Flame retardants are used to suppress or inhibit combustion processes in an effort to reduce the risk of fire. One class of flame retardants, polybrominated diphenyl ethers (PBDEs), has been found to be increasing in the environment and in human milk. Previous studies have shown that lower brominated PBDEs, tetra-, penta-, and hexabrominated diphenyl ethers, can cause developmental neurotoxic effects. The present study shows that the highly brominated PBDE 2,2',3,3',4,4',5,5',6,6'-decaBDE (PBDE 209) can be absorbed during neonatal life and induce developmental neurotoxic effects in adult mice, effects that also worsen with age. These effects seem to be inducible only during a defined critical period of neonatal life. Neonatal Naval Medical Research Institute (NMRI) male mice were exposed on day 3 to 2.22 or 20.1 mg PBDE 209/kg body weight, on day 10 to 1.34, 13.4, or 20.1 mg PBDE 209/kg body weight, or on day 19 to 2.22 or 20.1 mg PBDE 209/kg body weight, or to [U-14C]-2,2',3,3',4,4',5,5',6,6'-decaBDE. The oral neonatal administration of [U-14C]PBDE 209 on day 3, 10, or 19 showed that the compound distributes throughout the body and increases in the brain, from 24 h after administration to 7 days after administration, in 3-day-old and 10-day-old mice. The spontaneous behavior tests, observed in 2-, 4-, and 6-month-old mice, showed that the effect only occurred in mice exposed on day 3 and that this effect worsened with age. We conclude that more attention should be focused on the highly brominated PBDEs as possible developmental neurotoxic agents.

This article is available online at http://dmd.aspetjournals.org ABSTRACT:Among the group of polybrominated diphenyl ethers used as flame-retardants, the fully brominated diphenyl ether, decabromodiphenyl ether (decaBDE), is the most commonly used. Despite the large usage of decaBDE, neither the metabolic pathways nor the absorption have been addressed, and there are very few studies on its toxicology. In this work, it is shown that after a single oral dose of 14 C-labeled decaBDE to rats, at least 10% of the decaBDE dose is absorbed. The major excretion route in conventional rats is via feces that contained 90% of the decaBDE dose. The excretion in bile was close to 10% of the dose and represented mainly metabolites. It cannot be excluded that greater than 10% of the oral dose had been absorbed since 65% of the radioactivity excreted in feces was metabolites. The highest concentrations on a lipid weight basis were found in plasma and blood-rich tissues, and the adipose tissue had the lowest concentration of decaBDE. After derivatization of a phenolic fraction, gas chromatography-mass spectrometry (GC/MS) analyses indicated that metabolites with five to seven bromine atoms had formed, and they possessed a guaiacol structure (a hydroxy and a methoxy group) in one of the rings. In addition, traces of nonabrominated diphenyl ethers and monohydroxylated metabolites were found by GC/MS. Metabolites, characterized by their chemical properties, were interpreted to be covalently bound to macromolecules, either proteins or lipids. In addition, water solubility was suggested. The metabolic pathway was indicated to include a reactive intermediate.

Polybrominated diphenyl ethers (PBDEs) are used in large quantities as flame retardant additives. In a recent study, we have seen that neonatal exposure to some brominated flame retardants can cause permanent aberrations in spontaneous motor behavior that seem to worsen with age. In view of an increasing amount of PBDEs in mother's milk and in the environment, the present study was undertaken to investigate whether there is a critical and limited phase, during neonatal life, for induction of persistent neurotoxic effects of 2,2',4,4',5-pentaBDE (PBDE 99). Neonatal NMRI male mice were exposed on day 3, 10, or 19 to 8 mg 2,2',4,4',5-pentaBDE/kg body weight. Uptake and retention of 2,2',4,4',5-penta[(14)C]BDE were studied in the mouse brain after exposure to 1.5 M becquerel (Bq) 2,2',4,4',5-penta[(14)C]BDE /kg body weight (bw) on postnatal day 3, 10, or 19. Spontaneous motor behavior was observed in 4-month-old mice. Mice exposed to 2,2',4,4',5-pentaBDE on day 3 or 10 showed significantly impaired spontaneous motor behavior, whereas no effect was seen in mice exposed on day 19. Neonatal mice exposed to 2,2',4,4',5-penta[(14)C]BDE 99 on postnatal day 3, 10, or 19 were sacrificed 24 h or 7 days posttreatment. The amount of radioactivity, given as per mille ( per thousand) of total amount administered, was between 3.7 and 5.1 per thousand in the three different age categories at 24 h after administration. Seven days after the administration, 2,2',4,4',5-penta[(14)C]BDE or its metabolites could still be detected in the brain. The amount of radioactivity in the brain was not higher in mice exposed on day 3 or 10 when compared to exposure on day 19. Thus, the behavioral disturbances observed in adult mice following neonatal exposure to 2,2',4,4',5-pentaBDE are induced during a defined critical period of neonatal brain development.

1. The distribution and excretion of orally administered 14C-labelled 2,2',4,4'-tetrabromodiphenyl ether (TBDE) have been studied in rat and mouse. 2. TBDE was efficiently absorbed and stored in adipose tissue where high concentrations were observed in both species. 3. In the rat, 86% of the dose was retained after 5 days, while 14% was excreted via the faeces and < 0.5% via the urine. 4. The mouse excreted 20% of the dose via the faeces and 33% via the urine, the latter as a hydrophilic and labile metabolite. 5. Metabolites covalently bound to macromolecules and lipids were noted in tissues and faeces from both species. 6. The major individual compound was parent TBDE in the faeces and tissues although small amounts of five hydroxylated metabolites were indicated by GC-MS. 7. In plasma from both rat and mouse only a few of the hydroxylated metabolites were present, indicating selective retention of these metabolites.

1. 14C-TBBP-A (2,2-bis(4-hydroxy-3,5-dibromophenyl)propane) was administered orally to the conventional and bile-duct cannulated male Sprague-Dawley rat (2.0 mg/kg body weight). Urine, bile and faeces were collected daily for 72 h, and selected tissues were removed for distribution studies. 2. Faeces was the major route of elimination of TBBP-A in the conventional rat (91.7% of dose), and urine was a minor elimination route (0.3%). Enterohepatic circulation was suggested by biliary excretion of 71.3% and faecal excretion of 26.7% of the administered radioactivity in the bile-duct cannulated rat. 3. 14C-labelled residues in tissues were 2% in the conventional rat, and < 1% in the bile-duct cannulated rat. The large and small intestines contained the majority of the tissue 14C activity for both groups of rat. Levels of TBBP-A in liver were < 0.1% and in fat were below the level of quantification. 4. Three metabolites were characterized in 0-24 h bile samples. Glucuronic acid and sulphate ester conjugates were characterized by mass spectrometry. More than 95% of the extractable faecal 14C was identified as parent TBBP-A. 5. Negligible amounts of TBBP-A-derived 14C were associated with carrier proteins in the urine and bile.