Assessment of contamination and biomarker responses in two species of herons on the St. Lawrence river

This study was undertaken to validate potential biomarkers of exposure and effects due to chemical contaminants in breedingcolonies of the Great Blue Heron and the Black-crowned Night-Heron on the St. Lawrence River. Eggs and fledglings from both species were collected from many colonies along theRiver. The fledglings from colonies in freshwater and brackishwater were more contaminated by mercury and PCBs than those from estuarine and gulf colonies. With respect to fledglings ofthe two heron species, some morphometric and blood biochemicalmeasurements, including plasma thyroid hormones and retinol, were significantly different among colonies. Significant differences were also observed in liver retinoids, EROD and porphyrins among colonies. The results of this study suggestthat plasma retinoids and thyroid hormones are good biomarkersof exposure and effects, and are sufficiently sensitive to reflect local and regional variations in contamination. Along with the measure of contaminants in egg and plasma, they constitute non-invasive biomarkers which represent an importantcriteria for long term monitoring of wildlife species. It is concluded that the Great Blue Heron is an appropriate sentinelspecies in the surveillance network for the St. Lawrence River.