Toxic Trivalent Chromium Research Articles

Identification of Chromium Resistant Bacteria from Dry Fly Ash Sample of Mejia MTPS Thermal Power Plant, West Bengal, India.

Eight chromium resistant bacteria were isolated from a dry fly ash sample of DVC-MTPS thermal power plant located in Bankura, West Bengal, India. These isolates displayed different degrees of chromate reduction under aerobic conditions. According to 16S rDNA gene analysis, five of them were Staphylococcus, two were Bacillus and one was Micrococcus. The minimum inhibitory concentration towards chromium and the ability to reduce hexavalent chromium to trivalent chromium was highest in Staphylococcus haemolyticus strain HMR17. All the strains were resistant to multiple heavy metals (As, Cu, Cd, Co, Zn, Mn, Pb and Fe) and reduced toxic hexavalent chromium to relatively non toxic trivalent chromium even in the presence of these multiple heavy metals. All of them showed resistance to different antibiotics. In a soil microcosm study, S. haemolyticus strain HMR17 completely reduced 4 mM hexavalent chromium within 7 days of incubation.

Detoxification of hexavalent chromium by Leucobacter sp. uses a reductase with specificity for dihydrolipoamide.

Leucobacter sp. belongs to the metal stressed community and possesses higher tolerance to metals including chromium and can detoxify toxic hexavalent chromium by reduction to less toxic trivalent chromium. But, the mechanism of reduction of hexavalent chromium by Leucobacter sp. has not been studied. Understanding the enzyme catalyzing reduction of chromium is important to improve the species for application in bioremediation. Hence, a soluble reductase catalyzing the reduction of hexavalent chromium was purified from a Leucobacter sp. and characterized. The pure chromate reductase was obtained from the cell-free extract through hydrophobic interaction and gel filtration column chromatographic methods. It was a monomeric enzyme and showed similar molecular weights in both gel filtration (∼68 KDa) and SDS-PAGE (64 KDa). It reduced Cr(VI) using both NADH and NADPH as the electron donor, but exhibited higher activity with NADH. The optimal activity was found at pH 5.5 and 30 °C. The K(m) and V(max) for Cr(VI) reduction with NADH were 46.57 μM and 0.37 μmol min(-1) (mg protein) (-1), respectively. The activity was inhibited by p-hydroxy mercury benzoate, Ag(2+) and Hg(2+) indicating the role of thiol groups in the catalysis. The spectrophotometric analysis of the purified enzyme showed the absence of bound flavin in the enzyme. The N-terminal amino acid sequence and LC/MS analysis of trypsin digested purified enzyme showed similarity to dihydrolipoyl dehydrogenase. The purified enzyme had dihydrolipoyl dehydrogenase activity with dihydrolipoamide as the substrate, which suggested that Leucobacter sp. uses reductase with multiple substrate specificity for reduction of Cr(VI) detoxification.

Use of Experimental Factorial Design for Optimization of Hexavalent Chromium Removal by a Bacterial Consortium: Soil Microcosm Bioremediation

Hexavalent chromium Cr(VI) is regularly introduced into the environment through diverse anthropogenic activities. It is highly toxic, mutagenic and carcinogenic, and because of its solubility in water, chromate contamination can be difficult to contain. Bacteria can reduce chromate to insoluble and less toxic trivalent chromium Cr(III), and thus increasing attention is paid to chromate bioremediation to reduce its ecotoxicological impacts. In this study, the factorial design 23 was employed to optimize critical parameters responsible for higher Cr(VI) removal by a bacterial consortium. The factors considered were pH, temperature, and inoculum size at two markedly different levels. All three dependent variables have significant effect on Cr(VI) reduction. Optimal Cr(VI) removal by the bacterial consortium occurred at pH 9, temperature 37°C, and inoculum size OD = 3. Analysis of variance (ANOVA) showed a high coefficient of determination (R2) value of 0.984, thus ensuring a satisfactory adjustment of the second-order regression model with the experimental data. In addition, the effect of bioaugmentation of Cr(VI)-polluted soil microcosms with the bacterial consortium was investigated using the best factor levels. Contaminated soil by 20 and 60 mg/Kg of Cr(VI) showed reductions of 83% and 65% of initial Cr(VI) by the bacterial consortium, suggesting that this bacterial consortium might diminish phytoavailable Cr(VI) in soil and be useful for cleaning up chromium-contaminated sites.

