Dosimetric calculations for uranium miners for epidemiological studies

Radon Exposure, Clonal Hematopoiesis, and Stroke Susceptibility in the Women's Health Initiative

BACKGROUND AND OBJECTIVES

Studies suggest that clonal hematopoiesis of indeterminate potential (CHIP) may increase risk of hematologic malignancy and cardiovascular disease, including stroke. However, few studies have investigated plausible environmental risk factors for CHIP such as radon, despite the climate-related increases in and documented infrequency of testing for this common indoor air pollutant.The purpose of this study was to estimate the risk of CHIP related to radon, an established environmental mutagen.

METHODS

We linked geocoded addresses of 10,799 Women's Health Initiative Trans-Omics for Precision Medicine (WHI TOPMed) participants to US Environmental Protection Agency-predicted, county-level, indoor average screening radon concentrations, categorized as follows: Zone 1 (>4 pCi/L), Zone 2 (2-4 pCi/L), and Zone 3 (<2 pCi/L). We defined CHIP as the presence of one or more leukemogenic driver mutations with variant allele frequency >0.02. We identified prevalent and incident ischemic and hemorrhagic strokes; subtyped ischemic stroke using Trial of ORG 10172 in Acute Stroke Treatment (TOAST) criteria; and then estimated radon-related risk of CHIP as an odds ratio (OR) and 95% CI using multivariable-adjusted, design-weighted logistic regression stratified by age, race/ethnicity, smoking status, and stroke type/subtype.

RESULTS

The percentages of participants with CHIP in Zones 1, 2, and 3 were 9.0%, 8.4%, and 7.7%, respectively (ptrend = 0.06). Among participants with ischemic stroke, Zones 2 and 1 were associated with higher estimated risks of CHIP relative to Zone 3: 1.39 (1.15-1.68) and 1.46 (1.15-1.87), but not among participants with hemorrhagic stroke: 0.98 (0.68-1.40) and 1.03 (0.70-1.52), or without stroke: 1.04 (0.74-1.46) and 0.95 (0.63-1.42), respectively (pinteraction = 0.03). Corresponding estimates were particularly high among TOAST-subtyped cardioembolism: 1.78 (1.30-2.47) and 1.88 (1.31-2.72), or other ischemic etiologies: 1.37 (1.06-1.78) and 1.50 (1.11-2.04), but not small vessel occlusion: 1.05 (0.74-1.49) and 1.00 (0.68-1.47), respectively (pinteraction = 0.10). Observed patterns of association among strata were insensitive to attrition weighting, ancestry adjustment, prevalent stroke exclusion, separate analysis of DNMT3A driver mutations, and substitution with 3 alternative estimates of radon exposure.

DISCUSSION

The robust elevation of radon-related risk of CHIP among postmenopausal women who develop incident cardioembolic stroke is consistent with a potential role of somatic genomic mutation in this societally burdensome form of cerebrovascular disease, although the mechanism has yet to be confirmed.

Residential radon and characteristics of chronic obstructive pulmonary disease

It is not known whether residential radon exposure may be linked to the development of chronic obstructive pulmonary disease (COPD) and/or have an influence on the functional characteristics or exacerbations of COPD. The aim of this study was therefore to ascertain whether there might be an association between residential radon concentrations and certain characteristics of COPD. We analyzed COPD cases drawn from a case-control study conducted in an area of high radon exposure. Data were collected on spirometric pulmonary function variables, hospital admissions, and smoking. Radon measurements were taken using alpha-track-type CR-39 detectors individually placed in patients' homes. All statistical analyses were performed using the IBM SPSS v22 computer software program. The study included 189 COPD cases (79.4% men; median age 64 years). The median radon concentration was 157 Bq/m3. No differences were found between radon concentration and sex, age or severity of breathing obstruction as measured by FEV1%. It should be noted, however, that 48.1% of patients with FEV1% < 50 had radon concentrations below 100 Bq/m3, as compared to 35.6% with the same severity of obstruction who had over 300 Bq/m3. COPD cases with radon concentrations higher than > 600 Bq/m3 exhibited no different characteristics in lung function. Exposure to radon does not appear to have an influence on the clinical characteristics of smokers and ex-smokers with COPD. As exposure to residential radon increases, there is no trend towards a worsening of FEV1%. Further studies are thus needed to analyze this possible association in never-smokers with COPD.

The German Uranium Miners’ Biobank—A Biobank for OMICs Radiation Research

Systematic bio- and databanks are key prerequisites for modern radiation research to investigate radiation response mechanisms in the context of genetic, environmental and lifestyle-associated factors. This report presents the current status of the German Uranium Miners’ Biobank. In 2008, the bio- and databank was established at the Federal Office for Radiation Protection, and the sampling of biological materials from former uranium miners with and without lung cancer was initiated. For this purpose, various biological specimens, such as DNA and RNA, were isolated from blood samples as well as from formalin-fixed paraffin-embedded lung tissue. High-quality biomaterials suitable for OMICs research and the associated data on occupational radiation and dust exposure, and medical and lifestyle data from over 1000 individuals have been stored so far. Various experimental data, e.g., genome-wide SNPs, whole genome transcriptomic and miRNA data, as well as individual chromosomal aberration data from subgroups of biobank samples, are already available upon request for in-depth research on radiation-induced long-term effects, individual radiation susceptibility to lung cancer and radon-induced fingerprints in lung cancer. This biobank is the first systematic uranium miners´ biobank worldwide that is suitable for OMICs research on radiation-exposed workers. It offers the opportunity to link radiation-induced perturbations of biological pathways or processes and putative adverse outcome(s) by OMICs profiling at different biological organization levels.

