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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.
Tire wear particles (TWP) have been identified as one of the major sources of microplastics (MPs), and few studies have focused on their environmental behaviors and impacts. However, a thorough characteristic and toxicity assessment associated with environmentally persistent free radicals (EPFRs) on the photoaged TWP is missing. In this study, we investigated EPFRs in the process of TWP photoaging and evaluated their toxicity using in vitro bioassays. Our results showed that a total of around 1.0 × 1017 spins/g EPFRs (g-factors ranging 2.00308-2.00318) was formed on TWP with 60 days of light irradiation, which contained more than 29% of reactive EPFRs (r-EPFRs). Using macrophages as model cells for bioassays, TWP-associated EPFRs trigged endpoints, including the decrease of cell viability (27 to 45%) and the increase of oxidative stress response (46-93%) and inflammatory factor secretion. The enhancement of TWP toxicity with photoaging was confirmed to be attributed to the generated EPFRs combined with other TWP's chemical compositions (e.g., various metals and organics). Most importantly, the toxicity of photoaged TWP was closely correlated with the generated r-EPFRs, which induced reactive oxidant species (ROS) generation. This study provides direct evidence of toxicity on the photoaged TWP particles, revealing the potential contributions of EPFRs to the adverse effect on human health and highlighting the need for an improved understanding of the impacts of EPFRs on the risk assessment of TWP released into the environment.
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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.
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Tire wear particles, a common type of microplastic found on roads and in waterways, become more toxic after exposure to sunlight. This study found that sunlight-aged tire particles generate persistent free radicals that damaged the nervous system of test organisms, reducing movement and lowering levels of key brain chemicals like dopamine and serotonin. These findings suggest that weathered tire particles may pose a greater neurotoxic risk than fresh ones.
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Researchers reviewed how environmental aging — via photooxidation, mechanical abrasion, and biodegradation — transforms tire wear particles by increasing surface area and polarity, promoting additive leaching and the formation of reactive free radicals, collectively amplifying ecological toxicity beyond what fresh particles alone would cause.
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Researchers examined how UV exposure and natural aging change the ability of tire wear particles to release polycyclic aromatic hydrocarbons in soil. They found that UV aging increased the surface reactivity of the particles and altered how readily these toxic compounds could be absorbed by living organisms. The study suggests that weathered tire particles in roadside soils may pose greater health risks than fresh ones.
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