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ARTICLE
Year : 2011  |  Volume : 34  |  Issue : 2  |  Page : 129-136  

Measurement of radioactivity and hence define the radiological risk associated with the Chittagong city site coastal sediment containing all types of wastes (mills, factories, industries, and municipalities) in Bangladesh


1 Department of Physics, University of Chittagong, Chittagong, Bangladesh
2 Radioactivity Testing and Monitoring Laboratory, Bangladesh Atomic Energy Commission, Chittagong Medical College Hospital Campus, Chittagong, Bangladesh

Date of Web Publication12-Jul-2012

Correspondence Address:
Md. Kowsar Alam
Department of Physics, University of Chittagong, Chittagong
Bangladesh
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Source of Support: None, Conflict of Interest: None


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  Abstract 

The research work was carried out with an aim to determine the radiological threat to the inhabitants of Chittagong city in Bangladesh. To investigate the radiological threat, the activity concentrations of naturally occurring radionuclides 238 U, 232 Th, 226 Ra, and 40 K were measured in the sediment samples collected from three locations of the major drainages (Chaktai Khal and Karnaphuli River) of Chittagong city. The activity concentrations of all the elements were found to be higher than those of the world average values. In the samples studied, the artificial radionuclide 137 Cs has not been detected. The radiation doses from where the samples were collected were measured directly by employing beta-gamma survey meter (model: LUDLUM 44-9). The average values of the radiological parameters calculated from the activity concentrations of the radionuclides mentioned in the sediment samples were found to be higher than those of the corresponding world average values. The results of the present research were compared with the corresponding results obtained in other locations of Bangladesh as well as in different countries published in different journals.

Keywords: Broad energy germanium detector, Gamma spectrometry, Natural radioactivity, Radiological parameters


How to cite this article:
Alam M, Chakraborty S R, Rahman AR, Deb A K, Kamal M, Bhuian S I. Measurement of radioactivity and hence define the radiological risk associated with the Chittagong city site coastal sediment containing all types of wastes (mills, factories, industries, and municipalities) in Bangladesh. Radiat Prot Environ 2011;34:129-36

How to cite this URL:
Alam M, Chakraborty S R, Rahman AR, Deb A K, Kamal M, Bhuian S I. Measurement of radioactivity and hence define the radiological risk associated with the Chittagong city site coastal sediment containing all types of wastes (mills, factories, industries, and municipalities) in Bangladesh. Radiat Prot Environ [serial online] 2011 [cited 2020 Aug 6];34:129-36. Available from: http://www.rpe.org.in/text.asp?2011/34/2/129/98402


  1. Introduction Top


Environmental background radiation consists of natural and man-made radioactivity. It has been estimated that on average, 85% of the radiation to which humans are exposed is from natural sources and 15% is from man-made sources (UNSCEAR, 2000). Therefore, it is said that most of the ionizing radiation that people are exposed to nowadays comes from natural rather than man-made sources. Moreover, some natural radionuclide activity concentrations in the terrestrial environment are gradually increasing from fossil fuels' combustion, phosphate industry, and the use of fertilizers. Natural radioactivity is mainly due to the presence of primordial radionuclides such as 232 Th, 235 U, 238 U, 40 K, and 87 Rb (UNSCEAR, 2000). However, the highest contribution made to this radioactivity is by great number of decay products of 232 Th and 238 U. It has been estimated that soil is the main reservoir of man-made radionuclide's formed by nuclear activities. [1] 137 Cs deposited in soil causes internal irradiation by inhalation and by ingestion of contaminated food, or secondly, through external irradiation from photon emissions from surface soil. The objectives of the current study were: (1) to assess the radioactivity levels of the Karnaphuli River sediment containing municipal and industrial wastes of Chittagong city, and (2) to assess the corresponding radiological threat to the inhabitants of the Chittagong city associated with the municipal and industrial waste deposited in the sediment of the Karnaphuli River.


