Miner studies and radiological protection against radon

Radon and lung cancer: Current status and future prospects

Beyond tobacco smoking, radon takes its place as the second most significant contributor to lung cancer, excluding hereditary and other biologically related factors. Radon and its byproducts play a pivotal role in exposing humans to elevated levels of natural radiation. Approximately 10-20 % of lung cancer cases worldwide can be attributed to radon exposure, leading to between 3 % and 20 % of all lung cancer-related deaths. Nevertheless, a knowledge gap persists regarding the association between radon and lung cancer, impeding radon risk reduction initiatives globally. This review presents a comprehensive overview of the current state of research in epidemiology, cell biology, dosimetry, and risk modeling concerning radon exposure and its relevance to lung cancer. It also delves into methods for measuring radon concentrations, monitoring radon risk zones, and identifying priorities for future research.

Lifetime excess absolute risk for lung cancer due to exposure to radon: results of the pooled uranium miners cohort study PUMA

The Pooled Uranium Miners Analysis (PUMA) study is the largest uranium miners cohort with 119,709 miners, 4.3 million person-years at risk and 7754 lung cancer deaths. Excess relative rate (ERR) estimates for lung cancer mortality per unit of cumulative exposure to radon progeny in working level months (WLM) based on the PUMA study have been reported. The ERR/WLM was modified by attained age, time since exposure or age at exposure, and exposure rate. This pattern was found for the full PUMA cohort and the 1960 + sub-cohort, i.e., miners hired in 1960 or later with chronic low radon exposures and exposure rates. The aim of the present paper is to calculate the lifetime excess absolute risk (LEAR) of lung cancer mortality per WLM using the PUMA risk models, as well as risk models derived in previously published smaller uranium miner studies, some of which are included in PUMA. The same methods were applied for all risk models, i.e., relative risk projection up to <95 years of age, an exposure scenario of 2 WLM per year from age 18-64 years, and baseline mortality rates representing a mixed Euro-American-Asian population. Depending upon the choice of model, the estimated LEAR per WLM are 5.38 × 10-4 or 5.57 × 10-4 in the full PUMA cohort and 7.50 × 10-4 or 7.66 × 10-4 in the PUMA 1960 + sub-cohort, respectively. The LEAR per WLM estimates derived from risk models reported for previously published uranium miners studies range from 2.5 × 10-4 to 9.2 × 10-4. PUMA strengthens knowledge on the radon-related lung cancer LEAR, a useful way to translate models for policy purposes.

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 5 years 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/100 WLM was 2.50 (95% confidence interval (CI) 0.81; 4.18) and 6.92 (95% CI < 0; 16.59) among miners with attained age < 55 years, time since exposure 5-14 years, and annual exposure rates < 0.5 WL 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, 20-30 years 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 and lung cancer in the pooled uranium miners analysis (PUMA): highly exposed early miners and all miners

OBJECTIVES

Radon is a ubiquitous occupational and environmental lung carcinogen. We aim to quantify the association between radon progeny and lung cancer mortality in the largest and most up-to-date pooled study of uranium miners.

METHODS

The pooled uranium miners analysis combines 7 cohorts of male uranium miners with 7754 lung cancer deaths and 4.3 million person-years of follow-up. Vital status and lung cancer deaths were ascertained between 1946 and 2014. The association between cumulative radon exposure in working level months (WLM) and lung cancer was modelled as the excess relative rate (ERR) per 100 WLM using Poisson regression; variation in the association by temporal and exposure factors was examined. We also examined analyses restricted to miners first hired before 1960 and with <100 WLM cumulative exposure.

RESULTS

In a model that allows for variation by attained age, time since exposure and annual exposure rate, the ERR/100 WLM was 4.68 (95% CI 2.88 to 6.96) among miners who were less than 55 years of age and were exposed in the prior 5 to <15 years at annual exposure rates of <0.5 WL. This association decreased with older attained age, longer time since exposure and higher annual exposure rate. In analyses restricted to men first hired before 1960, we observed similar patterns of association but a slightly lower estimate of the ERR/100 WLM.

CONCLUSIONS

This new large, pooled study confirms and supports a linear exposure-response relationship between cumulative radon exposure and lung cancer mortality which is jointly modified by temporal and exposure factors.

Effects of spatial variation in dose delivery: what can we learn from radon-related lung cancer studies?

