Radon and Natural Ventilation in Newer Danish Single-Family Houses

Abstract To investigate the effect of ventilation on indoor radon (²²²Rn), simultaneous measurements of radon concentrations and air change rates were made in 117 Danish naturally ventilated slab-on-grade houses built during the period 1984–1989. Radon measurements (based on CR-39 alpha-track detectors) and air change rate measurements (based on the perfluorocarbon tracer technique; PFT) were in the ranges 12–620 Bq m^?3 and 0.16?0.96 h^?1, respectively. Estimates of radon entry rates on the basis of such time-averaged results are presented and the associated uncertainty is discussed. It was found that differences in radon concentrations from one house to another are primarily caused by differences in radon entry rates whereas differences in air change rates are much less important (accounting for only 80,0% of the house-to-house variation). In spite of the large house-to-house variability of radon entry rates it was demonstrated, however, that natural ventilation does have a significant effect on the indoor radon concentration. Most importantly, it was found that the group of houses with an air change rate above the required level of 0.5 h^?1 on average had an indoor radon concentration that was only 50% (0.5±0.1) of that of the group of houses with air change rates below 0.5 h^?1. The reducing effect of increased natural ventilation on the indoor radon concentration was found to be due mainly to dilution of indoor air. No effect could be seen regarding reduced radon entry rates.     

Temporal and small-scale spatial variability of Rn gas in a soil with a high gravel content

To quantify the small-scale spatial and long-term temporal variability of the ²²²Rn concentration in a typical soil with a high gravel content, we monitored this radionuclide every week for 1 year, at 0.5 m and 1.0 m depth at nine sampling positions in a 20×20-m field, and at the four corners of a 1×1-m plot within this field. The data show that the ²²²Rn soil gas concentrations exhibited a spatial variability which is characterised in the 20×20-m field by coefficients of variation from 20 to 30% at 0.5 m depth, and from 15 to 20% at 1.0 m depth. Within the 1×1-m plot, these values were at both depths only 5–10%. In the winter months, the ²²²Rn soil gas concentration was higher at 0.5 m depth compared to that at 1.0 m depth. However, in the summer months, the opposite behavior was observed. Time series analysis of the data showed that the ²²²Rn concentrations in the soil gas determined at a given position and depth is strongly correlated with the preceding observation at this point. In addition, strong cross-correlations are present between the ²²²Rn concentration time series observed at different positions and depths. The above results are used to calculate the probability for estimating, within a given deviation, the annual mean ²²²Rn soil gas concentration from a single measurement on an arbitrary day of a given month at a limited number of sampling positions only. Because the ²²²Rn concentration in the soil gas can vary considerably even within 1 month, ²²²Rn measurement obtained only once in a given month (especially in January and February) cannot be used to obtain a good estimate of the mean annual radon concentration, even if a large number of samples in the field are taken.     

Indoor 222Rn in Tennessee Valley Houses: Seasonal,Building, and Geological Factors

A two-season survey of indoor ²²²Rn concentrations was conducted in 226 occupied houses in Roane County, TN, during 1985 and 1986. A similar survey of 86 houses in Madison County, AL, was conducted in 1988 and 1989. Alpha track detectors were placed in each of the houses for three or more months during the winter heating season. Detectors were placed at the same sampling sites during the following cooling season. In this study, comparisons were made between winter and summer sampling times and between building types. For the data from Madison County, additional comparisons were made among regions of the county that differed in geological characteristics, especially the thickness of overburden above the Chattanooga Shale layer a geological stratum that has high concentrations of ²²⁶Ra and is widely found in the southeastern United States. The geometric means of summer and winter measurements in Roane County were 33 and 54 Bq m^?3, respectively. For Madison County, the summer and winter geometric means were 121 and 88 Bq m^?3, respectively. The winter ²²²Rn concentrations for houses in Roane Coutuy exceeded summer ²²²Rn concentrations, as is generally the case for houses in the US. For houses in Madison County, we found the opposite and atypical situation of higher ²²²Rn concentrations in the summertime. ²²²Rn concentrations differed significantly among groups of houses in distinguishable regions of Madison County. Substructure and other building factors had no observable effect on indoor ²²²Rn concentrations found in this study.     

