Lonicera japonica

Lonicera japonica...
5 downloads 11 Views 631KB Size
Subscriber access provided by University of Newcastle, Australia

Article

Degradation dynamics and dietary risk assessments of two neonicotinoid insecticides during Lonicera japonica planting, drying and tea brewing processes Qingkui Fang, Yanhong Shi, Haiqun Cao, Zhou Tong, Jinjing Xiao, Min Liao, Xiangwei Wu, and Rimao Hua J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b04658 • Publication Date (Web): 08 Feb 2017 Downloaded from http://pubs.acs.org on February 9, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Journal of Agricultural and Food Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 26

Journal of Agricultural and Food Chemistry

1

Degradation dynamics and dietary risk assessments of two

2

neonicotinoid insecticides during Lonicera japonica planting, drying

3

and tea brewing processes

4

Qingkui Fang1, a, Yanhong Shi1, b, Haiqun Cao*, a, Zhou Tonga, Jinjing Xiaoa, Min Liaoa, Xiangwei

5

Wub, Rimao Huab

6

a School of Plant Protection, Provincial Key Laboratory for Agri-Food Safety, Anhui Agricultural

7

University, Hefei 230036, China.

8

b School of Resource & Environment, Provincial Key Laboratory for Agri-Food Safety, Anhui

9

Agricultural University, Hefei, 230036, China.

10

* Corresponding Author. Email address: [email protected]

11

1

The first two authors contributed equally to this work.

12 13 14 15 16 17 18 19 20 21 22

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

23

Abstract

24

The degradation dynamics and dietary risk assessments of thiamethoxam and thiacloprid

25

during Lonicera japonica planting, drying and tea brewing processes were systematically

26

investigated using high-performance liquid chromatography. The half-lives of thiamethoxam and

27

thiacloprid were 1.0-4.1 d in the honeysuckle flowers and leaves, degradation rate constants k

28

ranged from -0.169 to -0.696. And the safety interval time was 7 d. The sun- and oven-drying

29

(70 °C) percent digestions were 59.4-81.0% for the residues, which were higher than the shade-

30

and oven-drying percent at lower temperatures (30, 40, 50 and 60 °C, which ranged from 37.7% to

31

57.0%). The percent transfer of thiamethoxam and thiacloprid were 0-48.4% and 0-25.2%,

32

respectively, for the different tea brewing conditions. Based on the results of this study, abiding by

33

the safety interval time is important and using reasonable drying methods and tea brewing

34

conditions can reduce the transfer of thiamethoxam and thiacloprid to humans.

35 36

Key words: Lonicera japonica, neonicotinoid insecticide, degradation dynamics, dietary risk

37

assessment, drying method, tea brewing condition

38 39 40 41 42 43 44

ACS Paragon Plus Environment

Page 2 of 26

Page 3 of 26

Journal of Agricultural and Food Chemistry

45

1. Introduction

46

Honeysuckle, the flowering buds of Lonicera japonica Thunb. (Caprifoliaceae), is one of the

47

most popular traditional Chinese medicinal herbs and contains a variety of biologically active

48

ingredients, including polyphenols, saponins, volatile oils, and iridoids.1,2 Pharmacological studies

49

have shown that the bioactive ingredients of honeysuckle possess broad-spectrum antibacterial,

50

antiviral, anti-inflammatory, hepatoprotective and choleretic properties that enhance the immune

51

system.3-7 Honeysuckle is also used in indigenous beverages in Korea and China.1 Because L.

52

japonica is prone to attack by several pests and diseases, many pesticides are used to protect crops,

53

which can result in pesticide residues in agriproducts.

54

Thiamethoxam and thiacloprid are systemic, contact and chloronicotinyl neonicotinoid

55

insecticides that act as an agonist on postsynaptic nicotinic acetylcholine receptors and modify

56

insect behavior, resulting in death. They are widely used as insecticides for controlling aphids,

57

thrips, diamondback moths and white flies.8,9 Residues of these two pesticides, which are

58

potentially hazardous to consumers, can be found in L. japonica and environmental samples due to

59

the high prevalence of aphids on L. japonica plantings.10-12 Therefore, it is necessary to study the

60

degradation dynamics and dietary risk assessments of thiamethoxam and thiacloprid in L. japonica

61

to assure human and environmental safety.

62

There have been several studies of the residue behavior and dietary risk assessment of

63

pesticides in agriproducts and environmental samples. Yu et al.13 reported the residual dynamics of

64

thiacloprid in the medical herbs marjoram, thyme, and chamomile. Abd-Alrahman14 investigated

65

the residue and dissipation kinetics of thiamethoxam in potato plants and soil in a field ecosystem.

