Assessments of radioactivity concentration of natural radionuclides and radiological hazard indices in sediment samples from the East coast of Tamilnadu, India with statistical approach

Marine Pollution Bulletin xxx (2015) xxx–xxx

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Assessments of radioactivity concentration of natural radionuclides and radiological hazard indices in sediment samples from the East coast of Tamilnadu, India with statistical approach R. Ravisankar a,⇑, J. Chandramohan b, A. Chandrasekaran c, J. Prince Prakash Jebakumar d, I. Vijayalakshmi e, P. Vijayagopal e, B. Venkatraman e a

PG & Research Department of Physics, Government Arts College, Thiruvannamalai 606603, Tamil Nadu, India Department of Physics, E.G.S. Pillay Engineering College, Nagapattinam 611002, Tamil Nadu, India c Department of Physics, SSN College of Engineering, Kalavakkam, Chennai 603110, Tamil Nadu, India d Coastal and Environmental Engineering, National Institute of Ocean Technology, Pallikaranai, Chennai 600100, Tamil Nadu, India e Radiological Safety Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamil Nadu, India b

a r t i c l e

i n f o

Article history: Received 16 April 2015 Revised 15 May 2015 Accepted 21 May 2015 Available online xxxx Keywords: Natural radioactivity Sediment Gamma ray spectrometry Radiological parameters Multivariate statistical analysis

a b s t r a c t This paper reports on the distribution of three natural radionuclides 238U, 232Th and 40K in coastal sediments from Pattipulam to Devanampattinam along the East coast of Tamilnadu to establish baseline data for future environmental monitoring. Sediment samples were collected by a Peterson grab samples from 10 m water depth parallel to the shore line. Concentration of natural radionuclides were determined using a NaI(Tl) detector based c-spectrometry. The mean activity concentration is 62.21, 14.29 and 360.23 Bq kg1 for 238U, 232Th and 40K, respectively. The average activity of 232Th, 238U and 40K is lower when compared to the world average value. Radiological hazard parameters were estimated based on the activity concentrations of 238U, 232Th and 40K to find out any radiation hazard associated with the sediments. The radiological hazard parameters such as radium equivalent activity (Raeq), absorbed gamma dose rates in air (DR), the annual gonadal dose equivalent (AGDE), annual effective dose equivalent (AEDE), external hazard index (Hex) internal hazard index (Hin), activity utilization index (AUI) and excess lifetime cancer (ELCR) associated with the radionuclides were calculated and compared with internationally approved values and the recommended safety limits. Pearson correlation, principal component analysis (PCA) and hierarchical cluster analysis (HCA) have been applied in order to recognize and classify radiological parameters in sediments collected at 22 sites on East coast of Tamilnadu. The values of radiation hazard parameters were comparable to the world averages and below the recommended values. Therefore, coastal sediments do not to pose any significant radiological health risk to the people living in nearby areas along East coast of Tamilnadu. The data obtained in this study will serve as a baseline data in natural radionuclide concentration in sediments along the coastal East coast of Tamilnadu. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction Radioactivity is common in rocks, soil, beach sand, sediment and riverbed soil, in rivers and oceans, and even in our building materials and houses. Naturally occurring radioactive materials generally contain primordial radionuclides, left over since the creation of the earth (UNSCEAR, 1982). The naturally existing radionuclides like 238U, 232Th and 40K are present everywhere in the Earth’s crust. Radium-226 (226Ra, uranium series progeny), Radium-228 (228Ra, thorium series progeny) and potassium-40 (40K) are of most ⇑ Corresponding author. E-mail address: [email protected] (R. Ravisankar).

concern due to theirs high solubility and mobility. The knowledge of the concentrations and distributions of these radionuclides are of interest since it provides useful information in the monitoring of environmental contamination by natural radioactivity (Yii et al., 2009). The activity of natural radionuclides in soil and sediment depends mainly on the types of rocks from which they originate. These radionuclides pose exposure risks externally due to their c-ray emissions and internally due to radon and its progeny (UNSCEAR, 1988). Hence, humans should be aware of their natural environment with regard to the radiation effects due to the naturally occurring and induced radioactive elements. The study of the distribution of primordial radionuclides allows the understanding of the

http://dx.doi.org/10.1016/j.marpolbul.2015.05.058 0025-326X/Ó 2015 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Ravisankar, R., et al. Assessments of radioactivity concentration of natural radionuclides and radiological hazard indices in sediment samples from the East coast of Tamilnadu, India with statistical approach. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/ j.marpolbul.2015.05.058

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R. Ravisankar et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx

Fig. 1. Location Map.

Table 1 Latitude and longitude of Locations. S. No.

Sample ID

Latitude (N)

Longitude (E)

Locations

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

PPM DVN MAM KKM KPM VPC TPM MKM OKM APT KPK FBH KMU GCM ABH MPT PBH KEP PPT KIP TKA DPM

12°400 51.270 0 N 12°390 19.320 0 N 12°370 55.530 0 N 12°340 56.330 0 N 12°300 57.520 0 N 12°270 58.970 0 N 12°240 42.280 0 N 12°210 26.510 0 N 12°190 35.890 0 N 12°160 19.800 0 N 12°120 42.650 0 N 12°90 2.750 0 N 12°40 59.370 0 N 12°20 45.840 0 N 11°590 51.980 0 N 11°570 43.220 0 N 11°560 38.160 0 N 11°540 23.610 0 N 11°520 45.440 0 N 11°500 23.500 0 N 11°460 28.210 0 N 11°440 41.370 0 N

80°150 19.350 0 E 80°140 49.680 0 E 80°140 13.140 0 E 80°130 22.370 0 E 80°11’50.570 0 E 80°110 16.290 0 E 80°90 48.290 0 E 80°60 52.670 0 E 80°50 44.700 0 E 80°30 16.000 0 E 80°10 32.400 0 E 79°590 11.440 0 E 79°550 53.550 0 E 79°560 46.860 0 E 79°550 31.390 0 E 79°520 42.650 0 E 79°520 17.450 0 E 79°510 49.370 0 E 79°510 19.750 0 E 79°510 54.440 0 E 79°490 31.030 0 E 79°490 23.010 0 E

Pattipulam Devaneri Mahabalipuram Kokilamedu Kalpakkam Veppancheri Thenpattinam Mudaliyarkuppam Odiyurkuppam Alampara fort Kaipanikuppam French beach Koonimedu Ganapathichettikulam Auroville beach Muthiyalpet Pondy beach Keerapalayam Puthupettai Kirumampakkam Thazhankuda Dhevanampattinam

radiological implication of these elements due to the gamma ray exposure of the body and irradiation of lung tissue from inhalation of radon and its daughters (Alam et al., 1999; Singh et al., 2005). Knowledge about the distribution of radioactivity present in natural materials enables one to assess any possible radiological hazard to mankind by the use of such materials.

