Farmed salmon contains far more toxic chemicals than wild salmon - high enough to suggest that fish-eaters limit how much they eat, US researchers said yesterday.
The culprit is "salmon chow" - the feed given to the captive fish, the researchers report in this week's issue of the journal Science.
Many health experts urge people to eat fish such as salmon because it contains healthy fats, especially the omega-3 fatty acids that can lower the risk of heart disease and perhaps have other health benefits, too.
The team at Indiana University, University at Albany, Cornell University and elsewhere analysed toxic contaminants in 700 farmed and wild salmon taken from markets in 16 cities in Europe and North America.
They looked for 13 different chemicals known to build up in the flesh of fish, including polychlorinated biphenyls or PCBs, dioxins and toxaphene. Some are pesticides, others are industrial by-products, and many are known or suspected cancer-causing agents.
Farmed salmon taken from markets in Frankfurt, Edinburgh, Paris, London, Oslo, Boston, San Francisco, and Toronto had the highest levels, and the researchers said consumers should eat no more than one-half to one meal of salmon per month. A meal was a quarter of a kilogramme of uncooked meat.
Farmed salmon from supermarkets in Los Angeles, Washington, DC, Seattle, Chicago, New York and Vancouver had toxins high enough to suggest that people eat no more than two salmon meals a month, based on US Environmental Protection Agency standards.
In contrast, it would be safe to eat up to eight meals a month of wild salmon, they said. Other groups note that walnuts, flaxseeds and other non-fish sources are rich in omega-3s.
Many chemicals can build up in the body, staying for years or even a lifetime. But the body also processes some out, so experts can figure out a safe or acceptable level of intake.
Mr Charles Santerre, a food and nutrition expert at Indiana's Purdue University, said the study in fact showed that farmed salmon is safe. - (Reuters)