Concentrations of the artificial radionuclide Caesium-137 in Baltic Sea fish

	Authors: HELCOM MORS Project Group

The indicator shows the concentrations of the man-made radionuclide Cs-137 in herring, flounder and plaice from the Baltic Sea since 1984.

Key message

Overall the levels of radioactivity in the Baltic Sea water, sediments and biota have shown declining trends since the Chernobyl accident in 1986, which caused significant fallout over the area. Radioactivity is now slowly transported from the Baltic Sea to the North Sea via Kattegat. Minor amounts of radioactivity from Sellafield are transported in the opposite direction. Routine discharges of radioactivity from nuclear power plants in the Baltic Sea area are small and only detectable locally.

Results and assessment

The most significant source of artificial radioactivity in the Baltic Sea is the fallout from the Chernobyl accident. The total input of 137Cs from Chernobyl to the Baltic Sea was estimated at 4700 TBq.

Other important sources are global fallout from atmospheric nuclear weapons tests performed during the late 1950s and early 1960s and discharges from nuclear reprocessing plants in Western Europe, Sellafield and La Hague. At present the latter sources have become of minor radiological importance, due to significant reduction of discharges from Sellafield during recent years.

The predominant radionuclide in terms of activity in the discharges from the nuclear power plants and research reactors in the Baltic Sea region is H-3. The total discharges of H-3 from local sources have amounted to 2400 TBq and those of other beta-gamma emitting radionuclides to about 20 TBq. The total discharges of alpha-emitting radionuclides have been 0.0001 TBq.
The dose rates to individuals from the regions of the Bothnian Sea and Gulf of Finland are predicted to be larger than from any other area in the Baltic Sea due to the pattern of fallout from the Chernobyl accident. The dose rates are predicted to have peaked in 1986 at a value of 0.2 mSv y^-1.

The total collective dose from man-made radioactivity in the Baltic Sea is estimated at 2600 manSv of which about two thirds (1700 manSv) originate from Chernobyl fallout, about one quarter (650 manSv) from fallout from nuclear weapons testing, about 8% (200 manSv) from European reprocessing facilities, and about 0.04% (1 manSv) from nuclear installations bordering the Baltic Sea area.
Dose rates and doses from natural radioactivity dominate except for the year 1986 where the individual dose rates from Chernobyl fallout in some regions of the Baltic Sea approached that from natural radioactivity.

The maximum annual dose since 1950 to individuals from any critical group in the Baltic Sea area is estimated at 0.2 mSv y^-1, which is below the dose limit of 1 mSv y^-1 for the exposure of the general public set out in the EU Basic Safety Standards, 1996. It is unlikely that any individual has been exposed from marine pathways at a level above this dose limit considering the uncertainties involved in the assessment. Doses to man due to liquid discharges from nuclear power plants in the Baltic Sea area are estimated at or below the levels mentioned in the Basic Safety Standards to be of no regulatory concern (individual dose rate of 10 µSv y^-1 and collective dose of 1 manSv). It should be noted that the assumptions made throughout the assessment were chosen to be realistic and not conservative. Consequently, this also applies to the estimated radiation doses to man.

Figure 1. Cesium-137 in herring muscle, annual mean values 1984-2000, Bq/kg

Figure 2. Cs-137 in plaice and flounder muscle, annual mean values 1984-2000, Bq/kg

Metadata

Data source

HELCOM MORS-PRO Database

Description of data

The data are obtained from the monitoring programmes carried out by the countries around the Baltic Sea and give activity concentrations of Cs-137 in fish in units of Bq kg-1 fresh weight.

Geographical coverage

The data cover all regions of the Baltic Sea.

Temporal coverage

The data cover the years since 1984.
Methodology and frequency of data collection
Dried or ashed samples of fish muscle are analysed in the laboratory for content of radiocaesium by gamma-ray spectrometry. Samples are collected annually.

Methodology and data treatment

The data are analytical results.

The radiological consequences of radioactivity in the Baltic Sea have been assessed based on information on input and observed levels of radioactivity in the Baltic Sea. Doses to man were calculated with a model covering the north Atlantic waters including the Baltic Sea. The model includes the dispersion of radionuclides in the marine environment, the transfer of radionuclides to biota, and the calculation of doses to individuals and populations exposed to radionuclides in fish.

Doses were calculated to members of the public from the ingestion of radionuclides in fish caught in the Baltic Sea area and from exposure to radioactivity in coastal areas. The calculations include source contributions from nuclear weapons testing, the Chernobyl accident, the two European reprocessing plants Sellafield and La Hague, and nuclear installations bordering the Baltic Sea area.

Dose rates from man-made radioactivity to individual members of the public were calculated based on rates of annual intake and beach occupancy time.

Collective committed doses to members of the public were calculated based on predicted concentrations of radionuclides in biota and coastal sediments.
Doses from naturally occurring radioactivity in seafood were calculated on a similar basis and compared with the doses from man-made radioactivity due to marine pathways.

Quality information

Intercomparisons of laboratory analyses of radiocaesium in different sample types from the Baltic Sea are carried out on a regular basis thus ensuring a high quality of the analytical results including good agreement across laboratories.

Reliability, accuracy, robustness, uncertainty (at data level)

The data are considered of high quality and thus reliable.
Further work required (for data level and indicator level)
Continue monitoring programmes.

Further work required (for data level and indicator level)

Continue monitoring programmes.