Effect of decontamination and processing on insecticide residues in grape (Muscat Hamburg)

Field and laboratory experiments were conducted to study the effect of simple decontamination methods and processing on imidacloprid, dimethoate, and emamectin benzoate residues in grapes and their processed products by liquid chromatography-mass spectrometry. Among the decontamination methods evaluated, washing with NaCl (2%) solution was effective for reducing imidacloprid (77.55%), dimethoate (83.27%), and emamectin benzoate (77.28%) residues in mature grapes. No metabolites (omethoate and 6-chloronicotinic acid) were detected in both decontamination and processing studies. The grapes were processed into various products, including fresh juice, squash, and raisin, following the standard effective steps for each product. Washing with NaCl (2%) solution for decontamination was included as an additional step in the standard protocol and resulted in substantial removal of surface residues of the selected insecticides. The processing factor calculated was less than one for all the products.


Introduction
Grape (Vitis vinifera L.) is an important, non-climacteric fruit crop that grows on perennial and deciduous woody vines. Globally, India ranks seventh in grape production. In 2019-2020, 2.93 MT of grapes were produced in an area of 147,000 ha (productivity of 21 MT ha −1 ). In Tamil Nadu, grape is cultivated on 2200 hectares of land, with a production of 58.93 MT and productivity of 27.27 MT ha −1 (DAC & FW 2019). In commercial cultivation, numerous insect pests damage vineyards and there are about 60 different types of insects attack grapes (Wadhi & Batram 1964). Farmers most commonly rely on pesticides to control these pests and grapes take up nearly 7% of the pesticides used in agriculture (Zengln & Karaca 2018).
Grape is one such fruit consumed in raw form as well after processed into squash, juice, wine, and raisins (Heshmati et al. 2020). Consumption of fresh grapes accounts for 74.5% of total production and more than 22.5% is used for producing juice, raisin, and wine ). Due to the high consumption of grapes, a survey on the pesticide usage pattern was conducted in the important grape-growing districts of Tamil Nadu (India). It was found that farmers use dimethoate (93.33%) and imidacloprid (75%) as primary plant protection chemicals (Jayabal et al. 2020). Imidacloprid is recommended for pest management in grapes by the Central Insecticide Board and Registration Committee of India (CIBRC 2021). It is also widely used by grape farmers across the world (Hogg et al. 2021;Daane et al. 2020). Dimethoate is registered under CIB & RC to control aphids, mealybugs, hoppers, and stem borers in various fruit crops, including mango, banana, citrus, apple, fig, and apricot (CIBRC 2021). However, the survey found that farmers used it extensively in grapes. Additionally, emamectin benzoate is often used indiscriminately against different types of grape insect pests and is also registered and recommended by CIB & RC for usage in grapes to control thrips.
Insecticides applied during the fruit growth period may evaporate more quickly because of the growth dilution Responsible Editor: Ester Heath effect, and those applied later are more likely to persist in the economically valuable parts (fruit), depending on the nature of the pesticide. The presence of pesticide residues in grapes was reported in several studies (Arora et al. 2008;Mohapatra et al. 2011;Reddy et al. 2021Reddy et al. , 2022Mahdavi et al. 2022). Generally, processing a fresh commodity into value-added products affects the nature and magnitude of pesticide residues and might increase or decrease the residues in the processed product (Schusterova et al. 2021). The processing factor (PF) is used to quantify the risk of pesticide residue intake, especially for processed food products (Thekkumpurath et al. 2020). The extent of reduction or removal of pesticide residues is determined by elements such as the chemical characteristics of the pesticides, the kind of food commodity, the processing stage, and the duration of contact between the pesticide and the food. Processing (washing, peeling, boiling, and juicing) can considerably reduce pesticide residues (Han et al. 2013;Lopez-Fernandez et al. 2013;Heshmati et al. 2020;Corrias et al. 2021;Rahimi et al. 2021;Shokoohi et al. 2022).
Most of the studies on pesticide residues in grapes focused on the vine-to-wine conversion process. Given the large-scale use of the abovementioned insecticides, the extensive consumption of the processed products of grapes, such as fresh juice, squash, and raisin, and the lack of published studies for the selected insecticides on the effect of processing on pesticides in grapes, this study was conducted to determine the effectiveness of simple decontamination approaches and the effect of processing on residues of selected insecticides.

