EFFECTS OF 3,3',4,4',5-PENTACHLOROBIPHENYL (PCB-126) AND 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN (TCDD) INJECTED INTO THE YOLKS OF CHICKEN (GALLUS-DOMESTICUS) EGGS PRIOR TO INCUBATION

The yolks of White Leghorn chicken (Gallus domesticus) eggs were injec ted prior to incubation with either 3,3',4,4',5-pentachlorobiphenyl (P CB 126) at doses ranging from 0.1 to 12.8 mu g/kg egg or 2,3,7,8-tetra chlorodibenzo-p-dioxin (TCDD) at doses ranging from 0.04 to 0.64 mu g/ kg egg. Chicks were subjected to necropsy within 24 h of hatching. The brain, bursa, heart, liver, and spleen were removed and weighed. Asse ssment of the rate of hatching indicated an LD(50)+/-S.E. of 2.3+/-0.1 9 mu g/kg egg (7.1+/-0.58 nmol/kg egg) for PCB 126 and 0.15+/-0.012 mu g/kg egg (0.47+/-0.037 nmol/kg egg) for TCDD. No significant differen ces in the incidence of developmental abnormalities (structural defect s and edema) were observed in TCDD-exposed embryos, while PCB 126 caus ed significantly more developmental abnormalities at 3.2, 6.4, and 12. 8 mu g/kg egg than the vehicle control. PCB 126 caused lower hatchling weights and greater relative brain, heart, and liver weights when com pared to the vehicle control group at a dose of 3.2 mu g/kg egg which is greater than the LD(50). TCDD at 0.08 mu g/kg egg caused relative b ursa weights to be less than those of the vehicle control. A toxic equ ivalency factor (TEF) of 0.07 was determined for PCB 126 in relation t o TCDD based on overt lethality.