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Latitudinal variation and residence time of 137Cs in Indian coastal environment
MPB-07164; No of Pages 6 Marine Pollution Bulletin xxx (2015) xxx–xxx
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Latitudinal variation and residence time of 137Cs in Indian coastal environment S.J. Sartandel, S.K. Jha ⁎, R.M. Tripathi Health Physics Division, Bhabha Atomic Research Center, Mumbai 400 085, India
a r t i c l e
i n f o
Article history: Received 25 March 2015 Received in revised form 18 August 2015 Accepted 1 September 2015 Available online xxxx Keywords: 137 Cs activity concentration Pre-concentration Coastal surface water Effective half-life
a b s t r a c t Anthropogenic 137Cs activity concentration, in surface sea water along the western and eastern coast of India has been estimated using the in-situ pre-concentration approach. Activity levels of 137Cs ranges from 0.09– 1.30 Bq m−3 with an overall mean of 0.69 ± 0.29 Bq m−3. Latitudinal variation and higher depletion in activity concentration of 137Cs at few locations were observed. Temporal change of 137Cs in sea water along Indian coast unveils a lower effective half-life of 13.8 ± 0.7 y in comparison to Asia Pacific regional sea water. The results prevailed that the spatial distribution confers no fresh input of 137Cs in Indian coastal region. © 2015 Elsevier Ltd. All rights reserved.
Marine environment is a major sink for anthropogenic radionuclides from global fallout, released during nuclear weapons tests performed on a large scale mainly by US and former USSR during 1960s, nuclear accident and discharges from the nuclear power plants (Povinec et al., 2003a; UNSCEAR, 2000). The activity concentration of 137Cs in the Indian coastal marine environment can be traced due to global fallout (Jha et al., 2003). The concentrations of global fallout radionuclide in sea water were measured since 1950s with an aim to assess the radiological impact from Nuclear weapon test on the marine environment and humans. Considering the usefulness of these studies, fallout radionuclide's have been used as a tracer to investigate the movement of water mass in the world oceans. The Indian Ocean plays a significant role in the global circulation of water mass. Perceptive of the coastal processes too play remarkable role in the protection of the marine environment against contamination due to anthropogenic sources. A global thermohaline circulation (conveyer belt) has been proposed as global ocean circulation model connecting the ocean basins with surface warm water and bottom cold water (Schmitz, 1995). A transport of warm surface water from North Pacific through Indonesian via Indian Ocean is well documented (Gordon et al., 2003). The Indian Ocean represents the most fragile part of the global ocean circulation because of its flow via Southern Ocean. This circulation pattern may be responsible for migration of anthropogenic radionuclide from one part of the ocean to another. Number of studies have been conducted for understanding the flux of anthropogenic radionuclide's in the Indian Oceans encompassed under Geochemical Ocean Section (GEOSECS) program in 1978 and
⁎ Corresponding author. E-mail address: [email protected] (S.K. Jha).
1998 (Povinec et al., 2003b; Mulsow et al., 2003), World Ocean Circulation Experiment (WOCE) program and marine survey in the region of Arabian Sea, by Department of Ocean Development (DOD) and National Institute of Oceanography during July–August 1983 (Sadarangani et al., 1990). Sensitive insight of the 137Cs activity concentration had not been revealed for Indian Ocean during these programs. The ineffectiveness in estimating the activity concentration of 137Cs in the forecasted region along India were mainly due to the number of constraints viz., requirement of large volume samples, cumbersome chemical separation, time constraint, financial constraint etc. During IAEA's Worldwide Marine Radioactivity Studies (WOMARS, 1995–2003), limited studies were carried out in Indian Oceans to understand the spatial variation of 137Cs in the Indian coastal region. Later Asia Pacific Marine Radioactivity Database (ASPAMARD) was developed jointly by IAEA Regional Co-operative Agreement and United Nation Development Program with the objectives to characterize the fate and behavior of key radionuclide contaminants in the regional sea. Input for most of the data contributed in ASPAMARD was through the project IAEA RAS/7/011, which focused on generating benchmark data on 137Cs activity concentration in coastal area. In this paper, we have attempted to trace the anthropogenic 137Cs activity concentration in sea water of Indian coastal region. This study will also help in understand the existing levels of 137Cs and its depletion from surface seawater. In terms of marine environment, India has a coastline of about 8000 km, an Exclusive Economic Zone (EEZ) of 2.02 million km2 adjoining the continental regions and the offshore lands and a very wide range of coastal ecosystems characterized by unique biotic and abiotic properties and processes (Venkataraman, 2003). The Indian Ocean differs from the Atlantic and Pacific Oceans in its limited northward extent to only 25°N. Indian subcontinent divides the Indian Ocean in the north into two tropical basins namely Arabian Sea (west) and Bay of Bengal
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Please cite this article as: Sartandel, S.J., et al., Latitudinal variation and residence time of 137Cs in Indian coastal environment, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.09.007
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(east) both being located within the same latitude and under the direct influence of monsoon. The Bay of Bengal is one of the largest freshwater and sediment input sites of the world oceans (Milliman and Meade, 1983). It is surrounded on three sides by land masses. The semi-enclosed nature of bay and its proximity to the equator makes it different from the ocean. Along the east coast of Indian border in the Bay of Bengal, six large river drains from India and the seventh one, Irrawaddy from Myanmar. The coastal area surrounding Indian peninsula consists of shallow coastal zone where both current and mixing process is intense. It is also under the influence of river runoff, intertidal effect, and contrast nature of shoreline (bare rocks to extensive mud flats), seasonal variability of physical and biological phenomena, man-made constructions and pollutant discharges. Contemplating the above facts, sampling was carried out at the sea water depth of minimum 10 m. The desirable depth for sampling was achieved at the distance of 2 to 3 km from the coastal shore, reached by a motor boat along with inbuilt in-situ preconcentration sampling assembly. It was also ensured from salinity measurement, that sampling points are away from coastal influences. For the present study, thirty locations along the coast of India, as shown in Fig. 1, were studied. The coastal sampling points from 1 to 8 in the Arabian sea marked as Region I covering the coastal area of Gujarat and Maharashtra states (GJ & MH) are known for high salinity as compared to Bay of Bengal (Vinayachandran and Kurian, 2008). The locations from 9 to 16 considered in Region II (Fig. 1) cover the coastal area of Karnataka and Kerala states (KA & KL). Region III represents the remaining locations 17 to 30 in the Bay of Bengal and covers the coastal areas of four states Tamil
Nadu (TN), Andhra Pradesh (AP), Orissa (OR) and West Bengal (WB). The selected sampling locations also include the coastal regions of operating Indian nuclear power plants. Surface seawater was pumped up, from an average depth of 1 m and passed through sampling assembly containing micro-wound filter cartridge inserted in the filter housing. Pumped water passed through 5 cartridges arranged in a series. First three filter cartridges of pore size 10 μm, 5 μm, and 0.5 μm respectively were arranged for ensuring complete isolation of the suspended material like silt, plankton etc., and remaining two were one μm pore size copper ferrocyanide coated cartridges for adsorption of cesium isotope in dissolved phase (Sartandel et al., 2012). Two coated cartridges were connected in series for determining the adsorption efficiency of 137Cs. At each location approximately 1000 l of sea water was pumped at the flow rate of a 4–5 l/min. After pre-concentration, the cartridges were packed in well-labeled polyethylene bags and brought to the laboratory for further processing. Simultaneously two/three sets of samples were collected to confirm the uniformity of measurement by this method. The pre-concentrated copper ferrocyanide cartridges were ashed in a furnace at 400 °C and filled in a standard plastic container of 4.2 cm × 4.0 cm (DxH). N-type high purity germanium coaxial detector Detector System (GmbH DSG make) with 50% relative efficiency and a resolution of 2.0 keV, coupled with 8 K MCA was used for the gamma spectrometric analysis. Natural background due to cosmic and surrounding terrestrial radioactivity was reduced by enclosing the detector system in a 7.5 cm thick low background lead shielding arrangement. The analysis of acquired gamma ray spectrum was carried out with the
Fig. 1. Sampling location around the Indian coast.
