Bioremediation of Soils Polluted with Hexavalent Chromium Using Bacteria

Abstract

Chromium (Cr) is a highly toxic metal that is continually being accumulated in the environment through natural processes and anthropogenic activities. Also, with the advent of industrialisation, the release of untreated effluent enables uncontrolled Cr to spread beyond groundwater and aquatic systems. United States Environment Protection Agency (USEPA) has marked Cr as a “Class A” pollutant, as one among the 17 hazardous chemicals posing a serious threat to mankind. Unlike trivalent chromium Cr(III), which is essential in trace amounts, hexavalent chromium Cr(VI) is a highly toxic form of chromium that persists in the soil owing to its high mobility. Also, its high bioavailability and solubility exert toxic effects including carcinogenicity in humans and mutagenicity/teratogenicity in most organisms. This chapter provides an overview of the popular remediation strategies (physical, chemical and biological) employed in the detoxification of Cr(VI). In recent times, biological mediated detoxification strategy is the most pursued due to its environmental friendly and sustainable approach. Some members of bacteria show chromium resistance and successfully reduce Cr(VI) to Cr(III), which is a less toxic form. Physicochemical factors, immobilisation of bacterial cells and genetic engineering strategies are described and compared to offer evidences which further enhances the bioremediation efficiency by attaining resistance towards Cr(VI) and biotransforming Cr(VI) to less toxic Cr(III).