Bioavailability and mass balance studies of a commercial pentabromodiphenyl ether mixture in male Sprague-Dawley rats

Mechanisms of Male Reproductive Toxicity of Polybrominated Diphenyl Ethers

Polybrominated diphenyl ethers (PBDE) are a group of flame retardants used in a variety of artificial materials. Despite being phased out in most industrial countries, they remain in the environment and human tissues due to their persistence, lipophilicity, and bioaccumulation. Populational and experimental studies demonstrate the male reproductive toxicity of PBDEs including increased incidence of genital malformations (hypospadias and cryptorchidism), altered weight of testes and other reproductive tissues, altered testes histology and transcriptome, decreased sperm production and sperm quality, altered epigenetic regulation of developmental genes in spermatozoa, and altered secretion of reproductive hormones. A broad range of mechanistic hypotheses of PBDE reproductive toxicity has been suggested. Among these hypotheses, oxidative stress, the disruption of estrogenic signaling, and mitochondria disruption are affected by PBDE concentrations much higher than concentrations found in human tissues, making them unlikely links between exposures and adverse reproductive outcomes in the general population. Robust evidence suggests that at environmentally relevant doses, PBDEs and their metabolites may affect male reproductive health via mechanisms including AR antagonism and the disruption of a complex network of metabolic signaling.

Emerging environmental pollutants hydroxylated polybrominated diphenyl ethers: From analytical methods to toxicology research

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are of particular concern due to their ubiquitous distribution and adverse health effects. Significant progress has been made in the characterization of OH-PBDEs by using mass spectrometry (MS). In this review, we summarize applications of MS-based techniques in detection, environmental and biota distribution, and potential health risk effects, hoping to unfold an overall picture on account of current knowledge of OH-PBDEs. The analytical methodologies are discussed from sample pretreatment to MS analysis. The methods including gas chromatography-MS (GC-MS), liquid chromatography-MS (LC-MS), and ion mobility spectrometry-MS (IMS-MS) are discussed. GC-MS is the most frequently adopted method in the analysis of OH-PBDEs due to its excellent chromatographic resolution, high sensitivity, and strong ability for unknown identification. LC-MS has been widely used for its high sensitivity and capability of direct analysis. As a newly developed technique, IMS-MS provides high specificity, which greatly facilitates the identification of isomers. OH-PBDEs pervasively existed in both abiotic and biotic samples, including humans, animals, and environmental matrices. Multiple adverse health effects have been reported, such as thyroid hormone disruption, estrogen effects, and neurotoxicity. The reported potential pathological mechanisms are also reviewed. Additionally, MS-based metabolomics, lipidomics, and proteomics have been shown as promising tools to unveil the molecular mechanisms of the toxicity of OH-PBDEs. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Rat liver epigenome programing by perinatal exposure to 2,2',4'4'-tetrabromodiphenyl ether

Perinatal exposures to polybrominated diphenyl ethers permanently reprogram liver metabolism and induce a nonalcoholic fatty liver disease-like phenotype and insulin resistance in rodents. Aim: To test if these changes are associated with altered liver epigenome. Materials & methods: Expression of small RNA and changes in DNA methylation in livers of adult rats were analyzed following perinatal exposure to 2,2',4,4'-tetrabromodiphenyl ether, the polybrominated diphenyl ether congener most prevalent in human tissues. Results: We identified 33 differentially methylated DNA regions and 15 differentially expressed miRNAs. These changes were enriched for terms related to lipid and carbohydrate metabolism, insulin signaling, Type-2 diabetes and nonalcoholic fatty liver disease. Conclusion: Changes in the liver epigenome are a likely candidate mechanism of long-term maintenance of an aberrant metabolic phenotype.

Mass balance study of brominated flame retardants in female captive peregrine falcons

