ABSTRACT
Pleistocene aquifers are key for lowering the chronic exposure of the rural population to arsenic. Too little is known, however, about the sources of reactive carbon that maintain reducing conditions in these low-arsenic aquifers. This matters as enhanced supply of reactive carbon due to perturbations in groundwater flow could potentially release arsenic to groundwater. To shed light on this process, our team measures the radiocarbon content of labile microbial matter (RNA) and compares it to the radiocarbon content of potential sources of reactive carbon. Results to date suggest that recent recharge supplies reactive carbon in the dissolved form rather than the sediment, possibly in part in the form of methane. This dynamic situation suggests arsenic concentration could vary of time and should be monitored in vulnerable areas.
