- Email: [email protected]
Indoor radon variations in central Iran and its geostatistical map
Atmospheric Environment 102 (2015) 220e227
Contents lists available at ScienceDirect
Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv
Indoor radon variations in central Iran and its geostatistical map Kamal Hadad*, Javad Mokhtari* Department of Nuclear Engineering, Shiraz University, Shiraz, Iran
h i g h l i g h t s A thorough 2 year indoor radon survey in central Iran (covering an area of 80,000 km2). Analysis of indoor radon level variability. Estimation of population effective dose from radon. Presentation of radon geostatistical spatial distribution map for central Iran.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 September 2014 Received in revised form 16 November 2014 Accepted 4 December 2014 Available online 5 December 2014
We present the results of 2 year indoor radon survey in 10 cities of Yazd province in Central Iran (covering an area of 80,000 km2). We used passive diffusive samplers with LATEX polycarbonate films as Solid State Nuclear Track Detector (SSNTD). This study carried out in central Iran where there are major minerals and uranium mines. Our results indicate that despite few extraordinary high concentrations, average annual concentrations of indoor radon are within ICRP guidelines. When geostatistical spatial distribution of radon mapped onto geographical features of the province it was observed that risk of high radon concentration increases near the Saqand, Bafq, Harat and Abarkooh cities, this depended on the elevation and vicinity of the ores and mines. © 2014 Published by Elsevier Ltd.
Keywords: Indoor radon SSNTD ICRP Geostatistical map Radon prone areas Yazd
1. Introduction The radon maps in many European countries and North America has been obtained and published (Wilkening, 1986; Crameri et al., 1989; Andam, 1992; Miles, 1998), such studies have started to pick up during past two decades in parts of Asia (Narayana et al., 1998; Mui and Wong, 2004; Singh et al., 2005; Badhan et al., 2010; Rafique et al., 2010), Latin America (Canoba et al., 2001; ~es et al., 2003; Espinosa and Gammage, 2003; Hadler Magalha et al., 2008) and Africa (Abo-Elmagd et al., 2007; Lindsay et al., 2008; El-Zaher, 2011; Saad et al., 2013). Radon measurements started in Iran since 1968 (Taghizadeh and Eftekharnejad 1968). The atomic energy organization of Iran (AEOI) has developed measurement techniques since 1988 (Sohrabi and Solaymanian, 1988; Sohrabi, 1999). Indoor radon
* Corresponding authors. E-mail addresses: [email protected] (K. Hadad), javadmokhtari67@gmail. com (J. Mokhtari). http://dx.doi.org/10.1016/j.atmosenv.2014.12.013 1352-2310/© 2014 Published by Elsevier Ltd.
measurements have been accelerated during past two decades in Iran as well as other developing countries. The importance of indoor radon brought to the attention of local governments, have provided sufficient funds for such studies. Example of these studies are: 1 Measurement of Radon Concentration in dwellings around the hot spring in the north west of Iran was investigated using Passive method. The radon levels in the majority of measurements reported less than the lowest limit recommended action level by ICRP (Karamdoust et al., 1993). 2 The indoor radon in 1124 samplers in northern Iran were monitored using both passive and active measurements by solid state nuclear track detectors (SSNTDs) with CR-39 polycarbonate and PRASSI Portable radon Gas Surveyor. The mean value of radon level during the year in Lahijan, Ardabil, Sar-Ein and Namin were 163, 240, 160 and 144 Bq/m3, respectively (Hadad et al., 2007).
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227
3 The Indoor radon concentrations in 30 homes in western Iran were measured using CR-39 alpha track-etch detectors. The average radon concentration and the effective dose equivalent were 108 Bq/m3 and 2.7 mSv/y, respectively. They stated that the maximum radon concentration in Hamadan occurred during the winter period with lower concentrations during the autumn (Gillmore and Jabarivasal, 2010) 4 The radon level of residential dwellings in Shiraz were assessed using Solid State Nuclear Track Detectors (SSNTD), CR-39 polycarbonate films. The annual average indoor radon concentration was 94 ± 52 Bq/m3 and annual effective doses were less than the limitation value recommended by ICRP (Hadad et al., 2011). 5 The indoor radon concentration in 150 apartments in Mashhad city were surveyed by PRASSI Portable radon Gas Surveyor. Result showed about 94.7% of apartments had radon concentration less than 100 Bq/m3 (Mowlavi et al., 2012). 6 The radon levels in 650 homes during the year in the Sari province were obtained using dosimeters DOSEman. The amounts of radon were 28.615 Bq/m3, 27.20 Bq/m3, 27.07 Bq/m3 and 36.95 Bq/m3 in the spring, summer, autumn and winter, respectively. The study has concluded that the average radon concentration was higher in winter than other seasons (Rahimi and Nikpour, 2013). 7 Using portable radon gas surveyor, the radon level of 84 dwellings basement in the city of Yazd were measured in 15 min periods. Despite vicinity of Yazd uranium mines of Saghand (180 Km from Yazd city) the average Radon concentrations of the basements was found to be 137.36 Bq/m3 (Bouzarjomehri and Ehrampoosh, 2008). In the present study, the authors examine radon concentration inside dwellings of the major cities in Yazd Province. The parameters that affect radon concentration variations including building's location, age and residents literacy levels are determined. This work can help to prepare the Iran Radon Map. 1.1. Study area, geographic and historic features the Yazd area The province is located in the central part of Iran, and covers an estimated area of 80,000 km2. It consists of ten townships, 21 cities, 19 districts and 51 villages. Neighboring the important provinces of Fars, Isfahan, Khorasan and Kerman make the province a major cross road in central Iran. The bordering deserts of Kavir-e-Loot,
221
Kavir-e Namak and Dasht-e Kavir, as well as a scanty rainfall give the province a dry climate. The existence of deserts and floating sand are the main geographical features of this province. The inexplicable silence of the desert attracts those who love profound beauties of nature. Yazd province holds a diversity of geodynamic environments like volcanic arcs, metamorphic complexes, and plutonic bodies with their associated hydrothermal mineralization. Therefore, the amount of geological and exploration studies on this province are very high and considerable. This province is one of the exceptional areas on which systematic studies are conducted in both regional and thematic ones. The existence of basement rocks (Bafq-Posht-eBadam zone), volcanic arc (Urumiyah-Bazman zone), and rift zones (Bafq-Posh-e-Badam zone) created a high mineral resource potentials for this province. Exploration studies are conducted in two regional and thematic ways. In this paper we present the results of 24 months radon measurements in dwellings of Yazd province. 10 major cities whose populations exceeded 50,000 were surveyed. Fig. 1 shows the location of Yazd in Iran.
