Hexavalent Chromium Contamination Research Articles

Chromium contamination accentuates changes in the microbiome and heavy metal resistome of a tropical agricultural soil.

The impacts of hexavalent chromium (Cr) contamination on the microbiome, soil physicochemistry, and heavy metal resistome of a tropical agricultural soil were evaluated for 6 weeks in field-moist microcosms consisting of a Cr-inundated agricultural soil (SL9) and an untreated control (SL7). The physicochemistry of the two microcosms revealed a diminution in the total organic matter content and a significant dip in macronutrients phosphorus, potassium, and nitrogen concentration in the SL9 microcosm. Heavy metals analysis revealed the detection of seven heavy metals (Zn, Cu, Fe, Cd, Se, Pb, Cr) in the agricultural soil (SL7), whose concentrations drastically reduced in the SL9 microcosm. Illumina shotgun sequencing of the DNA extracted from the two microcosms showed the preponderance of the phyla, classes, genera, and species of Actinobacteria (33.11%), Actinobacteria_class (38.20%), Candidatus Saccharimonas (11.67%), and Candidatus Saccharimonas aalborgensis (19.70%) in SL7, and Proteobacteria (47.52%), Betaproteobacteria (22.88%), Staphylococcus (16.18%), Staphylococcus aureus (9.76%) in SL9, respectively. Functional annotation of the two metagenomes for heavy metal resistance genes revealed diverse heavy metal resistomes involved in the uptake, transport, efflux, and detoxification of various heavy metals. It also revealed the exclusive detection in SL9 metagenome of resistance genes for chromium (chrB, chrF, chrR, nfsA, yieF), cadmium (czcB/czrB, czcD), and iron (fbpB, yqjH, rcnA, fetB, bfrA, fecE) not annotated in SL7 metagenome. The findings from this study revealed that Cr contamination induces significant shifts in the soil microbiome and heavy metal resistome, alters the soil physicochemistry, and facilitates the loss of prominent members of the microbiome not adapted to Cr stress.

Study on the remediation of hexavalent chromium groundwater by zero-valent iron

This study investigates the potential problems of zero-valent iron remediation of hexavalent chromium contamination by varying the type and dosage of zero-valent iron, finding a suitable zero-valent iron reaction material for application in actual remediation sites, and determining the dosage of zero-valent iron so that it can achieve remediation results without causing waste. To further investigate the effect of petroleum hydrocarbon contaminants on the remediation effect, the petroleum hydrocarbon contaminants were mixed with hexavalent chromium solution and a suitable amount of zero-valent iron was added.

Light intensity effect on the performance of Rhodobacter capsulatus in removal of chromium from effluent

The research aims to evaluate an unusual photosystem removing hexavalent chromium and total chromium contamination from the effluent by bioremediation (Rhodobacter capsulatus). Biomass and pigments (bacteriochlorophyll and carotenoid) production through different light intensities (dark, 800 lx, 3,200 lx, 5,670 lx, and 8,000 lx) were verified. The cultures were inoculated in 250 mL Erlenmeyer and operated under anaerobic conditions for 192 h. RCV medium with hexavalent chromium (10 mg/L, 30 mg/L, 60 mg/L, 90 mg/L, and 110 mg/L) was used. The findings show there was complete removal of hexavalent chromium. The increase in light intensity reduced the time for removal. Concerning total chromium, maximum removal occurred under 5,670 lx at low initial concentrations of hexavalent chromium of 10 mg/L (80.2 %), 30 mg/L (89.3 %), and 60 mg/L (77.0 %). Furthermore, the increase in light intensity up to 5,670 lx favored cell growth and pigment production. At 5,670 lx, there was a 230 % increase in biomass content in the culture with an initial concentration of 60 mg/L of hexavalent chromium. The final pigment contents were 2.22 mg/m3 (bacteriochlorophyll) and 1.44 mg/m3 (carotenoid).

