Radioactivity in Building Materials of Pudukkottai Geological Region, Tamil Nadu, India

Transcription

1 Earth Syst Environ (2017) 1:4 DOI /s y ORIGINAL ARTICLE Radioactivity in Building Materials of Pudukkottai Geological Region, Tamil Nadu, India G. Sankaran Pillai 1 K. Jeevarenuka 2 P. Shahul Hameed 3 Received: 6 February 2017 / Accepted: 10 May 2017 / Published online: 23 May 2017 Ó Springer International Publishing Switzerland 2017 Abstract Background Since Pudukkottai district is naturally endowed with variety of building material resources such as stones, bricks, sand etc. These building materials are also exported to other district. So analysis of natural radioactivity in these building materials is important before these put into construction purpose. Purpose WHO reported that indoor radon accumulation from soil and building materials is one of the major factors for human lung disorders. The main objective of the present study is to measure Naturally Occurring Radioactive Materials (NORM) in building materials of Pudukkottai and to assess the possible radiological risk. Methods A total of 118 samples of building materials have been investigated for 238 U,, and employing a NaI(Tl) detector. Results The mean Ra eq activity of the building materials maintained the following descending order: Stone (299 ± 206 Bq kg -1 ) [ Soil (145 ± 54 Bq kg -1 ) Sand and Cement (117 ± 28 Bq kg -1 ) [ Brick (110 ± 26 Bq kg -1 ). The present study identified seven stone quarries recorded Ra eq higher than the permissible limit ([370 Bq kg -1 ) as set by UNSCEAR, All other building materials mined and used from this district & G. Sankaran Pillai sankaranpillai521@gmail.com Radiological Safety Division, Indira Gandhi Centre for Atomic Research, Kalpakkam , Tamil Nadu, India Department of Civil Engineering, Shivani Engineering College, Tiruchirappalli, , Tamil Nadu, India Environmental Research Center, J.J.College of Engineering and Technology, Tiruchirappalli , Tamil Nadu, India recorded low Ra eq activity. Important radiological parameters such as ADRA, I c and H in were also calculated. Conclusion The results indicated that there is no elevated radioactivity observed in the studied materials. Therefore, it is concluded that the building materials used in the above mentioned district will not pose any hazard in terms of radioactivity. Keywords Natural radioactivity Pudukkottai Building materials Gamma ray spectrometry Radium equivalent Hazard indices 1 Introduction The soil and rocks of the earth contain substances which are naturally radioactive and provide natural radiation exposures. The most important radioactive elements which occur in the soil and in rocks are the long-lived primordial isotopes of potassium ( ), uranium ( 238 U), and thorium ( ). Since these primordial radionuclides are ubiquitous in the earth crust, therefore, it is impossible to eliminate radiation exposure altogether, i.e., man cannot possibly avoid natural radioactivity from the environment. These radioisotopes are occurring in almost all the building materials but in different concentration. Radon contributes about 55% of dose received by man (UNSCEAR 1993). The radiation level due to natural radioactivity is about 2.4 msv year -1 and the estimated worldwide average activity of,, and in the earth s crust to be 32, 45, and 412 Bq kg -1, respectively (UNSCEAR 2008). It should be mentioned that human beings have poor radiation resistant behavior (lethal dose = 4 Sv) as compared to other mammals. Therefore, additional exposures have to be measured and compared with respect to the

2 4 Page 2 of 12 G. S. Pillai et al. natural radiation exposure. Furthermore, it is important to estimate the potential risk from radiation from the environment. Since man spent about 80% in indoor environment, therefore, it is important to measure radioactivity level in building materials of any particular region. In US, about 16,000 24,000 lung cancer deaths occurred in 2008 among the nonsmokers due to indoor radon (Samet et al. 2009). Kolb and Schismer (1978) reported that the external gamma radiation exposure was about 33% higher in indoor as compared to outdoor. Radioactivity of building materials in Taiwan was studied by Chang et al. (1974) and concluded that wood frame houses contain very little radioactivity and provide some shielding from natural sources in the underlying soil. However, the byproduct from the processing of phosphate rock such as gypsum and fly ash from thermal power plant recorded maximum