Preparation of standard solutions
Individual stock solutions containing 400 mg/L of imidacloprid, 6-CNA, and emamectin benzoate were prepared in HPLC grade acetonitrile by adding 10.17, 10.11, and 10.24 mg of the respective analytical standards into a volumetric flask (25 mL), separately. Stock solutions of dimethoate and omethoate (400 mg/L) were prepared using LCMS grade methanol by independently weighing 10.05 and 10.33 mg of the analytical standards. To prepare secondary stock solutions (40 mg/L) of each pesticide, about 2.5 mL of each stock solution was added to a volumetric flask (25 mL). A working standard mixture (10 mg/L) was made from the secondary stock solution. From the mixed standard solution, linearity and spiking standard solutions in the range of 0.005-0.1 mg/L were prepared through serial dilution. All standard solutions were stored at − 20 °C in a deep freezer until further use.

Field experiments
In February 2021, experiments were conducted in the fields of farmers in the Theni district of Tamil Nadu, India (9° N, 76° E, and 375 m above the mean sea level), following good agricultural practices. The trials were conducted separately in a 50 m 2 plot that had not been treated previously with selected insecticides, and the treatment plots had three replicates. A buffer zone of 10 m was maintained between each treatment plot. The commercial formulations of imidacloprid 17.8 SL, dimethoate 30 EC, and emamectin benzoate 5 SG were applied on grapes (Muscat Hamburg variety) using a Spraywell-SW16C-2 battery-operated knapsack sprayer at harvest to evaluate decontamination methods in mature grapes and the impact of processing on pesticide residues in commodities made from fresh grapes after a single-dose (53, 445, and 11 g a.i ha −1 ) and a double-dose (106, 890, and 22 g a.i ha −1 ) treatment (Table S5).

Collection and preparation of samples
The grape berries (0.5 kg) were picked from vines at random to analyze the residues of the insecticides applied. The samples were collected after two hours of spraying, transported to the laboratory in an icebox, and stored at − 5 °C. The samples were homogenized using a high-volume blade homogenizer (Robot-Coupe) for the analysis of insecticide residues. The berries were processed (Srivastava and Kumar 2005) into juice, squash, and raisins (Fig. 1a).

Mature berries
The modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) procedure was adopted and validated for the analysis of insecticide residues in grapes (Anastas- siades et al. 2003). To 10 g of a homogenized sample taken in a centrifuge tube (50 mL), 10 mL of acetonitrile was added and vigorously agitated for 1 min. After adding 4 g of anhydrous magnesium sulfate and 1 g of sodium chloride, the mixture was gently mixed, followed by centrifugation at 6000 rpm for 10 min. After centrifugation, 6 mL of the sample was transferred to a 15-mL polypropylene centrifuge tube containing 10 mg GCB, 100 mg PSA, and 600 mg MgSO4, vortexed for 1 min, followed by centrifugation at 3000 rpm for 10 min. Then, 1 mL of the sample was transferred to autosampler vials and filtered through a membrane syringe filter (0.2 µm) without evaporation.

Juice, squash, and raisin
The samples were processed using the QuEChERS approach, which was developed by Pohorecka et al. (2012). A representative sample (10 g) of each product (juice, squash, and raisin) was taken in a 50-mL centrifuge tube and agitated for 1 min using a vortexer after adding 10 mL ultrapure water. After vortexing, 10 mL acetonitrile and 2 mL n-hexane were added and gently vortexed for 1 min. Approximately 4 g of anhydrous MgSO4, 1 g of NaCl, 1 g of sodium citrate dibasic sesquihydrate, and 1 g of anhydrous tri-sodium citrate dihydrate were added, vortexed, and centrifuged at 7600 rpm for 5 min. The upper supernatant (6 mL) after centrifugation was transferred to a 15-mL centrifuge tube containing 100 mg PSA, 600 mg anhydrous MgSO4, and 20 mg GCB. The mixture was vortexed for 1 min, followed by centrifugation at 8100 rpm for 1 min. Finally, 1 mL of the sample was taken and filtered using a membrane syringe filter (0.2 µm) before transferring it into 1 mL autosampler vials for LC-MS analysis to evaluate the residues of imidacloprid and emamectin benzoate.

