CYTOCHROME-P450 AND ORGANOCHLORINE CONTAMINANTS IN BLACK-CROWNED NIGHT-HERONS FROM THE CHESAPEAKE BAY-REGION, USA

Black-crowned night-heron (Nycticorax nycticorax) offspring were colle cted from a relatively uncontaminated coastal reference site (next to Chincoteague National Wildlife Refuge, VA, USA) and two sites in the C hesapeake Bay watershed (Baltimore Harbor, MD and Rock Creek Park, Was hington, DC, USA). Hepatic microsomal activities of benzyloxyresorufin -O-dealkylase and ethoxyresorufin-O-dealkylase were significantly elev ated (up to sixfold and ninefold induction, respectively) in pipping e mbryos from the Baltimore Harbor colony compared to the reference site , whereas values in embryos from the Rock Creek Park colony were inter mediate. Concentrations of organochlorine pesticides and metabolites i n pipping embryos from both sites in the Chesapeake watershed were gre ater than at the reference site but below the known threshold for repr oductive impairment. However, concentrations of 10 arylhydrocarbon rec eptor-active polychlorinated biphenyl (PCB) congeners and estimated to xic equivalents were up to 37-fold greater in embryos collected from t hese two sites in the Chesapeake Bay region, with values for toxic con geners 77 and 126 exceeding those observed in pipping heron embryos fr om the Great Lakes. Monooxygenase activity of pipping embryos was asso ciated with concentrations of several organochlorine pesticides, total PCBs, arylhydrocarbon receptor-active PCB congeners, and toxic equiva lents (r = 0.30-0.59), providing further evidence of the value of cyto chrome P450 as a biomarker of organic contaminant exposure. Organochlo rine contaminant levels were greater in 10-d-old nestlings from Baltim ore Harbor than the reference site but had no apparent effect on monoo xygenase activity or growth. These findings demonstrate induction of c ytochrome P450 in pipping black-crowned night-heron embryos in the Che sapeake Bay region, probably by exposure to PCB congeners of local ori gin, and the accumulation of organochlorine pesticides and metabolites in nestling herons from Baltimore Harbor. Biomonitoring with addition al waterbird species (e.g., bald eagle, common tern, great blue heron) that appear to be more sensitive to PCBs than black-crowned night-her ons is recommended to document health of waterbirds and remediation of the Chesapeake Bay.