Researchers from the University of Connecticut, Woods Hole Oceanographic Institution, and Harvard University plan to address three questions related to the global biogeochemical mercury (Hg) and selenium (Se) cycles, namely (1) what are the abiotic and biotic mechanisms for formation of methylated Hg and Se compounds in the upper ocean?; (2) what is the role of photochemical reactions in air-sea exchange of Hg and Se?; and (3) how are the biogeochemical cycles of Hg and Se related? To attain their goal, the scientists will participate in a cruise of opportunity to the Tropical North Pacific, as well as carry out laboratory culture and controlled incubation experiments. Samples collected during the cruise will be used to determine the speciation of Hg and Se, as well as obtain measurements of photochemical status (i.e., UV, ozone, light levels, chemical (i.e., natural organic matter, redox metals), and biological (i.e., chlorophyll a, phytoplankton composition,proteomics, estimates of carbon mineralization) properties. The laboratory culture and controlled incubation experiments will be used to determine the specific pathways for Hg and Se compound formation and degradation, especially the role of photochemical transformations, as well as assess the importance of Se as a binding ligand for Hg in the marine environment. Lastly, the researchers will continue to develop the oceanic sub-model of the GEOS-Chem global biochemical Hg model to include the cycling of Se and will use the model to ascertain the importance of various processes of conversion and evasion in the global cycles of these two elements.

As regards broader impacts, this study has societal benefits because it would improve our understanding on how mercury enters seafood which impacts human health. Results from the research would be included in curriculum material. One graduate student from the University of Connecticut, one postdoc from Harvard University, and one graduate student from Woods Hole Oceanographic Institution would be supported and trained as part of the project.

Project Report

Mercury and selenium are two elements found in trace concentrations in ocean water and biota. One, selenium, is an essential nutrient while the other is a potent toxin that can build up to alarmingly levels in fish. Previous research has suggested that the behavior in the environment of these two very different elements are in some ways entwined. For example, across a wide range of fish, when selenium concentrations in their tissues are high, the mercury concentrations are low, and vice versa. The cause of this behavior is unknown, but if explored could potentially offer a way to deal with the ever increasing concentrations of mercury in seafood. During this project, lead by researchers at the University of Connecticut, the Woods Hole Oceanographic Institution had a few research questions to address. These included 1) whether or not seleno-cysteine, a selenium containing amino acid, could increase the rate at which mercury is transformed into the highly bioaccumulative form monomethylmercury by enhancing the rate at which mercury enters bacteria who can perform the methylation; 2) whether another form of selenium, dimethylselenide, can directly methylate without bacteria and 3) whether there are detectable amounts of seleno-cysteine in seawater. Through our research, we found that none of these appear true. This interesting result suggests that the mercury-selenium interaction described above likely is the result of processes that occur within foodwebs, and allows further research to focus on those lines of investigation.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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Donald L. Rice
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Woods Hole Oceanographic Institution
Woods Hole
United States
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