Around Semipalatinsk nuclear test site: progress of dose estimations relevant to the consequences of nuclear tests (a summary of 3rd Dosimetry Workshop on the Semipalatinsk nuclear test site area, RIRBM, Hiroshima University, Hiroshima, 9-11 of March, 2005)

Comparison of external dose estimates using different retrospective dosimetry methods in the settlements located near Semipalatinsk Nuclear Test Site, Republic of Kazakhstan

For correct assessment of health risks after low-dose irradiation, calculation of radiation exposure estimates is crucial. To verify the calculated absorbed doses, instrumental methods of retrospective dosimetry are used. We compared calculated and instrumental-based estimates of external absorbed doses in the residents of Dolon, Mostik and Cheremushki villages, Kazakhstan, affected by the first nuclear weapon test performed at the Semipalatinsk Nuclear Test Site (SNTS) on August 29, 1949. The 'instrumental' doses were retrospectively estimated using the Luminescence Retrospective Dosimetry (LRD) and Electron Spin Resonance (ESR) methods. Correlation between the calculated individual cumulative external absorbed whole-body doses based on typical input data and ESR-based individual doses in the same people was strong (r = 0.782). It was even stronger between the calculated doses based on individual questionnaires' input data and the ESR-based doses (r = 0.940). Application of the LRD method is useful for validation of the calculated settlement-average cumulated external absorbed dose to air. Reconstruction of external exposure can be supplemented with the data from later measurements of soil contamination with long-lived radionuclides, such as, 137Cs. Our results show the reliability of the calculational method used for the retrospective assessment of individual external doses.

Background Level of Unstable Chromosome Aberrations in the Kazakhstan Population: A Human Biomonitoring Study

Kazakhstan is known as a country with a complex radioecological situation resulting from different sources such as a natural radiation background, extensive activities of the industrial system of the former Soviet Union and a well-known testing of nuclear power weapons occurred in the Semipalatinsk Test Site (STS) area. The present study focuses on the assessment of the background of dicentric chromosomes in Kazakhstan’s population, which is the starting point in the dose assessment of irradiated people, since the baseline level of spontaneous dicentrics can vary significantly in different populations. In this context, aiming to determine the background frequency of chromosome aberrations in the population of Kazakhstan, considering the heterogeneity of natural radiation background levels of its large territory, a selection of 40 control subjects living in four cities of North, South, West and East Kazakhstan was performed. The cytogenetic study on the selected groups showed fairly low background frequency values of chromosome aberrations (0.84 ± 0.83 per 1000 cells), comparable with other data in the literature on general populations, reporting background frequency values between 0.54 and 2.99 per 1000 cells. The obtained results should be taken into account when constructing the dose–effect calibration curve used in cytogenetic biodosimetry, as a “zero” dose point, which will reduce the uncertainty in quantifying the individual absorbed dose in emergency radiological situations.

Eurados review of retrospective dosimetry techniques for internal exposures to ionising radiation and their applications

This work presents an overview of the applications of retrospective dosimetry techniques in case of incorporation of radionuclides. The fact that internal exposures are characterized by a spatially inhomogeneous irradiation of the body, which is potentially prolonged over large periods and variable over time, is particularly problematic for biological and electron paramagnetic resonance (EPR) dosimetry methods when compared with external exposures. The paper gives initially specific information about internal dosimetry methods, the most common cytogenetic techniques used in biological dosimetry and EPR dosimetry applied to tooth enamel. Based on real-case scenarios, dose estimates obtained from bioassay data as well as with biological and/or EPR dosimetry are compared and critically discussed. In most of the scenarios presented, concomitant external exposures were responsible for the greater portion of the received dose. As no assay is available which can discriminate between radiation of different types and different LETs on the basis of the type of damage induced, it is not possible to infer from these studies specific conclusions valid for incorporated radionuclides alone. The biological dosimetry assays and EPR techniques proved to be most applicable in cases when the radionuclides are almost homogeneously distributed in the body. No compelling evidence was obtained in other cases of extremely inhomogeneous distribution. Retrospective dosimetry needs to be optimized and further developed in order to be able to deal with real exposure cases, where a mixture of both external and internal exposures will be encountered most of the times.

