Linda Birnbaum, the EPA's chief of experimental toxicology, told Science magazine that the study gives consumers valuable information: "I think we can begin to make informed choices about what kind of fish to eat."
The salmon industry and study authors found common ground on one point. Both want the FDA to revisit its standards of these contaminants in salmon and collaborate with the EPA to end consumer confusion.
But FDA officials said they preferred to focus on current efforts to lower levels of dioxins and other contaminants in all food sources, rather than diverting their attention to updating their standards for farmed fish.
The study draws attention to the different approach to health advisories by the different agencies. While the EPA only considers human health risks, the FDA is required by law to consider a range of factors, including the economic impacts of its standards on the food production system.
This was the fourth study to compare levels of PCBs and other contaminants in wild and farmed salmon.
The first three studies involved a tiny sampling, examining PCBs and dioxins in 10 fish or fewer because of the high costs of testing each fish. Their results were dismissed by the industry as shoddy work or too small to be meaningful.
Two years ago, the Pew Charitable Trusts awarded $2.5 million to the team of university scientists for a more definitive study, which tested 700 fish bought from markets across Europe and North America -- including Los Angeles -- and from wholesalers selling for all major producers.
Industry representatives question Pew's motivation for the study.
They point out that Pew previously financed projects by environmental groups to scrutinize problems associated with salmon farming, including the spread of pollution, disease and the depletion of wild fish stocks used to feed carnivorous fish grown in pens.
"They found they cannot get rid of salmon farming, so they're trying to scare consumers away," said Alex Trent, executive director of Salmon of the Americas, an industry group.
It's a charge denied by both Pew and the scientists, who said Pew had no influence over their results.
Testing farmed and wild salmon for 50 contaminants, the scientists noted a big difference in 13 of 14 organochlorine pollutants, including banned pesticides, PCBs and dioxins.
Farmed salmon from Scotland and the Faroe Islands were the most contaminated. The study recommends less than one-half meal a month of these fish.
Salmon grown in British Columbia and Washington were cleaner, but the least contaminated were from farms in Chile. The researchers said these fish can be eaten once a month without exceeding EPA guidelines.
The difference, the researchers confirmed, is the feed. Testing fish oil and meal used to feed penned salmon, the researchers found that the oil from fish caught in the South Pacific, far away from the industrialized north, was the cleanest.
None of this is news to salmon farmers. "Our farmers routinely test salmon for PCBs and other contaminants," Trent said.
"We used to be much higher. And every year it comes down. .... We're getting cleaner fish oil and meal." Ultimately, Trent said, the industry hopes to figure out how to switch from fish oil to soybean or canola oil, which will wipe out the contaminant issue.