Exposure to radon progeny results in heterogeneous dose distributions in many different spatial scales. The aim of this review is to provide an overview on the state of the art in epidemiology, clinical observations, cell biology, dosimetry, and modelling related to radon exposure and its association with lung cancer, along with priorities for future research. Particular attention is paid on the effects of spatial variation in dose delivery within the organs, a factor not considered in radiation protection. It is concluded that a multidisciplinary approach is required to improve risk assessment and mechanistic understanding of carcinogenesis related to radon exposure. To achieve these goals, important steps would be to clarify whether radon can cause other diseases than lung cancer, and to investigate radon-related health risks in children or persons at young ages. Also, a better understanding of the combined effects of radon and smoking is needed, which can be achieved by integrating epidemiological, clinical, pathological, and molecular oncology data to obtain a radon-associated signature. While in vitro models derived from primary human bronchial epithelial cells can help to identify new and corroborate existing biomarkers, they also allow to study the effects of heterogeneous dose distributions including the effects of locally high doses. These novel approaches can provide valuable input and validation data for mathematical models for risk assessment. These models can be applied to quantitatively translate the knowledge obtained from radon exposure to other exposures resulting in heterogeneous dose distributions within an organ to support radiation protection in general.

Nonmalignant respiratory disease mortality in male Colorado Plateau uranium miners, 1960-2016

BACKGROUND

To evaluate trends of nonmalignant respiratory disease (NMRD) mortality among US underground uranium miners on the Colorado Plateau, and to estimate the exposure-response association between cumulative radon progeny exposure and NMRD subtype mortality.

METHODS

Standardized mortality ratios (SMRs) and excess relative rates per 100 working level months (excess relative rate [ERR]/100 WLM) were estimated in a cohort of 4021 male underground uranium miners who were followed from 1960 through 2016.

RESULTS

We observed elevated SMRs for all NMRD subtypes. Silicosis had the largest SMR (n = 52, SMR = 41.4; 95% confidence interval [CI]: 30.9, 54.3), followed by other pneumoconiosis (n = 49, SMR = 39.6; 95% CI: 29.6, 52.3) and idiopathic pulmonary fibrosis (IPF) (n = 64, SMR = 4.77; 95% CI 3.67, 6.09). SMRs for silicosis increased with duration of employment; SMRs for IPF increased with duration of employment and calendar period. There was a positive association between cumulative radon exposure and silicosis with evidence of modification by smoking (ERR/100 WLM≥10 pack-years  = 0.78; 95% CI: 0.05, 24.6 and ERR/100 WLM<10 pack-years  = 0.01; 95% CI: -0.03, 0.52), as well as a small positive association between radon and IPF (ERR/100 WLM = 0.06, 95% CI: 0.00, 0.24); these associations were driven by workers with prior employment in hard rock mining.

CONCLUSIONS

Uranium mining workers had excess NMRD mortality compared with the general population; this excess persisted throughout follow-up. Exposure-response analyses indicated a positive association between radon exposure and IPF and silicosis, but these analyses have limitations due to outcome misclassification and missing information on occupational co-exposures such as silica dust.

Application of radon (222Rn) as an environmental tracer in hydrogeological and geological investigations: An overview

Radon (²²²Rn) is a colourless, odourless, inert, and radioactive noble gas (t_1/2 = 3.8 days) that emanates from rocks and soils as a result of the alpha decay of its parent, radium (²²⁶Ra) in the decay series of uranium-238, is the focus of this study. Radon is produced in the crystal lattice of the minerals and emanates out through alpha recoil. It dissolves in water, and is also found in soil and air. Its distribution in water is more pertinent for scientific investigations. It can be measured by various methods. Certain properties of radon enable it to serve as an ideal tracer, viz., short-half life, inertness, high abundance in groundwater than surface water, preferential partitioning, sensitivity to sudden changes in subsurface conditions, non-invasiveness etc. This paper reviews the state-of-the-art techniques on the measurement of dissolved radon in water and its potential applications as a tracer and precursor in several hydrogeological and geological applications like understanding the surface water - groundwater interactions, hydrograph separation of streams, estimation of Submarine Groundwater Discharge (SGD), study of hydrodynamics and water balance of lakes, earthquake predictions, locating geological structures (faults/lineaments), geochemical explorations, NAPL contamination studies etc. Among the various applications presented, radon based approach is found to be more reliable in water resources domain than seismic precursory studies. The interpretations based on radon study in the above applications will pave the way for the improved understanding of the hydrological processes, and thus, help the planners and water managers for the sustainable development and management of water resources.

Interaction between occupational radon exposure and tobacco smoke: a systematic review

INTRODUCTION

: The risk of lung cancer from radon exposure was small compared to tobacco smoking (BEIR VI), but the relationship between these two carcinogenic agents has yet to be quantitatively estimated. The objective of this systematic review was to evaluate the last evidences on the role of radon occupational exposures and tobacco smoke on lung cancer risk.

AREAS COVERED

: Thirteen articles were selected using two different databases, PubMed and Scifinder, and were limited to those published from 2010 to 2021. The reference list of selected studies was reviewed to identify other relevant papers.

