Heating treatment schemes for enhancing chelant-assisted phytoextraction of heavy metals from contaminated soils

Recent research has shown that chelant-assisted phytoextraction approaches often require a high dosage of chelant applied to soil. The present study focused on optimization of phytoremediation processes to increase the phytoextraction efficiency of metals at reduced chelant applications. Pot experiments were carried out to investigate the effects of increased soil temperature on shoot uptake of heavy metals by corn (Zea mays L.) and mung bean (Vigna radiat L. Wilczek) from heavy metal-contaminated soils. After the application of S,S-ethylenediaminedisuccinic acid or ethylenediaminetetra-acetic acid, soils were exposed to high temperatures (50 or 80 degrees C) for 3 h, which significantly increased the concentration of heavy metals in shoots. The heating treatment 2 d after the chelant addition resulted in higher concentrations of metals compared with those treatments 2 d before or simultaneously with the chelant application. Irrigation with 100 degrees C water 2 d after the chelant addition, or irrigation with 100 degrees C chelant solutions directly, also resulted in significantly higher phytoextraction of metals in the two crops compared with 25 degrees C chelant solutions. In addition. a novel application method to increase soil temperature using underground polyvinyl chloride tubes would increase the chelant-assisted extraction efficiency of Cu approximately 10- to 14-fold in corn and fivefold in mung bean compared with those nonheating treatments. In a field experiment, increasing soil temperature 2 d after chelant addition also increased the shoot Cu uptake approximately fivefold compared with those nonheating treatments. This new technique may represent a potential, engineering-oriented approach for phytoremediation of metal-polluted soils.