Vol 64, No 5 (2024)

In the second part of the review on estimates of excess relative risks (ERR) per 1 Gy/Sv for mortality from diseases of the circulatory system (ICD-9: 390–459; ICD-10: I00–I99) after irradiation, a combined analysis and meta-analysis was carried out for nuclear industry workers of various countries. The completeness of the sample at the end of 2021 appeared to be exhaustive. The combined analysis of the data consisted in assessing the average for the sample after eliminating outliers from it; ERR per 1 Gy/Sv was 0.20 (95% CI: 0.11; 0.30). The meta-analysis was performed on the full sample, without removing outliers. Some heterogeneity was identified, so a Random effect model was used for the meta-analysis, and the ERR per 1 Gy/Sv was 0.11 (95% CI: 0.01; 0.22). The mean value of ERR per 1 Gy/Sv obtained here only for nuclear industry workers, as well as the result of the meta-analysis, did not differ much from the data of M.P. Little and co-workers (2010–2016) for heterogeneous samples from different populations. At the same time, the data for ‘Mayak’ PA on mortality from circulatory pathologies in general, and not for their individual types, indicate lower risks for external exposure (Azizova TV et al., 2018): ERR per 1 Gy/Sv was 0.04 (95% CI: –0.00; 0.09). All listed risks from the point of view of classical epidemiology, when using the common Monson scale for relative risks (RR), should be considered either ignorable (RR = = 1.0–1.2) or weak (RR = 1.2–1.5). An estimation of the absolute risk of mortality from circulatory pathologies for a hypothetical group of 100,000 nuclear workers who each accumulated a dose of 1 Gy, based on data on the baseline mortality of men from these pathologies for the United States, showed an increase of 1400 deaths over 20 years of employment. However, recalculation for the real average dose accumulated by workers in different countries (31.1 mSv; Koterov A.N. et al., 2021) revealed an insignificant increase in mortality at 0.6% of the baseline level, which risk cannot be taken into account for such multifactorial pathologies. The results obtained in the second part of the presented study: a) reinforce the conclusion made in Report 1 about the advisability of adhering to the dose threshold of 0.5 Gy for circulatory pathologies mortality established by UNSCEAR, ICRP, NCRP, BEIR, etc.; b) they indicate very low, negligible risks of mortality from circulatory pathologies attributed to the radiation factor for nuclear industry workers in recent decades and for most of those even in the previous period; c) they show that for the real activity and health protection of the majority of workers in the nuclear industry, the determination/calculation of the radiation risks of mortality from circulatory pathologies is of an exclusively theoretical nature. These conclusions are important, among other things, for expert advices on establishing the causality of occupational pathologies in nuclear industry workers.

It is known that ionizing radiation can damage the genetic apparatus of a cell not only through direct exposure, but also through the induction of oxidative stress. Thus, oxidation of guanine (G) nitrogenous base by oxidative stress products can result in G:C>T:A and G:C>C:G type transversions in the tumor growth suppressor gene TR53. Somatic and inherited variants of the TP53 gene, in its turn, are of great importance in the development of malignant neoplasms. Therefore, the aim of the study was to analyze the G:C>T:A and G:C>C:G transversions of the TP53 gene in peripheral blood cells of individuals affected by chronic low-dose rate exposure. The paper presents the results of the analysis of the spectrum of TP53 gene sequence variants based on G:C>T:A and G:C>C:G transversions in peripheral blood cells of the Techa riverside residents of the Chelyabinsk and Kurgan Oblasts, affected by chronic low-dose rate exposure in the 1950s. The range of individual values of the accumulated absorbed dose to red bone marrow due to external gamma radiation and ⁹⁰Sr ranged from 2.1 to 2742.0 mGy (mean value – 605.4 ± 191.9 mGy (M ± SE)). As a result of the study, 7 different variants of the TP53 gene based on the G:C>T:A and G:C>C:G transversions, which are single nucleotide replacements, were identified in the examined individuals. All detected variants were present in the IARC TP53 Database and had no clinical significance as “pathogenic” or “probably pathogenic”. Differences in the frequencies of carriers of detected TP53 gene variants between the comparison group and the main group did not reach a statistically significant level/ were not statistically significant.

