BEIR VI radon: The rest of the story

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.

Correlative links between natural radiation and life expectancy in the US population

The linear no-threshold (LNT) hypothesis is still the ruling concept which dictates the radiation protection health policy and regulations. However, more and more studies show that not only that low dose radiation pose no danger to our health, but also exhibits clear beneficial health effects. Here, we evaluated the correlative links of the natural sources of radiation-terrestrial radiation (TR), cosmic radiation (CR), and Radon-222, with life expectancy, the most integrative index of population health. The results of this study show that the different sources of natural radiation display positive correlative links to life expectancy, which is in line with the hypothesis of radiation hormesis.

The level of free-circulating mtDNA in patients with radon-induced lung cancer

OBJECTIVE

According to the World Health Organization, radon is the second leading cause of lung cancer after smoking. Cell free circulating mitochondrial DNA (cf mtDNA) have been used not only as a biomarker of carcinogenesis but also as a biomarker of exposure to radiation, but nothing is known about changes in the level of cf mtDNA following radon exposure. Therefore, the purpose of this study was to estimate the cf mtDNA copy number as a biomarker of the response to radon exposure in lung cancer pathogenesis.

METHODS

207 subjects were examined including 41 radon-exposed lung cancer patients, 40 lung cancer patients without radon exposure and 126 healthy controls exposed/not exposed to high level of radon. Total cell free circulating DNA from blood samples was extracted and used to detect cell free circulating mitochondrial DNA copy number by quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

Our data indicate that the level of cf mtDNA in the radon-induced lung cancer patients was significantly higher than that of the other study participants. There was a significant difference in the level of cf mtDNA in the blood plasma of healthy volunteers exposed and not exposed to high doses of radon. Moreover, in healthy volunteers living in areas with high radon levels, the mtDNA copy number was higher than that in patients with lung cancer who were not exposed to high doses of radon.

CONCLUSION

Our study provides evidence for a possible role of cf mtDNA as a promising biomarker of lung cancer induced by exposure to high dose of radon.

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.

Study, measurement and mitigation of radon activity concentration in the School of Computer Science ofA Coruñain the North West of Spain

A study of the radon activity concentration was carried out at the School of Computer Science of 'Universidade da Coruña' (UDC, Spain). For this purpose, building location, the type of soil and the construction materials were analysed. Subsequently, the radon activity concentration was determined using two different techniques: measurement in situ with an on-site ionization chamber detector (short term) and measurement with trace detectors (long term). Based on the results obtained, and according with the Spanish Law (Spanish Official Bulletin-Boletín Oficial del Estado, of 21 December 2011, IS-33 Instruction), corrective works were performed, consisting on the installation of a forced ventilation system underneath the extent of the suspended floor in order to mitigate the high radon specific activity in the building. Four months and 3 years after the works, new measurements were carried out in order to verify the effectiveness of the new ventilation system, obtaining a decrease of the radon gas values ranging between 87% and 90%, which confirmed long term effectivity.

Analysis of Indoor Radon Data Using Bayesian, Random Binning, and Maximum Entropy Methods

Three statistical methods: Bayesian, randomized data binning and Maximum Entropy Method (MEM) are described and applied in the analysis of US radon data taken from the US registry. Two confounding factors-elevation of inhabited dwellings, and UVB (ultra-violet B) radiation exposure-were considered to be most correlated with the frequency of lung cancer occurrence. MEM was found to be particularly useful in extracting meaningful results from epidemiology data containing such confounding factors. In model testing, MEM proved to be more effective than the least-squares method (even via Bayesian analysis) or multi-parameter analysis, routinely applied in epidemiology. Our analysis of the available residential radon epidemiology data consistently demonstrates that the relative number of lung cancers decreases with increasing radon concentrations up to about 200 Bq/m³, also decreasing with increasing altitude at which inhabitants live. Correlation between UVB intensity and lung cancer has also been demonstrated.

A radon chamber specifically designed for environmentally relevant exposures of small animals

In order to facilitate direct testing of the biological effects of radon, we designed and constructed a 3.1 m³ radon chamber specifically for radon exposures to small animals. The chamber is designed to operate as a sealed enclosure with a controlled atmosphere containing a known concentration of radon and its radioactive decay products. Sensors for air flow rate, temperature, humidity, HEPA filter and differential pressure ensure an optimal environment for exposure subjects. The radon gas is supplied to the chamber from a generator containing Radium-226 in a dilute acid solution. Air containing radon can be pumped continuously using a constant flow rate to maintain a steady state supply. The source flow rate was partitioned to achieve a chamber concentration at 200 Bq/m³ (R² = 0.9341) or 1000 Bq/m³ (R² = 0.9715). Small particles are injected into the re-circulating air stream via a particle generator to provide condensation nuclei for attachment of radon decay products as they form in the chamber atmosphere. Particles measured at 0.3 μm, 0.5 μm and 5.0 μm averaged concentrations 5.7 ± 0.6 × 10⁷/m³, 2.5 ± 0.7 × 10⁷/m³ and 2.3 ± 2.4 × 10³/m³, respectively. A desired Equilibrium Factor can easily be achieved by varying the air circulation rate through the chamber. The Equilibrium Factor ranged from 0.4 to 0.8 at 200 Bq/m³ and 0.5 to0.6 at 1000 Bq/m³. The chamber was designed to conduct short term exposures to assess the acute cellular changes induced by radon exposure. To our knowledge, this is currently the only radon chamber designed specifically to investigate environmentally relevant exposure time and doses of radon gas and decay products in small animal models.

The downfall of the linear non-threshold model

The linear non-threshold model (LNTM) is a theoretical dose-response function as a result of extrapolating the late effects of high-dose exposure to ionizing radiation to the low-dose range, but there is great uncertainty about its validity. The acceptance of LNTM as the dominant probabilistic model have survived to the present day and it is actually the cornerstone of current radiation protection policies. In the last decades, advances in molecular and evolutive biology, cancer immunology, and many epidemiological and animal studies have cast serious doubts about the reliability of the NLTM, as well as suggesting alternative models, like the hormetic theory. Considering the given evidences, a discussion between the involved scientific societies and the regulatory commissions is promtly required in order to to reach a redefiniton of theradiation protection basis, as it would be specially crucial in the medical field.

Combined effect of alpha particles and cigarette smoke on human lung epithelial cells in vitro

Purpose: The combined toxicity of alpha particles and cigarette smoke to the critical cells in the lungs was investigated to assess the risk of smoking workers who handle naturally occurring radioactive materials. Materials and methods: The toxicity of alpha particles and cigarette smoke extract (CSE) was evaluated in terms of DNA double-strand break (DSB) induction and clonogenic cell death of human lung epithelial cells in vitro. The cells were exposed to alpha particles at doses of up to 0.25 Gy for gamma-H2AX assay and from 1.25 Gy to 5 Gy for clonogenic assay. CSE exposure of the cells was facilitated in the culture medium at CSE concentrations ranging from 1% to 12%. Additional experiments were performed using mouse endothelial cells for comparison. Results: The increases in the levels of DNA DSBs were linearly dependent on radiation dose and CSE concentration. The CSE-treated cells also responded with a linearly increasing number of DNA DSBs to the radiation dose. Both human lung epithelial cells and mouse endothelial cells showed exponential decreases in clonogenic surviving fraction as the dose from alpha particle exposure increased. Both cells responded with the clonogenic surviving fractions decreasing in a linear proportion to the CSE concentration in the culture medium. Conclusion: In our experimental in vitro setup, CSE treatment and alpha particle exposure affected the cells in an additive manner either for DNA DSB production or for clonogenic cell death induction.