Keywords: radioadaptive response, low-dose radiation, radiation workers, nuclear power plants, low radiation, risk estimation, Iran, cancer incidence, leukemia incidence, radiation dose limits, adaptive response, radiation protection, nuclear energy, nuclear safety
Open questions regarding implications of radioadaptive response in the estimation of the risks of low-level exposures in nuclear workers
Substantial data indicate that increased levels of chromosome aberrations in lymphocytes can be used to predict cancer risk in humans. One may conclude that a dose of ionising radiation sufficient to produce a certain level of cell damage increases production of antioxidants and repair enzymes that decrease either the frequency of chromosome aberrations or the cancer risk. People in some areas of Ramsar, a city in northern Iran, receive an annual radiation dose from background radiation that is more than five times higher than the 20 mSv yr-1 that is permitted for radiation workers. If an annual radiation dose of a few hundred mSv is detrimental to health, causing genetic abnormalities or an increased risk of cancer, it should be evident in these people, while cytogenetic studies show no significant differences between people in the high background compared to people in normal background areas. Although there is not yet solid epidemiological information, most local physicians in Ramsar report anecdotally there is no increase in the incidence rates of cancer or leukemia in their area. On the other hand, there are no data to indicate a significant increase of cancer incidence in other High Background Radiation Areas (HBRAs) around the world. Furthermore, several studies show a significant decrease of cancer death rates in areas with high backgrounds. To assess the possible induction of an adaptive response, an in vitro challenge dose of 1.5 Gy of gamma rays was administered to the lymphocytes of the inhabitants as well as those of a neighbouring area. Lymphocytes of Ramsar residents showed a significantly reduced radiation sensitivity for chromosome aberrations compared to those of residents in normal background areas. Given the apparent lack of ill effects in the populations of these high dose-rate areas, these data further suggest that current dose limits are overly conservative.