Cerium is the most abundant of rare-earth metals found in the Earth’s crust. Several Ce-carbonate, -phosphate, -silicate, and -(hydr)oxide minerals have been historically mined and processed for pharmaceutical uses and industrial applications. Of all Ce minerals, cerium dioxide has received much attention in the global nanotechnology market due to their useful applications for catalysts, fuel cells, and fuel additives. A recent mass flow modeling study predicted that a major source of CeO2 nanoparticles from industrial processing plants (e.g., electronics and optics manufactures) is likely to reach the terrestrial environment such as landfills and soils. The environmental fate of CeO2 nanoparticles is highly dependent on its physcochemical properties in low temperature geochemical environment. Though there are needs in improving the analytical method in detecting/quantifying CeO2 nanoparticles in different environmental media, it is clear that aquatic and terrestrial organisms have been exposed to CeO2 NPs, potentially yielding in negative impact on human and ecosystem health. Interestingly, there has been contradicting reports about the toxicological effects of CeO2 nanoparticles, acting as either an antioxidant or reactive oxygen species production-inducing agent). This poses a challenge in future regulations for the CeO2 nanoparticle application and the risk assessment in the environment.

No abstract

Cerium (Ce)-based compounds, such as CeO₂ nanoparticles (NPs), have received much attention in the last several years due to their popular applications in industrial and commercial uses. Understanding the impact of CeO₂ NPs on nutrient cycles, a subchronic toxicity study of CeO₂ NPs on soil-denitrification process was performed as a function of particle size (33 and 78 nm), total Ce concentration (50-500 mg L(-1)), and speciation [Ce(IV) vs. Ce(III)]. The antimicrobial effect on the soil-denitrification process was evaluated in both steady-state and zero-order kinetic models to assess particle- and chemical-species specific toxicity. It was found that soluble Ce(III) was far more toxic than Ce(IV)O₂ NPs when an equal total concentration of Ce was evaluated. Particle size-dependent toxicity, species-dependent toxicity, and concentration-dependent toxicity were all observed in this study for both the steady-state and the kinetic evaluations. Changes in physicochemical properties of Ce(IV)O₂ NPs might be important in assessing the environmental fate and toxicity of NPs in aquatic and terrestrial environments.

Ceria (CeO) has received much attention in the global nanotechnology market due to its useful industrial applications. Because of its release to the environment, the chemical fate of ceria nanoparticles (NPs) becomes important in protecting the agricultural and food systems. Using experimental biogeochemistry and synchrotron-based X-ray techniques, the fate of ceria NPs (30 and 78 nm) in an agricultural soil (mildly acidic Taccoa entisols) was investigated as a function of exchangeable Ce(III) concentration (0.3 and 1.56 mM/kg in small and large NPs, respectively) under anoxic and oxic conditions. Both ceria NPs strongly adsorbed (>98%) in soils. Under the anoxic condition, the reduction of Ce(IV) was more pronounced in small NPs, whereas the greater concentration of exchangeable Ce(III) in large NPs facilitated the formation of Ce(III) phosphate/oxalate surface precipitates that suppressed the electron transfer reaction. The study shows the importance of redox-ligand complexation controlled chemical fate of ceria NPs in an agricultural soil.