Health Risks Associated with Radionuclides in Soil Materials

Radionulides in soils from natural and man-made sources constitute a direct route of exposure to humans. The most significant part of the total exposure is due to natural radiation. Soil- or rock-borne radionuclides generate a significant component of the background radiation people are exposed to. Naturally occurring radionuclides with half-lives comparable with the age of the earth and their corresponding decay products existing in terrestrial material, such as thorium (232Th), uranium (238U, 235U) and potassium (40K), are of great importance. Their spatial distribution depends on geological parent materials and plays an important role for radiation protection. Another source of exposure to natural radiation is expressed through high energy cosmic ray particles in earth’s atmosphere. Additional amounts of natural radionuclides are released into the environment through human activities such as mining and milling of mineral ores, processing and enrichment, nuclear fuel fabrications, and handling of the fuel cycle tail end products. Radionuclides produced by humans originate from nuclear industrial activities, nuclear reactor accidents, or military activities. The most important man-made radionuclide is cesium (137Cs) with a half-life of 30.17 years, which is released from nuclear fission and activation processes. A large amount of 137Cs was released into the atmosphere during the nuclear weapons tests in the 1950s and 1960s. Atmospheric deposition of this 137C has made it a typical background component of northern hemisphere top soils. The most severe civil nuclear reactor accidents, which also released large quantities of 137Cs, occurred at Chernobyl (April 26, 1986) and Fukushima Daiichi (March 11, 2011) power stations. During the years after those weapon tests and reactor accidents, the bioactivity and environmental mobility of 137Cs declined markedly, resulting in large changes in contamination of soils, surface water and foodstuffs.