Little is known about brominated flame retardant (BFR) dynamics in birds, especially large molecules such as decabromodiphenyl ether (BDE-209). In particular, bioaccumulation from food and transfer dynamics to eggs are poorly understood. Therefore, an input-output mass balance study of tri-decaBDEs, DBDPE and HBCDD was performed in three female peregrine falcons from a captive breeding program by analyzing their naturally contaminated food (quail, chicken (cockerels)), plasma, feces and eggs. Predominant BFRs in cockerels and quail were BDE-209 and DBDPE, as well as HBCDD in quail. The predominant BFRs found in falcon plasma were BDE-209, -153 and -183, in eggs, HBCDD, BDE-209 and -153 and in feces, BDE-209. Mean absorption efficiencies (AE) for the tetra-octabrominated BDEs ranged from 84-100% and 70% for HBCDD. The AEs for BDE-206, -207, -208 and -209 varied due to the large variability seen for feces fluxes. All egg/plasma ratios for BDEs were similar and greater than one (range 1.1-2.7), including for BDE-209, indicating efficient transfer from females to the eggs. Excretion via egg-laying was approximately 6.0-29% of the initial, pre-breeding body burden of individual penta-decaBDE congeners, (15-45% for BDE-206). HBCDD was not detected in plasma but was found in eggs, also indicating efficient transfer and excretion via eggs. Input fluxes from food exceeded the output fluxes (feces, eggs) indicating considerable metabolism for tetra-octaBDEs, possibly also for the nona-decaBDEs and HBCDD. Bioaccumulation factors calculated from lipid weight concentrations in plasma and food (BAFp) were highest for BDE-208 (31), -153 (23), -209 (19) and -207 (16) and from eggs and food (BAFe), were highest for HBCDD (140), BDE-153 (41), -208 (42), BDE-207 (24) and BDE-209 (21). BAFe and BAFp values were below 10 for BDE-47, -99 and -100. For one falcon, egg results were available from three different years and estimated half-lives were 65 d (BDE-99), 624 d (BDE-153), 31 d (BDE-154), 349 d (BDE-183), 77 d (BDE-196) and 89 d (BDE-197).

Developmental Exposure to 2,2',4,4'-Tetrabromodiphenyl Ether Induces Long-Lasting Changes in Liver Metabolism in Male Mice

Polybrominated diphenyl ethers (PBDEs) were used as flame-retardant additives in a wide range of polymers. The generations born when environmental concentrations of PBDEs reached their maximum account in the United States for one-fifth of the total population. We hypothesized that exposure to PBDEs during sensitive developmental windows might result in long-lasting changes in liver metabolism. The present study was based on experiments with CD-1 mice and human hepatocellular carcinoma cells (human hepatoma cell line, HepG2). Pregnant mice were exposed to 0.2 mg/kg 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) from gestation day 8 until postnatal day 21. The metabolic health-related outcomes were analyzed on postnatal day 21 and postnatal week 20 in male offspring. Several groups of metabolic genes, including ribosomal and mitochondrial genes, were significantly upregulated in the liver at both points. Genes regulated via mechanistic target of rapamycin (mTOR) pathway, the gatekeeper of metabolic homeostasis, were whether up- or downregulated at both measurement points. On postnatal day 21, but not week 20, both mTOR complexes in the liver were activated, as measured by phosphorylation of their targets. mTOR complexes were also activated by BDE-47 in HepG2 cells in vitro. The following changes were observed at week 20: a decreased number of polyploid hepatocytes, suppressed cytoplasmic S6K1, twofold greater blood insulin-like growth factor-1 and triglycerides, and 2.5-fold lower expression of fatty acid uptake membrane receptor CD36 in liver tissue. Thus, perinatal exposure to environmentally relevant doses of BDE-47 in laboratory mice results in long-lasting changes in liver physiology. Our evidence suggests involvement of the mTOR pathway in the observed metabolic programming of the liver.

From the city to the Lake: loadings of PCBs, PBDEs, PAHs and PCMs from Toronto to Lake Ontario

Loadings from Toronto, Canada to Lake Ontario were quantified and major sources and pathways were identified, with the goal of informing opportunities for loading reductions. The contaminants were polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs) and polycyclic musks (PCMs). Loadings were calculated from measured concentrations for three major pathways: atmospheric processes, tributary runoff, and wastewater treatment plant (WWTP) effluents. Although atmospheric deposition to the Great Lakes has received the greatest attention, this was the dominant loading pathway for PCBs only (17 ± 5.3 kg/y or 66% of total loadings). PCB loadings reflected elevated urban PCB air concentrations due to, predominantly, primary emissions. These loadings contribute to consumption advisories for nearshore fish. PBDE loadings to the lake, again from mainly primary emissions, were 48% (9.1 ± 1.3 kg/y) and 42% (8.0 ± 5.7 kg/y) via tributaries and WWTPs, respectively, consistent with emissions deposited and subsequently washed-off of urban surfaces and emissions to the sewage system. PAHs loadings of 1600 ± 280 kg/y (71%) from tributaries were strongly associated with vehicle transportation and impervious surfaces. PCM loadings were 83% (±140 kg/y) from WWTP final effluent, reflecting their use in personal care products. Opportunities for source reduction lie in reducing the current inventories of in-use PCBs and PBDE-containing products, reducing vehicle emissions of PAHs and use of PAHs in the transportation network (e.g., pavement sealants), and improving wastewater treatment technology.

