EPA/600/R-12/047F2 | August 2012 | www.epa.gov
United States
Environmental Protection
Agency
Inhalation Health Effect Reference Values
for Ethylbenzene (CASRN 100-41-4)
hLC
H
CASRN 100-41-4
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC
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August 2012
Inhalation Health Effect Reference Values for Ethylbenzene
(CASRN: 100-41-4)
Overview
The reader is strongly encouraged to read Section 1 of the following report for critical
background information regarding the health effect reference values discussed in this summary:
Graphical Arrays of Chemical-Specific Health Effect Reference Values for Inhalation Exposures
[FinalReport] (U.S. EPA. 2009). This report is available on-line at
http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=211003.
In general, inhalation health effect reference values have been included which have been
developed and formally reviewed by an authoritative governing body (government agency or
professional association) for use in assessments of risk to support regulatory decision-making.
This is a review of existing reference values, including the basis for each of the reference values
as provided in the available technical support documents for those values, along with some basic
contextual references; this is not a comprehensive review of the health effects literature for ethyl
benzene.
General Properties
Ethylbenzene (CeHs^Hs)); MW = 106.2) is flammable as a liquid or vapor, has very
low solubility in water, and mixes well with most organic solvents (NLM, 1998). Ethylbenzene
is also known as ethylbenzol, and phenylethane. Ethylbenzene has an aromatic odor similar to
that of gasoline, with an odor threshold that varies between individuals, ranging from 2 to
200 ppm. Ethyl benzene becomes a vapor more slowly than the other BTEX solvents (Vapor
Pressure = 9.6 mm Hg at 25 degrees Celsius), with a vapor which is denser than air (Vapor
Density = 3.66; air = 1). Ethyl benzene tends to partition into organic solvents [Octanol/Water
Partition Coefficient (log Kow) = 3.15] and fatty tissues once absorbed by the body. Commercial
grade xylene contains between 6% to 15% ethylbenzene.
Production and Uses
Most ethyl benzene is used as a precursor in the production of styrene, but is also used as
a solvent, feedstock for other chemical production, and as a component of gasoline. Xylene is
one of the so-called BTEX aromatics (benzene, toluene, ethylbenzene, and xylene). Global
production of ethylbenzene in 2010 was approximately 29.2 million metric tons (SRI, 2011).
Exposure Potential
The Toxic Release Inventory (TRI) for the 2010 reporting year (U.S. EPA. 2010)
reported a total of 2,413,967 pounds of ethyl benzene were emitted to air from all industrial
sources in the United States, with 1,382,187 pounds emitted from point sources (stacks, vents,
ducts, or pipes) and 1,031,780 pounds coming from fugitive sources (equipment leaks,
evaporative losses from surface impoundments and spills, and releases from building ventilation
systems). Ambient air concentrations in the United States have been reported to range from 0.5
ppb (2.2 |ig/m3) in remote rural areas to greater than 150 ppb (> 650 |ig/m3) near industrial
facilities and roadways (NLM, 1998).
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August 2012
Potential Health Effects
Acute exposures to ethyl benzene have been associated with various effects including eye
and airway irritation, narcosis, and headache and sleepiness. Longer term and chronic exposures
may lead to ototoxicity (effects on hearing), general developmental toxicity, cellular alterations
and necrosis in the liver, testicular toxicity, and nephrotoxicity.
Cancer Potential
The U.S. EPA (1991) found that ethylbenzene was "not classifiable as to human
carcinogenicity" based on a lack of animal bioassays and human studies; however, an update to
the 1991 assessment is currently in preparation and there is a potential for that classification to
change. The International Agency for Research on Cancer (IARC, 2000) assessed the cancer
potential and found that "Ethylbenzene is possibly carcinogenic to humans (Group 2B). " The
American Conference of Governmental Industrial Hygienists (ACGPL 2007) found ethyl
benzene to be classified as "A3; Confirmed animal carcinogen with unknown relevance to
humans."
