EFFECTS OF 3,3',4,4',5-PENTACHLOROBIPHENYL AND 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN INJECTED INTO THE YOLKS OF DOUBLE-CRESTED CORMORANT (PHALACROCORAX-AURITUS) EGGS PRIOR TO INCUBATION

Double-crested cormorant (Phalacrocorax auritus) eggs were injected wi th either 3,3',4,4',5-pentachlorobiphenyl (polychlorinated biphenyl [P CB] 126; 70-698 mu g/kg egg) or 2,3,7,8-tetrachloradibenzo-p-dioxin (T CDD; 1.3-11.7 mu g/kg egg) prior to incubation. These compounds were i njected into the yolks of cormorant eggs collected from incomplete clu tches at isolated colonies on Lake Winnipegosis, Manitoba, Canada. Egg s were incubated for approximately 26 to 28 d. After hatching the brai n, bursa, heart, liver, and spleen were dissected and weighed. Torsos were preserved in formalin for examination of the gonads. Median letha l doses (LD50s) calculated from mortality data at hatching were 177 an d 4.0 mu g/kg egg for PCB 126 and TCDD, respectively. No significant d ifferences were found in the incidence of developmental abnormalities in any of the treatment groups. Bursa weights were significantly less in the greatest (11.7 mu g/kg egg) TCDD group compared to the vehicle control group. Spleen weights were significantly less in the 349 mu g PCB 126/kg egg and the 5.4 and 11.7 mu g TCDD/kg egg groups when compa red to the vehicle control group. No histological alterations of the g onads were found. Hepatic ethoxyresorufin-O-deethylase activity in all PCB 126 and TCDD dose groups was significantly greater compared to th e control activity. The toxic equivalency factor for PCB 126 was 0.02.