Arsenic is quite abundant in the terrestrial crust [4], being present in a variety of compounds of different toxicities, depending on its ox- idation state in the compound [5]. Mercury as a free element is rarely encountered in nature, but is well distributed in the terrestrial crust at low concentrations and also in a variety of compounds of different toxicities. Anthropogenic activities, including solid wastes facilities and deposits, are responsible for the introduction and distribution of As and Hg in the environment.