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In Ovo induction of hepatic ethoxyresorufin o-deethylase activity by 2,3,7,8-tetrachlorodibenzo-P-dioxin in four avian species Sanderson, John Thomas


The Canadian Wildlife Service monitors levels of polychiorinated aromatic hydrocarbons in great blue heron (Ardea herodias) and double-crested cormorant (Phalacrocorax auritus) eggs in British Columbia (B.C.) as biological indicators of environmental contamination. This thesis assessed the spatial and temporal effects of environmental contamination with polychiorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs) on hepatic microsomal ethoxyresorufin 0-deethylase (EROD) activities and other biological parameters in heron hatchlings from colonies in B.C and cormorant hatchlings from colonies across Canada. Also, the induction of hepatic EROD activities by environmental levels of polychiorinated aromatic hydrocarbons were compared to in ovo dose-response studies, using 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), in the laboratory. Finally, the differences in EROD-inducing potency of TCDD among avian species were compared with the affinities of TCDD for the avian hepatic Ah receptors. In the herons, levels of PCDDs and PCDFs had decreased considerably since 1988, particularly in the Crofton colony. Concomitantly, there was a decrease in hepatic EROD activity and incidence of chick edema, an increase in body weight and organ weights, and improvement of the reproductive success of the Crofton colony. The reduction in severity of the effects observed in the contaminated colonies in the recent collections, accompanied by the decline in levels of PCDDs and PCDFs, was consistent with the dose-response relationships determined in 1988. Regression analysis demonstrated a significant positive relationship between hepatic EROD activity (pmole/minlmg protein) and TCDD level =(2O.r49; p

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