Study On Fallout Radioactivity In The Sudanese Red Sea Coastal Environment

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Rifaat Kabbashi, Hassona
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The activity concentration of fallout radionuclides v.z.,238Pu ,239+240Pu, 241Am,137Cs and 90Sr has been measured in some species of multicellular marine algae, sea grass, coral fishes and shellfish, and surface sediments collected from the fringing reef at different locations along the Sudanese coast of the Red Sea. Coral reef fishes were collected from the local market at Port Sudan taking into account the most popular and available species and their 137Cs, 210Pb and 210Po activity concentrations were measured to estimate the committed effective dose to population due to consumption. The measurements were carried out using alpha-particle spectrometry, high-resolution gamma spectrometry, gas-flow proportional counter and liquid scintillation. In the sediments analyzed, the activity concentration averaged 2.65±1.3 (238Pu), 47.96 ± 26.3 (239+240Pu), 19.1± 6.5 (241Am), 273 ± 157 (137Cs) and 140.8±73.9 (90Sr) mBq/kg dry weight. Activity concentration ratios were 0.066±0.041 (238Pu: 239+240Pu), 0.22±0.04 (239+240Pu:137Cs), and 0.43±0.1 (241Am:239+240Pu). These values are typical of those reported in the literature from the regions unaffected directly by nuclear accidents or nuclear reprocessing plant discharges and can thus be attributed to global fallout. Average activity concentrations (mBq/kg Dry weight) in marine algae from different locations were found to be 20.1±14.1, 21.6±13.3 and 8.5±3.8 (239+240Pu), 6.2±4.0, 11.7±6.1 and 5.1±3.5 (241Am) and 688±242, 868±713 and 116±14.8 (137Cs) for brown, red and green algae, respectively. These results were found to be consistent and a decrease trend is noticeable towards the south from Portsudan and comparable to global fallout origin values. High levels of 137Cs observed in brown and red algae seem to confirm that algae are responsive to the soluble phase of constituents in the ambient medium more than the elements associated to particulate matter. Algae are known to be effective bioindicators for monitoring the anthropogenic radioactivity in the marine environment and from the results obtained in this study, brown algae (Cystoseria species) and red algae (Lauranthia species) suggested their suitability to be used as a bioindicators. Plutonium isotopes were measured in some species of coral fishes and shellfish samples from the fringing reefs area at Port Sudan. Activity concentrations of both 238Pu ,239+240Pu in fish are close to detection limits, while shellfish show values an order of magnitude higher relative to coral fish species. The lowest concentration for 239+240Pu was met in the molluscs species Tridacnica (2.4) and the highest value was met in the coral species Favites. Activity concentrations of 210Po and 137Cs were determined in 31 different species of Red Sea coral fishes. For better understanding of the influence of feeding habit on the availability of these two nuclides, the fishes were classified based on feeding habit into three categories as carnivores, omnivores and herbivores. Data have shown that for both 210Po and 137Cs there is no any discrepancy in uptake among three classes that could be attributed to the feeding habit. Committed Effective Dose (CED) from 137Cs and 210Po due to consumption of coral reef fishes was assessed from their respective activity concentration values measured in aforementioned 31 species of coral fishes using dose conversion factors (DRCFs). On the average, CED (µSv/y) values were found to be 0.012 (carnivores), 0.01 (omnivores) and 0.01 (herbivores) for 137Cs contributing about 0.4% of the total dose. While for 210Po, it was found to be 3.47, 4.81 and 4.14 (µSv/y) in carnivores, omnivores and herbivores, respectively, which represent 99.6% of the total dose. The results of CED suggest that the dose received by Sudanese population from the consumption of marine fishes is rather small compared to similar data reported from FAO fishing grounds around the globe and the contribution of 137Cs is negligible compared to 210Po
Study,Fallout ,Radioactivity ,Sudanese,Red Sea,Coastal,Environment