Abstract: The widespread use of chromium (Cr) has a deleterious impact on the environment. A number of pathways, both biotic and abiotic in character, determine the fate and speciation of Cr in soils. Chromium exists in two predominant species in the environment: trivalent [(Cr(III)] and hexavalent [Cr(VI)]. Of these two forms, Cr(III) is nontoxic and is strongly bound to soil particles, whereas Cr(VI) is more toxic and soluble and readily leaches into groundwater. The toxicity of Cr(VI) can be mitigated by reducing it to Cr(III) species. The authors compared results for the chicken manure biochar with acid-activated black carbon from a weedy species (Solanum elaeagnifolium Cav.). Results showed that the activated black carbon reduced all of the Cr(VI) to Cr(III) within 6 to 10 d, whereas the chicken manure biochar reduced between 198 and 219 mg kg−1 over the 14-d incubation; the estimated half-life for Cr(VI) reduction by biochar was between 10.7 and 11.4 d. Although biochar did not fully reduce Cr(VI) to Cr(III) within the timeframe of the study, results appear promising that both biochar and acid activated black carbons could play a role in reducing Cr(VI) in contaminated soils. Organic carbon sources, such as black carbon (BC) and biochar, were tested for their potential in reducing Cr(VI) in acidic and alkaline contaminated soils. An alkaline soil was selected to monitor the phytotoxicity of Cr(VI) in sunflower plant. In conclusion the showed that using BC resulted in greater reduction of Cr(VI) in soils compared with biochar. This is attributed to the differences in dissolved organic carbon and functional groups that provide electrons for the reduction of Cr(VI). When increasing levels of Cr were added to soils, both microbial respiration and plant growth decreased. The application of BC was more effective than biochar in increasing the microbial population and in mitigating the phytotoxicity of Cr(VI). The net benefit of BC emerged as an increase in plant biomass and a decrease in Cr concentration in plant tissue. Consequently, it was concluded that BC is a potential reducing amendment in mitigating Cr(VI) toxicity in soil and plants. [Choppala, G.K., N.S. Bolan, M. Megharaj, Z. Chen and R. Naidu. (2012). The influence of biochar and black carbon on reduction and bioavailability of chromate in soils. J. Environ. Qual. 41:1175–1184. doi:10.2134/jeq2011.0145] ${imageDescription} Comment
