Cytogenetic consequences of chronic irradiation in rodent populations inhabiting the Eastern Ural Radioactive Trace zone

Chromosome instability in bone-marrow cells and ⁹⁰Sr accumulation in the bone tissue are studied in rodents (Apodemus (Sylvaemus) uralensis Pall., 1811 and Apodemus agrarius Pall., 1771)* inhabiting the Eastern Ural Radioactive Trace (EURT) zone (Kyshtym radiation accident 1957) and adjacent areas of the Urals. Intensive mutagenic process in both species from impact plots (soil pollution by ⁹⁰Sr, 2322–16690 kBq/m²) is found. Significant positive correlation of the frequency of aberrant cells and the concentration of ⁹⁰Sr is shown. Possible causes of the lack of resistance to long-term mutagenic factors (over 100 generations in the 50 years since the accident), such as migration of animals and the specific configuration of the EURT zone (an extended narrow territory with a sharply falling gradient of radionuclide pollution), which considerably decrease the probability that certain changes will be fixed and inherited in a series of generations of rodents, are discussed.     

On the problem of radioadaptation in small mammals (ecological specialization of species, radioresistance, hemopoiesis, immunity)

The data illustrating ambivalent nature of radioresistance of rodents having different ecological specialization: wood mice (Apodemus uralensis Pallas 1811) and mole-voles (Ellobius talpinus Pallas 1770) to acute (laboratory experiment) and chronic (long-term inhabiting the East Ural Radioactive Trace - EURT) radiation action are presented. These species are greatly distinguished by a way of life, a migratory activity, an average life span etc. Numerous immunological, hematological disturbances were found in more radioresistant wood mice inhabiting in radioactively-polluted biogeocenosis (density of pollution 90Sr - 18.5 MBq/m2 = 500 Ci/km2). On the contrary there are no pathological shifts in more radiosensitive mole-voles from the EURT zone (density of pollution 90Sr - 37 MBq/m2 = 1000 Ci/km2). Comparative analysis of the hematological and immunological parameters and absorbed dose loads in rodents from radiocontaminated environment testify about the possibility of radioadaptation in a series of generations in Ellobius talpinus Pall. The leading role in development of radioadaptation of mole-voles belongs to ecophysiological peculiarities of the species.     

Chromosomal instability in rodents from the EURT territory: interspecies comparison

The common vole (Microtus arvalis) and the mole vole (Ellobius talpinus) were trapped in the Eastern Urals Reserve (initial soil pollution 500-1000 Ci/km2) where many dozens of generations came to pass after the 1957 accident in the plant "Mayak" and in the Middle and South Urals and Transurals localities with global level of the 90Sr pollution. At present the average internal dose rate from 90Sr was 0.413 mGy/day in M. arvalis and 0.985 mGy/day in E. talpinus. The total accumulated doses from external and internal sources were 0.4-0.5 Gy per year. Frequencies of cell with chromosome aberrations and gaps and rates of aneuploidy and polyploidy were analyzed. In the common vole from EURT, the frequency of aberrant cells was significantly higher (4.57%) than in three control populations (0.44-0.86%). In the mole vole, all the cytogenetic parameters did not exceed the control ones. Absence of the genomic response in E. talpinus could be caused by the protective activity of melanin-related metabolites or by heritable factors, which may have arisen as a result of mutagenic pressure and have spread in the population in question both by selection and genetic drift, due to considerable isolation of local demes of E. talpinus.     

Analysis of microsatellite DNA in rodents from Eastern Urals Radioactive Trace zone and contiguous territories

The variability of four microsatellite loci of rodents, caught from the head part of Eastern Urals Radioactive Trace (EURT), along with the rodents inhabiting contiguous zone with background radiation level and distant reference territory, was analyzed for the first time. Differences in the parameters of genetic diversity between northern red-backed voles from the EURT zone and from the reference population were detected. An increase in some indices of genetic diversity in animals from a contiguous to the EURT zone was found; this is probably associated with animal migration and configuration of the area of pollution. A transfer of radiation-induced effects to the contiguous territories and a decrease in the possibility of fixation of adaptations in a series of generations of mobile rodent species in the area of local radioactive pollution are consequences of migrations. The results of the study make it possible to recommend microsatellite markers for the analysis of radiation-induced effects in rodents as model objects of radioecological monitoring.     

