Polystyrene microplastics enhance oxidative dissolution but suppress the aquatic acute toxicity of a commercial cadmium yellow pigment under simulated irradiation

Abstract

Commercial cadmium yellow (CdS) pigment widely coexist with microplastics (MPs) in surface water, thus it is important to understand how MPs affect CdS pigment stability and toxicity under irradiation. Herein, the dissolution of CdS pigment (k_release = 0.118 h^-1) under irradiation was visibly increased to 0.144 h^-1 by polystyrene (PS) MPs, due to reactive species generation such as ¹O₂, •OH and ³PS* , while O₂^•- was unimportant to this process. The O₂, humic acid, photoaging status of PS MPs could promote PS MPs-related CdS pigment dissolution rate by modifying reactive species generation. However, the CO₃^2-, PO₄^3- and alkaline condition significantly decreased the dissolution rate to 0.091, 0.053 and 0.094 h^-1, respectively, through modifying free Cd²⁺ stability. Comparably, PS MPs-related CdS pigment dissolution was relatively slow in natural water samples (k_release = 0.075 h^-1). PS MPs at environmental concentration can also promote CdS pigment dissolution and Cd²⁺ release, but suppress acute toxicity of CdS pigment to zebrafish larvae as increasing 10 h survival from 65% to 85% by adsorbing the Cd²⁺ and decreasing Cd²⁺ bioavailability. This study emphasized the environmental risks and human safety of CdS pigment should be carefully evaluated in the presence of PS MPs in aquatic environments.

Keywords: Aquatic toxicity; CdS pigment; Microplastics; Oxidative dissolution; Reactive species.