Dosimetric Comparison of Exposure Pathways to Human Organs and Tissues in Radon Therapy

Three therapeutic applications are presently prescribed in the radon spas in Gastein, Austria: exposure to radon in a thermal bath, exposure to radon vapor in an exposure chamber (vapor bath), and exposure to radon in the thermal gallery, a former mine. The radiological exposure pathways to human organs and tissues in these therapeutic radon applications are inhalation of radon and radon progeny via the lungs, radon transfer from water or air through the skin, and radon-progeny deposition on the skin in water or air. The objectives of the present study were to calculate radon and radon-progeny doses for selected organs and tissues for the different exposure pathways and therapeutic applications. Doses incurred in red bone marrow, liver, kidneys, and Langerhans cells in the skin may be correlated with potential therapeutic benefits, while doses to the lungs and the basal cells of the skin indicate potential carcinogenic effects. The highest organ doses among the three therapeutic applications were produced in the thermal gallery by radon progeny via inhalation, with lung doses of 5.0 mSv, and attachment to the skin, with skin doses of 4.4 mSv, while the radon contribution was less significant. For comparison, the primary exposure pathways in the thermal bath are the radon uptake through the skin, with lung doses of 334 μSv, and the radon-progeny attachment to the skin, with skin doses of 216 μSv, while the inhalation route can safely be neglected.

Indoor Radon Exposure and COPD, Synergic Association? A Multicentric, Hospital-Based Case-Control Study in a Radon-Prone Area

BACKGROUND

COPD is a multifactorial disease which causes considerable mortality and morbidity worldwide. Previous studies assessing the possible relationship between indoor radon exposure and COPD have shown inconclusive results.

METHODS

A multicentric, hospital-based, case-control study was conducted in a Spanish radon-prone area. COPD cases were confirmed by spirometry and controls were selected due to trivial surgery or procedures not related to tobacco consumption. All participants had to have lived for at least 15 years in the same dwelling. Radon measurements were conducted individually in dwellings using alpha-track detectors. Results were obtained using multivariate logistic regression.

RESULTS

189 cases and 747 controls took part. There was no significant association between residential radon concentrations and COPD onset with a OR of 1.12 (95%CI 0.41-3.06) for individuals exposed to more than 200Bq/m³ compared to those exposed to less than 50Bq/m³. Heavy smokers seem to increase their COPD risk if exposed to higher radon concentrations vs those exposed to lower concentrations. There was a statistically significant synergy index between radon exposure and tobacco consumption, S-index 11.60 (95%CI 3.71-36.26). Indoor radon concentration was higher in never/light smokers with COPD compared to controls.

CONCLUSIONS

No association between indoor radon and COPD has been observed. However, there might be some effect modification on the COPD risk in heavy smokers when high radon exposure is present. This is supported by the additive synergy observed. Also, a possible association between indoor radon and COPD onset in never and light smokers needs to be further studied.

Mortality among uranium miners in North America and Europe: the Pooled Uranium Miners Analysis (PUMA)

BACKGROUND

The Pooled Uranium Miners Analysis (PUMA) study draws together information from cohorts of uranium miners from Canada, the Czech Republic, France, Germany and the USA.

METHODS

Vital status and cause of death were ascertained and compared with expectations based upon national mortality rates by computing standardized mortality ratios (SMRs) overall and by categories of time since first hire, calendar period of first employment and duration of employment as a miner.

RESULTS

There were 51 787 deaths observed among 118 329 male miners [SMR = 1.05; 95% confidence interval (CI): 1.04, 1.06]. The SMR was elevated for all cancers (n = 16 633, SMR = 1.23; 95% CI: 1.21, 1.25), due primarily to excess mortality from cancers of the lung (n = 7756, SMR = 1.90; 95% CI: 1.86, 1.94), liver and gallbladder (n = 549, SMR = 1.15; 95% CI: 1.06, 1.25), larynx (n = 229, SMR = 1.10; 95% CI: 0.97, 1.26), stomach (n = 1058, SMR = 1.08; 95% CI: 1.02, 1.15) and pleura (n = 39, SMR = 1.06; 95% CI: 0.75, 1.44). Lung-cancer SMRs increased with duration of employment, decreased with calendar period and persisted with time since first hire. Among non-malignant causes, the SMR was elevated for external causes (n = 3362, SMR = 1.41; 95% CI: 1.36, 1.46) and respiratory diseases (n = 4508, SMR = 1.32; 95% CI: 1.28, 1.36), most notably silicosis (n = 814, SMR = 13.56; 95% CI: 12.64, 14.52), but not chronic obstructive pulmonary disease (n = 1729, SMR = 0.98; 95% CI: 0.93, 1.02).

