Aminopyridine modified Spirulina platensis biomass for chromium(VI) adsorption in aqueous solution.

PubMed

Bayramoglu, Gulay; Akbulut, Aydin; Arica, M Yakup

Chemical modification of Spirulina platensis biomass was realized by sequential treatment of algal surface with epichlorohydrin and aminopyridine. Adsorptive properties of Cr(VI) ions on native and aminopyridine modified algal biomass were investigated by varying pH, contact time, ionic strength, initial Cr(VI) concentration, and temperature. FTIR and analytical analysis indicated that carboxyl and amino groups were the major functional groups for Cr(VI) ions adsorption. The optimum adsorption was observed at pH 3.0 for native and modified algal biomasses. The adsorption capacity was found to be 79.6 and 158.7 mg g(-1), for native and modified algal biomasses, respectively. For continuous system studies, the experiments were conducted to study the effect of important design parameters such as flow rate and initial concentration of metal ions, and the maximum sorption capacity was observed at a flow rate of 50 mL h(-1), and Cr(VI) ions concentration 200 mg L(-1) with modified biomass. Experimental data fitted a pseudo-second-order equation. The regeneration performance was observed to be 89.6% and 94.3% for native and modified algal biomass, respectively.

Remediation of chromium-slag leakage with electricity cogeneration via a urea-Cr(VI) cell

PubMed Central

Yu, Binbin; Zhang, Huimin; Xu, Wei; Li, Gang; Wu, Zucheng

2014-01-01

Chromium pollution has been historically widespread throughout the world. Most available remediation technologies often require energy consumption. This study is aimed to develop electrochemical remediation for Cr(VI) in chromium-slag leakage with self-generated electricity. Dynamic leaching experiments of chromium-slag samples were conducted to survey the release and leaching behavior of Cr(VI). Based on previous work, a unique urea-Cr(VI) was designed, in which urea was employed as the fuel and Cr(VI) from the leakage of the dichromate slag served as the oxidant. Furthermore, the electrochemical results showed that the removal percent of Cr(VI) was more than 96% after 18 h with the leakage Cr(VI) concentration of 2.69 mM. The open circuit potential (OCP) varied in the range of 1.56 ~ 1.59 V under different initial Cr(VI) leakage concentrations. The approach explores the feasibility of the promising technique without the need of energy input for simultaneous chromium-slag remediation and generation of electricity. PMID:25168513

[Identification of hexavalent chromium reducing bacteria Cr4-1 and optimization of its reduction conditions].

PubMed

Zhu, Peilei; Jiao, Shilin; Jiang, Pu; Zeng, Xin; Luo, Qifang; Wang, Lin

2015-03-01

To identify the hexavalent chromium reduction Cr4-1, and to study the better conditions of the bacterial growth and its Cr(VI) reduction. The physiological and biochemical methods and 16s rDNA sequencing were used for identification of bacteria Cr4-1. The influence of temperature, pH, initial Cr (VI) concentration and shaking speed on bacterial growth and Cr (VI) reduction were studied. Mass balance analysis was used to analyze the end products of the reduction reaction. A Cr(VI) reducing bacteria Cr4-1, screened from acclimated activated sludge, was identified as Bacillus cereus. The appropriate conditions of bacterial growth was 25 °C, pH 7 to 8, shaking speed 150 r/min, while the suitable conditions for Cr(VI) reduction was 35 °C, pH 8 to 9. When the initial Cr(VI) concentration increased from 20 mg/L to 60 mg/L, the reduction rate decreased gradually. Under the suitable reducing conditions, when the initial concentration of Cr (VI) was 30 mg/L, the reduction rate could up to 100% in 9 h. The end product was soluble trivalent chromium. Strain Cr4-1 had a good effect on Cr (VI) reduction and the final product was soluble trivalent chromium.

Oxidative dissolution of pyrite surfaces by hexavalent chromium: Surface site saturation and surface renewal

NASA Astrophysics Data System (ADS)

Graham, Andrew M.; Bouwer, Edward J.

2012-04-01

In-situ reduction of toxic Cr(VI) to nontoxic Cr(III) represents an important natural attenuation process for Cr(VI)-impacted environments. This study investigates the stoichiometry and kinetics of Cr(VI) reduction by pyrite, a reduced iron-sulfur mineral ubiquitous in recent estuarine and marine sediments. Pyrite suspensions at surface loadings of 0.28-2.10 m2/L (typical of estuarine or marine sediments) were capable of completely reducing 7-120 μM Cr(VI) on the timescale of minutes to days, with the time to reaction completion decreasing with increasing pyrite loading, decreasing initial Cr(VI) concentration, and decreasing suspension pH. Analysis of metal species (Cr and Fe) and sulfur species in solution and at the mineral surface indicated that Cr(VI) oxidatively dissolved the pyrite surface, releasing ferrous iron and sulfate into solution as the reaction progressed. Surface disulfide groups were postulated as the Cr(VI)-reactive surface entity. Net production or consumption of aqueous Fe(II) was shown to depend upon the relative rates of proton-promoted Fe(II) release, Fe(II) release due to oxidative dissolution of pyrite in the presence of Cr(VI), and Fe(II) consumption due to homogeneous reaction with Cr(VI). Kinetics of Cr(VI) reduction by pyrite displayed a biphasic pattern, and the time to reaction completion increased dramatically with increasing initial Cr(VI) concentration. Rapid Cr(VI) removal occurred early in the reaction progress, attributable to Cr(VI) loss under an adsorption-limited regime. Slow, approximately zero-order, Cr(VI) removal occurred over the bulk of the time courses, and corresponded to Cr(VI) removal under surface site saturation conditions. Stoichiometric Cr(VI) reduction was able to proceed under surface site limited conditions owing to regeneration of reactive surface sites following desorption/dissolution of oxidized surface products, as demonstrated in repeat Cr(VI)-spiking experiments. The role of surface passivation was evaluated by comparing rates of Cr(VI) reduction in the presence and absence of the Cr(III)-complexing agent citrate. While citrate addition significantly enhanced Cr(III) solubility, rates of Cr(VI) reduction were only marginally accelerated, suggesting that Cr(OH)3(s) coatings did not completely block access of Cr(VI) to reactive surface sites on pyrite. Given the rapid rates of Cr(VI) reduction with pyrite under pH and surface coverage conditions typical of natural environments, we propose that Cr(VI) reduction by pyrite be considered in fate and transport models for Cr in contaminated sediments.

Experimental Monitoring of Cr(VI) Bio-reduction Using Electrochemical Geophysics

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

Birsen Canan; Gary R. Olhoeft; William A. Smith

2007-09-01

Many Department of Energy (DOE) sites are contaminated with highly carcinogenic hexavalent chromium (Cr(VI)). In this research, we explore the feasibility of applying complex resistivity to the detection and monitoring of microbially-induced reduction of hexavalent chromium (Cr(VI)) to a less toxic form (Cr(III)). We hope to measure the change in ionic concentration that occurs during this reduction reaction. This form of reduction promises to be an attractive alternative to more expensive remedial treatment methods. The specific goal of this research is to define the minimum and maximum concentration of the chemical and biological compounds in contaminated samples for which themore » Cr(VI) - Cr(III) reduction processes could be detected via complex resistivity. There are three sets of experiments, each comprised of three sample columns. The first experiment compares three concentrations of Cr(VI) at the same bacterial cell concentration. The second experiment establishes background samples with, and without, Cr(VI) and bacterial cells. The third experiment examines the influence of three different bacterial cell counts on the same concentration of Cr(VI). A polarization relaxation mechanism was observed between 10 and 50 Hz. The polarization mechanism, unfortunately, was not unique to bio-chemically active samples. Spectral analysis of complex resistivity data, however, showed that the frequency where the phase minimum occurred was not constant for bio-chemically active samples throughout the experiment. A significant shifts in phase minima occurred between 10 to 20 Hz from the initiation to completion of Cr(VI) reduction. This phenomena was quantified using the Cole-Cole model and the Marquardt-Levenberg nonlinear least square minimization method. The data suggests that the relaxation time and the time constant of this relaxation are the Cole-Cole parameters most sensitive to changes in biologically-induced reduction of Cr(VI).« less

Biosorption of hexavalent chromium from aqueous medium with Opuntia biomass.

PubMed

Fernández-López, José A; Angosto, José M; Avilés, María D

2014-01-01

The biosorption of hexavalent chromium from aqueous solutions by Opuntia cladodes and ectodermis from cactus fruits was investigated. Both types of biomass are considered low-cost, natural, and ecofriendly biosorbents. Batch experiments were carried out to determine Cr(VI) biosorption capacity and the efficiency of the biosorption process under different pH, initial Cr(VI) concentration, and sorbent dosage. The biosorption of Cr(VI) by Opuntia biomass was highly pH dependent, favoring higher metal uptake at low pH. The higher biosorption capacity was exhibited at pH 2. The optimal conditions were obtained at a sorbent dosage of 1 g L(-1) and initial metal concentration of 10 mg L(-1). Biosorption kinetic data were properly fitted with the pseudo-second-order kinetic model. The rate constant, the initial biosorption rate, and the equilibrium biosorption capacity were determined. The experimental equilibrium data obtained were analyzed using two-parameter isotherm models (Langmuir, Freundlich, and Temkin). The Langmuir maximum monolayer biosorption capacity (q max) was 18.5 mg g(-1) for cladodes and 16.4 mg g(-1) for ectodermis. The results suggest that Opuntia biomass could be considered a promising low-cost biosorbent for the ecofriendly removal of Cr(VI) from aqueous systems.

The oxidation of Cr(III) to Cr(VI) in the environment by atmospheric oxygen during the bush fires.

PubMed

Panichev, N; Mabasa, W; Ngobeni, P; Mandiwana, K; Panicheva, S

2008-05-30

The presence of Cr(VI) in soils and plants of remote unpolluted areas can be explained by partial oxidation of Cr(III) with atmospheric oxygen during seasonable bush fires, which are rather frequent event in South Africa. Experiments with thermal treatment of a veld grass, Hyperthelia dissoluta, in muffle furnace at high temperature, followed by electrothermal atomic absorption spectrometry (ETAAS) determination of chromium, show a remarkable increase in Cr(VI) concentration from initial 2.5 to 23.2% after the treatment of grass ash at 500 degrees C and to 58.1% at 900 degrees C. Before ETAAS determination, the two chromium species of interest were separated by the treatment of samples with 0.1M Na2CO3. Thermodynamic calculations confirm the possibility of Cr(III) to Cr(VI) oxidation with atmospheric oxygen at high temperature in alkaline media, which is typical for vegetation ash. Analysis of field samples show that percent of Cr(VI), in respect to the total amount of chromium increased from initial 2.5% in grass to 9.3% in ash of grass. Without oxidation the percent of Cr(VI) in grass and ash of grass should be a constant value. After the fire Cr(VI) concentration in top soil (0-3 cm) increased from 0.3+/-0.05 to 1.8+/-0.5 microg g(-1) and the total Cr from 26+/-9 to 69+/-14 microg g(-1). The reason for the appearance of additional amount of Cr on top soil can be explained by condensation of chromium species from flame and shouldering ash on a soil surface. The results of studies demonstrate that Cr(VI) is formed by Cr(III) oxidation with atmospheric oxygen at high temperature during bush fires.

Chromium (Ⅵ) removal from aqueous solutions through powdered activated carbon countercurrent two-stage adsorption.

PubMed

Wang, Wenqiang

2018-01-01

To exploit the adsorption capacity of commercial powdered activated carbon (PAC) and to improve the efficiency of Cr(VI) removal from aqueous solutions, the adsorption of Cr(VI) by commercial PAC and the countercurrent two-stage adsorption (CTA) process was investigated. Different adsorption kinetics models and isotherms were compared, and the pseudo-second-order model and the Langmuir and Freundlich models fit the experimental data well. The Cr(VI) removal efficiency was >80% and was improved by 37% through the CTA process compared with the conventional single-stage adsorption process when the initial Cr(VI) concentration was 50 mg/L with a PAC dose of 1.250 g/L and a pH of 3. A calculation method for calculating the effluent Cr(VI) concentration and the PAC dose was developed for the CTA process, and the validity of the method was confirmed by a deviation of <5%. Copyright © 2017. Published by Elsevier Ltd.

[Investigation of concentration levels of chromium(VI) in bottled mineral and spring waters by high performance ion chromatography technique with application of postcolumn reaction with 1,5-diphenylcarbazide and VIS detection].

PubMed

Swiecicka, Dorota; Garboś, Sławomir

2008-01-01

The aim of this work was optimization and validation of the method of determination of Cr(VI) existing in the form of chromate(VI) in mineral and spring waters by High Performance Ion Chromatography (HPIC) technique with application of postcolumn reaction with 1,5-diphenylcarbazide and VIS detection. Optimization of the method performed with the use of initial apparatus parameters and chromatographic conditions from the Method 218.6 allowed to lowering detection limit for Cr(VI) from 400 ng/l to 2 ng/l. Thanks to very low detection limit achieved it was possible to determine of Cr(VI) concentrations in 25 mineral and spring waters presented at Polish market. In the cases of four mineral and spring waters analyzed, determined Cr(VI) concentrations were below of quantification limit (< 4 ng/l) but simultaneously in another mineral and spring waters the concentrations of chromium(VI) were determined in the range of 5.6 - 1281 ng/l. The fact of existence of different Cr(VI) concentrations in investigated waters could be connected with secondary contamination of mineral and spring waters by chromium coming from metal installations and fittings. One should be underlined that even the highest determined concentration level of chromium(VI) was below of the maximum admissible concentration of total chromium presented in Polish Decree of Minister of Health from April 29th 2004. Therefore after taking into account determined in this work concentration of Cr(VI), the consumption of all waters analyzed in this study does not lead to essential human health risk.

Zeolitic imidazolate framework-8 for efficient adsorption and removal of Cr(VI) ions from aqueous solution.

PubMed

Niknam Shahrak, Mahdi; Ghahramaninezhad, Mahboube; Eydifarash, Mohsen

2017-04-01

Heavy metals are emerging toxic pollutants in which the development of advanced materials for their efficient adsorption and separation is thus of great significance in environmental sciences point of view. In this study, one of the zinc-based zeolitic imidazolate framework materials, known as ZIF-8, has been synthesized and used for chromium(VI) contaminant removal from water for the first time. The as-synthesized ZIF-8 adsorbent was characterized with different methodologies such as powder X-ray diffraction (XRD), thermo-gravimetric analysis, FT-IR, nuclear magnetic resonance spectroscopy, and UV-Vis spectra of solid state. Various factors affecting removal percentage (efficiency) are experimentally investigated including pH of solution, adsorbent dosage, contact time and initial concentration of Cr(VI) to achieve the optimal condition. The obtained results indicate that the ZIF-8 shows good performance for the Cr(VI) removal from aqueous solution so that 60 min mixing of 2 g of ZIF-8 adsorbent with the 2.5 ppm of Cr(VI) solution in a neutral environment will result in the highest separation efficiency around 70%. The time needed to reach the equilibrium (maximum separation efficiency) is only 60 min for a concentration of 5 mg L -1 . Structure stability in the presence of water is also carefully examined by XRD determination of ZIF-8 under different contact times in aqueous solution, which suggests that the structure is going to be destructed after 60 min immersed in solution. Electrostatic interaction of Cr(VI) anions by positively charged ZIF-8 is responsible for Cr(VI) adsorption and separation. Moreover, equilibrium adsorption study reveals that the Cr(VI) removal process using ZIF-8 nicely fits the Langmuir and Toth isotherm models which mean the adsorbent has low heterogeneous surface with different distributions of adsorption energies during Cr(VI) adsorption. Equilibrium adsorption capacity is observed around 0.25 for 20 mg L -1 of initial Cr(VI) solutions.

Biosorption of Cr(VI) in Aqueous Solution using Microorganisms: Comparison of the Use of Rhizopus oryzae, Bacillus firmus, and Trichoderma viride

NASA Astrophysics Data System (ADS)

Safitri, Anna; Mahardini, Putri; Prasetyawan, Sasangka; Roosdiana, Anna

2018-01-01

In this work, the study of biosorption of Cr(VI) from aqueous solution was conducted using Rhizopus oryzae, Bacillus firmus, and Trichoderma viride as microorganisms that can absorb Cr(VI). The research is focused on determination of optimum conditions including pH, the number of R. oryzae, B. firmus, and T. viride (inoculums), and initial concentrations of Cr(VI) used. Optimum pH was obtained at pH 5, 4.5 and 6, for biosorption of Cr(VI) with R. oryzae, B. firmus, and T. viride, respectively, in the capacity of 45.3%, 24.5%, and 90.3%. The highest amount of Cr(VI) adsorbed for biosorption with R. oryzae, B. firmus, and T. viride, were 55.4%, 18.5%, and 74.5%, respectively, using 6-mL inoculums. The equilibrium concentrations achieved for R. oryzae, B. firmus, and T. viride were 60 mg/mL, 40 mg/mL, and 40 mg/mL, with the amount of Cr(VI) adsorbed were 32.4%, 28.2%, and 89.3%, respectively. The adsorption capacity for R. oryzae, B. firmus, and T. viride were 45.3 mg/1×106 colonies, 36.2 mg/1×106 cells, and 77.8 mg/1×106 colonies, respectively. Overall, the biosorbents effectivity order in the biosorption process of Cr(VI) are T. viride > R. oryzae > B. firmus.

Biosorption of Hexavalent Chromium from Aqueous Medium with Opuntia Biomass

PubMed Central

2014-01-01

The biosorption of hexavalent chromium from aqueous solutions by Opuntia cladodes and ectodermis from cactus fruits was investigated. Both types of biomass are considered low-cost, natural, and ecofriendly biosorbents. Batch experiments were carried out to determine Cr(VI) biosorption capacity and the efficiency of the biosorption process under different pH, initial Cr(VI) concentration, and sorbent dosage. The biosorption of Cr(VI) by Opuntia biomass was highly pH dependent, favoring higher metal uptake at low pH. The higher biosorption capacity was exhibited at pH 2. The optimal conditions were obtained at a sorbent dosage of 1 g L−1 and initial metal concentration of 10 mg L−1. Biosorption kinetic data were properly fitted with the pseudo-second-order kinetic model. The rate constant, the initial biosorption rate, and the equilibrium biosorption capacity were determined. The experimental equilibrium data obtained were analyzed using two-parameter isotherm models (Langmuir, Freundlich, and Temkin). The Langmuir maximum monolayer biosorption capacity (q max) was 18.5 mg g−1 for cladodes and 16.4 mg g−1 for ectodermis. The results suggest that Opuntia biomass could be considered a promising low-cost biosorbent for the ecofriendly removal of Cr(VI) from aqueous systems. PMID:24982975

Removal of hexavalent chromium in soil and groundwater by supported nano zero-valent iron on silica fume.

PubMed

Li, Yongchao; Jin, Zhaohui; Li, Tielong; Li, Shujing

2011-01-01

Silica fume supported-Fe(0) nanoparticles (SF-Fe(0)) were prepared using commercial silica fume as a support. The feasibility of using this SF-Fe(0) for reductive immobilization of Cr(VI) was investigated through batch tests. Compared with unsupported Fe(0), SF-Fe(0) was significantly more active in Cr(VI) removal especially in 84 wt% silica fume loading. Silica fume had also been found to inhibit the formation of Fe(III)/Cr(III) precipitation on Fe nanoparticles' surface, which was increasing the deactivation resistance of iron. Cr(VI) was removed through physical adsorption of Cr(VI) onto the SF-Fe(0) surface and subsequent reduction of Cr(VI) to Cr(III). The rate of reduction of Cr(VI) could be expressed by pseudo first-order reaction kinetics. The rate constant increased with the increase in iron loading but decreased with the increase in initial Cr(VI) concentration. Furthermore, column tests showed that the SF-Fe(0) could be readily transported in model soil.

Effect of Organic Substrates on the Photocatalytic Reduction of Cr(VI) by Porous Hollow Ga2O3 Nanoparticles

PubMed Central

Liu, Jin; Gan, Huihui; Wu, Hongzhang; Zhang, Xinlei; Zhang, Jun; Li, Lili; Wang, Zhenling

2018-01-01

Porous hollow Ga2O3 nanoparticles were successfully synthesized by a hydrolysis method followed by calcination. The prepared samples were characterized by field emission scanning electron microscope, transmission electron microscope, thermogravimetry and differential scanning calorimetry, UV-vis diffuse reflectance spectra and Raman spectrum. The porous structure of Ga2O3 nanoparticles can enhance the light harvesting efficiency, and provide lots of channels for the diffusion of Cr(VI) and Cr(III). Photocatalytic reduction of Cr(VI), with different initial pH and degradation of several organic substrates by porous hollow Ga2O3 nanoparticles in single system and binary system, were investigated in detail. The reduction rate of Cr(VI) in the binary pollutant system is markedly faster than that in the single Cr(VI) system, because Cr(VI) mainly acts as photogenerated electron acceptor. In addition, the type and concentration of organic substrates have an important role in the photocatalytic reduction of Cr(VI). PMID:29690548

Stabilization of nanoscale zero-valent iron (nZVI) with modified biochar for Cr(VI) removal from aqueous solution.

PubMed

Dong, Haoran; Deng, Junmin; Xie, Yankai; Zhang, Cong; Jiang, Zhao; Cheng, Yujun; Hou, Kunjie; Zeng, Guangming

2017-06-15

Three types of modified biochar (BC) were produced respectively with acid (HCl) treatment (HCl-BC), base (KOH) treatment (KOH-BC) and oxidation (H 2 O 2 ) treatment (H 2 O 2 -BC) of raw biochar. Both the raw biochar and modified biochars supported zero valent iron nanopartilces (nZVI) (i.e. nZVI@BC, nZVI@HCl-BC, nZVI@KOH-BC and nZVI@H 2 O 2 -BC) were synthesized and their capacities for Cr(VI) removal were compared. The results showed that the nZVI@HCl-BC exhibited the best performance and the underlying mechanisms were discussed. The surface elemental distribution maps of the nZVI@HCl-BC after reaction with Cr(VI) showed that Fe, Cr and O elements were deposited on the surface of HCl-BC evenly, indicating that the formed Cr(III)/Fe(III) could settle on the surface of HCl-BC uniformly rather than coated only on the nZVI surface. This reveals that the supporter HCl-BC could also play a role in alleviating the passivation of nZVI. Besides, the effects of mass ratio (nZVI/HCl-BC), pH, and initial Cr(VI) concentration on Cr(VI) removal were examined. At lower mass of HCl-BC, nZVI aggregation cannot be fully inhibited on the surface of HCl-BC, whereas excessive biochar can block the active sites of nZVI. Additionally, it was found that Cr(VI) removal by nZVI@HCl-BC was dependent on both pH and initial Cr(VI) concentration. Copyright © 2017 Elsevier B.V. All rights reserved.

Evaluation of the bioremoval of Cr(VI) and TOC in biofilters under continuous operation using response surface methodology.

PubMed

Leles, Daniela M A; Lemos, Diego A; Filho, Ubirajara C; Romanielo, Lucienne L; de Resende, Miriam M; Cardoso, Vicelma L

2012-06-01

In the present study, the bioremoval of Cr(VI) and the removal of total organic carbon (TOC) were achieved with a system composed by an anaerobic filter and a submerged biofilter with intermittent aeration using a mixed culture of microorganisms originating from contaminated sludge. In the aforementioned biofilters, the concentrations of chromium, carbon, and nitrogen were optimized according to response surface methodology. The initial concentration of Cr(VI) was 137.35 mg l(-1), and a bioremoval of 85.23% was attained. The optimal conditions for the removal of TOC were 4 to 8 g l(-1) of sodium acetate, >0.8 g l(-1) of ammonium chloride and 60 to 100 mg l(-1) of Cr(VI). The results revealed that ammonium chloride had the strongest effect on the TOC removal, and 120 mg l(-1) of Cr(VI) could be removed after 156 h of operation. Moreover, 100% of the Cr(VI) and the total chromium content of the aerobic reactor output were removed, and TOC removals of 80 and 87% were attained after operating the anaerobic and aerobic reactors for 130 and 142 h, respectively. The concentrations of cells in both reactors remained nearly constant over time. The residence time distribution was obtained to evaluate the flow through the bioreactors.

Laboratory investigations of the effects of nitrification-induced acidification on Cr cycling in vadose zone material partially derived from ultramafic rocks

USGS Publications Warehouse

Mills, Christopher T.; Goldhaber, Martin B.

2012-01-01

Sacramento Valley (California, USA) soils and sediments have high concentrations of Cr(III) because they are partially derived from ultramafic material. Some Cr(III) is oxidized to more toxic and mobile Cr(VI) by soil Mn oxides. Valley soils typically have neutral to alkaline pH at which Cr(III) is highly immobile. Much of the valley is under cultivation and is both fertilized and irrigated. A series of laboratory incubation experiments were conducted to assess how cultivation might impact Cr cycling in shallow vadose zone material from the valley. The first experiments employed low (7.1 mmol N per kg soil) and high (35 mmol N kg− 1) concentrations of applied (NH4)2SO4. Initially, Cr(VI) concentrations were up to 45 and 60% greater than controls in low and high incubations, respectively. After microbially-mediated oxidation of all NH4+, Cr(VI) concentrations dropped below control values. Increased nitrifying bacterial populations (estimated by measurement of phospholipid fatty acids) may have increased the Cr(VI) reduction capacity of the vadose zone material resulting in the observed decreases in Cr(VI). Another series of incubations employed vadose zone material from a different location to which low (45 meq kg− 1) and high (128 meq kg− 1) amounts of NH4Cl, KCl, and CaCl2 were applied. All treatments, except high concentration KCl, resulted in mean soil Cr(VI) concentrations that were greater than the control. High concentrations of water-leachable Ba2 + (mean 38 μmol kg− 1) in this treatment may have limited Cr(VI) solubility. A final set of incubations were amended with low (7.1 mmol N kg− 1) and high (35 mmol N kg− 1) concentrations of commercial liquid ammonium polyphosphate (APP) fertilizer which contained high concentrations of Cr(III). Soil Cr(VI) in the low APP incubations increased to a concentration of 1.8 μmol kg− 1 (5 × control) over 109 days suggesting that Cr(III) added with the APP fertilizer was more reactive than naturally-occurring soil Cr(III).

Highly active nanoscale zero-valent iron (nZVI)-Fe3O4 nanocomposites for the removal of chromium(VI) from aqueous solutions.

PubMed

Lv, Xiaoshu; Xu, Jiang; Jiang, Guangming; Tang, Jie; Xu, Xinhua

2012-03-01

For the first time, nanoscale zero-valent iron (nZVI)-Fe(3)O(4) nanocomposites, prepared by an in situ reduction method, are employed for chromium(VI) removal in aqueous environment. 96.4% Cr(VI) could be removed by these novel materials within 2h under pH of 8.0 and initial Cr concentration of 20 mg L(-1), compared with 48.8% by bare nFe(3)O(4) and 18.8% by bare nZVI. Effects of several factors, including mass composition of nZVI-Fe(3)O(4) nanocomposites, initial pH and Cr(VI) concentration, were evaluated. The optimal ratio of nFe(3)O(4) to nZVI mass lies at 12:1 with a fixed nZVI concentration of 0.05 g L(-1). Low pH and initial Cr(VI) concentration could increase both the Cr(VI) removal efficiency and reaction rate. Corresponding reaction kinetics fitted well with the pseudo second-order adsorption model. Free energy change (ΔG) of this reaction was calculated to be -4.6 kJ mol(-1) by thermodynamic study, which confirmed its spontaneous and endothermic characteristic. The experimental data could be well described by the Langmuir and Freundlich model, and the maximum capacity (q(max)) obtained from the Langmuir model was 100 and 29.43 mg g(-1) at pH 3.0 and 8.0, respectively. The reaction mechanism was discussed in terms of the mutual benefit brought by the electron transfer from Fe(0) to Fe(3)O(4). Copyright © 2011 Elsevier Inc. All rights reserved.

Visible-light-enhanced Cr(VI) reduction at Pd-decorated silicon nanowire photocathode in photoelectrocatalytic microbial fuel cell.

PubMed

Han, He-Xing; Shi, Chen; Zhang, Nan; Yuan, Li; Sheng, Guo-Ping

2018-10-15

Hexavalent chromium (Cr(VI)) is a prominent toxic metal with significant adverse human health effects. Photocatalytic reduction of Cr(VI) to less-toxic trivalent chromium (Cr(III)) is a promising method for removing Cr(VI) from aquatic environments. However, this technique often suffers from electron-hole recombination of semiconductors and poor reduction efficiency. The photoelectrocatalytic microbial fuel cell (Photo-MFC), which can use wastewater and light to recover electricity, has recently been proven to improve the separation of photocarriers of semiconductors and enhance cathodic reduction of pollutants. Here, the reduction of Cr(VI) was investigated in a Photo-MFC with a Pd-decorated p-type silicon nanowire (Pd/SiNW) photocathode and a bioanode under visible light. The Cr(VI) reduction efficiency reached 98.7% in 8 h under visible light, which was much higher than that under dark condition (56.2%) and open-circuit condition (19.4%). The enhanced Cr(VI) removal was mainly attributed to the synergistic effect of Pd/SiNW photocathode and bioanode. Cr(VI) reduction in the Photo-MFC fitted well with pseudo-first-order kinetics. The kinetics constants and reduction efficiencies of Cr(VI) decreased with the increase of pH, initial Cr(VI) concentration and external resistance. This work provides a promising alternative to mitigate Cr(VI) pollution in aquatic environments. Copyright © 2018 Elsevier B.V. All rights reserved.

Fabrication of a novel NiFe2O4/Zn-Al layered double hydroxide intercalated with EDTA composite and its adsorption behavior for Cr(VI) from aqueous solution

NASA Astrophysics Data System (ADS)

Deng, Lin; Shi, Zhou; Wang, Li; Zhou, Shiqing

2017-05-01

A novel magnetic NiFe2O4/Zn-Al layered double hydroxide intercalated with EDTA composite (NiFe2O4/ZnAl-EDTA LDH) was prepared through modified coprecipitation method and employed for adsorptive removal of Cr(VI) from aqueous solution. The adsorbents were characterized using Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), and X-ray photoelectron spectroscopy (XPS). Factors affecting the Cr(VI) adsorption, such as initial solution pH, adsorbent dosage, contact time, initial Cr(VI) concentration, temperature and coexisting ions, were studied systematically. Experiments results show that the magnetic NiFe2O4/ZnAl-EDTA LDH exhibits high adsorption efficiency within a wide pH range of 3.0-7.0 (R>80% at Cr(VI) concentration 50 mg L-1, contact time 360 min, and adsorbent dosage 2 g/L) and quick separation property. The adsorption process is fitted well with the Langmuir isotherm and pseudo-second-order kinetic model. The maximum theoretical adsorption capacity is found to be 77.22 mg g-1 at pH 6.0 and 318 K. The positive ΔH value (2.907 kJ mol-1) and negative ΔG value (-4.722 kJ mol-1) at 298-318 K reveals that the adsorption process is feasible, spontaneous and endothermic. Coexisting anions (PO43-, SO42-, CO32-, HCO3-, Cl-, and NO3-) have no significant effect on Cr(VI) removal. The mechanism study indicates that the adsorption of Cr(VI) onto NiFe2O4/ZnAl-EDTA LDH mainly involves electrostatic attraction and ion exchange interaction. It is interesting to note that a proportion of Cr(VI) adsorbed on the adsorbent surface are reduced to Cr(III) during the adsorption process. Results from this study demonstrate the potential utility of the magnetic NiFe2O4/ZnAl-EDTA LDH that could be developed into a viable technology for efficient removal of Cr(VI) from aqueous solution.

New generation ion-imprinted nanocarrier for removal of Cr(VI) from wastewater

NASA Astrophysics Data System (ADS)

Uygun, Murat; Feyzioğlu, Esra; Özçalışkan, Emir; Caka, Müşerref; Ergen, Aygen; Akgöl, Sinan; Denizli, Adil

2013-08-01

The purpose of this study was to prepare a novel ion-imprinted nanoparticle to remove Cr(VI) ions from waste water. For this, Cr(VI) ions were complexed with 2-methacryloylamido histidine (MAH) and then Cr(VI)-imprinted poly(HEMAH) nanoparticles were synthesized by surfactant-free emulsion polymerization technique. The templates, Cr(VI) ions, were removed from the nanoparticles using 0.1 M of HNO3 solution. The specific surface area of the Cr(VI)-imprinted poly(HEMAH) nanoparticles was found to be 1,397.85 m2/g, and the particle size was calculated as 155.3 nm. These Cr(VI)-imprinted nanoparticles were used for the adsorption/desorption of Cr(VI) ions from its aqueous solutions. The effects of initial Cr(VI) concentration and medium pH on the Cr(VI) adsorption capacity were also studied. The maximum adsorbed amount of Cr(VI) on the imprinted nanoparticles was found to be 3,830.58 mg/g nanoparticle in pH 4.0. In order to investigate the selectivity of the imprinted nanoparticle, adsorption studies were repeated using Cr(III) ions. The selectivity results demonstrated that Cr(VI)-imprinted poly(HEMAH) nanoparticles showed high affinity for the Cr(VI) ions than Cr(III). The Cr(VI)-imprinted nanoparticles were used several times without decreasing their Cr(VI) adsorption capacities.

Biodegradation of the metallic carcinogen hexavalent chromium Cr(VI) by an indigenously isolated bacterial strain

PubMed Central

Mishra, Susmita

2010-01-01

Background: Hexavalent chromium [Cr(VI)], a potential mutagen and carcinogen, is regularly introduced into the environment through diverse anthropogenic activities, including electroplating, leather tanning, and pigment manufacturing. Human exposure to this toxic metal ion not only causes potential human health hazards but also affects other life forms. The World Health Organization, the International Agency for Research on Cancer, and the Environmental Protection Agency have determined that Cr(VI) compounds are known human carcinogens. The Sukinda valley in Jajpur District, Orissa, is known for its deposit of chromite ore, producing nearly 98% of the chromite ore in India and one of the prime open cast chromite ore mines in the world (CES, Orissa Newsletter). Materials and Methods: Our investigation involved microbial remediation of Cr(VI) without producing any byproduct. Bacterial cultures tolerating high concentrations of Cr were isolated from the soil sample collected from the chromite-contaminated sites of Sukinda, and their bioaccumulation properties were investigated. Strains capable of growing at 250 mg/L Cr(VI) were considered as Cr resistant. Results: The experimental investigation showed the maximum specific Cr uptake at pH 7 and temperature 30°C. At about 50 mg/L initial Cr(VI) concentrations, uptake of the selected potential strain exceeded 98% within 12 h of incubation. The bacterial isolate was identified by 16S rRNA sequencing as Brevebacterium casei. Conclusion: Results indicated promising approach for microbial remediation of effluents containing elevated levels of Cr(VI). PMID:20976016

Adsorption Effectivity Test of Andisols Clay-Zeolite (ACZ) Composite as Chromium Hexavalent (Cr(VI)) Ion Adsorbent

NASA Astrophysics Data System (ADS)

Pranoto; Masykur, A.; Nugroho, Y. A.

2018-03-01

Adsorption of chromium hexavalent (Cr(VI)) ion in aqueous solution was investigated. This research was purposed to study the influence of the composition of ACZ, temperature activation, and contact time against adsorption capacity of Cr(VI) ion in aqueous solution. Determination of adsorption effectivity using several parameter such as composition variation of ACZ, contact time, pH, activation temperature, and concentration. In this research, andisol clay and zeolite has been activated with NaOH 3 M and 1 M, respectively. Temperature variation used 100, 200, and 400°C. While composition variation ACZ used 0:100, 25:75, 50:50, 75:25, 100:0. The pH variation was used 2 – 6 and concentration variation using 2, 4, 6, 8, 10, and 12 ppm. Characterization in this research used such as UV-Vis, Surface Area Analyzer (SAA) and Acidity Analysis. Result of this research is known that optimum composition of ACZ was 50:50 with calcination temperature 100°C. Optimum adsorption of Cr(VI) at pH 4 with removal percentage 76.10 % with initial concentration 2 ppm and adsorption capacity is 0.16 mg/g. Adsorption isotherm following freundlich isotherm with value Kf = 0.17 mg/g and value n is 0.963. Based on results, ACZ composite can be used as Cr(VI) ion adsorbents in aqueous solutions.

Thermodynamic analysis of Cr(VI) extraction using TOPO impregnated membranes.

PubMed

Praveen, Prashant; Loh, Kai-Chee

2016-08-15

Solid/liquid extraction of Cr(VI) was accomplished using trioctylphosphine oxide impregnated polypropylene hollow fiber membranes. Extraction of 100-500mg/L Cr(VI) by the extractant impregnated membranes (EIM) was characterized by high uptake rate and capacity, and equilibrium was attained within 45min of contact. Extraction equilibrium was pH-dependent (at an optimal pH 2), whereas stripping using 0.2M sodium hydroxide yielded the highest recovery of 98% within 60min. The distribution coefficient was independent of initial Cr(VI) concentration, and the linear distribution equilibrium isotherm could be modeled using Freundlich isotherm. The mass transfer kinetics of Cr(VI) was examined using pseudo-second-order and intraparticle diffusion models and a mass transfer mechanism was deduced. The distribution coefficient increased with temperature, which indicated endothermic nature of the reaction. Enthalpy and entropy change during Cr(VI) extraction were positive and varied in the range of 37-49kJ/mol and 114-155J/mol, respectively. The free energy change was negative, confirming the feasibility and spontaneity of the mass transfer process. Results obtained suggest that EIMs are efficient and sustainable for extraction of Cr(VI) from wastewater. Copyright © 2016 Elsevier B.V. All rights reserved.

Natural biosorbents (garlic stem and horse chesnut shell) for removal of chromium(VI) from aqueous solutions.

PubMed

Parlayıcı, Şerife; Pehlivan, Erol

2015-12-01

The biosorption of Cr(VI) by the garlic stem (GS)-Allium sativum L. and horse chesnut shell (HCS)-Aesculus hippocastanum plant residues in a batch type reactor was studied in detail for the purpose of wastewater treatment. The influence of initial Cr(VI) concentration, time, and pH was investigated to optimize Cr(VI) removal from aqueous solutions and equilibrium isotherms and kinetic data. This influence was evaluated. The adsorption capacity of the GS and the HCS for Cr(VI) was determined with the Langmuir and Freundlich isotherm models, and the data was fitted to the Langmuir. The adsorption capacity of the GS and the HCS was found to be 103.09 and 142.85 mg/g of adsorbent from a solution containing 3000 ppm of Cr(VI), respectively. The GS's capacity was considerably lower than that of the HCS in its natural form. Gibbs free energy was spontaneous for all interactions, and the adsorption process exhibited exothermic enthalpy values. The HCS was shown to be a promising biosorbent for Cr(VI) removal from aqueous solutions.

Catalytic role of Cu(II) in the reduction of Cr(VI) by citric acid under an irradiation of simulated solar light.

PubMed

Li, Ying; Chen, Cheng; Zhang, Jing; Lan, Yeqing

2015-05-01

The catalytic role of Cu(II) in the reduction of Cr(VI) by citric acid with simulated solar light was investigated. The results demonstrated that Cu(II) could significantly accelerate Cr(VI) reduction and the reaction obeyed to pseudo zero-order kinetics with respect to Cr(VI). The removal of Cr(VI) was related to the initial concentrations of Cu(II), citric acid, and the types of organic acids. The optimal removal of Cr(VI) was achieved at pH 4, and the rates of Cu(II) photocatalytic reduction of Cr(VI) by organic acids were in the order: tartaric acid (two α-OH groups, two -COOH groups)>citric acid (one α-OH group, three -COOH groups)>malic acid (one α-OH group, two -COOH groups)>lactic acid (one α-OH group, one -COOH group)≫succinic acid (two -COOH groups), suggesting that the number of α-OH was the key factor for the reaction, followed by the number of -COOH. The formation of Cu(II)-citric acid complex could generate Cu(I) and radicals through a pathway of metal-ligand-electron transfer, promoting the reduction of Cr(VI). This study is helpful to fully understanding the conversion of Cr(VI) in the existence of both organic acids and Cu(II) with solar light in aquatic environments. Copyright © 2015 Elsevier Ltd. All rights reserved.

Enhanced Cr(VI) removal by polyethylenimine- and phosphorus-codoped hierarchical porous carbons.

PubMed

Chen, Shixia; Wang, Jun; Wu, Zeliang; Deng, Qiang; Tu, Wenfeng; Dai, Guiping; Zeng, Zheling; Deng, Shuguang

2018-08-01

The amino- and phosphorus-codoped (N,P-codoped) porous carbons derived from oil-tea shells were facilely fabricated through a combination of phosphoric acid (H 3 PO 4 ) activation and amino (polyethylenimine, PEI) modification method. The as-synthesized carbon adsorbents were systematically characterized and evaluated for Cr(VI) removal in aqueous solutions. The relationship between adsorbent properties and adsorption behaviors was illustrated. Moreover, the influences of contact time, initial Cr(VI) concentration, pH, coexisting anions and temperature were also investigated. The adsorption behavior of Cr(VI) could be perfectly described by the pseudo-second-order kinetic model and Sips adsorption model. The maximum adsorption capacity of Cr(VI) on the carbon adsorbents synthesized in this work was 355.0 mg/g, and this excellent Cr(VI) capacity could be sustained with other coexisting anions. In addition to high surface area and suitable pore size distribution, the high Cr(VI) removal capacity is induced by rich heteroatoms incorporation and the Cr(VI) removal mechanism was clearly illustrated. Furthermore, the continuous column breakthrough experiment on obtained N,P-codoped carbon was conducted and well fitted by the Thomas model. This work revealed that PEI modification and P-containing groups could significantly enhance Cr(VI) adsorption capacity and make these N,P-codoped biomass-derived carbons potent adsorbents in practical water treatment applications. Copyright © 2018 Elsevier Inc. All rights reserved.

Synthesis, characterization and application of Lagerstroemia speciosa embedded magnetic nanoparticle for Cr(VI) adsorption from aqueous solution.

PubMed

Srivastava, Shalini; Agrawal, Shashi Bhushan; Mondal, Monoj Kumar

2017-05-01

Lagerstroemia speciosa bark (LB) embedded magnetic nanoparticles were prepared by co-precipitation of Fe 2+ and Fe 3+ salt solution with ammonia and LB for Cr(VI) removal from aqueous solution. The native LB, magnetic nanoparticle (MNP), L. speciosa embedded magnetic nanoparticle (MNPLB) and Cr(VI) adsorbed MNPLB particles were characterized by SEM-EDX, TEM, BET-surface area, FT-IR, XRD and TGA methods. TEM analysis confirmed nearly spherical shape of MNP with an average diameter of 8.76nm and the surface modification did not result in the phase change of MNP as established by XRD analysis, while led to the formation of secondary particles of MNPLB with diameter of 18.54nm. Characterization results revealed covalent binding between the hydroxyl group of MNP and carboxyl group of LB particles and further confirmed its physico-chemical nature favorable for Cr(VI) adsorption. The Cr(VI) adsorption on to MNPLB particle as an adsorbent was tested under different contact time, initial Cr(VI) concentration, adsorbent dose, initial pH, temperature and agitation speed. The results of the equilibrium and kinetics of adsorption were well described by Langmuir isotherm and pseudo-second-order model, respectively. The thermodynamic parameters suggest spontaneous and endothermic nature of Cr(VI) adsorption onto MNPLB. The maximum adsorption capacity for MNPLB was calculated to be 434.78mg/g and these particles even after Cr(VI) adsorption were collected effortlessly from the aqueous solution by a magnet. The desorption of Cr(VI)-adsorbed MNPLB was found to be more than 93.72% with spent MNPLB depicting eleven successive adsorption-desorption cycles. Copyright © 2016. Published by Elsevier B.V.

Inhibition of the nitrification process in activated sludge by trivalent and hexavalent chromium, and partitioning of hexavalent chromium between sludge compartments.

PubMed

Novotnik, Breda; Zuliani, Tea; Ščančar, Janez; Milačič, Radmila

2014-06-01

The input of wastewater treatment plants (WWTPs) may contain high concentrations of Cr(III) and Cr(VI), which can affect nitrogen removal. In the present study the influence of different Cr(III) and Cr(VI) concentrations towards activated sludge nitrification was studied. To better understand the mechanisms of Cr(VI) toxicity, its reduction, adsorption and uptake in activated sludge was investigated in a batch growth system. Quantification of Cr(VI) was performed by speciated isotope dilution inductively coupled plasma mass spectrometry. It was found that Cr(VI) concentrations above 1.0 mg L(-1) and Cr(III) concentrations higher than 50 mg L(-1) negatively affected nitrification. Speciation studies indicated almost complete reduction of Cr(VI) after 24h of incubation when Cr(VI) concentrations were lower than 2.5 mg L(-1), whereas for Cr(VI) added to 5 mg L(-1) around 40% remained unreduced. The study of the partitioning of Cr in the activated sludge was performed by the addition of Cr(VI) in concentrations of 2.5 and 5.0 mg L(-1). Results revealed that Cr was allocated mainly within the intercellular compartments, whereas intracellular and adsorbed Cr represented less than 0.1% of the Cr sludge concentrations. Cr(VI) was reduced in all compartments, the most efficiently (about 94%) within the intracellular and intercellular fractions. The extent of reduction of adsorbed Cr was 92% and 80% for 2.5 and 5.0mg of Cr(VI) L(-1), respectively. The results of present investigation provide a new insight into the toxicity of Cr species towards activated sludge nitrification, which is of significant importance for the management of WWTPs in order to prevent them from inflows containing harmful Cr(VI) concentrations. Copyright © 2014 Elsevier Ltd. All rights reserved.

A study of the kinetics and isotherms for Cr(VI) adsorption in a binary mixture of Cr(VI)-Ni(II) using hierarchical porous carbon obtained from pig bone.

PubMed

Li, Chengxian; Huang, Zhe; Huang, Bicheng; Liu, Changfeng; Li, Chengming; Huang, Yaqin

2014-01-01

Cr(VI) adsorption in a binary mixture Cr(VI)-Ni(II) using the hierarchical porous carbon prepared from pig bone (HPC) was investigated. The various factors affecting adsorption of Cr(VI) ions from aqueous solutions such as initial concentration, pH, temperature and contact time were analyzed. The results showed excellent efficiency of Cr(VI) adsorption by HPC. The kinetics and isotherms for Cr(VI) adsorption from a binary mixture Cr(VI)-Ni(II) by HPC were studied. The adsorption equilibrium described by the Langmuir isotherm model is better than that described by the Freundlich isotherm model for the binary mixture in this study. The maximum adsorption capacity was reliably found to be as high as 192.68 mg/g in the binary mixture at pH 2. On fitting the experimental data to both pseudo-first- and second-order equations, the regression analysis of the second-order equation gave a better R² value.

Studies on uptake of trivalent and hexavalent chromium by maize (Zea mays).

PubMed

Mishra, S; Singh, V; Srivastava, S; Srivastava, R; Srivastava, M M; Dass, S; Satsangi, G P; Prakash, S

1995-05-01

Pot culture experiments were carried out to study the uptake and translocation of chromium from irrigation water when supplied in its trivalent and hexavalent states to maize plants grown in soil and sand culture. The uptake of chromium was observed to increase with increase in the concentration for both oxidation states of chromium. For the root, the observed order of uptake was CrIII sand > CrVI sand > CrIII soil > CrVI soil, whereas in the lower shoot, upper shoot and fruit the order was CrVI sand > CrVI soil > CrIII sand > CrIII soil. Significantly high uptake of chromium by roots in the sand culture (CrIII treatment) is attributed to the effect of root exudates and degradation products on the mobilization of CrIII. In aerial parts of the plants a higher uptake was observed when the initial supply was CrVI. The trends observed are explained on the basis of the redox behaviour of chromium.

Quantifying Cr(VI) Production and Export from Serpentine Soil of the California Coast Range

DOE PAGES

McClain, Cynthia N.; Fendorf, Scott; Webb, Samuel M.; ...

2016-11-22

Here, hexavalent chromium (Cr(VI)) is generated in serpentine soils and exported to surface and groundwaters at levels above health-based drinking water standards. Although Cr(VI) concentrations are elevated in serpentine soil pore water, few studies have reported field evidence documenting Cr(VI) production rates and fluxes that govern Cr(VI) transport from soil to water sources. We report Cr speciation (i) in four serpentine soil depth profiles derived from the California Coast Range serpentinite belt and (ii) in local surface waters. Within soils, we detected Cr(VI) in the same horizons where Cr(III)-minerals are colocated with biogenic Mn(III/IV)-oxides, suggesting Cr(VI) generation through oxidation bymore » Mn-oxides. Water-extractable Cr(VI) concentrations increase with depth constituting a 7.8 to 12 kg/km 2 reservoir of Cr(VI) in soil. Here, Cr(VI) is produced at a rate of 0.3 to 4.8 kg Cr(VI)/km 2/yr and subsequently flushed from soil during water infiltration, exporting 0.01 to 3.9 kg Cr(VI)/km 2/yr at concentrations ranging from 25 to 172 μg/L. Although soil-derived Cr(VI) is leached from soil at concentrations exceeding 10 μg/L, due to reduction and dilution during transport to streams, Cr(VI) levels measured in local surface waters largely remain below California’s drinking water limit.« less

Quantifying Cr(VI) Production and Export from Serpentine Soil of the California Coast Range.

PubMed

McClain, Cynthia N; Fendorf, Scott; Webb, Samuel M; Maher, Kate

2017-01-03

Hexavalent chromium (Cr(VI)) is generated in serpentine soils and exported to surface and groundwaters at levels above health-based drinking water standards. Although Cr(VI) concentrations are elevated in serpentine soil pore water, few studies have reported field evidence documenting Cr(VI) production rates and fluxes that govern Cr(VI) transport from soil to water sources. We report Cr speciation (i) in four serpentine soil depth profiles derived from the California Coast Range serpentinite belt and (ii) in local surface waters. Within soils, we detected Cr(VI) in the same horizons where Cr(III)-minerals are colocated with biogenic Mn(III/IV)-oxides, suggesting Cr(VI) generation through oxidation by Mn-oxides. Water-extractable Cr(VI) concentrations increase with depth constituting a 7.8 to 12 kg/km 2 reservoir of Cr(VI) in soil. Here, Cr(VI) is produced at a rate of 0.3 to 4.8 kg Cr(VI)/km 2 /yr and subsequently flushed from soil during water infiltration, exporting 0.01 to 3.9 kg Cr(VI)/km 2 /yr at concentrations ranging from 25 to 172 μg/L. Although soil-derived Cr(VI) is leached from soil at concentrations exceeding 10 μg/L, due to reduction and dilution during transport to streams, Cr(VI) levels measured in local surface waters largely remain below California's drinking water limit.

[Preparation of nano zero-valent iron/Sargassum horneri based activated carbon for removal of Cr (VI) from aqueous solution].

PubMed

Zeng, Gan-Ning; Wu, Xiao; Zheng, Lin; Wu, Xi; Tu, Mei-Ling; Wang, Tie-Gan; Ai, Ning

2015-02-01

Nanoscale zero-valent iron supported on Sargassum horneri activated carbon (NZVI/SAC) was synthesized by zinc chloride activation and incipient wetness method, and characterized with X-ray diffraction (XRD), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). XRD confirmed the existence of nano zero-valent iron, and SEM revealed that the material consisted of mainly 30-150 nm spherical particles aggregated into chains of individual units. The valence state of iron conformed with the nuclear-shell model. The effects of NZVI loading on AC, pH and the initial concentration of Cr(VI) on the removal of Cr(VI) were investigated. The final Cr(VI) removal percentage was up to 100% under the following conditions: 30 degrees C, pH = 2, NZVI/SAC dosage of 2 g x L(-1) and the amounts of NZVI loaded on SAC of 30%. And the equilibrium time was 10 minutes. These results showed that NZVI/SAC could be potentially applied for removal of high concentration Cr(VI). By analyzing the chemical change of NZVI/ SAC, we demonstrated that Cr(VI) was mainly reduced to insoluble Cr (III) compound in the reaction when pH was less than 4, and adsorbed by NZVI and SAC when pH was over 4.

Removal of hexavalent chromium upon interaction with biochar under acidic conditions: mechanistic insights and application.

PubMed

Choudhary, Bharat; Paul, Debajyoti; Singh, Abhas; Gupta, Tarun

2017-07-01

Chromium pollution of soil and water is a serious environmental concern due to potential carcinogenicity of hexavalent chromium [Cr(VI)] when ingested. Eucalyptus bark biochar (EBB), a carbonaceous black porous material obtained by pyrolysis of biomass at 500 °C under oxygen-free atmosphere, was used to investigate the removal of aqueous Cr(VI) upon interaction with the EBB, the dominant Cr(VI) removal mechanism(s), and the applicability to treat Cr(VI)-contaminated wastewater. Batch experiments showed complete removal of aqueous Cr(VI) at pH 1-2; sorption was negligible at pH 1, but ~55% of total Cr was sorbed onto the EBB surface at pH 2. Detailed investigations on unreacted and reacted EBB through Fourier transform infrared spectroscopy and X-ray photoelectron spectrometry (XPS) indicate that the carboxylic groups in biochar played a dominant role in Cr(VI) sorption, whereas the phenolic groups were responsible for Cr(VI) reduction. The predominance of sorption-reduction mechanism was confirmed by XPS studies that indicated ~82% as Cr(III) and ~18% as Cr(VI) sorbed on the EBB surface. Significantly, Cr(VI) reduction was also facilitated by dissolved organic matter (DOM) extracted from biochar. This reduction was enhanced by the presence of biochar. Overall, the removal of Cr(VI) in the presence of biochar was affected by sorption due to electrostatic attraction, sorption-reduction mediated by surface organic complexes, and aqueous reduction by DOM. Relative dominance of the aqueous reduction mechanism depended on a critical biochar dosage for a given electrolyte pH and initial Cr(VI) concentration. The low-cost EBB developed here successfully removed all Cr(VI) in chrome tanning acidic wastewater and Cr(VI)-contaminated groundwater after pH adjustment, highlighting its potential applicability in effective Cr(VI) remediation.

Sorption of Cr(VI), Cu(II) and Pb(II) by growing and non-growing cells of a bacterial consortium.

PubMed

Sannasi, P; Kader, J; Ismail, B S; Salmijah, S

2006-03-01

This paper reports the sorption of three metallic ions, namely Cr(VI), Cu(II) and Pb(II) in aqueous solution by a consortium culture (CC) comprising an acclimatised mixed bacterial culture collected from point and non-point sources. Metal sorption capability of growing and non-growing cells at initial pH of between 3 and 8 in the 1-100mg/L concentration range were studied based on Q(max) and K(f) values of the Langmuir and linearised Freundlich isotherm models, respectively. Maximal metal loading was generally observed to be dependent on the initial pH. Growing cells displayed significant maximal loading (Q(max)) for Pb(II) (238.09 mg/g) and Cu(II) (178.87 mg/g) at pH 6 and at pH 7 for Cr(VI) (90.91 mg/g) compared to non-growing cells (p < 0.05). At the pH range of 6-8, growing cells showed higher loading capacity compared to non-growing cells i.e. 38-52% for Cr, 17-28% for Cu and 3-17% for Pb. At lower metal concentrations and at more acidic pH (3-4) however, non-growing cells had higher metal loading capacity than growing cells. The metal sorption capacity for both populations were as follows: Pb(II) > Cu(II) > Cr(VI).

Hexavalent Chromate Reductase Activity in Cell Free Extracts of Penicillium sp.

PubMed Central

Arévalo-Rangel, Damaris L.; Cárdenas-González, Juan F.; Martínez-Juárez, Víctor M.; Acosta-Rodríguez, Ismael

2013-01-01

A chromium-resistant fungus isolated from contaminated air with industrial vapors can be used for reducing toxic Cr(VI) to Cr(III). This study analyzes in vitro reduction of hexavalent chromium using cell free extract(s) of the fungus that was characterized based on optimal temperature, pH, use of electron donors, metal ions and initial Cr(VI) concentration in the reaction mixture. This showed the highest activity at 37°C and pH 7.0; there is an increase in Cr(VI) reductase activity with addition of NADH as an electron donor, and it was highly inhibited by Hg2+, Ca2+ and Mg2+, and azide, EDTA, and KCN. PMID:24027493

Adsorption characteristics of hexavalent chromium on HCB/TiO2

NASA Astrophysics Data System (ADS)

Zhang, Li; Zhang, Yonggang

2014-10-01

Sol-gel method was adopted to prepare HCB/TiO2 and its adsorption ability of hexavalent chromium, Cr(VI), and removal from aqueous solution were investigated. The samples were characterized by Power X-ray diffraction (XRD) and a transmission electron microscope (TEM) which showed that the TiO2 was deposited on the surface of HCB. FTIR was used to identify the changes of the surface functional groups before and after adsorption. Potentiometric titration method was used to characterize the zero charge (pHpzc) characteristics of the surface of HCB/TiO2 which showed more acidic functional groups containing. Batch experiments showed that initial pH, absorbent dosage, contact time and initial concentration of Cr(VI) were important parameters for the Cr(VI) adsorption studies. The Freundlich isotherm model better reflected the experimental data better. Cr(VI) adsorption process followed the pseudo-second order kinetic model, which illustrated chemical adsorption. The thermodynamic parameters, such as Gibbs free energy (ΔG), changes in enthalpy change (ΔH) and changes in entropy change (ΔS) were also evaluated. Negative value of free energy occurred at temperature range of 25-45 °C, so Cr(VI) adsorption by HCB/TiO2 is spontaneous. Desorption results showed that the adsorption capacity could maintain 80% after five cycles. The maximum adsorption capacity for Cr(VI) was at 27.33 mg g-1 in an acidic medium, of which the value is worth comparable with other low-cost adsorbents.

Cr(VI) reduction from contaminated soils by Aspergillus sp. N2 and Penicillium sp. N3 isolated from chromium deposits.

PubMed

Fukuda, Tsubasa; Ishino, Yasuhiro; Ogawa, Akane; Tsutsumi, Kadzuyo; Morita, Hiroshi

2008-10-01

Aspergillus sp. N2 and Penicillium sp. N3 are chromate-resistant filamentous fungi that were isolated from Cr(VI) contaminated soil based on their ability to decrease hexavalent chromium levels in the growth medium. After 120 h of growth in a medium containing 50 ppm Cr(VI) at near neutral pH, Aspergillus sp. N2 reduced the Cr(VI) concentration by about 75%. Penicillium sp. N3 was able to reduce the Cr(VI) concentration by only 35%. However, Penicillium sp. N3 reduced the Cr(VI) concentration in the medium by 93% under acidic conditions. Interestingly, the presence of Cu(II) enhanced the Cr(VI) reducing ability of Aspergillus sp. N2 and Penicillium sp. N3 at near neutral pH. Aspergillus sp. N2 and Penicillium sp. N3 reduced the Cr(VI) concentration in the growth medium to a virtually undetectable level within 120 h. For both Aspergillus sp. N2 and Penicillium sp. N3, mycelial seed cultures were more efficient at Cr(VI) reduction than conidium seed cultures. The mechanisms of Cr(VI) reduction in Aspergillus sp. N2 and Penicillium sp. N3 were enzymatic reduction and sorption to mycelia. Enzymatic activity contributed significantly to Cr(VI) reduction. Aspergillus sp. N2 and Penicillium sp. N3 reduced the levels of Cr(VI) in polluted soil samples, suggesting that these strains might be useful for cleaning up chromium-contaminated sites.

Polyethylenimine functionalized Fe3O4/steam-exploded rice straw composite as an efficient adsorbent for Cr(VI) removal

NASA Astrophysics Data System (ADS)

Zhang, Shengli; Wang, Zhikai; Chen, Haoyu; Kai, Chengcheng; Jiang, Man; Wang, Qun; Zhou, Zuowan

2018-05-01

Polyethyleneimine functionalized Fe3O4/steam-exploded rice straw composite (Fe3O4-PEI-SERS), which combines magnetic separation with adsorption of PEI functionalized biosorbent, was successfully prepared via a simple glutaraldehyde crosslinking method. Its adsorption potential for the removal of Cr(VI) was systematically studied in batch mode. Results showed that Cr(VI) adsorption on Fe3O4-PEI-SESERS was highly pH-dependent, and the optimum pH was 2.0. The time to reach equilibrium was related to initial Cr(VI) concentration and was 1 and 6 h for 200 and 300 mg/L of Cr(VI), respectively. The adsorption system followed pseudo-second-order kinetic model and Langmuir isotherm. Its maximum adsorption capacity was 280.11, 317.46 and 338.98 mg/g at 25, 35 and 45 °C, respectively. The competitive uptake from coexisting ions (K+, Na+, Cu2+, Cl- and NO3-) was insignificant except SO42-. After six adsorption/desorption cycles, the adsorbent retained good adsorption capacity. The Cr(VI) removal involved its partial reduction into Cr(III). Due to the properties of high adsorption capacity, strong magnetic responsiveness, good reusability and Cr(VI) detoxification, the Fe3O4-PEI-SESERS has a potential application in Cr(VI) removal from wastewater.

Cr(VI) Adsorption on Red Mud Modified by Lanthanum: Performance, Kinetics and Mechanisms

PubMed Central

Cui, You-Wei; Li, Jie; Du, Zhao-Fu; Peng, Yong-Zhen

2016-01-01

Water pollution caused by the highly toxic metal hexavalent chromium (Cr(VI)) creates significant human health and ecological risks. In this study, a novel adsorbent was used to treat Cr(VI)-containing wastewater; the adsorbent was prepared using red mud (RM) generated from the alumina production industry and the rare earth element lanthanum. This study explored adsorption performance, kinetics, and mechanisms. Results showed that the adsorption kinetics of the RM modified by lanthanum (La-RM), followed the pseudo-second-order model, with a rapid adsorption rate. Cr(VI) adsorption was positively associated with the absorbent dose, pH, temperature, and initial Cr(VI) concentration; coexisting anions had little impact. The maximum Cr(VI) adsorption capacity was 17.35 mg/g. Cr(VI) adsorption on La-RM was a mono-layer adsorption pattern, following the Langmuir isotherm model. Thermodynamic parameters showed the adsorption was spontaneous and endothermic. The adsorption of Cr(VI) on La-RM occurred as a result of LaOCl formation on the RM surface, which in turn further reacted with Cr(VI) in the wastewater. This study highlighted a method for converting industrial waste into a valuable material for wastewater treatment. The novel absorbent could be used as a potential adsorbent for treating Cr(VI)-contaminating wastewater, due to its cost-effectiveness and high adsorption capability. PMID:27658113

A Comparative Study of Raw and Metal Oxide Impregnated Carbon Nanotubes for the Adsorption of Hexavalent Chromium from Aqueous Solution

PubMed Central

Qureshi, Muhammad I.; Al-Baghli, Nadhir

2017-01-01

The present study reports the use of raw, iron oxide, and aluminum oxide impregnated carbon nanotubes (CNTs) for the adsorption of hexavalent chromium (Cr(VI)) ions from aqueous solution. The raw CNTs were impregnated with 1% and 10% loadings (weight %) of iron oxide and aluminum oxide nanoparticles using wet impregnation technique. The synthesized materials were characterized using scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Batch adsorption experiments were performed to assess the removal efficiency of Cr(VI) ions from water and the effects of pH, contact time, adsorbent dosage, and initial concentration of the Cr(VI) ions were investigated. Results of the study revealed that impregnated CNTs achieved significant increase in the removal efficiency of Cr(VI) ions compared to raw CNTs. In fact, both CNTs impregnated with 10% loading of iron and aluminum oxides were able to remove up to 100% of Cr(VI) ions from aqueous solution. Isotherm studies were carried out using Langmuir and Freundlich isotherm models. Adsorption kinetics of Cr(VI) ions from water was found to be well described by the pseudo-second-order model. The results suggest that metallic oxide impregnated CNTs have very good potential application in the removal of Cr(VI) ions from water resulting in better environmental protection. PMID:28487625

Modeling biosorption of Cr(VI) onto Ulva compressa L. from aqueous solutions.

PubMed

Aid, Asma; Amokrane, Samira; Nibou, Djamel; Mekatel, Elhadj; Trari, Mohamed; Hulea, Vasile

2018-01-01

The marine biomass Ulva compressa L. (ECL) was used as a low-cost biosorbent for the removal of Cr(VI) from contaminated aqueous solutions. The operating variables were optimized: pH ∼ 2, initial concentration of 25 mg/L, solid/liquid ratio of 6 g/L and a temperature of 50 °C, leading to an uptake elimination of 96%. A full factorial experimental design technique enabled us to obtain a mathematical model describing the Cr(VI) biosorption and to study the main effects and interactions among operational parameters. The equilibrium isotherm was analyzed by the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models; it has been found that the adsorption process follows well the Langmuir model. Kinetic studies showed that the pseudo-second order model describes suitably the experimental data. The thermodynamic parameters indicated an endothermic heat and a spontaneity of the Cr(VI) biosorption onto ECL.

Utility of Ochrobactrum anthropi YC152 in a Microbial Fuel Cell as an Early Warning Device for Hexavalent Chromium Determination.

PubMed

Wang, Guey-Horng; Cheng, Chiu-Yu; Liu, Man-Hai; Chen, Tzu-Yu; Hsieh, Min-Chi; Chung, Ying-Chien

2016-08-16

Fast hexavalent chromium (Cr(VI)) determination is important for environmental risk and health-related considerations. We used a microbial fuel cell-based biosensor inoculated with a facultatively anaerobic, Cr(VI)-reducing, and exoelectrogenic Ochrobactrum anthropi YC152 to determine the Cr(VI) concentration in water. The results indicated that O. anthropi YC152 exhibited high adaptability to pH, temperature, salinity, and water quality under anaerobic conditions. The stable performance of the microbial fuel cell (MFC)-based biosensor indicated its potential as a reliable biosensor system. The MFC voltage decreased as the Cr(VI) concentration in the MFC increased. Two satisfactory linear relationships were observed between the Cr(VI) concentration and voltage output for various Cr(VI) concentration ranges (0.0125-0.3 mg/L and 0.3-5 mg/L). The MFC biosensor is a simple device that can accurately measure Cr(VI) concentrations in drinking water, groundwater, and electroplating wastewater in 45 min with low deviations (<10%). The use of the biosensor can help in preventing the violation of effluent regulations and the maximum allowable concentration of Cr(VI) in water. Thus, the developed MFC biosensor has potential as an early warning detection device for Cr(VI) determination even if O. anthropi YC152 is a possible opportunistic pathogen.

Banana peel: a green and economical sorbent for the selective removal of Cr(VI) from industrial wastewater.

PubMed

Memon, Jamil R; Memon, Saima Q; Bhanger, Muhammad I; El-Turki, Adel; Hallam, Keith R; Allen, Geoffrey C

2009-05-01

This study describes the use of banana peel, a commonly produced fruit waste, for the removal of Cr(VI) from industrial wastewater. The parameters pH, contact time, initial metal ion concentration, and temperature were investigated and the conditions resulting in rapid and efficient adsorption (95% within 10 min) were determined. The binding of metal ions was found to be pH dependent with the optimal sorption occurring at pH 2. The retained species were eluted with 5 mL of 2M H(2)SO(4). To elucidate the mechanism of the process, total amounts of chromium and Cr(VI) were analyzed using flame atomic absorption and ultraviolet-visible (UV-vis) spectroscopic techniques, respectively. The Langmuir and Dubinin-Radushkevich (D-R) isotherms were used to describe the partitioning behavior for the system at different temperatures. Kinetics and thermodynamics of Cr(VI) removal by banana peel were also studied. The influence of diverse ions on the sorption behavior revealed that only Fe(II) ions (of those tested) suppressed the sorption of Cr(VI) ions to some extent. The method was applied for the removal of Cr(VI) from industrial wastewater.

Sulfate and chromate increased each other's uptake and translocation in As-hyperaccumulator Pteris vittata.

PubMed

de Oliveira, Letúzia M; Gress, Julia; De, Jaysankar; Rathinasabapathi, Bala; Marchi, Giuliano; Chen, Yanshan; Ma, Lena Q

2016-03-01

We investigated the effects of chromate (CrVI) and sulfate on their uptake and translocation in As-hyperaccumulator Pteris vittata. Plants were exposed to 1) 0.1 mM CrVI and 0, 0.25, 1.25 or 2.5 mM sulfate or 2) 0.25 mM sulfate and 0, 0.5, 2.5 or 5.0 mM CrVI for 1 d in hydroponics. P. vittata accumulated 26 and 1261 mg kg(-1) Cr in the fronds and roots at CrVI0.1, and 2197 and 1589 mg kg(-1) S in the fronds and roots at S0.25. Increasing sulfate concentrations increased Cr root concentrations by 16-66% and helped CrVI reduction to CrIII whereas increasing CrVI concentrations increased frond sulfate concentrations by 3-27%. Increasing sulfate concentrations enhanced TBARS concentrations in the biomass, indicating oxidative stress caused lipid peroxidation in plant cell membranes. However, addition of 0.25-2.5 mM sulfate alleviated CrVI's toxic effects and decreased TBARS from 23.5 to 9.46-12.3 μmol g(-1) FW. Though CrVI was supplied, 78-96% of CrIII was in the biomass, indicating efficient CrVI reduction to CrIII by P. vittata. The data indicated the amazing ability of P. vittata in Cr uptake at 289 mg kg(-1) h(-1) with little translocation to the fronds. These results indicated that P. vittata had potential in Cr phytoremediation in contaminated sites but further studies are needed to evaluate this potential. The facts that CrVI and sulfate helped each other in uptake by P. vittata suggest that CrVI was not competing with sulfate uptake in P. vittata. However, the mechanisms of how sulfate and CrVI enhance each other's accumulation in P. vittata need further investigation. Published by Elsevier Ltd.

Effect of multi-wall carbon nanotubes on Cr(VI) reduction by citric acid: Implications for their use in soil remediation.

PubMed

Zhang, Yali; Yang, Jiewen; Zhong, Laiyuan; Liu, Liming

2018-06-06

The potential application of carbon nanotubes (CNTs) in waste water treatment and their effect on the fate of heavy metals in the environments have attracted wide attention. However, the influence of CNTs on the reduction of Cr(VI) to Cr(III) in soils remains unknown. In this study, Cr(VI) adsorption by carboxylated or hydroxylated multi-walled carbon nanotubes (MWCNT-COOH or MWCNT-OH) was investigated together with their catalytic effect on Cr(VI) reduction by citric acid. Across the initial concentration range examined (5-60 mg/L), the adsorption capacity of Cr(VI) by MWCNT-COOH and MWCNT-OH (pH 5.0) could reach to 8.09 and 7.85 mg/g, respectively. With the decrease in pH, the Cr(VI) adsorption by both MWCNTs increased, while their difference in adsorption capacity became more pronounced, evidenced by that the percentage of Cr(VI) adsorbed by MWCNT-COOH can be 1.3-fold higher than that of MWCNT-OH at a pH of 3.2. The Cr(VI) adsorption kinetics could be well described by pseudo-second-order (R 2  > 0.95) and intra-particle diffusion models (R 2  > 0.98). MWCNT-OH or MWCNT-COOH could accelerate the reduction of 0.1 mM Cr(VI) by 1.0 mM citric acid, with the first-order rate constant of 0.0325 and 0.0147 h -1 , respectively. This finding was explained as that the reactivity of citric acid might be enhanced with its adsorption on the MWCNT surfaces. The catalysis of the functionalized CNTs on the Cr(VI) reduction was inhibited as the pH increased. The addition of MWCNTs to an oxisol can enhance the Cr(VI) reduction because the final concentration of aqueous Cr(III), compared with that without addition of MWCNTs, increased from 20.7 to 32.6 μM. Meanwhile, re-adsorption of aqueous Cr(III) onto the solid surfaces was also observed. The results above are important for understanding on the effect of CNTs on the fate of Cr(VI) and how they can be used to remediate Cr(VI)-polluted soils.

Reduction of Cr(VI) to Cr(III) by green rust - sulphate

NASA Astrophysics Data System (ADS)

Skovbjerg, L.; Stipp, S.

2003-04-01

Chromium is widely used in industrial processes such as leather tanning, electro-plating and as colour pigments. Unfortunately, hexavalent chromium is both toxic and very soluble so it can be a problem for groundwater resources. Given the right redox conditions, however, Cr(VI) can be reduced to trivalent chromium, which is much less soluble and is an essential trace nutrient. Fe(II), an element common in soil and sediments under anaerobic conditions, can serve as a reducing agent for Cr(VI). Green Rust (GR) is a layered Fe(II),Fe(III)-hydroxide with various anions compensating charge in the interlayers. It is very effective in reducing Cr(VI) to Cr(III). GR exists in nature and is thought to be precursor for the formation of Fe(III)-oxides and oxyhydroxides at the redox boundary. It may be that the formation of GR is a key process in the effectiveness of reactive barriers for groundwater remediation that are based on Fe(0). The purpose of this work is to investigate the mechanisms controlling Cr(VI) reduction by Green Rust, to examine the effect of Cr adsorption and incorporation on GR morphology and composition, and to define the role of parameters such as interlayer anion, initial Cr(VI) concentration and time. We are using freshly synthesised material that has not been dried to avoid structural changes that may accompany dehydration and rehydration. X-Ray Diffraction (XRD) is used to characterise mineral structural changes and Atomic Force Microscopy (AFM), to examine changes in morphology as reactions take place. By adjusting the concentration of Cr(VI), we can control the rate of surface change and we can observe the nanoscale particles directly.

Heavy Metal Resistances and Chromium Removal of a Novel Cr(VI)-Reducing Pseudomonad Strain Isolated from Circulating Cooling Water of Iron and Steel Plant.

PubMed

Zhang, Jian-Kun; Wang, Zhen-Hua; Ye, Yun

2016-12-01

Three bacterial isolates, GT2, GT3, and GT7, were isolated from the sludge and water of a circulating cooling system of iron and steel plant by screening on Cr(VI)-containing plates. Three isolates were characterized as the members of the genus Pseudomonas on the basis of phenotypic characteristics and 16S rRNA sequence analysis. All isolates were capable of resisting multiple antibiotics and heavy metals. GT7 was most resistant to Cr(VI), with a minimum inhibitory concentration (MIC) of 6.5 mmol L -1 . GT7 displayed varied rates of Cr(VI) reduction in M2 broth, which was dependent on pH, initial Cr(VI) concentration, and inoculating dose. Total chromium analysis revealed that GT7 could remove a part of chromium from the media, and the maximum rate of chromium removal was up to 40.8 %. The Cr(VI) reductase activity of GT7 was mainly associated with the soluble fraction of cell-free extracts and reached optimum at pH 6.0∼8.0. The reductase activity was apparently enhanced by external electron donors and Cu(II), whereas it was seriously inhibited by Hg(II), Cd(II), and Zn(II). The reductase showed a K m of 74 μmol L -1 of Cr(VI) and a V max of 0.86 μmol of Cr(VI) min -1  mg -1 of protein. The results suggested that GT7 could be a promising candidate for in situ bioremediation of Cr(VI).

Relationship of Hydrogen Bioavailability to Chromate Reduction in Aquifer Sediments

PubMed Central

Marsh, Tamara L.; McInerney, Michael J.

2001-01-01

Biological Cr(VI) reduction was studied in anaerobic sediments from an aquifer in Norman, Okla. Microcosms containing sediment and mineral medium were amended with various electron donors to determine those most important for biological Cr(VI) reduction. Cr(VI) (about 340 μM) was reduced with endogenous substrates (no donor), or acetate was added. The addition of formate, hydrogen, and glucose stimulated Cr(VI) reduction compared with reduction in unamended controls. From these sediments, an anaerobic Cr(VI)-utilizing enrichment was obtained that was dependent upon hydrogen for both growth and Cr(VI) reduction. No methane was produced by the enrichment, which reduced about 750 μM Cr(VI) in less than six days. The dissolved hydrogen concentration was used as an indicator of the terminal electron accepting process occurring in the sediments. Microcosms with sediments, groundwater, and chromate metabolized hydrogen to a concentration below the detection limits of the mercury vapor gas chromatograph. In microcosms without chromate, the hydrogen concentration was about 8 nM, a concentration comparable to that under methanogenic conditions. When these microcosms were amended with 500 μM Cr(VI), the dissolved hydrogen concentration quickly fell below the detection limits. These results showed that the hydrogen concentration under chromate-reducing conditions became very low, as low as that reported under nitrate- and manganese-reducing conditions, a result consistent with the free energy changes for these reactions. The utilization of formate, lactate, hydrogen, and glucose as electron donors for Cr(VI) reduction indicates that increasing the availability of hydrogen results in a greater capacity for Cr(VI) reduction. This conclusion is supported by the existence of an enrichment dependent upon hydrogen for growth and Cr(VI) reduction. PMID:11282599

Fe(0)-Fe3O4 nanocomposites embedded polyvinyl alcohol/sodium alginate beads for chromium (VI) removal.

PubMed

Lv, Xiaoshu; Jiang, Guangming; Xue, Xiaoqin; Wu, Donglei; Sheng, Tiantian; Sun, Chen; Xu, Xinhua

2013-11-15

In this study, Fe(0)-Fe3O4 nanocomposites embedded polyvinyl alcohol (PVA)/sodium alginate (SA) beads were synthesized, which exhibited an excellent physical properties and catalytic reactivity, and a robust performance of post-separation (complete separation using a simple grille) and reusability (efficiency of 69.8% after four runs) in Cr(VI) removal. 5.0 wt% PVA with 1.5 wt% SA was the optimal proportion for beads molding, and the followed acidification and reduction treatments were critical to ensure high mechanical strength and high Cr(VI) removal ability of beads. Effects of Fe(0) and Fe3O4 mass fraction, initial pH and Cr(VI) concentration on final removal efficiency were also evaluated. Merely 0.075 wt% Fe(0) together with 0.30 wt% Fe3O4 was sufficient to deal with 20 mg L(-1) Cr(VI) solution. The efficiency decreased from 100 to 79.5% as initial Cr(VI) increased from 5 to 40 mg L(-1), while from 99.3 to 76.3% with increasing pH from 3.0 to 11.0. This work provides a practical and high-efficient method for heavy metal removal from water body, and simultaneously solves the problems in stabilization, separation and regeneration of Fe(0) nanoparticles. Copyright © 2013 Elsevier B.V. All rights reserved.

Utility of Ochrobactrum anthropi YC152 in a Microbial Fuel Cell as an Early Warning Device for Hexavalent Chromium Determination

PubMed Central

Wang, Guey-Horng; Cheng, Chiu-Yu; Liu, Man-Hai; Chen, Tzu-Yu; Hsieh, Min-Chi; Chung, Ying-Chien

2016-01-01

Fast hexavalent chromium (Cr(VI)) determination is important for environmental risk and health-related considerations. We used a microbial fuel cell-based biosensor inoculated with a facultatively anaerobic, Cr(VI)-reducing, and exoelectrogenic Ochrobactrum anthropi YC152 to determine the Cr(VI) concentration in water. The results indicated that O. anthropi YC152 exhibited high adaptability to pH, temperature, salinity, and water quality under anaerobic conditions. The stable performance of the microbial fuel cell (MFC)-based biosensor indicated its potential as a reliable biosensor system. The MFC voltage decreased as the Cr(VI) concentration in the MFC increased. Two satisfactory linear relationships were observed between the Cr(VI) concentration and voltage output for various Cr(VI) concentration ranges (0.0125–0.3 mg/L and 0.3–5 mg/L). The MFC biosensor is a simple device that can accurately measure Cr(VI) concentrations in drinking water, groundwater, and electroplating wastewater in 45 min with low deviations (<10%). The use of the biosensor can help in preventing the violation of effluent regulations and the maximum allowable concentration of Cr(VI) in water. Thus, the developed MFC biosensor has potential as an early warning detection device for Cr(VI) determination even if O. anthropi YC152 is a possible opportunistic pathogen. PMID:27537887

Application of a surfactant-assisted dispersive liquid-liquid microextraction method along with central composite design for micro-volume based spectrophotometric determination of low level of Cr(VI) ions in aquatic samples.

PubMed

Sobhi, Hamid Reza; Azadikhah, Efat; Behbahani, Mohammad; Esrafili, Ali; Ghambarian, Mahnaz

2018-05-09

A fast, simple, low cost surfactant-assisted dispersive liquid-liquid microextraction method along with central composite design for the determination of low level of Cr(VI) ions in several aquatic samples has been developed. Initially, Cr(VI) ions present in the aqueous sample were readily reacted with 1,5‑diphenylcarbazide (DPC) in acidic medium through complexation. Sodium dodecyl sulfate (SDS), as an anionic surfactant, was then employed as an ion-pair agent to convert the cationic complex into the neutral one. Following on, the whole aqueous phase underwent a dispersive liquid-liquid microextraction (DLLME) leading to the transfer of the neutral complex into the fine droplet of organic extraction phase. A micro-volume spectrophotometer was used to determine Cr(VI) concentrations. Under the optimized conditions predicted by the statistical design, the limit of quantification (LOQ) obtained was reported to be 5.0 μg/L, and the calibration curve was linear over the concentration range of 5-100 μg/L. Finally, the method was successfully implemented for the determination of low levels of Cr(VI) ions in various real aquatic samples and the accuracies fell within the range of 83-102%, while the precision varied in the span of 1.7-5.2%. Copyright © 2018. Published by Elsevier B.V.

Hexavalent chromium exposure and control in welding tasks.

PubMed

Meeker, John D; Susi, Pam; Flynn, Michael R

2010-11-01

Studies of exposure to the lung carcinogen hexavalent chromium (CrVI) from welding tasks are limited, especially within the construction industry where overexposure may be common. In addition, despite the OSHA requirement that the use of engineering controls such as local exhaust ventilation (LEV) first be considered before relying on other strategies to reduce worker exposure to CrVI, data on the effectiveness of LEV to reduce CrVI exposures from welding are lacking. The goal of the present study was to characterize breathing zone air concentrations of CrVI during welding tasks and primary contributing factors in four datasets: (1) OSHA compliance data; (2) a publicly available database from The Welding Institute (TWI); (3) field survey data of construction welders collected by the Center for Construction Research and Training (CPWR); and (4) controlled welding trials conducted by CPWR to assess the effectiveness of a portable LEV unit to reduce CrVI exposure. In the OSHA (n = 181) and TWI (n = 124) datasets, which included very few samples from the construction industry, the OSHA permissible exposure level (PEL) for CrVI (5 μg/m(3)) was exceeded in 9% and 13% of samples, respectively. CrVI concentrations measured in the CPWR field surveys (n = 43) were considerably higher, and 25% of samples exceeded the PEL. In the TWI and CPWR datasets, base metal, welding process, and LEV use were important predictors of CrVI concentrations. Only weak-to-moderate correlations were found between total particulate matter and CrVI, suggesting that total particulate matter concentrations are not a good surrogate for CrVI exposure in retrospective studies. Finally, in the controlled welding trials, LEV reduced median CrVI concentrations by 68% (p = 0.02). In conclusion, overexposure to CrVI in stainless steel welding is likely widespread, especially in certain operations such as shielded metal arc welding, which is commonly used in construction. However, exposure could be substantially reduced with proper use of LEV.

Exposure to hexavalent chromium in welders: Results of the WELDOX II field study.

PubMed

Pesch, Beate; Lehnert, Martin; Weiss, Tobias; Kendzia, Benjamin; Menne, Eleonore; Lotz, Anne; Heinze, Evelyn; Behrens, Thomas; Gabriel, Stefan; Schneider, Wolfgang; Brüning, Thomas

2018-03-12

Exposure to hexavalent chromium (Cr(VI)) has been primarily studied in chromate production. Here, we measured personal exposure to respirable Cr(VI) together with airborne and urinary Cr and Ni in welders to explore levels and associations between various measures of exposure. Shift concentrations of Cr(VI), Cr, and Ni were measured in respirable welding fumes in 50 men who used either gas metal arc welding (GMAW) (n = 24) or tungsten inert gas welding (TIG) (n = 19) as their major technique. Cr and Ni were determined in pre- and post-shift urine samples. Concentrations below the limit of quantification (LOQ) were multiply imputed. Spearman correlation coefficients (rs) were calculated with 95% confidence intervals (CIs) to explore associations between the exposure variables, and regression models were applied to estimate the effect of the parent metal on the urinary concentration. Regarding the respirable Cr(VI), 62% of the measurements were below the LOQ, the 75th percentile was 0.50 µg m-3, and 8 out of 50 (16%) welders exceeded 1 µg m-3. The highest shift concentration that occurred as a result of shielded metal arc welding (SMAW) was 180 µg m-3. The Cr(VI) content in total Cr ranged from 4 to 82% (median 20%), although the concentration correlated with total Cr (rs 0.55, 95% CI 0.46; 0.64). The correlation between Cr(VI) and Ni was weaker (rs 0.42, 95% CI 0.34; 0.51) than that between total Cr and Ni in welding fumes (rs 0.83, 95% CI 0.74; 0.92). Both Cr(VI) and total Cr influenced the urinary Cr concentrations in post-shift samples (P = 0.0008 and P ≤ 0.0001, respectively). The airborne shift exposure was a weaker determinant than the Cr content in pre-shift urine samples, which strongly correlated with post-shift urinary Cr (rs 0.78, 95% CI 0.69; 0.87). The Cr(VI) content in total Cr varied considerably in welding fumes. The majority of welders using GMAW or TIG presented with shift concentrations of respirable Cr(VI) below 1 µg m-3. However, very high Cr(VI) concentrations may occur, for example in SMAW. The urinary concentration of total Cr, cannot be used to precisely determine the shift concentration of respirable Cr(VI) in welders.

Chromate and phosphate inhibited each other's uptake and translocation in arsenic hyperaccumulator Pteris vittata L.

PubMed

de Oliveira, Letúzia M; Lessl, Jason T; Gress, Julia; Tisarum, Rujira; Guilherme, Luiz R G; Ma, Lena Q

2015-02-01

We investigated the effects of chromate (CrVI) and phosphate (P) on their uptake and translocation in As-hyperaccumulator Pteris vittata (PV). Plants were exposed to 1) 0.10 mM CrVI and 0, 0.25, 1.25, or 2.50 mM P or 2) 0.25 mM P and 0, 0.50, 2.5 or 5.0 mM CrVI for 24 h in hydroponics. PV accumulated 2919 mg/kg Cr in the roots at CrVI₀.₁₀, and 5100 and 3500 mg/kg P in the fronds and roots at P₀.₂₅. When co-present, CrVI and P inhibited each other's uptake in PV. Increasing P concentrations reduced Cr root concentrations by 62-82% whereas increasing CrVI concentrations reduced frond P concentrations by 52-59% but increased root P concentrations by 11-15%. Chromate reduced P transport, with more P being accumulated in PV roots. Though CrVI was supplied, 64-78% and 92-93% CrIII were in PV fronds and roots. Based on X-ray diffraction, Cr₂O₃ was detected in the roots confirming CrVI reduction to CrIII by PV. In short, CrVI and P inhibited each other in uptake and translocation by PV, and CrVI reduction to CrIII in PV roots served as its detoxification mechanism. The finding helps to understand the interactions of P and Cr during their uptake in PV. Published by Elsevier Ltd.

Ni0 encapsulated in N-doped carbon nanotubes for catalytic reduction of highly toxic hexavalent chromium

NASA Astrophysics Data System (ADS)

Yao, Yunjin; Zhang, Jie; Chen, Hao; Yu, Maojing; Gao, Mengxue; Hu, Yi; Wang, Shaobin

2018-05-01

N-doped carbon nanotubes encapsulating Ni0 nanoparticles (Ni@N-C) were fabricated via thermal reduction of dicyandiamide and NiCl2·6H2O, and used to remove CrVI in polluted water. The resultant products present an excellent catalytic activity for CrVI reduction using formic acid under relatively mild conditions. The CrVI reduction efficiency of Ni@N-C was significantly affected by the preparation conditions including the mass of nickel salt and synthesis temperatures. The impacts of several reaction parameters, such as initial concentrations of CrVI and formic acid, solution pH and temperatures, as well as inorganic anions in solution on CrVI reduction efficiency were also evaluated in view of scalable industrial applications. Owing to the synergistic effects amongst tubes-coated Ni0, doped nitrogen, oxygen containing groups, and the configuration of carbon nanotubes, Ni@N-C catalysts exhibit excellent catalytic activity and recyclable capability for CrVI reduction. Carbon shell can efficiently protect inner Ni0 core and N species from corrosion and subsequent leaching, while Ni0 endows the Ni@N-C catalysts with ferromagnetism, so that the composites can be easily separated via a permanent magnet. This study opens up an avenue for design of N-doped carbon nanotubes encapsulating Ni0 nanoparticles with high CrVI removal efficiency and magnetic recyclability as low-cost catalysts for industrial applications.

Higher adsorption capacity of Spirulina platensis alga for Cr(VI) ions removal: parameter optimisation, equilibrium, kinetic and thermodynamic predictions.

PubMed

Gunasundari, Elumalai; Senthil Kumar, Ponnusamy

2017-04-01

This study discusses about the biosorption of Cr(VI) ion from aqueous solution using ultrasonic assisted Spirulina platensis (UASP). The prepared UASP biosorbent was characterised by Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer-Emmet-Teller, scanning electron spectroscopy and energy dispersive X-ray and thermogravimetric analyses. The optimum condition for the maximum removal of Cr(VI) ions for an initial concentration of 50 mg/l by UASP was measured as: adsorbent dose of 1 g/l, pH of 3.0, contact time of 30 min and temperature of 303 K. Adsorption isotherm, kinetics and thermodynamic parameters were calculated. Freundlich model provided the best results for the removal of Cr(VI) ions by UASP. The adsorption kinetics of Cr(VI) ions onto UASP showed that the pseudo-first-order model was well in line with the experimental data. In the thermodynamic study, the parameters like Gibb's free energy, enthalpy and entropy changes were evaluated. This result explains that the adsorption of Cr(VI) ions onto the UASP was exothermic and spontaneous in nature. Desorption of the biosorbent was done using different desorbing agents in which NaOH gave the best result. The prepared material showed higher affinity for the removal of Cr(VI) ions and this may be an alternative material to the existing commercial adsorbents.

Measurement of Soluble and Total Hexavalent Chromium in the Ambient Airborne Particles in New Jersey

PubMed Central

Huang, Lihui; Yu, Chang Ho; Hopke, Philip K.; Lioy, Paul J.; Buckley, Brian T.; Shin, Jin Young; Fan, Zhihua (Tina)

2015-01-01

Hexavalent chromium (Cr(VI)) in ambient airborne particulate matter (PM) is a known pulmonary carcinogen and may have both soluble and insoluble forms. The sum of the two forms is defined as total Cr(VI). Currently, there were no methods suitable for large-scale monitoring of total Cr(VI) in ambient PM. This study developed a method to measure total Cr(VI) in ambient PM. This method includes PM collection using a Teflon filter, microwave extraction with 3% Na2CO3-2% NaOH at 95°C for 60 minutes, and Cr(VI) analysis by 1,5-diphenylcarbazide colorimetry at 540 nm. The recoveries of total Cr(VI) were 119.5 ± 10.4% and 106.3 ± 16.7% for the Cr(VI)-certified reference materials, SQC 012 and SRM 2700, respectively. Total Cr(VI) in the reference urban PM (NIST 1648a) was 26.0 ± 3.1 mg/kg (%CV = 11.9%) determined by this method. The method detection limit was 0.33 ng/m3. This method and the one previously developed to measure ambient Cr(VI), which is soluble in pH ~9.0 aqueous solution, were applied to measure Cr(VI) in ambient PM10 collected from three urban areas and one suburban area in New Jersey. The total Cr(VI) concentrations were 1.05–1.41 ng/m3 in the winter and 0.99–1.56 ng/m3 in the summer. The soluble Cr(VI) concentrations were 0.03–0.19 ng/m3 in the winter and 0.12–0.37 ng/m3 in the summer. The summer mean ratios of soluble to total Cr(VI) were 14.3–43.7%, significantly higher than 4.2–14.4% in the winter. The winter concentrations of soluble and total Cr(VI) in the suburban area were significantly lower than in the three urban areas. The results suggested that formation of Cr(VI) via atmospheric chemistry may contribute to the higher soluble Cr(VI) concentrations in the summer. PMID:26120324

Chromium (VI) purification using pine sawdust in batch systems

NASA Astrophysics Data System (ADS)

Politi, Dorothea; Sidiras, Dimitris

2012-12-01

Pine sawdust, a waste generated in furniture industry, has been used as low-cost potential adsorbent. This low-cost adsorbent was used for the removal of chromium (VI) from an aqueous solution. The kinetics of adsorption and extent of adsorption at equilibrium are dependent on the physical and chemical characteristics of the adsorbent and adsorbate. The effect of hydrogen ion concentration, contact time, adsorbent dose and initial concentration of adsorbate on the uptake of chromium were studied in batch experiments. The adsorption data has been correlated with Lagergren - Eldridge pseudofirst order kinetic model. The efficiency of adsorbent material for the removal of Cr(VI) was found to be between 13.1 and 95.6%, respectively. These results depend on the conditions of pH, contact time, sawdust dose and Cr(VI) concentration.

Determination of hexavalent chromium concentration in industrial waste incinerator stack gas by using a modified ion chromatography with post-column derivatization method.

PubMed

Miyake, Yuichi; Tokumura, Masahiro; Iwazaki, Yuta; Wang, Qi; Amagai, Takashi; Horii, Yuichi; Otsuka, Hideyuki; Tanikawa, Noboru; Kobayashi, Takeshi; Oguchi, Masahiro

2017-06-16

An ion chromatography with post-column derivatization with 1,5-diphenylcarbazide (IC-DPC) analytical method was modified to enable measurement of trace-level hexavalent chromium (Cr(VI)) in air. One of the difficulties in determining trace levels of Cr(VI) in air with conventional IC-DPC methods is co-elution of the solvent and ion peaks due to high concentrations of ionic compounds in the extract. However, by using gradient elution rather than isocratic elution we were able to fully resolve the Cr(VI) ion peak from the solvent peak without the need for diluting the extract, which would have reduced the minimum quantifiable level of the method. With this method, we were able to detect Cr(VI) in air at concentrations of 5.3ng/m 3 (assuming a sampling volume of 1m 3 and a final solution volume of 10mL). Recovery tests at three different concentrations of Cr(VI) (50, 250, 1000ng) were performed with or without fly ash; recovery rates at all the concentrations of Cr(VI), with or without fly ash, ranged from 68% to 110% (mean±relative standard deviation, 96%±11%), and there were no differences in recovery rates with respect to the presence or absence of fly ash. Finally, we used the developed method to determine the concentration of Cr(VI) in stack gases collected from eight industrial waste incinerators located in Japan. The concentration of Cr(VI) in the stack gases ranged from below the method quantification limit to 3100ng/m 3 . The highest concentrations of Cr(VI) detected in the stack gases were two to three orders of magnitude higher than that in ambient air in Japan. Copyright © 2017 Elsevier B.V. All rights reserved.

Toxic metals biosorption by Jatropha curcas deoiled cake: equilibrium and kinetic studies.

PubMed

Rawat, Anand P; Rawat, Monica; Rai, J P N

2013-08-01

The equilibrium sorption of Cr(VI) and Cu(II) from aqueous solution using Jatropha curcas deoiled cake, has been studied with respect to adsorbent dosage, contact time, pH, and initial metal concentration in batch mode experiments. Removal of Cu(II) by deoiled cake was greater than that of Cr(VI). The adsorbent chemical characteristics, studied by Fourier transform-infrared analysis, suggested that the presence of Cr(VI) and Cu(II) in the biomass influenced the bands corresponding to hydroxyl and carboxyl groups. Desorption studies revealed that maximum metals recovery was achieved by HNO3 followed by CH3COOH and HCl. The Freundlich isotherm model showed good fit to the equilibrium adsorption data. The adsorption kinetics followed the pseudo-second-order model, which provided the best correlation for the biosorption process, and suggested that J. curcas deoiled cake can be used as an efficient biosorbent over other commonly used sorbents for decontamination of Cr(VI)- and Cu(II)-containing wastewater.

