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Global Occurrence and Ecological Risk Assessment of 6PPD and 6PPD-Quinone: Derivation of PNECs Using Species Sensitivity Distribution
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The tire-derived chemical 6PPD-quinone poses significantly greater ecological risk than its parent compound 6PPD, with mortality-based risk probabilities reaching 11.4% globally and lethal thresholds for salmonids in the nanogram-per-liter range. As a transformation product of tire rubber that co-occurs with tire wear particles and microplastics in roadway runoff, 6PPD-Q represents a high-priority emerging contaminant threatening aquatic biodiversity.
Tire antioxidant N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) and its transformation product 6PPD-quinone (6PPD-Q) have recently been recognized as emerging contaminants of global concern due to their widespread occurrence and high toxicity to aquatic organisms. Although the rapidly accumulating monitoring and toxicological data suggesting substantial ecological risks, a quantitative and cross-species assessment framework remains lacking. Here, we compiled 77 reported concentration records of 6PPD and 6PPD-Q from 21 studies worldwide and assembled 991 toxicity endpoints across 34 species to derive Predicted No-Effect Concentrations (PNECs) by species sensitivity distributions (SSDs) and probabilistic ecological risk estimates. Both compounds were ubiquitously detected in surface waters, with 6PPD-Q frequently exceeding the concentration of its parent compound. Salmonids exhibited exceptional sensitivity to 6PPD-Q, with lethal thresholds in the nanogram-per-liter range, whereas tolerance varied markedly among non-salmonid taxa. Model-averaged SSDs yielded mortality-based hazardous concentrations for 5% of species (HC5) of 24.3 µg/L for 6PPD and 0.0559 µg/L for 6PPD-Q, corresponding to PNECs of 4.87 and 0.0112 µg/L, respectively. Probabilistic risk characterization indicated negligible global risk for 6PPD, whereas 6PPD-Q exhibited elevated risk potential, with mortality-based overall risk probabilities reaching 11.4%. Risk levels followed the pattern of surface runoff > river waters > wastewater effluent, and were higher in North America and Europe than in Asia. Regional differences in species sensitivity and environmental exposure contributed to substantial uncertainties, underscoring the need for localized PNEC derivation and expanded toxicity datasets, particularly for transformation products. This study provides the first integrated global SSD-based benchmarks for 6PPD and 6PPD-Q, offering a quantitative foundation for monitoring, regulation, and ecological protection of tire-derived contaminants.
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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.
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.
Not Just a Fish Killer: Multi-Organ Toxicity and Mechanisms of 6PPD-Quinone
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6PPD-Quinone, a rubber tire antioxidant byproduct found in stormwater runoff, causes multi-organ toxicity across species via oxidative stress, inflammation, and metabolic disruption—and has now been detected in human urine. As a tire-derived contaminant closely linked to microplastic pollution from road wear particles, 6PPD-Q represents an emerging chemical hazard requiring urgent regulatory attention.
Comprehensive review on environmental pollution caused by 6PPD-quinone and remediation strategies
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A comprehensive review of 6PPD-quinone — a tire wear chemical that causes mortality in coho salmon — surveys its environmental fate, bioaccumulation through the food chain, and potential remediation strategies including alternative antioxidant compounds and nano-modified materials. Tire wear particles are a major source of microplastic pollution, and understanding toxic co-chemicals like 6PPD-quinone is essential for assessing the full health burden of tire-derived microplastic contamination.
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This review examines 6PPD, a rubber tire antioxidant, and its toxic transformation product 6PPD-quinone, which has been detected in air, water, and dust and shown to cause developmental, reproductive, neurological, and genetic harm to organisms at environmentally relevant concentrations.
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