright © 2015 Elsevier Ltd. All rights reserved.

Precipitation pathways for ferrihydrite formation in acidic solutions

DOE PAGES

Zhu, Mengqiang; Khalid, Syed; Frandsen, Cathrine; ...

2015-10-03

In this study, iron oxides and oxyhydroxides form via Fe 3+ hydrolysis and polymerization in many aqueous environments, but the pathway from Fe 3+ monomers to oligomers and then to solid phase nuclei is unknown. In this work, using combined X-ray, UV–vis, and Mössbauer spectroscopic approaches, we were able to identify and quantify the long-time sought ferric speciation over time during ferric oxyhydroxide formation in partially-neutralized ferric nitrate solutions ([Fe 3+] = 0.2 M, 1.8 < pH < 3). Results demonstrate that Fe exists mainly as Fe(H 2O) 6 3+, μ-oxo aquo dimers and ferrihydrite, and that with time, themore » μ-oxo dimer decreases while the other two species increase in their concentrations. No larger Fe oligomers were detected. Given that the structure of the μ-oxo dimer is incompatible with those of all Fe oxides and oxyhydroxides, our results suggest that reconfiguration of the μ-oxo dimer structure occurs prior to further condensation leading up to the nucleation of ferrihydrite. The structural reconfiguration is likely the rate-limiting step involved in the nucleation process.« less

Pyrolysis of the mixture of MSWI fly ash and sewage sludge for co-disposal: Effect of ferrous/ferric sulfate additives.

PubMed

Hu, Yuyan; Yang, Fan; Chen, Fangfang; Feng, Yuheng; Chen, Dezhen; Dai, Xiaohu

2018-05-01

Co-pyrolysis with sewage sludge was proved to be an efficient pre-treatment for sanitary landfill of municipal solid waste incineration (MSWI) fly ash (FA). In this study, to improve the stabilization effect of heavy metals, mixed ferrous/ferric sulfate was added into the FA/SS mixture before pyrolysis. To examine the feasibility of the landfill of co-pyrolysis char, toxicity characteristic leaching procedure (HJ/T300) was conducted. In addition, physio-chemical characteristics of char were also tested to explain the stability of heavy metals, including the speciation, mineralogical composition and the morphological features of them. The results indicated that within the range that the obtained char could meet the standard for landfill (GB16889-2008), the appropriate addition of mixed ferrous/ferric sulfates benefit to raising the FA ratio in the FA/SS mixture. The maximum ratio of 67 wt% is achieved when the additive was 1.5 wt% of dried SS (based on iron element) and the pyrolysis temperature was 500 °C. Copyright © 2018 Elsevier Ltd. All rights reserved.

Oxygenation of the Mesoproterozoic ocean and the evolution of complex eukaryotes

NASA Astrophysics Data System (ADS)

Zhang, Kan; Zhu, Xiangkun; Wood, Rachel A.; Shi, Yao; Gao, Zhaofu; Poulton, Simon W.

2018-05-01

The Mesoproterozoic era (1,600-1,000 million years ago (Ma)) has long been considered a period of relative environmental stasis, with persistently low levels of atmospheric oxygen. There remains much uncertainty, however, over the evolution of ocean chemistry during this period, which may have been of profound significance for the early evolution of eukaryotic life. Here we present rare earth element, iron-speciation and inorganic carbon isotope data to investigate the redox evolution of the 1,600-1,550 Ma Yanliao Basin, North China Craton. These data confirm that the ocean at the start of the Mesoproterozoic was dominantly anoxic and ferruginous. Significantly, however, we find evidence for a progressive oxygenation event starting at 1,570 Ma, immediately prior to the occurrence of complex multicellular eukaryotes in shelf areas of the Yanliao Basin. Our study thus demonstrates that oxygenation of the Mesoproterozoic environment was far more dynamic and intense than previously envisaged, and establishes an important link between rising oxygen and the emerging record of diverse, multicellular eukaryotic life in the early Mesoproterozoic.

Bioconcentration and arsenic speciation analysis in ragworm, Hediste diversicolor (Muller 1776).

PubMed

Gaion, Andrea; Scuderi, Alice; Pellegrini, David; Sartori, Davide

2013-01-01

This study focused on bioconcentrations of arsenic in Hediste diversicolor (Müller 1776) after exposure to three different molecule solutions: arsenate, dimethyl-arsinate and arsenobetaine. Speciation analysis was carried out after exposing the organisms to these solutions in order to investigate their arsenic biotransformation capacity. Arsenic reached to the maximum level in these tissues after 15 days' exposure to a solution of 100 μg L(-1) of arsenobetaine, although a significant increase was obtained in worms exposed to arsenate. Speciation analysis shows that trimethyl-arsine oxide is the slowest detoxification phase recorded in experiment.

Selenium speciation in seleniferous agricultural soils under different cropping systems using sequential extraction and X-ray absorption spectroscopy.

PubMed

Qin, Hai-Bo; Zhu, Jian-Ming; Lin, Zhi-Qing; Xu, Wen-Po; Tan, De-Can; Zheng, Li-Rong; Takahashi, Yoshio

2017-06-01

Selenium (Se) speciation in soil is critically important for understanding the solubility, mobility, bioavailability, and toxicity of Se in the environment. In this study, Se fractionation and chemical speciation in agricultural soils from seleniferous areas were investigated using the elaborate sequential extraction and X-ray absorption near-edge structure (XANES) spectroscopy. The speciation results quantified by XANES technique generally agreed with those obtained by sequential extraction, and the combination of both approaches can reliably characterize Se speciation in soils. Results showed that dominant organic Se (56-81% of the total Se) and lesser Se(IV) (19-44%) were observed in seleniferous agricultural soils. A significant decrease in the proportion of organic Se to the total Se was found in different types of soil, i.e., paddy soil (81%) > uncultivated soil (69-73%) > upland soil (56-63%), while that of Se(IV) presented an inverse tendency. This suggests that Se speciation in agricultural soils can be significantly influenced by different cropping systems. Organic Se in seleniferous agricultural soils was probably derived from plant litter, which provides a significant insight for phytoremediation in Se-laden ecosystems and biofortification in Se-deficient areas. Furthermore, elevated organic Se in soils could result in higher Se accumulation in crops and further potential chronic Se toxicity to local residents in seleniferous areas. Copyright © 2017 Elsevier Ltd. All rights reserved.

Effect of Phosphate on U(VI) Sorption to Montmorillonite: Ternary Complexation and Precipitation Barriers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Troyer, Lyndsay D.; Maillot, Fabien; Wang, Zheming

Phosphate addition is a potential treatment method to lower the solubility of U(VI) in soil and groundwater systems by causing U(VI) phosphate precipitation as well as enhancing adsorption. Previous work has shown that iron oxide surfaces may facilitate the nucleation of U(VI) phosphate minerals and, that under weakly acidic conditions, phosphate also enhances U(VI) adsorption to such phases. Like iron oxides, clays are important reactive phases in the subsurface but little is known about the interaction of U(VI) and phosphate with these minerals. The effect of aqueous phosphate on U(VI) binding to Wyoming montmorillonite (SWy-2) in air-equilibrated systems was investigated.more » Equilibrium U(VI) uptake to montmorillonite was determined at pH 4, 6 and 8 at discrete initial phosphate concentrations between 0 and 100 μM. The observed behavior of U(VI) indicates a transition from adsorption to precipitation with increasing total uranium and phosphate concentrations at all pH values. At the highest phosphate concentration examined at each pH value, a barrier to U(VI) phosphate nucleation is observed. At lower concentrations, phosphate has no effect on macroscopic U(VI) adsorption. To assess the mechanisms of U(VI)-phosphate interactions on smectite surfaces, U(VI) speciation was investigated under selected conditions using laser-induced fluorescence spectroscopy (LIFS) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Samples above the precipitation threshold display EXAFS and LIFS spectral signatures consistent with the autunite family of U(VI) phosphate minerals. However, at lower U(VI) concentrations, changes in LIFS spectra upon phosphate addition suggest that U(VI)-phosphate ternary surface complexes form on the montmorillonite surface at pH 4 and 6 despite the lack of a macroscopic effect on adsorption. The speciation of solid-associated U(VI) below the precipitation threshold at pH 8 is dominated by U(VI)-carbonate surface complexes. This work reveals that ternary complexation may occur without a macroscopic signature, which is attributed to phosphate not appreciably binding to smectite in the absence of U(VI), with U(VI) surface complexes serving as the sole reactive surface sites for phosphate. This study shows that phosphate does not enhance U(VI) adsorption to smectite clay minerals, unlike oxide phases, and that a barrier to homogeneous nucleation of U(VI) phosphates was not affected by the presence of the smectite surface« less

Iron speciation and isotope fractionation during silicate weathering and soil formation in an alpine glacier forefield chronosequence

