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Natural radioactivity concentrations and dose assessment in coastal sediments along the East Coast of Tamilnadu, India with statistical approach
CHNAES-00662; No of Pages 10 Acta Ecologica Sinica xxx (2019) xxx
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Natural radioactivity concentrations and dose assessment in coastal sediments along the East Coast of Tamilnadu, India with statistical approach E. Devanesan a,d, J. Chandramohan b, G. Senthilkumar c, N. Harikrishnan d, M. Suresh Gandhi e, Sanjay S. Kolekar f, R. Ravisankar d,⁎ a
Department of Physics, Dhivya Arts & Science College, Chetpet, Tamilnadu 606801, India Department of Physics, Aries Arts and Science College for women, Karunkuzhi, Vadalur, Tamilnadu 607 302, India c Department of Physics, University College of Engineering Arni, Thatchur, Tamilnadu 632326, India d Post Graduate and Research Department of Physics, Government Arts College, Tiruvannamalai, Tamilnadu 606603, India e Department of Geology, University of Madras, Guindy Campus, Chennai, Tamilnadu 600025, India f Department of Chemistry, Shivaji University, Kolhapur, Maharashtra 416004, India b
a r t i c l e
i n f o
Article history: Received 21 April 2019 Received in revised form 23 June 2019 Accepted 28 June 2019 Available online xxxx Keywords: Sediment Gamma ray spectrometry Radiological parameters Statistical analysis
a b s t r a c t The present study was conducted to determine the activity concentration of 238U, 232Th and 40K in coastal sediments samples from Poombuhar to Karaikal along East coast of Tamilnadu, India using gamma ray spectrometry. The average activity concentration for 238U, 232Th and 40K were obtained as 36.82 (Bq kg−1), 50.11(Bq kg−1) and 320.38 (Bq kg−1), respectively. These obtained results were used to calculate the radiological hazard parameters like radium equivalent activity (Raeq), absorbed gamma dose rate (DR), the annual effective dose equivalent (AEDE), Annual gonadal dose equivalent (AGDE), Activity utilization index (AUI), External hazard index (Hex), Internal hazard index (Hin), Gamma representative level index (RLI) and Excess lifetime cancer risk (ELCR). The computed radiological parameters values are compared with the internationally approved recommended values. The multivariate statistical method is used to simplify and organize large data sets to indicate natural associations between samples and variables. © 2019 Ecological Society of China. Published by Elsevier B.V. All rights reserved.
1. Introduction In universe, all living organisms including man are constantly exposed to varying degrees of ionizing radiation from naturally occurring radioactive materials (NORMs) in the environment and radionuclides generated by human activities which is called technologically enhanced naturally occurring radioactive materials (TENORM). The naturally occurring radioactive materials (NORMs) are found in various geological formations such as soil, rocks, water, sediments, air and in some building materials [1]. Many artificial sources of radiation have been introduced since the discovery of X-rays and radioactivity at the end of the nineteenth century, and particularly since the exploitation of the process of nuclear fission in the middle of the twentieth century. Also radionuclides enter the environment during nuclear weapon testing, nuclear accidents, medical and industrial radiation applications. These artificial sources now add a significant contribution to the total radiation exposure of the population.
The contribution of radiation from soil to human exposure can either be whole body due to external radiation originating directly from primordial radionuclides present in soil or internal due to inhalation [2]. The internal exposure to radiation affecting the respiratory track is due to radon and its decay products which emanate from soil, sediment and building materials [3]. Radionuclides may be transferred from soils to plants, animals and finally to man. The study of the distribution of radionuclide helps in the determination of the radiological health implication of exposure to gamma rays and inhalation of radon and its daughter products. In the present work an attempt has been made to assess the natural radioactivity and radiological hazard due to the exposure to gamma radiation from the coastal sediment samples collected from Poombuhar to Karaikal along the South East Coast of Tamilnadu, India. 2. Materials and methods 2.1. Sample collection
⁎ Corresponding author. E-mail address: [email protected] (R. Ravisankar).
Sediment samples were collected by a Peterson grab sampler along the Bay of Bengal coastline, from Poombuhar to Karaikal along the
https://doi.org/10.1016/j.chnaes.2019.06.001 1872-2032/© 2019 Ecological Society of China. Published by Elsevier B.V. All rights reserved.
Please cite this article as: E. Devanesan, J. Chandramohan, G. Senthilkumar, et al., Natural radioactivity concentrations and dose assessment in coastal sediments along the East Coast o..., Acta Ecologica Sinica, https://doi.org/10.1016/j.chnaes.2019.06.001
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E. Devanesan et al. / Acta Ecologica Sinica xxx (2019) xxx
South East Coast of Tamilnadu, India during premonsoon condition. Fig. 1 shows the location map of the study area. The grab sampler collects sediment layer from the seabed along the 20 stations. Table 1 lists the geographical latitude and longitude for the sampling locations of the study area. Uniform quantity of sediment samples were collected from all the sampling stations. Each sample of about 2 kg was kept in a thick plastic bag.
3. Results and discussions 3.1. Activity concentrations
The samples were air dried at1050C to a constant weight. After homogenization, samples were sieved through 1 mm mesh-sized sieve to remove stone, pebbles and other macro-impurities. The homogenized sample was packed in a standard 250 ml airtight PVC plastic container. 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 to allow radioactive secular equilibrium to be attained between 238U (226Ra) and 232Th (228Ra) and their progenies [4].
Table 2 gives the results of natural radionuclide concentrations in the collected sediment samples of the study area. The range and average values (in brackets) of the activities for 238U, 232Th and 40K are 24.35–55.74 (36.82), 22.11–86.39 (50.11) and 223.78–395.43 (320.38) Bq kg−1, respectively. The mean values are slightly higher than the corresponding worldwide average values which are 35 and 30 Bq kg−1 for 238U, 232Th and lower value of 400 Bq kg−1 for 40K. Measured activities of the radionuclides differed widely, as activity levels in the marine environment depend on their physical, chemical and geochemical properties and the environment [5]. The high values of the 232 Th observed in the sediment samples collected from the locations of PPR, PVG, PCG, PKM-1 & PKK-1 may be due to the presence of heavy minerals such illmenite, zircon etc., as revealed from the geological studies. Table 3 lists the comparison of activity concentrations of present work with regional area of Tamilnadu.
2.3. Gamma spectrometric analysis
3.2. Evaluation of radiological hazard effects
All samples were subjected to gamma spectral analysis with a counting time of 10,000 s. A 3“ x 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 kg−1 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, 238 U 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 kg−1, respectively for a counting time of 10, 000 s.
Different known radiation health hazard indices analysis has been used in radiation studies to arrive at a better and safer conclusion on the health status of a radiated or irradiated person and environment in recent studies [11]. To assess the radiation hazards associated with the studied sediment samples, the following nine quantities have been defined.
2.2. Sample preparation
3.2.1. Radium equivalent activity (Raeq) The radium equivalent activity (Raeq) was computed in this work in order to assess the gamma radiation risk to human being. This activity
Fig. 1. Location Map of the Study Area.
Please cite this article as: E. Devanesan, J. Chandramohan, G. Senthilkumar, et al., Natural radioactivity concentrations and dose assessment in coastal sediments along the East Coast o..., Acta Ecologica Sinica, https://doi.org/10.1016/j.chnaes.2019.06.001
E. Devanesan et al. / Acta Ecologica Sinica xxx (2019) xxx
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Table 1 The Geographical latitude and longitude for the sampling locations of the study area. S·No
Locations
Sample ID
Latitude (N)
Longitude (E)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Poombuhar ChinnaVaanagiri Vaanagiri Chinnangudi Pillaiperumalnallur Vellaikoil Tharangampadi Cheranjampadi Mandapaputhur Akkampettai-I Akkampettai-II Keelakasakudimedu-I Keelakasakudimedu-II Kilinjalmedu Karaikalmedu Ammantherumedu-I Ammantherumedu-II Karaikal-I Karaikal-II Karaikal-III
PPR PCV PVG PCG PPM PVK PTP PCP PMP PAP-1 PAP-2 PKM-1 PKM-2 PKJ PKL PAT-1 PAT-2 PKK-1 PKK-2 PKK-3
11° 9′ 1.0836″ N 11° 7′ 5.5776″ N 11° 7′ 10.7652″ N 11° 5′ 32.1504″ N 11° 4′ 21.8028″ N 11° 2′ 3.2496″ N 11° 1′ 37.182″ N 10° 59′ 59.658″ N 10° 59′ 8.2464″ N 10° 56′ 56.3784″ N 10° 56′ 56.0724″ N 10° 56′ 26.5684″ N 10° 56′ 10.5681″ N 10° 56′ 23.6148″ N 10° 56′ 24.2196″ N 10° 55′ 54.2192″ N 10° 55′ 43.2188″ N 10° 55′ 31.584″ N 10° 55′ 30.432″ N 10° 55′ 30.1296″ N
79° 50′ 37.248″ E 79° 50′ 49.2828″ E 79° 50′ 47.328″ E 79° 50′ 32.5212″ E 79° 49′ 59.1492″ E 79° 51′ 15.5484″ E 79° 50′ 13.6752″ E 79° 51′ 0.7164″ E 79° 51′ 4.4244″ E 79° 50′ 54.6144″ E 79° 51′ 17.172″ E 79° 51′ 10.7384″ E 79° 51′ 6.7382″ E 79° 50′ 50.9064″ E 79° 51′ 11.9196″ E 79° 51′ 07.9136″ E 79° 51′ 10.9192″ E 79° 50′ 16.8216″ E 79° 50′ 16.8396″ E 79° 50′ 18.8484″ E
index provides a useful guideline in regulating the safety standards on radiation protection for the general public residing in the area under investigation. It is the most widely used index to assess the radiation hazards and can be calculated using Equation [12–15].
and the outdoor occupancy of 0.2 as proposed by UNSCEAR [19]. The annual effective dose rate was calculated using the formula.
