Radiation Protection Dosimetry (2014), Vol. 162, No. 3, pp. 410 – 415 Advance Access publication 29 December 2013

doi:10.1093/rpd/nct344

SEASONAL INDOOR RADON CONCENTRATION IN ESKISEHIR, TURKEY H. Sogukpinar1, E. Algin2,*, C. Asici1, M. Altinsoz1 and H. Cetinkaya3 1 Graduate School of Sciences, Eskisehir Osmangazi University, Eskisehir TR-26480, Turkey 2 Department of Physics, Eskisehir Osmangazi University, Eskisehir TR-26480, Turkey 3 Department of Physics, Dumlupinar University, Kutahya TR-43100, Turkey *Corresponding author: [email protected]

Indoor radon concentrations are subject to seasonal variation, which directly depends on weather conditions. The seasonal indoor radon concentrations were measured and the annual effective dose was estimated for the city centre of Eskisehir, Turkey. In order to reflect annual averages measurements were performed over all seasons (winter, spring, summer and autumn) including also the entire year. Measurements were carried out using Kodak-Pathe LR 115 Type II passive alpha track detectors in 220 different houses. A total of 534 measurements including measurements of different seasons were taken between 2010 and 2011. The radon concentrations for winter ranged from 34 to 531 Bq m23, for spring ranged from 22 to 424 Bq m23, for summer ranged from 25 to 320 Bq m23, and for autumn ranged from 19 to 412 Bq m23. Yearly measurements ranged from 19 to 338 Bq m23. In this study the average annual effective total dose from radon and its decay products was calculated to be 3.398 mSv y21.

INTRODUCTION Radon is a naturally occurring radioactive noble gas which is colourless, odourless, tasteless and not detectable by human sense. Radon and its isotopes are regularly produced by uranium and thorium, which occur in the Earth crust in different amounts. Radon has three naturally occurring isotopes: 222Rn, 220 Rn and 219Rn. The most stable isotope is 222Rn, which is the decay product of 226Ra. 222Rn has a halflife of 3.82 d. The other two isotopes (220Rn and 219 Rn) have very short half-lives (55.6 and 3.96 s, respectively), and generally ignored in radon measurements. Radon is the most important source of ionising radiation in natural origin. Radon is considered the second most significant cause of lung cancer after smoking(1). Because radon has a half life longer than breathing times, most of it is inhaled and exhaled before decaying. However, immediate daughters of radon (218Po, 214Pb, 214Bi and 214Po) can attach to surfaces of aerosols and then these aerosols can be inhaled and deposited on epithelial surfaces in the lungs; hereby their alpha radiation affects the tissue. In most houses, indoor radon concentrations are subject to seasonal variation with a maximum in winter and a minimum in summer. In winter time indoor air temperature is higher than outside, and this temperature difference results in a lower atmospheric pressure indoors relative to outdoors. This causes the transport of radon from the ground into the building if a route exists. The indoor radon concentration depends on a large number of factors which includes local geology, soil permeability, building structure, lifestyle characteristics and outside climate(2).

GEOLOGY AND CLIMATE OF THE SURVEYED AREA Radon measurement has been carried out in the city centre of Eskisehir, Turkey (Figure 1). Eskisehir is situated in the northwestern Turkey within the longitudes of 308310 E and latitudes of 398470 N. The city has a population of 631.905, and covers an area of 2.678 km2 (788 m above the sea level). Its adjacent provinces are Bilecik to the northwest, Ku¨tahya to the west, Afyon to the southwest, Konya to the south, Ankara to the east and Bolu to the north. Eskisehir has relatively cold winters with an average of 08C (32.08F), and hot, dry summers with an average of 308C (86.08F). Rainfall occurs mostly during the spring and autumn. Semi-arid climate of Eskisehir’s high altitude and its dry summers cause nightly temperatures 7 –108C lower than daily temperatures. Precipitation is relatively low, although it can be observed throughout the year. Eskisehir is found in a valley. Porsuk River runs from west to east over it. The area consists of Quaternary aged alluvial deposits having mostly gravel, silt and clay. The thickness of the alluvium is 100 m in the central part of the plain and 30–40 m near its boundary(3). Eskisehir is on a tectonic fault zone which extends 400 km from Bursa to the west of Lake Tuz(4). MATERIALS AND METHODS The main objective of this study was to measure the indoor radon concentrations in the dwellings of the city centre of Eskisehir to search for seasonal variations of radon concentrations and to estimate the