Simultaneous removal of Cu(II) and Cr(VI) by Mg-Al-Cl layered double hydroxide and mechanism insight.

PubMed

Yue, Xianyang; Liu, Weizhen; Chen, Zuliang; Lin, Zhang

2017-03-01

Mg-Al-Cl layered double hydroxide (Cl-LDH) was prepared to simultaneously remove Cu(II) and Cr(VI) from aqueous solution. The coexisting Cu(II) (20mg/L) and Cr(VI) (40mg/L) were completely removed within 30min by Cl-LDH in a dosage of 2.0g/L; the removal rate of Cu(II) was accelerated in the presence of Cr(VI). Moreover, compared with the adsorption of single Cu(II) or Cr(VI), the adsorption capacities of Cl-LDH for Cu(II) and Cr(VI) can be improved by 81.05% and 49.56%, respectively, in the case of coexisting Cu(II) (200mg/L) and Cr(VI) (400mg/L). The affecting factors (such as solution initial pH, adsorbent dosage, and contact time) have been systematically investigated. Besides, the changes of pH values and the concentrations of Mg 2+ and Al 3+ in relevant solutions were monitored. To get the underlying mechanism, the Cl-LDH samples before and after adsorption were thoroughly characterized by X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. On the basis of these analyses, a possible mechanism was proposed. The coadsorption process involves anion exchange of Cr(VI) with Cl - in Cl-LDH interlayer, isomorphic substitution of Mg 2+ with Cu 2+ , formation of Cu 2 Cl(OH) 3 precipitation, and the adsorption of Cr(VI) by Cu 2 Cl(OH) 3 . This work provides a new insight into simultaneous removal of heavy metal cations and anions from wastewater by Cl-LDH. Copyright © 2016. Published by Elsevier B.V.

Nb2O5 nanowires in-situ grown on carbon fiber: A high-efficiency material for the photocatalytic reduction of Cr(VI).

PubMed

Du, Yucheng; Zhang, Shihao; Wang, Jinshu; Wu, Junshu; Dai, Hongxing

2018-04-01

Niobium oxide nanowire-deposited carbon fiber (CF) samples were prepared using a hydrothermal method with amorphous Nb 2 O 5 ·nH 2 O as precursor. The physical properties of the samples were characterized by means of numerous techniques, including X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), UV-visible spectroscopy (UV-vis), N 2 adsorption-desorption, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy. The efficiency for the removal of Cr(VI) was determined. Parameters such as pH value and initial Cr(VI) concentration could influence the Cr(VI) removal efficiency or adsorption capacity of the Nb 2 O 5 /carbon fiber sample obtained after hydrothermal treatment at 160°C for 14hr. The maximal Cr(VI) adsorption capacity of the Nb 2 O 5 nanowire/CF sample was 115mg/g. This Nb 2 O 5 /CF sample also showed excellent photocatalytic activity and stability for the reduction of Cr(VI) under UV-light irradiation: the Cr(VI) removal efficiency reached 99.9% after UV-light irradiation for 1hr and there was no significant decrease in photocatalytic performance after the use of the sample for 10 repeated cycles. Such excellent Cr(VI) adsorption capacity and photocatalytic performance was related to its high surface area, abundant surface hydroxyl groups, and good UV-light absorption ability. Copyright © 2017. Published by Elsevier B.V.

Porous p-NiO/n-Nb2O5 nanocomposites prepared by an EISA route with enhanced photocatalytic activity in simultaneous Cr(VI) reduction and methyl orange decolorization under visible light irradiation.

PubMed

Hashemzadeh, Fatemeh; Gaffarinejad, Ali; Rahimi, Rahmatollah

2015-04-09

Porous NiO/Nb2O5 nanocomposites with Ni/Nb molar ratio of 0.4, 0.8 and 1.2 have been obtained via the EISA route using P123 copolymer as organic template, and are assigned as NiNb0.4, NiNb0.8 and NiNb1.2, respectively. For comparison, pure Nb2O5 sample assigned as NiNb0.0 was also synthesized by the same method. Structural and textural features of the as prepared samples were investigated by XRD, FTIR, FE-SEM, EDX, UV-vis DRS and BET techniques. The results indicated that the porous p-NiO/n-Nb2O5 junction nanocomposites were formed and coupling of NiO with Nb2O5 resulted a remarkable red shift in the optical response of the nanocomposite samples. The photocatalytic properties of the nanocomposite samples, and also synthesized pure Nb2O5 (NiNb0.0) and commercial Nb2O5 as reference catalysts were evaluated for the first time by simultaneous Cr(VI) reduction and MO decolorization in aqueous suspension under visible light irradiation at pH 2. NiNb0.4 was found to be the most active photocatalyst, which might be attributed to the extended absorption in the visible light region and the effective photogenerated electron-hole separation by the photosynergistic effects of the p-NiO/n-Nb2O5 composite powder. The photocatalytic efficiency of the most active photocatalyst, NiNb0.4, was found to be rather low for either single Cr(VI) solution or single MO solution. However, the photocatalytic reduction of Cr(VI) and photocatalytic decolorization of MO proceed more rapidly for the coexistence system of Cr(VI) and MO than for the single process, showing synergetic effect between the reduction and decolorization reactions. The effects of initial concentration of Cr(VI), MO and the initial pH value on the rate of simultaneous photoreactions over NiNb0.4 sample, were also investigated. The Cr(VI) and MO removal rates were further enhanced by increasing MO and Cr (VI) concentration to an optimal value, respectively, and/or decreasing solution pH. Copyright © 2014 Elsevier B.V. All rights reserved.

Removal of Cr(VI) ions by sewage sludge compost biomass from aqueous solutions: Reduction to Cr(III) and biosorption

NASA Astrophysics Data System (ADS)

Chen, Huixia; Dou, Junfeng; Xu, Hongbin

2017-12-01

Sewage sludge compost biomass was used as a novel biosorbent to remove hexavalent chromium from water. Surface area analysis, scanning electron microscopy, fourier-transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and point zero charge was applied to study the microstructure, compositions and chemical bonding states of the biomass adsorbent. Effects of contact time, biomass dosage, agitation speed, pH, the initial concentration of Cr(VI) and Cr(Ⅲ) on its adsorption removal were also performed in the batch experiments. A model describing adsorption, desorption and reduction phenomena during the sorption process has been referenced to model Cr(VI) sorption onto sewage sludge compost biomass. The result of characterization test shows that adsorption of Cr(VI) onto sewage sludge compost biomass followed by the partial reduction to Cr(Ⅲ) by biomass groups such as hydroxyl, carboxyl, and amino groups. The absorption kinetics model in the description of adsorption-coupled reduction of Cr(VI) fits successfully the kinetic data obtained at different temperatures and describes the kinetics profile of total, hexavalent and trivalent chromium. The study shows that sewage sludge compost biomass could be used as a potential biosorbent for removal of hexavalent chromium from wastewaters.

Modelling biological Cr(VI) reduction in aquifer microcosm column systems.

PubMed

Molokwane, Pulane E; Chirwa, Evans M N

2013-01-01

Several chrome processing facilities in South Africa release hexavalent chromium (Cr(VI)) into groundwater resources. Pump-and-treat remediation processes have been implemented at some of the sites but have not been successful in reducing contamination levels. The current study is aimed at developing an environmentally friendly, cost-effective and self-sustained biological method to curb the spread of chromium at the contaminated sites. An indigenous Cr(VI)-reducing mixed culture of bacteria was demonstrated to reduce high levels of Cr(VI) in laboratory samples. The effect of Cr(VI) on the removal rate was evaluated at concentrations up to 400 mg/L. Following the detailed evaluation of fundamental processes for biological Cr(VI) reduction, a predictive model for Cr(VI) breakthrough through aquifer microcosm reactors was developed. The reaction rate in batch followed non-competitive rate kinetics with a Cr(VI) inhibition threshold concentration of approximately 99 mg/L. This study evaluates the application of the kinetic parameters determined in the batch reactors to the continuous flow process. The model developed from advection-reaction rate kinetics in a porous media fitted best the effluent Cr(VI) concentration. The model was also used to elucidate the logistic nature of biomass growth in the reactor systems.

Ethylenediamine grafted to graphene oxide@Fe3O4 for chromium(VI) decontamination: Performance, modelling, and fractional factorial design

PubMed Central

Xu, Jiawen; Wu, Cuiyu; Deng, Jianbin; Liao, Wenwei; Ling, Yuxiang; Yang, Yuanxiu; Zhao, Yina; Zhao, Yunlin; Hu, Xi; Wang, Hui; Liu, Yunguo

2017-01-01

A method for grafting ethylenediamine to a magnetic graphene oxide composite (EDA-GO@Fe3O4) was developed for Cr(VI) decontamination. The physicochemical properties of EDA-GO@Fe3O4 were characterized using HRTEM, EDS, FT-IR, TG-DSC, and XPS. The effects of pH, sorbent dose, foreign anions, time, Cr(VI) concentration, and temperature on decontamination process were studied. The solution pH can largely affect the decontamination process. The pseudo-second-order model is suitable for being applied to fit the adsorption processes of Cr(VI) with GO@Fe3O4 and EDA-GO@Fe3O4. The intra-particle diffusion is not the rate-controlling step. Isotherm experimental data can be described using the Freundlich model. The effects of multiple factors on the Cr(VI) decontamination was investigated by a 25−1 fractional factorial design (FFD). The adsorption process can significantly be affected by the main effects of A (pH), B (Cr(VI) concentration), and E (Adsorbent dose). The combined factors of AB (pH × Cr(VI) concentration), AE (pH × Adsorbent dose), and BC (Cr(VI) concentration × Temperature) had larger effects than other factors on Cr(VI) removal. These results indicated that EDA-GO@Fe3O4 is a potential and suitable candidate for treatment of heavy metal wastewater. PMID:29084287

Modulation of hexavalent chromium toxicity on Οriganum vulgare in an acidic soil amended with peat, lime, and zeolite.

PubMed

Antoniadis, Vasileios; Zanni, Anna A; Levizou, Efi; Shaheen, Sabry M; Dimirkou, Anthoula; Bolan, Nanthi; Rinklebe, Jörg

2018-03-01

Dynamics of chromate (Cr(VI)) in contaminated soils may be modulated by decreasing its phytoavailability via the addition of organic matter-rich amendments, which might accelerate Cr(VI) reduction to inert chromite (Cr(III)) or high-cation exchange capacity amendments. We studied Cr(VI) phytoavailability of oregano in a Cr(VI)-spiked acidic soil non-treated (S) and treated with peat (SP), lime (SL), and zeolite (SZ). The addition of Cr(VI) increased the concentrations of Cr(VI) and Cr(III) in soils and plants, especially in the lime-amended soil. The plant biomass decreased in the lime-amended soil compared to the un-spiked soil (control) due to decreased plant phosphorus concentrations and high Cr(VI) concentrations in root at that treatment. Oregano in the peat-amended soil exhibited significantly less toxic effects, due to the role of organic matter in reducing toxic Cr(VI) to Cr(III) and boosted plant vigour in this treatment. In the lime-amended soil, the parameters of soil Cr(VI), soil Cr(III), and root Cr(III) increased significantly compared to the non-amended soil, indicating that Cr(VI) reduction to Cr(III) was accelerated at high pH. Added zeolite failed to decreased Cr(VI) level to soil and plant. Oregano achieved a total uptake of Cr(III) and Cr(VI) of 0.275 mg in plant kg -1 soil in a pot in the non-amended soil. We conclude that peat as soil amendment might be considered as a suitable option for decreasing Cr(VI) toxicity in soil and plant, and that oregano as tolerant plant species has a certain potential to be used as a Cr accumulator. Copyright © 2017 Elsevier Ltd. All rights reserved.

The cytotoxicity and genotoxicity of particulate and soluble hexavalent chromium in leatherback sea turtle lung cells.

PubMed

Speer, Rachel M; Wise, Catherine F; Young, Jamie L; Aboueissa, AbouEl-Makarim; Martin Bras, Mark; Barandiaran, Mike; Bermúdez, Erick; Márquez-D'Acunti, Lirio; Wise, John Pierce

2018-05-01

Hexavalent chromium [Cr(VI)] is a marine pollution of concern as recent studies show it has a global distribution, with some regions showing high Cr concentrations in marine animal tissue, and it is extensively used. Leatherback sea turtles (Dermochelys coriacea) are an endangered marine species that may experience prolonged exposures to environmental contaminants including Cr(VI). Human activities have led to global Cr(VI) contamination of the marine environment. While Cr(VI) has been identified as a known human carcinogen, the health effects in marine species are poorly understood. In this study, we assessed the cytotoxic and genotoxic effects of particulate and soluble Cr(VI) in leatherback sea turtle lung cells. Both particulate and soluble Cr(VI) induced a concentration-dependent increase in cytotoxicity. Next, using a chromosome aberration assay, we assessed the genotoxic effects of Cr(VI) in leatherback sea turtle lung cells. Particulate and soluble Cr(VI) induced a concentration-dependent increase in clastogenicity in leatherback sea turtle lung cells. These data indicate that Cr(VI) may be a health concern for leatherback sea turtles and other long-lived marine species. Additionally, these data provide foundational support to use leatherback sea turtles as a valuable model species for monitoring the health effects of Cr(VI) in the environment and possibly as an indicator species to assess environmental human exposures and effects. Copyright © 2018 Elsevier B.V. All rights reserved.

Adsorption of Cr(VI) on cerium immobilized cross-linked chitosan composite in single system and coexisted with Orange II in binary system.

PubMed

Zhu, Tianyi; Huang, Wei; Zhang, Lingfan; Gao, Jie; Zhang, Wenqing

2017-10-01

In this work, cerium immobilized cross-linked chitosan (CTS-Ce) composite, employed as an efficient adsorbent for Cr(VI) in single system and coexisted with Orange II (OII) in binary system, was prepared by co-precipitation method. The as-obtained adsorbent was characterized by FTIR, SEM, EDS and XPS before and after adsorption. The adsorption behaviors of Cr(VI) in single and binary system were systematically studied. The maximum adsorption capacity of Cr(VI) on CTS-Ce (202.8mg/g) was calculated by Langmuir equation in single metal system, but it decreased to 112.9mg/g with initial concentration of 100mg/L OII in binary system at pH 2 and 293K. The adsorption data for Cr(VI) followed the Langmuir model in single system, while fitted Temkin model well in binary system. In both single and binary system, the kinetics of adsorption exhibited pseudo-second order behavior and adsorption capacity increased with increasing temperature. Moreover, the data of thermodynamic parameters (ΔG°<0, ΔH°>0) indicated that the adsorption was a spontaneous and endothermic process. Besides, |ΔG Cr |>|ΔG Cr-OII | at the same temperature further suggested that Cr(VI) was adsorbed on the CTS-Ce composite faster in binary system than in single system. Copyright © 2017 Elsevier B.V. All rights reserved.

Statistical Analysis of Main and Interaction Effects on Cu(II) and Cr(VI) Decontamination by Nitrogen-Doped Magnetic Graphene Oxide

NASA Astrophysics Data System (ADS)

Hu, Xinjiang; Wang, Hui; Liu, Yunguo

2016-10-01

A nitrogen-doped magnetic graphene oxide (NMGO) was synthesized and applied as an adsorbent to remove Cu(II) and Cr(VI) ions from aqueous solutions. The individual and combined effects of various factors (A: pH, B: temperature, C: initial concentration of metal ions, D: CaCl2, and E: humic acid [HA]) on the adsorption were analyzed by a 25-1 fractional factorial design (FFD). The results from this study indicated that the NMGO had higher adsorption capacities for Cu(II) ions than for Cr(VI) ions under most conditions, and the five selected variables affected the two adsorption processes to different extents. A, AC, and C were the very important factors and interactions for Cu(II) adsorption. For Cr(VI) adsorption, A, B, C, AB, and BC were found to be very important influencing variables. The solution pH (A) was the most important influencing factor for removal of both the ions. The main effects of A-E on the removal of Cu(II) were positive. For Cr(VI) adsorption, the main effects of A and D were negative, while B, C, and E were observed to have positive effects. The maximum adsorption capacities for Cu(II) and Cr(VI) ions over NMGO were 146.365 and 72.978 mg/g, respectively, under optimal process conditions.

Single, simultaneous and consecutive biosorption of Cr(VI) and Orange II onto chemically modified masau stones.

PubMed

Albadarin, Ahmad B; Solomon, Samuel; Kurniawan, Tonni Agustiono; Mangwandi, Chirangano; Walker, Gavin

2017-12-15

Novel and low cost chemically modified masau stone (CMMS) was investigated for its biosorption of an anionic azo dye, Orange II (OII), and toxic hexavalent chromium (Cr(VI)) from aqueous systems: individually, simultaneously and consecutively. XPS and FTIR analyses indicated the introduction of quaternary-Nitrogen to the CMMS surface after activation with epichlorohydrin (etherifying agent) and diethylenetriamine (crosslinking agent). The effects of pH, contact time and initial concentration (C o ), and loading order on mechanisms of biosorption/reduction of OII and Cr(VI) onto CMMS were examined in detail. Several analytical techniques were employed to characterise the physio-chemical properties of the CMMS and determine the biosorption mechanisms. The pseudo second order and redox models were able to adequately predict the kinetics of biosorption. The Langmuir maximum OII biosorption capacity (q max ) was calculated as 136.8 mg/g for the dye onto the Cr(VI)-loaded CMMS consecutive system at C o  = 100 mg/dm 3 . The q max for the Cr(VI) system was found to be 87.32 mg/g at the same C o max. This reveals that the biosorption of OII and Cr(VI) mainly takes place via two different mechanisms i.e. hydrogen bonding and electrostatic attraction for the dye, and biosorption-coupled reduction for Cr(VI). Copyright © 2017 Elsevier Ltd. All rights reserved.

Isotherm Modelling, Kinetic Study and Optimization of Batch Parameters Using Response Surface Methodology for Effective Removal of Cr(VI) Using Fungal Biomass

PubMed Central

Chidambaram, Ramalingam

2015-01-01

Biosorption is a promising alternative method to replace the existing conventional technique for Cr(VI) removal from the industrial effluent. In the present experimental design, the removal of Cr(VI) from the aqueous solution was studied by Aspergillus niger MSR4 under different environmental conditions in the batch systems. The optimum conditions of biosorption were determined by investigating pH (2.0) and temperature (27°C). The effects of parameters such as biomass dosage (g/L), initial Cr(VI) concentration (mg/L) and contact time (min) on Cr(VI) biosorption were analyzed using a three parameter Box–Behnken design (BBD). The experimental data well fitted to the Langmuir isotherm, in comparison to the other isotherm models tested. The results of the D-R isotherm model suggested that a chemical ion-exchange mechanism was involved in the biosorption process. The biosorption process followed the pseudo-second-order kinetic model, which indicates that the rate limiting step is chemisorption process. Fourier transform infrared (FT-IR) spectroscopic studies revealed the possible involvement of functional groups, such as hydroxyl, carboxyl, amino and carbonyl group in the biosorption process. The thermodynamic parameters for Cr(VI) biosorption were also calculated, and the negative ∆Gº values indicated the spontaneous nature of biosorption process. PMID:25786227

Chromium(VI) sorption efficiency of acid-activated banana peel over organo-montmorillonite in aqueous solutions.

PubMed

Ashraf, Anam; Bibi, Irshad; Niazi, Nabeel Khan; Ok, Yong Sik; Murtaza, Ghulam; Shahid, Muhammad; Kunhikrishnan, Anitha; Li, Dongwei; Mahmood, Tariq

2017-07-03

In the present study, we examined sorption of chromate (Cr(VI)) to acid-activated banana peel (AABP) and organo-montmorillonite (O-mont) as a function of pH, initial Cr(VI) concentration at a sorbent dose of 4 g L -1 and at 20 ± 1°C in aqueous solutions. In sorption edge experiments, maximum Cr(VI) removal was obtained at pH 3 after 2 hours by AABP and O-mont (88% and 69%). Sorption isotherm data showed that the sorption capacity of AABP was higher than O-mont (15.1 vs. 6.67 mg g -1 , respectively, at pH 4). Freundlich and Langmuir models provided the best fits to describe Cr(VI) sorption onto AABP (R 2 = 0.97) and O-mont (R 2 = 0.96). Fourier transform infrared spectroscopy elucidated that for AABP mainly the -OH, -COOH, -NH 2 , and for O-mont intercalated amines and -OH surface functional groups were involved in Cr(VI) sorption. The scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX) analyses, although partly, indicate that the (wt. %) proportion of cations (e.g., Ca, Mg) in AABP decreased after Cr(VI) sorption. This may be due to ion exchange of chromite (Cr(III)) (produced from Cr(VI) reduction) with cationic elements in AABP. Also, Cr(VI) desorption (using phosphate solution) from AABP was lower (29%) than that from O-mont (51%) up to the third regeneration cycle. This bench scale comparative study highlights that the utilization of widely available and low-cost acid-activated biomaterials has a greater potential than organo-clays for Cr(VI) removal in aqueous media. However, future studies are warranted to precisely delineate different mechanisms of Cr(VI) sorption/reduction by acid-activated biomaterials and organo-clays.

Occurrence of Cr(VI) in drinking water of Greece and relation to the geological background.

PubMed

Kaprara, E; Kazakis, N; Simeonidis, K; Coles, S; Zouboulis, A I; Samaras, P; Mitrakas, M

2015-01-08

This study provides a survey on potential Cr(VI) exposure attributed to drinking water in Greece. For this reason, a wide sampling and chemical analysis of tap waters from around 600 sites, supplied by groundwater resources, was conducted focusing on areas in which the geological substrate is predominated by ultramafic minerals. Results indicate that although violations of the current chromium regulation limit in tap water are very rare, 25% of cases showed Cr(VI) concentrations above 10 μg/L, whereas Cr(VI) was detectable in 70% of the samples (>2 μg/L). Mineralogy and conditions of groundwater reservoirs were correlated to suggest a possible Cr(VI) leaching mechanism. Higher Cr(VI) values are observed in aquifers in alluvial and neogene sediments of serpentine and amphibolite, originating from the erosion of ophiolithic and metamorphic rocks. In contrast, Cr(VI) concentration in samples from ophiolithic and metamorphic rocks was always below 10 μg/L due to both low contact time and surface area, as verified by low conductivity and salt concentration values. These findings indicate that under specific conditions, pollution of water by Cr(VI) is favorable by a slow MnO2-catalyzed oxidation of soluble Cr(III) to Cr(VI) in which manganese products [Mn(III)/Mn(II)] are probably re-oxidized by oxygen. Copyright © 2014 Elsevier B.V. All rights reserved.

Chromium(VI) generation in vadose zone soils and alluvial sediments of the southwestern Sacramento Valley, California: a potential source of geogenic Cr(VI) to groundwater

USGS Publications Warehouse

Mills, Christopher T.; Morrison, Jean M.; Goldhaber, Martin B.; Ellefsen, Karl J.

2011-01-01

Concentrations of geogenic Cr(VI) in groundwater that exceed the World Health Organization’s maximum contaminant level for drinking water (50 μg L−1) occur in several locations globally. The major mechanism for mobilization of this Cr(VI) at these sites is the weathering of Cr(III) from ultramafic rocks and its subsequent oxidation on Mn oxides. This process may be occurring in the southern Sacramento Valley of California where Cr(VI) concentrations in groundwater can approach or exceed 50 μg L−1. To characterize Cr geochemistry in the area, samples from several soil auger cores (approximately 4 m deep) and drill cores (approximately 25 m deep) were analyzed for total concentrations of 44 major, minor and trace elements, Cr associated with labile Mn and Fe oxides, and Cr(VI). Total concentrations of Cr in these samples ranged from 140 to 2220 mg per kg soil. Between 9 and 70 mg per kg soil was released by selective extractions that target Fe oxides, but essentially no Cr was associated with the abundant reactive Mn oxides (up to ~1000 mg hydroxylamine-reducible Mn per kg soil was present). Both borehole magnetic susceptibility surveys performed at some of the drill core sites and relative differences between Cr released in a 4-acid digestion versus total Cr (lithium metaborate fusion digestion) suggest that the majority of total Cr in the samples is present in refractory chromite minerals transported from ultramafic exposures in the Coast Range Mountains. Chromium(VI) in the samples studied ranged from 0 to 42 μg kg−1, representing a minute fraction of total Cr. Chromium(VI) content was typically below detection in surface soils (top 10 cm) where soil organic matter was high, and increased with increasing depth in the soil auger cores as organic matter decreased. Maximum concentrations of Cr(VI) were up to 3 times greater in the deeper drill core samples than the shallow auger cores. Although Cr(VI) in these vadose zone soils and sediments was only a very small fraction of the total solid phase Cr, they are a potentially important source for Cr(VI) to groundwater. Enhanced groundwater recharge through the vadose zone due to irrigation could carry Cr(VI) from the vadose zone to the groundwater and may be the mechanism responsible for the correlation observed between elevated Cr(VI) and NO3- source concentrations in previously published data for valley groundwaters. Incubation of a valley subsoil showed a Cr(VI) production rate of 24 μg kg−1 a−1 suggesting that field Cr(VI) concentrations could be regenerated annually. Increased Cr(VI) production rates in H+-amended soil incubations indicate that soil acidification processes such as nitrification of ammonium in fertilizers could potentially increase the occurrence of geogenic Cr(VI) in groundwater. Thus, despite the natural origin of the Cr, Cr(VI) generation in the Sacramento Valley soils and sediments has the potential to be influenced by human activities.

An exploratory study on low-concentration hexavalent chromium adsorption by Fe(III)-cross-linked chitosan beads

PubMed Central

Zhang, Yuanjing; Qian, Jin; Xin, Xu; Hu, Sihai; Zhang, Shuai; Wei, Jianguo

2017-01-01

In this study, Fe(III)-cross-linked chitosan beads (Fe(III)-CBs) were synthesized and employed to explore the characteristics and primary mechanism of their hexavalent chromium (Cr(VI)) adsorption under low concentration Cr(VI) (less than 20.0 mg l−1) and a pH range from 2.0 to 8.0. Batch tests were conducted to determine the Cr(VI) adsorption capacity and kinetics, and the effects of pH and temperature on the adsorption under low concentration Cr(VI) and a pH range from 2.0 to 8.0. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy were employed to explore the characteristics of Fe(III)-CBs and their Cr(VI) adsorption mechanisms. The results show that, unlike the adsorption of other absorbents, the Cr(VI) adsorption was efficient in a wide pH range from 2.0 to 6.0, and well described by the pseudo-first-order model and the Langmuir–Freundlich isotherm model. The capacity of Cr(VI) adsorption by Fe(III)-CBs was as high as 166.3 mg g−1 under temperature 25°C and pH 6.0. The desorption test was also carried out by 0.1 mol l−1 NaOH solution for Fe(III)-CBs regeneration. It was found that Fe(III)-CBs could be re-used for five adsorption–desorption cycles without significant decrease in Cr(VI) adsorption capacity. Ion exchange was confirmed between functional groups (i.e. amino group) and Cr(VI) anions (i.e. CrO42−). The amino-like functional groups played a key role in Cr(VI) distribution on the Fe(III)-CBs surface; Cr(VI) adsorbed on Fe(III)-CBs was partially reduced to Cr(III) with alcoholic group served as electron donor, and then formed another rate-limiting factor. So, Fe(III)-CBs has a good prospect in purifying low concentration Cr(VI) water with a pH range from 2.0 to 6.0. PMID:29291084

Removal of Hexavalent Chromium by Adsorption on Microwave Assisted Activated Carbon Prepared from Stems of Leucas Aspera

NASA Astrophysics Data System (ADS)

Shanmugalingam, A.; Murugesan, A.

2018-05-01

This study reports adsorption of Cr(VI) ions from aqueous solution using activated carbon that was prepared from stems of Leucas aspera. Eight hundred and fifty watts power of microwave radiation, 12 min of radiation time, 60% of ZnCl2 solution and 24 h of impregnation time are the optimal parameters to prepare efficient carbon effective activated carbon. It was designated as MWLAC (Microwave assisted Zinc chloride activated Leucas aspera carbon). Various adsorption characteristics such as dose of the adsorbent, agitation time, initial Cr(VI) ion concentration, pH of the solution and temperature on adsorption were studied for removal of Cr(VI) ions from aqueous solution by batch mode. Also the equilibrium adsorption was analyzed by the Langmuir, Freundlich, Tempkin and D-R isotherm models. The order of best describing isotherms was given based on R2 value. The pseudo-second-order kinetic model best fitted with the Cr(VI) adsorption data. Thermodynamic parameters were also determined and results suggest that the adsorption process is a spontaneous, endothermic and proceeded with increased randomness.

Chromium Biosorption from Cr(VI) Aqueous Solutions by Cupressus lusitanica Bark: Kinetics, Equilibrium and Thermodynamic Studies.

PubMed

Netzahuatl-Muñoz, Alma Rosa; Cristiani-Urbina, María del Carmen; Cristiani-Urbina, Eliseo

2015-01-01

The present study investigated the kinetics, equilibrium and thermodynamics of chromium (Cr) ion biosorption from Cr(VI) aqueous solutions by Cupressus lusitanica bark (CLB). CLB total Cr biosorption capacity strongly depended on operating variables such as initial Cr(VI) concentration and contact time: as these variables rose, total Cr biosorption capacity increased significantly. Total Cr biosorption rate also increased with rising solution temperature. The pseudo-second-order model described the total Cr biosorption kinetic data best. Langmuir´s model fitted the experimental equilibrium biosorption data of total Cr best and predicted a maximum total Cr biosorption capacity of 305.4 mg g(-1). Total Cr biosorption by CLB is an endothermic and non-spontaneous process as indicated by the thermodynamic parameters. Results from the present kinetic, equilibrium and thermodynamic studies suggest that CLB biosorbs Cr ions from Cr(VI) aqueous solutions predominantly by a chemical sorption phenomenon. Low cost, availability, renewable nature, and effective total Cr biosorption make CLB a highly attractive and efficient method to remediate Cr(VI)-contaminated water and wastewater.

Chromium (VI) biosorption by Saccharomyces cerevisiae subjected to chemical and thermal treatments.

PubMed

De Rossi, Andrea; Rigon, Magali Rejane; Zaparoli, Munise; Braido, Rafael Dalmas; Colla, Luciane Maria; Dotto, Guilherme Luiz; Piccin, Jeferson Steffanello

2018-05-28

The potential of chemically and thermally treated Saccharomyces cerevisiae as biosorbents for chromium (VI) was investigated in this work. The presence of this toxic metal in industrial effluents is harmful to the environment, so, it is important to develop environmental friendly methods for Cr(VI) removal from these effluents. Biosorption using microorganisms such as S. cerevisiae is a viable treatment option because this biomass is easily available as a residue of fermentation industries. In this study, the affecting variables on Cr(VI) biosorption were studied by constructing biosorption isotherms, using lyophilized yeast subjected to chemical and thermal treatments. S. cerevisiae was able to remove 99.66% of Cr(VI) from effluents by biosorption. The significant variables affecting biosorption were pH, initial Cr(VI) concentration, and contact time. The biosorption isotherms were represented by the Freundlich model for the untreated biomass, BET model for the chemically treated biomass, and Langmuir model for the heat-treated biomass. Thermal treatment increased the biosorption affinity of the biomass for chromium, while the chemical treatment facilitated the formation of a multilayer.

Chromium Biosorption from Cr(VI) Aqueous Solutions by Cupressus lusitanica Bark: Kinetics, Equilibrium and Thermodynamic Studies

PubMed Central

Netzahuatl-Muñoz, Alma Rosa; Cristiani-Urbina, María del Carmen; Cristiani-Urbina, Eliseo

2015-01-01

The present study investigated the kinetics, equilibrium and thermodynamics of chromium (Cr) ion biosorption from Cr(VI) aqueous solutions by Cupressus lusitanica bark (CLB). CLB total Cr biosorption capacity strongly depended on operating variables such as initial Cr(VI) concentration and contact time: as these variables rose, total Cr biosorption capacity increased significantly. Total Cr biosorption rate also increased with rising solution temperature. The pseudo-second-order model described the total Cr biosorption kinetic data best. Langmuir´s model fitted the experimental equilibrium biosorption data of total Cr best and predicted a maximum total Cr biosorption capacity of 305.4 mg g-1. Total Cr biosorption by CLB is an endothermic and non-spontaneous process as indicated by the thermodynamic parameters. Results from the present kinetic, equilibrium and thermodynamic studies suggest that CLB biosorbs Cr ions from Cr(VI) aqueous solutions predominantly by a chemical sorption phenomenon. Low cost, availability, renewable nature, and effective total Cr biosorption make CLB a highly attractive and efficient method to remediate Cr(VI)-contaminated water and wastewater. PMID:26352933

Selective and sensitive speciation analysis of Cr(VI) and Cr(III), at sub-μgL-1 levels in water samples by electrothermal atomic absorption spectrometry after electromembrane extraction.

PubMed

Tahmasebi, Zeinab; Davarani, Saied Saeed Hosseiny

2016-12-01

In this work, electromembrane extraction in combination with electrothermal atomic absorption spectrometry (ET-AAS) was investigated for speciation, preconcentration and quantification of Cr(VI) and Cr(III) in water samples through the selective complexation of Cr(VI) with 1,5-diphenylcarbazide (DPC) as a complexing agent. DPC reduces Cr(VI) to Cr(III) ions and then Cr(III) species are extracted based on electrokinetic migration of their cationic complex (Cr(III)-DPC) toward the negative electrode placed in the hollow fiber. Also, once oxidized to Cr(VI), Cr(III) ions in initial sample were determined by this procedure. The influence of extraction parameters such as pH, type of organic solvent, chelating agent concentration, stirring rate, extraction time and applied voltage were evaluated following a one-at-a-time optimization approach. Under optimized conditions, the extracted analyte was quantified by ETAAS, with an acceptable linearity in the range of 0.05-5ngmL -1 (R 2 value=0.996), and a repeatability (%RSD) between 3.7% and 12.2% (n=4) for 5.0 and 1.0ngmL -1 of Cr(VI), respectively. Also, we obtained an enrichment factor of 110 that corresponded to the recovery of 66%. The detection limit (S/N ratio of 3:1) was 0.02ngmL -1 . Finally, this new method was successfully employed to determine Cr(III) and Cr(VI) species in real water samples. Copyright © 2016. Published by Elsevier B.V.

Exposure to Hexavalent Chromium Resulted in Significantly Higher Tissue Chromium Burden Compared With Trivalent Chromium Following Similar Oral Doses to Male F344/N Rats and Female B6C3F1 Mice

PubMed Central

Collins, Bradley J.; Stout, Matthew D.; Levine, Keith E.; Kissling, Grace E.; Fennell, Timothy R.; Walden, Ramsey; Abdo, Kamal; Pritchard, John B.; Fernando, Reshan A.; Burka, Leo T.; Hooth, Michelle J.

2010-01-01

In National Toxicology Program 2-year studies, hexavalent chromium [Cr(VI)] administered in drinking water was clearly carcinogenic in male and female rats and mice, resulting in small intestine epithelial neoplasms in mice at a dose equivalent to or within an order of magnitude of human doses that could result from consumption of chromium-contaminated drinking water, assuming that dose scales by body weight3/4 (body weight raised to the 3/4 power). In contrast, exposure to trivalent chromium [Cr(III)] at much higher concentrations may have been carcinogenic in male rats but was not carcinogenic in mice or female rats. As part of these studies, total chromium was measured in tissues and excreta of additional groups of male rats and female mice. These data were used to infer the uptake and distribution of Cr(VI) because Cr(VI) is reduced to Cr(III) in vivo, and no methods are available to speciate tissue chromium. Comparable external doses resulted in much higher tissue chromium concentrations following exposure to Cr(VI) compared with Cr(III), indicating that a portion of the Cr(VI) escaped gastric reduction and was distributed systemically. Linear or supralinear dose responses of total chromium in tissues were observed following exposure to Cr(VI), indicating that these exposures did not saturate gastric reduction capacity. When Cr(VI) exposure was normalized to ingested dose, chromium concentrations in the liver and glandular stomach were higher in mice, whereas kidney concentrations were higher in rats. In vitro studies demonstrated that Cr(VI), but not Cr(III), is a substrate of the sodium/sulfate cotransporter, providing a partial explanation for the greater absorption of Cr(VI). PMID:20843897

Exposure to hexavalent chromium resulted in significantly higher tissue chromium burden compared with trivalent chromium following similar oral doses to male F344/N rats and female B6C3F1 mice.

PubMed

Collins, Bradley J; Stout, Matthew D; Levine, Keith E; Kissling, Grace E; Melnick, Ronald L; Fennell, Timothy R; Walden, Ramsey; Abdo, Kamal; Pritchard, John B; Fernando, Reshan A; Burka, Leo T; Hooth, Michelle J

2010-12-01

In National Toxicology Program 2-year studies, hexavalent chromium [Cr(VI)] administered in drinking water was clearly carcinogenic in male and female rats and mice, resulting in small intestine epithelial neoplasms in mice at a dose equivalent to or within an order of magnitude of human doses that could result from consumption of chromium-contaminated drinking water, assuming that dose scales by body weight(3/4) (body weight raised to the 3/4 power). In contrast, exposure to trivalent chromium [Cr(III)] at much higher concentrations may have been carcinogenic in male rats but was not carcinogenic in mice or female rats. As part of these studies, total chromium was measured in tissues and excreta of additional groups of male rats and female mice. These data were used to infer the uptake and distribution of Cr(VI) because Cr(VI) is reduced to Cr(III) in vivo, and no methods are available to speciate tissue chromium. Comparable external doses resulted in much higher tissue chromium concentrations following exposure to Cr(VI) compared with Cr(III), indicating that a portion of the Cr(VI) escaped gastric reduction and was distributed systemically. Linear or supralinear dose responses of total chromium in tissues were observed following exposure to Cr(VI), indicating that these exposures did not saturate gastric reduction capacity. When Cr(VI) exposure was normalized to ingested dose, chromium concentrations in the liver and glandular stomach were higher in mice, whereas kidney concentrations were higher in rats. In vitro studies demonstrated that Cr(VI), but not Cr(III), is a substrate of the sodium/sulfate cotransporter, providing a partial explanation for the greater absorption of Cr(VI).

Occurrence of hexavalent chromium in ground water in the western Mojave Desert, California

USGS Publications Warehouse

Ball, J.W.; Izbicki, J.A.

2004-01-01

About 200 samples from selected public supply, domestic, and observation wells completed in alluvial aquifers underlying the western Mojave Desert were analyzed for total dissolved Cr and Cr(VI). Because Cr(VI) is difficult to preserve, samples were analyzed by 3 methods. Chromium(VI) was determined in the field using both a direct colorimetric method and EPA method 218.6, and samples were speciated in the field for later analysis in the laboratory using a cation-exchange method developed for the study described in this paper. Comparison of the direct colorimetric method and EPA method 218.6 with the new cation-exchange method yielded r2 values of 0.9991 and 0.9992, respectively. Total dissolved Cr concentrations ranged from less than the 0.1 ??g/l detection limit to 60 ??g/l, and almost all the Cr present was Cr(VI). Near recharge areas along the mountain front pH values were near neutral, dissolved O2 concentrations were near saturation, and Cr(VI) concentrations were less than the 0.1 ??g/l detection limit. Chromium(VI) concentrations and pH values increased downgradient as long as dissolved O 2 was present. However, low Cr(VI) concentrations were associated with low dissolved O2 concentrations near ground-water discharge areas along dry lakes. Chromium(VI) concentrations as high as 60 ??g/l occurred in ground water from the Sheep Creek fan alluvial deposits weathered from mafic rock derived from the San Gabriel Mountains, and Cr(VI) concentrations as high as about 36 ??g/l were present in ground water from alluvial deposits weathered from less mafic granitic, metamorphic, and volcanic rocks. Chromium(III) was the predominant form of Cr only in areas where dissolved O2 concentrations were less than 1 mg/l and was detected at a median concentration of 0.1 ??g/l, owing to its low solubility in water of near-neutral pH. Depending on local hydrogeologic conditions and the distribution of dissolved O2, Cr(VI) concentrations may vary considerably with depth. Samples collected under pumping conditions from different depths within wells show that Cr(VI) concentrations can range from less than the 0.1 ??g/l detection limit to 36 ??g/l in a single well and that dissolved O2 concentrations likely control the concentration and redox speciation of Cr in ground water.

Hexavalent and total chromium at low reporting concentrations in source-water aquifers and surface waters used for public supply in Illinois, 2013

USGS Publications Warehouse

Mills, Patrick C.; Cobb, Richard P.

2015-01-01

There was a weak positive relation (ρ = 0.23) between concentrations of Cr(VI) and Cr(T) in untreated water samples, with a much stronger positive relation (ρ = 0.86 and ρ = 0.90, respectively) in samples collected soon after treatment and near the endpoint of distribution. The stronger relation and greater similarity between Cr(VI) and Cr(T) concentrations in treated water samples indicate that Cr(VI) represents a greater proportion of the measured concentrations of Cr(T) in treated waters than in untreated waters. The analysis of spikes and other quality-assurance samples indicate uncertainties associated with obtaining or confirming consistently accurate analytical results for Cr(VI) at near the applied reporting limit of 0.02 µg/L.

Accumulation, depuration dynamics and effects of dissolved hexavalent chromium in juvenile Japanese medaka (Oryzias latipes).

PubMed

Chen, Hongxing; Guo, Zhongbao; Zhou, Yu; Li, Dan; Mu, Lei; Klerks, Paul L; Luo, Yongju; Xie, Lingtian

2018-02-01

We previously demonstrated that chronic exposure to hexavalent chromium (Cr(VI)) causes a variety of adverse effects in the Japanese medaka (Oryzias latipes). The present study investigated the transition of acute to chronic effects by assessing the influences of Cr(VI) exposure concentration and exposure duration on Cr accumulation and their effects on fish growth and antioxidant physiology. Juvenile fish were exposed to 0.05, 0.5, 4 or 8mg/L Cr(VI) for 28 days. Endpoints were evaluated on days 3, 7, 14, 21 and 28. In addition, Cr depuration was examined for fish from two exposure groups (0.5 and 8mg/L). Chromium accumulation was rapid initially, then continued at a slower rate till the end of the exposure period without showing signs of reaching a steady state. Depuration patterns differed between the two exposure groups, but both reached 50% in 14 days. The rapid initial accumulation was accompanied by increased lipid peroxidation and elevated activities of antioxidants (e.g., GST, SOD and CAT). Activities of these enzymes had mostly returned to baseline levels by day 7, but there was no evidence of further cellular damage from ROS. Effects on fish length and weight continued to be evident over the 28-day exposure period. Our study suggest that the initial effects of Cr(VI) exposure may not be a good predictor of more-chronic effects in fish as a consequence of an efficient acclimation response by the antioxidant system that limits ROS-mediated toxicity. Copyright © 2017 Elsevier Inc. All rights reserved.

Bio-reduction of Cr(VI) by exopolysaccharides (EPS) from indigenous bacterial species of Sukinda chromite mine, India.

PubMed

Harish, R; Samuel, Jastin; Mishra, R; Chandrasekaran, N; Mukherjee, A

2012-07-01

Chrome mining activity has contributed intensively towards pollution of hexavalent chromium around Sukinda Valley, Orissa, India. In an attempt to study the specific contribution of exopolysaccharides (EPS) extracted from indigenous isolates towards Cr(VI) reduction, three chromium (VI) tolerant strains were isolated from the effluent mining sludge. Based on the tolerance towards Cr(VI) and EPS production capacity, one of them was selected for further work. The taxonomic identity of the selected strain was confirmed to be Enterobacter cloacae (showing 98% similarity in BLAST search to E. cloacae) through 16S rRNA analysis. The EPS production was observed to increase with increasing Cr(VI) concentration in the growth medium, highest being 0.078 at 100 mg/l Cr(VI). The extracted EPS from Enterobacter cloacae SUKCr1D was able to reduce 31.7% of Cr(VI) at 10 mg/l concentration, which was relevant to the prevailing natural concentrations at Sukinda mine effluent sludge. The FT-IR spectral studies confirmed the surface chemical interactions of hexavalent chromium with EPS.

Reduction of hexavalent chromium by fasted and fed human gastric fluid. II. Ex vivo gastric reduction modeling

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

Kirman, Christopher R., E-mail: ckirman@summittoxi

To extend previous models of hexavalent chromium [Cr(VI)] reduction by gastric fluid (GF), ex vivo experiments were conducted to address data gaps and limitations identified with respect to (1) GF dilution in the model; (2) reduction of Cr(VI) in fed human GF samples; (3) the number of Cr(VI) reduction pools present in human GF under fed, fasted, and proton pump inhibitor (PPI)-use conditions; and (4) an appropriate form for the pH-dependence of Cr(VI) reduction rate constants. Rates and capacities of Cr(VI) reduction were characterized in gastric contents from fed and fasted volunteers, and from fasted pre-operative patients treated with PPIs.more » Reduction capacities were first estimated over a 4-h reduction period. Once reduction capacity was established, a dual-spike approach was used in speciated isotope dilution mass spectrometry analyses to characterize the concentration-dependence of the 2nd order reduction rate constants. These data, when combined with previously collected data, were well described by a three-pool model (pool 1 = fast reaction with low capacity; pool 2 = slow reaction with higher capacity; pool 3 = very slow reaction with higher capacity) using pH-dependent rate constants characterized by a piecewise, log-linear relationship. These data indicate that human gastric samples, like those collected from rats and mice, contain multiple pools of reducing agents, and low concentrations of Cr(VI) (< 0.7 mg/L) are reduced more rapidly than high concentrations. The data and revised modeling results herein provide improved characterization of Cr(VI) gastric reduction kinetics, critical for Cr(VI) pharmacokinetic modeling and human health risk assessment. - Highlights: • SIDMS allows for measurement of Cr(VI) reduction rate in gastric fluid ex vivo • Human gastric fluid has three reducing pools • Cr(VI) in drinking water at < 0.7 mg/L is rapidly reduced in human gastric fluid • Reduction rate is concentration- and pH-dependent • A refined PK model is used to characterize inter-individual variability in Cr(VI) gastric reduction capacity.« less

Biological versus mineralogical chromium reduction: potential for reoxidation by manganese oxide.

PubMed

Butler, Elizabeth C; Chen, Lixia; Hansel, Colleen M; Krumholz, Lee R; Elwood Madden, Andrew S; Lan, Ying

2015-11-01

Hexavalent chromium (Cr(vi), present predominantly as CrO4(2-) in water at neutral pH) is a common ground water pollutant, and reductive immobilization is a frequent remediation alternative. The Cr(iii) that forms upon microbial or abiotic reduction often co-precipitates with naturally present or added iron (Fe), and the stability of the resulting Fe-Cr precipitate is a function of its mineral properties. In this study, Fe-Cr solids were formed by microbial Cr(vi) reduction using Desulfovibrio vulgaris strain RCH1 in the presence of the Fe-bearing minerals hematite, aluminum substituted goethite (Al-goethite), and nontronite (NAu-2, Clay Minerals Society), or by abiotic Cr(vi) reduction by dithionite reduced NAu-2 or iron sulfide (FeS). The properties of the resulting Fe-Cr solids and their behavior upon exposure to the oxidant manganese (Mn) oxide (birnessite) differed significantly. In microcosms containing strain RCH1 and hematite or Al-goethite, there was significant initial loss of Cr(vi) in a pattern consistent with adsorption, and significant Cr(vi) was found in the resulting solids. The solid formed when Cr(vi) was reduced by FeS contained a high proportion of Cr(iii) and was poorly crystalline. In microcosms with strain RCH1 and hematite, Cr precipitates appeared to be concentrated in organic biofilms. Reaction between birnessite and the abiotically formed Cr(iii) solids led to production of significant dissolved Cr(vi) compared to the no-birnessite controls. This pattern was not observed in the solids generated by microbial Cr(vi) reduction, possibly due to re-reduction of any Cr(vi) generated upon oxidation by birnessite by active bacteria or microbial enzymes. The results of this study suggest that Fe-Cr precipitates formed in groundwater remediation may remain stable only in the presence of active anaerobic microbial reduction. If exposed to environmentally common Mn oxides such as birnessite in the absence of microbial activity, there is the potential for rapid (re)formation of dissolved Cr(vi) above regulatory levels.

Hexavalent chromium removal in contaminated water using reticulated chitosan micro/nanoparticles from seafood processing wastes.

PubMed

Dima, Jimena Bernadette; Sequeiros, Cynthia; Zaritzky, Noemi E

2015-12-01

Chitosan particles (CH) were obtained from seafood processing wastes (shrimp shells) and physicochemically characterized; deacetylation degree of CH was measured by Infrared Spectroscopy (FTIR) and potentiometric titration; polymer molecular weight was determined by intrinsic viscosity measurements. Reticulated micro/nanoparticles of chitosan (MCH) with an average diameter close to 100nm were synthesized by ionic gelation of chitosan using tripolyphosphate (TPP), and characterized by SEM, size distribution and Zeta-potential. Detoxification capacities of CH and MCH were tested analyzing the removal of hexavalent chromium Cr(VI) from contaminated water, at different initial chromium concentrations. The effect of pH on adsorption capacity of CH and MCH was experimentally determined and analyzed considering the Cr(VI) stable complexes (anions) formed, the presence of protonated groups in chitosan particles and the addition of the reticulating agent (TPP). Chitosan crosslinking was necessary to adsorb Cr(VI) at pH<2 due to the instability of CH particles in acid media. Langmuir isotherm described better than Freundlich and Temkin equations the equilibrium adsorption data. Pseudo-second order rate provided the best fitting to the kinetic data in comparison to pseudo-first order and Elovich equations. Chemical analysis to determine the oxidation state of the adsorbed Cr, showed that Cr(VI) was adsorbed on CH particles without further reduction; in contrast Cr(VI) removed from the solution was reduced and bound to the MCH as Cr(III). The reduction of toxic Cr(VI) to the less or nontoxic Cr(III) by the reticulated chitosan micro/nanoparticles can be considered a very efficient detoxification technique for the treatment of Cr(VI) contaminated water. Copyright © 2015 Elsevier Ltd. All rights reserved.

Escherichia coli NemA is an efficient chromate reductase that can be biologically immobilized to provide a cell free system for remediation of hexavalent chromium.

PubMed

Robins, Katherine J; Hooks, David O; Rehm, Bernd H A; Ackerley, David F

2013-01-01

Hexavalent chromium is a serious and widespread environmental pollutant. Although many bacteria have been identified that can transform highly water-soluble and toxic Cr(VI) to insoluble and relatively non-toxic Cr(III), bacterial bioremediation of Cr(VI) pollution is limited by a number of issues, in particular chromium toxicity to the remediating cells. To address this we sought to develop an immobilized enzymatic system for Cr(VI) remediation. To identify novel Cr(VI) reductase enzymes we first screened cell extracts from an Escherichia coli library of soluble oxidoreductases derived from a range of bacteria, but found that a number of these enzymes can reduce Cr(VI) indirectly, via redox intermediates present in the crude extracts. Instead, activity assays for 15 candidate enzymes purified as His6-tagged proteins identified E. coli NemA as a highly efficient Cr(VI) reductase (k(cat)/K(M)= 1.1×10(5) M(-1) s(-1) with NADH as cofactor). Fusion of nemA to the polyhydroxyalkanoate synthase gene phaC from Ralstonia eutropha enabled high-level biosynthesis of functionalized polyhydroxyalkanoate granules displaying stable and active NemA on their surface. When these granules were combined with either Bacillus subtilis glucose dehydrogenase or Candida boidinii formate dehydrogenase as a cofactor regenerating partner, high levels of chromate transformation were observed with only low initial concentrations of expensive NADH cofactor being required, the overall reaction being powered by consumption of the cheap sacrificial substrates glucose or formic acid, respectively. This system therefore offers promise as an economic solution for ex situ Cr(VI) remediation.

Escherichia coli NemA Is an Efficient Chromate Reductase That Can Be Biologically Immobilized to Provide a Cell Free System for Remediation of Hexavalent Chromium

PubMed Central

Robins, Katherine J.; Hooks, David O.; Rehm, Bernd H. A.; Ackerley, David F.

2013-01-01

Hexavalent chromium is a serious and widespread environmental pollutant. Although many bacteria have been identified that can transform highly water-soluble and toxic Cr(VI) to insoluble and relatively non-toxic Cr(III), bacterial bioremediation of Cr(VI) pollution is limited by a number of issues, in particular chromium toxicity to the remediating cells. To address this we sought to develop an immobilized enzymatic system for Cr(VI) remediation. To identify novel Cr(VI) reductase enzymes we first screened cell extracts from an Escherichia coli library of soluble oxidoreductases derived from a range of bacteria, but found that a number of these enzymes can reduce Cr(VI) indirectly, via redox intermediates present in the crude extracts. Instead, activity assays for 15 candidate enzymes purified as His6-tagged proteins identified E. coli NemA as a highly efficient Cr(VI) reductase (kcat/KM  = 1.1×105 M−1s−1 with NADH as cofactor). Fusion of nemA to the polyhydroxyalkanoate synthase gene phaC from Ralstonia eutropha enabled high-level biosynthesis of functionalized polyhydroxyalkanoate granules displaying stable and active NemA on their surface. When these granules were combined with either Bacillus subtilis glucose dehydrogenase or Candida boidinii formate dehydrogenase as a cofactor regenerating partner, high levels of chromate transformation were observed with only low initial concentrations of expensive NADH cofactor being required, the overall reaction being powered by consumption of the cheap sacrificial substrates glucose or formic acid, respectively. This system therefore offers promise as an economic solution for ex situ Cr(VI) remediation. PMID:23527133

A revised model of ex-vivo reduction of hexavalent chromium in human and rodent gastric juices

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

Schlosser, Paul M., E-mail: schlosser.paul@epa.gov; Sasso, Alan F.

Chronic oral exposure to hexavalent chromium (Cr-VI) in drinking water has been shown to induce tumors in the mouse gastrointestinal (GI) tract and rat oral cavity. The same is not true for trivalent chromium (Cr-III). Thus reduction of Cr-VI to Cr-III in gastric juices is considered a protective mechanism, and it has been suggested that the difference between the rate of reduction among mice, rats, and humans could explain or predict differences in sensitivity to Cr-VI. We evaluated previously published models of gastric reduction and believe that they do not fully describe the data on reduction as a function ofmore » Cr-VI concentration, time, and (in humans) pH. The previous models are parsimonious in assuming only a single reducing agent in rodents and describing pH-dependence using a simple function. We present a revised model that assumes three pools of reducing agents in rats and mice with pH-dependence based on known speciation chemistry. While the revised model uses more fitted parameters than the original model, they are adequately identifiable given the available data, and the fit of the revised model to the full range of data is shown to be significantly improved. Hence the revised model should provide better predictions of Cr-VI reduction when integrated into a corresponding PBPK model. - Highlights: • Hexavalent chromium (Cr-VI) reduction in gastric juices is a key detoxifying step. • pH-dependent Cr-VI reduction rates are explained using known chemical speciation. • Reduction in rodents appears to involve multiple pools of electron donors. • Reduction appears to continue after 60 min, although more slowly than initial rates.« less

Pilot scale treatment of chromite ore processing residue using sodium sulfide in single reduction and coupled reduction/stabilization processes.

PubMed

Velasco, Antonio; Ramírez, Martha; Hernández, Sergio; Schmidt, Winfried; Revah, Sergio

2012-03-15

Single Cr(VI) reduction and coupled reduction/stabilization (R/S) processes were evaluated at pilot scale to determine their effectiveness to treat chromite ore processing residue (COPR). Sodium sulfide was used as the reducing agent and cement, gypsum and lime were tested as the stabilizing agents. The pilot experiments were performed in a helical ribbon blender mixer with batches of 250 kg of COPR and mixing time up to 30 min. Na2S/Cr(VI) mass ratios of 4.6, 5.7 and 6.8 were evaluated in the single reduction process to treat COPR with Cr(VI) concentration of ≈4.2 g/kg. The R/S process was tested with a Na2S/Cr(VI) mass ratio of 5.7 and including stabilizing agents not exceeding 5% (w/w(COPR)), to treat COPR with a Cr(VI) content of ≈5.1g/kg. The single reduction process with a ratio of 6.8, reached Cr(VI) reduction efficiencies up to 97.6% in the first days, however these values decreased to around 93% after 380 days of storage. At this point the total Cr level was around 12.5 mg/L. Cr(VI) removal efficiencies exceeding 96.5% were reached and maintained during 380 days when the coupled R/S process was evaluated. Total Cr levels lower than 5 mg/l were attained at the initials days in all R/S batch tested, however after 380 days, concentrations below the regulatory limit were only found with gypsum (2%) as single agent and with a blend of cement (4%) and lime (1%). These results indicated that the coupled R/S process is an excellent alternative to stabilize COPR. Copyright © 2011 Elsevier B.V. All rights reserved.

Leachability of Cr(VI) and other metals from asphalt composites with addition of filter dust.

PubMed

Vahcic, Mitja; Milacic, Radmila; Mladenovic, Ana; Murko, Simona; Zuliani, Tea; Zupancic, Marija; Scancar, Janez

2008-12-01

The potential use of filter dust in asphalt composites for road construction was investigated. Filter dust contains high concentrations of metals, of which Cr(VI) and Pb are leached with water. Compact and ground asphalt composites with addition of 2% of filter dust by mass were studied. In order to evaluate their environmental impact, leachability tests were performed using water and salt water as leaching agents. The concentrations of Cr(VI) and Pb were determined in leachates over a time period of 182 days. The results indicated that Pb was not leached with leaching agents from asphalt composites. Cr(VI) was also not leached with leaching agents from compact asphalt composites. However, in ground asphalt composites, Cr(VI) was leached with water in concentrations up to 220 microg L(-1) and in salt water up to 150 microg L(-1). From the physico-mechanical and environmental aspects, filter dust can be used as a component in asphalt mixtures.

Natural and man-made hexavalent chromium, Cr(VI), in groundwater near a mapped plume, Hinkley, California—study progress as of May 2017, and a summative-scale approach to estimate background Cr(VI) concentrations

USGS Publications Warehouse

Izbicki, John A.; Groover, Krishangi D.

2018-03-22

This report describes (1) work done between January 2015 and May 2017 as part of the U.S. Geological Survey (USGS) hexavalent chromium, Cr(VI), background study and (2) the summative-scale approach to be used to estimate the extent of anthropogenic (man-made) Cr(VI) and background Cr(VI) concentrations near the Pacific Gas and Electric Company (PG&E) natural gas compressor station in Hinkley, California. Most of the field work for the study was completed by May 2017. The summative-scale approach and calculation of Cr(VI) background were not well-defined at the time the USGS proposal for the background Cr(VI) study was prepared but have since been refined as a result of data collected as part of this study. The proposed summative scale consists of multiple items, formulated as questions to be answered at each sampled well. Questions that compose the summative scale were developed to address geologic, hydrologic, and geochemical constraints on Cr(VI) within the study area. Each question requires a binary (yes or no) answer. A score of 1 will be assigned for an answer that represents data consistent with anthropogenic Cr(VI); a score of –1 will be assigned for an answer that represents data inconsistent with anthropogenic Cr(VI). The areal extent of anthropogenic Cr(VI) estimated from the summative-scale analyses will be compared with the areal extent of anthropogenic Cr(VI) estimated on the basis of numerical groundwater flow model results, along with particle-tracking analyses. On the basis of these combined results, background Cr(VI) values will be estimated for “Mojave-type” deposits, and other deposits, in different parts of the study area outside the summative-scale mapped extent of anthropogenic Cr(VI).

Control of occupational exposure to hexavalent chromium and ozone in tubular wire arc-welding processes by replacement of potassium by lithium or by addition of zinc.

PubMed

Dennis, John H; French, Michael J; Hewitt, Peter J; Mortazavi, Seyed B; Redding, Christopher A J

2002-01-01

Hexavalent chromium [Cr(VI)] and ozone are produced in many arc-welding processes. Cr(VI) is formed when welding with chromium-containing alloys and is a suspected carcinogen. Ozone is formed by the action of ultraviolet light from the arc on oxygen and can cause severe irritation to the eyes and mucous membranes. Previous work has demonstrated that reduction of sodium and potassium in manual metal arc-welding electrodes leads to substantial reductions in Cr(VI) concentrations in the fume as well as a reduction in the fume formation rate. In this paper replacement of potassium by lithium in a tubular wire welding electrode (self-shielding flux-cored) is shown to give reductions in Cr(VI) concentrations and fume formation rates. Previous work has also demonstrated that use of a tubular wire (metal cored) containing 1% zinc can, under certain conditions, result in a reduction in Cr(VI) formation rate and in ozone concentration near the arc but with a rise in the total fume formation rate. The effects of different shield gases and different levels of zinc are examined. An experimental chromium-containing tubular wire with 1% zinc was used with the following shield gases: argon, Argoshield 5, Argoshield 20, Helishield 101, Ar + 2% CO2, Ar + 5% CO2, Ar + 1% O2 and Ar + 2% O2. The wire gave > 98% reduction in Cr(VI) formation rate compared to the control wire provided the shield gas contained no oxygen. When the shield gas did contain oxygen, 1% zinc enhanced Cr(VI) formation rate, resulting in more than double the rates measured when welding with the control wire. Experiments with zinc concentrations, from 0.018 to 0.9% using Helishield 101, gave results indicating that there is an optimum zinc concentration from the point of view of Cr(VI) reduction. Implications of the use of lithium or zinc on the overall exposure risk are discussed.

Removal of Cr(VI) by surfactant modified Auricularia auricula spent substrate: biosorption condition and mechanism.

PubMed

Dong, Liying; Jin, Yu; Song, Tao; Liang, Jinsong; Bai, Xin; Yu, Sumei; Teng, Chunying; Wang, Xin; Qu, Juanjuan; Huang, Xiaomei

2017-07-01

Auricularia auricula spent substrate (AASS) modified by didodecyldimethylammonium bromide(DDAB) was used as adsorbent to remove Cr(VI) from aqueous solution. Based on a single-factor experiment and response surface methodology, the optimal conditions were adsorbent dosage of 1.5 g/L, pH value of 4.0, initial Cr(VI) concentration of 19 mg/L, temperature of 25 °C, biosorption time of 120 min, rotational speed of 150 r/min, respectively, under which biosorption capacity could reach 12.16 mg/g compared with unmodified AASS (6.058 mg/g). DDAB modification could enlarge the specific surface area and porous diameter of the adsorbents, and supply hydrophilic and hydrophobic groups capable of adsorbing at the interfaces. In addition, DDAB increased ionic exchange and complex formation demonstrated by variations of elemental contents, shifts of carboxyl, amine groups, hydroxyl, alkyl chains, and phosphate groups as well as the crystal structure of the Cr-O compounds. Variations of peaks and energy in XPS analysis also testified the reduction of Cr(VI) to Cr(III).The biosorption behavior of modified AASS was in line with Langmuir and Freundlich isotherm equation. The final regeneration efficiency was 62.33% after three biosorption-desorption cycles. Apparently, DDBA is a eximious modifier and DDBA-modified AASS was very efficient for Cr(VI) removal.

[Adsorptive Stabilization of Soil Cr (VI) Using HDTMA Modified Montmorillonite].

PubMed

2016-03-15

A series of organo-montomorillonites were prepared using Na-montomorillonite and hexadecyl trimethyl ammonium bromide (HDTMA). The organo-montomorillonites were then investigated for the remediation of Cr(VI) contaminated soils. FT-IR, XRD, SEM and N2 -BET, CEC, Zeta potential measurement were conducted to understand the structural changes of montmorillonites as different amounts of HDTMAs were added as modifier. The characterization results indicated that the clay interlayer spacing distance increased from 1. 25 nm to 2. 13 nm, the clay surface roughness decreased, the clay surface area reduced from 38.91 m² · g⁻¹ to 0.42 m² · g⁻¹, the clay exchangeable cation amount reduced from 62 cmol · kg⁻¹ to 9.9 cmol · kg⁻¹ and the clay surface charge changed from -29.1 mV to 5.59 mV as the dosage of HDTMA in montmorillonite was increased. The TCLP (toxicity characteristic leaching procedure) was used to evaluate the leachate toxicity of Cr(VI). The effects of the initial soil Cr(VI) concentration, montmorillonites dosage, reaction time and HDTMA modification amount were investigated, respectively. The results revealed that modification of montmorillonites would manifest an attenuated physical adsorptive effect and an enhanced electrostatic adsorptive effect on Cr(VI), suggesting electrostatic effect was the major force that resulted in improved Cr(VI) adsorption onto HDTMA modified montmorillonites.

Simultaneous determination of Cr(III) and Cr(VI) in tannery wastewater using low pressure ion chromatography combined with flow injection spectrophotometry

NASA Astrophysics Data System (ADS)

Chen, Shujuan; Zhang, Xinshen; Yu, Lingyun; Wang, Li; Li, Hui

2012-03-01

Trivalent and hexavalent chromium have been successfully separated and determined using low pressure ion chromatography combined with flow injection spectrophotometric analysis (LPIC-FIA). A column packed with crosslinking starch microspheres was used for on-line separation of Cr(III) from Cr(VI) in a flow-injection system because of its absorptive effect on Cr(III). To determine the concentration of Cr(III) and Cr(VI) in samples, we used 3.0 mmol/L nitric acid to elute adsorbed Cr(III) from the column and then used ceric sulfate-sulfuric acid as oxidant to convert all Cr(III) into Cr(VI). Then, Cr(VI) directly came from the samples and Cr(VI) came from Cr(III) successively formed a amaranthine complex with diphenycarbazide and the complex shows a maximum absorption at 530 nm. Analytical parameters including the concentration of eluent and oxidant solution, oxidizing temperature, length of oxidizing reaction coil, reaction coil and injection coil, interfering effects, etc., were optimized. The limit of detection was 1.25 μg/L for Cr(VI) and 3.76 μg/L for Cr(III). The linear relationship between absorption with the concentration of Cr(VI) and Cr(III) was 0.001-1.000 mg/L and 0.030-1.000 mg/L with correlation coefficients of 0.9995 and 0.9994, respectively. The relative standard deviation of Cr(VI) and Cr(III) was 1.21% and 1.66%, respectively (n = 10). Major cations and anions did not show any interference. We validated this method through certified reference materials and through measuring the recovery in tannery wastewater.

Effect of seasonality and Cr(VI) on starch-sucrose partitioning and related enzymes in floating leaves of Salvinia minima.

PubMed

Rosa, Mariana; Prado, Carolina; Chocobar-Ponce, Silvana; Pagano, Eduardo; Prado, Fernando

2017-09-01

Effects of seasonality and increasing Cr(VI) concentrations on leaf starch-sucrose partitioning, sucrose- and starch-related enzyme activities, and carbon allocation toward leaf development were analyzed in fronds (floating leaves) of the floating fern Salvinia minima. Carbohydrates and enzyme activities of Cr-exposed fronds showed different patterns in winter and summer. Total soluble sugars, starch, glucose and fructose increased in winter fronds, while sucrose was higher in summer ones. Starch and soluble carbohydrates, except glucose, increased under increasing Cr(VI) concentrations in winter fronds, while in summer ones only sucrose increased under Cr(VI) treatment. In summer fronds starch, total soluble sugars, fructose and glucose practically stayed without changes in all assayed Cr(VI) concentrations. Enzyme activities related to starch and sucrose metabolisms (e.g. ADPGase, SPS, SS and AI) were higher in winter fronds than in summer ones. Total amylase and cFBPase activities were higher in summer fronds. Cr(VI) treatment increased enzyme activities, except ADPGase, in both winter and summer fronds but no clear pattern changes were observed. Data of this study show clearly that carbohydrate metabolism is differently perturbed by both seasonality and Cr(VI) treatment in summer and winter fronds, which affects leaf starch-sucrose partitioning and specific leaf area (SLA) in terms of carbon investment. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

Combination of cathodic reduction with adsorption for accelerated removal of Cr(VI) through reticulated vitreous carbon electrodes modified with sulfuric acid-glycine co-doped polyaniline.

PubMed

Mo, Xi; Yang, Zhao-hui; Xu, Hai-yin; Zeng, Guang-ming; Huang, Jing; Yang, Xia; Song, Pei-pei; Wang, Li-ke

2015-04-09

Improving the reduction kinetics is crucial in the electroreduction process of Cr(VI). In this study, we developed a novel adsorption-electroreduction system for accelerated removal of Cr(VI) by employing reticulated vitreous carbon electrode modified with sulfuric acid-glycine co-doped polyaniline (RVC/PANI-SA-GLY). Firstly, response surface methodology confirmed the optimum polymerization condition of co-doped polyaniline for modifying electrodes (Aniline, sulfuric acid and glycine, respectively, of 0.2 mol/L, 0.85 mol/L, 0.93 mol/L) when untraditional dopant glycine was added. Subsequently, RVC/PANI-SA-GLY showed higher Cr(VI) removal percentages in electroreduction experiments over RVC electrode modified with sulfuric acid doped polyaniline (RVC/PANI-SA) and bare RVC electrode. In contrast to RVC/PANI-SA, the improvement by RVC/PANI-SA-GLY was more significant and especially obvious at more negative potential, lower initial Cr(VI) concentration, relatively less acidic solution and higher current densities, best achieving 7.84% higher removal efficiency with entire Cr(VI) eliminated after 900 s. Current efficiencies were likewise enhanced by RVC/PANI-SA-GLY under quite negative potentials. Fourier transform infrared (FTIR) and energy dispersive spectrometer (EDS) analysis revealed a possible adsorption-reduction mechanism of RVC/PANI-SA-GLY, which greatly contributed to the faster reduction kinetics and was probably relative to the absorption between protonated amine groups of glycine and HCrO4(-). Eventually, the stability of RVC/PANI-SA-GLY was proven relatively satisfactory. Copyright © 2015 Elsevier B.V. All rights reserved.

A new cation-exchange method for accurate field speciation of hexavalent chromium

USGS Publications Warehouse

Ball, J.W.; McCleskey, R. Blaine

2003-01-01

A new method for field speciation of Cr(VI) has been developed to meet present stringent regulatory standards and to overcome the limitations of existing methods. The method consists of passing a water sample through strong acid cation-exchange resin at the field site, where Cr(III) is retained while Cr(VI) passes into the effluent and is preserved for later determination. The method is simple, rapid, portable, and accurate, and makes use of readily available, inexpensive materials. Cr(VI) concentrations are determined later in the laboratory using any elemental analysis instrument sufficiently sensitive to measure the Cr(VI) concentrations of interest. The new method allows measurement of Cr(VI) concentrations as low as 0.05 ??g 1-1, storage of samples for at least several weeks prior to analysis, and use of readily available analytical instrumentation. Cr(VI) can be separated from Cr(III) between pH 2 and 11 at Cr(III)/Cr(VI) concentration ratios as high as 1000. The new method has demonstrated excellent comparability with two commonly used methods, the Hach Company direct colorimetric method and USEPA method 218.6. The new method is superior to the Hach direct colorimetric method owing to its relative sensitivity and simplicity. The new method is superior to USEPA method 218.6 in the presence of Fe(II) concentrations up to 1 mg 1-1 and Fe(III) concentrations up to 10 mg 1-1. Time stability of preserved samples is a significant advantage over the 24-h time constraint specified for USEPA method 218.6.

A Green Microbial Fuel Cell-Based Biosensor for In Situ Chromium (VI) Measurement in Electroplating Wastewater.

PubMed

Wu, Li-Chun; Tsai, Teh-Hua; Liu, Man-Hai; Kuo, Jui-Ling; Chang, Yung-Chu; Chung, Ying-Chien

2017-10-27

The extensive use of Cr(VI) in many industries and the disposal of Cr(VI)-containing wastes have resulted in Cr(VI)-induced environmental contamination. Cr(VI) compounds are associated with increased cancer risks; hence, the detection of toxic Cr(VI) compounds is crucial. Various methods have been developed for Cr(VI) measurement, but they are often conducted offsite and cannot provide real-time toxicity monitoring. A microbial fuel cell (MFC) is an eco-friendly and self-sustaining device that has great potential as a biosensor for in situ Cr(VI) measurement, especially for wastewater generated from different electroplating units. In this study, Exiguobacterium aestuarii YC211, a facultatively anaerobic, Cr(VI)-reducing, salt-tolerant, and exoelectrogenic bacterium, was isolated and inoculated into an MFC to evaluate its feasibility as a Cr(VI) biosensor. The Cr(VI) removal efficiency of E. aestuarii YC211 was not affected by the surrounding environment (pH 5-9, 20-35 °C, coexisting ions, and salinity of 0-15 g/L). The maximum power density of the MFC biosensor was 98.3 ± 1.5 mW/m² at 1500 Ω. A good linear relationship ( r ² = 0.997) was observed between the Cr(VI) concentration (2.5-60 mg/L) and the voltage output. The developed MFC biosensor is a simple device that can accurately measure Cr(VI) concentrations in the actual electroplating wastewater that is generated from different electroplating units within 30 min with low deviations (-6.1% to 2.2%). After treating the actual electroplating wastewater with the MFC, the predominant family in the biofilm was found to be Bacillaceae (95.3%) and was further identified as the originally inoculated E. aestuarii YC211 by next generation sequencing (NGS). Thus, the MFC biosensor can measure Cr(VI) concentrations in situ in the effluents from different electroplating units, and it can potentially help in preventing the violation of effluent regulations.

A Green Microbial Fuel Cell-Based Biosensor for In Situ Chromium (VI) Measurement in Electroplating Wastewater

PubMed Central

Wu, Li-Chun; Tsai, Teh-Hua; Liu, Man-Hai; Kuo, Jui-Ling; Chang, Yung-Chu

2017-01-01

The extensive use of Cr(VI) in many industries and the disposal of Cr(VI)-containing wastes have resulted in Cr(VI)-induced environmental contamination. Cr(VI) compounds are associated with increased cancer risks; hence, the detection of toxic Cr(VI) compounds is crucial. Various methods have been developed for Cr(VI) measurement, but they are often conducted offsite and cannot provide real-time toxicity monitoring. A microbial fuel cell (MFC) is an eco-friendly and self-sustaining device that has great potential as a biosensor for in situ Cr(VI) measurement, especially for wastewater generated from different electroplating units. In this study, Exiguobacterium aestuarii YC211, a facultatively anaerobic, Cr(VI)-reducing, salt-tolerant, and exoelectrogenic bacterium, was isolated and inoculated into an MFC to evaluate its feasibility as a Cr(VI) biosensor. The Cr(VI) removal efficiency of E. aestuarii YC211 was not affected by the surrounding environment (pH 5–9, 20–35 °C, coexisting ions, and salinity of 0–15 g/L). The maximum power density of the MFC biosensor was 98.3 ± 1.5 mW/m2 at 1500 Ω. A good linear relationship (r2 = 0.997) was observed between the Cr(VI) concentration (2.5–60 mg/L) and the voltage output. The developed MFC biosensor is a simple device that can accurately measure Cr(VI) concentrations in the actual electroplating wastewater that is generated from different electroplating units within 30 min with low deviations (−6.1% to 2.2%). After treating the actual electroplating wastewater with the MFC, the predominant family in the biofilm was found to be Bacillaceae (95.3%) and was further identified as the originally inoculated E. aestuarii YC211 by next generation sequencing (NGS). Thus, the MFC biosensor can measure Cr(VI) concentrations in situ in the effluents from different electroplating units, and it can potentially help in preventing the violation of effluent regulations. PMID:29076985

Distribution and bioavailability of Cr in central Euboea, Greece

NASA Astrophysics Data System (ADS)

Megremi, Ifigeneia

2010-06-01

Plants and soils from central Euboea, were analyzed for Cr(totai), Cr(VI), Ni, Mn, Fe and Zn. The range of metal concentrations in soils is typical to those developed on Fe-Ni laterites and ultramafic rocks. Their bioavailability was expressed in terms of concentrations extractable with EDTA and 1 M HNO3, with EDTA having a limited effect on metal recovery. Cr(VI) concentrations in soils evaluated by alkaline digestion solution were lower than phytotoxic levels. Chromium and Ni — and occasionally Zn — in the majority of plants were near or above toxicity levels. Cr(VI) concentrations in plants were extremely low compared to total chromium concentrations. Cr(total) in ground waters ranged from <1 μg.L-1 to 130 μg.L-1, with almost all chromium present as Cr(VI). With the exception of Cr(total) and in some cases Zn, all elements were below regulatory limits for drinking water. On the basis of Ca, Mg, Cr(total) and Si ground waters were classified into three groups: Group(I) with Cr concentrations less than 1 μg.L-1 from a karstic aquifer; Group(II) with average concentrations of 24 μg.L-1 of Cr and relatively high Si associated with ophiolites; and Group(III) with Cr concentrations of up to 130 μg.L-1, likely due to anthropogenic activity. Group(III) is comparable to ground waters from Assopos basin, characterized by high Cr(VI) concentrations, probably due to industrial actrivities.

Toxic hexavalent chromium reduction by Bacillus pumilis, Cellulosimicrobium cellulans and Exiguobacterium

NASA Astrophysics Data System (ADS)

Rehman, Fatima; Faisal, Muhammad

2015-05-01

Three bacterial strains Bacillus pumilis, Cellulosimicrobium cellulans and Exiguobacterium were investigated when grown in Luria-Bertani (LB) medium at 500 μg/mL Cr(VI). The hexavalent chromium reduction was measured by growing the strains in DeLeo and Ehrlich (1994) medium at 200 and 400 μg/mL K2CrO4. The optimal Cr (VI) reduction by strains B. pumilis, Exigubacterium and C. cellulans was 51%, 39%, and 41%, respectively, at an initial K2CrO4 concentration of 200 μg/mL at pH 3 and temperature 37°C. At an initial chromate concentration of 400 μg/mL, the Cr(VI) reduction by strains B. pumilis, Exigubacterium and C. cellulans was 24%, 19%, and 18%, respectively at pH 3 at 37°C after 24 h. These strains have ability to reduce toxic hexavalent chromium to the less mobile trivalent chromium at a wide range of different environmental conditions and can be useful for the treatment of contaminated wastewater and soils.

Cr(VI) Occurrence and Geochemistry in Water From Public-Supply Wells in California

DOE PAGES

Izbicki, John A.; Wright, Michael T.; Seymour, Whitney A.; ...

2015-08-18

Hexavalent chromium, Cr(VI), in 918 wells sampled throughout California between 2004 and 2012 by the Groundwater Ambient Monitoring and Assessment Program—Priority Basin Project (GAMA—PBP) ranged from less than the study reporting limit (SRL) of 1 microgram per liter (μg/L) to 32 μg/L. Statewide, Cr(VI) was reported in 31 percent of sampled wells and equaled or exceeded the recently established (2014) California Maximum Contaminant Level (MCL) for Cr(VI) of 10 μg/L in 4 percent of sampled wells. Cr(VI) data collected for regulatory purposes overestimate Cr(VI) occurrence. Ninety percent of chromium was present as Cr(VI), which was detected more frequently and atmore » higher concentrations in alkaline (pH > 8), oxic water, and more frequently in agricultural and urban land uses compared to native land uses. Chemical, isotopic (tritium and carbon-14), and noble-gas data show high Cr(VI) in water from wells in alluvial aquifers in the southern California deserts result from long groundwater-residence times and geochemical reactions such as silicate weathering that increase pH, while oxic conditions persist. High Cr(VI) in water from wells in alluvial aquifers along the west-side of the Central Valley results from high-chromium abundance in source rock eroded to form those aquifers, and areal recharge processes (including irrigation return) that mobilize chromium from the unsaturated zone. Cr(VI) co-occurred with oxyanions having similar chemistry, including vanadium, selenium, and uranium. Cr(VI) was positively correlated with nitrate, consistent with increased concentrations in areas of agricultural land use and mobilization of chromium from the unsaturated zone by irrigation return.« less

Cr(VI) occurrence and geochemistry in water from public-supply wells in California

USGS Publications Warehouse

Izbicki, John; Wright, Michael; Seymour, Whitney A.; McCleskey, R. Blaine; Fram, Miranda S.; Belitz, Kenneth; Esser, Bradley K.

2015-01-01

Hexavalent chromium, Cr(VI), in 918 wells sampled throughout California between 2004 and 2012 by the Groundwater Ambient Monitoring and Assessment-Priority Basin Project (GAMA-PBP) ranged from less than the study reporting limit of 1 microgram per liter (μg/L) to 32 μg/L. Statewide, Cr(VI) was reported in 31 percent of wells and equaled or exceeded the recently established (2014) California Maximum Contaminant Level (MCL) for Cr(VI) of 10 μg/L in 4 percent of wells. Cr(VI) data collected for regulatory purposes overestimated Cr(VI) occurrence compared to spatially-distributed GAMA-PBP data. Ninety percent of chromium was present as Cr(VI), which was detected more frequently and at higher concentrations in alkaline (pH ≥ 8), oxic water; and more frequently in agricultural and urban land uses compared to native land uses. Chemical, isotopic (tritium and carbon-14), and noble-gas data show high Cr(VI) in water from wells in alluvial aquifers in the southern California deserts result from long groundwater-residence times and geochemical reactions such as silicate weathering that increase pH, while oxic conditions persist. High Cr(VI) in water from wells in alluvial aquifers along the west-side of the Central Valley results from high-chromium in source rock eroded to form those aquifers, and areal recharge processes (including irrigation return) that can mobilize chromium from the unsaturated zone. Cr(VI) co-occurred with oxyanions having similar chemistry, including vanadium, selenium, and uranium. Cr(VI) was positively correlated with nitrate, consistent with increased concentrations in areas of agricultural land use and mobilization of chromium from the unsaturated zone by irrigation return.

Adsorption behavior comparison of trivalent and hexavalent chromium on biochar derived from municipal sludge.

PubMed

Chen, Tan; Zhou, Zeyu; Xu, Sai; Wang, Hongtao; Lu, Wenjing

2015-08-01

In this work, static equilibrium experiments were conducted to distinguish the adsorption performance between the two valence states of chromium on biochar derived from municipal sludge. The removal capacity of Cr(VI) is lower than 7mg/g at the initial chromium concentration range of 50-200mg/L, whereas that of Cr(III) higher than 20mg/g. It indicates that Cr(III) is much easier to be stabilized than Cr(VI). No significant changes in the biochar surface functional groups are observed before and after the adsorption equilibrium, demonstrating the poor contribution of organic matter in chromium adsorption. The main mechanism of heavy metal adsorption by biochar involves (1) surface precipitation through pH increase caused by biochar buffer ability, and (2) exchange between cations in solution (Cd(2+)) and in biochar matrix (e.g. Ca(2+) and Mg(2+)). The reduction of Cr(VI) to Cr(III) is necessary to improve removal efficiency of chromium. Copyright © 2015 Elsevier Ltd. All rights reserved.

Synergistic effect of chickpea plants and Mesorhizobium as a natural system for chromium phytoremediation.

PubMed

Velez, Pilar A; Talano, Melina A; Paisio, Cintia E; Agostini, Elizabeth; González, Paola S

2017-09-01

The presence of chromium in soils not only affects the physiological processes of plants but also the microbial rhizosphere composition and metabolic activities of microorganisms. Hence, the inoculation of plants with Cr(VI)-tolerant rhizospheric microorganisms as an alternative to reduce Cr phytotoxicity was studied. In this work, chickpea germination was reduced by Cr(VI) concentrations of 150 and 250 mg/L (6 and 33%, respectively); however lower Cr(VI) concentrations negatively affected the biomass. On the other hand, its symbiont, Mesorhizobium ciceri, was able to grow and remove different Cr(VI) concentrations (5-20 mg/L). The inoculation of chickpea plants with this strain exposed to Cr(VI) showed a significantly enhanced plant growth. In addition, inoculated plants accumulated higher Cr concentration in roots than those noninoculated. It is important to note that Cr was not translocated to shoots independently of inoculation. These results suggest that Mesorhizobium's capability to remove Cr(VI) could be exploited for bioremediation. Moreover, chickpea plants would represent a natural system for phytoremediation or phytostabilization of Cr in situ that could be improved with M. ciceri inoculation. This strategy would be considered as a phytoremediation tool with great economic and ecological relevance.

Speciation of Cr(VI) in environmental samples in the vicinity of the ferrochrome smelter.

PubMed

Sedumedi, Hilda N; Mandiwana, Khakhathi L; Ngobeni, Prince; Panichev, Nikolay

2009-12-30

The impact of ferrochrome smelter on the contamination of its environment with toxic hexavalent chromium, Cr(VI), was assessed by analyzing smelter dusts, soil, grass and tree barks. For the separation of Cr(VI) from Cr(III), solid samples were treated with 0.1M Na(2)CO(3) and filtered through hydrophilic PDVF 0.45 microm filter prior to the determination of Cr(VI) by electrothermal atomic absorption spectrometry (ET-AAS). Ferrochrome smelter dust was found to contain significant levels of Cr(VI), viz. 43.5 microg g(-1) (cyclone dust), 2710 microg g(-1) (fine dust), and 7800 microg g(-1) (slimes dust) which exceeded the maximum acceptable risk concentration (20 microg g(-1)). The concentration of Cr(VI) in environmental samples of grass (3.4+/-0.2), soil (7.7+/-0.2), and tree bark (11.8+/-1.2) collected in the vicinity of the chrome smelter were higher as compared with the same kind of samples collected from uncontaminated area. The results of the investigation show that ferrochrome smelter is a source of environmental pollution with contamination factors of Cr(VI) ranging between 10 and 50.

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

Izbicki, John A.; Wright, Michael T.; Seymour, Whitney A.

Hexavalent chromium, Cr(VI), in 918 wells sampled throughout California between 2004 and 2012 by the Groundwater Ambient Monitoring and Assessment Program—Priority Basin Project (GAMA—PBP) ranged from less than the study reporting limit (SRL) of 1 microgram per liter (μg/L) to 32 μg/L. Statewide, Cr(VI) was reported in 31 percent of sampled wells and equaled or exceeded the recently established (2014) California Maximum Contaminant Level (MCL) for Cr(VI) of 10 μg/L in 4 percent of sampled wells. Cr(VI) data collected for regulatory purposes overestimate Cr(VI) occurrence. Ninety percent of chromium was present as Cr(VI), which was detected more frequently and atmore » higher concentrations in alkaline (pH > 8), oxic water, and more frequently in agricultural and urban land uses compared to native land uses. Chemical, isotopic (tritium and carbon-14), and noble-gas data show high Cr(VI) in water from wells in alluvial aquifers in the southern California deserts result from long groundwater-residence times and geochemical reactions such as silicate weathering that increase pH, while oxic conditions persist. High Cr(VI) in water from wells in alluvial aquifers along the west-side of the Central Valley results from high-chromium abundance in source rock eroded to form those aquifers, and areal recharge processes (including irrigation return) that mobilize chromium from the unsaturated zone. Cr(VI) co-occurred with oxyanions having similar chemistry, including vanadium, selenium, and uranium. Cr(VI) was positively correlated with nitrate, consistent with increased concentrations in areas of agricultural land use and mobilization of chromium from the unsaturated zone by irrigation return.« less

Genesis of Cr(VI) in Sri Lankan soils and its adsorptive removal by calcined gibbsite

NASA Astrophysics Data System (ADS)

Rajapaksha, A. U.; Wijesundara, D. M.; Vithanage, M. S.; Ok, Y. S.

2012-12-01

Hexavalent chromium is highly toxic to biota and considered as a priority pollutant. Industrial sources of Cr(VI) include leather tanning, plating, electroplating, anodizing baths, rinse waters, etc. In addition, weathering of ultramafic rocks rich in chromium, such as serpentine, is known to Cr(VI) sources into natural water. The Cr(III) is the most stable in the environment, however, conversion of Cr(III) into Cr(VI) occurs in soil due to presence of naturally occurring minerals such as manganese dioxides. We investigated the amount of Cr(VI) recorded from the soils from anthropogenically and naturally contaminated soils (serpentine soils) in Sri Lanka and the removal efficacy of Cr(VI) by calcined gibbsite (Al oxides). The effect of pH on Cr(VI) adsorption was determined by adjusting the pH in the range of 4-10. In the experiments, the adsorbent concentration was kept at 1 g/l of solution containing 10 mg/l Cr(VI) at 25 0C. Total chromium recorded were around 11,000 mg kg-1 and 6,000 mg kg-1 for serpentine soil and tannery waste-contaminated soil, respectively. Although total Cr was high in the contaminated soils, Cr(VI) concentration was only about 28 mg kg-1 and 210 mg kg-1 in the serpentine and tannery soils, respectively. The calcined gibbsite has maximum adsorption of 85 % around pH 4 and adsorption generally decreased with increase of pH.

Method for in situ or ex situ bioremediation of hexavalent chromium contaminated soils and/or groundwater

DOEpatents

Turick, C.E.; Apel, W.W.

1997-10-28

A method of reducing the concentration of Cr(VI) in a liquid aqueous residue comprises the steps of providing anaerobic Cr(VI) reducing bacteria, mixing the liquid aqueous residue with a nutrient medium to form a mixture, and contacting the mixture with the anaerobic Cr(VI) reducing bacteria such that Cr(VI) is reduced to Cr(III). The anaerobic Cr(VI) reducing bacteria appear to be ubiquitous in soil and can be selected by collecting a soil sample, diluting the soil sample with a sterile diluent to form a diluted sample, mixing the diluted sample with an effective amount of a nutrient medium and an effective amount of Cr(VI) to form a mixture, and incubating the mixture in the substantial absence of oxygen such that growth of Cr(VI) sensitive microorganisms is inhibited and growth of the anaerobic Cr(VI) reducing bacteria is stimulated. A method of in situ bioremediation of Cr(VI) contaminated soil and/or groundwater is also disclosed. 10 figs.

Method for in situ or ex situ bioremediation of hexavalent chromium contaminated soils and/or groundwater

DOEpatents

Turick, Charles E.; Apel, William W.

1997-10-28

A method of reducing the concentration of Cr(VI) in a liquid aqueous residue comprises the steps of providing anaerobic Cr(VI) reducing bacteria, mixing the liquid aqueous residue with a nutrient medium to form a mixture, and contacting the mixture with the anaerobic Cr(VI) reducing bacteria such that Cr(VI) is reduced to Cr(III). The anaerobic Cr(VI) reducing bacteria appear to be ubiquitous in soil and can be selected by collecting a soil sample, diluting the soil sample with a sterile diluent to form a diluted sample, mixing the diluted sample with an effective amount of a nutrient medium and an effective amount of Cr(VI) to form a mixture, and incubating the mixture in the substantial absence of oxygen such that growth of Cr(VI) sensitive microorganisms is inhibited and growth of the anaerobic Cr(VI) reducing bacteria is stimulated. A method of in situ bioremediation of Cr(VI) contaminated soil and/or groundwater is also disclosed.

Removal of Cr(VI) by nanoscale zero-valent iron (nZVI) from soil contaminated with tannery wastes.

PubMed

Singh, Ritu; Misra, Virendra; Singh, Rana Pratap

2012-02-01

The illegal disposal of tannery wastes at Rania, Kanpur has resulted in accumulation of hexavalent chromium [Cr(VI)], a toxic heavy metal in soil posing risk to human health and environment. 27 soil samples were collected at various depths from Rania for the assessment of Cr(VI) level in soil. Out of 27 samples, five samples had shown significant level of Cr(VI) with an average concentration of 15.84 mg Kg(-1). Varied doses of nanoscale zero-valent iron (nZVI) were applied on Cr(VI) containing soil samples for remediation of Cr(VI). Results showed that 0.10 g L(-1) nZVI completely reduces Cr(VI) within 120 min following pseudo first order kinetics. Further, to test the efficacy of nZVI in field, soil windrow experiments were performed at the contaminated site. nZVI showed significant Cr(VI) reduction at field also, indicating it an effective tool for managing sites contaminated with Cr(VI).

Chromium Is Elevated in Fin Whale (Balaenoptera physalus) Skin Tissue and Is Genotoxic to Fin Whale Skin Cells

PubMed Central

Wise, Catherine F.; Wise, Sandra S.; Thompson, W. Douglas; Perkins, Christopher; Wise, John Pierce

2015-01-01

Hexavalent chromium (Cr(VI)) is present in the marine environment and is a known carcinogen and reproductive toxicant. Cr(VI) is the form of chromium that is well absorbed through the cell membrane. It is also the most prevalent form in seawater. We measured the total Cr levels in skin biopsies obtained from healthy free-ranging fin whales from the Gulf of Maine and found elevated levels relative to marine mammals in other parts of the world. The levels in fin whale biopsies ranged from 1.71 ug/g to 19.6 ug/g with an average level of 10.07 ug/g. We also measured the cytotoxicity and genotoxicity of Cr(VI) in fin whale skin cells. We found that particulate and soluble Cr(VI) are both cytotoxic and genotoxic to fin whale skin cells in a concentration-dependent manner. The concentration range used in our cell culture studies used environmentally relevant concentrations based on the biopsy measurements. These data suggest that Cr(VI) may be a concern for whales in the Gulf of Maine. PMID:25805270

Microbial Fuel Cell Inoculated with Ochrobactrum Tritici KCC210 for Chromium (VI) Measurement in Electroplating Wastewater

NASA Astrophysics Data System (ADS)

Kuo, Jongtar; Kuo, Juiling; Cheng, Chiuyu; Chung, Yingchien

2018-01-01

Many methods/techniques have been developed for Cr(VI) measurement, but they are often conducted offsite or/and cannot provide real-time for Cr(VI) monitoring. A microbial fuel cell (MFC) is a self-sustaining device and has great potential as a biosensor for in situ Cr(VI) measurement, especially for wastewater generated from different electroplating units. In this study, Ochrobactrum tritici KCC210, a facultatively anaerobic, Cr(VI)-reducing, and exoelectrogenic bacterium, was isolated and inoculated into the MFC to evaluate its feasibility as a Cr(VI) biosensor. The results indicated that O. tritici KCC210 exhibited high adaptability to pH, and temperature under anaerobic conditions. The maximum power density of the MFC biosensor was 17.5±0.9 mW/m2 at 2,000 Ω. A good linear relationship was observed between the Cr(VI) concentration (10-80 mg/L) and voltage output. The stable performance of the MFC biosensor indicated its potential as a reliable biosensor system. Moreover, the developed MFC biosensor is a simple device that can accurately measure Cr(VI) concentrations in the actual electroplating wastewater generated from different electroplating units within 15 min with low deviations (-1.8% to 7.8%) in comparison with the values determined using standard method. Thus, the MFC biosensor can measure Cr(VI) concentrations in situ in the effluents and has potential as an early warning detection device.

Nitrification inhibition by hexavalent chromium Cr(VI)--Microbial ecology, gene expression and off-gas emissions.

