BHT, butylated hydroxytoluene, is a synthetic antioxidant that may be added to fish oil to limit rancidity of the fat.

Fish oil is used as an ingredient in fish feed, and consequently BHT may be present in fish feed. BHT is authorised as a food additive for many types of food such as sauces, chewing gum and food oils, but, in seafood, it only occurs in farmed fish that have been raised on feed containing BHT. BHT is the most prevalent among the synthetic antioxidants that is found in farmed salmon fillets.

Harmful effects

BHT has not been found to have harmful effects on humans, but studies on rats have shown that it may be carcinogenic if consumed at high doses.

Threshold values

There are no maximum levels for BHT in fish. The acceptable daily intake for BHT derived by the European Food Safety Authority is 0.25 mg per kg body weight per day. A large portion (300 grams) of farmed salmon would contribute approximately 15 per cent of the acceptable daily intake of BHT.

Threshold values in fish feed

In fish feed, the maximum level for the sum of synthetic antioxidants (EQ, BHA, BHT, PG and OG) is 150 milligrams per kilograms of feed. The levels of BHT in fish feed is monitored by the Norwegian Food Safety Authority in a feed monitoring programme, no feeds analysed to date have contained BHT levels which exceed the maximum level.

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