Genetic monitoring of natural Drosophila populations in radiation contaminated regions of Belarus

Genetic monitoring of natural Drosophila melanogaster populations inhabiting regions of Belarus with different radiation background (Vetka and Svetilovichi villages), radonuclide-contaminated after the Chernobyl accident, compared with populations from the Berezinsky biosphere reserve (the control area) were conducted. The dominant and recessive lethal mutation levels and genetic structure of the populations were analyzed for frequencies of F- and S-alleles of Adh (alcohol dehydrogenase) of Gpdh (glycerinophosphate dehydrogenase) and Sod (superoxide dismutase) loci. Populations inhabiting the regions with high radiation background exhibited higher frequency of lethal mutations and higher heterozygosity than those from the control area. Moreover, higher frequency of polymorphous Sod locus S-allele was detected in these populations. Apparently, Sod S-alleles are more adaptively valuable under conditions of high radiation background, because as is known, superoxide dismutase is an effective radioprotector at all levels molecular, cellular and organism. Adaptation of populations to stress impacts was analyzed, since 1998. Nonspecific adaptation of natural Drosophila melanogaster populations from Vetka and Svetilovichi villages of Gomel region was reveled. They are higher adapted than the control population from the Berezinsky biosphere reserve to both ionizing radiation effect and to chemical mutagen EMS. After laboratory cultivation within 6-8 generations without irradiation adaptation to radiation in the population from radiocontaminated regions remained. The content of samples from the control natural drosophila population in the laboratory conditions is an environmental stress that led to the formation of nonspecific adaptation within 6-8 generations to unfavorable factors, including ionizing radiation. It should be taken into account that the population adaptation is formed via death of sensitive genotypes at various ontogenesis stages.     

Galactic Factors,the Young Sun,the Earth,and the Biophysics of Living Systems

The effects of radiation from the young Sun and galactic cosmic rays on the physical conditions on the early Earth are significantly underestimated in studies of the problems related to the origin and evolution of the biosphere. This review considers the dynamics of solar and galactic processes over the 4.56 billion years of the existence of the Solar System. These factors substantially affected the development of adaptive technologies in ancient and modern living systems. The features of biosphere development are considered for the early Earth under the young Sun, which was fainter, but more flare active. The radiation spectrum of the young Sun is discussed together with the paradoxical mismatch between the solar radiation spectrum and the chlorophyll adsorption spectrum. Ways of solving the paradox are proposed. The role of solar radiation is important when studying models of the early biosphere of the Earth and hypothetical biospheres of giant planet satellites and exoplanets.

     

Environmental radiation as the conditioning factor for the survival of yeast Saccharomyces cerevisiae

Whether natural radiation can be a conditioning factor for the growth and survival of a living organism was investigated using diploid yeast S. cerevisiae D7. Yeast cells were conditioned by growing them continuously for at least 100 generation in 3 different radiation background such as i) ambient radiation (1.1 mSv/y), ii) sub-ambient radiation (0.44 mSv/y, within a shielded chamber) and iii) an elevated background radiation (88 and 880 mSv/y in a gamma-field). At the end, the cells were challenged with 60Co gamma, 100 Gy and the viable fractions were determined. Conditioning the cells in 880 mSv/y and in ambient radiation, enabled the cells to reduce the deleterious effect of the challenging dose significantly (P < 0.05) compared to that of sub-ambient radiation. The cellular viability of yeast cultures seems to be influenced by the prevailing radiation background, apart from starvation. Comparatively, a rapid decline in viability was noticed when the cultures were incubated for 60 days in the shielded chamber. The results indicate that some amount of radiation equivalent to background level or little above is needed to confer fitness in biological systems against stress factors, including radiation. The adaptive dose for the diploid yeast was also determined by single exposure. The priming dose ranged from 0.01 to 1.2 Gy. An adaptive dose of 0.25 or 0.4 Gy, almost nullified the deleterious effect of the challenging dose. The adaptive response may have a greater role in the field of cancer therapy and in radiation risk assessment. Understanding the response of an organism at different radiation-background will be helpful for successful space management.     

