Modified QuEChERS Method for the Determination of Multiclass Pesticide Residues in Fruit Samples Utilizing High-Performance Liquid Chromatography

Levels of organochlorine pesticides in onion and tomato samples from selected towns of Jimma Zone, Ethiopia

This study aimed to determine residues of organochlorine pesticides (OCPs) in tomato and onion samples collected from selected markets in the Jimma zone. A QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method was used for sample preparation followed by gas chromatography-mass spectrometry (GC-MS) for OCPs analysis. The method used showed wide linear ranges from 5-50 μg/L for all eight pesticides, with R2 values ≥ 0.992. The LOD values for the pesticides tested ranged from 0.14 μg/kg for p,p'-DDE to 2.40 μg/kg for p,p-DDT. LOQ values ranged from 0.46 μg/kg for p,p-DDE to 8.32 μg/kg for p,p'-DDT. The recoveries ranged from 74.84 - 109.45 % except for β-BHC (67.82 %). While most of the OCPs in the onion and tomato samples met European Union (EU) and Codex standards, some exceeded the limits. Methoxychlor and p,p'-DDT in onions, and methoxychlor, p,p'-DDT, α-BHC, and δ-BHC in some tomatoes, were detected above the permitted levels. Specific OCPs were not detected in some samples including aldrin in Meki Tomato (Mek-T), γ-chlordane in Agaro Tomato (Ag-T), and p,p'-DDE in Gera Tomato (Ger-T). The residual concentrations of OCPs varied among the samples. Among tomatoes, Gera had the highest percentage of detected OCPs contaminants (37 %), followed by Agaro (34.34 %) and Meki (28.55 %). Similarly, Sire onion (SrO) had the highest percentage of detected OCPs (28 %) compared to Minjer (25.16 %), Shewa Robit (25.10 %), and Sudan onion (22.25 %). In conclusion, most tomato and onion samples analyzed in this study contained OCP residues highlighting the importance of conducting a consumer health risk assessment.

Strategy of In Situ Electrochemical Regulation for Highly Enhanced Nonenzymatic Sensing of Carbaryl

Specific and sensitive sensing of most pesticide residues relies on enzymes such as acetylcholinesterase and advanced materials, which need to be loaded on the surface of working electrodes, leading to instability, uneven surface, tedious process, and high cost. Meanwhile, employing certain potential or current in electrolyte solution could also modify the surface in situ and overcome these drawbacks. However, this method is only regarded as electrochemical activation widely applied in the pretreatment of electrodes. In this paper, by means of regulating the electrochemical technique and its parameters, we prepared a proper sensing interface and derivatized the carbaryl (a carbamate pesticide) hydrolyzed form (1-naphthol) to enhance sensing by 100 times within several minutes. After regulation I by chronopotentiometry with 0.2 mA for 20 s or chronoamperometry with 2 V for 10 s, abundant oxygen-containing groups form and the ordered carbon structure is destroyed. Sweeping from -0.5 to 0.9 V through cyclic voltammetry for only one segment, following regulation II, the composition of oxygen-containing groups changes and the disordered structure is alleviated. Finally, on the constructed sensing interface, test by regulation III through differential pulse voltammetry from 0.8 to -0.4 V, resulting in derivatization of 1-naphthol during 0.8-0 V, followed by electroreduction of the derivative at around -0.17 V. Compared with the electro-oxidation peak at 0.5 V in previous reports, it is essential to improve specificity, even toward several other carbamate pesticides with similar structures. Hence, the in situ electrochemical regulation strategy has demonstrated great potential for effective sensing of electroactive molecules.

Multiclass Pesticide Residue Analysis in Fruit and Vegetable Samples by Combining Acetone-Based Salting-Out Assisted Extraction with Dispersive Liquid-Liquid Microextraction

Isolation and enrichment of multiclass pesticides’ residue, namely, fungicides (benalaxyl), herbicides (atrazine), carbamate insecticides (carbofuran), organophosphate insecticides (chlorpyrifos), organochlorine insecticides (4,4′-DDT), and pyrethroid insecticides (bifenthrin), were made by combining acetone-based salting-out assisted extraction with the dispersive liquid-liquid microextraction (SADLLME) method, followed by high-performance liquid chromatography-diode array detection (HPLC-DAD). The effect of the type and volume of the extraction solvent in the pretreatment step, the volume of the disperser solvent (acetone extract), the type and volume of the extraction solvent, pH, and salt addition in the DLLME procedure was studied. Good coefficient of determination (R2 ≥ 0.9964) was obtained for all the target analytes. The limits of detection and quantification limits were between 2.1 and 4.5 and 5.7 and 12.9 µg/kg, respectively, with adequate enrichment factors ranging from 37.6 to 191. The recoveries of spiked blank tomato ranged from 86.8 to 109.5%. The limit of quantification of the proposed method was lower than the maximum residue limits set by the European Union. The repeatability and reproducibility of precisions ranged between 2.9 and 8.0 and 4.9 and 9.5%, respectively. The optimized and validated method was applied to quantify pesticides in tomato, pear, apple, and melon obtained from different markets. However, all target compounds studied in this work were not detected in any real samples applied. Overall, the work results revealed that the proposed method is useful for the sample extraction and preconcentration of the target analytes from fruits and vegetables.