EXPERT OPINION

: Seven papers included in this systematic review did not deal with the multiplicative or the additive type of interaction between radon exposure and smoking habit. Six papers discussed the nature of this interaction with a prevalence of the sub-multiplicative model compared to the additive one. Altogether, smoking adjustment did not change significantly lung cancer risk. The included studies might constitute a starting point for updating the models for risk assessment in occupational and residential scenarios, promoting concomitantly the exposure reduction to radon and other cofactors, as recently introduced by Italian Legislative Decree number 101 of 31 July 2020, an application of Euratom Directive 59/2013.

Lung Cancer and Radon: Pooled Analysis of Uranium Miners Hired in 1960 or Later

BACKGROUND

Despite reductions in exposure for workers and the general public, radon remains a leading cause of lung cancer. Prior studies of underground miners depended heavily upon information on deaths among miners employed in the early years of mine operations when exposures were high and tended to be poorly estimated.

OBJECTIVES

To strengthen the basis for radiation protection, we report on the follow-up of workers employed in the later periods of mine operations for whom we have more accurate exposure information and for whom exposures tended to be accrued at intensities that are more comparable to contemporary settings.

METHODS

We conducted a pooled analysis of cohort studies of lung cancer mortality among 57,873 male uranium miners in Canada, Czech Republic, France, Germany, and the United States, who were first employed in 1960 or later (thereby excluding miners employed during the periods of highest exposure and focusing on miners who tend to have higher quality assessments of radon progeny exposures). We derived estimates of excess relative rate per 100 working level months (ERR/100 WLM) for mortality from lung cancer.

RESULTS

The analysis included 1.9  million person-years of observation and 1,217 deaths due to lung cancer. The relative rate of lung cancer increased in a linear fashion with cumulative exposure to radon progeny (ERR/100 WLM = 1.33 ; 95% CI: 0.89, 1.88). The association was modified by attained age, age at exposure, and annual exposure rate; for attained ages < 55    y , the ERR/100 WLM was 8.38 (95% CI: 3.30, 18.99) among miners who were exposed at ≥ 35   years of age and at annual exposure rates of < 0.5 working levels. This association decreased with older attained ages, younger ages at exposure, and higher exposure rates.

DISCUSSION

Estimates of association between radon progeny exposure and lung cancer mortality among relatively contemporary miners are coherent with estimates used to inform current protection guidelines. https://doi.org/10.1289/EHP10669.

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.

EFFECTIVE DOSE COEFFICIENTS FOR RADON AND PROGENY: A REVIEW OF ICRP AND UNSCEAR VALUES

The International Commission on Radiological Protection (ICRP) publishes guidance on protection against radon exposure in homes and workplaces. ICRP Publication 137 recommends a dose coefficient of 3 mSv per mJ h m-3 (~10 mSv WLM-1) to be used in most circumstances of radon exposure, for workers in buildings and in underground mines. Recently, United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reviewed radon epidemiology and dosimetry and concluded that its established dose coefficient of 1.6 mSv per mJ h m-3 (5.7 mSv WLM-1) should be retained for use in its comparisons of radiation exposures from different sources in a population. This paper explains and compares the reviews of the scientific evidence from UNSCEAR and ICRP. It is shown that the UNSCEAR and ICRP reviews are consistent and support the use of the ICRP reference dose coefficients for radiation protection purposes. It is concluded that the ICRP dose coefficient should be used to calculate doses to workers.

Lung cancer risk and effective dose coefficients for radon: UNSCEAR review and ICRP conclusions

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has provided a detailed and authoritative update of its reviews of the epidemiology and dosimetry of radon and progeny. Lifetime risk of lung cancer calculated using data for several miner cohorts were 2.4-7.5 × 10^-4per working level month (WLM) of radon-222 progeny exposure for a mixed male/female population and 3.0-9.6 × 10^-4per WLM for a male population. Dosimetric models gave mean values of effective dose coefficients from radon-222 progeny of 12 mSv per WLM for mines, 16 mSv per WLM for indoor workplaces and 11 mSv per WLM for homes. The lifetime risk coefficient used by the International Commission on Radiological Protection (ICRP) is 5 × 10^-4per WLM and it has recently recommended an effective dose coefficient for radon-222 and progeny of 3 mSv per mJ h m^-3(about 10 mSv per WLM) for most circumstances of exposure. The ICRP risk and dose coefficients are supported by the UNSCEAR review and provide a clear and firm basis for current international advice and standards for protection from radon. Notwithstanding this evidence and the ICRP advice, UNSCEAR will continue to use a lower value of effective dose coefficient of 5.7 mSv per WLM for assessments of population exposures.