Scholarly article on topic 'Activity of 210Po and 210Pb in the riverine environs of coastal Kerala on the southwest coast of India'

Activity of 210Po and 210Pb in the riverine environs of coastal Kerala on the southwest coast of India Academic research paper on "Earth and related environmental sciences"

CC BY-NC-ND
0
0
Share paper
Keywords
{" 210Po" / " 210Pb" / Sediment / River / Kerala}

Abstract of research paper on Earth and related environmental sciences, author of scientific article — N. Venunathan, Y. Narayana

Abstract The paper presents the systematic investigations on the activity concentrations of 210Po and 210Pb in the riverine environs of Bharathapuzha, Periyar and Kallada, the three major rivers of coastal Kerala. The radionuclides 210Po and 210Pb in sediment and water samples were separated using radiochemical methods and activity was counted using scintillation based alpha counting system. The mean value of 210Po activity in sediment samples was found to be 3.4 Bq kg−1, 40.0 Bq kg−1 and 22.5 Bq kg−1 in Bharathapuzha, Periyar and Kallada river respectively. The mean value of 210Pb activity was found to be 13.5 Bq kg−1, 88.7 Bq kg−1 and 60.8 Bq kg−1 in the sediment samples of Bharathapuzha, Periyar and Kallada river respectively. The activity ratio 210Po/210Pb shows that the radionuclides 210Po and 210Pb are not in equilibrium in the riverine environs and the accumulation of 210Pb in sediment is greater than that of 210Po. The disequilibrium between 210Po and 210Pb and the higher activity of 210Pb indicates the presence of unsupported 210Pb in the sediments. A significant correlation was observed between the concentrations of these radionuclides and organic matter content and clay minerals of the sediment samples. The low activity of 210Po and 210Pb was observed in the dissolved phase due to the removal of these particle reactive radionuclides from solution to particle. High Kd value for 210Po and 210Pb in water column indicates that there is a strong adsorption of these radionuclides on to the suspended particles in the aquatic environment, where suspended particulate matter acts as a carrier to transport and removal of 210Po and 210Pb from their site of production.

Academic research paper on topic "Activity of 210Po and 210Pb in the riverine environs of coastal Kerala on the southwest coast of India"

CÔ

Journal of

ëj adiation m\. ese arch & Applied Sciences

HOSTED BY

ELSEVIER

Available online at www.sciencedirect.com

ScienceDirect

Journal of Radiation Research and Applied

Sciences

journal homepage: http://www.elsevier.com/locate/jrras

Activity of Po and Pb in the riverine environs ^CrossMark of coastal Kerala on the southwest coast of India

N. Venunathan*, Y. Narayana

Department of Studies in Physics, Mangalore University, Mangalagangothri, 574199 Karnataka, India

ARTICLE INFO

ABSTRACT

Article history:

Received 21 December 2015 Accepted 6 May 2016 Available online 24 May 2016

Keywords:

210Po 210Pb

Sediment

Kerala

The paper presents the systematic investigations on the activity concentrations of 210Po and 210Pb in the riverine environs of Bharathapuzha, Periyar and Kallada, the three major rivers of coastal Kerala. The radionuclides 210Po and 210Pb in sediment and water samples were separated using radiochemical methods and activity was counted using scintillation

based alpha counting system. The mean value of 210Po activity in sediment samples was found to be 3.4 Bq kg-1,40.0 Bq kg-1 and 22.5 Bq kg-1 in Bharathapuzha, Periyar and Kallada river respectively. The mean value of 210Pb activity was found to be 13.5 Bq kg-1, 88.7 Bq kg-1 and 60.8 Bq kg-1 in the sediment samples of Bharathapuzha, Periyar and Kallada river respectively. The activity ratio 210Po/210Pb shows that the radionuclides 210Po and 210Pb are not in equilibrium in the riverine environs and the accumulation of 210Pb in sediment is greater than that of 210Po. The disequilibrium between 210Po and 210Pb and the higher activity of 210Pb indicates the presence of unsupported 210Pb in the sediments. A significant correlation was observed between the concentrations of these radionuclides and organic matter content and clay minerals of the sediment samples. The low activity of

210Po and 210Pb was observed in the dissolved phase due to the removal of these particle reactive radionuclides from solution to particle. High Kd value for 210Po and 210Pb in water column indicates that there is a strong adsorption of these radionuclides on to the suspended particles in the aquatic environment, where suspended particulate matter acts as a carrier to transport and removal of 210Po and 210Pb from their site of production. Copyright © 2016, The Egyptian Society of Radiation Sciences and Applications. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

Natural radionuclides are present at low concentration in soil, water, air and food. The level of terrestrial environmental radiation depends primarily on the geological and geographical conditions and can be different levels in the soils of each different geological region (Karadeniz, Karakurt,

& Akal, 2015). The radionuclides 210Po and 210Pb, widely present in the terrestrial environment, are the final long lived radionuclides in the decay of 238U in the earth's crust. Their presence in the atmosphere is due to the decay of 222Rn diffusing from the ground. These radionuclides return to earth's surface as a result of dry fallout or are washed out in rain (Ozden, Ugur, Esetlili, Esetlili, & Kurucu, 2013). The distribution and behavior of 210Po in the marine environment

* Corresponding author. Tel.: +91 9446169002. E-mail address: venunathan.nittoor@gmail.com (N. Venunathan).

