EDTA enhanced heavy metal phytoextraction: metal accumulation, leaching and toxicity

Synthetic chelates such as ethylene diamine tetraacetic acid (EDTA) have been shown to enhance phytoextraction of some heavy metals from contaminated soil. In a soil column study, we examined the effect of EDTA on the uptake of Pb, Zn and Cd by Chinese cabbage (Brassica rapa), mobilization and leaching of heavy metals and the toxicity effects of EDTA additions on plants. The most effective was a single dose of 10 mmol EDTA kg−1 soil where we detected Pb, Zn and Cd concentrations that were 104.6, 3.2 and 2.3-times higher in the aboveground plant biomass compared to the control treatments. The same EDTA addition decreased the concentration of Pb, Zn and Cd in roots of tested plants by 41, 71 and 69%, respectively compared to concentrations in the roots of control plants. In columns treated with 10 mmol kg−1 EDTA, up to 37.9, 10.4 and 56.3% of initial total Pb, Zn and Cd in soil were leached down the soil profile, suggesting high solubility of heavy metals-EDTA complexes. EDTA treatment had a strong phytotoxic effect on the red clover (Trifolium pratense) in bioassay experiment. Moreover, the high dose EDTA additions inhibited the development of arbuscular mycorrhiza. The results of phospholipid fatty acid analyses indicated toxic effects of EDTA on soil fungi and increased environmental stress of soil microfauna.