Hibernation concentrates chemicals.

Some pollutants build up in grizzly bears even as they doze through the winter, tests of the animals' hair and fat indicate.

Hibernating bears don't drink, eat, or excrete waste, so food- and waterborne contaminants neither enter nor leave their bodies. Nevertheless, chemical concentrations in the animals' fat may change as they use up that energy source.

The body converts some compounds into water-soluble metabolites that get excreted in urine. In a slumbering grizzly, such metabolites might accumulate.

Researchers led by Peter S. Ross, a Sidney, British Columbia-based mammal toxicologist with the government agency Fisheries and Oceans Canada, tested 11 grizzlies in the fall of 2003 and 14 others the following spring. In the March 15 Environmental Science & Technology, Ross, Jennie Christensen, and their colleagues report that many pollutants increased in concentration in body fat, while some decreased.

For example, the overall concentration of polychlorinated biphenyls (PCBs) more than doubled. Polychlorinated diphenyl ether concentrations increased by 58 percent. However, concentrations of certain PCBs and other contaminants declined, suggesting that they had been metabolized.

Some of the pollutants whose concentrations increased in shrinking fat stores--but none that decreased--are typically metabolized by an enzyme that may be suppressed during hibernation, the researchers found.

Ross' team notes that the bears' diets created two distinct contamination patterns in the fall--one in fish-eating bears and another in bears living far from water. The distinctive patterns blurred during hibernation, as metabolic processes erased the differences in pollutants within the bodies of bears in the two groups.--B.H.