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Residual characteristics and safety assessment of the insecticides spiromesifen and chromafenozide in lettuce and perilla

This study was performed to investigate the residual characteristics, safety assessment, and pre-harvest interval (PHI) of spiromesifen and chromafenozide in lettuce (Latuca sativa L.) and perilla (Perilla frutescens (L.) Britton) leaves. Samples were harvested periodically, extracted using QuEChERS method, and analyzed by LC-MS/MS. Average recoveries of spiromesifen and its metabolite BSN2060-enol and chromafenozide were ranged from 80.6 to 107.9%, with relative standard deviation < 10%. Spiromesifen and cromafenozide initial residues in lettuce were dissipated to 81.45 and 95.52% after 7 days, with half-lives of 2.89 and 1.69 days respectively. Values in perilla leaves were 76.68 and 61.27% after the same period, with half-lives of 4.25 and 6.30 days, respectively. Risk assessment results showed that %ADI (acceptable daily intake) of spiromesifen and chromafenozide was 6.83 and 0.56, in lettuce and 4.60 and 0.25% in perilla leaves, respectively. Theoretical maximum daily intakes of spiromesifen and chromafenozide were 67.49 and 3.43%, respectively, indicating that residues of both compounds pose no considerable health risks to consumers. This study provides data for setting maximum residue limits and PHIs for the safe use of spiromesifen and chromafenozide in lettuce and perilla.


Result and discussion
Method validation. The validation of the analytical method was carried out by evaluating different parameters including linearity, accuracy, precision, and method limits of quantification (MLOQ). The linearity of the seven-point matrix-matched calibration curve over the range of 0.01 to 1.0 mg/kg was excellent with a regression coefficient (R 2 ) of 0.99 for all compounds (Fig S1 and S2). The recoveries of spiromesifen, BSN2060-enol, and chromafenozide at 0.1 and 0.5 mg/kg fortification levels ranged between 88.2 to 101.9%, 97.3 to 103.2%, and 95. 6 to 100.8%, respectively, in lettuce (Table S1). The respective values in perilla leaves were 78.0 to 99.9%, 77.8 to 87.5%, and 99.4 to 113.5% (Table S1). The repeatability expressed as the RSD of the analyzed samples (n = 3) was below 10% for all compounds. The MLOQ of all analytes was 0.01 mg/kg. There were no interfering peaks found around the retention times of the target compounds in spiked and control samples, showing that the method was specifically accurate. The MLOQs and average recovery data of the test compounds are shown in Table 1.

