Application of solid-phase extraction and liquid chromatography–mass spectrometry to the determination of neonicotinoid pesticide residues in fruit and vegetables

Silver Core Coated with Molecularly Imprinted Polymer as Adsorbent in Pipet-Tip Solid Phase Extraction for Neonicotinoids Determination from Coconut Water

In this work, we report an innovative adsorbent named Ag-MPS@MIP that has a core@shell structure, i.e., silver nanoparticles modified with 3-methacryloxypropyltrimethoxysilane as the core and molecularly imprinted polymer based on methacrylic acid as its shell. Thiamethoxam, imidacloprid, and acetamiprid were extracted from coconut water samples using Ag-MPS@MIP in pipet-tip solid phase, prior to high-performance liquid chromatography analysis. The separation was carried out on isocratic mode using a mobile phase consisting of C18 column (Phenomenex, 150 mm × 4.6 mm, 5 μm), ultrapure water acidified with 0.3% phosphoric acid:acetonitrile (78:22, v/v), flow rate at 1.0 mL min-1, injection volume of 10 μL, temperature of 25 °C, and wavelength at 260 nm. The adsorbent and precursor materials were properly characterized by different instrumental techniques. The main factors affecting the recovery of analytes from coconut water samples by pipet-tip solid phase were optimized, such as sample volume (250 μL), sample pH (pH = 5.0), ionic strength (1%, m/v), washing solvent (300 μL ultrapure water), volume and type of eluent (500 μL methanol), amount of adsorbent (15 mg), cycle of percolation-dispensing (1×), and reuse (5×). Thereby, the neonicotinoids presented extraction recoveries between 82.80 and 96.36%, enrichment factor of 5, linearity ranged from 15 to 4000 ng mL-1, correlation coefficient (r) > 0.99, limit of detection of 5 ng mL-1, satisfactory selectivity, stability, and proper precision (RSD%: 0.52-9.64%) and accuracy (RE%: -5.19-6.45%). The method was successfully applied to real samples of coconut water.

A fast and simple procedure for the synthesis of a zinc and 1,4-benzene dicarboxylic acid metal-organic framework and its evaluation as a sorbent for dispersive micro solid phase extraction of pesticide residues

In this work, Zn-1,4-benzenedicarboxylate metal-organic framework was synthesized by a simple hydrothermal process and used in dispersive micro solid phase extraction of some pesticide from various fruit juice and water samples. Seven widely consumed pesticides in agriculture (chlorpyrifos, haloxyfop-R-methyl, oxadiazon, diniconazole, clodinafop-propargyl, fenpropathrin, and fenaxoprop-p-ethyl) were selected as target analytes. In this work, dispersive micro solid phase extraction was followed by a liquid phase microextraction method to achieve more enrichment of the analytes, and the enriched analytes were quantified using a gas chromatography-flame ionization detector. The sorbent was authenticated by Fourier transform infrared spectrophotometry, X-ray diffraction, energy dispersive X-ray analysis, and scanning electron microscope imaging. The factors affecting the extraction efficiency of the developed method were investigated, and the validation of the method under the optimized extraction conditions presented satisfactory results for precision and trueness, with limits of detection and quantification in the ranges of 0.50-0.90 and 1.5-2.7 μg L-1, respectively. Enrichment factors and extraction recoveries were in the ranges of 239-392% and 47-78%, respectively. One river water and some fruit and vegetable juice samples were analyzed by the recommended method, and the obtained recoveries were between 90% and 102%.

Determination of biochemical and histopathological changes on testicular and epididymis tissues induced by exposure to insecticide Imidacloprid during postnatal development in rats

BACKGROUND

Imidacloprid is a neonicotinoid insecticide belonging to the chloronicotinyl nitroguanidine chemical family. Toxicity of IMD for mammals in scientific studies has shown high mutagenic, immunotoxic, teratogenic and neurotoxic effects. The present study was designed to assess the toxic effects of imidacloprid (IMD) on the testicular and epididymis tissues as well as testosterone levels of neonatal male rats.

METHODS

Neonatal male rats from postnatal day (PND) 1 to PND 26 were consecutively administered with different concentrations of IMD (1, 5 and 10 mg/kg) subcutaneously. The effect of IMD on body and organ weight, lipid profile, histopathological alterations, oxidative stress and altered testosterone levels were assessed in the testis and plasma.

RESULTS

The results of body weight gain showed a significant difference in group 4 (10 mg/kg) animals as compared to the control. A significant increase in total cholesterol and triglycerides, while a decrease in high-density lipoprotein concentrations was evident. Similarly, a significant decrease in concentrations of antioxidant enzymes (CAT and SOD) among all the IMD-treated groups was evident, when compared to the control. Increased production of ROS was also noticed in the highest-dose treatment group. Further, we observed that IMD-treated rats indicated histopathological changes in the testis and epididymis along with a significant decrease in the plasma testosterone concentrations among IMI-treated groups in contrast to the control. Histological examination of the testis of IMD-treated neonatal male rats also showed decreased spermatogenesis in the treated groups when compared to the control. Furthermore, an increase in lumen diameter and a decrease in epithelial height of seminiferous tubules were also observed in IMD-treated rats in comparison with the control.

CONCLUSION

It is concluded that sub-chronic exposure to IMD in neonatal male rats may induce histopathological changes in reproductive tissues and damage normal testicular functions via inducing oxidative stress, decrease in body weight, disturbing normal blood lipid profile and testosterone concentration. IMD exposure can induce pathophysiological effects calls for further evaluation of this widely used insecticide.

Effects of Neonicotinoid Pesticide Metabolic Compounds on Medaka (Oryzias latipes) Embryo Development

Neonicotinoids, including imidacloprid, are pesticides that resemble nicotine and undergo slight chemical alterations through metabolic changes in the environment. However, the effects of these metabolites on organisms remain unknown. In this study, we assessed the developmental processes of medaka embryos exposed to neonicotinoid metabolites. The target compounds were imidacloprid metabolites: 2-chloro-5-pyridine carbaldehyde (CPC) and 6-chloronicotinic acid (6-CNA). Medaka embryos within 6 h of fertilization were exposed to the compounds, and their developmental processes were observed under a stereomicroscope. Medaka embryos exposed to 5 mg/L CPC showed no abnormalities compared to the controls. Contrastingly, medaka embryos exposed to 10, 15, and 20 mg/L CPC showed abnormalities such as thrombus formation, asymmetry, disorganized development of the eyeballs, and low blood flow. This trend was more pronounced at higher CPC concentrations. On the other hand, embryos exposed to 80 and 160 mg/L 6-CNA showed no abnormalities until day 7 of exposure. However, on day 8 of exposure, sudden embryo death was observed. Both compounds may have bound to acetylcholine receptors as agonists; however, their effects were different. CPC caused abnormal development and 6-CNA caused inhibition of hatching gland development and/or synthesis of the hatching enzyme.

