Alpine ponds as overlooked hotspots of microplastic hazards: Evidence from the Eastern Qinghai-Tibetan Plateau

Ponds are vital freshwater ecosystems that support biodiversity, nutrient cycling, yet their vulnerability to emerging contaminants like microplastics (MPs) remain poorly understood. This study investigated the characteristics, diversity, drivers, and ecological risks of MPs in surface water and sediments of ponds across the Eastern Qinghai-Tibetan Plateau (EQTP). Sampling sites were categorized into zones of Low (LAZ), Medium (MAZ), and High (HAZ) Anthropogenic Intensity to assess spatial variations. MPs were ubiquitous, with concentrations ranging from 1.11 to 594.44 items L^-1 in water and 5.44-1016.11 items kg^-1 dry weight in sediment. Abundance followed the order HAZ > MAZ > LAZ, directly linking microplastic pollution to anthropogenic pressure. Predominant MPs were fibers and small (<500 μm) polyethylene fragments, indicating advanced degradation and high bioavailability. Diversity was greater in HAZ and MAZ, than in LAZ, suggesting atmospheric deposition as a secondary source. MP concentrations correlated positively with temperature and negatively with altitude, highlighting the combined role of climate and human activity. Risk assessments revealed higher ecological hazards in HAZ and MAZ due to high-hazard polymers. While HAZ ponds exhibited contamination levels comparable to global reports, LAZ and MAZ remained lower. Our findings establish these alpine ponds as overlooked microplastic hotspots and highlight the urgent need for stricter waste management and their recognition as critical environmental sentinels.