Environmental Geochemistry and Human Health Risk Assessment of Potentially Toxic Elements in Urban Soils in the Vicinity of a Pb Fire-Assay Laboratory in Ouagadougou, Burkina Faso

A total of 30 topsoil, subsoil samples, and 11 new and used cupels were collected around a Pb fusion fire-assay laboratory in Ouagadougou, Burkina Faso, and their physico-chemical parameters and major and potentially toxic (PTE) element concentrations were determined. The results showed that the soil samples in the immediate vicinity of the used-cupel disposal site were highly polluted with Pb (up to 8900 mg/kg). Cluster analysis identified the used-cupels as the primary source of Pb, As, Cr, Cu, Ni, and Ca contamination of topsoils. Furthermore, principal component analysis revealed that abundance and mobility of Cr, Cu, Ni, and Pb were likely controlled by clay and Fe- and Al-oxyhydroxides, whereas that of As and Mn appeared to be a function of pH and oxido-reduction reactions. With pollution loading indices higher than unity, the status of all the sampling sites ranged from very high to moderate polluted. Similarly, the used-cupel disposal site had a very high average ecological risk index compared to the two relatively distant sites. Lead, As, and Cr proved to have non-carcinogenic effects on children in all sites, whereas these elements only showed non-carcinogenic effects on adults in the used-cupel disposal site. Direct ingestion was the major pathway of PTE exposure. The carcinogenic risk index for all sites and all elements exceeded the threshold. Moreover, the average total carcinogenic risk indices for Cr, Ni, As, and Pb in all sites were high enough to pose lifetime cancer risks to the exposed population with the used-cupel disposal site having the highest average value. Urgent remediation is necessary to prevent the spread of pollution to larger areas.