Plastic is an indispensable material essential for modern human life. With highly increasing demand for plastic use, however, environmental contamination by plastic litters has become an emerging issue. Globally, large quantity of used plastics is landfilled or emitted directly to the aquatic and terrestrial environments, albeit a part of the plastics is recycled or incinerated as energy source. In particular, microplastic debris that are smaller than 5 mm are considered to be emerging contaminants of global concern. In the past decade, however, most of the researches on impacts of microplastic contamination have been focused on the marine ecosystem, whereas very limited ones on the terrestrial ecosystem. Soil can be considered as a major sink and a carrier of microplastic contaminants to the aquatic environment. Most sources of microplastics in the soil environment are entered via a variety of routes and subsequent fragmented and spread to the surrounding environments, vertically and horizontally. In addition, there are negative impacts on soil biota, which in turn would cause concerns of human health by affecting the food web. Here, we provide an overview of characteristics, research trend, analytical methods, migration and degradation processes, effects on soil biogeochemistry, and interaction with soil organisms of microplastics suggesting the importance of ongoing research impacts of microplastics on the terrestrial ecosystem.

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.

Urban agriculture has been recently highlighted with the increased importance for recreation in modern society; however, soil quality and public health may not be guaranteed because of continuous exposure to various pollutants. The objective of this study was to evaluate the soil quality of urban agriculture by soil microbial assessments. Two independent variables, organic and inorganic fertilizers, were considered. The activities of soil enzymes including dehydrogenase, β-glucosidase, arylsulfatase, urease, alkaline and acid phosphatases were used as indicators of important microbial mediated functions and the soil chemical properties were measured in the soils applied with organic or inorganic fertilizer for 10 years. Fatty acid methyl ester analysis was applied to determine the soil microbial community composition. Relatively higher microbial community richness and enzyme activities were found in the organic fertilizers applied soils as compared to the inorganic fertilizers applied soils. Principal component analysis explained the positive influence of organic fertilizers on the microbial community. The application of organic fertilizers can be a better alternative compared to inorganic fertilizers for the long-term health and security of urban agriculture.