United States
Environmental Protection
1=1 m m Agency
EPA/690/R-14/003F
Final
7-10-2014
Provisional Peer-Reviewed Toxicity Values for
1,3 -Dibromobenzene
(CASRN 108-36-1)
Superfund Health Risk Technical Support Center
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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AUTHORS, CONTRIBUTORS, AND REVIEWERS
CHEMICAL MANAGERS
Evisabel A. Craig, PhD
National Center for Environmental Assessment, Cincinnati, OH
Q. Jay Zhao, PhD, DABT
National Center for Environmental Assessment, Cincinnati, OH
PRIMARY INTERNAL REVIEWERS
Paul G. Reinhart, PhD, DABT
National Center for Environmental Assessment, Research Triangle Park, NC
Ambuja Bale, PhD, DABT
National Center for Environmental Assessment, Washington, DC
Questions regarding the contents of this document may be directed to the U.S. EPA Office of
Research and Development's National Center for Environmental Assessment, Superfund Health
Risk Technical Support Center (513-569-7300).
1
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TABLE OF CONTENTS
COMMONLY USED ABBREVIATIONS AND ACRONYMS iii
BACKGROUND 1
DISCLAIMERS 1
QUESTIONS REGARDING PPRTVs 1
INTRODUCTION 2
REVIEW OF POTENTIALLY RELEVANT DATA (NONCANCER AND CANCER) 4
HUMAN STUDIES 7
ANIMAL STUDIES 7
Oral Exposures 7
Inhalation Exposures 7
Short-Term-Duration Studies 7
OTHER DATA (SHORT-TERM TESTS, OTHER EXAMINATIONS) 8
Other Toxicity Studies (Exposures Other than Oral or Inhalation) 10
Acute Studies 10
Short-Term-Duration Studies 11
Toxicokinetics Studies 12
Genotoxicity Studies 13
DERIVATION 01 PROVISIONAL VALUES 13
DERIVATION OF ORAL REFERENCE DOSES 14
Feasibility of Deriving Subchronic and Chronic p-RfDs 14
DERIVATION OF INHALATION REFERENCE CONCENTRATIONS 14
Feasibility of Deriving Subchronic and Chronic p-RfCs 14
CANCER WEIGHT-OF-EVIDENCE DESCRIPTOR 15
DERIVATION OF PROVISIONAL CANCER RISK VALUES 15
APPENDIX A. SCREENING PROVISIONAL VALUES 16
APPENDIX B. DATA TABLES 28
APPENDIX C. BENCHMARK DOSE MODELING RESULTS 29
APPENDIX D. REFERENCES 30
li
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COMMONLY USED ABBREVIATIONS AND ACRONYMS
a2u-g
alpha 2u-globulin
MN
micronuclei
ACGIH
American Conference of Governmental
MNPCE
micronucleated polychromatic
Industrial Hygienists
erythrocyte
AIC
Akaike's information criterion
MOA
mode-of-action
ALD
approximate lethal dosage
MTD
maximum tolerated dose
ALT
alanine aminotransferase
NAG
N-acetyl-P-D-glucosaminidase
AST
aspartate aminotransferase
NCEA
National Center for Environmental
atm
atmosphere
Assessment
ATSDR
Agency for Toxic Substances and
NCI
National Cancer Institute
Disease Registry
NOAEL
no-observed-adverse-effect level
BMD
benchmark dose
NTP
National Toxicology Program
BMDL
benchmark dose lower confidence limit
NZW
New Zealand White (rabbit breed)
BMDS
Benchmark Dose Software
OCT
ornithine carbamoyl transferase
BMR
benchmark response
ORD
Office of Research and Development
BUN
blood urea nitrogen
PBPK
physiologically based pharmacokinetic
BW
body weight
PCNA
proliferating cell nuclear antigen
CA
chromosomal aberration
PND
postnatal day
CAS
Chemical Abstracts Service
POD
point of departure
CASRN
Chemical Abstracts Service Registry
POD[adj]
duration-adjusted POD
Number
QSAR
quantitative structure-activity
CBI
covalent binding index
relationship
CHO
Chinese hamster ovary (cell line cells)
RBC
red blood cell
CL
confidence limit
RDS
replicative DNA synthesis
CNS
central nervous system
RfC
inhalation reference concentration
CPN
chronic progressive nephropathy
RfD
oral reference dose
CYP450
cytochrome P450
RGDR
regional gas dose ratio
DAF
dosimetric adjustment factor
RNA
ribonucleic acid
DEN
diethylnitrosamine
SAR
structure activity relationship
DMSO
dimethylsulfoxide
SCE
sister chromatid exchange
DNA
deoxyribonucleic acid
SD
standard deviation
EPA
Environmental Protection Agency
SDH
sorbitol dehydrogenase
FDA
Food and Drug Administration
SE
standard error
FEV1
forced expiratory volume of 1 second
SGOT
glutamic oxaloacetic transaminase, also
GD
gestation day
known as AST
GDH
glutamate dehydrogenase
SGPT
glutamic pyruvic transaminase, also
GGT
y-glutamyl transferase
known as ALT
GSH
glutathione
SSD
systemic scleroderma
GST
glutathione -S -transferase
TCA
trichloroacetic acid
Hb/g-A
animal blood-gas partition coefficient
TCE
trichloroethylene
Hb/g-H
human blood-gas partition coefficient
TWA
time-weighted average
HEC
human equivalent concentration
UF
uncertainty factor
HED
human equivalent dose
UFa
interspecies uncertainty factor
i.p.
intraperitoneal
UFh
intraspecies uncertainty factor
IRIS
Integrated Risk Information System
UFS
subchronic-to-chronic uncertainty factor
IVF
in vitro fertilization
UFd
database uncertainty factor
LC50
median lethal concentration
U.S.
United States of America
LD50
median lethal dose
WBC
white blood cell
LOAEL
lowest-observed-adverse-effect level
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PROVISIONAL PEER-REVIEWED TOXICITY VALUES FOR
1,3-DIBROMOBENZENE (CASRN 108-36-1)
BACKGROUND
A Provisional Peer-Reviewed Toxicity Value (PPRTV) is defined as a toxicity value
derived for use in the Superfund Program. PPRTVs are derived after a review of the relevant
scientific literature using established Agency guidance on human health toxicity value
derivations. All PPRTV assessments receive internal review by a standing panel of National
Center for Environment Assessment (NCEA) scientists and an independent external peer review
by three scientific experts.
The purpose of this document is to provide support for the hazard and dose-response
assessment pertaining to chronic and subchronic exposures to substances of concern, to present
the major conclusions reached in the hazard identification and derivation of the PPRTVs, and to
characterize the overall confidence in these conclusions and toxicity values. It is not intended to
be a comprehensive treatise on the chemical or toxicological nature of this substance.
The PPRTV review process provides needed toxicity values in a quick turnaround
timeframe while maintaining scientific quality. PPRTV assessments are updated approximately
on a 5-year cycle for new data or methodologies that might impact the toxicity values or
characterization of potential for adverse human health effects and are revised as appropriate. It is
important to utilize the PPRTV database (http://hhpprtv.ornl.gov) to obtain the current
information available. When a final Integrated Risk Information System (IRIS) assessment is
made publicly available on the Internet (www.epa.gov/iris). the respective PPRTVs are removed
from the database.
DISCLAIMERS
The PPRTV document provides toxicity values and information about the adverse effects
of the chemical and the evidence on which the value is based, including the strengths and
limitations of the data. All users are advised to review the information provided in this
document to ensure that the PPRTV used is appropriate for the types of exposures and
circumstances at the site in question and the risk management decision that would be supported
by the risk assessment.
Other U.S. Environmental Protection Agency (EPA) programs or external parties who
may choose to use PPRTVs are advised that Superfund resources will not generally be used to
respond to challenges, if any, of PPRTVs used in a context outside of the Superfund program.
