Cadmium, copper, and lead adsorption and desorption in oxisol samples pre-treated with phophorus

The movement of trace elements in soils is closely related to factors that contribute to their retention in the solid phase, for instance adsorbed anions. In the present work, it was evaluated the effect of phosphorus (P) pre-treatment on adsorption and desorption of Cd, Cu, and Pb in A and B horizon samples of two Latosol (Oxisols): a Yellow-Red Latosol and a Dark-Red Latosol. The P pre-treatment consisted of reacting soils samples for 72 h with 10.75 mmol L-1 Ca(H2PO4,)(2).H2O (soil:solution ratio of 1:1.5). For adsorbing the metals, samples of pre-treated and non pre-treated soil material were pre-equilibrated with 5 mmol L-1 Ca(NO3)(2) (soil:solution ratio of 1:67, pH 5.5), and then reacted, individually, with 0.450 mmol L-1 Cu(NO3)(2), Cd(NO3)(2), or Pb(NO3)(2), (final soil:solution ratio of 1:100). Phosphorus pre-treatment increased the adsorption of all metals, particularly in B-horizon samples. The increased adsorption indicates that the presence of P in these soils may contribute to reduce Cd, Cu and Pb availability. The amount of metal adsorbed followed the sequence Pb greater than or equal to Cu much greater than Cd. Regarding the fraction of desorbed metal (desorbed metal / adsorbed metal), it was smaller in the previously P treated samples, except for Cu, whose desorption was not influenced by the pre-treatment with P.