Radon epidemiology and nuclear track detectors: Methods, results and perspectives

An important achievement of nuclear track detectors is that they render it possible to measure a large number of radon concentrations. These are necessary for epidemiological studies aimed to estimate the lung cancer risk due to exposure to radon and its decay products in dwellings. Many case–control studies were conducted in the last 15 years in Europe, North America and China, in order to avoid the uncertainties associated with the risk extrapolation from epidemiological studies on miners exposed in underground mines. In this review paper, the main methodological issues of these studies are introduced: confounding factors, the impact of radon exposure uncertainties on the estimated risk, the retrospective assessment of radon exposure through the measurement of surface concentration on glass objects, the interaction between radon and smoking, statistical methods to analyze data and combine studies, etc. As regards the estimated risk of lung cancer, the main characteristics and results of each study are reported and discussed, together with the results of meta-analyses and, most importantly, of the three recently published analyses that pool 2 Chinese, 7 North American, and 13 European studies. Finally, some conclusions are given and a brief reference is made to ongoing studies.     

Comparison of radon exposure assessment results: Po surface activity on glass objects vs. contemporary air radon concentration

Radon exposure assessment in case–control studies on radon and lung cancer is generally based on contemporary radon concentration measurements, which can be affected by significant changes in the building structures or in living habits. Another method to estimate the radon exposure of the subjects is the recently developed retrospective dosimetry technique based on the ²¹⁰Po surface activity from glass objects. In order to compare the results obtained by the two methods, a study has been carried out in a sample of 26 dwellings in Rome, with radon concentration values ranging from 28 to 623 Bqm⁻³. Retrospective detectors based on CR-39 and LR 115 were exposed on 50 glass objects in bedrooms and living rooms. The correlation factor between the two sets of data, after removing six extreme values, is 0.67, which is similar to results obtained in other validation studies of similar sample size. The correlation increases to 0.83 if the 21 objects exposed in non-smoky dwellings are selected, while it vanishes to −0.01 for the 23 objects exposed in smoky dwellings, suggesting quite larger variations of plate-out in presence of environmental tobacco smoke.     

Quality assurance program for LR 115 based radon concentration measurements in a case-control study: description and results

A case-control study on lung cancer and radon exposure in dwellings has been carried out in Lazio, a high indoor radon region of Central Italy. A total of about 400 cases and 400 controls were recruited and radon concentration was measured in a total of about 1850 dwellings. In each dwelling, radon concentration measurement devices were placed in both the main bedroom and living room for two consecutive six-month periods. Each radon device, enclosed in a sealed polyethylene bag, contains two LR 115 detectors, each being covered by a thin absorber to reduce the alpha-energy within the detector sensitive range. A quality assurance program, described in this paper, was applied in order to reduce radon concentration measurement uncertainty, which have a significant impact on the results of an epidemiological study. The reported internal quality control and intercomparison results are compared with the results of other studies, and show that the radon measurement precision and accuracy obtained in this study can be considered quite good.     

Indoor radon survey in Eastern Sicily

Inhalation of radon (Rn-222) and its progeny is one of the most significant sources of natural radiation exposure of the population. Nowadays, high radon exposures have been shown to cause lung cancer and many governments all over the world have therefore recommended that radon exposures in dwellings and indoor workplaces should be limited. Radon levels in buildings vary widely from area to area depending on local geology. This paper presents the results of a long-term survey of radon concentrations carried out from 2005 till 2010 in schools and dwellings of Eastern Sicily, using the solid-state nuclear track detector (SSNTD) technique. The investigated area shows medium-high indoor radon concentrations, higher than the Italian average of about 70 Bq/m³, with peaks of 500 Bq/m³ or more in buildings near active faults. Fortunately, only a small fraction of the measurements, about 1.5% of total, was found greater than EU and Italian action limits for indoor and workplaces.     

