EVALUATING MERCURY CONTAMINATION IN FISH: A MULTI-MODEL APPROACH

Since the industrial revolution, mercury concentration in the atmosphere has increased substantially, largely due to anthropogenic inputs from coal-fired power plants (Pacyna and Pacyna 2006; Schuster and others 2002). Owing to the ease with which mercury is transported in the atmosphere and its long residence time, contamination in freshwater and marine ecosystems has become a global problem (Trudel and Rasmussen 2006).  After atmospheric mercury enters waterbodies it is chemically transformed by bacteria to methylmercury, the organic, highly toxic form of mercury that biomagnifies in aquatic food webs and constitutes a threat to wildlife and humans (Holloway and Weech 2003). The mechanisms associated with mercury methlyation and accumulation in fish tissue remain poorly understood, and health officials are often forced to recommend fairly nonspecific fish consumption advisories.  Our study addresses this problem through a comprehensive, statewide synthesis of data on fish mercury contamination in North Carolina and the environmental factors associated with methylmercury production and transport through aquatic food webs.  Using data collected by the North Carolina Department of Environment and Natural Resources, the U.S. Environmental Protection Agency, and others, we examined the relationships between a suite of biotic and abiotic factors and tissue mercury concentrations in fish from North Carolina water bodies (Sackett and other 2009). Multivariate tests were conducted to create predictive statistical models relating environmental variables to mercury levels in fish, and Akaike's Information Criterion was used to examine the relative strengths of candidate models. The best model in our analyses (R² = 0.81) included species, fish trophic status, ecoregion (areas of general similarity in ecosystems and in the type, quality, and quantity of environmental resources), and pH. Other important drivers of mercury accumulation were land use patterns (the percentage of the subbasin that is agricultural) and site type (swamps versus lakes, rivers, and bays).  Although previous investigations have indicated similar individual relationships, our study is unique in examining the relative importance of a large number of biotic and abiotic variables across a range of environments, ecosystems, and species. The results of these analyses should help policymakers in making risk assessment decisions and serve as a template for future investigations.

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Sackett, D.K., Aday, D.D., Rice, J.A.; and Cope, W.G., 2009, A statewide assessment of

mercury dynamics in North Carolina waterbodies and fish: Transaction of the American Fishery Society, v. 138, p. 1328-1341.

Schuster, P.F., Krabbenhoft, D.P., Naftz, D.L., Cecil, L.D., Olson, M.L., Dewild, J.F.,

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