Dissipation kinetics, pre-harvest residue limits, and dietary risk assessment of the systemic fungicide metalaxyl in Swiss chard grown under greenhouse conditions.

The residual behavior of the systemic fungicide, metalaxyl, in Swiss chard cultivated at two different locations under greenhouse conditions was investigated using high-performance liquid chromatography coupled with an ultraviolet detector (HPLC-UVD). Samples were randomly collected over 14 days and extracted using acetonitrile, partitioned using solid sodium chloride, and a solid-phase extraction (SPE) NH2 cartridge was used for cleanup. The linearity over a concentration range 0.05-50 mg/L was excellent with a coefficient of determination (R2) of 0.9997. The recovery rate ranged from 77.05 to 88.92% with relative standard deviations (RSDs) ≤ 10.74, and the limits of detection (LOD) and quantification (LOQ) were 0.0033 and 0.01 mg/kg, respectively. The initial (2 h after application) deposits were 4.69 and 5.90 mg/kg for sites 1 and 2, respectively, which increased to 4.95 and 6.57 mg/kg, respectively, one day post-application, owing to the systemic properties of the fungicide. The dissipation half-life was 5.3 and 6.0 days for sites 1 and 2, respectively. The pre-harvest residue limit (PHRL) suggested that if 55.38 and 47.23 mg/kg was applied 10 days before harvest or 33.28 and 30.73 mg/kg was applied 5 days before harvest (for sites 1 and 2, respectively) then the concentration will fall below the maximum residue limit (MRL = 20.0 mg/kg) at the time of harvest. The dietary risk assessment, estimated as hazard quotient (RQ%), indicate that metalaxyl can be safely used in/on Swiss chard, with no hazardous effects expected for consumers.

The disappearance rate and risk assessment of thiacloprid residues in Asian pear using liquid chromatography confirmed with tandem mass spectrometry.

This study was undertaken to quantify the residue levels and propose the dissipation kinetics of thiacloprid formulated as suspension concentrate in field-incurred Asian pears grown under two different open-field conditions. Samples were extracted with 20% distilled water in acetonitrile; partitioned with brine water and dichloromethane; and purified with a Florisil solid phase extraction cartridge. The analyte was identified with an LC ultraviolet detector, and field-incurred samples were confirmed using LC-MS/MS. The calibration curve was linear over the range 0.05-5.0 mg/L with a satisfactory coefficient of determination (R2 = 0.9994). The limits of detection and limits of quantification (LOQ) were 0.003 and 0.01 mg/kg, respectively. The recovery rate fortified to blank samples at LOQ, 10× LOQ, and the maximum residue limit (MRL) were between 73.7 and 86.2% with relative standard deviation ≤9.0%. The residual concentrations at both sites were considerably lower than the MRL (0.7 mg/kg) set by the Korean Ministry of Food Drug Safety, with biological half-lives of 5.0 and 7.4 days, for sites 1 and 2, respectively. From the pre-harvest residue limit curve, it was predicted that if the residues were <1.13 or 1.40 mg/kg 10 days before harvest, the residue level would be lower than the MRL during harvest. Risk assessment on day 0 showed an acceptable daily intake (%) of 13.0% and 11.0% for sites 1 and site 2, respectively, which indicates that the residual amounts are not hazardous to the Korean population.

Comparative Biological Half-Life of Penthiopyrad and Tebufenpyrad in Angelica Leaves and Establishment of Pre-Harvest Residue Limits (PHRLs).

To prevent pesticides from exceeding maximum residue limits (MRLs) in crops during export and shipment, it is necessary to manage residue levels during the pre-harvest stages. Therefore, the Republic of Korea establishes pre-harvest residue limits (PHRLs) per crop and pesticide. This study was conducted to set PHRLs for penthiopyrad and tebufenpyrad in angelica leaves, where the exceedance rates of MRLs are expected to be high. The LOQ of the analytical method used was 0.01 mg/kg and it demonstrated good linearity, with a correlation coefficient of 0.999 or higher within the quantitation range of 0.005 to 0.5 mg/kg. The recovery and storage stability accuracy values were in the range of 94.5-111.1%, within the acceptable range (70-120%, RSD ≤ 20%). The matrix effect for both pesticides was in the medium-to-strong range, and it did not significantly impact the quantitative results as a matrix-matched calibration method was employed. Using the validated method, residue concentrations of penthiopyrad 20 (%) EC and tebufenpyrad 10 (%) EC were analyzed. Both pesticides exhibited a decreasing residue trend over time. In Fields 1-3 and their integrated results, the biological half-life was within 2.6-4.0 days for penthiopyrad and 3.0-4.2 days for tebufenpyrad. The minimum value of the regression coefficient in the dissipation curve regression equation was selected as the dissipation constant. The selected dissipation constants for penthiopyrad in Fields 1-3 and their integration were 0.1221, 0.2081, 0.2162, and 0.1960. For tebufenpyrad, the dissipation constants were 0.1451, 0.0960, 0.1725, and 0.1600, respectively. The dissipation constant was used to calculate PHRL per field. Following the principles of the PHRL proposal process, residue levels (%) on PHI dates relative to MRLs were calculated, and fields for proposing PHRLs were selected. For penthiopyrad, since the residue level (%) was less than 20%, the PHRL for Field 3 with the largest dissipation constant was proposed. For tebufenpyrad, as the residue level (%) exceeded 80%, the PHRL proposal could not established. It is deemed necessary to reassess the MRL and 'guidelines for safe use' for tebufenpyrad in angelica leaves.

Dissipation kinetics, pre-harvest residue limits, and hazard quotient assessments of pesticides flubendiamide and fluopicolide in Korean melon (Cucumis melo L. var. makuwa) grown under regulated conditions in plastic greenhouses.

The dissipation kinetics, pre-harvest residue limits, and hazard quotient (HQ) assessments of the pesticides flubendiamide and fluopicolide were conducted for Korean melon (Cucumis melo L. var. makuwa) cultivated at two different sites. A single extraction and cleanup procedure was carried out using acetone (partitioned with dichloromethane) and amino solid-phase extraction cartridges, respectively. Residue analysis was performed by HPLC with ultraviolet detection. Both pesticides showed excellent linearity with correlation coefficients of 0.9999 and 0.9996 for flubendiamide and fluopicolide, respectively. The accuracy (expressed as recovery %) at three spiking levels was 92.0-103.6 and 82.8-105.3%, and the precision (expressed as relative standard deviation) was 1.7-3.4 and 2.7-5.3% for flubendiamide and fluopicolide, respectively. The initial residues of flubendiamide/fluopicolide were 0.326/0.376 and 0.206/0.298 mg/kg at sites 1 and 2, respectively. These amounts were substantially lower than the maximum residue limits (MRLs = 1 and 0.5 mg/kg for flubendiamide and fluopicolide, respectively) established by the Korean Ministry of Food and Drug Safety. The half-lives of flubendiamide were 5.8 and 6.5 days, and those of fluopicolide were 6.7 and 9.1 days at sites 1 and 2, respectively. The shorter half-lives were attributed to seasonal variations (higher temperatures) and enzymatic and metabolic profiling. The risk assessment HQs of flubendiamide were 0.217/0.249 on day 0, which decreased to 0.102/0.168 on day 5, and to 0.065/0.88 on day 10; the HQ values for fluopicolide were 0.029/0.042, 0.022/0.025, and 0.010/0.019 on day 0, day 5, and day 10, for sites 1/2, respectively. From this data, we concluded that the fruits could be consumed safely.