Hexavalent chromium contamination in groundwater and its implication to human health: a Monte Carlo model approach in Indonesia

Hexavalent chromium contamination in groundwater and its implication to human health: a Monte Carlo model approach in Indonesia

Enhanced phytoremediation of hexavalent chromium contamination in phosphate mining wasteland by a phosphate solubilizing bacterium

Soil chromium (Cr) contamination poses a significant threat to the environment and public health. A phosphate solubilizing bacterial strain Bacillus megaterium PMW-03 was used to enhance the phytoremediation of Cr(VI) contamination by Pteris vittata in phosphate mining wasteland in this study. The results showed that the strain PMW-03 could promote the solubilization of phosphate rock (PR) and the removal of Cr(VI) by Pteris vittata in the phosphate mining wasteland. Compared with the groups not inoculated with PMW-03, the available phosphate content in the rhizosphere soil of the inoculated groups increased by 17.6% and 24.9%, respectively (in the group with Cr(VI) added and the group with Cr(VI) and PR added), and the available Cr(VI) content decreased by 28.2%, 25.2% and 33.4%, respectively. In addition, the strain PMW-03 also promoted the growth of Pteris vittata by secreting indole acetic acid (IAA) and siderophore, promoting Pteris vittata to produce chlorophyll, increasing the concentration of soluble phosphate and reducing the concentration of Cr(VI) in root and shoot. The results of metagenomic analysis showed that changes in biological community structure, enrichment of related functional abundances, and activation of genes (FTH1, FTL, HSP90A, glgP, htpG, glnA, and GLUD1_2) located in microbes contributed to the microbial-phytoremediation of Cr(VI) contamination. These results provide a reference for future research on the microbial-phytoremediation of Cr(VI) contamination in phosphate mining wasteland.

Analysis of Hydrogeochemical Characteristics and Origins of Chromium Contamination in Groundwater at a Site in Xinxiang City, Henan Province

Hexavalent chromium contamination in groundwater has become a very serious and challenging problem. Identification of the groundwater chemical characteristics of the sites and their control mechanisms for remediation of pollutants is a significant challenge. In this study, a contaminated site in Xinxiang City, Henan Province, was investigated and 92 groundwater samples were collected from the site. Furthermore, the hydrogeochemical characteristics and the distribution patterns of components in the groundwater were analyzed by a combination of multivariate statistical analysis, Piper diagram, Gibbs diagram, ions ratio and hydrogeochemical simulation. The results showed that the HCO3-Cl-Mg-Ca type, SO4-HCO3-Na type, and HCO3-Mg-Ca-Na type characterize the hydrogeochemical composition of shallow groundwater and HCO3-Cl-Mg-Ca type, HCO3-Na-Mg type, and HCO3-SO4-Mg-Na-Ca type characterize the hydrogeochemical composition of deep groundwater. Ion ratios and saturation index indicated that the groundwater hydrogeochemical characteristics of the study area are mainly controlled by water–rock action and evaporative crystallization. The dissolution of halite, gypsum and anhydrite, the precipitation of aragonite, calcite and dolomite, and the precipitation of trivalent chromium minerals other than CrCl3 and the dissolution of hexavalent chromium minerals occurred in groundwater at the site. The minimum value of pH in groundwater at the site is 7.55 and the maximum value is 9.26. The influence of pH on the fugacity state of minerals was further investigated. It was concluded that the saturation index of dolomite, calcite, aragonite and MgCr2O4 increases with the increase of pH, indicating that these minerals are more prone to precipitation, and the saturation index of Na2Cr2O7, K2Cr2O7 and CrCl3 decreases with the increase of pH, implying that Na2Cr2O7, K2Cr2O7 and CrCl3 are more prone to dissolution. The saturation index of the remaining minerals is less affected by pH changes. The study can provide a scientific basis for groundwater remediation.

Evaluating toxic element contamination sources in groundwater bodies of two Mediterranean sites.

