Analyses of combined mortality data on workers at the Hanford Site, Oak Ridge National Laboratory, and Rocky Flats Nuclear Weapons Plant

An important objective of studies of workers exposed occupationally to chronic low doses of ionizing radiation is to provide a direct assessment of health risks resulting from this exposure. This objective is most effectively accomplished by conducting combined analyses that allow evaluation of the totality of evidence from all study populations. In this paper, combined analyses of mortality in workers at the Hanford Site, Oak Ridge National Laboratory, and Rocky Flats Nuclear Weapons Plant are presented. These combined analyses provide no evidence of a correlation between radiation exposure and mortality from all cancer or from leukemia. Of 11 other specific types of cancer analyzed, multiple myeloma was the only cancer found to exhibit a statistically significant correlation with radiation exposure. Estimates of the excess risk of all cancer and of leukemia, based on the combined data, were negative. Upper confidence limits based on the combined data were lower than for any single population, and were similar to estimates obtained from recent analyses of A-bomb survivor data. These results strengthen support for the conclusion that estimates obtained through extrapolation from high-dose data do not seriously underestimate risks of low-dose exposure, but leave open the possibility that extrapolation may overestimate risks.     

Cytogenetic analyses by fluorescence in situ hybridization (FISH) in hospital workers occupationally exposed to low levels of ionizing radiation

An occupationally exposed population has been studied to evaluate the suitability of FISH painting techniques to detect chronic exposures to very low doses of ionizing radiation by the analysis of translocations. Whole-chromosome painting probes for chromosomes 1, 4 and 11 in combination with a pancentromeric probe have been employed. For comparison, a matched control population has also been studied. The mean genomic frequencies per 100 cells of total translocations in the control and exposed populations were 0.90 +/- 0.12 and 1.04 +/- 0.11, respectively. In the occupationally exposed population, no correlation between the frequencies of translocations and the doses received was found. When the two populations were compared, no significant differences were observed for the frequencies of the different chromosomal abnormalities examined. The absence of differences between control and exposed populations could be attributed to the very low-dose exposures recorded in the occupationally exposed population and to the wide range of individual frequencies of translocations observed.     

A cytogenetic study of nuclear power plant workers using the micronucleus-centromere assay.

A cytogenetic study was performed in 215 nuclear power plant workers occupationally exposed to radiation using the micronucleus-centromere assay for peripheral blood lymphocytes. As control population served administrative staff with yearly doses below 1 mSv. The increase of the micronucleus frequency with age, observed in the non-smoking control population, is mainly due to an enhanced number of centromere-positive micronuclei, pointing to an increased chromosome loss. No differences in the number of micronuclei, centromere-positive and centromere-negative micronuclei between smokers and non-smokers are observed. An analysis of the micronucleus data vs. the dose accumulated over the 10 years preceding the venepuncture shows no significant clastogenic or aneuploidogenic effects of the exposure in the studied population which is representative for workers in the nuclear industry at present. According to the linear fits to our data an increase of the micronucleus frequency pro rata 0.5 per 1000 binucleated cells per year, related to the centromere-negative micronuclei, may be expected for workers with the maximal tolerable dose of 20 mSv/year.     

Stable intrachromosomal biomarkers of past exposure to densely ionizing radiation in several chromosomes of exposed individuals

A multicolor banding (mBAND) fluorescence in situ hybridization technique was used to investigate the presence inhuman populations of a stable biomarker-intrachromosomal chromosome aberrations-of past exposure to high-LET radiation. Peripheral blood lymphocytes were taken from healthy Russian nuclear workers occupationally exposed from 1949 onward to either plutonium, gamma rays or both. Metaphase spreads were produced and chromosomes 1 and 2 were hybridized with mBAND FISH probes and scored for intra-chromosomal aberrations. A large yield of intrachromosomal aberrations was observed in both chromosomes of the individuals exposed to high doses of plutonium, whereas there was no significant increase over the (low) background control rate in the population who were exposed to high doses of gamma rays.Interchromosome aberration yields were similar in both the high plutonium and the high gamma-ray groups. These results for chromosome 1 and 2 confirm and extend data published previously for chromosome 5. Intrachromosomal aberrations thus represent a potential biomarker for past exposure to high-LET radiations such as alpha particles and neutrons and could possibly be used as a biodosimeter to estimate both the dose and type of radiation exposure in previously exposed populations.     

