Carbon, hydrogen and nitrogen stable isotope fractionation allow characterizing the reaction mechanisms of 1H-benzotriazole aqueous phototransformation

1H-benzotriazole is part of a larger family of benzotriazoles, which are widely used as lubricants, polymer stabilizers, corrosion inhibitors, and anti-icing fluid components. It is frequently detected in urban runoff, wastewater, and receiving aquatic environments. 1H-benzotriazole is typically resistant to biodegradation and hydrolysis, but can be transformed via direct photolysis and photoinduced mechanisms. In this study, the phototransformation mechanisms of 1H-benzotriazole were characterized using multi-element compound-specific isotope analysis (CSIA). The kinetics, transformation products, and isotope fractionation results altogether revealed that 1H-benzotriazole direct photolysis and indirect photolysis induced by OH radicals involved two alternative pathways. In indirect photolysis, aromatic hydroxylation dominated and was associated with small carbon (epsilon(C) = -0.65 +/- 0.03%o), moderate hydrogen (epsilon(H) = -21.6 parts per thousand), and negligible nitrogen isotope enrichment factors and led to hydroxylated forms of benzotriazole. In direct photolysis of 1H-benzotriazole, significant nitrogen (epsilon(N) = -8.4 +/- 0.4 to -4.2 +/- 0.3 parts per thousand) and carbon (epsilon(C) = -4.3 +/- 0.2 to -1.64 +/- 0.04 parts per thousand) isotope enrichment factors indicated an initial N-N bond cleavage followed by nitrogen elimination with a C-N bond cleavage. The results of this study highlight the potential for multi-element CSIA application to track 1H-benzotriazole degradation in aquatic environments.

Automated summary

The phototransformation mechanisms of 1H-benzotriazole involve two alternative pathways: direct photolysis and indirect photolysis. Direct photolysis leads to N-N bond cleavage followed by nitrogen elimination with C-N bond cleavage. Indirect photolysis mainly results in aromatic hydroxylation, forming hydroxylated forms of benzotriazole.