Radionuclides are found naturally at very low concentrations in soils and therefore natural radioactivity is a common occcurence. Their activity levels vary greatly, depending on soil type. However, there are certain areas (high background radiation areas HBRA’s, rich in monazite, ilmenite, rutile, zircon minerals ) that have high background radiation levels, which can be dangerous for animal and human health Some examples of these areas include : Ramsar - Iran, Guarapari – Brazil, Kerala and Orissa – India, Minjingu – Tanzania, Yangjiang – China, Oklo – Gabon, etc. The most important natural radioactive nuclides are 40 K 238 U and Th.
The production of man made radioactive nuclides began in 1941. Amongst this group radionuclides are also extremely toxic. Nuclear reactors produce elements such as 3H, 129I, 239Pu, 90Sr to name a few, which also have their own radiation α, β, ɣ. Atmospheric fall out has been produced since 1945 by the use of nuclear weapons, weapons testing and nuclear power station accidents (e.g.Kyshtym, 1957, and Chernobyl, 1986 – Russia, Fukushima, 2011 - Japan). Nuclear wastes concentrated in repositories, even the encapsulated wastes, can not be guaranteed to remain stable and safe.
An environmental concern about the growing dissemination of radionuclides in soils and through the terrestrial food chain is vital as it can affect both animals and people. It is necessary to monitor, map and model the spatial structure of effected areas. Extensive studies of natural and technogenic geochemical fields and soil characteristics (soil type, components and properties : oxides, phosphates, clays, humus types, pH, redox potential, etc.) are necessary. It is very important to understand the behaviour and fate of radionuclides in soil horizons and especially in relation with the terrestrial food chain, the pollution mechanisms and the best and recent findings in remediation techniques.