Radiation epidemiological analysis of late effects of population exposure at northern part of east ural radioactive trace

Population residing in the northern part of the Chelyabinsk oblast and the south eastern part of the Sverdlovsk oblast of Russia affected to accidental exposure since 1957. The territory (East Ural Radioactive Trace - EURT) was contaminated after explosion of container with highly radioactive wastes at the Mayak Production Association. Studies of health effects of exposure in the southern, head part of EURT are conducted in the Ural Research and Practical Center of Radiation Medicine (U.R.P.R.M.). In the 1990's U.R.P.C.R.M. formed a cohort of EURT within Chelyabinsk oblast (14,500 cases and 19,400 external controls). The cohort was followed in 1957-1987 and the results of the study are discussed by Crestinina et al. First results of study on exposure late health effects among rural population in the northern part of the EURT are presented in this paper. Firstly, or the period 1958-2000 a statistically significant increase in cancer mortality associated with accidental exposure at EURT area was observed in the critical group of population of the Kamensky district, Sverdlovsk Region (65 cancer deaths among 691 cases, 90% CI 18-144). The finding is in agreement with the results of a radiation epidemiological study in the southern head part of EURT and model radiation risk assessments. E.R.R. normalized to colon dose is 1.3 Gy-1 (90 % CI 0.36-2.9 Gy-1). Secondly, analysis of the age and temporal factors influence on solid cancers radiation risk allows conclusion on decline of radiation risk in time. At present considerable number of additional radiation-induced cancer deaths are unlikely to appear. Radiation risk of solid cancers realizes at most during 30 post-accident years. Radiation risk declines with age at first exposure and not appeared in the age group >60. Derived age and time dependencies generally agree with results of other radiation epidemiological studies. Thirdly, continuation and development of radiation epidemiological study of the population residing in the northern part of EURT is of a certain interest for investigating radiation induced heath effects. The retrospective epidemiologic dosimetric register of the deceased in the northern part of EURT presented here may be considerably expanded by data on Kamenst-Uralsky and other districts of the Sverdlovsk Region contaminated following the accident of 1957 in 'Mayak' plant. Finally, when continuing the studies based on the register, potential sources of uncertainty should be considered in a more detail and it is necessary to conduct special studies to improve dosimetric methods of dose reconstruction for the territory under study. The work is supported by Russian Foundation for Basic Research (grant RFBR 05- 08-01401)