Assessment of Elemental Content and Associated Radiological Exposure in Sand Beds of Tiva River, Kitui County

Abstract

The geological structure of the river Tiva basin in Kitui County indicates heavy mineral sands like zircon, ilmenite, and hematite, associated with naturally occurring radioactive materials (NORM) from primordial radionuclides (40K, 238U, and 232Th) in the grains. Natural and anthropogenic activities may raise radiation exposure levels, posing risks to both the residents and the environment. This study aimed to establish baseline radioactivity, exposure levels, and heavy metal concentrations in river Tiva sand samples. Three sections (upstream at Kauwi, midstream at Tanganyika Bridge, and downstream at Tiva Bridge) were selected. 77 samples (58 in 2017 and 19 in 2018) underwent analysis using hyperpure germanium (HPGe) gamma-ray and energy-dispersive X-ray fluorescence (EDXRF) spectrometry. A follow-up survey in 2018 assessed external gamma dose rates using a GIS-enabled portable radiation detector. The average activity concentrations in upstream, midstream, and downstream sections respectively were: 238U (1.5 Bq kg-1, 30 Bq kg-1, 23.5 Bq kg-1), 232Th (20.5 Bq kg-1, 15.5 Bq kg-1, 20 Bq kg-1), 40K (598 Bq kg-1, 646 Bq kg-1, 578 Bq kg-1). Compared to global averages, 238U and 232Th levels were lower, while 40K levels were up to 1.6 times higher. Mean gamma dose rates 1 meter above the ground were 164±36 nGy/h, 149±42 nGy/h, and 124±22 nGy/h for the three sites. Elemental analysis revealed Fe (30000±300ppm) and K (14700±800ppm) as the richest elements, with a strong positive correlation among Fe, Mn, and Zn suggesting a common origin. Negative correlations were observed between Zr and K (-0.57), Zr and Sr (-0.65), and Zr and Rb (-0.72) indicating diverse origins. Principal component analysis explored multivariate relationships, showing a spatial distribution where Ti and Zn were more abundant upstream, while Fe was evenly distributed. The findings provide valuable reference data for radioactivity mapping and future radiological investigations, aiding the formulation of radioprotection and riverine environmental management policies.