Optimization of EDTA and citric acid for risk assessment in the remediation of lead contaminated soil

Abstract

So far, more attention has been mostly paid to the effects of the chelates application to improve phytoextraction efficiency, but less information is available about their effects on the rhizosphere enzyme activities. A greenhouse study was conducted to investigate the effect of EDTA and citric acid (CA) (3 and 5 mmol/kg) on the Pb accumulation in plant organs, the dehydrogenase, urease and alkaline phosphomonoesterase activities, geometric mean of enzyme activities (GMea), total enzyme activity (TEA), and Shannon's diversity index. The application of EDTA harmed plant growth, whereas CA treatments improved plant growth. The 3 and 5 mmol/kg EDTA enhanced Pb accumulation in shoots by 2.6–6 and 1.7–3 times, respectively, in comparison with the control. Pb accumulation in roots after the CA application was significantly higher than control and EDTA treatments. The high dose of EDTA reduced the dehydrogenase and urease activities, GMea, TEA, and diversity of enzyme activities. In contrast, the low dose of EDTA increased the dehydrogenase and alkaline phosphomonoesterase activities, and enzyme-based indices compared with control treatment. In both high and low concentrations, CA significantly stimulated enzyme activities of the rhizosphere, as well as the enzyme-based indices, compared with control and EDTA treatments. CA increased Pb accumulation in the root while did not elevate Pb translocation to the shoot, and also improved the rhizosphere enzyme activities. Thus, we conclude that: i) the effect of EDTA on the Pb phytoextraction and rhizosphere enzyme activities depended on the dosage of EDTA used; ii) CA can be a more suitable choice to increase Pb phytostabilization due to enhancement of the rhizosphere microbial activities.