Residue Behavior Of Imidacloprid In The Leaves And Flowers Of Pumpkin And Its Effects On Bees

In order to study the residue behavior of imidacloprid in pumpkin leaves and flowers and the effects of residues of imidacloprid in pumpkin on the bee health and honey safety, this study design and implement the dynamic experiment of imidacloprid residues in pumpkin leaves and flowers, and investigate the effects of the different experimental conditions on the regulation of imidacloprid residues. At the same time, the methods of analyzing pesticides residues were established, including the detection of imidacloprid residues in pumplin leaves and flowers and six new neonicotinoid pesticides(containing imidacloprid) residues in honey. Afterwards, the experimental samples were detected and the residual dynamic of imidacloprid in pumpkin leaves and flowers was evaluated. While the acute contact toxicity and acute oral toxicity of imidacloprid residues in pumpkin leaves and flowers to honey bees. The results of this study are as follows:1.The method of detecting and analyzing imidacloprid in pumpkin leaves and flowers was established and the method performance was evaluated. The calibration curves were linear in the range of 1-200 μg/L and the determination coefficients(r2) were 0.998-0.999 for imidacloprid. The recoveries of imidacloprid in pumpkin leaves and flowers at three spiked levels of 5 μg/kg, 10 μg/kg and 50 μg/kg were 84.1%-105.4%, while the relative standard deviation were 4.0%-16.3%. The limits of detection of pumpkin flowers and leaves were 1 μg/kg and 2 μg/kg respectively, and the limits of quantification were 5 μg/kg for imidacloprid in pumpkin leaves and flowers. This method is suitable for the detection of imidacloprid residues in pumpkin leaves and flowers samples.2.When the pumpkin was treated with root drench, the residual degradation dynamic of imidacloprid on the leaves and flowers of pumpkin under different factor of applying pesticide(such as, the application timing, dosage and environment) was studied. In pot experiment, when the application dosage were 0.05 g ai/plant and 0.1 g ai/plant, the residue of imidacloprid on the leaves of pumpkin were 6.56-34.07 mg/kg and 13.64-83.49 mg/kg, and the half- life were 8.0 day and 11.55 day respectively. We can know that the imidacloprid residue in the leaves is proportional to the pesticide dosage. And when the higher dosage imidacloprid was applied, its digestion rate is slower and half- life is longer. In the outdoor experiment, when the application dosage were 0.01125 g ai/plant and 0.045 g ai/plant, the maximum residual of imidacloprid on the leaves of pumpkin were 0.0722 mg/kg and 0.5548 mg/kg, and the half- life were both 2 day. At the same time, the maximum residual of imidacloprid on the flowers of pumpkin were 0.0272 mg/kg and 0.1356 mg/kg, and the half- life were 6.0 day and 9.0 day respectively. It shows that when there were two dose imidacloprid applied, the digestion rate of imidacloprid was close in the leaves, while the digestion rate of higher dosage imidacloprid was slower in the flowers. When the imidacloprid applying dose was same, imidacloprid residue and digestion rate in flowers were lower than that in leaves. The results indicate that imidacloprid has good systemic activity, and its residue in the pumpkin leaves and flowers is proportional to the applying dosage, also the transmission rate and digestion rate of imidacloprid were affected by the factor of applying pesticide(such as, the application time, dosage and environment).3.The influence of imidacloprid residue in the flowers of pumpkin to bee was studied, including the toxicity evaluation and risk assessment.(1) The hazard quotient(HQ) was used as the risk evaluation index. HQ=AR/LD50, AR is the proposed dosage of pesticide(g ai/hm2), and LD50 is the acute oral half death dosage of bee(0.0037 μg/bee). The HQ of imidacloprid is 4054, which is more than 2500, so the imidacloprid that applied on the honey plant has high risk to the bee.(2) According to the existing toxicology data and experimental data, the result of residual exposure assessment based on the exposure assessment method show that: the ratio of the NOEC and imidacloprid residue was more than 1, except the third day after applying lower dosage pesticide, so the chronic toxicity risk to bees is acceptable. Meanwhile the ratio of the NOEC and imidacloprid residue was less than 1, and the chronic toxicity risk of imidacloprid to bees is high.(3) The exposure risk of imidacloprid to bee was assessed by the exposure toxicity ratio(ETR, toxic/exposure levels), ETR= LD50/RI. RI is the residue of imidacloprid in the flowers, and LD50 is the level of imidacloprid that make bee acute oral half death(0.0037 μg/bee). The value of ETR was 0.03-1.54 that less than 10, and it was calculated by the residue of imidacloprid in flowers. It showed that imidacloprid in the pumpkin flowers has potentially exposure risk to bee under this experiment conditions.4.The method of detecting and analyzing six new neonicotinoid pesticides(including imidacloprid) residues in honey was established and the method performance was evaluated. The homogeneous liquid- liquid extraction was adopted as sample pretreatment method and the ultra performance liquid chromatography tandem mass spectrometry was used as detection method. The calibration curves were linear in the range of 0.2-100 μg/L and the determination coefficients(r2) were 0.9981-0.9997 for six new neonicotinoid pesticides. The recoveries of six new neonicotinoid pesticides in honey at three spiked levels of 1 μg/kg, 5 μg/kg and 50 μg/kg were 76.99%-105.89%, while the relative standard deviation were 2.37%-19.77%. The limits of detection were 0.2 μg/kg-0.4 μg/kg for six new neonicotinoid pesticides, and the limits of quantification were 1 μg/kg for six new neonicotinoid pesticides in honey. This method is suitable for the detection of six new neonicotinoid pesticides residues in honey samples. Ten honey samples from supermarket were monitored by established method, and six new neonicotinoid pesticides were not detected.