MERCURY IN WATERSHEDS FROM LAKE ERIE TO THE GULF OF MEXICO: USING PUBLIC DATABASES TO DETERMINE RELATIONSHIPS BETWEEN LENGTH (AGE) AND MERCURY IN LARGE FISH

Mercury is a toxic element that, when found in its methylmercury form, can lead to neurological impairment in humans. It is especially harmful for young children and women that are pregnant or nursing. Approximately 6%-8% of women of childbearing age have blood levels of mercury that are higher than the EPA's reference dose of 0.1 microgram/kg/day. Methylmercury is especially dangerous in that it bioaccumulates to a greater degree than other forms of mercury. Concentrations of methylmercury in fish, especially larger fish that are higher on the food chain, are customarily four orders of magnitude greater than concentrations found in water. Due to the health threat that mercury poses in the environment, the EPA maintains a database of research conducted by various states and tribal organizations. This NLFWA data set was received by the EPA in 2002 and can be accessed on the EPA's website. It provides a treasure trove of data that has largely been underutilized. Over 62,000 samples were obtained of mercury levels in fish, collected at 7,617 sites during 9,266 sampling events. Some of the data is problematic, but much of it is useful. For this particular study, the focus was placed on mercury sampled in fish tissues from 4 large predator fish, the largemouth bass, northern pike, catfish (blue, bullhead, channel, and flathead), and walleye. The database contained 17,388 individual records for mercury levels in tissues of largemouth bass, 9,017 records for northern pike, 5,624 records for the catfish species, and 10,835 records for walleye across the nation. The highest value of mercury measured in northern pike tissue was 2.1ppm, recorded in Michigan in 1989; walleye tissue concentrations reached 7.59ppm in Pennsylvania in 1993. Mercury concentrations tend to increase with fish size (a proxy for age), which is expected due to its bioaccumulation tendencies. Concentrations also display variability by season, likely due to changes in fish growth and nutrition.