A new study says some of Alas-ka's pristine and remote lakes are getting polluted with industrial PCBs through an unlikely source: sockeye salmon.
The fish pick up the chemicals in the northern Pacific Ocean and then return to the lakes to spawn. Then they die, their bodies releasing the pollutant and raising PCB concentration in the lake sediment more than sevenfold in some cases, researchers conclude in today's issue of the journal Nature.
It's not yet clear whether the pollution is affecting the wildlife in the lakes by weakening their disease resistance or causing other effects, said researcher Jules Blais of the University of Ottawa in Ontario, Canada.
The lakes are too far from human populations to pose any hazard to people, and the PCB concentrations in the lake sediments are too low to justify cleanup projects in any case, he said.
Blais said his work found the salmon themselves don't contain enough PCBs to be hazardous if eaten.
An Alaska state environmental official said the study's conclusions about the lakes would have to be confirmed by further research.
Blais said the study shows what can happen if enormous numbers of the fish concentrate in small lakes, but it focuses on extreme examples of that and doesn't represent Alaska lakes or rivers in general.
''Maybe the message here is that when we release these chemicals into the environment, a lot of unexpected things can happen,'' Blais said.
PCBs polychlorinated biphenyls concentrate in food chains, and killer whales near British Columbia have accumulated worrisome levels apparently by eating contaminated salmon and seals, he said.
Blais and colleagues chose eight lakes on Kodiak Island and the nearby Alaska mainland that have a wide range of densities of spawning salmon. They collected samples of lake sediment during 1995, 1997, 1998 and 2002.
They found that in general, the higher the concentration of spawning salmon a lake had, the higher the PCB concentration in its sediment. That suggests the salmon were responsible for the variation in PCB levels.
Kristin Ryan, director of environmental health at the Alaska State Department of Environmental Conservation, said more research is needed to see if the salmon idea is true. PCB pollution in Arctic areas like Alaska is generally blamed on transport of the chemicals through the atmosphere, she said.
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