The use of NTA for lead phytoextraction from soil from a battery recycling site

摘要

The application of synthetic aminopolycarboxylic acids to soil increases metal solubility, and therefore enhances phytoextraction. However, synthetic chelants degrade poorly in soil, and metal leaching threatens human and animal health. The aim of this study is to assess the use of a biodegradable chelant (NTA) for Pb phytoextraction from a soil contaminated by battery-casing disposal. EDTA was also included in the experiment to assess the behavior of a non-degradable chelant. Each synthetic chelant was applied to soil pots cultivated with maize plants at rates of 0,2,5,10, and 20 mmol kg~(-1). Soil samples were extracted with CaCl_2 and by sequential extraction for Pb. In addition, a soil column experiment was set up to study the leaching of Pb from the chelant-amended soil. The results showed that both NTA and EDTA were highly effective in solubilizing Pb from soil. The Pb distribution into soil fractions after chelant addition followed the sequence: Ex (exchangeable) > OM (organic matter) > AFeOx (amorphous iron oxides) >CFeOx (crystalline iron oxides). The 5 mmol kg~(-1) dose of EDTA increased the Pb concentration in maize shoots to 1.1%, but it promoted unacceptable Pb leaching rates. On the other hand, the results showed that phytoremedi-ating the site using 5 mmol kg~(-1) NTA could be feasible with no environmental effects due to Pb leaching over a five-year period.