Microplastic Contamination Hotspots in the Sakarya, a Major Anatolian River: Evidence from Water and Sediment

Rivers are important pathways for the transport of microplastics from terrestrial environments to aquatic ecosystems; however, data from major freshwater systems in Türkiye remain limited. This study aimed to determine the abundance, characteristics, and transport potential of microplastics in the Sakarya River, one of the largest freshwater systems in Türkiye. Surface water and sediment samples were collected from 10 stations along approximately 800 km of the river. Microplastics were quantified and classified according to polymer type. Annual transport was estimated using instantaneous concentrations and long-term average flow rates. Microplastic abundance ranged from 0–166.7 particles/m³ in surface water and 0–40 particles/kg in sediment. Inputs from tributaries draining densely populated areas significantly increased microplastic pollution. Ten polymer types were identified, with PET and PVC being dominant. Annual microplastic transport was estimated at approximately 10¹¹ particles. The Sakarya River exhibits significant microplastic contamination. These findings provide critical information for developing environmentally sound waste management practices and long-term environmental planning strategies.