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
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.
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
The indicator is applicable in the waters of all countries bordering the
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
Concentrations of contaminants
D8C1 Within coastal, territorial
and areas beyond territorial waters the concentration of contaminants do not
exceed the threshold values
Contaminants in fish and seafood
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
HELCOM (2017) Radioactive substances: Cesium-137 in fish and
surface seawater. HELCOM core indicator report. Online. [Date Viewed], [Web
II component - Core indicator report – web-based version July 2017 (pdf)