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.     

Radon and thoron exposures for cave residents in Shanxi and Shaanxi provinces

Measurements of natural radiation were carried out in cave dwellings distributed in the Chinese loess plateau. Those dwellings are located in Shanxi and Shaanxi provinces. Radon and thoron gas concentrations were measured using a passive integrating radon-thoron discriminative detector. Concentrations of thoron decay products were estimated from measurements of their deposition rates. A detector was placed at the center of each dwelling for 6 months and replaced with a fresh one for another 6 months. Measurements were conducted in 202 dwellings from August 2001 through August 2002. A short-term measurement was conducted during the observation period. In addition, gamma-ray dose rates were measured both indoors and outdoors with an electronic pocket dosimeter. Radioactivities in soil were determined by gamma-ray spectrometry with a pure germanium detector. Among 193 dwellings, indoor radon concentrations ranged from 19 to 195 Bq m(-3) with a geometric mean (GM) of 57 Bq m(-3), indoor thoron concentrations ranged from 10 to 865 Bq m(-3) with a GM of 153 Bq m(-3), and indoor equilibrium equivalent thoron concentrations ranged from 0.3 to 4.9 Bq m(-3) with a GM of 1.6 Bq m(-3). Arithmetic means of the gamma-ray dose rates were estimated to be 140 nGy h(-1) indoors and 110 nGy h(-1) outdoors. The present study revealed that the presence of thoron is not negligible for accurate radon measurements and thus that special attention should be paid to thoron and its decay products for dose assessment in such an environment. More systematic studies are necessary for a better understanding of thoron and its decay products.     

Calculation of the 1995 lung cancer incidence in the Netherlands and Sweden caused by smoking and radon: risk implications for radon

A two-mutation carcinogenesis model was used to calculate the expected lung cancer incidence caused by both smoking and exposure to radon in two populations, i.e. those of the Netherlands and Sweden. The model parameters were taken from a previous analysis of lung cancer in smokers and uranium miners and the model was applied to the two populations taking into account the smoking habits and exposure to radon. For both countries, the smoking histories and indoor radon exposure data for the period 1910-1995 were reconstructed and used in the calculations. Compared with the number of lung cancer cases observed in 1995 among both males and females in the two countries, the calculations show that between 72% and 94% of the registered lung cancer cases may be attributable to the combined effects of radon and smoking. In the Netherlands, a portion of about 4% and in Sweden, a portion of about 20% of the lung cancer cases (at ages 0-80 years) may be attributable to radon exposure, the numbers for males being slightly lower than for females. In the Netherlands, the proportions of lung cancers attributable to smoking are 91% for males and 71% for females; in Sweden, the figures are 70% and 56%, respectively. The risk from radon exposure is dependent on gender and cigarette smoking: the excess absolute risk for continuous exposure to 100 Bq m-3 ranges between 0.003 and 0.006 and compares well with current estimates, e.g. 0.0043 of the International Commission on Radiological Protection (ICRP). The excess relative risk for continuous exposure to 100 Bq m-3 shows a larger variation, ranging generally between 0.1 for smokers and 1.0 for non-smokers. The results support the assumption that exposure to (indoor) radon, even at a level as low as background radiation, causes lung cancer proportional to the dose and is consistent with risk factors derived from the miners data.     

Distribution of 222Rn in groundwater and estimation of resulting radiation dose to different age groups: A case study from Bangalore City

Ingesting waters holding high levels of natural occurring radioactive element like Radon would contribute to increase in the effective dose received by people followed by an increased prevalence of cancer. The current study is an attempt to describe the extent of contribution of ²²²Rn to natural background radiation and the resultant effective dose to public of different age groups. In order to do so, 65 groundwater samples from selected parts of Bangalore city were collected and analyzed for radon activity using RAD7 radon monitor coupled with RAD H₂O accessories. The radon activity was in the range of 3.05–696 Bq/L (mean: 91.39 Bq/L) and 92.31% of the groundwater samples recorded elevated radon concentration above the United States environmental protection agency (USEPA's) Maximum Contaminant Level (MCL) value of 300 pCi/L, corresponding to 11.1 Bq/L. The mean annual effective dose contribution of people falling under different age groups (viz., infants, children, teens: males and females, adults: males and females, pregnant and lactating women) due to ingestion of water-borne ²²²Rn ranged from 0.082 to 0.444 mSv/y and was found to be higher in all the age groups of males compared to respective female age groups, but well within the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and World Health Organization (WHO) proposed limit of 1 mSv/y.     