Mature berries
A modified QuEChERS was used similar to the procedure followed for imidacloprid and emamectin benzoate residues in mature berries, except for the use of 20 mL ethyl acetate instead of acetonitrile in the initial steps. Finally, 2 mL of the aliquot was evaporated to near dryness under a gentle stream of nitrogen gas in a low volume concentrator at 40 °C, and the residue was redissolved in 1.0 mL methanol, filtered using a membrane syringe filter (0.2 µm), and transferred into 1.0 mL autosampler vials.

Juice, squash, and raisin
The method developed by Pohorecka et al. (2012) was used with modifications. Acetonitrile was replaced with 20 mL ethyl acetate for extraction of the residues. The final 2 mL of aliquot was evaporated to near dryness under a gentle stream of nitrogen gas in a low volume concentrator at 40 °C. The residue was redissolved in 1.0 mL methanol, filtered through a membrane syringe filter (0.2 µm), and transferred into 1.0 mL autosampler vials.

LC-MS apparatus and chromatographic conditions
The residues of the compounds were detected, estimated, and confirmed using a Shimadzu 2020 series LCMS equipped with a reverse phase C 18 (Eclipse plus-Agilent) column (250 mm length × 4.6 mm internal diameter, 5 µm particle size) at a column oven temperature of 40 °C. The mobile phase, flow rate, and instrument parameters are presented in Table S4.

Method validation parameters
For estimating the residues in grapes, the method was validated using the SANTE guidelines (SANTE 2019) and evaluated for factors such as linearity, the limit of quantification (LOQ), the limit of detection (LOD), recovery, precision, repeatability, and the matrix effect. The acceptability of the methods regarding reproducibility was determined by HorRat (Horwitz ratio) for intra-laboratory precision, calculated using the formula mentioned below (Horwitz & Albert 2006).
The expected RSD was calculated using the formula PRSD = 2 C −0.15 , where C is the mass fraction.
The matrix effect (ME) was assessed based on the formula given below (Dong et al. 2018).

Decontamination of residues
Grape berries were decontaminated for 1 min using simple methods (T 1 -tap water washing, T 2 -washing in sodium chloride water (2%), T 3 -dipping in tamarind water (2%), T 4 -dipping in lemon water (2%), T 5-dipping in lukewarm water, T 6 -dipping in ozonized water (0.2 ppm), and no treatment (control)). The solutions of sodium chloride, tamarind, and lemon juice were prepared by mixing 20 g of each in a 1000-mL beaker. Ozonized water was produced using an ozone generator (L30G model manufactured by Faraday Ozone Products Private Limited) by high-frequency corona discharge technology using oxygen as the feed gas that was supplied by the oxygen generator. Following the treatment, the berries were air-dried and processed for analyzing the residues.

Processing factor
For each step of processing, PF was computed as the ratio of the pesticide residue level in the processed products to the pesticide residue level in raw commodities (Scholz et al. 2017). A PF below one indicates a reduction in the residue in the processed product, while a PF greater than one implies a concentration effect (BfR 2021).

Risk assessment
To evaluate the safety of the studied insecticides for the consumers of grapes and raisins, especially children, the maximum permissible intake (MPI [mg person −1 day −1 ]) was compared to their dietary exposure (TMDI [mg person −1 day −1 ]). The MPI was estimated by multiplying the acceptable daily intake (ADI) of the pesticide by the average body weight (NIN 2021) of a child (16 kg) and an adult (60 kg). The dietary intake was determined by multiplying an average per capita consumption of 0.15 kg of grapes (NIN 2021) and 0.0043 kg of raisins per day (NSSO 2001) with residue levels in the sample. Since no standard data for the consumption of juice and squash were available, the assessment of risk was not performed for juice and squash.

Results and discussion
Different methods were used for extracting the residues of imidacloprid and dimethoate from grapes and their processed products (Table S6). The mobile phase for extracting dimethoate and imidacloprid was also optimized with different formic acid compositions (0, 0.01%, 0.05%, and 0.1%).
In the mobile phase of 0.05% formic acid with methanol, the peak shape of dimethoate improved considerably. However, at 0.1% formic acid concentration with acetonitrile mobile phase, the peak shape and signal intensities of imidacloprid were better than those obtained with 0.01% and 0.05% formic acid.