Emergency Response Values
The Emergency Response reference values for ethylbenzene are limited to the Acute
Exposure Guideline Levels (AEGLs); no Emergency Response and Planning Guideline (ERPG)
values have been developed for ethylbenzene. The AEGL-1 value was based on upper
respiratory irritation, and mild effects on the central nervous system (CNS); no duration scaling
was performed due to the irritant effects that are not expected to change over the course of an
exposure of up to 8 hours. Both the AEGL-2 and -3 used a physiologically-based
pharmacokinetic (PBPK) model to extrapolate from observations in rats to humans, and to
perform duration scaling. The assumption is that the CNS response observed following
ethylbenzene exposure is directly related to the concentration of ethylbenzene reaching the brain,
and that venous blood concentrations correlate with brain concentrations. For the AEGL-2, the
venous blood concentration (Cv) of ethylbenzene following a 4-hour exposure to 2180 ppm
would be expected to provide an internal dose measurement correlating with the minimum
narcotic response. Similarly for the AEGL-3 derivation, a 6-hour exposure to 2000 ppm was
established to provide an internal dose measurement correlating with the nonlethal response. The
PBPK model was exercised to determine the internal dose (Cv) producing the respective effect in
rats, then the human PBPK model was run for each defined AEGL time point to determine the
equivalent exposure concentration producing the target Cv in humans. The total uncertainty
factor (UF) applied in deriving values for all three AEGL levels was equal to 3: the AEGL-1 was
based on human observations with an intraspecies UF of 3 deemed appropriate because direct
acting irritant effects at the portal of entry are not expected to vary between individuals; for both
the AEGL-2 and -3, the use of a PBPK model negated the need to apply an interspecies factor,
and an intraspecies factor of 3 was applied due to the mode of action of ethylbenzene being
similar to anesthetic chemicals, where a variation of 2-3 fold has been well documented (NRC,
2001). It should also be noted that the Interim Technical Support Document (TSD) for
Ethylbenzene (NAC/AEGL, 2009) makes the following statement regarding the potential for
additional effects from potentially repeated exposures in the data adequacy discussion for the
AEGL-2: "It is acknowledged that the resulting AEGL 2 values may not be protective of
ototoxicity which occurs after repeated exposures, however no data are available to assess this
endpoint following a single exposure to ethylbenzene." It should also be noted that the AEGL-2
values are less than a factor of 2 lower than the AEGL-3 values, denoting a very thin margin
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August 2012
between the two; extra caution should be exercised if exposure concentrations begin to approach
and have the potential to exceed AEGL-2 levels.
Occupational Exposure Limits (OELs)
The occupational values for ethylbenzene are all in strong concordance, with the time-
weighted average (TWA) values from three organizations all being equal to one another, and the
same being the case for the short-term exposure limits (STEL) values from two of those
organizations. The TWA values include the recommended exposure level (REL) developed by
the National Institute for Occupational Safety and Health (NIOSH); the permissible exposure
limit (PEL) developed by the Occupational Safety and Health Administration (OSHA); and the
Threshold Limit Value (TLV®) developed by the American Conference of Governmental
Industrial Hygienists (ACGIH). The STEL values for ethylbenzene were developed by NIOSH
and AGGIH. The most completely documented set of these occupational values are those
developed by ACGIH, with those of NIOSH being the next most complete, but more publically
available. There is only limited documentation on the basis for the OSHA PEL-TWA value.
These traditional occupational reference values are only slightly higher in concentration than the
AEGL-1 values, which anticipate that occupational exposures are generally to a healthy adult
work force. The same study (Bardodej andBardodejova, 1961) was used in the derivation of
both the AEGL-1 and the ACGIH TLV-STEL, with no uncertainty factors (UFs) applied for the
for the TLV-STEL and a UF of 3 applied for the AEGL-1 to account for inter-individual
variability.
