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Behavior of 210Po and 210Pb in high background areas of coastal Kerala on the south west coast of India
ARTICLE IN PRESS
Applied Radiation and Isotopes 64 (2006) 396–401 www.elsevier.com/locate/apradiso
Behavior of 210Po and 210Pb in high background areas of coastal Kerala on the south west coast of India Y. Narayana, P.K. Shetty, K. Siddappa Department of Studies in Physics, Mangalore University, Mangalagangothri, 574199, India Received 19 May 2005; received in revised form 6 August 2005; accepted 7 August 2005
Abstract This paper deals with the distribution and behavior of 210Po and 210Pb in beach sand and surface soil samples from the Quilon district of Kerala. Beach sand and soil samples were collected and analyzed for 210Po and 210Pb radionuclides using standard radiochemical analytical techniques. Mean activities of 210Po and 210Pb were found to be maximum in the samples collected at 20 m away from waterline. Among the beach sand samples, the activities of radionuclide were found to be maximum for samples from most of the regions of Chavara and few regions of Neendakara. The activity of 210Po was found to vary from 2.4 to 20.5 Bq kg 1 with a mean value of 8.3 Bq kg 1 at the water line, 2.5–19.9 Bq kg 1 with a mean value of 10.2 Bq kg 1 at 20 m away from the waterline, and 2.1–6.7 Bq kg 1 with a mean value of 3.5 Bq kg 1 at 40 m away from waterline. The respective values found for 210Pb were from 1.2 to 48.2 Bq kg 1 with a mean value of 14.9, 11.3–34.2 Bq kg 1 with a mean value of 19.8 Bq kg 1 and 2.3 to 18.3 Bq kg 1 with a mean value of 8.7 Bq kg 1. The depth profile study indicated the mean activity of 210Po to decrease with depth for samples collected 20 m away from waterline whereas the activity slightly increases with depth 40 m away from sea. The activity concentration of 210Po and 210Pb in surface beach sand shows good correlation, with a correlation coefficient 0.81. r 2005 Elsevier Ltd. All rights reserved. Keywords: Polonium-210; Lead-210; Kerala; Sand and soil
1. Introduction High natural background radiation areas are of special interest, indicating anomalous conditions in their geological features and consequently in the background radiation levels. One of the prime sources of high background radiation level is the presence of radioactive monazite. One of the regions in India within which high background radiation levels have been reported is from the coastal areas of Quilon district in Kerala. Monazite sands are known to contain thorium with some amount of 238U and 40K (Eisenbud, 1987). The radionuclides 210Po and 210Pb are the final radioactive members of the 238U series and are widely present in the environment, due to the decay of 222Rn in the atmosphere, Corresponding author. Tel.: +91 824 2287363; fax: +91 824 2287367.
E-mail address: [email protected] (Y. Narayana). 0969-8043/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2005.08.016
contributing about 8% of the natural radiation exposure to humans (United Nations Scientific Committee on the Effects of Atomic Radiation, 1988). However data available on the distribution of 210Po and 210Pb in sand and soils of high background radiation areas is sparse. In view of this, detailed studies on the radiation level and radionuclide activity concentration in different environmental matrices of high background area have been undertaken. As a part of this programme, the distribution and enrichment of 210 Po and 210Pb were studied in the region identified above. The soil and beach sand samples collected from different depths in the Karunagapalli, Chavara, Neendakara and Kollam beach areas were analysed for 210Po and 210Pb activity. An attempt is made in this investigation to study the distribution, enrichment, vertical profile, and activity ratios of 210Po and 210Pb and the influence of organic matter content on these radionuclides in surface soil and beach sand samples.
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whose temperature was maintained at 550 1C. The organic matter percentage was then calculated by weight loss. The clay content was also measured.
2. Materials and methods 2.1. Sample collection The study area covers the Quilon district of Kerala on the south west coast of India, extending over a coastal length of about 30 km (Fig. 1). Standard techniques were followed in the collection of samples. Sand samples were collected from the sea water line, 20 m and 40 m away from the waterline at each sampling location. The samples were taken from depth intervals of 0–10, 10–20 and 20–30 cm, except for that at the waterline where sand was collected from the surface (0–10 cm). The surface soil samples were also collected from inland regions of the beach area, about 1 km away from the shoreline. For soil sampling, undisturbed ground surfaces situated away from public roads and building were selected. The samples were individually collected in polythene bags and brought to the laboratory for analysis. 2.2. Organic matter and clay content measurement The ignition method was employed in the measurement of organic matter percentage in the soil sample (Lee and Lee, 1997). The samples were oven-dried in a furnace
2.3. Sample processing and activity measurement The electrochemical deposition method was employed for determination of 210Po (Iyengar et al., 1990), both for soil and sand samples. The sand and soil samples were dried in an oven at 110 1C until a constant dry weight was obtained. From the fresh and dry weight, the moisture content was calculated. The dried samples were leached with 4 M HNO3 and then the organic matter present in the sample was destroyed by digestion by adding a HNO3+ H2O2 mixture in small increments to obtain a white residue. Each sample was then converted into a 0.5 M HCl medium. 210Po in the solution was deposited onto a silver disc at 97 1C for 6 h (Iyengar et al., 1990). The disc was then washed with distilled water, rinsed with alcohol, dried under an infrared lamp and the a activity was counted using a ZnS(Ag) alpha counter of 30% efficiency (manufactured by the Electronic Corporation of India Limited, Hydarabad). The activity of 210Pb was estimated through 210Po, allowing the 210Po-plated solution for a period of 12 months to build up the 210Po from 210Pb (Iyengar et al., 1990).
