A MASS BALANCE FEEDING STUDY OF A COMMERCIAL OCTABROMODIPHENYL ETHER MIXTURE IN RATS

Authors: Huwe, Janice; Hakk, Heldur; Lorentzsen, Margaret

Submitted to: Organohalogen Compounds
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2002
Publication Date: 1/1/2002
Citation: Huwe, J.K., Hakk, H., Lorentzsen, M.K. 2002. A mass balance feeding study of a commercial octabromodiphenyl ether mixture in rats. Organohalogen Compounds. 58:229-232.

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. Although highly brominated compounds (hexa to decaBDEs) account for 90% of the PBDE production, only the lower brominated compounds are generally reported in wildlife. Reasons for this may include lack of bioavailability of the highly brominated compounds to animals, rapid excretion by animals, instability in the environment, or analytical limitations that prevent detection. This study was conducted to obtain information on the bioavailability and excretion of several highly brominated PBDEs in animals and to evaluate the analytical detection methods. Rats were chronically exposed to low levels of a commercial octabromodiphenyl ether product containing hexa to nonaBDEs. After three weeks of exposure, tissues and excreta were analyzed for PBDEs. All of the hexa to octa compounds were bioavailable to the rats, but bioavailability decreased with increasing bromination. NonaBDE was not found in any tissues or excreta, indicating either that the analytical methods were not sensitive enough or that nonaBDE was unstable. Rats were able to quickly excrete and metabolize most of the dosed PBDEs. From this study, it appears that highly brominated PBDEs are bioavailable to animal systems under certain conditions and that metabolism can occur. Negative findings in wildlife may be explained by other factors such as instability of these compounds in the environment or non-optimal modes of exposure.

Technical Abstract: 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. Although highly brominated congeners (octaBDE and decaBDE formulations) account for 90% of the PBDE production, only the lower brominated congeners are generally reported in biota. The purpose of this study was to conduct a mass balance feeding experiment in rats to determine whether bioavailability, metabolism, instability, or analytical problems may be the reason that highly brominated congeners do not appear in wild life. Rats were dosed with low amounts of a commercial octabromodiphenyl ether mixture for 21 days. The octaBDE formulation consisted of hexa to nonaBDEs. The carcasses, livers, and feces from control and dosed rats were quantitated for PBDEs by high resolution GC-MS using an isotope dilution method. Bioavailability was measured by the amount of the dose remaining in the carcass and liver 24 h after the last exposure. Bioavailability decreased with increasing bromination: 60% for hexaBDE, 30% for heptaBDEs, and 20% for octaBDEs. NonaBDE was not detected in any samples, indicating either that the analytical methods were not sensitive enough or that nonaBDEs are highly metabolized or unstable. Fecal excretion accounted for 20 40% of most of the dosed congeners. Approximately 40% of the dosed hepta and octaBDEs were not recovered suggesting that metabolic transformations had occurred in the rat. From this study, it appears that highly brominated PBDEs are bioavailable to animal systems under certain conditions and that metabolism does occur. Their lack of occurrence in wildlife, may be explained by other factors such as instability in the environment or non-optimal modes of exposure.