EPA/600/R-12/047F1 | August 2012 | www.epa.gov
United States
Environmental Protection
Agency
Chemical-Specific Reference Values
for Benzene (CASRN 71-43-2)
CASRN 71-43-2
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
Chemical-Specific Reference Values for Benzene
(CASRN 71-43-2)
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
benzene.
General Properties
Benzene (CeH6; MW = 78.11) is a clear colorless liquid with a characteristic sweet odor
at low concentrations, and is disagreeable and irritating at high levels (Cavender, 1994). Benzene
is known by a large number of synonyms (annulene, coal naphtha, cyclohexatriene, fenzen
[Czech], mineral naphtha, motor benzol, NCI-C55276, phene, phenyl hydride, pyrobenzol,
pyrobenzole) and by the registered trade name Polystream. Benzene readily becomes a vapor
(Vapor Pressure = 94.8 mm Hg at 25 degrees Celsius), and the vapor is denser than air (Vapor
Density = 2.8; air = 1). Benzene is moderately soluble in water but tends to partition into
organic solvents [Octanol/Water Partition Coefficient (log Kow) = 2.13] and fatty tissues once
absorbed by the body (NLM. 1998).
Production and Uses
Benzene is industrially the most important of the so-called BTEX aromatics (benzene,
toluene, ethylbenzene, and xylene). In industrial chemistry, benzene forms the basis for a great
variety of aromatic intermediates and for the group of cycloaliphatic compounds. Benzene is
used as the basis for the manufacture of plastics, synthetic rubber, dyestuffs, resins, raw materials
for detergents, and plant protection agents, and is used extensively as a solvent. Global benzene
consumption in 2010 was 40,000 tons (i.e., 80 billion pounds)
(http://www.chemsystems.com/about/cs/news/items/PPE%20PCMD%20Aromatics%202011 .cfin,
accessed 28 June 2012).
Exposure Potential
Benzene has historically been a major component in gasoline, but the percent benzene
content in gasoline has been declining due to regulatory pressure. In 2007, the average benzene
content in gasoline was 1.06% (by volume) and it is expected to be reduced to 0.62 vol% by
2015 (U.S. EPA. 201 Oa). The Toxics Release Inventory for 2010 (U.S. EPA. 201 Ob) reported
3,909,186 pounds of benzene were emitted to air from all industrial sources in the United States,
with 2,362,313 pounds emitted from point sources (stacks, vents, ducts, or pipes) and 1,546,872
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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 1.4 ppb (4.5 |ig/m3) in
remote rural areas, with concentrations up to 34 ppb (109 |ig/m3) near industrial facilities and
roadways, and up to 32 ppm (102 mg/m3) near service stations (NLM, 1998). Benzene is also
present in tobacco smoke and has been detected in the expired air of smokers (Cavender, 1994).
Potential Health Effects
Benzene is responsible for various toxicity effects including central nervous system
(CNS) depression, eye and airway irritation, general developmental toxicity, genotoxicity, and
bone marrow toxicity which may result in carcinogenesis (leukemia).
Cancer Potential
Benzene is classified as a "known" human carcinogen (Category A) under the Risk
Assessment Guidelines of 1986 (U.S. EPA, 2000). Under the revised Carcinogen Risk
Assessment Guidelines (U.S. EPA, 2005), benzene is characterized as a known human
carcinogen for all routes of exposure based upon convincing epidemiologic evidence of a causal
association between human exposure and cancer, as well as supporting evidence from animal
studies. The International Agency for Research on Carcinogens (IARC, 1998) found that "There
is sufficient evidence that benzene is carcinogenic to man."
Consideration of Peak versus Continuous Exposure
It is important to note that rather than cumulative exposures to low concentrations, it is
repeated peak benzene exposures which have been deemed determinative of bone marrow
toxicity with a greater potential for leukemia. This was noted in the documentation for the
Threshold Limit Value Short-term Exposure Limit (TLV-STEL) developed by the American
Conference of Governmental Industrial Hygienists (ACGIH, 2007), where it states:
"A TLV-STEL of 2.5 ppm is recommended to protect against excess risk of leukemia due to the
dose-rate-dependent hematopoietic toxicity of benzene" (Schnatter et al., 1996). The dose-rate
dependent toxicity of benzene indicates that peak exposures may be of greatest concern;
however, ACGIH also states that cumulative exposures over time must still be considered and
also lowered the TLV-TWA from 1.0 ppm to 0.5 ppm.
