A PILOT PHYTOREMEDIATION SYSTEM FOR THE DECONTAMINATION OF LEAD-POLLUTED SOILS

摘要

Phytoremediation is an emerging, environmentally-sound technique based on the use of plants (typically metal hyperaccumulators) able to transfer large quantities of metals from the soil to their aerial parts. We are currently testing a three year pilot phytoremediation system in a field (near Spezia, Italy) polluted by lead concentrations in the order of 300-1500 mg/Kg soil dry weight. The aim is to monitor the soil-decontamination efficiency of three plant species, i.e. maize (Zea mays), sunflower (Helianthus annuus), and indian mustard (Brassica juncea). The experiments were performed in the field and in lysimeters (1 x 1 x 0.8 m~3) filled with contaminated soil from the field. During the first year, a chelating agent (ethylene diamine tetracetic acid, EDTA) was added to the soil in the lysimeters in order to increase Pb in the soil solution while monitoring metal mobility. Total lead in the soil, its concentration in the soil solution (close to the roots) and in the plants were monitored by Atomic Absorption Spectroscopy (AAS). Preliminary results demonstrated that the addition of EDTA (5 mmol/kg dry weight of soil) substantially increased lead accumulation in the plants. Maximum Pb concentration was found in the leaves, while the stems did not show any significant increase in lead even after intensive treatment with EDTA. In the lysimeters, mobile lead in the soil solution (near the plant roots) returned to the initial level within a few weeks from the EDTA treatment. The information collected will support the elaboration of a phytoremediation strategy that may be applied on a larger scale and possibly also in decontamination of sites polluted by other metals.