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Microplastic Ingestion by Wild Fish Across an Urbanization Gradient in a Megacity River: A Case Study of the Suzhou River, Shanghai
Summary
Scientists found tiny plastic bits in the guts of over 70% of fish tested from Shanghai's Suzhou River, with fish from more urban, city-center areas carrying noticeably more plastic than those from quieter suburban stretches. Most of these particles were small, clear plastic fibers — the kind that could come from synthetic clothing or urban runoff — and since these are fish that people may eventually eat, the findings raise questions about how much plastic pollution moves from city waterways into the food we consume.
Microplastic (MP) pollution in highly urbanized rivers poses increasing ecological risks; however, the ingestion characteristics of wild fish across urbanization gradients remain insufficiently understood. In this study, gastrointestinal suspected microplastic ingestion was investigated in a diverse fish assemblage (n = 310, 10 species) collected from core urban, intermediate urban, and suburban reaches of the Suzhou River, Shanghai. A total of 496 visually identified suspected microplastics were detected, with an overall detection rate of 71.29% and a mean abundance of 1.60 ± 1.67 items/individual. Statistical analyses revealed significant spatial variation in suspected microplastic abundance (p < 0.05), with fish from the core urban area (2.08 ± 1.77 items/individual) and intermediate urban area (1.87 ± 1.80 items/individual) exhibiting significantly higher levels than those from suburban reaches (1.27 ± 1.50 items/individual). In contrast, differences associated with feeding habits and habitat layers were not statistically significant (p > 0.05). In the indicator species Coilia nasus, gastrointestinal suspected microplastic abundance showed a significant positive correlation with both body length (R2 = 0.205, p < 0.001) and body weight (R2 = 0.153, p < 0.005). Morphological characterization indicated that small-sized (≤1 mm, 79.47%), transparent fibres predominated among the detected particles. Overall, these findings suggest an association between urbanization and fish suspected microplastic exposure, although downstream accumulation likely co-drives this spatial pattern. Furthermore, differences associated with specific ecological traits were not statistically significant and require further targeted investigation. This study provides baseline ecological evidence for understanding microplastic exposure in urban river ecosystems and highlights the importance of integrated long-term monitoring for ecological risk assessment and management of emerging pollutants.