Dose-effect relationship of dicentric and ring chromosomes in lymphocytes of individuals living in the high background radiation areas in China

Assessment of natural radioactivity levels and hazard indicators in Tarakeshwor Municipality, Nepal through in-situ technique and multivariate analysis

The evaluation of primordial radionuclide concentrations in rapidly urbanized and concrete-laden areas through the importation of construction materials from various regions of Nepal is both important and essential. This study utilized a portable gamma-ray spectrometer (PGIS 2) to analyze the distribution of three natural radionuclides: uranium (238U), thorium (232Th), and potassium (40K) in Tarakeshwor Municipality, Kathmandu, Nepal. The measured dose rates ranged from 70.22 nSv hr-1 to 163.66 nSv hr-1, with an average of 124.65±20.29 nSv hr-1, surpassing the global average of 59 nSv hr-1. The activity concentrations of 40K, 238U, and 232Th exceeded global averages, indicating relatively higher natural radioactivity concentrations in the region. Specifically, the average values for 40K, 238U, and 232Th were 935.26±172.30 Bq kg-1, 80.47±15.53 Bq kg-1, and 80.44±18.58 Bq kg-1, respectively. The calculated radium equivalent (Ra eq ) ranged from 132.26 to 351.22 Bq kg-1, and the annual gonadal equivalent dose (A G E D ) varied from 372.61 to 1028.81 μSv yr-1. The annual effective dose rates for indoor and outdoor environments were 0.54±0.09 mSv yr-1 and 0.15±0.03 mSv yr-1, respectively, both exceeding the global average. The representative level index (RLI) within the study area averaged 1.96±0.32, indicating an elevated radiation risk. The excess lifetime cancer risk (E L C R ) values for outdoor and indoor environments were 0.52× 10 - 3 ±0.09 × 10 - 3 and 1.87 × 10 - 3 ±0.31× 10 - 3 , respectively, surpassing the world average. Additionally, external hazard indices (H ex ) ranged from 0.36 to 0.59, while internal hazard indices (H in ) ranged from 0.38 to 1.20, both indicating values higher than UNSCEAR recommendations. These findings underscore the necessity for further experimental analysis employing ex-situ equipment. The data generated in this study can provide a valuable baseline for future assessments and interventions in radiation risk management guidelines within the country.

Persons chronically exposed to low doses of ionizing radiation: A cytogenetic dosimetry study

The dosimetry and control of exposure for individuals chronically exposed to ionizing radiation are important and complex issues. Assessment may be optimized by evaluating individual adaptation and radiosensitivity, but it is not possible for a single model to account for all relevant parameters. Our goal was to develop approaches for the calculation of doses for persons chronically exposed to ionizing radiation, taking their radiosensitivities into consideration. On the basis of ex vivo radiation of blood samples, dose-effect models were constructed for dose ranges 0.01-2.0 and 0.01-0.4 Gy, using different cytogenetic criteria. The frequencies of "dicentric chromosomes and rings" at low doses are too low to have predictive value. The different responses of subjects to radiation made it possible to categorize them according to their radiosensitivities and to generate separate dose-effect curves for radiosensitive, average, and radioresistant individuals, reducing the amount of error in retrospective dosimetry.

Frequencies of Chromosome Aberrations are Lower in Splenic Lymphocytes from Mice Continuously Exposed to Very Low-Dose-Rate Gamma Rays Compared with Non-Irradiated Control Mice

Chromosome aberrations have been one of the most sensitive and reliable biomarkers of exposure to ionizing radiation. Using the multiplex fluorescence in situ hybridization (M-FISH) technique, we compared the changes, over time, in the frequencies of translocations and of dicentric chromosomes in the splenic lymphocytes from specific pathogen-free (SPF) C3H/HeN female mice continuously exposed to 0.05 mGy/day (18.25 mGy/year) gamma rays for 125 to 700 days (total accumulated doses: 6.25-35 mGy) with age-matched non-irradiated controls. Results show that the frequencies of translocations and of dicentric chromosomes increased significantly over time in both irradiated and non-irradiated control mice, and that the frequencies were significantly lower, not higher, in the irradiated mice, which differs from our previous reports of increased chromosome aberration frequencies at higher radiation dose rates of 1 mGy/day and 20 mGy/day. These results will be useful when considering the radiation risk at very low-dose rates comparable to regulatory dose limits.