66

Some researchers have reported on the effects of handling and processing pesticide residues in raw

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

67

cucumber,15 button crimini,16 olive oil,17 and camellia oil18. There are recent studies of the effect

68

of tea brewing conditions on pesticide residues in herbal tea and tea.19-24 These studies found

69

several critical controlling factors, such as tea variety, tea/water ratio, tea brewing time, and

70

washed or unwashed tea. However, there is an issue with these studies that must be addressed. The

71

entire process, from pesticide application to commercial and home processing to final

72

consumption, should be studied rather than examining residue behavior and dietary risk

73

assessment separately.

74

The aim of this research was to develop a systematic study that (i) investigates the

75

degradation dynamics of pesticide residues in L. japonica; (ii) studies the effects of honeysuckle

76

drying methods on the percent digestion of pesticide residues; and (iii) evaluates the effects of

77

honeysuckle brewing conditions on the percent transfer of pesticides. We hope that this systematic

78

research will aid in understanding how the proportions of degradation and percent transfer of the

79

pesticides in L. japonica planting, drying and tea brewing processes affect dietary risk. We used

80

high-performance liquid chromatography (HPLC) to determine thiamethoxam and thiacloprid

81

residues and investigate the degradation dynamics and dietary risk assessments of thiamethoxam

82

and thiacloprid in L. japonica planting, drying and tea brewing processes. The results of this work

83

will not only contribute to establishing adequate monitoring of thiamethoxam and thiacloprid

84

residues and their use in pest management strategies in Chinese herbs but also provide significant

85

guidance to the systematic study of degradation dynamics and dietary risk assessments in other

86

contaminated agriproducts.

87

2. Materials and Methods

88

2.1 Chemicals and Instruments

ACS Paragon Plus Environment

Page 4 of 26

Page 5 of 26

Journal of Agricultural and Food Chemistry

89

Thiamethoxam and thiacloprid were purchased from Dr. Ehrenstorfer (Augsburg, Germany).

90

Acetonitrile (liquid chromatography grade) as well as acetonitrile, petroleum ether, dichlomethane,

91

and acetone (analytical grade) were all purchased from the Chinasun Specialty Products Co., Ltd.

92

(Jiangsu, China). Anhydrous sodium sulfate and sodium chloride were obtained from the

93

Sinopharm Group Chemical Reagent Co., Ltd. (Shanghai, China). A Florisil solid-phase extraction

94

(SPE) column (1000 mg·6 mL-1) was purchased from Agela Technologies (Tianjin, China).

95

High-performance liquid chromatography (HPLC) was performed using a Shimadzu

96

LC-20AT instrument (Shimadzu, Japan). An HC-C18 column (4.6×250 mm, 5 µm) was used from

97

Agilent Technologies (Palo Alto, CA, USA). An EYELA N-1100 rotary evaporator was used from

98

the Shanghai Ailang Instruments Co., Ltd. (Shanghai, China). A SC-3610 low-speed centrifuge

99

was used from Anhui Zhongke Zhongjia Scientific Instruments Inc. (Anhui, China). A KQ-5200

100

ultrasonic cleaner was used from the Kunshan Ultrasonic Instrument Co., Ltd. (Shanghai, China).

101

A SQ-2119B multifunctional food processing instrument was used from the Shanghai Shuaijia

102

Electronic Technology Co., Ltd. (Shanghai, China). A DHG-9070A electrothermal oven

103

thermostat blast was used from the Shanghai Yiheng Science and Technology Co., Ltd. (Shanghai,

104

China). An LM-02 Chinese medicine grinder was used from the Zhejiang Dahai medicine factory

105

Instrument (Zhejiang, China).

106

2.2 Field trials of residue degradation dynamics

107

Field trials were carried out at the Sijiyuyang L. japonica planting base in Tongcheng City

108

(31°N, 117°E), Anhui Province, China. During the experiment, the temperature was 20-35 °C and

109

the rainfall was light. A plot size of 20 m2 was selected for the control and each treatment of the

110

pesticide under study, in a treatment plot is about 10 honeysuckle plants, leaving two rows of

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

111

bushes as guard rows between the control plot and the different treatment plots. The two pesticides

112

(thiamethoxam and thiacloprid) were sprayed at two times of the recommended dosages [i.e., the

113

recommended doses for aphid control were 56.25 g a.i. hm-2 (thiamethoxam) and 102.5 g a.i. hm-2

114

(thiacloprid), leading to 112.5 g a.i. hm-2 (thiamethoxam) and 205 g a.i. hm-2 (thiacloprid)] in three

115

replicates using a hand-operated knapsack sprayer with a recommended formulation volume of 15

116

L hm-2. The use of five-point sampling method, 0.5 kg honeysuckle flower samples and 0.5 kg leaf

117

samples were then picked at 2 h and 1, 3, 5, 7, 14 and 21 days.

