Polar Bears in Trouble

ABC News
Posted July 23, 2003

Melting Ice and Chemical Contaminants Putting Kings of the Arctic at Risk

By Amanda Onion — The mightiest predator in the remotest corner of the globe appears to be falling prey to a double dose of environmental ills. The source: The far-away industrialized world.

The Arctic polar bear faces retreating ice packs at Earth's northern polar cap, which have jeopardized the animal's ability to hunt seal, leading to weight loss, studies show. And now a range of chemical contaminants blown in from industrialized regions appear to be collecting in the bear's remaining fat stores.

The combination, say scientists, threatens the animal's longevity.

"As the animals lose fat, the remaining fat has higher concentrations of pollution," said Andrew Derocher, a polar bear expert with the University of Alberta in Edmonton, Canada. "When you start to add one stressor to another, the detrimental effect can become much greater."

Derocher, who has studied polar bears in the Arctic for the past seven years with the Norwegian Polar Institute, assessed recently that retreating ice flows at Earth's northern reaches could drive the polar bear to extinction within 100 years.

Melting Fishing Rafts, Giant Chemical Sink

The bears, whose Latin name, Ursus maritimus, means "sea bear," evolved about 200,000 years ago from brown bear and use sea ice as a floating platform to catch prey — mainly seal. Studies suggest this polar ice has been retreating at a rate of about 9 percent per decade.

Meanwhile, as the top predator in the harsh ecosystem at the top of the world, the polar bear is unusually vulnerable to ingesting a slew of chemical contaminants.

Weather mapping has shown the cool Arctic regions act as a giant sink for air streams flowing from all points south. In what is known as the grasshopper effect, chemicals repeatedly evaporate and condense, falling back to the ground.

Many end up at the Arctic, after rising and falling and riding thousands of miles on cool air streams. As air streams reach the frigid regions around the North Pole, moisture cools, condenses and falls to Earth. The chemicals then linger for long periods in snow and ice at the pole since low temperatures prevent evaporation. Here they can be ingested by wildlife.

The evidence can be found in polar bear fat.

A single bear can consume 100 pounds of blubber at one sitting — mostly from seals. For the bears, their generous bulk is critical for staying warm. But in a process known as bioaccumulation, each animal they eat can magnify the amount of toxins stored in their fat.

The chemicals are taken up by plankton (microscopic plants) and are passed along to copepods (microscopic animals), to fish, to seals and finally to polar bears.

"Most animals can't metabolize these chemicals so they tend to build up and increase 10 times at each step in the food chain," explains Ross Norstrom, a leading polar bear expert who has worked as a toxicologist with the Canadian Wildlife Service and is now a professor at Carleton University in Ottawa, Canada. "By the time you get to the polar bear, you've got an intense concentration."

Chemical Cocktails

For just over 30 years, scientists have been tranquilizing polar bears in the wild and extracting blood and fat samples. Since polar bears can weigh up to nearly 2,000 pounds and have a mouthful of sharp, jagged teeth, the process of extracting samples must be delicately conducted.

"Sometimes we have to take blood from a vein under the tongue because it's so hard to get to any other veins because of all their fat," said Ross.

These tests have shown that the bear, particularly those in the European arctic, have concentrations of chemical contaminants at levels as high as 80 parts per million.

Some of the contaminants include the industrial chemicals called PCBs, which were once used widely to insulate electric transformers and capacitors. They were banned in the United States and Canada in the mid-1970s but are still used in some parts of the Third World. The compounds are slow to degrade and float in the air and permeate water.

One recent study by scientists at the University of Lancaster, in England and the Norwegian Institute for Air Research calculated an estimated 1.3 million tons of PCBs were made between the 1930s and the 1990s and the majority of the contaminant remains at large.

"It was clear PCB levels were stabilizing in the 1980s and '90s," said Derocher. "But there are new leakages of the materials into the environment every day. And the vast majority is lying in wait to enter the environment."

Scientists have also found traces of DDT, another persistent chemical compound that was used as a pesticide and has been banned for about 30 years in the United States, Canada and Europe. But the chemical is still used in the equatorial zones where malaria, a mosquito-borne disease remains a serious threat to public health.

On the Contaminant Trail

Some contaminants appear to be from newer sources. Ross says that traces of fire retardant chemicals known as PBDEs have been found in the bears. These compounds are still applied to furniture and construction material in the United States.

Another group of compounds identified was, until recently, one of the key elements of Scotchguard. The parent company, 3M, removed the chemicals from their product in May of 2000, due to concerns about its effect on the environment.

"The problem is there are so many chemicals out there that the research hasn't been done on their effects," said Theo Colborn, senior scientist with the World Wildlife Fund, a nonprofit environmental group based in Washington, D.C. and co-author of the controversial 1996 book, Our Stolen Future, which detailed damaging effects from low-level exposure to chemicals.

The Chemical Manufacturers Association's literature suggests some positive news: the flow of chemicals into the environment is on the wane. Since 1987 the U.S. chemical industry reduced by 49 percent releases of toxic chemicals to the environment, according to reports for the Environmental Protection Agency.

As researchers try and keep track of chemicals entering the environment, biologists are struggling to understand their effects on animals like the polar bear. One effect may be a weakened immune system.

"It's a little bit like cancer," said Derocher about the chemicals' effects. "You don't see it and it's only evident once the symptoms manifest themselves."

Struggling for the Big Picture

To test the animals' resistance to disease, Derocher and colleagues sampled populations of about 30 polar bears in Norway and northern Canada and injected them with vaccines commonly used in farm animals. After five weeks, they recaptured the animals and measured the level of antibodies in their blood.

"The take-home message was those individuals with higher pollution traces in their blood had a lower response to the vaccines," said Derocher, who published the work recently in the journal, Science of the Total Environment. "They produced fewer antibodies."

Other work has suggested that cubs of mothers with high levels of contaminants in their fat are more likely to die during their first year than cubs of mothers with low levels. Ross explains that cubs may be particularly vulnerable since polar bear milk is about 30 percent fat so any contaminants stores in the mother's fat is passed down to nourish her young.

But Ross points out that, thanks to the Arctic's remote location and often hostile working conditions, research there is still young and it remains difficult to reach any solid conclusions.

So far about 24 years of data has recorded the receding ice levels at the polar cap, but a lack of long-term data limits researcher's ability to identify whether the melting is part of a natural, temporary cycle or a more permanent effect linked to global warming.

And even though early studies suggest contaminants may be weakening polar bear populations, more work needs to be done to be certain.

"There's a lot 'noise' in data from the Arctic," said Derocher, referring to multiple factors that must be considered when analyzing data. "And we very rarely have the full picture."

Either way, if both trends continue, Derocher fears the king of the Arctic could become mere legend.

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