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Residues and dissipation of thepesticide emamectin benzoate underEgyptian field condition: a case studyFarag Malhata, Abd El-Salam Fayza, Naglaa M. Loutfyb & MohamedTawfic Ahmedb

a Central Agricultural Pesticide Laboratory, Pesticide Residues andEnvironmental Pollution Department, Agriculture Research Center,Giza, Egyptb Faculty of Agriculture, Suez Canal University, Ismailia, EgyptAccepted author version posted online: 14 Nov 2013.Publishedonline: 19 Dec 2013.

To cite this article: Farag Malhat, Abd El-Salam Fayz, Naglaa M. Loutfy & Mohamed TawficAhmed (2013) Residues and dissipation of the pesticide emamectin benzoate under Egyptianfield condition: a case study, Toxicological & Environmental Chemistry, 95:7, 1099-1107, DOI:10.1080/02772248.2013.865908

To link to this article: http://dx.doi.org/10.1080/02772248.2013.865908

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Residues and dissipation of the pesticide emamectin benzoate under

Egyptian field condition: a case study

Farag Malhata, Abd El-Salam Fayza, Naglaa M. Loutfyb and Mohamed Tawfic Ahmedb*

aCentral Agricultural Pesticide Laboratory, Pesticide Residues and Environmental PollutionDepartment, Agriculture Research Center, Giza, Egypt; bFaculty of Agriculture, Suez CanalUniversity, Ismailia, Egypt

(Received 30 September 2013; accepted 8 November 2013)

A simple, rapid analytical procedure for the quantification of emamectin benzoate intomato was developed using high performance liquid chromatography with fluorescencedetector (HPLC-FLD). Emamectin benzoate residues were extracted from tomatosamples with n-hexane:ethyl acetate (1:1, v/v). The method involved derivatizationusing trifluoroacetic anhydride and 1-methylimidazole, prior to analysis by HPLC-FLD.Limit of quantification of this method was found to be 0.01 mg/kg, while limit ofdetection was 0.005 mg/kg. The dissipation of emamectin benzoate on tomato wasstudied, and half-life (t1/2) was estimated in a field study carried out at three differentlocations. Emamectin benzoate was sprayed on tomato at recommended dosage.Samples of tomato were collected at 0, 1, 3, 7, 10, and 15 days after treatment. The t1/2of emamectin benzoate when applied at the recommended doses in tomato wasapproximately 2.5 days. The residue of emamectin benzoate reached below the maximalresidue limit (MRL) 10 days after spraying at the tested dosage. Hence, a safe pre-harvest interval of 10 days is suggested before harvesting of tomato. This study wouldalso be helpful for the Egypt government to establish the MRL of emamectin benzoatein tomatoes and provide guidance on the proper and safe use of this insecticide.

Keywords: emamectin benzoate; pesticide residue; tomato; dissipation; food safety

Introduction

Tomato (Lycopersicon esculentum Mill.), the world’s largest grown vegetable crop, occu-

pies an important place in the economy of human societies because of its high nutritive

value and widespread production in different agroclimatic conditions (Frusciante et al.

2000). Tomatoes are an important source of lycopene (Sharma and Maguer 1996), a

powerful antioxidant that acts as an anticarcinogen (Arab and Steck 2000) as well as

provide vitamins A, B, and C, potassium, iron, and calcium. In Egypt, the annual tomato

production is approximately 10 million tons (FAO 2007). On average, 350,000 feddan

(feddan ¼ 0.42 hectare), representing 40% of the area cultivated with vegetable crops,

are used to grow tomatoes each year. A number of diseases frequently infest the tomato

crop at all stages of its development. Intensive pesticide applications may be required to

keep these diseases below the economic thresholds.

Emamectin benzoate, an insecticide, was shown to possess high efficacy in controlling

lepidopteran insects attacking tomatoes (Tomlin 2009). However, extensive applications

may lead to undesirable side effects on human health and environmental quality. Ema-

mectin benzoate (40-deoxy-40-epimethylamino-40-deoxyavermectin B1 benzoate,

*Corresponding author. Email: motawfic@tedata.net.eg

� 2013 Taylor & Francis

Toxicological & Environmental Chemistry, 2013

Vol. 95, No. 7, 1099–1107, http://dx.doi.org/10.1080/02772248.2013.865908

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Figure 1) has a high translaminar or local systemic efficacy that provides residual activity

against foliar-feeding insects. Emamectin benzoate is a mixture of two analogs (B1a:B1b

� 9:1), which differ by one methylene (CH2) unit on the C-25 side chain, wherein B1a

contains a sec-butyl group and B1b contains an isopropyl group.