PubMed

Kim, Young Mo; Park, Hongkeun; Chandran, Kartik

2016-04-01

The goal of this study was to investigate the responses in the physiology, microbial ecology and gene expression of nitrifying bacteria to imposition of and recovery from Cr(VI) loading in a lab-scale nitrification bioreactor. Exposure to Cr(VI) in the reactor strongly inhibited nitrification performance resulting in a parallel decrease in nitrate production and ammonia consumption. Cr(VI) exposure also led to an overall decrease in total bacterial concentrations in the reactor. However, the fraction of ammonia oxidizing bacteria (AOB) decreased to a greater extent than the fraction of nitrite oxidizing bacteria (NOB). In terms of functional gene expression, a rapid decrease in the transcript concentrations of amoA gene coding for ammonia oxidation in AOB was observed in response to the Cr(VI) shock. In contrast, transcript concentrations of the nxrA gene coding for nitrite oxidation in NOB were relatively unchanged compared to Cr(VI) pre-exposure levels. Therefore, Cr(VI) exposure selectively and directly inhibited activity of AOB, which indirectly resulted in substrate (nitrite) limitation to NOB. Significantly, trends in amoA expression preceded performance trends both during imposition of and recovery from inhibition. During recovery from the Cr(VI) shock, the high ammonia concentrations in the bioreactor resulted in an irreversible shift towards AOB populations, which are expected to be more competitive in high ammonia environments. An inadvertent impact during recovery was increased emission of nitrous oxide (N2O) and nitric oxide (NO), consistent with recent findings linking AOB activity and the production of these gases. Therefore, Cr(VI) exposure elicited multiple responses on the microbial ecology, gene expression and both aqueous and gaseous nitrogenous conversion in a nitrification process. A complementary interrogation of these multiple responses facilitated an understanding of both direct and indirect inhibitory impacts on nitrification. Copyright © 2016 Elsevier Ltd. All rights reserved.

Distribution of chromium species in a Cr-polluted soil: presence of Cr(III) in glomalin related protein fraction.

PubMed

Gil-Cardeza, María L; Ferri, Alejandro; Cornejo, Pablo; Gomez, Elena

2014-09-15

The accumulation of Cr in soil could be highly toxic to human health; therefore Cr soil distribution was studied in rhizosphere soils from Ricinus communis and Conium maculatum and bare soil (BS) from an industrial and urban area in Argentina. Total Cr, Cr(VI) and Cr(III) concentrations were determined in 3 soil fractions: total, extractable and associated to total-glomalin-related protein (T-GRSP). BS had the highest total Cr and total Cr(VI) concentrations. Total Cr(VI) concentration from both rhizosphere soils did not differ from the allowed value for residential area in Argentina (8 μg Cr(VI) g(-1) soil), while total Cr(VI) in BS was 1.8 times higher. Total Cr concentration in all the soils was higher than the allowed value (250 μg Cr g(-1) soil). Extractable and associated to T-GRSP Cr(VI) concentrations were below the detection limit. Cr(III) bound to T-GRSP was the highest in the BS. These findings are in agreement with a long term effect of glomalin in sequestrating Cr. In both plant species, total Cr was higher in root than in shoot and both species presented arbuscular mycorrhizal fungi (AMF). As far as we know, this is the first study that reports the presence of Cr in T-GRSP fraction of soil organic matter. These findings suggest that Cr mycorrhizostabilization could be a predominant mechanism used by R. communis and C. maculatum to diminish Cr soil concentration. Nevertheless, further research is needed to clarify the contribution of native AMF isolated from R. communis and C. maculatum rhizosphere to the Cr phytoremediation process. Copyright © 2014 Elsevier B.V. All rights reserved.

Environmental status of groundwater affected by chromite ore processing residue (COPR) dumpsites during pre-monsoon and monsoon seasons.

PubMed

Matern, Katrin; Weigand, Harald; Singh, Abhas; Mansfeldt, Tim

2017-02-01

Chromite ore processing residue (COPR) is generated by the roasting of chromite ores for the extraction of chromium. Leaching of carcinogenic hexavalent chromium (Cr(VI)) from COPR dumpsites and contamination of groundwater is a key environmental risk. The objective of the study was to evaluate Cr(VI) contamination in groundwater in the vicinity of three COPR disposal sites in Uttar Pradesh, India, in the pre-monsoon and monsoon seasons. Groundwater samples (n = 57 pre-monsoon, n = 70 monsoon) were taken in 2014 and analyzed for Cr(VI) and relevant hydrochemical parameters. The site-specific ranges of Cr(VI) concentrations in groundwater were <0.005 to 34.8 mg L -1 (Rania), <0.005 to 115 mg L -1 (Chhiwali), and <0.005 to 2.0 mg L -1 (Godhrauli). Maximum levels of Cr(VI) were found close to the COPR dumpsites and significantly exceeded safe drinking water limits (0.05 mg L -1 ). No significant dependence of Cr(VI) concentration on monsoons was observed.

Integrated Cr(VI) removal using constructed wetlands and composting.

PubMed

Sultana, Mar-Yam; Chowdhury, Abu Khayer Md Muktadirul Bari; Michailides, Michail K; Akratos, Christos S; Tekerlekopoulou, Athanasia G; Vayenas, Dimitrios V

2015-01-08

The present work was conducted to study integrated chromium removal from aqueous solutions in horizontal subsurface (HSF) constructed wetlands. Two pilot-scale HSF constructed wetlands (CWs) units were built and operated. One unit was planted with common reeds (Phragmites australis) and one was kept unplanted. Influent concentrations of Cr(VI) ranged from 0.5 to 10mg/L. The effect of temperature and hydraulic residence time (8-0.5 days) on Cr(VI) removal were studied. Temperature was proved to affect Cr(VI) removal in both units. In the planted unit maximum Cr(VI) removal efficiencies of 100% were recorded at HRT's of 1 day with Cr(VI) concentrations of 5, 2.5 and 1mg/L, while a significantly lower removal rate was recorded in the unplanted unit. Harvested reed biomass from the CWs was co-composted with olive mill wastes. The final product had excellent physicochemical characteristics (C/N: 14.1-14.7, germination index (GI): 145-157%, Cr: 8-10mg/kg dry mass), fulfills EU requirements and can be used as a fertilizer in organic farming. Copyright © 2014 Elsevier B.V. All rights reserved.

Dynamics of Chromium(VI) Removal from Drinking Water by Iron Electrocoagulation.

PubMed

Pan, Chao; Troyer, Lyndsay D; Catalano, Jeffrey G; Giammar, Daniel E

2016-12-20

The potential for new U.S. regulations for Cr(VI) in drinking water have spurred strong interests in improving technologies for Cr(VI) removal. This study examined iron electrocoagulation for Cr(VI) removal at conditions directly relevant to drinking water treatment. Cr(VI) is chemically reduced to less soluble Cr(III) species by the Fe(II) produced from an iron anode, and XANES spectra indicate that the Cr is entirely Cr(III) in solid-phases produced in electrocoagulation. The dynamics of Cr(VI) removal in electrocoagulation at pH 6 and pH 8 at both oxic and anoxic conditions can be described by a new model that incorporates Fe(II) release from the anode and heterogeneous and homogeneous reduction of Cr(VI) by Fe(II). Heterogeneous Cr(VI) reduction by adsorbed Fe(II) was critical to interpreting Cr(VI) removal at pH 6, and the Fe- and Cr-containing EC product was found to catalyze the redox reaction. Dissolved oxygen (DO) did not observably inhibit Cr(VI) removal because Fe(II) reacts with DO more slowly than it does with Cr(VI), and Cr(VI) removal was faster at higher pH. Even in the presence of common groundwater solutes, iron electrocoagulation lowered Cr(VI) concentrations to levels well below California's 10 μg/L.

Assessment of electrokinetic removal of heavy metals from soils by sequential extraction analysis.

PubMed

Reddy, K R; Xu, C Y; Chinthamreddy, S

2001-06-29

Electrokinetic remediation of metal-contaminated soils is strongly affected by soil-type and chemical species of contaminants. This paper investigates the speciation and extent of migration of heavy metals in soils during electrokinetic remediation. Laboratory electrokinetic experiments were conducted using two diverse soils, kaolin and glacial till, contaminated with chromium as either Cr(III) or Cr(VI). Initial total chromium concentrations were maintained at 1000mg/kg. In addition, Ni(II) and Cd(II) were used in concentrations of 500 and 250mg/kg, respectively. The contaminated soils were subjected to a voltage gradient of 1 VDC/cm for over 200h. The extent of migration of contaminants after the electric potential application was determined. Sequential extractions were performed on the contaminated soils before and after electrokinetic treatment to provide an understanding of the distribution of the contaminants in the soils. The initial speciation of contaminants was found to depend on the soil composition as well as the type and amounts of different contaminants present. When the initial form of chromium was Cr(III), exchangeable and soluble fractions of Cr, Ni, and Cd ranged from 10 to 65% in kaolin; however, these fractions ranged from 0 to 4% in glacial till. When the initial form of chromium was Cr(VI), the exchangeable and soluble fractions of Cr, Ni and Cd ranged from 66 to 80% in kaolin. In glacial till, however, the exchangeable and soluble fraction for Cr was 38% and Ni and Cd fractions were 2 and 10%, respectively. The remainder of the contaminants existed as the complex and precipitate fractions. During electrokinetic remediation, Cr(VI) migrated towards the anode, whereas Cr(III), Ni(II) and Cd(II) migrated towards the cathode. The speciation of contaminants after electrokinetic treatment showed that significant change in exchangeable and soluble fractions occurred. In kaolin, exchangeable and soluble Cr(III), Ni(II), and Cd(II) decreased near the anode and increased near the cathode, whereas exchangeable and soluble Cr(VI) decreased near the cathode and increased near the anode. In glacial till, exchangeable and soluble Cr(III), Ni(II), and Cd(II) were low even before electrokinetic treatment and no significant changes were observed after the electrokinetic treatment. However, significant exchangeable and soluble Cr(VI) that was present in glacial till prior to electrokinetic treatment decreased to non-detectable levels near the cathode and increased significantly near the anode. In both kaolin and glacial till, low migration rates occurred as a result of contaminants existing as immobile complexes and precipitates. The overall contaminant removal efficiency was very low (less than 20%) in all tests.

Kinetic and thermodynamic studies on the adsorption of heavy metals from aqueous solution by melanin nanopigment obtained from marine source: Pseudomonas stutzeri.

PubMed

Manirethan, Vishnu; Raval, Keyur; Rajan, Reju; Thaira, Harsha; Balakrishnan, Raj Mohan

2018-05-15

The difficulty in removal of heavy metals at concentrations below 10 mg/L has led to the exploration of efficient adsorbents for removal of heavy metals. The adsorption capacity of biosynthesized melanin for Mercury (Hg(II)), Chromium (Cr(VI)), Lead (Pb(II)) and Copper (Cu(II)) was investigated at different operating conditions like pH, time, initial concentration and temperature. The heavy metals adsorption process was well illustrated by the Lagergren's pseudo-second-order kinetic model and the equilibrium data fitted excellently to Langmuir isotherm. Maximum adsorption capacity obtained from Langmuir isotherm for Hg(II) was 82.4 mg/g, Cr(VI) was 126.9 mg/g, Pb(II) was 147.5 mg/g and Cu(II) was 167.8 mg/g. The thermodynamic parameters revealed that the adsorption of heavy metals on melanin is favorable, spontaneous and endothermic in nature. Binding of heavy metals on melanin surface was proved by Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). Contemplating the results, biosynthesized melanin can be a potential adsorbent for efficient removal of Hg(II), Cr(VI), Pb(II) and Cu(II) ions from aqueous solution. Copyright © 2018 Elsevier Ltd. All rights reserved.

Effect of trace metals and electron shuttle on simultaneous reduction of reactive black-5 azo dye and hexavalent chromium in liquid medium by Pseudomonas sp.

PubMed

Mahmood, Shahid; Khalid, Azeem; Arshad, Muhammad; Ahmad, Riaz

2015-11-01

This study demonstrates the role of electron shuttles and trace metals in the biotransformation of azo dye reactive black-5 and hexavalent chromium (CrVI) that are released simultaneously in tannery effluent. Previously isolated bacterial strain Pseudomonas putida KI was used for the simultaneous reduction of the dye (100 mg L(-1)) and CrVI (2 mg L(-1)) in a mineral salts medium (MSM). Among various trace metals, only Cu(II) had a stimulating effect on the bacterial-mediated reduction process. Application of electron shuttles such as hydroquinone and uric acid at a low concentration (1mM) had a positive effect on the reduction process and caused simultaneous reduction of 100% dye and 97% CrVI in 12-18 h. Mannitol, EDTA and sodium benzoate at all concentrations (ranging from 1 to 9 mM) showed an inhibitory effect on the reduction of reactive black-5 and CrVI. An inverse linear relationship between the velocity of reaction (V) and the concentration [S] of electron shuttles was observed. The results imply that both types and concentration of an electron shuttle and trace metals can affect the simultaneous reduction of reactive black-5 and CrVI. Copyright © 2014 Elsevier Ltd. All rights reserved.

Reduction of Hexavalent Chromium and Detection of Chromate Reductase (ChrR) in Stenotrophomonas maltophilia.

PubMed

Baldiris, Rosa; Acosta-Tapia, Natali; Montes, Alfredo; Hernández, Jennifer; Vivas-Reyes, Ricardo

2018-02-13

An Gram negative strain of S. maltophilia , indigenous to environments contaminated by Cr(VI) and identified by biochemical methods and 16S rRNA gene analysis, reduced chromate by 100%, 98-99% and 92% at concentrations in the 10-70, 80-300, and 500 mg/L range, respectively at pH 7 and temperature 37 °C. Increasing concentrations of Cr(VI) in the medium lowered the growth rate but could not be directly correlated with the amount of Cr(VI) reduced. The strain also exhibited multiple resistance to antibiotics and tolerance and resistance to various heavy metals (Ni, Zn and Cu), with the exception of Hg. Hexavalent chromium reduction was mainly associated with the soluble fraction of the cell evaluated with crude cell-free extracts. A protein of molecular weight around 25 kDa was detected on SDS-PAGE gel depending on the concentration of hexavalent chromium in the medium (0, 100 and 500 mg/L). In silico analysis in this contribution, revealed the presence of the chromate reductase gene ChrR in S. maltophilia , evidenced through a fragment of around 468 bp obtained experimentally. High Cr(VI) concentration resistance and high Cr(VI) reducing ability of the strain make it a suitable candidate for bioremediation.

Biomarkers of oxidative stress in electroplating workers exposed to hexavalent chromium.

PubMed

Pan, Chih-Hong; Jeng, Hueiwang Anna; Lai, Ching-Huang

2018-01-01

This study evaluates levels of biomarkers of oxidative DNA damage and lipid peroxidation in 105 male workers at 16 electroplating companies who had been exposed to hexavalent chromium (Cr(VI)). The study participants were 230 non-smoking male workers, comprising 105 electroplating workers who had been exposed to chromium and 125 control subjects who performed office tasks. Personal air samples, spot urine samples, hair samples, fingernail samples and questionnaires were used to quantify exposure to Cr(VI), oxidative DNA damage, lipid peroxidation, and environmental pollutants. Both the geometric mean personal concentrations of Cr(VI) of the Cr-exposed workers and the total Cr concentrations in the air to which they were exposed significantly exceeded those for the control subjects. The geometric mean concentrations of Cr in urine, hair and fingernails, and the urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), and malondialdehyde (MDA) levels in the Cr(VI) exposed workers exceeded those in the control subjects. Daily cumulative Cr(VI) exposure and urinary Cr were significantly correlated with urinary 8-OHdG levels following adjustments for covariates. A ten-fold increase in urinary Cr level was associated with a 1.73-fold increase in urinary 8-OHdG level. Daily cumulative Cr(VI) exposure and urinary Cr level were significantly correlated with urinary MDA level following adjustments for covariates. A ten-fold increase in urinary Cr was associated with a 1.45-fold increase in urinary MDA. Exposure to Cr(VI) increased oxidative DNA injury and the oxidative deterioration of lipids in electroplating workers.

Soil retention of hexavalent chromium released from construction and demolition waste in a road-base-application scenario.

PubMed

Butera, Stefania; Trapp, Stefan; Astrup, Thomas F; Christensen, Thomas H

2015-11-15

We investigated the retention of Cr(VI) in three subsoils with low organic matter content in laboratory experiments at concentration levels relevant to represent leachates from construction and demolition waste (C&DW) reused as unbound material in road construction. The retention mechanism appeared to be reduction and subsequent precipitation as Cr(III) on the soil. The reduction process was slow and in several experiments it was still proceeding at the end of the six-month experimental period. The overall retention reaction fit well with a second-order reaction governed by actual Cr(VI) concentration and reduction capacity of the soil. The experimentally determined reduction capacities and second-order kinetic parameters were used to model, for a 100-year period, the one-dimensional migration of Cr(VI) in the subsoil under a layer of C&DW. The resulting Cr(VI) concentration would be negligible below 7-70 cm depth. However, in rigid climates and with high water infiltration through the road pavement, the reduction reaction could be so slow that Cr(VI) might migrate as deep as 200 cm under the road. The reaction parameters and the model can form the basis for systematically assessing under which scenarios Cr(VI) from C&DW could lead to an environmental issue for ground- and receiving surface waters. Copyright © 2015 Elsevier B.V. All rights reserved.

Simultaneous chromate and sulfate removal by Streptomyces sp. MC1. Changes in intracellular protein profile induced by Cr(VI).

PubMed

Bonilla, José Oscar; Callegari, Eduardo Alberto; Delfini, Claudio Daniel; Estevez, María Cristina; Villegas, Liliana Beatriz

2016-11-01

The purpose of this study was to investigate the influence of increasing sulfate concentrations on chromium removal, to evaluate the effect of the presence of Cr(VI) on sulfate removal by Streptomyces sp. MC1 and to analyze the differential protein expression profile in the presence of this metal for the identification of proteins repressed or overexpressed. In the presence of Cr(VI) but in the absence of sulfate ions, bacterial growth was negligible, showing the Cr(VI) toxicity for this bacterium. However, the sulfate presence stimulated bacterium growth and Cr(VI) removal, regardless of its concentrations. Streptomyces sp. MC1 showed ability to remove chromium and sulfate simultaneously. Also, the sulfate presence favored the decrease of total chromium concentration from supernatants reaching a decrease of 50% at 48 h. In presence of chromium, seven proteins were down-expressed and showed homology to proteins involved in protein biosynthesis, energy production and free radicals detoxification while two proteins involved in oxidation-reduction processes identified as dihydrolipoamide dehydrogenase and S-adenosyl-l-methionine synthase were overexpressed. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electroreduction of Cr(VI) to Cr(III) on reticulated vitreous carbon electrodes in a parallel-plate reactor with recirculation.

PubMed

Rodriguez-Valadez, Francisco; Ortiz-Exiga, Carlos; Ibanez, Jorge G; Alatorre-Ordaz, Alejandro; Gutierrez-Granados, Silvia

2005-03-15

The reduction of Cr(VI) to Cr(III) is achieved in a flow-by, parallel-plate reactor equipped with reticulated vitreous carbon (RVC) electrodes;this reduction can be accomplished by the application of relatively small potentials. Treatment of synthetic samples and field samples (from an electrodeposition plant) results in final Cr(VI) concentrations of 0.1 mg/L (i.e., the detection limit of the UV-vis characterization technique used here) in 25 and 43 min, respectively. Such concentrations comply with typical environmental legislation for wastewaters that regulate industrial effluents (at presenttime = 0.5 mg/L for discharges). The results show the influence of the applied potential, pH, electrode porosity, volumetric flow, and solution concentration on the Cr(VI) reduction percentage and on the required electrolysis time. Values for the mass transfer coefficient and current efficiencies are also obtained. Although current efficiencies are not high, the fast kinetics observed make this proposed treatment an appealing alternative. The lower current efficiency obtained in the case of a field sample is attributed to electrochemical activation of impurities. The required times for the reduction of Cr(VI) are significantly lower than those reported elsewhere.

Environmental conditions affecting exopolysaccharide production by Pseudomonas aeruginosa, Micrococcus sp., and Ochrobactrum sp.

PubMed

Kiliç, Nur Koçberber; Dönmez, Gönül

2008-06-15

Three different chromium-resistant microorganisms (Pseudomonas aeruginosa, Micrococcus sp., and Ochrobactrum sp.) were tested with regard to their EPS production at different pH levels, temperatures, Cr(VI) concentrations, and incubation periods. The optimum pH level was 7 for P. aeruginosa and Micrococcus sp., while it was 8 for Ochrobactrum sp. according to the highest EPS amount at 100 mg/L Cr(VI) concentration. The highest production of EPSs by the three bacteria was obtained under different environmental conditions. P. aeruginosa produced the highest EPS (863.3 mg/L) after incubation for 96 h on media with 50 mg/L Cr(VI) at 20 degrees C, Micrococcus sp. gave the highest yield (444.6 mg/L) after incubation for 72 h on media with 100 mg/L Cr(VI) at the same temperature, and Ochrobactrum sp. had the highest production (430.5 mg/L) on media with 150 mg/L Cr(VI) at 30 degrees C at the end of 48 h of incubation.

Hexavalent chromium content in stainless steel welding fumes is dependent on the welding process and shield gas type.

PubMed

Keane, Michael; Stone, Samuel; Chen, Bean; Slaven, James; Schwegler-Berry, Diane; Antonini, James

2009-02-01

Occupational exposure to welding fumes is a known health hazard. To isolate elements in stainless steel welding fumes with high potential for adverse health outcomes, fumes were generated using a robotic gas metal arc system, using four shield gases of varying oxygen content. The objective was to measure Cr(VI) concentrations in a broad spectrum of gas metal arc welding processes, and identify processes of exceptionally high or low Cr(VI) content. The gases used were 95% Ar/5% O(2), 98% Ar/2% O(2), 95% Ar/5%CO(2), and 75% He/25% Ar. The welder was operated in axial spray mode (Ar/O(2), Ar/CO(2)), short-circuit (SC) mode (Ar/CO(2) low voltage and He/Ar), and pulsed axial-spray mode (98% Ar/2% O(2)). Results indicate large differences in Cr(VI) in the fumes, with Ar/O(2) (Pulsed)>Ar/O(2)>Ar/CO(2)>Ar/CO(2) (SC)>He/Ar; values were 3000+/-300, 2800+/-85, 2600+/-120, 1400+/-190, and 320+/-290 ppm respectively (means +/- standard errors for 2 runs and 3 replicates per run). Respective rates of Cr(VI) generation were 1.5, 3.2, 4.4, 1.3, and 0.46 microg/min; generation rates were also calculated in terms of microg Cr(VI) per metre of wire used. The generation rates of Cr(VI) increased with increasing O(3) concentrations. Particle size measurements indicated similar distributions, but somewhat higher >0.6 microm fractions for the short-circuit mode samples. Fumes were also sampled into 2 selected size ranges, a microspatter fraction (>or=0.6 microm) and a fine (<0.6 microm) fraction; analysis indicated that Cr(VI) is primarily associated with particles <0.6 microm. The conclusion of the study is that Cr(VI) concentrations vary significantly with welding type and shield gas type, and this presents an opportunity to tailor welding practices to lessen Cr(VI) exposures in workplaces by selecting low Cr(VI)-generating processes. Short-circuit processes generated less Cr(VI) than axial-spray methods, and inert gas shielding gave lower Cr(VI) content than shielding with active gases. A short circuit He/Ar shielded process and a pulsed axial spray Ar/O(2) process were both identified as having substantially lower Cr(VI) generation rates per unit of wire used relative to the other processes studied.

Treatment of Cr(VI)-containing wastewaters with exopolysaccharide-producing cyanobacteria in pilot flow through and batch systems.

PubMed

Colica, Giovanni; Mecarozzi, Pier Cesare; De Philippis, Roberto

2010-08-01

Seven exopolysaccharide-producing cyanobacteria were tested with regard to their capability to remove Cr(VI) from the wastewater of a plating industry. The cyanobacterium which showed, under lab conditions, the most promising features with regard to both Cr(VI) removal (about 12 mg of Cr(VI) removed per gram of dry biomass) and growth characteristics (highest growth rate and simplest culture medium) was Nostoc PCC7936. Furthermore, in lab experiments, it was also found that a HCl pretreatment is essential to abate the concentration of Cr(VI) in solution and that the viability of the biomass is not necessary. Subsequently, three pilot devices were tested, one batch (a dialysis cell) and two flow-through systems (a filter press and a column filled with quartz grain). The best performances were obtained with the filter press, where it was observed a sharp decrease in the concentration of Cr(VI), partly due to the adsorption of the metal by the biomass (about 50%) and partly due to its reduction to Cr(III). The results are discussed in terms of the role played by the different components (biomass and polysaccharide) of the cyanobacterial cultures in the removal of Cr(VI).

Mobilization of Cr(VI) from chromite ore processing residue through acid treatment.

PubMed

Tinjum, James M; Benson, Craig H; Edil, Tuncer B

2008-02-25

Batch leaching studies on chromite ore processing residue (COPR) were performed using acids to investigate leaching of hexavalent chromium, Cr(VI), with respect to particle size, reaction time, and type of acid (HNO(3) and H(2)SO(4)). Aqueous Cr(VI) is maximized at approximately 0.04 mol Cr(VI) per kg of dry COPR at pH 7.6-8.1. Cr(VI) mobilized more slowly for larger particles, and the pH increased with time and increased more rapidly for smaller particles, suggesting that rate limitations occur in the solid phase. With H(2)SO(4), the pH stabilized at a higher value (8.8 for H(2)SO(4) vs. 8.0 for HNO(3)) and more rapidly (16 h vs. 30 h), and the differences in pH for different particle sizes were smaller. The acid neutralization capacity (ANC) of COPR is very large (8 mol HNO(3) per kg of dry COPR for a stable eluate pH of 7.5). Changes to the elemental and mineralogical composition and distribution in COPR particles after mixing with acid indicate that Cr(VI)-bearing solids dissolved. However, concentrations of Cr(VI) >2800 mg kg(-1) (>50% of the pre-treatment concentration) were still found after mixing with acid, regardless of the particle size, reaction time, or type of acid used. The residual Cr(VI) appears to be partially associated with poorly-ordered Fe and Al oxyhydroxides that precipitated in the interstitial areas of COPR particles. Remediation strategies that use HNO(3) or H(2)SO(4) to neutralize COPR or to maximize Cr(VI) in solution are likely to require extensive amounts of acid, may not mobilize all of the Cr(VI), and may require extended contact time, even under well-mixed conditions.

Removal of Cr(VI) from Water Using a New Reactive Material: Magnesium Oxide Supported Nanoscale Zero-Valent Iron

PubMed Central

Siciliano, Alessio

2016-01-01

The chromium pollution of water is an important environmental and health issue. Cr(VI) removal by means of metallic iron is an attractive method. Specifically, nanoscopic zero valent iron (NZVI) shows great reactivity, however, its applicability needs to be further investigated. In the present paper, NZVI was supported on MgO grains to facilitate the treatments for remediation of chromium-contaminated waters. The performances and mechanisms of the developed composite, in the removal of hexavalent chromium, were investigated by means of batch and continuous tests. Kinetic studies, under different operating conditions, showed that reduction of Cr(VI) could be expressed by a pseudo second-order reaction kinetic. The reaction rate increased with the square of Fe(0) amount, while it was inversely proportional to the initial chromium concentration. The process performance was satisfactory also under uncontrolled pH, and a limited influence of temperature was observed. The reactive material was efficiently reusable for many cycles without any regeneration treatment. The performances in continuous tests were close to 97% for about 80 pore volume of reactive material. PMID:28773785

Removal of Cr(VI) from Water Using a New Reactive Material: Magnesium Oxide Supported Nanoscale Zero-Valent Iron.

PubMed

Siciliano, Alessio

2016-08-06

The chromium pollution of water is an important environmental and health issue. Cr(VI) removal by means of metallic iron is an attractive method. Specifically, nanoscopic zero valent iron (NZVI) shows great reactivity, however, its applicability needs to be further investigated. In the present paper, NZVI was supported on MgO grains to facilitate the treatments for remediation of chromium-contaminated waters. The performances and mechanisms of the developed composite, in the removal of hexavalent chromium, were investigated by means of batch and continuous tests. Kinetic studies, under different operating conditions, showed that reduction of Cr(VI) could be expressed by a pseudo second-order reaction kinetic. The reaction rate increased with the square of Fe(0) amount, while it was inversely proportional to the initial chromium concentration. The process performance was satisfactory also under uncontrolled pH, and a limited influence of temperature was observed. The reactive material was efficiently reusable for many cycles without any regeneration treatment. The performances in continuous tests were close to 97% for about 80 pore volume of reactive material.

Reduction of hexavalent chromium in water samples acidified for preservation

USGS Publications Warehouse

Stollenwerk, K.G.; Grove, D.B.

1985-01-01

Reduction of hexavalent chromium, Cr(VI), in water samples, preserved by standard techniques, was investigated. The standard preservation technique for water samples that are to be analyzed for Cr(VI) consists of filtration through a 0.45-??m membrane, acidification to a pH < 2, and storage in plastic bottles. Batch experiments were conducted to evaluate the effect of H+ concentration, NO2, temperature, and dissolved organic carbon (DOC) on the reduction of Cr(VI) to Cr(III). The rate of reduction of Cr(VI) to Cr(III) increased with increasing NO2, DOC, H+, and temperature. Reduction of Cr(VI) by organic matter occurred in some samples even though the samples were unacidified. Reduction of Cr(VI) is inhibited to an extent by storing the sample at 4??C. Stability of Cr(VI) in water is variable and depends on the other constituents present in the sample. Water samples collected for the determination of Cr(VI) should be filtered (0.45-??m membrane), refrigerated, and analyzed as quickly as possible. Water samples should not be acidified. Measurement of total Cr in addition to Cr(VI) can serve as a check for Cr(VI) reduction. If total Cr is greater than Cr(VI), the possibility that Cr(VI) reduction has occurred needs to be considered.The rate of reduction of Cr(VI) to Cr(III) increased with increasing NO//2, DOC, H** plus , and temperature. Reduction of Cr(VI) by organic matter occurred in some samples even though the samples were unacidified. Reduction of Cr(VI) is inhibited to an extent by storing the sample at 4 degree C. Stability of Cr(VI) in water is variable and depends on the other constituents present in the sample. Water samples collected for the determination of Cr(VI) should be filtered (0. 45- mu m membrane), refrigerated, and analyzed as quickly as possible. Water samples should not be acidified. Measurement of total Cr in addition to Cr(VI) can serve as a check for Cr(VI) reduction. If total Cr is greater than Cr(VI), the possibility that Cr(VI) reduction has occurred needs to be considered.

Reduction and removal of Cr(VI) from aqueous solutions using modified byproducts of beer production.

PubMed

Cui, Haojie; Fu, Minglai; Yu, Shen; Wang, Ming Kuang

2011-02-28

Biosorption, as an effective and low-cost technology treating industrial wastewaters containing Cr(VI), has become a significant concern worldwide. In this work, acid-modified byproducts of beer production (BBP) were used to remove Cr(VI) from aqueous solutions. Removal of Cr(VI) increases as the pH is decreased from 4.0 to 1.5, but the maximum of total Cr removal is obtained in a pH range from 2.0 to 2.5. Nearly 60% of the initial Cr(VI) (100 mg L(-1)) was adsorbed or reduced to Cr(III) within the first 10 min at pH 2.0. The Cr(VI) removal capability of acid-modified BBP materials was almost completely retained after regenerating with acid. FT-IR and XPS spectra revealed that carboxylate and carboxyl groups on the surface of modified BBP materials play a major role in Cr(VI) binding and reduction, whereas amide and other groups play a minor role in the Cr(VI) removal process. Copyright © 2010 Elsevier B.V. All rights reserved.

Toxic effect of Cr(VI) in presence of n-TiO2 and n-Al2O3 particles towards freshwater microalgae.

PubMed

Dalai, Swayamprava; Pakrashi, Sunandan; Bhuvaneshwari, M; Iswarya, V; Chandrasekaran, N; Mukherjee, Amitava

2014-01-01

The reactivity and toxicity of the soluble toxicants in the presence of the engineered nanomaterials is not well explored. In this study, the probable effects of TiO2 and Al2O3 nanoparticles (n-TiO2, n-Al2O3) on the toxicity of Cr(VI) were assessed with the dominant freshwater algae, Scenedesmus obliquus, in a low range of exposure concentrations (0.05, 0.5 and 1μg/mL). In the presence of 0.05μg/mL n-TiO2, the toxicity of Cr(VI) decreased considerably, which was presumably due to the Cr(VI) adsorption on the nanoparticle surface leading to its aggregation and precipitation. The elevated n-TiO2 concentrations (0.5 and 1μg/mL) did not significantly influence Cr(VI) bio-availability, and a dose dependent toxicity of Cr(VI) was observed. On the other hand, n-Al2O3 did not have any significant effect on the Cr(VI) toxicity. The microscopic observations presented additional information on the morphological changes of the algal cells in the presence of the binary toxicants. The generation of reactive oxygen species (ROS) suggested contribution of oxidative stress on toxicity and LDH release confirmed membrane permeability of algal cells upon stress. Copyright © 2013 Elsevier B.V. All rights reserved.

Accelerated redox reaction between chromate and phenolic pollutants during freezing.

PubMed

Ju, Jinjung; Kim, Jaesung; Vetráková, Ľubica; Seo, Jiwon; Heger, Dominik; Lee, Changha; Yoon, Ho-Il; Kim, Kitae; Kim, Jungwon

2017-05-05

The redox reaction between 4-chlorophenol (4-CP) and chromate (Cr(VI)) (i.e., the simultaneous oxidation of 4-CP by Cr(VI) and reduction of Cr(VI) by 4-CP) in ice (i.e., at -20°C) was compared with the corresponding reaction in water (i.e., at 25°C). The redox conversion of 4-CP/Cr(VI), which was negligible in water, was significantly accelerated in ice. This accelerated redox conversion of 4-CP/Cr(VI) in ice is ascribed to the freeze concentration effect occurring during freezing, which excludes solutes (i.e., 4-CP and Cr(VI)) and protons from the ice crystals and subsequently concentrates them in the liquid brine. The concentrations of Cr(VI) and protons in the liquid brine were confirmed by measuring the optical image and the UV-vis absorption spectra of cresol red (CR) as a pH indicator of frozen solution. The redox conversion of 4-CP/Cr(VI) was observed in water when the concentrations of 4-CP/protons or Cr(VI)/protons increased by 100/1000-fold. These results corroborate the freeze concentration effect as the reason for the accelerated redox conversion of 4-CP/Cr(VI) in ice. The redox conversion of various phenolic pollutants/Cr(VI) and 4-CP/Cr(VI) in real wastewater was successfully achieved in ice, which verifies the environmental relevance and importance of freezing-accelerated redox conversion of phenolic pollutants/Cr(VI) in cold regions. Copyright © 2017 Elsevier B.V. All rights reserved.

Enhanced adsorption of chromium onto activated carbon by microwave-assisted H(3)PO(4) mixed with Fe/Al/Mn activation.

PubMed

Sun, Yuanyuan; Yue, Qinyan; Mao, Yanpeng; Gao, Baoyu; Gao, Yuan; Huang, Lihui

2014-01-30

FeCl3, AlCl3 and MnCl2 were used as the assisted activation agent in activated carbon preparation by H3PO4 activation using microwave heating method. The physico-chemical properties of activated carbons were investigated by scanning electron microscope (SEM), N2 adsorption/desorption, Boehm's titration, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). To investigate the adsorption performances of chromium onto these newly developed activated carbons, a batch of experiments were performed under different adsorption conditions: solution pH, initial Cr(VI) ion concentration, contact time and co-existing ions. The results suggested that carbon with MnCl2 as assisted activation agent displayed the highest BET surface area (1332m(2)/g) and the highest pore volume (1.060cm(3)/g). FeCl3, AlCl3 and MnCl2 had successfully improved Cr(VI) adsorption and activated carbon with FeCl3 as assisted activation agent exhibited the best uptake capacity. To study the transformation of Cr(VI) in adsorption process, total chromium in the aqueous solution was also recorded. The ratio of the amount of Cr(VI) to Cr(III) on each adsorbent was explained by XPS analysis results. Both the co-existing salts (Na2SO4 and NaNO3) demonstrated promoted effects on Cr(VI) removal by four carbons. The pseudo-second-order model and Freundlich equation displayed a good correlation with adsorption data. Copyright © 2013 Elsevier B.V. All rights reserved.

Redox Conversion of Chromium(VI) and Arsenic(III) with the Intermediates of Chromium(V) and Arsenic(IV) via AuPd/CNTs Electrocatalysis in Acid Aqueous Solution.

PubMed

Sun, Meng; Zhang, Gong; Qin, Yinghua; Cao, Meijuan; Liu, Yang; Li, Jinghong; Qu, Jiuhui; Liu, Huijuan

2015-08-04

Simultaneous reduction of Cr(VI) to Cr(III) and oxidation of As(III) to As(V) is a promising pretreatment process for the removal of chromium and arsenic from acid aqueous solution. In this work, the synergistic redox conversion of Cr(VI) and As(III) was efficiently achieved in a three-dimensional electrocatalytic reactor with synthesized AuPd/CNTs particles as electrocatalysts. The AuPd/CNTs facilitated the exposure of active Pd{111} facets and possessed an approximate two-electron-transfer pathway of oxygen reduction with the highly efficient formation of H2O2 as end product, resulting in the electrocatalytic reduction of 97.2 ± 2.4% of Cr(VI) and oxidation of 95.7 ± 4% of As(III). The electrocatalytic reduction of Cr(VI) was significantly accelerated prior to the electrocatalytic oxidation of As(III), and the effectiveness of Cr(VI)/As(III) conversion was favored at increased currents from 20 to 150 mA, decreased initial pH from 7 to 1 and concentrations of Cr(VI) and As(III) ranging from 50 to 1 mg/L. The crucial intermediates of Cr(V) and As(IV) and active free radicals HO(•) and O2(•-) were found for the first time, whose roles in the control of Cr(VI)/As(III) redox conversion were proposed. Finally, the potential applicability of AuPd/CNTs was revealed by their stability in electrocatalytic conversion over 10 cycles.

Cytotoxic and genotoxic potential of Cr(VI), Cr(III)-nitrate and Cr(III)-EDTA complex in human hepatoma (HepG2) cells.

PubMed

Novotnik, Breda; Ščančar, Janez; Milačič, Radmila; Filipič, Metka; Žegura, Bojana

2016-07-01

Chromium (Cr) and ethylenediaminetetraacetate (EDTA) are common environmental pollutants and can be present in high concentrations in surface waters at the same time. Therefore, chelation of Cr with EDTA can occur and thereby stable Cr(III)-EDTA complex is formed. Since there are no literature data on Cr(III)-EDTA toxicity, the aim of our work was to evaluate and compare Cr(III)-EDTA cytotoxic and genotoxic activity with those of Cr(VI) and Cr(III)-nitrate in human hepatoma (HepG2) cell line. First the effect of Cr(VI), Cr(III)-nitrate and Cr(III)-EDTA on cell viability was studied in the concentration range from 0.04 μg mL(-1) to 25 μg mL(-1) after 24 h exposure. Further the influence of non-cytotoxic concentrations of Cr(VI), Cr(III)-nitrate and Cr(III)-EDTA on DNA damage and genomic stability was determined with the comet assay and cytokinesis block micronucleus cytome assay, respectively. Cell viability was decreased only by Cr(VI) at concentrations above 1.0 μg mL(-1). Cr(VI) at ≥0.2 μg mL(-1) and Cr(III) at ≥1.0 μg mL(-1) induced DNA damage, while after Cr(III)-EDTA exposure no formation DNA strand breaks was determined. Statistically significant formation of micronuclei was induced only by Cr(VI) at ≥0.2 μg mL(-1), while no influence on the frequency of nuclear buds nor nucleoplasmic bridges was observed at any exposure. This study provides the first evidence that Cr(III)-EDTA did not induce DNA damage and had no influence on the genomic stability of HepG2 cells. Copyright © 2016 Elsevier Ltd. All rights reserved.

Hexavalent chromium is cytotoxic and genotoxic to hawksbill sea turtle cells

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

Wise, Sandra S., E-mail: sandra.wise@maine.edu; Maine Center for Toxicology and Environmental Health, University of Southern Maine, Science Building, 96 Falmouth Street, Portland, ME 04103; Department of Applied Medical Science, University of Southern Maine, Science Building, 96 Falmouth Street, Portland, ME 04103

Sea turtles are a charismatic and ancient ocean species and can serve as key indicators for ocean ecosystems, including coral reefs and sea grass beds as well as coastal beaches. Genotoxicity studies in the species are absent, limiting our understanding of the impact of environmental toxicants on sea turtles. Hexavalent chromium (Cr(VI)) is a ubiquitous environmental problem worldwide, and recent studies show it is a global marine pollutant of concern. Thus, we evaluated the cytotoxicity and genotoxicity of soluble and particulate Cr(VI) in hawksbill sea turtle cells. Particulate Cr(VI) was both cytotoxic and genotoxic to sea turtle cells. Concentrations ofmore » 0.1, 0.5, 1, and 5 μg/cm{sup 2} lead chromate induced 108, 79, 54, and 7% relative survival, respectively. Additionally, concentrations of 0, 0.1, 0.5, 1, and 5 μg/cm{sup 2} lead chromate induced damage in 4, 10, 15, 26, and 36% of cells and caused 4, 11, 17, 30, and 56 chromosome aberrations in 100 metaphases, respectively. For soluble Cr, concentrations of 0.25, 0.5, 1, 2.5, and 5 μM sodium chromate induced 84, 69, 46, 25, and 3% relative survival, respectively. Sodium chromate induced 3, 9, 9, 14, 21, and 29% of metaphases with damage, and caused 3, 10, 10, 16, 26, and 39 damaged chromosomes in 100 metaphases at concentrations of 0, 0.25, 0.5, 1, 2.5, and 5 μM sodium chromate, respectively. These data suggest that Cr(VI) may be a concern for hawksbill sea turtles and sea turtles in general. - Highlights: • Particulate Cr(VI) is cytotoxic and clastogenic to hawksbill sea turtle cells. • Soluble Cr(VI) is cytotoxic and clastogenic to hawksbill sea turtle cells. • Cr(VI) may be a risk factor for hawksbill sea turtle health.« less

Column study of Cr(VI) removal by cationic hydrogel for in-situ remediation of contaminated groundwater and soil

NASA Astrophysics Data System (ADS)

Tang, Samuel C. N.; Yin, Ke; Lo, Irene M. C.

2011-07-01

Column experiments were conducted for examining the effectiveness of the cationic hydrogel on Cr(VI) removal from groundwater and soil. For in-situ groundwater remediation, the effects of background anions, humic acid (HA) and pH were studied. Cr(VI) has a higher preference for being adsorbed onto the cationic hydrogel than sulphate, bicarbonate ions and HA. However, the adsorbed HA reduced the Cr(VI) removal capacity of the cationic hydrogel, especially after regeneration of the adsorbents, probably due to the blockage of adsorption sites. The Cr(VI) removal was slightly influenced by the groundwater pH that could be attributed to Cr(VI) speciation. The 6-cycle regeneration and reusability study shows that the effectiveness of the cationic hydrogel remained almost unchanged. On average, 93% of the adsorbed Cr(VI) was recovered in each cycle and concentrated Cr(VI) solution was obtained after regeneration. For in-situ soil remediation, the flushing water pH had an insignificant effect on the release of Cr(VI) from the soils. Multiple-pulse flushing increased the removal of Cr(VI) from the soils. In contrast, more flushing water and longer operation may be required to achieve the same removal level by continuous flushing.

Removal of hexavalent chromium in carbonic acid solution by oxidizing slag discharged from steelmaking process in electric arc furnace

NASA Astrophysics Data System (ADS)

Yokoyama, Seiji; Okazaki, Kohei; Sasano, Junji; Izaki, Masanobu

2014-02-01

Hexavalent chromium (Cr(VI)) is well-known to be a strong oxidizer, and is recognized as a carcinogen. Therefore, it is regulated for drinking water, soil, groundwater and sea by the environmental quality standards all over the world. In this study, it was attempted to remove Cr(VI) ion in a carbonic acid solution by the oxidizing slag that was discharged from the normal steelmaking process in an electric arc furnace. After the addition of the slag into the aqueous solution contained Cr(VI) ion, concentrations of Cr(VI) ion and total chromium (Cr(VI) + trivalent chromium (Cr(III)) ions decreased to lower detection limit of them. Therefore, the used slag could reduce Cr(VI) and fix Cr(III) ion on the slag. While Cr(VI) ion existed in the solution, iron did not dissolve from the slag. From the relation between predicted dissolution amount of iron(II) ion and amount of decrease in Cr(VI) ion, the Cr(VI) ion did not react with iron(II) ion dissolved from the slag. Therefore, Cr(VI) ion was removed by the reductive reaction between Cr(VI) ion and the iron(II) oxide (FeO) in the slag. This reaction progressed on the newly appeared surface of iron(II) oxide due to the dissolution of phase composed of calcium etc., which existed around iron(II) oxide grain in the slag.

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

Panagiotakis, I.; Dermatas, D.; Vatseris, C.

We conducted a forensic investigation with the aim of decoupling the contribution of geogenic and anthropogenic Cr(VI) sources in the wider area of Thiva. Groundwater and topsoil samples were collected from two Cr(VI) groundwater plumes of 160 μg/L and 75 μg/L. A series of evidence support the view that the origin of Cr(VI) detected in groundwater is mainly geogenic. These are: (a) the presence of Cr in topsoil of the wider area, (b) the moderate Cr(VI) groundwater concentrations, (c) the high Ni levels within the Cr(VI) plumes, (d) the predominance of Mn(IV), which is a prerequisite for Cr(III) oxidation tomore » Cr(VI), and (e) the absence of co-contaminants. This study also revealed that, although both Cr(VI) plumes are clearly of geogenic origin, the plume with the elevated Cr(VI) values, in the north of Thiva town, exhibits also an anthropogenic component, which can potentially be attributed to the alkaline environment associated with the old uncontrolled landfill of Thiva and the industrial cluster located in this area.« less

Experimental Determination of Isotopic Fractionation of Chromium(III) During Oxidation by Manganese Oxides

NASA Astrophysics Data System (ADS)

Bain, D. J.; Bullen, T. D.

2004-12-01

In environmental conditions, chromium (Cr) exists in either the immobile, micronutrient trivalent form (Cr(III)) or the mobile, toxic hexavalent (Cr(VI)) form. Cr(VI) quickly reduces upon encountering Fe(II) or soil organic material (SOM). Therefore, it is often assumed that human Cr additions to terrestrial systems will impact localized areas and natural sources pose minimal threat to human or ecosystem health. However, oxidation and mobilization of Cr(III) by common manganese (Mn) oxides is less understood, especially in field settings. Moreover, Cr(VI)'s anionic form should enhance mobility through Fe- and SOM-poor soil and saprolite matrices. The variety of redox environments along a flowpath makes Cr source identification difficult with only concentration and speciation data. However, Cr has four stable isotopes (50, 52, 53, and 54), and characteristic fractionations during redox transformations might allow clarification of sources and flowpaths. For example, Cr(VI) reduction by a variety of reductants discriminates against heavy Cr, resulting in an increasingly heavy Cr(VI) fraction as reduction proceeds (α Cr(III)-Cr(VI) ˜ 0.996). Measurement of isotopic fractionation in other environmental Cr transformations, including oxidation, is necessary to understand Cr fate and transport. Recent estimates of isotopic fractionation between Cr aqueous species based on theoretical considerations indicate that at equilibrium α Cr(III)-Cr(VI) ˜ 0.994. To test this theoretical prediction, we are assessing the isotopic variability of aqueous Cr during oxidation of Cr(III) on MnO2 materials such as birnessite in laboratory experiments. Initial results indicate that the isotopic composition of the product Cr(VI) ranges from -2.50 to +0.71 ‰ δ 53Cr, suggesting an important role for kinetic isotope effects during the initial oxidation process. Large fluctuations in isotopic composition continue after dissolved Cr(VI) and Cr(III) ratios stabilize and net Cr(VI) production rates are very slow. Moreover, the Cr(VI) isotopic composition fluctuates between heavy and light compositions several times over the course of reaction. Overall, however, the long term trend appears to be toward the equilibrium fractionation predicted by theory. This adds further credence to hypothesized multiple oxidation pathways existing in the system and suggests that multiple processes with off-setting fractionations are driving the system. If these results are representative of natural systems, environmental Cr samples that have been oxidized or been oxidized/reduced multiple times along a flowpath, will have isotopic compositions that vary widely, depending predominantly on sample collection time. In turn, this suggests that Cr isotopic compositions alone will not clarify Cr fate and transport, especially at larger scales (e.g., catchments), and other geochemical and hydrologic constraints will be required.

Effects of sediment characteristics on the toxicity of chromium(III) and chromium(VI) to the amphipod, Hyalella azteca

USGS Publications Warehouse

Besser, J.M.; Brumbaugh, W.G.; Kemble, N.E.; May, T.W.; Ingersoll, C.G.

2004-01-01

We evaluated the influence of sediment characteristics, acid-volatile sulfide (AVS) and organic matter (OM), on the toxicity of chromium (Cr) in freshwater sediments. We conducted chronic (28-42-d) toxicity tests with the amphipod Hyalella azteca exposed to Cr(VI) and Cr(III) in water and in spiked sediments. Waterborne Cr(VI) caused reduced survival of amphipods with a median lethal concentration (LC50) of 40 ??g/L. Cr(VI) spiked into test sediments with differing levels of AVS resulted in graded decreases in AVS and sediment OM. Only Cr(VI)-spiked sediments with low AVS concentrations (<1 ??mol/g) caused significant amphipod mortality. Waterborne Cr(III) concentrations near solubility limits caused decreased survival of amphipods at pH 7 and pH 8 but not at pH 6. Sediments spiked with high levels of Cr(III) did not affect amphipod survival but had minor effects on growth and inconsistent effects on reproduction. Pore waters of some Cr(III)-spiked sediments contained measurable concentrations of Cr(VI), but observed toxic effects did not correspond closely to Cr concentrations in sediment or pore waters. Our results indicate that risks of Cr toxicity are low in freshwater sediments containing substantial concentrations of AVS.

High-capacity adsorption of Cr(VI) from aqueous solution using a hierarchical porous carbon obtained from pig bone.

PubMed

Wei, Shaochen; Li, Dongtian; Huang, Zhe; Huang, Yaqin; Wang, Feng

2013-04-01

A hierarchical porous carbon obtained from pig bone (HPC) was utilized as the adsorbent for removal of Cr(VI) from aqueous solution. The effects of solution pH value, concentration of Cr(VI), and adsorption temperature on the removal of Cr(VI) were investigated. The experimental data of the HPC fitted well with the Langmuir isotherm and its adsorption kinetic followed pseudo-second order model. Compared with a commercial activated carbon adsorbent (Norit CGP), the HPC showed an high adsorption capability for Cr(VI). The maximum Cr(VI) adsorption capacity of the HPC was 398.40 mg/g at pH 2. It is found that a part of the Cr(VI) was reduced to Cr(III) on the adsorbent surface from desorption experiment data. The regeneration showed adsorption capacity of the HPC can still achieve 92.70 mg/g even after fifth adsorption cycle. Copyright © 2013 Elsevier Ltd. All rights reserved.

Control of exposure to hexavalent chromium concentration in shielded metal arc welding fumes by nano-coating of electrodes.

PubMed

Sivapirakasam, S P; Mohan, Sreejith; Santhosh Kumar, M C; Thomas Paul, Ashley; Surianarayanan, M

2017-04-01

Background Cr(VI) is a suspected human carcinogen formed as a by-product of stainless steel welding. Nano-alumina and nano-titania coating of electrodes reduced the welding fume levels. Objective To investigate the effect of nano-coating of welding electrodes on Cr(VI) formation rate (Cr(VI) FR) from a shielded metal arc welding process. Methods The core welding wires were coated with nano-alumina and nano-titania using the sol-gel dip coating technique. Bead-on plate welds were deposited on SS 316 LN plates kept inside a fume test chamber. Cr(VI) analysis was done using an atomic absorption spectrometer (AAS). Results A reduction of 40% and 76%, respectively, in the Cr(VI) FR was observed from nano-alumina and nano-titania coated electrodes. Increase in the fume level decreased the Cr(VI) FR. Discussion Increase in fume levels blocked the UV radiation responsible for the formation of ozone thereby preventing the formation of Cr(VI).

Study on the DNA-protein crosslinks induced by chromium (VI) in SPC-A1

NASA Astrophysics Data System (ADS)

Liu, Yanqun; Ding, Jianjun; Lu, Xiongbing; You, Hao

2018-01-01

Objective: This study was designed to investigate the effect of chromium (VI) on DNA-protein crosslinks (DPC) of SPC-A1 cells. Methods: We exposed SPC-A1 cells were cultured in 1640 medium and treated with the SPC-A1 cells in vitro to different concentrations of Hexavalent chromium Cr(VI) for 2h, the KC1-SDS precipitation assay were used to measure the DNA-protein cross-linking effect. Results: All the different concentrations of Cr(VI) could cause the increase of DPC coefficient in SPC-A1 cells. But this effect was not significant (P>0.05) at low concentrations; while in high concentration Cr(VI) induced SPC-A1 cells could produce DNA-protein cross-linking effect significantly (P<0.05). Conclusions: chromium (VI) could induce DNA-protein crosslink.

Influence of pH on Cr(VI) ions removal from aqueous solutions using carboxymethyl cellulose-based hydrogel as adsorbent

NASA Astrophysics Data System (ADS)

Anah, L.; Astrini, N.

2017-03-01

The major problem in heavy metal pollution is that these metals are not biodegradable and accordingly accumulate in the bodies of living organisms, causing dangerous diseases and serious cell disorder. According to World Health Organization (WHO), the long term exposure of Cr(VI) levels of over 0.1 ppm causes respiratory problems, liver and kidney damage, and carcinogenicity.Due to its easy operation and of various cheap adsorbents development, adsorption has been proved to be efficient and most economically attractive technique and feasible to the removal of toxic heavy metal from wastewater. The study aimed to report the removal of Cr(VI) ions from aqueous solutions through adsorption process using carboxymethyl cellulose-graft-poly(acrylic acid) (CMC-g-PAA) hydrogel as adsorbent.Effect of pH was studied to remove hexavalent chromium.Graft copolymerization of poly(acrylic acid) onto carboxymethyl cellulose was carried out in the presence of benzoyl peroxide redox initiator and methylenbisacrylamide as crosslinker agent. Batch experiments were carried out to investigate the effects ofinitial pH.The adsorption of Cr(VI) ions as a function of pH was conducted in the initial pH range of 1 to 8. The results indicated that acidic pH strongly favored the adsorption. The optimum pH for adsorption of Cr(VI) ranged from 1 to 3, and the maximum uptake of Cr(VI) from the solution was 6.53 mg/g at pH 1 and 30°C. FTIR spectroscopy, SEM analyses were performed on the adsorbent before and after Cr(VI) binding. All analyses confirmed the complexation of Cr(VI) ions on the adsorbent.

Microbial Reduction of Chromate in the Presence of Nitrate by Three Nitrate Respiring Organisms

PubMed Central

Chovanec, Peter; Sparacino-Watkins, Courtney; Zhang, Ning; Basu, Partha; Stolz, John F.

2012-01-01

A major challenge for the bioremediation of toxic metals is the co-occurrence of nitrate, as it can inhibit metal transformation. Geobacter metallireducens, Desulfovibrio desulfuricans, and Sulfurospirillum barnesii are three soil bacteria that can reduce chromate [Cr(VI)] and nitrate, and may be beneficial for developing bioremediation strategies. All three organisms respire through dissimilatory nitrate reduction to ammonia (DNRA), employing different nitrate reductases but similar nitrite reductase (Nrf). G. metallireducens reduces nitrate to nitrite via the membrane bound nitrate reductase (Nar), while S. barnesii and D. desulfuricans strain 27774 have slightly different forms of periplasmic nitrate reductase (Nap). We investigated the effect of DNRA growth in the presence of Cr(VI) in these three organisms and the ability of each to reduce Cr(VI) to Cr(III), and found that each organisms responded differently. Growth of G. metallireducens on nitrate was completely inhibited by Cr(VI). Cultures of D. desulfuricans on nitrate media was initially delayed (48 h) in the presence of Cr(VI), but ultimately reached comparable cell yields to the non-treated control. This prolonged lag phase accompanied the transformation of Cr(VI) to Cr(III). Viable G. metallireducens cells could reduce Cr(VI), whereas Cr(VI) reduction by D. desulfuricans during growth, was mediated by a filterable and heat stable extracellular metabolite. S. barnesii growth on nitrate was not affected by Cr(VI), and Cr(VI) was reduced to Cr(III). However, Cr(VI) reduction activity in S. barnesii, was detected in both the cell free spent medium and cells, indicating both extracellular and cell associated mechanisms. Taken together, these results have demonstrated that Cr(VI) affects DNRA in the three organisms differently, and that each have a unique mechanism for Cr(VI) reduction. PMID:23251135

Biosorption of Cr(VI) by coconut coir: spectroscopic investigation on the reaction mechanism of Cr(VI) with lignocellulosic material.

PubMed

Shen, Ying-Shuian; Wang, Shan-Li; Huang, Shiuh-Tsuen; Tzou, Yu-Min; Huang, Jang-Hung

2010-07-15

In this study, the removal mechanism of Cr(VI) from water by coconut coir (CC) was investigated using X-ray photoelectron spectroscopy (XPS), Cr K-edge X-ray absorption near edge structure (XANES) and FTIR spectroscopy. The results showed that, upon reaction with CC at pH 3, Cr(VI) was reduced to Cr(III), which was either bound to CC or released back into solution. As revealed by the FTIR spectra of CC before and after reacting with Cr(VI), the phenolic methoxyl and hydroxyl groups of lignin in CC are the dominant drivers of Cr(VI) reduction, giving rise to carbonyl and carboxyl groups on CC. These functional groups can subsequently provide binding sites for Cr(III) resulting from Cr(VI) reduction. In conjunction with forming complexes with carbonyl and carboxyl groups, the formation of Cr(III) hydroxide precipitate could also readily occur as revealed by the linear combination fitting of the Cr K-edge XANES spectrum using a set of reference compounds. The phenolic groups in lignin are responsible for initiating Cr(VI) reduction, so lignocellulosic materials containing a higher amount of phenolic groups are expected to be more effective scavengers for removal of Cr(VI) from the environment. 2010 Elsevier B.V. All rights reserved.

Isolation and characterization of a chromium-resistant bacterium Serratia sp. Cr-10 from a chromate-contaminated site.

PubMed

Zhang, Kundi; Li, Fuli

2011-05-01

A novel bacterium, Cr-10, was isolated from a chromium-contaminated site and capable of removing toxic chromium species from solution by reducing hexavalent chromium to an insoluble precipitate. Sequence analysis of 16S rRNA gene of strain Cr-10 showed that it was most closely related to Serratia rubidaea JCM 1240(T) (97.68%). Physiological and chemotaxonomic data also supported that strain Cr-10 was identified as Serratia sp., a genus which was never specially reported chromate-resistant before. Serratia sp., Cr-10 was tolerant to a concentration of 1,500 mg Cr(VI) L(-1), which was the highest level reported until now. The optimum pH and temperature for reduction of Cr(VI) by Serratia sp. Cr-10 were found to be 7.0 and 37 °C, respectively. The Cr(VI) reduction was significantly influenced by additional carbon sources, and among them fructose and lactose offered maximum reduction, with a rate of 0.28 and 0.25 mg Cr(VI) L(-1) h(-1), respectively. The cell-free extracts and filtrate of the culture were able to reduce Cr(VI) while concentration of total chromium remained stable in the process, indicating that the enzyme-catalyzed mechanism was applied in Cr(VI) reduction by the isolate. Additionally, it was found that there was hardly any chromium on the cell surface of the strain, further supporting that reduction, rather than bioadsorption, plays a major role in the Cr(VI) removal.

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

Du Preez, S. P.; Beukes, J. P.; Van Dalen, W. P. J.

The production of ferrochrome (FeCr) is a reducing process. However, it is impossible to completely exclude oxygen from all of the high-temperature production process steps, which may lead to unintentional formation of small amounts of Cr(VI). The majority of Cr(VI) is associated with particles found in the off-gas of the high-temperature processes, which are cleaned by means of venturi scrubbers or bag filter dust (BFD) systems. BFD contains the highest concentration of Cr(VI) of all FeCr wastes. In this study, the solubility of Cr(VI) present in BFD was determined by evaluating four different BFD samples. The results indicate that themore » currently applied Cr(VI) treatment strategies of the FeCr producer (with process water pH ≤ 9) only effectively extract and treat the water-soluble Cr(VI) compounds, which merely represented approximately 31% of the total Cr(VI) present in the BFD samples evaluated. Extended extraction time, within the afore-mentioned pH range, proved futile in extracting sparingly-soluble and water-insoluble Cr(VI) species, which represented approximately 34% and 35% of the total Cr(VI), respectively. Due to the deficiencies of the current treatment strategies, it is highly likely that sparingly water-soluble Cr(VI) compounds will leach from waste storage facilities (e.g. slimes dams) over time. Therefore, it is critical that improved Cr(VI) treatment strategies be formulated, which should be an important future perspective for FeCr producers and researchers alike.« less

Aqueous solubility of Cr(VI) compounds in ferrochrome bag filter dust and the implications thereof

DOE PAGES

Du Preez, S. P.; Beukes, J. P.; Van Dalen, W. P. J.; ...

2017-04-21

The production of ferrochrome (FeCr) is a reducing process. However, it is impossible to completely exclude oxygen from all of the high-temperature production process steps, which may lead to unintentional formation of small amounts of Cr(VI). The majority of Cr(VI) is associated with particles found in the off-gas of the high-temperature processes, which are cleaned by means of venturi scrubbers or bag filter dust (BFD) systems. BFD contains the highest concentration of Cr(VI) of all FeCr wastes. In this study, the solubility of Cr(VI) present in BFD was determined by evaluating four different BFD samples. The results indicate that themore » currently applied Cr(VI) treatment strategies of the FeCr producer (with process water pH ≤ 9) only effectively extract and treat the water-soluble Cr(VI) compounds, which merely represented approximately 31% of the total Cr(VI) present in the BFD samples evaluated. Extended extraction time, within the afore-mentioned pH range, proved futile in extracting sparingly-soluble and water-insoluble Cr(VI) species, which represented approximately 34% and 35% of the total Cr(VI), respectively. Due to the deficiencies of the current treatment strategies, it is highly likely that sparingly water-soluble Cr(VI) compounds will leach from waste storage facilities (e.g. slimes dams) over time. Therefore, it is critical that improved Cr(VI) treatment strategies be formulated, which should be an important future perspective for FeCr producers and researchers alike.« less

Modifications to EPA Method 3060A to Improve Extraction of Cr(VI) from Chromium Ore Processing Residue-Contaminated Soils

USGS Publications Warehouse

Mills, Christopher T.; Bern, Carleton R.; Wolf, Ruth E.; Foster, Andrea L.; Morrison, Jean M.; Benzel, William M.

2017-01-01

It has been shown that EPA Method 3060A does not adequately extract Cr(VI) from chromium ore processing residue (COPR). We modified various parameters of EPA 3060A toward understanding the transformation of COPR minerals in the alkaline extraction and improving extraction of Cr(VI) from NIST SRM 2701, a standard COPR-contaminated soil. Aluminum and Si were the major elements dissolved from NIST 2701, and their concentrations in solution were correlated with Cr(VI). The extraction fluid leached additional Al and Si from the method-prescribed borosilicate glass vessels which appeared to suppress the release of Cr(VI). Use of polytetrafluoroethylene vessels and intensive grinding of NIST 2701 increased the amount of Cr(VI) extracted. These modifications, combined with an increased extraction fluid to sample ratio of ≥900 mL g–1 and 48-h extraction time resulted in a maximum release of 1274 ± 7 mg kg–1 Cr(VI). This is greater than the NIST 2701 certified value of 551 ± 35 mg kg–1 but less than 3050 mg kg–1 Cr(VI) previously estimated by X-ray absorption near edge structure spectroscopy. Some of the increased Cr(VI) may have resulted from oxidation of Cr(III) released from brownmillerite which rapidly transformed during the extractions. Layered-double hydroxides remained stable during extractions and represent a potential residence for unextracted Cr(VI).

Large scale groundwater flow and hexavalent chromium transport modeling under current and future climatic conditions: the case of Asopos River Basin.

PubMed

Dokou, Zoi; Karagiorgi, Vasiliki; Karatzas, George P; Nikolaidis, Nikolaos P; Kalogerakis, Nicolas

2016-03-01

In recent years, high concentrations of hexavalent chromium, Cr(VI), have been observed in the groundwater system of the Asopos River Basin, raising public concern regarding the quality of drinking and irrigation water. The work described herein focuses on the development of a groundwater flow and Cr(VI) transport model using hydrologic, geologic, and water quality data collected from various sources. An important dataset for this goal comprised an extensive time series of Cr(VI) concentrations at various locations that provided an indication of areas of high concentration and also served as model calibration locations. Two main sources of Cr(VI) contamination were considered in the area: anthropogenic contamination originating from Cr-rich industrial wastes buried or injected into the aquifer and geogenic contamination from the leaching process of ophiolitic rocks. The aquifer's response under climatic change scenario A2 was also investigated for the next two decades. Under this scenario, it is expected that rainfall, and thus infiltration, will decrease by 7.7 % during the winter and 15 % during the summer periods. The results for two sub-scenarios (linear and variable precipitation reduction) that were implemented based on A2 show that the impact on the study aquifer is moderate, resulting in a mean level decrease less than 1 m in both cases. The drier climatic conditions resulted in higher Cr(VI) concentrations, especially around the industrial areas.

Sorption of chromium with struvite during phosphorus recovery.

PubMed

Rouff, Ashaki A

2012-11-20

Struvite (MgNH(4)PO(4)·6H(2)O; MAP) precipitation is a viable means of phosphorus (P) recovery from animal and human wastes. The behavior of metal contaminants such as chromium (Cr) during struvite precipitation, however, requires consideration. Here the influence of both Cr concentration and oxidation state on sorption is assessed. The Cr content of struvite precipitated in the presence of 1-100 μM Cr as Cr(III) (22.3-3030.1 mg/kg) was higher than that of solids from Cr(VI) (4.5-5.1 mg/kg) solutions. For 1-20 μM Cr(III) solids, scanning electron microscopy (SEM) revealed etch pit formation on struvite crystal surfaces, indicative of a surface interaction. The formation of an adsorbate was confirmed by X-ray absorption fine structure spectroscopy (XAFS). At initial concentrations ≥20 μM Cr(III), XAFS confirmed the formation of a Cr(OH)(3)·nH(2)O(am) precipitate. Fourier transform infrared (FT-IR) spectroscopy revealed that both Cr(III) and Cr(VI) sorption resulted in distortion of the PO(4)(3-) tetrahedra in the mineral structure. This, combined with SEM results revealed that even at low sorbed concentrations, the Cr impurity can affect the mineral surface and structure. Thus, the initial Cr concentration and oxidation state in wastes targeted for P recovery will dictate the final Cr content, the mechanism of sorption, and impact on the struvite structure.

Fabrication of core-shell Fe{sub 3}O{sub 4}@MIL-100(Fe) magnetic microspheres for the removal of Cr(VI) in aqueous solution

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

Yang, Qingxiang, E-mail: qxyangzz@163.com; Zhao, Qianqian; Ren, ShuangShuang

Facile regeneration of an adsorbent is very important for commercial feasibility. One typical highly porous metal-organic framework (MOF) materials based on MIL-100(Fe) and magnetic iron oxide particles (denoted as MMCs) with diameter about of 350 nm were successfully synthesized. The growth of MIL-100(Fe) shell on the surface of Fe{sub 3}O{sub 4} was utilized precursor as crystal seed via in-situ step hydrothermal reaction. It is a simple way to obtain well organized core-shell MOF composites, compared to the step-by-step method. MMCs were firstly used to uptake of Cr(VI) anions in aqueous solution. Adsorption experiments were carried out in batch sorption mode investigatingmore » with the factors of contact time (0–1000 min), pH (from 2 to 12), dose of adsorbent (4–25 mg), and initial Cr(VI) concentration (range from 10 to 100 ppm). - Graphical abstract: One typical highly porous metal-organic framework (MOF) materials based on MIL-100(Fe) and magnetic iron oxide particles (denoted as MMCs) were successfully synthesized. Utilizing Fe{sub 3}O{sub 4} precursor as crystal seed to grow MIL-100(Fe) shell by in-situ step hydrothermal reaction. It is a simple way to obtain core-shell MOF composites. MMCs could effectively uptake of Cr(VI) anions in aqueous solution. - Highlights: • Fe{sub 3}O{sub 4}@MIL-100(Fe) composites with core-shell structure were successfully prepared through a simple method. • The influence factors on Cr(VI) adsorption by Fe{sub 3}O{sub 4}@MIL-100(Fe) were investigated. • Cr(VI) can efficiently adsorbed by Fe{sub 3}O{sub 4}@MIL-100(Fe) composites from aqueous solution.« less

Hexavalent chromium reduction under fermentative conditions with lactate stimulated native microbial communities.

PubMed

Somenahally, Anil C; Mosher, Jennifer J; Yuan, Tong; Podar, Mircea; Phelps, Tommy J; Brown, Steven D; Yang, Zamin K; Hazen, Terry C; Arkin, Adam P; Palumbo, Anthony V; Van Nostrand, Joy D; Zhou, Jizhong; Elias, Dwayne A

2013-01-01

Microbial reduction of toxic hexavalent chromium (Cr(VI)) in-situ is a plausible bioremediation strategy in electron-acceptor limited environments. However, higher [Cr(VI)] may impose stress on syntrophic communities and impact community structure and function. The study objectives were to understand the impacts of Cr(VI) concentrations on community structure and on the Cr(VI)-reduction potential of groundwater communities at Hanford, WA. Steady state continuous flow bioreactors were used to grow native communities enriched with lactate (30 mM) and continuously amended with Cr(VI) at 0.0 (No-Cr), 0.1 (Low-Cr) and 3.0 (High-Cr) mg/L. Microbial growth, metabolites, Cr(VI), 16S rRNA gene sequences and GeoChip based functional gene composition were monitored for 15 weeks. Temporal trends and differences in growth, metabolite profiles, and community composition were observed, largely between Low-Cr and High-Cr bioreactors. In both High-Cr and Low-Cr bioreactors, Cr(VI) levels were below detection from week 1 until week 15. With lactate enrichment, native bacterial diversity substantially decreased as Pelosinus spp., and Sporotalea spp., became the dominant groups, but did not significantly differ between Cr concentrations. The Archaea diversity also substantially decreased after lactate enrichment from Methanosaeta (35%), Methanosarcina (17%) and others, to mostly Methanosarcina spp. (95%). Methane production was lower in High-Cr reactors suggesting some inhibition of methanogens. Several key functional genes were distinct in Low-Cr bioreactors compared to High-Cr. Among the Cr resistant microbes, Burkholderia vietnamiensis, Comamonas testosterone and Ralstonia pickettii proliferated in Cr amended bioreactors. In-situ fermentative conditions facilitated Cr(VI) reduction, and as a result 3.0 mg/L Cr(VI) did not impact the overall bacterial community structure.

Natural attenuation of Cr(VI) contaminated groundwater at two industrial sites in the eastern U.S.A.: A Cr isotope study

NASA Astrophysics Data System (ADS)

Novak, Martin; Hellerich, Lucas A.; Sebek, Ondrej; Andronikov, Alexandre; Chrastny, Vladislav; Curik, Jan; Stepanova, Marketa; Pacherova, Petra; Martinkova, Eva; Prechova, Eva; Veselovsky, Frantisek

2017-04-01

Hexavalent chromium [Cr(VI)], found in various compartments of the environment, has generated much interest due to its extreme toxicity and mobility. We studied natural attenuation of Cr(VI)-contaminated groundwater at one site in Connecticut (site A), and one site in New Jersey (site B), U.S.A. Shallow groundwater was contaminated by electroplating solutions at site A, and by water-soluble chromite ore-processing residues at site B. Site A had lower Cr(VI) concentrations of less than 1 mg L-1 in comparison to site B (200 mg L-1). Site A also had lower mean del53Cr values (1.4 per mil) than site B (2.9 per mil). Chromium isotope composition of the pollution sources (plating bath, ore) was known (del53Cr of 0.0 to 0.2 per mil). The positive Cr isotope shift from the pollution source Cr(VI) to groundwater Cr(VI) at both sites indicated that spontaneous Cr(VI) reduction to insoluble Cr(III) is under way. This process is removing toxicity from the groundwater. Del53Cr values of groundwater were strongly positively correlated with the concentration of dissolved organic carbon (DOC), but not with divalent Fe and Mn, indicating that DOC may be the main Cr-reducing agent. A Rayleigh model indicated that 30 and 57 % of the original contaminant may have been removed from the groundwater by natural attenuation at site A and B, respectively. Interestingly, del53Cr values of the residual Cr(VI) in the groundwater at site A decreased significantly over the past 15 years, during which the water is being extracted for chemical treatment. At present, older, less fractionated Cr(VI) may be extracted at site A.

Cathodic reduction of hexavalent chromium [Cr(VI)] coupled with electricity generation in microbial fuel cells.

PubMed

Wang, Gang; Huang, Liping; Zhang, Yifeng

2008-11-01

A novel approach to Cr(VI)-contaminated wastewater treatment was investigated using microbial fuel cell technologies in fed-batch mode. By using synthetic Cr(VI)-containing wastewater as catholyte and anaerobic microorganisms as anodic biocatalyst, Cr(VI) at 100 mg/l was completely removed during 150 h (initial pH 2). The maximum power density of 150 mW/m(2) (0.04 mA/cm(2)) and the maximum open circuit voltage of 0.91 V were generated with Cr(VI) at 200 mg/l as electron acceptor. This work verifies the possibility of simultaneous electricity production and cathodic Cr(VI) reduction.

Assessment of ferrous chloride and Portland cement for the remediation of chromite ore processing residue.

PubMed

Jagupilla, Santhi C; Wazne, Mahmoud; Moon, Deok Hyun

2015-10-01

Chromite Ore Processing Residue (COPR) is an industrial waste containing up to 7% chromium (Cr) including up to 5% hexavalent chromium [Cr(VI)]. The remediation of COPR has been challenging due to the slow release of Cr(VI) from a clinker like material and thereby the incomplete detoxification of Cr(VI) by chemical reagents. The use of sulfur based reagents such as ferrous sulfate and calcium polysulfide to detoxify Cr(VI) has exasperated the swell potential of COPR upon treatment. This study investigated the use of ferrous chloride alone and in combination with Portland cement to address the detoxification of Cr(VI) in COPR and the potential swell of COPR. Chromium regulatory tests, X-ray powder diffraction (XRPD) analyses and X-ray absorption near edge structure (XANES) analyses were used to assess the treatment results. The treatment results indicated that Cr(VI) concentrations for the acid pretreated micronized COPR as measured by XANES analyses were below the New Jersey Department of Environmental Protection (NJDEP) standard of 20 mg kg(-1). The Toxicity characteristic leaching procedure (TCLP) Cr concentrations for all acid pretreated samples also were reduced below the TCLP regulatory limit of 5 mg L(-1). Moreover, the TCLP Cr concentration for the acid pretreated COPR with particle size ⩽0.010 mm were less than the universal treatment standard (UTS) of 0.6 mg L(-1). The treatment appears to have destabilized all COPR potential swell causing minerals. The unconfined compressive strength (UCS) for the treated samples increased significantly upon treatment with Portland cement. Copyright © 2015 Elsevier Ltd. All rights reserved.

Forensic investigation of a chromium(VI) groundwater plume in Thiva, Greece.

PubMed

Panagiotakis, I; Dermatas, D; Vatseris, C; Chrysochoou, M; Papassiopi, N; Xenidis, A; Vaxevanidou, K

2015-01-08

A forensic investigation was conducted with the aim of decoupling the contribution of geogenic and anthropogenic Cr(VI) sources in the wider area of Thiva. Groundwater and topsoil samples were collected from two Cr(VI) groundwater plumes of 160 μg/L and 75 μg/L. A series of evidence support the view that the origin of Cr(VI) detected in groundwater is mainly geogenic. These are: (a) the presence of Cr in topsoil of the wider area, (b) the moderate Cr(VI) groundwater concentrations, (c) the high Ni levels within the Cr(VI) plumes, (d) the predominance of Mn(IV), which is a prerequisite for Cr(III) oxidation to Cr(VI), and (e) the absence of co-contaminants. The present study also revealed that, although both Cr(VI) plumes are clearly of geogenic origin, the plume with the elevated Cr(VI) values, in the north of Thiva town, exhibits also an anthropogenic component, which can potentially be attributed to the alkaline environment associated with the old uncontrolled landfill of Thiva and the industrial cluster located in this area. Copyright © 2014 Elsevier B.V. All rights reserved.

[Treatment of wastewater containing Cr(VI) by LDH synthesizing in situ].

PubMed

Chen, Tian-hu; Feng, You-liang; Xu, Hui-fang; Peng, Shu-chuan; Huang, Chuan-hui; Tang, Shu-pei

2004-03-01

The objective of this work was to investigate the efficiency and factors impacting of removal Cr(VI) from wastewater by layer double hydroxide synthesizing in situ. Principle of the method may be described as follow: Mg2+ and Al3+ hydrolysis and forms Mg/Al-LDH by adding Mg2+, Al3+ and NaOH into wastewater containing Cr(VI), Cr(VI) anions are selectively intercalated into interlayer of LDH to balance positive structural charge. While Mg2+ and Al3+ co-precipitates and forms LDH, the Cr(VI) in wastewater is removal by settle of LDH synthesizing in situ, which are confirmed by analysis of X-ray diffraction on settle and chemical analysis on aqueous. The results indicate that factors of impacting on efficiency of removal Cr(VI) include in amount of adding Mg2+ and Al3+, Mg/Al ratio, pH and concentration of Cr(VI) in wastewater. The maximal removal efficiency of Cr(VI) can be reached when pH values are between 8.5 and 9, and Mg/Al ratios are between 1:1 and 2:1, meanwhile, Mg and Al added can be taken good use of. This technology has present extraordinary efficiency of wastewater treatment.

The effects of chromium(VI) on the thioredoxin system: Implications for redox regulation

PubMed Central

Myers, Charles R.

2014-01-01

Hexavalent chromium [Cr(VI)] compounds are highly redox active and have long been recognized as potent cytotoxins and carcinogens. The intracellular reduction of Cr(VI) generates reactive Cr intermediates, which are themselves strong oxidants, as well as superoxide, hydrogen peroxide, and hydroxyl radical. These probably contribute to the oxidative damage and effects on redox-sensitive transcription factors that have been reported. However, the identification of events that initiate these signaling changes has been elusive. More recent studies show that Cr(VI) causes irreversible inhibition of thioredoxin reductase (TrxR) and oxidation of thioredoxin (Trx) and peroxiredoxin (Prx). Mitochondrial Trx2/Prx3 are more sensitive to Cr(VI) treatment than cytosolic Trx1/Prx1, although both compartments show thiol oxidation with higher doses or longer treatments. Thiol redox proteomics demonstrate that Trx2, Prx3, and Trx1 are among the most sensitive proteins in cells to Cr(VI) treatment. Their oxidation could therefore represent initiating events that have widespread implications for protein thiol redox control and for multiple aspects of redox signaling. This review summarizes the effects of Cr(VI) on the TrxR/Trx system and how these events could influence a number of downstream redox signaling systems that are influenced by Cr(VI) exposure. Some of the signaling events discussed include the activation of apoptosis signal regulating kinase and MAP kinases (p38 and JNK) and the modulation of a number of redox-sensitive transcription factors including AP-1, NF-κB, p53, and Nrf2. PMID:22542445

Insights into controls on hexavalent chromium in groundwater provided by environmental tracers, Sacramento Valley, California, USA

USGS Publications Warehouse

Manning, Andrew H.; Mills, Christopher T.; Morrison, Jean M.; Ball, Lyndsay B.

2015-01-01

Environmental tracers are useful for determining groundwater age and recharge source, yet their application in studies of geogenic Cr(VI) in groundwater has been limited. Environmental tracer data from 166 wells located in the Sacramento Valley, northern California, were interpreted and compared to Cr concentrations to determine the origin and age of groundwater with elevated Cr(VI), and better understand where Cr(VI) becomes mobilized and how it evolves along flowpaths. In addition to major ion and trace element concentrations, the dataset includes δ18O, δ2H, 3H concentration, 14C activity (of dissolved inorganic C), δ13C, 3He/4He ratio, and noble gas concentrations (He, Ne, Ar, Kr, Xe). Noble gas recharge temperatures (NGTs) were computed, and age-related tracers were interpreted in combination to constrain the age distribution in samples and sort them into six different age categories spanning from <60 yr old to >10,000 yr old. Nearly all measured Cr is in the form of Cr(IV). Concentrations range from <1 to 46 μg L−1, with 10% exceeding the state of California’s Cr(VI) maximum contaminant level of 10 μg L−1. Two groups with elevated Cr(VI) (⩾5 μg L−1) were identified. Group 1 samples are from the southern part of the valley and contain modern (<60 yr old) water, have elevated NO3− concentrations (>3 mg L−1), and commonly have δ18O values enriched relative to local precipitation. These samples likely contain irrigation water and are elevated due to accelerated mobilization of Cr(VI) in the unsaturated zone (UZ) in irrigated areas. Group 2 samples are from throughout the valley and typically contain water 1000–10,000 yr old, have δ18O values consistent with local precipitation, and have unexpectedly warm NGTs. Chromium(VI) concentrations in Group 2 samples may be elevated for multiple reasons, but the hypothesis most consistent with all available data (notably, the warm NGTs) is a relatively long UZ residence time due to recharge through a deep UZ near the margin of the basin. A possible explanation for why Cr(VI) may be primarily mobilized in the UZ rather than farther along flowpaths in the oxic portion of the saturated zone is more dynamic cycling of Mn in the UZ due to transient moisture and redox conditions.

Flow-through Column Experiments and Modeling of Microbially Mediated Cr(VI) Reduction at Hanford 100H

NASA Astrophysics Data System (ADS)

Yang, L.; Molins, S.; Beller, H. R.; Brodie, E. L.; Steefel, C.; Nico, P. S.; Han, R.

2010-12-01

Microbially mediated Cr(VI) reduction at the Hanford 100H area was investigated by flow-through column experiments. Three separate experiments were conducted to promote microbial activities associated with denitrification, iron and sulfate reduction, respectively. Replicate columns packed with natural sediments from the site under anaerobic environment were injected with 5mM Lactate as the electron donor and 5 μM Cr(VI) in all experiments. Sulfate and nitrate solutions were added to act as the main electron acceptors in the respective experiments, while iron columns relied on the indigenous sediment iron (and manganese) oxides as electron acceptors. Column effluent solutions were analyzed by IC and ICP-MS to monitor the microbial consumption/conversion of lactate and the associated Cr(VI) reduction. Biogeochemical reactive transport modeling was performed to gain further insights into the reaction mechanisms and Cr(VI) bioreduction rates. All experimental columns showed a reduction of the injected Cr(VI). Columns under denitrifying conditions showed the least Cr(VI) reduction at early stages (<60 days) compared to columns run under other experimental conditions, but became more active over time, and ultimately showed the most consistent Cr(VI) reduction. A strong correlation between denitrification and Cr(VI) reduction processes was observed and was in agreement with the results obtained in batch experiments with a denitrifying bacterium isolated from the Hanford site. The accumulation of nitrite does not appear to have an adverse effect on Cr(VI) reduction rates. Reactive transport simulations indicated that biomass growth completely depleted influent ammonium, and called for an additional source of N to account for the measured reduction rates. Iron columns were the least active with undetectable consumption of the injected lactate, slowest cell growth, and the smallest change in Cr(VI) concentrations during the course of the experiment. In contrast, columns under sulfate-reducing/fermentative conditions exhibited the greatest Cr(VI) reduction capacity. Two sulfate columns evolved to complete lactate fermentation with acetate and propionate produced in the column effluent after 40 days of experiments. These fermenting columns showed a complete removal of injected Cr(VI), visible precipitation of sulfide minerals, and a significant increase in effluent Fe and Mn concentrations. Reactive transport simulations suggested that direct reduction of Cr(VI) by Fe(II) and Mn(II) released from the sediment could account for the observed Cr(VI) removal. The biogeochemical modeling was employed to test two hypotheses that could explain the release of Fe(II) and Mn(II) from the column sediments: 1) acetate produced by lactate fermentation provided the substrate for the growth of iron(III) and manganese(IV) oxide reducers, and 2) direct reduction of iron(III) and manganese(IV) oxides by hydrogen sulfide generated during sulfate reduction. Overall, experimental and modeling results suggested that Cr(VI) reduction in the sulfate-reducing columns occurred through a complex network of microbial reactions that included fermentation, sulfate reduction, and possibly the stimulated iron-reducing communities.

Comparative cytotoxicity and genotoxicity of particulate and soluble hexavalent chromium in human and sperm whale (Physeter macrocephalus) skin cells.

PubMed

Li Chen, Tânia; LaCerte, Carolyne; Wise, Sandra S; Holmes, Amie; Martino, Julieta; Wise, John Pierce; Thompson, W Douglas; Wise, John Pierce

2012-01-01

Chromium (Cr) is a global marine pollutant, present in marine mammal tissues. Hexavalent chromium [Cr(VI)] is a known human carcinogen. In this study, we compare the cytotoxic and clastogenic effects of Cr(VI) in human (Homo sapiens) and sperm whale (Physeter macrocephalus) skin fibroblasts. Our data show that increasing concentrations of both particulate and soluble Cr(VI) induce increasing amounts of cytotoxicity and clastogenicity in human and sperm whale skin cells. Furthermore, the data show that sperm whale cells are resistant to these effects exhibiting less cytotoxicity and genotoxicity than the human cells. Differences in Cr uptake accounted for some but not all of the differences in particulate and soluble Cr(VI) genotoxicity, although it did explain the differences in particulate Cr(VI) cytotoxicity. Altogether, the data indicate that Cr(VI) is a genotoxic threat to whales, but also suggest that whales have evolved cellular mechanisms to protect them against the genotoxicity of environmental agents such as Cr(VI). Copyright © 2011 Elsevier Inc. All rights reserved.

Chromium Isotopic Monitoring of HRC-Stimulated Bio-containment at the 100H Test Site, Hanford, Washington

NASA Astrophysics Data System (ADS)

Christensen, J. N.; Brown, S. T.; Brodie, E. L.; Chakraborty, R.; Conrad, M. E.; Long, P. E.; Faybishenko, B.; Hazen, T. C.

2007-12-01

Hexavalent Cr (Cr(VI)) groundwater contamination is a common problem in the U.S. associated with industrial activity (e.g. electroplating, tanning, paints, anti-corrosion). In the particular case of the Hanford Site, Washington, chromate was used primarily to inhibit corrosion in nuclear reactor cooling systems. During the active operation of the Hanford Site, disposal of waste water bearing chromate, and accidental releases to the vadose zone resulted in significant groundwater contamination with local concentrations near the Columbia river reaching over 1000 ppb Cr(VI). In an effort to test an effective bio-containment strategy for groundwater Cr(VI), a site was selected between the 100D and 100H reactor areas with modest concentrations (~100 ppb Cr(VI) over the past two decades). A slow-release 13C labeled polylactate amendment (HRCTM, Regenesis, Ltd.) was injected into groundwater within a sandy formation to stimulate bacterial activity in order to produce conditions that promote the reduction of dissolved Cr(VI) to insoluble Cr(III) complexes [1]. Since the injection of HRCTM in August 2004, groundwater Cr(VI) concentration has been locally below 1 ppb, and reducing conditions have been maintained to at least the present time. The isotopic composition of Cr can be fractionated during reduction from Cr(VI) to Cr(III) and so has the potential to be used as a monitor of hexavalent Cr reduction [2, 3]. This would provide a direct signature of Cr(VI) reduction, discernable from simple attenuation by dilution. In order to explore the use of Cr isotopic measurements for evaluating processes of Cr(VI) reduction, we have analyzed a series of samples in space and time for Cr isotopic composition (δ53Cr, permil deviation of sample 53Cr/52Cr from that of SRM970). Groundwater samples came from the HRC injection well, from multiple depths of three down-gradient wells, and from an up-gradient well. Samples from down-gradient wells have Cr that is isotopically fractionated relative to samples from the up-gradient well. Taken together, samples from a single sampling campaign yield an apparent fractionation of 2.2 ‰. Cr isotopic measurements of the latest samples (June, 2007) confirm continued reduction of Cr(VI) nearly three years after the introduction of HRCTM, suggesting the long-term effectiveness of this bio-stimulated containment strategy. [1] http://esd.lbl.gov/ERT/hanford100h/ [2] Ellis, AS, Johnson, TM and Bohlen, TD (2002) Science. 295:2060-2062. [3] Johnson, TM and Bohlen, TD (2004) Reviews in Mineralogy and Geochemistry, Vol. 55, p.289-317.

Germination and sporophytic development of Regnellidium diphyllum Lindman (Marsileaceae) in the presence of hexavalent chromium.

PubMed

Kieling-Rubio, M A; Droste, A; Windisch, P G

2010-12-01

Regnellidium diphyllum Lindman is a heterosporous fern, growing in aquatic environments and surrounding wetlands, which is assumed to be threatened by increasing water pollution and disappearance of its natural habitats. Among contaminants, hexavalent chromium - Cr(VI) - is known to be present in effluents from some leather tanning factories. Megaspore germination tests were performed using Meyer's solution, at concentrations 0 (control), 0.1, 0.5, 1, 5, 10, 15, 20, 30, 50, and 80 mg.L⁻¹, from a standard solution of Titrisol® 1000 mg.L⁻¹. The primary development of apomictic sporophytes was studied using solutions containing 0.025 to 4.8 mg.L⁻¹ of Cr(VI). The experiments were conducted in a growth chamber at 24 ± 1 ºC and for a 12-hour photoperiod under fluorescent lights, providing a nominal irradiance of 77 µmol.m⁻²/s. Significant differences in megaspore germination, with subsequent sporophytic development, were verified from 0.5 mg.L⁻¹ Cr(VI) concentration onwards. Growth of primary root and primary and secondary leaves was significantly reduced at 3.2 mg.L⁻¹ Cr(VI) concentration or higher. Considering the pollution from Cr(VI) in some areas of R. diphyllum natural occurrence, these data indicate that low reproductive rates and disappearance of populations are likely to occur in these situations.

Final Scientific/Technical Report--In-Situ Generation of Iron-Chromium Precipitates for Long Term Immobilization of Chromium at the Hanford Site

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

Butler, Elizabeth C.; Krumholz, Lee R.; Madden, Andrew S.

Hexavalent chromium (Cr(VI)) is a toxic ground water contaminant widespread at the Hanford site and many other industrial facilities. A common remediation method for Cr(VI) is in situ reduction/immobilization, in which soluble Cr(VI) is reduced to the less soluble trivalent Cr (Cr(III)). If iron (Fe) minerals are present during the process, Cr(III) precipitates as a mixed Fe(III)-Cr(III) (Fe-Cr) solid. The objective of this exploratory research was to obtain preliminary evidence about the relationships among the method of Cr(VI) reduction (i.e., abiotic or microbial), the properties of the resulting Fe-Cr precipitates, and their tendencies to release soluble Cr(VI) in the presencemore » of the common manganese oxide birnessite. The results of this exploratory research project show that the conditions of Cr(VI) reduction—specifically the ratio of Cr to Fe, and/or whether the Cr(VI) reductant is a mineral or a microorganism—can significantly affect the tendency of the resulting Fe-Cr precipitate to release Cr(VI) to the environment in the presence of birnessite. These results suggest the chosen remediation conditions have the potential to strongly influence not only the initial success of in situ Cr(VI) reduction/immobilization, but also the potential for successful long term sequestration of Cr in the form of stable soil precipitates.« less

Investigations on the nephrotoxicity and hepatotoxicity of trivalent and hexavalent chromium compounds.

PubMed

Dartsch, P C; Hildenbrand, S; Kimmel, R; Schmahl, F W

1998-09-01

In contrast to trivalent chromium (Cr(III)) compounds, hexavalent chromium ((Cr(VI)) compounds are oxidizing agents capable of directly inducing tissue damage and possessing carcinogenic, mutagenic and teratogenic potency. After oral or dermal absorption of Cr(VI), the kidney is the main target organ for chromium accumulation, which might result in acute tubular necrosis in humans. In contrast, an acute toxic effect of Cr(VI) on the liver has not yet been described. Therefore, we used two established epithelial cell lines from the kidney (Opossum kidney cells) and the liver (Hep G2 cells) to design an in vitro-assay which is able to examine acute toxic effects of chromium compounds. Cells of both cell lines were treated with various concentrations of Cr(III) and Cr(VI) ranging from 0.01 micromol/l to 1 mmol/l for 24 h. Thereafter, cell morphology, organization of the intracellular cytoskeleton, number of viable cells and mean cell volume were examined. The results show that Cr(VI), but not Cr(III), has an acute cytotoxic effect and causes a dose-dependent loss in cell viability. The effective dose that caused 50% of cell death was 5 micromol/l for kidney epithelial cells and 50 micromol/l for liver epithelial cells. This means that kidney epithelial cells are 10 times more sensitive towards Cr(VI) treatment than liver epithelial cells and this might explain the known nephrotoxicity in vivo. The loss in cell viability was accompanied by a rounding and detachment of the cells and a marked reduction of intracellular F-actin-containing stress fibers. Microtubules and intermediate-sized filaments were observed to be unaffected. Only in the case of kidney epithelial cells, a dose-dependent cell volume increase was observed after Cr(VI) treatment at concentrations up to 50 micromol/l. At higher concentrations, the cell volume decreased due to the high number of cells undergoing lysis and the appearance of cellular fragments. Various chloride channel blockers with different specificities, molecular structures and inhibitory potentials were tested for their ability to prevent Cr(VI)-induced cell damage. None of the channel blockers was able to inhibit cell damage, suggesting that the uptake of Cr(VI) through the general anion transport system of the cell membrane might be only one facet of cellular uptake and toxification. The data presented here not only confirm the different organ-specific effects of Cr(III) and Cr(VI), but also provide a basis for future experiments on the understanding of acute toxicity of Cr(VI) compounds. Moreover, the results demonstrate that the designed in vitro-assay might be a useful tool to prove whether non-toxic Cr(III) can be oxidized to Cr(VI) under specific industrial conditions (for example, in the leather or chrome industry).

Improved Atmospheric Sampling of Hexavalent Chromium

PubMed Central

Torkmahalleh, Mehdi Amouei; Yu, Chang-Ho; Lin, Lin; Fan, Zhihua (Tina); Swift, Julie L.; Bonanno, Linda; Rasmussen, Don H.; Holsen, Thomas M.; Hopke, Philip K.

2015-01-01

Hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) are the primary chromium oxidation states found in ambient atmospheric particulate matter. While Cr(III) is relatively nontoxic, Cr(VI) is toxic and exposure to Cr(VI) may lead to cancer, nasal damage, asthma, bronchitis, and pneumonitis. Accurate measurement of the ambient Cr(VI) concentrations is an environmental challenge since Cr(VI) can be reduced to Cr(III) and vice versa during sampling. In the present study, a new Cr(VI) sampler (Clarkson sampler) was designed, constructed, and field tested to improve the sampling of Cr(VI) in ambient air. The new Clarkson Cr(VI) sampler was based on the concept that deliquescence during sampling leads to aqueous phase reactions. Thus, the relative humidity of the sampled air was reduced below the deliquescence relative humidity (DRH) of the ambient particles. The new sampler was operated to collect Total Suspended Particles (TSP), and compared side-by-side with the current National Air Toxics Trends Stations (NATTS) Cr(VI) sampler that is utilized in the United States Environmental Protection Agency (USEPA) air toxics monitoring program. Side-by-side field testing of the samplers occurred in Elizabeth, NJ during the winter and summer of 2012. The average recovery values of Cr(VI) spikes after 24 hour sampling intervals during summer and winter sampling were 57 and 72%, respectively, for the Clarkson sampler, while the corresponding average values for NATTS samplers were 46% for both summer and winter sampling, respectively. Preventing the ambient aerosol collected on the filters from deliquescing is a key to improving the sampling of Cr(VI). PMID:24344574

Novel method of vulnerability assessment of simple landfills area using the multimedia, multipathway and multireceptor risk assessment (3MRA) model, China.

