This study reports on the spatial distributions of naturally occurring 238U, 232Th, 40K, 222Rn, and 220Rn from sediments across the coastal zone of the Bay of Bengal (BoB). The mean values of 238U, 232Th, and 40K activity are 23.42, 80.95, and 292.49 Bq kg−1, and the 220Rn surface mass exhalation rate value of 1,225.33 was calculated by 2.54 mBq kg−1h−1. The radionuclide concentration range in all the samples estimated in the coastal region was 220Rn > 40K > 232Th > 238U and the radiological risk parameters (Raeq, DR, AEDE, AGDE, Iɤr, AUI, Hex, Hin, and ELCR) were higher in the Kanyakumari region and lower in the Puducherry region of the BoB. The radionuclide levels of 232Th, 238U, and 220Rn displayed a strong step of positive association with all parameters of radiological hazards through constants of r > 0.75. This showed that radiation risks were correlated with, and regulated by, 238U and 232Th concentrations. Therefore, coastline sediments do not pose any serious hazard, and the statistics obtained from this analysis will serve as the reference data for the activity of natural radionuclides in sediments across the coastal zone of the BoB.

  • Naturally occurring radioactive material (NORM) concentration in the marine sediments was measured.

  • 220Rn > 40K > 232Th > 238U as novel proxies for quantifying the sediment source.

  • Investigation of radiological parameters around the coastal zone.

  • Radiological hazards were found to be less than the recommended value.

  • This research is the first detailed database for this area and will be the radiological baseline.

In general, primordial radionuclides that have been left over since the planet was formed are naturally occurring radioactive materials (UNSCEAR 1982), and they are found in several environmental compartments (Avwiri et al. 2012). Awareness of the applications and distributions of radionuclides is necessary due to their contribution to radioactivity pollution in the environment (Yii et al. 2009). Due to 222Rn and its falloff chain products, Naturally occurring radioactive material (NORM) may threaten the environment (UNSCEAR 1988).

Radiation is widespread in our surroundings due to naturally occurring sources such as radioactive substances from terrestrial origin found in rocks, soil, food, and water, as well as radionuclides from cosmic sources produced by the destruction of heavy nuclei with other particles in the environment (Orosun et al. 2021). Terrestrial radionuclides vary spatially and temporally, owing to the prevailing climatic conditions and local geology, which determine the kind of rock and soil. Coastlines are an important economic and biological zone on Earth, serving as a popular destination for recreation and agriculture. Shore sediments also provide home for crabs, bivalves, and various other rare aquatic creatures (Xinming & Wuhui 2018). The levels of 238U, 232Th, and 40K in sediments along the coastlines from around the world have been thoroughly recorded (Omeje et al. 2021; Pandion & Arunachalam 2022; Pandion et al. 2024).

The primordial radionuclide analysis makes it possible to consider the radiological effects of these due to its possibility of interference with living beings (Alam et al. 1999; Singh et al. 2005). In aquatic environments, sediments play an important role; therefore, observation of radiological studies can contribute to the improved conservation of aquatic resources (Matishov & Matishov 2004). The scattering of natural and anthropogenic radioactivity within the seafloor is correlated to grain size (Noureddine et al. 2003). Many authors have recorded natural measurements of radioactivity in marine sediments in various amounts across the globe (Mohanty et al. 2004; Akram et al. 2006; Alatise et al. 2008; Amekudzie et al. 2011; Tari et al. 2013) and also along the coastline of the Bay of Bengal (BoB) (Sivakumar et al. 2014; Ravisankar et al. 2015; Harikrishnan et al. 2018; Devanesan et al. 2020). And then, Sivakumar et al. (2014) provide a related measurement of the measurable radioactivity for the study zone that can be supportive in future epidemiological studies. The calculated NORM factor results are associated with the worldwide permitted suggested values (Devanesan et al. 2020).

Natural radiation exposes the world's population to radionuclides from other sources such as sediments and cosmic radiation, as well as internal radiation from radionuclides. Sediment has been identified as a medium that can provide valuable information about ecological and geochemical pollution by radionuclides (Zakaly et al. 2021). This study looked at the radioactive content of radionuclides in beach sediment, the minimal detectable activity (MDA), and the uncertainty. Radiological metrics such as the external hazard index, absorbed dose rate, radium equivalent activity, and annual effective dose were calculated to evaluate the population's likely radiological hazards and radiation risks (Shahrokhi et al. 2021).

The assessment of natural radionuclide activity due to gamma emissions from the marine zones should be investigated regularly. The activity of NORM 238U, 232Th, 40K, and 220Rn from the deposits of the BoB coastal zone, Southeast coast of India was recorded in this study, and is intended to deliver useful evidence for estimating human radiation exposure and observing the NORM in the region. The goal of this study is to assess NORM concentration and the radiological risk parameters associated with coastal deposits around the BoB coastal zone, India. Furthermore, statistical investigations (Pearson correlation and Cluster factor) conducted with the radioactivity concentration limits were found to explain the current relationships between them.

Study area

The BoB is a part of the Indian Ocean. It covers around 839,000 square miles (2,173,000 km2) and is bordered by Sri Lanka, India, Bangladesh, Myanmar, and the northern Malay Peninsula. It is approximately 1,000 miles (1,600 km) broad, with an average depth reaching 8,500 feet (2,600 m). Many major rivers flow into it, including the Godavari, Krishna, Cauvery, Ganges, and Brahmaputra. The only islands in the bay are the Andaman and Nicobar Islands, which separate it from the Andaman Sea to the southeast. It has traditionally been navigated by Indian and Malaysian traders, with Chinese maritime trade dating back to the 12th century. Vasco da Gama made the first European journey into a bay in 1498.

