Photoinduced degradation of three azole compounds from 3rd EU watchlist monitored by high-resolution higher-order mass spectrometry – Part I: A mechanistic study

Abstract

• Nine new degradation and transformation products of azoles were identified. • HR-MS and HR-MS/MS revealed structures from hydroxyl radical and photo-absorption induced reactions. • Direct and indirect mechanism of degradation could be discerned. Pesticides are found in water bodies worldwide. Among them, there are azoles which are used as fungizides. Hence, tebuconazole, imazalil and penconazole have been included into the 3 rd EU watchlist to survey their presence in water bodies. Pesticides mostly enter the aquatic environment through leaching from agriculture, fruit washing or via conventional sewage water treatment plants, which are often not able to completely eliminate these pesticides. Advanced purification processes have become intensely researched. The advanced oxidation process, UVC and UVA irradiation and addition of the radical scavenger tert -butanol, was investigated using high-resolution higher-order mass spectrometry to gain kinetic and mechanistic insight. Structure elucidation of degradation and transformation products revealed fragments and also multiple hydroxylated intermediates depending on the UV source and the presence of radical scavenger. Hydroxyl radical-induced indirect degradation was found to dominate a direct photoreaction pathway induced by photo-absorption by the initial substance. The indirect mechanism did not occur during UVA irradiation due to the lack of hydroxyl radicals. The radical scavenger decelerated or prevented degradation. In total, nine new degradation and transformation products were identified. Mass spectrometry revealed product structures of the pesticides substituted with one or more hydroxyl radical groups, cyclization and substitution of chlorine by a hydroxyl radical.