Microplastic characteristics in rivers and lakes across the Tibetan Plateau

Microplastics have emerged as one of the most significant threats to the Earth's ecosystems due to their persistence, ability to carry high loads of contaminants, and biotoxicity. The Tibetan Plateau is a hotspot for global biodiversity conservation, but its ecosystem is fragile. This study systematically investigated the characteristics, distribution, sources, and ecological risk of microplastics in rivers and lakes across the Tibetan Plateau using the Laser Direct Infrared Imaging Spectroscopy (LDIR). The results indicated that the mean abundances of microplastics in water and sediments were 4250 items/m3 (n=50) and 3750 items/kg (n=44), respectively. Microplastics with small sizes (50-200 mu m), characterized by transparent and white fragments, were predominant. The most common polymers identified were polyamide (PA), polyurethane (PU), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE). Water sampling sites near urban/suburban effluent outfalls showed high levels of contamination. Microplastics in water are primarily derived from sewage effluent and atmospheric deposition. No single driver has been identified as the key factor influencing the spatial distribution of microplastics in water. The abundance of microplastics in sediments was significantly negatively correlated with the distance to the nearest city/town (p<0.01, R= -0.56) and significantly positively correlated with precipitation (p<0.01, R=0.60). Discarded or landfilled plastic waste is a major source of microplastics in sediments, which accumulate through transport by stormwater runoff caused by precipitation. Three ecological risk assessment models for microplastics were applied, and the high proportion of hazardous polymers such as PU, PVC, and PA was found to be responsible for the high ecological risk in the study area. This study provides an accurate and detailed exploration of the characteristics, sources, and spatial distribution of microplastic pollution by advanced automatic detection method in rivers and lakes on the Tibetan Plateau.