Benzotriazole is part of a larger family of benzotriazoles which are widely used as antifreezes, corrosion inhibitors and UV-stabilizers in many commercial and industrial applications. It is frequently detected in urban runoff, wastewater, and receiving aquatic environments. In surface waters, benzotriazole is typically resistant to biodegradation and hydrolysis, but can be transformed via direct photolysis and photoinduced mechanisms, e.g., by reactive species formed from dissolved organic molecules. Compound-specific isotope analysis (CSIA) is a promising tool to track and quantify contaminant transformation in the environment. Due to the highly reaction-specific isotope fractionation patterns, CSIA can provide direct evidence of contaminant transformation and has the potential to provide insights into transformation mechanisms. In addition, measuring changes of isotope ratios of more than one element can help identify the relative contribution of different reaction mechanisms. Using multi-element CSIA, we found that the direct photolysis of benzotriazole resulted in significant N and C isotope fractionation, associated with the detection of transformation products such as aniline, 3-aminophenol, phenazine, and 1,6-phenazinediol. The results indicate a N-N bond fission yielding an imine compound in the rate-limiting step. The contribution of two pathways, i.e. hydroxylation and N elimination, was dependent on the pH, with hydroxylation being relevant only at low pH, when benzotriazole is in its neutral form. During indirect photolysis, formation of hydroxybenzotriazole suggested an oxidative attack by an OH radical on the benzene ring. The observed small C, moderate H, and negligible N isotope fractionation in the UV/H<sub>2</sub>O<sub>2</sub> system revealed that the formation of an O-C bond at the benzene ring was the rate-limiting step. The results of this study highlight the great potential for multi-element CSIA application to track benzotriazole transformation in surface water.

Mutli-element compound-specific isotope analysis reveal pathways of benzotriazole aqueous phototransformation

ACS Spring 2022

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