Impact of 6PPD-quinone: The Urgent Need for Action and Safer Alternatives
All human actions, from constructing cities, growing crops, or manufacturing goods, have a complex web of interactions with the environment. Thousands of chemicals and their derivatives are released into the environment, yet most of them are unknown and do not have detailed information on their toxicity. Recent research into the newly identified pollutant, 6PPD-quinone (6PPD-Q), has brought attention to its alarming effects, including its ability to rapidly kill coho salmon and its potential risks to fetal development in pregnant mice through placental transfer.
These findings emphasize the urgent requirement for additional research into the environmental and physiological impacts of 6PPD-Q, alongside the implementation of regulatory procedures and source management. 6PPD-Q is a derivative of the chemical 6PPD (N-(1,3-dimethylbutyl)-N'-phenyl-p- phenylenediamine), commonly used in tyre manufacturing to protect against environmental degradation. 6PPD is used in tyres at concentrations ranging from 0.4% to 2% by mass, gradually diffuses within rubber materials, and becomes available for gas-phase reactions upon exposure.
During tire wear, 6PPD reacts with oxidants like ozone (O3), and it forms 6PPD-Q, a potentially harmful byproduct released into the environment, eventually finding its way into water bodies through rainfall runoff. Estimations indicate that the annual generation of 6PPDQ resulting from tyre tread wear in the United States may range from 26 to 1900 metric tons. This signifies a notable environmental discharge that requires further attention and mitigation strategies. In response to these concerns, there is a critical need to pursue the development of substitute antioxidants that are safe for both human health and the environment. The U.S. Tyre Manufacturers Association (USTMA) has identified five possible alternatives to 6PPD that warrant further evaluation, highlighting the importance of ongoing research and development efforts in this area.
In addition to the development of alternative antioxidants, increasing attention is being directed towards the development of removal technologies to address the environmental impact of 6PPD-Q. These technologies are aimed at reducing the concentration of 6PPD-Q in water bodies and alleviating their detrimental effects on aquatic ecosystems and human health. One promising approach involves adsorption, wherein 6PPD-Q molecules are attracted and adhered to the surface of adsorbents, such as magnetic single-layer nano-MXene. Moreover, ongoing research is exploring innovative approaches for the removal of 6PPD-Q, with a particular focus on advanced oxidation processes. These processes utilize highly reactive oxidizing species to degrade pollutants and render them less harmful to the environment.
Overall, the development of effective removal technologies for 6PPD-Q and other pollutants is imperative for safeguarding aquatic ecosystems and protecting human health. By implementing these technologies, we can significantly reduce the concentration of pollutants in water bodies, thereby mitigating their adverse impacts on the environment. Furthermore, research and development efforts in this field will drive innovation and enhance the efficiency of removal technologies, further advancing the protection of aquatic ecosystems and human well-being.
Reference
Lo, B.P., Marlatt, V.L., Liao, X., Reger, S., Gallilee, C., Ross, A.R.S. and Brown, T.M. (2023), Acute Toxicity of 6PPD-Quinone to Early Life Stage Juvenile Chinook (Oncorhynchus tshawytscha) and Coho (Oncorhynchus kisutch) Salmon. Environ Toxicol Chem, 42: 815-822.
Transformation Product Formation upon Heterogeneous Ozonation of the Tire Rubber Antioxidant 6PPD (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine), Ximin Hu, Haoqi Nina Zhao, Zhenyu Tian, Katherine T. Peter, Michael C. Dodd, and Edward P. Kolodziej, Environmental Science & Technology Letters 2022 9 (5), 413-419,