Analysis and Monitoring of Indoor Radon Concentrations of 37 Kindergartens - Beijing Municipality, China, 2023.

Introduction: Radon (222Rn or 222radon) is a radioactive gas emitted from building materials, foundations, and soil. Children are especially susceptible to radon exposure, underscoring the need to assess indoor radon levels in kindergartens. This study monitored radon concentrations in 37 Beijing kindergartens from June to October 2023. Methods: A random sample of 37 kindergartens was selected from 18 administrative districts in Beijing. The indoor radon concentration was measured using the solid track accumulation method, with radon detectors continuously monitored over a 3-month period. Results: The mean indoor radon level in 37 kindergartens, observed at 252 monitoring points, was 84.3 Bq/m3, with values varying from 12.9 to 263.5 Bq/m3. About 20.2% of points showed radon levels between 100.0 and 200.0 Bq/m3, while 2.4% exceeded 200.0 Bq/m3. Notably, radon levels were significantly elevated on the ground floor compared to the upper floors. Conclusion: Indoor radon levels in 37 kindergartens remained below the national standard limit of 300.0 Bq/m3 for buildings (GB/T 16146-2015). Nonetheless, 18.9% of the kindergartens exceeded the 100.0 Bq/m3 limit set for new constructions. It is advised to improve radon monitoring in kindergartens and consider developing a national standard for maximum permissible radon levels in such facilities.

Impact of Indoor Radon Exposure on Lung Cancer Incidence in Slovenia.

Indoor radon is an important risk factor for lung cancer, as 3-14% of lung cancer cases can be attributed to radon. The aim of our study was to estimate the impact of indoor radon exposure on lung cancer incidence over the last 40 years in Slovenia. We analyzed the distribution of lung cancer incidence across 212 municipalities and 6032 settlements in Slovenia. The standardized incidence ratios were smoothed with the Besag-York-Mollie model and fitted with the integrated nested Laplace approximation. A categorical explanatory variable, the risk of indoor radon exposure with low, moderate and high risk values, was added to the models. We also calculated the population attributable fraction. Between 2.8% and 6.5% of the lung cancer cases in Slovenia were attributable to indoor radon exposure, with values varying by time period. The relative risk of developing lung cancer was significantly higher among the residents of areas with a moderate and high risk of radon exposure. Indoor radon exposure is an important risk factor for lung cancer in Slovenia in areas with high natural radon radiation (especially in the southern and south-eastern parts of the country).

Improved data analysis techniques for calculating more accurate radon and thoron exhalation rates from building interior solid walls.

The impacts of mathematical models and associated parameters on radon (222Rn) and thoron (220Rn) exhalation rates based on in-situ testing at building interior solid walls were demonstrated to improve data analysis techniques. The results showed that the heterogeneity of their activity concentrations within the measurement system was more significant for thoron than radon. The diurnal variation in indoor radon should be considered for better data quality. In conclusion, a model should be appropriately made and selected under the purposes and accuracy requirements of the exhalation test.

Radon exposure risks among residents proximal to gold mine tailings in Gauteng Province, South Africa: a cross-sectional preliminary study protocol.

Gold mine tailings, a legacy of the mining industry, harbors significant amount of radon gas, a classified human carcinogen. Radon exposure, especially near tailings, is a significant public health threat, potentially leading to increased risk of lung cancer, leukemia, and chronic obstructive pulmonary disease (COPD). These health problems are often associated with lower survival rates and significant financial burdens. This ongoing research aim to evaluating the relationship between indoor radon exposure and lung cancer, leukemia, and COPD risks among residents proximal to gold mine tailings in Gauteng Province, South Africa. This cross-sectional preliminary study focus on two distinct groups: Riverlea (exposed group, <2 km to Gold mine tailings) and Orlando East (unexposed group, >2 km to Gold mine tailings). Indoor radon levels is measured using AlphaE monitors, while health risks (lung cancer, leukemia, and COPD) linked to exposure are evaluated through interview-administered questionnaire and secondary data from Gauteng Health Department. Of the 476 residents randomly selected for this study, 300 have already participated, with balanced representation from both the exposed and unexposed groups. The study will compare indoor radon levels and health outcomes between the two groups. This study's results could aid in creating targeted interventions and policies to mitigate indoor radon exposure risks and safeguard vulnerable communities from this significant public health hazard.

