Abundance, distribution, and ecological risks of microplastics in urban and agricultural topsoil of Mian-Ab Plain, Iran

Although the presence of MPs in the environment has been widely studied, their spatial distribution, polymer types, and potential health risks in arid agricultural soils remain underexplored, particularly in Middle Eastern regions. This study provides a comprehensive analysis of MPs using visual, SEM–EDS, and Raman techniques, and introduces the first GIS-based mapping of MP contamination in an arid plain in Iran. In this study, composite soil samples (n = 102) were collected from the rural and agricultural areas. A combination of visual observations by stereo-microscopy, scanning electron microscopy (SEM) – Energy-dispersive X-ray spectroscopy (EDS), and Raman micro-spectroscopy was conducted to quantify and characterize MPs in soil samples. The spatial distribution of MPs was analyzed using the Inverse Distance Weighting (IDW) interpolation method in GIS, which revealed distinct contamination hotspots. The IDW results indicated that urbanized regions, particularly S9, S6, and S11, exhibited the highest MPs concentrations, while lower levels were detected in predominantly agricultural zones (S10, S12, and S5). The total MPs loading in the studies soil was 11.93 ± 0.9 items kg⁻1of surface soil. The MPs had various morphologies (fiber, pellet, fragment, and spherule shapes), colors (white-transparent, yellow-orange, red-pink, blue-green and black-grey colors), and sizes (< 100 µm up to ≥ 1000 µm). Black-grey fibers in size less than 100 μm were the dominant MPs in soil samples. SEM–EDS analysis revealed trace elements (C, N, O, Na, P, Si) on MP surfaces, indicating possible pollutant adsorption. Identified polymers (PET, PS, PP, Nylon) suggest mixed domestic and agricultural sources. The Hazard Index (HI) was at risk level III (10 ≤ HI < 100), and the PLI index showed moderate pollution (class III). Estimated ingestion exposure indicated higher risk for children (0.871 MPs/year) than adults (0.435 MPs/year). These findings underscore the need for better waste management and reduced plastic use in agriculture to limit soil contamination and exposure risks.