Dissipation Law And Environmentally Toxicological Effects Of Herbicide Acetochlor In Rice Field Ecosystem

The residual detection method of acetochlor in rice and other samples, and the degradation law of acetochlor in rice plant and in the environment were studied and the activity of urease, catalase and proteinase affected by acetochlor and toxicity of acetochlor for the tadpole were investigated, which provided scientific basis for making use of acetochlor in the field and comprehensively assessed the ecological security of acetochlor. The main results were as follows:(1) The paper established the residual extraction method, the purification extraction method and GC-ECD detection method for acetochlor in rice, rice plant, soil, and water samples. Acetochlor existed in rice plant, rice was extracted by dichloromethane, with pressure reduction and pressure filtration, the extracts were concentrated, purified and detected by rotary densifier, Florisil column and GC-ECD respectively. Acetochlor in soil was extracted by methanol, with pressure reduction and pressure filtration and constant volume of petroleum ether, and was subjected to gas chromatography with ECD. Average recoveries of residual detection method of acetochlor in rice, rice plant, soil, water samples were 92.5%~98.7%,87.2%~96.8%, 83.6%~93.7%,94.0%~99.3%, while the coefficients of variation were 5.46%~7.45%,3.80%~7.66%,2.70%~6.41%,3.46%~7.54%, respectively.(2) Residual dynamics of acetochlor in rice plant, soil and water samples of Changsha, Liuyang, Hangzhou and Fuyang were studied. The results showed that the degradation ratio of acetochlor in rice field was high in the natural environment. Half-lives of acetochlor in rice plant, soil, water samples in the cities above were 1.06-1.47d,2.01-2.42d and 0.91-1.81d, respectively. Twenty-one days after fertilizing, none acetochlor was detected in rice soil, plant and rice in the natural environment, and it was not about to cause cumulative residual pollution.(3) Through laboratory imitation experiment, the activity of urease, catalase and proteinase affected by acetochlor for the tadpole were studied. The result showed that the urease was inhibited when treated with low concentration of acetochlor (1.0mg/kg,5.0mg/kg). For the experiment of catalase activity, it showed "inhabitation-stimulation-normal state" and "inhabitation-normal state" process when the concentration of acetochlor were 1mg/kg,5mg/kg,20mg/kg and 50 mg/kg, respectively. For the experiment of proteinase activity, the value of proteinase activity was reduced slowly first and then stimulated when the concentration of acetochlor were lmg/kg and 5mg/kg. However, acetochlor of 20mg/kg and 50 mg/kg cause it reduced constantly, and then rarely stimulated.(4) The toxicity of acetochlor influenced on Bufo gargarizans tadpole was investigated. Results of the experiment of acute toxicity showed that LD50 of acetochlor in 24h,48h and 96h were 43.81mg/L,41.78mg/L and 39.07mg/L,respectively. The SC of acetochlor was 11.40 mg/L. It concluded that the toxicity of acetochlor is low. The tadpole appeared the characteristics of normal motionlessness, abnormal motionlessness, normal movement and abnormal movement. Results of the experiment of sub-acute toxicity also presented the same four features above, however, the characteristics of abnormal motionlessness and movement were different from that of acute toxicity.