Chemical composition, sources, and health risks assessment of PM₁₀ and PM₂.₅-bound metals at an industrial site in Nigeria

Abstract

Particulate matter (PM) pollution from industrial activities is a growing environmental and public health concern, particularly in sub-Saharan Africa; where metal recycling factories (MRFs) are expanding due to increasing urbanization and metal waste generation. However, data on the chemical composition of PM and associated health risks in this region, especially in countries like Nigeria, remain limited. The present study investigates the chemical composition-including water-soluble inorganic ions, sugars, and potentially toxic elements (PTEs), and evaluates the health risks of PM₂.₅ and PM₁₀ collected during wet and dry seasons from an industrial hub in Nigeria dominated by MRFs. The average concentrations of PM₂.₅ (27 ± 8 µg/m³) and PM₁₀ (109 ± 38 µg/m³) in the dry season exceeded the WHO Air Quality Guidelines (15 µg/m³ for PM₂.₅; 45 µg/m³ for PM₁₀), highlighting severe seasonal air quality issues. Major water-soluble ions included SO₄²⁻, Cl⁻, NO₃⁻, Na⁺, Ca²⁺, and K⁺, with NH₄⁺, C₂O₄²⁻, and Mg²⁺ present in smaller amounts. The elevated ion concentrations point to anthropogenic sources, primarily MRFs. Principal component analysis (PCA) identified crustal materials and anthropogenic emissions (from MRFs and cement factories) as major contributors to PM-bound elements. Trace metals such as Cr, Cu, Mo, Ni, Pb, and Zn showed high enrichment, with MRF activities being the dominant source. Health risk assessments using hazard quotient (HQ) and hazard index (HI) indicated non-carcinogenic risks were within acceptable limits (<1.0) for most metals in both children and adults. Carcinogenic risks were also below the permissible range (1 × 10⁻⁶ to 1 × 10⁻⁴). However, Pb posed a near-threshold risk in children, with HQ (0.81) and HI (0.84), suggesting the need for regulatory attention to prevent potential lead toxicity in this area. Stricter regulations and monitoring of MRF activities are crucial to mitigate PM pollution and associated health risks, ensuring a safer and healthier environment for communities in Nigeria.