METHYLMERCURY CYCLING IN URBANIZED AND OFFSHORE REGIONS OF THE U.S. ATLANTIC CONTINENTAL MARGIN

Methylmercury (MMHg) is the form of Hg that bioaccumulates and biomagnifies in marine food webs, notably piscivorous fish, and represents the primary human health concern related to Hg in the environment. Most fish consumed by humans is of marine origin, and the coastal zone, including biologically productive upwelling regions, supports most marine fish productivity. Benthic Hg methylation on the continental shelf and slope is a potentially significant contributor of MMHg to the marine environment, including biota and the open ocean. Thus, and given the limited information and knowledge regarding Hg distributions and biogeochemistry between near-shore and pelagic regions, we have been investigating processes and reactions affecting the cycling of MMHg in sediments, biota, and waters encompassing the important urbanized/impacted estuarine environments of Long Island Sound and New York/New Jersey Harbor and a broad portion of continental shelf and slope of the northwestern Atlantic Ocean. Our approaches have been mechanistic and designed to allow the results to be applicable to other regions of the coastal zone. Here, principal and unifying findings will be presented. These include evidence for a key role played by the triad of Hg loadings, sedimentary particulate organic matter (i.e., quantity and quality), and sulfur chemistry (i.e., speciation, ligands and redox transition regions) in governing the net benthic production of MMHg. Specific MMHg budgets for LIS (dominated by benthic MMHg production) and NY/NJ Harbor (fluvial MMHg fluxes are the major source) will be presented, and the euthrophication-Hg methylation hypothesis illustrated. Finally, these findings will be compared with recent data from our studies of MMHg cycling on the shelf and slope of the NW Atlantic.