The estimation of ionizing irradiation impact on Vicia cracca cenopopulations growing on the territory contaminated with the wastes of radium production

The radiation exposure on cenopopulations Vicea cracca L. growing on the territory contaminated with the wastes of radium production was estimated. The relationship between the chromosome aberration in seedlings root tip cells and irradiation dose was found to be linear. The significant cytogenetic effects in chronically irradiated Vicia cracca cenopopulation are observed at doses (equal to 0.006-0.7 Gy) 10 times upward the natural radiation background level. The reduced reproductive success (significantly increased embryonic lethal mutation level) is observed at weighted absorbed doses (equal to 0.2-0.7 Gy) up to 200-700 times higher than the natural radiation background level. It is showh, that the radiation hygienic standards of permissible exposure are noticeably stricter that the radioecological limits.     

居民食用大亚湾海洋生物所致内照射剂量研究

内照射剂量的估算在剂量防护中是十分重要的。对居民由于食入大亚湾核污染海洋生物所导致的内照射剂量给出一个评价方法是十分必要的。在对潮流污染扩散进行数值模拟的基础上,得出放射性核素浓度场的分布,进一步给出一个内照射剂量估算方法。根据这一估算方法,可以简便的估算出每个居民由于食入大亚湾海洋生物所致的辐射剂量。估算结果表明,每人每年由于食入大亚湾海洋生物所导致的内照射剂量在10^-6~10^-9Sv之间,低于人类每年人均受到的本底辐射。     

Oxidative stress in broad bean (Vicia faba L.) induced by static magnetic field under natural radioactivity

The investigation was performed to evaluate the influence of the static magnetic field on oxidative stress in Vicia faba cultivated in soil from high background natural radioactivity in Iran. Soil samples were collected from Ramsar, Iran where the annual radiation absorbed dose from background radiation is substantially higher than 20 mSv/year. The soil samples were then divided into 2 separate groups including high and low natural radioactivity. The plants were continuously exposed to static magnetic field of 15 mT for 8 days, each 8h/day. The results showed that in the plants cultivated in soils with high background natural radioactivity and low background natural radioactivity the activity of antioxidant enzymes as well as flavonoid content were lower than those of the control. Treatment of plants with static magnetic field showed similar results in terms of lowering of antioxidant defense system and increase of peroxidation of membrane lipids. Accumulation of ROS also resulted in chromosomal aberration and DNA damage. This phenomenon was more pronounced when a combination of natural radiation and treatment with static magnetic field was applied. The results suggest that exposure to static magnetic field causes accumulation of reactive oxygen species in V. faba and natural radioactivity of soil exaggerates oxidative stress.     

Ultraviolet radiation screening compounds

Amongst the diversity of methods used by organisms to reduce damage caused by ultraviolet (UV) radiation, the synthesis of UV-screening compounds is almost ubiquitous. UV-screening compounds provide a passive method for the reduction of UV-induced damage and they are widely distributed across the microbial, plant and animal kingdoms. They share some common chemical features. It is likely that on early earth strong selection pressures existed for the evolution of UV-screening compounds. Many of these compounds probably had other physiological roles, later being selected for the efficacy of UV screening. The diversity in physiological functions is one of the complications in studying UV-screening compounds and determining the true ecological importance of their UV-screening role. As well as providing protection against ambient UV radiation, species with effective screening may also be at an advantage during natural ozone depletion events. In this review the characteristics of a wide diversity of UV-screening compounds are discussed and evolutionary questions are explored. As research into the range of UV-screening compounds represented in the biosphere continues, so it is likely that the properties of many more compounds will be elucidated. These compounds, as well as providing us with insights into natural responses to UV radiation, may also have implications for the development of artificial UV-screening methods to reduce human exposure to UV radiation.     

Variation in chronic radiation exposure does not drive life history divergence among Daphnia populations across the Chernobyl Exclusion Zone

Ionizing radiation is a mutagen with known negative impacts on individual fitness. However, much less is known about how these individual fitness effects translate into population‐level variation in natural environments that have experienced varying levels of radiation exposure. In this study, we sampled genotypes of the freshwater crustacean, Daphnia pulex, from the eight inhabited lakes across the Chernobyl Exclusion Zone (CEZ). Each lake has experienced very different levels of chronic radiation exposure since a nuclear power reactor exploded there over thirty years ago. The sampled Daphnia genotypes represent genetic snapshots of current populations and allowed us to examine fitness‐related traits under controlled laboratory conditions at UK background dose rates. We found that whilst there was variation in survival and schedules of reproduction among populations, there was no compelling evidence that this was driven by variation in exposure to radiation. Previous studies have shown that controlled exposure to radiation at dose rates included in the range measured in the current study reduce survival, or fecundity, or both. One limitation of this study is the lack of available sites at high dose rates, and future work could test life history variation in various organisms at other high radiation areas. Our results are nevertheless consistent with the idea that other ecological factors, for example competition, predation or parasitism, are likely to play a much bigger role in driving variation among populations than exposure to the high radiation dose rates found in the CEZ. These findings clearly demonstrate that it is important to examine the potential negative effects of radiation across wild populations that are subject to many and varied selection pressures as a result of complex ecological interactions.     

