Microplastics in road runoff: occurrence, properties and transport modelling

Almost 10 % of the annual production of plastics ends up in our oceans. As a result, microplastics (MP) have been detected in organisms at all levels of the marine food chain. It is estimated that 70–80 % of marine MP originates from land-based sources, transported mainly via rivers. Studies on MP in freshwater are just starting to emerge, and observations of MP are alarming as we are dependent on freshwaters for drinking water and food production. An inventory of MP sources in the Swedish environment identified surface runoff from urban areas as a major pathway. The major contributors to MP in urban runoff are traffic-related. However, there are very few reports on MP in road runoff and in stormwater systems. This project aims at closing the knowledge gap on the occurrence and characteristics of MP in road runoff, and on the fate of MP in stormwater systems and transport to receiving waters. Through collection and analysis of runoff and sediment from different road surfaces, abundance and properties of road-related MP are investigated. The results are used to develop a model that describes the transport of MP from roads, through open stormwater systems and closed sewers, to receiving surface waters. This will give us understanding of where in the stormwater system or receiving waters MP tend to accumulate, as well as where in the system and which mitigation measures should be implemented to efficiently decrease the input of MP from road runoff to the water environment.