QUESTIONS REGARDING PPRTVs
Questions regarding the contents and appropriate use of this PPRTV assessment should
be directed to the EPA Office of Research and Development's National Center for
Environmental Assessment, Superfund Health Risk Technical Support Center (513-569-7300).
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INTRODUCTION
1,3-Dibromobenzene (CASRN 108-36-1), also known as meta-dibromobenzene
(w-dibromobenzene), appears as a clear, colorless to light-yellow liquid. It is used in various
organic syntheses. 1,3-Dibromobenzene is an irritant that can cause inflammation and burns to
the eyes and skin. It is stable but flammable and its combustion can lead to irritating, corrosive,
and/or toxic fumes. The molecular formula of 1,3-dibromobenzene is CtsFUBri (see Figure 1).
Table 1 provides a list of its physicochemical properties.
Br
Figure 1. Structure of 1,3-Dibromobenzene
Table 1. Physicochemical Properties of 1,3-Dibromobenzene (CASRN 108-36-1)
Property (unit)
Value
Boiling point (°C)
218-2193
Melting point (°C)
-T
Density at 25°C (g/inL)
1.9523
Log P (unitless)
3.75b
Vapor pressure (mm Hg at 25 °C)
0.269b
pH (unitless)
Not available
Solubility in water (mg/L at 35°C)
67.5b
Relative vapor density (air = 1)
8.16a
Molecular weight (g/mol)
235.9a
aChemicalBook (accessed on 7-22-2013).
bNLM (accessed on 7-22-2013).
A summary of available toxicity values for 1,3-dibromobenzene from U.S. EPA and
other agencies/organizations is provided in Table 2.
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Table 2. Summary of Available Toxicity Values for 1,3-Dibromobenzene
(CASRN 108-36-1)
Source/Parameter3
Value
(Applicability)
Notes
Reference
Date
Accessed
Noncancer
ACGIH
NV
NA
ACGIH (2013)
N/A
ATSDR
NV
NA
ATSDR (2013)
N/A
Cal/EPA
NV
NA
Cal/EPA (2014.
2013)
4-17-2014b
NIOSH
NV
NA
NIOSH (2010)
NA
OSHA
NV
NA
OSHA (2011.
2006s)
NA
IRIS
NV
NA
U.S. EPA
4-17-2014
Drinking water
NV
NA
U.S. EPA
(2012a)
NA
HEAST
NV
NA
U.S. EPA
(2011a)
NA
CARA HEEP
NV
Noncancer toxicity values were not
derived due to inadequate
noncancer data and lack of
carcinogenicity studies on the
chemical.
U.S. EPA (1994)
NA
WHO
NV
NA
WHO
4-14-2014
Cancer
IRIS
NV
NA
U.S. EPA
4-14-2014
HEAST
NV
NA
U.S. EPA
(2011a)
NA
IARC
NV
NA
IARC (2013)
NA
NTP
NV
NA
NTP (2011)
NA
Cal/EPA
NV
NA
Cal/EPA (2013.
2011)
NA
aSources: ACGIH = American Conference of Governmental Industrial Hygienists; ATSDR = Agency for Toxic
Substances and Disease Registry; Cal/EPA = California Environmental Protection Agency; CARA = Chemical
Assessments and Related Activities; HEAST = Health Effects Assessment Summary Tables; HEEP = Health and
Environmental Effects Profile; IARC = International Agency for Research on Cancer; IRIS = Integrated Risk
Information System; NIOSH = National Institute for Occupational Safety and Health; NTP = National
Toxicology Program; OSHA Occupational Safety and Health Administration; WHO = World Health
Organization.
bThe Cal/EPA Office of Environmental Health Hazard Assessment (OEHHA) Toxicity Criteria Database
(http ://oehha. ca. gov/tcdb/index. asp) was also reviewed and found to contain no information on
1,3 -Dibromobenzene.
NA = not applicable; NV = not available.
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Literature searches were conducted on sources published from 1900 through April 2014
for studies relevant to the derivation of provisional toxicity values for 1,3-dibromobenzene
(CASRN 108-36-1). The following databases were searched by chemical name, synonyms, or
CASRN: ACGM, ANEUPL, AT SDR, BIOSIS, Cal/EPA, CCRIS, CDAT, ChemlDplus, CIS,
CRISP, DART, EMIC, EPIDEM, ETICBACK, FEDRIP, GENE-TOX, HAPAB, HERO, HMTC,
HSDB, I ARC, INCHEM IPCS, IP A, ITER, IUCLID, LactMed, NIOSH, NTIS, NTP, OSHA,
OPP/RED, PESTAB, PPBIB, PPRTV, PubMed (toxicology subset), RISKLINE, RTECS,
TOXLINE, TRI, U.S. EPA IRIS, U.S. EPA HEAST, U.S. EPA HEEP, U.S. EPA OW, and
U.S. EPA TSCATS/TSCATS2. The following databases were searched for toxicity values or
exposure limits: ACGM, AT SDR, Cal EPA, U.S. EPA IRIS, U.S. EPA HEAST, U.S. EPA
HEEP, U.S. EPA OW, U.S. EPA TSCATS/TSCATS2, NIOSH, NTP, OSHA, and RTECS.
REVIEW OF POTENTIALLY RELEVANT DATA
(NONCANCER AND CANCER)
Table 3 provides an overview of the relevant databases for studies on
1,3-dibromobenzene and includes all potentially relevant, repeated-dose, short-term-duration
studies (no sub chronic-duration or longer-term-duration studies have been located). All
statistical comparisons were made at the 5% level of statistical significance (p < 0.05), unless
noted otherwise.
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Table 3. Summary of Potentially Relevant Data for 1,3-Dibromobenzene (CASRN 108-36-1)
Category
Number of
Male/Female, Strain,
Species, Study Type,
Study Duration
Dosimetry
Critical Effects
NOAEL
BMDL/
BMCL
LOAEL
Reference
Comments
Human
1. Oral
No data
2. Inhalation
No data
Animal
1. Oral
Short-term
4-6 female Wistar
rats, gavage, 7 days
0, 70, 135,
270, or
400 mg/kg
Increased ALA-D (135- and
270-mg/kg dose groups only)
and increased ALA-S (all dose
groups except for 70 mg/kg)
activities
ND
NC
ND
Szvmanska
(1996)
No hepatic lesions were
found.
Short-term
4-6 female Wistar
rats, gavage, 28 days
0, 5, 25, or
125 mg/kg
Increased serum GGT activity
(25- and 125-mg/kg dose
groups only), and porphyrinuria
ND
NC
ND
Szvmanska
(1996)
Increased GSH level as a
compensatory effect. No
hepatic lesions were
observed.
Subchronic
No data
Chronic
No data
Developmental
No data
Reproductive
No data
Carcinogenic
No data
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Table 3. Summary of Potentially Relevant Data for 1,3-Dibromobenzene (CASRN 108-36-1)
Category
Number of
Male/Female, Strain,
Species, Study Type,
Study Duration
Dosimetry
Critical Effects
NOAEL
BMDL/
BMCL
LOAEL
Reference
Comments
2. Inhalation
No data
ALA-D = delta-aminolevulinate dehydratase; ALA-S = delta-aminolevulinate synthase; GGT = L-y-glutamyltransferase; GSH = glutathione; NC = not calculated;
ND = not determined.
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HUMAN STUDIES
No studies have been identified.
ANIMAL STUDIES
No sub chronic-duration, chronic-duration, developmental toxicity, reproductive toxicity,
or carcinogenicity studies on 1,3-dibromobenzene exposure (via the oral or inhalation route)
were identified. A few short-term-duration gavage studies were located and are discussed below.
Oral Exposures
The effects of oral exposure of animals to 1,3-dibromobenzene via gavage have been
evaluated in two short-term-duration, repeated-dose toxicity studies (Szymanska. 1996).
