Electrochemistry Coupled to Mass Spectrometry and in silico Methods As an Alternative Strategy for Neonicotinoid Pesticides Ecotoxicity Assessment
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2025-07-11 |
| Journal | ECS Meeting Abstracts |
| Authors | Ranil Clement Temgoua Tonleu, Matthias Koch |
Abstract
Section titled āAbstractāThe widespread occurrence of neonicotinoid insecticides and their transformation/degradation products (TPs) in the aquatic environment raises health and environmental concerns. As a consequence, pesticides and, to a lesser degree, their degradation products are monitored by authorities both in surface waters and drinking waters. In this study, we propose an alternative non-enzymatic approach that combines electrochemistry (EC) with liquid chromatography (LC), gas chromatography (GC), mass spectrometry (MS), and in silico methods to evaluate the ecotoxicity of pesticides. The formation of degradation products from electrochemical reactors (EC) of the three neonicotinoid insecticides imidacloprid (IMI, first generation), clothianidin (CLO, second generation), and dinotefuran (DINO, third generation), and their toxicity effects were investigated. Firstly, electrochemical experiments were conducted using three primary methodological approaches: cyclic voltammetry (CV) and linear sweep voltammetry (LSV) for investigating electrochemical behavior and controlled-potential coulometry (CPC) for electrosynthesis. Three distinct electrochemical cell configurations were employed: the Āµ-PrepCell and ReactorCell for direct coupling with mass spectrometry (MS), and the SynthesisCell for batch electrosynthesis. These experiments utilized glassy carbon (GC) and boron-doped diamond (BDD) electrodes. Secondly, the chemical structures of the main EC-degradation products were identified using gas chromatography coupled with mass spectrometry and liquid chromatography-mass spectrometry (GC-MS and LC-MS/MS). Structural elucidation of the neonicotinoid insecticidesā reduction products was based on retention time, m/z ratio in positive mode, and fragmentation pattern. Nitration and reduction were identified as key processes in the electrochemical degradation of neonicotinoids. The reduction of the nitro group resulted in the formation of desnitro-insecticides, which are less toxic and often more biodegradable. In addition to previously known transformation products common to those observed during environmental degradation (e.g., 6-chloronicotinic acid, nitrosimine, imidacloprid-NTG, olefin, urea, guanidinium dihydrogen, and -hydroxy), new degradation products were identified. The ecotoxicity of neonicotinoid insecticides and the proposed TPs was estimated using two complementary in silico models: the Ecological Structure-Activity Relationships (ECOSAR) model and the Toxicity Estimation Software Tool (T.E.S.T.). While ECOSAR provided rapid estimates of ecotoxicity across three trophic levels (fish, Daphnia, and green algae), T.E.S.T. played a pivotal role in refining these predictions by offering additional insights into the acute and chronic toxicological profiles of the TPs. T.E.S.T.ās capabilities for quantitative structure-activity relationship (QSAR) analysis allowed for a deeper understanding of the specific chemical properties influencing toxicity. The combined use of these models underscored an important finding: that the electrochemical transformation products are at least as toxic, if not more so, than the parent compounds. Electrochemical mass spectrometry hyphenated techniques represent an accessible, rapid, and reliable tool to elucidate the reductive degradation of neonicotinoids, including reactive degradation products and conjugates. Coupled with advanced in silico tools such as T.E.S.T. and ECOSAR, this approach provides a comprehensive framework for evaluating the environmental impact of pesticides and their degradation products, paving the way for more sustainable pesticide monitoring and management practices.