levels of uranium and thorium. Radioactivity in soil has been studied in many regions of the world (Faanu et al. 2011; Taskin et al. 2009; Amrani and Tahtat 2001; Kolo et al. 2012; Hameed et al. 2014; UNSCEAR 2000) to obtain data on natural radioactivity, which can be used to establish if and where local controls are needed. Such data also enrich the global data bank on radioactivity that will allow a more accurate estimation of global average values of dosimetric quantities. Hewamanna et al. (2001) studied radioactivity in clay bricks of Sri Lanka, El-Shershaby (2002) in granite of north eastern desert of Egypt, Kovler et al. (2002) measured natural radionuclides in building materials of Isreal, Stoulos et al. (2003) in Greece, Xinwei (2005) in China, Ademola and Oguneletu (2005) in Nigeria, Anjos et al. (2005) in Brazil granites, Tsabaris et al. (2007) in albanian sediment, Turthan (2008) in Turkey, and radioactivity of some domestic and imported building materials from south Eastern Europe by Krstic et al. (2007). Natural radioactivity distribution in bricks of Pakistan, Greece, China, Algeria, Sri Lanka, and Kuwait was already reported by Faheem and Mujahid (2008), Papaefthymiou and Gouseti (2008), Xinwei (2005), Amrani and Tahtat (2001), Hewamanna et al. (2001), and Bou-Rabee and Bem (1996), respectively. Beretka and Mathew (1985) measured radioactivity in cements of Australia. A similar kind of study was undertaken by Khan and Khan (2001) in Pakistan. Urbanization and quality-of-life style lead to increase the mining and production of building materials. India is the second largest cement producer (6% share of world cement production) after China. In India, the work on the radioactivity in soil and other building materials is scattered. Mishra and Sadasivan (1971) surveyed natural radioactivity levels in soil. However, Kumar et al. (2003) reported natural radioactivity in construction material. Kumar et al. (1999) also worked on natural radioactivity in building materials and industrial by-products. Radioactivity in commercial building materials of Kerala was reported by Pereira et al. (2011). In Tamil Nadu, assessment of radioactivity in the building materials is scanty (Ravisankar et al. 2012; Pillai et al. 2016). However, data on radioactivity in construction materials of Pudukkottai district are totally lacking. Such data are vital in identifying building materials releasing radioactivity beyond the permissible limit and use of them for construction purpose could be avoided. The objective of the present work is to investigate the natural radioactivity distribution in building materials and related radiological risk assessment to general public of Pudukkottai. 2 Study Area and Sample Collection Pudukkottai (in tamil kottai means made by rocks) district lies between and east longitude and between and of the north latitude. The district covers an area of 4663 km 2 and had a population of 1,618,345 in 2011 with a coastline of 42 km. Thirumayam fort, Sittanavasal cave paginating, and Narthamalai rock cut temples are some notable historical places in this district. At present, this district is composed of 11 taluks (Fig. 1). This district is enriched with many stone quarries (Geological survey of India 2006). The stones were directly sampled from 21 stone quarries located in the district. As many as 55 virgin soil samples, 22 cultivated soil samples and 6 sand samples were collected. Besides these, the man made building materials such as bricks (8 no.) and fly ashbased Portland cement (6 no.) were also sampled for the present study. The bricks are directly sampled from brick kiln, while commercially available various brands of cement are collected directly from the market. Global Positioning System was used to locate the exact location of sampling stations (Garmin, e-trex10, USA make). The samples were collected based on the IAEA (2004) guidance. The collected building materials were powdered and sieved and a fine powder with a particle size less than 2 mm was obtained. Then, the samples were packed and sealed in an air-tight plastic container and stored for 30 days to attain radioactive equilibrium between Ra-226 and its daughter products. These samples were analyzed for natural radioactivity measurement using gamma ray spectrometry. 3 Materials and Methods Gamma ray spectrometry has been used for many years to measure the specific radionuclides activity in a given sample. This technique is an important tool in the field of environmental radioactivity measurements due to its high

