Since the Covid-19 pandemic, 129 billion masks have been consumed each month worldwide. Fate of masks not only include waste disposal sites and natural environments, but masks made from synthetic fibers may release micro(nano)plastics (MNPLs) that may reach respiratory tracts. However, degradation rate of MNPLs generated from masks have been unknown.

Here, we simulated the photolysis of surgical masks made from polypropylene equivalent to 900 days. Size-fractionated MNPL formation was quantified using vibrational spectroscopic imaging, and mask deformation and morphology were characterized with correlative microscopy. Three layers of masks did not exhibit signs of degradation from hydroxyl and carbonyl groups, however, the outer layer exhibited a linear increase in crystallinity calculated from the peak height of two characteristic bands, indicating that degradation started from amorphous regions. However, for microplastics > 10 μm, both groups were observed, and mass concentration was 10 mg/item calculated from FTIR imaging data. Fine microplastics <10 μm were imaged and fitted as ellipses, and the most abundant aspect ratio was 2. Nanoplastics (<1 μm) with an average size of 149 (59) nm were detected by SEM/STEM and Raman spectroscopy. Cluster analyses on spectra categorized three groups, suggesting different additives (e.g., dyes) were added. This study detected nanoplastics from degraded masks, which have major implications for their environmental fate and human health effects.