Structural elucidation and estimation of the acute toxicity of the major UV–visible photoproduct of fludioxonil – detection in both skin and flesh samples of grape

Abstract

Ultraviolet (UV)-visible irradiation of fludioxonil was investigated with two photoreactors using either a mercury or xenon vapor lamp. In both cases, it led to the formation of only one photoproduct in significant amount: 2-(2,2-difluorobenzo[d][1,3]dioxol-4-yl)-2-(nitrosomethylene)-4-oxobutanenitrile, which has been characterized using Liquid Chromatography - High Resolution - Tandem Mass Spectrometry (LC-HR-MS/MS) coupling. A photolysis pathway has been proposed to rationalize its formation in degassed water. In vitro bioassays on Vibrio fischeri bacteria showed that UV-vis irradiation of an aqueous solution of fludioxonil significantly increases its toxicity. Because no other by-product was detected in significant amount, the photoproduct mentioned above may be considered mainly responsible for this increase in toxicity. Grape berries treated with a 50 ppm aqueous solution of fludioxonil were submitted to UV-visible irradiation under laboratory conditions. The fungicide and photoproduct were detected in both skin and flesh of berries, even after they have been rinsed with water. The ability of the photoproduct to pass through the fruit skin is comparable with that of fludioxonil. These results are of concern for consumers because they mean that water tap rinsing does not lead to efficient removing of both compounds.

Impact of Unadorned Carbon Nitride on Photodegradation and Bioavailability of Multifungicides in the Environment

“…The dissociation pathways and the photoproducts of all fungicides were produced by combined full scan analysis and the ESI MRM method (Figure S2–S9). One of the main photoproduct of fludioxonil found was 2-(2,2-difluorobenzo­[ d ]­[1,3]­dioxol-4-yl)-2-(nitrosomethylene)-4-oxobutanenitrile (product I, m / z 280), which is identical with the photoproduct of fludioxonil produced by direct UV–vis photolysis . For hexaconazole, m / z 330 is detected, which could be three possible structures depending on the −OH group substitution .…”

“…Identification of the Main Photodegradation Products. As far as we know, there is no literature regarding the 29 For hexaconazole, m/z 330 is detected, which could be three possible structures depending on the −OH group substitution. 30 Triazole fungicides epoxiconazole and difenoconazole both had main photoproduct formation, resulting from an electron rearrangement occurring on an epoxy group, which is excited by visible light.…”

Isomerization of fenbuconazole under UV‐visible irradiation – chemical and toxicological approaches

“…The triazole group has been assumed to be the most likely ionization site given its low ionization energy. Ionization of the conjugated amino group has been shown to be the main ionization site of fludioxonil, a fungicide of the same class as fenbuconazole . Cyclization may arise through bond formation between the ionized nitrogen atom and (i) a carbon atom of the chlorophenyl group, leading to photoproducts 1 to 4 ; (ii) a carbon atom of the phenyl group, leading to photoproducts 5 to 7 ; or (iii) the nitrogen atom of the cyano group, leading to photoproduct 8 (see Fig.…”

Photodegradation of Fludioxonil and Other Pyrroles: The Importance of Indirect Photodegradation for Understanding Environmental Fate and Photoproduct Formation

“…Chromatographic separation was performed using a C18 column with a H 2 O/ACN (+0.1% formic acid) gradient. The HRMS was operated using a reference standard of Agilent Frag622 and in negative electrospray ionization over a mass range of 100–3000 Da with the following instrument parameters: 4.5 kV capillary, −0.5 kV end plate offset, 1.5 kVpp collision cell frequency, 1.6 bar nebulizer, and 200 °C dry heater temperature …”

“…Laser pulses were directed at a 1 cm quartz cuvette containing 1–3 mM fludioxonil in acetonitrile with and without 3MAP as a sensitizer (400 μM). Solutions were sparged before and during the experiment with either Ar or O 2 to determine the effect of O 2 on lifetime or to quench solvated electrons. , Time windows up to 10 μs (1 ns time resolution) were used to fit the (bi)­exponential decay of the short-lived singlet excited state and/or radical cation of fludioxonil. Data collection times of 5–10 min afforded sufficient signal-to-noise ratios.…”