Volumen 65 (2020): Edición 2 (June 2020)

A national radon survey was performed recently in all buildings of pre-university education in Montenegro. During the school year 2016/2017, radon (²²²Rn) was measured with passive detectors (Radosys, RSFV type) in 2855 ground-floor rooms of 468 buildings. The average 9-month radon activity concentrations above the level of 300 Bq/m³ were found in 728 rooms, which belong to 213 buildings, while in 111 rooms, belonging to 47 buildings, they were above 1000 Bq/m³. Radon concentrations in the educational buildings, averaged over all sampled ground-floor rooms in a building, range from 16 Bq/m³ to 2810 Bq/m³, with arithmetic mean (AM) = 275 Bq/m³. They follow a log-normal distribution with geometric mean (GM) = 174 Bq/m³ and geometric standard deviation (GSD) = 2.58. There are 135 buildings with average indoor radon concentrations on the ground floor above 300 Bq/m³ and 18 buildings where they are above 1000 Bq/m³. The influence of the nine factors (climate, urban/rural area, age of building, number of stories, building materials, basement, foundation slab, window frames, and heating) on radon concentrations in the buildings was analysed by univariate (UVA) and multivariate (MVA) methods. The univariate analysis revealed the significant relationship of the four factors: age of buildings, basement, building materials, and window frames with radon concentrations on the ground floor in the buildings, while multivariate analysis added to those factors urban/rural area and number of stories, but excluded building materials as a factor influencing significantly radon concentrations.

Four years of observations of radon, meteorology and atmospheric pollution was used to demonstrate the efficacy of combined diurnal and synoptic timescale radon-based stability classification schemes in relating atmospheric mixing state to urban air quality in Zgierz, Central Poland. Nocturnal radon measurements were used to identify and remove periods of non-stationary synoptic behaviour (13–18% of each season) and classify the remaining data into five mixing states, including persistent temperature inversion (PTI) conditions, and non-PTI conditions with nocturnal conditions ranging from well mixed to stable. Mixing state classifications were performed completely independently of site meteorological measurements. World Health Organization guideline values for daily PM_2.5/PM₁₀ were exceeded only under strong PTI conditions (3–15% of non-summer months) or often under non-PTI stable nocturnal conditions (14–20% of all months), when minimum nocturnal mean wind speeds were also recorded. In non-summer months, diurnal amplitudes of NO (CO) increased by the factors of 2–12 (3–7) from well-mixed nocturnal conditions to PTI conditions, with peak concentrations occurring in the morning/evening commuting periods. Analysis of observations within radon-derived atmospheric mixing ‘class types’ was carried out to substantially clarify relationships between meteorological and air quality parameters (e.g. wind speed vs. PM_2.5 concentration, and atmospheric mixing depth vs. PM₁₀ concentration).

Underground water is one of the main sources of radon for households. This article focuses on the estimation and removal of radon from underground water using the technology and inorganic sorbents developed by EKSORB Ltd., Russia for liquid radioactive waste treatment in the nuclear power industry. The article presents the results of tests of a system for the removal of radon and radon daughters from water patented by EKSORB. This is achieved by filtering water through RATZIR sorbent, followed by periodic load regeneration. Over a period of three years, the plant is successful in removing radon from the water that had an initial radon content of approximately 1500 Bq/L to less than 60 Bq/L, without releasing radon to indoor/outdoor air.

