Zinc oxide nanoparticles dissolution and toxicity enhancement by polystyrene microplastics under sunlight irradiation.

Zinc oxide nanoparticles (ZnO NPs) dissolution is a critical process for the transformation and toxicity of ZnO NPs in aquatic environments. However, the effect of microplastics (MPs) on dissolution and toxicity of ZnO NPs under sunlight irradiation is still lacking. Herein, the dramatic increase in sunlight-induced ZnO NPs dissolution by polystyrene (PS) MPs was proven, which was attributed to the increase in h+-dependent and proton-dependent ZnO NPs dissolution by PS MPs, yielding 1O 2 generation inhibition and acid release, respectively. The sizes, functional groups and aging status of PS MPs and pH were characteristic ZnO NPs dissolution through modifying 1O 2 , •OH and O 2 •− generation and acid release. Furthermore, the ZnO NPs dissolution affected by PS MPs also occurred in three realistic water samples, which were mainly governed by dissolved organic matter (DOM) and CO 3 2−, rather than Cl− or SO 4 2−. The PS MPs (1 μg/mL) dramatically altered the Zn2+:ZnO ratio in ZnO NPs suspension after 96 h of sunlight irradiation and presented vehicle effects on Zn2+, which in turn significantly increased the ion-related toxicity of ZnO NPs to Daphnia magna. Based on the PS MPs enhanced dissolution and toxicity of ZnO NPs, the effects of PS MPs on the environmental risk assessment of ZnO NPs should be seriously considered in freshwater environments under sunlight irradiation. [Display omitted] • PS MPs promote sunlight-induced ZnO NPs dissolution. • PS MPs modify ZnO NPs dissolutions in natural waters. • PS MPs increase the Zn2+:ZnO ratio. • PS MPs enhance ions-rated toxicity of ZnO NPs. • PS MPs present vehicle effects on Zn2+. [ABSTRACT FROM AUTHOR]