Aging MPs in aquatic ecosystems: a review on occurrence, interactions, vector effects, and ecotoxicology

The aging process of microplastics (MPs) in aquatic ecosystems allows them to enter organisms through mechanisms such as direct ingestion, bioaccumulation, and as pollutant carriers, which can induce toxic effects. This study presents a bibliometric review of research on aged MPs in aquatic ecosystems using CiteSpace software, the results indicate that the prominent contributions of U.S. researchers to foundational studies on aquatic aged MPs, but also emphasizes the central position of British institutions in promoting global research partnerships. While Chinese researchers have published a substantial number of papers, they have not yet fully established a bridging role in international academic networks. Knowledge dissemination remains largely confined to relatively closed domestic collaboration cycles. This paper also reviews how the adsorption and degradation behaviors of pollutants by aged MPs are jointly regulated by the inherent properties of the material (including polymer type and particle size) and the parameters of the environmental medium (such as pH, salinity, and organic matter content). The surface of aged MPs selectively enriches functional genes related to biofilm formation and promotes the horizontal transfer of drug resistance genes. In additional, aged MPs exacerbates their toxic effects on organisms by accelerating the release of additives and influencing the adsorption and environmental degradation behaviors of co-existing pollutants. Given the numerous unresolved scientific challenges-such as the unclear transport mechanisms of aged MP particles in aquatic environments and the poorly understood co-transport behavior of complex pollutants-there is a pressing need to promote further research through enhanced interdisciplinary and international collaboration.