Atmospheric microplastics at a southern China metropolis: Occurrence, deposition flux, exposure risk and washout effect of rainfall

Atmospheric microplastics (AMPs) have raised much concern for public health due to their potential for exposure. In this study, temporal distribution, characteristics and exposure risk of AMPs were studied in the urban area of Guangzhou, a metropolis in Southern China, and the washout effect of rainfall on AMPs was investigated. It was found that AMP abundances in Guangzhou were in a range of 0.01–0.44 items/m3, with higher abundance in the wet season (0.19 ± 0.01 items/m3) than in the dry season (0.15 ± 0.02 items/m3). The distribution of AMPs did not correspond to that of common air pollutants (e.g., PM2.5 and PM10), implying that their pollution sources might be distinct. In Guangzhou, a total of 1.26 × 1011 items AMPs are in the air every year, and annual inhalation exposure of adults was estimated to be in the range of 79.65–3.50 × 103 items. The annual deposition flux of AMPs is 65.94 ± 7.53 items/m2/d, and the deposition flux in the wet season (84.00 ± 6.95 items/m2/d) was much greater than that in the dry season (47.88 ± 8.35 items/m2/d). Furthermore, rainfall has an effective mechanism for removing AMPs from the atmosphere, with an average washout ratio of (19.39 ± 6.48) × 104 for rainfall washing AMPs out. Compared to moderate rain (2.5–10 mm/h) and heavy rain (10–50 mm/h), light rain (rainfall intensity <2.5 mm/h) had a better washout effect. This study contributes to the evaluation of AMP exposure risk and understanding of AMP environmental behavior and fate by providing long-term monitoring data on AMPs and quantifying the washout effect of rainfall on AMPs for the first time.