Thus far there are relatively few data on the risk of leukemia among those who were exposed to external radiation during cleanup operations following the Chornobyl nuclear accident, and results have not been consistent. To investigate this issue further, we assembled a cohort of 110,645 male cleanup workers from Ukraine and identified cases of leukemia occurring during the period 1986 to 2000. Detailed interviews were conducted and individual bone marrow doses were estimated using a new time-and-motion method known as RADRUE (Realistic Analytical Dose Reconstruction with Uncertainty Estimate). See companion paper II for a detailed description of the dosimetry. For the initial analyses we used a nested case-control approach with a minimum of five controls per case, matched for year of birth, oblast (region) of registration and residence. All identified cases were reviewed by an international panel of experts.The dose-response analysis and results are given in companion paper III.

In 1986, when an explosion accident occurred at the Chernobyl, Ukraine nuclear power plant, a large number of people were exposed to significant amounts of ionizing radiation. During the time between 1986 and 1992, peripheral blood samples were obtained from 102 people who either were on site during the emergency or were brought to Chernobyl shortly thereafter to assist in the cleanup of radioactive contaminants and isolate the damaged reactor from the environment. These blood samples plus samples from 13 unexposed Soviet individuals were analyzed by flow cytometry using the allele-loss somatic mutation assay for glycophorin A. Results of these assays show that the frequency of N/O variant red cells increased in proportion to the estimated radiation exposure of each individual. The radiation dose-response function derived from this population closely resembles that determined previously for atomic bomb survivors whose blood samples were obtained and analyzed 40 years after their exposure. This suggests comparable mutation induction per unit dose for these two populations and long-term persistence of the mutational damage. In addition, measurements on multiple blood samples from each of 10 donors taken over a 7-year period showed no significant changes in N/O variant cell frequencies, confirming the persistence of radiation-induced somatic mutations in long-lived bone marrow stem cells.

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No abstract

Selective cytogenetic monitoring of the highest priority groups of Chernobyl disaster victims has been carried out since 1987. In 1992-1993, 125 liquidators (irradiated mainly in 1986) and 42 persons recovering from acute radiation sickness of the second and third degrees of severity were examined. Cytogenetic effects (an elevated level of unstable as well as stable markers of radiation exposure) were found in all groups, which showed a positive correlation with the initial degree of irradiation severity even 6-7 y after the accident. Comparative scoring of conventional staining vs. G-banding in 10 liquidators showed the identical rate of unstable aberrations. At the same time, the yield of stable aberrations for G-banded slides exceeded the frequency for conventional staining. In order to study possible mutagenic activity of chronic low levels of irradiation, the cytogenetic monitoring of some critical groups of the population (especially children and occupational groups--tractor drivers and foresters) living in areas of the Ukraine contaminated by radionuclides was carried out. In all the examined groups, a significant increase in the frequency of aberrant metaphases, chromosome aberrations (both unstable and stable), and chromatid aberrations was observed. Data gathered from groups of children reflect the intensity of mutagenic impact on the studied populations and demonstrate a positive correlation with the duration of exposure. Results of cytogenetic examination of adults confirmed the importance of considering the contribution of occupational radiation exposure to genetic effects of Chernobyl accident factors on the population of contaminated areas. Results of our investigations demonstrated the possibility of evaluating the mutagenic impact of acute and long-term irradiation of different intensities on somatic cells of persons undergoing radiation exposure due to the Chernobyl accident and confirmed the need to introduce new informative genetic methods [especially fluorescence in situ hybridization (FISH)] for reliable retrospective cytogenetic dosimetry of radiation exposure in Chernobyl accident victims.