Study On Behavior Of Thiocyclam And Its Effects In The Tobacco Field

Thiocyclam is a kind of pesticide what is belong to nereistoxin and plays the role of inhibitor to acetylcholine receptors. It kills insect by acts on the synaptosomes of insect nervous systems which makes the insect nerve impulses blocked at synapses. It has good control effect on a variety of crops on the leaf-eating insects, borer pests and sucking pests.This study analyzed the residual and degradation of thiocyclam systematically in tobacco soil and leaves. Its adsorption was probed in the five kinds of soil tested.It was very important to assess the safety of thiocyclam after it was applied in tobacco filed, and to provide some fundamental data for scientific application of thiocyclam.The main conclusions were as follows:1Thiocyclam has little effect on the growth of the tobacco plants, and the main chemical composition has no significant difference between the controlled plants and the reference plant. Spraying low concentrations of thiocyclam would not cause phytotoxicity, however, lightly phytotoxicity could be observed latterly while sprayed high concentrations of thiocyclam.2The method of GC analysis of thiocyclam was established. The thiocyclam residues in tobacco leaves and soils were analyzed by Gas Chromatography (FPD). In this method the residues of thiocyclam were extracted with HCl and transformed into nereistoxin in alkali aqueous, then calculated the content of thiocyclam in tobacco. The minimum detectable amount of thiocyclam was5×10-11g.while the minimum residue in tobacco soil, fresh and dry leaves were0.005mg/kg,0.005mg/kg and0.001mg/kg, respectively. Results showed that the fortified recoveries in different samples ranged from76.4%to99.45%and relative standard deviation ranged from1.77%to6.00%when the added concentration of thiocyclam ranged from0.05to5.00mg/kg.3Field experiments were carried out to reveal residue dynamics and final residue of thiocyclam in tobacco leaf and soil in Changsha and Qingdao. Results showed that the half-lives in soil and leaves ranged in2.30～2.84days and2.86～4.14days, respectively. It means that thiocyclam is degradable pesticide.The final residue results showed that the ultimate residue in dry leaves was lower than0.1mg/kg at an interval of7d. According to the results, when50%soluble powder of thiocyclam were sprayed in tobacco field for four times according to the recommended dose of600g.hm-2(300a.i.g.hm-2), the safe period of thiocyclam in tobacco leaves could be set as7d.4The adsorption equilibrium times of thiocyclam were24hours. The adsorption of thiocyclam in five kinds of tobacco soils could be described with the Freundlich isotherm equation, and its adsorption was physical adsorption. The adsorption of thiocyclam was strongest in the black soil from Heilongjiang; the adsorption was weakest in the soil from Hunan; pH played an important role in the adsorption, at different pH values the adsorption of thiocyclam were different.