Residual Degradation Of Thiophanate-methyl And Carbendazim On Citrus And Its Adsorption In Biochar

In order to clearly understand the residual risk and harm of thiophonate-methyl and its metabolite carbendazim in citrus,and to practically remediate and control the polluted water caused by thiop ho nate-methyl.In this paper,the method of simultaneous analysis and determination of thiop ho nate-methyl and carbendazim in citrus was studied and established by adding recovery experiment and using the detection technology of high performance liquid chromatography-MS/MS.On this basis,field experiments were carried out to study the residual degradation of thiop ho nate-methyl and carbendazim metabolite in citrus after 50%thiop ho nate-methyl and pyraclostrobin suspending agent was applied in citrus orchards,and the residual risk was evaluated.In addition,the adsorption process of thiophonate-methyl and carbendazim in water by five kinds of biochar tested and the possible influence of water quality conditions on the adsorption process were studied by batch equilibrium method under indoor conditions.The main conclusions are as follows:(1)Simultaneous analysis and determination of thiophonate-methyl and carbendazim residues in citrus samples:citrus samples were extracted with acetonitrile,the extract was purified by PSA dispersion solid phase extraction,and detected by HPLC-MS/MS.When the concentration of thiophonate-methyl was 0.5,1.0 and 5.0 mg/kg,the recovery rate of thiophonate-methyl in citrus pulp was 89-111%,the coefficient of variation was 2-5%,85-109%and 4-6%respectively.The recovery of carbendazim in citrus pulp was 76-104%,and the coefficient of variation was 3-6%.In citrus fruit,the recovery was 76-103%,and the coefficient of variation was 3-7%.The quantitative limits of thiophonate-methyl and carbendazim in citrus fruit and pulp were 0.05 mg/kg,and the quantitative limits of thiop ho nate-methyl and carbendazim were 1×10-9 mg/kg.The sensitivity and accuracy of this method meet the relevant technical requirements of pesticide residue analysis and detection in China,and can be applied in practiceThe slope ratios of thiophonate-methyl and carbendazim in citrus fruit matrix were 1.1 and 1.2,respectively,indicating that there was a matrix inhibition effect in the whole fruit,while the slope ratios in pulp matrix were almost 1,indicating that there was no obvious matrix inhibition effect in the pulp(2)Degredation of thiophonate-methyl and carbendazim in citrus:The degradation of thiophonate-methyl and carbendazim in citrus pulp and fruit accorded with the first-order chemical kinetics equation(Ct=C0·e-kt).The half-life of thiop ho nate-methyl in citrus fruit was 3.3-19.3 d,13.9-19.3 d in pulp,3.3-7 d in Carbendazim and 3.6-6 d in citrus pulp 2 d;This indicated that thiophonate-methyl and carbendazim were easily digested in citrus and did not cause residual pollution.(3)The residual amount of thiophonate-methyl in citrus fruit was<0.05-0.506 mg/kg at 21 d after the last application,and<0.05-0.561 mg/kg in citrus flesh,and<0.05-0.818 mg/kg at 21 d after the Carbendazim last application,and<0.05-0.734 mg/kg in citrus flesh.The residual amount of thiophonate-methyl in citrus fruit was<0.05-0.482 mg/kg at 28 d after the last application,and<0.05-0.293 mg/kg in citrus flesh,and<0.05-0.473 mg/kg at 28 d after the last application,and<0.05-0.416 mg/kg in citrus flesh.(4)According to the residue degredation test results of 50%thiophonate-methyl and pyraclostrobin suspending agent on Citrus in 12 representative areas of China,combined with the residue registration of thiophonate-methyl and carbendazim in China and the per capita dietary structure of Chinese residents,the daily intake of thiophonate-methyl in the general population was calculated to be 0.68 mg,accounting for 36%of the daily allowable intake of carbendazim.1.17 mg,accounting for 62%of the daily allowable intake,the results showed that thiophonate-methyl and carbendazim did not pose a greater risk to the health of the general population.The reasonable suggestion of 50%thiop ho nate-methyl and pyraclostrobin suspending agent in citrus is that 50%thiophonate-methyl and pyraclostrobin suspending agent is used to control carbon blight in citrus.Its effective ingredient dosage is 400 mg/kg(dosage of preparation is 1250 times liquid),three times,each time interval is 7 d,and the safe interval is 21 d.(5)The adsorption equilibrium time of thiop ho nate-methyl and carbendazim on five kinds of biochar tested ranged from 2.0 h to 24.0 h.The pseudo-second-order kinetic equation was the best one for the adsorption kinetics of thiophonate-methyl and carbendazim,and the fitting effect of the other two equations was not good.The isothermal adsorption process was best characterized by Linear and Freundlich adsorption(both of which reached significant level),while the Langumir adsorption model was not good enough to describe the adsorption kinetics.Significant level).The adsorption isotherms of thiophonate-methyl and carbendazim were closer to "S" than "L".Among the five kinds of biochar tested,sawdust-coal biochar was the most obvious,followed by sugarcane biochar slightly,and rice straw biochar was the worst.Among them,pH value and temperature also had a greater impact on the adsorption effect.The larger the pH value,the better the adsorption effect of thiop ho nate-methyl,the smaller the pH value,the better the adsorption effect of carbendazim,and the higher the temperature,the better the adsorption effect.But in the end,sawdust-coal biochar and bagasse biochar are the best adsorbents.The influence of water quality conditions on the adsorption of thiop ho nate-methyl and carbendazim by five tested biochars:for the adsorption of thiop ho nate-methyl and carbendazim by changing the types of salt ions in water,adding strong acid and alkali salts will slightly increase the adsorption capacity,which is related to the salting out of inorganic salts and the degree of ion electrolysis.Adding strong acid and weak alkali salts will benefit the adsorption of carbendazim,and adding alkaline salts will benefit the adsorption of carbendazim.The ionization degree of salt ions can improve adsorption effect.