Fig. 1. Map showing sample locations.
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3.2. Vertical profile of
3. Results and discussions 3.1. Variation of
210
Po and
210
Pb activity in sand
The results of measurement of 210Po and 210Pb activity concentrations for surface beach sand samples (0–10 cm), taken at different distances from the sea waterline, are given in Table 1. As can be seen, the activity of 210Po varies from 2.4 to 20.5 Bq kg 1 with a mean value of 8.3 Bq kg 1 at the water line, 2.5–19.9 Bq kg 1 with a mean value of 10.2 Bq kg 1 at 20 m away from the waterline, and 2.1–6.7 Bq kg 1 with a mean value of 3.5 Bq kg 1 at 40 m away from waterline. The maximum activity was found for Chavara beach sand, while the minimum was found for samples obtained at Karunagarapalli. The mean activity of 210 Po was found to be maximum in samples collected at 20 m away from waterline. It can also be seen that the respective activities of 210Pb are from 1.2 to 48.2 Bq kg 1 with a mean value of 14.9, 11.3–34.2 Bq kg 1 with a mean value of 19.8, and 2.3–18.3 Bq kg 1 with a mean value of 8.7 Bq kg 1. Again, the maximum activity was observed at Chavara beach sand, while the minimum activity of 210Pb was found in Kollam beach sand. The mean activity of 210 Pb was found to be maximum for samples collected 20 m away from waterline.
Table 1 The activity concentration and activity ratios of
210
Po and
Po and
210
Pb
The results of measurement of 210Po and 210Pb activity concentrations at different depths in beach sand samples are given in Table 2. The mean values of activity of 210Po at 20 m away from waterline were found to be 10.2, 8.0 and 7.7 Bq kg 1 for the depth intervals of 0–10, 10–20 and 20–30 cm respectively. The mean values of activity of 210Po were 3.5, 3.7 and 4.7 Bq kg 1 for the depth intervals of 0–10, 10–20 and 20–30 cm respectively at 40 m away from waterline. The respective mean values of activity of 210Pb are also recorded. The mean values of activity of 210Pb were found to be 19.8, 42.6 and 35.8 Bq kg 1 for the depth intervals of 0–10, 10–20 and 20–30 cm respectively, at 20 m away from waterline. The mean values of activity of 210Pb were 8.7, 9.0 and 8.8 Bq kg 1 for the depth intervals of 0–10, 10–20 and 20–30 cm respectively at 40 m away from waterline. The mean value of 210Po decreases with depth for the samples collected 20 m away from waterline whereas the activity increases slightly with depth 40 m away from sea waterline. The 210Po and 210Pb activity in beach sand samples is relatively low. This may be due to very low percentage of clay and organic matter, as clay and organic matter content will be washed away due to continuous wave action. The activity of 210Po and 210Pb
210
Pb in surface beach sand at different distances from sea water line
Activity (Bq kg 1)
Location
At water line
Karunagapalli Chavara Neendakara Kollam Mean Range
210
Location
Po and
20 m away from water line 210
210
210
210
210
210
210
210
2.470.3 20.570.8 6.470.5 4.170.8
3.270.4 48.271.2 7.170.5 1.270.3
0.6 2.3 0.9 3.4
2.570.3 19.970.8 10.270.6 8.270.6
11.970.7 21.870.9 34.271.1 11.370.7
0.2 0.9 0.2 0.7
2.170.5 2.570.3 6.770.5 2.870.4
9.870.6 4.370.4 18.370.8 2.370.5
0.2 0.6 0.4 1.2
8.3 2.4–20.5
14.9 1.2–48.2
1.8 0.6–3.4
10.2 2.5–19.9
19.8 11.3–34.2
0.5 0.2–0.9
3.5 2.1–6.7
8.7 2.3–18.3
Pb
Po/210Pb
40 m away from water line
210
Po
Table 2 Variation of
210
Po
Po/210Pb
Pb
Po
Po/210Pb
Pb
0.6 0.2–1.2
210
Pb activities with depth
Activity (Bqkg 1) 20 m away from water line 210
210
Po
0–10 cm
40 m away from water line Pb