Optimized LCMS parameters
Instrument conditions were optimized using a single quadrupole LC-MS to identify, confirm, and quantify the selected insecticide residues in mature grapes, grape juice, squash, and raisin.

Validation of the method
Linearity, LOQ, LOD, recovery, precision, and the matrix effect were estimated following the SANTE (2019) guidelines for the validation of the analytical method used to identify and quantify the imidacloprid, 6-CNA, dimethoate, omethoate, and emamectin benzoate residues in grapes.
(a) Linearity: The linearity of the method was assessed at concentrations of 0.005, 0.01, 0.025, 0.05, 0.075, and 0.1 mg/kg with three replicate injections per concentration for all grape matrices. Matrix-matched and solvent standards (Tables S1, S2, and S3) had correlation coefficients (r 2 ) greater than 0.99 for imidacloprid, 6-CNA, dimethoate, omethoate, and emamectin benzoate. (b) Limit of detection (LOD) and limit of quantification (LOQ): The LOD and LOQ were established by comparing the signal-to-noise ratio of 3 and 10 to the background noise of a blank sample. The LOD and LOQ were confirmed as 0.005 and 0.01 µg/g, respectively.
The proposed LOQ (0.01 mg/kg) of the method was below the maximum residue limit  (Tables 1, 2, and 3). The HorRat (Horwitz ratio) of imidacloprid, 6-CNA, dimethoate, omethoate, and emamectin benzoate was less than 0.5 at all the spiked levels in grape matrices and was within the permitted range of 0.5 to 2.0, as suggested by the SANTE (2019) standards. Thus, the intra-laboratory precision and accuracy of the analytical method were acceptable. (e) Matrix effects: The matrix-matched standard solutions were prepared with different grape matrices separately, including mature grapes, juice, squash, and raisins, to obtain more realistic results. The calculated matrix effect ranged from 1.68 to 8.73% (i.e., < 20%) in the spiked mature grape, juice, squash, and raisin samples.

Decontamination of insecticide residues in mature grape berries
Various decontamination methods were used to study their effect on insecticide residues by exposing the mature grape berries for 1 min (Figs. S1, S2, and S3). Among the decontamination methods used, washing with 2% NaCl solution removed the highest content of insecticide residues (68.30%), and the next-best treatment was lukewarm water (60.00%) at the recommended dose (53 g a.i ha −1 ) of imidacloprid. Similarly, for a double-dose (106 g a.i   , and 0.2 ppm ozonized water (64.38%) were effective. The highest removal (77.48%) of emamectin benzoate residues was observed in 2% NaCl solution, while lukewarm water removed 68.06% of the residues for a single-dose (11 g a.i ha −1 ) emamectin benzoate treatment. For a double-dose (22 g a.i ha −1 ) treatment, 2% NaCl solution removed the maximum level of residues (73.45%), followed by a lukewarm water treatment (62.71%). The results indicated that treatment for 1 min using 2% NaCl solution was highly effective in reducing all the tested doses of insecticides, including imidacloprid, dimethoate, and emamectin benzoate residues, in mature grape berries. Sodium chloride is a potent electrolyte that interacts with pesticide residues and reduces their concentration. Pesticides with high water solubility can easily be removed from the fruits when they are dipped in a salt solution (Pallavi et al. 2021). Washing with salt water (2%) solution for 10 min effectively decontaminated the samples and removed 51.80-72.80% of acephate, chlorpyriphos, quinalphos, and bifenthrin residues in grapes (Reddy and Rao 2002, 2004). The oxidant nature of the washing solution (alkaline, acidic, or neutral), the surfactant activity, the pH, and the interference of negatively or positively charged ions might influence the removal of residues from the berries.

Effect of processing on insecticide residues during juice, squash, and raisin preparation
During product preparation, samples were taken at each step of processing and analyzed for residues. The PFs of juice, squash, and raisin preparation for imidacloprid, dimethoate, and emamectin benzoate are presented in Table 4.

