Inhalation dose assessment of indoor radon progeny using biokinetic and dosimetric modeling and its application to Jordanian population

High indoor radon concentrations in Jordan result in internal exposures of the residents due to the inhalation of radon and its short-lived progeny. It is therefore important to quantify the annual effective dose and further the radiation risk to the radon exposure. This study describes the methodology and the biokinetic and dosimetric models used for calculation of the inhalation doses exposed to radon progeny. The regional depositions of aerosol particles in the human respiratory tract were firstly calculated. For the attached progeny, the activity median aerodynamic diameters of 50 nm, 230 nm and 2500 nm were chosen to represent the nucleation, accumulation and coarse modes of the aerosol particles, respectively. For the unattached progeny, the activity median thermodynamic diameter of 1 nm was chosen to represent the free progeny nuclide in the room air. The biokinetic models developed by the International Commission on Radiological Protection (ICRP) were used to calculate the nuclear transformations of radon progeny in the human body, and then the dosimetric model was applied to estimate the organ equivalent doses and the effective doses with the specific effective energies derived from the mathematical anthropomorphic phantoms. The dose conversion coefficient estimated in this study was 15 mSv WLM⁻¹ which was in the range of the values of 6-20 mSv WLM⁻¹ reported by other investigators. Implementing the average indoor radon concentration in Jordan, the annual effective doses were calculated to be 4.1 mSv y⁻¹ and 0.08 mSv y⁻¹ due to the inhalation of radon progeny and radon gas, respectively. The total annual effective dose estimated for Jordanian population was 4.2 mSv y⁻¹. This high annual effective dose calculated by the dosimetric approach using ICRP biokinetic and dosimetric models resulted in an increase of a factor of two in comparison to the value by epidemiological study. This phenomenon was presented by the ICRP in its new published statement on radon.     

Detection of 210Po on filter papers 16 years after use for the collection of short-lived radon progeny in a room

Radon gas was allowed to accumulate in its radium source and then injected into a 36 m(3) test room, resulting in an initial radon concentration of 15 kBq m(-3). Filter papers were used to collect the short-lived radon progeny and thus to measure the Potential Alpha Energy Concentration (PAEC) in-situ in the year 1984 at different times and conditions according to the experimental design. The radon progeny collected on the filter papers were studied as a function of aerosol particle concentration ranging from 10(2)-10(5) particles cm(-3) in three different experiments. The highest aerosol particle concentration was generated by indoor cigarette smoking. Those filters were stored after the experiment, and were used after 16 years to study the activity of the radon long-lived alpha emitter progeny, (210)Po (T(1/2)=138 days). This isotope is separated from the short-lived progeny by (210)Pb beta emitter with 22.3 years half-life. After 16 years' storage of these filters, each filter paper was sandwiched and wrapped between two CR-39 nuclear track detectors, to put the detectors in contact with the surfaces of different filters, for 337 days. Correlation between the PAEC measured using filter papers in the year 1984 and the activity of long-lived alpha emitter (210)Po on the same filter papers measured in the year 2000 were studied. The results of the (210)Po activity showed a very good correlation of 0.92 with the PAEC 16 years ago. The results also depict that the PAEC and (210)Po activity in indoor air increased with the increase of aerosol particle concentration, which shows the attachment of short-lived radon progeny with the aerosol particles. The experiment proves that indoor cigarette smoking is a major source of aerosol particles carrying radon progeny and, thus, indoor cigarette smoking is an additional source of internal radiation hazard to the occupants whether smoker or non-smoker.     

Radon survey in Greece--risk assesment

A large scale radon survey using track etch detectors has been carried out from 1995 to 1998 in Greece in order to estimate the radon concentrations in Greek dwellings and the exposure of the Greek population to radon. The total data set consisted of 1,277 samples. Residential potential alpha energy concentration values ranged between (0.024 +/- 0.009) and (8 +/- 1) WLM per year (P < 0.05) and effective doses between (0.09 +/- 0.04) and (28 +/- 4) mSv (P < 0.05). The mean lifetime risk for the Greek population due to radon was found to be 0.4%.     