Inhalation Exposures
No studies have been identified.
Short-Term-Duration Studies
Szymanska (1996)
In a 7-day repeated-dose study, Szymanska (1996) administered daily doses of
1,3-dibromobenzene via gavage. Female Wistar rats (4-6 per dose group) were treated with 0,
70, 135, 270, or 400 mg/kg of 1,3-dibromobenzene or l,3-dibromo[3H]-benzene (purity not
specified) in sunflower oil. The control group received either sunflower oil or no gavage.
Animals were sacrificed 24 hours after the administration of the seventh dose and the liver was
excised for histological examination as well as to determine enzyme levels. The activity of
alanine aminotransaminase (ALT) and L-y-glutamyltransferase (GGT) were determined in
serum. The levels of glutathione (GSH) and malondialdehyde (MDA) as well as the activity of
5-aminolevulinate dehydratase (ALA-D) and synthase (ALA-S) were determined in liver. The
study author reported a 50% increase in liver GSH for the 70-mg/kg dose group. In addition,
ALT activity did not correlate with the change in GSH levels. There was a statistically
significant increase of ALT in the 270-mg/kg dose group only. The activities of ALA-D
(135- and 270-mg/kg dose groups only) and ALA-S (all dose groups except for 70 mg/kg) also
increased. There were no statistically significant changes in GGT activity or MDA levels. No
hepatic lesions were observed.
In another short-term-duration (28-day repeated-dose) study, Szymanska (1996)
administered daily doses of 1,3-dibromobenzene via gavage. Female Wistar rats (4-6 per dose
group) were treated with 0, 5, 25, or 125 mg/kg of 1,3-dibromobenzene (purity not specified) in
each dose group. The control group received either sunflower oil alone or no gavage. Control
animals were kept in two types of cages: (1) metabolic cages (n = 14; Control Group 1) and
(2) normal breeding cages (n = 21; Control Group 2). Treated animals were kept in metabolic
cages beginning at 24 hours before the start of the investigation. Animals were sacrificed 24
hours after the administration of 7, 14, 21, or 28 doses. Livers were excised for histological
examination and to determine enzyme levels. Increased GSH levels were observed in the
125-mg/kg dose group starting on Day 7. There was also a statistically significant increase in
GGT activity for the mid- and high-dose groups. ALT activity did not change significantly in
any of the dose groups. There was no statistically significant change in ALA-D in any of the
dose groups on Day 28 (some statistically significant changes on Day 7 only). For ALA-S, a
statistically significant decrease was observed in the 5-mg/kg dose group only. For liver MDA
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concentrations, the results were ambiguous in terms of the types of control groups used. Control
Group 1 had much higher MDA levels than Control Group 2. All test groups had lower MDA
concentrations than Control Group 1 and higher MDA concentrations than Control Group 2. The
study author concluded that the change in MDA concentrations was likely a stress-induced effect
due to the changing of cages rather than treatment related. No hepatic lesions were observed.
In addition to the liver parameters mentioned above, Szymanska (1996) also examined
liver iron levels and concentrations of 5-animolevulinic acid (ALA-U) and porphyrins in urine.
There were no significant changes in iron concentrations in the rat liver in any of the dose
groups. At the end of Week 4, however, there was a statistically significant decrease of excreted
ALA-U in urine for the 25-mg/kg dose group. The study author also observed that several
urinary porphyrins (i.e., tetracarboxy-, pentacarboxy-, and heptacarboxyporphyrins) were
increased following repeated exposure to 1,3-dibromobenzene (Day 28), mostly at the higher
doses. Because increased porphyrins were not accompanied by an increased excretion of
ALA-U, the study author concluded that short-term exposure to 1,3-dibromobenzene produced
porphyrinuria only and not porphyria in rats. Due to the short duration and differences observed
between the two control groups, the 7-day and 28-day studies by Szymanska (1996) are not
suitable for the derivation of a provisional reference dose (p-RfD). The study author did not
identify any effect levels or median lethal dose (LD50) values, and neither a NOAEL nor a
LOAEL are determined for this PPRTV assessment.
OTHER DATA (SHORT-TERM TESTS, OTHER EXAMINATIONS)
Other studies that examined 1,3-dibromobenzene but are not appropriate for the selection
of a point of departure (POD) are described here. These studies are not adequate for the
determination of p-RfD, provisional reference concentration (p-RfC), provisional oral slope
factor (p-OSF), or provisional inhalation unit risk (p-IUR) values but provide supportive data
supplementing a weight-of-evidence (WOE) approach. These may include genotoxicity,
metabolism/toxicokinetic, and studies using routes of exposure other than the oral or inhalation
route (see Table 4).
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Table 4. Other Studies
Test
Materials and Methods
Results
Conclusions
References
Other toxicity
studies
(exposures other
than
oral or
inhalation)
Male BALB/c mice
(4-12 per dose group);
single i.p. injection (0, 150,
300, or 600 mg/kg) of 1,2-,
1,3- ,or 1,4-dibromobenzene.
Decreased glutathione (GSH) and increased malondialdehyde
(MDA) levels in liver; increased gamma-glutamyltransferase
(GGT) activities with all three isomers.
Increased serum glutamate pyruvate transaminase (GPT) and
hepatic necrosis in the central lobular zone with 1,2- and
1,3-dibromobenzene but not 1,4-dibromobenzene.
1,2- and 1,3-Dibromobenzene
appear to have more pronounced
effects on the liver than
1,4-dibromobenzene.
Szvmanska et al.
(1996)
Female Wistar rats (4-6 per
dose group); single i.p.
injection (0, 40, 100, 300, or
600 mg/kg) of
1,3 -dibromobenzene.
Reduced GSH levels, increased alanine aminotransferase (ALT)
and GGT activities, and increased MDA concentration (two
highest dose groups only).
This study did not indicate whether the liver was histologically
examined.
1,3-Dibromobenzene induces liver
enzyme changes in rats.
Szvmanska
(1996)
Male Outbred Imp BALB/c
mice (4-12 per dose group);
single i.p. injection (0, 150,
300, or 600 mg/kg) of 1,2,4-
or 1,3,5-tribromobenzene,
1,2,4,5 -tetrabromobenzene,
bromobenzene, or
hexabromobenzene.
Results from this study were compared to those from a previous
studv with dibromobenzenes (Szvmanska et al.. 1996).
All brominated compounds decreased liver GSH levels and
increased GGT activity as well as MDA levels in the liver, but
these effects were more pronounced with dibromobenzenes and
bromobenzene.
The acute hepatotoxicity of
bromobenzenes decreases with the
increase in the number of bromine
atoms.
Szvmanska
(1998)
Male BALB/c mice (4-5 per
dose group); i.p. injection (0,
30, 60, 80, or 140 mg/kg) of
1,3-dibromobenzene or
seven other brominated
benzenes for 7 days.
Increased relative liver weight (liver-to-body weight ratio) and
increased MDA concentration in all brominated benzenes.
Steatosis was observed for some brominated benzenes but not
for 1,3-dibromobenzene.
Liver effects were observed
following repeated exposure to
brominated benzenes.
Szvmanska et al.
(1998)
Metabolism/
Toxicokinetic
Female Outbred IMP:Wist
rats (4 per dose group);single
i.p. injection (100 or
300 mg/kg) of
1,3-dibromobenzene (no
controls identified).
An average of 79.3% of 1,3-dibromobenzene and its
metabolites was excreted in urine. The highest concentration
of 1,3-dibromobenzene was found in the liver, kidneys, and fat
tissue.
Urine is the main route of
excretion for 1,3-dibromobenzene.
Saoota et al.
(1999)
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Other Toxicity Studies (Exposures Other than Oral or Inhalation)
The effects of intraperitoneal (i.p.) exposure of animals to 1,3-dibromobenzene have been
evaluated in three acute, single-injection studies (Szymanska. 1998. 1996; Szymanska et al..