The use of track registration detectors to reconstruct contemporary and historical airborne radon (RN) and radon progeny concentrations for radon-lung cancer epidemiologic study

Epidemiologic studies that investigate the relationship between radon and lung cancer require accurate estimates for the long-term average concentrations of radon progeny in dwellings. Year-to-year and home-to-home variations of radon in domestic environments pose serious difficulties for reconstructing an individual's long-term radon-related exposure. The use of contemporary radon gas concentrations as a surrogate for radon-related dose introduces additional uncertainty in dose assessment. Studies of glass exposed in radon chambers and in a home show that radon progeny deposited on, and implanted in, glass hold promise for reconstructing past radon concentrations in a variety of atmospheres. We developed an inexpensive track registration detector for the Iowa Radon Lung Cancer Study (IRLCS) that simultaneously measures contemporary airborne radon concentrations, surface deposited alpha activity density, and implanted ²¹⁰Po activity density. The implanted activity is used to reconstruct the cumulative radon and radon progeny exposure from the age of the glass and the ratios of the contemporary deposited activiteis to airborne radon gas activity. We placed over 2500 of these detectors in more than 1000 homes and retrieved 97% of them after a one-year exposure period. A preliminary analysis of the 1280 detectors that have undergone quality assurance review shows that the modules are meeting their accuracy and precision goals (10%). There is good correlation (r²0.5) between the total radon exposure estimated from contemporary radon gas measurements and historical average reconstructed from the implanted ²¹⁰Po surface activity. The linear regression slope of the airborne radon exposure to implanted activity is the same as the room model slope based on typical room parameters. This correlation improves (r²0.7) when the deposited surface activity measurements are added to the linear regression. Thus, track-registration detectors can contribute to accurate radon-related dose assessment in epidemiologic studies. Additional work is planned to incorporate the deposited activities in a more sophisticated reconstruction model.     

Thoron in the environment and its related issues

Since radon is internationally noted as the second cause of lung cancer, many countries are trying about to solve the problem worldwide. In addition, a new evidence of lung cancer risk has been recently found out with a low level below 200 Bq m⁻³. Thus the action level will have to be set lower than before. Importance of radon exposure has been further recognized and accurate radon concentrations will be required. Recently thoron has also been recognized from the viewpoint of accurate radon measurements. The present paper describes specification of the NIRS radon and thoron chambers, passive measurement technique of radon and thoron and thoron interference on radon measurements from both experimental studies and field experiences on epidemiological study area.      

An affordable proxy of representative national survey on radon concentration in dwellings: Design,organisation and preliminary evaluation of representativeness

Representative national surveys in dwellings are important to unbiasedly evaluate the exposure of the general population to radon. In Italy, a representative national survey was conducted from 1989 to 1996, which involved about 5600 dwellings in 232 towns. Later on, some Regions carried out more detailed surveys, but a new national survey in dwellings is necessary in order to obtain a more thorough estimate of radon concentration distribution over the Italian territory. The need to make this survey in an affordable way led to implement a new approach based on the collaboration between the Istituto Superiore di Sanità and a national company with workplaces and employees' homes throughout the country. The intent is to carry out a proxy of a population representative survey by measuring radon concentration in the homes of a random sample of the company employees. The realisation of this survey was affordable, thanks to the availability of corporate e-mail for each employee, intranet service, and company internal mail service. A dedicated web procedure and e-questionnaires allowed to automatically manage the contact with employees and to collect their data, which were both cost- and time-saving. Using this e-mail contact approach, 53% of contacted employees consented to participate in the survey. Radon concentration passive measuring devices were distributed to about 7000 dwellings, using about 14000 CR-39 detectors (two measured rooms per dwelling). In order to reduce costs, the devices were exposed for 12 months instead of two consecutive 6-month periods (as with the former national survey). A first checking of the actual representativeness of the sample was done by comparing characteristics of dwellings and occupants in the sample with corresponding data from the latest National Census. This was accomplished thanks to the fact that the questions in the survey questionnaire were tailored to the categories adopted for the Census questionnaire. A preliminary comparison showed that, at national level, the Italian dwellings are quite well represented by the sample.     

