Bondar Y. The radiobiological effects of chronic ionizing irradiation of Scots pine (Pinus sylvestris L.) in the Chornobyl NPP exclusion zone

In the dissertation the results of complex researches are presented which describe the radiobiological effects of the chronic ionizing irradiation to the Scots pine plantations growing at the sites contaminated with the radioactive substances as a result of the Chornobyl NPP accident. For this purpose the distribution and dynamics of the 137Cs and 90Sr radionuclide activities in various organs and tissues of the pine trees were determined. The dose rates to the trees' apical meristem at the three experimental sites were calculated using the dosimetric model that took into account irradiation from both external sources and incorporated 137Cs and 90Sr radionuclides. The absorbed dose rates to the apical meristem of pine varied in the range from 4,5 mGy?yr-1 at the site near Ivankiv city to several Gy?yr-1 for the trees growing at the trenches in Red Forest. The frequency of the morphological changes in the trees of the experimental array (cancelling the apical domination) was determined. The fraction of cells with aberrations in the apical meristem of the seed germs was quantified. For the actual conditions of the Chornobyl radioactive contamination the dose-effect dependencies were formulated for the morphological changes (various types of cancelling the apical domination during development of the pines' crown) and cytogenetic damages (aberrations of cells of the apical meristem of the seed germs) at the chronic irradiation of Scots pine (Pinus sylvestris L.). These dependencies can be applied for normalization of the permissible levels of irradiation to biota as well as for development of the theoretical approaches to interpretation of the radiobiological effects.