Radiation biology. Radioecology

The effect of γ-radiation including low doses on the mitotic index and root growth endpoints of Allium cepa (L.) seedlings in different intervals of the recovery time after irradiation were studied. Onion seedlings were irradiated with ¹³⁷Cs point γ-sources of various activity, including radioactive microparticles of the Yenisei River floodplain. According to the results of 7 experiments, the inhibitory effect of γ-irradiation on onion root growth was observed in the dose range from 0.1 to 21 Gy in the time interval of the recovery period of up to 6 days, by the 10th day the damaging effect of γ-irradiation persisted mainly at absorbed doses of 5.2 Gy. A detailed examination of root growth inhibition in the time interval from 1 to 6 days of the experiment allowed us to determine that a sharp inhibition of root growth began on day 4 at absorbed doses of 2.5–10.7 Gy, and at the same time a decrease in proliferative activity in the apical meristem of the root was observed. The results of a factor analysis of the experiment on the dynamics of inhibition of primary root length and mitotic index after irradiation are presented.

Imperfection of radioactive waste storage technologies in the initial period of Mayak Production Association operation in 1950s led to a long-term radioactive contamination of the vast territories of the Southern and Middle Urals in Russia. In 2024, it was 30 years since the beginning of the collaborative studies of Russian and American scientists in the framework of the Project 1.1 performed under the aegis of the Joint Coordinating Committee for Radiation Effects Research. A number of science and technology tasks arise while assessing the individual exposure doses for the members of epidemiological cohorts, viz. Techa River Cohort, EURT Cohort, Cohort of the Exposed Population Offspring, and Cohort of Southern Urals Population Exposed to Radiation (SUPER cohort), the latter being established in recent years. These tasks have been accomplished owing to the collaboration. The paper describes the main tasks and methodology of dosimetric studies in the Southern Urals as well as the most prominent scientific achievements. For instance, development of the dosimetry system to calculate exposure doses for people of different sex and age based on the radionuclide measurement results in human organs and tissues. The participants of the Project 1.1 have received an invaluable experience of conducting joint scientific research. The obtained estimates of the radiogenic risk will ultimately be used in the provision of radiation safety of the population around the globe.

An analysis was performed on the effects of radiation exposure on hydrobionts (phytoplankton, zooplankton, zoobenthos) of a freshwater body — Lake Urus Kul, located in the near zone of the accident at the "Mayak" radiochemical chemical plant — over a period of 50 years after the entry of radionuclides into the lake. The radiation doses received by these organisms during their lifetime were estimated. It was shown that in the lake subjected to radiation exposure, phytoplankton, zooplankton, and macrozoobenthos are characterized by significantly lower diversity and biomass, and large-sized forms that received high doses after the accident at the Mayak Chemical Combine were absent. The replacement of large-sized forms of biota species is most pronounced in macrozoobenthos, where species diversity decreased most significantly — from 12 to 7 species, which allows for consideration of macrozoobenthos as a critical group of aquatic organisms. The intensity of doses on hydrobionts decreased rapidly and reached ecologically tolerable limits 5–10 years after the lake's contamination. The restoration of the ecosystem's structure was occurring rather slowly. This suggests that the ecosystem of the affected lake was pushed back to an earlier stage of succession and the restoration of this water body's ecosystem after a radiation exposure is a long-term process.

The work studied the vertical distribution of Cs-137 in the trunk of Scots pine (Pinus sylvestris L.), grown in the Bryansk region, contaminated with technogenic radionuclides as a result of the Chernobyl accident. The Cs-137 content was measured in samples of bark and wood from a 10-meter section of a model tree with a step of 10 cm using the gamma spectrometric method. The activity concentration of Cs-137 in tree bark varies from 741 to 5362 Bq kg⁻¹, in wood — from 134 to 792 Bq kg⁻¹. The average value transfer factors of Cs-137 from soil to tree bark was 1.9 × 10⁻³ m² kg⁻¹, and to wood — 0.4 × 10⁻³ m² kg⁻¹. It has been established that the vertical distribution of Cs-137 in the bark and wood of a tree represents harmonic oscillations with a period of 1 meter, which are described by the Fourier equation. The distribution of Cs-137 in the bark and wood of a tree has the same characteristics throughout the entire volume of the tree, regardless of its side. The period of oscillations does not correlate with the formation of annual rings and the formation of whorls, which does not exclude the relationship between the distribution of Cs-137 and self-oscillatory processes in the tree, which determine root pressure through the intake and release of water in the root cells.

An assessment of cytogenetic effects in populations of wheatgrass (Agropyron cristatum L.) was carried out at 45 points of site "4A" of the Semipalatinsk test site (Kazakhstan), which did not differ in soil characteristics and heavy metal contamination, but contrasted in the level of radioactive contamination. At site "4A" in 1953–1957 combat radioactive substances were tested. The specific activity of ⁹⁰Sr radionuclide in wheatgrass changed from < 1 × 10² to 9.7 × 10⁵ Bq/kg. It was found that the frequency of aberrant cells increases linearly in the dose range from natural background to 1.4 Gy. The main contribution to the formation of cytogenetic effects in the common wheatgrass is made by double bridges, which confirms the radiation nature of the observed effects.