Geological and climatic influences on natural radioactivity in drinking water and their health impacts: a study of Dessie and Kombolcha towns, Ethiopia

This study examines the geological and climatic factors that influence natural radioactivity levels in drinking water from Dessie and Kombolcha towns in Ethiopia's northern plateau. The basaltic and sedimentary mudrock formations of the region contain high levels of natural radionuclide elevated natural radionuclide levels, while climatic factors such as precipitation, soil moisture, and humidity enhance their mobility and transport into water sources. Kombolcha, situated at a Lower altitude geographically, exhibits higher radionuclide concentrations for ²³⁸U and ²³²Th. All measured values are almost greater than the global permissible values 0.5 mBq/L and 0.05 mBq/L respectively, especially for samples collected from running water. This is due to surplus and downward transport along the Borkena River from Dessie to Kombolcha, which is intensified by climatic conditions and rainfall. ⁴⁰K shows high activity values in samples from underground and spring water in both towns, even if its global permissible value is clearly not known in ingestion food type. Uranium's greater solubility compared to thorium results in higher activity levels above 0.5 mBq/L, across both towns in this study. Radiation dose assessments reveal significant health risks, particularly in spring and headwater areas. Annual effective doses exceed the permissible values recommended by international guidelines like IAEA and ICRP in both towns which is 1 mSv/yr. These findings suggest potential long-term health risks, with recommendations for continuous monitoring and mitigation measures to protect public health in the two towns and downstream from the Ethiopian northern plateau.