The Driver-Pressure-State-Impact-Response (DPSIR) framework is applied for assessing the pressures and impacts on groundwater bodies of two Mediterranean sites (Megara and Oropos-Kalamos basins). The study areas present joint driving forces (drivers) and pressures. The main driving forces in the areas studied mainly include geology, agricultural activities, and urban development, while the main pressures mainly include the weathering of ultramafic rock masses, application of agrochemicals, and groundwater abstractions for irrigation and drinking uses. Hexavalent chromium (Cr+6), chromium total (Crtotal), manganese (Mn), and nitrate (NO3-) contamination of groundwater bodies are attributed to both anthropogenic and lithological sources. Elevated Crtotal (up to 70.3 μg L-1), Mn (up to 87.7 μg L-1), and NO3- (up to 411 mg L-1) contents are recorded for groundwater samples in Megara basin. High Crtotal (up to 34.3 μg L-1), Cr6+ (up to 27.9 μg L-1), Mn (up to 132.5 μg L-1), and NO3- (up to 30 mg L-1) are also observed for groundwater samples in the Oropos-Kalamos basin. The major response actions needed for the management options of groundwater bodies are discussed. Among the proposed remedial measures, the installation of a continuous groundwater monitoring network and the control in the usage of nitrogen fertilizers seems to be the most effective and tangible for immediate action.

Different Pathways for Cr(III) Oxidation: Implications for Cr(VI) Reoccurrence in Reduced Chromite Ore Processing Residue.

Hexavalent chromium contamination is a global environmental issue and usually reoccurs in alkaline reduced chromite ore processing residues (rCOPR). The oxidation of Cr(III) solids in rCOPR is one possible cause but as yet little studied. Herein, we investigated the oxidation of Cr(OH)3, a typical species of Cr(III) in rCOPR, at alkaline pH (9-11) with δ-MnO2 under oxic/anoxic conditions. Results revealed three pathways for Cr(III) oxidation under oxic conditions: (1) oxidation by oxygen, (2) oxidation by δ-MnO2, and (3) catalytic oxidation by Mn(II). Oxidations in the latter two were efficient, and oxidation via Pathway 3 was continuous and increased dramatically with increasing pH. XANES data indicated feitknechtite (β-MnOOH) and hausmannite (Mn3O4) were the reduction products and catalytic substances. Additionally, a kinetic model was established to describe the relative contributions of each pathway at a specific time. The simulation outcomes showed that Cr(VI) was mainly formed via Pathway 2 (>51%) over a short time frame (10 days), whereas in a longer-term (365 days), Pathway 3 predominated the oxidation (>78%) with an increasing proportion over time. These results suggest Cr(III) solids can be oxidized under alkaline oxic conditions even with a small amount of manganese oxides, providing new perspectives on Cr(VI) reoccurrence in rCOPR and emphasizing the environmental risks of Cr(III) solids in alkaline environments.

Hazardous Waste Disposal in Stromatolitic-Limestone Terrain and Hexavalent Chromium Contamination in Chhattisgarh State, India.

Background.Hexavalent chromium-containing waste from chromite ore processing is a major environmental health hazard due to its high toxicity. There have been instances of improper and unsafe disposal of this waste, leading to environmental health hazards.Objectives.The objective of the present study was to identify the cause of yellow colored water discharge and reported health issues in nearby residents and cattle. In addition, it investigated the improper disposal of chromite ore processing residue (COPR), a hazardous waste, in an abandoned quarry in stromatolitic-limestone terrain in central-east India.Methods.Standard methods of analysis of water and wastewater were used for the analyses of variables, including hexavalent chromium (Cr(VI)), pH, sulfate (SO42−), chlorine (Cl−), total hardness, calcium (Ca(II)), magnesium (Mg(II)), alkalinity and sodium (Na(I)) with proper sampling, quality assurance, and quality control protocols. Onsite Cr(VI) was analyzed using a chromium testing kit, and in the laboratory by atomic absorption spectrophotometry.Results.Large-scale contamination of surface and groundwater was noted due to the migration of hexavalent chromium-contaminated yellow colored leachate. High levels of hexavalent chromium were noted in the samples. The maximum Cr(VI) concentration observed was 1050 mg/L in leachate, 22 mg/L in surface water and 0.26 mg/L in the groundwater sample. Acute health effects were noted in cattle and by residents who consumed the highly contaminated water.Conclusions.A large volume of discharge of hexavalent chromium contamination from the COPR landfill was found, indicating the absence of containment features in the design (double high-density polyethylene liners, clay, leachate collection). Disposal of COPR in an abandoned limestone mine is inadvisable. The highly fractured stromatolitic-limestone environment at the study site was found to offer almost no resistance to the mobilization of Cr(VI) due to the absence of organic or eukaryotic deposition in the stromatolitic environment. It was also noted that the drainage pattern of the area facilitates a possible translocation of contaminated discharge to the nearby river system. Nearby residents were unaware of the adverse impacts of the contaminated leachates and were using the contaminated water for bathing, washing, etc. Applicable Indian governmental regulations regarding the construction of hazardous waste landfills were found to be insufficient with respect to the use of inactive limestone mines as landfill sites.Competing Interests.The authors declare no competing financial interests.

