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ORIGINAL ARTICLE
Year : 2014  |  Volume : 37  |  Issue : 3  |  Page : 150-156  

Radon exhalation rate from the building materials of Tiruchirappalli district (Tamil Nadu State, India)


1 Department of Chemistry, Jamal Mohamed College, Tiruchirappalli, Tamil Nadu, India
2 Environmental Research Centre, J. J. College of Engineering and Technology, Tiruchirappalli, Tamil Nadu, India
3 Radiological Safety Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu, India

Date of Web Publication10-Apr-2015

Correspondence Address:
P Shahul Hameed
Environmental Research Centre, J. J. College of Engineering and Technology, Tiruchirappalli 620 009, Tamil Nadu
India
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Source of Support: Project Funded by Atomic Energy Regulatory Board, Governmet of India, Mumbai (Project No.: AERB/CSRP/45/05/2010)., Conflict of Interest: None


DOI: 10.4103/0972-0464.154869

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  Abstract 

Tiruchirappalli district has enriched resources of building materials such as stone, granite, sand, brick, cement, etc., which are also supplied to the neighboring districts. Since radon is considered as one of the causative factors for human lung diseases, the measurement of the radon level in these building materials is imperative for the assessment. The samples of building materials were collected from their original sources spread over Tiruchirappalli district. The sealed can technique with solid state nuclear track detector (SSNTD) was employed for the measurement of radon exhalation. The activity concentrations of radon in sedimentary rocks analyzed ranged from 13.2 Bq/m 3 to 218.0 Bq/m 3 with the geometric mean activity of 46.3 Bq/m 3 . However, radon concentrations in igneous rocks are distinctly higher than those of sedimentary rocks and ranged from 95.6 Bq/m 3 to 1140 Bq/m 3 with the geometric mean activity concentration of 392.6 Bq/m 3 . The radon exhalation from sand, brick, and cement were found to be non-uniform (sand: 119.8-656 Bq/m 3 , brick: 31-558 Bq/m 3 , cement: 172-300 Bq/m 3 ). The activity concentration of radon in these building materials follow a descending order: Granite > sand > cement > brick > sand stone. The mass and surface exhalation (E M and E A ) rates also follow the same order. The study concludes that since the radon exhalation from the building materials was less than the International Commission on Radiological Protection limit of 1500 Bq/m 3 , they do not pose any radiological risk.

Keywords: Building materials, radon exhalation, solid state nuclear track detector, Tiruchirappalli


How to cite this article:
Pillai G S, Mazhar Nazeeb Khan S M, Hameed P S, Balasundar S. Radon exhalation rate from the building materials of Tiruchirappalli district (Tamil Nadu State, India). Radiat Prot Environ 2014;37:150-6

How to cite this URL:
Pillai G S, Mazhar Nazeeb Khan S M, Hameed P S, Balasundar S. Radon exhalation rate from the building materials of Tiruchirappalli district (Tamil Nadu State, India). Radiat Prot Environ [serial online] 2014 [cited 2020 Jun 6];37:150-6. Available from: http://www.rpe.org.in/text.asp?2014/37/3/150/154869


  Introduction Top


The building materials derived from rocks and soil contains the natural radionuclides such as uranium ( 238 U) and thorium ( 232 Th) and their daughter products and singly occurring potassium ( 40 K). The external exposure is caused by direct gamma radiation while the internal radiation exposure is caused by inhalation of radon ( 222 Rn, a daughter product of 226 Ra) and thoron ( 220 Rn, a daughter product of 224 Ra). Radon ( 222 Rn) is an alpha emitter with a half-life of 3.82 days and decays into a series of short-lived alpha-emitting daughter products, which are largely responsible for human internal radiation exposure affecting respiratory tract, (EC-1999). [1] About 70% of the radon in the living rooms originates from the building materials and also due to poor ventilation Stoop et al. 1998; [2] Sonkawade et al. 2005. [3] Hence, construction materials can be significant sources of indoor radon in addition to soil and water. Knowledge of radioactivity present in building materials enables one to assess any possible radiological risk to human health (Kumar et al. 2003). [4] The International Commission on Radiological Protection (ICRP) 1993 [5] recommended that the permissible limit of radon concentration for dwellings is 200-600 Bq/m 3 and for work places is 1100-1500 Bq/m 3 .

