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ORIGINAL ARTICLE
Year : 2019  |  Volume : 42  |  Issue : 3  |  Page : 102-106  

Distribution and enrichment of 210Po and210Pb in the environment of Mangalore, Southwest Coast of India


1 Department of Physics, Payyanur College, Kannur, Kerala, India
2 Department of Physics, SJC Institute of Technology, Chickballapur, Karnataka, India
3 Department of Physics, Mangalore University, Mangalore, Karnataka, India

Date of Submission28-Mar-2019
Date of Decision24-Apr-2019
Date of Acceptance11-Jun-2019
Date of Web Publication06-Nov-2019

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


DOI: 10.4103/rpe.RPE_12_19

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  Abstract 


The article deals with the distribution and enrichment of210Po and210Pb in soil samples of Mangalore, Southwest Coast of India. The soil samples collected from the region were analyzed for210Po and210Pb activity using radiochemical analytical technique to understand the distribution and enrichment of these radionuclides. The210Po activity in soil in the environment of Mangalore varies from 1.5 to 26.9 Bq/kg with a mean value of 12.6 Bq/kg and that of210Pb varies in the range 7.6–67.5 Bq/kg with a mean value of 38.9 Bq/kg. The mean210Po/210Pb ratio observed was 0.3, and it shows that the radionuclides210Po and210Pb are not in equilibrium and the accumulation of210Pb in soil is more compared to210Po. A good correlation exists between the activities of210Po and210Pb with correlation coefficient r = 0.7. The absorbed gamma dose in the environment of the region varies from 39.4 to 78.8 nGyh−1, with a mean value of 48.2 nGyh−1. The activity of both210Po and210Pb in soil almost certainly depends on the physicochemical parameters of the soil. The results of the systematic studies on the distribution and enrichment of210Po and210Pb and the absorbed gamma dose rate in air are presented and discussed in this article.

Keywords: 210Pb,210Po, enrichment, radionuclide, soil


How to cite this article:
Prakash V, Vineethkumar V, Rajashekhara K M, Narayana Y. Distribution and enrichment of 210Po and210Pb in the environment of Mangalore, Southwest Coast of India. Radiat Prot Environ 2019;42:102-6

How to cite this URL:
Prakash V, Vineethkumar V, Rajashekhara K M, Narayana Y. Distribution and enrichment of 210Po and210Pb in the environment of Mangalore, Southwest Coast of India. Radiat Prot Environ [serial online] 2019 [cited 2019 Nov 12];42:102-6. Available from: http://www.rpe.org.in/text.asp?2019/42/3/102/270437




  Introduction Top


Mangalore, an important region of Southwest Coast of India, is poised to become a center of major industrial activity with the operation oil refineries and petrochemical complexes, chemical and fertilizer factories, and various other industries. Most of these industrial activities are concentrated in a stretch of about 10 km. Hence, detailed studies on radiation level and distribution and enrichment of radionuclides in the environment of the region have relevance in understanding the radiation effects on the environment and human health. In view of this, detailed studies on radiation level and radionuclide distribution have been carried out in Mangalore region.[1] As part of the study, soil samples collected from the region were analyzed for210 Po and210 Pb activity concentration to understand the distribution and enrichment of these radionuclides in the region.

The radionuclides210 Po and210 Pb are among the most important natural radionuclides of Uranium series from a radioecological point of view. Both210 Po and210 Pb are of great concern for reasons mainly because of their large contribution to the natural radiation dose received by many species. The radionuclide210 Po is one of the most toxic alpha-emitting natural radionuclides and an important contributor to the internal exposure of the human population. Baseline information on the activity concentration of these radionuclides is important to understand the internal exposure to the human population due to these radionuclides. The correlation between the activities of210 Po and210 Pb and the dependence of physicochemical parameters present in the soil on the activity concentration of these radionuclides were studied. Detailed gamma radiation level survey was also carried out in the environment of the region using portable plastic scintillometer. The results of these investigations are presented and discussed in this article.


