CPES-WA had been frozen at –20°C since 2004 before they were analyzed in 2007/2008. Although we anticipate some degradation of pesticides in certain food samples that undoubtedly would underestimate the true pesticide residues, it is difficult to quantify the magnitude. Fourth, the data reported here are limited by the small number of food samples that we collected from a total of 46 children on 5 different days across two seasons, and cannot be generalized to the overall popula- tion of children. Finally, although the collec- tion of 24-hr duplicate food samples has been a common research method used to provide surrogate measurements of dietary pesticide exposure (Bradman et al. 2007; Fenske et al. 2002; MacIntosh et al. 2001; Melnyk et al. 1997), it is not known whether the 24-hr duplicate food samples provide valid estimates of the true levels of pesticide residues in foods actually consumed by children. Overall, the levels of pesticide residues detected in the CPES food samples were simi- lar to levels reported by the PDP; however, two CPES food samples and one MBA item exceeded reported PDP levels. These two CPES food samples probably represented a large single exposure for each child. The fact that two CPES children had a single exposure exceeding the PDP reported data highlights both the challenge in monitoring and man- aging dietary pesticide risks and the need to improve the PDP approach to more accurately capture real-world exposures. In fact, our com- parison with the PDP data set was limited by the commodities that the PDP included in their reports. In both CPES study years, the PDP data analyzed only approximately one- third of the foods consumed by the CPES children. Although the PDP is the most com- prehensive data set representing pesticide food residues in the United States, it does not test all foods, particularly foods that are commonly consumed by children, despite its increased focus on children’s foods in response to the FQPA. Furthermore, many commonly consumed foods are not tested every year by the PDP. These limitations threaten the suc- cess of conducting representative dietary pes- ticide exposure, risk assessments in infants and children (as mandated by FQPA), and trend analysis of dietary exposure risks. The PDP database provides a basis for esti- mating pesticide dietary exposures and risks when combined with food consumption infor- mation and information on the toxicological potency of individual pesticides. This prac- tice has been adapted by the Environmental Working Group (EWG) in their annual Shopper’s Guide to Pesticides reports (EWG 2009), in which commonly consumed fruits and vegetables, surveyed by the Total Diet Study, are ranked based on the pesticide resi- due data published by the PDP. As stated by EWG, the philosophy behind the Shopper’s Guide is to “give consumers the information they need to make choices in order to reduce pesticides in their diets.” Instead of conducting complex dietary pesticide risk assessments, the Shopper’s Guide provides a qualitative com- parison on the overall load of pesticides found on commonly eaten fruits and vegetables. We found that 5 and 6 of the top 12 most consumed food commodities by CPES-WA (apple, peach, grape, carrots, and lettuce) and by CPES-GA children (strawberries, apple, pear, carrots, spinach, and peach), respectively, are among the top 12 most contaminated food items ranked by the Shopper’s Guide’s published in 2009. In fact, all of the top 12 most contaminated food items listed in the Shopper’s Guide’s were consumed at different frequencies by the CPES children. Because some of the high-pesticide-risk commodities, such as peaches, grapes, and pears, are usually not available to the consumers year round, sea- sonal variations in dietary pesticide exposures and risks may not be captured by risk assessors if seasonality is not taken into account when defining common dietary consumption pat- terns. We found support for this hypothesis in a recent study in which we found that CPES Table 6. MBA of OP and pyrethroid insecticide residues in fresh produce and fruit juice items commonly consumed by the CPES-WA children. Pesticide residue (ng/g) Study season Summer 2003 Fall 2003 Food content Cherriesa Honeydew melon Grapea Nectarinea Strawberriesa Lemonade Strawberriesa Orange Strawberriesa Peacha Grapea OP Methamidophos (3) Methamidophos (1) Chlorpyrifos (1) Methamidophos (2) Chlorpyrifos (363) Methamidophos (trace) Ethion (1) Chlorpyrifos (3) Methamidophos (12) Chlorpyrifos (22) All the food samples were purchased in Washington State between 2003 and 2004. aOne of the 12 most pesticide-contaminated food items surveyed in 2008–2009 (EWG 2009). Environmental Health Perspectives • volume 118 | number 11 | November 2010 Pyrethroid Esfenvalerate (71) Bifenthrin (93) Pesticide residues in children’s diets children consumed more seasonal food com- modities, such as apples, peaches, nectarines, melon, grapes, pears, and strawberries, than did NHANES children in the same age range (Riederer et al. 2009). For food without sea- sonality, such as cow’s milk, apple juice, and orange juice, consumption differences were not apparent. Our comparisons illustrated how food consumption data collected in a cross-sectional manner, such as those of the NHANES, may not adequately capture sea- sonal variability in children’s dietary habits, and those measurement errors will no doubt be carried forward to the risk assessment steps. Among the 44 duplicate food samples con- taining detectable pesticide residues, we found 11 OP and 3 pyrethroid insecticides, and 16 of these duplicate food samples (7%) contained more than one pesticide (OP or pyrethroids). Among the food samples with detectable pes- ticide residues, we found much higher levels of pyrethroid insecticides than OP pesticides. This finding is consistent with the tolerances for pyrethroid insecticides that are generally higher than for OP insecticides, and with the residues reported by PDP (Table 5). In addi- tion, the higher pyrethroid insecticide residues may have resulted from excessive use of pyre- throid insecticides in the field to battle insect resistance problems. OP pesticide residues were detected more often in the CPES-WA food samples, whereas pyrethroid pesticides were detected more often in the CPES-GA food samples. The possible explanations for this finding may stem from contamination of foods resulting from residential use (Melnyk et al. 2009) of pyrethroid insecticides in the South/ Southeast region, regional differences in agri- cultural practices, or changes in pesticide use over time. If this pattern holds true, it suggests that it is necessary to conduct dietary pesticide exposure and risk assessments based on geo- graphic location. In addition to the seasonal nature of food consumption patterns among CPES children as reported in our recent study (Riederer et al. 2009), the findings of multiple pesticide residues in single food commodities and the geographical differences in the type of pesticides further demonstrate the complexity of conducting overall dietary pesticide exposure and risk assessments. Although the pesticide residue levels meas- ured in CPES were all below U.S. EPA tol- erance levels (U.S. EPA 2010), it should be acknowledged that tolerances were established at on a per chemical per crop basis in order to ensure the best practice of pesticide uses in the field. Also, tolerance levels are intended for monitoring residues in raw produce at the farm gate, before washing, shipping, storage, marketing, and food preparation (Olden and Guthrie 2000). Furthermore, those toler- ance levels do not consider exposure to mul- tiple pesticides with common mechanisms of 1629