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Reclaimed water in road cleaning: An unrecognized risk for toxic 6PPD-Q formation from tire wear waste
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Researchers found that washing roads with reclaimed water instead of rainwater accelerates the aging of tire wear particles and significantly increases conversion of the tire additive 6PPD into its more toxic transformation product 6PPD-quinone, suggesting that urban water reuse practices may inadvertently amplify the release of a compound acutely lethal to coho salmon.
Tire wear particles (TWPs) are a major source of microplastic pollution, particularly due to toxic additives like N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its transformation product, 6PPD-quinone (6PPD-Q). However, the mechanisms governing 6PPD transformation in TWPs are not yet fully understood. This study investigates photo-aging of TWPs as solid waste under simulated road conditions, focusing on how reclaimed water versus rainwater influences aging and 6PPD/6PPD-Q release. Sunlight and road exposure altered TWPs properties, characterized by surface fragmentation, increased hydrophilicity, and oxygen-containing functional groups. Following three weeks of aging in reclaimed water, the carbonyl index (CI) and hydroxyl index (HI) increased by 323.75% and 72.82%, respectively. The surface O/C ratio rose from 0.149 in pristine TWPs to 0.207 in the reclaimed water group and 0.161 in the rainwater group. This oxidation process was also accompanied by an increased abundance of reactive oxygen species. Under reclaimed water aging conditions, the concentrations of O, O, and •OH increased significantly by 82.95%, 33.72%, and 6.69%, respectively. Leaching experiments revealed a gradual decrease in 6PPD concentration during aging, accompanied by a significant increase in its conversion product 6PPD-Q. Pearson analysis revealed strong positive correlations between 6PPD-Q formation and C=O (r = 0.65, p = 0.003), O (r = 0.44, p = 0.031), and •OH (r = 0.65, p = 0.01). These findings indicate that tire wear solid waste management is highly sensitive to external conditions, with reclaimed water in road cleaning promoting 6PPD-Q formation. This underscores the need to reassess water reuse practices in urban maintenance to mitigate hazardous emissions.
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The Tire Wear Compounds 6PPD-Quinone and 1,3-Diphenylguanidine in an Urban Watershed
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Researchers re-analyzed archived water samples from an urban Canadian river and detected the tire-wear chemical 6PPD-quinone at concentrations exceeding the lethal threshold for coho salmon during storm events, confirming that tire-derived contaminants enter urban waterways in kilogram-scale loads during rainfall.
Treading Water: Tire Wear Particle Leachate Recreates an Urban Runoff Mortality Syndrome in Coho but Not Chum Salmon.
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Leachate from tire tread wear particles was found to cause acute mortality in coho salmon following rain events, reproducing the 'urban runoff mortality syndrome' seen in wild fish — while chum salmon were unaffected. The responsible chemical was identified as 6PPD-quinone, a tire additive, demonstrating that microplastic-related chemical leachates can devastate specific wildlife populations.
Spatiotemporal distribution and environmental risk assessment of 6PPDQ in the Schuylkill River
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Researchers tracked a toxic chemical called 6PPDQ, which forms when a common tire additive reacts with ozone, in the Schuylkill River in Pennsylvania. The chemical, carried by tire wear particles and microplastics, was found at levels that could harm aquatic life, particularly species like coho salmon. This study highlights how tire-derived microplastic pollution introduces dangerous chemicals into freshwater systems that communities rely on.
Environmental impact of tire and road wear particle residue on gammarids and potential ecological consequences
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Researchers investigated the ecotoxicological effects of tire and road wear particles (TRWPs) on freshwater gammarids, finding toxicity from both physical particle effects and leachable compounds including 6PPD-quinone. Combined chemical and physical exposure produced greater harm than either alone, with implications for stormwater runoff management.
Environmental and Human Health Risks of 6PPD and 6PPDQ: Assessment and Implications.
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This review synthesized current knowledge on 6PPD and its tire-derived quinone derivative 6PPDQ, focusing on their environmental distribution, transformation, human exposure pathways, and ecological toxicity. The authors found that 6PPDQ in particular poses significant risks to aquatic organisms, including coho salmon.
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