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Inhalation dose due to Rn-222, Rn-220 and their progeny in indoor environments
Author’s Accepted Manuscript Inhalation dose due to Rn-222, Rn-220 and their progeny in indoor environments Anand Giri, Deepak Pant
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To appear in: Applied Radiation and Isotopes Received date: 9 April 2017 Revised date: 19 October 2017 Accepted date: 23 November 2017 Cite this article as: Anand Giri and Deepak Pant, Inhalation dose due to Rn-222, Rn-220 and their progeny in indoor environments, Applied Radiation and Isotopes, https://doi.org/10.1016/j.apradiso.2017.11.027 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Inhalation dose due to Rn-222, Rn-220 and their progeny in indoor environments
Anand Giri, Deepak Pant* School of Earth and Environmental Sciences, Waste Management Laboratory, Central University of Himachal Pradesh, Dharamshala, Himachal Pradesh – 176215;
Radon (Rn-222), thoron (Rn-220) and its progeny are the natural radioactive gases emitted everywhere in different concentration. These carcinogenic substances were known to be responsible for lung cancer. Human exposure of these gases in an indoor environment was principally dependent on the house types like concrete, slate, mud-tin etc. Rate of exposure is also influenced by unplanned construction and associated poor ventilation.The study of inhalation dose with house type and the associated indoor environment were important to study the exposure due to natural ionising radiation.In this study, we report the results from passive measurement of indoor radon, thoron and their progeny concentrations in Bilaspur district of Himachal Pradesh, India. The measurement was performed at selected 95 dwellings, based on outdoor ambient gamma level and type of houses. Highest inhalation dose due to indoor radon, thoron and their progeny were found in mud houses in comparison to other concrete, slate and tin type of houses. The average annual inhalation dose thus found due to exposure to radon and thoron varies from 0.1 to 0.5mSv/y in the concrete, 0.3 to 0.6 in mud and slate type of houses whereas 0.1 to 0.4 in mud-tin type. The estimated average value of radon, thoron and their progeny concentrations were used to estimate total annual inhalation dose.
Keywords: ventilation; construction; inhalation dose; ionising radiation; indoor radon
1. Introduction Rn-222, Rn-220 and their progeny are the major contribution to inhalation doses received by the human population (Ramola et al., 2016).The exposure to radon and its progeny has been identified as the second most significant cause of lung cancer after smoking (WHO 2009).The value of indoor and outdoor exposer can be varied and the study of indoor value is important due to its apparent health implications in particular dwellings. Radon (222Rn), thoron (220Rn) and their decay products are present in the indoor atmosphere since their parent nuclei radium and thorium are present in the soil, natural construction and building materials. Out of the total radiation exposure in India, nearly 97.7% is from natural sources and the remaining 2.3% is from man-made sources of radiation (Narayanan et al., 1991). Internal and external radiation exposure from construction and building materials creates prolonged exposure situations to those individuals who spend more than 80% of their time in indoors (ICRP, 1999). The internal (inhalation) radiation exposure is mainly due to
222
Rn, and marginally to
220
Rn, and their short-lived daughter nuclei, exhaled from building
materials and ground soil into the indoor environment. Radon in the natural environment is quickly diluted and continual dispersion with the air and no cause to health hazard but whenever it enters into the indoor, it accumulates in the houses due to improper dilution and dispersion of gases and can caused lung cancer to the people living in the dwellings (Khan, 2000).The major source of radon in the indoor air is the presence of radioactive uranium in the soil, rocks beneath the surface of the house, drinking water, building material and cooking gas (Ramola et al., 2005).
222
Rn itself has no
hazardous issue but its short-lived daughter nuclei Polonium isotopes (212Po and
214
Po) can be
hazardous, if the gas is inhaled, densely ionizing alpha particles emitted by the short-lived decay nuclei of radon (212Po and 214Po) can interact with biological tissue in the lungs and results in to lung
cancer (Sevc et al., 1976; Singh et al., 2015) , it is therefore important to understand that origin and migration of Radon (222Rn), and its decay products in indoors for human health hazard purpose. The concentrations of indoor radon and its progeny also vary from geology, architectural style, porosity of the surrounding soil, building layout and ventilation conditions of the building. In the present study radiation monitoring was followed by using, LR-115 detectors in pin-hole cup dosimeters in 95 dwellings by passive measurement technique (Sahoo et al., 2013) to monitor annual inhalation dose due to radon, thoron and its progeny in the study area. 2. Materials and methods 2.1 Geology of the study area The present study (Fig 1) was conducted in the dwellings of Bilaspur district in Himachal Pradesh (H. P.), located on Siwalik ranges of Lesser Himalaya. It lies between north latitude 31°18’00” and 31°55’00” and east longitude 75°55’00” and 76°28’00” and falls in a survey of India degree sheet No.53A. The Bilaspur district is situated in Satluj valley in the outer hills and covers area of 1,167 sq. km. Its boundaries touch Hamirpur, Una, Mandi, and Solan districts of H. P. Most of the area in the district is covered with alluvial soil and non-calcic brown soil. 2.2 Building characteristics. Most of the houses in the surveyed area are cemented and semi-ventilated andonly a few are mud type with poor ventilation. Mud type houses were further distinguished in two types with difference in roof with slate or tin. Generally rural traditional houses are plastered with mud, cow dung, bhusa (straw) or husk plaster. The most construction materials like mud, rocks, cement, sand, bricks, marble and concrete have been used for building construction. Most of the cemented houses in the surveyed area have a single storey while most of the mud houses are of double. The mud-type
