Imazalil Degradation upon Applying Ozone-Transformation Products, Kinetics, and Toxicity of Treated Aqueous Solutions

The elimination of the pesticide imazalil (IMZ) spiked into ultra-pure water as well as into wastewater applying ozone (O-3) and the identification of transformation products was investigated. O-3 under hydroxyl radical suppression conditions reacted rapidly with the aliphatic double bond or the imidazole ring in IMZ, yielding several transformation products by partial oxidation. The structures of four oxidation products not yet described were characterized and identified after liquid chromatography coupled with high resolution, high mass accuracy, mass and tandem mass spectrometry (LC/MS and -MSn) in ultrapure water. For two identified transformation products, generated via direct ozone attack on IMZ, formation pathways were proposed. In wastewater, only two of those transformation products were observed. Kinetics studies for the reaction of IMZ with O-3, evaluated by the competition kinetic method, resulted in a second-order rate constant k(O3,IMZ) similar to (1.02 +/- 0.03) x 10(5) M-1 s(-1) at pH 6.6 +/- 0.2, indicating that IMZ is completely transformed during the ozonation process. Tests of acute toxicity were performed applying a solution of IMZ in ultrapure water or treated wastewater to Daphnia magna. In both cases the decrease of toxicity was observed after ozone treatment.