The State Scientific Automated Medical Registry, Kazakhstan: an important resource for low-dose radiation health research

Direct quantitative assessment of health risks following exposure to ionizing radiation is based on findings from epidemiological studies. Populations affected by nuclear bomb testing are among those that allow such assessment. The population living around the former Soviet Union's Semipalatinsk nuclear test site is one of the largest human cohorts exposed to radiation from nuclear weapons tests. Following research that started in the 1960s, a registry that contains information on more than 300,000 individuals residing in the areas neighboring to the test site was established. Four nuclear weapons tests, conducted from 1949 to 1956, resulted in non-negligible radiation exposures to the public, corresponding up to approximately 300 mGy external dose. The registry contains relevant information about those who lived at the time of the testing as well as about their offspring, including biological material. An international group of scientists worked together within the research project SEMI-NUC funded by the European Union, and concluded that the registry provides a novel, mostly unexplored, and valuable resource for the assessment of the population risks associated with environmental radiation exposure. Suggestions for future studies and pathways on how to use the best dose assessment strategies have also been described in the project. Moreover, the registry could be used for research on other relevant public health topics.

Increased prevalence of essential hypertension in areas previously exposed to fallout due to nuclear weapons testing at the Semipalatinsk Test Site, Kazakhstan

This study examines the association between environmental radiation exposure and essential hypertension in a series of investigated geographical districts adjacent to the Semipalatinsk nuclear test site in Kazakhstan. The sample consists of 2000 volunteers participants in screening examinations in three administrative districts close to the nuclear test site, which was carried out as part of the Government Programs on Environmental Health Hazard. The cross-sectional study compares prevalence ratios in a population sample with long-term exposure in the low and intermediate dose range. Age-adjusted odds ratios for hypertension were found significantly increased with higher exposure groups. After accounting for main cardiovascular risk factors into the model and stratifying by gender, the prevalence odds ratios for radiation remained significantly increased, with a significant dose-response effect observed for some but not all subgroups. The results support existing evidence of cardiovascular health effects of radiation exposure and of persisting environmental health issues that require attention in both epidemiological surveys and healthcare provision.

Cytogenetic abnormalities of the descendants of permanent residents of heavily contaminated East Kazakhstan

More than 400 nuclear explosion tests were conducted at the Semipalatinsk Nuclear Test Site (SNTS) and significant radioactive substances were released. The long-term consequences of the activities at the SNTS and the appearance of any hereditary effects remain insufficiently studied about 25 years after the test site was closed. The population living in villages near the SNTS are considered to have been heavily exposed to external and internal radiation. This study aims to perform an assessment and comprehensive cytogenetic analysis of the inhabitants living near the SNTS, and their first-(F1) and second-(F2) generation children. Residents of the East Kazakhstan region living in the area covered by the former SNTS were included in the study. To evaluate the hereditary effects of nuclear testing, comprehensive chromosome analyses were performed in lymphocytes using conventional Giemsa and fluorescent in situ hybridization methods in 115 F1 and F2 descendants in the villages of Dolon and Sarzhal, which were heavily contaminated. The parents of the subjects had permanently lived in the villages. A higher number of stable-type chromosome aberrations such as translocations was found in these residents than in 80 residents of the control area, Kokpecty, which indicates the possibility that radiation had biological effects on the exposed subjects.

Studies of Health Effects from Nuclear Testing near the Semipalatinsk Nuclear Test Site, Kazakhstan

The nuclear bomb testing conducted at the Semipalatinsk nuclear test site in Kazakhstan is of great importance for today's radiation protection research, particularly in the area of low dose exposures. This type of radiation is of particular interest due to the lack of research in this field and how it impacts population health. In order to understand the possible health effects of nuclear bomb testing, it is important to determine what studies have been conducted on the effects of low dose exposure and dosimetry, and evaluate new epidemiologic data and biological material collected from populations living in proximity to the test site. With time, new epidemiological data has been made available, and it is possible that these data may be linked to biological samples. Next to linking existing and newly available data to examine health effects, the existing dosimetry system needs to be expanded and further developed to include residential areas, which have not yet been taken into account. The aim of this paper is to provide an overview of previous studies evaluating the health effects of nuclear testing, including some information on dosimetry efforts, and pointing out directions for future epidemiologic studies.

