A study on the level of terrestrial gamma and gross alpha activity in Gulf of Mannar, South coast of India, Tamil Nadu

Raju Krishnamoorthy; O Basith; M Jamal Mohamed Jaffer

doi:10.4103/rpe.rpe_21_22

ORIGINAL ARTICLE

Year : 2022 | Volume : 45 | Issue : 3 | Page : 153-157

A study on the level of terrestrial gamma and gross alpha activity in Gulf of Mannar, South coast of India, Tamil Nadu

Raju Krishnamoorthy¹, O Basith¹, M Jamal Mohamed Jaffer²
¹ Department of Zoology, Environmental Research Laboratory, Jamal Mohamed College (Affiliated to Bharathidasan University), Tiruchirappalli, Tamil Nadu, India
² Department of Physics, Jamal Mohamed College, Tiruchirappalli, Tamil Nadu, India

Date of Submission	11-Aug-2022
Date of Decision	16-Nov-2022
Date of Acceptance	20-Feb-2023
Date of Web Publication	18-May-2023

Correspondence Address:
Raju Krishnamoorthy
Department of Zoology, Environmental Research Laboratory, Jamal Mohamed College (Affiliated to Bharathidasan University), Tiruchirappalli - 620 020, Tamil Nadu
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/rpe.rpe_21_22

Abstract

This study presents the results of outdoor ambient gamma and gross alpha activity of Gulf of Mannar, and these measurements were carried out using Scintillation Counter (UR-705). Results showed that the terrestrial Gamma radiation levels of the Gulf of Mannar ranged from 4.10 μR/h to 76.33 μR/h. The Gross alpha radioactivity levels of the Gulf of Mannar ranged between 3.67 Bq/kg and 51.34 Bq/kg. The calculated ambient gamma and gross alpha activity were found to be lower than the world average. Gamma absorbed dose rates in air outdoors were calculated to be in the range between 35.67 nGy/h and 664.07 nGy/h with an arithmetic mean of 98.98 ± 20.54 nGy/h. This value is lower than the population-weighted world-averaged of 60 nGy/h. Inhabitants of Northern Gulf of Mannar are subjected to external gamma Annual dose exposure ranging between 0.30 and 5.65 mGy/y with an arithmetic mean of 0.84 ± 0.17 mGy/y.

Keywords: Gross alpha, Gulf of Mannar, terrestrial gamma radiation

How to cite this article:
Krishnamoorthy R, Basith O, Mohamed Jaffer M J. A study on the level of terrestrial gamma and gross alpha activity in Gulf of Mannar, South coast of India, Tamil Nadu. Radiat Prot Environ 2022;45:153-7

How to cite this URL:
Krishnamoorthy R, Basith O, Mohamed Jaffer M J. A study on the level of terrestrial gamma and gross alpha activity in Gulf of Mannar, South coast of India, Tamil Nadu. Radiat Prot Environ [serial online] 2022 [cited 2023 Jun 2];45:153-7. Available from: https://www.rpe.org.in/text.asp?2022/45/3/153/377230

Introduction

Radioactivity is a part of our earth and has existed all along. Naturally occurring radioactive materials are present in its crust, the floors and walls of our homes, schools, or offices, and in the food, we eat and drink. There are radioactive gases in the air we breathe. Our own bodies-muscles, bones, and tissue-contain naturally occurring radioactive elements. Man has always been exposed to natural radiation arising from the earth as well as from outside the earth. The radiation we receive from outer space is called cosmic radiation or cosmic rays.^[1] We also receive exposure from man-made radiation, such as X-rays, radiation used to diagnose diseases and for cancer therapy. The fallout from nuclear explosives testing, and small quantities of radioactive materials released to the environment from coal and nuclear power plants, are also sources of radiation exposure to man. The radionuclides decay at a characteristic rate that remains constant regardless of external influences, such as temperature or pressure. The time that it takes for half the radionuclides to disintegrate or decay is called half-life. This differs for each radioelement, ranging from fractions of a second to billions of years. For example, the half-life of Iodine 131 is 8 days, but for Uranium 238, which is present in varying amounts all over the world, it is 4.5 billion years. Potassium 40, the main source of radioactivity in our bodies, has a half-life of 1.42 billion years.^[2]