Raeq Bq Kg−1 ¼ AU þ 1:43ATh þ 0:077AK
AEDE mSvy−1 ¼ DR x 0:00123
ð1Þ
where AU, ATh and AK are the activity concentrations of 238U, 232Th & 40K (Bq kg−1), respectively. The radium equivalent activity (Raeq) in these sediment samples ranges from 87.70 Bq kg−1 (PAP-2) to 185.21 Bq kg−1 (PKM-1) with a mean value of 133.14 Bq kg−1 (Table 2) which is less than the recommended maximum value of 370 Bq kg−1(NEA-OCED [16]). It indicates that no radiological hazards associated with the sediments. Fig. 2 shows the locations Vs Activity concentration and Radium equivalent activity (Bq kg−1). 3.2.2. Absorbed gamma dose rate (DR) The absorbed dose rate is important in radiation risk analysis since it measures the amount of radiation deposited per unit time. The contribution of natural radionuclides to the absorbed dose rate in air (DR) depends on the activity concentration of 238U, 232Th, and 40K. The absorbed dose rate (DR) in air at average gonad height of one meter above the surface of ground due to the natural radionuclides 238U, 232Th and 40K was estimated using the formula given as ([17,18].)
DR nGyh
−1
¼ 0:462AU þ 0:604ATh þ 0:042AK
ð2Þ
where AU, ATh and AK are the activity concentrations of 238U, 232Th & 40K (Bq kg−1), respectively. The range of absorbed dose rate in air due to natural radionuclides in the studied area is 41.51 (PAP-2) – 82.93 (PKM-1) nGyh−1, respectively with the mean of 60.73 nGyh−1. From Table 2, it is clear that mean value of absorbed dose rate in the studied area is higher than the world average absorbed gamma dose rate of 84 nGyh−1 [19]. The high values noticed in some locations of the study area could be explained as due to the presence of heavy mineral in the study area which may be monazite containing 232Th in significant quantity. This may enhance the activity concentrations which reflect the higher value of the absorbed dose rate. 3.2.3. Annual effective dose equivalent (AEDE) The annual effective dose due to the natural radionuclides in the samples was estimated using the dose conversion coefficient that convert the absorbed dose rate in air to the effective dose (0.7 Sv Gy−1)
−1 AEDE ¼ DR nGyh x 8760 h x 0:2 x 0:7SvGy−1 x 10−6 ð3Þ
The annual effective dose equivalent (Table 2) ranged between 0.051 (PAP-2) and 0.102 (PKM-1) with a mean value of 0.0746 mSv y−1. Therefore, the obtained mean value from this study area (0.0746 mSv y−1) is well lower than the 0.46 mSv y−1 for normal background radiation area [20]. This indicates that the sediment samples satisfy the criteria for a radiation safety point of view. 3.2.4. Annual gonadal dose equivalent (AGDE) Annual gonadal dose equivalent (AGDE) measures of the genetic significance of the yearly dose equivalent received by the population's reproductive organs (gonads). The annual gonadal dose equivalent (AGDE) due to the activity concentration of 238U, 232Th and 40K was calculated using the following formula [21]. AGDE mSvy−1 ¼ 3:09AU þ 4:18ATh þ 0:314AK
ð4Þ
The AGDE values are presented in Table 2. The annual gonadal dose equivalent obtained ranged between 0.291 (PAP-2) and 0.577 (PKM-1) with a mean value of 0.422 mSv y−1. The average value of the AGDE 0.422 mSv y−1 is slightly higher than UNSCEAR value 0.3 mSvy−1 reported as the world value [22]. Fig. 3 shows the locations Vs Annual Effective Dose Rate (AEDE) (mSvy−1) and Annual gonadal dose equivalent (AGDE) (mSv y−1). 3.2.5. Activity utilization index (AUI) The calculation of dose rates in air from different combinations of the three radionuclides in sediments by applying the appropriate conversion factors, an activity utilization index (AUI) is calculated for the usage of construction materials that is given by the following formula [23]. AUI ¼
AU 50 Bq=kg
fU þ
ATh Ak f Th þ fK 50 Bq=kg 500 Bq=kg
ð5Þ
where AU, ATh and AK are activity concentrations (in Bq kg−1) of 238U, 232 Th and 40K and fU, fTh, and fK are the fractional contributions to the
Please cite this article as: E. Devanesan, J. Chandramohan, G. Senthilkumar, et al., Natural radioactivity concentrations and dose assessment in coastal sediments along the East Coast o..., Acta Ecologica Sinica, https://doi.org/10.1016/j.chnaes.2019.06.001
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E. Devanesan et al. / Acta Ecologica Sinica xxx (2019) xxx
Table 2 Activity Concentration, Radium Equivalent activity(Raeq), Gamma dose rate(DR), AEDE, AGDE, AUI, External hazard index(Hex), Internal hazard index(Hin), RLI and Excess life time cancer risk(ELCR) in coastal sediment samples of Tamilnadu, India. Locations Name
Sample ID
238
Poombuhar ChinnaVaanagiri Vaanagiri Chinnangudi Pillaiperumalnallur Vellaikoil TharangamPadi Cheranjampadi Mandapaputhur Akkampettai-I Akkampettai-II Keelakasakudimedu-I Keelakasakudimedu-II Kilinjalmedu Karaikalmedu Ammantherumedu-I Ammantherumedu-II Karaikal-I Karaikal-II Karaikal-III MEAN MIN MAX
PPR PCV PVG PCG PPM PVK PTP PCP PMP PAP-1 PAP-2 PKM-1 PKM-2 PKJ PKL PAT-1 PAT-2 PKK-1 PKK-2 PKK-3
40
(Bqkg−1)
Absorbed Gamma Dose Rate (DR) (nGyh−1)
307.19 304.53 294.54 395.43 272.69 283.22 223.78 388.96 352.61 333.01 350.69 352.16 361.96 280.52 265.26 346.17 329.63 363.59 254.7 347.03 320.38 223.78 395.43
145.52 121.99 142.66 156.71 111.29 120.51 132.07 123.54 144.96 110.06 87.70 185.21 125.80 120.63 148.62 104.42 138.62 161.75 142.59 138.13 133.14 87.70 185.21
65.33844 55.4667 64.39044 71.31002 51.00318 55.79128 59.4711 57.27322 66.14256 50.87672 41.51838 82.937 58.1778 55.26944 67.06772 48.93586 62.77136 73.37966 64.33122 63.15274 60.73 41.51 82.93
Activity Concentration (Bqkg−1) U
24.35 26.6 33.92 34.64 35.6 55.74 39.51 35.49 39.65 31.15 29.08 34.56 40.7 41.9 44.9 39.14 27.67 40.72 42.63 38.34 36.82 24.35 55.74
232
Th
68.19 50.31 60.18 64.07 38.25 30.04 52.68 40.63 54.66 37.25 22.11 86.39 40.02 39.95 58.25 27.01 59.84 65.06 56.19 51.1 50.11 22.11 86.39
K
Ra(equ)
AEDE (mSv y−1)
AGDE (mSvy−1)
AUI
Hex
Hin
RLI
ELCR X 10−3
0.080366 0.068224 0.0792 0.087711 0.062734 0.068623 0.073149 0.070446 0.081355 0.062578 0.051068 0.102013 0.071559 0.067981 0.082493 0.060191 0.077209 0.090257 0.079127 0.077678 0.0746 0.051 0.102
0.455505 0.386894 0.447673 0.497434 0.354423 0.385602 0.41166 0.400075 0.460306 0.355192 0.290991 0.57707 0.405254 0.383423 0.464457 0.341157 0.437817 0.510489 0.445558 0.439648 0.422 0.291 0.577
1.0743 0.8789 1.0650 1.1270 0.8137 0.9015 1.0201 0.8512 1.0561 0.7656 0.5650 1.3923 0.8897 0.8931 1.1407 0.7168 1.0060 1.1925 1.0939 1.0005 0.972 0.565 1.392
0.3940 0.3302 0.3862 0.4242 0.3012 0.3260 0.3575 0.3343 0.3923 0.2978 0.2372 0.5015 0.3404 0.3264 0.4023 0.2824 0.3753 0.4378 0.3860 0.3738 0.360 0.236 0.500
0.4588 0.4013 0.4769 0.5168 0.3968 0.4762 0.4635 0.4296 0.4987 0.3814 0.3155 0.5936 0.4498 0.4391 0.5228 0.3878 0.4491 0.5469 0.5003 0.4767 0.360 0.236 0.500
1.0490 0.8835 1.0243 1.1353 0.8016 0.8608 0.9394 0.9022 1.0460 0.8022 0.6488 1.3291 0.9128 0.8658 1.0587 0.7618 1.0026 1.1645 1.0159 0.9980 0.960 0.648 1.329
0.281282 0.238784 0.277201 0.30699 0.219569 0.240181 0.256023 0.246561 0.284744 0.219024 0.178737 0.357044 0.250455 0.237935 0.288727 0.210669 0.270231 0.315899 0.276946 0.271873 0.261 0.178 0.357
Table 3 Comparison of Activity concentrations of present work with Regional level. S. No
Activity concentrations (Bq kg−1)
Locations
238
North East Coast of Tamilnadu, India Pattipulam to Devanampattinam, Tamilnadu, India Pulicatlake to Vadanemmeli, Tamilnadu, India Thazhankuda to Kodiyakkarai Tamilnadu, India Periyakalapet to Parangipettai, Tamilnadu, India Poombuhar to Karaikal, Tamilnadu, India
Activity Concentration and Radium Equivalent Activity (Bqkg−1)
1 2 3 4 5 6
400
232
U
8.39 ± 4.87 2.21 10.14 3.30 – 36.815
U
Th
Th
24.52 ± 4.73 14.29 35.02 40.45 85.67 50.109
K
References 40
K
274.87 ± 25.58 360.23 425.8 389.28 425.72 320.384
Ramasamy et al. [6] Chandramohan et al. [7] Tholkappian et al. [8] Sivakumar et al. [9] Harikrishnan et al. [10] Present Work
Ra eq
350 300 250 200 150 100 50 0
Location ID Fig. 2.. Locatin Vs Activity concentration and Radium equivalent activity (Bq kg−1).
