Dust storms as a means of transport for microplastics in the atmosphere

Airborne microplastic is a new area of research in the microplastic domain. Recently, microplastic presence was reported in areas remote from any urban, industrial, and agricultural sources. This reveals the role of the atmosphere in the transport and dispersion of microplastics. Dust storms can shift significant quantities of soil particles and associated microplastics, especially in arid and semi-arid regions. This study reports the presence, characteristics, and potential sources of microplastics in a severe dust storm in Shiraz, southern Iran, in May 2018. Using the method adopted by Bergmann et al. (2019), 22 dust samples were collected from parked cars directly after the event. Dust samples were analyzed for microplastic using the density extraction method and Raman Spectroscopy. The hybrid Lagrangian and Eulerian model of HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) was used for back trajectory analysis in order to determine the origin of air masses.

Results showed that MP concentrations ranged from 0.04 to 1.06 particles per g of dust. In total, 485 microplastics were detected in all dust samples. The main shape of microplastics was fibrous and polymer makeup was dominated by nylon, polypropylene, and polyethylene terephthalate. Scanning Electron Microscope (SEM) images revealed different degrees of weathering in microplastics. Results of modeling together with the geochemical evidence suggested that the Arabian Peninsula constitutes the principal distal and transboundary source. Results also estimated that about 2 * 10¹² microplastics could be transported by such a dust event. According to the literature on MP concentrations in urban dust and remote arid soils, it was estimated that between 0.1 and 5% of MPs in the dust samples were originated from local sources, and the remainder arose from more distant sources. The outcome of this study is proving the atmospheric transport of microplastic far beyond its sources and a potential pathway for microplastics to the oceans and land through dust storm events.