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Standardizing microplastic quantification by scanning electron microscopy: Structural performance of filter membranes and implications from bottled drink analysis
Summary
Scientists testing how labs count microplastics in bottled drinks found that the type of filter used to trap these tiny plastic bits can seriously skew the results—some filters cause plastic particles to clump together or get stuck, making counts unreliable. They identified one filter type (called PCTE) that gives the most accurate, consistent counts, which matters because reliable measurement is the first step to understanding how much plastic we're actually consuming and whether it poses health risks.
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.