Behavior And Effect Of Avermectin In Paddy Field

Avermectin is a high-efficient biological pesticide that has been used extensively in agriculture and husbandry. The behavior and effect of avermectin in Paddy field were studied in this thesis in order to provide some fundamental data for assessing the environment safety assessment and scientific application of avermectin. The main conclusions obtained are listed as follows:(1) An analytical method about residue determination of avermectin paddy water, soil, straw, rice hull and brown rice by HPLC.Samples were extracted with methanol, purified on liquid-liquid partition and the extract was purified by a chromography column of florisil, subsequently detected by high performance liquid chromatograph with ultraviolet detector. Detectable limits of avermectin residue in paddy water, soil, plants, rice hulls and rice were 0.001 mg/L,0.005,0.005,0.005,0.005 mg/kg. The result shows that when HPLC adopts 245 nra as scan wavelength, and the mixture of methanol and water according to appropriate proportion as flowing phase, the parameters such as accuracy, repetition and precision et al for the method are all good to satisfy the essential rules of pesticide residue determination.(2) The study on the degradation behavior of Avermectin in moist soil and waterlogged soil under laboratory condition.The degradation of Avermectin in the two kinds of soils environment conforms to the chemical reaction series. The average half-life of digestion Avermectin in the moist soil and waterlogged soil were 17.20 d and 13.51 d respectively.(3) Avermectin 3.2%EC was applied in paddy for two years in Changsha, Hangzhou and Guiyang, the results of degradation dynamic of Avermectin revealed that the degradation dynamics of Avermectin accorded with Ct=Coe"kt in paddy water, soil and plant, moreover it had high correlation. The average degradation half-lives of Avermectins were 2.52 days in paddy water,2.61 days in paddy soil and 1.86 days in paddy plant. This result indicated that Avermectin could be easily degradable in paddy. The final residue experiment of Avermectin in brown rice showed that when the 7th day after the last applied, the residues of Avermectin were less than 0.01 mg/kg. So Avermectin 3.2% EC was applied on the condition of the experiment, the safety interval period was at least 21 days. It suggested that the MRL of Avermectin in rice was 0.01 mg/kg.(4)In order to assess the eco-environmental effects and toxicity of avermectin overall correctly, a static experiment is made to probe into the study of the acute toxicity and joint toxicity of avermectins, Cd2+,Cr6+,Mn2+ to Tadpole. The results of the acute toxicity indicate that:the safe concentration of avermectin, Cd2+,Cr6+,Mn2+ to Tadpole are as follows:0.0004,0.6146,12.873 8.223.781 5 mg/L. The results of the joint toxicity show that:the joint toxicity of Avermectins and Cd2+ for 96 h were synergism; The joint toxicity of avermectins and Cd6+ for 96 h were antagonism; The joint toxicity of Avermectins and Mn2+ for 96h were antagonism. This is consequence for the environmental risk assessment should associate with the joint toxicity of heavy metal and other materials.(5) In order to assess the eco-environmental effects and toxicity of avermectins overall correctly, a static experiment is made to probe into the study of the acute toxicity and joint toxicity of avermectins, butachlor, difenoconazole, SDBS to Tadpole. The results of the acute toxicity indicate that:the safe concentration of avermectin, butachlor, difenoconazole, SDBS to Tadpole are as follows:0.0004,0.0380.0.437 1,143.897 8 mg/L. The results of the joint toxicity show that:the joint toxicity of Avermectin and butachlor for 96h were antagonism; the joint toxicity of avermectin and difenoconazole for 96 h were synergism; the joint toxicity of Avermectin and SDBS for 72 h were synergism, but at 96h were antagonism.