Please cite this article as: Sartandel, S.J., et al., Latitudinal variation and residence time of 137Cs in Indian coastal environment, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.09.007
S.J. Sartandel et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
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Table 1 Results of analysis of 134Cs and 137Cs in Internationally organized Proficiency Test. Proficiency Test
Radionuclide
Matrix
IAEA-RCA RAS/7/021 proficiency test
134
Sea water
Cs 137 Cs 137 Cs 137 Cs 137 Cs
Korea Research Institute of Standards and Science IAEA-CU-2007-04 IAEA-TEL-2011-04
RICE Spinach Spiked water1 Spiked water2 soil Spiked water Spiked water
137
IAEA-TEL-2012-03 IAEA-TEL-2014-03
Cs Cs 137 Cs 134 Cs 137 Cs 137 Cs 134
Spiked Seaweed Sediment
help of software PHAST (BARC make) and the net area was converted to activity in Bq m−3. IAEA reference material IAEA-330 spinach and IAEA154 whey powder in the similar geometry as that of the sample were used for efficiency calibration of the spectrometer. Absolute detector efficiency value was calculated using prominent gamma energy 661.6 keV of 137 Cs. Background and sample counting time were kept the same to ensure good counting statistics. The activity levels for 137Cs in the measured samples were computed using the following equation Activity
Bq m‐3 ¼
ðN−BÞ ðT γ ε0 ðEÞ ε V Þ
N — gross counts; B — background counts; T — counting time (sec); γ — gamma emission probability; ε'(E) — photopeak efficiency of detector; ε — cartridge collection efficiency; V — Volume of Sea water in m3;
Activity (Bq kg−1) Target Value
Laboratory Value
0.0734 ± 0.0013 0.1003 ± 0.0011 3.04 ± 0.29 1415.9 ± 89 3.1 ± 0.1 4.4 ± 0.1 14.4 ± 0.6 102.5 ± 0.75 21.4 ± 0.2 12.06 ± 0.1 8.27 ± 0.2 22.96 ± 0.45 12.0 ± 0.4
0.0707 ± 0.0043 0.1027 ± 0.0064 3.1 ± 0.3 1235.0 ± 35 3.39 ± 0.21 4.72 ± 0.11 13.7 ± 0.3 100.6 ± 3.2 21.32 ± 0.5 12.14 ± 0.21 8.58 ± 0.88 23.25 ± 1.1 13.45 ± 0.7
C2 cartridge collection efficiency ε was calculated as ¼ 1− C1 where C1 and 137 −3 Cs in Bq m retained in the first and second C2 are the activity of cartridge. Minimum detection limit (95% degree of confidence) was estimated for counting time of 1000 min using the statistical law (IAEA, 1989). The detection limit 0.02 Bq m−3 for 137Cs was achieved by this technique. Details of the method, including calibration were discussed elsewhere (Sartandel et al., 2012). For estimating salinity and temperature of water, a refractometer and a bucket thermometer were used. The method adopted for present work was validated during proficiency test organized in the frame of the IAEA Technical Cooperation project RAS/7/021, “Marine benchmark study on the possible impact of Fukushima radioactive releases in the Asia Pacific Region” (Jha et al., 2013). The quality control/assurance of analysis carried out at the laboratory has been confirmed by participating in the proficiency tests organized by the IAEA ALMERA network and other international
Table 2 137 Cs activity concentration in surface sea water along the coast of India. Sample code
Region
Sampling Location
No. of samples
Latitude °N
Longitude °E
Mean Activity Concentration (Bq m−3)
Salinity (%ο)
Temperature (οC)
SW1 SW2 SW3 SW4 SW5 SW6 SW7 SW8
Region I
Okha Pore Bandar Diu Nava Bandar Daman Tarapur Alibagh Murud Ratnagiri
3 2 3 3 3 2 3 3
22.49 21.62 20.72 20.48 19.86 18.63 18.28 16.98
27.0 27.1 27.0 27.2 27.0 27.1 27.0 27.3
Region II
Karwar Udpi Mangalore Kasarkode Kozhikode Appuzha Kollam Trivendram
3 3 3 3 3 3 3 3
14.79 13.31 12.97 12.47 11.25 9.43 8.87 8.47
35.6 35.4 35.5 35.5 35.4 35.2 35.2 35
27.5 27.6 27.8 27.7 27.8 28.0 28.1 28.2
SW17 SW18 SW19 SW20 SW21 SW22 SW23 SW24 SW25 SW26 SW27 SW28 SW29 SW30
Region III
Nagarcoil Kanyakumari Tuticorin Rameshwaram Karikal Pondichery Chennai Nallore Machhilipatnam Vishakhapattanam Srikakulam Puri Paradweep Digha
3 3 3 3 3 3 3 3 3 3 3 3 2 2
8.09 8.05 8.78 8.99 10.88 11.91 13.06 14.26 16.17 17.69 18.20 19.78 21.31 21.58
0.78 ± 0.07 0.81 ± 0.07 0.73 ± 0.06 0.80 ± 0.09 0.73 ± 0.06 0.73 ± 0.07 0.67 ± 0.06 0.63 ± 0.06 0.74 ± 0.06 0.37 ± 0.03 0.73 ± 0.06 0.27 ± 0.02 0.36 ± 0.03 0.56 ± 0.05 0.36 ± 0.03 0.61 ± 0.05 0.55 ± 0.05 0.48 ± 0.16 1.30 ± 0.13 1.21 ± 0.10 0.89 ± 0.06 0.96 ± 0.07 1.09 ± 0.15 1.03 ± 0.11 0.97 ± 0.07 0.45 ± 0.04 0.24 ± 0.02 0.35 ± 0.04 0.09 ± 0.01 0.78 ± 0.06 0.75 ± 0.06 0.77 ± 0.06 0.78 ± 0.37
39.8 36.8 36.9 36.7 36.6 36.1 36.0 35.7
SW9 SW10 SW11 SW12 SW13 SW14 SW15 SW16
68.98 69.58 71.08 72.77 72.65 72.74 72.88 73.21 Mean 74.07 74.66 74.77 74.97 75.74 76.30 76.55 76.89 Mean 77.43 77.55 78.25 79.21 79.91 79.88 80.33 80.27 81.28 83.35 83.99 85.86 86.98 87.53 Mean
34.8 34.8 34.4 34.2 34.9 34.7 34.6 34.7 33.4 32.4 32 30.4 29.7 29.6
28.3 28.4 28.5 28.1 27.6 27.50 27.3 27.1 26.9 26.9 26.8 26.9 26.8 26.9
Please cite this article as: Sartandel, S.J., et al., Latitudinal variation and residence time of 137Cs in Indian coastal environment, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.09.007
