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The real threat of emergency situations in Ukraine dictates the need to take into account the experience of previous radiation accidents, during which a significant part of the population was exposed to low-dose radiation. In such a case clinical manifestations of irradiation were mostly absent, while the danger of stochastic (carcinogenic) effects remained. Therefore, at present, the strategy of radiation protection of the population should be aimed at revising and choosing effective and low-toxic anti-radiation means. The main criterion for the development of stochastic consequences of exposure is radiation-induced genome instability, which is a promoter of carcinogenesis. The use of radiomitigators, which are able to weaken the harmful effect of ionizing radiation on critical highly radiosensitive systems of the human body, is promising. Our research showed the radiomitigative effect of inosine in cultured human T-lymphocytes on the genetic level with the significant decrease in the frequency of gamma-induced chromosome aberrations. The results experimentally justified an expediency of use of radiomitigators in the conditions of an emergency situation to minimize the occurrence and development of stochastic effects in population.

The 1986 accident at the Chernobyl Nuclear Power Plant led to large-scale changes in the environmental situation. The purpose of our study was to conduct a comparative analysis of the morphological states of the dentition of individuals living in regions exposed to radiation to determine the groups at risk for the main classes of dental anomalies. We believe our results will support the development of a differentiated system for dental rehabilitation and follow-up of individuals exposed to radiation. The prevalence rate of dental anomalies was studied in 1,889 patients of both sexes divided by age in accordance with dentition formation stages and by regions of residence in accordance with the 137 Cs soil-contamination level. A statistically significant decrease was observed in the number of patients with normal dentition for their age among those who had been exposed to prenatal radiation. A sharp increase in combined dental anomalies was revealed in patients who lived in regions with a 137 Cs soil-contamination level ranging from 555 to 1665 GBq/km 2 ; concomitantly, multidirectional fluctuations were observed in the numbers of tooth and occlusion anomalies. Among the examined population, the most severe pathology of the oral organs was found in prenatally irradiated patients (born between April 26, 1986, and April 30, 1987). The prevalence of dental anomalies is interrelated not only with the level of radioactive contamination in the soil of the dwelling area, but also with the age of the surveyed individuals at the moment of the accident., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Objective: Determination of the peculiarities of ultrastructural changes and metabolism of reactive forms of oxy gen and nitrogen in the tissues of the myocardium, aorta and portal vein of the radiosensitive BALB/c mice due long term exposure to the complex of radionuclides of Chоrnobyl fallout (ejection) and low intensity low dose γ irradiation., Materials and Methods: Experimental studies were performed on 60 mice female radiosensitive lines BALB/c with a body weight of 20-22 g, which were divided into 3 groups: I group (control) animals age 6-9 months which were born and lived their lives in Kyiv vivarium under conditions natural radioactive background; ІІ - animals age 6 months, which were born and lived in the Chornobyl exclusion zone throughout their lives; ІІІ - animals, which from 3 months of age for 6 months were constantly located in cages with flat ionizing radiation sources and exposed to external γ irradiation in a total dose of 0.43 Sv. Animals of II and III groups were kept in the vivarium of the Institute for Safety Problems of Nuclear Power Plants of the National Academy of Sciences of Ukraine (Chornobyl). Mice of the BALB/c lines are sensitive to radiation: for males LD 50/30 < 5.7 Gy, for females - 5.85 Gy., Results and Conclusions: The peculiarities of structural and functional changes in the organs of the cardiovascular system (CVS) and mechanisms of the development of oxidative and nitrosatitative stress due long term exposure to the complex of radionuclides of the Chornobyl fallout (ejection) and low intensity low dose γ radiation based on the study of ultrastructural organization and metabolism of reactive oxygen species (ROS) and nitrogen (NRS) of the atri al cardiomyocytes (CMC), the aortic endothelium and portal vein of the BALB/c mice. Found that the permanent expo sure to low doses of radiation changes occur, including the dominant mechanism is to run a CMC apoptosis and endothelial cells of the aorta and portal vein. It is shown that the development of oxidative stress accompanied by increased activity of ROS metabolism that occurs due to activation of nucleotide and lipid superoxide generators. Found that under these conditions the development of nitrosative stress is due to the activation of inducible NO syn thesis enzyme iNOS and inhibit its synthesis constitutive eNOS enzyme. High levels of simultaneous generation of superoxide and NO, bindting, lead to the formation of toxic peroxynitrite, which initiates the process of apoptosis., (I. V. Horot, M. M. Tkachenko.)