Transfer of PBDEs from e-waste to aqueous media

Experiments and analysis were carried out by contacting e-waste with distilled water and leachate from a major urban landfill. Contacting of crushed e-waste from different eras with leachate in a custom built end-over-end contactor led to appreciable mass transfer of Polybrominated diphenyl ethers (PBDEs) to the aqueous phase. Temperature had limited influence for the limited range (10-25°C) investigated. Lower pH (in the range 4 to 9) generally resulted in higher transfer of PBDEs to the aqueous phase. Exposing e-waste to distilled water in the same contactor led to lower, but still appreciable PBDE analysed concentrations, than for leachate, probably due to dislodgement of fine dust from the surface of the e-waste particles.

Brominated diphenyl ether (BDE) levels in liver, adipose, and milk from adult and juvenile rats exposed by gavage to the DE-71 technical mixture

Brominated diphenyl ethers (BDEs) are used as flame retardants in consumer products. Rodent studies indicate that the liver, thyroid, and nervous system of developing animals are targets of BDEs. To explore the relationship between exposure and health in developing animals, BDE accumulation in adult and juvenile rats was examined in conjunction with changes in liver weight and serum thyroxine (T4). Adult (F0) rats received the commercial BDE mixture DE-71 by gavage at doses of 0.5, 5, and 25 mg kg(-1) body weight (bw)/day for 21 weeks. F0 rats were mated and exposure continued throughout breeding, pregnancy, lactation, and postweaning until the pups (F1 generation) reached postnatal day (PND) 42. Milk was collected from lactating dams. Adipose and liver samples were collected from F0 and F1 males and females for BDE congener analysis. Congener prevalence in rat tissues mimicked congener prevalence in wildlife and humans. Tissue concentrations of all congeners except BDE-153 were lower than would be expected based on dose proportionality, confirming that BDE-153 has a high capacity for bioaccumulation. BDEs were transferred from maternal tissues to milk during lactation. Milk congener profiles differed from maternal tissue profiles indicating that degree of bromination and maternal sequestration influenced BDE transfer to milk. Female F1 rats accumulated more BDEs than F1 males, indicating that female rats were less able to metabolize and/or excrete BDEs. Significant effects on liver weight and serum T4 levels were observed in adults and juveniles in the middle and high dose groups, corresponding to BDE levels in the μg g(-1) range. Although it remains to be determined how human liver and thyroid are affected by exposure to much lower BDE levels, the present study confirmed that gender and reproductive status influence BDE accumulation in tissues and BDE transfer to the neonate via milk.

Application of mass spectrometry in the analysis of polybrominated diphenyl ethers

This review summarized the applications of mass spectrometric techniques for the analysis of the important flame retardants polybrominated diphenyl ethers (PBDEs) to understand the environmental sources, fate and toxicity of PBDEs that were briefly discussed to give a general idea for the need of analytical methodologies. Specific performance of various mass spectrometers hyphenated with, for example, gas chromatograph, liquid chromatograph, and inductively coupled plasma (GC/MS, LC/MS, and ICP/MS, respectively) for the analysis of PBDEs was compared with an objective to present the information on the evolution of MS techniques for determining PBDEs in environmental and human samples. GC/electron capture negative ionization quadrupole MS (GC/NCI qMS), GC/high resolution MS (GC/HRMS) and GC ion trap MS (GC/ITMS) are most commonly used MS techniques for the determination of PBDEs. New analytical technologies such as fast tandem GC/MS and LC/MS become available to improve analyses of higher PBDEs. The development and application of the tandem MS techniques have helped to understand environmental fate and transformations of PBDEs of which abiotic and biotic degradation of decaBDE is thought to be one major source of Br(1-9)BDEs present in the environment in addition to direct loading from commercial mixtures. MS-based proteomics will offer an insight into the molecular mechanisms of toxicity and potential developmental and neurotoxicity of PBDEs.

