Automobile Spray Paint Dust and Human Health: A Multi-Site Environmental Health Risk Assessment of Carcinogenic and Non-Carcinogenic Effects in South-Eastern Nigeria

Informal automobile spray-painting operations release metal-laden dust, posing occupational and residential health risks. Seasonal variations, receptor-specific exposure, and metal composition influence non-carcinogenic and carcinogenic hazards, yet data from South-Eastern Nigeria remain limited. This study quantified heavy-metal exposure in automobile spray-paint dust, assessed receptor-specific non-carcinogenic (HI) and carcinogenic (ILCR) risks, examined seasonal and metal-specific trends, and evaluated source attribution to inform evidence-based interventions. Forty dust samples were collected from 20 workshops across Owerri and Okigwe during rainy and dry seasons. Samples were sieved (<100 µm for ingestion, <45 µm for dermal exposure), digested, and analyzed for Pb, Cd, Cr, Ni, Zn, Fe, Cu, and Mn using FAAS/GFAAS/ICP-MS. Deterministic and probabilistic Monte Carlo models estimated receptor-specific Hazard Index (HI) and Incremental Lifetime Cancer Risk (ILCR). Statistical analyses included paired t-tests, Wilcoxon tests, correlation matrices, PCA, and regression to assess inter-metal relationships, seasonal variation, and source attribution. Dermal HI exceeded 1 for all workers in both seasons (rainy: 96.4 ± 12.3; dry: 122.3 ± 14.6), while nearby residents had lower but notable HI (rainy: 68.7 ± 10.5; dry: 84.5 ± 12.7). Ingestion HI remained below or near 1 for all receptors. Total ILCR (TCGLR) for workers ranged from 1.26 × 10⁻² (rainy) to 1.91 × 10⁻² (dry), and for residents from 8.6 × 10⁻³ to 1.21 × 10⁻². Cadmium and nickel dominated the cumulative risk. Dry-season exposures were higher, but paired t-tests and Wilcoxon tests indicated no statistically significant seasonal differences (p>0.05). PCA grouped Cd, Ni, and Pb into a high-risk cluster, while Zn, Cu, and Fe formed a background cluster. Regression analysis indicated a proportional relationship between total metal concentration and dermal HI (R²=0.18). Informal spray-painting environments in South-Eastern Nigeria pose significant non-carcinogenic and carcinogenic risks to workers and nearby residents, particularly via dermal exposure to Cd and Ni. Short-term interventions include PPE and dust suppression; mid-term, improved ventilation and metal substitution; long-term, regulatory enforcement, workshop formalization, and continuous monitoring. Findings emphasize season- and metal-specific risk, highlighting the need for adaptive occupational and environmental health strategies to protect both workers and communities.