The resistance of the micromycetes to β-irradiation had been studied. The study was conducted on two species: Cladosporium sphaerospermum Penz. and Alternaria alternata (Fr.) Keissl., each of them was represented by six strains. Half of strains were isolated from the inner locations of the "Shelter" object (SO), which were characterized by different levels of radionuclide contamination. For C. sphaerospermum strains maximum resistance to β-radiation was observed among 20-day-old cultures. The greatest resistance to β-radiation had been demonstrated by two strains: 5-1 (isolated from SO location with the highest level of contamination) and 852 (control). For A. alternata strains maximum resistance to β-radiation was observed among 40-day-old cultures. As the most resistant were characterized 56 and 105 isolates from the SO inner location with a high level of the radionuclide contamination. Based on the obtained results we concluded about high resistance to irradiation of both studied species of anamorphic fungi, which achieved through different life strategies: C. sphaerospermum strains survive due to rapid and abundant formation of conidia, whereas conidia of A. alternata strains are formed slowly, but they have greater advantage under irradiation due to their multicellular structure and large sizes.

Unlabelled: The objective was to study the immunogenetic component contribution to the formation of post-radiation effects in the long-term period after radiation exposure at the level of the human immune response as a prognostic criterion for risk assessment of radiation-associated somatic diseases. Study object was the convalescents of acute radiation syndrome (ARS) of the first grade of severity, 88 patients with a similar radiation history but with unconfirmed ARS, 73 patients being the liquidators of the Chornobyl accident consequences (LCAC) with chronic ischemic heart disease (HIHD), 65 patients LCAC without HIHD, 120 non-exposed patients with HIHD, 256 patients with oncohematological diseases and 500 healthy people - a population control., Results: Markers of risk of realization of genetic predisposition to oncohematological and cardiovascular disease in these groups were identified on the basis of study of immunological, hematological and molecular genetic disorders in relation to immunogenetic factors., Conclusion: These data indicate that realization of HLA-genetic predisposition to the disease is one of the radiation associated multifactorial pathology pathways, and presence of radiosensitivity markers in pheno/genotype enhances the realization risk of pathological process under irradiation., (Minchenko Zh. M., Djagil I. S., Dmytrenko O. O., Dmytrenko I. V., Shljahtichenko T. Ju., Gavrylenko T. I., Bilyj D. O., Homenko V. I., Bebeshko V. G., 2013.)

Natural populations of Drosophila melanogaster and Hirundo rustica that reside at the territories with different levels of radioactive pollution were investigated. The levels of visible mutations, sex-linked mutations and gonad reduction of Drosophila and the rate of interphase markers of chromosomal instability in erythrocytes of birds were selected as parameters for population monitoring. The results point out to possible reverse dependence among the level of chromosomal instability of birds, the rate of lethal mutations in sex chromosome of Drosophila and the density of radioactive pollution.

The health effects of ionizing radiation on human populations are often analyzed using epidemiological statistical methods. Because of the complexity of the health consequences of ionizing radiation and the prolonged period during which the consequences emerge, we propose to evaluate these health effects using mathematical models that are based on the best theoretical reasoning and prior biological evidence about disease mechanisms. We believe this will improve the ability of the model to identify health effects and reduce erroneous inferences.

Adaptation is a complex process by which populations of organisms respond to long-term environmental stresses by permanent genetic change. Here we present data from the natural "open-field" radiation adaptation experiment after the Chernobyl accident and provide the first evidence of the involvement of epigenetic changes in adaptation of a eukaryote-Scots pine (Pinus silvestris), to chronic radiation exposure. We have evaluated global genome methylation of control and radiation-exposed pine trees using a method based on cleavage by a methylation-sensitive HpaII restriction endonuclease that leaves a 5' guanine overhang and subsequent single nucleotide extension with labeled [3H] dCTP. We have found that genomic DNA of exposed pine trees was considerably hypermethylated. Moreover, hypermethylation appeared to be dependent upon the radiation dose absorbed by the trees. Such hypermethylation may be viewed as a defense strategy of plants that prevents genome instability and reshuffling of the hereditary material, allowing survival in an extreme environment. Further studies are clearly needed to analyze in detail the involvement of DNA methylation and other epigenetic mechanisms in the complex process of radiation stress and adaptive response.