Reconstruction of radionuclide intakes for the residents of East Urals Radioactive Trace (1957–2011)

The East Urals Radioactive Trace (EURT) was formed after a chemical explosion in the radioactive waste-storage facility of the Mayak Production Association in 1957 (Southern Urals, Russia) and resulted in an activity dispersion of 7.4?×?10¹⁶ Bq into the atmosphere. Internal exposure due to ingestion of radionuclides with local foodstuffs was the main factor of public exposure at the EURT. The EURT cohort, combining residents of most contaminated settlements, was formed for epidemiological study at the Urals Research Center for Radiation Medicine, Russia (URCRM). For the purpose of improvement of radionuclide intake estimates for cohort members, the following data sets collected in URCRM were used: (1) Total β-activity and radiochemical measurements of ⁹⁰Sr in local foodstuffs over all of the period of interest (1958–2011; n?=?2200), which were used for relative ⁹⁰Sr intake estimations. (2) ⁹⁰Sr measurements in human bones and whole body (n?=?338); these data were used for average ⁹⁰Sr intake derivations using an age- and gender-dependent Sr-biokinetic model. Non-strontium radionuclide intakes were evaluated on the basis of ⁹⁰Sr intake data and the radionuclide composition of contaminated foodstuffs. Validation of radionuclide intakes during the first years after the accident was first carried out using measurements of the feces β-activity of EURT residents (n?=?148). The comparison of experimental and reconstructed values of feces β-activity shows good agreement. ⁹⁰Sr intakes for residents of settlements evacuated 7–14 days after the accident were also obtained from ⁹⁰Sr measurements in human bone and whole body. The results of radionuclide intake reconstruction will be used to estimate the internal doses for the members of the EURT cohort.     

Radiation dose rates estimation and allozyme variability in the population of the northern red-backed vole (Clethrionomys rutilus) from the East-Ural Radioactive Trace

The paper estimates the external (due to radionuclides accumulated in the soil) and internal (due to incorporated radionuclides) exposure of rodents that live in the head of the East Urals Radioactive Trace (EURT). It is shown that in the last decades the dose rates were lower than the values that lead to a doubling the number of mutations in the allozyme loci in mammals. The variability of the eight allozyme loci in populations of northern red-backed voles from the EURT zone and their neighboring plots, as well as the territories of the Urals and Trans-Urals with background levels of radioactive contamination, are analyzed. No differences in the pattern and frequency of allozymes that would distinguish the EURT samples from a number of other populations of the Urals, were found. In the control sample “Sysert’,” “unique” for the Ural populations of northern red-backed voles, alleles of the loci Got and Sod were marked, conspecific to a closely related species-the bank vole. This fact can be regarded as evidence of recent cross-species hybridization.     

Evaluation of cytophysiological state of testis in forest voles living in the radioactively contaminated areas

We made a cytophysiological analys of testis in Clethrionomus rutilus and Apodemus sylvaticus inhabiting a contaminated area of the East Ural Radioactive Trace (EURT). The study showed that in the norm these species differed in the total number of cells of spermatogenous epithelium, due to interspecific difference. In the sampling plot a concentration of 90Sr in Clethrionomus rutilus was 2 times higher than that in Apodemus sylvaticus. Maximum destructive changes in endocrine and exocrine (seminiferous tubules) section of testis and increased proliferation activity of spermatogenous epithelium were observed in Clethrionomus rutilus.Increased proliferation activity was found as a compensatory-protective reaction which promote the maintenance of the germ cell number. Such changes were not observed in Apodemus sylvaticus.     

