Combined effects of polystyrene microplastics and natural organic matter on the accumulation and toxicity of copper in zebrafish

As emerging contaminants, microplastics (MPs) are predicted to act as vectors for other contaminants and their combined effects are largely unknown. In this study, the combined effects of MPs and natural organic matter (NOM) on the accumulation and toxicity of copper (Cu) in zebrafish (Danio rerio) were investigated. As a result, small-size MPs could absorb more Cu than large-size MPs. The presence of NOM promoted Cu adsorption on MPs in the pH range of 6-8. Our results demonstrate that the combination of MPs and NOM increased Cu accumulation in the livers and guts in a size-depended manner. Correspondingly, the results of biochemical test showed that MPs and NOM could aggravate Cu-toxicity in the livers and guts, which is manifested in the increased levels of malonaldehyde (MDA) and metallothionein (MT) and decreased levels of superoxide dismutase (SOD). Furthermore, the results of transcriptomic analysis suggested that such aggravation of toxicity was mainly attributed to the inhibition of Cu-ion transport and the enhanced oxidative stress. Since the co-existence of MPs and NOM in the environment is inevitable, their enhancement effects on the bioaccumulation and toxicity of other pollutants such as heavy metals deserve more attention.