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PubMed2001

Radon risk management: the future challenge for the nuclear community.

The short-lived decay products (Rn-d) of radon gas (222Rn, 220Rn) have been identified as a health hazard in occupational exposure situations, as well as a public health risk in general. Decisions will have to be made concerning the initiation and scale of national Rn-mitigation programmes. In view of the potentially significant socio-economic impact of such programmes, it is recommended to proceed from the current approach based on Rn-d risk assessment to the integrated approach of radon risk management (RRM). A seven-step RRM is proposed, ranging from the selection of an action level based on an incremental risk-reduction, to the conduct of auditing procedures, monitoring the RRM-outreach factor.

Air Pollutants, Radioactive↗
PubMed2001

Numerical modelling of radon-222 entry into houses: an outline of techniques and results.

Numerical modelling is a powerful tool for studies of soil gas and radon-222 entry into houses. It is the purpose of this paper to review some main techniques and results. In the past, modelling has focused on Darcy flow of soil gas (driven by indoor-outdoor pressure differences) and combined diffusive and advective transport of radon. Models of different complexity have been used. The simpler ones are finite-difference models with one or two spatial dimensions. The more complex models allow for full three-dimensional and time dependency. Advanced features include: soil heterogeneity, anisotropy, fractures, moisture, non-uniform soil temperature, non-Darcy flow of gas, and flow caused by changes in the atmospheric pressure. Numerical models can be used to estimate the importance of specific factors for radon entry. Models are also helpful when results obtained in special laboratory or test structure experiments need to be extrapolated to more general situations (e.g. to real houses or even to other soil-gas pollutants). Finally, models provide a cost-effective test bench for improved designs of radon prevention systems. The paper includes a summary of transport equations and boundary conditions. As an illustrative example, radon entry is calculated for a standard slab-on-grade house.

Air Pollutants, Radioactive↗
PubMed2001

Radon exposure and lung cancer risk--Czech cohort study on residential radon.

Epidemiological evidence of lung cancer risk from radon is based mainly on studies of men employed underground in mines where exposures are relatively high in comparison to indoor exposure. Nevertheless, direct evidence of risk from residential radon is desirable. In 1990, a study was started comprising 12,000 inhabitants of an area with elevated radon concentrations. The mean level in the houses was higher than general mean of the country by a factor of five. In the period 1961-1995, a total of 173 lung cancers were observed. Comparing to nationally expected numbers (E), the observed number (O) of cases is elevated (O/E = 1.11), in contrast to generally low figures for cancers other than lung (O/E = 0.85). Lung cancer risk related to cumulative exposures experienced in the past 5-24 or 5-35 years were both significant. In relation to standard radon progeny concentration 100 Bq/m3, the excess relative risk coefficient was 0.103 (95% CI, 0.039-0.168), the value somewhat lower than findings in other indoor studies.

Air Pollutants, Radioactive↗
PubMed2001

Approaches to the assessment of long term exposure to radon and its progeny.

In recent years, a number of case-control epidemiological studies have taken place and others are in progress to evaluate the lung cancer risk to the general population from exposure to radon and its short-lived progeny in the indoor residential environment. While it is actually long term exposure over past decades to radon progeny by inhalation that dominates lung doses, for a number of practical reasons it is radon gas that is measured in these studies. Because the risk from radon and its progeny results from cumulative exposure over past decades rather than from contemporary exposure, it is necessary to reconstruct the historical exposures of subjects. A number of factors limit the accuracy of this approach of which the following are perhaps the most important: the mobility and residential history of the subjects; radon exposures elsewhere; and changes that may have occurred in the radon levels in current and previous residences. Measurement techniques to assist in making more direct retrospective assessments of radon exposure have appeared in the recent past and are the subject of this paper. These are based on the measurement of the long-lived radon progeny 210Po trapped in household artefacts such as glass or porous and spongy materials. In vivo measurements of skeletal 210Pb in exposed persons is also a method that is currently being investigated as a means to assess historical exposures to radon. The advantages and disadvantages of these methods are described here as well as their potential in future radon epidemiological studies.

Air Pollutants, Radioactive↗
PubMed2001

Experience from retrospective radon exposure estimations for individuals in a radon epidemiological study using solid-state nuclear track detectors.