Generating Monoclonal Antibodies against Buprofezin and Developing Immunoassays for Its Residue Detection in Tea Samples

The synthesis of a hapten and antigen for the preparation of a monoclonal antibody (mAb) for buprofezin is described. The recognition mechanism of hapten and buprofezin by monoclonal antibodies (mAb-19F2) is described. The effectiveness of the mAb-19F2 immunoassay technique was assessed, and the effective detection of buprofezin in tea samples was achieved through the establishment of indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and colloidal gold immunochromatography assay (GICA). The mAb-19F2 subtype was IgG1, with an IC50 of 1.8 ng/mL and a linear range (IC20-IC80) of 0.6-5.4 μg/L, and had a cross-reaction rate of less than 0.18% with 29 other pesticides (neonicotinoids and insect growth regulators). The study identified π-π stacking interactions between hapten and TYR-61 at the mAb-19F2 site and alkyl/phosphate interactions with TRP-105 and ARG-103. The ic-ELISA had an IC50 of 12.9 ng/mL in green tea and 5.65 ng/mL in black tea, with a recovery rate of 92.4%-101.0% and RSD of 2.1%-4.8%. The GICA had a limit of detection (LOD) was 500 ng/mL, with the complete disappearance of the test lines visible to the naked eye. The limit of quantitation (LOQ, IC20) was determined to be 16.8 ng/mL. Additionally, the developed GICA showed no cross-reactivity with neonicotinoid pesticides. The recovery rate of tea spiked recovered samples was 83.6%-92.2%, with an RSD of 5.3%-12.6%, and the results were consistent with the LC/MS method. This study is important for the real-time detection of buprofezin residues to ensure food safety and human health.

Magnetic relaxation switch sensor based on aptamer-modified poly-L-lysine-ferroferric oxide magnetic nanoparticles and graphene oxide for the determination of insecticides in vegetables

A simple and effective graphene oxide-magnetic relaxation switch (GO-MRS) sensor that combines graphene oxide (GO) and aptamer-modified poly-L-lysine(PLL)-Fe₃O₄ nanoparticles (Fe₃O₄@PLL-Apt NPs) was designed for the detection of acetamiprid (ACE). In this sensor, Fe₃O₄@PLL-Apt NPs acted as a relaxation signal probe and GO facilitated the generation of relaxation signal changes (dispersion/aggregation shift), while the aptamer is a molecular component that recognizes ACE. This GO-assisted magnetic signal probe improves the stability of magnetic nanoparticles in solution and enhances their sensitivity to small molecules while avoiding cross-reactions. Under optimal conditions, the sensor exhibits a wide working range (10-80 nM) and low detection limit (8.43 nM). The spiked recoveries ranged from 96.54 to 103.17%, with a relative standard deviation (RSD) of less than 2.3%. In addition, the performance of the GO-MRS sensor matched that of the standard method (liquid chromatography-mass spectrometry (LC-MS)), indicating that the GO-MRS sensor is suitable for the detection of ACE in vegetables.

Phytotoxic effect of the insecticide imidacloprid in Phaseolus vulgaris L. plant and evaluation of its bioaccumulation and translocation by electrochemical methods

The objective of this work is to study the toxicological effect of the imidacloprid (IMD) on common bean plants (Phaseolus vulgaris L) when used at high doses and its quantification by electrochemical method. Common bean plants were exposed to increasing concentrations of IMD and the different plant tissues were subjected to various analyses. The IMD detection in different tissues of the bean plant was performed after extraction on the metallic silver electrode using square wave voltammetry. The analytical and calibration parameters (Slope, correlation coefficient, linear range, detection limit and relative standard deviation) were calculated for the different plant tissues. The effect of different doses (5.0 × 10^-3 to 5.0 × 10^-2 mol L^-1) of IMD was evaluated on germination, seedling (vigour, growth) and photosynthetic pigments in the bean plant. The results indicate that germination rate and seed vigour index reduced significantly (p ≤ 0.05) only in the applied concentrations above the recommended dose. A similar effect of IMD was observed on seedling development in term of roots length, plant length, number of leaves and number of nods. Concerning pigments content, chlorophyll a, b and total chlorophyll maximally decreased by 95.26%, 80.44% and 82.15% respectively at high applied dose. The bioaccumulation and translocation behaviour of IMD in bean plant was investigated, revealing that the IMD can be bioaccumulated in roots and can easily be translocated into stems and leaves.

Nanofibrous Online Solid-Phase Extraction Coupled with Liquid Chromatography for the Determination of Neonicotinoid Pesticides in River Waters

Polymeric nano- and microfibers were tested as potential sorbents for the extraction of five neonicotinoids from natural waters. Nanofibrous mats were prepared from polycaprolactone, polyvinylidene fluoride, polystyrene, polyamide 6, polyacrylonitrile, and polyimide, as well as microfibers of polyethylene, a polycaprolactone nano- and microfiber conjugate, and polycaprolactone microfibers combined with polyvinylidene fluoride nanofibers. Polyimide nanofibers were selected as the most suitable sorbent for these analytes and the matrix. A Lab-In-Syringe system enabled automated preconcentration via online SPE of large sample volumes at low pressure with analyte separation by HPLC. Several mat layers were housed in a solvent filter holder integrated into the injection loop of an HPLC system. After loading 2 mL sample on the sorbent, the mobile phase eluted the retained analytes onto the chromatographic column. Extraction efficiencies of 68.8–83.4% were achieved. Large preconcentration factors ranging from 70 to 82 allowed reaching LOD and LOQ values of 0.4 to 1.7 and 1.2 to 5.5 µg·L⁻¹, respectively. Analyte recoveries from spiked river waters ranged from 53.8% to 113.3% at the 5 µg·L⁻¹ level and from 62.8% to 119.8% at the 20 µg·L⁻¹ level. The developed methodology proved suitable for the determination of thiamethoxam, clothianidin, imidacloprid, and thiacloprid, whereas matrix peak overlapping inhibited quantification of acetamiprid.

