Effects of Industrial and Domestic Wastewater Treatment Plants on Microplastic Pollution in an Urban River in Türkiye

Microplastic (MP) contamination in inland aquatic systems is a growing environmental concern due to its persistence and potential ecological impacts. This study provides a comprehensive assessment of the occurrence, composition, and seasonal dynamics of MPs in two urban rivers—Nif Creek and Gediz River—in western Türkiye, which receive treated and untreated effluents from domestic and industrial wastewater treatment plants (WWTPs). A total of 20 river water and 3 sediment sampling stations were monitored across four seasons. MP concentrations ranged from 7 to 146 particles/L in water and from 9,867 to 136,177 particles/kg in sediments, with the highest abundances observed near WWTP outfalls and urban infrastructure. Polypropylene was the dominant polymer in water (59.1%) and WWTP effluents (44.4%), while polyethylene was most prevalent in sediments (60.2%). MPs were primarily within the 0.1–0.5 mm size range and were predominantly transparent in colour. Statistical analyses indicated significant positive correlations between MP abundance and key water quality parameters, including chemical oxygen demand, total suspended solids, and selected heavy metals (e.g., Zn, Cd, Ni). The polymeric composition of MPs reflected both urban and industrial sources, with variations in polymer profiles linked to spatial and seasonal factors. Compared to values reported in European freshwater systems, MP levels in the studied rivers were considerably higher, underscoring the need for improved wastewater management and targeted monitoring efforts in urban river basins.