Science - January 15, 2004

‘Salmon research is not a red herring’

A recent report by American toxicologists in Science on the levels of toxins in farmed salmon has caused commotion in the national and international press. According to the article it is only safe to eat salmon a couple of times a year. Wb asked Professor Frans Kok of the sub-department of Human Nutrition how serious the matter is.

“It’s certainly serious. The Americans examined seven hundred samples of salmon from all over the world for more than fifty different organochloride compounds. Fourteen of these, including PCBs, dieldrin, lindane and dioxins were found to be present in higher concentrations in farmed salmon. Salmon from Europe, farmed in Scotland, the Faro Islands and Norway, scores especially badly. Organochloride compounds, produced by industry and agriculture, can be dangerous. In the long term they probably increase the risk of cancer; in the short term they can interfere with the development of the endocrine system, the immune system and the brain. This makes them particularly dangerous for pregnant women and mothers who are breastfeeding. The concentrations of these compounds were so high that it means you should only occasionally eat the salmon found on supermarket shelves.

You can’t just dismiss these research results. The reaction from the food industry in the international press has been that the researchers have exaggerated the seriousness of their findings. The researchers have used the guidelines of the American EPA in formulating their advice, and this only takes into account the risks and not the health benefits of a high intake of fish fatty acids, say industry spokesmen. If the guidelines of the FDA are used, the results are less alarming. This might be the case, but you can’t get away with things so easily.

We recently published an article in the New England Journal of Medicine on the relationship between heart attacks and fish consumption. We measured the amount of omega-3 fatty acids stored in subcutaneous fat tissue and the concentration of mercury in the toenails, to see if the levels could be used to predict the chance of someone having a heart attack. Omega-3 fatty acids probably reduce the chance of a heart attack, while increased mercury levels mean an increased chance of a heart attack. Our research results suggest that mercury and fatty acids increase each other’s effect. The Americans did not look at mercury levels. They focused on the differences between wild and farmed salmon, and it was already known that both types contain equal amounts of mercury.

Something needs to be done, and fast. One the one hand you have consumers who regard fish as poison with fins, a view that is slowly changing thanks to information campaigns on the positive health effects of fish. But this kind of alarming news undermines this work. The Americans have already shown that the farmed fish become polluted through the feed they get, so it is possible to do something about this. Monitoring can be made stricter, or we can increase the use of plant material for the omega-3 fatty acids, such as transgenic canola oil, although I wonder whether Europe will accept this. The fact remains, we have to do something. This research is not a red herring; otherwise it wouldn’t be in Science.

Willem Koert

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