3 Radioactivity in Building Materials of Pudukkottai Geological Region, Tamil Nadu, India Page 3 of 12 4 Fig. 1 Sampling stations for stone (St), Soil (So), and cultivated Soil (Cs) in Pudukkottai district resolution, large photo peak efficiency, and it can measure different radionuclides in a single spectrum. This technique is working either scintillation [NaI (Tl) detector] or semiconductor (HPGe detector) principle. Both these detectors have their own advantages and disadvantages. NaI(Tl) detectors offer higher detection efficiency and it can be operated at room temperature, while HPGe provide superior energy resolution, but it can be performed only at liquid nitrogen temperature. HPGe detector measures the individual counts of the radionuclides, while NaI(Tl) detector measures the counts by stripping spectrum. For the present study, a NaI(Tl) detector was used for the measurement of natural radionuclides in building materials. The detailed description of the detector was already documented by Pillai et al. (2015). The background spectrum was obtained for 20,000 s. From that spectrum, the Minimum Detectable Activity (MDA) was calculated. The samples were also counted for 20,000 s. The gross counts of were noted directly by its own gamma line at 1461 kev, whereas 238 U and counts were recorded from their daughter radionuclides, namely, 214 Bi (1764 kev) and 208 Tl ( kev), respectively. The MDA was 2.03 Bq kg -1 for, 4.7 Bq kg -1 for, and 18.9 Bq kg -1 for K-40. The confidence level of the obtained result was 95%. 3.1 Radium Equivalent (Ra eq ) Radium equivalent (Ra eq ) activity has been used to express the total activity of any given environmental matrices (Beretka and Mathew 1985). The Ra eq activity in Bq kg -1 is calculated on the assumption 370 Bq kg -1 of or 259 Bq kg -1 of or 4810 Bq kg -1 of, which produces the same gamma dose rate: Bq kg 1 ¼ ARa þ 1:43A Th þ 0:077 A K ; ð1þ Ra eq

4 4 Page 4 of 12 G. S. Pillai et al. Table 1 Activity concentrations of primordials in stones of Pudukkottai district Sampling station Station code Activity concentration (Bq kg -1 ) Ra eq (Bq kg -1 ) D (ngy h -1 ) I c H ex Nartamalai St1 MDA 158 ± ± Irumbali St2 38 ± ± ± Perambur St3 32 ± ± ± Kulathur St4 MDA MDA 92 ± Melur St5 MDA 151 ± ± Moodampatti St6 14 ± ± ± Keeranur St7 MDA 133 ± ± Annavasal St8 27 ± ± ± Rajagiri St9 52 ± ± ± Kudumiyanmalai St10 15 ± ± ± Virallimalai St11 33 ± ± ± Nathampannai St12 37 ± ± ± Iluppur St13 MDA 5 ± 7 96 ± Gandarvakottai St14 MDA 32 ± ± Ganapathipuram St15 27 ± ± ± Mudukkulam St16 MDA 281 ± ± Ponnamaravathy St17 39 ± ± ± Kottaiyur St18 MDA 28 ± ± Valayampatti St19 6 ± 8 23 ± 7 93 ± Peranur St20 MDA 157 ± ± Pilangudi St21 MDA 13 ± 7 97 ± Range B B Mean ± SD 16 ± ± ± ± ± ± ± 0.55 where A U, A Th, and A K are the activities of,, and, respectively. The safe value of Ra eq in building materials is reported to be less than 370 Bq kg -1 to limit the annual effective dose to 1 msv for the general public (UNSCEAR 2008). 3.2 Absorbed Dose Rate in Air (ADRA) External terrestrial gamma dose rate was calculated from the concentrations of the radionuclides in building material. ADRA in ngy h -1 at 1 m above the ground level was calculated using equation (UNSCEAR 2008): ADRA ¼ 0:461A Ra þ 0:623A Th þ 0:417A K : ð2þ 3.3 Gamma Index (I c ) Another radiation hazard index, called the gamma activity concentration index, I c, has been defined by the European Commission (EC 1999) and is given as below: I c ¼ A Ra =300 þ A Th =200 þ A K =3000: ð3þ The index I c is correlated with the annual dose rate due to the excess external gamma radiation caused by superficial material. Values of index I c B 2 correspond to a dose rate criterion of 0.3 msv year -1, whereas 2 \ I c B 6 corresponds to a criterion of 1 msv year -1. The material with I c [ 6 should be avoided, since these values corresponds to dose rates higher than 1 msv year -1 which is the highest value of dose rate recommended for population (International Commission on Radiological Protection 2009). 3.4 External Hazard Index (H ex ) The external hazard index is another criterion to assess the radiological suitability of a building material. Beretka and Mathew (1985) prescribed the following equation to assess the external hazard: H ex ¼ C Ra =370 þ C Th =259 þ C K =4810 1; ð4þ where C Ra, C Th, and C K are the activity concentrations in Bq kg -1 of,, and. For the safe use of a material in the construction of dwellings, the above criterion was proposed (H in B 1).