2. Material and method 2.1. Annual radon concentrations Indoor radon sampling was carried out in 10 cities of Yazd province during two years. The map of this region is shown in Fig. 1. Sampling stations were chosen to be able to analyze the radon variation with population density, building age and elevation from see levels. Solid State Nuclear Track Detectors (SSNTD) with Lexan™ polycarbonate films was used as passive sampling instrument. The sampler consists of a 2.5 2.5 cm film placed inside a plastic diffusive holder. The sampler has been developed by Atomic Energy Organization of Iran (AEOI) and the detection, chemical etching and track density measurements and calibration have been fully explained in previous works in Ramsar (Sohrabi, 1999), Ardabil (Hadad et al., 2007), Shiraz (Hadad et al., 2011). The sensitivity of Lexan polycarbonate detector is 0.016 (tracks cm2/Bq m3day) and based on background counts, a minimum detection level (MDL) of 6 Bq/m3 was achievable (Hadad and Doulatdar, 2008). Houses in 10 major cities in Yazd province were chosen in random to include different geological structures. In the Yazd city,
Fig. 1. Location Of Yazd province in central Iran.
222
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227
both old and new quarters were sampled to examine the construction type and dwelling ages on radon levels. In isolated houses, radon detector was placed in a bedroom or a living room. In multistory buildings, one detector was exposed in each flat. Our total data set of all cities in 2 years. The obtained results were compared with information collected in previous national and international surveys. 2.2. The dose calculation The UNSCEAR-2000 model is used to estimate the annual mean effective dose (mSv/y) due to indoor radon (UNSCEAR, 2000).
D ¼ C F H T F0
(1)
where C is the indoor radon concentration (in Bq/m3), F is the equilibrium factor (0.4 for indoor measurement (EPA 2008)), H is the occupancy factor (0.8 for indoor measurement), T is the hours for a year (365.25 24 ¼ 8766 h y1), and F 0 is the dose conversion factor for the whole body dose calculation (9.0 nSv per Bq m3 h1) (ICRP, Publication 50, 1987). 2.3. The geostatistical analysis Geostatistical maps have commonly been developed to map the variation of environmental variables (Nejadkoorki et al., 2011). Radon geostatistical maps have been produced to determine areas with high levels of radon. Radon geostatistical maps show a reliable relation between the geostatistical maps and geographical features; consequently the geographical features studies will be helpful in order to predict of the radon levels in different areas. Radon geostatistical maps could also predict the areas higher reserves of natural uranium. The GPS (Geographic Positioning System) of every sampling station were recorded for data mapping. The measured radon concentrations and its data location were processed as contour maps by using the minimum curvature method to estimate unknown values. The values of the planar regression model at the data locations were subtracted from the data values. For planar regression an ordinary least-squares fit Z(X, Y) ¼ AX þ BY þ C was used, where A, B, and C are the Parameter Values. The minimum curvature algorithm was used to generate the surface that interpolates the residuals at the grid nodes and solves the modified bi-harmonic differential equation with tension:
1 Ti V2
V2 Z Ti V2 Z ¼ 0
(2)
curvature method (Smith and Wessel, 1990). After the geostatistical analyses result plotted onto geographical features of the area. The geostatistical analyses were carried out by using the Golden Software Surfer 10(refs). 3. Results and discussion Table 1 shows the annual median, geometric mean, arithmetic mean radon concentrations with corresponding standard deviations and doses from 222Rn in 10 cities of Yazd province. The annual arithmetic mean and geometric mean radon concentration in old quarters and new quarters of Yazd province for two years compares in Fig. 2. Old quarters have higher annual arithmetic mean radon activity concentration of 97.1 ± 54.0 and 101.8 ± 43.3 Bq/m3 for first year and second year, respectively. These levels marginally exceed the new WHO recommendation of 100 Bq/m3(WHO, 2009). The annual arithmetic mean and geometric mean radon concentrations in different floors of multistory buildings of Yazd province for two years is plotted in Fig. 3. Basements and ground floors have the highest averaged annual radon activity concentration compared with other floors. The annual arithmetic mean radon concentrations in basement and ground floor are 92.5 ± 46.2 and 95.1 ± 54.8 Bq/m3 for first year and 137.5 ± 33.7 and 99.8 ± 41.7 Bq/ m3 for second year, respectively. These results indicate that the radon level in basements and ground floors are marginal to the WHO recommendations. Fig. 4 displays the importance of dwelling age for reduction of indoor radon concentration. The older buildings Because of old construction materials had higher radon levels with highest arithmetic mean of 109 ± 70.9 and 106 ± 42.1 Bq/m3 for first year and second year, respectively. As a result, radon levels in the older buildings exceeds WHO recommendation of 100 Bq/m3. Fig. 5 shows the variation of annual arithmetic mean and geometric mean radon concentration with literacy level of head of household of Yazd province for two years. As could be seen from this figure, the Pre-high school literacy level have the highest radon concentrations while post graduate literacy level have lowest with annual arithmetic mean radon concentrations 99 ± 44.4 and 75.9 ± 48.8 Bq/m3 for first year and 109.8 ± 41.9 and 78.7 ± 27.1 for second year, respectively. Dwelling age, construction materials and
Table 1 Annual median, geometric mean (GM), arithmetic mean (AM) radon concentration and doses in 10 cities of Yazd province. AM (Bq/m3) GM (Bq/m3) Median (Bq/ m3)
Boundary conditions on edges are
! v2 Z þ 1 Tb vn2
! vZ ¼ 0; Tb vn
v V2 Z ¼0 vn
Taft
(3)
(4)
and on the corners:
v2 Z ¼0 vXvY
(5)
where n is the boundary normal, V2 is the Laplacian operator, Ti is the internal tension and Tb is the boundary tension. Final interpolated surface was produced by adding the values of the planar regression model at the grid nodes to the interpolated residuals. Smith and Wessel have been fully described the minimum
First year Second year Ashkezar First year Second year Mehriz First year Second year Harat First year Second year Bafq First year Second year Tabas First year Second year Yazd First year Second year Meybod First year Second year Ardakan First year Second year Abarkooh First year Second year
126 104 70 85 92 75 86 122 70 115 63 116 88 87 93 121 93 118 98 83
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
67 48 25 26 24 33 24 38 30 44 17 50 35 38 45 48 19 43 35 43
113 93 66 82 89 69 83 118 65 109 61 106 81 78 81.85 112.44 91 109 91 73
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
2 2 2 1 1 1 1 1 2 1 1 1 1 2 2 2 1 2 2 2
109 126 76 88 94 63 82 109 62 95 63.5 107 87 80.5 93 118.5 87.75 122 102.5 71
Dose (mSv/ y) 3.2 2.6 1.8 2.2 2.3 1.9 2.2 3.1 1.8 2.9 1.6 2.9 2.2 2.2 2.4 3.1 2.3 3.0 2.5 2.1
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227
223
Fig. 2. Annual averaged radon concentration variations in old quarters and new quarters of Yazd province for two years; (a) arithmetic mean, (b) geometric mean. The error bars are 1 SD based on replicates.
