Chemical controls on abiotic and biotic release of geogenic arsenic from Pleistocene aquifer sediments to groundwater

Abstract

Over 150 million people in South and Southeast Asia consume unsafe drinking water from arsenic-rich Holocene aquifers. Although use of As-free water from Pleistocene aquifers is a potential mitigation strategy, such aquifers are vulnerable to geogenic As pollution, placing millions more people at potential risk. The goal of this research was to define chemical controls on abiotic and biotic release of geogenic As to groundwater. Batch incubations of sediments with natural chemical variability from a Pleistocene aquifer in Cambodia were conducted to evaluate how interactions among arsenic, manganese and iron oxides, and dissolved and sedimentary organic carbon influenced As mobilization from sediments. The addition of labile dissolved organic carbon produced the highest concentrations of dissolved As after >7 months, as compared to sediment samples incubated with sodium azide or without added carbon, and the extent of As release was positively correlated with the percent of initial extractable Mn released from the sediments. The mode of As release was impacted by the source of DOC supplied to the sediments, with biological processes responsible for 81% to 85% of the total As release following incubations with lactate and acetate but only up to 43% to 61% of the total As release following incubations with humic and fulvic acids. Overall, cycling of key redox-active elements and organic-carbon reactivity govern the potential for geogenic As release to groundwater, and results here may be used to formulate better predictions of the arsenic pollution potential of aquifers in South and Southeast Asia.

Processes governing arsenic retardation on Pleistocene sediments: Adsorption experiments and model‐based analysis

“…Water Resources Research 10.1002/2017WR020551 including organic acids, amino acids, sugars, phenols, and other compounds which are known to form solution complexes with divalent ions, such as Mn 21 [Gillispie et al, 2016;Norvell, 1988], sorbed on Mn-oxide minerals naturally present in the Pleistocene sediments [Eiche et al, 2008]. This could further result in the oxidation of dissolved As(III), as observed in our pH experiments.…”

“…Migrating groundwater from shallow Holocene aquifers into Pleistocene aquifers contains large amount of dissolved organic carbon (DOC) [ Harvey et al ., ]. The DOC is composed of various organic ligands including organic acids, amino acids, sugars, phenols, and other compounds which are known to form solution complexes with divalent ions, such as [ Gillispie et al ., ; Norvell , ], sorbed on Mn‐oxide minerals naturally present in the Pleistocene sediments [ Eiche et al ., ]. This could further result in the oxidation of dissolved As(III), as observed in our pH experiments.…”

Predicting geogenic Arsenic in Drinking Water Wells in Glacial Aquifers, North‐Central USA: Accounting for Depth‐Dependent Features

“…Recent models for As‐affected aquifers in Southeast Asia have elucidated similar influential factors and variables (groundwater age, organic carbon, aquifer, depth, etc. ; Biswas et al, ; Biswas, Bhattacharya, et al, ; Biswas, Neidhardt, et al, ; Desbarats et al, ; Gillispie et al, ; McArthur et al, , , ; Mihajlov et al, ) related to modeled As hazard in aquifers (Biswas, Neidhardt, et al, ; Bonsor et al, ; Hoque et al, , , ; Mahmud et al, ; Mukherjee et al, ; Podgorski et al, ).…”

Si and Water Management Drives Changes in Fe and Mn Pools that Affect As Cycling and Uptake in Rice

“…Most at-risk populations are individuals with low body mass, those who consume high quantities of rice, and those who also ingest iAs via drinking water [7]. In an effort to devise approaches to minimize As entry into the human food chain, many studies have been conducted to understand how As is released from soils and sediments to water [8][9][10][11][12][13][14][15][16], where it can be taken up by rice roots. It has become clear that plant-availability of As in rice paddy agroecosystems is intimately tied to biogeochemical Fe and Mn cycling [17,18].…”