Studies of microplastics (MPs) in remote, trans-boundary and alpine rivers are currently lacking. To understand the sinks and transport mechanisms of MPs, this study investigated the distributions and sources of MPs in the surface waters and sediments of five tributaries of the Koshi River (KR), a typical alpine river in the Himalayas between China and Nepal. Mean abundances of MPs in water and sediment were 202 +/- 100 items/m3 and 58 +/- 27 items/kg, dry weight, respectively. The upstream tributary, Pum Qu in China, had the smallest abundance of MPs, while the middle tributary, Sun Koshi in Nepal, had the greatest abundance. Compared to international values in rivers, contamination of the KR with MPs was low to moderate. Fibers represented 98% of all MP particles observed, which consisted of polyethylene, polyethyleneterephthalate, polyamide, polypropylene, and polystyrene. Blue and black MPs were prevalent, and small MPs (<1 mm) accounted for approximately 60% of all MPs. Atmospheric transmission and deposition were considered to be the principal sources of MPs in the upstream tributary. The results imply that point sources associated with mostly untreated sewage effluents and solid wastes from households, major settlements, towns, and cities were most important sources of MPs in the KR. Non-point sources from agricultural runoff and atmospheric transport and deposition in the middle stream tributaries also contribute a part of microplastics, while the least amount was from fishing in the downstream tributary. Urbanization, agriculture, traffic, and tourism contributed to pollution in the KR by MPs. Equations to predict abundances of MPs based on river altitudes revealed that different trends were affected by both natural and human factors within the KR basin. This study presents new insights into the magnitude of MP pollution of a remote alpine river and provides valuable data for developing MP monitoring and mitigation strategies in similar environments worldwide.

Microplastics have recently been detected in the atmosphere of urban, suburban, and even remote areas far away from source regions of microplastics, suggesting the potential long-distance atmospheric transport for microplastics. There still exist questions regarding the occurrence, fate, transport, and effect of atmospheric microplastics. These questions arise due to limited physical analysis and understanding of atmospheric microplastic pollution in conjunction with a lack of standardized sampling and identification methods. This paper reviews the current status of knowledge on atmospheric microplastics, the methods for sample collection, analysis and detection. We review and compare the methods used in the previous studies and provide recommendations for atmospheric microplastic sampling and measurement. Furthermore, we summarize the findings related to atmospheric microplastic characteristics, including abundance, size, shapes, colours, and polymer types. Microplastics occur in the atmosphere from urban to remote areas, with an abundance/deposition spanning 1-3 orders of magnitude across different sites. Fibres and fragments are the most frequently reported shapes and the types of plastic which generally aligns with world plastic demand. We conclude that atmospheric microplastics require further research and greater understanding to identify its global distributions and potential exposure to human health through further field sampling and implementation of standardized analytical protocols.

Microplastics are widely detected in terrestrial environments. However, microplastic features in the soil of remote areas are still sparse. In this study, microplastic pollution in soil across the Tibetan Plateau was systematically investigated. The results revealed that microplastic was ubiquitous in the soil of the Tibetan Plateau with an average abundance of 47.12 items/kg-dry weight (range: 5-340 items/kg). Compared with the published data of soil microplastic pollution in other regions, the microplastic pollution in the Tibetan Plateau was relatively low. Fibers represented 43.54% of microplastic particles detected, followed by fragments (32.20%) and films (23.78%). They mainly consisted of polyvinyl chloride, polyethylene, polypropylene, and polystyrene. Transparent and white microplastics were prevalent, and small microplastics (50-500 mu m) occupied approximately 66% of all microplastics. High values of microplastics were found near Lhasa, Naqu, and Linzhi. Furthermore, microplastic pollution was found to be negatively related to the distance to the nearest city (p < 0.01), wind velocity (p = 0.014), altitude (p = 0.181), yet positively related to precipitation (p = 0.024). This work presents new insights into the magnitude of microplastics contamination in the soil across the Tibetan Plateau and supplies valuable data for future research on ecotoxicology, ecosystem impacts, and earth system feedback of microplastics on terrestrial ecosystems.