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ORIGINAL ARTICLE
Year : 2019  |  Volume : 42  |  Issue : 3  |  Page : 96-101  

Investigation on the enrichment of radionuclides in an endosulfan-affected area, Enmakaje Panchayath, Kasargod


Department of Studies and Research in Physics, Payyanur College, Kannur, Kerala, India

Date of Submission05-Jun-2019
Date of Decision11-Jun-2019
Date of Acceptance23-Jul-2019
Date of Web Publication06-Nov-2019

Correspondence Address:
V Prakash
Department of Studies and Research in Physics, Payyanur College, Kannur . 670 327, Kerala
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/rpe.RPE_19_19

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  Abstract 


In the present study, systematic analysis of radionuclides concentration and radiological parameters of sediment samples collected from the banks of Kodankari stream situated in Enmakaje Panchayath, Kasargod, has been carried out. A total of twenty sediment samples were collected and analyzed for activity concentration of radionuclides, namely,40K,226Ra, and232Th using high-purity germanium detector. The activity concentration of226Ra ranges from 30.5 to 56 Bq/kg with a mean value of 41.6 Bq/kg, activity concentration of232Th ranges from 100.5 to 220 Bq/kg with a mean value of 144.4 Bq/kg, and activity concentration of40K ranges from 19.1 to 98.6 Bq/kg with a mean value of 64.7 Bq/kg. The radiological parameters such as absorbed dose, annual effective dose (indoor and outdoor), radium equivalent activity, and internal and external exposure indices were calculated and compared with the recommended safety limits prescribed by various agencies. The results of the systematic analysis are presented and discussed in detail in the manuscript.

Keywords: 226Ra,232Th,40K, enrichment, radiological parameters, radionuclides


How to cite this article:
Ramesh S, Vineethkumar V, Sayooj V V, Prakash V. Investigation on the enrichment of radionuclides in an endosulfan-affected area, Enmakaje Panchayath, Kasargod. Radiat Prot Environ 2019;42:96-101

How to cite this URL:
Ramesh S, Vineethkumar V, Sayooj V V, Prakash V. Investigation on the enrichment of radionuclides in an endosulfan-affected area, Enmakaje Panchayath, Kasargod. Radiat Prot Environ [serial online] 2019 [cited 2019 Nov 22];42:96-101. Available from: http://www.rpe.org.in/text.asp?2019/42/3/96/270440




  Introduction Top


Radionuclides are the part of every environmental matrix and are found in varying concentration. Naturally occurring radioactive isotopes in the environment come from singly occurring40 K and radionuclides of uranium and thorium series. These radioactive isotopes are present in rocks, sands, soils, sediments, and all other environmental matrices. The decay of naturally occurring radionuclides in soil/sediment produces the gamma radiation field and the sources of terrestrial gamma radiation are the decay products of thorium and uranium series and radionuclides like40 K.[1] Natural radiation is the largest contributor to external dose to the world population and the radionuclides that are part of air, soil, building materials, rocks, vegetation, and food contain varying amounts of radioactivity.[2] Hence, the assessment of gamma radiation dose from natural sources has greater importance. Environmental radioactivity and external exposure due to gamma radiation occur at different levels in nature, and it varies geographically due to geological changes in each region.[3]

Between 1976 and 2000, the plantation corporation of Kerala aerially sprayed endosulfan on cashew plantation covering 11 grama panchayaths of Kasargod district, Kerala.[4] Various types of biological disorders such as neurobehavioral disorders, congenital disorders, cancers, and gynecological abnormalities can be seen at the nearby villages of Kerala Plantation Corporation in Kasargod district.[5] These chronic disorders were present after the cashew plantation started their operations. Various studies have been carried out in this region by different agencies both from government and private, but these studies do not have a common conclusion. The major controversy arises on regarding health issues raised in this region is due to endosulfan or not.