Fig. 3. Annual averaged radon concentration variations in different floors of multistory buildings of Yazd province for two years; (a) arithmetic mean, (b) geometric mean. The error bars are 1 SD based on replicates.
Fig. 4. Variation of annual averaged radon concentration with dwelling age of Yazd province for two years; (a) arithmetic mean, (b) geometric mean. The error bars are 1 SD based on replicates.
224
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227
Fig. 5. Biennial variation of annual averaged radon concentration with the literacy level of head of household; (a) arithmetic mean, (b) geometric mean. The error bars are 1 SD based on replicates.
air conditioning methods depends on financial condition and attitude. Usually, people with higher education have better financial position and attitude. Biennial averaged geostatistical spatial distribution of radon is mapped onto geographical features of the Yazd province in Fig. 6. Fig. 6 indicates that radon concentration decrease in deserts while increases with elevation and vicinity of the ores and mines. Average radon concentrations in all areas of the Yazd province are marginal to the ICRP (or WHO) guidelines. Fig. 7 illustrates measurement point locations and biennial averaged geostatistical spatial distribution of radon plotted onto
map of the Yazd city as the most populated city of the Yazd province. Average radon concentrations in densely populated areas of the Yazd city are within ICRP guidelines. Figs. 8 and 9 represent the areas prone to high indoor radon levels in the Yazd province and Yazd city, respectively. In this figures radon concentration above the thresholds of 120 Bq/m3 is given as Radon Prone Areas (RPA). Fig. 8 shows that risk of high radon concentration is increased near the Saqand, Bafq, Harat and Abarkooh cities. Saghand uranium mine is located in the north part of Yazd province with a longitude of 55.24 E and latitude 32.53 N. There are mines with relatively rich uranium ore near the Bafq city
Fig. 6. Biennial averaged geostatistical spatial distribution of radon mapped onto measurement point locations and geographical features of the Yazd province.
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227
225
Fig. 7. Biennial averaged geostatistical spatial distribution of radon plotted onto measurement point locations and map of the Yazd city.
Fig. 8. Radon prone areas (RPA) in the Yazd province.
at the South of the Yazd province with a longitude of 55.40 E and latitude 31.61 N. Radon gas releases from the decay uranium, which is present in all rocks at various levels. Accordingly, radon concentration increases near mines, particularly uranium mines. Harat and Abarkooh in the southwestern of the Yazd province are the highest cities of the province with altitude of 1600 and 1510 m above sea level, respectively. Similar studies in other countries have shown sites located on highlands had mostly higher radon
concentration due to geological reasons, for example Borgoni et al. (2010) found that municipalities located close to the Alps have a higher probability of being radon prone. 4. Conclusions Using SSNTD technique and during a period of two years, the indoor radon concentrations in Yazd province located in central
226
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227
Fig. 9. Possible map of areas at risk of high radon concentration in the Yazd city.