Zeolite H-Beta as a Dispersive Solid-Phase Extraction Sorbent for the Determination of Eight Neonicotinoid Insecticides Using Ultra-High-Performance Liquid Chromatography—Tandem Mass Spectrometry

In this study, a dispersive solid-phase extraction (DSPE) pretreatment procedure using zeolite H-Beta as a sorbent was exploited for the determination of eight neonicotinoids in bottled water and honey products based on ultra-high-performance liquid chromatography–tandem mass spectrometry analysis. The zeolite H-Beta was demonstrated to be a suitable sorbent for neonicotinoid insecticides, even after 10 recycles of reuse. The method performance was evaluated by the linearity (R2 ≥ 0.998), recovery (71–108%), precision (0.1–7.8%), limit of detection (0.05–0.1 ng/mL) and limit of quantification (0.1–0.2 ng/mL), which suggested excellent stability and high sensitivity with the use of the DSPE procedure. The method was further successfully applied in the test of neonicotinoid insecticides in 34 samples. Zeolite H-Beta shows promise as an efficient and practical material for monitoring neonicotinoid insecticides in bottled water and multiplex honey matrices.

Facile Detection and Quantification of Acetamiprid Using a Portable Raman Spectrometer Combined with Self-Assembled Gold Nanoparticle Array

Rapid and facile determination of pesticides is critically important in food and environmental monitoring. This study developed a self-assembled gold nanoparticle array based SERS method for highly specific and sensitive detection of acetamiprid, a neonicotinoid pesticide that used to be difficult in SERS analysis due to its low affinity with SERS substrates. SERS detection and quantification of acetamiprid was conducted with self-assembled gold nanoparticle arrays at the interface of chloroform and water as the enhancing substrate. Since targets dissolved in chloroform (organic phase) also have access to the hot-spots of Au NP array, the developed method exhibited good sensitivity and specificity for acetamiprid determination. Under the optimal conditions, SERS intensities at Raman shifts of 631 cm−1 and 1109 cm−1 displayed a good linear relationship with the logarithm concentration of acetamiprid in the range of 5.0 × 10−7 to 1.0 × 10−4 mol/L (0.11335 ppm to 22.67 ppm), with correlation coefficients of 0.97972 and 0.97552, respectively. The calculated LOD and LOQ of this method were 1.19 × 10−7 mol/L (0.265 ppb) and 2.63 × 10−7 mol/L (0.586 ppb), respectively, using SERS signal at 631 cm−1, and 2.95 × 10−7 mol/L (0.657 ppb) and 3.86 × 10−7 mol/L (0.860 ppb) using SERS signal at 1109 cm−1, respectively. Furthermore, the developed SERS method was successfully applied in determining acetamiprid on the surface of apple and spinach. This method offers an exciting opportunity for rapid detection of acetamiprid and other organic pesticides considering its advantages of simple preparation process, good specificity and sensitivity, and short detection time (within 1 h).

Recyclable nitrogen-containing chitin-derived carbon microsphere as sorbent for neonicotinoid residues adsorption and analysis

Chitin-derived three-dimensional nanomaterials has tremendous potential in pesticide residue analysis as an attractive green substitute for toxic solvents. The work presented herein focuses on constructing the environmentally friendly nitrogen-containing chitin-derived carbon microspheres (N-CCMP) for the efficient adsorption of neonicotinoid pesticides (NPs) including acetamiprid, clothianidin, imidacloprid and thiamethoxam. The N-CCMP displayed hierarchical porous structure, uniform size distribution, and excellent specific surface area of 680.8 m²  g^-1. The N-CCMP with N-heterocyclic ring structure and surface oxygen functional groups exhibited good affinity to NPs, which was beneficial for the rapid adsorption. Then, the N-CCMP were utilized as sorbent in extraction of NP residues. Under the optimum conditions, the relative recoveries in water and juice sample were in the range of 85 %-116 % and 74 %-108 %, with relative standard deviations (RSDs) of 0.1 %∼5.2 % and 0.7 %∼5.2 %, respectively. The extraction performance of N-CCMP were still over 80 % after 5 times of reuse.

Review of sample preparation methods for chromatographic analysis of neonicotinoids in agricultural and environmental matrices: From classical to state-of-the-art methods

This review specifically examines the development of sample preparation methods for residue analyses of neonicotinoid insecticides in agricultural and environmental matrices. Pesticide residue analysis is fundamentally important to ensure the safety of foods and processed foods of plant and animal origin, and to preserve the environment, particularly soil and water. For the development of pesticide residue analysis, the sample preparation process is an important key to maximizing the analytical performance of highly sensitive and accurate chromatographic instruments and to acquiring reliable analytical results. This review outlines sample preparation methods that have been proposed to date for extraction of neonicotinoids that might remain in a complicated sample matrix in quantitatively trace amounts, and for cleaning up, to the greatest extent possible, the interfering components that coexist in the sample extract.

A low-background fluorescent aptasensor for acetamiprid detection based on DNA three-way junction-formed G-quadruplexes and graphene oxide

A simple fluorescence detection platform has been established for acetamiprid assay based on DNA three-way junctions (TWJs), which can triple the fluorescence signal without any other amplification. It is designed with three single-stranded DNAs (ssDNA), each of which contains one-third or two-thirds of the G-quadruplex sequence at each end. Upon the addition of acetamiprid, the conformation of the aptamer-containing double-stranded DNA (dsDNA) changes from its original conformation and releases a strand of ssDNA. This ssDNA, with the other two ssDNAs, can assemble into DNA TWJs, and the three pairs of the branched ends of the DNA TWJs are adjacent to each other, allowing them to form three units of G-quadruplexes. Hence, the fluorescence of N-methyl mesoporphyrin IX (NMM) is lighted by the nascent G-quadruplexes. Graphene oxide (GO) is then added to minimize the detection background by absorbing the free NMM and non-target-induced ssDNA. The proposed strategy can assay acetamiprid in a wide linear range of 0-500 nM with a detection limit of 5.73 nM. More importantly, this assay platform demonstrates high potential for acetamiprid assay in food control and environmental monitoring.