PubMed

Yuan, Ying; He, Xiao-Song; Xi, Bei-Dou; Wei, Zi-Min; Tan, Wen-Bing; Gao, Ru-Tai

2016-11-01

Vulnerability assessment of simple landfills was conducted using the multimedia, multipathway and multireceptor risk assessment (3MRA) model for the first time in China. The minimum safe threshold of six contaminants (benzene, arsenic (As), cadmium (Cd), hexavalent chromium [Cr(VI)], divalent mercury [Hg(II)] and divalent nickel [Ni(II)]) in landfill and waste pile models were calculated by the 3MRA model. Furthermore, the vulnerability indexes of the six contaminants were predicted based on the model calculation. The results showed that the order of health risk vulnerability index was As > Hg(II) > Cr(VI) > benzene > Cd > Ni(II) in the landfill model, whereas the ecology risk vulnerability index was in the order of As > Hg(II) > Cr(VI) > Cd > benzene > Ni(II). In the waste pile model, the order of health risk vulnerability index was benzene > Hg(II) > Cr(VI) > As > Cd and Ni(II), whereas the ecology risk vulnerability index was in the order of Hg(II) > Cd > Cr(VI) > As > benzene > Ni(II). These results indicated that As, Hg(II) and Cr(VI) were the high risk contaminants for the case of a simple landfill in China; the concentration of these in soil and groundwater around the simple landfill should be strictly monitored, and proper mediation is also recommended for simple landfills with a high concentration of contaminants. © The Author(s) 2016.

Adsorption of toxic metal ion Cr(VI) from aqueous state by TiO2-MCM-41: equilibrium and kinetic studies.

PubMed

Parida, Kulamani; Mishra, Krushna Gopal; Dash, Suresh Kumar

2012-11-30

This paper deals with the immobilization of various weight percentage of TiO(2) on mesoporous MCM-41, characterization of the materials by X-ray diffraction (XRD), nitrogen adsorption-desorption, Fourier Transform Infrared (FTIR) analysis, UV-vis diffuse reflectance spectroscopy (DRS) and evaluation of the adsorption capacity toward Cr(VI) removal. It is found that the MCM-41 structure retained after loading of TiO(2) but the surface area and pore diameter decreased due to pore blockage. Adsorption of Cr(VI) from aqueous state was investigated on TiO(2)-MCM-41 by changing various parameters such as pH, metal ion concentration, and the temperature. When TiO(2) loading was more than 20 wt.%, the adsorption activity (25)TiO(2)-MCM-41 reduced significantly due to considerable decrease in the surface area. It is also observed that TiO(2) and neat MCM-41 exhibits very less Cr(VI) adsorption compared to TiO(2)-MCM-41. The adsorption of Cr(VI) onto (20)TiO(2)-MCM-41 at pH~5.5 and temperature 323 K was 91% at 100mg/L Cr(VI) metal ion concentration in 80 min. The experimental data fitted well to Langmuir and Freundlich isotherms. The adsorption of Cr(VI) on TiO(2)-MCM-41 followed a second order kinetics with higher values of intra-particle diffusion rate. Thermodynamic parameters suggested that the adsorption process is endothermic in nature and desorption studies indicated a chemisorption mode. Copyright © 2012 Elsevier B.V. All rights reserved.

Quantitative aspects of contact allergy to chromium and exposure to chrome-tanned leather.

PubMed

Hansen, Malene Barré; Rydin, Stefan; Menné, Torkil; Duus Johansen, Jeanne

2002-09-01

The potential of trivalent and hexavalent chromium to induce and elicit allergic contact dermatitis and the degree of chromium exposure from leather products are reviewed. Chromium dermatitis is often due to exposure in the occupational environment, with cement being one of the most common chromium sources. However, consumer products such as chromium(III)-tanned leather products are also an important source of chromium exposure. Apart from Cr(III), which is used for tanning, leather often also contains trace amounts of Cr(VI), which is formed by oxidation of Cr(III) during the tanning process. In a recent study of the Cr(VI) content of leather products bought on the Danish market, 35% of such articles had a Cr(VI) content above the detection limit of 3 p.p.m., ranging from 3.6 p.p.m. to 14.7 p.p.m. Leachable Cr(III) was detected at levels of 430-980 p.p.m. An examination of available dose-response studies showed that exposure to occluded patch test concentrations of 7-45 p.p.m. Cr(VI) elicits a reaction in 10% of the chromium-sensitive patients. When reviewing repeated open exposure studies, it is seen that either exposure to 5 p.p.m. Cr(VI) in the presence of 1% sodium lauryl sulfate (SLS) or exposure to 10 p.p.m. Cr(VI) alone both elicit eczema in chromium-sensitive patients. The eliciting capacity of Cr(III) has not been systematically investigated but, compared to Cr(VI), much higher concentrations are needed to elicit eczema.

Effects of common groundwater ions on chromate removal by magnetite: Importance of chromate adsorption

DOE PAGES

Meena, Amanda H.; Arai, Yuji

2016-04-29

Reductive precipitation of hexavalent chromium (Cr(VI)) with magnetite is a well-known Cr(VI) remediation method to improve water quality. The rapid (< a few hr) reduction of soluble Cr(VI) to insoluble Cr(III) species by Fe(II) in magnetite has been the primary focus of the Cr(VI) removal process in the past. However, the contribution of simultaneous Cr(VI) adsorption processes in aged magnetite has been largely ignored, leaving uncertainties in evaluating the application of in situ Cr remediation technologies for aqueous systems. In this study, effects of common groundwater ions (i.e., nitrate and sulfate) on Cr(VI) sorption to magnetite were investigated using batchmore » geochemical experiments in conjunction with X-ray absorption spectroscopy. As a result, in both nitrate and sulfate electrolytes, batch sorption experiments showed that Cr(VI) sorption decreases with increasing pH from 4 to 8. In this pH range, Cr(VI) sorption decreased with increasing ionic strength of sulfate from 0.01 to 0.1 M whereas nitrate concentrations did not alter the Cr(VI) sorption behavior. This indicates the background electrolyte specific Cr(VI) sorption process in magnetite. Under the same ionic strength, Cr(VI) removal in sulfate containing solutions was greater than that in nitrate solutions. This is because the oxidation of Fe(II) by nitrate is more thermodynamically favorable than by sulfate, leaving less reduction capacity of magnetite to reduce Cr(VI) in the nitrate media. X-ray absorption spectroscopy analysis supports the macroscopic evidence that more than 75 % of total Cr on the magnetite surfaces was adsorbed Cr(VI) species after 48 h. In conclusion, this experimental geochemical study showed that the adsorption process of Cr(VI) anions was as important as the reductive precipitation of Cr(III) in describing the removal of Cr(VI) by magnetite, and these interfacial adsorption processes could be impacted by common groundwater ions like sulfate and nitrate. The results of this study highlight new information about the large quantity of adsorbed Cr(VI) surface complexes at the magnetite-water interface. It has implications for predicting the long-term stability of Cr at the magnetite-water interface.« less

Modacrylic anion-exchange fibers for Cr(VI) removal from chromium-plating rinse water in batch and flow-through column experiments.

PubMed

Lee, Seung-Chan; Kang, Jin-Kyu; Sim, Eun-Hye; Choi, Nag-Choul; Kim, Song-Bae

2017-11-10

The aim of this study was to investigate Cr(VI) removal from chromium-plating rinse water using modacrylic anion-exchange fibers (KaracaronTM KC31). Batch experiments were performed with synthetic Cr(VI) solutions to characterize the KC31 fibers in Cr(VI) removal. Cr(VI) removal by the fibers was affected by solution pH; the Cr(VI) removal capacity was the highest at pH 2 and decreased gradually with a pH increase from 2 to 12. In regeneration and reuse experiments, the Cr(VI) removal capacity remained above 37.0 mg g -1 over five adsorption-desorption cycles, demonstrating that the fibers could be successfully regenerated with NaCl solution and reused. The maximum Cr(VI) removal capacity was determined to be 250.3 mg g -1 from the Langmuir model. In Fourier-transform infrared spectra, a Cr = O peak newly appeared at 897 cm -1 after Cr(VI) removal, whereas a Cr-O peak was detected at 772 cm -1 due to the association of Cr(VI) ions with ion-exchange sites. X-ray photoelectron spectroscopy analyses demonstrated that Cr(VI) was partially reduced to Cr(III) after the ion exchange on the surfaces of the fibers. Batch experiments with chromium-plating rinse water (Cr(VI) concentration = 1178.8 mg L -1 ) showed that the fibers had a Cr(VI) removal capacity of 28.1-186.4 mg g -1 under the given conditions (fiber dose = 1-10 g L -1 ). Column experiments (column length = 10 cm, inner diameter = 2.5 cm) were conducted to examine Cr(VI) removal from chromium-plating rinse water by the fibers under flow-through column conditions. The Cr(VI) removal capacities for the fibers at flow rates of 0.5 and 1.0 mL min -1 were 214.8 and 171.5 mg g -1 , respectively. This study demonstrates that KC31 fibers are effective in the removal of Cr(VI) ions from chromium-plating rinse water.

Occupational Exposure to Chromium of Assembly Workers in Aviation Industries.

PubMed

Genovese, G; Castiglia, L; Pieri, M; Novi, C; d'Angelo, R; Sannolo, N; Lamberti, M; Miraglia, N

2015-01-01

Aircraft are constructed by modules that are covered by a "primer" layer, which can often contain hexavalent chromium [Cr(VI)], known carcinogen to humans. While the occupational exposure to Cr(VI) during aircraft painting is ascertained, the exposure assessment of assembly workers (assemblers) requires investigations. Three biological monitoring campaigns (BM-I,II,III) were performed in an aviation industry, on homogeneous groups of assemblers (N = 43) and controls (N = 23), by measuring chromium concentrations in end-shift urine collected at the end of the working week and the chromium concentration difference between end- and before-shift urines. BM-I was conducted on full-time workers, BM-II was performed on workers after a 3-4 day absence from work, BM-III on workers using ecoprimers with lower Cr(VI) content. Samples were analyzed by atomic absorption spectroscopy and mean values were compared by T-test. Even if Cr concentrations measured during BM-I were lower than Biological Exposure Indices by ACGIH, statistically significant differences were found between urinary Cr concentrations of workers and controls. Despite 3-4 days of absence from work, urinary chromium concentrations measured during BM-II were still higher than references from nonoccupationally exposed populations. In the BM-III campaign, the obtained preliminary results suggested the efficacy of using ecoprimers. The healthcare of workers exposed to carcinogenic agents follows the principle of limiting the exposure to "the minimum technically possible". The obtained results evidence that assemblers of aviation industries, whose task does not involve the direct use of primers containing Cr(VI), show an albeit slight occupational exposure to Cr(VI), that must be carefully taken into consideration in planning suitable prevention measures during risk assessment and management processes.

Enhanced sequestration of Cr(VI) by nanoscale zero-valent iron supported on layered double hydroxide by batch and XAFS study.

PubMed

Sheng, Guodong; Hu, Jun; Li, Hui; Li, Jiaxing; Huang, Yuying

2016-04-01

Herein, the reduction of nanoscale zero-valent iron (NZVI) and adsorption of layered double hydroxides (LDH) to sequester Cr(VI) were well combined by the immobilization of NZVI onto LDH surface (NZVI/LDH). The characterization results revealed that LDH decreased NZVI aggregation and thus increased Cr(VI) sequestration. The batch results indicated that Cr(VI) sequestration by NZVI/LDH was higher than that of NZVI, and superior to the sum of reduction and adsorption. The LDH with good anion exchange property allowed the adsorption of Cr(VI), facilitating interfacial reaction by increasing the local concentration of Cr(VI) in the NZVI vicinity. X-ray absorption near edge structure (XANES) results indicated that Cr(VI) was almost completely reduced to Cr(III) by NZVI/LDH, but Cr(VI) was partly reduced to Cr(III) by NZVI with a trace of Cr(VI) adsorbed on corrosion products. The coordination environment of Cr from extended X-ray absorption fine structure (EXAFS) analysis revealed that LDH could be a good scavenger for the insoluble products produced during reaction. So, the insoluble products on NZVI could be reduced, and its reactivity could be maintained. These results demonstrated that NZVI/LDH exhibits multiple functionalities relevant to the remediation of Cr(VI)-contaminated sites. Copyright © 2016 Elsevier Ltd. All rights reserved.

Control of exposure to hexavalent chromium and ozone in gas metal arc welding of stainless steels by use of a secondary shield gas.

PubMed

Dennis, John H; French, Michael J; Hewitt, Peter J; Mortazavi, Seyed B; Redding, Christopher A J

2002-01-01

Previous work has demonstrated that the shield gas composition in gas metal arc welding can have a considerable effect on hexavalent chromium [Cr(VI)] concentration in the fume and on ozone concentrations near the arc. Normally a single shield gas is used. This paper describes a double shroud torch that allows used of concentric shield gases of different compositions. A solid stainless steel wire was used for welding. The double shroud torch used secondary shield gases containing small amounts of the reducing agents NO and C2H4. The Cr(VI) concentration in the fume and ozone concentration at a fixed point relative to the arc were measured and compared with results when using a single shield gas. Use of the reducing agents in secondary shielding using the double shroud torch was found to offer advantages for ozone concentration reduction compared with use in a conventional torch, but this was not found to be an advantage for reducing Cr(VI) concentrations.

Removal of Cr(VI) from Aqueous Environments Using Micelle-Clay Adsorption

PubMed Central

Qurie, Mohannad; Khamis, Mustafa; Manassra, Adnan; Ayyad, Ibrahim; Nir, Shlomo; Scrano, Laura; Bufo, Sabino A.; Karaman, Rafik

2013-01-01

Removal of Cr(VI) from aqueous solutions under different conditions was investigated using either clay (montmorillonite) or micelle-clay complex, the last obtained by adsorbing critical micelle concentration of octadecyltrimethylammonium ions onto montmorillonite. Batch experiments showed the effects of contact time, adsorbent dosage, and pH on the removal efficiency of Cr(VI) from aqueous solutions. Langmuir adsorption isotherm fitted the experimental data giving significant results. Filtration experiments using columns filled with micelle-clay complex mixed with sand were performed to assess Cr(VI) removal efficiency under continuous flow at different pH values. The micelle-clay complex used in this study was capable of removing Cr(VI) from aqueous solutions without any prior acidification of the sample. Results demonstrated that the removal effectiveness reached nearly 100% when using optimal conditions for both batch and continuous flow techniques. PMID:24222757

Method for the determination of chromium in feed matrix by HPLC.

PubMed

Umesh, Balakrishnan; Rajendran, Rajendra Moorthy; Manoharan, Muthu Tamizh

2015-11-01

An improved method for the chromatographic separation and determination of chromium (III) and (VI) [ CRIII AND CRVI: ] in mineral mixtures and feed samples has been developed. The method uses precolumn derivatization using ammonium pyrrolidinedithiocarbamate ( APD: ) followed by reversed-phase liquid chromatography to separate the chromium ions. Both Cr(III) and Cr(VI) species are chelated with ammonium pyrrolidinedithiocarbamate prior to separation by mixing with acetonitrile and 0.5 mmol acetate buffer (pH 4.5). Optimum chromatographic separations were obtained with a polymer-based reversed-phase column (Kinetex, 5 μ, 250 × 4.5 mm, Phenomenex, Torrance, CA) and a mobile phase containing acetonitrile and water (7:3). Both Cr(III) and Cr(VI) ion concentrations were directly determined from the corresponding areas in the chromatogram. The effect of analytical parameters, including pH, concentration of ligand, incubation temperature, and mobile phase, was optimized for both chromium complexes. The range of the procedure was found to be linear for Cr(III) and Cr(VI) concentrations between 0.125 and 4 μg/mL (r² = 0.9926) and 0.1 and 3.0 μg/mL (r² = 0.9983), respectively. Precision was evaluated by replicate analysis in which the percentage relative standard deviation values for chromium complex were found to be below 4.0. The recoveries obtained (85-115%) for both Cr(III) and Cr(VI) complexes indicated the accuracy of the developed method. The degradation products, as well as the excipients, were well resolved from the chromium complex peak in the chromatogram. Finally, the new method proved to be suitable for routine analysis of Cr(III) and Cr(VI) species in raw materials, mineral mixtures, and feed samples. © 2015 Poultry Science Association Inc.

Quantification of the toxic hexavalent chromium content in an organic matrix by X-ray photoelectron spectroscopy (XPS) and ultra-low-angle microtomy (ULAM)

NASA Astrophysics Data System (ADS)

Greunz, Theresia; Duchaczek, Hubert; Sagl, Raffaela; Duchoslav, Jiri; Steinberger, Roland; Strauß, Bernhard; Stifter, David

2017-02-01

Cr(VI) is known for its corrosion inhibitive properties and is, despite legal regulations, still a potential candidate to be added to thin (1-3 μm) protective coatings applied on, e.g., electrical steel as used for transformers, etc. However, Cr(VI) is harmful to the environment and to the human health. Hence, a reliable quantification of it is of decisive interest. Commonly, an alkaline extraction with a photometric endpoint detection of Cr(VI) is used for such material systems. However, this procedure requires an accurate knowledge on sample parameters such as dry film thickness and coating density that are occasionally associated with significant experimental errors. We present a comprehensive study of a coating system with a defined Cr(VI) pigment concentration applied on electrical steel. X-ray photoelectron spectroscopy (XPS) was employed to resolve the elemental chromium concentration and the chemical state. Turning to the fact that XPS is extremely surface sensitive (<10 nm) and that the lowest commonly achievable lateral resolution is a number of times higher than the coating thickness (∼2 μm), a bulk analysis was achieved with XPS line scans on extended wedge-shaped tapers through the coating. For that purpose a special sample preparation step performed on an ultra-microtome was required prior to analysis. Since a temperature increase leads to a reduction of Cr(VI) we extend our method on samples, which were subjected to different curing temperatures. We show that our proposed approach now allows to determine the elemental and Cr(VI) concentration and distribution inside the coating.

Efficacy of mangrove leaf powder for bioremediation of chromium (VI) from aqueous solutions: kinetic and thermodynamic evaluation

NASA Astrophysics Data System (ADS)

Sathish, Thadikamala; Vinithkumar, N. V.; Dharani, G.; Kirubagaran, R.

2015-06-01

Biosorption of heavy metals by bio-materials has been posited as a potential alternative to the existing physicochemical technologies for detoxification and recovery of toxic and valuable metals from wastewaters. In this context, the role of mangrove leaf powder (MLP) as biosorbent for chromium removal was investigated. In the present study, the effect of process parameters such as particle size, solution pH, initial concentration of Cr(VI) ion and adsorbent dose on chromium removal by MLP was investigated. The maximum sorption was observed at particle size 0.5 mm and pH 2.0. The adsorption data follow the pseudo second-order kinetics model. The isotherms denote that Langmuir model is the best fitted than Freundlich model. The maximum adsorption capacity ( Q 0) of 60.24 mg/g of Cr(VI) at 30 min on MLP was determined using the Langmuir model. The adsorption isotherm model indicates that the chromium is adsorbing as monolayer on the surface of MLP with heterogeneous energetic distribution of active sites. Various thermodynamic parameters, such as Gibb's free energy (∆ G °), enthalpy (∆ H °) and entropy (∆ S °) have been calculated. The thermodynamic data revealed that the adsorption of chromium ions onto MLP is endothermic in nature and a spontaneous process. The results of the present study suggest that MLP is an effective bioremediation measure for removal of high concentration of Cr(VI) in waste waters.

Study on Cr(VI) Leaching from Cement and Cement Composites

PubMed Central

Palascakova, Lenka; Kanuchova, Maria

2018-01-01

This paper reports an experimental study on hexavalent chromium leaching from cement samples and cement composites containing silica fume and zeolite additions that were subjected to various leaching agents. The water-soluble Cr(VI) concentrations in cements ranged from 0.2 to 3.2 mg/kg and represented only 1.8% of the total chromium content. The presence of chromium compounds with both chromium oxidation states of III and VI was detected in the cement samples by X-ray photoelectron spectroscopy (XPS). Leaching tests were performed in a Britton-Robinson buffer to simulate natural conditions and showed increased dissolution of Cr(VI) up to 6 mg/kg. The highest amount of leached hexavalent chromium was detected after leaching in HCl. The findings revealed that the leaching of chromium from cements was higher by 55–80% than that from the cement composites. A minimum concentration was observed for all cement samples when studying the relationship between the soluble Cr(VI) and the cement storage time. PMID:29690550

Study on Cr(VI) Leaching from Cement and Cement Composites.

PubMed

Estokova, Adriana; Palascakova, Lenka; Kanuchova, Maria

2018-04-22

This paper reports an experimental study on hexavalent chromium leaching from cement samples and cement composites containing silica fume and zeolite additions that were subjected to various leaching agents. The water-soluble Cr(VI) concentrations in cements ranged from 0.2 to 3.2 mg/kg and represented only 1.8% of the total chromium content. The presence of chromium compounds with both chromium oxidation states of III and VI was detected in the cement samples by X-ray photoelectron spectroscopy (XPS). Leaching tests were performed in a Britton-Robinson buffer to simulate natural conditions and showed increased dissolution of Cr(VI) up to 6 mg/kg. The highest amount of leached hexavalent chromium was detected after leaching in HCl. The findings revealed that the leaching of chromium from cements was higher by 55⁻80% than that from the cement composites. A minimum concentration was observed for all cement samples when studying the relationship between the soluble Cr(VI) and the cement storage time.

Comparative Study of Chromium(VI) Removal from Simulated Industrial Wastewater with Ion Exchange Resins

NASA Astrophysics Data System (ADS)

Li, Xiaofan; Shi, Shaoyuan; Cao, Hongbin; Li, Yuping; Xu, Dongyao

2018-06-01

Ion exchange process is an alternative technique for removal of heavy metal ions from industrial wastewater. The main aim of this paper is to evaluate the performance of different ion exchange resins in removing Cr(VI) from wastewater. The effects of resin types and dosage, initial pH were examined systemically. The results showed that the performance of different resins had obvious difference for the removal of the Cr(VI) ions, in which the type of functional groups of the resin was the main factor. The SEM images indicated that the micro-morphology of resins before and after adsorption of the Cr(VI) presented a little difference. The EDS analysis showed that the adsorbed Cr(VI) was uniformly distributed at the surface of the resins with formation of oxygen-containing groups. The adsorption isotherms and kinetics of Cr(VI) by the different resins are also discussed.

Effects of common groundwater ions on chromate removal by magnetite: importance of chromate adsorption.

PubMed

Meena, Amanda H; Arai, Yuji

2016-01-01

Reductive precipitation of hexavalent chromium (Cr(VI)) with magnetite is a well-known Cr(VI) remediation method to improve water quality. The rapid (

Nano iron oxide impregnated in chitosan bead as a highly efficient sorbent for Cr(VI) removal from water.

PubMed

Lu, Jianbo; Xu, Kai; Yang, Jinmei; Hao, Yarong; Cheng, Fang

2017-10-01

Using Fe(III) salts and chitosan, nano iron oxide impregnated in chitosan bead (NIOC) was successfully synthesized for aqueous Cr(VI) detoxification via sol-gel technique without any additional crosslinking agent. NIOC characterization demonstrated that the iron in NIOC mainly existed as nano akaganeite (β-FeOOH) and complex with chitosan. Intraparticle diffusion was the major rate-limiting step. The maximal adsorption capacity was 69.8mg/g (pH 5.0, 20°C). Normal concentration of coexisting anions (SO 4 2- , CO 3 2- , SiO 3 2 -) showed insignificant competition, whereas PO 4 3- suppressed the Cr(VI) sorption. Cr(VI)-loaded NIOC could be effectively regenerated by alkaline solutions. Column adsorption runs using granular NIOC could effectively treat about 1600 bed volumes of Cr(VI) solution (from 3.7mg Cr/L in influent to <0.5mg Cr/L in effluent). The Cr(VI) removal mechanisms involved the direct sorption of Cr(VI) (electrostatic attraction and ligand exchange), reduction of Cr(VI) into Cr(III) and re-sorption of Cr(III) via chelation on NIOC surface. Copyright © 2017 Elsevier Ltd. All rights reserved.

IN-SITU CR(VI) SOURCE AND PLUME TREATMENT USING A FERROUS IRON BASED REDUCTANT

EPA Science Inventory

A large volume of chromite ore processing residue (COPR) generated from ferrochrome production operations is present at the Macalloy Corporation Superfund site in Charleston, S.C. Groundwater hexavalent chromium (Cr(VI)) concentrations in the approximately 20 acre-foot COPR satu...

IN-SITU CR(VI) SOURCE AND PLUME TREATMENT USING A FERROUS IRON-BASED REDUCTANT

EPA Science Inventory

A large volume of chromite ore processing residue (COPR) generated from ferrochrome production operations is present at the Macalloy Corporation Superfund site in Charleston, S.C. Groundwater hexavalent chromium (Cr(VI)) concentrations in the approximately 20 acre-foot COPR sat...

Comparison of three sampling and analytical methods for the determination of airborne hexavalent chromium.

PubMed

Boiano, J M; Wallace, M E; Sieber, W K; Groff, J H; Wang, J; Ashley, K

2000-08-01

A field study was conducted with the goal of comparing the performance of three recently developed or modified sampling and analytical methods for the determination of airborne hexavalent chromium (Cr(VI)). The study was carried out in a hard chrome electroplating facility and in a jet engine manufacturing facility where airborne Cr(VI) was expected to be present. The analytical methods evaluated included two laboratory-based procedures (OSHA Method ID-215 and NIOSH Method 7605) and a field-portable method (NIOSH Method 7703). These three methods employ an identical sampling methodology: collection of Cr(VI)-containing aerosol on a polyvinyl chloride (PVC) filter housed in a sampling cassette, which is connected to a personal sampling pump calibrated at an appropriate flow rate. The basis of the analytical methods for all three methods involves extraction of the PVC filter in alkaline buffer solution, chemical isolation of the Cr(VI) ion, complexation of the Cr(VI) ion with 1,5-diphenylcarbazide, and spectrometric measurement of the violet chromium diphenylcarbazone complex at 540 nm. However, there are notable specific differences within the sample preparation procedures used in three methods. To assess the comparability of the three measurement protocols, a total of 20 side-by-side air samples were collected, equally divided between a chromic acid electroplating operation and a spray paint operation where water soluble forms of Cr(VI) were used. A range of Cr(VI) concentrations from 0.6 to 960 microg m(-3), with Cr(VI) mass loadings ranging from 0.4 to 32 microg, was measured at the two operations. The equivalence of the means of the log-transformed Cr(VI) concentrations obtained from the different analytical methods was compared. Based on analysis of variance (ANOVA) results, no statistically significant differences were observed between mean values measured using each of the three methods. Small but statistically significant differences were observed between results obtained from performance evaluation samples for the NIOSH field method and the OSHA laboratory method.

Hexavalent chromium reduction potential of Cellulosimicrobium sp. isolated from common effluent treatment plant of tannery industries.

PubMed

Bharagava, Ram Naresh; Mishra, Sandhya

2018-01-01

Present study deals with the isolation and characterization of a bacterium capable for the effective reduction of Cr(VI) from tannery wastewater. Based on the 16S rRNA gene sequence analysis, this bacterium was identified as Cellulosimicrobium sp. (KX710177). During the Cr(VI) reduction experiment performed at 50, 100, 200,and 300mg/L of Cr(VI) concentrations, the bacterium showed 99.33% and 96.98% reduction at 50 and 100mg/L at 24 and 96h, respectively. However, at 200 and 300mg/L concentration of Cr(VI), only 84.62% and 62.28% reduction was achieved after 96h, respectively. The SEM analysis revealed that bacterial cells exposed to Cr(VI) showed increased cell size in comparison to unexposed cells, which might be due to either the precipitation or adsorption of reduced Cr(III) on bacterial cells. Further, the Energy Dispersive X-ray (EDX) analysis showed some chromium peaks for cells exposed to Cr(VI), which might be either due to the presence of precipitated reduced Cr(III) on cells or complexation of Cr(III) with cell surface molecules. The bacterium also showed resistance and sensitivity against the tested antibiotics with a wide range of MIC values ranging from 250 to 800mg/L for different heavy metals. Thus, this multi-drug and multi-metal resistant bacterium can be used as a potential agent for the effective bioremediation of metal contaminated sites. Copyright © 2017 Elsevier Inc. All rights reserved.

Stratification of welding fumes and grinding particles in a large factory hall equipped with displacement ventilation.

PubMed

Niemelä, R; Koskela, H; Engström, K

2001-08-01

The purpose of the study was to investigate the performance of displacement ventilation in a large factory hall where large components of stainless steel for paper, pulp and chemical industries were manufactured. The performance of displacement ventilation was evaluated in terms of concentration distributions of welding fumes and grinding particles, flow field of the supply air and temperature distributions. Large differences in vertical stratification patterns between hexavalent chromium (Cr(VI)) and other particulate contaminants were observed. The concentration of Cr(VI) was notably lower in the zone of occupancy than in the upper part of the factory hall, whereas the concentrations of total airborne particles and trivalent chromium (Cr(III)) were higher in the occupied zone than in the upper zone. The stratification of Cr(VI) had the same tendency as the air temperature stratification caused by the displacement flow field.

Cr(VI) adsorption from electroplating plating wastewater by chemically modified coir pith.

PubMed

Suksabye, Parinda; Thiravetyan, Paitip

2012-07-15

Coir pith samples were chemically modified by grafting with acrylic acid for the removal of Cr(VI) from electroplating wastewater. The presence of acrylic acid on the coir pith surface was verified by a scanning electron microscope with an electron dispersive x-ray spectrometer (SEM/EDX), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TG). The carbonyl groups (C==O) from the carboxylic acids (COOH) increased on the coir pith surface after grafting with acrylic acid. In addition, the thermal stability of the acrylic acid-grafted coir pith also improved. The optimum conditions for grafting the acrylic acid on the coir pith consisted of 2 M acrylic acid and 0.00125 M ceric ammonium nitrate (CAN, as an initiator). The maximum Cr(VI) removal (99.99 ± 0.07%) was obtained with the following conditions: a 1.3% (w/v) dosage of acrylic acid-grafted coir pith, a system pH of 2, a contact time of 22 h, a temperature of 30 °C, a particle size of <150 μm and an initial Cr(VI) of 1,171 mg l(-1). At system pH of 2, Cr(VI) in the HCrO(4)(-) form can be adsorbed with acrylic acid-grafted coir pith via an electrostatic attraction. The adsorption isotherm of 2 M acrylic acid-grafted coir pith exhibited a good fit with the Langmuir isotherm. The maximum Cr(VI) adsorption capacity of the 2 M acrylic acid-grafted coir pith was 196.00 mg Cr(VI) g(-1) adsorbent, whereas for coir pith without grafting, the maximum Cr(VI) removal was 165.00 mg Cr(VI) g(-1) adsorbent. The adsorption capacity of the acrylic acid-grafted coir pith for Cr(VI) was higher compared to the original coir pith. This result was due to the enhancement of the carbonyl groups on the coir pith surface that may have involved the mechanism of chromium adsorption. The X-ray absorption near edged structure (XANES) and desorption studies suggested that most of the Cr(III) that presented on the acrylic acid-grafted coir pith was due to the Cr(VI) being reduced to Cr(III) on the adsorbent surface. FTIR confirmed the involvement of the carbonyl groups (C==O) and the methoxy groups (OCH3) in the mechanism of chromium adsorption. Thermodynamic study, such as enthalpy (ΔH), free energy (ΔG) and entropy change (ΔS) indicated that the overall adsorption process was endothermic, spontaneous and randomness. In addition, the adsorption process was favored at high temperatures. Copyright © 2012 Elsevier Ltd. All rights reserved.

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

Zhang, Ping; Van Nostrand, Joy D.; He, Zhili

Cr(VI) is a widespread environmental contaminant that is highly toxic and soluble. Previous work indicated that a one-time amendment of polylactate hydrogen-release compound (HRC) reduced groundwater Cr(VI) concentrations for >3.5 years at a contaminated aquifer; however, microbial communities responsible for Cr(VI) reduction are poorly understood. Here in this study, we hypothesized that HRC amendment would significantly change the composition and structure of groundwater microbial communities, and that the abundance of key functional genes involved in HRC degradation and electron acceptor reduction would increase long-term in response to this slowly degrading, complex substrate. To test these hypotheses, groundwater microbial communities weremore » monitored after HRC amendment for >1 year using a comprehensive functional gene microarray. The results showed that the overall functional composition and structure of groundwater microbial communities underwent sequential shifts after HRC amendment. Particularly, the abundance of functional genes involved in acetate oxidation, denitrification, dissimilatory nitrate reduction, metal reduction, and sulfate reduction significantly increased. The overall community dynamics was significantly correlated with changes in groundwater concentrations of microbial biomass, acetate, NO 3 -, Cr(VI), Fe(II) and SO 4 2-. Finally, our results suggest that HRC amendment primarily stimulated key functional processes associated with HRC degradation and reduction of multiple electron acceptors in the aquifer toward long-term Cr(VI) reduction.« less

Effect of Humic Acid on the Removal of Chromium(VI) and the Production of Solids in Iron Electrocoagulation.

PubMed

Pan, Chao; Troyer, Lyndsay D; Liao, Peng; Catalano, Jeffrey G; Li, Wenlu; Giammar, Daniel E

2017-06-06

Iron-based electrocoagulation can be highly effective for Cr(VI) removal from water supplies. However, the presence of humic acid (HA) inhibited the rate of Cr(VI) removal in electrocoagulation, with the greatest decreases in Cr(VI) removal rate at higher pH. This inhibition was probably due to the formation of Fe(II) complexes with HA that are more rapidly oxidized than uncomplexed Fe(II) by dissolved oxygen, making less Fe(II) available for reduction of Cr(VI). Close association of Fe(III), Cr(III), and HA in the solid products formed during electrocoagulation influenced the fate of both Cr(III) and HA. At pH 8, the solid products were colloids (1-200 nm) with Cr(III) and HA concentrations in the filtered fraction being quite high, while at pH 6 these concentrations were low due to aggregation of small particles. X-ray diffraction and X-ray absorption fine structure spectroscopy indicated that the iron oxides produced were a mixture of lepidocrocite and ferrihydrite, with the proportion of ferrihydrite increasing in the presence of HA. Cr(VI) was completely reduced to Cr(III) in electrocoagulation, and the coordination environment of the Cr(III) in the solids was similar regardless of the humic acid loading, pH, and dissolved oxygen level.

Nanoadduct relieves: Alleviation of developmental toxicity of Cr(VI) due to its spontaneous adsorption to Mg(OH)2 nanoflakes.

PubMed

Wang, Zhiping; Li, Chunhui; Mu, Yan; Lin, Zhang; Yi, Anji; Zhang, Qiu; Yan, Bing

2015-04-28

During pregnancy, both the mother and fetus are vulnerable to environmental pollution by particulate matters and chemicals. Although the toxicity of free pollutants has been frequently reported, the impact of nanoparticle/pollutant adducts on the vulnerable pregnant population remains unclear. In this study, pregnant mice were orally exposed to Mg(OH)2 nanoflakes and nanoflakes adsorbed with Cr(VI) anions during the peri-implantation and organogenesis stages of pregnancy at doses that did not induce systemic toxicity or pregnancy complications. The nano-Mg(OH)2/Cr(VI) adducts formation reduced fetal developmental toxicity compared with the toxicity induced by the same concentration of free Cr(VI) anions. Copyright © 2015 Elsevier B.V. All rights reserved.

Validation of an electrothermal atomization atomic absorption spectrometry method for quantification of total chromium and chromium(VI) in wild mushrooms and underlying soils.

PubMed

Figueiredo, Estela; Soares, M Elisa; Baptista, Paula; Castro, Marisa; Bastos, M Lourdes

2007-08-22

An ETAAS method was validated to quantify total Cr and Cr(VI) in mushrooms and the underlying soils. The method includes a sample pretreatment for total Cr dissolution using a wet acid digestion procedure and a selective alkaline extraction for Cr(VI). The limits of detection were, expressed in microg/L, 0.15 and 0.17 for total Cr and Cr(VI), respectively. The linearity ranges under the optimized conditions were 0.15-25.0 and 0.17-20.0 microg/L for total Cr and Cr(VI), respectively. The limits of quantification were, expressed in microg/g of dry weight, 0.0163 and 0.0085 for total and hexavalent chromium, respectively. The precision of the instrumental method for total Cr and Cr(VI) was lower than 1.6%, and for the analytical method, it was lower than 10%. The accuracy of the method for Cr(VI) quantification was evaluated by the standard additions method, with the recoveries being higher than 90% for all of the added concentrations. For total Cr, certified reference materials (lichen CRM 482 and soil sample NCS ZC73001) were used. An interference study was also carried out in a mushroom simulated matrix, and it was verified that the deviations of the expected values were lower than 4.0% for both total Cr and Cr(VI). The validated method was applied to the evaluation of total Cr and Cr(VI) in 34 wild mushrooms and 34 respective underlying soil samples collected in two different regions of Portugal (Beira Interior and TrAs-os-Montes), with different locations regarded as noncontaminated or contaminated areas. The species were identified by a mycologist and subdivided into 10 genera and 15 species: Amanita (rubescens, muscaria, and ponderosa), Boletus (regius), Lactarius (deliciosus, vellereus, and piperatus), Suillus (granulatus and luteus), Tricholoma (acerbum), Agaricus (sylvicola), Volvariella (gloiocephala), Lecopaxillus (giganteus), Macrolepiota (procera), and Psilocybe (fascicularis). The mean values found for total Cr were 1.14 and 1.11 microg/g of dry weight, and for Cr(VI), the mean values were 0.103 and 0.143 microg/g of dry weight for cap and stalk, respectively. For soils, the mean concentrations found were, for total Cr, 84.0 microg/g and, for Cr(VI), 0.483 microg/g. The bioconcentration factors (BCFs) based on dry weight for cap and stalk were determined, and the values found, for both total Cr and Cr(VI), were always <1, although for hexavalent chromium, the BCFs were 10 times higher than for total chromium.

Biological groundwater treatment for chromium removal at low hexavalent chromium concentrations.

PubMed

Mamais, Daniel; Noutsopoulos, Constantinos; Kavallari, Ioanna; Nyktari, Eleni; Kaldis, Apostolos; Panousi, Eleni; Nikitopoulos, George; Antoniou, Kornilia; Nasioka, Maria

2016-06-01

The objective of this work is to develop and evaluate biological groundwater treatment systems that will achieve hexavalent chromium reduction and total chromium removal from groundwater at hexavalent chromium (Cr(VI)) groundwater concentrations in the 0-200 μg/L range. Three lab-scale units operated, as sequencing batch reactors (SBR) under aerobic, anaerobic and anaerobic-aerobic conditions. All systems received groundwater with a Cr(VI) content of 200 μg/L. In order to support biological growth, groundwater was supplemented with milk, liquid cheese whey or a mixture of sugar and milk to achieve a COD concentration of 200 mg/L. The results demonstrate that a fully anaerobic system or an anaerobic-aerobic system dosed with simple or complex external organic carbon sources can lead to practically complete Cr(VI) reduction to Cr(III). The temperature dependency of maximum Cr(VI) removal rates can be described by the Arrhenius relationship. Total chromium removal in the biological treatment systems was not complete because a significant portion of Cr(III) remained in solution. An integrated system comprising of an anaerobic SBR followed by a sand filter achieved more than 95% total chromium removal thus resulting in average effluent total and dissolved chromium concentrations of 7 μg/L and 3 μg/L, respectively. Copyright © 2016 Elsevier Ltd. All rights reserved.

Hexavalent Chromium Cr(VI) Up-Regulates COX-2 Expression through an NFκB/c-Jun/AP-1–Dependent Pathway

PubMed Central

Zuo, Zhenghong; Cai, Tongjian; Li, Jingxia; Zhang, Dongyun; Yu, Yonghui

2012-01-01

Background: Hexavalent chromium [Cr(VI)] is recognized as a human carcinogen via inhalation. However, the molecular mechanisms by which Cr(VI) causes cancers are not well understood. Objectives: We evaluated cyclooxygenase-2 (COX-2) expression and the signaling pathway leading to this induction due to Cr(VI) exposure in cultured cells. Methods: We used the luciferase reporter assay and Western blotting to determine COX-2 induction by Cr(VI). We used dominant negative mutant, genetic knockout, gene knockdown, and chromatin immunoprecipitation approaches to elucidate the signaling pathway leading to COX-2 induction. Results: We found that Cr(VI) exposure induced COX-2 expression in both normal human bronchial epithelial cells and mouse embryonic fibroblasts in a concentration- and time-dependent manner. Deletion of IKKβ [inhibitor of transcription factor NFκB (IκB) kinase β; an upstream kinase responsible for nuclear factor κB (NFκB) activation] or overexpression of TAM67 (a dominant-negative mutant of c-Jun) dramatically inhibited the COX-2 induction due to Cr(VI), suggesting that both NFκB and c-Jun/AP-1 pathways were required for Cr(VI)-induced COX-2 expression. Our results show that p65 and c-Jun are two major components involved in NFκB and AP-1 activation, respectively. Moreover, our studies suggest crosstalk between NFκB and c-Jun/AP-1 pathways in cellular response to Cr(VI) exposure for COX-2 induction. Conclusion: We demonstrate for the first time that Cr(VI) is able to induce COX-2 expression via an NFκB/c-Jun/AP-1–dependent pathway. Our results provide novel insight into the molecular mechanisms linking Cr(VI) exposure to lung inflammation and carcinogenesis. PMID:22472290

Effect of chromium (VI) on the multiple nitrogen removal pathways and microbial community of aerobic granular sludge.

PubMed

Zheng, Xiao-Ying; Lu, Dan; Wang, Ming-Yang; Chen, Wei; Zhou, Gan; Zhang, Yuan

2017-06-12

The frequent appearance of Cr(VI) significantly impacts the microbial metabolism in wastewater. In this study, long-term effects of Cr(VI) on microbial community, nitrogen removal pathways and mechanism of aerobic granular sludge (AGS) were investigated. AGS had strong resistance ability to 1.0 mg/L Cr(VI). 3.0 mg/L Cr(VI) increased the heterotrophic-specific ammonia uptake rate (HSAUR) and heterotrophic-specific nitrate uptake rate (HSNUR) transiently, whereas 5.0 mg/L Cr(VI) sharply decreased the specific ammonia uptake rate (SAUR), specific nitrate uptake rate (SNUR) and simultaneous nitrification denitrification rate (SNDR). It was found that Cr (VI) has a greater inhibitory effect on autotrophic nitrification (ASAUR), and the maximal inhibition rate (IR) was 139.19%. Besides, the inhibition of Cr (VI) on nitrogen removal process belongs to non-competitive inhibition. Cr(VI) had a weaker negative impact on heterotrophic bacteria compared with that on autotrophic bacteria. Denaturing gradient gel electrophoresis analyses suggest that Acidovorax sp., flavobacterium sp., uncultured soil bacterium, uncultured nitrosospira sp., uncultured prokaryote, uncultured β-proteobacterium and uncultured pseudomonas sp. were the dominant species. The inhibition of Cr(VI) on nitrite-oxidizing bacteria was the strongest, followed by ammonia-oxidizing bacteria and denitrifying bacteria. Linear correlations between bacterial count and biomass-specific uptake rate were observed when the Cr(VI) concentration exceeded 3 mg/L. This study revealed the effect of Cr(VI) on nitrification is more serious than that on denitrification. Autotrophic and heterotrophic nitrification, heterotrophic denitrification and simultaneous nitrification denitrification played a significant role on nitrogen removal under Cr(VI) stress.

The influence of electrode type on electrocoagulation process for removal of chromium (VI) metal in plating industrial wastewater

NASA Astrophysics Data System (ADS)

Prasetyaningrum, Aji; Jos, Bakti; Dharmawan, Yudhy; Prabowo, Bilal T.; Fathurrazan, Muh.; Fyrouzabadi

2018-05-01

Chromium (VI) is one of the major metallic pollutants in plating industrial wastewater. Cr(VI) is one of toxic metal that cause serious threat to human health and the environment because its non-biodegradable. Among the technologies for removing these pollutants, electrocoagulation can be considered as an effective method. This method have some advantages such as less amount of produced sludge and high efficiency in removal of pollutants.This research intended to study the effects of type of electrode on the degree of Cr(VI) removal from wastewater of plating industry using electrocoagulation method. This laboratory research conducted with 3 types of electrode (aluminum, stainless and combination of both electrode). Synthetic chromium wastewater was prepared at the initial concentration of 100 mg L-1. The process was conducted at pH 3. The electricity current was setting at 3 Ampere. The variable of time of electrocoagulation at 1 and 2 hours. After performing the process on electrochemical cells, samples analyzed by the UV-Vis spectrophotometer regarding amount of Cr(VI) metals. The results showed that aluminium was the best performance electrode at variable of 2 hours with 26% of reduction of Cr(VI)metal content in plating industrial waste water.

A highly sensitive and selective electrochemical sensor for determination of Cr(VI) in the presence of Cr(III) using modified multi-walled carbon nanotubes/quercetin screen-printed electrode.

PubMed

Sadeghi, Susan; Garmroodi, Aziz

2013-12-01

A novel screen-printed carbon electrode modified with quercetin/multi-walled carbon nanotubes was fabricated for determination of Cr(VI) in the presence of excess of Cr(III) without any pretreatment. The method is based on accumulation of the quercetin-Cr(III) complex generated in situ from Cr(VI) at the modified electrode surface in an open circuit followed by differential pulse voltammetry detection. The new method allowed selective determination of Cr(VI) in the presence of Cr(III). The influence of various parameters affecting the adsorptive stripping voltammetry performance was investigated. Under the optimum conditions, the calibration plot was found to be linear in the Cr(VI) concentration range from 1.0 to 200 μmol(-1) with a limit of detection(S/N=3) of 0.3 μmol L(-1). The relative standard deviation (RSD%) of seven replicates of the current measurements for a 50 μmol(-1) of Cr(VI) solution was 3.0%. The developed electrode displayed a very low or no sensitivity to alkali, alkali-earth and transition metal cations and was successfully applied for the determination of Cr(VI) in drinking water samples. © 2013.

Modeling hexavalent chromium removal in a Bacillus sp. fixed-film bioreactor.

PubMed

Nkhalambayausi-Chirwa, Evans M; Wang, Yi-Tin

2004-09-30

A one-dimensional diffusion-reaction model was developed to simulate Cr(VI) reduction in a Bacillus sp. pure culture biofilm reactor with glucose as a sole supplied carbon and energy source. Substrate utilization and Cr(VI) reduction in the biofilm was best represented by a system of (second-order) partial differential equations (PDEs). The PDE system was solved by the (fourth-order) Runge-Kutta method adjusted for mass transport resistance using the (second-order) Crank-Nicholson and Backward Euler finite difference methods. A heuristic procedure (genetic search algorithm) was used to find global optimum values of Cr(VI) reduction and substrate utilization rate kinetic parameters. The fixed-film bioreactor system yielded higher values of the maximum specific Cr(VI) reduction rate coefficient and Cr(VI) reduction capacity (kmc = 0.062 1/h, and Rc = 0.13 mg/mg, respectively) than previously determined in batch reactors (kmc = 0.022 1/h and Rc = 0.012 mg/mg). The model predicted effluent Cr(VI) concentration well with 98.9% confidence (sigmay2 = 2.37 mg2/L2, N = 119) and effluent glucose with 96.4 % confidence (sigmay(w)2 = 5402 mg2/L2, N = 121, w = 100) over a wide range of Cr(VI) loadings (10-498 mg Cr(VI)/L/d). Copyright 2004 Wiley Periodicals, Inc.

Remediation of hexavalent chromium spiked soil by using synthesized iron sulfide particles.

PubMed

Li, Yujie; Wang, Wanyu; Zhou, Liqiang; Liu, Yuanyuan; Mirza, Zakaria A; Lin, Xiang

2017-02-01

Carboxymethyl cellulose (CMC) stabilized microscale iron sulfide (FeS) particles were synthesized and applied to remediate hexavalent chromium (Cr(VI)) spiked soil. The effects of parameters including dosage of FeS particles, soil moisture, and natural organic matter (NOM) in soil were investigated with comparison to iron sulfate (FeSO 4 ). The results show that the stabilized FeS particles can reduce Cr(VI) and immobilize Cr in soil quickly and efficiently. The soil moisture ranging from 40% to 70% and NOM in soil had no significant effects on Cr(VI) remediation by FeS particles. When molar ratio of FeS to Cr(VI) was 1.5:1, about 98% of Cr(VI) in soil was reduced by FeS particles in 3 d and Cr(VI) concentration decreased from 1407 mg kg -1 to 16 mg kg -1 . The total Cr and Cr(VI) in Toxicity Characteristic Leaching Procedure (TCLP) leachate were reduced by 98.4% and 99.4%, respectively. In FeS particles-treated soil, the exchangeable Cr fraction was mainly converted to Fe-Mn oxides bound fraction because of the precipitation of Cr(III)-Fe(III) hydroxides. The physiologically based extraction test (PBET) bioaccessibility of Cr was decreased from 58.67% to 6.98%. Compared to FeSO 4 , the high Cr(VI) removal and Cr immobilization efficiency makes prepared FeS particles a great potential in field application of Cr(VI) contaminated soil remediation. Copyright © 2016 Elsevier Ltd. All rights reserved.

Chromium isotope variation along a contaminated groundwater plume: a coupled Cr(VI)- reduction, advective mixing perspective

NASA Astrophysics Data System (ADS)

Bullen, T.; Izbicki, J.

2007-12-01

Chromium (Cr) is a common contaminant in groundwater, used in electroplating, leather tanning, wood preservation, and as an anti-corrosion agent. Cr occurs in two oxidation states in groundwater: Cr(VI) is highly soluble and mobile, and is a carcinogen; Cr(III) is generally insoluble, immobile and less toxic than Cr(VI). Reduction of Cr(VI) to Cr(III) is thus a central issue in approaches to Cr(VI) contaminant remediation in aquifers. Aqueous Cr(VI) occurs mainly as the chromate (CrO22-) and bichromate (HCrO2-) oxyanions, while Cr(III) is mainly "hexaquo" Cr(H2O)63+. Cr has four naturally-occurring stable isotopes: 50Cr, 52Cr, 53Cr and 54Cr. When Cr(VI) is reduced to Cr(III), the strong Cr-O bond must be broken, resulting in isotopic selection. Ellis et al. (2002) demonstrated that for reduction of Cr(VI) on magnetite and in natural sediment slurries, the change of isotopic composition of the remnant Cr(VI) pool was described by a Rayleigh fractionation model having fractionation factor ɛCr(VI)-Cr(III) = 3.4‰. We attempted to use Cr isotopes as a monitor of Cr(VI) reduction at a field site in Hinkley, California (USA) where groundwater contaminated with Cr(VI) has been under assessment for remediation. Groundwater containing up to 5 ppm Cr(VI) has migrated down-gradient from the contamination source through the fluvial to alluvial sediments to form a well-defined plume. Uncontaminated groundwater in the aquifer immediately adjacent to the plume has naturally-occurring Cr(VI) of 4 ppb or less (CH2M-Hill). In early 2006, colleagues from CH2M-Hill collected 17 samples of groundwater from within and adjacent to the plume. On a plot of δ53Cr vs. log Cr(VI), the data array is strikingly linear and differs markedly from the trend predicted for reduction of Cr(VI) in the contaminated water. There appear to be two groups of data: four samples with δ53Cr >+2‰ and Cr(VI) <4 ppb, and 13 samples with δ53Cr <+2‰ and Cr(VI) >15 ppb. Simple mixing lines between the groundwater samples having <4 ppb Cr(VI), taken to be representative of regional groundwater, and the contaminated water do not pass through the remainder of the data, discounting a simple advective mixing scenario. We hypothesize a more likely scenario that involves both Cr(VI) reduction and advective mixing. As the plume initially expands downgradient, Cr(VI) in water at the leading edge encounters reductant in the aquifer resulting in limited Cr(VI) reduction. As a result of reduction, δ53Cr of Cr(VI) remaining in solution at the leading edge increases along the "reduction" trend from 0 to ~+2‰. Inevitable mixing of this water at the leading edge with regional groundwater results in a suitable mixing end-member to combine with Cr(VI) within the plume in order to explain the bulk of the remaining data. Neither Cr(VI) reduction nor advective mixing of plume and regional groundwaters can explain the data on their own, implying an interplay of at least these two processes during plume evolution. Ellis, A.S., Johnson, T.M. and Bullen, T.D. 2002, Science, 295, 2060-2062.

Adsorption of hexavalent chromium from synthetic and electroplating effluent on chemically modified Swietenia mahagoni shell in a packed bed column.

PubMed

Rangabhashiyam, S; Nandagopal, M S Giri; Nakkeeran, E; Selvaraju, N

2016-07-01

Packed bed column studies were carried out to evaluate the performance of chemically modified adsorbents for the sequestration of hexavalent chromium from synthetic and electroplating industrial effluent. The effects of parameters such as bed height (3-9 cm), inlet flow rate (5-15 mL/min), and influent Cr(VI) concentration (50-200 mg/L) on the percentage removal of Cr(VI) and the adsorption capacity of the adsorbents in a packed bed column were investigated. The breakthrough time increased with increasing bed height and decreased with the increase of inlet flow rate and influent Cr(VI) concentration. The adsorption column models such as Thomas, Adams-Bohart, Yoon-Nelson, and bed depth service time (BDST) were successfully correlated with the experimental data. The Yoon-Nelson and BDST model showed good agreement with the experimental data for all the studied parameter conditions. Results of the present study indicated that the chemically modified Swietenia mahagoni shell can be used as an adsorbent for the removal of Cr(VI) from industrial wastewater in a packed bed column.

Lethal and sub-lethal effects on the Asian common toad Duttaphrynus melanostictus from exposure to hexavalent chromium.

PubMed

Fernando, Vindhya A K; Weerasena, Jagathpriya; Lakraj, G Pemantha; Perera, Inoka C; Dangalle, Chandima D; Handunnetti, Shiroma; Premawansa, Sunil; Wijesinghe, Mayuri R

2016-08-01

Chromium discharged in industrial effluents frequently occurs as an environmental pollutant, but the lethal and sub-lethal effects the heavy metal might cause in animals exposed to it have been insufficiently investigated. Selecting the amphibian Duttaphrynus melanostictus, we carried out laboratory tests to investigate the effects of short and long term exposure to hexavalent chromium (Cr(VI)) in both tadpoles and adult toads. The concentrations used were 0.002, 0.02, 0.2, 1.0 and 2.0mg/L, the first three corresponding to field levels. In vitro exposures were also carried out using toad erythrocytes and Cr(VI) concentrations of 0.0015, 0.003, 0.015, 0.03, 0.15mg/L. Mortality, growth retardation, developmental delays and structural aberrations were noted in the metal-treated tadpoles, with increasing incidence corresponding to increase in Cr(VI) level and duration of exposure. Many of the sub-lethal effects were evident with long term exposure to environmentally relevant levels of the toxicant. Changes in selected blood parameters and erythrocyte morphometry were also detected in Cr(VI) exposed toads, indicating anaemic and leucopenic conditions. In the genotoxicity study, DNA damage indicated by comet assay and increased micronuclei frequency, occurred at the low Cr(VI) concentrations tested. The multiple deleterious effects of exposure to chromium signal the need for monitoring and controlling the discharge of chromium to the environment. The dose-dependency and genotoxic effects observed in this widely distributed Asian toad indicates its suitability for monitoring heavy metal pollution in aquatic systems. Copyright © 2016 Elsevier B.V. All rights reserved.

Morphological and transcriptional responses of Lycopersicon esculentum to hexavalent chromium in agricultural soil.

PubMed

Li, Shi-Guo; Hou, Jing; Liu, Xin-Hui; Cui, Bao-Shan; Bai, Jun-Hong

2016-07-01

The carcinogenic, teratogenic, and mutagenic effects of hexavalent chromium (Cr[VI]) on living organisms through the food chain raise the immediate need to assess the potential toxicological impacts of Cr(VI) on human health. Therefore, the concentration-dependent responses of 12 Cr(VI)-responsive genes selected from a high-throughput Lycopersicon esculentum complementary DNA microarray were examined at different Cr concentrations. The results indicated that most of the genes were differentially expressed from 0.1 mg Cr/kg soil, whereas the lowest-observable-adverse-effect concentrations of Cr(VI) were 1.6 mg Cr/kg soil, 6.4 mg Cr/kg soil, 3.2 mg Cr/kg soil, and 0.4 mg Cr/kg soil for seed germination, root elongation, root biomass, and root morphology, respectively, implying that the transcriptional method was more sensitive than the traditional method in detecting Cr(VI) toxicity. Dose-dependent responses were observed for the relative expression of expansin (p = 0.778), probable chalcone-flavonone isomerase 3 (p = -0.496), and 12S seed storage protein CRD (p = -0.614); therefore, the authors propose the 3 genes as putative biomarkers in Cr(VI)-contaminated soil. Environ Toxicol Chem 2016;35:1751-1758. © 2015 SETAC. © 2015 SETAC.

Influence of oxygenation on chromium redox reactions with manganese sulfide (MnS(s)).

PubMed

Wadhawan, Amar R; Livi, Kenneth J; Stone, Alan T; Bouwer, Edward J

2015-03-17

Manganese sulfide (MnS(s)) minerals exist in sulfidic environments and can have unique reactive abilities because of sulfide, which is a known reductant, and Mn, the oxyhydroxides of which are known oxidants. This study elucidated the role of MnS(s) in controlling Cr speciation with implications on its fate and toxicity in the natural environment, specifically sulfidic sediments that undergo biogeochemical changes due to sediment resuspension during dredging, bioturbation, and flood events. In continuously mixed batch reaction experiments, aqueous CrVI reduction under anaerobic conditions occurred primarily on the surface of MnS(s) displaying a biphasic behavior- the initial rapid removal of CrVI from solution was followed by a slow decline due to surface passivation by reaction products, mainly sorbed or precipitated CrIII. The reaction progress increased with MnS(s) surface area loading but decreased on increasing CrVI concentration and pH, suggesting that surface site regeneration through product desorption was the rate-controlling mechanism. Below circum-neutral pH, higher solubility of MnS(s) resulted in additional CrVI reduction by reduced sulfur species in solution, whereas increased CrIII solubility lowered surface passivation allowing for more reactive sites to participate in the reaction. Aeration of MnS(s) at pH≥7 caused the formation of a heterogeneous MnIII(hydr)oxide that was composed of hausmanite and manganite. CrVI reoccurrence was observed on aeration of CrVI-spiked MnS(s) from the oxidation of product CrIII. The reoccurrence at pH≥7 was attributed to the oxidation of product CrIII by MnIII(hydr)oxide, whereas the reoccurrence at pH<7 was hypothesized from the oxidation of product CrIII by intermediate aqueous MnIII and/or sulfur species. Just as with Cr, MnS(s) may play an important role in speciation, fate, and transport of other environmental contaminants.

Natural and induced reduction of hexavalent chromium in soil

NASA Astrophysics Data System (ADS)

Leita, Liviana; Margon, Alja; Sinicco, Tania; Mondini, Claudio; Valentini, Massimiliano; Cantone, Pierpaolo

2013-04-01

Even though naturally elevated levels of chromium can be found naturally in some soils, distressing amounts of the hexavalent form (CrVI) are largely restricted to sites contaminated by anthropogenic activities. In fact, the widespread use of chromium in various industries and the frequently associated inadequate disposal of its by-products and wastes have created serious environmental pollution problems in many parts of the world. CrVI is toxic to plants, animals and humans and exhibits also mutagenic effects. However, being a strong oxidant, CrVI can be readily reduced to the much less harmful trivalent form (CrIII) when suitable electron donors are present in the environment. CrIII is relatively insoluble, less available for biological uptake, and thus definitely less toxic for web-biota. Various electron donors in soil can be involved in CrVI reduction in soil. The efficiency of CrVI reducing abiotic agents such as ferrous iron and sulphur compounds is well documented. Furthermore, CrVI reduction is also known to be significantly enhanced by a wide variety of cell-produced monosaccharides, including glucose. In this study we evaluated the dynamics of hexavalent chromium (CrVI) reduction in contaminated soil amended or not with iron sulphate or/and glucose and assessed the effects of CrVI on native or glucose-induced soil microbial biomass size and activity. CrVI negatively affected both soil microbial activity and the size of the microbial biomass. During the incubation period, the concentration of CrVI in soil decreased over time whether iron sulphate or/and glucose was added or not, but with different reduction rates. Soil therefore displayed a natural attenuation capacity towards chromate reduction. Addition of iron sulphate or/and glucose, however, increased the reduction rate by both abiotic and biotic mechanisms. Our data suggest that glucose is likely to have exerted an indirect role in the increased rate of CrVI reduction by promoting growth of indigenous microbial biomass, while iron sulphate exerted a direct abiotic role.

Enhanced performance of hexavalent chromium reducing cathodes in the presence of Shewanella oneidensis MR-1 and lactate.

PubMed

Xafenias, Nikolaos; Zhang, Yue; Banks, Charles J

2013-05-07

Biocathodes for the reduction of the highly toxic hexavalent chromium (Cr(VI)) were investigated using Shewanella oneidensis MR-1 (MR-1) as a biocatalyst and performance was assessed in terms of current production and Cr(VI) reduction. Potentiostatically controlled experiments (-500 mV vs Ag/AgCl) showed that a mediatorless MR-1 biocathode started up under aerated conditions in the presence of lactate, received 5.5 and 1.7 times more electrons for Cr(VI) reduction over a 4 h operating period than controls without lactate and with lactate but without MR-1, respectively. Cr(VI) reduction was also enhanced, with a decrease in concentration over the 4 h operating period of 9 mg/L Cr(VI), compared to only 1 and 3 mg/L, respectively, in the controls. Riboflavin, an electron shuttle mediator naturally produced by MR-1, was also found to have a positive impact in potentiostatically controlled cathodes. Additionally, a microbial fuel cell (MFC) with MR-1 and lactate present in both anode and cathode produced a maximum current density of 32.5 mA/m(2) (1000 Ω external load) after receiving a 10 mg/L Cr(VI) addition in the cathode, and cathodic efficiency increased steadily over an 8 day operation period with successive Cr(VI) additions. In conclusion, effective and continuous Cr(VI) reduction with associated current production were achieved when MR-1 and lactate were both present in the biocathodes.

Cytotoxic and clastogenic effects of soluble and insoluble compounds containing hexavalent and trivalent chromium.

PubMed Central

Levis, A. G.; Majone, F.

1981-01-01

Cr(III) and Cr(VI) compounds of varying solubilities have been tested in vitro for their ability to inhibit cell growth and nucleic acid and protein syntheses in BHK cells, to induce alterations in the mitotic cycle in HEp cells, and to increase the frequency of chromosomal aberrations and sister chromatid exchanges (SCE) in CHO cells. All Cr(VI) compounds, and particularly those containing soluble Cr(VI), such as potassium dichromate and zinc yellow, differentially inhibit macromolecular syntheses in BKH cells, that of DNA being always the most affected. Among Cr(III) compounds, which generally have very low cytotoxicity, chromite is particularly active, and inhibits cell growth and DNA synthesis even more than the poorly soluble Cr(VI) compounds. Preincubation in growth medium, with or without metabolizing cell cultures, solubilizes considerable amounts of Cr(VI) from zinc yellow and chromite, but significant amounts are also obtained from the most insoluble Cr(VI) pigments. When BHK cells are treated with such preincubated solutions, reduction of soluble Cr(VI) to Cr(III) by cell metabolites is seen with all Cr(VI) compounds, accompanied by decreased cytotoxicity. The same differences between Cr(VI) and Cr(III) compounds apply to the cytotoxic effects on mitosis of HEp cells and the clastogenic effects on CHO cells. The activity of chromite, the only Cr(III) pigment capable of significantly increasing the frequency of SCE, is due to contamination with soluble Cr(VI). In contrast to the very low cytotoxicity of Cr(III), much higher chromium levels are detected in the cells incubated with soluble Cr(III) than with the same concentrations of soluble Cr(VI). 50% and 75% of chromium accumulated in the cells during treatments with Cr(VI) and Cr(III) respectively remains firmly bound to the cells, even when they are incubated for up to 48 h in normal growth medium. Chromium accumulated in the cells after treatment with Cr(III) is most probably bound to the cell membrane, whereas some of the Cr(VI) is transported through the cell membrane and reduced in the cell nucleus. The results of the present investigation are in agreement with those obtained with the same Cr(VI) and Cr(III) compounds in mutagenicity assays in bacteria and carcinogenicity tests in rodents. A re-evaluation of the mechanisms of chromium carcinogenisis is proposed. PMID:7272188

Evaluation of chromium in red blood cells as an indicator of exposure to hexavalent chromium: An in vitro study.

PubMed

Devoy, Jérôme; Géhin, Antoine; Müller, Samuel; Melczer, Mathieu; Remy, Aurélie; Antoine, Guillaume; Sponne, Isabelle

2016-07-25

Chromium(VI) compounds are classified as carcinogenic to humans. Whereas chromium measurements in urine and whole blood (i.e., including plasma) are indicative of recent exposure, chromium in red blood cells (RBC) is attributable specifically to Cr(VI) exposure. Before recommending Cr in RBC as a biological indicator of Cr(VI) exposure, in-vitro studies must be undertaken to assess its reliability. The present study examines the relationship between the chromium added to a blood sample and that subsequently found in the RBC. After incubation of total blood with chromium, RBC were isolated, counted and their viability assessed. Direct analysis of chromium in RBC was conducted using Atomic Absorption Spectrometry. Hexavalent, but not trivalent Cr, was seen to accumulate in the RBC and we found a strong correlation between the Cr(VI) concentration added to a blood sample and the amount of Cr in RBC. This relationship appears to be independent of the chemical properties of the human blood samples (e.g., different blood donors or different reducing capacities). Even though in-vivo studies are still needed to integrate our understanding of Cr(VI) toxicokinetics, our findings reinforce the idea that a single determination of the chromium concentration in RBC would enable biomonitoring of critical cases of Cr(VI) exposure. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Hexavalent Chromium Induces Chromosome Instability in Human Urothelial Cells

PubMed Central

Wise, Sandra S.; Holmes, Amie L.; Liou, Louis; Adam, Rosalyn M.; Wise, John Pierce

2016-01-01

Numerous metals are well-known human bladder carcinogens. Despite the significant occupational and public health concern of metals and bladder cancer, the carcinogenic mechanisms remain largely unknown. Chromium, in particular, is a metal of concern as incidences of bladder cancer have been found elevated in chromate workers, and there is an increasing concern for patients with metal hip implants. However, the impact of Cr(VI) on bladder cells has not been studied. We compared chromate toxicity in two bladder cell lines; primary human urothelial cells and hTERT-immortalized human urothelial cells. Hexavalent chromium (Cr(VI)) induced a concentration- and time-dependent increase in chromosome damage in both cell lines, with the hTERT-immortalized cells exhibiting more chromosome damage than the primary cells. Chronic exposure to Cr(VI) also induced a concentration-dependent increase in aneuploid metaphases in both cell lines which was not observed after a 24 h exposure. Aneuploidy induction was higher in the hTERT-immortalized cells. When we correct for uptake, Cr(VI) induces a similar amount of chromosome damage and aneuploidy suggesting that the differences in Cr(VI) sensitivity between the two cells lines were due to differences in uptake. The increase in chromosome instability after chronic chromate treatment suggests this may be a mechanism for chromate-induced bladder cancer specifically and may be a mechanism for metal-induced bladder cancer in general. PMID:26908176

Ecotoxicology of Hexavalent Chromium in Freshwater Fish: A Critical Review

PubMed Central

Velma, Venkatramreddy; Vutukuru, S.S.; Tchounwou, Paul B.

2010-01-01

Chromium (Cr) is a naturally occurring element found in rocks, animals, plants, and soil, predominantly in its insoluble trivalent form [Cr(III)]. Intense industrialization and other anthropogenic activities have led to the global occurrence of soluble Cr(VI), which is readily leached from soil to groundwater or surface water, in concentrations above permissible levels. The ecotoxicology of Cr(VI) is linked to its environmental persistence and the ability to induce a variety of adverse effects in biologic systems, including fish. In aquatic ecosystems, Cr(VI) exposure poses a significant threat to aquatic life. This paper reviews the fate and transport of Cr(VI) in the environment and its acute and chronic effects on fish. We also discuss Cr(VI) toxicity at the cellular, biochemical, and genetic levels. An attempt is made in this review to comprehend the staggered data on the toxic effects of Cr(VI) to various species of fish. Such data are extremely useful to the scientific community and public officials involved in health risk assessment and management of environmental contaminants as a guide to the best course of action to restore ecosystems and, in turn, to preserve human health. PMID:19658319

Emissions of chromium (VI) from arc welding.

PubMed

Heung, William; Yun, Myoung-Jin; Chang, Daniel P Y; Green, Peter G; Halm, Chris

2007-02-01

The presence of Cr in the +6 oxidation state (Cr[VI]) is still observed in ambient air samples in California despite steps taken to reduce emissions from plating operations. One known source of emission of Cr(VI) is welding, especially with high Cr-content materials, such as stainless steels. An experimental effort was undertaken to expand and update Cr(VI) emission factors by conducting tests on four types of arc-welding operations: gas-metal arc welding (GMAW), shielded metal arc welding (SMAW), fluxcore arc welding, and pulsed GMAW. Standard American Welding Society hood results were compared with a total enclosure method that permitted isokinetic sampling for particle size-cut measurement, as well as total collection of the aerosol. The fraction of Cr(VI) emitted per unit mass of Cr electrode consumed was determined. Consistent with AP-42 data, initial results indicate that a significant fraction of the total Cr in the aerosol is in the +6 oxidation state. The fraction of Cr(VI) and total aerosol mass produced by the different arc welding methods varies with the type of welding process used. Self-shielded electrodes that do not use a shield gas, for example, SMAW, produce greater amounts of Cr(VI) per unit mass of electrode consumed. The formation of Cr(VI) from standard electrode wires used for welding mild steel was below the method detection limit after eliminating an artifact in the analytical method used.

Preparation and Cr(VI) removal performance of corncob activated carbon.

PubMed

Li, Hongyan; Gao, Pei; Cui, Jianguo; Zhang, Feng; Wang, Fang; Cheng, Jici

2018-05-12

Corncob activated carbon (CCAC) was prepared by a H 3 PO 4 activation method. The optimum conditions for the preparation of CCAC were determined by orthogonal experiments. The effects of pH, reaction time, CCAC dosage, and hexavalent chromium (Cr(VI)) concentrations on Cr(VI) removal by CCAC were studied. Corn straw activated carbon (CSAC) was also prepared using the optimum preparation conditions determined for CCAC. The properties of samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results showed that the optimum preparation conditions for CCAC were as follows: a mass of corncob of 10 g; a mass ratio of corncob to H 3 PO 4 of 1:2; a 5% H 3 BO 3 content of 10 mL; an impregnation time of 45 min; a carbonization temperature of 500 °C. The optimum conditions for the removal of Cr(VI) were as follows: pH < 9; temperature, 308 K; rotation speed, 150 r min -1 ; reaction time, 60 min; CCAC dosage, 1 g L -1 . The Cr(VI) removal rate was above 98%, and the maximum adsorption capacity of CCAC was 9.985 mg g -1 . The concentration of residual Cr(VI) in water was less than 0.05 mg L -1 . FTIR showed that the surfaces of the samples had more oxygen-containing functional groups, which promoted the adsorption. XRD showed that CCAC and CSAC had similar peaks and that these peaks promoted the adsorption of Cr(VI). BET indicated that the number of pores in the samples followed the order CCAC > CSAC > CAC. SEM showed that the CCAC surface had a more porous structure, which enhanced adsorption. EDS showed that the C contents of CCAC and CSAC were much higher than that of CAC. Cr(VI) adsorption on CCAC followed quasi-second-order kinetics and was in accordance with a Langmuir adsorption isotherm, with monolayer adsorption. The adsorption reaction was endothermic, where higher temperatures increased the degree of spontaneous reaction.

A Novel Early Warning System Based on a Sediment Microbial Fuel Cell for In Situ and Real Time Hexavalent Chromium Detection in Industrial Wastewater.

PubMed

Zhao, Shuai; Liu, Pu; Niu, Yongyan; Chen, Zhengjun; Khan, Aman; Zhang, Pengyun; Li, Xiangkai

2018-02-22

Hexavalent chromium (Cr(VI)) is a well-known toxic heavy metal in industrial wastewater, but in situ and real time monitoring cannot be achieved by current methods used during industrial wastewater treatment processes. In this study, a Sediment Microbial Fuel Cell (SMFC) was used as a biosensor for in situ real-time monitoring of Cr(VI), which was the organic substrate is oxidized in the anode and Cr(VI) is reduced at the cathode simultaneously. The pH 6.4 and temperature 25 °C were optimal conditions for the operation. Under the optimal conditions, linearity (R² = 0.9935) of the generated voltage was observed in the Cr(VI) concentration range from 0.2 to 0.7 mg/L. The system showed high specificity for Cr(VI), as other co-existing ions such as Cu 2+ , Zn 2+ , and Pb 2+ did not interfere with Cr(VI) detection. In addition, when the sediment MFC-based biosensor was applied for measuring Cr(VI) in actual wastewater samples, a low deviation (<8%) was obtained, which indicated its potential as a reliable biosensor device. MiSeq sequencing results showed that electrochemically active bacteria ( Geobacter and Pseudomonas ) were enriched at least two-fold on the biofilm of the anode in the biosensor as compared to the SMFC without Cr(VI). Cyclic voltammetry curves indicated that a pair of oxidation/reduction peaks appeared at -111 mV and 581 mV, respectively. These results demonstrated that the proposed sediment microbial fuel cell-based biosensor can be applied as an early warning device for real time in situ detection of Cr(VI) in industrial wastewaters.

Treatment of Alkaline Cr(VI)-Contaminated Leachate with an Alkaliphilic Metal-Reducing Bacterium.

PubMed

Watts, Mathew P; Khijniak, Tatiana V; Boothman, Christopher; Lloyd, Jonathan R

2015-08-15

Chromium in its toxic Cr(VI) valence state is a common contaminant particularly associated with alkaline environments. A well-publicized case of this occurred in Glasgow, United Kingdom, where poorly controlled disposal of a cementitious industrial by-product, chromite ore processing residue (COPR), has resulted in extensive contamination by Cr(VI)-contaminated alkaline leachates. In the search for viable bioremediation treatments for Cr(VI), a variety of bacteria that are capable of reduction of the toxic and highly soluble Cr(VI) to the relatively nontoxic and less mobile Cr(III) oxidation state, predominantly under circumneutral pH conditions, have been isolated. Recently, however, alkaliphilic bacteria that have the potential to reduce Cr(VI) under alkaline conditions have been identified. This study focuses on the application of a metal-reducing bacterium to the remediation of alkaline Cr(VI)-contaminated leachates from COPR. This bacterium, belonging to the Halomonas genus, was found to exhibit growth concomitant to Cr(VI) reduction under alkaline conditions (pH 10). Bacterial cells were able to rapidly remove high concentrations of aqueous Cr(VI) (2.5 mM) under anaerobic conditions, up to a starting pH of 11. Cr(VI) reduction rates were controlled by pH, with slower removal observed at pH 11, compared to pH 10, while no removal was observed at pH 12. The reduction of aqueous Cr(VI) resulted in the precipitation of Cr(III) biominerals, which were characterized using transmission electron microscopy and energy-dispersive X-ray analysis (TEM-EDX) and X-ray photoelectron spectroscopy (XPS). The effectiveness of this haloalkaliphilic bacterium for Cr(VI) reduction at high pH suggests potential for its use as an in situ treatment of COPR and other alkaline Cr(VI)-contaminated environments. Copyright © 2015, Watts et al.

A Novel Early Warning System Based on a Sediment Microbial Fuel Cell for In Situ and Real Time Hexavalent Chromium Detection in Industrial Wastewater

PubMed Central

Zhao, Shuai; Liu, Pu; Niu, Yongyan; Chen, Zhengjun; Khan, Aman; Zhang, Pengyun; Li, Xiangkai

2018-01-01

Hexavalent chromium (Cr(VI)) is a well-known toxic heavy metal in industrial wastewater, but in situ and real time monitoring cannot be achieved by current methods used during industrial wastewater treatment processes. In this study, a Sediment Microbial Fuel Cell (SMFC) was used as a biosensor for in situ real-time monitoring of Cr(VI), which was the organic substrate is oxidized in the anode and Cr(VI) is reduced at the cathode simultaneously. The pH 6.4 and temperature 25 °C were optimal conditions for the operation. Under the optimal conditions, linearity (R2 = 0.9935) of the generated voltage was observed in the Cr(VI) concentration range from 0.2 to 0.7 mg/L. The system showed high specificity for Cr(VI), as other co-existing ions such as Cu2+, Zn2+, and Pb2+ did not interfere with Cr(VI) detection. In addition, when the sediment MFC-based biosensor was applied for measuring Cr(VI) in actual wastewater samples, a low deviation (<8%) was obtained, which indicated its potential as a reliable biosensor device. MiSeq sequencing results showed that electrochemically active bacteria (Geobacter and Pseudomonas) were enriched at least two-fold on the biofilm of the anode in the biosensor as compared to the SMFC without Cr(VI). Cyclic voltammetry curves indicated that a pair of oxidation/reduction peaks appeared at −111 mV and 581 mV, respectively. These results demonstrated that the proposed sediment microbial fuel cell-based biosensor can be applied as an early warning device for real time in situ detection of Cr(VI) in industrial wastewaters. PMID:29470394

Magnetic solid-phase extraction combined with graphite furnace atomic absorption spectrometry for speciation of Cr(III) and Cr(VI) in environmental waters.

PubMed

Jiang, Hong-mei; Yang, Ting; Wang, Yan-hong; Lian, Hong-zhen; Hu, Xin

2013-11-15

A new approach of magnetic solid phase extraction (MSPE) coupled with graphite furnace atomic absorption spectrometry (GFAAS) has been developed for the speciation of Cr(III) and Cr(VI) using zincon-immobilized silica-coated magnetic Fe3O4 nanoparticles (Zincon-Si-MNPs) as the MSPE absorbent. Cr(III) was quantitatively reserved on the absorbent at pH 9.1 while total Cr was reserved at pH 6.5. The absorbed Cr species were eluted by using 2 mol/L HCl and detected by GFAAS. The concentration of Cr(VI) could be calculated by subtracting Cr(III) from total Cr. All the parameters affecting the separation and extraction efficiency of Cr species such as pH, extraction time, concentration and volume of eluent, sample volume and influence of co-existing ions were systematically examined and the optimized conditions were established accordingly. The detection limit (LOD) of the method was 0.016 and 0.011 ng mL(-1) for Cr(III) and Cr(VI), respectively, with the enrichment factor of 100 and 150. The precisions of this method (Relative standard deviation, RSD, n=7) for Cr(III) and Cr(VI) at 0.1 ng mL(-1) were 6.0% and 6.2%, respectively. In order to validate the proposed method, a certified reference material of environmental water was analyzed, and the result of Cr speciation was in good agreement with the certified value. This MSPE-GFAAS method has been successfully applied for the speciation of Cr(III) and Cr(VI) in lake and tap waters with the recoveries of 88-109% for the spiked samples. Moreover, the MSPE separation mechanism of Cr(III) and Cr(VI) based on their adsorption-desorption on Zincon-Si-MNPs has been explained through various spectroscopic characterization. © 2013 Elsevier B.V. All rights reserved.

Biogenic nano-magnetite and nano-zero valent iron treatment of alkaline Cr(VI) leachate and chromite ore processing residue

PubMed Central

Watts, Mathew P.; Coker, Victoria S.; Parry, Stephen A.; Pattrick, Richard A.D.; Thomas, Russell A.P.; Kalin, Robert; Lloyd, Jonathan R.

2015-01-01

Highly reactive nano-scale biogenic magnetite (BnM), synthesized by the Fe(III)-reducing bacterium Geobacter sulfurreducens, was tested for the potential to remediate alkaline Cr(VI) contaminated waters associated with chromite ore processing residue (COPR). The performance of this biomaterial, targeting aqueous Cr(VI) removal, was compared to a synthetic alternative, nano-scale zero valent iron (nZVI). Samples of highly contaminated alkaline groundwater and COPR solid waste were obtained from a contaminated site in Glasgow, UK. During batch reactivity tests, Cr(VI) removal from groundwater was inhibited by ∼25% (BnM) and ∼50% (nZVI) when compared to the treatment of less chemically complex model pH 12 Cr(VI) solutions. In both the model Cr(VI) solutions and contaminated groundwater experiments the surface of the nanoparticles became passivated, preventing complete coupling of their available electrons to Cr(VI) reduction. To investigate this process, the surfaces of the reacted samples were analyzed by TEM-EDX, XAS and XPS, confirming Cr(VI) reduction to the less soluble Cr(III) on the nanoparticle surface. In groundwater reacted samples the presence of Ca, Si and S was also noted on the surface of the nanoparticles, and is likely responsible for earlier onset of passivation. Treatment of the solid COPR material in contact with water, by addition of increasing weight % of the nanoparticles, resulted in a decrease in aqueous Cr(VI) concentrations to below detection limits, via the addition of ⩾5% w/w BnM or ⩾1% w/w nZVI. XANES analysis of the Cr K edge, showed that the % Cr(VI) in the COPR dropped from 26% to a minimum of 4–7% by the addition of 5% w/w BnM or 2% w/w nZVI, with higher additions unable to reduce the remaining Cr(VI). The treated materials exhibited minimal re-mobilization of soluble Cr(VI) by re-equilibration with atmospheric oxygen, with the bulk of the Cr remaining in the solid fraction. Both nanoparticles exhibited a considerable capacity for the remediation of COPR related Cr(VI) contamination, with the synthetic nZVI demonstrating greater reactivity than the BnM. However, the biosynthesized BnM was also capable of significant Cr(VI) reduction and demonstrated a greater efficiency for the coupling of its electrons towards Cr(VI) reduction than the nZVI. PMID:26109747

Biogenic nano-magnetite and nano-zero valent iron treatment of alkaline Cr(VI) leachate and chromite ore processing residue

DOE PAGES

Watts, Mathew P.; Coker, Victoria S.; Parry, Stephen A.; ...

2014-12-11

Highly reactive nano-scale biogenic magnetite (BnM), synthesized by the Fe(III)-reducing bacterium Geobacter sulfurreducens, was tested for the potential to remediate alkaline Cr(VI) contaminated waters associated with chromite ore processing residue (COPR). The performance of this biomaterial, targeting aqueous Cr(VI) removal, was compared to a synthetic alternative, nano-scale zero valent iron (nZVI). Samples of highly contaminated alkaline groundwater and COPR solid waste were obtained from a contaminated site in Glasgow, UK. During batch reactivity tests, Cr(VI) removal from groundwater was inhibited by ~25% (BnM) and ~50% (nZVI) when compared to the treatment of less chemically complex model pH 12 Cr(VI) solutions.more » In both the model Cr(VI) solutions and contaminated groundwater experiments the surface of the nanoparticles became passivated, preventing complete coupling of their available electrons to Cr(VI) reduction. To investigate this process, the surfaces of the reacted samples were analyzed by TEM-EDX, XAS and XPS, confirming Cr(VI) reduction to the less soluble Cr(III) on the nanoparticle surface. In groundwater reacted samples the presence of Ca, Si and S was also noted on the surface of the nanoparticles, and is likely responsible for earlier onset of passivation. Treatment of the solid COPR material in contact with water, by addition of increasing weight % of the nanoparticles, resulted in a decrease in aqueous Cr(VI) concentrations to below detection limits, via the addition of ≥5% w/w BnM or ≥1% w/w nZVI. XANES analysis of the Cr K edge, showed that the % Cr(VI) in the COPR dropped from 26% to a minimum of 4–7% by the addition of 5% w/w BnM or 2% w/w nZVI, with higher additions unable to reduce the remaining Cr(VI). The treated materials exhibited minimal re-mobilization of soluble Cr(VI) by re-equilibration with atmospheric oxygen, with the bulk of the Cr remaining in the solid fraction. Both nanoparticles exhibited a considerable capacity for the remediation of COPR related Cr(VI) contamination, with the synthetic nZVI demonstrating greater reactivity than the BnM. Furthermore, the biosynthesized BnM was also capable of significant Cr(VI) reduction and demonstrated a greater efficiency for the coupling of its electrons towards Cr(VI) reduction than the nZVI.« less

Inhibition of nitrate reduction by chromium (VI) in anaerobic soil microcosms

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

Kourtev, P. S.; Nakatsu, C. H.; Konopka, Allan

2009-10-01

Chromium (VI) is often found as a co-contaminant at sites polluted with organic compounds. We used microcosms amended with glucose or protein, nitrate and increasing concentrations of chromium to study nitrate reduction in Cr(VI) polluted soils. Organic carbon stimulated bacterial activity, but the addition of Cr(VI) caused a lag and then slower rates 5 of CO2 accumulation. Nitrate reduction only occurred after Cr(VI) had been reduced. Bacterial activity was again inhibited when Cr(VI) was added a second time; thus not all Cr-sensitive bacteria were removed in the first phase. Glucose and protein selected for relatively similar bacterial communities, as assayedmore » by PCR-DGGE of the 16S rRNA gene; this selection was modified by the addition of 10 Cr(VI). Cr-resistant bacteria isolated from microcosms were closely related to members of Bacillus, Enterococcus and Propionibacterium sp. Our results indicate that carbon utilization and nitrate reduction in these soils in the presence of Cr(VI) are contingent upon the reduction of the added heavy metal by a limited subset of the bacterial community. The amount of Cr(VI) required to inhibit nitrate reduction was 10-fold less than for aerobic catabolism of the same 15 substrate. We hypothesize that the resistance level of a microbial process is directly related to the diversity of microbes capable of conducting it.« less

Enhanced removal of toxic Cr(VI) in tannery wastewater by photoelectrocatalysis with synthetic TiO2 hollow spheres

NASA Astrophysics Data System (ADS)

Zhao, Yang; Chang, Wenkai; Huang, Zhiding; Feng, Xugen; Ma, Lin; Qi, Xiaoxia; Li, Zenghe

2017-05-01

Owing to the acute toxicity and mobility, the Cr(VI) in tannery wastewater is a huge threat to biological and environmental systems. Herein, an effective photoelectrocatalytic reduction of Cr(VI) was carried out by applying electric field to photocatalysis of as-prepared TiO2 spheres. The synthesis of spherical TiO2 catalytic materials with hollow structure and high surface areas was based on a self-assembly process induced by a mixture of organic acetic acid and ethanol. The possible formation mechanism of TiO2 spheres was proposed and verified by acid concentration-dependent and temperature-dependent experiments. It was found that the reaction rate constant of photoelectrocatalytic reduction of Cr(VI) exhibited an almost 3 fold improvement (0.0362 min-1) as compared to that of photocatalysis (0.0126 min-1). As a result, the mechanism of photoelectrocatalytic reduction of Cr(VI) was described according to the simultaneous determination of Cr(VI), Cr(III) and total Cr in the system. In addition, the effect of pH value and voltage of potential were also discussed. Moreover, this photoelectrocatalysis with TiO2 hollow spheres exhibited excellent activity for reduction of Cr(VI) in actual tannery wastewater produced from three different tanning procedures. These attributes suggest that this photoelectrocatalysis has strong potential applications in the treatment of tannery pollutants.

Aqueous Cr(VI) reduction by electrodeposited zero-valent iron at neutral pH: acceleration by organic matters.

PubMed

Liu, Junxi; Wang, Chuan; Shi, Jianying; Liu, Hong; Tong, Yexiang

2009-04-15

This work investigated the effect of co-existing organic matters on aqueous Cr(VI) reduction by electrodeposited zero-valent iron (ED Fe(0)) at neutral pH. The ED Fe(0) prepared in a solution containing mixture of saccharin, L-ascorbic acid and sodium dodecyl sulfate showed higher activity in reducing the aqueous Cr(VI) at neutral pH than that prepared without any organic presence. XRD and SEM indicated that the structure of ED Fe(0) was significantly improved to nano-scale by the presence of organic mixture in the preparation solution. Further, the ED Fe(0) activity in the Cr(VI) reduction at neutral pH was increased by the co-existence of citric acid or oxalic acid in the chromate solution. Electrochemical impedance spectroscopy (EIS) demonstrated that the corrosive current increased with the concentration of organic matter in the reaction solution. With the co-existing organic matters in the preparation solution, the ED Fe(0) corroded more rapidly due to its nano-size, thus the Cr(VI) reduction by the ferrous iron was accelerated. With the co-existing organic matters in the reaction solution, the Cr(VI) reduction was accelerated by a Fe(II) complex as the main electron donor, and a prevention of the passivation due to the Fe(III) and Cr(III) complexes also accelerated the Cr(VI) reduction.

Study on Adsorption of Chromium (VI) by Activated Carbon from Cassava Sludge

NASA Astrophysics Data System (ADS)

Yang, Jinhui; Li, Chuanshu; Yang, Bin; Kang, Sijun; Zhang, Zhen

2018-03-01

In this paper, a new type of adsorbent prepared by waste sludge from alcohol production industry was used to adsorb Cr (VI) in activated carbon from cassava sludge. A series of static adsorption experiments were carried out on the initial concentration of solution Cr (VI), pH value of solution, adsorption time and dosage of adsorbent. The results of single factor experiments show that the removal rate of Cr (VI) increases with the initial concentration of Cr(VI), while the adsorption amount is opposite. When the pH value of the solution is low, the adsorption effect of activated carbon is better.The adsorption time should be controlled within 40-60min. When the activated carbon dosage is increased, the removal rate increases but the adsorption capacity decreases.

Adverse effects and bioconcentration of chromium in two freshwater rotifer species.

PubMed

Hernández-Ruiz, Esmeralda; Alvarado-Flores, Jesús; Rubio-Franchini, Isidoro; Ventura-Juárez, Javier; Rico-Martínez, Roberto

2016-09-01

Bioaccumulation of trivalent (CrIII) and hexavalent chromium (CrVI), and its adverse effects were studied in two rotifer species: Brachionus calyciflorus (two different strains), and Lecane quadridentata. Median Lethal Concentration (LC50) at 24 h of both species showed that CrVI is highly toxic: LC50 ranges from 4.7 × 10(-5) to 4 × 10(-6) mg L(-1)), compared with CrIII: LC50 ranges from 0.64 to 1.279 mg L(-1). Using the LC50 as an exposure concentration, and using atomic absorption, the bioconcentration factor (BCF) was obtained and BCFs of rotifers exposed to CrIII are four orders of magnitude lower than BCFs of rotifers exposed to CrVI. The effect of Cr on the elemental composition of the two species of rotifers in their structures by X-ray microanalysis by energy dispersion showed that Cr is found in intoxicated rotifers, but not in control rotifers. The basal immunoreactivity to metallothioneins is greater in B. calyciflorus than L. quadridentata. The immunoreactivity to metallothioneins decreases in B. calyciflorus when is exposed to CrIII, in contrast in L. quadridentata the immunoreactivity to metallothioneins increase when is exposed to CrIII, and the immunoreactivity to CrVI in L. quadridentata decrease. A mechanism is proposed in which the harder lorica of L. quadridentata acts as a barrier and accumulator of CrVI, and allows for attenuating responses like metallothionein production in L. quadridentata. Instead, in B. calyciflorus the lack of a harder lorica allows for deeper penetration of CrVI, and no time to produce attenuating measures. Copyright © 2016 Elsevier Ltd. All rights reserved.

Nano-sized Fe2O3/Fe3O4 facilitate anaerobic transformation of hexavalent chromium in soil-water systems.

PubMed

Zhang, Yaxian; Li, Hua; Gong, Libo; Dong, Guowen; Shen, Liang; Wang, Yuanpeng; Li, Qingbiao

2017-07-01

The purpose of this study is to investigate the effects of nano-sized or submicro Fe 2 O 3 /Fe 3 O 4 on the bioreduction of hexavalent chromium (Cr(VI)) and to evaluate the effects of nano-sized Fe 2 O 3 /Fe 3 O 4 on the microbial communities from the anaerobic flooding soil. The results indicated that the net decreases upon Cr(VI) concentration from biotic soil samples amended with nano-sized Fe 2 O 3 (317.1±2.1mg/L) and Fe 3 O 4 (324.0±22.2mg/L) within 21days, which were approximately 2-fold of Cr(VI) concentration released from blank control assays (117.1±5.6mg/L). Furthermore, the results of denaturing gradient gel electrophoresis (DGGE) and high-throughput sequencing indicated a greater variety of microbes within the microbial community in amendments with nano-sized Fe 2 O 3 /Fe 3 O 4 than the control assays. Especially, Proteobacteria occupied a predominant status on the phylum level within the indigenous microbial communities from chromium-contaminated soils. Besides, some partial decrease of soluble Cr(VI) in abiotic nano-sized Fe 2 O 3 /Fe 3 O 4 amendments was responsible for the adsorption of nano-sized Fe 2 O 3 /Fe 3 O 4 to soluble Cr(VI). Hence, the presence of nano-sized Fe 2 O 3 /Fe 3 O 4 could largely facilitate the mobilization and biotransformation of Cr(VI) from flooding soils by adsorption and bio-mediated processes. Copyright © 2017. Published by Elsevier B.V.

Origin of hexavalent chromium in groundwater: The example of Sarigkiol Basin, Northern Greece.

PubMed

Kazakis, N; Kantiranis, N; Kalaitzidou, K; Kaprara, E; Mitrakas, M; Frei, R; Vargemezis, G; Tsourlos, P; Zouboulis, A; Filippidis, A

2017-09-01

Hexavalent chromium constitutes a serious deterioration factor for the groundwater quality of several regions around the world. High concentrations of this contaminant have been also reported in the groundwater of the Sarigkiol hydrological basin (near Kozani city, NW Greece). Specific interest was paid to this particular study area due to the co-existence here of two important factors both expected to contribute to Cr(VI) presence and groundwater pollution; namely the area's exposed ophiolitic rocks and its substantial fly ash deposits originating from the local lignite burning power plant. Accordingly, detailed geochemical, mineralogical, hydro-chemical, geophysical and hydrogeological studies were performed on the rocks, soils, sediments and water resources of this basin. Cr(VI) concentrations varied in the different aquifers, with the highest concentration (up to 120μgL -1 ) recorded in the groundwater of the unconfined porous aquifer situated near the temporary fly ash disposal site. Recharge of the porous aquifer is related mainly to precipitation infiltration and occasional surface run-off. Nevertheless, a hydraulic connection between the porous and neighboring karst aquifers could not be delineated. Therefore, the presence of Cr(VI) in the groundwater of this area is thought to originate from both the ophiolitic rock weathering products in the soils, and the local leaching of Cr(VI) from the diffused fly ash located in the area surrounding the lignite power plant. This conclusion was corroborated by factor analysis, and the strongly positively fractionated Cr isotopes (δ 53 Cr up to 0.83‰) recorded in groundwater, an ash leachate, and the bulk fly ash. An anthropogenic source of Cr(VI) that possibly influences groundwater quality is especially apparent in the eastern part of the Sarigkiol basin. Copyright © 2017 Elsevier B.V. All rights reserved.

Biosorption of chromium (VI) from aqueous solutions and ANN modelling.

