Last updated 10 March 2023

Caesium-137 (Cs-137) is a radioactive substance with a half-life of about 30 years. Cs-137 is soluble in sea water and mainly follows the ocean currents. It can attach to sediment. It is necessary to monitor and document the levels of caesium due to a large number of potential sources of future radioactive pollution and the great economic importance fishing in the Barents Sea has for Norway as an export nation.

Radioactivity in fish
Photo: Stein Ø. Nilsen / Norwegian Polar Institute

What is being monitored?

Radioactivity in fish

The levels of Cs-137 in cod from the Barents Sea have been low and generally below 1 Becquerel per kg wt wight since measurements began in the 1990s. The levels in fish from Norwegian waters are low and constitute no risk for public health or the environment.
(Cite these data: Norwegian Radiation and Nuclear Safety Authority, Institute of Marine Research (2023). Caesium-137 in fish, wet weight. Environmental monitoring of Svalbard and Jan Mayen (MOSJ). URL:

Details on these data

Last updated10 March 2023
Update intervalYearly
Next updateFebruary 2024
Commissioning organizationMinistry of Climate and Environment
Executive organizationNorwegian Radiation and Nuclear Safety Autority
Institute of Marine Research
Contact personsJustin Gwynn
Hilde Elise Heldal


The fish are weighed, filleted and freeze dried before being measured by high-resolution gamma spectrometry (HpGe detector). The pre-treatment is described in more detail in the Norwegian Radiation and Nuclear Safety Autority’s quality assurance ­system for gamma spectrometric analyses.

Experience has shown that there is little variation in the observed concentrations of radioactivity from Cs-137 in fish. This suggests that there is quite a good balance between the concentrations in sea water and fish muscle, and that seasonal variations and variations in the size and age of the fish have little significance. It is assumed that different groups of fish bio concentrate Cs-137 to differing degrees.

The sampling has therefore been confined to members of the cod family, cod, saithe and haddock, which show little mutual variation in the levels.

The actual measurements may be uncertain because the levels observed are sometimes close to the detection limit of the method and the size of the sample used.


At the Norwegian Radiation and Nuclear Safety Autority, samples are analysed using a method that has been accredited in accordance with ISO 17025.

Reference level and action level

The limit for seafood is 600 Bq/kg.

Following the Chernobyl disaster, the Norwegian Food Safety Authority set limits for how much radioactive caesium marketed food is permitted to contain. If the content is above the limits, the food is taken off the market.

Status and trend

Levels of anthropogenic radionuclides in the marine environment off northern Norway are at present low, and the time trends show that the concentrations are either relatively constant or declining. The current levels of Cs-137 in cod from the Barents Sea are up to ten times lower than were observed in the 1980s and 1990s.

Causal factors

The reduction of anthropogenic radionuclides in the Barents Sea and the Svalbard region in recent decades is mainly due to a reduction in discharges from the reprocessing plants at Sellafield (Great Britain) and Cap de la Hague (France). In addition, ongoing processes like physical decay, dilution and sedimentation have led to a reduction of all the important sources of anthropogenic radionuclides (global fallout, Chernobyl disaster and discharges from reprocessing plants).


Cs-137 can accumulate in marine organisms and marine food chains, but to a lesser degree than in the terrestrial environment.

Fish can take up Cs-137 directly from the water and via their food, and it can accumulate in their muscle tissue. Since fish in salt water take up significantly less Cs-137 than fish in fresh water, the concentrations measured are low.

It is most important for the Norwegian fishing industry that northern waters are monitored because any radioactive pollution may have negative consequences for the industry.

Considering the low concentrations of Cs-137 being measured in Barents Sea cod, eating such cod will have no detrimental effect on human health. The Norwegian Food Safety Authority has set an upper limit of 600 Bq/kg for Cs-137 in seafood, which is identical with the EU limit for imported foodstuffs. The levels of Cs-137 measured in Barents Sea cod are at present generally under 0.2 Bq/kg.

Based on the current situation, without new sources of radioactive pollution, it is expected that levels of anthropogenic radionuclides in the Norwegian marine environment will continue to drop.

About the monitoring

Caesium-137 (Cs-137) is a radioactive substance with a half-life of about 30 years. The sources of this pollution are mainly

  • fallout from the nuclear weapon tests in the atmosphere in the 1950s and 1960s,
  • radioactive fallout linked to the Chernobyl disaster in 1986, and
  • discharges from the reprocessing plant at Sellafield in Great Britain.

Even though Cs-137 is soluble in sea water and hence is transported by ocean currents, it can also be deposited in sediments. A large fraction of the discharge from Sellafield is deposited in sediments in the Irish Sea through the years. Remobilised Cs-137 from sediments from this area constitutes a fraction of the observed Cs-137 in Norwegian waters.

The substance can be directly absorbed by the fish from the surrounding waters, or supplied through its feeding behaviour, where it is accumulated in muscle tissue. The uptake of caesium-137 is significantly lower in saltwater fish than in fish living in fresh water and concentrations are therefore comparatively low.

There is a need to monitor and document the levels owing to the large number of potential sources of future radioactive pollution in the north and the great economic importance fish from the Barents Sea have for Norway as an export nation.

Places and areas

Relations to other monitoring

Monitoring programme

International environmental agreements

  • OSPAR Convention
    International cooperation to protect the marine environment of the North-East Atlantic.

Voluntary international cooperation

  • Norwegian-Russian Environmental Monitoring Programme

Related monitoring

  • None

Further reading



  1. Gwynn, J. P., Heldal, H. E., Gäfvert, T., Blinova, O., Eriksson, M., Sværen, I., … & Rudjord, A. L. (2012). Radiological status of the marine environment in the Barents Sea. Journal of environmental radioactivity113, 155-162.
  2. Skjerdal, H., Heldal, H.E., Gäfvert, T., Gwynn, J., Strålberg, E., Sværen, I., … & Rudjord, A.L. (2015). Radioactivity in the Marine Environment 2011. Results from the Norwegian Marine Monitoring Programme (RAME). StrålevernRapport 2015:3. Norwegian Radiation Protection Authority (NRPA). 45 pp.
  3. Skjerdal, H., Heldal, H.E., Gwynn, J., Strålberg, E., Møller, B., Liebig, P.L., … & Haanes, H. (2017). Radioactivity in the Marine Environment 2012, 2013 and 2014. Results from the Norwegian Marine Monitoring Programme (RAME). StrålevernRapport 2017:13. Norwegian Radiation Protection Authority (NRPA). 39 pp.