Exposure to Hexabromocyclododecanes (HBCDs) via Dust Ingestion, but Not Diet, Correlates with Concentrations in Human Serum: Preliminary Results

BACKGROUND: Hexabromocyclododecane (HBCD) is a high-production-volume chemical used as flame retardant in polystyrene insulation and textiles. Because it is not chemically bound to the polymer, HBCD can migrate into the environment, contaminating indoor dust and foodstuff. OBJECTIVES: We examined for the first time the relationship between combined exposure to three HBCD isomers (Sigma HBCDs) via ingestion of food (duplicate diets) and indoor dust and HBCD concentrations in serum for 16 Belgian adults (20-25 years of age). We also determined the chiral signatures of HBCDs to advance understanding of source-to-human enantioselective degradation and/or metabolism. METHODS: Concentrations and chiral signatures of alpha-, beta-, and gamma-HBCD in duplicate diets, dust, and serum were measured by liquid chromatography/tandem mass spectrometry. RESULTS: Dietary intakes of Sigma HBCDs were 1.2-20 ng/day (average, 7.2 ng/day), whereas those estimated under average (20 mg dust/day) and high (50 mg dust/day) dust ingestion scenarios were 1.1-15 ng/day (average intake, 3.2 ng/day) and 2.8-38 ng/day (average intake, 8.0 ng/day) respectively. Concentrations of Sigma HBCDs measured in blood serum were < 0.5 to 11 ng/g lipid weight (1w) (average, 2.9 ng/g 1w). gamma-HBCD dominated in food, whereas alpha-HBCD dominated in dust and was the sole isomer in serum. Although exposure via dust ingestion correlated significantly (p < 0.01) with concentrations in serum, no such correlation was evident with dietary exposure (p > 0.1). Although no enantioselective enrichment was detected in either dust or diet, substantial enrichment of (-)alpha-HBCD was observed in serum. CONCLUSIONS: Serum concentrations of HBCDs were correlated with the exposure via dust, but not via dietary ingestion. The enrichment of the (-)alpha-HBCD enantiomer in humans appears to be due to in vivo enantioselective metabolism/excretion rather than ingestion of dust or diet.