Inorganic sulfur and mercury speciation in the water level fluctuation zone of the Three Gorges Reservoir, China: The role of inorganic reduced sulfur on mercury methylation

• Published in: Environmental pollution (1987) Vol. 237; pp. 1112 - 1123
• Main Authors: Liu, Jiang, Jiang, Tao, Wang, Feiyue, Zhang, Jinzhong, Wang, Dingyong, Huang, Rong, Yin, Deliang, Liu, Zeyan, Wang, Jinzhu
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.06.2018
• Subjects: Environmental Sciences; Mercury methylation; Miljövetenskap; Polysulfides; Sulfur biogeochemistry; The Three Gorges Reservoir; The Yangtze River; Water level fluctuation zone; Polysulfides; The Three Gorges Reservoir; Mercury methylation; Sulfur biogeochemistry; The Yangtze River; Water level fluctuation zone
• ISSN: 0269-7491; 1873-6424; 1873-6424
• DOI: 10.1016/j.envpol.2017.11.045

The water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) in China is a unique geomorphological unit that undergoes annual flooding and drying alternation cycle. The alternating redox conditions within the WLFZ are expected to result in dynamic cycling of reduced sulfur species, which could affect mercury (Hg) methylation due to the high affinity of reduced sulfur species to both inorganic divalent mercury (Hg(II)i) and methylmercury (MeHg). Variations of inorganic sulfur species (measured as acid volatile sulfide, chromium reductive sulfur, elemental sulfur, and water-soluble sulfate), total mercury (THg) and MeHg were studied at two typical WLFZ sites in the TGR from July 2015 to June 2016. Whereas the water-soluble sulfate contents stayed essentially constant, the reduced inorganic sulfur contents varied greatly as the water level changed. Compared with the control soils, the MeHg contents in the WLFZ soils increased, suggesting that water level fluctuations accelerated the methylation process of Hg(II)i. In situ Hg(II)i-methylation also appeared to occur in the sub-layer of the drained sediment during the draw-down season. The significant correlation between MeHg and elemental sulfur (S(0)) further suggests that polysulfides may have played a role in Hg(II)i-methylation by increasing the bioavailable Hg(II)i content in the WLFZ of the TGR. [Display omitted] •Reduced inorganic sulfur exhibits dynamic concentration changes within the water level fluctuation zone (WLFZ).•Elemental sulfur (S(0)) was produced during the flooding and drying rotation.•In situ methylation of Hg may occur in the drained soil within the WLFZ.•A significant correlation was found between MeHg and S(0) within the WLFZ.•Polysulfides can increase the bioavailable Hg species within the WLFZ. The water level fluctuations of the Three Gorges Reservoir accelerated the methylation process of inorganic divalent mercury (Hg(II)i), and polysulfides may have played a role in this process by increasing the bioavailable Hg(II)i content.