Accumulation of 90Sr in the bone tissue of the northern mole vole, living in the head part of the East Ural Radioactive Trace

Deposition of 90Sr in a bone tissue of the northern mole-vole (Ellobius talpinus Pallas, 1770) living in the head part of the East Ural Radioactive Trace (EURT) (density of pollution by 90Sr 37 MBq/m2 - 1000 Ci/km2) was investigated. Features of the rodent are digging (underground) way of life, family organization of settlements and weak migratory activity. Authentic (p < 0.01) interfamily distinctions in concentration 90Sr are revealed on the background of absence of sexual and are features of accumulation the radionuclides inside separate families, thus individual parameters differ in 7 times. It is established, that the level of accumilation of 90Sr is comparable with that in other species of small mammals in this territory. Age inversion of accumulation of 90Sr earlier found out in other species of mammals on the EURT is confirmed.     

The adaptive strategy of rodent populations living in conditions of radioactive and chemical environmental pollution

The comparative analysis of demographic, morphological and physiological processes in mouselike rodents in pollution zones (90Sr + 90Y, 137Cs) on East-Ural radioactive track (EURT) and (Cu + Cd + Pb + Zn + SO2) on a site near copper-smelting factory is carried out. The direct (not mediated) defeat of animals by an irradiation leads to inherited adaptation (density preservation, tolerance increase to pollution, migration decrease and so forth). The mediated defeat of animals at pollution by metals influences animals as a result of degradation of a vegetative cover, reducing a forage reserve, shelters and reproduction places. Population is decreasing, migration is increasing. Hence, population reacts onto direct defeat of animals or on inhabitancy locuses degradation, id est unspecifically, without dependence from the physical and chemical nature of pollution.     

The characteristics of 90Sr accumulation and elimination in residents of the Urals region in the period of 1957-1988

A number of radiation accidents occurred at the "Mayak" plutonium production complex (Southern Urals, Russia) in 1950-60s that resulted in environmental contamination of large territories in the Southern and Middle Urals with long-lived radionuclides (90Sr, 137Cs). The results of long-term radiological monitoring were compiled into special databases at the Urals Research Center for Radiation Medicine, which allow the study of 90Sr behaviour in the environment and its accumulation in the human body. Retrospective analysis of the data on postmortem measurements of 90Sr in bones performed on residents of the Urals region over 1957-1988 were conducted for the first time. A time-dependence of 90Sr accumulation in the human body upon its density in soils was observed. Age and gender characteristics of 90Sr retention in bones were studied. It was shown that the levels of 90Sr in residents of large territories north and north-east of Chelyabinsk region, and of bordering territories of Sverdlovsk region were several times higher than the average values for the Russian Federation. Based on the measurements the direct dependence of 90Sr content in the skeleton on 90Sr density in soils was observed 30 years after the 1957 accident (the so called "Kyshtym accident"). However, for individual settlements this dependence may be weakened as a result of the influence of different biological and social factors. No influence of gender on 90Sr accumulation in the skeleton was found in the study. The analysis of age characteristics of 90Sr accumulation in bone, as influenced by skeleton growth and maturation, showed maximal levels of 90Sr from global fallout to be accumulated in bones of the persons born in 1949-1955.     

The cradle of the Russian radioecology (to the 50th anniversary of the Kyshtym radiation accident)

On September 29, 1957, at a nuclear industry facility (Production Association "Mayak"), there was a large radiation accident resulting in the release of radioactive wastes into the environment and the formation of the East-Urals Radioactive Trail (EURT). Within the EURT and there established in 1958 an Experimental Scientific Research Station (ESRS) which came to be known as alma mater of domestic radioecology, various comprehensive long-term investigations had been carried out. The main results of these 50-year investigations have been summarized for a broad range of problems on radionuclide migration in the natural environment and ionizing radiation effects on biota, as well as problems of environmental protection. In addition to the studies of the in situ behavior of released during the accident anthropogenic radionuclides (primarily 90Sr, the main dose-forming radionuclide within the EURT), at the ESRS large experiment have been performed to study migration and biological effects on agricultural plants and animals of man-made radionuclides (especially fresh mixtures of fission products) introduced to the natural environment. Results of ESRS experiments are described on irradiation of natural biogeocenoses from a powerful source of ionizing radiation (1.2 x 10(15) Bq 137Cs). The first unique experience is described of remediation of radioactively contaminated areas with emphasis on agricultural radioecology. The importance of the EURT and ESRS radioecological studies for the development of radioecology as a science is stressed.     