Washing fresh tea leaves before picking decreases pesticide residues in tea

BACKGROUND

The use of pesticides during tea plant cultivation helps agricultural production and prevents and controls pests, diseases and weeds. It is of the utmost importance to balance pesticide application with tea quality, safety and consumer health. The uptake of pesticides into plants may lead to the presence of residues that are hazardous to human health, especially for some foliar-applied insecticides. The movability or penetration behavior of a pesticide remains unknown after it has been sprayed on a tea leaf.

RESULTS

Two organophosphate (acephate, trichlorfon) and three neonicotinoid pesticides (imidacloprid, thiamethoxam and acetamiprid) were confirmed with respect to their removal from the treated fresh leaves of tea saplings via washing in a phytotron. Four of the targets have little penetrative ability into tea leaves, mainly existing (> 92%) on the tea leaf surface, except for trichlorfon (> 70%), for 30 days. With higher vapor pressures, trichlorfon and acetamiprid had relatively higher penetration ratios of 8.63-29.60% and 0.28-8.03% respectively. Two organophosphate insecticides were found to degrade more quickly, with lower final amounts of residues on and in the whole leaf compared to the neonicotinoid pesticides. In a field test, these residues could be reduced by 45-72% after a pre-harvest interval of 3 days, and by 16-89% after 7 days, when the fresh tea shoots were sprayed with 2 or 4 L m^-2 water.

CONCLUSION

Pesticides with different structures have different penetration abilities on the tea leaf surface, and some pesticides in commercial tea can be reduced by spraying with water before fresh leaves are picked. © 2020 Society of Chemical Industry.

Evaluation of supercritical fluid extraction for the determination of neonicotinoid pesticides in green onion

A supercritical fluid extraction (SFE) method was presented for the determination of neonicotinoid pesticides in green onion. We optimized the SFE parameters, namely the pressure, temperature, type and concentration of the modifier solvent, and extraction time, by testing on the incurred green onion applied with four commercial neonicotinoid formulations at the harvesting stage. The analytical values of the four neonicotinoids, obtained by 5 min dynamic SFE with a 25% (v/v) methanol/supercritical carbon dioxide mixture at 80 °C and 25 MPa, were in good agreement with those obtained by solid-liquid extraction using a homogenizer. This latter homogenization method is employed as a Japanese official method for the analysis of pesticide residues in food. The SFE-to-homogenization analytical value ratios were in the range 98.8-100.0%. Spike-and-recovery testing with spiked green onion was also performed by optimized SFE. The ratios of the analytical-to-spiked concentrations for six neonicotinoids obtained by the SFE method were 96.1-102.1% for 0.4 mg/kg and 93.9-104.1% for 4.0 mg/kg spiking levels. These values satisfied the Japanese validation guidelines for the testing method of pesticides in food. These results indicate that SFE is applicable for the analysis of neonicotinoids in green onion and enables automatic extraction with a small amount of solvent.

Physiological effects of thiamethoxam on Zea mays and its electrochemical detection using a silver electrode

BACKGROUND

The aim of this work is the detection and quantification of bioaccumulated thiamethoxam (THM) in Zea mays at a silver electrode using square-wave voltammetry. Thiamethoxam bioaccumulation and plant development were followed for 10 days from germination to seedling growth. Germination rate, accumulation rate, root length, and plant length were used as indicators. All experiments were carried out using several concentrations of THM (5.0 × 10^-4 , 1.0 × 10^-3 , 5.0 × 10^-3 , 3.4 × 10^-2 and 5.0 × 10^-2 mol L^-1 ).

RESULTS

The results confirm that Zea mays was sensitive to this insecticide and that germination and growth inhibition were dose dependent. The efficiency and utility of the proposed method were discussed. The current intensity increases linearly with an increase in the THM bioaccumulated in Zea mays. After 10 days,the recovery results of the extraction of THM from zea Mayes samples spiked with different concentrations were encouraging. The detection and quantification limits were found to be 9.58 × 10^-6 mol L^-1 (3*SD/B) and 3.13 × 10^-5 mol L^-1 (10*SD/B). The precision was 2.67% for eight repetitions in a solution of 3.5 × 10^-4 mol L^-1 THM. Histological tests were also performed to confirm the effect of THM on the plant and showed that exposure to THM induced a net histological modification in the primary root tissue of Zea mays.

CONCLUSION

The use of THM can affect the quality of the plant crop yield, and its accumulation in edible plants could pose a potential risk for human and animal health if the insecticide intake were to exceed the recommended tolerable limits. © 2019 Society of Chemical Industry.

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

This study proposes a practical and precise method for the simultaneous analysis of seven neonicotinoid pesticides in agricultural products using liquid chromatography-tandem mass spectrometry from two different approaches. First, the applicability of a cleanup cartridge, comprised of a polymer sorbent consisting of a styrene-divinylbenzene copolymer with N-containing polar groups and methacrylate, in food samples was demonstrated for the first time. Second, applying an internal standard (IS) calibration method at a lower cost was considered by changing the timing of the IS addition and selecting the minimum number of ISs by referring on the matrix effect. The proposed method resulted in excellent recoveries in all tested matrices (brown rice, grapes, and peanuts) at a spiked concentration of 0.01 mg/kg. Subsequently, a residue analysis of hagobou (young burdock) was conducted. Imidacloprid was detected at 0.02 mg/kg, and the recoveries calculated in parallel with the analysis were satisfactory.