To ensure that the pesticide use is performed according to good agricultural practices

protecting consumer health, regulatory authorities established tolerances, or maximal

residue limits (MRL), in treated crops. In addition, the MRL regulations require a pre-

harvest interval (PHI) to ensure that dissipation of a pesticide is below the proposed MRL

at harvest time (Karmakar and Kulshrestha 2009). Every year new pesticides are intro-

duced into the market with a growing need to develop new methods for their determina-

tion, or to integrate them into existing methods. For many years, analysis of pesticides in

vegetables has been performed employing gas chromatography (GC) especially coupled

with nitrogen phosphorus detector, electron capture detector (Fern�andez, Pico, and Manes

2002; Tadeo et al. 2004), and mass spectrometry (MS) (Beyer and Biziuk 2008; Ferrer

et al. 2005; Stajnbaher and Zupancic-Kralj 2003), or tandem mass spectrometery (MS/

MS) (Granby, Andersen, and Christensen 2004; Soler, Manes, and Pico 2004). High per-

formance liquid chromatography (HPLC) coupled to other less powerful detectors, that

are, however, easier to acquire and use (Kaihara et al. 2000; Martinez-Galera et al. 2001;

Paiga et al. 2009; Malhat 2013) is useful and preferable for polar, low volatile, and/or

thermolabile compounds that are not directly determinable by GC.

Various HPLC methods with ultraviolet (UV) detection, fluorescence detector (Hichs

et al. 1997; Roudaut 1998; Valenzuela, Popa, and Redobdo 2001; Wang et al. 2007; Kot-

tiappan and Anandham 2012), or MS (Liu et al. 2012; Wang et al. 2012) have been used

for determination of emamectin benzoate. As HPLC-FLD has good sensitivity and selec-

tivity, it is the current method of choice for analysis of emamectin benzoate residues, and

selected as a residue analytical method by the US Environmental Protection Agency

(2010). Most of the above methods require tedious sample preparation such as liquid–liq-

uid extraction or solid phase extraction even with the use of HPLC-MS. Therefore, there

Figure 1. Molecular structure of emamectin benzoate.

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is a need for simple and reliable analytical methods capable for determining residues of

emamectin benzoate.

To the best of our knowledge, studies on the dissipation behavior of emamectin ben-

zoate on tomatoes under field conditions, which is essential to evaluate its persistence and

fate in the environment, have not been reported. The objective of this study was to investi-

gate the dissipation kinetics of emamectin benzoate in tomatoes under Egyptian field con-

ditions using HPLC-FLD and thereby provide an assessment for scientific and safe use of

emamectin benzoate.

Material and methods

Materials

Emamectin benzoate standards were obtained from the Central Agricultural Pesticide

Laboratory (Dokki, Egypt), and purity was certified by the supplier to be greater than

99%. Commercial formulation 5% emamectin benzoate wettable granule (WG) was

obtained from Syngenta Agro Co. (Giza, Egypt). All solvents, acetonitrile, ethyl acetate,

methanol, and n-hexane were purchased from Merck (Darmstadt, Germany) and were of

HPLC grade. Trifluoroacetic anhydride and 1-methylimidazole were obtained from

Aldrich Chemical Co. (Milwaukee, WI). Water was distilled and filtered through a Milli-

Q-apparatus prior to use.

Preparation of standard solutions

Standard stock solution (100 mg/ml) was prepared by dissolving an appropriate quantity

of emamectin benzoate in acetonitrile. The stock solution was stored in dark at �20 �C.Fortification levels and calibration solutions for HPLC analysis were prepared via further

dilution with acetonitrile, achieving concentrations ranged from 0.005 to 1 mg/ml. The

calibration curve for emamectin benzoate was obtained by plotting the peak area against

the concentration of the corresponding calibration standard. Fortification and calibration

standard solutions were stored at 4 �C. The precision in the conditions of repeatability

(for five analyses in a single day) and intermediate precision (for five analyses on 5 differ-

ent days) were determined separately for a standard concentration of 0.01 mg/ml emamec-

tin benzoate.

Field trial study

Field trials for the determination of emamectin benzoate residue in tomatoes were con-

ducted in Menof, Miet-Gamer, and Kaha areas in the Nile valley. Trials were conducted

in separate plots measuring 40 m2 each in three replicates. None of the plots had been

treated with emamectin benzoate in the past. To ensure the reliability of the experimental

results, field management was carried out in accordance with the local conventional

method.

