Cd2+, Cu2+, and Pb2+ sorption, desorption and migration in Fluvisols

The aim of this work was to assess and compare the mono and bimetallic Cd2+, Cu2+ and Pb2+ sorption and desorption capacities as well as the sorption hysteresis in two different types of Fluvisols. The migration of cations through the profiles was evaluated, along with the dependence on soil properties of mono and bimetallic Cd2+, Cu2+ and Pb2+ fixation, hysteresis and mobility. Sorption irreversibility and migration of the studied cations through the profiles were evaluated, by means of hysteresis and migration indexes calculated from retention capacity values (Kr) proposed and validated in a previous work. The results showed that the sorption and retention capacities of the A horizons were higher than those of C and that the individual sorption and retention capacities were greater than the competitive capacities. The highest values of sorption and retention capacities were those for Pb2+, followed by Cu2+ and Cd2+. Mn oxides, organic matter and, consequently, ECEC were the components and properties that most highly influenced Pb2+ monometal and competitive sorption and retention. Cd2+ did not interfere with Pb2+ or Cu2+ sorption and retention. Organic matter content was only correlated with the sorption hysteresis of Pb2+, in accordance with the high Pb2+ fixation capacity of in this component and its lower capacity to retain Cu2+ and Cd2+. Tidalic Fluvisols retained only 0.4 and 0.2% of added Cd2+ when competing with Cu2+ and Pb2+, respectively. However, more than 60% of the added Pb2+, and over 47% of the added Cu2+ were retained. The Pb2+ retained in competition with Cu2+ was 98.2 in TF and 47% in the Umbric Fluvisol, whereas the retained Cu2+ was 93.8 and 29.9% respectively. These retention and Cd2+ mobility indicated that there is a possibility of heavy metals transferring to subsurface waters and, through these, of contamination and even of these metals entering the food chain.