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Table 3 Comparison of 137Cs activity concentration in Asia Pacific Regional Sea water. Cs Activity concentration (Bq m−3)
Region
137
Arabian Sea Bay of Bengal Indian Ocean Exclusive Economic Zone of east coast peninsular Malaysia (surface sea water) Philippines (Sulu sea) (depth of sample taken 5 m) Straits of Malacca (depth of sample taken 5 m) South China Sea (depth of sample taken 2.5 m) Gulf of Thailand Vietnam (1999–2002) Korea (surface sea water) Indian coastal Region
2.8–2.9 0.12–0.39 1.45–2.23 3.40–5.89 1.47–3.22 2.4–3.8 2.33–4.42 2.94–4.01 0.68–3.67 1.64–4.48 0.09–1.30
organizations. Table 1 shows the analytical performance evaluation of the analyzed samples in various matrices. The laboratory results are in good agreement with the target value. The performance evaluation in the IAEA proficiency tests confirms the reliability and traceability of the analytical measurement result of the laboratory. Table 2 gives the spatial distribution of 137Cs (decay corrected to Jan 2014) in surface water along with temperature and salinity for locations along the coast of Arabian Sea (Region I and II) and Bay of Bengal (Region III) in Indian Ocean. Table 3 compares the observed activity concentration of 137Cs in Indian coastal marine environment with 137 Cs activity concentration in Asia Pacific regional sea water. The range of 137Cs activity concentration (0.09–1.3 Bq m−3) in the present study was observed to be at lower side of range 0.26–11.47 Bq m−3 as appeared in the ASPAMARD (Duran et al., 2004). The 137Cs activity concentration v/s latitude was plotted to have a better representation of spatial variation, covering the entire region along the coast of India. 137Cs activity concentration in surface sea water in Region I (17°N to 22.5°N) along the Arabian Sea depicts uniform distribution (Fig. 2). This may be attributed to geochemical properties of 137Cs, favoring a stay of 137Cs in sea water particularly in dissolved form with negligible scavenging to the sediment (Nikano and Povinec, 2003). Variation of 137Cs activity concentration in sea water reflected in Region II (8°N to 15°N) may be due to factors such as scavenging to sediment, biogeochemical processes or primary productivity prevailing in the region (Livingston and Povinec, 2002). Fig. 3 gives the 137 Cs distribution along latitude 8°N to 21.6°N in Region III along the east coast of the country. The latitude band from 14°N to 19.25°N reflects higher depletion of cesium from sea water which could be due to high biological productivity prevailing in the area or scavenging to the sediment. The 137Cs activity concentration in the remaining locations of Region III
References IAEA TECDOC, 1429, 2005 Alam et al., 1996 Povinec et al., 2003b, 2011 Zaharudin et al., 2011 Yii and Zaharudin, 2007 Yii and Zaharudin, 2004 Yii and Zaharudin, 2004 Mahapanyawong et al., 1992 Lujaniene et al., 2004 Kim et al., 1997 Present study
(0.75–0.78 Bq m − 3 ) was observed to be similar to the values in Region I. To understand the temporal variation of 137Cs in surface sea water, published 137Cs activity concentration in surface sea water for locations adjoining Indian subcontinent were used. Table 4 gives the temporal variation of 137Cs activity concentration which includes results published by various authors for region adjoining Indian subcontinent. Sreekumaran et al. (1968) had carried study for surface seawater samples from the Arabian Sea and the Bay of Bengal during Indian Program of International Indian Ocean Expedition, 1962–63 and Angria Bank Expedition, 1964. Miyake et al. (1988) studied various locations in Bay of Bengal and Andaman during an expedition on cruise R. V. Hakaho in 1976 and 1977. Bourlat et al. (1996) reported 137Cs activity concentration ranging from 1.6–2.3 Bq m− 3 for Southwestern Indian Ocean from the survey in 1994. During the expedition of Indian Ocean Transect carried out in 1998, Povinec et al. (2003b) reported 137Cs activity concentration in surface water from 1.45–1.77 Bq m− 3 (for locations 5°N60°E–12°N50°E in proximity to Indian subcontinent). IAEA Worldwide marine radioactivity studies (WOMARS) carried out in Indian Oceans reported mean 137Cs surface water activity concentration level of 1.6 Bq m− 3 as on 2000. In this case, latitudinal Box 15 of published data was considered for locations in proximity to the Indian subcontinent (Povinec et al., 2004). In general, the concentration of 137Cs in surface water appears to decrease exponentially with time. Therefore, temporal variation of their concentrations in surface water may be described by flux model (Hirose et al., 1992). dc ¼ −K C dt where C is the concentration of given radionuclide's at time t and K is the flux coefficient. Here flux coefficient K = k + λ; the removal
Fig. 2. 137Cs in surface water in Region I and II along the west coast of Indian.