PubMed

Nag, Soma; Mondal, Abhijit; Bar, Nirjhar; Das, Sudip Kumar

2017-08-01

The use of sustainable, green and biodegradable natural wastes for Cr(VI) detoxification from the contaminated wastewater is considered as a challenging issue. The present research is aimed to assess the effectiveness of seven different natural biomaterials, such as jackfruit leaf, mango leaf, onion peel, garlic peel, bamboo leaf, acid treated rubber leaf and coconut shell powder, for Cr(VI) eradication from aqueous solution by biosorption process. Characterizations were conducted using SEM, BET and FTIR spectroscopy. The effects of operating parameters, viz., pH, initial Cr(VI) ion concentration, adsorbent dosages, contact time and temperature on metal removal efficiency, were studied. The biosorption mechanism was described by the pseudo-second-order model and Langmuir isotherm model. The biosorption process was exothermic, spontaneous and chemical (except garlic peel) in nature. The sequence of adsorption capacity was mango leaf > jackfruit leaf > acid treated rubber leaf > onion peel > bamboo leaf > garlic peel > coconut shell with maximum Langmuir adsorption capacity of 35.7 mg g -1 for mango leaf. The treated effluent can be reused. Desorption study suggested effective reuse of the adsorbents up to three cycles, and safe disposal method of the used adsorbents suggested biodegradability and sustainability of the process by reapplication of the spent adsorbent and ultimately leading towards zero wastages. The performances of the adsorbents were verified with wastewater from electroplating industry. The scale-up study reported for industrial applications. ANN modelling using multilayer perception with gradient descent (GD) and Levenberg-Marquart (LM) algorithm had been successfully used for prediction of Cr(VI) removal efficiency. The study explores the undiscovered potential of the natural waste materials for sustainable existence of small and medium sector industries, especially in the third world countries by protecting the environment by eco-innovation.

Zinc Chromate Induces Chromosome Instability and DNA Double Strand Breaks in Human Lung Cells

PubMed Central

Xie, Hong; Holmes, Amie L.; Young, Jamie L.; Qin, Qin; Joyce, Kellie; Pelsue, Stephen C.; Peng, Cheng; Wise, Sandra S.; Jeevarajan, Antony S.; Wallace, William T.; Hammond, Dianne; Wise, John Pierce

2014-01-01

Hexavalent chromium Cr(VI) is a respiratory toxicant and carcinogen, with solubility playing an important role in its carcinogenic potential. Zinc chromate, a water insoluble or ‘particulate’ Cr(VI) compound, has been shown to be carcinogenic in epidemiology studies and to induce tumors in experimental animals, but its genotoxicity is poorly understood. Our study shows that zinc chromate induced concentration-dependent increases in cytotoxicity, chromosome damage and DNA double strand breaks in human lung cells. In response to zinc chromate-induced breaks, MRE11 expression was increased and ATM and ATR were phosphorylated, indicating that the DNA double strand break repair system was initiated in the cells. In addition, our data show that zinc chromate-induced double strand breaks were only observed in the G2/M phase population, with no significant amount of double strand breaks observed in G1 and S phase cells. These data will aid in understanding the mechanisms of zinc chromate toxicity and carcinogenesis. PMID:19027772

Self-assembly modified-mushroom nanocomposite for rapid removal of hexavalent chromium from aqueous solution with bubbling fluidized bed.

PubMed

Xu, Fei; Liu, Xu; Chen, Yijiao; Zhang, Ke; Xu, Heng

2016-05-18

A self-assembled modified Pleurotus Cornucopiae material (SMPM) combined with improved Intermittent Bubbling Fluidized Bed (IBFB) was investigated to remove the hexavalent chromium ions in aqueous solution. After the modification, the powder-like raw material gradually self-assembled together to SMPM, which had crinkly porous structure, improved the Cr-accommodation ability in a sound manner. Optimized by Taguchi method, Cr(VI) removal efficiency was up to 75.91% and 48.01% for 100 mg/L and 500 mg/L initial concentration of Cr(VI), respectively. Results indicated that the metal removal was dependent on dosage of adsorbent, particle diameter and treatment time. The experimental data obtained from the biosorption process was successfully correlated with Freundlich isotherm model. Thermodynamic study indicated the endothermic nature of the process. The results confirmed that self-assembly modified Pleurotus Cornucopiae material could be applied for the removal of heavy metal from wastewater in continuous fluidized bed process.

Beneficial role of hydrophytes in removing Cr(VI) from wastewater in association with chromate-reducing bacterial strains Ochrobactrum intermedium and Brevibacterium.

PubMed

Faisal, Muhammad; Hasnain, Shahida

2005-01-01

This study deals with the use of three chromium-resistant bacterial strains (Ochrobactrum intermedium CrT-1, Brevibacterium CrT-13, and CrM-1) in conjunction with Eichornia crassipes for the removal of toxic chromium from wastewater. Bacterial strains resulted in reduced uptake of chromate into inoculated plants as compared to noninoculated control plants. In the presence of different heavy metals, chromium uptake into the plants was 28.7 and 7.15% less at an initial K2CrO4 concentration of 100 and 500 microg ml(-1) in comparison to a metal free chromium solution. K2CrO4 uptake into the plant occurred at different pHs tested, but maximum uptake was observed at pH 5. Nevertheless, the bacterial strains caused some decrease in chromate uptake into the plants, but the combined effect of plants and bacterial strains conduce more removal of Cr(VI) from the solution.

Self-assembly modified-mushroom nanocomposite for rapid removal of hexavalent chromium from aqueous solution with bubbling fluidized bed

PubMed Central

Xu, Fei; Liu, Xu; Chen, Yijiao; Zhang, Ke; Xu, Heng

2016-01-01

A self-assembled modified Pleurotus Cornucopiae material (SMPM) combined with improved Intermittent Bubbling Fluidized Bed (IBFB) was investigated to remove the hexavalent chromium ions in aqueous solution. After the modification, the powder-like raw material gradually self-assembled together to SMPM, which had crinkly porous structure, improved the Cr-accommodation ability in a sound manner. Optimized by Taguchi method, Cr(VI) removal efficiency was up to 75.91% and 48.01% for 100 mg/L and 500 mg/L initial concentration of Cr(VI), respectively. Results indicated that the metal removal was dependent on dosage of adsorbent, particle diameter and treatment time. The experimental data obtained from the biosorption process was successfully correlated with Freundlich isotherm model. Thermodynamic study indicated the endothermic nature of the process. The results confirmed that self-assembly modified Pleurotus Cornucopiae material could be applied for the removal of heavy metal from wastewater in continuous fluidized bed process. PMID:27188258

Self-assembly modified-mushroom nanocomposite for rapid removal of hexavalent chromium from aqueous solution with bubbling fluidized bed

NASA Astrophysics Data System (ADS)

Xu, Fei; Liu, Xu; Chen, Yijiao; Zhang, Ke; Xu, Heng

2016-05-01

A self-assembled modified Pleurotus Cornucopiae material (SMPM) combined with improved Intermittent Bubbling Fluidized Bed (IBFB) was investigated to remove the hexavalent chromium ions in aqueous solution. After the modification, the powder-like raw material gradually self-assembled together to SMPM, which had crinkly porous structure, improved the Cr-accommodation ability in a sound manner. Optimized by Taguchi method, Cr(VI) removal efficiency was up to 75.91% and 48.01% for 100 mg/L and 500 mg/L initial concentration of Cr(VI), respectively. Results indicated that the metal removal was dependent on dosage of adsorbent, particle diameter and treatment time. The experimental data obtained from the biosorption process was successfully correlated with Freundlich isotherm model. Thermodynamic study indicated the endothermic nature of the process. The results confirmed that self-assembly modified Pleurotus Cornucopiae material could be applied for the removal of heavy metal from wastewater in continuous fluidized bed process.

A MIXED CHEMICAL REDUCTANT FOR TREATING HEXAVALENT CHROMIUM IN A CHROMITE ORE PROCESSING SOLID WASTE

EPA Science Inventory

We evaluated a method for delivering ferrous iron into the subsurface to enhance chemical reduction of Cr(VI) in a chromite ore processing solid waste (COPSW). The COPSW is characterized by high pH (8.5 -11.5), high Cr(VI) concentrations in the solid phase (up to 550 mg kg-1) and...

Studies on the optimum conditions using acid-washed zero-valent iron/aluminum mixtures in permeable reactive barriers for the removal of different heavy metal ions from wastewater.

PubMed

Han, Weijiang; Fu, Fenglian; Cheng, Zihang; Tang, Bing; Wu, Shijiao

2016-01-25

The method of permeable reactive barriers (PRBs) is considered as one of the most practicable approaches in treating heavy metals contaminated surface and groundwater. The mixture of acid-washed zero-valent iron (ZVI) and zero-valent aluminum (ZVAl) as reactive medium in PRBs to treat heavy metal wastewater containing Cr(VI), Cd(2+), Ni(2+), Cu(2+), and Zn(2+) was investigated. The performance of column filled with the mixture of acid-washed ZVI and ZVAl was much better than the column filled with ZVI or ZVAl alone. At initial pH 5.4 and flow rates of 1.0 mL/min, the time that the removal efficiencies of Cr(VI), Cd(2+), Ni(2+), Cu(2+), and Zn(2+) were all above 99.5% can keep about 300 h using 80 g/40 g acid-washed ZVI/ZVAl when treating wastewater containing each heavy metal ions (Cr(VI), Cd(2+), Ni(2+), Cu(2+), and Zn(2+)) concentration of 20.0 mg/L. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to characterize ZVI/ZVAl before and after reaction and the reaction mechanism of the heavy metal ions with ZVI/ZVAl was discussed. Copyright © 2015 Elsevier B.V. All rights reserved.

The treatment of chromium containing wastewater using electrocoagulation and the production of ceramic pigments from the resulting sludge.

PubMed

Tezcan Un, Umran; Onpeker, Suzan Eroglu; Ozel, Emel

2017-09-15

This research experimentally investigates the treatment of authentic electroplating wastewater with high Cr(VI) content by electrocoagulation with the obtained sludge being reused as a raw material to produce inorganic pigments. A zero waste process is introduced to help conserve resources and to minimize environmental effects. The effects of operational parameters on electrocoagulation are determined in a batch stirred reactor using an iron electrode. The best performance was observed when a current density 20 mA/cm 2 , pH 2.4 and 0.05 M NaCl electrolyte were maintained. The initial Cr(VI) concentration of 1000 mg/L was almost completely abated (∼100%) at an energy cost of 2.68 kWh/m 3 , fulfilling the EPA guideline of 2.77 mg/L within a single step process. The sludge was characterized using XRD and XRF showing that the sludge is a rich source of iron and chromium and can be reused to produce value added ceramic pigments. Pigments prepared in this way appeared to be reddish brown and black color in transparent glaze and were also characterized using XRD and XRF. In this study, a zero waste process is successfully introduced with ∼100% Cr(VI) removal, with subsequent reuse of the resulting sludge. Copyright © 2017 Elsevier Ltd. All rights reserved.

Box-Behnken experimental design for chromium(VI) ions removal by bacterial cellulose-magnetite composites.

PubMed

Stoica-Guzun, Anicuta; Stroescu, Marta; Jinga, Sorin Ion; Mihalache, Nicoleta; Botez, Adriana; Matei, Cristian; Berger, Daniela; Damian, Celina Maria; Ionita, Valentin

2016-10-01

In this study bacterial cellulose-magnetite composites were synthesised for the removal of chromium(VI) from aqueous solutions. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the bacterial cellulose-magnetite composites and to reveal the uniform dispersion of nanomagnetite in the BC matrix. Magnetic properties were also measured to confirm the magnetite immobilization on bacterial cellulose membrane. The effects of initial Cr(VI) concentration, solution pH and solid/liquid ratio upon chromium removal were examined using the statistical Box-Behnken Design. Because of the possibility of magnetite dissolution during chromium(VI) adsorption, the degree of iron leaching was also analysed in the same conditions as Cr(VI) adsorption. From the factors affecting chromium(VI) adsorption the most important was solution pH. The highest Cr(VI) removal efficiency was observed at pH 4, accompanied by the lowest iron leaching in the solution. The adsorption experiments also indicated that the adsorption process of chromium(VI) is well described by Freundlich adsorption model. Our results proved that the BC-magnetite composites could be used for an efficient removal of chromium(VI) from diluted solutions with a minimum magnetite dissolution during operation. Copyright © 2016 Elsevier B.V. All rights reserved.

Diverse anaerobic Cr(VI) tolerant bacteria from Cr(VI)-contaminated 100H site at Hanford

NASA Astrophysics Data System (ADS)

Chakraborty, R.; Phan, R.; Lam, S.; Leung, C.; Brodie, E. L.; Hazen, T. C.

2007-12-01

Hexavalent Chromium [Cr(VI)] is a widespread contaminant found in soil, sediment, and ground water. Cr(VI) is more soluble, toxic, carcinogenic, and mutagenic compared to its reduced form Cr(III). In order to stimulate microbially mediated reduction of Cr(VI), a poly-lactate compound HRC was injected into the chromium contaminated aquifers at site 100H at Hanford. Based on the results of the bacterial community composition using high-density DNA microarray analysis of 16S rRNA gene products, we recently investigated the diversity of the dominant anaerobic culturable microbial population present at this site and their role in Cr(VI) reduction. Positive enrichments set up at 30°C using specific defined anaerobic media resulted in the isolation of an iron reducing isolate strain HAF, a sulfate reducing isolate strain HBLS and a nitrate reducing isolate, strain HLN among several others. Preliminary 16S rDNA sequence analysis identifies strain HAF as Geobacter metallireducens, strain HLN as Pseudomonas stutzeri and strain HBLS as a member of Desulfovibrio species. Strain HAF isolated with acetate as the electron donor utilized propionate, glycerol and pyruvate as alternative carbon sources, and reduced metals like Mn(IV) and Cr(VI). Growth was optimal at 37°C, pH of 6.5 and 0% salinity. Strain HLN isolated with lactate as electron donor utilized acetate, glycerol and pyruvate as alternative carbon sources, and reduced metals like Mn(IV) and Cr(VI). Optimal growth was observed at 37°C, at a pH of 7.5 and 0.3% salinity. Anaerobic active washed cell suspension of strain HLN reduced almost 95 micromolar Cr(VI) within 4 hours relative to controls. Further, with 100 micromolar Cr(VI) as the sole electron acceptor, cells of strain HLN grew to cell numbers of 4.05X 107/ml over a period of 24hrs after an initial lag, demonstrating direct enzymatic Cr(VI) reduction by this species. 10mM lactate served as the sole electron donor. These results demonstrate that Cr(VI) immobilization at the Hanford 100H site could be mediated by direct microbial metabolism apart from indirect chemical reduction of Cr(VI) by end products of microbial activity.

Hexavalent chromium, a lung carcinogen, confers resistance to thermal stress and interferes with heat shock protein expression in human bronchial epithelial cells.

PubMed

Abreu, Patrícia L; Cunha-Oliveira, Teresa; Ferreira, Leonardo M R; Urbano, Ana M

2018-03-16

Exposure to hexavalent chromium [Cr(VI)], a lung carcinogen, triggers several types of cellular stresses, namely oxidative, genotoxic and proteotoxic stresses. Given the evolutionary character of carcinogenesis, it is tempting to speculate that cells that survive the stresses produced by this carcinogen become more resistant to subsequent stresses, namely those encountered during neoplastic transformation. To test this hypothesis, we determined whether pre-incubation with Cr(VI) increased the resistance of human bronchial epithelial cells (BEAS-2B cells) to the antiproliferative action of acute thermal shock, used here as a model for stress. In line with the proposed hypothesis, it was observed that, at mildly cytotoxic concentrations, Cr(VI) attenuated the antiproliferative effects of both cold and heat shock. Mechanistically, Cr(VI) interfered with the expression of two components of the stress response pathway: heat shock proteins Hsp72 and Hsp90α. Specifically, Cr(VI) significantly depleted the mRNA levels of the former and the protein levels of the latter. Significantly, these two proteins are members of heat shock protein (Hsp) families (Hsp70 and Hsp90, respectively) that have been implicated in carcinogenesis. Thus, our results confirm and extend previous studies showing the capacity of Cr(VI) to interfere with the expression of stress response components.

A plan for study of hexavalent chromium, CR(VI) in groundwater near a mapped plume, Hinkley, California, 2016

USGS Publications Warehouse

Izbicki, John A.; Groover, Krishangi D.

2016-01-22

The Pacific Gas and Electric Company (PG&E) Hinkley compressor station, in the Mojave Desert 80 miles northeast of Los Angeles, is used to compress natural gas as it is transported through a pipeline from Texas to California. Between 1952 and 1964, cooling water used at the compressor station was treated with a compound containing chromium to prevent corrosion. After cooling, the wastewater was discharged to unlined ponds, resulting in contamination of soil and groundwater in the underlying alluvial aquifer (Lahontan Regional Water Quality Control Board, 2013). Since 1964, cooling-water management practices have been used that do not contribute chromium to groundwater.In 2007, a PG&E study of the natural background concentrations of hexavalent chromium, Cr(VI), in groundwater estimated average concentrations in the Hinkley area to be 1.2 micrograms per liter (μg/L), with a 95-percent upper-confidence limit of 3.1 μg/L (CH2M-Hill, 2007). The 3.1 μg/L upper-confidence limit was adopted by the Lahontan Regional Water Quality Control Board (RWQCB) as the maximum background concentration used to map the plume extent. In response to criticism of the study’s methodology, and an increase in the mapped extent of the plume between 2008 and 2011, the Lahontan RWQCB (Lahontan Regional Water Quality Control Board, 2012) agreed that the 2007 PG&E background-concentration study be updated.The purpose of the updated background study is to evaluate the presence of natural and man-made Cr(VI) near Hinkley, Calif. The study also is to estimate natural background Cr(VI) concentrations in the aquifer upgradient and downgradient from the mapped Cr(VI) contamination plume, as well as in the plume and near its margins. The study was developed by the U.S. Geological Survey (USGS) in collaboration with a technical working group (TWG) composed of community members, the Independent Review Panel (IRP) Manager (Project Navigator, Ltd.), the Lahontan RWQCB, PG&E, and consultants for PG&E.&E.

Chromium genotoxicity: a double-edged sword

PubMed Central

Nickens, Kristen P.; Patierno, Steven R.; Ceryak, Susan

2010-01-01

Certain forms of hexavalent chromium [Cr(VI)] are known respiratory carcinogens that induce a broad spectrum of DNA damage. Cr(VI)-carcinogenesis may be initiated or promoted through several mechanistic processes including, the intracellular metabolic reduction of Cr(VI) producing chromium species capable of interacting with DNA to yield genotoxic and mutagenic effects, Cr(VI)-induced inflammatory/immunological responses, and alteration of survival signaling pathways. Cr(VI) enters the cell through nonspecific anion channels, and is metabolically reduced by agents including ascorbate, glutathione, and cysteine to Cr(V), Cr(IV), and Cr(III). Cr(III) has a weak membrane permeability capacity and is unable to cross the cell membrane, thereby trapping it within the cell where it can bind to DNA and produce genetic damage leading to genomic instability. Structural genetic lesions produced by the intracellular reduction of Cr(VI) include DNA adducts, DNA strand breaks, DNA-protein crosslinks, oxidized bases, abasic sites, and DNA inter- and intrastrand crosslinks. The damage induced by Cr(VI) can lead to dysfunctional DNA replication and transcription, aberrant cell cycle checkpoints, dysregulated DNA repair mechanisms, microsatelite instability, inflammatory responses, and the disruption of key regulatory gene networks responsible for the balance of cell survival and cell death, which may all play an important role in Cr(VI) carcinogenesis. Several lines of evidence have indicated that neoplastic progression is a result of consecutive genetic/epigenetic changes that provide cellular survival advantages, and ultimately lead to the conversion of normal human cells to malignant cancer cells. This review is based on studies that provide a glimpse into Cr(VI) carcinogenicity via mechanisms including Cr(VI)-induced death-resistance, the involvement of DNA repair mechanisms in survival after chromium exposure, and the activation of survival signaling cascades in response to Cr(VI) genotoxicity. PMID:20430016

Bacterial reduction of Cr(VI) at technical scale--the Malaysian experience.

PubMed

Zakaria, Zainul Akmar; Ahmad, Wan Azlina; Zakaria, Zainoha; Razali, Firdausi; Karim, Norsuhada Abdul; Sum, Mohamad Md; Sidek, Mohd Saufi Mohd

2012-07-01

The bacterial reduction of Cr(VI) from industrial wastewater was evaluated using a 2.0-m(3) bioreactor. Liquid pineapple waste was used as a nutrient for the biofilm community formed inside the bioreactor. The use of rubber wood sawdust as packing material was able to immobilize more than 10(6) CFU mL(-1) of Acinetobacter haemolyticus cells after 3 days of contact time. Complete reduction of 15-240 mg L(-1) of Cr(VI) was achieved even after 3 months of bioreactor operation. Cr(VI) was not detected in the final effluent fraction indicating complete removal of Cr from solution from the flocculation/coagulation step and the unlikely re-oxidation of Cr(III) into Cr(VI). Impatiens balsamina L. and Gomphrena globosa L. showed better growth in the presence of soil-sludge mixture compared to Coleus scutellarioides (L.) Benth. Significant amounts of Cr accumulated at different sections of the plants indicate its potential application in Cr phytoremediation effort. The bacterial-based system was also determined not to be detrimental to human health based on the low levels of Cr detected in the hair and nail samples of the plant operators. Thus, it can be said that bacterial-based Cr(VI) treatment system is a feasible alternative to the conventional system especially for lower Cr(VI) concentrations, where sludge generated can be used as growth supplement for ornamental plant as well as not detrimental to the health of the workers.

Chromium cycling in soils and water: links, gaps, and methods.

PubMed

Bartlett, R J

1991-05-01

The major links in the cycling of chromium in soils and in natural waters are between chromium(III) and chromium (VI). Between the larger links are lesser links involving processes of mobilization and oxidation of CrIII and reduction of CrVI. The gaps are mainly in our understanding of the factors that control these processes. If soluble CrIII is added to an "average" soil, a portion of it will become immediately oxidized by manganese oxides to CrVI. The rest of the CrIII may remain reduced for long periods of time, even in the presence of electron-accepting manganese oxides. However, this less available CrIII can be mobilized by low molecular weight organic complexers and then oxidized where redox conditions are optimal. Usually part of any CrVI added to a soil or sediment will be reduced instantly, especially under acid conditions. On the other hand, high concentrations of polluting CrVI may quickly exhaust the readily available reducing power of the matrix material and excess CrVI, the thermodynamically stable form in air, may persist for years in soils or lagoons without reduction. Cleanup of chromium pollution must involve the surrounding of both CrIII and CrVI with excesses of slowly available reducing substances and sealing them permanently from inputs of atmospheric oxygen. Monitoring the effectiveness of the measures is mandatory, but fortunately the chemical testing for CrVI in soil and water is simple and problem free compared with most colorimetric determinations.

Hexavalent chromium is cytotoxic and genotoxic to hawksbill sea turtle cells.

PubMed

Wise, Sandra S; Xie, Hong; Fukuda, Tomokazu; Douglas Thompson, W; Wise, John Pierce

2014-09-01

Sea turtles are a charismatic and ancient ocean species and can serve as key indicators for ocean ecosystems, including coral reefs and sea grass beds as well as coastal beaches. Genotoxicity studies in the species are absent, limiting our understanding of the impact of environmental toxicants on sea turtles. Hexavalent chromium (Cr(VI)) is a ubiquitous environmental problem worldwide, and recent studies show it is a global marine pollutant of concern. Thus, we evaluated the cytotoxicity and genotoxicity of soluble and particulate Cr(VI) in hawksbill sea turtle cells. Particulate Cr(VI) was both cytotoxic and genotoxic to sea turtle cells. Concentrations of 0.1, 0.5, 1, and 5μg/cm(2) lead chromate induced 108, 79, 54, and 7% relative survival, respectively. Additionally, concentrations of 0, 0.1, 0.5, 1, and 5μg/cm(2) lead chromate induced damage in 4, 10, 15, 26, and 36% of cells and caused 4, 11, 17, 30, and 56 chromosome aberrations in 100 metaphases, respectively. For soluble Cr, concentrations of 0.25, 0.5, 1, 2.5, and 5μM sodium chromate induced 84, 69, 46, 25, and 3% relative survival, respectively. Sodium chromate induced 3, 9, 9, 14, 21, and 29% of metaphases with damage, and caused 3, 10, 10, 16, 26, and 39 damaged chromosomes in 100 metaphases at concentrations of 0, 0.25, 0.5, 1, 2.5, and 5μM sodium chromate, respectively. These data suggest that Cr(VI) may be a concern for hawksbill sea turtles and sea turtles in general. Copyright © 2014 Elsevier Inc. All rights reserved.

Hexavalent Chromium Is Cytotoxic and Genotoxic to Hawksbill Sea Turtle Cells

PubMed Central

Wise, Sandra S.; Xie, Hong; Fukuda, Tomokazu; Thompson, W. Douglas; Wise, John Pierce

2014-01-01

Sea turtles are a charismatic and ancient ocean species and can serve as key indicators for ocean ecosystems, including coral reefs and sea grass beds as well as coastal beaches. Genotoxicity studies in the species are absent, limiting our understanding of the impact of environmental toxicants on sea turtles. Hexavalent chromium (Cr(VI)) is a ubiquitous environmental problem worldwide, and recent studies show it is a global marine pollutant of concern. Thus, we evaluated the cytotoxicity and genotoxicity of soluble and particulate Cr(VI) in hawksbill sea turtle cells. Particulate Cr(VI) was both cytotoxic and genotoxic to sea turtle cells. Concentrations of 0.1, 0.5, 1, and 5 μg/cm2 lead chromate induced 108, 79, 54, and 7 percent relative survival, respectively. Additionally, concentrations of 0, 0.1, 0.5, 1, and 5 μg/cm2 lead chromate induced damage in 4, 10, 15, 26, and 36 percent of cells and caused 4, 11, 17, 30, and 56 chromosome aberrations in 100 metaphases, respectively. For soluble Cr, concentrations of 0.25, 0.5, 1, 2.5, and 5 μM sodium chromate induced 84, 69, 46, 25, and 3 percent relative survival, respectively. Sodium chromate induced 3, 9, 9, 14, 21, and 29 percent of metaphases with damage, and caused 3, 10, 10, 16, 26, and 39 damaged chromosomes in 100 metaphases at concentrations of 0, 0.25, 0.5, 1, 2.5, and 5 μM sodium chromate, respectively. These data suggest that Cr(VI) may be a concern for hawksbill sea turtles and sea turtles in general. PMID:24952338

Hexavalent chromium removal and bioelectricity generation by Ochrobactrum sp. YC211 under different oxygen conditions.

PubMed

Chen, Chih-Yu; Cheng, Chiu-Yu; Chen, Ching-Kuo; Hsieh, Min-Chi; Lin, Ssu-Ting; Ho, Kuo-Ying; Li, Jo-Wei; Lin, Chia-Pei; Chung, Ying-Chien

2016-01-01

Bioremediation is an environmentally friendly method of reducing heavy metal concentration and toxicity. A chromium-reducing bacterial strain, isolated from the vicinity of an electroplate factory, was identified as Ochrobactrum sp. YC211. The efficiency and capacity per time of Ochrobactrum sp. YC211 for hexavalent chromium (Cr(VI)) removal under anaerobic conditions were superior to those under aerobic conditions. An acceptable removal efficiency (96.5 ± 0.6%) corresponding to 30.2 ± 0.8 mg-Cr (g-dry cell weight-h)(-1) was achieved by Ochrobactrum sp. YC211 at 300 mg L(-1) Cr(VI). A temperature of 30°C and pH 7 were the optimal parameters for Cr(VI) removal. By examining reactivated cells, permeabilized cells, and cell-free extract, we determined that Cr(VI) removal by Ochrobactrum sp. YC211 under anaerobic conditions mainly occurred in the soluble fraction of the cell and can be regarded as an enzymatic reaction. The results also indicated that an Ochrobactrum sp. YC211 microbial fuel cell (MFC) with an anaerobic anode was considerably superior to that with an aerobic anode in bioelectricity generation and Cr(VI) removal. The maximum power density and Cr(VI) removal efficiency of the MFC were 445 ± 3.2 mW m(-2) and 97.2 ± 0.3%, respectively. Additionally, the effects of coexisting ions (Cu(2+), Zn(2+), Ni(2+), SO4(2-), and Cl(-)) in the anolyte on the MFC performance and Cr(VI) removal were nonsignificant (P > 0.05). To our knowledge, this is the first report to compare Cr(VI) removal by different cells and MFC types under aerobic and anaerobic conditions.

Removal of Cr6 + and Ni2+ from aqueous solution using bagasse and fly ash.

PubMed

Rao, M; Parwate, A V; Bhole, A G

2002-01-01

Raw bagasse and fly ash, the waste generated in sugar mills and boilers respectively have been used as low-cost potential adsorbents. Raw bagasse was pretreated with 0.1N NaOH followed by 0.1N CH3COOH before its application. These low-cost adsorbents were used for the removal of chromium and nickel from an aqueous solution. The kinetics of adsorption and extent of adsorption at equilibrium are dependent on the physical and chemical characteristics of the adsorbent, adsorbate and experimental system. The effect of hydrogen ion concentration, contact time, sorbent dose, initial concentrations of adsorbate and adsorbent and particle size on the uptake of chromium and nickel were studied in batch experiments. The Sorption data has been correlated with Langmuir, Freundlich and Bhattacharya and Venkobachar adsorption models. The efficiencies of adsorbent materials for the removal of Cr(VI) and Ni(II) were found to be between 56.2 and 96.2% and 83.6 and 100%, respectively. These results were obtained at the optimized conditions of pH, contact time, sorbent dose, sorbate concentration of 100 mg/l and with the variation of adsorbent particles size between 0.075 and 4.75 mm. The order of selectivity is powdered activated carbon > bagasse > fly ash for Cr(VI) removal and powdered activated carbon > fly ash > bagasse for Ni(II) removal.

Biosorption of Cr(VI) and As(V) at high concentrations by organic and inorganic wastes

NASA Astrophysics Data System (ADS)

María Rivas Pérez, Ivana; Paradelo Núñez, Remigio; Nóvoa Muñoz, Juan Carlos; Arias Estévez, Manuel; José Fernández Sanjurjo, María; Álvarez Rodríguez, Esperanza; Núñez Delgado, Avelino

2016-04-01

The potential reutilization of several wastes as biosorbents for As(V) and Cr(VI) has been assessed in batch-type experiments. The materials studied were one inorganic: mussel shell, and three organic: pine bark, oak ash and hemp waste. Batch experiments were performed in order to determine the removal capacity of the wastes under conditions of high As(V) and Cr(VI) loads. For this, 3 g of each waste material were added with 30 mL NaNO3 0.01 M dissolutions containing 0, 0.5, 1.5, 3 and 6 mmol As(V) L-1 or Cr(VI) L-1, prepared from analytical grade Na2HAsO4 or K2Cr2O7. The resulting suspensions were shaken for 24 h, centrifuged and filtered. Once each batch experiment corresponding to the sorption trials ended, each individual sample was added with 30 mL of NaNO3 0.01 M to desorb As(V) or Cr(VI), shaken for 24 h, centrifuged and filtered as in the sorption trials. Oak ash showed high sorption (>76%) and low desorption (<7%) for As(V), which was lower on mussel shell (<31%), hemp waste (<16%) and pine bark (<9.9%). In turn, pine bark showed the highest Cr(VI) sorption (>98%) with very low desorption (<0.5%), followed by oak ash (27% sorption), and hemp waste and mussel shell, that presented very low Cr(VI) sorption (<10%). Sorption data for both elements were better described by the Freundlich than by the Langmuir model. The variable results obtained for the removal of the two anionic contaminants for a given sorbent suggest that different mechanisms govern removal from the solution in each case. In summary, oak ash would be an efficient sorbent material for As(V), but not for Cr(VI), while pine bark would be the best sorbent for Cr(VI) removal.

The use of stable isotopes for Cr(VI) determination in silty-clay soil solution.

PubMed

Zuliani, Tea; Sčančar, Janez; Milačič, Radmila

2013-09-01

In assessing the environmental hazard of Cr(VI) present in soil, exchangeable Cr(VI) is important, since it can be easily washed out from the upper part of the soil into subsurface soil, surface and ground water, and taken up by plants. The aim of this study was to evaluate the degree of species interconversion that may occur during the extraction of exchangeable Cr(VI) from silty-clay soil with phosphate buffer in order to establish an extraction method that would be effective, accurate and with minimal or no species interconversions. The Cr(VI) concentration in soil extracts was determined by speciated isotope dilution inductively coupled plasma mass spectrometry (SID-ICP-MS). The study was performed on soil samples from a field treated with tannery waste for 17 years. Samples were spiked by enriched stable isotopic solutions of (50)Cr(VI) and (53)Cr(III) that were added to phosphate buffers (0.1 M KH2PO4-K2HPO4 (pH 7.2) and/or 0.1 M K2HPO4 (pH 8)). To optimize extraction, mechanical shaking and/or ultrasound-assisted extraction were compared. The separation and detection of Cr species was performed by high-performance liquid chromatography (HPLC) ICP-MS. When mechanical shaking was applied, 90 % reduction of Cr(VI) was induced by extraction with 0.1 M KH2PO4-K2HPO4, while with 0.1 M K2HPO4 reduction was around 40 %. To shorten the extraction time and the possibility of species interconversions, ultrasound-assisted extraction was further applied only with 0.1 M K2HPO4. For total extraction of exchangeable Cr(VI) with a maximum 10 % reduction of Cr(VI), five consecutive ultrasound-assisted extractions were needed.

Evaluation of on-line desalter-inductively coupled plasma-mass spectrometry system for determination of Cr(III), Cr(VI), and total chromium concentrations in natural water and urine samples

NASA Astrophysics Data System (ADS)

Sun, Y. C.; Lin, C. Y.; Wu, S. F.; Chung, Y. T.

2006-02-01

We have developed a simple and convenient method for the determination of Cr(III), Cr(VI), and the total chromium concentrations in natural water and urine samples that use a flow injection on-line desalter-inductively coupled plasma-mass spectrometry system. When using aqueous ammonium chloride (pH 8) as the stripping solution, the severe interference from sodium in the matrix can be eliminated prior to inductively coupled plasma-mass spectrometry measurement, and the Cr(VI) level can be determined directly. To determine the total concentration of Cr in natural water and urine samples, we used H 2O 2 or HNO 3 to decompose the organic matter and convert all chromium species into the Cr(VI) oxidation state. To overcome the spectral interference caused by the matrix chloride ion in the resulting solutions, we employed cool plasma to successfully suppress chloride-based molecular ion interference during the inductively coupled plasma-mass spectrometry measurement. By significantly eliminating interference from the cationic and anionic components in the matrices prior to the inductively coupled plasma-mass spectrometry measurement, we found that the detection limit reached 0.18 μg L - 1 (based on 3 sigma). We validated this method through the analysis of the total chromium content in two reference materials (NIST 1643c and 2670E) and through measuring the recovery in spiked samples.

Ultratrace Determination of Cr(VI) and Pb(II) by Microsample Injection System Flame Atomic Spectroscopy in Drinking Water and Treated and Untreated Industrial Effluents

PubMed Central

Baig, Jameel Ahmed; Kazi, Tasneem Gul; Elci, Latif; Afridi, Hassan Imran; Khan, Muhammad Irfan; Naseer, Hafiz Muhammad

2013-01-01

Simple and robust analytical procedures were developed for hexavalent chromium (Cr(VI)) and lead (Pb(II)) by dispersive liquid-liquid microextraction (DLLME) using microsample injection system coupled with flame atomic absorption spectrophotometry (MIS-FAAS). For the current study, ammonium pyrrolidine dithiocarbamate (APDC), carbon tetrachloride, and ethanol were used as chelating agent, extraction solvent, and disperser solvent, respectively. The effective variables of developed method have been optimized and studied in detail. The limit of detection of Cr(VI) and Pb(II) were 0.037 and 0.054 µg/L, respectively. The enrichment factors in both cases were 400 with 40 mL of initial volumes. The relative standard deviations (RSDs, n = 6) were <4%. The applicability and the accuracy of DLLME were estimated by the analysis of Cr(VI) and Pb(II) in industrial effluent wastewater by standard addition method (recoveries >96%). The proposed method was successfully applied to the determination of Cr(VI) and Pb(II) at ultratrace levels in natural drinking water and industrial effluents wastewater of Denizli. Moreover, the proposed method was compared with the literature reported method. PMID:24163779

Enhanced chromium adsorption capacity via plasma modification of natural zeolites

NASA Astrophysics Data System (ADS)

Cagomoc, Charisse Marie D.; Vasquez, Magdaleno R., Jr.

2017-01-01

Natural zeolites such as mordenite are excellent adsorbents for heavy metals. To enhance the adsorption capacity of zeolite, sodium-exchanged samples were irradiated with 13.56 MHz capacitively coupled radio frequency (RF) argon gas discharge. Hexavalent chromium [Cr(VI)] was used as the test heavy metal. Pristine and plasma-treated zeolite samples were soaked in 50 mg/L Cr solution and the amount of adsorbed Cr(VI) on the zeolites was calculated at predetermined time intervals. Compared with untreated zeolite samples, initial Cr(VI) uptake was 70% higher for plasma-treated zeolite granules (50 W 30 min) after 1 h of soaking. After 24 h, all plasma-treated zeolites showed increased Cr(VI) uptake. For a 2- to 4-month period, Cr(VI) uptake increased about 130% compared with untreated zeolite granules. X-ray diffraction analyses between untreated and treated zeolite samples revealed no major difference in terms of its crystal structure. However, for plasma-treated samples, an increase in the number of surface defects was observed from scanning electron microscopy images. This increase in the number of surface defects induced by plasma exposure played a crucial role in increasing the number of active sorption sites on the zeolite surface.

Effective treatment of alkaline Cr(VI) contaminated leachate using a novel Pd-bionanocatalyst: Impact of electron donor and aqueous geochemistry

PubMed Central

Watts, Mathew P.; Coker, Victoria S.; Parry, Stephen A.; Thomas, Russell A.P.; Kalin, Robert; Lloyd, Jonathan R.

2015-01-01

Palladium catalysts offer the potential for the effective treatment of a variety of priority reducible pollutants in natural waters. In this study, microbially synthesized magnetite nanoparticles were functionalized with Pd(0), creating a highly reactive, magnetically recoverable, nano-scale catalyst (Pd-BnM). This was then investigated for the treatment of model Cr(VI) contaminated solutions at a range of pH values, and also alkaline Cr(VI) contaminated leachates from chromite ore processing residue (COPR); a contaminant issue of global concern. The sample of COPR used in this study was obtained from a site in Glasgow, UK, where extensive Cr(VI) contamination has been reported. In initial experiments Pd-BnM was supplied with H2 gas or formate as electron donors, and Cr(VI) removal from model synthetic solutions was quantified at various pH values (2–12). Effective removal was noted at neutral to environmentally relevant alkaline (pH 12) pH values, while the use of formate as an electron donor resulted in loss of performance under acidic conditions (pH 2). Reaction kinetics were then assessed with increasing Pd-BnM loading in both model pH 12 Cr(VI) solutions and the COPR leachate. When formate was used as the electron donor for Pd-BnM, to treat COPR leachate, there was significant inhibition of Cr(VI) removal. In contrast, a promotion of reaction rate, was observed when H2 was employed. Upon sustained reaction with model Cr(VI) solutions, in the presence of excess electron donor (formate or H2), appreciable quantities of Cr(VI) were removed before eventual inactivation of the catalyst. Faster onset of inactivation was reported in the COPR leachates, removing 4% and 64% of Cr(VI) observed from model Cr(VI) solutions, when formate and H2 were used as electron donors, respectively. XAS, TEM-EDX and XPS analysis of the catalysts that had been inactivated in the model solution, showed that the surface had an extensive covering of reduced Cr(III), most likely as a CrOOH phase. COPR reacted catalysts recorded a lower abundance of Cr(III) alongside a high abundance of the leachate components Ca and Si, implicating these elements in the faster onset of inactivation. PMID:26146457

Activated carbon with excellent chromium(VI) adsorption performance prepared by acid-base surface modification.

PubMed

Liu, S X; Chen, X; Chen, X Y; Liu, Z F; Wang, H L

2007-03-06

In the present work, activated carbon (AC) with excellent Cr(VI) adsorption performance especially at low concentrations was prepared by an acid-base surface modification method. Raw activated carbon (AC(0)) was first oxidized in boiling HNO(3) (AC(1)), then treated with a mixture of NaOH and NaCl (AC(2)). Batch equilibrium and continuous column adsorption were conducted to evaluate the adsorption performance. Boehm titration, elemental analysis, and N(2)/77K adsorption isotherm methods were used to characterize the surface properties and pore structure of modified ACs. The results revealed that the modified AC exhibited excellent Cr(VI) adsorption performance in terms of adsorption capacity and adsorption rate: AC(2)>AC(1)>AC(0). Modification caused S(BET) to decrease and the total number of surface oxygen acidic groups to increase. HNO(3) oxidization produced positive acid groups, and subsequently NaOH treatment replaced H(+) of surface acid groups by Na(+), and the acidity of AC decreased. The main cause of higher Cr(VI) adsorption capacity and rate for AC(2) was the presence of more oxygen surface acidic groups and suitable surface acidity. HNO(3)-NaOH modification shows potential for the preparation of high quality AC for the effective removal of low concentrations of Cr(VI).

Homologous Recombination Repair Signaling in Chemical Carcinogenesis: Prolonged Particulate Hexavalent Chromium Exposure Suppresses the Rad51 Response in Human Lung Cells

PubMed Central

Qin, Qin; Xie, Hong; Wise, Sandra S.; Browning, Cynthia L.; Thompson, Kelsey N.; Holmes, Amie L.; Wise, John Pierce

2014-01-01

The aim of this study was to focus on hexavalent chromium, [Cr(VI)], a chemical carcinogen and major public health concern, and consider its ability to impact DNA double strand break repair. We further focused on particulate Cr(VI), because it is the more potent carcinogenic form of Cr(VI). DNA double strand break repair serves to protect cells against the detrimental effects of DNA double strand breaks. For particulate Cr(VI), data show DNA double strand break repair must be overcome for neoplastic transformation to occur. Acute Cr(VI) exposures reveal a robust DNA double strand break repair response, however, longer exposures have not been considered. Using the comet assay, we found longer exposures to particulate zinc chromate induced concentration-dependent increases in DNA double strand breaks indicating breaks were occurring throughout the exposure time. Acute (24 h) exposure induced DNA double strand break repair signaling by inducing Mre11 foci formation, ATM phosphorylation and phosphorylated ATM foci formation, Rad51 protein levels and Rad51 foci formation. However, longer exposures reduced the Rad51 response. These data indicate a major chemical carcinogen can simultaneously induce DNA double strand breaks and alter their repair and describe a new and important aspect of the carcinogenic mechanism for Cr(VI). PMID:25173789

Prenatal exposure to chromium induces early reproductive senescence by increasing germ cell apoptosis and advancing germ cell cyst breakdown in the F1 offspring.

PubMed

Sivakumar, Kirthiram K; Stanley, Jone A; Arosh, Joe A; Pepling, Melissa E; Burghardt, Robert C; Banu, Sakhila K

2014-04-01

Hexavalent chromium (CrVI), one of the more toxic heavy metals, is widely used in more than 50 industries such as chrome plating, welding, wood processing and tanneries. As one of the world's leading producers of chromium compounds, the U.S. is facing growing challenges in protecting human health against multiple adverse effects of CrVI. CrVI is rapidly converted to CrIII intracellularly, and can induce apoptosis through different mechanisms. Our previous studies demonstrated postnatal exposure to CrVI results in a delay or arrest in follicle development and puberty. Pregnant rats were treated with 25 ppm potassium dichromate (CrVI) from gestational day (GD) 9.5 to 14.5 through drinking water, placentae were removed on GD 20, and total Cr was estimated in the placentae; ovaries were removed from the F1 offspring on postnatal day (PND)-1 and various analyses were performed. Our results show that gestational exposure to CrVI resulted in (i) increased Cr concentration in the placenta, (ii) increased germ cell apoptosis by up-regulating p53/p27-Bax-caspase-3 proteins and by increasing p53-SOD-2 co-localization; (iii) accelerated germ cell cyst (GCC) breakdown; (iv) advanced primordial follicle assembly and primary follicle transition and (v) down regulation of p-AKT, p-ERK and XIAP. As a result of the above events, CrVI induced early reproductive senescence and decrease in litter size in F1 female progeny. Published by Elsevier Inc.

Prenatal exposure to chromium induces early reproductive senescence by increasing germ cell apoptosis and advancing germ cell cyst breakdown in the F1 offspring

PubMed Central

Sivakumar, Kirthiram K.; Stanley, Jone A.; Arosh, Joe A.; Pepling, Melissa E.; Burghardt, Robert C.; Banu, Sakhila K.

2014-01-01

Hexavalent chromium (CrVI), one of the more toxic heavy metals, is widely used in more than 50 industries such as chrome plating, welding, wood processing and tanneries. As one of the world’s leading producers of chromium compounds, the U.S. is facing growing challenges in protecting human health against multiple adverse effects of CrVI. CrVI is rapidly converted to CrIII intracellularly, and can induce apoptosis through different mechanisms. Our previous studies demonstrated postnatal exposure to CrVI results in a delay or arrest in follicle development and puberty. Pregnant rats were treated with 25 ppm potassium dichromate (CrVI) from gestational day (GD) 9.5 to 14.5 through drinking water, placentae were removed on GD 20, and total Cr was estimated in the placentae; ovaries were removed from the F1 offspring on postnatal day (PND)-1 and various analyses were performed. Our results show that gestational exposure to CrVI resulted in (i) increased Cr concentration in the placenta, (ii) increased germ cell apoptosis by up-regulating p53/p27–Bax–caspase-3 proteins and by increasing p53–SOD-2 co-localization; (iii) accelerated germ cell cyst (GCC) breakdown; (iv) advanced primordial follicle assembly and primary follicle transition and (v) down regulation of p-AKT, p-ERK and XIAP. As a result of the above events, CrVI induced early reproductive senescence and decrease in litter size in F1 female progeny. PMID:24530425

Identification of the main mechanisms involved in the tolerance and bioremediation of Cr(VI) by Bacillus sp. SFC 500-1E.

PubMed

Ontañon, Ornella M; Fernandez, Marilina; Agostini, Elizabeth; González, Paola S

2018-06-01

Chromium pollution is a problem that affects different areas worldwide and, therefore, must be solved. Bioremediation is a promising alternative to treat environmental contamination, but finding bacterial strains able to tolerate and remove different contaminants is a major challenge, since most co-polluted sites contain mixtures of organic and inorganic substances. In the present work, Bacillus sp. SFC 500-1E, isolated from the bacterial consortium SFC 500-1 native to tannery sediments, showed tolerance to various concentrations of different phenolic compounds and heavy metals, such as Cr(VI). This strain was able to efficiently remove Cr(VI), even in the presence of phenol. The detection of the chrA gene suggested that Cr(VI) extrusion could be a mechanism that allowed this strain to tolerate the heavy metal. However, reduction through cytosolic NADH-dependent chromate reductases may be the main mechanism involved in the remediation. The information provided in this study about the mechanisms through which Bacillus sp. SFC 500-1E removes Cr(VI) should be taken into account for the future application of this strain as a possible candidate to remediate contaminated environments.

A hydrological and geochemical analysis of chromium mobilization from serpentinized ultramafic rocks and serpentine soils at the McLaughlin Natural Reserve, Lake County, California

NASA Astrophysics Data System (ADS)

McClain, C.; Maher, K.; Fendorf, S.

2011-12-01

California recently adopted the nation's first Public Health Goal (PHG) for hexavalent chromium (Cr(VI)) in drinking water (0.02 μg/L) because recent studies show that Cr(VI) may be carcinogenic through ingestion. Approximately one third of drinking water sources in California tested for Cr(VI) have levels above 1 μg/L and thus may pose a risk to human health. Cr(VI) can enter drinking water directly from anthropogenic sources or from the release of Cr(III) in natural geogenic sources such as rocks, sediments and soils, and subsequent oxidation to Cr(VI) by manganese oxides. Ultramafic rocks and related soils and sediments have elevated Cr and Mn concentrations compared to other rock types. To study the release of Cr(VI) to water from geogenic sources we examined the local hydrology, groundwater, surface water, soils and sediment compositions within a serpentinized ultramafic terrain along Hunting Creek, a tributary to Putah Creek, at the McLaughlin Natural Reserve in the California Coast Ranges. The hydrology of the site is dominated by fracture flow: groundwater wells were screened in fractured serpentinite, and springs emanating from fractured serpentinite bedrock contribute to the baseflow of Hunting Creek. Soil profiles and bedrock were analyzed for major and trace elements by XRF to assess the fate of Cr during weathering and the distribution of manganese oxides. These factors, along with mineral surface areas, microbial activity, water content, and flow dynamics, collectively control the oxidation of Cr(III). The prevalence of Mg-HCO3 waters at this site indicates that waters are primarily interacting with serpentinites. Pyroxenes are slightly to highly undersaturated and amorphous silica is saturated. Smectite clays, chlorite, and hydromagnesite are supersaturated, indicating formation of secondary mineral phases is favorable and could lead to the inclusion of Cr(III). Total Cr concentrations in surface and groundwater vary from 0.1-26 μg/L and Cr(VI) concentrations vary from < 2.5-22 μg/L, where the highest concentrations were found in seeps emanating from fractured serpentinite and in tributaries to Hunting Creek. Aqueous Cr is mostly present as Cr(VI) (likely CrO42- and MgCrO4), which is consistent with the high pH (7.98-8.72). A reactive transport approach, constrained by solid and fluid data, was used to assess the geochemical transformations that occur along flow paths in order to evaluate the coupling between hydrologic and biogeochemical processes. Similar ultramafic rocks and terrains occur in belts along the Coast Range and the Foothills to the Sierra Nevada and in the Klamath Mountains. Creeks and rivers draining these ultramafic terrains have transported Cr-bearing sediments to the Central Valley, (and other densely populated sedimentary basins and alluvial plains) where they are now widely distributed both at the surface and buried underground, interlaced with aquifer materials. This study highlights the importance of using a holistic approach that considers multiple length scales to understand the factors that control Cr distribution and speciation in natural waters.

Assessment of the mutagenic potential of Cr(VI) in the oral mucosa of Big Blue® transgenic F344 rats.

PubMed

Thompson, Chad M; Young, Robert R; Suh, Mina; Dinesdurage, Harshini R; Elbekai, Reem H; Harris, Mark A; Rohr, Annette C; Proctor, Deborah M

2015-08-01

Exposure to high concentrations of hexavalent chromium [Cr(VI)] in drinking water was associated with an increased incidence of oral tumors in F344 rats in a 2-year cancer bioassay conducted by the National Toxicology Program. These tumors primarily occurred at 180 ppm Cr(VI) and appeared to originate from the gingival mucosa surrounding the upper molar teeth. To investigate whether these tumors could have resulted from a mutagenic mode of action (MOA), a transgenic mutation assay based on OECD Test Guideline 488 was conducted in Big Blue(®) TgF344 rats. The mutagenic oral carcinogen 4-nitroquinoline-1-oxide (4-NQO) served as a positive control. Mutant frequency was measured in the inner gingiva with adjacent palate, and outer gingiva with adjacent buccal tissue. Exposure to 10 ppm 4-NQO in drinking water for 28 days increased mutant frequency in the cII transgene significantly, from 39.1 ± 7.5 × 10(-6) to 688 ± 250 × 10(-6) in the gingival/buccal region, and from 49.8 ± 17.8 × 10(-6) to 1818 ± 362 × 10(-6) in the gingival/palate region. Exposure to 180 ppm Cr(VI) in drinking water for 28 days did not significantly increase the mutant frequency in the gingival/buccal (44.4 ± 25.4 × 10(-6)) or the gingival/palate (57.8 ± 9.1 × 10(-6)) regions relative to controls. These data indicate that high (∼180,000 times expected human exposure), tumorigenic concentrations of Cr(VI) did not significantly increase mutations in the gingival epithelium, and suggest that Cr(VI) does not act by a mutagenic MOA in the rat oral cavity. © 2015 Wiley Periodicals, Inc.

Comparative toxicogenomic analysis of oral Cr(VI) exposure effects in rat and mouse small intestinal epithelia

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

Kopec, Anna K.; Thompson, Chad M.; Kim, Suntae

2012-07-15

Continuous exposure to high concentrations of hexavalent chromium [Cr(VI)] in drinking water results in intestinal tumors in mice but not rats. Concentration-dependent gene expression effects were evaluated in female F344 rat duodenal and jejunal epithelia following 7 and 90 days of exposure to 0.3–520 mg/L (as sodium dichromate dihydrate, SDD) in drinking water. Whole-genome microarrays identified 3269 and 1815 duodenal, and 4557 and 1534 jejunal differentially expressed genes at 8 and 91 days, respectively, with significant overlaps between the intestinal segments. Functional annotation identified gene expression changes associated with oxidative stress, cell cycle, cell death, and immune response that weremore » consistent with reported changes in redox status and histopathology. Comparative analysis with B6C3F1 mouse data from a similarly designed study identified 2790 differentially expressed rat orthologs in the duodenum compared to 5013 mouse orthologs at day 8, and only 1504 rat and 3484 mouse orthologs at day 91. Automated dose–response modeling resulted in similar median EC{sub 50}s in the rodent duodenal and jejunal mucosae. Comparative examination of differentially expressed genes also identified divergently regulated orthologs. Comparable numbers of differentially expressed genes were observed at equivalent Cr concentrations (μg Cr/g duodenum). However, mice accumulated higher Cr levels than rats at ≥ 170 mg/L SDD, resulting in a ∼ 2-fold increase in the number of differentially expressed genes. These qualitative and quantitative differences in differential gene expression, which correlate with differences in tissue dose, likely contribute to the disparate intestinal tumor outcomes. -- Highlights: ► Cr(VI) elicits dose-dependent changes in gene expression in rat intestine. ► Cr(VI) elicits less differential gene expression in rats compared to mice. ► Cr(VI) gene expression can be phenotypically anchored to intestinal changes. ► Species-specific and divergent changes are consistent with species-specific tumors.« less

Chromium isotope fractionation in ferruginous sediments

NASA Astrophysics Data System (ADS)

Bauer, Kohen W.; Gueguen, Bleuenn; Cole, Devon B.; Francois, Roger; Kallmeyer, Jens; Planavsky, Noah; Crowe, Sean A.

2018-02-01

Ferrous Fe is a potent reductant of Cr(VI), and while a number of laboratory studies have characterized Cr isotope fractionation associated with Cr(VI) reduction by ferrous iron, the expression of this fractionation in real-world ferrous Fe-rich environments remains unconstrained. Here we determine the isotope fractionation associated with Cr(VI) reduction in modern ferrous Fe-rich sediments obtained from the previously well studied Lake Matano, Indonesia. Whole core incubations demonstrate that reduction of Cr(VI) within ferruginous sediments provides a sink for Cr(VI) leading to Cr(VI) concentration gradients and diffusive Cr(VI) fluxes across the sediment water interface. As reduction proceeded, Cr(VI) remaining in the overlying lake water became progressively enriched in the heavy isotope (53Cr), increasing δ53Cr by 2.0 ± 0.1‰ at the end of the incubation. Rayleigh distillation modelling of the evolution of Cr isotope ratios and Cr(VI) concentrations in the overlying water yields an effective isotope fractionation of εeff = 1.1 ± 0.2‰ (53Cr/52Cr), whereas more detailed diagenetic modelling implies an intrinsic isotope fractionation of εint = 1.80 ± 0.04‰. Parallel slurry experiments performed using anoxic ferruginous sediment yield an intrinsic isotope fractionation of εint = 2.2 ± 0.1‰. These modelled isotope fractionations are corroborated by direct measurement of the δ53Cr composition on the upper 0.5 cm of Lake Matano sediment, revealing an isotopic offset from the lake water of Δ53Cr = 0.21-1.81‰. The data and models reveal that effective isotope fractionations depend on the depth at which Cr(VI) reduction takes place below the sediment water interface-the deeper the oxic non-reactive zone, the smaller the effective fractionation relative to the intrinsic fractionation. Based on the geochemistry of the sediment we suggest the electron donors responsible for reduction are a combination of dissolved Fe(II) and 0.5 M HCl extractable (solid phase) Fe(II). Our results are in line with the range of intrinsic fractionation factors observed for such phases in previous laboratory studies. We suggest that intrinsic isotope fractionations of around 1.8‰, may be broadly characteristic of ferruginous environments, but we note that the partitioning of ferrous Fe between dissolved and solid phases may modulate this value. These results indicate that seawater δ53Cr is only captured with high-fidelity by ferruginous sediments when oxygen penetration, and therefore the upper boundary of the zone of Cr(VI) reduction, extends to more than 10 cm below the sediment-water-interface, as can be the case in sediments deposited below oligotrophic waters. In more productive regions, with thinner oxic zones, ferruginous sediments would record δ53Cr as much as 1.8‰ lower than seawater δ53Cr. This implies that a range of sediment δ53Cr compositions, that include that of the igneous silicate earth (ISE), are possible even when seawater is isotopically heavier than the ISE.

Comparative cytotoxicity and genotoxicity of soluble and particulate hexavalent chromium in human and hawksbill sea turtle (Eretmochelys imbricate) skin cells

PubMed Central

Young, Jamie L.; Wise, Sandra S.; Xie, Hong; Zhu, Cairong; Fukuda, Tomokazu; Wise, John Pierce

2015-01-01

Chromium is both a global marine pollutant and a known human health hazard. In this study, we compare the cytotoxicity and genotoxicity of both soluble and particulate chromate in human and hawksbill sea turtle (Eretmochelys imbricata) skin fibroblasts. Our data show that both soluble and particulate Cr(VI) induce concentration-dependent increases in cytotoxicity, genotoxicity, and intracellular Cr ion concentrations in both human and hawksbill sea turtle fibroblasts. Based on administered concentration, particulate and soluble Cr(VI) were more cytotoxic and clastogenic to human cells than sea turtle cells. When the analysis was based on the intracellular concentration of Cr, the data showed the response of both species was similar. The one exception was the cytotoxicity of intracellular Cr ions from soluble Cr(VI), which caused more cytotoxicity in sea turtle cells (LC50=271 uM) that human cells (LC50=471 uM), but its clastogenicity was similar between the two species. Thus, adjusting for differences in uptake indicated the explanation for the difference in potency was mostly due to uptake rather than differently affected mechanisms. Overall these data indicate sea turtles may be a useful sentinel for human health responses to marine pollution. PMID:26440299

Comparative cytotoxicity and genotoxicity of soluble and particulate hexavalent chromium in human and hawksbill sea turtle (Eretmochelys imbricata) skin cells.

PubMed

Young, Jamie L; Wise, Sandra S; Xie, Hong; Zhu, Cairong; Fukuda, Tomokazu; Wise, John Pierce

2015-12-01

Chromium is both a global marine pollutant and a known human health hazard. In this study, we compare the cytotoxicity and genotoxicity of both soluble and particulate chromate in human and hawksbill sea turtle (Eretmochelys imbricata) skin fibroblasts. Our data show that both soluble and particulate Cr(VI) induce concentration-dependent increases in cytotoxicity, genotoxicity, and intracellular Cr ion concentrations in both human and hawksbill sea turtle fibroblasts. Based on administered concentration, particulate and soluble Cr(VI) were more cytotoxic and clastogenic to human cells than sea turtle cells. When the analysis was based on the intracellular concentration of Cr, the data showed that the response of both species was similar. The one exception was the cytotoxicity of intracellular Cr ions from soluble Cr(VI), which caused more cytotoxicity in sea turtle cells (LC50=271μM) than that of human cells (LC50=471μM), but its clastogenicity was similar between the two species. Thus, adjusting for differences in uptake indicated that the explanation for the difference in potency was mostly due to uptake rather than differently affected mechanisms. Overall these data indicate that sea turtles may be a useful sentinel for human health responses to marine pollution. Copyright © 2015 Elsevier Inc. All rights reserved.

Biochemical studies of rat lung following exposure to potassium dichromate or chromium-rich welding fume particles.

PubMed

White, L R; Hunt, J; Richards, R J; Eik-Nes, K B

1982-04-01

Rats were examined for biochemical changes at the lung surface and in lung tissue 1, 4, and 13 weeks after a single instillation of the soluble of insoluble fraction of stainless steel welding particles, or potassium dichromate containing concentrations of hexavalent chromium (CrVI) equivalent to those found in the welding particles. Most of the toxicity of the welding particles 1 week after instillation could be related to the content of soluble CrVI, though the insoluble particles also produced changes at the alveolar surface. The regression of inflammatory changes 4 and 13 weeks after instillation was probably due to the removal of soluble components such as CrVI from the lung.

Papaya Seeds as A Low-Cost Sorbent for Removing Cr(VI) from The Aqueous Solution

NASA Astrophysics Data System (ADS)

Rahmawati, Atik; Marwoto, Putut; Karunia Z, Anita

2016-08-01

The presence of chromium (VI) contaminants and their toxicity in aqueous streams important environmental problems. Adsorption is one of the effective techniques that can be used for removing metal from wastewater. This research was initiated by preparing sorbent from papaya seeds and determining its functional group contents by using FT-IR. The adsorption process was carried out in a batch method. The study of adsorption aspects involved the pH, initial Cr (VI) concentration and contact time between Cr (VI) and sorbent. FT IR analysis results showed that the main functional groups are carbonyl, hydroxyl, and carboxylic. It was also found that the effective pH for Cr (VI) uptake is 2.0 and increasing contact time would increase the Cr (VI) uptake. In addition, the equilibrium was reached after 40 minutes interaction and the increase of initial chromium (VI) concentration would increase the sorbent uptake percentage. All these results indicated that papaya seed is a potential sorbent for removing Cr (VI) from aqueous solutions.

Effect of deacetylation on property of electrospun chitosan/PVA nanofibrous membrane and removal of methyl orange, Fe(III) and Cr(VI) ions.

PubMed

Habiba, Umma; Siddique, Tawsif A; Talebian, Sepehr; Lee, Jacky Jia Li; Salleh, Areisman; Ang, Bee Chin; Afifi, Amalina M

2017-12-01

In this study, effect of degree of deacetylation on property and adsorption capacity of chitosan/polyvinyl Alcohol electrospun membrane has been investigated. Resulting nanofibers were characterized by FESEM, FTIR, XRD, TGA, tensile testing, weight loss test and adsorption test. FESEM result shows, finer nanofiber was fabricated from 42h hydrolyzed chitosan and PVA blend solution. FTIR and XRD result showed a strong interaction between chitosan and polyvinyl alcohol. Higher tensile strength was observed for the nanofiber having 42h hydrolyzed chitosan. Blend solution of chitosan/PVA having low DD chitosan had higher viscosity. The nanofibrous membrane was stable in distilled water, acidic and basic medium. The isotherm study shows that the adsorption capacity (q m ) of nanofiber containing higher DD chitosan was higher for Cr(VI). In contrary, the membrane containing chitosan with lower DD showed the higher adsorption capacity for Fe(III) and methyl orange. Moreover, the effect of DD on removal percentage of adsorbate was dependent on the initial concentration of the adsorbate. Copyright © 2017 Elsevier Ltd. All rights reserved.

Radiation-induced graft polymerization for the preparation of a highly efficient UHMWPE fibrous adsorbent for Cr(VI) removal

NASA Astrophysics Data System (ADS)

Gao, Qianhong; Hua, Jiangtao; Li, Rong; Xing, Zhe; Pang, Lijuan; Zhang, Mingxing; Xu, Lu; Wu, Guozhong

2017-01-01

A novel fibrous adsorbent containing amine and quaternary ammonium groups was prepared by radiation-induced graft of glycidyl methacrylate (GMA) onto ultra-high molecular weight polyethylene (UHMWPE) fiber and further modifying with triethylenetetramine (TETA) and glycidyl trimethylammonium chloride (GTA). The ATR-IR spectra and SEM observation demonstrated that amine and quaternary ammonium groups were immobilized onto the surface of UHMWPE fiber. The principal factors affecting the adsorption of Cr(VI) ions have been investigated including pH of the aqueous solution, contact time, temperature and coexisting anions. This novel fibrous adsorbent could effectively adsorb Cr(VI) in the range of pH 1-9, and the maximum adsorption capacity reached 295 mg/g at pH 3 and 25 °C based on the Langmuir isotherm. It was found that adsorption equilibrium could be achieved within 2 h for initial Cr(VI) of 100 mg/L, following the pseudo-second order model. The effect of coexisting anions (including SO42-, H2PO4-, NO3-and Cl-) on the uptake of Cr(VI) was investigated in detail. Additionally, the adsorption saturated fiber could be regenerated by soaking in 0.5 mol/L NaOH solution, and the adsorption performance of this adsorbent could be maintained at 90% after eight cycles of adsorption-desorption. ATR-IR and XPS analysis revealed that Cr(VI) ions were adsorbed on the fiber adsorbent through ion exchange mechanism.

Characterization and Quantification of Hexavalent Chromium and Other Toxic Metals in the Air of Communities Surrounding Metal Processing Facilities

NASA Astrophysics Data System (ADS)

Pikelnaya, O.; Polidori, A.; Low, J.

2017-12-01

Hexavalent chromium [Cr(VI)] and other toxic metals are often emitted during metal forging, cutting, grinding and plating operations. In the South Coast Air Basin (SCAB) many of such operations are conducted by relatively small facilities intertwined within residential communities in the cities of Paramount, Compton, Long Beach and Anaheim. In response to the city of Paramount community members' complaints of "metallic" odors, the South Coast Air Quality Management District (SCAQMD) initiated a local air sampling study for toxic metals, which found elevated Cr(VI) and nickel levels in the community downwind of selected metal processing facilities. SCAQMD worked with these facilities to reduce the emissions from their metal grinding operations, which resulted in substantial reduced nickel levels, but did not reduce Cr(VI) levels. In order to fully understand the source(s) of these emissions, SCAQMD has been deploying portable samplers for Cr(VI) monitoring throughout the city of Paramount since October 2016. During this presentation we will discuss the results of more than a year of Cr(VI) analyses of samplers collected throughout the City of Paramount, as well as data from a continuous metal monitor deployed at one of the sites. We will also discuss options and challenges for expanding of Cr(VI) monitoring to other communities in the SCAB that are adjacent to metal forging and grinding operations; and explore emerging new technologies to address such monitoring challenges.

RESULTS FROM RECENT SCIENCE AND TECHNOLOGY INVESTIGATIONS TARGETING CHROMIUM IN THE 100D AREA HANFORD SITE WASHINGTON USA

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

PETERSEN SW; THOMPSON KM; TONKIN MJ

2009-12-03

Sodium dichromate was used in Hanford's 100D Area during the reactor operations period of 1950 to 1964 to retard corrosion in the reactor cooling systems. Some of the sodium dichromate was released to the environment by spills and/or leaks from pipelines used to deliver the chemical to water treatment plants in the area. As a result, hexavalent chromium [Cr(VI)] has migrated through the vadose zone to the groundwater and contaminated nearly 1 km{sup 2} of groundwater to above the drinking water standard of 48 {micro}g/L. Three technology tests have recently been completed in this area to characterize the source areamore » of the plumes and evaluate alternative methods to remove Cr(VI) from groundwater. These are (1) refine the source area of the southern plume; (2) test electrocoagulation as an alternative groundwater treatment technology; and (3) test the ability to repair a permeable reactive barrier by injecting micron or nanometer-size zero-valent iron (ZVI). The projects were funded by the US Department of Energy as part of a program to interject new technologies and accelerate active cleanup. Groundwater monitoring over the past 10 years has shown that Cr(VI) concentrations in the southern plume have not significantly diminished, strongly indicating a continuing source. Eleven groundwater wells were installed in 2007 and 2008 near a suspected source area and monitored for Cr(VI) and groundwater levels. Interpretation of these data has led to refinement of the source area location to an area of less than 1 hectare (ha, 2.5 acres). Vadose zone soil samples collected during drilling did not discover significant concentrations of Cr(VI), indicating the source is localized, with a narrow wetted path from the surface to the water table. Electrocoagulation was evaluated through a pilot-scale treatability test. Over 8 million liters of groundwater were treated to Cr(VI) concentrations of {le}20 {micro}g/L. The test determined that this technology has the potential to treat Cr(VI) to these low levels, but system reliability and operational complexity rendered electrocoagulation less cost effective than the baseline technology of ion exchange. Laboratory and field tests were conducted to evaluate the practicality of injecting ZVI into the aquifer to increase the lifespan and effectiveness of an existing permeable reactive barrier. From a database of 30 ZVI materials, 6 were chosen and tested in the laboratory to determine their geochemical and physical performance under simulated 100D aquifer conditions. The best-performing ZVI was injected into the aquifer and met the primary goals of communicating the iron at least 7 meters from the injection point and reducing the aquifer to transform mobile Cr(VI) to trivalent chromium Cr(III), which is effectively immobile in the aquifer.« less

On the removal of hexavalent chromium from a Class F fly ash.

PubMed

Huggins, F E; Rezaee, M; Honaker, R Q; Hower, J C

2016-05-01

Coarse and fine samples of a Class F fly ash obtained from commercial combustion of Illinois bituminous coal have been exposed to two long-term leaching tests designed to simulate conditions in waste impoundments. ICP-AES analysis indicated that the coarse and fine fly ash samples contained 135 and 171mg/kg Cr, respectively. Measurements by XAFS spectroscopy showed that the ash samples originally contained 5 and 8% of the chromium, respectively, in the hexavalent oxidation state, Cr(VI). After exposure to water for more than four months, the percentage of chromium as Cr(VI) in the fly-ash decreased significantly for the coarse and fine fly-ash in both tests. Combining the XAFS data with ICP-AES data on the concentration of chromium in the leachates indicated that, after the nineteen-week-long, more aggressive, kinetic test on the coarse fly ash, approximately 60% of the Cr(VI) had been leached, 20% had been reduced to Cr(III) and retained in the ash, and 20% remained as Cr(VI) in the ash. In contrast, during the six-month-long baseline test, very little Cr was actually leached from either the coarse or the fine fly-ash (<0.1mg/kg); rather, about 66% and 20%, respectively, of the original Cr(VI) in the coarse and fine fly-ash was retained in the ash in that form, while the remainder, 34% and 80%, respectively, was reduced and retained in the ash as Cr(III). The results are interpreted as indicating that Cr(VI) present in Class F fly-ash can be reduced to Cr(III) when in contact with water and that such chemical reduction can compete with physical removal of Cr(VI) from the ash by aqueous leaching. Copyright © 2016 Elsevier Ltd. All rights reserved.

Biofilm Shows Spatially Stratified Metabolic Responses to Contaminant Exposure

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

Cao, Bin; Majors, Paul D.; Ahmed, B.

2012-11-01

The objective of this study was to elucidate the spatiotemporal responses of live S. oneidensis MR-1 biofilms to U(VI) (uranyl, UO22+) and Cr(VI) (chromate, CrO42-), important environmental contaminants at DOE contaminated sites. Toward this goal, we applied noninvasive nuclear magnetic resonance (NMR) imaging, diffusion, relaxation and spectroscopy techniques to monitor in situ spatiotemporal responses of S. oneidensis biofilms to U(VI) and Cr(VI) exposure in terms of changes in biofilm structures, diffusion properties, and cellular metabolism. Exposure to U(VI) or Cr(VI) did not appear to change the overall biomass distribution but caused changes in the physicochemical microenvironments inside the biofilm asmore » indicated by diffusion measurements. Changes in the diffusion properties of the biofilms in response to U(VI) and Cr(VI) exposure imply a novel function of the extracellular polymeric substances (EPS) affecting the biotransformation and transport of contaminants in the environment. In the presence of U(VI) or Cr(VI), the anaerobic metabolism of lactate was inhibited significantly, although the biofilms were still capable of reducing U(VI) and Cr(VI). Local concentrations of Cr(III)aq in the biofilm suggested relatively high Cr(VI) reduction activities at the top of the biofilm, near the medium-biofilm interface. The depth-resolved metabolic activities of the biofilm suggested higher diversion effects of gluconeogenesis and C1 metabolism pathways at the bottom of the biofilm and in the presence of U(VI). This study provides a noninvasive means to investigate spatiotemporal responses of biofilms, including surface-associated microbial communities in engineering, natural and medical settings, to various environmental perturbations including exposure to environmental contaminants and antimicrobials.« less

Physiological mechanisms to cope with Cr(VI) toxicity in lettuce: can lettuce be used in Cr phytoremediation?

PubMed

Dias, Maria Celeste; Moutinho-Pereira, José; Correia, Carlos; Monteiro, Cristina; Araújo, Márcia; Brüggemann, Wolfgang; Santos, Conceição

2016-08-01

This research aims at identifying the main deleterious effects of Cr(VI) on the photosynthetic apparatus and at selecting the most sensitive endpoints related to photosynthesis. To achieve this goal, we used lettuce (Lactuca sativa), a sensible ecotoxicological crop model. Three-week-old plants were exposed to 0, 50, 150 and 200 mg L(-1) of Cr(VI). These concentrations ranged from levels admitted in irrigation waters to values found in several Cr industry effluents and heavily contaminated environments. After 30 days of exposure, plants accumulated Cr preferably in roots and showed nutritional impairment, with decreases of K, Mg, Fe and Zn in both roots and leaves. Cr(VI)-exposed plants showed decreased levels of chlorophyll (Chl) a and anthocyanins, as well as decreased effective quantum yield of photostystem II (ΦPSII) and photochemical Chl fluorescence quenching (qp), but increases in the non-photochemical Chl fluorescence quenching (NPQ) and in the de-epoxidation state (DEP) of the xanthophyll cycle. Net CO2 assimilation rate (P N ) and RuBisCO activity were mostly impaired in the highest Cr(VI) concentration tested. Concerning the final products of photosynthesis, starch content was not affected, while soluble sugar contents increased. These alterations were accompanied by a reduction in protein content and in plant growth. Our results support that endpoints related to the photosynthesis photochemical processes (ΦPSII and the qp) and the content of anthocyanins are sensitive predictors of Cr(VI) toxicity. The advantages of using these parameters as biomarkers for Cr toxicity in plants are discussed. Finally, we report that, despite showing physiological disorders, L. sativa plants survived and accumulated high doses of Cr, and their use in environmental/decontamination studies is open to debate.

Electro-migration of heavy metals in an aged electroplating contaminated soil affected by the coexisting hexavalent chromium.

PubMed

Zhang, Weihua; Zhuang, Luwen; Tong, Lizhi; Lo, Irene M C; Qiu, Rongliang

2012-02-01

Cr(VI) was often reported to oxidize soil organic matter at acidic environments due to its high ORP, probably thus changing cationic metal species bound to soil organic matter, and influencing their electro-migration patterns. However, such an effect on the electro-migration was not confirmed in most previous studies. Therefore, this study applied a fixed voltage direct current field on an aged electroplating contaminated clayed soil, with a special interest in the direct or indirect influence of Cr(VI) on the electro-migration of other coexisting metals. After 353 h electrokinetic process, 81% of Zn, 53% of Ni and 22% of Cu in the original soil were electro-migrated into the electrolyte, and most of the remaining concentrated near the cathode. The Cr(VI) oxidized some soil organic matter along its migration pathway, with a pronounced reaction occurred near the anode at low pHs. The resulting Cr(III) reversed its original movement, and migrated towards the cathode, leading to the occurrence of a second Cr concentration peak in the soil. Metal species analyses showed that the amount of metals bound to soil organic matter significantly decreased, while a substantial increase in the Cr species bound to Fe/Mn (hydro-)oxides was observed, suggesting an enhancement of cationic metal electro-migration by the reduction of Cr(VI) into Cr(III). However, the Cr(VI) may form some stable lead chromate precipitates, and in turn demobilize Pb in the soil, as the results showed a low Pb removal and an increase in its acid-extractable and residual fractions after electrokinetic remediation. Copyright © 2011 Elsevier Ltd. All rights reserved.

Hexavalent chromium induces chromosome instability in human urothelial cells

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

Wise, Sandra S.; Holmes, Amie L.; Department of Radiation Oncology, Dana Farber Cancer Institute, 450 Brookline Ave., Boston, MA 02215

Numerous metals are well-known human bladder carcinogens. Despite the significant occupational and public health concern of metals and bladder cancer, the carcinogenic mechanisms remain largely unknown. Chromium, in particular, is a metal of concern as incidences of bladder cancer have been found elevated in chromate workers, and there is an increasing concern for patients with metal hip implants. However, the impact of hexavalent chromium (Cr(VI)) on bladder cells has not been studied. We compared chromate toxicity in two bladder cell lines; primary human urothelial cells and hTERT-immortalized human urothelial cells. Cr(VI) induced a concentration- and time-dependent increase in chromosome damagemore » in both cell lines, with the hTERT-immortalized cells exhibiting more chromosome damage than the primary cells. Chronic exposure to Cr(VI) also induced a concentration-dependent increase in aneuploid metaphases in both cell lines which was not observed after a 24 h exposure. Aneuploidy induction was higher in the hTERT-immortalized cells. When we correct for uptake, Cr(VI) induces a similar amount of chromosome damage and aneuploidy suggesting that the differences in Cr(VI) sensitivity between the two cells lines were due to differences in uptake. The increase in chromosome instability after chronic chromate treatment suggests this may be a mechanism for chromate-induced bladder cancer, specifically, and may be a mechanism for metal-induced bladder cancer, in general. - Highlights: • Hexavalent chromium is genotoxic to human urothelial cells. • Hexavalent chromium induces aneuploidy in human urothelial cells. • hTERT-immortalized human urothelial cells model the effects seen in primary urothelial cells. • Hexavalent chromium has a strong likelihood of being carcinogenic for bladder tissue.« less

Hexavalent Chromium Causes the Oxidation of Thioredoxin in Human Bronchial Epithelial Cells

PubMed Central

Myers, Judith M.; Antholine, William E.; Myers, Charles R.

2008-01-01

Hexavalent chromium [Cr(VI)] species such as chromates are cytotoxic. Inhalational exposure is a primary concern in many Cr-related industries and their immediate environments, and bronchial epithelial cells are directly exposed to inhaled Cr(VI). Chromates are readily taken up by cells and are reduced to reactive Cr species which may also result in the generation of reactive oxygen species (ROS). The thioredoxin (Trx) system has a key role in the maintenance of cellular thiol redox balance and is essential for cell survival. Cells normally maintain the cytosolic (Trx1) and mitochondrial (Trx2) thioredoxins largely in the reduced state. Redox western blots were used to assess the redox status of the thioredoxins in normal human bronchial epithelial cells (BEAS-2B) incubated with soluble Na2CrO4 or insoluble ZnCrO4 for different periods of time. Both chromates caused a dose- and time-dependent oxidation of Trx2 and Trx1. Trx2 was more susceptible in that it could all be converted to the oxidized form, whereas a small amount of reduced Trx1 remained even after prolonged treatment with higher Cr concentrations. Only one of the dithiols, presumably the active site, of Trx1 was oxidized by Cr(VI). Cr(VI) did not cause significant GSH depletion or oxidation indicating that Trx oxidation does not result from a general oxidation of cellular thiols. With purified Trx and thioredoxin reductase (TrxR) in vitro, Cr(VI) also resulted in Trx oxidation. It was determined that purified TrxR has pronounced Cr(VI) reducing activity, so competition for electron flow from TrxR might impair its ability to reduce Trx. The in vitro data also suggested some direct redox interaction between Cr(VI) and Trx. The ability of Cr(VI) to cause Trx oxidation in cells could contribute to its cytotoxic effects, and could have important implications for cell survival, redox-sensitive cell signaling, and the cells' tolerance of other oxidant insults. PMID:18328613

The Reduction of Cr(VI) to Cr(III) by Natural Fe-Bearing Minerals: A Synchrotron XAS Study

NASA Astrophysics Data System (ADS)

Xu, H.; Guo, X.; Ding, M.; Migdissov, A. A.; Boukhalfa, H.; Sun, C.; Roback, R. C.; Reimus, P. W.; Katzman, D.

2017-12-01

Cr(VI) in the form of CrO42- is a pollutant species in groundwater and soils that can pose health and environmental problems. Cr(VI) associated with use as a corrosion inhibitor at a power plant from 1956-1972 is present in a deep groundwater aquifer at Los Alamos National Laboratory. A potential remediation strategy for the Cr contamination is reduction of Cr(VI) to Cr(III) via the acceptance of electrons from naturally occurring or induced Fe(II) occurring in Fe-bearing minerals. In this work, using synchrotron-based X-ray techniques, we investigated the Cr reduction behavior by Fe-bearing minerals from outcrop and core samples representative of the contaminated portion of the aquifer. Samples were exposed to solutions with a range of known Cr (VI) concentrations. XANES and EXAFS spectra showed that all the Cr(VI) had been reduced to Cr(III), and micro XRF mapping revealed close correlation of Cr and Fe distribution, implying that Fe(II) in minerals reduced Cr(VI) in the solution. Similar behavior was observed from in-situ XANES measurements on Cr reduction and adsorption by mineral separates from the rock samples in Cr(VI)-bearing solutions. In addition, to obtain reference parameters for interpreting the data of natural samples, we collected Cr and Fe EXAFS spectra of Cr(III)-Fe(III) hydroxide solid solutions, which show progressive changes in the local structure around Cr and Fe over the whole series.

Combined abiotic and biotic in-situ reduction of hexavalent chromium in groundwater using nZVI and whey: A remedial pilot test.

PubMed

Němeček, Jan; Pokorný, Petr; Lacinová, Lenka; Černík, Miroslav; Masopustová, Zuzana; Lhotský, Ondřej; Filipová, Alena; Cajthaml, Tomáš

2015-12-30

The paper describes a pilot remediation test combining two Cr(VI) geofixation methods - chemical reduction by nanoscale zero-valent iron (nZVI) and subsequent biotic reduction supported by whey. Combination of the methods exploited the advantages of both - a rapid decrease in Cr(VI) concentrations by nZVI, which prevented further spreading of the contamination and facilitated subsequent use of the cheaper biological method. Successive application of whey as an organic substrate to promote biotic reduction of Cr(VI) after application of nZVI resulted in a further and long-term decrease in the Cr(VI) contents in the groundwater. The effect of biotic reduction was observed even in a monitoring well located at a distance of 22 m from the substrate injection wells after 10 months. The results indicated a reciprocal effect of both the phases - nZVI oxidized to Fe(III) during the abiotic phase was microbially reduced back to Fe(II) and acted as a reducing agent for Cr(VI) even when the microbial density was already low due to the consumed substrate. Community analysis with pyrosequencing of the 16S rRNA genes further confirmed partial recycling of nZVI in the form of Fe(II), where the results showed that the Cr(VI) reducing process was mediated mainly by iron-reducing and sulfate-reducing bacteria. Copyright © 2015 Elsevier B.V. All rights reserved.

Reactive oxygen species mediate Cr(VI)-induced carcinogenesis through PI3K/AKT-dependent activation of GSK-3β/β-catenin signaling

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

Son, Young-Ok; Pratheeshkumar, Poyil; Wang, Lei

Cr(VI) compounds are known human carcinogens that primarily target the lungs. Cr(VI) produces reactive oxygen species (ROS), but the exact effects of ROS on the signaling molecules involved in Cr(VI)-induced carcinogenesis have not been extensively studied. Chronic exposure of human bronchial epithelial cells to Cr(VI) at nanomolar concentrations (10–100 nM) for 3 months not only induced cell transformation, but also increased the potential of these cells to invade and migrate. Injection of Cr(VI)-stimulated cells into nude mice resulted in the formation of tumors. Chronic exposure to Cr(VI) increased levels of intracellular ROS and antiapoptotic proteins. Transfection with catalase or superoxidemore » dismutase (SOD) prevented Cr(VI)-mediated increases in colony formation, cell invasion, migration, and xenograft tumors. While chronic Cr(VI) exposure led to activation of signaling cascades involving PI3K/AKT/GSK-3β/β-catenin and PI3K/AKT/mTOR, transfection with catalase or SOD markedly inhibited Cr(VI)-mediated activation of these signaling proteins. Inhibitors specific for AKT or β-catenin almost completely suppressed the Cr(VI)-mediated increase in total and active β-catenin proteins and colony formation. In particular, Cr(VI) suppressed autophagy of epithelial cells under nutrition deprivation. Furthermore, there was a marked induction of AKT, GSK-3β, β-catenin, mTOR, and carcinogenic markers in tumor tissues formed in mice after injection with Cr(VI)-stimulated cells. Collectively, our findings suggest that ROS is a key mediator of Cr(VI)-induced carcinogenesis through the activation of PI3K/AKT-dependent GSK-3β/β-catenin signaling and the promotion of cell survival mechanisms via the inhibition of apoptosis and autophagy. - Highlights: • Chronic exposure to Cr(VI) induces carcinogenic properties in BEAS-2B cells. • ROS play an important role in Cr(VI)-induced tumorigenicity of BEAS-2B cells. • PI3K/AKT/GSK-3β/β-catenin signaling involved in Cr(VI) carcinogenesis. • The inhibition of apoptosis and autophagy contributes to Cr(VI) carcinogenesis.« less

Cr(VI) transport via a supported ionic liquid membrane containing CYPHOS IL101 as carrier: system analysis and optimization through experimental design strategies.

PubMed

Rodríguez de San Miguel, Eduardo; Vital, Xóchitl; de Gyves, Josefina

2014-05-30

Chromium(VI) transport through a supported liquid membrane (SLM) system containing the commercial ionic liquid CYPHOS IL101 as carrier was studied. A reducing stripping phase was used as a mean to increase recovery and to simultaneously transform Cr(VI) into a less toxic residue for disposal or reuse. General functions which describe the time-depending evolution of the metal fractions in the cell compartments were defined and used in data evaluation. An experimental design strategy, using factorial and central-composite design matrices, was applied to assess the influence of the extractant, NaOH and citrate concentrations in the different phases, while a desirability function scheme allowed the synchronized optimization of depletion and recovery of the analyte. The mechanism for chromium permeation was analyzed and discussed to contribute to the understanding of the transfer process. The influence of metal concentration was evaluated as well. The presence of different interfering ions (Ca(2+), Al(3+), NO3(-), SO4(2-), and Cl(-)) at several Cr(VI): interfering ion ratios was studied through the use of a Plackett and Burman experimental design matrix. Under optimized conditions 90% of recovery was obtained from a feed solution containing 7mgL(-1) of Cr(VI) in 0.01moldm(-3) HCl medium after 5h of pertraction. Copyright © 2014 Elsevier B.V. All rights reserved.

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

Zhang, Hailin; Li, Ping; Wang, Zheming

Boehmite (γ-AlOOH) was synthesized to selectively adsorb V(V) from K 2CrO 4-KVO 3-H 2O solutions with highly concentrated Cr(VI) and low concentration V(V). The synthesized γ-AlOOH has a BET surface area of 433.2 m 2/g and an average pore size of 3.5 nm. It possesses a maximum adsorption capacity of V(V) of 1.53 mmol/g from K 2CrO 4-KVO 3-H 2O solutions. The adsorption of V(V) onto γ-AlOOH follows the Langmuir isotherm model and pseudo-second-order kinetics equation by forming innersphere complexes while the Cr(VI) adsorption forms both inner-sphere and outer-sphere chromate complexes depending on solution pH. The γ-AlOOH was further synthesizedmore » in situ by adding HNO 3 into the K 2CrO 4-KAlO 2- KVO 3-H 2O solutions and then used for synchronous adsorption of V(V) and Cr(VI), resulting in increased adsorption capacity of V(V) of 2.88 mmol/g and decreased adsorption capacity of Cr(VI) to 0.073 mmol/g, respectively. In the latter process, adsorption pH values were adjustable, and adsorption reached equilibrium instantaneously, supporting a novel in situ synthesis and adsorption integration strategy with adjustable surface charge of adsorbent and disappearance of diffusion effect.« less

Remediation of Cr(VI)-Contaminated Soil Using the Acidified Hydrazine Hydrate.

PubMed

Ma, Yameng; Li, Fangfang; Jiang, Yuling; Yang, Weihua; Lv, Lv; Xue, Haotian; Wang, Yangyang

2016-09-01

Acidified hydrazine hydrate was used to remediate Cr(VI)-contaminated soil. The content of water-soluble Cr(VI) in contaminated soil was 4977.53 mg/kg. The optimal initial pH of hydrazine hydrate solution, soil to solution ratio and molar ratio of Cr(VI) to hydrazine hydrate for remediation of Cr(VI)-contaminated soil were 5.0, 3:1 and 1:3, respectively. Over 99.50 % of water-soluble Cr(VI) in the contaminated soil was reduced at the optimal condition within 30 min. The remediated soil can keep stable within 4 months. Meanwhile the total phosphorus increased from 0.47 to 4.29 g/kg, indicating that using of acidified hydrazine hydrate is an effective method to remediate Cr(VI)-contaminated soil.

Optimizing Cr(VI) and Tc(VII) remediation through nano-scale biomineral engineering

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

Cutting, R. S.; Coker, V. S.; Telling, N. D.

2009-09-09

To optimize the production of biomagnetite for the bioremediation of metal oxyanion contaminated waters, the reduction of aqueous Cr(VI) to Cr(III) by two biogenic magnetites and a synthetic magnetite was evaluated under batch and continuous flow conditions. Results indicate that nano-scale biogenic magnetite produced by incubating synthetic schwertmannite powder in cell suspensions of Geobacter sulfurreducens is more efficient at reducing Cr(VI) than either biogenic nano-magnetite produced from a suspension of ferrihydrite 'gel' or synthetic nano-scale Fe{sub 3}O{sub 4} powder. Although X-ray Photoelectron Spectroscopy (XPS) measurements obtained from post-exposure magnetite samples reveal that both Cr(III) and Cr(VI) are associated with nanoparticlemore » surfaces, X-ray Magnetic Circular Dichroism (XMCD) studies indicate that some Cr(III) has replaced octahedrally coordinated Fe in the lattice of the magnetite. Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) measurements of total aqueous Cr in the associated solution phase indicated that, although the majority of Cr(III) was incorporated within or adsorbed to the magnetite samples, a proportion ({approx}10-15 %) was released back into solution. Studies of Tc(VII) uptake by magnetites produced via the different synthesis routes also revealed significant differences between them as regards effectiveness for remediation. In addition, column studies using a {gamma}-camera to obtain real time images of a {sup 99m}Tc(VII) radiotracer were performed to visualize directly the relative performances of the magnetite sorbents against ultra-trace concentrations of metal oxyanion contaminants. Again, the magnetite produced from schwertmannite proved capable of retaining more ({approx}20%) {sup 99m}Tc(VII) than the magnetite produced from ferrihydrite, confirming that biomagnetite production for efficient environmental remediation can be fine-tuned through careful selection of the initial Fe(III) mineral substrate supplied to Fe(III)-reducing bacteria.« less

A Comparison of Cytotoxicity and Oxidative Stress from Welding Fumes Generated with a New Nickel-, Copper-Based Consumable versus Mild and Stainless Steel-Based Welding in RAW 264.7 Mouse Macrophages

PubMed Central

Badding, Melissa A.; Fix, Natalie R.; Antonini, James M.; Leonard, Stephen S.

2014-01-01

Welding processes that generate fumes containing toxic metals, such as hexavalent chromium (Cr(VI)), manganese (Mn), and nickel (Ni), have been implicated in lung injury, inflammation, and lung tumor promotion in animal models. While federal regulations have reduced permissible worker exposure limits to Cr(VI), this is not always practical considering that welders may work in confined spaces and exhaust ventilation may be ineffective. Thus, there has been a recent initiative to minimize the potentially hazardous components in welding materials by developing new consumables containing much less Cr(VI) and Mn. A new nickel (Ni) and copper (Cu)-based material (Ni-Cu WF) is being suggested as a safer alternative to stainless steel consumables; however, its adverse cellular effects have not been studied. This study compared the cytotoxic effects of the newly developed Ni-Cu WF with two well-characterized welding fumes, collected from gas metal arc welding using mild steel (GMA-MS) or stainless steel (GMA-SS) electrodes. RAW 264.7 mouse macrophages were exposed to the three welding fumes at two doses (50 µg/ml and 250 µg/ml) for up to 24 hours. Cell viability, reactive oxygen species (ROS) production, phagocytic function, and cytokine production were examined. The GMA-MS and GMA-SS samples were found to be more reactive in terms of ROS production compared to the Ni-Cu WF. However, the fumes from this new material were more cytotoxic, inducing cell death and mitochondrial dysfunction at a lower dose. Additionally, pre-treatment with Ni-Cu WF particles impaired the ability of cells to phagocytize E. coli, suggesting macrophage dysfunction. Thus, the toxic cellular responses to welding fumes are largely due to the metal composition. The results also suggest that reducing Cr(VI) and Mn in the generated fume by increasing the concentration of other metals (e.g., Ni, Cu) may not necessarily improve welder safety. PMID:24977413

A comparison of cytotoxicity and oxidative stress from welding fumes generated with a new nickel-, copper-based consumable versus mild and stainless steel-based welding in RAW 264.7 mouse macrophages.

PubMed

Badding, Melissa A; Fix, Natalie R; Antonini, James M; Leonard, Stephen S

2014-01-01

Welding processes that generate fumes containing toxic metals, such as hexavalent chromium (Cr(VI)), manganese (Mn), and nickel (Ni), have been implicated in lung injury, inflammation, and lung tumor promotion in animal models. While federal regulations have reduced permissible worker exposure limits to Cr(VI), this is not always practical considering that welders may work in confined spaces and exhaust ventilation may be ineffective. Thus, there has been a recent initiative to minimize the potentially hazardous components in welding materials by developing new consumables containing much less Cr(VI) and Mn. A new nickel (Ni) and copper (Cu)-based material (Ni-Cu WF) is being suggested as a safer alternative to stainless steel consumables; however, its adverse cellular effects have not been studied. This study compared the cytotoxic effects of the newly developed Ni-Cu WF with two well-characterized welding fumes, collected from gas metal arc welding using mild steel (GMA-MS) or stainless steel (GMA-SS) electrodes. RAW 264.7 mouse macrophages were exposed to the three welding fumes at two doses (50 µg/ml and 250 µg/ml) for up to 24 hours. Cell viability, reactive oxygen species (ROS) production, phagocytic function, and cytokine production were examined. The GMA-MS and GMA-SS samples were found to be more reactive in terms of ROS production compared to the Ni-Cu WF. However, the fumes from this new material were more cytotoxic, inducing cell death and mitochondrial dysfunction at a lower dose. Additionally, pre-treatment with Ni-Cu WF particles impaired the ability of cells to phagocytize E. coli, suggesting macrophage dysfunction. Thus, the toxic cellular responses to welding fumes are largely due to the metal composition. The results also suggest that reducing Cr(VI) and Mn in the generated fume by increasing the concentration of other metals (e.g., Ni, Cu) may not necessarily improve welder safety.

Simultaneous analysis of Cr(III), Cr(VI), and chromium picolinate in foods using capillary electrophoresis-inductively coupled plasma mass spectrometry.