Peer review under responsibility of The Egyptian Society of Radiation Sciences and Applications. http://dx.doi.org/10.1016/j.jrras.2016.05.002

1687-8507/Copyright © 2016, The Egyptian Society of Radiation Sciences and Applications. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

have been under study for many years, primarily due to its enhanced bio-accumulation, its strong affinity for binding with certain internal tissues, and its importance as a contributor to natural radiation dose received by marine biota as well as humans consuming seafood (Fowler, 2011). Due to its half-life of about 22.3 years, 210Pb has proved to be an important nuclide for studying the sedimentary processes (Mahmood, Ishak, Bakar, Ishak, & Mohamed, 2011). Since 210Pb has a short residence time in atmosphere, it falls into lake or ocean, tends to bury in sediment and over a few months becomes permanently fixed on the sediment particles (Tee, Ahmad, & Mohamed, 2003). In water-marine environment 210Pb is scavenged by suspended particulate matter by several mechanisms and accumulated in the sediments (Aycik, Citaku, Erten, & Salihoglu, 2004). Since 210Po and 210Pb contribute about 8% of the natural radiation exposure to humans (UNSCEAR, 1988), it is important to acquire and analyze base line data about the concentrations of these ra-dionuclides in the terrestrial and aquatic environment.

The southwest coast of Kerala is one of the known high background radiation areas of the world. Studies reported in literature suggest that the source of radionuclides in the high background radiation area can be traced to the rocks in the catchment area of the major rivers. The radionuclides released during the weathering of these rocks are transported by rivers to the sea and subsequently deposited on the beach areas. Different geo-chemical processes influence the interaction of dissolved radionuclide with suspended matter and sediments. Sedimentation and resuspension are of importance for controlling the two-way migration of radionuclide from water column to sediments and vice-versa (Monte et al., 2005). So it is important to study the nature and transport of radionuclides in river environment. In view of this, an attempt was made to study the transport and distribution of 210Po and 210Pb in sediment, water and suspended particulate matter of major rivers of coastal Kerala, namely, Bhar-athapuzha, Periyar and Kallada. To understand the affinities of these radionuclides for particulate matter, the distribution coefficients (Kd) for 210Po and 210Pb were studied and reported. Correlation between the activities of 210Po and 210Pb and the influence of physico-chemical parameters on the speciation of these radionuclides in the riverine environs was analyzed. The results of these investigations are presented and discussed in this paper.

2. Materials and methods

2.1. Study area

In the present study sediment samples were collected from three major rivers of coastal Kerala namely, Bharathapuzha, Periyar and Kallada (Fig. 1). Bharathapuzha is the second longest river in Kerala (209 km) with catchment area of 4400 km2 within Kerala. It originates from Anamalai Hills in Western Ghats and discharges into Arabian Sea along coastal Kerala. It originates in a charnockite territory and flows through mignatite terrain. The hinterland consists of crystalline rocks of Archean age and sediments of Tertiary age. The Crystalline includes charnockite and khondalite, granite

Fig. 1 - Map showing sampling locations.

gneisses and granite traversed by basic rocks. Charnockite is wide spread in hill ranges of Western Ghats. Hornblende and biotite gneisses occur locally and are derived by retrograde metamorphism and mignatization of biotite gneiss Khonda-litic rocks are exposed in south Kerala. Latterite is the product of residual chemical weathering of both crystalline rocks and Tertiary sediments and forms flat topped hills and ridges between the foothills of Western Ghats and Arabian Sea.

The Periyar River has a length of 244 km and is the longest river in Kerala, with drainage area 5398 km2. It is formed by confluence of large number of streams originating from Sivagiri Hills in Western Ghats and discharges into Kodun-gallur Lake which opens to Arabian Sea. The river originates and follows through a metamorphic terrain consisting of charnockite garnet-sillimanite gneiss, garnet-biotite and hornblende-biotite gneiss besides magnetite and granite. Angamali to Kochi is the most industrialized zone of Periyar river basin. There are over 50 large and medium industries in this region. The industries such as monazite processing plant and fertilizer factory operate in the bank of this river. These industries also discharge waste to this river. The monazite and phosphate rock is known to contain trace levels of Uranium and its decay products.

The Kallada River has a length of 121 km with catchment area about 1699 km2. The river on its course encounters a number of geological formations, namely charnokiltes and khondalites, joins Astamudi Lake which opens to Arabian Sea. The river Kallada discharges into the Arabian Sea near Chavara, the known high background radiation area. These

high background radiation areas are formed due to the deposition of monazite mineral, which contain radioactive thorium.