A study of indoor radon levels in Indian dwellings,influencing factors and lung cancer risks

Passive integrating solid state nuclear track detectors (SSNTDs) were used to study the Radon-222 (Rn) concentrations in Indian dwellings. The study was made in 300 dwellings in the cities of Lucknow and Kanpur in northern India. The influence of some factors e.g. age of the house, number of floors and ventilation conditions, etc. on indoor Rn concentrations were studied. The equilibrium factor in 65 dwellings were also investigated. Average Rn concentrations in living rooms were found to be 34±8 Bq.m⁻³ and 40±10 Bq.m⁻³ respectively, with equilibrium factors of 0.35 and 0.38. Assuming an occupancy factor of 0.8, the annual average effective dose equivalents in living rooms of the two places are estimated as 0.8 and 1.0 mSv respectively.The average life-time risks of lung cancer for radon exposure of the Lucknow and Kanpur populations at home would be about 0.26% and 0.34% respectively and the mean relative loss of life expectancies were 0.06% and 0.074% respectively.     

Indoor radon and lung cancer: a case-control study

Lung-cancer risk to the general population from indoor radon remains controversial, although studies of radon exposure have established that radon decay products have been a cause of lung cancer among miners.

For the case group of patients, suffering from lung cancer, and the control group distributions of the number of homes with high indoor levels of radon were compared with the log-normal distribution, the empirical frequency distribution of the control group obeyed the theoretical log-normal distribution.

Using the ratio of frequencies of the case group to the control groups, or the relative frequencies, an association between the relative frequencies and indoor radon concentrations was found, and a positive correlation coefficient was obtained, thus enabling the rate of lung cancer to be estimated for certain indoor radon concentrations.

The significant difference between the mean radon levels for the case sample and the control led to the conclusion that patients with lung cancer lived in homes with radon concentrations which were significantly higher than those of Osijek’s inhabitants for the control sample.     

Indoor radon and lung cancer: a case-control study

Lung-cancer risk to the general population from indoor radon remains controversial, although studies of radon exposure have established that radon decay products have been a cause of lung cancer among miners. For the case group of patients, suffering from lung cancer, and the control group distributions of the number of homes with high indoor levels of radon were compared with the log-normal distribution, the empirical frequency distribution of the control group obeyed the theoretical log-normal distribution. Using the ratio of frequencies of the case group to the control groups, or the relative frequencies, an association between the relative frequencies and indoor radon concentrations was found, and a positive correlation coefficient was obtained, thus enabling the rate of lung cancer to be estimated for certain indoor radon concentrations. The significant difference between the mean radon levels for the case sample and the control led to the conclusion that patients with lung cancer lived in homes with radon concentrations which were significantly higher than those of Osijek's inhabitants for the control sample.     

Measurement of radon and thoron concentration by using LR-115 type-II plastic track detectors in the environ of Brahmaputra Valley, Assam, India

Radon/thoron and their progeny concentrations were measured in different types of dwellings at different locations around industrial areas, cities and rural areas of Brahmaputra Valley of Assam by using LR-115 (type-II) plastic detector. Radon levels of different dwellings were analysed with reference to the nature of building materials, ventilation patterns and the types of underlying soil. The results were discussed under the light of exposure limits set by ICRP. The average concentrations of indoor radon and thoron varied from 39.5 to 215.2 Bqm⁻³ and 12.9 to 37.6 Bqm⁻³, respectively. The estimated inhalation dose due to radon, thoron and their daughter products in the study areas varied from 0.53 to 1.00 μSvh⁻¹.     

