Occupational Radon Exposure Research Articles

DNA methylome profiling in occupational radon exposure miners using an Illumina Infinium Methylation EPIC BeadChip.

A causal relationship between occupational radon exposure in underground miners and lung cancer risk has been demonstrated through large cohort epidemiological studies. However, the mechanisms by which radon exposure causes adverse effects on lung tissue remain unclear. Epigenetic alterations such as DNA methylation may provide new insights into interactions at molecular levels induced by prolonged radon exposure. We used the Illumina Infinium Human Methylation 850K BeadChip to detect and compare genome-wide DNA methylation profiles in peripheral blood samples from underground miners (n=14) and aboveground workers (n=9). The average concentration of radon in underground workplaces was significantly higher than that of aboveground places (1,198Bq·m-3 vs 58Bq·m-3, p<0.001). A total of 191 differentially methylated positions (DMPs) corresponding to 104 hub genes were identified when |Δβ|≥0.1 and p<0.05, with 107 hypermethylated sites and 84 hypomethylated sites. GO and KEGG analysis revealed that differentially methylated genes between underground miners and aboveground workers were prominently enriched in pathways/networks involved in neurotransmitter regulation, immunomodulatory effects and cell adhesion ability. Furthermore, methylation changes of selected genes FERMT1, ALCAM, HLA-DPA1, PON1 and OR2L13 were validated by pyrosequencing, which may play vital roles in these biological processes induced by radon. In summary, the DNA methylation pattern of the underground miners exposed to radon was distinct from that of the aboveground workers. Such abnormalities in the genomic DNA methylation profile associated with prolonged radon exposure are worth studying in terms of neuro- and immune-system regulation, as well as cell adhesion ability in the future.

Updated risk models for lung cancer due to radon exposure in the German Wismut cohort of uranium miners, 1946-2018.

UNSCEAR recently recommended that future research on the lung cancer risk at low radon exposures or exposure rates should focus on more contemporary uranium miners. For this purpose, risk models in the German Wismut cohort of uranium miners were updated extending the follow-up period by 5years to 1946-2018. The full cohort (n = 58,972) and specifically the 1960 + sub-cohort of miners first hired in 1960 or later (n = 26,764) were analyzed. The 1960 + sub-cohort is characterized by low protracted radon exposure of high quality of measurements. Internal Poisson regression was used to estimate the excess relative risk (ERR) for lung cancer per cumulative radon exposure in Working Level Months (WLM). Applying the BEIR VI exposure-age-concentration model, the ERR/100WLM was 2.50 (95% confidence interval (CI) 0.81; 4.18) and 6.92 (95% CI < 0; 16.59) among miners with attained age < 55years, time since exposure 5-14years, and annual exposure rates < 0.5WL in the full (n = 4329 lung cancer deaths) and in the 1960 + sub-cohort (n = 663 lung cancer deaths), respectively. Both ERR/WLM decreased with older attained ages, increasing time since exposure, and higher exposure rates. Findings of the 1960 + sub-cohort are in line with those from large pooled studies, and ERR/WLM are about two times higher than in the full Wismut cohort. Notably, 20-30years after closure of the Wismut mines in 1990, the estimated fraction of lung cancer deaths attributable to occupational radon exposure is still 26% in the full Wismut cohort and 19% in the 1960 + sub-cohort, respectively. This demonstrates the need for radiation protection against radon.

RADON CONCENTRATION MEASUREMENT AND DOSE ESTIMATION IN NON-URANIUM MINES IN CHINA (2019-21).

The radon concentration in selected non-uranium mines from 2019 to 2021 in China are presented. By using of solid-state nuclear track detector, a total of 110 non-uranium mines in 13 provinces and autonomous regions were monitored, and the data were analyzed according to the mineral categories. The arithmetic mean of radon concentration in underground metal mines and nonmetallic mines were 1180 and 162Bq m-3, respectively, and the standard deviations were 2850 and 151Bq m-3, respectively. Correspondingly, the average annual effective dose of metal miners was 12.7mSv and that of nonmetal miners was 1.75mSv. It was noted that the radon concentration in some metal mines is not optimal in China. It is suggested that the ventilation should be strengthened in some metal mines. Besides, it is still necessary to control occupational radon exposure of non-uranium miners as low as reasonably achievable, and non-uranium mines should be managed by classification.