Iran is investigated. The indoor radon levels variability with different parameters including building's location, age, floor and residents literacy levels have been measured. The minimum curvature algorithm has been employed to generate radon geostatistical spatial distribution maps. Based on our results, the indoor radon levels of Yazd dwellings are marginal to the ICRP and WHO recommendations. Consequently, radon control actions are needed to lower the radon levels. The results also verified the common facts about radon accumulation on residential dwellings as: The indoor radon levels increases with aging buildings, also the average indoor radon concentration in old quarters is higher than new quarters. The average indoor radon concentration is affected significantly by floor levels, increases when the floor level decreases, the highest radon concentration was observed in the basements and ground floors. The new findings specific to Yazd province are: With increasing the literacy level of household heads, the radon levels are reduced. Higher radon concentrations have been observed in Saqand, Bafq, Harat and Abarkooh cities. Radon prone areas decrease in lowlands while increase with higher elevations and mines vicinity. References Abo-Elmagd, M., Metwally, S., El-Fiki, S., Eissa, H., Salama, E., 2007. Passive and active measurements of radon-related parameters inside ancient Egyptian tombs in Luxor. Radiat. Meas. 42 (1), 116e120. Andam, A., 1992. Indoor and soil radon measurements in a tropical climate. Int. J. Radiat. Appl. Instrum. Part D Nucl. Tracks Radiat. Meas. 20 (2), 371e375. Badhan, K., Mehra, R., Sonkawade, R.G., 2010. Measurement of radon concentration in ground water using RAD7 and assessment of average annual dose in the environs of NITJ, Punjab, India. Indian J. Pure Appl. Phys. 48, 508e511. Borgoni, R., Quatto, P., Som a, G., Bartolo, D., 2010. A geostatistical approach to define guidelines for radon prone area identification. Stat. Methods Appl. 19 (2), 255e276. Bouzarjomehri, F., Ehrampoosh, M.H., 2008. Radon level in dwellings basement of Yazd-Iran. Iran. J. Radiat. Res. 6 (3), 141e144. pez-Herrera, M., Vasquez, R., Moreno, V., Lo pez, F., et al., Canoba, A., Espinosa, G., Lo
2001. Indoor radon measurements and methodologies in Latin American countries. Radiat. Meas. 34 (1e6), 483e486. Crameri, R., Brunner, H.H., Buchli, R., Wernli, C., Burkart, W., 1989. Indoor Rn levels in different geological areas in Switzerland. Health Phys. 57 (1), 29e38. El-Zaher, M.A., 2011. Seasonal variation of indoor radon concentration in dwellings of Alexandria city, Egypt. Radiat. Prot. Dosim. 143 (1), 56e62. Espinosa, G., Gammage, R.B., 2003. A representative survey of indoor radon in the sixteen regions in Mexico City. Radiat. Prot. Dosim. 103 (1), 73e76. Gillmore, G.K., Jabarivasal, N., 2010. A reconnaissance study of radon concentrations in Hamadan city, Iran. Nat. Hazards Earth Syst. Sci. 10 (4), 857e863. Hadad, K., Hakimdavoud, M., Hashemi-Tilehnoee, M., 2011. Indoor radon survey in Shiraz-Iran using developed passive measurement method. Iran. J. Radiat. Res. 9 (3), 175e182. Hadad, K., Doulatdar, R., Mehdizadeh, S., 2007. Indoor radon monitoring in Northern Iran using passive and active measurements. J. Environ. Radioact. 95 (1), 39e52. Hadad, K., Doulatdar, R., 2008. U-series concentration in surface and ground water resources of Ardabil Province. Radiat. Prot. Dosim. 130 (3), 309e318. Hadler, J., Neman, R., Iunes, P., Pereira, O., Paulo, S., 2008. Indoor radon and radon progeny survey at Campinas Brazil using CR-39: final results. Radiat. Meas. 43, S440eS444. ICRP, 1987. ICRP publication 50. Lung cancer risk from indoor exposures to radon daughters. In: Annals of the ICRP, vol. 17. Pergamon Press, Oxford. Karamdoust, N., Afarideh, H., Hatami, P., 1993. Radon measurement in dwellings around the hot spring in the north west of Iran. Nucl. Tracks Radiat. Meas. 22 (1e4), 351e353. Lindsay, R., Newman, R., Speelman, W., 2008. A study of airborne radon levels in Paarl houses (South Africa) and associated source terms, using electret ion chambers and gamma-ray spectrometry. Appl. Radiat. Isotopes 66 (11), 1611e1614. ~es, M., Amaral, E., Sachett, I., Rochedo, E., 2003. Radon-222 in Brazil: an Magalha outline of indoor and outdoor measurements. J. Environ. Radioact. 67 (2), 131e143. Miles, J., 1998. Mapping radon-prone areas by Lognormal modeling of house radon data. Health Phys. 74 (3), 370e378. Mowlavi, A.A., Fornasier, M.R., Binesh, A., Denaro, M.D., 2012. Indoor radon measurement and effective dose assessment of 150 apartments in Mashhad, Iran. Environ. Monit. Assess. 184 (2), 1085e1088. Mui, K.W., Wong, L.T., 2004. Evaluation on different sampling schemes for assessing indoor radon level in Hong Kong. Atmos. Environ. 38 (39), 6711e6723. Narayana, Y., Somashekarappa, H., Karunakara, N., Balakrishna, K., Siddappa, K., Kumar, S., et al., 1998. Seasonal variation of indoor radon levels in coastal Karnataka on the south-west coast of India. Radiat. Meas. 29 (1), 19e25. Nejadkoorki, F., Nicholson, K., Hadad, K., 2011. The design of long-term air quality monitoring networks in urban areas using a spatiotemporal approach. Environ. Monit. Assess. 172 (1e4), 215e223. Rafique, M., Rahman, S., Rahman, S.U., Jabeen, S., Shahzad, M.I., Rathore, M.H., 2010. Indoor radon concentration measurement in the dwellings of district Poonch (Azad Kashmir), Pakistan. Radiat. Prot. Dosim. 138 (2), 158e165. Rahimi, S., Nikpour, B., 2013. Measurement of radon concentration of air samples and estimating radiation dose from radon in Sari province. Univers. J. Public Health 1 (2), 26e31. Saad, A., Abdallah, R., Hussein, N., 2013. Radon exhalation from Libyan soil samples measured with the SSNTD technique. Appl. Radiat. Isotopes 72, 163e168.
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227 Singh, S., Mehra, R., Singh, K., 2005. Seasonal variation of indoor radon in dwellings of Malwa region, Punjab. Atmos. Environ. 39 (40), 7761e7767. Smith, W.H., Wessel, P., 1990. Gridding with continuous curvature splines in tension. Geophysics 55 (3), 293. Sohrabi, M., Solaymanian, A., 1988. Indoor radon level measurements in some regions of Iran. Int. J. Radiat. Appl. Instrum. Part D Nucl. Tracks Radiat. Meas. 15 (1e4), 613e616. Sohrabi, M., 1999. New developments on electrochemical etching processes at the atomic energy organization of Iran. Radiat. Meas. 31 (1e6), 115e120.
227
Taghizadeh, N., Eftekharnejad, J., 1968. Geological Survey of Iran, Report on Radioactivity in Ramsar Area. University of Tehran, Iran. UNSCEAR, 2000. United Nations Scientific Committee on the Effects of Atomic Radiation. Source and Effects of Ionizing Radiation. United Nations, New York. Wilkening, M., 1986. Seasonal variation of indoor 222Rn at a location in the southwestern United States. Health Phys. 51, 427e436. World Health Organization, 2009. WHO Handbook on Indoor Radon: a Public Health Perspective. World Health Organization.
