United States
Environmental Protection
1=1 m m Agency
EPA/690/R-13/016F
Final
7-26-2013
Provisional Peer-Reviewed Toxicity Values for
Nitromethane
(CASRN 75-52-5)
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
Harlal Choudhury, DVM, PhD, DABT
National Center for Environmental Assessment, Cincinnati, OH
Dan D. Petersen, PhD, DABT
National Center for Environmental Assessment, Cincinnati, OH
DRAFT DOCUMENT PREPARED BY
ICF International
9300 Lee Highway
Fairfax, VA 22031
PRIMARY INTERNAL REVIEWERS
Dan D. Petersen, PhD, DABT
National Center for Environmental Assessment, Cincinnati, OH
Suryanarayana V. Vulimiri, BVSc, PhD, DABT
National Center for Environmental Assessment, Washington, DC
This document was externally peer reviewed under contract to
Eastern Research Group, Inc.
110 Hartwell Avenue
Lexington, MA 02421-3136
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).
li

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TABLE OF CONTENTS
COMMONLY USED ABBREVIATIONS	iv
BACKGROUND	1
DISCLAIMERS	1
QUESTIONS REGARDING PPRTVs	1
INTRODUCTION	2
REVIEW OF POTENTIALLY RELEVANT DATA (CANCER AND NONCANCER)	4
HUMAN STUDIES	10
Oral Exposures	10
Inhalation Exposures	10
ANIMAL STUDIES	11
Oral Exposures	11
Inhalation Exposures	12
OTHER DATA (SHORT-TERM TESTS, OTHER EXAMINATIONS)	22
Tests Evaluating Carcinogenicity, Genotoxicity, and/or Mutagenicity	27
Other Toxicity Studies (Exposures Other Than Oral or Inhalation)	27
Short-Term Studies	27
Metabolism/Toxicokinetic Studies	27
Mode-of-Action/Mechanistic Studies	28
Immunotoxicity	28
Neurotoxicity	28
DERIVATION 01 PROVISIONAL VALUES	28
DERIVATION OF ORAL REFERENCE DOSES	29
Derivation of Subchronic and Chronic Provisional RfD (p-RfD)	29
DERIVATION OF INHALATION REFERENCE CONCENTRATIONS	29
Derivation of Subchronic Provisional RfC (Subchronic p-RfC)	29
Derivation of Chronic Provisional RfC (Chronic p-RfC)	34
CANCER WEIGHT-OF-EVIDENCE (WOE) DESCRIPTOR	40
MODI: OI -ACTION DISCI SSION	40
DERIVATION OF PROVISIONAL CANCER POTENCY VALUES	40
Derivation of Provisional Oral Slope Factor (p-OSF)	40
Derivation of Provisional Inhalation Unit Risk (p-IUR)	40
APPENDIX A. PROVISIONAL SCREENING VALUES	43
APPENDIX B. DATA TABLES	44
APPENDIX C. BMD OUTPUTS	63
APPENDIX D. REFERENCES	73
in

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COMMONLY USED ABBREVIATIONS
BMC
benchmark concentration
BMCL
benchmark concentration lower bound 95% confidence interval
BMD
benchmark dose
BMDL
benchmark dose lower confidence limit
HEC
human equivalent concentration
HED
human equivalent dose
IUR
inhalation unit risk
LOAEL
lowest-observed-adverse-effect level
LOAELadj
LOAEL adjusted to continuous exposure duration
LOAELhec
LOAEL adjusted for dosimetric differences across species to a human
NOAEL
no-ob served-adverse-effect level
NOAELadj
NOAEL adjusted to continuous exposure duration
NOAELhec
NOAEL adjusted for dosimetric differences across species to a human
NOEL
no-ob served-effect level
OSF
oral slope factor
p-IUR
provisional inhalation unit risk
POD
point of departure
p-OSF
provisional oral slope factor
p-RfC
provisional inhalation reference concentration
p-RfD
provisional oral reference dose
RfC
inhalation reference concentration
RfD
oral reference dose
UF
uncertainty factor
UFa
interspecies uncertainty factor
UFC
composite uncertainty factor
UFd
database uncertainty factor
UFh
intraspecies uncertainty factor
UFl
LOAEL-to-NOAEL uncertainty factor
UFS
subchronic-to-chronic uncertainty factor
WOE
weight of evidence
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PROVISIONAL PEER-REVIEWED TOXICITY VALUES FOR
NITROMETHANE (CASRN 75-52-5)
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 flittp://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 (http://www.epa.eov/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
Nitromethane, CAS No. 75-52-5, is a nitroparaffin. Nitromethane is primarily used in
rocket and racing fuel as a gasoline additive and is also widely used as an industrial solvent. It
can be produced by high-temperature, vapor-phase nitration of propane or methane using nitric
acid in a free-radical reaction or by the interaction of sodium nitrite and sodium chloroacetate
(HSDB, 2010). A table of physicochemical properties is provided below (see Table 1). The
molecular formula for nitromethane is CH3NO2 (see Figure 1).
ch3—no2
Figure 1. Nitromethane Structure
Table 1. Physicochemical Properties of Nitromethane (CASRN 75-52-5)a
Property (unit)
Value
Boiling point (°C)
101.1
Melting point (°C)
-28.5
Relative density (g/cm3 at 20°C)
1.1371
Vapor pressure (mmHg at 25°C)
35.8
pH (unitless, 0.01M aqueous solution)
6.12
Solubility in water (mg/L at 25°C)
1.11 x 105
Relative vapor density (air =1)
2.11
Molecular weight (g/mol)
61.04
aHSDB (2010).
A summary of the available toxicity values for Nitromethane from U.S. EPA and other
agencies/organizations is provided below (see Table 2).
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Table 2. Summary of Available Toxicity Values for Nitromethane (CASRN 75-52-5)
Source/Parameter"
Value
(Applicability)
Notes
Reference
Date Accessed
Noncancer
ACGIH
8-hr TLV-TWA =
20 ppm
NA
ACGIH (2008)
NA
ATSDR
NV
NA
ATSDR
7-22-2013
Cal/EPA
NV
NA
Cal/EPA (2012)
NA
NIOSH
NV
NIOSH did submit comments to
OSHA regarding its "Proposed Rule
on Air Contaminants" (29 CFR
1910, Docket No. H-020)
questioning whether the OSHA PEL
for nitromethane was "adequate to
protect workers from recognized
health hazards" (NIOSH, 2011b)
NIOSH (2011a)
NA
OSHA
8-hr PEL-TWA =
100 ppm
NA
OSHA (2006)
NA
IRIS
NV
NA
U.S. EPA
7-22-2013
Drinking water
NV
HEEP declined to derive noncancer
toxicity values due to inadequate
data on noncancer effects and
potential carcinogenic effects of the
chemical
U.S. EPA
(2011a)
NA
HEAST
NV
NA
U.S. EPA
(2011b)
NA
CARA HEEP
NV
NA
U.S. EPA (1994,
1985)
NA
WHO
NV
NA
WHO
7-22-2013
Cancer
IRIS
NV
NA
U.S. EPA
7-22-2013
HEAST
NV
NA
U.S. EPA
(2011b)
NA
IARC
Group 2B, "Possibly
Carcinogenic to
Humans "
Based on sufficient animal
carcinogenicity evidence
IARC (2000)
NA
NTP
"Reasonably
Anticipated to be a
Human
Carcinogen"
In the key study that supports this
classification, increased mammary
gland tumors in female rats,
increased benign and malignant
tumors in the Harderian gland and
lung of male and female mice, and
liver tumors in female mice were
observed (NTP, 1997).
NTP (2011)
NA
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Table 2. Summary of Available Toxicity Values for Nitromethane (CASRN 75-52-5)
Source/Parameter"
Value
(Applicability)
Notes
Reference
Date Accessed
Cal/EPA
NSRL =39 ng/day
Cancer Potency =
0.18 mg/kg-dayb

Cal/EPA (2007)
NA
aSources: American Conference of Governmental Industrial Hygienists (ACGIH); Agency for Toxic Substances and
Disease Registry (ATSDR); California Environmental Protection Agency (Cal/EPA); National Institute for
Occupational Safety and Health (NIOSH); Occupational Safety and Health Administration (OSHA); Chemical
Assessments and Related Activities (CARA); Health and Environmental Effects Profile (HEEP); World Health
Organization (WHO); Integrated Risk Information System (IRIS); Health Effects Assessment Summary Tables
(HEAST); International Agency for Research on Cancer (IARC); National Toxicology Program (NTP).
bThis value was derived from NTP (1997) using "Route to Route" extrapolation.
IDLH= immediately dangerous to life or health; NA = not applicable; NSRL = no significant risk level; NV = not
available; PEL-TWA = permissible exposure level-time weighted average; REL-TWA = recommended exposure
level-time weighted average; TLV-TWA = threshold limit value-time weighted average.
Literature searches were conducted on sources published from 1900 through June 2013,
for studies relevant to the derivation of provisional toxicity values for nitromethane, CAS No.
75-52-5. Searches were conducted using EPA's Health and Environmental Research Online
(HERO) database of scientific literature. HERO searches the following databases: AGRICOLA;
American Chemical Society; BioOne; Cochrane Library; DOE: Energy Information
Administration, Information Bridge, and Energy Citations Database; EBSCO: Academic Search
Complete; GeoRef Preview; GPO: Government Printing Office; Informaworld; IngentaConnect;
J-STAGE: Japan Science & Technology; JSTOR: Mathematics & Statistics and Life Sciences;
NSCEP/NEPIS (EPA publications available through the National Service Center for
Environmental Publications [NSCEP] and National Environmental Publications Internet Site
[NEPIS] database); PubMed: MEDLINE and CANCERLIT databases; SAGE; Science Direct;
Scirus; Scitopia; SpringerLink; TOXNET (Toxicology Data Network): ANEUPL, CCRIS,
ChemlDplus, CIS, CRISP, DART, EMIC, EPIDEM, ETICBACK, FEDRIP, GENE-TOX,
HAPAB, HEEP, HMTC, HSDB, IRIS, ITER, LactMed, Multi-Database Search, NIOSH, NTIS,
PESTAB, PPBIB, RISKLINE, TRI; and TSCATS; Virtual Health Library; Web of Science
(searches Current Content database among others); World Health Organization; and Worldwide
Science. The following databases outside of HERO were searched for toxicity values: ACGIH,
ATSDR, 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
(CANCER AND NONCANCER)
Table 3 provides an overview of the relevant database for nitromethane and includes all
potentially relevant repeated short-term-, subchronic-, and chronic-duration studies. NOAELs,
LOAELs, and BMDL/BMCLs are provided in HED/HEC units for comparison except that oral
noncancer values are not converted to HEDs and are identified in parentheses as (Adjusted)
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rather than HED/HECs. Principal studies are identified in bold. Following the table, important
aspects of all the studies in the table are provided in the same order as the table. Reference can
be made to details provided in Table 3. The phrase "statistical significance," used throughout the
document, indicates a value of <0.05.
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Table 3. Summary of Potentially Relevant Data for Nitromethane (CASRN 75-52-5)
Category
Number of
Male/Female, Strain,
Species, Study Type,
Study Duration
Dosimetry"
Critical Effects
NOAEL"
BMDL/
BMCLa
LOAEL'
Reference
(Comments)
Notesb
Human
1. Oral (mg/kg-d)a
Acute0
1/0, age 18, oral
ingestion, case study,
single ingestion
NR
Neurological symptoms
NDr
DU
NDr
Fernandez et al.
(2008)
PR
Short-termd
ND
Long-term6
ND
Chronicf
ND
2. Inhalation (mg/m3)a
Acute0
ND
Short-termd
1/1, age 23 and 26 yr,
inhalation, occupational
case study, 1-2 mo
25-50
(mean =32)
Neurological symptoms
NDr
DU
NDr
Page et al.
(2001)
PR
Long-term0
ND
Chronicf
ND
Reproductive
ND
Carcinogenicity
ND
Animal
1. Oral (mg/kg-d)a
Subchronic
10/0, albino rat, drinking
water, 15 wk
0, 131,280s
(Adjusted)
Mortality, reduced body weight, and
reduced water consumption
NDr
DU
131 (FEL)
Weatherby
(1955)
PR
Chronic
ND
Developmental
ND
Reproductive
ND
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Table 3. Summary of Potentially Relevant Data for Nitromethane (CASRN 75-52-5)
Category
Number of
Male/Female, Strain,
Species, Study Type,
Study Duration
Dosimetry"
Critical Effects
NOAEL"
BMDL/
BMCLa
LOAEL'
Reference
(Comments)
Notesb
Carcinogenicity
ND
2. Inhalation (mg/m3)a
Short-term
5/5, F344 rat, whole
body inhalation, 6 hr
12 min/d, 5 d/wk, 16 d
(12 exposures)
M: 0, 5.7, 11.2,
22.1,43.5, 86.lh
F: 0,4.5,8.9,
17.7,35.3,69.7
Degeneration of the olfactory
epithelium of the nasal turbinates1
M: 11.2
F: 8.9
DU
M: 22.1
F: 17.7
NTP (1997)
PR

