|Year : 2011 | Volume
| Issue : 2 | Page : 96-103
A post-tsunami study on the distribution and bioaccumulation of natural radionuclides in Pichavaram mangrove environment (South East Coast of India) and dose to local human population
G Satheeshkumar1, P Shahul Hameed2, M Meeramaideen3, V Kannan4
1 PG and Research Department of Zoology, Periyar E.V.R. College, Tiruchirappalli, India
2 Environmental Research Centre, J.J. College of Engineering and Technology, Tiruchirappalli, India
3 Environmental Research Lab, Department of Zoology, Jamal Mohamed College, Tiruchirappalli, India
4 Ex - Environmental Survey Laboratory, Department of Atomic Energy, Kalpakkam, Tamil Nadu, India
|Date of Web Publication||12-Jul-2012|
PG and Research Department of Zoology, Periyar E.V.R. College, Tiruchirappalli
Source of Support: None, Conflict of Interest: None
The paper reports the impact of the December 26, 2004 Sumatra Tsunami on the radioactivity profile in the environment of Pichavaram Mangroves (South East Coast of India) and bioaccumulation of two toxic radionuclides 210 Po and 210 Pb in seafood organisms and possible dose transfer to local fisherman population through seafood intake. The present study (Post-Tsunami) recorded low levels in all radiological parameters analyzed with respect to primordials in sediments and 210 Po and 210 Pb in water, sediment, and seafood organisms as compared with the Pre-Tsunami data. The mean activity of 238 U and 232 Th recorded in the present study were 12.2 Bq/kg and 11.7 Bq/kg, respectively. The activity of 210 Po in water was less (1.4 mBq/l) than that of 210 Pb (2.7 mBq/l). In contrast, the activity of 210 Po in sediment was distinctly higher (3.3 Bq/kg) than that of 210 Pb (1.7 Bq/kg). The shell fishes (Prawn, Crab, Bivalves, and Squid) accumulated more 210 Po (16.4 Bq/kg) and 210 Pb (2.7 Bq/kg) than the fin fishes ( 210 Po: 6.9 Bq/kg; 210 Pb: 1.5 Bq/kg). The results indicated that fin fishes as seafood were relatively less radioactive compared with shell fishes. About 90% Committed Effective Dose Equivalent to fisherman population due to seafood intake was from 210 Po (712 μSv/y) and 10% from 210 Pb (78 μSv/y). The higher dose transfer to Pichavaram fisherman was attributed to relatively more seafood consumption. A low-level background radiation in the Post-Tsunami environment of Pichavaram Mangroves was due to the hydrodynamics of the Tsunami waves which removed the Pichavaram sediments loaded with monazites and other particles containing radionuclides.
Keywords: Bioaccumulation, dose transfer, mangroves, radionuclides in fishes, 210 Po and 210 Pb
|How to cite this article:|
Satheeshkumar G, Hameed P S, Meeramaideen M, Kannan V. A post-tsunami study on the distribution and bioaccumulation of natural radionuclides in Pichavaram mangrove environment (South East Coast of India) and dose to local human population. Radiat Prot Environ 2011;34:96-103
|How to cite this URL:|
Satheeshkumar G, Hameed P S, Meeramaideen M, Kannan V. A post-tsunami study on the distribution and bioaccumulation of natural radionuclides in Pichavaram mangrove environment (South East Coast of India) and dose to local human population. Radiat Prot Environ [serial online] 2011 [cited 2022 Jan 17];34:96-103. Available from: https://www.rpe.org.in/text.asp?2011/34/2/96/98394
| 1. Introduction|| |
Pichavaram mangrove ecosystem is located about 220 km south of Chennai city on the southeast coast of India. The mangroves are specialized coastal region characterized by rich growth of salt-tolerant trees and offer protection to sea shore from damages caused by storms, wave action, and erosion and provide a safe breeding place to variety of fishes, birds, crustaceans, and shell fishes. The mangrove has been intensively studied with respect to water quality, bioresources,  bioactive substances,  and pollutants like pesticides and heavy metals.  However, there is no adequate scientific data on the radioactivity profile of this unique coastal environment which has a rich living resource, except the work of Raja  and Shahul Hameed. 
