Martijn van Praagh

The widespread contamination of urban soils by airborne microplastics (MPs) is an emerging environmental issue, particularly in urban allotment gardens with home-grown food. This study investigates the vertical distribution of MP in three such gardens in Berlin, Germany, over 90 days. Soil samples were collected at three depths (0-1 cm, 1–15 cm, and 15–30 cm) and analyzed for MP composition and occurrence. Results showed that fibers were the dominant morphology of MPs, with the highest occurrence found in surface layers (0-1 cm). MPs amount decreased with soil depth, and fibers showed limited vertical penetration. We also identified 19 different polymer using Optical PhotoThermal InfraRed (OPTIR) spectroscopy, with polyethylene terephthalate (PET), polyester (PES), and polyethylene (PE) being the most frequent. Temporal variation in MP deposition was observed, with a significant peak at 90 days. Environmental factors, including PM2.5 concentration, precipitation, and wind velocity, played a role in MP deposition. Increased precipitation and concentration of PM2.5 explained increased MP deposition, while wind velocity was negatively correlated to MP deposition. These findings highlight the pervasive presence of MPs in urban soils and suggest that environmental conditions significantly influence MP distribution. Understanding these dynamics is essential for assessing the long-term ecological impacts of MPs on soil health in urban environments.