CONCLUSIONS

Whereas there are important obstacles to the ability to detect adverse effects of occupational exposures via SMR analyses, PUMA provides evidence of excess mortality among uranium miners due to a range of categories of cause of death. The persistent elevation of SMRs with time since first hire as a uranium miner underscores the importance of long-term follow-up of these workers.

Indoor Radon Exposure and COPD, Synergic Association? A Multicentric, Hospital-Based Case-Control Study in a Radon-Prone Area

BACKGROUND

COPD is a multifactorial disease which causes considerable mortality and morbidity worldwide. Previous studies assessing the possible relationship between indoor radon exposure and COPD have shown inconclusive results.

METHODS

A multicentric, hospital-based, case-control study was conducted in a Spanish radon-prone area. COPD cases were confirmed by spirometry and controls were selected due to trivial surgery or procedures not related to tobacco consumption. All participants had to have lived for at least 15 years in the same dwelling. Radon measurements were conducted individually in dwellings using alpha-track detectors. Results were obtained using multivariate logistic regression.

RESULTS

189 cases and 747 controls took part. There was no significant association between residential radon concentrations and COPD onset with a OR of 1.12 (95%CI 0.41-3.06) for individuals exposed to more than 200Bq/m3 compared to those exposed to less than 50Bq/m3. Heavy smokers seem to increase their COPD risk if exposed to higher radon concentrations vs those exposed to lower concentrations. There was a statistically significant synergy index between radon exposure and tobacco consumption, S-index 11.60 (95%CI 3.71-36.26). Indoor radon concentration was higher in never/light smokers with COPD compared to controls.

CONCLUSIONS

No association between indoor radon and COPD has been observed. However, there might be some effect modification on the COPD risk in heavy smokers when high radon exposure is present. This is supported by the additive synergy observed. Also, a possible association between indoor radon and COPD onset in never and light smokers needs to be further studied.

Miner studies and radiological protection against radon

Fundamental estimates of radon-associated health risk have been provided by epidemiological studies of miners. In total, approximately 15 studies have been conducted worldwide since the 1960s. These results have contributed directly to radiological protection against radon. The present article summarises the main results, with a focus on analyses of miners exposed more recently, estimates of radon lifetime attributable risk, and interaction between radon and smoking. The potential for the upcoming Pooled Uranium Miner Analysis project to further improve our knowledge is discussed.

Radon and cancer mortality among underground uranium miners in the Příbram region of the Czech Republic

BACKGROUND

This study aims to estimate the association between radon and site-specific cancer mortality among a large contemporary cohort of male uranium miners.

METHODS

Annual occupational radon exposure was estimated based on a worker's duration of underground mining in a year and estimates of potential alpha energy of radon progeny in their location of work. Cancer mortality over the period 1977-1992 was ascertained for a cohort of 16 434 male underground uranium miners employed in the Czech Republic between 1946 and 1992. Poisson regression was used to estimate relationships between cumulative radiation exposure (in working level months [WLM]) and site-specific cancer mortality.

RESULTS

Radon is positively associated with lung cancer mortality (excess relative rate [ERR] per 100 WLM = 0.2; 95% confidence interval [CI]: 0.10, 0.37). The best fit of the dose-response relationship between radon and lung cancer mortality was linear and estimates of radon-lung cancer associations varied by windows of time-since-exposure. Positive associations between radon and several types of cancer other than lung cancer were identified, notably chronic lymphocytic leukemia (CLL) (ERR/100 WLM = 0.24; 95% CI: [not determined [ND], 5.10]) and extrathoracic cancer (ERR/100 WLM = 0.12; 95% CI: [ND, 0.69]). We observed no associations between radon and stomach cancer, nor between radon and several hematopoietic cancer subtypes.

CONCLUSIONS

This study confirms the established radon-lung cancer association and suggests that radon may also be associated with other types of cancer mortality. Further investigations of extrathoracic and CLL cancer, with the aim of obtaining more precise estimates, are warranted to understand associations between radon and cancers other than lung.

PUMA - pooled uranium miners analysis: cohort profile

OBJECTIVES

Epidemiological studies of underground miners have provided clear evidence that inhalation of radon decay products causes lung cancer. Moreover, these studies have served as a quantitative basis for estimation of radon-associated excess lung cancer risk. However, questions remain regarding the effects of exposure to the low levels of radon decay products typically encountered in contemporary occupational and environmental settings on the risk of lung cancer and other diseases, and on the modifiers of these associations. These issues are of central importance for estimation of risks associated with residential and occupational radon exposures.

METHODS

The Pooled Uranium Miner Analysis (PUMA) assembles information on cohorts of uranium miners in North America and Europe. Data available include individual annual estimates of exposure to radon decay products, demographic and employment history information on each worker and information on vital status, date of death and cause of death. Some, but not all, cohorts also have individual information on cigarette smoking, external gamma radiation exposure and non-radiological occupational exposures.