The topography of the BoB is primarily determined by the U-shaped basin, which opens to the Indian Ocean to the south. However, it is extremely simple in the bay's center. The bay's head from the Ganges Deltaic region is relatively flat and narrow, cut only by the submarine canyon. In fact, submerged valleys intersect with plain-type topographical features in many places. Figure 1 shows the study area map, and Supplementary Table S1 shows the sample location sites with coordinates in the study area. The back-barrier morphology includes stranded coast ridges, palaeo bays, palaeo-barriers, and palaeo-tidal flats among other geomorphic units. These characteristics were developed mostly as a result of the coast's recent and ongoing emergence, and they revealed that the internal shelf had a variety of sand and silt with modest quantities of clay, which was approximately 4%. Mixed river/dune/beach characteristics influence depositional ecosystems, and sediments are poorly segregated. Any human activity along the coast is likely to disrupt littoral processes. As a result, the current research focuses on determining the effects of man-made construction and its effect on radionuclide distribution.
Figure 1

Study area map.

Sediment provenance in the BoB is thought to be primarily a terrestrial detritus material, with relatively modest contributions from marine autogenously organic matter, wind dust, and volcanic material (Ye et al. 2022). Recent studies have demonstrated that materials from Indian rivers contribute more than 20% to the BoB (Sun et al. 2020); nevertheless, it is unclear how these materials have evolved over time. Yet only a few investigations have been undertaken on this subject. As a result, in this study, we comprehensively analyses the features of clay minerals in core BoB-79 deposits from the southern BoB, quantify the impact of materials from different river provenances, and reveal the response of particle provenance changes to sea level fluctuations and Indian monsoon.

Sampling methodology

Mud samples were collected around the coastal region of the BoB. To collect these samples, initial locations were chosen randomly, and later, sites were determined at regular intervals (Table 1). Mud samples were obtained by a Petersen grab sampler, which was used around the coastline along the 12 stations to ensure minimal disruption of the upper layer. An equal amount of mud sample was obtained from all locations. Every single sample weighing approximately 2.5 kg was held in a flexible pouch. Sediment samples were placed in a flexible pouch and stored for analysis. Then they removed the gravel, twigs, and other external particles. The samples collected were dehydrated at a temperature of 110 °C and weighed continuously.

Table 1

Activity concentrations of radionuclides with their uncertainties, radium equivalent activity, gamma dose rate, and annual effective dose rate in coastal sediments at the Bay of Bengal coastal zone

StationActivity concentration (Bq kg−1)
Raeq (Bq kg−1)Gamma dose rate (DR) (nGy h−1)Annual effective dose rate (mSv y−1)
40K238U232Th220Rn222Rn
Kanyakumari 415.18 ± 04 19.21 ± 08 121.71 ± 05 2,044 ± 39 BDL 181.14 99.82 0.542 
Puducherry 154.11 ± 03 10.11 ± 06 54.90 ± 08 1,547 ± 81 BDL 81.22 44.30 0.205 
Chennai 345.04 ± 04 22.35 ± 07 68.18 ± 04 1,635 ± 60 BDL 126.70 65.99 0.456 
Nellore 241.25 ± 03 18.25 ± 09 111.03 ± 02 1,415 ± 34 BDL 155.70 85.62 0.326 
Amalapuram 398.35 ± 07 35.84 ± 05 94.41 ± 02 1,322 ± 45 BDL 176.33 90.31 0.540 
Vishakhapatnam 387.65 ± 08 28.04 ± 08 85.75 ± 07 991 ± 61 BDL 155.69 81.02 0.517 
Gopalpur 314.84 ± 07 14.44 ± 05 59.52 ± 04 1,121 ± 33 BDL 104.41 55.84 0.409 
Puri 254.66 ± 09 12.41 ± 04 70.92 ± 04 743 ± 32 BDL 108.27 59.26 0.333 
Bhitarkanika 198.74 ± 11 31.01 ± 02 79.80 ± 05 1,146 ± 27 BDL 139.44 70.87 0.287 
Digha 264.24 ± 05 19.14 ± 03 38.05 ± 02 948 ± 19 BDL 85.76 42.92 0.351 
Kakdwip 211.65 ± 09 36.24 ± 04 98.45 ± 07 578 ± 07 BDL 166.57 85.09 0.311 
Sundarban 324.25 ± 08 34.04 ± 05 88.75 ± 04 1,214 ± 16 BDL 162.39 82.94 0.446 
StationActivity concentration (Bq kg−1)
Raeq (Bq kg−1)Gamma dose rate (DR) (nGy h−1)Annual effective dose rate (mSv y−1)
40K238U232Th220Rn222Rn
Kanyakumari 415.18 ± 04 19.21 ± 08 121.71 ± 05 2,044 ± 39 BDL 181.14 99.82 0.542 
Puducherry 154.11 ± 03 10.11 ± 06 54.90 ± 08 1,547 ± 81 BDL 81.22 44.30 0.205 
Chennai 345.04 ± 04 22.35 ± 07 68.18 ± 04 1,635 ± 60 BDL 126.70 65.99 0.456 
Nellore 241.25 ± 03 18.25 ± 09 111.03 ± 02 1,415 ± 34 BDL 155.70 85.62 0.326 
Amalapuram 398.35 ± 07 35.84 ± 05 94.41 ± 02 1,322 ± 45 BDL 176.33 90.31 0.540 
Vishakhapatnam 387.65 ± 08 28.04 ± 08 85.75 ± 07 991 ± 61 BDL 155.69 81.02 0.517 
Gopalpur 314.84 ± 07 14.44 ± 05 59.52 ± 04 1,121 ± 33 BDL 104.41 55.84 0.409 
Puri 254.66 ± 09 12.41 ± 04 70.92 ± 04 743 ± 32 BDL 108.27 59.26 0.333 
Bhitarkanika 198.74 ± 11 31.01 ± 02 79.80 ± 05 1,146 ± 27 BDL 139.44 70.87 0.287 
Digha 264.24 ± 05 19.14 ± 03 38.05 ± 02 948 ± 19 BDL 85.76 42.92 0.351 
Kakdwip 211.65 ± 09 36.24 ± 04 98.45 ± 07 578 ± 07 BDL 166.57 85.09 0.311 
Sundarban 324.25 ± 08 34.04 ± 05 88.75 ± 04 1,214 ± 16 BDL 162.39 82.94 0.446 