Initial deposition and dissipation characteristics of insecticides.
The initial residue is a theoretical concentration of insecticides that could be deposited on crops. The calculation was carried out based on the Table 1. Average recoveries and MLOQs of insecticides in lettuce and perilla leaves. MLOQ method limit of quantitation, RSD relative standard deviation. www.nature.com/scientificreports/ 0-day residues (residue detected after two hours of insecticides application), considering the active ingredient concentration percentage in the pesticide formulation, dilution factors, and type of the formulations used 12 . The results in Table 2 indicated that the initial residues of spiromesifen and chromafenozide in lettuce were 136.90 and 107.20 mg/kg, respectively. While the initial residues of spiromesifen and chromafenozide in perilla leaves were 189.75 and 136.90 mg/kg, respectively. In both crops, the initial residues of spiromesifen were slightly higher than that of chromafenozide. These findings agree with previous studies in the context that the initial residues of pesticides in crops depend on several factors such as the active ingredient (AI), formulation, dilution factor, and type of crop 13 . The AI used in this study was spiromesifen SC 20% and chromafenozide EC 5%, it may be assumed that the higher initial residues of spiromesifen are due to the high concentration of AI present in the formulation products 4 . Pesticide formulation has major effects on its penetration through the leaf surface and dissipation. Generally, SC formulations retained better than wettable powder (WP) form 4 . The insecticide formulations used in the current study were spiromesifen SC and chromafenozide EC, which are considered to have good adhesion and easy penetration into the crops contributing to high initial residues 14 . Moreover, spiromesifen and chromafenozide were applied on lettuce and perilla leaves under similar environmental conditions, however, the initial residues in perilla leaves were higher than that of lettuce, which might be attributed to the hairy leaf of the perilla plant 15 .
The dissipation rate and half-lives of pesticides provide an important index to assess the behavior in plants. The dissipation of spiromesifen and chromafenozide in lettuce and perilla leaves were found following the firstorder kinetics model with a correlation coefficient between 0.93 and 0.97 (Figs. 1, 2). As the duration from last insecticide application to sampling time increased, spiromesifen and chromafenozide residue levels decreased. The initial residues of spiromesifen and cromafenozide in lettuce were dissipated to an extent of 81.45 and 95.52% after 7 days, with the half-lives of 2.89 and 1.69 days, respectively. Similarly, the initial residues of spiromesifen and cromafenozide in perilla leaves were dissipated to 76.68 and 61.27% after 7 days, with the half-lives of 4.25 and 6.30 days, correspondingly. The half-life period of spiromesifen and cromafenozide in lettuce and perilla leaves was less than a week. Sharma et al. 16 and Chauhan et al. 17 have observed a similar pattern of spiromesifen and cromafenozide half-life. They reported that spiromesifen have a half-life of 5.64 days in cucumber, 3 days in eggplant, 5 to 6 days in apple, and 5 days in tea 16,17 . In other studies, chromafenozide has been reported to have a half-life of 3.53 to 4.07 days in strawberries and 3.5 days in tomatoes 10,18 . The dissipation of pesticides in plants is affected by various factors including, physicochemical properties, initial concentration, characteristics of the crop species, frequency of application, and environmental factors 19,20 . Besides the degradation of the pesticide Table 2. Initial residues of spiromesifen a and chromafenozide in lettuce and perilla leaves. a Total residues of spiromesifen (mg/kg) = spiromesifen + (BSN2060 residue × 1.36). www.nature.com/scientificreports/ itself due to environmental factors, the growth-dilution effect of crops plays a substantial role in dissipation 14 .
Several studies have reported that the dilution effect caused by crop growth is a major factor that contributes to the decline of pesticides 19 . In another study, Jeon et al. 21 discovered that the decreasing residual level of bifenthrin in perilla leaves over time was due to the growth of the plant. Furthermore, Kim et al. 22 reported that the halflives of chlorpyrifos and procymidone in lettuce were 1.2 to 1.5 days and 1.3 to 2.6 days, respectively and the major cause of the decrease over time was the growth dilution factor. In this study, although spiromesifen and chromafenozide were similarly applied to lettuce and perilla leaves, the rate of degradation of both insecticides in lettuce was faster than that in perilla leaves. Such differences could be correlated to the growth characteristics of the two crops 15 . This result suggests that the dissipation and half-life of pesticide residues can vary based on crop variety.

