Effect of microplastics and nanoplastics in gastrointestinal tract on gut health: A systematic review.

INTRODUCTION: Microplastics (MPs) and nanoplastics (NPs) are pervasive environmental contaminants with growing concerns about their ingestion through food and water sources. Although animal studies suggest adverse health effects, direct mechanistic evidence in human gastrointestinal (GI) systems remains limited. In vitro models using human GI cell lines and organoids offer a physiologically relevant platform for investigating the effects of MPs and NPs on human health. However, existing findings are fragmented and lack systematic synthesis. This systematic review aims to consolidate and critically analyse current evidence on the biological effects of MPs and NPs in human GI in vitro studies. MATERIALS AND METHODS: Articles were selected from a previously conducted systematic search across Scopus and PubMed databases. Studies excluded from the prior review but relevant to MPs and NPs effects on human GI cells were re-screened under newly defined inclusion and exclusion criteria. RESULTS: A total of 30 studies were included. MPs and NPs were shown to induce size- and concentration-dependent biological effects, including increased cellular uptake, oxidative stress, mitochondrial dysfunction, inflammation, and apoptosis. Smaller particles consistently exhibited greater cellular internalisation and biological effects. These effects mainly occurred at high concentrations. Under chronic exposure, most studies reported minimal or no significant effects except for cell viability. CONCLUSION: This review provides the first comprehensive synthesis of in vitro evidence on the biological effects of MPs and NPs in human GI models. It advances mechanistic understanding and outlines future directions to strengthen health risk assessment, inform strategies for disease prevention, and guide public health policies addressing microplastic exposure.