Non-Destructive Extraction and Separation of Nano- and Microplastics from Environmental Samples by Density Gradient Ultracentrifugation

Nano-/microplastics (NMPs, particle diameter < 5 mm) are widespread emerging pollutants causing diverse impacts on organisms due to their sizes, shapes, and chemical properties. Despite the fast increase in NMP research, an effective method to separate and identify NMP types from environmental samples is still lacking. Here, we developed a simple and effective approach for the non-destructive extraction and separation of various types of NMPs from environmental samples by density gradient ultracentrifugation (DGU). For the first time, DGU was capable to separate various NMPs from the complex matrix with high selectivity (100%), purity (93%), and applicability. Through a gradually changing density of the density gradient medium by changing the concentrations or volumes of CsCl/water solution (from 0.00065 to 0.01989 g cm-3 mm-1), various NMPs (with particle sizes as little as 50 nm) could be extracted and separated from soil samples with high recovery (78.5-96.0%). We confirmed the effectiveness and compatibility of DGU through a correct identification of all types of NMPs separated from artificial soil samples with Raman spectroscopy, simultaneous thermal analysis (STA), and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). DGU is compatible with all analytical processes compared to other existing methods with much less sample pretreatment time (0.5 h). Overall, DGU is an effective and cheap method (2.2 USD/sample) to separate NMPs from environmental samples such as soil and water and, hence, can facilitate research on NMPs related to terrestrial and marine environments as well as human health.