​​​​​​​​​​​​​​Key message

This core indicator evaluates the state of the environment using the concentration of the radioactive isotope cesium-137 (137Cs) in herring, flatfish and surface waters. Good status is achieved when concentrations reach levels measured before the Chernobyl accident in 1986 when the biota of the Baltic Sea received the most significant contribution to their level of artificial radionuclides, predominantly in the form of 137Cs.

The indicator presents a status evaluation using data from 2011-2015.

In general, the activity concentrations of radioactive isotope cesium-137 (137Cs) in herring, flatfish and surface waters are still above the pre-Chernobyl levels which constitute the boundary for good status – threshold values.


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Key message figure 1: Status assessment results based on evaluation of concentrations of cesium-137 in herring and flatfish. The assessment is carried out using Scale 2 HELCOM assessment units (defined in the HELCOM Monitoring and Assessment Strategy Annex 4). Click to enlarge Cesium 137 in herring or flatfish.

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Key message figure 2: Status assessment results based evaluation of concentrations of cesium-137 in seawater. The assessment is carried out using Scale 2 HELCOM assessment units (defined in the HELCOM Monitoring and Assessment Strategy Annex 4). Click​ to enlarge.


For herring, good status is only achieved in the Arkona Basin, the Bay of Mecklenburg, the Kiel Bay and the Kattegat. For flatfish, good status is also achieved in the Arkona Basin, the Kiel Bay, the Great Belt and the Kattegat. All other assessed sub-basins are characterized by not-good status. For surface waters, good status is not achieved in any of the sub-basins.

Time series analyses show that the 137Cs activity concentrations in herring, flatfish and surface waters in the Baltic Sea basins are decreasing and approaching pre-Chernobyl levels. It is expected that good status may be reached in the Baltic Sea by about 2020 - 2025.

The confidence of the indicator status evaluation is considered to be high.

The indicator is applicable in the waters of all countries bordering the Baltic Sea.


Relevance of the core indicator

The radionuclide cesium-137 (137Cs) is the greatest contributor to the level of artificial radionuclides in the Baltic Sea, where the level of 137Cs contamination is still higher than in any other oceans of the world. The main source of 137Cs deposited to the Baltic Sea stems from the accident at the Chernobyl nuclear power plant in 1986. The 137Cs was introduced into the Baltic seawater by atmospheric deposition and, to a lesser extent, through riverine input. 137Cs introduced to the Baltic Sea is bioaccumulated in marine flora and fauna and is eventually deposited in the marine sediments. Therefore 137Cs activity concentrations are the key factors in an assessment of the radiological hazard to marine organisms and humans (Nielsen et al. 1999). Both are highly interconnected as the dominating exposure pathway of humans from man-made radioactivity in the Baltic Sea is related to the ingestion of 137Cs in fish.


Policy relevance of the core indicator

 ​BSAP segment and objectivesMSFD descriptor and criteria

Primary link

Hazardous substances

  • Radioactivity at pre-Chernobyl level

D8 Concentrations of contaminants

D8C1 Within coastal, territorial and areas beyond territorial waters the concentration of contaminants do not exceed the threshold values

Secondary link


 

 

D9 Contaminants in fish and seafood

D9C1 The level of contaminants in edible tissues of seafood caught or harvested in the wild does not exceed maximum levels which are the threshold values


Cite this indicator

HELCOM (2017) Radioactive substances: Cesium-137 in fish and surface seawater. HELCOM core indicator report. Online. [Date Viewed], [Web link].

ISSN 2343-2543

Download full indicator report

HOLAS II component - Core indicator report – web-based version July 2017 (pdf)