Distribution and Health-Risk Assessment of Polychlorinated Biphenyl Congeners in Soils from E-Waste and Automobile Dismantling Sites

Abstract

The uncontrolled dismantling of electronic waste and end-of-life vehicles in low- and middle income countries has emerged as a significant, yet inadequately quantified, source of persistent organic pollutants to the terrestrial environment. This study characterised the distribution, congener-specific profile and human health-risk implications of nineteen polychlorinated biphenyl (PCB) congeners in topsoils collected from three informal electronic-waste (e-waste) dumpsites and two automobile-dismantling sites in the densely populated metropolis of Lagos, Nigeria. Ten composite topsoil samples (0–15 cm) were subjected to ultrasonic solvent extraction, sulphuric acid and acidified silica-gel clean-up, and quantification by gas chromatography with electron capture detection. The sum of the nineteen target congeners (ΣPCB₁₉) ranged from 81.99 to 6111 ng g⁻¹, with the highest burden recorded at an e-waste site (NGK-S8) and the lowest at a peripheral point of another e-waste site (AR-S9), illustrating extreme small-scale spatial heterogeneity driven by the location of burning and dismantling micro-hotspots. Every sample exceeded the former USSR ambient-soil limit of 60 ng g⁻¹, and three samples exceeded the Canadian residential-soil guideline of 1300 ng g⁻¹. PCB 66, PCB 87 and PCB 153 were detected in every sample (100% frequency), whereas the complete suite of nineteen congeners co-occurred only at OWN-S5. All target congeners were non-dioxin-like, and the profile was dominated by penta- through hepta chlorinated homologues consistent with weathered technical Aroclor-type formulations and thermal degradation during open burning. Deterministic health-risk modelling, based on soil ingestion, revealed hazard-index values exceeding unity for numerous congeners at the Alaba Rago, New-Garage Gidan Kwali and Owode Onirin sites, with maxima of 18.43 (PCB 18) and 17.69 (PCB 31). Estimated incremental lifetime cancer risks exceeded the USEPA benchmark of 10⁻⁶ for nearly all detected congeners and surpassed 10⁻⁵ in most cases, reaching 7.37×10⁻⁴ for PCB 18 at NGK. These findings demonstrate that informal e-waste and automobile recycling constitutes a serious and immediate soil-contamination and public-health hazard in Lagos, warranting remediation, regulatory enforcement and longitudinal biomonitoring of exposed populations.