Simultaneous analysis of seven neonicotinoid pesticides in agricultural products involving solid-phase extraction and surrogate compensation using liquid chromatography-tandem mass spectrometry

Fast neonicotinoid quantification in honey using the one-point internal calibration approach

Neonicotinoids, a highly effective class of insecticides used worldwide, have been identified as a major cause of concern for biodiversity. To assess the ecological and environmental consequences of neonicotinoids' use, reliable analytical methodologies, including calibration approaches, are needed. Here, we compared the performance of internal calibration (IC) using a single concentration of stable isotope-labeled standard (SIL) with classical multipoint external calibration (EC) for the quantification of six neonicotinoids in honey. IC showed acceptable levels of trueness (86.3% - 116.0%) and precision (1.4% - 20.8%), although slight biases were observed at very low concentrations compared to EC. When applied to 32 original honey samples, both approaches showed strong agreement (R2 > 0.998) with proportional biases lower than 5%. These results highlight the possibility of implementing IC to simplify quantification in liquid chromatography-mass spectrometry-based pesticide applications.

Characterization of The Permeation Properties of Membrane Filters and Sorption Properties of Sorbents Used for Polar Organic Chemical Integrative Samplers

Polar organic chemical integrative samplers (POCIS) are promising devices for measuring the time-weighted average concentrations of hydrophilic compounds in aquatic environments. However, the mechanisms underlying compound uptake by POCIS remain unclear. We investigated the permeation kinetics of polyethersulfone and polytetrafluoroethylene membrane filters, and the sorption kinetics of Oasis HLB (Waters), Envi-Carb (Supelco), and Oasis WAX (Waters) sorbents. The log octanol-water partition coefficient (KOW) values of the 19 targeted compounds ranged from -0.55 to 6.0. The overall mass-transfer coefficients were negatively correlated with KOW, indicating that interactions between hydrophobic compounds and the membrane inhibit permeation. The sorption rate coefficient showed no correlation with KOW and depended on the type of sorbent used. These results imply that the uptake of highly hydrophilic compounds by POCIS is determined by both the membrane and the sorbent kinetics; however, membrane kinetics dominate the uptake of hydrophobic compounds. Environ Toxicol Chem 2024;43:2115-2121. © 2024 SETAC.

Investigation of variability in the matrix effect on stable isotope-labeled internal standards in liquid chromatography-tandem mass spectrometry analysis of 25 pesticides in vegetables

The matrix effects (ME) in simultaneous analysis of pesticide residue using liquid chromatography-tandem mass spectrometry (LC-MS/MS) were evaluated by comparing the slopes of matrix-matched and reagent-only calibrations of four types of vegetable samples. Both the sampling and measurement variances of the ME were also determined using one-way analysis of variance. Substantial ion suppression (ME<-20%) was observed in komatsuna, spinach, and tomato when a modified Japanese official method was implemented. The ME magnitude varied significantly due to sample variability for some pesticides, but it varied by no more than 4% as a result of analytical procedure variance. This study also showed that the addition of stable isotope-labeled internal standards at low concentrations improved the recovery of pesticides from samples at various residue levels. The findings of this study highlight the importance and practical application of internal standards and the matrix-matched calibration method in residue analysis using LC-MS/MS.

Evaluation of convolutional neural network for non-destructive detection of imidacloprid and acetamiprid residues in chili pepper (Capsicum frutescens L.) based on visible near-infrared spectroscopy

Consumption of agricultural products with pesticide residue is risky and can negatively affect health. This study proposed a nondestructive method of detecting pesticide residues in chili pepper based on the combination of visible and near-infrared (VIS/NIR) spectroscopy (400-2498 nm) and deep learning modeling. The obtained spectra of chili peppers with two types of pesticide residues (acetamiprid and imidacloprid) were analyzed using a one-dimensional convolutional neural network (1D-CNN). Compared with the commonly used partial least squares regression model, the 1D-CNN approach yielded higher prediction accuracy, with a root mean square error of calibration of 0.23 and 0.28 mg/kg and a root mean square error of prediction of 0.55 and 0.49 mg/kg for the acetamiprid and imidacloprid data sets, respectively. Overall, the results indicate that the combination of the 1D-CNN model and VIS/NIR spectroscopy is a promising nondestructive method of identifying pesticide residues in chili pepper.

