PCBs Imperil Polar Bears’ Fertility

Scientists worry that polar bears on remote Arctic islands are giving birth to fewer cubs because industrial toxins from North America and Europe are poisoning their favorite food, seal blubber.

Causing particular concern are polychlorinated biphenyls, or PCBs. The cancer-causing compounds once widely used in plastics and electrical insulation were banned in the United States in the 1970s and are restricted under international agreements such as the North Sea Agreement mandating destruction of all materials containing PCBs by 1999.

PCBs, which don’t dissolve in soil or water, also build up in animal fat and have been blamed for infertility in some species. Now the toxins have been recorded in disturbing amounts in polar bears, said Oystein Wiig, a polar bear specialist at the Norwegian Polar Institute.

Wiig tracked 14 likely mother bears, expecting 11 or 12 to give birth this past spring. Only five did.

It will take several years to determine whether the high levels of PCBs were to blame, he said, “but when you see it together with low reproduction, there is reason to be concerned.”

Some 20,000 to 40,000 polar bears inhabit the Arctic and at least 2,000 roam the wind-swept fiords, mountains and tundra of Norway’s Arctic Svalbard archipelago, Wiig said.

Tests showed much higher levels of the toxins in Svalbard’s polar bears than in their North American cousins, said Janneche Skaare, a toxicologist who tests samples taken by Wiig.

“We couldn’t understand why the polar bears at Svalbard would be more affected than those in Canada, which is a more polluted area,” Skaare said.

“But Svalbard is the center for air and water currents from the United States and Europe, as well as eastern Europe via Russia,” said Skaare, who heads the toxicology and chemistry department at the Norwegian College of Veterinary Medicine and the National Veterinary Institute.

Wind and water currents--including a branch of the warm Gulf Stream and flows from polluted rivers in northern Russia--bring toxic pollutants to the out-of-the-way islands.

Even low concentrations, like those found near Svalbard, build up in the food chain. PCBs dissolve readily in animal fat, such as blubber, and stay there, Skaare said. And, she said, “If a polar bear has a choice, it will eat the blubber of seals. It must eat large amounts of seal fat.”

Fat samples Skaare tested from Svalbard’s polar bears averaged 30 parts per million of PCBs, or 10 times the average reported by researchers who examined Alaska’s polar bears, and five times that found in Canadian bears.

“Some of the individual polar bears on Svalbard had 80 or 90 parts per million,” she said. “We reckon anything over 50 causes damage.”

Such levels in seals weaken their immune systems and cause sterility by deforming the uterus or Fallopian tubes, which prevent eggs from descending, Wiig said.

“We can hope that we are wrong, but the information we have from other animals shows an effect,” Skaare said.

Wiig tracks polar bears by helicopter and each year and studies about 40 of the off-white giants on the Svalbard islands by shooting them with tranquilizer darts.

While the 440- to 880-pound bears snooze, he collects fat samples with an instrument that resembles an apple corer. He also tags some with radio collars.

The collars, placed this year on 25 polar bears, transmit signals by satellite to the zoologist’s Oslo office that alert him to such developments as a bear’s impending motherhood.

“Only pregnant females go into hibernation,” Wiig explained. “If they move, they are not in hibernation. If they are in hibernation, they are going to have a cub.”