Distribution of microplastics in soil. A case study from a Swiss agricultural field

Abstract

Most of the plastic production as well as consumption occurs on land, but the terrestrial environment has received less attention compared to marine ecosystems when it comes to research on microplastic pollution. If plastic stays in the soil for a longer period time, it starts to decompose, but the particles are rarely fully removed from the environment. Plastic fragments can later be found in the form of microplastic particles. These microplastics can change the physical structure of the native soil and limit its capacity to hold water. They also affect plants by reducing root growth and nutrient uptake. Current studies found that factors like human and biological activity, soil properties and polymer characteristics are determining the transport behaviour of microplastic particles in soil, but there is still not enough research explaining the mobility of microplastic particles. This project reviewed existing literature and summarized the already available information on the relation between soil and microplastic. The collected information contributed to the projects own study were microplastics particles from an agricultural field were researched, to understand how the particles migrate into natural soil. The project worked on the research questions: (1) If the microplastic particles can penetrate deeper soil layers. (2) If so, what factors determine the transport of the particles. The field was analysed on its pH value, elements and soil organic carbon content. An extraction of microplastic particles was done as well, however, due to machine unavailability the identification and quantification of the particles could not be completed. The results from the few samples of the field showed similar outcome as the data from studies. The properties of the microplastic particles play a big role in the distribution. Properties like density, shape, size and hydrophobicity lead to different outcomes in the particle migration. Experiments from studies showed that PE (Polyethylene) particles, which had a higher density and low hydrophobicity, were able to migrate more and reach deeper levels in the soil. This statement could be confirmed, since PE was the polymer type that was found the most in the examined field as well. The chemical and physical properties of the soil determined the behaviour of particles too. The Fe/Al oxide content in the soil increased the accumulation of particles, which could not be confirmed, based on the few samples that were completed in this project. The analysed samples confirmed that particles were able to penetrate into 90 cm deep soil layer. To sum up, the project has gathered a set of data from research and field work, which can be used for further analysis, as soon as all the samples have been identified with their microplastic particles.