|Year : 2021 | Volume
| Issue : 2 | Page : 67-72
Distribution of natural and artificial radioactivity concentration in soils of two districts (Ballia and Deoria) of Uttar Pradesh, India
Deepak Kumar1, YP Gautam1, AK Sharma1, Vineet Kumar1, AR Tripathi1, S Kumar1, J Kumar1, IV Saradhi2, A Vinod Kumar2
1 Environmental Survey Laboratory, Narora Atomic Power Station, Bulandshahr, Uttar Pradesh, India
2 Environmental Monitoring and Assessment Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
|Date of Submission||18-Jun-2021|
|Date of Decision||20-Jul-2021|
|Date of Acceptance||28-Jul-2021|
|Date of Web Publication||23-Oct-2021|
Environmental Survey Laboratory, Narora Atomic Power Station, Narora, Bulandshahr - 202 389, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
This paper presents the activity concentrations of naturally occurring radionuclide 226Ra, 232Th, and 40K and the anthropogenic radionuclide, 137Cs in soil samples collected from Ballia and Deoria district of Uttar Pradesh, India. The mean activity concentrations of radionuclides in 43 soil samples from the two districts were measured using HPGe gamma spectrometry system. The activity level in soil samples varied from 23 to 50 Bq/kg with a mean of 30 Bq/kg for 226Ra, 30–74 Bq/kg with a mean of 47 Bq/kg for 232Th, 287–728 Bq/kg with a mean of 466 Bq/kg for 40K, and ≤0.1–1.4 Bq/kg with a mean of 0.4 Bq/kg for137Cs. The mean activity of naturally occurring 226Ra and 232Th is comparable with the international values reported by UNSCEAR while concentration of 40K is slightly higher. 137Cs activity is found to be comparable with the activities reported at other parts of India. Correlation of 226Ra and 40K activity with 232Th activity was observed as 0.85 and 0.75, respectively. A positive correlation (0.71) between 40K and 137Cs was found in the present study. The absorbed gamma dose rates in air were in the range of 44.6–98.3 nGy/h with a mean of 63.4 nGy/h, while the annual effective dose rates were observed in the range of 54.7–120.6 μSv/y with a mean of 77.8 μSv/y. The average value of radium equivalent activity in soil was 136.9 Bq/kg. This study provides a baseline data of natural radioactivity and 137Cs activity in soils of these two districts.
Keywords: Absorbed dose, annual effective dose rate, environmental radioactivity, HPGe gamma spectrometry system, soil
|How to cite this article:|
Kumar D, Gautam Y P, Sharma A K, Kumar V, Tripathi A R, Kumar S, Kumar J, Saradhi I V, Kumar A V. Distribution of natural and artificial radioactivity concentration in soils of two districts (Ballia and Deoria) of Uttar Pradesh, India. Radiat Prot Environ 2021;44:67-72
|How to cite this URL:|
Kumar D, Gautam Y P, Sharma A K, Kumar V, Tripathi A R, Kumar S, Kumar J, Saradhi I V, Kumar A V. Distribution of natural and artificial radioactivity concentration in soils of two districts (Ballia and Deoria) of Uttar Pradesh, India. Radiat Prot Environ [serial online] 2021 [cited 2021 Dec 8];44:67-72. Available from: https://www.rpe.org.in/text.asp?2021/44/2/67/329135
| Introduction|| |
Environmental radioactivity and the associated external exposure due to gamma radiation depend primarily on the geological and geographical conditions, and appear at different levels in the soils of each region in the world. It is crucial to determine the natural radioactivity of 226Ra, 232Th, and 40K and man-made radioactivity due to testing of nuclear weapons introduced in the environment. Among the man-made released radionuclides, 137Cs is one of the most important anthropogenic radionuclide. Around 25% of the total 137Cs released by the testing of nuclear weapons and other atmospheric emissions were deposited in the southern hemisphere.
Background level and baseline distribution of radioactivity in soils are monitored worldwide with the aim of providing useful information to assess human exposure to radiation, epidemiological studies and to build a “reference” database that can be useful to identify hotspots, and to evaluate changes of environmental radioactivity caused due to nuclear, industrial, or other human activities.
The objective of the present study is to carry out the radiological mapping to establish the baseline data on background radiation field and global fallout level of radioactivity in the soils at Ballia and Deoria district Uttar Pradesh. Data are generated as a part of emergency preparedness to identify the naturally occurring hot spots in public domain, if any.
| Materials and Methods|| |
Ballia and Deoria are two neighboring districts, situated in the eastern part of the state Uttar Pradesh, India, as shown in [Figure 1] and are located at the North latitude and East longitude are 25°23″–27°11″ and 82°38″–84°39″, respectively. Ghaghara and Ganga rivers that flow through the districts, old and younger alluvium constitutes the major physiography of districts. The average rainfall in the district is 983 mm.
