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Fundamental Mechanisms and Transformations

This research focuses on an improved fundamental understanding of the geochemical processes that control Hg speciation and complexation reactions, which may ultimately dictate Hg reactivity, bioavailability and methylation and demethylation in the environment. Our emphasis will be on the dominant, coupled geochemical processes and investigate rates and mechanisms of reactions occurring in the Hg-contaminated water and sediments. We will investigate the effect of dissolved organic matter, Fe, and particulate matter in Hg redox transformation, speciation, and catalyzed photochemical redox transformation and demethylation. It will progress to incorporate other geochemical reactive species based on field investigations and modeling results. Our goals are to: determine if reactive Hg species, such as weakly bound Hg-dissolved organic matter and Hg-inorganic complexes, are precursors to the formation of strongly bound Hg-dissolved organic matter complexes or particulates, what are the key geochemical parameters, such as dissolved organic matter with varying chemical and structural characteristics, in controlling the rates and mechanisms of the chemical and redox transformation of Hg, its speciation and bioavailability for methylation, and what controls the rates and mechanisms of photochemical redox transformation and demethylation.