Background Ionizing Radiation in Two Petroleum Institutions of Southern Nigeria: A Spatial–Statistical Evaluation

Background ionizing radiation (BIR) is a major contributor to public exposure, yet its spatial statistical characterization in institutional environments of Southern Nigeria remains limited. This study evaluated BIR across two Campuses-Federal University of Petroleum Resources (FUPRE) and Petroleum Training Institute (PTI) in Effurun, Delta State. Measurements were conducted at 20 sampling points per campus using a Digilert-100 radiation monitor. Exposure rates in FUPRE ranged from 0.007 to 0.025 mR h⁻¹, with a mean of 0.014 ± 0.005 mR h⁻¹, slightly exceeding the UNSCEAR reference value of 0.013 mR h⁻¹. PTI recorded lower values (0.002–0.015 mR h⁻¹; mean 0.007 ± 0.004 mR h⁻¹), well below international thresholds. Derived hazard indices confirmed higher values at FUPRE (EDR = 1.21 ± 0.46 mSv y⁻¹; ADR = 125.28 ± 47.76 nGy h⁻¹; AEDE = 0.15 ± 0.06 mSv y⁻¹; ELCR = 0.54 ×10⁻³) compared to PTI (EDR = 0.61 ± 0.30 mSv y⁻¹; ADR = 63.08 ± 30.64 nGy h⁻¹; AEDE = 0.08 ± 0.04 mSv y⁻¹; ELCR = 0.26 × 10⁻³). Spatial analysis revealed weak positive autocorrelation (Moran’s I: FUPRE = 0.1737, PTI = 0.0839; p = 0.0610), with variogram modeling identifying spherical and linear structures for FUPRE and PTI, respectively. Kriging maps highlighted localized hotspots at FUPRE, while PTI exhibited uniform distribution. Monte Carlo simulations (10,000 iterations, lognormal, 5% uncertainty) validated predictive robustness. Radiological Risk Index classification showed FUPRE with very low (3 points), low (11 points), and moderate (6 points) risk zones, whereas PTI was dominated by very low (13 points) and low (7 points). Comparative analysis positioned the study area (mean BIR = 0.012 mR h⁻¹; ADR = 104.4 nGy h⁻¹) within the lower to mid-range of exposure levels across Southern Nigeria. Overall, both campuses remain radiologically safe, though FUPRE requires continued monitoring due to localized enhancements linked to construction activities. These findings provide a reliable baseline for environmental radiation monitoring in petroleum-based institutional environments and support regulatory decision-making for radiological safety in Southern Nigeria.