Towards understanding the stability of environmentally relevant nano plastics in aqueous environments

Shylesh, Shreya (2025) Towards understanding the stability of environmentally relevant nano plastics in aqueous environments. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Shreya Shylesh (19MS117)) 19MS117_Thesis_file.pdf Restricted to Repository staff only Download (2MB)

Abstract

The presence of nanoplastics in aquatic environments has become a significant concern due to their ecotoxicological consequences. Nanoplastics possess distinct physical, chemical, and biological properties compared to larger plastic fractions. These include altered transport behavior, surface functionalization, and the ability to penetrate cell membranes and induce toxicity. Additionally, the aggregation and settling of nanoplastics are strongly influenced by water chemistry. Therefore, the colloidal stability of nanoplastics is a primary determinant of their environmental fate. This study focuses on the generation of environmentally relevant expanded polystyrene nanoplastics (eNPs) using a top-down approach and investigates their stability under varying conditions of ionic strength, dissolved organic matter (DOM), surfactants, and the combined effects of ionic strength and DOM. Stability was assessed by monitoring changes in turbidity over a period of seven days and by employing dynamic light scattering (DLS) techniques. Results indicate that ionic strength increases the rate of aggregation and settling of eNPs by screening electrostatic repulsion, and CaCl₂ induces greater instability compared to NaCl. The highest aggregation and settling occur with the combination of CaCl2 and humic acid, followed by CaCl2 alone. The greatest stabilization is observed in the presence of humic acid. The combination of NaCl and humic acid also stabilized the solution compared to NaCl alone. The anionic surfactant SDS stabilized the eNPs as its concentration increased. The cationic surfactant CTAB stabilized the eNPs at 300 mg/L but caused destabilization at 10 and 2000 mg/L. The destabilization at 2000 mg/L may be attributed to depletion forces induced by excessive free micelles in the solution. The results reflect that aggregation and settling of NPs generated from EPS undergo very gradual aggregation in most cases, which is in disagreement with the majority of studies on the environmental fate of nanoplastics and are may remain suspended or may mobilize easily, which may further affect the organisms living within the water column.

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