Polychlorinated Biphenyls, or PCBs, are persistent, cancer-causing chemicals that were widely used from the 1930s to the 1970s and are now banned in North America.

A 2004 study in Science showed that concentrations of contaminants are significantly higher in farmed salmon than in wild, and that eating farmed Atlantic salmon may pose health risks that detract from the positive effects of fish consumption.

While a great deal of research on chemical contaminants in farmed salmon has isolated a single persistent organic pollutant (i.e., PCB’s), consumers also need to be concerned about interactions between chemicals. In the 2004 study, Global Assessment of Organic Contaminants in Farmed Salmon, 13 persistent organic pollutants were found.

Each of these chemicals measured 10 times greater in farmed salmon than in their wild counterparts with some regional variations. The levels In BC’s farmed salmon was found to be lower than others. The chemicals include: PCB’s, dieldrins, toxaphenes, dioxins and chlorinated pesticides. Almost all of the contaminants found in farmed salmon are known as “probable” or “possible” human carcinogens according to the United States Environmental Protection Agency (USEPA).

Using the US EPA consumption advisory for cancer, the following consumption restrictions for the general public are advised for farmed salmon:

• North America - 1 serving every 2.5 months
• South America - 1 serving per month
• Europe - 1 serving every 5 months

A 2005 study published in the Journal of Nutrition compared the health benefits of farmed salmon to health risks. The study found that consumers, especially young children and women of child-bearing age, concerned about health impairments—such as reduction in IQ and other cognitive and behavioral effects—can minimize their exposure to cancer causing contaminants by choosing wild salmon or by selecting other sources of omega fatty acids.

Research published in the Journal of the American Medical Association in October 2006, encourages the overall consumption of seafood for its health benefits. However, the study still provides evidence showing wild salmon as a less contaminated source of omega-3 than farmed salmon.

References

Foran, J.A. D.H. Good, D.O. Carpenter, MC Hamilton, BA Knuth, and S.J. Schwager. (2005). Quantitative Analysis of the Benefits and Risks of Consuming Farmed and Wild Salmon. Journal of Nutrition. 135:2639-2643. (view abstract)

Mozaffarian, D. and E.A. Rimm. (2006). Fish Intake, Contaminants, and Human Health: Evaluating the Risks and Benefits. Journal of the American Medical Association. 296(15): 1885-1899. (view abstract)