Naturally occurring radionuclides in gold-mining-impacted aquatic systems of the Lake Victoria Goldfields, Tanzania: An ERICA-based radiological risk assessment

Gold-mining activities in the Lake Victoria Goldfields (LVGF), Tanzania, have raised concerns about riverine pollution and the accumulation of naturally occurring radionuclides (NORs) in aquatic ecosystems, yet information on their ecological implications remains limited. This study assessed the activity concentrations of 238 U, 235 U, 234 U, 232 Th, 230 Th and 226 Ra in water and sediments of the Mara River, Mori River, and associated tributaries, and evaluated the radiological risk to aquatic biota. A total of 40 water and 42 sediment samples were collected in March and August 2024 and the activity concentrations of selected radionuclides were determined by radiochemical separation followed by alpha spectrometry. ERICA Tool was used to estimate radiological risk to aquatic biota. Elevated 234 U/ 238 U activity ratios (>1) indicated preferential mobilisation of 234 U through alpha-recoil. The sediment-bound 238 U exceeded the UNSCEAR worldwide average by approximately 8-11 times along the Mara River and up to about fourteen-fold in the tributaries. Total dose rates to aquatic biota ranged from 3.70 μGy h −1 to 197 μGy h −1 , with the highest values for zooplankton, insect larvae, bivalve, and gastropod, exceeding the ERICA screening levels of 10 μGy h −1 by approximately twenty - fold, with 226 Ra dominating exposure. A sensitivity assessment supported their prioritisation for refined assessment. As no biological effects or radionuclide concentrations in biota were directly measured, the results constitute screening estimates of exposure under the selected scenario. The dataset provides baseline information for targeted monitoring and further assessment of aquatic biota.