The knowledge of the concentrations and distributions of the radionuclides is of interest, since it provides useful information in the monitoring of environmental radioactivity. The concentration of radionuclides in marine sediments can provide very useful information on the source, transport mechanisms and environmental fate of radionuclides. This information is required for successful long-term marine environmental radiation monitoring and assessment. Obtaining activity concentrations of natural radionuclides are useful not only for the above-mentioned reasons, but also for radiation risk assessment. Hence the estimation of radiation hazard parameters in marine sediments can reflect the health hazards due to natural radiation from nearby terrestrial areas as well as the hazards to people who handle these sediments. To address these problems, assessment of radioactivity concentration in the marine environment is essential. Natural radioactivity measurements in coastal sediments in different parts of the world were reported by many authors (Akram et al., 2006; Mohanty et al., 2004; Alatise et al., 2008; Amekudzie et al., 2011; Tari et al., 2013). Therefore, the measurement of natural radioactivity due to gamma rays from the coastal areas should be regularly examined. This paper reports the activity concentrations of natural radionuclides 238U, 232Th and 40K, for coastal sediments from Pattipulam to Devanampattinam along East coast of Tamilnadu, India and to provide useful information for estimation of the radiation exposures of human being and in monitoring of environmental radioactivity at that area. The objective of this paper is to evaluate the radiological hazards due to natural radioactivity associated with coastal sediments by calculating radium equivalent activity (Raeq), absorbed dose rate (DR), annual effective dose equivalent (AEDE), annual gonadal dose equivalent (AGDE), activity utilization index (AUI), excess

Please cite this article in press as: Ravisankar, R., et al. Assessments of radioactivity concentration of natural radionuclides and radiological hazard indices in sediment samples from the East coast of Tamilnadu, India with statistical approach. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/ j.marpolbul.2015.05.058

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Table 2 Activity concentrations of radionuclides with their uncertainties, radium equivalent activity, gamma dose rate and annual effective dose rate in coastal sediment samples of East coast line of study area. Sample ID

Activity Concentration (Bq kg1) 238

PPM DVN MAM KKM KPM VPC TPM MKM OKM APT KPK FBH KMU GCM ABH MPT PBH KEP PPT KIP TKA DPM Mean BDL = 62.21 for

232

U

BDL 37.02 ± 12.24 BDL BDL BDL BDL BDL BDL BDL BDL BDL BDL BDL BDL BDL BDL BDL BDL BDL BDL BDL BDL 62.21 238

U; 62.11 for

40

Th

52.89 ± 5.83 643.77 ± 13.73 86.05 ± 6.46 75.78 ± 6.36 35.31 ± 5.33 27.65 ± 5.28 42.8 ± 5.66 11.25 ± 4.61 BDL 11.99 ± 4.65 BDL BDL BDL BDL BDL 12.06 ± 4.50 BDL BDL 14.67 ± 4.76 14.29 ± 4.64 BDL 45.32 ± 5.47 14.29 232

Th, 8.5 for

Ra(eq) (Bq kg1)

Gamma dose rate (DR) (nGy h1)

Annual effective dose rate (mSv y1)

111.54 992.19 155.36 144.40 86.86 71.12 91.21 41.76 32.88 46.95 29.05 28.37 30.18 31.13 32.27 46.74 34.49 34.37 47.14 45.98 29.80 92.62 102.56

95.22 778.13 127.96 120.54 76.36 62.96 77.99 38.78 33.09 43.89 29.10 28.39 30.28 31.26 32.45 43.65 34.76 34.63 43.05 42.00 29.88 78.48 86.95

0.1169 0.9550 0.1570 0.1479 0.0937 0.0773 0.0957 0.0476 0.0406 0.0539 0.0357 0.0348 0.0372 0.0384 0.0398 0.0536 0.0427 0.0425 0.0528 0.0515 0.0367 0.0963 0.1067

K

437.63 ± 27.96 449.08 ± 44.40 390.94 ± 28.40 439.32 ± 28.62 443.56 ± 27.05 381.42 ± 27.03 360.99 ± 27.20 304.65 ± 24.25 359.18 ± 24.87 358.39 ± 25.08 309.34 ± 23.45 300.5 ± 23.93 324.04 ± 24.02 336.38 ± 23.92 351.14 ± 24.85 354.36 ± 24.25 380.09 ± 25.18 378.48 ± 24.95 311 ± 24.68 303.09 ± 24.05 319.11 ± 22.74 332.49 ± 25.95 360.23

40

K.

Fig. 2. Locations Vs activity concentration and radium equivalent activity (Bq kg1).

lifetime cancer (ELCR), hazard indices (Hex and Hin), alpha index (Ic) and gamma representative level index (RLI). Further the multivariate Statistical analyses (Pearson Correlation, Cluster and Factor analysis) were carried out with the obtained parameters from the radioactivity concentration to know the existing relations between them.