1996) and one short-term-duration, repeated-injection study. The results are reported in
Szymanska et al. (1998) and Szymanska (1996).
Acute Studies
Szymanska et al. (1996)
Szymanska et al. (1996) conducted an acute toxicity study of 1,2-, 1,3-, and
1,4-dibromobenzene isomers in male BALB/c mice. Single doses of 0, 150, 300, or 600 mg/kg
in sunflower oil (purity not reported) were administered to 4-12 male mice per dose group by
i.p. injection. The control group (n = 28-30) received no injections or were injected with
sunflower oil only. Livers were removed and blood was collected at different time intervals: 2,
4, 12, 24, 48, 72, and 120 hours after injection. Treatment-related effects included decreased
GSH levels in the first 24 hours after administration at the two highest doses (up to
90% decrease), a statistically significant increase in MDA in the liver, and increases in GGT in
all three isomers. Increased GPT activities and an increase in the incidence of hepatic necrosis
(as determined in histopathology) were observed with 1,2- and 1,3-dibromobenzene but not
1,4-dibromobenzene. The results of this study indicated that all three isomers are acutely
hepatotoxic, with 1,3- and 1,2-dibromobenzene being more toxic (based on more pronounced
incidences of hepatic necrosis in the central lobular zone) than 1,4-dibromobenzene (no
statistically significant change from the control group; caused necrosis only in individual
hepatocytes). Neither effect levels nor LDsos were determined by the study authors.
Szymanska (1996)
In addition to the short-term-duration oral studies in rats, Szymanska (1996) conducted
an acute single-dose study. Female Wistar rats (4-6 per dose group) were administered 0, 40,
100, 300, or 600 mg/kg of 1,3-dibromobenzene (purity not specified) in sunflower oil by i.p.
injection. The control rats (n = 21-22) received either sunflower oil alone or no injection.
Heavy depletion of liver GSH was observed at the high doses. Even at the low doses, there was
a statistically significant decrease in GSH levels. However, GSH levels eventually went up in all
dose groups, and in some cases, increased above control levels after 24 hours of administration.
The study author stated that these increases in GSH may indicate either an adaptation or
compensatory effect. Serum ALT increased slightly within a short time after the administration
of 1,3-dibromobenzene but then fluctuated above and below control levels between 4 and
72 hours after administration. There was a statistically significant increase in GGT activity
within 4 hours. A statistically significant increase in liver MDA concentration was observed in
the highest dose group only (up to 12 hours after administration). The study author did not
indicate whether morphological examinations were conducted to detect hepatic lesions
(necrosis), as previously observed in the mouse study (Szymanska et al.. 1996). In terms of
acute hepatotoxicity, a species-specific difference (rats vs. mice) could exist; however, the study
author did not speculate on reasons for this possible difference.
Szymanska (1998)
Szymanska (1998) conducted another acute single-dose hepatotoxicity study for multiple
brominated benzenes (bromobenzene, 1,2,4-tribromobenzene, 1,3,5-tribromobenzene,
1,2,4,5-tetrabromobenzene, and hexabromobenzene) in male Outbred Imp BALB/cJ mice in an
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attempt to find a relationship between chemical structure and hepatotoxic effects. Single doses
of 0, 150, 300, or 600 mg/kg in sunflower oil (purity not reported) were administered to
4-12 male mice per dose group by i.p. injection. The control mice received either sunflower oil
alone or no injection. Similar to the other acute single-dose i.p. studies (Szymanska. 1996;
Szymanska et al.. 1996). Szymanska (1998) found that all examined compounds (i.e.,
bromobenzene, 1,2,4-tribromobenzene, 1,3,5-tribromobenzene, 1,2,4,5-tetrabromobenzene, and
hexabromobenzene) lowered liver GSH levels shortly after the administration. The results were
compared with data for dibromobenzenes (1,2-, 1,3-, and 1,4-dibromobenzene) obtained from an
earlier study (Szymanska et al.. 1996). Statistically significant changes (30- to 120-fold
increases) in ALT activity were observed for bromobenzene, 1,2-dibromobenzene,
1.3-dibromobenzene, and 1,2,4-tribromobenzene. All brominated compounds produced an
increase in GGT activity in serum and MDA concentration in the liver. As stated in the
Szymanska et al. (1996) study and summarized in Szymanska (1998). increased incidence of
hemorrhagic necrosis in the liver central lobular zone was observed for 1,3-dibromobenzene.
Finally, Szymanska (1998) concluded that in mice ".. .acute toxicity of bromobenzenes decreases
with the increase of the number of bromine atoms in the molecule" (p. 97). Neither effect levels
nor LDsos were determined.
Short-Term-Duration Studies
Szymanska et al. (1998)
In a follow-up study, Szymanska et al. (1998) conducted another short-term-duration
(7-day repeated dose) study in male BALB/c mice. Szymanska et al. (1998) reported the effects
on selected indicators of liver impairment after repeated administration of mono- and
polybromobenzenes. Szymanska et al. (1998) administered 1,3-dibromobenzene along with
seven other brominated benzenes (i.e., bromobenzene, 1,2-dibromobenzene,
1.4-dibromobenzene, 1,2,4-tribromobenzene, 1,3,5-tribromobenzene, 1,2,4,5-tetrabromobenzene,
and hexabromobenzene; purity not specified) daily via i.p. injection in sunflower oil in volumes
of 0.2 ml per 20 g body weight of mice. The mice (4-5/group) were exposed to 0, 30, 60, 80, or
140 mg/kg in each dose group. The control mice received either sunflower oil only or no
injection. Because the study authors found no difference between the control groups, they chose
the pooled controls that received no injection for comparison with other treatment groups.
Changes in relative liver weight (liver-to-body weight ratio) were observed for all brominated
benzenes.
For exposure to 1,3-dibromobenzene, relative liver weight increased in the 60-, 80-, and
140-mg/kg dose groups, but these changes were not dose dependent. For histopathological
changes, distinct steatosis in the peripheral lobular zone was observed for 1,4-dibromobenzene,
1,2,4-tribromobenzene, 1,3,5-tribromobenzene, 1,2,4,5-tetrabromobenzene, and
hexabromobenzene but not 1,3-dibromobenzene. For exposure to 1,3-dibromobenzene, the GSH
level was statistically significantly increased in the 80-mg/kg dose group only; no depletion of
the GSH level was observed in any of the dose groups (the study authors stated that this may
explain the lack of hepatic necrosis). There was also a statistically significant increase in liver
MDA level at the highest dose of 1,3-dibromobenzene (140 mg/kg). ALA-S was significantly
decreased after exposure to 1,2-dibromobenzene and 1,3-dibromobenzene. 1,4-Dibromobenzene
decreased ALA-S in the lower doses and increased ALA-S in the higher doses. For ALA-D, the
study authors claimed there were no statistically significant changes for any of the brominated
benzenes. The activity of ALT—another key indicator for necrotic changes of hepatocytes—was
not affected by any of the brominated benzenes.
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Szymanska et al. (1998) stated that there was an apparent "shift" from single exposure to
repeated exposure in terms of hepatotoxic effects, with necrosis occurring after single-dose
exposure and the less severe steatosis occurring after repeated exposure (observed for other
brominated benzenes but not observed for 1,3-dibromobenzene directly). These findings are
consistent with the interpretation by Chakrabarti (1991) that, . .repeated doses of
bromobenzene may by means of inducing microsomal enzymes and GSH levels accelerate the
process of bromobenzene metabolism and/or may intensify repair/regeneration processes in the
cell" (as cited in Szymanska et al.. 1998. p. 28). In addition, instead of necrosis in the liver and
associated increases in ALT and GGT activities in the serum observed in the acute single-dose
studies in mice, the study authors found changes in heme synthesis and subsequent
porphyrogenic effects in the repeated dose studies.