NASA Astrophysics Data System (ADS)

Kiczka, Mirjam; Wiederhold, Jan G.; Frommer, Jakob; Voegelin, Andreas; Kraemer, Stephan M.; Bourdon, Bernard; Kretzschmar, Ruben

2011-10-01

The chemical weathering of primary Fe-bearing minerals, such as biotite and chlorite, is a key step of soil formation and an important nutrient source for the establishment of plant and microbial life. The understanding of the relevant processes and the associated Fe isotope fractionation is therefore of major importance for the further development of stable Fe isotopes as a tracer of the biogeochemical Fe cycle in terrestrial environments. We investigated the Fe mineral transformations and associated Fe isotope fractionation in a soil chronosequence of the Swiss Alps covering 150 years of soil formation on granite. For this purpose, we combined for the first time stable Fe isotope analyses with synchrotron-based Fe-EXAFS spectroscopy, which allowed us to interpret changes in Fe isotopic composition of bulk soils, size fractions, and chemically separated Fe pools over time in terms of weathering processes. Bulk soils and rocks exhibited constant isotopic compositions along the chronosequence, whereas soil Fe pools in grain size fractions spanned a range of 0.4‰ in δ 56Fe. The clay fractions (<2 μm), in which newly formed Fe(III)-(hydr)oxides contributed up to 50% of the total Fe, were significantly enriched in light Fe isotopes, whereas the isotopic composition of silt and sand fractions, containing most of the soil Fe, remained in the range described by biotite/chlorite samples and bulk soils. Iron pools separated by a sequential extraction procedure covered a range of 0.8‰ in δ 56Fe. For all soils the lightest isotopic composition was observed in a 1 M NH 2OH-HCl-25% acetic acid extract, targeting poorly-crystalline Fe(III)-(hydr)oxides, compared with easily leachable Fe in primary phyllosilicates (0.5 M HCl extract) and Fe in residual silicates. The combination of the Fe isotope measurements with the speciation data obtained by Fe-EXAFS spectroscopy permitted to quantitatively relate the different isotope pools forming in the soils to the mineral weathering reactions which have taken place at the field site. A kinetic isotope effect during the Fe detachment from the phyllosilicates was identified as the dominant fractionation mechanism in young weathering environments, controlling not only the light isotope signature of secondary Fe(III)-(hydr)oxides but also significantly contributing to the isotope signature of plants. The present study further revealed that this kinetic fractionation effect can persist over considerable reaction advance during chemical weathering in field systems and is not only an initial transient phenomenon.

A Study of Iron-Nitrogen-Carbon Fuel Cell Catalysts: Chemistry - Nanostructure - Performance

NASA Astrophysics Data System (ADS)

Workman, Michael J., Jr.

Fuel cells have the potential to be a pollution-free, low-cost, and energy efficient alternative to the internal combustion engine for transportation and small-scale stationary power applications. The current state of fuel cell technology has already achieved two of these three lofty goals. The remaining barrier to wide-scale deployment is the high cost, which is primarily caused by dependence on large amounts of platinum to catalyze the energy conversion reactions. To overcome this barrier and facilitate the integration of fuel cells into mainstream applications, research into a new class of catalyst materials that do not require platinum is needed. There has been a significant amount of research effort directed toward the development of platinum-group metal free (PGM-free) catalysts, yet there is a lack of consensus on both the engineering parameters necessary to improve the technology and the fundamental science that would facilitate rational design. I have engaged in research on PGM-free catalysts based on inexpensive and abundant reagents, specifically: nicarbazin and iron. Catalysts made from these precursors have previously proven to be among the best PGM-free catalysts, but their continued advancement suffered from the same lack of understanding that besets all catalysts in this class. The work I have performed address both engineering concerns and fundamental underlying principles. I present results demonstrating correlations between physical structure, chemical speciation, and synthesis parameters, as well as addressing active site chemistry and likely locations. My research presented herein introduces new morphology analysis techniques and elucidates several key structure-to-property characteristics of catalysts derived from iron and nicarbazin. I discuss the development and application of a new length-scale specific surface analysis technique that allows for analysis of well-defined size ranges from a few nm to several microns. The existing technique of focused ion beam tomography is modified and optimized for platinum-group metal free catalyst layers, facilitating direct observation of catalyst integration into catalyst layers. I present evidence supporting the hypothesis that atomically dispersed iron coordinated with nitrogen are the dominant active sites in these catalysts. Further, that the concentration of surface oxides in the carbon structure, which can be directly influenced by synthesis parameters, correlates with both the concentration of active sites in the material and with fuel cell performance. Catalyst performance is hindered by the addition of carbon nanotubes and by the presence of metallic iron. Evidence consistent with the catalytic active sites residing in the graphitic plane is also presented.

Linking benthic microbial community dynamics to diel redox variations in a near shore costal environment, Héeia Fishpond

NASA Astrophysics Data System (ADS)

Frank, K. L.; Rogers, K. L.; Wheat, C. G.; Alegado, R.

2016-12-01

Microbes play crucial roles in mediating biogeochemical cycling in coastal marine habitats. In shallow coastal ecosystems, excess primary productivity and respiration of pelagic phototrophic organisms generate striking diel variations in dissolved oxygen concentrations, leading to substantial vertical migration of redox transition zones in the sediment. However, the relationship between microbial community dynamics and the establishment of these geochemical gradients, especially over a diel time frame, remains poorly constrained. Here we examine the biogeochemical drivers of diel redox dynamics by integrating comprehensive geochemical, taxonomic, functional gene abundance, and thermodynamic datasets from Héeia Fishpond (HFP) sediment cores. HFP, an 88-acre tidally-influenced, shallow Hawaiian coastal estuarine system, is analogous to a large mesocosm embedded in a natural coastal environment, making it an ideal site for coastal biogeochemical studies. Taxonomic assessments of bacterial diversity via 16S rRNA genes revealed centimeter- scale variability with depth, with similar taxa present in all samples, but their relative abundances varied substantially among horizons. There were significant correlation between changes in geochemical composition and changes in community structure. Additionally, functional gene abundance was correlated with energy potential and aligned with activity. The taxanomic data and porewater geochemistry from HFP sediments suggest that redox variations observed in iron and sulfur speciation result from depth-related changes in microbial activity and community structure over a diel period. By linking community diversity to metabolic activity in the context of the geochemical environment, this research provides valuable insight into the connectivity of iron and sulfur metabolic modes.

Biogeochemical stability and reactions of iron-organic carbon complexes

NASA Astrophysics Data System (ADS)

Yang, Y.; Adhikari, D.; Zhao, Q.; Dunham-Cheatham, S.; Das, K.; Mejia, J.; Huang, R.; Wang, X.; Poulson, S.; Tang, Y.; Obrist, D.; Roden, E. E.

2017-12-01

Our core hypothesis is that the degradation rate of soil organic carbon (OC) is governed by the amount of iron (Fe)-bound OC, and the ability of microbial communities to utilize OC as an energy source and electron shuttle for Fe reduction that in turn stimulates reductive release of Fe-bound labile dissolved OC. This hypothesis is being systematically evaluated using model Fe-OC complexes, natural soils, and microcosm system. We found that hematite-bound aliphatic C was more resistant to reduction release, although hematite preferred to sorb more aromatic C. Resistance to reductive release represents a new mechanism that aliphatic soil OC was stabilized by association with Fe oxide. In other studies, pyrogenic OC was found to facilitate the reduction of hematite, by enhancing extracellular electron transport and sorbing Fe(II). For ferrihydrite-OC co-precipitates, the reduction of Fe and release of OC was closely governed by the C/Fe ratio in the system. Based on the XPS, XANES and XAFS analysis, the transformation of Fe speciation was heterogeneous, depending on the conformation and composition of Fe-OC complexes. For natural soils, we investigated the quantity, characteristics, and reactivity of Fe-bound OC in soils collected from 14 forests in the United States. Fe-bound OC contributed up to 57.8% of total OC in the forest soils. Under the anaerobic conditions, the reduction of Fe was positively correlated to the electron accepting capacity of OC. Our findings highlight the closely coupled dynamics of Fe and OC, with broad implications on the turnover of OC and biogeochemical cycles of Fe.

Temperature dependence and coupling of iron and arsenic reduction and release during flooding of a contaminated soil.

