Transformation of ceria nanoparticles in cucumber plants is influenced by phosphate

Transformation is a critical factor that affects the fate and toxicity of manufactured nanoparticles (NPs) in the environment and living organisms. This paper aims to investigate the effect of phosphate on the transformation of CeO2 NPs in hydroponic plants. Cucumber seedlings were treated with 2000 mg/L CeO2 NPs in nutrient solutions with or without adding phosphate (+P or -P) for 3 weeks. Large quantities of needle-like CePO4 was found outside the epidermis in the +P group. While in the -P group, CePO4 only existed in the intercellular spaces and vacuole of root cells. X-ray absorption near edge spectroscopy (XANES) indicates that content and percentage of Ce-carboxylates in the shoots of -P group (418 mg/kg, 67.5%) were much higher than those in the +P group (30.1 mg/kg, 21%). The results suggest that phosphate might influence the transformation process of CeO2 NPs in plants and subsequently their ultimate fate in the ecosystem.