Micro- and nanoplastic exposure and human health

Microplastics (MPs) and nanoplastics (NPs), collectively referred to as micro- and nanoplastics (MNPs), are pervasive environmental contaminants. In this review, MPs are defined as solid polymer-containing particles from 1 μm to 5 mm, whereas NPs range from 1 nm to < 1 μm. They originate from plastic degradation and the direct release of particles from industrial and consumer products. Human exposure occurs primarily through ingestion, inhalation, and dermal contact and may also occur through maternal-fetal transfer and medical materials. MNPs have been detected in human tissues and biological fluids, raising concerns about potential health effects; however, detection alone does not establish disease causation.

This review summarizes current knowledge on the sources, characteristics, exposure pathways, detection methods, and biological effects of MNPs. It critically integrates experimental, epidemiological, and analytical evidence to evaluate potential health risks and identify key knowledge gaps. Where evidence permits, MPs and NPs are discussed separately, and human observations are distinguished from in vitro and animal findings.

Experimental evidence suggests that MNP exposure may affect multiple biological systems through oxidative stress, inflammation, mitochondrial dysfunction, metabolic disturbance, and immune dysregulation. Adverse effects have been reported across multiple organ systems in experimental studies, whereas human epidemiological evidence remains limited and insufficient to establish causality. NPs may exhibit greater cellular uptake and biological-barrier translocation than larger MPs, depending on particle properties and biological context. Heterogeneity in particle characteristics, exposure scenarios, and analytical methods complicates cross-study comparisons and risk evaluation. Many mechanistic studies also use pristine model particles and exposure doses that may not reflect real-world conditions. Standardized detection and exposure assessment, environmentally relevant models, and well-designed human studies are therefore needed to clarify the long-term health implications of chronic low-dose MNP exposure and support future risk assessment.