In the frame of Radon rEal time monitoring System and Proactive Indoor Remediation (RESPIRE), a LIFE 2016 project funded by the European Commission, the contribution of building materials of volcanic origin to indoor radon concentration was investigated. First, total gamma radiation and related outdoor dose rates of geological materials in the Caprarola area (Central Italy) were measured to define main sources of radiation. Second, ²²²Rn and ²²⁰Rn exhalation rates of these rocks used as building materials were measured using an accumulation chamber connected in a closed loop with a RAD7 radon monitor. Among others, the very porous “Tufo di Gallese” ignimbrite provided the highest values. This material was then used to construct a scale model room of 62 cm × 50 cm × 35 cm (inner length × width × height, respectively) to assess experimental radon and thoron activity concentration at equilibrium and study the effects of climatic conditions and different coatings on radon levels. A first test was carried out at ambient temperature to determine experimental 222Rn and ²²⁰Rn equilibrium activities in the model room, not covered with plaster or other coating materials. Experimental ²²²Rn equilibrium was recorded in just two days demonstrating that the room “breaths”, exchanging air with the outdoor environment. This determines a dilution of indoor radon concentration. Other experiments showed that inner covers (such as plasterboard and different kinds of paints) partially influence ²²²Rn but entirely cut the short-lived ²²⁰Rn. Finally, decreases in ambient temperature reduce radon exhalation from building material and, in turn, indoor activity concentration.

The article describes three interlaboratory experiments concerning ²²²Rn determination in water samples. The first two experiments were carried out with the use of artificial radon waters prepared by the Laboratory of Radiometric Expertise (LER), Institute of Nuclear Physics, Polish Academy of Sciences in Kraków in 2014 and 2018. The third experiment was performed using natural environment waters collected in the vicinity of the former uranium mine in Kowary in 2016. Most of the institutions performing radon in water measurements in Poland were gathered in the Polish Radon Centre Network, and they participated in the experiments. The goal of these exercises was to evaluate different measurement techniques used routinely in Polish laboratories and the laboratories’ proficiency of radon in water measurements. In the experiment performed in 2018, the reference values of ²²²Rn concentration in water were calculated based on the method developed at LER. The participants’ results appeared to be worse for low radon concentration than for high radon concentrations. The conclusions drawn on that base indicated the weaknesses of the used methods and probably the sampling. The interlaboratory experiments, in term, can help to improve the participants’ skills and reliability of their results.

Objectives: Recent results of epidemiological and medical statistics studies of lung cancer and indoor radon in different regions of the world make a relevant new combined analysis of residential exposure health effects. In particular, new data were obtained by means of a meta-analysis of case-control studies as well as taking into account a confounding effect of human papillomavirus infection in studies of geographically aggregated data.

Materials and methods: Two sources of epidemiological data are considered: (1) studies of ecological design and (2) case-control studies. Ecological studies included the analysis performed for the USA counties and Russian oblasts with adjusting for the main confounders. Data on the case-control studies were gained from the meta-analysis of 31 individual studies with a weighting of obtained odds ratios according to the quality of radon exposure reconstruction and size of the reference group. Estimations of lung cancer excess relative risk (ERR) associated with indoor radon exposure are combined.

Results: Two types of epidemiological study design provided generally consistent EER estimations. The combined value of ERR due to radon exposure is 0.14 (90% CI: 0.10–0.18) per 100 Bq/m³.

Conclusion: Available geographically aggregated data in regions of Russia and the United States and the meta-analysis of case-control studies conducted in a large number of countries confirm the association of lung cancer with indoor radon exposure.

The exposure from radon, thoron, and thoron progeny was measured for 45 dwellings in high background radiation area in Takandeang, Indonesia with ambient dose equivalent rate ranging from 0.34 μSv h⁻¹ to 1.90 μSv h⁻¹. The measurement was taken using passive radon and thoron discriminative detector and thoron progeny detector. This measurement was taken from November 2018 to October 2019, and within one month the detector would be replaced with a new detector. The concentrations of radon, thoron, and thoron progeny were calculated as 42–490 Bq m⁻³, 20–618 Bq m⁻³, and 4–40 Bq m⁻³, respectively. The concentrations for outdoor were 49–435 Bq m⁻³, 23–457 Bq m⁻³, and 4–37 Bq m⁻³, respectively, and the annual effective dose was 9.8–28.6 mSv y⁻¹. Based on the result of Spearman’s correlations analysis between the indoor radon and thoron concentrations and between the indoor thoron progeny and thoron concentrations, we suggest that exposure to thoron cannot be predicted from exposure to radon, and the equilibrium equivalent thoron concentration has a large uncertainty when it is estimated from thoron concentration assuming a single thoron equilibrium factor.