In the report of Dr. Mohan Kumar, he pointed out that the health issues at this region may be due to the presence of heavy minerals and radionuclide concentration present in that region.[6] However, he failed to show any scientific proof to prove his argument and theory. More detailed and systematic investigation is needed to generate data and draw possible conclusions on basic dynamics of radioactivity in endosulfan-affected areas. In this context, investigation on distribution and enrichment of natural radionuclides in the sediment samples of endosulfan-affected areas assumes great significance. In view of the above and extensive literature survey, it is planned to analyze sediment samples collected from the banks of Kodankari stream of Swarga village and the systematic studies have been carried out to check the content of radionuclides, namely,226 Ra,232 Th, and40 K and compare the values with the concentration reported in other places. The sediment samples have been analyzed to understand the concentration of radionuclides in the region and if found higher, the health issues in the region may be attributed the radionuclides enrichment. In most of the literature, more focus was given to endosulfan and not on radionuclides content. In the present study, sediment sample analysis has not been linked to endosulfan spray and contamination due to radionuclides only given emphasis.


  Materials and Methods Top


Location of the study

The sediment samples were collected from the banks of Kodankari stream (12°37′21″N, 75°08′28″E, 839 m) situated in Enmakaje Panchayath, Kasargod, Kerala. [Figure 1] gives the sample collection spots and the region is about 40 km away from the Kasargod town. The length of stream is about 2 km, and it finally joins to the Chandragiri River.
Figure 1: Location map of the study area

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Sample collection and analysis

A total of twenty sediment samples weighing about 2–3 kg were collected from each sampling stations. Unused surface area was selected for sampling, the grass, root mat, stones, pebbles, plant material, and other wastes were removed from the samples. Sample collection was done at 30 cm depth, after thorough mixing. The samples were collected in polythene bags and brought to the laboratory for further analysis. The samples were processed following standard procedures.[7] The samples were cleaned and air-dried at room temperature and then dried in an oven at 110°C for 24 h till a constant dry weight is obtained. The dried samples were then sieved through 250 μm mesh and stored in airtight plastic containers for 30 days to prevent the escape of radiogenic gases radon (222 Rn) and thoron (220 Rn) and to allow radioactive equilibrium with their corresponding progeny.[8] The samples were then analyzed following standard techniques.

The activity concentration of226 Ra,232 Th, and40 K in the samples was determined using the gamma spectrometry employing a 38% relative efficiency p-type low-background high-purity germanium (HPGe) detector having an energy resolution 2.1 keV at 1.33 MeV (CANBERRA, USA). The spectrum was acquired and analyzed using a 16K multichannel analyzer (multiport, CANBERRA) and GENIE-2000 software (Mirion Technologies, Canberra, USA). The detector efficiency calibration was performed using the International Atomic Energy Agency (IAEA) quality assurance reference materials: RG U-238, RG Th-232, RG K-1, and SOIL-6 procured from IAEA. The standard materials and samples were collected in containers of uniform size and type so that detection geometry remains the same. The samples were counted long enough to reduce the counting error. The226 Ra activity was evaluated from the weighted mean of activity of three photo peaks of214 Bi (609.3, 1129.3, and 1764.5 keV) after applying the Compton corrections. In the case of232 Th, one photopeak of228 Ac (911.2 keV) and the photo peaks of208 Tl (583.1 and 2614.5 keV) were used in the same way. The activity of40 K was derived from the 1460.8 keV gamma line of this isotope.[8] The minimum detection level for the above detecting system was 0.62, 2.46 and 1.42 Bq/kg, respectively, for226 Ra,232 Th, and40 K for a counting time of 60,000 s and a sample weight of 300 g. The details of calibration of the detector, measurement techniques, and intercomparison measurements were already reported.[9],[10]

Calculation of radiological parameters

The radiological parameters, namely, absorbed dose rate, radium equivalent activity (Raeq), annual effective dose (AED) (indoor and outdoor), external and internal exposure index (IEI), radioactivity level index, and alpha index were calculated from the activity concentration, using the equations discussed below.

