Importance of AttachmentEfficiency in Determiningthe Fate of PS and PVC Nanoplastic Heteroaggregation with NaturalColloids Using a Multimedia Model

Here, we assessed the heteroaggregation of polystyrene (PS) and poly(vinyl chloride) (PVC) nanoplastics with SiO₂ as a model of natural colloids. Homoaggregation and heteroaggregation were evaluated as a function of CaCl₂ (0–100 mM) and natural organic matter (NOM) (50 mg L^–1) at a designated concentration of nanoplastics (200 μg L^–1). Critical coagulation concentrations (CCC) of nanoplastics were determined in homoaggregation and heteroaggregation experiments with SiO₂ and CaCl₂. The attachment efficiency (α) was calculated by quantifying the number of nanoplastics in the presence of CaCl₂, NOM, and SiO₂ using single-particle inductively coupled plasma mass spectrometry (spICP-MS) and pseudo-first-order kinetics. The calculated α was fed into the SimpleBox4Plastics model to predict the fate of nanoplastics across air, water, soil, and sediment compartments. Nanoplastics exhibited high stability against homoaggregation, while significant heteroaggregation with SiO₂ occurred at CaCl₂ concentrations above 100 mM. The influence of NOM was also evaluated, showing a reduction in heteroaggregation with SiO₂ for both nanoplastic types. Sensitivity analysis indicated that the degradation half-life of the tested nanoplastics had a more significant impact on persistence than did α. The results emphasize the environmental stability of nanoplastics, particularly in freshwater and soil compartments, and the critical role of NOM and emission pathways in determining their fate.