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Polar bears: Walking on thin ice January 17, 2006 6:29 AM

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Polar bears: Walking on thin ice Polar bears are under attack. Global warming and chemical pollution have affected their breeding and feeding patterns so severely that the big beasts of the Arctic could soon be extinct. Peter Marren reports Published: 16 January 2006

It's the old, old story. Back in the Sixties, agricultural pesticides such as DDT were used on an enormous scale without much regard to the environmental consequences. The result, in Britain, was a crash in the numbers of most of our top predators, such as otters, eagles and peregrines, after dangerous levels of pesticides accumulated in their body fat. DDT and other persistent chemicals have long been effectively banned. But, just as we hurried into things then, so our generation's rush to make a safer world for ourselves and our children has liberated a new generation of toxic chemicals into the environment.

The new DDT is known as polybrominated diphenyl ether (PBDE). Manufactured in the United States, it was widely used in the 1990s to coat electrical appliances, sofas, carpets and car seats to make them flameproof. The problem is that this chemical was designed to last the lifetime of the product, but in fact it lasts much longer. When sofas, carpets and car seats were thrown away, PBDE entered the rivers, the oceans and even the atmosphere.

The most prominent victim of the 1990s rush to safety is the much-loved polar bear. The Arctic, where all the world's polar bears live, is one of the great sinks of the planet. Chemical pollutants such as PBDE are carried towards the Arctic Ocean by the great continental rivers of Russia and Canada. PBDE already in the sea are wafted northwards by the currents. Even PBDE molecules in the air are carried there by winds, where they condense in the cold and fall to the ground in snow or hail.

Essentially the chemicals "biomagnify" as they move through the food chain from plankton to predator, so that long-lived top carnivores such as the polar bear accumulate the most concentrated amounts of them. In the case of DDT, the chemicals affected not only the general health of the animal but fatally reduced its capacity to breed. The chemically induced thin eggshells of polluted birds smashed before they could hatch.

Now Derek Muir of Environment Canada has found worryingly high amounts of PBDE in the body tissue of polar bears from right across the Arctic. They are higher in some areas than others, with Norway's Spitzbergen population having 10 times the level of the chemical as those in Alaska. Similar large quantities of PBDE have been found in Arctic killer whales. The long-term environmental effect of PBDE is unknown, but researchers suspect that it will damage the polar bear's immune systems, brain functions and bone strength. It also messes up the bear's sex hormones. One female bear on Spitzbergen had both male and female organs, a phenomenon often linked to chemical pollution.

This disaster could not have come at a worse time for the polar bear. The big beast of the Arctic, the largest land carnivore in the world, is already under stress from the results of climate change. Most of the bear's food comes from the sea. Its Latin name, Ursus maritimus, means "sea bear". They spend their time roaming the sea-ice along the frozen shores of the great northern land masses of Europe and America, hunting for seals in the channels and cracks where the ice is thinnest. During the Arctic summer, the bears follow the receding ice northwards. This means often having to swim from one ice floe to the next. This is normally not a problem for the sea bear, which can swim up to 15 miles in a calm sea.

Unfortunately, climate change has made life harder for polar bears. The sea ice is melting earlier and receding further northwards than ever before. The bears must therefore swim up to 60 miles in rough seas to reach it, and many are drowning on the way. Polar bears are strong swimmers, using their front legs to doggy-paddle with the back legs held flat as a rudder. They can swim for several hours without tiring, but they are built for paddling near the shore, and are vulnerable in heavy seas.

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