Oxidative stress in laboratory-incubated double-crested cormorant eggs collected from the Great Lakes

Double-crested cormorant (Phalacrocorax auritus) eggs were collected in 1998 from three sites on Lakes Huron and Superior and either analyzed for 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD)-like residues or artifically incubated. Some of the incubated eggs were injected with vitamin E (antioxidant) or piperonyl butoxide (CYPIA blocker) to examine the role of CYPIA and oxidative stress in normal bird development. Embryos (day 23) were analyzed for hepatic ethoxyresorufin O-deethylase (EROD) activity and different measures of oxidative stress. Glutathione-related parameters were also measured in brain. In contrast to the historical data, there were no statistically significant differences in concentrations of chlorinated dioxins, furans, dioxin-like PCBs, or total TCDD-equivalents (TEQs) in eggs among sites. Survival and incidence of abnormalities were comparable at all study sites. Slight differences in liver, heart, and egg weight were observed among sites. A greater incidence of eye deformities was observed in embryos treated with vitamin E. Treatment with the CYPIA blocker, piperonyl butoxide, decreased the body weights of embryos. EROD activities were similar at all locations, but measures of oxidative stress varied among locations. There were greater levels of oxidized glutathione and oxidative DNA damage at Little Charity Island in Saginaw Bay. There was relatively great interindividual variation in biochemical responses and significant interrelation of the parameters of oxidative stress. While exposure to PCDD/DF and PCBs does not seem to explain the observed oxidative stress, the potential of these compounds to cause the observed effects can not be completely excluded.