Biological and cellular responses of humans to high-level natural radiation: A clarion call for a fresh perspective on the linear no-threshold paradigm

There remains considerable uncertainty in obtaining risk estimates of adverse health outcomes of chronic low-dose radiation. In the absence of reliable direct data, extrapolation through the linear no-threshold (LNT) hypothesis forms the cardinal tenet of all risk assessments for low doses (≤ 100 mGy) and for the radiation protection principle of As Low As Reasonably Achievable (ALARA). However, as recent evidences demonstrate, LNT assumptions do not appropriately reflect the biology of the cell at the low-dose end of the dose-response curve. In this regard, human populations living in high-level natural radiation areas (HLNRA) of the world can provide valuable insights into the biological and cellular effects of chronic radiation to facilitate improved precision of the dose-response relationship at low doses. Here, data obtained over decades of epidemiological and radiobiological studies on HLNRA populations is summarized. These studies do not show any evidence of unfavourable health effects or adverse cellular effects that can be correlated with high-level natural radiation. Contrary to the assumptions of LNT, no excess cancer risks or untoward pregnancy outcomes have been found to be associated with cumulative radiation dose or in-utero exposures. Molecular biology-driven studies demonstrate that chronic low-dose activates several cellular defence mechanisms that help cells to sense, recover, survive, and adapt to radiation stress. These mechanisms include stress-response signaling, DNA repair, immune alterations and most importantly, the radiation-induced adaptive response. The HLNRA data is consistent with the new evolving paradigms of low-dose radiobiology and can help develop the theoretical framework of an alternate dose-response model. A rational integration of radiobiology with epidemiology data is imperative to reduce uncertainties in predicting the potential health risks of chronic low doses of radiation.

Committed effective dose and lifetime cancer risk due to ingestion of natural radionuclides in grains grown in an area of high background radiation

The current study aimed at estimating committed effective dose and cancer risk due to the intake of K-40, Ra-226, Ra-228 and Th-228 present in grains grown in an HBRA. The highest activity concentrations found were (606.2 ± 25.13), (8.07 ± 6.37), (10.01 ± 1.45), (43.97 ± 5.54) Bq.kg^-1 for K-40, Ra-226, Ra-228 and Th-228, respectively. The committed effective dose estimated was 0.5 mSv.y^-1, and the estimated cancer risk suggested that uninterrupted and unrestricted consumption of beans grown in this HBRA is not desirable.

Assessments of DNA Damage and Radiation Exposure Dose in Cattle Living in the Contaminated Area Caused by the Fukushima Nuclear Accident

Since the Fukushima nuclear accident in 2011, various abnormalities have been reported in animals living in the contaminated area. In the present study, we examined DNA damage in cattle living in the "difficult-to-return zone" by 8-hydroxy-2'-deoxyguanosine, comet, and micronucleus assays using their peripheral blood. The radiation exposure dose rate at the sampling time was approximately 0.25 or 0.38 mGy/day and the cumulative dose was estimated at approximately 1000 mGy. Significant increase in DNA damage was not detected by any of the three methods. As DNA damage is a stochastic effect of radiation, it might be occurring in animals living in the contaminated area. However, the present results suggest that radiation-induced DNA damage in the cattle did not increase to the level detectable by the assays we used due to the low dose rate in this area.

Assessment of chromosome aberrations in large Japanese field mice (Apodemus speciosus) in Namie Town, Fukushima

PURPOSE

After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in Japan on March 11 2011, the surroundings became contaminated with radionuclides. To understand the possible biological effects after chronic low dose-rate radiation in contaminated areas of Fukushima, we assessed the effects in large Japanese field mice (Apodemus speciosus) by means of chromosome aberration analysis.

MATERIALS AND METHODS

We collected A. speciosus in five sites around Namie Town, Fukushima (contaminated areas) and in two sites in Hirosaki City, Aomori (control areas, 350 km north of FDNPP) from autumn 2011 to 2013. The number of mice captured and ambient dose-rates were as follows: high (n = 11, 10.1-30.0 µGy h^-1), moderate (n = 10, 5.7-15.6 µGy h^-1), low (n = 12, 0.23-1.14 µGy h^-1) and control (n = 20, 0.04-0.07 µGy h^-1). After spleen extraction from rodents, spleen cell culture was performed to obtain metaphase spreads. Chromosome aberrations were assessed on Giemsa-stained metaphase spreads.

RESULTS

Although the mice in the contaminated areas were chronically exposed, there was no radiation-specific chromosome aberrations observed, such as dicentric chromosomes and rings. Some structural aberrations such as gaps and breaks were observed, and these frequencies decreased annually in mice from Namie Town.

