A Doctor’s Viewpoint: Chemical Contaminants and Farmed Salmon

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A Doctor’s Viewpoint: Chemical Contaminants and Farmed Salmon

Dr. David Carpenter, Healthy Child Science Advisory Committee

Saturday, April 28, 2007

Most salmon sold in supermarkets today come from fish farms. Farming of salmon has several advantages, in that they are available year round, and are less expensive than wild salmon. However farmed salmon contain levels of 13 fat-soluble persistent organic pollutants (POPs) that are on average ten times higher than those found in wild salmon.

The contaminants come from the feed fed the farmed fish, which is made from the fats and protein of trash fish.

So what are the health effects of eating a mixture of 13 POPs along with your farmed salmon? We applied U.S. Environmental Protection Agency cancer guidelines and advisories for frequency of fish consumption for three of these substances for which EPA has clear advisories, PCBs, toxaphene and dieldrin, making the assumption that the cancer risks were additive. We determined that on average one could only eat one meal of farmed salmon a month without increased risk of cancer. In the case of the most contaminated farmed salmon from Europe, the value would be one meal every four months! In contrast, wild salmon can safely be consumed up to eight meals per month.

While these are striking results, our estimation is clearly a large underestimate of the true risk. All of the other 11 POPs we analyzed are known to cause cancer, at least in animals. However we have not included these in our consumption advisories because EPA does not have clear standards for them. In addition we have not yet conducted any risk assessment for the non-cancer endpoints.

The greatest risk to human health from eating POPs-contaminated food is probably the detrimental non-cancer effects known to occur from exposure of the unborn child. Prenatal exposure to PCBs and dioxins results in an irreversible reduction in IQ in the child, reduced attention span, an increase in antisocial behavior, reduced immune system function and altered thyroid and sex steroid hormonal systems. The recent studies from Europe report that little boys exposed to these compounds prenatally are feminized.

The half-life of these compounds in the human body is the order of 10 years. Therefore if a 10-year-old girl eats a contaminated salmon, when she gets pregnant at age 20 she will have half of her contaminates still in her body to pass on to her child. In order to protect the fetus, it is critical that all females from the day of birth until the reproductive years are over, exercise care in what they eat.

The omega-3 fatty acids found in fish reduce the risk of cardiac arrhythmias and sudden cardiac death following a heart attack. However, omega-3 fatty acids have not been shown to have any protective effect against cancer, and young people are not at risk of heart attacks. There are many other sources of healthy omega-3 fatty acids, especially walnuts, wild fish and some cooking oils. One does not need to eat a contaminated fish to benefit from the omega-3 fatty acids. The solution is clearly that the salmon farming industry must stop feeding the salmon food that is contaminated with carcinogens. Until safe salmon reach the supermarket, consumers should restrict their consumption of farmed salmon.

Image Courtesy of Sam Beebe.