2. Materials and methods 2.1. Sampling and sample preparation Sediment samples were collected along the Bay of Bengal coastline, from Pattipulam to Devanampattinam coast during pre-monsoon condition. These samples were collected pre-monsoon season, when sediment texture and ecological conditions can be clearly observed, when erosional activities are predominant, and sediments were not transported from the river and estuary towards the beach and marine. In order to ensure minimum disturbance of the upper layer, samples were collected by a Peterson grab sampler from 10 m water depths parallel to the shoreline. The grab sampler collects 10 cm thick bottom sediment

layer from the seabed along the 22 stations (Fig. 1). Uniform quantity of sediment samples were collected from all the sampling stations located between an average interval of 3NM (Nautical mile). Each sample of about 2 kg was kept in a thick plastic bag. Care was taken to ensure that the collected sediments were not in contact with the metallic dredge of the sampler, and the top sediment layer was scooped with an acid washed plastic spatula. Sediment samples were stored in plastic bags and kept in refrigeration at 4 °C until analysis. Then pebbles, leaves and other foreign particles were removed. Table 1 represents the geographical latitude and longitude for the sampling locations at the study area. Sampling locations were selected to collect representative samples from all along the study area. The collected samples were brought to the laboratory, where they were dried at a temperature of 110 °C until constant weight. The dried samples were pulverized into a fine powder and sieved through a 200 mesh sieve for radioactivity analysis. A volume of 100 cm3 of each sample was then transferred to radon impermeable PVC cylindrical container of diameter 6.5 cm and height 7 cm. Containers were sealed tightly with vinyl tape around its screw neck to prevent possible escape of radon gases. Samples were then stored for a period of 4 weeks

Please cite this article in press as: Ravisankar, R., et al. Assessments of radioactivity concentration of natural radionuclides and radiological hazard indices in sediment samples from the East coast of Tamilnadu, India with statistical approach. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/ j.marpolbul.2015.05.058

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Table 3 Radiological parameters in coastal sediment samples of East coast line of study area.

3. Results and discussions 3.1. Activity concentrations of

Sample ID

Annual gonadal dose rate (lSvy1)

RLI (Icr)

Activity utilization index (AUI)

Hint

Hex

ELCR 103

PPM DVN MAM KKM KPM VPC TPM MKM OKM APT KPK FBH KMU GCM ABH MPT PBH KEP PPT KIP TKA DPM Mean

0.3653 2.9464 0.4893 0.4615 0.2937 0.2422 0.2991 0.1495 0.1284 0.1695 0.1128 0.1100 0.1174 0.1213 0.1259 0.1685 0.1350 0.1345 0.1658 0.1617 0.1158 0.3007 0.3325

0.8354 6.9839 1.1359 1.0654 0.6635 0.5455 0.6834 0.3303 0.2753 0.3736 0.2421 0.2362 0.2519 0.2601 0.2699 0.3716 0.2892 0.2882 0.3688 0.3597 0.2486 0.6896 0.762

0.6958 8.1563 1.0925 0.9725 0.4840 0.3862 0.5676 0.1817 0.0759 0.1951 0.0717 0.0710 0.0729 0.0740 0.0752 0.1957 0.0776 0.0775 0.2236 0.2183 0.0725 0.5956 0.6651

0.3071 2.7791 0.4255 0.3959 0.2405 0.1980 0.2522 0.1187 0.0948 0.1327 0.0844 0.0826 0.0875 0.0900 0.0931 0.1322 0.0991 0.0988 0.1332 0.1301 0.0864 0.2561 0.2872

0.3020 2.6887 0.4208 0.3910 0.2350 0.1924 0.2469 0.1129 0.0888 0.1270 0.0785 0.0766 0.0815 0.0841 0.0872 0.1264 0.0932 0.0928 0.1275 0.1244 0.0805 0.2508 0.2777

0.4090 3.3423 0.5496 0.5177 0.3280 0.2704 0.3350 0.1666 0.1421 0.1885 0.1250 0.1220 0.1301 0.1343 0.1394 0.1875 0.1493 0.1488 0.1849 0.1804 0.1284 0.3371 0.3735

to bring 222Rn and its short-lived daughter products into equilibrium with 226Ra.

2.2. Gamma spectrometric analysis All samples were subjected to gamma spectral analysis with a counting time of 10,000 s. A 3’’  3’’ NaI(Tl) detector was employed with adequate lead shielding which reduced the background by a factor of about 95%. The concentrations of various radionuclides of interest were determined in Bq kg1 using the count spectra. The gamma-ray photo peaks corresponding to 1.46 MeV (40K), 1.76 MeV (214Bi) and 2.614 MeV (208Tl) were considered in arriving at the activity of 40K, 238U and 232Th in the samples. The detection limit of NaI(Tl) detector system for 40K, 238U and 232Th are 8.5, 2.21 and 2.11 Bq kg1 respectively for a counting time of 10,000 s.

238

U,

232

Th and

40

K in the sediments

The activity concentrations of 238U, 232Th and 40K together with their average values for the sediment samples are shown in Table 2. All values are given in Bq kg1 of dry weight. The range and mean values (in brackets) of the activities for 238U, 232Th and 40 K are 62.21–37.02 (62.21), 62.11–643.7 (14.29) and 300.5– 449.08 (360.23) Bq kg1, respectively. In the present study more than 95% of the samples show BDL for activity concentration of 238 U, hence mean value of uranium is taken as 62.21, since activity concentration of uranium at Devaneri (DVN) is considered as an outlier. Similarly 59% of samples show BDL for thorium concentration. All the BDL values are replaced by half of detection limit and then mean value was calculated for thorium concentration. Measured activities of the radionuclides differed widely, as activity levels in the marine environment depend on their physical, chemical and geo-chemical properties and the environment (Mora et al., 2004). Fig. 2 shows the variation of activity concentration at different sampling locations. Variation among the radioactivity concentration for different locations has been observed. It may be due to geological condition and drainage pattern of the study area location. According to Harb (2008), large variation of radionuclides in beach sediments may be due to the continuous wave action, as the waves reaches up to about 10 m from the waterline during high tide and results in the fresh deposition of heavy minerals along the seashore. In all samples, activity concentrations were in the order 40 K > 232Th > 238U. 40K dominates over the other isotopes because it is the most abundant in continental rocks and it is elevated in many light minerals (Radi Dar and El-Saharty, 2013). 232Th was higher than 238U in all samples. This could be related to their difference in chemical speciation and solubility in a natural environment. 232Th is insoluble and also preferentially accumulated on the particular phases relative to 238U (Papaefthymiou et al., 2013; Alfonso et al., 2014). The high value for 232Th activity concentration observed in Devaneri (DVN) in the study area could be explained due to the presence of black sands, which are enriched in the mineral monazite containing a significant amount of 232Th. The enrichment occurs because the specific gravity of monazite allows its

Table 4 Comparison of activity concentration of present work with other countries. S. No.