Sample collection and processing
A total of 43 numbers of representative soil samples (i.e. S1–S43) from different locations of the two districts were collected from an undisturbed open area of one square meter. The area was cleared of grass and debris, and sample of top layer soil up to 5 cm was collected. The collected samples were dried in an oven at 100°C–110°C for about 24 h and sieved through a 2-mm mesh size sieve to remove stone, pebbles, and other macro-impurities. The homogenized soil samples were filled in airtight plastic container up to fixed height and weight. The container was sealed hermetically externally using cellophane tape to prevent the escape of radiogenic gases 222Rn and 220Rn and kept aside for about a month to ensure secular equilibrium between 232Th and 226Ra with their daughter products.
The equilibrated samples were analyzed by gamma spectrometry using 50% relative efficiency, P-type HPGe detector coupled to ITECH instruments make digital pulse processing MCA system. The system was calibrated for energy and efficiency using spiked soil sample and liquid standards containing 137Cs, 60Co, 133Ba, and 40K and verified by analysis of IAEA reference material such as IAEA-375 soil. Samples were counted for 24 h, and activity of 226Ra was determined by taking the weighted mean of their decay products: 214Bi (609 and 1120 keV) and 214Pb (352 keV). Similarly, the activity of 232Th was determined by taking the weighted mean of their decay products: 208Tl (583 and 2614 keV), 212Pb (238 keV), and 228Ac (911 keV).
The activity concentration per unit mass (A) of each sample was calculated using equation (1):
Where ƞ is measured photopeak efficiency, I is the gamma-ray intensity, t is sample counting time (s), and m is sample weight (kg).
Absorbed dose rate
The gamma dose rate in air was determined from 212Pb, 208Tl, 212Bi, and 228Ac for 232Th series and from 214Pb, 214Bi for 226Ra series. The contribution of natural radionuclides to the absorbed dose rate (D) in air at 1 m above ground depends on concentration of terrestrial gamma emitting radionuclides that are uniformly distributed in soil. The dose can be calculated using absorbed dose rate conversion factors, using the equation (2):
Where Ci (Bq/kg) concentration of radionuclides, DCF is dose conversion factor (nGy/h/Bq/kg) values for 226Ra = 0.462, 232Th = 0.604, and 40K = 0.0417, respectively.
Radium equivalent activity
The radium equivalent concentration (Bq/kg) is common index used to compare the specific activities of material containing 226Ra, 232Th, and 40K. It can be expressed as given in equation (3):
Where ARa, ATh, and AK are specific activities (Bq/kg) of 226Ra, 232Th, and 40K, respectively. The radium equivalent concentration (Raeq) was calculated based on the estimation that 370 Bq/kg of 226Ra, 259 Bq/kg of 232Th, and 4810 Bq/kg of 40K all producing same gamma dose rate.
Annual effective dose rate
The annual effective dose rate (AEDR) for outdoor and indoor dose occupancy factor were estimated using absorbed gamma dose rate with conversion coefficient from absorbed dose in air to effective dose, equation (4):
Where OC = occupancy factor (fraction of time spent indoor and outdoor) is 0.8 and 0.2, respectively. The results obtained are scaled by a factor of 0.7 to convert absorbed dose in air to effective dose received by adults.
| Results and Discussion|| |
The activity concentration (Bq/kg) of naturally occurring radionuclides such as 226Ra, 232Th, 40K, and the anthropogenic radionuclide 137Cs occurring due to nuclear fallout were determined in the soil samples from Ballia and Deoria districts, and results are given in the [Table 1]. The activity concentrations in the soil samples collected from Ballia and Deoria ranges from 23 to 50 Bq/kg for 226Ra with mean of 30 Bq/kg, 30 to 74 Bq/kg for 232Th with mean of 47 Bq/kg, and 287 to 728 Bq/kg for 40K with mean of 466 Bq/kg.
|Table 1: Natural radioactivity in soil sample of Ballia and Deoria (Bq/kg)|
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The 232Th/226Ra ratio ranged from 1.3 to 1.9 with a mean of 1.5. Mohanty et al. reported 232Th/226Ra in soil samples in Kaiga region as 0.8–5.1.
