Impacts of Pandemic-Associated Plastic Waste on Microplastics in Ambient PM_2.5

Microplastics (MPs) are a rising environmental and health concern, and the COVID-19 pandemic has increased plastic waste, particularly single-use plastics. While the impacts of pandemic-associated plastic waste on multiple environmental matrices (e.g., water and soil) have been well documented, its effects on MPs in atmospheric fine particles (PM_2.5) remain unclear. In this study, we analyzed the MPs in ambient PM_2.5 collected from urban Xi'an before, during, and after the COVID-19 pandemic in both summer and winter. Mean MP concentrations during and after the pandemic were three times higher than prepandemic levels, irrespective of the season. Transparent and white polypropylene and polyethylene terephthalate fibers dominated during and after the pandemic, while prepandemic MPs were more diverse in polymer types and colors. These results indicate a strong impact of pandemic-associated waste, especially discarded face masks, on the abundance and characteristics of MPs in ambient PM_2.5. Additionally, a positive correlation was found between MPs and ambient ozone, suggesting the potential for ozone to degrade plastics and release MPs into the air. Multiple-path particle dosimetry calculations revealed that MPs primarily deposit in the extrathoracic region of people across all age groups. However, teenagers and younger individuals showed increased susceptibility to deposition in tracheobronchial and pulmonary regions. Based on the estimated daily dose, inhalation of MPs from ambient PM_2.5 is proposed to be a significant exposure pathway for humans. Overall, our study highlights the substantial impacts of pandemic-associated plastic waste on MPs in ambient PM_2.5 and their potential implications for human exposure.