Characterization and Modeling of Indoor PM2.5-Bound Benzo[a]Pyrene Concentration in Public Schools: A Comparative Study of Oredo and Uhunmonde Local Government Areas, Edo State, Nigeria

Abstract

Indoor air quality (IAQ) has emerged as a critical concern for student health and well-being, as PM2.5 can transport toxic compounds like benzo[a]pyrene (B[a]P), posing significant health risks to vulnerable populations such as school children. This study compares indoor air quality in public schools between Oredo (urban LGA) and Uhunmwonde (rural LGA) in Edo State, Nigeria. Fortyeight PM2.5 samples were collected from eight sampling sites with meteorological parameters over one year. PM2.5 mass concentrations were determined gravimetrically, and samples were analyzed for PAH compounds using gas chromatography with Mass Spectroscopy (GC-MS). Data underwent multivariate analysis to determine source contributions and develop a predictive model for B[a]P concentrations using PM2.5 and meteorological parameters. Oredo classrooms exhibited substantially higher PM2.5 levels (45.3–63.7 μg/m³) than Uhunmwonde (21.7–30.8 μg/m³). Similarly, total PM2.5-bound PAH concentrations were higher in Oredo (1.27–1.47 μg/m³) than Uhunmwonde (1.14–1.19 μg/m³). High-molecular-weight (5–6-ring) PAHs dominated profiles at both locations, with Oredo showing a slightly greater proportion (3.06%) of these heavy PAHs. Principal component analysis (PCA) and diagnostic ratios indicated vehicular combustion (gasoline and diesel traffic) as the primary PAH source at both locations, with minor biomass or petroleum evaporation contributions. Estimated incremental lifetime cancer risks (ILCR) from PM2.5-bound PAHs were higher in Oredo than Uhunmwonde (adult ILCR: 1.3×10⁻⁵ vs. 9.5×10⁻⁶ for 24h exposure). Predictive models using PM2.5 and weather parameters achieved 91–96% accuracy, with robust regression providing the best fit. These findings highlight clear spatial differences, with Oredo schools facing substantially higher indoor PM2.5 and PAH contamination than Uhunmwonde schools.