Results indicate that the mean concentration levels measured in Ballia and Deoria soil are comparable with other region of India. Average concentration of 226Ra, 232Th, and 40K in soil of Ballia and Deoria is comparable with the average data published in UNSCEAR, 2000 for East Asian region. 137Cs radionuclides concentration in soil of the two districts ranged ≤0.1–1.3 Bq/kg with the average value of 0.4 Bq/kg. A survey in 33 soils of São Paulo state, 0–20 cm depth, found an average concentration value of 1.9 Bq/kg (values ranging from <0.3 to 4.1 Bq/kg). Rana et al. have reported 137Cs in soil sample of Tummalapalle, Andhra Pradesh, 0.15–3.42 Bq/kg with mean value of 1.34 Bq/kg. Ribeiro et al. reported concentration value of 137Cs ranged 0.51–1.25 Bq/kg in soil samples of the Rio de Janeiro state of Brazil.
Linear regression analysis shows good correlation in the soil samples activity of Ballia and Deoria for 232Th versus 226Ra (R2 = 0.85), for 232Th versus 40K (R2 = 0.75) as shown in [Figure 2] and [Figure 3]. Furthermore, a positive correlation (R2 = 0.71) was observed between 40K and 137Cs activity in soil sample of Ballia and Deoria in [Figure 4]. 40K and137Cs activity in soil sample is useful for estimation of discrimination factor and their transfer factor. Concentration of 137Cs in soil depends on organic content matter and clay content of the soil and migration depends on rainfall and transfer to vegetation. Soil having higher potassium content have less transfer of cesium to vegetation, thus results in higher cesium level in soil, which is observed from the correlation between 40K and 137Cs activity, in soil sample is useful.
|Figure 2: Linear regression analysis of 232Th versus 226Ra activity in soil sample of Ballia and Deoria|
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|Figure 3: Linear regression analysis of 232Th versus 40K activity in soil sample of Ballia and Deoria|
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|Figure 4: Linear regression analysis of 40K versus 137Cs activity in soil sample of Ballia and Deoria|
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The absorbed gamma dose rate at 1 m above ground in outdoor air was calculated from concentration of radionuclides of 226Ra and 232Th series and of 40K using the equation-1 and the computed values for the two districts ranged as 44.6–98.3 nGy/h with mean value of 63.4 nGy/h which is comparable the corresponding population-weighted global average dose rate of 60 nGy/h. The Raeq computed for all the locations under study of the two districts ranges from 95.3 to 212.3 Bq/kg which is quite low compared to the recommended limit of 370 Bq/kg.
The AEDR was computed and found to be in the range of 54.7–120.6 μSv/y, with an average value of 77.8 μSv/y, which is comparable with world average value of 70 μSv/y. [Table 2] presents the details of absorbed dose rate, radium equivalent activity, and AEDR for the two districts for outdoor and indoor occupancy.
|Table 2: Absorbed dose, radium equivalent activities, and annual effective dose rates for Ballia and Deoria|
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It can be seen from [Table 2] that the mean absorbed dose in both the districts is almost same of the order of 64.4 and 60.8 nGy/h, respectively, which is slightly higher than world average value of 51 nGy/h. The annual effective outdoor dose rate for both the districts was found to be 78.9 and 74.5 μSv/y, respectively.
[Table 3] presents the comparison of 226Ra, 232Th, 40K, and 137Cs activity in soil of Ballia and Deoria with other parts of India and world. It is observed that the estimated dose rate at Ballia and Deoria from 226Ra, 232Th, and 40K content in soil is comparable with that estimated at Narora, Uttar Pradesh, Gorakhpur, Haryana estimated, and Kaiga, Karnataka.
|Table 3: Comparison of Ra 226, Th 232, K 40, and Cs 137 activity concentration in soil sample and dose rate due to natural radioactivity of Ballia and Deoria with different parts of India and world|
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[Figure 5] illustrates the relative contributions to total absorbed dose in outdoor air due to 226Ra series, 232Th series, and 40K present in the soil. The relative contribution to dose due to 232Th was 46% followed by the contribution due to 40K and 226Ra series elements as 31% and 23%, respectively.
|Figure 5: Relative contribution to total absorbed dose in air due to 226Ra series, 232Th series, and 40K content in soil|
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| Conclusions|| |
The mean radioactivity levels in both the neighboring district Ballia and Deoria soil due to naturally occurring 226Ra and 40K concentration are comparable with those of worldwide soil but 232Th is slightly higher. The absorbed dose rate in air was found to be in the range of 44.6–98.3 nGy/h with mean of 63.4 nGy/h, which is comparable with corresponding population-weighted value of 60 nGy/h. The estimated dose rate at Ballia and Deoria are comparable with the estimated value at Gorakhpur, Haryana and Narora, Uttar Pradesh. 137Cs in soil of Narora site is comparable with the values of present study and is at fallout level.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3]