Rapid ultrasensitive detection of hexavalent chromium in soil and groundwater by a microProbing imaging platform

Using iron sulfate (Fe (II)) to restore hexavalent chromium (Cr (VI)) in soil solution, while different pH, action conditions and various reaction time, to study the reduction effect of ferrous iron on hexavalent chromium in soil. It is showed that Fe (II) could restore all of Cr (VI) basically at pH=7 in anaerobic condition. At the same time, the participation of oxygen would affect the reduction ability of Fe (II) to Cr (VI) with time goes on. In the absence of oxygen condition, the reduction effect is more stable, and under aerobic conditions, the reduction effect is precarious.

Soil humic acids may favour the persistence of hexavalent chromium in soil

Removal of hexavalent chromium in soil by lignin-based weakly acidic cation exchange resin

Surface soil containing 25,100 mg/kg total Cr [12,400 mg/kg Cr(VI)] obtained from a Superfund site was used in laboratory microcosm studies to evaluate the potential for aerobic reduction of Cr(VI) by the indigenous soil microbial community. Hexavalent chromium in soil was reduced by as much as 33% (from 1840 to 1240 mg/L) within 21 days under enrichment conditions. Reduction of Cr(VI) in this system was biologically mediated and depended on the availability of usable energy sources. Mass balance studies suggested that the microbial populations removed Cr(VI) from the soil solutions by reduction. Indigenous microbial soil communities even with no history of Cr(VI) contamination were capable of mediating this process. However, Cr(VI) removal was not observed when microbial populations from a sewage sludge sample were added to the soil microcosms. The results suggest that Cr(VI)-reducing microbial populations are widespread in soil, and thus the potential exists for in situ remediation of environmentally significant levels of Cr( VI) contamination.

The toxicity and mobility of chromium in the environment greatly depends upon its speciation. The reduction of hexavalent chromium to trivalent chromium in a soil environment was examined by spiking three soil types (sandy, clayey, and organic soils) with a common wood preservative solution known as chromated copper arsenate (CCA). Chromium in the CCA preservative solution exists in the hexavalent form. The total and hexavalent chromium concentrations (mg/kg) were measured over a period of 11 months. Leachable chromium concentrations (mg/L) were assessed using the synthetic precipitation leaching procedure (SPLP). The degree and rate of hexavalent chromium reduction were similar for the sand and clayey soil, but much greater for the organic soil. Most of the chromium reduction occurred within the first month of the experiment. At the end of the experiment, approximately 50% of the hexavalent chromium was converted to the trivalent form in the sand and clayey soils. Hexavalent chromium concentrations were below detection in the organic soil at the end of the experiment. Nearly all of the chromium observed in the SPLP leachates was in the form of hexavalent chromium. Chromium leaching was thus greatest in the sand and clay soils where the hexavalent chromium persisted. The results indicate that hexavalent chromium in soils can persist for considerable time periods, in particular in soils with low organic matter content. #Present affiliation for Jinkun Song: Graduate Research Assistant, Department of Civil Engineering, Texas A&M University, Texas 77843. **Present affiliation for Yong-Chul Jang: Assistant Professor, Department of Environmental Engineering, Chungnam National University, Daejeon 305-764, South Korea.

Environmentally available hexavalent chromium in soils and sediments impacted by dispersed fly ash in Sarigkiol basin (Northern Greece).

The presence of hexavalent chromium in soil poses a grave hazard to the environment and human health. This study explores the effectiveness, mechanism, and economic viability of remediation of Cr(VI)-contaminated soil by hydrazine. Soil-phase batch kinetic experiments were performed to examine the feasibility of reducing Cr(VI) while finding the effects of relevant process parameters, such as initial Cr(VI) concentration, hydrazine dosage, pH, soil-to-water ratio, and temperature. The materials were thoroughly characterized to gain insight into the mechanism. TCLP tests were done to affirm the immobilization stability. Complete Cr(VI) reduction was achieved within 3 h using a moderate 326% excess of hydrazine at neutral pH. Sonication of the soil mixed with hydrazine using a probe-type sonicator accelerated the reduction of Cr(VI) to Cr(III). Kinetic data could be adequately fitted in a second-order rate model, where the rate constant shows a linear dependency on the soil-to-water ratio. Additionally, the logarithmic rate constant demonstrates linearity within the pH range. The leaching toxicity of Cr(VI) and Crtotal complied with the USEPA regulatory limit and remained stable for 75 d. Hydrazine alone and its combination with ultrasound are sustainable and economically feasible for effective remediation of Cr(VI)-contaminated soil. The statistical analysis using RSM indicated a 99.4% reduction, aligning closely with the calculated optimized value. The optimal process conditions are easy to implement for field application at a competitive cost compared to other reductants. A simplified economic analysis was done to check the competitive acceptability of the technique, considering the construction cost of the remediation plant and its daily operational and maintenance expenses. The results show that the proposed technique will be a competitive one for field applications for the remediation of soil contaminated with Cr(VI). The data and kinetic rate equation will be useful for the process design of the remediation of soil contaminated with Cr(VI).

