Variations in the redox state of As and Fe measured by X-ray absorption spectroscopy in aquifers of Bangladesh and their effect on As adsorption

Itai, Takaaki; Takahashi, Yoshio; Seddique, Ashraf Ali; Maruoka, Teruyuki; Mitamura, Muneki

doi:10.1016/j.apgeochem.2009.09.026

Cited by 30 publications

(17 citation statements)

References 65 publications

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“…The high end might over-estimate the extent of As adsorption, because the sediment-water ratio used in the batch adsorption experiments was lower than in the actual aquifer (Limousin et al, 2007). Even a K d of 1.5 L/kg is a factor of 2–3 lower than the value of predicted from 1 M P-extractions of As from grey Bangladesh sediment for the southern portion of the transect (3–15 L/kg) and results from previous studies across the Bengal Basin (van Geen et al, 2008 and Itai et al 2010), suggesting that P-extractions over-estimate the proportion of exchangeable As in aquifer sands. The push–pull derived K d using the single-porosity model of 0.15 L/kg provides a plausible lower bound for As adsorption.…”

Section: Discussioncontrasting

confidence: 58%

“…Similar observations were reported by Jung et al (2012) using grey riverbank sands. Itai et al (2010) also conducted a series of batch adsorption experiments and saw no evidence of saturation for groundwater As concentrations less than 1000 µg/L. These results suggest that a linear distribution coefficient, K d , adequately represents both adsorption and desorption of As in reducing aquifers at ambient groundwater As concentrations.…”

Section: Discussionmentioning

confidence: 82%

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Reversible adsorption and flushing of arsenic in a shallow, Holocene aquifer of Bangladesh

Radloff

Zheng

Stute

et al. 2017

Applied Geochemistry

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The spatial heterogeneity of dissolved arsenic (As) concentrations in shallow groundwater of the Bengal Basin has been attributed to transport of As (and reactive carbon) from external sources or to the release of As from within grey sand formations. We explore the latter scenario in this detailed hydrological and geochemical study along a 300 m transect of a shallow aquifer extending from a groundwater recharge area within a sandy channel bar to its discharge into a nearby stream. Within the 10–20 m depth range, groundwater ages along the transect determined by the 3H–3He method increase from <10 yr in the recharge area to a maximum of 40 yr towards the stream. Concentrations of groundwater As within the same grey sands increase from 10 to 100 to ∼500 µg/L along this transect. Evidence of reversible adsorption of As between the groundwater and sediment was obtained from a series of push–pull experiments, traditional batch adsorption experiments, and the accidental flooding of a shallow monitoring well. Assuming reversible adsorption and a distribution coefficient, Kd, of 0.15–1.5 L/kg inferred from these observations, a simple flushing model shows that the increase in As concentrations with depth and groundwater age at this site, and at other sites in the Bengal and Red River Basins, can be attributed to the evolution of the aquifer over 100–1000 years as aquifer sands are gradually flushed of their initial As content. A wide range of As concentrations can thus be maintained in groundwater with increases with depth governed by the history of flushing and local recharge rates, without external inputs of reactive carbon or As from other sources.

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Section: Discussioncontrasting

confidence: 58%

Section: Discussionmentioning

confidence: 82%

Reversible adsorption and flushing of arsenic in a shallow, Holocene aquifer of Bangladesh

Radloff

Zheng

Stute

et al. 2017

Applied Geochemistry

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“…As a first step a better understanding of the solid phase speciation of As and Fe in the sediments should be sought. Our current knowledge is based on bulk sediment analysis , sequential extraction data (Dowling et al, 2002;Akai et al, 2004;Swartz et al, 2004), and spectroscopic techniques like EXAFS and XANES (Polizzotto et al, 2006;Itai et al, 2010). Currently, there is not much information concerning the mineralogy of the Fe-oxides in the Holocene aquifer sediments to which As is supposed to be associated (Akai et al, 2004;Polizzotto et al, 2006;Rowland et al, 2008).…”

Section: Introductionmentioning

confidence: 98%

Mobilization of arsenic and iron from Red River floodplain sediments, Vietnam

Postma

Jessen

Huệ

et al. 2010

Geochimica et Cosmochimica Acta

126

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“…Linking As reactivity and speciation to the identity, relative quantity, and reactivity of Fe-bearing minerals in the river basins of South and Southeast Asia is needed to understand the distribution and transport of As. Moreover, efforts to this end have concentrated in the Bengal Basin (Akai et al, 2004;Datta et al, 2009;Ghosh et al, 2006;Hasan et al, 2009;Itai et al, 2010;Polizzotto et al, 2006;Polizzotto et al, 2005;Seddique et al, 2008;Seddique et al, 2011;Swartz et al, 2004;Uddin et al, 2011), and to a lesser extent in the Red River Delta (Vietnam) (Phuong et al, 2012;Postma et al, 2010;Postma et al, 2007) and Datong Basin (China) (Xie et al, 2009a;Xie et al, 2009b;Xie et al, 2011;Xie et al, 2008). Little is known about mineralogical aspects of the Mekong Delta influencing dissolved As concentrations (Kocar et al, 2008;Rowland et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Reactivity and speciation of mineral-associated arsenic in seasonal and permanent wetlands of the Mekong Delta

Stuckey

Schaefer

Benner

et al. 2015

Geochimica et Cosmochimica Acta

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Millions of people in the deltaic regions of S/SE Asia regularly consume As contaminated groundwater. Arsenic persists within these groundwaters despite being flushed by several pore volumes of recharge, indicative of an in-situ solid phase source. Despite the importance of this solid phase source, the identity and reactivity of the minerals hosting and releasing As in the deltaic aquifers remain poorly constrained. Here we seek to define the chemistry and reactivity of As and its host minerals in aquifer sediments recharged by both seasonally saturated and permanent wetlands on the Mekong Delta of Cambodia. Sediment cores were retrieved to depths of up to 30 m. Selective extractions on near-surface sediments (to depths of 4-6 m) indicate that more than a third (27-50%) of the Fe in the profile is "reducible" (citrate-bicarbonate-dithioniteextractable)-nominally consisting of Fe(III) oxides. The Fe(III) oxide fraction was approximately the same under seasonal wetlands (mean = 39%) compared with sediments from beneath permanent wetlands (mean = 37%). Correspondingly, Fe Kedge extended X-ray absorption fine structure (EXAFS) spectra analysis indicates that the Fe mineral phases are predominantly goethite and hematite (30-50%). Analysis of solid phase As speciation by X-ray absorption near edge structure (XANES) spectroscopy showed arsenate in the shallowest sediments (upper 1 and 4 m of seasonal and permanent wetlands), and arsenite and/or As sulfides as the dominant phases in the deeper sediments. The reducible As fraction ranged from 17-42 % of the total As at both sites. The exception was found in a peat layer at 6 m beneath the seasonal wetland, in which only 1% of the total As was reducible. Arsenian pyrite was the predominant form of As in the peat. Thus, a pool of As hosted by reducible mineral phases persists in sediments below both the seasonal and permanently saturated wetland sites.

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Variations in the redox state of As and Fe measured by X-ray absorption spectroscopy in aquifers of Bangladesh and their effect on As adsorption

Cited by 30 publications

References 65 publications

Reversible adsorption and flushing of arsenic in a shallow, Holocene aquifer of Bangladesh

Reversible adsorption and flushing of arsenic in a shallow, Holocene aquifer of Bangladesh

Mobilization of arsenic and iron from Red River floodplain sediments, Vietnam

Reactivity and speciation of mineral-associated arsenic in seasonal and permanent wetlands of the Mekong Delta

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