Trends and patterns of PCB,DDE, and mercury contamination in bald eagle nestlings in the upper Midwest

We analyzed concentrations and trends of DDE, total PCBs, and mercury in bald eagle (Haliaeetus leucocephalus) nestlings at six study areas in the upper Midwest, 2006–2015, and long-term trends at two Lake Superior sites, 1989–2015. Eaglet plasma from the Apostle Islands in Lake Superior had the highest concentrations of DDE (geometric mean GM]?=?10.6?μg/L), and DDE concentrations decreased at 5.8% per year across the region from 2006 to 2015, and at 5.5% per year at Lake Superior sites from 1989 to 2015. Concentrations of the sum of 75 PCB congeners (ΣPCB₇₅) were highest at Pools 3 and 4 of the Mississippi River (GM?=?114.8?μg/L) and did not decline significantly region-wide (all study areas together) between the years of 2006 and 2011. However, at Lake Superior, ΣPCB₇₅ declined from 1995 to 2011 along the south shore at 3.6% per year, with a non-significant decline at the Apostle Islands. Concentrations of mercury in nestling breast feathers were highest at the upper St. Croix River (GM?=?6.66?μg/g wet weight). At Lake Superior study areas, mercury declined at 1.6% per year from 1991 to 2015; however, from 2006 to 2015 we found no significant trend at one of these same study areas and mercury concentrations apparently increased at two study areas. Mean concentrations of contaminants were below levels associated with significant impairment of reproduction at all sites and mean reproductive rates were?>?1.4 young per nest. However, increasing concentrations of mercury in some areas, combined with relatively high concentrations at some nests, suggest that continued monitoring of mercury should be a management priority.