total dose rate in air due to gamma radiation from the actual concentrations of these radionuclides. In the NEA-OECD [16] Report, typical activities per unit mass of 238U, 232Th, and 40K in area AU, ATh and AK are referred to be 50, 50 and 500 Bq kg−1,respectively. The activity utilization index of the sediment samples are calculated using the above formula. The calculated values (Table 2) vary from 0.565 (PAP-2) to
1.392 (PKM-1) with an average of 0.972. This value shows that AUI b2 for all locations which corresponds to an annual effective dose b0.3 mSv y−1 [24]. This indicates that these sediments can be safely used for construction.
Please cite this article as: E. Devanesan, J. Chandramohan, G. Senthilkumar, et al., Natural radioactivity concentrations and dose assessment in coastal sediments along the East Coast o..., Acta Ecologica Sinica, https://doi.org/10.1016/j.chnaes.2019.06.001
AEDE (mSvy-1) & AGDE (mSvy-1)
E. Devanesan et al. / Acta Ecologica Sinica xxx (2019) xxx
AEDE
0.6
5
AGDE
0.5 0.4 0.3 0.2 0.1 0
Location ID Fig. 3. Locations Vs Annual Effective Dose Rate AEDE (mSv y−1) and Annual gonadal dose equivalent AGDE (mSv y−1).
3.2.6. External hazard index (Hex) The external hazard index is obtained from Raeq expression through the supposition that its maximum value allowed (equal to unity) corresponds to the upper limit of Raeq (370 Bq·kg−1). The external hazard index (Hex) is measured by equation [25]. Hex ¼
AU ATh AK þ þ 370 Bq=Kg 259 Bq=Kg 4810 Bq=Kg
ð6Þ
The calculated value of the external hazard index for the studied samples is presented in Table 2. The Hex values ranged from 0.236 (PAP-2) to 0.500 (PKM-1) with an average value of 0.360. Also it was found that all the values of Hext is well below the criterion limit of ≤1 (NEA-OCED [16]). This indicated that there were no elevated radiological health hazards to the people living in nearby terrestrial areas of the
sampling sites. Table 4 lists the comparison of Radiological parameters of present work with other countries. 3.2.7. Internal hazard index (Hin) The external exposure is caused by direct gamma radiation whereas internal exposure is caused by the inhalation of radon (222Rn), thoron (220Rn) and their short-lived decay products [39]. The internal exposure to radon and its daughter products is quantified by the internal hazard index (Hin) which is given by the equation [40]. Hin ¼
AU ATh Ak þ þ 185 Bq=kg 259 Bq=kg 4810 Bq=kg
ð7Þ
The obtained values of Hin (Table 2) are less than unity indicating that the internal hazard is well below the recommended limit (NEAOCED [16]). The above results indicate that the internal hazard is
Table 4 Comparison of radiological parameters of present work with other countries. S. Name No
238 232 40 U Th K (Bq kg−1) (Bq kg−1) (Bq kg−1)
Raeq (Bqkg−1)
DR AEDE AGDE AUI (nGyh−1) (mSv y−1) (mSvy−1)
Hext
Hin
RLI (Iγr)
ELCR
Reference
1
29.6 ± 16.3 24.7
6 ± 6.1
–
–
–
–
–
–
–
–
–
Sam et al. [26]
31.4
158.4 ± 161.9 427.5
101.2
41.6
–
–
–
–
–
–
–
61
49
537
176
63
–
–
–
0.49
–
–
–
El-Mamoney et al. [27] Abdi et al. [28]
–
108.6
29.78
9
77.02
0.09
–
–
0.48
–
–
–
–
–
420 ± 90
–
–
–
–
330.70 ± 107 646.8159
30.69
0.04
–
–
1.04 ± 0.20 0.48
–
16.19 ± 8.68 48.755
0.39 ± 0.07 0.17
–
–
143.1 ± 27.7 63.81
–
–
78.0179
0.382725
–
–
0.447928 –
1.22
–
59.77 ± 3.43 62.96
0.07
–
–
–
–
0.95
–
0.08
–
–
0.37
–
–
–
86
41
0.051
0.299
–
0.2
0.3
0.3
0.17
189.6 ± 2.5 34 ± 5
53.5 ± 1.2 30 ± 3
767.96 ± 27.71 490.59 ± 81.04 478 ± 27.3 725 ± 21
122.89 ± 7.40 135.29
–
31.14 ± 5.58 48.57 ± 3.43 19 ± 2.5
331.4
181.51
0.24
1.186
0.25
0.93
1.41
2.47
0.83
320 ± 10
83
39
0.047
0.273
–
0.2
–
–
–
8.64 ± 2.49 36.82
13.77 ± 4.61 50.11
141.64 ± 43.01 320.38
39.24
18.88
0.02
–
–
0.11
0.13
0.30
–
133.14
60.73
0.0746
0.422
0.972 0.360
2 3 4 5 6 7 8 9 10 11 12 13 14
Sudanese Red Coast,sudan Egyptian coast of red sea, Egypt Southern Coast Of The Caspian Sea, Iran Coast of Greater Accra, Ghana East Coast Peninsular, Malaysia Red sea,Egypt Aden Coast on Gulf of Aden, South of Yemen Charfassion Island, Bhola, Bangladesh Inani Beach, Cox's Bazar, Bangladesh Safaga Coast of Red Sea, Egypt Coast of Ndokwa East, Delta State, Nigeria Tema Harbour Greater Accra, Ghana Suez Canal region in Egypt Present Study Area, Poombuhar to Karaikal, East Coast of Tamilnadu
46.32817 19.34 ± 4.37 –
0.21
0.459 0.960
Amekudzie et al. [29] Wo et al. [30] Mahmoud et al. [31] Harb et al. [32] Nizam et al. [33] Ahmed et al. [34] Uosif et al. [35] Ononugbo et al. [36] Benjamin et al. [37] Fares [38]
0.261 Present work
- Not Available.
