Pollution conundrum has fishy solution

To understand why industrial chemicals taint even uninhabited Arctic regions thousands of miles from where the pollutants were released, scientists have focused on air pollution. Many organic pollutants leapfrog the globe, periodically vaporizing from sites on the surface to ride the winds in a slow, polar-bound trek.

 Few scientists had considered biological means of transport, yet ecotoxicologists now report that much of the DDT, polychlorinated biphenyls (PCBs), and other persistent organic chemicals in one seemingly pristine lake arrived via spawning salmon.

 A research team headed by Goran Ewald of Lund University in Sweden compared organic pollutants in grayling -- a top predator and game fish -- from two neighboring Alaskan lakes: Round Tangle, which is self-contained, and Lower Fish, which drains into the final leg of a spawning run for sockeye salmon. Grayling in Lower Fish Lake have up to four times the concentrations of organic pollutants in their fat as grayling in the salmonfree lake, the team reports in the just-published March Arctic.

 Ewald explains that the salmon go to sea after spending a year or two in the freshwater lake. A few years later, they return to the lake to spawn. His team collected the fish throughout their 410-kilometer migration from the Gulf of Alaska.

 Analyses showed that as the fish burned fat to power their trip home, they didn't metabolize the pollutants in it. Instead, the chemicals became concentrated in the remaining fat. After spawning, the fish died, and their roe and carcasses introduced these pollutants into the food chain of Lower Fish Lake. Concentrations in the water, expected to be low, were not measured.

 Ewald's team reports that the proportions of DDT breakdown products and PCBs in Lower Fish Lake grayling match the pattern in salmon rather than the concentrations present in the air. Since the data show that both lakes received equivalent inputs of airborne pollutants, the grayling in Lower Fish Lake must be picking up most of their pollutants "from eating the fish and roe," Ewald says.

"This finding is exciting and really important," says Derek C.G. Muir of Environment Canada's National Water Research Institute in Burlington, Ontario. "It might explain much of the variation [in pollution] in regions where there are a lot of migratory fish," he says. It could also help regulators identify areas that might need more stringent advisories to limit consumption of tainted fish.

 In reality, people know little about freshwater-spawning marine fish, observes Phyllis Weber Scannell of the Alaska Department of Fish and Game in Fairbanks. For instance, biologists had thought that the repeat-spawning Dolly Varden char stay in local ocean waters between successive Alaskan migrations. In fact, some fish tagged in Alaska by her group later visited Russia. "What an opportunity for picking up pollutants," she speculates.