A 28-Day Oral Dose Toxicity Study Enhanced to Detect Endocrine Effects of Hexabromocyclododecane in Wistar Rats

Kinetic study of γ-hexabromocyclododecane orally given to laying hens (Gallus domesticus). "Transfer of HBCD in laying hens"

INTRODUCTION

High concentrations of hexabromocyclododecane (HBCD) sometimes recorded in free-range hens' eggs are thought to be due to soil ingestion. Of the three stereoisomers of HBCD (α-, β-, and γ-HBCD), γ-HBCD is the main component in the commercial mixture, as well as in environmental matrices, whereas the isomer profile is α-dominated in biota. In fish and in mammals, this shift is thought to be due to a rapid elimination of γ-HBCD and to its bioisomerization to the more persistent α-HBCD. The aim of the current controlled study was to better understand the fate of ingested HBCD in laying hens. The isomer profile in soil being γ-dominated, excretion kinetics of γ-HBCD into egg yolk, and accumulation in liver and in abdominal fat were investigated.

MATERIALS AND METHODS

Forty-eight laying hens were individually housed and fed with a spiked diet containing 1.1-ng γ-HBCD per gram for 21 days and with a clean diet for the following 18 days. Hens were sequentially slaughtered throughout the 39-day experiment. α-, β-, and γ-HBCD were analyzed in egg yolk, in abdominal fat, and in liver by LC-MS/MS. α- and γ-HBCD were quantified in the three tissues, while β-HBCD was never quantified.

RESULTS AND CONCLUSION

Kinetics of the two isomers suggests that γ-HBCD is rapidly biotransformed and eliminated, and partly isomerized into the more persistent α-HBCD. Carry-over rate of ingested γ-HBCD to egg yolk was estimated at 1.2%. Estimated half-lives of γ-HBCD in egg yolk, in abdominal fat, and in liver were 2.9, 13, and 0.41 days, respectively.

Tri-decabrominated diphenyl ethers and hexabromocyclododecane in indoor air and dust from Stockholm microenvironments 1: levels and profiles

Indoor air (gas and particle phase) and dust samples were collected from 10 houses, 44 apartments, 10 day care centers, 10 offices, 17 new cars and two car dealership halls from Stockholm, Sweden, and analyzed for polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD). Median ΣPBDE concentrations in air were 330, 58, 4000, 14000 and 510 pg/m(3) in houses, apartments, day care centers, offices and cars, respectively. Median ΣPBDE concentrations in dust were 510, 1400, 1200, 1200 and 1400 ng/g in houses, apartments, day care centers, offices and cars, respectively. HBCD was detected in most dust samples (median range, 45-340 ng/g) but only in a few air samples (median range, <1.6-2.0 pg/m(3)). For all microenvironments, the brominated flame retardant (BFR) found in highest concentration in air was ΣDecaBDE, primarily BDE-209, followed by ΣPentaBDE, and in dust, ΣDecaBDE, followed by HBCD (offices, day care centers, cars) or ΣPentaBDE (houses, apartments). Positive correlations were found between matched air and dust samples for ΣPentaBDE, but not for ΣDecaBDE.

Analysis of brominated flame retardants in house dust

The main objective of this study was to create a robust analytical method to analyse the flame retardants decabromodiphenylether (BDE-209), hexabromocyclododecane (HBCD), and tetrabromobisphenol-A (TBBPA) in house dust in order to estimate the degree of contamination of indoor environment. A liquid chromatography method equipped with a UV-detector and electro spray-tandem mass spectrometry was used to achieve this result. Applying an external calibration for BDE-209, an internal calibration for TBBPA, and a standard addition method for HBCD low limits of quantification were obtained. The analytical procedure was carried out under exclusion of UV-light as the target compounds potentially degrade when being exposed to UV-light. Empirical data were obtained in addition to the dust samples to estimate potential influences of apartment characteristics. A weak correlation between the number of electric devices and TBBPA was found.

Hexabromocyclododecane: current understanding of chemistry, environmental fate and toxicology and implications for global management

Hexabromocyclododecane (HBCD) is a globally produced brominated flame retardant (BFR) used primarily as an additive FR in polystyrene and textile products and has been the subject of intensified research, monitoring and regulatory interest over the past decade. HBCD is currently being evaluated under the Stockholm Convention on Persistent Organic Pollutants. HBCD is hydrophobic (i.e., has low water solubility) and thus partitions to organic phases in the aquatic environment (e.g., lipids, suspended solids). It is ubiquitous in the global environment with monitoring data generally exhibiting the expected relationship between proximity to known sources and levels; however, temporal trends are not consistent. Estimated degradation half-lives, together with data in abiotic compartments and long-range transport potential indicate HBCD may be sufficiently persistent and distributed to be of global concern. The detection of HBCD in biota in the Arctic and in source regions and available bioaccumulation data also support the case for regulatory scrutiny. Toxicity testing has detected reproductive, developmental and behavioral effects in animals where exposures are sufficient. Recent toxicological advances include a better mechanistic understanding of how HBCD can interfere with the hypothalamic-pituitary-thyroid axis, affect normal development, and impact the central nervous system; however, levels in biota in remote locations are below known effects thresholds. For many regulatory criteria, there are substantial uncertainties that reduce confidence in evaluations and thereby confound management decision-making based on currently available information.

Associations between brominated flame retardants in human milk and thyroid-stimulating hormone (TSH) in neonates

BACKGROUND

Brominated flame retardants (BFRs) have been in widespread use in a vast array of consumer products since the 1970s. The metabolites of some BFRs show a structural similarity to thyroid hormones and experimental animal studies have confirmed that they may interfere with thyroid hormone homeostasis. A major concern has been whether intrauterine exposure to BFRs may disturb thyroid homeostasis since the fetal brain is particularly susceptible to alterations in thyroid hormones. However, few reports on newborns have been published to date.

OBJECTIVES

To evaluate the association between BFRs and neonatal thyroid-stimulating hormone (TSH).

METHODS

We studied six polybrominated diphenyl ethers (PBDEs) measured in milk samples from 239 women who were part of the "Norwegian Human Milk Study" (HUMIS), 2003-2006. Hexabromocyclododecane (HBCD) and BDE-209 were measured in a subset of the women (193 and 46 milk samples, respectively). The milk was sampled at a median of 33 days after delivery. TSH was measured in babies three days after delivery as part of the routine national screening program for early detection of congenital hypothyroidism. Additional information was obtained through the Medical Birth Registry and questionnaires to the mothers.

