Comparative phytotoxicity of undoped and Er-doped ZnO nanoparticles on Lemna minor L.: changes in plant physiological responses

The present study is the first research on the phytotoxicological effects of Er-doped zinc oxide nanoparticles (NPs) on duckweed (Lemna minor L.), as a model aquatic floating macrophyte. It concentrated on the comparison of the physiological effects of different concentrations of undoped and Er-doped zinc oxide NPs on L. minor. Pure and Er-doped zinc oxide samples were synthesized through a sonochemical method and their morphology and chemical composition were studied by scanning electron microscopy and energy dispersive X-ray analysis. Plant growth, photosynthetic pigment contents, and antioxidant enzyme activities were investigated as indices to assess the effects and toxicity of the NPs on L. minor. Moreover, the dissolution of Zn2+ from the suspensions of NPs was investigated to clearly determine whether the Zn2+ released from the NPs was the main source of their toxicity to the plant. The results showed significant changes in the physiological parameters of the plant in response to the treatments. The negative effects of treatments on the growth of L. minor, in order, were Zn2+ >> ZnO-NPs >> EZO-NPs >> bulk-ZnO. The activity of superoxide dismutase was remarkably increased by increasing the concentration of the contaminants in the plant.