Analysis of Heavy Metals, Minerals and Radionuclides in Heavy Sands From Tiva and Mwita Syano Rivers, Kitui County

Abstract

Rivers have been and always will be the source of livelihood to many people, wildlife and aquatic organisms across the world. They are the sources of water for household use, irrigation and watering of both domestic and wild animals. They also provide a home to both aquatic animals and plants. In addition, human activities such as farming and sand mining for both minerals and for building and construction industries among others are carried out in the rivers during the dry spell. Owing to these and many more importance, proper management and exploitation of rivers are of great concern for the welfare of all its dependants. This research focused on characterizing sands from Tiva and Mwita Syano Rivers in Kitui County. The objective of this research was to analysis river sands for the presence of mineral sands, radionuclides and heavy metals. Ten sand samples collected from river Mwita Syano were analyzed for mineralogical content using the XRD technique while thirty-nine sand samples from the same were analyzed for the presence of heavy metals using EDXRF respectively. Finally, thirty-five sand samples from river Tiva were analyzed for the presence of radionuclides by high-resolution gamma radiation spectrometry using HP Ge detector. The XRD analysis of river Mwita Syano sand samples indicated the presence of minerals: albite, diopside, hornblende, microcline, quartz, magnetite, orthoclase and ilmenite. The average amount of quartz was the highest with 52.7 % while orthoclase had the lowest with an average of 1.1 % indicating the potentiality of heavy sands as a source of some of the 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 of river Tiva sands 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 observed high 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 accepted international commission on radiological protection limits except for representative index level. vi The most abundant element in heavy sands was iron followed by titanium. Manganese, vanadium, lead, copper, zinc, chromium, zircon, cobalt and strontium were found to be present in parts per million. In addition, nickel and arsenic mean concentrations were below the minimum detection limits. The average concentrations of heavy metals except those of Pb and Zn exceeded the sediments’ recommended values of Wisconsin Guidelines on Consensus-Based Sediment Quality. The mean concentrations of Fe, Zn and Pb were found to be less than the values of ‘average shale’ while the rest exhibited higher values. Most of the enrichment factors (EFs) calculated ranged from 0.24 to 3.77, indicating deficiency to moderate enrichment of heavy sands by heavy metals. The river sands were found to be very highly enriched with Co (EF of 17.36). The geo-accumulation index (Igeo) calculated showed Igeo of -3.0 for Pb on the lower side and 3.15 for Co on the upper side corresponding to unpolluted to strongly polluted with the respective heavy metals.