International Research Fellowship Program: The Influence of Sulfur Cycling on Mercury Methylation in Rice Paddies in the Mining Areas Guizhou Province, China

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0802014RothenbergThe International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twenty-four month research fellowship by Dr. Sarah Rothenberg to work with Dr. Xinbin Feng at State Key Laboratory of Environmental Geochemistry in Guiyang, China.Guizhou Province, located in southwestern China, is highly contaminated with mercury (Hg) due to historical mining of cinnabar, industrial runoff, artisinal zinc smelting, incineration of municipal wastes, and reliance on coal-burning power plants to fuel economic growth and heat residential homes. Hg runoff and residues have contaminated the air, water, soil, as well as agricultural products, including rice. Even though most human exposure to Hg occurs through the consumption of fish, Hg exposure may also occur through the ingestion of rice, and this exposure pathway may be important in countries where rice is a staple. Like wetlands, rice paddies are potential hot spots for the conversion of inorganic Hg to toxic mono-methylmercury (MMHg). The PI is conducting a study to determine under which hydrologic and biogeochemical regimes highest MMHg concentrations occur in rice paddies, which may be used to develop mitigation strategies. There are two research components. (1) The PI is characterizing sulfur cycling and Hg methylation within irrigation water, anoxic pore water and sediments within at least four rice paddies, half using traditional methods of irrigation and half using water saving methods. (2) The PI is also deploying a series of embedded sensor networks within the same four rice paddies in the early spring and in the late summer to coincide with the start and end of the rice growing season. Time series sensor measurements of oxygen redox potential and pH will be correlated with pore water MMHG levels to determine under which conditions MMHg production is highest. This study will answer the following questions: Are rice paddies hot spots for Hg methylation? How does sulfur cycling in the surface soil, anoxic bulk soil, and rhizosphere affect Hg methylation? Are there differences between flooded rice paddies and rice paddies that employ water-saving methods? How do temporal/seasonal changes in pore water oxidation-reduction potential (ORP) and pH affect Hg speciation?This project serves as a bridge between US and Chinese researchers, and is also collaborative, bringing together environmental scientists, engineers and computer scientists to focus on an critical environmental problem.