Effects of washing methods on indoxacarb contamination and acute exposure assessment in Welsh onions (Allium fistulosum L.)

Abstract

Pesticides are commonly used to control pests during crop production to increase productivity. In this study, we investigated the effects of washing methods on indoxacarb (pesticide) levels in Welsh onions. Welsh onions exposed to indoxacarb at a concentration threefold higher (0.3 kg a.i./ha) than the recommended rate were processed using five washing methods: running washing (RW), immersive washing (IW), RW after IW (IW-RW), RW after IW with vegetable wash (IW/VW-RW), and industrial washing (AS-IW). Among the washing methods, AS-IW showed the highest reduction rate of 70.8–81.9%. Simple water washing reduced pesticide residues, with longer times and higher frequencies resulting in greater reductions. Acute exposure assessment revealed that the percentage of acute reference dose (%ARfD) for all age and sex groups decreased from 0.59 to 0.96% before washing to 0.11–0.76% after washing, confirming reduced pesticide risk. Conclusively, washing effectively reduces pesticide residues in Welsh onions and lower pesticide-related health risks.

Introduction

Welsh onion (Allium fistulosum L.) is a highly consumed seasoning vegetable similar to kimchi cabbage, radish, and hot pepper in South Korea, with an average intake of 10.77 g in 2021 (KHIDI, 2024; RDA, 2018). However, they are susceptible to various pests and diseases such as leaf blight, rust, beet armyworm, and cabbage moth, making the application of pesticides essential for pest control (RDA, 2024b). To ensure safety, the maximum residue limits (MRLs) of pesticides have been established and pesticides must be applied according to safe use standards. Currently, 138 MRLs have been established for Welsh onions in South Korea (MFDS, 2024; RDA, 2024a).

Consumers are exposed to pesticides through the consumption of agricultural products containing pesticide residues. Currently, six cases of pesticide nonconformity in Welsh onions were reported in Seoul and five in Gyeonggi Province in 2023 (GIHE, 2023; SIHE, 2023). Although Welsh onions are primarily consumed in processed form in South Korea, they are also eaten raw as shredded Welsh onions (pachae), increasing consumers concern about pesticide residues (RDA, 2018; Woo et al., 2010). Welsh onions are consumed after removing dirt-covered roots and outer leaves, washing, and cooking in various ways such as stir-frying, stewing, and braising (Chung et al., 2019; Joo and Shin, 2005; RDA, 2018). Washing is a fundamental process for preparing agricultural products before consumption and can be effectively utilized to remove pesticide residues from crops such as Welsh onions (Hwang et al., 2015; Kwon et al., 2013).

Notably, several studies have been performed on the effects of washing methods on the levels of pesticide residues. For example, Hwang et al. (2015) reported that washing with water bath, running water, and 1% neutral detergent decreased etofenprox residue in spring onions (Allium fistulosum) by 21.6, 43.9, and 28.5%, respectively. Additionally, Kim and Lee (2014) reported that soaking in water and agitating for 2 min decreased chlorantraniliprole and ethaboxam residues in Chinese cabbage by 84 and 75%, respectively. Kim et al. (2020) reported that immersive washing, running washing, and immersive washing after running washing reduced azoxystrobin residues in lettuce by 75.3, 38.9, and 68.0%, respectively. Park et al. (2022) examined the effects of five washing methods and found that soaking in 0.1% neutral detergent for 5 min and rinsing three times with fresh water decreased pesticide residues in spinach by 54.63%. Kwak et al. (2019) investigated the effects of three washing solvents (water, detergent, and soju alcohol) and two washing methods (immersive and ultrasonic washing) on the levels of 10 pesticides in strawberries and found that immersive washing with detergent, soju, and water decreased the pesticide residues by 42.5, 41.7, and 41.3%, respectively. Additionally, ultrasonic washing with soju, water, and detergent decreased the residues by 40.2, 38.6, and 36.9%, respectively. Boscalid showed a relatively superior reduction rate (61.6–71.9%) than the other pesticides (9.2–66.2%), indicating variability in washing efficiency depending on the individual pesticides. Guardia-Rubio et al. (2007) reported that the total concentration of five pesticide residues, including diuron, in olives decreased from 0.003–0.699 mg/kg to ≤ 0.105 mg/kg after washing and stirring in water for 1 min, with diuron showing the maximum reduction of 93.9%. Moreover, simple washing for 2 min decreased isoprothiolane and fthalide residues in brown and polished rice by 18.5–59.5 and 9.7–41.7%, respectively (Hwang et al., 2013). Collectively, these studies indicate that simple washing can remove substantial amount of pesticide residues. However, the effects of various washing methods and conditions on the levels of pesticide residues in Welsh onions remains unclear.

