Heavy metal concentrations in consecutive saturation extracts of dredged sediment derived surface soils

Heavy metals in upland, dredged-material disposal sites are of concern. Metal mobility and availability are closely related to the composition of the liquid phase. To appraise changes in pore-water metal concentrations (Cd, Cu, Pb, Zn) after continued leaching, surface soil samples from abandoned metal-contaminated dredged-sediment disposal sites were subjected to consecutive saturation extracts. For an ‘alternating dry and wetʹ moisture regime, where soils were allowed to dry between extractions, metal concentrations varied randomly in the consecutive extracts. For a ‘continuously wetʹ moisture regime, metal concentrations decreased when reducing conditions were being established and then remained constant at a lower level than in the alternating dry and wet moisture regime. Potential short-term hazards (15–40 years) related to metal migration were estimated from the observed leaching behavior. Although metal concentrations in the saturation extracts of the oxidized soils were above levels found in the pore-water of clean soils, metal migration is estimated to be limited. However, an enhanced availability of Cd, Cu, and Zn for organisms living in these soils must be anticipated.