Enhancing the Phytoextraction of Cd, Cu, Pb, and Zn by Portulaca oleracea in a Heavily Contaminated Soil Using Low Molecular Weight Organic Substances: Is Phytoremediation Viable?

Phytoremediation can be accelerated if contaminated soils are amended with releasing agents. We tested four such materials, citric acid (CA), EDTA, oxalic acid (OA), and tartaric acid (TA) at two doses, 20 and 40 mmol kg⁻¹, amended in a pot experiment to a heavily contaminated soil cultivated with purslane (Portulaca oleracea). We found that Cd extracted with DTPA remained unchanged in all treatments compared to the control except for the treatment of added EDTA at 40 mmol kg⁻¹ (“EDTA-40”). Similar was the case with Cu, Pb, and Zn. As a consequence, Cd in the aboveground plant material increased significantly from 1.21 (control) to 3.84 at EDTA-40 and 3.55 at EDTA-20 (mg kg⁻¹). Similar was the case with all other metals, with Pb exhibiting an impressive fivefold increase to 280.35 mg kg⁻¹ at EDTA-40 from the control. We conclude that EDTA was the most successful releasing agent among those tested, especially for Pb and Zn. However, we come to the conclusion that, based on calculations of the required time to meaningfully reduce soil metals contents, phytoremediation is not a practical option for extremely metal-elevated soils. These findings should be verified under field conditions.