Residues and Dietary Risk Assessments of 2,4-D Isooctyl Ester, Metribuzin, Acetochlor, and 2-Ethyl-6-methylaniline in Corn or Soybean Fields

Since 2,4-dichlorophenoxy acetic acid (2,4-D) was discovered in the 1940s, 2,4-D and its derivatives remain among most commonly used herbicides in the world. There have been recent increases in using 2,4-D products in a combination with other herbicides such as metribuzin and acetochlor to control noxious weeds. However, accurate analysis of 2,4-D isooctyl ester remains to be improved due to long analysis time and rapid conversion of the ester to acid (i.e., under-reporting residues). In this work, a simple hydrolysis procedure was introduced to provide a quantitative hydrolytic rate of the ester (>95%) and did not affect the other pH-sensitive compounds. Analysis parameters and sample pretreatments were optimized for improved selectivity and accuracy. The hydrolysis-QuEChERS (quick, easy, cheap, effective, rugged, and safe) technique for multidetermination of 2,4-D isooctyl ester, metribuzin, acetochlor, and 2-ethyl-6-methylaniline in corn and soybeans via high performance liquid chromatography-tandem mass spectrometry was established. The method had average recoveries of 74-109% with relative standard deviations ≤13.5% and limits of quantifications (LOQs) of 0.05 mg/kg. The terminal residues of these compounds found in real edible matrixes were less than the corresponding LOQs at harvest time. The risk quotients were far below 100%, indicating a low health risk to consumers.

Identification, Quantification, and Stereoselective Degradation of Triazole Fungicide Cyproconazole in Two Matrixes through Chiral Liquid Chromatography-Tandem Mass Spectrometry

Systematic investigation of cyproconazole, including absolute stereochemistry, fungicidal activity, quantification in two matrixes, and stereoselective degradation in cucumber, are conducted in this study. By virtue of vibrational circular dichroism (VCD) spectroscopy, absolute configurations of four stereoisomers were identified to be (2R,3R)-(+)-, (2R,3S)-(+)-, (2S,3S)-(-)-, and (2S,3R)-(-)-cyproconazoles. Then four stereoisomers exhibited stereoselective fungicidal activities against Fusarium graminearum Schw and Magnaporthe oryzae, and the order of fungicidal activity was (2S,3S)-(-)-stereoisomer > the stereoisomer mixture > (2S,3R)-(-)-stereoisomer > (2R,3R)-(+)-stereoisomer > (2R,3S)-(+)-stereoisomer. Moreover, chiral liquid chromatography-tandem mass spectrometry was used to identify and quantify cyproconazole stereoisomers in soil and cucumber matrixes. Good linearity (R² ≥ 0.99) and recoveries (86.79-92.47%, RSD ≤ 3.94%) for them were achieved, individually. Furthermore, stereoselective degradation of four cyproconazole stereoisomers was observed in cucumber and the order of degradation rate was (2R,3R)-(+)-cyproconazole > (2S,3S)-(-)-cyproconazole > (2R,3S)-(+)-cyproconazole > (2S,3R)-(-)-cyproconazole. We envision that such systematic assessments of chiral fungicides at an enantiomeric level would provide valuable information in future studies involving enantioselective physiological, metabolic, and toxicological activities.

Antibody-free colorimetric detection of chlorothalonil in cucumberviathe inhibition of an enzyme-triggered reaction

Currently known rapid determination of fungicides usually relies on antibody-based immunoassay. This paper reports a simple antibody-free colorimetric assay for chlorothalonil via the inhibition of an enzyme-triggered reaction. The enzymatic activity of glyceraldehyde-3-phosphate dehydrogenase was significantly inhibited by chlorothalonil, and the color change of NBT-PMS system induced from NADH formation was suppressed, which could be used indirectly to assay chlorothalonil. The limit of detection (LOD) was 0.05 μM with a linear range from 0.5 to 10 μM, and the detection of 1 μM chlorothalonil in solution was achieved with a naked-eye readout. In addition, the colorimetric measurement results of the cucumber samples showed a good recovery rate, although the sensitivity was less effective than the instrumental method. Nevertheless, the results demonstrates that the chlorometric method provides potential opportunities for reliable, cost-effective quantitative detection for chlorothalonil residues in vegetables.

Colorimetric detection of chlorothalonil in cucumber via the inhibition of an enzyme-triggered reaction.