Microbial ecology of arsenic‐mobilizing C ambodian sediments: lithological controls uncovered by stable‐isotope probing

Abstract

Summary Microbially mediated arsenic release from H olocene and P leistocene C ambodian aquifer sediments was investigated using microcosm experiments and substrate amendments. In the H olocene sediment, the metabolically active bacteria, including arsenate‐respiring bacteria, were determined by DNA stable‐isotope probing. After incubation with 13 C‐acetate and 13 C‐lactate, active bacterial community in the Holocene sediment was dominated by different G eobacter spp.‐related 16S rRNA sequences. Substrate addition also resulted in the enrichment of sequences related to the arsenate‐respiring S ulfurospirillum spp. 13 C‐acetate selected for ArrA related to G eobacter spp. whereas 13 C‐lactate selected for ArrA which were not closely related to any cultivated organism. Incubation of the P leistocene sediment with lactate favoured a 16 S rRNA ‐phylotype related to the sulphate‐reducing D esulfovibrio oxamicus DSM 1925, whereas the ArrA sequences clustered with environmental sequences distinct from those identified in the H olocene sediment. Whereas limited A s( III ) release was observed in P leistocene sediment after lactate addition, no arsenic mobilization occurred from H olocene sediments, probably because of the initial reduced state of A s, as determined by X‐ray Absorption Near Edge Structure. Our findings demonstrate that in the presence of reactive organic carbon, A s( III ) mobilization can occur in P leistocene sediments, having implications for future strategies that aim to reduce arsenic contamination in drinking waters by using aquifers containing P leistocene sediments.

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