Salmon raised in ocean net pens and fed high-fat diets of concentrated fishmeal pellets contain worrying levels of toxic chemicals and could pose a health risk to humans, especially the young and old or those with compromised immune systems, according to two different studies comparing wild and farmed varieties.
The farmed salmon samples tested by two independent researchers in Canada and England showed 10 times more contaminants, most notably polychlorinated biphenyls, than were detected in wild species. Scientists traced the contamination to the feed, which comes from bait fish trawled from the world's oceans in vast quantities by industrial fleets. Concentrating the nutritional value of these fish into pellets to produce the high-protein diet for farmed salmon also appears to concentrate toxins.
For the Canadian study, "Preliminary Examination of Contaminant Loadings in Farmed Salmon, Wild Salmon and Commercial Salmon," researchers analyzed five commercial salmon feeds, four farmed salmon and four wild salmon (one chinook, one chum, two sockeyes) from the Pacific Coast. The data and findings were published in the February issue of Chemosphere, a peer-reviewed environmental science journal.
"The results were very clear," said Michael Easton, a Vancouver, B.C.-based geneticist and ecotoxicology expert. "Farmed fish and the feed that they were fed appeared to have a much higher level of contamination with respect to PCBs, organochlorine pesticides and polybrominated diphenyl ethers than did wild fish. In fact it was very noticeable."
In a report released earlier this year, Miriam Jacobs, a researcher in the toxicology group at the University of Surrey in England, detected PCBs in Scottish farmed salmon. The levels sometimes exceeded the recommended maximum daily dietary intake set by the British government.
Farmed salmon comprise 50 percent to 60 percent of the world salmon market, compared with just 1 percent 10 years ago, according to Productive Trade Resources, a Vashon Island, Wash.-based company that helps small- and medium-size enterprises find markets for food products.
Fish farming is also a growing and lucrative business. There are more than 5,000 farms worldwide from Norway to Thailand producing more than 30 million metric tons of fish per year valued at about $50 billion, according to the World Aquaculture Society. Those numbers are expected to double in the next two decades, the organization predicts.
Spokesmen for the industry have pointed to holes in the analysis, but Easton said the results warrant further research. Charles R. Santerre, associate professor, Department of Foods and Nutrition, Purdue University, West Lafayette, Ind., in a letter to the editors of Chemosphere, pointed out that the levels of PCBs detected were still below those considered dangerous by the U.S. Food and Drug Administration.
In a recent analysis by Ireland's Food Safety Authority, researchers found farmed salmon to have higher levels of toxic pollutants, but the amounts were below those deemed safe by European legislation.
Natural Foods Merchandiser volume XXIII/number 7/p. 12