The status of the Baltic Sea marine environment in terms of contamination by hazardous substances is assessed using several core indicators. Each indicator focuses on one important aspect of the complex issue. In addition to providing an indicator-based evaluation of the status of radioactivity in the Baltic Sea, this indicator also contributes to the overall integrated hazardous substances assessment.
The core indicator on cesium-137 in fish and surface waters addresses the Baltic Sea Action Plan's (BSAP) hazardous substances segment's ecological objective 'Radioactivity at pre-Chernobyl level'.
The HELCOM Monitoring of Radioactive Substances (MORS) Expert Group has been working to implement the Helsinki Convention on matters related to the monitoring and assessment of radioactive substances in the Baltic Sea based on HELCOM Recommendation 26/3 Monitoring of Radioactive Substances.
The core indicator also addresses the following qualitative descriptors of the MSFD for determining good environmental status (European Commission 2008):
and the following criteria of the Commission Decision (European Commission 2010a):
The core indicator also supports the implementation of the Euratom Treaty, of which all EU Member States are signatories. The Euratom Treaty requires actions in relation to monitoring and effects of discharges on neighbouring states.
A worldwide study on marine radioactivity has shown that the Baltic Sea has the highest average 137Cs levels in surface water compared to other marine areas of the world (IAEA 2005). Levels of radionuclides in marine biota are linked to the corresponding levels in seawater and sediments, via accumulation through food chains. Anthropogenic radionuclides, including 137Cs, entering seawater can be bioaccumulated and/or adsorbed on suspended particulate matter (composed mainly of plankton and mineral particles), which accumulates in bottom sediments. Radionuclides can also be accumulated by higher flora and fauna organisms.
The complexity of food chains increases with the trophic level of the species considered. Fish are mainly exposed to radionuclides and accumulate them through their food sources, not from water. Predators such as cod and pike, have shown the highest 137Cs levels, but there was some delay in reaching their maximum values after 1986, when compared to the trends in seawater. In the long-term, 137Cs time trends in biota closely follow the trends in seawater (Zalewska & Suplińska 2013).
The harmful effects of 137Cs on marine organisms are related to the emission of ionizing radiation, which can lead to internal damage, i.e. the effects are observed at the cellular level. It is difficult to establish unequivocally which 137Cs concentrations can be considered as harmless because of the complexity of reactions of individual organisms to its effects. Especially in the presence of other hazardous substances the effects of radionuclides could be intensified (synergetic effects). Taking into account the present concentration levels in Baltic Sea biota, no effects on animal health by 137Cs are expected as the lowest effect levels observed in fish are more than three orders of magnitude higher compared to the measured doses to these animals (according to ICRP 2008).
Ingestion of 137Cs with fish is the dominating exposure pathway of humans to man-made radioactivity in the Baltic Sea. Therefore, 137Cs concentrations in herring, plaice and flounder can be suitable as indicators for man-made radioactivity in the Baltic Sea. Internationally recommended maximal permitted concentrations of 137Cs in foodstuff are in the range 100–1250 Bq/kg (European Commission 2012, 2010b).
Substances, litter and energy
- Input of other substances (e.g. synthetic substances, non-synthetic substances, radionuclides) – diffuse sources, point sources, atmospheric deposition, acute events.
The development and use of nuclear power for military and peaceful purposes has resulted in the production of a number of man-made radioactive substances and their release into the environment. For example, even the routine operations of nuclear power plants cause small controlled discharges of radioactive substances, but accidents at nuclear power plants can release considerable amounts of radioactivity into the environment. Artificial radionuclides of particular concern to man and the environment, including 137Cs, are formed by nuclear fission.
137Cs reaches the Baltic Sea waters from different sources (such as atmospheric fallout, river discharges, and controlled liquid and gaseous discharges from working nuclear facilities) and becomes distributed within other compartments of the marine environment. Radioactive fallout from the Chernobyl accident in 1986 is the dominating source for 137Cs in the Baltic Sea.
The total collective dose of radiation from 137Cs in the Baltic Sea is estimated at 2,600 manSv, of which about two thirds (1,700 manSv) originated from the Chernobyl fallout, about one quarter (650 manSv) from the 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 have been dominant except for the year 1986 where the individual dose rates from the Chernobyl fallout in some regions of the Baltic Sea approached those from natural radioactivity.
Since 1950, the maximum annual equivalent dose to individuals from any critical group in the Baltic Sea area due to 137Cs is estimated at 0.2 mSv y-1. This value is lower than the doses that humans receive from natural radionuclides in foodstuffs, which are e.g. 0.215- 0.521 mSv in Germany (BfS 2014), and much lower than the dose limit of 1 mSv y-1 set for the exposure of members of the public in the IAEA - International Basic Safety Standards (IAEA 1996). Considering the uncertainties involved in the assessment, it is unlikely that any individual has been exposed from marine pathways at a level above this dose limit. 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.