Historical trends of heavy metals and stable lead isotopes in beluga (Delphinapterus leucas) and walrus (Odobenus rosmarus rosmarus) in the Canadian Arctic

Historical trends of trace metal concentrations and stable Pb isotopes in teeth were determined to assess whether the current high concentrations of Cd and other heavy metals in marine mammals of the Canadian Arctic are a natural phenomenon, or are due to the long-range transport of industrial pollution. In beluga (Delphinapterus leucas) from the Mackenzie Delta in the western Arctic, significant decreases in Pb isotope ratios indicate that the animals have been exposed to anthropogenic Pb since at least the mid-17th to late-18th centuries, well prior to the Industrial Revolution, coinciding with a period of substantial lead-silver smelting in Central Europe. A more recent decline in Pb ratios between 1775 AD and the present is consistent with the incorporation of industrial Pb from Europe and Eurasia into beluga. In contrast, walrus (Odobenus rosmarus rosmarus) near Igloolik in the eastern Arctic showed no isotopic evidence of anthropogenic Pb. In both species, the present concentrations of Cd and most other metals in teeth are similar to or significantly lower than historical specimens, indicating that the current Cd levels in these marine mammals are in all probability natural, despite the elevated rates of aeolian metal deposition in Arctic regions. This incongruity may be explained by the process of ‘biodepletion’ (restricted transfer) of anthropogenic metals through food webs, previously reported in several marine food chains.