Models of radon exhalation from building structures: General and case-specific solutions.

Assessing the radon activity that exhales from building structures is crucial to identify the best strategies to prevent radon from entering a building or reducing its concentration in the inhabited spaces. The direct measurement is extremely difficult, so the common approach has consisted in developing models describing the radon migration and exhalation phenomena for building porous materials. However, due to the mathematical complexity of comprehensively modelling the radon transport phenomenon in buildings, simplified equations have been mostly adopted until now to assess the radon exhalation. A systematic analysis of the models applicable to radon transport has been carried out and it has resulted in four models differing in the migration mechanisms - only diffusive or diffusive and advective - and the presence of inner radon generation. The general solutions have been obtained for all the models. Moreover, three case-specific sets of boundary conditions have been formulated to account for all the actual scenarios occurring in buildings: both perimetral and partition walls and building structures in direct contact with soil or embankments. The corresponding case-specific solutions obtained serve as a key practical tool to improve the accuracy in assessing the contribution of building materials to indoor radon concentration according to the site-specific installation conditions in addition to the material inner properties.

Extreme reverse seasonal variations of indoor radon concentration and possible implications on some measurement protocols and remedial strategies.

Indoor radon levels in dwellings are typically higher in cold months than in warm ones. The indoor radon concentration might experience an inverse seasonal behaviour - i.e., radon levels much higher in summer than in winter - under specific circumstances. In the framework of a study on long-term variations of annual radon concentration carried out in some tens of dwellings in Rome and surrounding small towns, two dwellings with very high - up to extreme - reverse seasonal variations were accidently discovered. These dwellings were located in a volcanic area, and they are both south-oriented and located on the lower part of a hill. In one of them, radon concentration was monitored by a continuous radon monitor for two years to find out when the greatest rises in radon levels occur. The indoor radon concentration resulted to experience extremely rapid, i.e. very few hours, increases up to 20 000 Bq m-3 during the spring period (i.e., April, May, and June especially). After about ten years from the first observation, the indoor radon concentration of the same house was monitored again for about five years: radon concentration peaks previously observed were found to be unchanged in terms of absolute values, duration, rising time and occurrence period. These reverse seasonal variations may lead to significant underestimation of the actual annual average radon concentration in case of measurements lasting less than one year if performed during the cold season and especially when seasonal correction factors are used. Moreover, these results suggest adopting specific measurement protocol and remediation strategies in houses having some peculiar characteristics, mainly regarding orientation, position, and attachment to the ground.

Impact of temporal variability of radon concentration in workplaces on the actual radon exposure during working hours.

For workplaces where significant diurnal variations in radon concentrations are likely, measurements to evaluate average radon concentration during working hours could be useful for planning an optimized protection of workers according to the 2013/59/Euratom Directive. However, very few studies on this subject, generally limited to periods of few weeks, have been published. Therefore, a study has been conducted to evaluate the actual long-term radon exposure during working hours for a sample of 33 workplaces of four different types (postal offices, shops, restaurants, municipal offices), mainly located at the ground floor, and with expected considerable air exchange rate occurring during working hours due to frequent entrance/exit of persons or mechanical ventilation. The results show that the difference between the average radon level during working hours and that one during the whole day is about 20% on average and ranges from 0 to 50%. These observed differences, generally smaller compared with those found in other similar studies, are nearly the same if the analysis is restricted to workplaces with annual radon level higher than 300 Bq m-3, and therefore natural or mechanical ventilation normally present during working hours of the monitored workplaces cannot be considered an effective mitigation measure. However, the costs and time-response characteristics of the active monitors, as those used for the present study, will probably allow using more frequently a similar measurement strategy in workplaces.

SHORT-TERM ANNUAL VARIATIONS OF RADON CONCENTRATION IN WORKPLACES: SOME RESULTS IN A RESEARCH INSTITUTE.

