The study, using Environmental Protection Agency (EPA) health guidelines, concluded that while consumers could safely eat four to eight meals of wild salmon a month, consumption of more than one eight-ounce portion of farmed salmon a month in most cases poses an "unacceptable cancer risk."

People in Washington, New York, Los Angeles, Chicago and Seattle should not eat farmed salmon more than once or twice a month, the study advises.

The study of 700 store-bought samples from Frankfurt, Germany; Edinburgh, Scotland; Paris; London; and Oslo, Norway, generally were the most contaminated, while samples from stores in New Orleans and Denver were the least contaminated.

The two-year, $2.4 million study, funded by the Pew Charitable Trust and published yesterday in the journal Science, is the latest blow to the commercial-fish industry, already suffering from growing concerns about elevated levels of mercury in tuna and shellfish.

Rebuttals

Officials of the Food and Drug Administration (FDA) and the fishing industry immediately took issue with the findings. They said the contaminant levels in salmon have declined by 90 percent since the 1970s and the remaining "trace levels" do not warrant consumers denying themselves the high protein and cardiovascular health benefits of eating salmon.

"We've looked at the levels found ... and they do not represent a health concern," said Terry Troxell, director of the FDA's Office of Plant and Dairy Food and Beverages. "In the end, our advice is not to alter consumption of farmed or wild salmon."

In addition, the study tested salmon raw, with the skin on. Grilling the fish without its skin removes a significant amount of PCBs, dioxins and other pollutants stored in fish fat, the FDA noted.

The Pew study "will likely over-alarm people in this country," said Eric Rimm of the Harvard School of Public Health, a specialist on nutrition and chronic disease. "To alarm people away from fish because of some potential, at this point undocumented, risk of long-term cancer — that does worry me."

EPA or FDA?

On average, farmed salmon has concentrations of health-threatening contaminants 10 times greater than those found in wild salmon, according to the study. EPA guidelines say that, if a person eats fish twice a week, it should contain no more than 4 to 6 parts per billion of PCBs. The study found that PCB levels in farmed salmon sold in the United States and Canada averaged about five times that amount: 30 parts per billion.

None of the levels exceeded standards set in 1984 by the U.S. Food and Drug Administration for commercially sold fish.

"Just because the contaminants we found do not exceed FDA levels, that doesn't mean they are safe for consumers to eat them," said Dr. David Carpenter, one of the study's six co-authors and a professor of environmental health and toxicology at the University of New York at Albany.

Aside from a slightly elevated cancer risk from these potential carcinogens, he said, the chief concern is that pregnant women can pass on these contaminants — which build up in body fat and linger for decades — to their fetuses, impairing IQ and immune function.

The study also calls for the need to label whether salmon is wild or farm-raised. No law requires such labeling, although "Atlantic" salmon almost certainly comes from a farm because wild Atlantic salmon are extremely rare due to overfishing.

Farmed fish are believed to contain higher concentrations of contaminants than wild fish largely because they are fed a meal that consists of ground-up fish tainted with the contaminants, while wild salmon feed on smaller fish and tiny aquatic organisms.

Alex Trent, executive director of Salmon of the Americas, a group representing farmed-salmon producers in the United States, Canada and Chile, said his industry doesn't discount some of the health problems associated with PCB contamination of farmed salmon. However, he said, meat and dairy products, when eaten in large quantities, pose similar problems, and consumers would be foolish to deny themselves the health benefits of salmon.

Raising salmon in floating pens, a practice that began only two decades ago, has helped the fish's popularity to soar. More than half the world's salmon now is farmed and available year-round, while wild salmon generally is available June through October. Farm-raised salmon sells for about $4 or $5 a pound compared with $15 for wild salmon, Trent said.

Many farmers in the United States, Canada and Chile slowly are replacing some of the fish oil in salmon feed with soybean and canola oil to address the pollutants, he said.

"PCB levels are coming down 10 to 20 percent a year," Trent said. "Every year we take more steps."

In Washington state, Pan Fish U.S.A. operates farms that raise 8,000 to 9,000 metric tons of Atlantic salmon annually off Port Angeles, Anacortes and Bainbridge Island. It's roughly a $30 million industry — a fraction of the size of the industry in British Columbia. There, more than 80 fish farms across the western edge of Vancouver Island produce more than 70,000 tons of salmon, most of it headed straight for the United States.

Representatives of that industry argued yesterday that the research published in Science was misleading.

"There are five different species of Pacific salmon, and three of them eat lower on the food chain than Atlantic salmon do, so their contaminant numbers automatically are going to be lower, but they're not the ones we buy in the store," said Washington state Sen. Dan Swecker, R-Rochester, who represents Pan Fish through the Washington Fish Growers Association. "The fish we buy are coho and chinook, and those have similar levels, at least with PCBs."

In 1998, a study by the Washington Department of Fish and Wildlife found PCB levels in wild chinook in Puget Sound were actually higher than those found in farmed fish. Earlier studies suggest there are elevated PCB levels in premium Copper River Delta salmon, too, said Mary Ellen Walling, executive director of the British Columbia Salmon Farmers Association, in Campbell River, B.C.

"I don't want to get pulled in to the farmed versus wild debate," Walling said. "It's important to put this in the context that PCBs, unfortunately, just exist in the food chain.

"We're doing everything we can as an industry: We're re-sourcing our fish oil and fish meal for fish feed from the least contaminated sources possible. ... But the fact is, these are trace elements and they're in wild fish, too."

Alternatives faulted

Both also argued that fish made up such a small portion of the average consumer's diet already that "the vast majority of PCBs in the diet come from beef, poultry and dairy," Swecker said. "The last thing we ought to do is reduce the consumption of fish."

One in two Americans will die of cardiovascular disease, a far bigger risk than the cancer concern, said nutritionist Alice Lichtenstein of the Agriculture Department's Human Nutrition Research Center at Tufts University.

Still, the study does raise a concern that needs more attention, she said: "The bottom-line message is to continue to eat fish but consume a variety of different types."

Compiled with information from The Washington Post, Associated Press, the Los Angeles Times and Seattle Times staff reporter Craig Welch.