Radioactivity measurement

The samples were obtained from various water depths parallel to the shoreline of 5 km along the BoB. Radioactivity of the sediments measured by a high purity germanium detector (HPGe) and 222Rn and 220Rn were determined by the RAD7 radon detector. For radioactivity analysis, the dehydrated samples remained crushed into fine particles and were separated completely using a 200 mm sieve. A volume of 100 cm3 per sediment was moved to a cylindrical radon airtight PVC bottle with a diameter of 6.5 cm and an elevation of 7 cm. These bottles were securely closed around the screw neck with vinyl tape to avoid the potential escape of radon gases. To match radon and its short-term offspring products with 226Ra, the sediment samples were then kept sealed for a retro of 4 weeks to attain stability. Then, these samples were subjected to gamma spectroscopy investigation to calculate their activity using a HPGe Nuvia tech instrument, India. 222Rn and 220Rn analyses used the Durridge RAD7 Radon detector (RAD7) Insrukart Pvt Limit, India. The device is an advanced resolution sensor for the peak of 1,332 keV of 60Co. The resolution of the peak zone is carried out in APTEC NRC app. The concentration of 40K is estimated from 1,460.8 keV and Bi (609.3 keV).

Electronic radon detector measurements RAD7

The RAD7 detector was used to calibrate and accurately determine radon and thoron concentrations. Three sensitivities are built into the RAD7 firmware. The RAD7 detector is calibrated by exposing it to a known activity of 222Rn (or 220Rn) and measuring the total rates. The two radon sensitivities are determined by radon calibration. Thoron sensitivity is determined via a different calibration. Several modifications and calculations can be performed to the bare count rates in the three windows to calculate more precise radon and thoron concentrations. RAD7 does some of these corrections automatically, and the data have been recorded using DURRIDGE's CAPTURE program.

NORM hazard calculations

Radium equivalent concentration (Raeq)

NORM comparable operation is a catalog implemented to reflect a single quantity of the particular actions of 238U, 232Th, and 40K, taking into consideration an explanation of the radiological risk related to them, calculated using Equation (1) (Beretka & Matthew 1985):
(1)

The basic activity of 238U, 232Th, and 40K are AU, ATh, and AK. 370 Bq kg−1 of 238U, 259 Bq kg−1 of 232Th, and 4,810 Bq kg−1 of 40K are expected to generate the same NORM dose rate here because of radon and its daughters.

Estimation of radiation hazard effects

Absorbed gamma level (DR)

The numbers of conversion influences for converting uranium 238, potassium 40, and thorium 232 activity deliberations to dose levels (Bq kg−1) are 0.462, 0.042, and 0.604, correspondingly (2) (UNSCEAR 2000):
(2)
where DR, AU, AK, and ATh are the particular activities of absorbed gamma dose, uranium, potassium, and thorium (Bq kg−1).

Yearly effective dosage equivalent (AEDE)

The yearly effective dosage equivalent was compared with the absorbed dosage (DR) values using the formulae (3) & (4) (UNSCEAR, 2000):
(3)
(4)

Annual gonadal dosage equivalent (AGDE)

By taking the activities of NORM into consideration, the yearly gonadal dosage equivalent was determined using the method provided by (5) (Mamont-Ciesla et al. 1982):
(5)

Gamma illustrative level index (Iɤr)

The gamma illustrative radionuclide risk level of natural radionuclide connected sediment samples was measured using a method based on the (Iɤr) hazard radiation index (6) (NEA-OECD 1979; Alam et al. 1999):
(6)

Action utilization index (AUI)

An action utilization catalogue is built for the use of building materials using the following formula that is used to analyze the measurement of the dosage amounts in the air from various mixtures of the three NORM in sediment, and the necessary conversion factors are applied, following the study of (7) (Chandrasekaran et al. 2014):
(7)
where AU, ATh, and AK are Uranium 238, Potassium 40, and Thorium 232 concentrations (in Bq kg−1). fU, fTh, and fK are the slight influences on the overall exposure level in the air due to gamma radioactivity. Typical actions for each unit mass of NORM in the AU, ATh, and AK sediments are discussed as 50, 50, and 500 Bq kg−1, correspondingly, in the NEA-OECD (1979) study.

Radiation risk indices

Outer (Hex) and inner (Hin) hazard index

This index is used to determine a material's radiological suitability. The primary intend of this catalog is to restrict the radioactivity dosage to an equal limit of 1 mSv y−1 for the admissible dose (8) (ICRP 60; Al-Hamarneh & Awadallah 2009) and to be considered using the calculation:
(8)
To hold the radioactivity risk to be negligible, the result of Hex must be a smaller amount than unity. If Hex < 1, it means that the material-use practices are healthy and do not induce any higher level of radioactivity exposure. The internal hazard index (Hin) will measure this hazard by (9) (Beretka & Matthew 1985; Xinwei 2005):
(9)

Extra lifetime tumor hazard (ELCR)

The extra lifetime tumor hazard for a lifespan is estimated with the calculation:
(10)
Where the gross annual effective dosage equivalent is AEDE, DL and RF, lifespan (70 y) and hazard issue (Sv1), (Taskin et al. 2009) also discussed about the fatal hazard of tumor indicating 0.05 based on the ICRP guidelines. ICRP 60 utilizes the public result of 0.05 to indicate (Taskin et al. 2009).

