Bioaccumulation of mercury in the aquatic food chain of walleye (Stizostedion vitreum) in Lake Siskiwit, northern Wisconsin, United States

The Great Lakes fishery is highly utilized, despite known contamination. The Great Lakes Region has experienced elevated amounts of atmospheric deposition of mercury, with many of its water bodies having documented levels of mercury (ASTDR 1999, Dellinger 2004, Greib et al. 1990, Kleinert and Degurse 1971). The chemical characteristics of methylmercury contribute to high rates of absorption (highly lipophilic and readily crosses biological membranes) and low rates of elimination. As a result of the properties of methylmercury, 60-90% of the mercury in fish is methylmercury (O\u27Neill 1993). Methylmercury is taken in by fish from food sources, through the gills (Haydon and Barron 1990), and by absorption through the skin (Hayton, & Barron, 1990); The Ojibwa Tribal members depend on the fish from this area as a valuable component of their diet and economic health (Dellinger 2004). Lake Siskiwit, located in the Great Lakes region, has some of the highest documented levels of mercury in fish of any lake ever studied (Dellinger et al. 1995, Dellinger 2004, Gerstenberger et al. 1993, WDNR 1999). Based on the United States Food and Drug Association (USDA) action level of 0.5 ppm for human fish consumption, the Wisconsin Department of Natural Resources (WDNR) and Local Tribes issued a fish consumption advisory for Lake Siskiwit in 1993 (Advisory No. 950) that is still active. The advisory calls for no consumption of walleye, by pregnant women and children; The key findings of this study involve prey species of the walleye food chain. This study identified a significant inverse relationship for Perca flavescens between mercury concentrations (ppm) and both total mass (mg) and total length (mm), inconsistent with the previous findings within the literature. It also detected mercury concentrations in all seven species of invertebrate samples, through the method of whole organism analysis. Through the calculations of an analytical model, Amphipoda was identified at the potential key contributor to mean mercury concentrations in yellow perch and therefore walleye, however further analysis would be necessary to raise confidence levels