Radionuclides 210Pb and 210Po are found in small quantities in most soils and sediments as part of Uranium decay series. They are also produced as natural fallout from atmosphere by radioactive decay of 222Rn. The main sources 210Pb and 210Po in sediments is the decay of 226Ra in the sediment matrix and the wet and dry precipitation from air and rinse from soil and rock materials and their runoff with interstitial water to rivers. Therefore the activity of 210Pb and 210Po in riverine environs largely depends on the local geology in the catchment areas of the river and the kind of industrial discharge operating on the river bank.

Sample collection and processing

Sampling stations were identified along the length of the river with a distance of about 10-20 km between them, keeping in view of the local geology and ready accessibility. The sediment samples were collected using a grab sampler. The samples used in the study were collected from the top layer (<15 cm deep) of sediments representing fresh sediments. Three to four grabs were collected from a cross section at a distance 5-10 m from the river bank and they are pooled together. The samples were collected in polythene bags and brought to laboratory for further processing.

The ignition method was employed in the measurement of organic matter percentage in the samples. The oven dried samples were kept in a muffle furnace for about 24 h, whose temperature was maintained at 550 °C. The organic matter percentage was then calculated using weight loss method on ignition (Lee & Lee, 1997). The sediment pH was measured using standard procedure. In the present study 10 g dried sediment sample was taken and 100 ml distilled water was added to make a suspension of 1:10 w/v dilution. The pH of the sample was measured using m pH system 361 (Narayana & Rajashekara, 2010a, 2010b).

For separation of sand silt and clay fractions, about 20 g sediments were taken from the samples. Organic matter was then removed by oxidizing with 30% H2O2 and carbonate material was subsequently dissolved using 10% acetic acid. After washing 2-3 times, sand was separated by wet sieving using ASTM 230 sieve. The residual fraction was used for pipette analysis to obtain the percentage of silt and clay based on Stokes law (Roy, 1987).

The electrochemical deposition method was employed for the determination of 210Po activity (Iyengar, Ganapathy, Kannan, Rajan, & Rajaram, 1990). The sediment samples were dried in an oven at 110 °C until a constant dry weight was obtained. About 20 g of each sample was leached with 4 M HNO3 and then the organic matter present in the samples was destroyed by adding 3:1 mixture of HNO3 and HClO4 in small increments till white residue appears. The samples were then converted to 1 M HCl medium and 210Po in the solution was deposited on a silver disc using magnetic stirrer at 97 ° C for 6 h (Iyengar et al., 1990; Narayana, Shetty, & Siddappa, 2006). The disc was then washed with distilled water, rinsed with alcohol, dried under infrared lamp and then alpha activity was counted on both sides using a ZnS(Ag) alpha counter of 30%

efficiency. The chemical recovery of 210Po was determined using 209Po as yield tracer by alpha spectrometry (Narayana & Rajashekara, 2010a, 2010b). The percentage recovery ranged from 85% to 95% with a mean value 90%. The activity was then calculated using the formula,

,„ „ , 100 100

A = (S±SD) x — x — ;

1000 W

where S - net count per second, SD - standard deviation, E -efficiency of alpha counter, EP - percentage plating efficiency, W - dry weight of the sample in grams.

The activity of 210Pb was estimated through 210Po by allowing the 210Po plated solution for a period of 12 months to build up the 210Po from 210Pb (Iyengar et al., 1990).

For the analysis of water samples, about 40 l of water was collected from each sampling location and samples were filtered to separate suspended particles through pre-weighed Whatman filter paper (pore size 0.45 mm). The solution was brought into acidic condition (pH ~2) by adding HCl. About 5 ml iron carrier was added to the water sample and stirred for about 30 min. Ammonia solution was added till the solution become base (pH ~9). The thick Ferric chloride precipitate formed was then dissolved in 1 N HCl and 210Po in the solution was deposited on a silver disc using magnetic stirrer at 97 °C for 6 h (Kavitha, Chandrashekara, & Paramesh, 2015). The activity of 210Pb in water samples was estimated by re-growth of210Po.

Results and discussions

3.1. Activity of 210Po and 210Pb in sediment samples

The activity of 210Po and 210Pb in sediment samples of Bhar-athapuzha, Periyar and Kallada river is shown in Figs. 2-4. The physico-chemical parameters of the sediment samples are presented in Table 1. In the sediment samples of Bhar-athapuzha 210Po activity varied from 2.1 Bq kg-1 to 4.8 Bq kg-1 with mean value 3.4 Bq kg-1 and the activity of 210Pb varied from 9.3 Bq kg-1 to 20.8 Bq kg-1 with mean value 13.5 Bq kg-1. In the Periyar river sediment the 210Po activity varied in the range 10.7 Bq kg-1 to 58.9 Bq kg-1 with mean value 40.0 Bq kg-1 and the 210Pb activity ranged from 18.5 Bq kg-1 to

40 60 80 100 120 140 Distance from Origin (Km)

Fig. 2 - Variation of 210Po and 210Pb activity with distance from origin - Bharathapuzha river.

