Mobility and Bioavailability of Chromium in the Environment: Physico-Chemical and Microbial Oxidation of Cr (III) to Cr (VI)

Abstract

The physico-chemical and microbial characteristics in soil was investigated in order to study the mobility and bioavailability of Chromium in the environment. In the present investigation the role of soil microbes along with some physico-chemical agents (UV ray, Mn and Fe) were studied for possible oxidation of Cr(III) to Cr(VI) in laboratory conditions. Photochemical oxidation of Cr(III) to Cr(VI) was found to be significantly high at the surface level of the soil studied (conversion of Cr6+ in control soil was calculated as 0.15 mg kg-1 dry weight). Metal catalyst also contributed to oxidation of chromium in soil. Conversion of Cr6+ by metal catalysis ranged between 0.00 and 0.08 mg kg-1 dry weight (mean 0.05 mg kg-1 dry weight). However, metal catalysts such as, Fe and Mn together or these metals alone were not as efficient as the microbes or the UV mediated conversion during the given period of exposure (two weeks). The data indicates that microbial conversion of Cr(III) to Cr(VI) varied from 0.12 – 0.18 mg kg-1 dry weight, while mean was 0.14 mg kg-1 dry weight. Since, at the plant root zone, where the UV penetration is negligible, metal catalysts could be inferred to be not much efficient in conversion of Cr(III) to Cr(VI) as compared to microbes. Therefore, the present findings suggested that microbial mediated conversion is the preferred pathway and consequently responsible for root uptake of chromium by plants.