Forests in the East Ural Radioactive Trace: structure, spatial distribution, and the 90Sr inventory 63 years after the Kyshtym accident.

On 29 September 1957, the so-called Kyshtym accident occurred at the USSR's first nuclear weapons plutonium production facility. The East Ural State Reserve (EUSR) was established in the most contaminated part of the radioactive trace, where a substantial part of the forests died in the first years after the accident. The purpose of our study was to evaluate the natural restoration of forests and to verify and update the taxonomic parameters that characterize the current state of forest stands in the EUSR. Data on the forest inventory of 2003 and results of our research of 2020 performed by the same methods on 84 randomly selected sites served as the basis for this work. We developed models to approximate growth dynamics and then updated the 2003 taxation-related forest data for the entire EUSR. According to these models and ArcGIS construction of new data, forest-covered lands make up 55.8% of the whole EUSR territory. The proportion of birch forests in the forest-covered lands is 91.9%; 60.7% of wood resources are located in mature and overmature (81-120-year-old) birch forests. The total timber stock in the EUSR is > 1385 thousand tons. It was revealed that ~ 4.2 × 1014 Bq of 90Sr is situated within the EUSR. The main stock of 90Sr is found in soils. The 90Sr stock in the stands is ~ 1.6-3.0% of the total content in the forests. Only a part of the EUSR forest stands can be used for practical applications.

Accumulation of 90SR by Betula pendula within the East Ural Radioactive Trace zone.

This study was conducted in 2010-2020 at the head of the East Ural Radioactive Trace (EURT), which was formed in 1957 as a result of the Kyshtym accident at the Mayak Production Association. The main contaminant in this zone is the long-lived radionuclide Strontium-90 (90Sr). Secondary forests dominated by silver birch (Betula pendula) occupy 45% of the EURT area. Concentration of 90Sr in birch leaves and small branches was higher than that in the trunks. The 90Sr content in birch sapwood varied slightly in the radial direction and did not depend on tree age. This was due to the dynamic equilibrium of the migration processes responsible for the accumulation and horizontal transfer of 90Sr. The 90Sr concentration increases in false heartwood, which is formed as a result of the secondary metabolism of dying parenchyma in the inner part of sapwood and is characterised by a high content of ash elements. The concentration of radionuclides in the aboveground organs of birch increased and the aggregated transfer factors (Tag) decreased with an increase in the soil contamination density, in accordance with the power function. The reasons for these patterns are also discussed.

Effects of environmental low-dose irradiation on functional-metabolic organ responses in a natural mouse population (Apodemus agrarius Pallas, 1771) within the East Urals Radioactive Trace (EURT) area, Russia.

HYPOTHESIS: The level of radiation-induced functional metabolic reactivity can differ among organs (spleen, liver and myocardium) and reproductive-sexual groups (breeding and non-breeding under-yearlings: females and males). MATERIALS AND METHODS: We analyzed Apodemus agrarius individuals captured in the zone of the East Urals Radioactive Trace (EURT, Russia). In this area, concentrations are 90Sr and 137Cs at 10,000 and 1000 Bq/kg, respectively, in a layer of soil not deeper than 10 cm. Comparative analysis was based on six biochemical parameters including the glycolysis level, peroxidation of lipids, H2O2-oxidoreductase status and concentrations of protein, DNA and RNA in tissues. RESULTS: External and internal doses of 137Cs and 90Sr for A. agrarius varied by an order of magnitude, from 0.013 to 0.177 mGy/d. The level of radiation exposure was found to not differ among females but it differed between the two male reproductive groups (breeding < non-breeding under-yearlings). Sexually mature males received a significantly lower dose than females. An increase in the dose rate correlated with an increase in all biochemical indicators, thus indicating high level of tissue metabolic functions. The reproductive status of females did not affect their radiation-induced organ response rate, whereas the response to radiation of breeding males was more than 1.5-fold higher than that of non-breeding males and 2-fold higher than that of females. CONCLUSIONS: We believe that the variation of the dose load is due to migration processes: breeding males are more likely to migrate than females and therefore have less contact with radionuclides. The higher the response to radiation of breeding males can be explained by a hormonal factor: testosterone causes radiosensitivity. The reactivity of the tissues examined (myocardium < liver < spleen) develops apparently in accordance with the degree of their 'staticity' in accordance with the law of radiosensitivity of Bergonié and Tribondeau.

Genetic structure of a widespread alpine shrub Rhododendron aureum (Ericaceae) across East Asia.