90Sr and 137Cs in higher aquatic plants of some water basins on the East-Urals Radioactive Trace: species features of radionuclide concentration

The paper summarizes the results from radioecological studies of a number of water basins located on the East-Urals Radioactive Trace (EURT), as exemplified by the lakes Large Ighish, Small Ighish and Shablish which are included in the medium-distance and remote zone of the EURT. The lake Misyash which is situated in the opposite direction from the release vector and has been only contaminated due to global fallouts has been used as a control water basin. The current species composition of the high aquatic plants and species-specific concentration of 90Sr and 137Cs in them was studied, also, the radionuclide accumulation and discrimination coefficients were estimated.     

Migrations of Rodents in the Zone of Local Radioactive Contamination at Different Phases of Population Dynamics and Their Consequences

Migrations of rodents in the zone of local radioactive contamination (East Urals Radioactive Trace, Southern Urals) at different phases of population dynamics are analyzed for the first time. The absence of any isolation of the rodents in the zone of this radioactive trace is convincingly demonstrated and the migration distances are estimated. As is shown, migration decreases the probability for transfer and fixation of adaptations in the chain of generations in vagile rodent species and increases the within-population genetic diversity of animals in adjacent regions. The need to consider the migration factor in a wide range of studies on assessment of biological effects in the zones of local technogenic contamination is confirmed.     

Lipid peroxidation in the liver of mice on the territories of East Ural radioactive trace

The researches were conducted on rodents from territories of the East Ural radioactive trace. The 90Sr activity of ground was 2 Ci/km2, 500 Ci/km2, 800 Ci/km2 (experimental plots) and on control territory--0.2 Ci/km2. In the liver of animals living on the polluted territories the activation of catalase and glutathionreductase, the increase in antioxidative activity and appropriate reduction of lipid peroxidation processes were observed. For 40 years after Kyshtym accident (70-100 generations of animals) the adaptive reaction have formed.     

Adaptation of small mammals to radiocontaminated environment: Oxidative metabolism and radioresistance

Differences in radioresistance and oxidative metabolism parameters in rodents of different ecological specialization in the East Ural radioactive trace (EURT) area are shown. Northern mole voles (radiosensitive species) exhibit a pronounced resistance to chronic exposure to radiation, living in a series of generations in a radioactive environment, whereas pigmy wood mice (radioresistant species) are less resistant in the EURT area due to their migration activity. Thus, under the EURT area conditions, northern mole voles realize the genotypic radioadaptation, whereas pigmy wood mice realize the physiological radioadaptation, the key role in which is played by the ecological and physiological characteristics and the lifestyle of animals.     

Ecology of <Emphasis Type="Italic">Hepaticola hepatica</Emphasis> infection in rodents in southern West Siberia

The paper analyzes data of the long-term monitoring of Hepaticola hepatica (Bancroft, 1893) Hall, 1916 prevalence in rodents in subtaiga small-leaf forests of the Northern Baraba lowland (the Severnyi raion of Novosibirsk oblast). The study found that the prevalence was (10.4 ± 1.02)% in Arvicola terrestris L., 1758; 4.5% in Microtus agrestis L., 1761; 3.4% in M. oeconomus Pall.,1776; 1.4% in Clethrionomys glareolus Schreb., 1780; 1.0% in C. rutilus Pall., 1779; and 0.2% in Apodemus agrarius Pall., 1771. A. terrestris was shown to become dominant in rodent communities during its outbreaks and play the main role in completing the life cycle of the parasite. During low density of A. terrestris, the H. hepatica reservoir in the biocenosis is maintained by other rodent species.     

