Dissolution and Retention Process of CeO2 Nanoparticles in Soil with Dynamic Redox Conditions

The time-course association of soil physicochemical properties and fate of CeO2 nanoparticles (NPs) is not well understood. This study for the first time investigated the dissolution and retention of CeO2 NPs (<25 nm) during soil short-term (6 h) and long-term (30 d) aging processes with dynamic redox conditions. Under the additional reductant-induced initial reductive condition, theoretically, up to 220 parts per thousand of Ce(IV) was temporarily reductively dissolved within 10 min, accompanied by a slow retention process (180 min) of Ce species in soil solutions. Conversely, the dissolution and slow retention of Ce species were not significant in soil solutions without added reductant. X-ray absorption near edge spectroscopy (XANES) shows that most of Ce species were present as Ce(IV) (94.0%-97.8%) in all soils after a long-term aging process. These results indicate that the soil dynamic redox conditions induced by oxidant/reductant intrinsically determined the different time-course dissolution and retention of CeO2 NPs, highlighting the occasional reductive condition in soil solution that may contribute to the migration and diffusion of Ce species. The time-course study should be also adopted to develop a comprehensive understanding of the nano-soil interactions.

Automated summary

This study investigated the dissolution and retention of CeO2 nanoparticles in soil under dynamic redox conditions, highlighting the influence of occasional reductive conditions on the migration and diffusion of Ce species. Results showed that reductant-induced initial reductive conditions led to temporary reductive dissolution of Ce(IV), followed by slow retention, while dissolution and retention were not significant without added reductant. XANES analysis revealed that most Ce species existed as Ce(IV) after long-term aging, indicating that soil redox conditions determined the behavior of CeO2 NPs. Time-course studies are important for understanding nano-soil interactions.