Investigations of the Radioactive Presence and Heavy Metallic Materials in Merowe Dam Area ()
1. Introduction
There are many different groups concerned about the assessment of the general environmental impact, before, during or after, of the construction of the dam to present an independent evaluation of the environmental impact to the surrounding reservoir such as: induced water quality, hydrology and water balance [1]. Also, there was a committee to declare the consequences of dam failure in terms of losing life and damage to property or services as well as environmental damage [2]. Furthermore, there are many studies that classify downstream hazard and take consideration of environmental damages. This would address situation where the reservoir contains materials which may be harmful to human. Added to that, different concerns of ionizing radiation background were assessed. This survey leads the fact that there are some raw materials used in construction when they product it may contain radioactive material or natural occurring radioactive material (NORM) during or after production processes led to possible multiplication effects [3].
Merowe dam is one of the strategically national schemes built in North Sudan, also known as Merowe high dam or Hamdab dam. It is a multi-purpose hydro project that is considered a large dam near Merowe town and it’s about 370 kilometers north of the city of Khartoum [4]. Several foreign institutions are currently involved in salvage archaeology in the region under the umbrella of Merowe Dam Archaeological Salvage Project (MDASP). Resettlement and compensation were mainly offered to Manasir, Hamadab and Amri tribes [5]. Merowe dam constrained again several local settlements to be displaced in desert regions and famous archaeological sites like Napata besides the Merowe dam [6].
There are several environmental studies done in Sudan, and take consider about radiation survey including assessing radiation background to compare results with the recommendations of the International Commission on Radiological Protection (ICRP) [7]. Also, some cases refer the low dose level of natural occurring radioactive materials NORM [8]; for instance to previous studies in Sudan, there were geographical information system (GIS), predictive mapping of terrestrial gamma radiation in the northern state, of Sudan. The result presents the evaluation of absorbed dose in air due to gamma-emitting nuclides from 238U and 232Th series, 40K and 137Cs from soil sample in different location. Activity concentrations were 19 ± 4 (238U), 47 ± 11 (232Th), 317 ± 65 (40K) and 2.26 Bq·kg−1 for 137Cs. On average, the values obtained fall within a narrow range of 44 and 53 nGy·h−1 [9]. In addition, the assessment of terrestrial gamma radiation in Sudan, Sam and co-authors conducted study on calculations of the external exposure due to gamma radiation from the ground. From the results of the measurements of radionuclide activity concentrations in the soil at various locations in Sudan, the average exposure was found to be 45 nGy·h−1, corresponding to the annual dose equivalent of 278 mSv·y−1 [10]. Also in the western region, Darfur state, specifically in Jebel Mun, the activity concentrations of 238U, 232Th and 40K were found to range from 39 - 253 Bq·kg−1, 41 - 527 Bq·kg−1 and 77 - 3027 Bq·kg−1, respectively [11]. In additions, in Sinnar State, measurements were carried out using high-resolution gamma-spectrometry; on average, the activity concentrations obtained were 38 ± 8 (232Th), 17 ± 2 (226Ra), 174 ± 19 (40K) and 0.9 ± 0.2 Bq·kg−1 for the fallout radionuclide 137Cs. The average value obtained here for 232Th is slightly higher than the corresponding world-average [12].
During the Merowe dam construction, there were a lot of social media news providing uncertain/unconfirmed information about existence of the radioactive materials. It may grieve inside the body of dam during construction. The aims of this investigation ascertain a denial of the argument or confirm this information by using several physical techniques.
2. Materials and Methods
Two radiation survey-meters (RadDose-RDS-120 and Idintifineder) were used in different position, to calculated absorbed dose rate in air at a height of 1 m above ground surface and corresponding annual effective dose was estimated [13], and different samples were collected in order to investigate the existence of heavy metals and natural occurring radioactive material (NORM).
