Relationships among cytochromes P450 and dioxin equivalents in pipping heron embryos from Virginia, the Great Lakes and San Francisco Bay

Pipping black-crowned night-heron (Nycticorax nycticorax) embryos were collected from undisturbed (Chincoteague National Wildlife Refuge, VA) and industrialized (Cat Island, Green Bay, WI; San Francisco Bay, CA) locations. Hepatic P450 associated monooxygenases (AHH, EROD, BROD, ECOD) and P450 proteins (CYP1A, CYP2B) were induced up to 85-fold, and were associated with burdens of total PCBs and 11 AHH-active PCB congeners. Dioxin equivalents (TCDD-EQs) of sample extracts, derived by bioassay (H4I1E rat hepatoma cell) and mathematically (product of PCB congener concentration and relative TCDD potency), revealed greatest TCDD-EQs in Cat Island samples. TCDD-EQs were associated with P450s, especially BROD, EROD and CYP1A (r2 = 0.35 to 0.66). TCDD-EQs derived by bioassay were highly correlated with TCDD-EQs derived mathematically (r2 = 0.58 to 0.67) . Multiple regressions were also performed to investigate relationships among P450s and PCB congeners. In summary, these data demonstrate that hepatic P450s of heron embryos are biomarkers of exposure to dioxin-like compounds and provide further evidence that this species has considerable value for assessing wetland and estuarine contamination.