Spatio-Temporal Patterns and Ecological Implications of Microplastic Contamination in Benthic Fish from the Tongkou River, China

Microplastic pollution in rivers is a critical environmental threat that harms aquatic life. To understand the abundance, physical characteristics, and polymer types of microplastics, this study examined the intestinal tract of four fish groups (three individual species: Saurogobio dabryi, Squalidus argentatus, and Hemibarbus labeo; and a pooled group of four loach species: Paramisgurnus dabryanus, Triplophysa bleekeri, Oreias dabryi, and Paracobitis variegatus) collected from the Tongkou River in October 2023 and November 2024 using tissue digestion methods across different river sections. The results revealed that every single fish contained microplastics, with contamination levels significantly higher downstream than upstream. Over the study period, total microplastic counts dropped by 32 percent from 2023 to 2024. Most of the collected pellets were thin threads and small fragments measuring under one millimeter, composed mainly of common plastics and cellulose. These findings demonstrate that freshwater fish are widely exposed to small plastic fibers, showing distinct geographic and yearly trends. Ultimately, this research provides essential baseline data to help authorities develop effective strategies to reduce plastic pollution in freshwater ecosystems and protect aquatic wildlife.