Absorption and biotransformation of polybrominated diphenyl ethers DE-71 and DE-79 in chicken (Gallus gallus), mallard (Anas platyrhynchos), American kestrel (Falco sparverius) and black-crowned night-heron (Nycticorax nycticorax) eggs

We recently reported that air cell administration of penta-brominated diphenyl ether (penta-BDE; DE-71) evokes biochemical and immunologic effects in chicken (Gallus gallus) embryos at very low doses, and impairs pipping (i.e., stage immediately prior to hatching) and hatching success at 1.8mugg(-1) egg (actual dose absorbed) in American kestrels (Falco sparverius). In the present study, absorption of polybrominated diphenyl ether (PBDE) congeners was measured following air cell administration of a penta-BDE mixture (11.1mug DE-71g(-1) egg) or an octa-brominated diphenyl ether mixture (octa-BDE; DE-79; 15.4mug DE-79g(-1) egg). Uptake of PBDE congeners was measured at 24h post-injection, midway through incubation, and at pipping in chicken, mallard (Anas platyrhynchos), and American kestrel egg contents, and at the end of incubation in black-crowned night-heron (Nycticorax nycticorax) egg contents. Absorption of penta-BDE and octa-BDE from the air cell into egg contents occurred throughout incubation; at pipping, up to 29.6% of penta-BDE was absorbed, but only 1.40-6.48% of octa-BDE was absorbed. Higher brominated congeners appeared to be absorbed more slowly than lower brominated congeners, and uptake rate was inversely proportional to the log K(ow) of predominant BDE congeners. Six congeners or co-eluting pairs of congeners were detected in penta-BDE-treated eggs that were not found in the dosing solution suggesting debromination in the developing embryo, extraembryonic membranes, and possibly even in the air cell membrane. This study demonstrates the importance of determining the fraction of xenobiotic absorbed into the egg following air cell administration for estimation of the lowest-observed-effect level.

Mini-review: polybrominated diphenyl ether (PBDE) flame retardants as potential autism risk factors

Brominated flame retardants, including Polybrominated diphenyl ethers (PBDEs) have been used at increasing levels in home furnishings and electronics over the past 25 years. They have also become widespread environmental pollutants. High PBDE levels have been detected in food, household dust, and indoor air, with subsequent appearance in animal and human tissues. This minireview summarizes studies on the extent to which these compounds can act as potent thyroid hormone mimetics, and emerging studies on long-term neurological effects of acute administration of PBDEs during development. When these data are considered in combination with the extensive literature on stage-dependent effects of thyroid hormone on aspects of brain development that are also implicated in autistic brains, a hypothesis that PBDEs might also serve as autism risk factors emerges. Studies designed to explicitly test this hypothesis will require chronic exposure paradigms, and specific body burden and behavioral monitoring in animal models. Such testing may help to prioritize extensive human epidemiological studies, as well as offer protocols for evaluation of future compounds.

Assessment of the bioaccessibility of polybrominated diphenyl ethers in foods and the correlations of the bioaccessibility with nutrient contents

Bioaccessibility of a contaminant in foods is the fraction of the contaminant mobilized from the food matrices during gastrointestinal digestion. In the present paper, the bioaccessibility of polybrominated diphenyl ethers (PBDEs) in 13 types of foods, including fish, meat, rice, flour, and vegetables, was determined using an in vitro digestion method. The bioaccessibility obtained ranged from 2.6% to 41.3%. It was found that the bioaccessibility of PBDEs exhibited positive correlations with fat and carbohydrate contents and negative correlations with protein and dietary fiber contents in the foods. Fat was the most important factor affecting the bioaccessibility of PBDEs. The mechanism underlying the correlations was discussed in view of partition of PBDEs between liquid and solid phases. To our knowledge, this is the first article systematically investigating the bioaccessibility of PBDEs in foods and demonstrating the influence of the food constituents on the bioaccessibility of PBDEs.

The potential of selected brominated flame retardants to affect neurological development