  2. Materials and Methods Top


2.1. Study area and sampling

Chittagong (22°20'01.89" N and 91°50'06.15" S at Court building of Chittagong city) is in the south-east district of Bangladesh. It is the second largest city of Bangladesh and situated on the banks of the Karnaphuli River. The Karnaphuli River originates in the lofty ranges of the Lusai Hills of Assam in India at 22°53' N and 92°27' E and discharges into the Bay of Bengal at 22°12' N and 91°47' E (at Patenga), winding a zigzag course of some 231 km through the districts of Chittagong and Chittagong Hill Tracts and receiving a large number of tributaries. In this study, a total of 25 samples were collected from three regions, namely, (1) around the 3 rd Karnaphuli Bridge (KB), (2) the Chaktai Khal (CK), and (3) the Fishari ghat (FG). The second and the third locations are one of the main drainages of Chittagong city and its estuary at Karnaphuli River. Among the 25 samples, 1-14 samples were collected around 2 km of the 3 rd KB or The Shah Amanat bridge, 15-21 samples were collected around 1.5 km of the CK, and 22-25 samples were collected around 1 km of the FG region. All of the samples were collected using a rotating cylindrical plastic corer and the geographical locations of all sampling points were recorded by using GPS of model GPSmap 76CSx, GARMIN. The baseline location of study area and location of sampling points on Google earth map are shown in [Figure 1] and [Figure 2], respectively.
Figure 1: Baseline map of the study area

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Figure 2: The sampling location of three study areas with the corresponding sample identification codes

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2.2. Gamma spectrometry and analytical procedures

An overview of preparation technique of all the samples used in the present study is given in [Figure 3]. The present research work had been performed by using a high-resolution gamma spectrometry of Canberra brand Broad Energy Germanium Detector (BEGe) system of detector model BE3820 and serial number 09078305, having relative efficiency of 38%. The full-energy peak efficiency curve was plotted by measuring the reference samples IAEA/RGU-1 (U ore), IAEA/RGTh-1 (Th ore), and IAEA/RGK-1 (K sulfate), from which the counting efficiencies of the gamma ray peaks were measured. [2] The spectrum acquisition and analysis were performed by the Canberra software of Genie 2000. The geometry of the counting samples was the same as that of the standard samples and the counting time for all the samples was 10,000 seconds. The background count due to naturally occurring radionuclides in the environment around the detector was subtracted from each sample count. Corrections were also made for self-absorption of the gamma radiation by the samples. [3],[4] The results were expressed with the confidence limit or standard deviation of ±1σ.
Figure 3: Flowchart of the sample preparation

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  3. Experimental Working Formulae Top


In the present study, the formulae given in Appendix A had been used for the calculation of the activity concentrations of the samples and the corresponding radiological hazard parameters. They are as follows:

  • The counting efficiency of the detector was calculated by using the formula [5] of Eq. (B.1).
  • Specific activities of the natural radionuclides presented in the sediment samples had been calculated by using the formula [6] of Eq. (B.2).
  • The formula for calculating the outdoor absorbed dose rate in air at 1 m above the ground surface (in nGy/h) using the conversion factors (UNSCEAR, 1988) is shown in Eq. (B.3).
  • The indoor contribution is assumed to be 1.2 times higher than the outdoor dose (UNSCEAR, 1988), [7] which is shown in Eq. (B.4).
  • The formula related to the annual effective dose equivalent Deff from outdoor terrestrial gamma radiation is shown in Eq. (B.5). [3]
  • For indoor exposure, using an occupancy factor of 0.8, [3] the annual effective dose equivalent was calculated by Eq. (B.6).
  • The total annual effective dose equivalent from terrestrial radiation is the sum of outdoor and indoor annual effective dose equivalents.
  • The formulae for calculating the radium equivalent activity [8] Ra eq and the representative level index, [9],[10],[11] Iγr in the present research used are shown in Eq. (B.7) and (B.8).
  • The formulae [8] for calculating the external radiation hazard, H ext , and internal radiation hazard, H int , are shown in Eq. (B.9) and (B.10).



