Polystyrene microplastics sunlight-induce oxidative dissolution, chemical transformation and toxicity enhancement of silver nanoparticles

The coexistence of microplastics (MPs) and nanomaterials has been increasingly studied, but the influence of MPs on the chemical transformation of nanomaterials remains unclear. Herein, it was demonstrated that polystyrene (PS) MPs induce the oxidative dissolution, transformation and toxicity of silver nanoparticles (Ag NPs) under simulated sunlight irradiation. The PS MPs induced the oxidation dissolution of pristine Ag NPs by O-1(2), center dot OH and/or acid release and simultaneously reduced the released Ag+ to secondary Ag NPs by O-2(center dot-). The sizes, functional groups and ageing status of the PS MPs and pH characterized secondary Ag NPs formation. Secondary formation of Ag NPs induced by PS MPs also occurred in realistic water and was governed by dissolved organic matter (DOM) and Cl-, rather than SO42- or CO32-. Moreover, PS MPs remarkably promoted Ag+ release, altered the Ag+:Ag-0 ratio, and presented vehicle effects on Ag+ toxicity to Daphnia magna. The concentration addition model demonstrated that the ion-related toxicity of Ag NPs was significantly increased by PS MPs. Therefore, PS MPs induced the oxidative dissolution, transformation and toxicity enhancement of Ag NPs under sunlight irradiation, and accordingly, the coexistence of PS MPs and Ag NPs in freshwater environments should be seriously considered.

Automated summary

This study found that polystyrene microplastics can induce the oxidative dissolution, transformation, and toxicity enhancement of silver nanoparticles under simulated sunlight irradiation. Similar processes also occurred in realistic water. This has important implications for the coexistence of polystyrene microplastics and silver nanoparticles in freshwater environments.