| A multi-residue analytical method for determination (thiamethoxam, imidacloprid, acetamiprid, thiacloprid) of 4 neonicotinoid insecticides in Lonicera japonica(bud, leave, soil and infusion) was developed in this dissertation. The dissipation dynamics and final residues of thiamethoxam and thiacloprid in honeysuckle under field conditions was investigated, and a suggestion of reasonable application of the pesticides was presented by residual safety assessment. The degradation of the 4 pesticides residues during different drying processes was discussed. Then the transfer of residues from honeysuckle tea to infusion in different soaking conditions were studied. The main results are as follows.1. The multi-residue analytical methods for neonicotinoids in the bud, leaves, soil and infusionThe flos lonicerae, leave and soil samples were extracted with acetonitrile by mechanical shaking and cleaned up by Florisil SPE. But the cooled infusion extract was subjected to partitioning with dichloromethane. All the samples were detected by HPLC-DAD. As the fortified concentration were 0.1～1 mg·kg-1 (leave, soil) and 0.05～1mgkg-1(bud, infusion), the average recoveries of thiamethoxam, imidacloprid, acetamiprid and thiacloprid in the bud were ranged between 81.7%-95.5%,82.4-89.1%, 80.8-94.4% and 80.6-99.2% respectively. The coefficient of variation were 3.3%-5.6%, 4.0-5.5%,4.4-6.7%,2.3-10.5%. And the recoveries of 4 neonicotinoids were ranged between 85.1-94.5%,84.6-87.3%,85.1-87.9% and 85.3-91.2%, the coefficient of variation were 1.2-4.7%,0.5-2.5%,1.7-4.2%,2.3-4.2%. The average recoveries of thiamethoxam in leave and soil respectively were 81.8-99.5% and 83.8-97.4%. The coefficient of variation were 5.5-12.0% and 2.6-3.9%. The average recoveries of thiacloprid in leave and soil respectively were 84.8%-98.2% and 77.8-96.4%. The coefficient of variation were 2.0-7.9% and 4.0-6.3%. These results showed that the accuracy and sensitivity of the method meet the requirement of pesticide residue analysis.2. Dynamic and final residues of thiamethoxam and thiacloprid in honeysuckle fieldThe results showed that the dissipation of the two pesticides in bud, leave and soil followed the first order kinetics. The half-life values of thiamethoxam and thiacloprid in the bud, leave and soil were 2.23d, 1.00d,1.81d and 4.10d,1.13d,1.63d when the dosages were 112.5g(ai)·hm-2 and 205g(ai)·hm-2 respectively. This shows that the two pesticides had a rapid degradation rate in honeysuckle field.The results of final residues showed that the terminal residues levels of the pesticides were below 0.05mg·kg-1 after pre-harvest interval of 14 days. Considering the manufacture and dietary means of honeysuckle, refer to the maximum residue limits of the two pesticides in other crops(The maximum residues of thiamethoxam and thiacloprid established by China are 0.5 and 1 mg·kg-1, respectively), we think it is reasonable that the MRLs of the two pesticides in honeysuckle were 1 mg·kg-1. It is also suggested the security harvest time was 14d or more than 14 days.3. Influence on neonicotinoids residues in Honeysuckle by different drying treatmentsThe 3 different drying methods were applied to fresh honeysuckle, and the influence on neonicotinoids residues in Honeysuckle by different drying measures was studied. The residue degradation rate of thiamethoxam, imidacloprid, acetamiprid and thiacloprid in the 3 different drying processes were respectively 49.3-54.4%,33.4-40.5%,55.4-66.4%, 54.1-57.0%(shade-drying); 60.8-64.9%,51.7-53.8%,64.5-71.9%,59.4-60.7%(sun-drying); 40.3-81.0%,30.9-78.3%,25.1-78%,37.7-77.3%(oven-drying) of the initial leveL It may be bound up with the water-so lubility and vapour pressure of the different pesticides for the differences of the degradation in same drying process. The pesticide with higher water-solubility and vapour pressure may degrade fester. The temperature and illumination were the main factors for the degradation of pesticides in different drying measures. High temperature and strong light can promote the degradation of pesticides.4. Influence on the transfer of pesticides from honeysuckle tea to infusion in different soaking conditions.The transfer of pesticides from honeysuckle tea to infusion in different soaking conditions (different initial content of pesticides, tea/water ratio, infusing times, infusing duraion, uncovered cup) were studied. There was a obviously different effects for the transfer of pesticides to the tea infusion in different brewing conditions.In these infusing process, the transfer of the 4 pesticides from honeysuckle tea to infusion decreased significantly with the increaseing of dosage. The transfer rate of the 4 neonicotinoids were respectively ranged between 30.7-42.1%(thiamethoxam), 19.8-26.3%(imidacloprid),34.8-55.1%(acetamiprid) and 16.1-23.4%(thiacloprid). The transfer of the 4 pesticides increased with the decreaseing of the tea/water ratio(1:30-1:100). The transfer rates were respectively 8.8-31.5%,7.7-20.7%,6.5-33.8% and 12.4-16.5%. The transfer of the 4 pesticides were up to 30.68%,17.57%,32.83% and 12.54% at the first infusing process. Respectively accounted for 89.1%,100%,87.8%, and 82.0% of the three total transfer. And the transfer rates of the 4 pesticides may firstly increase and then remain stable or decrease slightly with the increasing of the infusing duration. The transfer rates were respectively 16.4-30.7%,10.8-18.5%,14.4-33.8% and 12.9-17.5%. The transfer percentages of the 4 pesticides in the uncovered cup were 3.1-6.1%,4.4-5.1%,2.8-5.2% and 2.4-2.5% lower than the transfer of pesticides in covered cup. Thus it can be seen that the transfer rates were closely related to different infusion conditions. The result of this study will provide a scientific basis for evaluating the dietary exposure levels of the neonicotinoids in honeysuckle. |
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