Mercury in Blood of Children Exposed to Historical Residues from Metallurgical Activity

The fate of most of the Hg used to obtain Ag through amalgamation in colonial America is uncertain. Residues of this process are often unsecured, and the environmental risk they pose is frequently unknown. The aim of this study is to assess the exposure of the children population of the town of Cedral in North Central Mexico to Hg associated with uncontrolled historical amalgamation residues (tailings). Tailings were partially reprocessed in the twentieth century to obtain the remaining Ag and Hg, modifying the chemical forms of Hg in the residue and producing inorganic Hg compounds. Earlier reports show high concentrations of Hg in the soils and in the two main deposits of metallurgical waste in Cedral. A moderate level of exposure to Hg (geometric mean 3.5 µg L −1 ) was identified in blood samples from school-age children. A result assessment shows the importance of inhalation as a significant exposure route as well as the bioavailability of the Hg chemical form. Hg 0 content in gaseous elemental mercury (GEM) reaches concentrations of up to 1793 ng m −3 in the atmosphere and, due to a low bioavailability, probably contributes only in small proportion to human exposure. Inorganic Hg compounds in the tailings generated during the reprocessing procedure are contained in the particulate fraction in the atmosphere (PM2.5; mean concentration 23.6 ng m −3 ) and may contribute in a higher proportion than GEM to human exposure, due to its higher bioavailability.