Human and Environmental Risk Assessment of Polycyclic Aromatic Hydrocarbons in Automobile Repair Workshop Sites: A Case Study from Cameroon, Central Africa

Abstract

This study aimed to evaluate the concentration, vertical distribution, sources, and potential human health risks of polycyclic aromatic hydrocarbons (PAHs) in soils from informal automobile repair workshops across different geological settings in Cameroon, Central Africa. A cross-sectional environmental assessment involving field sampling, laboratory analysis, and quantitative health risk modeling. The study was conducted at six automobile repair workshops located in Bamenda, Buea, and Douala, Cameroon, representing volcanic, ferralitic, and alluvial soil types, respectively. Soil sampling and laboratory analysis were carried out during the dry season. Composite soil samples were collected at three depth intervals (0–15 cm, 15–30 cm, and 30–60 cm) from each workshop and corresponding control sites. Sixteen priority PAHs were extracted using ultrasonic extraction and quantified by gas chromatography–mass spectrometry. Source identification was performed using molecular diagnostic ratios. Carcinogenic risk to adult workers was assessed using benzo[a]pyrene toxic equivalency (BaP-TEQ) and total cancer risk (TCR) models for ingestion, dermal contact, and inhalation exposure pathways, respectively. Total PAH concentrations ranged from 110 to 3,780 µg/kg in workshop soils, compared to 22–226 µg/kg in control soils. Surface soils generally showed higher PAH levels, although enhanced vertical migration was observed in alluvial soils. High-molecular-weight PAHs dominated most samples, indicating mainly combustion-related inputs with additional petrogenic contributions. BaP-TEQ values ranged from 19.5 to 65.9 µg/kg. Total cancer risk values ranged from 1.8 × 10-7 to 6.3 × 10-7, all below acceptable risk thresholds. Automobile repair workshop soils in Cameroon are contaminated with PAHs at levels exceeding background concentrations; however, associated carcinogenic risks to adults are currently negligible. The findings highlight the influence of soil type on PAH mobility and emphasize the need for routine monitoring and improved environmental management in informal workshop settings.