FACTORS AFFECTING CHEMICAL AND BIOLOGICAL REDUCTION OF HEXAVALENT CHROMIUM IN SOIL

Hexavalent chromium [Cr(VI)] is a common environmental pollutant that is mobile in soils and is a known mutagen. The trivalent form [Cr(III)] has no known mutagenic properties and is highly insoluble and immobile above pH 5.5. Reduction to the trivalent state thus represents an effective mechanism for detoxification and immobilization of Cr(VI) in soil/water systems. In this study, we conducted experiments to examine various parameters involving aerobic reduction of Cr(VI) in a field soil. We found that organic matter content, bioactivity, and oxygen status were important factors. Under optimum conditions, the soil reduced 96% of added Cr(VI) under aerobic, field-moist conditions. The pH of the system was shown to have little effect. Both biological and nonbiological processes were influential, and, of 20 chromate-resistant bacterial cultures isolated from soils, 9 were found to actively reduce Cr(VI) to Cr(III) in liquid media. Our study suggests that organic-amended soils can readily reduce Cr(VI) and could promote excellent removal efficiency either as a primary treatment technique, or in conjunction with bioreactor-type wastewater treatment systems.