Study On Degradation Of 33% Imidacloprid-?-Cyhalothrinin SC In Citrus And Soil And Its Effect On Quality

This research establishes an analytical method for detecting imidacloprid and?-cyhalothrin in citrus?whole fruit,pulp,peel?and soil matrix at the same time by an optimized-mode of QuEChERS pretreatment method combined with UPLC-MS/MS analysis technology.The storage stability in citrus and soil matrix was investigated.And the dissipation dynamics and terminal residues study of 33%imidacloprid-?-cyhalothrin suspension in citrus and soil were carried out in Chongqing,Hunan and Guangxi from2016 to 2017.Based on the recommended dosage and frequency of application of early stage test results,the study on the effect of pesticide application on the nutritional quality of citrus was conducted.The purpose of the experiment is to get a reference for guiding agricultural production using 33%imidacloprid-?-cyhalothrin suspension in the citrus industry by a safe and rationa way,while guaranteeing agricultural production safety,monitoring fruit quality and ensuring that consumers can be protected from unsafe food.The main findings are as follows:An analytical method was developed for detecting imidacloprid and?-cyhalothrin in citrus?whole fruit,pulp,peel?and soil matrix at the same time by an optimized-mode of QuEChERS pretreatment method combined with UPLC-MS/MS analysis technology.Samples were extrated by 1%acetic acid-acetonitrile?as extractant?,MgSO₄ and NaCl?as salting-out agent?with ultrasonic assisted,purified by PSA?as purifying agent?and detected by UPLC-MS/MS.The experimental results show that the linear relationship between the integrated ion peak area and the target concentration of imidacloprid and?-cyhalothrin within the range of 0.2-2000?g/L is good,and the correlation coefficient R² is 0.9993⁰.9997,LODs are 0.0008⁰.002 mg/kg,LOQs are 0.002⁰.005 mg/kg;with spiked level of the two at 0.01,0.1,1,2 mg/kg,the average recovery of imidacloprid and?-cyhalothrin was 80.7%-107.0%,and the RSD was 0.5%-13.1%,indicating that this method has a good recovery and precision,which can meet detection pesticide residues of imidacloprid and?-cyhalothrin in citrus and soil matrix.The storage stability of imidacloprid and?-cyhalothrin in citrus and soil matrix under-18°C conditions was investigated.The results showed that the degradation rate of imidacloprid in different citrus substrates was 1%to 14%in the storage period of0-24 weeks,and the degradation rate in soil matrix was 1%-13%,both lower than 30%,indicating imidacloprid was stable in citrus and soil matrix?within 24 weeks?;the degradation rate of?-cyhalothrin in different citrus substrates was 2.5%to 25%,and the degradation rate in soil matrix was 2.5%to 17.5%,both below 30%,indicating that?-cyhalothrin is relatively stable in citrus and soil matrices?within 24 weeks?.All this indicates that test datas from samples of citrus and soil containig imidacloprid and?-cyhalothrin which stored under-18°C freezing conditions can meet the regulations?NY/T 3094—2017?within a 24-week storage period.In order to ensure the accuracy and reliability of the test results of pesticide residue in the plant source,all samples should be tested as soon as possible after collection.During the period of 2016 to 2017,the dissipation dynamics and terminal residues study of 33%imidacloprid-?-cyhalothrin suspension in citrus and soil were carried out in Chongqing,Hunan and Guangxi by the manners of good agricultural practices.The results showed that the dissipation dynamics of imidacloprid and?-cyhalothrin in citrus accorded with the first-order kinetic digestion mode and half-lives were 8.2 d-9.8 d,5.5d-7.6 d,and final residual degradation rate was above 92%.The dissipation dynamics dynamics of imidacloprid and?-cyhalothrin in soil accords with the first-order kinetic digestion mode,and half-lives are 10.8 d-24.8 d,11.4 d-21.0 d,and the residual final degradation rate is above 79%.The terminal residues indicated that the amounts of final residues was positively correlated with the dosage,the number of application and the interval of harvesting.The residues of the two were mainly distributed in peel,followed by whole fruit and pulp.About 28 days later after the last application,the residues of imidacloprid and?-cyhalothrin in fruits was lower than the MRL value specified in GB2763—2016,and dietary risk assessment showed that risks of residues were acceptabled.Therefore,it is recommended that 33%imidacloprid-?-cyhalothrin suspension should be applied in 1000-fold dilution?330 a.i.mg/kg?and can be applied up to 2 times in one citrus production cycle with 10-days application interval and 28-days harvest interval.Based on the recommended dosage?330 a.i.mg/kg?and frequency?2 times?of application of early stage test results,the study on the effect of pesticide application on the nutritional quality of citrus was conducted.Results show that citrus samples treated with insecticides have different effects on quality parameters of citrus.For example,the total content of flavonoids in pulp was promoted.And the ratio of sugar to acid and the total content of flavonoids in peel was reduced.And part of it also appears to enhance the fluctuation of a certain substance content and so on.The effect of applying this insecticide on the nutritional quality of citrus fruits is complicated,and further research is needed.