RESULTS

The PBDE concentrations in human milk in Norway were comparable to concentrations reported from other European countries and Asia, but not the US and Canada where levels are approximately one order of higher magnitude. We observed no statistically significant associations between BDE-47, 99, 153, 154, 209 and HBCD in human milk and TSH in models adjusted for possible confounders and other environmental toxicants including polychlorinated biphenyls (PCBs).

CONCLUSIONS

We did not observe an association between TSH and exposure to HBCD and PBDEs within the exposure levels observed.

Disruptive effects of persistent organohalogen contaminants on thyroid function in white whales (Delphinapterus leucas) from Svalbard

We analysed levels of 56 organohalogen contaminants (OHCs) including brominated flame retardants, polychlorinated biphenyls (PCBs), and organochlorine pesticides in the blubber of white (beluga) whales (Delphinapterus leucas) from Svalbard, Norway (N=12; 6 adults [5 males and 1 female] and 6 subadults [4 males and 2 females]) collected in 1996-2001. We also measured circulating levels of thyroid hormones (THs) and thyroid stimulating hormone (TSH) in the whales. The results confirm that OHC levels in these white whales are among the highest levels recorded in wildlife from Svalbard, and at the high end of the range when compared to white whales from the North American Arctic. A projection to latent structure (PLS) model (subadults and adult males grouped together) revealed that known or suspected thyroid disruptive contaminants (polybrominated diphenylether [PBDE]-28, -47, -99, -100, and -154, hexachlorobenzene [HCB], and PCB-105) were negatively correlated with circulating levels of total thyroxin (TT4), free T4 (FT4) and free triiodothyronine (FT3). Most of these negative relationships were also confirmed using partial correlations controlling for length (and thus age) of the whales. The positive correlations of TT4, FT4 and FT3 with hexabromocyclododecane (HBCD), α-hexachlorocyclohexane (α-HCH), chlorinated bornanes CHB-40 and CHB-62 revealed by the PLS model were not confirmed by partial correlations. TH levels in the present study appeared to be somewhat lower than levels measured in beluga whales from the Canadian Arctic. However, we were not able to determine if this was caused by different levels of OHCs, or differences in biological factors (e.g. age, sex, moulting status, and season) and analytical methods between the studies. Although the sample sizes were low and statistical models cannot depict the biological cause-effect relationships, this study suggests negative influences of specific OHCs, particularly PBDEs, on thyroid hormone levels in white whales. The impact this might have on individual and population health is unknown.

Dietary intake of hexabromocyclododecane diastereoisomers (α-, β-, and γ-HBCD) in the Belgian adult population

A study was performed to assess exposure of the Belgian population to HBCD diastereoisomers. Measurements of HBCD were performed by UPLC-MS/MS, on 45 composite samples from 5 major food groups: dairy (products), meat (products), eggs, fish (products) and a group of "other" products. The medium bound estimated average daily intake (EDI) of ΣHBCD in the Belgian population was 0.99 ng kg(-1)bw d(-1). The diastereoisomer contribution to the mean EDI showed a predominance of γ-HBCD at 67%, followed by α-HBCD at 25% and 8% for β-HBCD. These results are consistent with the pattern found in the two food groups contributing the most to the EDI: meat (products) and the group of "other" products. Anyway, it has to be noted that diastereomeric distribution of HBCD can change due to bioisomerisation in biological material. Levels of HBCD diastereoisomers found in Belgian food samples of animal origin were low in comparison with those found in other EU countries and the resulting EDI was substantially below the proposed thresholds.

Temporal trends of polybrominated diphenyl ethers and hexabromocyclododecane in Swedish Peregrine Falcon (Falco peregrinus peregrinus) eggs

A temporal trend study of brominated flame retardants in eggs from peregrine falcon (Falco peregrinus peregrinus), a terrestrial bird of prey, is presented. Eggs collected between 1974 and 2007 were analyzed for the major constituents of the Penta-, Octa- and Decabromodiphenyl ether technical products (BDE-47, -99, -100, -153, -183 and -209), and hexabromocyclododecane (HBCD). Concentrations of BDE-99, -100, -153, -183, -209 and HBCD increased from 1974 to 2000. After the early 2000s, BDE-99, -100, -153 and -183 concentrations decreased, whereas BDE-209 and HBCD concentrations continued to increase. No temporal trend was detected for BDE-47. Rates of increase also differed, with BDE-99 and -100 increasing 3-fold between the 1980s and mid-1990s, and BDE-153 and -183 increasing approximately 10-fold during the same period. The average yearly increase was 15% and 11% for BDE-209 and HBCD, respectively, based on log-linear regression trends. There is a change in BDE congener patterns over time, with a shift from the predominance of BDE-99 and -47 until the late 1980s, to BDE-153 becoming the predominant congener later on. BFR temporal trends in Swedish peregrine falcon eggs reflect European BFR usage patterns.

Biomonitoring-based risk assessment for hexabromocyclododecane (HBCD)

Hexabromocyclododecane (HBCD) is a brominated flame retardant compound that has been the subject of recent interest and risk assessment efforts due to its detection in a variety of environmental media and in human biological matrices. Because the exposure pathways for HBCD may be varied and exposure estimation uncertain, biomonitoring for HBCD in humans shows promise as a means of reflecting integrated human exposures to HBCD with lower uncertainty than through estimation of external exposures via multiple pathways. Data from numerous biomonitoring studies of HBCD over the past decade indicate that the central tendency of lipid-adjusted serum and human milk concentrations is approximately 1ng/g lipid, with upper bound levels of approximately 20 ng/g lipid. Recent risk assessment evaluations from Health Canada and the European Union have identified points of departure of 10 and 20mg/kg day, respectively, from rat repeated dose studies. The corresponding measured or estimated lipid-adjusted tissue concentrations in the laboratory animals at these points of departure range from 120,000 to 190,000 ng/g lipid. In comparison to these concentrations, the biomonitored human serum and milk concentrations indicate margins of exposure (MOEs) of 6000 to more than 100,000, which are greatly in excess of target MOE values. The use of internal dose measures (both from measurements of tissue concentrations in animal toxicology studies and from human biomonitoring studies) provides risk managers with highly relevant exposure information that is less uncertain than estimated external doses.

