Nontargeted Screening Unveils Structural Diversity and Environmental Pervasiveness of p-Phenylenediamine Antioxidant-Derived Quinones: Evidence from End-of-Life Tires and Road Dust Contamination

The environmental occurrence of toxic p-phenylenediamine antioxidant-derived quinones (PPD-Qs) is closely correlated with the emission of rubber from tire wear. The nontargeted screening of tire particles can facilitate the early identification of unknown or unrecognized PPD-Qs of concern in the environment. Here, we performed targeted and nontargeted screening for potential PPD-Qs in end-of-life tires and verified the presence of newly identified PPD-Qs in environment samples. In 20 end-of-life tires, seven target PPD-Qs were detected, with the total concentration range of 9.30 to 95.0 μg/g, in which N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone (6PPD-Q), N,N′-di(o-tolyl)-p-phenylenediamine quinone (DTPD-Q), and N,N′-diphenyl-p-phenylenediamine quinone (DPPD-Q) were dominant. Using a characteristic fragment-based nontargeted screening strategy, a novel PPD-Q, N-phenyl-o-tolyl-N′-phenyl-p-phenylenediamine quinone (PTPD-Q), three PPD-Q structural isomers with a 2,5-diamino-1,2-benzoquinone skeleton structure, and a diphenylamine ring cleavage product of 6PPD were first identified and/or confirmed in tire particles. In particular, PTPD-Q was abundant in urban road dust, with a detection frequency of 93% and a median concentration (5.07 ng/g) comparable to that of DTPD-Q (5.56 ng/g). In combination with predicted data using the EPI Suite tool and the reported experimental evidence, PTPD-Q may persist in the environment and exhibit toxicity to aquatic organisms while also having a low bioaccumulation potential. Correlation analysis and a degradation experiment indicated that PTPD oxidation was one source of PTPD-Q. This study provides first evidence on the ubiquitous presence of PTPD-Q in the environment and encourages researchers to take quick action to understand its environmental behavior, fate, and potential risk.