Radioactive substances occur naturally in the environment - mainly from the substances of which the solar system and the Earth were originally formed and partly from the Earth’s atmosphere by the slowing down of particles from the sun. The marine environment thus contains naturally occurring radionuclides. The development and use of nuclear power for military and peaceful purposes have however, resulted in the production of a number of man-made radioactive substances.
Man-made radionuclides of particular concern to man and the environment are 90Sr and 137Cs, which are both formed by nuclear fission. These radioisotopes have half-lives of about 30 years and remain in the environment for many years once released. Furthermore, 90Sr and137Cs are readily transported through food chains, since strontium and caesium have chemical similarities to calcium and potassium. These radionucleids may contaminate food and expose humans to radioactivity through ingestion.
The occurrence of man-made radioactive substances found in the Baltic Sea is due to four main events:
Thematic Assessment of long-term radioactivity in the Baltic Sea 2007-2010 (2013)
Radioactivity in the Baltic Sea - 1999-2006 HELCOM thematic assessment (2009)