Residues behavior and dietary exposure risk assessment of tebuconazole and pyraclostrobin in apple

Abstract:【Objective】The residue and degradation dynamics of tebuconazole and pyraclostrobin in apple were studied at twelve sites in one year. And the dietary exposure risk assessment concerning two compounds were estimated.【Methods】QuEChERS-HPLC-MS/MS method was established to detect te-buconazole and pyraclostrobin in apple fruits. The purification of sample was adjusted to the proportion of purifying agent. Samples were extracted by acetonitrile (Compared with methanol, acetonitrile was more efficient and safer as extraction solvent), and purified by a traditional purifying agent (20 mg graphitized carbon black (GCB)+40 mg primary secondary amine (PSA) and 150 mg anhydrous magnesium sulfate). Both compounds were optimized for separating under conditions of chromatography and mass spectrometry. The national estimated daily intake (NEDI) and risk index (RI) of six typical popula-tions were calculated【Results】The method established in this study greatly decreased the sample pre-treatment time and the separation efficiency of the two pesticides, the operation was practical, the peak shape was symmetrical, the response value was high and the reproducibility was perfect. In order to achieve efficient purification effect, PSA, PSA + GCB and multi-walled carbon nanotubes (MWCNTs) were investigated in the process of screening out different proportions of purification agents. The amount of purification agent was optimized for obtaining higher recovery. The extraction and purifica-tion of apple samples from different regions and varieties could achieve good purification effect.Through addition and recovery test, under three levels of addition (0.005, 0.5 and 2 mg·kg^-1), the aver-age inter-day recovery of tebuconazole in apple matrix was between 87% and 101%, the relative stan-dard deviation (RSDs) (n=5) was between 0.6% and 7.9%, the intra-day average recovery was 91%-100%, RSDs (n=15) were 1.0%-6.6%; the inter-day average recovery of pyraclostrobin in apple matrix was 87%-103%, RSDs (n=5) were 1.3%-7.0%, the average recovery was 93%-101% and RSDs (n=15) were less than 6.7%. Compared with other methods, the analytical method established in this study had higher recovery rate and versatility. In practical application group, it could realize rapid detection for a large number of samples from different regions. Moreover, the limit of quantitation about tebuconazoleand pyraclostrobin in apple matrix was 0.005 mg·kg^-1, which could be used to detect the distribution of two pesticides at low residue level. In this study, the effects of climate conditions and varieties were comprehensively considered. The results of degradation dynamics showed that the half-life period of the two fungicides in apple were faster (In the digestion test plots, the half-life periods of tebuconazole and pyraclostrobin were 9.4-21.7 d and 10.3-23.8 d, respectively), which were easily degradable pesti-cides (T1/2 < 30 d). The half-life periods of tebuconazole and pyraclostrobin in apple matrix were influ-enced by the climate conditions. At the same time, the adhesion of different varieties on apple directly affected the original deposition amount of pesticides, which was one of the important factors affecting pesticide residue behavior. The results of final residue test showed that the residues of tebuconazole and pyrazoxystrobin in apple were 0.010-0.191 mg·kg^-1 and 0.005-0.115 mg·kg^-1, respectively, 28 d and 35d after the last application, which were lower than the maximum residue limits of two pesticides in ap-ple. In addition, according to the final residue data from 12 places in one year, the dietary exposure risk of tebuconazole and pyraclostrobin in fresh apple fruits were calculated. The results showed that the di-etary exposure risk index of tebuconazole and pyraclostrobin in fresh apple fruits were less than 100%, and the dietary exposure risk was at an acceptable level. In this study, 12 experimental sites were select-ed, including main production areas in China. The varieties were local dominant varieties, and the re-sults were more realistic and universal.【Conclusion】QuEChERS-HPLC-MS/MS method can be used to detect tebuconazole and pyraclostrobin rapidly at the same time. It had prospects applied in the con-trol of raw materials of fresh and processed apples, pesticide residue detection of intermediate process-ing bodies, spot check of market food quality and national quarantine of imported and exported food. The results showed that the dietary exposure risk of fresh apple was acceptable in six different popula-tion, but age and gender had little effect on the overall exposure risk. In different age groups, the dietary exposure risk of 2-4-year-old children was significantly higher than that of additonal two groups, which was 3.3-5.6 times and 4.5-5.6 times of the other two groups, respectively. Therefore, in the future food risk assessment, we should take good care of individuals, such as children, women and pregnant wom-en. This study focused on the detection of residues in primary agricultural products, not the processing food. Cleaning, peeling, condensing, sterilization, fermentation and other processes involved in the pro-cessing of apple products could be used as the influencing factors of food residues. Therefore, if the pro-cessing factors were considered before the assessment of pesticide dietary exposure, more accurate risk assessment would be obtained. The results of this study had reference significance for guiding 40% pyraclostrobin · tebuconazole SC to determine the reasonable safety interval, and was important for the safety of fungicide application and dietary intake evaluation.