Subsurface Mobility of Organo–Cr(III) Complexes Formed during Biological Reduction of Cr(VI)

Hexavalent chromium [Cr(VI)] contamination of soil and groundwater is a major concern for some industrial sites as well as many United States Department of Energy sites. Bioreduction of Cr(VI) to less toxic and less mobile Cr(III) has received much attention as a viable method of remediation. However, bioreduction of Cr(VI) also produces soluble organo–Cr(III) complexes and little is known about the fate of these complexes in the environment. Cr(VI) was reduced abiotically in the presence of cellular organic compounds (malate, cysteine, and serine) and biotically in the presence of two test organisms (Cellulomonas ES6 and S. oneidensis MR1). The soluble organo–Cr(III) complexes formed were then introduced to soil columns to evaluate their sorption affinity and transport characteristics. The column data indicated that a significant fraction of the biologically derived organo–Cr(III) complexes are both soluble and mobile. Other complexes were observed to have limited mobility, indicating that a heterogeneous mixture of complexes are formed during biological reduction of Cr(VI).