CONCLUSION

These findings suggest that chromosome aberration analysis is useful to evaluate and monitor radiation effects in wild animals.

Investigation of the cumulative number of chromosome aberrations induced by three consecutive CT examinations in eight patients

In our previous study, we found that chromosomes were damaged by the radiation exposure from a single computed tomography (CT) examination, based on an increased number of dicentric chromosomes (Dics) formed in peripheral blood lymphocytes after a CT examination. We then investigated whether a cumulative increase in the frequency of Dics and chromosome translocations (Trs) formation could be observed during three consecutive CT examinations performed over the course of 3-4 years, using lymphocytes in peripheral bloods of eight patients (five males and three females; age range 27-77 years; mean age, 64 years). The effective radiation dose per CT examination estimated from the computational dosimetry system was 22.0-73.5 mSv, and the average dose per case was 40.5 mSv. The frequency of Dics formation significantly increased after a CT examination and tended to decrease before the next examination. Unlike Dics analysis, we found no significant increase in the frequency of Trs formation before and after the CT examination, and we observed no tendency for the frequency to decrease before the next CT examination. The frequency of Trs formation was higher than that of Dics formation regardless of CT examination. Furthermore, neither analysis of Dics nor Trs showed a cumulative increase in the frequency of formation following three consecutive CT examinations.

Is Induction of Anomalies in Lymphocytes of the Residents of High Background Radiation Areas Associated with Increased Cancer Risk?

Man has been exposed to different levels of natural background radiation since the creation of human life. There are inhabited areas around the world with extraordinary levels of natural background radiation. The level of natural radiation in these areas is up to two orders of magnitude higher than other places. Areas such as Yangjiang, China; Guarapari, Brazil; and Kerala, India are among the areas with high levels of natural radiation. Ramsar a coastal city in North Iran has some inhabited areas with the highest known levels of background radiation around the world. People who live in high background radiation areas (HBRAs) such as Ramsar do not record any detrimental biological effects. While some cytogenetic studies conducted in HBRAs have shown increased frequencies of unstable chromosome aberration, other investigations failed to find a significant difference. This short review is an attempt to verify if induction of chromosomal anomalies in the lymphocytes of the residents of high background radiation areas is associated with increased cancer risk.

Low dose or low dose rate ionizing radiation-induced health effect in the human

The extensive literature review on human epidemiological studies suggests that low dose ionizing radiation (LDIR) (≤100 mSv) or low dose rate ionizing radiation (LDRIR) (<6mSv/H) exposure could induce either negative or positive health effects. These changes may depend on genetic background, age (prenatal day for embryo), sex, nature of radiation exposure, i.e., acute or chronic irradiation, radiation sources (such as atomic bomb attack, fallout from nuclear weapon test, nuclear power plant accidents, ⁶⁰Co-contaminated building, space radiation, high background radiation, medical examinations or procedures) and radionuclide components and human epidemiological experimental designs. Epidemiological and clinical studies show that LDIR or LDRIR exposure may induce cancer, congenital abnormalities, cardiovascular and cerebrovascular diseases, cognitive and other neuropsychiatric disorders, cataracts and other eye and somatic pathology (endocrine, bronchopulmonary, digestive, etc). LDIR or LDRIR exposure may also reduce mutation and cancer mortality rates. So far, the mechanisms of LDIR- or LDRIR -induced health effect are poorly understood. Further extensive studies are still needed to clarify under what circumstances, LDIR or LDRIR exposure may induce positive or negative effects, which may facilitate development of new therapeutic approaches to prevent or treat the radiation-induced human diseases or enhance radiation-induced positive health effect.

Influence of anticoagulants and storage temperatures on blood counts and mitotic index of blood samples collected for cytogenetic biodosimetry

PURPOSE

In order to establish suitable protocols of blood culture to obtain sufficient numbers of metaphases for dicentric chromosome assay (DCA), we have examined the effect of storage temperature, storage time, and anticoagulant type.

MATERIALS AND METHODS

Peripheral blood was collected from five healthy donors with lithium heparin and ethylenediaminetetraacetic acid dipotassium salt (EDTA-2K). These samples were irradiated with X-rays at 3 Gy or sham; the samples were further divided into groups that were either stored at room temperature (RT) or 5.2 ± 1.0 °C. After 6, 24, 48, 72, and 168 h of storage, both blood counts and the mitotic index (MI) were analyzed.