Please cite this article as: E. Devanesan, J. Chandramohan, G. Senthilkumar, et al., Natural radioactivity concentrations and dose assessment in coastal sediments along the East Coast o..., Acta Ecologica Sinica, https://doi.org/10.1016/j.chnaes.2019.06.001
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E. Devanesan et al. / Acta Ecologica Sinica xxx (2019) xxx
AUI, Hex, Hin and RLI
AUI
Hex
Hin
RLI
1.4 1.2 1 0.8 0.6 0.4 0.2 0
Location ID Fig. 4. Locations Vs AUI, Hex, Hin and RLI.
below the critical value and has no significant radiation hazards associated with the sediments.
based on the radiation hazard index Iγr [41]. RLI ¼
3.2.8. Gamma representative level index (Iγ) The representative level index (Iγ) 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 [2]. The gamma radiation hazard level of the sediment samples associated with natural radionuclides were calculated using the formula,
ð8Þ
The calculated values of the representative level index vary from 0.648 (PAP-2) – 1.329 (PKM-1) with mean value of 0.960 (Table 2). The representative level index (Iγ) must be less than unity in order to keep the radiation hazard insignificant [6]. The mean (Iγ) value (0.960) in the study area is below than the recommended value b1 indicated that the sediments do not pose any hazardous (NEA-OCED [16]). Fig. 4 shows the locations Vs AUI, Hex, Hin and RLI. 3.2.9. Excess lifetime cancer risk (ELCR) The probability of cancer risk to any population from exposure to radiation is a measure of the Excess lifetime cancer risk (ELCR). The Excess lifetime cancer risk (ELCR) is calculated using below Eq. [42].
Table 5 Recommended safety limit for radiological parameters. Radionuclides
Recommended values
238
35 Bq kg−1 30 Bq kg−1 400 Bq kg−1 370 Bqkg−1 84nGyh−1 0.46 mSv y−1 0.3 mSv y−1 b2 ≤1 ≤1 b1 0.29 × 10−3
U 232 Th 40 K Radium equivalent Absorbed gamma dose rate (DR) Annual Effective Dose Equivalent (AEDE) Annual gonadal dose equivalent (AGDE) Activity Utilization Index (AUI) External hazard index (Hex) Internal hazard index (Hin) Gamma Representative Level Index (Iγr) Excess lifetime cancer risk (ELCR)
1 1 1 þ þ 150 AU 100 ATh 1500 AK
ELCR ¼ AEDE DL RF
ð9Þ
Where AEDE, DL and RF are the total annual effective dose equivalent, duration of life (70 yrs) and risk factor (Sv−1), i.e. fatal cancer risk per sievert, respectively. For stochastic effects, [43] uses values of 0.05 for the public [42]. From Table 2 the calculated ELCR values ranged from 0.178 × 10−3 (PAP-2) to 0.357 × 10−3 (PKM-1) with an average of 0.261 × 10−3, which is slightly higher than the worldwide recommended value of 0.29 × 10−3 [19]. Table 5 shows the recommended safety limit for radiological parameters. Fig. 5 shows the locations Vs Excess Life time cancer risk (ELCR).
ELCR x 10-3
ELCR 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0
Location ID Fig. 5. Locations Vs Excess Life time cancer risk (ELCR × 10−3).
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E. Devanesan et al. / Acta Ecologica Sinica xxx (2019) xxx
4. Multivariate statistical treatment The multivariate statistical method can also help to simplify and organize large data sets to indicate natural associations between samples and/or variables. Multivariate statistical methods are used to analyze the joint behavior of more than one random variable. The multivariate statistical method can be done using the SPSS.16.0 software. 1. Fundamental statistics 2. 3. 4. 5.
Histograms Pearson correlation Analysis Principal Components and Analysis Cluster Analysis
7
graph has no bell shaped form and its positive values indicate the positive skewness [45]. 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 [45,46]). The kurtosis value of activity concentrations of 238U and 232Th is positive indicates that the curve is more peaked than the normal curve (i.e.,) leptokurtic where as negative value of 40K shows that less peaked than the normal curve (i.e.,) platy kurtic.
4.1. Fundamental statistical of natural radionuclides
4.2. Histograms
Table 6 shows the basics statistics such as minimum, maximum, mean, standard deviation, variance, skewness and kurtosis of natural radionuclides from Poombuhar to Karaikal. In the present study, standard deviation of 238U, 232Th and 40K smaller than their mean value. This shows that concentration of uranium and thorium in sediment samples are high degree of uniformity [44]. Skewness data of natural radionuclide describes the degree of asymmetry of a distribution around its mean. Skewness refers to the 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. In the present study, the skewness of activity concentrations of 238U and 232Th radionuclides are positive, which shows that their distributions are asymmetric. The plotted
The frequency distribution of 238U, 232Th and 40K shown in Figs. 6–8. A plot showing the observed distribution of data points. The data range
Table 6 Basic statistical summary of coastal sediment samples, Tamilnadu, India. Variables
238
Mean Std. Deviation Variance Skewness Kurtosis Range Minimum Maximum Frequency distribution
36.81 7.23 52.27 0.518 1.265 31.39 24.35 55.74 Normal
U
232
Th
50.10 15.74 247.92 0.202 0.093 64.28 22.11 86.39 Log - Normal
Fig. 6. Frequency distribution of 238U.
40
K
320.38 46.75 2186 −0.326 −0.678 171.65 223.78 395.43 Normal
Fig. 7. Frequency distribution of 232Th.
Fig. 8. Frequency distribution of 40K.
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Table 7 Pearson correlation coefficients among the radionuclides and radiological parameters of the coastal sediment Samples, Tamilnadu, India.
U Th K Raequ DR AEDE AGDE AUI Hext Hint RLI ELCR
U
Th
K
DR
Raequ
AEDE
AGDE
AUI
Hext
Hint
RLI
ELCR
1 −0.224 −0.269 0.056 0.077 0.072 0.056 0.124 0.054 0.357 0.029 0.072
1 0.039 0.945 0.935 0.936 0.938 0.939 0.949 0.819 0.949 0.936
1 0.116 0.165 0.152 0.169 −0.035 0.114 0.025 0.157 0.152
1 0.999 1.000 1.000 0.982 0.999 0.956 0.999 1.000
1 0.999 0.998 0.988 1.000 0.952 0.999 0.999
1 1.000 0.982 0.999 0.956 0.999 1.000
1 0.979 0.998 0.951 0.999 1.000
1 0.988 0.962 0.981 0.982
1 0.952 0.999 0.999
1 0.943 0.956
1 0.999
1
is divided into a number of bins (i.e. intervals) and the number of data points that fall into each bin is summed up. The height of the bar in the histograms shows how many data points fall within the data range of the bin. The height of a rectangle is also equal to the frequency density of the interval. The plotted graph has no bell shaped form and its positive values indicate the positive skewness. The graph of 40K shows that these radionuclides demonstrate a normal (bell-shape) distribution. But 238U and 232Th exhibited some degree of multi-modality. This
Table 8 Factor ladings of radiological parameters. Variables
U Th K Raequ DR AEDE AGDE AUI Hext Hint RLI ELCR % of Variance Explained
Component 1
2
−0.014 0.975 0.052 0.993 0.987 0.988 0.987 0.989 0.994 0.926 0.992 0.988 80.43%
−0.273 −0.01 0.999 0.052 0.103 0.101 0.118 −0.087 0.062 −0.025 0.105 0.101 9.53%
multi-modal feature of the radio elements demonstrates the complexity of minerals in sediment samples. 4.3. Pearson correlations among radionuclides and radiological parameters The Pearson correlation coefficient is a measure of the strength of a linear association between two variables and is denoted by r. All the radiological parameters with 238U, 232Th and 40K are subjected into Pearson correlation analysis and obtained correlation coefficients are presented in Table 7. The correlation of 232Th with all radiological parameters showed a fairly positive correlation coefficient but very low degree of correlation was seen between 238U and 40K with all radiological parameters. This indicated that radiological hazards were associated and controlled by concentration of thorium 232Th and Potassium40K does not responsible for radiological hazards. Finally Pearson's correlation coefficient analysis suggested that natural radioactivity along the coastal area is may be due to the concentration of thorium only. 4.4. Factor Analysis (FA) among radionuclides and radiological parameters The principal component analysis is actually performed on the correlation matrix between different parameters followed by varimax rotation. Obtained principal components such as component 1 and 2 are given in Table 8 and shown in Fig. 9.
Fig. 9. Graphical representation of component 1 and component 2.
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Fig. 10. Shows the clustering of radioactive variables.