The relation between increased risk of lung cancer and exposure to indoor radon is assessed in epidemiological studies. Both the quality and reliability of smoking data and the radon exposure data are of primary importance. Contemporary measurement of radon concentration in the dwellings of individuals in a case-control study is traditionally used to assess past history of radon exposure. These assessments are somewhat unreliable since presently measured radon concentration might not be representative for a given location long ago. The measurement of long-lived decay products from 222Rn remaining indoors on hard surfaces, such as glass, makes it possible to assess the exposure to indoor radon. At the Swedish Radiation Protection Institute, a combination of two different solid-state nuclear track detectors has been developed to assess the 210Pb activity implanted in glass surfaces by measuring 210Po alpha activity. This detector (a RETRO detector) is used in the Swedish radon epidemiological case-control study of non-smokers with the aim to provide an alternative estimate of individual radon exposure and to evaluate the usefulness of RETRO measurements. A total of 576 different objects were found and 568 were measured. For 225 individuals, we measured two personal objects that had been in the same person's possession for more than 20 years. The standard deviation of the average radon concentration obtained from these two objects had a median value of 13 Bq/m3 indicating a precision of exposure of approximately 20%. The correlation between 210Po surface activity measured earlier and the mean values of radon concentrations in a number of Swedish dwellings is used to estimate the historical, average radon concentration. This average correlation factor seems also to be valid for measurements in the non-smoker epidemiological study.

Air Pollutants, Radioactive↗
PubMed2001

The Iowa radon lung cancer study--phase I: Residential radon gas exposure and lung cancer.

Exposure to high concentrations of radon (222Rn) progeny produces lung cancer in both underground miners and experimentally-exposed laboratory animals. The goal of the study was to determine whether or not residential radon exposure exhibits a statistically significant association with lung cancer in a state with high residential radon concentrations. A population-based, case-control epidemiologic study was conducted examining the relationship between residential radon gas exposure and lung cancer in Iowa females who occupied their current home for at least 20 years. The study included 413 incident lung cancer cases and 614 age-frequency-matched controls. Participant information was obtained by a mailed-out questionnaire with face-to-face follow-up. Radon dosimetry assessment consisted of five components: (1) on-site residential assessment survey; (2) on-site radon measurements; (3) regional outdoor radon measurements; (4) assessment of subjects' exposure when in another building; and (5) linkage of historic subject mobility with residential, outdoor, and other building radon concentrations. Histologic review was performed for 96% of the cases. Approximately 60% of the basement radon concentrations and 30% of the first floor radon concentrations of study participants' homes exceeded the US Environmental Protection Agency action level of 150 Bq m(-3) (4 pCi l(-1)). Large areas of western Iowa had outdoor radon concentrations comparable to the national average indoor value of 55 Bq m(-3) (1.5 pCi l(-1)). Excess odds of 0.24 (95% CI = -0.05-0.92) and 0.49 (95% CI = 0.03-1.84) per 11 WLM(5-19) were calculated using the continuous radon exposure estimates for all cases and live cases, respectively. Slightly higher excess odds of 0.50 (95% CI = 0.004-1.80) and 0.83 (CI = 0.11-3.34) per 11 WLM(5-19) were noted for the categorical radon exposure estimates for all cases and the live cases. A positive association between cumulative radon gas exposure and lung cancer was demonstrated using both categorical and continuous analyses. The risk estimates obtained in this study indicate that cumulative radon exposure presents an important environmental health hazard.

Adult↗
PubMed2001

Ventilation and radon transport in Dutch dwellings: computer modelling and field measurements.

In 1995 and 1996 radon concentrations and effective air flows were measured in approximately 1500 Dutch dwellings built between 1985 and 1993. The goal of this investigation was to describe the trend in the average radon concentration by supplementing the first survey on dwellings built up to 1984 and to quantify the contributions of the most important sources of radon. In the living room of new dwellings the average radon concentration was 28 Bq m(-3), which is 50% higher than in dwellings built before 1970. Measurements of effective air flows showed the most important source of radon in the living room of new dwellings to be the building materials, with an average contribution of 70%. The other 30% comprised outside air and air from the crawl space in equal quantities. The long-term increase in the indoor radon concentration is mainly due to improvements in insulation since 1970, resulting in a fourfold decrease in infiltration through the building shell. Model calculations, supplementing the field measurements, confirmed the dominant effect of increasing airtightness of dwellings compared to effects of the observed trend in the use of building materials.

Air Pollutants, Radioactive↗
PubMed2001

Radon permeability and radon exhalation of building materials.

