The Residue Of Imidacloprid And Thiamethoxam On Pumpkin And The Risk Assessment To Bees

In order to study the residue behavior of imidacloprid and thiamethoxam in pumpkin pollen and nectar and the effects of residues of imidacloprid and thiamethoxam in pumpkin on the bee health and nectar safety, this study design and implement the dynamic experiment of imidacloprid residues in pumpkin nectar,_pollen, flowers, leaves and soil and investigate the effects of the different experimental conditions on the regulation of imidacloprid and thiamethoxam residues. At the same time, the methods of analyzing pesticides residues were established, including the detection of imidacloprid residues in pumplin nectar,pollen, flowers,leves and soil. Afterwards, the experimental samples were detected and the residual dynamic of imidacloprid and thiamethoxam in pumpkin nectar, pollen, flowers, leaves and soil was evaluated. While the acute contact toxicity and acute oral toxicity of imidacloprid and thiamethoxam residues in pumpkin nectar and pollen to nectar bees. The results of this study are as follows:1. The method of detecting and analyzing imidacloprid and thiamethoxam in pumpkin nectar,pollen,flowers,leves and soil was established and the method performance was evaluated. The calibration curves were linear in the range of 1-500 μg/L and the determination coefficients (r2) were 0.999-1 for imidacloprid. The recoveries of imidacloprid and thiamethoxam in pumpkin at three spiked levels of 5 μg/kg,10 μg/kg and 100 μg/kg were73.44%-109.00%, while the relative standard deviation were 0.04%-17.38%. The limits of detection of pumpkins were 5μg/kg respectively, and the limits of quantification were 1μg/kg for imidacloprid and thiamethoxam in pumpkin nectar,pollen, flowers,leves and soil. This method is suitable for the detection of imidacloprid and thiamethoxam residues in pumpkin nectar,pollen, flowers,leves and soil samples.2. When the pumpkin was treated with root drench or spary experiment, the residual degradation dynamic of imidacloprid and thiamethoxam on the nectar,pollen, flowers,leves and soil of pumpkin under different factor of applying pesticide (such as, the application timing, dosage and environment), was studied. We can know that the imidacloprid and thiamethoxam residue in the leaves is proportional to the pesticide dosage. And when the higher dosage imidacloprid or thiamethoxam was applied, its digestion rate is slower and half-life is longer. It shows that when there were two modes imidacloprid or thiamethoxam applied, the digestion rate of root drench imidacloprid and thiamethoxam was slower in the pumpkin. When the applying dose was same, imidacloprid and thiamethoxam residue and digestion rate were soil>leave>flower>pollen>nectar. The results indicate that imidacloprid or thiamethoxam has good systemic activity, and its residue in the pumpkin nectar and pollen is proportional to the applying dosage, also the transmission rate and digestion rate of imidacloprid or thiamethoxam were affected by the factor of applying pesticide (such as, the application time, dosage and environment).3. The influence of imidacloprid and thiamethoxam 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/LDso, AR is the proposed dosage of pesticide (g ai/hm2), and LD50 is the acute oral half death dosage of bee. The HQ of imidacloprid and thiamethoxam are more than 2500, so the imidacloprid and thiamethoxam that applied on the nectar 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. When the pumpkin treated with spary experiment,imidacloprid and thiamethoxam chronic toxicity risk to bees can be ignored. When the pumpkin treated with root drench, imidacloprid and thiamethoxam on bees risk of chronic toxicity was unacceptabled. The more administration dose, the higher residual amount, the greater risk of chronic toxicity to bees.(3) The exposure risk of imidacloprid or thiamethoxam to bee was assessed by the exposure toxicity ratio (ETR, toxic/exposure levels), ETR= LD50/RI. RI is the residue of imidacloprid or thiamethoxam in the pollen or nectar, and LD50 is the level of imidacloprid or thiamethoxam that make bee acute oral half death. The value of imidacloprid in spary experiment of ETR was 0.62-8.00 that less than 10, and the thiamethoxam of ETR was 2.55-108.62.It was calculated by the residue of imidacloprid or thiamethoxam in pollen. The value of imidacloprid in root drench of ETR was 1.39～23.76, that thiamethoxam in the pumpkin nectar of ETR was 18.67～118.87. The value of imidacloprid in poleen by root drench of ETR was 0.11～3.15, that thiamethoxam of ETR was 0.93～40.91. It showed that imidacloprid in the pumpkin pollen has potentially exposure risk to bee under spray experiment conditions.