5/5, B6C3F, mouse,
whole body inhalation,
6 hr 12 min/d, 5 d/wk,
16 d (12 exposures)
M: 0, 6.6, 13.0,
25.6, 52.1,
103.7h
F: 0, 5.1, 10.2,
20.2, 40.9, 81.9
Degeneration of the olfactory
epithelium of the nasal turbinates1
M: 13.0
F: 10.2
DU
M: 25.6
F: 20.2
NTP (1997)
PR
Subchronic
10/10, F344 rat, whole
body inhalation, 6 hr
12 min/d, 5 d/wk, 13 wk
M: 0,6.6, 13.9,
27.1,53.0,
100. lh
F: 0, 4.8, 9.7,
19.2, 38.1,72.1
Degeneration of the olfactory
epithelium of the nasal turbinates1
M: 13.9
F: 9.7
DU
M: 27.1
F: 19.2
NTP (1997)
PR

10/0, Sprague-Dawley
rat, whole body
inhalation, 7 hr/d,
5 d/wk, 3 mo
0, 51, 388J
Decreased hematocrit and hemoglobin
levels
51
NCk
388
Lewis et al.
(1979)
PR

10/10, B6C3Fi mouse,
whole body inhalation,
6 hr 12 min/d, 5 d/wk,
13 wk
M: 0, 7.1,14.1,
28.0,55.7,
112.7h
F: 0,5.9,12.2,
24.9,48.0, 93.9
Degeneration of the olfactory
epithelium and hyaline droplets in
the respiratory epithelium of the
nasal turbinates'
5.9 (F)
1.31
12.2 (F)
NTP (1997)
PS, PR
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Table 3. Summary of Potentially Relevant Data for Nitromethane (CASRN 75-52-5)
Category
Number of
Male/Female, Strain,
Species, Study Type,
Study Duration
Dosimetry"
Critical Effects
NOAEL"
BMDL/
BMCLa
LOAEL'
Reference
(Comments)
Notesb
Subchronic
5/0, New Zealand white
rabbit, whole body
inhalation, 7 hr/d,
5 d/wk, 3 mo
0, 51, 388J
Decreased thyroxin levels
51
NCg
388
Lewis et al.
(1979)
PR
Chronic
10/0, Sprague-Dawley
rat, whole body
inhalation, 7 hr/d,
5 d/wk, 6 mo
0, 51, 388J
Increased relative thyroid weight
51
NCk
388
Lewis et al.
(1979)
PR

50/50, F344 rat, whole
body inhalation, 6 hr
12 min/d, 5 d/wk,
103 wk
0, 43, 87, 173J
No noncancer effects observed
173
DU
NDr
NTP (1997)
PR

40/40, Long-Evans rat,
whole body inhalation,
7 hr/d, 5 d/wk, 2 yr
0, 45.6, 89.01
No noncancer effects observed
89.0
DU
NDr
Griffin et al.
(1996)
PR

50/50, B6C3Fi mouse,
whole body inhalation,
6 hr 12 min/d, 5 d/wk,
103 wk
M: 0,22.2,
44.9,91.6h
F: 0,21.9,43.2,
87.9
Increased nonneoplastic nasal lesions
NDr
1.60
M: 22.2
F: 21.9
NTP (1997)
PS, PR

