Phytoextraction of Cu, Zn, and Pb Enhanced by Chelators with Vetiver (Vetiveria zizanioides): Hydroponic and Pot Experiments

Phytoextraction is a green remediation technology for clean-up contaminated soils. The effect of chelator application including EDTA, EDDS, and citric acid on phytoextraction of Cu, Zn, and Pb into high biomass vetiver (Vetiveria zizaniodides) was investigated in the hydroponic experiment and the pot experiment. In the hydroponic test, EDTA induced the most significant toxic symptom on vetiver compared to EDDS and citric acid. Obvious biofilm was attached in the rhizosphere of vetiver with the citric acid addition due to its serving as growth substrate while EDTA posed microbial toxicity to present clear solution. Sequential extraction results demonstrated that EDTA was better than EDDS and citric acid to change the adsorbed metal to loosely bound fraction which is more mobile and bioavailable. In the pot experiment, the critical finding was that vetiver has been demonstrated as a hyperaccumulator for treatment of EDDS with Cu; EDDS, citric acid, and EDTA with Zn; EDTA with Pb. EDDS and EDTA possess the viable phytoextraction ability and can be employed as an remediation alternative, though the groundwater leaching needs to be taken into serious consideration. 1. Introduction Heavy metals including Cu, Zn, and Pb from anthropogenic industrial operation are major pollution sources to cause soil contamination. Conventional physical-chemical technologies employed for heavy metals remediation including dig-and-dump, soil washing/flushing, and vitrification, are usually quite costly, energy consuming, and harmful to soil properties. In Taiwan, the most commonly used soil remediation for agricultural farmland was composed of vertical/horizontal soil mixing and redistribution for heavy metals (Cu, Zn, Ni, Pb, and Cr), while soil acid washing for health concerned heavy metals (Cd and Hg). Lots of debates concerned the effectiveness and soil property deterioration impact of these remediation technologies [1]. Phytoextration, a green remediation alternative removing metals by the use of plants, has drawn great attention and has offered a promising technology for heavy metal removal from soil [2, 3]. Phytoextraction can employ hyperaccumulators or plants with high biomass assisted by chelators. The success of phytoextraction employing hyperaccumulators is simply based on the ability to uptake and to retain metals within aerial parts. Hyperaccumulator species are plant aerial tissues that can contain >1000？mg/kg Cu, or Pb, and >10000？mg/kg Zn when grown in metal-rich soils. Hyperaccumulation species generally are slow growing and have small biomass [4]. Vetiver is