Therefore, we investigated the effects of washing methods and frequencies on the levels of the pesticide indoxacarb in Welsh onions and assessed the associated risks in humans. Indoxacarb was selected in this experiment because of its presence in vegetables (Lee, 2018; Moon, 2021; Yoon, 2020) and relatively high MRL of 2.0 mg/kg in Welsh onions (MFDS, 2024). Additionally, we assessed the acute exposure level associated with the consumption of pesticide-contaminated Welsh onion. Overall, it is anticipated that this study will provide information on the optimal washing method for effective pesticide removal to alleviate consumer concerns regarding pesticide residues.

Materials and methods

Pesticide standards and reagents

In this study, the reagents used in the pretreatment process included acetic acid (ACS reagent, ≥ 99.7%; Sigma-Aldrich, Taufkirchen, Germany), acetonitrile (HPLC grade, J.T. Baker, Center Valley, PA, USA), magnesium sulfate (MgSO₄, 99.5%; Guaranteed Reagent, JUNSEI, Tokyo, Japan), sodium acetate (NaOAc, 98.5%; Guaranteed Reagent, JUNSEI, Tokyo, Japan), and primary secondary amine (PSA, HPLC grade; Agilent Technology, Santa Clara, CA, USA). An indoxacarb standard with 97.37% purity was purchased from Dr. Ehrenstorfer GmbH (Augsburg, Germany). Formic acid (ACS reagent, ≥ 98%) and ammonium acetate (LC–MS grade, ≥ 99.0%) used for instrumental analysis were obtained Sigma-Aldrich (St. Louis, MO, USA). Distilled water and methanol for high-performance liquid chromatography (HPLC) were purchased from J.T. Baker (Center Valley, PA, USA).

Preparation of processed samples

Welsh onions (Allium fistulosum L. cv. Heukgeumjang) (Daeji Seed Co., Yongin, Korea) were cultivated in a field in Daedeok-myeon, Gimcheon-si, Gyeongbuk, South Korea. Indoxacarb application was performed three times between September 6 and 26, 2022, three weeks before harvest. To examine changes in indoxacarb residues during the washing process, indoxacarb was applied as 10% wettable powder at a rate of 0.3 kg ai/ha (Ammate, Kyung Nong, Seoul, Korea) three times at 7-day intervals at a concentration three times higher than the safety standard. After harvesting at 7 days after the final application, 1 cm above the root was cut, and the outer peels and damaged leaves were removed before washing.

Washing methods

Briefly, the washing methods for Welsh onions were based on previous reports (Kim et al., 2016; Lee, 2005). Five washing methods were employed: running washing (RW), immersive washing (IW), RW after IW (IW-RW), RW after IW with veggie wash (IW/VW-RW), and industrial washing involving slicing followed by immersive washing (IW after slicing, AS-IW). To examine the levels of pesticide residues, the onions were washed using the five washing methods at three durations (1, 2, and 3 min) and three washing frequencies (once, twice, and three times). A detailed description of each washing method is shown in Fig. 1. Notably, the pre-trimmed Welsh onions were washed in 10 batches (approximately 1 kg), dried at room temperature, and analyzed.

Fig. 1.

Detailed washing steps of Welsh onion used in this study

Running washing (RW)

Pre-trimmed Welsh onions were placed in a strainer and washed evenly on both sides for 1, 2, or 3 min under running water at a flow rate of 6 L/min.

Immersive washing (IW)

After immersing the pre-trimmed samples in 20 L of water for 1 min, the water was replaced with the same amount of fresh water once, twice, and three times by shaking 35 times for 30 s each time.

