Spatial and temporal evolution of groundwater arsenic contamination in the Red River delta, Vietnam: Interplay of mobilisation and retardation processes

Emiliano Stopelli; Vu T Duyen; Tran T Mai; Pham T K Trang; Pham H Viet; Alexandra Lightfoot; Rolf Kipfer; Magnus Schneider; Elisabeth Eiche; Agnes Kontny; Thomas Neumann; Martyna Glodowska; Monique Patzner; Andreas Kappler; Sara Kleindienst; Bhasker Rathi; Olaf Cirpka; Benjamin Bostick; Henning Prommer; Lenny H E Winkel; Michael Berg

doi:10.1016/j.scitotenv.2020.137143

Spatial and temporal evolution of groundwater arsenic contamination in the Red River delta, Vietnam: Interplay of mobilisation and retardation processes

Sci Total Environ. 2020 May 15:717:137143. doi: 10.1016/j.scitotenv.2020.137143. Epub 2020 Feb 5.

Authors

Emiliano Stopelli¹, Vu T Duyen², Tran T Mai², Pham T K Trang², Pham H Viet², Alexandra Lightfoot³, Rolf Kipfer³, Magnus Schneider⁴, Elisabeth Eiche⁴, Agnes Kontny⁴, Thomas Neumann⁵, Martyna Glodowska⁶, Monique Patzner⁷, Andreas Kappler⁷, Sara Kleindienst⁸, Bhasker Rathi⁹, Olaf Cirpka⁹, Benjamin Bostick¹⁰, Henning Prommer¹¹, Lenny H E Winkel¹², Michael Berg¹³

Affiliations

¹ Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department Water Resources and Drinking Water, 8600 Dübendorf, Switzerland. Electronic address: emiliano.stopelli@eawag.ch.
² Key Laboratory of Analytical Technology for Environmental Quality and Food Safety Control (KLATEFOS), VNU University of Science, Vietnam National University, Hanoi, Vietnam.
³ Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department Water Resources and Drinking Water, 8600 Dübendorf, Switzerland.
⁴ Institute of Applied Geosciences, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany.
⁵ Applied Geochemistry, Institute for Applied Geosciences, Technical University Berlin, 10587 Berlin, Germany.
⁶ Geomicrobiology, Center for Applied Geosciences, University of Tübingen, 72076 Tübingen, Germany; Microbial Ecology, Center for Applied Geosciences, University of Tübingen, 72074 Tübingen, Germany.
⁷ Geomicrobiology, Center for Applied Geosciences, University of Tübingen, 72076 Tübingen, Germany.
⁸ Microbial Ecology, Center for Applied Geosciences, University of Tübingen, 72074 Tübingen, Germany.
⁹ Hydrogeology, Center for Applied Geosciences, University of Tübingen, 72074 Tübingen, Germany.
¹⁰ Lamont-Doherty Earth Observatory, Columbia University, Palisades, 10964, NY, USA.
¹¹ CSIRO Land and Water, 6014 Floreat, Western Australia, Australia; School of Earth Sciences, University of Western Australia, Crawley, WA 6009, Australia.
¹² Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department Water Resources and Drinking Water, 8600 Dübendorf, Switzerland; Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, 8092 Zurich, Switzerland.
¹³ Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department Water Resources and Drinking Water, 8600 Dübendorf, Switzerland; UNESCO Chair on Groundwater Arsenic Within the 2030 Agenda for Sustainable Development, School of Civil Engineering and Surveying, University of Southern Queensland, QLD 4350, Australia. Electronic address: michael.berg@eawag.ch.

PMID: 32062264
DOI: 10.1016/j.scitotenv.2020.137143

Abstract

Geogenic arsenic (As) contamination of groundwater poses a major threat to global health, particularly in Asia. To mitigate this exposure, groundwater is increasingly extracted from low-As Pleistocene aquifers. This, however, disturbs groundwater flow and potentially draws high-As groundwater into low-As aquifers. Here we report a detailed characterisation of the Van Phuc aquifer in the Red River Delta region, Vietnam, where high-As groundwater from a Holocene aquifer is being drawn into a low-As Pleistocene aquifer. This study includes data from eight years (2010-2017) of groundwater observations to develop an understanding of the spatial and temporal evolution of the redox status and groundwater hydrochemistry. Arsenic concentrations were highly variable (0.5-510 μg/L) over spatial scales of <200 m. Five hydro(geo)chemical zones (indicated as A to E) were identified in the aquifer, each associated with specific As mobilisation and retardation processes. At the riverbank (zone A), As is mobilised from freshly deposited sediments where Fe(III)-reducing conditions occur. Arsenic is then transported across the Holocene aquifer (zone B), where the vertical intrusion of evaporative water, likely enriched in dissolved organic matter, promotes methanogenic conditions and further release of As (zone C). In the redox transition zone at the boundary of the two aquifers (zone D), groundwater arsenic concentrations decrease by sorption and incorporations onto Fe(II) carbonates and Fe(II)/Fe(III) (oxyhydr)oxides under reducing conditions. The sorption/incorporation of As onto Fe(III) minerals at the redox transition and in the Mn(IV)-reducing Pleistocene aquifer (zone E) has consistently kept As concentrations below 10 μg/L for the studied period of 2010-2017, and the location of the redox transition zone does not appear to have propagated significantly. Yet, the largest temporal hydrochemical changes were found in the Pleistocene aquifer caused by groundwater advection from the Holocene aquifer. This is critical and calls for detailed investigations.

Keywords: Arsenic geochemistry; Groundwater hydrochemistry; Methanogenic conditions; Redox transition; Reductive dissolution; Water isotopes.