houses were built with local mud and sandstone and most of them are less ventilated having one window. 2.3 Ambient gamma level The ambient gamma radiation levels indoors and outdoors in Bilaspur district were measured by using Gama Pocket Survey Meter (SARAD MKS-03D) and Scintillometer (SM 141D EC) (Sannappaa et al.,2003). Ambient gamma radiation map of the selected area was generated by the recording of ambient gamma level in the28 different villages of Bilaspur district (figure 2). 2.4 Pin-hole based twin cup dosimeters Indoor radon and thoron concentrations were measured using a single face for entry of radon (222Rn) and thoron (220Rn) gases from the environment. The design of dosimeter consists of the cylindrical plastic chamber of two equal compartments separated by acentral disc containing pin holes. The height and diameter of dosimeter were11×7cm and height of each chamber were 4.5cm, (Figure 3) (Eappen and Mayya, 2004; Sahoo et al., 2013).The LR-115 detector films were fixed at the end of each compartment dosimeter. The gas enters the lower radon and thoron chamber through a particulate filter and eventually diffuses to upper radon chamber. The dosimeter was hanged over on the ceiling of the selected houses at a height˃2 m from the floor and at least 10cm away from the adjacent walls for a period of about 4 months. Based on the gamma radiation map different radiation zones i.e. less than 10 (<10) and more than 10 (>10) were identified for further dosimeters installation in the study area.To study the seasonal variation of radon, thoron and progeny concentration, study was carried from December 2014 to January 2015 in three different seasons. 2.5 Direct radon and thoron progeny sensors The attached fraction of radon and thoron progeny was measured by direct radon and thoron progeny sensors (DTPS/DRPS; Fig 4) consisting of a 200 mesh type wire screens. These were made
of passive nuclear track detectors (LR-115) mounted with absorbers of appropriate thickness. 50 mm aluminized mylar act as absorber which selectively detects only 8.78 MeV alpha-particles emitted from 212Po (thoron progeny) was used for 220Rn progeny measurement; while for 222Rn progeny, the absorber aluminized mylar and cellulose nitrate combined together and effective thickness was 37 mm to detect mainly 7.67 MeV a-particles emitted from
214
Po (radon progeny) (Mishra et al., 2009).
The basic principle of operation of these sensors is that the LR115 detector detects the alpha particles emitted from an attached fraction of the progeny atoms (Leung et al., 2006; Mishra and Mayya, 2008; Singh et al., 2015). The exposed LR-115 detector films were etched by usingchemical process, using 2.5 N NaOH solution at 60 0C temperature for 90 min in etching bath. Then the etched films were washed, and the track density can be obtained by using the spark counter, which is an electronic counter operating at high voltage. The resulting average track densities were converted into radon, thoron and progeny concentrations. Equilibrium equivalent thoron concentration (EETC) and equilibrium equivalent radon concentration (EERC) are measured by deposition based Direct Progeny Sensor (DPS) in bare modes by calculating DTPS and track density. The absorber of DTPS is of comparatively larger thickness (50 µm) does not allow radon progeny to pass through it, than DRPS (37µm) which allows both radon progeny and thoron progeny to pass through it.
3. RESULTS AND DISCUSSION Average gamma level activity in the Bilaspur district lies in the range of 5.0 to13.0 µR/h (Table 1). Highest gamma level activity was recorded in Jamli and Nainadevi (12.0µR/h),Namhol area (13.0 µR/h) was recorded. The observed annual indoor radon concentration in concrete houses was found to vary from 10 to 280 Bq/m³ with an average value (avg) of 54 Bqm-3,while indoor radon
concentration in mud, slate, and mud-tin houses were found to vary from 32 to 186 (avg 82), 14 to 283 (avg68) and 27 to 134 (avg 65 Bqm-3) ,respectively. The annual indoor thoron concentration in concrete houses were found to vary from 10 to 313 (avg 62), while indoor thoron concentration in mud, slate, and mud-tin were found to vary from 11 to 275 (avg. 87), 12 to 260 (avg76) and 12.0 to 144 (avg 63Bqm-3), respectively (Table 2; fig 5). The average value of indoor thoron was slightly higher than indoor radon level emanation reasonably because of poor ventilation due to the unplanned construction of the building. The high indoor thoron level was found in some concrete houses, mud and slate houses due to the use of raw material from the surrounding thorium containing soil and slate for building construction in the study region. Furthermore, most of the deployment was in the basement and its floors made up of concrete and generally not covered by carpets or any other materials that can disturb radon and thoron flux from the cracks (Alharbi and Akber, 2015). The observed variation in indoor radon concentration may be lithological components like river and soil geology of the study area and the higher thoron concentration in the dwelling mainly due to the use of local raw building material like sandstone, rock, mud, brick, concrete, boulder etc. from the surrounding thorium-rich soil for the construction. 3.1 SEASONAL VARIATION The building construction materials, ventilation condition and seasonal variation in indoor radon, thoron, and progenies levels have been computed for all the 95 dwellings are illustrated in Fig 6 and table 3. It was observed that indoor radon, thoron, and progenies levels were higher in winter season than rainy and summer seasons, which may be due to the poor ventilation conditions because the doors and windows of the dwellings remain mostly closed of the times in winter season, as compared with summer and rainy season. In the summer seasons, radon and thoron concentration in the mud and slate type of houses were higher than winter seasons due to the villagers are regularly
