Chemicals and Heavy Metals / Study Finds Health Risks In Farmed Salmon

By Joan Lowy
Scripps Howard News Service
January 8, 2004

Farm-raised salmon have significantly higher levels of cancer-causing pollutants than wild salmon captured in the ocean and may pose health risks, according to a new study.

Contaminants in farmed salmon also may affect neurodevelopment in children, making it as risky as mercury-contaminated fish, one of the study's authors said.

The study, funded by the Pew Charitable Trusts' environment program and published Friday in the journal Science, measured PCBs and 49 other toxic contaminants in 700 samples of farmed and wild salmon from around the world. Previous studies measured PCBs alone in a few dozen farmed salmon.

European farmed salmon had greater amounts of the contaminants than North and South American farmed salmon, researchers found. However, farmed salmon in the Americas still had significantly higher contaminant levels than wild salmon.

PCBs (polychlorinated biphenyls), a group of industrial chemicals widely used in electrical transformers, were banned in 1979 after it was discovered they were accumulating in people and animals.

The study also found farmed salmon had higher levels of 13 other similarly toxic contaminants, including dioxin and several pesticides no longer used in the United States such as DDT, dieldrin and toxaphene. Dioxin is a general term for an extremely toxic group of chemicals that are byproducts of industrial processes and waste incineration.

Alex Trent, executive director of Salmon of the Americas, a trade association for the farmed salmon industry, said the PCB levels in the study are well below the Food and Drug Administration's tolerance level for fish.

The health benefits of eating farmed salmon _ which is high in certain fatty acids that can reduce the risk of heart disease _ outweigh the risk from contaminants, especially in relation to beef, Trent said.

However, the FDA's standard for PCBs in food is 40 times less restrictive than the Environmental Protection Agency's standard for human exposure to the chemical. Last month, 26 scientists said in an open letter to FDA Commissioner Mark McClelland that the agency's tolerance levels for PCBs, dioxin, pesticides and other food contaminants are grossly out of date and do not reflect current scientific studies.

Those studies show the contaminants can have health effects at much lower levels than was thought in the 1970s and 1980s when many of the levels were set, the scientists wrote. The FDA's tolerance level for PCBs, for example, was proposed in 1977 and adopted unchanged in 1984.

PCBs and other contaminants measured in the study tend to accumulate most in the flesh of larger animals at the top of the food chain. All are known or suspected to cause cancer in people. All are neurotoxins that can interfere with brain development and lower intelligence.

Using EPA guidelines adopted in 1998, researchers calculated that the combined concentration of PCBs, toxaphene and dieldrin would increase the risk of cancer by at least one additional case in 100,000 if consumers ate just half a quarter serving (two ounces) a month of the most contaminated European salmon. More than one serving a month of farmed salmon generally and more than two servings a month of store-bought salmon also increased the cancer risk.

By contrast, the study estimated that as many as eight servings a month of some types of wild salmon from Alaska and British Columbia can be consumed with no increased risk.

The study calculates the increased cancer risk for only three out of the 14 contaminants of greatest concern in farmed salmon because those are the only ones for which EPA has set risk guidelines, said Dr. David Carpenter of the State University of New York-Albany, a co-author of the study.

By not including other contaminants like DDT and dioxin in the risk assessment, "what we present in that paper is an underestimation of the true risk," Carpenter said.

The study results reported in Science do not include an assessment of the risks of neurodevelopmental disorders in children whose mothers eat farmed salmon. Those will be reported in a later paper, Carpenter said.

However, Carpenter said the neurodevelopmental risks from non-mercury contaminants in farmed salmon appear as great or greater than eating fish contaminated with mercury, another known neurotoxin that has been the recent focus of FDA attention.

The likely source of the contaminants is commercial salmon feed, which is made mostly from smaller fish, the study said.

Salmon farmers are "working with feed companies to find ways to eliminate these contaminants from farmed salmon and some success is being achieved," Salmon of the Americas said in a press statement.