The state-of-the-art on worldwide studies in some environments with elevated naturally occurring radioactive materials (NORM).

Direct observations and studies of the radiobiological and epidemiological effects of ionizing radiation from naturally occurring radioactive materials (NORM) on man, in particular in areas with elevated NORM, are becoming of prime concern in radiation protection. This is due to existing discrepancies in the application of the linear no-threshold theory in obtaining radiation risks at low doses by extrapolation from high dose to low dose using dose and dose-rate effective factors. Many areas in the world have elevated NORM caused either by the geological and geochemical structure of the soil, or by the radioactive content of the water flowing from hot springs and/or due to technologically enhanced radioactivity as well as due to cosmic rays. Such areas, with relatively large cohort sizes, have been the subject of intensive dosimetry, radiobiological and epidemiological studies. It is the purpose of this article to review: sources of NORM and human exposure, needs and problems in study of areas with elevated NORM; the criteria for their classification; some areas with elevated NORM and the results of related studies, and some conclusions and recommendations for unification of an approach in future studies aimed at obtaining better estimates of human radiation risk factors from the effects of ionizing radiation.