A Statewide Assessment of Mercury Dynamics in North Carolina Water Bodies and Fish

Abstract

AbstractMercury contamination of aquatic systems has received much attention recently because of potential health effects on humans and wildlife. Although the factors affecting mercury deposition, its conversion to biologically active methylmercury, and its bioaccumulation in aquatic systems have been identified, equivocal results for particular species and systems have hampered policy making. Our study addresses this problem through a comprehensive, statewide synthesis of the available data on fish mercury contamination in North Carolina and the environmental factors associated with methylmercury formation 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. Multivariate tests were conducted to create predictive models relating environmental variables to mercury levels in fish, and Akaike's information criterion was used to examine the relative strengths of the candidate models. The best model in our analyses (R2 = 0.81) included species, fish trophic status, ecoregion, 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 that we examined 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.