plaster of their own houses by the local mud and soil, while in the winter seasons plastering was not in the regular affair, due to working limitation in cold climatic conditon and generrally most of the room area covered by carpets or mat in winter seasons. Fan and air conditioner are generally not popular in mud and slate type of houses compared with concrete and responsible for the high value of radioactive gas concentration.In the mud houses, people mainly lived in the first floor (ground floor was used for animals), hence the variation of radiation due to ground soil was negligible rather than concrete houses.The average values of indoor radon, thoron, EETC and EERC in mud houses are relatively higher than other dwellings. This variation of indoor radiation in mud houses may be due to the unplanned construction of the mud houses and building material. The higher porosity ofthe material used for concentrations in the dwellings allowed more radon to diffuse inside the room (Ramola et al., 1998). 3.2 Inhalation dose Total inhalation effective dose of radon (TIDr) and thoron (TIDt) of study area along with their progeny were calculated by using thefollowing mathematical equation (UNSCEAR, 2008): TIDr(mSvy−1)=[(Cr×0.17)+(EECr×9)]×8760×0.8×10−6 TIDt(mSvy−1)=[(Ct×0.11)+(EECt×40)]×8760×0.8×10−6 Where, Cr and Ct are the radon and thoron concentrations in Bq/m3, respectively. 0.17 and 9; 0.11 and 40 are the sets of dose conversion factors for radon, thoron and its progeny concentrations, respectively.The conversion factor values lie between dosimetric and epidemiological dose. The occupancy factor has been considered 0.8 as the standard for the study region (exposure duration of one year; Mayya et al., 1998). The total inhalation dose variation in dwellings of this region is presented in fig7. It was observed that average annual inhalation dose
exposure of radon and thoron varies from 0.1 to 0.5 mSv/y in concrete houses, 0.3 to 0.7 in mud houses, 0.3 to 0.6 in slate houses and 0.2 to 0.4 mSv/y in mud-tin houses. 6. Conclusion: The measurement of indoor radon, thoron and their progeny in different types of the dwellings in the study area was carried out for seasonal variation. Measurement of the total inhalation doses received by human population due to natural radiation is an important parameter to check the public health and associated health harms. Furthermore the study concludes the following about the region: 1. radon, thoron levels inmud houses were found to be higher than in made of concrete, slate, and mud-tin dwellings. So human population in mud houses were in more health risk compared to other ; 2. thoron concentration was found to be slightly higher as compared to radon gas concentration in most of the dwellings. It gives a clue about the radioactivity due to material present inbuilding materials and the geology of the area; 3. annual average radon concentrations of most of thedwellings are less than the lower limit of the action level (200-300 Bq m-3), as recommended by ICRP in1993; 4. annual inhalation dose in all the dwellings were below 1msv/y for all houses –type and within the safe limits. Acknowledgement The authors are thankful to board of research in nuclear sciences, department of atomic energy, government of India for providing the financial assistance in the form of the research project via grant no 2013/36/64-BRNS/2618, and Dr. B K Sahoo for his support in the analysis.
4.REFERENCES Alharbi, S.H., Akber, R.A., 2015. Radon and thoron concentrations in public workplaces in Brisbane, Australia. J. Environ. Radioact. 144, 69–76. Bodansky, D., Robkin, M.A., Stadler, D.R., 1987. Indoor radon and its hazards. University of Washington Press, Seattle, WA. Eappen, K.P., Mayya, Y.S., 2004. Calibration factors for LR- 115 (type- II) based radon thoron discriminating dosimeter. Radiat. Meas. 38, 5–17. Evans, R.D., Harley, J.H., Mclean, A.S., Mills, W.A., Stewart, C.G., 1981. Estimate of risk from environmental exposure to radon-222 and its decay products. Nature 290, 98–100. Khan, A.J., (2000). A study of indoor radon levels in Indian dwellings, influencing factors and lung cancer risks. Radiation Measurements, 32(2), 87-92. Leung, S.Y.Y., Nikezic, D., Yu, K.N., 2006. Passive monitoring of the equilibrium factor inside a radon exposure chamber using bare LR 115 SSNTDs. Nucl. Instruments Methods Phys. Res. A 564, 319–323. doi:10.1016/j.nima.2006.04.031 Mayya, Y.S., Eappen, K.P., Nambi, K.S. V, 1998. Methodology for mixed field inhalation dosimetry in monazite areas using a twin-cup dosimeter with three track detectors. Radiat. Prot. Dosimetry 77, 177–184. Mishra, R., Mayya, Y.S., 2008. Study of a deposition-based direct thoron progeny sensor ( DTPS ) technique for estimating equilibrium equivalent thoron concentration ( EETC ) in indoor environment. Radiat. Meas. 43, 1408–1416. doi:10.1016/j.radmeas.2008.03.002 Mishra, R., Mayya, Y.S., Kushwaha, H.S., 2009. Measurement of 220 Rn / 222 Rn progeny deposition velocities on surfaces and their comparison with theoretical models. Aerosol Sci.
40, 1–15. doi:10.1016/j.jaerosci.2008.08.001 Narayanan, K.K., Krishnan, D., Ramu, M.C.S., 1991. Population Exposure to Ionising Radiation in India. ISRP Indian Soc. Radiat. Phys. Pressyanov, D.S., Guelev, M.G., Sharkov, B.G., 1995. Radon and radon progeny outdoors in avalley of enhanced natural radioactivity. Atmos. Environ. 29, 3433–3439. Ramola, R.C., Kandari, M.S., Rawat, R.B.S., Ramachandran, T. V, Choubey, V.M., 1998. A Study of seasonal variations of radon levels in different types of houses. J. Environ. Radioact. 39, 1–7. Ramola, R.C., Negi, M.S., Choubey, V.M., 2005. Radon and thoron monitoring in the environment of Kumaun Himalayas : survey and outcomes. J. Environ. Radioact. 79, 85–92. doi:10.1016/j.jenvrad.2004.05.012 Ramola, R. C., Prasad, M., Kandari, T., Pant, P., Bossew, P., Mishra, R., & Tokonami, S. (2016). Dose estimation derived from the exposure to radon, thoron and their progeny in the indoor environment. Scientific Reports, 6. Sahoo, B.K., Nathwani, D., Eappen, K.P., Ramachandran, T. V, Gaware, J.J., Mayya Y S, 2007. Estimation of radon emanation factor in Indian building materials. Radiation 42, 1422– 1425. Sahoo, B.K., Sapra, B.K., Kanse, S.D., Gaware, J.J., Mayya, Y.S., 2013. A new pin-hole discriminated 222Rn/220Rn passive measurement device with single entry face. Radiat. Meas. 58, 52–60. doi:10.1016/j.radmeas.2013.08.003 Sannappa, J., Chandrashekara, M.S., Sathish, L.A., Paramesh, L. and Venkataramaiah, P., 2003. Study of background radiation dose in Mysore city, Karnataka State, India. Radiation measurements, 37(1),55-65.
