A Pilot Study on Bioaccumulation and Tissue Distribution of Mercury in Barn Swallow (Hirundo rustica)

Although extensive research has been carried out on the occurrence of mercury (Hg) in biota, bioaccumulation and tissue distribution of Hg in songbirds have not been well characterized. In the present study, Hg was investigated in insects and barn swallows (Hirundo rustica) to explore the bioaccumulation characteristics of Hg. Hg in swallow feathers and tissues including muscle, liver, and bone was investigated to determine the tissue distribution of Hg. The concentrations of Hg were 1.39 ± 1.01 μg/g, 0.33 ± 0.09 μg/g, 0.47 ± 0.10 μg/g, and 0.23 ± 0.09 μg/g in feather, muscle, liver, and bone samples, respectively. The trophic magnification factor of Hg in swallows and insects was higher than 1. However, the Hg concentrations in swallow feathers were not significantly correlated with stable isotope values of carbon or nitrogen, which implies the complex food sources and exposure processes of Hg for swallows. Feathers had significantly higher concentrations of Hg than liver, muscle, and bone samples (p < 0.01 for all comparisons). Feather, muscle, bone, and other organs had fractions of 64.4 ± 11.9%, 6.07 ± 2.06%, 20.0 ± 8.19%, and 9.56 ± 2.96% in total body burden of Hg in swallows. Hg in feathers contributed more than half of Hg in the whole body for most swallow individuals. Swallows may efficiently eliminate Hg by molting, and the excretion flux of Hg and other contaminants via molting deserves more investigation.