Prokaryotic biosphere

The life philosophy aspects of natural sciences are discussed. The key role of prokaryotes in the origin, development, and existence of the biosphere is considered. It helps to understand how the penetration in the world of prokaryotes changes our notions of the place of biology in natural sciences.     

Electron paramagnetic resonance measurements of absorbed dose in teeth from citizens of Ozyorsk

In 1945, within the frame of the Uranium Project for the production of nuclear weapons, the Mayak nuclear facilities were constructed at the Lake Irtyash in the Southern Urals, Russia. The nuclear workers of the Mayak Production Association (MPA), who lived in the city of Ozyorsk, are the focus of epidemiological studies for the assessment of health risks due to protracted exposure to ionising radiation. Electron paramagnetic resonance measurements of absorbed dose in tooth enamel have already been used in the past, in an effort to validate occupational external doses that were evaluated in the Mayak Worker Dosimetry System. In the present study, 229 teeth of Ozyorsk citizens not employed at MPA were investigated for the assessment of external background exposure in Ozyorsk. The annually absorbed dose in tooth enamel from natural background radiation was estimated to be (0.7 ± 0.3) mGy. For citizens living in Ozyorsk during the time of routine noble gas releases of the MPA, which peaked in 1953, the average excess absorbed dose in enamel above natural background was (36 ± 29) mGy, which is consistent with the gamma dose obtained by model calculations. In addition, there were indications of possible accidental gaseous MPA releases that affected the population of Ozyorsk, during the early and late MPA operation periods, before 1951 and after 1960.     

Cancer incidence and mortality after low-dose radiation exposure: epidemiological aspects

Current recommendations for limiting exposure to ionizing radiation are based on the linear-no-threshold (LNT) model for radiation carcinogenesis under which every dose, no matter how low, carries with it some cancer risk. In this review, epidemiological evidences are discussed that the LNT hypothesis is incorrect at low doses. A large set of data was accumulated that showed that cancer risk after ordinarily encountered radiation exposure (natural background radiation, medical X-rays, etc.) is much lower than projections based on the LNT model. The discovery of the low-level radiation hormesis (stimulating effect) implies a non-linear dose-response curve in the low-dose region. The further studies in this field will provide new insights about the mechanisms of radiation carcinogenesis.     

Cancer incidence and mortality after low-dosage radiation exposure: Epidemiological aspects

Current recommendations for limiting exposure to ionizing radiation are based on the linear no-threshold (LNT) model for radiation carcinogenesis under which every dose, no matter how low, bears some cancer risk. In this review, epidemiological evidence is discussed that the LNT hypothesis is incorrect at low doses. A large set of data was accumulated that show that cancer risk after ordinarily encountered radiation exposure (natural background radiation, medical X-rays, etc.) is much lower than estimates based on the LNT model. The discovery of low-level radiation hormesis (stimulating effect) implies a non-linear dose-response curve in the low-dosage region. Further studies in this field will provide new insights into the mechanisms of radiation carcinogenesis.     

Estimation of background radiation doses for the Peninsular Malaysia’s population by ESR dosimetry of tooth enamel

Background radiation dose is used in dosimetry for estimating occupational doses of radiation workers or determining radiation dose of an individual following accidental exposure. In the present study, the absorbed dose and the background radiation level are determined using the electron spin resonance (ESR) method on tooth samples. The effect of using different tooth surfaces and teeth exposed with single medical X-rays on the absorbed dose are also evaluated. A total of 48 molars of position 6–8 were collected from 13 district hospitals in Peninsular Malaysia. Thirty-six teeth had not been exposed to any excessive radiation, and 12 teeth had been directly exposed to a single X-ray dose during medical treatment prior to extraction. There was no significant effect of tooth surfaces and exposure with single X-rays on the measured absorbed dose of an individual. The mean measured absorbed dose of the population is 34 ± 6.2 mGy, with an average tooth enamel age of 39 years. From the slope of a regression line, the estimated annual background dose for Peninsular Malaysia is 0.6 ± 0.3 mGy y⁻¹. This value is slightly lower than the yearly background dose for Malaysia, and the radiation background dose is established by ESR tooth measurements on samples from India and Russia.     

