Environmental impact of nuclear power materials decay, they release particles that can damage the body and lead to cancer, particularly cesium-137 and iodine-131. In the Chernobyl disaster, releases of cesium-137 contaminated land. Some communities, including the entire city of Pripyat, were abandoned permanently. One news source reported that thousands of people who drank milk contaminated with radioactive iodine developed thyroid cancer. The exclusion zone (approx. 30 km radius around Chernobyl) may have significantly elevated levels of radiation, which is now predominantly due to the decay of cesium-137, for around 10 half-lives of that isotope, which is approximately for 300 years. Due to the bioaccumulation of
Koeberg Alert strontium-90, which are responsible for most of the radioactivity of spent nuclear fuel Caesium-137 beta decays to barium-137m (a short-lived nuclear isomer) then to nonradioactive barium-137, and is also a strong emitter of gamma radiation. Caesium-137 has a very low rate of neutron capture and cannot be feasibly disposed of, but must be allowed to decay. The committee is also told how both the Tweelopiespruit and Wonderfonteinspruit in the Krugersdorp-Randfontein area have been contaminated by uranium mine tailings caused by South Africa's nuclear and mining industry. 16 March 2009, a leak of radioactive gases from Pelindaba is reported by NECSA.