In 2004, faced with incontrovertible evidence that polychlorinated biphenyls (PCBs) were contaminating the farthest reaches of the environment, the international community finally acted to ban the synthetic chemicals. A team led by Norwegian University of Science and Technology (NTNU) biologist Jenny Bytingsvik just published data from a ten-year follow up on a 1998 study of PCBs and polar bears which demonstrates that the ban is working.
PCB levels in polar bear plasma have dropped as much as 59% in cubs and 55% in their mothers. The lower levels remain above the threshold of concern for neurological problems, lowered intelligence levels, and fertility decreases among other effects. Of high concern in polar bears, PCBs interfere with proper operation of thyroid hormones, critical for metabolic control that is essential for survival in the harsh arctic homes of polar bears.
PCBs in Cubs via Polar Bear MilkPolar bear milk is high in fat, which makes the fat-loving PCBs dissolve into the milk and pass onto polar bear cubs easily. This puts cubs at even higher risk than adult polar bears, which get a lower level of PCBs in their diet, but concentrate these in their milk.
Once in the cubs, the PCBs are not metabolized as efficiently as in adult polar bears. Furthermore, the babies have less fat deposits which might store the chemical contaminants in harmless isolation, leaving greater concentrations of PCBs free to exert toxic effects on the cute and cuddly poster-babies for endangered species.
Promising Peak into FutureThe polar bears sampled for PCB levels all live in the Norwegian island archipelago of Svalbard, roughly 500 miles (800 km) south of the North Pole. Although the sampling in 1998 did not occur in exactly the same location as 2008, the researchers believe the results indicate an actual drop in exposures rather than differences in local environment.
The results, although still too high, offer hope for the future. With the ban that was started in highly developed nations now enforced internationally by the Stockholm Convention, researchers expect to see PCB levels continue to drop.