PubMed

Weber, Frank-Andreas; Hofacker, Anke F; Voegelin, Andreas; Kretzschmar, Ruben

2010-01-01

Arsenic (As) in soils and sediments is commonly mobilized when anoxic conditions promote microbial iron (Fe) and As reduction. Recent laboratory studies and field observations have suggested a decoupling between Fe and As reduction and release, but the links between these processes are still not well understood. In microcosm experiments, we monitored the formation of Fe(II) and As(III) in the porewater and in the soil solid-phase during flooding of a contaminated floodplain soil at temperatures of 23, 14, and 5 degrees C. At all temperatures, flooding induced the development of anoxic conditions and caused increasing concentrations of dissolved Fe(II) and As(III). Decreasing the temperature from 23 to 14 and 5 degrees C strongly slowed down soil reduction and Fe and As release. Speciation of As in the soil solid-phase by X-ray absorption spectroscopy (XAS) and extraction of the Fe(II) that has formed by reductive Fe(III) (hydr)oxide dissolution revealed that less than 3.9% of all As(III) and less than 3.2% of all Fe(II) formed during 52 days of flooding at 23 degrees C were released into the porewater, although 91% of the initially ascorbate-extractable Fe and 66% of the total As were reduced. The amount of total As(III) formed during soil reduction was linearly correlated to the amount of total Fe(II) formed, indicating that the rate of As(V) reduction was controlled by the rate of microbial Fe(III) (hydr)oxide reduction.

Toxic metal immobilization in contaminated sediment using bentonite- and kaolinite-supported nano zero-valent iron

NASA Astrophysics Data System (ADS)

Tomašević, D. D.; Kozma, G.; Kerkez, Dj. V.; Dalmacija, B. D.; Dalmacija, M. B.; Bečelić-Tomin, M. R.; Kukovecz, Á.; Kónya, Z.; Rončević, S.

2014-08-01

The objective of this study was to investigate the possibility of using supported nanoscale zero-valent iron with bentonite and kaolinite for immobilization of As, Pb and Zn in contaminated sediment from the Nadela river basin (Serbia). Assessment of the sediment quality based on the pseudo-total metal content (As, Pb and Zn) according to the corresponding Serbian standards shows its severe contamination, such that it requires disposal in special reservoirs and, if possible, remediation. A microwave-assisted sequential extraction procedure was employed to assess potential metal mobility and risk to the aquatic environment. According to these results, As showed lower risk to the environment than Pb and Zn, which both represent higher risk to the environment. The contaminated sediment, irrespective of the different speciation of the treated metals, was subjected to the same treatment. Semi-dynamic leaching test, based on leachability index and effective diffusion coefficients, was conducted for As-, Pb- and Zn-contaminated sediments in order to assess the long-term leaching behaviour. In order to simulate "worst case" leaching conditions, the test was modified using acetic and humic acid solution as leachants instead of deionized water. A diffusion-based model was used to elucidate the controlling leaching mechanisms; in the majority of samples, the controlling leaching mechanism appeared to be diffusion. Three different single-step leaching tests were applied to evaluate the extraction potential of examined metals. Generally, the test results indicated that the treated sediment is safe for disposal and could even be considered for "controlled utilization".

[XANES study of lead speciation in duckweed].

PubMed

Chu, Bin-Bin; Luo, Li-Qiang; Xu, Tao; Yuan, Jing; Sun, Jian-Ling; Zeng, Yuan; Ma, Yan-Hong; Yi, Shan

2012-07-01

Qixiashan lead-zinc mine of Nanjing was one of the largest lead zinc deposits in East China Its exploitation has been over 50 years, and the environmental pollution has also been increasing. The lead concentration in the local environment was high, but lead migration and toxic mechanism has not been clear. Therefore, biogeochemistry research of the lead zinc mine was carried out. Using ICP-MS and Pb-L III edge XANES, lead concentration and speciation were analyzed respectively, and duckweed which can tolerate and enriched heavy metals was found in the pollution area. The results showed that the lead concentration of duckweed was 39.4 mg x kg(-1). XANES analysis and linear combination fit indicated that lead stearate and lead sulfide accounted for 65% and 36.9% respectively in the lead speciation of duckweed, suggesting that the main lead speciation of duckweed was sulfur-containing lead-organic acid.

Rates of speciation and morphological evolution are correlated across the largest vertebrate radiation.

PubMed

Rabosky, Daniel L; Santini, Francesco; Eastman, Jonathan; Smith, Stephen A; Sidlauskas, Brian; Chang, Jonathan; Alfaro, Michael E

2013-01-01

Several evolutionary theories predict that rates of morphological change should be positively associated with the rate at which new species arise. For example, the theory of punctuated equilibrium proposes that phenotypic change typically occurs in rapid bursts associated with speciation events. However, recent phylogenetic studies have found little evidence linking these processes in nature. Here we demonstrate that rates of species diversification are highly correlated with the rate of body size evolution across the 30,000+ living species of ray-finned fishes that comprise the majority of vertebrate biological diversity. This coupling is a general feature of fish evolution and transcends vast differences in ecology and body-plan organization. Our results may reflect a widespread speciational mode of character change in living fishes. Alternatively, these findings are consistent with the hypothesis that phenotypic 'evolvability'-the capacity of organisms to evolve-shapes the dynamics of speciation through time at the largest phylogenetic scales.

Global cooling as a driver of diversification in a major marine clade

PubMed Central

Davis, Katie E.; Hill, Jon; Astrop, Tim I.; Wills, Matthew A.

2016-01-01

Climate is a strong driver of global diversity and will become increasingly important as human influences drive temperature changes at unprecedented rates. Here we investigate diversification and speciation trends within a diverse group of aquatic crustaceans, the Anomura. We use a phylogenetic framework to demonstrate that speciation rate is correlated with global cooling across the entire tree, in contrast to previous studies. Additionally, we find that marine clades continue to show evidence of increased speciation rates with cooler global temperatures, while the single freshwater clade shows the opposite trend with speciation rates positively correlated to global warming. Our findings suggest that both global cooling and warming lead to diversification and that habitat plays a role in the responses of species to climate change. These results have important implications for our understanding of how extant biota respond to ongoing climate change and are of particular importance for conservation planning of marine ecosystems. PMID:27701377

Computer simulations of sympatric speciation in a simple food web

NASA Astrophysics Data System (ADS)

Luz-Burgoa, K.; Dell, Tony; de Oliveira, S. Moss

2005-07-01

Galapagos finches, have motivated much theoretical research aimed at understanding the processes associated with the formation of the species. Inspired by them, in this paper we investigate the process of sympatric speciation in a simple food web model. For that we modify the individual-based Penna model that has been widely used to study aging as well as other evolutionary processes. Initially, our web consists of a primary food source and a single herbivore species that feeds on this resource. Subsequently we introduce a predator that feeds on the herbivore. In both instances we manipulate directly a basal resource distribution and monitor the changes in the populations. Sympatric speciation is obtained for the top species in both cases, and our results suggest that the speciation velocity depends on how far up, in the food chain, the focus population is feeding. Simulations are done with three different sexual imprintinglike mechanisms, in order to discuss adaptation by natural selection.

Global cooling as a driver of diversification in a major marine clade

NASA Astrophysics Data System (ADS)

Davis, Katie E.; Hill, Jon; Astrop, Tim I.; Wills, Matthew A.

2016-10-01

Climate is a strong driver of global diversity and will become increasingly important as human influences drive temperature changes at unprecedented rates. Here we investigate diversification and speciation trends within a diverse group of aquatic crustaceans, the Anomura. We use a phylogenetic framework to demonstrate that speciation rate is correlated with global cooling across the entire tree, in contrast to previous studies. Additionally, we find that marine clades continue to show evidence of increased speciation rates with cooler global temperatures, while the single freshwater clade shows the opposite trend with speciation rates positively correlated to global warming. Our findings suggest that both global cooling and warming lead to diversification and that habitat plays a role in the responses of species to climate change. These results have important implications for our understanding of how extant biota respond to ongoing climate change and are of particular importance for conservation planning of marine ecosystems.

Assessment of important SPECIATE Profiles in EPA’s Emissions Modeling Platform and Current Data Gaps (US EPA 2017 International Emissions Inventory Conference)

EPA Science Inventory

The US Environmental Protection Agency (EPA)’s SPECIATE database contains speciation profiles for both particulate matter (PM) and volatile organic compounds (VOCs) that are key inputs for creating speciated emission inventories for air quality modeling. The objective of th...

Fate of heavy metals during municipal solid waste incineration.

PubMed

Abanades, S; Flamant, G; Gagnepain, B; Gauthier, D

2002-02-01

A thermodynamic analysis was performed to determine whether it is suitable to predict the heavy metal (HM) speciation during the Municipal Solid Waste Incineration process. The fate of several selected metals (Cd, Pb, Zn, Cr, Hg, As, Cu, Co, Ni) during incineration was theoretically investigated. The equilibrium analysis predicted the metal partitioning during incineration and determined the impact of operating conditions (temperature and gas composition) on their speciation. The study of the gas composition influence was based on the effects of the contents of oxygen (reducing or oxidising conditions) and chlorine on the HM partitioning. The theoretical HM speciation which was calculated in a complex system representing a burning sample of Municipal Solid Waste can explain the real partitioning (obtained from literature results) of all metals among the various ashes except for Pb. Then, the results of the thermodynamic study were compared with those of characterisation of real incinerator residues, using complementary techniques (chemical extraction series and X-ray micro-analyses). These analysis were performed to determine experimentally the speciation of the three representative metals Cr, Pb, and Zn. The agreement is good for Cr and Zn but not for Pb again, which mainly shows unleachable chemical speciations in the residues. Pb tends to remain in the bottom ash whereas thermodynamics often predicts its complete volatilisation under chlorides, and thus its presence exclusively in fly ash.

