Small particles, large questions: unravelling the toxicity and potential health risks of PET micro-/nanoplastics

Despite the extensive use of polyethylene terephthalate (PET), the public health implications of its micro- and nanoparticles (MNPs) remain poorly understood, raising credible concerns about human exposure and health risks. We conducted a comprehensive literature search to synthesise evidence on human exposure to PET MNPs, their detection in human tissues and biological fluids, and the human-relevant toxicity of PET particles in vitro and in vivo. Studies consistently identify PET MNPs across consumer and environmental sources, and several investigations have detected PET in human matrices, supporting the plausibility of systemic translocation across biological barriers. Toxicological findings consistently indicate size- and shape-dependent uptake and effects: smaller particles exhibit greater cellular internalisation, reactivity, and biodistribution, with predominant oxidative, inflammatory, metabolic, and genotoxic responses, whereas larger microplastics more often provoke mechanical irritation. Key gaps include limited protocol harmonisation, unrealistic exposure levels, scarce long-term/kinetic data, and insufficiently standardised, well-characterised PET MNPs preparations. While evidence for exposure, detection in human matrices, and biological activity is growing, these deficits still hinder robust cross-study comparisons and clinically meaningful quantitative risk assessment.