Vol 63, No 1 (2023)

A review of two reports is devoted to the problem of the significance of excess relative risks (ERR) per 1 Gy/Sv for mortality from diseases of the circulatory system for various exposed groups from the standpoint of epidemiology and in terms of the effects of low doses of radiation. Report 1 provides an overview of reviews and meta-analyses, together with key studies, on this topic. In most sources, 2005–2021 (publications by M.P. Little with co-workers, and others) reveals an ideological bias towards the effects of low doses of radiation (noted in the titles or summaries of almost all papers), and often there was a lack of understanding about the upper limit of this range accepted by international organizations for low LET radiation (up to 0.1 Gy according to UNSCEAR, ICRP, BEIR, etc.). In selected M.P. Little and co-authors sources for reviews and meta-analyses observed both absurd ERR values per 1 Gy and incorrect recalculations of the risk estimated in the originals at 0.1 Gy. Examples of the incorrectness of such estimations are presented, since ERR per 1 Gy calculated for ranges of lower doses may differ from those for high dose ranges by many times, and this is a systemic phenomenon, despite all the declarations of a linear non-threshold concept. Selection of sources for meta-analyses used by M.P. Little and other authors (2010–2020) violates the principles of homogeneity (groups with radiotherapy (including children with tinea capitis) are combined with miners, liquidators of the Chernobyl accident, etc.), representing an illustration of a meme of critics of meta-analytical approaches (“combination of apples and oranges”). The values of ERR per 1 Gy obtained as a result of meta-analyses for diseases of the circulatory system in general and for their individual types according to epidemiological risk scales (R.R. Monson scale, 1980; 1990) are either insignificant (ERR = 0–0.2), or, rarely, located on the border of weak associations (ERR = 0.2–0.5). An analysis of data from reviews and meta-analyses on the topic did not reveal sources that investigated effects limited to low dose ranges. In almost all cases, with some exceptions (miners with radon exposure, cohorts with absurd risks, etc.), the upper limit of the range for groups in the samples was either medium (0.1–1 Gy) or high (>1 Gy). ) doses. An analysis of almost all publications on the topic of Mayak employees (T.V. Azizova with co-workers; 2010–2018; 31 sources) showed a lack of risk studies for groups with low doses of external exposure (up to 0.1 Gy), with the exception of works from 2014 and 2018, in which either reverse or weak effects were established in the absence of dose dependence. Thus, no samples in reviews and meta-analyses, as well as data for Mayak PA, provide material on the correspon-ding effect of low doses, despite the prevailing general idea of its “proof”. It was concluded that one should adhere to the statement of international organizations (USCEAR, ICRP, NCRP, BEIR, etc.) that the threshold for increasing mortality from diseases of the circulatory system is not less than 0.5 Gy, and then raise the issue of their radiation attribution for low doses impractical.

Computer simulations of the DNA damage are widely used due to their large application area. The computational methods to predict DNA breaks are based on molecular concepts about the formation of breaks, the geometric structure of DNA, as well as information about the distribution of absorbed energy in a DNA mo-lecule. Since the calculations use different postulates and algorithms, it is often difficult to make intercompa-rison between theoretical results in the literature. Due to the spread of experimental data on DNA breaks, the determination of parameters of DNA lesion models from the data is not straightforward. In this paper, a comparative analysis of two basic models of DNA structure, molecular and enlarged subvolume, various schemes for the formation of single- and double-strand DNA breaks, as well as different classifications of the break complexity after irradiation with protons and α-particles is performed. Numerical results on initial radiation-induced DNA damage due to direct and quasi-direct action demonstrate the dependence on variation of model parameters. The parameter values where the two models agree or differ are discussed.

The objective of the paper was to study the association between single nucleotide polymorphisms of genes involved in the cell cycle control (ATM rs664677, MDM2 rs2279744, CDKN1A rs1801270) and apoptosis (BCL-2 rs2279115, BAX rs4645878, TNFα rs361525) and the risk of solid cancer development in persons of different ethnicity exposed to chronic radiation. The study included 915 residents of the Techa riverside settlements belonging to two ethnic groups (Slavs and Turks) who were affected by chronic low dose rate exposure in the low to and medium dose range. 310 persons out of them had solid cancers. Genotyping of polymorphic regions of genes regulating cell cycle and apoptosis was performed by real-time PCR method. The study showed that the rs2279744*C allele of the MDM2 gene was associated with an increased risk of cancer development (OR = 2.29; 95% CI 1.23–4.28; p = 0.007), while the rs1801270*A allele of the CDKN1A gene showed a protective effect against cancer development (OR = 0.55; 95% CI 0.35–0.85; p = 0.01) in exposed individuals of the Turkic ethnic group. The combined effect of the identified polymorphisms and soft tissue exposure dose statistically significantly modifies the risk of cancer development in chronically exposed persons of the Turkic ethnic group, with the greatest contribution being made by the carriage of the rs2279744*C allele of the MDM2 gene.