10–20 cm 20–30 cm 0–10 cm
210
210
Po
10–20 cm 20–30 cm 0–10 cm
Pb
10–20 cm 20–30 cm 0–10 cm
Karunagapalli Chavara Neendakara Kollam
2.570.3 1.970.3 2.470.4 11.970.7 4.270.4 2.970.4 2.170.5 19.970.7 16.770.7 19.170.7 21.870.9 11.270.6 22.070.8 2.570.3 10.270.6 6.370.5 4.970.4 34.271.1 21.170.9 8.970.6 6.770.5 8.270.6 7.370.6 3.870.5 11.370.7 6.170.6 1.970.4 2.870.4
3.37.0.4 3.470.4 4.770.4 3.670.6
6.57.5 2.87.3 6.17.5 3.37.5
Mean Range
10.2 2.5–19.9
3.7 3.3–4.7
4.7 2.8–6.5
8 1.9–16.7
7.7 2.4–19
19.8 42.6 35.8 3.5 11.3–34.2 4.2–21.1 1.9–22.0 2.1–6.7
10–20 cm 20–30 cm
9.870.6 4.870.4 4.670.4 4.370.4 6.970.6 7.470.7 18.370.8 20.970.9 21.67.9 2.370.5 3.670.8 1.870.5 8.7 2.3–18.3
9 3.6–20.9
8.8 1.8–21.6
ARTICLE IN PRESS Y. Narayana et al. / Applied Radiation and Isotopes 64 (2006) 396–401 Table 3 210 Po and
210
399
Pb activities in surface soil samples Activity(Bq kg 1)
Location
210
Po/210Pb
Clay (%)
Organic matter (%)
0.63 0.45 0.54 1.59 0.48
1.16 0.75 0.69 2.29 1.49
210
210
Karunagapalli Chavara Neendakara Kollam Kayankulam
6.270.5 3.170.4 4.070.5 6.770.6 3.870.5
7.970.7 5.770.5 13.171.2 15.171.4 13.371.2
0.7 0.54 0.31 0.44 0.29
Mean: Range:
4.7 3.1–6.7
11 5.7–15.1
0.5 0.29–0.7
Po
Pb
was found be maximum in most of the regions at Chavara beach and for a few regions of Neendakara. This may be due to the net movement of heavy minerals towards the shore zone of Chavara (Prakash, 2000) and higher concentration of monazite placer deposits at Chavara beach. The littoral process and coastal configuration are also known to have a significant role in the concentration of heavies (Prakash et al., 1991). The activity of 210Po and 210 Pb was found to be maximum in the beach sand samples collected at 20 m away from the waterline. This might be due to the frequent fresh deposition of heavy minerals at this distance due to the continuous wave action. The mean values of both 210Po and 210Pb activity concentrations vary disproportionately with depth for the samples collected at 20 m away from waterline. However, the variation was marginal for samples collected at 40 m away from waterline. The depth profile study of 210Po in sand samples shows systematic variation in the activity with depth. 3.3. Activity of
210
Po and
210
Pb in soil
Results of the activity of 210Po and 210Pb in soil samples are given in Table 3. Among the soil samples, Kollam soil has the highest 210Po and 210Pb activity. This may be due to relatively high percentage of clay and organic matter. The activities of 210Po and 210Pb were found to be 6.7 and 15.1 Bq kg 1 respectively in Kollam soil. The activity of 210 Po varied from 3.1 to 6.7 Bq kg 1 with a mean value of 4.7 Bq kg 1. The activity of 210Pb varied from 5.7 to 15.1 Bq kg 1 with a mean value of 11.0 Bq kg 1. The 210Pb activity is higher compared to 210Po in the soil samples of the region. The 210Po and 210Pb content in the soil varied with soil type. The activity of 210Po and 210Pb has also been compared with the values reported for other regions (Table 4). Ibrahim and Whicker (1987) have reported values for activities of 210Po and 210Pb in some soils within the USA. The reported activities are 78.1 and 107.3 Bq kg 1 respectively. The reported value of 210Po and 210Pb for Kaiga soil (Karunakara, 1997) was 56.1 and 85.5 Bq kg 1 respectively. It is evident from the table that the activity of 210Po and 210 Pb in the present study area is low compared to that reported for other environs. This may be due to low
Table 4 Comparison of Present work
210
Pb and
210
Po activity in soil.
