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Metabolsim of a-and y~Hexabromocylododecane and Enantioselective Fractions of a-, B-, y-Isomers in Mice.
Citation:
DILIBERTO, J. J., H. Hakk, J. K. Huwe, D. T. Szabo, AND L. S. BIRNBAUM. Metabolsim of a-and y~Hexabromocylododecane and Enantioselective Fractions of a-, B-, y-Isomers in Mice. Presented at 30th International Symposium on Halogenated Persistent Organic Pollutants, San Antonio, TX, September 12 - 17, 2010.
Impact/Purpose:
To look at the selective metabolism and enantioselective absorption of gamma HBCD in mice.
Description:
Hexabromocyclododecane (HBCD) is the third-highest production volume brominated flame retardant (BFR). It is incorporated into expanded polystyrene foam used in thermal insulation of buildings, and currently is the only suitable BFR for this application. HBCD is an additive flame retardant, which allows it to be released from consumer products and because of this is considered a ubiquitous contaminant in environmental media and biota. HBCD is an enzyme inducer1, developmental neurotoxicant2, and endocrine disrupter3 in laboratory animals, and recent studies have suggested HBCD is also highly bioaccumulative4. Due to evidence of persistence and toxicity HBCD is currently being considered for a global ban under the framework of the Stockholm Convention on Persistent Organic Pollutants. Three major 1,2,5,6,9,I0-hexabromocyclododecane diastereoisomers, denoted as alpha (a), beta (B), and gamma (y). with the y-diastereoisomer predominating (>70%), comprise the commercial HBCD mixture. Both B-and y-HBCD can thermally convert to a-HBCDs, and it is speculated that in vivo metabolism may also convert the y-diastereoisomer to the a-diastereoisomer, which is the most prevalent HBCD diastereomer found in wildlife and humans6. The prevalence of a-HBCD as the major HBCD contaminant may be explained by differences in pharmacokinetic rates, where the y-diastereoisomer is metabolized and/or eliminated more rapidly than the a-diastereoisorner, or by isomerization of the y-diastereoisomer to the a-isomer. There are limited but emerging monitoring data identifying HBCD at the enantiomer levef 7,8. This is the first study to examine the enantiomer fractions after oral exposure of two main HBCD diastereomers, a-HBCD and y-HBCD, in the liver and feces using female mice as a mammalian model organism.