On average, our radiation exposure due to all-natural sources amounts to about 2.4 mSv a year-though this figure can vary, depending on the geographical location by several times. In homes and buildings, there are radioactive elements in the air. These radioactive elements are radon (Radon 222), thoron (Radon 220) and by-products formed by the decay of radium (Radium 226) and thorium present in many sorts of rocks, other building materials, and in the soil. By far the largest source of natural radiation exposure comes from varying amounts of uranium and thorium in the soil around the world. The radiation exposure due to cosmic rays is very dependent on altitude, and slightly on latitude: People who travel by air, thereby, increase their exposure to radiation.^[3] The environment normally has some amount of natural radioactivity resulting from cosmic rays, and ionizing radiations from naturally occurring radioactive substances in soil, air, water, and biota. These radiations provide the “background radiation” to which all living beings are exposed. Studies on natural radioactivity in India are largely made on marine ecosystem.^{[4],[5],[6],[7],[8],[9],[10],[11]} The present study was designed with the following objectives to study the distribution and the effects of natural radioactivity in the Gulf of Mannar.

Materials and Methods

Study area

The Gulf of Mannar lies between the South East coast of the Indian Peninsula and the West coast of Sri Lanka. Its S boundary lies between Cape Comorin, the South extremity of India, and Point de Galle, the South West point of Sri Lanka. The gulf is bounded North by Adam's Bridge, a chain of islets and rocks extending from the East end of Pamban Island to Mannar island about 16 miles south East. The Gulf of Mannar Biosphere Reserve covers an area of 10,500 km² of ocean, islands, and the adjoining coastline. The islets and coastal buffer zone includes beaches, estuaries, and tropical dry broadleaf forests, while the marine environments include seaweed communities, sea grass communities, coral reefs, salt marshes, and mangrove forests.

The National Centre for Coastal Research, an institute under the Ministry of Earth Sciences, in India, has a field research station in the Gulf of Mannar region, have found an alarming pattern of bleaching in the reefs in Mandapam, Kilakarai and Palk Bay. Researchers observed a pattern of bleaching in corals when the temperatures rose to between 32°C and 36°C. The Gulf of Mannar is known to harbor over 3600 species of flora and fauna, making it one of the richest coastal regions in Asia. In 1986, a group of 21 islets lying off the Tamil Nadu coast between Thoothukudi and Dhanushkodi were declared the Gulf of Mannar Marine National Park. The park and its 10 km buffer zone were declared a Biosphere Reserve in 1989. In the present study, 20 sampling stations were fixed in the Gulf of Mannar region [Table 1] and [Figure 1] and sample collections were done during the months December–February 2020.

Table 1: Terrestrial Gamma, gross alpha radioactivity levels in the different sampling stations of Gulf of Mannar

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Figure 1: Map showing the sampling station in Gulf of Mannar

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Collection of samples

Sediment samples were collected directly from the 20 sampling stations of Gulf of Mannar coastal region. Samplings were done in the intertidal to subtidal zone at a depth of 0.5–1.0 m about 30–50 m off the shore. Approximately 1 kg of sand was collected using an improvised hand-held dredger. The sediment samples were collected by Polythene Cover (Zip lock cover) of two kg capacity and brought to the laboratory for analysis of radioactivity.

Preparation of samples

The collected sediment samples were contain the extraneous materials such as plant parts, pebbles, and benthic fauna were strained out and the sediment samples were dried in sunlight for a day and an oven at 100°C for 24 h to remove the water content and the weight was measured. The dried samples were crushed to fine powder and then the sediment samples were sieved through a 0.5 mm mesh screen. One gram of sediment samples was subjected to analysis of radioactivity.

Determination of ambient gamma radioactivity

Environmental radioactivity measurements are necessary for determining the background radiation level due to natural radioactive sources of terrestrial and cosmic origins.^[12] Radionuclide activity concentration in soil is one of the main determinants of the natural background radiation. The present study is focused to survey the ambient gamma radiation measured by a scintillometer (UR-705). It is a rugged, lightweight, and portable scintillometer designed for radiometric, geophysical, and environmental reconnaissance survey.