We have shown that natural drosophila populations from the settlement Vetka of Gomel region with increased radiation background are more adapted to mutagenic effect of radiation than drosophila populations from Berezinsky reserve (the control). After the populations were placed into laboratory thermostat adaptation of Vetka population remained within 6-8 generations without irradiation. However the control population became more resistant too. So, the keeping of natural drosophila populations under laboratory conditions was a stress and led to unspecific adaptation the same as a low level of radiocontamination did. These facts should be considered in studying dynamics of the mutation level during radionuclide removal in animals caught in radiocontaminated regions and placed in vivaria conditions.

To study influence of "low radiodoses" on their early effects, the method to monitor peculiarities for human biochemphysic pathologies caused by technogenic chronic doses divided by natural constant radiation background doses (relative radiation loads as their ratios, RRL) has been developed. High radiolabile coupled system of harmful catabolites of the initiated lipoperoxic cascade with essential radioprotectors (vitamins A and E as natural antioxidants) as pathogenic significant test-objects were monitored. For exposed children low radiation technogenic doses were high enough as RRL to disturb and to dysregulate both systems. For evaluation of individual radiosensitivity significances of age for children especially, as of the biochemical status for both systems are shown. The approach permits to investigate pathologies of studied systems as primary factors for mechanisms of related radiogenic known somatic health secondary consequences and to use it for some important practical applications.

The results of long-term investigations of the effectivity of low level irradiation (below 0.5 Gy) carried out on the cells in culture and blood human lymphocytes (adults and children) have been brought. In the experiments conducted in the laboratory conditions and in the contaminated with radionuclides regions (after Chernobyl accident) the genomic instability have been discovered. The cell manifestations of the genomic instability have been registered in the progeny of irradiated cells as the decreasing of proliferative activity, the increasing of the frequency of cells with micronuclei, the increasing of cells with sister chromatid exchanges, the late cell death, the absence of the adaptive response ability, the enhancement of the radiosensitivity. The results of the investigations of the adaptive response of blood lymphocytes have been presented. It was shown that in all populations investigated there are individuals without the adaptive response and the individuals with the enhancement of radiosensitivity after adaptive irradiation (0.05 Gy). On the basis of own results and the data of literature the possible mechanisms of low level irradiation effects are discussed. The conclusion is that: a. The population with new properties can be formed after low level irradiation; b. The effects and mechanisms of this effect realization can be different from that after irradiation with high doses.

Methylobacterium extorquens, M. mesophilicum, and Bacillus subtilis strains were found to be resistant to gamma-radiation, irrespective of whether they were isolated from the alienated zone around the Chernobyl Nuclear Power Plant or outside this zone. The LD90 of Methylobacterium and B. subtilis strains with respect to gamma-radiation was 2.0-3.4 and 3.7-4.4 kGy, respectively, whereas their LD99.99 values were 4.5-6.9 and more than 10 kGy, respectively. The high threshold levels of gamma-radiation for Methylobacterium and B. subtilis imply the efficient functioning of DNA repair systems in these bacteria. Unlike Bacillus polymyxa cells, the cells of M. extorquens, M. mesophilicum, and B. subtilis were also resistant to desiccation. Pseudomonas sp., Nocardia sp., and nocardioform actinomycetes were sensitive to both gamma-radiation and desiccation. Similar results were obtained when the bacteria studied were exposed to hydrogen peroxide and ultraviolet radiation. The results obtained indicate that the bacteria that are resistant to gamma-radiation are also resistant to desiccation, UV radiation, and hydrogen peroxide. The possibility of using simple laboratory tests (such as the determination of bacterial resistance to UV light and desiccation) for the evaluation of bacterial resistance to gamma-radiation is discussed.

Over the period from 1998 to 2000 adaptation to unfavorable ecological factors was revealed to be formed in natural Drosophila melanogaster populations from various regions of Belarus with increased radiation background due to the Chernobyl accident. This adaptation was shown to be of non-specific character, since the populations from radiation regions were more resistant to the effect of not only factors of physical nature (irradiation), but also to that of chemical mutagen ethylmethanesulphonate. Assessment of population resistance was carried out by means of tests of dominant lethal mutations and recessive sex-linked lethal mutations.