Radon and thoron progeny concentration variability in relation to meteorological conditions at Bucharest (Romania)

The paper presents results of natural radioactivity levels in the atmosphere obtained for a 5 years period (1994-1999) at the Bucharest Environmental Radioactivity Surveillance Station (BERSS). The variability of radon and thoron progeny activity concentrations is analysed in relation to the local dynamics of the meteorological parameters (wind speed, air temperature, air pressure, cloud cover, relative humidity). The radon and thoron progeny concentrations display a daily and seasonal variation, with the highest values in the early morning and the lowest values in the afternoon. The outdoor radon progeny concentrations show maximum values in autumn and minimum values in spring-summer. The outdoor thoron progeny concentrations display maximum values in autumn and minimum values in winter. Significant statistical correlations with the meteorological parameters were obtained. The study on the temporal variability of natural atmospheric radioactivity near Bucharest is a starting point for further assessment of the radiological consequences resulting from human activities.     

Environmental radon studies using solid state nuclear track detectors

The results of radon activity recorded in 70 dwellings of Nurpur area, Kangra district, Himachal Pradesh, India are reported. LR-115 Type 2 films in the bare mode were exposed for four seasons of three months each covering a period of one year for the measurement of indoor radon levels. The calibration constant of 0.020 tracks cm(-2) d(-1) per Bq m(-3) has been used to express radon activity in Bq m(-3). The annual average indoor radon concentrations in 17 different villages of the area are found to vary from 168+/-46 to 429+/-71. Most of the indoor radon values lie in the range of action levels (200-600 Bq m(-3)) recommended by International Commission on Radiological Protection.     

Radon releases from Australian uranium mining and milling projects: assessing the UNSCEAR approach

The release of radon gas and progeny from the mining and milling of uranium-bearing ores has long been recognised as a potential radiological health hazard. The standards for exposure to radon and progeny have decreased over time as the understanding of their health risk has improved. In recent years there has been debate on the long-term releases (10,000 years) of radon from uranium mining and milling sites, focusing on abandoned, operational and rehabilitated sites. The primary purpose has been estimates of the radiation exposure of both local and global populations. Although there has been an increasing number of radon release studies over recent years in the USA, Australia, Canada and elsewhere, a systematic evaluation of this work has yet to be published in the international literature. This paper presents a detailed compilation and analysis of Australian studies. In order to quantify radon sources, a review of data on uranium mining and milling wastes in Australia, as they influence radon releases, is presented. An extensive compilation of the available radon release data is then assembled for the various projects, including a comparison to predictions of radon behaviour where available. An analysis of cumulative radon releases is then developed and compared to the UNSCEAR approach. The implications for the various assessments of long-term releases of radon are discussed, including aspects such as the need for ongoing monitoring of rehabilitation at uranium mining and milling sites and life-cycle accounting.     

Preliminary indoor radon risk assessment at the Poços de Caldas Plateau,MG-Brazil

This paper aims to present an assessment of the environmental radiological exposure at a Brazilian area of high natural radiation and discusses the indoor radon exposure risk. A survey of inhabitant exposures arising from the inhalation of radon progeny and external gamma exposure was conducted in urban and rural areas of the Po?os de Caldas Plateau, which is recognized worldwide as a high natural radiation region. The results of this survey indicated that highest radiation exposure was restricted to the rural area of Po?os de Caldas. The radiation exposure in urban locations was quite similar to the values observed in normal background areas in some Brazilian counties. By the application of a constant relative risk model, an additional 20% in the lifetime risk of lung cancer mortality due to the exposure to radon progeny was estimated at Po?os de Caldas. It was also estimated that 16% of all lung cancer deaths at Po?os de Caldas county could be attributable to radon exposure.     

