Aggregation dynamics of nanoplastics: insights through real world waste

Nanoplastics, typically smaller than thousand nanometers, originate from the degradation of plastic waste and pose significant threat to aquatic ecosystems by acting both as pollutants and as carriers for harmful contaminants. Understanding their colloidal behavior in aquatic environments is therefore critical. Unlike previous studies that used synthetic particles, this research examines nanoplastics generated from real-world plastic waste, providing a realistic representation of their environmental behavior. Polyethylene terephthalate (PET) and polystyrene (PS) nanoplastics, sourced from discarded water bottles and packaging, were synthesized (∼464 nm for PET; ∼483 nm for PS) and characterized using DLS, SEM, FTIR, and Raman spectroscopy. Aggregation behavior was evaluated via time-resolved DLS in NaCl and MgCl₂ solutions, revealing critical coagulation concentrations (CCCs) of 44.50 mM NaCl and 2.17 mM MgCl₂ for PET, and 33.82 mM NaCl and 2.21 mM MgCl₂ for PS. Aggregation was faster in the presence of divalent Mg²⁺ compared to monovalent Na⁺, and PS exhibited lower CCC values than PET, attributed to differences in hydrophobicity and surface chemistry. As predicted by Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the nanoplastics would remain stable in freshwater but would aggregate rapidly in saline environments. This dependence on electrolyte concentration indicates potentially enhanced mobility and persistence in rivers and lakes, while promoting sedimentation and pollutant accumulation in estuarine and marine systems. These shifts in aggregation behavior in aquatic environments have direct implications for nanoplastic transport pathways, ecological exposure, and long-term environmental risks.