Distribution of microplastics in soil by types of land use in metropolitan area of Seoul

Plastic pollution is becoming a significant problem in urban areas due to excessive use and careless disposal. While studies on microplastics are increasingly being conducted across various environments, research on microplastics in soil is limited compared to other areas. Microplastics entering the soil through various routes can stay there for a long period of time, threatening soil organisms and eventually humans. Therefore, this study was carried out to investigate the distribution characteristics of microplastics according to types of land use. For this purpose, a total of 54 soil samples were collected from agricultural land, residential areas, roadsides, parks, and forests. The analysis of microplastics in the soil by stereo microscopy showed that the average numbers of microplastics (particles/kg) in agricultural land, residential areas, roadsides, parks, and forests were 5047, 3646, 4987, 2673, and 1097, respectively. Various colors (black, red, green, blue, yellow, white, and transparent) and shapes (fragment, fiber, film, and sphere) of microplastics were found in soils. The combination of black x fragment plastics showed the highest frequency. Microplastics in soil samples from agricultural land, roadside, and residential areas with sizes between 20 µm and 500 µm were determined using Fourier transform infrared spectrometer (FT-IR) and analyzed by MP finder. The number of microplastics detected in the soil with sizes ranging between 20 µm and 500 µm was in the order of roadside > residential areas > agricultural land, which was different from the results by stereomicroscopy. Polyethylene (PE), polypropylene (PP), and polymethyl methacrylate (PMMA) were detected in soils from roadsides. Polyurethane (PU), cellulose acetate (CA), polyethylene terephthalate (PET), PP, and polystyrene (PS) were detected in soils from residential areas, with PU being the most frequently detected.