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Industrial chemicals are persistent organic pollutants (POPs) that come with all sorts of weird and scary effects. Cancer. Damage to the immune system. Interference with hormones. Reproductive and developmental abnormalities. Nervous system impacts. The list goes on.
Two POPs in particular have been associated with salmon: Polychlorinated Biphenyls (PCBs) and Dioxins. Both bioaccumulate, that is, they build up in the body to some toxic threshold that we cannot perceive until it's too late. In fact, researchers have found in mice that chronic consumption of farmed salmon with POPs causes insulin resistance and obesity .
Polychlorinated Biphenyls (PCBs)
PCBs are a group of about 200 man-made chemicals that were widely used in electrical equipment, lubricants, and plasticisers. PCBs were commercially produced in the U.S. from 1929 to 1979, when production was banned through legislation. Australia prohibited their importation from 1975. PCBs are associated with a variety of adverse health impacts on the immune system, reproductive effects, neurological problems, and endocrine impairment. The Doctors for the Environment Australia described PCBs this way in a Parliamentary submission: "In particular the bioaccumulation and contamination of the marine environment with polychlorinated biphenyls (PCBs) is of concern. PCBs are persistent, cancer-causing chemicals that continue to contaminate the environment and the food supply" .
The role of salmon as a dietary source of PCB contamination is contentious. A study of farmed salmon from American grocery stores found that farmed salmon have around 16 times the PCBs found in wild salmon, 4 times that found in beef, and more than 3 times that found in other seafood, leading the researchers to conclude that farmed salmon was likely "the most contaminated protein source in the U.S. food supply" . Another study of industrial contaminants in more than 2 metric tons of farmed and wild salmon from around the world found that the concentration of PCBs was eight times higher in farmed salmon than in wild-caught fish . However, later studies on salmon from Norway found that PCBs were higher in wild salmon than in farmed [5, 6].
To make the story even more complex, it appears that salmon are getting their PCBs from the fish oil and fish meal from the commercial feed in their diet . Moreover, salmon bioaccumulate PCBs in their fat (as do we). Health advice from Harvard is to avoid the skin of the salmon and the fat directly beneath it, as this is where the PCBs are most concentrated .
What about in Australia? Good question. We are not aware of any studies here. But because the feed comes from the same places, we must assume that contaminants in salmon overseas are in salmon here, until credibly demonstrated otherwise.
Dioxins are a family of highly toxic persistent environmental pollutants. They can cause cancer, reproductive and developmental problems, interfere with hormones, and impair the immune system. Dioxins are a by-product of industrial activities, combustion, pulp and and paper bleaching, and other activities.
Most of the studies detailed for PCBs above, also tested for dioxins. And similar patterns were found, that is to say, some found higher concentrations in farmed salmon, while others found higher concentration in wild salmon. The take-home message isn't about which is higher, but rather, that high concentrations of these highly toxic substances are found in salmon, which is marketed as a clean green healthy food source.
We welcome information on other chemicals that may be in farmed salmon to be brought to our attention.