Neither effect levels nor LDsos have been identified or determined in any of the studies in
this section, and none of the studies are suitable for the derivation of a p-RfD due to the route of
administration (i.p.), study duration (<90 days), and study design (e.g., metabolic cage vs.
normal breeding cage).
Toxicokinetics Studies
Sapota et al. (1999) investigated the toxicokinetic (distribution and excretion) properties
of 1,3-dibromobenzene in rats by radiotracing. Four female Outbred IMP:Wist rats per group
were administered 100 or 300 mg/kg of l,3-dibromobenzene-[3H] (purity not specified)
dissolved in olive oil via a single i.p. injection. The use of a control group was not reported.
Metabolites were identified and quantified by gas chromatography-mass spectrometry (GC-MS)
technique. Urine was the main route of excretion, where an average of 79.3% was excreted in
urine after 72 hours at a dose of 300 mg/kg, with 10% in feces. Similar (slightly lower)
absorption and excretion rates were also found at a dose of 100 mg/kg. Tissues examined
included the liver, kidneys, lung, adrenals, sciatic nerve, spleen, heart, brain, and fat. The
highest concentrations (radioactivity) of l,3-dibromobenzene-[3H] after administration at a dose
of 100 mg/kg were found in the liver, kidneys, and fat tissue. A similar pattern was observed for
the 300-mg/kg dose group. Several metabolites isolated from urine were identified by GC-MS:
unchanged (unconjugated) 1,3-dibromobenzene (18%), dibromophenols (34%),
dibromothiophenols (28%), dibromothioanisole (1.8%), bromophenol (5.5%),
bromohydroxythiophenols (5%), and bromohydroxythioanisole (7.5%). The study authors
concluded that there are three different metabolic pathways of 1,3-dibromobenzene: (1) ring
hydroxylation (dibromophenols), (2) glutathione conjugation (dibromothiophenols and
dibromothioanisole), and (3) hydrolytic dehalogenation (bromophenol, bromohydroxythiophenol
and bromohydroxythioanisole).
The study authors observed that approximately half of the metabolism products contain
sulfur, and this finding is consistent with earlier observations (Szymanska et al.. 1996) in which
the hepatic necrotic action of 1,3-dibromobenzene was accompanied by decreased hepatic GSH
levels. The study authors also concluded that 1,3-dibromobenzene has a relatively high turnover
rate (e.g., high level of excretion in urine) with minor levels of radiotracer 3H in the tissues for
longer time periods. Finally, they stated that 1,3-dibromobenzene is an acute hepatotoxicant in
rats and is also a potential nephrotoxicant (Sapota et al.. 1999).
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In a follow-up toxicokinetic study, Szymanska et al. (2002) compared the metabolism
and tissue distribution of 1,2- and 1,4-dibromobenzene isomers in female Outbred IMP:Wist rats.
The study used a similar protocol as detailed in Sapota et al. (1999). As with
1.3-dibromobenzene, urine is also the main route of excretion for both the 1,2- and
1.4-dibromobenzene isomers. Several metabolites isolated from urine were identified by
GC-MS for the 1,2- and 1,4-dibromobenzene isomers; they included unchanged (unconjugated)
parent compound (11 and 5%), dibromophenols (73 and 84%), dibromothiophenols (10 and 5%),
and bromophenols (0.7 and 1.9%). The study authors concluded that 1,2-dibromobenzene
(82.0%) excreted in urine after 72 hours for the 100-mg/kg dose group) was similar to
1,3-dibromobenzene (66.5%> excreted in urine for the 100-mg/kg dose group) (Sapota et al..
1999) in having a higher turnover rate than 1,4-dibromobenzene, which had a longer retention
time in the body (29.6%> excreted in urine for the 70-mg/kg dose group).
Genotoxicity Studies
No studies investigating the genotoxic effects of 1,3-dibromobenzene have been
identified.
DERIVATION OF PROVISIONAL VALUES
Table 5 below presents a summary of noncancer screening oral provisional reference
values derived using a surrogate approach (see Appendix A for details). Table 6 presents a
summary of cancer values. The toxicity values have been converted to human equivalent dose
(HED) units where appropriate.
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Table 5. Summary of Noncancer Reference Values
for 1,3-Dibromobenzene (CASRN 108-36-1)
Toxicity Type
(units)
Species/Sex
Critical Effect
Screening
p-Reference
Value
POD
Method
PODhed
UFc
Principal
Study
Screening
subchronic
p-RfD
(mg/kg-day)a
Rat/Male
Increased relative
liver weight and
hepatic
microsomal
enzyme induction
4 x 1(T3
NOAEL
1.2
300
Carlson
and Tardiff
(\ 977)
Screening
chronic p-RfD
(mg/kg-day)''
Rat/Male
Increased relative
liver weight and
hepatic
microsomal
enzyme induction
4 x 1(T4
NOAEL
1.2
3,000
Carlson
and Tardiff
(1977)
Subchronic
p-RfC
(mg/m3)
NDr
Chronic p-RfC
(mg/m3)
NDr
aA surrogate approach was applied. See Appendix A.
NDr = not determined
Table 6. Summary of Cancer Values for 1,3-Dibromobenzene (CASRN 108-36-1)
Toxicity Type
Species/Sex
Tumor Type
Cancer Value
Principal Study
p-OSF
None
p-IUR
None
DERIVATION OF ORAL REFERENCE DOSES
Feasibility of Deriving Subchronic and Chronic p-RfDs
No sub chronic-duration, chronic-duration, developmental toxicity, reproductive toxicity,
or carcinogenicity studies on 1,3-dibromobenzene exposure via the oral route were identified.
However, Appendix A of this document contains screening values (screening subchronic and
chronic p-RfDs) using a surrogate (e.g., structural and metabolic) approach, which may be of use
under certain circumstances. Please see Appendix A for details regarding the screening values.
DERIVATION OF INHALATION REFERENCE CONCENTRATIONS
Feasibility of Deriving Subchronic and Chronic p-RfCs
No sub chronic-duration, chronic-duration, developmental toxicity, reproductive toxicity,
or carcinogenicity studies on 1,3-dibromobenzene exposure via the inhalation route were
identified. No inhalation toxicity data have been identified for the derivation of a p-RfC for
1,3-dibromobenzene. Furthermore, no inhalation toxicity data were identified for any of the
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potential surrogates for 1,3-dibromobenzene, thus precluding derivation of screening subchronic
and chronic p-RfCs.
CANCER WEIGHT-OF-EVIDENCE DESCRIPTOR
Table 7 identifies the cancer WOE descriptor for 1,3-dibromobenzene (in bold).
Table 7. Cancer WOE Descriptor for 1,3-Dibromobenzene (CASRN 108-36-1)
Possible WOE
Descriptor
Designation
Route of Entry (Oral,
Inhalation, or Both)
Comments
"Carcinogenic to
Humans "
NA
NA
No studies pertaining to the carcinogenicity of
1,3-dibromobenzene in humans are available.
"Likely to be
Carcinogenic to
Humans "
NA
NA
No studies pertaining to the carcinogenicity of
1,3-dibromobenzene in multiple species of
animals are available.
"Suggestive
Evidence of
Carcinogenic
Potential"
NA
NA
No data are available regarding the
carcinogenic potential of 1,3-dibromobenzene
even in a single animal species.
"Inadequate
Information to
Assess
Carcinogenic
Potential"
Selected
Both
There is no pertinent information available
to assess the carcinogenic potential of
1,3-dibromobenzene.
"Not Likely to be
Carcinogenic to
Humans "
NA
NA
No data are available to suggest that
1,3-dibromobenzene is not likely to be a
carcinogen in humans following oral or
inhalation exposure.
NA= not applicable.
DERIVATION OF PROVISIONAL CANCER RISK VALUES
The lack of quantitative data on the carcinogenicity of 1,3-dibromobenzene precludes the
derivation of a quantitative estimate of cancer risk for either oral (p-OSF) or inhalation (p-IUR)
exposures.