Radiation dose from dissolved radon in potable waters of the Bangalore environment,South India

Potable waters from various locations of the Bangalore environment were investigated for their ²²²Rn concentrations by the emanometry method. About 94 groundwater (borewell) samples were analysed for ²²²Rn concentrations and found to vary in the range 5.3–283.4 Bq L^?1 with a mean value of 87 Bq L^?1. Frequency distribution showed the ²²²Rn concentration in a large number of samples in the range of 0–50 Bq L^?1. From the measured concentrations, the effective doses (lung and stomach) for the population of the region were estimated. The effective dose was found to vary from 42.6 to 2280.2 µSv y^?1 with a mean value 702.5 µSv y^?1. The effect of boiling of water showed a drastic reduction in the ²²²Rn concentration. The results of the present investigation are systematically analysed, compared with the literature values and discussed.     

Radon hazard in shallow groundwaters: Amplification and long term variability induced by rainfall

²²²Rn concentrations have been determined with a RAD7 radon detector in shallow groundwaters of the Pietramelara Plain, north-western Campania, southern Italy, where pyroclastic deposits, along with recent stream alluvial sediments, come in contact with Mesozoic carbonate reservoirs. The aim of this study has been to study the annual variation of ²²²Rn concentration in the shallow groundwaters, scarcely considered in the literature and of obvious relevance for radon hazard evaluation. Our results definitely show that ²²²Rn levels are characterized by a clear annual periodicity, strictly related to rainfall and water table levels, with a pronounced difference between the dry and the wet season. In this last case with concentrations increasing up to two orders of magnitude (up to two times the lower threshold given in the Recommendation 2001/928/EURATOM for public waters). In relation to this, experimental field data will be presented to demonstrate that this variability is due to purely hydrological mechanisms, mainly rinse out and discharge that control leaching efficiency. The detected cycle (Radon Hydrological Amplification Cycle, RHAC) has been generalized for the Mediterranean Tyrrhenian climate. The marked and seasonally persistent amplification in ²²²Rn levels poses the problem of evaluating the epidemiological risk brought up by this previously not yet reported mechanism. This mechanism, occurring in shallow groundwaters, very likely should strongly influence indoor radon levels via groundwater-soil-building exchange.     

Radon hazard in shallow groundwaters II: dry season fracture drainage and alluvial fan upwelling

²²²Rn concentrations have been measured in a well located on the edge of a large Pleistocene-Holocene fan and belonging to the shallow pyroclastic aquifer of the Pietramelara Plain, southern Italy. The aim of this study has been both to characterise the hydrological inputs that determine the influx of ²²²Rn to the shallow aquifer and to understand the correlations between ²²²Rn, major ions, physical-chemical parameters and rainfall. Results obtained from the time series indicate that the studied well shows a ²²²Rn variability that is inconsistent with a mechanism of pure hydrological amplification, such as described in Radon hazard in shallow groundwaters: Amplification and long term variability induced by rainfall (De Francesco et al., 2010a). On the contrary, in this well hydrological amplification appears to be mainly tied to the upwelling of alluvial fan waters, rich in radon, in response to pistoning from recharge in the carbonate substrate. This upwelling of alluvial fan waters occurs during almost the whole period of the annual recharge and is also responsible of the constant increase in ²²²Rn levels during the autumn-spring period, when both the water table level and weekly rainfall totals drop. Furthermore, a rapid delivery mechanism for ²²²Rn likely operates through fracture drainage in concomitance with the very first late summer-early autumn rains, when rainfall totals appear largely insufficient to saturate the soil storage capacity. Results obtained from this study appear to be particularly significant in both radon hazard zoning in relation to the shallow aquifer and possibly also for indoor radon, owing to possible shallow aquifer-soil-building exchanges. Moreover, both the spike-like events and the long wave monthly scale background fluctuations detected can also have potential significance in interpreting ²²²Rn time series data as seismic and/or volcanic precursors. Finally, ²²²Rn has proved to be an excellent tracer for hydrological inputs to the shallow aquifer when combined with major ions, physical-chemical data and geological and geomorphological controls.     