The deposition-based direct indoor ²²²Rn and ²²⁰Rn progeny measurement techniques are mostly affected by the indoor environmental conditions, such as the ventilation, concentration of condensation nuclei, and reactions with the structure and its furnishings. In this study, a theoretical model of a direct ²²²Rn and ²²⁰Rn progeny monitor based on allyl diglycol carbonate (ADC or CR-39) was established to analyse the factors that influence the detection process by using the parameter sensitivity analysis. The aerosol parameters contributed the highest to the variance, followed by the aerodynamic parameters. With respect to the result of the Spearman’s correlation analysis, the aerosol-related and the room-related parameters are positive, whereas the aerodynamic parameters – which affect the turbulence of indoor deposition – are negative. It means that both the attachment process and the deposition process of ²²²Rn and ²²⁰Rn progenies are important to the performance of the progeny monitor.

The population is continuously exposed to a background level of ionizing radiation due to the natural radioactivity and, in particular, with radon (²²²Rn). Radon gas has been classified as the second leading cause of lung cancer after tobacco smoke [1]. In the confined environment, radon concentration can reach harmful level and vary accordingly to many factors. Since the primary source of radon in dwellings is the subsurface, the risk assessment and reduction cannot disregard the identification of the local geology and the environmental predisposing factors. In this article, we propose a new methodology, based on the computation of the Gini coefficients at different spatial scales, to estimate the spatial correlation and the geographical variability of radon concentrations. This variability can be interpreted as a signature of the different subsurface geological conditions. The Gini coefficient computation is a statistical tool widely used to determine the degree of inhomogeneity of different kinds of distributions. We generated several simulated radon distributions, and the proposed tool has been validated by comparing the variograms based on the semi-variance computation with those ones based on the Gini coefficient. The Gini coefficient variogram is shown to be a good estimator of the inhomogeneity degree of radon concentration. Indeed, it allows to better constrain the critical distance below which the radon geological source can be considered as uniform at least for the investigated length scales of variability; it also better discriminates the fluctuations due to the environmental predisposing factors from those ones due to the random spatially uncorrelated noise.

The second most important source of indoor radon, after soil beneath dwelling, is building material. With the increase in environmental awareness and new energy-saving policies, residents tend to replace the existing windows with tighter windows, which leads to a decrease in air exchange rate and consequently an increase in indoor radon concentration. In case of low exchange rates, dose caused by inhalation of radon and its progeny can exceed external dose originating from the radium content in the surrounding building material. In this paper, surface exhalation rates of radon (²²²Rn) and thoron (²²⁰Rn) from typical building materials used for construction and interior decoration of houses in Serbia were investigated. Surface exhalation rate measurements were performed using the closed-chamber method, while concentrations of radon and thoron in the chamber were continuously measured using an active device, RTM1688-2, produced by SARAD® GmbH. Finally, the impact of the replacement of windows on the indoor radon concentration was estimated.

Continuous monitoring of natural gamma radiation in air has been carried out, during December 2014 – January 2018, with 1-min cyclic measurement in Prague, Czech Republic using a NaI(Tl) probe. The ²¹⁴Bi/²¹⁴Pb ratio as a tracer in rainwater has been investigated to study its variations related to both the ambient dose equivalent rate per hour and the amount of rainfall. A hybrid methodology for time series analysis, composed of the aggregation of two signal decomposition methods (multiple linear regression and empirical mode decomposition) and one forecasting method (support vector regression), has been applied to identify the anomalies in the studied signals in order to better find correlations among them. The results show a strong correlation between the ambient dose equivalent rate and the ²¹⁴Bi/²¹⁴Pb ratio values and between both these signals and rainfall amount ≥5 mm/h. Furthermore, the considered descendants of radon are mainly responsible for the overall ambient dose equivalent rate.