To investigate the biological effects of small dose ionizing radiation has been acquiring greater importance. The awareness of how and in what direction it show its modifying effects in small doses is an essential scientific basis for developing standards, living conditions under specific environmental conditions. Cultured Hela cells and DEF 4/21 fibroblasts were used to evaluate the biological effects of small-dose ionizing radiation, by examining the conditions under which it showed its modifying effect in small doses (0.1 Gy) in particular. Preexposure to small-dose radiation was shown to alter cell responses to subsequent radiation in large doses. The modifying effects of small-dose radiation turned out to depend on the interval of exposure to small and large doses. Sensitization was recorded at an interval of 2-3 min; an adaptive response was achieved when the interval increased up to 3-5 hours. Upon exposure, intercellular contacts contribute to the modifying effects of small-dose radiation. There was neither effect of sensitization nor adaptive response if single cells were exposed to radiation.

The main results of the 12-year radiation-genetic monitoring of radiobiological, cytogenetic, and genetic parameters in Pinus sylvestris forest plantation from the Chernobyl meltdown area are presented. The acute ionizing irradiation at doses > 1 Gy was shown to induce formation of morphoses and depressed growth; at doses > 2 Gy, the reproductive ability of the trees declined. The radiobiological parameters showed a linear or close to linear dose-dependence relationship. The acute irradiation at a dose of 0.5 Gy induced cytogenetic and genetic effects that were significantly higher than the corresponding control values. The relationship between the cytogenetic effects and the absorbed dose was exponential. The dependence of the mutation frequency at specific loci on the absorbed dose was described by a nonlinear curve. The results of cytogenetic analysis of seedlings obtained from seeds annually collected in zones of slight, moderate, and strong damage of Pinus sylvestris L. are presented.

This is probably the first report on intraspecific variation in radiation resistance for filamentous fungi. It was revealed that natural ("field") strains of the filamentous fungus Alternaria alternata are extremely variable in response to gamma-irradiation ranging from supersensitive to highly resistant to radiation. At the same time nearly all strains originating from the highly radiation-polluted reactor of the Chernobyl (Ukraine) Nuclear Power Plant possessed high radiation resistance. The genome structure of strains studied by universally primed polymerase chain reaction (UP-PCR) was found to be well conserved in "reactor" but not in "control" strains. The "reactor" strains appear to be genetically adapted to this high radiation habitat by means of selection, thus providing a natural source of genetically homogeneous fungal lineages., (Copyright 2000 Academic Press.)

Seventy strains of chemoorganotrophic bacteria isolated by our group in 1993-1994 from soil sampled in the zone around the Chernobyl Nuclear Power Plant (ChNPP) were studied with respect to their sensitivity to various stress factors damaging DNA. Bacillus subtilis, B. cereus (both spores and vegetative cells), Methylobacterium extorquens, M. mesophilicum, and unidentified pigmented bacteria were found to be the most resistant to ultraviolet (UV) radiation, exhibiting LD90 values of 40 to more than 211 J/m2. The same bacteria, as well as Bacillus polymyxa, were tolerant to hydrogen peroxide (lethal concentrations of H2O2 ranged from 0.3 to 1.0 M); i.e., UV-resistant strains were also tolerant to hydrogen peroxide and vice versa. Fluorescent pseudomonads were the most sensitive to both UV radiation and H2O2, showing LD90 from 6 to 18 J/m2 and a lethal concentration of H2O2 lower than 0.1 M. All of the soil samples collected in the alienated zone around the ChNPP, where the radioactivity of the soil had decreased from 1000 to 2 microCi/kg soil over the period from 1987 to 1995, contained not only resistant bacteria but also a small number of bacteria sensitive to UV radiation and H2O2.

In the frame of the emergency procedures in the case of an accident in a nuclear plant, this paper presents a survey of the information available on the risks related to the irradiation of the thyroid gland. Attention is focused on thyroid cancer resulting from an exposure to radioactive isotopes of iodine and especially and iodine-131. The consequences of the medical exposures as well as of the Hiroshima and Nagasaki irradiations are recalled first. Then the recently available informations on the effects on the populations exposed after the Tchernobyl accident are analysed more in details. Ten years after the accident, the most striking and the least questionable effects is a significant increase of the incidence of differentiated thyroid cancer in children, in the areas most exposed to the initial radioactive clouds. Young children are particularly vulnerable to this type of cancer which is of aggressive nature and shows a short latency period. These observations justify an iodine prophylaxis for the populations living in the vicinity of nuclear plants. Special attention should be paid to the protection of young children.