Hexabromocyclododecanes (HBCDs) in marine fishes along the Chinese coastline

This study reports concentrations of hexabromocyclododecanes (HBCDs) in two species of marine fish, large yellow croaker (Pseudosciaenacrocea) and silver pomfret (Pampusargenteus) (n = 46), from nine Chinese coastal cities (Dalian, Tianjin, Qingdao, Shanghai, Zhoushan, Wenzhou, Fuzhou, Quanzhou and Xiamen). HBCDs were detectable in all samples analyzed, indicating ubiquitous contamination of these compounds in the Chinese coastal environment. The average total HBCD concentration was 3.7 ng g⁻¹ lipid weight (range: 0.57-10.1 ng g⁻¹ lipid weight), which is relatively lower than other regions of the world, especially Europe, where HBCDs are intensively used. Among the three individual HBCD isomers (α-, β- and γ-HBCD) in all fish samples, the α-isomer showed a remarkable predominance (from 87.5% to 100% of total contribution), indicating its higher bioaccumulative potential. Geographically, the highest HBCD level present in fish was found in Dalian in northern China, and the lowest occurred in Wenzhou. Estimated daily intakes of HBCDs via fish consumption for the Chinese population were 0.004-1.00 ng kg body weight⁻¹ d⁻¹. These exposure levels were much lower than the effect levels.

Perinatal exposure to environmental contaminants detected in Canadian Arctic human populations changes bone geometry and biomechanical properties in rat offspring

Arctic inhabitants consume large proportions of fish and marine mammals, and are therefore continuously exposed to levels of environmental toxicants, which may produce adverse health effects. Fetuses and newborns are the most vulnerable groups. The aim of this study was to evaluate changes in bone geometry, mineral density, and biomechanical properties during development following perinatal exposure to a mixture of environmental contaminants corresponding to maternal blood levels in Canadian Arctic human populations. Sprague-Dawley rat dams were dosed with a Northern Contaminant Mixture (NCM) from gestational day 1 to postnatal day (PND) 23. NCM contains 27 contaminants comprising polychlorinated biphenyls, organochlorine pesticides, and methylmercury. Femurs were collected on PND 35, 77 and 350, and diaphysis was analyzed by peripheral quantitative computed tomography and three-point bending test, while femoral neck was assessed in an axial loading experiment. Dose-response modeling was performed to establish the benchmark dose (BMD) for the analyzed bone parameters. Exposure to the high dose of NMC resulted in short and thin femur with reduced mechanical strength in offspring at PND35. BMD of femur length, cortical area, and stiffness were 3.2, 1.6, and 0.8 mg/kg bw/d, respectively. At PND77 femur was still thin, but at PND350 no treatment-related bone differences were detected. This study provides new insights on environmental contaminants present in the maternal blood of Canadian Arctic populations, showing that perinatal exposure induces bone alterations in the young offspring. These findings could be significant from a health risk assessment point of view.

Halogenated flame retardants: do the fire safety benefits justify the risks?

Since the 1970s, an increasing number of regulations have expanded the use of brominated and chlorinated flame retardants. Many of these chemicals are now recognized as global contaminants and are associated with adverse health effects in animals and humans, including endocrine and thyroid disruption, immunotoxicity, reproductive toxicity, cancer, and adverse effects on fetal and child development and neurologic function. Some flame retardants such as polybrominated diphenyl ethers (PBDEs) have been banned or voluntarily phased out by manufacturers because of their environmental persistence and toxicity, only to be replaced by other organohalogens of unknown toxicity. Despite restrictions on further production in some countries, consumer products previously treated with banned retardants are still in use and continue to release toxic chemicals into the environment, and the worldwide use of organohalogen retardants continues to increase. This paper examines major uses and known toxic effects of commonly-used organohalogen flame retardants, replacements for those that have been phased out, their combustion by-products, and their effectiveness at reducing fire hazard. Policy and other solutions to maintain fire safety while reducing toxicity are suggested. The major conclusions are: (1) Flammability regulations can cause greater adverse environmental and health impacts than fire safety benefits. (2) The current options for end-of-life disposal of products treated with organohalogens retardants are problematic. (3) Life-cycle analyses evaluating benefits and risks should consider the health and environmental effects of the chemicals, as well as their fire safety impacts. (4) Most fire deaths and most fire injuries result from inhaling carbon monoxide, irritant gases, and soot. The incorporation of organohalogens can increase the yield of these toxic by-products during combustion. (5) Fire-safe cigarettes, fire-safe candles, child-resistant lighters, sprinklers, and smoke detectors can prevent fires without the potential adverse effects of flame retardant chemicals. (6) Alternatives to organohalogen flame retardant chemicals include using less flammable materials, design changes, and safer chemicals. To date, before evaluating their health and environmental impacts, many flame retardant chemicals have been produced and used, resulting in high levels of human exposure. As a growing literature continues to find adverse impacts from such chemicals, a more systematic approach to their regulation is needed. Before implementing new flammability standards, decision-makers should evaluate the potential fire safety benefit versus the health and environmental impacts of the chemicals, materials, or technologies likely to be used to meet the standard. Reducing the use of toxic or untested flame retardant chemicals in consumer products can protect human and animal health and the global environment without compromising fire safety.

Brominated flame retardants in the Arctic environment--trends and new candidates

Polybrominated diphenyl ethers (PBDEs) containing two to 10 bromines are ubiquitous in the Arctic, in both abiotic and biotic samples. Hexabromocyclododecane (HBCD) is also ubiquitous in the Arctic, with the gamma-HBCD isomer predominating in air, the alpha-HBCD isomer predominating in biota and similar concentrations of alpha-, beta- and gamma-HBCD found in marine sediments. Other brominated flame retardants (BFRs) found in some Arctic samples are polybrominated biphenyls (PBBs), tetrabromobisphenol A (TBBPA), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), hexabromobenzene (HxBBz), pentabromoethylbenzene (PBEB), pentabromotoluene (PBT), and 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH). Temporal trends of tetra- to heptaBDEs and HBCD show increasing concentrations or a tendency to levelling off depending on the matrix (air, sediment, biota) and location, but no uniform picture for the Arctic emerges. BDE-209 concentrations are increasing in air. PBDEs and HBCD spatial trends in seabirds and marine mammals are similar to those seen previously for polychlorinated biphenyls (PCBs), with highest concentrations found in organisms from East Greenland and Svalbard. These trends indicate western Europe and eastern North America as important source regions of these compounds via long range atmospheric transport and ocean currents. Latitudinal trends showed lower concentrations and fluxes of PBDEs at higher latitudes. The tetra-hexaBDEs and alpha-HBCD biomagnify in Arctic food webs. Results for BDE-209 are more conflicting, showing either only low or no biomagnification potential. PBDE and HBCD concentrations are lower in terrestrial organisms and higher in marine top predators such as some killer whale populations in Alaska and glaucous gulls from the Barents Sea area. Higher concentrations are seen near populated areas indicating local sources. Findings of BTBPE, HxBBz, PBEB, PBT and TBECH in seabirds and/or marine mammals indicate that these compounds reach the Arctic, most probably by long range atmospheric transport and accumulate in higher trophic level organisms and that increasing use as PBDE replacements will lead to increasing concentrations.