Determination gross alpha activity in samples

The gross alpha indicates the levels of radioactivity from all alpha-emitting radionuclides irrespective of individual contribution in the particular matrix. Measurements of gross alpha activity in various environmental matrices are considered important because these offers quick information on the radioactivity profile of any environment concerned. Such procedures are important preliminary steps in the radioactivity inventory of any ecosystem. The gross alpha activity in the biota and soil samples of the selected stations were measured after having been dried in an oven at 105°C to 110°C for 24 hrs. About 0.1–1.0 g (for alpha) of the powdered dry sample was uniformly spread over a clean background counted, Aluminium Planchette (3 cm diameter) using a micro sieve and the radioactivity was measured in alpha and beta counter.^[13],[14]

Derivation of the absorbed dose rates and effective dose rates

If natural radioactive nuclides are uniformly distributed in the ground, dose rates at 1 m above the ground surface are calculated by the following formula:^[15]

Dose rate (nGy/h) = Radiological concentration (Bq/kg) × Conversion factor (nGy/h/Bq/kg)

Nuclear instruments used

For the present investigation a Scintillation Counter manufactured by Nucleonix Systems (UR-705) and Alpha Counter System (Nucleonex-RC 605A, 33% Efficiency) were used for the estimation of Ambient Gamma and Gross Alpha activities of samples and this instrument is available in the Environmental Research Laboratory, P. G. and Research Department of Zoology, Jamal Mohamed College, Tiruchirappalli.

Results and Discussion

The terrestrial Gamma radiation levels of the Gulf of Mannar ranged from 4.10 μR/h (Vembar beach and Keelakarai) to 76.33 μR/h in Eruvadi. The result reveals the nonuniform distribution of Gamma radiation among the study area. During the survey period, an irregular distribution of radiation profile was observed. The terrestrial Gamma radiation levels of the Pulicat Lagoon ranged from 3.0 to 8.0 μR/h in lake region, 3.0–8.0 μR/h in mouth bar region and 5.0–16.0 μR/h in canal region.^[7] The activity of Gamma radiation in the Palk Strait sediments was ranged from 5 to 25 μR/h.^[6] The activity of Gamma radiation in the Puducherry costal sediments was ranged from 3.03 to 5.04 μR/h.^[16] The activity of Gamma radiation in Gulf of Mannar was ranged from 10 to 450 μR/h^[10] and the world range was 28–120 μR/h for normal background areas.^[17]

The average absorbed dose rates from outdoor terrestrial γ radiation at all the designated locations from Nandaprayag to Allahabad are referred. The values were found in the range of 81.33 ± 2.34 nSv/h to 144 ± 5.77 nSv/h with an average of 100.83 nSv/h. Terrestrial gamma radiation dose measurement and health hazard along river Alaknanda and Ganges in India.^[18] The geology of the local area plays an important role in the distribution of these radioactive elements. Environmental terrestrial gamma radiation dose rates were measured around the eastern coastal area of Odisha with the objective of establishing baseline data on the background radiation level. The values of the terrestrial gamma radiation dose rate vary significantly at different locations in the study area. The values of the terrestrial gamma dose rate ranged from 77 to 1651 nGy/h, with an average of 230 nGy/h.^[19]

The Gross alpha radioactivity levels of the Gulf of Mannar ranged from 5.50 Bq/kg (Mudukulathur) to 102.67 Bq/kg in Eruvadi. The result reveals the non uniform distribution of Gross alpha radioactivity among the study area. During the survey, an irregular distribution of radiation profile was observed. The gross alpha levels in the soil of Pulicat Lagoon were recorded in this study. The gross alpha activity in sediment were ranges from 1.38 to 10.08 mBq/g in lake region, 2.38–5.26 mBq/g in mouth bar region and 2.29–16.64 mBq/g in canal region.^[7] The gross alpha activity in the Puducherry costal sediments was ranged from 2.89 to 4.20 Bq/kg.^[16] The gross alpha activity in the Punnaikayal estuarine sediments was 73.2 Bq/kg.^[20] The gross alpha activity in the Palk Strait sediments mean value was ranged from 15.0 to 34.0 Bq/kg.^[4] The gross alpha activity in the Caddulore costal sediments was ranged from 10.1 to 14.80 Bq/kg.^[16] The Gross Alpha activity in Gulf of Mannar sediment samples was 86 mBq/g.^[10]