High radon concentrations indoors usually depend on the possibilities of radon penetration from the surrounding soil into the buildings. Radon concentrations in dwellings up to 100 kBq/m3 were found in some special regions (i.e. Schneeberg/Saxony, Umhausen/Tyrol), where the soil shows a high uranium content and additionally, a fast radon transport in the soil is possible. To reduce the radon exposure of the inhabitants in these 'radon prone areas' it is necessary to look for building and insulating materials with low radon permeability. We examined several building materials, like cements, concretes and bricks of different constitutions for their diffusion coefficients and their exhalation rates. The insulating materials, like foils and bitumen were tested also on their radon tightness. The measurements were performed with an online radon measuring device, using electrostatic deposition of 218Po ions onto a surface barrier detector and subsequent alpha spectroscopy. The mean diffusion lengths for the investigated building materials range from lower than 0.7 mm (i.e. for plastic foil), up to 1.1 m for gypsum. The diffusion length R was calculated from the diffusion coefficient D with R = square root(D/lambda). If the thickness of the material is more than 3 times the diffusion length, then it is called radon-tight. The mean 222Rn exhalation rates for the building materials varied between 0.05 and 0.4 mBq/m2s. The samples were investigated as stones, plates, blocks, foils, coatings, powders etc., no statement can be made about working at the construction site of a building. Also the fabrication and processing of the materials has to be considered, because the material characteristics may have changed.

Air Pollutants, Radioactive↗
PubMed2001

Size distribution, equilibrium ratio and unattached fraction of radon decay products under typical indoor domestic conditions.

In order to characterise the behaviour of radon decay products under domestic conditions, long-term measurements were carried out from May 1997 to April 1998 in a typical dwelling located in Brittany (France). In particular, the unattached fraction and equilibrium factor were continuously measured. Moreover, the size distributions of unattached and attached radon daughters were investigated by using specific instruments implemented in the laboratory. All these experiments were carried out under different typical aerosol conditions. The results evidenced the strong influence exerted by the characteristics (concentration, size) of ambient aerosol on these different parameters.

Aerosols↗
PubMed2001

Radiation performance index for Dutch dwellings: consequences for some typical situations.

This paper describes the new approach to control radiation exposure from natural sources to inhabitants of dwellings that is presently being considered in the Netherlands. The goal of this approach is to uphold the current rather favorable situation (average annual effective dose due to indoor radon and external radiation in dwellings is approx. 1 mSv). To achieve this goal a model is foreseen to predict the potential effective dose an inhabitant may receive from a dwelling on basis of its building plan. A scheme to calculate this dose is proposed in this paper. In future, such a scheme will be included in the Dutch Building Codes and houses to be built will be evaluated by using this scheme and comparing the results with, yet to be posed, limits to the potential effective dose.

Air Pollutants, Radioactive↗
PubMed2001

Results and conclusions of the Austrian radon mitigation project 'SARAH'.

The Austrian radon mitigation joint research project SARAH (supported by the Austrian Ministry of Economy and the Government of Upper Austria), a 2-year follow-up study of the Austrian National Radon Project (ONRAP), was started in 1996. The objectives of the research project were to find simple, cost-effective experimental methods for the characterisation of the radon situation in dwellings and to evaluate technically and economically the implementation of state of the art remedial actions for Austrian house types. After an intercomparison exercise of the assigned radon measuring instruments and detectors five houses were closely examined in regions with elevated radon levels in the federal state of Upper Austria. In this research work for the first time an extended Blower-Door method (which is conventionally used for determining the tightness of buildings) was successfully applied to radon diagnosis of buildings. In this paper the methods used for the radon diagnosis, the applied mitigation measures and the related technical and economical aspects are discussed. In conclusion of the results of this project a common strategy for solving the radon problem in Austria in the future is presented briefly.

Air Pollutants, Radioactive↗
PubMed2001

Measurements of deposition velocity of radon decay products for examination of the correlation between air activity concentration of radon and the accumulated Po-210 surface activity.

The retrospective determination of radon exposure levels in dwellings by means of the measurement of the Po-210 surface activity is subject to various uncertainties. These result partly from the values assumed for the equilibrium factor F and for the unattached fraction f(p), and, more importantly, from differences in the deposition velocities of short-lived decay products of Rn-222, caused by varying conditions of turbulence. In order to evaluate the actual range of the variation which occurs under German living conditions, measurements for the deposition velocity parameter were carried out in several dwellings in which increased levels of radon were present. The statistical evaluation of the measurements produced a mean deposition velocity of 1.7 m/h for Po-218 and 0.4 m/h for Pb-214, and a relative standard deviation in the measured values of as low as approximately 50%. This lay significantly below the uncertainty value expected from the literature and would seem to justify the retrospective determination of the radon exposure from Po-210 surface activity measurement for use in, for example, epidemiological studies.

Air Pollutants, Radioactive↗
PubMed2001

Correlation of 210Po implanted in glass with radon gas exposure: sensitivity analysis of critical parameters using a Monte-Carlo approach.