Several works have been carried out on primordial radioactivity in the building materials of Tamil Nadu using gamma ray spectrometry [6],[7],[8],[9],[10] and indoor radon measurements are reported by Babai et al. 2012 [11] and Kumar and Prasad 2007. [12] However, the study on radon activity and its exhalation rates from individual building materials are limited in India [13],[14] and totally wanting in Tamil Nadu. In general, rocks, cements, bricks, and sand are an important construction materials for houses and buildings in Tiruchirappalli district. However, data on radon exhalation rate in these construction materials are totally lacking. Hence, the present study was undertaken to generate a database on radon activity, surface and mass exhalation rate of building materials and assess the radiological risk in using them.


  Materials and methods Top


Study area

Tiruchirappalli district is located in the central part of Tamil Nadu and lies between 10° and 11°-30' Northern Latitude and between 77°-45' and 78°-50' Eastern longitude. It is the fourth largest district in Tamil Nadu and spread in an area of 4509 km 2 . According to the 2011 census, Tiruchirappalli had a population of 2,722,290 with the population density of 604 persons per km 2 . Tiruchirappalli district is naturally endowed with rich building material resources such as sand, stones, granites, cements and bricks, which are avidly utilized by several adjacent districts also, and the granites and cement are exported to other countries as well. In general, rocks are classified into three types namely igneous, Metamorphic and sedimentary based on their formation in the earth curst. However, igneous and sedimentary rocks are commonly found in Tiruchirappalli district.

Sample collections

The samples of building materials were collected from their original sources spread over Tiruchirappalli district. As such 14 sedimentary rock (sand stone) samples, nine igneous rocks (granite) samples, five sand samples, 10 brick samples were quarried from different quarries of Tiruchirappalli district [Figure 1]. The coordinates of each sampling site was recorded using a hand held GARMIN GPS (Global Positioning System, Model: ETrex 10, USA make). 11 cement samples were also collected from different dealers in Tiruchirappalli district. About 2 kg of the each building material was collected from each quarry. The solid matrix of the samples were powdered and sieved through 500 μm mesh. The samples were air-dried for several days to remove the moisture and unwanted foreign particles. The samples obtained were oven dried at 110°C until they reached a constant weight.
Figure 1: Map showing sampling stations

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Analysis

Radon ( 222 Rn) exhalation rate was measured adopting "can technique" following the method of Abu-Jard 1988. [15] In this method, the alpha emitting gaseous 222 Rn and their particulates progenies will be hitting and forming nuclear tracks on the sensitive surface of solid state nuclear track detector (SSNTD) (LR 115 film). 50 g of powdered building material was placed in plastic cylindrical can of 13 cm height and 9.4 cm diameter. The Kodak LR 115 film also known as SSNTD was fixed on the inner side of the lid with adhesive tape. The can is tightly closed and hermetically sealed such that the sensitive side of the detector (2.5 cm × 2.5 cm) always faced the specimen and it is exposed freely to the emerging radon and it's progenies in the remaining volume of the can [Figure 2]. The can was left for 90 days exposure. At the end of the exposure time, the LR 115 film (SSNTD) was removed and subjected to a chemical etching process in 2.5 N NaOH solutions at 60°C for 1½ h. The detector was washed with distilled water and air-dried. The detector is peeled off from their plastic base, and the registered tracks of alpha particles were counted using spark counter (model: PSC-SC1). The radon activity or integrated radon exposure inside the can was obtained using the sensitivity factor 0.021 tracks cm−2 /day Eappen and Mayya 2004. [16]
Figure 2: Can technique for radon measurement

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The integrated radon concentration can be calculated with the help of the formula Abu-Jard et al., 1988 [15]

(1)



Where T R is the number of tracks cm−2 , d is the time of exposure, K is the calibration factor (sensitivity factor) =0.021 tracks cm−2 /day/Bq/m 3 .

