Effects of HCO₃^- on Degradation of Toxic Contaminants of Emerging Concern by UV/NO₃

This study investigated the significant influence of HCO₃^- on the degradation of contaminants of emerging concern (CECs) during nitrate photolysis at 254 nm for water reuse applications. The second-order rate constants for the reactions between selected contaminants with carbonate radical (CO₃^•-) were determined at pH 8.8 and T = 20 °C: estrone ((5.3 ± 1.1) × 10⁸ M^-1 s^-1), bisphenol A ((2.8 ± 0.2) × 10⁸ M^-1 s^-1), 17α-ethynylestradiol ((1.6 ± 0.3) × 10⁸ M^-1 s^-1), triclosan ((4.2 ± 1.4) × 10⁷ M^-1 s^-1), diclofenac ((2.7 ± 0.7) × 10⁷ M^-1 s^-1), atrazine ((5.7 ± 0.1) × 10⁶ M^-1 s^-1), carbamazepine ((4.2 ± 0.01) × 10⁶ M^-1 s^-1), and ibuprofen ((1.2 ± 1.1) × 10⁶ M^-1 s^-1). Contributions from UV, reactive nitrogen species (RNS), hydroxyl radical (^•OH), and CO₃^•- to the CEC decomposition in UV/NO₃^- in the presence and absence of HCO₃^- were investigated. In addition, possible transformation products and degradation pathways of triclosan, diclofenac, bisphenol A, and estrone in UV/NO₃^-/HCO₃^- were proposed based on the mass (MS) and MS² spectra. Significant reduction in the cytotoxicity of bisphenol A was observed after the treatment with UV/NO₃^-/HCO₃^-.