Seasonal Indoor Radon Assessment and Estimation of Cancer Risk: A Case Study of Obafemi Awolowo University Nigeria.

Human exposure to indoor radon has been a subject of continuous concern due to its health implications, especially as it relates to lung cancer. Radon contaminates indoor air quality and poses a significant health threat if not abated/controlled. A seasonal indoor radon assessment of residential buildings of Obafemi Awolowo University was carried out to determine radon seasonal variability and to evaluate the cancer risk to the residents. AT-100 diffusion-based track detectors were deployed within living rooms and bedrooms for the radon measurement. During the rainy season, the average indoor radon concentration was 18.4 ± 10.1 Bq/m3, with higher concentrations observed in bedrooms compared to living rooms, whereas the average radon concentration was 19.0 ± 4.4 Bq/m3 in the dry season, with similar radon levels in living rooms and bedrooms. The potential alpha energy concentration values ranged from 1.62 to 7.57 mWL. The annual effective dose equivalent values were below the world average and recommended limits for public exposure. Of the three geological units underlying the residences, the buildings overlying the granite gneiss lithology have the highest radon concentrations with average value of 21.4 Bq/m3. The soil gas radon concentration to indoor radon concentration ratio over the granite gneiss lithology is 0.006. The estimated average lifetime cancer risk due to radon inhalation in the residences indicated a potential risk of cancer development in 178 persons in 100 000 population over a lifetime period. The average indoor radon concentrations were below the recommended limit, requiring no immediate remediation measures. Improved ventilation of residential apartments is recommended to minimize residents' risk to indoor radon.

Strategy and Metrological Support for Indoor Radon Measurements Using Popular Low-Cost Active Monitors with High and Low Sensitivity.

Traditionally, for indoor radon testing, predominantly passive measurements have been used, typically applying the solid-state alpha track-etch method for long-term and the charcoal method for short-term measurements. However, increasingly, affordable consumer-grade active monitors have become available in the last few years, which can generate a concentration time series of an almost arbitrary duration. Firstly, we argue that consumer-grade monitors can well be used for quality-assured indoor radon assessment and consequent reliable decisions. Secondly, we discuss the requirements of quality assurance, which actually allow for reliable decision-making. In particular, as part of a rational strategy, we discuss how to interpret measurement results from low-cost active monitors with high and low sensitivity with respect to deciding on conformity with reference levels that are the annual average concentration of indoor radon. Rigorous analysis shows that temporal variations in radon are a major component of the uncertainty in decision-making, the reliability of which is practically independent of monitor sensitivity. Manufacturers of low-cost radon monitors already provide sufficient reliability and quality of calibration for their devices, which can be used by both professional inspectors and the general public. Therefore, within the suggested measurement strategy and metrologically assured criteria, we only propose to clarify the set and values of the key metrological characteristics of radon monitors as well as to upgrade user-friendly online tools. By implementing clear metrological requirements as well as the rational measurement strategy for the reliable conformity assessment of a room (building) with radon safety requirements, we anticipate significant reductions in testing costs, increased accessibility, and enhanced quality assurance and control (QA/QC) in indoor radon measurements.

Influence of Human Activity on Radon Concentration, Indoor Air Quality, and Thermal Comfort in Small Office Spaces.

This article focuses on the influence of occupants on the concentration of contaminants (radon Rn-222 and CO2) as well as the thermal comfort parameters. A series of sensors were placed to measure the concentration of the contaminants, temperature, and relative humidity in the test room at the Institute of Nuclear Physics PAN in Krakow (IFJ PAN), Poland. The test room is an office that is typical of the offices used in the facility. The occupants that used the space kept a detailed diary of their entry, exit, and number of people entering. The results showed that the accumulation of contaminants in such spaces may be severe and risks the health and safety of occupants. The accumulation of CO2 was extremely noticeable and did not diminish to the background level between the re-entry of the occupants to the office. The same was consistent for the radon concentration. The study shows how ventilation methods and small changes in occupant work strategy may influence the contaminant concentration within a test zone.

Assessment of the Radioactivity, Metals Content and Mineralogy of Granodiorite from Calabria, Southern Italy: A Case Study.

