STRUCTURAL GENOMIC DAMAGE IN PLUTONIUM WORKERS N. V. Sotnik, T. V. Azizova, and S. V. Osovets Southern Urals Biophysics Institute, Ozyorskoe shosse 19, Ozyorsk, 456780, Russia ABSTRACT The research objective is assessment of structural genomic damages in plutonium workers. The study group included workers of the Mayak Production Association subjected to chronic occupational internal exposure to incorporated 239 Pu and/or external γ-rays. A lymphocyte culture of peripheral blood was chosen as an object of study. The yield of intrachromosomal exchange aberrations of chromosomal type on stained slides was analyzed using fluorescent in situ hybridization, mBAND. Linear relationships were revealed between (a) the total yield of chromosomal type aberrations (intra- and interchromosomal ones) and the absorbed dose from external exposure of the red bone marrow (RBM) to γ-rays, the absorbed dose from internal exposure of the RBM to α-radiation from incorporated 239 Pu, and 239 Pu body burden, and (b) the yield of intrachromosomal aberrations and an absorbed dose from internal exposure of the RBM to 239 Pu and 239 Pu body burden. Keywords: chromosomal aberrations, internal radiation, 239 Pu, external γ-radiation. INTRODUCTION Both stable and unstable chromosomal aberrations in the lymphocytes of the peripheral human blood are a sensitive and easily reproducible indicator of the radiation exposure [1, 2]. Owing to the fact that T-lymphocytes are long-living cells, a significant fraction of which are retained in the human bloodstream for several decades, a lymphocyte culture of the peripheral human blood is simple and unique model for studying of the induced mutagenesis. The low spontaneous level of chromosomal aberrations in the lymphocyte culture of the peripheral blood of healthy individuals and high radiosensitivity of the lymphocytes permit to find out the increasing of the frequency of induced chromosomal aberrations over the spontaneous level even under the effect of low dose ionizing radiations. The aim of this study was to estimate the frequency of chromosomal aberrations in the workers of the Mayak Production Association subject to occupational exposure using the mBAND method. MATERIALS AND METHODS The study group included 79 workers of the Mayak PA (50 men and 29 women). The main criteria for selecting the workers were as follows: (a) the 1945 – 1958 period of employment at the major factories of the Mayak PA; (b) the individual measured doses from external exposure to γ-rays and 239 Pu body burden. By the moment of the examination, the average age of the men was 71.1 ± 1.2 years, the age of the women was 73.7 ± 0.8 years, and the average age of the group was 72.1 ± 0.9 years. The workers of the reactor, plutonium, and radiochemical plants accounted for 44.3, 26.6, and 29.1%, respectively. The doses of external γ-exposure in the studied group varied from 0 to 3.5 Gy (the average value was 1.0 ± 0.1 Gy); the 239 Pu body burden was 0 – 12.3 kBq (the average value was 2.05 ± 0.37 kBq). The dose from external exposure to the RBM was within the range of 0 – 2.7 Gy (the average value was 0.86 ± 0.09 Gy); the absorbed dose to the RBM from incorporated 239 Pu was 0 – 0.8 Gy (the average value was 0.12 ± 0.02 Gy). The peripheral blood lymphocytes were cultured and chromosome slides were prepared according to the standard protocol [3]. Since the proliferative activity of the lymphocytes varied significantly in different individuals and depended on the conditions of cultivation and age of the examinees and radiation dose, the cultures were incubated for 62 – 72 h at 37°С. The mBAND hybridization of the slides was carried out according to the Xcyte lab manual MetaSystems protocol. The slides were analyzed with the help of a fluorescent microscope (using the set of DAPI, FITC, Texas Red, Spectrum Orange, DEAC, and Cy5 filters). Karyotyping was performed using the MetaSystems software (Germany). The observed frequency of intrachromosomal aberrations in chromosome 5 was converted to the whole genome according to the content of DNA in each chromosome. The statistical analysis of primary data was carried out by the standard method for linear regression analysis [4]. RESULTS AND DISSCUSSION Totally, 10 977 cells were analyzed in this study. Both interchromosomal (translocations, insertions, terminal deletions) and intrachromosomal aberrations (para- and pericentric inversions,