Indoor radon risk mapping of the Canary Islands using a methodology for volcanic islands combining geological information and terrestrial gamma radiation data.

Within the framework of the recent approval of the National Plan Against Radon by the Council of Ministers of the Spanish Government, one of its five axes focuses on the delimitation of priority action areas. In line with this objective, this paper presents the indoor radon risk maps of the Canary Islands. Due to the volcanic origin of the Canary Islands, there is a great deal of geological heterogeneity in the soils on which buildings settle, making it very difficult to delimit radon-risk areas in the process of creating maps. Following a methodology developed in previous works for a study area formed of a set of representative municipalities, this paper presents radon risk maps of the Canary Islands based on lithostratigraphic information and high-resolution terrestrial gamma radiation maps. The goodness of fit of these maps is verified based on a statistical analysis of indoor radon concentration measurements carried out at representative building enclosures. In order to analyse the level of risk to the population, these maps were combined with built up areas (urban fabric) maps and estimations of the annual effective doses due to radon was obtained by applying a dosimetric model. This methodology improves the capability to delimit indoor radon risk areas, with a greater margin of safety. In this respect, it is estimated that areas classified as low risk have indoor radon concentrations 41 % below the current reference level of 300 Bq/m3 established by national regulations in compliance with the precepts laid down in the European EURATOM Directive.

Time-efficient etching of LR-115 SSNTD film for indoor radon, thoron quantification.

LR-115 Solid State Nuclear Track Detector (SSNTD) is commonly utilized for quantifying indoor radon-thoron levels, by tallying the tracks formed in the films by exposure to these gases. Conventionally, sodium hydroxide (NaOH) is used to etch LR-115 films for 90 min at 60°C. However, this study suggests a time-efficient alternative approach utilizing potassium hydroxide (KOH) as the etchant. In an initial investigation, the bulk etch rates of KOH were examined at different normalities and temperatures, revealing that KOH exhibited nearly double the bulk etch rates compared to NaOH. Subsequently, a specially designed controlled experiment was conducted to assess the efficacy of the technique by enumerating the tracks generated in the films. Both etchants demonstrated very similar track counts for identical controlled exposures, indicating the reliability of the method. A consistent behavior was observed in the real-case scenario of LR-115 films exposed indoors to alpha particles from radon and its decay products. In both experiments, the etching with KOH for 45 min gave track densities comparable to standard NaOH etching for 90 min, highlighting the time efficiency of this method. Investigations were carried out into track shape and size features, aspects crucial to the measurement technique, using microscopic imaging of samples treated with both etchants. Strikingly similar track shapes and sizes were observed, affirming the consistency in the track measurement technique. Collectively, these findings suggest that KOH etchant reduces the etching time, presenting itself as a time-efficient method for quantifying radon and thoron track density.

Metrology for Indoor Radon Measurements and Requirements for Different Types of Devices.

Indoor radon measurements have been conducted in many countries worldwide for several decades. However, to date, there is a lack of a globally harmonized measurement standard. Furthermore, measurement protocols in the US (short-term tests for 2-7 days) and European Union countries (long-term tests for at least 2 months) differ significantly, and their metrological support is underdeveloped, as clear mathematical algorithms (criteria) and QA/QC procedures considering fundamental ISO/IEC concepts such as "measurement uncertainty" and "conformity assessment" are still absent. In this context, for many years, the authors have been advancing and refining the theory of metrological support for standardizing indoor radon measurements based on a rational criterion for conformity assessment within the ISO/IEC concepts. The rational criterion takes into account the main uncertainties arising from temporal variations in indoor radon and instrumental errors, enabling the utilization of both short- and long-term measurements while ensuring specified reliability in decision making (typically no less than 95%). The paper presents improved mathematical algorithms for determining both temporal and instrumental uncertainties. Additionally, within the framework of the rational criterion, unified metrological requirements are formulated for various methods and devices employed in indoor radon measurements.

