Size-dependent Effects of Polystyrene Micro- and Nanoplastics on Gastrointestinal Microbiota in Mice: Overlooked Axial Site-Specific Heterogeneity and Radial Mucosal-Luminal Compartment Divergence.

Accumulating evidence links micro- and nanoplastics (MNPs) exposure to gastrointestinal (GI) health impairment, especially via gut microbiota disruption. However, most studies focus on fecal or cecal luminal microbiota, neglecting the inherent spatial heterogeneity of the GI tract and distinct mucosal versus luminal microbial niche responses. In this study, multi-omics was applied to investigate the effects of polystyrene nanoplastics (PS-NPs, 100 nm) and microplastics (PS-MPs, 5 μm) on mouse GI microbiota following 4-week drinking water exposure. 16S rDNA sequencing revealed that MNPs altered mucosal microbiota across the stomach, jejunum, and cecum in a size- and site-specific manner: PS-MPs predominantly disrupted gastric mucosal communities, while PS-NPs dominated perturbations in the jejunal and cecal mucosa. Correlation analysis showed that these microbial dysbioses were significantly associated with hepatorenal functional impairment, as evidenced by elevated serum γ-glutamyl transferase, alanine aminotransferase, and lactate dehydrogenase activities. Strikingly, metagenomic sequencing showed that, in stark contrast to mucosal microbiota, PS-MPs exerted more pronounced effects on the structural and functional profiles of cecal luminal microbiota than PS-NPs. Consistently, untargeted metabolomics identified more differential metabolites in cecal contents of PS-MPs-exposed mice (288) than PS-NPs-exposed counterparts (213). Our results demonstrate that microbial niche heterogeneity and size-dependent effects are critical determinants of MNP gastrointestinal toxicity, which must be incorporated into health risk assessment to guide evidence-based pollution management.