PRELIMINARY RADON SURVEY IN GREECE (B) Panepistimioupoli , Athens Greece. Medicine, London SW7 2AZ U.K. Republic

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1 PRELIMINARY RADON SURVEY IN GREECE (B) A. Geranios 1, M. Kakoulidou 1, Ph. Mavroidi 2, S. Fischer 3, I. Burian 4 and J. Holecek 4 1 Nuclear and Particle Physics Section, Physics Department, University of Athens, Panepistimioupoli , Athens Greece 2 Graduate student, Environmental Technology, Imperial College of Science, Technology and Medicine, London SW7 2AZ U.K. 3 Astronomical Institute of the Academy of Sciences, Bocni II 1401, 14, Prague 4, Czech Republic 4 Institute for Testing and Disaster Medicine, Milin, Kamenna Czech Republic A preliminary indoor radon survey in Greece based on 258 passive detectors, to test the technique and the statistics, is presented. This paper is an extension of an initial survey (Geranios et al. 1999). The majority of the detectors were placed in schoolrooms and dwellings for a yearlong (June 1997-June 1998). The part of our sample concerning the northern region of Greece tends to indicate higher radon concentrations than the rest part of the country. The radon concentration distribution fits well to the theoretically expected lognormal. We have adopted a three level scheme to estimate the dose absorbed annually (0-99 Bq/m 3, Bq/m 3 and >200 Bq/m 3 ). Due to the small sample of detectors, we should not interpret this map as characterising whole geographic areas, but simply indicating the radon concentrations at the particular sites. In order to complete a national radon survey, a much denser sample is certainly needed. Key words: Indoor radon measurements INTRODUCTION It is well known that radon and its decay products are the most dominant component of natural radioactivity, to which man is exposed for his entire life. Therefore it is the major contributor to the effective dose (Cothern et al. 1987, Nazaroff et al. 1988, Cohen 1986, Christofides et al. 1993). Actually, the knowledge of radon concentration itself leads to the knowledge of the background radiation. The inhalation of radon decay products can cause lung cancer fatalities of which about is assumed to be in USA annually. It is thus believed that radon has been identified as the second leading cause of lung cancer, after smoking (Cothern et al. 1987, U.S.E.P.A. 1994). It is quite important to start measuring indoor radon levels and look for concentrations higher than the action level of 150 Bq/m 3 in order to take the appropriate remedial action (U.S.E.P.A. 1993). The corresponding action levels for European countries, which already have done a national survey, are higher but different from country to country. We considered the action level adopted by the States, since it represents a rather large number of population and a high homogeneity. TECHNIQUE Greece has not yet been scanned by a radon national survey. There are only some sporadic and local radon surveys made in the past (Anagnostakis et al. 1996, Papastefanou et al. 1997, Louizi 1997). For the present preliminary survey the track etched detector technique was used. The material, for this survey, is the nitrated type film Kodak LR-115, in open mode. By this technique, all alphas from radon itself and its progenies are counted. The etching procedure and the estimation of the concentration (Bq/m 3 with an uncertainty of 20%) were conducted by the radon facilities of 1081

2 the Institute for Testing and Disaster Medicine, Milin, Czech Republic (Burian, I., 1992). Figure 1 shows the dimensions and structure of the Kodak LR-115 detector used. METHODOLOGY Since all action levels correspond to the annual average of the radon gas concentration and the risk from the radon is accumulated slowly and expresses itself over a whole lifetime, we adopted the entire year period for measurements indoor radon. It is important to base decisions about remedial actions on a long-term average. Furthermore, because of the wide variations of radon concentrations from day to day and from season to season, it is evident that measurements be carried out over a long period of time. It was thus decided to leave all passive detectors measure for a whole year. A number of 500 detectors, provided by the above Institute were used for this study. Because of the limited capabilities of our group to survey such a large area and since the estimation of radon concentration in schools is our primary interest, we called upon the help of the Union of Higher Education of Greek Teachers. They assist us by placing the detectors in each part of Greece. Greece is divided into about 50 administrative regions, where there is a local office of the abovementioned union. About ten detectors were delivered to each of these 50 offices, for distributing them in ten different places covering possibly uniformly the whole region. An attached questionnaire, concerning the site of the detector, was given to each individual teacher, which had to be filled out and returned to us promptly after the placement. This practice has the advantage of minimal expenses, but the disadvantage of using unqualified people for this task with the possible consequence of getting back only a part of the initially sent detectors. In fact, the number of the evaluated detectors received was 258. After having experienced all those shortcomings, another practice was actually adopted for the organisation of our local next survey in Kalamata, Greece (Geranios et. al., 1999). For the preliminary radon survey, the major part of the 500 detectors was placed during the 1996 June-July period and most of them were collected after about one year. Some of them remained for a shorter or longer period and the corresponding concentration were adjusted according to the seasonal variation (Miles et al. 1996). The time distribution during which the detectors were exposed is shown in Figure 2. The adjusted concentrations from the 258 detectors were classified into three general categories according to their level. Table I shows those three categories and the number of measurements corresponding to the specified range. The lower limit of the last category coincides with some other proposed action levels (Miles 1994), and it is not necessarily recommended by the European Union. The points where the detectors were placed does not constitute a national survey map. It is obvious, that due to the practice used for the placement of the detectors, their geographic density is not uniform throughout Greece. For statistical testing, we calculated the differentiated and cumulative lognormal distribution and have plotted it together with the concentration obtained. Figures 3 and 4 show the above fits for differential and cumulative values, respectively. In this first sampling, the highest annual concentration found was about 700 Bq/m 3 and the detector was placed in a school. Much higher 1082

