MERCURY CONCENTRATIONS IN THE WATER AND PLANKTON, WESTERN LAKE ERIE

Mercury (Hg) contamination and bioaccumulation are among the primary pollutant concerns within the Great Lakes. Because the primary vector of Hg to humans is via fish consumption, the bioaccumulation of Hg within aquatic food chains is a major public health concern. Our goals were to evaluate the seasonal concentrations of Hg and methylmercury (MeHg) in the waters and Hg in the microplankton (20-202 µm) and macroplankton (<202 µm) of Western Lake Erie, and to better quantify the influence of both the Maumee and Detroit Rivers on Hg input to the lake. The lake was sampled 3 times (spring, summer and fall) in 4 locations (Detroit, Raisin, and Maumee River areas and the Sandusky Basin). River samples were collected approximately every 8 weeks. Mean lake concentrations were 2.0 ng/L for total Hg (HgT) and 0.41 ng/L for dissolved Hg (HgD). Only one lake water sample had a result above the 0.02 ng/L detection limit for MeHg. The riverine Hg concentrations for HgT and HgD for the Detroit River were 2.7 and 0.80 ng/L and for Maumee River were 4.8 and 1.8 ng/L, respectively. The nitrate concentrations of the Maumee were an order of magnitude higher than the Detroit River reflecting the agricultural land use of the watershed. Particulate Hg concentrations were two times lower in the Maumee compared to the Detroit River. Mean concentrations of Hg in the micro and macro plankton were 84 and 54 ng/g wet weight, respectively, with the highest concentration in macroplankton observed in the lake off the Raisin River. These values are within the range observed in other freshwater systems. The highest concentration of Hg in the macroplankton occurred in the summer while the highest concentration of Hg in the microplankton occurred in the fall.