Exposure and effects assessment of persistent organohalogen contaminants in arctic wildlife and fish

Persistent organic pollutants (POPs) encompass an array of anthropogenic organic and elemental substances and their degradation and metabolic byproducts that have been found in the tissues of exposed animals, especially POPs categorized as organohalogen contaminants (OHCs). OHCs have been of concern in the circumpolar arctic for decades. For example, as a consequence of bioaccumulation and in some cases biomagnification of legacy (e.g., chlorinated PCBs, DDTs and CHLs) and emerging (e.g., brominated flame retardants (BFRs) and in particular polybrominated diphenyl ethers (PBDEs) and perfluorinated compounds (PFCs) including perfluorooctane sulfonate (PFOS) and perfluorooctanic acid (PFOA) found in Arctic biota and humans. Of high concern are the potential biological effects of these contaminants in exposed Arctic wildlife and fish. As concluded in the last review in 2004 for the Arctic Monitoring and Assessment Program (AMAP) on the effects of POPs in Arctic wildlife, prior to 1997, biological effects data were minimal and insufficient at any level of biological organization. The present review summarizes recent studies on biological effects in relation to OHC exposure, and attempts to assess known tissue/body compartment concentration data in the context of possible threshold levels of effects to evaluate the risks. This review concentrates mainly on post-2002, new OHC effects data in Arctic wildlife and fish, and is largely based on recently available effects data for populations of several top trophic level species, including seabirds (e.g., glaucous gull (Larus hyperboreus)), polar bears (Ursus maritimus), polar (Arctic) fox (Vulpes lagopus), and Arctic charr (Salvelinus alpinus), as well as semi-captive studies on sled dogs (Canis familiaris). Regardless, there remains a dearth of data on true contaminant exposure, cause-effect relationships with respect to these contaminant exposures in Arctic wildlife and fish. Indications of exposure effects are largely based on correlations between biomarker endpoints (e.g., biochemical processes related to the immune and endocrine system, pathological changes in tissues and reproduction and development) and tissue residue levels of OHCs (e.g., PCBs, DDTs, CHLs, PBDEs and in a few cases perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonates (PFSAs)). Some exceptions include semi-field studies on comparative contaminant effects of control and exposed cohorts of captive Greenland sled dogs, and performance studies mimicking environmentally relevant PCB concentrations in Arctic charr. Recent tissue concentrations in several arctic marine mammal species and populations exceed a general threshold level of concern of 1 part-per-million (ppm), but a clear evidence of a POP/OHC-related stress in these populations remains to be confirmed. There remains minimal evidence that OHCs are having widespread effects on the health of Arctic organisms, with the possible exception of East Greenland and Svalbard polar bears and Svalbard glaucous gulls. However, the true (if any real) effects of POPs in Arctic wildlife have to be put into the context of other environmental, ecological and physiological stressors (both anthropogenic and natural) that render an overall complex picture. For instance, seasonal changes in food intake and corresponding cycles of fattening and emaciation seen in Arctic animals can modify contaminant tissue distribution and toxicokinetics (contaminant deposition, metabolism and depuration). Also, other factors, including impact of climate change (seasonal ice and temperature changes, and connection to food web changes, nutrition, etc. in exposed biota), disease, species invasion and the connection to disease resistance will impact toxicant exposure. Overall, further research and better understanding of POP/OHC impact on animal performance in Arctic biota are recommended. Regardless, it could be argued that Arctic wildlife and fish at the highest potential risk of POP/OHC exposure and mediated effects are East Greenland, Svalbard and (West and South) Hudson Bay polar bears, Alaskan and Northern Norway killer whales, several species of gulls and other seabirds from the Svalbard area, Northern Norway, East Greenland, the Kara Sea and/or the Canadian central high Arctic, East Greenland ringed seal and a few populations of Arctic charr and Greenland shark.

Toxicokinetics of the flame retardant hexabromocyclododecane gamma: effect of dose, timing, route, repeated exposure, and metabolism

Hexabromocyclododecane-gamma (γ-HBCD) is the predominate diastereoisomer in the commercial HBCD mixture used as a flame retardant in a wide variety of consumer products. Three main diastereoisomers, alpha (α), beta (β), and gamma (γ), comprise the mixture. Despite the γ-diastereoisomer being the major diastereoisomer in the mixture and environmental samples, the α-diastereoisomer predominates human tissue and wildlife. This study was conducted to characterize absorption, distribution, metabolism, and excretion parameters of γ-HBCD with respect to dose and time following a single acute exposure and repeated exposure in adult female C57BL/6 mice. Results suggest that 85% of the administered dose (3 mg/kg) was absorbed after po exposure. Disposition was dose independent and did not significantly change after 10 days of exposure. Liver was the major depot (< 0.3% of dose) 4 days after treatment followed by blood, fat, and then brain. γ-HBCD was rapidly metabolized and eliminated in the urine and feces. For the first time, in vivo stereoisomerization was observed of the γ-diastereoisomer to the β-diastereoisomer in liver and brain tissues and to the α- and β-diastereoisomer in fat and feces. Polar metabolites in the blood and urine were a major factor in determining the initial whole-body half-life (1 day) after a single po exposure. Elimination, both whole-body and from individual tissues, was biphasic. Initial half-lives were approximately 1 day, whereas terminal half-lives were up to 4 days, suggesting limited potential for γ-diastereoisomer bioaccumulation. The toxicokinetic behavior reported here has important implications for the extrapolation of toxicological studies of the commercial HBCD mixture to the assessment of risk.