Successful reduction of indoor radon activity concentration via cross-ventilation: experimental data and CFD simulations.

Advanced computational fluid dynamics (CFD) simulations are essential for predicting airflow in ventilated spaces and assessing indoor air quality. In this study, a focus was set on techniques for the reduction of indoor radon-222 activity concentration [Rn], and it is demonstrated how true-to-scale 3D CFD models can predict the evolution of complex ventilation experiments. A series of ventilation experiments in an unoccupied flat on the ground floor of a residential block in Bad Schlema (Saxony, Germany) were performed. Specifically, the 'Cross-ventilation 100 %' experiment resulted in room-specific [Rn] reductions from ∼3000 to ∼300 Bq m-3. We quantitatively interpreted the results of the ventilation experiment using a CFD model with a k-ϵ turbulent stationary flow model characterised by the used decentralised ventilation system. The model was coupled with a transient transport model simulating indoor [Rn]. In a first approach, the model overestimated the decrease in the starting of the experiment and the steady state. Adjusting the model parameters inflowing radon and inlet velocity the model results are in a good agreement with the experimental values. In conclusion, this paper demonstrates the potential of CFD modelling as a suitable tool in evaluating and optimising ventilation systems for an effective reduction of elevated [Rn].

Evaluation of Indoor Radon Activity Concentrations and Controls in Dwellings Surrounding the Gold Mine Tailings in Gauteng Province of South Africa.

Radon in dwellings is recognized as the primary source of natural radiation exposure to members of the public. In the West Rand District and Soweto in the Gauteng Province (South Africa), indoor radon (222Rn) mapping was carried out to assess the exposure levels of radon in dwellings around gold and uranium mining tailings dams. This study was conducted predominately during warm and cold seasons, using the solid-state nuclear track detectors. In summer months, the indoor radon levels measured in all areas ranged from below the lower limit of detection to 71 Bq/m3, with a mean value of 29 Bq/m3, whereas in winter, the levels ranged between 11 and 124 Bq/m3, with a mean value of 46 Bq/m3. Higher indoor radon levels are found in colder months (winter season) than warmer months (summer season). However, no dwellings with indoor radon levels that exceed the WHO (2009) recommended reference level of 100 Bq/m3 were found, except for one that was constructed directly on soil mixed with tailings material. It is recommended that residents should keep their indoor radon levels low through continuous ventilation so as to minimize the buildup of radon and the likelihood of increased health hazards associated with radon exposure.

Exploring statistical and machine learning techniques to identify factors influencing indoor radon concentration.

Radon is a radioactive gas with a carcinogenic effect. The malign effect on human health is, however, mostly influenced by the level of exposure. Dangerous exposure occurs predominantly indoors where the level of indoor radon concentration (IRC) is, in its turn, influenced by several factors. The current study aims to investigate the combined effects of geology, pedology, and house characteristics on the IRC based on 3132 passive radon measurements conducted in Romania. Several techniques for evaluating the impact of predictors on the dependent variable were used, from univariate statistics to artificial neural network and random forest regressor (RFR). The RFR model outperformed the other investigated models in terms of R2 (0.14) and RMSE (0.83) for the radon concentration, as a dependent continuous variable. Using IRC discretized into two classes, based on the median (115 Bq/m3), an AUC-ROC value of 0.61 was obtained for logistic regression and 0.62 for the random forest classifier. The presence of cellar beneath the investigated room, the construction period, the height above the sea level or the floor type are the main predictors determined by the models used.

Indoor radon concentrations in kindergartens in three Bulgarian districts.

