The addition of degradable chelating agents enhances maize phytoremediation efficiency in Cd-contaminated soils

Chelating agent-induced phytoremediation is a viable approach to completely remove heavy metals from soil. However, little attention has been paid to the interaction mechanisms between the concentration of the chelating agent and the application time on the physiological and biochemical properties of soil and plants. In this study, five chelating agents, namely ethylenediamine tetraacetic acid (EDTA), diethylenetriacetic acid (NTA), tetrasodium N, N-diacetate (GLDA), aspartate dibutyric acid ether (AES), and iminodisuccinic acid (IDSA), were used to support phytoremediation with maize and to explore the removal effect of Cd in soil. The results showed that chelating agent concentrations of 9 mmol kg^-1 significantly reduced the biomass of maize. Treatment with AES at a dose of 6 mmol kg^-1 significantly increased aboveground biomass, reaching a maximum of 0.92 g pot^-1 in all treatments. At an AES concentration of 6 mmol kg^-1, the highest shoot and root Cd levels of 7.79 and 9.86 mg kg^-1, respectively, were observed, which were 3.05 and 1.60 times higher than those of the control. Total Cd extraction followed the order AES (6 mmol kg^-1) > GLDA > NTA > EDTA > IDSA (3 mmol kg^-1). Chelating agent treatment significantly increased the activity of antioxidant enzymes and promoted plant growth. The self-degradation of AES significantly reduced soil pH, increased soil Cd activity, and promoted Cd uptake and transportation in maize.