RW after IW (IW-RW)

Briefly, three repetitions of IW were performed, followed by an additional RW procedure.

RW after IW with veggie wash (IW/VW-RW)

A commercial fruit and vegetable detergent (Jayeonpong, LG H&H Co., Seoul, Korea) was used according to the manufacturer's recommendations (0.15%). After mixing 30 mL of detergent with 20 L of water, the pre-trimmed samples were immersed following the same procedure for the IW-RW method.

Industrial washing process (IW after slicing, AS-IW)

This method followed the same initial procedure as that for IW-RW with an additional 3 min of washing under running water. Briefly, the samples were cut into 8 mm pieces, placed in a strainer and manually agitated 19 times for 30 s, followed by one, two, or three repetitions according to the IW method.

Pesticide residue analysis

After washing using various methods, 10 g of each air-dried sample was placed in a 50 mL centrifuge tube, followed by the addition of 10 mL of acetonitrile containing 1% acetic acid and constant shaking at 2000 rpm for 3 min to extract the mixture. Thereafter, 6 g of MgSO₄ and NaOAc (1.5 g) was added to the mixture, vigorously shaken for 1 min, and centrifuged at 4,000 rpm for 10 min at 4 °C to collect the supernatant. An aliquot of the supernatant (1 mL) was transferred to a 2 mL centrifuge tube containing 150 mg of MgSO₄ and 50 mg of PSA and vigorously mixed for 30 s. After centrifuging, the supernatant was filtered using a membrane filter (PTFE, 0.2 μm) to collect samples for ultra-performance liquid chromatography (UPLC).

UPLC was performed using Agilent 1290 Infinity II (Agilent Technologies, CA, USA) and 6470 Triple Quadrupole mass spectrometer (Agilent Technologies). The column was an Agilent Eclipse Plus C18 column (100 mm × 2.1 mm × 1.8 μm, Agilent), maintained at 40 °C, with a flow rate of 0.2 mL/min and a 2 μL injection volume. The mobile phases consisted of water containing 5 mM ammonium acetate and 0.1% formic acid (A) and methanol containing 5 mM ammonium acetate and 0.1% formic acid (B). The solvent gradient started with 90% A/10% B and was maintained for 3.0–5.5 min at 5% A/95% B, followed by 5.6–11.0 min at 2% A/98% B and the initial conditions for last 11.1–15.0 min. Multiple reaction monitoring (MRM) was performed in positive mode with the capillary voltage set to 3.5 kV. The drying gas flow rate and temperature were 9 L/min and 300 °C, respectively, the nebulizer gas pressure was 40 psi, and the sheath gas flow rate was 11 L/min at 350 °C. The precursor ion was 528.1 m/z, and the product ion of 249.0 m/z was used as the quantifier ion, while 218.0 m/z and 149.9 m/z were used as qualifier ions.

Method validation

The analytical method was validated based on the limit of quantification (LOQ), linearity, accuracy, and precision. Briefly, the LOQ was determined as the minimum detectable amount (ng) with a signal-to-noise ratio (S/N) ≥ 10, considering the sample injection volume (µL), sample weight (g), and final test solution volume (mL). Linearity was confirmed by constructing a calibration curve using matrix-matched calibration with standard solutions prepared from untreated Welsh onion extracts, and evaluating the coefficient of determination (R²). Recovery tests were conducted to verify the accuracy and precision of the analytical results. Indoxacarb standard was spiked into non-treated Welsh onions at three different concentrations: 0.01 mg/kg (1 × LOQ), 0.1 mg/kg (10 × LOQ), and 0.5 mg/kg (50 × LOQ). Each concentration was tested five times to assess reliability of the method.

