Abstract-Total Hg concentrations were determined in blood and feather samples of breeding common loons (Gavia immer) and their chicks from 24 lakes in Ontario with a range of water chemistry and fish Hg concentrations. In paired comparisons, males had significantly higher blood (p Ͻ 0.005) and feather (p Ͻ 0.05) Hg concentrations than their female mates. Sex differences in Hg concentrations were attributable to size differences between the two sexes and to the possible transfer of Hg to eggs by females during egg-laying. Significantly higher blood (p Ͻ 0.001) and feather (p Ͻ 0.01) Hg concentrations were found in adult loons compared to their chicks. Adult blood Hg concentrations were significantly correlated with those of their chicks (r ϭ 0.62, p Ͻ 0.05). Adult blood concentrations averaged about 13 times those of corresponding chicks. Both adult and chick blood Hg concentrations were positively correlated with fish Hg concentrations (r ϭ 0.71 and 0.51, respectively), indicating that adult loons in central Ontario, like their chicks, probably feed mainly on their breeding lakes and reflect the fish Hg concentrations of those lakes. Three of 24 lakes had 20-to 50-g fish (mainly perch and sunfish) with Hg concentrations at or exceeding the critical concentration (0.3-0.4 g/g wet weight or ϳ1-2 g/g dry weight) reported to cause reproductive impairment in loons. Monitoring Hg in blood (adult and chick) and feathers (chicks only) is useful for assessing the local bioavailability of methylmercury and the degree of current dietary Hg exposure in loons and other piscivorous birds.

Liver, kidney, and breast muscle tissue from common loons (Gavia immer) and common mergansers (Mergus merganser) from eastern Canada were analyzed for total Hg, organic Hg, and Se concentrations. In both species, Hg and Se concentrations were generally highest in liver, followed by kidney, then breast muscle. As total Hg concentrations increased in liver and kidney tissues, the fraction that was methylmercury (MeHg) decreased. Livers and kidneys with the highest total Hg concentrations (> 100 μg/g dry weight) had only 5 to 7% of the total as MeHg. Concentrations of MeHg were <10 μg\g (dry weight) regardless of the total Hg concentration in liver and kidney. In contrast, the proportion of MeHg in breast muscle remained high (80–100%) in both loons and mergansers regardless of total Hg concentration, which ranged from 0.7 to 35 μg\ (dry weight7rpar;. Strong positive correlations were observed between total Hg and Se concentrations, but not between MeHg and Se, in kidney and liver tissues for both loons and mergansers. Mercury concentrations were significantly higher (analysis of variance, p < 0.0001) in all three tissues of loons found in an emaciated condition compared with apparently healthy loons. Non‐emaciated loons had Hg concentrations comparable to those of healthy mergansers, and concentrations were lower than those associated with Hg toxicity in birds. The elevated Hg concentrations in emaciated loons may have contributed to their impaired conditions; alternatively, the wasting of their muscle and other tissues may have caused apparent tissue Hg concentrations to increase. In any case, total Hg concentrations in liver and/or kidney tissue are insufficient criteria for making toxicologically relevant judgments of possible Hg toxicity. Because of the varying degrees of apparent Hg demethylation in liver, kidney, and other tissues and the association of the resulting inorganic Hg with Se in an apparently stable, toxicologically inert complex, estimates of organic Hg and Se concentrations, in addition to total Hg, in these organs are recommended.

Abstract-Liver, kidney, and breast muscle tissue from common loons (Gavia immer) and common mergansers (Mergus merganser) from eastern Canada were analyzed for total Hg, organic Hg, and Se concentrations. In both species, Hg and Se concentrations were generally highest in liver, followed by kidney, then breast muscle. As total Hg concentrations increased in liver and kidney tissues, the fraction that was methylmercury (MeHg) decreased. Livers and kidneys with the highest total Hg concentrations (Ͼ100 g/g dry weight) had only 5 to 7% of the total as MeHg. Concentrations of MeHg were Ͻ10 g/g (dry weight) regardless of the total Hg concentration in liver and kidney. In contrast, the proportion of MeHg in breast muscle remained high (80-100%) in both loons and mergansers regardless of total Hg concentration, which ranged from 0.7 to 35 g/g (dry weight). Strong positive correlations were observed between total Hg and Se concentrations, but not between MeHg and Se, in kidney and liver tissues for both loons and mergansers. Mercury concentrations were significantly higher (analysis of variance, p Ͻ 0.0001) in all three tissues of loons found in an emaciated condition compared with apparently healthy loons. Non-emaciated loons had Hg concentrations comparable to those of healthy mergansers, and concentrations were lower than those associated with Hg toxicity in birds.