The influence of the cigarette smoke pollution and ventilation rate on alpha-activities per unit volume due to radon and its progeny

Alpha and beta activities per unit volume air due to radon, thoron and their decay products were evaluated in the air of various cafe rooms polluted by cigarette smoke. Both CR-39 and LR-115 type II solid state nuclear track detectors (SSNTD) were used. Equilibrium factors between radon and its progeny and thoron and its daughters have been evaluated in the air of the studied cafe rooms. The committed equivalent doses due to short-lived radon decay products were determined in different regions of the respiratory tract of non-smoker members of the public. The influence of cigarette smoke pollution, ventilation rate and exposure time on committed equivalent dose in the respiratory systems of non-smokers was investigated. Committed equivalent doses ranged from 1.15 x 10(-11)-2.7 x 10(-7) Sv.y(-1)/h of exposure in the extrathoracic region and from 0.8 x 10(-12)-1.7 x 10(-8) Sv.y(-1)/h of exposure in the thoracic region of the respiratory tract of non-smokers.     

Radon concentration in hospital buildings erected during the last 40 years in Białystok, Poland

The aim of the study was to compare radon concentrations in neighbouring hospital buildings which were constructed in different years during the period 1963-2000 and are located in areas with similar radon potential. The value of arithmetic mean (AM) radon concentration in soil gas amounted to 14,464 Bq m(-3). In a hospital built 40 years ago, the AM radon concentration in the cellar was 38.4+/-36.7 Bq m(-3) and on higher levels it was 17.1+/-10.3 Bq m(-3). In a hospital built 16 years ago, these values equaled 45.5+/-47.2 Bq m(-3) and 20.4+/-12.5 Bq m(-3), respectively. In the newest hospital, built three years ago, radon concentration (AM) in a cellar was 32.3+/-27.4 Bq m(-3) and the respective value on higher levels amounted to 20.4+/-12.6 Bq m(-3). When comparing radon concentrations in the cellars, no statistically significant differences were found. Similarly, no statistically significant differences were observed between radon concentrations measured on higher levels in investigated hospital buildings.     

Development of a technique for the measurement of the radon exhalation rate using an activated charcoal collector

A simple system to evaluate the 222Rn (radon) exhalation rate from soil has been improved. A sampling cuvette of 2.1 L is placed so that it covers the targeted ground soil, and radon emanating from the soil accumulates within the cuvette for 24 h. Its internal radon concentration is measured by the combination of an activated charcoal (PICO-RAD) and a liquid scintillation counting system. This study shows variations of the conversion factor (CF: unit Bq m(-3)/cpm) of PICO-RAD. The range of CF due to temperature (10-30 degrees C) was between -21% and +69%, and this due to humidity (30-90%) was between 0% and -15%. Humidity and radon concentration in the cuvette covering soil tended to saturate in a few hours. The above information was used to correct the CF for the evaluation. The improved system shows high reliability and can be easily applied to natural environments.     

Application of activated charcoal radon collectors in high humidity environments

Most commercially based activated charcoal radon collectors were designed for use in indoor environments. However, at present, they are often used for research in radon surveys in unique environments, such as in the bathrooms, underground areas, mines, caves and tunnels. In these environments, the relative humidity would be around 100%, and a change in the sensitivity of cpm(Bq m(-3))(-1)(radon) would occur. For this study, the reduction in the sensitivity of activated charcoal radon collector due to environmental humidity was investigated, and the data correction was discussed. Here, ST-100 (Pico-Rad) was selected as an example of a familiar activated charcoal radon collector. According to our performance test, the humidity of 90% (20 degrees C) resulted in a 15% reduction of the sensitivity for 24 h collection. The ST-100 user should discuss the necessity of data correction by comparing the change of sensitivity with other levels of estimation errors.     