PubMed

Chen, YiQuan; Chen, JinFa; Xi, Zhiming; Yang, Guidi; Wu, Zujian; Li, JianRong; Fu, FengFu

2015-05-01

We herein reported a method for the simultaneous detection of trace Cr(VI), Cr(III), and chromium(III) picolinate (CrPic) in foods using CE-ICP-MS together with ultrasonic-assisted extraction. The Cr(III) (Cr(3+) ) was chelated with trans-1,2-diaminocyclohexane-N,N,N´,N´-tetraacetic acid (DCTA) to form a single charged Cr-DCTA(-) complex. Then, Cr(VI) (CrO4 (2-) ), Cr-DCTA(-) , and CrPic were separated by CE within 8 min under a separation voltage of -13 KV followed by their monitoring with ICP mass spectrometer (ICP-MS). The proposed method is simple, effective, and sensitive. It has an instrument detection limit of 0.10, 0.18, and 0.20 ngCr/mL for Cr(VI), Cr(III), and CrPic, respectively. With the help of the methods, we have successfully determined Cr(VI), Cr(III), and CrPic in nutritional supplement (CrPic yeast tablet) with an RSD (n = 5) <6% and a recovery of 93-103%. The experimental results showed that CrPic was the main speciation of chromium in the nutritional supplement, with a concentration of 1514.6 μg Cr/g. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of hexavalent chromium on electron leakage of respiratory chain in mitochondria isolated from rat liver.

PubMed

Xie, Ying; Zhong, Caigao; Zeng, Ming; Guan, Lan; Luo, Lei

2013-01-01

In the present study, we explored reactive axygen species (ROS) production in mitochondria, the mechanism of hexavalent chromium (Cr(VI)) hepatotoxicity, and the role of protection by GSH. Intact mitochondria were isolated from rat liver tissues and mitochondrial basal respiratory rates of NADH and FADH2 respiratory chains were determined. Mitochondria were treated with Cr(VI), GSH and several complex inhibitors. Mitochondria energized by glutamate/malate were separately or jointly treated with Rotenone (Rot), diphenyleneiodonium (DPI) and antimycinA (Ant), while mitochondria energized by succinate were separately or jointly treated with Rot, DPI ' thenoyltrifluoroacetone (TTFA) and Ant. Cr(VI) concentration-dependently induced ROS production in the NADH and FADH2 respiratory chain in liver mitochondria. Basal respiratory rate of the mitochondrial FADH2 respiratory chain was significantly higher than that of NADH respiratory chain. Hepatic mitochondrial electron leakage induced by Cr(VI) from NADH respiratory chain were mainly from ubiquinone binding sites of complex I and complex III. Treatment with 50µM Cr(VI) enhances forward movement of electrons through FADH2 respiratory chain and leaking through the ubiquinone binding site of complex III. Moreover, the protective effect of GSH on liver mitochondria electron leakage is through removing excess H2O2 and reducing total ROS. Copyright © 2013 S. Karger AG, Basel.

Application of ICP-MS and HPLC-ICP-MS for diagnosis and therapy of a severe intoxication with hexavalent chromium and inorganic arsenic.

PubMed

Heitland, Peter; Blohm, Martin; Breuer, Christian; Brinkert, Florian; Achilles, Eike Gert; Pukite, Ieva; Köster, Helmut Dietrich

2017-05-01

ICP-MS and HPLC-ICP-MS were applied for diagnosis and therapeutic monitoring in a severe intoxication with a liquid containing hexavalent chromium (Cr(VI)) and inorganic arsenic (iAs). In this rare case a liver transplantation of was considered as the only chance of survival. We developed and applied methods for the determination of Cr(VI) in erythrocytes and total chromium (Cr) and arsenic (As) in blood, plasma, urine and liver tissue by ICP-MS. Exposure to iAs was diagnosed by determination of iAs species and their metabolites in urine by anion exchange HPLC-ICP-MS. Three days after ingestion of the liquid the total Cr concentrations were 2180 and 1070μg/L in whole blood and plasma, respectively, and 4540μg/L Cr(VI) in erythrocytes. The arsenic concentration in blood was 206μg/L. The urinary As species concentrations were <0.5, 109, 115, 154 and 126μg/L for arsenobetaine, As(III), As(V), methylarsonate (V) and dimethylarsinate (V), respectively. Total Cr and As concentrations in the explanted liver were 11.7 and 0.9mg/kg, respectively. Further analytical results of this case study are tabulated and provide valuable data for physicians and toxicologists. Copyright © 2017. Published by Elsevier GmbH.

Reduction of hexavalent chromium using Aerva lanata L.: elucidation of reduction mechanism and identification of active principles.

PubMed

Poonkuzhali, K; Rajeswari, V; Saravanakumar, T; Viswanathamurthi, P; Park, Seung-Moon; Govarthanan, M; Sathishkumar, P; Palvannan, T

2014-05-15

The effluent discharge treatment for controlling the environment from non biodegradable metal contaminants using plant extract is an efficient technique. The reduction of hexavalent chromium by abundantly available weed, Aerva lanata L. was investigated using batch equilibrium technique. The variables studied were Cr(VI) concentration, Aerva lanata L. dose, contact time, pH, temperature and agitation speed. Cyclic voltammetry and ICP-MS analysis confirmed the reduction of Cr(VI) to Cr(III). Electrochemical analysis proved that, the chromium has not been degraded and the valency of the chromium has only been changed. ICP-MS analysis shows that 100ng/L of hexavalent chromium was reduced to 97.01ng/L trivalent chromium. These results suggest that components present in the Aerva lanata L. are responsible for the reduction of Cr(VI) to Cr(III). The prime components ferulic acid, kaempherol and β-carboline present in the Aerva lanata L. may be responsible for the reduction of Cr(VI) as evident from LC-MS analysis. Copyright © 2014 Elsevier B.V. All rights reserved.

Adsorption behavior of Cr(VI) on modified natural zeolite by a new bolaform N,N,N,N',N',N'-hexamethyl-1,9-nonanediammonium dibromide reagent.

PubMed

Noroozifar, M; Khorasani-Motlagh, M; Gorgij, M N; Naderpour, H R

2008-07-15

The demand for effective adsorbents is to increase in response to the widespread recognition of the deleterious health effects of Cr(VI)-oxyanions exposure through drinking water. In this study, Cr(VI)-oxyanions uptake from aqueous solutions by a new bolaform N,N,N,N',N',N'-hexamethyl-1,9-nonanediammonium dibromide reagent-modified natural zeolitic materials from Zahedan, Iran, was investigated using batch technique. Spectrophotometry method was used for Cr determination. The Cr(VI)-solution concentration varied between 2 and 104 mg L(-1). It was shown that the Cr(VI) uptake strongly depended on pH. The maximum removal of Cr(VI) occurred in acidic media at pH<1.5. The amounts of Cr(VI) adsorbed increased with increase in dose of both adsorbents and their contact time. Based on results an adsorption mechanism has been suggested. The adsorption data for modified zeolite using the amine was consistent with Langmuir isotherm equation and the equilibrium data was analyzed using the Langmuir isotherm.

Utilization of ICP/OES for the determination of trace metal binding to different humic fractions.

PubMed

de la Rosa, G; Peralta-Videa, J R; Gardea-Torresdey, J L

2003-02-28

In this study, the use of inductively coupled plasma/optical emission spectrometry (ICP/OES) to determine multi-metal binding to three biomasses, Sphagnum peat moss, humin and humic acids is reported. All the investigations were performed under part per billion (ppb) concentrations. Batch pH profile experiments were performed using multi-metal solutions of Cd(II), Cu(II), Pb(II), Ni(II), Cr(III) and Cr(VI). The results showed that at pH 2 and 3, the metal affinity of the three biomasses exposed to the multi-metal solution that included Cr(III) presented the following order: Cu(II), Pb(II)>Ni(II)>Cr(III)>Cd(II). On the other hand, when Cr(VI) was in the heavy metal mixture, Sphagnum peat moss and humin showed the following affinity: Cu(II), Pb(II)>Ni(II)>Cr(VI)>Cd(II); however, the affinity of the humic acids was: Cu(II)>Pb(II), Cr(VI)>Ni(II)>Cd(II). The results demonstrated that pH values of 4 and 5 were the most favorable for the heavy metal binding process. At pH 5, all the metals, except for Cr(VI), were bound between 90 and 100% to the three biomasses. However, the binding capacity of humic acids decreased at pH 6 in the presence of Cr(VI). The results showed that the ICP/OES permits the determination of heavy metal binding to organic matter at ppb concentration. These results will be very useful in understanding the role of humic substances in the fate and transport of heavy metals, and thus could provide information to develop new methodologies for the removal of low concentrations of toxic heavy metals from contaminated waters.

Assessment of immunotoxicity in female Fischer 344/N and Sprague Dawley rats and female B6C3F1 mice exposed to hexavalent chromium via the drinking water.

PubMed

Shipkowski, Kelly A; Sheth, Christopher M; Smith, Matthew J; Hooth, Michelle J; White, Kimber L; Germolec, Dori R

2017-12-01

Sodium dichromate dihydrate (SDD), an inorganic compound containing hexavalent chromium (Cr(VI)), is a common environmental contaminant of groundwater sources due to widespread industrial use. There are indications in the literature that Cr(VI) may induce immunotoxic effects following dermal exposure, including acting as both an irritant and a sensitizer; however, the potential immunomodulatory effects of Cr(VI) following oral exposure are relatively unknown. Following the detection of Cr(VI) in drinking water sources, the National Toxicology Program (NTP) conducted extensive evaluations of the toxicity and carcinogenicity of SDD following drinking water exposure, including studies to assess the potential for Cr(VI) to modulate immune function. For the immunotoxicity assessments, female Fischer 344/N (F344/N) and Sprague Dawley (SD) rats and female B 6 C 3 F 1 mice were exposed to SDD in drinking water for 28 consecutive days and evaluated for alterations in cellular and humoral immune function as well as innate immunity. Rats were exposed to concentrations of 0, 14.3, 57.3, 172, or 516 ppm SDD while mice were exposed to concentrations of 0, 15.6, 31.3, 62.5, 125, or 250 ppm SDD. Final mean body weight and body weight gain were decreased relative to controls in 250 ppm B 6 C 3 F 1 mice and 516 ppm SD rats. Water consumption was significantly decreased in F344/N and SD rats exposed to 172 and 516 ppm SDD; this was attributed to poor palatability of the SDD drinking water solutions. Several red blood cell-specific parameters were significantly (5-7%) decreased in 250 ppm mice; however, these parameters were unaffected in rats. Sporadic increases in the spleen IgM antibody response to sheep red blood cells (SRBC) were observed, however, these increases were not dose-dependent and were not reproducible. No significant effects were observed in the other immunological parameters evaluated. Overall, exposure to Cr(VI) in drinking water had limited effects on the immune system in both rats and mice.

Genome-wide gene expression effects in B6C3F1 mouse intestinal epithelia following 7 and 90 days of exposure to hexavalent chromium in drinking water

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

Kopec, Anna K.; Kim, Suntae; Forgacs, Agnes L.

2012-02-15

Chronic administration of high doses of hexavalent chromium [Cr(VI)] as sodium dichromate dihydrate (SDD) elicits alimentary cancers in mice. To further elucidate key events underlying tumor formation, a 90-day drinking water study was conducted in B6C3F1 mice. Differential gene expression was examined in duodenal and jejunal epithelial samples following 7 or 90 days of exposure to 0, 0.3, 4, 14, 60, 170 or 520 mg/L SDD in drinking water. Genome-wide microarray analyses identified 6562 duodenal and 4448 jejunal unique differentially expressed genes at day 8, and 4630 and 4845 unique changes, respectively, in the duodenum and jejunum at day 91.more » Comparative analysis identified significant overlap in duodenal and jejunal differential gene expression. Automated dose–response modeling identified > 80% of the differentially expressed genes exhibited sigmoidal dose–response curves with EC{sub 50} values ranging from 10 to 100 mg/L SDD. Only 16 genes satisfying the dose-dependent differential expression criteria had EC{sub 50} values < 10 mg/L SDD, 3 of which were regulated by Nrf2, suggesting oxidative stress in response to SDD at low concentrations. Analyses of differentially expressed genes identified over-represented functions associated with oxidative stress, cell cycle, lipid metabolism, and immune responses consistent with the reported effects on redox status and histopathology at corresponding SDD drinking water concentrations. Collectively, these data are consistent with a mode of action involving oxidative stress and cytotoxicity as early key events. This suggests that the tumorigenic effects of chronic Cr(VI) oral exposure likely require chronic tissue damage and compensatory epithelial cell proliferation. Highlights: ► Mouse small intestine gene expression is highly responsive to hexavalent chromium [Cr(VI)]. ► Cr(VI) elicits more differential gene expression after 7 days of exposure than 90 days of exposure. ► Oral exposure to Cr(VI) leads to oxidative stress, cell cycle, lipid and immune dysregulation. ► Cr(VI) elicits dose-dependent changes in gene expression with an overall median EC{sub 50} of 47 mg/L SDD.« less

Mechanisms for the Reduction of Actinides and Tc(VII) in Geobacter sulfurreducens

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

Lloyd, Jonathan R.

2004-06-01

The mechanism of the reduction of U(VI) and Cr(VI) has now been studied in detail. Cr(VI) is reduced by one-electron transfer reactions to Cr(III), via a cell-bound Cr(V) intermediate identified by EPR spectroscopy. Studies with a cytochrome c7 mutant demonstrate that the electron transfer chain includes this protein which may be the terminal reductase for Cr(VI). Potential mechanisms of inhibition of Cr(III) precipitation, involving complex formation with organic acids commonly used as electron donors for metal reduction in the subsurface have also been identified. We have also initiated a collaboration with computational chemists led by Prof Ian Hillier in Manchester,more » to model metal binding to cytochrome c7, and subsequent electron transfer from the enzyme to the metal quantum mechanically.« less

Role of Bacillus subtilis Error Prevention Oxidized Guanine System in Counteracting Hexavalent Chromium-Promoted Oxidative DNA Damage

PubMed Central

Santos-Escobar, Fernando; Gutiérrez-Corona, J. Félix

2014-01-01

Chromium pollution is potentially detrimental to bacterial soil communities, compromising carbon and nitrogen cycles that are essential for life on earth. It has been proposed that intracellular reduction of hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)] may cause bacterial death by a mechanism that involves reactive oxygen species (ROS)-induced DNA damage; the molecular basis of the phenomenon was investigated in this work. Here, we report that Bacillus subtilis cells lacking a functional error prevention oxidized guanine (GO) system were significantly more sensitive to Cr(VI) treatment than cells of the wild-type (WT) strain, suggesting that oxidative damage to DNA is involved in the deleterious effects of the oxyanion. In agreement with this suggestion, Cr(VI) dramatically increased the ROS concentration and induced mutagenesis in a GO-deficient B. subtilis strain. Alkaline gel electrophoresis (AGE) analysis of chromosomal DNA of WT and ΔGO mutant strains subjected to Cr(VI) treatment revealed that the DNA of the ΔGO strain was more susceptible to DNA glycosylase Fpg attack, suggesting that chromium genotoxicity is associated with 7,8-dihydro-8-oxodeoxyguanosine (8-oxo-G) lesions. In support of this notion, specific monoclonal antibodies detected the accumulation of 8-oxo-G lesions in the chromosomes of B. subtilis cells subjected to Cr(VI) treatment. We conclude that Cr(VI) promotes mutagenesis and cell death in B. subtilis by a mechanism that involves radical oxygen attack of DNA, generating 8-oxo-G, and that such effects are counteracted by the prevention and repair GO system. PMID:24973075

Long-term stability of FeSO4 and H2SO4 treated chromite ore processing residue (COPR): Importance of H+ and SO42.

PubMed

Wang, Xin; Zhang, Jingdong; Wang, Linling; Chen, Jing; Hou, Huijie; Yang, Jiakuan; Lu, Xiaohua

2017-01-05

In this study, the long-term stability of Cr(VI) in the FeSO 4 and H 2 SO 4 (FeSO 4 -H 2 SO 4 ) treated chromite ore processing residue (COPR) after 400 curing days and the stabilization mechanisms were investigated. FeSO 4 -H 2 SO 4 treatment significantly reduced toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) Cr(VI) concentrations to lower than the regulatory limit of 1.5mgL -1 (HJ/T 301-2007, China EPA) even for the samples curing 400days, achieving an outstanding long-term stability. Our independent leaching tests revealed that H + and SO 4 2- have synergistic effect on promoting the release of Cr(VI), which would make Cr(VI) easier accessed by Fe(II) during stabilization. The contributions of H + and SO 4 2- to Cr(VI) release ratio were 25%-44% and 19%-38%, respectively, as 5mol H 2 SO 4 per kg COPR was used. X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and alkaline digestion analyses were also employed to interpret the possible stabilization mechanism. Cr(VI) released from COPR solid was reduced to Cr(III) by Fe(II), and then formed stable Fe x Cr (1-x) (OH) 3 precipitate. This study provides a facile and reliable scheme for COPR stabilization, and verifies the excellent long-term stability of the FeSO 4 -H 2 SO 4 treated COPR. Copyright © 2016 Elsevier B.V. All rights reserved.

Apoptosis of lymphocytes in the presence of Cr(V) complexes: role in Cr(VI)-induced toxicity.

PubMed

Vasant, C; Balamurugan, K; Rajaram, R; Ramasami, T

2001-08-03

Cr(VI) compounds have been declared as a potent occupational carcinogen by IARC (1990) through epidemiological studies among workers in chrome plating, stainless-steel, and pigment industries. Studies relating to the role of intermediate oxidation states such as Cr(V) and Cr(IV) in Cr(VI)-induced carcinogenicity are gaining importance. In this study, issues relating to toxicity elicited by Cr(V) have been addressed and comparisons made with those relating to Cr(VI) employing human peripheral blood lymphocytes. Lymphocytes have been isolated from heparinized blood by Ficoll-Hypaque density gradient centrifugation and exposed to Cr(V) complexes viz. sodium bis(2-ethyl-2-hydroxybutyrato)oxochromate(V), Na[Cr(V)O(ehba)(2)], 1 and sodium bis(2-hydroxy-2-methylbutyrato)oxochromate(V), Na[Cr(V)O(hmba)(2)], 2 and Cr(VI). The phytohemagglutinin (PHA)-induced proliferation of lymphocytes has been found to be inhibited by the two complexes of Cr(V) and chromate Cr(VI) in a time- and concentration-dependent manner. Viability of cells decreases in the presence of Cr(V). Apoptosis appears to be the mode of cell death in the presence of both Cr(V) and Cr(VI). Pretreatment of cells with antioxidants before exposure to chromium(V) complexes reverse apoptosis partially. Possibility for the formation and implication of reactive oxygen species in Cr(V)-induced apoptosis of human lymphocyte cells has been indicated in this investigation. The intermediates of Cr(V) and radical species in the biotoxic pathways elicited by Cr(VI) seems feasible. Copyright 2001 Academic Press.

Chromium recovery from exhausted baths generated in plating processes and its reuse in the tanning industry.

PubMed

Torras, Josep; Buj, Irene; Rovira, Miquel; de Pablo, Joan

2012-03-30

Chromium plating used for functional purposes provides an extremely hard, wear and corrosion resistant layer by means of electrolytic deposition. Typical layer thicknesses range between 2.5 and 500 μm. Chromium electroplating baths contain high concentrations of Cr(VI) with chromium trioxide (CrO(3)) as the chromium source. When because of technical or economic reasons a bath gets exhausted, a waste containing mainly chromium as dichromate as well as other heavy metals is generated. Chromium may then be purified for use in other industrial processes with different requirements. In this work, a sustainable system for using galvanic wastes as reagents in the leather tanning industry, thus reducing quantity of wastes to be treated, is presented. Metal cations present in the chromium exhausted bath were precipitated with NaOH. Then, the solution containing mainly soluble Cr(VI) was separated. By means of sodium sulphite in acidic conditions, Cr(VI) was reduced to Cr(III) as chromium (III) sulphate. From chromium (III) sulphate a basic Cr(III) sulphate may be obtained, which is one of most used compounds in the tanning industry. Cr(III) concentration in the final solution allows its reuse without concentration, but with a slight dilution. Copyright © 2012 Elsevier B.V. All rights reserved.

Development of analytical procedures for the determination of hexavalent chromium in corrosion prevention coatings used in the automotive industry.

PubMed

Séby, F; Castetbon, A; Ortega, R; Guimon, C; Niveau, F; Barrois-Oudin, N; Garraud, H; Donard, O F X

2008-05-01

The European directive 2000/53/EC limits the use of Cr(VI) in vehicle manufacturing. Although a maximum of 2 g of Cr(VI) was authorised per vehicle for corrosion prevention coatings of key components, since July 2007 its use has been prohibited except for some particular applications. Therefore, the objective of this work was to develop direct analytical procedures for Cr(VI) determination in the different steel coatings used for screws. Instead of working directly with screws, the optimisation of the procedures was carried out with metallic plates homogeneously coated to improve the data comparability. Extraction of Cr(VI) from the metallic parts was performed by sonication. Two extraction solutions were tested: a direct water extraction solution used in standard protocols and an ammonium/ammonia buffer solution at pH 8.9. The extracts were further analysed for Cr speciation by high-performance liquid chromatography (HPLC) inductively coupled plasma (ICP) atomic emission spectrometry or HPLC ICP mass spectrometry depending on the concentration level. When possible, the coatings were also directly analysed by solid speciation techniques (X-ray photoelectron spectroscopy, XPS, and X-ray absorption near-edge structure, XANES) for validation of the results. Very good results between the different analytical approaches were obtained for the sample of coating made up of a heated paint containing Zn, Al and Cr when using the extracting buffer solution at pH 8.9. After a repeated four-step extraction procedure on the same portion test, taking into account the depth of the surface layer reached, good agreement with XPS and XANES results was obtained. In contrast, for the coatings composed of an alkaline Zn layer where Cr(VI) and Cr(III) are deposited, only the extraction procedure using water allowed the detection of Cr(VI). To elucidate the Cr(VI) reduction during extraction at pH 8.9, the reactivity of Cr(VI) towards different species of Zn generally present in the coatings (metallic Zn and zinc oxide) was studied. The results showed that metallic Zn rapidly reduces Cr(VI), whereas this reaction is less evident in the presence of zinc oxide. Water was then retained for coatings containing metallic Zn.

Assessment of the mode of action underlying development of rodent small intestinal tumors following oral exposure to hexavalent chromium and relevance to humans

PubMed Central

Proctor, Deborah M.; Suh, Mina; Haws, Laurie C.; Kirman, Christopher R.; Harris, Mark A.

2013-01-01

Chronic exposure to high concentrations of hexavalent chromium (Cr(VI)) in drinking water causes intestinal adenomas and carcinomas in mice, but not in rats. Cr(VI) causes damage to intestinal villi and crypt hyperplasia in mice after only one week of exposure. After two years of exposure, intestinal damage and crypt hyperplasia are evident in mice (but not rats), as are intestinal tumors. Although Cr(VI) has genotoxic properties, these findings suggest that intestinal tumors in mice arise as a result of chronic mucosal injury. To better understand the mode of action (MOA) of Cr(VI) in the intestine, a 90-day drinking water study was conducted to collect histological, biochemical, toxicogenomic and pharmacokinetic data in intestinal tissues. Using MOA analyses and human relevance frameworks proposed by national and international regulatory agencies, the weight of evidence supports a cytotoxic MOA with the following key events: (a) absorption of Cr(VI) from the intestinal lumen, (b) toxicity to intestinal villi, (c) crypt regenerative hyperplasia and (d) clonal expansion of mutations within the crypt stem cells, resulting in late onset tumorigenesis. This article summarizes the data supporting each key event in the MOA, as well as data that argue against a mutagenic MOA for Cr(VI)-induced intestinal tumors. PMID:23445218

Examination of Cr(VI) treatment by zero-valent iron using in situ, real-time X-ray absorption spectroscopy and Cr isotope measurements

NASA Astrophysics Data System (ADS)

Jamieson-Hanes, Julia H.; Lentz, Adam M.; Amos, Richard T.; Ptacek, Carol J.; Blowes, David W.

2014-10-01

A series of replicate flow-through cell experiments was conducted to characterize Cr isotope fractionation during Cr(VI) treatment by granular zero-valent iron (ZVI). Synthetic groundwater containing 50 mg L-1 Cr(VI) was pumped upward through a custom-made cell packed with ZVI under anaerobic conditions. The geochemical evolution of the system was monitored using pH and redox measurements, while aqueous effluent samples were retained for analysis of cations and Cr isotopes. Real-time, in situ X-ray absorption near edge structure (XANES) spectroscopy collected via a Kapton® window in the cell provided additional information on the speciation of the reaction products. Increases in δ53Cr values corresponding to decreases in Cr(VI) concentration suggested the occurrence of redox processes. Spectroscopic results correlated well with the isotope data, indicating reduction of Cr(VI) to Cr(III). The isotope data did not appear to follow a single trend. A two-stage system was proposed to explain the complex isotope trend, where the rapid Cr removal was associated with very little fractionation (ε = -0.2‰), whereas slower removal was associated with a greater degree of fractionation (ε = -1.2‰ to -1.5‰). Reactive transport modeling was used to quantify distinct isotope fractionation values (ε), differentiated by a significant change in the Cr removal rate.

Remediation of hexavalent chromium contamination in chromite ore processing residue by sodium dithionite and sodium phosphate addition and its mechanism.

PubMed

Li, Yunyi; Cundy, Andrew B; Feng, Jingxuan; Fu, Hang; Wang, Xiaojing; Liu, Yangsheng

2017-05-01

Large amounts of chromite ore processing residue (COPR) wastes have been deposited in many countries worldwide, generating significant contamination issues from the highly mobile and toxic hexavalent chromium species (Cr(VI)). In this study, sodium dithionite (Na 2 S 2 O 4 ) was used to reduce Cr(VI) to Cr(III) in COPR containing high available Fe, and then sodium phosphate (Na 3 PO 4 ) was utilized to further immobilize Cr(III), via a two-step procedure (TSP). Remediation and immobilization processes and mechanisms were systematically investigated using batch experiments, sequential extraction studies, X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). Results showed that Na 2 S 2 O 4 effectively reduced Cr(VI) to Cr(III), catalyzed by Fe(III). The subsequent addition of Na 3 PO 4 further immobilized Cr(III) by the formation of crystalline CrPO 4 ·6H 2 O. However, addition of Na 3 PO 4 simultaneously with Na 2 S 2 O 4 (via a one-step procedure, OSP) impeded Cr(VI) reduction due to the competitive reaction of Na 3 PO 4 and Na 2 S 2 O 4 with Fe(III). Thus, the remediation efficiency of the TSP was much higher than the corresponding OSP. Using an optimal dosage in the two-step procedure (Na 2 S 2 O 4 at a dosage of 12× the stoichiometric requirement for 15 days, and then Na 3 PO 4 in a molar ratio (i.e. Na 3 PO 4 : initial Cr(VI)) of 4:1 for another 15 days), the total dissolved Cr in the leachate determined via Toxicity Characteristic Leaching Procedure (TCLP Cr) testing of our samples was reduced to 3.8 mg/L (from an initial TCLP Cr of 112.2 mg/L, i.e. at >96% efficiency). Copyright © 2017 Elsevier Ltd. All rights reserved.

Modeling of Cr(VI) Bioreduction Under Fermentative and Denitrifying Conditions

NASA Astrophysics Data System (ADS)

Molins, S.; Steefel, C.; Yang, L.; Beller, H. R.

2011-12-01

The mechanisms of bioreductive immobilization of Cr(VI) were investigated by reactive transport modeling of a set of flow-through column experiments performed using natural Hanford 100H aquifer sediment. The columns were continuously eluted with 5 μM Cr(VI), 5 mM lactate as the electron donor, and selected electron acceptors (tested individually). Here we focus on the two separate experimental conditions that showed the most removal of Cr(VI) from solution: fermentation and denitrification. In each case, a network of enzymatic and abiotic reaction pathways was considered to interpret the rate of chromate reduction. The model included biomass growth and decay, and thermodynamic limitations on reaction rates, and was constrained by effluent concentrations measured by IC and ICP-MS and additional information from bacterial isolates from column effluent. Under denitrifying conditions, Cr(VI) reduction was modeled as co-metabolic with nitrate reduction based on experimental observations and previous studies on a denitrifying bacterium derived from the Hanford 100H aquifer. The reactive transport model results supported this interpretation of the reaction mechanism and were used to quantify the efficiency of the process. The models results also suggest that biomass growth likely relied on a nitrogen source other than ammonium (e.g. nitrate). Under fermentative conditions and based on cell suspension studies performed on a bacterial isolate from the columns, the model assumes that Cr(VI) reduction is carried out directly by fermentative bacteria that convert lactate into acetate and propionate. The evolution to complete lactate fermentation and Cr(VI) reduction took place over a week's time and simulations were used to determine an estimate for a lower limit of the rate of chromate reduction by calibration with the flow-through column experimental results. In spite of sulfate being added to these columns, sulfate reduction proceeded at a slow rate and was not well constrained.

Optimizing the application of magnetic nanoparticles in Cr(VI) removal

NASA Astrophysics Data System (ADS)

Simeonidis, Konstantinos; Kaprara, Efthymia; Mitrakas, Manassis; Tziomaki, Magdalini; Angelakeris, Mavroidis; Vourlias, Georgios; Andritsos, Nikolaos

2013-04-01

The presence of heavy metals in aqueous systems is an intense health and environmental problem as implied by their harmful effects on human and other life forms. Among them, chromium is considered as an acutely hazardous compound contaminating the surface water from industrial wastes or entering the groundwater, the major source of drinking water, by leaching of chromite rocks. Chromium occurs in two stable oxidation states, Cr(III) and Cr(VI), with the hexavalent form being much more soluble and mobile in water having the ability to enter easily into living tissues or cells and thus become more toxic. Despite the established risks from Cr(VI)-containing water consumption and the increasing number of incidents, the E.U. tolerance limit for total chromium in potable water still stands at 50 μg/L. However, in the last years a worldwide debate concerning the establishment of a separate and very strict limit for the hexavalent form takes place. In practice, Cr(VI) is usually removed from water by various methods such as chemical coagulation/filtration, ion exchange, reverse osmosis and adsorption. Adsorption is considered as the simplest method which may become very effective if the process is facilitated by the incorporation of a Cr(VI) to Cr(III) reduction stage. This work studies the potential of using magnetic nanoparticles as adsorbing agents for Cr(VI) removal at the concentration levels met in contaminated drinking water. A variety of nanoparticles consisting of ferrites MFe2O4 (M=Fe, Co, Ni, Cu, Mn, Mg, Zn) were prepared by precipitating the corresponding bivalent or trivalent sulfate salts under controlled acidity and temperature. Electron microscopy and X-ray diffraction techniques were used to verify their crystal structure and determine the morphological characteristics. The mean particle size of the samples was found in the range 10-50 nm. Batch Cr(VI) removal tests were performed in aqueous nanoparticles dispersions showing the efficiency of ferrite nanoparticles to reduce Cr(VI) concentration below the regulation limit. The removal capacity is maximized for Fe3O4 nanoparticles due to the high reducing potential of the Fe2+ cations. Furthermore, their applicability was tested in a pilot-scale magnetic separator for the continuous flow removal of nanoparticles after water treatment that takes advantage of the magnetic properties. Acknowledgment This work was implemented within the framework of the Action «Supporting Postdoctoral Researchers» of the Operational Program "Education and Lifelong Learning" (Action's Beneficiary: General Secretariat for Research and Technology), and is co-financed by the European Social Fund (ESF) and the Greek State.

Environmental Presence of Hexavalent but Not Trivalent Chromium Causes Neurotoxicity in Exposed Drosophila melanogaster.

PubMed

Singh, Pallavi; Chowdhuri, D Kar

2017-07-01

A number of environmental chemicals are known to cause neurotoxicity to exposed organisms. Chromium (Cr), one of the major elements in earth's crust, is a priority environmental chemical depending on its valence state, and limited information is available on its neurotoxic potential. We, therefore, explored the neurotoxic potential of environmentally present trivalent- (Cr(III)) and hexavalent-Cr (Cr(VI)) on tested brain cell types in a genetically tractable organism Drosophila melanogaster along with its organismal response. Third instar larvae of w 1118 were fed environmentally relevant concentrations (5.0-20.0 μg/ml) of Cr(III)- or Cr(VI)-salt-mixed food for 24 and 48 h, and their exposure effects were examined in different brain cells of exposed organism. A significant reduction in the number of neuronal cells was observed in organism that were fed Cr(VI)- but not Cr(III)-salt-mixed food. Interestingly, glial cells were not affected by Cr(III) or Cr(VI) exposure. The tested cholinergic and dopaminergic neuronal cells were affected by Cr(VI) only with the later by 20.0 μg/ml Cr(VI) exposure after 48 h. The locomotor activity was significantly affected by Cr(VI) in exposed organism. Concomitantly, a significant increase in the level of reactive oxygen species (ROS) coupled with increased oxidative stress led to apoptotic cell death in the tested brain cells of Cr(VI)-exposed Drosophila, which were reversed by vitamin C supplementation. Conclusively, the present study provides evidence of environmental Cr(VI)-induced adversities on the brain of exposed Drosophila along with behavioral deficit which would likely to have relevance in humans and recommends Drosophila as a model for neurotoxicity.

Environmental impacts of asphalt mixes with electric arc furnace steel slag.

PubMed

Milačič, Radmila; Zuliani, Tea; Oblak, Tina; Mladenovič, Ana; Ančar, Janez Šč

2011-01-01

Electric arc furnace (EAF) steel slag can be used as an alternative high-quality material in road construction. Although asphalts with slag aggregates have been recognized as environmentally acceptable, there is a lack of data concerning the potential leaching of toxic Cr(VI) due to the highly alkaline media of EAF slag. Leaching of selected water extractable metals from slag indicated elevated concentrations of total chromium and Cr(VI). To estimate the environmental impacts of asphalt mixes with slag, leachability tests based on diffusion were performed using pure water and salt water as leaching agents. Compact and ground asphalt composites with natural aggregates, and asphalt composites in which the natural aggregates were completely replaced by slag were prepared. The concentrations of total chromium and Cr(VI) were determined in leachates over a time period of 6 mo. After 1 and 6 mo, the concentrations of some other metals were also determined in the leachates. The results indicated that chromium in leachates from asphalt composites with the addition of slag was present almost solely in its hexavalent form. However, the concentrations were very low (below 25 μg L) and did not represent an environmental burden. The leaching of other metals from asphalt composites with the addition of slag was negligible. Therefore, the investigated EAF slag can be considered as environmentally safe substitute for natural aggregates in asphalt mixes. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Removal of chromium (VI) using poly(methylacrylate) functionalized guar gum.

PubMed

Singh, Vandana; Kumari, Premlata; Pandey, Sadanand; Narayan, Tripti

2009-03-01

Using persulfate/ascorbic acid redox pair, poly(methylacrylate) was grafted on to guar gum and the conditions for the grafting were optimized. The copolymer sample having maximum %G was evaluated for the removal of Cr(VI) and the sorption conditions were optimized. The sorption was found pH dependent, pH 1.0 being the optimum value. Sorption data at pH 1.0 were modeled using both the Langmuir and Freundlich isotherms where the data fitted better to Freundlich isotherm. The equilibrium sorption capacity of 29.67mg/g was determined from the Langmuir isotherm. The sorption followed a pseudo-second-order kinetics with a rate constant 2.5x10(-4)gmg(-1) min(-1). The grafted product was also evaluated for Cr(VI) removal from local electroplating industrial waste water. The regeneration experiments revealed that the guar-graft-poly(methylacrylate) could be successfully reused for five cycles. In the present study conductivity measurements were used instead of conventional photometric method for determining Cr(VI) concentration in the equilibrium solutions and the results obtained have been compared with photometric method. Optimum Cr(VI) binding under highly acidic conditions indicated significant contribution of non electrostatic forces in the adsorption process.

Hexavalent chromium induces reactive oxygen species and impairs the antioxidant power of human erythrocytes and lymphocytes: Decreased metal reducing and free radical quenching ability of the cells.

PubMed

Husain, Nazim; Mahmood, Riaz

2017-08-01

The toxicity of hexavalent chromium [Cr(VI)] in biological systems is thought to be closely associated with the generation of free radicals and reactive oxygen species. These species are produced when Cr(VI) is reduced to its trivalent form in the cell. This process results in oxidative stress due to an imbalance between the detoxifying ability of the cell and the production of free radicals. We have studied the effect of potassium dichromate (K 2 Cr 2 O 7 ), a [Cr(VI)] compound, on the antioxidant power of human erythrocytes and lymphocytes under in vitro conditions. Incubation of erythrocytes and lymphocytes with different concentrations of K 2 Cr 2 O 7 resulted in a marked dose-dependent decrease in reduced glutathione and an increase in oxidized glutathione and reactive oxygen species levels. The antioxidant power of the cells was decreased, as determined by metal reducing and free radical quenching assays. These results show that [Cr(VI)] upregulates the generation of reactive oxygen species and, as a consequence, the cellular antioxidant defences are compromised. The resulting oxidative stress may contribute to Cr(VI)-induced cellular damage.

Golgi-Colonnier method: correlation of the degree of chromium reduction and pH change with quality of staining.

PubMed

Angulo, A; Merchán, J A; Molina, M

1994-03-01

We examined the role of chromium reduction in the Golgi-Colonnier method, correlating the quality of neuronal impregnation with the levels of hexavalent (CrVI) and trivalent (CrIII) chromium in the tissue and in the chromation fluid (CF). The concentrations of both chromium species were assessed by measuring spectrophotometrically the CrVI before and after oxidizing the sample and by calculating the ratio of CrVI to total chromium (chromium ratio, CrR). The CrR was almost identical in the tissue and the CF, decreasing exponentially during chromation due to a progressive consumption of CrVI to form CrIII. Satisfactory cell impregnation was obtained only when the CrR was 0.45-0.7, regardless of other factors. The CrR values could be accurately predicted by the pH increase of the CF; this increase has proven to be a most reliable criterion to decide the endpoint of the chromation process. The dependence of cell staining on the [CrIII], together with the well-known ability of this species to bridge proteins, suggests that the key event for cell impregnation is the cross-linking of neuronal proteins by CrIII polymers.

Hexavalent Chromium Generation within Naturally Structured Soils and Sediments

DOE PAGES

Hausladen, Debra M.; Fendorf, Scott

2017-01-13

Chromium(VI) produced from the oxidation of indigenous Cr(III) minerals is increasingly being recognized as a threat to groundwater quality. A critical determinant of Cr(VI) generation within soils and sediments is the necessary interaction of two low-solubility phases$-$Cr(III) silicates or (hydr)oxides and Mn(III/IV) oxides—that lead to its production. Here in this paper, we investigate the potential for Cr(III) oxidation by Mn oxides within fixed solid matrices common to soils and sediments. Artificial aggregates were constructed from Cr(OH) 3- and Cr 0.25Fe 0.75(OH) 3-coated quartz grains and either mixed with synthetic birnessite or inoculated with the Mn(II)-oxidizing bacterium Leptothrix cholodnii. In aggregatesmore » simulating low organic carbon environments, we observe Cr(VI) concentrations within advecting solutes at levels more than twenty-times the California drinking water standard. Chromium(VI) production is highly dependent on Cr-mineral solubility; increasing Fe-substitution (x = 0 to x = 0.75) decreases the solubility of the solid and concomitantly decreases total Cr(VI) generation by 37%. In environments with high organic carbon, reducing conditions within aggregate cores (microbially) generate sufficient Fe(II) to suppress Cr(VI) efflux. Our results illustrate Cr(VI) generation from reaction with Mn oxides within structured media simulating soils and sediments and provide insight into how fluctuating hydrologic and redox conditions impact coupled processes controlling Cr and Mn cycling.« less

Hexavalent Chromium Generation within Naturally Structured Soils and Sediments

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

Hausladen, Debra M.; Fendorf, Scott

Chromium(VI) produced from the oxidation of indigenous Cr(III) minerals is increasingly being recognized as a threat to groundwater quality. A critical determinant of Cr(VI) generation within soils and sediments is the necessary interaction of two low-solubility phases$-$Cr(III) silicates or (hydr)oxides and Mn(III/IV) oxides—that lead to its production. Here in this paper, we investigate the potential for Cr(III) oxidation by Mn oxides within fixed solid matrices common to soils and sediments. Artificial aggregates were constructed from Cr(OH) 3- and Cr 0.25Fe 0.75(OH) 3-coated quartz grains and either mixed with synthetic birnessite or inoculated with the Mn(II)-oxidizing bacterium Leptothrix cholodnii. In aggregatesmore » simulating low organic carbon environments, we observe Cr(VI) concentrations within advecting solutes at levels more than twenty-times the California drinking water standard. Chromium(VI) production is highly dependent on Cr-mineral solubility; increasing Fe-substitution (x = 0 to x = 0.75) decreases the solubility of the solid and concomitantly decreases total Cr(VI) generation by 37%. In environments with high organic carbon, reducing conditions within aggregate cores (microbially) generate sufficient Fe(II) to suppress Cr(VI) efflux. Our results illustrate Cr(VI) generation from reaction with Mn oxides within structured media simulating soils and sediments and provide insight into how fluctuating hydrologic and redox conditions impact coupled processes controlling Cr and Mn cycling.« less

Chromium speciation and fractionation in ground and surface waters in the vicinity of chromite ore processing residue disposal sites.

PubMed

Farmer, John G; Thomas, Rhodri P; Graham, Margaret C; Geelhoed, Jeanine S; Lumsdon, David G; Paterson, Edward

2002-04-01

Chromium concentrations of up to 91 mg l(-1) were found by ICP-OES for ground water from nine boreholes at four landfill sites in an area of S.E. Glasgow/S. Lanarkshire where high-lime chromite ore processing residue (COPR) from a local chemical works had been deposited from 1830 to 1968. Surface water concentrations of up to 6.7 mg l(-1) in a local tributary stream fell to 0.11 mg l(-1) in the River Clyde. Two independent techniques of complexation/colorimetry and speciated isotope dilution mass spectrometry (SIDMS) showed that Cr was predominantly (>90%) in hexavalent form (CrVI) as CrO4(2-), as anticipated at the high pH (7.5-12.5) of the sites. Some differences between the implied and directly determined concentrations of dissolved CrIII, however, appeared related to the total organic carbon (TOC) content. This was most significant for the ground water from one borehole that had the highest TOC concentration of 300 mg l(-1) and at which < 3% of Cr was in the form of CrVI. Subsequent ultrafiltration produced significant decreases in Cr concentration with decreasing size fractions, e.g. <0.45 microm, < 100 kDa, <30 kDa and < 1 kDa by the tangential-flow method. As this appeared related more to concentrations of humic substances than of TOC per se, horizontal bed gel electrophoresis of freeze-dried ultrafilter retentates was carried out to further characterise the CrIII-organic complex. This showed for the main Cr-containing fraction, 100 kDa-0.45 microm, that the Cr was associated with a dark brown band characteristic of organic (humic) matter. Comparison of gel electrophoresis and FTIR results for ultrafilter retentates of ground water from this borehole with those for a borehole at another site where CrVI predominated suggested the influence of carboxylate groups, both in reducing CrVI and in forming soluble CrIII-humic complexes. The implications of this for remediation strategies (especially those based on the addition of organic matter) designed to reduce highly mobile and carcinogenic Cr(VI)O4(2-) to the much less harmful CrIII as insoluble Cr(OH)3 are discussed.

Incorporation of zero valent iron nanoparticles in the matrix of cationic resin beads for the remediation of Cr(VI) contaminated waters.

PubMed

Toli, Aikaterini; Chalastara, Konstantina; Mystrioti, Christiana; Xenidis, Anthimos; Papassiopi, Nymphodora

2016-07-01

The objective of present study was to obtain the fixation of nano zero valent iron (nZVI) particles on a permeable matrix and evaluate the performance of this composite material for the removal of Cr(VI) from contaminated waters. The experiments were carried out using the cationic resin Dowex 50WX2 as porous support of the iron nanoparticles. The work was carried out in two phases. The first phase involved the fixation of nZVI on the resin matrix. The resin granules were initially mixed with a FeCl3 solution to obtain the adsorption of Fe(III). Then the Fe(III) loaded resin (RFe) was treated with polyphenol solutions to obtain the reduction of Fe(III) to the elemental state. Two polyphenol solutions were tested as reductants, i.e. green tea extract and gallic acid. Green tea was found to be inefficient, probably due to the relatively big size of the contained polyphenol molecules, but gallic acid molecules were able to reach adsorbed Fe(III) and reduce the cations to the elemental state. The second phase was focused on the investigation of Cr(VI) reduction kinetics using the nanoiron loaded resins (R-nFe). It was found that the reduction follows a kinetic law of first order with respect to Cr(VI) and to the embedded nanoiron. Compared to other similar products, this composite material was found to have comparable performance regarding reaction rates and higher degree of iron utilization. Namely the rate constant for the reduction of Cr(VI), in the presence of 1 mM nZVI, was equivalent to 1.4 h of half-life time at pH 3.2 and increased to 24 h at pH 8.5. The degree of iron utilization was as high as 0.8 mol of reduced Cr(VI) per mole of iron. It was also found that this composite material can be easily regenerated and reused for Cr(VI) reduction without significant loss of efficiency. Copyright © 2016 Elsevier Ltd. All rights reserved.

Reduction of aqueous chromate by Fe(II)/Fe(III) carbonate green rust: kinetic and mechanistic studies.

PubMed

Legrand, Ludovic; El Figuigui, Alaaeddine; Mercier, Florence; Chausse, Annie

2004-09-01

This work describes the heterogeneous reaction between FeII in carbonate green rust and aqueous chromate, in NaHCO3 solutions at 25 degrees C, and at pH values of 9.3-9.6. Evidence for reduction of CrVI to CrIII and concomitant solid-state oxidation of lattice FeII to FeIII was found from FeII titration and from structural analysis of the solids using FTIR, XRD, SEM, and XPS methods. Results indicate the formation of ferric oxyhydroxycarbonate and the concomitant precipitation of CrIII monolayers at the surface of the iron compound that induce passivation effects and progressive rate limitations. The number of CrIII monolayers formed at the completion of the reaction depends on [FeII]t=0, the molar concentration of FeII(solid) at t=0; on [n(o)]t=0, the molar concentration of reaction sites present at the surface of the solid phase at t=0; and on [CrVI]t=0, the molar concentration of CrVI at t=0. Kinetic data were modeled using a model based on the formation of successive CrIII monolayers, -(d[CrVI]/dt) = sigma(1)j k(i)[S] [CrVI]([n(i - 1)] - [n(i)]) with k(i)[S] (in s(-1) L mol(-1)), the rate coefficient of formation of CrIII monolayer i, and [n(i)] and [n(i - 1)], the molar concentration of CrIII precipitated in monolayer i and monolayer i - 1, respectively. Good matching curves were obtained with kinetic coefficients: k(1)[S] = 5-8 x 10(-4), k(2)[S] = 0.5-3 x 10(-5), and k(3)[S] about 1.7 x 10(-6) s(-1) m(-2) L. The CrVI removal efficiency progressively decreases along with the accumulation of CrIII monolayers at the surface of carbonate green rust particles. In the case of thick green rust particles resulting from the corrosion of iron in permeable reactive barriers, the quantity of FeII readily accessible for efficient CrVI removal should be rather low.

Bringing part of the lab to the field: On-site chromium speciation in seawater by electrodeposition of Cr(III)/Cr(VI) on portable coiled-filament assemblies and measurement in the lab by electrothermal, near-torch vaporization sample introduction and inductively coupled plasma-atomic emission spectrometry

NASA Astrophysics Data System (ADS)

Badiei, Hamid R.; McEnaney, Jennifer; Karanassios, Vassili

2012-12-01

A field-deployable electrochemical approach to preconcentration, matrix clean up and selective electrodeposition of Cr(III) and Cr(III) + Cr(VI) in seawater is described. Using portable, battery-operated electrochemical instrumentation, Cr species in seawater were electrodeposited in the field on portable coiled-filament assemblies made from Re. Assemblies with dried residues of Cr(III) or Cr(III) + Cr(VI) on them were transported to the lab for concentration determination by electrothermal, near-torch vaporization (NTV) sample introduction and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Electrodeposition offers selective species deposition, preconcentration and matrix clean up from seawater samples. For selective deposition, free Cr(VI) was electrodeposited at - 0.3 V and Cr(III) + Cr(VI) at - 1.6 V (both vs Ag/AgCl). Interestingly, at 0 V (vs Ag/AgCl) and in the absence of an electrodeposition potential only Cr(VI) was spontaneously and selectively adsorbed on the coil and reasons for this are given. Due to preconcentration afforded by electrodeposition, the detection limits obtained after a 60 s electrodeposition at the voltages stated above using buffered (pH = 4.7) artificial seawater spiked with either Cr(III) or Cr(VI) were 20 pg/mL for Cr(III) and 10 pg/mL for Cr(VI). For comparison, the detection limit for Cr obtained by pipetting directly on the coil 5 μL of diluted standard solution was 500 pg/mL, thus it was concluded that electrodeposition offered 40 to 60 fold improvements. Matrix clean up is required due to the high salt content of seawater and this was addressed by simply rinsing the coil with 18.2 MΩ water without any loss of Cr species. Reasons for this are provided. The method was validated in the lab using buffered artificial seawater and it was used in the field for the first time by sampling seawater, buffering it and immediately electrodepositing Cr species on portable assemblies on-site. Electrodeposition in the field addressed species transformation during sample pre-treatment. Such transformations occur due to sample acidification and may take place during transport and possibly storage prior to analysis. Thus, electrodeposition in the field is more reflective of Cr species concentration at the environmental conditions (e.g., temperature) at the time of sampling. It also opens up the possibility for shipping to the lab portable assemblies with Cr species on them rather than shipping large volumes of sample to the lab, thus also reducing shipping, handling and storage costs.

Chromium oxidation state mapping in human cells

NASA Astrophysics Data System (ADS)

Ortega, R.; Fayard, B.; Salomé, M.; Devès, G.; Susini, J.

2003-03-01

The widespread use of chromium in industrial applications such as chemical production of pigments, refractory brick production, tanning, metallurgy, electroplating, and combustion of fuels has lead to human occupational exposure and to its increased introduction into the environment. Hexavalent chromium compounds are established carcinogens but their mechanism of cell transformation is not known. Up to now, no microanalytical technique was sensitive enough to allow the observation of chromium distribution, and oxidation state identification, within isolated cells at carcinogenic concentrations. In this experiment, we used successfully the ID-21 X-ray microscope to map Cr(VI) and total Cr distributions in cells exposed in vitro to soluble, and insoluble, Cr(VI) compounds. Exposure to soluble compounds, weak carcinogens, resulted in a homogeneous intracellular distribution of Cr, confirming by in situ measurement that Cr is present in the cell nucleus. Cr(VI) was never detected in cells which suggests a mechanism of rapid intracellular reducticn. On the other hand, exposure to insoluble compounds, strong carcinogens, also resulted in a homogeneous distribution of reduced forms of Cr in cells, and their nucleus. However, in this case, Cr(VI)-rich structures were observed into the cells suggesting that carcinogenicity is enhanced when oxidation reactions due to Cr(VI) chronic exposure are associated to Cr-DNA alterations.

Cr(VI) removal by FeS-coated alumina, silica, and natural sand

NASA Astrophysics Data System (ADS)

Park, M.; Lee, S.; Jeong, H. Y.

2014-12-01

Removal of Cr(VI) was investigated using mackinawite (FeS)-coated mineral sorbents under anoxic conditions. The sorbents included alumina (Al), silica (WS), and natural sand (NS). By analysis of both solution and solid phases, all FeS-coated sorbents were found to reduce Cr(VI) into Cr(III). The sorption extent and mechanism of Cr(VI) strongly depended on the pH conditions. Only at pH 4.5, significant amounts of the dissolved Cr remained in the solution. Titration of dissolved Cr(III) and Fe(III) by NaOH solutions indicated that no bulk-phase precipitation occurred at pH 4.5. Also, the removal of Cr(VI) at pH 4.5 was the greatest by FeS-coated NS. Consistent with these, Cr-K edge EXAFS revealed that Cr was removed by FeS-coated NS via surface precipitation, and that it was immobilized by FeS-coated WS and Al by forming surface clusters. Regardless of FeS-coated sorbents, at pH 7.0 and pH 9.5, the initially added Cr(VI) was quantitatively removed from the solution phase. By EXAFS analysis, the Cr sorption by FeS-coated Al was mainly due to the bulk-phase precipitation of Cr(OH)3(s) or [Cr, Fe](OH)3(s). In case of FeS-coated WS and NS, the short Cr-Cr distance (~2.6 Å) at pH 7.0 and pH 9.5 was not simply accounted for by the bulk precipitation as either hydroxide (rCr-Cr ~ 3.0 Å), and it would rather result from the surface precipitation. Such a difference in the coordination structure among FeS-coated sorbents was likely due to in the lower surface area of the former available for the surface precipitation.

Delta Chromium-53/52 isotopic composition of native and contaminated groundwater, Mojave Desert, USA

USGS Publications Warehouse

Izbicki, John A.; Bullen, Thomas D.; Martin, Peter; Schroth, Brian

2012-01-01

Chromium(VI) concentrations in groundwater sampled from three contaminant plumes in aquifers in the Mojave Desert near Hinkley, Topock and El Mirage, California, USA, were as high as 2600, 5800 and 330 μg/L, respectively. δ53/52Cr compositions from more than 50 samples collected within these plumes ranged from near 0‰ to almost 4‰ near the plume margins. Assuming only reductive fractionation of Cr(VI) to Cr(III) within the plume, apparent fractionation factors for δ53/52Cr isotopes ranged from εapp = 0.3 to 0.4 within the Hinkley and Topock plumes, respectively, and only the El Mirage plume had a fractionation factor similar to the laboratory derived value of ε = 3.5. One possible explanation for the difference between field and laboratory fractionation factors at the Hinkley and Topock sites is localized reductive fractionation of Cr(VI) to Cr(III), with subsequent advective mixing of native and contaminated water near the plume margin. Chromium(VI) concentrations and δ53/52Cr isotopic compositions did not uniquely define the source of Cr near the plume margin, or the extent of reductive fractionation within the plume. However, Cr(VI) and δ53/52Cr data contribute to understanding of the interaction between reductive and mixing processes that occur within and near the margins of Cr contamination plumes. Reductive fractionation of Cr(VI) predominates in plumes having higher εapp, these plumes may be suitable for monitored natural attenuation. In contrast, advective mixing predominates in plumes having lower εapp, the highly dispersed margins of these plumes may be difficult to define and manage.

Innovative Use of Cr(VI) Plume Depictions and Pump-and-Treat Capture Analysis to Estimate Risks of Contaminant Discharge to Surface Water at Hanford Reactor Areas

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

Miller, Chuck W.; Hanson, James P.; Ivarson, Kristine A.

2015-01-14

The Hanford Site nuclear reactor operations required large quantities of high-quality cooling water, which was treated with chemicals including sodium dichromate dihydrate for corrosion control. Cooling water leakage, as well as intentional discharge of cooling water to ground during upset conditions, produced extensive groundwater recharge mounds consisting largely of contaminated cooling water and resulted in wide distribution of hexavalent chromium (Cr[VI]) contamination in the unconfined aquifer. The 2013 Cr(VI) groundwater plumes in the 100 Areas cover approximately 6 km2 (1500 acres), primarily in the 100-HR-3 and 100-KR-4 groundwater operable units (OUs). The Columbia River is a groundwater discharge boundary; wheremore » the plumes are adjacent to the Columbia River there remains a potential to discharge Cr(VI) to the river at concentrations above water quality criteria. The pump-and-treat systems along the River Corridor are operating with two main goals: 1) protection of the Columbia River, and 2) recovery of contaminant mass. An evaluation of the effectiveness of the pump-and-treat systems was needed to determine if the Columbia River was protected from contamination, and also to determine where additional system modifications may be needed. In response to this need, a technique for assessing the river protection was developed which takes into consideration seasonal migration of the plume and hydraulic performance of the operating well fields. Groundwater contaminant plume maps are generated across the Hanford Site on an annual basis. The assessment technique overlays the annual plume and the capture efficiency maps for the various pump and treat systems. The river protection analysis technique was prepared for use at the Hanford site and is described in detail in M.J. Tonkin, 2013. Interpolated capture frequency maps, based on mapping dynamic water level observed in observation wells and derived water levels in the vicinity of extraction and injection wells, are developed initially. Second, simulated capture frequency maps are developed, based on transport modelling results. Both interpolated and simulated capture frequency maps are based on operation of the systems over a full year. These two capture maps are then overlaid on the plume distribution maps for inspection of the relative orientation of the contaminant plumes with the capture frequency. To quantify the relative degree of protection of the river from discharges of Cr(VI) (and conversely, the degree of threat) at any particular location, a systematic method of evaluating and mapping the plume/capture relationship was developed. By comparing the spatial relationship between contaminant plumes and hydraulic capture frequency, an index of relative protectiveness is developed and the results posted on the combined plume/capture plan view map. Areas exhibiting lesser degrees of river protection are identified for remedial process optimization actions to control plumes and prevent continuing discharge of Cr(VI) to the river.« less

Processes affecting the remediation of chromium-contaminated sites.

PubMed

Palmer, C D; Wittbrodt, P R

1991-05-01

The remediation of chromium-contaminated sites requires knowledge of the processes that control the migration and transformation of chromium. Advection, dispersion, and diffusion are physical processes affecting the rate at which contaminants can migrate in the subsurface. Heterogeneity is an important factor that affects the contribution of each of these mechanisms to the migration of chromium-laden waters. Redox reactions, chemical speciation, adsorption/desorption phenomena, and precipitation/dissolution reactions control the transformation and mobility of chromium. The reduction of CrVI to CrIII can occur in the presence of ferrous iron in solution or in mineral phases, reduced sulfur compounds, or soil organic matter. At neutral to alkaline pH, the CrIII precipitates as amorphous hydroxides or forms complexes with organic matter. CrIII is oxidized by manganese dioxide, a common mineral found in many soils. Solid-phase precipitates of hexavalent chromium such as barium chromate can serve either as sources or sinks for CrVI. Adsorption of CrVI in soils increases with decreasing chromium concentration, making it more difficult to remove the chromium as the concentration decreases during pump-and-treat remediation. Knowledge of these chemical and physical processes is important in developing and selecting effective, cost-efficient remediation designs for chromium-contaminated sites.

Biosorption of Cr (VI), Cr (III), Pb (II) and Cd (II) from aqueous solutions by Sargassum wightii and Caulerpa racemosa algal biomass

NASA Astrophysics Data System (ADS)

Tamilselvan, Narayanaswamy; Saurav, Kumar; Kannabiran, Krishnan

2012-03-01

Heavy metal pollution is one of the most important environmental problems today. Biosorption is an innovative technology that employs biological materials to accumulate heavy metals from waste water through metabolic process or physicochemical pathways of uptake. Even though several physical and chemical methods are available for removal of heavy metals, currently many biological materials such as bacteria, algae, yeasts and fungi have been widely used due to their good performance, low cost and large quantity of availability. The aim of the present study is to explore the biosorption of toxic heavy metals, Cr(VI), Cr(III), Pb(II) and Cd(II) by algal biomass obtained from algae Sargassum wightii (brown) and Caulerpa racemosa (green). Biosorption of algal biomass was found to be biomass concentration- and pH-dependent, while the maximal biosorption was found at pH 5.0 and with the metal concentration of 100 mg L-1. S. wightii showed the maximal metal biosorption at the biomass concentration of 25 g L-1, followed by C. racemosa with the maximal biosorption at 30 g L-1. S. wightii showed 78% biosorption of Cr(VI), Cr(III), Pb(II) and Cd(II) ions. C. racemosa exhibited 85% biosorption of Cd(II) and Cr(VI), and 50% biosorption of Cr(III) and Pb(II). The results of our study suggest that seaweed biomass can be used efficiently for biosorption of heavy metals.

Low temperature reduction of hexavalent chromium by a microbial enrichment consortium and a novel strain of Arthrobacter aurescens.

PubMed

Horton, Rene' N; Apel, William A; Thompson, Vicki S; Sheridan, Peter P

2006-01-25

Chromium is a transition metal most commonly found in the environment in its trivalent [Cr(III)] and hexavalent [Cr(VI)] forms. The EPA maximum total chromium contaminant level for drinking water is 0.1 mg/l (0.1 ppm). Many water sources, especially underground sources, are at low temperatures (less than or equal to 15 Centigrade) year round. It is important to evaluate the possibility of microbial remediation of Cr(VI) contamination using microorganisms adapted to these low temperatures (psychrophiles). Core samples obtained from a Cr(VI) contaminated aquifer at the Hanford facility in Washington were enriched in Vogel Bonner medium at 10 Centigrade with 0, 25, 50, 100, 200, 400 and 1000 mg/l Cr(VI). The extent of Cr(VI) reduction was evaluated using the diphenyl carbazide assay. Resistance to Cr(VI) up to and including 1000 mg/l Cr(VI) was observed in the consortium experiments. Reduction was slow or not observed at and above 100 mg/l Cr(VI) using the enrichment consortium. Average time to complete reduction of Cr(VI) in the 30 and 60 mg/l Cr(VI) cultures of the consortium was 8 and 17 days, respectively at 10 Centigrade. Lyophilized consortium cells did not demonstrate adsorption of Cr(VI) over a 24 hour period. Successful isolation of a Cr(VI) reducing organism (designated P4) from the consortium was confirmed by 16S rDNA amplification and sequencing. Average time to complete reduction of Cr(VI) at 10 Centigrade in the 25 and 50 mg/l Cr(VI) cultures of the isolate P4 was 3 and 5 days, respectively. The 16S rDNA sequence from isolate P4 identified this organism as a strain of Arthrobacter aurescens, a species that has not previously been shown to be capable of low temperature Cr(VI) reduction. A. aurescens, indigenous to the subsurface, has the potential to be a predominant metal reducer in enhanced, in situ subsurface bioremediation efforts involving Cr(VI) and possibly other heavy metals and radionuclides.

Low temperature reduction of hexavalent chromium by a microbial enrichment consortium and a novel strain of Arthrobacter aurescens

PubMed Central

Horton, Rene' N; Apel, William A; Thompson, Vicki S; Sheridan, Peter P

2006-01-01

Background Chromium is a transition metal most commonly found in the environment in its trivalent [Cr(III)] and hexavalent [Cr(VI)] forms. The EPA maximum total chromium contaminant level for drinking water is 0.1 mg/l (0.1 ppm). Many water sources, especially underground sources, are at low temperatures (less than or equal to 15 Centigrade) year round. It is important to evaluate the possibility of microbial remediation of Cr(VI) contamination using microorganisms adapted to these low temperatures (psychrophiles). Results Core samples obtained from a Cr(VI) contaminated aquifer at the Hanford facility in Washington were enriched in Vogel Bonner medium at 10 Centigrade with 0, 25, 50, 100, 200, 400 and 1000 mg/l Cr(VI). The extent of Cr(VI) reduction was evaluated using the diphenyl carbazide assay. Resistance to Cr(VI) up to and including 1000 mg/l Cr(VI) was observed in the consortium experiments. Reduction was slow or not observed at and above 100 mg/l Cr(VI) using the enrichment consortium. Average time to complete reduction of Cr(VI) in the 30 and 60 mg/l Cr(VI) cultures of the consortium was 8 and 17 days, respectively at 10 Centigrade. Lyophilized consortium cells did not demonstrate adsorption of Cr(VI) over a 24 hour period. Successful isolation of a Cr(VI) reducing organism (designated P4) from the consortium was confirmed by 16S rDNA amplification and sequencing. Average time to complete reduction of Cr(VI) at 10 Centigrade in the 25 and 50 mg/l Cr(VI) cultures of the isolate P4 was 3 and 5 days, respectively. The 16S rDNA sequence from isolate P4 identified this organism as a strain of Arthrobacter aurescens, a species that has not previously been shown to be capable of low temperature Cr(VI) reduction. Conclusion A. aurescens, indigenous to the subsurface, has the potential to be a predominant metal reducer in enhanced, in situ subsurface bioremediation efforts involving Cr(VI) and possibly other heavy metals and radionuclides. PMID:16436214

Chronic exposure to particulate chromate induces spindle assembly checkpoint bypass in human lung cells.

PubMed

Wise, Sandra S; Holmes, Amie L; Xie, Hong; Thompson, W Douglas; Wise, John Pierce

2006-11-01

One of the hallmarks of lung cancer is chromosome instability (CIN), particularly a tetraploid phenotype, which is normally prevented by the spindle assembly checkpoint. Hexavalent chromium Cr(VI) is an established human lung carcinogen, and Cr(VI) induces tumors at lung bifurcation sites where Cr(VI) particles impact and persist. However, the effects of Cr(VI) on the spindle assembly checkpoint are unknown and little is known about prolonged exposure to particulate Cr(VI). Accordingly, we investigated particulate Cr(VI)-induced bypass of the spindle assembly checkpoint after several days of exposure in WHTBF-6 cells. We found that lead chromate indeed induces spindle assembly checkpoint bypass in human lung cells, as 72, 96, and 120 h treatments with 0.5 or 1 microg/cm2 lead chromate induced significant increases in the percentage of cells with aberrant mitotic figures. For example, treatment with 1 microg/cm2 lead chromate for 96 h induced 11, 12.3, and 14% of cells with premature anaphase, centromere spreading and premature centromere division, respectively. In addition, we found a disruption of mitosis with more cells accumulating in anaphase; cells treated for 96 h increased from 18% in controls to 31% in cells treated with lead chromate. To confirm involvement of the spindle assembly checkpoint, Mad2 expression was used as a marker. Mad2 expression was decreased in cells exposed to chronic treatments of lead chromate, consistent with disruption of the checkpoint. We also found concentration- and time-dependent increases in tetraploid cells, which continued to grow and form colonies. When cells were treated with chronic lead alone there was no increase in aberrant mitotic cells or polyploidy; however, chronic exposure to a soluble Cr(VI) showed an increase in aberrant mitotic cells and polyploidy. These data suggest that lead chromate does induce CIN and may be one mechanism in the development of Cr(VI)-induced lung cancer.

Chromium and fluoride sorption/desorption on un-amended and waste-amended forest and vineyard soils and pyritic material.

PubMed

Romar-Gasalla, Aurora; Santás-Miguel, Vanesa; Nóvoa-Muñoz, Juan Carlos; Arias-Estévez, Manuel; Álvarez-Rodríguez, Esperanza; Núñez-Delgado, Avelino; Fernández-Sanjurjo, María J

2018-05-22

Using batch-type experiments, chromium (Cr(VI)) and fluoride (F - ) sorption/desorption were studied in forest and vineyard soil samples, pyritic material, pine bark, oak ash, hemp waste and mussel shell, as well as on samples of forest and vineyard soil, and of pyritic material, individually treated with 48 t ha -1 of pine bark, oak ash, and mussel shell. Pine bark showed the highest Cr(VI) sorption (always > 97% of the concentration added) and low desorption (<1.5%). Pyritic material sorbed between 55 and 98%, and desorbed between 0.6 and 9%. Forest and vineyard soils, oak ash, mussel shell and hemp waste showed Cr(VI) sorption always < 32%, and desorption between 22 and 100%. Pine bark also showed the highest F - retention (sorption between 62 and 73%, desorption between 10 and 15%), followed by oak ash (sorption 60-69%, desorption 11-14%), forest soil (sorption 60-73%, desorption 19-36%), and pyritic material (sorption 60-67%, desorption 13-15%), whereas in vineyard sorption was 49-64%, and desorption 24-27%, and in hemp waste sorption was 26-36%, and desorption 41-59%. Sorption data showed better fitting to the Freundlich than to the Langmuir model, especially in the case of Cr(VI), indicating that multilayer sorption dominated. The addition of by-products to the forest and vineyard soils, and to the pyritic material, caused an overall increase in F - sorption, and decreased desorption. Furthermore, the pine bark amendment resulted in increases in Cr(VI) retention by both soils and the pyritic material. These results could be useful to favor the recycling of the by-products studied, aiding in the management of soils and degraded areas affected by Cr(VI) and F - pollution, and in the removal of both anions from polluted waters. Copyright © 2018 Elsevier Ltd. All rights reserved.

Airborne exposure to inhalable hexavalent chromium in welders and other occupations: Estimates from the German MEGA database.

PubMed

Pesch, Beate; Kendzia, Benjamin; Hauptmann, Kristin; Van Gelder, Rainer; Stamm, Roger; Hahn, Jens-Uwe; Zschiesche, Wolfgang; Behrens, Thomas; Weiss, Tobias; Siemiatycki, Jack; Lavoué, Jerome; Jöckel, Karl-Heinz; Brüning, Thomas

2015-07-01

This study aimed to estimate occupational exposure to inhalable hexavalent chromium (Cr(VI)) using the exposure database MEGA. The database has been compiling Cr(VI) concentrations and ancillary data about measurements at German workplaces. We analysed 3659 personal measurements of inhalable Cr(VI) collected between 1994 and 2009. Cr(VI) was determined spectrophotometrically at 540 nm after reaction with diphenylcarbazide. We assigned the measurements to pre-defined at-risk occupations using the information provided about the workplaces. Two-thirds of the measurements were below the limit of quantification (LOQ) and multiply imputed according to the distribution above LOQ. The 75th percentile value was 5.2 μg/m(3) and the 95th percentile was 57.2 μg/m(3). We predicted the geometric mean for 2h sampling in the year 2000, and the time trend of Cr(VI) exposure in these settings with and without adjustment for the duration of measurements. The largest dataset was available for welding (N = 1898), which could be further detailed according to technique. The geometric means were above 5 μg/m(3) in the following situations: spray painting, shielded metal arc welding, and flux-cored arc welding if applied to stainless steel. The geometric means were between 1 μg/m(3) and 5 μg/m(3) for gas metal arc welding of stainless steel, cutting, hard-chromium plating, metal spraying and in the chemical chromium industry. The exposure profiles described here are useful for epidemiologic and industrial health purposes. Exposure to Cr(VI) varies not only between occupations, but also within occupations as shown for welders. In epidemiologic studies, it would be desirable to collect exposure-specific information in addition to the job title. Copyright © 2015 Elsevier GmbH. All rights reserved.

Hexavalent Chromium Removal from Model Water and Car Shock Absorber Factory Effluent by Nanofiltration and Reverse Osmosis Membrane

PubMed Central

Bejaoui, Imen; Mouelhi, Meral; Hamrouni, Béchir

2017-01-01

Nanofiltration and reverse osmosis are investigated as a possible alternative to the conventional methods of Cr(VI) removal from model water and industrial effluent. The influences of feed concentration, water recovery, pH, and the coexisting anions were studied. The results have shown that retention rates of hexavalent chromium can reach 99.7% using nanofiltration membrane (NF-HL) and vary from 85 to 99.9% using reverse osmosis membrane (RO-SG) depending upon the composition of the solution and operating conditions. This work was also extended to investigate the separation of Cr(VI) from car shock absorber factory effluent. The use of these membranes is very promising for Cr(VI) water treatment and desalting industry effluent. Spiegler-Kedem model was applied to experimental results in the aim to determine phenomenological parameters, the reflection coefficient of the membrane (σ), and the solute permeability coefficient (Ps). The convective and diffusive parts of the mass transfer were quantified with predominance of the diffusive contribution. PMID:28819360

Hexavalent chromium availability and phytoremediation potential of Cichorium spinosum as affect by manure, zeolite and soil ageing.

PubMed

Antoniadis, Vasileios; Polyzois, Theologos; Golia, Evaggelia E; Petropoulos, Spyridon A

2017-03-01

Cichorium spinosum (spiny chicory) is a wild edible vegetable, and a possible suitable species for Cr(VI)-phytoremediation. There are three approaches for altering Cr(VI) dynamics: reduction to Cr(III) by organic matter addition, soil ageing, and Cr(VI) retention by high binding capacity materials added to soil, e.g., zeolite. Our aim was to assess spiny chicory as a phytoremediation species in relation to these three methods of altering Cr(VI) soil dynamics. There were 5 treatments: control (C); soil with 100 mg kg -1 Cr(VI) (S); soil with zeolite plus 100 mg kg -1 Cr(VI) (Z); soil with manure plus 100 mg kg -1 Cr(VI) (M); and soil added with 100 mg kg -1 Cr(VI) one year before this experiment (AS, "aged soil"). In soil, Cr(VI) was higher at S, while Z, M and AS were lower. In plant, Cr(VI) at Z, S, and AS were similar and significantly higher than M. This indicates that added manure decrease Cr(VI) availability to chicory due to the formation of organometallic complexes. However, chicory uptake amounted to 0.26-0.40 kg Cr(VI) ha -1 for Z, S, and AS, while uptake at M was lower. In conclusion, manure addition was more successful in decreasing Cr(VI) bioavailability, but it also slowed Cr(VI)-phytoremediation process. Copyright © 2016. Published by Elsevier Ltd.

Mechanism study of humic acid functional groups for Cr(VI) retention: Two-dimensional FTIR and 13C CP/MAS NMR correlation spectroscopic analysis.

PubMed

Zhang, Jia; Chen, Linpeng; Yin, Huilin; Jin, Song; Liu, Fei; Chen, Honghan

2017-06-01

Undissolved humic acid (HA) is known to substantially effect the migration and transformation of hexavalent chromium [Cr(VI)] in soils. The mechanisms of Cr(VI) retention in soils by undissolved HA have been reported; however, past studies are inconclusive about the types of HA functional groups that are involved in Cr(VI) retention and the retention mechanisms. Utilizing a two-dimensional correlation spectroscopy (2DCOS) analysis for FTIR and 13 C CP/MAS NMR, this study investigated the variations of HA function groups and molecular structures after reactions with aqueous Cr(VI) under different pH conditions. Based on the changing sequence of functional groups interpreted from the 2DCOS results, a four-step mechanism for Cr(VI) retention was determined as follows: (1) electrostatic adsorption of Cr(VI) to HA surface, (2) complexation of adsorbed Cr(VI) by carboxyl and ester, (3) reduction of complexed Cr(VI) to Cr(III) by phenol and polysaccharide, and (4) complexation of reduced Cr(III) by carboxylic groups. These functional groups that are involved in Cr(VI) retention were determined to occur in aromatic domains. Copyright © 2017 Elsevier Ltd. All rights reserved.

Acute and chronic effects of Cr(VI) on Hypsiboas pulchellus embryos and tadpoles.

PubMed

Natale, G S; Ammassari, L L; Basso, N G; Ronco, A E

2006-10-27

In the last few years there has been great concern about declines in the abundance of several species of amphibians around the world. Among amphibians, anurans have a biphasic life cycle, with aquatic tadpoles and generally terrestrial adults, and they have an extremely permeable skin, making them excellent indicators of the health of the environment. A number of different causes have been suggested for the global decline of anurans, the pollution of their habitat by chemical stressors being considered one of the major factors. Among chemical stressors, heavy metals are known for their high toxicity at very low concentrations. This study assessed short- (96 h, 'acute') and long-term (1272 h, 'chronic') exposure to Cr(VI) at lethal (3 to 90 mg 1(-1)) and sublethal concentrations (0.001 to 12 mg 1(-1)) on Hypsiboaspulchellus (previously called Hyla pulchella; see Faivovich et al. 2005) tadpoles (Fam. Hylidae) from central eastern Argentina. Fertilized eggs collected from a clean pond near La Plata (Buenos Aires Province) were used for acute and chronic toxicity testing. Assays were done under controlled laboratory conditions. Results of chronic exposure were used to assess the effect of factors such as toxicant concentration and age of organisms at the beginning of exposure on the response variables (growth, development and survival until metamorphosis). Results indicated a higher sensitivity to Cr(VI) of individuals first exposed as tadpoles than those first exposed as embryos during acute and chronic exposure. Exposure to the highest sublethal concentrations (6 to 12 mg 1(-1)) of the toxicant showed early inhibitory effects on growth of all treated organisms compensated at longer exposure periods with an increase in the growth rate compared to the control groups.

Biomonitoring of two types of chromium exposure in an electroplating shop.

PubMed

Pierre, Francis; Diebold, François; Baruthio, François

2008-01-01

This study is concerned with two specific chromium (Cr) exposure situations at a hard-process electroplating company. Its aims are to define variations in urinary Cr concentration and to clarify their exposure relationships. Airborne chromium exposure and urinary excretion were measured for a-one week period. The majority of the exposed population was divided into two groups distinguishing chromium plating and polishing functions. Analysis of airborne Cr distinguished water soluble Cr(VI), water total soluble Cr and water insoluble Cr. Volunteers provided 6-7 urine samples per day for a monitoring period of 7 days. Differences between the two groups appear in relation to the type of exposure. Low concentration water soluble Cr(VI) (5.3 microg/m3 maximum) in electroplating shops is practically undetected in other workshops. Water insoluble Cr present in low concentration in electroplating exceeds 1 mg/m3 in polishing shops. Total soluble Cr concentrations are similar in these two activities (3-10 microg/m3). In polishing, 0.4% of the Cr aerosol comprises soluble Cr. Urinary Cr varied according to a 24 h cycle in similar manner in both groups throughout the monitoring week. Minimum values (3-10 microg/g crea) occurred when starting a work shift, following by a rapid rise as soon as exposure commenced, whilst maximum values (12-30 microg/g crea) were recorded towards the end of the work shift. Although uncorrelated with soluble Cr(VI), urinary Cr (24 h) is effectively related to the soluble fraction of airborne chromium. In the case of chromium electroplating, correspondence between exposure and excretion appears to be governed by relationships different to those emerging from stainless steel welding, from which current biological limit values have been derived.

Evaluation of sequential extraction procedures for soluble and insoluble hexavalent chromium compounds in workplace air samples.

PubMed

Ashley, Kevin; Applegate, Gregory T; Marcy, A Dale; Drake, Pamela L; Pierce, Paul A; Carabin, Nathalie; Demange, Martine

2009-02-01

Because toxicities may differ for Cr(VI) compounds of varying solubility, some countries and organizations have promulgated different occupational exposure limits (OELs) for soluble and insoluble hexavalent chromium (Cr(VI)) compounds, and analytical methods are needed to determine these species in workplace air samples. To address this need, international standard methods ASTM D6832 and ISO 16740 have been published that describe sequential extraction techniques for soluble and insoluble Cr(VI) in samples collected from occupational settings. However, no published performance data were previously available for these Cr(VI) sequential extraction procedures. In this work, the sequential extraction methods outlined in the relevant international standards were investigated. The procedures tested involved the use of either deionized water or an ammonium sulfate/ammonium hydroxide buffer solution to target soluble Cr(VI) species. This was followed by extraction in a sodium carbonate/sodium hydroxide buffer solution to dissolve insoluble Cr(VI) compounds. Three-step sequential extraction with (1) water, (2) sulfate buffer and (3) carbonate buffer was also investigated. Sequential extractions were carried out on spiked samples of soluble, sparingly soluble and insoluble Cr(VI) compounds, and analyses were then generally carried out by using the diphenylcarbazide method. Similar experiments were performed on paint pigment samples and on airborne particulate filter samples collected from stainless steel welding. Potential interferences from soluble and insoluble Cr(III) compounds, as well as from Fe(II), were investigated. Interferences from Cr(III) species were generally absent, while the presence of Fe(II) resulted in low Cr(VI) recoveries. Two-step sequential extraction of spiked samples with (first) either water or sulfate buffer, and then carbonate buffer, yielded quantitative recoveries of soluble Cr(VI) and insoluble Cr(VI), respectively. Three-step sequential extraction gave excessively high recoveries of soluble Cr(VI), low recoveries of sparingly soluble Cr(VI), and quantitative recoveries of insoluble Cr(VI). Experiments on paint pigment samples using two-step extraction with water and carbonate buffer yielded varying percentages of relative fractions of soluble and insoluble Cr(VI). Sequential extractions of stainless steel welding fume air filter samples demonstrated the predominance of soluble Cr(VI) compounds in such samples. The performance data obtained in this work support the Cr(VI) sequential extraction procedures described in the international standards.

Effects of citrate on hexavalent chromium reduction by structural Fe(II) in nontronite

DOE PAGES

Liu, Xiaolei; Dong, Hailiang; Yang, Xuewei; ...

2017-09-23

Previous studies have shown that organic ligands could influence Cr(VI) reduction by aqueous Fe 2+ and pyrite. In this study, the effects of citrate on Cr(VI) reduction by structural Fe(II) in nontronite (NAu-2) were investigated at pH 6. Our results showed that the presence of citrate decreased the rate but increased the amount of Cr(VI) reduction. The decreased rate was likely due to competitive sorption of citrate and anionic dichromate (Cr 2O 7–) to NAu-2 surface sites, because sorption of dichromate appeared to be the first step for subsequent Cr(VI) reduction. The increased amount of Cr(VI) reduction was likely becausemore » citrate served as an additional electron donor to reduce Cr(VI) through ligand-metal electron transfer in the presence of soluble Fe 3+, which was possibly derived from dissolution of reduced NAu-2. Soluble Cr(III)-citrate complex was a possible form of reduced Cr(VI) when citrate was present. Without citrate, nanometer-sized Cr 2O 3 particles were the product of Cr(VI) reduction. In conclusion, our study highlights the importance of citrate on Cr(VI) reduction and immobilization when iron-rich smectite is applied to treat Cr(VI) contaminant in organic carbon rich environments.« less

Chromium (VI) ion adsorption by grafted cross-linked chitosan beads in aqueous solution - a mathematical and statistical modeling study.

PubMed

Igberase, E; Osifo, P; Ofomaja, A

2017-12-01

Chitosan outstanding qualities and efficient way of binding metal ions even to near zero concentration is the major reason for special attention. Modification of chitosan allows the polymer to be applied in numerous field of research. Depending on the modification techniques, chitosan possesses increased adsorption capacity. In this study chitosan beads (CS) were formulated from chitosan flakes, the beads were cross-linked with glutaraldehyde and thereafter grafted with ethyldiaminetetraacetic acid. The stability and amine concentration of the beads were determined. The chemical functionalities of the beads were obtained by Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis (TGA). However, in the adsorption studies with Cr(VI), the number of runs in the experiment was obtained by response surface methodology (RSM), and the maximum adsorption capacity (Q m ) from each run was determined from the Langmuir model. The results of the experiment showed that the non-modified beads were soluble at pH 1-4 and insoluble at pH 5, while the modified beads were insoluble at pH 1-6. The amine concentration of CS, CCS and grafted cross-linked chitosan beads (GCCS) were 4.4, 3.8 and 5.0 mmol/g, respectively. The point of zero charge (pH PZC ) of GCCS was found to be 4.4. The quadratic model was significant and adequate in describing the experimental data. The difference between experimental and predicted Q m was negligible. From the design matrix and results, increased Q m was achieved at pH 5, contact time 70 min, temperature 45°C, adsorbent dosage 5 g and initial concentration 70 mg/l. The desorption of the beads loaded with Cr(VI) was successful with 0.5 M HCl eluant and contact time of 180 min, leading to cost minimization.

Hydrogen ions and organic acids secreted by ectomycorrhizal fungi, Pisolithus sp1, are involved in the efficient removal of hexavalent chromium from waste water.

PubMed

Shi, Liang; Xue, Jiawang; Liu, Binhao; Dong, Pengcheng; Wen, Zhugui; Shen, Zhenguo; Chen, Yahua

2018-06-13

Pisolithus sp1 is an ectomycorrhizal (ECM) fungi that was chosen during a screening test of six strains of ECM fungi due to its ability to tolerate and remove hexavalent chromium (Cr(VI)). The physiological responses of Pisolithus sp1 to Cr(VI) exposure, the relationship between Pisolithus sp1 and exogenously added organic acids (EAOAs) or Na 3 VO 4 (H + -ATPase inhibitor) and the ability of Pisolithus sp1 to reduce Cr(VI) in liquid culture were also investigated. Hydrogen ions (H + ), which were produced directly by Pisolithus sp1, reduced the pH of the medium and played an important role in Cr(VI) reduction; however, Na 3 VO 4 significantly inhibited this process and resulted in a decrease in the Cr(VI) reduction rates. Organic acids were secreted after the reduction in Cr(VI) by Pisolithus sp1, and EAOAs did not significantly affect Cr(VI) reduction; those results revealed the secondary role of organic acids in Cr(VI) reduction. The Cr(VI) removal rate of Pisolithus sp1 approached 99% after Cr(VI) treatment for 12 days. Overall, 75% of the Cr(VI) removal was due to extracellular reduction and 24% was due to adsorption. The results of this study provide a strong basis for using Cr(VI)-tolerant and Cr(VI)-reducing fungi, as well as ectomycorrhiza, in the remediation of Cr(VI)-contaminated sites. Copyright © 2018 Elsevier Inc. All rights reserved.

Determination of hexavalent chromium in exhaled breath condensate and environmental air among chrome plating workers.

PubMed

Goldoni, Matteo; Caglieri, Andrea; Poli, Diana; Vettori, Maria Vittoria; Corradi, Massimo; Apostoli, Pietro; Mutti, Antonio

2006-03-15

Chromium speciation has attracted attention because of the different toxicity of Cr(III), which is considered relatively non-toxic, and Cr(VI), which can cross cell membranes mainly as a chromate anion and has been classified as a class I human carcinogen. The aims of the present study were to measure soluble Cr(VI) levels in environmental samples, to develop a simple method of quantifying Cr(VI) in exhaled breath condensate (EBC), and to follow the kinetics of EBC Cr(VI) in chrome plating workers.Personal air samples were collected from 10 chrome platers; EBC was collected from the same workers immediately after the work shift on Tuesday and before the work shift on the following Wednesday. Environmental and EBC Cr(VI) levels were determined by means of colorimetry and electrothermal absorption atomic spectrometry, respectively.The method of detecting Cr(VI) in environmental air was based on the extraction of the Cr(VI)-diphenylcarbazide (Cr(VI)-DPC) complex in 1-butanol, whereas EBC Cr(VI) was determined using a solvent extraction of Cr(VI) as an ion pair with tetrabutylammonium ion, and subsequent direct determination of the complex (Cr(VI)-DPC) in EBC.Kinetic data showed that airborne Cr(VI) was reduced by 50% in airway lining fluid sampled at the end of exposure and that there was a further 50% reduction after about 15 h. The persistence of Cr(VI) in EBC supports the use of EBC in assessing target tissue levels of Cr(VI).

Particles from bird feather: a novel application of an ionic liquid and waste resource.

PubMed

Sun, Ping; Liu, Zhao-Tie; Liu, Zhong-Wen

2009-10-30

The dissolution and regeneration of the waste chicken feathers in an ionic liquid of 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) were demonstrated for preparing chicken feather based particles. The structure and properties of the regenerated chicken feathers were investigated by FT-IR, XRD, SEM, BET and water contact angle. The crystallinity of the regenerated chicken feathers was decreased, and the content of beta-sheet was 31.71%, which was clearly lower than the raw feather (47.19%). The surface property of chicken feather changed from hydrophobicity to hydrophilicity after regenerated from [BMIM]Cl as indicated by the change of the water contact angle from 138 to 76 degrees . The chicken feather particles regenerated from [BMIM]Cl showed an excellent efficiency (63.5-87.7%) for removing Cr(VI) ions in wastewater at the concentrations from 2 to 80 ppm. The Freundlich constant (k(F)) for the adsorption of Cr(VI) ion by the particles of the regenerated chicken feather was four times larger than that of the raw chicken feather, the possible reason is the hydrophilic groups such as amino and carboxyl groups were tend to self-assemble towards surface when the dissolved CF were regenerated by water, amino group will partly hydrate to cationic amino and Cr(VI) ion occurs as an anion in the aqueous phase, so the cationic amino will adsorb the anionic Cr(VI) ion onto the RCF particles through electrostatic attraction. This work demonstrated a new application of the ionic liquid for dissolving chicken feather and a renewable application of waste chicken feather for removing Cr(VI) ion in water.

Duodenal crypt health following exposure to Cr(VI): Micronucleus scoring, γ-H2AX immunostaining, and synchrotron X-ray fluorescence microscopy

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

Thompson, Chad M.; Wolf, Jeffrey C.; Elbekai, Reem H.

2015-08-01

Lifetime exposure to high concentrations of hexavalent chromium [Cr(VI)] in drinking water results in intestinal damage and an increase in duodenal tumors in B6C3F1 mice. To assess whether these tumors could be the result of a direct mutagenic or genotoxic mode of action, we conducted a GLP-compliant 7-day drinking water study to assess crypt health along the entire length of the duodenum. Mice were exposed to water (vehicle control), 1.4, 21, or 180 ppm Cr(VI) via drinking water for 7 consecutive days. Crypt enterocytes in Swiss roll sections were scored as normal, mitotic, apoptotic, karyorrhectic, or as having micronuclei. Amore » single oral gavage of 50 mg/kg cyclophosphamide served as a positive control for micronucleus induction. Exposure to 21 and 180 ppm Cr(VI) significantly increased the number of crypt enterocytes. Micronuclei and γ-H2AX immunostaining were not elevated in the crypts of Cr(VI)-treated mice. In contrast, treatment with cyclophosphamide significantly increased numbers of crypt micronuclei and qualitatively increased γ-H2AX immunostaining. Synchrotron-based X-ray fluorescence (XRF) microscopy revealed the presence of strong Cr fluorescence in duodenal villi, but negligible Cr fluorescence in the crypt compartment. Together, these data indicate that Cr(VI) does not adversely effect the crypt compartment where intestinal stem cells reside, and provide additional evidence that the mode of action for Cr(VI)-induced intestinal cancer in B6C3F1 mice involves chronic villous wounding resulting in compensatory crypt enterocyte hyperplasia.« less

Modulation of sestrin confers protection to Cr(VI) induced neuronal cell death in Drosophila melanogaster.

PubMed

Singh, Pallavi; Chowdhuri, D Kar

2018-01-01

Increased oxidative stress is one of the major causes of hexavalent chromium [Cr(VI)], a heavy metal with diverse applications and environmental presence, induced neuronal adversities in exposed organism including Drosophila. Sestrin (sesn), an oxidative stress responsive gene, emerges as a novel player in the management of oxidative stress response. It is reported to be regulated by Target of rapamycin (TOR) and the former regulates autophagy and plays an important role in the prevention of neurodegeneration. Due to limited information regarding the role of sesn in chemical induced cellular adversities, it was hypothesized that modulation of sesn may improve the Cr(VI) induced neuronal adversities in Drosophila. Upon exposure of Cr(VI) (5.0-20.0 μg/ml) to D. melanogaster larvae (w 1118 ; background control), neuronal cell death was observed at 20.0 μg/ml of Cr(VI) concentration which was found to be reversed by targeted sesn overexpression (Elav-GAL4>UAS-sesn) in those cells of exposed organism by the induction of autophagy concomitant with decreased reactive oxygen species (ROS) level, p-Foxo-, p-JNK- and p-Akt-levels with decreased apoptosis. Conversely, after sesn knockdown (Elav-GAL4>UAS-sesn RNAi ) in neuronal cells, they become more vulnerable to oxidative stress and apoptosis. Furthermore, knockdown of sesn in neuronal cells of exposed organism resulted in decreased autophagy with increased TOR and p-S6k levels while overexpression of sesn led to their decreased levels suggestive of decreased anabolic and increased catabolic activity in neuronal cells shifting energy towards the augmentation of cellular repair. Taken together, the study suggests therapeutic implications of sesn against chemical induced neuronal adversities in an organism. Copyright © 2017 Elsevier Ltd. All rights reserved.

Chromium in urine, serum and red blood cells in the biological monitoring of workers exposed to different chromium valency states.

PubMed

Minoia, C; Cavalleri, A

1988-06-01

Using personal air sampling exposure to hexavalent and trivalent chromium was measured in 22 workers mainly exposed to Cr(VI) and in 15 workers mainly exposed to Cr(III) as basic chromium sulphate. Determination of Cr(VI) in the urine of all the subjects using a selective technique by ETA-AAS and liquid anion exchangers failed to show detectable amounts of the hexavalent form, the detection limit of the technique being 0.05 micrograms/L. A clear relationship between exposure and postshift urinary total chromium was found in subjects exposed to Cr(VI), while urinary levels in workers exposed to chromic sulphate high concentration proved lower. Determination of total chromium in serum and red blood cells showed a significant increase of chromium levels in erythrocytes of workers exposed to Cr(VI) while in subjects mainly exposed to Cr(III) an increase of the serum fraction was observed. The results demonstrate that Cr(III) is absorbed through the respiratory tract, but its kinetics and distribution in the body are not the same as for Cr(VI), and are not adequately monitored by short-term urinary determinations. Oxidation states of chromium largely influence uptake, mechanism of absorption, transport and organ distribution as well as toxicity of chromium-containing compounds. In particular, hexavalent derivatives are known to induce adverse effects, both acute and chronic, in occupationally exposed subjects, while there is little conclusive evidence for toxic effects caused by trivalent chromium compounds. Biological monitoring of exposure to chromium(VI) has usually been performed by determining total chromium levels in urine, whereas biological monitoring data in subjects occupationally exposed to Cr(III) are still scanty.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term chromium (VI) exposure increases phosphorus uptake by the extraradical mycelium of the arbuscular mycorrhizal fungus Rhizophagus irregularis MUCL 41833.

PubMed

Gil-Cardeza, María Lourdes; Calonne-Salmon, Maryline; Gómez, Elena; Declerck, Stéphane

2017-11-01

Hexavalent chromium is a potent carcinogen, while phosphorus is an essential nutrient. The role of arbuscular mycorrhizal fungi (AMF) in the uptake of P is well known and was also reported, at low levels, for Cr. However, it is unclear whether the uptake of Cr can impact the short-term uptake dynamics of P since both elements have a similar chemical structure and may thus potentially compete with each other during the uptake process. This study investigated the impact of Cr(VI) on short-term P uptake by the AMF Rhizophagus irregularis MUCL 41833 in Medicago truncatula. Bi-compartmented Petri plates were used to spatially separate a root compartment (RC) from a hyphal compartment (HC) using a whole plant in vitro culture system. The HC was supplemented with Cr(VI). Chromium(VI) as well as total Cr and P were monitored during 16 h within the HC and their concentrations determined by the end of the experiment within roots and shoots. Our results indicated that the uptake and translocation of Cr from hyphae to roots was a fast process: roots in which the extraradical mycelium (ERM) was exposed to Cr(VI) accumulated more Cr than roots of which the ERM was not exposed to Cr(VI) or was dead. Our results further confirmed that dead ERM immobilized more Cr than alive ERM. Finally our results demonstrated that the short exposure to Cr(VI) was sufficient to stimulate P uptake by the ERM and that the stimulation process began within the first 4 h of exposure. Copyright © 2017 Elsevier Ltd. All rights reserved.

Bioprocess development for hexavalent chromium reduction

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

Turick, C.E.; Apel, W.A.

1996-10-01

Hexavalent chromium (Cr(VI)) exists in the environment from anthropogenic activity and is regarded as a highly mobile and toxic pollutant. There is considerable interest in developing effective and efficient methods for the remediation of contaminated media. Many bacterial isolates have been demonstrated to metabolically reduce Cr(VI) to Cr(III), a much less toxic, more easily recoverable form of chromium. Aerobic and anaerobic cultures of Cr(VI) reducing bacteria were analyzed for their ability to reduce Cr(VI) prior to bioreactor design and scale up. Batch studies demonstrated Cr(VI) reduction rates with aerobic bacteria of up to 3 mg/hr/g dry cells, while anaerobic culturesmore » exhibited Cr(VI) reduction rates up to 22 mg/hr/g dry cells. An aerobic mixed culture of Cr(VI) reducing bacteria was chosen for bioreactor studies due to better rates of Cr(VI) reduction as well as the robust nature of the culture. These properties will allow for ease in bioprocess operation in the field.« less

Cr localization and speciation in roots of chromate fed Helianthus annuus L. seedlings using synchrotron techniques.

