Farm-Raised Salmon Linked to Contaminants
GINA KOLATA / NY Times 8jan04
[Global Assessment of Organic Contaminants in Farmed Salmon - Science v.303, 9jan04]
A new study of filets from 700 salmon, wild and farmed, finds that the farmed fish consistently have more PCB's and other contaminants, but still at levels far below the safety guidelines set by the federal government.
The study, the largest one so far to look at contaminants in the fish, is being published Friday in the journal Science. It found more than a sevenfold difference in PCB levels, with farmed salmon having an average of 36.63 parts per billion and wild salmon having 4.75. The authors advise people to limit their consumption of the popular fish, writing, "Although the risk/benefit computation is complicated, consumption of farmed Atlantic salmon may pose risks that detract from the beneficial effects of fish consumption."
Dr. Barbara Knuth, a study author who is chairwoman of the department of natural resources at Cornell University, explained, "It indicates that the vast majority of farmed-raised Atlantic salmon should be consumed at one meal or less per month."
More than 90 percent of the fresh salmon eaten in this country is farmed and sales have been growing by 10 to 20 percent a year, said Alex Trent, executive director of Salmon of the Americas, an industry group.
Dr. Terry Troxell, director of the FDA's office of plant and dairy foods and beverages, said most contaminants are found in the skin and the fat just beneath it. "Most people aren't eating the skin," he said. "And when salmon is cooked you lose a considerable amount of fat and so the levels go down quite a bit."
While the new study involved contaminants in raw filets, including skin, Dr. Troxell said even the levels in raw salmon were not worrisome. "We certainly don't think there's a public health concern here," he said. "Our advice to consumers is not to alter their consumption of farmed or wild salmon."
The agency's tolerance level for PCB's in salmon is 2,000 parts per billion, which is nearly 55 times the level found in the farmed fish. The Environmental Protection Agency has a lower tolerance level for fish caught in sport fishing, but defers to the FDA when it comes to setting levels for eating commercial fish.
The contaminants in the salmon study included PCB's, or polychlorinated biphenyls, a family of chemical compounds that were banned in the 1970's. The E.P.A. says they are a probable carcinogen though that has never been proven in humans. They were once used as coolants and lubricants and to make products like plastics and paints. The other contaminants were dioxins, formed, for example, when chlorine-containing chemicals, like plastics, are burned and two banned pesticides, toxaphene and dieldrin.
Salmon acquired the contaminants from their food. Farmed Atlantic salmon eat fish meal and oil from fish with higher levels of contaminants like PCB's. Wild salmon, living in the Pacific, eat fish and other organisms like shrimp with lower levels of the contaminants.
Mr. Trent said he did not believe that the levels of PCB's in farmed salmon posed a health risk. But, he added that the industry was working on ways to reduce those levels, substituting soybean oil for part of the fish oil in feed.
"The fact is that PCB's don't belong in any food and we are working very hard to get it out of our food," Mr. Trent said. But, he quickly added, the contaminants are in meats and dairy products, too. "If you put the same standards on milk, people would be allowed to drink five glasses of milk a week."
This study confirmed the findings of a smaller study on the safety of farmed salmon that was released last summer by an advocacy group, the Environmental Working Group. After buying 10 farmed salmon at supermarkets and having them analyzed for PCB's, the group concluded, in a small, unpublished study, that the levels were so high that people should eat farmed salmon no more than once a month.
The cancer risk associated with PCB's has been a point of contention for years. PCB's have not been proven to cause human cancer, and industry workers who would be typically exposed to higher levels have not been shown to suffer a higher rate of cancer, said Dr. Michael Gallo of the Cancer Institute at the Robert Wood Johnson Medical School. Dr. Gallo, who receives no money from the fish or chemical industry, added that PCB's are mixtures and some can cause cancer in laboratory rodents. In animals, some of the cancer-causing PCB's are blocked by others that do not cause cancer.
Other contaminants, like dioxins, can also block the effects of PCB's, said Dr. Stephen Safe, professor of toxicology at Texas A & M. In addition, some PCB's can antagonize dioxins and some chemicals in vegetables can block the cancer-causing effects of both PCB's and dioxins in laboratory tests.
"No one is really sure how important these interactions are in the real world," said Dr. Mark E. Hahn, a toxicologist at the Woods Hole Oceanographic Institution who has spent 20 years working on PCB's and dioxins with no industry support.
But, Dr. Hahn said, if you say you will not eat farmed salmon, then what? "What risk are you substituting?" he asked. "What else are you going to eat?"
The authors of the Science paper reached their conclusion about risk with what they characterized as the E.P.A.'s methods for assessing health effects of the contaminants in fish caught in sport fishing. The health risk they reported was from their assessment of the added risks of PCB's, dieldrin and toxaphene in the fish.
Dr. Troxell said the FDA would not do such a calculation. "We don't consider it correct to add the risks together for the three compounds unless you have the science to show they're based on the same mechanism of action," he said. "We're not aware of any science relating to that."
Dr. Knuth, the author of the new study, acknowledged the disagreements over how to assess risk and said the E.P.A. allowed for adding cancer risks. "That, of course, is a value judgment as to which you think is appropriate," she said.
Some, like Dr. Linda Birnbaum, director of the experimental toxicology division at the E.P.A., dismissed the arguments.
"You can spend a lot of time arguing about the numbers and the exact details, but in some ways I think it's more useful just to look at the levels," she said. "They are so much higher in farmed salmon. That gives you an indication that maybe there's something there that you don't want."
Dr. Birnbaum said, "Personally, I eat a fair amount of fish but I try to limit my consumption of farmed fish."
Dr. Hahn had a different view.
"I love salmon and I eat it a couple of times a month," he said. He read the Science paper carefully and said, "I'm not going to change my eating habits."
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