INDOOR RADON LEVELS IN PRIMARY SCHOOLS OF PATRAS, GREECE H. Papaefthymiou 1, * and C. D. Georgiou 2

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1 Radiation Protection Dosimetry (2007), Vol. 124, No. 2, pp Advance Access publication 17 May 2007 doi: /rpd/ncm180 INDOOR RADON LEVELS IN PRIMARY SCHOOLS OF PATRAS, GREECE H. Papaefthymiou 1, * and C. D. Georgiou 2 1 Division of Physical, Inorganic and Nuclear Chemistry, Department of Chemistry, University of Patras, Patras, Greece 2 Division of Genetics, Cell Biology and Development, Department of Biology, University of Patras, Patras, Greece Received 22 November 2006, revised 15 January 2007, accepted 29 January 2007 Radon activity concentrations have been measured in 53 from a total of 66 public primary schools throughout of Patras, Greece, during December 1999 to May 2000 using solid-state nuclear track detectors (LR-115 II). The indoor radon levels in the classrooms were generally low, ranging from 10 to 89 Bqm 23. The mean (arithmetic mean) indoor concentration was Bq m 23 and an estimated annual effective dose of msv y 21 was calculated for students and msv y 21 for teachers, assuming an equilibrium factor of 0.4 and occupancy factor of 12 and 14%, respectively. The research was also focused on parameters affecting radon concentration levels such as floor number of the classrooms and the age of the buildings in relation to building materials. INTRODUCTION Radon ( 222 Rn), a naturally occurring radioactive gas, constitutes the most important natural radiation exposure at many working places, schools and homes, and contributes more than half of the total natural ionizing radiation dose to world population (1). Educational buildings have attracted special interest as workplaces, not only because children are more sensitive to radon exposure than adults but as locations of high occupancy times for children. A number of radon surveys have been performed in schools in European countries. Although they concern a limited number of schools, except the Irish and Slovakia surveys, classrooms were found with radon concentration levels above the reference/action level (2 8). To our knowledge, only one survey is published in the literature concerning radon measurements in schools in Greece (9), while some surveys have been carried out in spas (10,11), in Kassandra mines and in the Athens underground railway (12). Patras is the third in size city of Greece with inhabitants, and is located in the north edge of the Peloponnese peninsula (southern Greece) (Figure 1). The objectives of this study were to determine the radon concentration levels in the classrooms of public primary schools in Patras area and mainly to estimate the contribution of school radon to the annual effective dose to students and teachers in primary schools. In addition, some factors affecting the indoor radon concentration, such as the influence of the floor number and the age of the *Corresponding author: epap@chemistry.upatras.gr buildings in relation to the constructed materials, were also examined. The radon measurements in schoolrooms were compared with the results found for dwellings in Patras (13), although residential and non-residential buildings, similar in construction, have quite different modes of ventilation. Peculiarities of the radon situation in schools compared with that in dwellings were also recorded. The survey was limited to primary schools, because these represent the greatest number of schools within the public school system in Greece. MATERIAL AND METHODS Sampling In the area of Patras, 66 primary public schools were in operation up to The children age ranges from 6 12 years. The first- and second-grades spend 5 h, while the other four grades spend 6 h in school. The school buildings differ in age, size and building materials. They have one or two and rarely three floors without basement and are heated by a hotwater central heating system, mainly from November to April. The ventilation is natural by windows and doors opened. During winter, doors and windows are opened in breaks, while during the other seasons the windows are more often opened. In the majority of schools, even in the cold period, a small window, near the ceiling, was always opened for better ventilation of the classroom. A number of 122 alpha-track detectors were prepared and distributed by ourselves in 53 from a total of 66 primary schools, for six consecutive months from December 1999 to May 2000 (the full school # The Author Published by Oxford University Press. All rights reserved. For Permissions, please journals.permissions@oxfordjournals.org

