Photodegradation of multiclass fungicides in the aquatic environment and determination by liquid chromatography-tandem mass spectrometry

Abstract

The photodegradation behaviour for nine widespread fungicides (benalaxyl, cyprodinil, dimethomorph, fenhexamide, iprovalicarb, kresoxim-methyl, metalaxyl, myclobutanil and tebuconazole) was evaluated in different types of water. Two different systems, direct UV photolysis and UVC/H₂O₂ advanced oxidation process (AOP), were applied for the photodegradation tests. For the monitoring of the target compound degradation, a method based on direct injection liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed. Several fungicide photodegradation by-products were tentatively identified by high-resolution mass spectrometry (HRMS) as well. For the photolysis studies, the efficiency of different types of radiation, UVC (λ = 254 nm) and UVA (λ = 365 nm), was compared. UVC photolysis provided the highest removal with a complete degradation for fenhexamide and kresoxim-methyl, and percentages between 48 and 78% for the other compounds, excluding iprovalicarb and myclobutanil with removals <35%, after 30 min of irradiation. Besides, the photodegradation tests were performed with different initial concentrations of fungicides, and the efficiency of two photoreactor systems was compared. In all cases, the kinetics followed pseudo-first order, and the half-life times could also be calculated. The addition of H₂O₂ under UVC light allowed an improvement of the reaction kinetics, especially for the most recalcitrant fungicides, obtaining in all cases removals higher than 82% in less than 6 min. Finally, in order to evaluate the suitability of the proposed systems, both UVC photolysis and UVC/H₂O₂ system were tested in different real water matrices (wastewater, tap water, swimming pool water and river water), showing that the UVC/H₂O₂ system had the highest removal efficiency in less than 6 min, for all water samples.

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