The consideration of peak exposures is important when attempting to compare the
emergency response reference values to the short-term occupational exposure limits (OELs), and
to the acute, non-emergency reference values for the general public. Acute Exposure Guideline
Level (AEGL) and Emergency Response Planning Guideline (ERPG) values are developed
under an assumption of once-in-a-lifetime exposure potential1. OELs are developed for
protection of an assumed healthy population of working-age adults, with a higher workplace
exposure level assumed during the work day, along with intermittent peak exposure events. Both
the short-term OELs and the acute general public reference values include consideration of the
1 "... [occupational exposure] limits are not easily or directly translated into emergency exposure limits for
exposures at high levels but of short duration, usually less than 1 hr, and only once in a lifetime for the general
population, which includes infants, children, the elderly, and persons with diseases, such as asthma, heart disease,
or lung disease." (From NRC (2001,192042), Standing Operating Procedures for Developing Acute Exposure
Guideline Levels, Page 2.)
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potential for events to occur more frequently than once-in-a-lifetime in their derivation, and in
the case of OELs, include provision for occurrence on a more regular basis.2
Emergency Response Values
The emergency response values for toluene include interim Acute Exposure Guideline
Level (AEGL) values and final Emergency Response Planning Guideline (ERPG) values for all
three severity levels (1 = mild, transient effects; 2 = irreversible effects or impeding ability to
escape; and 3 = threshold for life threatening effects).
The Technical Support Document for the benzene AEGL (NAC/AEGL, 2009) cites
effects on the CNS for both the AEGL-1 and AEGL-2. Developmental effects for the AEGL-2
were not considered because: "The developmental toxicity effects of benzene are considered to
be induced by repeated exposure and it is not likely that the same extent of effects will be induced
by a single exposure. Therefore, developmental toxicity will not be used for AEGL-2. " This
underscores the "once-in-a-lifetime" nature of the AEGLs and how effects appropriate for the
derivation of the AEGL values for benzene included that consideration.
The AEGL-3 for benzene was based on the "Highest reliable level without mortality
observed in rats (5940 ppm for 4h) " from the study of Molnar (1986). The final AEGL-3 values
were derived with application of a total uncertainty factor of 3 (no interspecies differences were
anticipated3 and a factor of 3 was applied because "experience with anesthetic gases have shown
that the variability between groups in the population does not vary by more than a factor 2-3 ");
duration extrapolation was accomplished using the Cn * t equation with n=2 for shorter and n=l
for longer durations. The ERPG-3 for benzene was established based on 10% of the rodent
LC50, with no other adjustments as noted in the ERPG documentation (AIHA, 2002), where it
states: "Exposure to benzene concentrations greater than 1000ppm have been tolerated. "
Occupational Exposure Limits (OELs)
Although ACGIH makes the point that peak exposures are critical for benzene toxicity in
setting the TLV-STEL (as stated earlier), it also notes that cumulative exposure over time must
still be considered and notes: " ...that exposure for a working lifetime at the current OSHA PEL
of 1 ppm, equivalent by this metric to 45 ppm-years, results in an unacceptable risk of leukemia"
and lowered the TLV-TWA from 1.0 ppm to 0.5 ppm.