2 INDOOR RADON IN SCHOOLS The track counting was performed manually with a slide projector (Kodak 5000) using an optimized technique (15). The calibration was performed by exposing a set of three diffusion chambers in a radon chamber maintained by the Nuclear Technology Laboratory in the national Technical University of Athens, Greece. The calculated calibration factor was tracks cm 22 per Bq h m 23. The relative statistical error (1s) of a single 6-month measurement at the average level of 40 Bq m 23, including the calibration error, was found to be 14%. Additional information on the detector arrangement, etching and counting procedures could be found elsewhere (13, 15). Figure 1. Map of Greece showing the location of Patras. year duration is 9 months). One detector was exposed inside a classroom on every floor of each school building, away from open windows and doors and in locations not accessible to students, to minimize loss during the measurement period. Measurements were made under normal operating conditions of the classrooms. A total of 114 measurements were finally performed, as eight detectors were lost or damaged. The majority of the investigated schools, randomly distributed throughout the city, are quite small, with only three to five rooms at the ground level. Although only one classroom has been tested on each floor for all schools, the variation in radon over the total surface is expected to be limited. Moreover, when the school consisted of several separate buildings, measurements were also performed in each of them. The overall percentage of the surveyed schools was 80%. Hence, the results concerning radon concentration levels could be considered as representative for Patras primary schools situation. RESULTS AND DISCUSSION Radon concentration levels The frequency distribution of the indoor radon concentrations for the 6-month-period of measurements is presented in Figure 2. Indoor radon concentration data usually follow a log-normal distribution (16,17). Although the distribution in Figure 2 is slightly skewed, the indoor radon concentration data found in this survey show a departure from log-normality (Kolmogorov Smirnov normality test: Z ¼ 1.142, P ¼ 0.071). Indoor radon measurements in kindergartens and play-schools of the Province of Parma did not follow the log-normal distribution (18). Moreover, data from a national radon survey in Irish schools also showed a departure from log-normality, which was attributed to the contribution of the outdoor radon to indoor concentration and possibly in random radon measurement uncertainties (8). The subtraction of outdoor radon from measured indoor values found in Irish survey improved significantly the log-normality of the data. It is worth to note that indoor radon data concerning dwellings and apartments in Patras area were found to follow log-normal distribution, but as stated earlier, the ventilation modes were quite different in houses compared with that in school classrooms. Methods Indoor air radon concentrations were measured by means of the passive track etching method with LR-115 SSNTD film, type II (Kodak-Pathé, France) in a closed-can arrangement (14). After 6-monthexposure, the detectors were subjected to chemical processing in a 2.5 N analytical grade sodium hydroxide solution at C, for 145 min in a constant temperature bath. After the etching, the detectors were washed for 30 min with running cool water, then with distilled water followed with a 50% water/alcohol solution and finally drying in the air. Figure 2. Distribution of the indoor radon concentrations in Patras (Greece) public primary schools. 173

3 Table 1. Summary statistics of radon concentration levels on different floors of classrooms. Average radon levels are also included. Indoor radon concentration level (Bq m 23) N AM+ SD GM + GSD Min Max Ground First floor Second floor Average N, number of cases; AM, arithmetic mean; SD, arithmetic standard deviation; GM, geometric mean; GSD, geometric standard deviation; min, minimum value; max, maximum value. H. PAPAEFTHYMIOU AND C. D. GEORGIOU Summary statistics of the radon concentration measurements in classrooms are presented in 1. This table lists the arithmetic and geometric means of radon concentration in each floor, together with the minimum and maximum values as well as the number of cases. The limited number of classrooms in the second floor might have induced a slight imprecision in the means calculated for this floor. The overall arithmetic and geometric means are also included in this table. As mentioned earlier, the distribution of the indoor radon concentrations was approximately normal. Thus, the arithmetic means were used for description and comparisons of results. As can be seen from Table 1, the radon concentration values vary from 10 to 89 Bq m 23. The winter spring arithmetic mean equals 35 Bq m 23 and the arithmetic standard deviation 16 Bq m 23, while the geometric mean equals 32 Bqm 23 and the geometric standard deviation 2 Bq m 23. As the measuring time was 6 months, we could assume that the arithmetic mean gives a good estimate of the average annual indoor radon concentration. The results compare well with those found for low-rise houses and apartments in Patras area from December 1996 to November The average annual arithmetic and geometric means were found to be 47 and 41 Bq m 23 for the houses, 32 and 28 Bq m 23 for the apartments and 43 and 38 Bq m 23 for all the dwellings, respectively (13). As is apparent from Table 1, all radon concentration values were found to be far below 400 Bq m 23, which is the implemented Greek action level value for work places (European Council Directive 96/29/Euratom) (19).It should be noted that the 6-month passive radon measurements provide an average radon concentration over the entire measurement period. This includes night, weekend and holiday periods during 174 which time the schools are closed and, as a result, higher radon concentrations may be present. The indoor radon concentrations in schools were classified according to: (a) floor level and (b) the age of the buildings, which is closely related to the type of construction material and to the building technique employed. The average radon concentrations measured in classrooms on different floors are summarized in Table 1. As can be seen from this table, there is a decrease in radon concentration from the ground to second floor level. The primary reason for this is the higher convective flow of soil gas into the ground classrooms, as they are not protected by a basement. The age of a building is related with the kind and quantity of material used and the building techniques. Building materials used in building construction are one of the factors which affected the indoor radon concentration levels. The school buildings were classified into three groups according to the age of the buildings: (a) buildings older than 70 years, (b) buildings with age between 20 and 69 years and (c) buildings newer than 20 years. In Greece, the old buildings were constructed with stones or/and fired clay bricks with small amounts of cement (group I). Moreover, Patras is located on a seismic area and is expected that the old buildings present larger and more cracks than modern ones. Recent buildings have thinner walls and are constructed with reinforced concrete and fired clay bricks (groups II and III). An essential difference between the last two groups is that group (III) contains buildings, which were constructed with concrete made by cement containing fly ash. Greek cement companies, from the beginning of the 1980s, use fly ash from lignite burning as an additive to Portland cement in percentages varying between 20 and 30%. The fly ash from Greek lignite power plants contains high activity concentrations, especially of 238 U and 226 Ra (20 23). This additive may enhance the radon exhalation from concrete, which will increase the indoor radon concentrations. The average radon concentrations measured in classrooms with different age are shown in Figure 3. The old buildings seems to have higher Figure 3. Variation of the indoor radon concentration in schools with the age of the buildings.

