Are farmed salmon fit fare?

In an analysis of salmon toxicants published 9 January 2004 in Science; a team led by environmental affairs professor Ronald Hites of Indiana University showed that farmed salmon contain significantly higher concentrations of 14 organochlorine contaminants such as polychlorinated biphenyls (PCBs) and dioxins than their counterparts caught in the wild. As a result, the investigators contend, farmed salmon may pose health risks to consumers, who should limit their intake of these fish and opt for the wild variety whenever possible.

The researchers measured contaminants in approximately 700 farmed and wild salmon from all over the world. Contaminant concentrations were significantly elevated in farmed Atlantic salmon compared to wild Pacific salmon (the two most commonly marketed types). Further, where the farmed salmon were raised made a big difference in their toxicant levels, with concentrations much higher in European fish than in North or South American salmon. The authors attribute these wide variations mainly to the fish oil/fish meal diet fed to farmed salmon, which was found to be contaminated in ranges corresponding to those found in the salmon.

Hites and colleagues assessed the relative human health risks of consuming the amounts of PCBs, toxaphene, and dieldrin found in farmed salmon by using the U.S. Environmental Protection Agency (EPA) approach for devising fish consumption advisories. This method, which the authors aver is more comprehensive than Food and Drug Administration (FDA) standards, aims to help consumers avoid long-term, bioaccumulative exposure that could contribute to the risk of cancer and other health effects.

For farmed salmon purchased in Boston, San Francisco, Toronto, and several European cities, the authors recommend no more than one meal (eight ounces of uncooked meat) per month. For fish purchased in several other U.S. cities, they recommend no more than two meals per month. Wild salmon, on the other hand, was deemed safe to consume up to eight times per month.

This contrast in consumption recommendations lies at the heart of the vigorous debate that has ensued since the publication of the study. Eric Rimm, an associate professor of epidemiology and nutrition at the Harvard School of Public Health, is concerned that the study will alarm U.S. consumers unnecessarily: "To alarm people away from fish because of some potential, at this point undocumented, risk of long-term cancer--that does worry me."

One FDA official reacted more bluntly. Terry Troxell, director of the FDA Office of Plant and Dairy Food and Beverages, told the 9 January 2004 Washington Post that "we've looked at the levels found ... and they do not represent a health concern. In the end, our advice is not to alter consumption of farmed or wild salmon."

The Science authors stoutly defend their conclusions. "We are certainly not telling people not to eat fish," says coauthor David Carpenter, a professor of environmental health and toxicology at the University at Albany, New York. "We're telling them to eat less farmed salmon."

Carpenter adds that noncancer end points such as neurobehavioral, endocrine disruptive, and immunotoxic effects may be even more important than cancer, and that consumers should consider risks versus benefits. "The only well-documented benefit of fish consumption is omega-3 fatty acids, which help to reduce sudden cardiac death following a heart attack," he says. "Young people are not at risk of heart attacks, but they are at risk of accumulating carcinogens which will cause cancer years later." Further, he says, females may pass such contaminants along to their children. Future papers by the team will address these issues.

The New York Times weighed in on the controversy in a 17 January 2004 editorial that concluded, "The real message of the study is that the fish farming industry needs to clean up its feeding materials to reduce the level of contaminants. It would also be desirable for salmon to be labeled clearly to show whether it was farmed or wild, and where it came from."

Others agree with the Times. The Environmental Working Group and the Center for Environmental Health filed notice soon after the Science paper's publication that they intend to sue the farmed salmon industry and several major grocery chains under a California statute requiring companies to notify consumers if their products contain hazardous levels of chemicals know to cause cancer or reproductive harm. Michael Green, executive director for the Center for Environmental Health, told the Associated Press, "Our goal is to challenge [the industry] to change their practices so their fish is safe to eat."