Assessment of Hexavalent Chromium Pollution in Buriganga and Dhaleshwari River Waterbodies Adjacent to Tannery Estates in Bangladesh

Recently, in Bangladesh, all tannery industries have been relocated to a new location exclusively established for leather processing industries with modern manufacturing facilities and effluent treatment plants with standard probations. Effluents generated from the tannery industries are now being disposed of into the surrounding river water bodies. In this study, our goal was to investigate the presence of chemical contaminants like hexavalent chromium (Cr6+) in the water bodies surrounding tannery industries and to understand the possible role played by the tannery effluents in contaminating the river water bodies with Cr6+. Result analysis revealed the presence of an amount of Cr6+ (ranging from 0.01 mg/L to 3.54 mg/L) in the surrounding water bodies, which was far above the maximum permissible limit of Cr6+ (0.05 mg/L for surface water), set by the Environmental Protection Agency. It is, therefore, plausible to assume that effluents from the tanneries play an important role in hexavalent chromium contamination of water bodies surrounding tannery industries.

Multiple exposure pathways and urinary chromium in residents exposed to chromium

BackgroundEnvironmental hexavalent chromium contamination in northeast China has been ongoing for over 60 years and health outcomes related with chromium (Cr) pollution were observed in polluted arears, but exposure pathways remains unclear. This study aims to evaluate the association between Cr exposure dose through multiple exposure pathways and Cr concentration in urine, and identify the most contributed pathway. MethodsWe used risk assessment tools with individual exposure parameters to estimate eight individual Cr exposure doses (CD) for three exposure routes (inhalation, ingestion, and dermal contact) with four environmental media (underground water, soil, household dust, and PM10 in ambient air) in 134 residents living in three chromium polluted villages. We used the covariate-adjusted standardized urinary Cr concentration (casUCr) as the internal Cr exposure biomarker. Ridge Regression, Weighted Quantile Sum Regression (WQS) and Bayesian Kernel Machine Regression (BKMR) models were used to assess the effect of overall eight CDs on urine Cr concentration and compare the contribution of each CD. ResultsIn the ridge regression analysis, Cr exposure through ingestion of dust (βstd = 0.418, p-value = 0.009), inhalation of dust (βstd = 0.384, p = 0.031) and dermal contact with soil (βstd = 0.264, p = 0.192) had the highest impact on casUCr. In the WQS model, the overall CDs demonstrated a non-significant positive association with casUCr. CDs of dust ingestion, air inhalation and dust inhalation had the largest contribution on casUCr when fitted in the WQS model. In the BKMR model, the hierarchical variable selection showed that casUCr was mainly affected by CDs of household dust and dermal contact with soil. CD of dermal contact with soil exhibited a negative association with casUCr, while CDs of dust showed positive or non-linear trend. ConclusionsThis research proposed a new method to calculate individual Cr exposure dose of multi-pathway and applied different statistical methods to identify predominant pathway. For this study, Cr exposure through dust has the strongest effect on Cr concentration in urine. The results could help conduct target interventions to reduce Cr intake, such as blocking dust exposure to reduce Cr uptake for villagers living in these contaminated areas.

