Sunlight-Induced Transformation of Tire Rubber Antioxidant N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) to 6PPD-Quinone in Water

Abstract

The huge consumption of the tire rubber antioxidant N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) has resulted in pervasive contamination in aquatic environments. More importantly, the transformation product of 6PPD, i.e., 6PPD-quinone (6PPD-Q), is raising increasing concerns due to its high toxicity to aquatic organisms. However, whether and how 6PPD-Q can be formed from 6PPD in aquatic environments remain unknown. Herein, we reported the transformation of 6PPD to 6PPD-Q in water under sunlight irradiation and elucidated the underlying mechanisms. In result, the transformation of 6PPD to 6PPD-Q in water was confirmed with a noteworthy molar yield of ∼1.01% within 90 min at pH 7.0 under simulated sunlight irradiation. The experimental observations, including transient and stable intermediate identification and reactive species quenching, evidenced that the transformation pathways started with photoexcitation of 6PPD and followed by generation of hydroxyl intermediates to form 6PPD-Q. This study revealed that sunlight-induced transformation of 6PPD could be an important origin of 6PPD-Q in aquatic environments, providing significant insights to the potentially underestimated ecological risks of 6PPD.

Screening of Tire-Derived Chemicals and Tire Wear Particles in a Road Tunnel Wash Water Treatment Basin

“…23 The concentrations of 6PPD were much higher than those reported elsewhere, e.g., 300− 14 300 ng/L in a German wastewater treatment plant 26 and 21−130 ng/L in road runoff from Pierce County (USA). 27 According to Zhou et al, 28 the presence of organic matter and sunlight may enhance the formation of 6PPD-Q in a continuous manner. Hence, the high levels of 6PPD in the discharged tunnel wash water are concerning.…”

Mechanistic Aspects of Photodegradation of Deoxynucleosides Induced by Triplet State of Effluent Organic Matter

“…A Q-SUN Xe-1 sunlight simulator equipped with an 1800 W xenon lamp and an optical filter with a 315 nm cutoff was used for the irradiation experiments. The total absolute irradiance spectrum of the sunlight simulator was measured using an Ocean Optics USB-4000 spectrometer with results shown in Figure S2c. , The intensity of the simulated sunlight irradiation in the range of 315–600 nm was determined to be 5.89 × 10 –5 Einstein·L –1 ·s –1 by p -nitroanisole/pyridine (Figure S4). …”

“…The total absolute irradiance spectrum of the sunlight simulator was measured using an Ocean Optics USB-4000 spectrometer with results shown in Figure S2c. 16,23 The intensity of the simulated sunlight irradiation in the range of 315−600 nm was determined to be 5.89 × 10 −5 Einstein•L −1 • s −1 by p-nitroanisole/pyridine (Figure S4). 24 Eighteen milliliters of solution containing 10 μM of each deoxynucleoside and 5.0 mg C •L −1 of EfOM or SRNOM was irradiated in a capped quartz container under simulated solar irradiation from the top xenon lamp (Figure S3).…”

Synthetic Antioxidants as Contaminants of Emerging Concern in Indoor Environments: Knowns and Unknowns

“…14,18 Recently, a few studies have elucidated the underlying phototransformation mechanisms of several OPAs and 6PPD through in-lab simulation. 65,66 However, the transformation products of most synthetic antioxidants have not been explored, which requires further study. Identifying novel contaminants from secondary sources (transformation products) in indoor dust is a significant challenge due to chemical and matrix complexity.…”

“…Previous studies have demonstrated that indoor dust contains only low concentrations of AO168. By contrast, very high concentrations of tris­(2,4-di- tert -butylphenyl) phosphate (AO168O), which is the oxidation product of AO168, have been observed in indoor dust. , The transformation products of synthetic antioxidants can be more toxic than their corresponding parent chemicals, particularly quinones such as BHT-Q and 6PPD-Q (derived from BHT and 6PPD, respectively). , Recently, a few studies have elucidated the underlying phototransformation mechanisms of several OPAs and 6PPD through in-lab simulation. , However, the transformation products of most synthetic antioxidants have not been explored, which requires further study. Identifying novel contaminants from secondary sources (transformation products) in indoor dust is a significant challenge due to chemical and matrix complexity.…”