Microplastics and Nanoplastics in Food: Dietary Toxicology Beyond Particle Counts

Microplastics (MPs) and nanoplastics (NPs) are ubiquitous contaminants in dietary sources, including seafood, table salt, infant formula, and drinking water. Recent stimulated Raman scattering microscopy has reported approximately 2.4 × 10⁵ MPs and NPs per liter in selected bottled-water samples. While these estimates remain contested and should not be generalized across products, they highlight the extent to which conventional analytical methods may underestimate nanoscale exposure. Current risk frameworks remain anchored to particle-count and mass-based metrics that do not capture reactive surface area, food-matrix interactions, or chemical cargo. This review examines dietary MP/NP toxicology through three underexplored dimensions: food matrix-particle interactions that transform particle surfaces before intestinal contact; potential engagement of endogenous intestinal transport pathways; and diet-dependent modulation of epithelial permeability. It integrates evidence across molecular, cellular, organ-level, and microbiome-mediated pathways, with emphasis on immune-metabolic dysregulation, endocrine disruption, hepatic toxicity, and neurodevelopmental risk. Key uncertainties include NP absorption kinetics in lipid-rich matrices, particle-facilitated chemical transfer, progressive corona remodeling during digestion, and the lack of standardized methods for detecting NPs in complex foods. In vitro and rodent studies support mechanistic links between NP exposure and NLRP3-associated inflammation, hepatic steatosis, endocrine disruption, and gut dysbiosis, but most use concentrations exceeding estimated human tissue levels. We propose a surface-area-normalized hazard quotient for surface-mediated endpoints as a complement to mass-based metrics, while recognizing that additive-leaching toxicity may require a separate mass-based framework.