To estimate variations in pesticide residue levels in crops, the variability factors (VFs, the 97.5th percentile of the residue levels in the sample divided by the average residue levels in the lot) in residue levels of acetamiprid and cypermethrin applied to cabbage and grapes were investigated, respectively. The VFs in the residue levels of both pesticides in cabbage (2.00 and 2.39, respectively) were clearly higher than those in grapes (1.82 and 1.63, respectively). Although the residue levels of both pesticides in grapes showed a normal distribution, those values in cabbage were slightly skewed at lower residue levels. Individual residue levels in grapes had a good agreement between acetamiprid and cypermethrin. In contrast, the distribution of cypermethrin residue levels in cabbage was slightly skewed at higher residue levels as compared to that of acetamiprid. These results indicate that the difference in the relative distribution of the two pesticides between cabbage and grapes might be due to the influence of various factors such as differences in crop species, plant cultivation methods, and physicochemical properties of the pesticides.
Cypermethrin residues in apples were evaluated to consider individual variations from sample-to-sample, eld-toeld, and edible-to-inedible portions. e VF (variability factor) values obtained from the 97.5th percentile and the mean pesticide residue levels of 130 individual apple samples were 1.76 and 1.75, respectively, and the highest residue level was approximately 10 times the lowest one. e results suggest that, in order to obtain reliable values of pesticide residue levels, a su cient number of samples is essential. Regarding eld-to-eld variability, the highest mean residue level from 8 orchards was approximately 2.3 times that of the lowest. e pesticide residue level determined for an entire fruit was slightly higher than that for the edible portions, and there was no signi cant statistical di erence between the two.
The uncertainty in pesticide residue levels (UPRL) associated with sampling size was estimated using individual acetamiprid and cypermethrin residue data from preharvested apple, broccoli, cabbage, grape, and sweet pepper samples. The relative standard deviation from the mean of each sampling size (n = 2 x , where x = 1–6) of randomly selected samples was defined as the UPRL for each sampling size. The estimated UPRLs, which were calculated on the basis of the regulatory sampling size recommended by the OECD Guidelines on Crop Field Trials (weights from 1 to 5 kg, and commodity unit numbers from 12 to 24), ranged from 2.1% for cypermethrin in sweet peppers to 14.6% for cypermethrin in cabbage samples. The percentages of commodity exceeding the maximum residue limits (MRLs) specified by the Japanese Food Sanitation Law may be predicted from the equation derived from this study, which was based on samples of various size ranges with mean residue levels below the MRL. The estimated UPRLs have confirmed that sufficient sampling weight and numbers are required for analysis and/or re-examination of subsamples to provide accurate values of pesticide residue levels for the enforcement of MRLs. The equation derived from the present study would aid the estimation of more accurate residue levels even from small sampling sizes.
To evaluate the influence of growing conditions on the pesticide residue in lettuce heads, we investigated the residue levels in open field and greenhouse conditions. A clear difference between the two growing conditions was observed for dinotefuran applied to the planting hole; the residue levels in the lettuce heads from the greenhouses were almost as high as those in the field samples. In contrast, no clear difference between the two growing conditions was observed for the other three pesticides applied to the foliage. The size reduction process for sample preparation also affected the variation in this residue data; the ranges between two size-reduced samples of dinotefuran were narrower than the values of the other three pesticides. Those results are part of the complex factors affecting the pesticide residue levels in lettuce heads in different growing conditions and with different types of application.
To find the effect of field-to-field variation in pesticide residue levels in Chinese cabbage and spinach, two residue datasets each were obtained from eight test fields in different years. Based on the obtained sixteen field datasets, the highest residue levels of five pesticides in Chinese cabbage and of three pesticides in spinach were 10.5 and 5.7 times higher than the lowest residue levels, respectively. The correlation of the pesticide residue levels in spinach samples between the data obtained in different years from the same six greenhouses was in good agreement (R 2 =0.8138). In contrast, there was no clear correlation between the pesticide residue levels in Chinese cabbage samples, which were grown in open fields. This different tendency observed in the residue data may be because of the difference in growing conditions. In addition, each datum of the pesticide residue was negatively correlated with the sample weight.
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