Award: OCE-1355770

Chemical reactions changing the forms (speciation) of dissolved mercury are important for determining this metal's transport and biological interactions in aquatic environments. The reactive oxygen species superoxide and hydrogen peroxide are produced both by microorganisms and sunlight in natural waters, and their role in changing mercury speciation is not well understood. The goal of the Colorado School of Mines portion of this collaborative grant was to quantify rates of mercury reactions involving reactive oxygen species. The challenge of our experimental design was that we wanted to perform experiments at mercury concentrations near natural levels, and we accomplished this using isotope-labeled mercury. Direct oxidation of zerovalent mercury by superoxide did not occur, but an indirect process involving superoxide may have led to some mercury oxidation in one sample. A significant direct reaction between mercury(II) and superoxide was observed in one water sample, but not in others, indicating that the reaction may depend on other compounds (such as organic ligands) present at variable concentrations in natural waters. We found no evidence that reactions involving hydrogen peroxide can change mercury speciation. We also found no evidence that manganese or copper can catalyze reactions of mercury with superoxide. The enzyme catalase was found to oxidize mercury while the coenzyme NADH was found to reduce mercury, which could complicate interpretation of experiments in which biota are present. Last Modified: 05/23/2017 Submitted by: Bettina M Voelker