RESULTS

The PUMA study represents the largest study of uranium miners conducted to date, encompassing 124 507 miners, 4.51 million person-years at risk and 54 462 deaths, including 7825 deaths due to lung cancer. Planned research topics include analyses of associations between radon exposure and mortality due to lung cancer, cancers other than lung, non-malignant disease, modifiers of these associations and characterisation of overall relative mortality excesses and lifetime risks.

CONCLUSION

PUMA provides opportunities to evaluate new research questions and to conduct analyses to assess potential health risks associated with uranium mining that have greater statistical power than can be achieved with any single cohort.

MECHANISTIC MODELING PREDICTS NO SIGNIFICANT DOSE RATE EFFECT ON HEAVY-ION CARCINOGENESIS AT DOSE RATES RELEVANT FOR SPACE EXPLORATION

Heavy ion-induced carcinogenesis is a challenge for human space exploration, and mechanistically-motivated mathematical models are needed to predict space-relevant low dose-rate risks, which are difficult to measure experimentally, based on data at higher dose rates. We present such a model, which quantifies targeted and non-targeted radiation effects. We fitted it to lung carcinogenesis data in radon-exposed miners and rats, which provide valuable information on carcinogenesis from protracted exposure to densely-ionizing radiation. We generated model-based estimates for the dose-rate-effect, relative to acute exposures, on heavy ion-induced carcinogenesis at doses/dose rates expected during a Mars mission. A small and not statistically-significant dose-rate effect was predicted: 1.00 (95% CI: 0.54, 1.40) for human data and for combined human and rat data 0.93 (0.06, 1.49). Consequently, heavy ion carcinogenesis estimates from moderate/high dose-rate experimental data may be applicable to doses/dose rates relevant for space exploration.

Residential radon and cancer mortality in Galicia, Spain

Residential radon exposure is a serious public health concern, and as such appears in the recommendations of European Code Against Cancer. The objective of this study was to assess the association between residential radon levels and mortality due to different types of cancer, using misaligned data analysis techniques. Mortality data (observed cases) for each of the 313 Galician municipalities were drawn from the records of the National Statistics Institute for the study period (1999-2008). Expected cases were computed using Galician mortality rates for 14 types of malignant tumors as reference, with a total of 56,385 deaths due to the tumors analyzed. The effect estimates of indoor radon (3371 sampling points) were adjusted for sociodemographic variables, altitude, and arsenic topsoil levels (1069 sampling points), using spatial/geostatistical models fitted with stochastic partial differential equations and integrated nested Laplace approximations. These models are capable of processing misaligned data. The results showed a statistical association between indoor radon and lung, stomach and brain cancer in women in Galicia. Apart from lung cancer (relative risk (RR)=1.09), in which a twofold increase in radon exposure led to a 9% rise in mortality, the association was particularly relevant in stomach (RR=1.17) and brain cancer (RR=1.28). Further analytical epidemiologic studies are needed to confirm these results, and an assessment should be made of the advisability of implementing interventions targeting such exposure in higher-risk areas.

238U CONTENT IN URINE OF URANIUM MINERS AND ITS MODELED VALUES

The aim of the study is to make a comparison of daily 238U excretion in urine among 115 active uranium miners and its modeled values obtained from inhalation intake of long-lived alpha emitters as measured by personal dosemeters and assessed by biokinetic models for different absorption parameters settings for inhaled uranium. A total of 144 spot samples of urine were collected. The 238U content was measured using high-resolution inductively coupled plasma mass spectrometry method. To obtain estimates of the daily excreted values, the daily values were calculated according to the expected daily excretion of creatinine assessed individually for each miner. When determining the relation between the experimentally found data and the modeled data, a high emphasis was placed on uncertainty of the both compared quantities. All the tested absorption parameters settings produced in average 1.4-4.7-fold higher values than the experimentally found values in the urine.

Recent aspects of uranium toxicology in medical geology

Uranium (U) is a chemo-toxic, radiotoxic and even a carcinogenic element. Due to its radioactivity, the effects of U on humans health have been extensively investigated. Prolonged U exposure may cause kidney disease and cancer. The geological distribution of U radionuclides is still a great concern for human health. Uranium in groundwater, frequently used as drinking water, and general environmental pollution with U raise concerns about the potential public health problem in several areas of Asia. The particular paleo-geological hallmark of India and other Southern Asiatic regions enhances the risk of U pollution in rural and urban communities. This paper highlights different health and environmental aspects of U as well as uptake and intake. It discusses levels of U in soil and water and the related health issues. Also described are different issues of U pollution, such as U and fertilizers, occupational exposure in miners, use and hazards of U in weapons (depleted U), U and plutonium as catalysts in the reaction between DNA and H₂O_2, and recycling of U from groundwater to surface soils in irrigation. For use in medical geology and U research, large databases and data warehouses are currently available in Europe and the United States.

