Our study suggests that handwipes may be a better matrix for examining exposure to contaminants found in dust than collecting dust itself, at least for the pentaBDE conge- ners evaluated in this study. Handwipes are potentially a more proximal measure of expo- sure than dust and may reflect exposure in more than one microenvironment. Handwipe samples are easier to collect and are more cost and time efficient than collecting dust. In addition, the best methods for collecting dust as a measure of exposure is not known; use of a less than optimal method should tend to diminish associations (Allen et al. 2008a). It may be easier to standardize collection of handwipes than to standardize collection of house dust given differences in vacuum clean- ers used to collect dust, areas vacuumed, and differences in how dust is sieved and stored. Certainly standardized methods for collec- tion and analysis of handwipes are needed, as is information on temporal variability in PBDE residues measured on the hands, per- haps through follow-up studies. Our estimates suggest that pentaBDE body burdens increased with age in our cohort, by approximately 61%/year for ∑BDE3 and 73%/year for BDE-153. This might reflect both accumulation over time and/or increased hand-to-mouth activities with age. However, studies on children’s hand-to-mouth behav- ior are limited. Some data suggest that there are no differences in hand-to-mouth behavior over the age range of 1–4 years, whereas others have reported higher hand-to-mouth activity in children < 2 years of age compared with children 2–5 years of age (Black et al. 2005; Tulve et al. 2002). ∑BDE3 concentrations in the serum of toddlers were inversely associated with paren- tal education, after controlling for handwipe levels, child age, and sex (However, because race and SES are associated in our cohort, they are difficult to disentangle). Furthermore, we found no significant differences in PBDE dust concentrations by race or parental education (data not shown), suggesting that the exposure difference is not driven solely by higher lev- els of PBDEs in dust from homes with lower SES. Few predictors have been found for pentaBDE concentrations in dust. A previous study (Allen et al. 2008b) reported no correla- tion with counts of foam-containing furniture in Boston homes, but found a strong corre- lation when bromine concentrations (mea- sured by X-ray fluorescence) were taken into account. The apparent SES-related differences in body burden of ∑BDE3 may be attribut- able to a number of factors that we did not take into account, including, for example, diet and differences in exposure patterns within or outside the home. More research is needed to understand the role of SES and race in deter- mining exposure to ∑BDE3. In marked contrast, BDE-153 in the serum of toddlers was positively associated with SES. However, this may at least be partly medi- ated by duration of breast-feeding, which is in turn associated with mother’s education in our population. The fact that BDE-153, but not ∑BDE3, was significantly associated with months of breast-feeding, combined with the Table 3. Regression analysis of predictors of PBDE concentrations in serum. ∑BDE3 Univariate Adjusted Coefficienta (95% CI) 1.34 (0.76, 2.38) p-Value 0.31 Coefficienta (95% CI) 1.61 (0.99, 2.62) aExponentiated beta-coefficients represent the multiplicative change in the serum concentration relative to the reference group for categorical variables, or per unit change for continuous variables (age, breast-feeding duration, time away from home). Environmental Health Perspectives • volume 120 | number 7 | July 2012 1053 PBDE exposure in U.S. toddlers lower correlations observed between BDE-153 in serum, handwipes, and dust levels, sug- gests that the sources and routes of exposure may differ between BDE 153 and BDEs 47, 99, and 100. Although BDEs 47, 99, 100 are commonly found in breast milk (Schecter et al. 2003; Wu et al. 2007), we did not find an asso- ciation between serum ∑BDE3 and months of breast-feeding, suggesting that indoor exposure is more important for these congeners in tod- dlers. The difference may be attributable to a relative enrichment of BDE-153 to the other congeners in breast milk versus dust (we did not sample breast milk in our study). A com- parison of our PBDE dust data to the data collected by Schecter et al. (2010) on PBDEs in breast milk does suggest that BDE-153 is more enriched in breast milk compared with BDE-47 when normalized to pentaBDE. Alternatively, this may also be attributable to a longer half-life for BDE-153 compared to the other BDE congeners. The human half-life of pentaBDE congeners has been only crudely estimated, not directly measured (Geyer et al. 2004). Similar to PCB-153, BDE-153 has a halogenation substitution pattern that results in low metabolic potential (Lupton et al. 2009). Therefore, serum levels of BDE-153 may be more reflective of cumulative exposures from in utero, infancy (e.g., breast milk), and dust exposures, whereas ∑BDE3 serum levels are likely attributable to more recent dust and dietary exposures. Major strengths of our study include a rela- tively large sample size for an exposure study of PBDEs as well as concomitant measurement of BDE-153 Adjusted Coefficienta (95% CI) 1.73 (1.05, 2.84) p-Value 0.03 1 1.85 (1.13, 3.03) 2.44 (1.51, 3.95) 0.01 0.0004 1.07 (1.04, 1.10) < 0.0001 Predictor Age (years) Child sex Female (referent) Male Father’s education No college degree (referent) College degree Mother’s education No college degree (referent) College degree Child’s race Nonwhite (referent) White Handwipe Low (referent) Medium High Dust Low (referent) Medium High Breast-feeding (months) Away from home (hr/week) 1 1.45 (0.90, 2.31) 1 0.50 (0.31, 0.78) 1 0.62 (0.38, 1.03) 1 0.53 (0.33, 0.84) 1 1.83 (1.11, 3.02) 3.66 (2.22, 6.05) 1 1.24 (0.70, 2.19) 1.78 (1.01, 3.15) 0.99 (0.95, 1.02) 1.00 (0.98, 1.01) 0.12 0.003 0.07 0.008 0.02 < 0.0001 0.45 0.05 0.41 0.50 p-Value 0.05 0.15 0.001 1 1.34 (0.90, 2.00) 1 0.48 (0.32, 0.74) 1 1.62 (1.01, 2.61) 2.94 (1.80, 4.79) 0.048 < 0.0001 Univariate Coefficienta (95% CI) 2.41 (1.38, 4.22) 1 1.37 (0.84, 2.23) 1 1.53 (0.94, 2.51) 1 1.80 (1.07, 3.03) 1 1.19 (0.72, 1.97) 1 1.70 (0.95, 3.04) 2.41 (1.37, 4.24) 1 1.34 (0.73, 2.48) 1.35 (0.75, 2.46) 1.07 (1.04, 1.11) 1.00 (0.99, 1.01) p-Value 0.002 0.21 0.09 0.03 0.48 0.07 0.003 0.34 0.31 < 0.0001 0.95