This article examines the results of a study of radon concentrations in kindergartens in three districts of north-western Bulgaria. For the period from December 2019 to May 2020, passive radon measurements were accomplished in 1490 premises of 130 kindergartens. The highest arithmetic mean (AM) value of 219 Bq m-3 and geometric mean (GM) value of 156 Bq m-3 radon concentration were found in the state kindergartens of the Vratsa district. The radon values for the remaining two districts are as follows: Lovech-AM = 156 Bq m-3 and GM = 114 Bq m-3; Montana-AM = 125 Bq m-3 and GM = 88 Bq m-3. The effects of various factors on the radon concentration including district, year of building construction, presence of basement, place of premise, wall, and floor interior covering materials, and presence of a ventilation system were investigated. Factor Analysis was used to assess the combined effects of those factors on indoor radon concentration. The results revealed three combinations of the investigated factors: the first combined the district in which the kindergartens were located and the materials used for the floor of the premises, the second combined the year of construction of the building and the presence of a building foundation, and the third combined the rest of the investigated factors. It is concluded that a regional assessment of predictors of radon variability is needed. The walls in kindergartens should not be covered by gypsum, and floors should not be made from materials that can easily develop cracks such as terra cotta. The installation of a ventilation system reduces the radon concentrations in the premises, which is of particular importance in cases where the measured value is above the national reference levels.

The Analysis of 222Rn and 220Rn Natural Radioactivity for Local Hazard Estimation: The Case Study of Cerveteri (Central Italy).

Radon (222Rn) is the second most common cause of lung cancer after smoking. As radon poses a significant risk to human health, radon-affected areas should be identified to ensure people's awareness of risk and remediation. The primary goal of this research was to investigate the local natural radioactivity (in soils, groundwater, and indoors) because of the presence of tuff outcrops (from middle-lower Pleistocene volcanic activity) that naturally produce radioactive gas radon at Cerveteri (Rome, Central Italy). The results of the radon survey highlighted moderate (>16,000 Bq/m3) but localized anomalies in soils in correspondence with a funerary site pertaining to the Etruscan Necropolis of Cerveteri, which extends over a volcanic rock plateau. Indoor radon measurements were performed at several tuff-made dwellings, and the results showed medium-low (<200 Bq/m3) values of indoor radon except for some cases exceeding the reference level (>300 Bq/m3) recommended by the 2013/59 Euratom Directive. Although no clinical data exist regarding the health effects of thoron (220Rn) on humans, the study of 220Rn average activity concentration in the soil gas survey reveals new insights for the interpretation of radon sources that can affect dwellings, even taking into account the considerable difference in the half-lives of 222Rn and 220Rn.

Extreme reverse seasonal variations of indoor radon concentration and possible implications on some measurement protocols and remedial strategies.

Indoor radon levels in dwellings are typically higher in cold months than in warm ones. The indoor radon concentration might experience an inverse seasonal behaviour - i.e., radon levels much higher in summer than in winter - under specific circumstances. In the framework of a study on long-term variations of annual radon concentration carried out in some tens of dwellings in Rome and surrounding small towns, two dwellings with very high - up to extreme - reverse seasonal variations were accidently discovered. These dwellings were located in a volcanic area, and they are both south-oriented and located on the lower part of a hill. In one of them, radon concentration was monitored by a continuous radon monitor for two years to find out when the greatest rises in radon levels occur. The indoor radon concentration resulted to experience extremely rapid, i.e. very few hours, increases up to 20 000 Bq m-3 during the spring period (i.e., April, May, and June especially). After about ten years from the first observation, the indoor radon concentration of the same house was monitored again for about five years: radon concentration peaks previously observed were found to be unchanged in terms of absolute values, duration, rising time and occurrence period. These reverse seasonal variations may lead to significant underestimation of the actual annual average radon concentration in case of measurements lasting less than one year if performed during the cold season and especially when seasonal correction factors are used. Moreover, these results suggest adopting specific measurement protocol and remediation strategies in houses having some peculiar characteristics, mainly regarding orientation, position, and attachment to the ground.

Evaluation of indoor 222Rn and 220Rn concentrations in Dakshina Kannada, Karnataka, India.