5/0, New Zealand white
rabbit, whole body
inhalation, 7 hr/d,
5 d/wk, 6 mo
0, 51, 388J
Decreased thyroxin levels
NDr
NCk
51
Lewis et al.
(1979)
PR
Developmental
ND
Reproductive
ND
Carcinogenicity
50/50, F344 rat, whole
body inhalation, 6 hr
12 min/d, 5 d/wk,
103 wk
0,43, 87,173j
Increased incidence of mammary
gland tumors
NA
NA
NA
NTP (1997)
PS, PR
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Table 3. Summary of Potentially Relevant Data for Nitromethane (CASRN 75-52-5)
Category
Number of
Male/Female, Strain,
Species, Study Type,
Study Duration
Dosimetry"
Critical Effects
NOAEL3
BMDL/
BMCLa
LOAEL3
Reference
(Comments)
Notesb
Carcinogenicity
40/40, Long-Evans rat,
whole body inhalation,
7 hr/d, 5 d/wk, 2 yr
0, 45.6, 89.01
No cancer effects observed
NA
NA
NA
Griffin et al.
(1996b)
PR
50/50, B6C3F, mouse,
whole body inhalation,
6 hr 12 min/d, 5 d/wk,
103 wk
0, 87, 173, 346J
Increased incidence of Harderian gland
and liver tumors; BMD based
Harderian gland adenomas or
carcinomas in males
NA
NA
NA
NTP (1997)
PR
""Dosimetry: NOAEL, BMDL/BMCL, and LOAEL values are converted to an adjusted daily dose (ADD in mg/kg-d) for oral noncancer effects and a human equivalent
concentration (HEC in mg/m3) for inhalation noncancer and carcinogenic effects. All long-term exposure values (4 wk and longer) are converted from a discontinuous
to a continuous exposure.
bNotes: IRIS = utilized by IRIS, date of last update; PS = principal study; PR = peer reviewed; NPR = not peer reviewed; NA = not applicable.
0 Acute = Exposure for 24 hours or less (U.S. EPA, 2002).
dShort-term = Repeated exposure for >24 h <30 d (U.S. EPA, 2002).
"Long-term = Repeated exposure for >30 d <10% lifespan (based on 70 years typical lifespan) (U.S. EPA, 2002).
fChronic = Repeated exposure for >10% lifespan (U.S. EPA, 2002).
8Daily doses were estimated from digitizing the data in the figure of weekly intakes provided in the study report.
hHECRESp = (ppm x MW ^ 24.45) x (hours per day exposed ^ 24) x (days per week exposed ^ 7) x regional gas dose ratio.
'Extra-respiratory effects were also observed, but the respiratory effects provided the lowest NOAEL/LOAEL.
jHECExresp = (ppm x MW ^ 24.45) x (hours per day exposed ^ 24) x (days per week exposed ^ 7) x blood:gas partition coefficient.
kBMD was not conducted on the data because the effects occurred at concentrations several fold higher than the critical effect in the principal study.
'HECexresp = mg/m3 x (hours per day exposed ^ 24) x (days per week exposed ^ 7) x blood:gas partition coefficient.
DU = data unsuitable; NA = not applicable; NC = not conducted; ND = no data; NDr = not determinable; NR = not reported.
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HUMAN STUDIES
Oral Exposures
The effects of oral exposure of humans to nitromethane have been evaluated in one case
study of an acute exposure (Fernandez et al., 2008). An 18-year-old male ingested an
undetermined amount of nitromethane fuel. He had generalized tonic-clonic seizures that
progressed to partial motor status epilepticus and was also hypertensive. A neurological exam
showed him to have mild left dysmetria in finger-to-nose testing, low frequency intention tremor,
broad-based gait, and inability to tandem-walk. An MRI revealed bilateral and symmetric
lesions in cerebellar white matter, tonsils, uvula, and colliculi. Initial therapy included valproic
acid, P-blockers, and clonidine to treat the symptoms. Valproic acid treatment continued. Eight
months after exposure there were no abnormalities observed during a clinical exam or in an MRI.
There were no other oral studies in humans identified.
Inhalation Exposures
The effects of subchronic inhalation exposure of humans to nitromethane have been
evaluated in two case reports on individuals exposed for 1 or 2 months (Page et al., 2001). An
investigation was initiated due to severe peripheral neuropathy in two workers in a headlight
subassembly plant. OSHA was called in to conduct an industrial hygiene inspection at the plant.
In the plant, nitromethane was used to clean off excess glue on the headlights. Nitromethane was
sprayed on, and because it was wiped off with a rag without the use of gloves, dermal exposure
occurred as well as inhalation exposure. However, in a separate study, Coulston International
Inc. (1990) found that very little nitromethane was absorbed dermally in rhesus monkeys. As
part of the investigation by Page et al. (2001), the air was sampled for nitromethane and ethyl
cyanoacrylate over a 2-day period. Nitromethane was measured in the personal breathing zone
of four workers cleaning headlights. Nitromethane levels ranged from 10-20 ppm
(25-50 mg/m3) with a mean of 12.75 ppm (32 mg/m3) as the 8-hour TWA. A 26-year-old
woman who cleaned the headlights with nitromethane began to note weakness in her hands, legs,
and feet within a month of beginning the job. She stopped working but felt worse 2 weeks later
and was admitted to the hospital. A neurological exam indicated that gastroscoleus and
brachioradialis reflexes were absent with weakness more severe distally and in the lower
extremities. An MRI did not reveal any abnormalities in the spinal cord. Laboratory tests did
not find any abnormalities, but serum immunoelectrophoresis showed an increased gamma
component, and a lumbar puncture showed elevated protein levels with a normal cell count. She
was eventually diagnosed with severe peripheral neuropathy and had only slight improvement
within 8 months. Four to five months later, a 23-year-old male began complaining about foot
numbness within 1.5 weeks of beginning work, which progressed over the next few weeks to
pain and swelling in both legs and feet. After about 6 weeks of employment as a headlight
cleaner, the man was admitted to the hospital. Peripheral neuropathy of the lower extremities
with normal testing on the upper extremities was observed. The individual demonstrated
diminished lower extremity reflexes, slightly decreased muscle strength on dorsiflexon of both
feet, and decreased sensation to pinprick up to the middle of the shin. Laboratory tests for this
individual were unremarkable, but symptoms persisted. Follow-up electrodiagnostic studies
found progressive denervation and severe axonal peripheral neuropathy. This individual had
significant, but not complete, improvement. No other inhalation studies in humans were
identified.
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ANIMAL STUDIES
Oral Exposures
The effects of oral exposure in animals to nitromethane have been evaluated in one
subchronic study (Weatherby, 1955).
Subchronic Studies
Weatherby (1955)
Weatherby (1955) exposed young male albino rats (10/treatment group) to 0, 0.1%,
0.25%, 0.5%), P/o, or 2% nitromethane (purity not reported) via drinking water for 15 weeks.
There is no indication that the dose formulations were measured for homogeneity, stability, or
concentration. It was stated that due to the slight solubility of nitromethane, emulsification with
methylcellulose was used. During the first week, animals did not drink the water with
concentrations >0.5%, and these groups were discontinued. However, several of the exposed
animals did die during this time (number not specified), and survivors were sacrificed for
microscopic examination of the tissues. The failure in these groups was attributed to refusal of
the water. Fluid intake was recorded daily, and the intake of nitromethane was calculated.
Intake levels were apparently measured on a per-cage basis, but the study report did not specify
how many rats were maintained per cage. The weekly intakes (mg nitromethane/kg-week) were
presented in the study report as a figure only and have been estimated by digitizing the data. The
weekly intakes divided by seven provide estimated daily intakes of 131 mg/kg-day for the
0.1% group and 280 mg/kg-day for the 0.25% group. Body weights were measured weekly.
Body weight and body-weight gain were lower than that of control animals in both nitromethane
groups, but this observation did not appear to dose related and may have been a function of
reduced fluid intake. Animals were stated to be in moderately good health at study termination.
Four of the 131-mg/kg-day animals and three of the 280-mg/kg-day animals died during
treatment. Due to destruction by their cage mates, the dead animals were not examined. At
study termination, all survivors were sacrificed, and tissues (heart, lungs, liver, spleen, kidney,
testes, adrenal gland, and small intestines) were examined microscopically. In the
131-mg/kg-day group, two of the six survivors had large hepatic cells with prominent nuclei. In
the 280-mg/kg-day group, two of the seven survivors had Malpighian corpuscles that appeared
more prominent than the normal spleens, and six of the survivors had a granular appearance in
the cytoplasm of the hepatic cells, less deeply stained hepatocytes, more prominent nuclei, and
lymphocytes in the periportal region. One of the 10 surviving controls had large hepatic cells
with prominent nuclei. No NOAEL or LOAEL can be determined because the lowest dose was a
frank effect level (FEL) due to mortality.
Chronic Studies
There is no suitable information to provide in this regard.
Developmental Studies
There is no suitable information to provide in this regard.
Reproductive Studies
There is no suitable information to provide in this regard.
Carcinogenicity Studies
There is no suitable information to provide in this regard.
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Inhalation Exposures
The effects of inhalation exposure of animals to nitromethane have been evaluated in a
short-term study in both rats and mice (NTP 1997), two subchronic studies in both rats and mice
(NTP, 1997; Lewis, 1979), chronic studies in rats and mice (NTP, 1997; Lewis, 1979) and rats
only (Griffin, 1996), and carcinogenicity studies in rats and mice (NTP, 1997) and rats only
(Griffin, 1996). All the reports provided information on multiple studies and are individually
discussed in this section.
Short-Term Studies
NTP (1997)
In the various substudies conducted by NTP (1997) summarized below, a small particle
detector (Type CN, Gardner Associates, Schenectady, NY) was used with and without animals in
the exposure chambers to ensure that nitromethane vapor, and not aerosol, was produced. The
purity of the chemical was analyzed by gas chromatography and carefully monitored during
exposures (details are provided on pages 21-23 of the study report).
For the short-term study, individually housed F344 rats (5/sex/treatment group) were
administered nitromethane (purity >98%) at concentrations of 0; 94; 188; 375; 750; or
1,500 ppm via whole body inhalation for 6 hours and 12 minutes (12 minutes was the time it
took to achieve 90% target concentration) a day, 5 days a week, for 16 days (total of
12 exposures). Chamber concentrations were routinely checked over the course of exposure.
Animals were observed twice a day for clinical signs of toxicity. Animals were weighed at study
initiation and on Days 8 and 16. At study termination, animals were necropsied, and the heart,
right kidney, liver, lungs, right testis, thymus, and thyroid glands were weighed. Histopathology
was conducted on respiratory tissues, brain, and sciatic nerve. Typical NTP statistical methods
were applied and were appropriate for the data.
All rats survived until study termination. Clinical signs were observed in the high-dose
group only and included increased preening, rapid breathing, hyperactivity early in the study, and
hypoactivity and loss of coordination near the end of the study in all animals of both sexes.
Although there were no statistically significant (p < 0.05) effects on body weight in any of the
groups, high-dose males had a significantly (p < 0.05) lower body-weight gain compared with
the controls (see Table B. 1). Necropsy body weight was significantly reduced in the high-dose
males (see Table B.2). Absolute and relative liver weights were significantly increased and
>10%) different from controls in female rats at concentrations >750 ppm. Relative liver weights
were significantly increased in all male treatment groups but were only >10% different from
controls at concentrations of 375 and 1,500 ppm (see Table B.2). Relative kidney weight was
significantly increased by >10% in high-dose males and females. In all males and all but one
female administered >375 ppm, there was degeneration of the olfactory epithelium of the nasal
turbinates with minimal to mild severity and degeneration of the sciatic nerve with severity
(minimal to moderate) increasing with exposure concentration (see Table B.3). Because
respiratory and extra-respiratory effects were observed, human equivalent concentrations (HECs)
are calculated for both effects. The average of initial and final body weight is used in the
calculation of HECs for respiratory effects. The HECs for respiratory effects are 5.7, 11.2, 22.1,
43.5, and 86.1 mg/m3 in males, respectively, and 4.5, 8.9, 17.7, 35.3, and 69.7 mg/m3 in females,
respectively, after adjusting for duration and multiplying by the regional gas dose ratio (RGDR)
for extra-thoracic effects. The RGDR is the ratio of the minute volumes to the applicable surface
areas of the lung in the two species respectively (see U.S. EPA 1994b, pages 4-44 through 4-64).
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This ratio is used to adjust the observed gas exposure level for interspecies dosimetric
differences. The NOAEL for respiratory effects is 11.2 mg/m3 in males and 8.9 mg/m3 in
3	3
females. The LOAEL for respiratory effects is 22.1 mg/m in males and 17.7 mg/m in females
based on degeneration of the olfactory epithelium in nasal turbinates. HECs for extra-respiratory
effects calculated by adjusting for duration and using the default blood:gas partition coefficient
of 1 since chemical-specific information is unavailable (see U.S.EPA 1994b). The
"3
corresponding values are 46, 91, 181, 363, and 726 mg/m in both sexes. The NOAEL for
systemic effects is 91 mg/m3, and the LOAEL is 181 mg/m3 based on degeneration of the sciatic
nerve in both sexes.
NTP (1997)
Individually housed male and female B6C3Fi mice (5/sex/treatment group) were
administered nitromethane (purity >98%) at concentrations of 0; 94; 188; 375; 750; or
1,500 ppm via whole body inhalation for 6 hours and 12 minutes a day, 5 days a week, for
16 days (total of 12 exposures). Chamber concentrations were routinely checked over the course
of exposure. Animals were observed twice a day for clinical signs of toxicity. Animals were
weighed at study initiation and on Days 8 and 16. At study termination, animals were
necropsied, and the heart, right kidney, liver, lungs, right testis, thymus, and thyroid glands were
weighed. Histopathology was conducted on respiratory tissues, brain, and sciatic nerve. Typical
NTP statistical methods were applied and were appropriate for the data.
All mice survived until study termination. Clinical signs were observed in the high-dose
group only and included hypoactivity and tachypnea of both sexes at the end of the study. There
were no treatment-related effects on body weight or gross pathology. Absolute liver weight was
>10% different from controls at all concentrations in both sexes, but relative liver weights were
statistically significant and >10% different from controls at concentrations >375 ppm in males
and >188 ppm in females (see Table B.4). All males and females administered >375 ppm had
degeneration of the olfactory epithelium of the nasal turbinates with minimal to mild severity.
Because respiratory and extra-respiratory effects were observed, HECs are calculated for both
effects. The average of initial and final body weight is used for the calculation of HECs for
respiratory effects. HECs for respiratory effects are 6.6, 13.0, 25.6, 52.1, and 103.7 mg/m in
males, respectively, and 5.1, 10.2, 20.2, 40.9, and 81.9 mg/m3 in females, respectively, after
adjusting for duration and multiplying by the RGDR for extra-thoracic effects. The NOAEL for
respiratory effects is 13.0 mg/m in males and 10.2 mg/m3 in females. The LOAEL for
3	3
respiratory effects is 25.6 mg/m in males and 20.2 mg/m in females based on degeneration of
the olfactory epithelium in nasal turbinates. HECs for extra-respiratory effects calculated by
adjusting for duration and using the default blood:gas partition coefficient of 1 (chemical-
specific information was unavailable) are 46, 91, 181, 363, and 726 mg/m3 in both sexes. The
3	3
NOAEL for systemic effects is 46 mg/m , and the LOAEL is 91 mg/m based on increased
relative liver weights in females.
Subchronic Studies
NTP (1997)
Individually housed male and female F344 rats (10/sex/treatment group) were
administered nitromethane (purity >98%) at concentrations of 0; 94; 188; 375; 750; or
1,500 ppm via whole body inhalation for 6 hours and 12 minutes a day, 5 days a week, for