220Rn surface mass exhalation rate

The successful quantity of the 220Rn surface breath level was carried out by closing the sediment samples in a 250 g airtight plastic container. This was followed by the equilibrium 220Rn calculation, the rate of variation of 220Rn activity focus, C (Bq m−3), given by (11) (Kanse et al. 2013) in the closed loop:
(11)
where JT is the level of 220Rn surface exhalation from the sediment in (Bq m−2s−1), V′ is the capacity in m3 found in the locked loop (i.e., the sum of the enduring volume of space, tube capacity, and detector capacity), λ is the falling-off constant of 220Rn (0.012464 s−1), and A is the chamber cross-section region. The 220Rn breath rate is given at equilibrium by the ensuing appearance in (12) (Sahoo et al. 2014):
(12)

The level of exhalation of thoron surface mass was calculated by Bq m−2h−1.

Statistical studies

The data from the analytical procedures were statistically handled with origin 2018 software. To determine the association between the sediment and the radionuclides in the environment, a multivariate analysis approach comprising the Pearson correlation matrix, principal component analysis (PCA), and cluster analysis was used.

NORM concentration in the coastal sediments

Table 1 gives the concentration of 238U, 232Th, 40K, 220Rn, and 222Rn, along with their average sediment sample values. The mean and standard deviation values are 292.49, (84.69), 23.42, (9.30), and 80.95, (24.08), respectively, for 238U, 232Th, and 40K. For 220Rn 1,225.33, (403.12), the exhalation rate (Bq m−2h−1) was calculated by the RAD7 radon detector. All the 222Rn activity concentrations were below the measurable limit. Activities of 238U are higher in Kakdwip (36.24 ± 04) and lesser in Puducherry (10.11 ± 06) in the current analysis. Figure 2 shows the natural radionuclides of 238U, 232Th, 40K, and 220Rn activity concentration at various sampling sites. The activity concentrations of 232Th are higher in Kanyakumari (121.71 ± 05) and lesser in Digha (38.05 ± 02), and those of 40K are higher in Kanyakumari (415.18 ± 04) and lesser in Puducherry (154.11 ± 03).
Figure 2

The natural radionuclides (238U, 232Th, 40K, and 220Rn) in the sediment samples.

Figure 2

The natural radionuclides (238U, 232Th, 40K, and 220Rn) in the sediment samples.

Close modal

Due to its smaller half-life (55 s), 220Rn was ignored, but recent studies have shown the important radiological significance of 220Rn because of its adverse health risk (Tokonami et al. 2008); to address this difficulty, it was agreed to conduct some additional measurements in the newly established straight radon and thoron progeny devices (Mishra et al. 2014). The activity concentrations of 220Rn are higher in Kanyakumari (2044 ± 39) and lesser in Kakdwip (578 ± 07) and those of 222Rn are below the detectable limit (BDL) throughout the station.

The calculated radionuclide activities varied widely, as the degree of activity in the coastal environment is subject to their physical, biological, geochemical, and environmental effects (Mora et al. 2004). There has been a difference in the concentration of radioactivity at various sites. This may be due to the environmental status and drainage design of the site of the study zone. According to Harb (2008), the persistent wave action may be due to the wide difference of radionuclides in the coastal sediments, as the waves reach up to around 10 m during high tide from the tideline, and result in new deposition of natural resources along the coastline.

The concentration range in all the samples was estimated as 220Rn > 40K > 232Th > 238U. Thoron (220Rn) is a naturally occurring radioactive gas that is continuously produced in rocks and sediment containing uranium and thorium primordial radionuclides. The mechanism by which radon and thoron escape and enter the atmosphere from the rock/soil matrix is called exhalation (Nazaroff & Nero 1988). Similar observations have been described (Inigo Valan et al. 2015). It is evident from the results of the mean activity present in the environment that 238U, 232Th, 40K, and 220Rn, as shown in Table 2, are lesser compared to the global average values.

Table 2

The comparison of activity concentration of the present work with other countries

