nano ZnO particles

The phytotoxicity of engineered nano-ZnO

PhD project of Xiaolin Chen

Supervisor:  Prof Marcel Jansen

The rapid development of nanotechnology has led to a rise in the large-scale production and commercial use of engineered nano-ZnO. Engineered/manufactured nano-ZnO are applied in a broad range of products such as drugs, paints, cosmetics, abrasive agents and insulators. This can result in the unintended exposure of human beings to nano-ZnO and will inevitably result in the release of nano-ZnO in to the environment. Thus, it is necessary to assess the risk of nano-ZnO to the environment.

The research by Xiaolin Chen explores the toxicity, and the mechanism of toxicity, of nano-ZnO using the aquatic, primary producer lesser duckweed (Lemna minor). Both short-term (one week) and long-term (six weeks) toxicity of nano-ZnO (uncoated) were determined. Results show that the toxicity of nano-ZnO added to the aquatic growth medium increases with increasing concentration and that toxicity accumulates with exposure time. A study of nano-ZnO dissolution reveals that the main reason for nano-ZnO toxicity on Lemna minor is the release of Zn ions. Nano-ZnO dissolution is pH dependent, and toxicity matches the release of Zn2+. Functional coating materials are commonly added to nano-ZnO particles to improve specific industrial applications. To test if coating materials contribute to nano-ZnO toxicity on lesser duckweed, the effect of silane coupling agent (KH550) coated nano-ZnO on Lemna minor was investigated. Results show that coating can decrease the release of Zn ions, which reduces toxicity to Lemna minor, in contrast to uncoated particles. Another commonly hypothesized reason for nano-ZnO toxicity is the formation of Reactive Oxygen Species (ROS) on the particles surface. As part of the research by Xiaolin Chen, the ROS formation induced by nano-ZnO was studied. Results show that nano-ZnO catalyze ROS formation and this can negatively affect duckweed growth.

In conclusion, our study has detailed potentially toxic effects of nano-ZnO on Lemna minor. This study also provides references for future research, and informs regulatory testing for nanoparticle toxicity. Specifically, the outcomes of this study emphasize the importance of exposure time, environmental parameters and coating material when analyzing nanoparticle toxicity. Firstly, impacts of longer exposure time should be studied. Secondly, environmental parameters such as pH and medium composition need to be considered when investigating nanoparticle toxicity. Lastly, coating of nanoparticles should always be considered in the context of their toxicity, and similar nanoparticles with different coatings require separate toxicity tests.