Bioaccessibility of potentially toxic elements in mine residue particles

Abstract

Mining companies used to abandon tailing heaps in countryside regions of Mexico and other countries. Mine residues (MRs) contain a high concentration of potentially toxic elements (PTE). The wind can disperse dust particles (<100 μm) and once suspended in the atmosphere, can be ingested or inhaled; this is a common situation in arid climates. Nowadays, there is little information on the risk of exposure to PTEs from particulate matter dispersed by wind. The pseudo-total PTE in bulk and fractionated MR after aqua regia digestion, the inhalable bioaccessibility with Gamble solution (pH = 7.4), and the gastric bioaccessibility with 0.4 M glycine solution at pH 1.5 were determined. As and Pb chemical species were identified by X-ray absorption near-edge structure (XANES) spectroscopy. The highest rate of dispersion was observed with 74–100 μm particles (104 mg m⁻² s⁻¹); in contrast, particles <44 μm had the lowest rate (26 mg m⁻² s⁻¹). The highest pseudo-total As (35 961 mg kg⁻¹), Pb (3326 mg kg⁻¹), Cd (44 mg kg⁻¹) and Zn (up to 4678 mg kg⁻¹) concentration was in the <20 μm particles and As in the 50–74 μm (40 236 mg kg⁻¹) particles. The highest concentration of inhaled bioaccessible As (343 mg kg⁻¹) was observed in the <20 μm fraction and the gastric bioaccessible As was 744 mg kg⁻¹, Pb was 1396 mg kg⁻¹, Cd was 19.2 mg kg⁻¹, and Zn was 2048 mg kg⁻¹. The predominant chemical As species was arsenopyrite (92%), while 54% of Pb was in the adsorbed form. Erodible particle matter is a potential risk for humans in case of inhalation or ingestion.