In this paper, an assessment of the natural radioactivity level, radon exhalation, metal contamination, and mineralogy of a granodiorite rock sample from Stilo, in the Calabria region, Southern Italy is presented as a case study. This rock was employed as a building material in the area under study. The specific activity of 226Ra, 232Th and 40K natural radioisotopes was assessed through high-purity germanium (HPGe) gamma-ray spectrometry. Then, several indices such as the absorbed gamma dose rate (D), the annual effective dose equivalent (AEDE), the activity concentration index (ACI) and the alpha index (Iα), were quantified to determine any potential radiological health risk related to radiation exposure from the analyzed rock. Furthermore, E-PERM electret ion chambers and inductively coupled plasma mass spectrometry (ICP-MS) measurements were carried out to properly quantify the radon exhalation rate and any possible metal pollution, respectively. In particular, to further address metal pollution factors, the geo-accumulation index (Igeo) was calculated to properly address the toxicity levels of the ecosystem originating from the detected metals. Finally, with the aim of successfully discriminating the provenance of such naturally occurring radionuclides, a combined approach involving X-ray diffraction (XRD) and µ-Raman spectroscopy was employed for the identification of the main radioisotope-bearing minerals characterizing the investigated granodiorite. The results achieved in this case study can be taken as the basis for further inquiries into background levels of radioactivity and chemical contamination in natural stone employed as building materials.

Radiological assessment of radon in groundwater of the northernmost Kashmir Basin, northwestern Himalaya.

This study investigates the radon concentration in groundwater in Kupwara, the northernmost district of the Kashmir valley. It further assesses the annual effective dose experienced by the district's diverse population-infants, children, and adults-attributable to both inhalation of airborne radon released from drinking water and direct ingestion. In addition to this, the calculation of gamma dose rate is also carried out at each of the sampling site of radon. A portable radon-thoron monitor and a portable gamma radiation detector were respectively employed to estimate the activity concentration of radon in water samples and to measure the gamma dose rate. The radon concentration was found to exhibit variability from a minimum of 2.9 BqL-1 to a maximum of 197.2 BqL-1, with a mean of 26.3 BqL-1 and a standard deviation of 23.3 BqL-1. From a total of 85 samples, 10.6% of the samples had radon activity concentrations exceeding the permissible limits of 40 BqL-1 set by the United Nations Scientific Committee on Effects of Atomic Radiations as reported by UNSCEAR (Sources and effects of ionizing radiation, 2008) and only 1.2% of the samples have radon activity concentration exceeding the permissible limits of 100 BqL-1 set by the World Health Organization as reported by WHO (WHO guidelines for drinking-water quality, World Health Organization, Geneva, 2008). The mean of the annual effective dose due to inhalation for all age groups as well as the annual ingestion dose for infants and children, surpasses the World Health Organization's limit of 100 µSv y-1 as reported by WHO (WHO guidelines for drinking-water quality, World Health Organization, Geneva, 2008). The observed gamma radiation dose rate in the vicinity of groundwater radon sites ranged from a minimum of 138 nSv h-1 to a maximum of 250 nSv h-1. The data indicated no significant correlation between the dose rate of gamma radiation and the radon levels in the groundwater. Radon concentration of potable water in the study area presents a non-negligible exposure pathway for residents. Therefore, the judicious application of established radon mitigation techniques is pivotal to minimize public health vulnerabilities.

Assessment of contamination level of radon (222Rn) in drinking water around Tulsishyam geothermal area and Savarkundla fault in Saurashtra, India.

This study aimed to estimate radon concentrations in groundwater and surface water to evaluate radon (222Rn) contamination in drinking water within the Amreli region of Saurashtra, Gujarat, India. Water samples from 84 sites, covering about 3000 km2, were analyzed using the RAD7 device from Durridge Instruments. Samples were collected in 250 ml radon-tight bottles. Radon concentrations ranged from 0.1 to 13.6 Bq/L, averaging 4.52 Bq/L. At three sites (P9, P29, P35), radon levels exceeded the USEPA limit of 11.1 Bq/L. P9 and P29 are near the Tulsishyam geothermal area, while P35 is close to the Savarkundla fault. Geothermal fluids in Tulsishyam may facilitate radon migration, and swarm-type earthquakes near Savarkundla could also contribute to radon migration. Concurrently, physicochemical parameters like Potential of Hydrogen (pH) and Total Dissolved Solid (TDS) were measured, with no significant correlation found between radon levels and these parameters. Samples were taken from tube wells with depths ranging from 105 to 750 feet, averaging 359 feet. A strong and significant correlation (0.83) was observed between radon concentration and water depth. Health risks from radon exposure were assessed by estimating annual effective dose rates for different age groups through ingestion and inhalation. In some instances, the annual effective dose rate surpassed the WHO-recommended value of 100 µSv/year. However, in most instances, the presence of radon in the water does not indicate a significant radiological risk.