RESULTS

Heparinized blood samples stored under cold conditions exhibited low white blood cell, lymphocyte, and platelet counts. EDTA-treated blood samples did not show such obvious changes in cell counts. After 6 h of storage, heparinized blood samples stored at RT had MI of 21.5-29.3%. Similar MI was obtained in the EDTA-washed group stored for 6, 24, 48, and 72 h.

CONCLUSIONS

Our study confirms that heparinized blood samples should be stored at RT to get sufficient metaphases for DCA, and that EDTA blood samples also can be used for blood culture after washing and storage under 5.2 ± 1.0 °C.

Frequency of chromosome aberrations among adult male individuals from high and normal level natural radiation areas of Kerala in the southwest coast of India

Chromosome aberration analysis was carried out in peripheral blood lymphocytes of adult male individuals from normal level natural radiation areas (NLNRA, ≤1.5 mGy/year, N = 27) and high level natural radiation areas (HLNRA, >1.5mGy/year, N = 70) of Kerala coast in southwest India. The mean age of individuals from NLNRA and HLNRA was 40.9 ± 9.4 and 43.7 ± 12.4 years, respectively, with an overall mean of 42.9 ± 11.6 (range: 18-80). Whole-blood cultures were set up and about 260 metaphases were scored per individual. The frequency of chromosome aberrations was calculated per 1000 cells. The overall basal frequency of unstable (dicentrics and rings), stable (translocations and inversions) and other (fragments and breaks) aberrations was 1.54 ± 0.25, 4.1 ± 0.40 and 6.66 ± 0.51, respectively. Individuals of NLNRA and HLNRA had statistically similar frequency of unstable (2.11 ± 0.64 v/s 1.39 ± 0.26; RR = 0.66; 95% CI: 0.33-1.33), stable (4.60 ± 0.94 v/s 3.97 ± 0.44; RR = 0.86; 95% CI: 0.55-1.36) and other (7.85 ± 1.23 v/s 6.36 ± 0.56; RR = 0.81; 95% CI: 0.57-1.15) chromosome aberrations. Frequencies of unstable, stable and other chromosome aberrations did not show any dose response after stratification of HLNRA samples into three dose groups (1.51-5.0 mGy/year, 5.01-10 mGy/year and >10.0 mGy/year). Smokers showed an increase in other chromosome aberrations (P < 0.001), but smoking was not associated with unstable and stable aberrations. Alcohol consumption and tobacco chewing had no significant association with any type of chromosome aberrations. In conclusion, chronic low dose radiation prevailing in Kerala coast did not show any significant effect on the basal frequency of chromosome aberrations among the adult population.

Dose-response curves for analyzing of dicentric chromosomes and chromosome translocations following doses of 1000 mGy or less, based on irradiated peripheral blood samples from five healthy individuals

In terms of biological dosimetry at the time of radiation exposure, the dicentric chromosome (Dic) assay (DCA) is the gold standard for assessing for the acute phase and chromosome translocation (Tr) analysis is the gold standard for assessing the chronic phase. It is desirable to have individual dose-response curves (DRCs) for each laboratory because the analysis criteria differ between laboratories. We constructed the DRCs for radiation dose estimation (with three methods) using peripheral blood (PB) samples from five healthy individuals. Aliquots were irradiated with one of eight gamma-ray doses (0, 10, 20, 50, 100, 200, 500 or 1000 mGy), then cultured for 48 h. The number of chromosome aberrations (CAs) was analyzed by DCA, using Giemsa staining and centromere-fluorescence in situ hybridization (centromere-FISH) and by chromosome painting (chromosome pairs 1, 2 and 4) for Tr analysis. In DCA, there was large variation between individuals in the frequency of Dics formed, and the slopes of the DRCs were different. In Tr analysis, although variation was observed in the frequency of Tr, the slopes of the DRCs were similar after adjusting the background for age. Good correlation between the irradiation dose and the frequency of CAs formed was observed with these three DRCs. However, performing three different biological dosimetry assays simultaneously on PB from five donors nonetheless results in variation in the frequency of CAs formed, especially at doses of 50 mGy or less, highlighting the difficulty of biological dosimetry using these methods. We conclude that it might be difficult to construct universal DRCs.