118

Final residue trials

119

The two pesticides were sprayed at two dosages (recommended dosage and two times of the

120

recommended dosage; 56.25 and 102.5 g a.i. hm-2 (thiamethoxam) and 112.5 and 205 g a.i. hm-2

121

(thiacloprid)) for three replicates. The plants were sprayed once every 7 days, with continuous

122

spraying three times. And then honeysuckle samples were collected on the 7th and 14th days after

123

the last application.

124

2.3. Sample extraction, cleanup, and HPLC analysis

125

2.3.1 Honeysuckle flower sample treatment

126

Honeysuckle flower samples (2.0 g) were extracted with 20 mL of acetonitrile by thoroughly

127

shaking for 30 min, centrifuging at 4,000×g for 5 min, and transferring the supernatant to a 150

128

mL separatory funnel. An additional 20 mL of acetonitrile was added to the samples and the

129

mixture was thoroughly shaken for 30 min and centrifuged at 4,000×g for 5 min. The supernatant

130

was transferred to the separatory funnel. Then, 30 mL of petroleum ether was added to the

131

separatory funnel, shaken for 2 min, and left standing for 5 min. The lower-layer liquid was

132

transferred to a 150 mL flask and concentrated close to dryness at 40 °C.

ACS Paragon Plus Environment

Page 6 of 26

Page 7 of 26

Journal of Agricultural and Food Chemistry

133

A Florisil SPE was activated with 3 mL of a petroleum ether:acetone (v/v=7:3) mixed

134

solution. The honeysuckle flower extract was washed with the mixed solution (2 mL×2) and

135

transferred to the SPE column, which was rinsed by the mixed solution (2 mL×2) to remove

136

interfering substances. The eluent was discarded. The SPE column was then eluted with

137

acetonitrile (3 mL×3), and the eluate was concentrated to dryness at 40 °C. The volume was set to

138

5 mL and placed in a volumetric flask with acetonitrile to await measurement.

139

2.3.2 Leaf sample treatment

140

Leaf samples (5.0 g) were extracted with 30 mL of acetonitrile by thoroughly shaking for 30

141

min. The samples were then centrifuged at 4,000×g for 5 min, and the supernatant was transferred

142

to a 150 mL separatory funnel. An additional 30 mL of acetonitrile was added to the samples, and

143

the mixture was thoroughly shaken for 30 min and centrifuged at 4,000×g for 5 min. The

144

supernatant was transferred to the separatory funnel and concentrated close to dryness at 40 °C.

145

A Florisil SPE was activated with 3 mL of a petroleum ether:acetone (v/v=7:3) mixed

146

solution. The leaf extract was washed with the mixed solution (2 mL×2) and transferred to the

147

SPE column, which was rinsed by the mixed solution (2 mL×2) to remove pigments and other

148

interfering substances. The eluent was discarded. The SPE column was then eluted with

149

acetonitrile (3 mL×3), and the eluate was concentrated to dryness at 40 °C. The volume was set to

150

5 mL and placed in a volumetric flask with acetonitrile to await measurement.

151

2.3.3 Tea infusion sample treatment

152

The boiling water was used for extraction, and after the tea infusion was cooled to room

153

temperature, 20 mL of the tea infusion was added to a separatory funnel along with 20 mL of a

154

NaCl saturated solution and 30 mL of dichloromethane. The mixture was thoroughly shaken for 2

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

155

min and left standing for 5 min; the organic phase was then transferred to a 150 mL flask. Another

156

20 mL of NaCl saturated solution and 30 mL of dichloromethane were added to the samples and

157

the mixture was thoroughly shaken for 2 min and left standing for 5 min; the organic phase was

158

then transferred to a 150 mL flask and concentrated close to dryness at 40 °C. The volume was set

159

to 5 mL and placed in a volumetric flask with acetonitrile to await measurement.

