Mobility of arsenic in a Bangladesh aquifer: Inferences from geochemical profiles, leaching data, and mineralogical characterization

Swartz, Christopher H.; Blute, Nicole; Badruzzman, Borhan; Ali, Ashraf; Brabander, Daniel J.; Jay, Jenny; Besancon, James; Islam, Shafiqul; Hemond, Harold F.; Harvey, Charles F.

doi:10.1016/j.gca.2004.04.020

Cited by 262 publications

(212 citation statements)

References 47 publications

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“…In the Mekong Delta, dramatic changes occurred in vegetation types, flooding patterns, hydraulic gradients, and mineral weathering (27,28). Evidence of these changes is seen in the abundance of ferric (hydr)oxides that give Pleistocene sands in Bangladesh their oft-noted brown or orange color (8,10,13,29,30). These oxidized deposits have a higher capacity for arsenic adsorption (4,21,31) and are associated with aquifers that are low in dissolved arsenic, which are found at greater depths in the Bengal Basin owing to higher sedimentation rates.…”

Section: Resultsmentioning

confidence: 99%

Release of arsenic to deep groundwater in the Mekong Delta, Vietnam, linked to pumping-induced land subsidence

Erban¹,

Gorelick²,

Zebker

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

237

126

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Deep aquifers in South and Southeast Asia are increasingly exploited as presumed sources of pathogen- and arsenic-free water, although little is known of the processes that may compromise their long-term viability. We analyze a large area (>1,000 km 2 ) of the Mekong Delta, Vietnam, in which arsenic is found pervasively in deep, Pliocene–Miocene-age aquifers, where nearly 900 wells at depths of 200–500 m are contaminated. There, intensive groundwater extraction is causing land subsidence of up to 3 cm/y as measured using satellite-based radar images from 2007 to 2010 and consistent with transient 3D aquifer simulations showing similar subsidence rates and total subsidence of up to 27 cm since 1988. We propose a previously unrecognized mechanism in which deep groundwater extraction is causing interbedded clays to compact and expel water containing dissolved arsenic or arsenic-mobilizing solutes (e.g., dissolved organic carbon and competing ions) to deep aquifers over decades. The implication for the broader Mekong Delta region, and potentially others like it across Asia, is that deep, untreated groundwater will not necessarily remain a safe source of drinking water.

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Section: Resultsmentioning

confidence: 99%

Release of arsenic to deep groundwater in the Mekong Delta, Vietnam, linked to pumping-induced land subsidence

Erban¹,

Gorelick²,

Zebker

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

237

126

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“…The shallow aquifer in Bangladesh is Ϸ30-m thick, with an area of Ϸ40,000 km 2 and a sediment As concentration of Ϸ3 mg/kg (1,22,23). Therefore, the sediment As inventory is estimated to be 7 ϫ 10 9 kg, assuming a 25% porosity and 2.5 g/cm 3 grain density.…”

Section: Discussionmentioning

confidence: 99%

Redox trapping of arsenic during groundwater discharge in sediments from the Meghna riverbank in Bangladesh

Datta

Mailloux

Jung

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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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°N) to the Bay of Bengal (22.5°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 sedimentbound 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.Ganges-Brahmaputra ͉ hyporheic zone ͉ natural reactive barrier ͉ submarine groundwater discharge ͉ XANES

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“…This may be one reason why there is no simple relationship between concentrations of Fe and As in anoxic groundwater (2,5,10,21,41). The limited impact of acetate on incubations of natural aquifer material suggests that the release of both Fe and As is not necessarily limited by the supply of organic substrate.…”

Section: Re-interpreting Spatial Patterns Of As In Groundwatermentioning

confidence: 99%

Mobilization of Arsenic During One-Year Incubations of Grey Aquifer Sands from Araihazar, Bangladesh

Radloff

Cheng

Rahman

et al. 2007

Environ. Sci. Technol.

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Elevated As concentrations in shallow groundwater pose a major health threat in Bangladesh and similarly affected countries, yet there is little consensus on the mechanism of As release to groundwater or how it might be influenced by human activities. In this study, the rate of As release was measured directly with incubations lasting 11 months, using sediment and groundwater collected simultaneously in Bangladesh and maintained under anaerobic conditions throughout. Groundwater and grey sediment were collected as diluted slurries between 5 and 38 m depth, a range over which ambient groundwater As concentrations increased from 20 to 100 μg L −1 . Arsenic was released to groundwater in slurries from 5 and 12 m depth at a relatively constant rate of 21 ± 4 (2 σ) and 23 ± 6 μg As kg −1 yr −1 , respectively. Amendment with a modest level of acetate increased the rate of As release only at 12 m (82 ± 18 μg kg −1 yr −1 ). Although the groundwater As concentration was initially highest at 38 m depth, no release of As was observed. These results indicate that the spatial distribution of dissolved As in Bangladesh and local rates of release to groundwater are not necessarily linked. Iron release during the incubations did not occur concurrently with As release, providing further confirmation that the two processes are not directly coupled. Small periodic additions of oxygen suppressed the release of As from sediments at all three depths, which supports the notion that anoxia is a prerequisite for accumulation of As in Bangladesh groundwater.

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Mobility of arsenic in a Bangladesh aquifer: Inferences from geochemical profiles, leaching data, and mineralogical characterization

Cited by 262 publications

References 47 publications

Release of arsenic to deep groundwater in the Mekong Delta, Vietnam, linked to pumping-induced land subsidence

Release of arsenic to deep groundwater in the Mekong Delta, Vietnam, linked to pumping-induced land subsidence

Redox trapping of arsenic during groundwater discharge in sediments from the Meghna riverbank in Bangladesh

Mobilization of Arsenic During One-Year Incubations of Grey Aquifer Sands from Araihazar, Bangladesh

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