Rapid urbanization drives increased emission of tire wear particles (TWPs) and the contamination of a transformation product derived from tire antioxidant, termed as N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone (6PPD-Q), with adverse implications for terrestrial ecosystems and human health. However, whether and how 6PPD-Q could be formed during the aging of TWPs in soils remains poorly understood.
In a study recently published in Environmental Science & Technology (2023, 57(14): 5978–5987), a research team led by Prof. ZHU Yong-Guan and AP LI Gang from the Institute of Urban Environment, the Chinese Academy of Sciences reported that the iron (Fe) reduction and TWP-harbored environmentally persistent free radicals (EPFRs) can facilitate 6PPD-Q formation during TWP aging processes in flooded soils.
The researchers observed an enhanced accumulation of 6PPD-Q in both sterilized and non-sterilized anaerobic flooded conditions during the 60- day TWP aging processes in soils, with a ~3.8-fold higher accumulation of 6PPD-Q in flooded soils than wet soils.
The researchers found a good correlation between the reduction from Fe(III) to Fe(II) and the transformation from 6PPD to 6PPD-Q under anaerobic conditions, which disappeared under the same conditions but with sterilization as pretreatment. The microbial iron reduction coupling 6PPD degradation was further verified as a plausible pathway for the biotic 6PPD-Q formation in flooded soils.
Combining with the uses of different reactive free radicals (ROS) quenchers, the researchers further pointed out that anaerobic flooded conditions were conducive to the EPFRs-induced formation of superoxide radicals (O2.-), which can further drive the abiotic formation of 6PPD-Q.
This work provides a plausible explanation for the occurrence of 6PPD-Q in anaerobic environments, such as flooded soils, sediments, and natural waters, and would be helpful to expand our understanding of the potential risk of TWPs to soil health.
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Figure 1. The mechanisms on the Fe reduction- and EPFRs transformation- dependent 6PPD-Q formation during TWP aging processes in flooded soils. Image by XU Qiao et al.
Contact: LI Gang
Institute of Urban Environment, Chinese Academy of Sciences
E-mail: gli@iue.ac.cn