Phytotoxicity and bioaccumulation of ZnO nanoparticles in Schoenoplectus tabernaemontani

The rapid development of nanotechnology will inevitably result in an increasing release of engineered nanoparticles (NPs) to wastewaters. In this study we investigated the fate and toxicity of ZnO NPs in aquatic plant mesocosms, as well as the potential for root accumulation and root-to-shoot translocation of these Zn NPs in the wetland plant Schoenoplectus tabernaemontani exposed to ZnO NPs. The growth of S. tabernaemontani in these hydroponic mesocosms was significantly inhibited by ZnO NPs (1000 mg L−1) compared to a control. Levels of Zn in the plant roots for the ZnO NP treatment ranged from 402 to 36 513 μg g−1, while values ranged from 256 to 9429 μg g−1 (dry weight) for Zn2+ treatment, implying that the uptake of Zn from ZnO NPs was substantially greater than that for Zn2+. The root uptake (of the initial mass of Zn in the solution) for ZnO NP treatment ranged from 8.6% to 43.5%, while for Zn2+ treatment they were 1.66% to 17.44%. The low values of the translocation factor for both ZnO NP (0.001-0.05) and Zn2+ (0.05-0.27) treatments implied that the potential for translocation of Zn NPs from roots to shoots was limited. ZnO NP distribution in the root tissues of S. tabernaemontani was confirmed by scanning electron microscopy (SEM). Transmission electron microscopy (TEM) demonstrated that ZnO NPs could pass through plant cell walls, and were present within the plant cells of S. tabernaemontani.