Experimental design

Each experimental treatment consisted of three replicate plots and a control plot, a buffer

area was used to separate each plot, and the area of each plot was 40 m2. Emamectin

benzoate 5% (proclaim uv 5 WG) was sprayed at the recommended dosage of

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3 g a.i.�feddan�1 during February 2013. The spray was carried out with a knap-sack hand

sprayer in the absence of precipitation.

Sampling and storage

Representative tomato samples were collected from each plot at 0 (2 hr after application),

1, 3, 7, 10, and 15 days, after the application of the pesticide. Samples were transported at

4 �C and in darkness in labeled polyethylene bags to the lab, where samples were proc-

essed and stored at �20 �C until analysis.

Analytical procedures

Sample extraction

The tomato samples were crushed vigorously in a blender. Four grams of homogenized

samples were extracted with 10 ml n-hexane:ethyl acetate and then vortexed for 5 min.

The extract was centrifuged for 10 min at 3000 g and 5 ml supernatant was transferred to

a spherical flask. The organic solvent was eliminated by a rotary evaporation and the

extract was re-dissolved in 0.5 ml acetonitrile for derivatization.

Derivatization

The sample and the standard solution were transferred to glass tubes, evaporated to dryness

at 35–40 �C under a gentle stream of nitrogen. The residues were dissolved in 0.2 ml ethyl

acetate and 1 ml acetonitrile, and 0.1 ml 1-methylimidazole was added. The tubes were

capped, contents vortexed, and all samples, standards, and freshly prepared in trifluoroace-

tic anhydride–acetonitrile (1:3, v/v) were placed in an icebox at ice temperature for

10 min. After cooling, 0.3 ml trifluoroacetic anhydride–acetonitrile (1:3, v/v) was added to

each sample and standard. Samples were capped and allowed to stand for 10 min. Each

sample or standard was diluted with acetonitrile to 2 ml for LC determination.

Instrumental analysis

Emamectin benzoate was determined using an Agilent 1260 HPLC with a fluorescence

detector, operated at an excitation and emission wavelength of 365 and 470 nm, respec-

tively, and a 250 � 4.6 mm id Zorbax C18 XDB column with 5 mm particle size. The

flow rate was 1.2 ml/min with an oven temperature of 40 �C and an injection volume of

20 ml. The mobile phase consisted of acetonitrile:water (95:5 v/v). The residues in the

real samples were tentatively identified by comparing the retention times (RT) of the sam-

ple peaks with the RT of injected standards. Emamectin benzoate is a mixture of B1a as

the main component and B1b as minor component. Therefore, the residue in crops are cal-

culated only using B1a.

Recovery assay

Recovery was performed by spiked blank tomato samples at three different concentration

levels (i.e., limit of quantification (LOQ), LOQ � 5, and LOQ � 50) of emamectin benzo-

ate as reported in Table 1, with five replicates for each level. Prior to the extraction step,

the spiked samples were allowed to settle for 2 hr at room temperature to distribute the

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pesticide evenly and ensure complete interaction with the sample matrix, and then proc-

essed according to the described procedure. The recoveries obtained with the extracted

spiked samples were compared with that of the matrix-matched calibration solutions.

Evaluation of matrix effect

Matrix-matched standard solution were prepared by evaporating to dryness portion of the

final extract solutions obtained from untreated tomato sample and taking up the remained

residue with the calibration solution and analyzed.

Data and statistical analysis

The dissipation dynamic and half-life of emamectin benzoate were determined by the

first-order kinetic equations Ct ¼ C0e�kt and t1/2 ¼ ln 2/k, respectively. Ct represents the

concentration of the pesticide residue at the time of t, C0 represents the initial deposits

after application, k is the degradation rate constant in days�1, and t1/2 is the half-life.

Results and discussion

Method validation

The method was validated by assessing linearity, recovery, precision, and specificity of

peak areas. The linearity of the calibration curve was established in the range 0.005–

1 mg/ml for emamectin benzoate with a correlation coefficient (R2) of calibration curve

> 0.999. The coefficient of variation (CV) pertaining to the repeatability and intermediate

precision for emamectin benzoate was 2.3 and 6%.

The limit of detection (LOD) and LOQ were defined, respectively, as the signal corre-

sponding to 3 and 10 times the noise ratio, determined experimentally from fortified sam-

ples. In this study, the LOD and LOQ were estimated to be 0.005 and 0.01 mg/kg,

respectively. The LOQ established allow for the identification and quantification of target

analyte below the maximal residue limit established by the European Union (0.02 mg/kg)

in tomato.

