Micro and nanoplastics pollution: Scientific progress, persistent gaps, and regulatory challenges

Micro and nanoplastics (MNPs) are ubiquitous contaminants of emerging concern in ecosystems. To provide a comprehensive overview of the current state of MNP research, its relationship with environments, emerging issues, limitations, and challenges, this scientometric review analyzed 16,578 primary studies from the Web of Science database across all years and languages. Machine learning-based refinement was applied to extract data on objective, conclusion, biological groups, study setting, biomarker techniques, and MNP types studied. Results showed that most research has focused on the effects of MNPs, followed by identification methods, contamination, and their association with other pollutants. Fish, microorganisms, and mammals were the most studied biological groups, while experimental scenario and aquatic systems were the most common study settings. A significant concern is the behavior of these particles after absorption, especially in humans, including their distribution and elimination, as well as the main routes of exposure, biological mechanisms, and effects on different organ systems. Despite substantial scientific efforts, gaps remain regarding synergistic effects, MNPs kinetics in organisms, and large-scale environment removal. MNPs are highly diverse, and their physicochemical characteristics and concentration directly influence behavior and toxicity. There is a need for studies on secondary MNPs that simulate environmentally realistic exposures and reflect real ecological conditions. Furthermore, the lack of methodological standardization in sampling, identification, and exposure procedures hampers comparability and the establishment of standardized protocols. This review discusses the global implications of MNP contamination.