Degradation Dynamics And Final Residues Of Thiamethoxam In Rice

With the improvement of people’s living standard,food contamination caused by pesticided was concerned by the public.China has been considered as the world’s leading producer and export of food.Rice(Oryza sativa L.)is the major food crop in China.In practice,reduplication applications of chemical pesticide are often necessary to protect the crop avoiding the infection by pathogens.Repeated applications could undoubtedly cause the problem of pesticide residue.Therefore,the problem of pesticide residues in rice has been widespread concerned in the world.Thiamethoxam oxazine,produced by Swiss syngenta crop protection co.,LTD.in 1991,and considered as the second generation of neonicotinoid insecticides,has the characteristics of high efficiency,low toxicity and broad-spectrum.It is mainly used for soil treatment and foliar spray,and has strong efficiency for control sap-sucking insects,as it can be absorbed by each part of the rice plant after its application.Therefore,thiamethoxam oxazine has become the common pesticide to control rice planthopper,aphids and leafhoppers.It has been applied on more than 115 species of crops in 64 countries.In this work,a simple and rapid method to detect the thiamethoxam oxazine residual in soil,rice,brown rice and chaff was established,meanwhile,the method was also used to study the degradation dynamic of thiamethoxam in paddy soil and rice.The main results were as follows: 1 analysis method of thiamethoxam residueIn this paper,a method to detect the thiamethoxam oxazine residual in soil,rice,brown rice and chaff was established.For soil and rice,with methanol as solvent extraction,mechanical oscillation extraction,5% of the water live off Florida silica column layer board purification,methanol,dichloromethane(V: V = 1:6)elution.Paddy water with acetonitrile as solvent extraction,liquid liquid distribution method to extract.In the solution under test thiamethoxam oxazine by high performance liquid chromatography(HPLC)method.Thiamethoxam lamictal in rice field water,the smallest of paddy soil and rice detection concentration were 0.01 mg/kg,0.03 mg/kg,0.05 mg/kg.The sensitivity,accuracy and precision of the method are to meet the requirements of the pesticide residue analysis.2 thiamethoxam lamictal in residue in rice research in motionSet thiamethoxam oxazine dissolve dynamic experiment and final residues of two parts,the recommended dose(18.75 g/hm~2 active ingredients),double recommended(28.125 g/hm~2 active ingredient)and blank control three processing.Digestion dynamic test 0 days after applying pesticide(2 h)after applying pesticide,1,3,5,7,14 and 21 days to collect plants,soil and paddy rice samples,the final residual test at 21 d and 28 d after applying pesticide and 35 d acquisition of rice plant,rice and soil samples,detection of thiamethoxam residue of oxazine.Dynamic experiment,the results show that the resolution thiamethoxam lamictal in rice plants,soil and paddy degradation rate faster,21 d basic completely degradation;And the final residual test,thiamethoxam oxazine has certain residue in rice plant and soil,but small residual amount,in the 35 d on paddy rice and rice husk and its residual amount is very small,when 21 d 35 d on rice and rice husk was no thiamethoxam oxazine checked out.3 thiamethoxam oxazine risk assessment on rice and rice huskAccording to the pesticide residues(JMPR)assessment experts joint conference,thiamethoxam oxazine per kilogram of body weight daily intake(ADI)0.02 mg,calculated according to weight 63 kg per capita in China,the daily intake of 1.26 mg per capita.According to the Chinese residents’ dietary guidelines(revised in 2011),grains and their products in our dietary structure,the per capita daily intake,adults generally is 250 ~ 400 g,combined with the research in this paper measured the brown rice thiamethoxam oxazine final residues of up to 1.0 mg/kg,deduce the per person per day through the grains and their products of thiamethoxam oxazine 0.4 mg,the maximum risk quotient(RQ)value is 0.32,the dietary exposure risk is low,belong to an acceptable level,safety level of the residue.4 rice thiamethoxam oxazine analysis of the degradation productsThrough the plant surface leacheate mass spectrometry analysis,according to thiamethoxam oxazine molecular structure,of thiamethoxam oxazine mass spectrogram a degradation products after parsing,in 1 day,3 days,five days,7 days of the plant surface gradually increase.According to the product of pyrolysis process,the degradation products may be one of the photolysis products.