Radioecological investigation of the soil cover of eastern Urals State radioactive reserve and neighboring areas

The contamination levels and spatial distribution of 90Sr and 137Cs in the soil cover of the Eastern Ural State Radioactive Reserve and neighboring areas have been studied. Situated in the Chelyabinsk region, the Reserve embraces the frontal part of the Eastern Urals Radioactive Trace. This Trace emerged in 1957 as a result of the nuclear accident at the Production Association "Mayak". In the studied areas, the content of radionuclides in soils decreases exponentially as the distance from the source of contamination increases. 90Sr received by the soil cover as a result of the accident in 1957 has remained the main contaminant of the Reserve central part (97% of the total contamination). Its contribution throughout western neighboring areas reduces up to 67%, which decreases the effect of 90Sr on the environment. Within eastern neighboring areas, soil is mainly contaminated by 137Cs received as a result of the wind disseminated dried sediments from the shores of Lake Karachay (1967) that was used for dumping high-level radioactive waste. Also observed was enrichment of forest litters with this radionuclide due to current atmospheric fallout.     

Remote effects in plant populations from zones of radiation and chemical pollution

A comparative research of dandelion seed progeny from the coenopopulations growing for a long time in a gradient of radioactive (zone of the East-Ural radioactive trace--EURT) or chemical (zone exposure Nizhny Tagil Metallurgical Plant--NTMP) pollution was carried out. It was revealed that the viability of seeds declined similarly in gradient of the man-caused stress regardless of its nature. Dandelion coenopopulations from the EURT zone, NTMP and the background area significantly differed in the qualitative and quantitative allozyme specifications. The analysis of clonal diversity revealed phenogenetic uniqueness of all coenopopulations. Study of F1-generation metal and radio resistance showed that the seed progeny from the impact EURT zone possessed a high viability but had hidden damage that led to a low resistance to additional man-caused influences. High viability of the seeds in the F1-generation from the NTMP zone combined with increased resistance to the provocative effects of radiation and heavy metals. Significant differences in responses to the "habitual" and "n ew" factors of influence, i.e. effect of pre-adaptation in samples from EURT and NTMP zones were not found.     

Parameters of peroxide oxidation of lipids and the system of its regulation in the tissues of Ellobius talpinus Pall,living on the territory of the East Urals Radioactive Trace

The peroxide oxidation of lipids and the systems of its regulation was tested in Ellobius talpinus Pall, living on the territory of the East Urals Radioactive Trace with the 90Sr contamination density of 1000 Ci/km2. The degree of sensitivity of the examined tissues and organs was revealed, the most considerable parameters were defined for marking radiosensitivity of the taken species, as well as the complex of parameters, allowing classifying an animal as an inhabitant of the clean or the contaminated territory. The found changes are considered as compensatory mechanisms for forming of nonspecific resistance.     

Genetic effects of the decay in Saccharomyces cerevisiae yeast cells of the radionuclide products of nuclear fuel fission. II. Lethal mutagenic effects and the nature of mutations induced by an equilibrium mixture of 90Sr-90Y and 89Sr

The lethal and mutagenic effects and the nature of mutations induced by 90Sr-90Y and 89Sr in cells of the yeast Saccharomyces cerevisiae were studied. The lethal efficiency was determined for 89Sr as (7,6 +/- 1,05) X 10(-5) decay-1, for 90Sr-90Y-(3,3 +/- 1,6) X 10(-4) decay-1. The mutagenic efficiency for ade1 and ade2 genes was determined for 89Sr as (8,3 +/- 2,5) X 10(-9) decay-1, for 90Sr-90Y-(2,9 +/- 1,5) X 10(-8) decay-1. For ade2 locus, the spectrum of mutations induced by 89Sr was a follows: one deletion, 17% of frameshifts and 83% of base pair substitutions--51% of transversions, 22% of GC-AT transitions and 10% of AT-GC transitions. The data of the present work suggest that 90Sr-90Y and 89Sr are very efficient physical mutagens. The relative mutagenic efficiency (RME) was estimated for radionuclides studied.