The loaded component-I has high positive loading of 232Th associated with all radiological parameters. The percentage of variance explained is 80.43%. This indicated that the total level of natural radioactivity in the study area is due to concentration of thorium (232Th) only. Similarly the loaded component-II has weak positive cum negative loading with 238 U and 40K. The percentage of variance explained is 9.53%. The negative loading variance indicates uranium and pottasium not controls the level of radiation exposure rate. According to Ravisankar et al. [45]. if the total variance is N70%, the fitted principal components to the data was good. In the present study the total explained variance is 89.96% to the radioactive data showed good. 4.5. Cluster analysis (CA) among Radionulides and radiological parameters There are different clustering techniques, but the hierarchical clustering is the one most widely applied in Earth Science [47]. The derived dendrogram is shown in Fig. 10. In this dendrogram, all 12 parameters are grouped into two statistically significant clusters. Cluster I consists 232Th and all important radiological parameters with high similarity. This shows that the total level of radioactivity in sediment mainly depends on the corresponding 232Th concentrations. Cluster II consists of 40K only, suggesting that concentration of potassium in sediments not contributing to the radiation hazard in the sediment sampling locations. The result of the cluster analysis is in good agreement and well matched with Pearson correlation analysis and principal component analysis. 5. Conclusion In this study, the gamma radiation has been measured to determine natural radioactivity of 238U, 232Th and 40K in sediment samples from Poombuhar to Karaikal along the East coast of Tamilnadu. All measured radiological parameters are less than permissible limit except in samples panaiyur, Kanathursunami and Vadanemeli. This may be due to the presence of rich distribution of black sands in the sediments.The multivariate statistical analysis showed that variation of radioactivity along the east coast of Tamilnadu depends on concentration of thorium and uranium. The data generated in this study will provide baseline data of natural radioactivity in the area under study and will be useful for authority in charge of implementation of radiation protection standards in the region and on the general population of host communities. Acknowledgements One of the author (R. Ravisankar) wishes to express his high gratitude to Dr. B. Venkatraman, Director, Radiation Safety & Environmental Group, Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam,
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Natural radioactivity concentrations and dose assessment in coastal sediments along the East Coast of Tamilnadu, India with statistical approach E. Devanesan a,d, J. Chandramohan b, G. Senthilkumar c, N. Harikrishnan d, M. Suresh Gandhi e, Sanjay S. Kolekar f, R. Ravisankar d,⁎ a
Department of Physics, Dhivya Arts & Science College, Chetpet, Tamilnadu 606801, India Department of Physics, Aries Arts and Science College for women, Karunkuzhi, Vadalur, Tamilnadu 607 302, India c Department of Physics, University College of Engineering Arni, Thatchur, Tamilnadu 632326, India d Post Graduate and Research Department of Physics, Government Arts College, Tiruvannamalai, Tamilnadu 606603, India e Department of Geology, University of Madras, Guindy Campus, Chennai, Tamilnadu 600025, India f Department of Chemistry, Shivaji University, Kolhapur, Maharashtra 416004, India b
a r t i c l e
i n f o
Article history: Received 21 April 2019 Received in revised form 23 June 2019 Accepted 28 June 2019 Available online xxxx Keywords: Sediment Gamma ray spectrometry Radiological parameters Statistical analysis
a b s t r a c t The present study was conducted to determine the activity concentration of 238U, 232Th and 40K in coastal sediments samples from Poombuhar to Karaikal along East coast of Tamilnadu, India using gamma ray spectrometry. The average activity concentration for 238U, 232Th and 40K were obtained as 36.82 (Bq kg−1), 50.11(Bq kg−1) and 320.38 (Bq kg−1), respectively. These obtained results were used to calculate the radiological hazard parameters like radium equivalent activity (Raeq), absorbed gamma dose rate (DR), the annual effective dose equivalent (AEDE), Annual gonadal dose equivalent (AGDE), Activity utilization index (AUI), External hazard index (Hex), Internal hazard index (Hin), Gamma representative level index (RLI) and Excess lifetime cancer risk (ELCR). The computed radiological parameters values are compared with the internationally approved recommended values. The multivariate statistical method is used to simplify and organize large data sets to indicate natural associations between samples and variables. © 2019 Ecological Society of China. Published by Elsevier B.V. All rights reserved.
1. Introduction In universe, all living organisms including man are constantly exposed to varying degrees of ionizing radiation from naturally occurring radioactive materials (NORMs) in the environment and radionuclides generated by human activities which is called technologically enhanced naturally occurring radioactive materials (TENORM). The naturally occurring radioactive materials (NORMs) are found in various geological formations such as soil, rocks, water, sediments, air and in some building materials [1]. Many artificial sources of radiation have been introduced since the discovery of X-rays and radioactivity at the end of the nineteenth century, and particularly since the exploitation of the process of nuclear fission in the middle of the twentieth century. Also radionuclides enter the environment during nuclear weapon testing, nuclear accidents, medical and industrial radiation applications. These artificial sources now add a significant contribution to the total radiation exposure of the population.
The contribution of radiation from soil to human exposure can either be whole body due to external radiation originating directly from primordial radionuclides present in soil or internal due to inhalation [2]. The internal exposure to radiation affecting the respiratory track is due to radon and its decay products which emanate from soil, sediment and building materials [3]. Radionuclides may be transferred from soils to plants, animals and finally to man. The study of the distribution of radionuclide helps in the determination of the radiological health implication of exposure to gamma rays and inhalation of radon and its daughter products. In the present work an attempt has been made to assess the natural radioactivity and radiological hazard due to the exposure to gamma radiation from the coastal sediment samples collected from Poombuhar to Karaikal along the South East Coast of Tamilnadu, India. 2. Materials and methods 2.1. Sample collection
⁎ Corresponding author. E-mail address: [email protected] (R. Ravisankar).
Sediment samples were collected by a Peterson grab sampler along the Bay of Bengal coastline, from Poombuhar to Karaikal along the
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E. Devanesan et al. / Acta Ecologica Sinica xxx (2019) xxx
South East Coast of Tamilnadu, India during premonsoon condition. Fig. 1 shows the location map of the study area. The grab sampler collects sediment layer from the seabed along the 20 stations. Table 1 lists the geographical latitude and longitude for the sampling locations of the study area. Uniform quantity of sediment samples were collected from all the sampling stations. Each sample of about 2 kg was kept in a thick plastic bag.
3. Results and discussions 3.1. Activity concentrations
The samples were air dried at1050C to a constant weight. After homogenization, samples were sieved through 1 mm mesh-sized sieve to remove stone, pebbles and other macro-impurities. The homogenized sample was packed in a standard 250 ml airtight PVC plastic container. 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 to allow radioactive secular equilibrium to be attained between 238U (226Ra) and 232Th (228Ra) and their progenies [4].
Table 2 gives the results of natural radionuclide concentrations in the collected sediment samples of the study area. The range and average values (in brackets) of the activities for 238U, 232Th and 40K are 24.35–55.74 (36.82), 22.11–86.39 (50.11) and 223.78–395.43 (320.38) Bq kg−1, respectively. The mean values are slightly higher than the corresponding worldwide average values which are 35 and 30 Bq kg−1 for 238U, 232Th and lower value of 400 Bq kg−1 for 40K. Measured activities of the radionuclides differed widely, as activity levels in the marine environment depend on their physical, chemical and geochemical properties and the environment [5]. The high values of the 232 Th observed in the sediment samples collected from the locations of PPR, PVG, PCG, PKM-1 & PKK-1 may be due to the presence of heavy minerals such illmenite, zircon etc., as revealed from the geological studies. Table 3 lists the comparison of activity concentrations of present work with regional area of Tamilnadu.
2.3. Gamma spectrometric analysis
3.2. Evaluation of radiological hazard effects
All samples were subjected to gamma spectral analysis with a counting time of 10,000 s. A 3“ x 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 kg−1 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, 238 U 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 kg−1, respectively for a counting time of 10, 000 s.
Different known radiation health hazard indices analysis has been used in radiation studies to arrive at a better and safer conclusion on the health status of a radiated or irradiated person and environment in recent studies [11]. To assess the radiation hazards associated with the studied sediment samples, the following nine quantities have been defined.
2.2. Sample preparation
3.2.1. Radium equivalent activity (Raeq) The radium equivalent activity (Raeq) was computed in this work in order to assess the gamma radiation risk to human being. This activity
Fig. 1. Location Map of the Study Area.
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E. Devanesan et al. / Acta Ecologica Sinica xxx (2019) xxx
3
Table 1 The Geographical latitude and longitude for the sampling locations of the study area. S·No
Locations
Sample ID
Latitude (N)
Longitude (E)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Poombuhar ChinnaVaanagiri Vaanagiri Chinnangudi Pillaiperumalnallur Vellaikoil Tharangampadi Cheranjampadi Mandapaputhur Akkampettai-I Akkampettai-II Keelakasakudimedu-I Keelakasakudimedu-II Kilinjalmedu Karaikalmedu Ammantherumedu-I Ammantherumedu-II Karaikal-I Karaikal-II Karaikal-III
PPR PCV PVG PCG PPM PVK PTP PCP PMP PAP-1 PAP-2 PKM-1 PKM-2 PKJ PKL PAT-1 PAT-2 PKK-1 PKK-2 PKK-3
11° 9′ 1.0836″ N 11° 7′ 5.5776″ N 11° 7′ 10.7652″ N 11° 5′ 32.1504″ N 11° 4′ 21.8028″ N 11° 2′ 3.2496″ N 11° 1′ 37.182″ N 10° 59′ 59.658″ N 10° 59′ 8.2464″ N 10° 56′ 56.3784″ N 10° 56′ 56.0724″ N 10° 56′ 26.5684″ N 10° 56′ 10.5681″ N 10° 56′ 23.6148″ N 10° 56′ 24.2196″ N 10° 55′ 54.2192″ N 10° 55′ 43.2188″ N 10° 55′ 31.584″ N 10° 55′ 30.432″ N 10° 55′ 30.1296″ N
79° 50′ 37.248″ E 79° 50′ 49.2828″ E 79° 50′ 47.328″ E 79° 50′ 32.5212″ E 79° 49′ 59.1492″ E 79° 51′ 15.5484″ E 79° 50′ 13.6752″ E 79° 51′ 0.7164″ E 79° 51′ 4.4244″ E 79° 50′ 54.6144″ E 79° 51′ 17.172″ E 79° 51′ 10.7384″ E 79° 51′ 6.7382″ E 79° 50′ 50.9064″ E 79° 51′ 11.9196″ E 79° 51′ 07.9136″ E 79° 51′ 10.9192″ E 79° 50′ 16.8216″ E 79° 50′ 16.8396″ E 79° 50′ 18.8484″ E
index provides a useful guideline in regulating the safety standards on radiation protection for the general public residing in the area under investigation. It is the most widely used index to assess the radiation hazards and can be calculated using Equation [12–15].
and the outdoor occupancy of 0.2 as proposed by UNSCEAR [19]. The annual effective dose rate was calculated using the formula.