Microbial Assisted Hexavalent Chromium Removal in Bioelectrochemical Systems

Groundwater is the environmental matrix that is most frequently affected by anthropogenic hexavalent chromium contamination. Due to its carcinogenicity, Cr(VI) has to be removed, using environmental-friendly and economically sustainable remediation technologies. BioElectrochemical Systems (BESs), applied to bioremediation, thereby offering a promising alternative to traditional bioremediation techniques, without affecting the natural groundwater conditions. Some bacterial families are capable of oxidizing and/or reducing a solid electrode obtaining an energetic advantage for their own growth. In the present study, we assessed the possibility of stimulating bioelectrochemical reduction of Cr(VI) in a dual-chamber polarized system using an electrode as the sole energy source. To develop an electroactive microbial community three electrodes were, at first, inserted into the anodic compartment of a dual-chamber microbial fuel cell, and inoculated with sludge from an anaerobic digester. After a period of acclimation, one electrode was transferred into a polarized system and it was fixed at −0.3 V (versus standard hydrogen electrode, SHE), to promote the reduction of 1000 µg Cr(VI) L−1. A second electrode, served for the set-up of an open circuit control, operated in parallel. Cr(VI) dissolved concentration was analysed at the initial, during the experiment and final time by spectrophotometric method. Initial and final microbial characterization of the communities enriched in polarized system and open circuit control was performed by 16S rRNA gene sequencing. The bioelectrode set at −0.3 V showed high Cr(VI) removal efficiency (up to 93%) and about 150 µg L−1 day−1 removal rate. Similar efficiency was observed in the open circuit (OC) even at about half rate. Whereas, purely electrochemical reduction, limited to 35%, due to neutral operating conditions. These results suggest that bioelectrochemical Cr(VI) removal by polarized electrode offers a promising new and sustainable approach to the treatment of groundwater Cr(VI) plumes, deserving further research.

Surface Water Pollution in the Middle Chinese Loess Plateau with Special Focus on Hexavalent Chromium (Cr6+): Occurrence, Sources and Health Risks

Due to the combined influence of unique natural environment and increasing human activities, water quality in the Chinese Loess Plateau is deteriorating. Hexavalent chromium (Cr6+) contamination is a critical water environmental issue in the loess areas. In this study, surface water, spring water, Quaternary phreatic water, and soil and rock samples were collected in the middle Chinese Loess Plateau to quantify the surface water pollution and its main affecting factors. Particularly, the occurrence and potential sources of Cr6+ as well as associated health risks in surface water were thoroughly investigated. The results show that Cr6+ is widely found in Luo River, Xingzi River, Wuding River and Bali River. The upper reaches of the Luo River are the main high-Cr6+ water distribution area. For Bali River, Wuding River, Xingzi River and the downstream of the Luo River, the values of Cr6+ in surface water were below the WHO drinking water limit (0.05 mg/L). The high Cr values in the soil and rock samples indicate that the loess and mudstone are important sources of high-Cr6+ water in the area. Groundwater which is characterized by high Cr6+ concentration is also an important factor affecting Cr6+ concentration in surface water which receives recharge from groundwater. In addition to Cr6+, TDS and nitrate are also important pollutants in surface water. The hydrochemical evolution of the surface water is controlled by rock weathering and evaporation crystallization. The health risk assessment results suggest that the inhabitants in the study area face high carcinogenic risks induced by Cr6+.

Assessment of groundwater geochemistry and diffusion of hexavalent chromium contamination in an industrial town of Italy

Groundwater contamination by hexavalent chromium (Cr (VI)) is currently a very serious and challenging issue. Therefore, in the present study, 108 shallow groundwater samples were collected during the years 2012 to 2015 (n = 27 samples each year) from an industrial town (Aosta) to assess the contamination status of the area. To evaluate the Cr (VI) concentration level, sources of pollutants and groundwater geochemistry of the study area, a combined approach of the multi-statistical and hydrogeochemical techniques were used. Furthermore, a geographic information system (GIS) was applied for the spatial distribution of Cr (VI) so that the most contaminated sites can be identified for a quick decision by policymakers. Results show that the groundwater chemistry was dominated by HCO3– and SO42− in the anionic chemistry and Ca2+ and Na+ in the cationic chemistry, while Ca-Mg-HCO3 and Ca-Mg-Cl-SO4 were the main water types during the years 2012–2015 in the study area. The central part and some north-eastern parts of the Aosta town groundwater was contaminated with Cr (VI) and are unsafe for drinking use. Concentration levels of Cr (VI) in the groundwater were 0.09 μg/L (lowest value) and 165 μg/L (highest value) in the years studied, and the spatial analysis shows the diffusion of Cr (VI) to north-east direction from the source. Contamination of Cr (VI) in the groundwater was due to the superficial slag deposits from a steel company within the study area. This study would be helpful for current and future water resource management in the area concerned.

