Gut microbiota responses to oral micro- and nanoplastic exposure in rodent models: a systematic review and evidence map of experimental paradigms

To synthesize rodent evidence on gut microbiota responses to oral micro-/nanoplastic exposure and map the exposure, microbiome, host response, and mechanistic paradigms through which this evidence has been generated. PubMed/MEDLINE, Scopus, Web of Science, and Embase were searched from inception and updated through September 2, 2026, with supplementary Google Scholar, gray literature, and citation searching. Eligible studies were oral rodent MP/NP experiments with gut microbiota outcomes. Two reviewers independently screened and extracted studies. Risk of bias was assessed with all ten SYRCLE domains. Heterogeneous findings were synthesized narratively and mapped by design and measurement level. Forty unique studies were included (37 mice and three rats). Polystyrene remained dominant (30/40), although PET, PLA, PE, PVC, and mixed/comparative polymer models broadened the evidence base. Beta diversity/community shifts were more consistent than a uniform decrease in alpha diversity, and no reproducible taxonomic dysbiosis signature emerged. Recent studies added metagenomics, direct metabolite/SCFA measurements, and pathway-directed experiments using FMT, microbiota depletion, or rescue interventions, strengthening causal inference for selected gut–organ pathways while leaving most findings associated. Rodent studies support biological plausibility for MP/NP-related perturbation of the gut ecosystem, but cross-study generalization remains limited by heterogeneous particles and dose metrics, polystyrene dominance, modified background designs, and incomplete reporting of experimental safeguards. Direct microbial functional measurements and explicit mechanistic tests now provide a stronger basis for future causal and translational work.