Polystyrene microplastics accelerate CuS dissolution and block Cu transfer in the Daphnia magna–zebrafish (Danio rerio) food chain under sunlight irradiation

Abstract

The toxicity of copper sulfide (CuS) in aquatic environments is limited by its high stability, and thus, environmental processes that promote Cu2+ release could potentially intensify its toxicity. Microplastics (MPs) are commonly detected in aquatic environments, and they can affect CuS dissolution under sunlight and pose a threat to biota, but the effects are poorly understood. This study shows that the reactive species (e.g., 1O2, OH and PS*) generated on the surfaces of polystyrene (PS) MPs strongly accelerated the oxidative dissolution of CuS under sunlight and increased the amount of Cu2+ released from CuS in ultrapure water by a factor of 2.95. Compared to virgin PS MPs, the mechanical abrasions on aged PS MPs promoted CuS dissolution by reactive species generation. However, increased levels of Cu2+ released by PS MPs were hardly noticeable in real water samples because Cu2+ release was extensively blocked by DOM, CO32−, pH and PO43−. Consequently, CuS predominantly showed particle-related toxicity in real water samples, and the PS MPs blocked the accumulation of Cu in D. magna as well as Cu transfer along the D. magna–zebrafish food chain. This study highlighted that PS MPs at environmentally relevant concentrations comparably promoted CuS dissolution but blocked Cu transfer along the food chain in real water. Thus, the impact of PS MPs on the transformation and toxicity of CuS in real water environments should be cautiously considered.