Changes in the metal mobility after repeated phytoextraction by Cd/Zn hyperaccumulator Sedum plumbizincicola

Phytoextraction is one of the most promising technologies for remediation of agricultural soils contaminated by heavy metal. Information of metal mobility changes during the phytoextraction process is helpful for understanding... [ view full abstract ]

Phytoextraction is one of the most promising technologies for remediation of agricultural soils contaminated by heavy metal. Information of metal mobility changes during the phytoextraction process is helpful for understanding the mechanisms of phytoremediation. Changes in metal mobility in the low and high level metal contaminated soils after phytoextraction by the Cd/Zn hyperaccumulator Sedum plumbizincicola were investigated. Kinetic extraction with EDTA was applied to assess heavy metal (Zn, Cd, Cu and Pb) mobilization and the two first-order reactions model was used to fit the heavy metal extraction data, which distinguished soil heavy metal into three fractions: readily labile (QM1), less labile (QM2) and non-labile (QM3). The results show that non-labile metals were the dominant fraction with the exception of Cd in low level polluted soil, and the readily metal predominated in high level polluted soil. Compared with the metal in contaminated soils without phytoextraction, the labile Zn and Cd (QM1 + QM2) in the soils with repeated phytoextraction by S. plumbizincicola decreased significantly, but the labile Cu and Pb (non-accumulated metals by S. plumbizincicola) were increased. In both contaminated soils, the readily labile fractions of Zn and Cd decreased markedly after repeated phytoextraction, but the readily labile Cu and Pb increased significantly. Besides, the non-labile of Zn, Cd, Cu and Pb decreased greatly in both contaminated soils after repeated phytoextraction. These results indicated repeated phytoextraction could decline the mobility of plant accumulated metal and transform non-labile metal to labile fractions, but increase the plant non-accumulated metal mobility.