[Separate Analysis of Loquat Fruit Pulp, Peel, and Pits to Calculate Pesticide Residue Levels in the Whole Commodity].

To evaluate the effects of handling "not detectable" residues (ND: <0.01 mg/kg) in the pulp and detectable residues in the pits on the calculation of pesticide residue in the whole fruit, residue levels in the pulp, peel, and pits of loquat fruits were separately analyzed. Following conventional Japanese agricultural practices, 16 pesticides were sprayed at the maximum application rates in three test fields. All target pesticides were detected at quantifiable levels in the peel (n=144). In contrast, the percentages of detected pesticides in the pulp and pits were 42% (n=61) and 36% (n=52), respectively. Most pesticide residues were present in the peel. For comparison, the pesticide residue levels in the whole fruits were determined based on three indices: the highest estimate (H), calculated using the measured residue levels in the pits and by replacing the ND residues in the pulp as the limit of quantification (LOQ) values; conventional estimate (C), calculated by neglecting all residues in the pits (0 mg/kg) and replacing the ND residues in the pulp as LOQ values; and the lowest estimate (L), calculated by neglecting all residues in the pits and the ND residues in the pulp (0 mg/kg). The L/C and H/C ratios ranged from 74% (L/C) to 106% (H/C). In seven of eighty-three cases with less than 90% difference, residue levels in the whole loquat fruits were low (≤0.06 mg/kg), with the actual range being equal to or below the minimum unit of 0.01. In comparison of three field datasets, the range of residue levels was estimated to be 2.77 mg/kg. Based on the results of separate analysis, handling of ND residues in the pulp and detectable residues in the pits did not significantly affect the calculated pesticide residue levels in the whole loquat fruits.

Influences of sample homogenization time and standing time before extraction on the determination of incurred pesticide residue levels in grapes.

To estimate the influence of sample processing with a blender, we conducted a homogeneity test using a bulk sample of pre-harvest grapes. Relative standard deviations (RSDs) were calculated from the concentrations of pesticides in the portions from the top, middle, and bottom of the homogenate with fine and rough particles. The results from adequate sample processing showed that the RSDs of the residue levels of all five pesticides in the fine-particle homogenate were lower than 10%. In contrast, the results under problematic conditions such as short blending times and long standing times after blending showed higher RSDs (>15%). The RSDs of nonpolar pesticides showed greater variabilities under the problematic conditions than those of polar pesticides. Separate analyses of the precipitate and supernatant phases suggested that the distribution bias of skin particles in the homogenate has a major effect on the concentration of nonpolar pesticides because of weighing errors in the extracted portions.

Influence of various parts of sweet corn ears on pesticide residue levels.

Pesticide residue levels in various parts of sweet corn ears were analyzed. For this purpose, five pesticides were sprayed on corn in two different fields, and the harvested samples were separated into four portions, namely kernels, cobs, silks, and husks. Each of these portions was then separately analyzed. Pesticide residues were predominantly distributed in the silk and husk portions, which constituted ≥91% of the whole crop, whereas relatively minimal residues remained in the kernel and cob portions. Further, residue distributions in the silks and husks were found to differ between the two fields. The calculated residue levels in kernels with the cob and silk were obviously higher than the residue levels in the kernel alone (max. >62 times different). This result suggests that the silk portion could greatly affect pesticide residue levels in the edible portion of corn.

Effect of sample preparation on the estimation of residue levels of sprayed pesticides in separate analyses of turnip roots and leaves: inclusion or exclusion of the root-shoot junction.

The effect of inclusion or exclusion of the root-shoot junction on the estimation of pesticide residue levels in turnip roots and leaves was investigated. Turnips grown at two experimental sites were sprayed with six pesticides. At residue analysis, the turnips were divided in three segments: roots (R), leaves (L), and root-shoot junctions (J). The highest pesticide residue amounts were found in leaves ≥93% of total, with minimal amounts in roots. Residue amounts in root-shoot junctions were intermediate between those of leaves and roots. Residue levels were calculated for the root plus root-shoot junction, and were higher than those in roots: (R+J)/R=1.0-9.0. In contrast, residue levels in the leaf plus root-shoot junction were lower than in leaves only: (L+J)/L=0.76-0.91. The results indicate that the position of the cut between root and leaves could greatly affect the estimated pesticide residue levels when roots and leaves are analyzed separately.

Effect of sampling size on the determination of accurate pesticide residue levels in Japanese agricultural commodities.

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.

Comparison of the variability in the levels of pesticide residue observed in Japanese cabbage and grape units.

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.