The vast territory of East Asia, including southwestern Beringia, is considered to have been almost ice free during the Pleistocene. Cold-resistant flora may have persisted in this region expanding or contracting its range during the climate cooling. Only a few plant genera have been studied with a sampling area across their entire geographic range in East Asia; therefore, the understanding of the biogeographic history of alpine flora in this region remains limited. In the present study, genetic variation and population structure in 21 populations of the alpine shrub Rhododendron aureum across its range in East Asia were assessed using 18 microsatellite loci. Phylogenetic analyses revealed three main genetic groups: Siberia, Northeast, and North Pacific. According to the geographical pattern of genetic diversity, the North Pacific group includes populations from Kamchatka, south of Russian Far East, and territories close to central Japan. This group is the most diverse and likely diverged earlier than the Siberia and Northeast groups. Ecological niche modeling predicts range expansion of this species during the period of cooling and, together with demographic history, suggests that the divergence between the three main genetic groups predated the Last Glacial Maximum. Similar to other cold-resistant species such as Larix sibirica and Juniperus communis, the pattern of genetic diversity of R. aureum supports the survival of the species at high latitudes during the Pleistocene with limited contribution of the southern populations to expansion of the species range to the Northeast region and Siberia.

Structural-functional modifications of the liver to chronic radioactive exposure in pygmy wood mouse (Apodemus uralensis) within the East-Urals Radioactive Trace.

The hepatic parameters (contents of glycogen, total lipids, nuclear and cytoplasmic proteins, DNA and RNA, fructose-6-phosphate, water, lipid peroxidation products, as well as activities of succinate dehydrogenase and glucose phosphate isomerase), radiometric data, and the relative population abundance of the pygmy wood mouse (Apodemus uralensis Pall., 1811) inhabiting natural (Middle Urals, Southern Urals, and Trans-Urals) areas and radioactivity territory (the EURT zone after of the Kyshtym accident in the South Urals in 1957) were analysed. Structural-functional modifications of the liver in A. uralensis from the EURT area are presented, taking into account irradiation power by dose-forming radionuclides (external and internal exposure to 137Cs and 90Sr), population size, and reproductive status (sexually immature and sexually mature yearlings, representing different ontogenetic patterns). The sexually immature mice from the EURT area can be considered to be the more sensitive (reactive) intrapopulation group to synergistic factors, such as radiation burden and population overabundance. The extent of structural-functional hepatic modification under current conditions of radionuclide exposure, in addition to the 60 year long effect of radioactive contamination in the EURT, can exceed the level of natural (geographic) variation observed in this species in the Urals region, which points to a long term evolutionary-ecological process.

East Urals Radioactive Trace: Dose-dependent functional-metabolic effects in the myocardium of the pygmy wood mouse (Apodemus uralensis) taking into account population size.

The population dynamics, radiometric data and biochemical parameters (concentrations of total lipids, proteins, DNA and RNA, activity of succinate dehydrogenase, glucose phosphate isomerase and catalase, as well as lipid peroxidation level) in the myocardium of the pygmy wood mouse (Apodemus uralensis Pall., 1811) inhabiting the area of the East Urals Radioactive Trace (EURT) were analyzed. The functional-metabolic radiation effects as a result external and internal exposure to 137Cs and 90Sr (unweighted total dose rate 0.04-0.5 mGy/day) are characterized by a reduction in lipid catabolism, mitochondrial oxidation and antioxidant defense, as well as the activation of anaerobic glycolysis as well as the protein-synthesizing and genetic apparatus. The data indicate the low efficiency of cell energy production and allow us to state that compensatory myocardial hypertrophy can improve myocardial contractile function. The level of the functional-metabolic response in pygmy wood mice in the EURT area increased with increasing whole-body radiation dose rate and was more pronounced with a large pygmy wood mouse population size. The harmful effects (cardiac decompensation stage) of synergies resulting from non-radiation and radiation factors manifest after population abundance above 30 ind./100 trap-day and a radiation burden above 0.1 mGy/day.

Stress-associated radiation effects in pygmy wood mouse Apodemus uralensis (Muridae, Rodentia) populations from the East-Urals Radioactive Trace.

This work is based on the comparative analysis of data obtained in the course of monitoring pygmy wood mouse populations (Apodemus uralensis Pallas, 1811) in the East-Urals Radioactive Trace (EURT) area and background territories. The effect of population size and its interaction with the radioactivity on biochemical parameters in the spleen and adrenal glands was studied. The concentrations of total lipids, proteins, DNA and RNA, activity of glucose-6-phosphate isomerase and catalase as well as the level of lipid peroxidation (LPO) were evaluated. The functional-metabolic shifts seen with large population sizes were characterized by delipidisation of adrenocortical cells, increased LPO as the main mechanism for steroidogenesis, growth of the protein components of the adrenal glands to maintain their hyperfunction, as well as immunosuppression associated with the restriction of carbohydrates providing splenocytes, reduction of DNA synthesis, and the development of a pro-/antioxidant imbalance. Reactivity of the neuroendocrine and hematopoietic systems of animals experiencing a high population density was higher in the EURT zone compared with the reference group. This difference can be explained by the additional stress from the chronic radiation exposure. The level of LPO, catalase activity, and DNA/protein ratio in the spleen and the total protein content in the adrenal glands were the most sensitive to the interaction of population size and radiation exposure. The harmful effect (distress) of the interaction of non-radiation and radiation factors can manifest when there is a population abundance above 30 ind./100 trap-day and a radiation burden which exceeds the lower boundary of the Derived Consideration Reference Levels, which is above 0.1 mGy/day.