The absorbed dose rate (D)

The biological effect, radiological effect, and clinical effects are directly related to the absorbed dose rate. Hence, the external outdoor absorbed gamma dose rates due to terrestrial gamma rays from the nuclides40 K,226 Ra, and232 Th at 1 m above the ground level was calculated based on the guideline provided by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), 2000.[11]

D = 0.462 CRa+ 0.604 CTh+ 0.0417 CK nGy/h

Where CRa, CTh, and CK, are the activities of226 Ra,232 Th, and40 K, respectively, in Bq/kg.

Radium equivalent activity

Radionuclides of226 Ra,232 Th and40 K are not homogeneously distributed in the sediment matrix. The inhomogeneous distribution of these naturally occurring radionuclides is due to disequilibrium between226 Ra and its decay products.[11]

Raeq= CRa+ 1.43 CTh+ 0.077 CK Bq/kg

Where CRa, CTh, and CK, are the activities of226 Ra,232 Th, and40 K, respectively, in Bq/kg.

Annual effective dose rate

The AED rate is determined by considering the conversion coefficient from absorbed dose in air to effective dose as 0.7 Sv/Gy and the indoor occupancy factor of 0.8 and the outdoor occupancy factor of 0.2 proposed by UNSCEAR 2000.[11] The AED was calculated from the equation,

Indoor (mSv/y) = D (nGy/h) × 8766/hy × 0.8 × 0.7

(Sv/Gy) × 10−6

Outdoor (mSv/y) = D (nGy/h) × 8766/hy × 0.2 × 0.7

(Sv/Gy) × 10−6

Where D is the absorbed dose rate in nGy/h.

External and internal exposure index

The external exposure index (EEI), due to the emitted gamma rays, from sediment samples was calculated using the relation.[12]

EEI = ([CRa/370] + [CTh/259] + [CK/4810])

The internal exposure to radon and its daughter products is quantified by IEI which is given by the equation.[12]

IEI = ([CRa/185] + [CTh/259] + [CK/4810])

Where CRa, CTh, and CK are the activity concentration of radium, thorium, and potassium, respectively.

Radioactivity level index (γ)

The radioactivity level index is used to represent the gamma radiation hazards associated with the natural radionuclides. The representative level index was obtained by the equation.[11]

Iγ= (CRa/150) + (CTh/100) + (CK/1500)

Where CRa, CTh, and CK are the activity concentration of radium, thorium, and potassium, respectively.

Alpha index (Iα)

The index is used for the assessment of internal hazard due to the radon inhalation originating from building materials and is defined by the equation,[11]

Iα= CRa/200

Where CRa is the activity concentration of radium and its recommended limit is 200 Bq/kg. Hence, for the safe use of building materials, the value of Iα chosen to be less than unity.


  Results and Discussion Top


The activity concentrations of the radionuclides (40 K,226 Ra, and232 Th) present in the collected samples are summarized in [Table 1]. The radiological parameters, namely, AED, Raeq, external exposure indices, internal exposure indices, radioactive indices, alpha indices, and indoor and outdoor AED calculated from the activity concentrations of40 K,226 Ra, and232 Th are summarized in [Table 2].
Table 1: Activity concentration of 40K, 226Ra, and 232Th

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Table 2: Radiological parameters of the samples

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[Figure 2] shows the variation of activity concentrations of40 K,226 Ra, and232 Th at different sampling locations. The activity concentration of40 K varies within the range 19.1 and 98.6 Bq/kg with a mean value 64.7 Bq/kg. The activity concentration of40 K is well within the reference value (Indian average value of K is 400 Bq/kg and world average value is 420 Bq/kg).[11] The activity concentration of226 Ra varies within the range 30.5 and 56.0 Bq/kg with a mean value 41.7 Bq/kg. The activity concentration of226 Ra is higher than the reference value (Indian average value of226 Ra is 28.7 Bq/kg and world average value is 33.0 Bq/kg).[11] The activity concentration of232 Th varies within the range 100.5 and 220 Bq/kg with a mean value 144.4 Bq/kg. The activity concentration of232 Th is higher than the reference value (Indian average value of232 Th is 63.83 Bq/kg and world average value is 45 Bq/kg).[11]
Figure 2: Variation of activity concentration at different sampling locations

