Copper and lead adsorption as influenced by organic matter in soils from a tropical toposequence with different chemical and mineralogical attributes

The aim of this work was to investigate the influence of the organic matter on copper and lead adsorption in soils with different physiochemical and mineralogical attributes. Suspensions (pH 6.0) of a Latosol, a Neosol and a Vertisol containing increasing amounts of copper or lead were used to obtain sorption isotherms while identical experiments were carried out with the soils previously treated with H₂O₂ to remove organic matter (OM). For the undisturbed soils, L-type and H-type isotherms were predominant for copper and lead respectively, showing that lead interacts more strongly with adsorption sites. For both metals, the non-linear Freundlich adsorption model revealed higher concentration of adsorption sites for Vertisol due to 2:1 clays. For the OM-removed soils, C-type isotherms were observed for copper with the permanence of less stable and more homogeneous sites. For this metal, a high correlation (R² = 0.997) was observed between the decrease of adsorbent sites and the loss of organic carbon, evidencing the central role of organic matter on copper complexation, while lead may be able to interact efficiently with both organic matter and soil minerals.