Riverscape genetics identifies replicated ecological divergence across an Amazonian ecotone.

PubMed

Cooke, Georgina M; Landguth, Erin L; Beheregaray, Luciano B

2014-07-01

Ecological speciation involves the evolution of reproductive isolation and niche divergence in the absence of a physical barrier to gene flow. The process is one of the most controversial topics of the speciation debate, particularly in tropical regions. Here, we investigate ecologically based divergence across an Amazonian ecotone in the electric fish, Steatogenys elegans. We combine phylogenetics, genome scans, and population genetics with a recently developed individual-based evolutionary landscape genetics approach that incorporates selection. This framework is used to assess the relative contributions of geography and divergent natural selection between environments as biodiversity drivers. We report on two closely related and sympatric lineages that exemplify how divergent selection across a major Amazonian aquatic ecotone (i.e., between rivers with markedly different hydrochemical properties) may result in replicated ecologically mediated speciation. The results link selection across an ecological gradient with reproductive isolation and we propose that assortative mating based on water color may be driving the divergence. Divergence resulting from ecologically driven selection highlights the importance of considering environmental heterogeneity in studies of speciation in tropical regions. Furthermore, we show that framing ecological speciation in a spatially explicit evolutionary landscape genetics framework provides an important first step in exploring a wide range of the potential effects of spatial dependence in natural selection. © 2014 The Author(s). Evolution © 2014 The Society for the Study of Evolution.

How does male–male competition generate negative frequency-dependent selection and disruptive selection during speciation?

PubMed Central

Border, Shana E

2018-01-01

Abstract Natural selection has been shown to drive population differentiation and speciation. The role of sexual selection in this process is controversial; however, most of the work has centered on mate choice while the role of male–male competition in speciation is relatively understudied. Here, we outline how male–male competition can be a source of diversifying selection on male competitive phenotypes, and how this can contribute to the evolution of reproductive isolation. We highlight how negative frequency-dependent selection (advantage of rare phenotype arising from stronger male–male competition between similar male phenotypes compared with dissimilar male phenotypes) and disruptive selection (advantage of extreme phenotypes) drives the evolution of diversity in competitive traits such as weapon size, nuptial coloration, or aggressiveness. We underscore that male–male competition interacts with other life-history functions and that variable male competitive phenotypes may represent alternative adaptive options. In addition to competition for mates, aggressive interference competition for ecological resources can exert selection on competitor signals. We call for a better integration of male–male competition with ecological interference competition since both can influence the process of speciation via comparable but distinct mechanisms. Altogether, we present a more comprehensive framework for studying the role of male–male competition in speciation, and emphasize the need for better integration of insights gained from other fields studying the evolutionary, behavioral, and physiological consequences of agonistic interactions. PMID:29492042

A study of method robustness for arsenic speciation in drinking water samples by anion exchange HPLC-ICP-MS.

PubMed

Day, Jason A; Montes-Bayón, María; Vonderheide, Anne P; Caruso, Joseph A

2002-08-01

Regulating arsenic species in drinking waters is a reasonable objective, since the various species have different toxicological impacts. However, developing robust and sensitive speciation methods is mandatory prior to any such regulations. Numerous arsenic speciation publications exist, but the question of robustness or ruggedness for a regulatory method has not been fully explored. The present work illustrates the use of anion exchange chromatography coupled to ICP-MS with a commercially available "speciation kit" option. The mobile phase containing 2 mM NaH(2)PO(4) and 0.2 mM EDTA at pH 6 allowed adequate separation of four As species (As(III), As(V), MMAA, DMAA) in less than 10 min. The analytical performance characteristics studied, including method detection limits (lower than 100 ng L(-1) for all the species evaluated), proved the suitability of the method to fulfill the current regulation. Other parameters evaluated such as laboratory fortified blanks, spiked recoveries, and reproducibility over a certain period of time produced adequate results. The samples analyzed were taken from water utilities in different areas of the United States and were provided by the U.S. EPA. The data suggests the speciation setup performs to U.S. EPA specifications but sample treatment and chemistry are also important factors for achieving good recoveries for samples spiked with As(III) as arsenite and As(V) as arsenate.

Influence of gene flow on divergence dating - implications for the speciation history of Takydromus grass lizards.

PubMed

Tseng, Shu-Ping; Li, Shou-Hsien; Hsieh, Chia-Hung; Wang, Hurng-Yi; Lin, Si-Min

2014-10-01

Dating the time of divergence and understanding speciation processes are central to the study of the evolutionary history of organisms but are notoriously difficult. The difficulty is largely rooted in variations in the ancestral population size or in the genealogy variation across loci. To depict the speciation processes and divergence histories of three monophyletic Takydromus species endemic to Taiwan, we sequenced 20 nuclear loci and combined with one mitochondrial locus published in GenBank. They were analysed by a multispecies coalescent approach within a Bayesian framework. Divergence dating based on the gene tree approach showed high variation among loci, and the divergence was estimated at an earlier date than when derived by the species-tree approach. To test whether variations in the ancestral population size accounted for the majority of this variation, we conducted computer inferences using isolation-with-migration (IM) and approximate Bayesian computation (ABC) frameworks. The results revealed that gene flow during the early stage of speciation was strongly favoured over the isolation model, and the initiation of the speciation process was far earlier than the dates estimated by gene- and species-based divergence dating. Due to their limited dispersal ability, it is suggested that geographical isolation may have played a major role in the divergence of these Takydromus species. Nevertheless, this study reveals a more complex situation and demonstrates that gene flow during the speciation process cannot be overlooked and may have a great impact on divergence dating. By using multilocus data and incorporating Bayesian coalescence approaches, we provide a more biologically realistic framework for delineating the divergence history of Takydromus. © 2014 John Wiley & Sons Ltd.

Erosive processes after tectonic uplift stimulate vicariant and adaptive speciation: evolution in an Afrotemperate-endemic paper daisy genus

PubMed Central

2014-01-01

Background The role of tectonic uplift in stimulating speciation in South Africa’s only alpine zone, the Drakensberg, has not been explicitly examined. Tectonic processes may influence speciation both through the creation of novel habitats and by physically isolating plant populations. We use the Afrotemperate endemic daisy genus Macowania to explore the timing and mode (geographic versus adaptive) of speciation in this region. Between sister species pairs we expect high morphological divergence where speciation has happened in sympatry (adaptive) while with geographic (vicariant) speciation we may expect to find less morphological divergence and a greater degree of allopatry. A dated molecular phylogenetic hypothesis for Macowania elucidates species’ relationships and is used to address the potential impact of uplift on diversification. Morphological divergence of a small sample of reproductive and vegetative characters, used as a proxy for adaptive divergence, is measured against species’ range distributions to estimate mode of speciation across two subclades in the genus. Results The Macowania crown age is consistent with the hypothesis of post-uplift diversification, and we find evidence for both vicariant and adaptive speciation between the two subclades within Macowania. Both subclades exhibit strong signals of range allopatry, suggesting that geographic isolation was important in speciation. One subclade, associated with dry, rocky environments at high altitudes, shows very little morphological and ecological differentiation but high range allopatry. The other subclade occupies a greater variety of habitats and exhibits far greater morphological differentiation, but contains species with overlapping distribution ranges. Conclusions Species in Macowania are likely to have diversified in response to tectonic uplift, and we invoke uplift and uplift-mediated erosion as the main drivers of speciation. The greater relative morphological divergence in sympatric species of Macowania indicates that speciation in the non-sympatric taxa may not have required obvious adaptive differences, implying that simple geographic isolation was the driving force for speciation (‘neutral speciation’). PMID:24524661

Cold Temperature Effects on Speciated VOC Emissions from Modern GDI Light-Duty Vehicles 1

EPA Science Inventory

In this study, speciated VOC emissions were characterized from three modern GDI light-duty vehicles. The vehicles were tested on a chassis dynamometer housed in a climate-controlled chamber at two temperatures (20 and 72 °F) using the EPA Federal Test Procedure (FTP) and a portio...

A COMPARISON OF URINARY ARSENIC SPECIATION VIA DIRECT NEBULIZATION AND ON-LINE PHOTOOXIDATION-HYDRIDE GENERATION WITH DETECTION BY INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY

EPA Science Inventory

Arsenic speciation continues to be important in assessing human and environmental exposure risk. Urinary arsenic analysis provides information on recent arsenic exposure. In this study, two sample introduction pathways: direct nebulization (DN) and hydride generation (HG) were ut...