Cytogenetic monitoring by use of the micronucleus assay among hospital workers exposed to low doses of ionizing radiation

The aim of this study was to assess occupationally induced chromosomal damage in a large population of hospital workers exposed to low doses of ionizing radiation. We used the cytokinesis-block micronucleus (CBMN) assay in the peripheral lymphocytes of 132 exposed workers compared with 69 controls matched for gender, age and smoking habits. The CBMN assay was combined with fluorescence in situ hybridization with a human pan-centromeric DNA probe in 32 exposed subjects and 30 controls randomly chosen from the initial populations. Occupational dosimetry records were collected over the last 10-year period and revealed very low exposure levels. The average binucleated micronucleated cell rate (BMCR) was significantly higher in the exposed subjects than in the controls (14.9 per thousand+/-8.1 versus 11.8 per thousand+/-6.5; P=0.011). About one-third of the micronuclei were centromere-negative in the exposed and control groups. BMCR significantly positively correlated with donor age in the exposed population; this correlation was at the border of significance in the control group. In the two groups, BMCR was significantly greater in females than in males, and the significant correlation between age and BMCR was observed in the female population, but not in the male one. No effect of smoking habits emerged. Univariate analysis revealed a possible influence of familial cancer history and diagnostic medical radiation dose (estimated from examinations reported in the questionnaire) on BMCR. Multiple regression analysis, taking into account all the previous confounding factors, showed that only occupational exposure status, gender and age had a significant effect on BMCR. In conclusion, the present study shows that chromosomal damage leading to micronucleated lymphocytes is more frequent in hospital workers exposed to ionizing radiation than in controls, despite the very low levels of exposure.     

Radiation Hazards Control in Survival Operations in the Event of a Nuclear War

The concepts of radiation protection in survival operations are explained, and procedures devised to control radiation hazards for the protection of the population and maintenance of the operating efficiency of survival operations personnel are presented.Radiation protection is a command function. The medical responsibility is to provide advice on the probable effects of radiation exposure in the light of existing knowledge of these effects in man.The major hazard is that of external exposure to penetrating gamma radiation. Radiation exposure guides indicate that persons may be exposed to not more than 100 r whole body radiation in a six-week period, or 200 r whole body radiation in a period in excess of six weeks, without loss of operational efficiency. Beta radiation from fallout deposited on skin or clothing may produce burns, but these injuries will not be incapacitating and can be controlled by simple procedures.The internal hazard is mainly from ingestion of food or water contaminated with radioactive material. For protection, only canned or packaged foods and water from covered or deep wells are consumed during the early days after a nuclear attack.     

An Evaluation of Different Methods in Epidemiologic Studies of Radiation Risks

The probability of detecting possible late effects of ionizing radiation in human populations depends on the size of exposure in the study population and on the epidemiologic evaluation method used. This is not only due to the mathematical or statistical properties of the method, but also to the choice of the control population, which may be either external (usually large) or internal (usually not so large). Moreover, the use of a large external control population often results in an increasing influence of selection factors expressing themselves e.g. through the ‘healthy worker’ effect. In this paper three different methods usually employed in follow-up studies are reviewed: the calculation of Standardized Mortality Ratios (SMR), a contingency table analysis based on Person-Years (PY) and the comparison of Cumulative Mean Doses (CMD) within different subcohorts. The methods are illustrated with a simple radiation risk model; nevertheless, most of the conclusions apply to non-radiation risk studies as well. The CMD-method is shown to be heavily selection sensitive.     

Semen Abnormalities,Sperm DNA Damage and Global Hypermethylation in Health Workers Occupationally Exposed to Ionizing Radiation

Background

Cytogenetic studies have demonstrated that low levels of chronic radiation exposure can potentially increase the frequency of chromosomal aberrations and aneuploidy in somatic cells. Epidemiological studies have shown that health workers occupationally exposed to ionizing radiation bear an increased risk of hematological malignancies.

Objectives

To find the influence of occupational radiation exposure on semen characteristics, including genetic and epigenetic integrity of spermatozoa in a chronically exposed population.

Methods

This cross sectional study included 134 male volunteers of which 83 were occupationally exposed to ionizing radiation and 51 were non-exposed control subjects. Semen characteristics, sperm DNA fragmentation, aneuploidy and incidence of global hypermethylation in the spermatozoa were determined and compared between the non-exposed and the exposed group.

Results

Direct comparison of the semen characteristics between the non-exposed and the exposed population revealed significant differences in motility characteristics, viability, and morphological abnormalities (P<0.05–0.0001). Although, the level of sperm DNA fragmentation was significantly higher in the exposed group as compared to the non-exposed group (P<0.05–0.0001), the incidence of sperm aneuploidy was not statistically different between the two groups. However, a significant number of hypermethylated spermatozoa were observed in the exposed group in comparison to non-exposed group (P<0.05).

