Sequential extraction and speciation of Ba, Cu, Ni, Pb and Zn in soil contaminated with automotive industry waste

Sequential extraction or fractionation of heavy metals in the solid phase and their speciation in soil solution are important tools for assessing changes resulting from land use and/or pollution. The distribution of the various forms of Ba, Cu, Ni, Pb and Zn was evaluated in soil samples taken from a polluted area, and the speciation of cations and anions in a soil solution contaminated with automotive industry waste. We evaluated the sequential extraction and speciation of Ba, Cu, Ni, Pb and Zn in a Leptosol associated with a Cambisol and contaminated with automotive industry waste. Soil samples were collected at 0-0.2 m (a mix of soil and waste); 0.2-0.4 m (waste only), and 0.4-0.6 m (soil only) both in the polluted area and in two contiguous unpolluted areas: a sugarcane plantation and a forest fragment. Total concentrations of metals in the polluted area were above limits for intervention established by European Community regulations. Cu was mostly distributed in the residual and in the oxide-bonded fractions, except for the waste-only sample, in which the carbonate-bonded fraction was significant. Zn was concentrated in the residual and carbonate-bonded fractions, while Ba, Ni and Pb predominated in the residual fraction of the contaminated samples. Metals in the soil solution were predominantly in the hydroxyl forms, except for Ba, which was mostly in the ionic form (Ba2+).