OICC Press Anthropogenic Pollution 2588-4646 10 1 2026 06 30 Quantitative and Qualitative Assessment of Microplastic Pollution in Urban Runoff Channels of Tehran Metropolitan Area 10.57647/AP.2026.1001.11 EN Fatemeh Karimi Department of Environment, NT.C., Islamic Azad University, Tehran, Iran Lida Salimi Department of Environment, NT.C., Islamic Azad University, Tehran, Iran Saeed Malmasi Department of Environment, NT.C., Islamic Azad University, Tehran, Iran Maryam Rafati Department of Environment, NT.C., Islamic Azad University, Tehran, Iran Journal Article 2026 06 30 Urban runoff is one of the main pathways for the transport of microplastics (MPs) to receiving environments. The present study was conducted with the aim of quantifying, investigating the physicochemical characteristics, and identifying the sources of microplastics in the surface water collection network of the Tehran metropolitan area. For this purpose, in order to understand seasonal effects, sampling was carried out at 34 stations during two hydrological periods, namely the wet and dry seasons. After particle extraction based on the standard NOAA protocol, a combination of morphological analysis using scanning electron microscopy (SEM) and polymer identification using spectroscopic techniques (FTIR/Raman) was employed. The findings showed that the average concentration of microplastics in the wet season (598 particles/L) was significantly higher than in the dry season (416 particles/L). In terms of morphology, fragmented particles (fragments), with a frequency of more than 50%, were the dominant form, and the highest particle density was observed in the size range of 1–20 μm. The polymer profile indicated the dominance of polyethylene (PE) and polypropylene (PP) with a frequency of 22.58%. This finding clearly confirms that, in addition to tire wear and environmental degradation of plastic waste, the interference and illegal connections of the sewage network to surface water channels are the main driving force of microplastic pollution in Tehran’s runoff. These findings highlight the urgent need for revising integrated urban infrastructure and developing source-control strategies to protect downstream water resources.