The Chernobyl accident and the Baltic Sea

The impact of the radioactive fallout caused by the accident at the Chernobyl NPP on the Baltic Sea is discussed in this paper. The fallout from Chernobyl was very unevenly distributed in the drainage area of the Baltic Sea; the Bothnian Sea and the eastern part of the Gulf of Finland received most of the deposition. This was reflected in the activity concentrations of the main fallout nuclides (especially 137Cs) that have been found in the marine environment of the Baltic Sea since then. The maximum concentrations that were detected soon after the fallout decreased significantly in a short time, and the distribution pattern of the Chernobyl-derived 137Cs has changed over the course of time as a consequence of river discharges, mixing of water masses, sea currents and sedimentation processes. Sea currents have transported caesium from the Gulf of Finland and the Gulf of Bothnia into the Baltic Proper and further out of the Baltic Sea into the North Sea. In addition, a considerable amount of 137Cs has been bound in the seabed of the Baltic Sea. In general, the concentrations of man-made radionuclides in the sediments have been at or below the concentrations of naturally-occurring radionuclides, and are not expected to cause harmful effects on the wildlife in the Baltic Sea. The exposure of the population to radiation caused by the ingestion of Baltic Sea fish after the Chernobyl accident was considered to be low compared with the mean annual exposure of Finns to radiation or to the dose caused by natural radionuclides in the sea. (orig.)