Mercury Speciation in Contaminated Soils from Old Mining Activities in Mexico Using a Chemical Selective Extraction
Irma Gavilán–García,1,3* Elvira Santos–Santos,1 Luis R. Tovar–Gálvez,3 Arturo Gavilán–García,2 Sara Suárez,1 and Jesús Olmos1
1 Unidad de Gestión Ambiental, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria 04510, Coyoacán, México D.F. Phone: (52–55) 5622–37–45, Fax: (52–55) 5622–37–45, *Responsible author: irmac@servidor.unam.mx.
2 Instituto Nacional de Ecología, Periférico 5000, Col. Insurgentes Cuicuilco, C.P. 04530, Delegación Coyoacán, México D.F. Phone: (52–55) 5424–64–39 FAX: (52–55) 5424–54–02.
3 Centro Interdisciplinario de Investigaciones y Estudios sobre Medio Ambiente y Desarrollo (CIIEMAD), Instituto Politécnico Nacional, Calle 30 de junio 1520, Col. Barrio La Laguna Ticomán, Delegación Gustavo A. Madero, México D.F.
]]> Received August 4, 2008
Abstract
Amalgamation was heavily used in mining since 1557 in Spanish Colonies. In Mexico and other parts of Latin–America, this process generated tailings which were left aside in the mine backyards. In the valley of Zacatecas, tailings were carried out of the mines due to the run–off from the mountains and contaminated most of the Zacatecan Valley which most important economic activity is agricultural (crop and livestock raising). The main concern in this area is the high level of total mercury found in previous studies. So far, various research studies have been conducted in Mexico to identify the contamination by total mercury in contaminated soils. However, research has not been developed to determine the available fraction by an analysis of the chemical species present in contaminated sites, which represent a risk to human health and the environment. The aim of this study is to develop a mercury sequential chemical extraction methodology with appropriate conditions for identifying: 1) water–soluble fraction, 2) elemental fraction, 3) interchangeable fraction, 4) strongly bound fraction, 5) organic fraction, 6) fraction as sulphides and 7) residual fraction. With this, it might be determined if the mercury species present in mining soils in the state of Zacatecas, Mexico represent a potential risk because of its mobility in the different environmental compartments. Results show that chemical species in the towns of Osiris and La Zacatecana (HgS and amalgamated mercury) have high stability and low mobility.
Key words: Mercury speciation, Soil contamination, Mining wastes, Chemical selective extraction.
Resumen
El proceso de amalgamación fue ampliamente utilizado en la minería desde 1557 en las colonias españolas. En México, y otras partes de América Latina, se generaron jales, los cuales fueron abandonados en los patios de las minas. En el valle de Zacatecas, los jales fueron arrastrados fuera de estos sitios, contaminando la mayor parte del valle, el cual tiene como actividad económica principal la agricultura. La principal preocupación en esta área es el alto nivel de mercurio encontrado en investigaciones anteriores. Hasta ahora, se han desarrollado diversos estudios en México para identificar la contaminación por mercurio total en suelos contaminados. Sin embargo, no se ha desarrollado investigación para determinar la fracción disponible mediante el estudio de las especies químicas presentes en sitios contaminados, lo cual representa un riesgo a la salud y al ambiente. El objetivo de este estudio es el desarrollo de una metodología de extracción química secuencial con las condiciones adecuadas para identificar: 1) fracción soluble en agua, 2) fracción elemental, 3) fracción intercambiable, 4) fracción fuertemente enlazada, 5) fracción orgánica, 6) fracción como sulfuros y 7) fracción residual. Con esto, se busca determinar si las especies de mercurio presentes en los suelos contaminados del estado de Zacatecas, México, representan un riesgo potencial por la movilidad de las especies en los diversos compartimentos ambientales. Los resultados muestran que las especies químicas presentes (HgS y mercurio amalgamado) tienen alta estabilidad y poca movilidad en las comunidades de Osiris y La Zacatecana.
Palabras clave: Especiación de mercurio, contaminación de suelo, residuos mineros, extracción química selectiva.
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Acknowledgments
The authors wish to thank: The Mexican National Institute of Ecology for financial and technical support; the Federal Office of the SEMARNAT in the State of Zacatecas for their technical support during field visits and sampling activities; the Mercury Programme of the United Nations Environmental Programme for financial support; and Project PAPIIT IN218305–2 <<Especiación de mercurio en jales de minería del estado de Zacatecas>> for financial support.
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