Altered thyroxine metabolism in rainbow trout (Oncorhynchus mykiss) exposed to hexabromocyclododecane (HBCD)

Hexabromocyclododecane (HBCD) is an additive flame retardant used in consumer and industrial applications. Our earlier work suggested that fish exposed to HBCD exhibited an increase in the rate of turnover of thyroxine (T4), the precursor molecule to the active thyroid hormone triiodothyronine (T3). To examine this further, juvenile rainbow trout were held in the laboratory and fed diets containing environmentally relevant concentrations of the individual alpha, beta or gamma isomers. Thirty-two days after feeding began, 20 fish from each group were gavaged with gelatin containing 1microCi [(125)I]-T4. Uptake of [(125)I]-T4 from the gut was low and recoveries of the initial [(125)I]-T4 were <10% after 2d and <3% and <2% after 6 and 14d respectively, with no differences among groups. However, measurements of the labeled T4 in tissues 2, 4, 6 and 14d after gavage showed that tissue disposition and elimination rates of the hormone were altered by HBCD. In particular, on day 14 after gavage feeding, there was significantly lower radioactivity in the thyroid of fish exposed to the HBCD isomers relative to the reference group. This implies that either there was lower iodide uptake by the gland in fish exposed to HBCD or that the rate of thyroid hormone turnover in HBCD treated fish was elevated. There was also a significantly higher type II outer ring deiodinase enzyme activity in livers of fish exposed to the beta and gamma isomers. Taken together, these results indicate that HBCD can potentially impact the thyroid system of fish.

Hexabromocyclododecane decreases tumor-cell-binding capacity and cell-surface protein expression of human natural killer cells

Hexabromocyclododecane (HBCD) is a flame retardant that decreases the lytic function of human natural killer (NK) cells. NK cells defend against tumor cells and virally infected cells. Thus, HBCD has the potential to increase cancer incidence and viral infections. NK cells must bind to their targets for lysis to occur. Thus, concentrations of HBCD that decrease lytic function were examined for their ability to alter NK binding to tumor targets. Levels of HBCD that caused a loss of binding function were examined for effects on expression of cell surface proteins needed for binding. NK cells exposed to HBCD for 24 h, 48 h or 6 days or to HBCD for 1 h followed by 24 h, 48 h or 6 days in HBCD-free media were examined for binding function and cell surface protein expression. The results indicated that exposure of NK cells to 10 microM HBCD for 24 h (which caused a greater than 90% loss of lytic function) caused a very significant decrease in NK cell binding function (70.9%), and in CD16 and CD56 cell-surface protein expression (57.8 and 24.6% respectively). NK cells exposed to 10 microM HBCD for 1 h followed by 24 h in HBCD-free media (which caused a 89.3% loss of lytic function) showed decreased binding function (79.2%), and CD 16 expression (48.1%). Results indicate that HBCD exposures decreased binding function as well as cell-surface marker expression in NK cells and that these changes may explain the losses of lytic function induced by certain HBCD exposures.

Spatial distribution of hexabromocyclododecanes (HBCDs), polybrominated diphenyl ethers (PBDEs) and organochlorines in bivalves from Japanese coastal waters

In order to elucidate the spatial distribution of brominated flame retardants (BFRs) in the Japanese coastal environment, hexabromocyclododecanes (HBCDs), polybrominated diphenyl ethers (PBDEs) and organochlorines (OCs: PCBs, DDTs, CHLs, HCHs, HCB) were determined in bivalves (oysters and mussels) collected from Japanese coastal waters. HBCDs and PBDEs were detected in all samples analyzed. Concentration ranges of HBCDs were 12-5200 ng g(-1) lipid wt., followed by PCBs (20-3100 ng g(-1))>PBDEs (3.1-86 ng g(-1) lipid wt.). The highest concentration of HBCDs was found in the Osaka region. This result indicates that HBCDs are ubiquitous and predominant compounds in bivalves from the Japanese coastal waters. Since no species differences between oysters and mussels were observed for the bioaccumulation properties of HBCDs and PBDEs, oysters could be utilized for BFR contamination monitoring worldwide as an alternative to mussels. Global comparisons between oysters and mussels showed that HBCD concentrations in Japan are among the highest levels reported from Asia and Europe. Estimated dietary exposures of HBCDs and PBDEs through seafood were 0.45-34 ng kg body weight(-1)d(-1), and 0.054-6.8 ng kg body weight(-1)d(-1), respectively. These exposure levels were more than 1000 times lower than the lowest observable effects or no observable adverse effects levels for HBCDs and PBDEs, respectively.

Exposure to hexabromocyclododecanes (HBCDs) via dust ingestion, but not diet, correlates with concentrations in human serum: preliminary results

BACKGROUND

Hexabromocyclododecane (HBCD) is a high-production-volume chemical used as flame retardant in polystyrene insulation and textiles. Because it is not chemically bound to the polymer, HBCD can migrate into the environment, contaminating indoor dust and foodstuff.

OBJECTIVES

We examined for the first time the relationship between combined exposure to three HBCD isomers (SigmaHBCDs) via ingestion of food (duplicate diets) and indoor dust and HBCD concentrations in serum for 16 Belgian adults (20-25 years of age). We also determined the chiral signatures of HBCDs to advance understanding of source-to-human enantioselective degradation and/or metabolism.

METHODS

Concentrations and chiral signatures of alpha-, beta-, and gamma-HBCD in duplicate diets, dust, and serum were measured by liquid chromatography/tandem mass spectrometry.

RESULTS

Dietary intakes of SigmaHBCDs were 1.2-20 ng/day (average, 7.2 ng/day), whereas those estimated under average (20 mg dust/day) and high (50 mg dust/day) dust ingestion scenarios were 1.1-15 ng/day (average intake, 3.2 ng/day) and 2.8-38 ng/day (average intake, 8.0 ng/day), respectively. Concentrations of SigmaHBCDs measured in blood serum were < 0.5 to 11 ng/g lipid weight (lw) (average, 2.9 ng/g lw). Gamma-HBCD dominated in food, whereas alpha-HBCD dominated in dust and was the sole isomer in serum. Although exposure via dust ingestion correlated significantly (p < 0.01) with concentrations in serum, no such correlation was evident with dietary exposure (p > 0.1). Although no enantioselective enrichment was detected in either dust or diet, substantial enrichment of (-)alpha-HBCD was observed in serum.

CONCLUSIONS

Serum concentrations of HBCDs were correlated with the exposure via dust, but not via dietary ingestion. The enrichment of the (-)alpha-HBCD enantiomer in humans appears to be due to in vivo enantioselective metabolism/excretion rather than ingestion of dust or diet.