Activity (Bq kg 1)
Region
Reference
3.6–45.2
Mangalore, India Kaiga, India USA Spain
Radhakrishna et al. (1995)
Kalpakkam, India Kaiga, India Ullal, India CPIC, Brazil USA
Iyengar et al. (1980)
210
Pb 5.7–15.1
85.5 107.3 15.4–820 210 Po 3.1–6.7
44.4 56.1 1.3–13.7 32.1–70 78.1
Karunakara (1997) Ibrahim and Whicker (1987) Aguirre and Leon (1997)
Karunakara et al. (2000) Radhakrishna et al. (1993) Santos et al. (1990) Ibrahim and Whicker (1987)
percentage of clay and organic matter (Table 3) in the soils of the region. 3.4. Activity ratios The mean values of activity ratios of 210Po to 210Pb in surface beach sand samples are 1.8, 0.5 and 0.6 at the waterline, 20 and 40 m away from waterline respectively. This clearly indicates 210Po and 210Pb are not in equilibrium in beach sand samples of this high background radiation area. Similarly, for soil samples there is also a lack of equilibrium, the mean value of activity ratios of 210 Po to 210Pb being 0.46 for surface soil. The observed disequilibrium between the two radionuclides in soil may due to the effective sequestering of 210Pb by organic matter (Durrance, 1986). 3.5. Correlation studies The activity concentration of 210Po and 210Pb in surface beach sand shows good correlation, with a correlation coefficient 0.81 (Fig. 2). Conversely, poor correlation is observed for surface soil samples (Fig. 3). The activity
ARTICLE IN PRESS Y. Narayana et al. / Applied Radiation and Isotopes 64 (2006) 396–401
400
7 6 activity (Bqkg-1)
40 r=0.81 30
20
210Po
210Pb
activity (Bqkg-1)
50
10
r=0.70 5 4 3 2 1
0 0
5
10 15 activity (Bqkg-1)
20
25
0
210Po
Fig. 2. Correlation between the activity of beach sand.
210
Po and
0 Pb in surface
2
2.5
210
Po and organic matter in
16
activity (Bqkg-1)
14 12 r=0.33 8
210Pb
activity (Bqkg-1)
1 1.5 Organic matter (%)
Fig. 4. Correlation between the activity of surface soil.
16
210Pb
0.5
210
4
r=0.62
12 10 8 6 4 2
0 0
1
2
3 4 5 210Po activity (Bqkg-1)
6
7
0 0
0.5
1 1.5 Organic matter (%)
2
2.5
Fig. 3. Correlation between the activity of 210Po and 210Pb in surface soil.
Fig. 5. Correlation between the activity of surface soil.
concentration of 210Po and 210Pb in surface soil varies from place to place. This could be due to the nature of soil and its physicochemical characteristics, including soil pH, humidity, and organic matter content. The organic matter content was determined in surface soil and the activity of 210 Po and 210Pb was correlated with organic matter content. The correlation graphs of 210Po and 210Pb with organic matter content are shown in Figs. 4 and 5 respectively. The correlation coefficients are 0.7 and 0.62 for 210Po and 210Pb respectively.
almost certainly depends on the organic matter content of the soil.
4. Conclusions The activity concentration of 210Pb is higher compared to 210Po activity in beach sand and in soil. The mean value of 210Po decreases with depth for samples collected 20 m away from waterline whereas the activity increases slightly with depth 40 m away from sea waterline. 210Po and 210Pb are not in equilibrium in high background area. The activity concentration of 210Po and 210Pb in surface soil
210
Pb and organic matter in
Reference Aguirre, M.A., Leon, G.M., 1997. Radioactive impact of phosphate ore processing in a wet Marshland in southwestern Spain. J. Environ. Radioactivity 34 (1), 45–57. Durrance, E.M., 1986. Radioactivity in geology; Principles and Applications. Ellis Horwood Ltd, Chichester. Eisenbud, M., 1987. Environmental radioactivity from natural, industrial and military sources, third ed. Academic Press Inc, New York. Ibrahim, S.A., Whicker, F.W., 1987. Plant accumulation and plant/soil concentration ratios of 210Po and 210Pb at various sites within a uranium mining and milling operation. Environ. Exp. Botany 27, 203–213. Iyengar, M.A.R., Rajan, M.P., Ganapathy, S., Kamath, P.R., 1980. Sources of natural radiation exposure in low monazite environment, Natural radiation environment III. In: Gesell, T.F., Lowder, W.M. (Eds.), Proceedings of the International Conference Houston, 1978. Vol. 2. Conf-780422, Technical Information Center, United States Department Of Energy, Oak Ridge, TN, pp. 1090–1106.