Many international and national regulations on radon in workplaces, including the 2013/59/Euratom Council Directive, are based on the annual average of indoor radon concentration, assuming it is representative of the long-term average. However, a single annual radon concentration measurement does not reflect annual variations (i.e. year-to-year variations) of radon concentration in the same location. These variations, if not negligible, should be considered for an optimized implementation of regulations. Unfortunately, studies on annual variations in workplaces can be difficult and time-consuming and no data have been published on scientific journals on this issue. Therefore, we carried out a study to obtain a first evaluation of short-term annual variations in workplaces of a research institute in Rome (Italy). The radon concentration was measured in 120 rooms (mainly offices and laboratories) located in 23 buildings. In each room, two 1-year long measurements were performed, with an interval between the two measurements of up to 3 years. The results show variability between the two 1-year long measurements higher than the variability observed in a sample of dwellings in the same area. Further studies are required to confirm the results and to extend the study to other types of workplaces.

REPRODUCIBILITY OF RADON-IN-WATER MEASUREMENTS BY EMANOMETRY TECHNIQUE.

The emanometry test method is one of the detection techniques of radon in water satisfying requirements of Directive 2013/51/Euratom with regards to the detection limit. Quality assurance (QA) procedures were developed and implemented for a measuring system relying on such a technique. These procedures mainly address the following: (i) the assembling of each component of the degassing circuit, (ii) the sample transfer from the transport container to the degassing vessel and (iii) the control of all the influencing quantities. Three identical measuring systems have been used to analyse in parallel 39 water samples with the aim to evaluate the effectiveness of QA procedures in terms of reproducibility. The results showed quite low variability (<15% for the 84% of measurements in the range 10-100 Bq L-1) among the three different measuring systems.

SPATIAL VARIABILITY OF INDOOR RADON CONCENTRATION IN SCHOOLS: IMPLICATIONS ON RADON MEASUREMENT PROTOCOLS.

The requirements about radon measurements in schools and public buildings included in most of the national and international legislations are generally restricted to all the rooms located at the ground floor and basement, assuming the soil beneath the building as the main source of indoor radon. In order to verify such an assumption for small buildings having at maximum two floors, a preliminary study was performed in 50 schools located in 15 municipalities of the Republic of Srpska. Results of this study suggest that a protocol requiring measurements at the ground floor only may be considered adequate. Due to the high radon spatial variability for rooms at the ground floor, it is preferable to require measurements in a high number of rooms (preferably in all of them) in order to assess the compliance with the reference level established by the legislation.

EVALUATION OF REPRESENTATIVENESS OF SAMPLES USED FOR INDOOR RADON SURVEYS.

The estimation of the indoor radon exposure of the population of a country is generally carried out by the means of surveys designed in order to have sample representativeness as a target (population-based survey). However, the estimates of radon concentration distributions could be affected by biases if sampling was not random or in case of differences between sample and target population characteristics. In this work, we performed a preliminary check of the representativeness of the sample used for the second Italian national survey aimed to evaluate radon concentration distribution in each Province. We found that sampled dwellings are mostly located in the main administrative centres, where average radon concentration is generally lower, as compared with the other towns of the Province. The potential source of bias identified in this work suggests to carefully control the occurrence of a sampling imbalance between 'main' cities and other cities of Province and to take it into account in data analysis.

Analytical method for evaluating (and correcting) the impact of outdoor radon concentration on the estimates of percentage of dwellings exceeding reference levels.

Outdoor radon concentration contributes to indoor radon levels, generally causing a shift from lognormal distribution of measured radon concentration data distribution, and it makes more challenging the estimation of radon distribution parameters on the basis of the lognormal assumption. In particular, lognormal assumption with no correction could lead to a significantly biased estimate of the percentage of dwellings exceeding a certain level, e.g. a reference level (RL), since this is based on biased estimates of geometric mean (GM) and geometric standard deviation (GSD) of radon concentration distribution. Subtracting to each measured data a constant outdoor radon level can usually compensate data distribution departure from log-normality (except for low radon levels), if the appropriate outdoor level value is chosen by means of a lognormal fit of the data. This approach - already (but not always) used in literature - cannot be applied in cases where all the data of radon concentrations are not available (e.g., for a review study). For these cases, this work presents an analytical method to quantitatively evaluate and correct the impact of outdoor on the lognormal distribution parameter estimates and, in particular, on the percentages of dwellings exceeding radon reference levels. The proposed method is applied to a number of possible situations, with different values of outdoor radon level, GM and GSD. The results show that outdoor radon levels generally produce an underestimation of the actual GSD parameter, which increases as the outdoor level increases, and in the worse cases, could lead to an underestimation higher than 50%. Consequently, if the outdoor contribution is not properly taken into account, the percentage of dwellings exceeding a certain RL is almost always underestimated, even by 80%-90% for RL equal to 300 Bq/m3. This could have implications for the classification of areas as regards radon concentration and for the estimation of avertable lung cancers attributable to radon levels higher than some possible RLs.

