INDOOR RADON EXPOSURE IN CLUJ-NAPOCA CITY, ROMANIA *

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1 INDOOR RADON EXPOSURE IN CLUJ-NAPOCA CITY, ROMANIA * K. SZACSVAI 1, C. COSMA 2, A. CUCOS 2 1 Sapientia Hungarian University of Transylvania, Faculty of Science and Arts, Department of Environmental Studies, 16 Deva Street, RO , Cluj-Napoca, Romania szacsvaikinga@gmail.com 2 Babes-Bolyai University, Faculty of Sciences and Engineering, 30 Fantanele Street, RO , Cluj-Napoca, Romania Received November 15, 2012 Radon and its decay products are the most important sources of natural radiation for the human exposure (UNSCEAR, 2000). As the second cause of lung cancer (after smoking), radon is received indoors, in houses and others buildings by the majority of the population exposed (ICRP, 1993). In the past decades, systematic radon surveys in dwellings were carried out all over the world (UNSCEAR 2000). Almost half of the radioactive dose is due to radon gas. The objective of this present study was to estimate the lung cancer risk induced by exposures to radon for a period of days in bedrooms at 1-1.5m distance from the floor. The mean measured radon concentration values were corrected for seasonal variations, depending on the time when detectors were exposed during the course of the year. The radon average concentration in the exanimate places was <C Rn > =112Bqm -3, C Rnmin = 9 Bqm -3 and C Rnmax =1127Bqm -3. The geometrical mean of radon, GM, in studied areas were found to be 68Bqm -3. Distribution of indoor radon concentration in homes was: 32,7% in C Rn [0-40 Bqm -3 ], 31,5% in C Rn [41-80 Bqm -3 ], 11% C Rn [ Bqm -3 ], 6,3% in C Rn [ Bqm -3 ], and 18,1% in C Rn [>160 Bqm -3 ]. Key words: indoor radon, solid track detector, lung cancer. 1. INTRODUCTION Radon, a naturally occurring radioactive gas, constitutes the most important natural radiation exposure in many dwellings and contributes with more than half to the total natural ionizing radiation dose of world s population [1]. Radon and radon progeny are present in dwellings air, representing the most important contribution to dose from natural sources of radiation. After smoking, radon represents the second most important risk cause of developing lung cancer. In Romania the first long time radon measurement were made by makrofol detectors [2] and in the last years with CR-39, track detectors [3]. The results * Paper presented at the First East European Radon Symposium FERAS 2012, September 2 5, 2012, Cluj-Napoca, Romania. Rom. Journ. Phys., Vol. 58, Supplement, P. S273 S279, Bucharest, 2013

2 S274 K. Szacsvai, C. Cosma, A. Cucos 2 recently reported for Romania in the literature were obtained by filtering method and they give an estimated value [4]. These results were essentially grab sample results and they are being confirmed by integrated measurements in order to obtain a reliable annual average exposure for Romanian houses. Previous data for equilibrium equivalent concentration (EEC) from 760 houses report a value of 25Bqm -3 [4]. Compared with other European countries this average indoor radon concentration is alike reported values in: Serbia 144 Bqm -3, Slovak Republic 104 Bqm -3, Hungary 73 Bqm -3, Slovenia 87 Bqm -3, Austria 97 Bqm -3, Spain 90 Bqm -3, Italy 70 Bqm -3. [5], [6] THE AIM OF THE STUDY The objectives of the present work were to determine the radon concentration levels in houses from Cluj-Napoca, and to analyze the main factors affecting indoor radon levels GEOGRAPHIC AND GEOLOGIC BACKGROUND OF THE STUDY Transylvania region is the north-western part of Romania, situated in the Carpathian arch, including also the western part of the West Carpathian Mountains with a total population of about inhabitants. Cluj-Napoca, as pointed in Fig. 1, is the second most populous city in Romania and is located in the north-western part of the country and in the central part of Transylvania. The city lies at the confluence of the Apuseni Mountains, the Someş plateau and the Transylvanian plain [7] (Figure 1). Fig. 1 Map of Romania showing the location of Cluj-Napoca.

