Heavy Metals and Hydrocarbons in Sediments from Three Lakes from San Miguel, Chiapas, Mexico A. Pascual-Barrera, G. Gold-Bouchot, V. Ceja-Moreno, M. del Rı´o-Garcı´a Marine Resources Department, CINVESTAV Unidad Merida, Km 6 Antigua Carretera a Progreso, Merida, Yucatan 97310, Mexico Received: 5 January 2004/Accepted: 15 July 2004