In order to detect NORM, 32 soil samples pulverized and packed in 1kg by mass in the cylindrical plastic containers of radius 3 inch and height 3.5 inch, which sits on the (3 inch × 3 inches) high purity germanium (HPGe) detector with geometry the containers are sealed for one week to ensure radioactive equilibrium between the parent radionuclides and their gaseous daughter decay products in the uranium and thorium series [14]. In term of existence heavy metallic elements experiment were carried out by using several devices, Energy Dispersive X ray Fluorescence (EDX8000) fundamental parameters(FP) method to the quantitative analysis were used [15], the first step should supply completely homogeneous and perfectly flat polished surface [16], for any unknown the analysis sensitivity coefficients were calculated by using standard samples, then unknown sample was analyzed the sensitivity coefficients, the closer the composition of the standard sample is to the composition of the unknown sample, the more precise the quantitative analysis, the sequences of the analysis are flowing: generation analysis conditions, analyzing the standard sample, calculating the sensitivity coefficient and analyzing the unknown sample (soil) [17].
The water and plant and un known samples were detected by using ICP 9000 atomic emission spectrometry for environmental purpose, an water and plant sample and gas chromatograph GC-2010 plus (Shimadzu cooperation) for unknown samples, the samples digestion was conducted the flowing process:
0.5 of sample was add to 5 ml of nitric acid to digestion container the mixture had let stand about 30 min, also 9.5 ml nitric acid and 0.5 ml hydrochloric acid were add and set container in microwave digester and digest approximately 1 hour after that the solution refrigerated and transferred to volumetric flask finally 25 ml were adjusted and eject in to device.
The analytical conditions for ICP-AES were: 1.2 Kw rad frequency power, 10 l/min plasma gas flow rate, 0.6 L/min auxiliary gas flow rate and 0.7 L/min carrier gas flow rate [18].
Data Collection Process
The Different samples were collected by using soil collection auger from waste hole near the dam was buried during dam construction and the local citizens were propagated about existence of radioactive materials in the buried hole. The survey was made over the hole and the hole was divided into four sectors.
3. Results
The investigation results were obtained by using two radiation survey-meters and several analytical devices (Inductively Coupled Plasma Emission spectrophotometer (ICPE-9000), Energy Dispersive X-ray Fluorescence (EDX-8000) devices and GAS chromatograph GC-2010 plus). All results were showing in Tables 1-3 and Figure 1 and Figure 2.
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Table 1. Soil, water, and plant sample screened by ICP device.
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Table 2. Unknown samples found in hole grave waste detected by using gas chromatograph GC-2010 plus.
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Figure 1. The percentage of Radiation dose in different location around the dam compared to the main value range reading 0.09 µSv/h.
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Figure 2. The percentage of radiation dose measurement reading in the both side of dam lake compared to total average reading 0.09 µSv/h.
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Table 3. The present of Natural occurring Radioactive Material in the soil samples.
4. Discussions
The calculated exposure falls within the global wide range of outdoor radiation exposure given in the UNSCEAR publications. The Screening analysis shown a present element such as Si, Ca, Ba, Fe, S, Co, for all samples as shown in Table 1 around the dam area this existence not different when compare over all Merowe area. Table 2 shows the present organic compound found in the buried hole near the dam, the existence revere to the human activity Mechanical workshop, car fuel, and construction martial like epoxide. Table 3, shows that, the level of Natural Occurring Radioactive Material in 32 soil sample around dam area is normal compared with previous studies [10] [11] [12]. The Result in Figure 1 indicates that, the percentage of the radiation dose in different location around the dam to the main value range reading 0.09 µSv/h according overall Sudan measurement were within the normal range. Finally, in Figure 2, it shows that The percentage of radiation dose measurement reading in the both side of the dam lake and average reading is 0.09 µSv/h, its normal reading.
5. Conclusion
Radioactivity and Heavy Metallic Materials in Merowe Dam Area were investigated by two radiation survey-meters and several analytical devices. Heavy metallic elements were detected in soil, water and plant. These elements may result from human activities. Current study confirmed that, the organic waste materials were buried inside the safety contained region and did not refer to any additive material buried from outside area. The radiation survey found that, the radiation dose is within the normal range 0.09 μSv/h.
Acknowledgements
The authors have many people to thank for their contribution to this work; in particular thanks are owed to participants at National committee who shared their idea and went step by step throughout the work until had finished. The author would like also to extend his thanks to the police officers in Regional Forensic Laboratory who provided helps throughout the samples analysis by ICP Caption Ahmed Altigani and First Luteant Hassan Mubark, and who was in charge for SEM Caption Abubakr A. Akasha. Finally, thanks to Mr. Alexander F. I. Osman and abdoulsakh Suleiman from Medical Physics & Laser Physics Department at Al-Neelain University for his revision and discussion.