Mapping soil microplastics across land uses: a baseline survey from northwestern Türkiye

The widespread use and improper management of plastics have led to increasing concern over microplastic (MP) contamination in terrestrial environments, particularly soils, which are recognized as major sinks for land-based plastic pollution. This study investigated the abundance, distribution, and characteristics of microplastics in soils from Sakarya Province, Türkiye, a region characterized by diverse land uses and significant industrial, residential, and agricultural activities. Soil samples were collected from ten sites representing different anthropogenic influences, including commercial areas, industrial zones, agricultural lands, construction sites, and recreational spaces. Samples were collected at a uniform depth of 15 cm and subjected to density separation using ZnCl₂ solution, followed by organic matter removal via Fenton oxidation. Microplastics were identified and quantified using Nile Red staining combined with fluorescence microscopy, while polymer types were determined using ATR-FTIR spectroscopy. Microplastics were detected in all soil samples, with abundances ranging from 225 to 7914 items per 50 g of dry soil, indicating widespread contamination. The highest concentrations were observed at sites associated with intensive human activities, such as construction and commercial areas, whereas lower abundances occurred in less disturbed garden, roadside, and recreational sites. Fibers, fragments, and films were the dominant MP shapes across all locations, though their relative contributions varied spatially, reflecting site-specific land use and anthropogenic pressures. The results indicate pronounced spatial heterogeneity in both the abundance and polymer composition of soil microplastics within the study area. Overall, this study highlights the strong influence of land use and human activity on microplastic contamination in soils and provides baseline data for understanding terrestrial microplastic pollution in urban-industrial regions of Türkiye.