Contaminant concentrations in bald eagles nesting on Lake Superior,the upper Mississippi River,and the St. Croix River

We measured concentrations of DDE, total PCBs, and mercury in bald eagle (Haliaeetus leucocephalus) nestlings at three locations in the upper Midwest: Lake Superior, the upper Mississippi River, and the St. Croix River, 2006–2008. We also analyzed trends in concentrations of these contaminants for eagles on the southern shore of Lake Superior, from 1989 to 2008, using the current and previously published data. Concentrations of DDE in nestling blood plasma samples were greatest on Lake Superior (geometric mean: 16.2 μg/kg, n = 29), whereas concentrations of total PCBs were highest in Mississippi River samples (88.6 μg/kg, n = 51). Mercury concentrations were highest along the upper St. Croix River (6.81 μg/g wet weight in feathers, n = 19). For Lake Superior, DDE concentrations declined significantly in nestling blood plasma samples from 1989 to 2008, an average of 3.0% annually. Similarly, total PCBs in Lake Superior eaglets decreased 4.0% annually from 1989 to 2008, and mercury concentrations in nestling feathers from Lake Superior nests also decreased significantly from 1991 to 2008, 2.4% per year. With the possible exception of mercury on the upper St. Croix River, mean concentrations in 2006–2008 of all three compounds were below levels associated with significant impairment of reproduction for all sites, and reproductive rates at all three sites averaged > 1.2 young per occupied territory, which is greater than the rate indicative of a healthy population.