Characteristics and long-term effects of stabilized nanoscale ferrous sulfide immobilized hexavalent chromium in soil

Distribution, origin and fate of chromium in soils in Guanajuato, Mexico

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

Chromium is released into the environment by a number of processes such as steel manufacturing, pulp processing, wood preservation, leather tanning, metal plating, metal cleaning and processing and alloy formation, mostly with-out proper treatment. As a consequence, elevated concentrations of chromium become a major threat to the environment. Among the different forms of chromium, hexavalent chromium is highly soluble in water, and mutagenic and carcinogenic. Recently, concern about Cr as an environmental pollutant has been escalating due to its build up to toxic levels in the environment as a result of various industrial and agricultural activities. In the present study, the hexavalent chromium was reduced into trivalent chromium from chromium contaminated (300 µg g -1 ) soil. The vermicompost and microbial cultures (Pseudomonas fluorescens and Trichoderma viride) were used for chromium detoxification studies. The chromium (VI) reduction was observed in best treatment like vermicompost alone reduced the chromium up to 85 per cent and vermicompost along with Pseudomonas fluorescens reduced the hexavalent chromium up to 84.6 per cent. The large amount of hexavalent chromium was detoxified due to application of vermicompost. The chromium hexavalent reduction was confirmed with maize plant uptake. The plants grown on the control soil (T1) had the highest content of Cr (39.2 µg g -1 ) and the plants grown on the soil with the application of Trichoderma viride (T9) had the lesser

The toxicity of chromium (Cr) to biota is related to its chemical forms and consequently to the redox conditions of soils. Hexavalent Cr[Cr(VI)] may undergo natural attenuation through reduction processes. In this study, the reduction kinetics of Cr(VI) in seven soils and its relationships with soil properties were investigated with laboratory incubation experiments. The results indicate that the reduction of Cr(VI) can be described by a first-order reaction. The reduction rates of Cr(VI) in the seven soils decreased in the order: Udic Ferrisols > Stagnic Anthrosols > Calcaric Regosols > Mollisol > Typic Haplustalf > Periudic Argosols > Ustic Cambosols. Simple correlation analysis revealed that the reduction of Cr(VI) in soils was positively related to organic matter content, dissolved organic matter content, Fe(II) content, clay fraction, and to the diversity index of the bacterial community but negatively correlated with easily reducible Mn content. Using stepwise regression, the reduction of Cr(VI) in soil could be quantitatively predicted by the measurement of dissolved organic matter content, Fe(II) content, pH, and soil particle size distribution, with a fitting level of 95.5%. The results indicated that the reduction of Cr(VI) in natural soils is not controlled by a single soil property but is the result of the combined effects of dissolved organic matter, Fe(II), pH, and soil particle size distribution.

Chromium (Cr) in the trivalent form (Cr III) is an important component of a balanced human and animal diet and its deficiency causes disturbance to the glucose and lipid metabolism in humans and animals. In contrast, hexavalent Cr (Cr VI) is a highly toxic carcinogen and may cause death to animals and humans if ingested in large doses. Recently, concern about Cr as an environmental pollutant has been escalating due to its build up to toxic levels in the environment as a result of various industrial and agricultural activities. In the present study, the hexavalent chromium was reduced into trivalent chromium from chromium contaminated (300 μg g) soil. In the presence of organic amendments (poultry manure) and microbial inoculants (Pseudomonas fluorescens and Trichoderma viride) the chromium (VI) reduction was observed in maximum in the poultry manure treatment (91%) whereas poultry manure with Pseudomonas fluorescens reduced the hexavalent chromium up to 90 %.

This study aimed to evaluate the total Cr and Cr(VI) contamination levels and assess the possible health risk of Cr(VI) in soils from a coal chemical industrial area in Northwest China. The contamination factor (CF) was used to calculate the total Cr and Cr(VI) contamination levels in soils from the study area. The highest concentration of Cr(VI) (69.58 mg/kg) was found in the top soil (0–20 cm) with the distance of 10 m to the coal cinder heap. The carcinogenic risk (CR) and hazard quotient (HQ) were estimated for health risk to workers by using “Chinese Technical Guidelines for Risk Assessment of Contaminated Sites (HJ 25.3-2014).” The results showed that the soils from the study area were moderately polluted by the total Cr and Cr(VI). There was no serious non-CR (HQ < 1). However, the CR values of Cr(VI) were significantly higher than the threshold value, indicating that workers are facing serious threat of Cr(VI). Inhalation (70.32%) was the main exposure pathway to CR, followed by dermal contact (20.64%), and then ingestion (9.04%). These results provide basic information of Cr(VI) pollution control and environment management in coal chemical industrial areas.

The mechanism of Cr(VI) immobilization in soils by organic substances are not well understood. In the present study, two crop residues (maize stalk and peanut shell) and their biochars obtained at various pyrolysis temperatures were prepared to investigate their influences on the immobilization of Cr(VI) in two contaminated soils via an incubation test and a bioassay. The results showed that Cr(VI) immobilization in soils was ascribed to dominant reduction (52–99%) coupled with secondary surface adsorption (1.2–48%) by organic substances. The maximum reduction capacity (Ym, 238 mg/kg) was found in an acidic brown soil with maize stalk amendment, secondly, with peanut shell amendment (Ym, 231 mg/kg). Their biochars presented a weaker capacity in reducing Cr(VI) to Cr(III) of soils than raw crop residues since carbonization accelerated the decomposition of oxygen-containing functional groups of organic substances. Soil properties, mainly soil pH, were negatively related to Cr(VI) reduction in soils remarkably, while concomitant anions in soils mainly the phosphate could compete with Cr(VI) for surfaces of soil particles and decrease Cr(VI) adsorption and subsequent reduction. The bioassay in pots with wheat seedlings further validated that maize stalk was a better organic substance for Cr(VI) immobilization and subsequent decrease of its bioavailability in contaminated soils than its biochar according to the results of wheat biomass and Cr contents in shoots and roots. Accordingly, to develop a cost-effective method for immobilizing Cr(VI) in contaminated soils, the raw maize stalk is more advantageous than the carbonaceous counterparts because no pyrolysis is required for the application.