Special Use Occupational Values
In addition to the standard occupational values, specialty occupational reference values
are also available in the form of the Spacecraft Maximum Acceptable Concentration (SMAC)
values, which were developed for exposures ranging from 1 hour to 180 days. The
documentation for the SMACs (NRC, 1996) is readily accessible from the National Academy of
Science web site. The SMACs are somewhat lower than the traditional occupational values to
account for the inability to escape exposure in the spacecraft environment.
General Public Values (Routine Non-emergency Exposures)
The reference values designed to protect the general public under normal exposure
conditions (not for emergency response) include the Minimal Risk Levels (MRLs) developed by
the Agency for Toxic Substances and Disease Registry (ATSDR) for acute (1-14 days),
intermediate (15-365 days), and chronic (>1 year) durations; and the California Reference
Exposure Levels (CA-REL) values developed by the Office of Environmental Health Hazard
Assessment (OEHHA), and the U.S. EPA reference concentration (RfC) values, both of which
are for chronic durations (>10% of lifespan, or >7 years). As shown in Table 1, the basis for each
of these general public reference values varied somewhat, as did the UFs applied in their
derivation.
All three ATSDR values were developed using a physiologically-based pharmacokinetic
(PBPK) model to estimate the ethylbenzene blood level in laboratory animals for each inhalation
concentration tested. Both the acute and intermediate MRL values were calculated using a single
standard deviation of the lower confidence limit of the benchmark dose (BMDLi.so) for the
ethylbenzene blood level causing effects to the auditory system (hearing). The BMDL blood
level was converted to an exposure calculation and adjusted for continuous exposure to arrive at
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August 2012
the human equivalent concentration (HEC), to which uncertainty factors were applied, thereby
deriving the final MRL value. The chronic MRL was calculated in a similar manner up to
estimating the ethylbenzene blood level, but the data were not amenable to BMD analysis so the
lowest observed adverse effect level (LOAEL) for progressive nephropathy (kidney failure) was
used as the basis to which HEC adjustments and UFs were applied to deriving the final chronic
MRL. A total UF of 30 was applied to the both the acute and intermediate MRLs (3 to account
for extrapolating from animals to humans, and 10 for variability among the human population);
an additional factor of 10 was applied to account for use of a LOAEL in the case of the chronic
MRL.
Nephropathy and body weight reduction in rats, and abnormally rapid growth
(hyperplasia) in the pituitary gland and effects on the liver in mice were the basis for the chronic
CA-REL, with adjustments to move from repeated to continuous exposures and a total UF of 30
applied to derive the final value.
The chronic RfC was based on the no observed adverse effect level (NOAEL) for
developmental toxicity in rats and rabbits, which was adjusted to account for repeated versus
continuous exposure to arrive at the NOAELHEC- A total UF of 300 (3 for use of an animal study;
10 for variability among humans; and 10 for database uncertainty due to the lack of chronic
studies or studies on multi-generational reproductive effects.
Summary
There is a high level of concordance among the occupational values for ethylbenzene, but
less so for the chronic reference values for the general public. The point of departure for the
chronic MRL and the chronic CA-REL were similar, but differences in adjusting from repeated
to continuous exposure and in the application of UFs lead to a difference of almost an order of
magnitude in final values. The final calculation of the chronic RfC (the oldest of these values)
lies between the other two chronic values. Two notes of caution regarding the AEGL emergency
response values should be heeded: (1) there is less than a two-fold difference between the
AEGL-2 and -3 values; and (2) the AEGL TSD notes a potential for ototoxicity (effects on the
auditory system) from repeated exposures near the AEGL-2 exposure concentration levels that
are not addressed for the AEGL due to the assumption that such exposures will be extremely rare
(i.e., "once-in-a-lifetime").