Surfactant-assisted enhancement of bioremediation rate for hexavalent chromium by water extract of Sajina (Moringa oleifera) flower

The presence of hexavalent chromium in waste water is a serious environmental problem due to its toxicity and carcinogenicity. Bioremediation is an efficient alternative to the conventional chemical methods of treatment. Bioremediation of toxic hexavalent chromium is done by the reduction of hexavalent chromium to relatively less toxic trivalent chromium. In this study, water extract of Sajina flower, which contains different types of reducing components such as sugar, amino acid, is used as reductant and the rate of bioremediation is increased by treatment with anionic and neutral surfactants. Here surfactants are used as catalyst in the bioremediation process. Sodiumdodecyl sulfate (SDS) is found to be the best catalyst. In the absence of surfactants, 60.37% of the total chromium(VI) is reduced within 285 h, whereas the removal percentage increases up to 96.25 and 99.37% in the presence of TX-100 and SDS, respectively, in minimum time.

Stability of biologically reduced chromium in soil

A large number of previous studies demonstrate that bacteria are able to transform hexavalent chromium (Cr(VI)) to less toxic trivalent chromium that is stabilized within soil rather than dissolved in groundwater. However, concern persists about the long-term stability of the chromium in these insoluble forms. The goal of this study was to determine the stability of chromium within soil after biotreatment. Laboratory columns packed with highly contaminated soil from a chromium plating site were used to simulate in situ conditions. Molasses, nitrate, and/or sulfate were added to artificial groundwater (GW) in order to stimulate naturally occurring bacteria in the soil to transform Cr(VI). Carbon consumption, nitrate reduction, and hydraulic conductivity decreases provided evidence of bioactivity as the main cause of reduced effluent Cr(VI) compared to columns without carbon and/or nitrate addition. Subsequent flushing of the biostabilized soil for 12–15 days with unamended GW maintained effluent Cr(VI) below 100μg/L compared to conditions without molasses addition where the effluent Cr(VI) concentrations always exceeded 655μg/L. In batch tests after biotreatment, the soil was equilibrated with three different types of aqueous solutions in order to determine the stability of the chromium. Equilibrium aqueous chromium concentrations were the lowest from the soil that was removed from columns treated with carbon and nitrate addition. The results demonstrate that biological activity stimulated by carbon and nitrate addition resulted in significant chromium stabilization to forms that were not readily desorbed from the soil.

Biochemical Treatment of Hydraulically Complex Hexavalent Chromium and Chlorinated Volatile Organic Plumes

AbstractGroundwater contaminated with hexavalent chromium (Cr+6) and chlorinated volatile organic compounds (cVOCs) presents unique in situ remedial challenges in an oxygen‐rich environment. On one hand, chemical oxidation would be effective in treating the cVOCs; however, it would not be appropriate to treat Cr+6. Biological treatment may be appropriate to treat the Cr+6; however, the cVOC degradation pathway within these mixed plumes is currently following an abiotic pathway with little to no daughter‐product production. Thus, a blended approach was needed to treat both constituents in situ in an effort to avoid a long‐term, costly pump‐and‐treat solution. This article evaluates an in situ biogeochemical stabilization/reduction strategy by injecting an inorganic carbon‐based remedial additive into the geologic and hydrogeologic environment to decrease concentrations within the commingled Cr+6 and cVOC plume. The concept involves creating favorable redox reducing conditions to shift the groundwater geochemical equilibrium from the more toxic Cr+6 to the less toxic trivalent chromium (Cr+3), with the final outcome being a conversion to chrome oxide that molecularly fixes to the soil grains. In addition, reducing conditions developed for chromium reduction should result in an increase in the available natural formation iron that should further enhance the natural abiotic reduction of cVOCs. © 2013 Wiley Periodicals, Inc.

Electrokinetic Enhanced Transport of Zero Valent Iron Nanoparticles for Chromium (vi) Reduction in Soils

Zero valent iron nanoparticles (nZVI) are a promising technology that could provide cost-effective solutions to soil and groundwater remediation. However, transport of nZVI is normally limited by their aggregation and settling, and with mobility being normally less than a few meters.The main research objective of this study is to find out if coupling electrokinetics and reactive iron nanoparticles can be an effective method for treating chromium contaminated clay soils. Direct current was used to enhance poly(acrylic acid), sodium salt (PAA) coated iron nanoparticles (PAA-nZVI) mobility in Cr(VI) spiked kaolin.A commercially available electrophoretic cell was modified for these experiments and equipped with internal auxiliary electrodes that allow to measure the redox potential directly in the clay. A constant potential of 5.0 V wasapplied across the test bed. Experimental results show that electrokinetics can enhance the delivery of nanoscale iron particles for the reduction of hexavalent chromium to the less toxic trivalent chromium. Direct current enhanced nZVI transport up to 74 % when compared with diffusion, maximum value found when comparing iron concentrations ratios. Activation of nZVI was also observed with a decrease in the redox potential of 531 mV, in average, after the injection point.

