Analysis of symmetrical translocations for retrospective biodosimetry in radiation workers of the Mayak nuclear-industrial complex (Southern Urals) using FISH-chromosome painting

Purpose: Frequencies of symmetrical translocations were determined by fluorescence in situ hybridization (FISH) for retrospective biodosimetry in workers occupationally exposed to external gamma -rays and internal plutonium at the Mayak nuclear-industrial complex (Southern Urals, Russia). Materials and methods : Chromosome analyses were carried out on peripheral lymphocytes from 75 Mayak workers who had received their main exposures between 1948 and 1963. Cumulative external gamma -ray doses between 0.02 and 9.91 Sv and plutonium burdens ranging between 0.26 and 18.5kBq are reported. As controls, 33 unexposed persons from noncontaminated areas of the Southern Urals were used. Wholechromosome painting probes for chromosomes 1, 4 and 12 were used simultaneously with a pancentromeric probe. Results : Compared with the control group, a significantly elevated translocation frequency was found for the total study group and for either of two subsets with (48 subjects) and without (27 subjects) plutonium incorporation. The dicentric frequency was not significantly different from the control level. In the pooled data set, translocation frequencies showed a significant dependence on cumulative external gamma -ray doses. Plutonium uptake had no substantial influence. Individual dose estimates for 21 cases exhibiting at least five translocations ranged between 0.5 and 1.8 Gy, which is substantially lower than the workers' registered personal doses. Conclusion : At 35-40 years after protracted exposure to low-dose rate external gamma -rays, the postulated lifetime stability of translocations cannot be confirmed. Apparently, the natural loss of translocation-bearing peripheral lymphocytes cannot be fully compensated so that a temporal decline even of transmissible aberrations takes place. As a consequence, individual retrospective biodosimetry estimates cannot be obtained reliably from the remaining fraction of translocations.