5 Radioactivity in Building Materials of Pudukkottai Geological Region, Tamil Nadu, India Page 5 of 12 4 Table 2 Activity concentrations of primordials in soils of Pudukkottai district Sampling station Station code Activity concentration (Bq kg -1 ) Ra eq (Bq kg -1 ) D (ngy h -1 ) I c H ex Viralimalai So1 14 ± 4 68 ± ± Kudumiyanmalai So2 13 ± 2 52 ± ± Rajagiri So3 5 ± 4 37 ± ± Annavasal So4 7 ± 4 43 ± ± Irumbali So5 8 ± 4 54 ± ± Nartamalai So6 8 ± 5 70 ± ± Kulathur So7 35 ± ± ± Keeranur So8 9 ± 4 81 ± ± Parambur So9 8 ± 4 58 ± ± Melur So10 7 ± 4 53 ± ± Kunnandarkovil So11 5 ± 4 78 ± ± Moodampatti So12 8 ± 5 52 ± ± Mudukkulam So13 10 ± 4 48 ± ± Nathamadaipatti So14 9 ± ± ± Gandarvakottai So15 5 ± 1 98 ± ± Thuvar So16 2 ± 1 35 ± ± Ambukovil So17 20 ± 5 52 ± ± Mangottai So18 24 ± 4 64 ± ± Karambakudi So19 9 ± ± ± Ganapathipuram So20 14 ± 5 87 ± ± Vannarapatti So21 16 ± 5 57 ± ± Varapur So22 15 ± 3 68 ± ± Puthambur So23 MDA 45 ± ± Mullur So24 14 ± 4 69 ± ± Nathampannai So25 6 ± ± ± Ponnamaravathy So26 24 ± ± ± Thenur So27 18 ± ± ± Sevalur So28 7 ± 4 58 ± ± Sundaram So29 21 ± ± ± Sithur So30 7 ± 4 48 ± ± Peraiyur So31 7 ± 4 34 ± ± Kottaiyur So32 13 ± 4 58 ± ± Neivasal So33 8 ± 6 59 ± ± Allanvayal So34 7 ± 4 43 ± ± Valayampatti So35 7 ± 4 64 ± ± Kayampatti So36 13 ± 4 65 ± ± Thiruvarangulam So37 3 ± 2 4 ± ± Settivayal So38 12 ± ± ± Kadalur So39 15 ± ± ± Pachikottai So40 9 ± 4 63 ± ± Kalangudi So41 9 ± 4 58 ± ± Kurumbur So42 8 ± 5 52 ± ± Melapattu So43 8 ± 5 50 ± ± Keelavijayapuram So44 5 ± 4 72 ± ± Vengur So45 42 ± 6 37 ± ± Vellatumangalam So46 7 ± 6 54 ± ± Thanikadu So47 5 ± 4 62 ± ±

6 4 Page 6 of 12 G. S. Pillai et al. Table 2 continued Sampling station Station code Activity concentration (Bq kg -1 ) Ra eq (Bq kg -1 ) D (ngy h -1 ) I c H ex Arasur So48 20 ± 4 87 ± ± Kumulur So49 18 ± 4 73 ± ± Peranur So50 17 ± 5 72 ± ± Veelimar So51 17 ± 3 77 ± ± Pilangudi So52 MDA 56 ± ± Nemmelivayal So53 9 ± 4 85 ± ± Perumanathur So54 6 ± 4 39 ± ± Seyyamam So55 8 ± 4 43 ± ± Range B Mean ± SD 12 ± 8 70 ± ± ± ± ± ± 0.15 Table 3 Activity concentrations of primordials in cultivated soils of Pudukkottai district Sampling station Station Code Activity concentration (Bq kg -1 ) Ra eq (Bq kg -1 ) D (ngy h -1 ) I c H ex Annavasal Cs1 7 ± 4 70 ± ± Kunnandarkovil Cs2 6 ± 5 57 ± ± Nartamalai Cs3 4 ± 3 68 ± ± Thuvar Cs4 18 ± 4 70 ± ± Gandarvakottai Cs5 6 ± 4 69 ± ± Mangottai Cs6 MDA 153 ± ± Nathamppannai Cs7 8 ± 4 84 ± ± Sevalur Cs8 7 ± 4 50 ± ± Ponnamaravathy Cs9 21 ± ± ± Peraiyur Cs10 6 ± 4 70 ± ± Kottaiyur Cs11 6 ± 4 42 ± ± Valayampatti Cs12 13 ± 3 99 ± ± Kalangudi Cs13 MDA 58 ± ± Thiruvarangulam Cs14 5 ± 4 85 ± ± Settivayal Cs15 9 ± 3 87 ± ± Vengur Cs16 7 ± 4 41 ± ± Melapattu Cs17 MDA 118 ± ± Kurumbur Cs18 6 ± 5 60 ± ± Peranur Cs19 7 ± 4 49 ± ± Kumulur Cs20 15 ± 1 99 ± ± Perumanathur Cs21 4 ± 3 51 ± ± Seyyamam Cs22 9 ± 5 98 ± ± Range B Mean ± SD 9 ± 4 77 ± ± ± ± ± ± Results and Discussion The activity concentrations of,, and measured for 118 building materials collected from Pudukkottai district were presented in Tables 1, 2, 3, 4, 5, and 6. As shown in Table 1, out of 21 stations, only 11 stations registered activity which ranged from 6 Bq kg -1 (St19) to 52 Bq kg -1 (St9) with an average value of 16 ± 16 Bq kg -1 and in the remaining ten stations registered MDA (B2.03 Bq kg -1 ). On the other hand, the

