Article

EEMs Characteristics of Dissolved Organic Matter and Their Implication in High Arsenic Groundwater of Jianghan Plain

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Abstract

Dissolved organic matter (DOM) is one of the key factors controlling the release of arsenic from sediment to groundwater. There are abundant surface water systems with rivers, lakes, streams and ponds in the Jianghan plain, densely covered by irrigation canals and ditches. The interactions between surface water and shallow groundwater may significantly affect the characteristics and strength of DOM in water. In order to elaborate the roles of DOM on arsenic mobilization in groundwater of Jianghan plain, this study analyzes surface water and groundwater samples using excitation-emission matrix spectroscopy (EEMs) and characterizes the dissolved organic matter of its functional groups, molecular, fluorescence using PARAFAC (parallel factor analysis). It is found that dissolved organic matter in Jianghan plain mainly includes three different components, of which C1 and C2 are humic-like substances and C3 is characterized by protein-like substances. The main components of dissolved organic matter in groundwater are C1 and C2, whilst the dissolved organic matter in surface water is mostly C2 and C3. Dissolved organic matter in groundwater dominated by terrestrial materials, promotes the mobilization of arsenic in two ways. (1) The humic substances act as an electron shuttle for microbial communities, promoting the microbially mediated oxidation of organic matter and reduction of Fe oxides with the release of arsenic and the production of large amounts of DOC (dissolved organic carbon)and HCO3⁻; (2) Complexation of As with DOM via the bridging of metal cations (such as Fe) enhances the mobility of As in groundwater. © 2017, Editorial Department of Earth Science. All right reserved.

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... Considerable proportion of oxidizable As (avg. 13.4%) was generally found in samples as the proclivity of HAsO 4 2 − and As(OH) 3 compounds for complexation with organic matters at high pH (Saada et al., 2003), and bridging of metal cations which may enhance the mobility of As (Lu et al., 2017;Li and Thornton, 1993). ...
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