Mechanistic insight into the degradation of 1H-benzotriazole and 4-methyl-1H-benzotriazole by •OH-based advanced oxidation process and toxicity assessment

Abstract

Benzotriazoles (BTs) are highly produced chemicals that are commonly used in the manufacture of aircraft de-icing/antifreeze fluids (ADAFs), coolants, etc. BTs have been detected in a variety of water environments, causing health hazards to aquatic species and humans. In this study, 1H-benzotriazole (BTri) and 4-methyl-1H-benzotriazole (4-TTri) were selected to investigate their degradation mechanisms in the aqueous phase initiated by ·OH using a theoretical calculation method. Addition reactions are the main type of reactions of ·OH with BTri and 4-TTri. The total rate constants for the reactions of BTri and 4-TTri with ·OH at 298 K are 8.26 × 10⁹ M^-1 s^-1 and 1.81 × 10¹⁰ M^-1 s^-1, respectively. The reaction rate constants increase as the temperature rises, indicating that rising temperatures promote the degradation of BTri and 4-TTri. 7-hydroxy-1H-benzotriazole (1-P1) and 4-hydroxy-benzotriazoles (1-P2) produced via multiple reaction pathways are important transformation products of BTri. After successive reactions with ·OH, 1-P1 and 1-P2 can be successively converted to 4,7-dihydroxy-1H-benzotriazole (1-P7), 4,7-dione-1H-benzotriazole (1-P8), and 1,2,3-triazole-4,5-dicarboxylic acid (1-P9), which is consistent with the product compositions detected in the experiments. The toxicity assessment indicated that the acute toxicity and chronic toxicity of the resulting transformation products are significantly reduced compared to BTri as the degradation process progressed, and ultimately showed no harm to all three aquatic organisms (fish, daphnia, and green algae). Hence, advanced oxidation processes (AOPs) can not only effectively remove BTs from water, but also reduce their toxic effects on aquatic organisms.

Keywords: AOP; Benzotriazoles; Oxidative degradation; Toxicity assessment; ·OH.