Exploring the Disparity in Indoor/Outdoor Time and Radon Exposure as Possible Factors Contributing to the Unexpected Increase in Lung Cancer Risk among Non-Smoking Women.

According to a NIH study, Lung cancer among individuals who have never smoked is more prevalent in women and occurs at an earlier age than in smokers. The rise in lung cancer rates among female non-smokers might be linked to radon inhalation and should be further investigated. Our theory is based on the differences in radon exposure between males and females, which can be attributed to the variations in time spent indoors versus outdoors. Over the past few years, the smoking rates have shown a steady decline in the United States and other developed countries. This decrease in smoking prevalence has led to a new shift in the primary risk factors associated with lung cancer. Although tobacco smoke historically served as the primary cause of lung cancer, the reduction in smoking rates has allowed other risk factors, such as radon exposure, to come to the forefront. Given that women in certain countries, on average, might spend more time indoors compared to men, they are potentially exposed to higher levels of radon. This increased exposure could explain the rising rates of lung cancer among female non-smokers. The theory is still in its nascent stages and requires further research and validation. However, if proven correct, it could significantly alter our understanding of lung cancer risk factors and lead to new prevention. It is therefore crucial to expedite the review and publication of this theory, given its potential implications for public health.

Inverse Probability Weighting to Estimate Impacts of Hypothetical Occupational Limits on Radon Exposure to Reduce Lung Cancer.

Radon is a known cause of lung cancer. Protective standards for radon exposure are derived largely from studies of working populations that are prone to healthy worker survivor bias. This bias can lead to under-protection of workers and is a key barrier to understanding health effects of many exposures. We apply inverse probability weighting to study a set of hypothetical exposure limits among 4,137 male, White and American Indian radon-exposed uranium miners in the Colorado Plateau followed from 1950 to 2005. We estimate cumulative risk of lung cancer through age 90 under hypothetical occupational limits. We estimate that earlier implementation of the current US Mining Safety and Health Administration annual standard of 4 working level months (implemented here as a monthly exposure limit) could have reduced lung cancer mortality from 16/100 workers to 6/100 workers (95% confidence intervals: 3/100, 8/100), in contrast with previous estimates of 10/100 workers. Our estimate is similar to that among contemporaneous occupational cohorts. Inverse probability weighting is a simple and computationally efficient way address healthy worker survivor bias in order to contrast health effects of exposure limits and estimate the number of excess health outcomes under exposure limits at work.

The correlation between indoor and soil gas radon concentrations in Kiraz district, Izmir.

