Chernobyl disaster substantial levels of caesium, which were believed to have been passed onto them during their consumption by wild boars, a significant number of which already contained radioactive particles above the allowed level. Like many other releases of radioactivity into the environment, the Chernobyl release was controlled by the physical and chemical properties of the radioactive elements in the core. Particularly dangerous are the highly radioactive fission products, those with high nuclear decay rates that accumulate in the food chain, such as some of the isotopes of iodine, caesium and strontium. Iodine-131 and caesium-137 are responsible for most of the radiation
Kyshtym disaster river, which had previously received 2.75 MCi (100 PBq) of deliberately dumped waste, and Lake Karachay, which had received 120 MCi (4,000 PBq). In the next 10 to 11 hours, the radioactive cloud moved towards the north-east, reaching from the accident. The fallout of the cloud resulted in a long-term contamination of an area of more than , depending on what contamination level is considered significant, primarily with caesium-137 and strontium-90. This area is usually referred to as the East-Ural Radioactive Trace (EURT). At least 22 villages were exposed to radiation from the disaster, with a total population of around