Evaluating a novel high-resolution X-ray computed tomography method for quantifying tire and road wear particle morphology.

Tire and road wear particles (TRWP) are the largest source of microplastics in terrestrial environments and accumulate particularly in roadside soils. Despite growing recognition of their ecological impacts, their internal structure remains poorly understood. We present a novel workflow for isolating and three-dimensionally characterizing environmentally derived TRWP using high-resolution X-ray micro-computed tomography (µCT). Roadside soils collected adjacent to national roads in central Germany underwent sequential density separation. Three TRWP identified by optical microscopy and two artificial tire wear particles were analyzed by µCT at 0.97 µm voxel resolution, enabling quantification of surface, volume, and pore-network morphology. Particles showed highly heterogeneous structures, ranging from dense and compact to extremely porous. Particle volume (0.011-0.042 mm³) and surface area (0.342-0.924 mm²) varied relatively little due to particle selection, whereas porosity, dominated by pores < 10 µm, ranged from 1.85 to 49.97%, including internal and external pores. Some particles displayed density gradients and denser outer layers, likely reflecting mineral incorporation. TRWP generally exhibited more complex surface textures than artificial particles. These results demonstrate µCT as a powerful tool for revealing TRWP internal architecture, improving morphological characterization and understanding of environmental behavior, potential microbial habitats, and long-term additive release in soil ecosystems.