7 Radioactivity in Building Materials of Pudukkottai Geological Region, Tamil Nadu, India Page 7 of 12 4 Table 4 Activity concentrations of primordials in sands of Pudukkottai district Sampling station Station code Activity concentration (Bq kg -1 ) Ra eq (Bq kg -1 ) D (ngy h -1 ) I c H ex Vellar River Sa1 5 ± 7 42 ± ± Agniyar River Sa2 10 ± 6 58 ± ± Koraiyar River Sa3 7 ± 2 38 ± ± Gundar River Sa4 10 ± 8 60 ± ± Pambar River Sa5 12 ± 6 68 ± ± Kuluvanar River Sa6 14 ± 1 76 ± ± Range Mean ± SD 10 ± 3 57 ± ± ± ± ± ± 0.08 Table 5 Activity concentrations of primordials in bricks of Pudukkottai district Sampling station Station code Activity concentration (Bq kg -1 ) Ra eq (Bq kg -1 ) D (ngy h -1 ) I c H ex Annavasal Br1 18 ± 5 65 ± ± Keeranur Br2 8 ± 4 52 ± ± Mudukkulam Br3 26 ± 6 32 ± ± Varapur Br4 18 ± 8 25 ± ± Peraiyur Br5 9 ± 5 58 ± ± Allanvayal Br6 8 ± 2 62 ± ± Settivayal Br7 14 ± 2 59 ± ± Perumanathur Br8 29 ± 6 28 ± ± Range Mean ± SD 16 ± 8 48 ± ± ± ± ± ± 0.07 Table 6 Activity concentrations of primordials in cements of Pudukkottai district Station Code Activity Concentration (Bq kg -1 ) Ra eq (Bq kg -1 ) D (ngy h -1 ) I c H ex Ce 1 29 ± 2 43 ± 5 74 ± Ce 2 39 ± 3 57 ± ± Ce 3 24 ± 2 47 ± 4 94 ± Ce 4 27 ± 1 54 ± 7 82 ± Ce 5 28 ± 2 46 ± 4 43 ± Ce 6 31 ± 2 87 ± ± Range Mean ± SD 30 ± 6 56 ± ± ± ± ± ± 0.08 concentration of was recorded in 20 stations, and the concentration varied from 5 Bq kg -1 (St13) to 387 Bq kg -1 (St17) with an average value of 163 ± 121 Bq kg -1 and the concentration of registered in all the stations which swung from 92 Bq kg -1 (St14) to 1119 Bq kg -1 (St1) with an average value of 299 ± 206 Bq kg -1. Of all the stone samples measured in this study, the activity concentrations of in all the samples were within that of the world average except the stations (St2, St9, St11, St12, and St17) (UNSCEAR 2008). The activity concentrations of and in St4, St13, St14, St18, St19, and St21 were within that of the world average of 45 and 412 Bq kg -1 and that in the remaining stations exceeded the world average. It is evident from Table 2 that the activity concentration of in soil

8 4 Page 8 of 12 G. S. Pillai et al. samples was varied from 2 Bq kg -1 (So16) to 42 Bq kg -1 (So45) with an average value of 12 ± 8Bqkg -1 and from 4 Bq kg -1 (So37) to 177 Bq kg -1 (So7) with an average value of 70 ± 33 Bq kg -1. The activity concentration of fluctuated from 187 Bq kg -1 (So3) to 676 Bq kg -1 (So7) with an average value of 436 ± 86 Bq kg -1. Of all the samples measured in this study, Kulathur (So7) and Vengur (So45) recorded the highest concentration of. The activity concentration of cultivated soil samples is presented in Table 3. It was evident from Table 3 that out of 22 stations, 19 stations registered ranging from 4 Bq kg -1 (Cs4 and Cs21) to 21 Bq kg -1 (Cs9) with an average value of 9 ± 4Bqkg -1 and in the remaining 3 stations registered MDA (B2.03 Bq kg -1 ). concentrations fluctuated from 41 Bq kg -1 (Cs16) to 153 Bq kg -1 (Cs6) with an average value of 77 ± 29 Bq kg -1 