Soil Geochemical Mapping with Environmental and Health Perspectives in the Region of San Luis De La Paz, Mexico

The soil is an essential element for human development (agriculture, settlements, mining, etc), however, it has been necessary many decades for a truly understanding of the necessity of geochemical mapping studies in order to assess the soil's role over the entire environment. In recent years, some Mexican institutions have started projects with the objective of studying the soil's geochemical landscape at the continental, national and regional scale. The Universidad Autónoma de San Luis Potosí (UASLP) is currently working on developing a soil geochemical mapping methodology at the regional scale, mainly with environmental and health perspectives. One of the study areas where this methodology has been applied is located in the county of San Luis de la Paz, Guanajuato (central Mexico).

This region, and specifically the area of Mineral de Pozos, was an old mining district, dating since XVII century. There it was established a 40x40 km grid, with a sampling density of 16 square kilometers (100 sampling points). After a near total digestion and ICP-MS analysis, the A horizon data showed geochemical anomalies for several potentially toxic elements like As (up to 1335 mg/kg), Cd (up to 54.25 mg/kg), Hg (up to 354 mg/kg), Pb (up to 5,935 mg/kg) and Se (up to 24 mg/kg).

The geochemical anomalies are located over the mineralized zones of Mineral de Pozos and Santa Gertrudis, but these two areas also have several waste rock deposits, that after being sampled showed the following maximum values: As (1,550 mg/kg), Cd (46.30 mg/kg), Hg (128 mg/kg), Pb (7,300 mg/kg) and Se (69 mg/kg).

Based on these results, the deposits represent a potential source of soil contamination, but at this point it is still difficult to differentiate the natural geochemical background from the anthropogenic impact caused by old mining and metallurgical activities.