ANCHORAGE — British Columbia grizzly bears that ate salmon grew more robust than their interior cousins, but took on something less desirable with the added calories -- concentrations of toxic chemicals.
Salmon-eating bears carried more persistent organic pollutants, probably blown into the North Pacific from Asia, according to a study by the Canadian government, the University of Victoria and the Raincoast Conservation Society.
Bears feeding on berries, roots, insects or meat away from the coast were not immune to the chemicals. Researchers found different kinds of organic pollutants, many heavier and probably of a more local origin, in their bodies.
"It's a bit of a tale of two food chains," said Peter Ross, an author of the study and a marine mammal toxicologist with the Institute of Ocean Sciences, part of Fisheries and Oceans Canada, in Sidney, British Columbia.
Ross researches the effects of persistent environmental contaminants in marine food chains.
Persistent organic pollutants are a group of unrelated chemicals that share unpleasant characteristics: They can take decades to break down. They accumulate in the fat of animals. They are created by humans for industrial purposes or as byproducts of processes, and they are toxic.
Some are highly mobile and can be picked up in water evaporation, blown by wind and deposited on the ground or in water around the world.
The Stockholm Convention on Persistent Organic Pollutants, a United Nations-sponsored treaty, seeks to restrict 12 chemicals commonly known as the "dirty dozen." The United States has not ratified the treaty, though the Bush administration promised to abide by it when it took effect in May 2004.
The chemicals include eight pesticides: aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex and toxaphene. Two industrial compounds, PCBs and hexachlorobenzene, are on the list, as are two byproducts of burning and industrial processes, dioxins and furans.
Some of the most notorious are PCBs, produced from 1929 through the 1970s and used commercially for heat resistance in products such as electric transformers. Ingestion of DDT by bald eagles almost exterminated the species because it thinned the birds' eggshells so much that the eggs broke before hatching. By 1963, there were only 417 known breeding pairs in the continental U.S. A ban on DDT has led to recovery of the eagle population, but the chemical's effects are so enduring that even now eagle shells are fragile.