The accident at the Chernobyl nuclear power station in 1986 led to the dispersal of large amounts of a variety of radioactive materials, most importantly uranium, plutonium, 137Cs, 131I and 90Sr, over very large distances estimated to reach as far as Sweden, Norway, Turkey and possibly the USA. As a consequence, the soil on which the radioactive materials fell was contaminated and the degree of contamination varied with distance from the station, the direction and strength of the wind and the amount of atmospheric scavenging by rainfall at that time. Some of the radioactive materials have left a significant impact on mankind in the form of chromosomal aberrations including trisomy, various forms of cancers and death, whilst others are still in the ground where they will remain for a prolonged period to continue to exert their effects. Likewise, microbes living in the soil and exposed to radioactive materials may have been affected in a number of ways; some perished, and others survived due to the acquisition of advantageous mutation. Six years after the accident, soil samples contaminated with different levels of radioactivity were obtained from five regions within a 30 km radius of the nuclear power plant. From these soil samples spore-forming bacilli were isolated, quantified, identified and tested for resistance to X-rays, UVC and 4-nitroquinoline 1-oxide (4NQO). As a control, spore-forming bacilli were obtained from 'Zeleny mys' (an area 50 km south-east of the power station and emitting basal levels of radioactivity). A mutant of Escherichia coli hyper-resistant to a variety of DNA-damaging agents and its parent strain were also included in the study. Analysis of results reveals that a proportion of isolates of the same species from near the power station and the E. coli mutant SA236 were more resistant to X-rays, UVC and 4NQO compared with isolates from the control site and the E. coli parent strain, KL14, respectively.

Phenomena of melanization of radioactively polluted soils, due to prevalence of melanin-containing species and positive radiotropism of some micromycetes have been found during monitoring of mycobiota of the 30-km alienation zone of the Chernobyl NPP for 10 years. To elucidate the contribution of the melanin system to the cell protection against irradiation, the influence of gamma-irradiation on the activity of protein synthesis in four Cladosporium cladosporioides (Fres.) de Vries strains has been investigated. Two strains isolated from radioactively polluted substrates were characterised by the presence of positive radiotropism. Laboratory strain 396 and its alb-mutant (with blocked melanin synthesis), did not possess this feature. The protein synthesizing activity was assayed by incorporation of 14C-leucine in the protein fraction of mycelium, grown during 7 days under continuous gamma-irradiation of low intensity and without it. The protein synthesis was activated in the radioactively treated mycelium of dark-pigmented C. cladosporioides strains and it was suppressed in similarly treated mycelium of alb-mutant of C. cladosporioides. The rate of 14C-leucine incorporation into biomass of investigated strains correlated with positive radiotropism. The dependence between protein synthesis intensity and the availability of melanin protection system in micromycetes is assumed.

Adaptive and stimulating effects of ionizing radiation occur at near natural doses. This disagrees with linear, no-threshold hypothesis on the dose/effect relationship, which is a basis of the current radiation protection. Vast literature demonstrates that such effects, usually known as hormetic ones, occur at molecular, cellular and population levels, and often result in increase longevity and decreased cancer incidence. Exposure to lower than natural radiation causes deficiency symptoms in protozoa and bacteria. Hormetic effects suggest that the current radiation protection regulations may be too conservative. After the Chernobyl accident, adverse health effects and vast material losses were induced in the former USSR by practical implementation of the ICRP radiation protection recommendations. A revision of the current approach to managing the risks of ionizing radiation is needed for the public interest.

Free radical melanin centers have been detected in the cell concentrate of bronchoalveolar lavage (BAL) of liquidator of Chernobyl NPP accident. To identify the nature of these centers the EPR technique and the fluorescent technique were used to study BAL of liquidators with lung chronic pathology, their blood, blood components as well as model melanin- and lipofuscin-containing systems: synthetic DOPA-melanin, human melanosome, human lipofuscin, human melanolipofuscin. I Besides that we have investigated the samples of fungi, extracted from lung phlegm of liquidators (Aspergillus niger, Aspergillus fumigatus, Aspergillus flavus, Penicillium Sp., Candida albicans) as well as the melanin, extracted from fungal conidium. It has been shown that the melanin centers found in BAL cells of liquidators is the melanin of melanin-synthesizing mutant fungi Aspergillus fumigatus and Aspergillus flavus. The prolonged gamma-irradiation at low dose rate and the effects of inhaled radioactive particles cause the adaptive mutation of micromycetes producing the chemo- and radioresistant population. We think that the radioactive dust and pathogenic mutant micromycetes were inhaled in lungs of liquidators during their work at the Chernobyl NPP. Thus, one of valid consequences of Chernobyl accident may be the wide fungous of human organs, in particularly, by Aspergillus mutant. The radiation-induced weakening of immune reactions of liquidators promotes the resistance of this fungus mutant infection.

