Latent Polyester Nanoplastics in Water Environments

Polyester fibers are the most consumed textile fibers, and nanoparticles of polyester fibers, i.e., polyethylene terephthalate polymer (PET-NPs), continuously enter natural water environments (Xu , <i>Environ. Sci. Technol.</i>, 2023). However, the reported concentrations of PET-NPs are only tens to hundreds of ng/L (Okoffo; ; Thomas, <i>J. Hazard. Mater.</i>, 2024 and Xu , <i>Environ. Sci. Technol.</i>, 2022). In this study, we developed a dialysis-ultrasonication-filtration method coupled with mass spectrometry to quantify dispersed and aggregated PET-NPs in water environments. Dispersed PET-NPs are widely present in the freshwater rivers and lakes of China with an average concentration of 2.23 μg/L, but they are rare in the saltwater. Much more PET-NPs are detected in the dialyzed and ultrasonicated samples, indicating the significant contribution of PET-NP aggregates in natural surface water. The total concentrations of PET-NPs in fresh lake water (average: 7.02 μg/L) are much higher than those in seawater (average: 1.71 μg/L). The lower critical coagulation concentration of PET-NPs indicates that they are more prone to aggregation than other nanoparticles. PET-NPs aggregate faster in seawater than in freshwater, and Na⁺ and Ca²⁺ significantly promote aggregation. Conversely, the higher dissolved organic matter in lake water inhibits the formation of large PET-NP aggregates. Therefore, more PET-NPs were present in fresh lake water and latent as small aggregates but fewer in seawater. Although the ecological risks of these latent PET-NPs are not yet clear, they are potential sources of dispersed nanoplastics.