Impact of constructional energy‐saving measures on radon levels indoors

Energy‐efficient building refurbishment has the aim of saving energy and thus reducing CO₂ emissions. Increased energy efficiency of a building often implies reduced air exchange. Together with other indoor air quality problems, this may lead to an increase in indoor radon concentration (Rn‐222). In order to investigate the extent of this problem, measurements of radon concentration in energy‐efficient refurbished and low‐energy houses (passive houses) were carried out. Track etch detectors were exposed in each type of building over a period of 1 year. A reference sample of non‐refurbished non‐passive buildings was drawn from the National Radon Database for comparison. Buildings were selected that have the same radon relevant properties and were built on comparable geological subsoil like those investigated. The reference sample was compiled in such a way that the measured values from the rooms on the ground floor of the refurbished and passive houses were each assigned a measured value from the database. The statistical analysis shows that the houses refurbished for energy efficiency have a wider distribution of radon concentrations indoors than the non‐refurbished ones. Both the mean value and the median of the radon concentration have nearly doubled in buildings refurbished for energy efficiency. The difference is statistically significant. On the other hand, there is no significant difference between the distributions of passive houses and houses not refurbished for energy efficiency.     

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.     

Radon measurement studies in workplace buildings of the Rawalpindi region and Islamabad Capital area, Pakistan

A survey concerning measurement of the indoor radon levels has been carried out in 105 workplaces of the Rawalpindi region and Islamabad Capital Territory using CR-39 based radon detectors. The main objective of this study was to assess the health hazard due to the indoor radon. CR-39 based NRPB type detectors were installed in offices/rooms located on first floors, ground floors and basements and were exposed to indoor radon for six months. The measured indoor radon concentration in the buildings surveyed ranged from 12 ± 5 to 293 ± 19 Bq m⁻³ with an overall mean value of 64 ± 32 Bq m⁻³. The highest mean radon concentration (113 ± 48 Bq m⁻³) was observed in the offices located in basements of the Rawalpindi city. The overall average annual effective dose in the studied workplaces was estimated to be 0.61 ± 0.30 mSv. The mean annual effective doses in basements, ground floor and first floor were found to be 0.87 ± 0.34 mSv, 0.55 ± 0.28 mSv, and 0.47 ± 0.29 mSv, respectively. These values are less than the action level recommended by International Commission on Radiological Protection.     

Calibration of a solid state nuclear track detector for the measurement of indoor levels of radon and its daughters

Time-integrated measurements of environmental radiation levels are commonly carried out using solid state nuclear track detectors (SSNTD). These detectors are particularly suitable for monitoring indoor radiation, however they should be calibrated for the measurement of the levels of radon (Rn) and its daughters likely to be found in dwellings. This paper reports the results of experiments conducted to calibrate cellulose nitrate film. LR-115 type II, which is used for the measurement of Rn levels in indoor environments of dwellings in India. The detector was exposed to varying concentrations of Rn inside an exposure chamber both in Bare and in Cup with membrane modes. We obtained calibration factors of 1.05 x 10(-3) tracks cm2 day-1 per pCi m-3 (2.84 x 10(-2) tracks cm-2 day-1 per Bq m-3) and 4.8 x 10(2) tracks cm-2 day-1 per WL of Rn.     

Population dose in the vicinity of old Spanish uranium mines

Regional surveys were conducted to determine exposure to natural sources of radiation for people in the vicinity of old Spanish uranium mines. The surveys evaluated indoor radon concentrations and outdoor and indoor external gamma dose rates. Indoor radon concentrations were measured in 222 dwellings by means of nuclear track-etched detectors. The terrestrial gamma ray dose rate was measured outdoors and indoors at a total of 256 points and 115 points, respectively. Estimates mean annual effective doses for the six areas studied ranged from 3.2 to 5.1 mSv per year, which is between 1.2 and 2 times higher than the average national value.     

Relevance of air conditioning for 222Radon concentration in shops of the Savona Province, Italy

Radon (222Rn) concentration was evaluated in shops of the Savona Province, Italy, between summer 2002 and winter 2002-2003. The main characteristics of each shops were recorded through a questionnaire investigating the ventilation rate and factors related to 222Rn precursors in the soil and the construction materials. The main variables that were related to radon concentration were the following: age of the building, level of the shop above ground, season of the year, wind exposure, active windows, and type of heating system. Shops equipped with individual air heating/conditioning systems exhibited radon concentrations that were three times higher than those of shops heated by centralized furnaces. Our data indicate that the level of pollution in the shops was of medium level, with an expected low impact on the salespersons' health. Only in wintertime, the action level of 200 Bq m(-3) for the confined environment was reached in 10 shops equipped with individual air heating/conditioning systems.     

