The soils of a high-traffic roadside ditch as a receptacle of macro-litter and microplastics

As urban roads represent a significant aspect of human activity, evaluating their impact as a source of macro-litter and microplastics is necessary to better understand plastic transfer in continental environments. In particular, the role of urban runoff in microplastic infiltration through soils remains to be assessed. One way to estimate the input of microplastics via road activity and determine the role played by urban runoff in their transport, is to focus on an infiltration ditch on the side of a road. In this study, the accumulation of macro-litter and the potential accumulation of microplastics in the soil of a seepage ditch on the side of a high traffic suburban road in the Parisian region were assessed. In addition, microplastic concentrations were measured at various depths in order to identify the role of infiltration as a pathway for microplastics. In order to study macro-litter, samples were collected along the edge of the ditch over a period of 8 months. Collected samples were weighed and characterized by composition and function. In the second half of 2021, an accumulation of 160 kg/km/year was estimated. This accumulation seems to be a combination of a continuous, diffuse input and the influence of a few specific and local events such as car accidents. In order to characterize microplastic infiltration in the ditch, soil samples were collected by manually coring at a depth up to 30 cm. A total of 10 cores were collected, each core was separated by depth into 4 samples at [0-5[, [5–15[, [15–25[, [25–35[ cm. After collection, microplastics were isolated from the samples and fully analysed using an automated Fourier Transform Infrared micro-Spectroscopy mapping analysis. Preliminary results show median microplastic concentrations of 24.6 MP/g in in the surface, versus 11.2 MP/g in the deeper layers, suggesting a limited infirltration. Also see: https://micro2022.sciencesconf.org/427070/document