Radon exposure and risk of neurodegenerative diseases among male miners in Ontario, Canada: A cohort study.

Environmental radon has been examined as a risk factor for neurodegenerative diseases in a small number of previous studies, but the findings have been inconsistent. This study aims to investigate the association between occupational radon exposure and neurodegenerative disease in a cohort of male miners with work experience in multiple ore types in Ontario, Canada. Radon exposure (1915-1988) was assessed using two job-exposure matrices (JEM) constructed from using historical records for 34,536 Ontario male miners. Neurodegenerative outcomes were ascertained between 1992 and 2018. Poisson regression models were used to estimate incidence rate ratios (RR) and 95% confidence intervals (CI) between cumulative radon exposure in working level months (WLM) and each neurodegenerative outcome. Levels of cumulative radon exposure showed variability among cohort members with a mean of 7.5 WLM (standard deviation 24.4). Miners in uranium mines or underground jobs had higher levels and more variability in exposure than workers in non-uranium work or surface jobs. Compared to the reference group (radon < 1 WLM), increased rates of Alzheimer's (RR 1.23, 95% CI 1.05-1.45) and Parkinson's disease (RR 1.43, 95% CI 1.08-1.89) were observed among workers with >1-5 WLM and >5-10 WLM, respectively, but not among higher exposed workers (>10 WLM). This study did not observe a positive monotonic dose-response relationship between cumulative radon exposure and Alzheimer's or Parkinson's disease in Ontario mining workers. There was no association observed with motor neuron disease.

Characterizing occupational radon exposure greater than 100Bq/m3 in a highly exposed country.

Radon is an established lung carcinogen concentrating in indoor environments with importance for many workers worldwide. However, a systematic assessment of radon levels faced by all workers, not just those with direct uranium or radon exposure, has not previously been completed. The objective of this study was to estimate the prevalence of workers exposed to radon, and the level of exposure (> 100-200Bq/m3, 200-400Bq/m3, 400-800Bq/m3, and > 800Bq/m3) in a highly exposed country (Canada). Exposures among underground workers were assessed using the CAREX Canada approach. Radon concentrations in indoor workplaces, obtained from two Canadian surveys, were modelled using lognormal distributions. Distributions were then applied to the susceptible indoor worker population to yield the number of exposed workers, by occupation, industry, province, and sex. In total, an estimated 603,000 out of Canada's 18,268,120 workers are exposed to radon in Canada. An estimated52% of exposed workers are women, even though they comprise only 48% of the labour force. The majority (68%) are exposed at a level of > 100-200Bq/m3. Workers are primarily exposed in educational services, professional, scientific and technical services, and health care and social assistance, but workers in mining, quarrying, and oil and gas extraction have the largest number of exposed workers at high levels (> 800Bq/m3). Overall, a significant number of workers are exposed to radon, many of whom are not adequately protected by existing guidelines. Radon surveys across multiple industries and occupations are needed to better characterize occupational exposure. These results can be used to identify exposed workers, and to support lung cancer prevention programs within these groups.

Indoor radon concentration measurements in workplaces and their impact on health risk assessment

Radon is the main source of exposure to ionizing radiation for the general population. In Italy, very little has been investigated to determine occupational radon exposure in workers. In this study, radon concentrations of various workplaces type were measured for 1 year using SSNTD CR-39. Q–Q plot and Shapiro–Wilks statistical test showed that radon concentrations are not log-normally distributed. The geometric mean of radon concentration was found to be 97 Bq/m3 with a geometric standard deviation of 3. The mean effective dose to workers has been calculated and found to be 1.4 mSv/y. Finally, for estimation of cancer risks, the lifetime risk and lung cancer cases per year per million have been calculated.

