Dynamics of the frequency of unstable chromosome exchanges in lymphocytes of chronically exposed residents of the Ural region

In the middle of the 20th century residents of the Ural region were affected by chronic radiation exposure in a wide dose range due to the release of liquid radioactive waste into the Techa River. The objective of the study was to investigate the dynamics of the frequency of unstable chromosome exchanges in chronically exposed residents of the Techa riverside settlements. Materials and Methods: The study covers the period from 1970s through 2019. The analysis is based on the published research describing the results of cytogenetic examination, as well as on the retrospective study of the cytogenetic database data. Nine groups of examined individuals were formed by periods of examination: five groups of exposed people and four comparison groups. To obtain the preparations, T-lymphocytes were cultivated to the metaphase stage and hypotonically treated; the metaphase plates were fixed, and the chromosome preparations were prepared. Results and Discussion: Results of the assessment showed a decrease in frequency of dicentrics and unstable chromosome exchanges over the period from 1970 through 2019. Most significant decline in the number of chromosome aberrations was observed starting from 1993, i.e. 40–50 years after the onset of exposure. Dicentrics are statistically significantly more frequent in the group of exposed people relative to the comparison group in the periods 1970-1993 (23-43 years after the onset of exposure), and 1993-1996 (46-49 years after the onset of exposure), as well as in the period from 2012 through 2019 (65-72 years after the onset of exposure). Conclusion: At present, frequency of dicentrics in exposed people remains statistically significantly increased relative to the comparison group members. State-of-the-art equipment and use of special software packages in the work of cytogeneticists made it possible to increase the number of analyzed cells in more than 3 times. It increased considerably the probability of chromosome aberration detection both in exposed and unexposed individuals.