In recent years, 210Po implanted in glass artefacts has been used as an indicator of the mean radon gas concentration in dwellings in the past. Glass artefacts have been selected in many dwellings and the alpha-recoil implanted 210Po concentration has been measured using various techniques. Some of these retrospective techniques use a model to estimate the retrospective radon gas on the basis of this surface 210Po activity. The accumulation of 210Po on glass surfaces is determined by the deposition regime over the exposure period. The 210Po activity is determined not only by the radon progeny deposition velocities, but by other room parameters such as ventilation rate, aerosol conditions and the surface to volume ratio of the room. Up to now in using room models, a nominal or 'base-case' scenario is used, i.e. a single value is chosen for each input parameter. In this paper a Monte-Carlo analysis is presented in which a probability distribution for each parameter is chosen, based on measurements quoted in the literature. A 210Po surface activity is calculated using a single value drawn from each of the parameter distributions using a pseudo-random number generator. This process is repeated n times (up to 20,000), producing n independent scenarios with corresponding 210Po values. This process permits a sensitivity analysis to be carried out to see the effect of changes in inputs on the model output.

Aerosols↗
PubMed2001

Mapping the geogenic radon potential in Germany.

Mapping the geogenic radon potential in Germany is a research project initiated by the German Federal Ministry for the Environment, Conservation and Reactor Safety. The project was aimed to develop a standard methodology for the estimation of a geogenic radon potential and to apply this method to map the region of Germany as an overview for planning purposes. The regionalisation results from a distance-weighted interpolation of the site-specific values of radon concentration in soil gas and in situ gas permeability of soils on a regular grid considering the corresponding geological units. The map of Germany in a scale of 1:2 million is based on the radon concentration in soil gas as an estimator of the geogenic radon potential assuming the 'worst case' of uniform highest permeability. The distribution is subdivided into categories of low (< 10 kBq/m3), medium (10-100 kBq/m3), increased (100-500 kBq/m3) and high (> 500 kBq/m3) radon concentration. High values occur especially in regions with granites and basement rocks of Paleozoic age, and are proven by measurements in 0.03% of the total area. Many of these regions are also known for their enhanced indoor values. The class with increased values takes a portion of 7.86% and likewise occurs mainly in regions with outcrops of folded and metamorphic basement, but also of some Meso- and Cenozoic sediments with increased uranium contents and/or higher emanation coefficients. For 67.3% of the country, the radon concentration is classified as 'medium', and an assignment to specific geological units cannot be made at the map scale considered. Low radon contents, where protective measures against radon are usually not considered, are found in the geologically rather homogeneous part of northern Germany with unconsolidated Cenozoic sediments, covering approximately 25% of the total country. It is of course not possible to predict the indoor radon concentration of single houses from these maps, because construction type and structural fabric of houses are essentially governing the extent to which subsoil radon potential affects the indoor concentration. Besides this, in places with site-specific geochemical, structural and soil-physical properties, local radon anomalies may occur which were not recorded in the course of the wide-meshed screening study.

Air Pollutants, Radioactive↗
PubMed2001

Mapping indoor radon-222 in Denmark: design and test of the statistical model used in the second nationwide survey.

In Denmark, a new survey of indoor radon-222 has been carried out, 1-year alpha track measurements (CR-39) have been made in 3019 single-family houses. There are from 3 to 23 house measurements in each of the 275 municipalities. Within each municipality, houses have been selected randomly. One important outcome of the survey is the prediction of the fraction of houses in each municipality with an annual average radon concentration above 200 Bq m(-3). To obtain the most accurate estimate and to assess the associated uncertainties, a statistical model has been developed. The purpose of this paper is to describe the design of this model, and to report results of model tests. The model is based on a transformation of the data to normality and on analytical (conditionally) unbiased estimators of the quantities of interest. Bayesian statistics are used to minimize the effect of small sample size. In each municipality, the correction is dependent on the fraction of area where sand and gravel is a dominating surface geology. The uncertainty analysis is done with a Monte-Carlo technique. It is demonstrated that the weighted sum of all municipality model estimates of fractions above 200 Bq m(-3) (3.9% with 95%-confidence interval = [3.4,4.5]) is consistent with the weighted sum of the observations for Denmark taken as a whole (4.6% with 95%-confidence interval = [3.8,5.6]). The total number of single-family houses within each municipality is used as weight. Model estimates are also found to be consistent with observations at the level of individual counties. These typically include a few hundred house measurements. These tests indicate that the model is well suited for its purpose.

Air Pollutants, Radioactive↗