Comprehensive Review of the Investigation of Anthropogenic and Naturally Occurring Radionuclides in Different Parts of Bangladesh

Authors attempt to depict a survey of anthropogenic 137Cs and naturally occurring radionuclides (226Ra, 228Th, 232Th, 214Bi, 208TI, 40K) in undistributed soil, water, ship scrapped materials such as metal, rubber and foam and tree bark of ship breaking area, cynoglossids i.e. tongue soles and tea leaves collected from different parts of Bangladesh for detecting health hazards, environmental protection and radiation safety of the public. The assessment of such radionuclides in these samples is utmost important due to nuclear test and accident, fallout and disposal of radioactive wastes. These radiotracers have been investigated by using laboratory-based Gamma Spectrometry for Food and Environmental Samples. The observation of activity concentrations for 137Cs, 226Ra, 228Th,232Th, 214Bi, 208TI and 40K have been presented in Bq.Kg-1. The others radiological parameters such as gamma ray dose rate (nGyh-1), Radium Equivalent Dose (Raeq) Bq.Kg-1, Representative Level Index (lr) Bq.Kg-1 and Transfer Factor (TF) %. The Radiation Hazard Index (Hx) Bq.Kg-1 also has been presented.


I. INTRODUCTION
Assessment of any release of radioactivity to the environment is important the protection of public health, especially if the released radioactivity can enter into the food chain. Assessment demands rapid, reliable and practical techniques for analysis of various radionuclides [1]. In this context, distribution of 137 Cs and naturally occurring radionuclides for soil and water samples in the Terrene of Goainghat and Jaintapur Area of Sylhet district and the same for soil samples at the site of the Rooppur Nuclear Power Plant has been presented [2,3]. In [4], describes the study of the radioactivity in soil and tea leaf and transfer factor of those radionuclides. The environmental radioactivity levels, both natural and anthropogenic, in the ship scrapped materials such as metal, rubber and foam and tree bark of ship breaking area of Bhatiari, Chittagong in the southern part of Bangladesh have been analyzed [5]. The study on 214 Bi, 208 TI, 40 K and 137 Cs in soil of Chittagong Hills, Bangladesh has been provided to ascertain the baseline data to assess the public exposure of that area [6]. The radionuclides concentration in the cynoglossids i.e. tongue soles collected from the Kutubdia channel of Bangladesh have been estimated. The study consists of the analysis of seasonal occurrence of these radionuclides along with hydrological parameters and biochemical constituents of their living area [7]. In [8], presents the Gamma radiation dose from the naturally occurring radioclides in soil of the Potenga Sea Beach area of Bangladesh. In Potenga Sea Beach soil samples, the activities of 226 Ra, 232 Th and 40 K have been found to be higher than that of world average values. The radioactivity of naturally occurring radionuclides in water and sediment samples collected from the Meghna-Dakatia River at Chandpur of Bangladesh has been measured. Thus, the external outdoor radiation dose rate, radium equivalent activities, Req and representative level index, lyr also have been estimated [9]. Activities of gamma-emitters 238 U, 226 Ra, 232 Th and 40 K in tap water samples of Dhaka city have been analyzed by using High-Purity Germanium (HPGe) coaxial detector(EG &ORTEC) coupled with Silena Emcaplus Multichannel Analyzer System. The estimated effective dose and annual effective dose due to intake of different radionuclides for various age groups also have been provided [10]. The current research motivated to the recent trend and development in Radiological Research in Bangladesh. A comprehensive review of the investigation of anthropogenic 137 Cs and naturally occurring radionuclides ( 226 Ra, 228 Th, 232 Th, 214 Bi, 208 Tl, 40 K) in undistributed soil, water, ship scrapped materials such as metal, rubber and foam and tree bark of ship breaking area, cynoglossids i.e. tongue soles and tea leaf collected from different parts of Bangladesh.
