Residue Degradation In Tobacco Leaves And Environmental Behavior Of Neonicotinoid Insecticide

Pesticides occupy an important position in agricultural production since birth, but the abuse of pesticides has also brought a series of problems. As a representative of the high efficiency, low toxicity and low residual pesticide, Neonicotinoids pesticide are widely used in recent years, but its security is always the hot topic of concern, the EU ban on neonicotinoids pesticide pushed it to the cusp of public opinion. In order to evaluate the safety of neonicotinoids pesticide used on tobacco and the environmental safety. studies were conducted on the effects of different applying pesticide factors on the final residue, effects of soil moisture, temperature, fortified concentration and soil microorganism on degradation of three neonicotinoids pesticide and the influence of three neonicotinoids pesticide to soil microbial enzyme activity and respiration action.The results as follows:(1) A new method was developed to detect imidacloprid, acetamiprid, thiacloprid, nitenpyram, thiamethoxam residues in tobacco and soil using HPLC-MS/MS, the effects of different applying pesticide factors on the final residue of the five neonicotinoids pesticide were studied. Tobacco and soil samples were extracted with acetonitrile, cleaned up using Qu ECh ERS method, detected by HPLC-MS/MS and quantitatively by external standard method. Result shows that average recoveries and the relative standard deviations(RSD) of the five neonicotinoids pesticide are in conformity with the guideline on pesticide residue trials. The limit of quantity(LOQ) of imidacloprid, acetamiprid and thiamethoxam were 0.001 mg/kg in soil and 0.005 mg/kg in tobacco leaves, the limit of quantity(LOQ) of thiacloprid and nitenpyram were 0.005 mg/kg in soil and 0.010 mg/kg in tobacco leaves. Field experiments were performed in Qingdao, Shandong province and Xichang, Sichuan province during 2013. Using the above method, the final residue of five neonicotinoids in tobacco leaves were detected. Result shows that: Under the experimental conditions, 21 days after the last treatment, the final residues of five neonicotinoids pesticide were blow the LOQ. Overall, the final residue of five neonicotinoids were increased with the increse of pesticide dosage and the number of trend, but there are differences between individual data showed the opposite rule. analysis the results of imidacloprid residues by SPSS, the results show that the sampling interval has a very significant impact on the final residue of imidacloprid, other single factor had no significant effect on that, A compound factor pesticide dose and sampling intervals has significant influence on final residues of imidacloprid and othes not.(2) Under laboratory conditions studied the effects of soil moisture, temperature, fortified concentration and soil microorganism on degradation of three neonicotinoids pesticide, result shows that, it was optimal for three neonicotinoids pesticide to degrade, when soil moisture was 60% FC, too much or too little are not conducive to the degradation;.It is not in the interest of the degradation of three neonicotinoids pesticide while the moisture was too low or too high. The speed of degradation in the sterilization process is obviously lower than that in non sterilized soil. Influence of p H on the degradation of three neonicotinoids pesticide significantly and degrade the fastest in nearly neutral conditions. The degradation was accelerated significantly when the temperature increase from 5°C to 35°C.(3) Thiacloprid, thiamethoxam and nitenpyram has a significant impact on the four kinds of soil enzyme activity. the influence of three neonicotinoids insecticide on soil enzyme activities at the fortifiled concentration of 1 mg/kg, 10 mg/kg as follows: inhibited during the early days, then promoted and finally returned to normal levels. This may be due to three neonicotinoids insecticide have the same chemical structure, mechanism of action and insecticidal activity.Three neonicotinoids insecticide have on long-term effects on soil, but the higher the concentration, the longer the recovery time.(4) The impact of thiacloprid, thiamethoxam and nitenpyram on soil respiration shows that: the influence of three neonicotinoids insecticide to soil respiration have the same tendency to soil enzyme activity at the fortifiled concentration of 1 mg/kg and 10 mg/kg, inhibited during the early days, then promoted and as higher as fortifiled concentration, the influence to the enzyme is more obviously.