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Polychlorinated dibenzodioxins (PCDD) and polychlorinated dibenzofurans (PCDF) are generally referred to as dioxins and furans. They are both organic environmental toxins that contain chlorine.

Today, dioxins and furans come mainly from incinerators, and there are 210 different dioxin compounds, of which 17 are normally measured. Ploychlorinated biphenyls, or PCBs, is a group of industrial chemicals that were developed in the 1920s. PCBs were used, among other things, in insulating oils, paint and coolants, but were banned in Norway in 1980.

Twelve of the 209 different PCB compounds are called dioxin-like PCBs, because these show the same mechanisms. Both dioxins and dioxin-like PCBs are discussed here. The non-dioxin-like PCBs are discussed on a separate page.

Dioxins

Harmful effects

Dioxins are fat-soluble and not very digestible, and they therefore accumulate in the bodies of humans, animals and fish. Dioxins are found in fat fish, meat, eggs and dairy products. In lean fish, they are mainly found in the liver.

Dioxins are carcinogenic and can cause foetal deformities. Acute exposure can also lead to an outbreak of spots on the skin.

Maximum levels

Not all dioxins and furans are equally toxic, which is why the various analysed compounds are converted into a degree of toxicity that can be summarised. This is called toxic equivalents (TEQ). The maximum value for total dioxins and furans is 3.5 ng TEQ/kg. Today, the levels in species such as herring and mackerel and farmed salmon are between 0.3 and 0.6 ng TEQ/kg.

Dioxins in fish feed

The main source of dioxins and furans in fish feed is fish oil and fishmeal. The upper threshold value for dioxins in fish feed is1.75 ng TEQ/kg feed.
Some of the dioxins and furans in the feed are transferred to the muscle tissue of fat fish and the liver of lean fish. Insignificant amounts are transferred from the feed to the environment.

Dioxin-like PCBs

Harmful effects

Dioxin-like PCBs are not very degradable, they are fat-soluble and therefore accumulate in the food chain and in the bodies of fish, animals and humans. Dioxin-like PCBs are found in fat fish, meat, dairy products and eggs. They are found in the muscle tissue of fat fish and in the liver of lean fish.

Dioxin-like PCBs are carcinogenic and can be transferred from the mother to the foetus, and can lead to foetal deformities. Acute exposure can lead to an outbreak of spots on the skin.

Maximum levels for total dioxins and dioxin-like PCBs

There is no separate maximum levels for dioxin-like PCBs in fish, but the threshold value for total dioxins and dioxin-like PCBs is 6.5 ng TEQ/ kg. Today, the levels in species such as herring and mackerel are around 1 ng TEQ/kg, and 0.5 ng TEQ/kg in farmed salmon. The tolerable weekly intake for total dioxins and dioxin-like PCBs is 14 pg TEQ/kg body weight per week. This means that a person weighing 60 kg can eat a portion of farmed salmon (150 grams) every day of the week without any risk to their health. This is also bearing in mind intake from other food.

Maximum levels for total dioxins and dioxin-like PCBs in fish feed

The main source of dioxins and dioxin-like PCBs in fish feed is fish oil and fishmeal. As plant ingredients are increasingly replacing fish oil and fishmeal, the levels of total dioxins and dioxin-like PCBs in feed and thereby farmed fish have fallen in recent years.

The maximum legal level for dioxins and dioxin-like PCBs in fish feed is 5.5 ng TEQ/kg feed. The levels that are found in fish feed have no impact on the health of the fish, but are found in the muscle tissue of fat fish and in the liver of lean fish.

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