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(Page 4 of 5)
The snow is clean. The air is clean. Even the water is clean. So where is this toxic trash coming from? Though PCBs were banned in the late 1970s in most of the world, the compounds, once widely used as insulating and cooling fluids in electrical equipment, are remarkably persistent. In a way, climate and geology conspire to transport PCBs to the Arctic, which in the view of some scientists, is becoming a sort of giant pollution sink. Prevailing winds sweep air pollution from eastern North America, Europe and Russia northward. Svalbard in particular is something of a crossroads, buffeted by three seas and the Arctic Ocean. In a phenomenon that scientists call the grasshopper effect, PCBs from, say, a discarded transformer on the Eastern Seaboard can repeatedly evaporate in warm weather, ride the wind and fall to the ground until they’ve hopscotched to the Arctic, where they land on snowfields and in frigid seas and are trapped. The chemicals work their way up the marine food chain, step-by-step. From water to plankton to crustaceans to cod to ringed seals to polar bears—with each link, PCBs can become 10 to 20 times more concentrated. Predators at the top of the chain thus take in the highest dosages. A polar bear can carry a million times the concentration of PCBs detected in seawater. And a mother that harbors contaminants in her fatty tissue passes them on to her suckling newborn. When newborn cubs feast on their mother’s milk, they feast upon her past.
Norwegian and Canadian scientists have recently linked a variety of effects in the bears to PCBs, including alterations in immune cells, antibodies, retinol, thyroid hormones, testosterone and progesterone. The scientists don’t know what these biological changes mean to the health of individual bears or the whole population. But they have recently amassed disturbing signs of trouble.
Scientists testing bears in Canada have found that concentrations of PCBs were three times higher in denning mothers that wound up losing their cubs than in mothers whose cubs survived. Skaare speculates that pollutants are taking a toll on Svalbard’s bears, too; they seem to den more often than other bears, about every two years instead of every three, which suggests that an unusual number of cubs are not surviving.
Evidence is also mounting that PCBs are suppressing the bears’ immunity to disease. The ability to rapidly produce large volumes of antibodies against viruses and infections is critical for survival. But polar bears with high amounts of PCBs can’t muster up many antibodies, and levels of the immune cells called lymphocytes are suppressed, according to Derocher and other researchers. Bears in Canada, which carry far less PCBs, produce more antibodies than Svalbard bears. Hinting at the capacity of PCBs to weaken the immune system with disastrous effects, a distemper virus wiped out some 20,000 PCB-laden seals in Europe in 1988.
Derocher has also documented altered levels of testosterone in male bears and progesterone in female bears, and he suspects that PCBs may be the reason for the disrupted reproductive hormones. He’s trying to determine whether PCB-carrying bears are also less fertile than other bears and whether the contaminants account for Svalbard’s pseudohermaphroditic bears. (Out of every 100 female bears captured, 3 or 4 also have the genital abnormality.) PCBs also seem to deplete the bears’ reserves of retinol, or vitamin A, which is critical for regulating growth.
Some scientists say that the polar bear population is lower than expected, and they wonder if PCBs are to blame for what they describe as a missing generation. Contaminant levels in Svalbard bears peaked in the late 1970s through the early ’90s. And studies showed that the bears had seven times more of some PCBs in their bodies in the early 1990s than in 1967. At the same time, researchers have found a dearth of bears born in Svalbard when pollution levels peaked. In one study, only 13 percent of Svalbard bears with cubs were over 15 years old, compared with 40 percent in Canada. Geir Wing Gabrielsen, director of ecotoxicology research at the Norwegian Polar Institute, says it is obvious that Svalbard bears have been weakened. “Everything indicates that the polar bear is being affected by these contaminants,” he said. “There are so many indications that there are population effects.”
Yet scientists remain cautious. Peter S. Ross of Canada’s Institute of Ocean Sciences, in Sidney, who is an authority on the effects of PCBs on marine mammals, says the evidence does not necessarily establish that the contaminants have caused the bears’ problems. Wild animals face so many natural and man-made challenges that it’s almost impossible to tease out one factor as the root problem. But Ross acknowledges that PCBs (and other pollutants) correlate with changes in animal physiology and have the potential to do harm.
Ross Norstrom, an environmental chemist at the Canadian Wildlife Service, worries most about the cubs. Perhaps cubs are dying from contamination, or perhaps the effect is more subtle, like altered hormones, Norstrom says. Weighing barely a pound at birth, a polar bear cub in Svalbard is hit with a blast of PCBs from its mother’s milk right when its immune and reproductive systems are developing. Norstrom believes that now, a quarter-century after PCBs were banned in most of the world, scientists are finally on the cusp of determining exactly what sorts of harm, if any, the chemicals have inflicted on the Arctic. The overall health of Svalbard’s bears is “at best unknown,” says Derocher, largely because of the difficulties of observing them in the wild.
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