Electrochemical detection of thiamethoxam in food samples based on Co3O4 Nanoparticle@Graphitic carbon nitride composite

Thiamethoxam is a class of neonicotinoid insecticide widely used in agriculture. Due to their high water solubility, thiamethoxam can be transported to surface waters and have the potential to be toxic to human life. Herein, a simple and robust method is presented for the detection of thiamethoxam based on hydrothermally synthesized nanoparticles of cobalt oxide into the graphitic carbon nitride composite (Co₃O₄@g-C₃N₄ NC). The materials were well characterized by XRD, FT-IR, XPS, FESEM, HRTEM, EDX, and UV-vis which provide crystalline nature, structure, and composition. The impedance measurement shows an intimate electrode/electrolyte interface by casting Co₃O₄@g-C₃N₄ onto a screen-printed carbon electrode (SPCE), delivering an interfacial resistance as low as 12.5 Ωcm². The cyclic voltammetry and differential pulse voltammetry measurements exhibit the nanocomposite as a superior electrocatalyst for the electrochemical detection of thiamethoxam and achieved a low detection limit of 4.9 nM with a wide linear range of 0.01-420 μM. The present work also demonstrates a promising strategy for electrochemical detection of thiamethoxam in real samples such as potato and brown rice.

A functionalized magnetic covalent organic framework for sensitive determination of trace neonicotinoid residues in vegetable samples

A functionalized magnetic covalent organic framework containing the nitro groups (Fe₃O₄@COF-(NO₂)₂) with core-shell structure was synthesized for magnetic solid phase extraction (MSPE) of six neonicotinoid insecticides residue in vegetable samples. The structure of Fe₃O₄@COF-(NO₂)₂ was investigated by various characterization techniques. The Fe₃O₄@COF-(NO₂)₂ exhibits the excellent thermal and chemical stability, high surface area (254.72 m² g^-1), total pore volume (0.19 cm³ g^-1), high magnetic responsivity (27.7 emu g^-1), which can be used as an ideal adsorbent for rapid isolation and enrichment of target analytes. A sensitive method was developed by using Fe₃O₄@COF-(NO₂)₂-based MSPE coupled with HPLC with UV detection. It offered good linearity within the range of 0.1-30 ng mL^-1, low limits of detection (S/N = 3) of 0.02-0.05 ng mL^-1. Furthermore, high enrichment factors of 170-250 for six neonicotinoid insecticides were obtained. The applicability of Fe₃O₄@COF-(NO₂)₂ is demonstrated for measuring trace neonicotinoid residues in vegetable samples with satisfactory recoveries, which ranged from 77.5 to 110.2%. The results indicated that the Fe₃O₄@COF-(NO₂)₂ microspheres offer great potential for efficient extraction of neonicotinoid insecticides from complex samples.

Health risk assessment of neonicotinoid insecticide residues in pistachio using a QuEChERS-based method in combination with HPLC-UV

There is an increasing need to address the potential risks arising from combined exposures to multiple residues from pesticides in the diet. Pesticide residue-related pollution is a problem that arises because of the increased use of pesticides in agriculture to meet the growing demands of food production. In this study, pesticide residue data were obtained based on an optimized extraction method. For this purpose, we established a method based on quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction for simultaneous determination of imidacloprid (IMI) and acetamiprid (ACT) in pistachio nuts. The parameters influencing the QuEChERS method were the sample-to-water ratio and adsorbent amounts. As a result, both were optimized to improve the recovery of the analytes as well as the clean-up efficiency of the pistachio matrix. Our results indicated that a freeze-out step and use of primary and secondary amines as an adsorbent led to much cleaner chromatograms with lower baseline drift, without using graphitized carbon black and C₁₈ -based adsorbent, which reduced both cost and time of analysis. Following extraction, the pesticide residues were separated and quantified by reverse-phase HPLC. For validation purposes, recovery studies were carried out using a concentration range from 20 to 2500 μg/L at nine levels. The suitable linearity, precision, and accuracy were obtained with HPLC-UV with recoveries of 70.37%-89.80% for IMI and 81.05%-113.57% for ACT, with relative standard deviations <12%. The validated method was successfully applied to the analysis of pistachio samples collected from a field trial to estimate maximum residue limits. There was no significant health risk for consumers via pistachio consumption.

A holistic study of neonicotinoids neuroactive insecticides-properties, applications, occurrence, and analysis

Among pesticides and foliar sprays involved in the treatment of seed, soil, and grass, also to crops, an important group is neonicotinoids. Neonicotinoid pesticides present similar properties with nicotine, but the mentioned compounds are less harmful for humans. Nevertheless, neonicotinoids are poisonous to insects and some invertebrates, which can act against insects' central nervous system, leading to their death. Moreover, neonicotinoids can affect the reproduction, foraging, and flying ability of honeybee and other insects including pollinators. In the present study, some neonicotinoids, such as imidacloprid, acetamiprid, clothianidin, thiacloprid, and thiamethoxam together with their toxic effects, have been presented. The Environmental Protection Agency (EPA) classifies these neonicotinoids as II and III class toxicity agents. Due to accumulation of these pesticides into the pollen of treated plants, especially due to their toxic effects against pollinators, the consequences of the occurrence of these insecticides have been discussed. Analytical aspects and methods involved in the isolation and determination of this class of pesticides have been presented in this contribution.

Quantitative analysis of acetamiprid and imidacloprid residues in tomato fruits under greenhouse conditions

A selective liquid chromatographic analytical method was studied for determination of two neonicotinoids, acetamiprid and imidacloprid, in tomato fruits under greenhouse conditions in Egypt. The fruits were extracted and cleaned up by QuEChERS method followed by HPLC determination. The method showed a good linearity with a determination coefficient (R²) of higher than 0.99 for the 0.0125-0.15 µg/mL concentration range. The method was validated using a blank tomato spiked at 5, 25 and 50 mg/kg and the recovery percentages were 83.71, 94.52 and 97.49% for acetamiprid and 88.59, 89.63 and 90.18% for imidacloprid, respectively. The rates of dissipation of both pesticides were studied and the preharvest intervals (PHIs) were calculated. Imidacloprid dissipated faster than acetamiprid and half-life periods were 1.30 and 2.07 days, respectively. Acetamiprid and imidacloprid residues were below the already established European maximum residue limits (EU MRLs) (0.5 mg/kg) 3 and 5 days after application, respectively.

Electrocatalytic activity of the metallic silver electrode for thiamethoxam reduction: application for the detection of a neonicotinoid in tomato and orange samples

BACKGROUND

Thiamethoxam (3-[(2-chloro-5-thiazolyl)methyl]tetrahydro-5-methyl-N-nitro-4H-1,3,5-oxadiazin-4-imine) belongs to a relatively new class of insecticides known as neonicotinoids, which can block irreversibly nicotinic acetylcholine receptors of the nervous system of insects. Its determination at trace levels is an acute analytical problem. Therefore, chromatography, spectroscopy, and electrochemical technics were reported. These last have several advantages (simple sensitive and less expensive). This work investigated the electro-reduction of Thiamethoxam using simple and rapid method in real samples using metallic silver electrode.

