Microplastics (MPs) have emerged as one of the most significant environmental pollutants in aquatic ecosystems, drawing increasing attention from researchers. Rivers are of strategic importance due to their role in connecting terrestrial and marine habitats and acting as a primary carrier of pollutants to the seas. The Sefidrud Dam, one of the largest dams in northern Iran, has a high potential for accumulating microplastics due to its ability to reduce the natural flow of water. In this study, the abundance and characteristics of microplastics in the surface waters and sediments of the Sefidrud Dam were investigated across five stations, including Emamzadeh Hashem, Siahroud Dam, Rostamabad, and Sefidrud Dam. Water samples were collected using plankton nets, and sediment samples were collected using a metal spoon. The samples were prepared by digesting organic materials with hydrogen peroxide and separating microplastics based on density differences using sodium chloride. Visual identification was conducted with a stereomicroscope, and polymer types were determined using FTIR.
The results showed that polyethylene, polystyrene, and polyester polymers were identified in all samples, with polyethylene being the dominant polymer in both water and sediment samples. The identified microplastics were found in filament, fragment, film, and pellet forms. The microplastics ranged in size from 500 to 5000 micrometers, with the size range of 1000 to 2000 micrometers being the most prevalent in both water and sediment samples. Specifically, 43.64% of the microplastics in the sediments fell within this size range. Microplastics were observed in various colors, with black, red, and green being the most dominant in both water and sediment samples. Black microplastics were most frequently found at the Siahroud station, with a frequency of 62.75%. This study provides new insights into the distribution and characteristics of microplastics in the region’s aquatic environments and aids