Road runoff pollution by polycyclic aromatic hydrocarbons and its contribution to river sediments

Particle-bound pollutants from road runoff and their entry into the river system were investigated and compared to river bottom sediments. The intensity of rainfall is responsible for the wash load, whereas the grain size distribution is controlled by the amount of rainfall and sorting processes near the sink traps of the streets. While the concentrations of suspended heavy metals show a familiar inverse relationship to particle size both in road runoff and river bottom sediments, the situation for polycyclic aromatic hydrocarbons (PAHs) is less clear. They are bimodally distributed. In street runoff, small molecules such as three-ring PAHs tend to be enriched in the fine sand fraction. Six-ring molecules show maximum concentrations in the fine silt fraction. In addition to chemical properties, the activation of both particle and PAH sources play an important role. After the input in the river system this pattern changes again. The chemical composition and structure of organic material become more significant than the sources, whereas its amount is only of minor importance.