  4. Results Top


The calculated mean activity concentrations of radionuclide's 238 U, 232 Th, 226 Ra, and 40 K were 45.32±4.44, 79.68±6.44, 61.02±9.33, and 856.88±59.45 Bq/kg, respectively, as given in [Table 1], and the corresponding graphical comparison is indicated in [Figure 4]. The activity concentrations of these radionuclides were found to range from 21.50±2.39 to 66.68±5.96, 41.52±3.53 to 106.62±8.42, 22.28±6.03 to 132.42±14.55, and 370.07±32.16 to 1207.40±76.82 Bq/kg, respectively. The anthropogenic radionuclide 137 Cs had not been detected in any sample. The comparison of the activity concentrations of radionuclide's 238 U, 232 Th, 226 Ra, and 40 K of the present study with regional, values of other countries of the world, and worldwide values [12] is given in [Table 2]. The mean activity concentrations of the radionuclides 238 U, 232 Th, 226 Ra, and 40 K of the present study were found to be higher than those of the worldwide values [12] as well as the world average values. [7] The graphical comparison of the mean specific activity concentrations of the radionuclides of the present study with regional values and worldwide values is shown in [Figure 5]. The calculated mean values of the radiological parameters, namely, radium equivalent activity, representative gamma level index, outdoor dose rate, indoor dose rate, outdoor annual effective dose, indoor annual effective dose, and total annual effective dose were found to be 240.94±23.12 Bq/kg, 1.77±0.17 Bq/kg, 115.82±10.81 nGy/h, 138.98±12.98 nGy/h, 0.14±0.02 mSv/year, 0.68±0.06 mSv/year, and 0.82±0.08 mSv/year, respectively. All these values of the radiological parameters were higher than those of the world average values. [7] The average of the measured value of the outdoor dose rate at 1 m height above the ground by using the beta-gamma survey meter of model LUDLUM: 44-9 was found to be 215.81±14.69 nGy/h. The directly measured dose rate was higher than that of the calculated value as given in [Table 3]. This is because during direct measurement, radiation dose due to cosmic radiation and other air-borne radiation including beta radiation had been included. The external radiation hazard index, Hext , and internal radiation hazard index, Hint , were found to be less than the recommended value of 1, which were 0.65±0.06 and 0.82±0.09, respectively. The comparison of the overall results of the present research work is shown in [Table 4].
Figure 4: Comparison of the mean activity concentrations of radionuclides 238U, 232Th, 226Ra, 40K, and 137Cs of all samples

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Figure 5: Comparison of mean activity concentrations of 238U, 232Th, 226Ra, and 40K with regional study and worldwide values

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Table 1: The comparative data of the mean activity concentrations of radionuclides 238U, 232Th, 226Ra, 40K, and 137Cs in all samples

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Table 2: Comparison of the mean activity concentrations of 238U, 232Th, 226Ra, and 40K (inBq/kg) of the present research work with regional values, values from other study areas of the world, and worldwide values

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Table 3: The comparative data of the measured and calculated dose rate at 1 m height above the ground

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Table 4: Comparison of results of the present study with corresponding world average values, worldwide values, and regional study values

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  5. Discussion Top


The present study shows the concentrations of Th- and U-series of radionuclide's ( 232 Th, 238 U, 226 Ra) and 40 K in the Karnaphuli River sediment. The specific activities of the radionuclides 232 Th, 238 U, 226 Ra, and 40 K in this river sediment were found to be higher than that of the world average as well as worldwide values.

The mean activity concentration of 232 Th in the Karnaphuli River sediment was found to be higher than those of Turkey, [16] Kirklareli, [15] Spain, [19] French rivers-1, [20] French rivers-2, [21] Iran, [22] China, [10] regional study, [13] Egypt. [28] It was about 1.77 times and 3.19 times higher than the worldwide value [12] and world average value, [7] respectively [Table 3]. However, the mean activity concentration of 232 Th was found to be lower than those of the Kestanbol, [17] South Cameroon, [24] India, [26] southern districts of Bangladesh, [27] China, [25] and northern districts of Bangladesh [Table 2]. [11]

The mean radioactivity level of 226 Ra in the Karnaphuli River sediment was found to be higher than those of Turkey, [16] Kirklareli, [15] Spain, [19] French rivers-1, [20] French rivers-2, [21] China, [10] regional study, [13] Egypt, [28] India, [26] and southern districts of Bangladesh, [27] although it was found to be lower than those of the Kestanbol, [17] Iran, [22] South Cameroon, [24] Louisiana, USA [18] and northern districts of Bangladesh [Table 2]. [11] It was found to be about 1.85 times and 2.44 times higher than the worldwide value [12] and world average value, [7] respectively [Table 3]. The present study showed that the average activity of 232 Th was 1.31 times higher than the average activity of 226 Ra in this river sediment.

