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Sulfur cycling-related biogeochemical processes of arsenic mobilization in the western Hetao basin, China: Evidence from multiple isotope approaches Huaming Guo, Yinzhu Zhou, Yongfeng Jia, Xiaohui Tang, Xiaofeng Li, Mengmeng Shen, Hai Lu, Shuangbao Han, Chao Wei, Stefan Norra, and Fucun Zhang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b03460 • Publication Date (Web): 31 Oct 2016 Downloaded from http://pubs.acs.org on November 1, 2016
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Environmental Science & Technology
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Sulfur cycling-related biogeochemical processes of arsenic mobilization in the
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western Hetao basin, China: Evidence from multiple isotope approaches
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Huaming Guo 1, *, Yinzhu Zhou1, Yongfeng Jia 1, Xiaohui Tang 2, Xiaofeng Li 1,
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Mengmeng Shen 1, Hai Lu 3, Shuangbao Han 4, Chao Wei 3, Stefan Norra 2, Fucun
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Zhang 4
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1. State Key Laboratory of Biogeology and Environmental Geology, School of Water
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Resources and Environment, China University of Geosciences (Beijing), Beijing
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100083, China
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2. Institute of Applied Geosciences, Karlsruhe Institute of Technology, Karlsruhe
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76131, Germany
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3. The National Institute of Metrology, Beijing 100013, P.R. China
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4. Center for Hydrogeology and Environmental Geology, China Geological Survey,
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Baoding 071051, Hebei, China
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* Corresponding author: Huaming Guo
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School of Water Resources and Environment,
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China University of Geosciences (Beijing),
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Beijing 100083, P. R. China
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Tel.: +86-10-8232-1366
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Fax: +86-10-8232-1081
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E-mail address:
[email protected] (H. Guo)
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Abstract
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The role of sulfur cycling in arsenic behavior under reducing conditions is not
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well-understood in previous investigations. This study provides observations of sulfur
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and oxygen isotope fractionation in sulfate and evaluation of sulfur cycling-related
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biogeochemical processes controlling dissolved arsenic groundwater concentrations
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using multiple isotope approaches. As a typical basin hosting high arsenic
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groundwater, the western Hetao basin was selected as the study area. Results showed
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that, along the groundwater flow paths, groundwater δ34SSO4, δ18OSO4 and δ13CDOC
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increased with increases in arsenic, dissolved iron, hydrogen sulfide and ammonium
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concentrations, while δ13CDIC decreased with decreasing Eh and sulfate/chloride.
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Bacterial sulfate reduction (BSR) was responsible for many of these observed changes.
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The δ34SSO4 indicated that dissolved sulfate was mainly sourced from oxidative
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weathering of sulfides in upgradient alluvial fans. The high oxygen-sulfur isotope
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fractionation ratio (0.60) may result from both slow sulfate reduction rates and
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bacterial disproportionation of sulfur intermediates (BDSI). Data indicate that both
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the sulfide produced by BSR and the overall BDSI reduce arsenic-bearing iron(III)
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oxyhydroxides, leading to the release of arsenic into groundwater. These results
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suggest that sulfur-related biogeochemical processes are important in mobilizing
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arsenic in aquifer systems.
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Key Words: Dual isotopes; Carbon isotopes; δ34Ssulfate; δ18Osulfate; Isotope
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fractionation; As; Aquifer; Sulfate
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■ INTRODUCTION
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High arsenic groundwater has been found worldwide, which has posed health risk
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to hundreds of millions of people due to its chronic poisoning effects.1 It is
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well-known that reductive dissolution of iron(III) oxyhydroxides leads to arsenic
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release from aquifer sediments under anoxic conditions.1-4 Biological reduction of
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iron(III) oxides would proceed concurrently with bacterial sulfate reduction (BSR)
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when the available iron(III) oxides had a low solubility. The released arsenic may be
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coprecipitated with sulfide produced by BSR.5, 6 In contrast, reduction of iron(III)
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oxyhydroxides by sulfur intermediates,7 a product formed during BSR, would
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mobilize the adsorbed arsenic. The formation of thioarsenate during BSR also results
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in arsenic mobility.8, 9 Accordingly, the geochemical behavior of dissolved sulfate
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plays an important role in arsenic mobilization and transport. However, sulfate
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concentrations in high arsenic groundwater show considerable differences between
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inland basins (50 µg/L. Arsenic(III) was the major arsenic species, with organic
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arsenic species (monomethyl- and dimethylarsenic, MMA and DMA) below detection
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limits (
