EPA/635/R-07/008F 

www.epa.gov/iris 

TOXICOLOGICAL REVIEW 

OF

DECABROMODIPHENYL ETHER 

(BDE-209) 

(CAS No. 1163-19-5) 

In Support of Summary Information on the 

Integrated Risk Information System (IRIS)

June 2008

U.S. Environmental Protection Agency

Washington, DC
ii

DISCLAIMER 

This document has been reviewed in accordance with U.S. Environmental Protection Agency 

policy and approved for publication. Mention of trade names or commercial products does not 

constitute endorsement or recommendation for use. 
iii

CONTENTS—TOXICOLOGICAL REVIEW OF

2,2',3,3',4,4',5,5',6,6'-DECABROMODIPHENYL ETHER (CAS No. 1163-19-5) 

LIST OF TABLES .......................................................................................................................... v

LIST OF FIGURES ....................................................................................................................... vi

LIST OF ACRONYMS ................................................................................................................ vii

FOREWORD ..................................................................................................................................ix

AUTHORS, CONTRIBUTORS, AND REVIEWERS .................................................................. x

1. INTRODUCTION...................................................................................................................... 1

2. CHEMICAL AND PHYSICAL INFORMATION ..................................................................... 3

3. TOXICOKINETICS................................................................................................................... 4

3.1. ABSORPTION ................................................................................................................... 4

3.1.1. Studies in Humans .................................................................................................. 4

3.1.2. Studies in Animals.................................................................................................. 4

3.2. DISTRIBUTION ................................................................................................................ 6

3.2.1. Studies in Humans .................................................................................................. 6

3.2.1.1 Data in Human Milk................................................................................... 7

3.2.1.2. Data in Human Blood............................................................................... 7

3.2.2. Studies in Animals.................................................................................................. 9

3.3. METABOLISM ................................................................................................................ 12

3.4. ELIMINATION ................................................................................................................ 15

3.4.1. Half-life Estimates ................................................................................................ 17

3.5. PHYSIOLOGICALLY BASED TOXICOKINETIC MODELS ...................................... 18

4. HAZARD IDENTIFICATION ................................................................................................. 19

4.1. STUDIES IN HUMANS—EPIDEMIOLOGY, CASE REPORTS, CLINICAL 

 TRIALS ........................................................................................................................... 19

4.2. SHORT-TERM, SUBCHRONIC, AND CHRONIC STUDIES AND CANCER 

BIOASSAYS IN ANIMALS—ORAL AND INHALATION .......................................... 19

4.2.1. Short-term and Subchronic Studies ...................................................................... 19

4.2.1.1. Studies in Rats........................................................................................ 19

4.2.1.2. Studies in Mice ....................................................................................... 22

4.2.2. Chronic Studies and Cancer Bioassays ................................................................ 22

4.2.2.1. Study in Rats .......................................................................................... 23

4.2.2.2. Study in Mice ......................................................................................... 26

4.3. REPRODUCTIVE/DEVELOPMENTAL STUDIES—ORAL AND INHALATION ..... 28

4.3.1. Studies in Rats...................................................................................................... 28

4.3.2. Studies in Mice..................................................................................................... 31

4.4. OTHER ENDPOINT-SPECIFIC STUDIES .................................................................... 35

4.4.1. Receptor Site Interactions .................................................................................... 35

4.4.1.1. Aryl Hydrocarbon Receptor Studies ...................................................... 35

4.4.1.2. Estrogen Receptor Studies ..................................................................... 37

4.4.1.3. Other Receptors ...................................................................................... 37
iv

4.4.2. Immunological Studies ......................................................................................... 37

4.4.3. Genotoxicity ......................................................................................................... 38

4.5. SYNTHESIS OF MAJOR NONCANCER EFFECTS ..................................................... 39

4.5.1. Oral ....................................................................................................................... 39

4.5.2. Inhalation .............................................................................................................. 40

4.5.3. Mode-of-Action Information ................................................................................ 40

4.6. EVALUATION OF CARCINOGENICITY ..................................................................... 43

4.6.1. Summary of Overall Weight of Evidence ............................................................ 43

4.6.2. Synthesis of Human, Animal, and Other Supporting Evidence ........................... 44

4.6.3. Mode-of-Action Information ................................................................................ 44

4.7. SUSCEPTIBLE POPULATIONS AND LIFE STAGES.................................................. 48

4.7.1. Possible Childhood Susceptibility ........................................................................ 48

4.7.2. Possible Gender Differences ................................................................................ 48

5. DOSE-RESPONSE ASSESSMENTS ..................................................................................... 50

5.1. ORAL REFERENCE DOSE (RfD) ................................................................................ 50

5.1.1. Choice of Principal Study and Critical Effect—with Rationale and 

 Justification .......................................................................................................... 50

5.1.2. Methods of Analysis ............................................................................................. 54

5.1.2.1. Benchmark Dose Modeling .................................................................... 54

5.1.3. RfD Derivation ..................................................................................................... 55

5.1.4. Previous RfD Assessment .................................................................................... 58

5.2. INHALATION REFERENCE CONCENTRATION (RfC) ............................................ 58

5.3. CANCER ASSESSMENT ............................................................................................... 58

5.3.1. Choice of Study/Data—with Rationale and Justification .................................... 58

5.3.2. Dose Adjustments ................................................................................................. 59

5.3.3. Extrapolation Method(s) ...................................................................................... 60

5.3.4. Oral Slope Factor .................................................................................................. 62

5.3.5. Previous Cancer Assessment ................................................................................ 63

6. MAJOR CONCLUSIONS IN THE CHARACTERIZATION OF HAZARD AND 

 DOSE RESPONSE ................................................................................................................ 64

6.1. HUMAN HAZARD POTENTIAL ................................................................................... 64

6.2. DOSE RESPONSE .......................................................................................................... 65

6.2.1. Noncancer/Oral .................................................................................................... 65

6.2.2. Cancer/Oral .......................................................................................................... 66

7. REFERENCES......................................................................................................................... 67

APPENDIX A: SUMMARY OF EXTERNAL PEER REVIEW AND PUBLIC 

 COMMENTS AND DISPOSITION ................................................................ A-1

APPENDIX B: BENCHMARK DOSE ANALYSIS OF NONCANCER ENDPOINTS ............B-1

APPENDIX C: BENCHMARK DOSE ANALYSIS OF CANCER ENDPOINTS ................... C-1
v

LIST OF TABLES 

Table 2-1. Physical properties and chemical identity of decaBDE ................................................ 3

Table 4-1. Oral short-term and subchronic toxicity studies for decaBDE in laboratory 

animals ..................................................................................................................... 20

Table 4-2. Oral chronic toxicity studies for decaBDE in laboratory animals .............................. 24

Table 4-3. Oral developmental and reproductive studies for decaBDE in laboratory 

animals ..................................................................................................................... 29

Table 4-4. Incidence of liver neoplastic nodules and carcinomas in rats fed decaBDE 

for 2 years ................................................................................................................ 46

Table 4-5. Incidence of nonneoplastic or neoplastic lesions in the liver and thyroid 

gland of mice fed decaBDE for 2 years ................................................................... 47

Table 5-1. BMDs for potential critical effect from chronic rat and mouse studies ..................... 55

Table 5-2. Cancer slope factors derived from BMDs for neoplastic effect from chronic 

rat and mouse studies using the multistage model .................................................. 61

Table B-1. Summary of BMD modeling results for thrombosis in the liver of male rats...........B-2

Table B-2. Summary of BMD modeling results for degeneration in the liver of male rats ........B-2

Table B-3. Summary of BMD modeling results for fibrosis in the spleen of male rats .............B-6

Table B-4. Summary of BMD modeling results for lymphoid hyperplasia in male rats ............B-7

Table B-5. Summary of BMD modeling results for centrilobular hypertrophy in the 

liver of male mice ...................................................................................................B-7

Table B-6. Summary of BMD modeling results for follicular cell hyperplasia in the 

thyroid of male mice ...............................................................................................B-8

Table C-1. Summary of BMD modeling results for increase in neoplastic nodules in 

the liver of male rats .............................................................................................. C-1

Table C-2. Summary of BMD modeling results for increases in neoplastic nodules or 

carcinomas (combined) in the liver of male rats ................................................... C-4

Table C-3. Summary of BMD modeling results for increases in neoplastic nodules in 

the liver of female rats ........................................................................................... C-7

Table C-4. Summary of BMD modeling results for increases in neoplastic nodules 
vi

and carcinomas (combined) in the liver of female rats ....................................... C-10

Table C-5. Summary of BMD modeling results for increases in thyroid follicular 

cell hyperplasia as a key event of thyroid tumor in male mice ........................... C-13

Table C-6. Summary of BMD modeling results for increases in combined 

hepatocellular adenomas or carcinomas in male mice ........................................ C-16

LIST OF FIGURES 

Figure 3-1. Proposed metabolic pathway for BDE-209. .............................................................. 13
vii 

LIST OF ACRONYMS 

AhR aryl hydrocarbon receptor 

AIC Akaike Information Criterion 

ALH amplitude of the lateral head displacement 

ATSDR Agency for Toxic Substances and Disease Registry 

AUC area under the curve 

BDE-209 decabromodiphenyl ether 

bDNA branched deoxyribonucleic acid 

BMD benchmark dose 

BMDL BMD 95% lower bound 

BMDS benchmark dose software 

BMR benchmark response 

CALUX Chemical-Activated LUciferase eXpression 

CAR constitutive androstane receptor 

CASRN Chemical Abstracts Service Registry Number 

CD25 interleukin-2-receptor α chain

cDNA complementary DNA 

Cmax maximum concentration 

CYP-450 cytochrome P-450 

decaBDE decabromodiphenyl ether 

DRE dioxin-responsive element

E2 17 -estradiol 

ED effective dose 

ER estrogen receptor 

EROD ethoxyresorufin O-deethylase 

FOB functional observational battery 

fw fresh weight

GC/MS gas chromatography/mass spectrometry

HED human equivalent dose

hexaBDE hexabromodiphenyl ether

i.v. intravenous

IRIS Integrated Risk Information System

LED 95% lower confidence limit for the effective dose

LOAEL lowest-observed-adverse-effect level

lw lipid weight

MMP mitochondrial membrane potential

MRL minimal risk level

mRNA messenger ribonucleic acid

NAS National Academy of Science

NOAEL no-observed-adverse-effect level

nonaBDE nonabromodiphenyl ether

NTP National Toxicology Program
 viii

octaBDE octabromodiphenyl ether 

PBDE polybrominated diphenyl ether 

PBPK physiologically based pharmacokinetic 

PCB polychlorinated biphenyl 

pentaBDE pentabromodiphenyl ether 

PND postnatal day 

PROD pentoxyresorufin O-deethylase

PXR pregnane X receptor

RfC reference concentration

RfD reference dose

RSD risk-specific dose

SXR steroid X receptor

T3 triiodothyronine

T4 thyroxine

TCDD 2,3,7,8-tetrachlorodibenzo-p-dioxin

tetraBDE tetrabromodiphenyl ether

triBDE tribromodiphenyl ether

TSH thyroid stimulating hormone

UDPGT uridine diphosphate glucuronyl transferase

UF uncertainty factor
ix 

FOREWORD 

The purpose of this Toxicological Review is to provide scientific support and rationale 

for the hazard and dose-response assessment in IRIS pertaining to chronic exposure to 

decabromodiphenyl ether. It is not intended to be a comprehensive treatise on the chemical or 

toxicological nature of decabromodiphenyl ether (BDE-209). 

This health assessment deals with BDE-209 of relatively high purity (≥94%) and does not 

deal with earlier commercial decabromodiphenyl ether mixtures containing lower proportions of 

decabromodiphenyl ether (e.g., 75% purity). In addition to BDE-209, IRIS health assessments 

have also been prepared for three other polybrominated diphenyl ether congeners: tetraBDE-47, 

pentaBDE-99, and hexaBDE-153. These four congeners are those for which toxicological 

studies suitable for dose-response assessments were available and are the ones most commonly 

found in the environment and human biological media. 

The intent of Section 6, Major Conclusions in the Characterization of Hazard and Dose 

Response, is to present the major conclulsions reached in the derivation of the reference dose, 

reference concentration and cancer assessment, where applicable, and to characterize the overall 

confidence in the quantitative and qualitative aspects of hazard and dose response by addressing 

the quality of data and related uncertainties. The discussion is intended to convey the limitations 

of the assessment and to aid and guide the risk assessor in the ensuing steps of the risk 

assessment process. 

For other general information about this assessment or other questions relating to IRIS, 

the reader is referred to EPA’s IRIS Hotline at (202) 566-1676 (phone), (202) 566-1749 (fax), or 

hotline.iris@epa.gov (email address). 
 x 

AUTHORS, CONTRIBUTORS, AND REVIEWERS 

CHEMICAL MANAGER 

Joyce Morrissey Donohue, Ph.D. 

Office of Water, Office of Science and Technology 

Health and Ecological Criteria Division 

U.S. Environmental Protection Agency 

Washington, DC 

AUTHORS 

Joyce Morrissey Donohue, Ph.D. 

Office of Water, Office of Science and Technology 

Health and Ecological Criteria Division 

U.S. Environmental Protection Agency 

Washington, DC

Hend Galal-Gorchev, Ph.D. 

Office of Water, Office of Science and Technology 

Health and Ecological Criteria Division 

U.S. Environmental Protection Agency 

Washington, DC 

Qiyu (Jay) Zhao, Ph.D. 

Toxicology Excellence for Risk Assessment 

Cincinnati, OH 

Bernard Gadagbui, Ph.D. 

Toxicology Excellence for Risk Assessment 

Cincinnati, OH 

Andrew Maier, Ph.D., CIH, DABT 

Toxicology Excellence for Risk Assessment 

Cincinnati, OH 

Toxicology Excellence for Risk Assessment staff performed work under Purchase Order 

4W-1550-NATX. 

OFFICE OF RESEARCH AND DEVELOPMENT CO-LEAD 

Samantha J. Jones, Ph.D. 

Office of Research and Development 

National Center for Environmental Assessment 

U.S. Environmental Protection Agency 

Washington, DC 
 xi 

REVIEWERS

This document has been reviewed by EPA scientists, interagency reviewers from other 

federal agencies, and the public, and peer reviewed by independent scientists external to EPA. A 

summary and EPA’s disposition of the comments received from the independent external peer 

reviewers and from the public is included in Appendix A of the Toxicological Review of 

2,2',3,3',4,4',5,5',6,6'-Decabromodiphenyl ether (BDE-209). 

INTERNAL EPA REVIEWERS 

Linda Birnbaum, Ph.D. 

Experimental Toxicology Division 

National Health and Environmental Effects Research Laboratory 

Office of Research and Development 

Karen Hogan, M.S. 

National Center for Environmental Assessment 

Office of Research and Development 

Tammy Stoker, Ph.D. 

Reproductive Toxicology Division 

National Health and Environmental Effects Research Laboratory 

Office of Research and Development 

EXTERNAL PEER REVIEWERS

Ahmed E. Ahmed, Ph.D. 

University of Texas Medical Branch 

Richard J. Bull, Ph.D. 

MoBull Consulting

Lucio G. Costa, Ph.D.

University of Washington

Ralph Kodell, Ph.D.

University of Arkansas for Medical Sciences

Deborah Rice, Ph.D. (chair)

State of Maine
1 

1. INTRODUCTION 

This document presents background information and justification for the Integrated Risk 

Information System (IRIS) Summary of the hazard and dose-response assessment of 

2,2',3,3',4,4',5,5',6,6'-decabromodiphenyl ether (BDE-209). IRIS Summaries may include oral 

reference dose (RfD) and inhalation reference concentration (RfC) values for chronic and other 

exposure durations, and a carcinogenicity assessment. 

The RfD and RfC, if derived, provide quantitative information for use in risk assessments 

for health effects known or assumed to be produced through a nonlinear (presumed threshold) 

mode of action. The RfD (expressed in units of mg/kg-day) is defined as an estimate (with 

uncertainty spanning perhaps an order of magnitude) of a daily exposure to the human 

population (including sensitive subgroups) that is likely to be without an appreciable risk of 

deleterious effects during a lifetime. The inhalation RfC (expressed in units of mg/m3) is 

analogous to the oral RfD, but provides a continuous inhalation exposure estimate. The 

inhalation RfC considers toxic effects for both the respiratory system (portal of entry) and for 

effects peripheral to the respiratory system (extrarespiratory or systemic effects). Reference 

values are generally derived for chronic exposures (up to a lifetime), but may also be derived for 

acute (≤24 hours), short-term (>24 hours up to 30 days), and subchronic (>30 days up to 10% of 

lifetime) exposure durations, all of which are derived based on an assumption of continuous 

exposure throughout the duration specified. Unless specified otherwise, the RfD and RfC are 

derived for chronic exposure duration. 

The carcinogenicity assessment provides information on the carcinogenic hazard 

potential of the substance in question and quantitative estimates of risk from oral and inhalation 

exposure may be derived. The information includes a weight-of-evidence judgment of the 

likelihood that the agent is a human carcinogen and the conditions under which the carcinogenic 

effects may be expressed. Quantitative risk estimates are derived from the application of a lowdose extrapolation procedure. If derived, the oral slope factor is a plausible upper bound on the 

estimate of risk per mg/kg-day of oral exposure. Similarly, an inhalation unit risk is a plausible 

upper bound on the estimate of risk per μg/m3 air breathed. 

Development of these hazard identification and dose-response assessments for BDE-209 

has followed the general guidelines for risk assessment as set forth by the National Research 

Council (1983). EPA guidelines and Risk Assessment Forum Technical Panel Reports that may 

have been used in the development of this assessment include the following: Guidelines for the 

Health Risk Assessment of Chemical Mixtures (U.S. EPA, 1986a), Guidelines for Mutagenicity 

Risk Assessment (U.S. EPA, 1986b), Recommendations for and Documentation of Biological 

Values for Use in Risk Assessment (U.S. EPA, 1988), Guidelines for Developmental Toxicity 
2 

Risk Assessment (U.S. EPA, 1991), Interim Policy for Particle Size and Limit Concentration 

Issues in Inhalation Toxicity (U.S. EPA, 1994a), Methods for Derivation of Inhalation Reference 

Concentrations and Application of Inhalation Dosimetry (U.S. EPA, 1994b), Use of the 

Benchmark Dose Approach in Health Risk Assessment (U.S. EPA, 1995), Guidelines for 

Reproductive Toxicity Risk Assessment (U.S. EPA, 1996), Guidelines for Neurotoxicity Risk 

Assessment (U.S. EPA, 1998), Science Policy Council Handbook: Risk Characterization (U.S. 

EPA, 2000a), Benchmark Dose Technical Guidance Document (U.S. EPA, 2000b), 

Supplementary Guidance for Conducting Health Risk Assessment of Chemical Mixtures (U.S. 

EPA, 2000c), A Review of the Reference Dose and Reference Concentration Processes (U.S. 

EPA, 2002), Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005a), Supplemental 

Guidance for Assessing Susceptibility from Early-Life Exposure to Carcinogens (U.S. EPA, 

2005b), Science Policy Council Handbook: Peer Review (U.S. EPA, 2006a), and A Framework 

for Assessing Health Risks of Environmental Exposures to Children (U.S. EPA, 2006b). 

The literature search strategy employed for this compound was based on the Chemical 

Abstracts Service Registry Number (CASRN) and at least one common name. Any pertinent 

scientific information submitted by the public to the IRIS Submission Desk was also considered 

in the development of this document. The relevant literature was reviewed through November 

2007. 
3 

2. CHEMICAL AND PHYSICAL INFORMATION 

Decabromodiphenyl ether (decaBDE or BDE-209) is a fully brominated diphenyl ether 

compound (i.e., 10 bromine atoms) used as a flame retardant. The composition of commercial 

decaBDE is almost exclusively the deca-substituted BDE-209 (typically ≥97%), the remainder 

being nonabromodiphenyl ether (nonaBDE); trace amounts of octabromodiphenyl ether 

(octaBDE) may be present (Schecter et al., 2003; American Chemistry Council, 2002; Hardy, 

2002). The composition of older decaBDE formulations, which are no longer commercially 

produced in the U.S., was approximately 77% decaBDE, 22% nonaBDE, and 1% octaBDE 

(Kociba et al., 1975). Physical and chemical properties of decaBDE (≥97% purity) are listed in 

Table 2-1. 

Table 2-1. Physical properties and chemical identity of decaBDE 

Physical property/chemical identity Reference

CASRN 1163-19-5 U.S. EPA (2004)

Synonyms 2,2',3,3',4,4',5,5',6,6'-decaBDE; BDE-209; decaBDE; 

benzene, 1,1'-oxybis[2,3,4,5,6,-pentabromo]-; 

decabromodiphenyl oxide; decabromodiphenyl ether; 

decabromobiphenyl ether; ether, 

bis(pentabromophenyl)

U.S. EPA (2004);

ATSDRa(2004)

Physical state Solid Hardy (2002)

Melting point, °C 300–310 ECBa(2003)

Boiling point, °C decomposes at >320°C ECB (2003)

Vapor pressure at 21°C, Pa 4.63 × 10–6 Hardy (2002)

Henry’s law constant:

atm m3/mol

(Pa m3 mol–1) at 25oC

1.93 × 10–8

0.04

Hardy (2002);

Cetin and Odabasi 

(2005)

Density, g/cm33.0 NASa(2000)

Water solubility at 25°C, μg/L <0.1 Hardy (2002)

Log Kow 6.3–12.6 Hardy (2002)

Log Koc 6.3 Hardy (2002)

Molecular weight 959.17 U.S. EPA (2004)

Chemical formula C12Br10O U.S. EPA (2004)

Chemical structure

O

Br

Br

Br

Br Br

Br

Br

Br

Br Br

aATSDR = Agency for Toxic Substances and Disease Registry; ECB = European Chemicals Bureau; NAS = National 

Academy of Science. 
4 

3. TOXICOKINETICS 

Data on the toxicokinetics of decaBDE in humans are limited to findings on the levels in 

serum and maternal milk that demonstrate it is absorbed from the environment and distributed to 

tissues. Several studies have been conducted to evaluate the absorption, distribution, 

metabolism, and elimination of decaBDE after oral or intravenous (i.v.) dosing in rats and mice. 

Absorption is low (7–26%) after oral exposure to rats. Following absorption, the highest levels 

are found in the liver, muscle, and skin. This differs from studies of the lower brominated 

congeners, where the highest levels are generally found in the adipose tissues. The available 

metabolic data apply exclusively to rats, where both debrominated and hydroxylateddebrominated species have been identified in plasma. In one study, the metabolites in the feces 

exceeded those that could be accounted for from bile, raising the possibility that some 

conversion of the parent compound may be mediated by the intestinal epithelium or microflora. 

This phenomenon was not reported for the lower brominated BDE congeners. Urinary excretion 

of decaBDE-209 is minimal in rats; no data are available for mice. In rats, some of the urinary 

radiolabel (18%) was bound to albumin. 

3.1. ABSORPTION 

3.1.1. Studies in Humans 

There are no direct studies of decaBDE absorption in humans. The data that demonstrate 

human absorption come from measurements of decaBDE in human biological media after 

anthropogenic exposures but do not provide information on the quantitative aspects of 

absorption or the kinetics of tissue distribution and retention. 

3.1.2. Studies in Animals 

Studies on BDE-209 absorption following oral dosing demonstrate its absorption 

potential. However, there were few direct measurements of absorbed dose, and absorption 

estimates are based on a combination of concentrations in blood and data on excretion. Among 

the several oral dosing studies, the percentage of an administered dose absorbed across the 

gastrointestinal tract ranged from approximately 7–26%. In some cases it was difficult to derive 

an accurate estimate of absorption because of the high proportion of the dose found in the feces 

(>90%) and the high percentage that was present as metabolites in feces. 

Sandholm et al. (2003) evaluated the bioavailability of unlabeled decaBDE in male 

Sprague-Dawley rats. One group of rats (n = 18) was dosed by gavage with unlabeled decaBDE 

(>98% purity) in dimethylamide/polyethylene glycol/water vehicle at 2 μmol/kg (1.9 mg/kg). 

Another group of rats (n = 18) was dosed intravenously via the tail vein with unlabeled decaBDE 
5 

at the same dose. At specific time intervals, blood samples from three rats per group were 

collected according to the following schedule: group 1 was sampled 1 hour and 24 hours after 

dosing; group 2 after 3 hours and 48 hours; group 3 after 6 hours and 72 hours; group 4 after 

96 hours; group 5 after 120 hours; and group 6 after 144 hours. Plasma samples were extracted, 

and decaBDE and its metabolites were quantified. Based on comparison to plasma levels (area 

under the curve [AUC]) following i.v. injections, the oral bioavailability (the percent of the dose 

reaching systemic circulation) was calculated to be 26% in the rat. The mean maximum plasma 

concentration (Cmax) following oral dosing was 264 pmol/mL in the 6-hour sample. 

One of the limitations of the absorption data for decaBDE is a lack of knowledge about 

the mechanism of gastrointestinal absorption. Passive diffusion across the lipid membrane 

appears to be restricted to lipophilic compounds with low molecular weight rather than high 

molecular weight compounds such as decaBDE. Accordingly, facilitated transport and/or uptake 

with dietary lipids by way of the chylomicrons may provide routes for absorption. 

In a gavage study by Morck et al. (2003), male Sprague-Dawley rats (n = 8) received 

3 μmol/kg (2.9 mg/kg) 14C-labeled decaBDE diluted with unlabeled compound (>98% purity, 

15 Ci/mol), prepared by dissolving the decaBDE labeled/unlabeled mixture in toluene, followed 

by sonication, suspension in Lutrol F127/soy phospholipone/water vehicle, and evaporation of 

the toluene by nitrogen flow. Four rats were sacrificed after 3 days and the other four rats after 

7 days. Urine and feces were collected at 24-hour intervals for 3 and 7 days, respectively, and 

assayed for radioactivity. Two additional male Sprague-Dawley rats were bile-duct-cannulated, 

treated similarly with 14C-labeled decaBDE, and sacrificed 3 days later. Bile from these rats was 

collected and assayed for radioactivity. 

Results indicated that in the conventional rats, about 90% of the dose was excreted in the 

feces within 3 days after a single oral dose of 14C-labeled decaBDE, and the majority of this 

radioactivity (65%) represented decaBDE metabolites. Radioactivity in bile collected from the 

cannulated rats accounted for 10% of the fecal excretion. Almost all of the excreted 

radioactivity in the bile represented metabolites, indicating that at least 10% of the decaBDE 

dose had been absorbed. It is also possible that greater than 10% of the oral dose may have been 

absorbed since 65% of the radioactivity excreted in the feces was in the form of metabolites. 

However, interpretation of the data is difficult. The relatively large amount of metabolites 

excreted in the feces could be due to a combination of biliary excretion of metabolites, 

metabolism of decaBDE by the microflora in the gastrointestinal tract, metabolism in the 

intestinal epithelium, and/or nonbiliary systemic secretion into the gut. 

Hughes et al. (2001) conducted a study to evaluate the in vitro dermal absorption of 

decaBDE in mice. In this study, the dorsal skin of female hairless (Crl:SKH1-hr–BR) mice was 

removed, cut to a thickness of 255 μm, and exposed in a flow-through diffusion cell system to 

carrier-free 14C-decaBDE (>98% purity; specific activity not provided) at doses of 6, 30, or 
6 

60 nmol. The percent dose absorbed as measured by the amount of material in the collecting 

chamber was determined at 6, 12, 18, and 24 hours. Very little compound passed through the 

skin sections; the percentages of dose reaching the receptor fluid in the collecting chamber after 

24 hours ranged from 0.07–0.34% and were inversely related to dose. 

For all three doses used in the experiment, the largest portion of the dose was taken up 

during the first 6 hours: 0.17%, 0.04%, and 0.03% of the applied 6, 30, and 60 nmol decaBDE 

doses, respectively. Results also showed that the 24-hour cumulative percent of the dose 

absorbed decreased with increasing applied dose, whereas the mass of chemical absorbed 

increased with increasing applied dose. This result suggests saturation of uptake at the higher 

doses. The authors calculated the total for the dose retained in the skin sections and transported 

to the receptor fluid as 20.5%, 3.3%, and 1.9% of the applied dose for 6, 30, and 60 nmol 

decaBDE, respectively. Most of the compound taken up in the 24-hour period was retained in 

the skin. The authors acknowledged that the in vitro results observed in this study using mouse 

skin may overestimate the amount of decaBDE that would be absorbed by human skin, given 

that the mouse skin is more permeable to several chemicals, at least in vitro, than rat, pig, or 

human skin. 

3.2. DISTRIBUTION 

BDE-209 has very low water solubility and a relatively high Kow. Accordingly, high 

distribution to adipose tissue might be expected. However, as indicated by the data that follow, 

that is not the case. Systemic distribution of hydrophilic metabolites, as well as molecular mass 

and favored conformation, may play a role in the limited uptake by adipocytes. The low uptake 

of decaBDE into tissue lipids makes it different from the less highly substituted, lower molecular 

weight polybrominated diphenyl ethers (PBDEs). 

3.2.1. Studies in Humans 

The human data described below come from monitoring of PBDEs in human populations 

rather than from measured dosing studies. The data demonstrate that humans are exposed to 

PBDEs and that absorption and distribution to some tissues occur. The data do not provide 

information on the quantitative aspects of absorption or the kinetics of tissue retention. Limited 

data are available on the occurrence of BDE-209 in human biological media. Data, described 

below, are available for human milk and blood samples and indicate a tendency for BDE-209 to 

distribute to these tissues. However, thorough distribution studies have not been conducted in 

humans, and therefore it is not known whether BDE-209 distributes to other tissues as well. The 

number of samples examined in various studies and countries is small, and therefore the data 

should not be construed as representative at the national level. 
7 

3.2.1.1 Data in Human Milk

In a study conducted in 2002 of levels of PBDEs in human milk in the U.S., 47 samples 

from Caucasian, African-American, and Hispanic nursing mothers 20–41 years of age and living 

in Texas were analyzed for 13 PBDE congeners (Schecter et al., 2003). Mean and median total 

concentrations of tribromodiphenyl ether (triBDE) through decaBDE were 74 and 34 ng/g lipid 

weight (lw). DecaBDE was present in these samples, with a mean concentration of 0.9 ng/g lw 

(1.2% of total PBDEs in the milk; median concentration not available), suggesting that some 

decaBDE is absorbed, distributed to mammary tissue, and secreted in human milk during 

lactation.

Milk samples were collected in 2003 from 40 first-time mothers with 8-week-old infants 

and residing in urban areas in the Pacific Northwest of the U.S. (Montana, Oregon, and 

Washington State) and British Columbia, Canada (She et al., 2007). Mean and median total 

concentrations of 12 tri- through decaBDE congeners were 96 and 50 ng/g lw, respectively. 

These values are substantially higher than the values reported in the study of Schecter et al. 

(2003) and could be due to the fact that the mothers in the later study had been nursing for 

longer periods of time. BDE-47 was found at the highest level, followed by hexabromodiphenyl 

ether (hexaBDE)-153 and pentabromodiphenyl ether (pentaBDE)-99 and -100. DecaBDE-209 

with mean and median concentrations of 0.8 and 0.4 ng/g lw, respectively, was a minor congener 

in breast milk. 

3.2.1.2. Data in Human Blood

Sjodin et al. (2001a) reported a finding of BDE-209 in serum samples collected from 

12 U.S. blood donors in 1988. The median concentration was <1 pmol/g lw with a range of 

<1–35 pmol/g lw (approximately <1–35 ng/g lw). These concentrations of BDE-209 were

comparable to blood levels collected 10 years later, in 1997, from non-occupationally exposed 

Swedish female cleaners (Sjodin et al., 1999). There is no demographic or questionnaire 

information on the donor; therefore, no information is available for assessing exposure sources.

Concentrations of tetrabromodiphenyl ether (tetraBDE) and penta-, hexa-, and decaBDE 

congeners were measured in serum samples collected during 2004 from a family residing in 

Berkeley, California (35- and 36-year-old father and mother, respectively, 5-year-old daughter, 

and 18-month-old son) (Fischer et al., 2006). The 18-month-old was exclusively breast-fed for 

6 months and was breast-feeding during the study period. PBDE levels for the sum of the five 

lower brominated congeners BDE-47, -99, -100, -153, and -154 were much higher in the infant 

(418 ng/g lw) and child (247 ng/g lw) than in their parents (mother 106 ng/g lw, father 64 ng/g 

lw). BDE-47 was the predominant congener for all ages, followed by hexaBDE-153, 

pentaBDE-100, pentaBDE-99, and hexaBDE-154. Levels of BDE-209 in the infant (233 ng/g 

lw) and child (143 ng/g lw) were unusually high compared with those in the parents (mother 
8 

14 ng/g lw, father 23 ng/g lw). The authors suspected house dust and breast milk to contribute 

appreciably to the child and infant exposures; however, no firm conclusions can be drawn from 

this study, given the small number of subjects investigated. 