3 3 Indoor radon exposure in Cluj-Napoca city, Romania S275 From a geological point of view, Transylvania mainly corresponds to a posttectonic depression, surrounded by the Alpine chain of the Carpathians. In the Eastern Carpathians, three main units can be separated: the Flysch zone, to the East, the Mesozoic and metamorphic rocks dominate the lithology. The western part of the chain consists of a mosaic of magmatic, metamorphic and sedimentary rocks [8]. 2. MEASUREMENT METHODS Solid state nuclear track detectors (SSNTDs) have been used for a long time for radon measurements [9], [10]. Every detectable α-particle produces in a SSNTD a single trail of damage, which, after chemical enlargement turns into narrow channel and is made visible under microscope. The latent tracks can be etched with the help of a suitable etching solution such as NaOH, or KOH under controlled conditions (temperature, time and etching agent concentration). SSNTDs exhibit different sensitivities; some of them are sensitive to alpha particles in the energy range of the particle emitted by radon and his progeny. Mostly, these SSNTDs are cellulose esters (nitrate and acetate) and polycarbonates like bisphenol-a polycarbonate and CR-39. Figure 2 a presents an etched CR-39 chip where visible tracks are shown. In Fig. 3 is presented the experimental search to find the best etching time. As it can be seen in this figure the time is as above mentioned. The development process requires an etching process with a 6.25 M solution of NaOH at a temperature of 90 0 C for 4.5h. Thus processed, we have evaluated measurements with RadoSys Fig. 2 Visible track in etched detector surface.

4 S276 K. Szacsvai, C. Cosma, A. Cucos 4 Fig. 3 The best etching time at development. 3. RESULTS AND DISCUSSIONS Indoor radon concentrations were measured in 254 dwellings in all quarters of Cluj-Napoca (Fig. 4) using CR-39 track detectors (Fig. 5) in bedrooms at a distance of m from the floor. After days exposure, detectors were subjected to chemical processing in a NaOH solution of 6.25 molar concentration, in a constant 90 0 C temperature bath, and etching time of 4.5 hours. After the etching, detectors were washed for 15 min with running cool distilled water and finally dried with hot air. After this process, we have evaluated measurements with RadoSys Radon concentrations (C Rn ) were calculated by the following relation: ( ρ F ) C Rn =, (1) t where: C Rn radon concentration (Bqm -3 ) ρ the track density (tracks mm -2 ), F calibration factor, F = 41.34(kBq h m -3 )/ (tracks mm -2 ) t exposure time (h). The mean measured radon concentration value (C Rn ) was corrected for seasonal variations, depending on the time when detectors were exposed during the course of the year [11]:

5 5 Indoor radon exposure in Cluj-Napoca city, Romania S277 3 C Rn = C summer (2) 2 The accuracy of this detection system was periodically checked by participation in national intercomparison campaigns [12]. Fig. 4 Cluj-Napoca s quaters with measurements places. Fig. 5 The CR-39 track detector used in measurements. The frequency distribution of the indoor radon concentrations for 200 daysperiod of measurements is presented in Figure 6.

6 S278 K. Szacsvai, C. Cosma, A. Cucos 6 Fig. 6 Distribution of the indoor radon concentration in Cluj-Napoca s houses. Summary statistics of the radon concentration measurements in dwellings are presented in Tabel 1. This table lists the arithmetic and geometric means of radon concentration, together with the minimum and maximum values as well as the number of cases. 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 9 to 1127 Bqm -3. The aritmethic mean equals 112 Bqm -3, while the geometric mean equals 68 Bqm -3. Table 1 Number of cases C Rnmin Summary statistics of radon concentration in dwellings C Rnmax AM GM Median In addition, some factors affecting the indoor radon concentration, such as the influence of the floor number and the age of the buildings in relation to the constructed materials, were also examined. They have one, two or three rooms, basement and are heated mostly by a hot water central heating system, mainly from November to March. The ventilation is natural, by opening windows and doors.

