Study On Effect Of Cooking On Two Fungicides Residues And Dietary Exposure Risk Assessment In Packchoi

The transformation of two systemic fungicide, metalaxyl and difenoconazole during processes of pakchoi were investigated. The simultaneous determination of metalaxyl and difenoconazole residues in different samples were developed. Then the effects of washing solutions and cooking modes on the elimination of metalaxyl and difenoconazole were investigated to achieve the processing factors. The dietary exposure assessment was also conducted by combining the dietary survey data of citizens from different ages and the residues of metalaxyl and difenoconazole in pakchoi from greenhouse.The main results are as follows:1. Determination of metalaxyl and difenoconazole were developed using gas chromatography-tandem mass spectrometry (GC-MS/MS) in oil sample, oil-free sample and soup sample. Modified QuEChERS was used for pretreatment of the oil sample and oil-free sample. C18 solid phase extraction catridge were used for purification and enrichment of soup sample. For three kinds of samples, the recoveries of metalaxyl ranged from 87.60% to 106.0%, RSD was 3.20%～10.21%; The recoveries of difenoconazole were78.81%～102.01%, RSD was 3.10%～12.55%.The limits of quantification (LOQs) were 0.5 μg/kg and 0.1 μg/kg, respectively. The correlation coefficient of metalaxyl and difenoconazole were 0.9951 and 0.9993, respectively(0.01～1mg/L). The method could satisfy the analysis.2. The effects of washing solutions such as tap water and detergent, NaCl, NaHCO3 and acetic acid solutions on the elimination of metalaxyl and difenoconazole in pakchoi from laboratory were investigated. The results indicated that the various solutions displayed different removal efficiency. In general, the removal efficiency was in order:detergent solution>NaCl solution>NaHCO3 solution> tap water>acetic acid solution. Taking the detergent residue into account,1% NaCl solution was selected as the better cleaning conditions. The removal efficiency of metalaxyl and difenoconazole was 65.88% and 84.88%, respectively under the optimum condition(1% NaCl solution for cleaning 20 min).3. The pakchoi from both greenhouse and laboratory were cleaned under the optimal washing conditions and then discussed the removal efficiency of the microwave, blanching and frying for the metalaxyl and difenoconazole. Processing factors were calculated and compared. Meanwhile, the processing factors of the pakchoi from greenhouse and laboratory were investigated. The results indicated that the removal efficiency of the metalaxyl and difenoconazole under cooking was in order:blanching> frying>microwave. The best cooking conditions is washing under 1% NaCl solution for cleaning 20 min and then blanching for 5 min. Comparing the processing factors of the pakchoi from greenhouse and laboratory, the results show that there was a certain gap between greenhouse and laboratory samples for metalaxyl under microwave, blanching and frying and for difenoconazole under microwave.4. Without processing the acute risk value(%ARfD) and chronic risk value {%CRJD) of metalaxyl in pakchoi were 7.01～15.46 and 42.70～94.16, respectively.The Values all lower than 100, belonging to the safe level; While the % ARfD and% CRfD of difenoconazole in pakchoi were 8.43～18.60 and 252.94～557.92. Displaying that chronic risk value belonging the dangerous level.5.After the process including washing and cooking, the %ARfD and %CRfD of metalaxyl were 0.3960～6.616 and 2.413～40.30, respectively.The values were significantly lower than that without processing. After washing, the cooking modes in reducing the dietary intake risk was in order to:blanching> frying>microwave; The %ARfD and %CRfD of difenoconazole after blanching and frying were 1.138-3.236 and 34.15～97.08, respectively, which were lower than that without processing. Especially the %CRfD was lower than 100,which reduced to the safe level. The %ARfD and %CRfD of difenoconazole after microwave were 2.220-4.897 and 67.60～146.90, respectively. The %CRfD was higher than 100, which still belong to the dangerous level. Processing could reduce the dietary intake risk of metalaxyl and difenoconazole in pakchoi.