The study of the complex of EPR characteristics of metabolic reactions involving free radicals and paramagnetic metal complexes revealed a pronounced dose-dependent dynamic SOS response of the most important life support systems of the body under General gamma irradiation. Studies in actively proliferating tissues of the ribonucleotide reductase enzyme using low-temperature EPR spectroscopy and parallel cytogenetic analysis of tissues and blood indicate initial radiation-induced trigger events that initiate the generation of DNA damage in hematopoietic organs. In the mechanism of the anti-radiation effect of radioprotectors, an increase in the activity of ribonucleotide reductase and the induction of deoxyribonucleotide synthesis is necessary for effective damage repair and DNA synthesis in cells of radiosensitive organs. The use of EPR biomarkers allowed us to justify the doses and modes of administration of radioprotectors to obtain optimal radio protection.

Early phenomenon on the potentiation of radioprotective properties of aminothiols (cystamine) during repeated application in the first 7 h of drug’s after-effect by increasing their activity by 2 times was discovered (B.I. Davydov, 1971, M.V. Vasin, V.V. Antipov, 1972). A hypothesis has been proposed to explain this phenomenon. The mechanism of radioprotective properties cystamine is associated with partial neutralization of oxygen effect with the development of reductive stress in the cell, which does not end after the cessation of protective effect of radioprotector. In the body, negative feedback mechanisms are implemented at the cell, which prevent full implementation of naked consequences of reductive stress. In it, the transcription factor HIF-1 plays a key role, which enhances the production of ATP due to glycolysis and, thereby, reduces the burden on oxidative phosphorylation processes under conditions of acute hypoxia with repeated use of cystamine over the first 7 h after the cessation of its radioprotective activity. There is an increase in metabolic shifts in the body with the development of deep hypothermia in animals up to 29°C rectal temperature which can lead to depletion of these restrictive mechanisms and, thereby allowing aminothiol to fully exhibit its protective properties without excluding the increase in its toxicity. In addition, this contributes to a more complete implementation of post-radiation repair of DNA. These processes contribute to a more complete realization of the affected repair of DNA breaks by providing more time for it in conditions of longer hypothermia and mitotic blockade under the action of cystamine.

The lower threshold values of the chronic exposure rate, above which negative radiobiological effects appear, are assessed and compared for mammals with low and high natural life expectancy. Dataset has been prepared, containing information on the observed radiobiological effects of chronic irradiation in mammals, depending on the dose rate. The dataset includes 118 records for mammals with high life expectancy and 92 records for mammals with low life expectancy. Data were analyzed with the nonparametric statistics. The lower threshold for deterministic radiation effects of chronic exposure for long-lived mammals is 0,1 mGy/day, with a 95% confidence interval 0.04 – 0.3 mGy/day. For mammals with a short natural life cycle, this threshold value is one order of magnitude higher – 1 mGy/day, with a 95% confidence interval of 0.5–1.1 mGy/day. It is concluded that the quantitative radiation safety criteria for long-lived and short-lived mammal species differ, which should be taken into account when assessing the ecological risk of radioactive contamination of the environment.

“Dose–response“ and “radioactivity level in the body–response” relationships that were set earlier for three types of chromosomal aberrations (dicentrics, stable aberrations and total aberrations) enabled the development of the biodosimetry system. This system allows the estimation of individual doses and ²³⁹Pu activity body levels in Mayak PA workers due to acute or chronic inhalation of plutonium compounds that are characterised by low transportability. The relative error of individual radiation doses absorbed in the lungs estimated by the biodosimetry system (based on stable CA and total CA) varied between 5.4 and 83.6% (with an average of 39.8%). On the other hand, the relative error in the individual estimate of ²³⁹Pu activity in the body due to chronic exposure similarly varied within a relatively narrow range: from 6.2 to 51.6% (the average of 42.8%). The relative uncertainty of the dose estimate for acute plutonium exposure averaged around 35%.

