Arsenite oxyanions affect CeO₂nanoparticle dissolution and colloidal stability

While highly reactive cerium oxide nanoparticles (CeO₂NPs) are widely used in industry, their transport in aquatic systems is not well understood. To fill this knowledge gap, the interactions of CeO₂NPs with arsenite (As³⁺), a toxic metalloid and potential co-present contaminant, were investigated with respect to CeO₂NP colloidal stability, dissolution, and surface redox reactions. Arsenite showed distinctive effects at different concentrations, with a high As³⁺concentration (10⁻⁴M) inducing 90% of CeO₂NPs to settle from solution after 8 hours, while lower As³⁺concentrations (10⁻⁵or 10⁻⁶M) led to only 20% of CeO₂NPs settling. The dissolution of NPs was most significant in the 10⁻⁵M As³⁺system owing to a lesser extent of aggregation, exposing more CeO₂surface for dissolution. In the three As³⁺concentration systems, >97% of aqueous arsenic remained as As³⁺over 6 hours. On the NP surface, adsorbed As^IIIwas oxidized to As^V, resulting in 58-70% of the adsorbed arsenic remaining as As^III. Simultaneously Ce^IVwas reduced to Ce^III, increasing Ce^IIIon the CeO₂NP surface from 17% (without arsenite) to 21-25% (with arsenite). Further mechanistic analyses revealed that the adsorption of arsenite was the main contributor to neutralizing the CeO₂NP surface potential, enhancing particle sedimentation. These findings suggest that the fate and transport of CeO₂NPs in our experimental systems are strongly affected by arsenite concentration and its adsorption on NPs. The results also highlight the importance of the interplay between NP aggregation, oxidation, and dissolution in predicting the behaviors of CeO₂NPs and associated toxic elements in aquatic systems.