RESULTS

Silver particles, known as effective catalysts in the reduction of nitro groups, were studied to explore their roles in the shift of thiamethoxam peak potential. Cyclic voltammetry, Tafel plot and electrochemical impedance spectroscopy analysis suggest that metallic silver electrodes have a significantly greater electrocatalytic activity in thiamethoxam electroreduction than glassy carbon electrodes and carbon paste electrodes. The electrocatalytic activity of metallic silver electrodes in thiamethoxam reduction was investigated by cyclic voltammetry and chronoamperometry. A linear variation in cathodic current with the square root of the scan rate was observed, suggesting that the process is diffusion controlled. Several supporting electrolytes were tested, and the best results were obtained with Britton-Robinson (BR) buffer, pH 10.4. A linear relationship between peak current and concentration was found in the range from 1.0 × 10^-5 to 1.0 × 10^-4  mol L^-1 using square wave voltammetry (SWV) with a correlation coefficient of 0.994. The detection limit and quantification limit were 5.49 × 10^-6 and 1.83 × 10^-5  mol L^-1 , respectively.

CONCLUSION

Silve metallic electrode exhibits efficient catalytic activity towards the Thiamethoxam reduction. The proposed electrode was then used for the determination of thiamethoxam in tomato anad orage juice samples. © 2019 Society of Chemical Industry.

Evaluation of pressurized liquid extraction for the determination of neonicotinoid pesticides in green onion

A pressurized liquid extraction (PLE) method was presented for the determination of six neonicotinoid pesticides, acetamiprid, clothianidin, dinotefuran, imidacloprid, thiacloprid, and thiamethoxam in green onion. The critical parameters of PLE, e.g. extraction solvent, temperature, pressure, number of cycles, and static extraction time, were optimized by test on the spiked green onion with six neonicotinoids and the incurred green onion applied with four commercial neonicotinoid insecticide formulations (acetamiprid, dinotefuran, imidacloprid, and thiamethoxam). As a result, the recoveries of six neonicotinoids obtained by one cycle PLE with acetonitrile at 140 °C and 50 bar for 10 min were 94.7-99.5%. These results were acceptable according to the validation guideline for testing method of agricultural chemicals in food by Ministry of Health, Labour, and Welfare in Japan. PLE was also validated by the test on the incurred green onion. The analytical values of four neonicotinoids obtained by PLE were good agreement with those obtained by solid-liquid extraction with homogenizer, which is employed for Japanese official method for the analysis of pesticide residues in food (the ratios of analytical values obtained by PLE to those obtained by solid-liquid extraction were 99.7-101.2%). These results indicate that PLE is applicable for the determination of neonicotinoids in green onion.

Aerobic Degradation of Clothianidin to 2-Chloro-methyl Thiazole and Methyl 3-(Thiazole-yl) Methyl Guanidine Produced by Pseudomonas stutzeri smk

Overuse of pesticides in agriculture may harm environmental and agricultural yields. Sustainable maintenance of soil fertility and management of the environment have become a concern due to the persistence of pesticides in the soil. Microbes have various mechanisms for the bioremediation of persistent organic pollutants from the environment. A bacterium that degrades clothianidin was isolated from the pesticide and applied to agricultural soil by the enrichment technique. The identity of the bacterium was determined by studying morphological, cultural, and biochemical characteristics and 16S rRNA gene sequences. The ability to metabolize clothianidin was confirmed using UV-visible spectrophotometric, chromatographic, and spectroscopic analyses. A Gram-negative bacterium, designated smk, isolated from clothianidin-contaminated soil was confirmed to be a member of Pseudomonas stutzeri. The biodegradation of clothianidin was studied using P. stutzeri smk. Approximately 62% degradation of clothianidin was achieved within two weeks when grown at 30°C and pH 7. The effects of various physicochemical parameters, including pH, temperature, and clothianidin concentrations, on catabolic rates were studied. The biodegradation studies using UV-Vis spectrophotometry, HPLC, FTIR, and LC-MS indicated the production of the following metabolites: 2-chloro-5-methyl thiazole (CMT), methyl nitroguanidine (MNG), methyl 3-[thiazole-yl], and methyl guanidine (TMG). Identification of specific degradation metabolites indicates that bioremediation of toxic neonicotinoid insecticides may be achieved by application of P. stutzeri smk.

A label-free and enzyme-free fluorescent aptasensor for sensitive detection of acetamiprid based on AT-rich dsDNA-templated copper nanoparticles

A label-free and enzyme-free aptasensor for sensitive assay of acetamiprid has been established using AT-rich double-stranded (ds) DNA-templated copper nanoparticles (CuNPs) as fluorescent probe. In this work, two hairpin DNA, HP1 and HP2, were elaborately designed with AT-rich DNA sequences in their loops. The aptamer of acetamiprid was located at the 3'-terminal of HP1, which was caged in the stem of HP1. Upon the addition of acetamiprid, the aptamer could combine with acetamiprid to form a target/aptamer complex, and thus its free 5'-terminal was released. Subsequently, the protruded 3'-terminal of HP2 could hybridize with the free 5'-terminal of HP1 to form a stable AT-rich dsDNA. When it interacted with Cu²⁺ and ascorbic acid (AA), the AT-rich dsDNA/CuNPs were generated with strong fluorescence, offering a "switch-on" detection of acetamiprid. The developed strategy could high selectively detect acetamiprid at the concentration as low as 2.37 nM. Moreover, the possibility of this strategy for the food sample analysis was also investigated. The obtained results demonstrate that the developed strategy has a promising application potential for acetamiprid assay in food safety fields.

