[Assessment of relative biological effectiveness of tritium using chromosome aberration frequency in human blood lymphocytes].

The aim of this work is to determine Relative Biological Effectiveness (RBE) of tritium beta-irradiation using chromosome aberration frequency in peripheral blood lymphocytes after radiation exposure in vitro and in vivo. The results of the experimental estimation of tritium beta-irradiation RBE in comparison with 60Co gamma-irradiation using analysis of unstable chromosome aberration frequencies in peripheral blood lymphocytes in reference to concrete conditions of the investigation were presented. It was demonstrated that tritium beta-irradiation is in total more effective than gamma-irradiation up to 1 Gy. RBE of tritium beta-irradiation was determined as 2.2 at minimum doses and decreased at higher doses (1 Gy) up to 1.25. For the first time results of the comparative analysis of frequencies of stable chromosome aberrations in two groups of professional nuclear workers (town Sarov) exposed to chronic tritium beta- and gamma-irradiation in remote period were presented. The grater RBE of tritium beta-irradiation was demonstrated. It has been estimated as 2.5.

[Cytogenetic examination of nuclear specialists exposed to chronic beta-radiation of tritium].

For the first time the cytogenetic examination of the group of nuclear specialists (79 persons) chronically exposed to tritium beta-radiation for a long period was carried out. The frequencies of unstable (conventional method) and stable (FISH-method) chromosome aberrations have been analyzed. 50 years after the beginning of working under the conditions of the increased radiation level the differences (in comparison with control values) were revealed for all cytogenetic parameters. The frequency of the radiation-specific markers (dicentrics and centric rings) exceeds more than 2-fold the control level. A significant but poor correlation between the frequency of unstable aberrations and the total absorbed dose (during the whole working period) was revealed. A retrospective estimation of irradiation doses for 14 nuclear workers was made by the frequency of stable chromosome aberrations. The obtained dose values ranged from 110 to 1250 mSv.

[The analysis of mutations at mini- and microsatellite DNA loci in the family members of a group of occupationally exposed to tritium and tritium oxide plant workers].

Mini/microsatellite (MNS/MCS) loci are efficient tools in solving basic and applied problems in different spheres of biology and medicine due to their unique characteristics - a high frequency of tandem repeats in combination with their wide variability. Specifically, they have been found use as potential markers of genetic effects of ionizing radiation on animals and on human. However there is no general agreement as to the influence of irradiation on the frequency of mutations in hypervariable repetitive DNA sequences up to now. The present work is the study of the mutation frequency at MCS/MNS loci in 19 families of workers occupationally exposed to chronic beta-radiation from tritium and tritium oxide (examined group), and in the control group included 23 families. The results have indicated that the average frequency of microsatellite mutations in the examined group made up 4.7% and exceeds about 7-fold the same parameter of the control group (0.7%). This differences is statistically significant (p = 0.004). The average frequency of minisatellite mutation in the examined group made up 3% while in the control group it was 2 time lower (1.5%), but this difference is not statistically significant. Mutations for 4 MCS and 2 MNS loci were revealed in two children from one family (the total reconstructed dose in their father was about 1000 mSv). If we exclude this family from statistical analysis the frequencies of MCS and MNS mutations in the children of nuclear workers do not statistically differ from the control values.

[Study of reparative DNA synthesis in lymphocytes of persons occupationally exposed to radiation]. / Izuchenie reparativnoso sinteza DNK v limfotsitakh professionalov-atomshchikov.

The UDS efficiency in lymphocytes of professionals chronically exposed to gamma/neutron radiation, as well as for a control cohort was estimated. A credible reduction of UV-induced UDS (KUV) index as compared to the control was demonstrated. This shows an invalid repair state of blood cells in professionals. As for the control cohort, the decreasing tendency of UDS index with age was found. The correlative analysis of UDS index dependence upon an absorbed dose (based on physical dosimetry data) revealed the trend towards repair index reduction along with a higher total absorbed doze, that is followed by UDS index coming onto a plateau. It was also demonstrated that after a sharp and/or accidental irradiation UDS index reduces as compared to permanent portioned irradiation. It was not observed the influence of smoking upon UDS efficiency in blood lymphocytes neither for control, nor for experimental group. The analysis of vitamin therapy of the both cohorts showed that such therapy raises UDS index of the control (i.e., non-professional) group. Besides, it was found out an additional positive effect of vitamin therapy, i.e. doze leveling in long-term perspective after irradiation. The most expressed KUV/doze correlation was characteristic for professionals, who do not take vitamins and do not smoke. This proves that in blood cells of professionals it is preserved a dependence of repair system invalidity upon the absorbed doze without similar external factors.

[Cytogenetic effect of small doses of tritium beta irradiation]. / Tsitogeneticheskii éffekt malykh doz beta-izlucheniia tritiia.

The effect of tritium beta-radiation within the dose range of 0.5 x 10(-3) = 0.6 Gy on human blood lymphocytes in vitro was investigated. Dose-effect correlation was determined by the frequency of aberrant cells and the sum of chromosome aberrations per 100 cells. As compared to a rated curve corresponding to a linear-quadratic model y = a + bD + cD2, experimental curves (showing correlation between cytogenetic indices and a dose) are of abnormal nature with a plateau in a dose range less than 7.5 x 10(-2) Gy. A big confidence interval of cytogenetic effect indices in a dose range less than 7.5 x 10(-2) Gy was shown to be determined by the number of analyzed metaphases. The proof of significance of a plateau on a dose-effect curve in regions of small doses (e.g. with a confidence interval of +/- 24%) necessitated analysis of no less than 10,000 metaphases per dose.

[Effect of pulse and prolonged x-rays in air and in nitrogen on the frequency of sex-linked recessive lethal mutations in Drosophila melanogaster]. / Izuchenie vliianiia impul'snogo i dlitel'nogo rentgenovskogo oblucheniia v vozdukhe i v azote na chastotu stseplennykh s polom retsessivnykh letal'nykh mutatsii u Drosophila melanogaster

The effect of X-irradiation on the frequency of recessive lethal mutations in Drosophila melanogaster sperm cells is studied. Drosophila males were X-irradiated in air and nitrogen in three units with doses rates of 4 X 10(9), 10(11) and 1.7 rad/sec at a dose of 2000 rad. It is found that the mutation frequency after the pulse irradiation was almost twice as low as that after prolonged irradiation. The oxygen effect is eliminated under pulse irradiation, and the data on pulse irradiation in air are similar to those on irradiation at a low dose rate in nitrogen. The data obtained are explained by the presence of short-lived oxygen-dependent damages which are not realized under pulse irradiation due to the lack of oxygen in the track volume.