Effects of weathering and rainfall conditions on the release of SiO2, Ag, and TiO2 engineered nanoparticles from paints

Abstract

Previous studies on the fate of engineered nanoparticles (ENPs) incorporated in paints mainly focused on the release of the particles as affected by a limited number of factors or monitoring their release from natural sources. In this study, the effects of four factors (i.e., weathering duration, water pH, rainfall duration and intensity) were investigated on the release of SiO2-ENPs, Ag-ENPs, and TiO2-ENPs from paints applied on panels. The static water immersion test showed that the concentrations of studied particles all increased with weathering duration. At low and high pH, SiO2-ENPs and Ag-ENPs showed a higher release, while the release of TiO2-ENPs was relatively high at low pH. With increased simulated rainfall duration, the concentration released decreased for Si, and the opposite was observed for Ag, while no obvious correlation was noted for Ti. With greater rainfall intensity, there was increasing release of all particles. In total, the releases of Ag-ENPs and TiO2-ENPs were extremely low and within the level of 21.32–42.16 μg L−1and 0.6–2.3 μg L−1, respectively, while the values for SiO2-ENPs were in the range of 7.5–12 mg L−1. Additionally, microscopic results highlighted that SiO2-ENPs were mainly released in the form of agglomerates, and only a small fraction was below 0.1 μm. Considering these influence factors together, conclusions may be made that weathering time and rainfall duration are more important in controlling release than water pH.