Polystyrene nanoplastics and benzo[a]pyrene co-exposure differentially impacts earthworm intra- and extracellular lysozyme

Current research lacks mechanistic insights into cross-hierarchical toxicity interactions between nanoplastics (NPs) and polycyclic aromatic hydrocarbons. This study innovatively integrated cellular oxidative stress responses with protein structure-activity relationships to elucidate polystyrene nanoplastics (PS NPs)' hierarchical-specific roles in co-contamination. Using an earthworm coelomocyte model exposed to Benzo[a]pyrene (BaP)/PS NPs with multispectral analysis, we systematically investigated impacts on redox homeostasis and lysozyme (LZM) functionality. Individual BaP exposure significantly reduced the GSH/GSSG ratio and triggered a sharp increase in ROS levels. In contrast, PS NPs co-exposure markedly attenuated intracellular ROS levels (up to 23.1 % reduction relative to BaP alone) while restoring lysozyme (LZM) activity from 67.3 % to 90.1 %. At molecular level, PS NPs synergized with BaP (80 μg/L) to decrease LZM catalytic activity from 86.9 % (BaP alone) to 83.5 % under co-exposure with 8 mg/L PS NPs, accompanied by α-helix elevation and Trp microenvironment perturbation that exacerbated active-site obstruction. These findings revealed PS NPs' dual toxicity profiles: cellular oxidative mitigation versus molecular-level synergistic inhibition. The established "intracellular alleviation-molecular interference" paradigm provided a theoretical foundation for developing a dual-parameter risk warning system integrating membrane integrity and enzyme conformational efficacy.