At the end of a food chain, polar bears accumulate toxic chemicals. Credit: Ø. WIIG

Female polar bears have provided researchers with an insight into the long-term health impact of pollutants.

In a study published on 1 November, a Norwegian team reveals that bears that roam long distances in their search for food tend to accumulate relatively high levels of industrial pollutants such as polychlorinated biphenyls (PCBs) in their bodies. This could be linked to the exceptional levels of hermaphroditism seen in some bear populations, although this connection has yet to be confirmed.

PCBs, which were widely used in electrical equipment until they were banned in most countries on health grounds, are extremely resistant to biodegradation. They accumulate in the food chain, even in remote locations, and then accrue at the chain's end — in polar bears, for example, which cannot easily metabolize or excrete the compounds.

The researchers tagged 54 female bears from the Svalbard archipelago and the nearby Barents Sea in the far north of Europe with satellite transmitters, and monitored their movements for several years. They found that some bears in off-coast habitats roam huge territories each year — up to 270,000 square kilometres — and accumulate significantly higher levels of PCBs in their fat, blood and milk than bears in smaller coastal or near-coastal habitats (G. H. Olsen et al. Environ. Sci. Technol. 37, 4919–4924; 2003).

“Long-distance migration costs immense energy,” says Øystein Wiig, a mammalogist at the University of Oslo's Zoological Museum and a co-author on the study. “The bears need to consume much more prey, and thus build up more PCBs.”

Particularly high pollutant concentrations were found in bears migrating to the Kara Sea, north of Russia. This indicates that there is massive pollution of Siberian rivers from contaminated industrial areas upstream, says Wiig.

PCBs are part of a group of pollutants known as endocrine disruptors, which may interfere with hormone function in humans and animals at relatively low doses. Earlier research suggests that the PCBs could be the cause of sexual anomalies found in polar bears — hermaphroditism has been seen in about 2% of the roughly 5,000-strong bear population in Svalbard (Ø. Wiig et al. J. Wildlife Dis. 34, 792–796; 1998).

But the link is tentative. “I'd rather not jump to conclusions. Hermaphrodites have also been found among brown bears that are free of PCBs,” says Aaron Fisk, a toxicologist at the University of Georgia in Athens, who investigates pollution in arctic wildlife.

The release of PCBs into the arctic environment is slowly decreasing, says Samantha Smith, who directs the arctic programme of the WWF, an environmental group. But she warns that a second wave of pollutants, now stored in arctic ice reservoirs, may be released if glaciers melt.