GEOC 4 |
| Prosun Bhattacharya1, Nirmal Tandukar2, Antonio A. Valero1, Gunnar Jacks1, and Arun B. Mukherjee3. (1) Department of Land and Water Resources Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden, (2) Department of Water Supply and Sewerage (DWSS), Panipokhari, Kathmandu, Nepal, (3) Department of Environmental Sciences, University of Helsinki, P.O. Box 27, FIN-00014 University of Helsinki, Finland |
| Mobilization of arsenic (As) in groundwater has become a focus of attention in recent years. Since a few years back, As is found as a geogenic contaminant in the groundwaters of the Terai Alluvial Plain (TAP) in southern Nepal. The source of As is natural and thought to be leached mainly due to weathering of As bearing minerals in the Himalayan range towards northern Nepal. In this study, the groundwater chemistry in the central part of the TAP in the district of Nawalparasi in southern Nepal has been investigated. TAP groundwaters are predominantly in a reducing character with high HCO3-, low SO42- and NO3- concentrations. Total arsenic (Astot) content in groundwater varied from 1.7 mg/L to as high as 404 mg/L, predominantly occurring as As(III) species. These groundwaters are characterized by elevated levels of dissolved Fe, Mn, NH4+ and DOC. The redox environment of the TAP alluvial aquifers seem to be controlled by several terminal electron accepting processes. Bacterial reduction of Fe3+ to Fe2+ ions, mobilize Fe as well as the adsorbed As along with dissimilatory reduction of As(V) to As(III). A characteristic feature of these reduced groundwaters is the elevated NH4+ concentrations, which shows positive correlation with Astot. The observed relationships between DOC, HCO3-, Fetot and Astot, supports the hypothesis of reductive dissolution of Fe-oxyhydroxides as the main mechanism of mobilization of As in the TAP aquifers. |
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Chemistry of Metals in Terrestrial and Aquatic Systems
8:00 AM-11:25 AM, Sunday, March 28, 2004 Marriott -- Marquis NE, Oral
Division of Geochemistry |