RADON REFERENCE LEVELS AND PRIORITY AREAS CONSIDERING OPTIMISATION AND AVERTABLE LUNG CANCERS.

Protection from radon exposure in workplaces and dwellings, as included in the latest relevant international regulations and recommendations, is based on the new concept of 'reference level' whose meaning is significantly different from that of previous 'action level' concept. In fact, whereas remedial actions had to be considered only for radon concentrations above the action level, actions to optimise radon exposure are requested with priority above reference level but optimisation should be applied also for radon concentrations below reference level. Similar considerations can be applied to the usually called 'Rn-prone' areas, which are here proposed to be regulated as 'priority' areas. The main implication of these new challenging concepts is a substantial increase of avertable lung cancer deaths, as it will be shown using Italian data. Some practical examples of possible policy actions fitting an approach based on these new concepts will also be given, which could be useful for the implementation of the Council Directive 2013/59/Euratom.

THE NATIONAL RADON ARCHIVE AS A USEFUL TOOL FOR DEVELOPING AND UPDATING THE NATIONAL RADON ACTION PLAN.

International recommendations and regulations require developing of National Radon Action Plans (NRAPs) to effectively manage the protection of workers and population from radon exposure. In Italy, a NRAP was published in 2002 and several activities have been carried out in this framework. Information and data regarding these and previous activities have been collected in a National Radon Archive (NRA). Activities carried out by institutionally involved institutes and agencies include several national and regional surveys, involving more than 50 000 indoor environments (dwellings, schools and workplaces), and remedial actions performed in ~350 buildings, largely in schools. Data collected in the NRA allowed also to estimate that lung cancer deaths attributable to radon exposure in Italy are ~3400 per year. On-going developments of the Italian NRA finalized to effectively use it as tool for developing, monitoring and updating the NRAP are also described.

The relation between radon in schools and in dwellings: A case study in a rural region of Southern Serbia.

Recognized as a significant health hazard, radon (Rn) has been given increasing attention for years. Surveys of different kinds have been performed in many countries to assess the intensity and the geographical extent of possible Rn problems. Common surveys cover mainly dwellings, the indoor place with highest occupancy, and schools, where people spend a large fraction of their lifetime and which can also be considered exemplary for Rn exposure at workplaces; it has however been observed that relating them is difficult. It was unclear whether residential Rn at a location, or in a region, can be predicted by Rn at a school of that location, or vice versa. To current knowledge, no general rule seems applicable, as few models to describe the relationship between Rn in dwellings and in schools have been developed. In Southern Serbia, a Rn survey in a predominantly rural region was based on measurements in primary schools. The question arose whether or to which degree the results can be considered as indicative or even representative for residential Rn concentrations. To answer the question an additional survey of indoor Rn concentrations in dwellings was initiated, designed and performed in Sokobanja district in 2010-2012 in a manner to be able to detect a relationship if it exists. In the study region, 108 dwellings in 12 villages and towns were selected, with one primary school each. In this paper, we investigate how a relation between Rn in schools and dwellings could be identified and quantified, by developing a model and using experimental data from both the above main and additional surveys. The key criterion is the hypothesis that the relation dwellings - schools, if it exists, is stronger for dwellings closer to a school than for those dwellings further away. We propose methods to test the hypothesis. As result, the hypothesis is corroborated at 95% significance level. More specifically, on town level (typical size about 1 km), the Rn concentration ratio dwelling/school is about 0.8 (geometrical mean), with geometrical standard deviation (GSD) about 1.9. For dwelling and school hypothetically in the same location, the ratio is estimated about 0.7 with GSD about 1.5. We think that the methodology can be applied to structurally similar problems. The results could be used to create "conditional maps" of Rn concentration in dwellings, i.e., for example a map of probabilities that indoor Rn concentrations in dwellings exceed 100 Bq/m3, as function of Rn concentration in the local school.