II. MATERIALS AND METHOD 2.1: Sample Collection Double identities should be placed on samples at collection time. It is advisable that a standard form with all relevant information such as date, location, fresh weight, weather, collector's name etc. to be filled up. Care should be taken that the sample is representative and suitable for specific purposes of the monitoring procedures [1]. In this context, M. N. Alam et al [2] study area was in Goainighat and Jaintapur of Sylhet disdrict located at 91 0 50 to 92 0 13 N and 24 0 56 to 25 0 12 E. The soil samples have been collected from 17 sites at a depth of 0-10 cm with the help of premeasured steel corer of size 10.5 cm dia and 25 cm height. Water samples have also been collected from 17 sites of natural reservoir corresponding to the location of soils, on the border area at a distance of 500 m to 4 km from each other during the period of September -October, 2000. The collected soils are of sedimentary rock and clay type and believe to be undistributed. Thereafter, N. Absar [4] research area was in Odalia tea Garden which was about 3000 sq. km situated in the hilly region of Fatickchari Chittagong disdrict of Bangladesh. Soil samples have been collected from 5 locations of the garden at a depth upto 20 cm from the surface and tea leaf sample for the same 5 locations [5].

2.2: Sample Preparation
Samples received in the laboratory may not in the proper physical form for analysis. They may require reduction in size, evaporating, drying of some form of homogenizing before taken for analysis. Some general consideration for handling and pretreatment of samples are needed. The samples with high levels of activity should be processed in a separate area from low level samples to avoid contamination [1]. All the soil samples M. N. Alam et al [2] have been dried in an oven at 110 0 C for 48 h, pulverized and passed through sieve, weighed and then packed in cylindrical plastic containers (6.5 cm 7.5 cm). They have been then sealed tightly with caps, wrapped with thick vinyl tape around their screw necks and stored for 4 weeks to allow secular equilibrium between 226 Ra, 232 Th and their daughter nuclei. Water samples were collected with 5-litre plastic jars from the natural reservoir. Each 5-litre water sample has been boiled to reduce its volume to 500 ml and packed into 500 ml cylindrical containers, sealed tightly and wrapped with thick vinyl tapes around their screw necks. These samples have been stored for 4 weeks too.

2.3: Measurement Procedure
The -ray activities of all the collected samples for 226 Ra, 232 Th, 214 Bi, 208 Tl, 40 K and 137 Cs have been analyzed by using a p-type coaxial lead shielded High Purity Germanium (HPGe) detector having relative efficiency of 30%, active volume 132 cm 3 , resolution (FWHM) of 1.85 KeV at 1332 KeV for 60 Co coupled with PCA and other accessories. The calibration of the peak efficiency of the detector was performed using IAEA reference samples 238 U (RGU-1), 232 Th (RGTh-1), 40 K (RGK-1) and 137 Cs (IAEA-152) [11]. The mentioned radiotracers were investigated by using a p-type coaxial lead shielded High Purity Germanium (HPGe) detector with Liquid Nitrogen (LN2) cooling having relative efficiency of 20%, resolution (FWHM) of 1.80 KeV at 1332 KeV for 60 Co coupled with DSA-1000, Genie-2000 GAA software and other accessories [3]. The radioactivities of the investigated samples were measured for 10,000s by using the same Gamma Spectrometry configuration as described in N. Absar [4]. The 226 Ra ( 238 U) activity was determined individually from the net area of peak at energies of 351.9 keV ( 214 Pb), 1120 keV ( 214 Bi) and 1764 keV ( 214 Bi). 214 Pb and 214 Bi are the decay products of 238 U series. Similarly, the 232 Th activity was determined from the counts at peak energies of 238.6 keV ( 212 Pb), 727 keV ( 212 Bi), 911 keV ( 228 Ac) and 583 keV ( 208 Tl) [5]. The 40 K and 137 Cs radionuclides have been measured from their respective ray energies 1460 KeV and 661.66 KeV respectively [1,12].

