Transport and deposition of microplastics and microrubbers during a dust storm (Sarakhs, northeast Iran)

Dust storms are important vehicles for the erosion and translocation of geogenic material in arid and semi-arid climates but little is known about their role in transporting microplastics (MPs). In this study, local soils (n = 20) and dusts deposited from a storm (n = 41) have been sampled from a remote region of northeastern Iran (Sarakhs) and the quantities and characteristics of MPs and microrubbers (MRs) determined using established techniques. In dusts, MPs and MRs were detected in 33 and 17 cases, respectively, with respective median and maximum concentrations of 0.48 and 23.0 MP g⁻¹ and 0.50 and 6.48 MR g⁻¹ and depositional fluxes of up to about 12 MP m⁻² h⁻¹ and 7 MR m⁻² h⁻¹. In soils, MPs and MRs were detected in ten and eight cases, respectively, with respective median and maximum concentrations of 0.25 and 1.90 MP g⁻¹ and 3.27 and 14.3 MR g⁻¹. Overall, the ratio of MPs in dusts to soils relative to MRs in dusts to soils was about 20, reflecting the greater mobility of the former type of particle. This can be attributed to the ready suspension and more favourable aerodynamic properties of fibrous MPs compared with fragmented MRs. A comparison of MPs in dusts and soils suggests a preferential long-range transport of fibres with certain characteristics (e.g., long, red and constructed of polypropylene), with HYSPLIT back trajectory modelling suggesting secondary (e.g., soil) sources to the south and southwest. Dust storms are important regional transporters of atmospheric MPs and MRs whose role is predicted to increase as desertification and the demands for potable water and plastics rise.