Chemical Fate of Cerium Oxide Nanoparticles in Soils.

Cerium-based compounds such as CeO₂ nanoparticles (NP) have received much attention in the last several years due to their popular applications in industrial and commercial uses. There is a growing concern about the environmental fate of released CeO₂ NPs, particularly their unintended impact in aquatic and terrestrial environments. To understand the chemical fate of CeO₂ NPs in soils, reactivity of CeO₂ NPs in agricultural soils (Taccoa entisols) were studied as a function of particle size (33 and 78 nm), redox condition, and aging time. Batch dissolution experiments show that CeO₂ NPs were only soluble at pH <5  under the oxic condition. The distribution coefficient for small and large NPs ranged from 5,101 to 102,039 L kg^-1, and from 5,356 to 71,427 L kg^-1, respectively, showing the strong sorption CeO₂ NPs in soils that is independent of particle size.  Furthermore, changes in chemical state of Ce (reduction of Ce(IV) to Ce(III)) was observed after 30d in reduced soils for small CeO₂ NPs. However, there was no significant changes in chemical speciation of Ce in the large CeO₂ NP reacted soils. The Ce chemical speciation and reactivity of CeO₂ in soils might be important in predicting the fate of CeO₂NPs to environment.