吸烟过程中重金属挥发量的测定

原子荧光光谱、石墨炉原子吸收光谱法测定了不同品牌香烟中重金属的本底值与香烟吸过后过滤嘴、烟头和烟灰中重金属的总残留量,并计算在吸烟过程中重金属的挥发量。结果表明,在吸烟过程中,香烟中砷和铅挥发性较小,且通过烟头及过滤嘴的吸附,对主动吸烟者及被动吸烟者造成危害甚微;而汞和镉的挥发性较大,且过滤嘴吸附量较小,故对主动吸烟者及被动吸烟者均可能造成危害。     

Radon levels in the volcanic region of La Garrotxa, Spain

A preliminary survey in the city of Olot, the main town of the volcanic region of La Garrotxa, showed that dwellings built on volcanic formations present higher indoor radon levels than dwellings on non-volcanic materials. The soil of the area is not especially rich in radium. However, some of the volcanic materials present very high permeability and therefore radon entering the houses might have travelled over long distances. In this paper we present indoor radon values measured in a larger survey carried out during April–July 2004. The influence of the volcanic materials found in the preliminary survey has been confirmed. The results obtained suggest the possibility that radon comes from the degassification of mantle through active faults. The values obtained in working places do not constitute a relevant radiological risk for workers.     

Indoor radon monitoring in some buildings surrounding the national Hydroelectric Power Corporation (NHPC) project at upper Siang in Arunachal Pradesh, India

In the present study measurement of radon and its progeny concentration has been undertaken in the buildings constructed in the surroundings of National Hydroelectric Power Corporation (NHPC). LR-115 Type-II solid state nuclear track detectors fixed on a thick flat card were exposed in bare mode. Track etch technique has been used to estimate the radon concentration in the rooms of some buildings. Annual effective dose has been calculated from the radon concentration to carry out the assessment of the variability of expected radon exposure of the population due to radon and its progeny. The radon levels in these dwellings vary from 9±4 to 472±28 Bq m⁻³ with an average value of 158±14.9 Bq m⁻³ whereas annual effective dose varies from 0.1±0.04 to 7±0.4 mSv y⁻¹ with an average value of 2.3±0.2 mSv y⁻¹. These values are below the recommended action levels.     

Indoor radon measurements in a Greek city located in the vicinity of lignite-fired power plants

This work presents indoor radon measurements in 42 dwellings in the city of Megalopolis, Southern Greece, located in the vicinity of 2 lignite-fired power plants and examines the effect of season, floor level and age of the dwellings on indoor radon concentration. The radon measurements have been carried out using the LR-115, type II and CR-39 alpha track detectors in “closed-can” geometry. The average annual indoor radon concentration (GM) was found to be 52 Bq m^?3, which is well below the recommended action level of the European Union. This value corresponds to an annual effective dose to the population of 1.3 ± 0.4 mSv. Season and age of the examined dwellings represent factors that affected significantly the indoor radon in Megalopolis, while the effect of floor level appeared to be not significant. Radium activity concentration values, measured by γ-ray spectrometry in 20 sub-samples of six soil cores (60–135 cm depth), collected from the surrounding area of the city, were found to be consistent with the Greek and world average values. Based on the results of this study, it is concluded that the effect of the lignite-fired power plants on indoor radon concentration in Megalopolis’ dwellings was not significant.     

Preliminary measurements of natural radioactivity at Madurai district of Tamilnadu, India

In dwellings, the radon and their daughter products contribute the largest fraction to the doses received from natural background radiation. In the present study, the radon levels at Madurai district of Tamilnadu have been measured initially for 15 dwellings using cellulose nitrate (C₆H₈O₉N₂) LR-115 type II (non-pelliculable) films and the dose assessment due to radon and its daughter product concentrations is calculated. These results were intercompared with other terrains viz. Jodhpur district of Rajasthan which is considered as semi-desert terrain and Jammu district of Jammu & Kashmir which is the hilly area. Also the natural radioactivity in soil samples of Madurai have been measured using NaI(Tl) detector based gamma spectrometry. From these radioactivity levels, the radium equivalent activity is calculated and a correlation between this and radon concentration has been tried out.     

