新农药哌虫啶在三种典型土壤中的吸附与淋溶研究

采用实验室模拟方法研究了烟碱类新农药哌虫啶在土壤生态系统中的降解动态及其对土壤微生物的影响.结果表明,哌虫啶的降解过程符合一级反应动力学方程,浓度为1、5和10 mg kg-1的哌虫啶在土壤中的降解半衰期为11.28 ~7.30 d.哌虫啶对土壤微生物的毒性作用与浓度正相关.施药后哌虫啶对土壤中细菌和放线菌的数量具有激活作用,3 d后,哌虫啶开始抑制土壤中细菌和放线菌的数量,施药后5 d内,哌虫啶促进了真菌的生长繁殖,10 d后表现为抑制真菌数量,有先促进后抑制细菌、真菌和放线菌的趋势.哌虫啶施入土壤后对土壤酶活性具有一定的影响,土壤碱性磷酸酶较酸性磷酸酶更敏感,哌虫啶具有抑制酸性磷酸酶和碱性磷酸酶的作用,这种抑制作用一直延续至试验的第20天;施药处理组对脲酶活性均有显著的抑制作用,并且浓度越大,抑制作用越强烈;哌虫啶对土壤脱氢酶具有显著的激活作用,哌虫啶对土壤过氧化氢酶影响作用较弱.总之哌虫啶在土壤中降解半衰期较短,属于易降解农药,10 mg kg-1浓度的哌虫啶对土壤微生物具有一定的毒性作用.

Adsorption and Leaching of Paichongding a New Pesticide in Three Typical Soils

IPP or Paichongding is a new type of neonicotinoid insecticide, high in effectiveness and broad in spectrum, developed jointly by the Jiangsu Kesheng Group Company Limited and the East China University of Science and Technology, it is intended to be used to control pests of fruit trees, vegetables, wheat, soybean, rice, corn and some other crops. It is, therefore, very important to study degradation dynamics and eco-toxicity of the pesticide to soil microorganisms. For that end, an in-lab simulation experiment was performed, using the SPE-HPLC( solid phase extraction and high efficiency liquid chromatography) method to determine residue of IPP in the soil; the dilution plate counting method to detect changes in number of soil microorganisms as affected by IPP; the p-nitro phenyl phosphate disodium salt hex hydrate method to determine phosphatase activity of the soil; the TTC (triphenyltetrazolium chloridel) method to determine dehydrase activity; the phenol sodium chromatometry method to determine urease activity; and potassium permanganate titration method to determine catalase activity. Results show that after the pesticide was applied at a rate of 1 mg kg^-1, 5 mg kg^-1 and 10 mg kg^-1, separately, its degradation rate in the soil reached 22.3%, 26.7% and 25.7% respectively, 3 days later and up to 50.5%, 47.2% and 64.3%, respectively, 10 days later; its degradation process in the soil could be well described with the first order kinetic equation; and its half life in the soil was found to be 11.28 d, 9.73 d and 7.30 d, respectively. Once applied into the soil, the substance did have some toxic effect on soil microorganisms and the higher the application rate, the more obvious the toxic effect. Its effect on actinomycetes was quite similar to that on bacteria, promoting firstly and then inhibiting. Two hours after its application, the substance began to stimulate propagation of bacteria and actinomycetes and the effect in the treatment high in application rate was very significant as compared with CK. However, 3 days later, it started to turn from stimulating to inhibiting growth of bacteria and actinomycetes, and the higher the application rate the more obvious the inhibitory effect. Twenty days after it was applied, its effect was not significant at all in the treatment low in application rate as compared with CK, but very in the treatment high in application rate. The effect of the pesticide on fungus was quite similar, promoting first and inhibiting afterwards. Within the first 5 days after its application, the pesticide stimulated growth and propagation of fungi and the effect was very significant in the treatment high in application rate, but 10 days later, the substance began to inhibit the growth of fungi, and the effect increased with rising application rate and became very significant when the rate was high as compared with CK. IPP, once applied into the soil, also had some effects on soil enzymes in activity. Soil alkaline phosphatase was more sensitive to the substance than acid phosphatase, and the effect on the former was significant 2 hours after the application. The activity of alkaline phosphatase was reduced by 24% in the treatment applied with 10 mg kg^-1of IPP. Three days after the application of the substance, the activity of acid phosphatase varied sharply between the treatments, and reduced 19.5% in the treatment applied with 10 mg kg^-1 of IPP. This inhibitive effect lasted on till the 20^th day. Urease activity was inhibited during the initial period of the experiment, and the effect increased with IPP application rate, but during the period from the 5^thto the 10^th day, no significant difference was observed between these treatments and CK. However, the inhibitive effect became obvious again during the period from the 15^th to the 20^th day. The experiment demonstrates that IPP does have some inhibitive effects on acid phosphatase, alkaline phosphatase and urease in activity, and some stimulating effect on dehydrogenase, and the higher the applicationrate, the more obvious the stimulating effect. Besides, the pesticide has some weak stimulating effect on catalase activity. To sum up, IPP is relatively short in half life, and hence belongs to the readily degradable kind of pesticide. It has some toxic effects on soil microbes even when only 10 mg kg^-1 is applied.