The genomic landscape at a late stage of stickleback speciation: High genomic divergence interspersed by small localized regions of introgression.

PubMed

Ravinet, Mark; Yoshida, Kohta; Shigenobu, Shuji; Toyoda, Atsushi; Fujiyama, Asao; Kitano, Jun

2018-05-01

Speciation is a continuous process and analysis of species pairs at different stages of divergence provides insight into how it unfolds. Previous genomic studies on young species pairs have revealed peaks of divergence and heterogeneous genomic differentiation. Yet less known is how localised peaks of differentiation progress to genome-wide divergence during the later stages of speciation in the presence of persistent gene flow. Spanning the speciation continuum, stickleback species pairs are ideal for investigating how genomic divergence builds up during speciation. However, attention has largely focused on young postglacial species pairs, with little knowledge of the genomic signatures of divergence and introgression in older stickleback systems. The Japanese stickleback species pair, composed of the Pacific Ocean three-spined stickleback (Gasterosteus aculeatus) and the Japan Sea stickleback (G. nipponicus), which co-occur in the Japanese islands, is at a late stage of speciation. Divergence likely started well before the end of the last glacial period and crosses between Japan Sea females and Pacific Ocean males result in hybrid male sterility. Here we use coalescent analyses and Approximate Bayesian Computation to show that the two species split approximately 0.68-1 million years ago but that they have continued to exchange genes at a low rate throughout divergence. Population genomic data revealed that, despite gene flow, a high level of genomic differentiation is maintained across the majority of the genome. However, we identified multiple, small regions of introgression, occurring mainly in areas of low recombination rate. Our results demonstrate that a high level of genome-wide divergence can establish in the face of persistent introgression and that gene flow can be localized to small genomic regions at the later stages of speciation with gene flow.

Chromosomal Speciation in the Genomics Era: Disentangling Phylogenetic Evolution of Rock-wallabies.

PubMed

Potter, Sally; Bragg, Jason G; Blom, Mozes P K; Deakin, Janine E; Kirkpatrick, Mark; Eldridge, Mark D B; Moritz, Craig

2017-01-01

The association of chromosome rearrangements (CRs) with speciation is well established, and there is a long history of theory and evidence relating to "chromosomal speciation." Genomic sequencing has the potential to provide new insights into how reorganization of genome structure promotes divergence, and in model systems has demonstrated reduced gene flow in rearranged segments. However, there are limits to what we can understand from a small number of model systems, which each only tell us about one episode of chromosomal speciation. Progressing from patterns of association between chromosome (and genic) change, to understanding processes of speciation requires both comparative studies across diverse systems and integration of genome-scale sequence comparisons with other lines of evidence. Here, we showcase a promising example of chromosomal speciation in a non-model organism, the endemic Australian marsupial genus Petrogale . We present initial phylogenetic results from exon-capture that resolve a history of divergence associated with extensive and repeated CRs. Yet it remains challenging to disentangle gene tree heterogeneity caused by recent divergence and gene flow in this and other such recent radiations. We outline a way forward for better integration of comparative genomic sequence data with evidence from molecular cytogenetics, and analyses of shifts in the recombination landscape and potential disruption of meiotic segregation and epigenetic programming. In all likelihood, CRs impact multiple cellular processes and these effects need to be considered together, along with effects of genic divergence. Understanding the effects of CRs together with genic divergence will require development of more integrative theory and inference methods. Together, new data and analysis tools will combine to shed light on long standing questions of how chromosome and genic divergence promote speciation.

Mercury Speciation by X-ray Absorption Fine Structure Spectroscopy and Sequential Chemical Extractions: A Comparison of Speciation Methods

USGS Publications Warehouse

Kim, C.S.; Bloom, N.S.; Rytuba, J.J.; Brown, Gordon E.

2003-01-01

Determining the chemical speciation of mercury in contaminated mining and industrial environments is essential for predicting its solubility, transport behavior, and potential bioavailability as well as for designing effective remediation strategies. In this study, two techniques for determining Hg speciation-X-ray absorption fine structure (XAFS) spectroscopy and sequential chemical extractions (SCE)-are independently applied to a set of samples with Hg concentrations ranging from 132 to 7539 mg/kg to determine if the two techniques provide comparable Hg speciation results. Generally, the proportions of insoluble HgS (cinnabar, metacinnabar) and HgSe identified by XAFS correlate well with the proportion of Hg removed in the aqua regia extraction demonstrated to remove HgS and HgSe. Statistically significant (> 10%) differences are observed however in samples containing more soluble Hg-containing phases (HgCl2, HgO, Hg3S2O 4). Such differences may be related to matrix, particle size, or crystallinity effects, which could affect the apparent solubility of Hg phases present. In more highly concentrated samples, microscopy techniques can help characterize the Hg-bearing species in complex multiphase natural samples.

Speciation of adsorbates on surface of solids by infrared spectroscopy and chemometrics.

PubMed

Vilmin, Franck; Bazin, Philippe; Thibault-Starzyk, Frédéric; Travert, Arnaud

2015-09-03

Speciation, i.e. identification and quantification, of surface species on heterogeneous surfaces by infrared spectroscopy is important in many fields but remains a challenging task when facing strongly overlapped spectra of multiple adspecies. Here, we propose a new methodology, combining state of the art instrumental developments for quantitative infrared spectroscopy of adspecies and chemometrics tools, mainly a novel data processing algorithm, called SORB-MCR (SOft modeling by Recursive Based-Multivariate Curve Resolution) and multivariate calibration. After formal transposition of the general linear mixture model to adsorption spectral data, the main issues, i.e. validity of Beer-Lambert law and rank deficiency problems, are theoretically discussed. Then, the methodology is exposed through application to two case studies, each of them characterized by a specific type of rank deficiency: (i) speciation of physisorbed water species over a hydrated silica surface, and (ii) speciation (chemisorption and physisorption) of a silane probe molecule over a dehydrated silica surface. In both cases, we demonstrate the relevance of this approach which leads to a thorough surface speciation based on comprehensive and fully interpretable multivariate quantitative models. Limitations and drawbacks of the methodology are also underlined. Copyright © 2015 Elsevier B.V. All rights reserved.

Speciation of mercury compounds by differential atomization - atomic absorption spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robinson, J.W.; Skelly, E.M.

This paper describes the dual stage atomization technique which allows speciation of several mercury-containing compounds in aqueous solution and in biological fluids. The technique holds great promise for further speciation studies. Accurate temperature control, expecially at temperatures less than 200/sup 0/C, is needed to separate the extremely volatile mercury halides and simple organomercurials from each other. Studies with mercury salts and EDTA, L-cysteine and dithioxamide demonstrate that this technique may be used to study the extent of complex formation. Investigations of biological fluids indicate that there is a single predominant form of mercury in sweat and a single predominant formmore » of mercury in urine. The mercury compound in urine is more volatile than that in sweat. Both quantitative and qualitative analyses are possible with this technique.« less

sources and processes identification for Zn cycling in the Seine river, France

NASA Astrophysics Data System (ADS)

gelabert, A.; Jouvin, D.; Morin, G.; Louvat, P.; Guinoiseau, D.; Benedetti, M. F.

2011-12-01

Because the availability of global freshwater stocks is predicted to become a major problem in a near future, new directives on water policy have been established in Europe. As a result, an accurate determination of the ecological status of the Seine river watershed is required. However, important evaluation limitation still exist, partly because the metal cycling in this system is not fully understood with for instance half the Seine river Zn not having clearly identified sources. Recent developments in isotopic measurements for new stable isotopes (Zn, Cu) allow many progresses in understanding the dynamics of metals in natural systems. But this technique alone does not always provide a precise distinction between mixing of water sources and biochemical processes able to induce isotopic fractionation. Along with an isotopic approach, this study propose to use XAS (X-ray Absorption Spectroscopy) to determine precisely the speciation of Zn complexes, and thus to define the proportion of water mixing vs. processes for Zn transfer in the watershed. A geographical sampling transect has been performed downstream Paris. Significant isotopic signature variations have been observed, varying from δ66Zn = 0.04 ± 0.04 to 0.18 ± 0.04 in the particulate part, and from δ66Zn= -0.28 ± 0.04 to 0.08 ± 0.04 for the dissolved part. The XAS analysis performed on the same samples at the Zn K-edge confirmed this heterogeneity by showing different speciations with a major contribution of sulfides, iron oxides and organic ligands. Interestingly, the wastewater treatment plant in Achères constitutes an important location in the system by contributing to the enrichment of heavy Zn to the Seine River particulate material. This change in isotopic signature follows a change in Zn speciation with decrease in sulfides contribution after Achères. A second important location is the confluence between the Seine and a minor river (Epte river) with a significant decrease in the δ66Zn for the particulate part. However, no major changes in Zn speciation have been observed. The cause for this isotopic decrease remains unclear but could be either 1) the mobilization of unknown sources, especially in this area (for the sampling point after the convergence) where the river is connected to numerous small lakes, or 2) the presence of biogeochemical processes able to induce a Zn isotopic fractionation. For instance, microorganisms present in freshwaters are known to be able to fractionate Zn during sorption processes, and they do not necessarily induce a change in the first shells of the Zn complexes if the sorbed metal was previously complexed with organic ligands in the river (fulvic substances with carboxylic or phenolic functional groups for instance). Although additional studies on the Seine river need to be conducted in order to reach a more complete understanding of this watershed functioning, these important results demonstrate the value of combining both the XAS and isotopic approaches in order to understand the behaviour of metals in such complex environments.

