Contemporary radiation doses to murine rodents inhabiting the most contaminated part of the EURT

Bone marrow dosimetry for mice: exposure from bone-seeking 89,90Sr

Studies of radiobiological effects in murine rodents exposed to internal radiation in the wild or in laboratory experiments require dosimetric support. The main problem of bone marrow (BM) dosimetry for bone-seeking β-emitters is dosimetric modeling, because the bone is a heterogeneous structure with complex microarchitecture. To date, there are several approaches to calculating the absorbed dose in BM, which mostly use rough geometric approximations. Recently, in the framework of studies of people exposed to ⁹⁰Sr in the Urals, a new approach (SPSD) has been developed. The aim of the current study was to test for the first time the possibility of extension of the SPSD approach elaborated for humans to mice. For this, computational phantoms of femur bones of laboratory animals (C57BL/6, C57BL/6 J, BALB/c, BALB/cJ) aged 5-8 weeks (growing) and > 8 weeks (adults) were created. The dose factors DF_Sr-90(BM ← TBV + CBV) to convert the Sr isotope activity concentration in a bone tissue into units of dose rate absorbed in the bone marrow were 1.75 ± 0.42 and 2.57 ± 0.93 μGy day^-1 per Bq g^-1 for growing and adult animals, respectively, while corresponding values for DF_Sr-89(BM ← TBV + CBV) were 1.08 ± 0.27 and 1.66 ± 0.67 μGy day^-1 per Bq g^-1, respectively. These results are about 2.5 times lower than skeleton-average DFs calculated assuming homogenous bone, where source and target coincide. The results of the present study demonstrate the possibility of application of the SPSD approach elaborated for humans to non-human mammals. It is concluded that the study demonstrates the feasibility and appropriateness of application of the SPSD approach elaborated for humans to non-human mammals. This approach opens up new prospects for studying the radiobiological consequences of red bone marrow exposure for both laboratory and wildlife mammals.

Hepatic effects of low-dose rate radiation in natural mouse populations (Apodemus uralensis and Apodemus agrarius): comparative interspecific analysis

Hypothesis: Natural mouse populations in radioactive contamination zone provide adequate information about dose loads and biological effects for 'non-human biota'. The comparative analysis of the responses of different species of mice allows us to reveal the possible variation in the effects of low-dose rate radiation relative to the ecological-physiological and functional-metabolic features of the species.Materials and methods: Objects of study - two sympatric rodent species [pygmy wood mouse (Apodemus uralensis Pallas, 1811) and striped field mouse (Apodemus agrarius Pallas, 1771)] caught on the territory of the East-Ural radioactive trace (EURT). The EURT zone is consequence the Kyshtym accident in South Urals in 1957. Nowadays, the main dose-forming radionuclide is β-emitting ⁹⁰Sr. The individual dose rate of impacted mice caused by internal exposure to ⁹⁰Sr varied from 0.021 to 0.152 mGy/day. The baseline functional-metabolic characteristics of the liver were researched: protein-, lipid-, and glycogen-synthesizing processes; glycolysis; aerobic synthesis of ATP; lipid peroxidation; and the H₂O₂-scavenging enzymatic status; and the functional activity of the genome.Results: The hepatic shifts for impacted populations are amplified with increasing dose rate of irradiation, regardless of which species is considered. But, the response of closely related species of rodents to irradiation is different both in the vector and the level (in A. agrarius sample was 2 time higher than that for A. uralensis).Conclusion: The radiation-induced hepatic shifts in A. uralensis from the EURT area correspond to the chronic response under stressful environmental conditions. The impacted population of A. agrarius can be considered the more reactive species to the radiation burden, demonstrating an acute effect. The interspecies contrast in the radiation response is associated with the original interspecies differences (background rodents' samples in 28 km from the impact study site), and also the degree of residency of the species in the impact plots.

Peculiarities of Hematopoiesis in small rodents from the Chornobyl Exclusion Zone on the background of extreme environment

Radiobiological investigations of natural populations of Myodes glareolus (bank vole) from the Chornobyl Exclusion Zone, namely within a highly radioactive site of the Red Forest were carried out. The complex of hematological and cytogenetic parameters of the bank voles inhabiting the contaminated site was studied before the site was flooded, in 2012, and after it drained, in 2015. A significant increase in micronucleated polychromatic erythrocytes, alterations in bone marrow and peripheral blood cell counts were observed in the population of 2015 in comparison with the group of 2012 and animals from the reference site. It is supposed that prolonged flooding has affected the features of radionuclide contamination of the experimental site as well as population characteristics and resulted in the increase of the genotoxic effects observed in the renewed population of bank voles exposed to chronic radiation.

