Assessment of microplastics under 20 μm in road dust using confocal laser scanning microscopy (CLSM) and pyrolysis-gas chromatography/mass spectrometry (Pyr-GC/MS)

Detecting microplastics (MPs) under 20 μm has been challenging, yet these tiny particles may pose significant threats to human health and the environment. They can be inhaled or ingested, potentially leading to respiratory diseases and gastrointestinal problems. This research proposed confocal laser scanning microscopy (CLSM) for identifying MPs smaller than 20 μm and to support its validity by comparing results to a typical gravimetric analysis for these small MPs in road dust samples using pyrolysis-gas chromatography/mass spectrometry (Pyr-GC/MS). A total of 30 road dust samples were collected from urban areas in Seoul and 15 samples from rural regions throughout South Korea. A strong agreement was observed between the results obtained from CLSM and Pyr-GC/MS, confirming the effectiveness of both methods in measuring MPs under 20 μm especially when polyolefins are dominating MPs. CLSM, coupled with BiofilmQ software, enabled precise volumetric analysis, while Pyr-GC/MS provided rapid identification of chemical compositions, suggesting that they are complementary. Mass concentrations of MPs in rural road dust (14.2±6.4 μg/g) were greater than those in urban road dust (7.8±4.6 μg/g), likely due to less stringent plastic waste management and increased agricultural plastic use in rural areas. This study builds upon prior volumetric imaging methods by enabling mass quantification of MPs under 20 μm using CLSM and validating the results against Pyr-GC/MS in real-world road dust samples.