CoII0IEDTA- 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 production and storage sites. Reduction of Co(III)EDTA(-) to Co(II)EDTA(2-) should decrease the mobility of Co-60 in natural environments by stimulating ligand displacement with Fe(lll) or AI(III) or by precipitation of CoSx in sulfidic environments. In this study, we examine direct(enzymatic) and indirect (metabolite) reduction processes of Co(III)EDTA(-) by the sulfate-reducing bacterium Desulfovibrio vulgaris. D. vulgaris reduces Co(III)EDTA(-) to Co(II)EDTA(2-), but growth using it as a terminal electron acceptor was not demonstrated. Rather than acting as a competing electron acceptor and limiting cobalt reduction, introducing sulfate with D. vulgaris enhances the reduction of Co(III)EDTA(-) as a result of sulfide production. Sulfide reduces Co(III)EDTA(-) in a pathway involving polysulfide formation and leads to a CoS precipitate. Thus, both direct and indirect (i.e., through the production of sulfide) microbial reduction pathways of Co(III)EDTA(-) may help to retard its migration within soils and waters.