*3.1. Method Validation*

In general, method validation was performed using each matrix. Table 3 shows the standard curve coefficients (R2), average recoveries, and relative standard deviations for the pesticides studied using each matrix. The LOQs for the ten pesticides (azoxystrobin, chlorantraniliprole, chlorfenapyr, diniconazole, fludioxonil, imidacloprid, indoxacarb, lufenuron, pyraclostrobin, and thiamethoxam) were defined as the concentrations produced from a S/N ratio of 10. The estimated LOD and the LOQ were 0.001–0.003 and 0.002–0.009 mg/kg, respectively. The LOQ was lower than the maximum residue limit (MRL) set by the Ministry of Food and Drug Safety of the South Korea (Table 1). Identical linearities with determination coefficients (R<sup>2</sup> > 0.999) were obtained from matrix-matched calibration of the blank and each matrix. The recovery rates were satisfactory, ranging from 87 to 115%, with an RSD of <8%. The RSD for five leafy vegetables never exceeded 20% according to the acceptance and rejection criteria of the SANTE guidelines. All mean values for recovery were within the acceptable range (70–120%).

**Table 3.** Regression coefficient (R2), LOQs, and average recoveries for ten pesticides in five leafy vegetables (n = 5).



*3.2. Differences in Efficiency by Type of Leafy Vegetable and Removal Method for the Reduction of Pesticide Residues*

In this study, ten pesticides with high detection rates were administered to five leafy vegetables. Thereafter, nine removal methods were applied. As various washing methods are applied for various dishes in Asian countries, including China and South Korea, a representative method for removing pesticide residues from leafy vegetables was tested. Since leafy vegetables are intended to be consumed following these treatments, their structure must remain more or less intact to maintain consumer acceptance. Figure S1 depicts images revealing the effect of the treatment on the appearance of the leafy vegetables. Except for blanching and boiling, all methods preserved the structural integrity of the leafy vegetables. Blanched or boiled leafy vegetables are consumed as soup or seasoned vegetables; therefore, consumers could accept them even if their structure is not retained.

The initial residue values for the pesticides found on artificially contaminated samples are outlined in Table S1: lettuce (4.45–34.81 mg/kg), perilla leaves (5.74–42.97 mg/kg), spinach (4.52–37.04 mg/kg), crown daisy (4.02–29.67 mg/kg), and ssamchoo (2.95–27.96 mg/kg). The reductions in the pesticide amount in the five vegetables are summarized in Table 4. The reduction range for the five leafy vegetables was 40.6–67.4%. The average reductions for each sample appeared in the following order: lettuce (67.4 ± 7.3%) > perilla leaves (59.8 ± 10.2%) > spinach (55.1 ± 13.8%) and crown daisy (54.3 ± 11.5%) > ssamchoo (40.6 ± 12.9%). Spinach and crown daisy showed no significant difference in their reductions. Lettuce had the highest reduction (57.5% (detergent)–82.5% (running water)), whereas ssamchoo had the lowest reduction (28.0% (NaHCO3)–59.7% (running water)). Overall, the reductions for each method were as follows: running water (77.0 ± 18.0%), boiling (59.5 ± 31.2%), alkaline water (56.4 ± 18.0%), blanching (54.9 ± 25.9%), ultrasonic cleaning (52.8 ± 18.7%), NaHCO3 (52.0 ± 19.2%), stagnant water (51.4 ± 16.4%), vinegar (51.2 ± 18.3%), detergent (43.7 ± 14.5%). Washing with running water led to the highest removal efficiency among all methods, whereas washing with detergent led to the lowest removal efficiency.

**Table 4.** Reduction of pesticide residues in five leafy vegetables using nine methods (means ± SD, n = 5).


The different letters indicate significant different (*p* < 0.05) and comparison of means were formed using Tukey's test.
