Between 1968 and 1980, 98 eggs were collected from active nests of the common loon (Gavia immer) in Ontario. Residues of ⌆DDT and PCB declined over this period while dieldrin and Hg appeared unchanged. Eggs collected in 1969 and 1970 had significantly thinner shells than eggs from a collection made before 1947. Between 1969 and 1979, 215 common loon carcasses were collected across Ontario, the result of having been drowned or shot or having died of diseases or unknown causes. Chemical analyses of 174 carcasses taken from healthy birds showed that adult loons accumulated higher levels of organochlorine and Hg residues than did juveniles. Tissues with high fat contents contained higher organochlorine levels while kidney, liver, and feathers had the highest Hg levels. Thirty loons were found to be emaciated with visibly lesser amounts of body fat and significantly lower levels of lipids in pectoral muscle tissue. Organochlorine but not Hg residues were one to two orders of magnitude higher in the wet tissues of emaciated birds than healthy birds. Higher residues of organochlorine chemicals were found in the uropygial gland, the oil secreted by this gland and belly and back feathers of emaciated birds when compared to healthy birds. It was concluded that losses of organochlorine chemical residues could occur through this gland. While Hg levels in feathers were elevated, Hg did not accumulate in the uropygial gland or in the secreted oil and was not the route for Hg content in feathers.
In emaciated birds, mean brain levels of ⌆DDT (primarily DDE) were between 25 and 49 Μg/g, dieldrin 0.5 to 1.2 Μg/g, PCB 39 to 63 Μg/g, and mercury 1.0 to 1.8 Μg/g. The mean brain levels in healthy birds were between 0.2 and 0.9 Μg/g ⌆DDT, 0.01 and 0.05 Μg/g dieldrin, 0.6 and 2.0 Μg/g PCB, and 0.4 and 0.6 Μg/g mercury.