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United States Department of Agriculture

Agricultural Research Service

Title: Metabolism, Tissue Disposition, and Excretion, of 1,2-Bis(2,4,6-Tribromophenoxy)ethane (Btbpe) in Male Sprague-Dawley Rats.

Authors
item Hakk, Heldur
item Larsen, Gerald
item Bowers, Joseph - ELECTROCHEMICALS INC

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 14, 2003
Publication Date: January 1, 2004
Citation: Hakk, H., Larsen, G.L., Bowers, J. 2004. Metabolism, tissue disposition, and excretion, of 1,2-bis(2,4,6-tribromophenoxy)ethane (btbpe) in male sprague-dawley rats. Chemosphere 54:1367-1374.

Interpretive Summary: 1,2-Bis(2,4,6-tribromophenoxy)ethane (BTBPE) is a common flame retardant used for plastics that require high manufacturing temperatures and UV light stability. The possibility exists that it could be leached from waste plastic and enter the environment, as has been observed with other flame retardants, although environmental levels have not been yet reported. The water solubility of BTBPE is very low, therefore, it would be expected to persist and be bioaccumulative. This purpose of this study was to measure the metabolic behavior of BTBPE in male rats for 3 days. BTBPE was not appreciably absorbed, as indicated by low daily urine and bile excretion, as well as low tissue retention. No parent was present in the radioactivity excreted in the urine or bile, therefore, metabolism of BTBPE was necessary for elimination via these routes. Lipophilic tissues contained the highest concentrations of BTBPE, e.g. thymus, adipose tissue, adrenals, lung, and skin. All other tissues contained less than 0.1% of the administered dose at 3 days. Feces was the major route of excretion, and over 92% was excreted in the first day. Extracted feces largely contained parent material, as characterized by mass spectrometry, however, characterized metabolites indicated that BTBPE underwent oxidation, oxidative debromination, and ether bridge cleavage. Feces also contained a substantial level of non-extractable BTBPE (>39% of 0-24h fecal 14C), an indication of metabolic activation to species which could bind to lipids and proteins. It was concluded that limited absorption and metabolism of BTBPE would occur by ingestion in mammals.

Technical Abstract: 1,2-Bis(2,4,6-tribromophenoxy)ethane (BTBPE) is a common flame retardant used for plastics that require high manufacturing temperatures and UV light stability. The possibility exists that BTBPE could be leached from waste plastic and enter the environment, as has been observed with other brominated flame retardants, although environmental levels have not yet been reported. The water solubility of BTBPE is extremely low, and it would, therefore, be expected to be accumulative in lipophilic tissues during exposure. This purpose of this study was to measure the metabolism, disposition, and excretion of BTBPE in male rats for 3 days. A single oral dose of [14C]BTBPE was administered to conventional and bile-duct cannulated male Sprague-Dawley rats. Tissue disposition, excretion and metabolism was determined. BTBPE was poorly soluble in lipophilic solutions, which made dose preparation difficult. The great majority of 14C (>94%) was excreted in the feces of both groups of rats at 72h, and tissue retention was minimal. Lipophilic tissues contained the highest concentrations of BTBPE, e.g. thymus, adipose tissue, adrenals, lung, and skin. Metabolites were excreted in the urine, bile and feces, but at a very low level. Fecal metabolites were identified by GC/MS, and suggested that BTBPE underwent oxidation, oxidative debromination, and ether bridge cleavage in male rats. Despite a limited quantity of stable metabolites extractable in the feces, non-extractable 14C levels were relatively high (39% of the 0-24h fecal 14C) which suggested that BTBPE could be metabolically activated in the rat and covalently bound to fecal proteins and/or lipids. It was concluded that limited absorption and metabolism of BTBPE would occur by ingestion in mammals.

Last Modified: 4/20/2014
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