The experiments in animals exposed in the area of increased radiation level around the Chernobyl NPP and the observational data on laringosyndrom and peripheral blood pattern of the people, who worked at the Chernobyl NPP in 1986-1987, have shown that it is possible to use some biogenic preparations (e.g. MIGI-K) for protection under chronic exposure to natural and technogenous ionizing radiation. MIGI-K preparation effectively enhances radioresistance as well as general resistance of the organism. It has important positive characteristics: it is non-toxic, there are no side effects and contra-indications for its peroral use as a nutriceutic, it has no mutagenic properties, it has not only radioprophylactic but also radiotherapeutic activity and pronounced cancerostatic activity. It is also important that MIGI-K has long-term effects on the organism resistance (up to 2 weeks after the ending of its month course), enhances the endogenous background of radioresistance, shows hemoregulatory effects, intensifies radionuclide efflux from organism. It can be stored under room temperature for several months without the loss of its activity. The data mentioned above let us to conclude that MIGI-K is adaptogenous preparation with wide spectrum of activity.

The consumption of food is an important pathway involved in the internal contamination of humans. The site-related critical foodstuffs can be grouped into three main categories: dairy products; aquatic animals, such as fish, molluscs and crustaceans; and other typical foods. The concentration factor plays a more important role than the amount of a certain food consumed. Semi-natural and natural ecosystems are of special interest in this context because they can provide critical pathways for radionuclide transfer to humans, and they can also act as temporary sinks or long-term sources for radionuclides deposited from the atmosphere. From the viewpoint of population health, another important role is played by the countermeasures. The reference values commonly adopted in radiation protection are conservative and they have been established for planning practices that could provide future sources of irradiation. After a large release of radionuclides, the evaluation of the problem must be as realistic as possible, otherwise the countermeasures will imply consequences worse than those produced by the accident itself (without any further intervention). This criterion was clearly stated by the International Commission on Radiological Protection but it was frequently neglected after the Chernobyl accident. The results of a survey on the number of induced abortions following this incident are reported. These suggest that moral and ethical problems are involved above and beyond any economical implications.

Historical experiments and observations in radioactively contaminated environments have documented radiation impacts on natural plant communities and animal populations. General findings from these studies are reviewed. Despite much information on the response of individual organisms to radiation in the laboratory, the database is more limited and the interpretations more complex for natural populations and communities exposed to radionuclides. These complications are discussed as they pertain to plants and animals in natural environments. Paradigms concerning the recovery of radiation-damaged communities and ecosystems, and areas of needed research are discussed.

The catastrophe at Chernobyl Atomic Power Station (ChAPS) of 1986 has created a natural model for studying the after-effects of prolonged action of radiation on the biota. Our work is aimed to estimate the variability of heterotrophic bacteria in the soil of 10-km zone of ChAPS which have formed as affected by prolonged action of radiation, as well as to create the corresponding collection of bacteria. Microbiological analysis of soils was carried out in 1993-1994 (in spring, summer, autumn), allowing for bacteria destroying different organic substance (in soil). It is shown that in the surface layer of soils (at the depth of 0-2 cm) the total number of cells of heterotrophic bacteria as well as the number of found species of bacteria is considerably less than in the control samples. Atypical distribution of bacteria in the soil profile was established. Indices of the species diversity of bacteria in these soils permit one to consider that microbe content of soil of the 10-km zone of the ChAPS has become considerably less after the disaster at the ChAPS in 1986 and has not recovered by 1993. A collection of various physiological groups of bacteria including representatives of Methylobacterium genus has been created. They have been isolated from the soils of 10-km zone of the ChAPS for following genetic investigations.

The frequency of irradiation-induced recessive lethals has been studied in chromosomes 1 and 2 of Drosophila melanogaster. It supposed, that the higher level of mutability may be explained in destabilization of genotype. The essential part in induction of genotype destabilization replies the genome instability mechanisms.

The results of series investigations of late effects after Chernobyl accident are discussed. Genomic instability induced by chronic irradiation of cultural cells in Chernobyl zone and in laboratory conditions have been studied. It was shown that low level prolonged irradiation result in increase of frequency of cells with micronuclei, giant cells, enhancement of radiosensitivity in descendents of early irradiated cells. Chronic low doses irradiation doesn't induce the adaptive response. Comparative investigation of adaptive response in blood lymphocytes of people (adults and children) living in Moscow and in regions polluted with radionuclides (5-40 ci/km2) after Chernobyl disaster have been conducted. In population from contaminated areas the frequency of individuals with definite adaptive response is decreased and there are individuals with increasing radiosensitivity after irradiation in conditioned dose. Chronic irradiation during living on contaminated areas don't induce the adaptive response.