Please cite this article as: Sartandel, S.J., et al., Latitudinal variation and residence time of 137Cs in Indian coastal environment, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.09.007
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Fig. 3. 137Cs in surface water in Region III along the east Coast of India.
Table 4 Temporal Variation of 137Cs activity concentration in surface sea water for region adjoining Indian subcontinent. Mean 137Cs activity concentration (Bq m−3)
Reference
Remark if any
1963 8.45 1964 7.85 1976 4.07
Sreekumaran et al., 1968 Sreekumaran et al., 1968 Miyake et al., 1988
1977 3.82
Miyake et al., 1988
1998 1.79
Povinec et al., 2003b
2000 1.6 2014 0.69
Povinec et al., 2004 Present study
Overall average activity concentration of 137Cs in surface sea water of Arabian Sea and Bay of Bengal Average activity concentration of 137Cs in surface sea water of Arabian Sea Average activity concentration of 137Cs in surface sea water of Indian Ocean for locations 0°N94°E–6°N95°E adjoining Indian subcontinent Average activity concentration of 137Cs in surface sea water of Indian Ocean for locations 0°N94°E–5°N98°E adjoining Indian subcontinent Average concentration of 137Cs in surface sea water for locations 0°N70°E–12°N50°E in proximity to Indian subcontinent during Indian Ocean Transect expedition. GLOMARD Database Latitudinal Box 15 in Indian Ocean
Year
rate of 137Cs in surface sea water, is the combination of the radioactive decay constant λ and the removal coefficient (k) of 137Cs in surface sea water. dc ¼ −kC−λC dt Solution is C = Coe− (k + λ)t. The removal coefficient (k) of 137Cs in surface seawater depends on radioelement chemistry, scavenging etc. The effective half-life of 137Cs in surface water can be calculated from flux coefficient K. Time series analysis of 137Cs concentration in surface water was evaluated using the data summarized in Table 4 to understand the effective half-life of 137Cs in the region associated to the Indian subcontinent. Fig. 4 gives the temporal change in the surface radionuclide
concentration expressed by an exponential function in time. The removal rate (K) of 137Cs was found to be 0.05 y−1 resulting, an effective halflife of 13.8 ± 0.7 y in the surface water. The observed removal rate of 137 Cs in surface water was higher than the reported removal rates of 0.016 y−1 in the Sulu and Indonesian Sea, 0.029 y−1 in the South China Sea, and 0.033 y− 1 in the Bay of Bengal and Andaman Sea (Yamada et al., 2006). The obtained effective half-life for 137Cs in the surface water was observed to be lower as compared to the values reported for Indian, Atlantic and Pacific oceans given in Table 5. The lower effective half-life of 137Cs in a coastal area reflects other processes apart from advection, diffusion, and radioactive decay, responsible for scavenging of 137Cs from sea water. Thus, the present study reveals the latitudinal variation in 137Cs activity concentration and enhanced scavenging process in few locations. This also may be one of the reasons of getting a lower mean effective half-life of 13.8 ± 0.7 y for 137Cs radionuclide in the coastal area. The spatial distribution results also confer no fresh input of 137Cs in Indian coastal region.
Acknowledgments The authors would like to thank Dr. B. N. Jagatap, Director Chemistry Group, BARC and Dr. K. S. Pradeepkumar, Associate Director, HS & EG, for their constant encouragement and support towards this work. Authors
Table 5 Effective half life of 137Cs in surface water of different oceans.
Fig. 4. Time series analysis of 137Cs activity concentration in surface water.
Oceans
Half life (years)
References
Indian Ocean Atlantic Ocean Pacific Ocean Mean of World Ocean Indian Coastal Region
20.3 ± 1.8 22.3 ± 2.4 15.9 ± 4.3 28.6 ± 2.1 13.8 ± 0.7
Povinec et al., 2005 IAEA TECDOC, 1429, 2005 IAEA TECDOC, 1429, 2005 IAEA TECDOC, 1429, 2005 (Present study)
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Nikano, M., Povinec, P.P., 2003. Modelling and distribution of Plutonium in Pacific Ocean. J. Environ. Radioact. 69, 85–106. Povinec, P.P., du Bois, P.B., Kershaw, P.J., Nies, H., Scotto, P., 2003a. Temporal and spatial trends in the distribution of Cs-137 in surface waters of Northern European Seas a record of 40 years of investigations. Deep-Sea Res. II Top. Stud. Oceanogr. 50 (17–21), 2785–2801. Povinec, P.P., Delfanti, R., Gastaud, J., La Rosa, J., Morgenstern, U., Oregioni, B., Pham, M.K., Salvi, S., Top, Z., 2003b. Anthropogenic radionuclides in the Indian Ocean Surface water — the Indian Ocean transect 1988. Deep-Sea Res. II 50, 2751–2760. Povinec, P.P., Hirose, K., Honda, T., Ito, T., Scott, M.E., Togawa, O., 2004. Spatial distribution of 3H, 90Sr, 137Cs and 239,240Pu in surface waters of the Pacific and Indian Oceans — GLOMARD database. J. Environ. Radioact. 76, 113–137. Povinec, P.P., Aarkrog, A., Buesseler, K.O., Delfanti, R., Hirose, K., Hong, G.H., Ito, T., Livingston, H.D., Nies, H., Noshkin, V.E., Shima, S., Togawa, O., 2005. 90Sr, 137Cs and 239,240 Pu concentration surface water time series in the Pacific and Indian Oceans WOMARS results. J. Environ. Radioact. 81, 63–87. Povinec, P.P., Ayoma, M., Fukasawa, M., Hirose, K., Komwha, K., Sanchez-Cabeza, J.A., Crastaud, J., Jeskovasky, M., Levy, I., Sykoru, I., 2011. 