The crucial role of intrinsic properties in determining the biological effects of CeO₂ nanocrystals

Nano ceria (nano-CeO₂) has been widely applied in various fields of industry and daily life, however, knowledge regarding the biological effects of nano-CeO₂ with different intrinsic physicochemical properties remains limited. In this study, we investigated the impact of nano-CeO₂ with different properties on the growth of a typical environmental species (romaine lettuce, Lactuca sativa L.) by exposing the plant to four types of CeO₂ (rod-like nano-CeO₂ (RNC), cubic nano-CeO₂ (CNC), spherical nano-CeO₂ (SNC) and commercial irregular CeO₂ (CIC)) during the germination stage. The results indicated that different types of CeO₂ exhibited varying inhibitory effects on plant growth. RNC and SNC significantly inhibited the elongation of roots and shoots, while CNC and CIC did not have a significant impact. We further examined the distribution and biotransformation of the four CeO₂ in plant tissues using transmission electron microscopy (TEM) and synchrotron X-ray absorption near edge structure (XANES). Specifically, the positively charged RNC and SNC were more readily adsorbed onto the root surface, and needle-like nanoclusters were deposited in the intercellular space inside the roots. The absolute content of Ce(III) in the roots romaine lettuce was in the order of RNC > SNC >> CNC >> CIC. The size and shape (i.e., exposed crystal surface) of the materials affected their reactivity and dissolution ratios, and zeta potentials affected their bioavailability, both of which influenced the overall contents of Ce³⁺ ions in plant tissues. Thus, these characteristics together led to different biological effects. These findings highlight the importance of considering the intrinsic properties of nano-CeO₂ when assessing their environmental and biological effects.