ARTICLE IN PRESS Y. Narayana et al. / Applied Radiation and Isotopes 64 (2006) 396–401 Iyengar, M.A.R., Ganapathy, S., Kannan, V., Rajan, M.P., Rajaram, S., 1990. Procedure manual, Workshop on environmental Radioactivity held at Kaiga, India. 16–18 April. Karunakara, N., 1997. Studies on radionuclide distribution and uptake in the environment of Kaiga, Ph D Thesis Mangalore University. Karunakara, N., Avadhani, D.N., Mahash, H..M., Soamshekarappa, H..M., Narayana, Y., Siddappa, K., 2000. Distribution and enrichment of 210Po in the environment of Kaiga in South India. J. Environ. Radioactivity 51, 349–362. Lee, M.H., Lee, C.W., 1997. Distribution and characteristics of 239,240Pu and 137Cs in the soil of Korea. J. Environ. Radioactivity 1, 1–16. Prakash, T.N., 2000. Sediment distribution and placer mineral enrichment in the inner shelf of Quilon, southwest coast of India. Indian journal of marine science 29, 120–127. Prakash, T.N., Raju, G.K., Prithviraj, M., 1991. Radioelement distribution in river, beach, and offshore areas and their significance to
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Chavara placer deposit, southern Kerala Coast of India. Geo-Marine Letters 11, 32–38. Radhakrishna, A.P., Somashekarappa, H.M., Narayana, Y., Siddappa, K., 1993. A new natural background radiation area on the southwest coast of India. Health Phys 65, 390–395. Radhakrishna, A.P., Somashekarappa, H.M., Narayana, Y., Siddappa, K., 1995. Distribution of some natural and artificial radionuclides in Mangalore environment of south India. J. Environ. Radioactivity 30 (1), 31–54. Santos, P.L., Gouvea, R.C., Dutta, I.R., Gouvea, V.A., 1990. Accumulation of 210Po in food stuffs cultivated in farms around Brazilian mining and milling facilities on Pocos de Caldas Plateau. J. Environ. Radioactivity 11, 141–149. United Nations Scientific Committee on the Effects of Atomic Radiation, 1988. Sources, effects and risks of ionising radiation, Report to the General Assembly New York: United Nations.
Applied Radiation and Isotopes 64 (2006) 396–401 www.elsevier.com/locate/apradiso
Behavior of 210Po and 210Pb in high background areas of coastal Kerala on the south west coast of India Y. Narayana, P.K. Shetty, K. Siddappa Department of Studies in Physics, Mangalore University, Mangalagangothri, 574199, India Received 19 May 2005; received in revised form 6 August 2005; accepted 7 August 2005
Abstract This paper deals with the distribution and behavior of 210Po and 210Pb in beach sand and surface soil samples from the Quilon district of Kerala. Beach sand and soil samples were collected and analyzed for 210Po and 210Pb radionuclides using standard radiochemical analytical techniques. Mean activities of 210Po and 210Pb were found to be maximum in the samples collected at 20 m away from waterline. Among the beach sand samples, the activities of radionuclide were found to be maximum for samples from most of the regions of Chavara and few regions of Neendakara. The activity of 210Po was found to vary from 2.4 to 20.5 Bq kg 1 with a mean value of 8.3 Bq kg 1 at the water line, 2.5–19.9 Bq kg 1 with a mean value of 10.2 Bq kg 1 at 20 m away from the waterline, and 2.1–6.7 Bq kg 1 with a mean value of 3.5 Bq kg 1 at 40 m away from waterline. The respective values found for 210Pb were from 1.2 to 48.2 Bq kg 1 with a mean value of 14.9, 11.3–34.2 Bq kg 1 with a mean value of 19.8 Bq kg 1 and 2.3 to 18.3 Bq kg 1 with a mean value of 8.7 Bq kg 1. The depth profile study indicated the mean activity of 210Po to decrease with depth for samples collected 20 m away from waterline whereas the activity slightly increases with depth 40 m away from sea. The activity concentration of 210Po and 210Pb in surface beach sand shows good correlation, with a correlation coefficient 0.81. r 2005 Elsevier Ltd. All rights reserved. Keywords: Polonium-210; Lead-210; Kerala; Sand and soil
1. Introduction High natural background radiation areas are of special interest, indicating anomalous conditions in their geological features and consequently in the background radiation levels. One of the prime sources of high background radiation level is the presence of radioactive monazite. One of the regions in India within which high background radiation levels have been reported is from the coastal areas of Quilon district in Kerala. Monazite sands are known to contain thorium with some amount of 238U and 40K (Eisenbud, 1987). The radionuclides 210Po and 210Pb are the final radioactive members of the 238U series and are widely present in the environment, due to the decay of 222Rn in the atmosphere, Corresponding author. Tel.: +91 824 2287363; fax: +91 824 2287367.
E-mail address: [email protected] (Y. Narayana). 0969-8043/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2005.08.016
contributing about 8% of the natural radiation exposure to humans (United Nations Scientific Committee on the Effects of Atomic Radiation, 1988). However data available on the distribution of 210Po and 210Pb in sand and soils of high background radiation areas is sparse. In view of this, detailed studies on the radiation level and radionuclide activity concentration in different environmental matrices of high background area have been undertaken. As a part of this programme, the distribution and enrichment of 210 Po and 210Pb were studied in the region identified above. The soil and beach sand samples collected from different depths in the Karunagapalli, Chavara, Neendakara and Kollam beach areas were analysed for 210Po and 210Pb activity. An attempt is made in this investigation to study the distribution, enrichment, vertical profile, and activity ratios of 210Po and 210Pb and the influence of organic matter content on these radionuclides in surface soil and beach sand samples.
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whose temperature was maintained at 550 1C. The organic matter percentage was then calculated by weight loss. The clay content was also measured.