Name of the country

Activity concentration (Bq kg1) 238

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Tamilnadu, India (Coastal sediment samples) Greateraccra, Ghana (coastal sediment) North east coast, Tamilnadu (Coastal sediment) Egypt red sea (Marine sediment) Bangaladesh (coastal sediment) Oman (marine sediment) Saudi coastline – Gulf of Aqaba (Coastal sediment) Karnataka (Sediment) Albania Spain Algeria Italy French Portugal (River Tejo) Hongkang Malaysia Greece Hungary (Sediment) India – East coast of Tamilnadu (coastal sediment) Worldwide

U

3.67 – 8.39 ± 4.87 – – 11.83–22.68 11.4 374 8–27 77–6401 11–25 42–70 9–62 – 44.1 – 29–110 28.67 BDL 35

232

Th

37.23 108.60 24.52 ± 4.73 16.19 ± 8.68 45.85 10.7–25.2 22.5 158 13–40 12–63 6–32 31–37 16–55 54–76 48.1 22 19–88 27.96 14.29 30

References 40

K

387.17 29.78 274.87 ± 25.58 330.70 ± 107 594.34 222.89–535.07 641.1 158 266–675 – 56–607 410–475 120–1026 – 625 189 152–1593 302.4 360.23 400

Ravisankar et al. (2014b) Amekudzie et al. (2011) Ramasamy et al. (2009) Mahmoud et al. (2012) Sabina et al. (2014) Zare et al. (2012) Al-Trabulsy et al. (2011) Radhakrishna et al. (1993) Tsabaris et al. (2007) Lozano et al. (2002) Benamar et al. (1997) Doretti et al. (1992) Lambrechts et al. (1992) Carreira and Sequeira (1988) Yu et al. (1994) Muhammad et al. (2011) Florou and Kriditis (1992) UNSCEAR (2000) Present work UNSCEAR (2000)

Please cite this article in press as: Ravisankar, R., et al. Assessments of radioactivity concentration of natural radionuclides and radiological hazard indices in sediment samples from the East coast of Tamilnadu, India with statistical approach. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/ j.marpolbul.2015.05.058

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mean value of 102.56 Bq kg1 (Table 2) which is less than the recommended maximum value of 370 Bq kg1 (Beretka and Matthew, 1985). All the values of Raeq in the studied samples are found to be lower than the criterion limit of 370 Bq kg1 (NEA-OECD, 1979) except Devaneri (DVN). It indicates that no significant radiological hazards are associated with the sediments. The recommended values for calculated radiological Parameters are given in Table 5. The mean value of radium equivalent activity (Raeq) is found to be lower when compared with Raeq value of the criteria limit (Table 5). Fig. 2 shows the variation of Radium equivalent activity (Raeq) and different locations.

Table 5 Recommended values for radiological parameters. Radiation indices

Recommended values

References

Radium equivalent activity (Raeq)

370 Bq kg1

NEA-OECD (1979) UNSCEAR (2000) UNSCEAR (1993) UNSCEAR (2000) UNSCEAR (2000) UNSCEAR (2000) UNSCEAR (2000)

1

Absorbed gamma dose rate

84 nGy h

Average annual external effective dose Gamma representative level index (Icr) External hazard index (Hex)

0.46 mSv y1 0.5

Internal hazard index (Hin)

<1

Excess lifetime cancer risk (ELCR)

0.29  103

<1

4. Evaluation of radiological hazard effects 4.1. Absorbed gamma dose rate (DR) To

concentration along beaches where lighter materials are swept away (Uosif et al., 2008) and anthropogenic inputs can release the additional amounts of natural radionuclides into the environment. From the results it is clear that the mean activity of 238U, 232 Th and 40K are lower when compared with worldwide average value as shown in Table 4. The average values of activity do not provide an exact indication of radiation hazard associated with the sediment. In order to determine the radiation hazard due to the natural radioactivity associated with the sediments different radiological parameters are estimated and the obtained values are compared with internationally recommended safety limits. 3.2. Radium equivalent activity (Raeq) Shore sediments and other raw materials are used in building and other construction works usually by the coastal dwellers. The natural radioactivity in these raw materials is usually determined from 238U, 232Th and 40K contents. Minerals from beach sand as well as soils and rejected light sands are used by industries and building construction firms. Hence the gamma-ray radiation hazards due to the specified radionuclides can be assessed using indices (NEA-OECD, 1979). Radium equivalent activity is an index that has been introduced to represent the specific activities of 238 U, 232Th and 40K by a single quantity, which takes into account the radiation hazards associated with them (Beretka and Matthew, 1985).

Raeq ðBq Kg1 Þ ¼ AU þ 1:43ATh þ 0:077AK

ð1Þ 238

232

40

where AU, ATh and AK are the specific activities of U, Th and K (Bq kg1), respectively. It has been assumed here that 370 Bq kg1 of 238U or 259 Bq kg1 of 232Th or 4810 Bq kg1 of 40K produce the same gamma dose rate. Raeq is related to the external c-dose and internal dose due to radon and its daughters. The radium equivalent activity (Raeq) in these sediment samples ranges from 28.37 Bq kg1 (FBH) to 992.19 Bq kg1 (DVN) with a

provide

a

characteristic

of

the

external

terrestrial

c-radiation, we have calculated the absorbed dose rate in outdoor air (nGy h1) at a height of 1 m above the ground surface. Absorbed gamma dose rate is amount of energy from ionizing radiations absorbed per unit mass per unit time of matter, expressed in Gray. The contribution of natural radionuclides to the absorbed dose rate in air (DR) depends on the natural specific activity concentration of 238U, 232Th and 40K. The greatest part of the gamma radiation comes from terrestrial radionuclides. There is a direct connection between terrestrial gamma radiation and radionuclide concentrations. If a radionuclide activity is known then its exposure dose rate in air at 1 m above the ground can be calculated (Kurnaz et al., 2007). The outdoor air-absorbed dose rate due to terrestrial gamma rays at 1 m above the ground were calculated from 238U, 232Th and 40K concentration values in soil assuming that the other radionuclides, such as 137Cs, 90Sr and 235U decay series can be neglected as they contribute very little to the total dose from environmental background. The dose conversion factors for converting the activity concentrations of 238U, 232Th and 40K into dose rates (nGy h1 per Bq kg1) are 0.462, 0.604 and 0.042 respectively (UNSCEAR, 2000). 1