S. No.Name of the countryActivity concentration (Bq kg−1)
References
238U232Th40K220Rn
Tamilnadu, India (Coastal sediment samples) 3.67 37.23 387.17 – Ravisankar et al. (2014)  
Heritage Gua Batu and Gua Mimpi of Maros Regency, South Sulawesi – – – 9.40 Dewang, et al. (2017)  
Greater Accra, Ghana (coastal sediment) – 37.23 108.60 29.78 Amekudzie et al. (2011)  
North east coast, Tamilnadu (Coastal sediment) 8 8.39 ± 4.87 24.52 ± 4.73 274.87 ± 25.58 – Ramasamy et al. (2009)  
Bangladesh (coastal sediment) – 45.85 594.34 – Ravisankar et al. (2015)  
Indian Stations in Antarctica – – – 5.17 ± 1.92 Prajith et al. (2019)  
Oman (marine sediment) 11.83–22.68 10.7–25.2 222.89–535.07 – Zare et al. (2012)  
Saudi coastline – Gulf of Aqaba (Coastal sediment) 11.4 22.5 641.1 – Al-Trabulsy et al. (2011)  
Albania 8–27 13–40 266–675 – Tsabaris et al. (2007)  
10 Spain 77–6,401 12–63 – – Lozano et al. (2002)  
11 Malaysia – 22 189 – Muhammad et al. (2012)  
12 Hungary (Sediment) 28.67 27.96 302.4  UNSCEAR (2000)  
13 Worldwide 35 30 400 – UNSCEAR (2000)  
14 Bay of Bengal coastal zone 22.94 168.85 299.14 2,243.33 Present work 
S. No.Name of the countryActivity concentration (Bq kg−1)
References
238U232Th40K220Rn
Tamilnadu, India (Coastal sediment samples) 3.67 37.23 387.17 – Ravisankar et al. (2014)  
Heritage Gua Batu and Gua Mimpi of Maros Regency, South Sulawesi – – – 9.40 Dewang, et al. (2017)  
Greater Accra, Ghana (coastal sediment) – 37.23 108.60 29.78 Amekudzie et al. (2011)  
North east coast, Tamilnadu (Coastal sediment) 8 8.39 ± 4.87 24.52 ± 4.73 274.87 ± 25.58 – Ramasamy et al. (2009)  
Bangladesh (coastal sediment) – 45.85 594.34 – Ravisankar et al. (2015)  
Indian Stations in Antarctica – – – 5.17 ± 1.92 Prajith et al. (2019)  
Oman (marine sediment) 11.83–22.68 10.7–25.2 222.89–535.07 – Zare et al. (2012)  
Saudi coastline – Gulf of Aqaba (Coastal sediment) 11.4 22.5 641.1 – Al-Trabulsy et al. (2011)  
Albania 8–27 13–40 266–675 – Tsabaris et al. (2007)  
10 Spain 77–6,401 12–63 – – Lozano et al. (2002)  
11 Malaysia – 22 189 – Muhammad et al. (2012)  
12 Hungary (Sediment) 28.67 27.96 302.4  UNSCEAR (2000)  
13 Worldwide 35 30 400 – UNSCEAR (2000)  
14 Bay of Bengal coastal zone 22.94 168.85 299.14 2,243.33 Present work 

The average concentration values do not deliver an exact indicator of the sediment-related radiation health risk. The radiological limits are assessed and the values obtained are related to the universally suggested protection limits to assess the radiation threat due to the NORM related to the sediments. Ravisankar et al. (2015) also reported that the radiation parameters in sediments at the East coast of Tamil Nadu, which are below the recommended values are safe and consistent with our study.

Radium equivalent activity (Raeq)

For the application in construction activities, marine sediments and other materials are typically used. A naturally occurring radionuclide is typically determined from the substances of 238U, 232Th, and 40K in these raw resources. The gamma radiation threats can, therefore, be measured using indices due to the radionuclides (NEA-OECD 1979). In these sediment samples, the radium comparable activity (Raeq) is higher in Kanyakumari (181.14) Bq kg−1 and lower in (81.22) (Bq kg−1) (Puducherry) with a mean result significance of 136.96 (Bq kg−1) (Table 1). This is lesser than the overall suggested results of 370 (Bq kg−1) (Beretka & Matthew 1985). The estimated Raeq in the samples tested was found to be lesser than the 370 (Bq kg−1) criterion limit (NEA-OECD 1979). It means that the sediments are not associated with any major radiological hazards. Supplementary Table S2 provides the suggested values for the measured radiological parameters. The mean importance of the radionuclide correspondent (Raeq) is lower compared to the suggested value (Supplementary Table S2).

Estimation of radiation threat belongings

Absorbed NORM dose level (DR)

The absorbed dosage level was outside the invisible gaseous substance surrounding the earth at an elevation of 1 m above the earth. DR provides a representation of outdoor radiation. The engrossed NORM dose frequency is the quantity of power absorbed period of matter from ionizing radiation, characterized in gray. The influence of natural radiation concentration on the absorbed dosage level in air (DR) is determined by the deliberation of uranium 238, potassium 40, and thorium 232 activity at a natural specific concentration. If a radiation concentration is known, the exposure amount level can be measured in the air at 1 m above the earth (Kurnaz et al. 2007). The outer invisible gaseous substance surrounding the earth's absorbed dose rate was determined from 238U, 232Th, and 40K sediment concentration values that attributed to 1 m above the earth surface, and other radium activity, such as cesium 137, strontium 90, and uranium 235 falling-off chain, can be ignored as they back slightly to the overall ecological amount.

In the studied region, the absorbed dosage level in the air due to NORM radiation activity is higher (99.82) (nGy h−1) in Kanyakumari and lower (42.92) (nGy h−1) in Digha, with an average of 71.99 (nGy h−1). It is clear from Table 1 that the mean rate of the absorbed dose level is somewhat upper than that of the ecosphere. The absorbed gamma dosage level was 84 nGy h−1 around the coastal zone (UNSCEAR 2000). Higher values may be due to the presence of black sand that improved with a significant amount of 232Th in mineral monazite, which can increase activity concentrations, indicating an advanced rate of the absorbed quantity level.

Yearly effective dose equal (AEDE)

The change constant from the absorbed dosage in the invisible gaseous substance surrounding the earth to the actual dose obtained by the grown person zero point 7 Sv Gy−1 and the out-of-doors tenancy factor (0.2) must be taken into account to measure the yearly effective dose rates. UNSCEAR (2000) suggests that 20 % of people are exposed to radiation in the outside environment. The AEDE of a location sample must be determined. The corresponding yearly effective dose acquired (Table 1) ranged from 0.20 (Puducherry) to 0.542 (Kanyakumari) with a mean rate of 0.39 mSv y−1. The mean AEDE rate for terrestrial NORM is 0.46 mSv y−1 in zones with natural upbringing radiation (UNSCEAR 1993). Consequently, the average rate of this research locations (0.38 mSv y−1) obtained is far below the ecosphere average significance. This shows that the dregs sediment follow the standards from a radioactivity protection perspective.

