Dry-surface versus aqueous photoaging of colored microplastics and their mediated co‑pollutant transformation differences

Although inorganic pigments are ubiquitous in daily-life plastics, their photochemical implications remain largely unexplored. Unlike traditional inert vectors, we report that colored microplastics (MPs) derived from commercial polyethylene bags act as photocatalysts, driving an efficient but previously unrecognized transformation of coexisting pollutants. Following 84-h simulated diurnal irradiation, five colored MPs accelerated sulfamethoxazole/tetracycline removal by 38.7-78.1% over natural photolysis under dry-surface and aqueous photoaging conditions, with metal‑rich blue/green surpassing metal‑depleted red/yellow/white. Photoelectrochemical and theoretical analyses revealed that redox-active metals (particularly Mn, Fe, Cr) outperform carbonyls in narrowing the bandgap and promoting charge separation; coupled with upshifted conduction bands and efficient O₂ activation, such dopants enable the rapid generation and diffusion of reactive oxygen species including ^•OH, O₂^•-, and ¹O₂ via Fenton-like and photosensitized reactions, culminating in superior decontamination. This work establishes that the environmental fates of colored MPs-particularly those enriched with redox‑active dopants-differ fundamentally from unpigmented polymers, thereby calling for a paradigm shift in risk assessment that transcends polymer‑centric and size‑centric frameworks to incorporate pigment photoredox activity.