Residue Characteristics And Dietary Risk Assessment Of The Main Fungicides In Tomatos

A method of multi-residues detection of pyraclostrobin, azoxystrobin, difenoconazole, dimethomorph, mancozeb, mancozeb and propineb in tomatos were established, and field trials were conducted in accordance with good agricultural practice (GAP) to explore their residue degradations under the agriculture climate and cropping system of Guangxi, in my area, and to assess the dietary risk. The main results obtained are as follows:1. A modified QuEChERS method combined with GC-ECD to determine the multi-residues of pyraclostrobin, difenoconazole, dimethomorph and azoxystrobin, a method of GC-FPD (with S filter) to indirectly determine the total residues of maneb, mancozeb and propineb, and a modified QuEChERS method by HPLC-UV to simultaneously determine ethylenethiourea (ETU) and propylenethiourea (PTU) were established. The separation effect of each target peak was good, with the linearity range of 0.01-5mg/L, and the limit of detection (LOD) were 0.003-0.038ng and the limit of quantification (LOQ) were 0.01-0.05mg/kg. And the average recovery ranges of tomato and cherry tomato were 70.5-120.0% and 70.8-119.8% with the relative standard deviations (RSD) between 2.2-6.3% and 3.1-7.1%, respectively. The three methods have high sensitivity, accuracy and precision to meet the requirements for pesticide residue analysis.2. The field trials of seven pesticides (pyraclostrobin ect) in taomatos were conducted. The dissipation dynamics of pyraclostrobin, difenoconazole, dimethomorph, azoxystrobin and 3 kinds DTCs in tomato and cherry tomato accorded with the first-order kinetics equation, and the half-lives was 12.7-17.8d and 10.8-11.8d,7.6-7.9d and 6.7-7.0d,6.6-6.9d and 5.4-5.5d, 6.3-6.6d and 5.9-6.2d,5.2d and 4.3-4.5d respectively. The final residues of the 5 kinds fungicides and ETU in tomato were negatively correlated with harvest time, and the amount of PTU were undetected. The residues of pyraclostrobin, dimethomorph, azoxystrobin and 3 kinds DTCs in cherry tomato were higher than tomato, while difenoconazole and ETU lower. However, some kinds of pesticide residues could be removed by washed, the removal rate of the 5 kinds fungicides, ETU and PTU in tomato were 4.9-100.0%, inferring that pyraclostrobin with larger internal absorption activity, and difenoconazole, dimethomorph and azoxystrobin with smaller internal absorption, but DTCs with no such property.3. The market monitoring of pyraclostrobin, difenoconazole, dimethomorph, azoxystrobin, 3 kinds DTCs and ETU, PTU in tomatos were conducted, with the detection rates between 16.7-83.3%, the concentration of 0.01-0.392mg/kg, and ETU and PTU were undetected. The residues of pyraclostrobin, dimethomorph and azoxystrobin in cherry tomato were higher than tomato, while difenoconazole and DTCs lower.4. The dietary risk assessment of the results of field trials and market monitoring were conducted. The acute risk of pyraclostrobin, difenoconazole, dimethomorph and ETU residues in tomatos to human body could be neglected; the chronic risk of pyraclostrobin, difenoconazole, dimethomorph, DTCs and ETU in tomatos under the corresponding PHI, and of pyraclostrobin, difenoconazole, dimethomorph and DTCs in saled tomatos were in a acceptable range.