Yearly gonadal dosage equal (AGDE)

It is an indicator of the hereditary importance of the annual dosage which is comparable to the generative body part of the populace earns (reproductive organ). In the same way, UNSCEAR considers the function of bones and external cells as tissues of concern (1988). Table 3 displays the AGDE values measured in this analysis, ranging from 301.16 (Digha) to 698.47 (Kanyakumari) μSv y−1, with an average rate of 502.61 μSv y−1. In general, the average standards go beyond the suggested restrictions, suggesting that the harmful hazards of such radionuclides are insignificant.

Table 3

Radiological parameters in coastal sediments at the Bay of Bengal coastal zone

StationAGDEGamma representative level index (Iɤr)Activity utilization index (AUI)HexHinELCRThoron surface exhalation rate
Kanyakumari 698.47 1.621 3.64 0.608 0.660 1.897 2,043.987 
Puducherry 309.11 0.719 1.608 0.271 0.298 0.717 1,546.987 
Chennai 462.39 1.060 2.500 0.395 0.455 1.596 1,634.987 
Nellore 596.25 1.392 3.068 0.528 0.577 1.141 1,414.987 
Amalapuram 630.46 1.448 3.401 0.544 0.641 1.89 1,321.987 
Vishakhapatnam 566.80 1.302 3.051 0.487 0.563 1.809 990.987 
Gopalpur 392.27 0.901 2.108 0.334 0.373 1.431 1,120.987 
Puri 414.75 0.961 2.175 0.360 0.393 1.165 742.987 
Bhitarkanika 491.78 1.137 2.613 0.433 0.517 1.004 1,145.987 
Digha 301.16 0.684 1.672 0.253 0.305 1.228 947.987 
Kakdwip 589.96 1.367 3.117 0.522 0.620 1.088 577.987 
Sundarban 577.97 1.330 3.104 0.502 0.594 1.561 1,213.987 
StationAGDEGamma representative level index (Iɤr)Activity utilization index (AUI)HexHinELCRThoron surface exhalation rate
Kanyakumari 698.47 1.621 3.64 0.608 0.660 1.897 2,043.987 
Puducherry 309.11 0.719 1.608 0.271 0.298 0.717 1,546.987 
Chennai 462.39 1.060 2.500 0.395 0.455 1.596 1,634.987 
Nellore 596.25 1.392 3.068 0.528 0.577 1.141 1,414.987 
Amalapuram 630.46 1.448 3.401 0.544 0.641 1.89 1,321.987 
Vishakhapatnam 566.80 1.302 3.051 0.487 0.563 1.809 990.987 
Gopalpur 392.27 0.901 2.108 0.334 0.373 1.431 1,120.987 
Puri 414.75 0.961 2.175 0.360 0.393 1.165 742.987 
Bhitarkanika 491.78 1.137 2.613 0.433 0.517 1.004 1,145.987 
Digha 301.16 0.684 1.672 0.253 0.305 1.228 947.987 
Kakdwip 589.96 1.367 3.117 0.522 0.620 1.088 577.987 
Sundarban 577.97 1.330 3.104 0.502 0.594 1.561 1,213.987 

NORM representative level index (Iɤr)

For estimating the amount of NORM threat related to the natural emitters in the sediments, the characteristic equal catalogue (Iɤr) of the deposit can be used. Due to the excess outer gamma radioactivity induced by superficial resources, this index is used to associate the yearly exposure rate and serves as a showing method for recognizing resources that may convert health hazards after being used as building resources (Jibiri & Okeyode 2012). The representative equal index values measured range from 0.719 (Puducherry) to 1.621 (Kanyakumari) with a mean value of 1.16 (Table 3). To maintain the radiation threat minimal, the illustrative equal index (Iɤr) must be smaller than unity. In the study area, the mean (Iɤr) value (2.04) is greater than the suggested value, suggesting that the sediments pose no significant radiation threat.

Action utilization index (AUI)

The samples’ activity utilization index is determined by the formula above. The values were measured (Table 3) at the range from 1.608 (Puducherry) to 3.64 (Kanyakumari) with a mean of 2.67. All of the values mean that the AUI is <2.5 mSv y−1 for all sites except Kanyakumari, which parallels a yearly actual dosage of >0.3 mSv y−1 for all sites except Kanyakumari (El-Gamal et al. 2007). This means that these samples can be recovered safely for building resources.

Radionuclide risk indices

Outer hazard index (Hex)

To estimate the risk of NORM activity in the external threat index (Ibrahim 1999), Table 3 shows the estimated result of the exterior risk index for the investigated samples. The Hex values ranged from 0.271 (Puducherry) to 0.608 (Kanyakumari) with a mean rate of 0.43. In this area, these sediments do not damage employees and farmers. In addition, the mean significance of the findings exposed that there were no raised radiation health risks to the public's breathing in the sampling sites in the surrounding terrestrial areas, and it is healthy for the public who handle the coastal sediments for construction. At Kanyakumari, the higher Hex value could remain as the complex drive of finer samples from the coastline areas.

Internal threat index (Hin)

Inner coverage to 222Rn besides its components is measured by calculating the inner risk index, in addition to the outward hazard index (Hin). It is also harmful to the respiratory organs to inhale alpha elements released from the temporary NORM. It was estimated that Hin means the value was 0.49 (Table 3), which is a lesser amount than the acceptable limit. The aforementioned findings show that the inner risk has a lesser value and the marine sediments are not interrelated with the major radionuclide hazards. The public living in close areas along the coastal zone of the BoB are unlikely to bear a radiation health hazard.