The NIOSH Occupational Safety and Health Guideline for Benzene "recommends that
benzene be controlled and handled as a potential human carcinogen in the workplace and that
exposure be reduced to the lowest feasible limit" and further states that the "NIOSH REL [of 0.1
ppm] is the lowest concentration detectable by current NIOSH-validated sampling and
analytical methods" (NIOSH, 1988). More recently developed analytical methods have
2 The ACGIH (2006) definition of a TLV-STEL states that "Exposures above the TLV-TWA up to the TLV-STEL
should be less than 15 minutes, should occur no more than four times per day, and there should be at least 60
minutes between successive exposures in this range. "
3 From the Benzene AEGL TSD (NAC/AEGL. 2009): "Because the mortality of benzene is caused by severe CNS
depression (paralysis of the respiratory center), this effect is correlated to the benzene level in the brain lipid
fraction ... This concentration will be related directly to a build-up of benzene in the tissue, which is directly related
to the inhalation rate ... Therefore, it is expected that humans require higher external concentrations compared to
rodents, to obtain a similar level of benzene in the blood or brain as is observed also for other VOC's
(trichloroethylene, toluene)... For this reason, an interspecies uncertainty factor ofl is used. "
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significantly greater sensitivity (NIOSH, 2003). In 1986 NIOSH used a cancer risk assessment to
derive a health-based NIOSH-REL (TWA) of 0.1 ppm. This corresponded to a cancer risk of
1:1000 for workers exposed to 0.1 ppm for a working lifetime (NIOSH. 1990. 1986).
Nonetheless, the NIOSH REL is less than an order of magnitude lower than the more recently
adopted TLV-TWA of 0.5 ppm (ACGffl. 2007).
A subset of OELs applicable only to workers in specific industries are mentioned here but
are not included in the following graphical array of reference values for benzene, nor in the table
showing details on value derivation. Appendix F of the NIOSH Pocket Guide (NIOSH, 2007)
states:
"The final OSHA Benzene standard in 1910.1028 applies to all occupational exposures to
benzene except some subsegments of industry where exposures are consistently under the action
level (i.e., distribution and sales of fuels, sealed containers and pipelines, coke production, oil
and gas drilling and production, natural gas processing, and the percentage exclusion for liquid
mixtures); for the exceptedsubsegments, the benzene limits in Table Z-2 apply (i.e., an 8-hour
TWA of 10 ppm, an acceptable ceiling of 25 ppm, and 50 ppm for a maximum duration of 10
minutes as an acceptable maximum peak above the acceptable ceiling). "
The related OSHA statute (Table Z-2) is cited in 29 CFR 1910.1028 and is available online at
http://www.osha.gov/pls/oshaweb/owadisp.show document?p id=10042&p table=STANDARDS.
Special Use Occupational Values
In addition to the standard occupational values, a set of special use occupational values
are also available for benzene which were developed by and/or reviewed by the National
Research Council (NRC): Spacecraft Maximum Acceptable Concentrations (SMACs) for
durations of 1 and 24 hours, and 7, 30, 180, and 1000 days; and values derived for submarine
crews - the Emergency Exposure Guideline Levels (EEGLs) for 1 and 24 hours, and the
Continuous Exposure Guideline Levels (CEGL) for 90 days. The EEGL values [40 ppm (12.8
mg/m3) for 1-hour and 3 ppm (9.6 mg/m ) for 24-hours] and the CEGL values [0.2 ppm (0.64
mg/m3) for 90 days) are fairly consistent with the AEGL-1 and traditional occupational TWA
values. Largely due to the confined working environment with no opportunity to be removed
from exposure, the 180 and 1000 day SMACs are lower than other occupational reference values
for similar durations. The SMACs for durations of 7-days or longer were based on concerns for
potential narcosis and neurotoxic effects, including hearing loss (ototoxicity) for the values.
General Public Values (Routine Non-emergency Exposures)
Values for the general public include California Reference Exposure Levels (CA-RELs,
developed by the Office of Environmental and Hazard Assessment - OEHHA) for both acute
(6 hours and shorter) and chronic (lifetime) durations; Minimal Risk Levels (MRLs) developed
by the Agency for Toxic Substances and Disease Registry (ATSDR) for chronic exposures
(periods longer than 1 year), intermediate durations of 15-364 days, and for durations of 1-14
days; and a chronic Reference Concentration (RfC) developed by the U.S. Environmental
Protection Agency (EPA) for the Integrated Risk Information System (IRIS) database.