2. Materials and methods 2.1. Sample collection The study area covers the Quilon district of Kerala on the south west coast of India, extending over a coastal length of about 30 km (Fig. 1). Standard techniques were followed in the collection of samples. Sand samples were collected from the sea water line, 20 m and 40 m away from the waterline at each sampling location. The samples were taken from depth intervals of 0–10, 10–20 and 20–30 cm, except for that at the waterline where sand was collected from the surface (0–10 cm). The surface soil samples were also collected from inland regions of the beach area, about 1 km away from the shoreline. For soil sampling, undisturbed ground surfaces situated away from public roads and building were selected. The samples were individually collected in polythene bags and brought to the laboratory for analysis. 2.2. Organic matter and clay content measurement The ignition method was employed in the measurement of organic matter percentage in the soil sample (Lee and Lee, 1997). The samples were oven-dried in a furnace
2.3. Sample processing and activity measurement The electrochemical deposition method was employed for determination of 210Po (Iyengar et al., 1990), both for soil and sand samples. The sand and soil samples were dried in an oven at 110 1C until a constant dry weight was obtained. From the fresh and dry weight, the moisture content was calculated. The dried samples were leached with 4 M HNO3 and then the organic matter present in the sample was destroyed by digestion by adding a HNO3+ H2O2 mixture in small increments to obtain a white residue. Each sample was then converted into a 0.5 M HCl medium. 210Po in the solution was deposited onto a silver disc at 97 1C for 6 h (Iyengar et al., 1990). The disc was then washed with distilled water, rinsed with alcohol, dried under an infrared lamp and the a activity was counted using a ZnS(Ag) alpha counter of 30% efficiency (manufactured by the Electronic Corporation of India Limited, Hydarabad). The activity of 210Pb was estimated through 210Po, allowing the 210Po-plated solution for a period of 12 months to build up the 210Po from 210Pb (Iyengar et al., 1990).
Fig. 1. Map showing sample locations.
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3.2. Vertical profile of
3. Results and discussions 3.1. Variation of
210
Po and
210
Pb activity in sand
The results of measurement of 210Po and 210Pb activity concentrations for surface beach sand samples (0–10 cm), taken at different distances from the sea waterline, are given in Table 1. As can be seen, the activity of 210Po varies from 2.4 to 20.5 Bq kg 1 with a mean value of 8.3 Bq kg 1 at the water line, 2.5–19.9 Bq kg 1 with a mean value of 10.2 Bq kg 1 at 20 m away from the waterline, and 2.1–6.7 Bq kg 1 with a mean value of 3.5 Bq kg 1 at 40 m away from waterline. The maximum activity was found for Chavara beach sand, while the minimum was found for samples obtained at Karunagarapalli. The mean activity of 210 Po was found to be maximum in samples collected at 20 m away from waterline. It can also be seen that the respective activities of 210Pb are from 1.2 to 48.2 Bq kg 1 with a mean value of 14.9, 11.3–34.2 Bq kg 1 with a mean value of 19.8, and 2.3–18.3 Bq kg 1 with a mean value of 8.7 Bq kg 1. Again, the maximum activity was observed at Chavara beach sand, while the minimum activity of 210Pb was found in Kollam beach sand. The mean activity of 210 Pb was found to be maximum for samples collected 20 m away from waterline.
Table 1 The activity concentration and activity ratios of
210
Po and
Po and
210
Pb
The results of measurement of 210Po and 210Pb activity concentrations at different depths in beach sand samples are given in Table 2. The mean values of activity of 210Po at 20 m away from waterline were found to be 10.2, 8.0 and 7.7 Bq kg 1 for the depth intervals of 0–10, 10–20 and 20–30 cm respectively. The mean values of activity of 210Po were 3.5, 3.7 and 4.7 Bq kg 1 for the depth intervals of 0–10, 10–20 and 20–30 cm respectively at 40 m away from waterline. The respective mean values of activity of 210Pb are also recorded. The mean values of activity of 210Pb were found to be 19.8, 42.6 and 35.8 Bq kg 1 for the depth intervals of 0–10, 10–20 and 20–30 cm respectively, at 20 m away from waterline. The mean values of activity of 210Pb were 8.7, 9.0 and 8.8 Bq kg 1 for the depth intervals of 0–10, 10–20 and 20–30 cm respectively at 40 m away from waterline. The mean value of 210Po decreases with depth for the samples collected 20 m away from waterline whereas the activity increases slightly with depth 40 m away from sea waterline. The 210Po and 210Pb activity in beach sand samples is relatively low. This may be due to very low percentage of clay and organic matter, as clay and organic matter content will be washed away due to continuous wave action. The activity of 210Po and 210Pb