160

HPLC analyses of the thiamethoxam and thiacloprid were followed measuring absorbance at

161

254 nm and 270 nm (UV), respectively. The mobile phase was acetonitrile:water (v/v=25:75) at a

162

flow rate of 1 mL·min-1. An HC-C18 column (4.6×250 mm, 5 µm) was used. The temperature of

163

the column oven was maintained at 30 °C with an injection volume of 20 µL.

164

2.4 Effect of drying method

165

To study the degradation of thiamethoxam and thiacloprid during the honeysuckle drying

166

process, the two pesticides were sprayed at two dosages [recommended dosage and two times of

167

the recommended dosage; 56.25 and 102.5 g active ingredient per square hectometer (a.i. hm-2)

168

thiamethoxam and 112.5 and 205 g a.i. hm-2 thiacloprid] using a recommended formulation

169

volume of 15 L hm-2. Honeysuckle samples were collected at 2 h post application when the

170

spraying mixture had dried.

171

The effects of the three drying methods on the degradation rate of the two pesticides were

172

investigated, including sun-, shade- and oven-drying. For shade-drying, 0.5 kg samples of low and

173

high concentrations of pesticides were spread over 1 m2 of area. Because the honeysuckle could

174

not be turned, proper indoor ventilation was ensured to keep the space relatively dry. For

175

sun-drying, 0.5 kg samples of low and high concentrations of pesticides were spread over 1 m2 of

176

area (the honeysuckle could not be turned). For oven-drying, the samples were placed in an oven

ACS Paragon Plus Environment

Page 8 of 26

Page 9 of 26

Journal of Agricultural and Food Chemistry

177

with the temperature set to 30, 40, 50, 60 and 70 °C (the honeysuckle could not be turned). All

178

treatments were performed until the samples were fully dry (i.e., the weight no longer changed).

179

2.5 Effects of tea brewing conditions of honeysuckle samples

180

Pesticide concentration, tea/water ratio (TWR), number of infusions, tea brewing time, and

181

covered or uncovered cups were investigated as the tea brewing conditions. The pesticide-free

182

honeysuckle sample was treated with the standard solution of pesticide. The samples were

183

separately sprayed with the pesticide solutions and left to stand at room temperature for 1 h. Tea

184

brewing refers to preparing a hot water infusion of the honeysuckle. Infusions were prepared with

185

tap water, using a stainless steel electric kettle to boil the tap water. Two grams of treated samples

186

were immersed in boiling water and allowed to stand at room temperature for 2-60 min. After tea

187

brewing, the infusions were filtered through an ordinary stainless steel tea strainer and cooled.

188

Both the infusions and the spent leaves after tea brewing were examined separately for residues.

189

The procedure was carried out in three replications.

190

Effect of Pesticide Concentration. The pesticide-free honeysuckle samples were separately

191

sprayed with three different concentrations of pesticide solutions and left to stand at room

192

temperature for 1 h. Two grams of three different concentrations of pesticide treated samples were

193

immersed in 100 mL of boiling water and then retained at room temperature for 10 min.

194

Effect of Number of Infusions. Two grams of samples were immersed in 100 mL of boiling

195

water and left at room temperature for 10 min. The liquid portion was decanted and collected in

196

another enclosed cup; this was the first infusion. Then, another 100 mL of boiling tap water was

197

poured into the original cup to brew the residual tea and to obtain a second infusion in the same

198

manner as the first tea brewing. A third infusion was also obtained by the same process.

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

199

Effect of Tea Brewing Time. Two grams of samples were immersed in 100 mL of boiling water

200

and left to stand at room temperature for 2, 5, 10, 15, 20, 30 and 60 min.

201

Effect of Tea/Water Ratio. Two grams of samples were immersed in 60, 100, 160 and 200 mL of

202

boiling water and left to stand at room temperature for 10 min. The ratios were 1/30, 1/50, 1/80

203

and 1/100 (w/v tea infusion).

204

Effect of Uncovered Cup. Two grams of samples were infused in 100 mL of boiling water,

205

enclosed in a 100 mL covered cup and left to stand at room temperature for 10 min. Another 2.0 g

206

sample was infused in 100 mL boiling water in a 100 mL uncovered cup and left to stand at room

207

temperature for 10 min.