Effective Doses of Employees at the Former Uranium Processing Plant MAPE Mydlovary, Czechoslovakia

Results are presented of a survey of almost 1000 dosimetric records of employees at the former uranium processing plant MAPE Mydlovary. Located ~20 km to the north-west of České Budějovice in South Bohemia, it was the place where most of the uranium ore mined in Czechoslovakia in the years from 1962 to 1991 was processed. The records refer to incorporation of short-lived radon progeny and long-lived radionuclides as well as external gamma exposure. The average annual doses calculated from the recorded data were 2.7 ± 1.4, 5.0 ± 3.1 and 1.7 ± 0.9 mSv from these three sources, respectively. Thus, the relative contributions of these components to the effective dose were 29 ± 6, 53 ± 14 and 18 ± 13% , respectively. This is different from the findings in an earlier study for the exposure of uranium miners, where the overall doses were similar, but over 50% was contributed by short-lived radon progeny. No legal limits applicable at the time were exceeded, as the inclusion of long-lived radionuclides in the dose calculations was not yet obligatory.

Residential radon and COPD. An ecological study in Galicia, Spain

PURPOSE

Radon is a human lung carcinogen but it might be linked with other respiratory diseases. We aimed to assess the relationship between residential radon exposure and COPD (chronic obstructive pulmonary disease) prevalence and hospital admissions at a municipal level.

MATERIALS AND METHODS

We designed an ecological study where we included those municipalities with at least three radon measurements. Using mixed Poisson regression models, we calculated the relative risk (RR) for COPD for each 100 Bq/m³ of increase in radon concentration and also the relative risk for COPD using a cut-off point of 50 Bq/m³. We did not have individual data on cigarette smoking and therefore we used a proxy (bladder cancer standardized mortality rate) that has proved to account for tobacco consumption. We performed separate analyses for sex and also sensitivity analysis considering age and rurality.

RESULTS

A total of 3040 radon measurements and 49,393 COPD cases were included. The relative risk for COPD prevalence was 0.95 (95% CI: 0.92-0.97) while for hospital admissions the RR was 1.04 (95% CI: 1.00-1.10) for each 100 Bq/m³. Relative risks were higher for women compared to men. Using a categorical analysis with a cut-off point of 50 Bq/m³, the RR for COPD prevalence was 1.06 (95% CI: 1.02-1.10) and for hospital admissions it was 1.08 (95% CI: 1.00-1.17) for women living in municipalities with more than 50 Bq/m³. All risks were also higher for women. No relevant differences were observed for age, rurality or other categories for radon exposure.

CONCLUSION

While the influence of radon on COPD prevalence is unclear depending on the approach used, it seems that residential radon might increase the risk of hospital admissions in COPD patients. Women have a higher risk than men in all situations. Since this is an ecological study, results should be interpreted cautiously.

The German Thorotrast Cohort Study: a review and how to get access to the data

It is well known that exposures like those from (226)Ra, (224)Ra and Thorotrast(®) injections increase the risk of neoplasia in bone marrow and liver. The thorium-based radioactive contrast agent Thorotrast(®) was introduced in 1929 and applied worldwide until the 1950s, especially in angiography and arteriography. Due to the extremely long half-life of several hundred years and the life-long retention of the thorium dioxide particles in the human body, patients suffer lifetime internal exposure. The health effects from the incorporated thorium were investigated in a few cohort studies with a German study being the largest among them. This retrospective cohort study was set up in 1968 with a follow-up until 2004. The study comprises 2326 Thorotrast patients and 1890 patients of a matched control group. For those being alive at the start of the study in 1968 follow-up was done by clinical examinations on a biannual basis. For the others, causes of death were collected in various ways. Additionally, clinical, radiological and biophysical studies of patients were conducted and large efforts were made to best estimate the radiation doses associated with incorporation of the Thorotrast. The aim of this paper is to describe the cohort, important results and some open questions. The data from the German Thorotrast Study are available to other interested researchers. Information can be found at http://storedb.org .

Residential radon exposure and risk of incident hematologic malignancies in the Cancer Prevention Study-II Nutrition Cohort

Dosimetric models show that radon, an established cause of lung cancer, delivers a non-negligible dose of alpha radiation to the bone marrow, as well as to lymphocytes in the tracheobronchial epithelium, and therefore could be related to risk of hematologic cancers. Studies of radon and hematologic cancer risk, however, have produced inconsistent results. To date there is no published prospective, population-based study of residential radon exposure and hematologic malignancy incidence. We used data from the American Cancer Society Cancer Prevention Study-II Nutrition Cohort established in 1992, to examine the association between county-level residential radon exposure and risk of hematologic cancer. The analytic cohort included 140,652 participants (66,572 men, 74,080 women) among which 3019 incident hematologic cancer cases (1711 men, 1308 women) were identified during 19 years of follow-up. Cox proportional hazard regression was used to calculate multivariable-adjusted hazard ratios (HRs) and corresponding 95% confidence intervals (CIs) for radon exposure and hematologic cancer risk. Women living in counties with the highest mean radon concentrations (>148Bq/m(3)) had a statistically significant higher risk of hematologic cancer compared to those living in counties with the lowest (<74Bq/m(3)) radon levels (HR=1.63, 95% CI:1.23-2.18), and there was evidence of a dose-response relationship (HRcontinuous=1.38, 95% CI:1.15-1.65 per 100Bq/m(3); p-trend=0.001). There was no association between county-level radon and hematologic cancer risk among men. The findings of this large, prospective study suggest residential radon may be a risk factor for lymphoid malignancies among women. Further study is needed to confirm these findings.

