Biodegradable Organic Carbon in Sediments of an Arsenic-Contaminated Aquifer in Bangladesh

Laboratory incubations of sediment collected from an arsenic-contaminated aquifer in Bangladesh revealed a hitherto undocumented pool of biodegradable sedimentary organic carbon. Sampling, homogenizing, handling, and/or experimentation with the sediment released organic carbon, causing dissolved organic carbon (DOC) concentrations to reach ∼150–250 mg/L when DOC was mixed with recharge water. The native sedimentary microbial community rapidly consumed the released carbon, producing methane, while no loss of DOC was observed in sterilized sediments. In both sterilized and native incubations, dissolved arsenic equilibrated with the sediment; arsenic concentrations initially dropped and then remained constant over the 180 day experiment. Collectively, these data suggest that in situ perturbations to the aquifer matrix could promote mobilization of bioavailable sedimentary organic carbon. Although this sedimentary organic carbon did not influence arsenic concentrations here, it represents a carbon source that could, in the presence of arsenic-bearing iron (hydr)oxides, fuel microbial reductive release of arsenic.