Mapping the biological effects of micro- and nanoplastics in mammalian intestinal models: a scoping review.

BACKGROUND: Micro- and nanoplastics (MNPLs) are increasingly recognized as emerging environmental contaminants with potential implications for gastrointestinal health. Although experimental research on intestinal MNPL toxicity has expanded rapidly, the available evidence remains highly heterogeneous with respect to experimental models, polymer composition, particle size, particle condition, exposure scenarios, and biological endpoints. Therefore, a structured evidence map is needed to clarify dominant methodological patterns and identify key knowledge gaps in the field. METHODS: This study was conducted as a scoping review in accordance with the Joanna Briggs Institute framework and the PRISMA-ScR guidelines. A comprehensive search was performed in PubMed, Scopus, and Web of Science to identify eligible original in vitro, ex vivo, and in vivo experimental research investigating the biological effects of MNPLs in mammalian intestinal models. Data were extracted and synthesized based on experimental models, particle characteristics, exposure scenarios, and toxicological outcomes. RESULTS: A total of 90 peer-reviewed studies were included from 3,540 initially identified records. The evidence base was strongly dominated by simplified experimental systems, with in vitro studies accounting for 88.9% of the included studies (n = 80/90). Caco-2-based systems represented the dominant experimental platform overall (52.2%, n = 47/90), while Caco-2 monoculture-like models accounted for 36.7% (n = 33/90). A pronounced polymer bias was observed, with polystyrene (PS) appearing in 60.0% of the included studies (n = 54/90). Nanoplastics were the most frequently investigated size category (60.0%, n = 54/90), and most studies relied on virgin particles (68.9%, n = 62/90). Across the literature, the most prominent evidence themes included oxidative stress and mitochondrial injury, uptake and translocation, barrier dysfunction and permeability changes, inflammation and immune signaling, and cell death- or DNA damage-related responses. CONCLUSION: This scoping review demonstrates that intestinal MNPL research has expanded rapidly but remains methodologically concentrated in simplified in vitro systems and dominated by a limited range of polymer types and particle conditions. Although existing studies have generated important mechanistic insights, future progress will depend on the broader use of physiologically representative intestinal models, environmentally relevant polymers, and more standardized physicochemical characterization protocols. These findings provide a structured evidence map to support more realistic and translationally relevant future studies. CLINICAL TRIAL NUMBER: Not applicable.