Clothianidin residues in green bean, pepper and watermelon crops and dietary exposure evaluation based on dispersive liquid-liquid microextraction and LC–MS/MS

Development of Green and Facile Sample Preparation Method for Determination of Seven Neonicotinoids in Fresh Vegetables, and Dissipation and Risk Assessment of Imidacloprid and Dinotefuran

A facile procedure for extracting and determining seven neonicotinoids was developed. Water was the only extraction solvent without phase separation and cleanup steps. The method was validated according to European Union standards, and the values obtained were compared with the criteria. The accuracy values were between 99.8% (thiamethoxam) and 106.8% (clothianidin) at the spiking levels of 0.01, 0.1, and 1 mg/kg in the tested matrices. The precision as pooled RSD values was ≤6.1% (intra-day) and ≤6.9% (inter-day). The limit of quantification was set and tested at 0.01 mg/kg. The matrix effect was evaluated, and all matrices had a suppressive effect. The matrix of the cucumber was the most effective, with -20.9% for dinotefuran and an average of -9.8% for all compounds, while the tomato matrix had the slightest effect. Real marketed samples were analyzed using the developed and QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) methods; the results were not significantly different. A supervised field trial was conducted in the open field to study the dissipation patterns of imidacloprid and dinotefuran in tomatoes. The dissipation of both compounds followed first-order kinetics. The half-life (T½) values were 3.4 and 2.5 days, with dissipation rates k of 0.2013 and 0.2781 days, respectively. Following the EU-MRL database, the calculated pre-harvest interval (PHI) values were 7 and 14 days for imidacloprid and dinotefuran, respectively, and 3 days for both compounds following Codex Alimentarius regulations. The risk of imidacloprid and dinotefuran residues was estimated from chronic and acute perspectives. The risk factors of dinotefuran were lower than those of imidacloprid. Nonetheless, the highest expected residues of both compounds were below the tolerance limits.

Development of competitive and noncompetitive immunoassays for clothianidin with high sensitivity and specificity using phage-displayed peptides

Clothianidin is a widely used pesticide that has been banned from outdoor use by the European Union due to its toxicity. To improve the sensitivity and specificity of existing clothianidin immunoassays, we developed competitive and noncompetitive immunoassays for clothianidin based on phage-displayed peptides. Cyclic 8-, 9-, and 10-residue peptide libraries were constructed using an optimized phagemid pComb-pVIII to prevent the loss of theoretical library diversity. Twenty-eight peptidomimetics and two anti-immunocomplex peptides were isolated through a blended panning process and used to develop competitive and noncompetitive phage enzyme-linked immunosorbent assays (P-ELISAs), respectively. After optimization, the half inhibition concentration (IC₅₀) and half saturation concentration (SC₅₀) of competitive and noncompetitive P-ELISAs were 3.83 ± 0.23 and 0.45 ± 0.02 ng/mL, respectively. Competitive P-ELISA showed 2.6-18.2% cross-reactivity with imidaclothiz, nitenpyram and imidacloprid. Importantly, noncompetitive P-ELISA, which has the best specificity and great sensitivity for clothianidin, showed no cross-reactivity with the analogs. The average recoveries of competitive and noncompetitive P-ELISAs were 73.8-104.1% and 76.6-102.2%, respectively, while the relative standard deviations were ≤ 11.0%. In addition, the results of P-ELISAs in the analysis of blind samples were consistent with those of high-performance liquid chromatography.

Residues, dissipation, and safety evaluation of pymetrozine-clothianidin mixture in strawberry

The residue detection method and field dissipation dynamics of the pymetrozine-clothianidin mixture in strawberries were investigated combining QuEChERS pretreatment and LC-MS/MS analysis to provide a reference for the safe use of pymetrozine and clothianidin mixture on strawberries. Good linearity (R2 > 0.999) was obtained for pymetrozine and clothianidin within the range of 0.005-1 μg mL-1. Method validations indicated that the recovery for pymetrozine and clothianidin was 84.2-101.4%, intra-day and inter-day repeatability ranged from 1.8 to 8.1% and from 4.1 to 7.0%, respectively. Following application of the recommended dose in field trials, pymetrozine and clothianidin dissipation followed first-order kinetics with half-lives of 6.8-13.9 days in strawberries at four locations. Moreover, owing to risk quotient < 100%, a mixture pesticide of 30% suspension concentrates (25% pymetrozine + 5% clothianidin) was unlikely to give rise to vital health concerns to humans following the recommended application guidelines. This study can be utilized in safety assessment and developing spray schedules for this mixed pesticide in strawberries.

Levels of residues and dietary risk assessment of the fungicides myclobutanil, penconazole, tebuconazole, and triadimenol in squash

Triazole fungicides may potentially harm human health. The 'quick, easy, cheap, effective, rugged, and safe' approach has become popular for extraction and cleanup during pesticide residue analysis. We aimed to (a) validate a method for the simultaneous determination of myclobutanil, penconazole, tebuconazole, and triadimenol in squash using LC-MS/MS and (b) determine the pre-harvest intervals (PHIs) and assess the related risk of consuming squash cultivated under open-field conditions in Saudi Arabia. Using acetonitrile as the extraction solvent and fourfold dilution in deionized water led to weak signal suppression (<-6.1%). The limits of quantitation ranged from 10 to 40 μg/kg. Mean recovery and relative standard deviation ranged from 81.7 to 96.3% and from 3.6 to 11.4%. The half-lives ranged from 2.22 to 3.83 days, and the dissipation followed first-order kinetics. The terminal residues of myclobutanil, penconazole, tebuconazole, and triadimenol were <0.771, <0.307, <0.459, and <0.954 mg/kg, respectively, 7 days after two or three applications of recommended dosages. The PHIs of 7.1-11.4, 8.7-13.1, 3.8-5.3, and 11.3-14.3 days are suggested after the application of the recommended dose and double the recommended dose. A consumer risk assessment based on estimated dietary intake indicated that the consumption of squash treated with the recommended doses does not pose a significant health risk.

Determination of thiamethoxam and its metabolite clothianidin residue and dissipation in cowpea by QuEChERS combining with ultrahigh-performance liquid chromatography-tandem mass spectrometry

The dissipation and residue levels of thiamethoxam and its metabolite clothianidin in cowpea were investigated under field conditions. Samples of cowpea were analyzed using a QuEChERS technique with ultra-performance liquid chromatography tandem mass spectrometry. The recoveries were 86.5-118.9% for thiamethoxam and 75.6-104.1% for clothianidin, with the coefficient of variation of < 13%. The water dispersible granule formulation of thiamethoxam was applied on cowpea at 30 and 45 g active ingredient ha^-1 in accordance with good agricultural practice. The half-life of thiamethoxam in cowpea was 0.8-1.6 days. The cowpea samples were gathered at 3, 7, and 10 days after the last application, and the residues of thiamethoxam in cowpea were < 0.005-0.054 mg kg^-1, while those of clothianidin were < 0.005-0.008 mg kg^-1. The final residues of thiamethoxam and clothianidin were below the European Union (EU) maximum residue level (0.3 mg kg^-1 for thiamethoxam; 0.2 mg kg^-1 for clothianidin) in cowpea after a preharvest interval (PHI) of 7 days. This study provided basic data on the use and safety of thiamethoxam and clothianidin in cowpea to help the Chinese government formulate a maximum residue level for thiamethoxam in cowpea.