This article does a clear and complete job of explaining the contamination issues with farm raised salmon versus wild caught salmon. Polychlorinated biphenyls (PCB’s) are “cancer causing chemicals that were banned in the United States in 1976 and are among the ‘dirty dozen’ toxic chemicals slated for global phase out.” The difficult issue is that they are persistent and therefore will continue to contaminate the environment long after their use is discontinued.
Toxins tend to bio-accumulate as you go up the food chain. This is the reason larger fish accumulate more toxins that smaller fish. In addition, toxins are fat soluble. The fishmeal designed to feed farm raised fish is designed to have high amounts of fish oil and therefore it consistently has higher levels of PCB’s. The referenced studies showed that farm raised fish have PCB levels five to ten times higher than wild caught fish.
The most confounding aspect of this discussion is the EPA and FDA health guidance levels. The wild caught fish fall under the EPA who updated its’ standards in 1999 to reflect recent research. The farm raised salmon falls under the jurisdiction of the FDA who have not updated their standards since 1984. The EPA standards are 500 times more protective than the FDA. This becomes an important issue to human health because salmon is the third most popular seafood consumed in the United States behind shrimp and tuna.
I would highly recommend the series of articles and the Environmental Working Group website as a resource for environmental issues. The mission of the Environmental Working Group is to use the power of public information to protect public health and the environment. EWG was founded in 1993 by Ken Cook and Richard Wiles.