Imidacloprid
In this study, 59.75-67.94% of imidacloprid residues were removed from grapes after washing with tap water for all the products and a strong correlation between water solubility (600 mg L −1 ) and the removal of imidacloprid was found (Malhat et al. 2021). Crushing/homogenization does not impact residues, but it speeds up processes like hydrolysis and the release of isolated enzymes and acids from the cuticle layer, thus reducing residues in the juice. During clarification of juice, a reduction of 14.32-21.55% of residues was recorded. This might be caused by the elimination of residues in the suspended particles due to the partitioning characteristics of the insecticide between pulp and juice. During juice preparation, pasteurization (80 °C for 10 min) led to the loss of imidacloprid residues (10.49%), which might be due to evaporation, hydrolysis, or thermal destruction during heating. Pasteurization was found to reduce imidacloprid residues (32.45%) during strawberry juice preparation (Hendawi et al. 2010) and also reduce 60.42-100% of imidacloprid residues in tomato juice and paste (Romeh et al. 2009). About 89.13-97.17% of residues were removed while processing grapes into juice in the current study. About 93.26-97.85% of imidacloprid residues were removed during the processing of apples into juice (Wang et al. 2016). Pesticide residues were significantly reduced during juice processing from apples, carrots, and lemons (Zabik et al. 2000;Burchat et al. 1998;Holland et al. 1994;Pappas et al. 2003;Rasmussen et al. 2003).
The addition of sugar syrup to pure juice reduced the residues (94.32%) as the water added to prepare the sugar syrup diluted the residues. A reduction of imidacloprid residues (82.66% and 66.55%) was observed in sweetened pulp and paste of winter jujube (Peng et al. 2014) and in strawberry syrup (50.64%) and jam preparation (84.41%), respectively (Hendawi et al. 2010). About 92.43-94.68% reduction in insecticide residues was found after the production of squash. The residues of imidacloprid in raisins were below the detectable level (< 0.01 mg kg −1 ) for a single dose of imidacloprid and 0.038 mg/kg for a double dose of imidacloprid (106 a.i ha −1 ). Evaporation and degradation while drying can significantly reduce the imidacloprid residues (Bajwa & Sandhu 2014). Thus, volatilization after drying can effectively remove pesticides with low K ow , and this was true for the studied chemical, imidacloprid, which has a low K ow (0.57). Concerning imidacloprid residues, 70% reduction in pomegranate anardana by hot oven air drying (Utture et al. 2012), 36.73% reduction during zucchini processing , 53% reduction in lettuce (Miguel et al. 2017), and 37% reduction in chili peppers (Noh et al. 2015) were reported during drying. Phosalone (68.04%) and ethion (69.55%) residues were removed during raisin preparation (Rahimi et al. 2021).