The radiosensitivity of cellular elements of megakaryocytic spring in accordance of their maturity has been evaluated on the basis of analysis of changes in thrombocyte level in peripheral blood of the Chernobyl disaster victims. The radiosensitivity of committed cellular elements of megakaryocytic spring by the criterion D0 is presumably 1.6-1.7 Gy(n = 1). More mature polyploid cells (megakaryoblasts, megakaryocytes) apparently are "absolutely" radioresistant and within the analysed range of doses (0.1-13.7 Gy) their function of thrombocyte producing remains intact. It has been proved that the rate of thrombocyte escape from peripheral blood rises with the acute radiation disease under going in the comparison with the norm that seriously affects the lifetime of thrombocytes. The transit time of megakaryocyte starting from primarily committed cell and ending with a cellular element, producing thrombocytes, is not a constant value. The normal transit time is approximately 28 days.

Radiation remains the only factor that has been shown unequivocally to cause (nonmedullary) thyroid cancer. Recent advances include the analysis of the dose-response relationship using data pooled from multiple studies. This analysis confirms that radiation-induced thyroid cancers continue to occur, with a maximum risk at approximately 30 years after exposure. Physicians asked to evaluate patients with a history of radiation exposure should attempt to estimate the dose from the history and should be familiar with the other risk factors. For some individuals, screening should include thyroid imaging, but the results of such imaging, especially with thyroid ultrasound, should be interpreted with caution. The treatment of radiation-induced thyroid cancers is based on the observation that they appear to be no more aggressive than thyroid cancers not associated with radiation. In the future, more information should emerge about the role of cancer genes and susceptibility factors in radiation-induced thyroid cancer.

Dietary intake, physical development and some indicator of health status of schoolchildren of Novosybkov (2th zone of strict control) and Vyshkov (3th zone) were studied. Energy and macronutrient intakes for schoolchildren can be considered adequate. Dietary intake intake of vitamins A, E, beta-carotene and especially C, and calcium were rather low. Low intakes of vitamin and calcium are results from low dietary consumption of milk and diary products, fruits and vegetables Physical development of Novosybkov's children is considered adequate and do not differ from that of Moscow's schoolchildren. The frequency of obese schoolchildren was seen in Novosybkov's children in comparison with Moscow's ones. On the contrary, among rural Vyshkov's children the high frequency of children with deficit of body mass was examined. The number of children relating to 2 or 3 groups of health was higher in Novosybkov than in Moscow. The data about higher prevalence of child morbidity were supported. One of risk factors of decreasing of children body toleration to low level of radiation are low level of vitamin intake and other defects of health nutrition.

Properties of morphogenesis, growth dynamics, anatomy and ultrastructure of wood and needle, reproductive processes in coniferous plants were studied under different level of radiation effect in the 10-km zone in 1986-1992. It was established that the full drying of pine forests began under absorbed dose 80-100 Gy/year. Threshold doses, after which repair processes were possible, reached to 10-12 Gy/year for Picea abies and 50 Gy/year for Pinus sylvestris. Three maine stages are revealed in dynamics of radiation damage and repair processes in studied conifers and their morphological and functional characteristic is presented.

The morphophysiological properties of two generations of seeds from chronically exposed agrocenoses of the Chernobyl NPP accident zone were investigated. The difference in reactions between exposed and control seeds to acute stimulating irradiation and to treatment with biologically active substances was shown. The relationship between the degree of radiation depression of the seed morphological development indexes and biometric characteristics of plants on the plots with different radioactive contamination was revealed.

The radiosensibility of erythropoietic tissue cells was estimated on the basis of analysis of erythrocyte and reticulocyte quantity changes in peripheral blood of the victims of the disaster on the Chernobyl NPP. The radiosensibility of blood cells was evaluated in accordance with their maturity (committed, committed-and-maturing and maturing pools). The population of erythropoietic tissue cells can be divided into two groups on the criterion of their radiosensibility. The first group demonstrates the highest level of radiosensibility varying from 0.5 to 1.73 Gy (n = 1). It includes the cells from primarily committed to basophilic normoblasts. The other group consisting of polychromatophils and oxyphils is more radioresistent. Do of these groups corresponds to their maturity and ascends from 4.7 to 12.9 Gy.

