Abstract
Arsenic groundwater contamination threatens the health of millions of people worldwide, particularly in South and Southeast Asia. In most cases, the release of arsenic from sediment was caused by microbial reductive dissolution of arsenic-bearing iron(III) minerals with organic carbon being used as microbial electron donor. Although in many arsenic-contaminated aquifers high concentrations of methane were observed, its role in arsenic mobilization is unknown. Here, using microcosms experiments and hydrogeochemical and microbial community analyses, we demonstrate that methane functions as electron donor for methanotrophs, triggering the reductive dissolution of arsenic-bearing iron(III) minerals, increasing the abundance of genes related to methane oxidation, and ultimately mobilizing arsenic into the water. Our findings provide evidence for a methane-mediated mechanism for arsenic mobilization that is distinct from previously described pathways. Taking this together with the common presence of methane in arsenic-contaminated aquifers, we suggest that this methane-driven arsenic mobilization may contribute to arsenic contamination of groundwater on a global scale.
Highlights
Arsenic groundwater contamination threatens the health of millions of people worldwide, in South and Southeast Asia
These symptoms are prevalent in populations living along river floodplains of South and Southeast Asia that rely on shallow groundwater wells for drinking water and irrigation[2,3]
In situ gas measurements demonstrated that the Total dissolved gas pressure (TDGP) correlates with As concentrations and CH4 accounts for the majority of detected gases in the groundwater (Fig. 1c)
Summary
Arsenic groundwater contamination threatens the health of millions of people worldwide, in South and Southeast Asia. Analysis of the in situ microbial community composition by 16S rRNA gene amplicon sequencing in aquifer sediments and groundwater (Fig. 2) showed that fermenting, methanogenic, and methanotrophic microorganisms dominated sediments and groundwater, suggesting that CH4 cycling occurs in this aquifer.
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