Hexabromocyclododecane decreases the lytic function and ATP levels of human natural killer cells

This study investigates the effect of hexabromocyclododecane (HBCD) on the lytic function of human natural killer (NK) cells and on ATP levels in NK cells. NK cells are capable of lysing tumor cells, virally infected cells, and antibody-coated cells. HBCD is a brominated cyclic alkane used primarily as an additive flame retardant. If HBCD interferes with NK cell function, this could increase risk of tumor development and/or viral infection. NK cells were exposed to various concentrations of HBCD for 24 and 48 h and 6 days before determining lytic function and ATP levels. ATP levels and lytic function were also determined in NK cells that were exposed to HBCD for 1 h followed by 24 and 48 h, and 6 days in HBCD-free media. The results indicated that exposure of NK cells to 10 microm HBCD for 24 h causes a very significant decrease in both NK cell lytic function and ATP levels (93.5 and 90.5%, respectively). Exposure of NK cells to 10 microm HBCD for 1 h followed by 24 h in HBCD-free media showed a progressive and persistent loss of lytic function (89.3%) as well as a decrease in ATP levels (46.1%). The results indicate that HBCD exposures decreased lytic function as well as ATP levels. However, a decrease in lytic function was not necessarily accompanied by a similar decrease in ATP. Importantly, these results also indicate that a brief (1 h) exposure to HBCD causes a progressive loss of lytic function over a 6 day period.

Bioaccumulative characteristics of hexabromocyclododecanes in freshwater species from an electronic waste recycling area in China

Hexabromocyclododecanes (HBCDs) are now emerging ubiquitous contaminants due to their wide usage, persistence and toxicities. To investigate the bioaccumulative characteristics of HBCDs, sediments, Winkle (Littorina littorea), crucian carp (Carassius carassius) and loach (Misgurnus anguillicaudatus) were collected from two streams near an E-waste dismantling site in China, and HBCD exposure test was then conducted on Chinese rare minnow. The concentration of HBCDs was 14 ng g(-1) dry weight in sediments, 186, 377 and 1791 ng g(-1) lipid weight in winkle, crucian carp and loach, respectively. gamma-HBCD was found to be the dominant diastereoisomer in the sediments (63% of total HBCDs). However, alpha-HBCD was selectively accumulated in the biotic samples and contributed to 77%, 63% and 63% of total HBCDs in winkle, crucian carp and loach, respectively. Moreover, an enrichment of (-)-enantiomers of alpha- and gamma-HBCD were found in the winkle. The reverse results were observed in the crucian carp and loach. Similar observations of diastereoisomeric and enantiomeric composition were obtained in Chinese rare minnow with those found in the crucian carp and loach. These results indicate that the freshwater species from the streams are contaminated by HBCDs. alpha-HBCD can be selectively accumulated in organisms and the accumulative characteristics are enantioselective among species.

Identification of hydroxylated metabolites of hexabromocyclododecane in wildlife and 28-days exposed Wistar rats

We studied the presence of hydroxylated metabolites of hexabromocyclododecane (HBCD) in three wildlife species (tern egg, seal, and flounder) and in Wistar rats exposed to 30 and 100 mg HBCD/kg bw/day for 28 days. A nondestructive extraction, fractionation, and cleanup method was developed to separate the hydroxylated HBCD metabolites from the biotic sample matrix. Four different groups of hydroxylated HBCD metabolites were identified in rat adipose, liver, lung, and muscle tissues by liquid and gas chromatography (LC and GC) combined with mass spectrometry (MS): monohydroxy metabolites of HBCD, pentabromocyclododecene (PBCDe), tetrabromocyclododecene (TBCDe), and dihydroxy-HBCD. Dihydroxy-PBCDe was identified by GC-MS but could not be confirmed by LCMS. Debromination of HBCD to PBCDe was another metabolic pathway observed. In tern eggs from the Western Scheldt the monohydroxy-HBCD was found and in the blubber of harbor seal (Wadden Sea) the monohydroxy metabolites of HBCD and PBCDe were found. No hydroxylated metabolites were detected in the tissue of flounder (Wadden Sea). To our knowledge, this is the first study to identify different hydroxylated metabolite groups of HBCD in rat and wildlife samples.

Technical pentabromodiphenyl ether and hexabromocyclododecane as activators of the pregnane-X-receptor (PXR)

Technical pentabrominated diphenyl ether (pentaBDE mix) is a mixture of polybrominated diphenyl ethers (PBDEs) which has been widely used as a flame retardant. Since its ban in several countries it has been replaced by other brominated flame retardants such as hexabromocyclododecane (HBCD). Both certain PBDE congeners and HBCD are present in environmental and human samples reflecting their persistent and bioaccumulative properties. PentaBDE mix and HBCD have recently been found to induce cytochrome P450 (CYP) 3 enzymes in rat liver. In this study we tested both technical pentaBDE mix and HBCD for their potency to induce CYP3A enzymes in rat hepatocytes in primary culture, and in rat H4IIE and human HepG2 hepatoma cells. In rat hepatocytes, HBCD was a more effective CYP3A1 inducer than pentaBDE mix, being less effective, however, than the prototype inducer dexamethasone. In human HepG2 cells, both compounds and the prototype inducer rifampicin were about equally effective. In contrast, in HepG2 cells, HBCD failed to induce luciferin-PFBE dealkylase, a common catalytic activity of a number of CYP3A enzymes, possibly reflecting enzyme inhibition. A significant induction of catalytic activity was observed in rat hepatocytes with both compounds. Analysis of a XREM-driven reporter gene activity in transfected cells confirmed that both compounds act as agonists of the human and rat pregnane-X-receptor, which was detectable in all cell types used.

Developmental toxicity of brominated flame retardants, tetrabromobisphenol A and 1,2,5,6,9,10-hexabromocyclododecane, in rat offspring after maternal exposure from mid-gestation through lactation

To evaluate developmental exposure effects of two brominated flame retardants, tetrabromobisphenol A (TBBPA) and 1,2,5,6,9,10-hexabromocyclododecane (HBCD), pregnant Sprague-Dawley rats were administered either chemical at doses of 100, 1000 or 10,000 ppm in a soy-free diet from gestation day 10 until the day 20 after delivery. Offspring exposed to TBBPA showed dose-unrelated slight decreases of serum triiodothyronine (T(3)) concentration at postnatal day 20, and there was no evidence of hypothyroidism-related neuronal mismigration and impaired oligodendroglial development as judged by morphometric analyses of NeuN-immunoreactive neuronal distribution in the hippocampal CA1, and area of corpus callosum as well as density of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase)-immunoreactive oligodendrocytes in the cingulate deep cortex at the adult stage. On the other hand, HBCD exerted a weak hypothyroidism evident with increases in thyroid weight, thyroid follicular cell hypertrophy and serum concentrations of thyroid-stimulating hormone as well as decreases of serum T(3) concentrations in offspring at 10,000 ppm at weaning. Increased thyroid weights and decreased serum T(3) concentrations were also observed in the adult stage from 1000 ppm. With regard to the effect on brain development, HBCD reduced density of CNPase-positive oligodendrocytes at 10,000 ppm, suggesting an impaired oligodendroglial development. Results thus suggest that TBBPA did not exert developmental brain effects, while HBCD did, and 100 ppm was determined to be the no-observed-adverse-effect level of HBCD from changes in thyroid parameters at the adult stage by maternal exposure, translating into 8.1-21.3mg/kg-d.

