Redox trapping of arsenic during groundwater discharge in sediments from the Meghna riverbank in Bangladesh
- 6 October 2009
- journal article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences of the United States of America
- Vol. 106 (40), 16930-16935
- https://doi.org/10.1073/pnas.0908168106
Abstract
Groundwater arsenic (As) is elevated in the shallow Holocene aquifers of Bangladesh. In the dry season, the shallow groundwater discharges to major rivers. This process may influence the chemistry of the river and the hyporheic zone sediment. To assess the fate of As during discharge, surface (0-5 cm) and subsurface (1-3 m) sediment samples were collected at 9 sites from the bank of the Meghna River along a transect from its northern source (25 degrees N) to the Bay of Bengal (22.5 degrees N). Bulk As concentrations of surface sediment averaged 16 +/- 7 mg/kg (n = 9). Subsurface sediment contained higher mean concentrations of As of 4,000 mg/kg (n = 14), ranging from 1 to 23,000 mg/kg As, with >100 mg/kg As measured at 8 sites. X-ray absorption near-edge structure spectroscopy indicated that As was mainly arsenate and arsenite, not As-bearing sulfides. We hypothesize that the elevated sediment As concentrations form as As-rich groundwater discharges to the river, and enters a more oxidizing environment. A significant portion of dissolved As sorbs to iron-bearing minerals, which form a natural reactive barrier. Recycling of this sediment-bound As to the Ganges-Brahmaputra-Meghna Delta aquifer provides a potential source of As to further contaminate groundwater. Furthermore, chemical fluxes from groundwater discharge from the Ganges-Brahmaputra-Meghna Delta may be less than previous estimates because this barrier can immobilize many elements.Keywords
This publication has 24 references indexed in Scilit:
- Near-surface wetland sediments as a source of arsenic release to ground water in AsiaNature, 2008
- Determining Rates of Change and Evaluating Group-Level Resiliency Differences in Hyporheic Microbial Communities in Response to Fluvial Heavy-Metal DepositionApplied and Environmental Microbiology, 2004
- Arsenic in groundwater of the Bengal Basin, Bangladesh: Distribution, field relations, and hydrogeological settingHydrogeology Journal, 2004
- Spatial variability of arsenic in 6000 tube wells in a 25 km2 area of BangladeshWater Resources Research, 2003
- Stratigraphic evolution of the late Holocene Ganges–Brahmaputra lower delta plainSedimentary Geology, 2003
- Controls on facies distribution and stratigraphic preservation in the Ganges–Brahmaputra delta sequenceSedimentary Geology, 2003
- A review of the source, behaviour and distribution of arsenic in natural watersApplied Geochemistry, 2002
- Large Groundwater Strontium Flux to the Oceans from the Bengal Basin and the Marine Strontium Isotope RecordScience, 2001
- Arsenic mobilization in the hyporheic zone of a contaminated streamWater Resources Research, 1999
- Distribution of arsenic in the natural environment with emphasis on rocks and soilsApplied Organometallic Chemistry, 1988