The mass exhalation and surface exhalation rate (E M and E A ) of radon is obtained from the following expressions of Mahur et al. 2008 [17]

(2)



(3)



Where C-is the integrated radon exposure (Bq/m 3 /h); V is the volume of air in can (~ 9.02 E−4 m 3 ); T is the time of exposure (~ 2160 h); λ is the decay constant for radon (7.55 E−3/h); A is surface area of the sample (~ 0.0069 m 2 ); M is the mass of the sample (~ 0.05 kg).


  Results and discussion Top


The activity concentrations of radon and exhalation rates in terms of mass and surface from building materials such as stone rocks, granites, bricks, sand and cements sand are presented in [Table 1] [Table 2] [Table 3] [Table 4]. It is evident from [Table 1], that in stone rocks, the radon activity concentrations varied from 13.2 Bq/m 3 (Kelavadi) to 218 Bq/m 3 (Thiruvellarai) with geometric mean value of 46.3 ×χ 2.25 Bq/m 3 . However, radon concentrations in granite rocks are distinctly higher than those of stone rocks and ranged from 95.6 Bq/m 3 (K. K. Nagar) to 1140 Bq/m 3 (Vilathupatti) with geometric mean value of 392.6×χ 2.1 Bq/m 3 . Next to granite the sand registered a higher radon concentration and found to vary from 119.8 Bq/m 3 (Iyan vaikal) to 656 Bq/m 3 (Ariyar river) with geometric mean of 267.9×χ 1.84 Bq/m 3 [Table 2], whereas, activity in bricks ranged from 31 Bq/m 3 (Thiruvanaikovil) to 558 Bq/m 3 (Malligaipuram) with geometric mean of 136.3 ×χ2.14 Bq/m 3 [Table 3]. The activity concentrations of radon in cement samples were found to vary from 172 Bq/m 3 (Orient cement) to 300 Bq/m 3 (Bharathi cement) with mean of 231.6 ± 35.8 Bq/m 3 [Table 4]. The activity concentrations of radon ( 222 Rn) in these building materials analyzed were nonuniform and follow a descending order: Granite > sand > cement > brick > sand stone. The lowest geometric mean value of radon (46.3×χ 2.25 Bq/m 3 ) was measured in stone rock and the highest geometric mean value of radon (392.6×χ 2.1 Bq/m 3 ) in granite. [Figure 3]a-d show the frequency distribution of the radon activities detected for the building materials analyzed. It can be observed from [Table 5] that the skewness and kurtosis co-efficient of granites, stone rocks, and bricks were not closer to the null value indicating the nonexistence of a normal distribution. However, in cement samples the skewness and kurtosis co-efficient (0.249 and 0.196) was much closer to the null value indicating a normal distribution.
Figure 3: Frequency distribution of radon activities detected for the building materials in the study area

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Table 1: Radon activity and radon exhalation rate in rock samples of Tiruchirappalli district


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Table 2: Radon activity and radon exhalation rate in river sands of Tiruchirappalli district


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Table 3: Radon activity and radon exhalation rate in bricks of Tiruchirappalli district


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Table 4: Radon activity and radon exhalation rate in cement samples of Tiruchirappalli district


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Table 5: Statistical data for radon concentration in building materials of Tiruchirappalli district


