Long-Term Exposure–Recovery to 20 nm Polystyrene Nanoplastic Particles Is Associated with Residual Nuclear Stress in a Marine Fish Cell Line

Nanoplastic particles are increasingly detected in aquatic environments, yet whether cellular stress responses persist after exposure cessation remains unclear. Here, Lateolabrax maculatus rostral (LMR) cells from spotted sea bass were continuously exposed for up to 30 passages (105 days) to nominal 20 nm carboxylated fluorescent polystyrene particles (20 μg/mL), followed by 10 particle-free passages (recovery). Long-term exposure was associated with reduced proliferation and pronounced changes in cell surface morphology and ultrastructure. Although NP-associated fluorescence became undetectable during recovery, several nuclear-associated alterations persisted throughout the 10-passage recovery period, including TEM-observed nuclear-envelope alterations, filamentous actin (F-actin) reorganization, and sustained elevation of phosphorylated H2AX (γ-H2AX) foci. Several nuclear pore complex (NPC) genes were downregulated during exposure and rebounded after particle removal, whereas the nuclear-to-cytoplasmic distribution of proliferating cell nuclear antigen (PCNA) remained shifted. Together, these findings indicate that prolonged exposure to this nanoscale polystyrene particle formulation was associated with nuclear stress responses that did not fully resolve within the 10-passage recovery window in fish cells. Because bulk-polymer and chemical-extract (leachate) controls were not included, nanoscale-specific effects cannot be distinguished from contributions of polymer chemistry, surface functionalization, fluorescent dye, or other formulation-related effects.