RADIOMETRIC ANALYSES OF ACTIVITY CONCENTRATIONS OF WELLS AND BOREHOLE WATER AND THE HEALTH IMPLICATION IN IJEBU-IGBO, OGUN STATE
This study assessed the natural radioactivity levels and associated radiological health risks in groundwater sources (boreholes and hand-dug wells) supplying residents of Ijebu-Igbo, Ogun State, Nigeria, where the population relies almost entirely on these sources for domestic water in the absence of a comprehensive municipal treatment scheme. Twenty-five (25) water samples were purposively collected from five sampling locations in each of five residential sections of the town (Atikori, Ojowo, Oke-Agbo, Oke-Alafia and Oke-Sopen), sealed in Marinelli beakers, and stored for forty days to attain secular equilibrium between parent and daughter radionuclides prior to counting. The activity concentrations of Uranium-238 (²³⁸U), Thorium-232 (²³²Th) and Potassium-40 (⁴⁰K) were determined by gamma-ray spectrometry using a High-Purity Germanium (HPGe) detector coupled to an 8192-channel multichannel analyser at the Nigerian Nuclear Regulatory Authority (NNRA) environmental laboratory, University of Ibadan. Radiological hazard indices – radium equivalent activity (Raeq), external hazard index (Hex), internal hazard index (Hin), absorbed dose rate (D), annual effective dose (AED) and excess lifetime cancer mortality risk (ELCMR) – were computed from the measured activities. Results showed mean activity concentrations of 53.60 ± 7.83 Bq/L for ²³⁸U, 4.81 ± 0.29 Bq/L for ²³²Th and 200.49 ± 10.19 Bq/L for ⁴⁰K. The mean Raeq (75.92 Bq/L), Hex (0.20) and Hin (0.34) were all below the reference limits of the World Health Organization (WHO), International Commission on Radiological Protection (ICRP) and International Atomic Energy Agency (IAEA). However, the mean AED of 1.30, 1.74 and 3.36 mSv/y for infants, adolescents and adults, respectively, exceeded the WHO reference level of 0.1 mSv/y, and one sampling point in Oke-Alafia recorded an anomalously high ²³⁸U concentration of 873.30 ± 121.87 Bq/L. The study concludes that groundwater in Ijebu-Igbo is largely radiologically safe for consumption, with the exception of the identified hotspot in Oke-Alafia. It is recommended that the affected borehole be investigated further and remediated, that residents of the affected area undergo periodic medical screening, and that routine radiometric monitoring of groundwater sources be instituted across the study area.