| In order to research the degradation and residue behavior of carbosulfan and its metabolites(including carbofuran and3-hydroxycarbofuran)in the tobacco field, and to explore the effect of pH, temperature, inorganic salts and chemical fertilizers on carbosulfan hydrolysis, a technical method of simultaneous analysis and detection to detect the residue of carbosulfan and its metabolites was established with added recovery experiment in soil planted tobacco, fresh tobacco leaves and flue-cured tobacco leaves of tobacco samples, and on this basis, the residue and digestion behavior of carbosulfan was probed systematically after25%carbosulfan·emamectin benzoate EW was applied in tobacco field by field experiment. In addition, the hydrolysis mechanism and pathways of carbosulfan was probed detailedly by laboratory simulation experiment. The main effect factor on the hydrolysis of carbosulfan was researched systematically. These studies not only provided a scientific basis to assess the environmental effect of carbosulfan, but also provided a important basic data to apply scientifically and rationally25%carbosulfan·emamectin benzoate EW. The main contents and results of this paper showed as follows:(1) A technical method was established to detect the residue of carbosulfan and its metabolites with added recovery experiment by gas chromatography-mass spectroetry (GC-MS) in tobacco samples, The mixture of acetone-petroleum ether (1:4, v/v) was extraction agent for the soil samples, and the mixture of acetone-acetonitrile (1:9, v/v) was as extraction agent for fresh tobacco leaves, and acetonitrile was as extraction agent for flue-cured tobacco leave, this above extraction of tobacco leaves was concentrated, and purified on Florisil column, the separation was performed on HP-5MS quartz elastic capillary column at programmed temperature, and detected by GC-MS. When the added concentration changed from0.05mg/kg to1.00mg/kg, the recoveries of carbosulfan ranged from77.25%to94.49%in soil planted tobacco,76.05%to101.13%in fresh tobacco leaves and80.56%to106.28%in flue-cured tobacco leaves, and its relative standard deviation was1.51%～4.17%,5.63%～7.30%and5.48%～9.20%, the recoveries of carbofuran ranged from86.57%to 98.78%in soil planted tobacco,71.36%to104.80%in fresh tobacco leaves and79.53%to98.88%in flue-cured tobacco leaves, and its relative standard deviation was1.79%～4.41%,2.44%～5.93%and3.02%～4.79%, the recoveries of3-hydroxycarbofuran ranged from73.85%to99.60%in soil planted tobacco,71.45%to110.40%in fresh tobacco leaves and76.42%to96.06%in flue-cured tobacco leaves, and its relative standard deviation was2.00%～6.13%,4.83%～9.14%and5.17%～6.57%. The minimum detectable concentration of carbosulfan was0.125μg/kg in soil planted tobacco, which was0.1μg/kg in fresh tobacco leaves and flue-cured tobacco leaves, that of carbofuran and3-hydroxycarbofuran was0.5μg/kg in soil planted tobacco,0.4μg/kg in fresh tobacco leaves and flue-cured tobacco leaves, the minimum detectable quantity of carbosulfan was1.0×10-12g, and that of carbofuran and3-hydroxycarbofuran was4.0×10-12g. These results indicated that this method are in line with the technical requirements for the analysis and detection of pesticide residue.(2) In2012and2013year, the degradation and residue of carbosulfan, carbofuran and3-hydroxycarbofuran was launched respectively after25%carbosulfan·emamectin benzoate EW was applied in Hunan Changsha and Shandong Qingdao. The results showed that the degradation dynamics of carbosulfan and its metabolites in soil planted tobacco and fresh tobacco all could conform to the requirement of the chemical reaction kinetic equation, the half-life of carbosulfan was2.81to4.62days in soil planted tobacco,1.71to1.88days in fresh tobacco leaves, the half-life of carbofuran (including carbofuran and3-hydroxy carbofuran sum, the same below) was2.85to4.13days in soil planted tobacco,1.90to2.26days in fresh tobacco leaves. These results showed that carbosulfan was degradable pesticide in tobacco field, when25%carbosulfan·mamectin benzoate EW was applied one time with the dosage of525g/ha and787.5g/ha in tobacco field, the results showed that carbosulfan had some residue in soil, and its metabolites such as carbofuran and3-hydroxycarbofuran had little residue. After applied75days, the residue of carbosulfan in flue-cured tobacco leaves was less than0.1μg/kg, and the residue of carbofuran in flue-cured tobacco leaves was0.0005mg/kg to0.0016mg/kg, this residue were less than tentative maximum residue limits value(0.05mg/kg) of carbosulfan in tobacco leaves (flue-cured tobacco leaves), so the reasonable use suggestion for25%carbosulfan·emamectin benzoate EW in tobacco field was that applying one time at dosage525g/ha before tobacco was transplanted, the safe interval of flue-cured tobacco leaves is75days.(3) The hydrolysis mechanism and pathways of carbosulfan was studied detailedly by indoor simulation experiment. The results showed thatthe hydrolysis products of carbosulfan were carbofuran and carbofuran phenol, and this was identified and detected by GC-MS, the N-S bond of carbosulfan molecular structure ruptured and generated carbofuran, and then generated carbofuran phenol through the hydrolysis of the ester carbonyl, oxidation or free radical reactions of benzofuran ring finally led the ring to be cracked. The benzofuran ring of carbosulfan molecule had an apparent electron-withdrawing function, it made the charge density of the ester carbonyl reduced, so that the charge of N-S bond in the molecular structure becomed unstable, therefore, carbosulfan hydrolyzed easily and generated carbofuran, the ester carbonyl of carbofuran molecule was attacked by the hydroxide anion(OH-) in alkaline solution, so that carbofuran hydrolyzed further, and generated carbofuran phenol.(4) The effect of the aqueous solution pH value, temperature, inorganic salt, chemical fertilizers on the hydrolysis of carbosulfan was preliminarily researched by indoor simulation experiment. The results showed that the hydrolysis rate of carbosulfan changed at different pH value, in alkaline solution it was lower than in acid solution or neuter solution, it accelerated with the increase of temperature, inorganic salts had some inhibition to the hydrolysis of carbosulfan, but this inhibition was not obvious, because of the salting-out effect, strong acid and strong base salts (NaCl, KCl, CaCl2, NaNO3) could inhibite the hydrolysis of carbosulfan, because NaHCO3was strong base and weak acid salt, it presented alkaline in aqueous solution, it also inhibited the hydrolysis of carbosulfan, urea presented weak alkaline in aqueous solution, so it had some inhibition to the hydrolysis of carbosulfan, KCl had a little effect to the hydrolysis of carbosulfan, potassium dihydrogen phosphate presented acidic in aqueous solution, so it had some promotion to the hydrolysis of carbosulfan. |