Accounting for shared and unshared dosimetric uncertainties in the dose response for ultrasound-detected thyroid nodules after exposure to radioactive fallout

Dosimetic uncertainties, particularly those that are shared among subgroups of a study population, can bias, distort or reduce the slope or significance of a dose response. Exposure estimates in studies of health risks from environmental radiation exposures are generally highly uncertain and thus, susceptible to these methodological limitations. An analysis was published in 2008 concerning radiation-related thyroid nodule prevalence in a study population of 2,994 villagers under the age of 21 years old between August 1949 and September 1962 and who lived downwind from the Semipalatinsk Nuclear Test Site in Kazakhstan. This dose-response analysis identified a statistically significant association between thyroid nodule prevalence and reconstructed doses of fallout-related internal and external radiation to the thyroid gland; however, the effects of dosimetric uncertainty were not evaluated since the doses were simple point "best estimates". In this work, we revised the 2008 study by a comprehensive treatment of dosimetric uncertainties. Our present analysis improves upon the previous study, specifically by accounting for shared and unshared uncertainties in dose estimation and risk analysis, and differs from the 2008 analysis in the following ways: 1. The study population size was reduced from 2,994 to 2,376 subjects, removing 618 persons with uncertain residence histories; 2. Simulation of multiple population dose sets (vectors) was performed using a two-dimensional Monte Carlo dose estimation method; and 3. A Bayesian model averaging approach was employed for evaluating the dose response, explicitly accounting for large and complex uncertainty in dose estimation. The results were compared against conventional regression techniques. The Bayesian approach utilizes 5,000 independent realizations of population dose vectors, each of which corresponds to a set of conditional individual median internal and external doses for the 2,376 subjects. These 5,000 population dose vectors reflect uncertainties in dosimetric parameters, partly shared and partly independent, among individual members of the study population. Risk estimates for thyroid nodules from internal irradiation were higher than those published in 2008, which results, to the best of our knowledge, from explicitly accounting for dose uncertainty. In contrast to earlier findings, the use of Bayesian methods led to the conclusion that the biological effectiveness for internal and external dose was similar. Estimates of excess relative risk per unit dose (ERR/Gy) for males (177 thyroid nodule cases) were almost 30 times those for females (571 cases) and were similar to those reported for thyroid cancers related to childhood exposures to external and internal sources in other studies. For confirmed cases of papillary thyroid cancers (3 in males, 18 in females), the ERR/Gy was also comparable to risk estimates from other studies, but not significantly different from zero. These findings represent the first reported dose response for a radiation epidemiologic study considering all known sources of shared and unshared errors in dose estimation and using a Bayesian model averaging (BMA) method for analysis of the dose response.

Mortality from cardiovascular diseases in the Semipalatinsk historical cohort, 1960-1999, and its relationship to radiation exposure

The data on risk of mortality from cardiovascular disease due to radiation exposure at low or medium doses are inconsistent. This paper reports an analysis of the Semipalatinsk historical cohort exposed to radioactive fallout from nuclear testing in the vicinity of the Semipalatinsk Nuclear Test Site, Kazakhstan. The cohort study, which includes 19,545 persons of exposed and comparison villages in the Semipalatinsk region, had been set up in the 1960s and comprises 582,656 person-years of follow-up between 1960 and 1999. A dosimetric approach developed by the U.S. National Cancer Institute (NCI) has been used. Radiation dose estimates in this cohort range from 0 to 630 mGy (whole-body external). Overall, the exposed population showed a high mortality from cardiovascular disease. Rates of mortality from cardiovascular disease in the exposed group substantially exceeded those of the comparison group. Dose-response analyses were conducted for both the entire cohort and the exposed group only. A dose-response relationship that was found when analyzing the entire cohort could be explained completely by differences between the baseline rates in exposed and unexposed groups. When taking this difference into account, no statistically significant dose-response relationship for all cardiovascular disease, for heart disease, or for stroke was found. Our results suggest that within this population and at the level of doses estimated, there is no detectable risk of radiation-related mortality from cardiovascular disease.

Reconstruction of local fallout composition and gamma-ray exposure in a village contaminated by the first USSR nuclear test in the Semipalatinsk nuclear test site in Kazakhstan