Magnetic field is able to change the biological activity of drugs, which can be used in medicine. Literature data on the increase in biological activity of prepared drugs under the influence of pulsed magnetic fields immediately before their administration have not been found. This article presents data on the increase in antibacterial activity of benzylpenicillin sodium salt after its treatment with pulsed magnetic field. The aim of the work is to investigate the reasons for the increase in biological activity of benzylpenicillin, to show the changes that occur in the molecule under the influence of a pulsed magnetic field. Exposure to magnetic field was carried out on powdered antibiotic on magnetic-pulse unit with magnetic field strength H = (0.09÷0.82) × 10⁶ A/m. The pulse shape was a damped sinusoid with frequency response f = 40 kHz and f = 51 kHz. Experimental methods of NMR-spectroscopy and IR-Fourier-spectroscopy were used in the studies. The shift in the value of chemical shifts (δ_H) and spin-spin interaction constants (²J_HH) of the signals of methylene protons of the benzyl substituent as a result of the magnetic field was found. The changes in the absorption bands of the N–H and C=O bonds of the amide grouping and the carbonyl group of the lactam cycle were detected by FTIR spectroscopy. The obtained spectral data allow us to conclude that the geometry of the benzylpenicillin sodium salt molecule in the amide fragment has changed under the influence of a pulsed magnetic field, which is probably the reason for the increase in antibacterial activity of the antibiotic.

The transformation of the hydrological regime of floodplains due to climate change and anthropogenic impact on water redistribution processes within natural landscapes can significantly impact the bioavailability of long-lived radioactive isotopes of cesium and strontium. A laboratory experiment demonstrated that varying the moisture content of alluvial soil within 40–100% from its full water-holding capacity leads to the redistribution of ¹³⁷Cs and ⁹⁰Sr between different chemical forms. Soil saturation with water increases the proportion of water-soluble ¹³⁷Cs, while the proportion of water-soluble ⁹⁰Sr decreases. The ion-exchangeable form of ¹³⁷Cs remains unaffected by soil moisture. The behavior of the ion-exchangeable form of ⁹⁰Sr in response to changes in soil moisture is dependent on soil characteristics: a significant increase in the proportion of ⁹⁰Sr was observed in sod-gley soil developed on sandy alluvium as soil moisture increased; however, this phenomenon was not observed in sod-gleyed soil developed on loamy alluvium. The proportion of ¹³⁷Cs extracted by sodium tetraphenylborate increases when alluvial soils are saturated with water. Similarly, the mobile form of ⁹⁰Sr behaves in the same manner, but when soil moisture reaches 100% of its full water-holding capacity in sod-gley soil, a sharp decrease in the proportion of the mobile form of this radionuclide is observed. Overall, there is a trend towards increased proportions of bioavailable forms of ¹³⁷Cs and ⁹⁰Sr in alluvial soils with increased moisture content, although the pecularities and magnitude of this phenomenon depend on the specific soil characteristics.

The study outlines the various factors that determine the impact of the accident at the “Mayak” chemical plant on agriculture as well as the unique characteristics of the radiation levels in the affected region. In order to guarantee preparedness for any operational response, it is crucial to establish an efficient management structure that can make swift and well-informed decisions. Additionally, having access to emergency plans, prognostic calculation tools, and suitable protocols for handling emergencies are equally essential. These crucial elements are all necessary to ensure that any unexpected event can be addressed promptly and effectively. An analysis of protective measures taken at various times after the Kyshtym accident has been carried out. The paper presents the formulated key takeaways from the Kyshtym accident that pertain to emergency preparedness, the execution of organizational and agrochemical protective measures in agricultural production, and the utilization of accumulated knowledge in both science and practical applications.