In: Causes and Effects of Heavy Metal Pollution ISBN 978-1-60456-900-1 Editor: Mikel L. Sanchez, pp. © 2008 Nova Science Publishers, Inc. Chapter 5 PHYTOCHELATINS IN THE WILD PLANTS FROM GUANAJUATO CITY – AN IMPORTANT SILVER AND GOLD MINING CENTER IN MEXICO Kazimierz Wrobel, Julio Alberto Landero Figueroa and Katarzyna Wrobel 1 Instituto de Investigaciones Científicas, Universidad de Guanajuato, L. de Retana N° 5, 36000 Mexico ABSTRACT Phytochelatins (PCs) are a group of small, metal-binding peptides that are biosynthesized by higher plants, some fungi and algae in the response to heavy metal exposure. One actual research topic focuses on better understanding the global effect that all elements present in natural environments exert on the PCs production by plants. In this work, PCs levels were evaluated in the wild plants, chronically exposed to low or moderate levels of heavy metals. The quantification of total PCs in plant extracts was carried out by HPLC with fluorimetric detection, after derivatization of free –SH groups with monobromobimane. Additionally, the distribution of metals in molecular mass (MM) fractions of these same extracts was studied by size exclusion chromatography with on-line UV and ICP-MS detection. All samples were collected in Guanajuato city (Mexico), which has long been an important silver and gold mining area. Among different metals reported in Guanajuato soils, lead, cadmium, copper and silver were selected in this study, because of their capability to induce phytochelatins in plants. The common plants from this region were analyzed, namely: Ricinus communis (castor bean), Tithonia diversifolia (Mexican sunflower) and Opuntia ficus (nopal). The analytical approach involved the ICP-MS analysis of total elements in soil, soil fractions and wild plants and also the evaluation of relationships between PCs, metal levels found in plants/soil and different soil parameters. 1 Corresponding autor: katarzyn@quijote.ugto.mx.