Photolysis of model emerging contaminants in ultra-pure water: Kinetics, by-products formation and degradation pathways

The photolysis of five frequent emerging contaminants (Benzotriazole, Chlorophene, N,N-diethyl-m-toluamide or DEET, Methylindole, and Nortriptyline HCl) was investigated in ultra-pure water under monochromatic ultraviolet radiation at 254 nm and by a combination of UV and hydrogen peroxide. The results revealed that the photolysis rates followed first-order kinetics, with rate constant values depending on the nature of the specific compound, the pH, and the presence or absence of the scavenger tert-butanol. Quantum yields were also determined and values in the range of 53.8 x 10(-3) - 9.4 x 10(-3) mol E-1 for Benzotriazole, 525 x 10(-3) - 469 x 10(-3) mol E-1 for Chlorophene, 2.8 x 10(-3) - 0.9 x 10(-3) mol E-1 for DEET, 108 x 10(-3) - 165 x 10(-3) mol E-1 for Methylindole, and 13.8 x 10(-3) - 15.0 x 10(-3) mol E-1 for Nortriptyline were obtained. The study also found that the UV/H2O2 process enhanced the oxidation rate in comparison to direct photolysis. High-performance liquid chromatography coupled to electrospray ionization quadrupole time-of-flight mass spectrometry (HPLC-ESI-QTOF-MS) technique was applied to the concentrations evaluation and further identification of the parent compounds and their by-products, which allowed the proposal of the degradation pathways for each compound. Finally, in order to assess the aquatic toxicity in the photo-degradation of these compounds, the Vibrio fischeri acute toxicity test was used, and the results indicated an initial increase of this parameter in all cases, followed by a decrease in the specific case of Benzotriazole, DEET, Methylindole, and Chlorophene. (c) 2012 Elsevier Ltd. All rights reserved.