The December 26, 2004 Sumatra Tsunami has caused greater devastation to east coast of India also. The numbers killed along the East Coast of India are put down at more than 10000 and the worst affected areas in Tamil Nadu are Nagapattinam, Cuddalore, and Cholechel. However, Pichavaram Mangroves region which is very close to Cuddalore (30 km) was not seriously affected because of dense protective mangrove vegetation.  The need for developing and maintaining the mangroves along the east coast to maintain coastal integrity and also to protect the coast from Tsunami, soil erosion, etc., was seriously felt. Since Tsunami deposited a huge volume of fresh sediment on the shore, which would modify the environmental radioactivity profile of the Pichavaram mangroves, a scientific study on impact of Tsunami on the distribution of primordial radionuclides in sediment and bioaccumulation of internal emitters in the seafood organisms was felt imperative.
Radioactivity in environmental matrices is due to the presence of primordial radionuclides ( 238 U, 232 Th, and 40 K) and their daughters. Lead-210 ( 210 Pb) and Polonium-210 ( 210 Po) belong to [238 U series and they are ubiquitous in environment. In aquatic environment, 210 Po and 210 Pb are transported and concentrated by physical, chemical, and biological processes. The study of bioaccumulation of 210 Po and 210 Pb in seafood organisms assumes importance because of their toxic nature and bioaccumulative behavior.  Consumption of food and drink are the main routes by which these radionuclides enter human body. 210 Po, an alpha emitter, causes considerably greater biological damage, as compared with the beta emitter, 210 Pb.  Evidences from literature indicate that these radionuclides are accumulated strongly by marine organism and transferred to man via food along a trophic chain.  Because of their ubiquitous nature and contribution to the total radioactive dose to human beings and animals,  it is imperative to study the accumulation of 210 Po and 210 Pb in marine organisms. Hence, the present study was undertaken during the Post-Tsunami period from March 2007 to February 2009, to generate a database on distribution of primordial radionuclides in sediment and bioaccumulation of 210 Po and 210 Pb in the seafood organisms from Pichavaram Mangroves and consequent dose transfer to local human population through seafood intake and to compare the data with the available pre-tsunami data.
| 2. Materials and Methods|| |
2.1. Description of the study area
Pichavaram mangroves (Lat. 11 0 27': Long. 79 0 47') consist of 51 small and large islets covering an area of 1 100 ha and are traversal by several creeks, gullies, rivulets, channels, and canals and lie within the Vellar-Coleroon estuarine complex.  For the present study, six sampling stations (S1-S6) were identified based on the accessibility and specific geomorphic features and spread over the entire mangrove stretch [Figure 1]. Water and sediment samples were collected from sampling stations. Seven species of shell fishes and ten species of fin fishes were chosen for the present study and collected from local fish market near Killai.
2.2. Analysis of Primordial Radionuclides
The sediment samples collected from each sampling site were first air dried and later dried in an oven at temperatures of 105-110 o C to get a constant dry weight. The samples were cooled and then sieved through 100 μm mesh. These samples were stored in airtight cylindrical plastic containers of 300 ml volume for 30 days to allow radioactive equilibrium of 238 U and 232 Th with their corresponding progenies. The concentrations of 238 U, 232 Th, and 40 K were determined using a High-Pure Germanium detector (HPGe) by counting the sample for a period of 20 hours to minimize the counting error. The activity of 238 U was evaluated from the 609 keV gamma line of 214 Bi and that of 232 Th from 911 keV gamma line of 228 Ac. For the determination of 238 U and 232 Th concentrations, it was assumed that these radionuclides were in secular equilibrium with their corresponding decay products.  The activity calculations were carried out following the methods of. 
2.3. Analysis of 210 Po in water samples
For the analysis of 210 Po, about 100 l of water sample was collected from each sampling station, filtered through a Whatman 40 filter paper, and acidified with concentrated HCl to pH 1. About 500 mg of ferric chloride (Iron carrier) was added to the acidified sample and 210 Po in the filtered water was collected as ferric hydroxide precipitate by slow addition of concentrated ammonia solution with rapid stirring until pH reached 9. Two repeat precipitations were carried out to completely remove 210 Po by Fe(OH) 3 . The precipitate carrying 210 Po was dissolved in 6N HCl and 210 Po was deposited on silver planchette by electrochemical exchange technique following the procedure of  and alpha counted, in Radiation Counting System (ECIL-RCS 4027-A) with ZnS(Ag) detector having a counting efficiency of 25% to 28% for a 239 Pu standard source.
