Microplastics in Urban Soils of İstanbul: Distribution Patterns and Seasonal Changes

Microplastics (MPs), although less studied compared to aquatic environments, pose a growing environmental threat to urban soil ecosystems under intense human activity. In this study, the spatial and seasonal distribution, abundance, and basic characteristics of microplastics in urban soils located in the European and Anatolian sides of İstanbul were evaluated for the first time using a comprehensive approach. Microplastics were extracted from surface soil samples collected from 11 different stations during the winter, spring, summer, and fall seasons using a density-based flotation method and classified under a stereomicroscope according to their shape, size, and colour characteristics. MPs were found at all sampling points, with concentrations ranging from 1001 to 1893 items/kg. The highest average MP abundance was determined in the spring season (1675 items/kg), while the lowest values were detected in the summer period. The vast majority of MPs were particles in the form of fibres <500 µm in size (66%), followed by fragments (25%) and films (7%). In terms of colour distribution, the dominance of blue-green tones is noteworthy. Statistical analyses revealed that seasonal variations had a significant effect on MP abundance (p<0.05) and that there was a strong positive correlation between total MP quantity and fiber-type MPs. The calculated Contamination Factor (CF) and Pollution Load Index (PLI) values indicate that urban soils in Istanbul generally have a “moderate” level of MP pollution. The findings reveal that urban land use and anthropogenic pressures play a decisive role in MP accumulation, and the study provides an important reference dataset for Istanbul.