On Thin Ice

It is late April, nine days since the return of the midnight sun, and a 450-pound polar bear and her cubs walk on the finger of a frozen fjord. Spring has arrived on the Norwegian archipelago of Svalbard, a favorite nursery for polar bears. About 670 miles from the North Pole, the mother bear lumbers along in her hunt for ringed seals, leaving a zigzagged path of 12-inch-wide craters followed by the smaller paw prints of her two young sons.

A few miles away, from the front seat of a helicopter, scientist Andy Derocher has spotted the family’s fresh trail. The chopper’s pilot loops, spins, and straddles the tracks, following their erratic path for several miles. “She’s running here,’’ Derocher tells the pilot, pointing to the edge of a craggy glacier. “I think she’s ahead of us here somewhere.”

One of the world’s leading polar bear experts, Derocher is monitoring the health of a species imperiled by a double whammy of toxic chemicals and global climate change. He and other wildlife biologists now predict that some populations of the world’s 22,000 to 25,000 polar bears could become extinct by the end of this century.

Born at Christmastime, cradled in pure white snow, polar bears emerge blind, toothless, a pound apiece, as feeble as kittens. Yet before they even leave the safety of their dens on Svalbard, polar bear cubs already harbor more pollutants in their bodies than most other creatures on the planet. Mother polar bears store a lifetime of chemicals in their fat and then bequeath them, via their milk, to their young.

Several hundred of the industrialized world’s most toxic chemicals, especially PCBs and organochlorine pesticides such as DDT, have transformed Svalbard and much of the Arctic into a giant chemical repository, and polar bears into its unintentional lab rats. Newcomers are joining the older chemicals there, including flame retardants called PBDEs and a compound used in the manufacture of Teflon. Originating mostly in North America and northern Europe, the pollutants hitchhike to Svalbard, Greenland, and other remote reaches of the Arctic on northbound winds and ocean currents. There, they magnify in animals each step up the food web, leaving polar bears, killer whales, and other top predators highly contaminated.

Scientific studies suggest that these extraordinary loads of chemicals are weakening polar bears, culling the old and the young. Their immune cells and antibodies have been suppressed, and their sex hormones, thyroid hormones, and even their bone composition have been altered. And perhaps most curious of all, small numbers of strange pseudohermaphroditic bears have been discovered. Of every 100 female bears captured on Svalbard, three or four have partial male genitalia.