Evaluation of radionuclide contaminations in water sources in Kaabong District

Abstract

This study investigates the activity concentrations of naturally occurring radionuclides and associated radiological health risks in borehole groundwater from Kaabong District, Uganda. The work is driven by concerns over ionizing radiation exposure in areas underlain by granitic and metamorphic rocks enriched in uranium and thorium. Groundwater samples from five sub-counties were analyzed using gamma-ray spectrometry with a NaI(Tl) detector to quantify 226Ra, 232Th, and 40K. Radiological parameters including absorbed dose rate (D), radium equivalent activity (Raeq), internal and external hazard indices (Hin, Hex), annual effective dose equivalent (AEDE), and excess lifetime cancer risk (ELCR) were determined following ICRP and UNSCEAR standards. Results reveal spatial variations in radionuclide concentrations, with some boreholes exceeding international reference levels. The absorbed dose rate ranged from 32.96 to 106.18 nGy h−1 (mean: 67.93 nGy h−1 ), while AEDE values (0.20–0.65 mSv y−1 ; mean: 0.39 mSv y−1 ) surpassed the recommended global limit of 0.07 mSv y−1 . Radium equivalent activity (75.42–249.70 Bq kg−1 ; mean: 158.60 Bq kg−1 ) and hazard indices (Hin = 0.49, Hex = 0.43) remained below unity, indicating that groundwater use does not pose significant radiological danger. ELCR values ranged from 0.00085 × 10−3 to 0.00295 × 10−3 (mean: 0.002 × 10−3), all well below the world average of 0.29 × 10−3. The negligible lifetime cancer risk is attributed to the relatively low concentrations of the most radiotoxic nuclides (226Ra and 232Th), coupled with small ingestion dose conversion factors. The district’s geology, dominated by weathered gneisses and low-radioelement sedimentary formations, further limits radionuclide mobility into groundwater. Comparisons with studies from Nigeria, Ethiopia, and Saudi Arabia show that Kaabong District exhibits generally lower radiological hazard levels. The findings highlight the importance of regular groundwater monitoring, public awareness, and mitigation strategies to safeguard community health.