Microbial mobilization of arsenic from sediments of the Aberjona watershed

Arsenic mobilization from aquatic sediments is an issue of concern, as water-borne arsenic can migrate into pristine areas, endangering aquatic organisms and people. Such mobilization in the Aberjona Watershed has distributed nearly 20 t of arsenic throughout river and lake sediments. To gain an understanding of possible biological mechanisms contributing to this transport mobilization of solid-phase arsenic was investigated in upper Aberjona sediment microcosms. Microcosms catalyzed rapid dissolution of arsenic from iron arsenate, a solid-phase surrogate for sedimentary arsenic, mobilizing 20-28% of the arsenic present. Sterilization prevented this transformation. Reduction of arsenate to arsenite accompanied iron arsenate dissolution, suggesting that reduction was driving dissolution. Sediment- conditioned, filter-sterilized medium showed no arsenic-transforming activity. A native enrichment culture of sulfate-reducing bacteria possessed one-fifth of the microcosm activity, while strain MIT-13, a native arsenate reducing microorganism, showed much greater activity dissolving 38% of the arsenic present. Furthermore, strain MIT 13 mobilized arsenic from presterilized, unamended upper Aberjona sediments. These observations indicate that a direct microbial arsenic-mobilizing activity exists in the sediments, show that strain MIT-13 is a strong arsenic transforming agent native to the sediments, and suggest that dissimilatory arsenic reduction may contribute to arsenic flux from anoxic sediments in the most arsenic- contaminated region of the Aberjona Watershed.