Bone structural parameters, dosimetry, and relative radiation risk in the beagle skeleton

A variety of morphometric and histomorphometric parameters such as the mass of bone and marrow, bone surface areas, percentage of bone volume, percentage of the surface that is trabecular, and percentage of surfaces that are forming and resting are calculated for all major parts of the beagle skeleton. The total bone surface of the beagle is estimated at 2.9 m2 with 53.7% of the surface area being associated with trabecular bone. There are about 4.5 x 10(9) bone-lining cells and about 1 x 10(9) osteoblasts. From the fractional retention in each part of the skeleton, the initial surface concentration of 239Pu after a single injection of 592 Bq/kg body wt (0.016 microCi/kg) on resting surfaces and at sites of bone formation is calculated for various values of the affinity ratios of trabecular/cortical and forming/resting surfaces. These estimated concentrations then yield dose rates as well as cumulative and collective doses to bone-lining cells and osteoblasts in the different parts of the skeleton. On the assumption that the relative risk of tumor induction is proportional to the collective dose to either bone-lining cells or osteoblasts, the frequency of tumor occurrence is calculated and compared to observed frequencies. Both hypotheses yield approximate agreement with experimental data for different ratios of trabecular/cortical radiation sensitivity, although the differences between some bones are statistically significant.     

Survival of clonogenic cells of Lewis lung carcinoma cells forming colonies in agar cultures in diffusion chambers during gamma-irradiation and exposure to gamma-neutron californium-252 irradiation

Clonogenic cells forming colonies in agar cultures in diffusion chambers and those isolated from subcutaneously transplanted Lewis lung carcinoma do not differ in their sensitivity to 60Co gamma-rays with respect to tumor growth stages. The dose-survival curves for all studied cells are S-shaped with a small shoulder. A cumulative dose-survival curve for malignant clonogenic cells is characterized by the average value of mean lethal dose D0 = 2.24 Gy and extrapolation number n = 2.0. When exposed to gamma-neutron-radiation (252Cf) malignant clonogenic cells exhibit a nearly exponential dose-survival curve with D0 = 0.56 Gy (with respect to a neutron component). The RBE of gamma-neutron radiation (252Cf) is 2.5.     

Physical and biological organ dosimetry analysis for international space station astronauts

In this study, we analyzed the biological and physical organ dose equivalents for International Space Station (ISS) astronauts. Individual physical dosimetry is difficult in space due to the complexity of the space radiation environment, which consists of protons, heavy ions and secondary neutrons, and the modification of these radiation types in tissue as well as limitations in dosimeter devices that can be worn for several months in outer space. Astronauts returning from missions to the ISS undergo biodosimetry assessment of chromosomal damage in lymphocyte cells using the multicolor fluorescence in situ hybridization (FISH) technique. Individual-based pre-flight dose responses for lymphocyte exposure in vitro to gamma rays were compared to those exposed to space radiation in vivo to determine an equivalent biological dose. We compared the ISS biodosimetry results, NASA's space radiation transport models of organ dose equivalents, and results from ISS and space shuttle phantom torso experiments. Physical and biological doses for 19 ISS astronauts yielded average effective doses and individual or population-based biological doses for the approximately 6-month missions of 72 mSv and 85 or 81 mGy-Eq, respectively. Analyses showed that 80% or more of organ dose equivalents on the ISS are from galactic cosmic rays and only a small contribution is from trapped protons and that GCR doses were decreased by the high level of solar activity in recent years. Comparisons of models to data showed that space radiation effective doses can be predicted to within about a +/-10% accuracy by space radiation transport models. Finally, effective dose estimates for all previous NASA missions are summarized.     

Preliminary dose estimation from indoor radon for the medical staff of Radiation Oncology and Nuclear Medicine

The aim of this preliminary study was to measure the indoor radon activity concentration in the houses and offices of Radiation Oncology and Nuclear Medicine staff at Dokuz Eylül University and to assess the results from a radiological perspective. LR-115 type II solid-state nuclear track detectors were installed in the homes and hospital and were exposed for 2 months. LR-115 type II detectors were etched for 90 min in 10% (2.5 M) NaOH solution at 60°C and radon activity concentration was determined from observed microscopic track densities. It was observed that measured indoor radon concentration ranged between 18 and 624 Bq/m³ with a geometric mean of 95 Bq/m³ in hospital, and between 22 and 560 Bq/m³ with a geometric mean of 129 Bq/m³ in homes. Estimates of the annual effective dose received by medical staff who participated in the study ranged between 0.76 and 8.79 mSv. On average, the hospital building contributed 41% to the annual effective dose. The reported values for radon concentrations and the corresponding estimated annual effective equivalent doses were within the limits recommended by the International Commission on Radiological Protection as well as the Turkish Atomic Energy Commission recommended limits for workplaces and houses.     

