Human Exposure to Micro- and Nanoplastics: Trans-Barrier Transport, Tissue Accumulation, and Health Risks

Micro- and nanoplastics (MNPs) as emerging pollutant are widespread in the environment. MNPs have been widely detected in human samples, with reported concentrations in human brain tissue reaching 298.5-47,730 μg/g. Furthermore, several clinical and epidemiological studies suggest that human exposure to MNPs may be associated with adverse health outcomes. These findings have raised growing concerns about the potential health risks of MNPs. This review summarizes current knowledge on the exposure pathways, occurrence and distribution, trans-barrier transport, toxicity, and health risks of MNPs in humans. Studies indicate the primary exposure pathways of MNPs to human including ingestion, inhalation, dermal contact, as well as direct exposure via intravenous injection and surgery. Moreover, MNPs can traverse multiple biological barriers such as intestinal barrier, blood-alveolar barrier, placental barrier, blood-testis barrier, and blood-brain barrier, resulting in accumulation in various tissues. Studies in vivo and in vitro demonstrate that MNPs cause multiple toxic effects. Notably, this review provides an integrated perspective on the continuous biological cascade from external exposure through internal processes to adverse health outcomes. In addition, we point out that future research should focus on improving identification techniques, performing long-term low-dose exposure assessments, and elucidating the underlying mechanisms.