Summary

Description

Mason Neck National Wildlife Refuge supports the largest great blue heron Ardea herodias rookery in the State of Virginia. The presence of bioaccumulative compounds such as polychlorinated biphenyls and DDT in fish collected from the Potomac River and tidal tributaries along the Refuge led to this study. The objective was to determine if there were any indications of pollutantinduced eggshell thinning or evidence of biochemical exposure to contaminants. We examined eggshell thickness and biomarkers of contaminant exposure in livers of embryos collected from the refuge and Coaches Island, a reference location in Chesapeake Bay. There was no evidence of eggshell thinning. Cytochrome P450 activity, measured as ethoxyresorufinOdealkylase EROD and benzyloxyresorufinOdealkylase BROD, was not significantly different in embryos from the two colonies. Biochemical indicators of oxidative stress can be reflected as changes in levels of reduced thiols, oxidized glutathione, and thiobarbituric reactive substances TBARS. Although there were significant differences in the levels of reduced glutathione GSH and total thiol TSH activities in the embryo livers, there were no statistically significant differences in TBARS, proteinbound sulthydryls PBSH, oxidized glutathione GSSG and the ratio of GSSG to GSH. In fact, the concentrations of GSH and TSH were higher in the Mason Neck birds relative to Coaches Island. Under conditions of increased oxidative stress at least one or more of the following would be expected: decreased concentrations of reduced thiols GSH and TSH, increased GSSG, and increased TBARS. In conclusion, we did not detect eggshell thinning or find evidence of a biochemical response to contaminant exposure in the Mason Neck great blue herons.