Toxicokinetics and Toxicological Implications of Eco- and Bio-Corona Formation on Micro- and Nanoplastics in Aquatic Systems.

Microplastics and nanoplastics are environmentally transformable interfaces rather than static particulate debris. After release into aquatic systems, photo-oxidation, mechanical abrasion, fragmentation, and biofilm-associated aging modify their surface chemistry, morphology, polarity, and reactivity. Simultaneously, natural organic matter, humic substances, extracellular polymeric substances, proteins, lipids, and microbial products adsorb onto plastic surfaces, forming eco-coronas that regulate aggregation, colloidal stability, contaminant partitioning, and desorption behavior. A central unresolved question is how eco-corona-coated particles are remodeled after organismal entry, how environmental coronas are exchanged into bio-coronas within mucus, gut, gill, and tissue microenvironments, and how these dynamic interfaces control the toxicokinetics of coexisting pollutants. This review synthesizes current evidence to define when weathered microplastics and nanoplastics act as vectors, sinks, amplifiers, or neutral carriers of co-pollutants. We emphasize internal exposure, bioaccessibility, residence time, and tissue distribution rather than nominal water concentrations or adsorption capacity alone. Classical modeling indicates that, for many hydrophobic organic contaminants, chemical flux from natural prey, sediments, and organic matter may exceed that from ingested plastics under typical environmental conditions, requiring scenario-specific interpretation. However, this logic should not be generalized to antibiotics, pharmaceuticals, metals, and per- and polyfluoroalkyl substances, whose interactions may depend on electrostatics, ionization, hydrogen bonding, cation bridging, corona chemistry, and gut-phase desorption. We propose a predictive framework linking plastic aging, eco-corona formation, bio-corona remodeling, partitioning/desorption kinetics, uptake, retention, translocation, and organism-level outcomes. Finally, within an explicitly aquatic scope, we outline minimum reporting requirements to improve comparability, mechanistic interpretation, and risk relevance in microplastic-mixture toxicology, including clearer reporting of particle-size class, size distribution, hydrodynamic diameter after corona formation, and size-dependent uptake or translocation outcomes.