The radioresistance of seeds of populations of Arabidopsis thaliana (L.) Heynh. growing for 5 years in the regions with different levels of radioactive contamination within 30 km zone of Chernobyl NPP was studied. The analysis of comparative radiosensitivity by root test was performed. It has been shown that plants from Arabidopsis population growing under chronic irradiation did not gain an increased radioresistance. The data obtained show that they are more radiosensitive.

Acute emotional stress in people is followed by changes in oral fluid composition (sialic acid, components of proteolytic system, lipid of peroxidation products). The possibility to use these indices for estimation of the psychoemotional stress in people is based.

On the basis of the data obtained from 61 cases of accidental exposure (0.1-12.5 Gy) at the Chernobyl A.P.S. the kinetics of acute radiation bone-marrow syndrome was analyzed and radiosensitivity of the entire spectrum of human granulocytic compartment cells was estimated. The radiosensitivity estimates were made by a "functional" criterion, developed by the authors, which was based on the comparative ability of irradiated and nonirradiated bone marrow cells of different maturity to produce peripheral blood neutrophils. Changes were found in physiology of myeloid cells during their maturation: the maturation mechanism, for cells of the committed pool, was "attached" to the division process, whereas these processes were independent for cells of the dividing and maturing pool. It is once again confirmed that the transit time of a maturing myeloid cell, to begin with the primarily committed one and to end with a peripheral blood neutrophil, is not constant and lasts normally for 32 days.

The frequency of micronuclei in erythrocyte cells from fish collected in six Swedish lakes with high concentrations of radiocaesium and other suspected natural and induced pollutants, was investigated. The frequency was enhanced in some lakes but was not correlated with caesium concentrations. Fish could prove to be interesting models for investigations of ionizing radiation effects at low doses because of their sensitivity.

The method of provocative gamma-irradiation was used to study the radiosensitivity of seeds of three first post-accident reproductions of Plantago lanceolata L. within the thirty kilometer zone of Chernobyl. The radiation injury was severer among seeds taken in 1987-1988 from the areas with a higher level of radioactive contamination.

Genetic effects of irradiation in males of wild house mice which were caught in the region of Chernobyl Nuclear Power Station were studied. The dose rate on the ground surface varied from 0.04 to 200 mR/h of gamma-irradiation. The increasing yield of dominant lethal mutations was only observed in males from the most contaminated sector. Reciprocal translocations were observed in spermatocytes of mice at all the levels of contamination. The rate of reciprocal translocations was relatively low and increased linearly with the elevation of the dose rate. The extent of testis damages increased also, as the dose rate grew. The frequency of abnormal sperm heads, the yield of recessive lethal mutations, litter size and radiosensitivity of the first progeny were not changed, depending on the dose rate.

The potential harm to a population exposed to radiation from a nuclear accident, such as the one that recently occurred at the Chernobyl plant in the Soviet Union, is of concern to many individuals. The average dose to a population is a useful index of harm (IH) only for linear, nonthreshold-type, quantal (i.e., all-or-none) effects. For such radiobiological effects, the expected harm to the population is linearly related to the average dose. However, for nonstochastic effects, it is not. An IH is proposed for threshold-type nonstochastic effects which is based on a form of the Weibull model where, at low to moderate doses, the individual risk at dose X = D/D50 is given by the approximation Risk = ln(2)XV; where D50 is the absorbed radiation dose that produces the specified effect in one-half the population, D is the absorbed radiation dose, and V is a positive parameter. The dose, X, is in units of the D50. Use of this form of the Weibull model is limited to doses such that X is small in comparison to 1. An IH for the population can be obtained by defining a new variable, P = XV, in dimensionless units, because the individual risk is linearly related to P at low and moderate doses. The average value for P (given by [P]) for an exposed population can be used as an IH for the population when the maximum value for P does not exceed 1. Both P and [P] can be regarded as theoretical doses. The average risk for the population in terms of the average dose [P] is given by ln(2)*[P], and the expected cases of nonstochastic effects among N individuals by N*ln(2)*[P]. As an example of the application of the average dose [P], the expected cases of temporary sterility in males among the approximately 135,000 people evacuated within 30 km of the Chernobyl plant is calculated to be about 200. The cases of sterility would be expected to come from those males exposed to doses to the testes of about 0.35 Gy or higher. No cases of sterility would be expected for individuals exposed to lower doses.