Zhang et al. (2021) described the mass concentrations of micropiastics (MPs) in landfill mineralized refuse using depolymerization-combined mass spectrometry technology and evaluated the separation efficiency of density flotation method which is commonly used in MPs research. Their results showed that approximately 70% of MPs could not be extracted during the flotation process and remained in the refuse residue. However, we doubt that direct depolymeriza-tion likely produced monomers from other compounds instead of real MPs and thus caused the overestimation of MPs concentration in mineralized refuse, leading to unreliable separation efficiency result. These points were further confirmed by calculation using their data, suggesting that there existed a self-contradiction. We think it is necessary to point out these scientific facts, in order to help clarify the understandings of MPs concept and analysis.
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