Detection of pesticide residues on intact tomatoes by carbon fiber ionization mass spectrometry

Trace and toxic pesticide residues may still remain on crops after harvest. Thus, maximum residual levels (MRLs) of pesticides on crops have been regulated. To determine whether the remaining pesticide residue level is below MRL, time-consuming sample pretreatment is needed prior to analysis of crop samples by suitable analytical tools. By elimination of sample pretreatment steps, a high-throughput method can be developed to determine the presence of pesticide residues directly on intact crops. Carbon fiber ionization mass spectrometry (CFI-MS) is effective in determining analytes with different polarities in solid, liquid, and vapor phases in open air. Moreover, the vapor derived from solid or liquid samples possessing high vapor pressure can be readily detected by CFI-MS. The setup of CFI-MS is straightforward. A carbon fiber (diameter of ~ 10 μm and length of ~ 1 cm) is placed close (~ 1 mm) to the inlet of the mass spectrometer applied with a high voltage (- 4.5 kV). No direct electrical contact applied on the carbon fiber is required. When placing the sample with certain vapor pressure underneath the carbon fiber, analyte ions derived from the sample can be readily detected by the mass spectrometer. Given that most pesticides possess a certain vapor pressure (~ 1.33 × 10^-5-~ 1.33 × 10^-4 Pa), we herein develop a qualitative and quantitative analysis method to determine pesticide residues on intact fruits such as tomato based on CFI-MS without requiring any sample pretreatment. Atrazine, ametryn, carbofuran, chlorpyrifos, isoprocarb, and methomyl were selected as model samples. Low limits of detection (at nM range) were achieved for the model pesticides using the current approach. Moreover, we demonstrated that the precision and accuracy of quantitative analysis of ~ 5% and ~ 2%, respectively, could be achieved using this approach. Graphical Abstract ᅟ.

Distribution of cyanobacteria and their interactions with pesticides in paddy field: A comprehensive review

Cyanobacteria, also known as blue green algae are one of the important ubiquitous oxygen evolving photosynthetic prokaryotes and ultimate source of nitrogen for paddy fields since decades. In past two decades, indiscriminated use of pesticides led to biomagnification that intensively harm the structure and soil functions of soil microbes including cyanobacteria. Cyanobacterial abundance biomass, short generation, water holding capacity, mineralizing capacity and more importantly nitrogen fixing have enormous potential to abate the negative effects of pesticides. Therefore, investigation of the ecotoxicological effects of pesticides on the structure and function of the tropical paddy field associated cyanobacteria is urgent and need to estimate the fate of interaction of pesticides over nitrogen fixations and other attributes. In this regard, comprehensive survey over cyanobacterial distribution patterns and their interaction with pesticides in Indian context has been deeply reviewed. In addition, the present paper also deals the molecular docking pattern of pesticides with the nitrogen fixing proteins, which helps in revealing the functional interpretation over nitrogen fixation process.

Simultaneous determination of nine neonicotinoids in human urine using isotope-dilution ultra-performance liquid chromatography-tandem mass spectrometry

Neonicotinoids (neonics), a class of systemic insecticides, have been frequently detected in pollen, vegetables, and fruits. Recently, an increasing concern has been aroused for human exposure to neonics. However, biological monitoring for quantifying body burden of neonics has rarely been reported. In this study, we developed an isotope-dilution ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) method to simultaneously quantify nine neonics, including acetamiprid (ACE), thiamethoxam (THIAM), imidacloprid (IMIP), clothianidin (CLO), flonicamid (FLO), thiacloprid (THIAC), dinotefuran (DIN), nitenpyram (NIT), and imidaclothiz (IMIT) in urine. The limits of quantification were 0.1 μg/L for ACE, FLO, DIN, NIT and IMIT, and 0.2 μg/L for THIAM, IMIP, CLO, and THIAC. The overall recoveries were 80.8-103%, 81.5-91.7% and 83.0-92.3% for QA/QC samples fortifying at 1, 25, and 100 μg/L levels, respectively. UPLC/MS/MS method was used to analyze urine samples obtained from 10 children in Hangzhou, China. The detection frequencies were 80% for ACE and IMIP, 70% for THIAM and CLO, 20% for DIN and IMIT and 10% for THIAC. FLO and NIT were not detected in those urine samples. The data provided here will be helpful for conducting biological monitoring of neonics exposure in the future.

Development and Validation of an Ultra-Sensitive UHPLC-MS/MS Method for Neonicotinoid Analysis in Milk

A very sensitive ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was developed and validated for the quantitation of the most common neonicotinoids (thiamethoxam, clothianidin, imidacloprid, acetamiprid, and thiacloprid) at trace levels in milk. Using fast and selective liquid-liquid extraction (LLE) starting from 0.5 mL of milk, lowest limits of quantitation (LLOQ) equal or lower than 10 pg/mL for all analytes were achieved. Precision and accuracy were evaluated at four different concentrations (5, 10, 500, and 10000 pg/mL) and ranged between 2 and 16% (RSD) and 77-125%, respectively. Extraction recoveries and matrix effects ranged between 64 and 76% and 88-98%, respectively. The method was applied to measure neonicotinoid levels in a series of conventional and organic Swiss milks as well as in human breast milk and commercial powdered milk. More than 90% of the samples tested positive for at least one neonicotinoid. However, all animal samples were far below the maximum residue limits authorized for human consumption with average total neonicotinoid levels of 16.1 ± 13.1 pg/mL. Human breast milks and powdered milks contained similar amounts of neonicotinoids. Taken together, our results demonstrate the high prevalence of neonicotinoids in milk from all origins, albeit at levels considered to be safe for human consumption.

A label-free triplex-to-G-qadruplex molecular switch for sensitive fluorescent detection of acetamiprid

The detection and monitoring of acetamiprid has drawn extensive attentions, due to their potential threat to human health. Herein, a simple, sensitive and label-free fluorescent assay based on triplex-to-G-qadruplex (TTGQ) molecular switch, was developed for the assay of acetamiprid in aqueous solution. In this detection, the proposed TTGQ molecule contained the acetamiprid aptamer sequence at its loop part and the triple-helix structure at its stem part. One single-stranded DNA grafted by two split G-rich DNA sequences at its two ends, participated in the assembly of the triplex part in TTGQ. In the presence of acetamiprid, TTGQ was dissociated, and the split G-rich DNA was released out to result in the fluorescent signal enhancement of a G-quadruplex's probe. By virtue of this TTGQ molecular switch, the proposed assay can sense acetamiprid at the concentration as low as 2.38 nM with excellent selectivity. Furthermore, the detection of acetamiprid in three kinds of foods extract demonstrated the high application potential of the detection platform in the field of food safety. Compared with the other reported strategies for acetamiprid assay, this triplex-to-G-qadruplex-based fluorescent molecular switch was just composed of two DNA probes without the labeling procedure, presenting a really simple and low-cost fluorescent detection for acetamiprid assay.

