Is road pavement wear a source of microplastics in stormwater runoff?

Urban stormwater runoff is a major route by which microplastics are spread in the environment. This environmental compartment includes various sources of microplastics such as atmospheric deposition, plastic litter, paints, building materials, and textiles. Another source of microplastics in stormwater is tire wear, which is often included together with road wear despite the latter's unknown contribution of microplastics. Pavements like concrete and asphalt have plastic polymers incorporated in them in order to improve their physical performance. Waste plastics like crumb rubber and microfibers have been used in asphalt and concrete pavement mixes instead of virgin plastics as a sustainability practice. However, pavement becomes abraded and worn over time from weathering and traffic exposure which generates tire and road particles. In this study, three parking lots and one road within the same conservation facility in Ontario, Canada that were made of asphalt, concrete, and recycled rubber were sampled for stormwater and for pavement specimens. Pavement specimens underwent specialized testing with a Hamburg Wheel track test to simulate tire abrasion. The chemical signature of pavement abrasion effluent was also evaluated. It was found that asphalt generated the most microparticles in stormwater with a median above 600 microparticles/L compared to concrete which had 216 microparticles/L and rubber with 115 microparticles/L. Pavement testing which isolated the effect of pavement degradation from other environmental factors, however found that rubber pavement released the most microparticles. Many types of plastics were identified with ATR-Fourier Transform Infrared spectroscopy from each pavement type including in particular polyester and rubber-associated plastics. The chemical signature of pavement abrasion effluent varied between pavement types. Our work demonstrates the need to consider microplastics generation during the selection of pavement additives and the choice of pavement types for different traffic loads. Also see: https://micro2024.sciencesconf.org/558531/document