W4 AM Environmental Fate of Mercury
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in Ballroom 4

(BAN-1117-832183) Exploring links between mercury cycling and hypoxia in the Gulf of Mexico.

Bank, M¹, Shine, J¹, Chesney, E², Rabalais, N², Jay, J³, Lincoln, R¹, Senn, D¹, ¹ Harvard School of Public Health, Department of Environmental Health, Boston, MA, USA² Louisiana Universities Marine Consortium, Chauvin, LA, USA³ Department of Civil and Environmental Engineering, Los Angeles, CA, USA

ABSTRACT- Mercury (Hg) pollution is a widespread and chronic environmental problem that has recently gained considerable attention from policymakers, public health officials, and natural resource managers. Methylmercury is the highly toxic form of Hg that readily bioaccumulates in fish and other biota. Humans are exposed to methylmercury primarily (> 60%) through consumption of fish from coastal marine environments. Coastal eutrophication is another global phenomenon that has garnered substantial attention over the last decade. Increased nutrient fluxes to coastal waters cause enhanced primary production, and, during seasonal stratification, can result in low-oxygen (hypoxic) bottom waters due to aerobic respiration of settling organic matter. Because mercury is primarily methylated by sulfate reducing bacteria (SRB) found in anaerobic sediments, it is reasonable to hypothesize that coastal eutrophication may influence mercury methylation rates in coastal sediments, although the relationship is complex. Up to a certain point, increased organic carbon flux to sediments should enhance mercury methylation in the sediments by stimulating sulfate reduction. However, elevated levels of organic carbon or sulfide can slow methylation rates by making Hg unavailable for uptake by SRB. In this study, we explore links between methylmercury and hypoxia in the Gulf of Mexico, which regularly experiences large-scale seasonal hypoxia. Sediment cores, porewater and gray snapper (Lutjanus griseus) and red snapper (Lutjanus campechanus) tissue samples were collected across a gradient of hypoxia frequency off the Louisiana coast to determine: 1) the spatial distribution of mercury levels and mercury speciation; and 2) if coastal eutrophication and hypoxia exert influences over mercury biomagnification and bioaccumulation in marine ecosystems. The potential cumulative and synergistic effects of mercury pollution, coastal eutrophication, and hypoxia on environmental health are also summarized.

Key words: mercury, biogeochemistry, hypoxia, fish