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

Abstract

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.

Keywords: LC-MS/MS; PHRL; QuEChERS; angelica leaves; penthiopyrad; tebufenpyrad.

Figure 1

Structural formulas of pyrazolecarboxamide-based pesticides. (a) Penthiopyrad and (b) tebufenpyrad. Dotted circles refer to the structure of the pyrazolecarboxamide series.

Figure 2

Experimental field planning. (a) Field location selection and (b) layout of the fields. In (a), #1 is Field 1 (Sancheong), #2 is Field 2 (Jeonju), and #3 is Field (Jecheon).

Figure 3

Chromatograms for pesticides. (a) Penthiopyrad matrix-matched standard at 0.025; (b) penthiopyrad recovery sample at 0.1 mg/kg; (c) penthiopyrad storage stability sample at 1 mg/kg; (d) blank sample without penthiopyrad; penthiopyrad residue sample at (e) 0 DAT and (f) 7 DAT; (g) tebufenpyrad matrix-matched standard at 0.025; (h) tebufenpyrad recovery sample at 0.1 mg/kg; (i) tebufenpyrad storage stability sample at 1 mg/kg; (j) blank sample without tebufenpyrad; tebufenpyrad residue sample at (k) 0 DAT and (l) 7 DAT. The red arrowhead indicates the peak detected at the retention time for each pesticide. The blank sample shows the retention time since no peaks were detected.

Figure 4

The dissipation curves of pesticide in each field and their integrated results. Sub-figures (a–d) are for penthiopyrad and (e–h) are for tebufenpyrad.

Figure 5

Weight and temperature of each field at 0 DAT. (a) Weight of angelica leaves and (b) field temperature.

Figure 6

After the final pesticide application, the growth rate of angelica leaves in each field during the initial period (0−5 DAT) for (a) penthiopyrad and (b) tebufenpyrad.

Figure 7

Dilution effects due to diameter growth and penthiopyrad residual dissipation curves reflecting the dilution effect. Graphs (a,d) represent data from Field 1; (b,e) are from Field 2, and (c,f) are from Field 3. (a–c) are the graphs for penthiopyrad and (d–f) are the graphs for tebufenpyrad. ‘Standard’ refers to the original residue concentration without accounting for the dilution effect. ‘Only pesticide’ refers to the residue concentration accounting for the dilution effect.

Figure 8

Process of proposing a PHRL.

Figure 9

PHRL curve of each field and their integrated average. (a) Penthiopyrad and (b) tebufenpyrad.