THE AUSTRIAN RADON PROJECT

Transcription

1 Radon in the Living Environment, 010 THE AUSTRIAN RADON PROJECT H. Friedmann 1), C. Atzmüller 2), L. Breitenhuber 3), P. Brunner 4), K. Fink 5), K. Fritsche 6), W. Hofmann 2), H. Kaineder 7), P. Karacson 8), V. Karg 9), P. Kindl 3), C. Kralik 9), J. Krischan 10), H. Lettner 2), F. J. Maringer 11), E. Nadschläger 7), W. Ringer 12), F. Schönhofer 9), P. Schönleitner 13), S. Sperker 7), H. Stadtmann 14), F. Steger 14), F. Steinhäusler 2), R. Winkler 2), 1)Institut für Radiumforschung und Kernphysik, University of Vienna, Boltzmanngasse 3, A-1090 Vienna, Austria, Tel. (+43 1) , FAX (+43 1) , 2)Institut für Physik und Biophysik, University of Salzburg, Austria; 3) Institut für Kernphysik, Technical University of Graz, Austria; 4) Institut für Analytische Chemie, University of Innsbruck, Austria; 5) Amt der Stmk. Landesregierung, Graz, Austria; 6) Amt der Vorarlberger Landesregierung, Bregenz, Austria; 7) Amt der Oberösterreichischen Landesregierung, Linz, Austria; 8) Amt der NÖ Landesregierung, St. Pölten, Austria; 9) Bundesanstalt für Lebensmitteluntersuchung und - forschung, Vienna, Austria; 10) Amt der Kärntner Landesregierung, Klagenfurt, Austria; 11)Bundesversuchs- und Forschungsanstalt Arsenal, Geotechnisches Institut, Vienna, Austria; 12)Bundesanstalt für Lebensmitteluntersuchung, Linz, Austria, 13) Amt der Salzburger Landesregierung, Salzburg, Austria; 14) Österreichisches Forschungszentrum Seibersdorf, Seibersdorf, Austria. The Austrian Radon Project (ARP) is aimed to investigate and measure systematically the indoor radon concentration in about 0.5% of all Austrian homes. With the information from this survey areas of enhanced indoor radon concentration can be identified and people living in such areas should be encouraged to mitigate their homes. The radon potential is introduced by normalizing the observed radon data to a standard situation. By mapping the radon potential an overview on the geological risk for enhanced indoor radon concentrations will be available. In the future a passage should be introduced into the building codes to consider the radon potential during the construction of houses to avoid radon problems in new buildings. Keywords: Radon, indoor air quality, radon mapping, radon measurements INTRODUCTION In 1991 the Austrian Ministry of Health and Consumer Protection initiated the Austrian Radon Project (ARP) with the aim of investigating the indoor radon concentration distribution and identifying areas of high radon risk in Austria. The project was planned to be executed in 3 phases. During the first phase (ARP-1) existing data on indoor radon measurements as well as data which may indicate high indoor radon levels (e.g. γ-dose-rate, U and Th concentration in the ground and sediments, Ra and Rn concentration in spring and ground water etc.) were collected and the strategy for a nation-wide survey was developed (completed in 1991). The second phase (ARP-2) was started in 1992 as a pilot project to test the proposed strategies. After a fine-tuning of the methods used during ARP-2 the nation-wide survey was launched in January 1995 and should be completed with end of There are two main aspects for the ARP which are closely connected to the recommendation of the Austrian Radiation Protection Commission (1992). According to these recommendations the annual mean radon concentration in new buildings should be kept below 200 Bq/m³ and remedial actions should be taken in existing dwellings with annual mean radon concentrations exceeding 400 Bq/m³. 85

