Contamination Risk Assessment and Distribution of Rare Trace Metal(loid)s in Surface Soil of Cerrito Blanco, Mexico using Various Contamination Indices

In many regions of the world, soil contamination of trace metal(loid)s has become a serious problem. Several studies have used contamination risk indices to identify potential risks arising from excessive pollution, but the majority of these analyses have only focused on anthropogenic sources, making data from these studies less meaningful than those from the added past mining sites, which are considered in the present study. The main objective of this study was to examine the contamination of rare trace metal(loid)s in surface soil near the vicinity of historical mining activities. The concentrations and contamination risks of five rare trace metal(loid)s (B, Ba, Sb, Sn, and V) in surface soils were analysed for 39 soil samples collected from the surrounding areas of the past mining areas of Cerrito Blanco, Matehuala in San Luis Potosi, Mexico. The region has a long history of mining activities that has resulted in the release of trace metal(loid)s into the environment. The evaluation of the contamination risk was performed using single standard indices (i.e., geo-accumulation index and contamination factor) and multi-element standard indices (i.e., degree of contamination, modified degree of contamination, pollution load index, metal pollution index, and Nemerow pollution index). The mean trace metal(loid)s concentration in surface soils followed in the decreasing order barium (Ba) > boron (B) > vanadium (V) > antimony (Sb) > tin (Sn), with corresponding values of 48.15, 12.37, 5.36, 1.62, and 1.58 mg/kg, respectively. Evaluated contamination indices revealed that most of the soil samples were not polluted and were below the reference value. The measured values obtained from these indices revealed that the contamination is only caused by past mining activities and natural geological formations. The GIS interpolation technique was used to assess the spatial distribution patterns and mapping process of trace metal(loid)s. However, the contaminated area was less than 10% of the studied area calculated using a traditional technique, which relies on the proportion of contaminated samples. The significance of this study lies on the processes contributing to soil contamination in Mexico's historical mining regions. The findings offer essential insights for developing appropriate remediation strategies and safeguards to improve soil quality. By considering not only anthropogenic sources but also historical mining activities, this work contributes to a more comprehensive understanding of soil contamination risks and broadens the scope of research in this field.