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Latent Polyester Nanoplastics in Water Environments
Summary
Researchers developed a new method to measure polyester nanoplastics in water and found that actual concentrations are much higher than previously reported. Using dialysis and ultrasonication to break up aggregated particles, they detected average PET nanoplastic concentrations of 7.02 micrograms per liter in freshwater lakes, revealing that most nanoplastics in natural water exist as aggregates rather than individual dispersed particles.
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 , Environ. Sci. Technol., 2023). However, the reported concentrations of PET-NPs are only tens to hundreds of ng/L (Okoffo; ; Thomas, J. Hazard. Mater., 2024 and Xu , Environ. Sci. Technol., 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.