Environmental and human health risk assessment of potentially toxic elements in soil, sediments, and ore-processing wastes from a mining area of southwestern Tunisia

Abstract

The occurrence and bioaccessibility of potentially toxic elements (PTEs) in soils and sediments are investigated by many studies, especially in territories exploited by mining and ore-processing activities, nearby agriculture-driven rural cities. Accordingly, the present study aimed at evaluating the geochemical properties, potential bioavailability, and risks for environment and human health of the most concerning PTEs of study area (Gafsa mining basin, Tunisia) such as Cd, Cr, and Zn in selected soil, sediment, and mining waste samples. The extraction of these solid matrixes by modified EU-BCR sequential extraction revealed that the most easily extractable fractions of each PTE were very low (first 2 steps, < 10%), Cd was mainly associated with the oxidizable phase (likely organic matter), and Cr and Zn were mostly found in residual mineral fraction (likely occluded in non-siliceous mineral phase). The total cumulative concentration of each metal was found to be higher in soil/sediment profiles and ore-processing wastes than in phosphate rocks, indicating a metal enrichment due to mining activities. The aqua regia extraction of representative sediment samples revealed that Cd, Cr, and Zn concentrations were higher than non-polluted sediment standards. In contrast, other elements as Cu, Mn, and Pb essentially arose from natural bedrocks. The Unified BARGE method was applied to assess the risk of ingestion by human beings and wild/domestic animals of contaminated sediment particulate prone to wind erosion and air dispersion in the arid conditions of study area. An higher oral bioaccessibility was found for Cd than Zn and Cr, most concerning in acid gastric phase than in sub-neutral intestinal environment.

Keywords: Bioaccessibility; Bioavailability; EU-BCR sequential extraction; Gafsa mining basin; Heavy metals; Unified BARGE Method (UBM).