The Infl uence of Biochar and Black Carbon on Reduction and Bioavailability of Chromate in Soils

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. Th e toxicity of Cr(VI) can be mitigated by reducing it to Cr(III) species. Th e objective of this study was to examine the eff ect of organic carbon sources on the reduction, microbial respiration, and phytoavailability of Cr(VI) in 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 sunfl ower plant. Our results showed that using BC resulted in greater reduction of Cr(VI) in soils compared with biochar. Th is is attributed to the diff erences 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. Th e application of BC was more eff ective than biochar in increasing the microbial population and in mitigating the phytotoxicity of Cr(VI). Th e net benefi t 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.