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- Ane Eide Kjæraas

Mercury as an environmental toxin

Mercury is found everywhere in the environment, both as a result of human activity and as a natural deposit. It can be detected at a background level even in places without human activity.

A drop of mercury can be seen in the sediment sample from the seabed surrounding U-864. (Photo: NCA)

This element can be transmitted through the food chain, primarily as the methylmercury produced in nature through interaction with organic material. Mercury is toxic to humans and other organisms both as vapour and in the form of methylmercury.

Mercury ranks among the environmental toxins being found globally in steadily increasing quantities, with burning of coal regarded as the primary source.

Metallic mercury

When U-864 was torpedoed in 1945, it could have been carrying as much as 67 tonnes of metallic mercury. As long as it remains in this form or is bound in rocks, this material has low toxicity.

Calculations have shown that leakage of mercury from the wreckage and the surrounding area into the water column could amount to four kilograms per year.


Human exposure to mercury vapour or other toxic mercury compounds is very unlikely, since it lies as deep as it does with the U-864 wreck (around 160 metres beneath the sea surface).

Should efforts be made to retrieve the mercury containers, direct exposure of the personnel taking part to mercury vapour and other compounds could pose a risk which must be handled.


Methylmercury forms in sediments and can be ingested by organisms living on the seabed. It is then transferred via the food chain to fish, crabs and other species consumed by humans. 

Fish take a particularly long time to excrete methylmercury, and contain more of this substance the older and larger they are and the further up the food chain they live.


  • Chemical symbol: Hg, one litre of mercury weight 13.6 kilograms.
  • U-864 primarily contains metallic mercury.
  • —Metallic metal is liquid from -38°C.
  • —Methylmercury is produced from interaction with organisms and toxic to humans, who may ingest it through the food chain.

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