  Materials and Methods Top


Sample collection

To determine the individual radionuclide activity concentration in soil of Mangalore, a large number of samples were collected from different sampling stations of Mangalore. In the present study, 16 soil samples were collected from Mangalore in a stretch of about 10 km, namely, Bejai (M1), Kottara (M2), Kodialbail (M3), Urva Store (M4), Car street (M5), Kudroli (M6), State Bank (M7), Bunder (M8), Attavar (M9), Jeppinamogaru (M10), Jeppu (M11), Ekkur (M12), Pumpwell (M13), Padil (M14), Kadri (M15), and Nanthoor (M16) locations. The map showing sampling locations is given in [Figure 1].
Figure 1: Map showing sampling stations

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For soil sampling, the unused surface area away from buildings, free from trees, was selected. About 1 m2 area was marked, grass and its root mat on the surface, stones were cleaned and soil from the top layer (up to 30 cm) was collected. Four samples, 100 m apart, were collected following the same procedure, and extraneous materials such as stones, pebbles, plant materials, root, and its mud portions were removed, pooled together, and mixed thoroughly. Then, cleaned and thoroughly mixed soil was divided into four equal parts and one part was collected as the representative sample (≈2 kg) in a polythene bag and brought to the laboratory for further analysis.

Sample processing

All the samples were carefully processed following standard procedures.[2],[3],[4] The samples were transferred to a porcelain tray and dried in an oven at 110°C till a constant dry weight is obtained. The dried sample was then sieved through 250-micron sieve and taken for analysis.

The electrochemical deposition method was employed for the determination of210 Po and210 Pb activity. About 20 g of each sample was leached with 4M HNO3 and then organic matter present in the samples was destroyed by adding 3:1 HNO3+ HClO4 mixture in small increments till white residue was obtained. The samples were then converted into 1M HCl medium and210 Po in the solution was deposited on a brightly polished background counted (both sides) silver disc using magnetic stirrer at 97°C for 6 h. The counts were noted on both sides using ZnS (Ag) alpha counter of 0.4 cpm background and 30% efficiency for the210 Po activity. From the total counts obtained from both sides, the activity concentration of210 Po was calculated.[4] The activity of210 Pb was estimated through210 Po by storing the210 Po-plated solution for a period of 12 months for the buildup of210 Po from210 Pb.

The physicochemical parameter like soil organic matter was measured employing standard methods.[5],[6] Moisture percentage of the sample was estimated gravimetrically as difference in wet and dry sample (100°C) method. The loss on ignition method was employed in the measurement of organic matter percentage in the soil sample. The oven-dried samples were kept in a muffle furnace for about 8 h whose temperature was maintained at 500°C. The organic matter percentage was then calculated gravimetrically as difference in weight. The pH is a scale of intensity of acidity or alkalinity and measures the concentration of hydrogen ions. About 10 g of soil sample was taken and 100 ml of distilled water added to make a suspension of 1:10 w/v dilution. In the present work, the pH of the sample was measured using μpH system 361. Initially, the system is calibrated using buffer solutions of pH 4.0 and pH 9.2. Then, the electrodes were washed with distilled water and dipped in the sample, and the readings were noted.


  Results and Discussion Top


Activity of210 Po and210 Pb and activity ratio

The results of the activities of210 Po and210 Pb and activity ratio in soil samples of the Mangalore region are given in [Table 1]. It can be seen from the table that the activity of210 Po varies from 1.5 to 26.9 Bq/kg with a mean value of 12.6 Bq/kg and that of210 Pb varies in the range 7.6–67.5 Bq/kg with a mean value of 38.9 Bq/kg.
Table 1: 210Po and 210Pb activity and activity ratio in Mangalore environment soil

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The maximum activity for both210 Po and210 Pb was found at Urva Store and the minimum activity for both210 Po and210 Pb at Padil. The highest210 Po and210 Pb activity at Urva Store is due to high organic matter content in the soil sample of the region. The lowest activity at Padil can be attributed to relatively low organic matter content in that sample. Both210 Po and210 Pb activity in soil was found to increase with increasing organic matter content. The mean210 Po/210 Pb ratio was observed to be 0.3 [Table 1]. The present results show that the radionuclides210 Po and210 Pb are not in equilibrium and the accumulation of210 Pb in soil is much more compared to210 Po. The higher activity of210 Pb in soil compared to210 Po may be due to the existence of210 Pb in the soil matrix for longer duration and removal of polonium from its site of production at relatively faster rate by chemical means.[7] The variation of210 Po and210 Pb activities in different sampling stations is shown in [Figure 2].
Figure 2: Variation of210Po and210Pb activity in the environment of Mangalore

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Physicochemical parameters

It is a well-established fact that any change in the radionuclide content of various components of the ecosystem depends on the interactions of large number of different factors. These include the nature of the radionuclide itself, the site-specific characteristics, physicochemical properties of the soil, variation in plant cover, and climatic conditions.