13 weeks. Chamber concentrations were routinely checked over the course of exposure.
Animals were observed twice a day for clinical signs of toxicity. Animals were weighed at study
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initiation, weekly, and at study termination. Blood was collected on Days 3 and 23 and at study
termination for hematology (hematocrit, hemoglobin, erythrocyte counts, nucleated erythrocyte
counts, mean cell volume [MCV], mean cell hemoglobin [MCH], mean cell hemoglobin
concentration [MCHC], platelet counts, total leukocyte count and differentials, and
methemoglobin) and clinical chemistry (blood urea nitrogen [BUN], creatinine, total protein,
albumin, globulin, alanine aminotransferase [ALT], alkaline phosphatase, creatine kinase,
sorbitol dehydrogenase, bile acid, thyroid-stimulating hormone [TSH], triiodothyronine, and
total and free thyroxine concentrations). At study termination, animals were necropsied, and the
heart, right kidney, liver, lungs, right testis, thymus, and thyroid glands were weighed. Complete
histopathology was conducted on control and high-dose animals. In addition, the following
tissues were examined in the lower concentrations until a no-effect level (NOEL) was reached:
bone marrow, lung, and nose in both sexes; and cecum, larynx, and testis in male rats. Sperm
samples were collected from the 0; 375-; 750-; and 1,500-ppm groups at study termination and
evaluated for sperm count and motility. The left cauda, epididymis, and testis were weighed.
Vaginal samples were collected for seven consecutive days before study termination and
evaluated for the relative frequency of estrous stages and for estrous cycle length.
Neurobehavioral tests (forelimb and hindlimb grip strength, tail flick latency, and startle
response) were conducted during Week 11. Typical NTP statistical methods were applied and
were appropriate for the data.
All rats survived until study termination. Clinical signs included hindlimb paralysis in all
high-dose males and females beginning on Day 21, and one male and four females in the
750-ppm group beginning on Day 63. There was a statistically significant decrease in terminal
body weight and body-weight gain in high-dose males (see Table B.5). There were several
changes in hematology in all treatment groups (see Table B.6). These animals developed
microcytic responsive anemia as indicated by mild-to-moderate decreases in hematocrit and
hemoglobin and minimal-to-moderate decreases in mean cell volume (see Table B.6). MCH
levels were also consistently decreased. The results were dose dependent but were most
prominent with concentrations >375 ppm. Although the increases in MCHC were less than 5%
from the control, the change was consistent. The study authors also reported several changes in
erythrocyte morphology related to damage and anemia (e.g., Heinz bodies, schistocytes,
polychromasia), but data were not provided. Hyperplasia in the bone marrow was observed at
concentrations of 750 and 1,500 ppm, supporting the hematology findings. There were also
consistent increases in platelets and methemoglobin mainly at concentrations of 750 and
1,500 ppm. Although there were changes in thyroid hormone levels on Day 23, this was a
transient effect in both males and females. Thyroid weight was increased in 1,500-ppm males
only, but only the relative weight was statistically significant, which is likely an effect of the
lower body weight in this group. There were no other biologically significant changes in organ
weights. At concentrations >375 ppm, there was degeneration of the olfactory epithelium of the
nasal turbinates with minimal-to-mild severity and degeneration of the sciatic nerve and spinal
cord with severity increasing with exposure concentration (see Table B.7). Grip strength was
only significantly reduced in high-dose males (hind and forelimb) and females (hindlimb) (see
Table B.8). There was a statistically significant decrease in absolute left cauda, epididymis, and
testis weight in high-dose males. Although this finding may be due to reduced body weight,
there also was a 15% decrease in sperm concentration, and sperm motility was significantly
decreased with concentrations of 750 and 1,500 ppm (see Table B.9). There were no
treatment-related changes in estrous cycle length or stages. Because respiratory and
extra-respiratory effects were observed, HECs are calculated for both effects. Because only
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initial and final body weights were provided, the average is used to estimate average body
weights for the calculation of HECs for respiratory effects. The HECs for respiratory effects are
6.6, 13.9, 27.1, 53.0, and 100.1 mg/m3 in males, respectively, and 4.8, 9.7, 19.2, 38.1, and
72.1	mg/m3 in females, respectively, after adjusting for duration and multiplying by the RGDR
for extra-thoracic effects. HECs for extra-respiratory effects calculated by adjusting for duration
and using the default blood:gas partition coefficient of 1 are 43, 87, 173, 346, and 691 mg/m3 in
both sexes. The NOAEL is 188 ppm, and the LOAEL is 375 ppm based on anemia accompanied
by changes in the bone marrow and histopathology of the nasal turbinates, sciatic nerve, and
spinal cord. Because the respiratory effects relay a lower HEC value, the study NOAEL is
13.9 mg/m3 in males and 9.7 mg/m in females, and the LOAEL is 27.1 mg/m in males and
"3
19.2	mg/m in females.
Lewis etal. (1979)
Male Sprague-Dawley rats (10/treatment group) were administered nitromethane (96.5%
pure with 1.5% nitroethane and 1.4% 2-nitropropane) at analytical concentrations of 0, 98 ± 5, or
745 ± 34 ppm via whole body inhalation, 7 hours a day, 5 days a week, for 3 months
(Lewis et al., 1979a). While Lewis et al. (1979) provided a peer-reviewed publication of the
data, the proprietary data were also available for review (Huntingdon Research Center, 1989).
Additional groups of 10 animals/concentration group were sacrificed at 2 days, 10 days, and
1 month. Animals were housed in groups of 10 in wire mess stainless-steel cages, which were
part of the exposure chamber. Chamber concentrations were measured hourly and recorded
twice a day. Animals were observed daily for overt signs of toxicity. Body weights were
obtained at regular intervals. At sacrifice, blood was collected for hematology (erythrocyte
counts [RBC], hematocrit, hemoglobin, prothrombin time, and methemoglobin) and clinical
chemistry (ALT, ornithine carbamyl transferase [OCT], and thyroxin). Animals were
necropsied, and select organs (brain, liver, kidneys, lungs, and thyroid) were weighed. Tissue
samples were obtained from the brain and lungs. The samples were weighed, dried, and weighed
again to determine the percent of water. Adrenals, bronchi, cerebellum, cerebral hemispheres,
eyes, kidneys, liver, lung, spleen, thyroid, and trachea were examined histologically.
Appropriate statistical methods (Bartlett's test for homogeneity of variance; one-way analysis of
variance followed by Student's /-test) were conducted on the data.
Not all the data were provided in Lewis et al. (1979). Data in the Huntingdon Research
Center (1989) report were not provided in any sort of order, were hard to find (tables were not in
order), and, in some cases, were not reported. Both sources were used for evaluation. There
were no clinical signs of toxicity noted and no treatment-related effects on mortality. There was
no difference in body weight between the low-dose group and controls. However, high-dose rats
were stated to have a slower weight gain that was statistically significant from the control
beginning around Week 8 (except during Week 13). Body-weight data were only provided in a
figure (even in the proprietary data), but the body weights do not appear to differ by more than
10%) at any time point during the 3 months. There was a statistically significant decrease in
hematocrit and hemoglobin levels in the high-dose group that began after 10 days of treatment
(see Table B. 10). There were no treatment-related changes in clinical chemistry. Additionally,
there were no treatment-related changes in organ weights, lung or brain edema, gross pathology,
or organ histopathology. Based on the absence of respiratory toxicity noted, the NOAEL and
LOAEL are selected based on extra-respiratory effects. The HECs for extra-respiratory effects
"3
adjusted for duration and a blood:gas partition coefficient of 1 are 51 and 388 mg/m ,
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3	3
respectively. Therefore, the NOAEL is 51 mg/m , and the LOAEL is 388 mg/m based on
consistent decreases in hematocrit and hemoglobin levels.
NTP (1997)
The 13-week component of the peer-reviewed mouse study by NTP (1997) is selected
as the principal study for the derivation of the subchronic p-RfC. Individually housed male
and female B6C3Fi mice (10/sex/treatment group) were administered nitromethane (purity
>98%) at concentrations of 0; 94; 188; 375; 750; or 1,500 ppm via whole body inhalation for
6 hours and 12 minutes a day, 5 days a week, for 13 weeks. Chamber concentrations were
routinely checked over the course of exposure. Animals were observed twice a day for clinical
signs of toxicity. Animals were weighed at study initiation, weekly, and at study termination. At
study termination, animals were necropsied, and the heart, right kidney, liver, lungs, right testis,
and thymus glands were weighed. Complete histopathology was conducted on control and
high-dose animals. In addition, tissues of the nose and spleen in both sexes were examined in
the lower concentrations until a NOEL was reached. Sperm samples were collected from the 0-;
375-; 750-; and 1,500-ppm groups at study termination and evaluated for sperm count and
motility. The left cauda, epididymis, and testis were weighed. Vaginal samples were collected
for seven consecutive days before study termination and evaluated for the relative frequency of
estrous stages and for estrous cycle length. Typical NTP statistical methods were applied and
were appropriate for the data.
All mice survived until study termination. There were no treatment-related clinical signs
or changes in body weight. There were statistically significant increases in the absolute and/or
relative kidney weight in all treatment groups except in low-dose females (see Table B.l 1).
Although the relative kidney weights in exposed males were >10% relative to controls at all
concentrations tested, relative kidney weight changes were not dose dependent and were only
>10%) in females at the highest concentration tested. Relative liver weights were also
significantly increased in males at concentrations >375 ppm. However, this response was not
dose dependent and was >10% only at concentrations of 750 and 1,500 ppm. Liver weights were
unaffected in female mice at any dose. There were no treatment-related changes in male
reproductive tissue weight or in sperm concentration, but there was a statistically significant
decrease in sperm motility at all concentrations examined (i.e., >375 ppm) (see Table B.12).
There was a dose-related increase in estrous cycle length at all concentrations examined (see
Table B. 12). At concentrations >375 ppm, there was degeneration of the olfactory epithelium of
the nasal turbinates with minimal to moderate severity and hyaline droplets in the respiratory
epithelium in all mice (see Table B. 13). Female mice also had a statistically significant increase
in the incidence of these lesions at 188 ppm. There was a significant increase in extramedullary
hematopoiesis in the spleens of high-dose males and females (see Table B. 13). Although
respiratory and extra-respiratory effects were observed, the NOAEL and LOAEL are based on
respiratory effects because they occurred at lower concentrations. Because only initial and final
body weights were provided, the average is used to calculate body weights for the calculation of
HECs for respiratory effects. The HECs for respiratory effects are 7.1, 14.1, 28.0, 55.7, and
112.7 mg/m3 in males, respectively, and 5.9, 12.2, 24.9, 48.0, and 93.9 mg/m3 in females,
respectively, after adjusting for duration and multiplying by the RGDR for extra-thoracic effects.
The NOAEL is 5.9 mg/m3 (94 ppm), and the LOAEL is 12.2 mg/m3 (188 ppm) based on
increased histopathology of the nasal turbinates in female mice.
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Lewis etal. (1979)
Male New Zealand white rabbits (5/treatment group) were administered nitromethane
(96.5% pure with 1.5% nitroethane and 1.4% 2-nitropropane) at analytical concentrations of 0,
98 ± 5, or 745 ± 34 ppm via whole body inhalation, 7 hours a day, 5 days a week, for 3 months
(Lewis et al., 1979b). While Lewis et al. (1979) provides a peer-reviewed publication of the
data, the proprietary data were also available for review (Huntingdon Research Center, 1989).
An additional group of 5 animals/concentration group was sacrificed after 1 month of treatment.
Animals were housed individually in wire mess stainless steel cages, which was part of the
exposure chamber. Chamber concentrations were measured hourly and recorded twice a day.
Animals were observed daily for overt signs of toxicity. Body weights were obtained at regular
intervals. At sacrifice, blood was collected for hematology (RBC, hematocrit, hemoglobin,
prothrombin time, and methemoglobin) and clinical chemistry (ALT, OCT, and thyroxin).
Animals were necropsied, and select organs (brain, liver, kidneys, lungs, and thyroid) were
weighed. Tissue samples were obtained from the brain and lungs. The samples were weighed,
dried, and weighed again to determine the percent of water. Adrenals, bronchi, cerebellum,
cerebral hemispheres, eyes, kidneys, liver, lung, spleen, thyroid, and trachea were examined
histologically. A Kruskal-Wallis one-way analysis of variance followed by a Mann-Whitney
U test was used on the data due to the small number of animals used.
Not all the data were provided in Lewis et al. (1979). Data in the Huntingdon Research
Center (1989) report were not provided in any sort of order, were hard to find (tables were not in
order), and, in some cases, were not reported. There were no clinical signs of toxicity noted and
no treatment-related effects on mortality or body weight. There was a statistically significant
increase in methemoglobin in high-dose rabbits at the 3-month time point only, and a statistically
significant decrease in hemoglobin in the high-dose rabbits at the 1-month time point only.
There were increases in OCT at both 1 and 3 months (see Table B. 14); however, this was not
noted at 6 months (see chronic studies below). Thyroxin levels were lower than the control
values at both 1 and 3 months but only achieved statistical significance in the high-dose group at
1 month (see Table B.14). Lungs of rabbits at 1 month had focal areas of moderate-to-
moderately severe hemorrhage and congestion of the alveolar and alveolar duct walls. This was
not stated to occur at 3 months. There were no other treatment-related changes in organ weights,
lung or brain edema, gross pathology, or organ histopathology. Based on the absence of
respiratory toxicity noted, the NOAEL and LOAEL are selected based on extra-respiratory
effects. The HECs for extra-respiratory effects adjusted for duration and a blood:gas partition
coefficient of 1 are 51 and 388 mg/m3, respectively. Therefore, the NOAEL is 51 mg/m3, and
"3
the LOAEL is 388 mg/m based on consistent decreases in thyroxin levels.
Chronic Studies
Lewis etal. (1979)
Male Sprague-Dawley rats (10/treatment group) were administered nitromethane
(96.5% pure with 1.5% nitroethane and 1.4% 2-nitropropane) at analytical concentrations of 0,
98 ± 5, or 745 ± 34 ppm via whole body inhalation, 7 hours a day, 5 days a week, for 6 months
(Lewis et al., 1979c). While Lewis et al. (1979) provides a peer-reviewed publication of the
data, the proprietary data were also available for review (Huntingdon Research Center, 1989).
This study was conducted in conjunction with the 3-month subchronic study discussed above,
and materials and methods were the same as those previously detailed.
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There were no treatment-related effects on mortality. There was no difference in body
weight between the low-dose group and the controls. High-dose rats had a slower weight gain,
with body weights stated to be statistically significantly different from the control beginning
around Week 8 (except during Week 13), but by study termination, body weight was similar to
the controls according to the figure in the study report. There was a statistically significant
decrease in hematocrit and hemoglobin levels in the high-dose group (see Table B.10). There
were no treatment-related changes in clinical chemistry and no treatment-related changes in lung