Changes in gene expression and assessment of DNA methylation in primary human hepatocytes and HepG2 cells exposed to the environmental contaminants-Hexabromocyclododecane and 17-beta oestradiol

We evaluated the effects of two putative non-genotoxic hepatic carcinogens, hexabromocyclododecane (HBCD) and 17-beta oestradiol (E(2)) on global and CpG promoter DNA methylation in both primary human hepatocytes and hepatocellular carcinoma (HepG2) cells. The mRNA gene expression levels of genes involved particularly in cell cycle were also evaluated and potential correlation with DNA methylation status examined. HBCD at 0.03 and 0.3 ng/mL did not produce statistically significant differences in global genomic methylation. However, E(2) (0.1 ng/mL) significantly lowered global DNA methylation levels in HepG2 cells by approximately 65% (P<0.01). In primary hepatocytes, the promoter regions of N-cym and ERalpha were methylated in both control and treated groups, signifying lack of promoter demethylation by both HBCD and E(2). Furthermore, CpG promoter methylation of RB1 was observed in HepG2 cells but this was unaffected by treatments. The remaining genes (p16, C-myc, H-ras, THRalpha, histone H3, TBK1 and TNFRalpha) were unmethylated in their CpG promoter regions in both test systems. Quantitative RT-PCR showed that HBCD at 0.03 ng/mL up-regulated the expression of N-cym whereas E(2) up-regulated the expression of ERalpha and THRalpha genes in primary hepatocytes. In HepG2 cells, the mRNA gene expression levels of p16, RB1 and N-cym were significantly down regulated by HBCD (0.03 ng/mL) and E(2) (0.1 ng/mL) while HBCD at 0.3 ng/mL, significantly down regulated the expression levels of N-cym, ERalpha and ERbeta genes. Thus, while both HBCD and E(2) may alter the expression of certain genes involved in proliferation, the mechanisms appear unrelated to DNA methylation.

Effects of hexabromocyclododecane and polybrominated diphenyl ethers on mRNA expression in chicken (Gallus domesticus) hepatocytes

Hexabromocyclododecane (HBCD) and polybrominated diphenyl ethers (PBDEs) are additive flame retardants used in a wide range of consumer products. Both compounds have been detected in free-living avian species, but toxicological and molecular end points of exposure are limited. An in vitro approach was used to compare concentration-dependent effects of HBCD and the commercial penta-brominated diphenyl ether mixture DE-71 on cytotoxicity and mRNA expression in cultured hepatocytes derived from embryonic chickens. Neither HBCD-alpha, HBCD-technical mixture (TM), nor DE-71 effected hepatocyte viability at the highest concentrations assessed (30-100 microM). Real-time RT-PCR assays were developed to quantify changes in mRNA abundance of genes associated with chicken xenobiotic-sensing orphan nuclear receptor activation, the thyroid hormone (TH) pathway, and lipid regulation. Exposure to >or= 1 microM HBCD-alpha and HBCD-TM resulted in significant upregulation of cytochrome P450 (CYP) 2H1 (fourfold to sevenfold) and CYP3A37 (5- to 30-fold) at 24 and 36 h. In contrast, 30 microM DE-71 caused a twofold increase of CYP2H1 only. UGT1A9 expression was only upregulated by HBCD-alpha to a maximum of fourfold at >or= 1 microM. Transthyretin, thyroid hormone-responsive spot 14-alpha, and liver fatty acid-binding protein were all significantly downregulated (up to sevenfold) for cells exposed to >or= 1 microM HBCD-alpha and HBCD-TM. DE-71 also downregulated these three target genes twofold to fivefold at concentrations >or= 3 microM. Taken together, our results indicate that xenobiotic-metabolizing enzymes and genes associated with the TH pathway and lipid regulation are vulnerable to HBCD and DE-71 administration in cultured avian hepatocytes and might be useful molecular markers of exposure.

Bone mineral density changes in relation to environmental PCB exposure

BACKGROUND

Bone toxicity has been linked to organochlorine exposure following a few notable poisoning incidents, but epidemiologic studies in populations with environmental organochlorine exposure have yielded inconsistent results.

OBJECTIVES

The aim of this study was to investigate whether organochlorine exposure was associated with bone mineral density (BMD) in a population 60-81 years of age (154 males, 167 females) living near the Baltic coast, close to a river contaminated by polychlorinated biphenyls (PCBs).

METHODS

We measured forearm BMD in participants using dual energy X-ray absorptiometry; and we assessed low BMD using age- and sex-standardized Z-scores. We analyzed blood samples for five dioxin-like PCBs, the three most abundant non-dioxin-like PCBs, and p,p'-dichloro-phenyldichloroethylene (p,p'-DDE).

RESULTS

In males, dioxin-like chlorobiphenyl (CB)-118 was negatively associated with BMD; the odds ratio for low BMD (Z-score less than -1) was 1.06 (95% confidence interval, 1.01-1.12) per 10 pg/mL CB-118. The sum of the three most abundant non-dioxin-like PCBs was positively associated with BMD, but not with a decreased risk of low BMD. In females, CB-118 was positively associated with BMD, but this congener did not influence the risk of low BMD in women.

CONCLUSIONS

Environmental organochlorine exposures experienced by this population sample since the 1930s in Sweden may have been sufficient to result in sex-specific changes in BMD.

New insights into the endocrine disrupting effects of brominated flame retardants

The objective of this review is to provide an overview of recent studies demonstrating the endocrine disrupting (ED) effects of brominated flame retardants (BFRs), while highlighting interesting data presented at the recent international BFR workshop in Amsterdam in April, 2007. A review written in 2002 was used as a starting point and about 60 publications published since 2003 were reviewed. New insights into the in vivo effects of BFRs on thyroid hormone, estrogen and androgen pathways in both mammalian and non-mammalian models are provided, and novel (in vitro) findings on the mechanisms underlying ED effects are highlighted. Special attention is also given to reports on neurotoxicological effects at relatively low doses of BFRs, although an endocrine-related mechanism is disputable. Convincing evidence has been published showing that BFRs and importantly, BFR metabolites, have the potential to disrupt endocrine systems at multiple target sites. While some studies suggest a wide margin of safety between effect concentrations in rodent models and levels encountered in humans and the environment, other studies demonstrate that exposure to low doses relevant for humans and wildlife at critical time points in development can result in profound effects on both endocrine pathways and (neuro)development.

