Phytoextraction of Lead from Soil from a Battery Recycling Site: The Use of Citric Acid and NTA

摘要

Phytoextraction is a soil remediation technique involving plants that concentrate heavy metals in their shoots, which may be removed from the area by harvest. The application of synthetic chelants to soil increases metal solubility, and therefore enhances phytoextraction. However, synthetic chelants degrade poorly in soil, and metal leaching poses a threat to human and animal health. The aim of this study is to assess the use of two biodegradable chelants (citric acid and nitrilotriacetic acid (NTA)) for Pb phytoextraction by maize from a soil contaminated by battery-casing disposal. In order to assess the behavior of a non-degradable chelant, ethylenediaminetetraacetic acid (EDTA) was also included in the experiment. The chelants NTA and EDTA were applied to soil pots at rates of 0, 3, 5, 7, and 10 mmol kg~(-1) of soil. The rates used to citric acid were 0, 5,10, 15, and 30 mmol kg~(-1). Maize plants were grown for 72 days and chelants were applied 9 days before harvest. Soil samples were extracted with CaCl_2 to assess the Pb solubility after chelants application. The results showed that NTA was more efficient than citric acid to solubilize Pb from soil; however, citric acid promoted higher net removal of Pb (120 mg pot~(-1)) than NTA (57 mg pot~(-1)). Thus, the use of citric acid, a biodegradable organic acid, could bernfeasible for enhancing the phytoextraction of Pb from the site studied with no environmental constraints.