Presently more than 100 million people in Asia are exposed to groundwater with arsenic (As) concentrations exceeding standards recommended by the World Health Organization. The governing biogeochemical processes controlling the release of As from sediments and potential secondary sinks remain in question. Further, it remains unclear whether a single mechanism or a combination of processes controls As cycling across the large affected geographic areas. Here we provide a detailed evaluation of aquifer chemistry within the Jianghan Plain of the Yangtze River, China, followed by a comparison of these results to other As affected regions of Asia. Groundwater As concentrations exceed 1000 �g L-1 in some locations within the Jianghan Plain and exhibit strong seasonal variability, complicating identification of As contaminated wells. The highest aqueous concentrations in the aquifer are co-located with As-rich, carbon-depleted sediment. Arsenic X-ray absorption spectroscopy (XAS) analysis of these sediments reveals that although As(III) is the dominant species throughout the profile, As appears to be accumulating in an oxidized layer ~20 m below the surface where the solid-phase arsenic concentration exceeds 100 mg kg-1. Batch incubations of sediment amended with 2 mM glucose or with deionized (DI) water demonstrates that the greatest As release is coincident with elevated solid-phase As at depths between 18 and 23 m. Glucose amendment enhances As release at these depths by a factor of approximately two compared to DI water, but marginally increases As liberation at other depths. XAS analysis of glucose amended sediment post-incubation shows that when sulfur is present, As transitions from an oxoanion to As-S precipitate, preventing As release to solution. In sulfur-depleted sediment As is released to solution following glucose amendment. Our results highlight the vulnerability of groundwater resources in the Jianghan Plain to changing geochemical conditions.

Susceptibility of groundwater As concentrations to changing geochemical conditions

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.