4 radon concentrations compared with those of groups (II) and (III), while classrooms of group (III) present higher radon concentrations than those of group (II). This could be explained by the higher permeability of the old constructions and the fly ash presence in group (III). Two-way analysis of variance (SPSS v.12) was used in order to examine the effect of building materials (three categories) and floor number (ground and first floor) in radon concentration level. Results indicated that no significant interaction between floor number and building materials regarding radon concentration was found (F ¼ 1.586, P ¼ 0.210). This means that the effect of building materials in ground floor was similar to that in the first floor. Regarding the floor number effect, significant difference was found between the ground and first floor (F ¼ 3.971, P ¼ 0.049). The same trend was also observed in an earlier study concerning the indoor radon levels in Patras dwellings (13). Moreover, non-significant effect of the age of the buildings in relation to building materials on radon concentration was found (F ¼ 0.864, P ¼ 0.424). Results from a number of radon surveys in schools that have been carried out in European countries are summarized in Table 2. As is shown in this table, schools in Slovak Republic and Patras, Greece present the lower radon concentration values. Table 2. Indoor radon concentration levels in schools from different European countries. Country Radon concentration (Bq m 23 ) AM SD GM References Ireland 93 Synnot et al. (8) (national survey) Belgium 120 Poffin et al. (2) Croatia Planinic et al. (3) Slovak Ďurčik et al. (4) Republic Slovenia Vaupotič et al. (5) (national survey) Italy Giorani et al. (7) (Pordenone Province) Italy Giorani et al. (7) (Trieste Province) Greece Geranios et al. (9) (Kalamata) Greece (Patras) Present study AM, arithmetic mean; SD, arithmetic standard deviation; GM, geometric mean. INDOOR RADON IN SCHOOLS 175 Moreover, classrooms with radon concentration levels above the EC action levels were found in the majority of surveys referred in Table 2. Dose estimates The six-month measurement period could be assumed as representative of the school population and was used to calculate the mean annual effective dose. Although for children, the dosimetric models indicate a bronchial dose per unit exposure which is up to a factor of 2 higher than for adults (24), the International Commission on Radiological Protection has not adopted a lifetime risk coefficient for children different from that for adults (25). To evaluate the effective dose to the students and teachers a conversion dose factor of 9 nsv Bq m 23,a mean equilibrium value of 0.4 and an occupancy factor of 12 and 14% for students and teachers (assuming the presence in classroom to be 1050 h for students and a total of 1225 h per year in school for teachers) were used, respectively (1,13). According to the above, the radon concentration values correspond to an annual effective dose ranging from 0.03 to 0.34 msv y 21 for students and 0.04 to 0.39 msv y 21 for teachers. The resulting annual effective dose calculated from the arithmetic mean was estimated to be and mSv y 21 for students and teachers, respectively. The estimated effective doses may be a little overestimated as the classrooms were closed during nights, weekends and holidays. Nevertheless, this possible dose overestimation is on the safe side from the radiation protection point of view. According to the results of a previous survey performed in dwellings (13), the mean annual effective dose for the citizens of Patras area was calculated to be msv y 21. The mean annual effective doses for students and teachers at home and school were added in order to get the total annual effective dose. These values lead to an average effective dose of and msv y 21 for students and teachers, respectively. CONCLUSIONS Six-month passive alpha track detector measurements were performed, in 53 from a total of 66 (80%) public primary schools in Patras area, to determine the indoor radon concentration and the effective dose for students and teachers. Results showed that all the surveyed classrooms had radon levels lower than the European Communities action level for workplaces (the higher recorded value was 89 Bq m 23 ). The average radon concentration in schools was found to be Bq m 23, which is similar to the value previously reported for Patras dwellings (38 Bq m 23 ) and corresponds to an annual effective dose of msv y 21 for students and

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