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Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
}
TY - JOUR
T1 - Dual in-aquifer and near surface processes drive arsenic mobilization in Cambodian groundwaters
AU - Richards, L.A.
AU - Magnone, D.
AU - Sültenfuß, J.
AU - Chambers, Lee
AU - Bryant, C.
AU - Boyce, A.J.
AU - van Dongen, B.E.
AU - Ballentine, C.J.
AU - Sovann, C.
AU - Uhlemann, S.
AU - Kuras, O.
AU - Gooddy, Daren C.
AU - Polya, D.A.
PY - 2019/4/1
Y1 - 2019/4/1
N2 - Millions of people globally, and particularly in South and Southeast Asia, face chronic exposure to arsenic from reducing groundwater in which arsenic release is widely attributed to the reductive dissolution of arsenic-bearing iron minerals, driven by metal reducing bacteria using bioavailable organic matter as an electron donor. However, the nature of the organic matter implicated in arsenic mobilization, and the location within the subsurface where these processes occur, remains debated. In a high resolution study of a largely pristine, shallow aquifer in Kandal Province, Cambodia, we have used a complementary suite of geochemical tracers (including 14C, 3H, 3He, 4He, Ne, δ18O, δD, CFCs and SF6) to study the evolution in arsenic-prone shallow reducing groundwaters along dominant flow paths. The observation of widespread apparent 3H-3He ages of <55 years fundamentally challenges some previous models which concluded that groundwater residence times were on the order of hundreds of years. Surface-derived organic matter is transported to depths of >30 m, and the relationships between age-related tracers and arsenic suggest that this surface-derived organic matter is likely to contribute to in-aquifer arsenic mobilization. A strong relationship between 3H-3He age and depth suggests the dominance of a vertical hydrological control with an overall vertical flow velocity of ~0.4 ± 0.1 m·yr−1 across the field area. A calculated overall groundwater arsenic accumulation rate of ~0.08 ± 0.03 μM·yr−1 is broadly comparable to previous estimates from other researchers for similar reducing aquifers in Bangladesh. Although apparent arsenic groundwater accumulation rates varied significantly with site (e.g. between sand versus clay dominated sequences), rates are generally highest near the surface, perhaps reflecting the proximity to the redox cline and/or depth-dependent characteristics of the OM pool, and confounded by localized processes such as continued in-aquifer mobilization, sorption/desorption, and methanogenesis. © 2018
AB - Millions of people globally, and particularly in South and Southeast Asia, face chronic exposure to arsenic from reducing groundwater in which arsenic release is widely attributed to the reductive dissolution of arsenic-bearing iron minerals, driven by metal reducing bacteria using bioavailable organic matter as an electron donor. However, the nature of the organic matter implicated in arsenic mobilization, and the location within the subsurface where these processes occur, remains debated. In a high resolution study of a largely pristine, shallow aquifer in Kandal Province, Cambodia, we have used a complementary suite of geochemical tracers (including 14C, 3H, 3He, 4He, Ne, δ18O, δD, CFCs and SF6) to study the evolution in arsenic-prone shallow reducing groundwaters along dominant flow paths. The observation of widespread apparent 3H-3He ages of <55 years fundamentally challenges some previous models which concluded that groundwater residence times were on the order of hundreds of years. Surface-derived organic matter is transported to depths of >30 m, and the relationships between age-related tracers and arsenic suggest that this surface-derived organic matter is likely to contribute to in-aquifer arsenic mobilization. A strong relationship between 3H-3He age and depth suggests the dominance of a vertical hydrological control with an overall vertical flow velocity of ~0.4 ± 0.1 m·yr−1 across the field area. A calculated overall groundwater arsenic accumulation rate of ~0.08 ± 0.03 μM·yr−1 is broadly comparable to previous estimates from other researchers for similar reducing aquifers in Bangladesh. Although apparent arsenic groundwater accumulation rates varied significantly with site (e.g. between sand versus clay dominated sequences), rates are generally highest near the surface, perhaps reflecting the proximity to the redox cline and/or depth-dependent characteristics of the OM pool, and confounded by localized processes such as continued in-aquifer mobilization, sorption/desorption, and methanogenesis. © 2018
KW - Arsenic
KW - Bioavailability
KW - Geochemical tracers
KW - Groundwater monitoring
KW - Groundwater quality
KW - Aquifers
KW - Biogeochemistry
KW - Biological materials
KW - Flow velocity
KW - Groundwater
KW - Groundwater resources
KW - Hydrogeology
KW - Organic minerals
KW - Water quality
KW - Arsenic mobilization
KW - Geochemical tracer
KW - Groundwater residence
KW - Hydrological controls
KW - Metal-reducing bacteria
KW - Reductive dissolution
KW - Hydrochemistry
KW - arsenic
KW - carbon 14
KW - ground water
KW - organic matter
KW - tracer
KW - tritium
KW - accumulation rate
KW - aquifer
KW - bioavailability
KW - desorption
KW - flow velocity
KW - groundwater pollution
KW - iron-reducing bacterium
KW - methanogenesis
KW - mobilization
KW - pollutant transport
KW - pollution monitoring
KW - water quality
KW - analytic method
KW - arsenic mobilization
KW - Article
KW - Cambodia
KW - chemical procedures
KW - dissolution
KW - environmental exposure
KW - priority journal
KW - quality control
KW - sediment
KW - water sampling
KW - Kandal
U2 - 10.1016/j.scitotenv.2018.12.437
DO - 10.1016/j.scitotenv.2018.12.437
M3 - Journal article
VL - 659
SP - 699
EP - 714
JO - Science of the Total Environment
JF - Science of the Total Environment
SN - 0048-9697
ER -