Biodosimetry of Persons Chronically Exposed to Low and Therapeutic Doses of Ionizing Radiation

Dynamic changes of the chromosomal aberrations and the DNA damage were analyzed in individuals exposed to low and therapeutic doses of radiation. The investigation included 37 persons living in areas where the radioactive sources were discovered 10–12 years ago. It was established by biodosimetry methods that the examined persons had absorbed dose of 0.2–0.7 Gy or had increased number of chromosomal aberrations, though insufficient to determine a dose. Clinical examination, chromosomal analysis, and assay of DNA damage by the comet (single-cell gel electrophoresis) assay were carried out. There was no correlation between the doses received 10 years ago and the cytogenetic changes with clinical outcome. The effect of the local fractionated gamma-irradiation with doses of 40–70 Gy was studied in cancer patients with localized head and neck tumors. The study of chromosomal abnormalities, the DNA damages by the comet assay, and the micronuclei detection of the buccal cells revealed a statistically significant correlation between the initial cytogenetic indices in cancer patients and their dynamic changes during and after the radiation exposure. In addition, the correlation was detected between the initial cytogenetic parameters and the functional stage of red blood system. Our results allow us to conclude that there is a need for further research to estimate the individual radiation risk to optimize and individualize the subsequent medical management of radiotherapy.

Lower prevalence but similar fitness in a parasitic fungus at higher radiation levels near Chernobyl

Nuclear disasters at Chernobyl and Fukushima provide examples of effects of acute ionizing radiation on mutations that can affect the fitness and distribution of species. Here, we investigated the prevalence of Microbotryum lychnidis-dioicae, a pollinator-transmitted fungal pathogen of plants causing anther-smut disease in Chernobyl, its viability, fertility and karyotype variation, and the accumulation of nonsynonymous mutations in its genome. We collected diseased flowers of Silene latifolia from locations ranging by more than two orders of magnitude in background radiation, from 0.05 to 21.03 μGy/h. Disease prevalence decreased significantly with increasing radiation level, possibly due to lower pollinator abundance and altered pollinator behaviour. Viability and fertility, measured as the budding rate of haploid sporidia following meiosis from the diploid teliospores, did not vary with increasing radiation levels and neither did karyotype overall structure and level of chromosomal size heterozygosity. We sequenced the genomes of twelve samples from Chernobyl and of four samples collected from uncontaminated areas and analysed alignments of 6068 predicted genes, corresponding to 1.04 × 10(7)  base pairs. We found no dose-dependent differences in substitution rates (neither dN, dS, nor dN/dS). Thus, we found no significant evidence of increased deleterious mutation rates at higher levels of background radiation in this plant pathogen. We even found lower levels of nonsynonymous substitution rates in contaminated areas compared to control regions, suggesting that purifying selection was stronger in contaminated than uncontaminated areas. We briefly discuss the possibilities for a mechanistic basis of radio resistance in this nonmelanized fungus.

Analysis of chromosome translocation frequency after a single CT scan in adults

We recently reported an increase in dicentric chromosome (DIC) formation after a single computed tomography (CT) scan (5.78-60.27 mSv: mean 24.24 mSv) and we recommended analysis of 2000 metaphase cells stained with Giemsa and centromere-FISH for dicentric chromosome assay (DCA) in cases of low-dose radiation exposure. In the present study, we analyzed the frequency of chromosome translocations using stored Carnoy's-fixed lymphocyte specimens from the previous study; these specimens were from 12 patients who were subject to chromosome painting of Chromosomes 1, 2 and 4. Chromosomes 1, 2 and 4 were analyzed in ∼5000 cells, which is equivalent to the whole-genome analysis of almost 2000 cells. The frequency of chromosome translocation was higher than the number of DICs formed, both before and after CT scanning. The frequency of chromosome translocations tended to be higher, but not significantly higher, in patients with a treatment history compared with patients without such a history. However, in contrast to the results for DIC formation, the frequency of translocations detected before and after the CT scan did not differ significantly. Therefore, analysis of chromosome translocation may not be a suitable assay for detecting chromosome aberrations in cases of low-dose radiation exposure from a CT scan. A significant increase in the frequency of chromosome translocations was not likely to be detected due to the high baseline before the CT scan; the high and variable frequency of translocations was probably due to multiple confounding factors in adults.