Various brominated flame retardants (BFR), including polybrominated diphenyl ether (PBDE) congeners, hexabromocyclododecane (HBCD), and tetrabromobisphenol A (TBBPA), are commonly used in household items and electronics and have been detected in the environment and/or the bodily fluids of people, including children. Some studies in animals suggest that exposure to PBDE congeners, HBCD, or TBBPA during the perinatal period may affect locomotor activity and/or memory and learning. Epidemiological studies showing similar effects in humans, however, are lacking. To assess whether an association exists between perinatal exposure and development of consistent neurobehavioral alterations, published animal studies investigating perinatal exposure to PBDE congeners, HBCD, or TBBPA with specific neurobehavioral evaluations-particularly, assessments of motor activity-were reviewed for consistency of results. Our analysis shows that although the majority of studies suggest that perinatal exposure affects motor activity, the effects observed were not consistent. This lack of consistency includes the type of motor activity (locomotion, rearing, or total activity) affected, the direction (increase or decrease) and pattern of change associated with exposure, the existence of a dose response, the permanency of findings, and the possibility of gender differences in response. Interestingly, Good Laboratory Practices (GLP)-compliant studies that followed U.S. Environmental Protection Agency (EPA)/Organization for Economic Cooperation and Development (OECD) guidelines for developmental neurotoxicity testing found no adverse effects associated with exposure to PBDE209, HBCD, or TBBPA at doses that were orders of magnitude higher and administered over longer durations than those used in the other studies examined herein. The lack of consistency across studies precludes establishment of a causal relationship between perinatal exposure to these substances and alterations in motor activity.

A mass balance of tri-hexabrominated diphenyl ethers in lactating cows

Beef and dairy products can be important vectors of human exposure to polybrominated diphenylethers (BDEs), and hence an understanding of BDE transfer from feed to cows' milk and tissue is important for BDE exposure assessment The fate of tri- to hexaBDEs in lactating cows exposed to a naturally contaminated diet was studied by analyzing feed, feces, and milk samples from a mass balance study. Tissue distribution was studied in one cowslaughtered afterthe experiment The carryover rates from feed to milk ranged from 0.15 to 0.35 for the major congeners. Lower values were observed for several of the tetrabrominated congeners, and this was attributed to metabolism. The dietary absorption efficiency decreased with increasing octanol-water partition coefficient of the BDE congener. The absorption behavior was consistent with a model based on chemical lipophilicity, but agreed less well with a model based on effective molecular diameter, and it violated Lipinski's "rule of 5". The lipid normalized concentrations were similar in all tissues analyzed including liver and milk, suggesting that tissue distribution is governed by partitioning into lipids. Overall, the behavior of the tri- to hexaBDEs was consistent with that observed for other classes of halogenated aromatic contaminants such as PCBs and PCDD/Fs, but it differed markedly from the behavior of the hepta- decaBDEs.

Tissue distribution of polybrominated diphenyl ethers in male rats and implications for biomonitoring

Polybrominated diphenyl ethers (PBDEs) are a class of widely used flame retardants which have been found to persist, bioaccumulate, and potentially affect development in animals. Exposure to PBDEs can be through both diet and the environment and is generally estimated by measuring PBDEs in blood, adipose tissue, muscle, or milk samples. Using rats as a model, we investigated tissue distribution of PBDEs after oral administration and evaluated a suitable matrix for body burden estimation. Male rats were administered dust or corn oil containing 8 or 6 microg PBDEs kg(-1) body wt, respectively, in the diet for 21 days (N=4 rats per treatment), and the concentration of 15 PBDEs were measured in various tissues, plasma, and feces. PBDEs were found in all tissues, including the brain, and showed no difference in distribution patterns between treatments for most PBDEs. Tri- to hexa-BDEs comprised >80% of the total PBDEs in the adipose, brain, kidney, lung, and residual carcass, but <40% in the liver and plasma. The ratio of the lipid-weight concentration of tri- to hexa-BDEs in adipose tissue, residual carcass, and plasma was 1:1:2. For the hepta- to nona-BDEs, lipid-weight concentrations increased from adipose tissue to residual carcass to plasma in the ratio 0.3:1:>4. BDE-209 was the dominant congener in the liver and plasma, but was not detected in the adipose tissue or carcass. In summary, the lower brominated congeners tended to distribute equally into lipids implying both adipose tissue and plasma would be suitable matrices for biomonitoring. Plasma was the best matrix for detection of the higher brominated congeners (especially BDE-209), although on a lipid-weight basis tended to overestimate the total body burdens.

Hydroxylation increases the neurotoxic potential of BDE-47 to affect exocytosis and calcium homeostasis in PC12 cells

BACKGROUND

Oxidative metabolism, resulting in the formation of hydroxylated polybrominated diphenyl ether (PBDE) metabolites, may enhance the neurotoxic potential of brominated flame retardants.

OBJECTIVE

Our objective was to investigate the effects of a hydroxylated metabolite of 2,2',4,4'-tetra-bromodiphenyl ether (BDE-47; 6-OH-BDE-47) on changes in the intracellular Ca2+ concentration ([Ca2+]i) and vesicular catecholamine release in PC12 cells.

