Abstract

As part of the Canadian Wildlife Service monitoring of great blue herons in British Columbia, eggs were collected from three colonies with low, intermediate, and high levels of PCDD and PCDF contamination: Nicomekl, Vancouver, and Crofton, respectively. One egg from each nest was used for chemical analysis by CC‐MS; the others were hatched. Liver microsomes were prepared from the heron chicks and used for determination of cytochrome P‐450‐dependent activities. No erythromycin N‐demethylase activity was found in any sample. Ethoxyresorufin O‐dealkylase activity in the Nicomekl group was similar to that in pigeons, a control altricial species. The ethoxyresorufin activity in the herons from the Crofton colony was 2.6‐fold higher than in the Nicomekl group. The Vancouver colony was intermediate. No difference among the three heron colonies was found in pentoxyresorufin O‐dealkylase activity, although levels were 20–33 times that in the pigeon. Chemical analysis was carried out on paired heron eggs. Vancouver and Crofton eggs contained 13.5 and 21 times the levels of 2,3,7,8‐TCDD compared to the Nicomekl group. The Crofton eggs contained higher levels of several other contaminants also. A highly significant correlation (p < .001) was found between ethoxyresorufin O‐dealkylase and 2,3,7,8,‐TCDD concentrations. The correlation coefficient did not change when ethoxyresorufin O‐dealkylase was compared to total chemical contamination using several toxic equivalency factors. Multiple regression analysis resulted in only one predictor variable for ethoxyresorufin O‐dealkylase: 2,3,7,8‐TCDD.