All humans are exposed to radon, the primary source of natural radiation, which can harm people due to natural processes rather than human activity. Thus, it is of significant importance to determine the levels of radon in indoor, soil gas, water, and outdoors. Radon concentration (CRn) was measured in Kiraz district, Izmir, and the correlation between the indoor and soil gas CRn values was investigated. The indoor CRn values measured in 40 randomly selected dwellings in Kiraz exhibited a wide range from 19.50 ± 2.50 to 204.70 ± 8.00 Bq m-3 with an average value of 61.11 ± 4.23 Bq m-3. The measured indoor CRn values were compared to the reference levels in the world to help control radon in the dwellings. Indoor CRn values were lower than the ICRP reference level of 300 Bq m-3 in all of the dwellings studied. Furthermore, in 34 dwellings (representing 85% of the total number of dwellings studied), indoor CRn values were lower than the WHO reference level of 100 Bq m-3. Health hazard indices, namely annual effective dose (AED) and excess lifetime cancer risk (ELCR), were also calculated for each dwelling and compared with internationally acceptable levels to estimate the risk to human health. The AED values varied from 0.49 ± 0.06 to 5.16 ± 0.20 mSv y-1 with an average value of 1.54 ± 0.11 mSv y-1, which exceeds the world average of 1.15 mSv y-1 as reported by UNSCEAR. The ELCR values ranged from 2.05 ± 0.26 × 10-3 to 21.55 ± 0.84 × 10-3 with an average value of 6.43 ± 0.44 × 10-3, exceeding the world average of 0.29 × 10-3 as reported by UNSCEAR. The soil gas CRn values measured exhibited a wide variation ranging from 129.25 ± 6.38 Bq m-3 to 6172.64 ± 44.06 Bq m-3 with an average value of 1291.79 ± 18.70 Bq m-3. The soil gas CRn values were less than 10,000 Bq m-3; hence, the research area is categorized as "low radon risk areas" according to Sweden Criteria, and so no special constructions are required in the studied area. When soil gas CRn values were compared to indoor CRn values, no linear relationship was found between the CRn values. However, a strong positive linear correlation was found between indoor and soil gas CRn values less than 200 Bq m-3 and 2500 Bq m-3, respectively.

Small ion pulse ionization chamber for radon measurement in underground space.

Radon, prevalent in underground spaces, requires continuous monitoring due to health risks. Traditional detectors are often expensive, bulky, and ill-suited for humid environments in underground spaces. This study presents a compact, cost-effective radon detector designed for long-term, online monitoring. It uses a small ionization chamber with natural airflow, avoiding the need for fans or pumps, and includes noise filtering and humidity mitigation. Featuring multi-point networking and easy integration capabilities, this detector significantly enhances radon monitoring in challenging, underground conditions.

Overview of radon gas in groundwater around the world: Health effects and treatment technologies.

The natural radioactive decay of uranium in rocks and soils gives rise to the presence of radon in groundwater. The existence of radon in groundwater at activity levels way higher than the reference limits set by US-EPA and WHO was widely covered in literature. The exposure to elevated levels of radon in ground and drinking water have been reported in literature to cause adverse health impacts. The aim of the present paper is to give an overview of radon gas in groundwater followed by the safe limits suggested by international organizations and agencies such as US-EPA and WHO. The paper also discusses the health effects associated with the exposure to radon levels and the estimation of the annual effective dose through ingestion and inhalation. This is followed by the radon levels around the world as well as the corresponding annual effective doses reported in literature. The determination techniques of radon levels in water covered in literature such as liquid scintillation counting, gamma-ray spectrometry and emanometry were also discussed and reviewed in the present work. Next, the paper sheds light on the most frequently used treatment techniques such as aeration, adsorption, filtration as well as biological techniques and evaluates their efficiency in mitigating radon levels in water. The paper also highlights the main precautions and future mitigation plans for radon in groundwater as well as delved onto future research perspectives of radon. It was found out that the type of rock played a key role in determining the radon levels. For instance, granitic rock types were reported to contribute to the elevation in the groundwater radon levels due to their characteristic permeability as a result of the formed fractures as well as their natural incorporation of high levels of uranium. Some of the reported radon levels in groundwater in literature were way higher than the guidelines set by the World Health Organization (WHO) for drinking water and US-EPA alternative higher maximum contaminant level. This review paper could be of importance to researchers working on the evaluation as well as the treatment of radon gas in water as it will provide a critical and state of the art review on radon gas in groundwater.

Characterization of radon gas transmission rate in pore structures of different rock layers by radon daughters inversion calculation.

