Influence of minerals from the tailings in the bioaccessibility of arsenic, lead, zinc and cadmium, in the mining district Zimapan, Mexico

The state of Hidalgo has been, through centuries, an important producer of gold, silver, lead, zinc and copper in Mexico, thanks to the exploitation of metallic resources of deposits of the skarn type, generating a great volume of residues (tailings) deposited in dams for over 450 years, which have not been rehabilitated or restored. The tailings present variable and complex mineralogy constituted by calcosilicates, sulfides and sulfosalts. Also, the concentrations of As, Sb, Se, Zn, Cu, Pb, Cd, Bi and Mn, are notable, considered potentially toxic elements (PTE). The mineralogic characterization by polarized optical microscope (POM), scanning electronic microscope (SEM) and microprobe (Mp), allowed determination of the primary and secondary mineralogy of the tailings. Additionally, the formation of ferric hidroxides and sulfates as products of the preferential alteration of pyrrhotite was identified, as well as ferric arsenates (scorodite and symplesite) as a result of border alterations of arsenopyrite. The bioaccessible content of arsenic, lead, cadmium and zinc was quantified using the PBET (Physiologically Based Extraction Test) method, for the gastric (pH 1.3) and intestinal (pH 7.0) phases. The bioaccessibility and percentage of bioaccessibility of arsenic and lead is highest in the gastric phase, while zinc and cadmium are variable in both phases.