Mountain Refugia Play a Role in Soil Arthropod Speciation on Madagascar: A Case Study of the Endemic Giant Fire-Millipede Genus Aphistogoniulus

PubMed Central

Wesener, Thomas; Raupach, Michael J.; Decker, Peter

2011-01-01

To elucidate the speciation mechanisms prevalent within hotspots of biodiversity, and the evolutionary processes behind the rise of their species-rich and endemic biota, we investigated the phylogeny of the giant fire-millipede genus Aphistogoniulus Silvestri, 1897, a Malagasy endemic. This study is the first comprehensive (molecular and morphological) phylogenetic study focusing on millipede (class Diplopoda) speciation on Madagascar. The morphological analysis is based on 35 morphological characters and incorporates ten described as well as two newly described species (A. rubrodorsalis n. sp. and A. jeekeli n. sp.) of Aphistogoniulus. The molecular analysis is based on both mitochondrial (COI and 16S), and nuclear genes (complete 18S rDNA), together comprised of 3031 base pairs, which were successfully sequenced for 31 individual specimens and eight species of Aphistogoniulus. In addition to the null-model (speciation by distance), two diversification models, mountain refugia and ecotone shift, were discovered to play a role in the speciation of soil arthropods on Madagascar. Mountain refugia were important in the speciation of the A. cowani clade, with three species occurring in the Andringitra and Ranomafana Mountains in the southeast (A. cowani), the Ambohijanahary and Ambohitantely Mountains in the mid-west (A. sanguineus), and the Marojejy Mountain in the northeast (A. rubrodorsalis n. sp.). An ecotone shift from the eastern rainforest to the unique subarid spiny forest of Mahavelo was discovered in the A. vampyrus - A. aridus species-pair. In the monophyletic A. diabolicus clade, evidence for divergent evolution of sexual morphology was detected: species with greatly enlarged gonopods are sister-taxa to species with normal sized gonopods. Among the large-bodied Spirobolida genera of Madagascar, Colossobolus and Sanguinobolus were found to be close sister-genera to Aphistogoniulus. Forest destruction has caused forest corridors between populations to disappear, which might limit the possible resolution of biogeographic analyses on Madagascar. PMID:22162998

Sympatric ecological speciation meets pyrosequencing: sampling the transcriptome of the apple maggot Rhagoletis pomonella

PubMed Central

2009-01-01

Background The full power of modern genetics has been applied to the study of speciation in only a small handful of genetic model species - all of which speciated allopatrically. Here we report the first large expressed sequence tag (EST) study of a candidate for ecological sympatric speciation, the apple maggot Rhagoletis pomonella, using massively parallel pyrosequencing on the Roche 454-FLX platform. To maximize transcript diversity we created and sequenced separate libraries from larvae, pupae, adult heads, and headless adult bodies. Results We obtained 239,531 sequences which assembled into 24,373 contigs. A total of 6810 unique protein coding genes were identified among the contigs and long singletons, corresponding to 48% of all known Drosophila melanogaster protein-coding genes. Their distribution across GO classes suggests that we have obtained a representative sample of the transcriptome. Among these sequences are many candidates for potential R. pomonella "speciation genes" (or "barrier genes") such as those controlling chemosensory and life-history timing processes. Furthermore, we identified important marker loci including more than 40,000 single nucleotide polymorphisms (SNPs) and over 100 microsatellites. An initial search for SNPs at which the apple and hawthorn host races differ suggested at least 75 loci warranting further work. We also determined that developmental expression differences remained even after normalization; transcripts expected to show different expression levels between larvae and pupae in D. melanogaster also did so in R. pomonella. Preliminary comparative analysis of transcript presences and absences revealed evidence of gene loss in Drosophila and gain in the higher dipteran clade Schizophora. Conclusions These data provide a much needed resource for exploring mechanisms of divergence in this important model for sympatric ecological speciation. Our description of ESTs from a substantial portion of the R. pomonella transcriptome will facilitate future functional studies of candidate genes for olfaction and diapause-related life history timing, and will enable large scale expression studies. Similarly, the identification of new SNP and microsatellite markers will facilitate future population and quantitative genetic studies of divergence between the apple and hawthorn-infesting host races. PMID:20035631

Characteristics and chemical compositions of particulate matter collected at the selected metro stations of Shanghai, China.

PubMed

Guo, Li; Hu, Yunjie; Hu, Qingqing; Lin, Jun; Li, Chunlin; Chen, Jianmin; Li, Lina; Fu, Hongbo

2014-10-15

A campaign was conducted to assess and compare the air quality at the different metro platforms at Shanghai City, focusing on particulate matter (PM) levels, chemical compositions, morphology and mineralogy, as well as species of iron. Our results indicated that the average PM₂.₅ concentrations for the three metro lines were 177.7 μg/m(3), 105.7 μg/m(3) and 82.5 μg/m(3), respectively, and the average PM1 concentrations for the three lines were 122.3 μg/m(3), 84.1 μg/m(3) and 59.6 μg/m(3), respectively. Fe, Mn, Cr, Cu, Sr, Ba and Pb concentrations in all of the sampling sites were significantly higher than that in the urban ambient air, implicating that these trace metals may be associated with the metro systems working. Individual airborne dusts were studied for morphology and mineralogy characteristics. The results revealed that the presence of most individual particles were with no definite shape and most of them were with a large metal content. Furthermore, Fe-rich particles had significantly higher abundance in the metro systems, which were more frequently encountered in the underground lines than the aboveground line. The 2D distribution map of an interested Fe-rich particle showed an uneven Fe distribution, implying that a hollow or core of other substance exists in the particle center during the formation process. Cluster analysis revealed that Fe-rich particles were possibly a mixture of Fe species. Fitting of X-ray absorption near-edge fine structure spectra (XANES) showed the main iron species within the particles collected from the three contrasting metro lines of Shanghai to be hematite, magnetite, iron-metal and mineral Fe. Hematite and mineral Fe were all found in three lines, while magnetite only existed in aboveground metro line. Iron-metal was determined in both the older and younger underground lines, based on the X-ray diffraction (XRD) analysis. As diverse Fe species have different physical-chemical characteristics and toxicity, the speciation of Fe-containing metro particles is important in the context of public health and control measures. Copyright © 2014. Published by Elsevier B.V.

The effects of redox fluctuation on iron-organic matter interactions in wet tropical soils

NASA Astrophysics Data System (ADS)

Bhattacharyya, A.; Campbell, A.; Lin, Y.; Nico, P. S.; Silver, W. L.; Pett-Ridge, J.

2016-12-01

Two-thirds of the C in the terrestrial biosphere is stored as soil organic C, and much of this is stabilized via iron (Fe) mineral-organic matter (OM) associations that are susceptible to redox effects. The rapid C cycling typical of wet tropical ecosystems- driven by ample moisture and temperature- may also be fueled by a characteristically dynamic redox environment. Yet the net result of altered tropical soil climate and fluctuating soil redox regimes on Fe-organic matter associations is poorly understood. In this study, we hypothesized that the timing of redox transitions (frequency of O2 introduction and ferrous iron (Fe2+) generation) will lead to differences in Fe (oxyhydr)oxide mineral crystallinity and C degradation rates and alter the proportion of organic C associated with iron minerals. Surface soils from a humid tropical forest in Puerto Rico were incubated for 44 days under four redox regimes: (1) static anoxic, (2) static oxic, (3) 4 days anoxic, 4 days oxic, and (4) 4 days anoxic, 8 days oxic. Replicate microcosms were harvested at multiple time points, including before and after a redox switch (oxic to anoxic or vice versa). Selective chemical extractions, bulk Fe K-edge EXAFS and STXM/NEXAFS spectromicroscopy were used to comprehensively probe treatment effects on Fe and C speciation. Static redox conditions had a significant effect on Fe2+ and dissolved organic carbon (DOC) concentrations, and prolonged anoxia promoted reductive dissolution of Fe-oxides and an increase in amorphous or short-range ordered (SRO) Fe oxides. Preferential dissolution of this less-crystalline Fe pool was more prominent during rapid redox switches from oxic to anoxic conditions, and coincided with increased DOC. Bulk Fe K-edge EXAFS spectroscopy identified Fe3+ as the dominant Fe species in all treatments and indicated O/N atoms in the first Fe co-ordination sphere and features similar to SRO Fe-oxide phases (e.g. ferrihydrite or nano-goethite) in the second co-ordination sphere. STXM/NEXAFS analyses indicated an increase in lignin-like biomolecules under static anoxic conditions, and a potential role of Fe-lignin interactions under strong reducing conditions. Our current findings highlight the necessity to explore natural redox-dynamic systems in greater detail in order to develop a better model for climate change.

