The Scale and Distribution of Microplastic Pollution in the Soils of a UK Urban Woodland

There is increasing evidence for the presence of microplastics within terrestrial soils, but little is known about their distributions at smaller spatial scales. This study investigated the small-scale distribution and characteristics of microplastics (500 µm—5 mm) in Epping Forest, an ancient woodland in London, UK. Soil samples were taken along transects within an open area and an adjacent forested area, at depths of 0–5 cm and 5–10 cm. Microplastics were found in all soil samples. Surface soil microplastic concentrations were significantly higher (p = 0.004) in the forested area (350—8000 particles kg−1; mean 2937 particles kg−1) than in the open area (133—900 particles kg−1; mean 543 particles kg−1) and exceed those that have been reported in more remote locations, as well as some agricultural soils. Elevated microplastic concentrations deeper into the forest suggest that this sheltered environment creates a preferential accumulation zone, whereas no clear spatial pattern was found in the open area. No significant difference in microplastic concentrations was found between soil depths. In both areas, fibres were the most common microplastic shape, and larger size classes (3–5 mm) were most abundant. Polyethylene terephthalate (PET) was the most common polymer identified by micro-FTIR analysis. Recreation, littering and diffuse atmospheric deposition are thought to be the main sources of microplastic pollution within the study area. These data represent, to our knowledge, the first recorded presence of microplastic pollution within UK woodland soils, and demonstrate that urban forest soils could represent significant sinks for microplastic pollution.