The Gross alpha and gross beta radioactivity in thirty environmental samples of soil, water, and vegetable were randomly collected from the different locations of Bheramara and Ishwardi, near the proposed Rooppur Nuclear Power Plant area, Kushtia and Pabna, Bangladesh. The Gross Alpha activity under investigation ranges from 1.13 to 5.66 Bq/kg with an average of 2.78 ± 0.16 Bq/kg for soil sample. This study will help to prepare baseline data for gross alpha radioactivity in the environmental sample which will be used as a fingerprint for the comparison of radioactivity level.^[21] Determination of the gross-alpha radioactivity of river soil and sediment samples was collected from Bendimahi River which originates near the Tendürek Mountain (Van, Turkey), its tributaries and Van Lake (Turkey). The gross-alpha activity concentrations in soil samples ranged from 0.800 to 4.277 Bq/g in May and 0.686–4.713 Bq/g in August, respectively. Concentrations ranging from 0.782 to 4.596 Bq/g in May and from 0.580 to 5.824 Bq/3 in August for gross-alpha radioactivity were observed in sediments, respectively.^[22]

Understanding natural radioactivity will enable us to check or limit the toxicity and hence risk to the individual and society of such exposed. The gross alpha radioactivity concentration in soil varies between 0.25 and 1.20 mBq/g.^[23] The concentrations of gross alpha radioactivity were analyzed in Holocene sediments of the Gulf of Izmir (Eastern Aegean Sea). The sediments were collected from four different locations affected by industrial activities, overpopulation, and shipping in the Gulf of İzmir. The obtained results show that natural gross alpha activity concentrations in the drilling cores range from 537 ± 77 to 1800 ± 207 Bq/kg. These results were compared with previous studies throughout the world, and the study could be a reference data for the future researches related to radiological mapping or environmental monitoring in the area.^[24] The present study indicates that the radiation dose received by to coastal population of Gulf of Mannar through seafood intake was less compared to those at Mumbai and Kalpaakam coast.

The absorbed dose rate of gamma radiation was calculated from ambient gamma levels in the selected station of Gulf of Mannar [Table 1]. The result showed that the sampling station 13 Eruvadi recorded the highest absorption rate 664.07 nGy/h. Whereas station 6 (Vember Beach) and 14 (Keelakarai) registered the lowest absorption rate 35.67 nGy/h, the mean absorbed dose rate was 98.98 ± 20.54 nGy/h. Outdoors Gamma absorbed dose rates were calculated and ranged between 32 nGy/h and 59.1 nGy/h with an arithmetic mean of 43.3 ± 9 nGy/h.^[25] The highest Annual dose in Gulf of Mannar was 5.65 mGy/h in Eruvadi and lowest value 0.30 mGy/h in Vambar beach and Keelarai. External annual effective dose ranged from 0.17 to 0.60 mSv/y with a mean value of 0.33 ± 0.05 mSv/y.^[26] The ambient gamma radiation in various regions of the world largely depends on the geological and geographical condition of the soil in the particular region of the world.^[17]

Acknowledgments

The authors are thankful to Dr. A. K. Khaza Nazeemudeen Sahib, Secretary and Correspondent, Dr. S. Ismail Mohideen, Principal and Dr. I. Joseph Antony Jerald, Head, P. G. and Research Department of Zoology (DST-FIST and DBT STAR funded), Jamal Mohamed College (Autonomous), Tiruchirappalli for Institutional support. We profoundly thank Science and Engineering Research Board (Ref. no YSS0000146/2016), Department of Science and Technology, Government of India, New Delhi for Instrument support.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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