Dimethoate
Tap water washing reduced 21.86-45.35% of the dimethoate residues for all the processed products. Washing reduced chlorpyrifos residues (21%) while processing apples (Kong et al. 2012). An increase in the residue was observed during pulping of berries from 0.397 to 0.425 mg/kg and 0.89 to 1.177 mg/kg for single-dose and double-dose dimethoate treatment, respectively, while preparing grape juice. Pulping, followed by clarification, increased the level of residues (0.393 to 0.435 mg/kg at the recommended dose and 0.767 to 0.846 mg/kg for a Table 4 Residues and processing factor of imidacloprid, dimethoate, and emamectin benzoate in grape juice, squash, and raisin double dose of dimethoate) during squash preparation and this was due to the high-water solubility (23,300 mg/L at 20 °C) and low octanol-water partition coefficient (0.7) of dimethoate. Moreover, dimethoate is xylem mobile due to its low log K ow value of 0.7 and phloem mobile due to its pK a of 2 (British Crop Protection Science Council, 2014). This is probably why dimethoate was removed less effectively by washing than other organophosphates (chlorpyriphos and parathion) and thus was present in the filtered juice. High concentrations of insecticides, like dimethoate in wine (Pazzirota et al. 2013), chlorpyrifos in apple juice (Kong et al. 2012), and quinalphos and chlorpyrifos in apple juice (Rasmussen et al. 2003) were also reported. Most of the dimethoate, omethoate, and quinalphos residues in tea (80.5-84.9%) were transferred into the tea infusion easily, as the transfer rate is positively correlated with water solubility and negatively correlated with the octanol-water partition coefficient (Ramezani & Shahriari 2015;Saber et al. 2016). Thus, pesticides with high water solubility (quinalphos, dimethoate, and hexaconazole) and low octanol-water partition coefficient easily accumulate in tea (Manikandan et al. 2009;Pan et al. 2015).
Mixing sugar syrup during squash production diluted the dimethoate residues by 63.08% in this study. Sugar dipping was reported to reduce the dimethoate (88%) and triazophos (46%) residues while processing kumquat . The residues of dimethoate during raisin production by oven drying increased from 0.441 to 0.499 and 1.07 to 1.623 mg/kg for a single dose and double dose of dimethoate, respectively, due to moisture loss, indicating an increase in the concentration of the residues. An increase in the concentration of dimethoate was probably because water loss in grapes was higher than the degradation rate of dimethoate during drying, and the left-over residue present after sugar syrup soaking treatment was probably bound to the matrix more firmly, thus, preventing its degradation during drying. A higher PF for hexythiazox (1.64) and bifenazate (1.12) was observed during raisin production (Thekkumpurath et al. 2020). Methamidaphos residues increased by three times in dried grapes after oven-drying (Athanasopoulos et al. 2005), and cypermethrin residues increased to 0.46 in grape raisins from 0.40 mg/kg (Lentza-rizos and Kokkinaki 2002). Dimethoate increased by 11% during the processing of dried kumquat fruit , and bifenthrin, lambda-cyhalothrin, and beta-cyfluthrin increased in dried shiitakes . The levels of some pesticide residues decreased during the processing of food commodities, but those pesticides (dimethoate, azoxystrobin, and pyrimethanil) did not have a preferential partitioning between the liquid and solid phases and might be concentrated in the final processed product (Čuš et al. 2010).

Emamectin benzoate
Tap water washing reduced the residues (43.15-61.82%) in all products of grapes that received single and double doses of insecticides. Filtration of pure juice by discarding the pulp and seed reduced the residues by 55.08-68.94% compared to unprocessed samples for both juice and squash. The poor transfer/presence of lower residues in filtered juice might be due to low water solubility (0.1 mg/L) and a high octanol coefficient (K ow = 5.0), as reported for emamectin benzoate, fenpropathrin, and propargite during tea brewing (Manikandan et al. 2009;Zhou et al. 2016). Pasteurization caused a reduction in the residues during juice preparation by 24.74%. The residues were below BDL at the recommended dose and 0.02 mg/kg in fresh juice of grapes treated with a double dose of emamectin benzoate, showing an overall reduction of 92.68%. Mixing sugar syrup with pure juice for squash production diluted the residues by 87.67%. Most of the residues (93.01%) during raisin preparation were removed by dipping/soaking in sugar syrup, which caused the residue level to fall below BDL after drying in a hot air oven. The fate of emamectin benzoate during the processing of grapes or other fruits has not been studied. In other crops, post-harvest processing and decoction of the Chinese medicinal plant mugua resulted in a reduction of emamectin benzoate by 99.94% (Xiao et al. 2021a, b) and in Chinese peony (PF = 0.06), reported by Xiao et al. (2021b). The above results indicated that physicochemical properties might strongly influence how far the residues are leached into the by-products of any food commodity.

