Atmospheric distribution and exposure implications of heavy metals around industrial, mining, and slum areas in Liberia

Abstract

This study evaluated the distribution, sources, and health risks of airborne As, Cd, Pb, and Hg in industrial, mining, and urban slum areas of Liberia. Eighty-one total suspended particulate samples were collected at source locations and at 100 m and 500 m distances. Metal concentrations were measured using atomic absorption spectrophotometry, with multivariate analysis, Positive Matrix Factorization (PMF), and Monte Carlo simulation applied for source apportionment and uncertainty assessment. The mining zone recorded the highest metal concentrations, including arsenic (0.102 mg/m³), lead (1.002 mg/m³), cadmium (0.016 mg/m³), and mercury (0.008 mg/m³). Metal concentrations declined significantly with distance, stabilizing at ≥100 m, where reductions of 55–80% were observed relative to the source.

Non-carcinogenic risk assessment showed that As, Cd, Pb, and Hg posed no significant health risk (HQ < 1) for both adults and children, although children exhibited relatively higher HQ values, suggesting greater vulnerability. Carcinogenic risks for As, Cd, and Pb remained below the permissible threshold (CR = 1.1 × 10⁻⁶–8.4 × 10⁻⁶), while Monte Carlo simulations confirmed risk stability, with exposure following the order industrial > mining > slum which reflects the differences in exposure frequency, population density, and intensity of human activities rather than concentration levels alone. Although current risks are minimal, continued unregulated emissions could pose long-term health concerns. Regular air quality monitoring and enforcing ≥100-m buffer zones around mining and industrial sites are recommended, alongside further research on seasonal and cumulative exposure pathways.