137Cs water profile in the south Indian Ocean. An evidence for accumulation of pollutants in subtropical gyre. Prog. Oceanogr. 89, 17–30. Sadarangani, S.H., Gogate, S.S., Chhapgar, B.F., Krishnamoorthy, T.M., 1990. Tritium level in Arabian Sea. Bull. Radiat. Prot. 13 (1), 47–50. Sartandel, S.J., Jha, S.K., Puranik, V.D., 2012. Constraints in Gamma Spectrometry analysis of fallout 137Cs in coastal marine environment of Arabian sea in India. J. Radioanal. Nucl. Chem. 292, 995–998. Schmitz, W.J., 1995. On the inter basin-scale thermoline circulation reviews Rev. Rev. Geophys. 33 (2), 151–174. Sreekumaran, C., Gogate, S.S., Doghi, G.R., Sastry, V.N., Viswanathan, R., 1968. Distribution of Cesium-137 and Strontium-90 in the Arabian Sea and Bay of Bengal. Proc. Indiana Acad. Sci. 8, 629–631. UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation), 2000. Sources and Effects of Ionizing Radiation; Annex J. Exposure and Effects of Chernobyl Accident. United Nations, New York. Report to General Assembly. Venkataraman, K., 2003. Natural aquatic Ecosystems of India. Thematic Working Group, The National Biodiversity Strategy Action Plan, India, pp. 1–275. Vinayachandran, P.N., Kurian, J., 2008. Modeling Indian ocean circulation Bay of Bengal fresh plume and Arabian Sea mini warm pool. Proceedings of the 12th Asian Congress of Fluid Mechanics, Korea. Yamada, M., Zheng, J., Wang, Z.-L., 2006. 137Cs, 239 + 240Pu and 240Pu/239Pu atom ratios in the surface waters of the western North Pacific Ocean, eastern Indian Ocean and their adjacent seas. Sci. Total Environ. 366, 242–252. Yii, M.W., Zaharudin, A., 2004. Determination of 137Cs in seawater surrounding peninsular Malaysia — a case study. Nucl. Relat. Tech. 1 (2), 17. Yii, M.W., Zaharudin, A., 2007. Concentration of 137Cs in sea water surrounding East Malaysia. J. Radioanal. Nucl. Chem. 274 (2), 323–329. Zaharudin, A., Zal, W.M., Hidayah, S., Yii, M., Bakar, A., 2011. Radioactivity in the exclusive economic zone of east coast peninsular Malaysia: distribution trends of Cs in surface seawater. J. Radioanal. Nucl. Chem. 287 (1), 329–334.
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Latitudinal variation and residence time of 137Cs in Indian coastal environment S.J. Sartandel, S.K. Jha ⁎, R.M. Tripathi Health Physics Division, Bhabha Atomic Research Center, Mumbai 400 085, India
a r t i c l e
i n f o
Article history: Received 25 March 2015 Received in revised form 18 August 2015 Accepted 1 September 2015 Available online xxxx Keywords: 137 Cs activity concentration Pre-concentration Coastal surface water Effective half-life
a b s t r a c t Anthropogenic 137Cs activity concentration, in surface sea water along the western and eastern coast of India has been estimated using the in-situ pre-concentration approach. Activity levels of 137Cs ranges from 0.09– 1.30 Bq m−3 with an overall mean of 0.69 ± 0.29 Bq m−3. Latitudinal variation and higher depletion in activity concentration of 137Cs at few locations were observed. Temporal change of 137Cs in sea water along Indian coast unveils a lower effective half-life of 13.8 ± 0.7 y in comparison to Asia Pacific regional sea water. The results prevailed that the spatial distribution confers no fresh input of 137Cs in Indian coastal region. © 2015 Elsevier Ltd. All rights reserved.
Marine environment is a major sink for anthropogenic radionuclides from global fallout, released during nuclear weapons tests performed on a large scale mainly by US and former USSR during 1960s, nuclear accident and discharges from the nuclear power plants (Povinec et al., 2003a; UNSCEAR, 2000). The activity concentration of 137Cs in the Indian coastal marine environment can be traced due to global fallout (Jha et al., 2003). The concentrations of global fallout radionuclide in sea water were measured since 1950s with an aim to assess the radiological impact from Nuclear weapon test on the marine environment and humans. Considering the usefulness of these studies, fallout radionuclide's have been used as a tracer to investigate the movement of water mass in the world oceans. The Indian Ocean plays a significant role in the global circulation of water mass. Perceptive of the coastal processes too play remarkable role in the protection of the marine environment against contamination due to anthropogenic sources. A global thermohaline circulation (conveyer belt) has been proposed as global ocean circulation model connecting the ocean basins with surface warm water and bottom cold water (Schmitz, 1995). A transport of warm surface water from North Pacific through Indonesian via Indian Ocean is well documented (Gordon et al., 2003). The Indian Ocean represents the most fragile part of the global ocean circulation because of its flow via Southern Ocean. This circulation pattern may be responsible for migration of anthropogenic radionuclide from one part of the ocean to another. Number of studies have been conducted for understanding the flux of anthropogenic radionuclide's in the Indian Oceans encompassed under Geochemical Ocean Section (GEOSECS) program in 1978 and
⁎ Corresponding author. E-mail address: [email protected] (S.K. Jha).
