Both natural and artificial radioactive substances are present in the sea.
Radioactive substances can be transported by ocean currents over long distances.
Low levels of artificial radioactivity in the sea
Levels of radioactive contamination in marine fish and shellfish are generally very low. This also applies to caesium-137, which is one of the most problematic artificial radioactive substances in the environment. This is partly because the contamination is diluted in these large bodies of water, but also because the salt (potassium) content of the sea causes the animals to absorb less radioactive caesium from the environment. Along the coast and in fjords, the levels may be slightly higher than in the open sea.
Radioactive substances can be transported by ocean currents, and spread over large distances.
The DSA monitors levels of radioactive substances in seawater, sediment and living organisms, and takes part in research expeditions with the Institute of Marine Research every year. Although the levels of radioactive substances in seafood are low, it is important to document the situation and monitor the trends in Norwegian waters, also considering that fish are an important export industry.
The graph below shows caesium-137 concentrations (Bq/kg fresh weight) in Atlantic cod in the Barents Sea and in two coastal areas in Northern Norway (near Finnmark and in Vestfjorden).
Click on the blue arrows to make the picture larger.
Sources of radioactive contamination
The largest sources of radioactive contamination in the sea are the Chernobyl accident in 1986, the atmospheric nuclear tests of the 1950s and 60s and releases from reprocessing plants for spent nuclear fuel in Europe (such as Sellafield in the UK and La Hague in France).
Along the Norwegian coast, ocean currents mainly go north, carrying contamination from the Baltic Sea and Europe. Outflows from the Baltic Sea, which was particularly contaminated after Chernobyl, still affect the level of caesium-137 in our waters. In the 1990s, the Sellafield plant in the UK increased its releases of the radioactive substance technetium-99, and we saw an increase in Norwegian seas. The radioactive releases have recently decreased, and the levels in seawater are low.
Human activities that lead to increased concentrations of naturally occurring radioactive substances are also classed as radioactive contamination. One such example is radium-226 and radium-228 released in connection with offshore petroleum extraction. This requires permission from the DSA, and the companies report their releases.
There are also potential future sources of radioactive contamination in our vicinity, including the sunken Soviet nuclear submarine Komsomolets, which went down in 1989 southwest of Bjørnøya. The submarine is located at a depth of 1700 metres, and samples of sediment and seawater are taken nearby each year to investigate the situation and look for possible leaks of radioactive material.
Natural radioactivity in the sea
Natural radioactive substances have always been present in the sea, and originate mainly from the earth’s crust. The substance that usually contributes the most to the radiation dose from seafood is polonium-210. Levels of this substance are often somewhat higher in seafood than in food produced on land, but they vary widely between species. The DSA is working to survey the levels in the species of fish and shellfish that are commonly consumed in Norway.