Increase in dicentric chromosome formation after a single CT scan in adults

Excess risk of leukemia and brain tumors after CT scans in children has been reported. We performed dicentric chromosome assay (DCAs) before and after CT scan to assess effects of low-dose ionizing radiation on chromosomes. Peripheral blood (PB) lymphocytes were collected from 10 patients before and after a CT scan. DCA was performed by analyzing either 1,000 or 2,000 metaphases using both Giemsa staining and centromere-fluorescence in situ hybridization (Centromere-FISH). The increment of DIC formation was compared with effective radiation dose calculated using the computational dosimetry system, WAZA-ARI and dose length product (DLP) in a CT scan. Dicentric chromosome (DIC) formation increased significantly after a single CT scan, and increased DIC formation was found in all patients. A good correlation between the increment of DIC formation determined by analysis of 2,000 metaphases using Giemsa staining and those by 2,000 metaphases using Centromere-FISH was observed. However, no correlation was observed between the increment of DIC formation and the effective radiation dose. Therefore, these results suggest that chromosome cleavage may be induced by one CT scan, and we recommend 2,000 or more metaphases be analyzed in Giemsa staining or Centromere-FISH for DCAs in cases of low-dose radiation exposure.

Cytogenetic studies for a group of people living in Japan 1 year after the Fukushima nuclear accident

In order to understand the potential health effect of radiation from Fukushima nuclear disaster, a group of people living in Japan during and after the accident were investigated 1 y after the accident. The venous blood samples were extracted in tune from 156 tested persons living in Tokyo and Niigata with average age of 42.4 ± 10.2 y old as well as 87 controls living in Beijing with similar age and sex proportion. Conventional chromosome culture and cytochalasin B micronucleus methods were applied. The unstable chromosome aberrations of 200 cells and micronuclei (MN) and micronuclei cells (MNC) of 1000 binucleated lymphocytes were analysed for each examined subject. The results showed that the frequencies ± SE (×100) of the dicentrics plus rings were 0.17 ± 0.024% and 0.13 ± 0.028% in the tested and control populations (p > 0.05), respectively. The frequencies of the extra acentrics were 0.21 ± 0.026% and 0.06 ± 0.018% in the tested and control groups (p < 0.01), respectively. The total chromosomal aberration frequencies of the tested and control groups were 0.40 ± 0.036% and 0.20 ± 0.034% (p < 0.01), respectively. The MN and MNC frequencies of the tested group were 29.25 ± 3.96 ‰ and 23.85 ± 4.23 ‰, and 25.30 ± 6.45 ‰ and 21.56 ± 3.99 ‰ for control group (p < 0.01). With the exception of dicentrics, there were significant differences (p < 0.01) between two groups in frequencies of chromosome aberration and MN. Generally, 1 y after the Fukushima nuclear accident, the dicentric frequencies had not increased in the 156 persons investigated in this study. The increase in chromatid aberrations, chromosomal acentrics and MN was induced but could not be directly linked to radiation exposures, as an excess of dicentric frequency is linked. However, the observed higher frequency of chromosomal alterations might be related to exposure to the low doses of ionising in this cohort. Consequently, it is recommended to assess the long-term health effects in this population.

Cancer and non-cancer mortality among Inhabitants in the high background radiation area of Yangjiang, China (1979-1998)

The present study aimed to evaluate the effects of high background radiation (HBR) on mortality. A cohort of 31,604 men and women aged 30-74 y living in the study area in Guangdong Province, China, was followed during the period 1979-1998. The information on deaths and migrations of cohort members was collected by visiting study areas every 3-4 y. Cumulative external radiation dose, lagged by 2 y for leukemia and 10 y for cancer excluding leukemia, was estimated for each individual based on hamlet-specific indoor and outdoor doses, and gender- and age-specific house occupancy factors. The follow-up study accumulated 736,942 person-years at risk and ascertained 6,005 deaths, including 956 cancer deaths and 4,525 non-cancer disease deaths. Mean cumulative radiation doses from natural radiation in the HBR and control area residents were 84.8 mGy and 21.6 mGy, respectively. Mortality due to leukemia (15 deaths) or cancer excluding leukemia (941 deaths) was not related to cumulative radiation dose. The excess relative risk (ERR) Gy of cancer excluding leukemia was estimated to be -1.01 (95% CI: -2.53, 0.95). In site-specific analysis, liver-cancer mortality was inversely related to the cumulative dose (p=0.002). Note, however, that liver cancer is well known for its difficulty in accurate diagnosis. The ERR Gy of cancer excluding leukemia and liver cancer was 0.19 (95% CI: -1.87, 3.04). Non-cancer disease mortality was not related to cumulative radiation dose either. The cumulative HBR dose was not related to the mortality due to cancer or all non-cancer diseases among residents in Yangjiang HBR areas.