Sjodin et al. (1999) investigated the exposure to PBDEs of Swedish workers by 

comparing blood PBDE concentrations collected in 1997 from personnel at an electronics 

dismantling plant, clerks working full time in front of computer screens, and a control group of 

hospital cleaning workers. Electronics dismantling involved grinding plastic goods in a 

shredder. This process releases airborne particulate matter from plastic parts containing 

brominated flame retardants. The investigators found decaBDE in the serum of individuals from 

all three groups (19–20 male and female subjects per group). The median BDE-209 

concentration in hospital cleaners was <0.7 pmol/g lw (<9.7 ng/g), with a range of ≤0.3–

3.9 pmol/g lw (≤0.3–3.7 ng/g), while the median BDE-209 concentration in computer clerks was 

<0.7 pmol/g lw (<0.7 ng/g), with a range of ≤0.3–8.0 pmol/g lw (≤0.3–7.8 ng/g). Plasma levels 

of BDE-209 were significantly higher in the electronics dismantling workers than in the other 

two groups with a median BDE-209 concentration of 5.0 pmol/g lw (4.8 ng/g, range <0.3–

9.9 pmol/g lw [<0.3–9.5 ng/g]). The higher BDE-209 concentration in the serum of the 

electronics dismantling workers was attributed to the relatively high total BDE-209 

concentration in the air of the dismantling hall (mean 36 ng/m3) and at the shredder (175 ng/m3) 

(Sjodin et al., 2001b). The presence of BDE-209 in the blood samples from these three groups 

of workers qualitatively indicated the bioavailability of BDE-209 in humans, even though this 

compound is not expected to be greatly bioavailable based on its high molecular mass. There 

was no correlation between plasma levels of BDE-209 with age or fish consumption (the only 

food evaluated in the study). The serum concentrations of all PBDE congeners decreased in 

electronic-dismantling workers after vacation. The median decreases, standardized to 30 days of 

leave, were 14% for BDE-47, -153, and -154, 30% for BDE-183, and 66% for BDE-209. These 

results indicate shorter half-lives of the more highly brominated diphenyl ethers. However, 

serum half-lives were not estimated by the authors. 

In another Swedish study, increased BDE-209 in the serum was also found in computer 

technicians who repair or partially dismantle computers (Jakobsson et al., 2002). The median 

BDE-209 concentration in groups of 19–20 subjects was 1.6 pmol/g lw (1.5 ng/g) in computer 

technicians, while it was <0.7 pmol/g lw (<0.7 ng/g) in hospital cleaners and computer clerks. A 

possible source of exposure is airborne dust particulate matter to which PBDEs strongly adsorb 

(Sjodin et al., 1999). 

Thuresson et al. (2005) assessed the exposure to PBDEs in Swedish workers engaged in 

manufacturing decaBDE flame-retarded rubber goods or electric cables. A referent group, 

abattoir (slaughterhouse) workers with no occupational exposure to PBDEs, was also 

investigated. The commercial decaBDE used was Saytex 102E, consisting mainly of BDE-209 
9 

with traces of nonaBDEs (BDE-206, -207, and -208) and unknown octaBDE congeners. 

Consumption of fatty fish was low in all three groups (median 0.5 meals/month), age ranged 

between 24 and 60 years, with a median of 40 years in all three groups, and each group consisted 

of approximately 20 subjects. The concentration of 12 PBDE congeners, ranging from tetra- to 

decaBDE, was measured in the serum samples of all individuals participating in the study. 

Elevated serum concentrations of octa-, nona-, and decaBDE were present in serum of workers 

handling decaBDE flame-retarded rubber. Serum concentrations of BDE-209 were up to 50- to 

100-fold higher than those of the referent group. In contrast, the serum concentrations of tetrato heptaBDEs were similar among rubber workers and referents. 

3.2.2. Studies in Animals 

No studies were identified regarding distribution of decaBDE in animals after inhalation 

exposure. Several rodent oral dosing studies were identified and are described below. 

Sandholm et al. (2003) evaluated the distribution of unlabeled decaBDE in male SpragueDawley rats. A group of rats (n = 18) was dosed by gavage with unlabeled decaBDE (>98% 

purity) in dimethylamide/polyethylene glycol 400/water vehicle at 2 μmol/kg (1.9 mg/kg). 

Another group of rats (n = 18) was dosed intravenously with the same dose of decaBDE. At 

specific time intervals, blood samples from three rats per group were collected for up to 

144 hours. Plasma samples were extracted, and decaBDE and its metabolites were quantified. 

Oral results indicated that the mean plasma Cmax was 264 pmol/mL (253 ng/g) at 6 hours after 

dosing and AUC was 12 nmol × hour/mL (11.5 μg × hour/mL). The results from the i.v. study 

indicated that the clearance was 0.60 mg/minute-kg and the apparent volume of distribution at 

steady state was 1.4 L/kg. Concentrations in other tissues were not measured; therefore, relative 

tissue distribution could not be determined. However, the identification of decaBDE in the 

plasma supports other studies, suggesting wide tissue distribution. 

Morck et al. (2003) evaluated the distribution of decaBDE (>98% purity) in male 

Sprague-Dawley rats after oral administration. Four rats were sacrificed 3 or 7 days after 

administration of 3 μmol/kg (2.9 mg/kg) of 14C-labeled and unlabeled decaBDE combined 

(15 Ci/mol). Liver, adipose tissue, lung, kidney, adrenal glands, skin, muscle, spleen, testis, 

thymus, heart, plasma, colon wall and contents, and small intestine wall and contents were 

collected. Radioactivity was determined in all tissues. Analysis of tissues and organs for 

radioactivity indicated that approximately 9% of the dose remained in the body at 3 and 7 days. 

On a fresh weight (fw) adjusted basis, the concentrations at 3 and 7 days were highest in the 

adrenal glands (1.25 and 0.41 nmol/g fw [1.2 and 0.4 μg/g]), liver (0.55 and 0.20 nmol/g fw 

[0.7 and 0.2 μg/g]), kidney (0.17 and 0.07 nmol/g fw [0.16 and 0.07 μg/g]), and heart (0.14 and 

0.05 nmol/g fw [0.13 and 0.05 μg/g]), respectively. On an lw basis, the plasma and liver had the 

highest concentrations of radiolabel (22 and 14.9 nmol/g lw [21 and 14 μg/g] on day 3 and 
10 

8.8 and 5.3 nmol/g lw [8.4 and 5.1 μg/g] on day 7, respectively), whereas adipose tissue, testis, 

thymus, spleen, small intestine wall, skin muscle, lung, kidney, adrenal, and heart had low 

concentrations. These results indicate that decaBDE was not readily distributed to lipid-rich 

tissues but rather was found in plasma and blood-rich tissues, including liver, kidney, heart, and 

intestinal wall. 

Huwe and Smith (2007) conducted a repeat dosing study of BDE-209 during which a 

group of 18 male Sprague-Dawley rats were given 0.36 μg/day BDE-209 in an oil-based 

supplement added to their diets for 21 days. Eight control animals received the same diet and 

oil-based supplement. At the end of dosing, groups of three animals were sacrificed on days 0, 

3, 7, 10, 14, and 21 of a follow-up period that began 24 hours after the last feeding of the treated 

diet. There was no collection of excreta during the feeding period. Twenty-four hours after the 

last feeding, the levels of BDE-209 in liver, plasma, gastrointestinal tract, and carcass were 

measured. The highest levels were found in the liver (48.2 ± 8.9 μg/g wet weight) and 

gastrointestinal tract (35.9 ± 8.5 μg/g wet weight). The amounts in plasma (3.6 ± 0.9 μg/g wet 

weight) and carcass (14.0 ± 4.0 μg/g wet weight) were lower. After the 21-day exposure, the 

tissues of the exposed rats contained levels of BDE-209 that were 10–20 times greater than those 

in control rats. In addition, hepta-, octa-, and nonaBDEs were isolated in tissues and were 

apparently formed via reductive debromination of BDE-209. Two of the octaBDE congeners 

(BDE-201 and -197) bioconcentrated in the tissues to a greater extent than the parent and other 

debrominated metabolites. Huwe and Smith (2007) made no attempt to determine if 

hydroxylated metabolites had been formed. These results differ from those for the tetra-, penta-, 

and hexaBDE congeners, where there is no evidence for debromination in the absence of 

hydroxylation. 

Viberg et al. (2003a) studied the distribution of decaBDE in mice. NMRI male mice (n = 

6–8) received a single oral dose (2.22 mg/kg) of 14C-decaBDE (40.5 μCi/kg) by gavage on 

postnatal day (PND) 3, 10, or 19. The animals were sacrificed 1 and 7 days after administration 

of the radiolabeled decaBDE, and the label in the brain, heart, and liver was measured. The 

highest concentrations as a percentage of the administered dose were seen in the liver, followed 

by the brain and heart. The authors did not state whether the radioactivity was that of the parent 

compound or its metabolites. 

One day after administration, the mean radioactivity in the liver of mice treated with 

radiolabeled decaBDE on PND 3, 10, or 19 was 12.6%, 9.4%, or 5.8% of the administered dose, 

respectively, whereas 7 days after administration, the radioactivity decreased significantly to 

4.8%, 4.6%, or 0.3%, respectively. The distribution to and retention by the liver was greater for 

the dosing on PNDs 3 and 10 than for the dosing on PND 19. One day after administration, mice 

treated on PNDs 3 and 10 had 0.5 and 0.4% of total activity administered, respectively, in the 

brain, and the radioactivity increased to 0.7 and 1.1%, respectively, 7 days after the dosing. In 
11 

contrast, mice treated with 14C-decaBDE on PND 19 had only 0.06% of the total radioactivity 

administered in the brain 1 and 7 days after administration. Significant age-dependent 

differences in distribution to the liver and developing brain were noted. On the other hand, the 

amount of radioactivity in the heart was minimally affected by age of the animal 24 hours after 

administration (0.28, 0.31, and 0.22% of the total dose was measured in the heart 24 hours after 

administration on PNDs 3, 10, and 19, respectively). After 7 days of administration, the 3-dayold and 10-day-old animals did not have significant changes in the amounts of radioactivity in 

the heart (0.34 and 0.32% of the total administered dose). The amount of radioactivity detected 

in the hearts of 19-day-old mice had decreased significantly to 0.08%. 

In a study by el Dareer et al. (1987) the liver of rats fed two diets containing low 

(0.0277%; 25 mg/kg) or high (4.8%; 4,400 mg/kg) amounts of 14C-labeled decaBDE contained 

0.45, 0.21, and 0.11% of the administered dose on days 1, 2, and 3 after administration of the 

low dose and 0.007, 0.007, and 0.016% after administration of the high dose, respectively. 

These data are also included in Appendix O of the National Toxicology Program (NTP) (1986) 

report. These results suggest saturation in uptake or distribution. High-pressure liquid 

chromatography and ultraviolet spectral analysis indicated that 81% of the radioactivity in the 

liver was decaBDE rather than metabolites. The maximum percent of dose in the organs and 

tissues obtained from the rats fed the lower dose of decaBDE (0.0277%) was in the following 

order: liver > skin > muscle > fat > blood > gut tissue > plasma > kidneys > lungs > spleen > 

brain. 

Hakk et al. (2002) investigated the disposition of decaBDE in rats. Groups of four male 

Sprague-Dawley rats (conventional rats) and bile-duct-cannulated rats (cannulated rats) were 

administered 14C-labeled decaBDE (>97% purity; 15 mCi/mol) in Lutrol F127/soya 

phospholipid/water vehicle as a single oral dose of 3 μmol/kg (2.9 mg/kg). Gastrointestinal 

mucosa, kidneys, liver, and lungs were collected from the animals 72 hours following dosing. 

Radioactivity content was assayed in tissue supernatants and protein-bound extracts. 

Radioactivity was also quantified from pellets obtained after centrifugation of homogenized 

tissues. In addition, binding of radiolabeled decaBDE and/or its metabolites to liver proteins 

was determined. Analysis of liver, lung, intestinal cells, and kidney tissues of noncannulated rats 

72 hours following decaBDE administration indicated that the majority (>45–80%) of the 

decaBDE-derived radioactivity was associated with the membrane fraction, whereas 0–29% and 

4–24% were associated with microsomal and soluble fractions, respectively. 

Collectively, these studies suggest wide tissue distribution, although relative distribution 

among various tissues differed across studies in adult rodents. Significant age-dependent 

differences in distribution to the undeveloped brain were noted. 
12 

3.3. METABOLISM 

Oral and i.v. studies suggest that decaBDE is metabolized through oxidative 

dehalogenation reactions to form phenolic metabolites and debrominated to form a 

variety of nona-, octa-, and heptaBDE congeners. This conclusion is based on the 

extensive presence of metabolites in the fecal matter and in blood. However, the sites of 

metabolism have not been identified. At least a portion is likely to occur in the liver. 

Extrahepatic metabolism may occur in the epithelium of the gastrointestinal tract or 

through preabsorption metabolism of decaBDE by the intestinal microflora. Figure 3-1 

provides a summary of the proposed metabolic pathway as derived from the metabolites 

that have been identified in plasma, tissues, and fecal material. 

It should be noted that some metabolites may be formed by intestinal microbes. The 

number of bromines removed will depend on whether the starting material is the parent or a 

partially debrominated metabolite. If absorption occurs with lipids via the chylomicrons, other 

tissues may also participate in metabolism. The identification of the feces as the major excretory 

pathway and the high percentage of metabolites present in the feces that cannot be accounted for 

through biliary excretion provide support for the hypothesis that the liver may not be the only 

site for metabolic conversions. 

Morck et al. (2003) studied decaBDE metabolism in rats given a single oral dose by 

gavage. Results indicated that in noncannulated rats about 90% of the dose was excreted in the 

feces within 3 days after a single oral dose of 14C-labeled decaBDE and the majority of this 

radioactivity (65%) represented decaBDE metabolites. Measurement of bile radioactivity 

indicated that close to 10% of the total dose was excreted in the bile during the same period, 

with almost all of the excreted dose in bile in the form of metabolites. 

Analysis of radiolabeled materials from tissues of these rats at day 3 after decaBDE 

administration revealed that 42% of the radioactivity in the liver represented solvent extractable 

lipid-bound metabolites and 30% was in the form of extractable unconjugated metabolites (4 and 

26% of which were hydroxylated and neutral metabolites, respectively). Twenty-seven percent 

of the radiolabel could not be extracted and was tissue bound. Only 1% of the extractable 

material was water soluble. A larger percentage (61%) of the radioactivity in the small intestine 

wall was tissue bound. Lipid-bound metabolites accounted for 7% of the label, water-soluble 

compounds for 11%, and unbound parent or metabolites for 20%. The percentage of the 

radiolabel found as water-soluble compounds in the intestinal wall was 10 times greater than the 

water-soluble metabolites in the liver, providing some support for the hypothesis that oxidative 

metabolism can occur in the intestinal mucosa. Most of the radioactivity (71–80%) in the lung, 

adipose tissue, and kidney was unbound parent or metabolites; 15–21% represented lipid-bound 

metabolites, and 1.5–8% was tissue bound. Formation of adducts was indicative of covalent 

and/or noncovalent interactions with cellular macromolecules. 
13 

Figure 3-1. Proposed metabolic pathway for BDE-209. 

Source: Derived from Huwe and Smith (2007), Sandholm et al. (2003), and Morck et al. (2003).

Sandholm et al. (2003) evaluated the metabolism of unlabeled decaBDE in male rats 

after gavage or i.v. injection. Blood samples were collected at specific intervals for up to 6 days. 

Pooled plasma samples from all 6 days were extracted and decaBDE and its metabolites were 

quantified. Analysis of the pooled samples indicated that the major neutral compound in the 

plasma was unmodified decaBDE with trace amounts of three nonaBDEs. Thirteen phenolic 

metabolites were determined in the plasma of both the orally and i.v. dosed rats, but only three 

phenolic metabolites were present in sufficiently high concentration for further analysis. These 

metabolites were characterized as a hydroxy-octaBDE, an hydroxy-nonaBDE, and an 

hydroxy/methoxy hexaBDE (Figure 3-1). The relative amount of each metabolite recovered was 

Br

Br

Excreted as 

parent 

compound

Br

Br

Br

O

Br

Br

Br

Br

Br Br

reduction

Br -1

Arene epoxide

intermediate

2 Br -1

Br

OH

Br

O

Br4 Br

Br

Br

Br -

Br

Br4

Br

O

Br

Br

Br Br

Z Br - Z = 1 or 2

Bry

O

Brx

x + y = 7 or 8

Br

OH

Br

O

Br3 Br

Br

Br

Br

Bry

(OH)2

O

Brx

OH

Br

O

Brx

Br

Methyl donor

x + y = 5, 6, or 7

x + y = 5, 6, or 7

CH3-O Bry

reduction
14 

not reported, but the concentration of phenolic radioactivity in the plasma collected 3 and 7 days 

after oral gavage was four times higher than that of the neutral compounds (i.e., the parent or 

debrominated decaBDE). The authors indicated that reductive debromination may be the first 

step in the metabolic pathway of decaBDE, followed by oxidation to form phenolic metabolites. 

It was also suggested that the hydroxy/methoxy metabolites were probably formed via an arene 

oxide hydrolyzed to a dihydrodiol and further rearomatized followed by a methylation reaction 

(Figure 3-1). 

In the study conducted by Morck et al. (2003), the unconjugated phenolic fractions 

isolated from the feces were examined by gas chromatography/mass spectrometry (GC/MS). 

Methoxyhydroxylated penta- to heptabrominated diphenyl ethers were identified. As was the 

case in the Sandholm et al. (2003) study, the methoxy and hydroxy substituents were on the same 

phenyl ring when both were present. In addition, trace amounts of debrominated metabolites 

and nonaBDEs were also found in the feces and bile (see Figure 3-1), indicating debromination 

may have been the first step in decaBDE metabolism. A small proportion of monohydroxylated 

metabolites was found in tissues and feces, indicating a role for reductive dehalogenation 

followed by an oxidation step or direct oxidative dehalogenation reactions. 

The plasma samples collected during the Morck et al. (2003) study were analyzed and 

reported by Sandholm et al. (2003). As was the case with the plasma samples collected by 

Sandholm et al. (2003), the neutral fraction was almost all BDE-209 with a small fraction of 

three nonaBDEs. Neutral compounds represented 19% of the plasma total in the samples drawn 

at 3 days and 21% in the samples collected at 7 days. The phenolic compounds in the plasma 

could not be purified enough to allow GC/MS analysis. 

Huwe and Smith (2007) identified nonhydroxylated metabolites found in feces and 

tissues after 21 days dosing with 0.36 μg/day BDE-209 in an oil-based supplement added to their 

diets. Only 5% of the parent dose was present in the body after 21 days of dosing. Three 

nonaBDEs (206, 207, and 208), four octaBDEs (196, 197, 201, and 203), and one heptaBDE 

(183) were identified in the body tissues. No attempt was made to determine if hydroxylated 

metabolites were present. The results are indicative of considerable fecal excretion during the 

dosing period. 

Intravenous administration of 1.07 mg/kg decaBDE to rats (el Dareer et al., 1987; NTP, 

1986) resulted in the major part of the dose (74%) being excreted as metabolites in feces. About 

63% of the excreted material in the feces was metabolites, and the remaining 37% was 

unchanged decaBDE. In these rats, 1% of the radioactivity in the bile was intact decaBDE, 

while 99% of the radioactivity excreted in the bile was in the form of metabolites. 

Animal studies indicated that decaBDE is a weak inducer of the phase I or phase II 

xenobiotic metabolizing enzymes responsible for oxidation and conjugation of many xenobiotic 

compounds (Darnerud et al., 2001). Zhou et al. (2001) conducted a study in weanling rats to 
15 

investigate the mechanism(s) by which decaBDE interferes with thyroid hormone homeostasis. 

In this study, Long-Evans female rats (eight animals/dose group) were orally administered 

decaBDE (>98% purity) in corn oil at doses of 0, 0.3, 1, 3, 10, 30, 60, or 100 mg/kg-day for 

4 consecutive days. Hepatic enzyme activities (ethoxyresorufin O-deethylase [EROD], a marker 

for cytochrome P-450 1A1 [CYP-1A1]; pentoxyresorufin O-deethylase [PROD], a marker for 

CYP-2B1) were measured. PROD activity increased only at 1 and 30 mg/kg-day. The lack of 

dose dependence was also found for EROD activity, where maximal induction was only 1.8-fold 

in the 1 mg/kg-day group, indicating that there were no significant or dose-related effects on 

CYP-1A1 or CYP-2B1. However, the presence of active EROD and PROD suggests that there 

may be some oxidative debromination of the decaBDE during metabolism, through the activity 

of CYP-1A1 and/or CYP-2B1. 

Pacyniak et al. (2007) evaluated the ability of BDE-209 to induce CYP-3A11, -2B10, and 

-1A1/2. Six C57BL/mice (10 weeks of age) were injected with doses of 10 or 100 μmol/kg 

(10 or 100 mg/kg) in corn oil for 4 days. The livers were removed 24 hours after the last dose 

and the levels of messenger ribonucleic acid (mRNA) measured by Northern blot and branched 

deoxyribonucleic acid (bDNA) analyses. The bDNA was considered to be the more accurate of 

the two assay systems. Northern blot analysis indicated that the levels of CYP-2B10 were 

induced three- and fivefold, respectively, at the two doses tested, while the bDNA results 

indicated 3.6-fold and sevenfold inductions. CYP-3A11 did not show a difference with respect 

to the dose administered but was induced 4-fold by the Northern blot analysis and 1.7-fold by the 

bDNA analysis. The two doses of PBDE-209 induced CYP 1A1/2 9- and 6-fold, respectively, by 

Northern blot analysis and 0.3- and 0.8-fold by bDNA analysis. 

3.4. ELIMINATION 

As has been mentioned previously, the excretion of decaBDE and its metabolites in rats 

is almost exclusively through the fecal and biliary routes. In toxicokinetic studies (Morck et al., 

2003; Hakk et al., 2002; el Dareer et al., 1987), the amounts excreted in urine have consistently 

been less than 1% of the dose (about 18% bound to albumin); biliary excretion has accounted for 

about 10% of the label found in the feces. There have been no studies that examined the 

excretion of BDE-209 in mice. Studies by Staskal et al. (2006) using BDE-47, -99, and -153 

found that urinary excretion in male mice involves binding with one or two major urinary 

excretory proteins. 

In one of the early toxicokinetic studies (el Dareer et al., 1987; NTP, 1986), the fate of 

decaBDE in male F344 rats was investigated. The study consisted of four substudies. In 

substudy one, groups of 2-month-old male F344 rats (three animals/group) were fed a standard 

diet containing unlabeled decaBDE (92% purity) on days 1–7 and 9–11 and the test diet 

containing 14C-labeled decaBDE (>98% purity) on day 8. The diets contained 0, 0.0250, 0.0509, 
16 

0.250, 0.487, 2.49, or 4.99% decaBDE. Based on the rat body weight information reported in 

el Dareer et al. (1987) and the average feed intake from the NTP (1986) report, the 

corresponding daily doses were 0, 27, 55, 272, 512, 2396, or 4577 mg/kg. Radioactivity was 

determined in feces collected daily on study days 9–12. 

In substudy two, rats were fed two diets containing low (0.0277% or 25 mg/kg) or high 

(4.80% or 4400 mg/kg) amounts of decaBDE or similar amounts of 14C-labeled decaBDE, using 

the same protocol as in the first substudy, except that groups of three rats were killed on study 

days 10, 11, or 12. Urine and feces were collected from each rat and analyzed for radioactivity. 

In substudy three, a group of rats (n = 3) was injected intravenously via the tail vein with 

1.07 mg/kg of 14C-labeled decaBDE; urine and feces were collected daily for 3 days and 

analyzed for radioactivity 72 hours after dosing. In the fourth substudy, bile-duct-cannulated rats 

(n = 5) were injected intravenously with 0.947 mg/kg of 14C-labeled decaBDE. Bile was 

collected over a 4-hour period. Radioactivity was determined in each pooled bile sample. 

The recovery of radioactivity in the feces ranged from 91–101% of the ingested dose in 

the first feeding study and 83–86% in the second feeding study, indicating that the recovery was 

not related to the dose of decaBDE or to the time of sacrifice (24, 48, or 72 hours) after 

consumption of 14C-labeled decaBDE within a specific substudy. (Note: no reasons were given 

for the differences in the radioactivity recovered in these two studies.) Greater than 99% of the 

radioactivity was recovered in the feces and gut contents. 

After i.v. dosing of 14C-labeled decaBDE (substudy three), 74% of the radioactivity was 

recovered in the feces and gut contents at 72 hours. About 63% of the excreted material in the 

feces was metabolites and the remaining 37% was unchanged decaBDE. In these rats, only 

traces of radioactivity were noted in the urine. In bile-duct-cannulated rats, 7.2% of the 

radioactivity intravenously administered appeared in the bile in 4 hours, 1% of which was intact 

decaBDE (i.e., 99% of the radioactivity excreted in the bile was in the form of metabolites). 

Together, these results show that the vast majority of an oral dose of decaBDE is excreted in the 

feces, mostly as unabsorbed material. 

Morck et al. (2003) administered orally 14C-radiolabeled decaBDE as a single 3 μmol/kg 

(2.9 mg/kg) dose in soy phospholipid/Lutrol F127/water vehicle to male Sprague-Dawley rats 

(i.e., conventional rats). An average of 90 and 91% of the radioactivity was excreted in the feces 

at 3 and 7 days, respectively. About 71% of the total dose was excreted in the first 24 hours, 

another 17% between 24 and 48 hours, and a further 2% between 48 and 72 hours. In bile-ductcannulated rats subjected to the same oral treatment, an average of 88% of the dose was excreted 

in the feces and 9.5% in the bile within 3 days. Less than 0.1% of the radioactivity was excreted 

in the urine. In the cannulated rats, 66% of the total dose was excreted in the feces in the first 

24 hours and another 19% during 24–48 hours. In the first 12 hours, 4.4% of the total dose was 

recovered in the bile, whereas 1.6, 2, and 0.4% of the total dose were excreted at 12–24, 24–48, 
17 

and 48–72 hour intervals, respectively. These results indicate that excretion of decaBDE via 

feces was the dominant route after the oral dose, and biliary excretion plays a major role in the 

systemic elimination of absorbed decaBDE. The urinary excretion of radioactivity was 

insignificant. 

In the Hakk et al. (2002) study described earlier, ≤0.02% of the administered decaBDE 

dose was excreted daily via the urine in both conventional and cannulated rats, with a total of 

0.033 and 0.047%, respectively, of the administered dose excreted over the 72-hour period. 

About 9% of the administered dose was excreted in the bile by 72 hours, 6% of which was 

eliminated within the first 24 hours, indicating that excretion via the bile was favored over that 

of urine. 

About 20% of the decaBDE-derived radioactivity in urine from noncannulated rats was 

protein bound at 72 hours (compared to >73% not associated with protein). Eighteen percent of 

the bound material was bound to albumin, a serum protein with the ability to bind (nonspecific 

protein binding) short chain fatty acids. In cannulated rats, 18.2% of the decaBDE-derived 

radioactivity was unbound, and all the remaining 68.3% was associated with albumin. Two 

polar metabolites were noted but not identified. Under the assumption that the bound materials 

are less polar than the unbound materials, this observation supports the concept that a substantial 

portion, but not all, of the metabolites in the fecal matter originate from the bile. 

About 90% of the biliary radiolabel was associated with an unidentified 79-kDa protein, 

with the percent of bound label decreasing from 94 to 87% in bile samples pooled at 

1–24 hours, 24–48 hours, and 48–72 hours. Approximately 17% of the protein-bound biliary 

radioactivity collected over the first 24 hours was parent compound (and the remainder was 

unidentified metabolites); no parent compound was detected at 48 and 72 hours. The percent of 

total bound label in the bile samples also declined over time. None of the label in the bile was 

found to be unbound. 

3.4.1. Half-life Estimates 

In computer technicians, the half-life of BDE-209 is estimated to be in the range of a 

week (Sjodin et al., 2003; Jakobsson et al., 2002); however, the data to support this estimate are 

limited. Sjodin et al. (1999) also found that the levels of BDE-209 in the blood of 

occupationally exposed Swedish workers decreased by 66% over a 30-day absence from the 

workplace. These authors did not present any half-life estimate in their publication. 

The half-lives of hepta- to decaBDE in human serum were estimated by using data from 

occupationally exposed workers sampled before, during, and after a vacation period (Thuresson 

et al., 2006). The half-lives were found to decrease with increasing bromination. The half-life 

of heptaBDE-183 was 94 days, while that for BDE-209 was 15 days. 
18 

Sandholm et al. (2003) evaluated the kinetics of unlabeled decaBDE in male rats. One 

group of rats was dosed orally by gavage with 2 μmol decaBDE/kg (1.9 mg/kg). Another group 

of rats was also dosed intravenously with unlabeled decaBDE at the same dose. At specific time 

intervals, blood samples from three rats per group were collected according to the following 

schedule: group 1 was sampled 1 hour and 24 hours after dosing, group 2 after 3 hours and 

48 hours, group 3 after 6 hours and 72 hours, group 4 after 96 hours, group 5 after 120 hours, and 

group 6 after 144 hours. Plasma samples were extracted and decaBDE and its metabolites were 

quantified. Results from animals orally dosed with unlabeled decaBDE indicated the mean Cmax

in plasma reached 264 pmol/mL (253 ng/g) at 6 hours after dosing and AUC was 

12 nmol × hour/mL (11.5 μg × hour/mL). The i.v. data indicated that the clearance was 

0.60 mg/minute-kg, and the apparent volume of distribution at steady state was 1.4 L/kg. 

Half-lives were determined from the slope of the total concentration-time curve by linear 

regression. The disposition of decaBDE in male rats after oral dosing was described by a twocompartment model with t1/2β and t1/2γ

 values of 6.9 hours and 51 hours, respectively. The results 

from the i.v. study were consistent with a three-compartment model with half-lives (t1/2α, t1/2β, 

and t1/2γ) of 1.6 hours, 12 hours, and 58 hours, respectively (Sandholm et al., 2003). This value 

is lower than the 15-day half-life for humans estimated by Thuresson et al. (2006).

Huwe and Smith (2007) modeled the distribution and elimination half-lives of parent 

BDE-209 and several debrominated nonhydroxylated metabolites based on assays of plasma, 

excreta, liver, and carcass over a 21-day period that followed 21 days of dosing with 0.36 μg/day. 

The BDE-209 data showed the best fit to a biphasic depletion pattern. The distribution half-lives 

were 1.0 and 1.2 days for liver and plasma, respectively. The elimination half-lives for the same 

tissues were 20.2 and 75.9 days, respectively. A plasma first order half-life for octaBDE-207 

(7.9 days) was twice that of BDE-209 (3.9 days). In the liver, the first order half-life estimates 

for congeners 208, 191, and 197 (~6 days) were greater than those for 206 and 207 (~1 day). 

First-order estimates for 207 and 196 were intermediate (4–5 days). These values reflect the 

behavior of the parent BDE-209 and the debrominated, nonhydroxylated metabolites after 

absorption, distribution, and excretion but do not reflect the distribution and elimination of the 

hydroxylated metabolites. 

3.5. PHYSIOLOGICALLY BASED TOXICOKINETIC MODELS 

Limited information is available on the absorption, distribution, metabolism, and 

excretion of decaBDE in experimental animals and in humans. A model for human metabolism 

has not been established. Extrapolation of results from laboratory animals to humans using 

physiologically based pharmacokinetic (PBPK) models is not possible at this time. 
19 

4. HAZARD IDENTIFICATION 

4.1. STUDIES IN HUMANS—EPIDEMIOLOGY, CASE REPORTS, CLINICAL TRIALS 

Studies of decaBDE levels in occupationally exposed groups or studies of decaBDE in 

human biological media did not include surveillance of health endpoints. 

4.2. SHORT-TERM, SUBCHRONIC, AND CHRONIC STUDIES AND CANCER 

BIOASSAYS IN ANIMALS—ORAL AND INHALATION 

Inhalation toxicological studies of decaBDE in experimental animals are not available. 

4.2.1. Short-term and Subchronic Studies 

The short-term and subchronic studies are summarized in Table 4-1. 

4.2.1.1. Studies in Rats

Zhou et al. (2001) conducted a study in weanling rats to investigate the mechanism(s) by 

which decaBDE interferes with thyroid hormone homeostasis. In this study, Long-Evans female 

rats (eight animals/dose group) were orally administered decaBDE (>98% purity) in corn oil at 

doses of 0, 0.3, 1, 3, 10, 30, 60, or 100 mg/kg-day for 4 consecutive days. Body weights were 

recorded and dosing volumes adjusted daily. Animals were sacrificed 1 day after the last dose. 

Serum total thyroxine (T4) and triiodothyronine (T3), serum thyroid stimulating hormone (TSH), 

and hepatic enzyme activities (EROD, a marker for CYP-1A1; PROD, a marker for CYP-2B1;

and T4-uridine diphosphate glucuronyl transferase [T4-UDPGT]) were measured (see section 3.3

for data on EROD and PROD). Short-term treatment with decaBDE did not cause any visible 

signs of toxicity or any effects on body-weight gain or liver-to-body-weight ratios at any dose 

level. DecaBDE (up to 100 mg/kg-day) had no effect on serum T4, T3, or TSH concentration or 

on hepatic UDPGT activity. Based on these observations, the highest dose of 100 mg/kg-day is 

identified as the no-observed-adverse-effect level (NOAEL).

Carlson (1980) conducted a study to evaluate the induction of xenobiotic metabolism in 

rats, following short-term administration of decaBDE. Groups of four male Sprague-Dawley rats 

were dosed orally with 0.1 mmol/kg-day (96 mg/kg-day) of decaBDE in corn oil for 14 days. 

