Study On Residue Dynamics Of Chlorothalonil And Its Metabolites In Cucurbita Maxima Duch. Ex Lam. And Soil

Cucurbita maxima Duch.ex Lam.is a popular low-calorie food.In the production of Cucurbita maxima Duch.ex Lam.,chemical control is an important measure to prevent and control diseases and pests in the production process of the winter squash,and thus the pesticide residue problem has always been of concern.In this paper,the chlorothalonil and its more toxic major decomposition product chlorothalonil-4-hydroxy as the object of study.A residue analysis method for the determination of chlorothalonil and its main metabolite chlorothalonil-4-hydroxy in cucurbita maxima Duch.ex Lam.and soils was established.The residual behavior of chlorothalonil and chlorothalonil-4-hydroxy was studied in order to provide a clear and safe use of bamboo shoots provides scientific basis.The main results were summarized as following:1.The analytical methods of chlorothalonil and chlorothalonil-4-hydroxy in cucurbita maxima Duch.ex Lam.and soil.The chlorothalonil in cucurbita maxima Duch.ex Lam.samples were extracted by acetonitrile for 2 min;Soil samples were extracted by acetonitrile for 30 min;Cleaned up with Florisil column;chlorothalonil in samples was determinated by GC with ECD.Determination conditions: Shimadzu GC-2010 plus gas chromatograph with ECD;Column: BR-5 column(30 m ×0.32 mm × 0.25 ?m);Sample volume: 1.0 ?L.The retention time of chlorothalonil was about 9.65 min.The limit of instrumental detection was 5.0 ng.The results of the adding recovery test show that: Three different concentrations of 0.01 mg/kg,0.1 mg/kg,1.0 mg/kg,10.0 mg/kg were fortified respectively in cucurbita maxima Duch.ex Lam.and soil.The average recoveries of chlorothalonil in cucurbita maxima Duch.ex Lam.were ranged between 71.68%~102.59%,and the RSD ranged between 1.86%~7.23%.The average recoveries and RSD in soil were ranged between 73.17%~97.98% and 4.51%~7.02%.The LOQ of chlorothalonil in cucurbita maxima Duch.ex Lam.and soil were all 0.01 mg/kg.The feasibility,accuracy and accuracy of the residue analysis method are all up to the requirement of pesticide residue analysis.The chlorothalonil-4-hydroxy in cucurbita maxima Duch.ex Lam.samples were extracted by acetonitrile and 0.5% phosphoric acid water solution for 2 min,cleaned up with Florisil column;Soil samples were extracted by acetonitrile,shaking and extraction for 30 min;chlorothalonil-4-hydroxy in samples was determinated by HPLC.Determination conditions: Agilent 1260 high performance liquid chromatography system;Column: Agilent HC-C18 column(4.6 mm×250 mm,5 ?m);Detector wavelength:245nm;Mobile phases: acetonitrile and 0.5% phosphoric acid water solution(75:25,v/v);Flow velocity:1.0 mL/min;Oven temperature: 35?,Sample volume: 20 ?L.The retention time of chlorothalonil was about 3.97 min.The limit of instrumental detection was 500 ng.The results of the adding recovery test show that: Three different concentrations of 0.1 mg/kg,1.0 mg/kg,5.0 mg/kg were fortified respectively in cucurbita maxima Duch.ex Lam.and soil.The average recoveries of chlorothalonil-4-hydroxy in cucurbita maxima Duch.ex Lam.were ranged between 77.49%~116.65%,and the RSD ranged between 1.76%~6.26%.The average recoveries and RSD in soil were ranged between 90.74%~98.51% and 1.31%~6.04%.The LOQ of chlorothalonil-4-hydroxy in cucurbita maxima Duch.ex Lam.and soil were all 0.1 mg/kg.The feasibility,accuracy and accuracy of the residue analysis method are all up to the requirement of pesticide residue analysis.2.Dispelling dynamics of chlorothalonil in cucurbita maxima Duch.ex Lam.and soilThe dissipation of chlorothalonil in cucurbita maxima Duch.ex Lam.and soil was studied in Anhui and Beijing in 2016.The residues of chlorothalonil amount of cucurbita maxima Duch.ex Lam.and soil was 0.3773 mg/kg and 0.9669 mg/kg in Anhui.The residual amount gradually decreases as time goes on,the digestion rate of chlorothalonil in cucurbita maxima Duch.ex Lam.and soil was 82.22% and 83.99% after 7 d,with the half-life of 6.86 d and 8.45 d.The residues of chlorothalonil amount of cucurbita maxima Duch.ex Lam.and soil was 0.3671 mg/kg and 2.2750 mg/kg in Beijing.The residual amount gradually decreases as time goes on,the digestion rate of chlorothalonil in cucurbita maxima Duch.ex Lam.and soil was 94.55% and 87.30% after 7 d,with the half-life of 4.88 d and 6.48 d.3.The final residue experiment of chlorothalonil in cucurbita maxima Duch.ex Lam.and soilIn 2016,seven test points in Anhui,Beijing,Shandong,Jiangsu,Hunan,Zhejiang and Hainan were applied at low dose(2200 g/ha),the residues of chlorothalonil and chlorothalonil-4-hydroxy were <LOQ~3.042 mg/kg in cucurbita maxima Duch.ex Lam.,seven test points were applied at high dose(3300 g/ha),the residues of chlorothalonil and chlorothalonil-4-hydroxy were <LOQ~3.724 mg/kg in cucurbita maxima Duch.ex Lam.As there was no MRL of chlorothalonil in cucurbita maxima Duch.ex Lam.in our country,refer to the MRL of Japan(5 mg/kg),the results show that it was safe used under the dosage of 2200 g/h and 3300 g/ha,after using chlorothalonil in 7 d,10 d,14 d,the total residue is not over standard,which is safe to use.