Naturally occurring radioactive gases which tend to build up (radon and thoron) in indoor environs can cause deleterious health effects including the development of lung cancer. The present study aims to measure 222Rn and 220Rn levels in dwellings in different seasons in the environs of Dakshina Kannada region of India. The 222Rn and 220Rn concentrations were measured in the monsoon, autumn, winter, and summer seasons using Solid State Nuclear Track Detector (SSNTD, LR-115 type II) films fixed in single-entry pinhole cylindrical twin-cup dosimeters. The higher 222Rn levels in indoors were observed during winter with an average concentration of 38.8 Bq m-3 and lower during summer with an average of 14.1 Bq m-3. The average indoor thoron concentration was also highest in winter with an average value of 25.5 Bq m-3 and lowest in summer with 8.8 Bq m-3. The annual inhalation dose ranged from 0.44 to 1.06 mSv year-1 with a mean value of 0.66 mSv year-1. The annual effective dose varied from 1.03 to 2.57 mSv year-1 with an average value of 1.59 mSv year-1. The assessed values have been contrasted with the limit suggested by the UNSCEAR and the ICRP and were found to be within the permissible level. The normality of frequency distribution curves of 222Rn and 220Rn concentrations was assessed by the Kolmogorov-Smirnov test.

Assessment of indoor radon exposure in South Korea.

The objective of this study is to update the national and regional indoor radon concentrations in South Korea and assess indoor radon exposure. Based on the previously published survey results and the collected measurement data of surveys conducted since 2011, a total of 9271 indoor radon measurement data covering 17 administrative divisions are finally used for analysis. The annual effective dose from the indoor radon exposure is calculated using dose coefficients recommended by the International Commission on Radiological Protection. The population-weighted average indoor radon concentration was estimated to be a geometric mean of 46 Bq m-3(GSD = 1.2) with 3.9% of all samples showing values exceeding 300 Bq m-3. The regional average indoor radon concentration ranged from 34 to 73 Bq m-3. The radon concentrations in detached houses were relatively higher than those in public buildings and multi-family houses. The annual effective doses to the Korean population due to indoor radon exposure were estimated to be 2.18 mSv. The updated values in this study might better represent the national indoor radon exposure level in South Korea because they contain more samples and cover a wider range of geographical areas than previous studies.

Spatial modeling of geogenic indoor radon distribution in Chungcheongnam-do, South Korea using enhanced machine learning algorithms.

Prolonged inhalation of indoor radon and its progenies lead to severe health problems for housing occupants; therefore, housing developments in radon-prone areas are of great concern to local municipalities. Areas with high potential for radon exposure must be identified to implement cost-effective radon mitigation plans successfully or to prevent the construction of unsafe buildings. In this study, an indoor radon potential map of Chungcheongnam-do, South Korea, was generated using a group method of data handling (GMDH) algorithm based on local soil properties, geogenic, geochemical, as well as topographic factors. To optimally tune the hyper-parameters of GMDH and enhance the prediction accuracy of modelling radon distribution, the GMDH model was integrated with two metaheuristic optimization algorithms, namely the bat (BA) and cuckoo optimization (COA) algorithms. The goodness-of-fit and predictive performance of the models was quantified using the area under the receiver operating characteristic (ROC) curve (AUC), mean squared error (MSE), root mean square error (RMSE), and standard deviation (StD). The results indicated that the GMDH-COA model outperformed the other models in the training (AUC = 0.852, MSE = 0.058, RMSE = 0.242, StD = 0.242) and testing (AUC = 0.844, MSE = 0.060, RMSE = 0.246, StD = 0.0242) phases. Additionally, using metaheuristic optimization algorithms improved the predictive ability of the GMDH. The GMDH-COA model showed that approximately 7 % of the total area of Chungcheongnam-do consists of very high radon-prone areas. The information gain ratio method was used to assess the predictive ability of considered factors. As expected, soil properties and local geology significantly affected the spatial distribution of radon potential levels. The radon potential map produced in this study represents the first stage of identifying areas where large proportions of residential buildings are expected to experience significant radon levels due to high concentrations of natural radioisotopes in rocks and derived soils beneath building foundations. The generated map assists local authorities to develop urban plans more wisely towards region with less radon concentrations.