The decaBDE was synthesized by the complete bromination of diphenyl ether and was reported

to be of ―high purity.‖ These animals were probably dosed every other day since the protocol 

stated that livers were collected from animals sacrificed 24 hours after the last (seventh) dose. 
20 

Table 4-1. Oral short-term and subchronic toxicity studies for decaBDE in laboratory animals

Study

Species, sex, and 

sample size

Route, dose, and 

duration Observed effects NOAEL LOAELa Comments

Zhou et al. 

(2001)

Rat, Long-Evans,

female weanling rats, 

8/dose group

Gavage (>98% purity);

0, 0.3, 1, 3, 10, 30, 60, 

or 100 mg/kg-day; 4 days

No observed dose-related 

effects on body weight or

liver weight or changes in T3

or T4 levels 

100 mg/kg-day Not identified

NTP 

(1986)

Rat, F344/N,

male and female,

5/sex/dose group

Diet (99% purity); 0, 

472, 928, 1,846, 4,569, 

or 9,326 mg/kg-day in 

males; 0, 538, 1,061, 

2,137, 5,323, or 10,853 

mg/kg-day in females; 14 

days

None 9,326 mg/kg-day 

in males;

10,853 mg/kgday in females

Not identified Survival, final mean 

body weights not 

adversely affected. 

Clinical signs or 

gross pathological

effects not noted. 

NTP 

(1986)

Rat, F344/N,

male and female,

10/sex/dose group

Diet (97–99% purity); 0, 

191, 372, 781, 1,536, or 

3,066 mg/kg-day in 

males; 0, 238, 504, 967, 

1,955, or 3,944 mg/kgday in females; 13 weeks

None 3,066 mg/kg-day 

in males;

3,994 mg/kg-day 

in females

Not identified Survival, final mean 

body weights not 

adversely affected. 

Clinical signs or 

gross pathological

effects not noted.

NTP 

(1986)

Mouse, B6C3F1,

male and female,

5/sex/dose group

Diet (99% purity);

0, 1,027, 2,143, 4,246, 

10,536, or 20,994 

mg/kg-day in males; 

0, 1,146, 2,286, 4,627, 

11,348, or 23,077 

mg/kg-day in females; 

14 days

None 20,994 mg/kgday in males; 

23,077 mg/kgday in females

Not identified Survival, final mean 

body weights not 

adversely affected.

NTP 

(1986)

Mouse, B6C3F1,

male and female,

10/sex/dose group

Diet (97–99% purity);

0, 666, 1,355, 2,659, 

5,278, or 10,233 mg/kgday in males; 0, 702, 

1,437, 2,899, 5,687, or 

11,566 mg/kg-day in 

females; 13 weeks

None 10,233 mg/kgday in males;

11,566 mg/kgday in females

Not identified Survival, final mean 

body weights not 

adversely affected. 

Clinical signs or 

gross pathological

examination did not 

show any effect.

a

LOAEL = lowest-observed-adverse-effect level. 
21 

 Detoxification of O-ethyl O-p-nitrophenyl phenylphosphonothioate, methylation of 

p-nitroanisole, levels of NADPH cytochrome c reductase and cytochrome P-450 (CYP-450), and 

activities of UDPGT and benzo[a]pyrene hydroxylase were determined in hepatic cytosol or 

microsomes. Serum sorbitol dehydrogenase measurements were also performed on blood 

samples collected from the tail vein. No significant changes were observed in these enzyme 

activities. DecaBDE significantly increased the liver-to-body-weight ratio, indicating liver 

enlargement. Sorbitol dehydrogenase activity in the serum was not altered by decaBDE, 

suggesting that liver necrosis had not occurred, although other common serum markers for liver 

damage were not measured. Because of limitations in the study design, these results are not 

adequate for use in the health assessment of decaBDE. 

NTP (1986) conducted a 14-day study in rats exposed to decaBDE. F344/N rats (five 

animals/sex/dose) were fed diets containing 0, 5,000, 10,000, 20,000, 50,000, or 100,000 ppm 

decaBDE (99% purity). Based on the reported body weight information NTP (1986) and U.S. 

EPA (1988) default food intake values for F344 male (0.018 kg food/day) and female (0.014 kg 

food/day) rats, the corresponding estimated average daily doses were 0, 472, 928, 1,846, 4,569, 

or 9,326 mg/kg-day in male rats and 0, 538, 1,061, 2,137, 5,323, or 10,853 mg/kg-day in female 

rats. Animals were observed daily and were weighed on days 1, 7, and 14. At the end of the 

exposure period, animals were necropsied and several organs and tissues were examined 

histologically. No mortality was observed in the rats during the course of the study. Exposure to 

decaBDE did not cause any clinical signs of toxicity or adversely affect the final mean body 

weights. Gross pathological effects were not noted in any animal at any dose level. The results 

of this study indicated a NOAEL of 9,326 mg/kg-day in male rats and 10,853 mg/kg-day in 

female rats. 

The subchronic effects of decaBDE (97–99% purity) on rats were also investigated in a 

13-week study (NTP, 1986). Groups of F344/N rats (10/sex/dose) were administered decaBDE 

in the diet at concentrations of 0, 3,100, 6,200, 12,500, 25,000, or 50,000 ppm for 13 weeks. 

Based on body-weight information in the NTP (1986) report and U.S. EPA (1988) default food 

intake values for F344 male (0.018 kg food/day) and female (0.014 kg food/day) rats, the 

corresponding estimated average daily doses were 0, 191, 372, 781, 1,536, or 3,066 mg/kg-day in 

male rats and 0, 238, 504, 967, 1,955, or 3,944 mg/kg-day in female rats. Animals were 

observed twice daily and body weight, feed consumption, clinical signs, and behavior were 

recorded once a week. A necropsy was performed on all animals, including those killed in 

extremis, with the exception of those excessively autolyzed or cannibalized. Histologic 

examination was performed on major organs and tissues from control and high-dose groups. No 

mortality was observed in rats fed decaBDE, and no clinical signs of toxicity were noted. 

Compound-related changes in body weight and feed consumption were not observed, and no 
22 

gross or macroscopic pathological effects were noted in any animal examined. The results 

indicate a NOAEL of 3,066 mg/kg-day in male rats and 3,944 mg/kg-day in female rats. 

4.2.1.2. Studies in Mice

A 14-day study (NTP, 1986) was also conducted in mice. B6C3F1 mice (five 

animals/sex/dose) were fed diets containing 0, 5,000, 10,000, 20,000, 50,000, or 100,000 ppm 

decaBDE (99% purity). Based on the reported body weight information (NTP, 1986) and U.S. 

EPA (1988) default food intake values for B6C3F1 male (0.0057 kg food/day) and female 

(0.0048 kg food/day) mice, the estimated average daily doses were 0, 1,027, 2,143, 4,246, 

10,536, or 20,994 mg/kg-day in male mice and 0, 1,146, 2,286, 4,627, 11,348, or 23,077 mg/kgday in female mice. Animals were observed daily and were weighed on days 1, 7, and 14. 

Necropsy was performed at the end of the exposure period, and several organs and tissues were 

examined histologically. Exposure to decaBDE up to 20,994 mg/kg-day in males and 

23,077 mg/kg-day in females showed no effects on survival or body weight, and there were no 

clinical signs of toxicity. No compound-related gross pathological effects were noted in any 

animal in any group. The results of this study indicate a NOAEL of 20,994 mg/kg-day in male 

mice and 23,077 mg/kg-day in female mice. 

B6C3F1 mice (10 animals/sex/dose) were fed diets containing 0, 3,100, 6,300, 12,500, 

25,000, or 50,000 ppm decaBDE (97–99% purity) for 13 weeks (NTP, 1986). Based on the 

mouse body weight information reported (NTP, 1986) and U.S. EPA (1988) default food intake 

values for B6C3F1 male (0.0057 kg food/day) and female (0.0048 kg food/day) mice, the 

corresponding estimated average daily doses were 0, 666, 1,355, 2,659, 5,278, or 10,233 mg/kgday in males and 0, 702, 1,437, 2,899, 5,687, or 11,566 mg/kg-day in females. Animals were 

observed twice daily and body weights, feed consumption, clinical signs, and behavior were 

monitored once a week. Necropsy was performed on all animals, including those killed in 

extremis, with the exception of those excessively autolyzed or cannibalized. Histologic 

examination was performed on the organs and tissues from control and high-dose groups. Only 

one male and one female mouse fed 12,500 ppm died in the course of the study. There were no 

clinical signs of toxicity, and no compound-related effects on body weight and feed consumption 

were observed. No gross or macroscopic pathological effects were noted in any animal at any 

dose. The results of this study indicated a NOAEL of 10,233 mg/kg-day in males and 

11,566 mg/kg-day in females. 

4.2.2. Chronic Studies and Cancer Bioassays 

NTP (1986) investigated the relationship between ingestion of decaBDE in rats and mice 

and tumor development. These chronic oral studies are summarized in Table 4-2. The decaBDE 

used in both rats and mice was 94–97% pure, with no detectable brominated dioxins or furans. 
23 

The major impurities in the decaBDE test material were isolated and identified as two 

unspecified congeners of nonaBDE. 

4.2.2.1. Study in Rats

Groups of 7- to 8-week-old male and female F344/N rats (50/sex/dose) were exposed to 

decaBDE (94–97% purity) in the diet at concentrations of 0, 25,000, or 50,000 ppm for 

103 weeks (NTP, 1986). Average daily doses of decaBDE as reported in the study were 0, 

1,120, or 2,240 mg/kg-day for male rats and 0, 1,200, or 2,550 mg/kg-day for female rats. The 

animals were observed twice daily and clinical signs were recorded once per week. Animals 

were weighed once a week for the first 12 weeks, once per month thereafter until week 100 or 

101, then every 2 weeks. Mean body weights were calculated for each group. In addition, feed 

consumption, morbidity, and mortality were monitored throughout the study period. Animals 

found moribund and animals that survived to the end of the study period were sacrificed. 

Complete necropsy was performed on all animals, including those found dead during the course 

of the study, unless they were excessively autolyzed or cannibalized. Gross and microscopic 

examinations were performed on major organs or tissues. 

No clinical signs of toxicity were observed in the treated rats. There were no significant 

differences in the mean body weight and feed consumption between treated and control animals. 

Survival of low-dose male rats was significantly lower than that of the controls after week 102, 

but the decrease was not considered to be compound related because the reduction in survival 

occurred late in the study and there was a lack of a dose effect. 

At necropsy, several nonneoplastic changes were observed. In the liver, an increase in 

the incidence of thrombosis was observed in high-dose male rats (1/50, 0/50, 9/49), with no such 

increase noted in low-dose males or in any female at any dose level. A dose-dependent, but not 

statistically significant, increase in the incidence of degeneration of the liver was also observed 

in treated male rats at incidence rates of 13/50, 19/50, and 22/49 in the control, low-dose, and 

high-dose groups, respectively. No liver degeneration was observed in female rats. In the 

spleen, an increased incidence of fibrosis was seen in males at low dose (8/50) and high dose 

(13/49) compared with 5/49 in controls, indicating a dose-dependent increase that was 

statistically significant only in the high-dose group. Hematopoiesis was observed at an increased 

incidence in the spleen of female rats (control 12/49, low dose 24/48, high dose 17/50), but the 

increase was not dose dependent or statistically significant at any dose level. No such increases 

were observed in males. In the mandibular lymph node, lymphoid hyperplasia increased in 

males in a dose-dependent manner (4/50, 6/50, and 13/49 in the control, low dose, and high dose, 

respectively), but the incidence reached statistical significance only at the high dose. 
24 

Table 4-2. Oral chronic toxicity studies for decaBDE in laboratory animals 

Study

Species, sex, and 

sample size

Route, dose, and 

duration Observed effects NOAEL LOAELa Comments

NTP 

(1986)

Rat, F344/N,

male and female,

50/sex/dose group

Diet (94–97% purity);

0, 1,120, or 2,240 

mg/kg-day for males; 0, 

1,200, or 2,550 mg/kgday for females; 2 years

Increased incidences of thrombosis (1/50, 0/50, 

9/49) and degeneration (13/50, 19/50, 22/49) in the 

liver of high-dose male rats; dose-dependent 

increase in splenic fibrosis in males with statistical 

significance at high dose; dose-dependent increase 

in lymphoid hyperplasia of the mandibular lymph 

nodes in males with statistical significance at high 

dose

Dose-related increase in liver neoplastic nodules 

statistically significant in low- and high-dose males 

and in high-dose females

1,120

mg/kg-day 

in males

2,550 

mg/kg-day 

in females

2,240

mg/kg-day 

in males

Not 

identified

Males, but not 

females, 

exhibited 

effects.

NTP 

(1986)

Mouse, B6C3F1,

male and female,

50/sex/dose group

Diet (94–97% purity);

0, 3,200, or 6,650 

mg/kg-day for males; 0, 

3,760, or 7,780 mg/kgday for females; 2 years

Increased incidences of granulomas in the liver of 

treated males (with statistical significance only at 

low dose); centrilobular hypertrophy in males (with 

significance at low and high doses); dosedependent increase in thyroid follicular cell 

hyperplasia (2/50, 10/50, 19/50) in males 

(significant at low and high doses); increase in the 

incidence of stomach ulcers in females at high dose

Increased incidence of hepatocellular adenoma or 

carcinoma (combined) in low-dose males; 

marginally but not statistically significant increase 

in the thyroid gland follicular cell adenomas or 

carcinomas (combined) in males

Not 

available in 

males

3,760 

mg/kg-day 

in females 

3,200 

mg/kg-day 

in males

7,780 

mg/kg-day 

in females

a

LOAEL = lowest-observed adverse-effect level. 
25 

 No incidence of lymphoid hyperplasia was reported in females at any dose level. An 

increased incidence of retinal degeneration was noted in low-dose female rats but not in highdose females or males at any dose level. This lesion was attributed to greater exposure of the 

female rats to fluorescent light and was not considered to be treatment related. Acanthosis 

(increased thickness of the epithelial surface) of the forestomach was observed at increased 

incidence in treated males but not in females, but the incidence was not significant. Both male 

and female rats demonstrated a dose-dependent decrease in the incidence of C-cell hyperplasia 

in the thyroid gland (12/50, 6/49, and 2/49 in males and 14/50, 7/49, and 2/50 in females at 

control, low-dose, and high-dose groups, respectively). Decreases in the C-cell hyperplasia 

would not be considered biologically adverse since other thyroid effects were not observed in 

these rats. No other significant pathological changes were observed. 

Histopathologic examination revealed a significant increase in the incidence of neoplasia 

in the rat, and several organs or tissues were adversely affected. There was a dose-dependent 

increase in the incidence of neoplastic nodules in the livers of both male and female rats. The 

incidence of these lesions was 1/50, 7/50, and 15/49 in males and 1/50, 3/49, and 9/50 in females 

in control, low-dose, and high-dose groups, respectively. The incidence reached statistical 

significance at both treatment doses in males and at the high dose in females. 

At the time the NTP (1986) study was conducted, the term neoplastic nodule was used to 

describe abnormal cellular masses in the livers of rats characterized by loss or distortion of 

normal cellular architecture (Maronpot et al., 1986). Some of those nodules would now be 

described as benign hepatocellular adenomas in rats (Wolf and Mann, 2005). However, there is 

no complete equivalency between the neoplastic nodule of the past and the hepatocellular 

adenoma term of today. Some of the neoplastic nodules from the NTP (1986) study might now 

be classified as foci of cellular alteration or hyperplasia rather than adenomas (Maronpot et al., 

1986). Adenomas and foci of cellular alteration are considered to be preneoplastic lesions, 

whereas hyperplastic lesions represent secondary nonneoplastic changes (Maronpot et al., 1986). 

The assumption that the hepatic neoplastic nodules from the NTP (1986) bioassay are equivalent 

to hepatic adenomas under the current NTP lexicon is a conservative interpretation of the data.

A slight increase in mononuclear cell leukemia in treated rats was observed with 

incidences in males of 30/50, 33/50, and 35/50 at control, low, and high doses, respectively, and 

in females of 14/50, 21/50, and 18/50 at control, low, and high doses, respectively. However, the 

increase was not considered to be biologically significant because of the marginal and 

insignificant increase in treated rats of both sexes and the high incidence in control rats. The 

incidence of hepatocellular carcinomas was low in male and female rats and was apparently not 

compound related. Other tumors observed included splenic sarcomas, pancreatic acinar cell 

adenomas, carcinomas in Zymbal’s gland, and osteosarcomas, but these were considered to be of 
26 

no significance because of high historical incidence, lack of dose-response trend in the tumor 

incidence, or lack of statistically significant responses. 

Based on the results from this 2-year study in rats (NTP, 1986), exposure to decaBDE in 

the diet did not cause compound-related effects on survival or any significant effects on body 

weight or food consumption. However, treatment resulted in several nonneoplastic changes at 

the high dose, including thrombosis and degeneration of the liver in males, fibrosis in the spleen 

in males, and lymphoid hyperplasia in the mandibular lymph node in males. Dose-dependent 

increases in the incidence of neoplastic nodules in liver of males and females provide some 

evidence of carcinogenicity of decaBDE in rats. Based on these results and on increased 

incidence of thrombosis and degeneration in the liver, splenic fibrosis, and lymphoid hyperplasia 

of the mandibular lymph nodes, a NOAEL for systemic toxicity was 1,120 mg/kg-day and the 

lowest-observed-adverse-effect level (LOAEL) was 2,240 mg/kg-day for males. Female rats 

appeared to be less sensitive to the systemic toxicity of decaBDE at the doses used in this study. 

Based on this finding, the NOAEL for systemic toxicity in females was 2,550 mg/kg-day, with 

no LOAEL established. The dose-related increase in nonmalignant liver tumors (neoplastic 

nodules) in both males and females provides some evidence of carcinogenicity of decaBDE in 

rats. 

4.2.2.2. Study in Mice

Groups of 9-week-old male and female B6C3F1 mice (50/sex/dose) were administered 

decaBDE (94–97% purity) in the diet at doses of 0, 25,000, or 50,000 ppm for 103 weeks (NTP, 

1986). Average daily doses of decaBDE as reported in the study were 0, 3,200, or 6,650 mg/kgday in male mice and 0, 3,760, or 7,780 mg/kg-day in female mice. The animals were observed 

twice daily, and clinical signs were recorded once per week. Animals were weighed once a 

week for the first 12 weeks and once per month thereafter. In addition, feed consumption, 

morbidity, and mortality were monitored throughout the study period. All survivors were 

sacrificed during weeks 112–113. Complete necropsy was performed on all animals, including 

those found dead during the course of the study, unless they were excessively autolyzed or 

cannibalized. Gross and microscopic examinations were performed on major organs or tissues. 

There were no significant differences in survival among any groups of mice of either sex 

at terminal sacrifice. However, loss of control male mice (presumably due to fighting) was 

significant during the first 15 months of the study. There were no compound-related clinical 

signs of toxicity or changes in body weight or food consumption. 

At necropsy, several nonneoplastic changes were observed in tissues of treated mice. In 

the liver, the incidence of granulomas in control, low-, and high-dose mice was 8/50, 22/50, and 

12/50 in males and 23/50, 27/50, and 24/50 in females, respectively. Although increases were 

observed in the treated animals of both sexes compared with controls, no consistent dose 
27 

response for this effect was evident, and the effect was not associated with a statistically 

significant positive trend. Thus, the toxicological significance of this effect is unclear. 

Significant increases in the incidence of centrilobular hypertrophy were also observed in the 

liver of male mice at high and low doses (0/50, 34/50, and 32/50 in the control, low dose, and 

high dose, respectively). Although the increases were comparable in the low- and high-dose 

males and were not observed in female mice at any dose level, the high incidence in the treated 

males indicates that the effect was treatment related. In the thyroid gland, a dose-dependent and 

statistically significant increase (at both dose levels) in the incidence of follicular cell 

hyperplasia was observed in males (2/50, 10/50, and 19/50, respectively, in the control, lowdose, and high-dose groups). In the females, the incidence was increased in the low- (9/50) and 

high- (7/49) dose groups compared to 4/50 in the control group, but the increase was not dose 

dependent or statistically significant at any dose level. Only high- but not low-dose female mice 

exhibited a significant increase in the incidence of stomach ulcers (1/50, 1/50, and 8/50 in the 

control, low-dose, and high-dose females, respectively). In males, the incidence in treated mice 

was comparable with that in control mice: 5/49, 3/50, and 5/50 in the control, low-dose, and 

high-dose males, respectively. 

Histopathological examination revealed a significantly increased incidence of neoplasia 

in mice, with the liver appearing to be the main target organ for decaBDE. In the liver, increases 

(although not statistically significant) in the incidence of hepatocellular adenoma were observed 

at similar rates in low- and high-dose males (4/50, 12/50, and 12/50 in control, low-dose, and 

high-dose groups, respectively). Other changes observed in male mice included an increased 

incidence of hepatocellular carcinoma (5/50, 14/50, and 8/50 in the control, low-dose, and highdose groups, respectively) that was not statistically significant at either dose. The combined 

incidence of hepatocellular adenomas or carcinomas in male mice, after correction for survival, 

significantly increased at low dose but not at high dose; the responses amounted to 8/50, 22/50, 

and 18/50 in control, low-dose, and high-dose groups, respectively. As indicated in the study 

report, these findings may have been influenced by the large number of early deaths in control 

male mice compared with treated mice, thereby decreasing the significance of the hepatocellular 

adenomas or carcinomas seen in the treated male mice. Consequently, the apparent statistically 

significant increase in the hepatocellular adenomas and carcinomas (combined) at the high dose 

(18/50 versus 8/50) based on regular rate comparison test (i.e., Fisher’s exact test) was no longer 

significant when the life table test or incidental tumor test was used to control for intercurrent 

mortality. The trend tests from the latter two tests also failed to show statistical significance in 

the combined hepatocellular adenomas or carcinomas in male rats. The incidence of 

hepatocellular adenomas or carcinomas (combined) in female mice was not statistically 

significant (8/50, 13/50, and 13/50 in control, low-, and high-dose mice, respectively). In the 

thyroid gland, follicular cell adenomas or carcinomas (combined) were slightly, but not 
28 

significantly, increased in treated mice of both sexes over the corresponding control mice; the 

incidence was 0/50, 4/50, and 3/50 in males and 1/50, 3/50, and 3/50 in females in the control, 

low-, and high-dose groups, respectively. 

These results from the NTP (1986) chronic carcinogenicity study in mice show that 

decaBDE treatment caused liver granulomas, liver hypertrophy, and thyroid gland follicular cell 

hyperplasia in males only and stomach ulcers only in females. Males, but not females, had a 

statistically significant increase in the incidence of hepatocellular adenomas and carcinomas at 

the low dose but not at the high dose. Based on these results and on increased incidence of liver 

granulomas and centrilobular hypertrophy and statistically significant and dose-dependent 

increases in the thyroid gland follicular cell hyperplasia in male mice administered 3,200 mg/kgday or higher, no NOAEL for systemic effects for males was established. Female mice were less 

sensitive to the systemic toxicity of decaBDE at the doses used in this study; however, the IRIS 

assessment authors identified a NOAEL for a portal-of-entry effect for females of 3,760 mg/kgday and a LOAEL of 7,780 mg/kg-day based on an increase in the incidence of stomach ulcers. 

4.3. REPRODUCTIVE/DEVELOPMENTAL STUDIES—ORAL AND INHALATION 

Reproductive/developmental toxicity studies are not available in humans by the oral or 

inhalation routes of exposure. No reproductive/developmental animal toxicity studies were 

identified by the inhalation route of exposure. Oral reproductive and developmental studies in 

experimental animals are summarized in Table 4-3. 

4.3.1. Studies in Rats 

Hardy et al. (2002) conducted a developmental toxicity study in rats by using a composite 

of three lots of a commercial flame retardant (97.34% decaBDE and 2.66% nonaBDE and 

octaBDE) produced by three manufacturers. In this study, Sprague-Dawley rats (25 mated 

females per dose group) were administered decaBDE in corn oil by gavage at doses of 0, 100, 

300, or 1,000 mg/kg-day during gestation days 0 through 19. Dams were observed daily for 

morbidity, mortality, and signs of injury. Maternal body weight, body-weight gain, and food 

consumption were monitored. Dams were sacrificed on day 20 of gestation, and liver weights, 

gravid uterine weights, and the number of corpora lutea, implants, fetuses, and resorptions were 

recorded. The placenta and fetuses were examined for gross abnormalities, and histologic 

examinations were performed.

All dams survived decaBDE treatment until scheduled sacrifice. There were no adverse 

treatment-related effects observed in maternal clinical findings, body weight, or body-weight 

gain. Although a slight but statistically significant increase in food consumption was observed at 

1,000 mg/kg-day at time intervals up to day 12 of gestation, the authors did not consider this 

indicative of an adverse effect of treatment. 
29 

Table 4-3. Oral developmental and reproductive studies for decaBDE in laboratory animals 

Study

Species, sex,

and sample size

Route, dose, and 

duration Observed effects NOAEL LOAEL Comments

Hardy et al. 

(2002)

Rat, SpragueDawley, 

pregnant female, 

25/dose group

Gavage (97.34% 

purity); 0, 100, 300, or 

1,000 mg/kg-day;

gestation days 0–19

No statistically significant maternal or 

developmental treatment-related effects

1,000 

mg/kg-day

Not 

identified

Viberg et al. 

(2007)

Rat, SpragueDawley, male, 20 

rats from 3–5 

litters/treatment 

group

Single dose gavage 

(>98% purity in 20% 

fat emulsion); 0, 6.7, 

or 20.1 mg/kg on PND 

3 

Significant dose-related disruption in 

habituation (changes in locomotion, 

rearing, and total activity) at 2 months 

in rats, following exposure to 6.7 and

20.1 mg/kg on PND 3

Not 

identified

6.7 mg/kg Single dose 

experiment

Viberg et al. 

(2003a)

Mouse, NMRI, 

male, 10 mice 

from 3–5 litters/ 

treatment group 

Single oral gavage 

(>99% purity in 20% 

fat emulsion); 0, 2.22, 

or 20.1 mg/kg (PNDs

3 and 19); 0, 1.34,

13.4, or 20.1 mg/kg 

(PND 10)

Significant dose-related disruption in 

habituation (changes in locomotion, 

rearing, and total activity) at 2, 4, and 6 

months in mice, following exposure to 

20.1 mg/kg on PND 3

2.22 mg/kg 20.1 mg/kg Single dose 

experiment

Tseng et al. (2006) Mouse, CD-1, 

male, 50/dose 

group

Oral gavage (98% 

purity in corn oil); 0, 

10, 100, 500, or 1,500 

mg/kg-day; PNDs 21–

70

Reduced amplitude of sperm lateral 

head displacement, reduced sperm 

mitochondrial membrane potential, 

increased sperm H2O2 generation

100 mg/kgday500 mg/kgday

Rice et al. (2007) Mouse, 

C57BL6/J, 3 

males and 3

females from 11–

13 

litters/treatment 

group 

Micropipette 

administration (99.5% 

purity in 20% fat 

emulsion); 0, 6, or 20 

mg/kg-day; PNDs 2–

15

Decreased number of male and female 

pups performing the palpebral reflex on 

PND 14, increased struggling behavior 

on PND 20, effects on grip strength on 

PNDs 14 and 16, effects on locomotor 

activity on PND 70

Not 

identified

6 mg/kg-day
30 

 No statistically significant differences were observed in maternal absolute or relative 

liver weights between treatment and control groups. At necropsy, gross examination of the dams 

revealed no adverse effect of treatment with decaBDE. Number of dams with viable fetuses, 

mean number of corpora lutea, number of implantation sites, percent preimplantation loss per 

dam, number of viable fetuses, and gravid uterine weights were not adversely affected by 

decaBDE treatment. 

A statistically significant increase in the mean number of early resorptions per dam was 

observed in the 1,000 mg/kg-day group compared to controls. Based on the lack of a consistent 

dose response for this effect (the mean number of early resorptions per dam was 0.6, 0.6, 0.5, 

and 1.4 at 0, 100, 300, and 1,000 mg/kg-day, respectively), lack of a statistically significant 

positive trend associated with the effect, and the historically high incidence of this effect (0.5–

1.4) for the laboratory, these effects are not considered to be of toxicological significance. 

Examination of the results indicated a marginal increase in the postimplantation loss/dam of 7 

and 9% at 300 and 1,000 mg/kg-day, respectively, compared with 4% in controls and at 100 

mg/kg-day. However, this effect was not associated with a statistically significant positive trend. 

A slight, but statistically not significant, decrease in the percentage of viable fetuses per implant 

was seen 

(96, 96, 93, and 91% in the control, 100, 300, and 1,000 mg/kg-day groups, respectively). Fetal 

body weights, crown-rump ratio, and fetal sex ratio were not different between treatment and 

control groups. No adverse decaBDE treatment-related effects were identified during fetal 

external, skeletal, or visceral examinations. DecaBDE treatment, therefore, did not produce any 

evidence of maternal or developmental toxicity up to the highest dose tested of 1,000 mg/kg-day. 

The NOAEL for maternal and developmental toxicity in this study was 1,000 mg/kg-day, the 

highest dose tested. 

BDE-209 (>98% purity) in a fat emulsion was administered by gavage to 3-day-old 

Sprague-Dawley rats at 0, 6.7, or 20.1 mg/kg (Viberg et al., 2007). A total of 20 rats were 

picked from three to five different litters in each treatment group. Motor activity was measured 

for a 60-minute period, divided into three 20-minute periods, in rats at the age of 2 months. 

Motor activity tests measured locomotion (horizontal movement), rearing (vertical movement), 

and total activity (all types of vibration within the test cage [i.e., those caused by rat movements, 

shaking/tremors, and grooming]). There were no clinical signs of toxicity in the BDE-209-

treated rats at any given time during the experimental period, nor was there any significant 

difference in body-weight gain or adult weight between controls and rats treated with BDE-209. 

In control rats, there was a distinct decrease in locomotion, rearing, and total activity at 2 months 

of age, indicating habituation in response to the diminishing novelty of the test chamber over the 

60-minute test period. Habituation is defined as the ability of the animals to adapt to a new 

environment and is characterized as initial investigation and exploration of their surroundings 
31 

followed by gradual acclimatization and acceptance of the new area. Two-month-old rats 

exposed to 20.1 mg/kg BDE-209 on PND 3 displayed significantly less activity for all three 

behavioral variables during the first 20-minute test period compared with controls, while during 

the third 20-minute period (40–60 minutes) they were significantly more active than the control 

animals. Rats receiving the low dose of BDE-209 (6.7 mg/kg) showed significantly increased 

locomotion activity during the second 20-minute period, significantly decreased rearing activity 

during the first and second 20-minute periods, and significantly higher total activity during the 

first and second 20-minute periods compared with the control rats. The LOAEL in this study 

was 6.7 mg/kg for significant changes in spontaneous motor behavior (locomotion, rearing, and 

total activity) in 2-month-old rats given BDE-209 on PND 3. 

Immediately after the spontaneous behavior tests, nicotine-induced behavior was studied 

to determine whether changes in spontaneous behavior in adult rats neonatally exposed to 

BDE-209 included effects on development of the cholinergic system and thereby altered the 

response in the adult animal to the cholinergic agent nicotine (Viberg et al., 2007). The rats 

were given a single subcutaneous injection of 80 μg nicotine base/kg, a dose known to cause an 

increase in activity in experimental animals, and were immediately tested again for nicotineinduced motor behavior with regard to locomotion, rearing, and total activity during another 

60-minute period divided into three 20-minute periods. 

Pair-wise testing between the nicotine-injected and saline-injected rats showed, as 

expected, a significant increase in response to nicotine in the neonatally vehicle-treated rats 

during the first 20-minute period (60–80 minutes) for all three variables (locomotion, rearing, 

and total activity). In contrast, the nicotine-injected rats exposed to 20.1 mg/kg of BDE-209 on 

PND 3 showed significantly decreased activity for all three tests (locomotion, rearing, and total 

activity) during the first 20-minute period (60–80 minutes) compared with the rats neonatally 

exposed to the high BDE-209 dose and injected with saline. The authors concluded that 

neonatal exposure to BDE-209 on PND 3 affects adult spontaneous behavior and also affects the 

cholinergic system, seen as changes in the adult rats’ response to the cholinergic agent nicotine. 

