Pérez Olvera, Ma. Antonia. 2008. “Concentration of Pb, Cd, Ni, and Zn in Polluted Soils and Their Transference to Broccoli Heads”. REVISTA TERRA LATINOAMERICANA 26 (3):215-25. https://terralatinoamericana.org.mx/index.php/terra/article/view/1345.