Leaching behaviour of Cd, Cu, Pb and Zn in surface soils derived from dredged sediments

Leaching of heavy metals from land-disposed dredged sediment spoils is a potential environmental hazard. The leaching behavior of Cd, Cu, Pb and Zn in surface soils sampled from abandoned dredged sediment disposal sites was assessed. Using simple mass-balance calculations, the significance of the leaching test results with respect to metal migration into underlying clean soil was appraised. The potential leachability, defined as the amounts released at constant pH 4, decreased in the order (% of total contents): Zn (58%)≈Cd (49%)>Cu (5%)≈Pb (2%). The kinetics of metal release were determined in a cascade shaking test using de-mineralized water acidified to pH 4 (HNO3). Metal concentrations in the leachates were low and metal migration was, assuming uniform convective flow, predicted to be of no environmental concern. It is emphasized that any long-term prediction of metal migration is uncertain.