Microplastics in the Lut and Kavir Deserts, Iran

Although microplastics (MPs) are ubiquitous environmental contaminants, little is known about their occurrence and behavior in the terrestrial setting. In this study, MPs have been isolated from soils collected from various geomorphological features (yardangs, sand dunes, moving sands, seasonal lakes) of the Kavir and Lut Deserts on the Iranian plateau. The number of MPs identified in 300 g samples ranged from zero (not detected) in several yardang tops to 25 on some yardang hillsides, with an overall average abundance of about 0.02 MP g^-1. The majority of MPs were of a fibrous nature with a size distribution (≤100 μm to ≥1000 μm) skewed toward the lower end, and analysis of a selection of particles by μ-Raman spectroscopy showed that polyethylene terephthalate and Nylon (polyamide) were the principal polymers. Scanning electron microscopy revealed intense degradation of some particles but limited weathering of others. With little evidence of meso- and macroplastics in the deserts, it appears that the majority of MPs are brought into these environments from distant sources via the wind, with smaller, seasonal contributions from runoff associated with the adjacent mountains. It is proposed that some windborne MPs are transported through the deserts relatively rapidly, while others are subject to internal recycling and significant photo-oxidation and mechanical weathering.