Stapleton et al. blood, handwipes, and house dust. Potential weaknesses of our analysis include ignoring sources of dietary exposure and measurement of handwipes and dust at a single point in time. It is unknown how variable PBDE levels on handwipes are in a single person, although they do depend on frequency of handwashing (Watkins et al. 2011). In a previous study of Boston homes, we found that PBDEs in dust sampled 6–8 months apart were highly cor- related (Allen et al. 2008a). Although the asso- ciations between PBDEs in serum, handwipes, and dust are most consistent with a hand-to- mouth exposure pathway following contact of hands with dust or PBDE-containing sur- face films, we cannot completely rule out der- mal exposure, absorption of pentaBDEs from vapor to skin (Weschler and Nazaroff 2008), or reverse causation (in which PBDEs are excreted from skin), although some of these pathways appear to be unlikely (Watkins et al. 2011). In conclusion, the results of our study sug- gest that toddlers have a significant amount of exposure to PBDEs from hand-to-mouth transfer. Children may also be exposed to other contaminants often found in house dust (e.g., polycyclic aromatic hydrocarbons, pesticides, perfluorinated compounds, other flame retar- dants) via hand-to-mouth activities. We also found striking differences in the relationships between SES and serum concentrations of dif- ferent congeners. Although serum BDE-153 was positively associated with mother’s educa- tion, this association may be mediated by dura- tion of breast-feeding. In contrast, BDEs 47, 99, and 100 were negatively associated with SES. Further research is needed to determine why SES factors are influencing PBDE expo- sure in children, which may help in mediating the potential health risks from exposure. Ref Rencs Allen JG, McClean MD, Stapleton HM, Webster TF. 2008a. Critical factors in assessing exposure to PBDEs via house dust. 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