Tyre and road wear particles (TRWP) are an important microplastics contributor to the environment, although direct observations along suggested pathways are virtually absent. There are concerns for both human health and ecosystems from TRWP exposure and leached chemicals. Due to great analytical challenges in detection and characterization, almost nothing is known about the physicochemical characteristics, occurrence, fate and transport of TRWP in the environment. Diverse tyre types exist for different seasons and vehicle profiles, and their formulations are undisclosed proprietary information.

Here we show TRWP dispersion in marine sediments, and a direct link between tyre formulation, tread hardness and TRWP emissions. Softer tyres with higher natural rubber and carbon black content generate higher particle wear. Sediment TRWP dominates the microplastics assemblage close to the city, while showing a much more steeply reducing concentration gradient with distance from the source, suggesting different transport behaviour compared to lower density microplastics. This implies that urbanized coastal ecosystems are impacted by the accumulating TRWP, with consequences for sediment ecosystems.