Concerted Uranium Research in Europe (CURE): toward a collaborative project integrating dosimetry, epidemiology and radiobiology to study the effects of occupational uranium exposure

The potential health impacts of chronic exposures to uranium, as they occur in occupational settings, are not well characterized. Most epidemiological studies have been limited by small sample sizes, and a lack of harmonization of methods used to quantify radiation doses resulting from uranium exposure. Experimental studies have shown that uranium has biological effects, but their implications for human health are not clear. New studies that would combine the strengths of large, well-designed epidemiological datasets with those of state-of-the-art biological methods would help improve the characterization of the biological and health effects of occupational uranium exposure. The aim of the European Commission concerted action CURE (Concerted Uranium Research in Europe) was to develop protocols for such a future collaborative research project, in which dosimetry, epidemiology and biology would be integrated to better characterize the effects of occupational uranium exposure. These protocols were developed from existing European cohorts of workers exposed to uranium together with expertise in epidemiology, biology and dosimetry of CURE partner institutions. The preparatory work of CURE should allow a large scale collaborative project to be launched, in order to better characterize the effects of uranium exposure and more generally of alpha particles and low doses of ionizing radiation.

Size distribution of aerosol particles produced during mining and processing uranium ore

The aerosol particle size distributions of uranium and its daughter products were studied and determined in the area of the Rožná mine, which is the last active uranium mine in the Czech Republic. A total of 13 samples were collected using cascade impactors from three sites that had the highest expected levels of dust, namely, the forefield, the end of the ore chute and an area close to workers at the crushing plant. The characteristics of most size distributions were very similar; they were moderately bimodal, with a boundary approximately 0.5 μm between the modes. The activity median aerodynamic diameter (AMAD) and geometric standard deviation (GSD) were obtained from the distributions beyond 0.39 μm, whereas the sizes of particles below 0.39 μm were not differentiated. Most AMAD and GSD values in the samples ranged between 3.5 and 10.5 μm and between 2.8 and 5.0, respectively. The geometric means of the AMADs and GSDs from all of the underground sampling sites were 4.2 μm and 4.4, respectively, and the geometric means of the AMADs and GSDs for the crushing plant samplings were 9.8 μm and 3.3, respectively. The weighted arithmetic mean of the AMADs was 4.9 μm, with a standard error of 0.7 μm, according to the numbers of workers at the workplaces. The activity proportion of the radon progeny to (226)Ra in the aerosol was 0.61.

Analysis of Genetic Damage in Lymphocytes of Former Uranium Processing Workers

The frequency of cells containing micronuclei (MN) and the presence of centromeres in these MN were analyzed in lymphocytes of 98 men from Southern Bohemia. Forty-six of them had worked at the uranium processing plant ‘MAPE Mydlovary' which was closed in 1991, and 52 men were controls from the same area. FISH using human pan-centromeric chromosome paint was employed to detect centromere-positive (CEN+) and -negative (CEN-) MN. A total of 1,000 binucleated cells (BNC) per participant were analyzed after cytochalasin B treatment. All BNC with MN (CEN+ or CEN-) were recorded. No differences were found between formerly exposed workers and the control group, neither in the total frequency of cells with MN per 1,000 BNC (mean levels ± SD, 9.1 ± 3.1 and 9.8 ± 2.5, respectively) nor in the percentage of CEN- MN, which were equal (50 ± 18 and 49 ± 17, respectively). Also, there was no difference between individuals living in the 3 villages closest to the uranium processing plant and those living further away. Considering the fact that effective doses of the workers at MAPE Mydlovary were overall similar to those of former uranium miners in whom higher frequencies of CEN- MN have been found more than 10 years after they had finished working underground, these results are somewhat surprising. A more detailed analysis of the exposures indicates that uranium miners received a greater percentage of their effective dose from the inhalation of radon and its daughters, whereas uranium processing workers received it from the incorporation of long-lived radioactive nuclides such as uranium. If, as has been suggested before, the higher level of DNA damage in miners is due to induced genomic instability, then this phenomenon may be related to radon exposure rather than exposure to uranium.

Health effects of occupational exposure to uranium: do physicochemical properties matter?

PURPOSE

Physicochemical properties of uranium, including isotopic composition and solubility, are determinants of its toxicity. We reviewed epidemiological studies in civilian and military workers known to be exposed to uranium with different physicochemical properties to investigate its long-term effects, such as cancerous and circulatory diseases.

MATERIALS AND METHODS

We systematically searched the Pubmed and the Scopus databases to identify studies of uranium- processing workers (published between 1980 and 2013) and veterans of the wars in the Persian Gulf and the Balkans (published between 1991 and 2013) in which defined outcomes, such as lung, lymphohematopoietic, kidney cancers, and circulatory diseases were examined. RESULTS from these studies in terms of risk of each health outcome (mortality or incidence) and analyses of dose-response relationship were examined to present the impact of uranium physicochemical properties on the observed results.