2 010 Radon in the Living Environment, Thus, the first aspect is to identify houses with elevated indoor radon concentration and to animate the inhabitants to reduce the radon concentration in their homes. The second aspect is to find areas where even in new buildings enhanced radon concentrations can be expected. For such areas certain construction regulations may be published in the future. STRATEGY During ARP-1 the strategy for the whole project was developed. Several decisions must be made very early: It was decided to measure the radon gas concentration instead of radon progeny concentration. This decision was based on the following considerations: Long term radon measurements are relatively cheap compared with long term progeny measurements which at that time could only be performed by active measurement techniques. On top of that, the usual progeny concentration determination methods measures only the attached fraction, which usually do not characterize the exposure. The dose the inhabitants are exposed to, can significantly be enhanced by the unattached fraction. Often the attached and the unattached fraction appear to be anticorrelated. Therefore, radon gas concentration may be a better measure of the exposure than the determination of the attached fraction of the radon progenies. Sample selection: Several decisions were necessary for the selection of the sample. According to our budget we considered to make measurements in one out of approx. 200 homes. The sample was taken statistically (from the telephone registry) and the density of the investigated homes was proportional to the density of inhabitants. This means we get more accurate results in dense populated areas than in areas with only a low number of inhabitants. This makes sense only up to a certain population density. So the density of investigated homes per inhabitant was substantially reduced in big cities with preferably multi story houses. With this selection of the sample the survey does not cover the whole country equally well as compared to a grid sample philosophy, however, the Austrian topography with large areas in the Alps with an extreme low population density are of only minor interest for a radon survey. A possible drawback of a stochastic sample was a low acceptance by the selected individuals and thus a low return rate of the distributed detectors was suspected. Therefore, several efforts were made to overcome these difficulties. Measurement techniques: There is no question about the advantages of one-year measurements. However, the project was funded only on successive one-year periods for the investigation of certain parts of Austria. This means that the preparation of the measurements, the measurements and the analysis of the data must be performed within approximately one year. Keeping this in mind SSNTD (System KfK) and electret detectors (e-perm) were used on basis of 3 months exposures. Additional measurements were made using charcoal detectors with liquid scintillation analysis (Picorad) on a 3-days basis. The measurements were performed in the primarily used rooms (usually living room and bedroom) to get an information on the actual radon exposure of the population. The geologic risk for enhanced radon concentration should be deduced in a second step by normalizing the measured data to a standard situation. REALIZATION The individuals selected from the telephone register were informed about the radon project by a letter from the state government. They were told that this investigation is of great importance for the health care of the country and they can have a free radon measurement in their home. Special 86

3 Radon in the Living Environment, 010 emphasis was given to the fact, that the participation in that program is voluntary. Finally it was mentioned that within the next 2 weeks an interviewer will come to distribute the detectors. The interviewers got a list of the selected persons with the additional advise that in case somebody refuses the investigation, the interviewer should try to make the measurements in the adjoining neighborhood. In all of the selected homes the radon concentration in the two most often used rooms was measured. In case of the three months measurements (long-term measurements), only one detector was placed in a room, in case of the charcoal detectors (3 days measurements) always two detectors were exposed in a room. Together with the detectors a one-page questionnaire was distributed with questions about the house type, type of construction materials, living style etc. Some of the questions were the same as asked during the last census. By comparing the frequency of answers on multiple choice questions, it can be checked if the selected sample is representative for the whole population. The long-term detectors were collected by the interviewers while the charcoal detectors were directly sent back from the householder to the laboratory. In the latter case an envelope with the address and a stamp fixed on the envelope was distributed with the detectors. The interviewers were asked to make a call to the homes with charcoal detectors 3 days after they had given the detectors to the householders. MEASUREMENT RESULTS All together approximately measurements were performed (including repeated and multiple measurements). The return rate was more than 95% and it could be proved that the sample selection was representative for the whole population. Generally the acceptance was better in rural areas compared to large cities. But even there a sufficient acceptance could be found. A systematic investigation on the reliability of measurements showed a rather surprising fact: Although repeated laboratory calibration test proved a sufficient reliability of all used detector systems with a good consistence of the calibration factors, field test showed rather strong variations. The mean values from measurements with different types of detectors in approximately 50 rooms showed good consistencies (within 15 to 20 %) however the measurement results from different detectors exposed in the same room (at the same time) deviated considerably. This was not surprising when comparing long-term with short-term measurements, however, even different measurement systems with long-term exposure showed variations up to a factor of two (Friedmann 1994). We concluded that within the three months exposure the detectors were moved to different places in the room with different mean radon concentrations (e.g. close to windows, doors etc.). This means that long-term measurements will not give reliable data for all homes, but good mean values for an area can be deduced, even with short-term measurements. In consequence short-term measurements were also used (Schönhofer 1995) because the survey should only map the radon situation for areas and it was not intended to get reliable result for single homes. The measured data represent the radon situation for the time of the detector exposure only. Additional measurements showed significant seasonal variations in the indoor radon concentrations. These seasonal effects can vary substantially. Usually the radon concentration in winter is higher than in summer, however, under certain situations a reverse effect is also possible. Nevertheless only a mean correction factor can be used to correct for such seasonal effects. So, a mean winter to summer ration of 2 was used for rural areas and a ratio of 1.4 for was used for larger towns (multi 87

