Submitted to: Chemosphere
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/9/2006
Publication Date: 6/30/2006
Citation: Huwe, J.K., Hakk, H., Lorentzsen, M.K. 2007. Bioavailability and mass balance studies of a commercial pentabromodiphenyl ether mixture in male Sprague-Dawley rats. Chemosphere 66:259-266. Interpretive Summary: Polybrominated diphenyl ethers (PBDE) are common flame retardants in polyurethane foam and high impact polystyrene. PBDE levels have been increasing in the environment for over 20 years. Two congeners are particularly prominent in environmental samples, i.e. tetrabromo BDE-47 and pentabromo BDE-99. However, the large scale production of these congeners as pentabromodiphenyl ether formulations has been sharply curtailed. The purpose of this study was to conduct a mass balance experiment in rats to obtain information on the bioavailability and bioaccumulation of both BDE-47 and 99. Rats were chronically exposed to low levels of a commercial pentabromodiphenyl ether mixture, and tissues and excreta were analyzed for PBDEs. Both BDE-47 and BDE-99 were highly bioavailable to the rats with <10% of the dose excreted in the feces. Approximately 50% of the dose remained in the animals; however, it appeared that significant metabolic transformation of the PBDEs had occurred. These results may help researchers further determine what the environmental fate of compounds such as BDE-47 and BDE-99 may be and the implications for their persistence in biota.
Technical Abstract: Polybrominated diphenyl ethers (PBDE) are common flame retardants used in polyurethane foam, high impact polystyrene, and textiles. The worldwide demand for PBDEs continues to increase and, as a result, PBDE levels in the environment also appear to be climbing. Two PBDE congeners that are particularly prominent in environmental samples are 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and 2,2',4,4',5-pentabromodiphenyl ether (BDE-99). These two congeners are major components in penta-BDE formulations which constitute a minor percentage (11%) of the commercial PBDE market. In order to determine the bioavailability and bioconcentrating potential of these PBDEs, we have conducted a mass balance experiment in rats dosed with low amounts of a commercial penta-BDE mixture for 21 days to mimic an environmental exposure. The carcasses, livers, and feces from control and dosed rats were quantitated for PBDEs by a high resolution GC-MS isotope dilution method. Approximately 50% of each of the dosed congeners was retained in the rats with the liver being a minor depot (1% of the dose). Fecal excretion accounted for 5-15% of the dosed congeners. A large percent of the dose (40-50%) was not recovered indicating that metabolic transformations had occurred in the rats. The relative congener distribution in each tissue was nearly identical to the congener distribution of the commercial mixture. Conclusions from the study suggest that the tetra- to hexa-BDEs present in commercial penta-BDE formulations are largely bioavailable to animals, that bioavailability in the rat is independent of bromination number, and that metabolism may occur to a large extent during a chronic exposure.