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The data on mass and surface exhalation rates of radon in the building materials analyzed were also presented in [Table 1] [Table 2] [Table 3] [Table 4]. The mean mass exhalation rate fluctuated from 6.2×χ 2.25 mBq/kg/h (stone rocks) to 31.5×χ2.24 mBq/kg/h (igneous rocks) while the mean surface exhalation rate from 46.2×χ 2.29 mBq/m/h (stone rocks) to 387.8×χ 2.1 mBq/m 2 /h (igneous rocks). The data are also indicating that the mass and surface exhalation rates were proportional to the activity concentration of radon. Among the building materials, higher radiation levels are associated with igneous rocks, like granite. However, some shale and phosphate rocks have relatively higher content of radionuclides and become more radioactive (UNSCEAR 2000) [18] Sediment sand of the river was formed through weathering and erosion of rock and soil by external forces such as flood wind, etc., In general sand, stones are harder than granite and hence the probability of weathering of granite rocks is higher than stone rocks. Hence, sands having higher activity concentration of radon next to granites. Cement is one of the most commonly used building materials for construction. Calcium carbonate (lime), silica, alumina, iron oxide and fly ash are the raw materials for the cement (Portland). Hence, the activity concentrations of radon in cement samples depend on the activity of constituents. However, addition of fly ash in cement also leads to high radon activity. Bricks are made from locally quarried soil and sand. The radon activity of bricks depends on the local geological and geographical condition. Mahur et al. 2009 [13] reported the radon activity for the beach sand samples of Chhatrapur (2116.6 Bq/m 3 ) and Chauhan 2011 [14] reported for the stones of the Aravali hills (1440 ± 134 Bq/m 3 ). These values are distinctly higher than the radon activity measured for sands and stones of Tiruchirappalli. The variation of radon concentrations in different building materials is due to the variation of concentrations of 238 U and 232 Th in the geological formation El-Arabi 2007 [19] The radionuclides linked minerals such as zircon, iron oxides, and fluorite play an important role in controlling the distribution of uranium and thorium. Zircon usually contains uranium and thorium concentrations, which ranged from 0.01% to 0.19% and 1% to 2% respectively Cuney et al. 1987 [20] Uranium in iron oxides is first trapped by adsorption Speer et al. 1981. [21] The high uranium content in the mineralized granite and pegmatite are attributed to the ability of iron oxide in them on adsorbing uranium. It is observed that the high percentage of U 3 O 8 and ThO 2 in granite were responsible for higher activity concentration of radon. Zircon typically contains 2-2000 g/t of 232 Th and 5-4000 g/t of 238 U Deer et al. 1997. [22] The average radon concentrations in building materials analyzed (stone rock: 46.3 Bq/m 3 , granite: 392.6 Bq/m 3 , sand: 267.9 Bq/m 3 , brick: 136.3 Bq/m 3 and cement: 229.1 Bq/m 3 ) were below the permissible level of 200-600 Bq/m 3 for dwellings recommended by the ICRP 1993 [5] and, therefore, the building materials are safe and do not pose any radiological risk.


  Conclusions Top


A preliminary database on the radon concentrations in commonly used building materials in Tiruchirappalli district is generated. The distribution of radon concentrations in building materials of this study region is not uniform. The high radon activity levels are found in granite type of rocks (igneous). The activity concentration of radon ( 222 Rn) in these building materials analyzed follow a descending order: Granite > sand > cement > brick > sand stone. All other radiological parameters like mass exhalation rate and surface exhalation rate are derived. The study concludes that the building materials analyzed were radiologically safe as compared to the permissible limit ICRP, 1993, and hence they do not pose any radiological risk.


  Acknowledgments Top


The authors thankfully acknowledge Atomic Energy Regulatory Board, Government of India, Mumbai for funding (Project No.: AERB/CSRP/45/05/2010) and Dr. B. Venkatraman, Head, Radiological Safety Division, Indira Gandhi Center for Atomic Research, Kalpakkam for technical support and Prof. K. Ponnusamy, Chairman, J. J. College of Engineering and Technology for providing facilities and Dr. S. Mohamed Salique, Principal Jamal Mohamed College for academic support.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]


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