Microplastic behaviors and ecological risks in extreme arid hypersaline ecosystems: Qarhan Salt Lake on the Qinghai-Tibet Plateau

Although numerous studies have examined microplastic (MP) environmental exposure and contaminant characteristics, understanding of MP pollution in extreme saline environments remains limited. This study systematically investigated the distribution, migration, and potential ecological risks of MPs in the ultra-saline Qarhan Salt Lake, where intensive resource development occurs. MPs were widely detected, with higher abundances concentrated in the core industrial zones, including factories, salt ponds, and the eastern shore of Dabuson Lake. This spatial pattern closely matched the distribution of industrial facilities, identifying salt lake industry as the primary source. Accelerated aging and fragmentation driven by strong thaw and high salinity produced dominant MPs of 20–50 μm fragments across water, soil, and sediment. Polymers exhibited medium‑selective enrichment: dense polyamide accumulated in surface soil, while low‑density polypropylene migrated readily in water, governed by polymer properties and regional wind–water dynamics. A site-specific risk ranking framework, the Comprehensive Environmental Risk Index (CERI), was developed to integrate multi-media MP risk information at the same sampling locations, revealing surface soil as a key MP accumulation center. Localized high risks occurred in salt ponds and industrial areas due to toxic polymers, with core high‑risk zones in industrial clusters, salt ponds, and river estuaries. These findings reveal unique MP migration and risk patterns shaped by the synergy of resource development and extreme environments, providing a scientific basis for precise risk management and sustainable development in salt lake regions.