PubMed

de la Rosa, Guadalupe; Castillo-Michel, Hiram; Cruz-Jiménez, Gustavo; Bernal-Alvarado, Jesús; Córdova-Fraga, Teodoro; López-Moreno, Laura; Cotte, Marine

2014-01-01

In order to gain knowledge on the potential use of Helianthus annuus L. for the remediation of Cr(VI) polluted waters, hydroponics experiments were set up to determine Cr uptake and tolerance in different Cr(VI)-sulfate conditions, and Cr biotransformations. Results indicated that Cr(VI) promoted seed germination, and plant tolerance was higher at younger plant stages. Cr uptake was dependent on sulfate concentrations. The highest Cr levels in roots and shoots (13,700 and 2,500 mg kg(-1) dry weight (DW), respectively) were obtained in 1 mM sulfate. The lowest Cr uptake in roots (10,600 mg kg(-1) DW) was observed in seedlings treated with no sulfate. In shoots, Cr concentration was of 1,500 mg kg(-1)DW for the 1 mM sulfate treatment, indicating a different level of interaction between chromate and sulfate in both tissues. For the first time, using micro X-ray florescence (muXRF), we demonstrated Cr reaches the root stele and is located in the walls of xylem vessels. Bulk and micro X-ray Absorption Near-Edge Structure (muXANES) results showed that Cr in the roots is mostly in the form of Cr(III) phosphate (80%), with the remainder complexed to organic acids. Our results suggest this plant species may serve for Cr(VI) rhizofiltration purposes.

Comparison of Field Groundwater Biostimulation Experiments Using Polylactate and Lactate Solutions at the Chromium-Contaminated Hanford 100-H Site

NASA Astrophysics Data System (ADS)

Hazen, T. C.; Faybishenko, B.; Beller, H. R.; Brodie, E. L.; Sonnenthal, E. L.; Steefel, C.; Larsen, J.; Conrad, M. E.; Bill, M.; Christensen, J. N.; Brown, S. T.; Joyner, D.; Borglin, S. E.; Geller, J. T.; Chakraborty, R.; Nico, P. S.; Long, P. E.; Newcomer, D. R.; Arntzen, E.

2011-12-01

The primary contaminant of concern in groundwater at the DOE Hanford 100 Area (Washington State) is hexavalent chromium [Cr(VI)] in Hanford coarse-grained sediments. Three lactate injections were conducted in March, August, and October 2010 at the Hanford 100-H field site to assess the efficacy of in situ Cr(VI) bioreductive immobilization. Each time, 55 gal of lactate solution was injected into the Hanford aquifer. To characterize the biogeochemical regimes before and after electron donor injection, we implemented a comprehensive plan of groundwater sampling for microbial, geochemical, and isotopic analyses. These tests were performed to provide evidence of transformation of toxic and soluble Cr(VI) into less toxic and poorly soluble Cr(III) by bioimmobilization, and to quantify critical and interrelated microbial metabolic and geochemical mechanisms affecting chromium in situ reductive immobilization and the long-term sustainability of chromium bioremediation. The results of lactate injections were compared with data from two groundwater biostimulation tests that were conducted in 2004 and 2008 by injecting Hydrogen Release Compound (HRC°), a slow-release glycerol polylactate, into the Hanford aquifer. In all HRC and lactate injection tests, 13C-labeled lactate was added to the injected solutions to track post-injection carbon pathways. Monitoring showed that despite a very low initial total microbial density (from <104 to 105 cells/mL), both HRC and lactate injections stimulated anaerobic microbial activity, which led to an increase in biomass to >107 cells/mL (including sulfate- and nitrate-reducing bacteria), resulting in a significant decrease in soluble Cr(VI) concentrations to below the MCL. In all tests, lactate was consumed nearly completely within the first week, much faster than HRC. Modeling of biogeochemical and isotope fractionation processes with the reaction-transport code TOUGHREACT captured the biodegradation of lactate, fermentative production of acetate and propionate, the evolution of 13C in bicarbonate, and the rate of sulfate reduction. In contrast to the slow-release HRC injections, no long-term effects of biostimulation and Cr bioreduction were observed in groundwater after the lactate injections. The presentation will address these patterns of the geochemical, δ13C of DIC, and biomass changes in groundwater before and after the polylactate and lactate injections.

Characterization of Long-term Stability of Sodium Dithionite for Evaluation of its Potential Utility for Cr(VI) Remediation at Los Alamos National Laboratory

NASA Astrophysics Data System (ADS)

Telfeyan, K.; Migdissov, A. A.; Reimus, P. W.

2017-12-01

Sodium dithionite (Na2S2O4) has proven to be an effective remediation agent in aquifers contaminated with Cr(VI). S2O42- rapidly reduces the Fe(III) in aquifer sediments to Fe(II), which then reduces aqueous Cr(VI) to insoluble Cr(III). Previous work demonstrated that the reaction products from this treatment have no long-lasting undesirable effects. However, current literature regarding the stability of dithionite in aqueous solution and its decomposition products, which are important for developing a practical treatment approach, is sparse and inconsistent. Furthermore, S2O42- treatment effectiveness depends on site-specific geochemical and hydrological conditions, so experiments using site-specific materials are necessary to develop an optimal treatment strategy. In this study, we conducted (1) batch aqueous-phase-only experiments aimed at elucidating dithionite lifetimes and decomposition products as a function of dithionite concentration and pH, (2) batch experiments at the most practical pH for a field deployment, with use of four different representations of site aquifer sediments to evaluate dithionite reaction rates in the presence of the sediments and to determine the reduction capacity of the treated sediments, and (3) column experiments to represent a field-scale deployment of dithionite and determine the Cr(VI) reduction capacity of the reduced sediments. The aqueous-phase-only batch experiments verified the presence of S2O42- in aqueous anoxic solution beyond 100 days at alkaline pH. Each sampling interval also recorded the concentration of decomposition products, which enabled the derivation of a possible hydrolysis/decomposition reaction. In the batch experiments with sediments, dithionite reacted more rapidly than in blank solutions, but measurable concentrations remained for over a month. Cr was then added to the reactors to determine the efficacy of treatment. Depending on the sediment type and concentration of dithionite, the treated sediments were able to remove between 100 and 1000 µg Cr per gram of sediment. Column experiments then determined that the dithionite treatment of aquifer sediments could treat over 30 pore volumes of contaminated water (900 ppb Cr) prior to any breakthrough of Cr, suggesting that S2O42- should be an effective treatment agent at this site.

Biotransformation of hexavalent chromium into extracellular chromium(III) oxide nanoparticles using Schwanniomyces occidentalis.

PubMed

Mohite, Pallavi T; Kumar, Ameeta Ravi; Zinjarde, Smita S

2016-03-01

To demonstrate biotransformation of toxic Cr(VI) ions into Cr2O3 nanoparticles by the yeast Schwanniomyces occidentalis. Reaction mixtures containing S. occidentalis NCIM 3459 and Cr(VI) ions that were initially yellow turned green after 48 h incubation. The coloration was due to the synthesis of chromium (III) oxide nanoparticles (Cr2O3NPs). UV-Visible spectra of the reaction mixtures showed peaks at 445 and 600 nm indicating (4)A2g → (4)T1g and (4)A2g → (4)T2g transitions in Cr2O3, respectively. FTIR profiles suggested the involvement of carboxyl and amide groups in nanoparticle synthesis and stabilization. The Cr2O3NPs ranged between 10 and 60 nm. Their crystalline nature was evident from the selective area electron diffraction and X-ray diffraction patterns. Energy dispersive spectra confirmed the chemical composition of the nanoparticles. These biogenic nanoparticles could find applications in different fields. S. occidentalis mediated biotransformation of toxic Cr(VI) ions into crystalline extracellular Cr2O3NPs under benign conditions.

Determination of hexavalent chromium in exhaled breath condensate and environmental air among chrome plating workers

PubMed Central

Goldoni, Matteo; Caglieri, Andrea; Poli, Diana; Vettori, Maria Vittoria; Corradi, Massimo; Apostoli, Pietro; Mutti, Antonio

2006-01-01

Chromium speciation has attracted attention because of the different toxicity of Cr(III), which is considered relatively non-toxic, and Cr(VI), which can cross cell membranes mainly as a chromate anion and has been classified as a class I human carcinogen. The aims of the present study were to measure soluble Cr(VI) levels in environmental samples, to develop a simple method of quantifying Cr(VI) in exhaled breath condensate (EBC), and to follow the kinetics of EBC Cr(VI) in chrome plating workers. Personal air samples were collected from 10 chrome platers; EBC was collected from the same workers immediately after the work shift on Tuesday and before the work shift on the following Wednesday. Environmental and EBC Cr(VI) levels were determined by means of colorimetry and electrothermal absorption atomic spectrometry, respectively. The method of detecting Cr(VI) in environmental air was based on the extraction of the Cr(VI)-diphenylcarbazide (Cr(VI)–DPC) complex in 1-butanol, whereas EBC Cr(VI) was determined using a solvent extraction of Cr(VI) as an ion pair with tetrabutylammonium ion, and subsequent direct determination of the complex (Cr(VI)–DPC) in EBC. Kinetic data showed that airborne Cr(VI) was reduced by 50% in airway lining fluid sampled at the end of exposure and that there was a further 50% reduction after about 15 h. The persistence of Cr(VI) in EBC supports the use of EBC in assessing target tissue levels of Cr(VI). PMID:17047732

Assessment of the chemical status of the alluvial aquifer in the Aosta Plain: an example of the implementation of the Water Framework Directive in Italy

NASA Astrophysics Data System (ADS)

Rotiroti, Marco; Fumagalli, Letizia; Stefania, Gennaro A.; Frigerio, Maria C.; Simonetto, Fulvio; Capodaglio, Pietro; Bonomi, Tullia

2015-04-01

The Italian Legislative Decree 30/09 (D.Lgs. 30/09) implements the EU Water Framework Directive (WFD) providing some technical guidelines to assess the chemical status of groundwater bodies. This work presents the estimation of the chemical status of the shallow aquifer in the Aosta Plain (Aosta Valley Region, NW Alpine sector, Italy) on the basis of the D.Lgs. 30/09. The study area covers ~40 km2 along the Dora Baltea River basin. The Aosta Plain hosts an alluvial aquifer formed of lacustrine, glacial, fluvio-glacial and fan deposits of Pleistocene and Holocene ages. The unconfined aquifer features a depth of ~80 m in the western part of the plain and ~20 in the eastern part due to the intercalation of a silty lacustrine layer. The aquifer is mainly recharged by precipitation, surface water and ice and snow melt. Previous studies revealed that SO4, Fe, Mn, Ni, Cr(VI) and PCE represent potential threats for groundwater quality in the Aosta Plain. The chemical status was calculated using the data collected during the 2012 by the Regional Environmental Protection Agency of the Aosta Valley Region from its groundwater quality monitoring network that includes 38 points. Each point was sampled up to four times. Since the D.Lgs. 30/09 excludes Fe and Mn from the assessment of the groundwater chemical status, the present work deals with SO4, Ni, Cr(VI) and PCE. Threshold values (TVs) were estimated on the basis of natural background levels (NBLs) for SO4, Ni and Cr(VI) whereas, for PCE, the reference value (REF) reported by the D.Lgs. 30/09 (i.e., 1.1 µg/L) was used as TV. The NBLs were calculated using the two approaches suggested by the EU research project BRIDGE, that are the pre-selection and the component separation. The TVs were evaluated using the following criteria: (a) if NBL < REF, then TV = (REF+NBL)/2 and (b) if NBL ≥ REF, then TV = NBL. The average between the NBL resulted from the pre-selection and the component separation was used in the TV estimation. Finally, the chemical status was defined comparing the annual average concentration in each monitoring point to the TV: if more than 20% of sampling points exceeded the TV for at least one chemical parameter then the chemical status was defined as poor, otherwise the status was defined as good. The NBLs resulted of 10.1 µg/L, 1.8 µg/L and 115 mg/L from pre-selection and 9.4 µg/L, 2.3 µg/L and 148 mg/L from component separation for Ni, Cr(VI) and SO4, respectively. The TVs calculated are 15 µg/L, 3.6 µg/L and 191 mg/L for Ni, Cr(VI) and SO4, respectively. The percentages of sampling points exceeding the TV were 5.3, 23.7, 5.3 and 2.7 for Ni, Cr(VI), SO4 and PCE, therefore the groundwater chemical status in the Aosta Plain in 2012 resulted poor due to the high concentration of Cr(VI). This work underlines the necessity for remediation strategies to reduce the Cr(VI) pollution in the Aosta Plain in order to achieve the good chemical status as required by the WFD.

Hydrothermal Carbonization of Microalgae (Chlorococcum sp.) for Porous Carbons With High Cr(VI) Adsorption Performance.

PubMed

Sun, Yuanyuan; Liu, Chang; Zan, Yifan; Miao, Gai; Wang, Hao; Kong, Lingzhao

2018-04-12

Porous carbon adsorbents were prepared from microalgae (Chlorococcum sp.) via directly hydrothermal carbonization coupled with KOH or NH 3 activation for Cr(VI) adsorption. KOH-activated porous carbons exhibit high Cr(VI) adsorption capacities than those obtained via NH 3 modification (370.37 > 95.70 mg/g). The superior Cr(VI) adsorption capacity is due to high surface areas (1784 m 2 /g) and pore volumes of porous carbon with mesoporous and macroporous structures. The Cr(VI) adsorption result was well fitted to the Langmuir model, showing that the removal of Cr(VI) was attributed to the monolayer adsorption of activity site on carbon surface.

Removal of Chromium from Soils Cultivated with Maize (Zea Mays) After the Addition of Natural Minerals as Soil Amendments.

PubMed

Μolla, A; Ioannou, Z; Mollas, S; Skoufogianni, E; Dimirkou, A

2017-03-01

The efficiency of natural minerals, i.e. zeolite, bentonite and goethite, regarding the retention of chromium, from maize was examined. Specifically, 1.0 kg of soil, 1.0 g of soil amendment and either 50 mg L -1 Cr(III) or 1 mg L -1 Cr(VI) were added in plant pots. Then, seeds of maize were cultivated. Each treatment was repeated three times. The statistical results of the experiments were analyzed by LSD test. Cr(III) addition in soil has shown that zeolite was the only amendment that increased the dry weight. Zeolite and bentonite reduced significantly the total chromium in plants after the addition of 50 mg L -1 Cr(III). The addition of Cr(VI) in soil has shown that bentonite was the only amendment that increased the dry weight of biomass and the plants' height. All soil amendments reduced to zero the total chromium concentration measured to plants after the addition of 1 mg L -1 Cr(VI).

Study on the properties of chromium residue-cement matrices (CRCM) and the influences of superplasticizers on chromium(VI)-immobilising capability of cement matrices.

PubMed

Shi, Hui-Sheng; Kan, Li-Li

2009-03-15

The study of cementitious activity of chromium residue (CR) was carried out to formulate the properties of chromium residue-cement matrices (CRCM) by blending CR with Ordinary Portland Cement (OPC). The particle size distribution, microstructures of CR were investigated by some apparatuses, and physical properties, leaching behavior of hexavalent chromium [Cr(VI)] of CRCM were also determined by some experiments. Three types of commonly used superplasticizers (sulphonated acetone formaldehyde superplasticizer (J1), polycarboxylate-based superplasticizer (J2) and naphthalene superplasticizer (J3)) were chosen to investigate their influences on the physical properties and the Cr(VI)-immobilisation in the leachate of the CRCM hardened pastes. The results show that the CR has a certain cementitious activity. The incorporation of CR improves the pore size distribution of CRCM. The Cr(VI) concentrations in the leachate of CRCM significantly decrease by incorporation of J2. Among three superplasticizers, J2 achieves lowest Cr(VI) leaching ratio. Based on this study, it is likely to develop CR as a potential new additive used in cement-based materials.

Synthesis of Bi nanowire networks and their superior photocatalytic activity for Cr(vi) reduction.

PubMed

Zhao, Jin; Han, Qiaofeng; Zhu, Junwu; Wu, Xiaodong; Wang, Xin

2014-09-07

Interconnected Bi nanowire networks were synthesized for the first time via a solvothermal route by using ethylene glycol (EG) as both a solvent and a reducing agent, and citric acid (CA) as a stabilizing agent at a molar ratio of CA/Bi(3+) = 5. Among various reaction conditions including the temperature, reaction time and precursor concentration, the molar ratio of CA/Bi(3+) was the dominant experimental parameter to influence the morphology and structures of the Bi crystals. Highly dispersed Bi microspheres and network-like Bi thick wires were obtained if the molar ratio of CA/Bi(3+) was changed to 2.5 and 10, respectively. As compared to other additives including trisodium citrate, cetyltrimethylammonium bromide (CTAB) and oxalic acid, good solubility of CA in EG together with its coordination effect played a crucial role in the formation of network-like Bi nanowires. The Bi nanowire networks exhibited excellent photocatalytic performance for Cr(vi) reduction. Cr(vi) was completely reduced to less toxic Cr(iii) after 8 min and 55 min of UV and visible-light irradiation, respectively.

Method of trivalent chromium concentration determination by atomic spectrometry

DOEpatents

Reheulishvili, Aleksandre N [Tbilisi, 0183, GE; Tsibakhashvili, Neli Ya [Tbilisi, 0101, GE

2006-12-12

A method is disclosed for determining the concentration of trivalent chromium Cr(III) in a sample. The addition of perchloric acid has been found to increase the atomic chromium spectrometric signal due to Cr(III), while leaving the signal due to hexavalent chromium Cr(VI) unchanged. This enables determination of the Cr(III) concentration without pre-concentration or pre-separation from chromium of other valences. The Cr(III) concentration may be measured using atomic absorption spectrometry, atomic emission spectrometry or atomic fluorescence spectrometry.

Stabilization of Cr(VI) from fine ferrochrome dust using exfoliated vermiculite.

PubMed

Mulange Wa Mulange, Delphin; Garbers-Craig, Andrie Mariana

2012-07-15

This study proved that vermiculite, a natural occurring mineral, can effectively remove and stabilize Cr(VI) from fine ferrochrome dust leachate. Batch adsorption studies were carried out to determine the effect of pH, contact time and adsorbent dose on the removal of Cr(VI). The process was found to be highly pH dependent. The optimum conditions for the Cr(VI) removal are at a pH of 1.5, contact time of 2h and adsorbent dose of 10gL(-1). The stability of the Cr(VI)-loaded vermiculite remained unchanged after 12 months, when the vermiculite was evaluated with the ASTM and TCLP Cr(VI) leach methods. However, Cr(VI) desorption did take place when the Acid Rain Test was used. The adsorption kinetic data fits the pseudo-second order model, while the equilibrium data of Cr(VI) adsorption onto vermiculite are best described by the Langmuir isotherm. The presence of hydrobiotite and biotite in the industrial vermiculite slightly decreased the degree of adsorption of Cr(VI). Copyright © 2012 Elsevier B.V. All rights reserved.

Removal of hexavalent Cr by coconut coir and derived chars--the effect of surface functionality.

PubMed

Shen, Ying-Shuian; Wang, Shan-Li; Tzou, Yu-Min; Yan, Ya-Yi; Kuan, Wen-Hui

2012-01-01

The Cr(VI) removal by coconut coir (CC) and chars obtained at various pyrolysis temperatures were evaluated. Increasing the pyrolysis temperature resulted in an increased surface area of the chars, while the corresponding content of oxygen-containing functional groups of the chars decreased. The Cr(VI) removal by CC and CC-derived chars was primarily attributed to the reduction of Cr(VI) to Cr(III) by the materials and the extent and rate of the Cr(VI) reduction were determined by the oxygen-containing functional groups in the materials. The contribution of pure Cr(VI) adsorption to the overall Cr(VI) removal became relatively significant for the chars obtained at higher temperatures. Accordingly, to develop a cost-effective method for removing Cr(VI) from water, the original CC is more advantageous than the carbonaceous counterparts because no pyrolysis is required for the application and CC has a higher content of functional groups for reducing Cr(VI) to less toxic Cr(III). Copyright © 2011 Elsevier Ltd. All rights reserved.

Oral Chromium Exposure and Toxicity

PubMed Central

Sun, Hong; Brocato, Jason

2015-01-01

Hexavalent chromium [Cr(VI)] is a known carcinogen when inhaled. However, inhalational exposure to Cr(VI) affects only a small portion of the population, mainly by occupational exposures. In contrast, oral exposure to Cr(VI) is widespread and affects many people throughout the globe. In 2008, the National Toxicology Program (NTP) released a 2-year study demonstrating that ingested Cr(VI) was carcinogenic in rats and mice. The effects of Cr(VI) oral exposure is mitigated by reduction in the gut, however a portion evades the reductive detoxification and reaches target tissues. Once Cr(VI) enters the cell, it ultimately gets reduced to Cr(III), which mediates its toxicity via induction of oxidative stress during the reduction while Cr intermediates react with protein and DNA. Cr(III) can form adducts with DNA that may lead to mutations. This review will discuss the potential adverse effects of oral exposure to Cr(VI) by presenting up-to-date human and animal studies, examining the underlying mechanisms that mediate Cr(VI) toxicity, as well as highlighting opportunities for future research. PMID:26231506

Kinetics and Products of Chromium(VI) Reduction by Iron(II/III)-Bearing Clay Minerals.

PubMed

Joe-Wong, Claresta; Brown, Gordon E; Maher, Kate

2017-09-05

Hexavalent chromium is a water-soluble pollutant, the mobility of which can be controlled by reduction of Cr(VI) to less soluble, environmentally benign Cr(III). Iron(II/III)-bearing clay minerals are widespread potential reductants of Cr(VI), but the kinetics and pathways of Cr(VI) reduction by such clay minerals are poorly understood. We reacted aqueous Cr(VI) with two abiotically reduced clay minerals: an Fe-poor montmorillonite and an Fe-rich nontronite. The effects of ionic strength, pH, total Fe content, and the fraction of reduced structural Fe(II) [Fe(II)/Fe(total)] were examined. The last variable had the largest effect on Cr(VI) reduction kinetics: for both clay minerals, the rate constant of Cr(VI) reduction varies by more than 3 orders of magnitude with Fe(II)/Fe(total) and is described by a linear free energy relationship. Under all conditions examined, Cr and Fe K-edge X-ray absorption near-edge structure spectra show that the main Cr-bearing product is a Cr(III)-hydroxide and that Fe remains in the clay structure after reacting with Cr(VI). This study helps to quantify our understanding of the kinetics of Cr(VI) reduction by Fe(II/III)-bearing clay minerals and may improve predictions of Cr(VI) behavior in subsurface environments.

Impact of Fe(III) as an effective electron-shuttle mediator for enhanced Cr(VI) reduction in microbial fuel cells: Reduction of diffusional resistances and cathode overpotentials.

PubMed

Wang, Qiang; Huang, Liping; Pan, Yuzhen; Quan, Xie; Li Puma, Gianluca

2017-01-05

The role of Fe(III) was investigated as an electron-shuttle mediator to enhance the reduction rate of the toxic heavy metal hexavalent chromium (Cr(VI)) in wastewaters, using microbial fuel cells (MFCs). The direct reduction of chromate (CrO 4 - ) and dichromate (Cr 2 O 7 2- ) anions in MFCs was hampered by the electrical repulsion between the negatively charged cathode and Cr(VI) functional groups. In contrast, in the presence of Fe(III), the conversion of Cr(VI) and the cathodic coulombic efficiency in the MFCs were 65.6% and 81.7%, respectively, 1.6 times and 1.4 folds as those recorded in the absence of Fe(III). Multiple analytical approaches, including linear sweep voltammetry, Tafel plot, cyclic voltammetry, electrochemical impedance spectroscopy and kinetic calculations demonstrated that the complete reduction of Cr(VI) occurred through an indirect mechanism mediated by Fe(III). The direct reduction of Cr(VI) with cathode electrons in the presence of Fe(III) was insignificant. Fe(III) played a critical role in decreasing both the diffusional resistance of Cr(VI) species and the overpotential for Cr(VI) reduction. This study demonstrated that the reduction of Cr(VI) in MFCs was effective in the presence of Fe(III), providing an alternative and environmentally benign approach for efficient remediation of Cr(VI) contaminated sites with simultaneous production of renewable energy. Copyright © 2016 Elsevier B.V. All rights reserved.

Development of phosphate rock integrated with iron amendment for simultaneous immobilization of Zn and Cr(VI) in an electroplating contaminated soil.

PubMed

Zhao, Ling; Ding, Zhenliang; Sima, Jingke; Xu, Xiaoyun; Cao, Xinde

2017-09-01

This study aims to develop an amendment for simultaneous immobilization of Zn and Cr(VI) in an abandoned electroplating contaminated soil. Nature phosphate rock was first activated with oxalic acid (O-PR) and then combined with FeSO 4 or zero-valent iron (ZVI) for immobilization of Zn and Cr(VI) from aqueous solutions. Finally, the optimized approach showing the highest immobilization ability in solution was applied in an electroplating contaminated soil. The O-PR combined with FeSO 4 was more effective in simultaneously removing Zn and Cr(VI) than the O-PR integrated with ZVI within the tested solution pH range of 5.5-8.5. Both O-PR with FeSO 4 and with ZVI removed over 95% of Zn from the solution; however, only 42-46% of Cr(VI) was immobilized by O-PR with ZVI, while O-PR with FeSO 4 almost precipitated all Cr(VI). Moreover, there were 75-95% Zn and 95-100% Cr(VI) remaining in the exhausted O-PR with FeSO 4 solid after toxicity characteristic leaching test (TCLP) while the exhausted O-PR with ZVI solid only retained 44-83% Zn and 32-72% Cr(VI). Zinc was immobilized mainly via formation of insoluble Fe-Zn phosphate co-precipitates, while iron-induced reduction of Cr(VI) into stable Cr(OH) 3 or Cr x Fe (1-x) (OH) 3 was responsible for Cr(VI) immobilization. Application of the O-PR integrated with FeSO 4 in the electroplating contaminated soil rapidly reduced the TCLP extractable Zn and Cr(VI) to below the standard limits, with decrease by 50% and 94%, respectively. This study revealed that combination of oxalic acid activated phosphate rock with FeSO 4 could be an effective amendment for remediation of Zn and Cr(VI) contaminated soil. Copyright © 2017 Elsevier Ltd. All rights reserved.

Tracing the tracks of genotoxicity by trivalent and hexavalent chromium in Drosophila melanogaster.

PubMed

Mishra, Manish; Sharma, Anurag; Negi, M P S; Dwivedi, U N; Chowdhuri, D Kar

2011-05-18

Mutagen sensitive strains (mus) in Drosophila are known for their hypersensitivity to mutagens and environmental carcinogens. Accordingly, these mutants were grouped in pre- and post-replication repair pathways. However, studying mutants belonging to one particular repair pathway may not be adequate for examining chemical-induced genotoxicity when other repair pathways may neutralize its effect. To test whether both pre-and post-replication pathways are involved and effect of Cr(III)- and Cr(VI)-induced genotoxicity in absence or presence of others, we used double mutant approach in D. melanogaster. We observed DNA damage as evident by changes in Comet assay DNA migration in cells of larvae of Oregon R(+) and single mutants of pre- (mei-9, mus201 and mus210) and post- (mei-41, mus209 and mus309) replication repair pathways and also in double mutants of different combinations (pre-pre, pre-post and post-post replication repair) exposed to increasing concentrations of Cr(VI) (0.0, 5.0, 10.0 and 20.0 μg/ml) for 48 h. The damage was greater in pre-replication repair mutants after exposure to 5.0 μg/ml Cr(VI), while effects on Oregon R(+) and post replication repair mutants were insignificant. Post-replication repair mutants revealed significant DNA damage after exposure to 20.0 μg/ml Cr(VI). Further, double mutants generated in the above repair categories were examined for DNA damage following Cr(VI) exposure and a comparison of damage was studied between single and double mutants. Combinations of double mutants generated in the pre-pre replication repair pathways showed an indifferent interaction between the two mutants after Cr(VI) exposure while a synergistic interaction was evident in exposed post-post replication repair double mutants. Cr(III) (20.0 μg/ml) exposure to these strains did not induce any significant DNA damage in their cells. The study suggests that both pre- and post-replication pathways are affected in Drosophila by Cr(VI) leading to genotoxicity, which may have consequences for metal-induced carcinogenesis. 2011 Elsevier B.V. All rights reserved.

Biosorption Potential of Bacillus salmalaya Strain 139SI for Removal of Cr(VI) from Aqueous Solution.

PubMed

Dadrasnia, Arezoo; Chuan Wei, Kelvin Swee; Shahsavari, Nasser; Azirun, Mohd Sofian; Ismail, Salmah

2015-12-03

The present study investigated the biosorption capacity of live and dead cells of a novel Bacillus strain for chromium. The optimum biosorption condition was evaluated in various analytical parameters, including initial concentration of chromium, pH, and contact time. The Langmuir isotherm model showed an enhanced fit to the equilibrium data. Live and dead biomasses followed the monolayer biosorption of the active surface sites. The maximum biosorption capacity was 20.35 mg/g at 25 °C, with pH 3 and contact time of 50 min. Strain 139SI was an excellent host to the hexavalent chromium. The biosorption kinetics of chromium in the dead and live cells of Bacillus salmalaya (B. salmalaya) 139SI followed the pseudo second-order mechanism. Scanning electron microscopy and fourier transform infrared indicated significant influence of the dead cells on the biosorption of chromium based on cell morphological changes. Approximately 92% and 70% desorption efficiencies were achieved using dead and live cells, respectively. These findings demonstrated the high sorption capacity of dead biomasses of B. salmalaya 139SI in the biosorption process. Thermodynamic evaluation (ΔG⁰, ΔH⁰, and ΔS⁰) indicated that the mechanism of Cr(VI) adsorption is endothermic; that is, chemisorption. Results indicated that chromium accumulation occurred in the cell wall of B. salmalaya 139SI rather than intracellular accumulation.

Biosorption Potential of Bacillus salmalaya Strain 139SI for Removal of Cr(VI) from Aqueous Solution

PubMed Central

Dadrasnia, Arezoo; Chuan Wei, Kelvin Swee; Shahsavari, Nasser; Azirun, Mohd Sofian; Ismail, Salmah

2015-01-01

The present study investigated the biosorption capacity of live and dead cells of a novel Bacillus strain for chromium. The optimum biosorption condition was evaluated in various analytical parameters, including initial concentration of chromium, pH, and contact time. The Langmuir isotherm model showed an enhanced fit to the equilibrium data. Live and dead biomasses followed the monolayer biosorption of the active surface sites. The maximum biosorption capacity was 20.35 mg/g at 25 °C, with pH 3 and contact time of 50 min. Strain 139SI was an excellent host to the hexavalent chromium. The biosorption kinetics of chromium in the dead and live cells of Bacillus salmalaya (B. salmalaya) 139SI followed the pseudo second-order mechanism. Scanning electron microscopy and fourier transform infrared indicated significant influence of the dead cells on the biosorption of chromium based on cell morphological changes. Approximately 92% and 70% desorption efficiencies were achieved using dead and live cells, respectively. These findings demonstrated the high sorption capacity of dead biomasses of B. salmalaya 139SI in the biosorption process. Thermodynamic evaluation (ΔG0, ΔH0, and ΔS0) indicated that the mechanism of Cr(VI) adsorption is endothermic; that is, chemisorption. Results indicated that chromium accumulation occurred in the cell wall of B. salmalaya 139SI rather than intracellular accumulation. PMID:26633454

Pilot Scale Production of Activated Carbon Spheres Using Fluidized Bed Reactor and Its Evaluation for the Removal of Hexavalent Chromium from Aqueous Solutions

NASA Astrophysics Data System (ADS)

Tripathi, Nagesh Kumar; Sathe, Manisha

2017-12-01

Large scale production of activated carbon is need of ongoing research due to its excellent adsorption capacity for removal of heavy metals from contaminated solutions. In the present study, polymeric precursor polystyrene beads [Brunauer Emmett Teller (BET) surface area, 46 m2/g; carbon content, 40.64%; crushing strength, 0.32 kg/sphere] were used to produce a new variant of activated carbon, Activated Carbon Spheres (ACS) in a pilot scale fluidized bed reactor. ACS were prepared by carbonization of polymeric precursor at 850 °C followed by activation of resultant material with steam. Prepared ACS were characterized using scanning electron microscope, CHNS analyzer, thermogravimetric analyzer, surface area analyzer and crushing strength tester. The produced ACS have 1009 m2/g BET surface area, 0.89 cm3/g total pore volume, 92.32% carbon content and 1.1 kg/sphere crushing strength with less than 1% of moisture and ash content. The ACS were also evaluated for its potential to remove hexavalent chromium [Cr(VI)] from contaminated solutions. The chromium removal is observed to be 99.1% at initial concentration 50 mg/l, pH 2, ACS dose 1 g/l, contact time 2 h, agitation 120 rpm and temperature 30 °C. Thus ACS can be used as an adsorbent material for the removal of Cr(VI) from contaminated solutions.

Utilization of modified corn silk as a biosorbent for solid-phase extraction of Cr(III) and chromium speciation.

PubMed

Yu, Hongmei; Pang, Jing; Wu, Mei; Wu, Qiaoli; Huo, Cuixiu

2014-01-01

The ues of corn silk modified with diluted nitric acid (HNO3-MCS) as a novel biosorbent has been established for solid-phase extraction of Cr(III) and chromium speciation in water samples. The functional groups of the HNO3-MCS surface are favorable for the adsorption of Cr(III). Effective extraction conditions were optimized in both batch and column methods. At pH 3.0 - 6.0, a discrimination of Cr(III) and Cr(VI) is achieved on the HNO3-MCS surface. Cr(III) ions are retained onto the HNO3-MCS surface, however, the adsorption of Cr(VI) is negligible under the same conditions. The adsorption isotherm of HNO3-MCS for Cr(III) has been demonstrated in accordance with a linear form of the Langmuir equation, and the maximum adsorption capacity is 35.21 mg g(-1). The well fitted linear regression of the pseudo-second order model showed the indication of a chemisorption mechanism for the entire concentration range. Thermodynamic studies have shown that the adsorption process is spontaneous and endothermic. The adsorbed Cr(III) was quantitatively eluted by a nitric acid solution with detection by flame atomic absorption spectrometry (FAAS). With a sample volume of 30 mL, a detection limit (3σ) of 0.85 μg L(-1) and a precision of 2.0% RSD at the 40 μg L(-1) level were achieved. The concentration of Cr(III) could be accurately quantified within a linear range of 3 - 200 μg L(-1). After Cr(VI) has been reduced to Cr(III) with hydroxylamine hydrochloride, the total amount of chromium was obtained, and the content of Cr(VI) was given by subtraction. The procedure was validated by analyzing chromium in a certified reference material (GBW (E) 080039). It was also successfully applied for the speciation of chromium in wastewater samples.

Effects of citrate on hexavalent chromium reduction by structural Fe(II) in nontronite

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

Liu, Xiaolei; Dong, Hailiang; Yang, Xuewei

Iron-bearing clay minerals and organic matter are two important components in natural environments that influence hexavalent chromium (Cr(VI)) reduction. Previous studies have shown that organic ligands could influence Cr(VI) reduction by aqueous Fe2+ and pyrite. However, the effects of organic ligands on Cr(VI) reduction by structural Fe(II) in clays are not well understood. In this study, the effects of citrate on Cr(VI) reduction by nontronite (NAu-2) were investigated under near neutral pH condition (pH=6). Our results showed that the presence of citrate decreased the rate but increased the amount of Cr(VI) reduction by structural Fe(II) in NAu-2. The decreased reactionmore » rate was likely due to competitive sorption of citrate and polyanionic dichromate (Cr2O7- ), because sorption of dichromate appeared to be the first step for subsequent Cr(VI) reduction. The increased amount of Cr(VI) reduction in the presence of citrate was likely because citrate provided additional reducing power through ligand-metal electron transfer in the presence of soluble Fe 3+ derived from dissolution of reduced NAu-2. Soluble Cr(III)-citrate complex was the possible form of reduced chromium when citrate was present. In contrast, nanometer-sized Cr2O3 particles were the product of Cr(VI) reduction by reduced NAu-2 without citrate. Our study highlights the importance of organic ligands on Cr(VI) reduction and immobilization when iron-bearing clay minerals are applied to treat Cr(VI) contaminant in organic matter rich environments.« less

Field method for the determination of hexavalent chromium by ultrasonication and strong anion-exchange solid-phase extraction.

PubMed

Wang, J; Ashley, K; Marlow, D; England, E C; Carlton, G

1999-03-01

A simple, fast, sensitive, and economical field method was developed and evaluated for the determination of hexavalent chromium (CrVI) in environmental and workplace air samples. By means of ultrasonic extraction in combination with a strong anion-exchange solid-phase extraction (SAE-SPE) technique, the filtration, isolation, and determination of CrVI in the presence of trivalent chromium (CrIII) and potential interferents was achieved. The method entails (1) ultrasonication in basic ammonium buffer solution to extract CrVI from environmental matrixes; (2) SAE-SPE to separate CrVI from CrIII and interferences; (3) elution/acidification of the eluate; (4) complexation of chromium with 1,5-diphenylcarbazide; and (5) spectrophotometric determination of the colored chromium-diphenylcarbazone complex. Several critical parameters were optimized in order to effect the extraction of both soluble (K2CrO4) and insoluble (PbCrO4) forms of CrVI without inducing CrIII oxidation or CrVI reduction. The method allowed for the dissolution and purification of CrVI from environmental and workplace air sample matrixes for up to 24 samples simultaneously in less than 90 min (including ultrasonication). The results demonstrated that the method was simple, fast, quantitative, and sufficiently sensitive for the determination of occupational exposures of CrVI. The method is applicable for on-site monitoring of CrVI in environmental and industrial hygiene samples.

Hexavalent Chromium Is Carcinogenic to F344/N Rats and B6C3F1 Mice after Chronic Oral Exposure

PubMed Central

Stout, Matthew D.; Herbert, Ronald A.; Kissling, Grace E.; Collins, Bradley J.; Travlos, Gregory S.; Witt, Kristine L.; Melnick, Ronald L.; Abdo, Kamal M.; Malarkey, David E.; Hooth, Michelle J.

2009-01-01

Background Hexavalent chromium [Cr(VI)] is a human carcinogen after inhalation exposure. Humans also ingest Cr(VI) from contaminated drinking water and soil; however, limited data exist on the oral toxicity and carcinogenicity of Cr(VI). Objective We characterized the chronic oral toxicity and carcinogenicity of Cr(VI) in rodents. Methods The National Toxicology Program (NTP) conducted 2-year drinking water studies of Cr(VI) (as sodium dichromate dihydrate) in male and female F344/N rats and B6C3F1 mice. Results Cr(VI) exposure resulted in increased incidences of rare neoplasms of the squamous epithelium that lines the oral cavity (oral mucosa and tongue) in male and female rats, and of the epithelium lining the small intestine in male and female mice. Cr(VI) exposure did not affect survival but resulted in reduced mean body weights and water consumption, due at least in part to poor palatability of the dosed water. Cr(VI) exposure resulted in transient microcytic hypochromic anemia in rats and microcytosis in mice. Nonneoplastic lesions included diffuse epithelial hyperplasia in the duodenum and jejunum of mice and histiocytic cell infiltration in the duodenum, liver, and mesenteric and pancreatic lymph nodes of rats and mice. Conclusions Cr(VI) was carcinogenic after administration in drinking water to male and female rats and mice. PMID:19479012

Microstructural analyses of Cr(VI) speciation in chromite ore processing Residue (COPR)

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

CHRYSOCHOOU, MARIA; FAKRA, SIRINE C .; Marcus, Matthew A.

2010-03-01

The speciation and distribution of Cr(VI) in the solid phase was investigated for two types of chromite ore processing residue (COPR) found at two deposition sites in the United States: gray-black (GB) granular and hard brown (HB) cemented COPR. COPR chemistry and mineralogy were investigated using micro-X-ray absorption spectroscopy and micro-X-ray diffraction, complemented by laboratory analyses. GB COPR contained 30percent of its total Cr(VI) (6000 mg/kg) as large crystals(>20 ?m diameter) of a previously unreported Na-rich analog of calcium aluminum chromate hydrates. These Cr(VI)-rich phases are thought to be vulnerable to reductive and pH treatments. More than 50percent of themore » Cr(VI) was located within nodules, not easily accessible to dissolved reductants, and bound to Fe-rich hydrogarnet, hydrotalcite, and possibly brucite. These phases are stable over a large pH range, thus harder to dissolve. Brownmilleritewasalso likely associated with physical entrapment of Cr(VI) in the interior of nodules. HB COPR contained no Cr(VI)-rich phases; all Cr(VI) was diffuse within the nodules and absent from the cementing matrix, with hydrogarnet and hydrotalcite being the main Cr(VI) binding phases. Treatment ofHBCOPRis challenging in terms of dissolving the acidity-resistant, inaccessible Cr(VI) compounds; the same applies to ~;;50percent of Cr(VI) in GB COPR.« less

Chemical and microbial remediation of hexavalent chromium from contaminated soil and mining/metallurgical solid waste: a review.

PubMed

Dhal, B; Thatoi, H N; Das, N N; Pandey, B D

2013-04-15

Chromium is a highly toxic non-essential metal for microorganisms and plants, and its occurrence is rare in nature. Lower to higher chromium containing effluents and solid wastes released by activities such as mining, metal plating, wood preservation, ink manufacture, dyes, pigments, glass and ceramics, tanning and textile industries, and corrosion inhibitors in cooling water, induce pollution and may cause major health hazards. Besides, natural processes (weathering and biochemical) also contribute to the mobility of chromium which enters in to the soil affecting the plant growth and metabolic functions of the living species. Generally, chemical processes are used for Cr- remediation. However, with the inference derived from the diverse Cr-resistance mechanism displayed by microorganisms and the plants including biosorption, diminished accumulation, precipitation, reduction of Cr(VI) to Cr(III), and chromate efflux, bioremediation is emerging as a potential tool to address the problem of Cr(VI) pollution. This review focuses on the chemistry of chromium, its use, and toxicity and mobility in soil, while assessing its concentration in effluents/wastes which becomes the source of pollution. In order to conserve the environment and resources, the chemical/biological remediation processes for Cr(VI) and their efficiency have been summarised in some detail. The interaction of chromium with various microbial/bacterial strains isolated and their reduction capacity towards Cr(VI) are also discussed. Copyright © 2013 Elsevier B.V. All rights reserved.

Determination of Cr(III) solids formed by reduction of Cr(VI) in a contaminated fractured bedrock aquifer: evidence for natural attenuation of Cr(VI)

EPA Science Inventory

Hexavalent chromium Cr(VI) is toxic and can be highly mobile in many aquifer systems. Redox reactions with naturally occurring minerals and organic compounds can reduce Cr(VI) to Cr(III), forming labile Cr(III) oxyhydroxide precipitates, which is a natural attenuation process. In...

A chronic oral reference dose for hexavalent chromium-induced intestinal cancer†

PubMed Central

Thompson, Chad M; Kirman, Christopher R; Proctor, Deborah M; Haws, Laurie C; Suh, Mina; Hays, Sean M; Hixon, J Gregory; Harris, Mark A

2014-01-01

High concentrations of hexavalent chromium [Cr(VI)] in drinking water induce villous cytotoxicity and compensatory crypt hyperplasia in the small intestines of mice (but not rats). Lifetime exposure to such cytotoxic concentrations increases intestinal neoplasms in mice, suggesting that the mode of action for Cr(VI)-induced intestinal tumors involves chronic wounding and compensatory cell proliferation of the intestine. Therefore, we developed a chronic oral reference dose (RfD) designed to be protective of intestinal damage and thus intestinal cancer. A physiologically based pharmacokinetic model for chromium in mice was used to estimate the amount of Cr(VI) entering each intestinal tissue section (duodenum, jejunum and ileum) from the lumen per day (normalized to intestinal tissue weight). These internal dose metrics, together with corresponding incidences for diffuse hyperplasia, were used to derive points of departure using benchmark dose modeling and constrained nonlinear regression. Both modeling techniques resulted in similar points of departure, which were subsequently converted to human equivalent doses using a human physiologically based pharmacokinetic model. Applying appropriate uncertainty factors, an RfD of 0.006 mg kg–1 day–1 was derived for diffuse hyperplasia—an effect that precedes tumor formation. This RfD is protective of both noncancer and cancer effects in the small intestine and corresponds to a safe drinking water equivalent level of 210 µg l–1. This concentration is higher than the current federal maximum contaminant level for total Cr (100 µg l–1) and well above levels of Cr(VI) in US drinking water supplies (typically ≤ 5 µg l–1). © 2013 The Authors. Journal of Applied Toxicology published by John Wiley & Sons, Ltd. PMID:23943231

Chromium sorption and Cr(VI) reduction to Cr(III) by grape stalks and yohimbe bark.

PubMed

Fiol, Núria; Escudero, Carlos; Villaescusa, Isabel

2008-07-01

In this work, two low cost sorbents, grape stalks and yohimbe bark wastes were used to remove Cr(VI) and Cr(III) from aqueous solutions. Batch experiments were designed to obtain Cr(VI) and Cr(III) sorption data. The mechanism of Cr(III) and Cr(VI) removal and Cr(VI) reduction to Cr(III) by the two vegetable wastes, has been investigated. Fourier transform infrared rays (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis on solid phase were performed to determine the main functional groups that might be involved in metal uptake and to confirm the presence of Cr(III) on the sorbent, respectively. Results put into evidence that both sorbents are able to reduce Cr(VI) to its trivalent form.

Evaluation of Solidification/Stabilization for Treating Contaminates Soils from the Frontier Hard Chrome Site

DTIC Science & Technology

1992-05-01

replicates were ɘ.020 mg/L. The chromium present was in the trivalent form. 139. Vendor 2. The replicate total chromium TCLP concentrations in the...criterion. The chromium present in the leachates was in the trivalent form, shown by concentrations of Cr(VI) of ɘ.020, ɘ.020, and 0.042 mg/L. 142...concentrations of total chromium were 4.7, 3.7, and 4.1 mg/L. Chromium is present in the trivalent form. The total chromium concentrations were below

Energy reserve modification in different age groups of Daphnia schoedleri (Anomopoda: Daphniidae) exposed to hexavalent chromium.

PubMed

Arzate-Cárdenas, Mario Alberto; Martínez-Jerónimo, Fernando

2012-07-01

Caloric content is a reliable biomaker of effect since it is modified by exposure to toxicants that can alter basal metabolism. Since organisms' age modifies how energy resources are allocated and modifies the activity of antioxidant enzymes, the response to toxic agents could be altered with age. Seven age groups of Daphnia schoedleri (0, 3, 5, 7, 14, 21, and 28-day-old) were exposed for 24h to two sublethal concentrations of Cr(VI): 1/25 and 1/5 of the 48 h EC(50) of each age group, to determine the age at which susceptibility to Cr(VI) is highest. To evaluate energy content, carbohydrate, protein and lipid reserves were quantified and antioxidant enzymes activity was assessed (SOD, CAT, GPx, and GR). Furthermore, an integrative approach was applied to evaluate both sets of responses and interpret them as a whole in a simply visual way, achieved by the integrated biomarker response approach. Results indicate that Cr(VI) induced significant differences in all age groups. Seven and 14-day-old organisms were exposed to the highest concentrations (based on their EC50) and showed greater tolerance to this metal. Susceptibility to the toxicant was highest in younger specimens in which energy requirements are greater due to high growth rates (basal metabolism), as a result of which more energy reserves are expended to satisfy demands in terms of growth and response to toxicants. Copyright © 2012 Elsevier B.V. All rights reserved.

Chromium Stable Isotope Fractionation - An Indicator of Hexavalent Chromium Reduction.

NASA Astrophysics Data System (ADS)

Ellis, A.; Johnson, T. M.; Bullen, T. D.

2001-12-01

Chromium is a common anthropogenic contaminant in surface water and ground water, and is also of interest in oceanography. It is redox-active; the two common valences in natural waters are Cr(VI), which is highly soluble and toxic, and Cr(III), which is relatively insoluble. Redox reactions thus control Cr mobility in aqueous solutions, and reduction of Cr(VI) to Cr(III) is the most important reaction controlling attenuation of Cr in groundwater. Our results show that Cr(VI) reduction favors the lighter isotopes and leads to enrichment of heavier isotopes in the remaining Cr(VI). Cr isotope measurements thus show great promise as indicators of Cr(VI) reduction. We report here the first measurements of the magnitude of Cr isotope fractionation during Cr(VI) reduction and variations in δ 53Cr values obtained from three contaminated sites. Experiments were conducted to measure Cr isotope fractionation during Cr(VI) reduction by suspensions of magnetite and unamended sediments from a local pond, Urbana, IL and San Francisco Estuary near Martinez, CA. Suspensions were incubated anaerobically with constant shaking, and complete Cr(VI) reduction occurred within a few days. Cr(VI) from intermediate time points in the experiments was purified via ion exchange and 53Cr/52Cr ratios were measured via TIMS with a double isotope spike. The instantaneous per mil fractionation, ɛ , was calculated assuming a Rayleigh fractionation model. The ɛ for Cr(VI) reduction on magnetite surfaces yielded a fractionation of -3.5 ‰ . The ɛ values for the pond and estuary sediments were -3.5 ‰ and -3.3 ‰ respectively. The size of this Cr isotope fractionation is encouraging, as current precision is 0.2 \\permil. δ 53Cr values in dissolved Cr(VI) from three contaminated sites range from 1.1 ‰ to 5.8 ‰ , suggesting that Cr(VI) reduction has occurred and has induced isotopic fractionation in these settings. δ 53Cr values measured from Cr(VI) in plating baths show little or no fractionation during plating operations during up to 5 years of use. These results demonstrate that Cr stable isotope analyses should be a highly practical indicator of the critical chromate reduction reaction, and an otherwise useful geologic and oceanographic tool.

Urinary chromium concentrations in humans following ingestion of safe doses of hexavalent and trivalent chromium: Implications for biomonitoring

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

Finley, B.L.; Scott, P.K.; Norton, R.L.

1996-08-09

This study evaluates the significance of increased urinary chromium concentrations as a marker of chromium exposure and potential health risk. Six human volunteers ingested trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)] at doses that are known to be safe but higher than typical levels. The following dosing regimen was used: d 1-7, 200 {mu}g/d chromium picolinate; d 8-10, Cr(VI) ingestion at the U.S. Environmental Protection Agency (EPA) reference dose (RfD) of 0.005 mg/kg/d; d 11-13, no dose; d 14-16, Cr(III) ingestion at the U.S. EPA RfD of 1.0 mg/kg/d; and 17-18, postdose. Findings are as follows: (1) ingestion of 200more » {mu}g/d of chromium picolinate yielded significantly elevated urine concentrations such that each participant routinely exceeded background, (2) ingestion of the Cr(VI) RfD (0.005 mg/kg/d) yielded individual mean urinary chromium levels (1.2-2.3 {mu}g/L) and a pooled mean urinary chromium level (2.4 {mu}g/L) that significantly exceeded background, and (3) ingestion of the Cr(III) RfD yielded no significantly exceeded background, and (3) ingestion of the Cr(III) RfD yielded no significant increase in urinary chromium concentrations, indicating that little, if any, absorption occurred. Our work identified three critical issues that need to be accounted for in any future studies that will use urinary chromium as a marker of exposure. First, a minimum urinary chromium concentration of approximately 2 {mu}g/L should be used as a screening level to critically identify individuals who may have experienced elevated exposures to chromium. Second, if Cr(III) levels in soils are known to be less than 80,000 ppm and the Cr(III) is insoluble, urinary chromium concentrations are not an appropriate marker of exposure. Third, newer forms of chromium supplements that contain organic forms of Cr(III) must be considered potential confounders and their contribution to residential chromium uptake must be carefully evaluated. 19 refs., 7 figs., 3 tabs.« less

Impact of wastewater derived dissolved organic carbon on reduction, mobility, and bioavailability of As(V) and Cr(VI) in contaminated soils.

PubMed

Kunhikrishnan, Anitha; Choppala, Girish; Seshadri, Balaji; Wijesekara, Hasintha; Bolan, Nanthi S; Mbene, Kenneth; Kim, Won-Il

2017-01-15

In this work, the effects of various wastewater sources (storm water, sewage effluent, piggery effluent, and dairy effluent) on the reduction, and subsequent mobility and bioavailability of arsenate [As(V)] and chromate [Cr(VI)] were compared using both spiked and field contaminated soils. Wastewater addition to soil can increase the supply of carbon, nutrients, and stimulation of microorganisms which are considered to be important factors enhancing the reduction of metal(loid)s including As and Cr. The wastewater-induced mobility and bioavailability of As(V) and Cr(VI) were examined using leaching, earthworm, and soil microbial activity tests. The rate of reduction of As(V) was much less than that of Cr(VI) both in the presence and absence of wastewater addition. Wastewater addition increased the reduction of both As(V) and Cr(VI) compared to the control (Milli-Q water) and the effect was more pronounced in the case of Cr(VI). The leaching experiment indicated that Cr(VI) was more mobile than As(V). Wastewater addition increased the mobility and bioavailability of As(V), but had an opposite effect on Cr(VI). The difference in the mobility and bioavailability of Cr(VI) and As(V) between wastewater sources can be attributed to the difference in their dissolved organic carbon (DOC) content. The DOC provides carbon as an electron donor for the reduction of As(V) and Cr(VI) and also serves as a complexing agent thereby impacting their mobility and bioavailability. The DOC-induced reduction increased both the mobility and bioavailability of As, but it caused an opposite effect in the case of Cr. Copyright © 2016 Elsevier Ltd. All rights reserved.

Catalytic effect of soil colloids on the reaction between CrVI and p-methoxyphenol.

PubMed

Zhou, D M; Chen, H M; Zheng, C R; Tu, C

2001-01-01

Adsorption of CrVI and p-methoxyphenol (PMP) on soil colloids at different pH media was studied. The resulting k1 and n of 1.89 x 10(2) and 0.53 (r2 = 0.99) and k2 and b of 0.13 and 1.25 x 10(3) (r2 = 0.96) were obtained from Freundlich (Q = k1Caqn) and Langmuir [Q = k2bCaq/(1 + k2Caq)] simulation equations, respectively, for CrVI adsorption on soil colloids (pH 4.20). The adsorption of PMP on soil colloids in pH 5.72 media was simulated by five different equations and the results indicated that the Fritz-Schluender one (r2 = 1.00) was the most suitable among them. Adsorption quantity of CrVI and PMP on colloids increased with increasing acidity in the pH range of 3.5-9.0. Study of CrVI adsorption kinetics indicated that the adsorption equilibrium of CrVI was reached rapidly within 2 h. In pure aqueous solution, CrVI reduction by PMP was observed only when the media's pH was lower than 4.0. Oxidation and reduction reaction between CrVI and p-methoxyphenol obviously occurred when soil colloids were involved in this system, even at pH > or = 7.0, which strongly suggested that minerals in soil colloids acted as catalysts to speed the reaction of CrVI and PMP. The oxidized product of PMP by CrVI, extracted by chloroform in acid media and analyzed by gas chromatography-mass spectrometry, was identified as benzoquinone. The reaction included two steps of one electron process.

Extraction of hexavalent chromium from chromated copper arsenate treated wood under alkaline conditions.

PubMed

Radivojevic, Suzana; Cooper, Paul A

2008-05-15

Information on chromium (Cr) oxidation states is essential for the assessment of environmental and health risks associated with the overall life-cycle of chromated copper arsenate (CCA) treated wood products because of differences in toxicity between trivalent [Cr(III)] and hexavalent [Cr(VI)] chromium compounds. Hypothetical Cr(VI) fixation products were investigated in CCA type C treated sawdust of aspen and red pine during or following preservative fixation by extraction with Cr(VI)-specific extractants. Cr(VI) was found only in alkaline extracts of treated wood. A major source of Cr(VI) was method-induced oxidation of fixed Cr(III) during alkaline extraction, as confirmed by demonstrated oxidation of Cr(III) from CrCl3 treated wood. Oxidation of nontoxic and immobile Cr(III) to toxic and mobile Cr(VI) was facilitated by the presence of wood at pH > 8.5. Thermodynamic equilibrium between Cr(III) and Cr(VI) is affected by pH, temperature, rates of dissolution of CrIII) compounds, and oxygen availability. Results of this study recommend against alkaline extraction protocols for determination of Cr(VI) in treated wood. This Cr oxidation mechanism can act as a previously unrecognized route for generation of hazardous Cr(VI) if CCA treated wood is exposed to alkaline conditions during its production, use, or waste management.

Study of Cr(VI) adsorption onto magnetite nanoparticles using synchrotron-based X-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Chen, Yen-Hua; Liu, Dian-Yu; Lee, Jyh-Fu

2018-04-01

In this study, the efficiency of Cr(VI) adsorption onto nano-magnetite was examined by batch experiments, and the Cr(VI) adsorption mechanism was investigated using synchrotron-based X-ray absorption spectroscopy. Magnetite nanoparticles with a mean diameter of 10 nm were synthesized using an inexpensive and simple co-precipitation method. It shows a saturation magnetization of 54.3 emu/g, which can be recovered with an external magnetic field. The adsorption data fitted the Langmuir adsorption isotherm well, implying a monolayer adsorption behavior of Cr(VI) onto nano-magnetite. X-ray absorption spectroscopy results indicate that the adsorption mechanism involves electron transfer between Fe(II) in nano-magnetite (Fe2+OFe3+ 2O3) and Cr(VI) to transform into Cr(III), which may exist as an Fe(III)-Cr(III) mixed solid phase. Moreover, the Cr(III)/Cr(VI) ratio in the final products can be determined by the characteristic pre-edge peak area of Cr(VI) in the Cr K-edge spectrum. These findings suggest that nano-magnetite is effective for Cr(VI) removal from wastewater because it can transform highly poisonous Cr(VI) species into nontoxic Cr(III) compounds, which are highly insoluble and immobile under environmental conditions.

Sequential Leaching of Chromium Contaminated Sediments - A Study Characterizing Natural Attenuation

NASA Astrophysics Data System (ADS)

Musa, D.; Ding, M.; Beroff, S.; Rearick, M.; Perkins, G.; WoldeGabriel, G. W.; Ware, D.; Harris, R.; Kluk, E.; Katzman, D.; Reimus, P. W.; Heikoop, J. M.

2015-12-01

Natural attenuation is an important process in slowing down the transport of hexavalent chromium, Cr(VI), an anthropogenic environmental contaminant, either by adsorption of Cr(VI) to sediments, or by reduction to nontoxic trivalent chromium, Cr(III). The capacity and mechanism of attenuation is explored in this sequential leaching study of different particle size fractions of chromium contaminated sediments and similar uncontaminated sediments from the regional aquifer near Los Alamos, New Mexico. Using this leaching protocol each sediment sample is split in two: one half is leached three times using a 0.1 M sodium bicarbonate/carbonate solution, while the second half is leached three times using a 0.01 M nitric acid, followed by two consecutively increasing magnitudes of nitric acid concentrations. Based on the amphoteric nature of chromium, alkaline leaching is used to establish the amount of Cr(VI) sorbed on the sediment, whereas acid leaching is used to establish the amount of Cr(III). The weak acid is predicted to release the attenuated anthropogenic Cr(III), without affecting Cr-bearing minerals. The sequential, stronger, acid is anticipated to leach Cr(III)-incorporated in the minerals. The efficiency and validation of the sequential leaching method is assessed by comparing the leaching behavior of bentonite and biotite samples, with and without loaded Cr(VI). A 97% chromium mass balance of leached Cr(VI)-loaded bentonite and biotite proves the viability of this method for further use on leaching contaminated sediments. By comparing contaminated and uncontaminated sediment leachate results, of chromium and other major and trace elements, the signature of anthropogenic chromium is determined. Further mineralogical characterization of the sediments provides a quantitative measure of the natural attenuation capacity for chromium. Understanding these results is pertinent in delineating the optimal procedure for the remediation of Cr(VI) in the regional aquifer near Los Alamos.

Comparison of in vivo genotoxic and carcinogenic potency to augment mode of action analysis: Case study with hexavalent chromium.

PubMed

Thompson, Chad M; Bichteler, Anne; Rager, Julia E; Suh, Mina; Proctor, Deborah M; Haws, Laurie C; Harris, Mark A

2016-04-01

Recent analyses-highlighted by the International Workshops on Genotoxicity Testing Working Group on Quantitative Approaches to Genetic Toxicology Risk Assessment-have identified a correlation between (log) estimates of a carcinogen's in vivo genotoxic potency and in vivo carcinogenic potency in typical laboratory animal models, even when the underlying data have not been matched for tissue, species, or strain. Such a correlation could have important implications for risk assessment, including informing the mode of action (MOA) of specific carcinogens. When in vivo genotoxic potency is weak relative to carcinogenic potency, MOAs other than genotoxicity (e.g., endocrine disruption or regenerative hyperplasia) may be operational. Herein, we review recent in vivo genotoxicity and carcinogenicity data for hexavalent chromium (Cr(VI)), following oral ingestion, in relevant tissues and species in the context of the aforementioned correlation. Potency estimates were generated using benchmark doses, or no-observable-adverse-effect-levels when data were not amenable to dose-response modeling. While the ratio between log values for carcinogenic and genotoxic potency was ≥1 for many compounds, the ratios for several Cr(VI) datasets (including in target tissue) were less than unity. In fact, the ratios for Cr(VI) clustered closely with ratios for chloroform and diethanolamine, two chemicals posited to have non-genotoxic MOAs. These findings suggest that genotoxicity may not play a major role in the cancers observed in rodents following exposure to high concentrations of Cr(VI) in drinking water-a finding consistent with recent MOA and adverse outcome pathway (AOP) analyses concerning Cr(VI). This semi-quantitative analysis, therefore, may be useful to augment traditional MOA and AOP analyses. More case examples will be needed to further explore the general applicability and validity of this approach for human health risk assessment. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Microbial interactions with chromium: basic biological processes and applications in environmental biotechnology.

PubMed

Gutiérrez-Corona, J F; Romo-Rodríguez, P; Santos-Escobar, F; Espino-Saldaña, A E; Hernández-Escoto, H

2016-12-01

Chromium (Cr) is a highly toxic metal for microorganisms as well as plants and animal cells. Due to its widespread industrial use, Cr has become a serious pollutant in diverse environmental settings. The hexavalent form of the metal, Cr(VI), is considered a more toxic species than the relatively innocuous and less mobile Cr(III) form. The study of the interactions between microorganisms and Cr has been helpful to unravel the mechanisms allowing organisms to survive in the presence of high concentrations of Cr(VI) and to detoxify and remove the oxyanion. Various mechanisms of interactions with Cr have been identified in diverse species of bacteria and fungi, including biosorption, bioaccumulation, reduction of Cr(VI) to Cr(III), and chromate efflux. Some of these systems have been proposed as potential biotechnological tools for the bioremediation of Cr pollution using bioreactors or by in situ treatments. In this review, the interactions of microorganisms with Cr are summarised, emphasising the importance of new research avenues using advanced methodologies, including proteomic, transcriptomic, and metabolomic analyses, as well as the use of techniques based on X-ray absorption spectroscopy and electron paramagnetic resonance spectroscopy.

Immunological pattern alteration in shoe, hide, and leather industry workers exposed to hexavalent chromium.

PubMed

Mignini, Fiorenzo; Tomassoni, Daniele; Traini, Enea; Vitali, Mario; Scuri, Stefania; Baldoni, Emilia; Grappasonni, Iolanda; Cocchioni, Mario

2009-12-01

The aim of this work was to assess the effects of hexavalent chromium [Cr(VI)] on shoe, leather, and hide industry workers, based on the assumption that Cr(VI) can behave as an environmental immunological "stressor." The immunological patterns of 84 male subjects were studied in relation to Cr(VI) hematic and urinary levels. Cr(VI) was measured through atomic absorption. Lymphocyte subsets, mitogen-mediated lymphocyte-proliferation, cytokine levels, and natural killer (NK) cytotoxic activity were also assayed. The urinary levels of the total amount of Cr(VI) were significantly higher in a subgroup of exposed subjects (group B) than in the control or in the lower exposed (group A). In group B, Cr(VI) caused a decrease in the density of glucocorticoid receptors (GR) on peripheral blood mononuclear cells (PBMC) and a increase of IL-6. Cr(VI) did not modify NK-mediated cytotoxicity, the plasmatic levels of inflammatory cytokines and related soluble receptors, and prostaglandin levels, while it tended to increase lymphocyte sensitivity to mitogens and the production of immunomodulant cytokines (IFN-gamma, IL-4, and IL-2). The experimental addition of Cr(VI) to the in vitro lymphocyte culture determined a significant inhibition of phagocytosis percentage, index, and killing percentage. These effects were neutralized by exogenous IFN-gamma. Cr(VI) could represent an environmental immunological stressor whose effects can be evaluated through laboratory surveys. The lymphocyte mitogen-induced proliferation, GR receptor on PBMC, and IL-6 plasma levels may represent a discriminating element between Cr(VI)-induced stress and other kinds of stress.

Occupational exposure to Cr(VI): comparison between chromium levels in lymphocytes, erythrocytes, and urine.

PubMed

Lukanova, A; Toniolo, P; Zhitkovich, A; Nikolova, V; Panev, T; Popov, T; Taioli, E; Costa, M

1996-01-01

The relationships between chromium (Cr) levels in lymphocytes, erythrocytes, urine, and ambient air were compared among 14 chrome-platers from a metallurgic plant in Bulgaria and two groups of local controls, one from the same heavily polluted industrial town as the chrome-platers (n = 11) and one from a seaside resort town 100 km away (n = 6). Among the chrome-platers, the Cr concentration in peripheral lymphocytes was positively correlated with total Cr and Cr(VI) levels in ambient air and with Cr excretion in urine. As compared to the controls, the chrome-platers had mean Cr levels in lymphocytes twice as high, in erythrocytes ninefold higher, and in urine fourfold to eightfold higher. Although Cr levels in urine and lymphocytes were similar between the two control groups, levels in erythrocytes were 3 times higher among subjects from the industrial area than among those from the seaside town. The study suggests that lymphocyte Cr could be a good indicator of the Cr body burden caused by high exposures to Cr(VI), such as in electroplating operations. In these conditions, erythrocyte Cr may be less useful, possibly owing to increased toxicity due to the high affinity of erythrocytes for Cr. However, when exposure is lower, such as in most environmental situations, erythrocyte Cr should provide a better and more sensitive index than lymphocyte Cr. By contrast, urinary Cr, which provides information on total Cr exposure, including Cr(III) from dietary and environmental sources, does not seem to be of value for studying occupational exposure to Cr(VI).

Carbon-dependent chromate toxicity mechanism in an environmental Arthrobacter isolate.

PubMed

Field, Erin K; Blaskovich, John P; Peyton, Brent M; Gerlach, Robin

2018-05-12

Arthrobacter spp. are widespread in soil systems and well-known for their Cr(VI) reduction capabilities making them attractive candidates for in situ bioremediation efforts. Cellulose drives carbon flow in soil systems; yet, most laboratory studies evaluate Arthrobacter-Cr(VI) interactions solely with nutrient-rich media or glucose. This study aims to determine how various cellulose degradation products and biostimulation substrates influence Cr(VI) toxicity, reduction, and microbial growth of an environmental Arthrobacter sp. isolate. Laboratory culture-based studies suggest there is a carbon-dependent Cr(VI) toxicity mechanism that affects subsequent Cr(VI) reduction by strain LLW01. Strain LLW01 could only grow in the presence of, and reduce, 50 μM Cr(VI) when glucose or lactate were provided. Compared to lactate, Cr(VI) was at least 30-fold and 10-fold more toxic when ethanol or butyrate was the sole carbon source, respectively. The addition of sulfate mitigated toxicity somewhat, but had no effect on the extent of Cr(VI) reduction. Cell viability studies indicated that a small fraction of cells were viable after 8 days suggesting cell growth and subsequent Cr(VI) reduction may resume. These results suggest when designing bioremediation strategies with Arthrobacter spp. such as strain LLW01, carbon sources such as glucose and lactate should be considered over ethanol and butyrate. Copyright © 2018 Elsevier B.V. All rights reserved.

Reduction of Cr(VI) under acidic conditions by the facultative Fe(III)-reducing bacterium Acidiphilium cryptum

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

David E. Cummings; Scott Fendorf; Rajesh K. Sani

2007-01-01

The potential for biological reduction of Cr(VI) under acidic conditions was evaluated with the acidophilic, facultatively metal-reducing bacterium Acidiphilium cryptum strain JF-5 to explore the role of acidophilic microorganisms in the Cr cycle in low-pH environments. An anaerobic suspension of washed A. cryptum cells rapidly reduced 50 M Cr(VI) at pH 3.2; biological reduction was detected from pH 1.7-4.7. The reduction product, confirmed by XANES analysis, was entirely Cr(III) that was associated predominantly with the cell biomass (70-80%) with the residual residing in the aqueous phase. Reduction of Cr(VI) showed a pH optimum similar to that for growth and wasmore » inhibited by 5 mM HgCl2, suggesting that the reaction was enzyme-mediated. Introduction of O2 into the reaction medium slowed the reduction rate only slightly, whereas soluble Fe(III) (as ferric sulfate) increased the rate dramatically, presumably by the shuttling of electrons from bioreduced Fe(II) to Cr(VI) in a coupled biotic-abiotic cycle. Starved cells could not reduce Cr(VI) when provided as sole electron acceptor, indicating that Cr(VI) reduction is not an energy-conserving process in A. cryptum. We speculate, rather, that Cr(VI) reduction is used here as a detoxification mechanism.« less

Sulphur alters chromium (VI) toxicity in Solanum melongena seedlings: Role of sulphur assimilation and sulphur-containing antioxidants.

PubMed

Singh, Madhulika; Kushwaha, Bishwajit Kumar; Singh, Samiksha; Kumar, Vipin; Singh, Vijay Pratap; Prasad, Sheo Mohan

2017-03-01

The present study investigates modulation in hexavalent chromium [Cr(VI) 25 μM] toxicity by sulphur (S; 0.5, 1.0 and 1.5 mM S as low (LS), medium (MS) and high sulphur (HS), respectively) in Solanum melongena (eggplant) seedlings. Biomass accumulation (fresh and dry weights), photosynthetic pigments, photosynthetic oxygen evolution and S content were declined by Cr(VI) toxicity. Furthermore, fluorescence characteristics (JIP-test) were also affected by Cr(VI), but Cr(VI) toxicity on photosystem II photochemistry was ameliorated by HS treatment via reducing damaging effect on PS II reaction centre and its reduction side. Enhanced respiration, Cr content and oxidative biomarkers: superoxide radical, hydrogen peroxide, lipid peroxidation and membrane damage were observed under Cr(VI) stress. Though Cr(VI) enhanced adenosine triphasphate sulfurylase (ATPS) and o-acetylserine(thiol)lyase (OASTL), glutathione-S-transferase (GST), glutathione reductase (GR) and ascorbate peroxidase (APX) activity, and content of total glutathione, cysteine and NP-SH, however, their levels/activity were further enhanced by S being maximum with HS treatment. The results show that Cr(VI) toxicity does increase under LS treatment while HS protected Cr(VI)-induced damaging effects in brinjal seedlings. Under HS treatment, in mitigating Cr(VI) toxicity, S assimilation and its associated metabolites such as cysteine, glutathione and NP-SH play crucial role. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

A fetal whole ovarian culture model for the evaluation of CrVI-induced developmental toxicity during germ cell nest breakdown

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

Stanley, Jone A.; Arosh, Joe A.; Burghardt, Robert C.

Prenatal exposure to endocrine disrupting chemicals (EDCs), including bisphenol A, dioxin, pesticides, and cigarette smoke, has been linked to several ovarian diseases such as premature ovarian failure (POF) and early menopause in women. Hexavalent chromium (CrVI), one of the more toxic heavy metals, is widely used in more than 50 industries. As one of the world's leading producers of Cr compounds, the U.S. is facing growing challenges in protecting human health against adverse effects of CrVI. Our recent findings demonstrated that in vivo CrVI exposure during gestational period caused POF in F1 offspring. Our current research focus is three-fold: (i)more » to identify the effect of CrVI on critical windows of great vulnerability of fetal ovarian development; (ii) to understand the molecular mechanism of CrVI-induced POF; (iii) to identify potential intervention strategies to mitigate or inhibit CrVI effects. In order to accomplish these goals we used a fetal whole ovarian culture system. Fetuses were removed from the normal pregnant rats on gestational day 13.5. Fetal ovaries were cultured in vitro for 12 days, and treated with or without 0.1 ppm potassium dichromate (CrVI) from culture day 2–8, which recapitulated embryonic day 14.5–20.5, in vivo. Results showed that CrVI increased germ cell/oocyte apoptosis by increasing caspase 3, BAX, p53 and PUMA; decreasing BCL2, BMP15, GDF9 and cKIT; and altering cell cycle regulatory genes and proteins. This model system may serve as a potential tool for high throughput testing of various drugs and/or EDCs in particular to assess developmental toxicity of the ovary. - Highlights: • CrVI (0.1 ppm, a regulatory dose) increased germ cell apoptosis of fetal ovaries. • CrVI (0.1 ppm) increased pro-apoptotic proteins. • CrVI (0.1 ppm) decreased cyclins and CDK1 and cell survival proteins. • CrVI (0.1 ppm) increased oxidative stress during fetal ovarian development. • We propose fetal ovarian culture model for high-throughput testing of heavy-metals.« less

Chronic Exposure to Zinc Chromate Induces Centrosome Amplification and Spindle Assembly Checkpoint Bypass in Human Lung Fibroblasts

PubMed Central

Holmes, Amie L.; Wise, Sandra S.; Pelsue, Stephen C.; Aboueissa, AbouEl-Makarim; Lingle, Wilma; Salisbury, Jeffery; Gallagher, Jamie; Wise, John Pierce

2010-01-01

Hexavalent chromium (Cr(VI)) compounds are known human lung carcinogens. Solubility plays an important role in its carcinogenicity with the particulate or insoluble form being the most potent. Of the particulate Cr(VI) compounds, zinc chromate appears to be the most potent carcinogen, however, very few studies have investigated its carcinogenic mechanism. In this study, we investigated the ability of chronic exposure to zinc chromate to induce numerical chromosome instability. We found no increase in aneuploidy after a 24 hour exposure to zinc chromate, but with more chronic exposures, zinc chromate induced concentration- and time-dependent increases in aneuploidy in the form of hypodiploidy, hyperdiploidy and tetraploidy. Zinc chromate also induced centrosome amplification in a concentration- and time-dependent manner in both interphase and mitotic cells after chronic exposure, producing cells with centriolar defects. Further, chronic exposure to zinc chromate induced concentration- and time-dependent increases in spindle assembly checkpoint bypass with increases in centromere spreading, premature centromere division and premature anaphase. Lastly, we found that chronic exposure to zinc chromate induced a G2 arrest. All together, these data indicate that zinc chromate can induce chromosome instability after prolonged exposures. PMID:20030412

Competitive adsorption of boric acid and chromate onto alumina in aqueous solutions.

PubMed

Demetriou, A; Pashalidis, I

2014-01-01

The competitive adsorption of boric acid and chromate from aqueous solutions by alumina has been investigated by spectrophotometry at pH 8, ionic strength = 0.0, 0.1 and 1.0 M NaClO4, T = 22 ± 3 °C and under normal atmospheric conditions. The experimental data show that addition of excess boric acid in the system leads to the increase of Cr(VI) concentration in solution, indicating the replacement of adsorbed chromate by boron on the alumina surface. Data evaluation results in the determination of the competition reaction constant and the formation constant of the Cr(VI) surface complexes, which are logKCr(VI)-B(III) = -3.5 ± 0.2 and logβ*Cr = 7.6 ± 0.3, respectively.

Exposure to particulate hexavalent chromium exacerbates allergic asthma pathology

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

Schneider, Brent C.; Department of Pharmacology and Physiology, The George Washington University, Washington, DC 20037; Constant, Stephanie L.

Airborne hexavalent chromate, Cr(VI), has been identified by the Environmental Protection Agency as a possible health threat in urban areas, due to the carcinogenic potential of some of its forms. Particulate chromates are produced in many different industrial settings, with high levels of aerosolized forms historically documented. Along with an increased risk of lung cancer, a high incidence of allergic asthma has been reported in workers exposed to certain inhaled particulate Cr(VI) compounds. However, a direct causal association between Cr(VI) and allergic asthma has not been established. We recently showed that inhaled particulate Cr(VI) induces an innate neutrophilic inflammatory responsemore » in BALB/c mice. In the current studies we investigated how the inflammation induced by inhaled particulate Cr(VI) might alter the pathology of an allergic asthmatic response. We used a well-established mouse model of allergic asthma. Groups of ovalbumin protein (OVA)-primed mice were challenged either with OVA alone, or with a combination of OVA and particulate zinc chromate, and various parameters associated with asthmatic responses were measured. Co-exposure to particulate Cr(VI) and OVA mediated a mixed form of asthma in which both eosinophils and neutrophils are present in airways, tissue pathology is markedly exacerbated, and airway hyperresponsiveness is significantly increased. Taken together these findings suggest that inhalation of particulate forms of Cr(VI) may augment the severity of ongoing allergic asthma, as well as alter its phenotype. Such findings may have implications for asthmatics in settings in which airborne particulate Cr(VI) compounds are present at high levels. -- Highlights: ► Allergic asthma correlated with exposure to certain inhaled particulate chromates. ► Direct causal association between Cr(VI) and allergic asthma not established. ► Cr exacerbated pathology and airway hyperresponsiveness in an OVA-challenged mouse. ► Particulate Cr(VI) may augment severity and alter phenotype of ongoing allergic asthma.« less

Chromium in Drinking Water: Sources, Metabolism, and Cancer Risks

PubMed Central

2011-01-01

Drinking water supplies in many geographic areas contain chromium in the +3 and +6 oxidation states. Public health concerns are centered on the presence of hexavalent Cr that is classified as a known human carcinogen via inhalation. Cr(VI) has high environmental mobility and can originate from anthropogenic and natural sources. Acidic environments with high organic content promote the reduction of Cr(VI) to nontoxic Cr(III). The opposite process of Cr(VI) formation from Cr(III) also occurs, particularly in the presence of common minerals containing Mn(IV) oxides. Limited epidemiological evidence for Cr(VI) ingestion is suggestive of elevated risks for stomach cancers. Exposure of animals to Cr(VI) in drinking water induced tumors in the alimentary tract, with linear and supralinear responses in the mouse small intestine. Chromate, the predominant form of Cr(VI) at neutral pH, is taken up by all cells through sulfate channels and is activated nonenzymatically by ubiquitously present ascorbate and small thiols. The most abundant form of DNA damage induced by Cr(VI) is Cr-DNA adducts, which cause mutations and chromosomal breaks. Emerging evidence points to two-way interactions between DNA damage and epigenetic changes that collectively determine the spectrum of genomic rearrangements and profiles of gene expression in tumors. Extensive formation of DNA adducts, clear positivity in genotoxicity assays with high predictive values for carcinogenicity, the shape of tumor–dose responses in mice, and a biological signature of mutagenic carcinogens (multispecies, multisite, and trans-sex tumorigenic potency) strongly support the importance of the DNA-reactive mutagenic mechanisms in carcinogenic effects of Cr(VI). Bioavailability results and kinetic considerations suggest that 10–20% of ingested low-dose Cr(VI) escapes human gastric inactivation. The directly mutagenic mode of action and the incompleteness of gastric detoxification argue against a threshold in low-dose extrapolation of cancer risk for ingested Cr(VI). PMID:21766833

Elemental sulfur amendment decreases bio-available Cr-VI in soils impacted by leather tanneries.

PubMed

Shi, Jingjing; Chen, Hualin; Arocena, Joselito M; Whitcombe, Todd; Thring, Ronald W; Memiaghe, Jeff Nze

2016-05-01

This study investigated the potential use of elemental S (S(0)) to convert Cr-VI to Cr-III which should decrease the bio-availability hence, toxicity of Cr-VI in soils. The bio-available fraction of Cr in soil was measured by phosphate buffer extraction (PBE) and the results showed that the fraction is about 10% of the total Cr-VI and varied from 12.8 to 42.5 mg kg(-1). The addition of 4.0 mg g(-1) S(0) decreased PBE Cr-VI to <0.4 mg kg(-1) limit established for Cr-VI toxicity in soils. Synchrotron-based X-ray absorption near-edge structure (XANES), X-ray fluorescence (XRF) and micro-XRD revealed that Cr-III was the dominant species (99% of total Cr) and Cr was retained by hematite and goethite in soil. Fe-containing minerals may have provided sufficient protection to render the dominant Cr-III species biochemically inert to redox processes in soils. It is concluded that S(0)amendment is a promising approach to remediate Cr-VI contaminated soils. Copyright © 2016 Elsevier Ltd. All rights reserved.

Anion-exchange high-performance liquid chromatography of water-soluble chromium (VI) and chromium (III) complexes in biological materials.

PubMed

Suzuki, Y

1987-04-10

A high-performance anion-exchange liquid chromatograph coupled to visible-range (370 nm) and UV (280 nm) detectors and an atomic-absorption spectrometer allowed the rapid determination of CrVI and/or complexes of CrIII in rat plasma, erythrocyte lysate and liver supernatant treated with CrVI or CrIII in vitro. CrVI in the eluates was determined using both the visible-range detector and atomic-absorption spectrometer (AAS). The detection limits of CrVI in standard solutions using these methods were 2 and 5 ng (signal-to-noise ratio = 2), respectively. Separations of the biological components and of CrIII complexes were monitored by UV and AAS analyses, respectively. Time-related decreases of CrVI accompanied by increases in CrIII complexes were observed, indicating the reduction of CrVI by some of the biological components. The reduction rates were considerably higher in the liver supernatant and erythrocyte lysate than in the plasma. These results indicate that the anion-exchange high-performance liquid chromatographic system is useful for simultaneous determination of CrVI and CrIII complexes in biological materials.

A highly sensitive and selective detection of Cr(VI) and ascorbic acid based on nitrogen-doped carbon dots.

PubMed

Zhang, Yuhua; Fang, Xian; Zhao, Hong; Li, Zengxi

2018-05-01

A highly sensitive and selective detection of hexavalent chromium (Cr(VI)) and ascorbic acid (AA) was proposed using nitrogen-doped carbon dots (N-CDs). In the absence of AA, the quantitative detection of Cr(VI) was realized through Cr(VI) acting as a quencher to quench the fluorescence of N-CDs by inner filter effect (IFE) and static quenching effect. Under the optimal conditions, the linear range for Cr(VI) detection was from 0.01 to 250μM with a detection limit of 5nM (S/N = 3). In the presence of AA, the fluorescence intensity could be rapidly enhanced compared with the fluorescence of N-CDs/Cr(VI) system since Cr(VI) can be reduced into trivalent chromium (Cr(III)) by AA. And a wide linear range for AA detection was obtained from 1 to 750μM. The detection limit was 0.3μM (S/N = 3). More importantly, this method can be successfully applied to the detection of Cr(VI) in real water samples, and AA in vitamins C tablets and human serum sample. Copyright © 2018 Elsevier B.V. All rights reserved.

Pyrolysis Treatment of Chromite Ore Processing Residue by Biomass: Cellulose Pyrolysis and Cr(VI) Reduction Behavior.

PubMed

Zhang, Da-Lei; Zhang, Mei-Yi; Zhang, Chu-Hui; Sun, Ying-Jie; Sun, Xiao; Yuan, Xian-Zheng

2016-03-15

The pyrolysis treatment with biomass is a promising technology for the remediation of chromite-ore-processing residue (COPR). However, the mechanism of this process is still unclear. In this study, the behavior of pyrolysis reduction of Cr(VI) by cellulose, the main component of biomass, was elucidated. The results showed that the volatile fraction (VF) of cellulose, ie. gas and tar, was responsible for Cr(VI) reduction. All organic compounds, as well as CO and H2 in VF, potentially reduced Cr(VI). X-ray absorption near-edge structure (XANES) spectroscopy and extended X-ray absorption fine-structure (EXAFS) spectroscopy confirmed the reduction of Cr(VI) to Cr(III) and the formation of amorphous Cr2O3. The remnant Cr(VI) content in COPR can be reduced below the detection limit (2 mg/kg) by the reduction of COPR particle and extension of reaction time between VF and COPR. This study provided a deep insight on the co-pyrolysis of cellulose with Cr(VI) in COPR and an ideal approach by which to characterize and optimize the pyrolysis treatment for COPR by other organics.

Hexavalent chromium-induced apoptosis of granulosa cells involves selective sub-cellular translocation of Bcl-2 members, ERK1/2 and p53

PubMed Central

Banu, Sakhila K.; Stanley, Jone A.; Lee, JeHoon; Stephen, Sam D.; Arosh, Joe A.; Hoyer, Patricia B.; Burghardt, Robert C.

2011-01-01

Hexavalent chromium (CrVI) has been widely used in industries throughout the world. Increased usage of CrVI and atmospheric emission of CrVI from catalytic converters of automobiles, and its improper disposal causes various health hazards including female infertility. Recently we have reported that lactational exposure to CrVI induced a delay/arrest in follicular development at the secondary follicular stage. In order to investigate the underlying mechanism, primary cultures of rat granulosa cells were treated with 10 μM potassium dichromate (CrVI) for 12 and 24 h, with or without vitamin C pre-treatment for 24 h. The effects of CrVI on intrinsic apoptotic pathway(s) were investigated. Our data indicated that CrVI: (i) induced DNA fragmentation and increased apoptosis, (ii) increased cytochrome c release from the mitochondria to cytosol, (iii) downregulated anti-apoptotic Bcl-2, Bcl-XL, HSP70 and HSP90; upregulated pro-apoptotic BAX and BAD, (iv) altered translocation of Bcl-2, Bcl-XL, BAX, BAD, HSP70 and HSP90 to the mitochondria, (v) upregulated p-ERK and p-JNK, and selectively translocated p-ERK to the mitochondria and nucleus, (vi) activated caspase-3 and PARP, and (vii) increased phosphorylation of p53 at ser-6, ser-9, ser-15, ser-20, ser-37, ser-46 and ser-392, increased p53 transcriptional activation, and downregulated MDM-2. Vitamin C pre-treatment mitigated CrVI effects on apoptosis and related pathways. Our study, for the first time provides a clear insight into the effect of CrVI on multiple pathways that lead to apoptosis of granulosa cells which could be mitigated by vitamin C. PMID:21262251

Hexavalent chromium-induced apoptosis of granulosa cells involves selective sub-cellular translocation of Bcl-2 members, ERK1/2 and p53

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

Banu, Sakhila K., E-mail: skbanu@cvm.tamu.edu; Stanley, Jone A.; Lee, JeHoon

Hexavalent chromium (CrVI) has been widely used in industries throughout the world. Increased usage of CrVI and atmospheric emission of CrVI from catalytic converters of automobiles, and its improper disposal causes various health hazards including female infertility. Recently we have reported that lactational exposure to CrVI induced a delay/arrest in follicular development at the secondary follicular stage. In order to investigate the underlying mechanism, primary cultures of rat granulosa cells were treated with 10 {mu}M potassium dichromate (CrVI) for 12 and 24 h, with or without vitamin C pre-treatment for 24 h. The effects of CrVI on intrinsic apoptotic pathway(s)more » were investigated. Our data indicated that CrVI: (i) induced DNA fragmentation and increased apoptosis, (ii) increased cytochrome c release from the mitochondria to cytosol, (iii) downregulated anti-apoptotic Bcl-2, Bcl-XL, HSP70 and HSP90; upregulated pro-apoptotic BAX and BAD, (iv) altered translocation of Bcl-2, Bcl-XL, BAX, BAD, HSP70 and HSP90 to the mitochondria, (v) upregulated p-ERK and p-JNK, and selectively translocated p-ERK to the mitochondria and nucleus, (vi) activated caspase-3 and PARP, and (vii) increased phosphorylation of p53 at ser-6, ser-9, ser-15, ser-20, ser-37, ser-46 and ser-392, increased p53 transcriptional activation, and downregulated MDM-2. Vitamin C pre-treatment mitigated CrVI effects on apoptosis and related pathways. Our study, for the first time provides a clear insight into the effect of CrVI on multiple pathways that lead to apoptosis of granulosa cells which could be mitigated by vitamin C.« less

IN SITU CR(VI) TREATMENT USING A FERROUS IRON-BASED REDUCTANT

EPA Science Inventory

Laboratory and field studies were conducted to evaluate the performance of a ferrous sulfate/ sodium hydrosulfite (dithionite) reductant blend in treating a hexavalent chromium (Cr(VI)) source area and Cr(VI) dissolved phase plume at a former industrial site in Charleston, South ...

Chromium removal from electroplating wastewater by coir pith.

PubMed

Suksabye, Parinda; Thiravetyan, Paitip; Nakbanpote, Woranan; Chayabutra, Supanee

2007-03-22

Coir pith is a by-product from padding used in mattress factories. It contains a high amount of lignin. Therefore, this study investigated the use of coir pith in the removal of hexavalent chromium from electroplating wastewater by varying the parameters, such as the system pH, contact time, adsorbent dosage, and temperature. The maximum removal (99.99%) was obtained at 2% (w/v) dosage, particle size <75microm, at initial Cr(VI) 1647mgl(-1), system pH 2, and an equilibrium time of 18h. The adsorption isotherm of coir pith fitted reasonably well with the Langmuir model. The maximum Cr(VI) adsorption capacity of coir pith at 15, 30, 45 and 60 degrees C was 138.04, 197.23, 262.89 and 317.65mgCr(VI)g(-1) coir pith, respectively. Thermodynamic parameters indicated an endothermic process and the adsorption process was favored at high temperature. Desorption studies of Cr(VI) on coir pith and X-ray absorption near edge structure (XANES) suggested that most of the chromium bound on the coir pith was in Cr(III) form due to the fact that the toxic Cr(VI) adsorbed on the coir pith by electrostatic attraction was easily reduced to less toxic Cr(III). Fourier transform infrared (FT-IR) spectrometry analysis indicated that the carbonyl (CO) groups and methoxy (O-CH(3)) groups from the lignin structure in coir pith may be involved in the mechanism of chromium adsorption. The reduced Cr(III) on the coir pith surface may be bound with CO groups and O-CH(3) groups through coordinate covalent bonding in which a lone pair of electrons in the oxygen atoms of the methoxy and carbonyl groups can be donated to form a shared bond with Cr(III).

Polyaniline coating with various substrates for hexavalent chromium removal

NASA Astrophysics Data System (ADS)

Qiu, Bin; Xu, Cuixia; Sun, Dezhi; Wang, Qiang; Gu, Hongbo; Zhang, Xin; Weeks, Brandon L.; Hopper, Jack; Ho, Thomas C.; Guo, Zhanhu; Wei, Suying

2015-04-01

Hexavalent chromium (Cr(VI)) contamination is increasingly serious in surface water and groundwater, therefore, its removal attracts increasing attention due to its highly toxic to human health. The cost effective and sustainable adsorbents are urgently needed for the remediation of Cr(VI) pollution. Polyanline (PANI), a conductive polymer, has demonstrated a great performance on Cr(VI) removal. But the recycling is the challenge for its application due to its small size. The PANI coating with various substrates is an effective approach to solve this problem. The synthesis methods and applications of the PANI coated magnetic Fe3O4, carbon fabric and cellulose composites for the Cr(VI) removal were reviewed. Finally, this review analyzed the Cr(VI) removal mechanisms by the PANI composites considering the substrate and the PANI coating.

Preparation of Silk Sericin/Lignin Blend Beads for the Removal of Hexavalent Chromium Ions.

PubMed

Kwak, Hyo Won; Shin, Munju; Yun, Haesung; Lee, Ki Hoon

2016-09-02

In the present study, novel adsorbents having high adsorption capability and reusability were prepared using agricultural by-products: silk sericin and lignin. Silk sericin and lignin blend beads were successfully prepared using simple coagulation methods for the removal of hexavalent chromium (Cr(VI)) from aqueous solution. A 1 M lithium chloride (LiCl)/dimethyl sulfoxide (DMSO) solvent system successfully dissolved both sericin and lignin and had sufficient viscosity for bead preparation. Compared to the conventional sericin bead adsorbent, sericin/lignin blend beads showed higher Cr(VI) adsorption capacity. The amount of lignin added to the adsorbent greatly affected the adsorption capacity of the beads, and a 50:50 sericin/lignin blend ratio was optimal. Adsorption behavior followed the Freundlich isotherm, which means the adsorption of Cr(VI) occurred on the heterogeneous surface. Cr(VI) adsorption capability increased with temperature because of thermodynamic-kinetic effects. In addition, over 90% of Cr(VI) ions were recovered from the Cr(VI) adsorbed sericin/lignin beads in a 1 M NaOH solution. The adsorption-desorption recycling process was stable for more than seven cycles, and the recycling efficiency was 82%. It is expected that the sericin/lignin beads could be successfully applied in wastewater remediation especially for hazardous Cr(VI) ions in industrial wastewater.

Preparation of Silk Sericin/Lignin Blend Beads for the Removal of Hexavalent Chromium Ions

PubMed Central

Kwak, Hyo Won; Shin, Munju; Yun, Haesung; Lee, Ki Hoon

2016-01-01

In the present study, novel adsorbents having high adsorption capability and reusability were prepared using agricultural by-products: silk sericin and lignin. Silk sericin and lignin blend beads were successfully prepared using simple coagulation methods for the removal of hexavalent chromium (Cr(VI)) from aqueous solution. A 1 M lithium chloride (LiCl)/dimethyl sulfoxide (DMSO) solvent system successfully dissolved both sericin and lignin and had sufficient viscosity for bead preparation. Compared to the conventional sericin bead adsorbent, sericin/lignin blend beads showed higher Cr(VI) adsorption capacity. The amount of lignin added to the adsorbent greatly affected the adsorption capacity of the beads, and a 50:50 sericin/lignin blend ratio was optimal. Adsorption behavior followed the Freundlich isotherm, which means the adsorption of Cr(VI) occurred on the heterogeneous surface. Cr(VI) adsorption capability increased with temperature because of thermodynamic-kinetic effects. In addition, over 90% of Cr(VI) ions were recovered from the Cr(VI) adsorbed sericin/lignin beads in a 1 M NaOH solution. The adsorption-desorption recycling process was stable for more than seven cycles, and the recycling efficiency was 82%. It is expected that the sericin/lignin beads could be successfully applied in wastewater remediation especially for hazardous Cr(VI) ions in industrial wastewater. PMID:27598142

Hematite enhances the removal of Cr(VI) by Bacillus subtilis BSn5 from aquatic environment.

PubMed

Ma, Shuai; Song, Chang-Shun; Chen, Yuefang; Wang, Fei; Chen, Hui-Lun

2018-06-05

In the present study, we investigated the removal of Cr(VI) and the associated bacterial activity in the systems containing Bacillus subtilis BSn5 (B. subtilis BSn5) and hematite. The microcalorimetry was used to study the effect of hematite on the normal physiological functions of B. subtilis BSn5 towards the removal of Cr(VI) for the first time. The results of the heat flux and the sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that hematite does not affect the normal physiological functions of B. subtilis BSn5, and can help the strains maintain their activity in the presence of Cr(VI). More importantly, the relative capacity and intensity of Cr(VI) and total Cr removal by B. subtilis BSn5 in the presence of hematite were higher than that in the absence of hematite. The enhancement effect could be associated with their mineral adsorption, biosorption, Fe(II) reduction, bioreduction and immobilization functions. This study demonstrates the possibility of reducing the toxicity of Cr(VI) and enhancing the Cr(VI) removal efficiency in contaminated environments using a combination of hematite and B. subtilis BSn5. Copyright © 2018 Elsevier Ltd. All rights reserved.

