Interactions between Plants and Rare Earth Oxide Nanoparticles

Rare earth oxide nanoparticles (REO NPs) can be released into the environment from various application routes, but their effects on the ecosystem are still little known. In this study, we exposed cucumber seedlings to suspensions of La2O3 and CeO2 NPs for 14 d. Phytotoxicity of the two REO NPs was assessed and their distribution and transformation in plant tissues were investigated. CeO2 NPs had no toxicity to cucumber at all tested concentrations, while La2O3 NPs showed significant inhibition on root elongation, biomass, as well as induced more ROS and cell death in roots. The different distribution and speciation of Ce and in plants were determined by synchrotron-based micro X-ray fluorescence microscopy (SR-XRF) and X-ray absorption spectroscopy (XAS). In the aerial parts, all of La was combined with phosphate or carboxylic group while only 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 cucumber plants.