Inhalation Dose Due to Indoor Radon

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1 International Journal of Pure and Applied Physics ISSN Volume 6, Number 3 (2010), pp Research India Publications Inhalation Dose Due to Indoor Radon S. Shobha 1, L.A. Sathish 2*, S. Sundareshan 3 and T.V. Ramachandran 4 1 Department of Physics, Basaveshwara Degree College, Bangalore, India 2 Department of Physics, Government Science College, Bangalore, India 3 Department of Physics, Vijaya Degree College, Bangalore, India 3 Ex-Environ. Assessment Div., Bhabha Atomic Research Center, Mumbai, India *Corresponding Author lasgayit@yahoo.com Abstract The 222 Rn and 220 Rn enter the atmosphere mainly by crossing the air interface of either soil-air or building materials. The existence of relatively high indoor concentration maintains a large 222 Rn, 220 Rn concentration gradient between the materials and open air. The present paper deals with the experimental measurement of 222 Rn, 220 Rn concentrations and the associated inhalation dose rates due to them in the dwellings of different characteristics. Higher dose rates were observed in lower volume houses and the houses with granite flooring. Keywords: Indoor Radon, Thoron, progeny, dose, dwellings. Introduction In recent years the concern has developed about possible associations of indoor radon exposure with cancers [1]. Outstanding issue now is the health effects of low levels of chronic radiation exposures. So far on definite trends are observed in the available studies and there exist a large variability in the effects obtained in different facilities and cohorts. Results of continuing studies would eventually lead to a definite picture of the corresponding dose response relationships and the risk estimates. In view of this, it is essential to have a clear image of these and an attempt is made to estimate the effective dose rates due to the exposure of indoor 222 Rn, 220 Rn and their progeny levels to the population of Bangalore city, India. Also, the observations were made to study the seasonal variations, dependence on different walls, floorings, rooms and range of volume of the houses. This type of study strengthens the results for specific area and adds up as a data bank for radon measurements.

2 258 S. Shobha et al Methods and Measurements Solid State Nuclear Track Detectors (SSNTD) and Spark Counter SSNTD based dosimeters were used for the measurement of radon and this is a good technique to study the long-term measurements [2]. The detailed description of experimental methodology and calibration procedure is available in the literature [3, 4]. Spark counter technique is applicable to plastic detectors, which provides a convenient, economical and fast method for track counting. This technique was developed by Cross and Tommasino [5] and is discussed by Garkani [6]. Results and Discussions About 150 dwellings in ten different locations of Bangalore city, India were selected on the basis of construction, age of the building, nature of walls, rooms and floorings to see the effective dose rates due to indoor 222 Rn, 220 Rn and their progeny levels in dwellings during different seasons of the year, and also for different walls, floorings, rooms and different volume of the houses. Seasonal variations and dose rates: The mean values of the 222 Rn and 220 Rn concentrations of all the studied locations during different seasons are shown in Fig. 1(a) and the annual effective dose rates in Fig. 1(b). The higher concentrations observed during winter season is may be due to the radioactive gases are trapped near to the surface because of temperature inversions. In summer, the higher rate of vertical mixing and dispersions lifts the aerosols to higher altitudes resulting in a decrease in the concentration near the ground level air [7]. Magalhaes et al [8] have observed a two order of magnitude of variability, with a maximum of 50 Bq m -3 in winter and a minimum of 0.5 Bq m -3 in summer months. In addition radon exhalation rate also decreases during monsoon as soil pores get filled by water and hence, resulting in lower concentration of 222 Rn and 220 Rn [9]. Wall wise variations and dose rates: The mean concentration of 222 Rn and 220 Rn levels in different walls are shown in Fig 2(a) and the respective dose rates in Fig 2(b). Higher concentrations and dose rates were observed in mud wall houses and lower in concrete walls. The concentrations were found to vary from wall to wall. The variation is may be due to the random distribution of radioactive rock species used ignorantly in the construction of houses [10]. Floor wise variations and dose rates: The higher concentrations of 222 Rn and 220 Rn were observed in granite flooring houses and lower in mosaic flooring and are shown in Fig. 3(a). Granite is rich of radium and it may be the reason for higher concentration of radon in granite flooring houses. The materials used for construction of buildings are sufficiently porous and allow radon to enter into the indoor atmosphere [11]. Granite samples show higher radon exhalation rate than mosaic. There is a positive correlation between radium content of

3 Inhalation Dose Due to Indoor Radon 259 granite with radon exhalation and its concentration [12]. The variations of dose rates in different floorings are shown in Fig. 3(b). The elevated levels were observed in the granite floorings and the lower in mosaic floorings. Room wise variations and dose rates: Variations of indoor 222 Rn and 220 Rn concentrations in different rooms of houses are shown in Fig 4 (a). The high concentrations were observed in bath room, bed room and lower in living rooms. One can clearly see in the figure that there is soaring concentration in bathroom compared to the other rooms of the houses. Bed rooms might be expected to be least ventilated, on the average based upon limited use patterns and bath rooms may receive some additional 222 Rn due to 222 Rn dissolved in water [13]. 222 Rn is shown to be released in spray from faucets or shower fixture [14]. Air in living rooms on the other hand is most readily diluted due to outdoor air blow. The variations of dose rate in different rooms of the houses are shown in figure 4(b). Higher dose rates were observed in bed room and bath rooms. Volume wise variations and dose rates: The volumetric variations of 222 Rn and 220 Rn are shown in Fig. 5(a). Higher concentrations were observed in lower volume room than in the higher volume room. The concentrations in a dwelling of volume m 3 ranged from 4 to 93Bq m -3. It is interesting to note that as the volume of room varies in geometric progression; there is no linear dependence on the concentrations. This clearly indicates that though the observations have been made almost for similar type of constructions and lifetime of the houses, but as the volume of the room increases the concentrations reduces exponentially and it becomes almost constant above the house volume 150 m 3. The regression coefficients for the exponential drops for 222 Rn and 220 Rn are 0.99 and 0.98 respectively. The variations of dose rates are shown in Fig. 5(b). The present work reveals that the dwellers of lower volume houses will expose themselves to the higher dose rates and is 4.4 times of the dose received in higher volume houses. Geometric means of indoor 222 Rn and 220 Rn levels in the study area are 23.0 and 20.0 Bqm -3 with GSDs 2.1 and 2.0 respectively. Cumulative frequencies against the radon/thoron values showed linear regression with correlation coefficient equals 1 for both the cases. A linear correlation with correlation coefficient nearing one indicates a common factor predominant in the various categories of rooms governing the gas concentrations in these houses. A correlation with dwellings volume and gas concentrations is attempted in this study. Inhalation dose is computed using UNSCEAR [15] dose conversion factors. Inhalation dose calculated from the total results varied from msv y -1 with a geometric mean of 1.34 msv y -1 (GSD 2.1)