40 60 80 100 120 140 Distance from Origin (Km)

Fig. 3 - Variation of 210Po and 210Pb activity with distance from origin - Periyar river.

90.0 80.0 5^70.0 ¿f 60.0 g 50.0 £■40.0

20 30 40 50 60 70 Distance from Origin (Km)

Fig. 4 - Variation of 210Po and 210Pb activity with distance from origin - Kallada river.

127.6 Bq kg-1with mean value 88.7 Bq kg-1. In the Kallada river the activity of 210Po in the sediment varied from 15.1 Bq kg-1 to 29.6 Bq kg-1 with mean value 22.5 Bq kg-1 and the activity of 210Pb varied from 35.9 Bq kg-1 to 81.9 Bq kg-1with mean value 60.8 Bq kg-1.

Both 210Po and 210Pb activity was found to be low in the samples of Bharathapuzha river sediment, compared with Periyar and Kallada river samples. This could be due to the low percentage of organic matter present in the samples of Bharathapuzha river sediment (Table 1). The relatively higher concentration of 210Po and 210Pb in Periyar river could be due to the inputs from untreated waste water from industrial and agricultural sources. The discharges from monazite ore processing plant and the fertilizer factory, which operates on the banks of the river contribute to the elevated levels of 210Po and

210Pb in this river environment. The monazite and phosphate rocks are known to contain trace levels of uranium, radium and their progeny including 210Po and 210Pb. The river Kallada discharges into the Arabian sea near Chavara, the known high background radiation area on the southwest coast of India. These high background areas are formed due to the monazite deposits, which contain radioactive thorium and their progeny. The source for the high background area has been traced to the rocks in the catchment areas of river Kallada. The thorium bearing monazite minerals released due to the weathering of rocks in the catchment areas are transported by the river to the sea and these minerals were subsequently deposited on the beach area due to the wave action of the sea.

However, the activity 210Po and 210Pb in the riverine environment of Kallada was found to be slightly less than in Periyar river. This indicates that the source and geochemical behavior of these radionuclides are different from that of thorium. There is an increasing trend in the activity of 210Po and 210Pb from the upper to lower reaches in the sediment samples of Kallada river (Fig. 3). The 210Po and 210Pb content in the sediment samples near estuarine environment of this river was found to be higher compared to the activity in the upper reaches of the riverine environment. This could be due to larger percentage of clay minerals present in the sediment samples of the estuarine environment compared to the clay content in the sediment samples of the upper reaches of this river (Rajashekara, Narayana, & Siddappa, 2008).

Activities of 210Po and 210Pb in the sediment samples were found to increase with organic matter and clay minerals in the samples (Table 1). The fine grain size fractions offer larger surface area for the adsorption of radionuclides. The pH value also effects adsorption process and solubilization of radio-nuclides in soil and sediments (Saxena, 1987). The pH value of sediment samples of the Bharathapuzha environment was found to vary from 6.8 to 7.7. For Periyar and Kallada river environments the pH ranged from 7.2 to 7.8 and 6.9 to 7.5 respectively. No significant correlation was found between the activity of 210Po and 210Pb with pH as the pH was near neutral and not very variable. The natural distribution of 210Po in the environment is integrally dependant on that of its progenitor 210Pb. With a half life of 22.3 years, the in growth of 210Pb is slow and its environmental transport largely controls the distribution of 210Po. If 222Rn decays in situ then the chemistry of 210Pb will largely control the fate of 210Po subsequently produced (Matthews, Kim, & Martin, 2007). In river system the concentration of 210Po and 210Pb in water and sediments depends on the geology of the watershed and weathering conditions (Ugur, Yeener, & Bassari, 2002), while the geochemistry of the parent 238U and its speciation also play a significant role (Skwarzec, Struminska, Borylo, & Falandysz, 2004). The natural linkage between 210Po and 210Pb explains why most studies of their environmental behavior consider the two nuclides together, often with special attention to their concentration ratios.

In the present study the mean value of activity ratio of 210Po and 210Pb was found to be 0.26, 0.47 and 0.37 respectively for Bharathapuzha, Periyar and Kallada rivers. The results show that these two radionuclides are not in equilibrium and the accumulation of 210Pb is much more compared to 210Po in the riverine environs. The observed disequilibrium between 210Po and 210Pb is due to biogeochemical process which controls the distribution of these nuclides. Higher activity of 210Pb compared to 210Po may be due to the longer duration of 210Pb that exists within a matrix and relatively faster removal of 210Po from its site of production by chemical means (Eisenbud, 1987; Narayana & Rajashekara, 2010a). The disequilibrium may also be due to the effective sequestering of 210Pb by organic matter (Durrance, 1986). The disequilibrium between 210Po and 210Pb and the higher activity of 210Pb indicate the presence of unsupported 210Pb in the sediments. This indicates that in addition to in-situ radioactive decay of 226Ra, the atmospheric precipitation of 222Rn also contributes to the activity of 210Pb in river sediments. Similar findings were also

Table 1 - Physico-chemical characteristics of sediment

reported by Parfenov (1974). The depositional flux of 210Pb at any given site depends on the 222Rn concentration in air and the scavenging efficiency by rain. Because 222Rn is a chemically inert gas that enters the atmosphere from geological materials, 210Pb is associated with submicron-size aerosols which are removed by precipitation and deposited on the earth's surface (Kanai, 2013). In water column it is readily removed to the bottom through adsorption on particulate matter within a week or a month (Kanai, 2013).

