HEPATIC ETHOXYRESORUFIN-O-DEETHYLASE ACTIVITY AND INDUCIBILITY IN WILD POPULATIONS OF DOUBLE-CRESTED CORMORANTS (PHALACROCORAX-AURITUS)

Microplate fluorometric techniques were used to measure ethoxyresorufi n O-deethylase (EROD) activity in hepatic microsomes and primary hepat ocyte cultures from individual wild double-crested cormorant (Phalacro corax auritus) embryos. Embryos were collected in 1993 and 1994 from H umboldt Bay and San Francisco Bay (CA, USA) and a reference site in co astal Oregon (USA). Median microsomal EROD activities in embryos colle cted from San Francisco Bay (in both 1993 and 1994) and from Humboldt Bay (1994) were four- to eightfold higher than the reference site medi an (Kruskal-Wallis, p < 0.05). This degree of induction suggests that cormorant embryos in the two California locations were exposed to conc entrations of dioxinlike compounds that are at the threshold for toxic effects in this species. Substantial variation in the EROD response i n cultured hepatocytes was observed between individuals, populations, and the two bird species tested (cormorants and chickens [Gallus gallu s]). Although most of the cormorant individuals displayed a consistent dose-response profile, a few individuals were uninducible, showing no appreciable increase over basal activity with increasing dose of indu cer. Composite dose-response curves for two cormorant colonies appeare d to be divergent in spite of small sample sizes, indicating that indu cibility can also vary at the population level. These observations sug gest that considerable variability in pollutant metabolism and sensiti vity associated with single enzyme systems may exist within wild popul ations and species.