Excess lifetime cancer hazard (ELCR)

Prospective cancer-causing special effects are categorized by assessing the risk of tumor occurrence from expected exposure consumptions and substance-specific dose-response data over a specific lifespan in a population. The additional threat of evolving tumors is due to exposure to a harmful material that occurs over an individual's lifetime (Ravisankar et al. 2014). The estimated ELCR values from Table 3 ranged from 0.717 (Puducherry) to 1.897 (Kanyakumari) with an average value of 1.37, which is significantly more complex than the suggested universal rate of 0.29103 (UNSCEAR 2000). The complex ELCR rate registered at Kanyakumari (1.897) may be attributable to the complex activity of NORM at this site. Table 4 provides an assessment of the radiological factors of the existing work with other countries.

Table 4

The comparison of radiological parameters of the present work with other countries

S. No.Name of the countryRa(eq) (Bq kg−1)DR (nGy h−1)AEDE (mSv y−1)AGDE (mSv y−1)RLI (Iɤr)HexHinReferences
Tamilnadu, India (Coastal sediment samples) 84.57 41.70 0.051 0.282 0.64 0.22 0.23 Ravisankar et al. (2014)  
Greater Accra, Ghana (Coastal sediment) 9.00 77.02 0.09 – 0.48 –  Amekudzie et al. (2011)  
North east coast Tamilnadu (Coastal sediment) – 30.15 0.15 – 0.48 0.17 – Ramasamy et al. (2009)  
Bangladesh (Coastal sediment) 121.27 55.15 0.14 – – 0.33 – Ravisankar et al. (2015)  
Oman (Marine sediment) 47.21–90.2 12.36–24.38 – – – 0.13–0.25 – Zare et al. (2012)  
Saudi coastline Gulf of Aqaba (Coastal sediment) 92.9 45.6 0.056 – – 0.13 0.28 Al-Trabulsy et al. (2011)  
Malaysia (Coastal sediment) 143.1 – – – 1.00 0.4 – Yii et al. (2011)  
Sudan Red Sea (Coastal sediment) 32.4 – – – 0.2 0.1 – Sam et al. (1998)  
Bay of Bengal coastal zone 288.67 125.15 0.15 870 2.04 0.77 0.83 Present work 
S. No.Name of the countryRa(eq) (Bq kg−1)DR (nGy h−1)AEDE (mSv y−1)AGDE (mSv y−1)RLI (Iɤr)HexHinReferences
Tamilnadu, India (Coastal sediment samples) 84.57 41.70 0.051 0.282 0.64 0.22 0.23 Ravisankar et al. (2014)  
Greater Accra, Ghana (Coastal sediment) 9.00 77.02 0.09 – 0.48 –  Amekudzie et al. (2011)  
North east coast Tamilnadu (Coastal sediment) – 30.15 0.15 – 0.48 0.17 – Ramasamy et al. (2009)  
Bangladesh (Coastal sediment) 121.27 55.15 0.14 – – 0.33 – Ravisankar et al. (2015)  
Oman (Marine sediment) 47.21–90.2 12.36–24.38 – – – 0.13–0.25 – Zare et al. (2012)  
Saudi coastline Gulf of Aqaba (Coastal sediment) 92.9 45.6 0.056 – – 0.13 0.28 Al-Trabulsy et al. (2011)  
Malaysia (Coastal sediment) 143.1 – – – 1.00 0.4 – Yii et al. (2011)  
Sudan Red Sea (Coastal sediment) 32.4 – – – 0.2 0.1 – Sam et al. (1998)  
Bay of Bengal coastal zone 288.67 125.15 0.15 870 2.04 0.77 0.83 Present work 

220Rn surface mass exhalation rates

The diffusion duration of 220Rn is just around 1 cm due to the low emitting radiation half-life of 220Rn (55.6 s). This implies that only the upper surface adds to the exhalation of 220Rn to the atmosphere, and thus, the breath rate is called the exhalation level of the surface. It can also be seen that the 220Rn mass breath rate can be altered by changing the geometry of the accumulator, but the surface breath rate (normalized concerning external area) was not modified (Kanse et al. 2013; Sahoo et al. 2014). The breath rate of thoron surface mass exhalation was from 577.987 (Kakdwip) to 2,043.987 (Kanyakumari) with a mean value of 1,225.320 (Bq m−2h−1). The thoron surface mass complaint radiological parameters are described in Table 3.

Descriptive statistics of NORM

Fundamental information such as maximum, minimum, average, distribution, standard deviation, difference of NORM, and radiological factors are shown in Supplementary Table S4. The measures of dispersion of a set of data standards are greater than the average rate. The standard deviations of 232Th are slightly higher than their mean value in the current study. The NORM and radiological parameter limits of 238U, 40K, 220Rn, Raeq, DR, AEDE, AGDE, Iɤr, AUI, Hex, Hin, and ELCR are less than the mean value of their distribution, suggesting a significant uniformity in the study.

Pearson correlations

By Pearson's correlation coefficient investigation, the linear association of NORM activity and the related radiological parameter limits are defined in Supplementary Table S5. The 238U with 232Th correlation exposed a reasonably extraordinary grade with an association constant of r > 0.75, indicating that their sediment gratified is primarily partial and regulated by the related sources of origin (Chandrasekaran et al. 2014). Among 40K, 238U, 232Th, and 220Rn, a low degree of correlation was seen, indicating that 40K has different sediment sources. The radionuclide levels of 232Th, 238U, and 220Rn displayed a strong step of positive association with all parameters of radiological hazards through constants of r > 0.75. This showed that radiation risks were correlated with and regulated by 238U and 232Th concentrations. A fragile association between potassium 40 and radiological risk parameters indicates that potassium concentration is not suggestively responsible for the radiological risk that was observed. In conclusion, Pearson's study of the association coefficient showed that the natural fallout in the shoreline region is due to 238U and 232Th concentrations.