Therefore, the study of physicochemical parameters of the soil constitutes one of the important aspects of the present study. Some of the physicochemical parameters, namely moisture content, organic matter content, pH, and electrical conductivity, were determined using standard procedure, and the results are presented in [Table 2].
Table 2: Soil physicochemical parameters in the environment of Mangalore

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Comparison of activity and correlation study

The mean210 Po and210 Pb activity in the present study area is low compared to that reported for Goa region and Black Forest and high compared to the high background radiation, Kerala [Table 3]. The210 Po and210 Pb concentration in the soil varied from place to place and with soil type. This could be due to the nature of soil and its physicochemical characteristics such as pH, humidity, and organic matter content.
Table 3: Comparison of 210Po and 210Pb activity with other environments

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The correlation study between activities of210 Po and210 Pb shows significant correlation with correlation coefficient r = 0.7 [Figure 3]. This indicates that individual activity of one radionuclide is a good predictor of the other. Similarly, in case of210 Pb, correlation coefficient of 0.8 was observed. A good correlation was observed between the210 Po activity and organic matter content in the soil with correlation coefficient 0.8. Similarly, in the case of210 Pb, a correlation coefficient of 0.7 was observed [Figure 4] and [Figure 5].
Figure 3: Correlation between the activity of210Po and210Pb

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Figure 4: Correlation between the activity of210Po and organic matter

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Figure 5: Correlation between the activity of210Pb and organic matter

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The absorbed gamma dose rate in air and in the environment of the region varies from 39.4 to 78.8 nGyh−1 with a mean value of 48.2 nGyh−1. The absorbed dose rates have also been measured to understand the spatial variation of radionuclide activity concentration. The average dose rate in the present study was less in comparison with the Indian average value of 56 nGyh−1 and world average value of 59 nGyh−1.[15]


  Conclusions Top


The maximum210 Po and210 Pb activity was found at Urva Store and minimum at Padil. No equilibrium exists between210 Po and210 Pb radionuclides. Both210 Po and210 Pb activity depends on the organic matter content of the soil. Both210 Po and210 Pb activity concentration varied with soil structure and soil type. The activity of both210 Po and210 Pb in soil almost certainly depends on the physicochemical parameters of the soil. A good correlation exists between the activities of210 Po and210 Pb. The radiation level follows almost a uniform pattern, with dose rates close to the mean value except in some sampling stations.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Iyengar MA, Rajan MP, Ganapathy S, Kamath PR. Sources of natural radiation exposure in a low monazite environment. In: Gesell TF, Lowder WM, editors. Natural Radiation Environment III. Proc. Int. Conf. Houston. Vol. 2. Oak Ridge, TN: Technical Information Center, United States Department of Energy; 1980. p. 1090-106.  Back to cited text no. 9
    
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Parfenov YuD. Polonium-210 in the environment and in the human organism. At Energy Rev 1974;12:75-143.  Back to cited text no. 11
    
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Schuttelkopf H, Kiefer H. The Radium-226 and polonium-210 concentration of the black forest. In: Vohra KG, Mishra UC, Pillai KC, Sadasivan S, editors. Natural Radiation Environment. Proc. 2nd Special Symp. Bombay, New Delhi: Wiley Eastern Ltd.; 1982. p. 194-200.  Back to cited text no. 12
    
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Narayana Y, Shetty PK, Siddappa K. Behavior of 210Po and 210Pb in high background areas of coastal Kerala on the south west coast of India. Appl Radiat Isot 2006;64:396-401.  Back to cited text no. 13
    
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    Figures

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

  [Table 1], [Table 2], [Table 3]



 

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