A study of North American, South American and European salmon has shown thatPCBs and other environmental toxins are present at higher levels in farm-raisedsalmon than in their wild counterparts
A study of North American, South American and European salmon has shown that PCBs and other environmental toxins are present at higher levels in farm-raised salmon than in their wild counterparts. The study authors say increased toxin levels in farm-raised salmon may pose health risks. The levels found in the study are however within the safety limits set by the World Health Organization, European Commission and the US Food and Drug Administration for fish. The study, which appears in Science, is the most comprehensive analysis to date of salmon toxin concentrations, claim its authors.
Farmed salmon production has increased 40-fold over the last two decades. Over half the salmon sold globally are raised in Northern Europe, Chile and North America. While the health benefits of eating salmon have been established by numerous studies, concerns about the fish's tendency to accumulate toxins have gone largely unaddressed. As fish eaters themselves, salmon occupy fairly high positions in their food chains and so tend to have higher concentrations of toxins in their bodies than herbivores.
Ronald Hites of Indiana University, USA and his colleagues measured organochlorine toxin levels in about 700 farmed and wild salmon. Farm-raised Atlantic salmon were purchased from retailers in England, Germany, Scotland, Norway, France, Canada and 10 locations in the USA and from wholesalers in North America, Chile and Europe. These samples were compared with samples of five wild Pacific salmon species -- Chinook, Coho, chum, pink and sockeye -- from three different regions in North America. Farmed Pacific salmon or wild Atlantic salmon were not used because fish from the two groups are difficult to obtain.
The researchers analyzed the concentrations of 14 organochlorine toxins in salmon from each collection site, using gas chromatographic high-resolution spectrometry. They studied polychlorinated biphenyls (PCBs), dioxins, toxaphene, dieldrin, hexachlorobenzene (HCB), lindane, heptachlor epoxide, cis-nonachlor, trans-nonachlor, gamma-chlordane, alpha-chlordane, Mirex, endrin and total DDT. Many of these toxins, including PCBs, dioxins and toxaphene, are each "reasonably anticipated to be a human carcinogen," according to a recent report by the U.S. Department of Health and Human Services.
The researchers found farm-raised Atlantic salmon had significantly higher levels of 13 toxins compared with wild Pacific salmon. Levels of all 14 toxins were significantly elevated in both European and North American farm-raised salmon when compared with wild Pacific salmon. Levels of only 6 toxins were significantly elevated in South American farm-raised salmon. Levels of two toxins (HCB and lindane) were actually significantly lower in farm-raised South American salmon than in wild salmon species.
The researchers also found toxin levels in European farm-raised salmon were significantly higher than in North American or South American farm-raised salmon. Levels of PCBs, dioxins, toxaphene and dieldrin were highest in farmed salmon from Scotland and the Faroe Islands and lowest in farmed salmon from Chile and Washington state, though Hites pointed out that even these comparatively uncontaminated South American salmon had high levels of other toxins.
The researchers applied U.S. Environmental Protection Agency fish consumption advisory methods to determine consumption recommendations. They calculated the maximum amount salmon that can be eaten before boosting cancer risk by more than 1 case per 100, 000. Only PCBs, dioxins, dieldrin and toxaphene were used to calculate consumption safety guidelines, because the researchers deemed these four toxins to most strongly impact human health.
Farmed salmon purchased in Frankfurt, Edinburgh, Paris, London, Oslo, Boston, San Francisco, and Toronto triggered consumption recommendations of 4-8 oz of uncooked salmon per month. Farmed salmon from supermarkets in Los Angeles, Washington, D.C., Seattle, Chicago, New York and Vancouver triggered a recommendation of no more than 16 oz per month. Farmed salmon from Denver and New Orleans supermarkets both triggered a consumption recommendation of 16 oz per month. Wild salmon could be consumed at levels as high as 64 oz.
Hites and his colleagues also measured toxin levels in the mixture of ground-up fish and oil fed to farm-raised salmon. They found a strong correlation between the toxins in the feed and salmon, suggesting toxins are passed into the salmon from their feed.
The UK Food Standards Agency (FSA) questions the study. John Krebs Chair of the FSA says "this study shows that the levels of dioxins and PCBs in salmon are within internationally recognised safety limits and confirms previous studies by the FSA." The Agency maintains its view that the benefits of eating fish outweigh the possible risks. It reiterates advice to eat at least 2 portions of fish per week, including one portion of oily fish such as salmon. The Agency says, "the study does not raise any food safety concerns."
The study has provoked an angry response from the fish farming industry, which says that the study is misleading and that the levels of toxin are within guidelines set by the EU, WHO and US Food and Drug Administration. Scottish Quality Salmon which represents about 65% of Scottish salmon farming says that use of the EPA guidelines is misleading as they are meant to be applied to non-commercial fish. However the industry is looking at ways to reduce organic contaminants in salmon from feed.
"Global Assessment of Organic Contaminants in Farmed Salmon," by R.A. Hites, J.A. Foran, D.O. Carpenter, M.C. Hamilton, B.A. Knuth and S.J. Schwager is published in Science (2004) 203:226-229.
Abstract available. Free registration required.
Contact: Ronald Hites, School of Public and Environmental Affairs, Indiana University, Bloomington, IN 47405, USA
Email: HitesR@Indiana.edu