Current problems of estimation of genetic risk of human exposure to radiation

The methodology of assessing the genetic risk of radiation exposure is based on the concept of "hitting the target" in development of which N.V. Timofeeff-Ressovsky has played and important role. To predict genetic risk posed by irradiation, the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has worked out direct and indirect methods of assessment, extrapolational, integral and populational criteria of risk analysis that together permit calculating the risk from human exposure on the basis of data obtained for mice. Laboratory mice are the main objects in studying radiation mutagenesis due to the fact that the data on the frequency of radiation-induced human mutations are rather scarce. The method of doubling dose based on the determination of a dose doubling the level of natural mutational process in humans is the main one used to predict the genetic risk. The evolution of views about the genetics risk of human exposure to radiation for last 40 years is considered. Till 1972 the main model for assessing the genetic risk was the "human/mouse" model (the use of data on the spontaneous human variability and data on the frequency of induced mutations in mice). In the period form 1972 till 1994 the "mouse/mouse" model was intensively elaborated in many laboratories. This model was also used in this period by UNSCEAR experts to analyze the genetic risk from human irradiation. Recent achievements associated with the study of the molecular nature of many hereditary human diseases as well as the criticism of number fundamental principles of the "mouse/mouse" model for estimating the genetic risk on a new basis. The estimates of risk for the different classes of genetic diseases have been obtained using the doubling-dose method. The estimate of doubling dose used in the calculations is 1 Gy for low dose/chronic low-LET radiation conditions.     

Effects of reduced natural background radiation on Drosophila melanogaster growth and development as revealed by the FLYINGLOW program

Natural background radiation of Earth and cosmic rays played a relevant role during the evolution of living organisms. However, how chronic low doses of radiation can affect biological processes is still unclear. Previous data have indicated that cells grown at the Gran Sasso Underground Laboratory (LNGS, L'Aquila) of National Institute of Nuclear Physics (INFN) of Italy, where the dose rate of cosmic rays and neutrons is significantly reduced with respect to the external environment, elicited an impaired response against endogenous damage as compared to cells grown outside LNGS. This suggests that environmental radiation contributes to the development of defense mechanisms at cellular level. To further understand how environmental radiation affects metabolism of living organisms, we have recently launched the FLYINGLOW program that aims at exploiting Drosophila melanogaster as a model for evaluating the effects of low doses/dose rates of radiation at the organismal level. Here, we will present a comparative data set on lifespan, motility and fertility from different Drosophila strains grown in parallel at LNGS and in a reference laboratory at the University of L'Aquila. Our data suggest the reduced radiation environment can influence Drosophila development and, depending on the genetic background, may affect viability for several generations even when flies are moved back to normal background radiation. As flies are considered a valuable model for human biology, our results might shed some light on understanding the effect of low dose radiation also in humans.     

Time-dependent changes of the physiological status of Bromus inermis Leyss. seeds from chronic low-level radiation exposure areas

The seed progeny of smooth brome (Bromus inermis Leyss.) were evaluated over a year for their viability, mutation rate, resistance to radiation and antioxidant status in response to chronic radiation exposure. Bromus inermis is found in the Eastern Ural Radioactive Trace (EURT) area and the background territories (surrounding territories that are used as controls as they only have natural background radiation). The absorbed doses by smooth brome from the EURT area were 1.5–18.5 times higher compared to background locations for parent plants and 1.1–11.6 times higher for the seed embryos. There are predictable and asynchronous changes in the survival of shoots and root growth rate between background populations and chronically irradiated samples. The provocative dose of 250 Gy is more damaging in the winter months, than in the summer and autumn. The frequency of anomalies in shoots varied in different months, with the biggest rate of mutation recorded in physiologically harsher period (autumn–winter). There is no correlation between resulting survival rate of shoots and their resistance to radiation. The intense activity of the antioxidant systems (estimated by the content of low molecular weight antioxidants) allowed faster growth of the shoots and reduced the number of abnormalities seen in development.     