Contents lists available at ScienceDirect
Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv
Indoor radon variations in central Iran and its geostatistical map Kamal Hadad*, Javad Mokhtari* Department of Nuclear Engineering, Shiraz University, Shiraz, Iran
h i g h l i g h t s A thorough 2 year indoor radon survey in central Iran (covering an area of 80,000 km2). Analysis of indoor radon level variability. Estimation of population effective dose from radon. Presentation of radon geostatistical spatial distribution map for central Iran.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 September 2014 Received in revised form 16 November 2014 Accepted 4 December 2014 Available online 5 December 2014
We present the results of 2 year indoor radon survey in 10 cities of Yazd province in Central Iran (covering an area of 80,000 km2). We used passive diffusive samplers with LATEX polycarbonate films as Solid State Nuclear Track Detector (SSNTD). This study carried out in central Iran where there are major minerals and uranium mines. Our results indicate that despite few extraordinary high concentrations, average annual concentrations of indoor radon are within ICRP guidelines. When geostatistical spatial distribution of radon mapped onto geographical features of the province it was observed that risk of high radon concentration increases near the Saqand, Bafq, Harat and Abarkooh cities, this depended on the elevation and vicinity of the ores and mines. © 2014 Published by Elsevier Ltd.
Keywords: Indoor radon SSNTD ICRP Geostatistical map Radon prone areas Yazd
1. Introduction The radon maps in many European countries and North America has been obtained and published (Wilkening, 1986; Crameri et al., 1989; Andam, 1992; Miles, 1998), such studies have started to pick up during past two decades in parts of Asia (Narayana et al., 1998; Mui and Wong, 2004; Singh et al., 2005; Badhan et al., 2010; Rafique et al., 2010), Latin America (Canoba et al., 2001; ~es et al., 2003; Espinosa and Gammage, 2003; Hadler Magalha et al., 2008) and Africa (Abo-Elmagd et al., 2007; Lindsay et al., 2008; El-Zaher, 2011; Saad et al., 2013). Radon measurements started in Iran since 1968 (Taghizadeh and Eftekharnejad 1968). The atomic energy organization of Iran (AEOI) has developed measurement techniques since 1988 (Sohrabi and Solaymanian, 1988; Sohrabi, 1999). Indoor radon
* Corresponding authors. E-mail addresses: [email protected] (K. Hadad), javadmokhtari67@gmail. com (J. Mokhtari). http://dx.doi.org/10.1016/j.atmosenv.2014.12.013 1352-2310/© 2014 Published by Elsevier Ltd.
measurements have been accelerated during past two decades in Iran as well as other developing countries. The importance of indoor radon brought to the attention of local governments, have provided sufficient funds for such studies. Example of these studies are: 1 Measurement of Radon Concentration in dwellings around the hot spring in the north west of Iran was investigated using Passive method. The radon levels in the majority of measurements reported less than the lowest limit recommended action level by ICRP (Karamdoust et al., 1993). 2 The indoor radon in 1124 samplers in northern Iran were monitored using both passive and active measurements by solid state nuclear track detectors (SSNTDs) with CR-39 polycarbonate and PRASSI Portable radon Gas Surveyor. The mean value of radon level during the year in Lahijan, Ardabil, Sar-Ein and Namin were 163, 240, 160 and 144 Bq/m3, respectively (Hadad et al., 2007).
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227
3 The Indoor radon concentrations in 30 homes in western Iran were measured using CR-39 alpha track-etch detectors. The average radon concentration and the effective dose equivalent were 108 Bq/m3 and 2.7 mSv/y, respectively. They stated that the maximum radon concentration in Hamadan occurred during the winter period with lower concentrations during the autumn (Gillmore and Jabarivasal, 2010) 4 The radon level of residential dwellings in Shiraz were assessed using Solid State Nuclear Track Detectors (SSNTD), CR-39 polycarbonate films. The annual average indoor radon concentration was 94 ± 52 Bq/m3 and annual effective doses were less than the limitation value recommended by ICRP (Hadad et al., 2011). 5 The indoor radon concentration in 150 apartments in Mashhad city were surveyed by PRASSI Portable radon Gas Surveyor. Result showed about 94.7% of apartments had radon concentration less than 100 Bq/m3 (Mowlavi et al., 2012). 6 The radon levels in 650 homes during the year in the Sari province were obtained using dosimeters DOSEman. The amounts of radon were 28.615 Bq/m3, 27.20 Bq/m3, 27.07 Bq/m3 and 36.95 Bq/m3 in the spring, summer, autumn and winter, respectively. The study has concluded that the average radon concentration was higher in winter than other seasons (Rahimi and Nikpour, 2013). 7 Using portable radon gas surveyor, the radon level of 84 dwellings basement in the city of Yazd were measured in 15 min periods. Despite vicinity of Yazd uranium mines of Saghand (180 Km from Yazd city) the average Radon concentrations of the basements was found to be 137.36 Bq/m3 (Bouzarjomehri and Ehrampoosh, 2008). In the present study, the authors examine radon concentration inside dwellings of the major cities in Yazd Province. The parameters that affect radon concentration variations including building's location, age and residents literacy levels are determined. This work can help to prepare the Iran Radon Map. 1.1. Study area, geographic and historic features the Yazd area The province is located in the central part of Iran, and covers an estimated area of 80,000 km2. It consists of ten townships, 21 cities, 19 districts and 51 villages. Neighboring the important provinces of Fars, Isfahan, Khorasan and Kerman make the province a major cross road in central Iran. The bordering deserts of Kavir-e-Loot,
221
Kavir-e Namak and Dasht-e Kavir, as well as a scanty rainfall give the province a dry climate. The existence of deserts and floating sand are the main geographical features of this province. The inexplicable silence of the desert attracts those who love profound beauties of nature. Yazd province holds a diversity of geodynamic environments like volcanic arcs, metamorphic complexes, and plutonic bodies with their associated hydrothermal mineralization. Therefore, the amount of geological and exploration studies on this province are very high and considerable. This province is one of the exceptional areas on which systematic studies are conducted in both regional and thematic ones. The existence of basement rocks (Bafq-Posht-eBadam zone), volcanic arc (Urumiyah-Bazman zone), and rift zones (Bafq-Posh-e-Badam zone) created a high mineral resource potentials for this province. Exploration studies are conducted in two regional and thematic ways. In this paper we present the results of 24 months radon measurements in dwellings of Yazd province. 10 major cities whose populations exceeded 50,000 were surveyed. Fig. 1 shows the location of Yazd in Iran.
