By Alex Kirby
BBC News Online environment correspondent
Evidence that the health of polar bears is being damaged by chemicals has been reinforced by new Arctic research.
Svalbard has as many bears as people (Image: Svein B Oppegaard)
The findings show biological changes in the hormone and immune systems of the bears are related to the levels of toxic contaminants in their bodies.
WWF, the global conservation campaign, says the data confirms the findings of other research in the last four years.
It says the chemicals may affect the bears' behaviour and breeding, and make them more vulnerable to infection.
The research is published in two academic journals: the Journal of Toxicology and Environmental Health, and Environmental Health Perspectives.
It was conducted by international teams of scientists in Canada and on Spitzbergen, the main island of the Svalbard archipelago in the high Arctic.
WWF is publicising the findings to support its campaign for more stringent laws to control chemicals.
The substances blamed for the damage are PCBs (polychlorinated biphenyls) and pesticides: the higher their level in the bears, the lower the level of antibodies found in their blood.
WWF says: "Toxic chemicals were also correlated with the steroid hormone cortisol and thyroid hormone levels in Svalbard polar bears.
"Reduced levels of antibodies leave bears more susceptible to infection. Altered hormone levels could result in a wide range of negative health impacts, such as development, behaviour, and reproductive problems."
Unable to cope
Dr Andrew Derocher, who has long experience in studying the bears' contamination, said: "The studies conducted on polar bears over the last few years all conclude that these animals are negatively affected by chemical pollution.
The bears' breeding may be affected (Image: Svein B Oppegaard)
"Most polar bears probably have several hundred man-made chemicals in their bodies and they have never evolved mechanisms to deal with them.
"The unintentional tinkering with the hormone and immune system of a polar bear is unlikely to be good for them."
WWF says that although the contaminants found in these studies are no longer widely used, they are slow to break down in the environment and can remain in water, ice, and soil for many years.
Brettania Walker of WWF's Arctic programme said: "Other contaminants, with similar properties, continue to be used on a day-to-day basis in manufacturing processes and products throughout the world.
Mother and cub in Canada (Image: Francois Pierrel)
In 2000 scientists on Svalbard said more than 1% of the islands' bears were hermaphroditic, showing the reproductive organs of both sexes.
PCBs were manufactured for use in electrical equipment, and although many countries have now banned them, there is a reservoir of the chemicals that has escaped into the environment.
Images copyright and courtesy of WWF-Canon and named photographers.