Retention of microplastic particles in road side ditches

This thesis is about microplastics. The first part studies at the possibility of using fluorescent staining as a method for identifying and quantifying microplastics from car tyres. Part two examines the ability of different ditch materials to retain microplastic. Here materials from the existing road ditch along Drøbakveien in Ås, and materials that correspond to requirements from the Norwegian Public Roads Administration, will be used. In this part of the thesis, the fluorescent microplastic particles from part one will be utilised. In order to answer to the research questions, an extensive literature study on microplastics, drainage systems and retention of microplastics in ditch materials, were conducted. Subsequently, experiments to stain particles from car tyres, and testing of ditch materials with particle suspension were conducted. Microscopy has also been a part of the process of analysing the results. For part one of the thesis, it quickly became clear that black particles from car tyres were not possible to fluoresce. The results indicate that the dye itself attaches to the particles, but that it is still impossible to see them in the fluorescent microscope. This may be due to the colour or density of the particles. For part two of the thesis, it was possible to see high retention of microplastic in materials from both existing and constructed road ditches. This result is based on an estimate of both inlet and outlet concentrations from the ditch materials. Here, there may be some margin of error in the estimates, but essentially the results will be representative of realistic results.