4.3.2. Studies in Mice 

Viberg et al. (2003a) assessed the potential of decaBDE to affect the developing central 

nervous system. The neurotoxic effects of decaBDE on spontaneous motor behavior of NMRI 

male mice were investigated in adult animals exposed to a single oral dose as neonates. Uptake 

of radiolabel by the brain of the neonatal mice orally administered 14C-labeled BDE-209 on PND 

3, 10, or 19 (i.e., at different stages of neonatal mouse brain development) was also measured to 

determine if there were age-related differences in tissue toxicokinetics that might correlate with 

the neurodevelopmental effects evaluated. 
32 

In this behavioral study, 3-day-old and 19-day-old male mice were given a single dose of 

0, 2.22, or 20.1 mg/kg body weight decaBDE (purity estimated to be >99%) in a 

20% (weight/weight) emulsion vehicle of egg lecithin-peanut oil and water. Ten-day-old mice 

received 0, 1.34, 13.4, or 20.1 mg/kg. The spontaneous behavior test (measuring locomotion, 

rearing, and total activity) was conducted in 10 mice randomly selected from the litters in each 

treatment group at 2, 4, and 6 months of age. There were three to five litters (four to seven 

males per litter) in each of the dose groups. The behavior variables were measured for a 60-

minute period divided into three consecutive 20-minute periods. In order to study timedependent changes in habituation, an habituation ratio was calculated by dividing the motor 

behavior measures from the 40- to 60-minute observation period by those from the 0- to 20-

minute period and multiplying by 100 for each of the three different variables: locomotion, 

rearing, and total activity. The habituation ratios from 2-, 4-, and 6-month-old mice within each 

treatment group were then compared. An increase in habituation ratio indicates decreased 

capability to habituate to a novel environment. Data for the three spontaneous behavior 

variables and habituation ratio are only available in graphic form and could not be used for 

quantitative assessment.1

Treatment with decaBDE caused no clinical signs of toxicity at any time during the 

experimental period. Body weight and body-weight gain were not significantly different 

between decaBDE- and vehicle-treated mice in the three different age groups. Control mice 

treated on PND 3, 10, or 19 exhibited normal habituation profiles. Pair-wise testing between 

adult mice exposed to 20.1 mg/kg on PND 3 and control groups indicated significant changes in 

all three spontaneous behavior variables at 2, 4, and 6 months of age. For the first 20 minutes, 

mice receiving 20.1 mg/kg displayed significantly less activity for locomotion, rearing, and total 

activity compared with controls. During the third 20-minute period, exposure of mice to 

20.1 mg/kg on PND 3 caused significantly more activity for locomotion, rearing, and total 

activity than the controls at 2, 4, and 6 months. The only effect noted in mice exposed to 

2.22 mg/kg was a significant decrease in total activity in the first 20-minute test period compared 

with the controls at 2 months of age. However, total activity returned to control level during the 

third 20-minute period. The lower dose of 2.22 mg/kg did not elicit any significant differences 

in these three variables compared with controls at 4 months of age. Lower activity was observed 

at 2.22 mg/kg during the first 20-minute period for the rearing variable at 6 months of age 

compared with controls, again returning to control level during the third 20-minute period. Mice 

exposed neonatally up to 20.1 mg on either PND 10 or 19 did not show any significant 

differences in any of the variables after 2, 4, or 6 months compared with controls. The authors 

 

1

Attempts to obtain numerical values and other information on the data from the authors were not successful. 
33 

indicated that the absence of effects on spontaneous activity in mice treated on PNDs 10 and 19 

suggests that there is a critical window for the induction of the observed behavioral disturbances. 

The habituation ratio calculated from the three spontaneous motor behavior variables 

(locomotion, rearing, and total activity) significantly increased after 2, 4, and 6 months of age in 

mice exposed on PND 3 to 20.1 mg/kg. Mice exposed on PND 3 to 2.22 mg/kg did not show a 

significant decrease in habituation capability with age. The decrease observed in the habituation 

capability in the adult mice exposed neonatally to the high dose indicated that the neurotoxic 

effect of neonatal decaBDE exposure was persistent and also worsened with age. The NOAEL 

in this study was 2.22 mg BDE-209/kg, and the LOAEL was 20.1 mg/kg for significant changes 

in spontaneous motor behavior and decreased habituation capability for locomotion, rearing, and 

total activity, worsening with increasing age. 

Neonatal exposure to 14C-decaBDE (specific activity 17.5 mCi/mmol) in mice on PND 3, 

10, or 19 revealed that the labeled substance was absorbed and distributed to the brain, heart, 

and liver. However, the amounts in the liver 24 hours after dosing on PNDs 3, 10, and 19 were 

12.6, 9.4, and 5.8%, respectively. The lower amount of BDE-209 measured as the dosing day 

occurred later suggests that gastrointestinal absorption may have decreased as the 

gastrointestinal tract matured over the first 19 days after birth. Only a small fraction of the dose 

reached the brain or heart 24 hours after dosing, especially with dosing on day 19 (see Viberg et 

al. [2003a] in section 3.2.2). However, results indicated that the amount of radioactivity 

increased significantly in the brain over a 7-day period in animals exposed on PNDs 3 and 10 but 

not in those exposed on PND 19. The radioactivity in the liver and heart was the same or 

decreased during the 7-day period following oral administration on PNDs 3, 10, and 19. The 

observed increase in radioactivity in the brain over the 7-day period suggests slow transport of 

decaBDE and/or its metabolites to the brain, which may account for the fact that administration 

on day 3 caused a more significant impact on habituation than administration on PND 10 or 19. 

The radiolabel data showed that the amount of decaBDE in the brain 24 hours after dosing on 

PNDs 3, 10, and 19 was 0.5, 0.4, and 0.06%, respectively. The radioactivity was significantly 

greater 7 days after BDE-209 administration on PNDs 3 and 10 compared with 24 hours after 

administration. The amount of radioactivity measured in the brain 7 days after dosing on PNDs 

3 and 10 (PNDs 10 and 17) was 0.7 and 1.1%, respectively. There was no change in the amount 

of radioactivity measured in the brain of animals 7 days after dosing on PND 19. 

Rice et al. (2007) examined the effects of BDE-209 (99.5% purity) on developmental 

milestones, sensorimotor behaviors, serum T4 levels, and locomotor activity in male and female 

C57BL6/J mice administered doses of 0, 6, or 20 mg/kg-day. The BDE-209, in a 20% egg 

lecithin/peanut oil/water emulsion, was administered to the pups from PNDs 2–15 by using a 

micropipette to avoid gavaging neonatal animals. There were no delays in postnatal 

developmental milestones (pinna detachment, incisor eruption, eye opening, vaginal opening, or 
34 

testes descent) from BDE-209 treatment in male or female mice. There were no effects of 

exposure on anogenital distance or crown-rump length. 

The authors developed a special functional observational battery (FOB), suitable for 

neonatal mice, to examine a series of home-cage, reflexive, and sensorimotor behaviors, 

measured on PND 14, 16, 18, or 20. Three of the FOB endpoints were affected by BDE-209 

exposure: palpebral reflex, forelimb grip, and struggling behavior during handling. On PND 14, 

significantly fewer male and female pups in the 6 and 20 mg/kg-day groups performed the 

palpebral reflex compared with controls. On PNDs 14 and 16, fewer male pups in the 20 mg/kgday group performed an effective forelimb grip compared with same-sex controls. Male and 

female pups in the 6 mg/kg-day group struggled significantly more on PND 20, while they were 

being handled for the FOB, compared with controls and the high-dose group. 

Rice et al. (2007) also examined the locomotor activity of male and female mice in a 

novel environment over a 2-hour period on PND 70 and at approximately 1 year of age (one 

male and one female from each of 9–13 litters were evaluated). Locomotor activity declined 

over the course of the 2-hour assessment in PND 70 males and in females in the control and 

treated groups. However, the rate of decline was significantly different (p = 0.04) in male mice 

exposed to 6 and 20 mg/kg-day compared with control animals, an effect that was most 

pronounced in the high-dose males during the first 1.5 hour of the 2-hour activity session. There 

was a non-dose-related decline in the locomotor activity in the female mice during the 2-hour 

activity session. Unlike the males, they became hypoactive compared with the controls. There 

was no effect of BDE-209 treatment on the locomotor activity of the 1-year old male and female 

mice. 

The effect of BDE-209 treatment on serum T4 in PND 21 offspring was also investigated 

in this study. A dose-related reduction in serum T4 in comparison with controls occurred in 

males but not in females. 

The LOAEL in this study was 6 mg/kg-day, the lowest dose tested, for decrease in the 

percent of male and female pups performing the palpebral reflex on PND 14, for increased 

struggling behavior of male mice on PND 20, for decreased T4 levels in male mice, and for 

effects on locomotor activity of male mice on PND 70. 

Tseng et al. (2006) studied the effects of BDE-209 on mouse sperm function, DNA 

content, and histopathology of the testes. CD-1 male mice (50/dose group) were fed decaBDE 

(98% purity) by gavage in corn oil at 0, 10, 100, 500, or 1,500 mg/kg-day from PNDs 21–70. 

Body weight, body-weight gain, and absolute and relative weights of the testis, epididymis, 

cauda epididymis, and seminal vesicle of treated animals were not significantly different from 

controls at sacrifice on PND 71. Morphology of the testicular tissues appeared normal in all 

treated groups compared with controls. DNA content in testis cells was unaffected by treatment 

with BDE-209. No significant differences in sperm motility (expressed as the ratio between the 
35 

number of motile sperm and total number of sperm), sperm count, or morphology were seen 

among the groups exposed to BDE-209 and the controls. Sperm motion velocity parameters 

were measured, including curvilinear velocity, straight-line velocity, and amplitude of the lateral 

head displacement (ALH). The only effect seen on sperm motion velocity was a significant 

decrease in ALH at 500 and 1,500 mg/kg-day. Significant increase in the generation of hydrogen 

peroxide in the sperm of sexually mature mice occurred at 500 and 1,500 mg/kg-day. The 

mitochondrial membrane potential (MMP) of sperm cells, a predictor of sperm fertility potential, 

was assessed using a lipophilic cationic compound, JC-1, which possesses the ability to 

differentially label mitochondria with high and low membrane potential (Gravance et al., 2001). 

Mice exposed to 500 and 1,500 mg/kg-day were found to have a significant decrease in high 

MMP sperm. In addition, the MMP was negatively and significantly associated with the 

generation of sperm hydrogen peroxide. The NOAEL in this study was 100 mg/kg-day and the 

LOAEL 500 mg/kg-day for decrease in ALH and MMP and increased generation of hydrogen 

peroxide in the sperm of adult mice. 

4.4. OTHER ENDPOINT-SPECIFIC STUDIES

4.4.1. Receptor Site Interactions 

Some studies of halogenated aromatic compounds show that they exert an influence on 

cells by interacting with membrane receptor sites and activating cellular transcription factors. 

Transcription factor complexes then initiate DNA synthesis, allowing the cell to respond to the 

extracellular signal by producing a series of mRNAs that in turn produce a variety of proteins. 

This process is termed signal transduction. The structural similarities between PBDEs and 

polychlorinated biphenyls (PCBs) suggest that PBDEs might activate the aryl hydrocarbon 

receptor (AhR) and the estrogen receptor (ER). Based on the data from the well-studied PCBs 

and dioxins, the activation of these receptors is associated with immunosupression, reproductive 

effects, and carcinogenesis (Klaassen, 1996; Bock, 1994), all endpoints of interest for PBDEs. 

Studies of receptor interactions of BDE-209 with the AhR, ER, pregnane X receptor (PXR), and 

steroid X receptor (SXR) are summarized in the sections that follow. As a group, these studies 

indicate that the ability of BDE-209 to activate signal transduction responses via the receptors 

studied is minimal or negligible. 

4.4.1.1. Aryl Hydrocarbon Receptor Studies

Although in vivo studies investigating mechanisms of liver toxicity in animals have not 

been identified, several in vitro systems have evaluated the ability of decaBDE to interact with 

the AhR by using liver tissues or cell lines. Brown et al. (2004) investigated the potential of 

decaBDE to bind to and activate the AhR (using a gel retardation assay) and the ability of 

decaBDE to induce the expression of dioxin-responsive genes (using the reporter gene based 
36 

Chemical-Activated Luciferase eXpression [CALUX] assay). The decaBDE used in this study 

was 85.5% purity, and the identities of the other components present in the preparation were not 

reported. Incubation of decaBDE with hepatic cytosol prepared from guinea pigs and 

subsequent incubation with [32P]-labeled dioxin-responsive element (DRE)-containing 

oligonucleotide, followed by resolution of the ligand:AhR:[32P]DRE complex by gel retardation 

analysis, indicated that decaBDE (20 μM) stimulated AhR-DNA binding but to a much lower 

level (26%) than 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). DecaBDE demonstrated some 

activity in the CALUX assay. Based on the results from gel retardation and reporter gene assays, 

decaBDE may induce AhR-dependent DNA binding and gene expression but with very low 

potency if the activity observed is solely attributable to decaBDE. However, the low but 

measurable activity may have been caused by contaminants since the test material was impure. 

The possible dioxin-like effects of decaBDE or induction of genes that encode 

metabolizing enzymes have also been investigated by Peters et al. (2004). AhR-mediated 

induction of CYP-1A1 and -1B1 were studied in human breast carcinoma MCF7 cells by using 

EROD activity as a marker for CYP-1A1 and -1B1 activity. DecaBDE (>98% purity) did not 

induce EROD activity and, therefore, was not found to be an AhR agonist in these cells 

incubated for 72 hours with decaBDE at concentrations that were not cytotoxic (up to 10 μM). 

Additionally, exposure of the cells to decaBDE did not induce mRNA levels of CYP-1A1 or 

-1B1, indicating no effect of decaBDE on AhR gene expression. 

Villeneuve et al. (2002) evaluated the dioxin-like potency of decaBDE (99% purity) at 

environmentally relevant concentrations (up to 500 ng/mL) by using in vitro luciferase assays 

with H4IIE-luc recombinant rat hepatoma cells. DecaBDE did not induce AhR-dependent gene 

expression. The authors calculated that most PBDEs, including decaBDE, were at least 

10,000 times less potent than TCDD for inducing AhR-mediated responses in vitro. 

The affinity of decaBDE for rat hepatic AhR was evaluated through competitive binding 

assays (Chen et al., 2001). Results indicated that decaBDE has no AhR-binding activity. The 

ability of decaBDE to induce hepatic CYP-450 enzyme activity by means of EROD assays in 

human, rat, chick, and rainbow trout cells was also determined in this study. Incubation of 

decaBDE (of unspecified purity) with cultures of primary rat hepatocytes, primary chick embryo 

hepatocytes, two human cell lines (hepatoma HepG2 and intestinal Caco-2), and one rat cell line 

(hepatoma H4IIE) showed that decaBDE did not induce EROD activity in any cell line tested. 

Moreover, decaBDE was almost completely inactive in a gel retardation assay, suggesting that 

decaBDE did not activate the AhR. 

Pullen et al. (2003) investigated the effect of decaBDE on CYP-450 activity in mouse 

hepatocytes. Incubation of decaBDE (of unspecified purity) with hepatocytes isolated from 

C57BL/6 mice for 24 hours did not induce CYP-1A1 (measured as EROD activity), indicating 

that decaBDE does not act as a specific ligand for the AhR and, thus, exerts no effect via the 
37 

AhR pathway as do many of the polycyclic aromatic hydrocarbons. Together, these studies 

suggest that decaBDE has very limited potential to activate the AhR signal transduction 

pathway, which is an important step in the mode of action through which many persistent 

aromatic hydrocarbons impact cell regulation and cell maintenance (Klaassen, 1996). 

4.4.1.2. Estrogen Receptor Studies

ER-mediated (estrogenic) effects of decaBDE at environmentally relevant concentrations 

were investigated by Villeneuve et al. (2002) in an in vitro luciferase assay system. Incubation 

of decaBDE (99% purity) at concentrations up to 500 ng/mL with MVLN recombinant human 

breast carcinoma cells for 72 hours showed that decaBDE did not exhibit estrogenic effects. 

Most PBDEs, including decaBDE, were at least 50,000 times less potent than 17β-estradiol (E2) 

for inducing ER-mediated gene expression. This study also examined the ability of decaBDE to 

displace E2 or testosterone from serum proteins in a competitive hormone displacement assay. 

Incubation of decaBDE at concentrations up to 2.5 μg/mL in the presence of 3H-estradiol or 3Htestosterone and hormone-stripped carp serum for 15 hours indicated that decaBDE did not 

cause any significant displacement of these hormones in vitro. These results suggest that 

decaBDE and other PBDEs are not likely to elicit E2-mediated gene expression at the exposure 

levels currently observed in fish and wildlife. 

4.4.1.3. Other Receptors

 Pacyniak et al. (2007) conducted a study of the PXR and its human counterpart SXR by 

using HepG2 cells transvested with the appropriate complementary DNA (cDNA), the receptor 

response elements, and a luciferase reporter vector. The cultured cells were exposed to 0, 0.1, 1, 

10, or 100 μM concentrations of BDE-209. With the PXR there was a very slight dose-related 

increase in relative luciferase activity that achieved significance for only the highest 

concentration. With the SXR, there was no impact of luciferase for any concentration other than 

the 100 mM preparation. Accordingly, BDE-209 appears to be a weak inducer for PXR and 

SXR. The authors also compared the response in PXR knock-out mice (10–12 weeks old) with 

the wild-type mice and found that CYP-3A11 was induced to a greater extent in the wild-type 

animals, indicating that BDE-209 seems to be a ligand for the PXR. However, even in the 

knock-out mice, some CYP-3A11 protein was identified, suggesting that the PXR was not the 

only receptor affected by BDE-209. The authors suggested that the persisting CYP-3A11 protein 

could be related to activation of the constitutive androstane receptor (CAR). 

4.4.2. Immunological Studies 

No in vivo studies that specifically evaluated the immunosuppressive effects of decaBDE 

have been identified. However, in chronic dietary studies, decaBDE has been found to induce 
38 

histological changes in lymphoid organs, including the spleen (fibrosis) and mandibular lymph 

nodes (hyperplasia) in male rats at a dose of 2,240 mg/kg-day (NTP, 1986). Although these 

histopathological changes may play an important role in flagging decaBDE for immunotoxicity, 

they are at the high end of the spectrum of doses evaluated, and the lack of studies to investigate 

the functional effects on immune cells from exposure to decaBDE precludes complete 

assessment of its immunotoxic potential. 

Only one study investigated the immunotoxic effects of decaBDE on intact lymphocytes. 

Pullen et al. (2003) isolated splenocytes from C57BL/6 mice and incubated the cells in culture 

with decaBDE (purity not specified). DecaBDE was not cytotoxic to these cells at 3 μmol/L. 

Treatment of cells for 48 hours with 3 μmol/L decaBDE did not cause attenuation of interleukin2-receptor α chain (CD25) expression (evaluated by immunohistochemistry and confocal 

microscopy or laser scanning cytometry). The lack of attenuation of CD25 expression suggests 

that decaBDE is not likely to alter a surface marker (which is essential for lymphocyte 

proliferation during immune response) and may not affect the immune system in an 

immunosuppressive manner. Pullen et al. (2003) also evaluated the potential of decaBDE to 

alter cytokine production. Results showed that decaBDE did not have any effect on the 

production of the cytokines IFN-γ, IL-2, IL-6, and IL-10, indicating that decaBDE does not 

interfere with the cells’ ability to synthesize protein.

4.4.3. Genotoxicity 

In vitro studies were conducted to evaluate the mutagenic potential of decaBDE (NTP, 

1986). DecaBDE was tested in Salmonella typhimurium TA98, TA100, TA1535, or TA1537 

strains up to 10,000 μg/plate in the presence or absence of exogenous metabolic system 

(S9 fractions) prepared from the livers of Aroclor 1254-induced male Sprague-Dawley rats or 

male Syrian hamsters. Results indicated that decaBDE was not mutagenic in the salmonella 

assay systems. 

The mutagenicity of decaBDE at doses of up to 10 μg/mL was evaluated in 

L5178Y/TK+/– mouse lymphoma cell assay system in the absence or presence of S9 prepared 

from the livers of Aroclor 1254-induced male F344/N rats. DecaBDE did not induce mutagenic 

potential in this assay system. DecaBDE at doses up to 500 μg/mL did not induce sisterchromatid exchanges or chromosomal aberrations in Chinese hamster ovary cells in the absence 

or presence of S9 prepared from the livers of Aroclor 1254-induced male Sprague-Dawley rats 

(NTP, 1986). 

Results from these studies provide evidence that parent decaBDE in the presence or 

absence of an exogenous liver metabolic system does not react directly or indirectly with DNA 

to cause gene mutations, DNA damage, or chromosomal effects. 
39 

4.5. SYNTHESIS OF MAJOR NONCANCER EFFECTS 

4.5.1. Oral 

Several studies have been conducted to evaluate the effects of decaBDE and to elucidate 

its mode of action. Long-term dietary studies conducted by NTP (1986) have identified 

nonneoplastic liver and thyroid histopathology, such as liver thrombosis and degeneration in 

male rats, and liver granulomas, centrilobular hypertrophy, and thyroid follicular cell hyperplasia 

in male mice. 

Neurobehavioral developmental effects on habituation were seen in adult male rats 

(Viberg et al., 2007) and adult male mice (Viberg et al., 2003a) given a single dose of BDE-209 

during the postnatal period. Male and female mice pups given BDE-209 during the neonatal 

period showed early effects on palpebral reflex, forelimb grip, and struggling behavior. 

Locomotor activity was also affected in young adult male mice (Rice et al., 2007). 

Behavioral disturbances observed in the mature rats and mice exposed to decaBDE as 

neonates (Rice et al., 2007; Viberg et al., 2007, 2003a) raise concern about possible 

developmental neurotoxicity in children. In the study by Viberg et al. (2003a), neonatal male

mice were given a single dose of decaBDE (up to 20.1 mg/kg) in a fat emulsion on PNDs 3, 10, 

or 19 and spontaneous motor behavior tests (measuring locomotion, rearing, and total activity) 

were conducted in the mice at 2, 4, or 6 months of age. In addition, an habituation ratio was also 

determined for each behavior variable at the tested ages. Exposure of 3-day-old mice to 

20.1 mg/kg decaBDE resulted in significant dose-related changes in all three spontaneous 

behavior variables at 2, 4, and 6 months of age. However, adult mice exposed neonatally up to 

20.1 mg on either PND 10 or 19 did not show any significant differences in any of the variables 

after 2, 4, or 6 months compared with controls. In the study in rats (Viberg et al., 2007), 

significant dose-related disruption in habituation (changes in locomotion, rearing, and total 

activity) was observed in 2-month-old rats, following exposure to BDE-209 at 6.7 and 

20.1 mg/kg on PND 3. 

Rice et al. (2007) used a similar approach in evaluating locomotor activity in groups of 

9–13 male and female C57BL6/J mice exposed to 6 or 20 mg/kg-day BDE-209 from PNDs 2–15 

and observed after placement in a novel environment on PND 70 during a 2-hour period. The 

exposed males showed greater activity than the controls throughout the observation period. 

Early in the period, the exposed male mice were hyperactive compared with controls; the 

difference between the exposed animals and controls declined with time but locomotor activity 

remained greater than that for the controls at the end of the 2-hour observation period. In the 

case of the females, the activity of all groups was similar for the first 45 minutes of exposure but 

the females became less active than the controls thereafter. The linear slope for the decline in 

activity among the exposed males was significantly different from that of controls; the 20 mg/kg 

group was affected to a greater extent than the 6 mg/kg group. The females on PND 70 and both 
40 

sexes when examined at 1 year after birth did not display similar dose-related differences in 

locomotor activity. 

Rice et al. (2007) also examined a number of developmental and behavioral parameters 

during the dosing period and for five days after dosing ceased. BDE-209 exposure did not 

impact the developmental endpoints evaluated (pinnae detachment, incisor eruption, eye 

opening, vaginal opening, testes descent). The behavioral parameters studied were selected as 

measures of home-cage, motor, and sensorimotor behaviors. There was no apparent impact on 

most measures of behavior; however, palpebral reflex, forelimb grip, and struggling during 

handling appeared to be impacted by BDE-209 exposure. There was a significantly poorer 

performance of the 20 mg/kg-day group in the palpebral reflex test on PND 14 and in the grip 

test (males only) on PND 16. On PND 20, the struggling behavior of the group exposed to 6 

mg/kg was significantly increased compared with the controls and 20 mg/kg-day group. 

The most striking dose-related trend in the Rice et al. (2007) study was the locomotive 

activity profile of males at PND 70. The direction of this trend differed from that observed by 

Viberg et al. (2007, 2003a). In the Rice et al. (2007) study, activity in the exposed and control 

mice decreased across the observation period, while in the Viberg et al. (2007, 2003a) studies 

activity increased across the observation period for the exposed animals compared with the 

controls. However, the exposure and testing conditions varied between the two studies and, thus, 

the two sets of results are not directly comparable. 

4.5.2. Inhalation 

No data are available on the toxicity of decaBDE by the inhalation route of exposure. 

4.5.3. Mode-of-Action Information 

Impaired development of the cholinergic system during the postnatal ―brain growth 

spurt‖ period has been offered as a plausible hypothesis for the observed neurodevelopmental 

impact of the PBDEs on adult responses to a novel environment (Viberg et al., 2007, 2003b). 

The authors described a critical window of vulnerability in development of the cholinergic 

system during postnatal development that in mice occurs in the first few weeks after birth with a 

peak at PND 10 (Viberg et al., 2003b). They hypothesize that any agent that caused a deficit in 

cholinergic receptors during this period could cause a hypoactive response to cholinergic 

stimulants, including exposure to a novel environment in adulthood. 

Viberg et al. (2007) tested this hypothesis in Sprague-Dawley rats. Two-month-old rats 

that had been exposed to vehicle, 6.7 mg/kg, or 20 mg/kg BDE-209 on PND 3 were given a 

subcutaneous injection of nicotine or saline solution. The vehicle control animals and animals in 

the 6.7 mg/kg dose group receiving the nicotine demonstrated the typical hyperactive response of 

mature rats when compared with the saline-injected rats during the 60–80 minute observation 
41 

period. Those given the 20.1 mg/kg dose were markedly hypoactive compared with the saline 

controls. These observations provide some support for the hypothesis that impaired prenatal 

development of the cholinergic system may play a role in the habituation deficits observed in 

adult rats and mice that were prenatally exposed to decaBDE during the critical window for 

system development. 

Other studies by the Eriksson/Viberg research team using PBDE compounds with four, 

five, and six bromines have shown effects on locomotion and habituation that are similar to 

those observed for the deca compound. However, in the study of BDE-99, when the timing of 

exposure was varied, the window of greatest vulnerability occurred on day 10 rather than on 

days 3 or 19 (Eriksson et al. 2002). Thus, the results for BDE-99 are different from those for 

decaBDE reported in Viberg et al. (2003a). However, the data from the radiolabel component of 

the study provide a rationale for the difference in the apparent window of vulnerability. Two 

contributing factors are observed. First, absorption from the gastrointestinal tract decreases as 

the neonatal mice age during their first few weeks of life. Thus, less of the decaBDE reaches the 

liver for distribution on days 10 and 19 than on day 3. Secondly, distribution to the brain is slow. 

The amount of radiolabel in the brain is higher (0.7%) when measured 7 days after dosing on 

PND 3 than when measured 24 hours after dosing (0.5%). The radioactivity measured 7 days 

after dosing was also higher than when measured 24 hours after dosing on PND 10 (0.4% at 

24 hours; 1.1% at 7 days). Less than 0.1% of the label reaches the brain when the compound is 

administered on day 19. While evidence exists that demonstrates BDE-209, as well as other 

PBDEs, interact at the neurological level, data are inadequate to determine the mode of action 

for BDE-209. 

DecaBDE caused thyroid gland follicular cell hyperplasia and thyroid tumors in male 

mice, effects that are indicative of thyroid toxicity (NTP, 1986). Based on these effects, 

decaBDE may share the general property of organohalogen compounds in which in vivo 

exposure in rodents results in reduction of serum total and free thyroid hormone (T4) levels 

(Legler and Brouwer, 2003). Thyroid hormone disruption has been hypothesized to arise from at 

least two different mechanisms, one of which is the induction of liver enzymes of different 

enzyme families, including CYP-1A1 and CYP-2B (McDonald, 2002). Induction of liver 

UDPGTs may increase the rate of T4 conjugation and excretion, which is believed to be a 

mechanism for TCDD-induced thyroid effects. An increase in the metabolism of T4 will result 

in enhanced excretion and thus a drop in its circulating levels. The other mechanism involves 

alteration of thyroid homeostasis through hormone mimicry. Potential thyroid toxicants may be 

metabolized by liver enzymes to metabolites that compete with the thyroid transport protein, 

transthyretin, a key protein involved in the transport of T4 through the blood and into the 

developing tissues in rodents. 
42 

Zhou et al. (2001) evaluated the interference of decaBDE with thyroid hormone 

homeostasis in weanling rats exposed to decaBDE (>98% purity) up to 100 mg/kg-day for 

4 consecutive days. Results indicated that decaBDE did not affect hepatic enzyme activities or 

serum T4, T3, TSH, and hepatic UDPGT activity at doses up to 100 mg/kg-day. Rice et al. 

(2007) also evaluated T4 levels in the blood of C57BL6/J mice (1 male, 1 female/litter) on 

PND 21 following exposure to 0.6 or 20 mg/kg-day BDE during PNDs 2–15. In this instance, 

there was a dose-related reduction in the T4 levels for males but not females. Despite the 

possibility of thyroid hormone involvement in the neurodevelopmental impact of BDE-209 on 

the habituation response in male mice exposed to a single dose on PND 3, there are no mode-ofaction data that link thyroid hormones to the neurobehavioral observations reported by Viberg et 

al. (2003a). 

In the chronic dietary studies conducted by NTP (1986), decaBDE has been found to 

induce histologic changes in lymphoid organs, including the spleen (fibrosis) and mandibular 

lymph nodes (hyperplasia), in rats. These histopathologic changes could flag decaBDE as a 

potential immunotoxicant. No in vivo functional immunotoxicity studies were identified. 

Results from an in vitro study investigating the immunotoxic effects of decaBDE indicated that 

decaBDE did not show any attenuation of CD25 expression or changes in cytokine production 

(Pullen et al., 2003). As such, decaBDE is unlikely to affect the immune system in an 

immunosuppressive manner. 

Several in vivo and in vitro studies have evaluated decaBDE for its potential to activate 

the AhR signal transduction pathway and to induce gene expression, resulting in increased phase 

I and phase II metabolism. Taken together, the in vivo and in vitro studies suggest that decaBDE 

has very low or no potential to bind the AhR. The inability of decaBDE to elicit CYP-450 

induction or AhR binding and gene expression, indicating lack of potential to activate the AhR 

signal transduction pathway, suggests that decaBDE may cause liver toxicity through a different 

mechanism and that the observed liver effects are not an adaptive effect related to enzyme 

induction. Results from the Morck et al. (2003) study indicated high concentration of tissuebound radioactivity in the liver, and the radioactivity was assumed to be bound to 

macromolecules. The authors asserted that binding occurred via reactive metabolites. 

Formation of such metabolites may be responsible for the liver toxicity observed on exposure to 

decaBDE. However, the enzymes responsible for decaBDE metabolism and reactive 

intermediates have not been identified. The existing data show tissue binding and are therefore 

not adequate to elucidate a potential role in the mode of action. 

A number of studies have also indicated that brominated flame retardants may interfere 

with estrogen pathways by binding to and activating ERs (Legler and Brouwer, 2003). No in 

vivo studies were identified that evaluated the specific estrogenic effects of decaBDE. 

Furthermore, specific effects attributable to estrogenic dysregulation were not identified in the 
43 

available animal studies, although some developmental toxicity endpoints were observed. 

Mechanistic studies do not support effects of decaBDE on ER pathways. 

4.6. EVALUATION OF CARCINOGENICITY 

4.6.1. Summary of Overall Weight of Evidence 

Under the Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005a), the descriptor 

―suggestive evidence of carcinogenic potential‖ is appropriate for decaBDE. This descriptor of 

the database is appropriate when the weight of evidence is suggestive of carcinogenicity and a 

concern for potential carcinogenic effects in humans is raised, but the data are judged not 

sufficient for a stronger conclusion. This descriptor covers a spectrum of evidence associated 

with varying levels of concern for carcinogenicity, ranging from a positive cancer result in the 

only study on an agent to a single positive cancer result in an extensive database that includes 

negative studies in other species. 

The weight of evidence of human carcinogenicity of decaBDE is based on (1) no studies 

of cancer in humans exposed to decaBDE; (2) a statistically significant increase in incidence of 

neoplastic nodules in the liver of low- and high-dose male rats and high-dose female rats; (3) a 

significantly increased incidence of hepatocellular adenoma or carcinoma (combined) in male 

mice at the low dose and marginally increased incidence at high dose; (4) a nonsignificantly 

increased incidence of hepatocellular adenoma or carcinoma (combined) in female mice; (5) a 

slightly greater (but statistically not significant) incidence of thyroid gland adenomas or 

carcinomas (combined) in dosed male and female mice; (6) a significantly increased incidence 

in male mice, at both doses, of follicular cell hyperplasia, considered by many as a precursor to 

thyroid tumors; and (7) an apparent absence of genotoxic potential. 

Based on the results of the chronic and genotoxicity studies, NTP (1986) concluded that 

there was ―some evidence of carcinogenicity‖ for male and female rats as shown by increased 

incidences of neoplastic nodules of the liver in low-dose males and high-dose groups of each 

sex. There was ―equivocal evidence of carcinogenicity‖ for male mice as shown by increased 

incidences of hepatocellular adenomas or carcinomas (combined) in only the low-dose group 

and slight increase of thyroid gland follicular cell adenomas or carcinomas (combined) in both 

dosed groups. There was ―no evidence of carcinogenicity‖ for female mice. Several 

nonneoplastic lesions were observed at increased incidences, the most notable being thyroid 

gland follicular cell hyperplasia in male mice. The weight of experimental evidence is on the 

strong end of the spectrum for the descriptor ―suggestive evidence of carcinogenic potential,‖

since there is suggestive evidence that decaBDE is carcinogenic for more than one species, sex, 

and site. Based on the weight of evidence, a dose-response assessment of the carcinogenicity of 

decaBDE is deemed appropriate 
44 

4.6.2. Synthesis of Human, Animal, and Other Supporting Evidence 

No information is available on the carcinogenicity of decaBDE in humans. Chronic 

dietary studies of decaBDE have been conducted in rats and mice (NTP, 1986), and 

carcinogenicity data are presented in Tables 4-4 and 4-5. DecaBDE caused substantial doserelated increases in neoplastic nodules in rats with statistical significance at the high dose in both 

sexes (Table 4-4). There were no statistically significant changes in hepatocellular carcinoma in 

either sex. Although there was a positive trend in mononuclear cell leukemia in male rats, the 

increase was marginal and not considered to be biologically significant due to the unusually high 

incidence in controls. 

