Aquifer-Scale Observations of Iron Redox Transformations in Arsenic-Impacted Environments to Predict Future Contamination

TitleAquifer-Scale Observations of Iron Redox Transformations in Arsenic-Impacted Environments to Predict Future Contamination
Publication TypeJournal Article
Year of Publication2020
AuthorsNghiem, AA, Shen, Y, Stahl, M, Sun, J, Haque, E, DeYoung, B, Nguyen, KN, Mai, TThi, Trang, PThi Kim, Pham, HViet, Mailloux, B, Harvey, CF, van Geen, A, Bostick, BC
JournalEnvironmental Science & Technology Letters
Volume7
Issue12
Pagination916 - 922
Date PublishedAug-12-2020
ISSN2328-8930
KeywordsBANGLADESH, BENGAL BASIN, groundwater, PLEISTOCENE AQUIFER, POLLUTION, RELEASE, RIVER DELTA, Sediment, TRANSPORT, VIETNAM
Abstract

Iron oxides control the mobility of a host of contaminants in aquifer systems, and the microbial reduction of iron oxides in the subsurface is linked to high levels of arsenic in groundwater that affects greater than 150 million people globally. Paired observations of groundwater and solid-phase aquifer composition are critical to understand spatial and temporal trends in contamination and effectively manage changing water resources, yet field-representative mineralogical data are sparse across redox gradients relevant to arsenic contamination. We characterize iron mineralogy using X-ray absorption spectroscopy across a natural gradient of groundwater arsenic contamination in Vietnam. Hierarchical cluster analysis classifies sediments into meaningful groups delineating weathering and redox changes, diagnostic of depositional history, in this first direct characterization of redox transformations in the field. Notably, these groupings reveal a signature of iron minerals undergoing active reduction before the onset of arsenic contamination in groundwater. Pleistocene sediments undergoing postdepositional reduction may be more extensive than previously recognized due to previous misclassification. By upscaling to similar environments in South and Southeast Asia via multinomial logistic regression modeling, we show that active iron reduction, and therefore susceptibility to future arsenic contamination, is more widely distributed in presumably pristine aquifers than anticipated.

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DOI10.1021/acs.estlett.0c0067210.1021/acs.estlett.0c00672.s00110.1021/acs.estlett.0c00672.s00210.1021/acs.estlett.0c00672.s00310.1021/acs.estlett.0c00672.s004