ASSESSMENT OF NATURALLY OCCURRING RADIOACTIVE MATERIALS AND RADIOLOGICAL RISKS IN SOILS AROUND THE KADUNA REFINING AND PETROCHEMICAL COMPANY, NIGERIA

Abstract

Industrial activities, particularly petroleum refining, have been identified as significant contributors to the enrichment of Naturally Occurring Radioactive Materials (NORMs) in surrounding environments. This study assessed the radiological impact of the Kaduna Refining and Petrochemical Company (KRPC) on the local soil environment. Soil samples were collected from 10 sampling points within the refinery operational area and one control site located approximately 2 km away. Activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K were determined using Thallium-activated Sodium Iodide [NaI(Tl)] gamma spectrometry. Results revealed that the mean activity concentrations of ²²⁶Ra (25.94 ± 14.97 Bq/kg) and ⁴⁰K (171.85 ± 63.27 Bq/kg) were below the UNSCEAR global averages of 35 Bq/kg and 400 Bq/kg, respectively. However, ²³²Th exhibited significant enhancement, with a mean concentration of 66.23 ± 27.32 Bq/kg, substantially exceeding both the control site (36.12 Bq/kg) and the UNSCEAR global average of 30 Bq/kg. Radiological hazard indices, including Absorbed Dose Rate (59.15 nGy/h), Annual Effective Dose Equivalent (0.0725 mSv/y), Radium Equivalent Activity (133.88 Bq/kg), and hazard indices (H_ex = 0.362, H_in = 0.432, I_γ = 0.950), all remained within internationally recommended safety limits. However, the Excess Lifetime Cancer Risk (1.140 × 10⁻³) exceeded the global average of 0.29 × 10⁻³, indicating a cumulative long-term health risk. Pearson correlation analysis revealed weak to negative correlations among the radionuclides, confirming anthropogenic interference through Technologically Enhanced Naturally Occurring Radioactive Materials (TENORM) from refinery operations. The study concludes that while no acute radiation hazard exists, sustained industrial exposure poses a latent public health vulnerability that requires regulatory intervention.