Chromosome aberrations in peripheral blood lymphocytes of individuals living in high background radiation areas of Ramsar, Iran

In order to investigate the biological effects of exposure to low-dose radiation and to assess the dose-effect relationship in residents of high background radiation areas (HBRAs) of Ramsar, cytogenetic investigation of unstable-type aberrations was performed in 15 healthy elderly women in a HBRA of Ramsar, Talesh mahalle, and in 10 elderly women living in a nearby control area with normal background radiation. In total, 77,714 cells were analyzed; 48,819 cells in HBRA residents and 28,895 cells in controls. On average, 3,108 cells per subject were analyzed (range 1,475-5,007 cells). Significant differences were found in the frequency of dicentric plus centric rings in 100 cells (0.207 ± 0.103 vs. 0.047 ± 0.027, p < 0.0005), total chromosome-type aberrations per 100 cells (0.86 ± 0.44 vs. 0.23 ± 0.17, p < 0.0005), and chromatid-type aberrations per 100 cells (3.31 ± 2.01 vs. 1.66 ± 0.63, p = 0.01) by the Mann-Whitney U test between HBRA and the control, respectively. Using chromosomal aberrations as the main endpoint to assess the dose-effect relationship in residents of HBRAs in Ramsar, no positive correlation was found between the frequency of dicentric plus centric ring aberrations and the cumulative dose of the inhabitants estimated by direct individual dosimetry; however, obvious trends of increase with age appeared in the control group. Based on these results, individuals residing in HBRAs of Ramsar have an increased frequency of detectable abnormalities in unstable aberrations.

The dose response of chromosome aberrations in human lymphocytes induced in vitro by very low-dose γ rays

This paper considers the dose-effect relationship for unstable chromosome aberration yields in human lymphocytes in very low-dose range. Data are presented for (60)Co γ-ray doses of 0, 10, 20, 40 and 1000 mGy. More than 5,000 metaphases were scored for each data point at the very low doses, and each cell was double-checked using a semi-automated metaphase finding/relocation system. Aberration yields of dicentrics plus centric rings followed an excellent linear dose response down to zero dose; the yields were significantly above the control frequency from 20 mGy.

Review and evaluation of updated research on the health effects associated with low-dose ionising radiation

While radiation health risks at low doses have traditionally been estimated from high-dose studies, we have reviewed recent literature and concluded that the mechanisms of action for many biological endpoints may be different at low doses from those observed at high doses; that acute doses <100 mSv may be too small to allow epidemiological detection of excess cancers given the background of naturally occurring cancers; that low-dose radiation research should use holistic approaches such as systems-based methods to develop models that define the shape of the dose-response relationship; and that these results should be combined with the latest epidemiology to produce a comprehensive understanding of radiation effects that addresses both damage, likely with a linear effect, and response, possibly with non-linear consequences. Continued research is needed to understand how radiobiology and epidemiology advances should be used to effectively model radiation worker risks.

Human exposure to high natural background radiation: what can it teach us about radiation risks?

Natural radiation is the major source of human exposure to ionising radiation, and its largest contributing component to effective dose arises from inhalation of (222)Rn and its radioactive progeny. However, despite extensive knowledge of radiation risks gained through epidemiologic investigations and mechanistic considerations, the health effects of chronic low-level radiation exposure are still poorly understood. The present paper reviews the possible contribution of studies of populations living in high natural background radiation (HNBR) areas (Guarapari, Brazil; Kerala, India; Ramsar, Iran; Yangjiang, China), including radon-prone areas, to low dose risk estimation. Much of the direct information about risk related to HNBR comes from case-control studies of radon and lung cancer, which provide convincing evidence of an association between long-term protracted radiation exposures in the general population and disease incidence. The success of these studies is mainly due to the careful organ dose reconstruction (with relatively high doses to the lung), and to the fact that large-scale collaborative studies have been conducted to maximise the statistical power and to ensure the systematic collection of information on potential confounding factors. In contrast, studies in other (non-radon) HNBR areas have provided little information, relying mainly on ecological designs and very rough effective dose categorisations. Recent steps taken in China and India to establish cohorts for follow-up and to conduct nested case-control studies may provide useful information about risks in the future, provided that careful organ dose reconstruction is possible and information is collected on potential confounding factors.

