Microplastic abundance and distribution in a Central Asian desert

Microplastic pollution is widespread, affecting even the remotest places on Earth. However, observational data on microplastic deposition in deserts, which comprise 21% of the total land area, are relatively rare. The current study aims to address the knowledge gap in terms of microplastic distribution in Asian deserts. The Badain Jaran Desert in Central Asia is the second largest desert in China. We investigated microplastic distribution and deposition on dunes and lakes of this desert. Microplastics were extracted from surface sediments to determine their characteristics and polymer types by microscopic inspection and μ-FTIR. The abundance of microplastics (detection limit is approximately 40 μm) in the uninhabited area ranged from 0.7 ± 1.5 to 11.7 ± 15.5 items/kg, with an average of 6.0 ± 15.4 items/kg. Fragments and fibers accounted for 77% and 23% of the total microplastics, respectively. Epoxy resin (28%), polyethylene terephthalate (25%), phenoxy resin (25%), and polyamide (9%) were the main polymer components, whose sizes were concentrated at 50-200 μm. Back-trajectory modeling was then performed to explore the possible source direction of the microplastics. The results showed that the microplastics mainly originated from the populated areas southeast of the desert, indicating long-distance atmospheric transport and deposition in deserts. The desert-edge zone with some tourism activity contained more microplastics (8.2 ± 17.9 items/kg) than the non-tourism zone (0.9 ± 1.6 items/kg), indicating a potential contribution from tourism. The abundance in the non-tourism zone (0.9 items/kg) can be used as a reference for microplastic background values in the Central Asian deserts, as this value is critical for simulating and predicting global microplastic yields.