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Received 21 June 2013; revised 2 December 2013; accepted 4 December 2013

SEASONAL INDOOR RADON CONCENTRATION IN ESKISEHIR

amount of annual dose absorbed by inhabitants. Measurements were carried out during the following periods: December 2010 to February 2011 (winter period), March 2011 to May 2011 (spring period), June 2011 to August 2011 (summer period) and September 2011 to November 2011 (autumn period), as well as for a period of 12 months. Kodak-Pathe LR 115 Type II detectors were distributed to 220 houses which were randomly selected in Eskisehir city centre. In each house six detectors were placed, i.e. two in living room and two in bedroom for seasonal measurements, and two in living room for annual measurement. Together with the detectors questionnaires and informative brochures were distributed to the inhabitants of the dwellings. The questionnaire included questions about the physical features of the dwelling and the living style of the occupants. The radon measuring device used in this study is an open (bare)-mode detector and consists of a plastic cup of 8.2 cm height, 6.5 cm diameter at one end and 4.4 cm at the other end, where an LR 115 detector with the ` 1.5 cm is fixed. At the end of dimensions of 1.5 cm each measurement period, detectors were collected and etched with 10 % NaOH solution at 608C for 95 min. Following the etching, the detectors were washed and dried. The tracks were manually counted under an optical microscope at a magnification of 100 times. Background track density was determined using 30 unexposed detectors and subtracted from the observed data. To determine the calibration factor a set of LR 115 detectors was installed for 1–5 d inside a radon calibration chamber with an equilibrium radon concentration of 3.2 kBq m23 at the Health Physics Department of the Çekmece Nuclear

Research and Training Centre, which participated in the National Radiological Protection Board of intercomparisons (1989, 1991, 1995 and 2000)(5). The observed track densities were related to radon concentration levels using calibration factor (0.117 Bq m23 tr21 cm2 d). For each house, the mean indoor radon concentration was estimated by averaging the measurements in the bedroom and in the living room. At the beginning of the survey, 170 track detectors were distributed to selected houses; however, the number of measurements in the following periods decreased since some householders moved or lost, mistreated or damaged the detectors. The seasonal average was calculated by adding the winter, spring, summer and autumn data and dividing it by four. For the comparison of the seasonally averaged data and data from yearly exposed detectors, only those houses from which both data are available were used. The lower detection limit (LD) was calculated using the expression LD ¼ 2.71þ3.29sB, where sB is the background standard deviation(6). The minimum detectable concentration (MDC) for radon corresponds to LD expressed in activity concentration units by using the calibration factor. For a 3-month exposure, MDC was estimated to be 4.1 Bq m23. RESULTS AND DISCUSSION Table 1 reports the descriptive statistics determined from the measurements of indoor radon concentration in 220 different dwellings for the four seasons. The indoor radon concentration follows log–normal distribution for each season as confirmed by the Kolmogorov– Simirnov normality test ( p . 0.05).

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Figure 1. Map of the surveyed area.

H. SOGUKPINAR ET AL. Table 1. Summary statistics for the radon concentration data for all houses (all floors). Sample

Winter

Spring

Summer

Autumn

Yearly

Seasonal average

n AM (Bq m23) SE (Bq m23) SD (Bq m23) Minimum (Bq m23) Maximum (Bq m23) GM (Bq m23) GSD