Geological controls to the indoor radon distribution in southern Belgium

Soils and rocks are the predominant source of indoor radon (Rn) in southern Belgium. We have studied the correlations between geological features and indoor Rn concentrations using an indoor Rn data set of approx. 1700 short-term measurements. The sediments in the study region are divided into 11 geological series or 43 stages and 16 rock types. The results show a striking relation between indoor Rn concentration and the geological factors.     

In situ gamma spectroscopy to characterize building materials as radon and thoron sources

In situ gamma spectroscopy is widely utilized to determine the outdoor gamma dose rate from the soil and to calculate the natural and artificial radionuclide concentration and their contribution to the dose rate. The application of in situ gamma spectroscopy in indoor environments can not supply quantitative information about activity concentration of radionuclides in building materials, but this technique can provide interesting information about building materials as radon source. In fact, a method based on analyses of gamma spectra data has been developed by the authors to provide, in field, quantitative estimation of disequilibrium in 226Ra and 228Ac sub-chains due to 222Rn and 220Rn exhalation. The method has been applied to data of gamma spectroscopy measurements carried out with HPGe detector (26%) in seven dwellings and one office in Rome. The first results of the data analysis show that, as regards especially the 226Ra sub-chain disequilibrium, different building materials (tuff, concrete, etc.) can show very different characteristics. If, in addition to the spectrometric data, other indoor environment parameters (indoor gamma dose rates, room dimensions, wall thickness, etc.) (Bochicchio et al., Radiat Prot Dosim 1994;56(1-4):137-140; Bochicchio et al., Environ Int 1996a;22:S633-S639) are utilized in a room model, an evaluation of 226Ra, 228Ac and 40K activity concentration and an indication of the exhalation features, by means of estimation of exhaled 222Rn activity concentration, can be achieved.     

House dust mites (Der p 1, Der f 1), cat (Fel d 1) and cockroach (Bla g 2) allergens in indoor work-places (offices and archives)

BACKGROUND: Exposure to indoor allergens has already been shown to occur in many public places, including workplaces, in several countries. Aim of this study was to measure the levels of house dust mites, cat and cockroach allergens in indoor workplaces (offices and archives) in Italy and to evaluate the possible relationships between allergen levels and building characteristics, type of ventilation, indoor relative humidity and temperature. METHODS: Der f 1 and Der p 1, Fel d 1, Bla g 2 were measured by ELISA in dust samples collected from floors or upholstered seats of 160 workplaces. RESULTS: Detectable Der p 1 levels were found in 86 (54%) workplaces Der f 1 in 87 (55%), Fel d 1 in 86 (54%) and Bla g 2 in 3 (1.9%). Der p 1 allergen concentrations expressed per weight were higher than the proposed sensitization thresholds in 7 samples, Der f 1 in 5, Fel d 1 in 6 and Bla g 2 in 3. The highest allergen levels were detected in samples from upholstered seats. A significant correlation was found between Der f 1 level on floors, expressed per surface, and indoor temperature (r = 0.39; P < 0.01). CONCLUSIONS: In our study we found that upholstered seats in workplaces in Italy may constitute a significant reservoir both of house dust mites and cat allergens. Exposure to these allergens in workplaces may represent a risk factor for elicitation of symptoms and/or induction/maintenance of inflammation in allergic individuals and might also constitute a risk factor for sensitization.     

Meteorological parameters contributing to variability in 222Rn activity concentrations in soil gas at a site in Sapporo, Japan

Continuous ²²²Rn monitoring in soil gas since November 22, 2004 has revealed variability in activity concentration with time in the semi-natural woods on the campus of Hokkaido University in Sapporo, Japan. Among various factors affecting soil radon levels and variability, temperature was found to be dominant during three seasons when activity concentrations of ²²²Rn showed a diurnal high and nocturnal low with a boundary around 10 o'clock in the morning. This pattern was disturbed by low pressure fronts with occasional rain. The activity gradually decreased as soil temperatures decreased from late November to mid-December. After the ground surface was completely covered with snow, soil radon levels became low with a small fluctuation. There were several peaks of ²²²Rn on the time-series chart in winter. Those peaks appearing in early winter and early spring may be interpreted by considering meteorological parameters. In a few cases, the radon activity suddenly increased with increasing pressure in the soil at a depth of 10 cm, which may be associated with subsurface events such as seismic activity in the area.     