In mice, insignificant increases in hepatocellular adenoma occurred in males at low 

(3,200 mg/kg-day) and high (6,650 mg/kg-day) doses compared with controls. The incidence of 

hepatocellular carcinoma was not significantly increased in male mice at either dose. In these 

male mice, however, significantly increased hepatocellular adenomas or carcinomas (combined) 

were observed in the low-dose group but only marginally increased in the high-dose group. An 

increased incidence of hepatocellular adenoma and carcinoma was also observed in the female 

mice; however, these changes were not statistically significant in either treated dose group. 

There was also a slight (but not statistically significant) increase in the incidence of thyroid 

tumors in mice of both sexes, but this was not observed in rats. The biological relevance of this 

finding in mice is supported by the accompanying increased incidence of follicular cell 

hyperplasia in male mice; the increase in hyperplasia in females was not statistically significant. 

The increased incidence of neoplastic nodules of the liver observed in male and female 

rats constitutes some evidence of carcinogenicity in treated rats, and this observation is 

supported by the significantly increased incidence of hepatocellular adenoma and carcinoma 

(combined) in low-dose male mice and nonsignificantly increased incidence in female mice. 

Although the study results from each individual species/sex combination were judged to be 

either ―some‖ or ―equivocal‖ evidence of carcinogenicity, a common target organ (liver) in two 

species and both sexes indicates a potential for decaBDE to cause cancer in treated animals. In 

addition to the liver cancer, slight increases in thyroid follicular cell tumors in mice were 

accompanied by hyperplasia. Based on the increasing agreement that hyperplasia is a stage of 

the thyroid follicular cell carcinogenic process (NAS, 2000; Hard, 1998; U.S. EPA, 1998b; Hill 

et al., 1989), decaBDE would be considered as eliciting a carcinogenic effect in a second target 

organ (i.e., the thyroid) in mice. 

4.6.3. Mode-of-Action Information 

Genotoxicity studies have found that decaBDE does not appear to be mutagenic since it 

did not induce gene mutations in S. typhimurium strains or in mouse L5178Y lymphoma cells. 

Also, decaBDE did not induce sister-chromatid exchanges or chromosomal aberrations in 
45 

Chinese hamster ovary cells in the presence or absence of metabolic activation systems (NTP, 

1986). 

There are no other studies of the carcinogenic mode of action of decaBDE. The mode of 

action is unknown. 
46 

Table 4-4. Incidence of liver neoplastic nodules and carcinomas in rats fed decaBDE for 2 years 

Males Females

Dose groups ppm 0 25,000 50,000 0 25,000 50,000

mg/kg-day 0 1,120 2,240 0 1,200 2,550

Number examined 50 50 50 50 50 50

Liver neoplastic nodules

Overall rates 1/50 (2%) 7/50 (14%)a15/49 (31%)a1/50 (2%) 3/49 (6%) 9/50 (18%)a

Adjusted rates 2.9% 27.1% 52.7% 2.5% 9.1% 24.4%

Terminal rates 1/35 (3%) 6/24 (25%) 13/26 (50%) 1/40 (3%) 3/33 (9%) 7/34 (21%)

Week of first observation 104 89 87 104 104 87

Historical incidence 3.5% 2.6%

Hepatocellular carcinoma

Overall rates 1/50 (2%) 1/50 (2%) 1/49 (2%) 0/50 (0%) 2/49 (4.1%) 0/50 (0%)

Liver neoplastic nodule or hepatocellular carcinoma

Overall rates 2/50 (4%) 8/50 (16%)a15/49 (31%)a1/50 (2%) 5/49 (10%) 9/50 (18%)a

Adjusted rates 5.2% 31.1% 52.7% 2.5% 15.2% 24.4%

Terminal rates 1/35 (3%) 7/24 (29%) 13/26 (50%) 1/40 (3%) 5/33 (15%) 7/34 (21%)

Week of first observation 97 89 87 104 104 87

a

Statistically significantly different from controls (p < 0.05), based on life table tests and incidental tumor tests. 

Source: NTP (1986).
47 

Table 4-5. Incidence of nonneoplastic or neoplastic lesions in the liver and thyroid gland of mice fed decaBDE 

for 2 years 

Males Females

Dose groups ppm 0 25,000 50,000 0 25,000 50,000

mg/kg-day 0 3,200 6,650 0 3,760 7,780

Number examined 50 50 50 50 50 50

Hepatocellular adenoma

Overall rates 4/50 (8%) 12/50 (24%) 12/50 (24%) 5/50 (10%) 10/50 (20%) 7/50 (14%)

Adjusted rates 19.0% 46.2% 39.0% 16.8% 31.2% 21.9%

Terminal rates 3/19 (16%) 11/25 (44%) 7/24 (29%) 4/27 (15%) 9/31 (29%) 7/32 (22%)

Week of first observation 81 100 60 83 102 103

Hepatocellular carcinoma

Overall rates 5/50 (10%) 14/50 (28%) 8/50 (16%) 3/50 (6%) 4/50 (8%) 7/50 (14%)

Adjusted rates 20.7% 42.9% 26.8% 10.7% 12.1% 20.8%

Terminal rates 1/19 (5%) 8/25 (32%) 4/24 (17%) 2/27 (7%) 3/31 (10%) 6/32 (19%)

Week of first observation 81 72 76 101 93 96

Hepatocellular adenoma or carcinoma

Overall rates 8/50 (16%) 22/50 (44%)a18/50 (36%) 8/50 (16%) 13/50 (26%) 13/50 (26%)

Adjusted rates 33.9% 67.7% 56.5% 26.7% 39.1% 39.1%

Terminal rates 4/19 (21%) 15/25 (60%) 11/24 (46%) 6/27 (22%) 11/31 (35%) 12/32 (38%)

Week of first observation 81 72 60 83 93 96

Thyroid gland

Hyperplasia, follicular cell 2/50 (4%) 10/50 (20%)a19/50 (38%)a4/50 (8%) 9/50 (18%) 7/49 (14%)

Follicular cell adenoma

Overall rates 0/50 (0%) 3/50 (6%) 3/50 (6%) 1/50 (2%) 3/50 (6%) 2/49 (4%)

Adjusted rates 0% 10.8% 12.5% 2.9% 7.8% 6.3%

Terminal rates 0/19 (0%) 2/25 (8%) 3/24 (13%) 0/27 (0%) 1/31 (3%) 2/32 (6%)

Week of first observation 90 103 95 80 103

Follicular cell adenoma or carcinoma (combined)

Overall rates 0/50 4/50 (8%) 3/50 (6%) 1/50 (2%) 3/50 (6%) 3/49 (6%)

Adjusted rates 0% 14.7% 12.5% 2.9% 7.8% 9.4%

Terminal rates 0 3/25 (12%) 3/24 (13%) 0/27 (0%) 1/31 (3%) 3/32 (9%)

Week of first observation 90 103 95 80 103

a

Statistically significantly different from controls (p < 0.05), based on life table tests and incidental tumor tests. 

Source: NTP (1986). 
48 

4.7. SUSCEPTIBLE POPULATIONS AND LIFE STAGES 

4.7.1. Possible Childhood Susceptibility 

As discussed in section 4.3.1, a gavage study (Hardy et al., 2002) in which rats were 

exposed in the diet to decaBDE (97.34% purity) during gestation days 0–19 reported no effects 

on number of dams with viable fetuses, mean number of corpora lutea, number of implantation 

sites, percent preimplantation loss per dam, number of viable fetuses, gravid uterine weights, 

fetal body weights, crown-rump ratio, and fetal sex ratio. No effects were reported during 

external, skeletal, or visceral examination of rat fetuses. The NOAEL in this study was 

1,000 mg/kg-day, the highest dose tested. In a study in male mice (Tseng et al., 2006) exposed 

to BDE-209 from PNDs 21–70 (see section 4.3.2), effects were seen on sperm function, DNA 

content, and histopathology of the testes at 500 mg/kg-day but not at 100 mg/kg-day. 

In a study in rats (Viberg et al., 2007), exposure of the animals to the lowest dose tested 

of 6.7 mg/kg-day BDE-209 on PND 3 resulted in significant changes in spontaneous motor 

behavior (locomotion, rearing, and total activity) in 2-month-old rats. In the study of Rice et al. 

(2007), effects on the palpebral reflex, struggling behavior and locomotor activity were seen in 

mice given the lowest dose of 6 mg/kg-day BDE-209 on PNDs 2–15. 

Neurobehavioral alterations were observed in mature mice when male mice were 

exposed to 20.1 mg/kg decaBDE as neonates on PND 3 but not on PNDs 10 and 19 (Viberg et 

al., 2003a). A significant increase in the amount of radioactivity in the brain on day 7 after 

exposure was noted when the neonates were exposed to 14C-decaBDE on PNDs 3 and 10 but not 

on PND 19 (Viberg et al., 2003a). The increase in the radioactivity in the brain, coupled with 

the behavioral disturbances on exposure to decaBDE on PND 3, suggests that differences may 

exist in the absorption and distribution of decaBDE among the 3-, 10-, and 19-day-old neonates. 

In addition, differences exist in the timing of the brain growth spurt in rodents (first few weeks 

after birth) and humans (starts in the sixth month of gestation and continues through the first 2 

years of life after birth). The significance of this difference with regard to the potential for 

effects on children from exposure to BDE-209 is not clear. Moreover, whether other targets of 

decaBDE (thyroid and liver) are more sensitive in children is unknown since the enzymes 

responsible for decaBDE metabolism have not been identified and the mechanisms for agedependent kinetic differences are not completely clear. Although no studies were identified that 

investigated placental transfer, decaBDE has been found in human breast milk, suggesting that 

newborns and infants have a potential source of exposure via this route. 

4.7.2. Possible Gender Differences 

All absorption studies following oral administration of decaBDE were conducted in male 

rats, precluding a comparison of kinetics in males versus females. There were no clear genderdependent differences in decaBDE toxicity in short-term and subchronic studies conducted in 
49 

both sexes of rats and mice (NTP, 1986). However, long-term exposure studies to decaBDE 

indicated that male rats may be more sensitive than females. Male rats exhibited nonneoplastic 

lesions, including liver thrombosis and degeneration, splenic fibrosis, and lymphoid hyperplasia, 

and male mice showed increased incidences of liver granulomas, hepatocellular hypertrophy, 

and thyroid follicular cell hyperplasia, while female rats and mice appeared to be refractory to 

these systemic effects of decaBDE at the tested doses (NTP, 1986). One exception was that 

female mice had a higher incidence of stomach ulcers than their male counterparts. Although a 

significantly increased incidence of liver neoplastic nodules was observed in both sexes of rats 

(NTP, 1986), hepatocellular carcinomas or adenomas were not significantly increased in male 

mice only. No gender-specific effects on reproductive organs were identified. 

The study of Rice et al. (2007) investigated several endpoints in male and female mice. 

In PND 21 offspring of mice treated with decaBDE on PNDs 2–15, a dose-related reduction in 

serum T4 was observed in males but not females. Development of forelimb grip strength was 

delayed at PND 16 in exposed males in the high-dose group but not in females. Struggling 

behavior was more apparent in males than in females, and effects on locomotor activity were 

observed on PND 70 in male mice but not in female mice. 

Overall, it appears that males may be more susceptible to some effects of decaBDE 

compared to females, although this is not true for all endpoints. Underlying mechanisms for the 

apparent differences in susceptibility have not been identified. 
50 

5. DOSE-RESPONSE ASSESSMENTS 

5.1. ORAL REFERENCE DOSE (RfD) 

5.1.1. Choice of Principal Study and Critical Effect—with Rationale and Justification 

Epidemiological studies or case reports are not available for decaBDE. 

Available animal studies of repeated oral exposure to decaBDE include a 4-day study in 

rats (Zhou et al., 2001), 14-day studies in rats and mice (NTP, 1986), 13-week studies in rats and 

mice (NTP, 1986), and 2-year studies in rats and mice (NTP, 1986). In addition, decaBDE was 

also tested for its toxicity in reproductive and developmental studies (Rice et al., 2007; Viberg et 

al., 2007, 2003a; Tseng et al., 2006; Hardy et al., 2002). The results from these studies are 

summarized in Tables 4-1, 4-2, and 4-3. Among the available studies, several potential principal 

studies for deriving an RfD were identified: the 2-year chronic studies in rats and mice (NTP, 

1986) and neurodevelopmental studies in rats and mice (Rice et al., 2007; Viberg et al., 2007, 

2003a). 

NTP (1986) reported a study of the chronic oral toxicity and carcinogenicity of decaBDE 

in rats. In the liver, an increase in the incidence of thrombosis was observed in high-dose male 

rats (2,240 mg/kg-day). A dose-dependent but statistically not significant increase in 

degeneration of the liver was also observed in treated male rats at incidences of 13/50, 19/50, 

and 22/49 in the control, low-dose, and high-dose groups, respectively. In the spleen, increased 

incidence of fibrosis was seen in males at the low dose (8/50) and high dose (13/49) compared to 

5/49 in controls; the effect was statistically significant only in the high-dose group. In the 

mandibular lymph node, lymphoid hyperplasia increased in males in a dose-dependent manner, 

but the incidence reached statistical significance only at the high dose. Based on these results, 

the NOAEL for systemic toxicity was 1,120 mg/kg-day, and the LOAEL was 2,240 mg/kg-day in 

male rats based on increased incidence of thrombosis and degeneration in the liver, splenic 

fibrosis, and lymphoid hyperplasia of the mandibular lymph nodes. Female rats appeared to be 

refractory to the systemic toxicity of decaBDE at the doses used in this study. Therefore, the 

NOAEL for systemic toxicity in females was 2,550 mg/kg-day, with no LOAEL established. 

The observed systemic toxicity of decaBDE in the 2-year study in rats is supported by 

observed liver effects at higher doses in a 2-year study in mice (NTP, 1986). Significant 

increases in the incidence of centrilobular hypertrophy were also observed in the liver of male 

mice at low and high doses (34/50, and 32/50, respectively) in comparison to controls (0/50). In 

the thyroid gland, a dose-dependent and statistically significant increase (at both dose levels) in 

the incidence of follicular cell hyperplasia was observed in male mice (control, 2/50; low dose, 

10/50; high dose, 19/50). In the females, this incidence increased in the low- and high-dose 

groups compared with the control group, but the increase was not dose dependent or statistically 
51 

significant at any dose level. High-dose female mice exhibited a significant increase in the 

incidence of stomach ulcers. Based on these results, no NOAEL for males was established. The 

LOAEL, based on increased incidence of centrilobular hypertrophy and a statistically significant 

and dose-dependent increase in thyroid gland follicular cell hyperplasia in male mice, was 

3,200 mg/kg-day or greater. Similar to the study in rats (NTP, 1986), female mice appeared to 

be refractory to the systemic toxicity of decaBDE at the doses used in this study. The study 

established a NOAEL of 3,760 mg/kg-day for portal-of-entry effects for females and a LOAEL of 

7,780 mg/kg-day based on a significant increase in the incidence of stomach ulcers. 

Viberg et al. (2003a) reported functional neurobehavioral effects of single-dose 

exposures to decaBDE. The neurotoxic effects of decaBDE on spontaneous motor behavior 

were investigated in adult NMRI male mice exposed to a single oral dose of decaBDE as 

neonates on PND 3, 10, or 19 (i.e., at different stages of neonatal mouse brain development). 

Pair-wise testing between adult mice exposed on PND 3 and control groups indicated significant 

dose-related changes in the habituation ratio calculated from three behavior variables 

(locomotion, rearing, and total activity) in mice exposed to 20.1 mg/kg and evaluated at 2, 4, and 

6 months of age; no statistically significant effect was seen at 2.22 mg/kg. Adult mice exposed 

neonatally up to 20.1 mg/kg on either PND 10 or 19 did not show any significant differences in 

any of the variables after 2, 4, or 6 months compared with controls. The authors indicated that 

the absence of changes in spontaneous activity in mice treated on PNDs 10 and 19 appears to 

suggest that there is a critical window for the induction of behavioral disturbances. The decrease 

observed in the habituation capability in the adult mice exposed neonatally to the high dose 

indicated that the neurotoxic effect of neonatal decaBDE exposure was persistent and also 

worsened with age. Based on these observations, the NOAEL in this study was 2.22 mg/kg and 

the LOAEL was 20.1 mg/kg. In the study in rats (Viberg et al., 2007), significant dose-related 

disruption in habituation (changes in locomotion, rearing, and total activity) was observed in 2-

month-old rats, following exposure to BDE-209 at 6.7 and 20.1 mg/kg on PND 3. A NOAEL 

was not identified in this study. 

Rice et al. (2007) examined the effects of BDE-209 (99.5% purity) on developmental 

milestones, sensorimotor behaviors, serum T4 levels and locomotor activity in male and female 

C57BL6/J mice administered doses of 0, 6, or 20 mg/kg-day from PNDs 2–15. An FOB suitable 

for neonatal mice was developed to examine a series of homecage, reflexive, and sensorimotor 

behaviors, measured on PND 14, 16, 18, or 20. Three of the FOB endpoints were affected by 

BDE-209 exposure: palpebral reflex, forelimb grip, and struggling behavior during handling. On 

PND 14, significantly fewer male and female pups in the 6 and 20 mg/kg-day groups performed 

the palpebral reflex compared with controls. On PNDs 14 and 16, fewer male pups in the 

20 mg/kg-day group performed an effective forelimb grip compared with same-sex controls. 

Male and female pups in the 6 mg/kg-day group struggled significantly more on PND 20, while 
52 

they were being handled for the FOB, compared with controls and the high-dose group. 

Locomotor activity in PND 70 males and females in the control and treated groups declined over 

the course of the 2-hour assessment. However, the rate of decline was significantly different 

(p = 0.04) in male mice exposed to 6 and 20 mg/kg-day compared with control animals. The 

effect was most pronounced in the high-dose males during the first 1.5 hours of the 2-hour 

activity session. A dose-related reduction in serum T4 in comparison with controls occurred in 

PND 21 males but not in females. The LOAEL in this study was 6 mg/kg-day, the lowest dose 

tested, for decrease in the percent of male and female pups performing the palpebral reflex on 

PND 14, for increased struggling behavior of male mice on PND 20, for decreased T4 levels in 

male mice, and for effects on locomotor activity of male mice on PND 70. 

Viberg et al. (2007) administered BDE-209 by gavage to 3-day-old Sprague-Dawley rats 

at 0, 6.7, or 20.1 mg/kg. A total of 20 rats were picked from three to five different litters in each 

treatment group. Motor activity, measured as locomotion (horizontal movement), rearing 

(vertical movement), and total activity (all types of vibration within the test cage [i.e., those 

caused by rat movements, shaking/tremors, and grooming]) was evaluated for a 60-minute 

period, divided into three 20-minute periods, in rats at the age of 2 months. In control rats, there 

was a distinct decrease in locomotion, rearing, and total activity, indicating habituation in 

response to the diminishing novelty of the test chamber over the 60-minute test period, at 

2 months of age. Two-month-old rats exposed to 20.1 mg/kg BDE-209 on PND 3 displayed 

significantly less activity for all three behavioral variables during the first 20-minute test period 

compared with controls, while during the third 20-minute period (40–60 minutes) they were 

significantly more active than the control animals. Rats receiving the low dose of BDE-209 

(6.7 mg/kg) showed significantly increased locomotion activity during the second 20-minute 

period, significantly decreased rearing activity during the first and second 20-minute periods, 

and significantly higher total activity during the first and second 20-minute periods compared 

with the control rats. The LOAEL in this study was 6.7 mg/kg for significant changes in 

spontaneous motor behavior (locomotion, rearing, and total activity) in 2-month-old rats given 

BDE-209 on PND 3. 

Of the three neurobehavioral studies, only Viberg et al. (2003a) identified a NOAEL. 

The NOAEL identified in Viberg et al. (2003a) was lower than the LOAELs identified in the 

neurobehavioral studies conducted by Viberg et al. (2007) and Rice et al. (2007). The Viberg et 

al. (2003a) study was therefore selected as the principal study for deriving the RfD. However, 

several considerations were weighed in making this decision. Concerns regarding the study 

design raise potential issues about full reliance on this study. The dosing regimen did not 

include gestation and lactation exposure (U.S. EPA, 1998a); only single doses were given. The 

study was conducted in male mice only. The protocol was unique and did not conform to health 

effects test guidelines for neurotoxicity screening battery or developmental neurotoxicity studies 
53 

(U.S. EPA, 1998a, c). While the study design appears to identify a developmental window of 

susceptibility, it is not adequate to determine the effect of longer dosing. However, the fact that 

the effects were observed after a single dose is a situation that increases concern regarding the 

impact of BDE-209 on neurological development. Translating the implications of these data to 

more traditional dosing regimens is problematic, particularly with regard to evaluating the 

implications of in utero and postnatal exposure. 

Another concern is that, based on the data provided in the published report, more than 

one pup per litter were used for the behavioral testing (10 mice were randomly selected from 

three to five different litters in each treatment group). Increasing the number of samples from 

each litter may bias the analyses towards false positives. The observed neurobehavioral effects 

may be attributable to differences in pups born to a single dam rather than related to treatment. 

Another concern regarding the study design was the limited number of neurobehavioral 

parameters that were assessed; the authors measured only indices related to motor activity 

(locomotion, rearing, and total activity). The absence of a full FOB that evaluates neurological 

and behavioral signs limits the ability to correlate the reported effects with other FOB 

parameters. Data from the FOB utilized in the Rice et al. (2007) study, also in mice, mitigate 

some concern related to its absence in the Viberg et al. (2003a) study. 

As indicated in the Guidelines for Neurotoxicity Risk Assessment (U.S. EPA, 1998a), it is 

assumed that an agent that produces detectable adverse neurotoxic effects in experimental 

animal studies will pose a potential hazard to humans. For BDE-209, in the absence of human 

evidence, data from experimental animal studies are used as the basis for the RfD. 

While study design limitations cloud the utility of this study, several additional 

considerations support the use of these data. Acute exposure to a highly lipophilic and long halflife chemical, such as BDE-209, will result in exposure that lasts much longer than just acutely. 

In addition, there are a wide variety of brain structures that have very limited critical windows 

during development. These short critical windows translate to susceptible periods of exposure 

that can be very short. 

The concept that exposure during critical periods of development can induce functional 

neurological effects later in development has been demonstrated with structurally related PBDE 

congeners, including tetra-, penta-, and hexaBDEs (Kuriyama et al., 2005; Viberg et al., 2005, 

2004a, b, 2003b, 2002; Ankarberg, 2003; Branchi et al., 2002; Eriksson et al., 2002, 2001). In 

addition, the study of Rice et al. (2007) strengthens the evidence that links the behavioral effects 

seen in mice to neonatal BDE-209 exposure. Therefore, the observed neurobehavioral effects in 

the Viberg et al. (2003a) study in mice and the Viberg et al. (2007) study in rats are biologically 

plausible, and exposure to BDE-209 may pose a potential hazard to humans (U.S. EPA, 1998a). 

Viberg et al. (2003b) have suggested that the animals are vulnerable only during the 

postnatal brain growth spurt that occurs in the first few weeks after birth in mice. In the case of 
54 

decaBDE, the identification of PND 3 as the most vulnerable window for exposure can be 

explained by the toxicokinetic data showing apparent absorption decreases during the first few 

weeks of life and slow distribution to the brain when the dosing occurs on PND 3 or 10. 

Although some radiolabel reaches the brain in the 24 hours after dosing, the amount increases 

over the 7-day period after dosing. After dosing on PND 19, less than 0.1% of the dose was 

found in the brain initially and after 7 days. These observations would explain the absence of 

effects in animals exposed later in the postnatal period as adults. 

Taken together, these considerations support the use of the Viberg et al. (2003a) study as 

a potential critical study for deriving the RfD for BDE-209. 

5.1.2. Methods of Analysis 

The published information presented by Viberg et al. (2007, 2003a) could not be used for 

benchmark dose (BMD) modeling; mean values for motor activity (locomotion, rearing, and 

total activity), habituation capability for 2-, 4-, and 6-month-old mice or rats, and standard 

deviations are only displayed graphically, and such values cannot be read with any accuracy 

from the graphs. Therefore, the NOAEL of 2.22 mg/kg is used as a point of departure for 

estimating the oral RfD for BDE-209. 

DecaBDE has very low water solubility and a relatively high Kow; therefore, preferential 

distribution to adipose tissue might be expected. This property raises concerns for accumulation 

of decaBDE in the body as a result of repeated exposure. However, limited data on the tissue 

distribution of decaBDE in experimental animals indicate that it is not readily distributed to 

adipose tissue (Morck et al., 2003). The limited deposition in the adipose tissue suggests that 

chronic accumulation may not be significant for BDE-209. The optimal way to address this 

issue would be to use a PBPK model to estimate the steady-state body burden in the lipid 

compartment after repeated exposure and examine the dose-response relationship based on the 

internal dose at the target tissues. No PBPK models of decaBDE were identified for humans or 

animals, and data on internal doses from existing toxicity studies are not adequate to support 

dose-response analysis. In the absence of these data, a dose-response analysis based on body 

burden was not included in this assessment. 

5.1.2.1. Benchmark Dose Modeling

Although the NOAEL from the Viberg et al. (2003a) study was selected as the critical 

endpoint for the RfD derivation, the dose-response data from the NTP (1986) study were 

modeled to determine the lower bound BMD (BMDL) for systemic toxicity. Details of the BMD 

modeling results are presented in Appendix B and summarized in this section. The following 

data sets from the NTP (1986) 2-year rat and mouse studies were selected for BMD modeling: 

thrombosis in the liver, liver degeneration, fibrosis in the spleen, and lymphoid hyperplasia in 
55 

male rats; centrilobular hypertrophy in the livers; and follicular cell hyperplasia in the thyroid of 

male mice. 

The BMD modeling was conducted using EPA’s BMD software (BMDS) version 1.3.2. 

The dose levels showing a change compared with control values exhibited responses at levels 

near 10%; therefore, all of the BMD analyses were conducted with the benchmark response 

(BMR) set to a 10% extra risk (U.S. EPA, 2000b). For each data set, all the dichotomous 

models, including gamma, logistic, log-logistic, multistage, probit, log-probit, quantal-linear, 

quantal-quadratic, and Weibull, available in the BMDS were used. BMD model fit was 

evaluated based on the goodness-of-fit p value (indicating global model fit), Akaike Information 

Criterion (AIC) (indicating model fit when controlling for number of model parameters), as well 

as local chi-square residual (indicating the model fit at the data point close to the preset BMR). 

Based on the model output, the models providing best model fit to the data were selected to 

estimate BMD10 and BMDL10. The BMD analyses results are summarized in Table 5-1. 

Based on the comparison of BMD modeling results for all the potential critical effects 

observed in chronic rat and mouse studies, the lowest BMDL10 is 406 mg/kg-day for liver 

degeneration effect in male rats. This value is much higher than the NOAEL of 2.22 mg/kg for 

the neurobehavioral changes observed in Viberg et al. (2003a). Because the graphic habituation 

data from the Viberg et al. (2003a) publication could not be used for BMD modeling, the 

NOAEL of 2.22 mg/kg is used as a point of departure for calculating the oral RfD. 

Table 5-1. BMDs for potential critical effect from chronic rat and mouse 

studies 

Endpoint Reference

NOAEL

(mg/kg-day)

LOAEL

(mg/kg-day)

BMD10

(mg/kg-day)

BMDL10

(mg/kg-day)

Thrombosis in the liver of male rats NTP (1986) 1,120 2,240 2,125 1,738

Liver degeneration in male rats NTP (1986) 2,240 N/Aa765 406

Splenic fibrosis in male rats NTP (1986) 1,120 2,240 1,446 1,001

Lymphoid hyperplasia in male rats NTP (1986) 1,120 2,240 1,538 1,165

Centrilobular hypertrophy in the liver 

of male mice NTP (1986) N/A 3,200 No model fit –

Follicular cell hyperplasia in the 

thyroid of male mice NTP (1986) N/A 3,200 1,670 1,190

aN/A = not available or cannot be estimated.

Source: NTP (1986). 

5.1.3. RfD Derivation 

Based on the neurobehavioral effects observed in the Viberg et al. (2003a) study, the 

NOAEL of 2.22 mg/kg is used as the point of departure for calculating the RfD. The following 

uncertainty factors (UFs) (U.S. EPA, 2002) are applied to the NOAEL of 2.22 mg/kg: 10 for 
56 

extrapolating animal data to humans (UFA interspecies variability), 10 for susceptible human 

subpopulation (UFH interhuman variability), and 3 for extrapolating from the single-dose to a 

lifetime exposure (UFS). The total composite UF = 10 × 10 × 3 = 300. 

A 10-fold UFA was used to account for laboratory animal to human interspecies 

differences. Although the toxicokinetics of decaBDE in animals have been evaluated, no 

adequate description of toxicokinetics of decaBDE in humans exists. The critical effect for 

deriving the RfD, altered behavior due to exposure during development, is expected to be 

relevant to humans. No quantitative data were identified to compare relative human and rodent 

sensitivity to these changes. However, given the longer period of brain development in humans 

as compared to rodents and the higher importance of cognitive function, it is appropriate to 

consider that humans may be more sensitive than rodents in the absence of specific data. Based 

on these considerations, the default UFA value of 10 was applied. 

A default intraspecies UFH of 10 was applied to account for variations in susceptibility 

within the human population (intrahuman variability). This factor accounts for the segment of 

the human population that may be more sensitive than the general population to exposure to 

BDE-209. A default value is warranted because insufficient information is currently available to 

assess human-to-human variability in BDE-209 toxicokinetics or toxicodynamics. 

A threefold UFS was used to adjust for exposure duration. For BDE-209, the principal 

study identified endpoints that, for the most part, reflect specific aspects of developmental 

physiology. The hypothesized window of susceptibility, proposed by the study authors, is based 

on the observation that the developmental neurotoxic effects observed following exposure to 

BDE-209 on PND 3 will not occur once the toxicokinetics of intestinal uptake and excretion 

have matured and the animal brain is developmentally less active (outside the window of 

susceptibility). The Eriksson/Viberg group has suggested that the period of maximum 

vulnerability for the developing cholinergic system that coincides with the most pronounced 

neurodevelopmental effects from BDE-99 exposure is from PNDs 10–14. However, for BDE209 the developmental neurotoxic effects were noted following exposure on PND 3 rather than 

on PNDs 10 or 19. It is likely that two factors contributed to this difference in the timing for the 

peak period of vulnerability. First, absorption from the gastrointestinal tract decreases as the 

neonatal mice age during their first few weeks of life; thus, less of the BDE-209 reaches the liver 

for distribution on PNDs 10 and 19 than on PND 3. Secondly, distribution to the brain is slow. 

The amount of radiolabel in the brain is 1.4- and 2.8-fold greater 7 days after dosing compared 

with 24 hours after dosing on PNDs 3 and 10. Even less reaches the brain when the BDE-209 is 

administered on day 19. The UFS was viewed as a dosing duration adjustment rather than simply 

a comparison of the effects of a subchronic to a chronic exposure. A threefold UFS was applied 

because the critical study dosed the animals only once within the hypothesized critical window, 

not because the chronic exposures would have exacerbated the impact on habituation. 
57 

A UFL for LOAEL-to-NOAEL extrapolation was not applied because a NOAEL was used 

as the point of departure. 

A UFD to account for deficiencies in the available decaBDE database was not necessary. 

Available animal studies on repeated oral exposure to decaBDE include 14-day studies in rats 

and mice (NTP, 1986), 13-week studies in rats and mice (NTP, 1986), and 2-year studies in rats 

and mice (NTP, 1986). A developmental and behavioral toxicity study in male and female mice 

was available (Rice et al., 2007), as well as a behavioral study in male rats (Viberg et al., 2007). 

A 7-week study (Tseng et al., 2006) of sperm functions in mice was also available. In addition, a 

standard developmental toxicity study in rats (Hardy et al., 2002) was identified for decaBDE. 

No multigeneration reproductive toxicity study or other study of reproductive function is 

available for pure decaBDE. This array of studies results in potential uncertainty regarding the 

reproductive toxicity of decaBDE. However, this potential uncertainty is adequately accounted 

for based on the following considerations. First, none of the well-conducted longer-term dosing 

studies identified effects on male or female reproductive organs. Second, no developmental or 

reproductive effects were observed at doses up to 1,000 mg/kg-day in rats (Hardy et al., 2002) 

and 100 mg/kg-day in mice (Tseng et al., 2006). The absence of effects in the available longerterm and developmental studies indicates that at least some aspects of reproductive organ 

toxicity or function are not affected at doses much higher than those that resulted in the 

neurological effects in neonates (Viberg et al., 2003a), although effects on mating and fertility 

are not evaluated in these studies. 

