Organochlorine and metal residues in eggs of waterfowl nesting on islands in Lake Michigan off Door County, Wisconsin, 1977-78.

One egg from each of 114 red-breasted merganser (Mergus serrator) nests in 1977 and 92 nests in 1978 was collected and later analyzed for organochlorines, polybrominated biphenyls (PBBs), polychlorinated styrenes (PCSs), and metals. One egg was also collected from each of the dabbling duck nests located. Twenty-nine of these eggs were analyzed for organochlorines and metals in 1977; 10 eggs were analyzed in 1978. All merganser eggs contained DDE, polychlorinated biphenyls (PCBs), and dieldrin; all but one egg collected in 1978 contained DDT. DDE and PCB levels had declined since 1975 to a geometric mean of 7.4 ppm DDE and 20 ppm PCBs in 1977 and 7.6 ppm DDE and 19 ppm PCBs in 1978. Dieldrin residues in eggs had not declined from 1975 levels; the geometric mean was 0.78 ppm in 1977 and 0.76 ppm in 1978. Other organochlorines were present at low levels. Mercury residues averaged greater than 0.50 ppm in merganser eggs and had not declined since 1975. Other metals were present at low levels. Dabbling ducks generally had much lower organochlorine and Hg residues than mergansers; DDE and PCBs were the only organochlorines present in the majority of eggs. Geometric means of PCBs and DDT in dabbling duck eggs did not exceed 2.0 ppm and 1.0 ppm, respectively. PBBs and PCSs were detected only in a few merganser eggs, at low levels. Eggshell thickness for red-breasted merganser eggs averaged 0.359 mm in 1977 and 0.355 mm in 1978, which is only 2%-3% below pre-1946 thicknesses. Mallard (Anas platyrhynchos) eggshell thicknesses averaged 0.331 mm in 1977 and 0.377 mm in 1978.