Widespread Microplastic Burden in the Endemic Freshwater Fish Squalius pursakensis Sarısu Stream, Türkiye: Evidence of Chronic Environmental Pressure and One Health Implications

Abstract

Microplastic (MP) pollution is increasingly recognized as a pervasive environmental stressor in freshwater ecosystems. This study evaluated the occurrence, characteristics, and ecological implications of MPs in the gastrointestinal tract of the endemic freshwater fish Squalius pursakensis from Sarısu Stream (Sakarya River Basin, Türkiye). MPs were detected in all examined individuals (n = 23), indicating a 100% prevalence. MP abundance ranged from 6 to 51 particles per individual, with a mean ± SD of 27.65 ± 11.49 MP/individual. Fibers were the dominant morphological type (48.5%), followed by fragments (33.5%), while particle sizes ranged from 0.1 to 0.3 mm and approximately 50% of the particles were transparent. Fourier-transform infrared spectroscopy identified six polymer types, with Nylon (PA6+PA66) as the predominant polymer (46.7%), followed by polypropylene and polyvinyl chloride A significant positive correlation between total length and MP abundance was observed in bivariate analysis (rs = 0.41, p = 0.004); however, this association was not retained in multivariate negative binomial modeling, suggesting that biometric traits did not independently predict MP burden. These findings provide baseline evidence of widespread MP exposure in an endemic freshwater fish from a semi-rural Anatolian watershed. Although potential textile- and wastewater-related inputs may contribute to the observed contamination, specific sources cannot be confirmed without environmental source-tracking. The findings, therefore, highlight the value of endemic freshwater species in MP monitoring and provide a basis for further investigation of the ecological implications of persistent MP exposure.