High arsenic groundwater in the Guide basin, northwestern China: Distribution and genesis mechanisms

Zhen Wang; Huaming Guo; Wei Xiu; Jiao Wang; Mengmeng Shen

doi:10.1016/j.scitotenv.2018.05.255

High arsenic groundwater in the Guide basin, northwestern China: Distribution and genesis mechanisms

Sci Total Environ. 2018 Nov 1:640-641:194-206. doi: 10.1016/j.scitotenv.2018.05.255. Epub 2018 May 30.

Authors

Zhen Wang¹, Huaming Guo², Wei Xiu³, Jiao Wang⁴, Mengmeng Shen⁴

Affiliations

¹ State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, PR China; MOE Key Laboratory of Groundwater Circulation and Evolution & School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, PR China.
² State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, PR China; MOE Key Laboratory of Groundwater Circulation and Evolution & School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, PR China. Electronic address: hmguo@cugb.edu.cn.
³ State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, PR China.
⁴ MOE Key Laboratory of Groundwater Circulation and Evolution & School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, PR China.

PMID: 29859436
DOI: 10.1016/j.scitotenv.2018.05.255

Abstract

High arsenic (As) groundwater has been found in Pliocene confined aquifers at depths from 100 to 300 m of the Guide basin, but little is known on the main hydrogeochemical processes leading to its elevated concentrations. Ninety-seven water samples and fifty-three sediment samples were collected for chemical and/or isotopic analysis. Concentrations of As in groundwater of confined aquifer range from 9.9 to 377 μg/L (average 109 μg/L), which generally show a sharply increasing trend along with NH₄⁺, HCO₃^-, CO₃^2- and TOC along the inferred flow path, while NO₃^-, SO₄^2-/Cl^- and redox potential (Eh) have decreasing trends. Results of sequential extraction show that As bound to amorphous and crystalline Fe oxide minerals are the main As forms, accounting for around 50% of total As in sediments. Reductive dissolution of As-bearing Fe(III) oxide minerals under reducing conditions in confined aquifers lead to the mobilization of As in groundwater. In addition, alkaline environment and high concentrations of HCO₃^- and CO₃^2- may make contributions to As enrichment in groundwater. High As groundwater in confined aquifer continuously flows out on the ground surface through tens of artesian wells, which may potentially contaminate low As groundwater in unconfined aquifer. Thus, further investigation is needed to evaluate long-term variations of water chemistry of low As groundwater and assess vulnerability of unconfined aquifer to As contamination.

Keywords: Arsenic enrichment; Confined aquifer; Guide basin; Hydrogeochemistry; Isotopes.