Biomonitoring-based risk assessment for hexabromocyclododecane (HBCD)

Hexabromocyclododecane (HBCD) is a brominated flame retardant compound that has been the subject of recent interest and risk assessment efforts due to its detection in a variety of environmental media and in human biological matrices. Because the exposure pathways for HBCD may be varied and exposure estimation uncertain, biomonitoring for HBCD in humans shows promise as a means of reflecting integrated human exposures to HBCD with lower uncertainty than through estimation of external exposures via multiple pathways. Data from numerous biomonitoring studies of HBCD over the past decade indicate that the central tendency of lipid-adjusted serum and human milk concentrations is approximately 1 ng/g lipid, with upper bound levels of approximately 20 ng/g lipid. Recent risk assessment evaluations from Health Canada and the European Union have identified points of departure of 10 and 20 mg/kg day, respectively, from rat repeated dose studies. The corresponding measured or estimated lipid-adjusted tissue concentrations in the laboratory animals at these points of departure range from 120,000 to 190,000 ng/g lipid. In comparison to these concentrations, the biomonitored human serum and milk concentrations indicate margins of exposure (MOEs) of 6000 to more than 100,000, which are greatly in excess of target MOE values. The use of internal dose measures (both from measurements of tissue concentrations in animal toxicology studies and from human biomonitoring studies) provides risk managers with highly relevant exposure information that is less uncertain than estimated external doses.