FISH-based analysis of stable translocations in a Techa river population

Purpose: Measurements of symmetrical translocations by fluorescence in situ hybridization (FISH) were performed for retrospective biodosimetry in a Techa River population exposed to external (gamma-rays) and internal (Sr-90, Cs-137) irradiation. Materials and methods: Chromosome analyses were carried out on peripheral lymphocytes from 73 radiation-exposed residents from settlements along the Techa River (Southern Urals, Russia) located 7-148 km downstream from the site of release of liquid radioactive waste from the plutonium production facility Mayak. Thirty-nine unexposed persons from non-contaminated areas were used as controls. Whole-chromosome painting probes for chromosomes 1, 4 and 12 were used simultaneously with a pancentromeric probe. Results: A significantly elevated mean translocation frequency compared with controls was found for the total study group and for either of two subgroups of inhabitants residing in villages of the upper regions of the Techa River (7-60 km) during 1950 to 1951, or in villages of the lower regions (78-148 km) until the time of blood sampling. Within the first subgroup, subjects born between 1937 and 1949 showed higher translocation frequencies than those born between 1914 and 1936. Collective biodosimetry estimates for the various groups were between 0.24 and 0.54 Gy. Individual dose estimates for seven subjects with at least five translocations ranged between 0.77 and 1.80 Gy and compared well with doses reconstructed on the basis of Sr-90 whole-body counts (WBC) and electronic paramagnetic resonance (EPR) measurements. Individual translocation frequencies from 40 subjects with existing WBC data and calculated cumulative red bone marrow doses below 0.6 Gy fall within the 95% prediction limits of the calibration curve. Conclusions: FISH-based translocation measurements can provide useful information for a retrospective biodosimetric interpretation. However, with the analysed number of cells, individual estimates required for a reliable evaluation of this highly variable exposure situation can be obtained only for a minority of subjects. In addition, influence of a temporal decline on the yield of stable translocations cannot be fully excluded.