Working with Arctic researchers from the Northwest Territories and Nunavut in Canada, as well as from Denmark, Greenland and the United States, Dr. Robert Letcher and his team investigated the influence of carbon and lipid sources on regional differences in liver trace element concentrations measured in polar bears from Alaskan, Canadian Arctic and East Greenland subpopulations. Their findings suggest that carbon and lipid sources for polar bears should be taken into account when assessing spatial and temporal trends of long-range transported trace elements.

A negative relationship between total mercury and carbon isotopes suggested that polar bears feeding in areas with higher riverine inputs of terrestrial carbon accumulate more mercury than bears feeding in areas with lower freshwater input.

Mercury concentrations were also positively related to a specific fatty acid biosynthesized in large amounts in microscopic crustaceans belonging to the Calanus genus called copepods. This result raises the hypothesis that the copepod species Calanus glacialis is an important link in the uptake of mercury in the marine food web and ultimately in polar bears.

Carbon and lipid sources were assessed using carbon isotope ratios in muscle tissue and fatty acid profiles in subcutaneous adipose tissue as chemical tracers. Unadjusted total mercury, selenium, and arsenic concentrations showed greater geographical variation among polar bear subpopulations compared with concentrations adjusted for carbon and lipid sources.

Routti, H., R.J. Letcher, E.W. Born, M. Branigan, R. Dietz, T.J. Evans, M.A. McKinney, E. Peacock, C. Sonne. 2012. Influence of carbon and lipid sources on variation of mercury and other trace elements in polar bears (Ursus maritimus). Environmental Toxicology and Chemistry 31: 2739–2747.

Contact: Dr. Robert Letcher, 613-998-6696, Ecotoxicology and Wildlife Health Division, Wildlife and Landscape Science Directorate