or brain edema, gross pathology, or organ histopathology. The only change in organ weight was
a statistically significant increase in absolute and relative thyroid weight in the high-dose group
that was dose related (see Table B.15). Based on the absence of respiratory toxicity noted, the
NOAEL and LOAEL are selected based on extra-respiratory effects. The HECs for
extra-respiratory effects adjusted for duration and a blood:gas partition coefficient of 1 are 51
3	3
and 388 mg/m , respectively. Therefore, the NOAEL is 51 mg/m , and the LOAEL is
388 mg/m3 based on an increase in relative thyroid weights.
NTP (1997)
Individually housed male and female F344 rats (50/sex/treatment group) were
administered nitromethane (purity >98%) at concentrations of 0, 94, 188, or 375 ppm via whole
body inhalation for 6 hours and 12 minutes a day, 5 days a week, for 103 weeks. Chamber
concentrations were routinely checked over the course of exposure. Animals were observed
twice a day for clinical signs of toxicity and weighed at study initiation, weekly through
Week 12, monthly from Week 15 through Week 91, then every 2 weeks until study termination,
and at study termination. At study termination, animals were necropsied. Complete
histopathology was conducted on all animals except that spinal cord and sciatic nerve were only
examined in control and high-dose animals (15/sex). Typical NTP statistical methods were
applied and were appropriate for the data.
There was no treatment-related effect on mortality. Besides tumor masses, there were no
clinical signs observed. There were no statistically significant changes in body weight compared
with the controls. However, the study authors noted that the high-dose group had a slightly
higher body weight than the control beginning around Week 23. The differences were not
statistically significant nor did they exceed a 10% difference from controls. The only noncancer
effect observed in rats was a slight increase in severity of the nephropathy that occurred in all
male rats (2.8, 2.9, 3.1, and 3.2 at 0, 94, 188, and 375 ppm, respectively). Based on the absence
of significant noncancer effects, the NOAEL and LOAEL are selected based on extra-respiratory
effects. The HECs for extra-respiratory effects adjusted for duration and a blood:gas partition
3	3
coefficient of 1 are 43, 87, and 173 mg/m , respectively. Therefore, the NOAEL is 173 mg/m ,
the highest concentration tested.
Griffin et al. (1996)
Male and female Long-Evans rats (40/sex/treatment group) were administered
nitromethane (96.26%) pure with 2.79% nitroethane and 0.62% 2-nitropropane) at concentrations
of 0, 100, or 200 ppm via whole body inhalation, 7 hours a day, 5 days a week, for 2 years
(Griffin et al., 1996). While Griffin et al. (1996) provided a peer-reviewed publication of the
study, the proprietary data were also available for review (Coulston International Inc., 1990).
Animals were individually housed in stainless-steel cages except during exposure periods when
they were placed in exposure chambers. Chamber concentrations were measured 3-4 times per
day, with average analytical results of 99.5 ppm (stated by the study authors to be equivalent to
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3	3
219 mg/m ) and 199.3 ppm (stated by the study authors to be equivalent to 427 mg/m ).
Animals were observed daily for overt signs of toxicity. Body weights were obtained weekly for
the first 6 months and every 2 weeks thereafter. At terminal sacrifice, blood was collected from
10 rats/sex/treatment group for hematology (RBC, leukocyte counts [WBC], MCV, hematocrit,
hemoglobin, and platelet counts) and serum clinical chemistry (aspartate aminotransferase
[AST], ALT, bilirubin, total protein, BUN, creatinine, sodium, and potassium). Animals were
necropsied, and select organs (brain, liver, kidneys, lungs, and heart) were weighed. Thirty-three
different tissues/organs were examined histologically in both sexes of rat. Appropriate statistical
methods were conducted on the data.
There were no clinical signs of toxicity noted. There were no treatment-related effects on
mortality. There were no treatment-related changes in body weight in male rats. Although
female rats in both treatment groups had statistically significant lower body weights compared to
the controls during the second half of the study, the results were not dose dependent and did not
exceed a 10% difference from the control. There were no treatment-related effects on
hematology. The only change noted in clinical chemistry was an increase in creatinine in the
200-ppm dose group. However, the increase was associated with the method used (i.e., Jaffe
reaction) as nitromethane in the plasma has been found to increase the reaction (De Leacy et al.,
1989). There were no treatment-related changes in organ weights, gross pathology, or organ
histopathology. Due to the absence of toxicity, the NOAEL and LOAEL are selected based on
extra-respiratory effects. The HECs for extra-respiratory effects adjusted for duration and a
"3
blood:gas partition coefficient of 1 are 45.6 and 89.0 mg/m , respectively. Therefore, the
NOAEL is 89.0 mg/m3, the highest concentration tested.
NTP (1997)
The 2-year component of the peer-reviewed mouse study by NTP (1997) is selected
as the principal study for the derivation of the chronic p-RfC. Individually housed male and
female B6C3Fi mice (50/sex/treatment group) were administered nitromethane (purity >98%) at
concentrations of 0, 188, 375, or 750 ppm via whole body inhalation for 6 hours and 12 minutes
a day, 5 days a week, for 103 weeks. Chamber concentrations were routinely checked over the
course of exposure. Animals were observed twice a day for clinical signs of toxicity. Animals
were weighed at study initiation, weekly through Week 12, monthly from Week 15 through
Week 91, then every 2 weeks until study termination, and at study termination. At study
termination, animals were necropsied. Complete histopathology was conducted on all animals
except that spinal cord and sciatic nerve were not examined. Typical NTP statistical methods
were applied and were appropriate for the data.
There was no treatment-related effect on mortality. Clinical signs observed included
swelling around the eyes and exophthalmos. This was stated to be consistent with Harderian
gland neoplasms, which occurred at a greater incidence in treated animals (see carcinogenicity
studies below). There were no statistically significant changes in body weight compared with
the controls. There were increases in liver lesions in female mice and nasal lesions in both sexes
(see Table B.16). The HECs for respiratory effects are 22.2, 44.9, and 91.6 mg/m in males,
-3
respectively, and 21.9, 43.2, and 87.9 mg/m in females, respectively, after adjusting for duration
and multiplying by the RGDR for extra-respiratory effects. No NOAEL can be determined. The
3	3
LOAEL is 22.2 mg/m in males and 21.9 mg/m in females based on increased incidence of nasal
lesions in both sexes of mice.
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Lewis etal. (1979)
Male New Zealand white rabbits (5/treatment group) were administered nitromethane
(96.5% pure with 1.5% nitroethane and 1.4% 2-nitropropane) at analytical concentrations of 0,
98 ± 5, or 745 ± 34 ppm via whole body inhalation for 7 hours a day, 5 days a week, for
6 months (Lewis et al., 1979d). While Lewis et al. (1979) provides a peer-reviewed publication
of the data, the proprietary data were also available for review (Huntingdon Research Center,
1989). This study was conducted in conjunction with the 3-month subchronic study discussed
above, and the materials and methods were the same as those previously detailed.
There were no treatment-related effects on mortality, body weight, hematology, lung or
brain edema, gross pathology, or organ histopathology. Thyroxin levels at both concentrations
were statistically significantly (p < 0.05) lower than the control (see Table B. 14). This was
accompanied by an increase in absolute and relative thyroid weight that did not achieve
statistical significance (see Table B.17). Based on the absence of respiratory toxicity noted, the
NOAEL and LOAEL are selected based on extra-respiratory effects. The HECs for
extra-respiratory effects adjusted for duration and a blood:gas partition coefficient of 1 are 51
and 388 mg/m3, respectively. Therefore, the LOAEL is 51 mg/m3 based on decreases in thyroxin
levels, which were accompanied by changes in organ weight. No NOAEL can be determined
from the data.
Developmental Studies
There are no developmental studies via oral or inhalation exposure to nitromethane.
However, Whitman et al. (1977) intraperitoneally injected 0.5 mL of a 1.5-M solution of
nitromethane in saline every third day beginning prior to pregnancy through gestation to albino
rats. Few details were provided on the dosing procedure. Controls were similarly treated with
saline. No differences were observed in the number of pups (dead or alive), pup body weight, or
dam behavior. Pups were maintained with mothers until weaning and behavioral maze tests
were conducted when pups were 2.5 months old. Nitromethane-exposed pups had significantly
more errors to criterion compared with the control animals.
Reproductive Studies
There are no multigeneration reproductive studies with nitromethane by either oral or
inhalation routes of exposure. However, the two 13-week studies by NTP (NTP, 1997)
examined some reproductive endpoints after inhalation exposure. In rats (NTP, 1997), there
were statistically significant decreases in absolute left cauda, epididymis, and testis weight at
1,500 ppm. Although this may be due to reduced body weight, there was a 15% decrease in
sperm concentration in high-dose males, and sperm motility was significantly decreased with
concentrations of 750 and 1,500 ppm (see Table B.9; NTP, 1997). Mice also had reduced sperm
motility (NTP, 1997), but there was no effect on reproductive tissue weight or sperm
concentration (see Table B. 12). There were no treatment-related changes in estrous cycle length
or estrous stages in female rats (NTP, 1997), but there was a dose-related increase in estrous
cycle length at all concentrations examined in female mice (see Table B.12; NTP, 1997).
Carcinogenicity Studies
NTP (1997)
The carcinogenicity component of the chronic peer-reviewed rat study by NTP
(1997) is selected as the principal study for the derivation of the p-IUR. Individually housed
male and female F344 rats (50/sex/treatment group) were administered nitromethane
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(purity >98%) at concentrations of 0, 94, 188, or 375 ppm via whole body inhalation for 6 hours
and 12 minutes a day, 5 days a week, for 103 weeks. Chamber concentrations were routinely
checked over the course of exposure. Animals were observed twice a day for clinical signs of
toxicity. Animals were weighed at study initiation, weekly through Week 12, monthly from
Week 15 through Week 91, then every 2 weeks until study termination, and at study termination.
At study termination, animals were necropsied. Complete histopathology was conducted on all
animals except that spinal cord and sciatic nerve were only examined in control and high-dose
animals (15/sex). Typical NTP statistical methods were applied and were appropriate for the
data.
There was no treatment-related effect on mortality. Besides tumor masses, there were no
clinical signs of toxicity observed. There were no statistically significant changes in body
weight compared with controls. However, the study authors noted that the high-dose group had
a slightly higher body weight than the control beginning around Week 23. The differences were
not statistically significant nor did they exceed a 10% difference from the control. There were
no treatment-related increases in tumors in male rats. There was an increase in tumors of the
mammary gland in females with concentrations of 188 and 375 ppm (see Table B. 18). The
incidence of mammary gland tumors in the 188- and 375-ppm groups also exceeded the
historical control data from inhalation studies. There were concerns raised that the slight
increase in body weight in the 375-ppm females was related to the increase in tumors observed in
the female rat. However, it was concluded that this was not the case. Based on the increase in
body weights, it would be predicted that there would be a 51% incidence of mammary gland
tumors, but the incidence was 82%. NTP determined that there was no evidence of
carcinogenicity in male rats, but there was clear evidence of carcinogenicity in female rats. The
HECs for extra-respiratory carcinogenic effects adjusted for duration and a blood:gas partition
-3
coefficient of 1 are 43, 87, and 173 mg/m , respectively.
Griffin et al. (1996)
Male and female Long-Evans rats (40/sex/treatment group) were administered
nitromethane (96.26%) pure with 2.79% nitroethane and 0.62% 2-nitropropane) at concentrations
of 0, 100, or 200 ppm via whole body inhalation for 7 hours a day, 5 days a week, for 2 years
(Griffin et al., 1996b). While Griffin et al. (1996) provides a peer-reviewed publication of the
data, the proprietary data were also available for review (Coulston International Inc., 1990). See
the chronic studies discussed above for details on the materials and methods. There was no
treatment-related effect on mortality. There were no statistically significant differences in
neoplastic lesions. However, two high-dose females had adenocarcinomas of the uterus, which
were not observed in either of the other groups. Because the incidence is low and there is no
dose response, it is not clear if this is related to treatment. Based on the absence of either
systemic or respiratory carcinogenicity, the NOAEL and LOAEL are selected based on
extra-respiratory effects. The HECs for extra-respiratory effects adjusted for duration and a
blood:gas partition coefficient of 1 are 45.6 and 89.0 mg/m , respectively. There is no evidence
of carcinogenicity.
NTP (1997)
Individually housed male and female B6C3Fi mice (50/sex/treatment group) were
administered nitromethane (purity >98%) at concentrations of 0, 188, 375, or 750 ppm via whole
body inhalation for 6 hours and 12 minutes a day, 5 days a week, for 103 weeks. Chamber
concentrations were routinely checked over the course of exposure. Animals were observed
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twice a day for clinical signs of toxicity. Animals were weighed at study initiation, weekly
through Week 12, monthly from Week 15 through Week 91, then every 2 weeks until study
termination, and at study termination. At study termination, animals were necropsied. Complete
histopathology was conducted on all animals except that spinal cord and sciatic nerve were not
examined. Typical NTP statistical methods were applied and were appropriate for the data.
There was no treatment-related effect on mortality. Clinical signs observed included
swelling around the eyes and exophthalmos. This was stated to be consistent with Harderian
gland neoplasms, which occurred at a greater incidence in treated animals. There were no
statistically significant changes in body weight compared with controls. There were increases in
the incidence of Harderian gland tumors in both sexes, liver tumors in females, and
alveolar/bronchiolar carcinomas in males (see Table B.19). Respiratory and systemic tumors
developed; therefore, HECs were calculated using both the respiratory and extra-respiratory
methods respectively, for respiratory tumors (adjusted for duration and multiplied by a RGDR)
and for extra-respiratory tumors (duration-adjusted and multiplied by a blood:gas partition
coefficient of 1) (U.S.EPA, 1994b). The HECs for respiratory carcinogenic effects are 359; 727;
and 1,484 mg/m3 in males and 355; 700; and 1,423 mg/m3 in females, respectively, based on the
area of the thoracic region and average body weights provided in the study report. The HECs for
extra-respiratory carcinogenic effects are 87, 173, and 346 mg/m3, respectively. The study
authors concluded that there was clear evidence of carcinogenicity in both sexes of mice.
OTHER DATA (SHORT-TERM TESTS, OTHER EXAMINATIONS)
The genotoxicity of nitromethane has been studied in several in vitro test systems (see
Table 4A). Little information on the toxicokinetics of nitromethane is available (Coulston
International Inc., 1990; Sakurai et al., 1980) and is presented in Table 4B. Further in-depth
details follow Tables 4A and 4B.
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Table 4A. Summary of Nitromethane Genotoxicity
Endpoint
Test System
Dose
Concentration"
Resultsb
Comments
References
Without
Activation
With
Activation
Genotoxicity studies in prokaryotic organisms
Reverse mutation
Salmonella typhimurium strains TA1537,
TA1535, TA100, TA1538, and/or TA98
with or without S9 metabolic activation
50,000 ng/plate