Determination of indoor radon and soil radioactivity levels in Giresun, Turkey

Indoor radon survey and gamma activity measurements in soil samples were carried out in the Giresun province (Northeastern Turkey). The result of analysis of variance showed a relationship between indoor radon and radium content in soil (R(2)=0.54). It was found that indoor radon activity concentration ranged from 52 to 360 Bq m(-3) with an average value of 130 Bq m(-3). A model built by BEIR VI was used to predict the number of lung cancer deaths due to indoor radon exposure. It was found that indoor radon is responsible for 8% of all lung cancer deaths occurring in this province. (137)Cs activity concentration was measured 21 years after the Chernobyl accident. The results showed that (137)Cs activity concentration ranged from 41 to 1304 Bq kg(-1) with an average value of 307 Bq kg(-1). The indoor radon results and the geology of the studied area were discussed. Annual effective doses to the both radionuclides of natural origin and (137)Cs were estimated.     

Estimation of radon concentrations in coal mines using a hybrid technique calibration curve

The results of epidemiological studies in various countries show that radon and its progeny cause carcinogenic effects on mine workers. Therefore, it becomes of paramount importance to monitor radon concentrations and consequently determine the radon dose rates in coal mines for the protection of coal miners. A new calibration curve was obtained for radon concentration estimation using hybrid techniques. A calibration curve was generated using 226Ra activity concentration measured by a HPGe detector-based gamma-ray spectrometer versus alpha-track-density rate due to radon and its progeny on CR-39 track detector. Using the slope of the experimentally determined curve in the units of Becqueral per kilogram (Bq kg-1) per unit alpha-track-density per hour (cm-2 h-1), radon concentrations (Bq m-3) were estimated using coal samples from various coal mines in two provinces of Pakistan, Punjab and Balochistan. Consequently, radon dose rates were computed in the simulated environment of the coal mines. Results of these computations may be considered with a caveat that the method developed in this paper provides only a screening method to indicate the radon dose in coal mines. It has been shown that the actual measurements of radon concentrations in the coal mines are in agreement with the estimated radon concentrations using the hybrid-technique calibration curve.     

Contribution of (222)Rn-bearing water to the occupational exposure in thermal baths

The present study investigates the short- and long-term effects of radon ((222)Rn) released from water on the progeny exposure in a thermal spa. For the purposes of this work, the Polichnitos spa was used as a case study. The bathroom was supplied with water containing 110-210 kBq m(-3) of (222)Rn. The (222)Rn concentration in air and the short-lived (222)Rn progenies in attached and unattached form were monitored into the bathroom and the surrounding premises. The equilibrium factor (F-factor) and the unattached fraction were estimated. The results of this study show that water flow during bath filling is by far the dominant mechanism by which (222)Rn is released in the air of the bathroom. The progeny exposure was correlated linearly with the (222)Rn concentration in the entering water. The annual effective dose received by a worker was found to be below the lower limit value of 3 mSv recommended by ICRP 65. The dose limit was exceeded only for water containing more than 300 kBq m(-3).     

The practical use of electrets in a public health radon remediation campaign

As part of a long-term assessment of domestic radon in Northamptonshire, England, a batch of 50 commercially available electrets was deployed for nearly 1,000 exposures, individual exposure periods ranging from one to eight weeks. Responsivity was comparable with that of recently-calibrated Durridge RAD-7 continuously-monitoring equipment. Voltage history analysis indicated mean voltage decay during manufacturers' QA assessment of 0.059+/-0.026 Vday(-1), increasing to 0.114+/-0.073 Vday(-1) during storage to first use and to 0.204+/-0.49 Vday(-1) during inter-deployment storage. At a representative elevated radon concentration of 500 Bqm(-3), the resulting perturbation is 3% over a 7-day deployment; at the typical mean Northamptonshire level of 80 Bqm(-3) it approaches 22%. Each electret can be used for up to 25 measurements, which makes the technology attractive for organisational use. It is not suited for deployment by individual householders.     

