Arsenic mobilization by anaerobic iron-dependent methane oxidation

In most cases, the release of arsenic (As) was shown to be caused by microbially catalyzed reductive dissolution of As-bearing Fe(III) (oxyhydr)oxide minerals with organic carbon being used as microbial electron and energy source6-8.

Although in many As-contaminated aquifers high concentrations of methane (CH4) were observed9-11, the role of CH4 for As mobilization is unknown. Here we demonstrate that CH4 functions as electron donor for methanotrophic microorganisms and triggers the reductive dissolution of As-bearing Fe(III) (oxyhydr)oxide minerals leading to As mobilization. In microcosms with As-bearing sediments from the Red River Delta amended with environmentally relevant concentrations of CH4 we found that CH4 triggers Fe(III) mineral reduction, supports the growth and activity of type-1 aerobic methanotrophs and archaea affiliating with Candidatus Methanoperedens, increases the abundance of methane oxidation mcrA and pmoA genes, and ultimately mobilizes significant amount of As into the water.