What contributes to human body burdens of halogenated flame retardants? : An experimental approach

Abstract: Flame retardants (FRs) are chemicals added to a broad range of consumer products such as textiles, electrical and electronic equipment, furniture and building material to meet flammability requirements. Most of these chemicals are additives that can continuously leach out from the applied products during usage. FRs are studied because of their abundance in indoor environments and concerns about their impact on human health. The restrictions on many brominated FRs have resulted in a need for their replacement with a variety of emerging halogenated FRs (EHFRs). Humans are exposed to these chemicals mainly through dust and diet ingestion, but there is still insufficient data about the relative importance of other exposure pathways. In this thesis, a Norwegian cohort of 61 adults (age 20-66, 16 males and 45 females) was studied for their exposure to legacy and emerging HFRs. Duplicate diet, stationary air, personal air, settled dust, hand wipe and serum samples were collected from the participants and analyzed for polybrominated diphenyl ethers (PBDEs), hexabromocyclododecanes (HBCDDs) and EHFRs. External exposures via dietary intake, air inhalation, dust ingestion and dermal exposure (in pg/kg body weight/day) were estimated from the measured concentrations. The intake values were then compared to elucidate which of these exposure pathways were most important for the Norwegian cohorts’ exposure to specific HFRs. Dietary intake was the predominant exposure route for most of the PBDE congeners and EHFRs, whereas dust ingestion contributed significantly to the exposure of some less volatile HFRs. Inhalation exposure was negligible for most of the target HFRs except for those with higher volatility, such as tetrabromoethylcyclohexane (DBE-DBCH), 2-bromoallyl 2,4,6-tribromophenyl ether (BATE) and 1,2,3,4,5-pentabromobenzene (PBBz). Dermal exposure seems to be a significant exposure pathway for HBCDDs and tetrabromobisphenol A (TBBPA) but the relevance of hand wipes to represent total dermal exposure remains uncertain. Overall, the median and 95th percentile total intakes for all target HFRs did not exceed the regulatory reference doses (RfD). Estimated serum concentrations were calculated from total intakes from all exposure pathways using a one compartment pharmacokinetic model and these were compared to measured concentrations. The estimated median serum BDE-47 and BDE-153 concentrations were slightly over-estimated by a factor of 5.5 and 4.3, respectively whereas BDE-197 and -209 were under-estimated by 1 to 2 orders of magnitude compared to the measured concentrations. Statistical analysis suggested that age, number of electronic equipment at home, certain dietary habits, hand washing and house cleaning frequency were possible contributors to HFR exposure.