Scientists from Norway have begun a long-term programme to tag and monitor polar bears which, they say, are under threat from pollution and climate change.

One problem is global warming, which many scientists believe is shrinking the Arctic ice shelf where the bears live.

The scientists are equally concerned about man-made chemicals entering the bears' food chain.

One of the research team, Andrew Derocher, told the BBC that the Arctic is being increasingly polluted by industrial chemicals which drift northwards on sea currents and the wind.

Because the chemicals bond well with fat, high levels build up in the blubber of seals which are the main diet of polar bears.

Initial studies show that fertility is being affected by the chemicals.

From the newsroom of the BBC World Service