To investigate the combined toxic effects of microplastics(MPs)and polycyclic aromatic hydrocarbons(PAHs)on aquatic organisms,the individual and combined exposures were conducted using Daphnia magna as the test organism.The polyethylene microplastics(PE-MPs)with particle size range of 1-10 μm and phenanthrene were selected as experimental materials.Six methods including the toxicity unit method,the additive index method,the mixed toxicity index method,the combination index method,the similarity index method,as well as the equiva-lent line method were employed to assess their combined mode of toxicity.The results demonstrated that both PE-MPs and phenanthrene posed significant immobilisation effects on D.magna,exhibiting a dose-response relation-ship along with a time-dependent correlation following a 48-hour period of individual exposure.The EC50 values were determined to be 5.07 mg·L-1 and 0.61 mg·L-1for PE-MPs and phenanthrene,respectively.Furthermore,there was an enhancement in the toxic effects caused by co-exposure conditions.Based on six evaluation methods,it was indicated that the combined toxic effects of PE-MPs and phenanthrene on D.magna were synergistic joint action.It was implied that MPs in aquatic environments could enhance the biological toxicity of PAHs to Clado-cera.The findings of this study provided valuable data and a reference for investigating the combined toxicity of MPs and other pollutants,thereby contributing to enhancing our understanding of the ecological risks of MPs in a-quatic environments.
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