7 7 Indoor radon exposure in Cluj-Napoca city, Romania S CONCLUSIONS The radon average concentration in the exanimate places was <C Rn >=112Bqm -3, C Rnmin =9Bqm -3 and C Rnmax =1127Bqm -3. The geometrical mean of radon, GM, in the studied areas were found to be 68Bqm -3. Distribution of indoor radon concentration in houses was: 32.7% for C Rn [0-40Bqm -3 ], 31.5% C Rn [41-80Bqm -3 ], 11% C Rn [81-120Bqm -3 ], 6.3% C Rn [ Bqm -3 ], and 18.1% for C Rn [>161Bqm -3 ]. As it can be concluded from Figure 1, in 85.7% of the cases the radon concentration values were found to be far below 200 Bqm -3, 12.6% of the cases were in the interval of Bqm -3, which is the implemented in UE. Outstanding values, more than 600 Bqm -3 was found in 2% of cases. The average annual radon concentrations for the investigated areas are in accordance with the integrated measurements in Transylvania [13], [14]. REFERENCES 1. UNSCEAR, 2000, Sources and effects of ionizing radiation, United Nations Scientific Committee on the effects of atomic radiation. Report to the General Assembly. United Nations, New York (2000). 2. C. Cosma, D. Ristoiu, T. Vaida, A. Poffijn, J. Miles, Integrating measurements of radon in dwellings in some Romanian regions, IRPA 9, April, Viena, pp (1996). 3. C. Cosma, K. Szacsvai, A. Dinu, D. Ciorba, Indoor radon and lung cancer risk in Romania, Studia Universitatis Babes-Bolyai, Geologia, 52(1), 10 (2007). 4. O. Iacob, C. Grecea, E. Botezatu, Population exposure to inhaled radon and thoron progeny. In the natural radiation environment, NRE-VII. J. P. Mc Laughlin, S.E. Simopoulos, F. Steinhausler (Eds), pp (2005). 5. G. Dubois, An overview of Radon survey in Europe EC, Joint Research Center Report, Luxembourg (2005). 6. Z. Gorjanacz, A. Varhegyi, T. Kovaçs, J. Somlai, Population dose exposure in the vicinity of closed Hungarian uranium mine, Rad. Prot. Dosimetry, 118, pp (2006). 7. Geografia judeţului Cluj INSSE - Direcţia Regională de Statistică Cluj. Retrieved I. Balintoni, N. Meszaros, I. Gyorfi, Transylvania-Depresion and Basins, Studia Universitatis Babes-Bolyai, Geologia, 42(1), 7 (1998). 9. R. L. Fleisher, P. B. Price, R. M. Walker, Nuclear Tracks in Solides: Principles and Applications, University of California Press, Berkley, S.A Durrani, R. K. Bulk, Solid State Nuclear Track Detection: Principles, Methods and Applications, Pergamon Press, Oxford (1987). 11. C. Cosma, K. Szacsvai, A. Dinu, D. Ciorba, T. Dicu, L. Suciu, Preliminary integrated indoor radon measurements in Transylvania (Romania). Isotopes in Environmental and Health Studies, Volume 45, Issue 3, pp , (2009). 12. C. Sainz, A. Dinu, T. Dicu, K. Szacsvai, C. Cosma, L. S., Quindos, Comparative risk assessment of residential radon exposures in two radon - prone areas, Stei (Romania) and Torrelodones (Spain). Science of the Total Environment 407, pp , (2009). 13. C. Cosma, D. Ciorba, A. Timar, K. Szacsvai, A. Dinu, Radon exposure and lung cancer risk in Romania, Journal of Environmental Protection and Ecology, Volume 10, Issue 1, pp , (2009). 14. L. A. Truta-Popa, A. Dinu, T. Dicu, K. Szacsvai, C. Cosma, W. Hoffmann, Preliminary lung cancer risk assessment of exposure to radon progeny for Transylvania, Romania, Health Physics, Volume 99, Issue 3, pp , (2010).