Determining the transmission rate of radon gas in overburden strata is crucial for conducting a comprehensive study of radon gas's longitudinal and long-distance migration mechanisms. This study investigates the mineral components of rocks in the underground strata of the mining area using the X-ray diffraction method. Additionally, it examines the pore structure parameters of the rocks at different depths using the low-temperature nitrogen adsorption method. This research introduces an approach to inversion calculate the radon gas transmission rate through the activity ratio of radon's characteristic daughters based on the decay law and activity balance of 210Po and 210Pb daughters. In addition, it determines the transmission rates of radon gas in overlying strata at various depths through this method. The relationship between the rock's mineral composition and pore structure is investigated, and the effects of pore structure and mineral composition on the radon gas transmission rate are analyzed. The findings indicated that the pore structure exerts a dual impact on radon gas transport: macropores serve as channels for upward radon gas transport, while micropores offer most of the adsorption area. In contrast, the radon gas transmission rate is indirectly influenced by the mineral composition content associated with the medium's adsorption capacity and pore structure. In the studied lithologies, an increase in quartz content promotes radon gas transmission, while an increase in clay mineral content impedes it. Finally, the mechanisms of radon gas transport, daughter adsorption, and the impacts of rock pore structure and mineral composition on the radon transmission rate are discussed.

The Bacau (Romania) phosphogypsum stacks as a source of radioactive threat: a case study.

For a detailed characterization of the 5.7 106 mt phosphogypsum (PG) stack in the vicinity of Bacau city, Romania, the air dose rate (ADR) was measured in 72 points covering the stack surface, while 10 samples of stack material were collected for future analysis. Radiometric determinations showed for the ADR values varying between 364 ± 53 and 489 ± 8 nSv/h, with some extreme values of 2775 ± 734 nSv/h, significantly exceeding 90 nSv/h, the average value reported for the Romanian territory. High-resolution gamma-ray spectroscopy (HRGS), performed on 10 samples collected from the entire PG stack evidenced only the presence of 226Ra as the major radioactive element with a specific activity varied between 820 ± 150 and 5278 ± 264 Bq/kg for hot spots. Further analysis performed on a similar number of samples by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX), evidenced, beside gypsum as the main component, traces of brushite (CaHPO4·2H2O) and ardealite (Ca2(PO3OH)(SO4)·4H2O), as well as the presence of small acicular celestine (SrSO4) agglomerates. XRF determinations of the mass fractions of major elements evidenced values such as SiO2 (2.31 ± 0.73 %), TiO2 (0.07 ± 0.01 %), Al2O3 (0.17 ± 0.04 %), Fe2O3 (0.87 ± 0.18 %), MnO (0.01 ± 0.01 %), MgO (0.17 ± 0.02 %), CaO (32.5 ± 0.82 %), Na2O (0.04 ± 0.04 %), K2O (0.05 ± 0.01 %), P2O5 (2.12 ± 0.51 %), LOI (20.2 ± 0.3 %), i.e. closer to literature reported data for PG of different provenience while the data concerning the distribution of 20 trace elements, including incompatible Sc, La, Ce, and Th were relatively closer to the upper continental crust (UCC).

Efficacy of zeolites in radon adsorption: state of the art and development of an optimized approach.

Radon is a radioactive noble gas omnipresent in the environment, being part of the 238U and 232Th decay chains present in the Earth's crust. The gas can easily leak through the ground but also be present in natural construction materials and migrate into indoor places where it can be a carcinogen when inhaled. Studying the content and removal of indoor radon is crucial for the evaluation and mitigation of its radiological risks to public health. For more than 100 years, the removal by adsorption of the radon has been performed on activated charcoal. There is little progress in the field of radon adsorption at ambient conditions; the main progress is in the use of zeolite materials, having well-defined three-dimensional porous structures and radiation resistance. This study concerns a report on the state of the art of the application of zeolites in radon adsorption. Furthermore, an optimized approach for measuring the radon content in indoor environments and, consequently, its removal has been proposed. Adsorption systems based on zeolites have the potential to replace activated charcoal as a material of choice, allowing to facilitate the development of simple and compact radon adsorption systems.

Short-Term vs. Long-Term: A Critical Review of Indoor Radon Measurement Techniques.