210
Pb in surface beach sand at different distances from sea water line
Activity (Bq kg 1)
Location
At water line
Karunagapalli Chavara Neendakara Kollam Mean Range
210
Location
Po and
20 m away from water line 210
210
210
210
210
210
210
210
2.470.3 20.570.8 6.470.5 4.170.8
3.270.4 48.271.2 7.170.5 1.270.3
0.6 2.3 0.9 3.4
2.570.3 19.970.8 10.270.6 8.270.6
11.970.7 21.870.9 34.271.1 11.370.7
0.2 0.9 0.2 0.7
2.170.5 2.570.3 6.770.5 2.870.4
9.870.6 4.370.4 18.370.8 2.370.5
0.2 0.6 0.4 1.2
8.3 2.4–20.5
14.9 1.2–48.2
1.8 0.6–3.4
10.2 2.5–19.9
19.8 11.3–34.2
0.5 0.2–0.9
3.5 2.1–6.7
8.7 2.3–18.3
Pb
Po/210Pb
40 m away from water line
210
Po
Table 2 Variation of
210
Po
Po/210Pb
Pb
Po
Po/210Pb
Pb
0.6 0.2–1.2
210
Pb activities with depth
Activity (Bqkg 1) 20 m away from water line 210
210
Po
0–10 cm
40 m away from water line Pb
10–20 cm 20–30 cm 0–10 cm
210
210
Po
10–20 cm 20–30 cm 0–10 cm
Pb
10–20 cm 20–30 cm 0–10 cm
Karunagapalli Chavara Neendakara Kollam
2.570.3 1.970.3 2.470.4 11.970.7 4.270.4 2.970.4 2.170.5 19.970.7 16.770.7 19.170.7 21.870.9 11.270.6 22.070.8 2.570.3 10.270.6 6.370.5 4.970.4 34.271.1 21.170.9 8.970.6 6.770.5 8.270.6 7.370.6 3.870.5 11.370.7 6.170.6 1.970.4 2.870.4
3.37.0.4 3.470.4 4.770.4 3.670.6
6.57.5 2.87.3 6.17.5 3.37.5
Mean Range
10.2 2.5–19.9
3.7 3.3–4.7
4.7 2.8–6.5
8 1.9–16.7
7.7 2.4–19
19.8 42.6 35.8 3.5 11.3–34.2 4.2–21.1 1.9–22.0 2.1–6.7
10–20 cm 20–30 cm
9.870.6 4.870.4 4.670.4 4.370.4 6.970.6 7.470.7 18.370.8 20.970.9 21.67.9 2.370.5 3.670.8 1.870.5 8.7 2.3–18.3
9 3.6–20.9
8.8 1.8–21.6
ARTICLE IN PRESS Y. Narayana et al. / Applied Radiation and Isotopes 64 (2006) 396–401 Table 3 210 Po and
210
399
Pb activities in surface soil samples Activity(Bq kg 1)
Location
210
Po/210Pb
Clay (%)
Organic matter (%)
0.63 0.45 0.54 1.59 0.48
1.16 0.75 0.69 2.29 1.49
210
210
Karunagapalli Chavara Neendakara Kollam Kayankulam
6.270.5 3.170.4 4.070.5 6.770.6 3.870.5
7.970.7 5.770.5 13.171.2 15.171.4 13.371.2
0.7 0.54 0.31 0.44 0.29
Mean: Range:
4.7 3.1–6.7
11 5.7–15.1
0.5 0.29–0.7
Po
Pb
was found be maximum in most of the regions at Chavara beach and for a few regions of Neendakara. This may be due to the net movement of heavy minerals towards the shore zone of Chavara (Prakash, 2000) and higher concentration of monazite placer deposits at Chavara beach. The littoral process and coastal configuration are also known to have a significant role in the concentration of heavies (Prakash et al., 1991). The activity of 210Po and 210 Pb was found to be maximum in the beach sand samples collected at 20 m away from the waterline. This might be due to the frequent fresh deposition of heavy minerals at this distance due to the continuous wave action. The mean values of both 210Po and 210Pb activity concentrations vary disproportionately with depth for the samples collected at 20 m away from waterline. However, the variation was marginal for samples collected at 40 m away from waterline. The depth profile study of 210Po in sand samples shows systematic variation in the activity with depth. 3.3. Activity of
210
Po and
210
Pb in soil
Results of the activity of 210Po and 210Pb in soil samples are given in Table 3. Among the soil samples, Kollam soil has the highest 210Po and 210Pb activity. This may be due to relatively high percentage of clay and organic matter. The activities of 210Po and 210Pb were found to be 6.7 and 15.1 Bq kg 1 respectively in Kollam soil. The activity of 210 Po varied from 3.1 to 6.7 Bq kg 1 with a mean value of 4.7 Bq kg 1. The activity of 210Pb varied from 5.7 to 15.1 Bq kg 1 with a mean value of 11.0 Bq kg 1. The 210Pb activity is higher compared to 210Po in the soil samples of the region. The 210Po and 210Pb content in the soil varied with soil type. The activity of 210Po and 210Pb has also been compared with the values reported for other regions (Table 4). Ibrahim and Whicker (1987) have reported values for activities of 210Po and 210Pb in some soils within the USA. The reported activities are 78.1 and 107.3 Bq kg 1 respectively. The reported value of 210Po and 210Pb for Kaiga soil (Karunakara, 1997) was 56.1 and 85.5 Bq kg 1 respectively. It is evident from the table that the activity of 210Po and 210 Pb in the present study area is low compared to that reported for other environs. This may be due to low
Table 4 Comparison of Present work
210
Pb and
210
Po activity in soil.
