Baseline biomonitoring of microplastic pollution in freshwater fish from the Chishui River, China: Insights into accumulation patterns and influencing factors

In recent years, there has been growing concern about microplastic pollution in aquatic environments worldwide owing to the possible threat to fish health and river ecosystem. Fish are important indicator organisms in rivers, and their microplastic contamination reflects the plastic pollution status of the river. In this study, we conducted the first biomonitoring of microplastic contamination in freshwater fishes from the Chishui River (primary tributary of the Yangtze River), analyzed microplastic abundance, shape, size, and polymer types in gills and intestinal contents of 31 fish species using laser direct infrared imaging spectrometer (LDIR). The main findings were: (1) A total of 32 types of polymers were identified in the fish, exceeding those detected in environmental compartments (16 in water and 10 in sediment). Chlorinated polyethylene (CPE) was identified as the predominant type of microplastic polymer across water, sediment and fish; (2) Microplastic abundance in the 31 fish species ranged from 22.5 to 940 items/g (mean 246.42 items/g) in gills and from 8.5 to 968.75 items/g (mean 231.73 items/g) in intestinal contents. The fish in Siluriformes represented significantly higher intestinal microplastic abundance (382.38 ± 334.44 items/g) than that in Cypriniformes (185.96 ± 167.10 items/g) (p < 0.05). Moreover, benthic fish represented significantly higher microplastic abundance in intestinal contents (391.50 ± 299.82 items/g) than pelagic fish (155.65 ± 107.93 items/g) (p < 0.05); (3) The abundance of smaller particles was consistently identified significantly higher than that of larger particles in water, sediment, and fish. Three shapes (fragment, pellet and fiber) of microplastics were detected in fish while only fragment and pellet were found in water and sediment; (4) The polymer hazard index (PHI) assessed based on the polymer-specific risk index were much varied ranging from 275.40 (Pelteobagrus fulvidraco) to 8382.32 (Acrossocheilus yunnanensis) in total suggesting the hazard risk level from III to V. The microplastics are hazardous substances, uptake of which could cause physical damage and chemical toxicity, threatening fish health. Thus the present study would establish the first evidence of microplastic contamination in fish from the Chishui River, providing critical baseline data for developing targeted mitigation strategies in the future.