In Silico Investigation of Selected Pesticides and Their Determination in Agricultural Products Using QuEChERS Methodology and HPLC-DAD

In this study, we considered some pesticides as active substances within formulations for the protection of plant-based food in the Republic of Serbia in silico, because these pesticides have not often been investigated in this way previously, and in an analytical way, because there are not very many available fast, cheap, and easy methods for their determination in real agricultural samples. Seven pesticides were detected in selected agricultural products (tomatoes, cucumbers, peppers, and grapes) using the QuEChERS methodology and HPLC-DAD. Standard curves for the investigated pesticides (chlorantraniliprole, methomyl, metalaxyl, thiacloprid, acetamiprid, emamectin benzoate, and cymoxanil) show good linearity, with R² values from 0.9785 to 0.9996. The HPLC-DAD method is fast, and these pesticides can be determined in real spiked samples in less than 15 min. We further characterized the pesticides we found in food based on physicochemical properties and molecular descriptors to predict the absorption, distribution, metabolism, elimination, and toxicity (ADMET) of the compounds. We summarized the data supporting their effects on humans using various computational tools to determine their potential adverse effects. The results of our prediction study show that all of the selected pesticides considered in this study have good oral bioavailability, and those with high toxicity, therefore, could be harmful to human health. Chlorantraniliprole was shown in a molecular docking study as a good starting point for a new Alzheimer's disease drug candidate.

Determination and dietary intake risk assessment of 35 pesticide residues in cowpea (Vigna unguiculata [L.] Walp) from Hainan province, China

The presence of pesticide residues in cowpea raises serious health concerns. In this study, a novel, sensitive, high-performance method was developed to simultaneously analyze the residues of 35 pesticides in cowpea samples from growing areas in the Hainan province of China, from November 2018 to June 2021. The method employs modified QuEChERS sample pretreatment coupled with gas chromatography-tandem mass spectrometry. The limits of quantification of the 35 pesticides in the cowpea matrix ranged from 1.0 to 8.0 μg/kg. Twenty-seven of the 35 pesticides were detected, twelve of which are banned for use on legumes in China. Residues for ten pesticides in 17.1% of the samples exceeded their MRLs, with the highest exceedance of 380% observed in difenoconazole. Moreover, 80.8% of the samples contained one or more pesticide residues, with the most frequently detected pesticide being chlorfenapyr with a detection rate of 46.3%. In addition, the pesticide triazophos was detected through different years and regions. Notably, the chronic dietary exposure risk (%ADI) of the detected pesticides, evaluated from the national estimated acceptable daily intake, was lower than 100% in Chinese people of different age groups.

Comparative Evaluation of the Polar Organic Chemical Integrative Sampler in Two Types of Validation Systems Simulating Peak Concentration Events

Polar organic chemical integrative sampler (POCIS) devices have been suggested for measuring time-weighted averages (TWAs) of contaminant concentrations resulting from chemical leak accidents in aquatic environments. However, the response of the POCIS device in the emergency condition in natural water remains unclear. The response of the POCIS device to contaminant fluctuation was investigated using a chamber test with tap water and a channel test with natural water. The fluctuation in the chamber and the channel simulated the condition of river water under a chemical leak scenario (maximum concentration: 1-10 μg L^-1 , half-life: 1 day). The target chemicals were neonicotinoid pesticides (dinotefuran, clothianidin, thiamethoxam, imidacloprid, acetamiprid, and thiacloprid) and bisphenol A. The ratio of the POCIS measured value to the TWA values of grab samplings (POCIS/TWA) for the channel test (temperature: 15 °C, flow velocity: 15 cm s^-1 ) ranged from 61% (clothianidin) to 133% (thiacloprid). The results indicated that the POCIS device could be effectively used as a monitoring device in an aquatic environment under the chemical leak scenario over a time period of more than14 days. In addition, the POCIS/TWA ratios obtained from the chamber test and the channel test were in the range of 50-150%. Thus, the chamber test could be used to evaluate the POCIS device at a low cost. Environ Toxicol Chem 2021;40:3010-3018. © 2021 SETAC.

