Nanomaterial-Enhanced Phytoremediation of Centella asiatica (L.) Urban in Cd-Contaminated Soils

High Resolution Image Download MS PowerPoint Slide This study investigates the effectiveness of titanium dioxide nanoparticles (TiO 2 NPs) on the uptake, accumulation, translocation, and phytoremediation efficiency of Cd by Centella asiatica (L.) Urban ( C. asiatica ). TiO 2 NPs at a concentration of 100 mg/kg were applied to soils contaminated with Cd at varying levels (10, 100 mg/kg). The Cd concentration in the roots of C. asiatica was increased by 4 times when grown in soils containing both TiO 2 NPs and Cd, compared with soil containing only Cd, indicating that TiO 2 NPs play an important role in facilitating Cd removal from the soil. TiO 2 aggregates were observed in the cortex cells and xylem regions in the roots. The adsorption of Cd onto TiO 2 aggregates was confirmed by scanning transmission electron microscopy (STEM)-energy-dispersive X-ray spectroscopy (EDS) analysis. Once translocated, TiO 2 aggregates were found to be distributed within the air space of mesophyll cells, and there is an internalization of TiO 2 aggregates within the cytoplasm of C. asiatica leaves. TiO 2 NPs were observed to be transformed into rodlike aggregates when they penetrated through barriers such as cell walls and cell membranes in the transportation process. In addition, it is found that negatively charged TiO 2 NPs were more efficiently translocated from roots to shoots of C. asiatica than positively charged ones. These findings suggested that the uptake, translocation, and distribution of TiO 2 NPs were closely related to the properties of TiO 2 NPs.