Mercury isotope variations between bioavailable mercury fractions and total mercury in mercury contaminated soil in Wanshan Mercury Mine, SW China Runsheng Yin a, b , Xinbin Feng a, ⁎, Jianxu Wang a, b , Zhengduo Bao a, b , Ben Yu a, b , Jiubin Chen a a State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China b Graduate University of Chinese Academy of Sciences, Beijing 100049, China abstract article info Article history: Accepted 17 April 2012 Available online xxxx Editor: J.D. Blum Keywords: Mercury Mercury isotope Water-soluble Thiosulphate extractable Soil In this study, a comparison of the mobility of soil mercury with two different extractable treatments (water- treated and (NH 4 ) 2 S 2 O 3 -treated) was carried out in soil samples collected from Wanshan Mercury Mine (WSMM), Guizhou, SW China. Substantially higher levels of mobilized Hg were found in (NH 4 ) 2 S 2 O 3 - extracted (1.22 to 2.41 μgg -1 ) compared to the water-extracted soil samples (0.05 to 0.49 μgg -1 ). To un- derstand the geochemical behavior of Hg during Hg mobilization, and to identify the potential hazard of Hg in soil, Hg isotope compositions of total Hg, water-soluble Hg and (NH 4 ) 2 S 2 O 3 -extractable Hg in WSMM soil were measured by using multiple collectors coupled plasma mass spectrometer (MC-ICP-MS). A large variation of mass-dependent fractionation (MDF) of Hg was observed (δ 202 Hg of -0.29–1.59‰) between the extractable Hg species and the total Hg in soil. Mass independent fractionation (MIF) in Δ 199 Hg ranged from -0.07 to 0.07‰, which were statistically insignificant. The experimental data (δ 202 Hg values) revealed that water-soluble (δ 202 Hg = 0.70 ± 0.13‰, n=8) and (NH 4 ) 2 S 2 O 3 -extractable (δ 202 Hg = 1.28 ± 0.25‰, n = 8) Hg species were enriched in heavier Hg isotopes by 0.72‰ and 1.30‰ relative to total Hg in soil sam- ples, respectively. The results suggest that the bioavailable fraction of Hg in soil possesses heavier Hg isotope values than total Hg in soil. To understand mercury isotope fractionation in the biogeochemical cycling pro- cesses in soil, it is of importance to measure Hg isotope compositions of different Hg species. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Mercury (Hg) is a global pollutant (Fitzgerald et al., 1998). Soil plays an important role in the global biogeochemical cycle of mercury because it acts both as a sink and a source of this metal to biota, atmo- sphere and hydrological compartments (Davidson et al., 2010). As a consequence of contamination from mercury mining and retorting activities, as well as excessive pesticide application and wastewater irrigation in agriculture, mercury pollution in soil is becoming a seri- ous problem worldwide (Wang et al., 2011). The geochemical behavior and distribution of Hg in the pedosphere is complex. Most Hg that is released into soil is adsorbed onto the solid phase of organic matter and onto soil minerals, such as sulphides and oxyhydroxides of iron and aluminum (Evans, 1989). A substantial frac- tion, however, undergoes physical (leaching, erosion, and volatiliza- tion) and biochemical transformations (methylation, photochemical and biological reduction) (Morel et al., 1998). Mobilization of Hg can occur through exchange reactions with sulfur-containing ligands and chloride ions, leading to enhanced Hg solubility in soil solution (Schuster, 1991). The mobilized Hg eventually forms complexes to dissolved organic constituents and reaches aquatic systems, where it can be exported to areas far away from the pollution source (Oliveira et al., 2001). The transformation of inorganic Hg into toxic methyl Hg (Me–Hg) can occur through biotic (Choi et al., 1994) and abiotic pro- cesses (Weber, 1993). Once formed, Me–Hg is biomagnified through the food chains and, in top predators such as fish, it can exceed safe levels for human consumption (Southworth et al., 2004). According to the ‘hard and soft’ acid‐base principle, mercury is regarded as a ‘soft metal’ (Pearson, 1963). It has a strong affinity for thiol groups and can be readily complexed to the thiosulphate ion (Wilkinson et al., 1987). Hg–thiosulphate complexes are mobile in soils (Wallschläger et al., 1998) and can enhance both Hg bioavailability in soil and Hg uptake by plants (Hinton and Veiga, 2001). In previous studies, thiosulphate-induced plant Hg accumulation has been pro- posed as a potential strategy for the removal of Hg from contaminated substrates. For instance, Brassica juncea was able to accumulate 40 μgg -1 of Hg in the shoot tissues following application of ammonium thiosulphate [(NH 4 ) 2 S 2 O 3 ] to mine tailings with Hg concentration of 2.8 μgg -1 (Moreno et al., 2004). Despite the application of chelated- enhanced phytoextraction (Lombi et al., 2001), the existence of the thiol-containing solutions in soil can dissolve the non-mobile Hg phase in soil, and enhance the leaching of Hg to groundwater. Hence, knowledge of the formation of Hg–thiosulphate complexes in soil is critical to evaluate its environmental risk (Moreno et al., 2005). Chemical Geology xxx (2012) xxx–xxx ⁎ Corresponding author. Tel.: + 86 851 5891356; fax: + 86 851 5891609. E-mail address: fengxinbin@vip.skleg.cn (X. Feng). CHEMGE-16514; No of Pages 7 0009-2541/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.chemgeo.2012.04.017 Contents lists available at SciVerse ScienceDirect Chemical Geology journal homepage: www.elsevier.com/locate/chemgeo Please cite this article as: Yin, R., et al., Mercury isotope variations between bioavailable mercury fractions and total mercury in mercury contaminated soil in Wanshan Mercury Mine, SW China, Chem. Geol. (2012), doi:10.1016/j.chemgeo.2012.04.017