Mortality of populations potentially exposed to ionising radiation, 1953-2010, in the closed city of Ozyorsk, Southern Urals: a descriptive study.

BACKGROUND The city of Ozyorsk (Southern Urals) was created as a secret city in 1945 and is a closed city until today. It housed workers of the earliest and one of the country's largest nuclear facilities. Workers of the nuclear reactors, radiochemical or reprocessing plants were exposed to high levels of ionising radiation in the early years of operation and possibly further exposed from inhalation of plutonium aerosols. METHODS The cause-of-death registry of Ozyorsk received paper copies of original death certificates of all deaths of residents of the city. Data were analysed for recent mortality rates (1998-2010) and time trends in age-standardised mortality rates between 1953 and 2010 of main groups of causes of deaths, in particular cancer. RESULTS Comparing workers of the three main plant types with the remainder of the Ozyorsk residents, and with national figures, all-cause mortality rates were lowest among workers, with ratios compared to national figures of 0.65 (men) and 0.56 (women), and compared to the other residents of 0.77 (men) and of 0.74 (women). For cancer overall, the differences were smaller in men (ratio between workers and national figures of 0.86) and there were no differences in women (ratio of 1.00), but ratios differed by cancer type. Most cancer deaths were however least common in the workers, including leukaemia. Over the last 60 years, all-cause mortality has gradually increased among men in all three groups but was stable among women, whereas cancer death rates have slightly declined in both sexes. CONCLUSIONS Healthy worker effect, relatively better living conditions in Ozyorsk and healthier lifestyles may explain the lower mortality rates in Ozyorsk. Overall mortality time trends in Ozyorsk were similar to the entire country. No apparent radiation-related effects were seen in this population-level analysis, but the radiation-related risks can be better addressed in individual-level studies.