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Figure 1. Inhalation health effect reference value array for ethylbenzene
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Office of Research and Development
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Ethylbenzene
August 2012
Table 1. Details on derivation of the available health effect reference values for inhalation exposure to ethylbenzene
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Reference
Value Name
AEGL-3
AEGL-2
AEGL-1
Duration
10 minutes
30 minutes
1 hour
4 hours
8 hours
10 minutes
30 minutes
1 hour
4 hours
8 hours
10 minutes
30 minutes
1 hour
4 hours
8 hours
Reference Value
(mg/m3)
20,400
11,000
7800
4400
4000
13,000
7000
4800
2900
2500
144
144
144
144
144
(ppm)
4700
2600
1800
1000
910
2900
1600
1100
660
580
33
33
33
33
33
Health Effect
The internal
dose producing a
non-lethal condition
in rats was
determined, then an
equivalent cone, was
determined for
humans via a PBPK
model
Narcosis in rats
Irritation of the
upper respiratory
tract and eye,
headache,
sleepiness, and
transient feelings of
drunkeness
Point of
Departure
2000 ppm
(rats, 6 h/d,
5 d/wk, for
3 days)
1500 ppm (4
hrs)
100 ppm
(8 hrs in
human
volunteers)
180 ppm
Qualifier1
No lethality
NOAEL
NOAEL
LOAEL
Principal
Study
Andersson
etal. (1981)
Molnar et al.
(1986)
Bardodei
and
Bardodejova
(1961)
Uncertainty
Factors2
Total UF = 3
UFA=1
UFH = 3
Total UF = 3
UFA=1
UFH = 3
Total UF = 3
UFH = 3
UFA=1
Notes on
Derivation
Application of
PBPK model
No duration
adjustment
Review
Status
Interim
(NAC/AEGL.
2009)
1 NOAEL - No observed adverse effect level; LOAEL - Lowest observed adverse effect level; HEC - Human equivalent concentration; BMCL - Benchmark
concentration, lower confidence limit, with criteria in subscript (e.g., 1-SD = one standard deviation)
2 UFH - inter-human variability; UFA - animal to human variability; UFL - LOAEL to NOAEL adjustment; UFS - subchronic to chronic adjustment;
UFDB - database uncertainty
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Ethylbenzene
August 2012
Occupational
Reference
Value Name
NIOSH
STEL
NIOSH
IDLH
ACGIH
TLV-STEL
ACGIH
TLV-TWA
NIOSH REL
(TWA)
OSHAPEL
(TWA)
SMACs
Duration
<10
minutes
30 minutes
<15
minutes
8 hour
TWA
10 hour
TWA
8 hour
TWA
1 hour
24 hour
7 day
30 day
Reference Value
(mg/m3)
435
3475
545
435
435
435
780
260
130
130
(ppm)
125
800
125
100
100
100
180
60
30
30
Health Effect
Irritation and
narcotic effects,
with potential for
chronic effects
Protection from
explosion;
Acute inhalation
toxicity data in
humans and animals
Potential for eye and
upper respiratory
irritation; also
protective for
narcosis
Eye, skin and upper
respiratory irritation
Irritant, narcotic,
and chronic effects
Eye and respiratory
irritation, headache,
sleepiness
Headache,
sleepiness
Eye and
respiratory
irritation,
testicular toxicity
Point of
Departure
Various
Various
125 ppm
400 ppm
NR
NR
180 ppm
(8-hr)
180 ppm
(8-hr)
100 ppm
(8-hr)
Qualifier1
NR
Effects
levels
LOAEL
(Human)
NOAEL
(Rabbit and
Monkey)
NA
NR
LOAEL
(Human,
n=ll)
LOAEL
(Human,
n=ll)
NOAEL
(Human,
n=9)
Principal
Study
NR
NIOSH
(19941
Bardodej
and
Bardodejova
(1961)
Wolfetal.
(1956)
NR
NR
Bardodej
and
Bardodejova
(19701
Uncertainty
Factors2
NA
NR
NR
NR
Total UF = 1
Total UF = 1
Total UF = 1
Total UF = 1
Notes on
Derivation
WOE
Approach
WOE
Approach;
10% of the
lower
explosive
limit of 0.8%
WOE
Approach
NR
NR
No duration
scaling.