and from 202 Bq kg -1 (Cs11) to 589 Bq kg -1 (Cs14) with an average value of 377 ± 121 Bq kg -1. The activity concentrations of 238 Uin all the samples were within the world average (UNSCEAR 2008). However, the activity concentrations of in all the samples exceeded the world average except in two stations (Cs11 and Cs16). Similarly, the activity concentrations of obtained for 15 stations within the world average. As seen from Table 4, the activity concentration of ranged from 5 Bq kg -1 (Sa1) to 14 Bq kg -1 (Sa6) with an average Fig. 2 Frequency distribution of 238 U,, and in building materials of Pudukkottai district

9 Radioactivity in Building Materials of Pudukkottai Geological Region, Tamil Nadu, India Page 9 of 12 4 Activity (Bq/kg) Radionuclides Ra-226 Th-232 K-40 Fig. 3 Natural radionuclides activity in building materials of Pudukkottai district value of 10 ± 43 Bq kg -1 and from 38 Bq kg -1 (Sa3) to 76 Bq kg -1 (Sa3) with an average value of 57 ± 15 Bq kg -1. The activity concentration of fluctuated from 280 Bq kg -1 (Sa3) to 433 Bq kg -1 (Sa6) with an average value of 362 ± 65 Bq kg -1. Of all the six sand samples measured in this study, the activity concentrations of in all the samples were within the world average (UNSCEAR 2008). The activity concentrations of in Sa1 and Sa 3 were within the world average 45 Bq kg -1 and the remaining four stations exceeded the world average. Similarly, activity concentrations obtained for the stations Sa5 and Sa6 were higher than the world average value of 412 Bq kg -1 (UNSCEAR 2008) remaining four stations within the world average. It is evident from Table 5, in brick sample, the concentration of oscillated from 8Bqkg -1 (Br6) to 29 Bq kg -1 (Br3) with an average value of 16 ± 8Bqkg -1 and from 25 Bq kg -1 (Br4) to 65 Bq kg -1 (Br1) with an average value of 48 ± 17 Bq kg -1. The activity concentration of from 215 Bq kg -1 (Br8) to 491 Bq kg -1 (Br 5) with an average value of 336 ± 105 Bq kg -1. Table 6 gives the values of the activity concentrations of primordial radionuclides in cement samples. The activity concentration of swung from 24 Bq kg -1 (Ce3) to 39 Bq kg -1 (Ce2) with an average value of 30 ± 6Bqkg -1 and from 43 Bq kg -1 (Ce 1) to 87 Bq kg -1 (Ce6) with an average value of 56 ± 16 Bq kg -1. The activity concentration of oscillated from 43 Bq kg -1 (Ce5) to 179 Bq kg -1 (Ce6) with an average value of 100 ± 52 Bq kg -1. Of all the six cement samples measured in this study, the activity levels of 238 U and in all the samples were within the world average, whereas the activity concentrations of in all the stations were higher the world average. The frequency distributions of,, and among the building materials of Pudukkottai district are presented in Fig. 2. The values of skewness coefficient obtained for,, and in the building materials for Pudukkottai district 1.32, 2.34, and 1.11, respectively. It is evident that the distribution of primordial radionuclides in the building materials was asymmetric and wide range. These asymmetric primordial radionuclides in the building material are attributed to wide verities of lithological components existing in the study area. concentration