ANALYSIS OF HEAVY METALS, MINERALS AND RADIONUCLIDES IN HEAVY SANDS FROM TIVA AND MWITA SYANO RIVERS, KITUI COUNTY

Rivers have been and always will be, the source of livelihood to many people, wildlife and aquatic organisms across the world. Farming and sand mining for both minerals and building and construction industries among others form part of human activities being carried out in the rivers. Rivers also provide water for household use, irrigation, and watering of both domestic and wild animals. The river provides a home to both aquatic animals and plants. Therefore, due to their immense importance, proper management is of great concern for the welfare of all its dependents.

This research focused on characterising sands from Tiva and Mwita Syano Rivers in Kitui County. The objectives of this research were to analysis heavy sands for the presence of mineral sands, radionuclides and heavy metals. Ten sand samples from river Mwita Syano were analysed for mineralogical content using the XRD technique, and thirty-nine sand samples from the same river were evaluated for the presence of heavy metals using EDXRF. Lastly, thirty-five sand samples from river Tiva were analysed for the presence of radionuclides by high-resolution gamma radiation spectrometry using HP Ge detector.

The XRD analysis of heavy sand samples indicated the presence of minerals: albite, diopside, hornblende, microcline, quartz, magnetite, orthoclase and ilmenite. The average percentage amount of minerals present in heavy sands varied as follows: quartz > albite > hornblende > ilmenite > diopside > magnetite > microcline > orthoclase with the highest being 52.7 % and the lowest being 1.1 % indicating the potentiality of heavy sands as a source of minerals. However, the viability of the heavy sands as the source of minerals requires additional knowledge on the size of the deposit, the cost of mineral separation, infrastructure network and marketing strategies. Hence, this research only opens up the gates for further detailed prospective research work.

The level of primordial radioactivity as evaluated by high-resolution gamma radiation spectrometry using HP Ge detector showed the mean specific activities of 238U, 232Th and that of 40K in heavy sands as 8.8 Bq kg-1, 199 Bq kg-1, and 329 Bq kg-1 respectively. The elevated radioactivity level of thorium is as results of the presence of monazites or heavy minerals bearing thorium atoms in their structures. The associated absorbed dose rate was 150 nGy h-1 which translates to 0.18 mSv yr-1 annual effective dose. The radiological hazard indices were found to be within the international commission on radiological protection recommended limits except for Iγ.

The mean concentration level of heavy metals (Fe, Ti, V, Mn, Cr, Cu, Co, Zn, Pb, Ni, As, Zr and Sr) were evaluated and their contamination levels assayed on the basis of enrichment factor and geo-accumulation index. The most abundant element was Fe. The average concentrations of heavy metals except those of Pb and Zn exceeded the recommended CBSQG values. The mean concentrations of Fe, Zn, Pb, Ni and As were found to be less than values of ‘average shale’ while the rest exhibited higher values. Most of the enrichment factors (EFs) calculated ranged from 0.17 to 3.77, indicating deficiency to moderate enrichment of heavy sands by heavy metals. The heavy sands were found to be very highly enriched by Co (EF of 17.36). The geo-accumulation index (Igeo) calculated showed Igeo of -3.51 for As on the lower side and 3.15 for Co on the upper side corresponding to unpolluted to strongly polluted with the respective heavy metals.

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