Isolation and characterization of an NAD+-degrading bacterium PTX1 and its role in chromium biogeochemical cycle

Microorganisms can reduce toxic chromate to less toxic trivalent chromium [Cr(III)]. Besides Cr(OH)(3) precipitates, some soluble organo-Cr(III) complexes are readily formed upon microbial, enzymatic, and chemical reduction of chromate. However, the biotransformation of the organo-Cr(III) complexes has not been characterized. We have previously reported the formation of a nicotinamide adenine dinucleotide (NAD(+))-Cr(III) complex after enzymatic reduction of chromate. Although the NAD(+)-Cr(III) complex was stable under sterile conditions, microbial cells were identified as precipitates in a non-sterile NAD(+)-Cr(III) solution after extended incubation. The most dominant bacterium PTX1 was isolated and assigned to Leifsonia genus by phylogenetic analysis of 16S rRNA gene sequence. PTX1 grew slowly on NAD(+) with a doubling time of 17 h, and even more slowly on the NAD(+)-Cr(III) complex with an estimated doubling time of 35 days. The slow growth suggests that PTX1 passively grew on trace NAD(+) dissociated from the NAD(+)-Cr(III) complex, facilitating further dissociation of the complex and formation of Cr(III) precipitates. Thus, organo-Cr(III) complexes might be an intrinsic link of the chromium biogeochemical cycle; they can be produced during chromate reduction and then further mineralized by microorganisms.

Application of a by-product of Lentinus edodes to the bioremediation of chromate contaminated water

The agricultural by-product of Lentinus edodes was used as a novel biosorbent for bioremediation of chromate contaminated waste water in the simulated experimental conditions. The contact time, particle size, biosorbent dosage and optimum pH range were investigated to optimize the sorption condition. The biosorption by the biomass was strongly affected by pH. At pH 1.0–2.5, all hexavalent chromium was diminished, either removed by the biosorbent or reduced to less toxic trivalent chromium even in very high concentration of 1000 mg/L. The adsorbed hexavalent chromium and reduced trivalent chromium were both linearly dependent on the initial chromium concentration. Most uptake of Cr occurred at pH around 4. The maximum uptake of chromium was 21.5 mg/g when simulated with Langmuir model, which showed the potential biosorption capacity of this biomaterial. The change of oxidation–reduction potential (ORP) during biosorption process revealed strong reduction ability of this biosorbent. Comparing analysis from Fourier transform infrared spectrums indicated that nitrogen oxide and carboxyl groups were increased after biosorption. The energy-dispersive X-ray microanalyzer revealed the mechanism of cation exchange during biosorption.

Various cells of the immune system and intestine differ in their capacity to reduce hexavalent chromium

The cells of the immune system form a strong line of defence against foreign substances. The present study was undertaken to investigate the capacity of different cells of Wistar rats to reduce potentially carcinogenic hexavalent chromium (Cr-VI) into less toxic trivalent chromium in vitro. 5×10 6 cells were incubated with 10 or 25 μg ml −1 of Cr (VI) in the form of K 2Cr 2O 7 at 37°C in the presence of 5% CO 2 in air. At various time periods the remaining amount of Cr (VI) was measured and the percentage of Cr (VI) reduced was calculated. Among the single cell suspensions from the splenic cells a peak reduction of 55% was observed with the total spleen cells, 40% with the B-lymphocyte-enriched subpopulation, 10% with T-lymphocytes and 24% with the macrophages. The reduction by splenic and peritoneal macrophages was similar. Total thymocytes reduced 54% of the Cr (VI). Since the most common route of entry of chromium is through drinking water and food, intestinal cells were also investigated. Among the intestinal cells the maximum reduction of 100% (of 10 μg ml −1) was observed with the upper villus cells and 72% with the middle villus cells while reduction was the least (4%) with the crypt cells. The reduction in the intestinal loop in situ was 100%. The time taken by each cell type for the peak reduction to Cr (VI) was markedly different. The findings thus show that the capacity of different cells in the body differs vastly in their capacity and time taken to reduce hexavalent chromium. The most efficient handling of Cr (VI) by the intestine, due to the presence of a variety of cells and bacteria, protects the body from its adverse effects.

