| Arsenic contamination of groundwater is a global health crisis, especially in Bangladesh where an estimated 40 million people are at risk (Smith, Lingas and Rahman 2000). The release of dissolved arsenic (As) into groundwater from geogenic arsenic bound to sediments (Anawar, et al. 2003) is thought to be influenced by dissolved organic matter (DOM) through several biogeochemical processes. Abiotically, DOM can promote the release of sediment bound As through the formation of DOM-As complexes (Redman, Macalady and Ahmann 2002) and competitive interactions between As and DOM for sorption sites on the sediment (Bauer and Blodau 2006). Additionally, groundwater DOM can serve as an electron acceptor yielding energy to support microbial growth (Lovey, et al. 1996), resulting in reduction of iron bound to sediments and consequently As mobilization (McArthur, et al. 2001). However, the exact role and nature of the DOM involved in As mobilization is yet to be resolved. The goal of this study is to understand the source of DOM and the DOM sorption processes that occur at depth. This study first performed an in-depth geochemical site analysis, followed by isolation of preparative quantities of fulvic acids from numerous groundwater samples from two field campaigns in the Araihazar region of Bangladesh. The groundwater and fulvic acid isolates where analyzed using fluorescence spectroscopy, elemental analysis, carbon-13 NMR, etc to understand the source and reactivity of the DOM. This study found that where there is high arsenic, there is a decrease in the fluorescence index and percent of protein-like fluorescence, suggesting a release of terrestrial DOM at depth. It is hypothesized that this terrestrial DOM, perhaps from the dissolution of sediment organic carbon, is driving the reductive dissolution processes which lead to As mobilization. |