Relationship between deposition and attachment rates in Jacobi room model

It is shown in this work that parameters of the Jacobi model, which describes behavior of short-lived radon progeny, are not independent. The relationship between deposition rate of attached radon progeny and attachment rate of their unattached fraction was determined in this paper. It was found that deposition rate increases when the attachment rate is smaller; this effect is more pronounced for larger friction velocity. The deposition rate of attached radon progeny is presented here as a function of friction velocity, ventilation and attachment rate. Deposition rate of attached fraction was estimated in the range 0.012-0.46 h⁻¹, when attachment rate varies from 10 h⁻¹ to 100 h⁻¹.     

Investigation of the potential for radon mitigation by operation of mechanical systems affecting indoor air

Mitigation of radon gas and radon progeny in buildings is based largely on reducing the pressure difference between the point of the radiation source and the point of entry to indoor air. This study identifies the influence of mechanical systems, of air-conditioning and 'wet' systems of central heating as potential remediation agents in the control of radon and progeny concentrations. Air-conditioning was found to reduce radon levels in a systematic way within a few hours of start-up, to a low fraction of the immediately preceding concentration. Central heating reduced the level by around 40% of the preceding high within a few hours of start-up. Importantly for health concerns, under operating conditions of both types of system the level of radon progeny was reduced to a greater extent than the radon progenitor.     

Measurements of summer radon and its progeny concentrations along with environmental gamma dose rates in Taiwan

The concentrations of 222Rn (radon) and its progeny with surrounding environmental gamma-dose rates were measured simultaneously inside and outside of buildings at 10 locations around Taipei and Hualien in Taiwan. For summer radon in Taiwan, indoor concentrations were estimated to be about 20 Bq m(-3) with about 90 nSv h- of environmental gamma, and outdoors, about 10 Bq m(-3) with about 70 nSv h(-1). The equilibrium factors were calculated to be 0.2-0.3 indoors and 0.3-0.4 outdoors. Indoor radon concentration had a weak positive correlation with gamma-dose rate. Since there is a possibility that high radon concentrations exist indoors during the cool season in Taiwan because of extremely low ventilation rates in the dwellings, a winter survey in January through February will be needed for future estimation of the annual effective dose.     

Bronchial dosimeters for radon progeny for Chinese males and females

Bronchial dosimeters have been designed for adult Chinese males and females for home and mine exposures, which can give the bronchial doses from radon progeny by direct measurements. The bronchial dosimeter for home exposures consists of five 400-mesh wire screens. With a sampling face velocity of 3.3 cm s(-1) for Chinese males and 2.7 cm s(-1) for Chinese females, the deposition pattern on the wire screens were found to satisfactorily match the variation of the dose conversion coefficients (in units of mSv WLM(-1)) with the size of radon progeny from 1 to 1000 nm. The bronchial dosimeter for mine exposures consists of four 250-mesh wire screens. With a sampling face velocity of 3.3 cm s(-1), the deposition pattern on the wire screens were found to satisfactorily match the variation of the dose conversion coefficients for both Chinese males and females. In this way, the bronchial dosimeters directly give the bronchial doses from the alpha counts recorded on the wire-screens.     

Experimental methods of determining the activity depth distribution of implanted 210Pb in glass

Glass is often used in radon surveys to estimate retrospective radon concentrations, as radon progenies are embedded in the upper surface layer. Experimental methods based on etching to determine the depth distribution of recoil-implanted 210Po in glass from radon decay in air is presented. By carefully controlling chemical concentrations and exposure time during which the glass is etched, stepwise removal of the surface material was possible. Two different etching agents, diluted HF/HNO3 and NaOH were utilised, with very similar results. Experimental recoil depths of 210Po agree with theoretical calculations from the literature. The maximum implantation depth obtained using this procedure was 100 +/- 20nm.