Establishment of import tolerance for the insecticide thiacloprid in strawberry

To promote exports, import tolerance (IT) of thiacloprid in strawberry was proposed using the Organization for Economic Cooperation and Development (OECD) maximum residue limit (MRL) calculator after conducting three different field trials. The pre-harvest interval of residual pattern and degradation dynamics of thiacloprid in strawberry were determined using ultra-performance liquid chromatography-tandem mass spectrometry. Samples were extracted with acetonitrile and a mixture of salts and dilution was performed for purification. A six-point matrix-matched calibration curve was constructed which provided excellent linearity with coefficient of determination (R² ) of 0.9998 or more. Detection and quantification limits were 0.003 and 0.01 mg/kg, respectively. The method was validated in quintuplicate at three different concentrations, which resulted in acceptable recovery ranging from 80.86% to 101.71% with relative standard deviation of 6.50 or less among the three field sites. The developed method was applied to the field-treated sample harvested at different intervals. In the pre-harvest interval trial, the amount of thiacloprid residues ranged from 0.24 to 0.70 mg/kg in field site 1 (Nonsan), 0.16 to 0.50 mg/kg in field site 2 (Sunchang), and 0.36 to 0.50 mg/kg in field site 3 (Sacheon). By contrast, in the degradation trial, the observed residues were 0.03-0.81 mg/kg in field site 1 and 0.02-0.48 mg/kg in field site 2. Consequently, the IT of thiacloprid in strawberry using the OECD MRL calculator was proposed as 2 mg/kg, which is exactly the same as the MRL established by the Republic of Korea. In conclusion, the residue study proposes 2.0 mg/kg as the MRL of thiacloprid in strawberries.

Bioinformatics of a Novel Nitrile Hydratase Gene Cluster of the N2-Fixing Bacterium Microvirga flocculans CGMCC 1.16731 and Characterization of the Enzyme

Microvirga flocculans CGMCC 1.16731 can degrade many cyano group-containing neonicotinoid insecticides. Here, its genome was sequenced, and a novel nitrile hydratase gene cluster was discovered in a plasmid. The NHase gene cluster (pnhF) has gene structure β-subunit 1, α-subunit, and β-subunit 2, which is different from previously reported NHase gene structures. Phylogenetic analysis of α-subunits indicated that NHases containing the three subunit (β1αβ2) structure are independent from NHases containing two subunits (αβ). pnhF was successfully expressed in Escherichia coli, and the purified PnhF could convert the nitrile-containing insecticide flonicamid to N-(4-trifluoromethylnicotinoyl)glycinamide. The enzymatic properties of PnhF were investigated using flonicamid as a substrate. Homology models revealed that amino acid residue β1-Glu56 may strongly affect the catalytic activity of PnhF. This study expands our understanding of the structures and functions of NHases and the enzymatic mechanism of the environmental fate of flonicamid.

Development and Calibration of the Polar Organic Chemical Integrative Sampler (POCIS) for Neonicotinoid Pesticides

Neonicotinoid pesticides are highly hydrophilic systemic insecticides that have been extensively used worldwide. To evaluate their environmental risks, the concentrations of these pesticides in the aquatic environment must be monitored. Although the polar organic chemical integrative sampler (POCIS) has proved to be a suitable passive sampler for many highly hydrophilic compounds, Oasis HLB (Waters) POCIS has shown limitations for the monitoring of neonicotinoid pesticides, such as short linear uptake ranges. In the present study we optimized POCIS for neonicotinoid pesticides by selecting suitable adsorbents and filters. The ENVI-Carb (Supelco) nonporous carbon-based adsorbent demonstrated a good balance between strong sorption and high recovery. Static renewal experiments showed that the our POCIS device using ENVI-Carb with a polyethersulfone membrane filter had a 3 d (dinotefuran) to 28 d (clothianidin, imidacloprid, acetamiprid, and thiacloprid) linear range, which is longer than that of HLB POCIS (≤1 [dinotefuran] to 14 d). The POCIS using ENVI-Carb with a polytetrafluoroethylene membrane had higher sampling rates (0.270 L/d [clothianidin] to 0.686 [imidacloprid] L/d) than those of the HLB POCIS for short-term deployment. The time-weighted average concentrations in actual river water measured by the new POCIS were in good agreement with those obtained by repeated grab sampling, within 30%. Moreover, POCIS detected 2 neonicotinoid pesticides that were not detected by grab sampling. Thus, the proposed POCIS is a promising tool for the monitoring of neonicotinoid pesticides. Environ Toxicol Chem 2020;39:1325-1333. © 2020 SETAC.