Radon levels and indoor air quality after application of thermal retrofit measures-a case study.

This study was conducted to evaluate the influence of thermal retrofit on radon levels in workrooms, and to determine whether the radon concentration in the building changes after the application of retrofit measures. In the first survey, digital Airthings Corentium Home radon detector was used for 1-month radon measurements during the heating season 2018/19. The daily averaged radon concentrations varied from 37 to 573Bq/m3 for 10 selected workrooms, while hourly averaged radon measurements showed extreme variations from 6 to 1603Bq/m3 due to radon fluctuations. In second survey, passive radon technique based on charcoal canister test kit was conducted in all basement workrooms in spring 2021. The averaged radon concentrations grouped according to flooring type in workrooms were 327Bq/m3 for parquet, 227Bq/m3 for ceramic tiles, 146Bq/m3 for vinyl flooring and 71Bq/m3 for laminate. Besides thermal insulation and airtight windows, noticeable differences in indoor radon concentration within the renovated building are primarily caused by different types of flooring. It includes various types of insulation from the ground/concrete slab: laminate, parquet (wood blocks), vinyl flooring, and ceramic tiles. Detailed analysis point out that laminate is more efficient way for radon protection than other types of flooring. An efficient ventilation system should be installed to avoid increasing occupational radon exposure and to provide healthy and comfortable indoor environment.

An Innovative Tool to Control Occupational Radon Exposure.

After smoking, indoor radon is the main contributor to lung cancer in many countries. The European Union (EU) Directive 2013/59/Euratom establishes a maximum reference level of 300 Bq/m3 of radon concentration in the workplace, and an effective dose limit of 20 mSv per year for workers. If the radon concentration in a workplace exceeds the reference level, constructive mitigation applies. When constructive mitigation is not feasible, we propose to keep workers’ effective dose below 6 mSv per year (category B of exposed workers) by controlling occupancy time. Setting the maximum annual dose at 6 mSv protects workers’ health and eases the regulatory requirements for employers. If multisite workers are present, each worker has to be monitored individually by tracking the time spent and the radon concentration at each worksite. This paper shows a software tool for employers to perform this complex tracking in an accurate, conservative, and transparent manner, and in compliance with the EU by-laws.

Radon in Finnish underground mines 2011–2019

Radon measurements in Finnish underground mines were started in 1972. Since 1992, regular radon inspections by the competent authority have been carried out in all underground mines. During these inspections, several grab samples are taken from the air, which are later measured in the laboratory. This is a follow-up survey of radon concentrations in the air of the underground mines. The average radon concentrations in the mines between the years 2011 and 2019 varied from 90 to 1100 Bq m−3. Overall, the occupational radon exposure in the Finnish underground mines has remained at a low level from the 1990s onwards. In recent years, high radon concentrations have been observed only in those mines where active mining has ceased. Compared to other recent studies in mines in other countries, radon concentrations in Finnish mines are approximately at the same level. Uncertainties relating to infrequent grab sampling have been recognised and the authority is now testing personal radon detectors that may be used for the exposure assessment in the future.

Long-term Lung Cancer Risk Associated with Sputum Atypia: A 27-Year Follow-up Study of an Occupational Lung Screening Cohort in Yunnan, China.

