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Current Status and Treatment Methods for the Emerging Trace Contaminant 6PPD-Q
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This review summarizes existing research on 6PPD-Q, a chemical formed from a tire rubber additive that can wash into waterways and persist there. It describes how the chemical forms, and compares chemical, biological, and adsorption methods studied for removing it from water.
The increasing global generation of tire wear particles (TWPs) has raised growing concerns regarding TWP-derived contaminants as important non-point source pollutants. Among these contaminants, N-(1,3- dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD), an antioxidant widely used in rubber products such as tires, and its oxidative transformation product, 6PPD-quinone (6PPD-Q), have attracted considerable attention because of their environmental occurrence, fate, and toxicity. This review provides a comprehensive overview of the environmental transformation pathways of 6PPD, the occurrence and fate of 6PPD-Q, and recently reported removal technologies. As a p-phenylenediamine (PPD)-type antioxidant, 6PPD preferentially reacts with ozone because of its low ionization potential, thereby protecting the olefinic double bonds in the rubber matrix from oxidative degradation. This transformation can occur through heterogeneous reactions on tire surfaces as well as photochemical and oxidative processes involving TWPs in aquatic environments. The resulting 6PPD-Q can be transported into aquatic systems via stormwater runoff and may persist and disperse in the environment because of its relatively high chemical stability. Reported removal technologies for 6PPD-Q can be broadly classified into chemical treatment, biological treatment, and adsorption processes. Chemical treatment relies on reactive species to degrade 6PPD-Q through structural transformation, including quinone-ring modification and C–N bond cleavage. Biological treatment involves the transformation and removal of 6PPD-Q through enzyme-mediated metabolic processes in microorganisms and plants, whereas adsorption using porous materials removes 6PPD-Q through interactions such as π–π interactions, hydrogen bonding, and coordination bonding. Future research should focus on developing treatment technologies that can be integrated with existing wastewater treatment systems while remaining economically feasible, together with long-term monitoring to better understand the environmental occurrence, transport, and fate of 6PPD-Q.
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Occurrence and hydrolytic stability of emerging tire wear contaminants in environmental waters and soils: A case study from northern Poland
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This study tested water and soil samples in northern Poland for chemicals that come from tire wear, including 6PPD-Q. The chemical 6PPD-Q was found in all water samples and was assessed as posing high ecological risk at every site tested.
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.
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 Occurrence, Influencing Factors, and Toxic Effects of 6PPD-Q
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Researchers reviewed the environmental distribution and toxicological effects of 6PPD-quinone (6PPD-Q), a tire antioxidant transformation product released with tire and road wear particles, finding it is ubiquitous across atmospheric, aquatic, and terrestrial compartments, bioaccumulates, and poses significant health risks through multiple exposure pathways, while proposing a source-reduction management framework.
Review of 6PPD-quinone environmental occurrence, fate, and toxicity in stormwater
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This review comprehensively assessed 6PPD-quinone, a toxic transformation product of a common tire rubber antioxidant, examining its environmental occurrence in stormwater, environmental fate, and toxicity to aquatic organisms and potential human health impacts.
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