The Acute CA-REL for benzene used developmental effects as the basis for derivation, in
contrast to the derivation of the AEGL-2 values noted earlier. The Acute CA-REL did not,
however, apply any duration extrapolation, and therefore is stated as a 6-hour value instead of
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the more commonly reported 1-hour value for acute CA-RELs. The California Office of
Environmental Health Hazard Assessment does not consider duration extrapolation for
developmental toxicants but instead considers the derived values as "not to exceed" at any time,
as noted in Section 4.4.6.3 (page 55 et seq.) of their Technical Support Document for the
Derivation of Noncancer Reference Exposure Levels (OEHHA, 2008b). Therefore, although the
Acute CA-REL for benzene is a 6-hour value, it is also applicable to shorter durations (e.g.,
1-hour). It is also important to note that the Acute CA-REL for benzene was derived for "severe
effects" because there were no good data upon which to derive a value for mild effects.
Most of the other general public health values (EPA Reference Concentration [RfC],
Chronic ATSDR MRLs, and Chronic CA-REL) were based on effects on the blood forming
capabilities of bone marrow, as shown in Table 1. The Acute and Intermediate ATSDR MRLs,
were based on decreases in immunological function related to white blood cell formation, and
hence also related to bone marrow toxicity.
An Inhalation Unit Risk (IUR) estimate was developed for cancer potential over the
range of 2.2 x 10~6 to 7.8 x 10~6 for an increase in the risk for an individual who is exposed for a
lifetime to 1 |ig/m3 benzene in air (U.S. EPA, 2000). From those IUR risk values, the exposure
levels resulting in a 1:1,000,000 (one in a million) risk of cancer range from 0.13 to 0.45 |ig/m3
(0.00013 to 0.00045 mg/m3), and exposure levels of 13 to 45 |ig/m3 (0.013 to 0.045 mg/m3)
result in a 1:10,000 risk range for cancer. In comparison, the exposure levels predictive of
potential increases in cancer incidence at the one in one million risk range are well below the
range of reference values for noncancer effects; however, exposures near the chronic RfC (0.03
mg/m3) are within the range of exposures predictive for an increased risk potential of one in
10,000 for leukemia. The exposure levels associated with those cancer risk levels are shown in
Figure 1 as ranges but are not covered in more detail in Table 1. This information is provided for
the reader to consider the balance of risks between both cancer and noncancer effects.
Summary
As noted earlier, effects on the blood forming capacity of bone marrow have been
identified as precursor events for leukemia. Therefore the majority of chronic reference values
for the general public and for workers are based on those effects. The organizations developing
the occupational also considered the potential for leukemia in their derivation of short-term and
ceiling values for workers. This concern is founded on the previous discussion on Consideration
of Peak versus Continuous Exposure presented earlier in this document. The effects on the CNS
are the key driver for the emergency response reference values; the application of a once-in-a-
lifetime exposure scenario in the development of those values diminishes the concern for the
potential development of cancer.
Comparisons among Acute Reference Values in Risk Screening
Risks from acute exposures which may occur on a intermittent basis (i.e., more
commonly than the once-in-a-lifetime scenario used with the emergency response values) are
most appropriately addressed by values designed for that purpose - namely, the acute California
RELs and the acute ATSDR MRLs. Emergency response values (such as the AEGLs and
ERPGs) are designed for rare, once-in-a-lifetime accidental releases; however, the one-hour
AEGL-1 and/or ERPG-1 is often used in screening assessments when no other value is available,
or as a "back-stop" value when a preferred screening reference value is exceeded to help identify
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August 2012
a level where effects may be "expected" in the exposed population. Occupational exposure levels
(OELs) are not typically used in characterizing public health risks. Occupational ceiling values
(typically 15 minutes or less) are commonly set at levels higher than a one-hour AEGL-1 or
ERPG-1 for most chemicals, and are not considered protective for the general public.