Sputum cytologic atypia is associated with increased lung cancer risk. However, little is known about the long-term magnitude and temporal trend of this risk. An extended follow-up was conducted in a prospective screening cohort among occupational tin miners in Yunnan, China. Sputum samples were collected prospectively at baseline and 7 annual screenings since enrollment. The associations between sputum cytologic results from baseline screening, the first 4 consecutive rounds of sputum screening, and lung cancer risk were analyzed by time-varying covariate Cox regression model. A moderate or worse cytologic result was associated with a significantly increased lung cancer risk. This relative hazard significantly decreased over time. Compared with negative screening results, the adjusted hazard ratios of baseline-moderate or worse atypia, at least one moderate or worse atypia in the first 4 consecutive screening rounds during the first 10 years of follow-up were 3.11 [95% confidence interval (CI): 2.37-4.07], 3.25 (95% CI: 2.33-4.54) respectively. This association was stronger for persistent atypia (adjusted hazard ratio = 17.55, 95% CI: 8.32-37.03); atypia identified in the recent screening rounds (adjusted HR = 4.14, 95% CI: 2.70-6.35), and those were old in age, had higher level of smoking, occupational radon, and arsenic exposure. In terms of histology, this increased risk was significant for squamous cell carcinoma and small cell lung cancer. Although decreasing over time, an increased lung cancer risk concerning moderate or worse sputum atypia can continue at least for 10 years. Sputum atypia might be helpful for identifying high-risk individuals for screening, surveillance, or chemoprevention of lung cancer.

Evaluation of occupational radon exposure and comparison with residential radon exposure in Canada—a population-level assessment

Radon is a naturally occurring radioactive gas and presents everywhere on the Earth at varying concentration in workplaces and at homes. With Canadian labour statistics, time statistics and more than 7600 long-term radon measurements in workplaces, occupational radon exposure is evaluated for all 20 job categories based on North American Industry Classification System. Results are compared with residential radon exposure based on more than 22 000 long-term radon tests conducted in Canadian homes. The average annual effective dose due to radon exposure in workplaces is 0.21 mSv, which is lower than the average annual effective dose of 1.8 mSv from radon exposure at home by a factor of eight. Due to relatively higher radon concentration in residential homes and longer time spent indoors at home, exposure at home contributes to 90% of workers’ total radon exposure (on average 1692 h in workplaces and 5852 h at homes). The analysis presented here is based on province-wide average radon exposures in various indoor and outdoor environments. Since the risk of developing lung cancer increases proportionally with increasing radon exposure, this evaluation indicates that on average reduction of radon levels in homes is very important and an effective way to reduce radon-induced lung cancers in Canada.

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

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

Estimating the burden of lung cancer in Canada attributed to occupational radon exposure using a novel exposure assessment method

ObjectiveExposure to radon causes lung cancer. The scope and impact of exposure among Canadian workers have not been assessed. Our study estimated occupational radon exposure in Canada and its associated lung cancer burden.MethodsExposed workers were identified among the working population during the risk exposure period (1961–2001) using data from the Canadian Census and Labour Force Survey. Exposure levels were assigned based on 12,865 workplace radon measurements for indoor workers and assumed to be 1800 mg/m3 for underground workers. Lung cancer risks were calculated using the Biological Effects of Ionizing Radiation (BEIR) VI exposure-age-concentration model. Population attributable fractions were calculated with Levin’s equation and applied to 2011 Canadian lung cancer statistics.ResultsApproximately 15.5 million Canadian workers were exposed to radon during the risk exposure period. 79% of exposed workers were exposed to radon levels < 50 Bq/m3 and 4.8% were exposed to levels > 150 Bq/m3. We estimated that 0.8% of lung cancers in Canada were attributable to occupational radon exposure, corresponding to approximately 188 incident lung cancers in 2011.ConclusionsThe lung cancer burden associated with occupational radon exposure in Canada is small, with the greatest burden occurring among those exposed to low levels of radon.

A Review of Radon Equilibrium Factors in Underground Mines, Caves, and Thermal Spas.

Radon equilibrium factor Feq is an important factor in radon progeny dose assessment. A review of published measurements of Feq shows a range of values from 0.1 to 1.0 reported in studies from more than 26 countries measured in 173 underground mines, and 136 show caves, tourist mines, and thermal spas. The average values of Feq are 0.38 in underground mines and 0.39 for show caves, tourist mines, and thermal spas. The wide range of Feq in those special workplaces suggests that location-, environment-, and operation-specific values are more appropriate than a recommended average value in the calculation of lung bronchial dose. This is especially important in mines or other typically high radon exposure locations because Feq can be used for recording an individual's occupational radon exposure or dose.