Chromium isotopes tracking the resurgence of hexavalent chromium contamination in a past-contaminated area in the Friuli Venezia Giulia Region, northern Italy

ABSTRACTThe origin of a resurgent hexavalent chromium contamination in groundwater from a phreatic aquifer in the Friuli Venezia Giulia Region plain was investigated by chromium isotopic systematics. The area underwent a severe Cr(VI) contamination by industrial effluents in 1997, when Cr(VI) concentration in groundwater reached 4500 µg/L. In subsequent years the contamination naturally attenuated, totally disappearing in 2003. A renewal of water contamination was observed in 2008, Cr(VI) reaching 1560 µg/L. The δ53Cr value in groundwater and extracts from sediments was measured in 2009–2011, and it ranges between −3.21 and +0.21‰ and between −4.71 and +1.26‰, respectively. Due to the lack of geogenic Cr-sources, these data are interpreted as evidence of the subsequent oxidation through Mn-oxides of the Cr(III) hosted in the aquifer and originated by the reduction of the original industrial chromates. Cr(III) is characterized by negative δ53Cr, starting from the δ53Cr value around zero of Cr(VI) in industrial effluents. Oxidation liberates soluble Cr(VI) which is transported by groundwater and permeated soils. The complex Cr-isotopic vs. concentration distribution reflects both the new Cr(VI) reduction and dilution processes in the aquifer system. From an environmental point of view, the data raise concerns regarding the potential impact of past Cr(VI)-contamination.

Abiotic reduction of Cr(VI) by humic acids derived from peat and lignite: kinetics and removal mechanism

Hexavalent chromium contamination of groundwater is a worldwide problem caused by anthropogenic and natural processes. We report the rate of Cr(VI) removal by two humic acids (extracted from Miocene age lignite and younger peat soil) in aqueous suspensions across a pH range likely to be encountered in terrestrial environments. Cr(VI) was reduced to Cr(III) in a first-order reaction with respect Cr(VI) concentration, but exhibited a partial order (~ 0.5) with respect to [H+]. This reaction was more rapid with the peat humic acid, where Cr(VI) reduction was observed at all pH values investigated (3.7 ≤ pH ≤ 10.5). 13C NMR and pyrolysis GC-MS spectroscopy indicate that the reaction results in loss of substituted phenolic moieties and hydroxyl groups from the humic acids. X-ray absorption spectroscopy indicated that at all pH values the resulting Cr(III) was associated with the partially degraded humic acid in an inner-sphere adsorption complex. The reaction mechanism is likely to be controlled by ester formation between Cr(VI) and phenolic/hydroxyl moieties, as this initial step is rapid in acidic systems but far less favourable in alkaline conditions. Our findings highlight the potential of humic acid to reduce and remove Cr(VI) from solution in a range of environmental conditions.

Rapid determination of hexavalent chromium in textiles by a novel ammonium pyrrolidine dithiocarbamate derivatization combined with UHPLC-MS/MS.

Hexavalent chromium is mainly determined by traditional spectrophotometry, atomic absorption spectrometry, and ion chromatography methods. In the present work, a reliable ultra high performance liquid chromatography with tandem mass spectrometry method was firstly developed for the determination of hexavalent chromium in textiles. The sample was extracted by acetic acid/sodium acetate buffer solution and followed by derivatization with ammonium pyrrolidine dithiocarbamate. The resulting derivative product was extracted by ethyl acetate, separated on a C18 column, and detected through electrospray ionization source in the positive mode with multiple reaction monitoring conditions. The derivatization reaction conditions were investigated and optimized. The developed method was validated in terms of the sensitivity, linearity range, matrix effects, recovery, accuracy, intra- and interday precision. Results showed that the calibration curves of pure solvent and matrix were linear over the selected concentration ranges of 0.1-20.0μg/L. The achieved instrument and method limit of quantification were 0.1 and 40.0μg/kg, respectively. Recoveries were calculated at three spiked concentrations and the values were between 92.2 and 103% with relative standard deviation values of 2.7-4.9% for intra-day precision and 6.1% for inter-day precision. Successful analysis of hexavalent chromium in practical textiles indicated that there was hexavalent chromium contamination in textiles.

