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

Marina Héry,Hervé Sanguin,Jonathan R Lloyd,Richard D Pancost,David A Cooke,Athanasios Rizoulis,David A Polya

doi:10.1111/1462-2920.12412

Abstract

Microbially mediated arsenic release from Holocene and Pleistocene Cambodian aquifer sediments was investigated using microcosm experiments and substrate amendments. In the Holocene 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 Geobacter spp.-related 16S rRNA sequences. Substrate addition also resulted in the enrichment of sequences related to the arsenate-respiring Sulfurospirillum spp. (13) C-acetate selected for ArrA related to Geobacter spp. whereas (13) C-lactate selected for ArrA which were not closely related to any cultivated organism. Incubation of the Pleistocene sediment with lactate favoured a 16S rRNA-phylotype related to the sulphate-reducing Desulfovibrio oxamicus DSM1925, whereas the ArrA sequences clustered with environmental sequences distinct from those identified in the Holocene sediment. Whereas limited As(III) release was observed in Pleistocene sediment after lactate addition, no arsenic mobilization occurred from Holocene sediments, probably because of the initial reduced state of As, as determined by X-ray Absorption Near Edge Structure. Our findings demonstrate that in the presence of reactive organic carbon, As(III) mobilization can occur in Pleistocene sediments, having implications for future strategies that aim to reduce arsenic contamination in drinking waters by using aquifers containing Pleistocene sediments.

Highlights

IntroductionIn South and South East Asia, where high concentrations of arsenic in groundwater are causing a humanitarian disaster (Smith et al, 2000), aquifer sediments have been studied largely in terms of their geological, mineralogical and geochemical characteristics (Acharyya et al, 2000; Berg et al, 2001; 2007; Polya et al, 2003; Ravenscroft et al, 2005; 2009; Zheng et al, 2005; Charlet and Polya, 2006; Buschmann et al, 2007; Rowland et al, 2008)
Limited As(III) release was observed in Pleistocene sediment after lactate addition, no arsenic mobilization occurred from Holocene sediments, probably because of the initial reduced state of As, as determined by X-ray Absorption Near Edge Structure
Our findings demonstrate that in the presence of reactive organic carbon, As(III) mobilization can occur in Pleistocene sediments, having implications for future strategies that aim to reduce arsenic contamination in drinking waters by using aquifers containing Pleistocene sediments

Summary

Introduction

In South and South East Asia, where high concentrations of arsenic in groundwater are causing a humanitarian disaster (Smith et al, 2000), aquifer sediments have been studied largely in terms of their geological, mineralogical and geochemical characteristics (Acharyya et al, 2000; Berg et al, 2001; 2007; Polya et al, 2003; Ravenscroft et al, 2005; 2009; Zheng et al, 2005; Charlet and Polya, 2006; Buschmann et al, 2007; Rowland et al, 2008). Studies based on arsenic-rich South East Asian sediments support the consensus that the oxidation of organics coupled to the reduction of As(V) sorbed to mineral surfaces plays a major role in As(III) mobilization in anoxic aquifers Profiling of the bacterial structure based on 16S ribosomal RNA (rRNA) gene phylogeny and the study of arsenate reductase genes in arsenic-rich sediments have emphasized the enrichment of metal-reducing Geobacter spp. The probable influence of Geobacter in arsenic biogeochemistry in groundwater has been highlighted recently by a transcriptomic approach (Giloteaux et al, 2013)

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