1998 (Povinec et al., 2003b; Mulsow et al., 2003), World Ocean Circulation Experiment (WOCE) program and marine survey in the region of Arabian Sea, by Department of Ocean Development (DOD) and National Institute of Oceanography during July–August 1983 (Sadarangani et al., 1990). Sensitive insight of the 137Cs activity concentration had not been revealed for Indian Ocean during these programs. The ineffectiveness in estimating the activity concentration of 137Cs in the forecasted region along India were mainly due to the number of constraints viz., requirement of large volume samples, cumbersome chemical separation, time constraint, financial constraint etc. During IAEA's Worldwide Marine Radioactivity Studies (WOMARS, 1995–2003), limited studies were carried out in Indian Oceans to understand the spatial variation of 137Cs in the Indian coastal region. Later Asia Pacific Marine Radioactivity Database (ASPAMARD) was developed jointly by IAEA Regional Co-operative Agreement and United Nation Development Program with the objectives to characterize the fate and behavior of key radionuclide contaminants in the regional sea. Input for most of the data contributed in ASPAMARD was through the project IAEA RAS/7/011, which focused on generating benchmark data on 137Cs activity concentration in coastal area. In this paper, we have attempted to trace the anthropogenic 137Cs activity concentration in sea water of Indian coastal region. This study will also help in understand the existing levels of 137Cs and its depletion from surface seawater. In terms of marine environment, India has a coastline of about 8000 km, an Exclusive Economic Zone (EEZ) of 2.02 million km2 adjoining the continental regions and the offshore lands and a very wide range of coastal ecosystems characterized by unique biotic and abiotic properties and processes (Venkataraman, 2003). The Indian Ocean differs from the Atlantic and Pacific Oceans in its limited northward extent to only 25°N. Indian subcontinent divides the Indian Ocean in the north into two tropical basins namely Arabian Sea (west) and Bay of Bengal
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Please cite this article as: Sartandel, S.J., et al., Latitudinal variation and residence time of 137Cs in Indian coastal environment, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.09.007
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(east) both being located within the same latitude and under the direct influence of monsoon. The Bay of Bengal is one of the largest freshwater and sediment input sites of the world oceans (Milliman and Meade, 1983). It is surrounded on three sides by land masses. The semi-enclosed nature of bay and its proximity to the equator makes it different from the ocean. Along the east coast of Indian border in the Bay of Bengal, six large river drains from India and the seventh one, Irrawaddy from Myanmar. The coastal area surrounding Indian peninsula consists of shallow coastal zone where both current and mixing process is intense. It is also under the influence of river runoff, intertidal effect, and contrast nature of shoreline (bare rocks to extensive mud flats), seasonal variability of physical and biological phenomena, man-made constructions and pollutant discharges. Contemplating the above facts, sampling was carried out at the sea water depth of minimum 10 m. The desirable depth for sampling was achieved at the distance of 2 to 3 km from the coastal shore, reached by a motor boat along with inbuilt in-situ preconcentration sampling assembly. It was also ensured from salinity measurement, that sampling points are away from coastal influences. For the present study, thirty locations along the coast of India, as shown in Fig. 1, were studied. The coastal sampling points from 1 to 8 in the Arabian sea marked as Region I covering the coastal area of Gujarat and Maharashtra states (GJ & MH) are known for high salinity as compared to Bay of Bengal (Vinayachandran and Kurian, 2008). The locations from 9 to 16 considered in Region II (Fig. 1) cover the coastal area of Karnataka and Kerala states (KA & KL). Region III represents the remaining locations 17 to 30 in the Bay of Bengal and covers the coastal areas of four states Tamil
Nadu (TN), Andhra Pradesh (AP), Orissa (OR) and West Bengal (WB). The selected sampling locations also include the coastal regions of operating Indian nuclear power plants. Surface seawater was pumped up, from an average depth of 1 m and passed through sampling assembly containing micro-wound filter cartridge inserted in the filter housing. Pumped water passed through 5 cartridges arranged in a series. First three filter cartridges of pore size 10 μm, 5 μm, and 0.5 μm respectively were arranged for ensuring complete isolation of the suspended material like silt, plankton etc., and remaining two were one μm pore size copper ferrocyanide coated cartridges for adsorption of cesium isotope in dissolved phase (Sartandel et al., 2012). Two coated cartridges were connected in series for determining the adsorption efficiency of 137Cs. At each location approximately 1000 l of sea water was pumped at the flow rate of a 4–5 l/min. After pre-concentration, the cartridges were packed in well-labeled polyethylene bags and brought to the laboratory for further processing. Simultaneously two/three sets of samples were collected to confirm the uniformity of measurement by this method. The pre-concentrated copper ferrocyanide cartridges were ashed in a furnace at 400 °C and filled in a standard plastic container of 4.2 cm × 4.0 cm (DxH). N-type high purity germanium coaxial detector Detector System (GmbH DSG make) with 50% relative efficiency and a resolution of 2.0 keV, coupled with 8 K MCA was used for the gamma spectrometric analysis. Natural background due to cosmic and surrounding terrestrial radioactivity was reduced by enclosing the detector system in a 7.5 cm thick low background lead shielding arrangement. The analysis of acquired gamma ray spectrum was carried out with the
Fig. 1. Sampling location around the Indian coast.
Please cite this article as: Sartandel, S.J., et al., Latitudinal variation and residence time of 137Cs in Indian coastal environment, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.09.007
S.J. Sartandel et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
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Table 1 Results of analysis of 134Cs and 137Cs in Internationally organized Proficiency Test. Proficiency Test
Radionuclide
Matrix
IAEA-RCA RAS/7/021 proficiency test
134
Sea water
Cs 137 Cs 137 Cs 137 Cs 137 Cs
Korea Research Institute of Standards and Science IAEA-CU-2007-04 IAEA-TEL-2011-04
