“It was previously widely thought that farmed salmon contained more environmental pollutants than wild salmon, but this proves not to be the case,” said Anne-Katrine Lundebye, senior scientist at the National Institute of Nutrition and Seafood Research (NIFES) in a press release.
The study has been published in the journal Environmental Research, under the title ‘Lower levels of persistent organic pollutants, metals and the marine omega-3-fatty acid DHA in farmed compared to wild Atlantic salmon (Salmo salar)’.
It was led by Lundebye, and researchers analysed levels of environmental pollutants and nutrients in wild and farmed salmon. The study showed that farmed salmon had lower levels of most environmental pollutants – including dioxins, PCBs, brominated flame-retardants and pesticides. Lundebye explains that the differences between wild and farmed is due to their diets.
“Fish are what they eat, both in terms of environmental pollutants and nutrients. This can be controlled in farmed fish, while what fish eat in the wild varies,” she said.
Changes in the composition of fish feed is one of the reasons for the relatively low level of organic pollutants in farmed salmon. Today’s fish feed contains less fish oil, which was previously the main source of many of the undesirable substances in the feed.
Both wild and farmed salmon in the study had relatively low levels of environmental pollutants, which were well below the maximum limit for those substances for which limits have been established. The research also shows that wild salmon has higher concentrations of the nutrients iron, copper, zinc and selenium, and that the composition of omega-3 and omega-6 is more beneficial in wild salmon than in farmed salmon.
“The omega-3 in farmed salmon still has a positive effect, even though there is a lower omega-3 to omega-6 ratio than in wild salmon,” said Lundebye.
Despite the different levels of nutrients and environmental pollutants in Norwegian farmed and wild salmon, Lundebye has no hesitation in recommending both types of salmon in our diets.
“Consumers have nothing to worry about because both types are a good source of omega-3 fatty acids and do not contain alarming levels of environmental pollutants. We can safely say that they are both healthy,” she says.
This study is extensive, using 100 samples of each type of salmon. The wild salmon were caught in the sea in Northern Norway, but Lundebye does not believe that the results would have been very different had the fish been caught elsewhere along the Norwegian coast.
“Since salmon migrates, where it is caught in the sea is probably of limited relevance. It has been previously shown that salmon from all areas of Norway use the Norwegian Sea as a feeding ground, and to some extent, the Barents Sea. Other studies show that salmon caught in one area have lived in entirely different areas of the sea, but we do not know precisely where the fish in our study have previously spent time. The reason why we have only used salmon from Northern Norway in this study is that most of the wild salmon fisheries occur there,” she says.
Questioning conventional wisdom
The most publicised study conducted on environmental pollutants in farmed and wild salmon was an American study published in the journal Science in 2004, which reported higher levels of environmental pollutants in the former.
However, Lundebye is sceptical about value of the 2004 study since the wild salmon sampled were Pacific salmon, while the farmed salmon were Atlantics. Lundebye explains that these two species have a different fat content and it is therefore difficult to compare them.
“It’s like comparing apples with pears. Comparing wild Pacific salmon with farmed Atlantic salmon is not scientifically justifiable because the two species’ have different fat contents. Since Atlantic salmon contains more fat, it will have higher levels of fat-soluble organic pollutants than Pacific salmon, regardless of whether it is farmed or wild,” she said.
Summary of the NIFES results
Lower levels of the following environmental pollutants were found in farmed salmon:
• brominated flame retardants
• the pesticides DDT, toxaphene, dieldrin, lindane, chlordane, hexachlorobenzene and mirex
Wild salmon had higher levels of the following nutrients:
• beneficial composition of omega fatty acids
Similar levels of the following environmental pollutants in farmed salmon and wild salmon:
• the pesticides endosulfan and pentachlorobenzene