The correlation between activity concentrations of 210Po and 210Pb shows a good correlation with correlation coefficient r = 0.74, r = 0.98 and r = 0.97 respectively for Bhar-athapuzha, Periyar and Kallada river (Figs. 5-7). The organic matter content was determined in the sediment samples and the activity of 210Po and 210Pb was correlated with organic matter content. The 210Po activity and organic matter content in the Bharathapuzha river were correlated with a good correlation coefficient of 0.95. A moderate correlation with correlation coefficient 0.63 was observed for 210Pb activity with organic matter in the Bharathapuzha river environment. For Periyar and Kallada rivers the correlations between 210Po activity and organic matter contents were found to be 0.94 and 0.96 respectively. The 210Pb activities of Periyar and Kallada rivers were correlated with organic matter with correlation coefficients of 0.95 and 0.90 respectively. The activity

concentration of 210Po and 210Pb in sediment samples depends on organic matter content in the samples.

The variation of 210Po activity and clay contents in sediment samples of Bharathapuzha, Periyar and Kallada rivers was correlated with coefficients of 0.92, 0.88 and 0.97 respectively. A low positive correlation (r = 0.53) was found between the activity of 210Pb and clay content in the sediment samples of Bharathapuzha river environment. For Periyar and Kallada river environments the corresponding correlations were found to be 0.91 and 0.93 respectively.

The results obtained in the present study are compared with values reported in the literature for other environs. Activity of 210Po and 210Pb obtained for Periyar and Kallada rivers is comparable with reported values of 65 Bq kg-1 and 63 Bq kg-1 for Breboviscica river sediment (Vreck, Benedik, & Pihlar, 2004) and 56 Bq kg-1of French river sediment (Descamps & Foulquier, 1998). The values obtained in this study are very low compared with the reported mean values of 311 Bq kg-1 (210Po) and 215 Bq kg-1 (210Pb) for the sediment samples of El Hamraween area of Red sea, Egypt (Salahel Din & Vesterbacka, 2012). The 210Po activity concentrations in Bharathapuzha river sediment samples are comparable with reported values of 4.5 Bq kg-1 to 17 Bq kg-1 for coastal region of UK (Mc Donald, Cook, & Baxter, 1992). The 210Pb activity in the Kallada river environment is comparable with the reported values of 27 Bq kg-1 to 91 Bq kg-1 for the sediment samples in the Izmir Bay, Turkey (Sacan et al., 2010).

3.2. Activity of 210Po and 210Pb in water

Activity of 210Po and 210Pb in the water samples collected from the rivers are presented in Fig. 8. The activity of 210Po in the water samples of Bharathapuzha river ranged from 18 to 43 mBq l-1 with a mean value 32 mBq l-1. The activity of 210Po in Periyar and Kallada river water samples was found to be in the range 92-179 mBq l-1 with mean value 146 mBq l-1 and 57-167 mBq l-1 with mean value 121 mBq l-1respectively. Activity of 210Pb in the water samples collected from Bhar-athapuzha, Periyar and Kallada rivers was found to be in range 42-88 mBq l-1 with mean value 71 mBq l-1, 120-198 mBq l-1 with mean value 171 mBq l-1 and 75-167 mBq l-1 with mean value 121 mBq l-1respectively. Water from these rivers is mainly used for irrigation and drinking purpose. So the annual

5.0 H-1-1-1-1-1-1

2.0 2.5 3.0 3.5 4.0 4.5 5.0 210Po Activity (Bq kg"1)

Fig. 5 - Correlation between 210Po and 210Pb activity -Bharathapuzha river.

samples.

River/sampling ; Organic pH Size fraction (%)

