Study On Residue Behaviors Of Typical Pesticides In Six Leafy Green Vegetables And Representative Commodities

Ilegal usage, incorrect usage of pesticides, pesticides application out of the label, and the lack of maximum residue limits are the core issues of agricultural products and food safety. Crops are classified and grouped accourding to their morphology and residue characteristics, representative commodities are chosen based on their commercial importance and the similarity of their morphology and residue characteristics to other related commodities in the group or suboup. Supervised field residue trials of representative commodities will be conducted according to good agriculture production, and the residues datas could be used in the residue extrapolation, which is a scientific and effective solution to resolve relative problems such as lack of pesticide registration on minor crop and the absence of maximum residue limits.In this study, a multi-residue method was built to determine of thiophanate-methyl, carbendazim, metalaxyl, fluazifop-P-butyl, azoxystrobin, buprofezin, methidathion, thiamethoxam, procymidone, chlorpyrifos, lambda-cyhalothrin, beta-cypermethrin in pakchoi, rape, crown daisy, amaranth, spinach, lettuce and celery. A quick, easy, cheap, effective, rugged and safe (QuEChERS) method was used in*sample preparation, thiophanate-methyl, carbendazim, metalaxyl, fluazifop-P-butyl, azoxystrobin, buprofezin, methidathion, thiamethoxam and procymidone were detected by liquid chromatography tandem mass spectrometry (LC-MS/MS), chlorpyrifos, lambda-cyhalothrin and beta-cypermethrin were determined by gas chromatography with electron capture detector (GC-ECD). The limits of quantification (LOQ) in all leafy vegetables were in the range of0.001-0.08mg/kg for all analytes and the average recoveries of all pesticides ranged from60.1%to118.6%. Good linearity was found for all pesticides with cofficients between0.991and1.00in a range of0.001-10.0mg/kg. The developed method was successfully used to determine the12pesticide residues in seven leafy vegetables.To select representative commodities in leafy green vegetables and for adorption in establishment of maximum residue limits of pesticides, supervised field residue trails of thiophanate-methyl, fluazifop-P-butyl, metalaxyl, chlorpyrifos and lambda-cyhalothrin on six leafy green vegetables including pakchoi, rape, crown daisy, amaranth, spinach and lettuce were designed and conducted in three places. It was found that almost all initial concentrations and maximal concentrations of pesticides in spinach and/or amaranth were higher than others with the same application dose, and the final residues for most pesticides in shinach and/or amaranth at the same preharvest interval (PHI) were higher. Spinach and/or amaranth were selected as representative crop in leafy green vegetables. In order to verify the accuracy of representative commodities selected, supervised field residue trials of azoxystrobin, fluazifop-P-butyl, buprofezin, methidathion, thiamethoxam, procymidone, beta-cypermethrin in the six leaf vegetables were conducted in three places. Initial concentrations, maximal concentrations and final residues were also used to compare. In addition to the part of higher final residues in crown daisy, the other results were consistent. In consideration of residue dynamics, initial concentrations and final residues, spinach and/or amaranth were recommended to select as representative commodities in leafy green vegetables. To investigate the influence of different planting seasons on the dissipation of pesticides, supervised field residue trails of thiophanate-methyl, metalaxyl, fluazifop-P-butyl, chlorpyrifos and lambda-cyhalothrin on six leafy green vegetables including pakchoi, rape, crown daisy, amaranth, spinach and lettuce were designed and conducted at two planting seasons (summer:between May and July; autumn:between August and October) in three places. The results showed that initial concentrations and maximal concentrations of most pesticides in six leafy green vegetables at autumn were higher that at summer. More than85%samples contained more pesticide residues at autumn at the same PHI in Shijiazhuang, and almost all samples had higher concentrations of pesticides at autumn at same PHI in Beijing. In order to verify the conclusion above, supervised field residue trails of azoxystrobin, fluazifop-P-butyl, buprofezin, methidathion, thiamethoxam, procymidone, beta-cypermethrin in the six leafy green vegetables were conducted at two planting seasons in Shijiazhuang, Beijing and Nanjing. For most pesticides, the initial concentrations and maximal concentrations at autumn were higher than that at summer with the same spray dose More than70%samples contained more pesticide residues at autumn at the same PHI. Analysis variance results showed that initial concentrations and half-lives of pesticides were influced by different planting seasons in a larger degree than the final residues.In order to investigate the effect of different spraying times on pesticide residues, supervised field residue trails of azoxystrobin, fluazifop-P-butyl, buprofezin, methidathion, thiamethoxam, procymidone, beta-cypermethrin in celery were conducted at two planting seasons. The experiments were designed for spraying one time and two times. Initial concentrantions, maximal concentrations and final concentrations of pesticides were considered in data analysis. The results of the experiments showed that half-lives of about64%pesticides were longer when sprayed two times (spraying pesticide interval was7days) than that sprayed one time at summer, and half-lives of about50%pesticides were longer when sprayed two times at autumn. The initial concentrations of azoxystrobin, buprofezin, methidathion, thiamethoxam, beta-cypermethrin in celery when spraying two times were higher than that when spraying one time at summer in Shijiazhuang, the initial concentrations of the seven pesticides when spraying two times were higher than that spraying one time at autumn, and the increase was higher at autumn especially to azoxystrobin and beta-cypermethrin. The results of Beijing were consistent with that of Shijiazhuang, initial concentrations of pesticides when spraying two times were higher than that when spraying one time in Beijing in addition to the azoxystrobin at summer. Approximately60%samples contained more pesticide residues when spraying two times at summer, while more than90%samples had higher concentrations of pesticides when spraying two times at autumn. There were no significant differences in initial concentrations, half-lives and final residues in celery with different spraying times.The dietary risk assessment of pesticides in six leafy green vegetables was conducted. The chronic assessment results of five pestides (carbendazim etc.) demonstrated that chronic dietary risk of spinach and amaranth (or leaf lettuce) was much higher; and the chronic assessment results of seven pesticides (azoxystrobin etc.) indicated that chronic dietary risk of spinach and amaranth (or crown daisy) was much higher. The acute assessment results of five pestides (carbendazim etc.) showed that acute dietary risk of spinach and/or amaranth was higher; and acute assessment results of seven pesticides (azoxystrobin etc.) presented that the acute dietary risk of spinach and/or amaranth was higher. Risk assessment is a comprehensive indicator in that it reflects the field experiment results and the dietary intake at same time. Spinach and/or amaranth could be recommended to select as representative commodities in according to the risk assessment results.