Photoinduced degradation of three azole compounds from 3rd EU watchlist monitored by high-resolution higher-order mass spectrometry – part II A critical in silico ecotoxicity assessment and application of ecotoxicity equivalents

The fungicides imazalil, penconazole and tebuconazole have been added to the 3rd EU watchlist due to their persistence and hazard to the environment. In vitro ecotoxicity studies against organisms such as Daphnia magna and Danio rerio have indicated the harmfulness. To prevent penetration of these substances into the aquatic environment, advanced cleaning stages are being tested for wastewater treatment plants, including ultraviolet radiation. Yet, the exposure of the compounds may result in transformation products whose ecotoxicity determination proves difficult due to the lack of reference standards. Alleviation comes from in silico methods such as quantitative structure activity relationship (QSAR) analysis and the determination of time-depended ecotoxicity equivalents (ETE) which combines chemical kinetics of the photoinduced degradation process and in silico predicted ecotoxicity of the transformation products. QSAR analysis was used to predict the ecotoxicity of the transformation products whose structures were elucidated with the help of high-resolution multifragmentation mass spectrometry. Predicted values were compared to the results of in vitro ecotoxicity assays from previous studies and found in agreement. All photoinduced products were described as subsequent or subsequent follow-up reaction products. Time-independent ETEs revealed that the degradation of the fungicide itself had the greatest effect on the ecotoxicity of the irradiated solution, as photoinduced transformation products were found of significantly lower amount in irradiated solution and of lesser ecotoxicological hazard than the fungicide. The method may help estimating the conditions needed for application of UV irradiation in an advanced purification step in wastewater treatment plants.