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APPENDIX A. SCREENING PROVISIONAL VALUES
For reasons noted in the main provisional peer-reviewed toxicity value (PPRTV)
document, it is inappropriate to derive provisional toxicity values for 1,3-dibromobenzene.
However, information is available for a related chemical, which although insufficient to support
derivation of a provisional toxicity value under current guidelines, may be of limited use to risk
assessors. In such cases, the Superfund Health Risk Technical Support Center summarizes
available information in an appendix and develops a "screening value." Appendices receive the
same level of internal and external scientific peer review as the PPRTV documents to ensure
their appropriateness within the limitations detailed in the document. Users of screening toxicity
values in an appendix to a PPRTV assessment should understand that there is considerably more
uncertainty associated with the derivation of an appendix screening toxicity value than for a
value presented in the body of the assessment. Questions or concerns about the appropriate use
of screening values should be directed to the Superfund Health Risk Technical Support Center.
APPLICATION OF AN ALTERNATIVE SURROGATE APPROACH
The surrogate approach allows for the use of data from related compounds to calculate
screening values when data for the compound of interest are limited or unavailable. Details
regarding searches and methods for surrogate analysis are presented in Wang et al. (2012).
Three types of potential surrogates (structural, metabolic, and toxicity-like) are identified to
facilitate the final surrogate chemical selection. The surrogate approach may or may not be
route-specific or applicable to multiple routes of exposure. In this document, it is limited to the
oral noncancer effects only, based on the available toxicity data. All information was considered
together as part of the final weight-of-evidence (WOE) approach to select the most suitable
surrogate both toxicologically and chemically.
Structural Surrogates (Structural Analogs)
1,3-Dibromobenzene is a halogenated compound belonging to the brominated benzene
class. Thus, an initial surrogate search focused on the identification of brominated benzenes with
toxicity values from the Integrated Risk Information System (IRIS), PPRTV, and Health Effects
Assessment Summary Tables (HEAST) databases to take advantage of the well-characterized
chemical-class information. Four brominated benzenes were found to have oral toxicity values
listed on IRIS: bromobenzene (U.S. EPA. 2009); 1,4-dibromobenzene (U.S. EPA. 1988a);
1,2,4-tribromobenzene (U.S. EPA. 1993); and hexabromobenzene (U.S. EPA. 1988b) (see
Tables A-l and A-3). Similarity scores for these chemicals were identified by searching for
structural analogs at least 50% similar to 1,3-dibromobenzene using the National Library of
Medicine's ChemlDplus database (NLM ). Out of the four brominated benzenes initially
obtained from IRIS, only 1,2,4-tribromobenzene had a similarity match of >50% to
1,3-dibromobenzene (55.92%>, see Table A-l). The remaining three potential surrogates had a
similarity score less than 50%. However, all four brominated benzenes were retained because of
the chemical-class specific information (e.g., common target organ and effect[s]). Table A-l
summarizes their physicochemical properties and structural similarity.
Although 1,2,4-tribromobenzene was found to be the most structurally similar to
1.3-dibromobenzene based on the ChemlDplus similarity score, 1,2,4-tribromobenzene was not
as similar to 1,3-dibromobenzene with regard to physicochemical properties. Instead,
1.4-dibromobenzene displayed the most similarity to 1,3-dibromobenzene with regard to
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physicochemical properties, followed by bromobenzene and 1,2,4-dibromobenzene (see
Table A-l). Hexabromobenzene displayed physicochemical properties that were the least similar
to 1,3-dibromobenzene (see Table A-l). Based on this information, the top three chemicals
considered as structural surrogates are bromobenzene, 1,4-dibromobenzene, and
1,2,4-tribromobenzene (see details below).
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Table A-l. Structural Similarity and Physicochemical Properties of 1,3-Dibromobenzene and Potential Surrogates3
Characteristic
1,3-Dibromobenzene
Bromobenzene
1,4-Dibromobenzene
1,2,4-Tribromobenzene
Hexabromobenzene
Structure
Br
^^^Br
Br
Br^^j^^Br
Br
CASRN
108-36-1
108-86-1
106-37-6
615-54-3
87-82-1
Similarity score (%)
100
<50
<50
55.92
<50
Molecular formula
C6H4Br2
C6H5Br
C6H4Br2
C6H3Br3
CeBr6
Molecular weight
235.9
157
235.9
314.8
551.5
Melting point (°C)
-7.00
-30.6
87.3
44.5
326
Boiling point (°C)
218
156
219
275
-
Vapor pressure (mm Hg at
25°C)
0.269
4.18
0.058
5.48 x 10-3
1.63 x 10-8
Henry's law constant
(atm-m3/mole at 25 °C)
1.24 x 10-3
2.47 x 10-3
8.93 x 10-4
3.41 x 10-4
2.81 x 10"5
Water solubility (mg/L)
67.5
446
20
4.9
1.60 x 10-4
Log Kowb
3.78
2.99
3.89
4.54
6.07
aNLM (accessed 7-22-2013).
bLu et al. (2000).
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Metabolic Surrogates
Toxicokinetic Data
The specific metabolism information for 1,3-dibromobenzene and the four potential
metabolic surrogates was based on the available metabolic information in the form of
metabolites detected in urine; Table A-2 displays a summary of these excretion data. Similar to
the analysis of physicochemical properties, hexabromobenzene was the least similar to
1,3-dibromobenzene in terms of metabolite profile; hence, it was concluded that
hexabromobenzene is not a suitable candidate to serve as a metabolic surrogate for
1,3-dibromobenzene. Bromobenzene, 1,4-dibromobenzene, and 1,2,4-tribromobenzene had the
same common metabolites as 1,3-dibromobenzene (i.e., bromophenols), and they were
considered as metabolic surrogates.
In a related but indirect metabolism study, Lupton et al. (2009) analyzed brominated
diphenyl ethers (BDEs) 47, 99, and 153 and identified their metabolites using human liver
microsomes. The study authors found that BDE 99 was metabolized primarily to dihydroxylated
BDE 99, but it was also metabolized to 2,4,5-tribromophenol, and 1,3-dibromobenzene to a
lesser extent (<2-8%). Because 1,3-dibromobenzene only accounts for a small amount of the
metabolites of BDE 99, BDE 99 was not considered as a potential metabolic surrogate for
1,3-dibromobenzene (BDE 99 also has a different toxic endpoint: neurotoxicity).
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Table A-2. Summary of Brominated Benzene Metabolites Detected in Urine
Chemical
Route
Species
Metabolites
Reference
Bromobenzene
i.p.
Rabbit
Bromophenols
Ruzo et al. (1916)
i.p.
Rat
Bromophenols and dihydrodiols
Miller et al. CI990s) and
Lertratananekoon and Hornine
(1987)
1,4 -Dibromobenzene
i.p.
Rabbit
Bromophenols
Ruzo et al. (1976)
i.p.
Rat
Bromophenols
Szvmariska et al. (2002)
1,2,4-Tribromobenzene
i.p.
Rabbit
Bromophenols
Ruzo et al. (1976)
Hexabromobenzene
oral
Rat
Bromobenzenes
Yamaeuchi et al. (1988)
1,3 -Dibromobenzene
i.p.
Rabbit
Three phenolic products—Due to small amounts of metabolites and
unavailability of authentic standards, these metabolites could not be
identified.
Ruzo et al. (1976)
i.p.
Rat
Bromophenols
Saoota et al. (1999)
i.p. = intraperitoneal.
