Tables 3 and 4 show distribution percen- tiles of concentrations of cis- and trans-DCCA, which were highly correlated with each other (r = 0.887; p < 0.001) and with 3PBA (r = 0.766; p = 0.02). However, the ratio of the cis- and trans-isomers of DCCA varied. 4F3PBA was detected in 3.2% and 0.6% of the urine samples analyzed in 1999–2000 and 2001–2002, respectively. Similarly, cis-DBCA was detected in 1.3% and 0.5% of the urine samples analyzed in 1999–2000 and 2001–2002, respectively. Both 4F3PBA and cis-DBCA were detected in too few of the samples tested to allow a reliable estima- tion of their distribution percentiles and GM concentrations. Discussion Although pyrethroid insecticides have largely replaced organophosphorus and carbam- ate insecticides as the most commonly used household insecticides, these are the first Table 4. Urinary concentrations of trans-DCCA in the general U.S. population, NHANES 1999–2002. Selected percentile (95% confidence interval) 75th 90th 95th Weighted detection (%) Category/survey years Total 1999–2000a 2001–2002a 1999–2000b 2001–2002b Age group 6–11 years 1999–2000a 2001–2002a 1999–2000b 2001–2002b 12–19 years 1999–2000a 2001–2002a 1999–2000b 2001–2002b 20–59 years 1999–2000a 2001–2002a 1999–2000b 2001–2002b ≥ 60 years 2001–2002a 2001–2002a Sex Male 1999–2000a 2001–2002a 1999–2000b 2001–2002b Female 1999–2000a 2001–2002a 1999–2000b 2001–2002b Race/ethnicity Non-Hispanic white 1999–2000a 2001–2002a 1999–2000b 2001–2002b Mexican American 1999–2000a 2001–2002a 1999–2000b 2001–2002b Non-Hispanic black 1999–2000a 2001–2002a 1999–2000b 0.56 (0.48–0.70) 0.43 (< LOD–0.56) 0.70 (0.61–0.78) 0.74 (< LOD–0.80) 0.97 (0.70–10.66) 0.47 (< LOD–0.76) 0.90 (0.64–1.39) 0.77 (< LOD–0.97) 0.71 (0.52–0.86) 0.49 (< LOD–0.67) 0.47 (0.38–0.55) 0.47 (< LOD–0.58) 0.50 (0.40–0.62) < LOD 0.74 (0.67–1.00) < LOD 0.46 (< LOD–0.63) 0.86 (< LOD–0.97) 0.56 (0.50–0.67) 0.42 (< LOD–0.50) 0.57 (0.50–0.67) 0.57 (< LOD–0.61) 0.55 (0.41–0.82) 0.44 (< LOD–0.63) 0.88 (0.72–1.11) 0.85 (< LOD–0.95) 0.56 (0.46–0.73) 0.41 (< LOD–0.58) 1.00 (0.76–1.12) 0.88 (< LOD–0.99) 0.47 (0.41–0.53) 0.41 (< LOD–0.51) 0.52 (0.44–0.64) 0.59 (< LOD–0.67) 0.78 (0.49–1.13) 0.59 (0.49–0.74) 0.50 (0.41–0.68) 1.40 (1.17–1.77) 1.18 (0.93–1.64) 1.56 (1.33–1.87) 1.47 (1.32–1.87) 2.91 (1.76–4.19) 1.39 (1.03–1.68) 1.85 (1.17–3.77) 1.40 (1.12–2.16) 2.07 (1.25–3.42) 1.20 (0.80–1.60) 1.02 (0.70–1.42) 0.85 (0.71–1.07) 1.17 (0.91–1.68) 1.17 (0.85–1.85) 1.75 (1.29–2.26) 1.87 (1.37–2.33) 1.13 (0.76–2.44) 1.92 (1.30–2.71) 1.28 (1.11–1.63) 1.12 (0.86–1.58) 1.23 (1.05–1.35) 1.22 (1.00–1.45) 1.77 (1.07–3.08) 1.23 (0.91–1.98) 1.87 (1.47–2.37) 1.75 (1.47–2.15) 1.41 (1.14–2.14) 1.18 (0.85–1.85) 2.15 (1.65–2.74) 2.14 (1.57–2.33) 1.23 (0.83–1.60) 0.86 (0.68–1.14) 1.01 (0.80–1.17) 1.04 (0.90–1.17) 1.84 (1.08–4.69) 1.26 (1.05–1.70) 1.08 (0.76–2.15) 3.42 (2.39–5.56) 2.60 (1.85–3.58) 2.65 (2.15–3.89) 2.62 (2.30–3.11) 4.19 (2.97–11.7) 2.50 (1.55–3.54) 3.67 (1.55–9.49) 2.55 (1.50–3.11) 4.28 (2.12–6.23) 2.01 (1.49–3.77) 1.56 (0.96–4.02) 1.29 (1.00–1.63) 2.94 (1.49–5.56) 2.56 (1.64–4.66) 3.13 (2.22–4.48) 2.89 (2.34–3.50) 4.27 (1.20–6.49) 3.31 (2.03–5.33) 2.25 (1.55–5.10) 2.44 (1.69–3.70) 2.15 (1.53–2.74) 2.33 (1.68–2.73) 4.19 (3.08–6.81) 2.62 (1.90–3.58) 3.65 (2.26–5.94) 2.98 (2.55–3.20) 3.89 (2.14–6.43) 2.64 (1.85–4.27) 4.48 (2.64–6.29) 3.16 (2.63–3.50) 1.87 (1.49–3.35) 1.57 (1.08–2.01) 1.47 (1.17–1.69) 1.40 (1.17–1.87) 4.69 (1.41–14.5) 2.25 (1.54–3.32) 2.15 (1.16–3.96) Sample size (n) 1,976 3,033 1,976 3,031 478 576 478 576 675 826 675 825 823 1,123 823 1,123 508 507 961 1,419 961 1,419 1,015 1,614 1,015 1,612 