Activity (Bq kg 1)
Region
Reference
3.6–45.2
Mangalore, India Kaiga, India USA Spain
Radhakrishna et al. (1995)
Kalpakkam, India Kaiga, India Ullal, India CPIC, Brazil USA
Iyengar et al. (1980)
210
Pb 5.7–15.1
85.5 107.3 15.4–820 210 Po 3.1–6.7
44.4 56.1 1.3–13.7 32.1–70 78.1
Karunakara (1997) Ibrahim and Whicker (1987) Aguirre and Leon (1997)
Karunakara et al. (2000) Radhakrishna et al. (1993) Santos et al. (1990) Ibrahim and Whicker (1987)
percentage of clay and organic matter (Table 3) in the soils of the region. 3.4. Activity ratios The mean values of activity ratios of 210Po to 210Pb in surface beach sand samples are 1.8, 0.5 and 0.6 at the waterline, 20 and 40 m away from waterline respectively. This clearly indicates 210Po and 210Pb are not in equilibrium in beach sand samples of this high background radiation area. Similarly, for soil samples there is also a lack of equilibrium, the mean value of activity ratios of 210 Po to 210Pb being 0.46 for surface soil. The observed disequilibrium between the two radionuclides in soil may due to the effective sequestering of 210Pb by organic matter (Durrance, 1986). 3.5. Correlation studies The activity concentration of 210Po and 210Pb in surface beach sand shows good correlation, with a correlation coefficient 0.81 (Fig. 2). Conversely, poor correlation is observed for surface soil samples (Fig. 3). The activity
ARTICLE IN PRESS Y. Narayana et al. / Applied Radiation and Isotopes 64 (2006) 396–401
400
7 6 activity (Bqkg-1)
40 r=0.81 30
20
210Po
210Pb
activity (Bqkg-1)
50
10
r=0.70 5 4 3 2 1
0 0
5
10 15 activity (Bqkg-1)
20
25
0
210Po
Fig. 2. Correlation between the activity of beach sand.
210
Po and
0 Pb in surface
2
2.5
210
Po and organic matter in
16
activity (Bqkg-1)
14 12 r=0.33 8
210Pb
activity (Bqkg-1)
1 1.5 Organic matter (%)
Fig. 4. Correlation between the activity of surface soil.
16
210Pb
0.5
210
4
r=0.62
12 10 8 6 4 2
0 0
1
2
3 4 5 210Po activity (Bqkg-1)
6
7
0 0
0.5
1 1.5 Organic matter (%)
2
2.5
Fig. 3. Correlation between the activity of 210Po and 210Pb in surface soil.
Fig. 5. Correlation between the activity of surface soil.
concentration of 210Po and 210Pb in surface soil varies from place to place. This could be due to the nature of soil and its physicochemical characteristics, including soil pH, humidity, and organic matter content. The organic matter content was determined in surface soil and the activity of 210 Po and 210Pb was correlated with organic matter content. The correlation graphs of 210Po and 210Pb with organic matter content are shown in Figs. 4 and 5 respectively. The correlation coefficients are 0.7 and 0.62 for 210Po and 210Pb respectively.
almost certainly depends on the organic matter content of the soil.
4. Conclusions The activity concentration of 210Pb is higher compared to 210Po activity in beach sand and in soil. The mean value of 210Po decreases with depth for samples collected 20 m away from waterline whereas the activity increases slightly with depth 40 m away from sea waterline. 210Po and 210Pb are not in equilibrium in high background area. The activity concentration of 210Po and 210Pb in surface soil
210
Pb and organic matter in
Reference Aguirre, M.A., Leon, G.M., 1997. Radioactive impact of phosphate ore processing in a wet Marshland in southwestern Spain. J. Environ. Radioactivity 34 (1), 45–57. Durrance, E.M., 1986. Radioactivity in geology; Principles and Applications. Ellis Horwood Ltd, Chichester. Eisenbud, M., 1987. Environmental radioactivity from natural, industrial and military sources, third ed. Academic Press Inc, New York. Ibrahim, S.A., Whicker, F.W., 1987. Plant accumulation and plant/soil concentration ratios of 210Po and 210Pb at various sites within a uranium mining and milling operation. Environ. Exp. Botany 27, 203–213. Iyengar, M.A.R., Rajan, M.P., Ganapathy, S., Kamath, P.R., 1980. Sources of natural radiation exposure in low monazite environment, Natural radiation environment III. In: Gesell, T.F., Lowder, W.M. (Eds.), Proceedings of the International Conference Houston, 1978. Vol. 2. Conf-780422, Technical Information Center, United States Department Of Energy, Oak Ridge, TN, pp. 1090–1106.
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