Micro- and Nanoplastics as Emerging Drivers of Liver Injury: Exposure, Evidence, and Mechanisms

Micro- and nanoplastics (MNPs) are emerging environmental contaminants of increasing relevance to human health. Growing evidence suggests that, following ingestion, inhalation, or, less convincingly, dermal exposure, MNPs may cross biological barriers, enter lymphatic and vascular compartments, and reach the liver. Owing to portal blood flow, sinusoidal architecture and Kupffer cell activity, the liver appears to be one of the principal sites of early particle sequestration. Human biomonitoring, ex vivo and postmortem studies have detected MNPs in blood and multiple organs, including the liver, although the currently available evidence remains limited and methodologically heterogeneous. Their identification relies on multistep analytical procedures that integrate sample pretreatment with FTIR, Raman spectroscopy, LD-IR, Py-GC-MS and supplementary imaging methods. However, each of these techniques presents significant limitations, particularly in the analysis of nanoplastics. Experimental studies indicate that MNPs may induce hepatic injury through oxidative stress, mitochondrial impairment, endoplasmic reticulum stress, inflammation, DNA damage, dysregulated lipid metabolism and disruption of the gut-liver axis, consequently contributing to steatosis, cholestatic anomalies and fibrosis. Consequently, MNPs should be considered potential contributors to liver pathology, although more comprehensive human data are still required.