Sevc, J., Kunz, E., Placek, V., 1976. Lung Cancer in Uranium Miners and Long-term Exposure to Radon Daughter Products. Health Phys. 30, 433–437. Singh, P., Singh, P., Singh, S., Sahoo, B.K., Sapra, B.K., Bajwa, B.S., 2015. A study of indoor radon, thoron and their progeny measurement in Tosham region Haryana, India. J. Radiat. Reasarch Appl. Sci. 8, 1–8. UNSCEAR, 2008. United Nations Scientific Committee on the Effect of Atomic Radiation., Report to the General Assembly. United Nation, New York. ICRP.(1999). Protection of the public in situations of prolonged radiation exposure. Publication 82, Ann. ICRP 29(1-2), Elsevier Sciences, B.V. International Commission on Radiological Protection ICRP (1992).Principles for Intervention for Protection of the Public in a Radiological Emergency.ICRP Publication 63.Ann. ICRP 22 (4). WHO
handbook
on
indoor
radon.(2009a).
A
public
Whqlibdoc.who.int/publications/2009/9789241547673_eng.pdf.
health
perspective.
Fig.1. Location of Study area
Fig.2. Gamma Radiation survey location map of study area
Fig.3. Pin-holes based twin cup dosimeter
Fig.4. Direct Radon and Thoron progeny sensors 100 Concentration (Bq m-3)
90 80 70 60
Radon
50
Thoron
40 30
EETC
20
EERC
10 0 Concrete
Mud
Slate
Mud -Tin
Houses Types
Fig. 5.Annual average indoor radon, thoron and progenies concentration in different type of houses
Concentration (Bq m-3
120 100 80 Concrete
60
Mud
40
Slate 20
Mud-tin
Summer
Rainy
EERC
EETC
Thoron
Radon
EERC
EETC
Thoron
Radon
EERC
EETC
Thoron
Radon
0
Winter
Fig.6. Seasonal variation of average indoor radon, thoron, EETC and EERC concentration.
Inhalation Dose (mSvy−1)
0.8 0.7 0.6 0.5 0.4
TIDr
0.3
TIDt
0.2 0.1 0 Concrete
Mud
Slate
Mud-Tin
Fig.7. Inhalation dose variation in dwellings
Name of Village:
GPS Coordinate
Gamma Level µR/hr
Long.
Lat.
Bhater
76º40'07.61”
31º 46’15.05”
706.72
9
9
9
Bhahari
76º39'54.65”
31º 32’16.68”
793.7
10
9
9.5
Ladhyani
76º40'07.61”
31º 30’13.93”
706.72
10
10
10
Chakrama
76º40'04.90”
31º 31’13.94”
712.3
9
9
9
Singaswin
76º37'25.97”
31º 24’50.72”
570.37
12
10
11
Barthin
76º38'43.16”
31º 25’16.52”
623.05
10
10
10
Dun
76º39'36.11”
31º 26’37.93”
634.99
10
10
10
Nihari
76º40'23.64”
31º 28’56.64”
665.71
9
9
9
Seu
76º40'57.22”
31º 28’32.74”
629.39
5
6
5.5
Ghumarwin
76º42'58.32”
31º 25’25.91”
584.45
5
5
5
Bager
76º43'44.39”
31º 24’13.86”
586.52
5
5
5
Height (meters
Min.
Max.
Avg.
Kandrour
76º45'37.33”
31º 23’27.32”
510.7
10
9
9.5
Barmana
76º49'44.68”
31º 25’10.24”
497.7
10
10
10
Thohru
76º48'50.69”
31º 20’11.41”
666.21
10
10
10
Gassour
76º48'57.67”
31º 18’30.81”
691.85
10
10
10
Kotla
76º49'00.58”
31º 16’36.73”
788.08
9
10
9.5
Namhol
76º51'49.98”
31º 15’22.13”
1182.4
13
13
13
Sagirthi
76º47'49.66”
31º 16’23.22”
804.91
6
6
6
Nauni
76º46'20.04”
31º 18’007.20”
618.6
10
10
10
Bilaspur
76º45'42.0”
31º 20’05.22”
570.36
7
7
7
Kothipura
76º47'00.83”
31º 17’27.25”
682.89
5
5
5
Charol
76º46'11.58”
31º 15’15.76”
697.36
10
10
10
Jamli
76º46'38.84”
31º 13’47.15”
657.32
12
12
12
Baner
76º44'56.37”
31º 14’07.57”
710.8
10
10
10
Nainadevi
76º32'05.68”
31º 18’30.45”
1073.07
13
13
13
Saloa
76º29'53.78”
31º 21’22.11”
661.53
10
10
10
Makri
76º29'02.47”
31º 22’44.73”
598.77
12
12
12
Bakhra
76º26'41.21”
31º 24’57.84”
482.46
10
10
10
Table.1. Ambient gamma radiation levels in different villages of Bilaspur District
Concrete
Mud
Slate
Mud -Tin
Radon
54.4
82.8
68.8
65.9
Thoron
62.3
87.9
76.2
63.3
EETC
0.29
0.94
0.89
0.49
7.4
9.3
8.8
5.4
EERC
Table.2. Annual average indoor radon, Thoron and progenies concentration
Summer
Concrete Min. Max.
Avg.
Min.
Mud Max.
Avg.
Min.
Slate Max.
Avg.
Mud-tin Min. Max. Avg.
