Novel PCB transport pathway discovered

When sockeye salmon return to their natal lakes to spawn and die, they bring with them PCBs accumulated during a lifetime in the northern Pacific Ocean, according to a study published by Canadian and U.S. researchers in the September 18 issue of Nature. Their decomposing bodies release these persistent industrial pollutants, increasing the PCB content in some Alaskan lake sediments by more than sevenfold.

“In the lakes that receive the highest salmon densities, we’re looking at 7 to 10 times the amount [of PCBs] traditionally assigned from atmospheric pathways,” says Jules Blais, a biologist at the University of Ottawa and one of the study’s coauthors. In some cases, he says, “We’re getting levels comparable to what you find in places like Lake Superior, which is surprising when you consider that these are remote Alaskan lakes.”

Blais and his colleagues extracted sediment cores from eight lakes during 1995, 1997, 1998, and 2002 for the PCB analysis. They also measured the types and concentrations of PCBs in the muscle tissue of returning sockeye salmon. PCB patterns and concentrations in lake sediments correlated with the density of returning salmon. In particular, PCB sediment concentrations in a lake that receives no salmon spawners were 10 times lower and included a greater proportion of lighter congeners, which are effectively transported by air.

The salmon themselves do not contain high enough PCB concentrations to warrant consumption advisories, Blais cautions, but the cumulative effect of millions of fish funneling into such small areas could be concentrating these chemicals in the food chain. (Nature 2003, 425, 255–256)