Pollution has impact on diet of grizzlies

British Columbia grizzly bears that feasted on 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, or POPs, 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.

Interior bears feeding on berries, roots, insects or meat were not immune to the chemicals. Researchers found different kinds of POPs, 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.

POPs are a name for 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’re toxic.

Some POPs are highly mobile. POPs can be picked up in water evaporation, blown by wind, and deposited on ground or 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 dozen 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’ egg shells so much that the eggs broke before hatching. By 1963, there only 417 known breeding pairs in the Lower 48 states. A ban on DDT has led to recovery of the eagle population.

In Alaska, researchers have studied POPs in polar bears and killer whales. The U.S. Geological Survey since the late 1980s has collected and archived tissue from Alaska marine mammals for possible future study, said the agency’s Steve Amstrup.

The British Columbia researchers analyzed hair and fat samples from 12 bears killed in 2003. Most were killed by hunters. A few were problem bears killed by game managers. Ross called it a reasonable study size because samples were high quality of known origin with body weight, sex and age of the animals recorded.

Researchers analyzed carbon and nitrogen isotopes in the bears’ hair to determine whether their primary diet was salmon, meat or vegetation. Measuring the changes in these isotopes along the hair’s length enabled researchers to estimate how much salmon was consumed by each bear over time, said lead author Jennie R. Christensen, a doctoral student at the University of Victoria.

Fat samples told them which POPs were present, and in what concentrations.

Bears that ate salmon, which themselves are carnivorous and susceptible to accumulating POPs in their fat, were exposed to older contaminants. Most of the contaminants named in the “dirty dozen,” including DDT, dieldrin and PCBs, were detected in the bears.

“The more salmon the bear was eating, the higher the contaminant load,” Christensen said.

The No. 1 contaminant was DDT derivatives. The source was likely countries in Asia and carried by prevailing winds.

“These are coming from a global source, the North Pacific Ocean,” Christensen said.

The finding underscores that even though dangerous contaminants are regulated in North America, they still can be generated on the other side of the world, blown into the oceans, taken up in marine food webs and brought onto land through salmon migration, Christensen said.

Interior bears showed lower concentrations of different kinds of pollutants, especially newer POPs called polybrominated diphenyl ethers. PBDEs are used as flame retardants. They’re used in furniture such as foam in chairs, automobiles, textiles, consumer electronics.

Heavier than the older POPs, they’re less likely to be blown long distances, suggesting they come from a local source, the researchers said. The exact source is not known.

Neither bear group was immediately threatened by the level of POPs. But the variation in amounts and types of POPs was significant.

“We were surprised by the margin of the difference between the two types of bears,” Ross said.

If there’s any immediate concern for bears, it could be with breeding sows. Bears fast as they den in quasi-hibernation, Ross said, relying on fat reserves to survive. As they slowly burn fat, the concentration of POPs increase. That raises concerns about developing fetuses, which rely on the sows for nutrients, hormones and antibodies, Ross said.

The chemicals could affect development of the skeleton, reproductive organs, immune system or brain of the fetus, Ross said.

POPs levels in the environment continue to be a threat. Former military installations and pulp mills can be regional sources, Ross said.

“These findings just reiterate how important it is to regulate these organic contaminants on a global level,” Christensen said. “Otherwise, the regulations are not really doing what they were set out to do.”

The findings will be published this monthin the scientific journal Environmental Science & Technology.