Polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p -dioxin equivalents in eggs of double-crested cormorants from a colony near Green Bay, Wisconsin, USA

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Great Lakes colonial waterbirds have experienced poor reproduction and a greater incidence of birth defects than those in remote areas. An egg was collected from each of 1,000 marked cormorant nests at Spider Island (Lake Michigan). Nine pools comprised of three eggs were randomly selected for instrumental quantification of polychlorinated biphenyls (PCB) congeners, calculation of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEq) and measurement of equivalents by bioassay (TCDD-EQ). PCB analysis of the nine samples was semi-automated with high performance liquid chromatography (HPLC) columns including a porous graphitic carbon column. TEqs were calculated from concentrations of PCB congeners and bioassay-derived toxic equivalency factors (TEfs), and TCDD-EQ were measured directly with an H4IIE bioassay. Total PCB concentrations ranged from 9.7 to 38 μg/g, wet weight (ww). Mean concentrations of PCB 77, 126, and 169 were 2, 7, and 1 ng/g, ww. The mean TEqs and TCDD-EQ were 150 and 350 pg/g, ww, respectively. Thus, PCB congeners contributed less than 50% of the total TCDD-EQs as measured by the bioassay.