Exposure Pathways, Systemic Distribution, and Health Implications of Micro- and Nanoplastics in Humans

Plastics have become integral to modern life; however, their widespread use and persistent nature have resulted in significant environmental contamination, especially by microplastics (MPs < 5 mm) and nanoplastics (NPs < 100 nm). These plastic particles can enter the human body via ingestion, inhalation, or dermal absorption, raising substantial concerns about their potential health impacts. Recent studies using zebrafish, rodent models, and human cell lines have begun to elucidate the mechanisms underlying micro- and nanoplastics (MNPs)-induced toxicity. These mechanisms include oxidative stress, inflammation, disruption of metabolic processes, neurotoxicity, reproductive dysfunction, and carcinogenicity. Despite these advances, significant knowledge gaps remain. There remains a lack of comprehensive reviews that systematically evaluate these effects across major human organ systems and address how MNPs cross biological barriers in the human body. This review addresses these gaps by summarizing the available evidence on MNPs’ toxicity, critically discussing their absorption, distribution, metabolism, and the associated cellular and molecular mechanisms of action. Furthermore, it outlines urgent research priorities, emphasizing the need for standardized analytical protocols, realistic exposure models, and extended epidemiological research to evaluate human health risks posed by MNPs accurately. In addition, the adoption of precautionary regulatory actions is recommended to mitigate exposure and safeguard public health.