208

2.6 Data analysis

209

The relationship between the two pesticide residues and time is Ct = C0e-kt, where Ct (mg/kg)

210

is the residue after time t, C0 (mg/kg) is the initial residue, and k is the dissipation rate constant

211

(d-1). This equation is widely used to assess the level of pesticides in agriproducts.25,26

212 213

The percent transfer of thiamethoxam and thiacloprid from tea infusion was calculated using the following formula:

transfer (%)

214

=

Ct × Vt C 0 × W0

× 100%

215

where Ct represents the concentration (µg/mL) of thiamethoxam and thiacloprid in the tea infusion,

216

Vt is the volume (mL) of the tea infusion, C0 is the content (µg/g) of thiamethoxam and thiacloprid

217

in the brewed tea, and W0 is the weight (g) of the tea used in the infusion.22

218

3. Results and discussion

219

3.1 Recovery study

220

The limits of detection (LOD) were determined as the sample concentration of thiamethoxam

ACS Paragon Plus Environment

Page 10 of 26

Page 11 of 26

Journal of Agricultural and Food Chemistry

221

and thiacloprid at a signal-to-noise ratio of 3:1 by HPLC. The LOD of thiamethoxam and

222

thiacloprid were both estimated at 0.01 mg kg-1 for the honeysuckle flower and leaf samples, and

223

0.01 mg L-1 for the tea infusion samples. The analyte recoveries and precision values obtained

224

from the validation study are summarized in Table 1. Thiamethoxam and thiacloprid were added

225

to the untreated control samples at 0.05, 0.1 and 1.0 mg kg-1 for the honeysuckle flower and tea

226

infusion and 0.1, 0.5 and 1.0 mg kg-1 for the leaves. For method validation, the control and treated

227

samples were analyzed under the same conditions. The mean values of five replicates at each

228

spiked level were recorded. The recoveries of thiamethoxam and thiacloprid ranged from 77.8% to

229

99.2%. The coefficients of variation (CV) were between 1.2% and 10.5% for the three samples.

230

Thus, these results demonstrate that the HPLC method can be used for sample determination.

231

3.2 Degradation dynamics of the pesticides in honeysuckle flowers and leaves

232

The data on degradation dynamics obtained for thiamethoxam and thiacloprid in the

233

honeysuckle flowers and leaves are shown in Figure 1. A gradual and continuous deterioration of

234

pesticide residues in the two treated samples was observed. The average residues of thiamethoxam

235

and thiacloprid in honeysuckle (Figure 1A) were 3.2 and 4.1 mg kg-1, respectively, after 2 h of the

236

application of two times of the recommended dosages and the residual amounts of the two

237

pesticides dissipated by 95.3% and 98.4%, respectively, after 7 days. The half-life values (t½) for

238

the degradation of thiamethoxam and thiacloprid in the honeysuckle were calculated to be 2.2 d

239

and 4.1 d (Table 2), respectively, after application of the recommended dosage, and the dynamics

240

are described by the equations C = 2.518e-0.3108t and C = 3.452e-0.169t, with R2 = 0.9184 and R2 =

241

0.8639, respectively. The average residues of thiamethoxam and thiacloprid in the leaves (Figure

242

1B) were 2.3 and 4.4 mg kg-1, respectively, after 2 h of the application of two times of the

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

243

recommended dosages, and the residual amount of the two pesticides dissipated by 96.5% and

244

91.0%, respectively, after 5 days. The half-lives of thiamethoxam and thiacloprid in the leaves was

245

1.0 d and 1.1 d (Table 2), respectively, and the dynamics are described by the equations C =

246

2.438e-0.696t, R2 = 0.9918 and C = 5.466e-0.613t, R2 = 0.8552, respectively. Based on previously

247

published studies27,28, sunlight, evaporation and rainfall elution are important factors affecting the

248

degradation of pesticides, especially sunlight photodegradation. The two pesticides faster

249

dissipated in leaves, because of the different structure of leaves and honeysuckle, when light,

250

rainfall and evaporation occurs, the surface area of the leaves was larger than that of honeysuckle.

251

When thiamethoxam and thiacloprid were applied at two times of the recommended dosages,

252

the initial deposits of thiamethoxam (2 h) were 3.2 mg kg-1 in the honeysuckle flowers and 2.3 mg

253

kg-1 in the leaves and the initial deposits of thiacloprid (2 h) were 4.1 mg kg-1 in the honeysuckle

254

flowers and 4.4 mg kg-1 in the leaves. The residuals of the two pesticides were evenly distributed

255

in the honeysuckle flowers and leaves.

256

3.3 Final residue of pesticides in honeysuckle

257

The final residues of thiamethoxam and thiacloprid were measured at 7 and 14 days after the

258

last application of the recommended and two times of dosages. The results are shown in Table 3.

259

Residues of thiamethoxam in the honeysuckle were undetectable (