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.

Hematological indicators in pygmy wood mouse Apodemus uralensis (Muridae, Rodentia) populations as markers of the environmental radiation exposure: East Urals radioactive trace (Russia)

The hematological effects of chronic radiation exposure in males of the pygmy wood mouse (Apodemus uralensis Pall., 1811) from the East Urals radioactive trace (EURT) area were assessed, taking into account population abundance and reproductive status (immature, ripening, and mature yearlings). For this purpose, we analyzed the morpho-functional characteristics of erythrocytes (red cell indices [MCV, MCH, MCHC], red cell count, activity of antioxidant enzymes [GSH-Px, CAT], lipid peroxidation, glycolysis, osmotic resistance, methaemoglobin content) and blood plasma components (free hemoglobin, total lipids, total cholesterol, and glucose) in the background territory and the EURT area; these areas have a density of soil contamination with ⁹⁰Sr of 12,851 and 198 kBq × m^-2, respectively (four and two order of magnitude higher than the background value). The data indicate the "hyperfunctional" state of the erythrocyte, aimed at activation of the gas transport function of blood in the radioactive environment. This, as a consequence, determines the insufficiency of energy supply of the cell defense system necessary to maintain the structural integrity of the membrane. Intensification of membrane lipid peroxidation, reduction of osmotic resistance and GSH-Px activity in red cells, an increase in the degree of intravascular hemolysis, and tendency towards erythropenia indicate the processes of accelerated aging of erythrocytes and their more pronounced destruction in the circulatory bed. The level of the hematological response increased with increasing radiation burden and was more pronounced with a large population size. The interaction effect of "overpopulation" and "radioactive pollution" was observed to a lesser degree for ripening males, and was very small for sexually mature animals. Immature males from the EURT head part with internal whole-body radiation doses of 0.0045-0.35 mGy/day can be considered as the most sensitive group to the factors synergy, including radiation damage and overabundance population.

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.

Heterogeneity of 90Sr radioactive contamination at the head part of the East Ural radioactive trace (EURT)

1: We measured ⁹⁰Sr concentrations and beta particle flux density (BPFD) in 44 soil samples collected from four soil profiles across a central transect on the head of the East Ural Radioactive Trace (EURT). The relationship between BPFD and ⁹⁰Sr concentration of each soil sample can be characterised by a linear regression model; ⁹⁰Sr concentration in the upper 12 cm soil layer can thus be assessed by measuring BPFD in the soil surface. 2: The BPFD on the soil surface was measured at 969 points at seven sites with linear dimensions ranging from 140 × 20 m to 140 × 320 m. The correspondence of ⁹⁰Sr concentration in the 12 cm soil layer with its BPFD value was calculated for each of these seven sites. Eighty (80) % of ⁹⁰Sr concentration measurements in the 12 cm soil layer in each model site differed by a factor of 2.0-5. The variability of ⁹⁰Sr concentration increased significantly in the 12 cm upper soil layer over territories with visual features of landscape disturbance (pits, trenches). The ratio of maximum to minimum concentration of ⁹⁰Sr varied from 6.1 to 6.6 in the 12 cm soil layer over territories without visual features of anthropogenic soil disturbance. 3: The ⁹⁰Sr concentration was measured in the skeletons of 34 juvenile Microtus oeconomus individuals weighing less than 12.5 g and trapped at the four model sites in July. The assessment of ⁹⁰Sr concentration in the 12 cm soil layer was conducted for each point where an animal was trapped. The relationship between ⁹⁰Sr concentration in soil and in the skeleton was characterised by a linear regression model with a determination coefficient of 0.51. 4: The concentration ratio for ⁹⁰Sr from soil to skeleton (CR_{skeleton-soil}) was 2.0 ± 0.1 for M. oeconomus over the territory of the EURT, which is consistent with the minimum value of the same CR_{skeleton-soil} for M. oeconomus from the Chernobyl area (Chesser et al., 2000).

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.