Origin of the different phytotoxicity and biotransformation of cerium and lanthanum oxide nanoparticles in cucumber

Abstract

To investigate how the physicochemical properties of nanoparticles (NPs) affect their biological and toxicological effects, we evaluated the phytotoxicity of CeO₂ and La₂O₃ NPs to cucumber (Cucumis sativus) plants and tried to clarify the relation between physicochemical properties of NPs and their behaviors. CeO₂ NPs had no phytotoxicity to cucumber at all tested concentrations, while La₂O₃ NPs showed significant inhibition on root elongation ( ≥ 2 mg/L), shoot elongation (at 2000 mg/L), root biomass ( ≥ 2 mg/L), and shoot biomass ( ≥ 20 mg/L), as well as induced more reactive oxygen species and cell death in roots (2000 mg/L). The different distribution and speciation of Ce and La in plants were determined by synchrotron-based micro X-ray fluorescence microscopy and X-ray absorption spectroscopy. In the aerial parts, all of La was combined with phosphate or carboxylic group, while a fraction of Ce was changed to Ce(III)–carboxyl complexes, implying that La₂O₃ acted as its ionic form, while CeO₂ displayed the behavior of particles or particle–ion mixtures. The higher dissolution of La₂O₃ than CeO₂ NPs might be the reason for their significant difference in phytotoxicity and transporting behaviors in cucumbers. To our knowledge, this is the first detailed study of the relation between the level of dissolution of NPs and their behaviors in plant systems.

• Biotransformation
• CeO₂ and La₂O₃ NPs
• dissolution
• phytotoxicity
• plants

Declaration of interest

The authors report no conflict of interest. The authors alone are responsible for the content and writing of this article.

This work was financially supported by the Ministry of Science and Technology of China (grant no. 2011CB933400 and 2013CB932703) and Ministry of Environmental Protection of China (grant no. 201209012). Project 11005118, 11275215, 11275218 and 11375009 was supported by National Natural Science Foundation of China.