Effects of Chelating Agents Addition on Ryegrass Extraction of Cadmium and Lead in Artificially Contaminated Soil

Abstract

This study investigated the removal of cadmium (Cd) and lead (Pb) from the soil through phytoremediation using ryegrass combined with chelating agents. Soil leaching experiments were employed to determine the extraction efficiencies of chelating agents, including ethylenediaminetetraacetic acid (EDTA), citric acid (CA), sodium glutamate tetra acetate (GLDA), oxalic acid (OA), and diethylenetriaminepentaacetic acid (DTPA) on Cd and Pb. Soil pot experiments were conducted to determine the effects of five different chelating agents—GLDA, EDTA, DTPA, CA, and OA—on the growth of ryegrass and the enrichment of Cd and Pb. The main findings were as follows: (1) the extraction efficiencies for Cd and Pb in soil were found to be GLDA > EDTA > DTPA > CA > OA and EDTA > DTPA > GLDA > CA > OA, respectively. (2) The aminopolycarboxylic acid class of chelating agents significantly reduced Cd and Pb contents in the weak acid extractable and reducible states in the studied soil, yet were less effective in the extraction of their residue state. Using chelating agents increased the proportion of residual heavy metals while reducing those in the weak acid extractable and reducible states in the soil, thereby mitigating the harmful effects of these heavy metals on the soil ecology.