The average activity concentration of 238 U in the Karnaphuli River sediment was found to be higher than those of the regional study, [13] Turkey, [16] French rivers-1, [20] French rivers-2, [21] Hungary, [23] Louisiana, USA, [18] and Republic of Ireland. [14] It was about 1.37 times and 1.81 times higher than the worldwide value [12] and world average value, [7] respectively [Table 3]. However, the mean activity concentration of 238 U was lower than those of the China [25] and Kestanbol [Table 2]. [17]

The specific radioactivity level of 40 K in the Karnaphuli River sediment was found to be higher than those of the Turkey, [16] Kirklareli, [15] Spain, [19] French rivers-1, [20] French rivers-2, [21] Iran, [22] regional study, [13] Egypt, [28] and southern districts of Bangladesh, [27] but the activity concentration of 40 K was found to be lower than those of the Kestanbol, [17] China, [10] South Cameroon, [24] northern districts of Bangladesh, [11] and India [Table 2]. [26] The specific activity of 40 K was found to be about 2.04 times and 2.32 times higher than the worldwide values [12] and world average values, [7] respectively [Table 3].

Although the radioactivity of Th, U-series radionuclides ( 232 Th, 238 U, 226 Ra), and 40 K was found in the Karnaphuli River sediment due to the natural distribution and disposal of municipal and industrial wastes of Chittagong city, no artificially produced anthropogenic radionuclide like 137 Cs had been detected in this river sediment samples. The un-detection of 137 Cs indicates that no nuclear test activities were carried out in that region and no fallout of 137 Cs radionuclide occurred.

The mean value of the representative level index Iγr , radium equivalent activity Ra eq , outdoor dose, indoor dose, indoor annual effective dose, outdoor annual effective dose, and total annual effective dose due to the radioactivity in the Karnaphuli River sediment were found to be higher than those of the world average [Table 3]. The average values were found to be about 2.69, 2.71, 2.12, 1.99, 2.005, 2.03, and 2.009 times higher than those of the world average, respectively [Table 3]. The mean value of the measured outdoor dose was 215.81±14.69 nGy/h, which was higher than that of the calculated outdoor dose at 1 m height above the ground, as given in [Table 4]. Because the dose rate was measured directly by using the beta-gamma survey meter of model LUDLUM: 44-9, which counted the environmental gamma radiations, cosmic radiations, as well as beta radiations from the environmental sources instantaneously. The calculated dose was based on the concentration of gamma emitting radionuclides only that are dealt with in the present study.

Again, the recommended value of the external and internal radiation hazard indices H ext and H int are one, [11] but in the sediment samples of the Karnaphuli River, the radiation hazard indices H ext and H int were 0.65 and 0.82, respectively [Table 3]. So, it does not pose any significant radiological threat to the inhabitants of the Chittagong city.


  6. Conclusions Top


Naturally occurring important radionuclides ( 238 U, 226 Ra, 232 Th, and 40 K) had been found in the sediment samples of Karnaphuli River and the artificial radionuclide 137 Cs had not been detected in any sample. The mean radioactivity levels of these radionuclides were higher than the respective world average values. These results showed that the mean outdoor dose rate in the study area was 115.82 nGy/h, which exceeded the world average value of 55 nGy/h. The total annual effective dose equivalent from terrestrial gamma radiation was 0.82 mSv of which 0.68 mSv was from indoor exposure and 0.14 mSv was from outdoor exposure. The recommended value of the radiation hazard indices H ext and H int is 1, but in the sediment samples of the study area, both the hazard indices were less than 1. Therefore, the present study area might not pose any radiological risk to the population of Chittagong city due to deleterious effects of ionizing radiation from the naturally occurring radioactive material (NORM) in the soils and sediments of the Karnaphuli River resulting from the natural distribution and disposal of municipal and industrial wastes of Chittagong city.

 
  References Top

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    Figures

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

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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5. Discussion
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