2. Material and method 2.1. Annual radon concentrations Indoor radon sampling was carried out in 10 cities of Yazd province during two years. The map of this region is shown in Fig. 1. Sampling stations were chosen to be able to analyze the radon variation with population density, building age and elevation from see levels. Solid State Nuclear Track Detectors (SSNTD) with Lexan™ polycarbonate films was used as passive sampling instrument. The sampler consists of a 2.5 2.5 cm film placed inside a plastic diffusive holder. The sampler has been developed by Atomic Energy Organization of Iran (AEOI) and the detection, chemical etching and track density measurements and calibration have been fully explained in previous works in Ramsar (Sohrabi, 1999), Ardabil (Hadad et al., 2007), Shiraz (Hadad et al., 2011). The sensitivity of Lexan polycarbonate detector is 0.016 (tracks cm2/Bq m3day) and based on background counts, a minimum detection level (MDL) of 6 Bq/m3 was achievable (Hadad and Doulatdar, 2008). Houses in 10 major cities in Yazd province were chosen in random to include different geological structures. In the Yazd city,
Fig. 1. Location Of Yazd province in central Iran.
222
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227
both old and new quarters were sampled to examine the construction type and dwelling ages on radon levels. In isolated houses, radon detector was placed in a bedroom or a living room. In multistory buildings, one detector was exposed in each flat. Our total data set of all cities in 2 years. The obtained results were compared with information collected in previous national and international surveys. 2.2. The dose calculation The UNSCEAR-2000 model is used to estimate the annual mean effective dose (mSv/y) due to indoor radon (UNSCEAR, 2000).
D ¼ C F H T F0
(1)
where C is the indoor radon concentration (in Bq/m3), F is the equilibrium factor (0.4 for indoor measurement (EPA 2008)), H is the occupancy factor (0.8 for indoor measurement), T is the hours for a year (365.25 24 ¼ 8766 h y1), and F 0 is the dose conversion factor for the whole body dose calculation (9.0 nSv per Bq m3 h1) (ICRP, Publication 50, 1987). 2.3. The geostatistical analysis Geostatistical maps have commonly been developed to map the variation of environmental variables (Nejadkoorki et al., 2011). Radon geostatistical maps have been produced to determine areas with high levels of radon. Radon geostatistical maps show a reliable relation between the geostatistical maps and geographical features; consequently the geographical features studies will be helpful in order to predict of the radon levels in different areas. Radon geostatistical maps could also predict the areas higher reserves of natural uranium. The GPS (Geographic Positioning System) of every sampling station were recorded for data mapping. The measured radon concentrations and its data location were processed as contour maps by using the minimum curvature method to estimate unknown values. The values of the planar regression model at the data locations were subtracted from the data values. For planar regression an ordinary least-squares fit Z(X, Y) ¼ AX þ BY þ C was used, where A, B, and C are the Parameter Values. The minimum curvature algorithm was used to generate the surface that interpolates the residuals at the grid nodes and solves the modified bi-harmonic differential equation with tension:
1 Ti V2
V2 Z Ti V2 Z ¼ 0
(2)
curvature method (Smith and Wessel, 1990). After the geostatistical analyses result plotted onto geographical features of the area. The geostatistical analyses were carried out by using the Golden Software Surfer 10(refs). 3. Results and discussion Table 1 shows the annual median, geometric mean, arithmetic mean radon concentrations with corresponding standard deviations and doses from 222Rn in 10 cities of Yazd province. The annual arithmetic mean and geometric mean radon concentration in old quarters and new quarters of Yazd province for two years compares in Fig. 2. Old quarters have higher annual arithmetic mean radon activity concentration of 97.1 ± 54.0 and 101.8 ± 43.3 Bq/m3 for first year and second year, respectively. These levels marginally exceed the new WHO recommendation of 100 Bq/m3(WHO, 2009). The annual arithmetic mean and geometric mean radon concentrations in different floors of multistory buildings of Yazd province for two years is plotted in Fig. 3. Basements and ground floors have the highest averaged annual radon activity concentration compared with other floors. The annual arithmetic mean radon concentrations in basement and ground floor are 92.5 ± 46.2 and 95.1 ± 54.8 Bq/m3 for first year and 137.5 ± 33.7 and 99.8 ± 41.7 Bq/ m3 for second year, respectively. These results indicate that the radon level in basements and ground floors are marginal to the WHO recommendations. Fig. 4 displays the importance of dwelling age for reduction of indoor radon concentration. The older buildings Because of old construction materials had higher radon levels with highest arithmetic mean of 109 ± 70.9 and 106 ± 42.1 Bq/m3 for first year and second year, respectively. As a result, radon levels in the older buildings exceeds WHO recommendation of 100 Bq/m3. Fig. 5 shows the variation of annual arithmetic mean and geometric mean radon concentration with literacy level of head of household of Yazd province for two years. As could be seen from this figure, the Pre-high school literacy level have the highest radon concentrations while post graduate literacy level have lowest with annual arithmetic mean radon concentrations 99 ± 44.4 and 75.9 ± 48.8 Bq/m3 for first year and 109.8 ± 41.9 and 78.7 ± 27.1 for second year, respectively. Dwelling age, construction materials and
Table 1 Annual median, geometric mean (GM), arithmetic mean (AM) radon concentration and doses in 10 cities of Yazd province. AM (Bq/m3) GM (Bq/m3) Median (Bq/ m3)
Boundary conditions on edges are
! v2 Z þ 1 Tb vn2
! vZ ¼ 0; Tb vn
v V2 Z ¼0 vn
Taft
(3)
(4)
and on the corners:
v2 Z ¼0 vXvY
(5)
where n is the boundary normal, V2 is the Laplacian operator, Ti is the internal tension and Tb is the boundary tension. Final interpolated surface was produced by adding the values of the planar regression model at the grid nodes to the interpolated residuals. Smith and Wessel have been fully described the minimum
First year Second year Ashkezar First year Second year Mehriz First year Second year Harat First year Second year Bafq First year Second year Tabas First year Second year Yazd First year Second year Meybod First year Second year Ardakan First year Second year Abarkooh First year Second year
126 104 70 85 92 75 86 122 70 115 63 116 88 87 93 121 93 118 98 83
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
67 48 25 26 24 33 24 38 30 44 17 50 35 38 45 48 19 43 35 43
113 93 66 82 89 69 83 118 65 109 61 106 81 78 81.85 112.44 91 109 91 73
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
2 2 2 1 1 1 1 1 2 1 1 1 1 2 2 2 1 2 2 2
109 126 76 88 94 63 82 109 62 95 63.5 107 87 80.5 93 118.5 87.75 122 102.5 71
Dose (mSv/ y) 3.2 2.6 1.8 2.2 2.3 1.9 2.2 3.1 1.8 2.9 1.6 2.9 2.2 2.2 2.4 3.1 2.3 3.0 2.5 2.1
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227
223
Fig. 2. Annual averaged radon concentration variations in old quarters and new quarters of Yazd province for two years; (a) arithmetic mean, (b) geometric mean. The error bars are 1 SD based on replicates.