Acute exposure assessment based on Welsh onion consumption

An exposure assessment of indoxacarb was conducted using the residual amounts before and after washing to calculate the estimated daily intake (EDI) according to age group and sex. Briefly, the daily intake was calculated using the extreme intake levels (99th percentile) per kg of body weight based on the 2021 national health statistics from the Korea National Health and Nutrition Examination Survey (KNHANES) (KHIDI, 2024). Notably, the acute reference dose (ARfD) of indoxacarb was set at 0.1 mg/kg bw/day (FAO and WHO, 2005). Considering pesticide residue levels and age- and sex-specific intake data, the EDI for each Welsh onion sample was calculated using the formula below:

$$\begin{array}{cc}\hfill \text{EDI}\left(\text{mg}/\text{kg}·\text{bw}/\text{day}\right)& =\text{Pesticide residual level}\left(\text{mg}/\text{kg}\right)\hfill \\ \hfill & \times \text{Intake per body weight by age group and gender}\left(\text{kg}/\text{kg}·\text{bw}/\text{day}\right)\hfill \\ \hfill \end{array}$$ 1

$$\%\text{ARfD}=\frac{\text{EDI}\left(\text{mg}/\text{kg}·\text{bw}/\text{day}\right)}{\text{ARfD}\left(\text{mg}/\text{kg}·\text{bw}/\text{day}\right)}\times 100$$ 2

Statistical analysis

All statistical analyses were performed using Statistical Analysis System (SAS version 9.4) based on results from triplicate samples. Significant differences between groups were determined using analysis of variance (ANOVA), followed by Duncan’s multiple range test. Statistical significance was set at P < 0.05.

Results and discussion

Method validation

In this study, the LOQ of indoxacarb in Welsh onions was 0.01 mg/kg and the determination coefficient (R²) of the calibration curve was 0.9993, indicating good linearity. Additionally, the recovery rates at three concentrations (0.01, 0.1, and 0.5 mg/kg) were 101.2, 97.1, and 102.0%, respectively, and the relative standard deviation (RSD) was < 1.5% (Table 1). Overall, the recovery rate and precision data met the Codex Alimentarius Commission guidelines (CAC/GL 40) (Codex, 2003), confirming the suitability of the analytical method used in this study.

Table 1.

Recovery of indoxacarb in Welsh onion (n = 5)

Compound	Fortification (mg/kg)	Recovery (%) Mean ± SDa	RSD (%)b	LOQc (mg/kg)
Indoxacarb	0.01	101.2 ± 0.8	0.7	0.01
	0.10	97.1 ± 1.2	1.2
	0.50	102.0 ± 0.8	0.8

^aSD: standard deviation

^bRSD: relative standard deviation

^cLOQ: limit of quantification

In previous studies, the reported recovery rates of indoxacarb in various vegetables were 73.9–77.3% for Brussels sprouts (An et al., 2022), 95.1–102.1% for broccoli (Yang et al., 2020), 90–96% for cauliflower (Takkar et al., 2011), and 92.1–105.1% for tomatoes (Sakthiselvi et al., 2020). Notably, the recovery rate of indoxacarb in Welsh onions in the present study (97.1–102.0%) was higher than that reported for Brussels sprouts by An et al. (2022). In the case of broccoli, cauliflower, and tomatoes, comparable recovery rates were achieved despite using additional cleanup steps involving florisil cartridges or the addition of graphitized carbon black to MgSO₄ and PSA. Therefore, the analytical method used in this study is considered suitable for analyzing Welsh onion samples, as it ensures reliable recovery via a relatively simple purification procedure.

Efficiency of washing methods in reducing pesticide residues

Table 2 shows the pesticide reduction efficiencies of the different washing methods for Welsh onions. Notably, RW, IW, and IW-RW methods decreased the pesticide residues by 20.8–44.4, 50.0–54.2, and 55.6–61.1%, respectively, indicating that an additional washing step after IW may enhance pesticide removal efficiency. Similarly, Park et al. (2022) reported that washing with running water for 5 min after immersion showed a superior cyantraniliprole reduction efficiency (27.3–42.9%) in spinach than RW (15.1–41.1%) and IW (19.6–41.5%) for 1, 3, and 5 min. In contrast, Hwang et al. (2015) reported that RW for 1 min exhibited a superior etofenprox reduction rate (43.0%) than IW for 1 min (21.6%). Importantly, this discrepancy in results could be attributed to differences in the washing processes. For example, the present study involved manual agitation during immersion, whereas this process was not employed by Hwang et al. (2015). Additionally, Kim et al. (2020) reported that RW for 3 s, IW for 1 min with two additional 30-s washes, and RW for 3 s after IW reduced azoxystrobin residues in lettuce by 38.9, 75.3, and 68.0%, respectively. Collectively, these results indicate that additional washing after immersion can significantly influence pesticide reduction efficiency.

