Radiological Characterization of Dredged Sediments from the Nun River, Nigeria, and their Implications for Building Material Use

Abstract

This study assesses the radiological safety of sediments obtained from dredging activities along the Nun River, Bayelsa State, Nigeria, where such materials are commonly used in residential construction. Given the potential contribution of naturally occurring radionuclides in building materials to indoor radiation exposure, the study is guided by radiation protection principles aimed at minimising exposure to ionising radiation. Sediment samples from ten locations in two Local Government Areas were analysed using a NaI(Tl) gamma spectrometry system. This study is the first extensive radiological characterisation of dredged sediments from the Nun River, Nigeria, and provides a critical baseline for the Niger Delta region. The mean activity concentrations of ⁴⁰K (402.22 Bq/kg) and ²³⁸U (28.10 Bq/kg) were within the limits set by UNSCEAR, whereas ²³²Th (6.04 Bq/kg) was significantly below the corresponding limit, a pattern characteristic of the mineralogy of the Niger Delta. The radiological hazard indices, including Raeq (mean 67.71 Bq/kg), Hₑₓ (mean 0.18), Hᵢₙ (mean 0.24), and Iγ (mean 0.50), were all below the internationally recommended safety limits. The gamma index (Iγ) ranged from 0.24 to 0.91, indicating that most Nun River sediments meet the initial screening criterion for use in construction applications. Multiple linear regression revealed that ⁴⁰K contributed the most to the variability of Iγ (β=0.486), followed by ²³⁸U (β=0.386) and ²³²Th (β=0.262); the model fit was excellent. Shared mineralogical controls were further suggested by strong correlations among the radionuclides. The results, particularly the hazard indices and Iγ, were well below unity, indicating that the sediments pose negligible indoor exposure risks.