Microplastic and nanoplastic accumulation in fish from Luzhou range of the upper Yangtze River: Trophic level and living water layer as key drivers

Microplastics (< 5 mm) and nanoplastics (< 1 μm) are concerning aquatic pollutants due to their small size and persistence, readily accumulating in fish and potentially impairing physiology. Understanding their uptake is crucial for assessing ecological risks in the upper Yangtze River. This study detected microplastics in water, sediments, and intestinal contents of 41 fish species from the Luzhou range using laser direct infrared (LDIR) imaging, and quantified nanoplastics in five species via pyrolysis gas chromatography-mass spectrometry (Py-GC-MS). Fluororubber (FKM) was the dominant polymer in fish (31.30 %). Microplastic abundance in intestinal contents ranged widely from 7.17 items/g (Xenocypris davidi) to 606.67 items/g (Silurus asotus). Abundance positively correlated with fish trophic level (Pearson's r = 0.35, p < 0.05) and was significantly higher in benthic versus pelagic fish. The potential hazard index (PHI) for microplastics in intestines ranged from 4.14 (Ancherythroculter wangi) to 6172.05 (Silurus asotus), indicating risk levels I to IV. Nanoplastics (PA66 and PVC) were quantified within fish bodies. This proves fish accumulate nanoplastics and highlights significant environmental and health concerns. The study enhances understanding of freshwater plastic pollution and aids fish protection in the upper Yangtze.