Hexavalent Chromium Sources and Distribution in California Groundwater.

Groundwater resources in California represent a confluence of high-risk factors for hexavalent chromium contamination as a result of industrial activities, natural geology, and, potentially, land use. Here, we examine state-wide links in California between groundwater Cr(VI) concentrations and chemicals that provide signatures for source attribution. In environmental monitoring wells, Cr(VI) had the highest co-occurrence and also clustered with 1,4-dioxane and several chlorinated hydrocarbons indicative of the metal plating industry. Additionally, hotspots of Cr(VI) co-occurring with bromoform result from volatile organic compound remediation using in situ chemical oxidation that inadvertently oxidizes naturally occurring Cr(III). In groundwater supply wells, which are typically free of industrial inputs, Cr(VI) correlates with dichlorodiphenyldichloroethylene (DDE), vanadium, and ammonia and clusters with nitrate and dissolved oxygen, suggesting potential links between agricultural activities and Cr(VI). Specific controls on Cr(VI) vary substantially by region: from the metal plating industry around Los Angeles and the San Francisco Bay areas to natural redox conditions along flow paths in the Mojave Desert and to correlations with agricultural practices in the Central Valley of California. While industrial uses of Cr lead to the most acute cases of groundwater Cr(VI) contamination, oxidation of naturally occurring Cr affects a larger area, more wells, and a greater number of people throughout California.

Alleviation of Cr(VI)-induced oxidative stress in maize (Zea mays L.) seedlings by NO and H2S donors through differential organ-dependent regulation of ROS and NADPH-recycling metabolisms

Chromium (Cr) contamination in soil is a growing concern in relation to sustainable agricultural production and food safety. Nitric oxide (NO) and, more recently, hydrogen sulfide (H2S) are considered to be new signalling molecules with biotechnological applications in the agronomical sector. Using 9-day-old maize (Zea mays) seedlings exposed to 200μM Cr(VI), the potential mitigating effects of exogenous NO and H2S on chromium-induced stress in maize seedlings were investigated in roots, cotyledons and coleoptiles. Analysis of Cr content, lipid peroxidation, antioxidant enzymes (catalase and superoxide dismutase isozymes), peroxisomal H2O2-producing glycolate oxidase and the main NADPH-regenerating system revealed that chromium causes oxidative stress, leading to a general increase in these activities in coleptiles and roots, with the latter organ being the most affected. However, cotyledons behaved in an opposite manner. Moreover, exogenous applications of NO and H2S to Cr-stressed maize seedlings triggered a significant response, involving the virtual restoration of the values for all these activities to those observed in unstressed seedlings, although their specific impact on ROS and NADPH-recycling metabolisms depends on the seedling organ involved. Taken together, the data indicate that gas transmitters, NO and H2S, which act as a defence against the negative effects of hexavalent chromium contamination, are alternative compounds with potential biotechnological applications.

ISOLATION AND CHARACTERIZATION OF CHROMIUM TOLERANT BACTERIA FROM TANNERY EFFLUENT AT DINDIGUL DISTRICT, TAMILNADU, INDIA

Hexavalent chromium contamination in environment became a serious problem in all over the world. The chromium, a toxic heavy metal, is a major contaminant in tannery wastes and their accumulation into the soil and water is an environmental issue particularly in Tamilnadu. Dindigul is the headquarters of leather tannery industry. Tannery effluent was collected from leather industry located at Dindigul district. Bacteria having tolerance to chromium has been isolated. A total of six species of chromium tolerant bacteria were isolated and their minimum inhibitory concentration of all the six isolates against hexavalent chromium was determined on nutrient agar supplemented with varying concentration of chromium from 100 ppm to 600 ppm. The bacterial strains were characterized by morphological, cultural and biochemical analysis. They were identified as Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus, Micrococcus species, Bacillus cereus and Bacillus licheniformis. The analysis of the results concluded that all the bacteria showed resistance against chromium with Minimum Inhibitory Concentration (MIC) values up to 100 mg/L.