Conclusions

We provide the first evidence on the detrimental effects of occupational radiation exposure on functional, genetic and epigenetic integrity of sperm in health workers. However, further studies are required to confirm the potential detrimental effects of ionizing radiation in these subjects.     

Sister chromatid exchanges in lymphocytes of nuclear medicine physicians

OBJECTIVE: The aim of this study was to assess whether occupational exposure to chronic, low doses of Iodine 131 (I-131) and Technetium 99m (Tc-99m) may lead to genotoxicity. Medical personnel occupied in nuclear medicine departments are occupationally exposed to low doses of I-131 and Tc-99m. The determination of the frequency of sister chromatid exchanges (SCEs) and of cells with a high frequency of SCEs (HFC) is considered to be a sensitive indicator for detecting genotoxic potential of mutagenic and carcinogenic agents. Therefore, we examined peripheral lymphocytes from nuclear medicine physicians for the presence of both SCE and HFC. METHODS: Sixteen exposed nuclear medicine physicians (non-smokers) were compared to 16 physicians (non-smokers) who had not been exposed to chemical or physical mutagens in their usual working environment at the same hospital. RESULTS: A statistically significant difference was found between SCE frequencies and HFC percentages measured in lymphocytes from the exposed and control groups. CONCLUSIONS: The present observation on the effect of chronic low doses of I-131 and Tc-99m indicates the possibility of genotoxic implications of this type of occupational exposure. Hence, the personnel who work in nuclear medicine departments should carefully apply the radiation protection procedures and should minimize, as low as possible, radiation exposure to avoid possible genotoxic effects.     

Micronuclei in humans induced by exposure to low level of ionizing radiation: influence of polymorphisms in DNA repair genes

Understanding the risks deriving from protracted exposure to low doses of ionizing radiation has remarkable societal importance in view of the large number of work settings in which sources of IR are encountered. To address this question, we studied the frequency of micronuclei (MN), which is an indicator of DNA damage, in a population exposed to low levels of ionizing radiation and in matched controls. In both exposed population and controls, the possible influence of single nucleotide polymorphisms in XRCC1, XRCC3 and XPD genes on the frequency of micronuclei was also evaluated. We also considered the effects of confounding factors, like smoking status, age and gender. The results indicated that MN frequency was significantly higher in the exposed workers than in the controls [8.62+/-2.80 versus 6.86+/-2.65; P=0.019]. Radiological workers with variant alleles for XRCC1 or XRCC3 polymorphisms or wild-type alleles for XPD exon 23 or 10 polymorphisms showed a significantly higher MN frequency than controls with the same genotypes. Smoking status did not affect micronuclei frequency either in exposed workers or controls, while age was associated with increased MN frequency in the exposed only. In the combined population, gender but not age exerted an influence on the yield of MN, being higher in females than in males. Even though there is a limitation in this study due to the small number of subjects, these results suggest that even exposures to low level of ionizing radiation could have genotoxic effects and that XRCC3, XRCC1 and XPD polymorphisms might contribute to the increased genetic damage in susceptible individuals occupationally exposed to chronic low levels of ionizing radiation. For a clear conclusion on the induction of DNA damage caused by protracted exposure to low doses of ionizing radiation and the possible influence of genetic polymorphism in DNA repair genes larger studies are needed.     

Effects of polycyclic aromatic hydrocarbons (PAHs) in environmental pollution on exogenous and oxidative DNA damage (EXPAH project): description of the population under study

The EXPAH project was a molecular epidemiology study whose aims were to evaluate the hypothesis that polycyclic aromatic hydrocarbons (PAHs) are a major source of genotoxic activities of organic mixtures associated with air pollution. Biomarkers of exposure, effects and susceptibility, and oxidative DNA damage were measured in three PAH-exposed populations from Prague (Czech Republic), Kosice (Slovakia) and Sofia (Bulgaria). Control populations were included from each city. In total 356 individuals were enrolled. A questionnaire was used to determine life style/dietary factors. Ambient air exposure was measured by stationary monitoring, and personal exposure monitoring was also carried out. The characteristics of the population are described in this paper together with their personal exposure to carcinogenic PAHs (c-PAHs). The dose of c-PAH exposure was found to vary between the occupationally exposed (e.g. policemen and bus drivers) and the control populations in each country, and also varied from country to country.     

Limitations and problems in deriving risk estimates for low-level radiation exposure.