Indoor Radon Levels in Homes and Schools in the Western Cape, South Africa-Results from a Schools Science Outreach Initiative and Corresponding Model Predictions.

We describe a school science outreach initiative that introduced learners to applied nuclear physics research by means of a two-day workshop that involved learners and teachers from 5 schools in the Western Cape province of South Africa. During this workshop, the participants were introduced to the naturally occurring, inert, colorless, and tasteless radioactive gas radon (222Rn). During the first day of the workshop, the participants were informed about the detrimental health impacts of inhaling radon and its daughter radionuclides and were shown how indoor radon activity concentrations can be measured using the electret ion chamber (EIC) technology. The learners were then each supplied with a short-term electret (E-PERM, Radelec, Frederick, MD, USA) and associated ion chamber to enable them to make radon measurements in their homes. The teachers in turn were supplied with EICs to enable them make radon measurements in their schools. The participants returned the EICs on the second day of the workshop, one week later. Here, the drop in the potential difference across each electret was measured in order to calculate the average indoor radon activity concentration. A total of 49 indoor radon concentrations were measured. The average indoor radon concentrations were 36 ± 26 Bqm-3 in homes and 41 ± 36 Bqm-3 in schools, while the highest concentration was found to be 144 Bqm-3. These levels were compared to predictions from a model that uses input information about the uranium content associated with the surface geology at each measurement location. The predictions compared well with the measured values.

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 573 Bq/m3 for 10 selected workrooms, while hourly averaged radon measurements showed extreme variations from 6 to 1603 Bq/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 327 Bq/m3 for parquet, 227 Bq/m3 for ceramic tiles, 146 Bq/m3 for vinyl flooring and 71 Bq/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.

Patterns of indoor radon concentrations, radon-hazard potential, and radon testing on a small geographic scale in Utah.

INTRODUCTION: Currently, there are no publicly-available estimates of indoor radon concentration at scales smaller than the county. Radon-hazard potential soil maps that reflect underlying geologic factors can be created at small geographic scale and linked to residential and census data. We determined the association between residential radon tests and high radon-hazard potential soil at the residential and block group levels using a large Utah-based dataset. We also identified characteristics of block groups with limited tests in the dataset. METHODS: We geocoded a dataset of residential radon tests obtained from 2001 to 2017 by a statewide educational program. We linked each location to maps of radon-hazard potential soil, the Environmental Protection Agency's (EPA) county radon zones. We also calculated the number of tests conducted in each block group and linked block groups to demographic data from the 2020 United States census. Log-linear and logistic models identified the association between residential home test results and 1) radon-hazard potential soil of each residence, 2) percent of residences on high radon-hazard potential soils in block groups, and 3) EPA's radon zones. We compared demographic characteristics among block groups with ≥5 or <5 residential tests in our dataset. RESULTS: Approximately 42% of homes in the dataset tested ≥4 pCi/L. We found significant positive associations for residential radon test results with 1) residential location on high radon-hazard potential soil and 2) block groups with >0% of residences on high radon-hazard potential soil. EPA radon zones were not associated with residential test results. Block groups with <5 tests had higher than the statewide median percentage of Hispanic residents (OR = 2.46, 95% CI = 1.89-3.21) and were located in rural counties. DISCUSSION: Radon-hazard potential soil has a significant association with residential home radon tests. More efforts are needed to improve radon testing in block groups that are rural and have greater percentages of racial minorities.

A case study on seasonal and annual average indoor radon, thoron, and their progeny level in Kohima district, Nagaland, India.

Indoor radon and thoron survey has been carried out in 50 dwellings under Kohima district, Nagaland, India, using the latest measurement technology. The survey has been carried out for a one-year period in 3 different seasons, and the dwellings were selected according to the building materials used for construction. Indoor radon and thoron concentrations, as well as their progeny, followed a predictable pattern with greater levels in the winter and lower levels in the summer. Concrete housing had greater radon and thoron concentrations than bamboo and semi-wood/bamboo homes. The equilibrium factor (E.F.) and inhalation dose due to radon, thoron, and their corresponding progeny were also studied in the present study.