Salmon raised in sea pens, particularly Atlantic salmon farmed in Europe, contain significantly more dioxins and other potentially cancer-causing pollutants than do salmon caught in the wild, according to a major study that tested samples from around the world.
Some health experts urged consumers not to panic, noting that levels were still far below health standards. And one of the study's authors emphasized that consumers should continue to eat plenty of fish but might want to avoid farmed salmon.
In their study released Thursday in the journal Science, the authors tied the chemical levels to fish food used in sea pens. Fish food is typically made from concentrated oil from other fish that absorbed chemicals in their fat during their lifetime. Wild salmon, on the other hand, have a more varied diet.
Eating more than one meal of farm-raised salmon per month, depending on its country of origin, could slightly increase the risk of getting cancer later in life, the researchers concluded.
The researchers urged that farmers change fish feed and that salmon be clearly labeled to indicate whether it is farmed or wild so consumers can make informed choices about which fish to eat.
But the Food and Drug Administration said the levels of pollutants found in salmon are too low for serious concern. The agency urged Americans not to let the new research frighten them into a diet change.
U.S. markets rely on Chile
The debate is sure to confuse consumers, who long have been told to eat fish at least twice a week because it helps prevent heart disease. Indeed, salmon is usually listed as a top choice because it is particularly high in heart-healthy omega-3 fatty acids and low in a completely different seafood contaminant, mercury.
Moreover, most farm-raised salmon sold in the United States is domestic or comes from Chile — where the pollutant level was not too much higher than that found in some wild-caught salmon.
The 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.”
Funded by the nonprofit Pew Charitable Trusts, the study tested salmon raw, with the skin on. Removing the skin and grilling it removes a significant amount of PCBs, dioxins and other pollutants stored in fish fat, the FDA noted.
The average dioxin level in farmed-raised salmon was as 11 times higher than that in wild salmon — 1.88 parts per billion compared with 0.17 ppb. For PCBs, the average was 36.6 ppb in farm-raised salmon and 4.75 in wild salmon.
The government does not have one set level of dioxins and PCBs that is considered safe in foods.
“We are certainly not telling people not to eat fish. ... We’re telling them to eat less farmed salmon,” said David Carpenter of the University at Albany, N.Y., who tested 700 salmon from around the world.
In setting consumption advice, Carpenter cited Environmental Protection Agency guidelines that are far stricter than the FDA’s legal limits.
Farmed salmon bought at markets in Frankfurt, Edinburgh, Paris, London, Oslo, Boston, San Francisco, and Toronto had the highest levels of four key pollutants, and the researchers said EPA risk assessment methods indicate consumers should eat no more than one-half to one meal of salmon per month. A meal was eight ounces of uncooked meat.
Farmed salmon from supermarkets in Los Angeles, Washington, D.C., Seattle, Chicago, New York and Vancouver had toxins high enough to suggest that people eat no more than two salmon meals a month.
In contrast, it would be safe to eat up to eight meals a month of wild salmon, the researchers said.
In terms of where farmed salmon was raised, those from Scotland and Denmark's Faroe Islands showed the highest levels.
The salmon farming industry points out that all the pollutant levels are well within the FDA’s legal limits and says other foods eaten far more often, such as beef, are greater sources of exposure.
Raising salmon in floating pens is an industry that began just two decades ago but has helped the fish’s popularity to soar, turning it from a seasonal to a year-round commodity. More than half the world’s salmon now is farmed. Farm-raised salmon sells for about $4 or $5 a pound compared with two or three times more for wild salmon, said Alex Trent of the trade group Salmon of the Americas.
Trent said many farmers in the United States, Canada and Chile are slowly replacing some of the fish oil in salmon feed with soybean and canola oil to address the pollutants.
“PCB levels are coming down 10 to 20 percent a year. Every year we take more steps,” he said.
That's exactly what activists like the Environmental Working Group are advocating. “These fish don’t have to be contaminated,” said EWG staffer Jane Houlihan.
Chemicals, fish and geography
Farm-raised salmon contained significantly higher concentrations of 13 pollutants, including dioxins, released when industrial waste is burned, and PCBs, once widely used as insulating material, according to the study.
As for the geographic difference in contaminant levels, ocean pollution follows a similar pattern. Europe was industrialized before North and then South America, and presumably each region uses salmon feed made of local ocean fish.
Animals absorb those pollutants through the environment, storing them in fat that people then eat. High levels are believed to increase the risk of certain cancers and, in pregnant or breast-feeding women, harm the developing brains of fetuses and infants.
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.
Carpenter acknowledged that for people with cardiovascular disease, the benefits of salmon would outweigh any added cancer risk.
Lichtenstein added, in any case, “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.”