Dellarco and Prival (1989)
also used flavin
mononucleotide in a
modified preincubation assay
to facilitate nitro reduction
and found negative results;
some pages of the Haskell
Laboratories study illegible;
0.5% stated to be half the
50% survival concentration
(Dow Chemical, 1975a)
Dow Chemical
(1975a); Haskell
Laboratories (2000);
Chiuetal. (1978);
Lofroth et al., (1986)
Mortelmans et al.
(1986); Dellarco and
Prival (1989); NTP
(1997); Gockeetal.
(1981a)
Reverse mutation
Preincubation modification of Salmonella
typhimurium strains TA98, TA100, TA102
200 |imol/platc


Concentrations
>500 |imol/platc were
cytotoxic and could not be
used
Dayal et al. (1989a)
Reverse mutation
Salmonella typhimurium strains TA98,
TA100, TA1535, TA1537 with or without
S9 activation
50 |iL/platc
+
+
Mutagenic in TA1535 only
Ong et al. (1980)
SOS repair
induction
ND
Genotoxicity studies in nonmammalian eukaryotic organisms
Mutation
Saccharomyces cerevisiae strain D4 with
and without metabolic activation
5%
-
-
5% stated to be half the
50% survival concentration
Dow Chemical
(1975b)
Recombination
induction
ND
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Table 4A. Summary of Nitromethane Genotoxicity
Endpoint
Test System
Dose
Concentration"
Resultsb
Comments
References
Without
Activation
With
Activation
Chromosomal
aberration
The Base test using Drosophila
melanogastex Berlin K (wild type) and Base
strains
125 mM