3 values are reported in other countries (Burian 1992). In both plots of Figs 3 and 4, the concentration interval is 10 Bq/m 3. It is easily seen that about 15% of the measurements exceed the assumed action level of 150 Bq/m 3 (U.S.E.P.A. 1993). RESULTS Inhalation of radon and its daughters may be followed by deposition of large amounts of energy in the lungs. Absorbed dose in the trancheobronchial epithelium is caused by the short-lived α-particle emitted by the decay products 218 Po and 214 Po. Before applying a dosimetry model, one should calculate the annual occupancy time spent by the householder or the inhabitant and the equilibrium factor; i.e. the extent to which radon daughters, which impart dose to the trancheobronchial epithelium, are in equilibrium with the parent radon. Because, we did not measure equilibrium factor, a value of 50% was taken arbitrarily. This same value was adopted for the survey in Cyprus too (Christofides et al. 1993) and it is not much different from values taken by other European countries (lowest value of 0.4). In addition, the used Kodak etched track detectors do not vary significantly their efficiency with equilibrium changes. The occupancy factor determination (percentage of the mean daily indoor residence time), although it was asked by the residents of the houses, is not an easy task. Normally, three occupancy habits should be taken into account: a. The residence in the dwelling, b. The residence in the work place and c. The residence outdoor. We can neglect the contribution of radon outdoor, but it is difficult to distinguish the dose received at home and the one received at the work place. In our case, a value of 0.65 was deemed, according to the questionnaire. Table I shows the classification of radon concentrations. The effective dose for each category is estimated separately assuming no plateout of radon decay products. For the calculation of the dose equivalent, one can use the Weidel or Jacobi model (Cothern et al. 1987, Jacobi 1964). As it is known, the two models yield different conversion coefficients (ratio of WLM to msv). However, since this difference is smaller than the occupancy uncertainty, we use the conversion factor proposed by ICRP 65 of 4 msv per WLM (ICRP 1992). It is rather complicate to estimate the relation between exposure in WLM (Working Level Months) and dose equivalent (Sv). There are several models, which compute cellular doses following inhalation of radon and its progenies, and it is not surprising that a number of approaches are adapted by various authors in order to conclude in a conversion factor between integral exposure (WLM) and the dose equivalent to radiosensitive cells. For example, the Weibel model applies a mathematical approach specifying the number of generations in the lung a constant ratio between the radii and length of all tubes of the lung, and other parameters (Cothern et al. 1987). Altshuler et al. (1964) proposed a conversion factor of Gy per WLM for mouth breathing. The Jacobi model (1964) for the same way of breathing estimates a similar factor of Gy per WLM. But, Haque et al. (1967) using the Weibel model derived a three times greater value (0.11 Gy per WLM). 1083

