Stapleton et al. significant associations between serum PBDEs and altered thyroid hormone levels in adults (Turyk et al. 2008) and pregnant women (Chevrier et al. 2010; Stapleton et al. 2011), and with motor, cognitive, and behavioral per- formances in children (Herbstman et al. 2010; Roze et al. 2009). This study was undertaken to better understand the variables contributing to PBDE exposure in young children, specifi- cally toddlers between 1 to 3 years of age, who have the highest hand-to-mouth activi- ties (Tulve et al. 2002). Our primary objec- tive was to estimate the influence of indoor exposure from house dust on serum PBDE levels in toddlers. A secondary objective was to explore the relationships between PBDE exposures and socioeconomic status (SES; e.g., race/ethnicity and parental education), because some researchers have suggested that SES may contribute to exposure disparities (Zota et al. 2010). Materials and Methods Participant recruitment. All aspects of this study were authorized by the Duke University Institutional Review Board before initiation, and all parents/guardians gave informed con- sent before sample collection. Recruitment was conducted through a pediatric clinic in Durham, North Carolina, and by letters mailed to patients of three local pediatric clin- ics in Durham. Families with children between the ages of 12–36 months, with no prior diag- noses of thyroid problems, were recruited for this study. Recruitment began in May 2009 and continued through November 2010. Sample collection. From every child a small blood sample (~ 4 mL blood) was col- lected by venipuncture. Children recruited through the pediatric clinic (n = 9) had a blood sample collected during their doctor’s appointment by laboratory staff. Participants recruited after responding to letters (n = 74) had their blood collected by a contract phle- botomist during the home visit. Every family participating in the study received a visit from our research team. During the home visit (between 0900 and 1700 hours) each family filled out a short questionnaire administered by a research staff member who collected information on the child and information on the parents’ education levels. A hand- wipe sample was collected from each child and a house dust sample was collected from the area of the home identified by the par- ent/guardian as the area in which the child spent the most active time. Handwipe and dust samples were collected using published methods (Allen et al. 2008a; Stapleton et al. 2008). Briefly, for handwipe sample collec- tions, sterile gauze wipes were first soaked in exactly 3.0 mL isopropyl alcohol. The entire surface area of the child’s hands (including 1050 top and bottom of fingers) was then wiped two times from fingers to the wrist. All wipes were investigator collected and then stored in pre-cleaned scintillation vials at –4°C until analysis. A Eureka Mighty-Mite vacuum cleaner (Model 3670) and crevice tool attach- ment were used to collect dust samples. Dust was captured by a cellulose extraction thimble (Whatman International, Maidstone, UK) inserted between the crevice tool and the vacuum tube extender and secured using a rubber O-ring. The equivalent of the entire floor-surface area for the room was vacuumed by gently drawing the crevice tool across the top of all surfaces. Cellulose thimbles used to collect the dust were removed from the vacuum, wrapped in foil, and stored in plastic bags at –4°C until analysis. Chemicals. Individual PBDE conge- ners used for analysis of the handwipes and house dust samples were purchased from AccuStandard, Inc. (New Haven, CT). 13C-2,2´,3,4,5,5´-hexachlorodiphenylether (CDE-141) and 13C-decabromodiphenyl- ether (13C-BDE-209) were purchased from Wellington Labs (Guelph, ON, Canada) and used as a recovery and internal standard, respectively. 4-Fluoro-2,3,4,6-tetrabromo- diphenylether (FBDE-69), purchased from Chiron (Trondheim, Norway), was used as an internal standard. All solvents and other mate- rials were HPLC grade or better. Serum analysis. Blood samples were trans- ferred to the laboratory on ice packs in a cooler and allowed to sit for 1–2 hr to facilitate clot- ting. They were then centrifuged at 3,000 rpm for 5 min to isolate the serum. Serum was transferred to pre-cleaned amber bottles and frozen at –20°C until analysis. Serum samples were analyzed for tri- to decaBDEs (11 con- geners) and lipids at the Centers for Disease Control and Prevention (CDC) using estab- lished methods (Sjödin et al. 2004, 2008). Handwipe analysis. The wipes were extracted and analyzed for PBDE congeners using a method reported by Stapleton et al. (2008). Handwipe samples were spiked with both FBDE-69 and 13C-BDE-209 before extraction as both a surrogate and internal standard. Dust analysis. Dust samples were sieved to < 500 µm and then extracted and ana- lyzed for PBDE congeners using a method reported by Allen et al. (2008a). Dust sam- ples were spiked with both FBDE-69 and 13C-BDE-209 before extraction as both a sur- rogate and internal standard. Quality control. Clean gauze pads and sodium sulfate were used as laboratory blanks for the handwipes and house dust, respec- tively. SRM 2585 (Organic Contaminants in House Dust; National Institute of Standards and Technology, Gaithersburg, MD) was used for quality assurance, to test performance of the dust extraction method for PBDEs. Handwipe and house dust PBDE measure- ments were blank subtracted using the average field (handwipe) or laboratory (house dust) blank measurement. BDEs 47, 99, 100, and 209 were routinely detected in the blanks, although at levels that were typically much lower (e.g., < 1% in dust and < 10% in wipes) than those of the samples, with values ranging from less than detection to a maximum of 4.6 ng for BDE-209. The method detection limits (MDL) for each sample type were deter- mined as three times the standard deviation of the appropriate blanks after subtracting the average blank level, and normalized to average extraction mass of the sample. The labora- tory instrument detection limit was used as the MDL (i.e., signal-to-noise response ratio of 3) in instances where congeners were not detected. Recovery of the internal standard, FBDE-69, averaged 102 ± 15% in the hand- wipe samples, and 86 ± 25% in the house dust samples. Recovery of 13C-BDE-209 in the handwipe extracts was variable for unknown reasons. It was detected in only 28% of the samples and averaged 56 ± 31% when detected. Recovery of the tri–decaBDE conge- ners in the dust SRM 2585 ranged from 85% to 133%. Statistical analysis. Values < MDL were assigned a value equal to half the detection limit for statistical analyses. PBDE measure- ments are reported in mass terms instead of molar units, because mass is more commonly used in the literature. Summary statistics were only computed for congeners with detection frequencies of ≥ 50%. To allow for com- parison of serum, handwipes, and dust using the same congeners, we refer to ∑pentaBDE throughout this paper as the sum of BDEs 47, 99, 100 and 153, and ∑BDE3 represents the sum of BDEs 47, 99, and 100. ∑BDE3 was calculated separately due to the differ- ent behavior of BDE-153 relative to BDEs 47, 99, and 100 observed in correlation and multivariate analyses. The distributions of PBDEs were assessed using histograms, Q-Q plots and Shapiro–Wilk tests and mea- sured PBDE values were log-transformed for analysis as distributions were much closer to log-normal than normal. Regression analy- ses were checked to confirm that residuals were homoscedastic and normally distributed. Pearson correlation coefficients were calcu- lated using log-transformed data. Univariate and multivariate models were used to exam- ine predictors of log-transformed serum ∑BDE3 and BDE-153. Variables examined included children’s sex, age (continuous variable), race, parents’ education levels (a measure of SES), duration of breast-feeding (continuous variable), time children spent away from home (hours/week), dust con- centrations, and handwipe levels. Education ovlume 120 | number 7 | July 2012 • Environmental Health Perspectives