Stability of CeO2 nanoparticles from paints and stains: insights under controlled and environmental scenarios

Abstract

Due largely to their ability to absorb UV light, cerium oxide (CeO₂) nanoparticles (NP) are now widely used in numerous surface coatings. The release of CeO₂ NP from the surface coatings and their subsequent fate in the environment is difficult to evaluate, and to-date, has either been modelled, estimated using elemental mass balances or measured under controlled laboratory conditions. Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) is emerging as one of the best techniques for detecting very small NP at very low concentrations in complex media such as natural waters, soils or biota. In this study, we first examined the role of different physicochemical properties (e.g., pH, ionic strength, and concentration of natural organic matter) on CeO₂ NP that were found in a paint and a stain. Their stability was then evaluated in rainwater over 30 days. Depending on the properties of the media, Ce NP concentrations in the paint decreased by 65–90%, whereas those in the stain decreased by 15–35% after 30 days. The loss was attributed to either dissolution or agglomeration/sedimentation. Finally, we quantified and characterized the release of both dissolved and particulate Ce from the two surface coatings under natural weathering conditions. In that case, Ce released from painted and stained panels was mainly shown to be in its dissolved metal forms. After 23 weeks of exposure, up to 15% of the Ce applied as paint and up to 35% of the Ce applied as stain were released into the precipitation. Nonetheless, no Ce NP beyond background levels were detected – all release appeared to be in the form of dissolved Ce.