Radioactivity in North Sea and Baltic Sea
Since the 1960s, seawater, marine suspended matter and marine sediment have initially been investigated for artificial radioactivity by the German Hydrographic Institute (DHI), and since 1990 by the Federal Maritime and Hydrographic Agency (BSH). The main sources of radioactivity are the fallout from atmospheric nuclear weapons tests, the discharges from the European nuclear fuel reprocessing plants (NRP) and the Chernobyl accident. These events occurred decades ago and the discharges of NRP are now very low. As a result, the activity concentrations of all major artificial radionuclides in German waters are very low. In the western Baltic Sea, however, the activity concentrations of Cs-137 are much higher than in the North Sea. It should be noted that the activity concentrations of natural radionuclides in the sea are considerably higher than those of artificial radionuclides.
Monitoring since 1961
Source of radioactivity in North Sea and Baltic Sea
Since 1961, the DHI and the BSH have been regularly monitoring the North Sea and Baltic Sea for artificial radioactive substances. Monitoring is also carried out in the North-East Atlantic and in the European North Sea. The fallout of atmospheric nuclear weapons tests in the 1950s and 1960s contaminated the marine environment worldwide. Even today, this source makes by far the largest contribution to the global inventory of artificial radionuclides. In later years, the North Sea was first massively contaminated by NRP discharges in Great Britain and France, and then the Baltic Sea by the Chernobyl accident.
Meanwhile, the contamination of the North Sea is at a historic low. This is a consequence of the decreasing discharges and the favourable hydrographic conditions. However, the situation in the Baltic Sea is fundamentally different. Due to the very low water exchange across the Danish straits, all pollutants remain in the Baltic Sea for a very long time. This also applies to the fallout of radiocaesium following the Chernobyl accident.
The sediment monitoring shows that the surface sediments of the Baltic Sea show significantly higher specific activities of Cs-137 than those of the North Sea. The primary reasonis the contamination remaining in the Baltic Sea from the Chernobyl accident. This effect is further intensified by the high proportion of fine-grained material in some quiet bays.
However, there is no reason to fear that the consumption of fish or other marine products will have any adverse effects on health. The resulting doses are only a small fraction of the dose from natural radiation exposure.
Cs-137 as a reference nuclide
The radioactivity measuring network of the BSH continuously measures and monitors the radioactive substances in the sea. In parallel, BSH research vessels carry out nuclide-specific monitoring of seawater, suspended matter and sediments. Cs-137 occupies a special role among artificial radionuclides because it is used as a long-lived radionuclide with a half-life of about 30 years as a reference nuclide in seawater. It is the most dose-relevant radionuclide in the ocean. It is transported by ocean currents over long distances and contributes significantly to the contamination of the marine food chain.