Anthropogenic influences on groundwater arsenic concentrations in Bangladesh

Neumann, Rebecca B.; Ashfaque, Khandaker N.; Badruzzaman, A. B. M.; Ali, Muhammad; Shoemaker, Julie K.; Harvey, Charles F.

doi:10.1038/ngeo685

Cited by 335 publications

(213 citation statements)

References 43 publications

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“…Although advected OC is used in the aquifer, the data reported here challenge the notion that young OC drawn down by irrigation pumping over the last 50 y has affected water quality in a rapidly recharged aquifer (3,4). In addition, the data place strict limits on the role that very old OC contained in petroleum (30), isolated peat strata (6), or ambient sedimentary carbon (7) play in driving microbial activity in reducing aquifers.…”

Section: Discussioncontrasting

confidence: 44%

mentioning

confidence: 99%

“…Given the connectivity between contaminated surface waters and aquifers, widespread pumping could redistribute As from the surface to depth (3,4) or between aquifers (5). This pumping could potentially also deliver reactive OC from ponds and latrines to depth, causing microbial reduction and As release (3,4). Fluorescent spectra of dissolved organic carbon (DOC), correlations between sedimentary organic carbon and As levels, and stratigraphy suggest, however, that reactive OC is derived from the sediment within the aquifer and therefore is primarily of geologic origin (6-8).…”

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confidence: 99%

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Advection of surface-derived organic carbon fuels microbial reduction in Bangladesh groundwater

Mailloux

Trembath‐Reichert

Cheung

et al. 2013

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

100

102

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Chronic exposure to arsenic (As) by drinking shallow groundwater causes widespread disease in Bangladesh and neighboring countries. The release of As naturally present in sediment to groundwater has been linked to the reductive dissolution of iron oxides coupled to the microbial respiration of organic carbon (OC). The source of OC driving this microbial reduction-carbon deposited with the sediments or exogenous carbon transported by groundwater-is still debated despite its importance in regulating aquifer redox status and groundwater As levels. Here, we used the radiocarbon ( 14 C) signature of microbial DNA isolated from groundwater samples to determine the relative importance of surface and sediment-derived OC. Three DNA samples collected from the shallow, high-As aquifer and one sample from the underlying, low-As aquifer were consistently younger than the total sediment carbon, by as much as several thousand years. This difference and the dominance of heterotrophic microorganisms implies that younger, surface-derived OC is advected within the aquifer, albeit more slowly than groundwater, and represents a critical pool of OC for aquifer microbial communities. The vertical profile shows that downward transport of dissolved OC is occurring on anthropogenic timescales, but bomb 14 C-labeled dissolved OC has not yet accumulated in DNA and is not fueling reduction. These results indicate that advected OC controls aquifer redox status and confirm that As release is a natural process that predates human perturbations to groundwater flow. Anthropogenic perturbations, however, could affect groundwater redox conditions and As levels in the future.A quifer redox status is a major factor affecting groundwater composition and its suitability for human consumption. The most egregious example is the dire health impact of elevated levels of arsenic (As) in groundwater drawn with inexpensive handpumped tube wells by more than 100 million villagers across South, Southeast, and East Asia (1, 2). Aquifer redox status is largely controlled by microbial respiration of organic carbon (OC) coupled to the utilization of terminal electron acceptors. Reduction of iron (Fe) oxides containing As coupled with the oxidation of OC is the dominant process causing the accumulation of As in groundwater (1), but there is no consensus on the source of OC that fuels these transformations. Such information is critical to understanding subsurface carbon cycling, redox reactions, and the vulnerability of groundwater aquifers to perturbation.Human perturbations have long been suggested to exacerbate the problem of elevated As in groundwater in several ways. Given the connectivity between contaminated surface waters and aquifers, widespread pumping could redistribute As from the surface to depth (3, 4) or between aquifers (5). This pumping could potentially also deliver reactive OC from ponds and latrines to depth, causing microbial reduction and As release (3, 4). Fluorescent spectra of dissolved organic carbon (DOC), correlations between sedimentary ...

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Section: Discussioncontrasting

confidence: 44%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Advection of surface-derived organic carbon fuels microbial reduction in Bangladesh groundwater

Mailloux

Trembath‐Reichert

Cheung

et al. 2013

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

100

102

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“…As such, our understanding of the extent and mechanisms of deep arsenic contamination has remained incomplete. Evidence suggests that deep contamination in the Mekong Delta focus area is unlikely to have been caused by the only presently acknowledged mechanism: pumping-induced vertical migration of arsenic or dissolved organic carbon (DOC), which can trigger arsenic release, from the surface or shallow subsurface (6,7,(19)(20)(21). The number of wells above 10 μg/L in the deep zone is seven times greater than in the shallow zone.…”

Section: Resultsmentioning

confidence: 95%

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.

226

122

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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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“…This As-contaminated groundwater is of concern due to both direct ingestion and the irrigation of soils for crop production. Concentrations of up to 10 mM (and slightly higher) have been reported in drinking water in Bangladesh (Frisbie et al, 2002;Ahsan et al, 2009;Neumann et al, 2010), while the average concentration of water used for irrigation in Jessore (Bangladesh) was 3 mM (FAO, 2006). Indeed, it is estimated that 0.9 to 1.36 Gg of As is brought onto arable land each year via groundwater extraction for irrigation (Ali, 2003).…”

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confidence: 99%

Examination of the Distribution of Arsenic in Hydrated and Fresh Cowpea Roots Using Two- and Three-Dimensional Techniques

et al. 2012

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Arsenic (As) is considered to be the environmental contaminant of greatest concern due to its potential accumulation in the food chain and in humans. Using novel synchrotron-based x-ray fluorescence techniques (including sequential computed tomography), short-term solution culture studies were used to examine the spatial distribution of As in hydrated and fresh roots of cowpea (Vigna unguiculata 'Red Caloona') seedlings exposed to 4 or 20 mm arsenate [As(V)] or 4 or 20 mm arsenite. For plants exposed to As(V), the highest concentrations were observed internally at the root apex (meristem), with As also accumulating in the root border cells and at the endodermis. When exposed to arsenite, the endodermis was again a site of accumulation, although no As was observed in border cells. For As(V), subsequent transfer of seedlings to an As-free solution resulted in a decrease in tissue As concentrations, but growth did not improve. These data suggest that, under our experimental conditions, the accumulation of As causes permanent damage to the meristem. In addition, we suggest that root border cells possibly contribute to the plant's ability to tolerate excess As(V) by accumulating high levels of As and limiting its movement into the root.

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Anthropogenic influences on groundwater arsenic concentrations in Bangladesh

Cited by 335 publications

References 43 publications

Advection of surface-derived organic carbon fuels microbial reduction in Bangladesh groundwater

Advection of surface-derived organic carbon fuels microbial reduction in Bangladesh groundwater

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

Examination of the Distribution of Arsenic in Hydrated and Fresh Cowpea Roots Using Two- and Three-Dimensional Techniques

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