The levels of radionuclides and trace elements in selected Kenyan coastal ecosystems
Hashim, N. O.
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Human activities all over the world have placed a growing demand for the environment to absorb the many forms of the wastes generated. These activities have lead to the deterioration of the state of the world environment including pollution by radionuclides and trace elements among other contaminants of the world's oceans. This project was aimed at evaluating the status of the Kenyan coastal ecosystems with reference to the levels of radioniclides and trace elements. The radioactivity and elemental concentrations in the sediment, plant and seawater samples from the areas of Mombasa Island, the north and coast of Kenya (Malindi and Gazi, respectively) have been determined. Gamma-ray spectrometry using HPGe detector and EDXRF spectrometry using a Si(Li) detector, were used respectively to measure the radioactivity and elemental concentrations in the samples. The measured specific activity and elemental concentrations in the samples. The measured specific activity and elemental concentrations in the samples. The measured specific activity and elemental concentration values are in close agreement (correlation coefficient, r0.99) with the certified values of two reference materials, IAEA SOIL - 375 and SOIL - 7, respectively. Sample preparation procedures were optimized for the reproducibility of the trace element measurements, while in gamma - ray spectrometry, the intensity distribution of the gamma radiation is assumed to be isotropic in the samples. An efficient methodology to determine the reproducibility of trace element measurements of environmental sample matrices (marine sediment and plant) has been developed in this work. Statistically designed measurements were carried out involving repeated trace element analyses of the samples. Analyses of variance (ANOVA) on the data show no variation in the measurements due to the instrumentation but there is variation due to the sample in homogeneity. The effective dose rates were calculated for human exposure to the gamma radiation from the radionuclides; 40K, 232Th and 238U in the sediments, and were found to be in the range (0.03-0.20) mSv y-1, which is below the ICRP limit of 1 mSv y-1 for members of the general public. The specific radioactivity of 137Cs was below the detection limit (2.9± 0.04) Bq/kg except in the samples from Mombasa with a range of (2.9-4.7) Bq/kg. The elemental analyses of the samples show that the levels of Th are in the range of (2.55-8.71)g/g in the sediments from Mombasa while it is below the detection limit (2.55 ± 0.08) g/g in the other samples. The levels of Pb (105.23 ± 5.56) g/g and Zn (813.67 ± 2.34) g/g were higher in the sediments from the Kibarani wastes dump site at Makupa creek of Mombasa by factors of 3-7 than those from the north and south coast respectively. The calculated elemental enrichment factors (EF>1) indicate anthropogenic inputs of these metals (Cu,Zn, Pb and Zr) in to the marine sediments at the wastes dump site. Further studies on the human exposure to radiation, particularly on the dose - to risk conversion factors (DRCF) are suggested for estimation of the human effects of the radiation from the environment. Monitoring of the levels of radionuclides and trace elements in the various coastal ecosystems and suitable models to study i) their spatial and time variation and ii) the meteorological conditions, are required to be carried out.