Dissipation And Residues Of 8% Kasugamycin-Benziothiazolinone WG In Citrus And Its Effect On Fruit Quality

As the largest fruit in the world,Citrus has beautiful colors,flavors,and high nutritional value,and is loved by people of all countries.However,it is susceptible to infections such as Huanglong disease,sore disease,ulcer disease and other diseases during planting,which seriously affects the yield and nutritional quality of citrus and has a huge impact on the citrus industry.As good environment-friendly fungicides,kasugamycin and benziothiazolinone have a good control effect on citrus ulcer disease,but there is little research on the combination of the two fungicides on citrus.In this study,a dispersive solid-phase extraction method was used to purify samples,and ultra-high performance liquid chromatography-tandem mass spectrometry?UPLC-MS/MS?was used to develop a method for simultaneous determination of the residues of kasugamycin and benziothiazolinone in citrus samples.Furthermore,the storage stability of kasugamycin and benziothiazolinone in citrus matrix was studied.In order to study the dissipation dynamics and terminal residue of 8%of kasugamycin-benziothiazolinone water dispersible granules on citrus in the filed conditions,a field trial of 2018 was carried out at 12 trail fields,and the dietary intake risk assessment of pesticide residues was conducted based on the test results,toxicology and dietary structure data.In addition,the effect of applying 8%of kasugamycin-benziothiazolinone water dispersible granules on the nutritional quality of citrus fruits were studied.The main research results of this article are as follows:1.An analytical method for simultaneous determination of kasugamycin and benziothiazolinone residues in citrus by dispersive solid-phase extraction combined with UPLC-MS/MS was developed.The two analytes spiked in citrus whole fruit and pulp were extracted with 0.5%formic acid and 0.5%aqueous ammonia in acetonitrile-water?7:3,v/v?,respectively,purified by C₁₈,and separated on Waters ACQUITY UPLC^?HSS T3 column.Gradient elution was carried out with methanol-0.2%aqueous formic acid as mobile phase,and multiple reaction monitoring mode?MRM?scanning was performed and quantified by matrix-matched standard curve external standard method.The results showed that the target compounds have a good linearity in the concentration range of 0.5-200?g/L,and the limits of detection ?LODs?was 0.006-0.04?g/kg,the limits of quantitation?LOQs?in the concentration range of 0.5-200?g/L.The three spiked recoveries were 73.4%-104%,and the relative standard deviations?RSD?were 1.6%-9.6%.The method is easy to operate and has high sensitivity,and is suitable for simultaneous determinations of residues of kasugamycin and benziothiazolinone in citrus.2.The storage stability of kasugamycin and benziothiazolinone in citrus whole fruit and pulp was studied under the storage temperature of-18?.The results showed that the degradation rates of kasugamycin and benziothiazolinone in the citrus matrix were 6.2%-23.9%and 4.5%-25.0%within 24 weeks,respectively.The degradation rates of two pesticides gradually increased with the increase of storage time,but were always less than 30%.The results indicated that kasugamycin and benziothiazolinone did not degrade significantly in the citrus according to the“Guideline for the stability testing of pesticide residues in stored commodities of plant origin”?NY/T 3094-2017?.In summary,the storage stability period of kasugamycin and thiamydone on the citrus substrate is 24 weeks.It should be measured within 24 weeks after the field sample is taken to accurately detect kasugamycin and benziothiazolinone.3.The dissipation dynamics and final residue tests of 8%kasugamycin-benziothiazolinone water dispersible granules in citrus fruits from twleve places including Chongqing,Hunan,Hubei and other regions in 2018 were studied,and their dietary intake risks were evaluated.The result of dissipation dynamics tests showed that the degredation of kasugamycin conformed to the first-order kinetic equation with a half-life of 14.44 days to 19.80 days when 80 mg a.i./kg of 8%of kasugamycin-benziothiazolinone water dispersible granules were sprayed once on Satsuma Mandarin and Newhall navel orange.And the degredation rate has reached about 70%at 28 days after the last application.However,the degredation of benziothiazolinone did not meet to the first-order kinetic equation,and the residual amount at 2 hours after application was lower than LOQ and fluctuated around LOQ subsequently.The result of final residue test showed that the final residues of kasugamycin and benziothiazolinone in the whole citrus fruit and pulp at 21d and 28d after the last application were less than the LOQ,far lower than the MRL when sprayed twice with 7 d interval on Satsuma Mandarin and Newhall navel orange.The results of dietary intake risk assessment indicate that the residual risk of the two fungicides on citrus pose a chronic risk to people of different ages,which is within an acceptable range.Therefore,it is recommended that the dosage of 8%kasugamycin-benziothiazolinone water dispersible granules on citrus is 80 mg a.i./kg with twice of applications and 7 d of application interval,and the harvest interval is 21d.4.The effects of 8%kasugamycin-benziothiazolinone water dispersible granules on citrus fruit nutritional quality were studied by applying twice with an interval of 7days at dose of 80 mg a.i./kg.The results showed that the application of the compound pesticide had no obvious effect on the appearance quality of citrus fruits,but can increase the total soluble solids?TSS?to the titratable acid?TA?and reducing sugar content,while reduce the TA,Vitamin C and total flavonoid content of citrus fruits to a certain extent.