It is well known that one of the factors that influence the indoor radon variability is the floor level of the buildings. Considering the fact that the main source of indoor radon is radon in soil gas, it is expected that the radon concentration decreases at higher floors. Thus at higher floors the dominant source of radon is originating from building materials, and in some cases there may be deviations from the generally established regularity. In such sense, we chose one freestanding single-family house with loft and other 16-floor high-rise residential building for this study. The indoor radon measurements were performed by two methods: passive and active. We used passive devices based on track-etched detectors: Radtrak² Radonova. For the short-term indoor radon measurements, we used two active devices: SN1029 and SN1030 (manufactured by Sun Nuclear Corporation). The first device was fixed in the living room at the ground level and the second was moved through the floors of the residential building. Every measuring cycle at the specified floor lasted seven days with the sampling time of 2 h. The results show two different indoor radon behaviours regarding radon variability due to floor level. In the single-family house with loft we registered intense difference between radon concentration in the ground level and loft, while in the high-rise residential building the radon level was almost the same at all floors, and hence we may conclude that radon originated mainly from building materials.

At the beginning of the year 2016, the representatives of the Polish Radon Centre decided to organize proficiency tests (PTs) for measurements of radon gas and radon decay products in the air, involving radon monitors and laboratory passive techniques. The Silesian Centre for Environmental Radioactivity of the Central Mining Institute (GIG), Katowice, became responsible for the organization of the PT exercises. The main reason to choose that location was the radon chamber in GIG with a volume of 17 m³, the biggest one in Poland. Accordingly, 13 participants from Poland plus one participant from Germany expressed their interest. The participants were invited to inform the organizers about what types of monitors and methods they would like to check during the tests. On this basis, the GIG team prepared the proposal for the schedule of exercises, such as the required level(s) of radon concentrations, the number and periods of tests, proposed potential alpha energy concentration (PAEC) levels and also the overall period of PT. The PT activity was performed between 6th and 17th June 2016. After assessment of the results, the agreement between radon monitors and other measurement methods was confirmed. In the case of PAEC monitors and methods of measurements, the results of PT exercises were consistent and confirmed the accuracy of the calibration procedures used by the participants. The results of the PAEC PTs will be published elsewhere; in this paper, only the results of radon intercomparison are described.

According to the new European Union Basic Safety Standards (EU-BSS), preparation of the National Radon Action Plan is obligatory for the Member States. One of the plan’s aims is to carry out an indoor radon survey to identify radon-prone areas. In the radon surveys, track detector methods are used. At the University of Pannonia (Veszprém, Hungary), a new scanner-based detector evaluation system has been developed. For the application of the new system, the selection of appropriate parameters is necessary. In this study, selection of the applied track detectors and setting of the etching conditions have been carried out. Two different types of allyl diglycol carbonate (ADC or CR-39) track detectors were investigated, taking into account the detector’s background and response during the exposure (determination of calibration factor). The Baryotrak’s background track density (0–1.5 tracks mm⁻²) was lower than that of the 0.8–4 tracks mm⁻². The response of the Tastrak was higher, but the deviation of the calibration factor was much higher (1.2–5.3 × 10⁻³ tracks mm⁻²/(Bq day m⁻³)) than in the case of the Baryotrak (1.4–2.8 × 10⁻³ tracks mm⁻²/(Bq day m⁻³)). After the systematic review of the etching system, a new method was developed. For the determination of the optimal track diameter, the argon fluoride (ArF) laser was applied to create tracks with diameters in the range of 10–100 μm. The optimum track size was in the range of 40–60 μm. On this basis, new etching conditions were determined: 6.25 M NaOH solution, a temperature of 90°C, and time period of 8 hours.

