Thyroid Hormones, Retinol and Clinical Parameters in Relation to Mercury and Organohalogen Contaminants in Great Blue Heron (Ardea herodias) Nestlings from the St. Lawrence River, Québec, Canada.

The exposure and effects of persistent environmental contaminants were investigated in great blue heron (Ardea herodias) nestlings sampled in 2001, 2002, 2006, and 2007 in freshwater and estuarine heronries along the St. Lawrence River, Québec (Canada). Biomarkers (retinoids, thyroid hormones, and clinical parameters) and contaminants (organochlorine contaminants, polychlorinated biphenyls (PCBs), brominated flame retardants (BFRs), and mercury (Hg)) were analyzed in blood, and Hg was analyzed in feathers (generally 9 nestlings per colony and 4 colonies per year). Feather Hg and most contaminants detected in blood were found in higher concentrations in birds from freshwater than estuarine colonies more distant from the pollution sources. Among freshwater colonies, Ile aux Hérons showed the highest levels of contaminants, with mean Hg concentrations of 8.4 and 0.55 mg/kg in feathers and plasma, respectively, and plasma ΣBFRs of 19.6 ng/g ww. The highest mean ΣPCBs, 56.5 ng/g ww, was measured at Grande Ile in 2001. The levels of contaminants in heron nestlings were generally below critical thresholds for adverse effects observed on reproduction or survival. Retinol, dehydroretinol (DROH), and thyroid hormone concentrations differed significantly among colonies. Retinol concentrations were negatively related to ΣPCBs, whereas DROH concentrations were negatively related to Hg and total and free triiodothyronine (T3) concentrations were negatively related to ΣBFRs. These results indicate that contaminants from the St. Lawrence River could impair the development and fitness of great blue heron nestlings and emphasize the need for more research on the great blue heron population to assess their health and nutritional status.