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Within a class of agrochemical residues, pesticides are significant concern due to their various adverse effects on people, animals and the environmental systems. Once they entered to food or to the environment, the parent compound is transformed to metabolites which have different toxicity profiles. Activities like food cooking and waste water treatment (WWT) may lead to produce more toxic metabolites than the parent substances.
Online coupling of electrochemistry with liquid chromatography mass spectrometry (EC-HPLC-MS) is one of the most promising and powerful techniques for metabolite studies which exploited widely for pharmaceuticals so far [1]. However, data on the application of EC-HPLC-MS to simulate environmental transformation products, the fate of contaminants and their metabolic pathways are rare. The oxidation of analyte of interest on the EC, separate the metabolites on HPLC and identifying them by MS gives enormous advantages to identify the contaminants transformation products [2]. Thus, applying this technique (EC-MS, EC-HPLC-MS, and HPLC-EC-MS) for transformation products of pesticide residues is urgently needed.
The main interest of this study will be investigating the electrochemical oxidative degradation products, simulating to in-vitro metabolites and transformation processes of selected pesticides in food and environmental samples. The parent pesticides’, like carbamates and abamectin, oxidation by EC, product metabolites identification and their fates will be discussed using electrochemistry coupled to HPLC-MS techniques.
Nowadays, electrochemistry coupled online to mass spectrometry (EC-MS) or to liquid chromatography-mass spectrometry (EC-LC-MS) is a technique of interest to investigate metabolic transformation of xenobiotics in living organisms. It enables the production of redox products in an electrochemical cell, the separation by an analytical column and the detection by mass spectrometry online. Furthermore, EC-LC-MS enables to determine short lived transformation products (TPs) and their bioconjugates in a fully automated way. Although the EC-MS selectivity is incomparable to enzymatic reactions, it is advantageous by reducing analysis time and matrix complexity compared to cytochrome based metabolism. However, in the development of EC-MS, most efforts are devoted for prediction of drug metabolism in the human body and there is very limited work on agrochemicals in general.
The main objective of this work was to develop an online EC-LC-MS method that could predict the metabolism of fluopyram (fungicide) and chlorpyrifos (insecticide). Oxidation products were produced by using a boron doped diamond electrode and characterized by either online LC-MS or offline LC-MS/MS. After incubation with rat and human liver microsomes, different targeted and suspected metabolites were identified by LC-MS/MS and high resolution-mass spectrometry (HR-MS) and compared with the EC based methods. Additionally, conjugation reactions with a variety of biomolecules such as glucoside and glutathione were investigated by trapping the oxidized species before entering to mass spectrometry.
In summary, phase-I metabolism by N-dealkylation, O-dealkylation, P-oxidation, hydroxylation and dearylation and phase-II metabolism by conjugation with glutathione mechanisms were successfully mimicked by EC-LC-MS. Fluopyram is primarily metabolized to 7- and 8-mono- hydroxyl, 7,8-di-hydroxyl and 2-trifluoromethyl benzamide, and chlorpyrifos is metabolized to chlorpyrifos oxon, trichloropyridinol, diethylthiophosphate and diethylphosphate.
Identifying the fate of agrochemicals is important to understand their potential risk for living organisms. We report here new photodegradation products (PPs) of the fungicide fluopyram. The PPs were produced by irradiating a fluopyram standard in 0.1% acetonitrile aqueous media by a 150-W medium pressure Hg-lamp that emits wavelengths between 200–280 nm. The structural elucidation of PPs was achieved by combining the retention time, isotopic pattern, targeted fragmentation, and accurate mass measurements using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and high resolution-MS (HRMS). In addition to previously known PPs, seven new PPs of fluopyram were identified in this work: mainly dihydroxyl and hydroxylimide fluopyram as well as mono, di, and trihydroxyl lactam. Additionally, two PPs were found to be formed by rearrangement after the loss of H2C=CH2. Hence, the results of the work contribute to extending the current knowledge regarding the photoinduced fate of agrochemicals, and fluopyram in particular.