Umbrella review on micro and nanoplastics: Mapping the scientific landscape

Micro- and nanoplastics (MNPs) are emerging contaminants widely distributed across environmental compartments and associated with potential ecological and human health risks. Given the rapid expansion of review literature on this topic, we conducted an umbrella review integrating scientometric mapping and thematic synthesis to evaluate research trends, methodological patterns, convergent evidence, and knowledge gaps in MNPs research. Review articles indexed in the Web of Science Core Collection up to June 2025 were analyzed using combined manual refinement, automated text-mining workflows, and CiteSpace network analyses. A total of 7,349 review articles were included. The results revealed strong thematic concentration around aquatic ecosystems, fish-based models, contamination studies, and adverse biological effects, particularly involving polyethylene, polystyrene, polypropylene, and polyethylene terephthalate. There was a broad consensus on the widespread environmental occurrence of MNPs and their potential to induce oxidative stress, inflammation, cytotoxicity, and bioaccumulation. However, substantial methodological heterogeneity and structural biases were identified, including the predominance of narrative reviews, limited taxonomic diversity, and inconsistent analytical and experimental approaches. Several domains remained comparatively underexplored, especially environmental transport, degradation pathways, microorganism interactions, combined exposure scenarios, and environmentally realistic conditions. In addition, terrestrial organisms, atmospheric systems, and less frequently studied polymer types remain insufficiently represented in the current review literature. Overall, this umbrella review demonstrates that, despite the rapid consolidation of MNPs research, important limitations persist regarding evidence integration, methodological standardization, and ecological representativeness. These findings highlight the need for more integrative, standardized, and ecologically relevant approaches capable of improving ecological risk assessment and advancing the understanding of MNPs dynamics and impacts across environmental systems.