Resumo

PEREZ-MARTINEZ, Isabel  e  MARTIN ROMERO, Francisco. Use of indirect parameters in the assessment of soil contamination by heavy metals in a mining area of San Luis Potosi, Mexico. Bol. Soc. Geol. Mex [online]. 2015, vol.67, n.1, pp.01-12. ISSN 1405-3322.

Tailings are a significant source of arsenic and heavy metals. When mining wastes are subjected to wind dispersal and water erosion, they may be the cause of widespread soil contamination. In this work, a mining area in the state of San Luis Potosi, Mexico, was selected to evaluate the use of magnetic susceptibility (MS), electrical conductivity (EC) and pH as alternative indicators for the delimitation of the spatial distribution of arsenic and heavy metals in mine wastes and soils contaminated by their dispersal. The MS, EC, pH and the total concentration of potentially toxic elements (PTE), such as arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), zinc (Zn) and iron (Fe), were determined in 107 waste and soil samples. Moreover, the concentration of major ions in solution was analyzed and XRD and SEM analyses were carried out. Finally the hazard index (HI) was assessed as a value showing the effect of joint presence of As, Cd and Pb in the area. The results indicate that higher values of MS, EC and total concentrations of PTE and the lowest pH values were determined in mining waste, confirming that they are a potential source of soil contamination of adjacent areas. Moreover, soils closest to residues yielded high values for these parameters. There was a strong linear correlation between the MS, pH and the total concentration of PTE and a lower correlation for the EC, which is determined by the presence of calcium sulfate (gypsum) as the main secondary mineral of oxidation processes in mining wastes. Also, the relationship between MS and PTE was determined by solid phases that were contained in the PTE (Fe minerals) with good magnetic response. The linear regression analysis for the hazard index (HI), MS, EC and pH indicates a significant linear correlation between HI and MS (0.82), and between HI and pH (- 0.81). However, only a weak linear correlation between HI and EC was found (r = 0.57). These results suggest that the EC will help to determine the source of contamination and the dispersion of the waste and the MS and pH help in the delineation of soil contamination as well as the assessment of the degree of contamination by mining waste in the study area.

Palavras-chave : magnetic susceptibility; electrical conductivity; pH; mine tailings; hazard index.