2% ethanol used as the
solvent
Gocke et al. (1981b)
Chromosomal
malsegregation
ND
Mitotic arrest
ND
Genotoxicity studies in mammalian cells—in vitro
Mutation
ND





Chromosomal
aberration
Micronucleus assay of Syrian hamster
embryo cells
In DMSO:
6.0 ng/mL
In media:
5,000 ng/mL


Reduction in cell numbers in
DMSO at 5.5 and 6.0 ng/mL;
no increased frequency in
micronuclei
Gibson etal. (1997);
Hazelton Washington
(1996)
Chromosomal
aberration
Transformation assay using Syrian hamster
embryo cells
4,000 iig/mL
+
+
Dose-related increase in the
number of morphological
transformed colonies; cells
incubated for 24 hr prior to
application of nitromethane;
incubation with nitromethane
lasted 24 hr
Kerckaert et al.
(1996); Brauninger
(1995)
Chromosomal
aberration
Abs test in Chinese hamster ovary cells with
or without S9 metabolic activation
5,000 |ig/mL
—
—
No induction of chromosome
aberrations
NTP (1997)
Sister chromatid
exchange (SCE)
Chinese hamster ovary cells with or without
S9 metabolic activation
5,000 |ig/mL
-
-
No induction of SCE
NTP (1997)
DNA damage
ND
DNA adduct
ND
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Table 4A. Summary of Nitromethane Genotoxicity
Endpoint
Test System
Dose
Concentration"
Resultsb
Comments
References
Without
Activation
With
Activation
Genotoxicity studies in mammals—in vivo
Chromosomal
aberration
Subchronic inhalation exposure of male and
female mice
1,500 ppmfor
13 wk

NA
No increased frequency of
micronucleated erythrocytes
in peripheral blood samples
NTP (1997)
Chromosomal
aberration
Micronucleus test on mouse bone marrow
1,830 mg/kg at 0
and 24 hr
-
NA
All treated mice survived;
animals sacrificed at 30 hr
Gocke et al. (1981c)
Sister chromatid
exchange (SCE)
ND
DNA damage
ND
DNA adduct
ND
Mouse
biochemical or
visible specific
locus test
ND
Dominant lethal
ND
Genotoxicity studies in subcellular systems
DNA binding
ND
aLowest effective dose for positive results, highest dose tested for negative results.
b+ = positive; ± = equivocal or weakly positive; ~ = negative; T = cytotoxicity; NA = not applicable; ND = no data; NDr = not determined; NR = not reported; NR/Dr =
not reported but determined from data.
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Table 4B. Other Studies
Test
Materials and Methods
Results
Conclusions
References
Carcinogenicity other
than oral/inhalation
ND
Other toxicity studies
(exposures other than
oral or inhalation)
Male and female BALB/c mice, hepatoxicity
test via intraperitoneal injection at 4.5, 6.7, or
9.0 mmol/kg; control mice injected with
NaCl; animals terminated at 24, 48, 72, or
96 hr after dosing; blood assays for sorbitol
dehydrogenase, alanine aminotransferase,
and aspartate aminotransferase
No abnormalities found in the enzyme
activities for mice dosed with 9 mmol/kg
Not toxic at 9 mmol/kg after 24,
48, 72, or 96 hr
Dayal et al.
(1989b)
Short-term studies
Rabbit, acute exposure (80 min) at 8 mg; no
information regarding control or study
methods provided
No significant effect on blood pressure or
respiration
No significant effect on blood
pressure or respiration
Machle and Scott
(1943)
Metabolism/
toxicokinetic
Two adult female rhesus monkeys; single
dermal exposure (300 |iL ether/ethanol
solution, 5.5% 14C-nitromethane) for 12 h.
No signs of toxicity reported; levels of
nitromethane recovered in urine, feces,
blood; absorption in skin considered to be
low
Not hazardous to human skin
Coulston
International Inc.
(1990)

