Integrated biogeochemical and hydrologic processes driving arsenic release from shallow sediments to groundwaters of the Mekong delta

Kocar, Benjamin D.; Polizzotto, Matthew L.; Benner, S. G.; Ying, Samantha C.; Ung, Mengieng; Ouch, Kagna; Samreth, Sopheap; Suy, Bunseang; Phan, Kongkea; Sampson, M.; Fendorf, Scott

doi:10.1016/j.apgeochem.2008.06.026

Cited by 150 publications

(105 citation statements)

References 46 publications

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“…Holocene clays are known to maintain high concentrations of dissolved arsenic over millennia (12,26). Modern climate features, notably tropical temperatures and precipitation, and high sea levels, are conducive to sustaining the biogeochemical conditions that are favorable to arsenic dissolution within Holocene clays.…”

Section: Resultsmentioning

confidence: 99%

“…Concurrently, clays lost some of their original solute load to diffusion through the limited connected pore network. Slow diffusion out of occluded pores and slow dissolution and desorption of the persistent solid-phase arsenic supply (12,33), however, maintained a continuous dissolved arsenic load in deep clays, as found elsewhere in much older aquitards (>70 Ma) (34). When low-arsenic, deep aquifers were overpumped during recent decades, clay compaction began, leading to water containing arsenic or possibly other, arsenicmobilizing solutes being squeezed out of dead-flow storage in confining clays to adjacent aquifers, a process taking a decade or more.…”

Section: Resultsmentioning

confidence: 99%

“…As a result, considerable attention has been paid to contamination mechanisms in Holocene units (up to ∼0.011 Ma in age), where affected wells are most commonly found, and to older Pleistocene units (∼0.011-2.6 Ma), where they are usually more rare (6)(7)(8)13). Little is known of arsenic occurrence in older Pliocene-Miocene-age (∼2.6-23 Ma) aquifers or in the thick sequences of interbedded confining clays (i.e., aquitards), which are known to mobilize high levels of dissolved arsenic in nearsurface Holocene clays (12).…”

mentioning

confidence: 99%

“…Dissolution is controlled by a suite of physicochemical conditions that vary widely within and among hydrogeologic units (9), largely as a result of variability in depositional and paleoclimatic conditions during their formation. Across basins, dissolved arsenic concentrations tend to be highest in the shallow (<100 m) subsurface (10), where the reactivity of host minerals and the organic carbon needed to dissolve them is also greatest (11,12). As a result, considerable attention has been paid to contamination mechanisms in Holocene units (up to ∼0.011 Ma in age), where affected wells are most commonly found, and to older Pleistocene units (∼0.011-2.6 Ma), where they are usually more rare (6)(7)(8)13).…”

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confidence: 99%

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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.

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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%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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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.

Self Cite

235

126

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“…In Cambodia, many studies have found high arsenic hazard in groundwater drinking water sources (Polya et al 2003(Polya et al , 2005Feldman et al 2007;Berg et al 2007;Buschmann et al 2007;Polya et al 2008;Sampson et al 2008;Kocar et al 2008;Quicksall et al 2008;Rowland et al 2008;Benner et al 2008;Sthiannopkao et al 2008;Polizzotto et al 2008). Human exposure has been demonstrated through studies of various biomarkers (Kubota et al 2006;Gault et al 2008) and cases of arsenic poisoning (arsenicosis) have been recorded by Mazumder et al (2009), amongst others.…”

Section: Labour Markets and Shadow Wage Ratesmentioning

confidence: 99%

Discrete Choice Experiments in Developing Countries: Willingness to Pay Versus Willingness to Work

Gibson

Rigby

Polya

et al. 2015

Environ Resource Econ

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A concern when conducting stated preference valuation studies in rural developing or very low income contexts is the use of monetary willingness to pay (WTP) estimates. In circumstances where cash incomes are extremely low, a significant proportion of the population are not engaged in waged labour and the exchange of goods or services is augmented through barter or work exchange, the role of money is likely to be different from that within an urban developed setting. As such, ability to pay using money may be impaired and downwardly biased when compared with other mediums of exchange. In recognition of this several studies have used hypothetical labour contributions as payment vehicles and a common finding is that households are more often willing to contribute labour than they are money. In this paper we present the results of a split sample DCE using money and labour contributions as payment vehicles for improved drinking water quality in Kandal Province, Cambodia. We find little differences between the payment vehicles in terms of attribute non-attendance, marginal utilities of attributes or derived welfare values. We argue that this provides support for the use of WTP in rural developing areas where there are functioning labour markets.

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Groundwater flow dynamics and arsenic source characterization in an aquifer system of West Bengal, India

Desbarats

Koenig

Pal

et al. 2014

Water Resources Research

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Numerical groundwater flow modeling, reverse particle tracking, and environmental tracers are used to locate the source of geogenic As affecting an aquifer in West Bengal. The aquifer is hosted by point-bar sands deposited in a meandering fluvial environment. Wells tapping the aquifer exhibit As concentrations up to 531 lg/L. High-As groundwaters are recharged in ponds marking an abandoned river channel. The source of As is traced to the underlying fine-grained channel-fill sediments. Arsenic release within these sediments is accompanied by a concomitant release of Br and DOC indicating that these species may be decay products of natural organobromines codeposited along with As. Mass transfer of As to the dissolved phase and its flushing from source sediments are described using a simplified reactive solute transport model. Based on this model, a characteristic reaction time for mass transfer is estimated at 6.7 years. Average groundwater residence times in the source are estimated to have declined from 16.6 to 6.6 years with the advent of intensive irrigation pumping. The ratio of residence and reaction times, a Damk€ ohler number, has declined correspondingly from 2.49 to 0.99, indicating a shift from transport to reaction rate limited As mobilization. Greater insight into the As problem in SE Asia may be achieved by shifting the focus of field investigations from aquifers to potential contamination sources in aquitards.

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Integrated biogeochemical and hydrologic processes driving arsenic release from shallow sediments to groundwaters of the Mekong delta

Cited by 150 publications

References 46 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

Discrete Choice Experiments in Developing Countries: Willingness to Pay Versus Willingness to Work

Groundwater flow dynamics and arsenic source characterization in an aquifer system of West Bengal, India

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