sampled in the Norwegian island archipelago of Svalbard, roughly 800 km south of the North Pole. Overall, Bytingsvik found that the levels of OH-PCBs in polar bear mothers dropped by 65 per cent over the 10-year span, while the levels of PCBs dropped by 55 per cent. In cubs, the levels of OH-PCBs dropped by 50 per cent, while levels of PCBs dropped by 59 per cent over the same period. Although the bears were not sampled in exactly the same location in 2008 as in 1998 (which might itself affect PCB levels), Bytingsvik believes that the findings mainly reflect changes in exposure levels over time.
Predicting the future?
While these figures are encouraging, Bytingsvik notes that the overall levels of OH-PCBs and PCBs in the cubs are still too high. As a comparison, the 2008 concentrations of OH-PCB in cubs was roughly 90-170 times higher than levels that are known to affect thyroid hormones in human babies.
"Polar bear cubs can be much more susceptible to the effects of these kinds of environmental contaminants than adults because they are in a vulnerable phase of growth and development," she says.
Bytingsvik's research is part of a larger international project to assess the condition of polar bears in the Arctic called Bear Health. The Norwegian leader of the project, Bjrn Munro Jenssen, is Bytingsvik's supervisor. He says her findings are definitely good news.
"PCBs are considered to be among the worst environment contaminants, so it's good to see that the levels have gone down," he said. "At the same time, we can't forget that animals in the Arctic are exposed to a number of other environmental pollutants that are carried northward on the wind or by ocean currents. On top of that, there's climate change. This creates big challenges for many species."
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