RESULTS

Twenty-seven articles were reviewed. There is some evidence for increased lung cancer risk among uranium-processing workers. The evidence is less strong for lymphohematopoietic cancer. We found that most of the studies insufficiently assessed the physicochemical properties of uranium and some of them used proxies for the exposure assessment and risk estimation analyses. Studies of veterans of the wars in the Persian Gulf and the Balkans are uninformative in respect to internal uranium exposure.

CONCLUSIONS

Existing epidemiological data on the physicochemical properties of uranium and associated health outcomes are inconclusive. Further studies among certain groups of uranium-processing workers (uranium-enrichment and fuel-fabrication workers) could contribute to our knowledge of the health effects of uranium with respect to its physicochemical properties.

Doses and lung cancer risks from exposure to radon and plutonium

PURPOSE

Epidemiological studies of the French uranium miners and the plutonium workers at the Mayak nuclear facility have provided excess relative risk (ERR) estimates per unit absorbed lung dose from alpha radiation. The aim of this paper was to review these two studies and to derive values of the relative biological effectiveness (RBE) of alpha particles for the induction of lung cancer.

MATERIALS AND METHODS

We examined and compared the dosimetry assumptions and methodology used in the epidemiological studies of uranium miners and the plutonium workers. Values of RBE were obtained by comparing risk coefficients including comparison of lifetime risks for a given population. To do this, preliminary calculations of lifetime risks following inhalation of plutonium were carried out.

RESULTS AND CONCLUSIONS

Published values of risk per unit dose following inhalation of radon progeny and plutonium were in agreement despite the very different dose distributions within the lungs and the different ways the doses were calculated. Values of RBE around 10-20 were obtained by comparing ERR values, but with wide uncertainty ranges. Comparing lifetime risks gave similar values (10, 19 and 21). This supports the use of a radiation weighting factor of 20 for alpha particles for radiation protection purposes.

Kidney cancer mortality and ionizing radiation among French and German uranium miners

The investigation of potential adverse health effects of occupational exposures to ionizing radiation, on uranium miners, is an important area of research. Radon is a well-known carcinogen for lung, but the link between radiation exposure and other diseases remains controversial, particularly for kidney cancer. The aims of this study were therefore to perform external kidney cancer mortality analyses and to assess the relationship between occupational radiation exposure and kidney cancer mortality, using competing risks methodology, from two uranium miners cohorts. The French (n = 3,377) and German (n = 58,986) cohorts of uranium miners included 11 and 174 deaths from kidney cancer. For each cohort, the excess of kidney cancer mortality has been assessed by standardized mortality ratio (SMR) corrected for the probability of known causes of death. The associations between cumulative occupational radiation exposures (radon, external gamma radiation and long-lived radionuclides) or kidney equivalent doses and both the cause-specific hazard and the probability of occurrence of kidney cancer death have been estimated with Cox and Fine and Gray models adjusted to date of birth and considering the attained age as the timescale. No significant excess of kidney cancer mortality has been observed neither in the French cohort (SMR = 1.49, 95 % confidence interval [0.73; 2.67]) nor in the German cohort (SMR = 0.91 [0.77; 1.06]). Moreover, no significant association between kidney cancer mortality and any type of occupational radiation exposure or kidney equivalent dose has been observed. Future analyses based on further follow-up updates and/or large pooled cohorts should allow us to confirm or not the absence of association.

Leukemia, lymphoma and multiple myeloma mortality (1950-1999) and incidence (1969-1999) in the Eldorado uranium workers cohort

Uranium workers are chronically exposed to low levels of radon decay products (RDP) and gamma (γ) radiation. Risks of leukemia from acute and high doses of γ-radiation are well-characterized, but risks from lower doses and dose-rates and from RDP exposures are controversial. Few studies have evaluated risks of other hematologic cancers in uranium workers. The purpose of this study was to analyze radiation-related risks of hematologic cancers in the cohort of Eldorado uranium miners and processors first employed in 1932-1980 in relation to cumulative RDP exposures and γ-ray doses. The average cumulative RDP exposure was 100.2 working level months and the average cumulative whole-body γ-radiation dose was 52.2 millisievert. We identified 101 deaths and 160 cases of hematologic cancers in the cohort. Overall, male workers had lower mortality and cancer incidence rates for all outcomes compared with the general Canadian male population, a likely healthy worker effect. No statistically significant association between RDP exposure or γ-ray doses, or a combination of both, and mortality or incidence of any hematologic cancer was found. We observed consistent but non-statistically significant increases in risks of chronic lymphocytic leukemia (CLL) and Hodgkin lymphoma (HL) incidence and non-Hodgkin lymphoma (NHL) mortality with increasing γ-ray doses. These findings are consistent with recent studies of increased risks of CLL and NHL incidence after γ-radiation exposure. Further research is necessary to understand risks of other hematologic cancers from low-dose exposures to γ-radiation.