In the case of benzene, however, the emergency response reference values (AEGLs and
ERPGs) have been established at concentrations that are much higher than the short-term
occupational exposure levels (OELs), with the one-hour ERPG-1 (50 ppm; 156 mg/m3) and
AEGL-1 (52 ppm; 170 mg/m3) values ten times higher than the highest short-term OEL - the 15-
minute OSHA Ceiling value (5 ppm; 15.6 mg/m3). The ACGIH TLV® ceiling value of 2.5 ppm
(8.0 mg/m3) is designed as "not to be exceeded at any time" (ACGIH. 2006). The NIOSH REL-
Short-term Exposure Limit of 1.0 ppm (3.2 mg/m3) is applicable "for any 15 minute period in a
workday" (NIOSH, 2007). This information calls into question the appropriateness of the one-
hour AEGL-1 or ERPG-1 values for benzene in screening risks for the general population
beyond the once-in-a-lifetime exposure scenarios for which they were designed.
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Benzene: Comparison of Reference Values
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Figure I. Available health effect reference values for inhalation exposure to benzene
7
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Benzene
August 2012
Table 1. Details on derivation of the available health effect reference values for inhalation exposure to benzene
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Reference
Value Name
AEGL-3
AEGL-2
AEGL-1
ERPG-3
ERPG-2
ERPG-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
1 hour
1 hour
1 hour
Reference Value
(nig/m3)
31,000
18,000
13,000
6500
3300
6500
3600
2600
1300
650
420
240
170
58
29
3190
470
156
(ppm)
9700
5600
4000
2000
990
2000
1100
800
400
200
130
73
52
18
9.0
1000
150
50
Health Effect
Highest dose
without mortality
within the AEGL
time frame - rats, 4-
h exposure.
Increase in
locomotor activity
with some
incoordination and
tremor - rats, 4-h
exposure.
No report of
symptoms in
humans exposed up
to 2 hours via
inhalation only
Lethality in mice
Observed
occupational levels
5 hr exposure;
headaches,
lassitude, and
general weakness
Transient
neurological effects
expected.
Mean threshold for
odor detection
Point of
Departure
5940 ppm
4000 ppm
110 ppm
10,000 ppm
1000 ppm
150 ppm
50 ppm
61 ppm
Qualifier
NOAEL
LOAEL
NOAEL
LC50
Estimated
NOAEL for
Level 3
effects
Estimated
NOAEL for
Level 2
effects
Estimated
LOAEL
Odor
threshold
Principal
Study
(Molnar et aL
1986)
(Molnar et a\..
1986)
(Srbova et aL
1950)
(Drew and
Fouts, 1974)
(Greenburg,
1926)
(Gerarde,
1960)
(Greenburg,
1926)
Uncertainty
Factors4
Total LTF = 3
UFA=1
UFH=3
Total LTF = 10
UFA=3
LTFH=3
Total LTF = 3
UFA=1
UFH=3
NR
NR
NR
Notes on
Derivation
Duration
adjustments: Cn
x t = k, where n
= 2 for shorter
and n = 1 for
longer durations
Note: ~10x
reduction from
LC50 to derived
value
Review
Status
Interim
(NAC/AEGL
2009)
Final
(AIHA, 2002)
1UFH - 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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Benzene
August 2012
Occupational
Reference
Value Name
ACGffl
TLV-STEL
OSHA-Ceiling
NIOSH STEL
NIOSHIDLH
ACGffl
TLV-TWA
NIOSH REL
(TWA)
OSHA PEL
(TWA)
EEGLs
CEGL
SMACs
Duration
Any
< 1 5 minutes
< 1 5 minutes
30 minutes
8 hour TWA
10 hour
TWA
8 hour TWA
1 hour
24 hour
90 day
1 hour
24 hour
7 day
30 day
180 day
1000 day
Reference Value
(mg/m3)
8.0
16
3.2
1600
1.6
0.32
3.2
128
96
0.64
32
96
1.6
0.32
0.22
0.042
(ppm)
2.5
5.0
1.0
500
0.5
0.1
1.0
40
3.0
0.2
10
3.0
0.5
0.1
0.07
0.013
Health Effect
Peak exposures
causing
hematopoietic
toxicity
NR
NR
Acute inhalation
toxicity data in
humans; Potential
carcinogen
Committee
interpretation of 3
papers analyzing
cumulative
exposure
(ppm-year) -
Pliofilm cohort
Potential
carcinogen; lowest
current detectable
level
NR
CNS Depression in
humans
Immunosuppression
and hematologic
effects in mice
Point of
Departure
20-25
ppm
NR
NR
500 ppm
45
ppm-years
(1 ppm for
45 years)
NR
NR
110 ppm
100 ppm
Qualifier
LOAEL
NR
NR
LOAEL
Judged to
be an
unaccept-
able risk
NR
NR
NOAEL
LOAEL
Principal
Study
(Schnatter et
aL 1996)
(Gerarde,
1960)
(NIOSH, 1996)
(Schnatter et
aL 1996)
(NIOSR 1988)
Srbova et al.