The other potential uncertainty in the database factor is immunotoxicity from exposure to 

decaBDE. The potential immunotoxicity was indicated by the observations of significant 

increases in spleen fibrosis and lymphoid hyperplasia in male rats treated with a high dose of 

decaBDE (NTP, 1986). However, no such changes occurred in female rats or in either sex of 

treated mice (NTP, 1986). In addition, an in vitro immunotoxicity study (Pullen et al., 2003) 

with mouse splenocytes suggested that decaBDE is not likely to affect the immune system in an 

immunosuppressive manner nor the production of the cytokines by these cells. Moreover, the 

proposed point of departure is based on the developmental neurobehavioral changes and 

immunotoxicity is not likely to occur at the current point of departure of 2.22 mg/kg, which is 

500-fold lower than the NOAEL for histopathologic changes in rat spleen and lymphoid in the 

NTP (1986) study. 

Based on the choice of the critical effect and UF selections, the oral RfD for decaBDE is 

calculated as follows: 

 RfD = NOAEL ÷ UF

 = 2.22 mg/kg ÷ 300 

 = 0.007 mg/kg-day or 7 μg/kg-day 
58 

5.1.4. Previous RfD Assessment 

An IRIS health assessment of decaBDE is available (U.S. EPA, 1989). The RfD is based 

on the study of Kociba et al. (1975) in which male and female Sprague-Dawley rats (25/sex/dose 

group) were treated with a commercial decaBDE (77.4% decabromodiphenyl oxide, 21.8% 

nonaBDE, and 0.8% octaBDE) at doses of 0, 0.01, 0.1, or 1.0 mg/kg-day for 2 years. Parameters 

examined were hematology, clinical chemistry, food consumption, organ weight, body weight, 

and incidence of histopathologic lesions. No significant differences among treatment and 

control groups were found. The NOAEL in this study was 1.0 mg/kg-day, the highest dose 

tested. A UF of 100 was applied to the NOAEL for both the expected intra- and interspecies 

variability to the toxicity of this chemical in lieu of specific data, resulting in a RfD of 0.01 

mg/kg-day or 10 μg/kg-day. Confidence in the RfD was considered low (The low doses and 

number of animals used in this study have been questioned as to their adequacy to determine the 

carcinogenic potential of this commercial decaBDE [NTP, 1986]). The previous RfD was not 

based on the NTP (1986) study because the final NTP report was not available at the time. 

The National Research Council of the National Academies of Science (NAS, 2000) 

derived a RfD for decaBDE based on the NTP (1986) study. The LOAEL for liver thrombosis 

and degeneration in male rats was 2240 mg/kg-day and the NOAEL 1120 mg/kg-day. The 

following UFs were applied: 10 for extrapolation from animals to humans, 10 for intraspecies 

variation, and 3 for database deficiency. Applying this total UF of 300 to the NOAEL of 

1120 mg/kg-day gives a RfD of 4.0 mg/kg-day. Confidence in this provisional RfD was 

considered medium to low. 

The Agency for Toxic Substances and Disease Registry (ATSDR, 2004) derived an 

intermediate oral minimal risk level (MRL) of 10 mg/kg-day based on the Hardy et al. (2002) 

study. No effects on any maternal or fetal endpoints were observed in any dose group. The 

NOAEL in this study was the highest dose tested of 1000 mg/kg-day. Applying a total UF of 100 

(10 for extrapolation from animals to humans and 10 for human variability), an intermediate oral 

MRL of 10 mg/kg-day was derived. 

5.2. INHALATION REFERENCE CONCENTRATION (RfC) 

No data are available for deriving a RfC for decaBDE. 

5.3. CANCER ASSESSMENT

5.3.1. Choice of Study/Data—with Rationale and Justification 

As discussed in section 4.6, the weight of evidence of human carcinogenicity of 

decaBDE is based on (1) no studies of cancer in humans exposed to decaBDE; (2) a significantly 

increased incidence of neoplastic nodules in the liver of low- and high-dose male rats and highdose female rats; (3) a significantly increased incidence of hepatocellular adenoma or carcinoma 
59 

(combined) in male mice at low dose and marginally increased incidence at high dose; (4) a 

nonsignificantly increased incidence of hepatocellular adenoma or carcinoma (combined) in 

female mice; (5) a slight (but statistically not significant) increase in incidence of thyroid gland 

adenomas or carcinomas (combined) in both male and female mice; (6) a significantly increased 

incidence in male mice of follicular cell hyperplasia, considered by many as a precursor to 

thyroid tumors; and (7) an apparent absence of genotoxic potential. All of the data supporting 

carcinogenicity were obtained from chronic studies in rats and mice (NTP, 1986). 

As discussed in section 4.6, the weight of evidence suggests that decaBDE shows 

―suggestive evidence of carcinogenic potential.‖ Support for tumorigenic effects in the liver of 

varying strengths is found in both sexes of rats and mice. In the NTP (1986) study, decaBDE 

caused a dose-dependent increased incidence of liver neoplastic nodules in rats with statistical 

significance at the high dose in both sexes (Table 4-4), indicating some evidence of 

carcinogenicity in treated rats. However, there were no significant changes in hepatocellular 

carcinoma in either sex. In mice, nonsignificant increases in hepatocellular adenoma or 

carcinoma occurred in male mice at low (3,200 mg/kg-day) and high (6,650 mg/kg-day) doses 

compared with controls. However, combined incidence of hepatocellular adenoma or carcinoma 

increased significantly in the low-dose group but not in the high-dose group. Increased 

incidence of hepatocellular adenoma and carcinoma was also observed in the female mice; 

however, these changes were not statistically significant. Similarly, although the increases in 

thyroid tumors were not statistically significant in either sex of mice, they were supported by 

increases in a precursor to thyroid tumors, follicular cell hyperplasia. 

Therefore, the NTP (1986) chronic studies in mice and rats were considered the basis for 

the quantitative cancer assessment. Liver and thyroid tumors were considered as possible bases 

for the quantitation. To select the most sensitive cancer endpoint as the point of departure to 

derive a cancer risk value, benchmark modeling was conducted for each tumor endpoint or 

related precursor (i.e., thyroid hyperplasia). The BMD analysis and corresponding results are 

summarized in the following sections. 

5.3.2. Dose Adjustments 

For the chronic rat study (NTP, 1986), the original oral doses were reported as 0, 1,120, 

and 2,240 mg/kg-day for males and 0, 1,200, and 2,550 mg/kg-day for females. Since there are 

not enough toxicokinetic data for conducting a quantitative interspecies extrapolation, a default 

dose conversion was used. Based on EPA’s Guidelines for Carcinogen Risk Assessment (U.S. 

EPA, 2005a), corresponding human equivalent doses (HEDs) were calculated by scaling animal 

daily applied doses experienced for a lifetime in proportion to body weight raised to the 0.75 

power. 
60 

A body weight (bw)3/4 scaling factor was used to convert the points of departure in the rat

study to HEDs, in accordance with the Guidelines for Carcinogen Risk Assessment (U.S. EPA, 

2005a). This procedure presumes that equal doses in these units (i.e., in mg/kg3/4-day), when 

administered daily over a lifetime, will result in equal lifetime risks of the critical effect across 

mammalian species (U.S. EPA, 1992). The HED may be calculated as follows (U.S. EPA, 

2005a, 1992):

 HED (mg/kg-day) = dose in animals (mg/kg-day) × (bwa/bwh)

0.25 

where: 

HED = human equivalent dose 

 dose = average daily dose in animal study 

 bwa = animal body weight (kg) 

 bwh = reference human body weight (70 kg) 

 Based on reported weekly body weight data for each dose group for male rats, average 

lifetime body weights were calculated as 383.9, 385.2, and 380.7 g for the control, low-, and 

high-dose groups, respectively. Using the calculated average lifetime rat body weight and a 

default human body weight of 70 kg, the corresponding HEDs were calculated as 0, 305.1, and 

608.3 mg/kg-day, respectively. Similarly, for female rats, average lifetime body weights were 

calculated as 247.9, 246.2, and 242.1 g for the control, low-, and high-dose groups, respectively. 

Based on the calculated body weight and default human body weight of 70 kg, corresponding 

HEDs were calculated as 0, 292.2, and 618.4 mg/kg-day, respectively. 

For the chronic mouse study (NTP, 1986), the only dose-response data on carcinogenicity 

available were obtained from male mice; therefore, the dose conversion was conducted for male 

mice only. The original oral doses for male mice were reported as 0, 3,200, and 6,650 mg/kgday. Since there are not enough toxicokinetic data for conducting a quantitative interspecies 

extrapolation, a default dose conversion was used. Based on reported weekly body weight data 

for each dose group, average lifetime body weights were calculated as 37.3, 37.4, and 37.0 g for 

control, low-, and high-dose groups, respectively. Based on these data on average lifetime 

mouse body weight and a default human body weight of 70 kg, corresponding HEDs were 

calculated by scaling animal daily applied doses experienced for a lifetime in proportion to body 

weight raised to the 0.75 power. The estimated HEDs are 0, 486.5, and 1,008.6 mg/kg-day, 

respectively. 

5.3.3. Extrapolation Method(s) 

U.S. EPA BMDS (version 1.40b) was used in the cancer endpoint BMD analysis. 

Following the guidelines for evaluation of data on tumorigenic responses, the cancer model 
61 

(a multistage model with a calculation function for slope factor) was used to calculate effective 

doses (EDs) for a tumor response within the range of observation and the lower confidence 

estimate on that dose. The lower confidence limit of the estimated dose for a BMR similar to 

the response observed in the low-dose group is used as a point of departure to estimate an oral 

slope factor (U.S. EPA, 2005a, b). 

All potential tumor endpoints with statistically significant responses in the rat and mouse 

chronic studies (NTP, 1986) were modeled in order to identify the most sensitive point of 

departure. Animals dying prior to week 53, before the first appearance of tumors, were censored 

from the group totals to adjust the incidence rates for early mortality. To adjust for differential 

mortality among treated male rats, censored data on neoplastic nodules or the combined 

neoplastic nodules and carcinomas in rats of both sexes were also modeled. The data on 

combined hepatic carcinomas and adenomas in male mice were modeled despite the fact that 

they did not show a good dose-response relationship because they were significantly increased in 

comparison with controls. A detailed description of the BMD modeling results is presented in 

Appendix C. The estimated cancer slope factors based on estimated EDs and their 95% lower 

confidence limits using the multistage model for each cancer endpoint are summarized in Table 

5-2. 

Table 5-2. Cancer slope factors derived from BMDs for neoplastic effect 

from chronic rat and mouse studies using the multistage model 

Endpoint Species

Cancer slope factor

(mg/kg-day)–1

Neoplastic nodules in the liver Male rat 0.0007

Neoplastic nodules or carcinomas (combined) in the liver Male rat 0.0007

Neoplastic nodules in the liver Female rat 0.0004

Neoplastic nodules or carcinomas (combined) in the liver Female rat 0.0005

Follicular cell hyperplasia in the thyroid Male mouse 0.0005

Adenomas or carcinomas (combined) in the liver Male mouse 0.0005

Source: NTP (1986). 

Neoplastic nodules and carcinomas were also modeled together because the two lesions 

could have a similar mode of action. Based on the estimated ED for each cancer endpoint, the 

most sensitive response is neoplastic nodule or carcinoma (combined) in the liver of male rats. 

The ED12 from the lower end of the range of observation is 263 mg/kg-day, and the 

corresponding 95% lower confidence limit for the effective dose (LED12) is 178 mg/kg-day. For 

neoplastic nodules or carcinomas in the liver of female rats, both censored and uncensored data 

resulted in higher LEDs than for this effect in male rats; therefore, the LED in females was not 

used as the point of departure. Similarly, the estimated LED for the follicular cell hyperplasia in 

the thyroid of male mice is also higher than that of neoplastic nodules or carcinomas (combined) 
62 

in the male rats. Thus, the lowest LED, 178 mg/kg-day for neoplastic nodules or carcinomas 

(combined) in the male rats, is selected as the point of departure for deriving an oral cancer slope 

factor. However, as stated earlier (section 4.2.2.1), the term neoplastic nodule is no longer used 

for rat liver tumors, and it is not possible to know if all lesions originally categorized as 

neoplastic nodules were preneoplastic under current guidelines. Some may have been 

nonneoplastic hyperplasia. Accordingly, there is some uncertainty in the calculated slope factor 

that should be considered when it is applied in quantitative risk assessment. 

5.3.4. Oral Slope Factor 

Although no human studies were available, two chronic rodent studies provide suggestive 

evidence of decaBDE-induced carcinogenicity. The data from these studies are adequate to 

support a quantitative cancer dose-response assessment. Even though the available evidence is 

suggestive of human carcinogenic potential, there is very limited information exploring the mode 

of action for any of the tumors reported in the animal chronic studies. While decaBDE was not 

mutagenic or genotoxic in various in vitro studies, there are no data to support alternative modeof-action hypotheses. In the absence of such data, a mode of action for BDE-209 could not be 

determined; therefore, extrapolation from the point of departure to lower doses is conducted by 

using a linear approach. 

Based on a comparison of estimated EDs for all the cancer endpoints observed in rat and 

mouse chronic studies (NTP, 1986), the neoplastic nodules or carcinomas (combined) in the 

liver of treated male rats are the most sensitive endpoint. Therefore, the LED12 of 178 mg/kgday estimated for this endpoint is used as a point of departure for calculating the cancer slope 

factor. 

For linear extrapolation, a straight line is drawn from the point of departure expressed as 

an HED to the origin to give a probability of extra risk. The slope of the line expresses extra risk 

per dose unit. For linear extrapolation, the slope of the line is 0.12/LED12. The central estimate, 

ED12, of exposure at 12% extra risk is 0.12/ED12. The slope of the linear extrapolation from the 

central estimate ED12 is 5 × 10–4, which is derived using 0.12/(263 mg/kg-day). For neoplastic 

nodules or carcinomas, the resulting oral cancer slope factor is 7 × 10–4 per mg/kg-day, which is 

derived using 0.12/(178 mg/kg-day). Since some of the neoplastic nodules might not progress to 

carcinomas, this oral risk estimate errs on the conservative side. Based on this slope factor, the 

dose associated with an excess cancer risk (risk-specific dose [RSD]) value is approximately as 

follows: RSD at 10–6 is 1 μg/kg-day; RSD at 10–5 is 10 μg/kg-day; and RSD at 10–4 is 100 μg/kgday. 

Doses for excess cancer risks of approximately 5 × 10–6

 or lower would be protective of 

neurodevelopmental effects since the RfD established on the basis of these effects is 7 μg/kg-day 

(see section 5.1.3). As explained above, there is some uncertainty in this slope factor because 
63 

some of the neoplastic nodules might have been nonneoplastic hyperplasia rather than 

preneoplastic foci of cellular alteration or hepatic adenomas. The combination of the 

hyperplastic nodules and carcinomas for the dose-response analysis leads to a conservative but 

protective slope factor. 

5.3.5. Previous Cancer Assessment 

The carcinogenicity of decaBDE was evaluated in IRIS (U.S. EPA, 1989). DecaBDE 

was classified in Group C, ―possible human carcinogen,‖ according to EPA cancer guidelines 

(U.S. EPA, 1986b). The basis of this classification was lack of human carcinogenicity data and 

limited evidence of carcinogenicity in animals, namely, significantly increased incidences of 

neoplastic liver nodules in male and female rats and increased incidences of hepatocellular 

adenomas or carcinomas (combined) in male mice (NTP, 1986). A quantitative estimate of 

carcinogenic risk from oral exposure was not derived in the IRIS assessment because the final 

NTP (1986) report was not available at the time. 

On the basis of the carcinogenicity studies in F344/N rats and B6C3F1 mice, NTP (1986) 

concluded that there was ―some evidence of carcinogenicity‖ for male and female rats as shown 

by increased incidences of neoplastic nodules of the liver in low-dose males and high-dose 

groups of both males and females. There was ―equivocal evidence of carcinogenicity‖ for male 

mice as shown by increased incidences of hepatocellular adenomas or carcinomas (combined) in 

the low-dose group and of thyroid gland follicular cell adenomas or carcinomas (combined) in 

both dosed groups. There was ―no evidence of carcinogenicity‖ for female mice receiving low 

or high dose of decaBDE in the diet. Several nonneoplastic lesions were observed at increased 

incidences, the most notable being thyroid gland follicular cell hyperplasia in male mice. 

The potential carcinogenicity of decaBDE was evaluated by NAS (2000) on the basis of 

the NTP (1986) study. Based on lack of human data and limited evidence of carcinogenicity in 

animals (i.e., significant increased incidences of neoplastic liver nodules in male and female rats 

and increased incidences of hepatocellular adenomas or carcinomas in male mice), NAS (2000)

concluded that decaBDE is a possible carcinogen in rats but has not concluded that it is a 

carcinogen in humans. Based on the incidence of hepatic neoplastic nodules in male rats (NTP, 

1986), a cancer slope factor of 9 × 10–4 per mg/kg-day was derived, applying the multistage 

model to censored data to adjust for differential mortality among treated rats. 
64 

6. MAJOR CONCLUSIONS IN THE CHARACTERIZATION OF 

HAZARD AND DOSE RESPONSE 

6.1. HUMAN HAZARD POTENTIAL 

Studies of toxicokinetics of decaBDE reveal that the chemical can be absorbed by the 

oral route to a limited extent, does not accumulate in tissues, and undergoes clearance, largely as 

a result of metabolism in the liver and excretion in the bile. 

Short-term and subchronic studies demonstrated low toxicity from oral exposure to 

decaBDE with NOAELs of 3,000 mg/kg-day or higher. NTP (1986) conducted a chronic toxicity 

and carcinogenicity dietary study in F344 rats. DecaBDE caused an increase in the incidence of 

thrombosis in the liver in high-dose male rats (2,240 mg/kg-day). A dose-dependent, but 

insignificant, increase in the incidence of degeneration of the liver was also observed in treated 

male rats. In the spleen, a dose-dependent increase (statistically significant in the high-dose 

group) in the incidence of fibrosis was observed in males. In the mandibular lymph node, 

lymphoid hyperplasia increased in males in a dose-dependent manner, but the incidence reached 

statistical significance only at the high dose. Histopathology examination also revealed a dosedependent increase in the incidence of neoplastic nodules in the liver in both male and female 

rats. Female rats appeared to be refractory to the systemic toxicity of decaBDE at the doses used 

in this study. 

The observed toxicity of decaBDE in the 2-year study in rats is further supported by the 

2-year mouse study conducted by NTP (1986). Significant increases in the incidence of 

centrilobular hypertrophy were observed in the liver of treated male mice. In the thyroid gland, a 

dose-dependent and statistically significant increase (at all dose levels) in the incidence of 

follicular cell hyperplasia was observed in male mice. In the females, the incidence increased in 

the low- and high-dose groups compared with the control group, but the increase was not 

statistically significant at any dose level. Female mice in the high-dose group exhibited a 

significant increase in the incidence of stomach ulcers. In addition, there were significant 

increases in the combined incidence of hepatocellular adenomas or carcinomas at both low and 

high doses in male mice. In the thyroid gland, follicular cell adenomas or carcinomas 

(combined) were slightly, but not significantly, increased in treated mice of both sexes. Similar 

to female rats, female mice appeared to be refractory to the systemic toxicity of decaBDE.

DecaBDE also has been shown to induce behavioral changes in several studies in mice

and rats (Viberg et al., 2007, 2003a; Rice et al., 2007). In the principal study selected, Viberg et 

al. (2003a) investigated the neurotoxic effects of decaBDE on spontaneous motor behavior of 

adult NMRI male mice when these animals were exposed to a single oral dose as neonates on 

PND 3, 10, or 19 (i.e., at different stages of neonatal mouse brain development). Pair-wise 
65 

testing between adult mice exposed on PND 3 and control groups indicated significant doserelated changes in all three spontaneous behavior variables at 2, 4, and 6 months of age. Adult 

mice exposed neonatally up to 20.1 mg on either PND 10 or 19 did not show any significant 

differences in any of the variables. These data suggested that there was a critical window for the 

induction of behavioral disturbances, and the neurotoxic effect of neonatal decaBDE exposure 

was persistent and also worsened with age in male mice. 

The appropriate hazard descriptor for decaBDE is ―suggestive evidence of carcinogenic 

potential‖ (U.S. EPA, 2005a, b). The weight-of-evidence of human carcinogenicity of decaBDE 

is based on (1) no studies of cancer in humans exposed to decaBDE; (2) a statistically significant 

increase in incidence of neoplastic nodules and a slight increase in incidence of carcinomas (not 

statistically significant) in the liver of low- and high-dose male rats and high-dose female rats; 

(3) a significantly increased incidence of hepatocellular adenoma or carcinoma (combined) in 

male mice at the low dose and marginally increased incidence at the high dose; (4) a 

nonsignificantly increased incidence of hepatocellular adenoma or carcinoma (combined) in 

female mice; (5) a slightly greater (but statistically not significant) incidence of thyroid gland 

adenomas or carcinomas (combined) in dosed male and female mice; (6) a significantly 

increased incidence in male mice, at both doses, of follicular cell hyperplasia, considered by 

many as a precursor to thyroid tumors; and (7) an apparent absence of genotoxic potential. 

The weight of experimental evidence is on the strong end of the spectrum for the 

descriptor ―suggestive evidence of carcinogenic potential,‖ since there is suggestive evidence 

that decaBDE is carcinogenic for more than one species, sex, and site. Based on the weight of 

evidence, a dose-response assessment of the carcinogenicity of decaBDE is deemed appropriate. 

6.2. DOSE RESPONSE 

6.2.1. Noncancer/Oral 

BMD modeling was conducted for all the potential critical effects observed in the rat and 

mouse chronic studies, including thrombosis in the liver, liver degeneration, fibrosis in the 

spleen, and lymphoid hyperplasia in male rats, as well as centrilobular hypertrophy in the livers 

and follicular cell hyperplasia in the thyroid of male mice. The data on neurobehavioral effects 

in the Viberg et al. (2003a) study could not be modeled because the data were presented 

graphically rather than numerically and thus were not amenable to BMD analysis. The lowest 

BMDL10 in rodent chronic studies is 383 mg/kg-day for liver degeneration effect in male rats. 

This value is much higher than the NOAEL level of 2.22 mg/kg for the neurobehavioral changes 

observed in mice (Viberg et al., 2003a). Therefore, the NOAEL of 2.22 mg/kg is used as a point 

of departure for calculating the oral RfD. A composite UF of 300 was applied to this effect level 

to account for the interspecies uncertainty (10-fold), intraspecies variation (10-fold), and 
66 

extrapolation of a single dose to a lifetime exposure (3-fold), yielding an RfD of 0.007 mg/kgday or 7 μg/kg-day. 

The available database included acute, short-term, subchronic, and chronic studies in two 

species. Also, there are developmental and reproductive studies (Tseng et al., 2006; Hardy et al., 

2002) in addition to the critical neurobehavioral study. Confidence in the principal study 

(Viberg et al., 2003a) is low because the study used a single dose during a period of 

neurodevelopmental vulnerability. In addition, only limited tests on motor activity were 

conducted in only male mice in the critical study by Viberg et al. (2003a). This study is 

strengthened by the results of Rice et al. (2007), where behavioral effects were identified in 

neonatally exposed PND 70 mice following a repeated postnatal dose protocol, and also by the 

results of the Viberg et al. (2007) study in rats. The Viberg et al. (2003a) study provides 

information on the most sensitive endpoint; therefore, using the NOAEL from this study as a 

point of departure to calculate the RfD is expected to provide adequate protection for humans. 

The overall confidence in the RfD assessment of BDE-209 is low. 

6.2.2. Cancer/Oral 

Although no human studies were available, two chronic rodent studies (NTP, 1986) 

provide suggestive evidence of decaBDE-induced carcinogenicity. The data from these studies 

are adequate to support a quantitative cancer dose-response assessment. There is very limited 

information exploring the mode of action for any of the tumors reported in the animal chronic 

studies. DecaBDE was not mutagenic or genotoxic in several in vitro studies, and there are no 

data to support a nongenotoxic mode-of-action hypothesis. In the absence of such data, 

extrapolation from the point of departure to lower doses is most appropriate using a linear 

approach. 

Based on a comparison of estimated EDs for all the cancer endpoints observed in rat and 

mouse chronic studies (NTP, 1986), the neoplastic nodule or carcinoma (combined) in the 

treated rats is the most sensitive endpoint. Therefore, the LED12 of 178 mg/kg-day estimated for 

this endpoint is used as a point of departure for calculating the cancer slope factor. For 

neoplastic nodules or carcinomas (combined), the resulting oral cancer slope factor is 7 × 10–4

per mg/kg-day. This slope factor assumes that all neoplastic nodules were preneoplastic cellular 

changes with the potential to become malignant. Based on this slope factor, the doses associated 

with excess cancer risks of 10–4, 10–5, and 10–6 are approximately 100, 10, and 1 μg/kg-day, 

respectively. There is some uncertainty in this estimate, given the fact that the tissues identified 

as neoplastic nodules may have included some lesions now categorized as nonneoplastic 

hyperplasia (Maronpot et al., 1986). 
67 

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6200.pdf. 

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online at http://www.epa.gov/OSA/spc/pdfs/prhandbk.pdf. 

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Environmental Protection Agency, Washington, DC. Available online at http://www.epa.gov/srs. 

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70:17765–18717. Available online at http://www.epa.gov/cancerguidelines. 

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early-life exposure to carcinogens. Risk Assessment Forum, Washington, DC; EPA/630/R-03/003F. Available online 

at http://www.epa.gov/cancerguidelines. 

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Office of Science Policy, Office of Research and Development, Washington, DC; EPA/100/B-06/002. Available 

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ethers on thyroid hormones and hepatic enzyme activities in weanling rats. Toxicol Sci 61:76–82.
A-1 

APPENDIX A: SUMMARY OF EXTERNAL PEER REVIEW AND PUBLIC 

COMMENTS AND DISPOSITION 

The ―Toxicological Review‖ for BDE-209 has undergone a formal external peer review 

performed by scientists in accordance with EPA guidance on peer review (U.S. EPA, 2006a, 

2000a). The external peer reviewers were tasked with providing written answers to general 

questions on the overall assessment and on chemical-specific questions in areas of scientific 

controversy or uncertainty. The external peer review for BDE-209 was conducted in concert 

with the external peer review of other PBDE congeners (i.e., BDE-47, BDE-99, and BDE-153), 

and some external peer review charge questions were specific to congeners other than BDE-209. 

External peer reviewer comments on all of the PBDEs and the Agency response are included 

below for completeness. A summary of significant comments made by the external reviewers 

and EPA’s responses to these comments arranged by charge question follow. In many cases the 

comments of the individual reviewers have been synthesized and paraphrased in development of 

Appendix A. Synthesis of comments from individual peer reviewers resulted in summaries that 

combine similar statements from peer reviewers that were mentioned in conjunction with more 

than one charge question. In such cases, the comment and its response have been placed under 

the most relevant charge question. Some of the peer review comments were not directly related 

to charge questions. Those comments are categorized as miscellaneous and placed after those 

related to the charge questions. EPA also received scientific comments from the public. These 

comments and EPA’s responses are included in a separate section of this appendix. 

The peer review of the ―Toxicological Review‖ for BDE-209 was coupled with the 

review of the documents for BDE- 47, -99, and -153. Accordingly, most of the charge questions 

address all four congeners. The responses to the charge questions in this appendix apply 

primarily to comments related to BDE-209. The charge to the external peer reviewers and final 

external peer review report (February 2007) pertaining to the toxicological reviews of the four 

polybrominated diphenyl ether congeners are available at 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=161970. The public comments received 

can be found at http://www.regulations.gov/fdmspublic/component/main under the Docket EPAHQ-ORD-2006-0838. 

EXTERNAL PEER REVIEWER COMMENTS 

The reviewers made several editorial suggestions to clarify specific portions of the text. These 

changes were incorporated in the document as appropriate and are not discussed further. 
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A. General Comments 

Charge Question 1. Are you aware of other published peer-reviewed toxicological studies not 

included in these toxicological reviews that could be of relevance to the health assessment of 

BDE-47, -99, -153, or -209?

Comment 1: Three reviewers stated that they were unaware of any other relevant studies that 

would contribute to the BDE-209 IRIS assessment. One reviewer identified potentially relevant 

additional literature: 

Jones-Ortazo, HA; et al. (2005) Environ. Sci. Technol. 39:5121-5130

Wilford, BH; et al. (2005) Environ. Sci. Technol. 39:7027-7035

Schecter, A; et al. (2005) J. Toxicol. Environ. Health Part A 68:501-513

Hites, RA; et al. (2004) Environ. Sci. Technol. 38:4945-4949

Schecter, A; et al. (2006) Environ. Health Perspect. 114:1515-1520

Fischer, D; et al. (2006) Environ. Health Perspect. 114:1581-1584

Bradman, A; et al. (2007) Environ. Health Perspect. 115:71-74

Kodavanti, PRS; Derr-Yellin, EC. (2002) Toxicol. Sci. 68:451-457

Kodavanti, PRS; et al. (2005) Toxicol. Sci. 88:181-192

Reistad, T; Mariussen, E. (2005) Toxicol. Sci. 87:57-65

Reistad, T; et al. (2006) Arch. Toxicol. 80:785-796

Response: The Agency reviewed and evaluated the studies recommended by the reviewer and 

has included the relevant studies for BDE-209. Fischer et al. (2006), Bradman et al. (2007), and 

Kodavanti et al. (2005) were found to be relevant and were added to the document. The 

remaining studies suggested by the reviewer fell outside the scope of the IRIS assessment (i.e., 

exposure data, commercial mixtures). Additionally, a new literature search was conducted to 

ensure that recently published relevant studies are included in the IRIS assessment. Four studies 

were added to the ―Toxicological Review‖ for BDE-209 as the result of the literature search 

(Huwe and Smith, 2007; Pacyniak et al., 2007; Rice et al., 2007; Thuresson et al., 2006). A 

description of these studies can be found in sections 3 and 4. 

B. Oral Reference Dose (RfD) Values 

Charge Question 2. Have the rationale and justification for deriving RfDs on the basis of the 

neurobehavioral toxicity studies been transparently and objectively described in the draft 
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toxicological reviews of BDE-47, -99, -153, and -209? Are there additional studies that should 

be considered for deriving the RfDs for any of the four PBDE congeners? 

Comment 1: Three reviewers stated that the rationale for deriving the RfD based on the 

neurobehavioral toxicity studies was clearly and transparently described. Two reviewers stated 

that the neurobehavioral effects are the only toxic effects that have been observed consistently in 

PBDE rodent studies. One of these reviewers noted that, although the rat and mouse bioassays 

by NTP (1986) provide suitable data, the neurobehavioral studies appeared to provide the most 

appropriate dose-response data on which to base the health assessment. None of the reviewers 

suggested additional studies that should be considered for deriving the RfD. 

Response: No response needed. 

Charge Question 3. Do you agree or disagree with EPA basing the health assessment of BDE47, -99, -153, and -209 to a large extent on the Eriksson/Viberg neurobehavioral studies? 

Comment 1: One reviewer supported the use of the Eriksson/Viberg neurobehavioral study as 

the basis for the derivation of the RfD, given the limited body of toxicological information 

available. Two reviewers noted that the studies are limited by the fact that they originated from 

the same laboratory. One reviewer was concerned that the experimental design of the principal 

study selected more than one pup per litter, ignoring the ―litter‖ effect. Treating littermates as 

independent experimental units could confuse dose effects with litter effects. Another reviewer 

was concerned with the specificity of the neurobehavioral data for developmental neurotoxicity 

and suggested that independent confirmation of the endpoints is essential. One peer reviewer 

identified the use of a single sex (male mice) as a limitation of the critical study that had not 

been identified in the ―Toxicological Review‖ discussion of study limitations. One of these 

reviewers stated that these limitations do not hinder the derivation of the RfD for BDE-209 but 

make the confidence low. Another reviewer noted that the neurobehavioral findings of this 

laboratory have been corroborated in a study examining BDE-99 (Kuriyama et al., 2005). None 

of the reviewers stated that the studies could not be used as the basis for the derivation of the 

RfD. 

Response: The ―Toxicological Review‖ contains a detailed summary of the concerns with the 

study design and methods utilized in the principal study (see section 5.1.1). A discussion of the 

use of only male mice in the study by Viberg et al. (2003a) has been added to the discussion in 

section 5.1.1 of the ―Toxicological Review.‖ Additionally, the neurobehavioral effects reported 

in Viberg et al. (2003a) are supported by a study in male and female mice that was published by 
A-4 

Rice et al. (2007) after the peer review, which used an expanded array of neurodevelopmental 

endpoints and dosing for 14 days. The neurodevelopmental findings from Viberg et al. (2003a) 

are also supported by an expanding body of literature for the BDE-47, -99 and -153 congeners 

(Viberg et al., 2007, 2005, 2004a, b, 2003b, 2002; Kuriyama et al., 2005; Eriksson et al., 2002, 

2001; Branchi et al., 2002) that details changes in motor and cognitive activity in rodents 

following administration of single or repeated perinatal doses of PBDEs. Some of the concerns 

associated with the methodology of the Eriksson/Viberg neurobehavioral studies are alleviated 

by other studies (Rice et al., 2007; Kuriyama et al., 2005; Branchi et al., 2002) using more 

traditional methodologies that have generated toxic effects similar to those reported by Viberg et 

al. (2003a). Results reported by Viberg et al. (2003a) for BDE-209 are similar to results reported 

by Eriksson et al. (2001) for BDE-47, Viberg et al. (2004b) and Kuriyama et al. (2005) for BDE99, and Viberg et al. (2003b) for BDE-153. Altogether, these studies support the findings of 

Viberg et al. (2003a) that exposure to BDE-209 in early developmental stages can result in 

lasting changes in the neurobehavioral activity of mice.

