| In order to study the residue, digestion and ecological environment effects of the avermectin pesticide after being used in tobacco field, and to understand its ecological environmental behavior and safety, to guide its scientific and rational application in tobacco field, a technical method of simultaneous analysis and detection was established to detect the residue of Avermectin and Emamectin Benzoate in tobacco samples based on added recovery experiment, and on this basis, the residue, digestion of Emamectin Benzoate in soil planted tobacco, flue-cured tobacco leaves and fresh tobacco leaves were researched systematically after25%Carbosulfan·Emamectin Benzoate EW was applied in the tobacco field, then put forward the scientific and reasonable recommendations on using this pesticide in the tobacco field. In addition, the adsorption behavior of Avermectin and Emamectin Benzoate in four kinds of clay mineral and its influence factors were probed. Moreover, the adsorption behavior and mechanism of Avermectin and Emamectin Benzoate in four kinds of Clay mineral was investigated by FTIR and XRD technology. The main conclusions in this paper were as follows:(1) A technical method was established to detect simultaneously the residue of Avermectin and Emamectin Benzoate in soil planted tobacco, flue-cured tobacco leaves and fresh tobacco leaves by HPLC-FD. The soil planted tobaccol sample was extracted with acetone, and the extract was re-extracted with dichloromethane, the re-extract of dichloromethane was volumed by chromatography acetonitrile after being concentrated. Flue-cured tobacco leaves sample and fresh tobacco leaves sample was extracted with acetonitrile (the extract of fresh tobacco leaves sample was Salting out), and the extract of acetonitrile was volumed by chromatography acetonitrile after being concentrated. Finally,the above volumed solution was derivatizated with Nitrogen methylimidazole and Trifluoroacetic anhydride, and detected by HPLC-FD. When the added concentration ranged from0.01mg/kg to1.OOmg/kg of Avermectin and Emamectin Benzoate, the recovery of Avermectin was80.12%～118.31%in soil planted tobacco,83.63%～114.36%in flue-cured tobacco leaves and99.37%～112.37%in fresh tobacco leaves, the relative standard deviation was0.93%～2.65%in soil planted tobacco,1.99%～3.65%in flue-cured tobacco leaves and2.18%～3.71%in fresh tobacco leaves. The recovery of Emamectin Benzoate was81.23%～104.33%in soil planted tobacco,84.58%～102.37%in flue-cured tobacco leaves and87.88%～105.69%in fresh tobacco leaves, the relative standard deviation was2.10%～3.52%in soil planted tobacco,1.49%～5.33%in flue-cured tobacco leaves and1.96%～2.37%in fresh tobacco leaves. The minimum detectable amount of Avermectin and Emamectin Benzoate was2.0X10-10g, and the minimum residue concentration was O.Olmg/kg in soil planted tobacco, flue-cured tobacco leaves and fresh tobacco leaves. These results indicated that this method was in line with the technical requirement for the analysis and detection the residue of pesticide, it could be applied to analyze and detect the residue of the actual sample.(2)Field experiments were carried out to reveal the residue dynamics and final residue of Emamectin Benzoate in tobacco field in Changsha and Qingdao after25%Carbosulfan· Emamectin Benzoate EW was applied. Results showed that the half-lives in soil planted tobacco was10.85～13.80days, and fresh tobacco leaves was9.85～12.03days, it means that Emamectin Benzoate was degradable pesticide. When25%Carbosulfan·Emamectin Benzoate EW was applied one time with the dosage of525g/ha and787.5g/ha in tobacco field, the results show that:after applied75days, the residue of Emamectin Benzoate in flue-cured tobacco leaves was LOQ(less than0.01mg/kg)～0.0339mg/kg, this residue was less than tentative maximum residue limits value(0.05mg/kg) of Emamectin Benzoate in tobacco leaves (flue-cured tobacco leaves). The reasonable application recommend of25%Carbosulfan·Emamectin Benzoate EW in tobacco field was that applying one time at dosage525g/ha before tobacco was transplanted, the safe interval of flue-cured tobacco leaves is75days.(3)The adsorption equilibrium time of Avermectin and Emamectin Benzoate in four kinds of clay mineral was24hours. The adsorption process could be described with Freundlich adsorption equation or Linear adsorption equation. The adsorption of Avermectin and Emamectin Benzoate was strongest in sepiolite, the second was montmorillonite, the third was attapulgite, and the weakest was kaolinite. The aqueous solution pH value played an important role in the adsorption, in acidic condition was inhibited, the more strongly the acidic conditions,the more obviously influence this inhibitory effect, but this inhibitory effect was not obvious in neutral or alkaline condition, and even negligible. The effect of aqueous solution temperature on the adsorption capacity was increased by temperature increasing, when the temperature reaches25℃, the adsorption rate was over90%. The adsorption of Avermectin and Emamectin Benzoate in four kinds of clay mineral were not. influenced in inorganic nitrogen of weak alkaline such as urea and ammonium bicarbonate, but it was inhibited in inorganic phosphate of weak acidulous such as dipotassium hydrogen phosphate and superphosphate, it was not obviously influenced in inorganic potash like potassium chloride and potassium nitrate when its concentrations was lower, but with the concentration increasing, this adsorption function would be inhibited.(4) Through comparing and analyzing the FTIR spectra and XRD patterns before and after adsorbed with Avermectin and Emamectin Benzoate in four kinds of clay mineral, it showed that Avermectin and Emamectin Benzoate could be adsorbed in the clay mineral by hydrogen bond, charge-dipole bond, coordination complexation, ion exchange and so on. Avermectin and Emamectin Benzoate could’t reach the inter layer of kaolinite and montmorillonite, only adsorbed on the surface by hydrogen bond and ion exchange, while Avermectin and Emamectin Benzoate not only adsorbed on the surface of attapulgite and sepiolite, but also could reach into the inter layer. |
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