station matter (%) Clay Silt Sand

Bharathapuzha

BT1 0.7 7.7 6.1 5.4 88.5

BT2 0.4 7.5 4.2 5.1 90.7

BT3 0.6 7.6 5.9 6.4 87.7

BT4 0.5 7.4 4.8 9.6 85.6

BT5 0.5 7.5 4.9 8.3 86.8

BT6 0.6 6.8 5.3 10.2 84.5

BT7 0.4 7.1 4.6 8.4 87.0

BT8 0.6 7.3 5.7 6.2 88.1

Range 0.4-0.7 6.8-7.7 4.2-6.1 5.1-10.2 84.5-90.7

Periyar

PT1 5.3 7.6 16.2 18.5 65.3

PT2 5.1 7.3 10.1 8.4 81.5

PT3 6.3 7.8 20.3 14.2 65.5

PT4 1.8 7.3 8.6 13.1 78.3

PT5 8.5 7.5 28.3 18.5 53.2

PT6 11.6 7.2 30.6 25.2 44.2

PT7 13.2 7.5 35.3 16.4 48.3

PT8 12.5 7.2 32.4 26.6 41.0

Range 1.8-13.2 7.2-7.8 8.6-35.3 8.4-26.6 41-81.5

Kallada

KT1 2.7 7.5 9.4 4.2 86.4

KT2 2.0 7.2 6.7 12.2 81.1

KT3 2.5 7.5 8.7 8.1 83.2

KT4 3.0 7.3 10.2 18.4 71.4

KT5 3.8 7.4 12.1 15.6 72.3

KT6 5.7 6.9 14.7 12.1 73.2

KT7 5.4 7.1 16.4 20.5 63.1

KT8 6.1 7.3 17.8 14.2 68.0

Range 2.0-6.1 6.9-7.5 6.7-17.8 4.2-20.5 63.1-86.4

Îf o<

140.0 120.0 100.0 80.0 60.0 40.0 20.0 0.0

r = 0.98

10.0 20.0 30.0 40.0 50.0 60.0 210Po Activity (Bq kg"1)

Fig. 6 - Correlation between 210Po and 210Pb activity -Periyar river.

90.0 80.0 S 70.0

•f" 60.0

% 50.0 «

s 40.0

r = 0.97

14.0 19.0 24.0 29.0

210Po Activity (Bq kg1)

Fig. 7 - Correlation between 210Po and 210Pb activity -Kallada river.

effective dose due 210Po injection in water was calculated on the basis of the conversion factor of 1.2 x 10-6 Sv Bq-1 for 210Po (Marbaniang, Poddar, Nongkynrih, & Khathing, 2010). The average value of the annual effective dose due to 210Po injection in drinking water was found to be 28, 128 and 83 mSv year-1 for Bharathapuzha, Periyar and Kallada river respectively. The values obtained for Periyar and Kallada rivers are higher than the recommended limit of 50 mSv year-1 (WHO, 1993).

Significant correlation was found between the activity of 210Po in sediments and water samples with correlation coefficient 0.92, 0.96 and 0.97 respectively for Bharathapuzha, Periyar and Kallada river environment. For 210Pb activity the corresponding correlation coefficients were found to be 0.46, 0.89 and 0.97 respectively for Bharathapuzha, Periyar and Kallada. This could be due to the release of 210Po and 210Pb from surface sediments via resuspension (Tanaka, Takeda, & Tsunogai, 1983).

3.3. Behavior of210Po and 210Pb in water column

B1 B2 B3 B4 B5 B6 B7 B8 PI P2 P3 P4 P5 P6 P7 P8 K1 K2 K3 K4 K5 K6 K7 K8 Bharathapuzha Periyar Kallada

Sampling Stations

Fig. 8 - Activity of 210Po and 210Pb in water samples.

physico-chemical aspects of the dissolved and particulate phase interaction. In this study distribution coefficient was calculated using the following equation (Saili & Mohamed, 2014).

Kd = Ap/(Ad x TSP)

where Ap is the activity of 210Po and 210Pb in the particulate phase (Bq kg-1), Ad is the activity of 210Po and 210Pb in the dissolved phase (Bq kg-1) and TSP is the total suspended particle (g l-1).

The Kd value for 210Po ranged from 13 x 106 to 64 x 106 l kg-1, 10 x 106 to 91 x 106 l kg-1 and 14 x 106 to 31 x 106 l kg-1 respectively for Bharathapuzha, Periyar and Kallada river. The Kd value for 210Pb was found to be in the range 12 x 106 to 62 x 1061 kg-1,11 x 106 to 88 x 1061 kg-1 and 30 x 106 to 54 x 106 l kg-1 respectively for Bharathapuzha, Periyar and Kallada river. High Kd value for 210Po and 210Pb indicates that there is a strong adsorption of these radionu-clides on to the suspended particles in the aquatic environment. Data obtained in this study showed a significant negative correlation between the Kd value and concentration of suspended particulate matter with correlation coefficient 0.72, 0.94 and 0.87 for 210Po and 0.70, 0.95 and 0.85 for 210Pb in Bharathapuzha, Periyar and Kallada river environment respectively. This inverse relation between Kd and concentration of TSP is commonly found for various metals (Wei & Murray, 1994). This correlation is attributed to the presence of colloidal ligand phase in the filter-passing fraction, and particle-particle interactions (Wei, Lin, Wen, & Sheu, 2012). This result showed that 210Po and 210Pb had an affinity to suspended particles in the riverine environment. Polonium-210 is generally found in natural water in the form of Po (IV), which is slightly soluble due to the hydrolysis of Po (IV) and the formation of colloids, and has a high affinity to the particulate phase (Ansoborlo et al., 2011). TSP plays an important role in controlling the scavenging of 210Po and 210Pb. The scavenging process by aggregation of colloidal matter and adsorption on to particulate matter influenced the mobilization of 210Po and 210Pb in the water column (Saili & Mohamed, 2014).

