Radon in Drinking Water from Laterite-Dominated Terrains of Yewa, Southwestern Nigeria: An Assessment of Radiological Health Risk

Abstract

Radon-222 (²²²Rn) is a naturally occurring radionuclide and a major contributor to radiation exposure via groundwater. Yewa South Local Government Area (LGA), Ogun State, Nigeria, has extensive lateritic weathering that may influence radionuclide occurrence, yet its groundwater radon levels remain insufficiently characterised. This study determined ²²²Rn concentrations in borehole drinking water, estimated age-specific annual cumulative effective dose (ACED), and evaluated excess lifetime cancer risk (ELCR) for adults. Twenty groundwater samples (10 for each location) were collected, with one control site at Bells University of Technology, Ota, and analysed using a RAD7 radon detector. ACED was computed using age-specific water-ingestion rates and ICRP Publication 158 dose coefficients. Adult ELCR was derived from ACED using a 70-year lifetime and a 5.5 × 10⁻² Sv⁻¹ risk factor. One-way ANOVA and Tukey's HSD test were used to compare groups. Mean ²²²Rn concentrations were 480.31 Bq/L (Abule Agbara) and 485.65 Bq/L (Ilobi Town), significantly exceeding the control (161 Bq/L; p < 0.001), with no significant difference between sites. Mean ACED was highest in infants (0.491 and 0.496 mSv y⁻¹), while adult ACED was 0.270 and 0.273 mSv y⁻¹, and the maximum ACED was 0.844 mSv y⁻¹. All ACED values remained below 1 mSv y⁻¹, whereas the mean adult ELCR (~9.5 × 10⁻⁴) exceeded the conventional 10⁻⁴ reference level. These findings indicate elevated radon exposure and increased estimated cancer risk relative to the conventional reference level, despite doses remaining below 1 mSv y⁻¹. Routine surveillance, protection of vulnerable age groups, and pre-consumption mitigation such as aeration are recommended.