The work is dedicated to the analysis of thermal sensitivity and efficiency of thermosensitization to γ-radiation of three cell lines of breast cancer of different molecular subtypes. It has been established that the cells of the studied lines differ in the sensitivity to hyperthermia and, as a result, in the effectiveness of thermoradiosensitization, which raises the question of finding criteria for assessing the rationale of using hyperthermia in each specific case. It has been shown that the level of heat-responsive expression of HSP70 gene and also the level of cell genomic instability can serve as such criteria. It was found that the efficiency of thermoradiosensitization is significantly higher in MDA-MB-231 cells compared to the cells of other studied lines. The data obtained suggest that the use of hyperthermia as a radiotherapy-sensitizing co-treatment may be particularly promising toward triple negative breast cancer.

The effect of nanosecond repetitively pulsed microwave radiation (RPM, 50–4000 pulses, pulse repetition rate of 13 Hz, peak power flux density of 140 W/cm², carrier frequency of 10 GHz) on the stimulation of me-senchymal stem cells (MSC) proliferation was studied. The effect of exposure was assessed by the change in the number of cells in the culture after a single irradiation with a different number of pulses. The most pronounced effect exerted by the impact with 100 and 50 pulses, and the effect is realized with a maximum speed after 24 hours.

An overview of data on thorium concentrations in terrestrial animals, as well as freshwater organisms is presented. Concentrations of ²³²Th in both animals and fish vary widely, reflecting environmental thorium concentrations. Thorium concentrations in the regions with a normal thorium background in animal tissues were in a range from 0.9 × 10^–4 to 2.1 × 10^–2 Bq/kg, and from 3.1 × 10^–2 to 1.4 × 10^–1 Bq/ kg in the areas with high thorium concentrations in the soil. Significantly higher values were observed in wild animals’ tissues. The highest ²³²Th concentrations were found to be in the skeleton, followed by lungs, kidneys, liver and finally muscles. It has been shown that thorium accumulation is higher in species occupying a higher position in the trophic chains. In areas with normal thorium background, the concentration of ²³²Th in fish can reach 1.0 × 10^–1 Bq/kg (fresh mass), and in areas of high thorium background this value can be up to 100 times higher. The obtained results show the importance of study on the thorium transfer along the food chains and the need to consider observed regularities when assessing the consequences of radioactive contamination of the environment.

The paper presents data on the concentration of tritium in the water of the river Pyshma, which is under the influence of the Beloyarsk NPP named after Kurchatov, and drinking water of settlements located in the coastal zone of the river. It was found that the content of radionuclide in the water of the river at a distance of up to 400 km below the dam of the Beloyarsk reservoir varies within 13–26 Bq/l and significantly decreases along the course of the river. In the coastal part of the river, above-background tritium pollution enters the drinking water of wells and chinks. It is shown that in water samples from wells, the tritium concentration significantly decreases with increasing depth and distance from the dam of the Beloyarsk reservoir; in the water of private wells, such a relationship was not reliably recorded. The concentration levels of tritium in the spring water of 7 settlements located along the Pyshma river at different distances from the dam of the Beloyarsk re-servoir, almost 2 times higher than in the water of deep chinks, have similar values and do not depend on the distance.

The paper presents the data on the content of plutonium (^239,240Pu) in the muscles of the Baikal grayling Thymallus baicalensis, inhabiting the middle reaches of the Yenisei River in the vicinity of the radioactive discharge point of the Mining and Chemical Combine, in 2011–2019. The content of ^239,240Pu in grayling muscles varied within 7–32 mBq/kg dry weight. Highest value was recorded in 2019, a year after the increase in the volume of controlled plutonium discharges. The ratio of activity concentrations ^239,240Pu/¹³⁷Cs in grayling muscles compared to the similar ratio in other hydrobionts of the Yenisei indicates a lower bioavailability of plutonium for fish.