Characterization of Regional Geochemical Anomalies within the Continental-Scale Pilot Transect in Mexico

In order to improve the lack of information about the spatial distribution of chemical elements in the soils of Mexico, the Mexican Geological Survey (SGM), the National Institute of Statistics, Geography and Informatics (INEGI) and the Autonomous University of San Luis Potosí (UASLP) have established a multidisciplinary team with the objective of creating a national program of geochemical mapping of soils. This program is part of the North American Soil Geochemical Landscapes Project, in partnership with the U.S. Geological Survey and the Geological Survey of Canada. Results will be presented from the Mexican pilot transect and from two regional mapping projects related with it.

The pilot study was conducted over a representative transect across the country (from the USA border at north to the Pacific Ocean at south), with a 40-km spacing. Samples from the A and C horizons of non-impacted soils were collected and the results let to identify broad-scale geochemical patterns. The soil parent material was the most relevant factor influencing the distribution of elements, followed by the influence of regional mineralization. There were some sampling sites with relatively high values of potentially toxic elements (PTE's) like As and Hg (up to 85.6 and 0.25 mg/kg respectively). The following step has consisted in developing regional geochemical mapping projects with environmental and health perspectives over specific areas within the transect. At the moment, two regional projects over a 40km grid with a 4-km sampling density have been completed, one in Mineral de Pozos region and other in the Altiplano Potosino region, both in Central Mexico. The resulting geochemical maps show with more detail the anomalous points identified within the transect, with areas up to 324 mg/kg As and 1.35 mg/kg Hg in the Altiplano and up to 1335 mg/kg As and 353 mg/kg Hg in Mineral de Pozos.