Study On Classification And Application Of Head Brassicas Vegetables Based On Residue Behaviors Of Typical Pesticides

Scientific regulation of pesticides requires a large amount of residue data, while limited resources could be used in supervised residue trials for each pesticide/crop combination, in which residue levels are investigated. Therefore, the situations that few pesticides are registered on minor crops and lack of Maximum Residue Limits (MRLs) are widely observed. It would be a useful way that pesticide registrations and MRLs setting could be carried out for crop group by utilizing the combined residue dataset of crop group or the representative commodity. In this thesis, residue behaviors of six pesticides on brassica vegetables were investigated. Commodity group was classified and different types of residue datasets of the Head Brassicas subgroup were evaluated in MRLs setting for the subgroup. Specified results are summarized as follows:A QuEChERS-LC-MS/MS and GC-ECD method for simultaneously analysis of thiophanate-mehtyl, carbendazim, metalaxyl, Fluazifop-P-butyl, chlorpyrifos and lambda-cyhalothim residues on five brassica vegetables (cabbage, red cabbage, kohlrabi, kale and brussels sprout) was developed and validated. At fortification levels of0.01,0.05and0.1mg/kg, it was shown that recoveries ranged from76.9%to117.4%with RSDs of3.7-10.8%(n=5) in all samples. The LOQs of six pesticides in five matrixes were all0.01mg/kg.Pesticide residues in cabbage at the application rates of both GAP and1.5*GAP were investigated. The result showed that a proportionality existed in residues from different application rates on condition that the residues were at measurable levels. Equation of linear regression of natural logarithms of residues was y=0.803x+0.4928, with a correlation coefficient of0.9346. The slope was close to1(theoretical value) and the calculated multiple from the concept (1.6) was close to1.5(theoretical value). Proportionality was obvious in chlorpyrifos and lambda-cyhalothim residues rather than thiophanate-methyl and metalaxyl residues, but linear relationships performed well in all residues. Results from field and storage were similar and it confirmed that environment did not affect the proportionality of residues in side-by-side trials. This result would be useful in utilizing residue data from different application rates of pesticides.Residue behaviors of six pesticides in five brassica vegetables were investigated. Half-lives of thiophanate-methyl, carbendazim, metalaxyl, chlorpyrifos, lambda-cyhalothrin and fluazifop-P-butyl in five brassica vegetables were0.9-6.1days,1.3-5.0days,0.9-6.9days,0.8-4.0days,1.4-6.2days and0.3-3.3days. Pesticides had the longest geo-mean half-life of2.1-3.5days in cabbage. Carbendazim and lambda-cyhalothim had the slowest dissipation in all five brassica vegetables. The lowest initial deposits of most pesticides were found on kohlrabi and the highest initial deposits were on kale or brussels sprouts.Commodity group was classified according to the results of comparison of residue data on different commodities and the morphology of five brassica vegetables. With the highest residue and different morphology, kale should not be classified into Head Brassicas subgroup. Cabbage, red cabbage and brussels sprouts could be classified into Head Brassicas as they had similar residue data and morphology. Though residues in kohlrabi were at low levels, it could be classified into Head Brassicas because it would not present health risk to customers. Therefore, an appropriate subgroup of Head Brassicas should include cabbage, red cabbage, kohlrabi and brussels sprouts. Cabbage should be selected as the representative commodity as it had the highest residues and largest production and consumption.Combined datasets of5pesticide residues in the subgroup of Head Brassicas were used in MRLs calculations with both NAFTA and OECD MRL calculators. The results of two calculators were similar. Acute and chronic risk assessments were carried out and the chronic and acute risk quotients were0-0.6%and0.4-54.1%, respectively. That both results were below100%indicated that no acute and chronic risk would be presented. Estimated MRLs based on the residue data of the representative commodity cabbage with residue extrapolation were evaluated by comparing to those from the residue datasets of the whole subgroup. The results showed that there were no difference between the two kinds of estimated MRLs of calculated carbendazim (sum of thiophanate-methyl and carbendaizm), metalaxyl, lambda-cyhalothirn and fluazifop-P-butyl based on datasets of representative commodity and the whole subgroup. Significant lower estimated MRL of chlorpyrifos was found in residue extrapolation based on the representative commodity:a MRL of0.06ing/kg compared to0.4mg/kg. This finding indicated that extra residue trials on crops within the commodity group should be carried out to comfirm the rational use when residue extrapolation was applied on pesticides like chlorpyrifos which might have high residue levels. While residue extrapolation in the other pesticides could be applied directly in the subgroup of Head brassicas.