|Year : 2011 | Volume
| Issue : 3 | Page : 193-196
Study of distribution of radionuclides in cultivated land in and around chikmagalur, Karnataka, India
S Manjunatha1, A Jayasheelan2, P Venkataramanaiah3
1 Department of Physics, PESITM, Shimoga, India
2 Department of Physics, GFGC, Sira, India
3 Department of Physics, PG Studies, Mysore, Karnataka, India
|Date of Web Publication||27-Sep-2012|
Department of Physics, PESITM, Shimoga
Source of Support: None, Conflict of Interest: None
Cultivation of land modifies soil characteristics and influences redistribution of radionuclides in topsoil. The concentrations of 210 Po and 210 Pb in the cultivated land of Chikmagalur were measured by wet ashing silver planchet electroplating alpha count method. The concentration of 226 Ra was determined using Emanometry Method. The samples were precipitated by chemical processes and the concentrations of 228 Ra measured using high efficiency low level background gas flow beta counter. The lowest activity of 226 Ra, 228 Ra 210 Po and 210 Pb recorded at study area were 6.1, 5.6, 12.9 and 20.6 Bq.Kg -1 and maxima were 47.7, 29.6, 71.2 and 120.5 Bq.Kg -1 and mean 13.8, 19.2, 28.6 and 1.8 Bq.Kg -1 respectively. The mean of ratios of 210 Po and 210 Pb in cultivated and uncultivated land were found to be 0.53 and 1.06 respectively. Concentrations of 226 Ra, 228 Ra and 210 Po in cultivated land found to be lower than that of undisturbed land but reverse in case of 210 Pb. Decrease in activities of 226 Ra, 228 Ra, and 210 Po in cultivated may due to wash out of 'floating fraction' with rainwater and the increase of activity of 210 Pb may be due to re-suspension. The 're-suspension factor' (K) increases for 226 Ra, 228 Ra, and 210 Po in cultivated and fertilizer added area, but not for 210 Pb. Also the concentrations of radionuclides were found to be high in comparison with global and Indian average.
Keywords: Floating fraction, Re-suspension factor, Polonium, Lead, Radium
|How to cite this article:|
Manjunatha S, Jayasheelan A, Venkataramanaiah P. Study of distribution of radionuclides in cultivated land in and around chikmagalur, Karnataka, India. Radiat Prot Environ 2011;34:193-6
|How to cite this URL:|
Manjunatha S, Jayasheelan A, Venkataramanaiah P. Study of distribution of radionuclides in cultivated land in and around chikmagalur, Karnataka, India. Radiat Prot Environ [serial online] 2011 [cited 2020 Sep 21];34:193-6. Available from: http://www.rpe.org.in/text.asp?2011/34/3/193/101720
| 1. Introduction|| |
In the present study, the concentrations of radionuclides, 226 Ra, 228 Ra 210 Po and 210 Pb and the ambient gamma levels with dose rate were measured in and around Chikmagalur region. Eleven geographically different locations around study area were selected; soil samples were collected in undisturbed and cultivated regions and analyzed. The main source of 210 Po in the environment is the exhalation of 222 Rn gas from the surface layers of the earth's crust. 210 Po poses potential risks to humans for internal radiation exposure by ingestion and inhalation, and 210 Po and 210 Pb have carcinogenic effects with respect to lung cancer. ,,,
| 2. Materials and Methods|| |
Soil samples from eleven different locations of Chikmagalur, were collected and analyzed in an attempt to study the influence of cultivation activities in the region of present study. The samples were oven dried over night at 50° C, sieved and used for radiometric measurements.
2.1 Ambient gamma radiation
The gamma radiation exposures have been measured using a highly sensitive GM type Environmental Radiation Monitor. About seventy points were selected in each area and the average gamma exposures were determined. The measured exposure rates have been converted to absorbed dose units using the relation 1mR.h -1 = 8.76nGy.  The results of gamma measurements have been summarized in [Table 1].