Effect of processing on residues after washing with 2% NaCl
Based on the results obtained in the decontamination experiment, washing with 2% NaCl solution for 1 min was found to be the most effective decontamination process for removing all the selected insecticide residues, including imidacloprid, dimethoate, and emamectin benzoate. A separate experiment was conducted to observe the effect of processing on residues in juice, squash, and raisin by including washing with 2% NaCl solution as an additional step in the standard protocol for the preparation of processed products. The details are summarized in Table 5.
The results indicated that NaCl washing strongly affected the residues and removed imidacloprid (64.70%), dimethoate (71.64%), and emamectin benzoate (62.76%). Subsequent tap water washing resulted in > 80% cumulative reduction of imidacloprid (89.59%), dimethoate (88.93%), and emamectin benzoate (84.41%) compared to the residue levels in the control. During juice preparation, the subsequent pulping and filtration of pure juice reduced 94.61% and 91.40% of imidacloprid and emamectin benzoate residues. Dimethoate residues increased from 0.106 to 0.174 mg/kg (recommended dose) and 0.141 to 0.198 mg/kg (double-dose), which might be due to its high-water solubility, as found in the experiment. Pasteurization of filtered juice resulted in 96.08%, 95.82%, and 91.40% removal of imidacloprid, dimethoate, and emamectin benzoate residues, respectively. The addition of sodium benzoate reduced the residues below the detectable level (< 0.01 mg kg −1 ) in juice for all insecticide treatments except for the treatment with a double dose of dimethoate. During squash preparation, 68.44%, 70.82%, and 65.50% residues of imidacloprid, dimethoate, and emamectin benzoate were reduced after washing with NaCl (2%) solution relative to the residue levels in the control. Further washing with tap water removed a substantial quantity of residues of imidacloprid (89.59%), dimethoate (86.88%), and emamectin benzoate (77.59%). Pulping of juice reduced imidacloprid (94.60%) and emamectin benzoate (90.52%) and increased dimethoate residues from 0.115 to 0.218 mg kg −1 (recommended dose) and 0.152 to 0.234 mg kg −1 (doubledose). The addition of sugar syrup caused the imidacloprid and emamectin benzoate residues to fall below BDL at the recommended dose and by 96.59% and 97.65% of the initial residues for a double dose treatment. About 97.33% of dimethoate residues were removed by mixing sugar syrup with filtered juice. The addition of tonovin and sodium benzoate reduced the residues to BDL at the recommended dose for all insecticides except for a double dose of dimethoate in squash (0.014 mg/kg). The dilution of residues after the addition of sodium benzoate was mainly due to the strong electrolytic nature of sodium.
During raisin preparation, 69.06%, 63.18%, and 57.92% imidacloprid, dimethoate, and emamectin benzoate residues, respectively were eliminated by washing with a 2% NaCl solution. Further washing with tap water reduced imidacloprid (89.59%), dimethoate (87.76%), and emamectin benzoate (75.73%) residues. Dipping in sugar syrup showed the maximum reduction of imidacloprid, dimethoate, and emamectin benzoate residues by 95.56%, 98.58%, and 93.82%, respectively, and a high concentration of residues in raisin was found for a double dose of dimethoate. However, the overall PF was below one in raisin for all the insecticides analyzed. Compared to a previous experiment, washing grapes with a 2% NaCl solution as part of the standard protocol provided a maximum reduction of residues in the final products. The results indicated that the transfer of residues into processed products of grapes is positively correlated with water solubility and negatively correlated with the octanol-water partition (log K ow ) coefficient. Monitoring of commercially available grape processed products for residues under laboratory conditions can be determined with further studies, if such studies are carried out concurrently.

Safety evaluation
Since grapes are commonly consumed, a risk assessment was performed for fresh grapes, decontaminated grapes (sodium chloride [2%]), and raisins. Consumption of fresh grapes after the application of dimethoate was not safe (MPI < TMDI) but safer (MPI > TMDI) after the application of imidacloprid and emamectin benzoate. After washing with NaCl solution, the grapes were safe (MPI > TMDI) for consumption. The results showed that the TMDI (Table S7) of all three insecticides for raisins was lesser than the MPI for both doses of insecticides, thus indicating that they are safe for consumption by adults and children. However, raisins were found to be safe only based on the MRL of dimethoate recommended by the FSSAI (2.0 mg kg −1 ) and not following the MRL recommended by the EU (0.01 mg kg −1 ), according to which these raisins might pose a risk to the health of consumers.

Conclusion
LC-MS was performed to detect imidacloprid, 6-CNA, dimethoate, omethoate, and emamectin benzoate residues in grapes and their processed products. Sodium chloride (2%) solution was found to be an effective decontaminant for reducing the imidacloprid, dimethoate, and emamectin benzoate residues in grapes. The residues in commercially prepared products were below the quantification level after, including NaCl washing in the standard protocol. This study showed that NaCl washing is an essential step in the preparation of processed products from grapes for reducing imidacloprid, dimethoate, and emamectin benzoate residues in grapes and consequently for lowering the risk to the health of consumers.

Declarations
Ethical approval and consent to participate Not applicable.

Competing interests
The authors declare no competing interests.