4 010 Radon in the Living Environment, story buildings) to normalize the measured data to an annual mean (Friedmann 1996). These observed mean winter to summer ratios are in good agreement with results from Switzerland and Germany. In Figure 1 the measured radon concentration can be seen, as well as the data converted to annual means. It is the typical log-normal density distribution function that can be expected in such surveys. The mean indoor radon concentration in the already investigated areas of Austria is approximately 125 Bq/m 3. The remaining areas (Vienna and Burgenland) will probably reduce the Austrian mean. THE RADON POTENTIAL The indoor radon concentration is not only influenced by the geological situation beneath the house but also by many other parameters, e.g., the location in the house, the living style of the inhabitants, the type and the construction of the house. As an example, the mean radon concentration in a town will generally be lower than in a rural area situated on the same type of soil, because a significant fraction of inhabitants of a town live in upper stories, where the radon concentration is usually much smaller than in the ground floor. In case of the construction of a new house the geological risk of the site should be taken in consideration. For this reason a new quantity must be introduced. To do this the measured data (converted to an annual mean) were normalized to a standard situation. The standard situation was defined as a measurement in a living or sleeping room in the ground floor, in a permanently used house with no or only partial basement, not higher than 2 stories, usually tight windows (no single plane windows), inhabited by two adults and less than two children. It can be shown that a normalization to a standard situation is possible for a log-normally distributed data set (Friedmann, 1994, 1995). The normalization factor (for each parameter used in the normalization process) is the ratio of the median of the radon concentration in the standard situation and the median in the situation to be normalized. E.g., to normalize a measurement made in the second floor to a measurement in the first floor, the data is multiplied by the ratio of the median of all ground floor measurements (in an area) and the median of all second floor measurements (in the same area). The radon concentration in the defined standard situation is called radon potential and indicates the radon risk from the ground stripped from all other influences of the measuring situation. For administrative reasons the radon potential is computed only for municipalities and is not mapped in connection with the geology (Friedmann 1996). The municipalities are classified according to their radon potential into 3 classes: Class I: radon potential < 200 Bq/m 3, Class II: radon potential between 200 and 400 Bq/m 3, Class III: radon potential > 400 Bq/m 3 A preliminary recommendation says that in class I no special construction precautions seem to be necessary, in class II areas several precautions should be taken and in class III radon-safe constructions seem necessary. The actual radon potential map can be seen in Figure 2. 88

