However experts had conflicting advice on whether the findings should cause consumers to change their eating habits.
The study blamed the pollutants’ presence on the food the farm-raised salmon eat and found that the fish farmed in Northern Europe contained the most pollutants, followed by North America and then Chile.
Eating more than one-quarter a serving of farm-raised salmon each month, depending on its country of origin, could slightly increase the risk of getting cancer later in life, the researchers reported. They considered a serving to be eight ounces of uncooked salmon.
Farmed salmon bought in the United States is most likely to be from Canada and Chile. The study reported that one-half a serving of Canadian farm-raised salmon would not raise cancer risks and that a full serving is safe when eating fish from Chile.
Other experts disagreed over how to interpret the findings. The U.S. Food and Drug Administration told the Associated Press that the levels of pollutants in farm-raised salmon are not high enough to raise serious concerns and urged Americans not to change their diets based on the study.
The FDA considers both safety and nutrition when setting acceptable pollution levels. The Science researchers instead used levels set by the Environmental Protection Agency, which only considers health risks.
The FDA also told the AP that since the study tested raw salmon with its skin, it overestimated the potential risk. Removing the skin and grilling it removes a significant amount of PCBs, dioxins and other pollutants stored in fish fat, the agency noted.
The study “will likely over-alarm people in this country,” Eric Rimm of the Harvard School of Public Health, told the AP.
“To alarm people away from fish because of some potential, at this point undocumented, risk of long-term cancer — that does worry me,” Rimm, a specialist on nutrition and chronic disease, continued.
The American Heart Association advises people to eat fish at least twice a week because it helps prevent heart disease. Salmon is often touted as a good choice because it is particularly high in heart-healthy omega-3 fatty acids and low in mercury, a seafood contaminant that can damage the central nervous system. Mercury levels were not measured as part of the Science study.
One in two Americans will die of cardiovascular disease, a far bigger risk than the cancer concern, nutritionist Alice Lichtenstein of the Agriculture Department’s Human Nutrition Research Center at Tufts University told the AP.
However she cautioned that “this was a beautiful study” that does raise a concern that needs more attention. “The bottom-line message is to continue to eat fish but consume a variety of different types,” she said.
For the study, researchers analyzed toxic contaminants in 700 farmed and wild salmon taken from supermarkets and wholesalers in Europe and North America.
“We think it’s important for people who eat salmon to know that farmed salmon have higher levels of toxins than wild salmon from the open ocean,” lead study author and environmental affairs professor Ronald Hites said in a statement.
Farm-raised salmon sells for about $4 or $5 a pound compared with $15 for wild salmon, Alex Trent of the trade group Salmon of the Americas told the AP.
The Science study lends support to findings reported last year by the Environmental Working Group, which said it found elevated PCB levels in farmed salmon filets taken from 10 U.S. grocery stores.
“This unquestionably large, new study strongly confirms earlier research, and it leaves little room for the farmed fish industry to argue away the problems of polluted farmed seafood,” the Environmental Working Group’s Jane Houlihan told Reuters.