DR ðnGy h Þ ¼ 0:462AU þ 0:604ATh þ 0:042AK

ð2Þ

The range of absorbed dose rate in air due to natural radionuclides in the studied area is 28.39 (FBH)–778.13(DVN) nGy h1 respectively with the mean of 86.95 nGy h1. From Table 2, it is clear that mean value of absorbed dose rate in the studied area is slightly higher than the world average absorbed gamma dose rate of 84 nGy h1 (UNSCEAR, 2000). In some locations such as Pattipulam (PPM), Devaneri (DVN), Mahabalipuram (MAM) and Kokilamedu (KKM) noticed higher value than the world average value. The high values could be explained as due to the presence of black sands, which are enriched in the mineral monazite containing a significant amount of 232Th may enhance the activity concentrations which reflect the higher value of the absorbed dose rate. The spectral investigations (FT-IR and XRD analysis) support

Fig. 3. Locations Vs absorbed gamma dose rate (nGy h1).

Please cite this article in press as: Ravisankar, R., et al. Assessments of radioactivity concentration of natural radionuclides and radiological hazard indices in sediment samples from the East coast of Tamilnadu, India with statistical approach. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/ j.marpolbul.2015.05.058

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Fig. 4. Locations Vs annual effective dose rate (mSv y1).

Fig. 5. Locations Vs annual gonadal dose equivalent (lSv y1).

Fig. 6. Locations Vs RLI & AUI.

Fig. 7. Locations Vs internal (Hin) & external hazard (Hex) Indices.

the statement and confirm the heavy mineral in these locations. Fig. 3 shows the variation of absorbed gamma dose rate in different locations.

proposed by UNSCEAR (2000) were used. The determination of AEDE of each site sample is very important. The annual effective dose equivalent in mSv y1 resulting from the absorbed dose values (DR) was calculated using the following formula (UNSCEAR, 2000)

4.2. Annual effective dose equivalent (AEDE) 1

In order to estimate the annual effective dose rates, one has to take into account the conversion coefficient from the absorbed dose in air to the effective dose received by adults (0.7 SvGy1) and the outdoor occupancy factor (0.2) which implies that people spend 20% of the time outdoors, on the average, around the world

AEDE ¼ DR ðnGy h Þ  8760 h  0:2  0:7 SvG y1  106 AEDEðmSv y1 Þ ¼ DR  0:00123

ð3Þ

The annual effective dose equivalent obtained (Table 2) ranged between 0.034 (FBH) and 0.955 (DVN) with a mean value of 0.106 mSv y1. In areas with the normal background radiation,

Please cite this article in press as: Ravisankar, R., et al. Assessments of radioactivity concentration of natural radionuclides and radiological hazard indices in sediment samples from the East coast of Tamilnadu, India with statistical approach. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/ j.marpolbul.2015.05.058

R. Ravisankar et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx

the average annual external effective dose from terrestrial radionuclides is 0.46 mSv y1 (UNSCEAR, 1993). Therefore, the obtained mean value from this study area (0.106 mSv y1) is well lower than the world average value. This indicates that the sediment samples satisfy the criteria for a radiation safety point of view. Fig. 4 shows the variation of annual effective dose equivalent in different locations.

7

4.5. Activity utilization index (AUI) In order to facilitate the calculation of dose rates in air from different combinations of the three radionuclides in sediments and by applying the appropriate conversion factors, an activity utilization index (AUI) is constructed for the usage of construction materials that is given by the following formula (Chandrasekaran et al., 2014; Ravisankar et al., 2014b)



     AU ATh AK fU þ f Th þ f 50 Bq=kg 50 Bq=kg 500 Bq=kg K

4.3. Annual gonadal dose equivalent (AGDE)

AUI ¼

It is a measure of the genetic significance of the yearly dose equivalent received by the population’s reproductive organs (gonads). In the same context, the activity of bone marrow and the bone surface cells are considered as the organs of interest by UNSCEAR (1988). Therefore, the annual gonadal dose equivalent (AGDE) due to the specific activities of 238U, 232Th and 40K was calculated using the following formula (Mamont-Ciesla et al., 1982)

where AU, ATh and AK are activity concentrations (in Bq kg1) of 238U, Th and 40K and fU, fTh, and fK are the fractional contributions to the total dose rate in air due to gamma radiation from the actual concentrations of these radionuclides. In the NEA-OECD (1979) Report, typical activities per unit mass of 238U, 232Th, and 40K in sediments AU, ATh and AK are referred to be 50, 50 and 500 Bq kg1 respectively. The activity utilization index of the sediment samples are calculated using the above formula. The calculated values (Table 3) vary from 0.071 (KPK) to 8.156 (DVN) with an average of 0.665. All the value shows that AUI is <0.3 mSv y1 for all locations except one location (DVN), which corresponds to an annual effective dose >0.3 mSv y1 (El-Gamal et al., 2007). This indicates that these sediments can be safely used for construction. Fig. 6 shows variation of activity utilization index (AUI) with different locations.

AGDEðlSv y1 Þ ¼ 3:09AU þ 4:18ATh þ 0:314AK

ð4Þ

The AGDE values are presented in Table 3. The overall average values of AGDE, is found to be 0.332 lSv y1. As can be seen, the average values do not, in general, exceed the permissible recommended limits, indicating that the hazardous effects of these radiations are negligible. Fig. 5 shows variation of annual gonadal dose equivalent (AGDE) in different locations.