4 260 S. Shobha et al Figure 1: Season wise 222 Rn, 220 Rn and Figure 2: Wall wise 222 Rn, 220 Rn and Figure 3: Floor wise 222 Rn, 220 Rn and Figure 4: Room wise 222 Rn, 220 Rn and Figure 5: Volume wise 222 Rn, 220 Rn and dose rate. Conclusions With the aim of estimations of dose rates in dwellings of different features of Bangalore city. The higher values were observed in lower volume house, granite

5 Inhalation Dose Due to Indoor Radon 261 flooring house, bath room, mud wall houses and during winter seasons. Among these the lower volume and granite flooring house inhabitants are exposed to higher dose. Hence, it is recommended that the lower volume houses should have good ventilation and they should avoid granites for floorings to reduce the effective dose rate. Acknowledgments The research work is sponsored by the University Grants Commission in the form of research grants under the Research Funding Council for major research project, X Plan, UGC, New Delhi (F.No.32-46/2006(SR) dated ). The cooperation extended by all the residents is highly appreciated and the support extended by all the principals of government science college, Bangalore for allowing us to carry out the research work in the test room is highly acknowledged. References [1] Allen, J. E, Henshaw, D. L., Keith, P. A., Fews, A. P., 1995, Fat cells in red bone marrow of human rib; their size and spatial distribution with respect to the radon-derived dose to the haemoniteic tissue Int J Bio 68, pp [2] Fleischer, R. L., 1998, Radon in the environment-opportunities and hazard Nuclear Tracks Radiation Measurements. 14, pp [3] Mayya, Y. S., Eappen, K. P., and Nambi, K. S. V., 1998, Methodology for mixed field inhalation dosimetry in monazite areas using a twin cup dosimeter with three track detectors Rad Prot Dosimetry 77, pp [4] Eappen, K. P., and Mayya, Y. S., 2004, Calibration factors for LR-115 (type II) based radon thoron discriminating dosimeter Radiat Meas, 38, pp [5] Cross, W. G., and Tommasino, L., 1970, Rapid reading technique for nuclear particle damage tracks in thin foils Radiation Effects, 5, pp [6] Garkani, D. A., 1989, Spark Counter for Alpha Particle Registration in Proceedings of International Workshop on Radon Monitoring in Radioprotection, Environmental Radioactivity and Earth Sciences. Eds L. Tommasino, G. Furlan, H. A. Khan and M. Monnin (Singapore: World Scientific) pp [7] Sesana, L., Caprioli, E., and Marcazzan, G. M., 2003, Long period study of outdoor radon concentration in Milan and correlation between its temporal variations and dispersion properties of atmosphere Journal of Environmental Radioactivity, 65, pp [8] Magalhaes, M. H., Amaral, E. C. S., Sachett, I., and Rochedo, 2003, Radon- 222 in Brazil: an outline of indoor and outdoor measurements Journal of Environmental Radioactivity ERR, 67, pp [9] Nagaraja, K., Prasad, B. S. N., Madhava, M. S., 2003, Chandrashekara MS, Paramesh L, Sannappa J, Pawar SD, Murugavelu P and Kamra AK Radiat Meas, 36, pp

6 262 S. Shobha et al [10] Kumar, J., Malhotra, R., Singh, J., Singh, S., 1994, 222 Rn measurements in dwellings in radioactive areas in Himachal Pradesh, India, using LR-115 Plastic Track Detectors Nucl Geophys, 6, pp [11] Gaso, M. I., Segovia, N., Pulinets, S., Leyva, A., Ponciano, G., Pena, P., 2005, Indoor radon and annual effective doses at a high altitude region in central Mexico J Appl Sci, 5, pp [12] Al-Jarallah, 2001, 222 Rn exhalation from granites used in Saudi Arabia J Env Radioact 53, pp [13] Sathish, L. A., Sannappa, J., Paramesh, L., Chandrashekara, M. S., and Venkataramaiah, P., 2006, Studies on the concentrations of radon/thoron and their progeny in houses of different types of floorings in Mysore city Env Geochem, 9, pp [14] Gessel, T. F., and Prichard, H. M., 1980, The concentration of 222 Rn in tap water to Indoor 222 Rn concentrations In: Natural Radiation Environment-III, Eds. Gessel TF, Prichard HM, Springfield, pp [15] UNSCEAR. 2000, Report to the General Assembly with Scientific Annexes, United Nations. Annexure B, pp

Elaine R. R. Rochedo

Elaine R. R. Rochedo Summary ICRP recommendations on exposure to radon New BSS requirements Comments Public Exposure General Some suggestions for a National Radon Program Radon -ICRP Reccommendations