Radon Thoron EETC EERC Radon Thoron
Rainy
EETC EERC Radon
Winter
Thoron EETC EERC
10.4 22 0.12 0.8 20.9 10.4 0.68 0.8 19.6 20.4 0.94 0.21
115.4 176.5 1.45 16.3 89.2 112.3 1.49 16.8 152.6 250.1 3.06 0.8
48.4 67 0.62 6.8 48.4 53.3 0.13 6.6 66.4 71 0.21
32 26.8 0.27 3.1 48.8 11.4 0.23 2.2 39.8 14 0.23
33.9
1.9
186 80.5 277.1 109.6 2.79 0.92 33.8 11.9 184.1 83.6 275.5 75 2.72 0.96 19.3 8.4 135.8 84.5 275.5 79.1 2.13 1.1 18.4
7.6
36.1 31.2 0.23 1.6 14.9 15.6 0.21 1 31.9 12.3 0.32
283.3 204.3 2.5 29.1 125.5 147.2 2.47 22.1 132.5 260 5.32
74.4 82.3 0.85 10.7 61.1 73.1 0.91 7.4 71 73.4 1.1
36.4 65.9 0.35 2 27.7 12 0.76 6.5 41.6 20.7 0.27
132.6 12.4 2.08 20.4 124.1 127.4 1.8 12.8 134 128.5 1.51
65.9 58.9 0.95 6.7 56.1 62.7 0.27 2.1 75.8 68.4 0.79
1.1
17.4
8.4
2
17.8
7.5
-3
Table 3- Seasonal variation of indoor radon, thoron and their progeny concentration (Bq m )
Highlights Comparative study of indoor radon, thoron and their progeny concentrations in different house types. Radon, thoron levels in mud houses were found to be higher compared with dwellings made of concrete, slate and mud-tin. In summer season radon and thoron concentration in the mud and slate type of houses were found higher than winter seasons.
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PII: DOI: Reference:
S0969-8043(17)30522-5 https://doi.org/10.1016/j.apradiso.2017.11.027 ARI8176
To appear in: Applied Radiation and Isotopes Received date: 9 April 2017 Revised date: 19 October 2017 Accepted date: 23 November 2017 Cite this article as: Anand Giri and Deepak Pant, Inhalation dose due to Rn-222, Rn-220 and their progeny in indoor environments, Applied Radiation and Isotopes, https://doi.org/10.1016/j.apradiso.2017.11.027 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Inhalation dose due to Rn-222, Rn-220 and their progeny in indoor environments
Anand Giri, Deepak Pant* School of Earth and Environmental Sciences, Waste Management Laboratory, Central University of Himachal Pradesh, Dharamshala, Himachal Pradesh – 176215;
Radon (Rn-222), thoron (Rn-220) and its progeny are the natural radioactive gases emitted everywhere in different concentration. These carcinogenic substances were known to be responsible for lung cancer. Human exposure of these gases in an indoor environment was principally dependent on the house types like concrete, slate, mud-tin etc. Rate of exposure is also influenced by unplanned construction and associated poor ventilation.The study of inhalation dose with house type and the associated indoor environment were important to study the exposure due to natural ionising radiation.In this study, we report the results from passive measurement of indoor radon, thoron and their progeny concentrations in Bilaspur district of Himachal Pradesh, India. The measurement was performed at selected 95 dwellings, based on outdoor ambient gamma level and type of houses. Highest inhalation dose due to indoor radon, thoron and their progeny were found in mud houses in comparison to other concrete, slate and tin type of houses. The average annual inhalation dose thus found due to exposure to radon and thoron varies from 0.1 to 0.5mSv/y in the concrete, 0.3 to 0.6 in mud and slate type of houses whereas 0.1 to 0.4 in mud-tin type. The estimated average value of radon, thoron and their progeny concentrations were used to estimate total annual inhalation dose.
Keywords: ventilation; construction; inhalation dose; ionising radiation; indoor radon
1. Introduction Rn-222, Rn-220 and their progeny are the major contribution to inhalation doses received by the human population (Ramola et al., 2016).The exposure to radon and its progeny has been identified as the second most significant cause of lung cancer after smoking (WHO 2009).The value of indoor and outdoor exposer can be varied and the study of indoor value is important due to its apparent health implications in particular dwellings. Radon (222Rn), thoron (220Rn) and their decay products are present in the indoor atmosphere since their parent nuclei radium and thorium are present in the soil, natural construction and building materials. Out of the total radiation exposure in India, nearly 97.7% is from natural sources and the remaining 2.3% is from man-made sources of radiation (Narayanan et al., 1991). Internal and external radiation exposure from construction and building materials creates prolonged exposure situations to those individuals who spend more than 80% of their time in indoors (ICRP, 1999). The internal (inhalation) radiation exposure is mainly due to
222
Rn, and marginally to
220
Rn, and their short-lived daughter nuclei, exhaled from building
materials and ground soil into the indoor environment. Radon in the natural environment is quickly diluted and continual dispersion with the air and no cause to health hazard but whenever it enters into the indoor, it accumulates in the houses due to improper dilution and dispersion of gases and can caused lung cancer to the people living in the dwellings (Khan, 2000).The major source of radon in the indoor air is the presence of radioactive uranium in the soil, rocks beneath the surface of the house, drinking water, building material and cooking gas (Ramola et al., 2005).
