Assessing the size transformation of nanoplastics in natural water matrices

Understanding the stability of NPs in different aqueous environments, related with their size is crucial for assessing their potential risks. This is influenced by several factors, including pH, ionic strength, and the presence of biomolecules, or dissolved organic matter (DOM). In this study, dispersions of NPs derived from common plastic waste materials, including polystyrene (PS), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), and polycarbonate (PC), were synthesized by a nanoprecipitation method with sizes: 189 +/- 7, 58 +/- 3, 123 +/- 4, 151 +/- 7 and 182 +/- 6 nm, respectively. Stability for a period of 14 days of these NPs was assessed in various natural water matrices. Different analytical techniques were used, including Asymmetric Flow Field-Flow Fractionation (AF4) coupled with UV-Vis and Dynamic Light Scattering (DLS) in series, batch DLS, Fourier-Transform Infrared Spectroscopy-Attenuated Total Reflection (FTIR-ATR), and Transmission Electron Microscopy (TEM). None of the studied NPs was stable in seawater and NPs were transformed in microplastics (MPs) by aggregation. PET was more prone to aggregation in all waters and PS was the most stable followed for PC, PVC and PMMA. However, bottle and tap waters maintained better the original size of NPs. For the most stable dispersion PS, the influence of heteroaggregation in tap and lagoon waters and aging from exposure to UV light in sea water were tested. In both cases, the stability over time was worse for PS. The results can contribute to a more comprehensive understanding of the fate and behaviour of NPs in natural aquatic environments, emphasizing the importance of studying a wide range of polymers.