2.4. Analysis of 210 Po in sediment samples
For the analysis of 210 Po in sediment, 10 g of the sample was ground to pass through 100-μm meshes and heated to 110 o C for 24 hours to remove moisture. The sample was then heated three times with concentrated HNO 3 evaporating to near dryness each time. The residue was evaporated with concentrated HCl repeatedly to convert to chloride medium and taken in 0.5N HCl for electrochemical deposition of 210 Po on to a silver (Ag) planchette  and alpha counted.
2.5. Analysis of 210 Po in shell and fin fishes
The biological samples (25 to 50 g) of muscle or soft tissue were wet processed repeatedly with oxidizing mixture made of HNO 3 and H 2 O 2 in 1 : 1 ratio till a white residue was obtained. The residue was dissolve in 0.5N HCl and made up to 300 ml and 210 Po was plated on a silver planchette by electrochemical displacement following the method of  and the activity alpha counted.
2.6. Analysis of 210 Pb in water, sediment and biological samples
The 210 Pb concentrations in water, sediment, and biological samples were determined by incubation method.  In this method, the final solutions used for electrochemical separation of 210 Po in various environmental samples were incubated for a period of 138 days (Equivalent to half-life period of 210 Po). After the incubation period, solutions were subjected to electrochemical deposition of 210 Po on a silver planchette. The planchette was removed, dried, and counted for alpha radiation. From the 210 Po concentration, 210 Pb concentration was deduced.
2.7. Assessment of committed effective dose
To assess the local dietary habits and per capita intake of diet components, a survey was carried out in the coastal population of Pichavaram, mostly comprising of fishermen, covering 150 families in three villages. From the data on the diet information survey and radioactivity of 210 Po and 210 Pb in seafood organisms, the dietary intake of 210 Po and 210 Pb were arrived at. The activity in Becquerel unit (Bq) is converted into Committed Effective Dose Equivalent (CEDE) in Sievert unit (Sv) by using the following conversion factor. 
210 Po: 1.2 × 10 -6 Sv/Bq
210 Pb: 6.9 × 10 -7 Sv/Bq
| 3. Results and Discussion|| |
3.1. Analysis of Primordial Radionuclides
The activity concentration of primordial radionuclides ( 238 U, 232 Th, and 40 K) in the coastal sediment of Pichavaram mangroves stations are presented in [Table 1]. The 238 U concentration in all six sampling stations of Pichavaram Mangroves ranged from 6 to19 Bq/kg with a mean value of 12.2 Bq/kg. The concentration of 232 Th ranged from 2 to 22 Bq/kg with a mean value of 11.7 Bq/kg. The activity ratio 232 Th/ 238 U ranged from 0.54 to 1.69 Bq/kg with a mean value of 0.9 Bq/kg. The activity of 40 K value fluctuated from 114 to 419 Bq/kg and the mean value was 265.0 Bq/kg.
|Table 1: Primordial Radionuclides in Sediment Samples of Pitchavaram Mangroves|
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The mean activity ratio of 238 U to 232 Th recorded in the present study was 0.9 Bq/kg. However, Raja  reported a higher ratio of 3.8 for the same environment indicating a significant change in the radioactivity profile of the environment. But, 40 K levels in these stations fluctuated from 114 to 419 Bq/kg which compares well with the pre-tsunami measurement of 40 K (150 to 242 Bq/kg by Raja.  But studies carried out in several regions of Indian coast revealed higher levels of 232 Th as compared with 238 U. Such studies were carried out for Kalpakkam coast by Kannan et al., for Gulf of Mannar by Ravikumar,  for Palk Strait by Shahul Hameed,  for Ullal beach by Narayanan et al., for Kerala coast by Ramachandran and Boban,  for East Coast of Tamil Nadu by Lakshmi et al., and for Kanyakumari by Rekhkutty et al.
All Indian average of 238 U, 232 Th, and 40 K are 14.8 Bq/kg, 18.31 Bq/kg, and 40.70 Bq/kg, respectively.  The world average of 238 U, 232 Th, and 40 K are 26 Bq/kg, 26 Bq/kg, and 370.0 Bq/kg, respectively. , If the values of present study are compared with all India average, 238 U and 232 Th concentrations are little lower while 40 K concentration is in higher level.