222
Rn itself has no
hazardous issue but its short-lived daughter nuclei Polonium isotopes (212Po and
214
Po) can be
hazardous, if the gas is inhaled, densely ionizing alpha particles emitted by the short-lived decay nuclei of radon (212Po and 214Po) can interact with biological tissue in the lungs and results in to lung
cancer (Sevc et al., 1976; Singh et al., 2015) , it is therefore important to understand that origin and migration of Radon (222Rn), and its decay products in indoors for human health hazard purpose. The concentrations of indoor radon and its progeny also vary from geology, architectural style, porosity of the surrounding soil, building layout and ventilation conditions of the building. In the present study radiation monitoring was followed by using, LR-115 detectors in pin-hole cup dosimeters in 95 dwellings by passive measurement technique (Sahoo et al., 2013) to monitor annual inhalation dose due to radon, thoron and its progeny in the study area. 2. Materials and methods 2.1 Geology of the study area The present study (Fig 1) was conducted in the dwellings of Bilaspur district in Himachal Pradesh (H. P.), located on Siwalik ranges of Lesser Himalaya. It lies between north latitude 31°18’00” and 31°55’00” and east longitude 75°55’00” and 76°28’00” and falls in a survey of India degree sheet No.53A. The Bilaspur district is situated in Satluj valley in the outer hills and covers area of 1,167 sq. km. Its boundaries touch Hamirpur, Una, Mandi, and Solan districts of H. P. Most of the area in the district is covered with alluvial soil and non-calcic brown soil. 2.2 Building characteristics. Most of the houses in the surveyed area are cemented and semi-ventilated andonly a few are mud type with poor ventilation. Mud type houses were further distinguished in two types with difference in roof with slate or tin. Generally rural traditional houses are plastered with mud, cow dung, bhusa (straw) or husk plaster. The most construction materials like mud, rocks, cement, sand, bricks, marble and concrete have been used for building construction. Most of the cemented houses in the surveyed area have a single storey while most of the mud houses are of double. The mud-type
houses were built with local mud and sandstone and most of them are less ventilated having one window. 2.3 Ambient gamma level The ambient gamma radiation levels indoors and outdoors in Bilaspur district were measured by using Gama Pocket Survey Meter (SARAD MKS-03D) and Scintillometer (SM 141D EC) (Sannappaa et al.,2003). Ambient gamma radiation map of the selected area was generated by the recording of ambient gamma level in the28 different villages of Bilaspur district (figure 2). 2.4 Pin-hole based twin cup dosimeters Indoor radon and thoron concentrations were measured using a single face for entry of radon (222Rn) and thoron (220Rn) gases from the environment. The design of dosimeter consists of the cylindrical plastic chamber of two equal compartments separated by acentral disc containing pin holes. The height and diameter of dosimeter were11×7cm and height of each chamber were 4.5cm, (Figure 3) (Eappen and Mayya, 2004; Sahoo et al., 2013).The LR-115 detector films were fixed at the end of each compartment dosimeter. The gas enters the lower radon and thoron chamber through a particulate filter and eventually diffuses to upper radon chamber. The dosimeter was hanged over on the ceiling of the selected houses at a height˃2 m from the floor and at least 10cm away from the adjacent walls for a period of about 4 months. Based on the gamma radiation map different radiation zones i.e. less than 10 (<10) and more than 10 (>10) were identified for further dosimeters installation in the study area.To study the seasonal variation of radon, thoron and progeny concentration, study was carried from December 2014 to January 2015 in three different seasons. 2.5 Direct radon and thoron progeny sensors The attached fraction of radon and thoron progeny was measured by direct radon and thoron progeny sensors (DTPS/DRPS; Fig 4) consisting of a 200 mesh type wire screens. These were made
of passive nuclear track detectors (LR-115) mounted with absorbers of appropriate thickness. 50 mm aluminized mylar act as absorber which selectively detects only 8.78 MeV alpha-particles emitted from 212Po (thoron progeny) was used for 220Rn progeny measurement; while for 222Rn progeny, the absorber aluminized mylar and cellulose nitrate combined together and effective thickness was 37 mm to detect mainly 7.67 MeV a-particles emitted from
214
Po (radon progeny) (Mishra et al., 2009).
The basic principle of operation of these sensors is that the LR115 detector detects the alpha particles emitted from an attached fraction of the progeny atoms (Leung et al., 2006; Mishra and Mayya, 2008; Singh et al., 2015). The exposed LR-115 detector films were etched by usingchemical process, using 2.5 N NaOH solution at 60 0C temperature for 90 min in etching bath. Then the etched films were washed, and the track density can be obtained by using the spark counter, which is an electronic counter operating at high voltage. The resulting average track densities were converted into radon, thoron and progeny concentrations. Equilibrium equivalent thoron concentration (EETC) and equilibrium equivalent radon concentration (EERC) are measured by deposition based Direct Progeny Sensor (DPS) in bare modes by calculating DTPS and track density. The absorber of DTPS is of comparatively larger thickness (50 µm) does not allow radon progeny to pass through it, than DRPS (37µm) which allows both radon progeny and thoron progeny to pass through it.