169 147 7.11 92 34 531 126 1.72

137 120 6.59 77 22 424 98 1.89

125 90 5.16 58 25 320 76 1.8

103 151 7.97 81 19 412 131 1.75

83 98 6.85 63 19 338 84 1.73

134 127 6.71 77 25 422 108 1.79

The arithmetic mean of the indoor radon concentrations for winter, spring, summer, autumn and yearly measurements (with SD in brackets) are 147 (92) Bq m23, 120 (77) Bq m23, 90 (58) Bq m23, 151 (81) Bq m23 and 98 (63) Bq m23, respectively. Figure 2 shows clearly higher indoor radon concentrations for winter and autumn periods than those in summer and spring periods. The autumn concentration was even higher than the winter season as opposed to the general tendency of winter concentration being the highest. This can be attributed to the colder temperatures for the autumn season of the year of 2011 than the temperatures for the preceding winter season. Thus, dwellings are more heated and ventilation is lower during the colder season which in turn results in lower indoor pressure and higher radon accumulation within the house. In Eskisehir, new houses either single unit or apartment floors are generally constructed with high isolation, having natural ventilation only in the kitchen. Moreover, most old houses have been renovated for high isolation to reduce heating bills in winter. Table 2 gives indoor radon concentration data from single unit houses or first floors and upper floors, respectively. It is evident from Figure 3 that high radon levels are found in either single unit houses or first floor levels. While there is a significant decrease in the radon concentration from the first floor to the second floor, the change in radon concentrations at upper floors is insignificant. This is because the main radon source for the first floor is the soil, and the radon sources for upper floors are building materials, tap water and the habits of the residents. If the main radon source is from building materials and water, high levels of indoor radon concentration may be reduced by increased ventilation. If the main source of indoor radon is soil and geology under building, active and passive soil depressurisation, regular ventilation and sealing of the surface can be done to reduce indoor radon concentration. The effect of floor level on the indoor radon levels in the different seasons was also investigated with the

Figure 2. Indoor radon concentration data with SE for each measurement period.

Fisher’s LSD test. For this analysis the authors used data from 382 houses which have all of the four season data available. The data analysis of all seasons shows that the indoor radon concentrations are significantly higher at the first floors (LSD, p , 0.0001). This result is consistent with the findings of other authors(7). Differences in the radon concentration between first floor and second floor are statistically insignificant at a 95 % confidence level for all seasons (LSD, p ¼ 0.66 for winter, p ¼ 0.38 for spring, p ¼ 0.62 for summer, p ¼ 0.72 for autumn). The radon concentrations at higher floors are relatively constant. In Figure 4 the seasonal average indoor radon concentrations are plotted together with yearly indoor radon measurements for selected 61 dwellings. The seasonal average radon concentrations were found to be higher than associated yearly measurements. Ninety per cent of 12-month exposed detectors gave significantly lower values due to dust accumulation on track detectors. The differences between the yearly and seasonally averaged radon concentrations were also examined for selected 61 houses, and statistically significant differences between the yearly and the seasonally averaged radon concentrations were found (t-test, p ¼ 0.0039). A similar result was obtained earlier elsewhere(7). Thus, detector sensitivity decreases with measurement time. Moisture is also a potential problem for bare-detector measurements. Namely, if

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n, number of dwellings; AM, arithmetic mean; SE, standard error of the means; SD, standard deviation; GM, geometric mean; GSD, geometric standard deviation.

SEASONAL INDOOR RADON CONCENTRATION IN ESKISEHIR Table 2. Summary statistics for radon concentration data for the first floor and floors except the first floor. Sample

Spring

Summer

Autumn

First floor

Except first floor

First floor

Except first floor

First floor

Except first floor

First floor

Except first floor

37 228 18.3 111 94 471 206 1.57

111 116 5.13 54 34 325 105 1.57

29 200 19.31 104 42 570 176 1.73

99 102 6.71 67 22 424 86 1.81

27 139 14.88 77 38 320 119 1.81

84 76 4.36 40 25 214 66 1.66

23 244 23.86 114 77 554 220 1.61

72 133 7.53 64 19 379 118 1.71

estimated for both cases. The black dot curve is the annual average for the seasonal measurements. This model should be considered as an approximation to the real data.