Residual characteristics of insecticides.
To obtain a proper protection regime, spiromesifen and chromafenozide were sprayed twice on lettuce and perilla leaves. The insecticides residue amount at various growth stages (0, 1, 3, 5, and 7 days after spraying) of lettuce and perilla were measured and the results are summarized in Table 3. The residues of spiromesifen were calculated as the sum of spiromesifen and its metabolite BSN2060-enol following RDA guidelines 23 . The residues of spiromesifen and chromafenozide in lettuce after 7 days were decreased from 27.07 to 5.50 mg/kg and 9.30 to 0.48 mg/kg, respectively. Similarly, perilla leaves after the same periods were decreased from 34.52 to 9.67 mg/kg (spiromesifen) and 12.40 to 5.26 mg/kg (chromafenozide). Several factors affect the residual characteristics of pesticides such as crop morphology, growth rate, and physicochemical properties of pesticides 14,24 . In this study, although the tendency of spiromesifen and chromafenozide to decrease over time was similar, the residual amounts of both compounds in perilla leaves were relatively higher than that of lettuce. This higher residual amount may be due to the morphological features of the crops, as perilla has hairy leaves while lettuce leaves had deep curves 25 . Thus, compared to curved leaves, the foliar sprays deposit a high amount of insecticide on hairy leaves 26 . The result of the present study is consistent with the previous study in which the amount of pesticide in hairy peaches was 1.9 times higher than that of without hair 27 . Moreover, a faster growth rate of crop increases the contribution of growth dilution to pesticide dissipation 14 . Hwang et al. 28 described that the wider leaf and rapid growth of lettuce consider as another factor that influences the residue of pesticides 28 . Another factor affecting the residual characteristics of pesticide are the physicochemical properties 29,30 . The log P value of pesticide is used as an index to predict the lipophilicity, and it has been reported that pesticides with a log P value greater than 1.0 have a good penetration property 31,32 . In the case of spiromesifen and chromafenozide the log P values were 4.55 and 2.7 respectively, which are considered to be easily penetrating the crop 33 . Therefore, it is assumed that the higher residues of spiromesifen detected in lettuce and perilla leaves are due to its high concentration of AI in the formulation products as well as 100-time higher log P value. Our results are consistent with the results of previous studies, which have reported that the initial residues, residual patterns, and biological half-life of pesticides are affected by crop morphology and physicochemical characteristics of pesticides 14,24,34 .
Safety assessment. The %ADI of spiromesifen and chromafenozide in lettuce and perilla leaves consumed by Koreans are shown in Table 4. Based on the data provided by the Korean Health Industry Development Institute (KHIDI) 35 , on average, 0.00615 kg/day of lettuce and 0.00276 kg/day of perilla leaves are consumed by the average Korean adult (60 kg weight). The ADI of spiromesifen set by the Korean authorities is 0.03 mg/kg/ body weight/day, and chromafenozide is 0.27 mg/kg/bodyweight/day 36 . The %ADI of spiromesifen and chromafenozide estimated in this study was 6.8333% and 0.5694% respectively in lettuce and 4.6000% and 0.2556% www.nature.com/scientificreports/ in perilla leaves. The previous study conducted by Chun and Kang 37 claims that the risk of the target pesticide is considered relatively low when %ADI value is less than 10%. TMDI, the sum of %ADI of spiromesifen and chromafenozide, was 67.4925% and 3.4315%, correspondingly. The potential risk to consumers occurs when the TMDI ratio exceeds 80%. Thus, no significant effects of spiromesifen and chromafenozide residues were found in lettuce and perilla leaves on human health due to relatively low values 37 .

Conclusion
This study determined the dissipation and residual characteristics of spiromesifen and chromafenozid in lettuce and perilla leaves using LC-MS/MS. The result indicated that both insecticides dissipated rapidly in both matrices under greenhouse conditions. The spiromesifen and chromafenozide residues in lettuce and perilla leaves dissipated following the first-order kinetics model with the half-lives of 2.89 and 1.69 days in lettuce and 4.25 and 6.30 days in perilla leaves, respectively. The dissipation of both tested insecticides in lettuce was faster than that in perilla leaves. The safety assessment, based upon the TMDI, demonstrated that following the recommended guidelines for insecticides used in this study, lettuce and perilla leaves could be consumed safely without health problems. The data provided by this study can contribute to the management and regulation of pesticide use in lettuce and perilla as well as help in the sustainable production of minor crops in Republic of Korea.