Table 2.

Residual amounts of indoxacarb in Welsh onions after various washing methods

Washing method		Residual level (mg/kg) Mean ± SD1	Loss (%)
Before washing		0.72 ± 0.02a	–
RW2	1 min	0.57 ± 0.03b	20.8
	2 min	0.43 ± 0.03c	40.3
	3 min	0.40 ± 0.02d	44.4
IW3	1 time	0.36 ± 0.01e	50.0
	2 time	0.33 ± 0.01f	54.2
	3 time	0.33 ± 0.01f	54.2
IW-RW4	1 min	0.32 ± 0.01f	55.6
	2 min	0.32 ± 0.02f	55.6
	3 min	0.28 ± 0.01gh	61.1
IW/VW-RW5	1 min	0.29 ± 0.01 g	59.7
	2 min	0.26 ± 0.01hi	63.9
	3 min	0.24 ± 0.02i	66.7
AS-IW6	1 time	0.21 ± 0.02j	70.8
	2 time	0.20 ± 0.01j	72.2
	3 time	0.13 ± 0.01 k	81.9

¹SD: standard deviation

²RW: running water washing

³IW: immersive washing

⁴IW-RW: running washing after immersive washing

⁵IW/VW-RW: running washing after immersive washing with veggie wash

⁶AS-IW: immersive washing after slicing

^a–kValues sharing the same superscript are not significantly different at P < 0.05

Additionally, pesticide removal efficiency was higher in the IW/VW-RW group (59.7–66.7%) than in the IW-RW group (55.6–61.1%). You and Lee (2011) reported that soaking in water, 5% acetic acid, 20% alcohol, and 0.15% detergent for 2 min with agitation and subsequent rinsing with fresh water for 2 min reduced the levels of five pesticides, including dichlorvos, in Chinese cabbage by 61.2–85.2, 61.2–83.6, 63.8–85.5, and 67.8–95.5%, respectively, with the 0.15% detergent wash showing the best residue reduction. Additionally, the log K_OW values of dichlorvos, fenarimol, edifenphos, cypermethrin, and fenvalerate were 1.90, 3.69, 3.83, 6.61, and 7.19. Moreover, the detergent showed a superior removal efficiency for lipophilic pesticides and a lesser effect on relatively water-soluble pesticides such as dichlorvos. Overall, these results suggest that surfactants in detergents can effectively dissolve both water- and lipid-soluble pesticides, thereby enhancing residue removal efficiency. Kim et al. (2022) investigated the effects of different washing methods for 1 min and rinsing (twice for 30 s each) on flubendiamide removal efficiency (log K_OW 4.2) in kale and found that the removal rates of the pesticide were higher with detergent (27.2%), calcium powder (30.2%), baking soda (31.7%), and vinegar (39.8%) than with water (15.9%). Collectively, these results indicate that the effectiveness of pesticide removal varies depending on the type and characteristics of washing auxiliaries. However, it is essential to follow the recommended usage levels and ensure thorough rinsing when using detergents to prevent residual detergents in agricultural products (Lee et al., 2021).

AS-IW is a modified method designed to replicate the industrial processing of Welsh onions in laboratory settings. Welsh onions were cut after IW-RW for 3 min and washed again by stirring 19 times for 30 s in fresh water. Among the five methods examined, the AS-IW method showed the highest pesticide reduction rate (70.8–81.9%). Importantly, the superior removal efficiency of the AS-IW method compared with the other methods (RW, IW, or IW-RW) could be attributed to the cutting and additional washing steps. Therefore, industrial washing methods, such as AS-IW, may be effective for ensuring pesticide safety management in agricultural processing operations.