The distribution coefficient (Kd) is widely used as an approach of understanding and determining the metals and radionuclides released in to the aquatic environment (Alam, Mohamed, Arifin, & Mokhtar, 2015). According to Abril and Fraga (1996), mathematical equation has been formulated to describe the behavior of selected contaminants based on

4. Conclusion

The radionuclides 210Po and 210Pb are not in equilibrium in the riverine environs of Bharathapuzha, Periyar and Kallada and the accumulation of 210Pb is higher than 210Po in the riverine

environs. The higher activity of 210Pb in the riverine environment when compared to 210Po can be attributed to the difference in the geochemical pathways of these two radionuclides. Significant correlations were observed between the activity concentration of 210Po and 210Pb for these rivers. This indicates that individual activity of one radionuclide is a good predictor of the other. The mean value of 210Po and 210Pb activity was found to be high for Periyar river sediment samples compared to Bharathapuzha and Kallada rivers. The higher activity in Periyar can be traced to industrial activities on the banks of the river. Good positive correlations exist between the activity concentration of 210Po and 210Pb with organic matter and clay contents in the samples of the Periyar and Kallada river environment. Polonium enrichment was found to increase with clay minerals and organic matter. No significant correlation was found between 210Po and 210Pb activities with pH in sediments. Organic matter plays an important role in the accumulation and enrichment of 210Po and 210Pb in the riverine environs. A significant negative correlation was found between Kd value and concentration of total suspended particles, which showed that 210Po and 210Pb had an affinity to suspended particles in the riverine environment. The suspended particulate matter plays an important role in controlling the scavenging of 210Po and 210Pb in water column.

REFERENCES

Abril, J. M., & Fraga, E. (1996). Some physical and chemical features of the variability of Kd distribution coefficients for radionuclides. Journal of Environmental Radioactivity, 30, 253-270.

Alam, L., Mohamed, C. A. R., Arifin, N. A. N., & Mokhtar, M. B. (2015). A study on seasonal variations of Po-210 levels in a coal burning power station area of Malaysia. Indian Journal of Geo-Marine Science, 44(3), 1-8.

Ansoborlo, E., Berard, P., Auwer, C. D., Leggett, R., Menetrier, F., Younes, A., et al. (2011). Review of chemical and radio toxicological properties of polonium for internal contamination purposes. Chemical Research in Toxicology, 25(8), 1551-1564.

Aycik, G. A., Citaku, D., Erten, H. N., & Salihoglu, I. (2004). Dating of Black Sea sediments from Romanian coast using natural 210Pb and fallout 137Cs. Journal of Radio Analytical and Nuclear Chemistry, 259(1), 177.

Descamps, B., & Foulquier, L. (1998). Radiation Protection Dosimetry, 24, 143-147.

Durrance, E. M. (1986). Radiation in geology; Principles and applications. Chichester: Ellis Horwood Ltd.

Eisenbud, M. (1987). Environmental radioactivity from natural, industrial and military sources (3rd ed.). California: Academic Press Inc.

Fowler, S. W. (2011). 210Po in the marine environment with emphasis on its behavior within the biosphere. Journal of Environmental Radioactivity, 102(5), 448-461.

Iyengar, M. A. R., Ganapathy, S., Kannan, V., Rajan, M. P., &

Rajaram, S. (16-18 April 1990). Procedure manual. Workshop on environmental radioactivity held at Kaiga, India.

Kanai, Y. (2013). High activity concentration of 210Pb and 7Be in sediments and their histories. Journal of Environmental Radioactivity, 124, 44-49.

Karadeniz, O., Karakurt, H., & Akal, C. (2015). Natural radionuclide activity in forest soil horizons of Mount IDA/Kazdagi, Turkey.

Environmental Monitoring and Assessment, 187. http://dx.doi.org/ 10.1007/s10661-015-4554-y.

Kavitha, E., Chandrashekara, M. S., & Paramesh, L. (201 5). 226Ra and 210Po concentration in drinking water of Cauvery river basin south interior Karnataka state, India. Journal of Radiation Research and Applied Sciences. http://dx.doi.org/10.1016/ j.jrras.2015.08.001.

Lee, M. H., & Lee, C. W. (1997). Distribution and characteristics of 239'240Pu and 137Cs in the soil of Korea. Journal of Environmental Radioactivity, 37(1), 1-16.

Mahmood, Z. U. W., Ishak, A. K., Bakar, N. S. A., Ishak, K., & Mohamed, C. A. R. (2011). Vertical distribution of 210Pb and 226Ra and their activity ratio in marine sediment core of the East Malaysia coastal waters. Journal of Radioanalytical Nuclear Chemistry, 289, 953-959.

Marbaniang, D. G., Poddar, R. K., Nongkynrih, P., & Khathing, D. T. (2010). 210-Polonium studies in some environmental and biological matrices of Domiasiat Uranium deposit area, West Khasi Hill, Meghalaya, India. Environmental Monitoring Assessment, 162, 347-353.

