1. Environmental Health Department, National Institute of Public Health, Cuernavaca, Morelos, Mexico
2. Center for Ecosystem Research, National Autonomous University of Mexico, and Interdisciplinary Group on Appropriate Rural Technology, Morelia, Michoacán, Mexico
3. Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
4. National Institute of Ecology, Mexico City, Mexico
5. International Agency for Research on Cancer, Lyon, France