ANNUAL EFFECTIVE DOSE

Figure 3. Indoor radon concentrations as a function of floor level for each season.

the humidity is high, temperature fall could cause condensation of moisture droplets on the detector foil, which would then act as an absorber for the alpha particle, and thus lower the track densities in an uncontrolled way(8). It has also been shown that the heat and humidity in the presence of oxygen in the air can affect the sensitivity of etched-track detectors while they are being used to measure radon. Seasonal dependence of radon concentration can be described approximately as a sinusoidal function(9). The fitting function for the seasonal data is defined by ln(CRn Þ ¼ y0 þ asin[2pðx  fÞ]

ð1Þ

where can be taken either as a free parameter or estimated annual average of radon, is the radon concentration Bq m23, f is the phase difference and x changes from 0 to 0.75. Figure 5 shows the fit results. The data are logarithms of the geometric means of the seasonal measurement data, the uncertainty bars are the standard error of the means (SE) of the ln(CRn). The red curve shows a fit either y0 as a free parameter or equal to the means of seasonal average, the same values were

For radon and decay products, the annual effective dose equivalent can be estimated from measured radon concentrations based on conversion factors given by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reports(10). A range of dose conversion factors are derived from epidemiological study and physical dosimetry. To calculate the annual effective dose, the dose conversion factor of 9 nSv (Bq m23 h)21, equilibrium factors of 0.4 for indoors and 0.6 for outdoors with an occupancy factor of 0.8 for indoors and 0.2 for outdoors were used, as established by UNSCEAR 2000 (see Table 3). Indoor radon concentrations generally follow log – normal distribution. Thus, the arithmetic mean is generally used for estimating average indoor radon concentration in a given area. To estimate the annual effective dose (DE, mSv y21) the following formula is used. DE ¼ CRn DQET

ð2Þ

where CRn (Bq m23) is the annual mean radon concentration (AM); D (nSv (Bq m23 h)21) is the dose conversion factor; Q is the indoor occupancy factor; E is the indoor radon equilibrium factor and T (h y21) is hours per year. The annual effective dose (mSv y21) for radon decay product for indoors:

413

Ein ¼ 127 Bq m3  9 nSv (Bq h m3 )1  0:8  0:4  8760 h y1 ¼ 3:21 mSv y1

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n AM (Bq m23) SE (Bq m23) SD (Bq m23) Minimum (Bq m23) Maximum (Bq m23) GM (Bq m23) GSD

Winter

H. SOGUKPINAR ET AL.

The annual effective dose (mSv y21) for radon dissolved in blood following inhalation for indoors and outdoors: Ein ¼ 127 Bq m3  0:17 nSv (Bq h m3 )1  0:8  8760 h y1 = 0:15 mSv y1 Eout ¼ 4 Bq m3 0.17 nSv (Bq h m3 )1 0.2  8760 h y1 = 0.00119 mSv y1

Figure 5. Fitting of a sinusoidal function to the natural logarithms of the seasonal geometric means. Table 3. The factors used in estimating annual effective dose: CRn is the annual mean radon concentration, D is the dose conversion factor, Q is indoor occupancy factor and E is the indoor radon equilibrium factor. Radon

Radon decay product

Outdoor Indoor Outdoor Indoor CRn (Bq m23) D nSv (Bq m23 h)21 E Q

4 0.17 — 0.2

127 0.17 — 0.8

4 9 0.6 0.2

127 9 0.4 0.8

The annual effective dose (mSv y21) for radon decay product for outdoors: Eout ¼ 4 Bq m3 9 nSv (Bq h m3 )1  0:2  0:6  8760 h y1 ¼ 0:037 mSv y1

In this study the average annual effective total dose from radon and its decay products was calculated to be 3.398 mSv y21. The world average is 1.15 mSv y21 (UNSCEAR, 2000). The annual effective dose equivalent ranged from 0.5 to 3.5 mSv y21. International Commission on Radiological Protection (ICRP) has recommended action level for annual effective dose between 3 and 10 mSv y – 1. Indoor radon measurements show that dose taken by people is around the lower limit of the action level or slightly less than the action level. CONCLUSION Radon concentration in most dwellings is subject to seasonal variation, and is generally maximum in winter and minimum in summer. To find annual indoor radon concentration it is better to increase the measurement period. Less than a year-long measurement does not reflect the correct radon concentration in a dwelling. In this study the annual indoor radon concentrations carried out in Eskisehir, Turkey, were reported covering 220 different dwellings with a total of 534 measurements. The number of dwellings was determined randomly in accordance with the population density. Measurements were carried out with LR-115 detectors over four seasons with a 3-month exposure period in each season. The arithmetic

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Figure 4. Yearly and seasonally averaged radon concentrations for 61 houses.

