Phytoextraction is one of the most promising technologies for the remediation of metal contaminated
soils. Changes in soil metal availability during phytoremediation have direct effects on removal efficiency
and can also illustrate the interactive mechanisms between hyperaccumulators and metal contaminated
soils. In the present study the changes in metal availability, desorption kinetics and speciation in four
metal-contaminated soils during repeated phytoextraction by the zinc/cadmium hyperaccumulator
Sedum plumbizincicola (S. plumbizincicola) over three years were investigated by chemical extraction and
the DGT-induced fluxes in soils (DIFS) model. The available metal fractions (i.e. metal in the soil solution
extracted by CaCl2 and by EDTA) decreased greatly by >84% after phytoextraction in acid soils and the
deceases were dramatic at the initial stages of phytoextraction. However, the decreases in metal
extractable by CaCl2 and EDTA in calcareous soils were not significant or quite low. Large decreases in
metal desorption rate constants evaluated by DIFS were found in calcareous soils. Sequential extraction
indicated that the acid-soluble metal fractionwas easily removed by S. plumbizincicola from acid soils but
not from calcareous soils. Reducible and oxidisable metal fractions showed discernible decreases in acid
and calcareous soils, indicating that S. plumbizincicola can mobilize non-labile metal for uptake but the
residual metal cannot be removed. The results indicate that phytoextraction significantly decreases metal
availability by reducing metal pool sizes and/or desorption rates and that S. plumbizincicola plays an
important role in the mobilization of less active metal fractions during repeated phytoextraction.