Low radon exposures and lung cancer risk: joint analysis of the Czech, French, and Beaverlodge cohorts of uranium miners

It is well established that high radon exposures increase the risk of lung cancer mortality. The effects of low occupational exposures and the factors that confound and modify this risk are not clear and are needed to inform current radiation protection of miners. The risk of lung cancer mortality at low radon exposures (< 100 working-level months) was assessed in the joint cohort analysis of Czech, French, and Canadian uranium miners, employed in 1953 or later. Statistical analysis was based on linear Poisson regression modeling with grouped cohort survival data. Two sensitivity analyses were used to assess potential confounding from tobacco smoking. A statistically significant linear relationship between radon exposure and lung cancer mortality was found. The excess relative risk per working-level month was 0.022 (95% confidence intervals: 0.013–0.034), based on 408 lung cancer deaths and 394,236 person-years of risk. Time since exposure was a statistically significant modifier; risk decreased with increasing time since exposure. A tendency for a decrease in risk with increasing attained age was observed, but this was not statistically significant. Exposure rate was not found to be a modifier of the excess relative risk. The potential confounding effect of tobacco smoking was estimated to be small and did not substantially change the radon–lung cancer mortality risk estimates. This joint cohort analysis provides strong evidence for an increased risk of lung cancer mortality from low occupational radon exposures. The results suggest that radiation protection measures continue to be important among current uranium miners.

RADON IN US WORKPLACES: A REVIEW.

Exposure to naturally occurring radon is unavoidable and is second only to smoking as a direct cause of lung cancer in the USA. The literature for existing information on US occupations that are prone to increased radon exposures was reviewed. Current recommendations and applicable protective standards against occupational radon exposure that are applicable to US workers are discussed. Exposure varied widely among several working populations, most of whom were employed in industries that were unrelated to the uranium fuel cycle. Radon protection standards differed among agencies and have not changed since the height of domestic uranium production in the 1970s. In contrast, European countries are adopting recommendations by the International Commission on Radiation Protection to set a reference level near a derived annual exposure of about one working level month, which is 25% of the level currently established for US miners.

Accounting for Berkson and Classical Measurement Error in Radon Exposure Using a Bayesian Structural Approach in the Analysis of Lung Cancer Mortality in the French Cohort of Uranium Miners.

Many occupational cohort studies on underground miners have demonstrated that radon exposure is associated with an increased risk of lung cancer mortality. However, despite the deleterious consequences of exposure measurement error on statistical inference, these analyses traditionally do not account for exposure uncertainty. This might be due to the challenging nature of measurement error resulting from imperfect surrogate measures of radon exposure. Indeed, we are typically faced with exposure uncertainty in a time-varying exposure variable where both the type and the magnitude of error may depend on period of exposure. To address the challenge of accounting for multiplicative and heteroscedastic measurement error that may be of Berkson or classical nature, depending on the year of exposure, we opted for a Bayesian structural approach, which is arguably the most flexible method to account for uncertainty in exposure assessment. We assessed the association between occupational radon exposure and lung cancer mortality in the French cohort of uranium miners and found the impact of uncorrelated multiplicative measurement error to be of marginal importance. However, our findings indicate that the retrospective nature of exposure assessment that occurred in the earliest years of mining of this cohort as well as many other cohorts of underground miners might lead to an attenuation of the exposure-risk relationship. More research is needed to address further uncertainties in the calculation of lung dose, since this step will likely introduce important sources of shared uncertainty.

Modeling Lung Carcinogenesis in Radon-Exposed Miner Cohorts: Accounting for Missing Information on Smoking.