The matrix effect of the present method was investigated by comparing standards in

solvent with matrix-matched standards for 5 replicates at the LOQ (0.01 mg/kg) level.

The relative response (response matrix/response solvent) was 1.01 for tomato. The results

showed that, no interfering endogenous peak appeared, and the matrix did not signifi-

cantly suppress or enhance the response of the instrument. In addition, the RT of the

tested analyte at the spiked samples matched those of the standard samples and the ana-

lyte were eluted as separate symmetric peaks. For emamectin benzoate, however, the

matrix effect was not significant and, hence, for quantification, the pure solvent-based cal-

ibration could be used. Figure 2 shows HPLC-FLD chromatograms of tomato samples.

Table 1. Recoveries of emamectin benzoate in tomato at various fortification levels.

Fortified level (mg�kg�1) (na ¼ 5) Recovery (%) CV (%)

0.01 101 6.90.05 96.4 4.50.5 99.2 2.3

aNumber of replicate.

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Figure 2. The chromatogram of emamectin benzoate: standard (0.01 mg�L�1) (A), tomato blank(B), and tomato spiked at 0.01 mg�kg�1 (C).

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The average recoveries% emamectin benzoate at 0.01 (LOQ), 0.05, and 0.5 mg/kg

fortification levels were 101%, 96.4%, and 99.2%, respectively. This complies with the

EU DG SANCO criterion (European Commission SANCO/2009/10684 2009), which

requires mean recoveries within the range 70%–120% and with relative standard devia-

tion (RSD) of less than 20%. The reproducibility of the recovery results, as indicated by

the relative standard deviations, suggested that extraction and derivatization procedure

was reliable enough for the analysis of emamectin benzoate residues in tomato. The aver-

age recovery values from the fortified samples were found to be more than 96%. There-

fore, the results have been presented as such without applying any correction factor.

The degradation of emamectin benzoate, applied at recommended rate i.e., 3 g per

feddan was studied at three different locations. Dissipation data are shown in Figure 3.

The initial residues were in the range of 0.207–0.099 mg/kg at all three locations. In

Miet-Gamer, the initial concentration was higher than that of the other two locations. The

amount of emamectin benzoate residue was below the LOQ of the method 15 days after

treatment in the three locations. Decline in the residues of emamectin benzoate may be

attributed to volatilization that occurred during the first days following application,

removal by weathering, heat decomposition, sunlight, UV radiation, or the complex

Figure 3. Dissipation curve of emamectin benzoate in tomato under field condition.

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condition (Spynu 1989). In addition, growth dilution factor also might have played a sig-

nificant role in residue decline (Tewary et al. 2005).

The dissipation dynamics of emamectin benzoate could be described by the following

first-order kinetics equation: C ¼ 0.1461e�0.2676t (Menof), C ¼ 0.0971e�0.2724t (Kaha),

and C ¼ 0.1934e�0.3085t (Miet-Gamer).

The climatic conditions of the three experiment sites are different, but the degradation

half-life (t1/2) of emamectin in tomato calculated from regression equation was 2.6, 2.5,

and 2.2 days in Menof, Kaha, and Miet-Gamer, respectively. Data suggest that the dissi-

pation of emamectin benzoate on tomato is not markedly affected by the weather. The

results are in agreement with data reported by Wang et al. (2012), who indicated that the

half-lives of emamectin benzoate in apple were 3.09 and 2.75 days in Beijing and Jiangsu,

respectively.

The MRL fixed in tomato for emamectin benzoate is 0.02 mg/kg (European Union

2013). From the residue results in field trail, at harvest time, the MRL in tomato at inter-

vals of 10 days was below 0.02 mg/kg. This result suggested that it is safe to harvest

10 days after applying the recommended dose of emamectin benzoate.

Conclusions

A few methods have been previously devised for the extraction of emamectin benzoate

from field sample. In the present study, the analyte was easily separated on a Zorbax col-

umn and detected via HPLC-FLD. Homogenization, extraction, and analysis of the

extract after derivatization yielded satisfactory detection limits. The compound was read-

ily separated, and the tomato matrix exerted no interference. Emamectin benzoate

degraded quickly in tomato in three different locations. The residue of emamectin benzo-

ate reached below the MRL 10 days after spraying at the tested dosage. Hence, a safe PHI

of 10 days is suggested before harvesting of tomato. The present finding suggests that

emamectin benzoate may be used in tomato safely with recommended dosage. This study

would also be helpful for the Egypt government to establish the MRL of emamectin ben-

zoate in tomato and to provide guidance on the proper and safe use of this insecticide.

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