Raeq Bq Kg−1 ¼ AU þ 1:43ATh þ 0:077AK
AEDE mSvy−1 ¼ DR x 0:00123
ð1Þ
where AU, ATh and AK are the activity concentrations of 238U, 232Th & 40K (Bq kg−1), respectively. The radium equivalent activity (Raeq) in these sediment samples ranges from 87.70 Bq kg−1 (PAP-2) to 185.21 Bq kg−1 (PKM-1) with a mean value of 133.14 Bq kg−1 (Table 2) which is less than the recommended maximum value of 370 Bq kg−1(NEA-OCED [16]). It indicates that no radiological hazards associated with the sediments. Fig. 2 shows the locations Vs Activity concentration and Radium equivalent activity (Bq kg−1). 3.2.2. Absorbed gamma dose rate (DR) The absorbed dose rate is important in radiation risk analysis since it measures the amount of radiation deposited per unit time. The contribution of natural radionuclides to the absorbed dose rate in air (DR) depends on the activity concentration of 238U, 232Th, and 40K. The absorbed dose rate (DR) in air at average gonad height of one meter above the surface of ground due to the natural radionuclides 238U, 232Th and 40K was estimated using the formula given as ([17,18].)
DR nGyh
−1
¼ 0:462AU þ 0:604ATh þ 0:042AK
ð2Þ
where AU, ATh and AK are the activity concentrations of 238U, 232Th & 40K (Bq kg−1), respectively. The range of absorbed dose rate in air due to natural radionuclides in the studied area is 41.51 (PAP-2) – 82.93 (PKM-1) nGyh−1, respectively with the mean of 60.73 nGyh−1. From Table 2, it is clear that mean value of absorbed dose rate in the studied area is higher than the world average absorbed gamma dose rate of 84 nGyh−1 [19]. The high values noticed in some locations of the study area could be explained as due to the presence of heavy mineral in the study area which may be monazite containing 232Th in significant quantity. This may enhance the activity concentrations which reflect the higher value of the absorbed dose rate. 3.2.3. Annual effective dose equivalent (AEDE) The annual effective dose due to the natural radionuclides in the samples was estimated using the dose conversion coefficient that convert the absorbed dose rate in air to the effective dose (0.7 Sv Gy−1)
−1 AEDE ¼ DR nGyh x 8760 h x 0:2 x 0:7SvGy−1 x 10−6 ð3Þ
The annual effective dose equivalent (Table 2) ranged between 0.051 (PAP-2) and 0.102 (PKM-1) with a mean value of 0.0746 mSv y−1. Therefore, the obtained mean value from this study area (0.0746 mSv y−1) is well lower than the 0.46 mSv y−1 for normal background radiation area [20]. This indicates that the sediment samples satisfy the criteria for a radiation safety point of view. 3.2.4. Annual gonadal dose equivalent (AGDE) Annual gonadal dose equivalent (AGDE) measures of the genetic significance of the yearly dose equivalent received by the population's reproductive organs (gonads). The annual gonadal dose equivalent (AGDE) due to the activity concentration of 238U, 232Th and 40K was calculated using the following formula [21]. AGDE mSvy−1 ¼ 3:09AU þ 4:18ATh þ 0:314AK
ð4Þ
The AGDE values are presented in Table 2. The annual gonadal dose equivalent obtained ranged between 0.291 (PAP-2) and 0.577 (PKM-1) with a mean value of 0.422 mSv y−1. The average value of the AGDE 0.422 mSv y−1 is slightly higher than UNSCEAR value 0.3 mSvy−1 reported as the world value [22]. Fig. 3 shows the locations Vs Annual Effective Dose Rate (AEDE) (mSvy−1) and Annual gonadal dose equivalent (AGDE) (mSv y−1). 3.2.5. Activity utilization index (AUI) The calculation of dose rates in air from different combinations of the three radionuclides in sediments by applying the appropriate conversion factors, an activity utilization index (AUI) is calculated for the usage of construction materials that is given by the following formula [23]. AUI ¼
AU 50 Bq=kg
fU þ
ATh Ak f Th þ fK 50 Bq=kg 500 Bq=kg
ð5Þ
where AU, ATh and AK are activity concentrations (in Bq kg−1) of 238U, 232 Th and 40K and fU, fTh, and fK are the fractional contributions to the
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Table 2 Activity Concentration, Radium Equivalent activity(Raeq), Gamma dose rate(DR), AEDE, AGDE, AUI, External hazard index(Hex), Internal hazard index(Hin), RLI and Excess life time cancer risk(ELCR) in coastal sediment samples of Tamilnadu, India. Locations Name
Sample ID
238
Poombuhar ChinnaVaanagiri Vaanagiri Chinnangudi Pillaiperumalnallur Vellaikoil TharangamPadi Cheranjampadi Mandapaputhur Akkampettai-I Akkampettai-II Keelakasakudimedu-I Keelakasakudimedu-II Kilinjalmedu Karaikalmedu Ammantherumedu-I Ammantherumedu-II Karaikal-I Karaikal-II Karaikal-III MEAN MIN MAX
PPR PCV PVG PCG PPM PVK PTP PCP PMP PAP-1 PAP-2 PKM-1 PKM-2 PKJ PKL PAT-1 PAT-2 PKK-1 PKK-2 PKK-3
40
(Bqkg−1)
Absorbed Gamma Dose Rate (DR) (nGyh−1)
307.19 304.53 294.54 395.43 272.69 283.22 223.78 388.96 352.61 333.01 350.69 352.16 361.96 280.52 265.26 346.17 329.63 363.59 254.7 347.03 320.38 223.78 395.43
145.52 121.99 142.66 156.71 111.29 120.51 132.07 123.54 144.96 110.06 87.70 185.21 125.80 120.63 148.62 104.42 138.62 161.75 142.59 138.13 133.14 87.70 185.21
65.33844 55.4667 64.39044 71.31002 51.00318 55.79128 59.4711 57.27322 66.14256 50.87672 41.51838 82.937 58.1778 55.26944 67.06772 48.93586 62.77136 73.37966 64.33122 63.15274 60.73 41.51 82.93
Activity Concentration (Bqkg−1) U
24.35 26.6 33.92 34.64 35.6 55.74 39.51 35.49 39.65 31.15 29.08 34.56 40.7 41.9 44.9 39.14 27.67 40.72 42.63 38.34 36.82 24.35 55.74
232
Th
68.19 50.31 60.18 64.07 38.25 30.04 52.68 40.63 54.66 37.25 22.11 86.39 40.02 39.95 58.25 27.01 59.84 65.06 56.19 51.1 50.11 22.11 86.39
K
Ra(equ)
AEDE (mSv y−1)
AGDE (mSvy−1)
AUI
Hex
Hin
RLI
ELCR X 10−3
0.080366 0.068224 0.0792 0.087711 0.062734 0.068623 0.073149 0.070446 0.081355 0.062578 0.051068 0.102013 0.071559 0.067981 0.082493 0.060191 0.077209 0.090257 0.079127 0.077678 0.0746 0.051 0.102
0.455505 0.386894 0.447673 0.497434 0.354423 0.385602 0.41166 0.400075 0.460306 0.355192 0.290991 0.57707 0.405254 0.383423 0.464457 0.341157 0.437817 0.510489 0.445558 0.439648 0.422 0.291 0.577
1.0743 0.8789 1.0650 1.1270 0.8137 0.9015 1.0201 0.8512 1.0561 0.7656 0.5650 1.3923 0.8897 0.8931 1.1407 0.7168 1.0060 1.1925 1.0939 1.0005 0.972 0.565 1.392
0.3940 0.3302 0.3862 0.4242 0.3012 0.3260 0.3575 0.3343 0.3923 0.2978 0.2372 0.5015 0.3404 0.3264 0.4023 0.2824 0.3753 0.4378 0.3860 0.3738 0.360 0.236 0.500
0.4588 0.4013 0.4769 0.5168 0.3968 0.4762 0.4635 0.4296 0.4987 0.3814 0.3155 0.5936 0.4498 0.4391 0.5228 0.3878 0.4491 0.5469 0.5003 0.4767 0.360 0.236 0.500
1.0490 0.8835 1.0243 1.1353 0.8016 0.8608 0.9394 0.9022 1.0460 0.8022 0.6488 1.3291 0.9128 0.8658 1.0587 0.7618 1.0026 1.1645 1.0159 0.9980 0.960 0.648 1.329
0.281282 0.238784 0.277201 0.30699 0.219569 0.240181 0.256023 0.246561 0.284744 0.219024 0.178737 0.357044 0.250455 0.237935 0.288727 0.210669 0.270231 0.315899 0.276946 0.271873 0.261 0.178 0.357
Table 3 Comparison of Activity concentrations of present work with Regional level. S. No
Activity concentrations (Bq kg−1)
Locations
238
North East Coast of Tamilnadu, India Pattipulam to Devanampattinam, Tamilnadu, India Pulicatlake to Vadanemmeli, Tamilnadu, India Thazhankuda to Kodiyakkarai Tamilnadu, India Periyakalapet to Parangipettai, Tamilnadu, India Poombuhar to Karaikal, Tamilnadu, India
Activity Concentration and Radium Equivalent Activity (Bqkg−1)
1 2 3 4 5 6
400
232
U
8.39 ± 4.87 2.21 10.14 3.30 – 36.815
U
Th
Th
24.52 ± 4.73 14.29 35.02 40.45 85.67 50.109
K
References 40
K
274.87 ± 25.58 360.23 425.8 389.28 425.72 320.384
Ramasamy et al. [6] Chandramohan et al. [7] Tholkappian et al. [8] Sivakumar et al. [9] Harikrishnan et al. [10] Present Work
Ra eq
350 300 250 200 150 100 50 0
Location ID Fig. 2.. Locatin Vs Activity concentration and Radium equivalent activity (Bq kg−1).