Fig. 3. Annual averaged radon concentration variations in different floors of multistory buildings of Yazd province for two years; (a) arithmetic mean, (b) geometric mean. The error bars are 1 SD based on replicates.
Fig. 4. Variation of annual averaged radon concentration with dwelling age of Yazd province for two years; (a) arithmetic mean, (b) geometric mean. The error bars are 1 SD based on replicates.
224
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227
Fig. 5. Biennial variation of annual averaged radon concentration with the literacy level of head of household; (a) arithmetic mean, (b) geometric mean. The error bars are 1 SD based on replicates.
air conditioning methods depends on financial condition and attitude. Usually, people with higher education have better financial position and attitude. Biennial averaged geostatistical spatial distribution of radon is mapped onto geographical features of the Yazd province in Fig. 6. Fig. 6 indicates that radon concentration decrease in deserts while increases with elevation and vicinity of the ores and mines. Average radon concentrations in all areas of the Yazd province are marginal to the ICRP (or WHO) guidelines. Fig. 7 illustrates measurement point locations and biennial averaged geostatistical spatial distribution of radon plotted onto
map of the Yazd city as the most populated city of the Yazd province. Average radon concentrations in densely populated areas of the Yazd city are within ICRP guidelines. Figs. 8 and 9 represent the areas prone to high indoor radon levels in the Yazd province and Yazd city, respectively. In this figures radon concentration above the thresholds of 120 Bq/m3 is given as Radon Prone Areas (RPA). Fig. 8 shows that risk of high radon concentration is increased near the Saqand, Bafq, Harat and Abarkooh cities. Saghand uranium mine is located in the north part of Yazd province with a longitude of 55.24 E and latitude 32.53 N. There are mines with relatively rich uranium ore near the Bafq city
Fig. 6. Biennial averaged geostatistical spatial distribution of radon mapped onto measurement point locations and geographical features of the Yazd province.
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227
225
Fig. 7. Biennial averaged geostatistical spatial distribution of radon plotted onto measurement point locations and map of the Yazd city.
Fig. 8. Radon prone areas (RPA) in the Yazd province.
at the South of the Yazd province with a longitude of 55.40 E and latitude 31.61 N. Radon gas releases from the decay uranium, which is present in all rocks at various levels. Accordingly, radon concentration increases near mines, particularly uranium mines. Harat and Abarkooh in the southwestern of the Yazd province are the highest cities of the province with altitude of 1600 and 1510 m above sea level, respectively. Similar studies in other countries have shown sites located on highlands had mostly higher radon
concentration due to geological reasons, for example Borgoni et al. (2010) found that municipalities located close to the Alps have a higher probability of being radon prone. 4. Conclusions Using SSNTD technique and during a period of two years, the indoor radon concentrations in Yazd province located in central
226
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227
Fig. 9. Possible map of areas at risk of high radon concentration in the Yazd city.