Dosimetric assessment of radon in a vegetable system

An alpha-dose calculation due to radon uptake in anthers of Tradescantia, clone 4430, has been performed. Probability distribution density of the dose in the pollen mother cells was calculated by means of a model that simulates the interaction of separate alpha-particles with these cells. It is shown that alpha-radiation from either radon or its decay products surrounding the buds does not reach pollen mother cells because of the short-range alpha-particles. However, it is suggested that radon diffuses through the gap structure of the bud to the anther from which a radon-gas adsorption process takes place. Absorbed-dose calculations in the anther are discussed as well as their relationship to the experimental results of micronucleus induction in pollen mother cells. The radon concentration interval used (0.85 kBq m(-3)-98.16 kBq m(-3)) is equivalent to the exposure to an average environmental radon concentration (40 Bq m(-3)) for 2.3 months or 22.1 years, respectively. The lowest radon concentration to induce micronuclei was 12.1 kBq m(-3), which is 15 times in excess of that adopted for old buildings in Canada.     

Cytogenetic analyses in peripheral lymphocytes of persons living in houses with increased levels of indoor radon concentrations

Published data concerning the effects of indoor radon exposure on the frequency of chromosome aberrations in peripheral lymphocytes of residents are contradictory. Possible reasons for this may be the low radon concentration in dwellings and/or the limited number of investigated persons. We therefore studied the relationship of domestic radon exposure and the occurrence of chromosome aberrations in peripheral lymphocytes in 61 persons living in houses with radon concentrations from 80 up to 13,000 Bq/m3. We analyzed 60,000 cells from fluorescence plus Giemsa (FPG)-stained slides. It could be clearly demonstrated that in groups of persons living in dwellings with indoor radon concentrations >200 Bq/m3 the number of cells containing dicentrics and/or centric rings (C(dic + cr)) (2.45 +/- 0.50 x 10(-3)) was significantly increased (p < 0.05) in comparison to the control level (1.03 +/- 0.15 x 10(-3)). However, there was no difference in the mean frequency of C(dic + cr) between the groups living in dwellings with higher radon concentrations. Using the fluorescence in situ hybridization (FISH) technique for the detection of translocations, we analyzed 23,315 cells in 16 persons of the highest exposed group (>5,000 Bq/m3). The observed frequency of translocations was 3.9 +/- 0.64 x 10(-3). In comparison to the control group (2.02 +/- 0.18 x 10(-3)), there was a slight but not statistically significant increase in the exposed group (P = 0.055). If, however, the age of the examined persons is taken into account, the values are significantly increased (P < 0.05) in the exposed persons older than 40 years in comparison to the age-matched controls. Since most of the translocations were found in stable cells, it is concluded that translocations are also induced in blood-forming tissue and are transmitted to peripheral blood.     

Comparison of antioxidative effects between radon and thoron inhalation in mouse organs

Radon therapy has been traditionally performed globally for oxidative stress-related diseases. Many researchers have studied the beneficial effects of radon exposure in living organisms. However, the effects of thoron, a radioisotope of radon, have not been fully examined. In this study, we aimed to compare the biological effects of radon and thoron inhalation on mouse organs with a focus on oxidative stress. Male BALB/c mice were randomly divided into 15 groups: sham inhalation, radon inhalation at a dose of 500 Bq/m³ or 2000 Bq/m³, and thoron inhalation at a dose of 500 Bq/m³ or 2000 Bq/m³ were carried out. Immediately after inhalation, mouse tissues were excised for biochemical assays. The results showed a significant increase in superoxide dismutase and total glutathione, and a significant decrease in lipid peroxide following thoron inhalation under several conditions. Additionally, similar effects were observed for different doses and inhalation times between radon and thoron. Our results suggest that thoron inhalation also exerts antioxidative effects against oxidative stress in organs. However, the inhalation conditions should be carefully analyzed because of the differences in physical characteristics between radon and thoron.

