Identification of groups at risk for mental and behavioral disorders among Chernobyl clean-up workers residing in the Kaluga oblast

Groups at risk for mental and behavioral disorders were identified among Chernobyl clean-up workers, liquidators, residing in the Kaluga oblast on the basis of excess risk values, calculated in the cohort comprised 82.5 thousand males, worked in the Chernobyl exclusion zone in 1986 and 1987. The follow-up lasted 27 years from 1986 through 2012. Average age of the workers at the beginning of the follow-up was 34 years, average cumulative dose of external radiation was 133 mGy. Duration of stay at the exclusion zone was accepted as surrogate variable connected to stress-induced factors of risk to develop mental and behavioral disorders. Cumulative external dose to a clean-up worker, not correlated to his stay at the exclusion zone, was used as radiation factor. Liquidators worked in the exclusion zone more than 6 weeks in 1986 and received cumulative external dose higher than 100 mGy, were assigned to the group at risk for mental and behavioral disorders (ICD-10: F00-F99). Risk values of stress-induced and radiation induced mental disorders were maximum in the first years after the accident. Within 4 years following the accident 44% of diseases detected in clean-up workers were mental and behavioral disorders caused by exposure to stress and radiation factors in the Chernobyl zone. Within the next four-year period the portion of excess cases was 17.9%. In eight years after the accident no statistically significant effect of stress and radiation factors on mental health of clean-up workers was registered. In the workers with cumulative dose exceeded 150 mGy saturation of the "dose-effect" was observed: values of relative risk in dose groups "150-200 mGy" and "above 200 mGy" were practically similar within each time period, they simultaneously reduced with time after the accident. "Dose-effect" relationship for mental and behavioral disorders is referred to medium-term tissue reactions. Among 864 clean-up workers of the Kaluga oblast, worked in the exclusion zone in 1986, 397 cases of mental and behavioral disorders were detected to the end of 2012, of them 44 cases (11%) could be caused by exposure of the clean-up workers to stress-induced and radiation factors during their stay at the Chernobyl zone. All excess cases of mental disorders were registered before 1994.