Polyethylene microplastics decrease the bioaccumulation and toxicity of picoxystrobin and azoxystrobin to microalgae Scenedesmus obliquus.

Fungicide residues can interact with microplastics (MPs) in the aquatic environment leading to mixed toxicity on phytoplankton. The investigation of biological effects obtained from combined fungicide and MPs is essential for proper evaluation of the ecological risks. Until now, the mechanisms that how polyethylene (PE) MPs altered the toxicity of picoxystrobin and azoxystrobin on microalgae Scenedesmus obliquus was unknown. Here, the impacts of PE-MPs on freely dissolved concentrations (C) of the 2 fungicides and their toxicity to microalgae growth were assessed after 96 h exposure. We found that the presence of PE-MPs reduced the bioaccumulation of picoxystrobin and azoxystrobin in microalgae through decreasing the fungicide C. Furthermore, inhibition effects on microalgae growth and chlorophyll generation was alleviated significantly in the combination of fungicide and PE-MPs compared with the fungicide alone. Specifically, 400 mg/L of 25 μm PE induced more profound influences than other treatments in terms of decreasing C, promoting growth rate, and increasing chlorophyll content that might be attributed to its higher adsorption capacity for the fungicides. Our results demonstrated the antagonism between the fungicides and PE-MPs, clarifying that PE-MPs functioned in lowering the bioavailability and acte toxicity of the 2 strobilurin fungcides to microalgae via physical adsorption especially under the small size and high level of PE-MPs. This study provides evidences that the existence of MPs is capable of influencing the toxicological behavior of fungicides in the environment, and can be a starting point for more sophisticated mechanism investigation of joint toxicity for fungicides and MPs.