5 Radon in the Living Environment, 010 CONCLUSIONS The mean indoor radon concentration in Austria is higher as primarily assumed. In addition, municipalities with elevated radon concentrations were also found in parts of Austria where it was not expected. Even a well known small radon-prone area (Ennemoser 1993, 1994) was found which proved the successful use of the stochastic sampling technique. Nevertheless 80% of all municipalities belong to radon potential class I, which means low risk areas, 15% belong to class II and only 5% belong to class III. It is clear, that statistical uncertainties have influenced the classifications. Therefore, in a second step, cluster analyses are used to indicate areas where additional measurements seem necessary. These measurements will be used to improve the radon potential map. ACKNOWLEDGEMENTS The work was funded by the Austrian Government (Budeskanzleramt). The authors thank all persons engaged in the measurements and data evaluation. Without their help this project would never have succeeded. REFERENCES [1] Austrian Radiation Protection Commission (Strahlenschutzkommission beim Bundesministerium für Gesundheit Sport und Konsumentenschutz): Richtwerte für die Radonkonzentration in Innenräume. 58.Sitzung am 29.Juni Forschungsberichte des Bundesministeriums für Gesundheit, Sport und Konsumentenschutz, Sektion III, 1994; 3/94. [2] Ennemoser O, Ambach W, Brunner P, Schneider P, Oberaigner W. Exposure to unusually high indoor radon levels. Lancet 1993; 341: [3] Ennemoser O, Ambach W, Auer T, Brunner P, Schneider P, Oberaigner W, Purtscheller F, Stingl V. High indoor radon concentraion in an Alpine region of western Tyrol. Health Phys. 1994; 67: [4] Friedmann H, Beck C, Breitenhuber L, Exler M, Gehringer P, Hamernik E, Hofmann W, Hubmer A, Kaineder H, Karg V, Kindl P, Korner M, Le Bail P, Lettner H, Maringer FJ, Mossbauer L, Nadschläger E, Oberlercher G, Pock K, Schönhofer F, Seiberl W, Sperker S, Stadtmann H, Steger F, Steinhäusler F, Tschurlovits M, Zimprich P. Ermittlung der Strahlenbelastung der österreichischen Bevölkerung durch Radonexposition und Abschätzung des damit verbundenen Lungenkrebsrisikos - Pilotprojekt. Beiträge - Forschungsberichte des Bundesministeriums für Gesundheit, Sport und Konsumentenschutz, Sektion III, 1994; 3/94. [5] Friedmann H, Breitenhuber L, Hamernik E, Hofmann W, Kaineder H, Karg V, Kindl P, Lettner H, Maringer FJ, Mossbauer L, Nadschläger E, Oberlercher G, Pock K, Schönhofer F, Seiberl W, Sperker S, Stadtmann H, Steger F, Steinhäusler F, Tschurlovits M. Das Österreichische Radonprojekt. Mitteilungen der Österr. Geolog. Ges. 1995; 88: [6] Friedmann H, Atzmüller C, Breitenhuber L, Hamernik E, Hofmann W, Kaineder H, Karacson P, Karg V, Kindl P, Kralik C, Lettner H, Maringer FJ, Mossbauer L, Nadschläger E, Oberlercher G, Pock K, Schönhofer F, Seiberl W, Sperker S, Stadtmann H, Steger F, Steinhäusler F, Tschurlovits M, Zimprich P. Environment International 1996; 22, Suppl. 1: ps677-s686. [7] Schönhofer F, Pock K, Friedmann H. Radon Surveys with Charcoal and Liquid Scintillation Counting. Field Experience and Comparison to other Techniques. Journal of Radioanalytical and Nuclear Chemistry. 1995; 193, No.2:

6 010 Radon in the Living Environment, Distribution of the Radon Concentration in Rooms Frequency Measured Data Annual Mean Log-Normal Distribution >1500 Radon Concentration in Bq/m³ Figure 1: Frequency distribution of the radon concentration in Austrian homes. Measured data - mean: 114 Bq/m 3, median: 62 Bq/m 3, maximum: 8325 Bq/m 3 ; extrapolated annual mean values mean: 127 Bq/m 3, median: 71 Bq/m 3, maximum: 7776 Bq/m 3 ; log-normal distribution fitted to the annual mean data mean: 128 Bq/m 3, median: 65 Bq/m 3, GSD:

7 Radon in the Living Environment, 010 Radon Potential Gemeinden no data Bq/m³ Bq/m³ > 400 Bq/m³ N Kilometer Figure 2: The radon potential in Austria. The radon potential is defined as the annual mean radon concentration in a standard situation (living room at ground level, no basement, etc.). 91

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