Radiological safety of drinking water sources in Nsukka metropolis based on natural radionuclide content

Background: Naturally occurring radionuclides in drinking water represent a significant pathway for internal exposure to ionizing radiation. Their occurrence is largely controlled by geological and hydrogeochemical conditions, and prolonged ingestion at elevated concentrations may pose potential health risks.
Objectives: This study aimed to determine the activity concentrations of key naturally occurring radionuclides in selected groundwater and surface water sources in Nsukka Metropolis, Enugu State, Nigeria, and to evaluate their radiological safety in line with international guidelines.
Methods: Six water samples were purposively collected from three surface water sources (Ohe Nsukka Lake, Ajiye Odenigbo Pond, and Iyi Mkpi Stream) and three groundwater sources (Asho Spring, Iyi Adoro Spring, and University of Nigeria Nsukka Borehole). Activity concentrations of potassium-40 (⁴⁰K), radium-226 (²²⁶Ra), and thorium-232 (²³²Th) were determined using standard gamma spectrometry at the Centre for Energy Research and Training (CERT), Ahmadu Bello University, Zaria. Descriptive statistical analyses (mean, range, and variability) were performed and results were compared with internationally recommended reference levels.
Results: The activity concentrations varied across sampling locations, reflecting underlying geological heterogeneity. Potassium-40 recorded the highest activity concentrations (44.09–81.14 Bq/L), followed by thorium-232 (16.20–30.02 Bq/L), while radium-226 exhibited the lowest levels (10.22–24.21 Bq/L). Relatively higher radionuclide concentrations were observed in Asho Spring and Ajiye Odenigbo samples, suggesting localized geogenic influences. Despite this variability, all measured values were below internationally recommended guideline limits for drinking water quality.
Conclusion: The findings indicate that the investigated water sources in Nsukka Metropolis are radiologically safe for domestic consumption under current conditions. This study provides important baseline, radionuclide-specific data for an urbanizing region in southeastern Nigeria and enhances the evidence base for environmental radioactivity assessment. Continued monitoring and incorporation of dose-based risk evaluation are recommended to ensure sustained compliance with international radiation protection standards.