The influence of biochar and black carbon on reduction and bioavailability of chromate in soils

University of South Australia, Australia.
Journal of Environmental Quality (Impact Factor: 2.35). 01/2012; DOI: 10.2134/jeq2011.0145

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 non-toxic and is strongly bound to soil particles, while Cr(VI) is more toxic, soluble and readily leaches into groundwater. The toxicity of Cr(VI) can be mitigated by reducing it to Cr(III) species. The objective of this study was to examine the effect of organic carbon sources on the reduction, microbial respiration and phytoavailability of Cr(VI) in soils. Organic carbon sources such as black carbon 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. Our results showed that using black carbon resulted in greater reduction of Cr(VI) in soils compared to biochar. This is attributed to the differences in dissolved organic carbon (DOC) 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 black carbon was more effective than biochar in increasing the microbial population and in mitigating the phytotoxicity of Cr(VI). The net benefit of black carbon emerged as an increase in plant biomass and a decrease in Cr concentration in plant tissue. Consequently, it was concluded that black carbon is a potential reducing amendment in mitigating Cr(VI) toxicity in soil and plants.

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