A critical review of micro- and nanoplastic permeation in the human body

Plastic products have been progressively integrated into every aspect of human life, and they are susceptible to fragmentation, leading to the release of micro- and nanoplastics (MNPs) to the surroundings. Not only are these persistent particles ubiquitous in the environment, but they have also been detected in food, beverages and ambient air, placing them in close contact with humans. Consequently, concerns have been raised on their potential impacts on human health. A growing number of studies have been reporting MNPs detection in various human tissues. Some have attempted to explore the correlation to impacts on human health, gaining significant societal attention. Whilst it is widely accepted that MNPs can enter humans via ingestion and inhalation, accurate identification and quantification have not been without challenges, and their fate in the human body is largely unknown. The objective of this review is to critically assess the potential for translocation of MNPs through the lens of human physiology. Here, we present a comprehensive synthesis of human cell studies, in vivo studies, biological pathways and the current state of human biomonitoring studies, to evaluate how MNPs migrate from entry points to systemic circulation and cross key physiological barriers. Our analysis highlights that larger microplastics are more easily detected with current techniques, though characterisation and quantification-oriented studies often lack adequate consideration for biological plausibility and physiological limits behind reported results. Studies that utilise thermal degradation mass spectrometric analysis are highly susceptible to matrix interference-induced inflated reports of MNP concentrations. Conversely, nanoplastics – sizes most likely to translocate and hence pose the greatest risk – remain underexplored due to analytical challenges, particularly the resolution limitations of spectroscopic techniques. This review provides a critical bridge between empirical detection and physiological relevance – a perspective that is largely absent from current research. We argue that such an integrated approach is essential to advance understanding of the behaviour and fate of MNPs in humans and more robust scientific evidence is needed to form a strong foundation for future research of plastics effects on human health.