Microplastics in the third pole of the world: Abundance and ecological risk assessment

Microplastics (MPs) pose a threat to the Tibetan Plateau's ecosystems. Previous studies focused mainly on lakes and specific river segments, lacking a basin-wide analysis. This study systematically examined the abundance, composition, and spatial distribution of MPs in surface waters, sediments, and sewage treatment plant tailwater in the Yarlung Zangbo River Basin (water samples through 100 µm sieve). MPs showed regional characteristics, with fibrous and fragmented forms, transparent and colored particles, and high proportions of PP and PE. Abundance was heterogeneous, higher downstream due to human activities. MPs levels in surface waters (390-1890 n/m³) and sediments (26-370 n/kg) were lower than in other regions. Sewage treatment plant tailwater was a significant MPs entry point. MPs abundance correlated with water bodies and sediments in the mainstream but less so in tributaries. It is proposed that MPs potentially originate from sources such as sewage discharge, tourism, cultivation, plastic ageing, and atmospheric transport. Water quality parameters influenced MP distribution, suggesting point source pollution impacts. MPs abundance decreased with altitude. Risk assessment showed class I PLI for surface water and sediments but high PHI and PERI for specific polymers, with the Nianchu River at highest risk. PVC and PA plastics require enhanced management.