RICE Spinach Spiked water1 Spiked water2 soil Spiked water Spiked water
137
IAEA-TEL-2012-03 IAEA-TEL-2014-03
Cs Cs 137 Cs 134 Cs 137 Cs 137 Cs 134
Spiked Seaweed Sediment
help of software PHAST (BARC make) and the net area was converted to activity in Bq m−3. IAEA reference material IAEA-330 spinach and IAEA154 whey powder in the similar geometry as that of the sample were used for efficiency calibration of the spectrometer. Absolute detector efficiency value was calculated using prominent gamma energy 661.6 keV of 137 Cs. Background and sample counting time were kept the same to ensure good counting statistics. The activity levels for 137Cs in the measured samples were computed using the following equation Activity
Bq m‐3 ¼
ðN−BÞ ðT γ ε0 ðEÞ ε V Þ
N — gross counts; B — background counts; T — counting time (sec); γ — gamma emission probability; ε'(E) — photopeak efficiency of detector; ε — cartridge collection efficiency; V — Volume of Sea water in m3;
Activity (Bq kg−1) Target Value
Laboratory Value
0.0734 ± 0.0013 0.1003 ± 0.0011 3.04 ± 0.29 1415.9 ± 89 3.1 ± 0.1 4.4 ± 0.1 14.4 ± 0.6 102.5 ± 0.75 21.4 ± 0.2 12.06 ± 0.1 8.27 ± 0.2 22.96 ± 0.45 12.0 ± 0.4
0.0707 ± 0.0043 0.1027 ± 0.0064 3.1 ± 0.3 1235.0 ± 35 3.39 ± 0.21 4.72 ± 0.11 13.7 ± 0.3 100.6 ± 3.2 21.32 ± 0.5 12.14 ± 0.21 8.58 ± 0.88 23.25 ± 1.1 13.45 ± 0.7
C2 cartridge collection efficiency ε was calculated as ¼ 1− C1 where C1 and 137 −3 Cs in Bq m retained in the first and second C2 are the activity of cartridge. Minimum detection limit (95% degree of confidence) was estimated for counting time of 1000 min using the statistical law (IAEA, 1989). The detection limit 0.02 Bq m−3 for 137Cs was achieved by this technique. Details of the method, including calibration were discussed elsewhere (Sartandel et al., 2012). For estimating salinity and temperature of water, a refractometer and a bucket thermometer were used. The method adopted for present work was validated during proficiency test organized in the frame of the IAEA Technical Cooperation project RAS/7/021, “Marine benchmark study on the possible impact of Fukushima radioactive releases in the Asia Pacific Region” (Jha et al., 2013). The quality control/assurance of analysis carried out at the laboratory has been confirmed by participating in the proficiency tests organized by the IAEA ALMERA network and other international
Table 2 137 Cs activity concentration in surface sea water along the coast of India. Sample code
Region
Sampling Location
No. of samples
Latitude °N
Longitude °E
Mean Activity Concentration (Bq m−3)
Salinity (%ο)
Temperature (οC)
SW1 SW2 SW3 SW4 SW5 SW6 SW7 SW8
Region I
Okha Pore Bandar Diu Nava Bandar Daman Tarapur Alibagh Murud Ratnagiri
3 2 3 3 3 2 3 3
22.49 21.62 20.72 20.48 19.86 18.63 18.28 16.98
27.0 27.1 27.0 27.2 27.0 27.1 27.0 27.3
Region II
Karwar Udpi Mangalore Kasarkode Kozhikode Appuzha Kollam Trivendram
3 3 3 3 3 3 3 3
14.79 13.31 12.97 12.47 11.25 9.43 8.87 8.47
35.6 35.4 35.5 35.5 35.4 35.2 35.2 35
27.5 27.6 27.8 27.7 27.8 28.0 28.1 28.2
SW17 SW18 SW19 SW20 SW21 SW22 SW23 SW24 SW25 SW26 SW27 SW28 SW29 SW30
Region III
Nagarcoil Kanyakumari Tuticorin Rameshwaram Karikal Pondichery Chennai Nallore Machhilipatnam Vishakhapattanam Srikakulam Puri Paradweep Digha
3 3 3 3 3 3 3 3 3 3 3 3 2 2
8.09 8.05 8.78 8.99 10.88 11.91 13.06 14.26 16.17 17.69 18.20 19.78 21.31 21.58
0.78 ± 0.07 0.81 ± 0.07 0.73 ± 0.06 0.80 ± 0.09 0.73 ± 0.06 0.73 ± 0.07 0.67 ± 0.06 0.63 ± 0.06 0.74 ± 0.06 0.37 ± 0.03 0.73 ± 0.06 0.27 ± 0.02 0.36 ± 0.03 0.56 ± 0.05 0.36 ± 0.03 0.61 ± 0.05 0.55 ± 0.05 0.48 ± 0.16 1.30 ± 0.13 1.21 ± 0.10 0.89 ± 0.06 0.96 ± 0.07 1.09 ± 0.15 1.03 ± 0.11 0.97 ± 0.07 0.45 ± 0.04 0.24 ± 0.02 0.35 ± 0.04 0.09 ± 0.01 0.78 ± 0.06 0.75 ± 0.06 0.77 ± 0.06 0.78 ± 0.37
39.8 36.8 36.9 36.7 36.6 36.1 36.0 35.7
SW9 SW10 SW11 SW12 SW13 SW14 SW15 SW16
68.98 69.58 71.08 72.77 72.65 72.74 72.88 73.21 Mean 74.07 74.66 74.77 74.97 75.74 76.30 76.55 76.89 Mean 77.43 77.55 78.25 79.21 79.91 79.88 80.33 80.27 81.28 83.35 83.99 85.86 86.98 87.53 Mean
34.8 34.8 34.4 34.2 34.9 34.7 34.6 34.7 33.4 32.4 32 30.4 29.7 29.6
28.3 28.4 28.5 28.1 27.6 27.50 27.3 27.1 26.9 26.9 26.8 26.9 26.8 26.9
Please cite this article as: Sartandel, S.J., et al., Latitudinal variation and residence time of 137Cs in Indian coastal environment, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.09.007
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Table 3 Comparison of 137Cs activity concentration in Asia Pacific Regional Sea water. Cs Activity concentration (Bq m−3)
Region
137
Arabian Sea Bay of Bengal Indian Ocean Exclusive Economic Zone of east coast peninsular Malaysia (surface sea water) Philippines (Sulu sea) (depth of sample taken 5 m) Straits of Malacca (depth of sample taken 5 m) South China Sea (depth of sample taken 2.5 m) Gulf of Thailand Vietnam (1999–2002) Korea (surface sea water) Indian coastal Region
2.8–2.9 0.12–0.39 1.45–2.23 3.40–5.89 1.47–3.22 2.4–3.8 2.33–4.42 2.94–4.01 0.68–3.67 1.64–4.48 0.09–1.30
organizations. Table 1 shows the analytical performance evaluation of the analyzed samples in various matrices. The laboratory results are in good agreement with the target value. The performance evaluation in the IAEA proficiency tests confirms the reliability and traceability of the analytical measurement result of the laboratory. Table 2 gives the spatial distribution of 137Cs (decay corrected to Jan 2014) in surface water along with temperature and salinity for locations along the coast of Arabian Sea (Region I and II) and Bay of Bengal (Region III) in Indian Ocean. Table 3 compares the observed activity concentration of 137Cs in Indian coastal marine environment with 137 Cs activity concentration in Asia Pacific regional sea water. The range of 137Cs activity concentration (0.09–1.3 Bq m−3) in the present study was observed to be at lower side of range 0.26–11.47 Bq m−3 as appeared in the ASPAMARD (Duran et al., 2004). The 137Cs activity concentration v/s latitude was plotted to have a better representation of spatial variation, covering the entire region along the coast of India. 137Cs activity concentration in surface sea water in Region I (17°N to 22.5°N) along the Arabian Sea depicts uniform distribution (Fig. 2). This may be attributed to geochemical properties of 137Cs, favoring a stay of 137Cs in sea water particularly in dissolved form with negligible scavenging to the sediment (Nikano and Povinec, 2003). Variation of 137Cs activity concentration in sea water reflected in Region II (8°N to 15°N) may be due to factors such as scavenging to sediment, biogeochemical processes or primary productivity prevailing in the region (Livingston and Povinec, 2002). Fig. 3 gives the 137 Cs distribution along latitude 8°N to 21.6°N in Region III along the east coast of the country. The latitude band from 14°N to 19.25°N reflects higher depletion of cesium from sea water which could be due to high biological productivity prevailing in the area or scavenging to the sediment. The 137Cs activity concentration in the remaining locations of Region III
