Polar bears on thinner ice.

McKinney, MA, E Peacock and RJ Letcher. 2009. Sea ice-associated diet change increases the levels of chlorinated and brominated contaminants in polar bears. Environmental Science and Technology 43(12):4334–4339.

Hudson Bay's polar bears are more contaminated with some pollutants now than in the past due to warmer temperatures that are melting ice sooner in the spring and forcing the bears to eat different food.

Even though global use of some persistent organic pollutants (POPs) is declining, the levels of some contaminants found in the polar bears in this study are increasing. These pollutants may be affecting their health and welfare.

Global climate change is affecting the Arctic and subarctic regions more than any other part of the planet. In the western Hudson Bay, Canada, air temperatures have increased an average of 1.5 degrees Celcius during the last 30 years. The summer ice breakup now occurs an average of 3 weeks earlier.

The warming is changing how these ecosystems function and is having a big effect on the polar bears living in the area. The burly, white bears rely on the sea ice for hunting seals and for mating. With a shorter ice season, the bears are skinnier, die younger and produce fewer pups.

Polar bears also accumulate POPs such as DDT, PCBs and flame retardants from their diets. The high levels of POPs in their bodies have been linked to impacts on their reproduction and immune system.

Researchers collected fat samples from mainly mature female polar bears living in western Hudson Bay seven times between 1991 – 2007. Nine to 15 samples were taken each time over the 17-year period and analyzed for a suite of POPs.

Two methods were used to understand the diets of the bears. The first looked at the fatty acid (a component of fats) fingerprint in the bears and compared them to possible prey species. The second used changes in the carbon signal of the samples.

Both methods showed that the polar bears have changed their diet over time with the declines in sea ice.  Fatty acid fingerprints revealed that the bears now eat more harbor and harp seals and fewer bearded seals than before.  This shift in diet resulted in higher levels of PCBs and flame retardants (but not the pesticides DDT or chlordane) in their tissues.

This study shows that climate change can not only affect the ecology and lifestyle of the polar bears, but that it can also increase pollutant levels in an already highly contaminated animal.