Chelate-assisted phytoextraction of lead from soil - A study on some parameters determining the efficiency

Background. Soil pollution with heavy metals is one of the major problems in industrial areas. Chelate-assisted phytoextraction has been proposed as an alternative to the high costs of the ex situ methodology df decontamination based on soil removal and treatment. The soil of the present study has a low - medium level of lead contamination (360 mg/kg dry soil) distributed by tillage works in the first 50 cm of soil. The aim of the present work was to study chelate agents capability to solubilise. Pb in the soil and the chelate induced Pb accumulation in Helianthus annuus plant in order to optimise some aspects of a chelate-assisted phytoextraction treatment. Methods. Different doses of chelate agents, ethylenediaminetetraacetic acid Dipotassium Salt, N-(2-hydroxyethyl)ethylenediaminetriacetic acid, Diethylenetriaminepentaacetic acid, N,N ' -DI(2-hydroxybenzil)ethylenediamine-N,N ' -diacetic acid Monohydrocloride Hydrate, nitrilotriacetic acid have been compared and the environmental impact of the best performing chelate treatment has been considered. For Pb solubilisation in soil the best performing chelate proved to be EDTA. The root absorption and translocation to the xylem of the Pb-chelate complexes were followed by the pressure chamber technique. Results. The Pb-EDTA and Pb-NTA complex were the best absorbed. For the EDTA and Pb-EDTA complex, the transpiration stream concentration factor has been determined. After EDTA treatment of the soil, the Pb absorbed in the plant was accumulated in the leaves, a low amount was in the stem. The Pb mobility in the soil after EDTA application was tested showing the possibility of leaching toward; deep layers and underground water. in addition EDTA solubilised micronutrients with possibility of leaching: and decrease in soil fertility.