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Structural Compactness Governs the Environmental Fate of Polystyrene Nanoplastics: Reaggregation Mechanisms in Laboratory-Scale Aquatic Systems.
Summary
Scientists studied how tiny plastic particles from polystyrene (smaller than the width of a human hair) behave in water under different conditions like saltiness and water movement. They found that these plastic particles can break apart and stick back together, staying suspended in water for long periods and traveling far distances through rivers and oceans. This matters because it means these microscopic plastics could spread widely through water systems and potentially end up in our drinking water and food chain.
Most previous studies have been largely been limited to simple stability assessments based on critical coagulation concentration, providing insufficient understanding of the particle size distribution and dynamic behavior of polystyrene nanoplastics (PS NPs, <1 μm,) under realistic environmental conditions such as salinity gradients in estuaries or flow-induced disturbances. To bridge this knowledge gap, we investigated the aggregation-disaggregation-reaggregation mechanisms of environmentally representative, non-functionalized PS NPs under various environmental conditions (pH, ionic strength, and dissolved organic matter) and physical perturbations. Real-time monitoring using a quartz crystal microbalance with dissipation enabled quantitative assessment of structural compactness and viscoelastic changes in PS NP aggregates. Our findings revealed that the final aggregate size increased by approximately 21.5% as the ionic strength rose from 100 to 600 mM. The coexistence of DOM significantly reduced the structural stiffness of the aggregates, resulting in a disaggregation degree of approximately 38.5% under physical disturbance and facilitating the redispersion of aggregates into nanometer-sized particles. Consequently, PS NPs are likely to persist as submicrometer dispersions over extended periods, highlighting their potential for long-range transport and widespread distribution within aquatic ecosystems.