The effects of Ethylenediamine disuccinic acid (EDDS) (0 and 5 mmol·kg-1) as a synthetic chemical amendment, vermicompost (0 and 5%w/w) as an organic amendment and their combined application were evaluated for the phytoextraction by sunflower (Helianthus annuus L.) of cadmium (Cd) and lead (Pb) at three artificial contamination levels in soils (0, 50, and 100 mg·kg-1 for Cd and 0, 100, and 200 mg·kg-1 for Pb). The results showed that the application of EDDS was the most effective method to increase Pb and Cd concentrations in both parts of the plant. The results also showed that the application of EDDS increased 9.27% shoot Pb content at 200 mg·kg-1 but decreased 15.95% shoot Cd content at 100 mg·kg-1 contamination level with respect to the respective controls. The bioavailable concentrations of Cd at 100 mg·kg-1 and Pb at 200 mg·kg-1 contamination level in the soil at the end of experiment increased 25% and 26%, respectively after the application of EDDS but vermicompost decreased 43.28% the bioavailable Pb concentration relative to their controls. Vermicompost increased the remediation factor index of Cd, thus making it the best treatment for the phytoextraction of Cd. The combined application of EDDS and vermicompost was the best amendment for Pb phytoextraction.
Keywords: Cd; EDDS; Pb; phytoextraction; sunflower; vermicompost.