Reduction of hexavalent chromium by fasted and fed human gastric fluid. I. Chemical reduction and mitigation of mutagenicity

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

De Flora, Silvio, E-mail: sdf@unige.it

Evaluation of the reducing capacity of human gastric fluid from healthy individuals, under fasted and fed conditions, is critical for assessing the cancer hazard posed by ingested hexavalent chromium [Cr(VI)] and for developing quantitative physiologically-based pharmacokinetic models used in risk assessment. In the present study, the patterns of Cr(VI) reduction were evaluated in 16 paired pre- and post-meal gastric fluid samples collected from 8 healthy volunteers. Human gastric fluid was effective both in reducing Cr(VI), as measured by using the s-diphenylcarbazide colorimetric method, and in attenuating mutagenicity in the Ames test. The mean (± SE) Cr(VI)-reducing ability of post-meal samplesmore » (20.4 ± 2.6 μg Cr(VI)/mL gastric fluid) was significantly higher than that of pre-meal samples (10.2 ± 2.3 μg Cr(VI)/mL gastric fluid). When using the mutagenicity assay, the decrease of mutagenicity produced by pre-meal and post-meal samples corresponded to reduction of 13.3 ± 1.9 and 25.6 ± 2.8 μg Cr(VI)/mL gastric fluid, respectively. These data are comparable to parallel results conducted by using speciated isotope dilution mass spectrometry. Cr(VI) reduction was rapid, with > 70% of total reduction occurring within 1 min and 98% of reduction is achieved within 30 min with post-meal gastric fluid at pH 2.0. pH dependence was observed with decreasing Cr(VI) reducing capacity at higher pH. Attenuation of the mutagenic response is consistent with the lack of DNA damage observed in the gastrointestinal tract of rodents following administration of ≤ 180 ppm Cr(VI) for up to 90 days in drinking water. Quantifying Cr(VI) reduction kinetics in the human gastrointestinal tract is necessary for assessing the potential hazards posed by Cr(VI) in drinking water. - Highlights: • Cr(VI) reduction capacity was greater in post-meal than paired pre-meal samples. • Cr(VI) reduction was rapid, pH dependent, and due to heat stable components. • Gastric fluid attenuates the mutagenicity of Cr(VI) and reduces risk of GI cancer. • The results are useful to quantitatively evaluate the fate of ingested Cr(VI).« less

TRANSPORT OF CHROMIUM AND SELENIUM IN A PRISTINE SAND AND GRAVEL AQUIFER: ROLE OF ADSORPTION PROCESSES

EPA Science Inventory

Field transport experiments were conducted in an oxic sand and gravel aquifer using Br (bromide ion), Cr (chromium, injected as Cr(VI)), Se (selenium, injected as Se(VI)), and other tracers. The aquifer has mildly acidic pH values and low concentrations of dissolved salts. Within...

Trivalent chromium solubility and its influence on quantification of hexavalent chromium in ambient particulate matter using EPA method 6800.

PubMed

Huang, Lihui; Yu, Chang Ho; Hopke, Philip K; Shin, Jin Young; Fan, Zhihua

2014-12-01

Measurement of carcinogenic Cr(VI) in ambient PM is challenging due to potential errors associated with conversion between Cr (VI) (a carcinogen) and Cr(III) (an essential nutrient). Cr(III) conversion is a particular concern due to its > 80% atomic abundance in total Cr. US. Environmental Protection Agency (EPA) method 6800 that uses water-soluble isotope spikes can be used to correct the interconversion. However, whether the enriched Cr(III) isotope spikes can adequately mimic the Cr(III) species originally in ambient PM is unknown. This study examined the water solubility of Cr(III) in ambient PM and discussed its influence on Cr(VI) measurement. Ambient PM10 samples were collected on Teflon filters at four sites in New Jersey that may have different Cr emission sources. The samples were ultrasonically extracted with 5 mL DI-H2O (pH 5.7) at room temperature for 40 min, and then analyzed by ion chromatography-inductively coupled plasma mass spectrometry (IC-ICPMS). Cr(III) was below detection limit (0.06 ng/m3) for all samples, suggesting water-soluble Cr(III) species, such as CrCl3, Cr(NO3)3, and amorphous Cr(OH)3, in the ambient PM were negligible. Therefore, the enriched 50Cr(III) isotope spike (in the form of Cr(NO3)3) could not mimic the original ambient Cr(III). Only the conversion of 53Cr(VI) (in the form of K2CrO4) was taken into account when correcting the interconversion. We then used NaHCO3-pretreated MCE filters (prespiked with enriched isotope species) to measure Cr(VI) in the ambient PM10. The samples were ultrasonically extracted at 60 C pH 9 solutions for 40 min followed by IC-ICPMS analysis. Due to the correction of Cr(VI) reduction, the Cr(VI) concentrations determined by EPA method 6800, 0.26 ± 0.16 (summer) and 0.16 ± 0.11(winter) ng/m3 (n = 64), were significantly greater than those by the external standard curve, 0.21 ± 0.17 (summer) and 0.10 ± 0.07 (winter) ng/m3 (n = 56) (p < 0.01, Student's t-test). Our study revealed that appropriate application of EPA method 6800 is important because it only applies to soluble fraction of Cr species in ambient PM. Implications: Accurate measurement of carcinogenic Cr(VI) in ambient PM is challenging due to conversion between Cr(VI) (a human carcinogen) and Cr(III) (a human essential nutrient). The conversion of CR(III) is of particular concern due to its dominant presence in total Cr (>80%). This study examined the water solubility of Cr(III) in ambient PM that was collected at four locations in New Jersey. Then we discussed the influence of Cr(III) solubility on the application of EPA method 6800, which utilizes enriched isotope spikes to correct the interconversion. Our results suggested that appropriate application of EPA method 6800 is important because it only applies to soluble fraction of Cr species.

Stability of Cr Remediation Products Linked to Duration of Bioremediation.

NASA Astrophysics Data System (ADS)

Miller, L. G.; Bobb, C.; Bennett, S.; Izbicki, J. A.

2017-12-01

Groundwater and alluvium beneath Hinkley Valley, Mojave Desert, California contain elevated levels of anthropogenic Cr(VI). In-situ remediation (ISR) using ethanol as an electron donor is employed at the site to reduce soluble, toxic, Cr(VI) to insoluble and non-hazardous Cr(III). We conducted year-long experiments to determine the fate of isotopically-labeled 50Cr tracer within microcosms consisting of sealed batch reactors containing aquifer material and groundwater from within and near the mapped Cr(VI) plume. Ethanol was added periodically to the reactors to drive biologically mediated reduction of Cr(VI). Reduction and sorption of 50Cr tracer on the solid matrix was examined by selective extractions designed to monitor operationally-defined weakly sorbed, specifically sorbed, amorphous, and well-crystalized strong-acid extractable phases. Recovery of the 50Cr tracer by ICP-MS analysis of each extract revealed the degree of mineralization of the added 50Cr. Initially, the tracer was distributed evenly between the aqueous and weakly sorbed phases, with little present in the strongly sorbed, amorphous or crystalline phases. After several months, most 50Cr was incorporated within the amorphous fraction and by one year increasing amounts were associated with the crystalline phase. Artificial substrates also were prepared as experimental controls. Artificial substrates showed similar trends; however less 50Cr was associated with amorphous Fe in acid-washed Ottowa sand coated with 2-line ferrihydrite than in aquifer sediments. Washed sand without ferrihydrite reacted with site water sorbed very little 50Cr, and no 50Cr was found in the amorphous fraction; however some was converted to the crystalline form with time. This suggests that groundwater-borne organisms alone were capable of reducing Cr(VI) to Cr(III) with ethanol in the absence of Fe(II). A planned metagenomics study of materials from these experiments is expected to highlight changes in microbial community composition and diversity as ISR progresses. Our experimental results bode well for the permanency of Cr sequestration by ISR; that is, Cr solubilization by re-oxidation may be less likely if reduced Cr is bound in more recalcitrant phases via extended reduction.

Mechanisms of hexavalent chromium resistance and removal by microorganisms.

PubMed

Joutey, Nezha Tahri; Sayel, Hanane; Bahafid, Wifak; El Ghachtouli, Naïma

2015-01-01

Chromium has been and is extensively used worldwide in multiple industrial processes and is routinely discharged to the environment from such processes. Therefore, this heavy metal is a potential threat to the environment and to public health, primarily because it is non-biodegradable and environmentally persistent. Chromium exists in several oxidation states, the most stable of which are trivalent Cr(Ill) and hexavalent Cr(VI) species. Each species possesses its own individual chemical characteristics and produces its own biological effects. For example, Cr (Ill) is an essential oligoelement for humans, whereas Cr(VI) is carcinogenic and mutagenic. Several chemical methods are used to remove Cr(VI) from contaminated sites. Each of these methods has advantages and disadvantages. Currently, bioremediation is often the preferred method to deal with Cr contaminated sites, because it is eco-friendly, cost-effective and is a "natural" technology. Many yeast, bacterial and fungal species have been assessed for their suitability to reduce or remove Cr(VI) contamination. The mechanisms by which these microorganisms resist and reduce Cr(VI) are variable and are species dependent. There are several Cr-resistance mechanisms that are displayed by microorganisms. These include active efflux of Cr compounds, metabolic reduction of Cr(VI) to Cr (ill), and either intercellular or extracellular prec1p1tation. Microbial Cr (VI) removal typically involves three stages: binding of chromium to the cell surface, translocation of chromium into the cell, and reduction of Cr(VI) to Cr (ill). Cr(VI) reduction by microorganisms may proceed on the cell surface, outside the cell, or intracellularly, either directly via chromate reductase enzymes, or indirectly via metabolite reduction of Cr(VI). The uptake of chromium ions is a biphasic process. The primary step is known as biosorption, a metabolic energyindependent process. Thereafter, bioaccumulation occurs, but is much slower, and is dependent on cell metabolic activity. Choosing an appropriate bioremediation strategy for Cr is extremely important and must involve investigating and understanding the key mechanisms that are involved in microbial resistance to and removal of Cr(VI).

Improved Bi Film Wrapped Single Walled Carbon Nanotubes for Ultrasensitive Electrochemical Detection of Trace Cr(VI).

PubMed

Ouyang, Ruizhuo; Zhang, Wangyao; Zhou, Shilin; Xue, Zi-Ling; Xu, Lina; Gu, Yingying; Miao, Yuqing

2013-12-15

We report here the successful fabrication of an improved Bi film wrapped single walled carbon nanotubes modified glassy carbon electrode (Bi/SWNTs/GCE) as a highly sensitive platform for ultratrace Cr(VI) detection through catalytic adsorptive cathodic stripping voltammetry (AdCSV). The introduction of negatively charged SWNTs extraordinarily decreased the size of Bi particles to nanoscale due to electrostatic interaction which made Bi(III) cations easily attracted onto the surface of SWNTs in good order, leading to higher quality of Bi film deposition. The obtained Bi/SWNTs composite was well characterized with electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), the static water contact angle and the voltammetric measurements. The results demonstrates the improvements in the quality of Bi film deposited on the surface of SWNTs such as faster speed of electron transfer, more uniform and smoother morphology, better hydrophilicity and higher stripping signal. Using diethylene triaminepentaacetic acid (DTPA) as complexing ligand, the fabricated electrode displays a well-defined and highly sensitive peak for the reduction of Cr(III)-DTPA complex at -1.06 V ( vs . Ag/AgCl) with a linear concentration range of 0-25 nM and a fairly low detection limit of 0.036 nM. No interference was found in the presence of coexisting ions, and good recoveries were achieved for the analysis of a river sample. In comparison to previous approaches using Bi film modified GCE, the newly designed electrode exhibits better reproducibility and repeatability towards aqueous detection of trace Cr(VI) and appears to be very promising as the basis of a highly sensitive and selective voltammetric procedure for Cr(VI) detection at trace level in real samples.

Improved Bi Film Wrapped Single Walled Carbon Nanotubes for Ultrasensitive Electrochemical Detection of Trace Cr(VI)

PubMed Central

Zhou, Shilin; Xue, Zi-Ling; Xu, Lina; Gu, Yingying; Miao, Yuqing

2014-01-01

We report here the successful fabrication of an improved Bi film wrapped single walled carbon nanotubes modified glassy carbon electrode (Bi/SWNTs/GCE) as a highly sensitive platform for ultratrace Cr(VI) detection through catalytic adsorptive cathodic stripping voltammetry (AdCSV). The introduction of negatively charged SWNTs extraordinarily decreased the size of Bi particles to nanoscale due to electrostatic interaction which made Bi(III) cations easily attracted onto the surface of SWNTs in good order, leading to higher quality of Bi film deposition. The obtained Bi/SWNTs composite was well characterized with electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), the static water contact angle and the voltammetric measurements. The results demonstrates the improvements in the quality of Bi film deposited on the surface of SWNTs such as faster speed of electron transfer, more uniform and smoother morphology, better hydrophilicity and higher stripping signal. Using diethylene triaminepentaacetic acid (DTPA) as complexing ligand, the fabricated electrode displays a well-defined and highly sensitive peak for the reduction of Cr(III)-DTPA complex at −1.06 V (vs. Ag/AgCl) with a linear concentration range of 0–25 nM and a fairly low detection limit of 0.036 nM. No interference was found in the presence of coexisting ions, and good recoveries were achieved for the analysis of a river sample. In comparison to previous approaches using Bi film modified GCE, the newly designed electrode exhibits better reproducibility and repeatability towards aqueous detection of trace Cr(VI) and appears to be very promising as the basis of a highly sensitive and selective voltammetric procedure for Cr(VI) detection at trace level in real samples. PMID:24771881

Differential effect of biochar upon reduction-induced mobility and bioavailability of arsenate and chromate.

PubMed

Choppala, Girish; Bolan, Nanthi; Kunhikrishnan, Anitha; Bush, Richard

2016-02-01

Heavy metals such as chromium (Cr) and arsenic (As) occur in ionic form in soil, with chromate [Cr(VI)] and arsenate As(V) being the most pre-dominant forms. The application of biochar to Cr(VI) and As(V) spiked and field contaminated soils was evaluated on the reduction processes [(Cr(VI) to Cr(III)] and [As(V) to As(III))], and subsequent mobility and bioavailability of both As(V) and Cr(VI). The assays used in this study included leaching, soil microbial activity and XPS techniques. The reduction rate of As(V) was lower than that of Cr(VI) with and without biochar addition, however, supplementation with biochar enhanced the reduction process of As(V). Leaching experiments indicated Cr(VI) was more mobile than As(V). Addition of biochar reversed the effect by reducing the mobility of Cr and increasing that of As. The presence of Cr and As in both spiked and contaminated soils reduced microbial activity, but with the addition of biochar to these soils, the microbial activity increased in the Cr(VI) contaminated soils, while it was further decreased with As(V) contaminated soils. The addition of biochar was effective in mitigating Cr toxicity by reducing Cr(VI) to Cr(III). In contrast, the conversion process of As(V) to As(III) hastened by biochar was not favourable, as As(III) is more toxic in soils. Overall, the presence of functional groups on biochar promotes reduction by providing the electrons required for reduction processes to occur as determined by XPS data. Copyright © 2015 Elsevier Ltd. All rights reserved.

Prolonged Particulate Hexavalent Chromium Exposure Suppresses Homologous Recombination Repair in Human Lung Cells

PubMed Central

Browning, Cynthia L.; Qin, Qin; Kelly, Deborah F.; Prakash, Rohit; Vanoli, Fabio; Jasin, Maria

2016-01-01

Abstract Genomic instability is one of the primary models of carcinogenesis and a feature of almost all cancers. Homologous recombination (HR) repair protects against genomic instability by maintaining high genomic fidelity during the repair of DNA double strand breaks. The defining step of HR repair is the formation of the Rad51 nucleofilament, which facilitates the search for a homologous sequence and invasion of the template DNA strand. Particulate hexavalent chromium (Cr(VI)), a human lung carcinogen, induces DNA double strand breaks and chromosome instability. Since the loss of HR repair increases Cr(VI)-induced chromosome instability, we investigated the effect of extended Cr(VI) exposure on HR repair. We show acute (24 h) Cr(VI) exposure induces a normal HR repair response. In contrast, prolonged (120 h) exposure to particulate Cr(VI) inhibited HR repair and Rad51 nucleofilament formation. Prolonged Cr(VI) exposure had a profound effect on Rad51, evidenced by reduced protein levels and Rad51 mislocalization to the cytoplasm. The response of proteins involved in Rad51 nuclear import and nucleofilament formation displayed varying responses to prolonged Cr(VI) exposure. BRCA2 formed nuclear foci after prolonged Cr(VI) exposure, while Rad51C foci formation was suppressed. These results suggest that particulate Cr(VI), a major chemical carcinogen, inhibits HR repair by targeting Rad51, causing DNA double strand breaks to be repaired by a low fidelity, Rad51-independent repair pathway. These results further enhance our understanding of the underlying mechanism of Cr(VI)-induced chromosome instability and thus, carcinogenesis. PMID:27449664

Sorption of Cr(III) and Cr(VI) to High and Low Pressure Synthetic Nano-Magnetite (Fe3O4)Particles

PubMed Central

Parsons, Jason G.; Hernandez, Jeffrey; Gonzalez, Christina M.; Gardea-Torresdey, J. L.

2014-01-01

The binding of Cr(III) and Cr(VI) to synthetic nano-magnetie particles synthesized under open vessel conditions and a microwave assisted hydrothermal synthesis techniques was investigated. Batch studies showed that the binding of both the Cr(III) and Cr(VI) bound to the nano-materials in a pH dependent manner. The Cr(III) maximized at binding at pH 4 and 100% binding. Similarly, the Cr(VI) ions showed a maximum binding of 100% at pH 4. The data from the time dependency studies showed for the most part the majority of the binding occurred within the first 5 minutes of contact with the nanomaterial and remained constant thereafter. In addition, the effects of the possible interferences were investigated which showed some effects on the binding of both Cr(III) and Cr(VI). However, the interferences never completely eliminated the chromium binding. Isotherm studies conducted at room temperature showed the microwave synthesized nanomaterials had a binding capacity of 1208 ± 43.9 mg/g and 555 ± 10.5 mg/g for Cr(VI) and Cr(III), respectively. However, the microwave assisted synthesized nanomaterials had capacities of 1705 ± 14.5 and 555± 10.5 mg/g for Cr(VI) and Cr(III), respectively. XANES studies showed the Cr(VI) was reduced to Cr(III), and the Cr(III) remained as Cr(III). In addition, the XANES studies indicated that the chromium remained coordinated in an octahedral arrangement of oxygen atoms. PMID:25097452

Exposure to Particulate Hexavalent Chromium Exacerbates Allergic Asthma Pathology

PubMed Central

Schneider, Brent C.; Constant, Stephanie L.; Patierno, Steven R.; Jurjus, Rosalyn A.; Ceryak, Susan M.

2011-01-01

Airborne hexavalent chromate, Cr(VI), has been identified by the Environmental Protection Agency as a possible health threat in urban areas, due to the carcinogenic potential of some of its forms. Particulate chromates are produced in many different industrial settings, with high levels of aerosolized forms historically documented. Along with an increased risk of lung cancer, a high incidence of allergic asthma has been reported in workers exposed to certain inhaled particulate Cr(VI) compounds. However, a direct causal association between Cr(VI) and allergic asthma has not been established. We recently showed that inhaled particulate Cr(VI) induces an innate neutrophilic inflammatory response in BALB/c mice. In the current studies we investigated how the inflammation induced by inhaled particulate Cr(VI) might alter the pathology of an allergic asthmatic response. We used a well-established mouse model of allergic asthma. Groups of ovalbumin protein (OVA)-primed mice were challenged either with OVA alone, or with a combination of OVA and particulate zinc chromate, and various parameters associated with asthmatic responses were measured. Co-exposure to particulate Cr(VI) and OVA mediated a mixed form of asthma in which both eosinophils and neutrophils are present in airways, tissue pathology is markedly exacerbated, and airway hyperresponsiveness is significantly increased. Taken together these findings suggest that inhalation of particulate forms of Cr(VI) may augment the severity of ongoing allergic asthma, as well as alter its phenotype. Such findings may have implications for asthmatics in settings in which airborne particulate Cr(VI) compounds are present at high levels. PMID:22178736

Removal of trivalent and hexavalent chromium by seaweed biosorbent

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

Kratochvil, D.; Volesky, B.; Pimentel, P.

1998-09-15

Protonated or Ca-form Sargassum seaweed biomass bound up to 40 mg/g of Cr(III) by ion exchange at pH 4. An ion-exchange model assuming that the only species taken up by the biomass was Cr(OH){sup 2+} successfully fitted the experimental biosorption data for Cr(III). The maximum uptake of Cr(VI) by protonated Sargassum biomass at pH 2 was explained by simultaneous anion exchange and Cr(VI) to Cr(III) reduction. At pH <2.0, the reduction of Cr(VI) to Cr(III) dominated the equilibrium behavior of the batch systems, which was explained by the dependence of the reduction potential of HCrO{sub 4}{sup {minus}} ions on themore » pH. At pH >2.0, the removal of Cr(VI) was linked to the depletion of protons in equilibrium batch systems via an anion-exchange reaction. The optimum pH for Cr(VI) removal by sorption lies in the region where the two mechanisms overlap, which for Sargassum biomass is in the vicinity of pH 2. The existence of the optimum pH for the removal of Cr(VI) may be explained by taking into account (a) the desorption of Cr(III) from biomass at low pH and (b) the effect of pH on the reduction potential of Cr(VI) in aqueous solutions. Seventy percent of Cr(VI) bound to the seaweed at pH 2 can be desorbed with 0.2 M H{sub 2}SO{sub 4} via reduction to Cr(III).« less

Degradation of TCE, Cr(VI), sulfate, and nitrate mixtures by granular iron in flow-through columns under different microbial conditions.

PubMed

Gandhi, Sumeet; Oh, Byung-Taek; Schnoor, Jerald L; Alvarez, Pedro J J

2002-04-01

Flow-through aquifer columns packed with a middle layer of granular iron (Fe0) were used to study the applicability and limitations of bio-enhanced Fe0 barriers for the treatment of contaminant mixtures in groundwater. Concentration profiles along the columns showed extensive degradation of hexavalent chromium Cr(VI), nitrate, sulfate, and trichloroethene (TCE), mainly in the Fe0 layer. One column was bioaugmented with Shevanella algae BRY, an iron-reducing bacterium that could enhance Fe0 reactivity by reductive dissolution of passivating iron oxides. This strain did not enhance Cr(VI), which was rapidly reduced by iron, leaving little room for improvement by microbial participation. Nevertheless, BRY-enhanced nitrate removal (from 15% to 80%), partly because this strain has a wide range of electron acceptors, including nitrate. Sulfate was removed (55%) only in a column that was bioaugmented with a mixed culture containing sulfate-reducing bacteria. Apparently, these bacteria used H2 (produced by Fe0 corrosion) as electron donor to respire sulfate. Most of the TCE was degraded in the zone containing Fe0 (50-70%), and bioaugmentation with BRY slightly increased the removal efficiency to about 80%. Microbial colonization of the Fe0 surface was confirmed by scanning electron microscopy.

Elimination of a pollution associated with chromic acid during the electro-deposition of Cr(III) using appropriate anodic and membrane materials in a double film bath.

PubMed

Jiang, Xiaojun; Chen, Wenchao; Xu, Hongbo

2009-01-01

A method using trivalent chromium has been used to replace hexavalent chromium for the electro-deposition of chromium. Using a tri-chamber bath system various anodic materials and membranes were evaluated to minimize the production of environmentally and health damaging chromic acid. By measuring the absorbance of Cr(VI) at 640 nm, the results indicate that the use of a titanium plated ruthenium (Ti-Ru) anode produces the least amount of chromic acid byproduct compared to lead-gold alloy and graphite anodes. The concentration of Cr(VI) in the immediate vicinity of the Ti-Ru anode decreased from 0.389 mg/L to 0 during a 40-min deposition period. The use of a Nafion(TM) quaternary cation exchange membrane portioning the buffer and anode selectively prevented Cr(III) from entering the anode compartment whilst allowing the migration of H(+) to maintain overall voltaic continuity. It has been demonstrated that the use of a Ti-Ru anode with a Nafion(TM) membrane can eliminate the production of chromic acid associated with the electro-deposition of chromium plate thereby preventing its health damaging exposure to plant operators and preventing discharge of Cr(VI) into the environment. Addition of a surfactant improved current efficiency by 34.7%.

Biosorption of hexavalent chromium from aqueous solutions by Macadamia nutshell powder

NASA Astrophysics Data System (ADS)

Pakade, Vusumzi Emmanuel; Ntuli, Themba Dominic; Ofomaja, Augustine Enakpodia

2017-10-01

Macadamia nutshell biosorbents treated in three different activating agents [raw Macadamia nutshell powder (RMN), acid-treated Macadamia nutshell (ATMN) and base-treated Macadamia nutshell (BTMN)] were investigated for the adsorption of hexavalent chromium [Cr(VI)] from aqueous solutions. Fourier transform infrared spectroscopy spectra of free and Cr(VI)-loaded sorbents as well as thermogravimetric analysis revealed that the acid and base treatments modified the surface properties of the sorbent. Surface characteristics were also evaluated by the scanning electron microscopy and surface area analyzer. The optimum conditions for the adsorption of Cr(VI) by sorbents were pH 2, contact time 10 h, adsorbent mass 0.2 g and concentration 100 mg L-1. The equilibrium data were fitted into the Langmuir, Freundlich, Redlich-Peterson and Sips isotherms, and no single model could clearly explain the sorption mechanism. Maximum binding capacities of 45.23, 44.83 and 42.44 mg g-1 for RMN, ATMN and BTMN, respectively, were obtained. The kinetic data were analyzed using the pseudo-first, pseudo-second and Elovich kinetic models, and it was observed that the pseudo-second-order model produced the best fit for the experimental data. Macadamia nutshell sorbents showed potential as low-cost adsorbent for the removal of Cr(VI) from aqueous solution.

Transport of chromium and selenium in a pristine sand and gravel aquifer: Role of adsorption processes

USGS Publications Warehouse

Kent, D.B.; Davis, J.A.; Anderson, L.C.D.; Rea, B.A.

1995-01-01

Field transport experiments were conducted in an oxic sand and gravel aquifer using Br (bromide ion), Cr (chromium, injected as Cr(VI)), Se (selenium, injected as Se(VI)), and other tracers. The aquifer has mildly acidic pH values and low concentrations of dissolved salts. Within analytical errors, all mobile Cr was present as Cr(VI). All mobile Se was probably present as Se(VI). Adsorption of Cr and Se onto aquifer sediments caused retardation of both tracers. Breakthrough curves for Cr and Se had extensive tails, which caused large decreases in their maximum concentrations relative to the nonreactive Br tracer after only 2.0 m of transport. A surface complexation model was applied to the results of laboratory studies of Cr(VI) adsorption on aquifer solids from the site based on adsorption onto hydrous ferric oxide. The modeling results suggested that the dominant adsorbents in the aquifer solids have lower affinities for anion adsorption than pure hydrous ferric oxide. The steep rising limbs and extensive tails observed in most of the breakthrough curves are qualitatively consistent with the equilibrium surface complexation model; however, slow rates of adsorption and desorption may have contributed to these features. Variations during transport in the concentrations of Cr, Se, and other anions competing for adsorption sites likely gave rise to variations in the extent of adsorption. Adequate description of the observed retardation of Cr and Se would require a coupled transport-adsorption model that can account for these effects. Companion experiments in the mildly reducing zone of the aquifer (Kent et al., 1994) showed a loss of Cr mass, probably resulting from reduction to Cr(III), and little retardation of mobile Cr and Se during transport; this contrast illustrates the influence of aquifer chemistry on the transport of redox-sensitive solutes.

Au and Pt selectively deposited on {0 0 1}-faceted TiO2 toward SPR enhanced photocatalytic Cr(VI) reduction: The influence of excitation wavelength

NASA Astrophysics Data System (ADS)

Wang, Wei; Lai, Min; Fang, Jiaojiao; Lu, Chunhua

2018-05-01

Anatase TiO2 nanosheets with {0 0 1}-{1 0 1} surface heterojunction is employed as the typical photocatalyst to study surface plasmon resonance (SPR) enhanced photocatalytic Cr(VI) reduction with the help of selectively deposited Au and Pt nanoparticles. By employing an UV LED with central wavelength of 365 nm and a green LED with central wavelength of 530 nm as the light sources, results indicate the single green LED has little positive effect on driving the photocatalytic Cr(VI) reduction. In contrast, Au SPR can significantly improve the photocatalytic Cr(VI) reduction efficiency when both the UV LED and green LED are simultaneously irradiated. The {0 0 1}-{1 0 1} surface heterojunction and Pt nanoparticles can further improve the Cr(VI) reduction efficiency because of the facilitated hot electrons' transfer. Our findings suggest that the synergistic effect among {0 0 1}-{1 0 1} surface heterojunction, Au/Pt selective deposition, and excitation wavelength is important for SPR enhanced photocatalytic Cr(VI) reduction activity.

Incineration of tannery sludge under oxic and anoxic conditions: study of chromium speciation.

PubMed

Kavouras, P; Pantazopoulou, E; Varitis, S; Vourlias, G; Chrissafis, K; Dimitrakopulos, G P; Mitrakas, M; Zouboulis, A I; Karakostas, Th; Xenidis, A

2015-01-01

A tannery sludge, produced from physico-chemical treatment of tannery wastewaters, was incinerated without any pre-treatment process under oxic and anoxic conditions, by controlling the abundance of oxygen. Incineration in oxic conditions was performed at the temperature range from 300°C to 1200°C for duration of 2h, while in anoxic conditions at the temperature range from 400°C to 600°C and varying durations. Incineration under oxic conditions at 500°C resulted in almost total oxidation of Cr(III) to Cr(VI), with CaCrO4 to be the crystalline phase containing Cr(VI). At higher temperatures a part of Cr(VI) was reduced, mainly due to the formation of MgCr2O4. At 1200°C approximately 30% of Cr(VI) was reduced to Cr(III). Incineration under anoxic conditions substantially reduced the extent of oxidation of Cr(III) to Cr(VI). Increase of temperature and duration of incineration lead to increase of Cr(VI) content, while no chromium containing crystalline phase was detected. Copyright © 2014 Elsevier B.V. All rights reserved.

Adsorption isotherm studies of chromium (VI) from aqueous solutions using sol-gel hydrotalcite-like compounds.

PubMed

Ramos-Ramírez, Esthela; Ortega, Norma L Gutiérrez; Soto, Cesar A Contreras; Gutiérrez, Maria T Olguín

2009-12-30

In under-developed countries, industries such as paint and pigment manufacturing, leather tanning, chrome plating and textile processing, usually discharge effluents containing Cr(VI) and Cr(III) into municipal sanitary sewers. It has been reported that Cr(VI) acts as a powerful epithelial irritant and as a human carcinogen. In the present work, hydrotalcite-like compounds with a Mg/Al ratio=2 were synthesized by the sol-gel method. The hydrotalcite-like compounds and their corresponding thermally treated products were characterized by powder X-ray diffraction, infrared spectroscopy and N(2) adsorption. The hydrotalcite-like compounds and the heated solids were used as adsorbents for Cr(VI) in aqueous solutions. Adsorption isotherm studies of Cr(VI) from aqueous solution are described. The adsorbent capacity was determined using the Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherm models. The Cr(VI) adsorption isotherm data fit best to the Langmuir isotherm model. The maximum Cr(VI) uptake by hydrotalcite and the heated solids was determined using the Langmuir equation and was found to range between 26 and 29 mg Cr(VI)/g adsorbent.

Microbial Community Phylogenetic and Functional Succession in Chromium-Reducing Aquifer-Derived Microcosms

NASA Astrophysics Data System (ADS)

Brodie, E. L.; Beller, H. R.; Goldfarb, K. C.; Han, R.; Santee, C. A.

2009-12-01

In situ reductive immobilization, whereby highly soluble Cr(VI) species are reduced to poorly soluble Cr(III) species, is a favored approach for remediating Cr-contaminated groundwater. How microbial populations respond phylogenetically and functionally to the injection of an organic electron donor to stimulate Cr(VI) reduction is unclear, as are the relative contributions of direct enzymatic Cr(VI) reduction versus indirect (e.g. sulfide-mediated) reduction. In this study, we inoculated anaerobic microcosms with groundwater from the Cr-contaminated Hanford 100H site (WA) and supplemented them with lactate and the electron acceptors nitrate, sulfate, and amorphous ferric oxyhydroxide. The microcosms progressed successively through nitrate-reducing, sulfate-reducing, and Fe(III)-reducing conditions, and after a second nitrate amendment, nitrate-dependent Fe(II)-oxidizing conditions. Cr(VI) reduction occurred during both the denitrification and the sulfate/iron reduction phases. DNA and RNA were harvested during each major biogeochemical phase and were subjected to PhyloChip analysis, qPCR, and transcript sequencing. Bacterial community succession followed a trajectory related to the sequential use of electron acceptors. During denitrification, bacterial communities were enriched in known denitrifiers within the Beta- and Gamma-proteobacteria and became phylogenetically clustered. Fermenters became enriched following nitrate reduction, preceding both iron and sulfate reduction. Iron reduction was stoichiometrically related to the formation of hydrogen sulfide and, although iron reducers were detected during this phase, their iron-reducing activity was not confirmed. Following the depletion of lactate and sulfate, iron reduction rates decreased and acetate and propionate concentrations stabilized, indicating a marginal contribution of acetate-coupled iron reduction. Rapid Fe(II) oxidation occurred following the nitrate amendment with a concomitant reduction of nitrate to nitrite and an increased abundance of Beta-proteobacterial species related to known anaerobic Fe(II)-oxidizing bacteria. To uncover the microbial mechanisms contributing to the biogeochemical complexity encountered, even under controlled laboratory incubations, requires alternatives to standard phylogenetic analyses. Our ongoing efforts in analyzing the community transcriptomes (mRNA) should provide valuable insight into the relative rates of direct versus indirect mechanisms of Cr(VI) immobilization in contaminated aquifers.

Facile preparation of magnetic mesoporous MnFe2O4@SiO2-CTAB composites for Cr(VI) adsorption and reduction.

PubMed

Li, Na; Fu, Fenglian; Lu, Jianwei; Ding, Zecong; Tang, Bing; Pang, Jiabin

2017-01-01

Chromium-contaminated water is regarded as one of the biggest threats to human health. In this study, a novel magnetic mesoporous MnFe 2 O 4 @SiO 2 -CTAB composite was prepared by a facile one-step modification method and applied to remove Cr(VI). X-ray diffraction, scanning electron microscopy, transmission electron microscopy, specific surface area, and vibrating sample magnetometer were used to characterize MnFe 2 O 4 @SiO 2 -CTAB composites. The morphology analysis showed that the composites displayed a core-shell structure. The outer shell was mesoporous silica with CTAB and the core was MnFe 2 O 4 nanoparticles, which ensured the easy separation by an external magnetic field. The performance of MnFe 2 O 4 @SiO 2 -CTAB composites in Cr(VI) removal was far better than that of bare MnFe 2 O 4 nanoparticles. There were two reasons for the effective removal of Cr(VI) by MnFe 2 O 4 @SiO 2 -CTAB composites: (1) mesoporous silica shell with abundant CTA + significantly enhanced the Cr(VI) adsorption capacity of the composites; (2) a portion of Cr(VI) was reduced to less toxic Cr(III) by MnFe 2 O 4 , followed by Cr(III) immobilized on MnFe 2 O 4 @SiO 2 -CTAB composites, which had been demonstrated by X-ray photoelectron spectroscopy results. The adsorption of Cr(VI) onto MnFe 2 O 4 @SiO 2 -CTAB followed the Freundlich isotherm model and pseudo-second-order model. Tests on the regeneration and reuse of the composites were performed. The removal efficiency of Cr(VI) still retained 92.4% in the sixth cycle. MnFe 2 O 4 @SiO 2 -CTAB composites exhibited a great potential for the removal of Cr(VI) from water. Copyright © 2016 Elsevier Ltd. All rights reserved.

The Intracellular Redox Stress Caused by Hexavalent Chromium is Selective for Proteins that Have Key Roles in Cell Survival and Thiol Redox Control

PubMed Central

Myers, Judith M.; Antholine, William E.; Myers, Charles R.

2011-01-01

Hexavalent chromium [Cr(VI)] compounds (e.g. chromates) are strong oxidants that readily enter cells where they are reduced to reactive Cr intermediates that can directly oxidize some cell components and can promote the generation of reactive oxygen and nitrogen species. Inhalation is a major route of exposure which directly exposes the bronchial epithelium. Previous studies with non-cancerous human bronchial epithelial cells (BEAS-2B) demonstrated that Cr(VI) treatment results in the irreversible inhibition of thioredoxin reductase (TrxR) and the oxidation of thioredoxins (Trx) and peroxiredoxins (Prx). The mitochondrial Trx/Prx system is somewhat more sensitive to Cr(VI) than the cytosolic Trx/Prx system, and other redox-sensitive mitochondrial functions are subsequently affected including electron transport complexes I and II. Studies reported here show that Cr(VI) does not cause indiscriminant thiol oxidation, and that the Trx/Prx system is among the most sensitive of cellular protein thiols. Trx/Prx oxidation is not unique to BEAS-2B cells, as it was also observed in primary human bronchial epithelial cells. Increasing the intracellular levels of ascorbate, an endogenous Cr(VI) reductant, did not alter the effects on TrxR, Trx, or Prx. The peroxynitrite scavenger MnTBAP did not protect TrxR, Trx, Prx, or the electron transport chain from the effects of Cr(VI), implying that peroxynitrite is not required for these effects. Nitration of tyrosine residues of TrxR was not observed following Cr(VI) treatment, further ruling out peroxynitrite as a significant contributor to the irreversible inhibition of TrxR. Cr(VI) treatments that disrupt the TrxR/Trx/Prx system did not cause detectable mitochondrial DNA damage. Overall, the redox stress that results from Cr(VI) exposure shows selectivity for key proteins which are known to be important for redox signaling, antioxidant defense, and cell survival. PMID:21237240

Understanding the role of clay minerals in the chromium(VI) bioremoval by Pseudomonas aeruginosa CCTCC AB93066 under growth condition: microscopic, spectroscopic and kinetic analysis.

PubMed

Kang, Chunxi; Wu, Pingxiao; Li, Yuewu; Ruan, Bo; Li, Liping; Tran, Lytuong; Zhu, Nengwu; Dang, Zhi

2015-11-01

Laboratory batch experiments were conducted to investigate the role of clay minerals, e.g., kaolinite and vermiculite, in microbial Cr(VI) reduction by Pseudomonas aeruginosa under growth condition in glucose-amended mediums as a method for treating Cr(VI)-contaminated subsurface environment such as soil. Our results indicated that glucose could acted as an essential electron donor, and clay minerals significantly enhanced microbial Cr(VI) reduction rates by improving the consumption rate of glucose and stimulating the growth and propagation of P. aeruginosa. Cr(VI) bioreduction by both free cells and clay minerals-amended cells followed the pseudo-first-order kinetic model, with the latter one fitting better. The mass balance analyses and X-ray photoelectron spectroscopy analysis found that Cr(VI) was reduced to Cr(III) and the adsorption of total chromium on clay minerals-bacteria complex was small, implying that Cr(VI) bioremoval was not mainly due to the adsorption of Cr(VI) onto cells or clay minerals or clay minerals-cells complex but mainly due to the Cr(VI) reduction capacity of P. aeruginosa under the experimental conditions studied (e.g., pH 7). Atomic force microscopy revealed that the addition of clay minerals (e.g. vermiculite) decreased the surface roughness of Cr(VI)-laden cells and changed the cell morphology and dimension. Fourier transform infrared spectroscopy revealed that organic matters such as aliphatic species and/or proteins played an important role in the combination of cells and clay minerals. Scanning electron microscopy confirmed the attachment of cells on the surface of clay minerals, indicating that clay minerals could provide a microenvironment to protect cells from Cr(VI) toxicity and serve as growth-supporting materials. These findings manifested the underlying influence of clay minerals on microbial reduction of Cr(VI) and gave an understanding of the interaction between pollutants, the environment and the biota.

Continuous flow operation with appropriately adjusting composites in influent for recovery of Cr(VI), Cu(II) and Cd(II) in self-driven MFC-MEC system.

PubMed

Li, Ming; Pan, Yuzhen; Huang, Liping; Zhang, Yong; Yang, Jinhui

2017-03-01

A self-driven microbial fuel cell (MFC) - microbial electrolysis cell (MEC) system, where electricity generated from MFCs is in situ utilized for powering MECs, has been previously reported for recovering Cr(VI), Cu(II) and Cd(II) with individual metals fed in different units of the system in batch operation. Here it was advanced with treating synthetic mixed metals' solution at appropriately adjusting composites in fed-batch and continuous flow operations for complete separation of Cr(VI), Cu(II) and Cd(II) from each other. Under an optimal condition of hydraulic residence time of 4 h, matching of two serially connected MFCs with one MEC, and fed with a composite of either 5 mg L -1 Cr(VI), 1 mg L -1 Cu(II) and 5 mg L -1 Cd(II), or 1 mg L -1 Cr(VI), 5 mg L -1 Cu(II) and 5 mg L -1 Cd(II), the self-driven MFC-MEC system can completely and sequentially recover Cu(II), Cr(VI) and Cd(II) from mixed metals. This study provides a true sustainable and zero-energy-consumed approach of using bioelectrochemical systems for completely recovering and separating Cr(VI), Cu(II) and Cd(II) from each other or from wastes or contaminated sites.

Cr isotope fractionation factors for Cr(VI) reduction by a metabolically diverse group of bacteria

NASA Astrophysics Data System (ADS)

Basu, Anirban; Johnson, Thomas M.; Sanford, Robert A.

2014-10-01

Reduction of Cr(VI) is an important process that determines the geochemical behavior, mobility and bioavailability of Cr in both terrestrial and marine environments. Many metabolically diverse microorganisms possess Cr(VI) reduction capacity. Cr(VI) reduction fractionates Cr isotopes and thus 53Cr/52Cr ratios can be used to monitor Cr(VI) reduction and redox conditions. The magnitude of isotopic fractionation (ε) for a variety of microbial reduction mechanisms must be known for accurate interpretation of observed shifts in 53Cr/52Cr ratios. We determined isotopic fractionation factors for Cr(VI) reduction by metal reducers Geobacter sulfurreducens and Shewanella sp. strain NR, a denitrifying soil bacterium Pseudomonas stutzeri DCP-Ps1, and a sulfate reducer Desulfovibrio vulgaris. All bacteria investigated in this study produced significant Cr isotope fractionation. The fractionation (ε) for G. sulfurreducens, Shewanella sp. (NR), P. stutzeri DCP-Ps1, and D. vulgaris were -3.03‰ ± 0.12‰, -2.17‰ ± 0.22‰, -3.14‰ ± 0.13‰, and -3.01‰ ± 0.11‰, respectively. Despite differences in microbial strains in this study, the ε did not vary significantly except for Shewanella sp. (NR). Our results suggest that strong isotopic fractionation is induced during Cr(VI) reduction under electron donor poor (∼300 μM) conditions.

Determination of chromium (VI) in primary and secondary fertilizer and their respective precursors.

PubMed

Krüger, Oliver; Fiedler, Francesca; Adam, Christian; Vogel, Christian; Senz, Rainer

2017-09-01

Hexavalent chromium species (Cr(VI)) are often carcinogenic, of high acute toxicity, highly mobile, and thus pose a severe risk to health and environment. Fertilizers usually contain significant amounts of chromium. Therefore, a reliable analysis of chromium and the fraction of Cr(VI) are crucial for safe use of fertilizers. This problem is expected to increase in the future, since more and more recycled fertilizers emerge due to increasing fertilizer demand and respective supply risks. However, existing analytical methods have been developed for conventional fertilizers and have to be tested whether they are suitable for the new materials. Thus, we performed a wet-chemical extraction for Cr(VI) on several matrices as well as respective quality control experiments including spiking with Cr(III) and Cr(VI) compounds. We found the Cr(VI) amounts to be below 2 mg/kg except for a thermally post-treated sewage sludge ash (SSA) that showed 12.3 mg/kg. The presence of organic matter e.g. in sludge or precipitated struvite caused a reduction of spiked Cr(VI) and thus no satisfying recovery for quality control. Cr(VI) reduction was also observed for SSA, presumably due to the presence of Fe(II) compounds. Even though the tested procedure can be hampered in some recycled fertilizer matrices, it might be adapted to be applicable also for these complex samples. Copyright © 2017 Elsevier Ltd. All rights reserved.

Chromium(III) and chromium(VI) release from leather during 8 months of simulated use

PubMed Central

Lidén, Carola

2016-01-01

Summary Background Chromium (Cr) release from Cr‐tanned leather articles is a major cause of Cr contact dermatitis. It has been suggested that Cr(VI) release from leather is not necessarily an intrinsic property of the leather, but is strongly dependent on environmental conditions. Objectives To test this hypothesis for long‐term (8 months) simulated use. Materials and methods The release of total Cr and Cr(VI) from Cr‐tanned, unfinished leather was analysed in subsequent phosphate buffer (pH 8.0) immersions for a period of 7.5 months. The effect of combined ultraviolet treatment and alkaline solution (pH 12.1) was tested. Dry storage [20% relative humidity (RH)] was maintained between immersions. Atomic absorption spectroscopy, X‐ray fluorescence and diphenylcarbazide tests were used. Results Cr(VI) release was dependent on previous dry storage or alkaline treatment, but not on duration or number of previous immersions. Cr(III) release decreased with time. Fifty‐two percent of the total Cr released during the last immersion period was Cr(VI). Cr(VI) release exceeded 9 mg/kg in all immersion periods except in the first 10‐day immersion (2.6 mg/kg). Conclusions Cr(VI) release is primarily determined by environmental factors (RH prior to immersion, solution pH, and antioxidant content). The RH should be kept low prior to testing Cr(VI) release from leather. PMID:27144948

Differential determination of chromium(VI) and total chromium in natural waters using flow injection on-line separation and preconcentration electrothermal atomic absorption spectrometry.

PubMed

Sperling, M; Yin, X; Welz, B

1992-03-01

A rapid, sensitive and selective method for the differential determination of CrIII and CrVI in natural waters is described. Chromium(vi) can be determined directly by flow injection on-line sorbent extraction preconcentration coupled with electrothermal atomic absorption spectrometry using sodium diethyldithiocarbamate as the complexing agent and C18 bonded silica reversed-phase sorbent as the column material. Total Cr can be determined after oxidation of CrIII to CrVI by potassium peroxydisulfate. Chromium(III) can be calculated by difference. The optimum conditions for sorbent extraction of CrVI and oxidation of CrIII to CrVI are evaluated. A 12-fold enhancement in sensitivity compared with direct introduction of 40 microliters samples was achieved after preconcentration for 60 s, giving detection limits of 16 ng l-1 for CrVI and 18 ng l-1 for total Cr (based on 3 sigma). Results obtained for sea-water and river water reference materials were all within the certified range for total Cr with a precision of better than 10% relative standard deviation in the range 100-200 ng l-1. The selectivity of the determination of CrVI was evaluated by analysing spiked reference materials in the presence of CrIII, resulting in quantitative recovery of CrVI.

Hexavalent chromium adsorption from aqueous solution using carbon nano-onions (CNOs).

PubMed

Sakulthaew, Chainarong; Chokejaroenrat, Chanat; Poapolathep, Amnart; Satapanajaru, Tunlawit; Poapolathep, Saranya

2017-10-01

The capacity of carbon nano-onions (CNOs) to remove hexavalent chromium (Cr(VI)) from aqueous solution was investigated. Batch experiments were performed to quantify the effects of the dosage rate, pH, counter ions, and temperature. The adsorption of Cr(VI) onto CNOs was best described by a pseudo-second order rate expression. The adsorption efficiency increased with increasing adsorbent dosage and contact time and reached equilibrium in 24 h. The equilibrium data showed better compliance with a Langmuir isotherm than a Freundlich isotherm. Effective removal of Cr(VI) was demonstrated at pH values ranging from 2 to 10. The adsorption capacity of Cr(VI) was found to be highest (82%) at pH 3.4 and greatly depended on the solution pH. We found that Cr(VI) adsorption decreased with increasing pH over the pH range of 3.4-10. The adsorption capacity increased dramatically when the temperature increased from 10 °C to 50 °C regardless of the amount of CNOs used. Cr(VI) removal decreased by ∼13% when Zn(II), Cu(II), and Pb(II) were present, while there were no significant changes observed when NO 3 - or SO 4 2- was present. The overall results support that CNOs can be used as an alternative adsorbent material to remove Cr(VI) in the water treatment industry. Copyright © 2017 Elsevier Ltd. All rights reserved.

Differential impact of ionic and coordinate covalent chromium (Cr)-DNA binding on DNA replication.

PubMed

Fornsaglio, Jamie L; O'Brien, Travis J; Patierno, Steven R

2005-11-01

The reactive species produced by the reduction of Cr(VI), particularly Cr(III), can form both ionic and coordinate covalent complexes with DNA. These Cr(III)-DNA interactions consist of Cr-DNA monoadducts, Cr-DNA ternary adducts, and Cr-DNA interstrand cross-links (Cr-ICLs), the latter of which are DNA polymerase arresting lesions (PALs). We sought to determine the impact of Cr-DNA interactions on the formation of replication blocking lesions in S. cerevisiae using a PCR-based method. We found that target sequence (TS) amplification using DNA isolated from Cr(VI)-treated yeast actually increased as a function of Cr(VI) concentration. Moreover, the enhanced TS amplification was reproduced in vitro using Cr(III)-treated DNA. In contrast, PCR amplification of TS from DNA isolated from yeast exposed to equitoxic doses of the inorganic DNA cross-linking agent cisplatin (CDDP), was decreased in a concentration-dependent manner. This paradox suggested that a specific Cr-DNA interaction, such as an ionic Cr-DNA complex, was responsible for the enhanced TS amplification, thereby masking the replication-blocking effect of certain ternary Cr-DNA adducts (i.e. interstrand cross-links). To test this possibility, we removed ionically associated Cr from the DNA using salt extraction prior to PCR analysis. This procedure obviated the increased amplification and revealed a dose-dependent decrease in TS amplification and an increase in Cr-PALs. These data from DNA analyzed ex vivo after treatment of intact cells indicate that ionic interactions of Cr with DNA result in increased DNA amplification whereas coordinate-covalent Cr-DNA complexes lead to formation of Cr-PALs. Thus, these results suggest that treatment of living cells with Cr(VI) leads to two modes of Cr-binding, which may have conflicting effects on DNA replication.

Evaluation of the effects of various culture condition on Cr (VI)reduction by Shewanella oneidensis MR-1 in a novel high-throughputmini-bioreactor

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

Tang, Yinjie J.; Laidlaw, David; Gani, Kishen

2006-03-16

The growth and Cr(VI) reduction by Shewanella oneidensisMR-1 was examined using a mini-bioreactor system that independentlymonitors and controls pH, dissolved oxygen, and temperature for each ofits 24, 10-mL reactors. Independent monitoring and control of eachreactor in the cassette allows the exploration of a matrix ofenvironmental conditions known to influence S. oneidensis chromiumreduction. S. oneidensis MR-1 grew in minimal medium without amino acidor vitamin supplementation under aerobic conditions but required serineand glycine supplementation under anaerobic conditions. Growth wasinhibited by dissolved oxygen concentrations>80 percent. Lactatetransformation to acetate was enhanced by low concentration of dissolvedoxygen during the logarithmic growth phase. Between 11 andmore » 35oC, thegrowth rate obeyed the Arrhenius reaction rate-temperature relationship,with a maximum growth rate occurring at 35oC. S. oneidensis MR-1 was ableto grow over a wide range of pH (6-9). At neutral pH and temperaturesranging from 30-35oC, S. oneidensis MR-1 reduced 100 mu M Cr(VI) toCr(III) within 20 minutes in the exponential growth phase, and the growthrate was not affected by the addition of chromate; it reduced chromateeven faster at temperatures between 35 and 39oC. At low temperatures(<25oC), acidic (pH<6.5), or alkaline (pH>8.5) conditions, 100mu M Cr(VI) strongly inhibited growth and chromate reduction. Themini-bioreactor system enabled the rapid determination of theseparameters reproducibly and easily by performing very few experiments.Besides its use for examining parameters of interest to environmentalremediation, the device will also allow one to quickly assess parametersfor optimal production of recombinant proteins or secondarymetabolites« less

Transient gestational exposure to drinking water containing excess hexavalent chromium modifies insulin signaling in liver and skeletal muscle of rat progeny.

PubMed

Shobana, Navaneethabalakrishnan; Aruldhas, Mariajoseph Michael; Tochhawng, Lalmuankimi; Loganathan, Ayyalu; Balaji, Sadhasivam; Kumar, Mani Kathiresh; Banu, Liaquat Alikhan Sheerin; Navin, Ajit Kumar; Mayilvanan, Chinnaiyan; Ilangovan, Ramachandran; Balasubramanian, Karundevi

2017-11-01

Chromium (Cr), an essential micronutrient potentiates insulin action, whereas excess hexavalent Cr (CrVI) acts as an endocrine disruptor. Pregnant mothers living in areas abutting industries using the metal and chromite ore dumps are exposed to ground water contaminated with Cr. Nevertheless, the impact of prenatal exposure to excess CrVI on insulin signaling in the progeny remains obscure. We tested the hypothesis "transient gestational exposure to drinking water containing excess CrVI may modify insulin signaling during postnatal life". Pregnant Wistar rats were given drinking water containing 50, 100 and 200 ppm CrVI (K 2 Cr 2 O 7 ) from gestational day 9-14 encompassing the period of organogenesis; the male progenies were tested at postnatal day 60. Neither fasting blood glucose nor oral glucose tolerance was altered in CrVI treated progeny. Nevertheless, western blot detection pointed out attenuated expression level of insulin receptor (IR), its downstream signaling molecules (IRS-1, pIRS-1 Tyr632 , Akt and pAkt Ser473 ) and organ specific glucose transporters (GLUT2 in liver and GLUT4 in gastrocnemius muscle), along with a significant increase in serum insulin level in male progenies exposed to CrVI. While 14 C-2-deoxy glucose uptake increased in the liver, the same decreased in the skeletal muscle whereas, 14 C-glucose oxidation recorded a consistent decrease in both tissues of CrVI exposed rats. These findings support our hypothesis and suggest that transient gestational exposure to excess CrVI may affect insulin signaling and glucose oxidation in the progeny, predictably rendering them vulnerable to insulin resistance. Copyright © 2017 Elsevier B.V. All rights reserved.

Enhancement of chromate reduction in soils by surface modified biochar.

PubMed

Mandal, Sanchita; Sarkar, Binoy; Bolan, Nanthi; Ok, Yong Sik; Naidu, Ravi

2017-01-15

Chromium (Cr) is one of the common metals present in the soils and may have an extremely deleterious environmental impact depending on its redox state. Among two common forms, trivalent Cr(III) is less toxic than hexavalent Cr(VI) in soils. Carbon (C) based materials including biochar could be used to alleviate Cr toxicity through converting Cr(VI) to Cr(III). Incubation experiments were conducted to examine Cr(VI) reduction in different soils (Soil 1: pH 7.5 and Soil 2: pH 5.5) with three manures from poultry (PM), cow (CM) and sheep (SM), three respective manure-derived biochars (PM biochar (PM-BC), CM biochar (CM-BC) and SM biochar (SM-BC)) and two modified biochars (modified PM-BC (PM-BC-M) and modified SM-BC (SM-BC-M)). Modified biochar was synthesized by incorporating chitosan and zerovalent iron (ZVI) during pyrolysis. Among biochars, highest Cr(VI) reduction was observed with PM-BC application (5%; w/w) (up to 88.12 mg kg -1 ; 45% reduction) in Soil 2 (pH 5.5). The modified biochars enhanced Cr(VI) reduction by 55% (SM-BC-M) compared to manure (29%, SM) and manure-derived biochars (40% reduction, SM-BC). Among the modified biochars, SM-BC-M showed a higher Cr(VI) reduction rate (55%) than PM-BC-M (48%) in Soil 2. Various oxygen-containing surface functional groups such as phenolic, carboxyl, carbonyl, etc. on biochar surface might act as a proton donor for Cr(VI) reduction and subsequent Cr(III) adsorption. This study underpins the immense potential of modified biochar in remediation of Cr(VI) contaminated soils. Copyright © 2016 Elsevier Ltd. All rights reserved.

Prolonged Particulate Hexavalent Chromium Exposure Suppresses Homologous Recombination Repair in Human Lung Cells.

PubMed

Browning, Cynthia L; Qin, Qin; Kelly, Deborah F; Prakash, Rohit; Vanoli, Fabio; Jasin, Maria; Wise, John Pierce

2016-09-01

Genomic instability is one of the primary models of carcinogenesis and a feature of almost all cancers. Homologous recombination (HR) repair protects against genomic instability by maintaining high genomic fidelity during the repair of DNA double strand breaks. The defining step of HR repair is the formation of the Rad51 nucleofilament, which facilitates the search for a homologous sequence and invasion of the template DNA strand. Particulate hexavalent chromium (Cr(VI)), a human lung carcinogen, induces DNA double strand breaks and chromosome instability. Since the loss of HR repair increases Cr(VI)-induced chromosome instability, we investigated the effect of extended Cr(VI) exposure on HR repair. We show acute (24 h) Cr(VI) exposure induces a normal HR repair response. In contrast, prolonged (120 h) exposure to particulate Cr(VI) inhibited HR repair and Rad51 nucleofilament formation. Prolonged Cr(VI) exposure had a profound effect on Rad51, evidenced by reduced protein levels and Rad51 mislocalization to the cytoplasm. The response of proteins involved in Rad51 nuclear import and nucleofilament formation displayed varying responses to prolonged Cr(VI) exposure. BRCA2 formed nuclear foci after prolonged Cr(VI) exposure, while Rad51C foci formation was suppressed. These results suggest that particulate Cr(VI), a major chemical carcinogen, inhibits HR repair by targeting Rad51, causing DNA double strand breaks to be repaired by a low fidelity, Rad51-independent repair pathway. These results further enhance our understanding of the underlying mechanism of Cr(VI)-induced chromosome instability and thus, carcinogenesis. © The Author 2016. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Inter-conversion of Chromium Species During Air Sampling: Effects of O3, NO2, SO2, Particle Matrices, Temperature and Humidity

PubMed Central

Huang, Lihui; Fan, Zhihua (Tina); Yu, Chang Ho; Hopke, Philip K.; Lioy, Paul J.; Buckley, Brian T.; Lin, Lin; Ma, Yingjun

2013-01-01

The inter-conversion between Cr(VI), a pulmonary carcinogen, and Cr(III), an essential human nutrient, poses challenges to the measurement of Cr(VI) in airborne particles. Chamber and field tests were conducted to identify the factors affecting Cr(VI)-Cr(III) inter-conversion in the basic filter medium under typical sampling conditions. In the chamber tests, isotopically enriched 53Cr(VI) and 50Cr(III) were spiked on diesel particulate matter (DPM) and secondary organic aerosol (SOA) that were pre-collected on a basic MCE filter. The filter samples were then exposed to clean air or the air containing SO2 (50 and 160 ppb), 100 ppb O3, or 150 ppb NO2 for 24 hours at 16.7 LPM flow rate at designated temperature (20 and 31°C) and RH (40% and 70%) conditions. Exposure to 160 ppb SO2 had the greatest effect on 53Cr(VI) reduction, with 53Cr(VI) recovery of 31.7 ± 15.8% (DPM) and 42.0 ± 7.9% (SOA). DPM and SOA matrix induced 53Cr(VI) reduction when exposed to clean air while reactive oxygen species in SOA could promote 50Cr(III) oxidation. Deliquescence when RH increased from 40% to 70% led to conversion of Cr(III) in SOA, whereas oxidized organics in DPM and SOA enhanced hygroscopicity and thus facilitated Cr(VI) reduction. Field tests showed seasonal variation of Cr(VI)-Cr(III) inter-conversion during sampling. Correction of the inter-conversion using USEPA method 6800 is recommended to improve accuracy of ambient Cr(VI) measurements. PMID:23550818

40 CFR 413.02 - General definitions.

Code of Federal Regulations, 2011 CFR

2011-07-01

... term CN,T shall mean cyanide, total. (c) The term Cr,VI shall mean hexavalent chromium. (d) The term... the concentration or mass of Copper (Cu), Nickel (Ni), Chromium (Cr) (total) and Zinc (Zn). (f) The... Pollution Control Act Amendments of 1972, 33 U.S.C. 1251 et. seq., as amended by the Clean Water Act of 1977...

40 CFR 413.02 - General definitions.

Code of Federal Regulations, 2010 CFR

2010-07-01

... term CN,T shall mean cyanide, total. (c) The term Cr,VI shall mean hexavalent chromium. (d) The term... the concentration or mass of Copper (Cu), Nickel (Ni), Chromium (Cr) (total) and Zinc (Zn). (f) The... Pollution Control Act Amendments of 1972, 33 U.S.C. 1251 et. seq., as amended by the Clean Water Act of 1977...

Electrophoretic deposition of carbon nanotube on reticulated vitreous carbon for hexavalent chromium removal in a biocathode microbial fuel cell

NASA Astrophysics Data System (ADS)

Fei, Kangqing; Song, Tian-shun; Wang, Haoqi; Zhang, Dalu; Tao, Ran; Xie, Jingjing

2017-10-01

For Cr(VI)-removal microbial fuel cell (MFC), a more efficient biocathode in MFCs is required to improve the Cr(VI) removal and electricity generation. RVC-CNT electrode was prepared through the electrophoretic deposition of carbon nanotube (CNT) on reticulated vitreous carbon (RVC). The power density of MFC with an RVC-CNT electrode increased to 132.1 ± 2.8 mW m-2, and 80.9% removal of Cr(VI) was achieved within 48 h; compared to only 44.5% removal of Cr(VI) in unmodified RVC. Cyclic voltammetry, energy-dispersive spectrometry and X-ray photoelectron spectrometry showed that the RVC-CNT electrode enhanced the electrical conductivity and the electron transfer rate; and provided more reaction sites for Cr(VI) reduction. This approach provides process simplicity and a thickness control method for fabricating three-dimensional biocathodes to improve the performance of MFCs for Cr(VI) removal.

Graphene/biofilm composites for enhancement of hexavalent chromium reduction and electricity production in a biocathode microbial fuel cell.

PubMed

Song, Tian-Shun; Jin, Yuejuan; Bao, Jingjing; Kang, Dongzhou; Xie, Jingjing

2016-11-05

In this study, a simple method of biocathode fabrication in a Cr(VI)-reducing microbial fuel cell (MFC) is demonstrated. A self-assembling graphene was decorated onto the biocathode microbially, constructing a graphene/biofilm, in situ. The maximum power density of the MFC with a graphene biocathode is 5.7 times that of the MFC with a graphite felt biocathode. Cr(VI) reduction was also enhanced, resulting in 100% removal of Cr(VI) within 48h, at 40mg/L Cr(VI), compared with only 58.3% removal of Cr(VI) in the MFC with a graphite felt biocathode. Cyclic voltammogram analyses showed that the graphene biocathode had faster electron transfer kinetics than the graphite felt version. Energy dispersive spectrometer (EDS) and X-ray photoelectron spectra (XPS) analysis revealed a possible adsorption-reduction mechanism for Cr(VI) reduction via the graphene biocathode. This study attempts to improve the efficiency of the biocathode in the Cr(VI)-reducing MFC, and provides a useful candidate method for the treatment of Cr(VI) contaminated wastewater, under neutral conditions. Copyright © 2016. Published by Elsevier B.V.

Adsorption of hexavalent chromium on cationic cross-linked starches of different botanic origins.

PubMed

Klimaviciute, Rima; Bendoraitiene, Joana; Rutkaite, Ramune; Zemaitaitis, Algirdas

2010-09-15

The influence of origin of native starch used to obtain cationic cross-linked starch (CCS) on the adsorption of Cr(VI) onto CCS has been investigated. CCS granule size is influenced by the botanic source of native starch. The equilibrium adsorption of Cr(VI) onto CCS was described by the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models. The more equal the adsorption energy of the quaternary ammonium groups in CCS granule as indicated by low value of change of Temkin adsorption energy DeltaE(T) the greater amount of Cr(VI) was adsorbed onto CCS. The value of DeltaE(T) decreased and sorption capacity of CCS increased with the decrease of CCS granule size and with the increase of number of amorphous regions in CCS granules. The affinity of dichromate anions increases and adsorption proceeds more spontaneously when Cr(VI) is adsorbed onto more amorphous CCS. Adsorption process of Cr(VI) onto such CCS is more exothermic and order of system undergoes major changes during adsorption. After the adsorption on CCS Cr(VI) could be regenerated by incineration at temperature of 800 degrees C. Copyright 2010 Elsevier B.V. All rights reserved.

A novel Pseudomonas gessardii strain LZ-E simultaneously degrades naphthalene and reduces hexavalent chromium.

PubMed

Huang, Haiying; Wu, Kejia; Khan, Aman; Jiang, Yiming; Ling, Zhenmin; Liu, Pu; Chen, Yong; Tao, Xuanyu; Li, Xiangkai

2016-05-01

Combined pollutants with polycyclic aromatic hydrocarbons (PAHs) and heavy metals have been identified as toxic and unmanageable contaminates. In this work, Pseudomonas gessardii strain LZ-E isolated from wastewater discharge site of a petrochemical company degrades naphthalene and reduces Cr(VI) simultaneously. 95% of 10mgL(-1) Cr(VI) was reduced to Cr(III) while 77% of 800mgL(-1) naphthalene was degraded when strain LZ-E was incubated in BH medium for 48h. Furthermore, naphthalene promotes Cr(VI) reduction in strain LZ-E as catechol and phthalic acid produced in naphthalene degradation are able to reduce Cr(VI) abiotically. An aerated bioreactor system was setup to test strain LZ-E's remediation ability. Strain LZ-E continuously remediated naphthalene and Cr(VI) at rates of 15mgL(-1)h(-1) and 0.20mgL(-1)h(-1) of 800mgL(-1) naphthalene and 10mgL(-1) Cr(VI) addition with eight batches in 16days. In summary, strain LZ-E is a potential applicant for combined pollution remediation. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Probing chromium(III) from chromium(VI) in cells by a fluorescent sensor

NASA Astrophysics Data System (ADS)

Hu, Xiangquan; Chai, Jie; Liu, Yanfei; Liu, Bin; Yang, Binsheng

2016-01-01

Cellular uptake of Cr(VI), followed by its reduction to Cr(III) with the formation of kinetically inert Cr(III) complexes, is a complex process. To better understand its physiological and pathological functions, efficient methods for the monitoring of Cr(VI) are desired. In this paper a selective fluorescent probe L, rhodamine hydrazide bearing a benzo[b]furan-2-carboxaldehyde group, was demonstrated as a red chemosensor for Cr(III) at about 586 nm. This probe has been used to probe Cr(III) which is reduced from Cr(VI) by reductants such as glutathione (GSH), vitamin C, cysteine (Cys), H2O2 and Dithiothreitol (DTT) by fluorescence spectra. Cr(VI) metabolism in vivo is primarily driven by Vc and GSH. Vc could reduce CrO42 - to Cr(III) in a faster rate than GSH. The indirectly detection limit for Cr(VI) by L + GSH system was determined to be 0.06 μM at pH = 6.2. Moreover, the confocal microscopy image experiments indicated that Cr(VI) can be reduced to Cr(III) inside cells rapidly and the resulted Cr(III) can be captured and imaged timely by L.

Cr(VI) sorption by free and immobilised chromate-reducing bacterial cells in PVA-alginate matrix: equilibrium isotherms and kinetic studies.

PubMed

Rawat, Monica; Rawat, A P; Giri, Krishna; Rai, J P N

2013-08-01

Chromate-resistant bacterial strain isolated from the soil of tannery was studied for Cr(VI) bioaccumulation in free and immobilised cells to evaluate its applicability in chromium removal from aqueous solution. Based on the comparative analysis of the 16S rRNA gene, and phenotypic and biochemical characterization, this strain was identified as Paenibacillus xylanilyticus MR12. Mechanism of Cr adsorption was also ascertained by chemical modifications of the bacterial biomass followed by Fourier transform infrared spectroscopy analysis of the cell wall constituents. The equilibrium biosorption analysed using isotherms (Langmuir, Freundlich and Dubinin-Redushkevich) and kinetics models (pseudo-first-order, second-order and Weber-Morris) revealed that the Langmuir model best correlated to experimental data, and Weber-Morris equation well described Cr(VI) biosorption kinetics. Polyvinyl alcohol alginate immobilised cells had the highest Cr(VI) removal efficiency than that of free cells and could also be reused four times for Cr(VI) removal. Complete reduction of chromate in simulated effluent containing Cu(2+), Mg(2+), Mn(2+) and Zn(2+) by immobilised cells, demonstrated potential applications of a novel immobilised bacterial strain MR12, as a vital bioresource in Cr(VI) bioremediation technology.

Adsorption and Reduction of Hexavalent Chromium on the Surface of Vivianite at Acidic Environment

NASA Astrophysics Data System (ADS)

HA, S.; Hyun, S. P.; Lee, W.

2016-12-01

Due to the rapid increase of chemical use in industrial activities, acid spills have frequently occurred in Korea. The acid spill causes soil and water acidification and additional problems such as heavy metal leaching from the soil. Hexavalent chromium (Cr(VI)) is relatively mobile in the environment and toxic and mutagenic. Monoclinic octa-hydrated ferrous phosphate, vivianite, is one of commonly found iron-bearing soil minerals occurring in phosphorous-enriched reducing environments. We have investigated reductive sorption of Cr(VI) on the vivianite surfaces using batch experimental tests under diverse groundwater conditions. Cr(VI) (5 mg/L) was added in 6.5 g/L vivianite suspension buffered at pH 5, 7, and 9, using 0.05 M HEPES or tris buffer solution, to check the effect of pH on the reductive sorption of Cr(VI) on the vivianite surface. The aqueous Cr(VI) removal was fastest at pH 5, followed by pH 7, and pH 9. The effect of ionic strength on the removal kinetics of Cr(VI) was negligible. It could be subsequently removed via sorption and reduction on the surface of vivianite of which reactive chemical species could be aqueous Fe(II), iron oxides, and metavivianite. Adsorption test was conducted using the same amount of Cr(III) to check the selectivity of chromium species on the vivianite surface for the reductive adsorption. Through Cr extraction test, amount of strong-bound Cr to vivianite is similar for Cr(III) and Cr(VI) injection but amount of weak-bound Cr is bigger for Cr(VI) injection. Reaction mechanism for the sorption and reductive transformation of Cr(VI) to Cr(III) species at reactive sites of vivianite surface are discussed based on surface complexation modeling and K-edge Fe X-ray absorption near edge structure (XANES) results. Since vivianite is reacted with Cr(VI), two smooth peaks of absorption edge changed to one sharp peak. Pre-edge that contains 1s-3d transition information tends to show high peak when reaction time is increased and pH is low. This fact indicated that the Fe(II) is oxidized to Fe(III) at the surface of viviante and this phenomena is optimized at pH 5 and longer elapsed time.

Self-sustained reduction of multiple metals in a microbial fuel cell-microbial electrolysis cell hybrid system.

PubMed

Li, Yan; Wu, Yining; Liu, Bingchuan; Luan, Hongwei; Vadas, Timothy; Guo, Wanqian; Ding, Jie; Li, Baikun

2015-09-01

A self-sustained hybrid bioelectrochemical system consisting of microbial fuel cell (MFC) and microbial electrolysis cell (MEC) was developed to reduce multiple metals simultaneously by utilizing different reaction potentials. Three heavy metals representing spontaneous reaction (chromium, Cr) and unspontaneous reaction (lead, Pb and nickel, Ni) were selected in this batch-mode study. The maximum power density of the MFC achieved 189.4 mW m(-2), and the energy recovery relative to the energy storage circuit (ESC) was ∼ 450%. At the initial concentration of 100 mg L(-1), the average reduction rate of Cr(VI) was 30.0 mg L(-1) d(-1), Pb(II) 32.7 mg L(-1) d(-1), and Ni(II) 8.9 mg L(-1) d(-1). An electrochemical model was developed to predict the change of metal concentration over time. The power output of the MFC was sufficient to meet the requirement of the ESC and MEC, and the "self-sustained metal reduction" was achieved in this hybrid system. Published by Elsevier Ltd.

Enhancement strategies for Cu(II), Cr(III) and Cr(VI) remediation by a variety of seaweed species.

PubMed

Murphy, V; Hughes, H; McLoughlin, P

2009-07-15

Various chemical treatments have been applied to six brown, red and green seaweed species with a view to enhancing their metal removal for Cu(II), Cr(III) and Cr(VI). Treatment with acetone resulted in the greatest enhancement for both cationic and anionic species with relatively low mass losses (15-35%), indicating its low risk to biomass operational stability. Cation binding was increased by 69%, while the total Cr removal was augmented by 15%. Cr(VI) binding was shown to be an adsorption-coupled reduction, whereby Cr(VI) was bound to the biomass surface at pH 2 and subsequently reduced to Cr(III). Acetone treatment also resulted in biomasses that were capable of converting up to 83% of Cr(VI) in solution to Cr(III). Blocking of carboxyl and amino functionalities had significant negative effects both on total Cr removal as well as percentage conversion of Cr(VI) to Cr(III). Results therefore indicated the significant role played by these moieties in metal binding to these seaweeds. Potentiometric titrations displayed agreement between the degree of esterification and the decrease in Cu(II) removal for Ulva spp. and Polysiphonia lanosa. FTIR analysis identified changes in biomass functionality and availability after chemical modification, the results of which were in agreement with metal removal studies. In conclusion, these biosorbents represent suitable candidates to replace conventional removal technologies for metal bearing wastewaters, in particular for the detoxification of hazardous Cr(VI) waste streams.

Matrix isolation with an ion transfer device for interference-free simultaneous spectrophotometric determinations of hexavalent and trivalent chromium in a flow-based system.

PubMed

Ohira, Shin-Ichi; Nakamura, Koretaka; Chiba, Mitsuki; Dasgupta, Purnendu K; Toda, Kei

2017-03-01

Chromium speciation by spectrophotometric determination of hexavalent chromium (Cr(VI)) with diphenylcarbazide (DPC) has several problems. These include: (1) the inability to directly detect trivalent chromium (Cr(III)) with DPC, (2) positive interference in Cr(VI) determination by other metal cations and (3) negative interference by any reducing agent present in the sample. These are addressed with an ion transfer device (ITD) in a flow injection analysis system. We previously developed the ITD for electrodialytic separations. Here we separate oppositely charged Cr(III) and Cr(VI) species by the ITD into two different acceptor solutions within ~5 s. The acceptor solutions consist of buffered H 2 O 2 to oxidize the Cr(III) to Cr(VI). Then DPC is added to either acceptor to measure Cr(III) and Cr(VI) spectrophotometrically. The system was optimized to provide the same response for Cr(VI) and Cr(III) with limits of detection (LODs, S/N=3) of 0.5 μg L -1 for each and a throughput rate of 30 samples h -1 . The ITD separation was also effective for matrix isolation and reduction of interferences. Potential cationic interferences were not transferred into the anionic Cr(VI) acceptor stream. Much of the organic compounds in soil extracts were also eliminated as evidenced from standard addition and recovery studies. Copyright © 2016 Elsevier B.V. All rights reserved.

Chromium(III) and chromium(VI) release from leather during 8 months of simulated use.

PubMed

Hedberg, Yolanda S; Lidén, Carola

2016-08-01

Chromium (Cr) release from Cr-tanned leather articles is a major cause of Cr contact dermatitis. It has been suggested that Cr(VI) release from leather is not necessarily an intrinsic property of the leather, but is strongly dependent on environmental conditions. To test this hypothesis for long-term (8 months) simulated use. The release of total Cr and Cr(VI) from Cr-tanned, unfinished leather was analysed in subsequent phosphate buffer (pH 8.0) immersions for a period of 7.5 months. The effect of combined ultraviolet treatment and alkaline solution (pH 12.1) was tested. Dry storage [20% relative humidity (RH)] was maintained between immersions. Atomic absorption spectroscopy, X-ray fluorescence and diphenylcarbazide tests were used. Cr(VI) release was dependent on previous dry storage or alkaline treatment, but not on duration or number of previous immersions. Cr(III) release decreased with time. Fifty-two percent of the total Cr released during the last immersion period was Cr(VI). Cr(VI) release exceeded 9 mg/kg in all immersion periods except in the first 10-day immersion (2.6 mg/kg). Cr(VI) release is primarily determined by environmental factors (RH prior to immersion, solution pH, and antioxidant content). The RH should be kept low prior to testing Cr(VI) release from leather. © 2016 The Authors. Contact Dermatitis published by John Wiley & Sons Ltd.

Correlation between bulk- and surface chemistry of Cr-tanned leather and the release of Cr(III) and Cr(VI).

PubMed

Hedberg, Yolanda S; Lidén, Carola; Odnevall Wallinder, Inger

2014-09-15

About 1-3% of the adult general population in Europe is allergic to chromium (Cr). The assessment of the potential release of Cr(III) and Cr(VI) from leather is hence important from a human health and environmental risk perspective. The Cr(VI) content in leather was recently restricted in the European Union. The aim of this study was to assess possible correlations between the bulk and surface chemistry of leather, released Cr(III) and Cr(VI), and capacities of co-released leather specific species to reduce and complex released Cr. Four differently tanned leathers were characterized by scanning electron microscopy with energy dispersive spectroscopy, X-ray photoelectron spectroscopy, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and the diphenylcarbazide colorimetric method. Their characteristics were compared with results on Cr(III) and Cr(VI) release into artificial sweat (ASW, pH<6.5) and phosphate buffer (PB, pH 7.5-8.0), measured by means of spectrophotometry and atomic absorption spectroscopy. Co-released leather-specific species were shown to reduce Cr(VI), both in ASW and in PB. Their reduction capacities correlated with findings of the surface content of Cr and of released Cr. Leather samples without this capacity, and with less aromatic surface groups visible by ATR-FTIR, revealed Cr(VI) both at the surface and in solution (PB). Copyright © 2014 The Authors. Published by Elsevier B.V. All rights reserved.

Enhanced removal of Cr(VI) from aqueous solution by supported ZnO nanoparticles on biochar derived from waste water hyacinth.

PubMed

Yu, Jiangdong; Jiang, Chunyan; Guan, Qingqing; Ning, Ping; Gu, Junjie; Chen, Qiuling; Zhang, Junmin; Miao, Rongrong

2018-03-01

Biochar derived from waste water hyacinth was prepared and modified by ZnO nanoparticles for Cr(VI) removal from aqueous solution with the aim of Cr(VI) removal and management of waste biomass. The effect of carbonization temperature (500-800 °C), ZnO content (10-50 wt%) loaded on biochar and contact time (0.17-14 h) on the Cr(VI) removal were investigated. It was found that higher than 95% removal efficiency of Cr(VI) can be achieved with the biochar loaded 30 wt% ZnO. The adsorption kinetics of the sorbent is consistent with the pseudo-second-order kinetic model and adsorption isotherm follows the Langmuir model with maximum adsorption capacity of 43.48 mg g -1 for Cr(VI). Multiple techniques such as XRD, XPS, SEM, EDX and FT-IR were performed to investigate the possible mechanisms involved in the Cr (VI) adsorption. The results show that there is precipitation between chromium ions and Zn oxide. Furthermore, the ZnO nanoparticles acts as photo-catalyst to generate photo-generated electrons to enhance the reduction of Cr(VI) to Cr(III). The as-prepared ZnO/BC possess good recyclability and the removal ratio remained at about 70% in the fifth cycle, which suggests that both contaminants removal and effective management of water hyacinth can be achieved by the approach. Copyright © 2017 Elsevier Ltd. All rights reserved.

Chromium VI and stomach cancer: a meta-analysis of the current epidemiological evidence.

PubMed

Welling, Roberta; Beaumont, James J; Petersen, Scott J; Alexeeff, George V; Steinmaus, Craig

2015-02-01

Chromium VI (hexavalent chromium, Cr(VI)) is an established cause of lung cancer, but its association with gastrointestinal cancer is less clear. The goal of this study was to examine whether the current human epidemiological research on occupationally inhaled Cr(VI) supports the hypothesis that Cr(VI) is associated with human stomach cancer. Following a thorough literature search and review of individual studies, we used meta-analysis to summarise the current epidemiological literature on inhaled Cr(VI) and stomach cancer, explore major sources of heterogeneity, and assess other elements of causal inference. We identified 56 cohort and case-control studies and 74 individual relative risk (RR) estimates on stomach cancer and Cr(VI) exposure or work in an occupation associated with high Cr(VI) exposure including chromium production, chrome plating, leather work and work with Portland cement. The summary RR for all studies combined was 1.27 (95% CI 1.18 to 1.38). In analyses limited to only those studies identifying increased risks of lung cancer, the summary RR for stomach cancer was higher (RR=1.41, 95% CI 1.18 to 1.69). Overall, these results suggest that Cr(VI) is a stomach carcinogen in humans, which is consistent with the tumour results reported in rodent studies. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

Hexavalent chromium reduction by bacterial consortia and pure strains from an alkaline industrial effluent.

PubMed

Piñón-Castillo, H A; Brito, E M S; Goñi-Urriza, M; Guyoneaud, R; Duran, R; Nevarez-Moorillon, G V; Gutiérrez-Corona, J F; Caretta, C A; Reyna-López, G E

2010-12-01

To characterize the bacterial consortia and isolates selected for their role in hexavalent chromium removal by adsorption and reduction. Bacterial consortia from industrial wastes revealed significant Cr(VI) removal after 15 days when incubated in medium M9 at pH 6·5 and 8·0. The results suggested chromium reduction. The bacterial consortia diversity (T-RFLP based on 16S rRNA gene) indicated a highest number of operational taxonomic units in an alkaline carbonate medium mimicking in situ conditions. However, incubations under such conditions revealed low Cr(VI) removal. Genomic libraries were obtained for the consortia exhibiting optimal Cr(VI) removal (M9 medium at pH 6·5 and 8·0). They revealed the dominance of 16S rRNA gene sequences related to the genera Pseudomonas/Stenotrophomonas or Enterobacter/Halomonas, respectively. Isolates related to Pseudomonas fluorescens and Enterobacter aerogenes were efficient in Cr(VI) reduction and adsorption to the biomass. Cr(VI) reduction was better at neutral pH rather than under in situ conditions (alkaline pH with carbonate). Isolated strains exhibited significant capacity for Cr(VI) reduction and adsorption. Bacterial communities from chromium-contaminated industrial wastes as well as isolates were able to remove Cr(VI). The results suggest a good potential for bioremediation of industrial wastes when optimal conditions are applied. Journal of Applied Microbiology © 2010 The Society for Applied Microbiology. No claim to Mexican Government works.

Contemplating the feasibility of vermiculate blended chitosan for heavy metal removal from simulated industrial wastewater

NASA Astrophysics Data System (ADS)

Prakash, N.; Soundarrajan, M.; Arungalai Vendan, S.; Sudha, P. N.; Renganathan, N. G.

2017-12-01

Wastewater contaminated by heavy metals pose great challenges as they are non biodegradable, toxic and carcinogenic to the soil and aquifers. Vermiculite blended with chitosan have been used to remove Cr(VI) and Cd(II) from the industrial wastewater. The results indicate that the vermiculite blended with chitosan adsorb Cr(VI) and Cd(II) from industrial waste water. Batch adsorption experiments were performed as a function of pH 5.0 and 5.5 respectively for chromium and cadmium. The adsorption rate was observed to be 72 and 71 % of chromium and cadmium respectively. The initial optimum contact time for Cr(VI) was 300 min with 59.2 % adsorption and 300 min for Cd(II) with 71.5 % adsorption. Whereas, at 4-6 there is saturation, increasing the solid to liquid ratio for chitosan biopolymers increases the number of active sites available for adsorption. The optimum pH required for maximum adsorption was found to be 5.0 and 5.5 for chromium and cadmium respectively. The experimental equilibrium adsorption data were fitted using Langmuir and Freundlich equations. It was observed that adsorption kinetics of both the metal ions on vermiculite blended chitosan is well be analyzed with pseudo-second-order model. The negative free energy change of adsorption indicates that the process was spontaneous and vermiculite blended chitosan was a favourable adsorbent for both the metals.

Differential Isotopic Fractionation during Cr(VI) Reduction by an Aquifer-Derived Bacterium under Aerobic versus Denitrifying Conditions

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

Han, R.; Qin, L.; Brown, S. T.

2012-01-27

We studied Cr isotopic fractionation during Cr(VI) reduction by Pseudomonas stutzeri strain RCH2. Finally, despite the fact that strain RCH2 reduces Cr(VI) cometabolically under both aerobic and denitrifying conditions and at similar specific rates, fractionation was markedly different under these two conditions (ε was ~2‰ aerobically and ~0.4‰ under denitrifying conditions).

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

Wu, Fen; Sun, Hong; Kluz, Thomas

Hexavalent chromium [Cr(VI)] is a human carcinogen that results in the generation of reactive oxygen species (ROS) and a variety of DNA lesions leading to cell death. Epigallocatechin-3-gallate (EGCG), the major polyphenol present in green tea, possesses potent antioxidative activity capable of protecting normal cells from various stimuli-induced oxidative stress and cell death. Here we demonstrated that co-treatment with EGCG protected human normal bronchial epithelial BEAS-2B cells from Cr(VI)-induced cell death in a dose-dependent manner. Cr(VI) induces apoptosis as the primary mode of cell death. Co-treatment of BEAS-2B cells with EGCG dose-dependently suppressed Cr(VI)-induced apoptosis. Fluorescence microscopic analyses and quantitativemore » measurement revealed that EGCG significantly decreased intracellular levels of ROS induced by Cr(VI) exposure. Using a well-established K{sup +}/SDS precipitation assay, we further showed that EGCG was able to dose-dependently reduce DNA–protein cross-links (DPC), lesions that could be partially attributed to Cr(VI)-induced oxidative stress. Finally, analyses of Affymetrix microarray containing 28,869 well-annotated genes revealed that, among the 3412 genes changed more than 1.5-fold by Cr(VI) treatment, changes of 2404 genes (70%) were inhibited by pretreatment of EGCG. Real-time PCR confirmed the induction of 3 genes involved in cell death and apoptosis by Cr(VI), which was eliminated by EGCG. In contrast, Cr(VI) reduced the expression of 3 genes related to cellular defense, and this reduction was inhibited by EGCG. Our results indicate that EGCG protects BEAS-2B cells from Cr(VI)-induced cytotoxicity presumably by scavenging ROS and modulating a subset of genes. EGCG, therefore, might serve as a potential chemopreventive agent against Cr(VI) carcinogenesis. -- Highlights: ► EGCG protected human normal bronchial epithelial BEAS-2B cells from Cr(VI)-induced cell death and apoptosis. ► EGCG significantly decreased intracellular levels of ROS induced by Cr(VI) exposure. ► EGCG reduced DNA-protein cross-links, lesions that could be partially attributed to Cr(VI)-induced oxidative stress. ► EGCG modulated 70% of the gene expression changes induced by Cr(VI) exposure.« less

Genesis of hexavalent chromium from natural sources in soil and groundwater.

PubMed

Oze, Christopher; Bird, Dennis K; Fendorf, Scott

2007-04-17

Naturally occurring Cr(VI) has recently been reported in ground and surface waters. Rock strata rich in Cr(III)-bearing minerals, in particular chromite, are universally found in these areas that occur near convergent plate margins. Here we report experiments demonstrating accelerated dissolution of chromite and subsequent oxidation of Cr(III) to aqueous Cr(VI) in the presence of birnessite, a common manganese mineral, explaining the generation of Cr(VI) by a Cr(III)-bearing mineral considered geochemically inert. Our results demonstrate that Cr(III) within ultramafic- and serpentinite-derived soils/sediments can be oxidized and dissolved through natural processes, leading to hazardous levels of aqueous Cr(VI) in surface and groundwater.

Genesis of hexavalent chromium from natural sources in soil and groundwater

PubMed Central

Oze, Christopher; Bird, Dennis K.; Fendorf, Scott

2007-01-01

Naturally occurring Cr(VI) has recently been reported in ground and surface waters. Rock strata rich in Cr(III)-bearing minerals, in particular chromite, are universally found in these areas that occur near convergent plate margins. Here we report experiments demonstrating accelerated dissolution of chromite and subsequent oxidation of Cr(III) to aqueous Cr(VI) in the presence of birnessite, a common manganese mineral, explaining the generation of Cr(VI) by a Cr(III)-bearing mineral considered geochemically inert. Our results demonstrate that Cr(III) within ultramafic- and serpentinite-derived soils/sediments can be oxidized and dissolved through natural processes, leading to hazardous levels of aqueous Cr(VI) in surface and groundwater. PMID:17420454

Chromium reduces the in vitro activity and fidelity of DNA replication mediated by the human cell DNA synthesome

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

Dai Heqiao; Liu Jianying; Malkas, Linda H.

2009-04-15

Hexavalent chromium Cr(VI) is known to be a carcinogenic metal ion, with a complicated mechanism of action. It can be found within our environment in soil and water contaminated by manufacturing processes. Cr(VI) ion is readily taken up by cells, and is recognized to be both genotoxic and cytotoxic; following its reduction to the stable trivalent form of the ion, chromium(Cr(III)), within cells. This form of the ion is known to impede the activity of cellular DNA polymerase and polymerase-mediated DNA replication. Here, we report the effects of chromium on the activity and fidelity of the DNA replication process mediatedmore » by the human cell DNA synthesome. The DNA synthesome is a functional multiprotein complex that is fully competent to carry-out each phase of the DNA replication process. The IC{sub 50} of Cr(III) toward the activity of DNA synthesome-associated DNA polymerases {alpha}, {delta} and {epsilon} is 15, 45 and 125 {mu}M, respectively. Cr(III) inhibits synthesome-mediated DNA synthesis (IC{sub 50} = 88 {mu}M), and significantly reduces the fidelity of synthesome-mediated DNA replication. The mutation frequency induced by the different concentrations of Cr(III) ion used in our assays ranges from 2-13 fold higher than that which occurs spontaneously, and the types of mutations include single nucleotide substitutions, insertions, and deletions. Single nucleotide substitutions are the predominant type of mutation, and they occur primarily at GC base-pairs. Cr(III) ion produces a lower number of transition and a higher number of transversion mutations than occur spontaneously. Unlike Cr(III), Cr(VI) ion has little effect on the in vitro DNA synthetic activity and fidelity of the DNA synthesome, but does significantly inhibit DNA synthesis in intact cells. Cell growth and proliferation is also arrested by increasing concentrations of Cr(VI) ion. Our studies provide evidence indicating that the chromium ion induced decrease in the fidelity and activity of synthesome mediated DNA replication correlates with the genotoxic and cytotoxic effects of this metal ion; and promotes cell killing via inhibition of the DNA polymerase activity mediating the DNA replication and repair processes utilized by human cells.« less

Chromium reduces the in vitro activity and fidelity of DNA replication mediated by the human cell DNA synthesome

PubMed Central

Dai, Heqiao; Liu, Jianying; Malkas, Linda H.; Catalano, Jennifer; Alagharu, Srilakshmi; Hickey, Robert J.

2009-01-01

Hexavalent chromium Cr(VI) is known to be a carcinogenic metal ion, with a complicated mechanism of action. It can be found within our environment in soil and water contaminated by manufacturing processes. Cr(VI) ion is readily taken up by cells, and is recognized to be both genotoxic and cytotoxic; following its reduction to the stable trivalent form of the ion, chromium(Cr(III)), within cells. This form of the ion is known to impede the activity of cellular DNA polymerase and polymerase-mediated DNA replication. Here, we report the effects of chromium on the activity and fidelity of the DNA replication process mediated by the human cell DNA synthesome. The DNA synthesome is a functional multiprotein complex that is fully competent to carry-out each phase of the DNA replication process. The IC50 of Cr(III) toward the activity of DNA synthesome-associated DNA polymerases α, δ and ε is 15, 45 and 125 μM, respectively. Cr(III) inhibits synthesome-mediated DNA synthesis (IC50 =88 μM), and significantly reduces the fidelity of synthesome-mediated DNA replication. The mutation frequency induced by the different concentrations of Cr(III) ion used in our assays ranges from 2–13 fold higher than that which occurs spontaneously, and the types of mutations include single nucleotide substitutions, insertions, and deletions. Single nucleotide substitutions are the predominant type of mutation, and they occur primarily at GC base-pairs. Cr(III) ion produces a lower number of transition and a higher number of transversion mutations than occur spontaneously. Unlike Cr (III), Cr(VI) ion has little effect on the in vitro DNA synthetic activity and fidelity of the DNA synthesome, but does significantly inhibit DNA synthesis in intact cells. Cell growth and proliferation is also arrested by increasing concentrations of Cr(VI) ion. Our studies provide evidence indicating that the chromium ion induced decrease in the fidelity and activity of synthesome mediated DNA replication correlates with the genotoxic and cytotoxic effects of this metal ion; and promotes cell killing via inhibition of the DNA polymerase activity mediating the DNA replication and repair processes utilized by human cells. PMID:19371627

Catalytic reduction of hexavalent chromium by a novel nitrogen-functionalized magnetic ordered mesoporous carbon doped with Pd nanoparticles.

PubMed

Li, Sisi; Tang, Lin; Zeng, Guangming; Wang, Jiajia; Deng, Yaocheng; Wang, Jingjing; Xie, Zhihong; Zhou, Yaoyu

2016-11-01

Hexavalent chromium Cr(VI) is a toxic water pollutant which can cause serious influence to the health of the human and animals. Therefore, developing new methods to remove hexavalent chromium in water attracts great attention of scholars. In our research, we successfully synthesized a new type of magnetic mesoporous carbon hybrid nitrogen (Fe-NMC) loaded with catalyst Pd nanoparticles (NPs), which performed excellent catalytic reduction efficiency toward Cr(VI). The characterization of Pd/Fe-NMC composite was investigated in detail using scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), and nitrogen adsorption-desorption measurements. According to the experimental results, we dealt with in-depth discussion and studied on the mechanism of hexavalent chromium removed by Pd/Fe-NMC composite. Furthermore, the batch experiments were conducted to investigate the catalytic reduction ability of composite. It was found that the chromium reduction process conforms to pseudo-first-order reaction kinetics model when the concentrations of chromium and sodium formate were low. It took only 20 min for the Pd/Fe-NMC composite to reach 99.8 % reduction of Cr(VI) (50 mg/L). The results suggested that the Pd/Fe-NMC composite may exhibit significantly improved catalytic activity for the hexavalent chromium reduction at industrial wastewater.

Electrophoretic deposition of carbon nanotube on reticulated vitreous carbon for hexavalent chromium removal in a biocathode microbial fuel cell.

PubMed

Fei, Kangqing; Song, Tian-Shun; Wang, Haoqi; Zhang, Dalu; Tao, Ran; Xie, Jingjing

2017-10-01

For Cr(VI)-removal microbial fuel cell (MFC), a more efficient biocathode in MFCs is required to improve the Cr(VI) removal and electricity generation. RVC-CNT electrode was prepared through the electrophoretic deposition of carbon nanotube (CNT) on reticulated vitreous carbon (RVC). The power density of MFC with an RVC-CNT electrode increased to 132.1 ± 2.8 mW m -2 , and 80.9% removal of Cr(VI) was achieved within 48 h; compared to only 44.5% removal of Cr(VI) in unmodified RVC. Cyclic voltammetry, energy-dispersive spectrometry and X-ray photoelectron spectrometry showed that the RVC-CNT electrode enhanced the electrical conductivity and the electron transfer rate; and provided more reaction sites for Cr(VI) reduction. This approach provides process simplicity and a thickness control method for fabricating three-dimensional biocathodes to improve the performance of MFCs for Cr(VI) removal.