Radon is a known carcinogen, and the accurate assessment of indoor levels is essential for effective mitigation strategies. While long-term testing provides the most reliable data, short-term testing (STT) offers a quicker and more cost-effective alternative. This review evaluated the accuracy of STT in predicting annual radon averages and compared testing strategies in Europe (where long-term measurements are common) and the United States (where STT is prevalent). Twenty (20) studies were systematically identified through searches in scientific databases and the grey literature, focusing on STT accuracy and radon management. This review revealed several factors that influence the accuracy of STT. Most studies recommended a minimum four-day test for initial screening, but accuracy varied with radon levels. For low levels (<75 Bq/m3), a one-week STT achieved high confidence (>95%) in predicting annual averages. However, accuracy decreased for moderate levels (approximately 50% success rate), necessitating confirmation with longer testing periods (3 months). High radon levels made STT unsuitable due to significant fluctuations. Seasonality also played a role, with winter months providing a more representative picture of annual radon averages. STT was found to be a useful method for screening low-risk areas with low radon concentrations. However, its limitations were evident in moderate- and high-level scenarios. While a minimum of four days was recommended, longer testing periods (3 months or more) were crucial for achieving reliable results, particularly in areas with potential for elevated radon exposure. This review suggests the need for further research to explore the possibility of harmonizing radon testing protocols between Europe and the United States.

Validation of a new sampler for radon gas measurements in surface water.

Radon gas (Rn-222) in water poses health risks due to radiation exposure, yet it's also an important tracer for studying natural systems. Sampling procedures for Rn-222 analysis are very sensitive to potential losses of the gas to the atmosphere. It requires a well-defined and properly validated protocol to ensure accuracy and reliability. A novel sampler was developed to collect surface water from a distance (e.g. from bridges), addressing logistic challenges posed by topography. The sampler, manually operated, ensures precise depth-specific sampling throughout the water column. A three-stage validation process (technical performance test, uncertainty estimations and preliminary test) was followed to validate the protocol.•The comparison of the technical procedure for analysis and measurement through Liquid Scintillation Counting is statistically robust (one-way ANOVA p-value = 0.96).•For the protocol proposed for Rn-222 determination, the estimated sampling and measurement uncertainties (k = 2) are respectively 5% and 15%. These are compatible with the literature and the laboratory's precision.•Preliminary tests, with meaningful patterns identified and possibly related to the river's hydrodynamics, revealed a very reliable protocol, even in low Rn-222 concentrations.Therefore, the sampler has demonstrated a good analytical reproducibility and was considered validated for Rn-222 determination in surface waters.

A transcranial multiple waves suppression method for plane wave imaging based on Radon transform.

Transcranial ultrasound imaging presents a significant challenge due to the intricate interplay between ultrasound waves and the heterogeneous human skull. The skull's presence induces distortion, refraction, multiple scattering, and reflection of ultrasound signals, thereby complicating the acquisition of high-quality images. Extracting reflections from the entire waveform is crucial yet exceedingly challenging, as intracranial reflections are often obscured by strong amplitude direct waves and multiple scattering. In this paper, a multiple wave suppression method for ultrasound plane wave imaging is proposed to mitigate the impact of skull interference. Drawing upon prior research, we developed an enhanced high-resolution linear Radon transform using the maximum entropy principle and Bayesian method, facilitating wavefield separation. We detailed the process of wave field separation in the Radon domain through simulation of a model with a high velocity layer. When plane waves emitted at any steering angles, both multiple waves and first arrival waves manifested as distinct energy points. In the brain simulation, we contrasted the characteristic differences between skull reflection and brain-internal signal in Radon domain, and demonstrated that multiples suppression method reduces side and grating lobe levels by approximately 30 dB. Finally, we executed in vitro experiments using a monkey skull to separate weak intracranial reflection signals from strong skull reflections, enhancing the contrast-to-noise ratio by 85 % compared to conventional method using full waveform. This study deeply explores the effect of multiples on effective signal separation, addresses the complexity of wavefield separation, and verifies its efficacy through imaging, thereby significantly advancing ultrasound transcranial imaging techniques.

Evaluation of accurate measurement methods for radon exhalation rate with advection effect and application in field.

In decommissioning of a uranium tailings pond, radon exhalation rates on a beach surface should meet regulatory standards. Accurate measurements of the radon exhalation rate are demanded. However, current studies fail to consider the impact of advection under temperature variations or pressure gradients caused by gas movement on measurements using an accumulation chamber. Two proposed methods were therefore evaluated to accurately measure radon exhalation rates on the loose medium surface under advective conditions. Repeated experiments were conducted on a laboratory experimental platform filled with uranium tailings sand under advective flow rates of 0.03 and 0.3 L/min to validate the stability and reliability. Deviations between measured and true values were 0.1-6.1 % and 6.3-29.2 % for the two methods, respectively. Subsequently, numerical simulation was used to analyze defects of traditional methods and mechanisms of the new methods. In a field study, all methods were compared, and a predictive map of radon exhalation rates was created using interpolated data from 20 random sites using the new method. Results from the proposed methods, compared with traditional ones, were closer to true values under advective conditions, and accurate assessment of beach surface treatment was expected.