3. RESULTS AND DISCUSSION Average gamma level activity in the Bilaspur district lies in the range of 5.0 to13.0 µR/h (Table 1). Highest gamma level activity was recorded in Jamli and Nainadevi (12.0µR/h),Namhol area (13.0 µR/h) was recorded. The observed annual indoor radon concentration in concrete houses was found to vary from 10 to 280 Bq/m³ with an average value (avg) of 54 Bqm-3,while indoor radon
concentration in mud, slate, and mud-tin houses were found to vary from 32 to 186 (avg 82), 14 to 283 (avg68) and 27 to 134 (avg 65 Bqm-3) ,respectively. The annual indoor thoron concentration in concrete houses were found to vary from 10 to 313 (avg 62), while indoor thoron concentration in mud, slate, and mud-tin were found to vary from 11 to 275 (avg. 87), 12 to 260 (avg76) and 12.0 to 144 (avg 63Bqm-3), respectively (Table 2; fig 5). The average value of indoor thoron was slightly higher than indoor radon level emanation reasonably because of poor ventilation due to the unplanned construction of the building. The high indoor thoron level was found in some concrete houses, mud and slate houses due to the use of raw material from the surrounding thorium containing soil and slate for building construction in the study region. Furthermore, most of the deployment was in the basement and its floors made up of concrete and generally not covered by carpets or any other materials that can disturb radon and thoron flux from the cracks (Alharbi and Akber, 2015). The observed variation in indoor radon concentration may be lithological components like river and soil geology of the study area and the higher thoron concentration in the dwelling mainly due to the use of local raw building material like sandstone, rock, mud, brick, concrete, boulder etc. from the surrounding thorium-rich soil for the construction. 3.1 SEASONAL VARIATION The building construction materials, ventilation condition and seasonal variation in indoor radon, thoron, and progenies levels have been computed for all the 95 dwellings are illustrated in Fig 6 and table 3. It was observed that indoor radon, thoron, and progenies levels were higher in winter season than rainy and summer seasons, which may be due to the poor ventilation conditions because the doors and windows of the dwellings remain mostly closed of the times in winter season, as compared with summer and rainy season. In the summer seasons, radon and thoron concentration in the mud and slate type of houses were higher than winter seasons due to the villagers are regularly
plaster of their own houses by the local mud and soil, while in the winter seasons plastering was not in the regular affair, due to working limitation in cold climatic conditon and generrally most of the room area covered by carpets or mat in winter seasons. Fan and air conditioner are generally not popular in mud and slate type of houses compared with concrete and responsible for the high value of radioactive gas concentration.In the mud houses, people mainly lived in the first floor (ground floor was used for animals), hence the variation of radiation due to ground soil was negligible rather than concrete houses.The average values of indoor radon, thoron, EETC and EERC in mud houses are relatively higher than other dwellings. This variation of indoor radiation in mud houses may be due to the unplanned construction of the mud houses and building material. The higher porosity ofthe material used for concentrations in the dwellings allowed more radon to diffuse inside the room (Ramola et al., 1998). 3.2 Inhalation dose Total inhalation effective dose of radon (TIDr) and thoron (TIDt) of study area along with their progeny were calculated by using thefollowing mathematical equation (UNSCEAR, 2008): TIDr(mSvy−1)=[(Cr×0.17)+(EECr×9)]×8760×0.8×10−6 TIDt(mSvy−1)=[(Ct×0.11)+(EECt×40)]×8760×0.8×10−6 Where, Cr and Ct are the radon and thoron concentrations in Bq/m3, respectively. 0.17 and 9; 0.11 and 40 are the sets of dose conversion factors for radon, thoron and its progeny concentrations, respectively.The conversion factor values lie between dosimetric and epidemiological dose. The occupancy factor has been considered 0.8 as the standard for the study region (exposure duration of one year; Mayya et al., 1998). The total inhalation dose variation in dwellings of this region is presented in fig7. It was observed that average annual inhalation dose
exposure of radon and thoron varies from 0.1 to 0.5 mSv/y in concrete houses, 0.3 to 0.7 in mud houses, 0.3 to 0.6 in slate houses and 0.2 to 0.4 mSv/y in mud-tin houses. 6. Conclusion: The measurement of indoor radon, thoron and their progeny in different types of the dwellings in the study area was carried out for seasonal variation. Measurement of the total inhalation doses received by human population due to natural radiation is an important parameter to check the public health and associated health harms. Furthermore the study concludes the following about the region: 1. radon, thoron levels inmud houses were found to be higher than in made of concrete, slate, and mud-tin dwellings. So human population in mud houses were in more health risk compared to other ; 2. thoron concentration was found to be slightly higher as compared to radon gas concentration in most of the dwellings. It gives a clue about the radioactivity due to material present inbuilding materials and the geology of the area; 3. annual average radon concentrations of most of thedwellings are less than the lower limit of the action level (200-300 Bq m-3), as recommended by ICRP in1993; 4. annual inhalation dose in all the dwellings were below 1msv/y for all houses –type and within the safe limits. Acknowledgement The authors are thankful to board of research in nuclear sciences, department of atomic energy, government of India for providing the financial assistance in the form of the research project via grant no 2013/36/64-BRNS/2618, and Dr. B K Sahoo for his support in the analysis.
4.REFERENCES Alharbi, S.H., Akber, R.A., 2015. Radon and thoron concentrations in public workplaces in Brisbane, Australia. J. Environ. Radioact. 144, 69–76. Bodansky, D., Robkin, M.A., Stadler, D.R., 1987. Indoor radon and its hazards. University of Washington Press, Seattle, WA. Eappen, K.P., Mayya, Y.S., 2004. Calibration factors for LR- 115 (type- II) based radon thoron discriminating dosimeter. Radiat. Meas. 38, 5–17. Evans, R.D., Harley, J.H., Mclean, A.S., Mills, W.A., Stewart, C.G., 1981. Estimate of risk from environmental exposure to radon-222 and its decay products. Nature 290, 98–100. Khan, A.J., (2000). A study of indoor radon levels in Indian dwellings, influencing factors and lung cancer risks. Radiation Measurements, 32(2), 87-92. Leung, S.Y.Y., Nikezic, D., Yu, K.N., 2006. Passive monitoring of the equilibrium factor inside a radon exposure chamber using bare LR 115 SSNTDs. Nucl. Instruments Methods Phys. Res. A 564, 319–323. doi:10.1016/j.nima.2006.04.031 Mayya, Y.S., Eappen, K.P., Nambi, K.S. V, 1998. Methodology for mixed field inhalation dosimetry in monazite areas using a twin-cup dosimeter with three track detectors. Radiat. Prot. Dosimetry 77, 177–184. Mishra, R., Mayya, Y.S., 2008. Study of a deposition-based direct thoron progeny sensor ( DTPS ) technique for estimating equilibrium equivalent thoron concentration ( EETC ) in indoor environment. Radiat. Meas. 43, 1408–1416. doi:10.1016/j.radmeas.2008.03.002 Mishra, R., Mayya, Y.S., Kushwaha, H.S., 2009. Measurement of 220 Rn / 222 Rn progeny deposition velocities on surfaces and their comparison with theoretical models. Aerosol Sci.
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handbook
on
indoor
radon.(2009a).
A
public
Whqlibdoc.who.int/publications/2009/9789241547673_eng.pdf.
health
perspective.