The representative level index Icr of the sediment may be used to estimate the level of gamma radiation hazard associated with natural gamma emitters in the sediments. This index is used to correlate the annual dose rate due to the excess external gamma radiation caused by superficial materials and acts as a screening tool for identifying materials that might become health concerns when used as construction materials (Jibiri and Okeyode, 2012). The gamma radiation hazard level of the sediment samples associated with natural radionuclides were calculated using the formula, based on the radiation hazard index Icr (NEA-OECD, 1979; Alam et al., 1999).

1 1 1 þ þ 150AU 100ATh 1500AK

232

5. Radiation hazard indices

4.4. Gamma representative level index (Icr)

RLI ¼

ð6Þ

ð5Þ

The calculated values of the representative level index vary from 0.2362 to 6.9839 with mean value of 0.7622 (Table 3). The representative level index (Icr) must be less than unity in order to keep the radiation hazard insignificant. The mean Icr value (0.7622) in the study area is below than the recommend value which indicates that the sediments do not pose any significant radiation hazard. Fig. 6 shows the variation of gamma representative level index (Icr) at different sampling locations.

5.1. External hazard index (Hex) The external hazard index is an evaluation of the hazard of the natural gamma radiation (Ibrahim, 1999). This index is used to assess the radiological suitability of a material. The prime objective of this index is to limit the radiation dose to the admissible dose equivalent limit of 1 mSv y1 (ICRP 60; Al-Hamarneh and Awadallah, 2009) and can be evaluated using the following equation,

Hex ¼

AU ATh AK þ þ 370 Bq=kg 259 Bq=kg 4810 Bq=kg

ð7Þ

The value of Hex must be lower than unity in order to keep the radiation hazard insignificant. If Hex < 1 implies that activities involving the use of materials are safe and do not attract any high levels of radiation exposure. The calculated value of the external hazard index for the studied samples is presented in Table 3. The Hex values ranged from 0.076 (FBH) to 2.688 (DVN) with an average value of 0.277. These sediments may not harm workers and peasants in this region. Further, the mean value of the results showed there were no elevated radiological health hazards to the people living in nearby terrestrial areas of the sampling sites and the people who handle the marine sediments for utilizing building

Fig. 8. Locations Vs excess lifetime cancer risk (ELCR).

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R. Ravisankar et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx

Table 6 Comparison of radiological parameters of present work with other countries. S. No. 1 2 3 4 5 6 7 8 9 10

Name of the country

Ra(eq) (Bq kg1)

DR (nGy h1)

AEDE (mSv y1)

AGDE (mSv y1)

RLI (Icr)

Hex

Hint

References

Tamilnadu, India (Coastal sediment samples) Greateraccra, Ghana (Coastal sediment) North east coast Tamilnadu (Coastal sediment) Egypt red sea (Marine sediment) Bangaladesh (Coastal sediment) Oman (Marine sediment) Saudi coastline Gulf of Aqaba (Coastal sediment) Malaysia (Coastal sediment) Sudan Red sea (Coastal sediment) India (East Coast of Tamilnadu)

84.57

41.70

0.051

0.282

0.64

0.22

0.23

Ravisankar et al. (2014b)

9.00

77.02

0.09

–

0.48

–

Amekudzie et al. (2011)

–

30.15

0.15

–

0.48

0.17

–

Ramasamy et al. (2009)

63.81 121.27 47.21–90.2 92.9

30.69 55.15 12.36–24.38 45.6

0.04 0.14 – 0.056

– – – –

0.48 – – –

0.17 0.33 0.13–0.25 0.13

0.21 – – 0.28

Mahmoud et al. (2012) Sabina et al. (2014) Zare et al. (2012) Al-Trabulsy et al. (2011)

143.1 32.4 102.56

– – 86.95

– – 0.1067

– – 0.3325

1.00 0.2 0.762

0.4 0.1 0.277

– – 0.287

Yii et al. (2011) Sam et al. (1998) Present work

Table 7 Summary of basic statistics of natural radionuclides (Bq kg1) in sediments. Variables

238

232

40

Minimum Maximum Mean Std. Deviation Variance Skewness Kurtosis Frequency distribution

BDL 37.02 BDL 7.89 62.29 4.69 22 Log-normal

BDL 643.7 14.29 135.3 18315.2 4.4 20.2 Log-normal

300.5 449.08 360.24 48.11 2314.29 0.62 0.67 Normal

U

Th

K

constructions is safe. The higher value of Hex in Devaneri may be due to the dynamic movement of finer sediments from coastal regions. Fig. 7 shows variation of Hex with different locations. 5.2. Internal hazard index (Hin) In addition to the external hazard index, internal exposure to radon and its products is quantified by estimating the internal hazard index (Hin). Inhalation of alpha particles emitted from the short-lived radionuclides radon (222Rn, the daughter product of 226 Ra) and thoron (220Rn, the daughter product of 224Ra) is also hazardous to the respiratory organs. This hazard can be quantified

Fig. 9. Frequency distribution of

238

by the internal hazard index (Hin) (Beretka and Matthew, 1985; Xinwei, 2005).

U.

Hin ¼

AU ATh Ak þ þ 185 Bq=kg 259 Bq=kg 4810 Bq=kg

ð8Þ

The average value of Hin has been determined to be 0.287 (Table 3) which is less than permissible limit. The above results indicate that the internal hazard is below the critical value and no significant radiation hazards are associated with the sediments and coastal sediments. They are unlikely to pose radiological health risk to the people living in nearby areas along the East coast of Tamilnadu, India. Fig. 7 shows variation of Hin with different locations. 5.3. Excess lifetime cancer risk (ELCR) Potential carcinogenic effects are characterized by estimating the probability of cancer incidence in a population of individuals for a specific lifetime from projected intakes (and exposures) and chemical-specific dose–response data (i.e., slope factors). The additional or extra risk of developing cancer is due to exposure to a toxic substance incurred over the lifetime of an individual (Ravisankar et al., 2014b). The excess lifetime cancer risk (ELCR) is calculated using the equation:

Fig. 10. Frequency distribution of

232

Th.

