non-linear phenomena in biological findings of the residents of high background radiation areas of ramsar

some areas of ramsar, a city in northern iran are among the world’s wellknown inhabited areas with highest levels of natural radiation. annual exposure levels in these areas are up to 260 mgy y‐1 and the mean exposure rate is about 10 mgy y‐1 for a population of about 2000 residents. if elevated levels of natural radiation as high as a few hundred msv per year is detrimental to health and leads to higher risks of genetic abnormalities and cancer, it should be evident in the residents of areas such as ramsar. however, it has been reported that no detrimental biological effects have ever been detected in high natural background radiation areas. some studies indicate that ramsar residents not only show a significant increase in dna repair but also demonstrate induction of radioadaptive response. there is currently a great debate over the shape of the dose‐response curve for stochastic effects such as mutations and cancer after exposure to low doses of ionizing radiation. linear‐no‐threshold (lnt) model predicts that every dose, no matter how low, carries some cancer risk. lack of any proven detrimental effect in the residents of high natural background radiation areas of ramsar may be due to the induction of nonlinear dose‐response relationships which are not compatible with the widely accepted lnt hypothesis.