Comparative Effects of ZnO Nanoparticles, ZnO Bulk Particles, and Zn2+ on Brassica napus After Long-Term Exposure: Changes in Growth, Biochemical Compounds, Antioxidant Enzyme Activities, and Zn Bioaccumulation

A wide variety of application of nanoparticles (NPs) in recent years has raised their possible entrance into the environment so that can affect living components of ecosystems. There is no comparative study on the long-term effects of a wide range of concentrations of NPs, related bulk particles (BPs), and corresponding metal ions on different traits of the plants. The present study has investigated comparative effects of zinc oxide (ZnO) NPs, ZnO BPs, and zinc ions (Zn2+) on rapeseed (Brassica napus L.) after long-term exposure to a wide range of concentrations. The inhibitory effects of treatments on the growth of B. napus were in the order Zn2+ >> ZnO BPs > ZnO NPs. Results showed the significant changes in the antioxidant enzyme activities, total chlorophyll, soluble proteins, proline, and soluble sugars of the leaves in response to the treatments. However, total phenolic compounds were not affected significantly by any treatment. Overall, in the present study, the toxicity of ZnO NPs on B. napus was lower than those of Zn2+ or ZnO BPs. Results indicate that adverse effects of ZnO NPs or BPs on B. napus may be due in part to the toxic effects of Zn2+ ions dissolution, probably induced by root exudates, or due o the physical interaction of ZnO particles with roots and induction of structural and functional disorders.