Based on these findings, applying industrial washing methods, such as AS-IW, is effective for processing operations. However, the relatively simple IW could still remove more than 50% of the pesticides when considering practicality for home use. Considering that Welsh onions are generally consumed after cooking rather than raw, further processing methods, such as heat treatment, are expected to enhance the removal of residual pesticides.

Changes in pesticide residue levels according to washing duration and frequency

Table 2 shows indoxacarb residue levels in Welsh onions under varying washing duration and frequency. Compared with the initial level of 0.72 mg/kg, RW for 1, 2, and 3 min significantly decreased indoxacarb residue levels by 20.8% (0.57 mg/kg), 40.3% (0.43 mg/kg), and 44.4% (0.40 mg/kg), respectively, indicating a significant decrease in residue levels with washing duration. In the case of IW-RW and IW/VW-RW, the residue levels were analyzed with and without fruit and vegetable detergents under different washing duration. Additionally, IW-RW for 1, 2, and 3 min decreased indoxacarb residue level to 0.32 mg/kg (55.6%), 0.32 mg/kg (55.6%), and 0.28 mg/kg (61.1%), respectively. Moreover, IW/VW-RW for 1, 2, and 3 min decreased indoxacarb levels to 0.29 mg/kg (59.7%), 0.26 mg/kg (63.9%), and 0.24 mg/kg (66.7%), respectively. Immersion in detergent for 1 min or more showed a similar reduction rate to that after 3 min of water immersion. Cui et al. (2023) reported that fluxapyroxad reduction rate in cucumber and cowpeas increased from 14.88–20.27% to 64.88–71.08% with increasing immersion duration in water from 1 to 10 min. Additionally, Park et al. (2022) found that cyantraniliprole reduction rate in spinach increased from 15.1–42.9% to 41.1–54.6% with increasing washing duration from 1 to 5 min, regardless of the washing method. Similarly, previous studies have shown that pesticide removal rates tend to increase with longer washing duration, regardless of the washing method.

Regarding washing frequency, IW decreased the concentration of the residues by 50.0% (0.36 mg/kg), 54.2% (0.33 mg/kg), and 54.2% (0.33 mg/kg) after 1, 2, and 3 repetitions, respectively. Additionally, AS-IW decreased the residue level to 0.21 mg/kg (70.8%), 0.20 mg/kg (72.2%), and 0.13 mg/kg (81.9%) after 1, 2, and 3 additional immersions. Even after a single washing process, AS-IW demonstrated a relatively higher pesticide removal efficiency than the other washing methods. Previous studies have shown that the reduction rates of four pesticides in crown daisy and lettuce increased from 7–80.1% after a single wash to 16.5–85.2% after three washes (Kim et al., 2016; Kwon et al., 2013). Additionally, the reduction rates of three pesticides, including indoxacarb, in perilla leaves increased from 61.1–84.9% after one wash to 64.5–91.3% after two washes by immersion (Seo et al., 2007). Collectively, these results suggest that repeated washing can effectively remove large amounts of pesticides.

In this study, the pesticide removal rate in Welsh onions ranged from 20.8 to 81.9% for all washing methods examined. Pesticide reduction rate in the groups (except AS-IW group) increased from 20.8% to over 40.3% and from 50.4% to 54.2% following an increase in washing duration and frequency, respectively. Overall, these findings indicate that pesticide removal efficiency may vary according to the washing method. Notably, this variation may be attributed to factors such as physical friction during the washing process, detergent use, physicochemical properties of the pesticides, and the morphological characteristics of agricultural products (Lee and Lee, 1997; Yang et al., 2012).

Consistent with previous findings (Cui et al., 2023; Kim et al., 2016; Kwon et al., 2013; Park et al., 2022; Seo et al., 2007), the largest portion of pesticide removal was observed after the first wash. This trend was attributed to the fact that the washing process primarily removes pesticides on the surface of agricultural products. Therefore, most of the residual pesticides are eliminated initially, causing a decrease in the amount removed in subsequent washing stages (Lee, 2005; Kim et al., 2023). Additionally, the pesticide removal efficiency of washing is influenced by the physicochemical properties of the pesticides. Pesticides with higher water solubility, as indicated by log K_OW < 2, are easily dissolved in water, and thus exhibit higher removal rates during washing. In contrast, lipophilic pesticides (log K_OW > 4) tend to bind to the cuticle layer of crops (Yang et al., 2022) or penetrate crops, depending on their permeability (You and Lee, 2011), making it difficult to remove them completely through simple water washing. Non-systemic pesticides, which primarily adhere to the crop surface, are effectively removed by washing, while systemic pesticides absorbed into the internal tissues of the crop may be challenging to eliminate solely by washing (Hanafi et al., 2016).