The removal of toxic metals from liquid effluents by ion exchange resins. Part I: Chromium(VI)/Sulphate/Dowex 1x8

The removal of chromium (VI) from sulphuric acid solutions using the Dowex 1x8 resin has been investigated. The influence of several variables such as the stirring speed, temperature, the sulphuric acid and metal concentrations in the aqueous phase and the variation of the amount of resin added has been studied. Various aqueous solutions were used for the elution of the metal. Although concentrated nitric acid elutes chromium, this can be best accomplished using hydrazine sulphate solutions which at the same time reduce the toxic Cr (VI) to the less toxic trivalent chromium state. Results obtained from batch experiments were applied to a continuous system using vertical columns. Moreover, an analytical application of the system in the determination of Cr (VI) presents in the leachate of an EAF dust was investigated by transfering the methodology to an on-line flow injection system.

Reduction of toxic chromate in an industrial effluent by use of a chromate‐reducing strain ofEnterobacter cloacae

Abstract Detoxification and removal of hexavalent chromium (chromate: CrO4 2−) in an industrial effluent was investigated using Enterobacter cloacae HO1. This bacterium could completely reduce chromate to less toxic trivalent chromium when appropiate nutrients were supplied to the effluent. The reduction rate was strongly dependent on the amount of added carbon and energy sources, and also on cell density. Since the reduced chromium readily formed insoluble chromium hydroxides, about 40% of the reduced chromium could be removed from the treated water by centrifugation.

Effect of cysteine on chromate resistance in the yeast Saccharomyces cerevisiae.

Saccharomyces cerevisiae strains defective in cysteine biosynthesis were more sensitive to chromate than their corresponding isogenic prototrophic strains. Chromate sensitivity of the cysteine-dependent strains was reduced when L-cysteine was added to the growth medium. The effect of L-cysteine on chromate sensitivity was, however, not specific to the cysteine-dependent strains but was general to all strains tested. That is, addition of L-cysteine to the growth medium containing chromate caused an increase of colony-forming ability of chromate-sensitive, normal and chromate-resistant strains. It was also shown that L-cysteine nonbiologically consumed chromate. From these results, we conclude that cysteine plays an essential role in defence of cells against chromate. We contend that cysteine chemically reduces toxic hexavalent chromium to less toxic trivalent chromium; detoxication of chromate by this mechanism takes place intracellularly as well as extracellularly.

Toxicity of trivalent chromium to early life stages of steelhead trout

AbstractAcute and early life stage toxicity tests were conducted with trivalent chromium and steelhead trout (Salmo gairdneri). A 96‐h LC50 of 4,400 μg/L chromium was obtained with two‐month‐old juvenile fish. Early life stage exposure from newly fertilized eggs to 30‐d post‐swimup produced complete mortality at 495 μg/L, and significantly reduced survival to hatch and to the end of the test at 157 and 89 μg/L, respectively. An early life stage test started with eyed eggs produced similar results, with hatching survival significantly reduced at 271 μg/L. An acute test conducted with fish surviving the early life stage test showed that no acclimation resulted from previous chromium exposure.

Persistence of four pyrethroid insecticides in a mineral and an organic soil.

Permethrin, cypermethrin, fenpropanate and fenvalerate (emulsifiable concentrates) were applied at 280 g AI/ha and incorporated into mineral and organic soil contained in small field plots. Radishes and carrots were grown to serve as indicators of insecticide uptake. Similar plots were treated with the same insecticides at 140 g AI/ha and the soil surface was left undisturbed following application. Soil cores were removed at appropriate intervals and the crops were harvested when mature. The insecticide concentration in all samples was determined by gas-liquid chromatography. The amount of insecticide in the soil declined rapidly to less than 50% of the initial value in 1 month or less for most material-soil-treatment combinations and within 2 months for all cases. Concentrations remained in excess of 0.01 ppm in the organic soil for at least six months for all material-treatment combinations but fell below this level over 2-5 months in the mineral soils. Organic soil incorporated fenvalerate was the most persistent combination overall with 25, 17 and 7% remaining at 6, 18 and 28 months respectively. The trans-isomers of permethrin and cypermethrin disappeared more quickly than the cis-isomers but the insecticidally active IR isomers were not preferentially degraded relative to the inactive 1S. No residues (less than 0.01 ppm) were found in the radish or carrot crops. First order disappearance rates were not constant for any of the combinations. A comparison of partial rate constants showed: 1) 0-1 mo rates were generally greater in mineral than organic soil, 2) 1-6 mo rates in organic soil were lower than 0-1 mo rates, 3) 1-6 mo rates for surface applications to organic soil were generally less than for incorporated applications. In laboratory experiments, 0-1 mo rates for fenvalerate disappearance in a mineral soil were 2-3x greater for 0.5 ppm than for 10 ppm while 1-6 mo rates were independent of insecticide concentration but were 1.5x greater for 0.5% moisture than for 5%.