Assessment of Naturally Occurring Radionuclides in the Saudi Gulf of Aqaba and Northern Eastern Red Sea

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Hussain Ali M., Al-Trabulsy
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University of Khartoum
Abstract The present study highlights and treats radioactivity levels of the naturally occurring radionuclides 226Ra, 228Ra, 238U, 232Th and 40K, the radioactivity of anthropogenic radionuclide 137Cs, concentration of heavy elements, physiochemical characteristics, radiological hazard indices and radon concentration in shore sediment samples collected along the Saudi Gulf of Aqaba and Northern Eastern Red Sea. Nineteen samples were collected from the Gulf of Aqaba coast, starting from the Saudi-Jordanian border down to the end of the Gulf at Tiran Strait (region-I). Additionally, 13 samples were collected from Tiran strait until further south at Duba city along the Red Sea coast (region-II). This allows a systematic comparison study between two environments of Gulf of Aqaba and Red Sea. Measurements of the activity concentrations of 226Ra, 228Ra, 40K and 137Cs Bq/kg (in dry weight) of the collected samples were carried out using gamma ray spectrometry based on a high-pure germanium coaxial detector (HPGe). The mean activities for 226Ra, 228Ra and 40K were found to be 11.4±1.5, 19.3±3.1 and 641±61 Bq/kg, respectively, for region-I and 8.4±1.9, 10.2±3.4 and 420±69, respectively, for region-II. The results showed that the mean activity of 226Ra and 228Ra is lower than the world average for both of them, whereas the mean value for 40K is about double the world average. The presence of 137Cs in the analyzed samples was low with a mean value of 4.7± 0.6 Bq/kg in region-I. It was detected only in one site in region-II with a value of 1.47 Bq/kg. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) technique was used to measure the total and leachable concentration of 238U, 232Th, 40K, in addition to the elements: Ag, Al, As, Ba, Be, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Se, V and Zn. The mean activity concentrations of 238U and 232Th were 17±1.7 and 22.5±3.7 Bq/kg respectively in region-I whereas in region-II the values were 22.1±2.4 and 9.8±3.4 Bq/kg respectively. The enrichment factor (EF) shows that all samples were extremely highly contaminated by selenium. The mean EF for the elements Ag, As, Cr and Sb showed significant contamination. The concentrations of uranium, thorium and potassium for water samples were close to the average concentrations in the oceans. They ranged between 2.5 to 8.4 with a mean value of 3.8±0.2=472;=549;g/l for U and 12 to 506 with a mean value of 473±15.5 mg/l for K. The concentration for Th was less than 0.01 =549;g/l for all samples. Moreover, physiochemical characteristics including: saturation percentage (SP), pH, electrical conductivity (ECe), cation exchange capacity (CEC), organic matter (OM) and content of clay, silt and sand have been determined. Indications for high correlation between most of the heavy elements were found. The linear correlation between heavy elements and most of NORM was generally significant. The radiological hazard indices of radium absorbed dose (D), annual effective dose (E), radium equivalent (Raeq), external hazard index (Hex), internal hazard index (Hin) and representative level index (I=543;) were computed as: 45.6±4.9 nGy/h, 56±6=472;=549;Sv/y, 92.9±10.3 Bq/kg, 0.13±0.01, 0.28±0.03 and 0.73±0.08, respectively in region-I and 27.3±4.9 nGy/h, 33.5±6=472;=549;Sv/y, 54.7±10 Bq/kg 0.07±0.01, 0.17±0.03 and 0.43±0.1, respectively in region-II. Concentration of Radon-222 was measured using Solid State Nuclear Detector (CR-39). The resulting concentration values varied widely from 95 to 390 with a mean value of 173±17.1 Bq/m3 in region-I while in region-II from 90 to 300 with a mean value of 136.6±16 Bq/m3. Some radon related parameters such as the effective radium content (Bq/kg), surface exhalation rate (mBq/m2 h), mass exhalation rate (mBq/kg h) and emanation power were computed. The correlation between radon exhalation rate with radium concentration shows strong correlation.
Naturally Occurring;Radionuclides;e Saudi Gulf of Aqaba and Northern Eastern ;Red Sea;