4 It should be emphasised that the dose absorbed by children in the trancheobronchial region is twice as much as that for adults. In Table II, adapted from (Cothern et al. 1987), the age-dependent relative dose rate for exposure to airborne radon progeny is given. DISCUSSION The estimated effective dose (Table I) can be strongly affected by several uncertainties, i.e. the measurement technique (calibration and reproducibility etching procedure), the location of the detector (each room gives generally different concentrations), the measurement period, the occupancy factor (strongly variable from inhabitant to inhabitant), the equilibrium factor (it may vary between 0.4 and 0.7) and the dose-exposure conversion factor. One could give the corresponding lung cancer risk, annual or for a lifetime, by adopting the two, nearly equal risks proposed by NCRP (National Council on Radiation Protection and Measurements) and ICRP (International Commission on Radiological Protection), the value being 10-2 WLM -1 y with an error of 50%, i.e. 100 per persons exposed to 1 WLM y -1 for life. One could sum up the WLMs received for the whole life, taking into account the latent period and the life expectancy (Lamarshe 1982). Epidemiological studies require a very careful unbiased sample of people. Habits like smoking, mask the relation between radon and lung cancer (Quindos et al 1991). This preliminary study, was ment to test the measuring technique and statistics of the sample. Nevertheless, we can say that higher concentrations then the action level are reported in the northern part of the country, probably due to the presence of underground uranium layers. The percentage of these concentrations is about 15% of the total sample. A much higher number of indoor measurements are required to get a complete national radon survey and to pinpoint the dwellings exceeding action level in order to take the appropriate remedial action. ACKNOWLEDGEMENTS The authors are indebted to O.L.M.E. (Teacher s Union of Higher Education), to some Greek colleagues of the Athens University, as well as to all the inhabitants of the dwellings in which radon concentration was measured. REFERENCES [1] Altshuler B, Nelson N, Kuschner M. Estimation of Lung Tissue Dose from the Inhalation of Radon and Daughters. Health Phys. 1964; 10: [2] Anagnostakis M, Hinis E, Simopoulos S, Angelopoulos M. Natural Radioactivity Mapping of Greek Surface Soils. NRE VI, Environment International. Suppl 1996; 22 Suppl 1: S3-S8. [3] Burian I. Radon Investigation in Czechoslovakia. Radiat. Prot. Dosim. 1992; 45: [4] Christofides S, Christodoulidis G. Airborne 222Rn Concentration in Cypriot Houses. Health Phys 1993; 64: [5] Cohen B. A National Survey of 222Rn in U.S. Homes and Correlating Factors. Health Phys. 1986; 51: [6] Cothern C, Smith J. Environmental Radon. Plenum, New York,

5 [7] Geranios A, Kakoulidou M, Mavroidi Ph, Fischer S, Burian I, Holecek J. Preliminary radon survey in Greece. Ad. Prot. Dosim. 1999; 81: [8] Geranios A, Kakoulidou M, Mavroidi Ph, Moschou, M., Fischer S, Burian I, Holecek J. [9]. [10] Haque A, Collison J. Radiation Dose to the Respiratory System Due to Radon and its Daughter Products. Health Phys. 1967; 13: [11] Jacobi W. The dose to the Human Respiratory tract by Inhalation of Shortlived 222 Rn and 220 Rn Decay Products. Health Phys 1964; 10: [12] ICRP, Recommendations of the International Commission on Radiological Protection. Publication 65, Pergamon Press UK, [13] Lamarshe J. Introduction to Nuclear Reactor Theory. Addison-Wesley, London, [14] Louizi A. Exposure of Greek Population from Indoor Radon Measurements. 1 st Southeastern- European Regional Radon Workshop 3-5 April 1997, Athens, Greece, in press. [15] Miles J. Mapping the Proportion of the Housing Stock Exceeding a Radon Reference Level. Radiat. Prot. Dosim. 1994; 56: [16] Miles J, Kendall G, Green B, Lomas P. UK Radon Policy. Annales de l Association belge de Radioprotection 1996; 21: [17] Nazaroff W, Nero A. Radon and its Decay Products in Indoor Air. John Wiley and Sons, New York, [18] Papastefanou K, Stoulos S, Manolopoulou M, Ioannidou A, Charalambus S. Indoor Radon Concentrations in Greek Apartment Dwellings. 1 rst Southeastern-European Regional Radon Workshop 3-5 April 1997, Athens, Greece, in press. [19] Quindos L, Soto J, Fernandes P, Rodenas C, Gomez J, Arteche J, Romero G, Madrid J. Radon and Lung Cancer in Spain. Radiat. Prot. Dosim. 1991; 36: [20] U.S.E.P.A. Radon Measurements in Schools. Office of Air Radiation Document. # E.P.A R [21] U.S.E.P.A. Radon in Schools. Office of Air Radiation Document. # E.P.A.402-F

6 Table I: Characteristic parameters for dose estimation Concentration, Bq/m 3 Mean Bq/m 3 St. deviat ion Number of measurements Occupancy factor Equilib rium factor WLM Effective Dose 1, msv Effective Dose 2, msv > All factors are given annually. 1 For adults 2 For children approximately double values according to Cothern et al Table II : The relative dose rate for different ages Age Ratio of rates Years To trancheob. Region * Adult 1 * To those for adults (Cothern, 1987) 1086

7 Figure 1: The detector used for the survey (etched track detector, cellulose nitrate Kodak LR 115) and its dimensions in mm. 1087

8 Figure 2: The measuring time distribution in days 1088

9 Figure 3: Geographical distribution of the measured points 1089

10 Figure 4: Experimental (continuous line) and expected (dotted line) distribution of radon concentrations % 0Percentage of measurements,% Concentration (Bq/m 3 ) Concentration, Bq/m Figure 5: Cumulative measured (continuous line) and expected (dotted line) radon concentrations in logarithmic scale. (For better viewing, the expected concentration is shifted vertically by 5%). 1090