The Production and Export of Bioavailable Iron from Ice Sheets - the Importance of Colloidal and Nanoparticulate Phases

NASA Astrophysics Data System (ADS)

Hawkings, J.; Wadham, J. L.; Tranter, M.; Raiswell, R.; Benning, L. G.; Statham, P. J.; Tedstone, A.; Nienow, P. W.; Telling, J.; Bagshaw, E.

2013-12-01

Glaciers cover approximately 10% of the world's land surface at present, but our knowledge of biogeochemical processes occurring beneath them is still limited, as is our understanding of their impact on downstream ecosystems via the export of nutrients in runoff. Recent work has suggested that glaciers are a primary source of nutrients to near coastal areas(1). For example, macronutrients, such as nitrogen and phosphorus, and micronutrients, such as iron, may support primary production(2,3). Nutrient limitation of primary producers is known to be prevalent in large sectors of the world's oceans and iron is a significant limiting nutrient in Polar waters(4,5). Significantly, large oceanic algal blooms have been observed in polar areas where glacial influence is large(6,7). Our knowledge of iron speciation, concentrations and export dynamics in glacial meltwater is limited due, in part, to problems associated with collecting trace measurements in remote field locations. For example, recent work has indicated large uncertainty in 'dissolved' meltwater iron concentrations (0.2 - 4000 μM(8,9)). There is currently a dearth of information about labile nanoparticulate iron in glacial meltwaters, as well as export dynamics from large ice sheet catchments. Existing research has focused on small catchment examples(8,10), which behave differently to larger catchments(11). Presented here is the first time series of daily variations in meltwater iron concentrations (dissolved, filterable colloidal/nanoparticulate and bioavailable suspended sediment bound) from two large contrasting glacial catchments in Greenland over the 2012 and 2013 summer melt seasons. We also present the first estimates of iron concentrations in Greenlandic icebergs, which have been identified as hot spots of biological activity in the open ocean(12,13). Budgets for ice sheets based on our data demonstrate the importance of glaciers in global nutrient cycles, and reveal a large and previously under-appreciated component of the global iron cycle. References 1 Hood, E. & Scott, D, Nat Geosci 1, 583-587 (2008) 2 Wadham, J. et al., Earth Env Sci T R So (2013) 3 Gerringa, L. J. A. et al., Deep-Sea Res Pt II 71-76, 16-31 (2012) 4 Martin, J. H. & Fitzwater, S. E., Nature 331, 341-343 (1988) 5 Martin, J. H., Fitzwater, S. E. & Gordon, R. M., Global Biogeochem Cy 4, 5-12 (1990) 6 Perrette, M., Yool, A., Quartly, G. D. & Popova, E. E., Biogeosciences 8, 515-524 (2011) 7 Frajka-Williams, E. & Rhines, P. B., Deep-Sea Res Pt I 57, 541-552 (2010) 8 Statham, P. J., Skidmore, M. & Tranter, M., Global Biogeochem Cy 22 (2008) 9 Mikucki, J. A. et al., Science 324, 397-400 (2009) 10 Bhatia, M. P. et al., Nat Geosci (2013) 11 Wadham, J. L. et al., Global Biogeochem Cy 24 (2010) 12 Smith, K. L. et al., Science 317, 478-482 (2007) 13 Raiswell, R. & Canfield, D. E., Geochemical Perspectives 1, 1-220 (2012)

Influence of iron redox cycling on organo-mineral associations in Arctic tundra soil

DOE PAGES

Herndon, Elizabeth; Oak Ridge National Lab.; AlBashaireh, Amineh; ...

2017-03-25

Arctic tundra stores large quantities of soil organic matter under varying redox conditions. As the climate warms, these carbon reservoirs are susceptible to increased rates of decomposition and release to the atmosphere as the greenhouse gases carbon dioxide (CO 2) and methane (CH 4). Geochemical interactions between soil organic matter and minerals influence decomposition in many environments but remain poorly understood in Arctic tundra systems and are not considered in decomposition models. The accumulation of iron (Fe) oxyhydroxides and organo- iron precipitates at redox interfaces may be particularly important for carbon cycling given that ferric iron [Fe(III)] species can enhancemore » decomposition by serving as terminal electron acceptors in anoxic soils or inhibit microbial decomposition by binding organic molecules. Here in this paper, we examine chemical properties of solid-phase Fe and organic matter in organic and mineral horizons within the seasonally thawed active layer of Arctic tundra on the North Slope of Alaska. Spectroscopic techniques, including micro-X-ray fluorescence ( XRF) mapping, micro-X-ray absorption near-edge structure ( XANES) spectroscopy, and Fourier transform infrared spectroscopy (FTIR), were coupled with chemical sequential extractions and physical density fractionations to evaluate the spatial distribution and speciation of Fe-bearing phases and associated organic matter in soils. Organic horizons were enriched in poorly crystalline and crystalline iron oxides, and approximately 60% of total Fe stored in organic horizons was calculated to derive from upward translocation from anoxic mineral horizons. Ferrihydrite and goethite were present as coatings on mineral grains and plant debris, and in aggregates with clays and particulate organic matter. Minor amounts of ferrous iron [Fe(II)] were present in iron sulfides (i.e., pyrite and greigite) in mineral horizon soils and iron phosphates (vivianite) in organic horizons. Concentrations of organic carbon in the organic horizons (28 ± 5% wt. % C) were approximately twice the concentrations in the mineral horizons (14 ± 2 % wt. C), and organic matter was dominated by base-extractable and insoluble organics enriched in aromatic and aliphatic moieties. Conversely, water-soluble organic molecules and organics solubilized through acid-dissolution of iron oxides comprised < 2% of soil organic C and were consistent with a mixture of alcohols, sugars, and small molecular weight organic acids and aromatics released through decomposition of larger molecules. Integrated over the entire depth of the active layer, soils contained 11± 4 kg m -2 low- density, particulate organic C and 19 ± 6 kg m -2 high-density, mineral-associated organic C, indicating that 63 ±19% of organic C in the active layer was associated with the mineral fraction. We conclude that organic horizons were enriched in poorly crystalline and crystalline iron oxide phases derived from upward translocation of dissolved Fe(II) and Fe(III) from mineral horizons. Precipitation of iron oxides at the redox interface has the potential to contribute to mineral protection of organic matter and increase the residence time of organic carbon in arctic soils. Our results suggest that iron oxides may inhibit organic carbon degradation by binding low-molecular-weight organic compounds, stabilizing soil aggregates, and forming thick coatings around particulate organic matter. Organic matter released through acid-dissolution of iron oxides could represent a small pool of readily-degradable organic molecules temporarily stabilized by sorption to iron oxyhydroxide surfaces. The distribution of iron in organic complexes and inorganic phases throughout the soil column constrains Fe(III) availability to anaerobic iron-reducing microorganisms that oxidize organic matter to produce CO 2 and CH 4 in these anoxic environments. Future predictions of carbon storage and respiration in the arctic tundra should consider such influences of mineral stabilization under changing redox conditions.« less

Influence of iron redox cycling on organo-mineral associations in Arctic tundra soil

NASA Astrophysics Data System (ADS)

Herndon, Elizabeth; AlBashaireh, Amineh; Singer, David; Roy Chowdhury, Taniya; Gu, Baohua; Graham, David