References IAEA TECDOC, 1429, 2005 Alam et al., 1996 Povinec et al., 2003b, 2011 Zaharudin et al., 2011 Yii and Zaharudin, 2007 Yii and Zaharudin, 2004 Yii and Zaharudin, 2004 Mahapanyawong et al., 1992 Lujaniene et al., 2004 Kim et al., 1997 Present study
(0.75–0.78 Bq m − 3 ) was observed to be similar to the values in Region I. To understand the temporal variation of 137Cs in surface sea water, published 137Cs activity concentration in surface sea water for locations adjoining Indian subcontinent were used. Table 4 gives the temporal variation of 137Cs activity concentration which includes results published by various authors for region adjoining Indian subcontinent. Sreekumaran et al. (1968) had carried study for surface seawater samples from the Arabian Sea and the Bay of Bengal during Indian Program of International Indian Ocean Expedition, 1962–63 and Angria Bank Expedition, 1964. Miyake et al. (1988) studied various locations in Bay of Bengal and Andaman during an expedition on cruise R. V. Hakaho in 1976 and 1977. Bourlat et al. (1996) reported 137Cs activity concentration ranging from 1.6–2.3 Bq m− 3 for Southwestern Indian Ocean from the survey in 1994. During the expedition of Indian Ocean Transect carried out in 1998, Povinec et al. (2003b) reported 137Cs activity concentration in surface water from 1.45–1.77 Bq m− 3 (for locations 5°N60°E–12°N50°E in proximity to Indian subcontinent). IAEA Worldwide marine radioactivity studies (WOMARS) carried out in Indian Oceans reported mean 137Cs surface water activity concentration level of 1.6 Bq m− 3 as on 2000. In this case, latitudinal Box 15 of published data was considered for locations in proximity to the Indian subcontinent (Povinec et al., 2004). In general, the concentration of 137Cs in surface water appears to decrease exponentially with time. Therefore, temporal variation of their concentrations in surface water may be described by flux model (Hirose et al., 1992). dc ¼ −K C dt where C is the concentration of given radionuclide's at time t and K is the flux coefficient. Here flux coefficient K = k + λ; the removal
Fig. 2. 137Cs in surface water in Region I and II along the west coast of Indian.
Please cite this article as: Sartandel, S.J., et al., Latitudinal variation and residence time of 137Cs in Indian coastal environment, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.09.007
S.J. Sartandel et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
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Fig. 3. 137Cs in surface water in Region III along the east Coast of India.
Table 4 Temporal Variation of 137Cs activity concentration in surface sea water for region adjoining Indian subcontinent. Mean 137Cs activity concentration (Bq m−3)
Reference
Remark if any
1963 8.45 1964 7.85 1976 4.07
Sreekumaran et al., 1968 Sreekumaran et al., 1968 Miyake et al., 1988
1977 3.82
Miyake et al., 1988
1998 1.79
Povinec et al., 2003b
2000 1.6 2014 0.69
Povinec et al., 2004 Present study
Overall average activity concentration of 137Cs in surface sea water of Arabian Sea and Bay of Bengal Average activity concentration of 137Cs in surface sea water of Arabian Sea Average activity concentration of 137Cs in surface sea water of Indian Ocean for locations 0°N94°E–6°N95°E adjoining Indian subcontinent Average activity concentration of 137Cs in surface sea water of Indian Ocean for locations 0°N94°E–5°N98°E adjoining Indian subcontinent Average concentration of 137Cs in surface sea water for locations 0°N70°E–12°N50°E in proximity to Indian subcontinent during Indian Ocean Transect expedition. GLOMARD Database Latitudinal Box 15 in Indian Ocean
Year
rate of 137Cs in surface sea water, is the combination of the radioactive decay constant λ and the removal coefficient (k) of 137Cs in surface sea water. dc ¼ −kC−λC dt Solution is C = Coe− (k + λ)t. The removal coefficient (k) of 137Cs in surface seawater depends on radioelement chemistry, scavenging etc. The effective half-life of 137Cs in surface water can be calculated from flux coefficient K. Time series analysis of 137Cs concentration in surface water was evaluated using the data summarized in Table 4 to understand the effective half-life of 137Cs in the region associated to the Indian subcontinent. Fig. 4 gives the temporal change in the surface radionuclide
concentration expressed by an exponential function in time. The removal rate (K) of 137Cs was found to be 0.05 y−1 resulting, an effective halflife of 13.8 ± 0.7 y in the surface water. The observed removal rate of 137 Cs in surface water was higher than the reported removal rates of 0.016 y−1 in the Sulu and Indonesian Sea, 0.029 y−1 in the South China Sea, and 0.033 y− 1 in the Bay of Bengal and Andaman Sea (Yamada et al., 2006). The obtained effective half-life for 137Cs in the surface water was observed to be lower as compared to the values reported for Indian, Atlantic and Pacific oceans given in Table 5. The lower effective half-life of 137Cs in a coastal area reflects other processes apart from advection, diffusion, and radioactive decay, responsible for scavenging of 137Cs from sea water. Thus, the present study reveals the latitudinal variation in 137Cs activity concentration and enhanced scavenging process in few locations. This also may be one of the reasons of getting a lower mean effective half-life of 13.8 ± 0.7 y for 137Cs radionuclide in the coastal area. The spatial distribution results also confer no fresh input of 137Cs in Indian coastal region.
Acknowledgments The authors would like to thank Dr. B. N. Jagatap, Director Chemistry Group, BARC and Dr. K. S. Pradeepkumar, Associate Director, HS & EG, for their constant encouragement and support towards this work. Authors
Table 5 Effective half life of 137Cs in surface water of different oceans.
Fig. 4. Time series analysis of 137Cs activity concentration in surface water.
Oceans
Half life (years)
References
Indian Ocean Atlantic Ocean Pacific Ocean Mean of World Ocean Indian Coastal Region
20.3 ± 1.8 22.3 ± 2.4 15.9 ± 4.3 28.6 ± 2.1 13.8 ± 0.7
Povinec et al., 2005 IAEA TECDOC, 1429, 2005 IAEA TECDOC, 1429, 2005 IAEA TECDOC, 1429, 2005 (Present study)
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Please cite this article as: Sartandel, S.J., et al., Latitudinal variation and residence time of 137Cs in Indian coastal environment, Marine Pollution Bulletin (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.09.007