Temporal separation of Cerenkov radiation and scintillation using artificial neural networks in Clinical LINACs

The irradiation of scintillator-fiber optic dosimeters by clinical LINACs results in the measurement of scintillation and Cerenkov radiation. In scintillator-fiber optic dosimetry, the scintillation and Cerenkov radiation responses are separated to determine the dose deposited in the scintillator volume. Artificial neural networks (ANNs) were trained and applied in a novel single probe method for the temporal separation of scintillation and Cerenkov radiation. Six dose profiles were measured using the ANN, with the dose profiles compared to those measured using background subtraction and an ionisation chamber. The average dose discrepancy of the ANN measured dose was 2.2% with respect to the ionisation chamber dose and 1.2% with respect to the background subtraction measured dose, while the average dose discrepancy of the background subtraction dose was 1.6% with respect to the ionisation chamber dose. The ANNs performance was degraded when compared with background subtraction, arising from an inaccurate model used to synthesise ANN training data.     

Effect of low and chronic radiation exposure: a case-control study of mental retardation and cleft lip/palate in the monazite-bearing coastal areas of southern Kerala

A population-based 1:3 age-matched case-control study was conducted during 2006-2009 to assess the role of high-level natural radiation (>1 mSv/year) on congenital mental retardation and cleft lip/palate in the southwest coastal area of Kerala. Dosimetry was carried out in the house where parents resided during conception and the subsequent two trimesters of pregnancy of the study subject. Conditional logistic regression did not suggest any statistically significant association of either mental retardation (n = 445) or cleft lip/palate (n = 116) with high-level natural radiation. The odds of mental retardation and cleft lip/palate among those exposed to high-level natural radiation relative to normal levels of natural background radiation (≤1 mSv/year) were 1.26 (95% CI: 0.91-1.73) and 0.56 (95% CI: 0.31-1.02), respectively, after controlling for gender and maternal age at birth of the study subject. The data did not suggest any dose-related trend in the risk of either mental retardation (P = 0.113) or cleft lip/palate (P = 0.908). Notwithstanding the use of a single dose estimate to reconstruct past radiation exposure and the complex etiology of congenital malformations, it may reasonably be concluded that the prevailing high-level natural radiation in the study area does not appear to increase the risk of either mental retardation or cleft lip/palate among offspring of parents staying in the area.     

Background gamma radiation and childhood cancer in Germany: an ecological study

The relationship of low-dose background gamma radiation and childhood leukaemia was investigated in a number of studies. Results from these studies are inconclusive. Therefore, in the present study 25 years of German childhood cancer data were analyzed using interpolated background annual gamma dose rate per community in an ecological study. The main question was leukaemia; as exploratory questions we investigate central nervous system (CNS) tumours, thyroid carcinomas and diagnoses less likely to be related to radiation. A Poisson regression model was applied and a fractional polynomial model building procedure. As the main sensitivity analysis a community deprivation index was included as a potential confounder. It was found that outdoor background gamma annual dose rates in Germany range roughly from 0.5–1.5 mSv/a with an average of 0.817 mSv/a. No association of annual ambient gamma dose rates with leukaemia incidence was found. Amongst the exploratory analyses, a strong association was found with CNS tumour incidence [rate ratio for 1.5 vs 0.5 mSv/a: 1.35; 95% confidence interval (1.17, 1.57)]. The community level deprivation index was not a confounder. It is concluded that the present study did not confirm an association of annual outdoor ambient gamma dose rate and childhood leukaemia, corresponding to some studies and contrasting others. An association with CNS incidence was found in the exploratory analyses. As this is an ecological study no causal interpretation is possible.     

Geochemical ecology and problems of health.

The state of health or disease is determined by the nature of the organism, the properties of the biosphere, the heterogeneity of its natural geochemical composition and changes brought about by technology (technogenic changes). For a systematic study of the conditions of health and endemic diseases we have suggested a system of biogeochemical regionalizing of the biosphere with the aid of biospheric taxa: regions of the biosphere, subregions of the biosphere, biogeochemical provinces. The main criteria of the regionalizing are biogenous cycles of chemical elements (links of the biogeochemical food chain from soil-forming rocks to man). An important criterion of the biogeochemical regionalizing is threshold concentrations of chemical elements. The organism regulates its metabolism within the ranges of chemical element concentration between the upper and lower thresholds (necessity range). When chemical elements are present in concentrations above the upper threshold and below the lower threshold, dysfunctions and endemic diseases are observed. Hence, the biogeochemical food chain allows us to establish critical links responsible for the state of health or endemic disease. Principles of optimizing the conditions of the environment and life have been worked out. The creation by us in the U.S.S.R. of biogeochemical maps relating conditions of the environment to biological reactions of organisms has proved a useful method of studying the ecological structure of the biosphere.