Some of the problems in determining the cancer risk of low-level radiation from studies of exposed groups are reviewed and applied to the study of Hanford workers by Mancuso, Stewart, and Kneale. Problems considered are statistical limitations, variation of cancer rates with geography and race, the "healthy worker effect," calendar year and age variation of cancer mortality, choosing from long lists, use of proportional mortality rates, cigarette smoking-cancer correlations, use of averages to represent data distributions, ignoring other data, and correlations between radiation exposure and other factors that may cause cancer. The current status of studies of the Hanford workers is reviewed.     

A cytogenetic study of men environmentally and occupationally exposed to airborne pollutants.

The level of sister-chromatid exchanges (SCE), high-frequency cells (HFC), chromosomal aberrations (CA) as well as the proliferation rate index (PRI) were measured in peripheral blood lymphocytes from three groups of volunteers. The environmentally exposed donors were residents from the vicinity of a coke factory; the occupationally exposed persons were cokery workers, while rural region inhabitants served as a control group. Compared with the control group, statistically significant increases of SCE and HFC, as well as decreased cell kinetics (PRI) were observed for both occupationally and environmentally exposed groups. The effect was especially pronounced when only smokers were taken into account. A statistically significant increase of CA was observed in the environmentally exposed group when CA including gaps (CA + G) were evaluated. The proportion of HFC was found to be the most sensitive method to detect genetic effects on the tested human population. This study demonstrates the usefulness of all 4 biomarkers (SCE, HFC, CA and PRI) in monitoring populations exposed to ambient pollution and clearly indicates effects from residential as well as occupational exposure to industrial air pollutants.     

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.     

Occupational exposure to low doses of ionizing radiation and cataract development: a systematic literature review and perspectives on future studies

Ionizing radiation is a well-known but little understood risk factor for lens opacities. Until recently, cataract development was considered to be a deterministic effect occurring at lens doses exceeding a threshold of 5–8 Gy. Substantial uncertainty about the level and the existence of a threshold subsists. The International Commission on Radiation Protection recently revised it to 0.5 Gy. Based on a systematic literature review of epidemiological studies on exposure to low levels of ionizing radiation and the occurrence of lens opacities, a list of criteria for new epidemiological studies was compiled, and a list of potential study populations was reviewed. Among 24 publications finally identified, six report analyses of acute exposures in atomic bomb survivors and Chernobyl liquidators, and the others report analyses of protracted exposures in occupationally, medically or accidentally exposed populations. Three studies investigated a dose threshold: in atomic bomb survivors, the best estimates were 1 Sv (95 % CI <0–0.8 Sv) regarding lensectomies; in survivors exposed as children, 0.6 Sv (90 % CI <0.0–1.2 Sv) for cortical cataract prevalence and 0.7 Sv (90 % CI 0.0–2.8 Sv) for posterior subcapsular cataract; and in Chernobyl liquidators, 0.34 Sv (95 % CI 0.19–0.68 Sv) for stage 1 cataract. Current studies are heterogeneous and inconclusive regarding the dose–response relationship. Protracted exposures and high lens doses occur in several occupational groups, for instance, in physicians performing fluoroscopy-guided interventional procedures, and in accidentally exposed populations. New studies with a good retrospective exposure assessment are feasible and should be initiated.     

Power and uncertainty analysis of epidemiological studies of radiation-related disease risk in which dose estimates are based on a complex dosimetry system: some observations

This paper discusses practical effects of dosimetry error relevant to the design and analysis of an epidemiological study of disease risk and exposure. It focuses on shared error in radiation dose estimates for such studies as the Hanford Thyroid Disease Study or the Utah Thyroid Cohort Study, which use complex dosimetry systems that produce multiple replications of possible dose for the cohort. We argue that a simple estimation of shared multiplicative error components through direct examination of the replications of dose for each person provides information useful for estimating the power of a study to detect a radiation effect and illustrate this with an example based on the doses used for the Hanford Thyroid Disease Study. Uncertainty analysis (construction of confidence intervals) can be approached in the same way in simple cases. We also offer some suggestions for Monte Carlo-based confidence intervals.     

Analysis of structural chromosome changes and SCE after occupational long-term exposure to electric and magnetic fields from 380 kV-systems

Summary Chromosome analyses were carried out in lymphocytes of 32 workers occupationally exposed for more than 20 years to 50 Hz alternating electric and magnetic fields in 380 kV switchyards. As compared with a control group of 22 workers of similar age and occupation but without field exposure neither the yields of structural chromosome changes nor the SCE-frequencies were increased. The difference of cytogenetic data after occupational exposure to ionizing radiation is discussed.     