Imidacloprid as reproductive toxicant and endocrine disruptor: investigations in laboratory animals

Imidacloprid, a neonicotinoid insecticide, has been used worldwide due to its selective toxicity for insects. Its residues may enter the food chain, which is why it is important to investigate the potential adverse effects of imidacloprid exposure. This review summarises current knowledge of the reproductive toxicity and disruptive endocrine effects of imidacloprid in laboratory animals. Investigations, conducted mostly on laboratory rats, have shown adverse effects of imidacloprid on the reproductive ability in both parental and offspring generation as well as on the development of the offspring. Like many pesticides, imidacloprid may also act as endocrine disrupting chemical (EDC). It may disrupt the metabolic homeostasis, contribute to obesity, and disrupt steroidogenesis by inhibiting cytochrome P450 (CYP) enzyme activities. All these adverse effects of imidacloprid may pose a serious risk for reproduction and development with long-term consequences in adulthood.

Contamination by neonicotinoid insecticides and their metabolites in Sri Lankan black tea leaves and Japanese green tea leaves

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A method for 7 neonicotinoids and 20 metabolites in tea was developed by LC–MS/MS.

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All seven neonicotinoids and ten of the metabolites were detected in Japanese tea.

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Dinotefuran and dinotefuran-urea were most abundant neonicotinoid and metabolite.

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The estimated MDIs of neonicotinoid insecticides were lower than the ADIs.

Tea is one of the world’s most popular beverages due to health promoting effects. Despite these, there have been concerns about the adverse effects of tea contamination by neonicotinoid insecticides. Only a handful of studies on neonicotinoid insecticides in tea have been carried out and this study was therefore performed to determine the concentrations of seven neonicotinoid insecticides and 20 metabolites in Japanese green tea leaves, and black tea leaves from Sri Lanka; and assess the Maximum Daily Intake (MDI) of neonicotinoid insecticides. From the results, the seven parent compounds were detected in Japanese tea leaves and beverages. Dinotefuran (3004 ng/g) was found at the highest level in green tea leaves. Ten of the 20 metabolites were detected in Japanese tea products. Dinotefuran-urea (92%) and thiacloprid-amide (89%) were most frequently detected in Japanese tea leaves. Clothianidin-urea (100 ng/g) was found at the highest level in green tea leaves. Neonicotinoid insecticides and metabolites were not detected in Sri Lankan black tea leaves. The concentrations and MDI of neonicotinoid insecticides in tea leaves were below the Maximum Residual Levels (MRLs) and Acceptable Daily Intakes (ADIs), respectively.

Simultaneous determination of neonicotinoid insecticides and insect growth regulators residues in honey using LC-MS/MS with anion exchanger-disposable pipette extraction

In this study, we developed an anion exchanger-disposable pipette extraction (DPX) method to detect the residual concentrations of eight neonicotinoid insecticides (dinotefuran, acetamiprid, clothianidin, thiacloprid, imidachloprid, imidaclothiz, nitenpyram, and thiamethoxam) and eight insect growth regulators (IGRs; triflumuron, cyromazine, buprofezin, methoxyfenozide, tebufenozide, chromafenozide, fenoxycarb, and RH 5849) in Chinese honey samples collected from different floral sources and different geographical regions using liquid chromatography tandem mass spectrometry (LC-MS/MS). QAE Sephadex A-25 was used as the anion exchanger in the DPX column for the purification and cleanup of honey samples. Analytes were eluted with a mixture of acetonitrile and 0.1 M HCl, and the elution was subjected to LC analysis. This method was thoroughly validated for its reproducibility, linearity, trueness, and recovery. Satisfactory recovery of pesticides was obtained ranging from 72% to 111% with intraday RSDs (n = 5) of 1%-10%. High linearity (R² ≥ 0.9987) was observed for all 16 pesticides. Limits of detection and quantification for all 16 compounds ranged from 0.3 to 3 μg/kg and from 1 to 10 μg/kg, respectively. Pesticide residues (9-113 μg/kg) were found in Chinese honey samples. The anion exchanger-DPX method was effective for removing sugars and retaining target analytes. Moreover, this method was highly reliable and sensitive for detecting neonicotinoids and IGRs in different floral sources of honey and will be applicable to matrixes with high sugar content.

Preconcentration of Trace Neonicotinoid Insecticide Residues Using Vortex-Assisted Dispersive Micro Solid-Phase Extraction with Montmorillonite as an Efficient Sorbent

In this work, we investigated montmorillonite for adsorption of neonicotinoid insecticides in vortex-assisted dispersive micro-solid phase extraction (VA-d-μ-SPE). High-performance liquid chromatography with photodiode array detection was used for quantification and determination of neonicotinoid insecticide residues, including thiamethoxam, clothianidin, imidacloprid, acetamiprid, and thiacloprid. In this method, the solid sorbent was dispersed into the aqueous sample solution and vortex agitation was performed to accelerate the extraction process. Finally, the solution was filtered from the solid sorbent with a membrane filter. The parameters affecting the extraction efficiency of the proposed method were optimized, such as amount of sorbent, sample volume, salt addition, type and volume of extraction solvent, and vortex time. The adsorbing results show that montmorillonite could be reused at least 4 times and be used as an effective adsorbent for rapid extraction/preconcentration of neonicotinoid insecticide residues. Under optimum conditions, linear dynamic ranges were achieved between 0.5 and 1000 ng mL^-1 with a correlation of determination (R²) greater than 0.99. Limit of detection (LOD) ranged from 0.005 to 0.065 ng mL^-1, while limit of quantification (LOQ) ranged from 0.008 to 0.263 ng mL^-1. The enrichment factor (EF) ranged from 8 to 176-fold. The results demonstrated that the proposed method not only provided a more simple and sensitive method, but also can be used as a powerful alternative method for the simultaneous determination of insecticide residues in natural surface water and fruit juice samples.