is relatively higher than that of both and (Fig. 3). The data also indicated that is uniformly distributed as compared to both uranium and thorium. This is because of high solubility and natural abundance of -40 as compared to 238 U and. However, concentration is always higher than that of. A good correlation existed between uranium and thorium in sand and stone (R 2 = 0.9 and 0.6), but there is no such correlation observed in soil and brick. This is may be due to sand and stones are enriched with inorganic (heavy minerals), whereas soil and bricks are organic species such as carbon mixed with the inorganic minerals. The natural radionuclides Fig. 4 Mean radium equivalent activity in building materials of Pudukkottai district

10 4 Page 10 of 12 G. S. Pillai et al. Fig. 5 Percentage composition of U-238, Th-232, and K-40 in building materials of Pudukkottai district distribution in soils and cultivated soils did not vary much (Fig. 4). Figure 5 shows the percentage of activity concentration of primordials in the building materials of Pudukkottai district. represented 2 4%, : 12 20%, and : 78 85%. The elevated level of and in cement could be attributed to the mixing of fly ash and phosphogypsum which are enriched source of and (Khalifa and El-Arabi 2005). In stones, radium equivalent activity ranged from 12 Bq kg -1 (St4) to 653 Bq kg -1 (St17) with a mean value of 299 ± 206 Bq kg -1. On the other hand, Ra eq of 55 soil samples fluctuated from 61 Bq kg -1 (So 45) to 340 Bq kg -1 (So7) with mean value of 145 ± 54 Bq kg -1. In cultivated soils, Ra eq swung from 83 Bq kg -1 (Cs 11) to 242 Bq kg -1 (Cs 6) with mean value of 145 ± 43 Bq kg -1, while in sand, Ra eq varied from 82 Bq kg -1 (Sa3) to 153 Bq kg -1 (Sa6) with mean value of 117 ± 28 Bq kg -1 and Ra eq value of bricks fluctuated from 71 Bq kg -1 (Br4) to 143 Bq kg -1 (Br1) with mean value of 110 ± 26 Bq kg -1. The Ra eq activity of the building materials of from Pudukkottai district maintained the following descending order: Stone [ Cultivated soil & Soil [ Sand and Cement [ Brick. The maximum activity was found in stone (Ra eq 299 Bq kg -1 ) and minimum in Brick (Ra eq 110 Bq kg -1 ). The variation in the concentration of primordials in building materials may be due to variation in geological formation and geochemical processes. It was observed that igneous rocks (granites) were predominant in Pudukkottai district (Geological survey of India 2006). The enrichment of monazite in igneous rock which was the source of thorium was responsible for the elevated radioactivity level in igneous rock as also reported by Hameed et al Itis noted from the literature data that minerals such as quartz, microline feldspar, and kaolinite are the major component responsible for the higher radioactivity content of rocks (Ramasamy et al. 2009). It can be concluded from the results that the radioactivity fluctuated widely even within a short distance; Hameed et al. (2014) also reported that the Ra eq activity could vary greatly even if two stations were separately by 5 km. The granites with high Ra eq values identified in the present study are not used as core construction material. However, they