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Photo-Fenton treatment of tire wear particles: structural evolution, mineralization, and the kinetic bottleneck of silica fillers
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In a lab test, a strong chemical oxidation process broke down tire tread particles in water, removing over 90% of their organic material. However, the particles' silica filler did not break down, forming a shell that slowed further breakdown and kept the particles' outer size intact.
Tire wear particles (TWPs) are a major source of aquatic microplastic pollution. Because conventional wastewater treatment plants struggle to fully mitigate their continuous release, Advanced Oxidation Processes (AOPs) are increasingly investigated as advanced water treatments for their elimination. This study evaluates the degradation of cryogenic milled tire tread (CMTT) particles of a passenger car tire, a reliable TWP proxy, using a homogeneous photo-Fenton process under ambient conditions to elucidate the structural evolution and mass transfer limitations of filler-loaded elastomers. Initial characterization revealed a silica-rich matrix containing leachable organic additives, including vulcanization accelerators and antiozonants. The photo-Fenton system demonstrated high efficiency, achieving a greater than 90% organic mass reduction and an 88% total organic carbon (TOC) mineralization in 24 h. Furthermore, thermal and spectroscopic analyses of the solid residues indicated selective polymer degradation, suggesting that natural rubber (NR) being is consumed significantly faster than the synthetic rubber (SBR/BR) fraction. Kinetic analysis showed that TWP organic conversion was well described by an ash layer diffusion-controlled Shrinking Core Model. Because the highly aggregated silica filler is non-oxidizable, it accumulates as the organic rubber degrades, forming a rigid physical barrier that maintains the initial macroscopic particle size. This continuously thickening silica layer impedes intraparticle diffusion of hydroxyl radicals, making it the primary kinetic bottleneck of the system. Ultimately, while the photo-Fenton treatment successfully mineralizes the polymeric fraction of TWPs, the specific inorganic filler formulation dictates the overall oxidation rate and leaves behind a persistent silica-rich shell. Ultimately, these findings suggest that while AOPs hold potential for advanced water treatment, their overall efficiency may be constrained by the persistent inorganic filler matrix. Furthermore, the applied photo-Fenton system could serve as a complementary accelerated aging tool to help simulate oxidative weathering and better understand the long-term degradation pathways of tire wear particles in aquatic ecosystems.
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A critical review of tire wear particles aging and ecotoxicological consequences in terrestrial environments: Insights into environmentally persistent free radicals
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This review synthesizes evidence on how tire wear particles age in terrestrial environments and the resulting ecological consequences. Researchers found that UV-induced aging generates environmentally persistent free radicals and reactive oxygen species that amplify soil toxicity, while biodegradation may reduce some risks. The study highlights that characterizing aged tire wear particles remains difficult due to their compositional complexity and calls for standardized analytical methods.
A study on the aquatic degradation of tire wear particles: Impact of environmental factors and material formulations
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This study investigated how tire wear particles degrade in aquatic environments, examining the effects of environmental factors such as UV exposure and water chemistry on particle breakdown. The results showed that aquatic degradation alters tire wear particles in ways that may increase their ecotoxicological risk.
Assessing the Biodegradability of Tire Tread Particles and Influencing Factors
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Researchers tested the biodegradability of tire tread particles under natural and UV-weathered conditions, finding that biodegradation was limited and that UV weathering affected the process. Tire wear particles persist in the environment and contribute to microplastic, chemical, and particulate matter pollution.
From elastomer microstructure to thermomechanically damaged nanocomposites: an insight into the parameters influencing the biodegradability of rubbers by natural microbial consortia
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Researchers examined how the complex rubber microstructure of tire and road wear particles—including carbon black, silica, and polymer cross-links—governs resistance to biodegradation by natural microbial consortia, finding that thermomechanical damage during road use alters particle morphology but that TRWP remain largely persistent beyond two years in environmental conditions.
In Vitro Assessment Reveals the Effects of Environmentally Persistent Free Radicals on the Toxicity of Photoaged Tire Wear Particles
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Researchers examined how tire wear particles change when exposed to sunlight and found that the aging process generates environmentally persistent free radicals on their surfaces. These radicals significantly increased the toxicity of the particles in laboratory cell tests, causing oxidative stress and DNA damage. The study suggests that weathered tire particles may be more harmful than freshly released ones, adding a new dimension to microplastic pollution concerns.
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