Are the Inhabitants of High Background Radiation Areas of Ramsar More Radioresistant

Backgroud/ Ramsar in northern Iran is among the world’s well-known areas with highest levels of natural radiation. Annual exposure levels in areas with elevated levels of natural radiation in Ramsar are up to 260 mGy y-1 and average exposure rates are about 10 mGy y-1 for a population of about 2000 residents. Due to the local geological features, which includes high levels of radium in rocks, soils, and groundwater, Ramsar residents are also exposed to high levels of alpha activity in the form of ingested radium and radium decay progeny as well as very high radon levels (over 1000 MBq m-3) in their dwellings. In some cases, the inhabitants of these areas receive doses much higher than the current ICRP-60 dose limit of 20 mSv y-1 set for radiation workers. The extraordinary levels of natural radiation in Ramsar prompted us to assess the radiation susceptibility of the residents. Venous blood samples were taken from 7 healthy blood donors of both sexes who lived in some areas of Ramsar with highest levels of natural radiation (dose rates were up to 155 µSv h-1) and 5 healthy persons from a nearby control area. Standard condition for cell cultivation, irradiation and analysis of chromosome aberrations was used. The cells were exposed to the challenge dose of 1.5 Gy of Co-60 gamma ray 48 hours after PHA stimulation. Using mean chromosomal aberration per cell (MCAPC), the expected numbers of aberrations were calculated. Lymphocytes of Ramsar residents when subjected to 1.5 Gy of Gamma rays, showed fewer chromosome aberrations compared to residents in a nearby control area. These findings clearly show that high levels of natural radiation may induce radioadaptive response. Interestingly, this radioadaptation phenomenon was found in individuals who received doses as much as a few hundred times more than the inhabitants of a nearby control area. More research is needed to precisely clarify if it is possible to relax the radiation protection guidelines for inhabitants who live in such areas.