The new radiation protection law in Germany, which came into effect 2018, puts greater emphasis on the protection against naturally occurring radiation, especially radon as a known health hazard. The law requires the delineation of radon priority areas, where prevention and remediation of high indoor radon concentrations should be taken with priority. In Germany, radiation protection is the administrative responsibility of the federal states. The state of Hesse has early on decided to fully survey the state for radon priority areas. To identify radon priority areas, the geogenic radon potential has to be determined. To achieve that radon, soil-gas measurements combined with soil permeability are a necessity. The University of Applied Sciences (THM) in Giessen is responsible for the radon soil-gas measurement campaign in Hessen. To achieve a statistically sound survey of the state of Hessen with an achievable amount of different measurement locations, and in the given time-frame, a geology-based concept has been designed. Taking into account the known geological information about geological structures in combination with the administrative counties, a survey strategy has been established. Prior known information regarding soil thickness, moisture, digability, and other technical limitations are used to determine the exact measuring locations. At every location, the radon activity in soil gas is measured. The soil permeability is determined for every measurement as well. Three measurements are performed at each location. Having completed the first set of measurements, the design criteria of the campaign and the practical experiences will be presented.

More than half of the total natural ionizing radiation dose received by the human population is caused by radon and thoron (Rn and Tn) and their progeny. To estimate the level of radiation due to radon and thoron and their progeny, an investigation was conducted in a residential area near the world’s largest open-pit mine of Bayan Obo in Inner Mongolia, China. The concentration of Rn, Tn, and their decay products in air and soil were studied by using AlphaGUARD, RAD7, and ERS-RDM-2S for a discrete period of time in three different locations. The average indoor concentration of radon and thoron was 62.6 ± 44.6 Bq/m³ and 108.3 ± 94.5 Bq/m3 respectively, and the outdoor concentration was 12.9 ± 6.3 Bq/m³ and 55.8 ± 18.5 Bq/m³, respectively. Relatively high concentrations were recorded in the area near to the mine, with a significant increasing trend observed in indoor thoron concentration. A prominent hotspot in thoron concentration was found in a single-story house with values 747 ± 150 Bq/m³. The equilibrium equivalent thoron concentration (EEC_Tn) varies from 0.48 Bq/m³ to 2.36 Bq/m³ with an arithmetic mean of 1.37 ± 0.64 Bq/m³, and comparatively higher than EEC_Rn. Concluding that the mining activity at Bayan Obo mine is significantly increasing the level of indoor thoron and its progeny in surroundings. It is suggested to further systematically investigate the indoor Rn and Tn progeny concentrations in the residential dwellings of the Bayan Obo mining area, and ²³²Th content of the building materials, to provide a basis for calculating the radiation dose.

The presence of uranium makes the Kowary area characterized by an increased concentration of radon in the air and the living houses. Measurements of periodic radon concentrations in dwellings of Kowary were carried out three times in the last 20 years. It can be observed that 20 years ago level of radon concentrations in houses of Kowary were lower than today. Measurements carried out in Kowary over 20 years have shown that residents are exposed to radon concentrations, which often exceed 300 Bq m⁻³ – a reference level recommended by the European Union. The present geometric mean of radon concentration in houses of Kowary (260 Bq m⁻³) exceeds the geometric mean of radon concentration of buildings in the rest of Poland (142 Bq m⁻³).

The continuous monitoring of ²²²Rn activity concentration, CO₂ concentration, and microclimatologic parameters (internal air temperature and relative humidity) in the Važecká Cave (Northern Slovakia) is being carried out at three monitoring stations, namely, Gallery, Lake Hall, and Entrance Hall. Radon activity concentration and CO₂ concentration exhibited a clear annual variation. The daily average of radon concentration ranged 1300–27 700 Bq/m³ at the Lake Hall station and 3600–42 200 Bq/m³ at the Gallery station. Radon reached its maximum in the summer months, from June to September. The annual maximum of CO₂ concentration is registered approximately one month later than radon maximum. The annual variation of radon and CO₂ is controlled by the seasonal change of ventilation regime associated with the seasonal variation of the difference between the temperature measured inside the cave and the atmospheric temperature.