Charge Question 4. Are the Eriksson et al. (2001) (BDE-47), Viberg et al. (2004b) (BDE-99), 

Viberg et al. (2003b) (BDE-153), and Viberg et al. (2003a) (BDE-209) studies appropriate for 

determining the point of departure? Have the strengths and weaknesses of the Viberg and 

Eriksson studies been appropriately characterized and considered?

Comment 1: All four reviewers believed that the Viberg et al. (2003a) BDE-209 study was

appropriate for determining the point of departure. One reviewer felt that these data were 

appropriate as long as the document emphasizes that the neurochemical data also show 

alterations in normal developmental patterns. Another reviewer noted that both Viberg et al. 

(2003a) and NTP (1986) provided data appropriate for determining a point of departure, with 

Viberg et al. (2003a) providing the lowest point of departure. None of the reviewers suggested 

an alternative study for determining the point of departure. Two reviewers explicitly stated that 

the strengths and weaknesses were identified and clearly presented.

Response: No response needed. 

Charge Question 5. Have the most appropriate critical effect and point of departure been 

selected? And has the rationale for the point of departure been transparently and objectively 

described? 

Comment 1: All four reviewers agreed with the selection of the neurobehavioral effects as 

critical effects and that these effects were appropriate for identifying a point of departure. One 
A-5 

of the reviewers felt that the neurochemical data also provided critical information and should be 

presented centrally rather than as supporting data. One reviewer stated that there was no 

correlation between PND of exposure and the concentration of the chemical in the brain. One 

reviewer added that decreased habituation might be as appropriate as or more appropriate than 

the habituation ratio as an indicator of toxicity, while another believed that the actual behavioral 

data, rather than the habituation ratio, should have been presented in the document. It was not 

clear for another reviewer why the actual data could not be recovered from the study authors to 

allow for dose-response modeling and BMD estimation, given that the studies were published 

fairly recently (2003). This reviewer recommended that the Agency attempt to recover the 

neurobehavioral toxicity data from the study authors. 

Response: The evidence of neurochemical interactions and the potential relationship with the 

neurobehavioral effects are highlighted in the mode-of-action section of the document (section 

4.5.3). The document presents the hypothesis proposed by the Eriksson/Viberg group in which 

the observed effects on locomotion and habituation are related to impaired development of the 

cholinergic system during the postnatal brain growth spurt; however, data are unavailable to 

determine the relevance of the neurochemical effects or to establish a mode of action. This 

conclusion has been added to section 4.5.3. In the case of BDE-209, the levels of radiolabel in 

the brain were higher following administration of equivalent doses on PND 3 or 10 compared to 

PND 19 (Viberg et al., 2003a). There are no measurements of levels of BDE-209 or the 

congeners in the brain or other tissues at the time of neurobehavioral testing at 2 or 4 months to 

show if any differences exist in the brain or other tissues at those time points. 

The actual motor activity components (locomotion, rearing, and total activity) that gave 

rise to the habituation ratios were reported in graphical form only and could not be reasonably 

estimated as presented, and the Agency’s attempts to obtain the raw data were unsuccessful. 

Thus, the habituation ratios, rather than the actual habituation data, served as the basis for 

determining the point of departure. 

Comment 2: Two reviewers thought that the rationale for the point of departure had been 

transparently and objectively described. Another reviewer felt the document provided clear 

rationalization for the selection of the point of departure. None of the reviewers stated that the 

rationale for the point of departure was not appropriately described. 

 

Response: No response needed. 

Comment 3: One reviewer noted that a BMDL would be better than a NOAEL for deriving an 

RfD. 
A-6 

Response: The Agency recognizes that a NOAEL can be limiting since it is highly dependent on 

the doses selected and the sample size and does not account for the dose-response curve. 

Alternatively, a BMDL is more independent of study design, takes into account the doseresponse curve, and, therefore, is preferable to a NOAEL as a point of departure. However, the 

data in the principal study for BDE-209 only allows for the identification of a NOAEL. The 

reporting is insufficient to provide the necessary information to perform BMD modeling and the 

Agency’s attempts to obtain the raw data were unsuccessful. 

Charge Question 6. Have the rationale and justification for each UF selected in the draft 

toxicological reviews of BDE-47, -99, -153, and -209 been transparently described? If the 

selected UFs are not appropriate, what alternative UFs would you suggest and what are the 

scientific rationales for those suggested? Does the database support the determinations of the 

RfDs for BDE-47, -99, -153, and -209? 

Note: The peer reviewers provided fairly extensive comments about the individual components 

of the combined UF. For that reason the following reviewer comments and EPA responses have 

been grouped by the area of uncertainty to which they apply. 

Comment 1: Two reviewers agreed that the document described the rationale and justification 

for each UF and another reviewer noted that the selection of the UFs was described in detail. 

The fourth reviewer felt that the document did not provide much explanation or justification for 

applying the default intraspecies UFH for BDE-209. 

Response: There is little information available on the effects of PBDEs in humans and in the 

absence of data there is no scientific rationale for moving away from the default value for the 

intraspecies UFH. Additional explanation for the intraspecies UFH was added to section 5.1.3. 

Comment 2: One reviewer suggested decreasing the interspecies UFA, considering the relatively 

specific and sensitive nature of the neurobehavioral and neurochemical measures compared with 

conventional endpoints. However, another reviewer felt that the 10-fold UFA was justifiable 

based on the lack of data on the mode of action in animals and humans. 

 

Response: The 10-fold UFA for interspecies uncertainty is retained based on the lack of modeof-action, pharmacokinetic, and human data that would sufficiently illustrate the similarities and 

differences for the effects of the PBDEs in animals and humans. Additional explanation for 

applying the default interspecies UFA was added to section 5.1.3. 
A-7 

Comment 3: Two reviewers suggested lowering the intrahuman UFH. One of these reviewers 

felt the relatively specific and sensitive nature of the neurobehavioral and neurochemical 

measures compared with conventional endpoints warranted a decrease in the UFH. The other 

reviewer recommended decreasing the 10-fold UFH to 3-fold based on the sensitivity of the test 

species population (neonates). 

Response: The 10-fold UFH for intraspecies uncertainty is retained based on the lack of 

information concerning the pharmacokinetics and mode of action of the BDE-209 in humans. In 

the absence of human data, the effects in potentially susceptible populations exposed to BDE209 cannot be determined. Additional explanation for applying the default intraspecies UFH was 

added to section 5.1.3. 

Comment 4: One reviewer disagreed with the treatment of a single-dose experiment as 

equivalent to a subchronic exposure when applying a UF to account for differences in exposure 

duration. This reviewer stated that the principal study needs to be treated as a single-dose study 

and not a subchronic study. The reviewer also felt that the threefold UFS was inappropriate and 

suggested raising the UFS from 3 to 10 to consider the extent to which the mother’s prepregnancy accumulated body burden would influence the developmental outcome, especially 

since these data are unavailable. One reviewer agreed with the application of a threefold UFS, 

recognizing that for the observed neurobehavioral effects the timing of exposure is more critical 

than the duration of exposure. This reviewer regards the UFS as accounting for uncertainty from 

lack of prenatal exposure rather than uncertainty regarding potential effects of chronic exposure. 

One reviewer suggested the threefold UFS may not be necessary, considering that exposure 

during a window of susceptibility indicates that chronic exposure may not necessarily result in 

greater adverse effects. 

Response: For BDE-209, the principal study identified endpoints that, for the most part, reflect 

specific aspects of developmental physiology. The hypothesized window of susceptibility, 

proposed by the study authors, is based on the observation that the developmental neurotoxic 

effects observed following exposure to BDE-209 on PND 3 will not occur once the 

toxicokinetics of intestinal uptake and excretion have matured and the animal brain is 

developmentally less active (outside the window of susceptibility). The Eriksson/Viberg group 

has suggested that the period of maximum vulnerability for the developing cholinergic system 

that coincides with the most pronounced neurodevelopmental effects from BDE-99 exposure is 

from PNDs 10–14. However, for BDE-209 the developmental neurotoxic effects were noted 

following exposure on PND 3 rather than on PNDs 10 or 19. It is likely that two factors 
A-8 

contributed to this difference in peak vulnerability. First, absorption from the gastrointestinal 

tract decreases as the neonatal mice age during their first few weeks of life, thus less of the 

BDE-209 reaches the liver for distribution on PNDs 10 and 19 than on PND 3. Secondly, 

distribution to the brain is slow. The amount of radiolabel in the brain is 1.4- and 2.8-fold 

greater 7 days after dosing compared with 24 hours after dosing on PNDs 3 and 10, respectively. 

Even less reaches the brain when the BDE-209 is administered on day 19. The UFS was viewed 

as a dosing duration adjustment rather than simply a comparison of the effects of a subchronic to 

a chronic exposure. A threefold UFS was applied because the critical study dosed the animals 

only once within the hypothesized critical window, not because the chronic exposures would 

have exacerbated the impact on habituation. 

In response to the comment about possible effects as the result of a maternal prepregnancy body burden, the Agency notes that, although the principal study did not include 

prenatal exposure, the maternal uptake and retention of BDE-209 during the prenatal period 

would be lower than that of the pups during the postnatal period of vulnerability because of the 

differences in toxicokinetics for mature versus neonatal animals. Support for the UFS is 

provided by the Hardy et al. (2002) study, where BDE-209 treatment did not produce any 

evidence of maternal or developmental toxicity up to the highest dose tested (1,000 mg/kg-day) 

despite exposure from gestation days 0 through 19. 

 

Comment 5: Two reviewers recommended raising the onefold database UFD to threefold. One 

of these reviewers based this decision on the use of a NOAEL rather than a BMDL as the point 

of departure. This reviewer felt that the absence of definitive data for dose-response modeling 

for the neurobehavioral effects reflects an inadequacy in the database, although if the endpoints 

could be modeled then a onefold UFD is acceptable. The other reviewer suggested raising the 

UFD to account for the lack of other developmental neurotoxicity studies. 

Response: EPA’s practice is to apply a database UFD, generally ranging from 1–10, in the 

health assessment to account for the potential for deriving an underprotective RfD as a result of 

an incomplete characterization of a chemical’s toxicity because of missing studies. In deciding 

to apply this factor to account for deficiencies in the available data set and in identifying its 

magnitude, EPA considers both the data lacking and the data available for particular organ 

systems as well as life stages. The database for BDE-209 contains subchronic and chronic 

toxicity studies as well as a traditional developmental study. Although the database lacks a twogeneration reproductive study, the absence of effects in the available longer-term and 

developmental studies indicates that at least some aspects of reproductive organ toxicity or 

function are not affected at doses much higher than those that resulted in the neurological effects 

observed in neonates in the principal study. Therefore, the Agency retains the onefold database 
A-9 

UFD. Calculating a BMDL rather than using a NOAEL for the point of departure would not 

impact the use of a database UF. 

Comment 6: Two reviewers believed the database supports the determination of the RfD but 

stated that the overall confidence in the RfD assessment is low. Another reviewer believed the 

database is very poor and suggested that the RfDs be acknowledged as temporary while waiting 

for additional studies that increase confidence. 

Response: The statement that the overall confidence in the RfD is low is included in the 

―Toxicological Review‖ in section 6.2. The Agency does not develop temporary RfDs for IRIS 

assessments. However, the availability of new information is one of the factors considered in 

selecting a chemical for reassessment. 

C. Body Burden Approach 

Charge Question 7. Are there adequate data for considering body burden as an alternative 

dose metric to administered doses in any of the RfD derivations?

Comment 1: All four reviewers agreed that the data were inadequate to consider body burden as 

an alternative dose metric for the derivation of the RfD. Two of the reviewers stated that body 

burden is a possible alternative but the data are too limited. 

Response: EPA examined the data on BDE-209 to determine if a body burden approach could 

be used for this congener during the development of the ―Toxicological Review.‖ It was 

determined that existing half-life, exposure, metabolite and mode-of-action data could not 

support a body burden calculation for this congener. 

Charge Question 8. Do you agree with the rationale described in the “Toxicological Review”

of BDE-209 that the data on the window of susceptibility of the cholinergic receptors to BDE209 tend to minimize body burden concerns?

Comment 1: Three reviewers stated that the question was unclear. One reviewer accepted the 

concept as a basis for the experimental design, given the available information. A second 

reviewer stated that there was no direct evidence that BDE-209 directly affects cholinergic 

receptors and suggested that the mechanism of the interaction must be complex and indirect. A 

third reviewer stated that although there are no definitive data on mode of action, this hypothesis 

is plausible. This reviewer acknowledges that the data on the window of susceptibility of the 
A-10 

cholinergic receptors to BDE-209 are suggestive but believes there are too many other 

possibilities for mode of action for this rationale to minimize body burden concerns. 

Response: Available mode-of-action data that describe the developmental neurotoxicity of 

BDE-209 are limited. The Eriksson/Viberg group, the principal study authors, have 

hypothesized that the observed effects on locomotion and habituation are related to impaired 

development of the cholinergic system during the postnatal brain growth spurt period based on 

studies of BDE-99 (Viberg et al., 2005, 2004a) and supported by studies with BDE-153 (Viberg 

et al., 2003b) and BDE-209 (Viberg et al, 2007, 2003a). They have further hypothesized that the 

sensitivity of the cholinergic system occurs in the vicinity of PND 10 and have tested this 

hypothesis by varying the time of dosing and observing differences in the habituation effect for 

BDE-99 and BDE-209 (Viberg et al., 2007; Eriksson et al., 2002). A difference in the impact of 

the time of dosing was observed between BDE-99 and BDE 209 and can be explained based on 

toxicokinetic factors (see section 4.5.3). The resulting deficit in cholinergic receptors persisted 

across the duration of testing and could cause an abnormal response to exposure to cholinergic 

stimulants in adulthood. The following statement has been added to the mode-of-action 

summary (section 4.5.3): ―While evidence exists that demonstrates BDE-209, as well as other 

PBDEs, interacts at the neurological level, data are inadequate to determine the mode of action 

for BDE-209.‖ 

D. Carcinogenicity Assessment 

Charge Question 9. Is the weight of evidence for the carcinogenicity of BDE-209 in the draft 

“Toxicological Review” appropriately described? Are there additional studies that should be 

included? 

Comment 1: Three reviewers commented that the weight of evidence for carcinogenicity of 

BDE-209 was appropriately described in the ―Toxicological Review.‖ One reviewer stated that 

the carcinogenicity study was completely and methodically described. This reviewer noted that 

the carcinogenicity study is over 25 years old and utilized very high doses that led to some toxic 

effects and animal deaths. None of the reviewers were aware of additional studies that should be 

included in the cancer assessment for BDE-209. 

Response: No response needed. 

Charge Question 10. Do the data support estimation of a cancer slope factor for BDE-209? If 

yes, is the rationale for the quantitative analysis objectively and transparently described, 
A-11 

considering the uncertainty in the data and the suggestive nature of the weight of evidence? 

Have the rationale and justification for the use of the linear low-dose extrapolation been 

objectively and transparently presented? 

Comment 1: One reviewer stated that the data appear to support estimation of a cancer slope 

factor, one reviewer stated that the data supports estimation, one reviewer did not specifically 

answer this question but, as mentioned below, did question the appropriateness of the study EPA 

used, and the fourth reviewer did not answer the question about the support for estimation of a 

cancer slope factor. One reviewer felt that the data supported the weight-of-evidence 

classification as ―suggestive of the carcinogenic potential.‖ One reviewer questioned the 

appropriateness of the NTP (1986) study for developing the cancer slope factor based on the 

utilization of very high doses and potentially limited absorption of BDE-209 and suggested that a 

new bioassay be conducted. This reviewer recognized the public comments on the 

carcinogenesis data, particularly the statements regarding the modest dose-response and the 

change, since the completion of the study, in criteria for classifying liver lesions in rats. This 

reviewer was less concerned with the scoring of neoplastic nodules as tumors because the 

nodules identified in chronic studies with exposure to a single compound are less likely to 

regress as compared with an initiation/promotion study. Regarding the change in classification 

criteria, another reviewer noted that the data supported the estimation of a cancer slope factor for 

BDE-209, with the assumption that the change in classification of the neoplastic nodules would 

not appreciably change the dose response. Two reviewers explicitly stated that the rationale for 

the quantitative analysis is transparently described. Two reviewers stated that the justification 

for the use of the linear low-dose extrapolation is objectively presented in the BDE-209 

assessment. One reviewer noted that the document did not include a rationale or justification, 

other than a reference to EPA guideline documents (U.S. EPA, 2005a, b), for the use of linear 

low-dose extrapolation. None of the reviewers disagreed with the estimation of the cancer slope 

factor or the use of linear low-dose extrapolation. 

Response: The Agency is aware of the deliberations concerning the significance of neoplastic 

nodules in interpreting cancer risk. In 1986, a significant change was made regarding the NTP

nomenclature for hepatoproliferative lesions of rats: lesions previously combined under the 

diagnosis of ―neoplastic nodules‖ were replaced with three terms: ―hepatocellular hyperplasia,‖ 

―foci of cellular alteration,‖ and ―hepatocellular adenoma.‖ The term ―hyperplasia‖ was 

reserved for proliferative lesions that were perceived to be secondary, nonneoplastic responses to 

degenerative changes in the liver. Foci of cellular alteration, hepatocellular adenoma, and 

hepatocellular carcinoma were considered to represent a spectrum of changes that are part of the 

carcinogenic process (Maronpot et al., 1986). It is recognized that not all neoplastic nodules 
A-12 

have the potential to progress to malignancy: some neoplastic nodules may regress following 

removal of a chemical stimulus, others may only be hyperplastic lesions, and still others may 

progress to hepatocellular carcinoma. Therefore, the exact contribution of neoplastic nodules to 

the overall incidence of carcinoma in the rat liver is not known with any certainty. However, an 

increase in neoplastic nodules in treated rats provides some indication that the liver may be at 

increased risk of cancer formation, and inclusion of the incidence of neoplastic nodules in the 

assessment of cancer risk is considered to be a conservative approach (U.S. EPA, 1986c). This 

change in nomenclature has been noted in the ―Toxicological Review‖ in sections 4.2, 4.6.2, and 

5.3.3 and in Table 4-2. 

 EPA acknowledges that toxicokinetic limitations on solubility and absorption may make 

external dose a poor indicator of systemic dose. However, there are no PBPK models for BDE209 that might be used to estimate internal dose. Thus, the only parameter available for 

modeling dose-response is the external dose. 

 The justification for using the linear low-dose extrapolation for deriving a cancer slope 

factor for BDE-209 is based on the absence of data available to determine the mode of action for 

BDE-209. This rationale is provided in section 5.3.4. 

Charge Question 11. Are there alternative modeling approaches that should have been 

considered instead of or in addition to the linear low-dose extrapolation approach?

Comment 1: None of the reviewers suggested that an alternative modeling approach should have 

been considered. One reviewer stated that all possible modeling approaches were explained and 

the model that best fit the experimental data was selected. Another reviewer noted that 

consideration of other modeling approaches is not necessary, considering the dose-response data 

are linear, the linear model adequately fits the data, and the data are inadequate to justify an 

alternative approach. 

Response: No response needed. 

Miscellaneous Comments 

Comment 1: Three reviewers felt that the assessment would benefit from the combination of the 

individual documents for the four congeners into one comprehensive document to compare and 

cohesively present the similarities and differences among the congeners. 
A-13 

Response: The Agency has recently completed IRIS assessments for four individual PBDE 

congeners: BDE-47, -99, -153, and -209 (see Foreword). These congeners were selected based 

on frequent detection in human tissues and the environment, availability of animal toxicological 

studies suitable for human health assessment, and their common occurrence in commercial 

PBDE mixtures. Although there is some repetition in the four documents, the available database 

is sufficiently different from one congener to another to support the separation of the four IRIS 

assessments. However, in response to the comments from the peer reviewers, the Agency has 

increased the text that compares the data on BDE-209 to those of the other congeners evaluated 

using comparable methodological approaches. 

Comment 2: One reviewer noted that the document failed to cite the purities of the radioactive 

chemicals in most of the studies, the position of the label, location of radioactivity in the brain, 

and the specific activities of the 14C compounds. Another reviewer questioned the reliance upon 

the 14C data and the intermixing with direct chemical measures. The reviewer felt that the 

conclusions drawn were challenging. 

Response: The requested data were added to the descriptions of the pertinent studies (in section 

3) when they were provided by the authors of the paper. Frequently, the position of the 

radiolabel was not specified. In a few cases the radiolabel was described as ―uniform,‖ 

suggesting that all carbons carried the radiolabel. If the authors of the paper used the term 

―uniform,‖ it has been added to the discussion of the study. No change was made if the authors 

of the paper did not comment on the position of the radiolabel. 

Comment 3: One reviewer was concerned that the doses and concentrations of the compound 

and the metabolites in biological tissues were presented in differing units (i.e., μmol, μg, percent 

of dose). 

Response: Doses and concentrations are reported as given by the authors. If a dose was given in 

molar or mole units per unit body weight, the doses have been provided parenthetically as mg/kg 

body weight values. Otherwise the units are those provided in the published papers. 

Comment 4: One reviewer suggested including proposed metabolic pathways to strengthen the 

fact that the lower brominated congeners could be obtained from the higher brominated ones. 

Response: A diagram of a proposed metabolic pathway has been included as Figure 3-1 in 

section 3.3. The diagram is based on the metabolites that have been identified in several studies. 

The metabolic pathway is described as ―proposed‖ and uncertainties are indicated. The 
A-14 

individual publications that provided data on metabolites are cited in the Figure 3-1. In cases 

where the data from one study are discussed in more than one section of the ―Toxicological 

Review,‖ a reference to the location of prior mention of the study is provided. 

Comment 5: One reviewer acknowledged that developmental neurotoxicity is consistently 

observed following exposure to the PBDEs despite very different patterns of metabolism, 

distribution, and persistence within the body. This reviewer recommended rationalizing the 

relative potency of the PBDEs, considering the differences in the extent of metabolism. 

Response: Information is currently insufficient to identify the relative potency of the four 

congeners. 

Comment 6: One reviewer suggested that the Agency provide conclusions on the extent of 

metabolism and the presence of metabolites in excreta for the PBDEs or provide a statement if 

conclusions cannot be drawn. One reviewer suggested the addition of a summary at the 

beginning of the toxicokinetics section to reduce potential confusion. 

Response: An overview to the toxicokinetics section and summary paragraphs have been added 

to section 3. 

Comment 7: One reviewer recommended improving the discussion of the possible 

debromination of BDE-209 to lower brominated congeners and questioned if environmental 

debromination should be mentioned. 

Response: Discussion of the potential debromination of BDE-209 to lower-brominated 

congeners can be found in sections 3.2.2 and 3.3, based on evidence observed in several studies 

(Huwe and Smith, 2007; Morck et al., 2003; Sandholm et al., 2003; Zhou et al., 2001). Data for 

environmental debromination falls outside the scope of the IRIS health assessment. 

Comment 8: One reviewer recommended presenting the receptor site interaction information in 

a summary table. 

Response: Tables were added to the toxicological reviews for BDE-47, -99, and -153 because 

there were data for multiple congeners for the tetra, penta, and hexa congeners. In the case of 

BDE-209, there is only one PBDE congener and there was no need to have a table to summarize 

the data. 
A-15 

Comment 9: One reviewer felt that the evolution of exposures that are different in the U.S. 

compared with other countries and the pattern of exposures are important issues and the studies 

need to be presented to support or refute these observations. 

Response: The Agency has provided information on exposure in the U.S. and other countries for 

comparison purposes. While the Agency agrees that exposure analysis is a critical component of 

risk assessment, a comprehensive presentation and analysis of exposure data are outside the 

scope of the IRIS health assessment. 

Comment 10: One reviewer stated that the large number of bromine atoms of the PBDEs can 

impart electrophilic and lipophilic properties to the aromatic ring of the chemical and also noted 

that oily vehicles (e.g., corn oil) were used in most of the in vitro and in vivo animal studies. 

This reviewer was concerned the vehicle could significantly alter the distribution and tissue 

uptake of the PBDEs between the oily vehicle and the biological system. These conditions could 

lead to decreased absorption and distribution with subsequent alteration in metabolism and 

excretion. 

Response: The lipohilicity of the BDE-209 is acknowledged in the ―Toxicological Review‖ as 

part of section 3 on toxicokinetics. It will be necessary to determine if absorption occurs via the 

chylomicrons along with the body lipids or via direct membrane transport before the full impact 

of the vehicle on absorption, distribution, metabolism, and elimination can be determined. The 

data are currently inadequate to determine the impact of the oily vehicle on the distribution and 

uptake of BDE-209. 

PUBLIC COMMENTS 

The public commenters made several editorial suggestions to clarify specific portions of the text. 

These changes were incorporated in the document as appropriate and are not discussed further. 

Comment 1: One public commenter suggested that the Agency consider a body burden 

approach. 

Response: The Agency presented this issue to the peer reviewers in the form of a charge 

question. In response to the charge question about use of a body burden approach for dose 

evaluation, the peer reviewers agreed that, whereas the body burden approach might be 

appropriate for some of the congeners given their lipophilicity and distribution to adipose tissue, 

data to support such an approach are not presently available. 
A-16 

Comment 2: Three public commenters from one group questioned the selection of Viberg et al. 

(2003a) as the principal study for the derivation of the RfD, and another public commenter 

disagreed with the selection of Viberg et al. (2003a). Critiques of the study were submitted by 

the three public commenters questioning the methods utilized by the principal study authors. 

These public commenters were concerned that the purity of the radiolabeled BDE-209 in Viberg 

et al. (2003a) was not reported and suggested that observed effects may have been induced by 

impurities rather than the parent compound. Two of these public commenters felt that applying 

the intraspecies UFH to account for sensitive populations when evidence for a sensitive 

subpopulation does not exist is overly conservative. One of the public commenters noted the use 

of inconsistent units of concentration within the document. 

Response: The Agency has included a detailed summary of the concerns with the experimental 

design and methods utilized in the principal study (see section 5.1.1). These issues were raised 

during the external peer review of the BDE-209 IRIS assessment. The peer reviewers 

acknowledged the limitations and concerns with the study; however, all of the peer reviewers 

agreed that this study was appropriate for derivation of the RfD for BDE-209 and that its 

limitations were transparently discussed in the ―Toxicological Review.‖ Additionally, the 

neurobehavioral effects reported in Viberg et al. (2003a) are supported by other data for BDE209 (Rice et al., 2007) and by an expanding body of literature for the PBDEs (Viberg et al., 

2007, 2005, 2004a, b, 2003b, 2002; Kuriyama et al., 2005; Eriksson et al., 2002, 2001; Branchi 

et al., 2002) that details changes in motor and cognitive activity in rodents following 

administration of single or repeated perinatal doses of PBDEs. A summary of Rice et al. (2007) 

has been added to the BDE-209 ―Toxicological Review‖ in section 4.3.2. 

In response to the radiolabel concerns, the purities and positions of the radiolabels, the 

specific activities of the 14C compounds, and the locations of radioactivity in the brain were 

added to the descriptions of the relevant studies (in section 3) when they were provided by the 

authors of the paper. Frequently, the position of the radiolabel was not specified and/or the 

radiolabel was inadequately described to allow for the detailed reporting. These data have been 

added to the document where available. 

 The 10-fold UFH for intraspecies uncertainty is retained based on the lack of information 

concerning the pharmacokinetics and mode of action of the PBDEs in humans. In the absence of 

human data, the effects in potentially susceptible populations exposed to PBDEs cannot be 

determined. Additional explanation for applying the default intraspecies UFH was added to 

section 5.1.3. 

In response to the statement regarding the inconsistent reporting of units of 

concentration, the Agency notes that the doses and concentrations that are in the ―Toxicological 
A-17 

Review‖ are reported as given by the authors. If a dose was given in molar or mole units per unit 

body weight, the doses have been provided parenthetically as mg/kg body weight values. 

Otherwise the units are those provided in the published papers. 

Comment 3: One public commenter suggested a revision of the absorption, distribution, 

metabolism, and elimination sections (section 3) of the IRIS assessment for BDE-209. 

Additionally, another public group identified weaknesses in several studies within section 3. 

Response: The toxicokinetics section (section 3) has been revised and updated to reflect recently 

published literature (Huwe and Smith et al., 2007; Pacyniak et al., 2007; Thuresson et al., 2006). 

An introduction to the toxicokinetics information has been added to section 3. The studies 

within this section have been reorganized to separate animal and human data in section 3.1. 

Comment 4: One public commenter disagreed with the conclusion that the database for BDE209 provides ―suggestive evidence of carcinogenic potential.‖ This commenter recommended 

adding a chronic study in rats administered BDE-209 (Kociba et al., 1975). Additionally, the 

public commenter noted the change in nomenclature for hepatoproliferative liver lesions in rats 

and the appropriateness of using the incidence of ―neoplastic nodules‖ for quantitative cancer 

risk assessment. 

Response: The external peer reviewers were asked to evaluate the weight of evidence for 

carcinogenic potential for BDE-209 and to determine if the database supported the estimation of 

a cancer slope factor. Three of the peer reviewers explicitly stated that the database was 

sufficient, and none of the reviewers disagreed with either the classification of ―suggestive 

evidence of carcinogenic potential‖ or the quantitative cancer assessment for BDE-209. Kociba 

et al. (1975) administered a commercial grade BDE-209 that possesses a lower purity than the 

analytical grade utilized in the majority of the studies described in the IRIS health assessment. 

This study was not included for comparison since it falls outside the scope of the IRIS health 

assessment for the pure BDE-209 congener. Please see the response to the external peer review 

Comment 1, under Charge Question 10, regarding the change in criteria for the classification of 

hepatoproliferative liver lesions. 
B-1 

APPENDIX B: BENCHMARK DOSE ANALYSIS OF NONCANCER ENDPOINTS 

The following data sets from the NTP (1986) 2-year rat and mouse studies were selected 

for BMD modeling: thrombosis in the liver, liver degeneration, fibrosis in the spleen, and 

lymphoid hyperplasia in male rats, as well as centrilobular hypertrophy in the liver and follicular 

cell hyperplasia in the thyroid of male mice.

BMD modeling was conducted by using EPA’s BMDS, version 1.3.2. All the BMD 

analyses were conducted with the BMR set to a 10% response (U.S. EPA, 2000b). For each data 

set, all the available dichotomous models, including gamma, logistic, log-logistic, multistage, 

probit, log-probit, quantal-linear, quantal-quadratic, and Weibull, available in the BMDS were 

used. BMD model fit was evaluated based on the goodness-of-fit p value (indicating global 

model fit), local chi-square residual (indicating the model fit at the data point close to the preset 

BMR), as well as AIC (indicating model fit when controlling for number of model parameters). 

Based on the model output, the model(s) providing best model fit to the data were selected to 

estimate BMD10 and BMDL10. In some cases, the BMDS gives exactly the same results for 

several different models. This occurs when model parameters are fixed at a boundary, yielding 

reduced models that are identical expressions for the probability of response. For example, 

when the power parameter in the Weibull or gamma model is fixed at 1 by BMDS or when the 

degree of the multistage model is set to 1 by the user, these models reduce to the quantal linear 

model. When this occurred, all the reduced models providing the same BMD results were 

considered as one model. 

Liver Thrombosis in Male Rats

The data (1/50, 0/50, and 9/49 for control, low dose, and high dose, respectively) on 

thrombosis in the liver of male rats treated with decaBDE (NTP, 1986) were modeled with EPA 

BMDS. The reported oral doses were 0, 1,120, and 2,240 mg/kg-day, respectively. The data 

were modeled with all the dichotomous models available in the BMDS, and modeling results are 

summarized in Table B-1. 

Based on these results, the models that did not demonstrate significant lack of fit for the 

data were obtained from three models (shown in bold in the table): gamma, log-logistic, and 

Weibull. These models provided relatively high goodness-of-fit p values and low AIC values. 

Based on these considerations, an average value of the BMDs estimated from these three models 

is used. For thrombosis in the livers of male rats, the average BMD10 is 2,125 mg/kg-day and the 

average BMDL10 is 1,738 mg/kg-day. 
B-2 

Table B-1. Summary of BMD modeling results for thrombosis in the liver of 

male rats 

Model

Goodness-of-fit

p value AIC BMD10 BMDL10

Gamma 0.31 61.9754 2,047 1,717

Log-logistic 0.32 61.9384 2,161 1,741

Logistic 0.04 65.0449 1,909 1,597

Multistage 0.07 66.1380 1,898 1,449.97

Log-probit N/A

a

63.9383 2,130 1,691.4

Probit 0.04 65.8039 1,869 1,513.96

Quantal-linear 0.02 69.4028 2,030 1,162.71

Quantal-quadratic 0.07 66.1380 1,898 1,449.97

Weibull 0.31 61.9384 2,166 1,757

 aN/A = not applicable. 

 Source: NTP (1986). 

Liver Degeneration in Male Rats

The data (13/50, 19/50, and 22/49 for control, low dose, and high dose, respectively) on 

degeneration in the liver of male rats treated with decaBDE (NTP, 1986) were modeled with 

EPA BMDS. The reported oral doses were 0, 1,120, and 2,240 mg/kg-day, respectively. The 

data were modeled with all the dichotomous models available in the BMDS, and modeling 

results are summarized in Table B-2. 

