Degradation of carbamazepine in ice with bromate and nitrite: Role of reactive nitrogen species

Abstract

Seasonal freezing of waters occurs during winter in cold regions. Bromate (BrO3–) is a disinfection by-product generated during water treatment, its interaction with emerging contaminants may be affected by freezing. Nitrite (NO2–) is widely distributed in the environment, whereas its effect on the interaction of emerging contaminants and BrO3– in ice may have been overlooked. Herein carbamazepine (CBZ) was selected as a model emerging contaminant to elucidate the role of reactive nitrogen species (RNS) in contaminant transformation during the reduction of BrO3– by NO2– in ice. Results indicated that freezing significantly enhanced CBZ degradation by BrO3–. The CBZ degradation by BrO3– and NO2– in ice was 25.4 %–27.8 % higher than that by BrO3–. Contributions of hydroxyl radical (•OH), bromine radical (•Br), and RNS to CBZ degradation in freezing/dark or sunlight systems were 8.1 % or 15.9 %, 25.4 % or 7.2 %, and 66.5 % or 76.9 %, respectively. Most CBZ was degraded by RNS generated during the reduction of BrO3– by NO2– in ice, resulting in 16.4 % of transformation products being nitro-containing byproducts. Hybrid toxicity of CBZ/BrO3–/NO2– system was reduced effectively after the freezing-sunlight process. This study can provide new insights into the environmental fate of emerging contaminants, BrO3–, and NO2– in cold regions.