Strontium 90 is an isotope of Strontium, a metal found naturally on Earth. A by-product of nuclear fission, Strontium 90 became a worldwide health concern as a result of fallout from atmospheric nuclear testing during the 1950s. Though current levels of this radioactive element in the environment are rather low, there is still some risk of exposure to Strontium 90 from nuclear power plants.
During the 1950s scientists began tracking the radioactive products of nuclear tests in the United States. The test of a thermonuclear bomb resulted in dust and debris becoming contaminated by the radioactivity produced by such an explosion. The explosion kicked this dust into the stratosphere where it remained for a short time before falling to the lower atmosphere. Strontium 90 (and other radioactive elements) then reached the earth in the form of rain. When analyzing the fallout from a nuclear explosion, scientists focused on Strontium 90 because of its chemical similarity to calcium. Unable to distinguish between calcium and Strontium 90, plants took in the Strontium isotope from rainfall, and animals, such as dairy cows, ate the plants. When people drank milk, they received a dose of the Strontium 90 that the cows had ingested. As this effect became apparent, scientists in the fifties like chemist Linus Pauling expressed concern over the atmospheric nuclear testing that the United States (U.S.) and the Union of Soviet Socialist Republics (U.S.S.R.) were each conducting. Fallout, including Strontium 90, from these tests could be found all over the world.
Just as plants soak up Strontium 90 because of its similarity to calcium, likewise the human body absorbs Strontium 90. Like calcium, it tends to become lodged in bones. With a half-life of 29.1 years, Strontium 90 has the potential to harm people for a while; as it decays, Strontium 90 can cause bone cancer or leukemia.
As the effects of Strontium 90 and fallout in general penetrated public awareness, American and Soviet politicians were under increasing pressure to end the nuclear testing that had led to the presence of Strontium 90 in the environment. In 1963 the U.S. and the U.S.S.R. signed a treaty banning atmospheric testing of nuclear weapons. This was heralded as a positive turning point in the Cold War. As a result of the treaty, the levels of Strontium 90 have dropped, and the accompanying risk of cancer and disease from Strontium 90 has declined.
Although most countries adhere to the ban on atmospheric nuclear testing, there is still a risk of exposure from nuclear power plants. Scientists have discovered that people living in proximity to nuclear power plants test positively for the presence of Strontium 90 in their teeth and bones. More seriously, an accident like the 1986 event at the nuclear power plant in Chernobyl in the U.S.S.R. can release radioactive elements like Strontium 90 into the environment.
Scientists have found positive uses for Strontium 90. It has been used as a tracer in various scientific studies, for instance, in revealing how fast blood flows from the heart to other parts of the body. Doctors have used Strontium 90 to treat eye and bone cancer. Strontium 90 can serve as a power source; the heat from its radioactive decay can generate power in places remote from humans, for instance, in navigational beacons or at weather stations.