595 1,278 595 1,277 691 767 691 767 518 764 518 33.1 26.4 33.1 26.4 42 28.8 42 28.8 39.2 31.3 39.2 31.3 30.4 24.7 30.4 24.7 27.9 27.9 33.7 26.1 33.7 26.1 32.6 26.7 32.6 26.7 32.7 25.5 32.7 25.5 30.2 25.8 30.2 25.8 41 36.7 41 Pyrethroid metabolites in the U.S. population population-based data reported for the general U.S. population. Because these pesticides are relatively nonvolatile, the primary source of exposure is believed to be through diet, with perhaps short episodes of exposure from resi- dential use of insect control products. Children had higher concentrations of pyrethroid insec- ticide metabolites than did adolescents and adults. These results are consistent with many other pesticide-related exposures and probably reflect differences in diet and behaviors (e.g., hand-to-mouth behaviors). Non-Hispanic blacks had higher concentrations than did the other race/ethnicity groups. This observation could potentially be an indicator of socioeco- nomic or housing status. Older homes and lower income households are likely to have more pests, requiring use of more household pesticides. Dietary differences could also account for the higher levels of pyrethroid pesticide metabolites. Concentrations of pyrethroid metabolites tended to be higher during the morning col- lection periods than during the afternoon or evening collection periods. We cannot plau- sibly explain this observation; however, this may underscore the need to have consistent collection times in future studies. The high correlation between 3PBA and cis- and trans-DCCA suggests that the parent pesticides resulting in U.S. population expo- sures were predominantly permethrin or cyper- methrin, which is consistent with U.S. pesticide use data. The low frequency of detection of 4F3PBA and cis-DBCA suggests that exposure to cyfluthrin and deltamethrin is infrequent. Interestingly, the ratio of trans-DCCA and cis-DCCA varied from 0.001 to > 5,800; however, the vast majority of our ratios ranged between 3 and 4. The ratio of trans- to cis- DCCA could vary based upon a variety of criteria, including product formulation, differ- ential metabolism, different half-lives in envi- ronmental media, different parent chemicals from which it was derived, exposure routes, and other factors. The only population-based data on these metabolites were generated in Germany during the last decade (Becker et al. 2006; Heudorf and Angerer 2001; Heudorf et al. 2006). Generally, the U.S. population-based data are consistent with those from the German stud- ies, where median values of 3PBA ranged from 0.04 ng/mL to 0.29 ng/mL, compared with our median levels of 0.25 ng/mL and 0.27 ng/mL for NHANES 1999–2000 and 2001– 2002, respectively. The frequencies of detection were relatively similar for cis- and trans-DCCA concentrations in the German studies and in our study of the U.S. population. 4F3PBA and cis-DBCA were detected more frequently in the German studies than in our U.S. study but were detected much less frequently than the other metabolites, similar to our data. 747 < LOD indicates less than the limit of detection for the uncorrected urine values, which may vary for some chemicals by year. The 50th percentile measures were all < LOD and are not shown here. GMs were not calculated (proportion of results below limit of detection was too high to provide any valid results). n-Values may differ if some information was missing for a particular subgroup. aVolume-based concentrations (ng/mL). bCreatinine-adjusted concentrations (μg/g creatinine). Environmental Health Perspectives • volume 118 | number 6 | June 2010