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Toxicity-Like Surrogates
Table A-3 summarizes available toxicity data for 1,3-dibromobenzene and the four
brominated benzenes identified as potential surrogates. All of the four brominated benzenes
induced liver effects (e.g., hepatocellular cytomegaly, increased liver-to-body-weight ratio,
hepatic microsomal enzyme induction, etc.). Furthermore, three of the brominated benzenes
(bromobenzene, 1,4-dibromobenzene, and 1,2,4-tribromobenzene) had critical effects involving
the liver. For hexabromobenzene, liver changes were observed (i.e., increased liver-to-body-
weight ratio and increased liver porphyrins at higher doses) but these were not the most sensitive
endpoints. From these long-term toxicity data, it is clear that the liver is a common target organ,
and liver effects are often times the most sensitive endpoint for the brominated benzene chemical
class. Also, the available acute and short-term toxicity studies similarly point to the liver as a
target organ for 1,3-dibromobenzene (Szymanska et al.. 1998; Szymanska. 1998. 1996;
Szymanska et al.. 1996). Hence, with respect to 1,3-dibromobenzene, the liver is likely to be the
target organ and liver effects the most sensitive endpoint for long-term toxicity.
Although Szymanska (1998) demonstrated that the acute toxicity of bromobenzenes in
mice is reduced when the number of bromine atoms is increased, comparison of median lethal
dose (LD50) values among bromobenzenes was inconclusive. The mouse LD50 values for
bromobenzene and 1,4-dibromobenzene were slightly higher than the mouse LD50 for
1.3-dibromobenzene, but there were no mouse LD50 data for 1,2,4-tribromobenzene or
hexabromobenzene to make a direct comparison (see Table A-3). Furthermore, an opposite
trend in the long-term toxicity of brominated benzenes in terms of their effect levels was
observed (see Table A-3) (i.e., the higher the number of bromine atoms, the more toxic the
chemical is chronically). This trend is consistent with later findings by Szymanska et al. (1998)
that there is an apparent "shift" from single exposure to repeated exposure in terms of
hepatotoxic effects from necrosis to less severe steatosis and porphyrogenic effects (Szymanska
et al.. 1998). This shift may occur because repeated doses of brominated benzenes could
accelerate the process of metabolism towards the formation of less toxic metabolites and/or may
intensify the repair/regeneration processes in cells (Szymanska et al.. 1998).
In vitro Hep ototoxicity Data
In addition to the in vivo data on the potential surrogates, in vitro measurements of
toxicity such as median lethal concentration (LC50) were also available. The human hepatocyte
LC50 of 1,3-dibromobenzene was most similar to the human hepatocyte LC50 of
1,2,4-tribromobenzene (488 vs. 475 [xM; see Table A-3). The rat hepatocyte toxicity data LC50
of 1,3-dibromobenzene was most similar to the rat hepatocyte LC50 of 1,4-dibromobenzene
(355 vs. 371 [xM; see Table A-3). The human and rat LC50S of bromobenzene were 2-3 times
higher than the LC50S of 1,3-dibromobenzene; these data suggest that 1,3-dibromobenzene could
be 2 to 3 times more toxic than bromobenzene in terms of in vitro toxicity. No comparison was
possible between hexabromobenzene and 1,3-dibromobenzene because there were no in vitro
human or rat hepatocyte toxicity data. Therefore, based on the similarities in in vitro toxicity
levels as well as critical effects involving the liver, 1,4-dibromobenzene and
1,2,4-tribromobenzene were considered toxicity-like surrogates.
In conclusion, an attempt was made to identify a suitable surrogate to derive toxicity
values for 1,3-dibromobenzene. Comparison of the potential surrogates (bromobenzene,
1.4-dibromobenzene, 1,2,4-tribromobenzene, and hexabromobenzene) was made based on their
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profiles of structural similarity, toxicokinetics, and tissue-specific toxicity. The chronic
reference doses (RfDs) for the four potential surrogates range from 2 x io~3 to
1 x 10"2 mg/kg-day, and therefore, use of any of these candidates would have resulted in a
comparable screening chronic provisional reference dose (p-RfD) for 1,3-dibromobenzene (see
Table A-3). The common target organ among the potential surrogates appears to be the liver,
with the kidneys as a likely secondary target organ for some brominated benzenes
(e.g., bromobenzene).
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Table A-3.
Comparison of Available Toxicity Data for 1,3-Dibromobenzene and Potential Surrogates
Characteristic
1,3-Dibromobenzene
Bromobenzene
1,4-Dibromobenzene
1,2,4-Tribromobenzene
Hexabromobenzene
Structure
Br
^^^Br
Br^^j^^Br
Br^^j^^Br
Br
Human hepatocyte toxicity LC50
(|iM)a
488 ±48.8
1.150 ±115
560 ± 56
475 ±37.5
NA
Rat hepatocyte toxicity LC50
(|iM)a
355 ±35.5
750 ± 75
371 ±37.1
214 ±21.4
NA
Mouse LD50 (mg/kg)b
2,250
2,700
3,120
NA
NA
Chronic RfD (mg/kg-day)
NA
8 x 10-3
1 x 10-2
5 x 10-3
2 x 10-3
Critical effect
NA
Hepatocellular
cytomegaly
Increased liver-to-body-
weight ratio and hepatic
microsomal enzyme
induction
Increased liver-to-body-
weight ratio and hepatic
microsomal enzyme
induction
Induced serum
carboxylesterase activity
POD (mg/kg-day)
NA
BMDL10: 24.1
NOAEL: 10
NOAEL: 5
NOAEL: 2
UFC
NA
3,000
1,000
1,000
1,000
Source
NA
U.S. EPA (2009)
U.S. EPA (1988a)
U.S. EPA (1993)
U.S. EPA (1988b)
aChan et al. (2007).
bNLM (accessed on 7-22-2013).
BMDL = benclimark dose lower confidence limit; LCso = median lethal concentration; LD50 = median lethal dose; NA = not available; NOAEL = no-observed-adverse-
effect level; POD = point of departure; UFC = composite uncertainty factor.
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Weight-of-Evidence (WOE) Approach
To select the best surrogate chemical based on all of the information from the three
surrogate types, the following considerations were used in a WOE approach: (1) biological and
toxicokinetic data are preferred over the structural data, (2) lines of evidence that indicate
pertinence to humans are preferred, (3) chemicals with more conservative/health protective
toxicity values may be favored, and (4) if there are no clear indications as to the best surrogate
chemical based on the first three considerations, then the candidate surrogate with the highest
structural similarity may be preferred.
In summary, bromobenzene, 1,4-dibromobenzene, and 1,2,4-tribromobenzene were
identified as structural surrogates; bromobenzene, 1,4-dibromobenzene, and
1,2,4-tribromobenzene were identified as metabolic surrogates; and 1,4-dibromobenzene and
1,2,4-tribromobenzene were identified as toxicity-like surrogates. Overall, based on the WOE of
all the information presented above, 1,2,4-tribromobenzene appears to be the most appropriate
surrogate for 1,3-dibromobenzene because of the following factors:
• More similar structurally
o Structural similarity of 55.92% (highest similarity score) using the National
Library of Medicine's ChemlDplus database (NLM)
• Similar toxicokinetic profile and target organ (see Table A-2 and A-3)
• Similar in vitro hepatotoxicity data (see Table A-3) (Chan et al.. 2007)
• More sensitive effect level (see Table A-3)
The 1,2,4-Tribromobenzene IRIS Summary (U.S. EPA. 1993) cited Carlson and Tardiff
(1977) as the principal study for the RfD.
Six male rats/group were dosed daily with 0, 2.5, 5 or 10 mg
1,2,4-tribromobenzene (TBB)/kg bw for 45 or 90 days. TBB was administered in
corn oilp.o. as 0.1% of body weight. Controls received corn oil only. Animals
were sacrificed at 45 or 90 days or after an additional 30-day recovery period
after 90 days of treatment. Body weight, liver weight, and hepatic microsomal
enzyme activity were measured. Liver-to-body weight ratios were increased
12-16% over controls for the rats treated at 10 mg/kg/day. Liver enzyme
activities were 1.4- to 3-fold that of controls for the same group. Full recovery to
baseline enzyme activity was observed after the 30-day recovery period; liver-to-
body weight ratios were only 7% greater than the control values. Similar results
were reported by Carlson (1979) in a follow-up study.