(1950)
Gill et al.
(1980)
Uncertainty
Factors4
NR
NR
NR
NR
NR
NR
NR
Total UF = 3
UFH=3
Total UF = 30
UFL=3
TTF — T,
U-TA J
UFH=3
Notes on
Derivation
Note: ~10x
reduction from
LOAEL
Assumed WOE
approach.
Rounded from
37 to 40 ppm
Rounded from
3.3 to 3 ppm
Review
Status
Final
(ACGLLL
2007)
Final
(NIOSH, 2007)
Final
(ACGIFL
2007)
Final
(NIOSH, 2007)
Final
(NRC, 2008a)
Final
(NRC, 2008b)
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Benzene
August 2012
General Public
Reference
Value Name
Acute
CA-REL
(Severe
Effects)
Acute ATSDR
MRL
Intermediate
ATSDR MRL
Chronic
CA-REL
Chronic
ATSDR MRL
Chronic RfC
(TRIS)
Duration
6 hour
1 -14 days
15-364
days
Chronic
Chronic
(> 1 year)
Chronic
Reference Value
(mg/m3)
1.3
0.029
0.019
0.06
0.0096
0.03
(ppm)
0.4
0.009
0.006
0.02
0.003
0.0094
Health Effect
Decreased fetal
body weights of
pregnant female rats
exposed 6-h/d, GD
6-15
Immunological
effects in exposed
mice
(6-h/d, 6 days)
Immunological
suppression effects
in rats
Hematological
effects for workers
with an average
exposure of 7.4
years (32% exposed
for more than 10
years)
B cell counts in
workers of shoe
manufacturing
industries in
Tianjin, China
Decreased
lymphocyte count
(Human
occupational
inhalation study, 8-
hrTWA)
Point of
Departure
40 ppm
10. 2 ppm
2.55 ppm
10 ppm
1.8 ppm
0.53 ppm
0.1 9 ppm
0.10 ppm
0.03 ppm
23 mg/m3
8.2 mg/m3
Qualifier
NOAEL
LOAEL
LOAELHEC
LOAEL
LOAELHEc
NOAEL
NOAELHEC
BMCL0.25sd
BMCLADJ
BMCL
BMCLHEC
Principal
Study
(Coate et al,
1984)
(Rozenetal.,
1984)
(Rosenthal and
Snvder, 1987)
(Tsaietal.,
1983)
(Lan et al..
2004)
(Rothman et
al.. 1996)
Uncertainty
Factors4
Total UF = 100
UFA=10
UFH = 10
Total UF = 300
UFL=10
UFA=3
UFH = 10
Total UF = 300
UFL=10
UFA=3
UFH=10
Total UF = 10
UFH = 10
Total UF = 10
UFH = 10
Total UF = 300
UFL=3
UFS=3
UFH = 10
UFDB = 3
Notes on
Derivation
No time
extrapolation
Adjustment:
(6-h/24-h)
Duration
adjusted:
(6-h/24-h) x
(5-d/7-d)
Adjustments:
occupational
breathing rate
(10m3 vs. 20m3)
and 5 days per
week.
Duration
adjusted:
(8-h/24-h) x
(6-d/7-d)
Adjustments:
occupational
breathing rate
(10m3 vs. 20m3)
and 5 days per
week.
Review
Status
Final
(OEHHA,
2008a)
Final
(ATSDR,
2007)
Final
(OEHHA,
2008a)
Final
(ATSDR,
2007)
(U.S. EPA,
2002)
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August 2012
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