Mercury is a heavy metal that occurs in different chemical forms. Organic mercury, also known as methylmercury, is most toxic.

Mercury occurs in nature and can come from sources such as volcanic eruptions or outgassing. Human activities such as mining and industry also lead to discharges of mercury. Mercury discharges have been stable in recent years.

Harmful effects

Methylmercury is transferred from pregnant women to their foetus and can lead to deformities in the child. It also affects the mental development of foetuses and infants and can lead to impaired learning ability and harm their motor skills.

Inorganic mercury is less available and less toxic. Less is absorbed by the body and it is accumulated in the kidneys and liver, and not in the brain. It therefore has less effect on the foetus.

Pregnant and breastfeeding women are advised to increase their intake of fish and other seafood, but should avoid species that contain a high level of methylmercury, such as large freshwater fish (pike and freshwater trout) and fish from particularly polluted areas.

Maximum levels

The most important sources of methylmercury in our diet are fish and other seafood. The maximum level for total mercury is 0.5 mg per kg for most fish species. For several predatory fish such as halibut and tuna, the maximum level is 1 mg per kg.

The tolerable weekly intake for inorganic mercury is four micrograms per kg body weight. For methylmercury, the limit is 1.3 micrograms per kg body weight per week.

Maximum levels in fish feed

Mercury occurs in fish feed, but farmed fish contain low levels of methylmercury. The legal maximum level in fish feed is 0.2 mg mercury per kilogram. The mercury levels fish are exposed to through today's commercial feed have no effect on fish health.

Methylmercury accumulates in the fish and is not transferred to the environment via the feed to any great extent.

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