Distribution and accumulation of mercury in tissues of captive‐reared common loon (Gavia immer) chicks

We determined the distribution and accumulation of Hg in tissues of common loon (Gavia immer) chicks maintained for up to 15 weeks on either a control diet with no added methylmercury chloride (MeHgCl) or one containing either 0.4 or 1.2 μg Hg (as MeHgCl)/g wet-weight food. Total Hg and MeHg tissue concentrations were strongly positively correlated (r2 > 0.95) with the amount of Hg delivered to individual chicks throughout the course of the experiment. The pattern of differential Hg concentration in internal tissues was consistent within each treatment: Liver > kidney > muscle > carcass > brain. Feather Hg concentrations were consistently higher than those of internal tissues and represented an important route of Hg elimination. Feather mass accounted for 4.3% ± 0.1% (average ± standard error) of body mass, yet 27.3% ± 2.6% of total Hg intake was excreted into feathers. Our calculations indicate that 26.7% ± 4.9% of ingested Hg was not accounted for and, thus, either was never absorbed or was absorbed and subsequently eliminated in feces. With the additional excretion into feathers, 54% of ingested Hg was excreted. Demethylation was evident in the liver at all treatment levels and in the kidneys of chicks dosed at 1.2 μg Hg/g. Mercury concentrations were strongly positively correlated (r2 ≥ 0.95) among internal tissues and with blood Hg concentration. Mercury concentrations of secondary feathers were moderately correlated (r2 = 0.82–0.93) with internal tissues. We supply regression models that may be used to provide perspective and a useful means of interpreting the variety of measures of Hg exposure reported in the literature.