Duration
adjusted using
Haber's Rule
Adjusted for
small sample
size
(n/100 = 0.3)
Review
Status
Final
(NIOSH.
20071
Final
(ACGIH.
2006)
Final
(NIOSH.
2007)
Final
Standard
(OSHA.
20061
Final
(NRC. 19961
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Ethylbenzene
August 2012
General Public
Reference
Value Name
Acute
ATSDR
MRL
Intermediate
ATSDR
MRL
Chronic
ATSDR
MRL
Chronic
CA-REL
Chronic RfC
(IRIS)
Duration
180 day
1 -14 days
15-365
days
Chronic
(> 1 year)
Chronic
Chronic
Reference Value
(mg/m3)
50
21.7
8.7
0.26
2.0
1.0
(ppm)
12
5.0
2.0
0.06
0.4
0.2
Health Effect
Testicular
toxicity
Compound Action
Potential auditory
shifts using an
internal dose metric
of time-averaged
arterial blood cone.
Auditory threshold
shifts and outer hair
cell loss
Increased severity of
chronic progressive
nephropathy in
female rats exposed
to 75 ppm and
higher
Nephrotoxicity,
body weight
reduction (rats)
hyperplasia of the
pituitary gland; liver
cellular alterations
and necrosis (mice)
Developmental
toxicity in rats and
rabbits
Point of
Departure
400 ppm
(7h/d;
5d/w;
186 d)
81.1 umol/L
154.26 ppm
19.94
umol/L
63.64 ppm
17.45 ppm
75 ppm
13 ppm
75 ppm
(6-h/d,
5d/wk,
103 weeks)
434 mg/nr1
(100 ppm)
4340 mg/m3
(1000 ppm)
Qualifier1
NOAEL
(Rabbit,
Monkey)
BMDLj.sD
HEC
BMDLj.sD
HEC
LOAELHEc
LOAEL
NOAELADJ
NOAEL
NOAELHEC
LOAEL
Principal
Study
Wolfetal.
(19561
Cappaert et
al. (20001
Gagnaire et
al. (2007)
(NTP, 1999)
Chan et al.
(1998) and
(NTP. 19901
Andrew et
al. (19811
and Hardin
etal. (19811
Uncertainty
Factors2
Total UF= 10
UFA=10
Total UF = 30
UFA = 3
UFH = 10
Total UF = 30
UFA = 3
UFH = 10
Total UF =
300
UFA = 3
UFH = 10
UFL = 10
Total UF = 30
UFA = 3
UFH = 10
Total UF =
300
UFA = 3
UFH = 10
UFDB = 10
Notes on
Derivation
Duration
adjusted using
Haber's Rule
PBPK model
used to
estimate
internal dose,
BMD analysis
results then
converted to
ppm for POD
PBPK models
used to
estimate
internal dose
metrics and
HECs were
adjusted for
intermittent
exposure
Duration
adjusted to
account for
6 h/dand
5d/wk
exposures
Database UF
due to absence
of multi-
generational
reproductive
and chronic
studies
Review
Status
Final
(ATSDR.
20101
Final
(OEHHA.
20001
Final
(U.S. EPA
1991)
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REFERENCES
Further Reading
U.S. EPA (U.S. Environmental Protection Agency). Ethylbenzene, Air Toxics Web Site.
http://www.epa.gov/ttnatw01/hlthef/ethylben.html
ACGIH (American Conference of Governmental Industrial Hygienists). (2006). Documentation
of the threshold limit values and biological exposure indices. Cincinnati, OH.
ACGIH (American Conference of Governmental Industrial Hygienists). (2007). 2007 TLVs and
BEIs: Based on the documentation of the threshold limit values for chemical substances
and physical agents and biological exposure indices. Cincinnati, OH.