3.2. The analysis of 210 Po and 210 Pb in water
The activity concentrations of 210 Po and 210 Pb in water and sediments samples collected from six sampling stations of Pichavaram Mangroves are presented in [Table 2]. The activity of 210 Po in water ranged from 1.2 to 1.6 mBq/l with mean value of 1.41±0.16 mBq/l. In contrast, the concentration of 210 Pb registered a distinct higher mean value of 2.7 mBq/l and it fluctuated between 2.0 mBq/l and 3.7 mBq/l. The mean 210 Po/ 210 Pb ratio for water samples was 0.53±0.13 mBq/l. It is evident that the activity concentrations of 210 Pb in water are always higher than that of 210 Po. Furthermore, it indicates that 210 Po concentration in the medium is always supported by concentration of the mother source, namely 210 Pb.
|Table 2: 210Po and 210Pb Activity in Water and Sediment Samples of Pitchavaram Mangroves|
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The 210 Po and 210 Pb concentrations of the Pichavaram Mangrove water were found to be lower than the values reported for Kalpakkam coast  ( 210 Po: 9.1 mBq/l and 210 Pb: 6.66 mBq/l) and Gulf of Mannar coast  ( 210 Po: 2.14 mBq/l and 210 Pb: 32.4 mBq/l). Pichavaram Mangrove values are comparable with the recorded values of Palk Strait coast ( 210 Po: 1.54 and 210 Pb: 2.7 mBq/l) by Bukhari et al.
3.3. Analysis of 210 Po and 210 Pb in sediment samples
The present study registered that 210 Po in sediment samples ranged from 2.6 to 4.0 Bq/kg (mean value, 3.3±0.56 Bq/kg) and activity of 210 Pb ranged from 1.2 to 2.6 Bq/kg (mean value, 1.7±0.52 Bq/kg). The activity ratios of 210 Po/ 210 Pb ranged from 1.52 to 3.00 (with mean value: 1.9±0.54).
The mean 210 Po and 210 Pb activity in sediment samples of Pichavaram Mangrove was less than the values reported for Kalpakkam coastal beach sediment  ( 210 Po: 44 Bq/kg and 210 Pb: 385 Bq/kg); Gulf of Mannar coastal sediments  ( 210 Po: 286.12 Bq/kg and 210 Pb: 35.3 Bq/kg); and Trombay coastal sediments  ( 210 Po: 784.1 Bq/kg and 210 Pb: 356.0 Bq/kg). However,  reported a comparable value (3.2 Bq/kg) for the 210 Pb in sediment of Palk Strait.
The 210 Po/ 210 Pb ratios for Pichavaram Mangrove sediments are always greater than 1, indicating the unsupported nature of 210 Po in the sediment. This means that 210 Po concentration in the sediment is also contributed by sources such as vegetation and decomposing organic matter besides 210 Pb parent. The higher activity in 210 Po in sediment serves as a baseline for the transfer of 210 Po to higher organisms. It is evident from the present study that the levels of 210 Po in the water and sediment of Pichavaram Mangroves are much lower than the adjacent marine provinces namely Gulf of Mannar, Palk Strait, and Bay of Bengal.
3.4. Analysis of 210 Po and 210 Pb in shell and fin fishes
[Table 3] presents the activity concentrations of 210 Po and 210 Pb in the seven species of shell fishes and ten fish species analyzed. In general, the mean concentrations of 210 Po (16.4 Bq/kg) and 210 Pb (2.7 Bq/kg) measured in shell fish species are distinctly higher than the mean values registered in fishes ( 210 Po: 6.85 Bq/kg and 210 Pb:1.5 Bq/kg). Among the seven shell fish species, molluscs in general and oysters in particular registered a maximum accumulation rate of 210 Po and 210 Pb. The data also indicated that fish as food organisms is less radioactive. 210 Po levels in the muscles of marine fish samples obtained in the present study were comparable with those obtained by  in Bombay coast (0.52 - 25.0 Bq/kg) and  in Kalpakkam coast (1.1 - 29.6 Bq/kg). It is interesting to note in any given species 210 Po concentration in muscle is distinctly higher than 210 Pb level. Hameed et al. reported that 210 Po has exhibited greater affinity to protein-rich muscle, whereas 210 Pb is a bone seeker and tends to accumulate in mineralized parts of animal body. The concentrations of 210 Po in muscle are important for the high rate of dose transfer to human beings.  The Concentration Factors (CF) of 210 Po in the seafood organisms analyzed revealed that 210 Po was avidly accumulated several thousand times the concentration in water (CF: 4.6×10 -3 ), whereas 210 Pb maintain a low-level CF (10×10 -2 ). The low-level accumulation of 210 Po and 210 Pb in fish muscle indicated that fishes are relatively safer seafood as compared with shell fishes.
