Evaluation of the aqueous phototransformation routes of phenyl ethyl azolic fungicides by liquid chromatography accurate mass spectrometry

Abstract Similarities and differences among the phototransformation routes of four azolic fungicides (diniconazole, DIN, imazalil, IMA; penconazole, PEN; and propiconazole, PRO) in surface water aliquots are investigated. Selected compounds share a common chemical structure consisting on dichlorophenyl and azolic rings connected through an ethylene bridge, which is substituted with different functionalities. Liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) was employed as analytical technique to follow the time-course of precursor fungicides and to detect and to identify their photo-transformation products (TPs). Under solar light, the substituents linked to the ethylene chain controlled the stability of the fungicides. Whilst PEN and PRO remained stable, DIN and IMA showed moderate reactivities, with half-lives (t 1/2 ) of 5.1 and 33.5 h, respectively. When exposed to UV (254 nm) radiation, all compounds were effectively degraded with t 1/2 in the range from seconds to a few minutes. Dechlorination followed by intramolecular cyclization, between phenyl and azolic rings, was identified as a common phototransformation route under UV irradiation. Depending on the length and the kind of the functionalities attached to the ethylene bridge, additional cyclization reactions are also possible. In-silico toxicity predictions pointed out to dechlorinated tricyclic TPs as the most concerning ones, with predicted lethal concentrations (LC 50 ) in the same range as the precursor fungicides.