total dose rate in air due to gamma radiation from the actual concentrations of these radionuclides. In the NEA-OECD [16] Report, typical activities per unit mass of 238U, 232Th, and 40K in area AU, ATh and AK are referred to be 50, 50 and 500 Bq kg−1,respectively. The activity utilization index of the sediment samples are calculated using the above formula. The calculated values (Table 2) vary from 0.565 (PAP-2) to
1.392 (PKM-1) with an average of 0.972. This value shows that AUI b2 for all locations which corresponds to an annual effective dose b0.3 mSv y−1 [24]. This indicates that these sediments can be safely used for construction.
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AEDE (mSvy-1) & AGDE (mSvy-1)
E. Devanesan et al. / Acta Ecologica Sinica xxx (2019) xxx
AEDE
0.6
5
AGDE
0.5 0.4 0.3 0.2 0.1 0
Location ID Fig. 3. Locations Vs Annual Effective Dose Rate AEDE (mSv y−1) and Annual gonadal dose equivalent AGDE (mSv y−1).
3.2.6. External hazard index (Hex) The external hazard index is obtained from Raeq expression through the supposition that its maximum value allowed (equal to unity) corresponds to the upper limit of Raeq (370 Bq·kg−1). The external hazard index (Hex) is measured by equation [25]. Hex ¼
AU ATh AK þ þ 370 Bq=Kg 259 Bq=Kg 4810 Bq=Kg
ð6Þ
The calculated value of the external hazard index for the studied samples is presented in Table 2. The Hex values ranged from 0.236 (PAP-2) to 0.500 (PKM-1) with an average value of 0.360. Also it was found that all the values of Hext is well below the criterion limit of ≤1 (NEA-OCED [16]). This indicated that there were no elevated radiological health hazards to the people living in nearby terrestrial areas of the
sampling sites. Table 4 lists the comparison of Radiological parameters of present work with other countries. 3.2.7. Internal hazard index (Hin) The external exposure is caused by direct gamma radiation whereas internal exposure is caused by the inhalation of radon (222Rn), thoron (220Rn) and their short-lived decay products [39]. The internal exposure to radon and its daughter products is quantified by the internal hazard index (Hin) which is given by the equation [40]. Hin ¼
AU ATh Ak þ þ 185 Bq=kg 259 Bq=kg 4810 Bq=kg
ð7Þ
The obtained values of Hin (Table 2) are less than unity indicating that the internal hazard is well below the recommended limit (NEAOCED [16]). The above results indicate that the internal hazard is
Table 4 Comparison of radiological parameters of present work with other countries. S. Name No
238 232 40 U Th K (Bq kg−1) (Bq kg−1) (Bq kg−1)
Raeq (Bqkg−1)
DR AEDE AGDE AUI (nGyh−1) (mSv y−1) (mSvy−1)
Hext
Hin
RLI (Iγr)
ELCR
Reference
1
29.6 ± 16.3 24.7
6 ± 6.1
–
–
–
–
–
–
–
–
–
Sam et al. [26]
31.4
158.4 ± 161.9 427.5
101.2
41.6
–
–
–
–
–
–
–
61
49
537
176
63
–
–
–
0.49
–
–
–
El-Mamoney et al. [27] Abdi et al. [28]
–
108.6
29.78
9
77.02
0.09
–
–
0.48
–
–
–
–
–
420 ± 90
–
–
–
–
330.70 ± 107 646.8159
30.69
0.04
–
–
1.04 ± 0.20 0.48
–
16.19 ± 8.68 48.755
0.39 ± 0.07 0.17
–
–
143.1 ± 27.7 63.81
–
–
78.0179
0.382725
–
–
0.447928 –
1.22
–
59.77 ± 3.43 62.96
0.07
–
–
–
–
0.95
–
0.08
–
–
0.37
–
–
–
86
41
0.051
0.299
–
0.2
0.3
0.3
0.17
189.6 ± 2.5 34 ± 5
53.5 ± 1.2 30 ± 3
767.96 ± 27.71 490.59 ± 81.04 478 ± 27.3 725 ± 21
122.89 ± 7.40 135.29
–
31.14 ± 5.58 48.57 ± 3.43 19 ± 2.5
331.4
181.51
0.24
1.186
0.25
0.93
1.41
2.47
0.83
320 ± 10
83
39
0.047
0.273
–
0.2
–
–
–
8.64 ± 2.49 36.82
13.77 ± 4.61 50.11
141.64 ± 43.01 320.38
39.24
18.88
0.02
–
–
0.11
0.13
0.30
–
133.14
60.73
0.0746
0.422
0.972 0.360
2 3 4 5 6 7 8 9 10 11 12 13 14
Sudanese Red Coast,sudan Egyptian coast of red sea, Egypt Southern Coast Of The Caspian Sea, Iran Coast of Greater Accra, Ghana East Coast Peninsular, Malaysia Red sea,Egypt Aden Coast on Gulf of Aden, South of Yemen Charfassion Island, Bhola, Bangladesh Inani Beach, Cox's Bazar, Bangladesh Safaga Coast of Red Sea, Egypt Coast of Ndokwa East, Delta State, Nigeria Tema Harbour Greater Accra, Ghana Suez Canal region in Egypt Present Study Area, Poombuhar to Karaikal, East Coast of Tamilnadu
46.32817 19.34 ± 4.37 –
0.21
0.459 0.960
Amekudzie et al. [29] Wo et al. [30] Mahmoud et al. [31] Harb et al. [32] Nizam et al. [33] Ahmed et al. [34] Uosif et al. [35] Ononugbo et al. [36] Benjamin et al. [37] Fares [38]
0.261 Present work
- Not Available.
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E. Devanesan et al. / Acta Ecologica Sinica xxx (2019) xxx
AUI, Hex, Hin and RLI
AUI
Hex
Hin
RLI
1.4 1.2 1 0.8 0.6 0.4 0.2 0
Location ID Fig. 4. Locations Vs AUI, Hex, Hin and RLI.
below the critical value and has no significant radiation hazards associated with the sediments.
based on the radiation hazard index Iγr [41]. RLI ¼
3.2.8. Gamma representative level index (Iγ) The representative level index (Iγ) 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 [2]. The gamma radiation hazard level of the sediment samples associated with natural radionuclides were calculated using the formula,
ð8Þ
The calculated values of the representative level index vary from 0.648 (PAP-2) – 1.329 (PKM-1) with mean value of 0.960 (Table 2). The representative level index (Iγ) must be less than unity in order to keep the radiation hazard insignificant [6]. The mean (Iγ) value (0.960) in the study area is below than the recommended value b1 indicated that the sediments do not pose any hazardous (NEA-OCED [16]). Fig. 4 shows the locations Vs AUI, Hex, Hin and RLI. 3.2.9. Excess lifetime cancer risk (ELCR) The probability of cancer risk to any population from exposure to radiation is a measure of the Excess lifetime cancer risk (ELCR). The Excess lifetime cancer risk (ELCR) is calculated using below Eq. [42].
