Role of chelating agents on release kinetics of metals and their uptake by maize from chromated copper arsenate-contaminated soil

Kinetic aspects of metal release were investigated to understand the effects of synthetic chelating agents (EDTA, EDDS and NTA) and low molecular weight (LMW) organic acids (oxalic and citric acids) on the release kinetics of Cr, Cu and As in chromated copper arsenate (CCA)-contaminated soil, as well as their uptake by maize (Zea mays L.). The results showed that the release of metals from soil was better described by parabolic diffusion, power function or simple Elovich model than by the first- and second-order models, indicating a heterogeneous diffusion of metals. Synthetic chelating agents afforded a higher release of Cu than that of LMW organic acids, whereas citric acid was the most effective chelating agent for Cr and As release. The most effective treatments for stimulating metal uptake in plant shoots were EDDS for Cu, EDTA for Cr, and citric acid for As, as indicated by the removal efficiencies of 0.046%, 0.036%, and 0.004%, respectively. However, Zea mays is not an attractive species for chelate-enhanced phytoremediation of CCA-contaminated soils due to its low phytoextraction rate, even in the presence of chelating agents and ligands.