Inhabited areas with high levels of natural radiation are found in Yangjiang, China, Kerala, India and Guarapari, Brazil. Ramsar, a northern coastal city in Iran, has some areas with one of the highest levels of natural radiation studied so far. The effective dose equivalents in very high background radiation areas (VHBRAs) of Ramsar in particular in Talesh Mahalleh are a few times higher than the dose limits for radiation workers. Inhabitants who live in this area receive annual doses as high as 132 mSv from external terrestrial sources. The basic aim of this paper is to answer the question on whether the findings on the health effects of prolonged exposure to very high levels of natural radiation contradict current ultra-conservative radiation protection regulations. In spite of the fact that at present there is no considerable radio-epidemiological data regarding the incidence of cancer in the inhabitants of VHBRAs of Ramsar, some of the local physicians strongly believe that the population living in these areas does not reveal increased solid cancer or leukemia incidences. As the majority of the inhabitants of Ramsar have lived there for many generations, we started a study to assess whether they developed a radio-adaptive response to high levels of natural radiation. Our results indicated that the frequency of chromosome aberrations (CA) in the lymphocytes of the inhabitants of VHBRAs after exposure to a challenge dose of 1.5 Gy Gamma rays was significantly lower than that of the inhabitants of a normal background radiation area (NBRA). No statistically significant difference was found in the background frequencies of chromosome aberrations between the inhabitants of VHBRAs and a neighboring NBRA. Futility of any urgent limiting regulations is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.