A prediction method for radon in groundwater using GIS and multivariate statistics

Radon (222Rn) in groundwater constitutes a source of natural radioactivity to indoor air. It is difficult to make predictions of radon levels in groundwater due to the heterogeneous distribution of uranium and radium, flow patterns and varying geochemical conditions. High radon concentrations in groundwater are not always associated with high uranium content in the bedrock, since groundwater with a high radon content has been found in regions with low to moderate uranium concentrations in the bedrock. This paper describes a methodology for predicting areas with high concentrations of 222Rn in groundwater on a general scale, within an area of approximately 185x145km2. The methodology is based on multivariate statistical analyses, including principal component analysis and regression analysis, and investigates the factors of geology, land use, topography and uranium (U) content in the bedrock. A statistical variable based method (the RV method) was used to estimate risk values related to different radon concentrations. The method was calibrated and tested on more than 4400 drilled wells in Stockholm County. The results showed that radon concentration was clearly correlated to bedrock type, well altitude and distance from fracture zones. The weighted index (risk value) estimated by the RV method provided a fair prediction of radon potential in groundwater on a general scale. Risk values obtained using the RV method were compared to radon measurements in 12 test areas (on a local scale, each of area 25x25km2) in Stockholm County and a high correlation (r=-0.87) was observed. The study showed that the occurrence and spread of radon in groundwater are guided by multiple factors, which can be used in a radon prediction method on a general scale. However, it does not provide any direct information on the geochemical and flow processes involved.     

Increased radon concentrations in classrooms used for pottery workshops.

In a pilot study of nine schools the radon (Rn) concentrations were measured systematically. The mean radon concentrations in the classrooms on the ground-floor and on higher floors was 52 Bq/m3, which is equivalent to the mean values in Central Europe. Several of the basement rooms used for handicraft lessons had significantly increased Rn levels with a mean concentration of 617 Bq/m3. In all other parts of the basement Rn levels were clearly lower with a mean concentration of 136 Bq/m3. In the rooms used for handicraft lessons numerous articles of pottery were on display. After removing these the Rn in air concentration was reduced to a mean value of 83 Bq/m3.     

Modelling the effect of air exchange on 222Rn and its progeny concentration in a tunnel atmosphere

The effect of air exchange on the concentration of 222Rn and its progeny in the atmosphere of the Roselend tunnel, in the French Alps, is estimated using a box modelling scheme. In this scheme, the atmosphere is divided into a small number of well mixed zones, separated by flow restricted interfaces, characterized by their exchange rate. A four-box model, representing the three sections of the tunnel present until 2001 and an adjacent inner room, accounts for the spatial variations of the background 222Rn concentration, and for the time structure of transient bursts observed regularly in this tunnel since 1995. A delay of the order of one day, observed during some transient bursts in the inner room with respect to the end of the tunnel, is accounted for if the bursts are assumed to be mainly generated in the end section of the tunnel, and stored temporarily in the inner room via air exchange. The measured radon concentration is reproduced by this model for an air exchange rate of 1.6x10(-6) s-1 between the room and the tunnel, in a context of a global ventilation rate of 10(-5) s-1 in the tunnel. Gradual onset and decay phases, varying from burst to burst, are also suggested. The equilibrium factor of 222Rn with its progeny, measured in 2002 with values varying from 0.60+/-0.05 to 0.78+/-0.06, is interpreted with a five-box model representing the five sections of the tunnel present after 2001. This model indicates that the equilibrium factor does not provide additional constraints on the air exchange rates, but the value of the deposition rate of the unattached short-lived radon progeny can be inferred, with results varying from 0.2 to 6 h-1 in the various sections. This study illustrates the benefits of a simple modelling tool to evaluate the effect of natural ventilation on 222Rn and its progeny concentration in underground cavities, which is important for radioprotection and for a reliable characterization of signatures of hydrogeological or geodynamical processes. Conversely, this study shows that 222Rn and progeny measurements provide a non-invasive method for characterizing natural ventilation conditions in delicate underground cavities, such as painted caves.