Epidemiological miner cohort data used to estimate lung cancer risks related to occupational radon exposure often lack cohort-wide information on exposure to tobacco smoke, a potential confounder and important effect modifier. We have developed a method to project data on smoking habits from a case-control study onto an entire cohort by means of a Monte Carlo resampling technique. As a proof of principle, this method is tested on a subcohort of 35,084 former uranium miners employed at the WISMUT company (Germany), with 461 lung cancer deaths in the follow-up period 1955-1998. After applying the proposed imputation technique, a biologically-based carcinogenesis model is employed to analyze the cohort's lung cancer mortality data. A sensitivity analysis based on a set of 200 independent projections with subsequent model analyses yields narrow distributions of the free model parameters, indicating that parameter values are relatively stable and independent of individual projections. This technique thus offers a possibility to account for unknown smoking habits, enabling us to unravel risks related to radon, to smoking, and to the combination of both.

Nonlinear dose-response relationship between radon exposure and the risk of lung cancer: evidence from a meta-analysis of published observational studies.

Although radon exposure (RE) has been confirmed to increase the risk of lung cancer (LC), questions remain about the shape of the dose-response relationship between RE and the risk of LC. We carried out a dose-response meta-analysis to investigate and quantify the potential dose-response association between residential and occupational exposure to radon and the risk of LC. All cohort and case-control studies published in English and Chinese on Embase, PubMed, and China National Knowledge Infrastructure (CNKI) digital databases through November 2013 were identified systematically. We extracted effect measures (relative risk, odds ratio, standardized mortality ratio, standardized incidence ratio, or standardized rate ratio) from individual studies to generate pooled results using meta-analysis approaches. We derived meta-analytic estimates using random-effects models taking into account the correlation between estimates. Restricted cubic splines and generalized least-squares regression methods were used to model a potential curvilinear relationship and to carry out a dose-response meta-analysis. Stratified analysis, sensitivity analysis, and assessment of bias were performed in our meta-analysis. Sixty publications fulfilling the inclusion criteria for this meta-analysis were finally included. Occupational RE was associated with LC [risk ratio 1.86, 95% confidence interval (CI)=1.67-2.09; I²=92.2%; 27 prospective studies], for pooled risk estimate of the: standardized mortality ratio [2.00 (95% CI=1.82-2.32)]; standardized incidence ratio [1.45 (95% CI=1.20-1.74)]; relative risk [2.10 (95% CI=1.64-2.69)]. In a subgroup analysis of uranium miners and residents exposed to occupational uranium, the summary risk was 2.23 (95% CI=1.86-2.68) and 1.23 (95% CI=1.05-1.44). The overall meta-analysis showed evidence of a nonlinear association between RE and the risk of LC (P(nonlinearity)<0.014); in addition, the point value of residential radon also improved the results quantitatively, where odds ratios were 1.11 (95% CI=1.07-1.15) and 1.21 (95% CI=1.14-1.29) when the radon concentration was at the point of 100 and 200 Bq/m³ compared with the lowest. For 17 prospective studies with at least three categories of occupational cumulative radon dose, the dose-risk model estimated a risk ratio of 1.26 (95% CI=1.21-1.30) for 100 working level months and 1.51 (95% CI=1.38-1.65) for 200 working level months, respectively. The assessment of risk of bias within individual studies and across studies indicated risk that was unlikely to alter these results markedly. This meta-analysis shows a nonlinear dose-response association between environmental RE and the risk of LC. This increased risk is particularly apparent when the cumulative exposure to radon is well beyond that resulting from exposure to the recommended limit concentration for a prolonged period of time.

Relative biological effectiveness of alpha particles at radon exposure.

The relative biological effectiveness (RBE) of alpha particles at radon exposure is estimated by comparison of radiation risks at external gamma exposure and radon exposure in different situations. For external gamma exposure, the BEIR VII model of radiation risk assessment was used. For occupational and indoor radon exposure, models such as BEIR VI, WISMUT, Tomasek's and combined miners population were considered. It was demonstrated that RBE values are strongly dependent on models of radiation risk assessment used for RBE calculation, sex of exposed peoples and age at the exposure. The average values of RBE in dependence on model of risk assessment choice are in the range from 1.5 to 12.0 for males and in the range from 0.34 to 2.7 for females.