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R. Ravisankar et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx

Fig. 11. Frequency distribution of

asymmetry or lack of symmetry in the shape of a frequency distribution. When a distribution is not symmetrical it is called a skewed distribution. Skewed distribution could either be positively or negatively skewed (Gupta, 2001). In the present study, the skewness of activity concentrations of 238U, 232Th and 40K radionuclides are positive, which shows that their distributions are asymmetric. The plotted graph has no bell shaped form and its positive values indicate the positive skewness. The frequency distribution of 238 U, 232Th and 40K are shown in Figs. 9–11. Kurtosis is a measure of peakedness. It is also a function of internal sorting or distribution. Depending upon the peakedness, it is named as mesokurtic, leptokurtic and platy kurtic. If the value of kurtosis is zero, it is known as normal curve or mesokurtic. When the kurtosis value is positive, the curve is more peaked than the normal curve i.e., leptokurtic whereas the negative value of kurtosis indicates less peaked than the normal curve i.e., platy kurtic (Gupta, 2001). In the present study, the kurtosis values of activity concentrations of 238U and 232Th are positive and it indicates that the curve is more peaked than the normal curve i.e., leptokurtic whereas negative kurtosis value of activity concentration of 40K indicates platy kurtic. This may due to uneven distribution of natural radionuclides in the samples of the study area.

40

K.

ELCR ¼ AEDE  DL  RF

ð9Þ 5.5. Pearson correlations

where AEDE, DL and RF are the total annual effective dose equivalent, duration of life (70 y) and risk factor (Sv1), i.e. fatal cancer risk per sievert, respectively. For stochastic effects, ICRP 60 uses values of 0.05 for the public (Taskin et al., 2009). From Table 3, the calculated ELCR values ranged from 0.122  103 (FBH) to 3.342  103 (DVN) with an average of 0.373  103, which is slightly higher than the worldwide recommended value of 0.29  103 (UNSCEAR, 2000). The higher ELCR value noticed in Devaneri (3.3423  103) may be due to the higher activity concentration of natural radionuclides in this location. Fig. 8 shows the locations and excess lifetime cancer risk (ELCR). Comparison of radiological parameters of present work with other countries is reported in Table 6.

The linear association relationship of radionuclides and associated radiological parameters was established using Pearson’s correlation coefficient analysis and summarized in Table 8. The correlation of 238U with 232Th showed a fairly high degree with a positive correlation coefficient of r > 0.75, suggesting that their content in sediments are mostly influenced and controlled by similar origin of sources (Ravisankar et al., 2014b; Chandrasekaran et al., 2015). A poor degree of correlation was seen between 40K and 238U, 232Th suggesting that 40K has dissimilar origin in sediments. The 232Th and 238U, radionuclide levels showed a high degree of positive correlation with all radiological hazard parameters with coefficients of r > 0.75. This indicated that radiological hazards were associated and controlled by concentration of uranium and thorium. A poor degree of correlation was observed between 40K and radiological hazard parameters suggesting concentration of potassium is not significantly responsible for radiological hazards. Finally Pearson’s correlation coefficient analysis suggested that natural radioactivity along the coastal area is due to concentration of uranium and thorium.

5.4. Descriptive statistics of natural radionuclides The basic statistics such as minimum, maximum, mean, standard deviation, variance, skewness and kurtosis of natural radionuclides are presented in Table 7. The standard deviation higher than the mean value indicates the low degree of uniformity and vice versa (Gupta, 2001; Ravisankar et al., 2014c). In the present study, standard deviation of 238U and 232Th are greater than their mean value. This shows that concentration of uranium and thorium in sediment samples has low degree of uniformity. The standard deviation of 40K is less than the mean value which indicates high degree of uniformity in their distribution. Skewness refers to the

5.6. Principal component analysis (PCA) To confirm the association of radiological parameters with natural radionuclides obtained from the Pearson correlation analysis, principal component analysis was performed for the present

Table 8 Pearson correlations between radionuclides and associated radiological hazards. Variables

238

232

238

1 0.982 0.412 0.982 0.982 0.982 0.983 0.982 0.984 0.983 0.982 0.982

1 0.512 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000

U 232 Th 40 K Raeq DR HR AGDE RLI AUI Hin Hex ELCR

U

Th

40

K

1 0.520 0.524 0.524 0.523 0.524 0.508 0.517 0.520 0.524

Raeq

DR

HR

AGDE

RLI

AUI

Hin

Hex

ELCR

1 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000

1 1.000 1.000 1.000 1.000 1.000 1.000 1.000

1 1.000 1.000 1.000 1.000 1.000 1.000

1 1.000 1.000 1.000 1.000 1.000

1 1.000 1.000 1.000 1.000

1 1.000 1.000 1.000

1 1.000 1.000

1 1.000

1

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Table 9 Rotated factor loadings of variables. Variables

Component-1

Component-2

238

0.975 0.963 0.261 0.960 0.959 0.959 0.959 0.959 0.964 0.961 0.960 0.959 85.33%

0.164 0.270 0.965 0.279 0.284 0.284 0.285 0.283 0.266 0.275 0.279 0.284 14.47%

232

U Th K

40

Raeq DR HR AGDE RLI AUI Hin Hex ELCR % of variance explained

Fig. 12. Graphical representation of component 1 (85.33%) and component 2 (14.47%).

sediments. The variables taken for this analysis are the same as for the Pearson correlation analysis. The principal component analysis is actually performed on the correlation matrix between different parameters followed by varimax rotation. Obtained important principal components such as component 1 and 2 are given in Table 9 and shown in Fig. 12. The principal component 1 extracted due to high positive lodgings of 238U and 232Th and associated all radiological parameters

with explained variance of 85.33%. This indicated that the total level of natural radioactivity in the study area is due to concentration of uranium and thorium. Similarly component 2 due to high positive loading of only 40K with explained variance of 14.47% but concentration of potassium does not control the levels of radioactivity. According to Ravisankar et al. (2014a) if the total variance is greater than 70%, the fitted principal component to the data was good. In the present study the total explained variance is 99.80% to the radioactive data. Also the result of principal component analysis is in good agreement with Pearson correlation analysis.

