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Thursday, 30 June 2005 TITLE Christopher S. Kim1, James J Rytuba, Gordon E Brown, Jr.3 1Department of Physical Sciences, Chapman University, Orange, CA 92866 2U.S. Geological Survey, Menlo Park, CA 94025 3Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305 Mercury contamination is widespread due both to point sources and the transport/distribution of Hg on regional and global scales. Since mercury compounds possess a wide range of solubilities in water, understanding the specific forms of mercury present in a contaminated sample and the factors that influence what forms are likely to be present is critical to predicting the mobility, reactivity, and potential bioavailability of mercury in the environment. Research by Dr. Christopher Kim of Chapman University and colleagues has resulted in the development of a sensitive technique which uses EXAFS spectroscopy to identify and quantify the proportions of different mercury species present in mercury-bearing samples; as applied to mine wastes from selected mercury and gold mine regions in California and Nevada, this represents the first in situ, non-destructive method by which to identify mercury speciation in natural samples. The results of this SSRL research reveal that geological environment plays an important role in which mercury phases are likely to appear, with hot-spring hydrothermal systems likely to deposit high proportions of soluble (and potentially more toxic) mercury chloride species. The roasting of mercury-bearing ore at temperatures approaching 600°C was found to have the effect of converting cinnabar (HgS, hex) to the more soluble metacinnabar (HgS, cub) species. Also, total mercury concentrations were found to increase dramatically with decreasing particle size in a heterogeneous mine waste, sometimes by nearly an order of magnitude. While this raises concern due to the higher transport potential for smaller particles, EXAFS analysis also found that the mercury associated with these particles is more likely to be present as relatively insoluble mercury sulfides rather than soluble mercury chlorides and oxides. This type of information will hopefully allow a higher degree of sophistication in assessing and prioritizing mine sites for remediation by agencies such as the Environmental Protection Agency and Bureau of Land Management.