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LEVELS OF PERSISTENT CONTAMINANTS IN BALD EAGLES NESTING ON THE ST. CROIX AND NAMEKAGON RIVERS, WITH COMPARISONS TO THE MISSISSIPPI RIVER AND LAKE SUPERIOR
Bill Route, National Park Service, Great Lakes Inventory and Monitoring Network
The Great Lakes Inventory and Monitoring Network is responsible for monitoring trends of selected ecological indicators at nine national parks in the upper Midwest. We are currently monitoring water quality, terrestrial vegetation, land birds, land cover and use, and a targeted group of persistent, bioaccumulative toxins (PBTs).
Network staff and partners sampled bald eagle nestlings in 2006 and 2007 to monitor levels of PBTs at the St. Croix National Scenic Riverway, the Mississippi National River and Recreation Area, and Apostle Islands National Lakeshore. For this paper we present data for three ecological areas: 1) the upper riverways, including the St. Croix and Namekagon rivers above St. Croix Falls; 2) the Greater Twin Cities area, including the Mississippi National River and the portion of the St. Croix below St. Croix Falls; and 3) Lake Superior, including the Apostle Islands and nearby shoreline. Blood and feather samples from 66 nestlings (32 in 2006, 34 in 2007) were analyzed for six contaminants: two that have been banned—PCBs and DDT (including metabolites DDE and DDD); two heavy metals—mercury and lead; and two emerging contaminants—polybrominated diphenyl ether (PBDE) and perfluorooctanyl sulfonate (PFOS). PBDEs and PFOS are widely used as flame retardants and water/stain repellents, respectively, and have come under increasing scientific and regulatory scrutiny.
PCBs and DDE continue to decline from highs in the 1970s, though concentrations are greater in nestlings from Lake Superior compared to the Greater Twin Cities and upper riverways. DDT was generally below detection limits, but was detected in three of 10 nestlings in 2006 and four of 12 in 2007 in Lake Superior nests. By comparison, at inland nests, DDT was found in one of 26 nestlings in 2006 and zero of 22 in 2007.
We found both PCBs and PBDEs in all nestlings sampled and found them to be higher in Lake Superior and Greater Twin Cities samples than those from the upper riverways. Our data suggest a near doubling of PBDEs in Lake Superior over the last five years. Levels of PFOS in 2006 were highest in nestlings from the Greater Twin Cites area, followed by Lake Superior, and lowest in the upper riverways. We found a significant reduction in levels of PFOS from 2006 to 2007 in eaglets from the Greater Twin Cities; yet levels remained about the same for Lake Superior nestlings.
The spatial distribution of mercury in bald eagle nestlings was nearly opposite of the other chemicals. It was highest in nestlings along the upper riverways where extensive areas of wetlands likely contribute to the production and availability of mercury. Lead concentrations were highest in nestlings from the Twin Cities area, but were generally low elsewhere.