METHODS

We measured vesicular catecholamine release and [Ca2+]i using amperometry and imaging of the fluorescent Ca2+-sensitive dye Fura-2, respectively.

RESULTS

Acute exposure of PC12 cells to 6-OH-BDE-47 (5 microM) induced vesicular catecholamine release. Catecholamine release coincided with a transient increase in [Ca2+]i, which was observed shortly after the onset of exposure to 6-OH-BDE-47 (120 microM). An additional late increase in [Ca2+]i was often observed at > or =1 microM 6-OH-BDE-47. The initial transient increase was absent in cells exposed to the parent compound BDE-47, whereas the late increase was observed only at 20 microM. Using the mitochondrial uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) and thapsigargin to empty intracellular Ca2+ stores, we found that the initial increase originates from emptying of the endoplasmic reticulum and consequent influx of extracellular Ca2+, whereas the late increase originates primarily from mitochondria.

CONCLUSION

The hydroxylated metabolite 6-OH-BDE-47 is more potent in disturbing Ca2+ homeostasis and neurotransmitter release than the parent compound BDE-47. The present findings indicate that bioactivation by oxidative metabolism adds considerably to the neurotoxic potential of PBDEs. Additionally, based on the observed mechanism of action, a cumulative neurotoxic effect of PBDEs and ortho-substituted polychlorinated biphenyls on [Ca2+]i cannot be ruled out.

Comparative absorption and bioaccumulation of polybrominated diphenyl ethers following ingestion via dust and oil in male rats

Household dust has been implicated as a major source of polybrominated diphenyl ether (PBDE) exposure in humans. This finding has important implications for young children, who tend to ingest more dust than adults and may be more susceptible to some of the putative developmental effects of PBDEs. Absorption parameters of PBDEs from ingested dust are unknown; therefore, the objectives of this study were to determine and to compare the uptake of PBDEs from either household dust (NIST Standard Reference Material 2585) or a corn oil solution. Male rats were administered dust or corn oil doses at 1 or 6 microg of PBDEs kg(-1) body wt in the diet for 21 days (n = 4 rats per group). The concentrations of 15 PBDEs were measured in adipose tissue and liver from each treatment group and showed that bioconcentration was congener dependent, but for the majority of congeners, the concentrations did not differ with either dose level or dose vehicle. Hepatic Cyp2b1 and 2b2 mRNA expression increased in rats receiving the higher PBDE doses, suggesting potential effects on metabolic activity. Retention of PBDEs in tissues ranged from <5% of the dose for BDE-209 to 70% for BDEs-47, 100, and 153 but generally did not differ between the high dust and high oil treatment groups. Excretion via the feces was significantly lower in the high oil dosed rats suggesting differences in absorption, excretion, and/or metabolism. The present study shows that PBDEs in dust are readily bioavailable and are biologically active, as indicated by increased transcription of hepatic enzymes.

Accumulation, whole-body depletion, and debromination of decabromodiphenyl ether in male sprague-dawley rats following dietary exposure

Decabromodiphenyl ether (BDE-209) isthe major component in the flame-retardant formulation DecaBDE which is incorporated into numerous consumer goods ranging from upholsteries to electronics. Because of the high volume of DecaBDE produced, its presence in consumer products and the environment, and the finding of BDE-209 in the blood of exposed workers, the extent of bioavailability, persistence, and potential debromination are important issues. To measure the bioconcentration, distribution, reductive debromination, and whole-body half-lives of BDE-209 after multiple low doses in an animal model, we dosed rats with a commercial DecaBDE (0.3 microg/g of diet) for 21 days and measured tissue polybrominated diphenyl ether levels during a 21 day withdrawal period. BDE-209, three nona-BDEs, and four octa-BDEs accumulated in the rats and distributed proportionately throughout the body. Only 5% of the total BDE-209 dose was present as parent compound in the rats after 21 days of dosing and <4% in the feces, suggesting extensive metabolism. A nona-BDE (BDE-207) and two octa-BDEs (BDEs-201 and -197) appeared to form via meta-debromination(s) of BDE-209 to a minimal extent (1% of the total BDE-209 dose). The wholebody half-lives tended to increase with decreasing bromination; however, two octa-BDEs, presumably forming from debromination, increased in the rats after 21 days of withdrawal and demonstrated the potential for BDE-209 to form more persistent lipophilic compounds in vivo.