Brominated flame retardants as possible endocrine disrupters

Brominated flame retardants (BFR) are endocrine disrupters in experimental systems, both in vitro and in vivo. Although BFR effects on thyroid hormones are well confirmed, studies of effects on oestrogen/androgen systems are fewer but today growing in numbers. The effects of BFR on other hormone systems are still unknown. Hormonal effect levels in animals start from ca 1 mg/kg b.w., but there are exceptions: effects on spermatogenesis, suggesting hormonal causes, have been observed at a low dose (60 microg/kg b.w.) of a polybrominated diphenyl ether (PBDE) congener, BDE-99. It could be concluded that hormonal effects are of importance in risk assessment, and in some cases where effects are seen at low levels safety margins may be insufficient. One additional uncertainty is the lack of reliable human data that could be used to support animal BFR observations. In spite of the recent regulation of PBDE production, levels of both PBDE and of other BFR groups are still present in environmental samples. Thus, we have to deal with the possible effects of human BFR exposure for times to come. In order to reduce BFR exposure, the routes of exposure should be carefully examined and ways to reduce levels in major exposure routes considered.

Brominated flame retardants in fish and shellfish - levels and contribution of fish consumption to dietary exposure of Dutch citizens to HBCD

In order to determine the contamination with brominated flame retardants (BFR) in fish regularly consumed by Dutch citizens, 44 samples of freshwater fish, marine fish, and shellfish were analyzed for polybrominated diphenyl ethers (PBDE), tetrabromobisphenol-A (TBBP-A) and its methylated derivative (me-TBBP-A), and hexabromocyclododecane (HBCD), including its alpha-, beta- and gamma-diastereomers. The highest BFR concentrations were found in pike-perch and eel from the highly industrialized and urbanized rivers Rhine and Meuse. The sum concentrations of BDE 28, 47, 99, 100, 153, 154, 183, 209, and brominated biphenyl (BB) 153 and HBCD (selection based on The European Food Safety Authority monitoring recommendation) ranged from below quantification limits to 17 ng/g wet weight (ww) in marine fish and in freshwater fish from 0.6 ng/g ww in pike-perch to 380 ng/g ww in eel. The BDE congener profile in all fish and shellfish samples is dominated by BDE 47, followed by BDE 99, except for eel in which BDE 100 is higher than BDE 99. BDE 209 was detected in two mussel samples, most likely due to BDE 209 contaminated particulate matter in their intestines. Total-HBCD (as determined by GC/electron capture negative ion (ECNI)-MS) was detected in 22 out of the 44 samples in concentrations between 0.20 ng/g in marine fish and 230 ng/g ww in eel. Three HBCD diastereomers were determined by HPLC/ESI-MS/MS. alpha-HBCD was the prevalent congener in most fish samples, followed by gamma-HBCD. beta-HBCD, TBBP-A and me-TBBP-A were only detected in a few samples and at low concentrations. A considerable difference was found between HBCD results obtained from GC/ECNI-MS and HPLC/ESI-MS/MS: the GC/ECNI-MS results were 4.4 times higher, according to regression analysis. There is hardly any data on human dietary exposure to HBCD available. We have estimated the fish-related dietary exposure of HBCD for the average Dutch population. The medium bound intake was estimated at 8.3 ng/day for a 70-kg person (0.12 ng/kg bodyweight/day). For this estimation, we relied mostly on HPLC/ESI-MS/MS data as we argue that these results are more accurate than those obtained by GC/ECNI-MS.

Biotransformation enzymes and thyroid axis disruption in juvenile rainbow trout (Oncorhynchus mykiss) exposed to hexabromocyclododecane diastereoisomers

Juvenile rainbow trout (Oncorhynchus mykiss) were fed either a reference diet or one of three diets enriched with alpha, beta, or gamma diastereoisomers of hexabromocyclododecane (HBCD, C12H18Br6) for 56 days. This exposure period was followed by 112 days during which all fish were fed the reference diet. Potential effects of HBCD on phase I and II biotransformation enzyme activities and thyroid axis disruption were examined. Disruption of the thyroid axis was most evident in the gamma-HBCD exposed group, as indicated by lower circular FT4 and higher FT3 as well as an increase in thyroid epithelial cell height. However, fish fed the alpha-HBCD enriched diet also exhibited altered glucuronyltransferase activity and thyroid epithelial cell heights and the beta-HBCD group had altered FT4 and FT3 and glucuronyltransferase activity. T4ORD activity was not affected after 14 days, but was significantly lower among all HBCD exposed fish compared to the reference fish after 56 days. Results from these experiments indicate that all isomers have the potential to disrupt thyroid homeostasis.

A 28-day oral dose toxicity study enhanced to detect endocrine effects of a purified technical pentabromodiphenyl ether (pentaBDE) mixture in Wistar rats

A 28-day subacute oral toxicity study was performed in Wistar rats with a purified preparation of the commercial pentabromodiphenyl ether (pentaBDE), DE-71. The applied OECD407 protocol was enhanced for endocrine and immune parameters, and to enable benchmark dose analysis. A vehicle control group and 7 dose groups were included, which received 0.27, 0.82, 2.47, 7.4, 22.2, 66.7 or 200 mg pentaBDE/kg bw/d (mkd). The liver appeared to be a key target organ, showing a marked increase of weight and centrilobular hepatocellular hypertrophy, probably due to the observed induction of P450 enzymes, notably CYP1A and CYP2B. A marked decrease of circulating total thyroxine (TT4) and an increase of plasma cholesterol were probably secondary to the liver effects. Furthermore, dose-dependently decreased weight of epididymis, seminal vesicles, and prostate, as well as sperm head deformities in males, and induction of CYP17 activity in adrenals in females were observed, all possibly related to anti-androgenic activity. Finally, we observed a substantial increase of large unstained cells in the blood and a decrease of apolar retinoids in the liver. All these effects had benchmark doses at the lower confidence bound (BMDL) in the low- or mid-dose range, but particular sensitive, potentially adverse effects were TT4 decrease (BMDLs 1.1 in males and 1.8 mkd in females), and decrease of hepatic apolar retinoids (BMDLs 0.5 mkd in males and 2.3 mkd in females). These results contribute to refinement of the hazard identification of pentaBDE and improved risk assessment of human exposure to this industrial chemical and environmental pollutant.