2.2 Determination of 210 Po and 210 Pb
Polonium was extracted by wet ashing method. Soil sample containing polonium was digested using conc. Nitric acid and later with HCl, A brightly polished silver planchet is kept in contact with the solution containing polonium while constant stirring for six hours, the polonium activity gets deposited on the surface of the silver planchet. The activity on both sides was counted in a low background alpha counting system. The average recovery was found to be 92.94%. The concentration of 210 Po was calculated using formula used by earlier researchers. ,,,, The sample solution after estimation of 210 Po was preserved for 6-8 months for sufficient growth of 210 Po from 210 Pb. , Then the 210 Po was re-estimated as described already. From the 210 Po activity, knowing its growth factor, the 210 Pb activity was calculated using the same equation used for the determination of 210 Pb.
2.3 Determination of 226 Ra and 228 Ra
Estimation of 226 Ra by emanometry has been adopted with some modifications by earlier researchers. , Radium in different soil samples was extracted into solution. Approximately 40 ml was transferred to the radon bubbler. Air was sucked through the sample solution for about 5 minutes using a vacuum pump to scrub it. This would purge the solution of dissolved 222 Rn. The solution in the bubbler was then allowed to stand for a known period of about 3 - 5 half-lives of 222 Rn, by connecting a scintillation cell and photomultiplier assembly, 226 Ra activity was calculated.  The efficiency of this method found to be 79.4 ± 2.25%. The values of 226 Ra obtained by emanometry were verified by HPGe detector from environment survey lab of Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam. The concentration of 228 Ra was determined by radiochemical method using low level background beta counter used by earlier researcher.  The overall efficiency of this method was found to be 80%.
| 3. Results and Discussion|| |
Relatively higher dose rates were recorded at Devagondanahalli and Kalasapura, the mean absorbed gamma dose 233 and 191nGy.h -1 respectively with the corresponding annual dose of 2.0 and 1.8 mGy.h -1 receptively. These higher doses may be attributed to the presence of granitic outcrops and since these places lie near the region of U-QPC (Uranium Quartz Pebble Conglomerate) occurrences. The average annual dose of other areas put together was 0.882 mGy.h -1 with standard deviation of 0.182 mGy.h -1 .
[Table 2] shows the concentrations of 226 Ra and 228 Ra. The highest activity, 47.7 Bq.kg -1 was observed at Magadi Kyamara and the lowest at Esharahalli when 226 Ra isotope was considered. The ratio of 228 Ra/ 226 Ra varied widely from 0.6 to 4.7. One of the reasons for this may be the mixing in layers of the soil during cultivation.
[Table 3] shows the concentrations of 210 Po and 210 Pb in the cultivated and uncultivated land. The highest activity 71.2 Bqkg -1 was observed at Magadi Kyamara and lowest was 12.9Bqkg -1 at Kalasapura. Further, the mean ratio of 210 Po and 210 Pb in cultivated land is less than that of the uncultivated land. This indicates that the increased concentrations of 210 Pb in cultivated land in comparison with uncultivated land, whereas it was reverse in the case of 210 Po. The variation in distribution of the two radionuclides is quite wide. The cultivated soils are loosely bound and they can easily be mixed with water. The 'Floating Fraction' serves as the source of all chemical elements. These particles get washed out along with rainwater. This natural process may be one of the reasons for the decrease in activities of 226 Ra, 228 Ra, and 210 Po in cultivated and fertilizer added soil. The increase of activity of 210 Pb may be due to resuspension.  The variation of concentrations of 210 Po and 210 Pb in different locations of the study area are shown in [Figure 1].
|Figure 1: Variation of concentrations of 210Po and 210Pb in different locations of Chikmagalur district|
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|Table 3: Concentration of 210Po and 210Pb in cultivated and uncultivated land|
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| 4. Conclusion|| |
The higher gamma radiation doses in the some regions of the study area were due to the presence of granitic outcrops and the proximity of U-QPC region. The cultivation process, which mixes the soil, was the main reason for the wide variation of 228 Ra and 226 Ra ratio. The increase of activity of 210 Pb may be due to re-suspension factor ('K'). This factor characterizes the relationship between surface and air borne contamination. The 'K' factor increases for 226 Ra, 228 Ra, and 210 Po in cultivated, fertilized area, but not for 210 Pb.
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[Table 1], [Table 2], [Table 3]