吸烟、辐射与肺癌

肺癌是危害人类生命的主要癌种之一,诱发肺癌的第一位因素是吸烟,第二位因素是吸入氡及其子体后的内照射． Lung cancer is one of the main killers to mankind in all kinds of cancers.The first factor inducing lung cancer is cigarette smoking. The second factor is the internal exposures from the intake of Radon and its airborne decay products.     

Radon and thoron levels,their spatial and seasonal variations in adobe dwellings – a case study at the great Hungarian plain

Radon and thoron isotopes are responsible for approximately half of the average annual effective dose to humans. Although the half-life of thoron is short, it can potentially enter indoor air from adobe walls. Adobe was a traditional construction material in the Great Hungarian Plain. Its major raw materials are the alluvial sediments of the area. Here, seasonal radon and thoron activity concentrations were measured in 53 adobe dwellings in 7 settlements by pairs of etched track detectors. The results show that the annual average radon and thoron activity concentrations are elevated in these dwellings and that the proportions with values higher than 300 Bq m^?3 are 14–17 and 29–32% for radon and thoron, respectively. The calculated radon inhalation dose is significantly higher than the world average value, exceeding 10 mSv y^?1 in 7% of the dwellings of this study. Thoron also can be a significant contributor to the inhalation dose with about 30% in the total inhalation dose. The changes of weather conditions seem to be more relevant in the variation of measurement results than the differences in the local sedimentary geology. Still, the highest values were detected on clay. Through the year, radon follows the average temperature changes and is affected by the ventilation, whereas thoron rather seems to follow the amount of precipitation.     

Inter-comparison of three techniques for radon activity measurements

In this paper the results of an inter-comparison employing three distinct techniques for measuring indoor radon activities are discussed: (i) NRPB–SSI dosimeter, a diffusion chamber, CR-39 based, calibrated in a controlled radon chamber; (ii) a diffusion chamber, CR-39 based, calibrated via nuclear emulsion; (iii) canister with activated charcoal. Totally 39 dwellings of Poços de Caldas city (Minas Gerais State, Brazil), located in a high natural radioactivity region, have been monitored during a six months period.

Dosimeters (i) and (ii) were exposed continuously in all of 39 dwellings and dosimeter (iii) was exposed in 10 of them, randomly chosen. In this case the individual exposures lasted around 5 days and 4 equally time spaced exposures were made in each dwelling. Results produced by techniques (i) and (ii) show a great level of concordance. Individual results of technique (iii) for each residence show great fluctuations, but their mean results statistically agree with the other techniques. So our results indicate that active charcoal technique can be used to study average term radon variation (in few days), but its individual results cannot reflect long-term indoor radon activity.     

A comparative study of indoor radon levels and inhalation dose in some areas of Punjab and Haryana, India

Indoor radon concentrations have been measured for two consecutive half-year periods in a wide range of dwellings of some regions of Punjab and Haryana states. The objective was to find correlation between the variations of indoor radon levels with the sub-soil, local geology, type of building materials, etc. of the two regions. So keeping this in view the indoor radon measurements have been carried out in the dwellings of different villages around the Tusham ring complex, Bhiwani District, Haryana, known to be composed of acidic volcanics and the associated granites along with some villages of Amritsar District, Punjab. The indoor radon concentration in the dwellings around Tusham (Haryana) have been found to be varying from 120.5±95 to 915.2±233 Bq m⁻³, whereas it ranges from 60.0±37 to 235.6±96 Bq m⁻³ for the dwellings of Punjab. The ²²²Rn concentration observed at most of locations particularly around Tusham ring complex region is higher than that of all the villages studied in Punjab region. Local geology including embedded granitic rocks, sub-soil, etc. as well as building materials having higher radioactive content are the major contributors for the higher indoor radon levels observed in the dwelling around Tusham, where few dwellings have higher radon concentrations than the ICRP, 1993 recommendations. The annual effective dose equivalent has also been estimated for each location of the both regions, which has been found to be varying from 1.0 to 17.2 mSv/y.