Notably, the pesticide used in this study (indoxacarb) is a non-systemic pesticide that primarily adheres to the crop surface, making it easily removed through washing. However, it is highly lipophilic, with a log K_OW value of 4.65 (Turner, 2015), which may hinder its complete removal via washing with only water. Although the reduction rate of indoxacarb in this study ranged from 20.8 to 81.9%, an average reduction of 55.1% (40.3–66.7%) was achieved after 2–3 min or 2–3 times of washing, regardless of the washing method. Wang et al. (2023) reported that soaking in washing solutions (water, 3% green tea, 3% salt, or 3% vinegar) for 5 min and rinsing under running water for 1 min after immersion decreased indoxacarb residue in strawberries by 10.7 and 28.5%, respectively. Additionally, the above treatments reduced spirotetramat, a systemic pesticide with a log K_OW value of 2.5, by 54.1 and 67.1%, respectively, indicating that water-soluble pesticides were more readily eliminated during the washing process. Pesticide reduction rate in lettuce, perilla leaves, spinach, crown daisy, and samchoo (Brassica lee ssp. namai) varied depending on the crop type following a 5-min immersion, with an average removal rate of 55.2% for indoxacarb (Yang et al., 2022). Additionally, pesticides with high log K_OW values, such as chlorfenapyr, diniconazole, indoxacarb, fludioxonil, pyraclostrobin, and lufenuron, were not easily removed. Our study showed that although indoxacarb is a lipophilic pesticide, it was effectively removed (maximum reduction rate, 81.9%), indicating that effective pesticide removal can be achieved through appropriate washing conditions and the use of detergents. Collectively, these results indicate that although pesticides can be removed to a certain extent through the washing process, their reduction rates may vary depending on multiple factors, including the physicochemical properties of the pesticides, morphological characteristics of the agricultural products, and the washing methods employed.

Acute exposure assessment of indoxacarb based on Welsh onion consumption

An acute exposure assessment of indoxacarb was conducted using the residue levels before and after washing (Table 3). Based on the extreme daily intake (99th percentile) derived from the Korea National Health and Nutrition Examination Survey, the acute exposure assessment showed that the %ARfD of unwashed Welsh onions ranged from 0.81 to 0.82% by sex and from 0.59 to 0.96% by age group. Despite considering extreme intake levels, %ARfD for all age groups and sexes was < 1%, indicating no significant risk. Among age groups, the %ARfD values were 0.69% (1–2 years), 0.59% (3–5 years), 0.75% (6–11 years), 0.69% (12–18 years), 0.96% (19–29 years), 0.69% (30–49 years), 0.81% (50–64 years), and 0.91% (≥ 65 years). Among these, the 19–29 years group showed the highest %ARfD, possibly due to the higher Welsh onion intake (0.00133 kg/kg·bw/day) than the other age groups (0.00082–0.00126 kg/kg·bw/day). Additionally, there was no significant difference in %ARfD between males and females. A comparison based on washing methods showed that the %ARfD were as follows: RW (0.33–0.76%), IW (0.27–0.48%), IW-RW (0.23–0.43%), IW/VW-RW (0.20–0.39%), and AS-IW (0.11–0.28%). In the sex groups, the %ARfD were as follows: RW (0.45–0.65%), IW (0.37–0.41%), IW-RW (0.31–0.36%), IW/VW-RW (0.27–0.33%), and AS-IW (0.15–0.24%). Consistent with previous findings (Majed et al., 2024), indoxacarb residue levels and %ARfD showed a decreasing trend with each washing method, and the washing process effectively reduced acute risk. Andrade et al. (2015) examined the effects of preservation duration (60 days) and washing for 1 min (tap water, boiling water, and 10% vinegar) on azoxystrobin, fenazaquin, and indoxacarb risk in grape leaves and found that the hazard index of the three pesticides decreased from 0.0321–0.3690 before processing to 0.0020–0.2920 after preservation and 0.0191–0.3260 after washing. Our study showed that although indoxacarb was applied a three-times the recommended rate at 7-day intervals, the residue level before washing (0.72 mg/kg) was lower than the MRL (2.0 mg/kg) established for Welsh onions in South Korea. Considering that the pesticide exposure level in crops grown according to standard safe-use practices is reportedly at a safe level (An et al., 2019; Jin et al., 2018), it can be concluded that the residue levels and associated risks of pesticides present in Welsh onions distributed in the market are significantly low. However, the monitoring results for pesticide residues in domestic agricultural products indicate a high frequency of pesticide detection in vegetables. Previous studies have reported pesticide residue levels exceeding the MRL in some crops such as coriander, chard, perilla leaves, and Welsh onions (GIHE, 2023; Gwon et al., 2024; Lee et al., 2024). Therefore, consumers should wash their agricultural products thoroughly before cooking and consumption. Conclusively, all washing methods examined effectively decreased the %ARfD of indoxacarb in Welsh onions to < 0.76% for all age groups and sexes, thereby contributing to consumer safety. In particular, AS-IW is an effective approach for pesticide safety management in industrial processing. For home use, performing IW at least once can effectively remove more than 50% of pesticide residues from Welsh onions.