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The absorbed dose ranges from 76.0 to 151.6 nGy/h with an average value of 106.7 nGy/h. The absorbed dose was found higher than the world average value (57 nGy/h).[10] The Raeq varies within the range 178.1 and 360.56 Bq/kg with a mean value 253.1 Bq/kg. It is clear that the Raeq is low compared with the permissible limit (370 Bq/kg).[11]

The value of EEI ranges from 0.48 to 0.97 with a mean value 0.68 is less than unity. The IEI ranges from 0.57 to 1.02 with a mean value 0.79 is less than unity. Even when it exceeds unity, it does not cause any significant exposure so as to result in any kind of adverse health effects. To cause any kind of adverse health effects, the index should approximately exceed about a million.[12] The value of radioactive index ranges from 1.24 to 2.52 with an average value of 1.76. The alpha index varies within the range 0.15–0.28 with a mean value 0.21. The indoor AED ranges from 0.34 to 0.84 mSv/y with a mean value of 0.58 mSv/y. The indoor AEDs rate is slightly higher than world average value (0.48 mSv/y). The outdoor AED ranges from 0.09 to 0.21 mSv/y with a mean value of 0.14 mSv/y. The outdoor AED is seen to be higher than the world average value of 0.07 mSv/y.[11] The comparison of the activity of natural radionuclides with other environs of India is presented in [Table 3].
Table 3: Comparison of the activity concentration 40K, 226Ra, and 232Th with other regions of India

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The correlation between the activity concentration of40 K,226 Ra, and232 Th were studied [Figure 3], [Figure 4], [Figure 5]. From the study, it can be pointed out that no proper correlation is observed between the concentrations of radionuclides measured from the samples. The correlations between the activities of radionuclides were insignificant.
Figure 3: Correlation between40K and226Ra

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Figure 4: Correlation between232Th and40K

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Figure 5: Correlation between232Th and226Ra

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  Conclusions Top


In this study, the analysis of radioactivity was carried out for the samples collected from the banks of Kodankari stream situated in Enmakaje Panchayath, Kasargod. The HPGe gamma spectrometric measurement technique is used to analyze the activity concentrations of40 K,226 Ra, and232 Th. The radiological parameters, namely, absorbed dose rate, Raeq, indoor and outdoor AED, internal and external hazard index, alpha indices, and radioactive level index were calculated from the activity. The activity concentration of40 K is well within the permissible limit and the activity concentration of226 Ra and232 Th are higher than the recommended permissible limits. The correlation between the activities of radionuclides is insignificant. The radiological parameters are well within the permissible limit except for indoor and outdoor AED rate. The radionuclide232 Th is the dominant gamma-emitting sources in the sediment samples. The radionuclides concentration varied from place to place due to the presence of different geological and geochemical processes in the region. The sediments weathered from the rock are rich in radioactive minerals may influence the activity concentration of the radionuclides. More systematic studies are needed to understand the various processes influencing the activity concentration in the endosulfan spread area.

Acknowledgment

The first author is thankful to Dr. Mohan Kumar and Mr. Ambikasudhan Mangad for providing detailed information regarding the sampling location. He is also thankful to Dr. Karunakara N., (Coordinator, Centre for Advanced Research in Environmental Radioactivity, Mangalore University) for extending the HPGe facility for the sample analysis. Thanks are also due to the natives of Enmakaje Panchayath, Kasargod district, who have helped us to understand the geology of the area and endosulphan-related issues.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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