Toxicity of zinc oxide nanoparticles to zebrafish embryo: A physicochemical study of toxicity mechanism

The biological impact of engineered nanomaterials released into the aquatic environment is a major concern. In this work, the properties of ZnO nanoparticles (nano-ZnO, 30 nm) were characterized in a water suspension (E3 medium), and a zebrafish 96-h post fertilization (hpf) embryo-larval test was performed to assess the toxicity of nano-ZnO suspension. Nano-ZnO was found to readily form aggregates with different sizes; small aggregates (142.4-517.7 nm) were still suspended in E3 medium, but large aggregates (>1 μm) quickly deposited on the bottom of 24-well plates; nano-ZnO was partially dissolved to Zn species (Zn_(dis)) in E3 medium. In the nano-ZnO suspension, small aggregates, Zn_(dis), and large aggregates might jointly exert influence on the development of zebrafish embryos. The embryo toxicity test revealed that nano-ZnO killed zebrafish embryos (50 and 100 mg/L), retarded the embryo hatching (1-25 mg/L), reduced the bodylength of larvae, and caused tail malformation after the 96 hpf exposure. Zn_(dis) only partially contributed to the toxicity of nano-ZnO. This research highlights the need to further investigate the ecotoxicity of nano-ZnO in the water environment.