Phytotoxicity of 6PPD and its oxidized product 6PPD-Q on pakchoi (Brassica rapa L. ssp. chinensis)

Abstract

N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) and N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone (6PPD-Q) are the derivatives of tire wear particles (TWPs) that can enter the agricultural environment. Their negative consequences on the agricultural environment remain unknown, particularly their toxic effects on edible plants. In this experiment, the toxicity of different concentrations of 6PPD and 6PPD-Q on pakchoi (Brassica rapa L. ssp. chinensis) was explored by hydroponics. The results revealed that seed germination was inhibited by 6PPD and 6PPD-Q to various degrees. However, we observed an increase in the fresh weight of pakchoi seedling. Environmental concentration (1 μg L⁻¹) of 6PPD and 6PPD-Q significantly increased ROS levels and caused changes in antioxidant enzyme activities. The MDA content of pakchoi was significantly elevated under 6PPD-Q treatment, indicating severe oxidative damage. These results demonstrated the phytotoxicity induced by 6PPD and 6PPD-Q, which is of great significance for assessing their potential ecological risks in the environment.