5.7. Cluster analysis (CA) In order to determine the influence of natural radionuclides in the levels of natural radioactivity in sediments, the cluster analysis was carried out using SPSS (version 16) software. Cluster analysis (CA) is a multivariate technique, whose primary purpose is to classify the objects of the system into categories or clusters based on their similarities, and the objective is to find an optimal grouping for which the observations or objects within each cluster are similar, but the clusters are dissimilar from each other. The dendrogram visually displays the order in which parameters or variables combine to form clusters with similar properties. The most similar objects are first grouped, and these initial groups are merged according to their similarities. Similarity is a measure of distance between clusters relative to the largest distance between any two individual variables. One hundred percent similarity means the clusters were zero distance apart in their sample measurements, while the similarity of zero percent means the cluster areas are as disparate as the least similar region (Ravisankar et al., 2014b; Chandrasekaran et al., 2014). In CA single linkage method along with correlation coefficient distance is applied. Table 8 lists the rotated factor loadings of variables. The derived dendrogram is shown in Fig 13. From the dendrogram, an interesting relation between the radioisotopes and radiological parameters can be assessed. In this dendrogram all 12 parameters are grouped into two statistically significant clusters. All the clusters are formed on the basis of existing similarities. Cluster I consists of natural radionuclides (238U and 232Th) and all important radiological parameters with high similarity. This shows that the total level of radioactivity in sediment mainly depends on the corresponding 238U and 232Th concentrations. Cluster II consists of only 40K suggesting that concentration of potassium in sediments not contributing the radiation hazard in the sediment sampling locations. These results are in good agreement with Pearson correlation and principal component analysis.

Fig. 13. The clustering of radioactive variables.

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R. Ravisankar et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx

6. Conclusion The activity concentrations of 238U, 232Th and 40K in sediment samples collected from Pattipulam to Devanampattinam along East coast of Tamilnadu, India were analyzed using c-ray spectrometer containing NaI(Tl) detector. The variation in concentration of natural radionuclides at different sampling locations may be due to sediment particle size. Radiological hazard parameters were estimated based on the activity concentrations of 238U, 232 Th and 40K. Among the investigated samples, Devaneri (DVN) showed higher specific activities for 238U, 232Th and 40K and radiological parameters most probably due to presence of heavy mineral. However, the results of radiation hazard indices reflect that the investigated area of East coast of Tamilnadu seems to be radiologically safe for human being. From the multivariate statistical analysis, the Pearson’s correlation coefficient analysis suggested that natural radioactivity along the coastal area due to concentration of uranium and thorium and the results of principal component analysis is in good agreement with Pearson correlation analysis. Cluster analysis indicates that 40 K in sediments is not contributing to the radiation hazard in the sampling locations and is also in good agreement with Pearson correlation and principal component analysis. The present study has pointed out the area under study need further studies in order to understand better the origin and distribution of naturally occurring radionuclides. The results may be used as a reference data for monitoring. Acknowledgements We are sincerely thanks to Dr. M.T. Jose, Head, Radiological Safety Section, Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam for his keen interest and permission to avail Gamma Ray Spectrometer and Mr. R. Mathiarasu, Scientific Officer, RSD, IGCAR for his technical help in counting the samples. One of the author (J. Chandramohan) is highly indebted to the Management, E.G.S. Pillay Engineering College, Nagapattinam-611 002, Tamilnadu, India for allowing him to pursue the Doctoral degree for the sake of improvement of his career. References Akram, M., Qureshi, R.M., Ahmad, N., Solaija, T.J., 2006. Gamma-emitting radionuclides in the shallow marine sediments off the Sindh coast, Arabian Sea. Radiat. Prot. Dosi. 118, 440–447. Alam, M.N., Chowdhury, M.I., Kamal, M., Ghose, S., Islam, M.N., Mustafa, M.N., Miah, M.M.H., Ansary, M.M., 1999. The 226Ra, 232Th and 40K activities in beach sand minerals and beach soils of Cox’s Bazar, Bangladesh. J. Environ. Radioact. 46, 243–250. Alatise, O.O., Babalola, I.A., Olowofela, J.A., 2008. Distribution of some natural gamma emitting radionuclides in the soils of the coastal areas of Nigeria. J. Environ. Radioact. 99, 1746–1749. Alfonso, J.A., Perez, K., Palacios, D., Handt, H., LaBrecque, J.J., Mora, A., Vasquez, Y., 2014. Distribution and environmental impact of radionuclides in marine sediments along the Venezuelan coast. J. Radioanal. Nucl. Chem. 300, 219–224. Al-Hamarneh, I.F., Awadallah, M.I., 2009. Soil radioactivity levels and radiation hazard assessment in the highlands of northern Jordan. Radiat. Meas. 44, 102– 110. Al-Trabulsy, H.A., Khater, A.E.M., Habbani, F.I., 2011. Radioactivity levels and radiological hazard indices at the Saudi coast line of the Gulf of Aqaba. Radiat. Phys. Chem. 80, 343–348. Amekudzie, A., Emi-Reynolds, G., Faanu, A., Darko, E.O., Awudu, A.R., Adukpo, O., Quaye, L.A.N., Kpordzro, R., Agyemang, B., Ibrahim, A., 2011. Natural radioactivity concentrations and dose assessment in shore sediments along the coast of greater Accra, Ghana. W. Appl. Sci. Jour. 13, 2338–2343. Benamar, M.A., Zerrouki, A., Idiri, Z., Tobbeche, S., 1997. Natural and artificial levels in sediments in Algiers Bay. Appl. Radiat. Isot. 48 (8), 1161–1164. Beretka, J., Matthew, P.J., 1985. Natural radioactivity of Australian building materials. Industrial wastes and by-products. Health Phys. 48, 87–95. Carreira, M.C.U., Sequeira, M.M.A., 1988. 226Ra and 228Ac in a fresh water ecosystem. Radiat. Prot. Dosim. 24 (1), 133–137. Chandrasekaran, A., Ravisankar, R., Senthilkumar, G., Thillaivelavan, K., Dhinkaran, B., Vijayagopal, P., Bramha, S.N., Venkatraman, B., 2014. Spatial distribution and

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Please cite this article in press as: Ravisankar, R., et al. Assessments of radioactivity concentration of natural radionuclides and radiological hazard indices in sediment samples from the East coast of Tamilnadu, India with statistical approach. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/ j.marpolbul.2015.05.058