After the disintegration of the USSR in end of 1991, it became possible for foreign scientists to visit Kazakhstan, in order to investigate the radiological consequences of nuclear explosions that had been conducted at the Semipalatinsk nuclear test site (SNTS). Since the first visit in 1994, our group has been continuing expeditions for soil sampling at various areas around SNTS. The current level of local fallout at SNTS was studied through γ-spectrometry for (137)Cs as well as α-spectrometry for (239,240)Pu. Average values of soil inventory from wide areas around SNTS were 3,500 and 3,700 Bq m(-2) for (137)Cs and (239,240)Pu, respectively, as of January 1, 2000. The average level of (137)Cs is comparable to that in Japan due to global fallout, while the level of (239,240)Pu is several tens of times larger than that in Japan. Areas of strong contamination were found along the trajectories of radioactive fallout, information on which was declassified after the collapse of the USSR. Our recent efforts of soil sampling were concentrated on the area around the Dolon village heavily affected by the radioactive plume from the first USSR atomic bomb test in 1949 and located 110 km east from ground zero of the explosion. Using soil inventory data, retrospective dosimetry was attempted by reconstructing γ-ray exposure from fission product nuclides deposited on the ground. Adopting representative parameters for the initial (137)Cs deposition (13 kBq m(-2)), the refractory/volatile deposition ratio (3.8) and the plume arrival time after explosion (2.5 h), an absorbed dose in air of 600 mGy was obtained for the 1-year cumulative dose in Dolon village, due to the first bomb test in 1949. Considering possible ranges of the parameters, 350 and 910 mGy were estimated for high and low cases of γ-ray dose in air, respectively. It was encouraging that the deduced value was consistent with other estimations using thermal luminescence and archived monitoring data. The present method can be applied to other settlements affected by local fallout from SNTS.

Thyroid cancer following nuclear tests in French Polynesia

BACKGROUND

Between 1966 and 1974, France conducted 41 atmospheric nuclear tests in Polynesia, but their potential health effects have not previously been investigated.

METHODS

In a case-control study, we compared the radiation exposure of almost all the French Polynesians diagnosed with differentiated thyroid carcinoma between 1981 and 2003 (n=229) to the exposure of 373 French Polynesian control individuals without cancer from the general population. Radiation exposures were estimated using measurements after the nuclear tests, age at time of each test, residential and dietary information.

RESULTS

The average thyroid dose before 15 years of age was about 1.8 mGy, and 5% of the cases and 3% of the controls received a dose above 10 mGy. Despite this low level of dose, and after adjusting for ethnic group, level of education, body surface area, family history of thyroid cancer and number of pregnancies for women, we observed an increasing risk (P=0.04) of thyroid cancer with increasing thyroid dose received before age of 15 years, which remained after excluding non-aggressive differentiated thyroid micro-carcinomas. This increase of risk per unit of thyroid radiation dose was higher (P=0.03) in women who later experienced four or more pregnancies than among other women.

CONCLUSION

The risk estimate is low, but is based on limited exposure data. The release of information on exposure, currently classified, would greatly improve the reliability of the risk estimation.

EPR dosimetry with tooth enamel: A review

When tooth enamel is exposed to ionizing radiation, radicals are formed, which can be detected using electron paramagnetic resonance (EPR) techniques. EPR dosimetry using tooth enamel is based on the (presumed) correlation between the intensity or amplitude of some of the radiation-induced signals with the dose absorbed in the enamel. In the present paper a critical review is given of this widely applied dosimetric method. The first part of the paper is fairly fundamental and deals with the main properties of tooth enamel and some of its model systems (e.g., synthetic apatites). Considerable attention is also paid to the numerous radiation-induced and native EPR signals and the radicals responsible for them. The relevant methods for EPR detection, identification and spectrum analyzing are reviewed from a general point of view. Finally, the needs for solid-state modelling and studies of the linearity of the dose response are investigated. The second part is devoted to the practical implementation of EPR dosimetry using enamel. It concerns specific problems of preparation of samples, their irradiation and spectrum acquisition. It also describes how the dosimetric signal intensity and dose can be retrieved from the EPR spectra. Special attention is paid to the energy dependence of the EPR response and to sources of uncertainties. Results of and problems encountered in international intercomparisons and epidemiological studies are also dealt with. In the final section the future of EPR dosimetry with tooth enamel is analyzed.

Twinning in the offspring of parents with chronic radiation exposure from nuclear testing in Kazakhstan

The population of the Semipalatinsk region of Kazakhstan was chronically exposed to radioactive fallout from above-ground nuclear tests conducted during 1949-1956 by the Soviet Union. We investigated the effect of radiation exposure and other factors on risks of twinning overall and of same- and different-sex twinning and hence estimated dizygotic and monozygotic twinning rates in 11,605 deliveries around Semipalatinsk, 141 of which were twin, to 3992 mothers exposed to fallout during 1949-1956. Overall, the same-sex twinning rate was 7.85 [95% confidence interval (CI): 6.24, 9.47] per 1000 and the opposite-sex twinning rate was 4.45 (95% CI: 3.23, 5.67). Twinning rates did not differ significantly between radiation exposure categories, parental age at main radiation exposure, or year of birth. Different-sex, but not same-sex, twinning increased with maternal age (P(trend) = 0.04) but not with other demographic factors and was increased soon after radiation exposure [OR = 4.08 (95% CI: 1.11, 15.07)] for births occurring within 5 years compared with more than 20 years after exposure; this effect was similar in villages with low and high radiation exposure, however, so interpretation is uncertain.