Andersson, K; Fuxe, K; Nilsen, OG; Toftgard, R; Eneroth, P; Gustafsson, JA. (1981). Production
of discrete changes in dopamine and noradrenaline levels and turnover in various parts of
the rat brain following exposure to xylene, ortho-, meta-, and para-xylene, and
ethylbenzene. Toxicol Appl Pharmacol 60: 535-548.
Andrew, FD; Buschbom, RL; Cannon, WC; Miller, RA; Montgomery, LF; Phelps, DW; Sikov,
MR. (1981). Teratologic assessment of ethylbenzene and 2-ethoxyethanol. Richland,
WA: Battelle. http://www.ntis.gov/search/product.aspx?ABBR=OTS0516210
ATSDR (Agency for Toxic Substances and Disease Registry). (2010). Toxicological Profile for
Ethylbenzene [ATSDR Tox Profile]. Atlanta, GA: U.S. Department of Health and
Human Services, Public Health Service.
http://www.atsdr.cdc.gov/ToxProfiles/tp.asp?id=383&tid=66
Bardodej, Z; Bardodejova, E. (1961). [Usefulness and application of exposure tests]. CeskHyg
6: 537-545.
Bardodej, Z; Bardodejova, E. (1970). Biotransformation of ethyl benzene, styrene, and alpha-
methylstyrene in man. Am Ind Hyg Assoc J 31: 206-209.
http://dx.doi.org/10.1080/0002889708506230
Cappaert, NLM; Klis, SFL; Baretta, AB; Muijser, H; Smoorenburg, GF. (2000). Ethyl benzene-
induced ototoxicity in rats: A dose-dependent mid-frequency hearing loss. J Assoc Res
Otolaryngol 1: 292-299. http://dx.doi.org/10.1007/sl01620010050
Chan, PC; Hasemani, JK; Mahleri, J; Aranyi, C. (1998). Tumor induction in F344/N rats and
B6C3F1 mice following inhalation exposure to ethylbenzene. Toxicol Lett 99: 23-32.
Gagnaire, F; Langlais, C; Grossmann, S; Wild, P. (2007). Ototoxicity in rats exposed to
ethylbenzene and to two technical xylene vapours for 13 weeks. Arch Toxicol 81: 127-
143. http://dx.doi.org/10.1007/s00204-006-0124-y
Hardin, BD; Bond, GP; Sikov, MR; Andrew, FD; Beliles, RP; Niemeier, RW. (1981). Testing of
selected workplace chemicals for teratogenic potential. Scand J Work Environ Health 7:
66-75.
IARC (International Agency for Research on Cancer). (2000). Some industrial chemicals. Lyon,
France. http://monographs.iarc.fr/ENG/Monographs/vol77/index.php
Molnar, J; Paksy, KA; Naray, M. (1986). Changes in the rat's motor behaviour during 4-hr
inhalation exposure to prenarcotic concentrations of benzene and its derivatives. Acta
Physiol 67: 349-354.
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NAC/AEGL. (2009). Interim AEGL Technical Support Document for Ethylbenzene.
Washington DC: U.S. EPA.
http://www.epa.gov/oppt/aegl/pubs/ethylbenzene_interim_sep_09.vl.pdf
NIOSH (National Institute for Occupational Safety and Health). (1994). Ethyl benzene - IDLH
Documentation. Cincinatti, OH: National Institute for Occupational Saftey and Health.
http://www.cdc.gov/niosh/idlh/100414.html
NIOSH (National Institute for Occupational Safety and Health). (2007). NIOSH pocket guide to
chemical hazards. (2005-149). Cincinnati, OH. http://www.cdc.gov/niosh/docs/2005-149/
NLM (National Institutes of Health, National Library of Medicine). (1998). Hazardous
Substances Data Bank (HSDB). Available online at http://toxnet.nlm.nih.gov (accessed
October 6, 2009).
NRC (National Research Council). (1996). Spacecraft maximum allowable concentrations for
selected airborne contaminants: Volume 3. Washington, DC.
http://www.nap.edu/catalog.php7record id=5435
NRC (National Research Council). (2001). Standing operating procedures for developing acute
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