Wet Deposition of Globally Transportable Microplastics (<25 µm) Hovering over the Megacity of Beijing.

Microplastics of size <25 µm possess globally transportable features, but the impact of precipitation on their transport remains unclear. Here, microplastics were detected in all 10 studied rainfalls in Beijing, with <25 µm microplastics present in 8 rainfalls. Interestingly, microplastic abundance (7590-136,778 items·m-3) was tentatively linked to maximum rainfall intensity, with <25 µm microplastics making up 39.6 (±27.5)% of the total count. The composition of <25 µm microplastics differed from that of larger microplastics, although both mainly comprised polystyrene, polyethylene, and polypropylene. The microplastic communities differed among rainfalls, suggesting that atmospheric transport is a highly dynamic process. The first rainfall exhibited the highest microplastic abundance and community diversity after long-term exposure to dry atmospheric environment. The deposited microplastics were unstable and highly fragmented according to the conditional fragmentation model. The wet deposition rate of the microplastics was calculated as 2-463 µg·m-2 (146-8629 items·m-2) per rain, amounting to 25.44 tons per annum in Beijing. Although <25 µm microplastics represented a negligible proportion (0.00-1.24%) of the overall mass load of microplastics, their numerical abundance was high. Our results demonstrate that precipitation is an effective mechanism for removing airborne microplastics, which may enter urban soils and waters, exacerbate microplastic burdens in the environment, and cause potential risk for human health.

Occurrence, stability and source identification of small size microplastics in the Jiayan reservoir, China.

Microplastics (MPs) in terrestrial aquatic ecosystems has received increasing attention. However, its footprints in reservoirs are poorly documented compared to those in rivers and lakes, especially for small-sized microplastics (<300 µm, SMPs). This study investigated the whole size spectrum of MPs contamination, classified by shape and polymer type, in surface waters and sediments at the Jiayan reservoir, one of the cascade reservoirs in the Upper Yangtze River in western China. High concentrations of MPs were detected in all surface water and sediment samples. The MPs abundances ranged from 1.10 × 104 to 6.17 × 104 items/m3 (average 2.75 × 104 ± 2.33 × 104 items/m3) in the surface water and 2.60 × 103 to 1.57 × 104 items/kg (average 6.90 × 103 ± 5.96 × 103 items/kg) in the sediment. The SMPs accounted for 80% of the total MPs particles, and were dominated by polyethylene (PE) fragment. Small-sized PE was the main contributor to the high abundance of MPs in the Jiayan reservoir. Neglecting SMPs not only leads to an underestimation of the degree of risk, but also causes misjudgment of the major morphology, components, and sources. The conditional fragmentation model analysis showed the stability of MPs increased from the fibers to fragments and fibers tend to disintegrate into smaller particles. Agricultural activities and atmospheric deposition were the main sources of MPs in the Jiayan reservoir. This study indicates that the reservoirs are presumably hotspots for MPs accumulation, and the fate of SMPs in the cascade reservoirs deserves more attention for further studies.