|Table 3: Activity Concentrations of 210Po and 210Pb in Sea Food Organisms from Pitchavaram Mangroves and Dose to Local Human Population|
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The data generated on the activity concentrations of the 210 Po and 210 Pb in the muscles of seafood organisms from Pichavaram mangroves are used to calculate the total amount of radiation dose transfer to human being consuming them as CEDE.
In the present study, CEDE to fisherman community due to dietary intake of 210 Po was estimated to be 712 μSv/y and of 210 Pb to be 78 μSv/y (Total: 790 μSv/y). Internal radiation dose to the public from 210 Po due to consumption of seafood from Bombay Harbour Bay varied from 2.1 to 40.0 μSv/y.  Rajan et al. estimated the dose transfer due to 210 Po through seafood at Kalpakkam environment to be 36.3 μSv/y and  reported a dose of 1 011 μSv/y from 210 Po through seafood intake in Palk Strait coastal population. The higher dose transfer to Pichavaram fisherman population was attributed to higher intake of seafood, particularly oysters and clams which rarely gets into the diet of urban population of Mumbai and Kalpakkam.  reported CEDE due to dietary intake of 210 Po, in fisherman population of Gulf of Mannar coast, a high background radiation area, was estimated to be 2888 μSv/y. From the present study, it was evident that despite the low background radiation level in Pichavaram, fisherman population got relatively higher dose due to higher seafood consumption.
Of all the natural radioemitters, 210 Po constitutes the main source (>90%) of the internal radiation to which human beings are subjected. , The dose result of present study also confirmed this trend and it recorded about 90% of dose from 210 Po (712 μSv/y) and 10% from 210 Pb (78 μSv/y).
3.5. Comparison of present study with Pre-Tsunami data
The environmental radioactivity study in Pichavaram Mangroves was carried out for the pre-tsunami period by Raja  and Shahul Hameed and Raja.  A comparison of the data of present study with pre-tsunami data is made in [Table 4]. It is evident that the present study (post-tsunami) recorded low levels in all radiological parameters analyzed with respect to primordials in sediment, 210 Po and 210 Pb in water, sediment, and seafood organisms. The calculation of dose transfer to local human population due to dietary intake in seafood organisms also indicated a lower dose as compared with the pre-tsunami data. The important reason attributed to such reduced level of radioactivity in Pichavaram is the hydrodynamics of Tsunami waves which removed huge quantities of beach materials that have been built up over a few decades. Furthermore, it dumped a thick blanket of black sands. Hence, the radiological profile becomes modified reducing background radiation level of the environment. In earlier study, the 232 Th concentration is always higher than 238 U. The 232 Th/ 238 U ratio was recorded to be 3.8. But the present study recorded a low level of 232 Th/ 238 U ratio (0.9). The monazite in the beach sediment is the major source of Thorium. Seralathan et al. have made sedimentological study in the Tsunami-affected Tamil Nadu coast including Pichavaram and reported that the Tsunamigenic sediment of Pichavaram mangroves contained abundant heavy minerals and opaques like ilmenite, magnetite, grants, zircon, and flaky minerals like chlorite, biolite, actinolite, and tromolite. However, the enrichment of monazite in the Tsunamigenic sediment is not reported. It is evident that Tsunami waves had washed the Pichavaram sediment loaded with monazite and other particulates containing radionuclides, thus reducing the background radiation of the ecosystem.
|Table 4: Comparison of Post-Tsunami Radiological Data with Pre-Tsunami Data in Pitchavaram Mangrove Environment|
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| 4. Acknowledgements|| |
The authors gratefully acknowledge Board of Research in Nuclear Sciences, Department of Atomic Energy, Govt. of India, for funding the research work and Prof. K. Ponnusamy, Chairman, J.J. Group of Institutions for support and facilities.
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[Table 1], [Table 2], [Table 3], [Table 4]