Experimental constraints on redox-induced arsenic release and retention from aquifer sediments in the central Yangtze River Basin

Yanhua Duan; Michael V Schaefer; Yanxin Wang; Yiqun Gan; Kai Yu; Yamin Deng; Scott Fendorf

doi:10.1016/j.scitotenv.2018.08.205

Experimental constraints on redox-induced arsenic release and retention from aquifer sediments in the central Yangtze River Basin

Sci Total Environ. 2019 Feb 1:649:629-639. doi: 10.1016/j.scitotenv.2018.08.205. Epub 2018 Aug 17.

Authors

Yanhua Duan¹, Michael V Schaefer², Yanxin Wang³, Yiqun Gan⁴, Kai Yu⁴, Yamin Deng⁵, Scott Fendorf⁶

Affiliations

¹ School of Environmental Studies, China University of Geosciences, 430074 Wuhan, China; Earth System Science Dept., Stanford University, Stanford, CA 94305, United States.
² Earth System Science Dept., Stanford University, Stanford, CA 94305, United States; Environmental Science Dept., University of California-Riverside, 900 University Ave, Riverside, CA 92521, United States.
³ School of Environmental Studies, China University of Geosciences, 430074 Wuhan, China; State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 430074 Wuhan, China. Electronic address: yx.wang@cug.edu.cn.
⁴ School of Environmental Studies, China University of Geosciences, 430074 Wuhan, China; State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 430074 Wuhan, China.
⁵ Geological Survey, China University of Geosciences, 430074 Wuhan, China.
⁶ Earth System Science Dept., Stanford University, Stanford, CA 94305, United States. Electronic address: fendorf@stanford.edu.

PMID: 30176474
DOI: 10.1016/j.scitotenv.2018.08.205

Abstract

The consumption of arsenic (As) contaminated groundwater affects the health of almost 20 million people in China. Unlike the preponderance of observations within the deltas of South and Southeast Asia, groundwater As concentrations in the central Yangtze River Basin, China, vary by up to an order of magnitude seasonally. In order to decipher the cause of seasonal release and retention of As between sediments and groundwater, we conducted batch sediment incubations under varying (imposed) redox conditions. Incubations were conducted under both N₂ and O₂ gas purges to simulate conditions observed within the field. In all cases, anoxic conditions resulted in As release to solution while As was removed from solution under oxic conditions. These experiments confirm that anoxia is a prerequisite for As mobilization into groundwater from Yangtze River Basin sediments. Alternating redox conditions resulted in Fe minerals dissolution, transformation, crystallization, and precipitation, and subsequent As release and retention in the system. More importantly, aquifer sediments at depths >15 m release As through multiple redox cycles without an exogenous electron donor (carbon source), organic matter in the sediments is sufficiently reactive to support microbial reduction of As(V) and Fe(III). These results provide direct evidence for previously described mechanisms explaining the observed seasonal variation of groundwater As concentrations in the central Yangtze River Basin, where seasonal changes in surface and groundwater levels drive changes in redox conditions and thus As concentrations.

Keywords: Arsenic mobilization; Central Yangtze River basin; Multiple redox cycles; Seasonal variation.