SEASONAL INDOOR RADON CONCENTRATION IN ESKISEHIR

ACKNOWLEDGEMENTS The authors would like to thank the referees for their valuable comments and reading the manuscript carefully. FUNDING This work was supported by Eskisehir Osmangazi University Scientific Research Project ( project no: 2010/19014).

REFERENCES 1. RPII and NCRI health risks due to exposure to radon in homes in Ireland—the implications of recently published data joint statement by the Radiological Protection Institute of Ireland and National Cancer Registry of Ireland. Radiological Protection Institute of Ireland, p. 10 (2005). 2. Gunby, J. A., Darby, S. C., Miles, J. C. H., Green, B. M. R. and Cox, D. R. Factors affecting indoor radon concentrations in the United Kingdom. Health Phys. 64, 2–12 (1993). 3. Kac¸arog˘lu, F. and Gu¨nay, G. Groundwater nitrate pollution in an alluvium aquifer, Eskis¸ehir urban area and its vicinity, Turkey. Environ. Geol. 31, 178– 184 (1997). 4. Kocyigit, A. Orta Anadolu’nun genel neotektonik o¨zellikleri ve depremsellig˘i. Haymana-Tuzgolu-Ulukısla Basenleri uygulamali calisma calistayi (workshop title), Turkiye Petrol Jeologlari Dernegi (TPJD) Special Issue 5, 1-26 (in Turkish with English abstract) (2000). 5. Ko¨ksal, E. M., Çelebi, N., Ataksor, B., Ulug, A., Tas¸delen, M., Kopuz, G., Akar, B. and Karabulut, M. T. A survey of 222Rn concentrations in dwellings of Turkey. J. Radioanal. Nucl. Chem. 259(2), 213–216 (2004). 6. Currie, L. A. Limits for qualitative detection and quantitative determination. Anal. Chem. 40(3), 586–593 (1968). 7. Matiullah, S. R. and Ghauri, B. M. Comparison of seasonal and yearly average indoor radon levels using CR-39 detectors. Radiat. Meas. 45(2), 247–252 (2010). 8. Durrani, S. A. and Ilic, R. Radon measurements by etched track detectors: applications to radiation protection, earth sciences and the environment. World Scientific (1997). 9. Stojanovska, Z., Januseski, J., Bossew, P., Zunic, Z. S., Tollefsen, T. and Ristova, M. Seasonal indoor radon concentration in FYR of Macodenia. Radiat. Meas. 46, 602–610 (2011). 10. UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation). Sources and biological effects of ionizing radiation. 2000 Report. United Nations (2000).

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means of indoor radon concentrations for winter, spring, summer, autumn and yearly measurements (with SD in brackets) were found to be 147 (92) Bq m23, 120 (77) Bq m23, 90 (58) Bq m23, 151 (81) Bq m23, and 98 (63) Bq m23, respectively. The indoor radon concentrations of all houses follow log– normal distribution as confirmed by the Kolmogorov–Simirnov normality test. The results of Fisher’s LSD test showed statistically significant differences between the indoor radon concentration of the first floor and that of the second floor. The annual indoor radon concentrations obtained from the seasonal average and from the yearly measurement were different (t-test, p ¼ 0.0039). The annual indoor radon concentration calculated from the seasonal measurements was found to be 127 Bq m23. This result is more than the world average value of 40 Bq m23. The Turkish Atomic Energy Agency set the action level to be 400 Bq m23. The radon concentration in a dwelling with 400 Bq m23 corresponds to the absorbed radiation dose of 10 mSv y21. The ICRP set the action level for the annual effective doses of 3–10 mSv. The estimated annual effective dose was found to be 3.398 mSv, which is higher than the world average (1.15 mSv).

Seasonal indoor radon concentration in Eskisehir, Turkey.

Indoor radon concentrations are subject to seasonal variation, which directly depends on weather conditions. The seasonal indoor radon concentrations ...
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