2.4: Results and Discussion
Radiological parameters are very important for ensuring the public health and safety (reducing environmental radiation exposer), environmental protection and radioecological control. According to N. Alam et al [2], the activity concentration of 137 Cs in soil and water of the sampling area have been observed as 4.12  0.32 to 30.53  0.88 Bq.kg -1 with an average value of 13.23  6.76 Bq.kg -1 and 1.0  0.34 to 1.72  0.61 Bq.L -1 . The activity concentration S. Roy et al [3] of 137 Cs in seven soil samples out of thirty of the Rooppur Nuclear Power Plant (RNPP) sampling area have been observed as 3.46  0.48 to 5.86  0.61 Bq.kg -1 with an average value of 4.22  0.78 Bq.kg -1 . In N. Absar [4] research, the average activity concentration of 137 Cs in the soil samples has been obtained as 2.84  0.27 Bq.kg -1 whereas the 137 Cs for tea samples was not present in all samples, therefore, no uptake has been recorded. Barua, et al [5] obtained the lower limit of detection for 137 Cs was 0.043679 Bq.kg -1 . In N. Alam et al [6], the activity concentration of 137 Cs in soil of Chittagong Hills varies from 1.08  0.14 to 4.25  0.48 Bq.kg -1 with an average value of 2.66 Bq.kg -1 . According to J. Ferdous et al [10], no activity concentration of 137 Cs in tap water of Dhaka City has been detected.
N. Alam et al [2], continued with the activity concentration of naturally occurring radionuclides like 226 [7], the range of 226 Ra activity has been measured as 9 ± 2 to 20 ± 5 Bq.kg -1 fresh weight (fw) with maximum in the edible portion of c. cynoglossus and minimum in the whole body of c. lingua. Seasonal variation of activity of radionuclides in different body parts of cynoglossids also have presented. Afterwards, the activity concentration of 232 Th has been found in the range 8 ± 1 to 17 ± 4 Bq.kg -1 fw with highest in the whole body of c. cynoglossus and lowest in the whole body of p. bilineata.Then, the range of 228 Th activity has been measured as 4 ± 1 to 14 ± 4 Bq.kg -1 fw with maximum in the offal of c. bilineatus and minimum in the edible portion of c. cynoglossus. At last, the radionuclides concentration of 40 K in the different body parts of cynoglossids i.e. tongue soles on a fw basis also have been detected as 81 ± 11 Bq.kg -1 to 227 ± 19 Bq.kg -1 fw with highest in the whole body of c. bilineatus and lowest in the edible portion of c. cynoglossus. Following S. Ghose et al [8] , mean the activities of 226  and all natural origin for bulk samples have been recommended by IAEA as 100 Bq.kg -1 and 1000 Bq.kg -1 respectively; only exception in 40 K which is 10000 Bq.kg -1 [13]. The absorbed dose rate in air one meter above the ground surface due to the radionuclides 226 Ra, 232 Th, and 40 K of soil has been estimated using the formula given by Where CRA , CTH and CK are the average activity concentrations of 226 Ra, 232 Th, and 40 K of soil samples in Bqkg -1 [14]. The dose rate N. Alam et al [2] due to 226 Ra, 232 Th, and 40 K of soil samples varied in the ranges from 59.66 to 89.84 nGyh -1 , with an average value of 74.76 nGyh -1 , which is higher than the world average value of 52 nGyh -1 . The dose rate S. Roy et al [3] due to 226 Ra, 232 Th, and 40 K of soil samples varied in the ranges from 50.90 to 103.46 nGyh -1 , with an average value of 69.45 nGyh -1 . According to N. Absar [4] research, the dose rate that has been calculated of 71.14 nGyh -1 is to be treated as outdoor dose that yielded annual effective dose much below the permissible limit of 1.0 mSv.y -1 recommended by the International Commission on Radiation Protection (ICRP) for general population [15]. The dose rate in S. Ghose et al
The annual effective dose equivalent Deff from outdoor terrestrial gamma radiation is given by Where 0.2 is the outdoor dose occupancy factor and 0.7 Sv.Gy -1 is the quotient of effective dose equivalent rate to absorbed dose rate in air [17].
