The degradation of profenofos and phoxim in banana fruit and peel

Abstract: 【Objective】The objective of the study is to understand the degradation dynamics and final resi-due of profenofos and phoxim in banana fruit and in the peel. The degradation of profenofos and phoxim infruit and peel followed the first order kinetic equation(Ct=C0ekt). According to the equation,the half-life(T1/2) and 99% elimination time(T0.99) in the fruit and peel of these two pesticides were computed. The safeuses of profenofos and phoxim on banana were evaluated.【Methods】Three experimental plots in the ba-nana plantation were set. They were allocated to three treatments: the control without pesticide,applica-tion at the recommended dose,and the application at a dose that doubled recommended dose. Each plothad 6 banana strains,and the pesticides were prepared by water and applied by spray. 40% profenofoswas diluted by 1 000 or 500 times while 15% Avi · phoxim by 1 500 or 750 times with water. The dynam-ics of residue was studied in a one-spray experiment,where banana samples were collected 0,1,3,5,8,14 and 21 d after applying pesticides. The final residue experiment involved spraying pesticides twotimes with an interval of 15 days,and banana samples were collected 20,30,40 and 50 d after the sec-ond spray. During sampling,one finger was sampled each from hand 1,3,5 and 7 from top to bottom inthe banana clusters,and each time a total of 24 fingers were collected for each treatment. Banana sampleswere dissected into fruit and skin and separately mashed. 20 g sample was put into a 100 m L triangularflask,to which 50 m L acetone and appropriate amount of anhydrous sodium sulfate were added to remove the moisture,and the mixture was shaken for 1 h. After filtration with solid-phase extraction,the filtratewas condensed by nitrogen blow,dissolved in 1 mL acetone,and then determined for pesticide residuesusing gas chromatography. The pesticide residue in the sample collected on the day of applying was set asthe original residue,and the residue levels in the rest samples were compared with the original residue toget the degradation rate. The dissipation equation was fitted to the first order kinetics equation.【Results】The results indicated that the original residue levels of profenofos and phoxim in the peel were higher thanin banana fruit. The original residues of profenofos in the fruit and peel were 0.964 2 mg·kg^-1 and 1.756 7mg·kg^-1,respectively,and residues of phoxim in banana fruit and skin were 0.385 9 mg·kg^-1 and 0.461 7mg·kg^-1,respectively. In addition,the original residue levels of these two pesticides were affected bydose applied,they were higher in the doubled dose than the recommended dose. Correlation analysis withSPSS 19.0 revealed strong correlations(P<0.01) between applying dosage of two pesticides and the origi-nal residues in the fruit and peel. With time,the residues of phoxim and profennofos in banana fruit andskin decreased significantly,but the degradation rates were different in the two parts of banana. Phoximwas undetectable in the fruit 14 d after application(detection limit is 0.015 mg·kg^-1),suggesting all phox-im residue in banana fruit had been degraded by day 14. But in the skin,full degradation took 21 d. Incase of profenofos,it could not be detected in the fruit 14 at day(detection limit is 0.008 mg·kg-1),sug-gesting it was fully degraded in banana fruit 14 d after applying. However,in skin,up to 97.33% of resi-due was degraded at day 21. Comparison between T1/2and T0.99 of the two pesticides revealed that that thedegradation rate of phoxim was faster than profenofos. The degradation coefficient k was similar in thesame fruit parts when pesticides were applied at recommend dose and at doubled dose. But the degrada-tion coefficient k was different in different parts of banana,it being greater in fruit than in the peel. In ad-dition,the degradation of profenofos and phoxim in the fruit and peel proved to follow the first order kinet-ic equation(Ct=C0ekt). The experimental results also showed that the degradation coefficient(︱k︱) of pro-fenofos in the fruit and skin was(0.444 3±0.053 8)and(0.191 7±0.011 5),respectively. In bananafruit,the T1/2and T0.99 of profenofos ranged from 1.4 d to1.8 d and from 9.2 d to 11.7 d,respectively;andin the skin T1/2and T0.99 ranged from 3.4 d to 3.8 d and from 22.7 d to 25.6 d,respectively. The degrada-tion coefficient(︱k︱) of phoxim in the fruit and peel was(0.568 5±0.011 2)and(0.217 8±0.013 8),re-spectively. In fruit,the T1/2and T0.99 of phoxim were1.2 d and in the range from 7.9 d to 8.3 d,respective-ly;and in the skin the T1/2and T0.99 ranged from 3.0 d to 3.4 d and from 19.9 d to 22.6 d,respectively.The final residue test showed that profenofos and phoxim were readily degraded in banana,and the finalresidue of two pesticides in the peel was greater than in the fruit. 20 days after the second spray,the twopesticides could not be detected in the fruit,but they were not detected in the skin 40 days and 50 days af-ter the second spray,respectively.【Conclusion】The results indicated that profenofos and phoxim werereadily degraded in banana,and the degradation rates of these two pesticides in the fruit were higher thanin the peel. The phoxim maximum residue limit(MRL) in berries is 0.05 mg·kg^-1 and profenofos maximumresidue limit(MRL) in apple is 0.05 mg·kg^-1. Taking this value as residue limit,banana fruit became safe9 days after phoxim spraying,and in case of profenofos,it was 12 d. Therefore,if 15% avi·phoxim oiland 40% profenofos are applied according to the conventional method and at the recommended dosage thebanana produced can meet pollution-free requirements and the quality and safety of final product canmeet the requirements of the NY/T 750-2011.