A registry for exposure and population health in the Altai region affected by fallout from the Semipalatinsk nuclear test site

A registry of the rural population in the Altai region exposed to fallout from nuclear tests at the Semipalatinsk test site (STS) was established more than four decades after the first Soviet nuclear explosion on August 29, 1949. Information about individuals living in an exposed and a control area was collected using all available local sources, such as kolkhoz documentation, school registries, medical treatment records and interviews with residents. As a result, a database comprising an exposed group of 39 179 individuals from 53 Altai region villages, 6769 external and 3303 internal controls was compiled. For several settlements, effective dose estimates reached the level of 1.5 Sv, while the average effective dose estimate in the exposed group was 340 mSv. Dosimetric data, vital status information and health records gathered at rayon and village medical facilities are held in the registry. Cause-of-death information for deceased residents is obtained from death registration forms archived at the Altai region vital statistics office. At present, a follow-up of approximately 40% of the population exposed in 1949 has been done. More will be added by searching for migrants to the larger towns of the Altai region, i.e. Barnaul, Rubtsovsk and Biisk. In order to assess the influence of radiation exposure, analytical studies with a case-control design for stomach and lung cancer are currently being prepared. The number of known cases is sufficient to detect an odds ratio of 1.5 at the 95% confidence level. Epidemiological studies in populations affected by fallout from STS may be equally important to the atomic bomb survivors’ study for the direct quantification of radiation effects. The range of exposure rates experienced will extend the acute high-dose-rate findings from Hiroshima/Nagasaki towards acute and protracted lower exposures, which are more relevant for radiation protection issues. Received: 3 March 1999 / Accepted in revised form: 8 June 1999     

mFISH analysis of chromosome aberrations in workers occupationally exposed to mixed radiation

We performed a study on the presence of chromosome aberrations in a cohort of plutonium workers of the Mayak production association (PA) with a mean age of 73.3 ± 7.2 years to see whether by multi-color fluorescence in situ hybridization (mFISH) translocation analysis can discriminate individuals who underwent occupational exposure with internal and/or external exposure to ionizing radiation 40 years ago. All Mayak PA workers were occupationally exposed to chronic internal alpha-radiation due to incorporated plutonium-239 and/or to external gamma-rays. First, we obtained the translocation yield in control individuals by mFISH to chromosome spreads of age-matched individuals and obtained background values that are similar to previously published values of an international study (Sigurdson et al. in Mutat Res 652:112–121, 2008). Workers who had absorbed a total dose of >0.5 Gy external gamma-rays to the red bone marrow (RBM) displayed a significantly higher frequency of stable chromosome aberrations relative to a group of workers exposed to <0.5 Gy gamma-rays total absorbed RBM dose. Thus, the translocation frequency may be considered to be a biological marker of external radiation exposure even years after the exposure. In a group of workers who were internally exposed and had incorporated plutonium-239 at a body burden >1.48 kBq, mFISH revealed a considerable number of cells with complex chromosomal rearrangements. Linear associations were observed for translocation yield with the absorbed RBM dose from external gamma-rays as well as for complex chromosomal rearrangements with the plutonium-239 body burden.     

Analysis of genome instability in offspring of Mayak workers’ families: Minisatellite CEB

Genome instability transmission in offspring was analyzed in order to evaluate the risk of delayed genetic effects of exposure in 95 family triplets in which only fathers experienced prolonged occupational radiation exposure. The mean total preconceptive absorbed dose (TPAD) of external gamma radiation in the paternal gonads was 1.65 ± 0.080 Gy (dose range of 0.57–5.70 Gy), and the mean TPAD of internal alpha radiation from incorporated plutonium-239 in the gonads was 0.0015 ± 0.0003 Gy (dose range 0.000–0.015 Gy). The control group consisted of 50 family triplets in which parents were not occupationally exposed. The mutation process was studied using PCR based on hypervariable minisatellite marker CEB1 (chromosome 2, 2q37.3). The paternal type of inheritance of mutations for minisatellite CEB1 was found in 80% of cases. The analysis revealed a statistically significant increase in minisatellite CEB1 mutations in the common group of families in which fathers experienced prolonged occupational radiation exposure and in the group of families in which fathers were exposed to radiation in a dosage range of 0.5–1.0 Gy as compared to the control, reaching a significance level of p = 0.109 and p = 0.058, respectively. The dose threshold of mutation detection in the offspring of Mayak PA workers was estimated.