Iran is investigated. The indoor radon levels variability with different parameters including building's location, age, floor and residents literacy levels have been measured. The minimum curvature algorithm has been employed to generate radon geostatistical spatial distribution maps. Based on our results, the indoor radon levels of Yazd dwellings are marginal to the ICRP and WHO recommendations. Consequently, radon control actions are needed to lower the radon levels. The results also verified the common facts about radon accumulation on residential dwellings as: The indoor radon levels increases with aging buildings, also the average indoor radon concentration in old quarters is higher than new quarters. The average indoor radon concentration is affected significantly by floor levels, increases when the floor level decreases, the highest radon concentration was observed in the basements and ground floors. The new findings specific to Yazd province are: With increasing the literacy level of household heads, the radon levels are reduced. Higher radon concentrations have been observed in Saqand, Bafq, Harat and Abarkooh cities. Radon prone areas decrease in lowlands while increase with higher elevations and mines vicinity. References Abo-Elmagd, M., Metwally, S., El-Fiki, S., Eissa, H., Salama, E., 2007. Passive and active measurements of radon-related parameters inside ancient Egyptian tombs in Luxor. Radiat. Meas. 42 (1), 116e120. Andam, A., 1992. Indoor and soil radon measurements in a tropical climate. Int. J. Radiat. Appl. Instrum. Part D Nucl. Tracks Radiat. Meas. 20 (2), 371e375. Badhan, K., Mehra, R., Sonkawade, R.G., 2010. Measurement of radon concentration in ground water using RAD7 and assessment of average annual dose in the environs of NITJ, Punjab, India. Indian J. Pure Appl. Phys. 48, 508e511. Borgoni, R., Quatto, P., Som a, G., Bartolo, D., 2010. A geostatistical approach to define guidelines for radon prone area identification. Stat. Methods Appl. 19 (2), 255e276. Bouzarjomehri, F., Ehrampoosh, M.H., 2008. Radon level in dwellings basement of Yazd-Iran. Iran. J. Radiat. Res. 6 (3), 141e144. pez-Herrera, M., Vasquez, R., Moreno, V., Lo pez, F., et al., Canoba, A., Espinosa, G., Lo
2001. Indoor radon measurements and methodologies in Latin American countries. Radiat. Meas. 34 (1e6), 483e486. Crameri, R., Brunner, H.H., Buchli, R., Wernli, C., Burkart, W., 1989. Indoor Rn levels in different geological areas in Switzerland. Health Phys. 57 (1), 29e38. El-Zaher, M.A., 2011. Seasonal variation of indoor radon concentration in dwellings of Alexandria city, Egypt. Radiat. Prot. Dosim. 143 (1), 56e62. Espinosa, G., Gammage, R.B., 2003. A representative survey of indoor radon in the sixteen regions in Mexico City. Radiat. Prot. Dosim. 103 (1), 73e76. Gillmore, G.K., Jabarivasal, N., 2010. A reconnaissance study of radon concentrations in Hamadan city, Iran. Nat. Hazards Earth Syst. Sci. 10 (4), 857e863. Hadad, K., Hakimdavoud, M., Hashemi-Tilehnoee, M., 2011. Indoor radon survey in Shiraz-Iran using developed passive measurement method. Iran. J. Radiat. Res. 9 (3), 175e182. Hadad, K., Doulatdar, R., Mehdizadeh, S., 2007. Indoor radon monitoring in Northern Iran using passive and active measurements. J. Environ. Radioact. 95 (1), 39e52. Hadad, K., Doulatdar, R., 2008. U-series concentration in surface and ground water resources of Ardabil Province. Radiat. Prot. Dosim. 130 (3), 309e318. Hadler, J., Neman, R., Iunes, P., Pereira, O., Paulo, S., 2008. Indoor radon and radon progeny survey at Campinas Brazil using CR-39: final results. Radiat. Meas. 43, S440eS444. ICRP, 1987. ICRP publication 50. Lung cancer risk from indoor exposures to radon daughters. In: Annals of the ICRP, vol. 17. Pergamon Press, Oxford. Karamdoust, N., Afarideh, H., Hatami, P., 1993. Radon measurement in dwellings around the hot spring in the north west of Iran. Nucl. Tracks Radiat. Meas. 22 (1e4), 351e353. Lindsay, R., Newman, R., Speelman, W., 2008. A study of airborne radon levels in Paarl houses (South Africa) and associated source terms, using electret ion chambers and gamma-ray spectrometry. Appl. Radiat. Isotopes 66 (11), 1611e1614. ~es, M., Amaral, E., Sachett, I., Rochedo, E., 2003. Radon-222 in Brazil: an Magalha outline of indoor and outdoor measurements. J. Environ. Radioact. 67 (2), 131e143. Miles, J., 1998. Mapping radon-prone areas by Lognormal modeling of house radon data. Health Phys. 74 (3), 370e378. Mowlavi, A.A., Fornasier, M.R., Binesh, A., Denaro, M.D., 2012. Indoor radon measurement and effective dose assessment of 150 apartments in Mashhad, Iran. Environ. Monit. Assess. 184 (2), 1085e1088. Mui, K.W., Wong, L.T., 2004. Evaluation on different sampling schemes for assessing indoor radon level in Hong Kong. Atmos. Environ. 38 (39), 6711e6723. Narayana, Y., Somashekarappa, H., Karunakara, N., Balakrishna, K., Siddappa, K., Kumar, S., et al., 1998. Seasonal variation of indoor radon levels in coastal Karnataka on the south-west coast of India. Radiat. Meas. 29 (1), 19e25. Nejadkoorki, F., Nicholson, K., Hadad, K., 2011. The design of long-term air quality monitoring networks in urban areas using a spatiotemporal approach. Environ. Monit. Assess. 172 (1e4), 215e223. Rafique, M., Rahman, S., Rahman, S.U., Jabeen, S., Shahzad, M.I., Rathore, M.H., 2010. Indoor radon concentration measurement in the dwellings of district Poonch (Azad Kashmir), Pakistan. Radiat. Prot. Dosim. 138 (2), 158e165. Rahimi, S., Nikpour, B., 2013. Measurement of radon concentration of air samples and estimating radiation dose from radon in Sari province. Univers. J. Public Health 1 (2), 26e31. Saad, A., Abdallah, R., Hussein, N., 2013. Radon exhalation from Libyan soil samples measured with the SSNTD technique. Appl. Radiat. Isotopes 72, 163e168.
K. Hadad, J. Mokhtari / Atmospheric Environment 102 (2015) 220e227 Singh, S., Mehra, R., Singh, K., 2005. Seasonal variation of indoor radon in dwellings of Malwa region, Punjab. Atmos. Environ. 39 (40), 7761e7767. Smith, W.H., Wessel, P., 1990. Gridding with continuous curvature splines in tension. Geophysics 55 (3), 293. Sohrabi, M., Solaymanian, A., 1988. Indoor radon level measurements in some regions of Iran. Int. J. Radiat. Appl. Instrum. Part D Nucl. Tracks Radiat. Meas. 15 (1e4), 613e616. Sohrabi, M., 1999. New developments on electrochemical etching processes at the atomic energy organization of Iran. Radiat. Meas. 31 (1e6), 115e120.
227
Taghizadeh, N., Eftekharnejad, J., 1968. Geological Survey of Iran, Report on Radioactivity in Ramsar Area. University of Tehran, Iran. UNSCEAR, 2000. United Nations Scientific Committee on the Effects of Atomic Radiation. Source and Effects of Ionizing Radiation. United Nations, New York. Wilkening, M., 1986. Seasonal variation of indoor 222Rn at a location in the southwestern United States. Health Phys. 51, 427e436. World Health Organization, 2009. WHO Handbook on Indoor Radon: a Public Health Perspective. World Health Organization.