**4. Conclusion**

The amount of As and Pb detected in this study showed levels that were above the national criteria (NOM-147-SEMARNAT/SSA1–2004) mainly for the distances of 0–100 m, which reflects the danger of these elements for the environment. The historical mining activity in this site has left large amounts of mine tailings rich in heavy metals exposed to the elements, which are currently causing a problem of contamination and health impacts of soil, plants, animals and humans. The levels identified in this study justify immediate intervention in the area close to the tailings, followed by long-term monitoring for the protection of human and ecological receptors, as well as avoiding the mobility of contaminants to different environmental matrices (water and sediments).

**Conflict of interest**

**Author details**

S.L.P., México

**References**

Donaji J. González-Mille<sup>1</sup>

Ángeles Martínez-Toledo4

César A. Ilizaliturri-Hernández2

de San Luis Potosí, S.L.P., México

The authors declare that there is no conflict of interest regarding the publication of this chapter.

Evaluation of the Biological Activity of Soil in a Gradient Concentration of Arsenic and Lead…

1 Cátedras Consejo Nacional de Ciencia y Tecnología (CONACyT), Universidad Autónoma

3 Facultad de Química, Universidad Veracruzana, Campus Coatzacoalcos, Veracruz, México 4 Facultad de Ingeniería, Área de Ciencias de la Tierra, Universidad Autónoma de San Luis Potosí,

5 Instituto de Geología, Universidad Autónoma de San Luís Potosí (UASLP), S.L.P., Mexico

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2 Centro de Investigación Aplicada en Ambiente y Salud (CIAAS), CIACyT-Facultad de

, María del Carmen Cuevas-Díaz3

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, María E. García-Arreola5

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, Guillermo Espinosa-Reyes2

, Leticia Carrizalez-Yáñez2

\*

Medicina, Universidad Autónoma de San Luis Potosí, S.L.P., México

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\*Address all correspondence to: ilizaliturri\_ca@hotmail.com

The contamination by heavy metals and the effect of the mining activities in Villa de la Paz over time have caused for the physical–chemical properties (organic matter, electrical conductivity and pH), of the soils developed on the mining residues, to be significantly different to those of soils without the influence of pollution. These properties are involved in the interactions between microorganisms, enzymes and roots of plants, which are responsible for maintaining adequate soil health. It is recommended to carry out tests to evaluate the degree of degradation in at least 1 km around the mining waste to identify the alterations caused by the mining activity punctually and thus propose methods of soil recovery.

The biological activity of the soils presented a strong affectation due to the presence of heavy metals, which proved its usefulness as an indicator for rapid, reliable and low-cost evaluation. Levels such as those registered in the evaluated sites reduce the biological activity of soil in an alarming way, affecting their health, as well as the biogeochemical cycles and the environmental services that this provides. It was determined that metals are not the only ones who can negatively affect enzymatic activity, but also electrical conductivity and pH can interact in the phenomenon of inhibition. The organic matter with its capacity of immobilization of heavy metals promotes the increase of enzymatic activity.

The general pattern of inhibition for the area was urease>glucosidase>arylsulfatase>dehydrog enase>phosphatase>respiration; the latter being the least sensitive to inhibition. The continuous monitoring of parameters in this area is recommended. The alteration of these enzymes could be interrupting the biogeochemical cycles, as well as the material and energy flows of the ecosystems, making it more difficult to recover key processes for the maintenance of life such as the fixation of nitrogen and CO2 .