Reassessment of individual dosimetry of long-lived alpha radionuclides of uranium miners through experimental determination of urinary excretion of uranium

Urinary excretion of uranium of 40 uranium miners was determined by the high-resolution inductively coupled mass spectrometry method. The concentration of uranium in the urine of the miners was converted to daily excretion of (238)U either under the assumption that the daily urinary excretion is 1.6 l or daily urinary excretion of creatinine is 1.7 g and compared with the excretion of (238)U calculated with a biokinetic model. Input data to the excretion model were derived from personal three- component ALGADE dosemeters, using the component for the estimation of inhalation of long-lived alpha radionuclides. Experimentally found contents of uranium in the urine of uranium miners are generally lower than the modelled ones, which means that the dosimetric approach is conservative. The uncertainty of inhalation intakes, derived from the measurements of filters from personal dosemeters, and the uncertainty of the concentration of uranium in the urine are discussed.

Radiation dose dependent risk of liver cancer mortality in the German uranium miners cohort 1946-2003

An increased risk of mortality from primary liver cancers among uranium miners has been observed in various studies. An analysis of the data from a German uranium miner cohort (the 'Wismut cohort') was used to assess the relationship with ionising radiation. To that end the absorbed organ dose due to high and low linear energy transfer radiation was calculated for 58 987 miners with complete information on radiation exposure from a detailed job-exposure matrix. 159 deaths from liver cancer were observed in the follow-up period from 1946 to 2003. Relative risk models with either linear or categorical dependence on high and low linear energy transfer radiation liver doses were fitted by Poisson regression, stratified on age and calendar year. The linear trend of excess relative risk in a model with both low and high linear transfer radiation is -0.8 (95% confidence interval (CI): -3.7, 2.1) Gy(-1) and 48.3 (95% CI: -32.0, 128.6) Gy(-1) for low and high linear energy transfer radiation, respectively, and thus not statistically significant for either dose. The increase of excess relative risk with equivalent liver dose is 0.57 (95% CI: -0.69, 1.82) Sv(-1). Adjustment for arsenic only had a negligible effect on the radiation risk. In conclusion, there is only weak evidence for an increase of liver cancer mortality with increasing radiation dose in the German uranium miners cohort considered. However, both a lack of statistical power and potential misclassification of primary liver cancer are issues.

Micronuclei in lymphocytes from currently active uranium miners

Micronuclei can be used as markers of past radiation exposure, but only few studies have dealt with uranium miners. In this paper, we report on micronuclei in lymphocytes from individuals currently working at Rožná, Czech Republic, the last functioning uranium mine in the European Union. A modified micronucleus-centromere test was applied to assess the occurrence of micronuclei in stimulated lymphocytes, as well as their content in terms of whole chromosomes or fragments. Compared with unexposed individuals, the miners had higher frequencies of micronucleus-containing lymphocytes and higher percentages of micronuclei without centromeres, and the differences were significant for both parameters (0.74 ± 0.60 vs. 0.50 ± 0.42, p = 0.017 and 49 ± 44 vs. 12 ± 21, p = 0.0002; means ± standard deviations). There were also significant correlations between one or other of these parameters on the one hand and various dose values on the other, in particular with a 'retrievable' dose, that is, a dose whose effect should still be recognisable in lymphocytes assuming a half-life of 3 years. The 'retrievable' dose at which a doubling of the micronucleus frequency was observed was around 35 mSv, corresponding to a total dose of 90 mSv received while working in the mines. Altogether, our data show that the micronucleus-centromere test is a valuable tool for the assessment of past radiation exposure in uranium miners. The scatter in the data is of course far too great to allow individual dosimetry, but for groups of a few dozen exposed individuals, the method can be used to monitor doses clearly below 100 mSv.

Risk of lung cancer mortality in relation to lung doses among French uranium miners: follow-up 1956-1999

The aim of this study was to assess the risk of lung cancer death associated with cumulative lung doses from exposure to α-particle emitters, including radon gas, radon short-lived progeny, and long-lived radionuclides, and to external γ rays among French uranium miners. The French "post-55" sub-cohort included 3,377 uranium miners hired from 1956, followed up through the end of 1999, and contributing to 89,405 person-years. Lung doses were calculated with the ICRP Human Respiratory Tract Model (Publication 66) for 3,271 exposed miners. The mean "absorbed lung dose" due to α-particle radiation was 78 mGy, and that due to the contribution from other types of radiation (γ and β-particle radiation) was 56 mGy. Radon short-lived progeny accounted for 97% of the α-particle absorbed dose. Out of the 627 deaths, the cause of death was identified for 97.4%, and 66 cases were due to lung cancer. A significant excess relative risk (ERR) of lung cancer death was associated with the total absorbed lung dose (ERR/Gy = 2.94, 95% CI 0.80, 7.53) and the α-particle absorbed dose (4.48, 95% CI 1.27, 10.89). Assuming a value of 20 for the relative biological effectiveness (RBE) of α particles for lung cancer induction, the ERR/Gy-Eq for the total weighted lung dose was 0.22 (95% CI: 0.06, 0.53).