Table B-2. Summary of BMD modeling results for degeneration in the liver 

of male rats 

Model

Goodness-of-fit

p value AIC BMD10 BMDL10

Gamma 0.83 195.178 779 422

Log-logistic 0.89 195.148 707 344

Logistic 0.71 195.269 929 600

Multistage 0.83 195.178 779 422

Log-probit 0.51 195.555 1,161 718

Probit 0.72 195.259 914 584

Quantal-linear 0.83 195.178 779 422

Quantal-quadratic 0.42 195.779 1,363 962

Weibull 0.83 195.178 779 422

 Source: NTP (1986). 

Based on the goodness-of-fit p value, none of the models demonstrated lack of fit. The 

best model fit for the data was obtained from five models (shown in bold in the table): gamma, 

log-logistic, multistage, quantal-linear, and Weibull. These models provided high goodness-of-
B-3 

fit p values and low AIC values. However, among the five models, gamma, multistage, quantallinear, and Weibull were reduced to a single identical model. Based on these considerations, an 

average value of the BMDs estimated from the log-logistic model and the common reduced 

model are used. For degeneration in the livers of male rats, the average BMD10 is 765 mg/kgday and the average BMDL10 is 406 mg/kg-day. 
B-4 

Liver Degeneration in Male Rats (NTP, 1986)

10% BMR

 ==================================================================== 

 Log-Logistic Model $Revision: 2.1 $ $Date: 2000/02/26 03:38:20 

$ 

 Input Data File: C:\BMDS\DATA\RATS.(d) 

 Gnuplot Plotting File: C:\BMDS\DATA\RATS.plt 

 Thu Nov 25 12:11:49 2004 

 ==================================================================== 

 BMDS MODEL RUN 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 

The form of the probability function is: 

P[response] = background+(1-background)/[1+EXP(-intercept-slope*Log(dose)] 

Dependent variable = resp1 

Independent variable = Dose 

Slope parameter is restricted as slope >= 1 

Total number of observations = 3 

Total number of records with missing values = 0 

Maximum number of iterations = 250 

Relative Function Convergence has been set to: 1e-008 

Parameter Convergence has been set to: 1e-008 

User has chosen the log transformed model 

Default Initial Parameter Values 

background = 0.26 

intercept = -8.66331 

slope = 1 

Asymptotic Correlation Matrix of Parameter Estimates 

( *** The model parameter(s) -slope have been estimated at a boundary point, 

or have been specified by the user, and do not appear in the correlation 

matrix ) 

background intercept 

background 1 -0.69 

intercept -0.69 1 

 

 
B-5 

Parameter Estimates 

Variable Estimate Std. Err.

background 0.262212 0.0603288

intercept -8.75859 0.569357

slope 1 NA

NA - Indicates that this parameter has hit a bound implied by some inequality 

constraint and thus has no standard error. 

Analysis of Deviance Table 

Model Log(likelihoo

d)

Deviance Test DF P-value

Full model -95.5647

Fitted model -95.5739 0.0184518 1 0.8919

Reduced model -97.5646 3.99968 2 0.1354

 AIC: 195.148 

Goodness of Fit Scaled 

Dose Est._Prob Expected Observed Size Residual

0.0000 0.2622 13.111 13 50 -0.03556

1120.0000 0.3726 18.630 19 50 0.1081

2240.0000 0.4543 22.259 22 49 -0.07432

Chi-square = 0.02 DF = 1 P-value = 0.8919

Benchmark Dose Computation

Specified effect = 0.1

Risk Type = Extra risk 

Confidence level = 0.95

BMD = 707.234

BMDL = 344.083

0.2

0.3

0.4

0.5

0.6

0 500 1000 1500 2000

dose

Log-Logistic Model with 0.95 Confidence Level

12:11 11/25 2004

BMDL BMD

 

Log-Logistic

BMD Lower Bound
B-6 

Splenic Fibrosis in Male Rats

The data (5/49, 8/50, and 13/49 for control, low dose, and high dose, respectively) on 

fibrosis in the spleen of male rats treated with decaBDE (NTP, 1986) were modeled with EPA 

BMDS. The reported oral doses were 0, 1,120, and 2,240 mg/kg-day, respectively. The data 

were modeled with all the dichotomous models available in the BMDS, and modeling results are 

summarized in Table B-3. 

Table B-3. Summary of BMD modeling results for fibrosis in the spleen of 

male rats 

Model

Goodness-of-fit 

p value AIC BMD10 BMDL10

Gamma N/A

a

139.172 1,464 700

Log-logistic N/A 139.172 1,463 644

Logistic 0.92 137.183 1,427 1,018

Multistage 0.69 137.336 1,236 690

Log-probit 0.87 137.197 1,519 1,017

Probit 0.88 137.195 1,393 968

Quantal-linear 0.69 137.336 1,236 690

Quantal-quadratic 0.80 137.233 1,612 1,176

Weibull N/A 139.172 1,470 700

aN/A = not applicable. 

Source: NTP (1986). 

Based on these results, the logistic, multistage, log-probit, probit, quantal-linear, and 

quantal-quadratic models did not show significant lack of fit for the data. The lowest AIC values 

were obtained with three models: logistic, log-probit, and probit (shown in bold in the table). 

Based on these considerations, an average value of the BMDs estimated from these three models 

is used. For fibrosis in the spleen of male rats, the average BMD10 is 1,446 mg/kg-day and the 

average BMDL10 is 1,001 mg/kg-day. 

Lymphoid Hyperplasia in Male Rats

The data (4/50, 6/50, and 13/49 for control, low dose, and high dose, respectively) on 

lymphoid hyperplasia in male rats treated with decaBDE (NTP, 1986) were modeled with EPA 

BMDS. The reported oral doses were 0, 1,120, and 2,240 mg/kg-day, respectively. The data 

were modeled with all the dichotomous models available in the BMDS, and modeling results are 

summarized in Table B-4. 

Based on these results, the models that adequately fit the data were the logistic, 

multistage, probit, quantal-linear, and quantal-quadratic. The quantal-quadratic model (shown in 

bold in the table) provided a relatively high goodness-of-fit p value and the lowest AIC value. 
B-7 

Based on these considerations, the BMD and BMDL estimates from this model are selected. For 

lymphoid hyperplasia of male rats, the BMD10 is 1,538 mg/kg-day and the BMDL10 is 

1,165 mg/kg-day. 

Table B-4. Summary of BMD modeling results for lymphoid hyperplasia in 

male rats 

Model

Goodness-of-fit 

p value AIC BMD10 BMDL10

Gamma N/A

a

127.266 1,601 765

Log-logistic N/A 127.266 1,608 725

Logistic 0.62 125.512 1,404 1,063

Multistage 0.36 126.122 1,207 707

Log-probit N/A 127.266 1,575 1,032

Probit 0.57 125.59 1,364 1,007

Quantal-linear 0.36 126.122 1,207 707

Quantal-quadratic 0.86 125.298 1,538 1,165

Weibull N/A 127.266 1,620 765

aN/A = not applicable. 

Source: NTP (1986). 

Centrilobular Hypertrophy in the Livers of Male Mice 

The data (0/50, 34/50, and 32/50 for control, low dose, and high dose, respectively) on 

centrilobular hypertrophy in the liver of male mice treated with decaBDE (NTP, 1986) were 

modeled with EPA BMDS. The reported oral doses were 0, 3,200, and 6,650 mg/kg-day, 

respectively. The data were modeled with all the dichotomous models available in the BMDS, 

and modeling results are summarized in Table B-5. 

Table B-5. Summary of BMD modeling results for centrilobular hypertrophy 

in the liver of male mice 

Model

Goodness-of-fit 

p value AIC

Local chi-square 

residual BMD10 BMDL10

Gamma 0.005 140.455 2.48 479 389

Log-logistic 0.094 134.65 1.44 258 180

Logistic 0 166.133 3.87 1,286 1,046

Multistage 0.005 140.455 0.7 479 389

Log-probit 0.004 140.591 2.22 839 676

Probit 0 165.095 4.03 1,253 1,036

Quantal-linear 0.005 140.455 2.48 479 389

Quantal-quadratic 0 164.89 5.08 1,612 1,451

Weibull 0.005 140.455 2.48 479 389

Source: NTP (1986). 
B-8 

Based on the BMD modeling results from all the models used, none of the available 

dichotomous models in the BMDS provided satisfactory data fit because all the goodness-of-fit 

p values are less than 0.1. This unsatisfactory model fit is due to the nonmonotonic dose 

response for this particular endpoint. Therefore, BMD and BMDL estimated from these model 

fits cannot be used. 

Follicular Cell Hyperplasia in the Thyroid of Male Mice

The data (2/50, 10/50, and 19/50 for control, low dose, and high dose, respectively) on 

follicular cell hyperplasia in the thyroid of male mice treated with decaBDE (NTP, 1986) were 

modeled with EPA BMDS. The reported oral doses were 0, 3,200, and 6,650 mg/kg-day, 

respectively. The data were modeled with all the dichotomous models available in the BMDS, 

and modeling results are summarized in Table B-6. 

Table B-6. Summary of BMD modeling results for follicular cell hyperplasia 

in the thyroid of male mice 

Model

Goodness-of-fit 

p value AIC

Local chi-square 

residual BMD10 BMDL10

Gamma N/A

a

139.241 0 2,040 1,196

Log-logistic N/A 139.241 <0.01 2,089 1,008

Logistic 0.34 138.147 0.70 2,989 2,430

Multistage 0.76 137.337 –0.09 1,670 1,190

Log-probit 0.66 137.436 0.34 2,561 1,977

Probit 0.44 137.846 0.59 2,792 2,265

Quantal-linear 0.76 137.337 –0.25 1,670 1,190

Quantal-quadratic 0.26 138.466 0.96 3,135 2,598

Weibull N/A 139.241 0.00002 2,022 1,196

aN/A = not applicable. 

Source: NTP (1986). 

Based on these results, the logistic, multistage, log-probit, probit, quantal-linear, and 

quantal-quadratic models showed adequate fit of the data. The multistage and quantal-linear 

models (shown in bold in the table) provided adequate goodness-of-fit p values and the lowest 

AIC values. Since both models provided the same data fit, the BMDs estimated from these 

models are identical. For follicular cell hyperplasia in the thyroid of male mice, the BMD10 is 

1,670 mg/kg-day and the BMDL10 is 1,190 mg/kg-day. 
C-1 

APPENDIX C: BENCHMARK DOSE ANALYSIS OF CANCER ENDPOINTS 

All the potential cancer endpoints in the rat and mouse chronic studies (NTP, 1986) 

expressed as responses from all the animals treated were modeled, and BMD modeling results 

are summarized below. All the cancer endpoints are modeled with the cancer model in the 

BMDS, version 1.40b. 

Neoplastic Nodules in the Liver of Male Rats

In the rat chronic study (NTP, 1986), there was a dose-dependent increase in the 

incidences of neoplastic nodules in the livers of male rats. The incidences of the lesion were 

1/50, 7/50, and 15/49 for control, low dose, and high dose, respectively. The original oral doses 

were 0, 1,120, and 2,240 mg/kg-day, and the corresponding HEDs are 0, 305.1, and 608.3 mg/kgday, respectively. These incidence data on neoplastic nodules in male rats were modeled by 

using the multistage model as recommended for a tumorigenic endpoint, and the modeling 

results are summarized in Table C-1. 

Table C-1. Summary of BMD modeling results for increase in neoplastic 

nodules in the liver of male rats 

Model

Goodness-of-fit 

p value AIC ED12.2 LED12.2

Multistage 0.58 114.935 250 174

 Source: NTP (1986). 

The low-dose group resulted in an incidence of 7/50, which corresponds to 12.2% extra 

risk. Therefore, the cancer ED at an extra risk of 12.2% was estimated to be 250 mg/kg-day, and 

the corresponding LED is 174 mg/kg-day. The slope factor at the 12.2% extra risk is 0.0007 per 

mg/kg-day. 
C-2 

Neoplastic nodules in the liver of male rats (NTP, 1986) 

BMR=12.2% extra risk

==================================================================== 

 Cancer Model. (Version: 1.2; Date: 10/20/2005) 

 Input Data File: C:\BMDS140B\UNSAVED1.(d) 

 Gnuplot Plotting File: C:\BMDS140B\UNSAVED1.plt

Thu Dec 01 00:38:02 2005

==================================================================== 

BMDS MODEL RUN 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The form of the probability function is: 

P[response] = background + (1-background)*[1-EXP(-beta1*dose^1)]

The parameter betas are restricted to be positive

Dependent variable = response

Independent variable = dose

Total number of observations = 3

Total number of records with missing values = 0

Total number of parameters in model = 2

Total number of specified parameters = 0

Degree of polynomial = 1

Maximum number of iterations = 250

Relative Function Convergence has been set to: 1e-008

Parameter Convergence has been set to: 1e-008

Default Initial Parameter Values 

Background = 0.0063916

Beta(1) = 0.000566746

Asymptotic Correlation Matrix of Parameter Estimates

Background Beta(1)

Background 1 -0.73

Beta(1) -0.73 1

Parameter Estimates

95.0% Wald Confidence Interval

Variable Estimate Std. Err Lower Conf. 

Limit

Upper Conf. 

Limit

Background 0.0190343 0.127925 -0.231695 0.269764

Beta(1) 0.000520805 0.000351251 -0.000167635 0.00120924

Analysis of Deviance Table 

Model Log(likelihood) # Param's Deviance Test 

d.f.

P-value

Full model -55.3119 3

Fitted model -55.4674 2 0.311055 1 0.577

Reduced model -63.9318 1 17.2399 2

0.0001805

AIC: 114.935 
C-3 

Goodness of Fit 

 Scaled 

Dose Est._Prob Expected Observed Size Residual

0.0000 0.0190 0.933 1 49 0.070

305.1000 0.1632 8.158 7 50 -0.443

608.3000 0.2854 13.984 15 49 0.321

Chi^2 = 0.30 d.f. = 1 P-value = 0.5811

Benchmark Dose Computation

Specified effect = 0.122

Risk Type = Extra risk 

Confidence level = 0.95

BMD = 249.822

BMDL = 173.541

BMDU = 401.462

Taken together, (173.541, 401.462) is a 90% two-sided confidence interval for 

the BMD

Cancer Slope Factor = 0.000703004

0

0.1

0.2

0.3

0.4

0.5

0 100 200 300 400 500 600

dose

Cancer Model with 0.95 Confidence Level

00:38 12/01 2005

BMDL BMD

 

Cancer

Linear extrapolation
C-4 

Neoplastic Nodules or Carcinomas (Combined) in the Liver of Male Rats

The data (2/50, 8/50, and 15/49 for control, low dose, and high dose, respectively) on 

neoplastic nodules or carcinomas (combined) in the liver of male rats treated with decaBDE 

(NTP, 1986) were also modeled with BMDS. The modeling results are summarized in 

Table C-2. 

Table C-2. Summary of BMD modeling results for increases in neoplastic 

nodules or carcinomas (combined) in the liver of male rats 

Model

Goodness-of-fit 

p value AIC ED12.4 LED12.4

Multistage 0.71 125.18 263 178

 Source: NTP (1986).

The low-dose group resulted in an incidence of 8/50, which corresponds to 12.4% extra 

risk. Therefore, the cancer ED at an extra risk of 12.4% was estimated to be 263 mg/kg-day, and 

the corresponding LED is 178 mg/kg-day. The slope factor at the 12.4% extra risk is 0.0007 per 

mg/kg-day.
C-5 

Neoplastic Nodules or Carcinomas (Combined) in the Liver of Male Rats (NTP, 

1986)

BMR=12.4% extra risk

==================================================================== 

 Cancer Model. (Version: 1.2; Date: 10/20/2005) 

 Input Data File: C:\BMDS140B\UNSAVED1.(d) 

 Gnuplot Plotting File: C:\BMDS140B\UNSAVED1.plt

Thu Dec 01 00:51:35 2005

==================================================================== 

BMDS MODEL RUN 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The form of the probability function is: 

P[response] = background + (1-background)*[1-EXP(-beta1*dose^1)]

The parameter betas are restricted to be positive

Dependent variable = response

Independent variable = dose

Total number of observations = 3

Total number of records with missing values = 0

Total number of parameters in model = 2

Total number of specified parameters = 0

Degree of polynomial = 1

Maximum number of iterations = 250

Relative Function Convergence has been set to: 1e-008

Parameter Convergence has been set to: 1e-008

Default Initial Parameter Values 

Background = 0.0312973

Beta(1) = 0.00053218

Asymptotic Correlation Matrix of Parameter Estimates

Background Beta(1)

Background 1 -0.73

Beta(1) -0.73 1

Parameter Estimates

95.0% Wald Confidence Interval

Variable Estimate Std. Err. Lower Conf. Limit Upper Conf. 

Limit

Background 0.039023 0.127636 -0.21114 0.289186

Beta(1) 0.000503605 0.000358293 -0.000198637 0.00120585

Analysis of Deviance Table 

Model Log(likelihoo

d)

# 

Param's

Deviance Test d.f. P-value

Full model -60.5216 3

Fitted 

model

-60.5898 2 0.136394 1 0.7119

Reduced 

model

-67.2168 1 13.3904 2 0.001237

 AIC: 125.18 
C-6 

Goodness of Fit 

 Scaled 

Dose Est._Prob. Expected Observed Size Residual

0.0000 0.0390 1.912 2 49 0.065

305.1000 0.1759 8.795 8 50 -0.295

608.3000 0.2926 14.337 15 49 0.208

 

Chi^2 = 0.13 d.f. = 1 P-value = 0.7136

Benchmark Dose Computation

Specified effect = 0.124

Risk Type = Extra risk 

Confidence level = 0.95

BMD = 262.883

BMDL = 177.57

BMDU = 464.193

Taken together, (177.57 , 464.193) is a 90% two-sided confidence interval for 

the BMD

Cancer Slope Factor = 0.000698317

0

0.1

0.2

0.3

0.4

0.5

0 100 200 300 400 500 600

dose

Cancer Model with 0.95 Confidence Level

00:51 12/01 2005

BMDL BMD

 

Cancer

Linear extrapolation
C-7 

Neoplastic Nodules in the Liver of Female Rats

In the rat chronic study (NTP, 1986), there was also a dose-dependent increase in the 

incidences of neoplastic nodules in the livers of female rats. The incidences of the lesion were 

1/50, 3/49, and 9/50 for control, low dose, and high dose, respectively. The original oral doses 

were 0, 1,200, and 2,550 mg/kg-day, and the corresponding HEDs are 0, 292.2, and 618.4 mg/kgday, respectively. The modeling results are summarized in Table C-3. 

Table C-3. Summary of BMD modeling results for increases in neoplastic 

nodules in the liver of female rats 

Model

Goodness-of-fit 

p value AIC ED4.2 LED4.2

Multistage 0.44 84.15 171 103

 Source: NTP (1986). 

The low-dose group resulted in an incidence of 3/49, which corresponds to 4.2% extra 

risk. Therefore, the cancer ED at an extra risk of 4.2% was estimated to be 171 mg/kg-day, and 

the corresponding LED is 103 mg/kg-day. The slope factor at the 4.2% extra risk is 0.0004 per 

mg/kg-day. 
C-8 

Neoplastic Nodules in the Liver of Female Rats (NTP, 1986)

BMR=4.2% extra risk

==================================================================== 

 Cancer Model. (Version: 1.2; Date: 10/20/2005) 

 Input Data File: C:\BMDS140B\UNSAVED1.(d) 

 Gnuplot Plotting File: C:\BMDS140B\UNSAVED1.plt

Thu Dec 01 01:12:25 2005

==================================================================== 

BMDS MODEL RUN 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The form of the probability function is: 

P[response] = background + (1-background)*[1-EXP(-beta1*dose^1)]

The parameter betas are restricted to be positive

Dependent variable = response

Independent variable = dose

Total number of observations = 3

Total number of records with missing values = 0

Total number of parameters in model = 2

Total number of specified parameters = 0

Degree of polynomial = 1

Maximum number of iterations = 250

Relative Function Convergence has been set to: 1e-008

Parameter Convergence has been set to: 1e-008

Default Initial Parameter Values 

Background = 0.00569581

Beta(1) = 0.000290683

Asymptotic Correlation Matrix of Parameter Estimates

Background Beta(1)

Background 1 -0.73

Beta(1) -0.73 1

Parameter Estimates

 95.0% Wald 

Confidence Interval

Variable Estimate Std. Err. Lower Conf. Limit Upper Conf. 

Limit

Background 0.0173602 0.122542 -0.222817 0.257538

Beta(1)

0.000250587

0.000317551 -0.000371802 0.000872976

 Analysis of Deviance Table 

Model Log(likelihood

)

# 

Param's

Deviance Test 

d.f.

P-value

Full model -39.7575 3

Fitted model -40.074 2 0.633004 1 0.4263

Reduced model -44.1226 1 8.73022 2 0.01271

 AIC: 84.148 
C-9 

Goodness of Fit 

 Scaled 

Dose Est._Prob. Expected Observed Size Residual

0.0000 0.0174 0.868 1 50 0.143

292.2000 0.0867 4.250 3 49 -0.635

618.4000 0.1584 7.921 9 50 0.418

Chi^2 = 0.60 d.f. = 1 P-value = 0.4394

Benchmark Dose Computation

Specified effect = 0.042

Risk Type = Extra risk 

Confidence level = 0.95

BMD = 171.228

BMDL = 103.205

BMDU = 388.232

Taken together, (103.205, 388.232) is a 90% two-sided confidence interval for 

the BMD

Cancer Slope Factor = 0.000406959

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 100 200 300 400 500 600

dose

Cancer Model with 0.95 Confidence Level

01:12 12/01 2005

BMDL BMD

 

Cancer

Linear extrapolation
C-10 

Neoplastic Nodules and Carcinomas (Combined) in the Liver of Female Rats 

The data (1/50, 5/49, and 9/50 for control, low dose, and high dose, respectively) on 

neoplastic nodules or carcinomas (combined) in the liver of female rats treated with decaBDE 

(NTP, 1986) were also modeled. The original oral doses were 0, 1,200, and 2,550 mg/kg-day, 

and the corresponding HEDs are 0, 292.2, and 618.4 mg/kg-day, respectively. The modeling 

results are summarized in Table C-4. 

Table C-4. Summary of BMD modeling results for increases in neoplastic 

nodules and carcinomas (combined) in the liver of female rats 

Model

Goodness-of-fit 

p value AIC ED8.4 LED8.4

Multistage 0.96 93.24 301 186

 Source: NTP (1986). 

The low-dose group resulted in an incidence of 5/49, which corresponds to 8.4% extra 

risk. Therefore, the cancer ED at an extra risk of 8.4% was estimated to be 301 mg/kg-day, and 

the corresponding LED is 186 mg/kg-day. The slope factor at the 8.4% extra risk is 0.0005 per 

mg/kg-day.
C-11 

Neoplastic Nodules and Carcinomas (Combined) in the Liver of Female Rats 

(NTP, 1986) 

BMR=8.4% extra risk

==================================================================== 

 Cancer Model. (Version: 1.2; Date: 10/20/2005) 

 Input Data File: C:\BMDS140B\UNSAVED1.(d) 

 Gnuplot Plotting File: C:\BMDS140B\UNSAVED1.plt

Thu Dec 01 01:23:38 2005

==================================================================== 

BMDS MODEL RUN 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The form of the probability function is: 

P[response] = background + (1-background)*[1-EXP(-beta1*dose^1)]

The parameter betas are restricted to be positive

Dependent variable = response

Independent variable = dose

Total number of observations = 3

Total number of records with missing values = 0

Total number of parameters in model = 2

Total number of specified parameters = 0

Degree of polynomial = 1

Maximum number of iterations = 250

Relative Function Convergence has been set to: 1e-008

Parameter Convergence has been set to: 1e-008

Default Initial Parameter Values 

Background = 0.0211024

Beta(1) = 0.000288051

Asymptotic Correlation Matrix of Parameter Estimates

Background Beta(1)

Background 1 -0.75

Beta(1) -0.75 1

Parameter Estimates

95.0% Wald Confidence Interval

Variable Estimate Std. Err. Lower Conf. Limit Upper Conf. 

Limit

Background 0.0202022 0.128079 -0.230828 0.271232

Beta(1) 0.000291122 0.000344031 -0.000383167 0.00096541

Analysis of Deviance Table 

Model Log(likelihood) # Param's Deviance Test 

d.f.

P-value

Full model -44.6193 3

Fitted model -44.6208 2 0.0030289

1

1 0.9561

Reduced 

model

-48.6567 1 8.07484 2 0.01764

 AIC: 93.2416 
C-12 

Goodness of Fit 

Scaled 

Dose Est._Prob. Expected Observed Size Residual

0.0000 0.0202 1.010 1 50 -0.010

292.2000 0.1001 4.905 5 49 0.045

618.4000 0.1816 9.081 9 50 -0.030

Chi^2 = 0.00 d.f. = 1 P-value = 0.9560

Benchmark Dose Computation

Specified effect = 0.084

Risk Type = Extra risk 

Confidence level = 0.95

BMD = 301.382

BMDL = 186.131

BMDU = 676.695

Taken together, (186.131, 676.695) is a 90% two-sided confidence interval for 

the BMD

Cancer Slope Factor = 0.000451296

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 100 200 300 400 500 600

dose

Cancer Model with 0.95 Confidence Level

01:23 12/01 2005

BMDL BMD

 

Cancer

Linear extrapolation
C-13 

Thyroid Follicular Cell Hyperplasia in Male Mice 

In the mouse chronic study (NTP, 1986), there were slight increases in follicular cell 

adenomas or carcinomas (combined) accompanied by significant increase in follicular cell 

hyperplasia in male mice. Because the follicular cell hyperplasia is considered a stage of the 

thyroid cell carcinogenic process, this endpoint was also modeled as a cancer endpoint. 

Therefore, the data (2/50, 10/50, and 19/50 for control, low dose, and high dose, respectively) on 

follicular cell hyperplasia in the thyroid of male mice treated with decaBDE (NTP, 1986) were 

modeled. The original oral doses were 0, 3,200, and 6,650 mg/kg-day, and the corresponding 

HEDs are 0, 486.5, and 1,008.6 mg/kg-day, respectively. The modeling results are summarized 

in Table C-5. 

Table C-5. Summary of BMD modeling results for increases in thyroid 

follicular cell hyperplasia as a key event of thyroid tumor in male mice 

Model

Goodness-of-fit 

p value AIC ED16.7 LED16.7

Multistage 0.75 137.34 440 313

 Source: NTP (1986). 

The low-dose group resulted in an incidence of 10/50, which corresponds to 16.7% extra 

risk. Therefore, the cancer ED at an extra risk of 16.7% was estimated to be 440 mg/kg-day, and 

the corresponding LED is 313 mg/kg-day. The slope factor at the 16.7% extra risk is 0.0005 per 

mg/kg-day. 
C-14 

Thyroid Follicular Cell Hyperplasia in Male Mice (NTP, 1986) 

BMD:16.7%

 ==================================================================== 

 Cancer Model. (Version: 1.2; Date: 10/20/2005) 

 Input Data File: C:\BMDS140B\UNSAVED1.(d) 

 Gnuplot Plotting File: C:\BMDS140B\UNSAVED1.plt 

 Thu Dec 01 01:32:16 2005 

 ==================================================================== 

 BMDS MODEL RUN 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 

The form of the probability function is: 

P[response] = background + (1-background)*[1-EXP(-beta1*dose^1)] 

The parameter betas are restricted to be positive 

Dependent variable = response 

Independent variable = dose 

Total number of observations = 3 

Total number of records with missing values = 0 

Total number of parameters in model = 2 

Total number of specified parameters = 0 

Degree of polynomial = 1 

Maximum number of iterations = 250 

Relative Function Convergence has been set to: 1e-008 

Parameter Convergence has been set to: 1e-008 

Default Initial Parameter Values 

Background = 0.0304923 

Beta(1) = 0.000434152 

Asymptotic Correlation Matrix of Parameter Estimates 

Background Beta(1) 

Background 1 -0.72 

Beta(1) -0.72 1 

Parameter Estimates 

95.0% Wald Confidence Interval 

Variable Estimate Std. Err. Lower Conf. Limit Upper Conf. 

Limit

Background 0.0386341 0.126668 -0.209631 0.2869

Beta(1)

0.000415702

0.000222182 -1.97658e-005 0.00085117

Analysis of Deviance Table 

Model Log(likelihood) # Param's Deviance Test 

d.f.

P-value

Full model -66.6205 3

Fitted model -66.6699 2 0.0987661 1 0.7533

Reduced 

model

-76.426 1 19.6109 2 <.0001

 AIC: 137.34 
C-15 

Goodness of Fit 

 Scaled 

Dose Est._Prob. Expected Observed Size Residual

0.0000 0.0386 1.932 2 50 0.050

486.5000 0.2147 10.733 10 50 -0.252

1008.6000 0.3679 18.394 19 50 0.178

Chi^2 = 0.10 d.f. = 1 P-value = 0.7544

Benchmark Dose Computation

Specified effect = 0.167

Risk Type = Extra risk 

Confidence level = 0.95

BMD = 439.549

BMDL = 313.299

BMDU = 685.676

Taken together, (313.299, 685.676) is a 90% two-sided confidence interval for 

the BMD

Cancer Slope Factor = 0.000533037

0

0.1

0.2

0.3

0.4

0.5

0 200 400 600 800 1000

dose

Cancer Model with 0.95 Confidence Level

01:32 12/01 2005

BMDL BMD

 

Cancer

Linear extrapolation
C-16 

Combined Incidence of Hepatocellular Adenomas or Carcinomas in Male Mice

In the mouse chronic study (NTP, 1986), there were significant increases in combined 

hepatocellular adenomas or carcinomas in male mice. Therefore, the data (8/50, 22/50, and 

18/50 for control, low dose, and high dose, respectively) on combined hepatocellular adenomas 

or carcinomas of male mice treated with decaBDE (NTP, 1986) were modeled. The original 

oral doses were 0, 3200, and 6650 mg/kg-day, and the corresponding HEDs are 0, 486.5, and 

1008.6 mg/kg-day, respectively. The modeling results are summarized in Table C-6. 

Table C-6. Summary of BMD modeling results for increases in combined 

hepatocellular adenomas or carcinomas in male mice 

Model

Goodness-of-fit 

p value AIC ED33.3 LED33.3

Multistage 0.03 186.5 1154 680

 Source: NTP (1986). 

The low-dose group resulted in an incidence of 22/50, which corresponds to 33.3% extra 

risk. Therefore, the cancer ED at an extra risk of 33.3% was estimated to be 1,154 mg/kg-day, 

and the corresponding LED is 680 mg/kg-day. The slope factor at the 33.3% extra risk is 0.0005 

per mg/kg-day. 
C-17 

Combined Incidence of Hepatocellular Adenomas or Carcinomas in Male Mice 

(NTP, 1986) 

BMR=33.3% extra risk

==================================================================== 

 Cancer Model. (Version: 1.2; Date: 10/20/2005) 

 Input Data File: C:\BMDS140B\UNSAVED1.(d) 

 Gnuplot Plotting File: C:\BMDS140B\UNSAVED1.plt

Thu Dec 01 01:47:16 2005

==================================================================== 

BMDS MODEL RUN 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The form of the probability function is: 

P[response] = background + (1-background)*[1-EXP(-beta1*dose^1)]

The parameter betas are restricted to be positive

Dependent variable = response

Independent variable = dose

Total number of observations = 3

Total number of records with missing values = 0

Total number of parameters in model = 2

Total number of specified parameters = 0

Degree of polynomial = 1

Maximum number of iterations = 250

Relative Function Convergence has been set to: 1e-008

Parameter Convergence has been set to: 1e-008

 Default Initial Parameter Values 

 Background = 0.235837

 Beta(1) = 0.000263218

Asymptotic Correlation Matrix of Parameter Estimates

Background Beta(1)

Background 1 -0.77

Beta(1) -0.77 1

Parameter Estimates

95.0% Wald Confidence Interval

Variable Estimate Std. Err. Lower Conf. Limit Upper Conf. 

Limit

Background 0.19695 0.125592 -0.0492049 0.443105

Beta(1) 0.000350822 0.00026836 -0.000175153 0.000876797

Analysis of Deviance Table 

Model Log(likelihood) # Param's Deviance Test 

d.f.

P-value

Full model -88.9509 3

Fitted model -91.2692 2 4.63657 1 0.0313

Reduced 

model

 -94.0304 1 10.159 2 0.006223

Goodness of Fit 

Scaled 

Dose Est._Prob. Expected Observed Size Residual

0.0000 0.1970 9.848 8 50 -0.657

486.5000 0.3230 16.148 22 50 1.770

1008.6000 0.4363 21.813 18 50 -1.087
C-18 

Chi^2 = 4.75 d.f. = 1 P-value = 0.0293 

Benchmark Dose Computation

Specified effect = 0.333

Risk Type = Extra risk 

Confidence level = 0.95

BMD = 1154.33

BMDL = 680.241

BMDU = 3796.73

Taken together, (680.241, 3796.73) is a 90% two-sided confidence interval for 

the BMD

Cancer Slope Factor = 0.000489532

0.1

0.2

0.3

0.4

0.5

0.6

0 200 400 600 800 1000 1200

dose

Cancer Model with 0.95 Confidence Level

01:47 12/01 2005

BMDL BMD

 

Cancer

Linear extrapolation