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Toxic effects of environmentally persistent free radicals (EPFRs) on the surface of tire wear particles on freshwater biofilms: The alleviating role after sewage-incubation-aging
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Researchers investigated how tire wear particles affect freshwater biofilms, which are communities of microorganisms that play important roles in aquatic ecosystems. They found that reactive chemical compounds on the surface of fresh tire particles caused significant toxicity, reducing photosynthesis and biological activity in the biofilms. The study suggests that aging in sewage environments reduces the toxicity of tire wear particles by breaking down these harmful surface chemicals.
The aquatic ecological risks posed by the surface-active components of tire wear particles (TWPs) are not fully understood. This study aimed to determine the acute (24 h exposure) aquatic toxicity effects of TWPs on freshwater biofilms in terms of total organic carbon (TOC), chlorophyll-a (Chl-a) abundance, quantum yield ( ФM ), and adenosine triphosphate (ATP). Three types of TWP were tested: TWPs produced via the typical wear of tires and roads (i.e., rolling friction (R-TWPs) and sliding friction (S-TWPs)) and cryogenically milled tire treads (C-TWPs). The results showed that the surface structural properties of the three TWPs differed significantly in morphology, bare composition, functional groups, and surface-active components (environmental persistent free radicals). The exposure of biofilms to the TWPs increased TOC and ATP at low concentrations (1 mg L −1 ) but inhibited them at high concentrations (50 mg L −1 ). All TWP types inhibited biofilm photosynthesis (reduced Chl-a and ФM ) and altered the community structure of algae to varying degrees; in addition, the toxicity mechanisms of the TWPs contributed to the accumulation of reactive oxygen species and cell membrane (or cell-wall) fragmentation, leading to lactate dehydrogenase release. S-TWPs were the most toxic because their surface carried the highest environmental persistent free radicals . R-TWPs were the second most toxic, which was attributed to their smaller particle size. The toxicity of all TWPs was tested after sewage incubation aging. The results showed that the toxicity of all TWPs reduced as the sewage covered their surface components and active sites. This process also reduced the differences in toxicity among the TWPs. This study filled a research gap in our understanding of aquatic toxicity caused by the surface structural properties of tire microplastics and has implications for the study of microplastic biotoxicity mechanisms. • Pristine surface properties of TWPs are tire and road wear conditions-dependent • TWPs can inhibit the photosynthetic system of freshwater biofilms even at 1 mg L −1 • The surface EPFRs of TWPs are the main cause of their acute biofilm toxicity • Sewage aging can cover and shield the active EPFRs on the surface of TWPs
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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.
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.
Electrochemical-oxidative dualism: Decoupling the acute effects of lake water-aged tire wear particles on periphytic biofilm-mediated denitrification
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This study examined how freshly generated and lake water-aged tire wear particles (TWPs) of different types affect denitrification in periphytic biofilms. Neither fresh nor aged TWPs altered nitrate removal or denitrification gene abundance, despite aging increasing the electron exchange capacity and free radical content of particles.
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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Researchers found that environmental aging of tire wear particles increases their toxicity to marine microalgae beyond that of fresh particles, with aged particles triggering greater oxidative stress, photosynthesis disruption, and metabolic changes in the algae.
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