Spatial Distribution and Health Risk Assessment of Natural Radionuclides from Water Samples of Lake Kyoga, Namasale Uganda

The occurrence of naturally occurring radionuclides in freshwater systems represents an important environmental and public health concern due to potential radiation exposure through water consumption. This baseline screening study assessed the activity concentrations, spatial distribution, and age-dependent radiological health risks of selected natural radionuclides in surface water from the Namasale section of Lake Kyoga, Uganda. Sixteen sampling locations were distributed across four land-use zones representing fishing shoreline areas, agricultural runoff zones, domestic/livestock water-use areas, and relatively undisturbed open-water control sites. Water samples were analyzed using gamma spectrometry for 226 Ra, 228 Ra, 40 K, and 210 Pb, and alpha spectrometry for 238 U and 234 U. Measured radionuclide concentrations showed significant spatial variability (p < 0.05), with generally elevated activities in agricultural and domestic zones relative to control areas. Potassium-40 recorded the highest activity concentrations due to its natural abundance, while uranium isotopes exhibited the expected natural disequilibrium pattern ( 234 U > 238 U), indicating geochemically controlled mobility. Pearson correlation, principal component analysis, and spatial interpolation further suggested that radionuclide distribution is influenced by combined geogenic and land-use-related factors. Adult annual effective dose (AED) values ranged from 61.21 to 97.79 µSv yr -1 , remaining below the World Health Organization guideline level of 100 µSv yr -1 , although age-dependent assessment indicated proportionally higher vulnerability for children and infants. Radium isotopes were the dominant contributors to ingestion dose across all populations. Excess lifetime cancer risk values indicated generally low-to-borderline radiological concern under conservative exposure assumptions rather than critical health risk. Although current radionuclide levels do not indicate substantial immediate radiological hazards, the observed spatial variability highlights the importance of continued monitoring, particularly in agriculturally and domestically influenced zones. This study provides important baseline radiological data for Lake Kyoga and supports sustainable freshwater management, environmental surveillance, and future multi-seasonal investigations in Uganda.