Materials and methods
Chemicals and materials. Analytical standard (> 99% purity) of spiromesifen, BSN2060-enol, and chromafenozide were purchased from AB Solution Co., Ltd., Hwaseong-si, Gyeonggi-do, Republic of Korea. HPLC grade water and acetonitrile were supplied by Merck, Darmstadt, Germany. QuEChERS kit (4.0 g magnesium sulfate, 1.0 g sodium chloride, 1.0 g sodium citrate tribasic dihydrate, 0.5 g disodium citrate sesquihydrate) were  Table 4. TMDI and %ADI of spiromesifen and chromafenozide in lettuce and perilla leaves. MRL maximum residue limit, EDI estimated daily intake, TMDI theoretical maximum daily intake. Field experiments. The trials were carried out in a greenhouse farm during the season 2018 at two different sites (with approximately 24 km distance between both sites) located in Chuncheon and Hongcheon-gun, Gangwon-do, Republic of Korea following the method described by the Organization for Economic Co-operation and Development (OECD) 38 . The field test of lettuce (Latuca sativa L.) crop was conducted in Chuncheon city, and perilla (Perilla frutescens (L.) Britton) crop in Hongcheon city. The area of each field was divided into two plots (treatment and control). The treatment plots were further divided into three replicates (subplots 33 m 2 ). The control plot was separated by a buffer zone of 3 m 2 from the treated site. To minimize spray overlap, buffer zones (1 m) were set up between subplots. The commercial products of spiromesifen 20% SC diluted 2000 times and chromafenozide 5% EC diluted 1000 times were sprayed twice at 7-days intervals using an automatic sprayer. After the second spray samples (lettuce and perilla leaves) were collected from each subplot at 0 (2 h after spraying), 1, 3, 5, and 7 days according to the Korean RDA 23 method. Thirty samples 1.0 kg each from the collected crop were placed in polyethylene bag and labeled. After collection, the samples were transported to the laboratory, where they were chopped and homogenized. The homogenized samples were kept frozen at − 20 °C until analysis.

Insecticides Crops MRL (mg/kg) Daily intake (g/day) EDI (mg/kg) %ADI TMDI (%)
We confirm all plant samples used in the current work comply with the IUCN Policy Statement on Research Involving Species at Risk of Extinction and the Convention on the Trade in Endangered Species of Wild Fauna and Flora.
Samples pretreatment. A QuEChERS method was used for the extraction of the targeted compounds from lettuce and perilla leaves. A 10 g of previously homogenized samples were weighed into a 50 mL polypropylene centrifuge tube and mixed with 10 mL of water followed by 10 mL of acetonitrile. The samples were shaken at 1500 rpm in a shaker machine for 10 min. Then commercial QuEChERS kit was added, and the mixtures were shaken vigorously for 2 min in a shaker. Subsequently, the samples were centrifuged at 3584 g-force for 10 min. After centrifugation, the supernatant was filtered with a 0.22 μm membrane filter and transferred into the glass vial for instrumental analysis.
The calculation of spiromesifen total residues. The total residues in lettuce and perilla samples were calculated using Eq. (1) 23 .
Initial deposition calculation. The initial residues of spiromesifen and chromafenozide deposition in lettuce and perilla leaves were calculated from 0-day according to Eq.   www.nature.com/scientificreports/ concentrations levels (0.1 mg/L) and (0.5 mg/L) in 10 g control samples and were quantified by comparing the response of analytes in samples with response in calibration standard solutions prepared in matrix. The repeatability expressed as the relative standard deviation (RSD) of the analyzed samples was calculated from three repetitions. The MLOQ was calculated by Eq. (3) taking into consideration the following factors: the instrument limit of detection, volume of extraction solvent, injection volume, dilution factor, and sample amount 39,40 .
where A: instrument limit of detection, B: volume of extraction solvent, C: injection volume, D: dilution factor, E: sample amount.
Half-life calculation. The dissipation patterns of spiromesifen and chromafenozide in lettuce and perilla leaves over time were found following the first-order kinetics model 28 . The half-life was determined by the following equation: where C t is the concentration of the insecticide, C 0 represents the initial residue concentration of insecticide, t is the time (days) after insecticide application, and k is the constant rate.
Safety assessment. In this study, the safety assessments (percent acceptable daily intake; %ADI) of the target insecticides that are consumed with lettuce and perilla leaves were calculated by the ratio of estimated daily intake (EDI) to acceptable daily intake (ADI). The EDI was calculated using insecticide concentration and average consumption of food commodities per person per day. In addition, the theoretical maximum daily intakes (TMDIs) of both insecticides were calculated using the maximum residue limits (MRLs) and average body weight (60 kg) of adults in Republic of Korea. TMDIs were calculated following the equation described by Kim et al. 41 .

Data availability
Data are presented in the manuscript and available as support information.