Sorption of cadmium, zinc and copper in dominant soils of the Zagreb aquifer system, Croatia

Contamination of soils with potentially toxic metals (PTMs) is an environmental problem. In this study, sorption of cadmium (Cd), zinc (Zn) and copper (Cu) in four soil profiles (two Fluvisols, one Gleysol, and one Cambisol), representing the dominant soils of the Zagreb aquifer system, were studied using a multi element laboratory batch test. Mathematical expressions were applied to establish the relationship between the concentration of the adsorbent in the liquid phase and the solid phase at equilibrium and in laboratory conditions. The study revealed that the investigated soils have a higher capacity to sorb Cu than Zn and Cd. The most significant physicochemical characteristics of soils, influencing sorption, are pH, carbonate content (minerals) and organic matter. Although all PTMs in all analyzed soils had a similar sorption capacity, the variation of sorption was higher in the siltic soils (Fluvisois) compared with the texturally finer (loamic) Gleysol and Cambisol soils, as well as in the subsoil horizons compared with the topsoils. Results indicate that sorption of PTMs is more influenced by physicochemical characteristics at different soil depths than by soil type, which is confirmed with a higher affinity for Zn and Cd bonding in the topsoil horizons. Also, it has been shown that Cd may pose more of a threat to soils and ground-water due to its toxicity and relatively high mobility in comparison with Zn and Cu.