Matthews, K. M., Kim, C. K., & Martin, P. (2007). Determination of Po in environmental materials: A review of analytical methodology. Applied Radiation and Isotopes, 65, 267-279.

Mc Donald, P., Cook, G. T., & Baxter, M. S. (1992). Natural and anthropogenic radioactivity in coastal region of UK. Radiation Protection Dosimetry, 45, 707-710.

Monte, L., Boyer, P., Brittain, J. E., Hakanson, L., Lepicard, S., & Smithy, J. T. (2005). Review and assessment of models for predicting the migration of radionuclides through rivers. Journal of Environmental Radioactivity, 79, 273-296.

Narayana, Y., & Rajashekara, K. M. (2010a). Study of 210Po and 210Pb in riverine environments of Coastal Karnataka. Journal of Environmental Radioactivity, 110(6), 468-471.

Narayana, Y., & Rajashekara, K. M. (2010b). The importance of physico-chemical parameters on the speciation of natural radionuclides in riverine ecosystem. Journal of Environmental Radioactivity, 101(11), 958-964.

Narayana, Y., Shetty, P. K., & Siddappa, K. (2006). Behaviour of 210Po and 210Pb in high background areas of coastal Kerala on the south west coast of India. Applied Radiation and Isotopes, 64(3), 396-401.

Ozden, B., Ugur, A., Esetlili, T., Esetlili, B. S., & Kurucu, Y. (2013). Assessment of the effects of physical-chemical parameters on 210Po and 210Pb concentrations in cultivated and uncultivated soil from different areas. Geoderma, 19, 7-11.

Parfenov, Y. D. (1974). Polonium-210 in the environment and in the human organism. Atomic Energy Review, 12, 75-143.

Rajashekara, K. M., Narayana, Y., & Siddappa, K. (2008).

Distribution of 210Po and 210Pb in the riverine environs of Coastal Karnataka. Journal of Radioanalytical and Nuclear Chemistry, 277(2), 379-388.

Roy, C. L. (1987). A practical approach to sedimentology. London and Boston: Alan and Unwin.

Sacan, S., Ugur, A., Sunlu, U., Buyukisik, B., Aksu, M., & Sunlu, F. S. (2010). The 210Po and 210Pb levels in surface sediment samples in the Imzir Bay (Aegean Sea-Turkey). Environmental Monitoring and Assessment, 161, 575-582.

Saili, N. A. B., & Mohamed, C. A. R. (2014). Behavior of 210Po and 210Pb in shallow water region of Mersing estuary, Johor, Malaysia. Environment Asia, 7(2), 7-18.

Salahel Din, K., & Vesterbacka, P. (2012). Radioactivity levels in some sediment samples from Red Sea and Baltic Sea. Radiation Protection Dosimetry, 148(1), 101-106.

Saxena, M. M. (1987). Environmental analysis of water, soil and air (p. 134). India: Agro Botanical Publishers.

Skwarzec, B., Struminska, D. I., Borylo, A., & Falandysz, J. (2004). Intake of 210Po, 234U and 238U radionuclides in beer in Poland. Journal of Radioanalytical and Nuclear Chemistry, 261(3), 661-663.

Tanaka, N., Takeda, Y., & Tsunogai, S. (1983). Biological effect on removal of Th-234, Po-210 and Pb-210 from surface water in Funka Bay, Japan. Geochimica et Cosmochimica Acta, 47(10), 1783-1790.

Tee, L. T., Ahmad, Z., & Mohamed, C. A. R. (2003). Estimation of sedimentation rates using 210Pb and 210Po at the coastal water of Sabah, Malaysia. Journal of Radioanalytical and Nuclear Chemistry, 256(1), 115-120.

Ugur, A., Yeener, G., & Bassari, A. (2002). Trace metals and 210Po (210Pb) concentration in mussel (Mytilus galloprouincialis) consumed at western Anatolia. Applied Radiation and Isotopes, 57, 565-571.

UNSCEAR. (1988). Sources, effects and risk of ionizing radiation. Report to the General Assembly. New York, USA.

Vreck, P., Benedik, L., & Pihlar, B. (2004). Determination of 210Po and 210Pb in sediment and soil latches and in biological materials using a Sr-resin column and evaluation of column reuse. Applied Radiation and Isotopes, 60, 717-723.

Wei, C. L., Lin, S. Y., Wen, L. S., & Sheu, D. D. D. (2012).

Geochemical behavior of 210Po and 210Pb in the nearshore waters of western Taiwan. Marine Pollution Bulletin, 64, 214-220.

Wei, C. L., & Murray, J. W. (1994). The behavior of scavenging isotopes in marine anoxic environments: Lead-210 and Polonium-210 in water column of the Black Sea. Geochimica et Cosmochimica Acta, 58, 1795-1811.

WHO. (1993). Guidelines for drinking water quality. Geneva: World Health Organization.