Already imperiled by melting ice and a brew of toxic chemicals, polar bears throughout the Arctic, particularly in remote dens near the North Pole, face an additional threat as flame retardants originating largely in the United States are building up in their bodies, according to an international team of wildlife scientists.
The flame retardants are one of the newest additions to hundreds of industrial compounds and pesticides carried to the Arctic by northbound winds and ocean currents. Accumulating in the fatty tissues of animals, many chemicals grow more concentrated as larger creatures eat smaller ones, turning the Arctic’s top predators and native people into some of the most contaminated living organisms on Earth.
In urban areas, particularly in North America, researchers already have shown that levels of flame retardants called polybrominated diphenyls, or PBDEs, are growing at a rapid pace in people and wildlife. Although they have been found in much lower concentrations in the Arctic, scientists say their toxic legacy will persist there for years because they are slow to break down, particularly in cold climates.
In polar bears, the effects are unknown. But in tests on laboratory animals, PBDEs disrupted thyroid and sex hormones and damaged developing brains, impairing motor skills and mental abilities, including memory and learning.
Scientists say that other industrial chemicals with properties similar to PBDEs are already weakening the bears’ immune systems, altering their bone structure, skewing their sex hormones and perhaps even causing small numbers of hermaphroditic bears.
What remains uncertain, however, is whether those physiological changes are killing bears or reducing their populations. Some experts suspect that many cubs, which are contaminated by their mother’s milk, are not surviving.
An even more immediate threat to the world’s 20,000 to 25,000 polar bears is global climate change, which is melting their hunting grounds. Bears in Canada’s western Hudson Bay -- the most well-researched population -- declined from 1,100 in 1995 to fewer than 950 in 2004. In Alaska, wildlife biologists for the first time have documented that polar bears are drowning. Scientists predict that some populations could become extinct by the end of the century as more sea ice melts.
Derek Muir of Canada’s National Water Research Institute, who led the new research, said the geographical patterns in contamination suggest that the East Coast of North America and northwestern Europe are the primary sources of the flame retardants.
The most highly contaminated bears are in eastern Greenland and Norway’s Svalbard islands, where the chemicals are about 10 times more concentrated than in bears in Alaska and four times more than in Canada, according to new research published in December in the journal Environmental Science and Technology.
A major denning area, Svalbard is a national refuge where hunting is prohibited, but scientists at the Norwegian Polar Institute say its bear population is not thriving, and older females aren’t producing cubs.
The team of scientists from Canada, Norway, Denmark and Alaska, who tested 139 bears captured in 10 locations, found that some brominated flame retardants magnify from prey to predator at an extraordinary rate. One compound was 71 times more concentrated in polar bears than in ringed seals, their major food source.
Manufacturing industries in the United States use large volumes of PBDEs in furniture, carpet padding, electronics and plastics. The most abundant PBDE in the bears comes from a compound called penta, used primarily in North America to make foam furniture cushions fire-resistant.
The only U.S. manufacturer of penta and another PBDE called octa ended their production in 2004 after the compounds began building up in human breast milk and Europe and California banned their use. Yet stockpiles remain, as well as products that contain penta, octa and other flame retardants, so the chemicals are still hitchhiking to the Arctic on northbound winds.
Michael Ikonomou of Canada’s Institute of Ocean Sciences reported some good news last year. Although the flame retardants had been doubling every four to five years in Arctic ringed seals from 1981 to 2000, they have stabilized as the bans on the two compounds go into effect. Muir said he expects “a quick downturn” in the polar bear levels as factories stop using stockpiles. He warned, however, that other industrial chemicals are starting to turn up in Arctic creatures.
The geographical patterns of the flame retardants mirror those of a much older contaminant -- PCBs, or polychlorinated biphenyls. Although banned by industrialized nations in the 1970s, PCBs persist in the environment for decades, and remain the most abundant and worrisome contaminant in polar bears, particularly in the Norwegian and Russian Arctic.
Muir, who has been documenting Arctic wildlife contamination for 20 years, said the flame retardants probably are coming from the same areas as PCBs and arriving in the Arctic via the same pathways -- primarily northbound winds blowing chemicals across the Atlantic from the United States, Canada and northern Europe.
If the chemicals were originating in Asia, contamination would be higher in the Alaskan bears.
In June in Seattle, 40 wildlife scientists representing all five nations that contain polar bear populations adopted a resolution declaring that the bears are “susceptible to the effects of pollutants,” and those effects could be worsened by the stresses of global warming. They agreed that chemicals probably are causing diseases and changes in the tissues, organs and bone density of bears in eastern Greenland. Denmark, which owns the self-governed territory of Greenland, was chosen to coordinate a circumpolar study of the role of pollution in harming bears’ vital organs and other bodily systems.
Geir Gabrielsen, the Norwegian Polar Institute’s director of research on the environmental impacts of toxic chemicals, said all the industrial compounds and pesticides probably combine to alter the physiology of polar bears as well as Arctic seabirds. Glaucous gulls in Svalbard have shown signs of reproductive, behavioral and developmental stress, perhaps from PCBs and other contaminants that alter their thyroid hormones. Chemical loads are also high in Arctic foxes and whales.
“PCBs, pesticides, brominated and fluorinated compounds are the greatest threat to top predators in the Svalbard area,” he said.
Virtually every animal and person tested on Earth contains traces of brominated flame retardants, scientists say. Americans have the highest levels found so far, and many U.S. women carry concentrations in their breast milk that are close to the amounts that altered the brains of newborn mice in lab tests.
Marine mammals in North America’s urbanized areas, particularly killer whales and belugas, are 100 times more contaminated with PBDEs than Arctic creatures. Canada’s polar bears, however, contain more than the nation’s grizzly bears because their diet is almost entirely meat, particularly fatty meat that builds up chemicals. Killer whales have the highest concentrations in the Arctic.
In addition to the brominated flame retardants, perfluorinated compounds used to manufacture Teflon and formerly used in Scotchgard have been detected in polar bears in Greenland, Canada and Alaska, and a PBDE compound called deca, used in large volumes in electronics, is in the blood of Svalbard bears.
The new study also detected another flame retardant used in building materials and household furnishings, called HBCD, or hexabromocyclododecane, in Arctic bears. Chemists had thought it had a low potential to migrate long distances but now believe it is spreading globally.
“It is a chemical that needs to be watched,” Muir said, “because it does biomagnify in the aquatic food webs and appears to be a widespread pollutant.”