Table 3.

Acute risk assessment of indoxacarb residues in Welsh onion after various washing methods

Washing method		%ARfD
		Gender groups		Age groups
		Male (All ages)	Female (All ages)	1–2 year	3–5 year	6–11 year	12–18 year	19–29 year	30–49 year	50–64 year	More than 65 year
Before washing		0.81	0.82	0.69	0.59	0.75	0.69	0.96	0.69	0.81	0.91
RWa	1 min	0.64	0.65	0.55	0.47	0.59	0.55	0.76	0.55	0.64	0.72
	2 min	0.48	0.49	0.41	0.35	0.45	0.41	0.57	0.41	0.49	0.54
	3 min	0.45	0.46	0.38	0.33	0.42	0.38	0.53	0.38	0.45	0.50
IWb	1 time	0.40	0.41	0.35	0.30	0.37	0.35	0.48	0.35	0.41	0.45
	2 time	0.37	0.38	0.32	0.27	0.34	0.32	0.44	0.32	0.37	0.42
	3 time	0.37	0.38	0.32	0.27	0.34	0.32	0.44	0.32	0.37	0.42
IW-RWc	1 min	0.36	0.36	0.31	0.26	0.33	0.31	0.43	0.31	0.36	0.40
	2 min	0.36	0.36	0.31	0.26	0.33	0.31	0.43	0.31	0.36	0.40
	3 min	0.31	0.32	0.27	0.23	0.29	0.27	0.37	0.27	0.32	0.35
IW/VW-RWd	1 min	0.32	0.33	0.28	0.24	0.30	0.28	0.39	0.28	0.33	0.37
	2 min	0.29	0.30	0.25	0.21	0.27	0.25	0.35	0.25	0.29	0.33
	3 min	0.27	0.27	0.23	0.20	0.25	0.23	0.32	0.23	0.27	0.30
AS-IWe	1 time	0.24	0.24	0.20	0.17	0.22	0.20	0.28	0.20	0.24	0.26
	2 time	0.22	0.23	0.19	0.16	0.21	0.19	0.27	0.19	0.23	0.25
	3 time	0.15	0.15	0.12	0.11	0.14	0.12	0.17	0.12	0.15	0.16

^aRW: running water washing

^bIW: immersive washing

^cIW-RW: running washing after immersive washing

^dIW/VW-RW: running washing after immersive washing with veggie wash

^eAS-IW: immersive washing after slicing

Funding

This research was supported by a grant (22192MFDS322) from Ministry of Food and Drug Safety in 2022.

Declarations

Conflict of interest

The authors declare no conflict of interest.