The annual effective dose due to intake of 238 U, 226 Ra, 232 Th and 40 K in tap water samples of Dhaka city for five age groups are 104.10, 87.90, 75.73, 63.19 and 73.38 Sv.y -1 for 1 year, 5 year, 10 year, 15 year and above 18 year respectively in J. Ferdous et al [10]. These values are significantly lower than both the World Health Organization (WHO) and the International Commission on Radiological Protection (ICRP) limits.
The annual effective dose equivalent Deff from indoor exposure is given by: Where 0.8 has been used as the occupancy factor [17]. Therefore, the total annual effective dose equivalent from terrestrial radiation is sum of outdoor and indoor annual effective dose equivalent.
The -ray radiation hazards due to the radionuclides 226 Ra, 232 Th, and 40 K of soil samples has been assessed by two different indices. The most widely used radiation hazard index , Raeq , can be derived from the following formula: = + ( Where CRA, CTH and CK are the average activity concentrations of 226 Ra, 232 Th, and 40 K in Bq.kg -1 respectively [18]. The values of Raeq for N. Alam et al [2] in soils varied from 121. 8 [4]. Barua, et al [5] calculated the Raeq in the range of 21-145 Bq.kg -1 except one scrapped metal from engine (760 Bq.kg -1 ) is of radiological concern indeed. The Raeq for S. Ghose et al [8]  Absar [4]. The lr for S. Ghose et. Al [8] due to 226 Ra, 232 Th, and 40 K in soil samples of high and low tide lines varied in the ranges from 0.6 -3.0 and 0.7 -2.0 Bq.kg -1 respectively. The value of lr for the sediments sample has been obtained in the range of 0.70  0.32 to 1.21  0.46 Bq.kg -1 with mean value of 0.95  0.28 Bq.kg -1 in M. I. Chowdhury et al [9]. The Transfer Factor (TF) is defined by the following equation: The transfer mechanism of radionuclides, represented by TF, is widely used to describe the soil-to-plant transfer of radionuclides through plant roots. The concentration of a nuclide in a plant or plant part (in Bq.kg -1 , dry weight), is assumed to be linearly related to its concentration in soil within the rooting zone also in Bq.kg -1 , dry weight) [20].
TF value in excess of unity imply active bioaccumulation of the activity. The values less than unity mean either strong binding of the radionuclides with soil, little or no accumulation in the plant [4].
The external radiation hazard index Hext and internal radiation hazard index Hint has been calculated by using the following formula: Where, the numerical quantities of equations (8) and (9) are in units of Bq.kg -1 and AU, ATh and AK are the activity concentrations of the radionuclides 238 U, 232 Th, and 40 K respectively [21]. The values of Hext and Hint have been observed in the ranges from 0.30 0.08 to 0.50 0.08 and 0.62 0.10 to 0.39 0.10 with the mean value of 0.41 0.08 and 0.51 0.10 respectively in N. Absar [4]. The Hext in Barua, et al [5] varied from 0.06 to 0.39. Since these values are lower than unity, the external radiation hazard in the ship breaking area is low.
The radon mass exhalation rate is calculated by following the equation given below = . Where, .

III. CONCLUSION
The recent trend and development in the Radiological Research in Bangladesh has been presented in this study. Firstly, a chronological survey of the investigation of anthropogenic 137 Cs and naturally occurring radionuclides ( 226 Ra, 228 Th, 232 Th, 214 Bi, 208 Tl, 40 K) in undistributed soil, water, ship scrapped materials such as metal, rubber and foam and tree bark of ship breaking area, cynoglossids i.e. tongue soles and tea leaf collected from different parts of Bangladesh has been provided. Afterwards, the matter of sample collection, sample preparation and measurement procedure has been depicted as well. At the end, radioactivity analysis of the samples has been presented for detecting health hazards to ensure public health and safety.