Principal component analysis

The PCA for the present sediments was performed to ratify the suggestion of radiological limits with NORM found from the Pearson correlation study. The variables in use for this study are the same as the correlation investigation of Pearson on the association conditions between various parameters followed by varimax rotation, and the PCA is performed. In Supplementary Table S3, essential main components such as components 1 and 2 have been obtained and are shown in Figure 3. Due to the high positive lodging of 232Th, the main component 1 was extracted and entirely radiological parameter limits were correlated with an explained modification of 73.51%. This showed that the overall amount of natural fallout radionuclides was due to thorium accumulation in the study region. Similarly, component 2 with an explained variance of 14.93% is due to great positive loading of 40K, 220Rn, and 238U, but potassium concentration does not regulate the radioactivity levels. The key component of the data was fine, conferring towards (Ravisankar et al. 2014), if the entire modification was larger than 70%. The total explained variance of the radioactive data in the present study is 100.00%. The finding of the key component study is also in strong agreement with the analysis of the Pearson correlation.
Figure 3

The graphical representation of principal component analysis.

Figure 3

The graphical representation of principal component analysis.

Close modal

Cluster analysis (CA)

A cluster study was carried out using origin (2021) software in mandate to assess the effect of NORM and radiological parameters in sediments. The instruction in which limits or variables syndicate to form the clusters through comparable assets is visually displayed by a dendrogram. The most related objects are first grouped, and according to their similarities, these initial classes are combined. The similarity is the amount of the expanse of any two individual variables between clusters comparative to the greatest expanse. One hundred percent similarity means that, in their sample quantities, the clusters were 0 distance apart, while 0% similarity means that the cluster zones are as dissimilar as the minimum comparable zone (Chandrasekaran et al. 2014). In CA, the single connection form is used beside the distance coefficient of correlation. Rotated factor loadings of variables are mentioned in Supplementary Table S3. In Figure 4, a derived dendrogram is shown. A significant relationship between the NORM and radiological parameter limits can be evaluated from the dendrogram. In total, 11 parameters are gathered in this dendrogram and are classified into 2 statistically important clusters. Based on the existing similarities, all clusters are formed. Cluster I contains NORM (238U, 232Th, and 40K) and is in high similarity with all essential radiation factors. This specifies that the overall sediment NORM level is primarily influenced by the corresponding action of 238U, 232Th, and 40K. Cluster II contains just 220Rn showing that the focus of thoron in sediments in the sediment sampling locations does not contribute to the radiation threat. These findings are in strong agreement with the association between Pearson and principal constituent analyses.
Figure 4

The cluster of radioactive variables at different places. 1. Kanyakumari, 2. Puducherry, 3. Chennai, 4. Nellore, 5. Amalapuram, 6. Vishakhapatnam, 7. Gopalpur, 8. Puri, 9. Bhitarkanika. 10. Digha, 11. Kakdwip, and 12. Sundarban.

Figure 4

The cluster of radioactive variables at different places. 1. Kanyakumari, 2. Puducherry, 3. Chennai, 4. Nellore, 5. Amalapuram, 6. Vishakhapatnam, 7. Gopalpur, 8. Puri, 9. Bhitarkanika. 10. Digha, 11. Kakdwip, and 12. Sundarban.

Close modal

The sediment samples were evaluated for 238U, 232Th, and 40K activity using an HPGe detector, while 222Rn and 220Rn samples were analyzed using a RAD 7 detector in the sediments from the coast of the BoB region. The levels of natural radionuclides may vary depending on the size of the sediment particles at each sampling site. Radiological risk limits were computed based on the concentrations of 238U, 232Th, 40K, 222Rn, and 220Rn and were found to be safe when compared to international norms.

Using Pearson correlation coefficient analysis of 238U with 232Th revealed a reasonably exceptional grade through a positive relationship constant of r > 0.75, suggesting that their sediment is mainly partial and influenced by the associated sources of origin, and the PCA results are in strong agreement with the Pearson results. Cluster analysis demonstrates that all essential radiological characteristics are highly similar, suggesting that there is no radiation concern. Both Pearson and PCA support these conclusions. The results of radiation risk indices show that the region around the BoB coastline zone is ecologically safe for living things.

The current inquiry has revealed that additional research is required to better understand the source and dispersal of NORM in the region under investigation. The findings can be utilized as the reference data in monitoring and are strongly recommended for the sequential extraction and speciation studies of radionuclides to understand the binding fractions and mobility of radionuclides to the surrounding environment and quantification of the pollution history through geochronological studies to determine the age of the sediment at the time of deposition.

The authors are grateful to SRM Institute of Science and Technology, Kattankulathur-603203, for providing infrastructure and continuous support to carry out this work. The authors extend their appreciation to the Researchers Supporting Project number RSPD2024R686, King Saud University, Riyadh, Saudi Arabia.

K.P.: Conceptualization, Writing – original draft, Writing – review & editing. K.D.A. and B.R.: Investigation, Data creation, Writing – original draft, Writing – review & editing, Project administration. A.-R.Z.G. and B.M.A.: Writing– review & editing. S.K., R.P.S., and M.C.: Data creation. S.W.C.: Writing – review.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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