In-field evaluation of the impact of ageing and fading effects on annual radon concentration measurements for two different techniques.

Measurements covering a 1 year period are often used and required by legislation to assess the average radon concentration within a house or a workplace. This kind of long-term measurement-generally carried out with techniques based on nuclear track detectors-can be affected by a reduction in sensitivity due to ageing and fading of latent tracks during the exposure period, thus resulting in an underestimation of the actual average concentration. In order to evaluate in field conditions the ageing and fading effects on annual radon concentration measurements, two different studies in a large sample of rooms in dwellings (162) and in workplaces (432) were conducted using two different techniques (detector and track read-out system): (i) CR-39 plastics readout with a fully automated image analysis system, and (ii) LR 115 films with a spark-counter for track counting. Study design and data analysis aimed to evaluate both the average and the variability of ageing and fading effects in real conditions, and to reduce and separate the contribution of measurement uncertainty to the observed variability. For the CR-39 based technique, the results show that radon concentration measurements over a 12month period are on average about 16% lower than those evaluated with measurements of two consecutive 6 month periods, implying the need for a correction factor to avoid measurement bias (i.e. underestimation) due to ageing and fading effects. The observed variability of ageing and fading effects among the sampled rooms is not negligible (coefficient of variation about 18%), although a considerable fraction is attributable to measurement uncertainty, which is presumably not related to ageing and fading. For the technique based on LR 115 spark counting, ageing and fading do not significantly affect the results of radon concentration measurement.

Geographical distribution of the annual mean radon concentrations in primary schools of Southern Serbia - application of geostatistical methods.

Between 2008 and 2011 a survey of radon ((222)Rn) was performed in schools of several districts of Southern Serbia. Some results have been published previously (Zunic et al., 2010; Carpentieri et al., 2011; Zunic et al., 2013). This article concentrates on the geographical distribution of the measured Rn concentrations. Applying geostatistical methods we generate "school radon maps" of expected concentrations and of estimated probabilities that a concentration threshold is exceeded. The resulting maps show a clearly structured spatial pattern which appears related to the geological background. In particular in areas with vulcanite and granitoid rocks, elevated radon (Rn) concentrations can be expected. The "school radon map" can therefore be considered as proxy to a map of the geogenic radon potential, and allows identification of radon-prone areas, i.e. areas in which higher Rn radon concentrations can be expected for natural reasons. It must be stressed that the "radon hazard", or potential risk, estimated this way, has to be distinguished from the actual radon risk, which is a function of exposure. This in turn may require (depending on the target variable which is supposed to measure risk) considering demographic and sociological reality, i.e. population density, distribution of building styles and living habits.

Radon in indoor air of primary schools: a systematic survey to evaluate factors affecting radon concentration levels and their variability.

UNLABELLED: In order to optimize the design of a national survey aimed to evaluate radon exposure of children in schools in Serbia, a pilot study was carried out in all the 334 primary schools of 13 municipalities of Southern Serbia. Based on data from passive measurements, rooms with annual radon concentration >300 Bq/m(3) were found in 5% of schools. The mean annual radon concentration weighted with the number of pupils is 73 Bq/m(3), 39% lower than the unweighted 119 Bq/m(3) average concentration. The actual average concentration when children are in classrooms could be substantially lower. Variability between schools (CV = 65%), between floors (CV = 24%) and between rooms at the same floor (CV = 21%) was analyzed. The impact of school location, floor, and room usage on radon concentration was also assessed (with similar results) by univariate and multivariate analyses. On average, radon concentration in schools within towns is a factor of 0.60 lower than in villages and at higher floors is a factor of 0.68 lower than ground floor. Results can be useful for other countries with similar soil and building characteristics. PRACTICAL IMPLICATIONS: On average, radon concentrations are substantially higher in schools in villages than in schools located in towns (double,on average). Annual radon concentrations exceeding 300 Bq/m3 were found in 5% of primary schools (generally on ground floors of schools in villages). The considerable variability of radon concentration observed between and within floors indicates a need to monitor concentrations in several rooms for each floor. A single radon detector for each room can be used provided that the measurement error is considerable lower than variability of radon concentration between rooms.