Characterization of the ultraviolet-visible photoproducts of thiophanate-methyl using high performance liquid chromatography coupled with high resolution tandem mass spectrometry-Detection in grapes and tomatoes.

UV-visible irradiation of thiophanate-methyl (TM) led to the formation of nine photoproducts that were characterized by high performance liquid chromatography coupled with high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Although carbendazime has been reported in the literature to be the major metabolite and photoproduct of thiophanate-methyl, it was not detected in this study. However, an isomer of carbendazime referred as PP2, which was unambiguously characterized owing to CID experiments, was found in great abundance. Grape berries and cherry tomatoes treated with aqueous solutions of thiophanate-methyl were submitted to irradiation under laboratory conditions. TM and PP2 were detected in both peel and flesh of berries. The ability of TM and PP2 to pass through the fruit skin has been shown to be highly compound and matrix dependent. In vitro bioassays on Vibrio fischeri bacteria showed that the global ecotoxicity of the TM solution increases significantly with the irradiation time. PP2 should likely contribute to this ecotoxicity enhancement since in silico estimations for Daphnia magna provide a LC50 value seven times lower for PP2 than for the parent molecule.

Isomerization of fenbuconazole under UV-visible irradiation - chemical and toxicological approaches.

RATIONALE: Fenbuconazole is a fungicide commonly used for the protection of vineyards, vegetables and grain crops. Under UV-visible irradiation, it undergoes isomerization through various cyclization processes. Isomeric structures were elucidated by liquid chromatography/high-resolution multiple-stage mass spectrometry (LC/HR-MS(n) ) coupling. The potential toxicities of these isomers were estimated by in silico tests. METHODS: Aqueous solutions of fenbuconazole and grapes treated with this fungicide were irradiated in a self-made reactor equipped with a mercury vapor lamp. Analyses were carried out using high-performance liquid chromatography (HPLC) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS). High-resolution m/z measurements, multiple-stage mass spectrometry and isotopic labeling experiments allowed structural elucidation of the isomers of fenbuconazole. In silico toxicity estimations were carried out using the T.E.S.T. RESULTS: Seven isomers of fenbuconazole were detected after irradiation of the fungicide in aqueous solution; the major ones were also detected in the flesh of treated grapes irradiated under laboratory conditions. Elucidation of their chemical structures owing to high resolution measurements and multi-stage collision induced dissociation experiments allowed confirmation of photo-transformation pathways mainly dominated by cyclization processes. Photo-induced isomers exhibited higher potential toxicities than fenbuconazole for Daphnia magna and fathead minnow species. CONCLUSIONS: UV-visible irradiation of fenbuconazole in aqueous solution and on grapes leads to the formation of isomers, all of which being potentially much more toxic than the parent fungicide.

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.

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.

Ultraviolet-vis degradation of iprodione and estimation of the acute toxicity of its photodegradation products.

The UV-vis photodegradation of iprodione in water was investigated with a high pressure mercury lamp photoreactor. Five photoproducts of iprodione were characterized by LC-HR-MS/MS and isotopic labeling; none of them has been reported in previous studies. Three of them result from the elimination of one or two chlorine atoms followed by hydroxy or hydrogen addition while the two others are cyclic isomers of iprodione. An ICR mass spectrometer was used for by-products identification; concentrations of photoproducts were estimated with a triple quadrupole instrument, using iprodione-D5 as an internal standard. Phototransformation mechanisms were postulated to rationalize photoproducts formation. In silico QSAR toxicity predictions were conducted with the Toxicity Estimation Software Tool (T.E.S.T.) considering oral rat LD50, mutagenicity and developmental toxicity. Low oral rat LD50 values of 350 mg/kg and 759 mg/kg were predicted for cyclic isomers of iprodione, compared to that of the parent molecule (2776 mg/kg). Toxicity estimations exhibited that all the iprodione photoproducts could be mutagenic while the parent compound is not. In vitro assays on Vibrio fischeri were achieved on both irradiated and non-irradiated aqueous solutions of iprodione and on HPLC fractions containing isolated photoproducts. Phenolic photoproducts were shown to be mainly responsible for toxicity enhancement with EC50 values of 0.3 and 0.5 ppm, for the bi- and mono-phenolic compounds issued from chlorine elimination.

UV-visible degradation of boscalid--structural characterization of photoproducts and potential toxicity using in silico tests.

RATIONALE: Boscalid is a carboximide fungicide mainly used for vineyard protection as well as for tomato, apple, blueberry and various ornamental cultivations. The structural elucidation of by-products arising from the UV-visible photodegradation of boscalid has been investigated by gas chromatography/multi-stage mass spectrometry (GC/MS(n) ) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) couplings. The potential toxicities of transformation products were estimated by in silico calculations. METHODS: Aqueous solutions of boscalid were irradiated up to 150 min in a self-made reactor equipped with a mercury lamp. Analyses were carried out using a gas chromatograph coupled with an ion trap mass spectrometer operated in both electron ionization (EI) and chemical ionization (CI) modes and a liquid chromatograph coupled with a quadrupole time-of-flight (Q-TOF) mass spectrometer operated in electrospray ionization (ESI) mode. Multiple-stage collision-induced dissociation (CID) experiments were performed to establish dissociation pathways of ions. The QSAR (Quantitative Structure-Activity Relationship) T.E.S.T. program allowed the estimation of the toxicities of the by-products. RESULTS: Eight photoproducts were investigated. Chemical structures were proposed not only on the interpretation of multi-stage CID experiments, but also on kinetics data. These structures led us to suggest photodegradation pathways. Three photoproducts were finally detected in Lebanon in a real sample of grape leaves for which routine analysis had led to the detection of boscalid at 4 mg kg(-1). CONCLUSIONS: With one exception, the structures proposed for the photoproducts on the basis of mass spectra interpretation have not been reported in previous studies. In silico toxicity predictions showed that two photoproducts are potentially more toxic than the parent compound considering oral rat LD50 while five photoproducts may induce mutagenic toxicity. With the exception of one compound, all photoproducts may potentially induce developmental toxicity.

Separation of xanthines in hydro-organic and polar-organic elution modes on a titania stationary phase.

Hydrophilic interaction LC was investigated in hydro-organic and nonaqueous elution modes on a titania column by using a set of N-methyl xanthines as neutral polar probes. To get information regarding the mechanisms that are behind the discrimination of these analytes in hydrophilic interaction, we focused our study on the type and amount of organic modifier as a critical yet rarely explored mobile phase parameter. Several alcohols such as methanol, ethanol, and isopropanol were studied as substitutes to acetonitrile in hydro-organic elution mode. Compared to silica, the investigation of the eluotropic series of these alcohols on titania highlighted a different implication in the retention mechanism of the xanthine derivatives. At low amounts of protic solvents, the adsorption mainly characterized the retention of analytes on bare silica; whereas mixed interactions including adsorption and ligand exchange were identified on native titania. To investigate the peculiar behavior of alcohols on the metal oxide, methanol, ethanol, and ethylene glycol were tested in replacement of water in polar-organic elution mode. Distinctive effects on the chromatographic retention and selectivity of xanthines were noticed for the dihydric alcohol, which was found to be a stronger eluting component than water on titania.