     

Evaluation of radon effects on lung cancer development

In order to evaluate the effect of indoor exposure to radon and thoron on the development of lung cancer in the population of two towns of Sverdlovsk Region, epidemiologic studies were conducted using a multifactarial method of analysis. Both towns, Pervouralsk and Karpinsk, are located within the geological area with the gamma-radiation exposure dose ranging from 5 to 12 mu r/hr, and are characterized by an increased cancer incidence rate--323.1 and 364.6 cases per 100,000 of population, respectively. The mean values of the voluminous indoor activity (VA) of radon in Pervouralsk and Karpinsk were 23 and 75 Bq/m3 (with maximal indices of radon VA being 395 and 739 Bq/m3), equivalent equilibrium concentrations (EEC) of residential radon and thoron were 0.6 and 2.5 Bq/m3 (maximal indices of EEC of thoron being 5 and 13 Bq/m3), respectively. The results of multifactorial analysis of 22 different lung cancer risk factors carried out using the pattern recognition method proved that the contribution of thoron and radon in the development of lung cancer in the population of Pervouralsk and Karpinsk was not significant--0.5 and 0.6%, respectively. The calculations performed in a monofactorial model of risk evaluation BEIR VI gave different results--11-16% and 35-52% for the towns of Pervouralsk and Karpinsk, respectively. The discussion of the results provides arguments for the reliability and adequacy of the application of multifactorial method of radiation risk evaluation as compared to the traditionally applied monofactorial method.     

The conversion of exposures due to radon into the effective dose: the epidemiological approach

The risks and dose conversion coefficients for residential and occupational exposures due to radon were determined with applying the epidemiological risk models to ICRP representative populations. The dose conversion coefficient for residential radon was estimated with a value of 1.6 mSv year^?1 per 100 Bq m^?3 (3.6 mSv per WLM), which is significantly lower than the corresponding value derived from the biokinetic and dosimetric models. The dose conversion coefficient for occupational exposures with applying the risk models for miners was estimated with a value of 14 mSv per WLM, which is in good accordance with the results of the dosimetric models. To resolve the discrepancy regarding residential radon, the ICRP approaches for the determination of risks and doses were reviewed. It could be shown that ICRP overestimates the risk for lung cancer caused by residential radon. This can be attributed to a wrong population weighting of the radon-induced risks in its epidemiological approach. With the approach in this work, the average risks for lung cancer were determined, taking into account the age-specific risk contributions of all individuals in the population. As a result, a lower risk coefficient for residential radon was obtained. The results from the ICRP biokinetic and dosimetric models for both, the occupationally exposed working age population and the whole population exposed to residential radon, can be brought in better accordance with the corresponding results of the epidemiological approach, if the respective relative radiation detriments and a radiation-weighting factor for alpha particles of about ten are used.     

Alkaline single cell gel electrophoresis and human biomonitoring for genotoxicity: a study on subjects with residential exposure to radon.

Based on theoretical estimates and various correlation studies, it has been suggested that ingestion of radon in drinking water represents an increased risk for cancer. Such a risk has never been conclusively shown in epidemiological or experimental animal studies, however, and it has been questioned whether the radon level in the drinking water is of any significance in terms of overall radon exposure. Using primary DNA damage as a biological marker for an ongoing exposure to ionising radiation, the present study was undertaken to investigate whether people with different types of residential radon exposures differed with regard to their levels of DNA damage in circulating lymphocytes. DNA damage was measured in coded blood samples from 125 residents living in 45 households with different levels of radon-222 in the drinking water (10-2410 Bq/l) and indoor air (35-1025 Bq/m3) using alkaline single cell gel electrophoresis (the 'Comet' assay). Increased levels of radon in indoor air (>200 Bq/m3) were found to be associated with an increased level of DNA damage in peripheral lymphocytes (P相似文献   

Expression of blood serum proteins and lymphocyte differentiation clusters after chronic occupational exposure to ionizing radiation

This study aimed to assess effects of chronic occupational exposure on immune status in Mayak workers chronically exposed to ionizing radiation (IR). The study cohort consists of 77 workers occupationally exposed to external gamma-rays at total dose from 0.5 to 3.0 Gy (14 individuals) and workers with combined exposure (external gamma-rays at total dose range 0.7–5.1 Gy and internal alpha-radiation from incorporated plutonium with a body burden of 0.3–16.4 kBq). The control group consists of 43 age- and sex-matched individuals who never were exposed to IR, never involved in any cleanup operations following radiation accidents and never resided at contaminated areas. Enzyme-linked immunoassay and flow cytometry were used to determine the relative concentration of lymphocytes and proteins. The concentrations of T-lymphocytes, interleukin-8 and immunoglobulins G were decreased in external gamma-exposed workers relative to control. Relative concentrations of NKT-lymphocytes, concentrations of transforming growth factor-β, interferon gamma, immunoglobulins A, immunoglobulins M and matrix proteinase-9 were higher in this group as compared with control. Relative concentrations of T-lymphocytes and concentration of interleukin-8 were decreased, while both the relative and absolute concentration of natural killers, concentration of immunoglobulins A and M and matrix proteinase-9 were increased in workers with combined exposure as compared to control. An inverse linear relation was revealed between absolute concentration of T-lymphocytes, relative and absolute concentration of T-helpers cells, concentration of interferon gamma and total absorbed dose from external gamma-rays in exposed workers. For workers with incorporated plutonium, there was an inverse linear relation of absolute concentration of T-helpers as well as direct linear relation of relative concentration of NKT-lymphocytes to total absorbed red bone marrow dose from internal alpha-radiation. In all, chronic occupational IR exposure of workers induced a depletion of immune cells in peripheral blood of the individuals involved.     

