Evaluation of Radiological Risks From Radionuclides in Fish and Sediment of Eleyele Reservoir, Ibadan, Nigeria.

Abstract

The Eleyele Reservoir is a critical water resource and a source of food and livelihood for Ibadan's local fishers. However, the reservoir has faced a lot of environmental pollution. Therefore, this study investigated the radiological risk associated with fish and sediment samples from Eleyele Reservoir in Ibadan using a NaI(Tl) gamma-ray spectrometer. Sediment samples were taken from upstream and downstream locations, characterised by different levels of waste and water clarity. The average activity concentrations for⁴⁰K, ²²⁶Ra and ²³²Th in the sediment samples were found to be 597.75 ± 27.50, 40.66 ± 5.75 and 261.84 ± 5.75 Bq kg^-1, respectively, for the upstream and 114.92 ± 5.96, 16.11 ± 2.29 and 81.48 ± 2.29 Bq kg^-1, for the downstream; while 0.22 mSv/year was calculated for the annual effective dose. The absorbed dose rate has an overall mean of 181 nGy/h, which is significantly higher than the global average value of 59 nGy/h. The radiological hazard indices of the sediment from Eleyele's Reservoir (downstream) slightly exceeded the recommended limits for construction purposes. The mean activity concentrations of 244.69 ± 13.33, 21.65 ± 1.83, and 27.76 ± 1.56 Bq kg^-1 for ⁴⁰K, ²²⁶Ra and ²³²Th, respectively, were obtained for the fish samples. The highest Bioaccumulation Factor (BAF) value for ⁴⁰K was found in the flesh of Oreochromis niloticus (1.64). The highest Committed Effective Ingestion Dose (CEID) of 24.13 mSv was obtained in Sanotherodon melanothron Gut, suggesting a significant long-term radiological hazard if consumed frequently, and the lowest CEID (1.98 mSv) was in Gymnarchus niloticus whole fish. Generally, the radiological indices are within safe limits, indicating no appreciable radiological threat to the local population consuming fish from the Reservoir. However, periodic monitoring of sediment and aquatic life is advised, especially downstream, to track long-term changes and mitigate potential exposure risks.