Radon-222 signatures of atmospheric dynamics in the Pech Merle Painted Cave, France: Consequences for management and conservation.

Radon-222, a radioactive noble gas with a half-life of 3.8 days produced by radium-226, is a health hazard in caves, but also a powerful tracer of atmospheric dynamics. Here we show how airborne radon-222 can be analysed in a cave with multiple openings, the Pech Merle Cave in South-West France. This two-level cave hosts prehistoric remains and Gravettian paintings in its lower level. Radon concentration, monitored at 15 points with one-hour sampling intervals for more than one year, including two points for more than three years, showed mean values from 1274 ± 11 to 5281 ± 20 Bq m-3, with transient values above 15,000 Bq m-3. Seasonal variations were observed, with a weak normal cycle (low in winter) at two points in the upper level and a pronounced inverse seasonal cycle (low in summer) at the other points in the cave. The radon-222 source (effective radium-226 concentration, ECRa) was measured in the laboratory for floor deposits, soil and rock samples. While ECRa values obtained for rocks and speleothems are smaller than 1 Bq kg-1, most ECRa values for soils are larger than 10 Bq kg-1. Quantitative modelling confirms that the floor fillings inside the cave are responsible for the stationary lower concentrations, while the higher concentrations observed in winter are explained by percolation of outside air, which collects radon-222 as it passes through the soil layers. In addition, Stored Available Radon (SAR) is sufficient to account for transient variations. While air currents occur when visitors enter the cave or when the cave is deliberately ventilated, the climatic processes revealed by their radon-222 signatures appear to be essentially natural. These processes, enhanced by global climate change, could cause or accelerate the deterioration of prehistoric paintings. Radon-222 source analysis using ECRa-based modelling and SAR appears essential for the preservation of underground heritage.

Effective dose assessment due to inhalation of 222Rn, 220Rn, and their progeny: highlighting the major contribution of thoron in a thoron-prone area in Cameroon.

To assess public exposure to radon, thoron, and their progeny, measurements were conducted in 50 dwellings within the bauxite-rich area of Fongo-Tongo in western Cameroon. Passive integrating radon-thoron discriminative detectors (specifically RADUET) were employed for radon and thoron measurements. Additionally, concentrations of short-lived radon and thoron progeny were estimated using Direct Radon Progeny Sensors (DRPSs) and Direct Thoron Progeny Sensors (DTPSs) based on LR-115 detectors. The findings revealed indoor radon concentrations ranging from 31 to 123 Bq m-3 with a geometric mean (GM) of 62 Bq m-3, and indoor thoron concentrations ranging from 36 to 688 Bq m-3 with a GM of 242 Bq m-3. The Equilibrium Equivalent Radon Concentration (EERC) ranged from 3 to 86 Bq m-3 with a GM of 25 Bq m-3, while the Equilibrium Equivalent Thoron Concentration (EETC) ranged from 1.2 to 12.5 Bq m-3 with a GM of 7.6 Bq m-3. Notably, all dwellings recorded radon concentrations below 100 Bq m-3. Arithmetic means of radon and thoron equilibrium factors were calculated as 0.47 and 0.04, respectively. To assess annual effective doses from radon and thoron inhalation, equilibrium factors were used along with direct measurements of EERC and EETC. The differences observed in annual effective doses were 4.5% for radon and 42.5% for thoron. Furthermore, the contribution of thoron and its decay products to the annual effective dose from radon, thoron, and their progeny ranged from 12 to 94%, with an average contribution of 58%. Thus, this study found that the effective dose due to thoron inhalation in the study area exceeded that due to radon inhalation. It is concluded that, when evaluating radiation doses and health risks, it is crucial to consider both thoron and its progeny alongside radon and its progeny. This underscores the importance of considering direct measurements for accurately estimating radiation doses.