were used for paving open space, closing drainage and as fencing post and hence rigorous human exposure as indoor gamma radiation was naturally avoided. The mean absorbed gamma dose rate for building materials, namely, soils, cultivated soil, sand, brick, and cement, was *54 ngy h -1 which is less than the permissible limit of 55 ngy h -1. However, the mean absorbed gamma dose rate calculated for stones (132 ngy h -1 ) was higher than the world average indicating an elevated level of gamma radiation in the stones of Pudukkottai district. The analysis revealed that H ex and I c calculated for the building materials were well within the safety limit (B1). Principal component analysis (PCA) is a powerful statistical tool, which is used widely in environmental Fig. 6 Screen plot

11 Radioactivity in Building Materials of Pudukkottai Geological Region, Tamil Nadu, India Page 11 of 12 4 Table 7 Extraction method: principal component analysis applications. PCA is simplifying the complex and diverse relationships that exist among a set of observed variables by revealing common and unobservable factors. This method is applied to the data matrix for reducing the data to an easily interpretable form. The significance of principal components of primordial radionuclides were indicated by screen plot of eigen values (Fig. 6). The sharp decline in values from the first to second components indicates that most of the variability of the data can be accounted for the first component ( ) which represents 83.03% of the total variation of the data (Table 7). 5 Conclusions Component Variables Factor 1 Radium Thorium Potassium Ra eq ADRA I c H ex % of variance explained One component extracted A total of 118 building materials sampled from Pudukkottai district for the analysis of natural radioactivity employing gamma ray spectrometry. There is a wide variation in,, and activities. The Ra eq activity in the building materials formed the following sequence: Stone [ Cultivated soil and Soil [ Sand and Cement [ Brick. The present study identified seven stone quarries of granite rocks, namely, Annavasal, Rajagiri, Viralimalai, Narthamppannai, Ganapathipuram, Mudukulam, and Ponnamaravathy which registered Ra eq value (Range Bq kg -1 ) higher than the permissible limit. Although these granites were not used in core construction, the radiological risk to human population living closer to these granite rocks needed to be further investigated by cytogenetic studies among the quarry miners. Overall, the mean Ra eq activity of samples collected in Pudukkottai is well below the recommended value and does not pose any radiological risk to the general public. Acknowledgements The authors would like to acknowledge Atomic Energy Regulatory Board, Govt. India for funding (Project No: AERB/CSRP/45/05/2010) and Shri. R. Mathiyarasu, HSEG, IGCAR for his technical support. References Ademola JA, Oguneletu PO (2005) Radionuclide content of concrete building blocks and radiation dose rates in some dwellings in Ibadan, Nigiria. J Environ Radioact 81: Amrani D, Tahtat M (2001) Natural radioactivity in Algerian building materials. 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