On the behaviour of selected triazole fungicides in the environment and under technical conditions

In order to ensure acceptable crop yield the use of plant protection products is inevitable. Triazole fungicides are a class of pesticides often used against a variety of fungal diseases in plants. During application an involuntary introduction into soil and surface water is possible, as well as a subsequent leaching into groundwater. In these environmental compartments the fungicides are subject to transformation reactions, metabolisation by (micro-)organisms and can also undergo widespread transport through adsorption onto particles. Since ground and surface waters are also used for drinking water production the pesticides may enter drinking water facilities where they can undergo technical transformations. These processes may result in the formation of transformation products (TP) which are often more polar than the parent compound and may exhibit differing toxicological properties. This highlights the necessity for the identification of relevant TP. During this study potential oxidative TP of the triazole fungicides propiconazole and difenoconazole in soil and water were identified using model reactions with Fenton’s reagent and electrochemical conversion. For analysis of the TP gaschromatography coupled to mass spectrometry (GC/MS) as well as liquid chromatography coupled to either tandem mass spectrometry (LC/MS/MS) or high resolution mass spectrometry (LC/HRMS) were applied. TP were identified by comparison of mass spectra and retention times with those of authentic standards, if available. Both propiconazole and difenoconazole were transformed into their corresponding ketone. Additionally, monoand dihydroxylated species as well as cleavage products were postulated. Follow-up experiments investigated the behaviour of the triazole fungicides under technical conditions found in water treatment plants. Neither chlorination nor ozonation resulted in a significant reduction of analyte concentration. However, irradiation with energy-rich UV-light lead to fast transformation of the substances. Some TP which also occured in the aforementioned model reactions could be detected during this process. These results were compared to the behaviour of the analytes when irradiated with simulated global irradiation with or without the addition of humic substances. The latter were characterised physico-chemically and either used as purchased or isolated from soil and suspended particulate matter. A strong relation between the humic substance content and the conversion rate could be demonstrated. This holds for irradiated soils as well. Furthermore, the triazole fungicides were incubated with iron-/manganese-oxidising bacteria. Yet, no change in analyte concentration after a sampling period of four weeks was evident. Finally, the affinity of difenoconazole towards microplastics was investigated which resulted in a ready sorption of the analyte to all employed materials. Hence, a long-range transport of difenoconazole on the base of this mechanism might be possible.