Radionuclide Basics: Strontium-90
Strontium (chemical symbol Sr) is a silvery metal that rapidly turns yellowish in air. Naturally occurring strontium is not radioactive. The most common man-made radioactive form of strontium is strontium-90 (Sr-90). Strontium-90 is produced commercially through nuclear fissionfissionThe splitting of an atomic nucleus into at least two other nuclei with the release of a relatively large amount of energy. Fissioning that occurs without any outside cause is called "spontaneous fission." for use in medicine and industry. It also is found in the environment from nuclear testing that occurred in the 1950s and 1960s as well in nuclear reactor waste.
Strontium-90 is widely dispersed in the environment and the food chain from atmospheric testing of nuclear weapons in the 1950s and 1960s. Radioactive decayRadioactive decayThe process in which an unstable (radioactive) nucleus emits radiation and changes to a more stable isotope or element. is the only way of decreasing the amount of Sr-90 in the environment. It has been slowly decaying since then, current levels from these tests are very low.
Plants or crops growing in or near contaminated soil may take up small amounts of Sr-90 from the soil. Animals may ingest Sr-90 when eating plants.
Everyone is exposed to small amounts of Sr-90, since it is widely dispersed in the environment and the food chain. Strontium-90 was widely dispersed in the 1950s and 1960s in falloutfalloutRadioactive material in the air from a nuclear explosion that will cool into dust-like particles and fall to the ground. from the atmospheric testing of nuclear weapons.
Strontium-90 is also found in waste from nuclear reactors. The accident at the Chernobyl nuclear power plant introduced a large amount of Sr-90 into the environment. Strontium-90 was also released during the 2011 Japanese nuclear incident at the Fukushima Daiichi Nuclear Power Plant. No significant amount of Sr-90 reached the United States from either incident. Learn more about EPA’s historical responses to radiological emergencies like Fukushima and Chernobyl on the Planning and Past Responses page.
Strontium-90 can be inhaled, but ingestion in food and water is the greatest health concern. Once in the body, Sr-90 acts like calcium and is readily incorporated into bones and teeth, where it can cause cancers of the bone, bone marrow, and soft tissues around the bone. Because Sr-90 acts like calcium, milk monitoring will be important after a large release.