Chemical Characteristics Of Dissolved Humic Substances From Arsenic-Rich Shallow Groundwater In Bangladesh
Simone, Bailey E 1 ; Legg, Teresa 2 ; McKnight, Diane 3 ; Nemergut, Diana 4 ;Zheng , Yan 5 ; Mladenov, Natalie 6
1 University of Colorado at Boulder
2 University of Colorado at Boulder
3 University of Colorado at Boulder
4 University of Colorado at Boulder
5 Queens College
6 University of Colorado at Boulder
Dissolved organic material present in groundwater has been shown to play a significant role in mobilizing arsenic through several pathways in Bangladesh aquifers and other regions with As-rich sediments (Bauer, 2006). Firstly, labile organic substrates may stimulate the growth of heterotrophic bacteria, resulting in anoxic conditions, which drives the use of alternate electron acceptors beyond oxygen, such as nitrate and ferric iron present in oxides in sediment (Mladenov, 2008; Horneman, 2004). Another potentially important pathway is the electron shuttling by dissolved humic substances where the quinone moieties in the humic substances are reduced by microbial processes (Van Geen, 2004). These reduced humic molecules transfer electrons to ferric iron in iron oxides along the flow path. This redox cascade promotes the release of arsenic and potentially other toxic metals. Although all humic substances studied have shown some electron shuttling capability, there is a large variation among fulvic and humic acids of different origins. We have isolated preparative quantities of fulvic and transphilic acid from two well depths at a site in Bangladesh with high arsenic concentrations in the groundwater, as well as surface water. The fluorescence characteristics of these samples, which were modeled using parallel factor analysis (PARAFAC) indicate that a terrestrial source of DOM is released concurrently with high arsenic concentrations.
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