2017-06-01

Arctic tundra stores large quantities of soil organic matter under varying redox conditions. As the climate warms, these carbon reservoirs are susceptible to increased rates of decomposition and release to the atmosphere as the greenhouse gases carbon dioxide (CO2) and methane (CH4). Geochemical interactions between soil organic matter and minerals influence decomposition in many environments but remain poorly understood in Arctic tundra systems and are not considered in decomposition models. The accumulation of iron (Fe) oxyhydroxides and organo-iron precipitates at redox interfaces may be particularly important for carbon cycling given that ferric iron [Fe(III)] species can enhance decomposition by serving as terminal electron acceptors in anoxic soils or inhibit microbial decomposition by binding organic molecules. Here, we examine chemical properties of solid-phase Fe and organic matter in organic and mineral horizons within the seasonally thawed active layer of Arctic tundra on the North Slope of Alaska. Spectroscopic techniques, including micro-X-ray fluorescence (μXRF) mapping, micro-X-ray absorption near-edge structure (μXANES) spectroscopy, and Fourier transform infrared spectroscopy (FTIR), were coupled with chemical sequential extractions and physical density fractionations to evaluate the spatial distribution and speciation of Fe-bearing phases and associated organic matter in soils. Organic horizons were enriched in poorly crystalline and crystalline iron oxides, and approximately 60% of total Fe stored in organic horizons was calculated to derive from upward translocation from anoxic mineral horizons. Ferrihydrite and goethite were present as coatings on mineral grains and plant debris, and in aggregates with clays and particulate organic matter. Minor amounts of ferrous iron [Fe(II)] were present in iron sulfides (i.e., pyrite and greigite) in mineral horizon soils and iron phosphates (vivianite) in organic horizons. Concentrations of organic carbon in the organic horizons (28 ± 5 wt.% C) were approximately twice the concentrations in the mineral horizons (14 ± 2 wt.% C), and organic matter was dominated by base-extractable and insoluble organics enriched in aromatic and aliphatic moieties. Conversely, water-soluble organic molecules and organics solubilized through acid-dissolution of iron oxides comprised <2% of soil organic C and were consistent with a mixture of alcohols, sugars, and small molecular weight organic acids and aromatics released through decomposition of larger molecules. Integrated over the entire depth of the active layer, soils contained 11 ± 4 kg m-2 low-density, particulate organic C and 19 ± 6 kg m-2 high-density, mineral-associated organic C, indicating that 63 ± 19% of organic C in the active layer was associated with the mineral fraction. We conclude that organic horizons were enriched in poorly crystalline and crystalline iron oxide phases derived from upward translocation of dissolved Fe(II) and Fe(III) from mineral horizons. Precipitation of iron oxides at the redox interface has the potential to contribute to mineral protection of organic matter and increase the residence time of organic carbon in arctic soils. Our results suggest that iron oxides may inhibit organic carbon degradation by binding low-molecular-weight organic compounds, stabilizing soil aggregates, and forming thick coatings around particulate organic matter. Organic matter released through acid-dissolution of iron oxides could represent a small pool of readily-degradable organic molecules temporarily stabilized by sorption to iron oxyhydroxide surfaces. The distribution of iron in organic complexes and inorganic phases throughout the soil column constrains Fe(III) availability to anaerobic iron-reducing microorganisms that oxidize organic matter to produce CO2 and CH4 in these anoxic environments. Future predictions of carbon storage and respiration in the arctic tundra should consider such influences of mineral stabilization under changing redox conditions.

Influence of iron redox cycling on organo-mineral associations in Arctic tundra soil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herndon, Elizabeth; Oak Ridge National Lab.; AlBashaireh, Amineh

Arctic tundra stores large quantities of soil organic matter under varying redox conditions. As the climate warms, these carbon reservoirs are susceptible to increased rates of decomposition and release to the atmosphere as the greenhouse gases carbon dioxide (CO 2) and methane (CH 4). Geochemical interactions between soil organic matter and minerals influence decomposition in many environments but remain poorly understood in Arctic tundra systems and are not considered in decomposition models. The accumulation of iron (Fe) oxyhydroxides and organo- iron precipitates at redox interfaces may be particularly important for carbon cycling given that ferric iron [Fe(III)] species can enhancemore » decomposition by serving as terminal electron acceptors in anoxic soils or inhibit microbial decomposition by binding organic molecules. Here in this paper, we examine chemical properties of solid-phase Fe and organic matter in organic and mineral horizons within the seasonally thawed active layer of Arctic tundra on the North Slope of Alaska. Spectroscopic techniques, including micro-X-ray fluorescence ( XRF) mapping, micro-X-ray absorption near-edge structure ( XANES) spectroscopy, and Fourier transform infrared spectroscopy (FTIR), were coupled with chemical sequential extractions and physical density fractionations to evaluate the spatial distribution and speciation of Fe-bearing phases and associated organic matter in soils. Organic horizons were enriched in poorly crystalline and crystalline iron oxides, and approximately 60% of total Fe stored in organic horizons was calculated to derive from upward translocation from anoxic mineral horizons. Ferrihydrite and goethite were present as coatings on mineral grains and plant debris, and in aggregates with clays and particulate organic matter. Minor amounts of ferrous iron [Fe(II)] were present in iron sulfides (i.e., pyrite and greigite) in mineral horizon soils and iron phosphates (vivianite) in organic horizons. Concentrations of organic carbon in the organic horizons (28 ± 5% wt. % C) were approximately twice the concentrations in the mineral horizons (14 ± 2 % wt. C), and organic matter was dominated by base-extractable and insoluble organics enriched in aromatic and aliphatic moieties. Conversely, water-soluble organic molecules and organics solubilized through acid-dissolution of iron oxides comprised < 2% of soil organic C and were consistent with a mixture of alcohols, sugars, and small molecular weight organic acids and aromatics released through decomposition of larger molecules. Integrated over the entire depth of the active layer, soils contained 11± 4 kg m -2 low- density, particulate organic C and 19 ± 6 kg m -2 high-density, mineral-associated organic C, indicating that 63 ±19% of organic C in the active layer was associated with the mineral fraction. We conclude that organic horizons were enriched in poorly crystalline and crystalline iron oxide phases derived from upward translocation of dissolved Fe(II) and Fe(III) from mineral horizons. Precipitation of iron oxides at the redox interface has the potential to contribute to mineral protection of organic matter and increase the residence time of organic carbon in arctic soils. Our results suggest that iron oxides may inhibit organic carbon degradation by binding low-molecular-weight organic compounds, stabilizing soil aggregates, and forming thick coatings around particulate organic matter. Organic matter released through acid-dissolution of iron oxides could represent a small pool of readily-degradable organic molecules temporarily stabilized by sorption to iron oxyhydroxide surfaces. The distribution of iron in organic complexes and inorganic phases throughout the soil column constrains Fe(III) availability to anaerobic iron-reducing microorganisms that oxidize organic matter to produce CO 2 and CH 4 in these anoxic environments. Future predictions of carbon storage and respiration in the arctic tundra should consider such influences of mineral stabilization under changing redox conditions.« less

Modeling low-temperature geochemical processes: Chapter 2

USGS Publications Warehouse

Nordstrom, D. Kirk; Campbell, Kate M.

2014-01-01

This chapter provides an overview of geochemical modeling that applies to water–rock interactions under ambient conditions of temperature and pressure. Topics include modeling definitions, historical background, issues of activity coefficients, popular codes and databases, examples of modeling common types of water–rock interactions, and issues of model reliability. Examples include speciation, microbial redox kinetics and ferrous iron oxidation, calcite dissolution, pyrite oxidation, combined pyrite and calcite dissolution, dedolomitization, seawater–carbonate groundwater mixing, reactive-transport modeling in streams, modeling catchments, and evaporation of seawater. The chapter emphasizes limitations to geochemical modeling: that a proper understanding and ability to communicate model results well are as important as completing a set of useful modeling computations and that greater sophistication in model and code development is not necessarily an advancement. If the goal is to understand how a particular geochemical system behaves, it is better to collect more field data than rely on computer codes.

Shedding Light on the Grey Zone of Speciation along a Continuum of Genomic Divergence.

PubMed

Roux, Camille; Fraïsse, Christelle; Romiguier, Jonathan; Anciaux, Yoann; Galtier, Nicolas; Bierne, Nicolas

2016-12-01

Speciation results from the progressive accumulation of mutations that decrease the probability of mating between parental populations or reduce the fitness of hybrids-the so-called species barriers. The speciation genomic literature, however, is mainly a collection of case studies, each with its own approach and specificities, such that a global view of the gradual process of evolution from one to two species is currently lacking. Of primary importance is the prevalence of gene flow between diverging entities, which is central in most species concepts and has been widely discussed in recent years. Here, we explore the continuum of speciation thanks to a comparative analysis of genomic data from 61 pairs of populations/species of animals with variable levels of divergence. Gene flow between diverging gene pools is assessed under an approximate Bayesian computation (ABC) framework. We show that the intermediate "grey zone" of speciation, in which taxonomy is often controversial, spans from 0.5% to 2% of net synonymous divergence, irrespective of species life history traits or ecology. Thanks to appropriate modeling of among-locus variation in genetic drift and introgression rate, we clarify the status of the majority of ambiguous cases and uncover a number of cryptic species. Our analysis also reveals the high incidence in animals of semi-isolated species (when some but not all loci are affected by barriers to gene flow) and highlights the intrinsic difficulty, both statistical and conceptual, of delineating species in the grey zone of speciation.