Co(II0I)EDTA(-) reduction by Desulfovibrio vulgaris and propagation of reactions involving dissolved sulfide and polysulfides

The migration of Co-60, dominantly via transport of Co-EDTA complexes, into surface water and groundwater is a recognized concern at many nuclear prod uction and storage sites. Reduction of Co(III)EDTA(-) to Co(II)EDTA(2-) sho uld decrease the mobility of Co-60 in natural environments by stimulating l igand displacement with Fe(lll) or AI(III) or by precipitation of CoSx in s ulfidic environments. In this study, we examine direct(enzymatic) and indir ect (metabolite) reduction processes of Co(III)EDTA(-) by the sulfate-reduc ing bacterium Desulfovibrio vulgaris. D. vulgaris reduces Co(III)EDTA(-) to Co(II)EDTA(2-), but growth using it as a terminal electron acceptor was no t demonstrated. Rather than acting as a competing electron acceptor and lim iting cobalt reduction, introducing sulfate with D. vulgaris enhances the r eduction of Co(III)EDTA(-) as a result of sulfide production. Sulfide reduc es Co(III)EDTA(-) in a pathway involving polysulfide formation and leads to a CoS precipitate. Thus, both direct and indirect (i.e., through the produ ction of sulfide) microbial reduction pathways of Co(III)EDTA(-) may help t o retard its migration within soils and waters.