The radiobiology/radiation protection interface in healthcare

The current knowledge of radiation effects is reviewed and implications for its application in healthcare considered. The 21st L H Gray conference gathered leading experts in radiobiology, radiation epidemiology, radiation effect modelling, and the application of radiation in medicine to provide an overview of the subject. The latest radiobiology research in non-targeted effects such as genomic instability and the bystander effect challenge the old models, but the implications for health effects on humans are uncertain. Adaptive responses to external stresses, of which radiation is one, have been demonstrated in cells and animal models, but it is not known how these might modify human dose-effect relationships. Epidemiological evidence from the Japanese A-bomb survivors provides strong evidence that there is a linear relationship between the excess risk of cancer and organ dose that extends from about 50 mSv up to 2.5 Sv, and results from pooled data for multiple epidemiological studies indicate that risks extend down to doses of 20 mSv. Thus linear extrapolation of the A-bomb dose-effect data provides an appropriate basis for radiological protection standards at the present time. Risks from higher dose diagnostic procedures fall within the range in which health effects can be demonstrated. There is therefore reason for concern about the rise in the number of computed tomography (CT) scans performed in many countries, and in particular the use of CT for screening of asymptomatic individuals. New radiotherapy techniques allow high dose radiation fields to be conformed more effectively to target volumes, and reduce doses to critical organs, but they tend to give a higher and more uniform dose to the whole body which may increase the risk of second cancer. It is important that radiation protection practitioners keep abreast of developments in understanding of radiation effects and advise the medical community about the implications of fundamental research when planning medical applications for the future.

Microbe-mineral interactions in naturally radioactive beach sands from Espirito Santo, Brazil: experiments on mutagenicity

Previous studies on naturally radioactive materials suggested that they can have a mutagenic effect on plants (growing in sands in Kerala, South West India), and on bats (dwelling in an abandoned underground mine of primary monazite ore in Namaqualand, Western Cape, South Africa). We hypothesised, based on previous theoretical work, that radioactive sands would not induce mutants in microorganisms over time scales typical of doubling times in the natural environment. The potential of exceptionally monazite (Th)-rich mineral sands collected from the coast of Espirito Santo, Brazil to induce single-point reversion in Escherichia coli cultures (both repair-competent and repair-deficient strains) was tested using the tryptophan reverse mutation assay. The results show that at least on a short-term scale (1-7 days), the monazite-rich sands did not cause an increase in reversion above background.

Mineral radioactivity in sands as a mechanism for fixation of organic carbon on the early Earth

Irradiation of organic molecules by mineral radioactivity is a feasible alternative to cosmic irradiation to precipitate solid organic carbon-rich matter on the early Earth. Radioactive (uranium- and thorium-rich) minerals have been concentrated at the Earth's surface, and accumulated accretionary coatings of carbon due to irradiation, since early Archean times. The organic accretion process could have occurred at the surface or in the sub-surface, and is independent of a terrestrial or extraterrestrial source for the carbon.

An introductory overview of the epidemiological study on the population at the high background radiation areas in Yangjiang, China

The epidemiological study on the residents of the high background radiation areas in Yangjiang, China was started by Chinese scientists in 1972 and continued until 1986. In 1991, Japanese scientists recognized the importance of the work and a joint feasibility study was conducted with revised protocols. The feasibility study matured to a cooperative project involving both Chinese and Japanese scientists in 1992, which currently is still in progress. The project was divided into three phases; the first being from 1992 to 1995, the second from 1995-1998 and the third from 1998 to 2001. The results of the first phase were reported previously in 1996. The present paper is a historical overview of the studies before the cooperation and the first two phases. Remarks are made on the detailed data on dosimetry, cytogenetic studies and cancer epidemiology of a series of the papers in this supplemental issue. Some problems such as paradoxical observations between cytogenetic results and cancer mortality, and the importance of the high background study in risk assessment are discussed.

Chromosome translocation in residents of the high background radiation areas in southern China

We performed a cytogenetical study using chromosome painting analysis on 9 residents of the naturally high background radiation areas (HBRA) and 8 residents of the control areas in southern China. The estimated dose (air kerma) of each resident measured by an electric pocket dosimeter showed 2.20-4.23 mGy/year in HBRA and 0.56-0.70 mGy/year in the control areas. A total of 14,096 cells (1,566 cells/case) in the former and 17,522 cells (2,190 cells/case) in the latter were analyzed. Children, both in HBRA and in the control areas, had translocations at low frequencies. The frequency of translocations among elder individuals varied widely and it was not possible to detect dose effect although it was detected in dicentrics. The effect of radiation on the induction of chromosome aberrations, which have a statistically potential risk of causing malignant or congenital diseases, seems to be less significant than those of metabolic factors and/or mutagenic agents (excluding radiation) even in HBRA in China.