Fig.1. Location of Study area
Fig.2. Gamma Radiation survey location map of study area
Fig.3. Pin-holes based twin cup dosimeter
Fig.4. Direct Radon and Thoron progeny sensors 100 Concentration (Bq m-3)
90 80 70 60
Radon
50
Thoron
40 30
EETC
20
EERC
10 0 Concrete
Mud
Slate
Mud -Tin
Houses Types
Fig. 5.Annual average indoor radon, thoron and progenies concentration in different type of houses
Concentration (Bq m-3
120 100 80 Concrete
60
Mud
40
Slate 20
Mud-tin
Summer
Rainy
EERC
EETC
Thoron
Radon
EERC
EETC
Thoron
Radon
EERC
EETC
Thoron
Radon
0
Winter
Fig.6. Seasonal variation of average indoor radon, thoron, EETC and EERC concentration.
Inhalation Dose (mSvy−1)
0.8 0.7 0.6 0.5 0.4
TIDr
0.3
TIDt
0.2 0.1 0 Concrete
Mud
Slate
Mud-Tin
Fig.7. Inhalation dose variation in dwellings
Name of Village:
GPS Coordinate
Gamma Level µR/hr
Long.
Lat.
Bhater
76º40'07.61”
31º 46’15.05”
706.72
9
9
9
Bhahari
76º39'54.65”
31º 32’16.68”
793.7
10
9
9.5
Ladhyani
76º40'07.61”
31º 30’13.93”
706.72
10
10
10
Chakrama
76º40'04.90”
31º 31’13.94”
712.3
9
9
9
Singaswin
76º37'25.97”
31º 24’50.72”
570.37
12
10
11
Barthin
76º38'43.16”
31º 25’16.52”
623.05
10
10
10
Dun
76º39'36.11”
31º 26’37.93”
634.99
10
10
10
Nihari
76º40'23.64”
31º 28’56.64”
665.71
9
9
9
Seu
76º40'57.22”
31º 28’32.74”
629.39
5
6
5.5
Ghumarwin
76º42'58.32”
31º 25’25.91”
584.45
5
5
5
Bager
76º43'44.39”
31º 24’13.86”
586.52
5
5
5
Height (meters
Min.
Max.
Avg.
Kandrour
76º45'37.33”
31º 23’27.32”
510.7
10
9
9.5
Barmana
76º49'44.68”
31º 25’10.24”
497.7
10
10
10
Thohru
76º48'50.69”
31º 20’11.41”
666.21
10
10
10
Gassour
76º48'57.67”
31º 18’30.81”
691.85
10
10
10
Kotla
76º49'00.58”
31º 16’36.73”
788.08
9
10
9.5
Namhol
76º51'49.98”
31º 15’22.13”
1182.4
13
13
13
Sagirthi
76º47'49.66”
31º 16’23.22”
804.91
6
6
6
Nauni
76º46'20.04”
31º 18’007.20”
618.6
10
10
10
Bilaspur
76º45'42.0”
31º 20’05.22”
570.36
7
7
7
Kothipura
76º47'00.83”
31º 17’27.25”
682.89
5
5
5
Charol
76º46'11.58”
31º 15’15.76”
697.36
10
10
10
Jamli
76º46'38.84”
31º 13’47.15”
657.32
12
12
12
Baner
76º44'56.37”
31º 14’07.57”
710.8
10
10
10
Nainadevi
76º32'05.68”
31º 18’30.45”
1073.07
13
13
13
Saloa
76º29'53.78”
31º 21’22.11”
661.53
10
10
10
Makri
76º29'02.47”
31º 22’44.73”
598.77
12
12
12
Bakhra
76º26'41.21”
31º 24’57.84”
482.46
10
10
10
Table.1. Ambient gamma radiation levels in different villages of Bilaspur District
Concrete
Mud
Slate
Mud -Tin
Radon
54.4
82.8
68.8
65.9
Thoron
62.3
87.9
76.2
63.3
EETC
0.29
0.94
0.89
0.49
7.4
9.3
8.8
5.4
EERC
Table.2. Annual average indoor radon, Thoron and progenies concentration
Summer
Concrete Min. Max.
Avg.
Min.
Mud Max.
Avg.
Min.
Slate Max.
Avg.
Mud-tin Min. Max. Avg.
Radon Thoron EETC EERC Radon Thoron
Rainy
EETC EERC Radon
Winter
Thoron EETC EERC
10.4 22 0.12 0.8 20.9 10.4 0.68 0.8 19.6 20.4 0.94 0.21
115.4 176.5 1.45 16.3 89.2 112.3 1.49 16.8 152.6 250.1 3.06 0.8
48.4 67 0.62 6.8 48.4 53.3 0.13 6.6 66.4 71 0.21
32 26.8 0.27 3.1 48.8 11.4 0.23 2.2 39.8 14 0.23
33.9
1.9
186 80.5 277.1 109.6 2.79 0.92 33.8 11.9 184.1 83.6 275.5 75 2.72 0.96 19.3 8.4 135.8 84.5 275.5 79.1 2.13 1.1 18.4
7.6
36.1 31.2 0.23 1.6 14.9 15.6 0.21 1 31.9 12.3 0.32
283.3 204.3 2.5 29.1 125.5 147.2 2.47 22.1 132.5 260 5.32
74.4 82.3 0.85 10.7 61.1 73.1 0.91 7.4 71 73.4 1.1
36.4 65.9 0.35 2 27.7 12 0.76 6.5 41.6 20.7 0.27
132.6 12.4 2.08 20.4 124.1 127.4 1.8 12.8 134 128.5 1.51
65.9 58.9 0.95 6.7 56.1 62.7 0.27 2.1 75.8 68.4 0.79
1.1
17.4
8.4
2
17.8
7.5
-3
Table 3- Seasonal variation of indoor radon, thoron and their progeny concentration (Bq m )
Highlights Comparative study of indoor radon, thoron and their progeny concentrations in different house types. Radon, thoron levels in mud houses were found to be higher compared with dwellings made of concrete, slate and mud-tin. In summer season radon and thoron concentration in the mud and slate type of houses were found higher than winter seasons.