The re-establishment of hypersensitive cells in the crypts of irradiated mouse intestine

Within 3-6 h of small doses of radiation (gamma-rays) the number of dead cells (apoptotic cells) in the crypts of the small intestine reaches peak values. These return to normal levels only after times later than 1 day. After higher doses elevated levels of cell death persist for longer times. The dead cells first occur most frequently at the lower positions of the crypt (median value for the distribution of apoptotic fragments is about cell position 6). At later times more dead cells are observed at higher positions. Two doses of radiation separated by various time intervals have been used to investigate when after irradiation the cell population susceptible to acute cell death is re-established. Dead cells were scored 3 or 6 h after the second dose. The yield of dead cells after two doses represents the sum of the dead cells produced by, and persisting from, the first dose and new apoptotic cells induced by the second dose. Since the temporal and dose-dependence aspects of the dead-cell yield after the first dose alone is known, the additional dead cells attributable to the second dose alone can be determined by subtraction. Within 1-2 days of small doses (0.5 Gy) the sensitive cells, recognized histologically as apoptotic cells, are re-established at the base of the crypt (around cell position 6). After higher doses (9.0 Gy) they are not re-established until about the fourth day after irradiation. Even in the enlarged regenerating crypts the sensitive cells are found at the same position at the crypt base. It has been estimated that the crypt contains five or six cells that are susceptible to low doses (0.5 Gy) (hypersensitive cells) and up to a total of only seven or eight susceptible cells that can be induced by any dose to enter the sequence of changes implicit in apoptosis. Between 4 and 10 days after an initial irradiation of 9.0 Gy the total number of susceptible cells increased from seven to eight to about 10 to 13 per crypt.     

Pretreatment with oxygen species increases the resistance of mammalian cells to hydrogen peroxide and gamma-rays

Pretreatment of Chinese hamster ovary (CHO) or H4 (rat hepatoma) cells with low non-toxic doses of H2O2 or xanthine-xanthine oxidase renders the cells more resistant to the toxic effect of H2O2 and gamma-rays. This increased resistance is observed both in exponentially growing and in plateau-phase cells. Cells pretreated with xanthine-xanthine oxidase are less mutated than control cultures when challenged with ionizing radiation. The number of DNA single-strand breaks (measured by nucleoid sedimentation) induced by a high dose of gamma-rays or H2O2 is lower in cells pretreated with xanthine-xanthine oxidase compared to control cultures. However, the pretreatment does not modify the rate of DNA single-strand breaks rejoining in cells challenged with H2O2 or gamma-rays. The catalase activity is not modified in pretreated cells, but the superoxide dismutase activity is increased about 2-fold.     

Temporal variation of thoron decay product concentration in the atmosphere and comparison with radon decay product concentration

Seasonal and long-term variation of the airborne ²¹²Pb concentration, representative of the equilibrium equivalent concentration of thoron decay products (EEC_Rn220), was investigated from 1989 through 1996 at a semi-natural location in southern Germany. Continuous measurement yielded a long-term average concentration of 0.082 Bq m^–3, while daily mean concentrations varied from ≤0.01 to 0.34 Bq m^–3. An average annual effective dose of 1.4 mSv due to outdoor thoron progeny concen-tration was estimated. This is about 2% of the dose due to the average short-lived radon progeny concentration (EEC_Rn222) of 8.4 Bq m^–3 measured for this location in the same period. In most years the seasonal pattern of ²¹²Pb activity concentration in the atmosphere is characterized by two maxima: the first in May and the second one in September. Low concentrations are observed from November through February of each year. This is in contrast to the behaviour of the short-lived ²²²Rn progeny which exhibit enhanced concentrations exactly during these months. The most probable reason for the different temporal behaviour of ²¹²Pb is the extremely reduced flux of thoron gas from the ground during the winter months. Received: 19 August 1997 / Accepted in revised form: 22 January 1998