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 immobi le above pH 5.5. Reduction to the trivalent state thus represents an e ffective 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 s oil. We found that organic matter content, bioactivity, and oxygen sta tus 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 nonbio logical processes were influential, and, of 20 chromate-resistant bact erial cultures isolated from soils, 9 were found to actively reduce Cr (VI) to Cr(III) in liquid media. Our study suggests that organic-amend ed 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.