90Sr in mammal teeth from contaminated areas in the former Soviet Union measured by imaging plates

Imaging plates sensitive to beta rays were used to obtain the images of 90Sr in tooth samples taken from mammals collected in contaminated areas of the former Soviet Union. The average concentrations of 90Sr in the samples were determined by comparing the intensities of the luminescence using a single crystal of KCl. The results showed that the determined 90Sr concentration has a positive correlation with the soil contamination levels in the South Ural region. Tooth samples from both inside of the Semipalatinsk nuclear test site and the villages nearby have detectable amounts of 90Sr, indicating the possible presence of residual soil contamination. The present study demonstrates that using imaging plates is a very sensitive method to detect 90Sr in teeth as well as to estimate low-level 90Sr contamination in soil.

High frequency of AML1/RUNX1 point mutations in radiation-associated myelodysplastic syndrome around Semipalatinsk nuclear test site

It is known that bone marrow is a sensitive organ to ionizing radiation, and many patients with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) have been diagnosed in radiation-treated cases and atomic bomb survivors in Hiroshima and Nagasaki. The AML1/RUNX1 gene has been known to be frequently mutated in MDS/AML patients among atomic bomb survivors and radiation therapy-related MDS/AML patients. In this study, we investigated the AML1 mutations in radiation-exposed patients with MDS/AML among the residents near the Semipalatinsk Nuclear Test Site (SNTS), where the risk of solid cancers and leukemias was increased due to the radiation effects. AML1 mutations were identified in 7 (39%) of 18 radiation-exposed MDS/AML patients. In contrast, no AML1 mutation was found in 13 unexposed MDS/AML cases. The frequency of AML1 mutations in radiation-exposed patients with MDS/AML was significantly higher compared with unexposed patients (p < 0.05).We also found a significant correlation between individual estimated doses and AML1 mutations (p < 0.05). Considering these results, AML1 point mutations might be a useful biomarker that differentiates radio-induced MDS/AML from spontaneous MDS/AML.

Iodine-129 measurements in soil samples from Dolon village near the Semipalatinsk nuclear test site

Dolon village, located about 60 km from the border of the Semipalatinsk nuclear test site, is known to be heavily contaminated by the first USSR atomic bomb test in August 1949. Soil samples around Dolon were taken in October 2005 in an attempt to evaluate internal thyroid dose arising from incorporation of radioiodine isotopes (mainly (131)I). Iodine-129 in soil was measured by using the technique of accelerator mass spectrometry. The (129)I/(127)I atom ratios measured were in the range from 3.3 x 10(-9) to 3.3 x 10(-7). These values were within the range of the current background level ( approximately 10(-9) to 10(-7)) in the environment, including contributions from the global fallout of atmospheric nuclear tests and local fallout of nuclear facilities. The (129)I atom accumulated level in soil ranged from 1.28 x 10(13) to 1.59 x 10(14) atoms m(-2), the average (8.0 x 10(13)) of which was higher than the background level of (2-5) x 10(13). From the relationship between (129)I and( 137)Cs (corrected for background and decay from 1949 to 2005) accumulated levels, the background level of (129)I and the (129)I/(137)Cs ratio around Dolon were estimated to be (6.4 +/- 0.4) x 10(13) atoms m(-2) and 0.25 +/- 0.16, respectively. This (129)I/(137)Cs ratio is almost similar to the fission yield ratio for (239)Pu fast fission (0.24).

EPR TOOTH DOSIMETRY OF SNTS AREA INHABITANTS

The determination of external dose to teeth of inhabitants of settlements near the Semipalatinsk Nuclear Test Site (SNTS) was conducted using the EPR dosimetry technique to assess radiation doses associated with exposure to radioactive fallout from the test site. In this study, tooth doses have been reconstructed for 103 persons with all studied teeth having been formed before the first nuclear test in 1949. Doses above those received from natural background radiation, termed "accident doses", were found to lie in the range from zero to approximately 2 Gy, with one exception, a dose for one person from Semipalatinsk city was approximately 9 Gy. The variability of reconstructed doses within each of the settlements demonstrated heterogeneity of the deposited fallout as well as variations in lifestyle. The village mean external gamma doses for residents of nine[ settlements were in the range from a few tens of mGy to approximately 100 mGy.