Table 5 Recommended safety limit for radiological parameters. Radionuclides
Recommended values
238
35 Bq kg−1 30 Bq kg−1 400 Bq kg−1 370 Bqkg−1 84nGyh−1 0.46 mSv y−1 0.3 mSv y−1 b2 ≤1 ≤1 b1 0.29 × 10−3
U 232 Th 40 K Radium equivalent Absorbed gamma dose rate (DR) Annual Effective Dose Equivalent (AEDE) Annual gonadal dose equivalent (AGDE) Activity Utilization Index (AUI) External hazard index (Hex) Internal hazard index (Hin) Gamma Representative Level Index (Iγr) Excess lifetime cancer risk (ELCR)
1 1 1 þ þ 150 AU 100 ATh 1500 AK
ELCR ¼ AEDE DL RF
ð9Þ
Where AEDE, DL and RF are the total annual effective dose equivalent, duration of life (70 yrs) and risk factor (Sv−1), i.e. fatal cancer risk per sievert, respectively. For stochastic effects, [43] uses values of 0.05 for the public [42]. From Table 2 the calculated ELCR values ranged from 0.178 × 10−3 (PAP-2) to 0.357 × 10−3 (PKM-1) with an average of 0.261 × 10−3, which is slightly higher than the worldwide recommended value of 0.29 × 10−3 [19]. Table 5 shows the recommended safety limit for radiological parameters. Fig. 5 shows the locations Vs Excess Life time cancer risk (ELCR).
ELCR x 10-3
ELCR 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0
Location ID Fig. 5. Locations Vs Excess Life time cancer risk (ELCR × 10−3).
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4. Multivariate statistical treatment The multivariate statistical method can also help to simplify and organize large data sets to indicate natural associations between samples and/or variables. Multivariate statistical methods are used to analyze the joint behavior of more than one random variable. The multivariate statistical method can be done using the SPSS.16.0 software. 1. Fundamental statistics 2. 3. 4. 5.
Histograms Pearson correlation Analysis Principal Components and Analysis Cluster Analysis
7
graph has no bell shaped form and its positive values indicate the positive skewness [45]. 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 [45,46]). The kurtosis value of activity concentrations of 238U and 232Th is positive indicates that the curve is more peaked than the normal curve (i.e.,) leptokurtic where as negative value of 40K shows that less peaked than the normal curve (i.e.,) platy kurtic.
4.1. Fundamental statistical of natural radionuclides
4.2. Histograms
Table 6 shows the basics statistics such as minimum, maximum, mean, standard deviation, variance, skewness and kurtosis of natural radionuclides from Poombuhar to Karaikal. In the present study, standard deviation of 238U, 232Th and 40K smaller than their mean value. This shows that concentration of uranium and thorium in sediment samples are high degree of uniformity [44]. Skewness data of natural radionuclide describes the degree of asymmetry of a distribution around its mean. Skewness refers to the 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. In the present study, the skewness of activity concentrations of 238U and 232Th radionuclides are positive, which shows that their distributions are asymmetric. The plotted
The frequency distribution of 238U, 232Th and 40K shown in Figs. 6–8. A plot showing the observed distribution of data points. The data range
Table 6 Basic statistical summary of coastal sediment samples, Tamilnadu, India. Variables
238
Mean Std. Deviation Variance Skewness Kurtosis Range Minimum Maximum Frequency distribution
36.81 7.23 52.27 0.518 1.265 31.39 24.35 55.74 Normal
U
232
Th
50.10 15.74 247.92 0.202 0.093 64.28 22.11 86.39 Log - Normal
Fig. 6. Frequency distribution of 238U.
40
K
320.38 46.75 2186 −0.326 −0.678 171.65 223.78 395.43 Normal
Fig. 7. Frequency distribution of 232Th.
Fig. 8. Frequency distribution of 40K.
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E. Devanesan et al. / Acta Ecologica Sinica xxx (2019) xxx
Table 7 Pearson correlation coefficients among the radionuclides and radiological parameters of the coastal sediment Samples, Tamilnadu, India.
U Th K Raequ DR AEDE AGDE AUI Hext Hint RLI ELCR
U
Th
K
DR
Raequ
AEDE
AGDE
AUI
Hext
Hint
RLI
ELCR
1 −0.224 −0.269 0.056 0.077 0.072 0.056 0.124 0.054 0.357 0.029 0.072
1 0.039 0.945 0.935 0.936 0.938 0.939 0.949 0.819 0.949 0.936
1 0.116 0.165 0.152 0.169 −0.035 0.114 0.025 0.157 0.152
1 0.999 1.000 1.000 0.982 0.999 0.956 0.999 1.000
1 0.999 0.998 0.988 1.000 0.952 0.999 0.999
1 1.000 0.982 0.999 0.956 0.999 1.000
1 0.979 0.998 0.951 0.999 1.000
1 0.988 0.962 0.981 0.982
1 0.952 0.999 0.999
1 0.943 0.956
1 0.999
1
is divided into a number of bins (i.e. intervals) and the number of data points that fall into each bin is summed up. The height of the bar in the histograms shows how many data points fall within the data range of the bin. The height of a rectangle is also equal to the frequency density of the interval. The plotted graph has no bell shaped form and its positive values indicate the positive skewness. The graph of 40K shows that these radionuclides demonstrate a normal (bell-shape) distribution. But 238U and 232Th exhibited some degree of multi-modality. This
Table 8 Factor ladings of radiological parameters. Variables
U Th K Raequ DR AEDE AGDE AUI Hext Hint RLI ELCR % of Variance Explained
Component 1
2
−0.014 0.975 0.052 0.993 0.987 0.988 0.987 0.989 0.994 0.926 0.992 0.988 80.43%
−0.273 −0.01 0.999 0.052 0.103 0.101 0.118 −0.087 0.062 −0.025 0.105 0.101 9.53%
multi-modal feature of the radio elements demonstrates the complexity of minerals in sediment samples. 4.3. Pearson correlations among radionuclides and radiological parameters The Pearson correlation coefficient is a measure of the strength of a linear association between two variables and is denoted by r. All the radiological parameters with 238U, 232Th and 40K are subjected into Pearson correlation analysis and obtained correlation coefficients are presented in Table 7. The correlation of 232Th with all radiological parameters showed a fairly positive correlation coefficient but very low degree of correlation was seen between 238U and 40K with all radiological parameters. This indicated that radiological hazards were associated and controlled by concentration of thorium 232Th and Potassium40K does not responsible for radiological hazards. Finally Pearson's correlation coefficient analysis suggested that natural radioactivity along the coastal area is may be due to the concentration of thorium only. 4.4. Factor Analysis (FA) among radionuclides and radiological parameters The principal component analysis is actually performed on the correlation matrix between different parameters followed by varimax rotation. Obtained principal components such as component 1 and 2 are given in Table 8 and shown in Fig. 9.
Fig. 9. Graphical representation of component 1 and component 2.
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E. Devanesan et al. / Acta Ecologica Sinica xxx (2019) xxx
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Fig. 10. Shows the clustering of radioactive variables.
The loaded component-I has high positive loading of 232Th associated with all radiological parameters. The percentage of variance explained is 80.43%. This indicated that the total level of natural radioactivity in the study area is due to concentration of thorium (232Th) only. Similarly the loaded component-II has weak positive cum negative loading with 238 U and 40K. The percentage of variance explained is 9.53%. The negative loading variance indicates uranium and pottasium not controls the level of radiation exposure rate. According to Ravisankar et al. [45]. if the total variance is N70%, the fitted principal components to the data was good. In the present study the total explained variance is 89.96% to the radioactive data showed good. 4.5. Cluster analysis (CA) among Radionulides and radiological parameters There are different clustering techniques, but the hierarchical clustering is the one most widely applied in Earth Science [47]. The derived dendrogram is shown in Fig. 10. In this dendrogram, all 12 parameters are grouped into two statistically significant clusters. Cluster I consists 232Th and all important radiological parameters with high similarity. This shows that the total level of radioactivity in sediment mainly depends on the corresponding 232Th concentrations. Cluster II consists of 40K only, suggesting that concentration of potassium in sediments not contributing to the radiation hazard in the sediment sampling locations. The result of the cluster analysis is in good agreement and well matched with Pearson correlation analysis and principal component analysis. 5. Conclusion In this study, the gamma radiation has been measured to determine natural radioactivity of 238U, 232Th and 40K in sediment samples from Poombuhar to Karaikal along the East coast of Tamilnadu. All measured radiological parameters are less than permissible limit except in samples panaiyur, Kanathursunami and Vadanemeli. This may be due to the presence of rich distribution of black sands in the sediments.The multivariate statistical analysis showed that variation of radioactivity along the east coast of Tamilnadu depends on concentration of thorium and uranium. The data generated in this study will provide baseline data of natural radioactivity in the area under study and will be useful for authority in charge of implementation of radiation protection standards in the region and on the general population of host communities. Acknowledgements One of the author (R. Ravisankar) wishes to express his high gratitude to Dr. B. Venkatraman, Director, Radiation Safety & Environmental Group, Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam,
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