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Sampling, Sorting, and Characterizing Microplastics in Aquatic Environments with High Suspended Sediment Loads and Large Floating Debris
Published on: July 28, 2018
Standardizing microplastic quantification by scanning electron microscopy: Structural performance of filter membranes
Qian Zhang1, Xinyan Xu1, Dengke Zhang1
1State Key Laboratory of Water Pollution and Green Resource Recycling, School of the Environment, Nanjing University, Nanjing, 210023, China.
Abstract:
Filtration methods are widely used for microplastic (MP) isolation, yet filter membrane selection can introduce substantial bias into MP quantification. In this study, five types of membranes, classified as single-layer-hole [polycarbonate track-etched (PCTE)], multilayer-fiber [polytetrafluoroethylene (PTFE) and glass fiber (GF)], and multilayer-hole [mixed cellulose esters (MCE) and nylon (NY)], were systematically compared for MP quantification. Particle abundance was quantified by scanning electron microscopy (SEM)-based visual counting on membranes. Polystyrene (PS) microspheres exhibited superior dispersion on single-layer-hole (PCTE) and multilayer-fiber (PTFE) membranes. However, partial particle embedding occurred in multilayer-fiber membranes (PTFE and GF), whereas pronounced aggregation occurred on multilayer-hole membranes (MCE and NY). Accordingly, PCTE exhibited the most stable quantification performance across PS concentrations and pH conditions, with RSD values of 3.05-17.68%. Application to bottled drinks further showed that PCTE improved the differentiation of particle abundance among brands. LDIR analysis indicated that the collected particles from bottled drinks consisted of both MPs, mainly polyethylene terephthalate, polyethylene, polybutadiene rubber, and polyvinyl chloride, as well as non-MPs (54.50% - 81.29%). Overall, selection of appropriate membranes is critical for MP quantification, and single-layer-hole PCTE membranes are recommended for reliable visual counting and improved comparability across studies.
Insights
Choosing the right filter membrane is crucial for accurate microplastic (MP) quantification. Single-layer-hole polycarbonate track-etched (PCTE) membranes offer the most reliable results for visual counting and inter-study comparisons.
Area of Science:
- Environmental Science
- Analytical Chemistry
- Materials Science
Background:
- Microplastic (MP) isolation relies heavily on filtration methods.
- Filter membrane choice significantly impacts MP quantification accuracy.
- Existing studies lack systematic comparisons of different membrane types.
Purpose of the Study:
- To systematically compare five common filter membrane types for microplastic quantification.
- To evaluate the impact of membrane structure on particle dispersion, embedding, and aggregation.
- To identify the most suitable membrane for reliable MP quantification and analysis.
Main Methods:
- Five membrane types were tested: polycarbonate track-etched (PCTE), polytetrafluoroethylene (PTFE), glass fiber (GF), mixed cellulose esters (MCE), and nylon (NY).
- Polystyrene microspheres were used to assess dispersion and quantification performance under varying concentrations and pH.
- Scanning electron microscopy (SEM) was employed for visual counting.
- Laser direct infrared (LDIR) analysis was used for particle identification in bottled drinks.
Main Results:
- Single-layer-hole (PCTE) and multilayer-fiber (PTFE) membranes showed superior polystyrene microsphere dispersion.
- Multilayer-fiber membranes (PTFE, GF) exhibited partial particle embedding, while multilayer-hole membranes (MCE, NY) showed pronounced aggregation.
- PCTE membranes demonstrated the most stable quantification performance (RSD 3.05-17.68%) and improved differentiation of particle abundance in bottled drinks.
- Particles in bottled drinks comprised 54.50%-81.29% non-microplastics, with identified microplastics including PET, PE, PBR, and PVC.
Conclusions:
- Filter membrane selection is critical for accurate microplastic quantification.
- Single-layer-hole PCTE membranes are recommended for reliable visual counting due to superior particle dispersion and minimal artifacts.
- PCTE membranes enhance comparability of microplastic data across different studies and sample types.
