Effects of EDTA on solubility of cadmium, zinc, and lead and their uptake by rainbow pink and vetiver grass

Rainbow pink (Dianthus chinensis), a potential phytoextraction plant, can accumulate high concentrations of Cd from contaminated soils. Vetiver grass (Vetiver zizanioides) has strong and long root tissues and is a potential phytostabilization plant since it can tolerate and grow well in soils contaminated with multiple heavy metals. Soil was moderately artificially contaminated by cadmium (20 mg/kg), zinc (500 mg/kg), and lead (1000 mg/kg) in pot experiments. Three concentrations of Na2–EDTA solution (0, 5, and 10 mmol/kg soil) were added to the contaminated soils to study the influence of EDTA solution on phytoextraction by rainbow pink or phytostabilization by vetiver grass. The results showed that the concentrations of Cd, Zn, and Pb in a soil solution of rainbow pink significantly increased following the addition of EDTA (p<0.05). The concentrations of Cd and Pb in the shoots of rainbow pink also significantly increased after EDTA solution was applied (p<0.05), but the increase for Zn was insignificant. EDTA treatment significantly increased the total uptake of Pb in the shoot, over that obtained with the control treatment (p<0.001), but it did not significantly increase the total uptake of Cd and Zn. The concentrations of Zn and Pb in the shoots of rainbow pink are significantly correlated with those in the soil solution, but no relationship exists with concentrations in vetiver grass. The toxicity of highly contaminating metals did not affect the growth of vetiver grass, which was found to grow very well in this study. Results of this study indicate that rainbow pink can be considered to be a potential phytoextraction plant for removing Cd or Zn from metal-contaminated soils, and that vetiver grass can be regarded as a potential phytostabilization plant that can be grown in a site contaminated with multiple heavy metals.