Single and Sequential Extractions of Heavy Metals in Soils From Mining and Smelting Areas in Brazil.

Mining and smelting activities have been pointed out as a potential source of heavy metal contamination, which might pose a threat to human health and ecological systems. This study investigated single and sequential extractions of Zn, Pb, and Cd in soils affected by mining and smelting activities in Brazil. Soils from a Zn mining area (soils A, B, C, D, E, and the control soil) and a tailing from a smelting area were collected in Minas Gerais State, Brazil. These samples were subjected to single (using Mehlich I solution) and sequential extractions. The targeted components (soil phase) in each fraction were considered to be: F₁, exchangeable; F₂, carbonate; F₃, easily reducible oxides; F₄, organic matter; F₅, reducible oxides; and F₆, residual fraction. Zinc and Cd, in soil samples from the mining area, were found mainly associated with carbonate forms. This same pattern did not occur for Pb. Moreover, the Fe-Mn oxides and residual fractions had important contributions for Zn and Pb in those soils. For the tailing from the smelting area, more than 70% of Zn and Cd were released in the exchangeable fraction, showing a much higher mobility and availability of these metals at this site. These differences in terms of mobility might be due to different chemical forms of the metals in those two sites, which are attributable to natural occurrence as well as ore processing. Sponsored by Fapemig, CNPq, and Capes.