Although no overt liver toxicity was demonstratedfor TBB, bromobenzene
mixtures at higher doses cause acute hepatic necrosis. The mechanism of
bromobenzene toxicity has been studied in detail and involves conversion of the
parent compound to toxic intermediates by hepatic microsomal enzymes.
Induction of these enzymes can potentiate the toxicity of bromobenzenes and other
similarly-activated compounds.
The uncertainty factor includes factors for interspecies variability, subchronic-to-
chronic exposure duration extrapolation, and intrahuman variability.
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Low confidence levels were assigned to both the study and the database because
of the lack of adequate toxicity parameters in the critical study, the lack of
chronic toxicity data in general, and a degree of uncertainty about the
significance of the effects. Low confidence in the RfD follows.
An updated literature search from 2004 to 2013 was performed for
1,2,4-tribromobenzene and one additional subchronic study was identified. Dodd et al. (2012)
treated 10 male Sprague-Dawley rats/dose with 1,2,4-tribromobenzene via gavage for either 5
days, 2, 4, or 13 weeks at 0, 2.5, 5, 10, 25, or 75 mg/kg-day. This study only focused on liver
effects and did not evaluate any other possible endpoints of toxicity. The study authors
identified a no-observed-adverse-effect level (NOAEL) of 5 mg/kg-day based on increased liver
weight and increased incidence of hepatocyte hypertrophy. This coincides with the NOAEL of
5 mg/kg-day identified from Carlson and Tardiff (1977) which is used as the point of departure
(POD) in the IRIS assessment of 1,2,4-tribromobenzene.
ORAL TOXICITY VALUES
Derivation of Screening Subchronic Provisional Reference Dose (Screening Subchronic
p-RfD)
Based on the overall surrogate approach presented in this PPRTV assessment, the
Integrated Risk Information System (IRIS) POD for 1,2,4-tribromobenzene (a NOAEL of
5 mg/kg-day) established in 1993 and based on increased relative liver weight (liver-to-body-
weight ratio) and hepatic microsomal enzyme induction in male Sprague-Dawley rats from a
90-day study (Carlson and Tardiff. 1977) is recommended as the surrogate POD for
1,3-dibromobenzene. No duration adjustment was performed for the doses reported in the
principal study because Carlson and Tardiff (1977) did not report the treatment schedule used.
The data are not amenable to BMD modeling; thus, calculation of a BMDL is precluded.
As described in the EPA's Recommended Use of Body Weight314 as the Default Method in
Derivation of the Oral Reference Dose (U.S. EPA. 201 lb), the POD from the 90-day
1,2,4-tribromobenzene study by Carlson and Tardiff (1977) in rats is converted to a human
equivalent dose (HED) through an application of a dosimetric adjustment factor (DAF) derived
as follows:
DAF = (BWa1/4 - BWh1/4)
where
DAF = dosimetric adjustment factor
BWa = animal body weight
BWh = human body weight
Using a BWa of 0.25 kg for rats and a default BWh of 70 kg for humans (U.S. EPA.
1988c). the resulting DAF is 0.24. Applying this DAF to the NOAEL identified in the rat study
yields a surrogate PODhed as follows:
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Surrogate PODhed = NOAEL (mg/kg-day) x DAF
= NOAEL (mg/kg-day) x 0.24
= 5 mg/kg-day x 0.24
= 1.2 mg/kg-day
As described by Wang et al. (2012). the uncertainty factors typically applied to the
chemical of concern are the same as those applied to the surrogate unless additional information
is available. The IRIS assessment for the 1,2,4-tribromobenzene surrogate was performed prior
to the recommended use of BW3/4 scaling for noncancer effects (U.S. EPA. 2011b) and prior to
the application of a database uncertainty factor (UFd). Thus, the composite UF (UFc) for
1,3-dibromobenzene has been adjusted and differs from that of the surrogate. To derive a
screening subchronic p-RfD for 1,3-dibromobenzene, a UFc of 300 has been applied to the
surrogate PODhed. The screening subchronic p-RfD for 1,3-dibromobenzene is derived as
follows:
Screening Subchronic p-RfD = Surrogate PODhed ^ UFc
= 1.2 mg/kg-day -^300
= 4 x 10"3 mg/kg-day
Table A.4 summarizes the uncertainty factors for the screening subchronic p-RfD for
1,3 -dibromobenzene.
Table A-4. Uncertainty Factors for the Screening Subchronic p-RfD for
1,3-Dibromobenzene
UF
Value
Justification
UFa
3
A UFa of 3 (10°5) has been applied to account for uncertainty in characterizing the
toxicodynamic differences between rats and humans following oral 1,3-dibromobenzene
exposure. The toxicokinetic uncertainty has been accounted for by calculation of a HED
through application of a DAF as outlined in the EPA's Recommended Use of Body
Weishf/4 as the Default Method in Derivation of the Oral Reference Dose ('U.S. EPA.
2011b).
UFd
10
A UFd of 10 has been applied because there are no acceptable two-generation
reproductive toxicity or developmental toxicity studies via the oral route.
UFh
10
A UFh of 10 has been applied for inter-individual variability to account for human-to-
human variability in susceptibility in the absence of quantitative information to assess
the toxicokinetics and toxicodynamics of 1,3-dibromobenzene in humans.
UFl
1
A UFl of 1 has been applied for LOAEL-to-NOAEL extrapolation because the POD is a
NOAEL
UFS
1
A UFS of 1 has been applied because a subchronic-duration study was selected as the
principal study.
UFC
300
Composite UF.
Derivation of Screening Chronic Provisional Reference Dose (Screening Chronic p-RfD)
The surrogate POD used to derive a screening chronic p-RfD is the same as the surrogate
POD (PODhed =1.2 mg/kg-day) used to derive the screening subchronic p-RfD above. To
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derive a screening chronic p-RfD, a UFc of 3,000 has been applied to the surrogate PODhed.
The screening chronic p-RfD for 1,3-dibromobenzene is derived as follows:
Screening Chronic p-RfD = Surrogate PODhed ^ UFc
= 1.2 mg/kg-day ^ 3,000
= 4 x 10"4 mg/kg-day
Table A. 5 summarizes the uncertainty factors for the screening chronic p-RfD for
1,3 -dibromobenzene.
Table A.5. Uncertainty Factors for the Screening Chronic p-RfD for 1,3-Dibromobenzene
UF
Value
Justification
UFa
3
A UFa of 3 (10°5) has been applied to account for uncertainty in characterizing the
toxicodynamic differences between rats and humans following oral
1,3-dibromobenzene exposure. The toxicokinetic uncertainty has been accounted for
by calculation of a HED through application of a DAF as outlined in the EPA's
Recommended Use of Body Weight3/4 as the Default Method in Derivation of the Oral
Reference Dose (U.S. EPA. 201 lb).
UFd
10
A UFd of 10 has been applied because there are no acceptable two-generation
reproductive toxicity or developmental toxicity studies via the oral route.
UFh
10
A UFh of 10 has been applied for inter-individual variability to account for human-to-
human variability in susceptibility in the absence of quantitative information to assess
the toxicokinetics and toxicodynamics of 1,3-dibromobenzene in humans.
UFl
1
A UFl of 1 has been applied for LOAEL-to-NOAEL extrapolation because the POD
is a NOAEL.
UFS
10
A UFS of 10 has been applied to account for the extrapolation from less than chronic
exposure because no chronic-duration toxicity studies are available to evaluate
chronic systemic toxicity.
UFC
3,000
Composite UF.
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APPENDIX B. DATA TABLES
No data tables are presented.
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APPENDIX C. BENCHMARK DOSE MODELING RESULTS
There are no BMD modeling outputs.
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