Hydrophilicity and Material Type Govern the Aqueous Release of Rubber-Derived Chemicals: Insights from Extractables and Leachables of Road-Related Materials

Rubber-derived chemicals (RDCs) are primarily released into the environment from tires, posing significant risks to the ecosystem. However, there is limited knowledge about the emerging RDC components and release from a broader range of road-related materials. In the current study, we performed a comprehensive investigation into the RDC formulations and leaching behaviors of six road-related materials. The mass fraction in extractables followed the descending order: tires (average ∑35RDC 1080 μg/g) > speed bumps (90.3 μg/g) > traffic cones (37.4 μg/g) > water pipes (4.25 μg/g) > asphalt concrete (0.37 μg/g) > foam boards (0.33 μg/g). N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, 1,3-benzothiazole, and N,N′-dicyclohexylurea emerged as the top three RDCs. While RDCs in leachables exhibited lower levels, the average leaching ratios from tires, speed bumps, water pipes, and asphalt concrete into rainwater exceeded 65%, indicating substantial leaching potential. The hydrophilicity (log KOW) of RDCs played a key role in their leaching behavior, with compounds exhibiting lower log KOW values demonstrating higher leaching efficiency. The annual emissions of tire wear particles and RDCs thereof in China were estimated at 1,282,537 and 1385 tons, respectively. Our study illustrated that road-related materials are crucial contributors to urban RDC pollution, highlighting the urgent need for developing environmentally friendly materials.