Study On Degradation And Residual Behavior Of Metolachlor And Its Effects In The Tobacco Field

Metolachlor is a kind of amide herbicides, which is recommended as a herbicide in our country, and which is used in most areas planted tobacco. In order to evaluate whether it is risks to the eco-environment in tobacco, this paper has systematically studied the effects of metolachlor and its preparations on the growth and quality of tobacco, the residual degradation in tobacco and soil after it was applied in tobacco field, its transportation in "soil-tobacco" system, and its adsorption in the soil planted tobacco. These studies were very important for the comprehensively and accurately assess the safety of metolachlor after it was applied in tobacco field, and to guid its scientific application in the process of tobacco production; while these studies would provide a scientific basis for cigarette company to choose high-quality tobacco. The main conclusions were as follows:(1) Under the natural conditions of Hunan Changsha, this herbicide inhibit the growth of tobacco plants in the front of spraying metolachlor, and its high concentrations is more than its low concentration; this herbicide could promote the growth of tobacco plants in the later, and its high concentrations is more than its low concentration. while there was a certain promoting on the yield of tobacco leaves, and a little effect on the main chemical composition of tobacco leaves.(2) The degradation of metolachlor followed a equation of one-grade chemical reaction dynamics in the tobacco leaves and soils planted tobacco, and its degradation half-life of metolachlor was 10.30 d,11.12 d in soil planted tobacco from Hunan Changsha and Shandong Qingdao respectively, its half-life was 9.47 d,8.49d in tobacco leaves respectively. This showed that metolachlor is a easily degradable pesticides (T1/2<30 d). When 72% metolachlor EC was 1500ml/hm2, in the tobacco leaves its residues ranged from 0.004 mg/kg to 0.031mg/kg in Hunan Changsha and from 0.007 mg/kg to 0.045 mg/kg in Shandong Qingdao respectively affter the mature of tobacco leaves; when 72% metolachlor EC was 2250ml/hm2, in the tobacco leaves the residue of metolachlor ranged from 0.009mg/kg to 0.043mg/kg in Hunan Changsha and from O.Ollmg/kg to 0.058mg/kg in Shandong Qingdao respectively affter the mature of tobacco leaves. The residues of metolachlor in tobacco leaves were lower than the corresponding MRL value (0.1mg/kg), so it was concluded that it is safe that the dose of 72% metolachl EC was used in the tobacco fields.(3) In the system of "Soil-tobacco," the metolachlor can transport from soil planted tobacco to tobacco leaves, and the order of residues in different position of tobacco leaves were:lower leaves> middle leaves> upper leaves; the residues of metolachlor in tobacco leaves would reduce by the process of curing to tobacco leaves.(4) The adsorption of metolachlor in five kinds of soil planted tobacco was consistent well with the Freundlich isotherm equation; the adsorption of metolachlor was strongest in the cinamon soil from Shandong Qingdao, and its mobility was weakest; the adsorption was weakest in the red soil from Hunan Changsha, and its mobility was strongest; the major factor which affect the adsorption of metolachlor was the organic matter content in physical and chemical properties of soil; the free energy of adsorption of metolachlor in five kinds of the tested soil was less than 40 kJ/mol, what indicates that the adsorption of metolachlor in soil belonged to physical adsorption process.