Total Hg concentrations were determined in blood and feather samples of breeding common loons (Gavia immer) and their chicks from 24 lakes in Ontario with a range of water chemistry and fish Hg concentrations. In paired comparisons, males had significantly higher blood (p Ͻ 0.005) and feather (p Ͻ 0.05) Hg concentrations than their female mates. Sex differences in Hg concentrations were attributable to size differences between the two sexes and to the possible transfer of Hg to eggs by females during egg-laying. Significantly higher blood (p Ͻ 0.001) and feather (p Ͻ 0.01) Hg concentrations were found in adult loons compared to their chicks. Adult blood Hg concentrations were significantly correlated with those of their chicks (r ϭ 0.62, p Ͻ 0.05). Adult blood concentrations averaged about 13 times those of corresponding chicks. Both adult and chick blood Hg concentrations were positively correlated with fish Hg concentrations (r ϭ 0.71 and 0.51, respectively), indicating that adult loons in central Ontario, like their chicks, probably feed mainly on their breeding lakes and reflect the fish Hg concentrations of those lakes. Three of 24 lakes had 20-to 50-g fish (mainly perch and sunfish) with Hg concentrations at or exceeding the critical concentration (0.3-0.4 g/g wet weight or ϳ1-2 g/g dry weight) reported to cause reproductive impairment in loons. Monitoring Hg in blood (adult and chick) and feathers (chicks only) is useful for assessing the local bioavailability of methylmercury and the degree of current dietary Hg exposure in loons and other piscivorous birds.

Abstract:We examined the flow of mercury (Hg) from benthic invertebrates to fishes in lakes with contrasting fish community structure. The study was carried out in two whole lakes in southcentral Ontario in 1992. Both were remote from direct sources of contamination and were chosen because of their physical and chemical similarities. Although the fish communities in the two lakes were qualitatively similar, the total number of fishes in Ranger Lake was an order of magnitude smaller than that in Mouse Lake. As a result of the lower net predation from benthivorous fishes, documented in earlier studies, Ranger Lake benthic invertebrate populations were significantly higher. However, benthic invertebrate taxa in Mouse Lake were generally larger and had higher Hg concentrations. This was partly attributed to the stunted growth of Mouse Lake fishes, which did not allow them to prey on larger benthos as a result of gape limitations. Despite the lower Hg concentrations in Ranger Lake benthos, total benthic invertebrate Hg pools were higher in this lake as a result of its higher total benthic invertebrate biomass. However, the transfer of total Hg from benthic invertebrates to fishes was higher in Mouse Lake due to the higher consumption rates of benthivorous fishes.Résumé : Nous avons examiné le flux du mercure (Hg) des invertébrés benthiques aux poissons dans des lacs ayant des communautés de poissons de structure différente. L'étude a été réalisée dans deux lacs entiers dans le centre-sud de l'Ontario en 1992. Les deux lacs étaient éloignés des sources de contamination directe et ils ont été choisis en raison de leur ressemblance du point de vue physique et chimique. Bien que les communautés de poissons dans les deux lacs aient été semblables du point de vue qualitatif, le nombre total de poissons dans le lac Ranger était inférieur d'un ordre de grandeur à celui du lac Mouse. À cause de la prédation nette inférieure attribuable aux poissons benthivores, documentée dans des études antérieures, les populations d'invertébrés benthiques du lac Ranger étaient substantiellement plus importantes. Cependant, les représentants des taxons d'invertébrés benthiques du lac Mouse étaient généralement de taille plus grande et avaient des concentrations de Hg plus élevées. Cette situation était en partie attribuable à la croissance arrêtée des poissons du lac Mouse, qui ne leur permettait pas de consommer les organismes benthiques plus gros en raison d'une ouverture maximale de la bouche insuffisante. Malgré les concentrations de Hg inférieures dans le benthos du lac Ranger, les pools de Hg chez les invertébrés benthiques étaient plus importants dans ce lac en raison de sa biomasse totale en invertébrés benthiques plus élevée. Toutefois, le transfert de Hg des invertébrés benthiques aux poissons était plus élevé dans le lac Mouse en raison du taux de consommation plus élevé des poissons benthivores. [Traduit par la Rédaction]