Nitromethane aerobically incubated with
liver microsomes isolated from male
Sprague-Dawley rat livers treated with
phenobarbital or 3-methylcholanthrene
Formaldehyde produced from
nitromethane via NADPH-independent
reaction; nitromethane did not result in a
substrate-binding difference spectrum in
the oxidized rat liver microsomal
suspension, but peaked at 437 nm,
indicating cytochrome P450-NO complex
production
Nitrite, formaldehyde, and
cyclohexanone are the major
reaction products of nitromethane
in activated rat liver microsomes in
the presence of NADPH and
dioxygen; study authors speculated
that a special form of cytochrome
P450 was necessary to cleave the
C-N bond
Sakurai et al.
(1980)
Mode of action/
mechanistic
ND
Immunotoxicity
ND
Neurotoxicity
ND
ND = no data.
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Tests Evaluating Carcinogenicity, Genotoxicity, and/or Mutagenicity
As seen in Table 4A, the majority of the genotoxicity (e.g., clastogenicity, mutagenicity)
studies were negative. There was only one study (Ong et al., 1980) using the Ames assay that
found a positive result in one strain (TA 1535) of Salmonella typhimurium. Negative results
were also observed in Saccharomyces cerevisiae (Dow Chemical, 1975) and Drosophila
melanogaster (Gocke et al., 1981). Chromosomal aberrations were not observed in Syrian
hamster embryo cells using the micronucleus assay (Gibson et al., 1997; Hazleton Washington,
1996) but were observed as a dose-related increase in morphological-transformed colonies in the
transformation assay (Kerkaert et al., 1996; Brauninger, 1995). Chromosomal aberrations were
not observed in Chinese hamster ovary cells using either an Abs test or sister chromatid
exchange test (NTP, 1997). Chromosomal aberrations were also not observed in mouse bone
marrow using the micronucleus test (NTP, 1997; Gocke et al., 1981).
Other Toxicity Studies (Exposures Other Than Oral or Inhalation)
Dayal et al. (1989b) compared the potential hepatotoxicity of 2-nitropropane,
nitromethane, and nitroethane following intraperitoneal injection. Biochemical and
histopathological effects in male and female BALB/c mice were assessed following
intraperitoneal injection of nitromethane at doses 0, 4.5, 6.7, or 9.0 mmol/kg in saline. Animals
were sacrificed 24, 48, 72, or 96 hours after dosing, and blood was collected via cardiac
puncture. Assays were performed for sorbitol dehydrogenase, alanine aminotransferase, and
aspartate aminotransferase enzymes. Livers were investigated for biochemical effects. No liver
abnormalities or other toxicity were reported in mice after treatment with 9-mmol/kg
nitromethane. Results were not reported for the other doses.
Short-Term Studies
Machle and Scott (1943) examined the blood pressure and respiration of rabbits when
exposed to nitromethane and other mononitroparaffins at 8 mg for 80 minutes. Although details
of the study were lacking, the study authors reported no significant effect on rabbit blood
pressure or respiration.
Metabolism/Toxicokinetic Studies
In a toxicokinetic study, Coulston International Inc. (1990) conducted a skin absorption
study on two female rhesus monkeys. Animals were administered a single dose of 5.5%
14C-nitromethane (in a 300-|iL ether/ethanol solution) to shaved intact skin on the back for
12 hours. The dosed area was occluded with a plastic foil patch and taped until removal at the
end of the 12-hour dosing period. Upon removal of the application patch, the skin was cleaned
with acetone and soap to remove any remaining test material. The patch and swab were
extracted with ethanol and acetone, respectively, and then the extracts were assayed for
radioactivity. Blood, urine, and feces were collected while animals were held in metabolism
cages for 72 hours after dosing and assayed for radioactivity. Skin and subcutaneous fat were
removed and assayed for radioactivity. Skin samples were examined histologically. No toxicity
was reported by the study authors. Feed and water consumption as well as feces and urine output
were low during the first 12 hours but returned to normal after animals were returned to their
cages. No change in body weight was reported. Skin samples did not reveal any sign of skin
damage or irritation. The study authors considered the level of radioactivity detected in blood
plasma (37.8 ng/mL and 40.3 ng/mL average maximum per 1 mL blood plasma) and
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erythrocytes (40.8 ng/g and 44.3 ng/g maximum) of the two monkeys to be low. Due to the low
level of absorption after a high concentration level, study authors concluded that nitromethane is
not hazardous to human skin.
Sakurai et al. (1980) investigated the metabolism of nitromethane in liver microsomes
isolated from rats pretreated with phenobarbital or 3-methylcholanthrene in the presence of
nicotinamide adenine dinucleotide phosphate (NADPH) and dioxygen (O2). Male
Sprague-Dawley rats were pretreated with either phenobarbital (80 mg/kg for 3 days) or
3-methylcholanthrene (20 mg/kg for 2 days). The microsomal fraction was then isolated from
the livers of the pretreated rats and incubated in the presence of NADPH and dioxygen. The
results of the incubation indicated a linear production of nitrite and formaldehyde.
Cyclohexanone was also identified as a reaction product of nitromethane. The specific activity
(±S.E.M) for denitrification of nitromethane by rat liver microsomal monooxygenases was
reported as 0.2 ±0.1 nmol/mg protein-min. The study authors reported that the addition of
nitromethane to oxidized rat liver microsomal suspensions resulted in a peak of 437 nm, which is
outside the normal substrate-binding spectrum. Further, the study authors explained the peak as
the formation of the cytochrome P450-NO complex. Additionally, the study authors also
reported that the oxidized rat liver microsomes produced formaldehyde from nitromethane in an
independent NADPH reaction.
Mode-of-Action/Mechanistic Studies
There is insufficient information to determine the mode of action.
Immunotoxicity
There is no suitable information to provide in this regard.
Neurotoxicity
There is no suitable information to provide in this regard.
DERIVATION OF PROVISIONAL VALUES
Tables 5 and 6 present a summary of noncancer reference and cancer values,
respectively, for nitromethane. IRIS data are indicated in the tables, if available.
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Table 5. Summary of Noncancer Reference Values for Nitromethane (CASRN 75-52-5)
Toxicity Type (Units)
Species/Sex
Critical Effect
p-Reference
Value
POD
Method
POD
UFC
Principal
Study
Subchronic p-RfD
(mg/kg-d)
NDr
Chronic p-RfD
(mg/kg-d)
NDr
Subchronic p-RfC
(mg/m3)
Mouse/F
Hyaline droplets
in the respiratory
epithelium
4 x 10"3
BMCL10
1.31
300
NTP
(1997)
Chronic p-RfC (mg/m3)
Mouse/F
Hyaline
degeneration in
the respiratory
epithelium
5 x 10"3
BMCL10
1.60
300
NTP
(1997)
NDr = not determinable.
Table 6. Summary of Cancer Values for Nitromethane (CASRN 75-52-5)
Toxicity Type
Species/Sex
Tumor Type
Cancer Value
Principal
Study
p-OSF
NDr
p-IUR
Rat/F
Combined mammary gland
fibroadenoma, adenoma, and
carcinoma
8.8 x HP' (mg/m3)-1
NTP (1997)
NDr = not determinable.
DERIVATION OF ORAL REFERENCE DOSES
Derivation of Subchronic and Chronic Provisional RfD (p-RfD)
No subchronic or chronic p-RfD value can be derived because no adequate,
well-described studies are available.
Justification
There is a single subchronic oral study available for nitromethane (Weatherby, 1955).
The lowest dose administered (i.e., 0.1%) caused mortality in 4 of the 10 animals tested. Due to
cannibalism of the dead animals, it was not possible to determine cause of death. Because the
lowest dose administered was considered an FEL, it is not possible to use this study to derive a
p-RfD.
DERIVATION OF INHALATION REFERENCE CONCENTRATIONS
Derivation of Subchronic Provisional RfC (Subchronic p-RfC)
There are several studies available for the derivation of the subchronic p-RfC (see
Table 7). The study by NTP (1997) in mice is selected as the principal study. This study was
peer reviewed and GLP compliant. NTP (1997) examined numerous endpoints in both sexes in
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two species (i.e., rats and mice). Details are provided in the "Review of Potentially Relevant
Data" section. Among the available and acceptable studies, the NTP (1997) subchronic study in
mice represents the lowest POD for developing a subchronic p-RfC. The critical endpoint is
hyaline droplets in the respiratory epithelium of the nasal turbinates in female mice. The NTP
(1997) studies included histopathologic evaluations of the upper respiratory tract, additionally,
histopathological lesions of the nasal tract were observed in rats and mice after 16 days (NTP,
1997) and 13 weeks (1997), with possible progression noted in the 2-year studies (NTP, 1997).
The hyaline droplets in the respiratory epithelium are selected as the critical effect because, in
addition to being the most sensitive effect in the most sensitive species (mice), it was a lesion of
progressing severity. Hyaline droplets of the respiratory epithelium were not noted after 16 days
of exposure but were observed after 13 weeks of exposure and progressed to degeneration of the
respiratory epithelium after 2 years of exposure. In addition, the severity of the hyaline droplets
was stated to increase with concentration, ranging from mild in the lower concentrations to
moderate at the highest concentration. Degeneration of the olfactory epithelium also occurred at
the same concentrations as hyaline droplets in the respiratory epithelium. Benchmark dose
(BMD) analysis has been conducted on both endpoints (hyaline droplets and degenerative
lesions) only in mice; these same nasal lesions were also observed in the rats but occurred at
greater concentrations. The hyaline droplets in the respiratory epithelium have a lower BMCL.
However, this endpoint models better when the highest two concentrations are dropped due to
maximal response observed in the top three concentrations. Also occurring at higher
nitromethane concentrations was anemia noted by decreased hematocrit and hemoglobin levels
as well as other hematological effects, effects to the thyroid (increased thyroid weight and
decreased thyroxin levels), and other histological lesions in both species. Relative liver weights
were increased in female mice after 16 days of exposure at the same concentration that caused
the nasal effects (i.e., 188 ppm). BMD analyses have not been conducted on these endpoints.
Histopathology in the 16-day rat and mouse studies and the 13-week rat study was not amenable
to BMD analysis due to unsuitable dose-response data.
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Table 7. Summary of Relevant Inhalation Subchronic Toxicity Studies for Nitromethane
Reference
Species,
#/Sex (M/F)
Exposure
(ppm)
Frequency/
Duration
NOAEW
(mg/m3)
LOAELAI)lb
(mg/m3)
Critical Endpoint
NTP (1997)
Rat, 5/5
0; 94; 188; 375; 750; 1,500
6.2 hr, 5 d/wk,
16 d
8.9
17.7
Degeneration of the olfactory
epithelium of the nasal
turbinates in females
NTP (1997)
Mouse, 5/5
0; 94; 188; 375; 750; 1,500
6.2 hr, 5 d/wk,
16 d
10.2
20.2
Degeneration of the olfactory
epithelium of the nasal
turbinates in females
NTP (1997)
Rat, 10/10
0; 94; 188; 375; 750; 1,500
6.2 hr, 5d/wk,
13 wk
9.7
19.2
Degeneration of the olfactory
epithelium of the nasal
turbinates in females
NTP (1997)
Mouse, 10/10
0; 94; 188; 375; 750; 1,500
6.2 hr, 5 d/wk,
13 wk
5.9
11.8
Degeneration of the olfactory
epithelium and hyaline droplets
in the respiratory epithelium of
the nasal turbinates in females
Lewis et al. (1979)
Rat, 10/0
0, 98, 745
7 hr/d, 5 d/wk,
3 mo
51
388
Decreased hematocrit and
hemoglobin levels
Lewis (1979)
Rabbit, 5/0
0, 98, 745
7 hr/d, 5 d/wk,
3 mo
51
388
Decreased thyroxin levels
"NOAELA|,[ is the HEC value for respiratory or extra-respiratory effects; HECresp = ppm x (molecular weight ^ 24.45) x (hours exposed per day ^ 24) x (days
dosed total days) x RGDR; RGDRs were based on average body weights from the study reports and the surface area of the respiratory area affected;
HECexresp = PPm x (molecular weight ^ 24.45) x (hours exposed per day ^ 24) x (days dosed ^ total days) x blood:gas partition coefficient.
YOAELadj is the HEC value for respiratory or extra-respiratory effects; HECresp = ppm x (molecular weight ^ 24.45) x (hours exposed per day ^ 24) x (days
dosed total days) x RGDR; RGDRs were based on average body weights from the study reports and the surface area of the respiratory area affected;
HECexresp = PPm x (molecular weight ^ 24.45) x (hours exposed per day ^ 24) x (days dosed ^ total days) x blood:gas partition coefficient.
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The following dosimetric adjustments have been made for inhalation with an
EXPOSURE,,,,,,, for respiratory effects. The RGDR is the ratio of the respiratory minute volumes
divided by the surface areas of the extra-thoracic pulmonary region (where the effect occurred)
in mice and humans, respectively, and is used in calculating the HEC (U.S. EPA, 1994b). The
example shown below is for the second lowest dose.
(EXPOSUREhec, extra-thoracic)n = PPm x (ppm conversion) x (average daily dose) x
RGDR
= ppm x (MW ^ 24.45) x ([hours exposed ^ 24 hours]
x [days exposed per week study days per week]) x
RGDR
= 188 x (61.04 -h 24.45) x (6.2 - 24) x (5 - 7) x 0.136
= 11.8 mg/m3
Where:
RGDR = (Ve SA)a ^ (Ve ^ SA)h; Ve = minute volume (m3/day); SA = surface area
of the extra-thoracic region (m ); calculated using average body weights
from the study report
= (0.0408 -h 0.0003) -h (20 - 0.02)
= 0.136
All available dichotomous models in the EPA Benchmark Dose Software (BMDS
version 2.1.2) have been fit to the data on hyaline droplets in the respiratory epithelium in female
mice following exposure to nitromethane for 13 weeks (see Table 8). A benchmark response
(BMR) of 10% extra risk above the control mean has been used to estimate the BMD (U.S. EPA,
2010).
Table 8. Incidence Data for Female B6C3Fi Mice Treated with
Nitromethane for 13 Weeks—Used for BMD Analysis"
(PPM)n
(EXPOSUREhec extra-thoracic)n
(mg/m )
Number of
Subjects
Response
0
0
10
0
94
5.9
10
2
188
11.8
10
9**
375
24.9
10
10**
750
48.0
10
10**
1500
93.9
10
10**
aNTP (1997).
**Statistically significant difference from control (p < 0.01) using Fisher's exact test as performed by the study
authors.
Table 9 summarizes the BMDS model results for the respiratory epithelium hyaline
droplet data in female mice. The curve and BMDS output for the selected model only are
provided in Appendix C. The BMDS Multistage model with a benchmark concentration lower
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"3
bound 95% confidence interval BMCLiohec, extra-thoracic of 1.31 mg/m is selected. For the models
that provided adequate fit (using goodness-of-fittest;p> 0.1), the Akaike Information Criterion
(AIC) values are close, and the BMCLs are within 3-fold of each other; therefore, the model with
the lowest AIC is selected. Table 10 summarizes the uncertainty factors applied.
Table 9. Model Predictions for Respiratory Epithelial Hyaline Droplets
in Female B6C3Fi Mice"
Model
Goodness-of-Fit
p-V alueb
AIC for Fitted
Model
BMC10
(mg/m3)
BMCL10
(mg/m3)
Conclusions
Multistage
1.00
18.556
4.431
1.31
Selected as lowest AIC value for
POD with a range of 1.314-3.126
Weibull
1.00
20.510
4.709
2.14
Not selected
Probit
0.99
20.549
4.755
2.54
Not selected
Logistic
0.96
20.659
4.825
2.73
Not selected
Log-logistic
0.98
20.569
5.078
3.11
Not selected
Log-probit
1.00
20.517
5.121
3.13
Not selected
aNTP (1997).
bChi-square p-valuc = /j-value from chi-square test for lack of fit. Values <0.1 fail to meet conventional
goodness-of-fit criteria.
AIC = Akaike Information Criteria; BMC = benchmark concentration; BMCL lower confidence limit (95%) on the
benchmark concentration; BMCi0 = BMC at a response rate of 10% incidence, extra risk.
-3
A POD of 1.31 mg/m is determined by BMD analysis. The subchronic p-RfC for
nitromethane, based on a BMCLiohec, extra-thoracic of 1.31 mg/m3 in female mice, is derived as
follows:
Sllbchronic p-RfC	BIVICLlOin.C, extra-thoracic ' UFc
= 1.31 mg/m3 300
= 4 x 10 3 mg/m3
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Table 10. Uncertainty Factors for Subchronic p-RfC of Nitromethane
UF
Value
Justification
UFa
3
A UFa of 3 is applied for animal-to-human extrapolation to account for the toxicodynamic
portion of the UFA because the toxicokinetic portion (100 5) has been addressed in dosimetric
conversions.
ufd
10
A UFd of 10 is applied because there are no acceptable two-generation reproductive studies or
developmental studies by this route of exposure.
UFh
10
A UFh of 10 is applied for intraspecies differences to account for potentially susceptible
individuals in the absence of information on the variability of response to humans.
ufl
1
A UFl of 1 is applied because the POD was developed using a BMCL.
UFS
1
A UFS of 1 is applied because a subchronic study was utilized.
UFC
<3000
300
Composite uncertainty factor
The confidence of the subchronic p-RfC for nitromethane is medium as explained in
Table 11 below.
Table 11. Confidence Descriptors for Subchronic p-RfC for Nitromethane
Confidence Categories
Designation"
Discussion
Confidence in study
H
The study by NTP (1997) provided sufficient details, used
sufficient numbers of animals, examined both sexes, and
examined numerous endpoints including both portal-of-entry and
systemic endpoints. In addition, NTP (1997) examined two
species (rats and mice) and conducted short-term studies to
determine appropriate doses for the subchronic study.
Confidence in database
M
Although there are several short-term, subchronic, chronic, and
carcinogenicity studies available, there are no acceptable
reproductive or developmental studies available for nitromethane.
Confidence in subchronic
p-RfCb
M
The overall confidence is medium because the confidence in the
database is medium.
"L = low; M = medium; H = high.
bThe overall confidence cannot be greater than lowest entry in the table.
Derivation of Chronic Provisional RfC (Chronic p-RfC)
There are several studies available for the derivation of the chronic p-RfC (see Table 12).
The study by NTP (1997) is selected as the principal study for derivation of the chronic p-RfC.
This study was peer reviewed and GLP compliant. NTP (1997) examined numerous endpoints
in both sexes of two species (i.e., rats and mice). Details are provided in the "Review of
Potentially Relevant Data" section. Among the available and acceptable studies, this study
represents the lowest POD for developing a chronic p-RfC. The critical effect is hyaline
degeneration of the respiratory epithelium of the nasal turbinates in female mice. Only the NTP
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(1997) studies included histopathologic evaluations of the upper respiratory tract, but
histopathological lesions of the nasal tract were observed in rats and mice after 16 days,
13 weeks, as well as in mice after 2 years (NTP, 1997). As stated previously, the hyaline
degeneration of the respiratory epithelium is a progressive lesion with hyaline droplets observed
after 13 weeks of exposure in mice. There was also a concentration-related increase in severity
of the nasal lesions. Degeneration of the olfactory epithelium also occurred at the same
concentration as the hyaline degeneration of the respiratory epithelium. BMD analysis has been
conducted on both the degeneration in the olfactory epithelium and the hyaline degeneration in
the respiratory epithelium (both in the nasal turbinates) in mice, but hyaline degeneration of the
respiratory epithelium is the most sensitive effect. The NTP studies also found signs of anemia
including decreased hematocrit and hemoglobin levels and effects on the thyroid (increased
thyroid weight and decreased thyroxin levels), but these effects occurred at higher
concentrations. Because these effects occurred at higher HECs than the nasal effects observed in
the 2-year mouse study, BMD analyses have not been conducted on these endpoints.
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Table 12. Summary of Relevant Inhalation Chronic Toxicity Studies for Nitromethane
Reference
Species,
#/Sex (M/F)
Exposure
(ppm)
Frequency/
Duration
NOAEW
(mg/m3)
LOAELAI)lb
(mg/m3)
Critical Endpoint
NTP (1997)
Rat, 50/50
0, 94, 188, 375
6.2 hr, 5 d/wk,
103 wk
173
NDr
No noncancer effects observed,
but tumors were observed at
87 mg/m3
NTP (1997)
Mouse, 50/50
0, 188, 375, 750
6.2 hr, 5 d/wk,
103 wk
NDr
21.9
Increase in nonneoplastic nasal
lesions in females
Griffin et al. (1996)
Rat, 40/40
0, 100, 200
7 hr, 5 d/wk, 2 yr
89.0
NDr
No noncancer effects observed
Lewis et al. (1979)
Rat, 10/0
0, 98, 745
7 hr/d, 5 d/wk,
6 mo
51
388
Increase in relative thyroid
weight
Lewis et al. (1979)
Rabbit, 5/0
0, 98, 745
7 hr/d, 5 d/wk,
6 mo
NDr
51
Decreased thyroxin levels
:iNOAELA[,j is the HEC value for respiratory or extra-respiratory effects; HECresp = ppm x (molecular weight ^ 24.45) x (hours exposed per day ^ 24) x
(days dosed total days) x RGDR; RGDRs were based on average body weights from the study reports and the surface area of the respiratory area affected;
HECexresp = PPm x (molecular weight ^ 24.45) x (hours exposed per day ^ 24) x (days dosed ^ total days) x blood:gas partition coefficient.
LO AEL U)[ is the HEC value for respiratory or extra-respiratory effects; HECresp = ppm x (molecular weight ^ 24.45) x (hours exposed per day ^ 24) x (days dosed ^
total days) x RGDR; RGDRs were based on average body weights from the study reports and the surface area of the respiratory area affected;
HECexresp = PPm x (molecular weight ^ 24.45) x (hours exposed per day ^ 24) x (days dosed ^ total days) x blood:gas partition coefficient.
NDr = not determinable.
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Based on its physical properties, nitromethane is a Category 2 gas. This is supported by
the observation of both respiratory (direct contact) and extra-respiratory (systemic) effects in the
studies that examined endpoints inclusive of both effects. Therefore, dosimetric conversions are
based on the endpoint observed and differ for respiratory and extra-respiratory effects. Note that
the RGDR used in dosimetric conversions is different from the subchronic-duration derivation
because of the difference in average body weights at 13 weeks versus 103 weeks.
The following dosimetric adjustments have been made for inhalation with an
EXPOSURE,,,,,,, for respiratory effects. The example shown is for the lowest dose.
(EXPOSUREhec, resp)ii = ppm x (ppm conversion) x (average daily dose) x RGDR
= ppm x (MW ^ 24.45) x ([hours exposed ^ 24] x [days
exposed ^ study duration]) x RGDR
= 188 x (61.04 -h 24.45) x (6.2 - 24) x (5 - 7) x 0.254
= 22.0 m«/m3
Where:
RGDR = (Ve SA)a ^ (Ve ^ SA)h; Ve = minute volume (m3/day); SA = Surface Area
of the extra-thoracic region (m2); calculated using average body weights
from the study report
= (0.0763 -h 0.0003) - (20 - 0.02)
= 0.254
The following dosimetric adjustments have been made for inhalation with an
EXPOSUREppm for extra-respiratory effects. Data for calculating a specific blood:gas partition
coefficient were not available; therefore, a value of 1 is employed.
EXPOSUREhec, exresp — PPm x (PPm conversion) x (average daily dose) x
blood:gas partition coefficient
= ppm x (MW ^ 24.45) x ([hours exposed ^ 24] x [days
exposed ^ study duration]) x blood:gas partition coefficient
= 188 x (61.04 -h 24.45) x (6.2 - 24) x (5 - 7) x 1
= 86.6 mg/m3
All available dichotomous models in the EPA Benchmark Dose Software (BMDS
version 2.1.2) have been fit to the hyaline degeneration of the respiratory epithelium data in
female mice following exposure to nitromethane for 2 years (see Table 13). A BMR of
10% extra risk above the control mean is used to estimate the BMD (U.S. EPA, 2010).
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Table 13. Incidence Data for Hyaline Degeneration of the Respiratory Epithelium in
Female B6C3Fi Mice Treated with Nitromethane for 2 Years—Used for BMDS Analysis3
(PPM)n
(EXPOSUREhec,resp)
(mg/m3)
Number of Subjects
Response
0
0
50
16
188
22.0
49
39**
375
43.9
50
50**
750
87.8
50
50**
aNTP (1997).
**Statistically significant difference from control (p < 0.01) using Fisher's exact test as performed by the study
authors.
Table 14 summarizes the BMDS model results for the data in female mice. The curve
and BMDS output for the selected model only are provided in Appendix C. The BMDS
Multistage model with a BMCLiohec, resp of 1.60 mg/m3 is selected. Following EPA guidance
(U.S. EPA, 2012), for the models that provided an adequate fit (using goodness-of-fit test;
p > 0.1), the AIC values are close, but the BMCLs are not within 3-fold of each other; therefore,
the model with the lowest BMCL is selected. Table 15 summarizes the uncertainty factors
applied.
Table 14. Model Predictions for Hyaline Degeneration of the
Respiratory Epithelium in Female B6C3Fi Mice"
Model
Goodness-of-Fit
p-V alueb
AIC for
Fitted Model
BMC10
(mg/m3)
BMCL10
(mg/m3)
Conclusion
Multistage
1.00
116.283
9.734
1.60
Selected as lowest BMCL value for
POD with a range of 1.602-8.373
Logistic
0.47
118.672
2.810
2.19
Not selected
Probit
0.66
117.579
2.885
2.33
Not selected
Weibull
1.00
118.276
11.437
2.90
Not selected
Log-probit
1.00
118.276
17.188
6.85
Not selected
Log-logistic
1.00
116.276
18.523
8.37
Not selected
aNTP (1997).
bChi-square p value = p-valuc from chi-square test for lack of fit. Values <0.1 fail to meet conventional goodness-
of-fit criteria.
AIC = Akaike Information Criteria; BMC = benchmark concentration; BMCL lower confidence limit (95%) on
the benchmark concentration; BMCio = BMC at a response rate of 10% incidence, extra risk.
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The POD in this study is a BMCLiohec, resp of 1.60 mg/m3. The chronic p-RfC for
nitromethane, based on a BMCLiohec, resp of 1.60 mg/m3 in female mice, is derived as follows:
Chronic p-RfC = BMCLiohec, resp UFc
= 1.60 mg/m3 300
= 5 x 10 3 mg/m3
Table 15. Uncertainty Factors for Chronic p-RfC of Nitromethane
UF
Value
Justification
ufa
3
A UFa of 3 is applied for animal-to-human extrapolation to account for the toxicodynamic
portion of the UFA because the toxicokinetic portion (100 5) has been addressed in dosimetric
conversions.
ufd
10
A UFd of 10 is applied because there are no acceptable two-generation reproductive studies or
developmental studies by this route of exposure.
UFh
10
A UFh of 10 is applied for intraspecies differences to account for potentially susceptible
individuals in the absence of information on the variability of response to humans.
ufl
1
A UFl of 1 is applied for using a POD based on a BMCL.
UFS
1
A UFS of 1 is applied because a chronic study was utilized.
UFC
<3000
300
Composite uncertainty factor
The confidence of the chronic p-RfC for nitromethane is medium as explained in
Table 16 below.
Table 16. Confidence Descriptors for Chronic p-RfC for Nitromethane
Confidence Categories
Designation"
Discussion
Confidence in study
M
The study by NTP (1997) provided sufficient details, used
sufficient numbers of animals, examined both sexes, and
examined numerous endpoints including both portal-of-entry and
systemic endpoints. In addition, NTP (1997) examined two
species (rats and mice) and selected doses based on shorter
duration studies. However, the lowest dose tested was a LOAEL.
Confidence in database
M
Although there are several short-term, subchronic, chronic, and
carcinogenicity studies available, there are no reproductive or
developmental studies available for nitromethane.
Confidence in chronic
p-RfCb
M
The overall confidence is medium because the confidence in the
database is medium.
aL = low; M = medium; H = high.
bThe overall confidence cannot be greater than the lowest entry in table.
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CANCER WEIGHT-OF-EVIDENCE (WOE) DESCRIPTOR
Table 17 identifies the cancer WOE descriptor for nitromethane. As there are statistically
significant increases in tumors in more than one species (rats and mice) and in both sexes of
mice, the cancer WOE descriptor is "Likely to Be Carcinogenic to Humans " (U.S. EPA, 2005)
for the inhalation route of exposure. Because no carcinogenicity studies on nitromethane via the
oral route of exposure have been identified, the cancer WOE descriptor for the oral route is
"Inadequate Information to Assess Carcinogenic Potential".
Table 17. Cancer WOE Descriptor for Nitromethane
Possible WOE
Descriptor
Designation
Route of entry
(oral, inhalation,
or both)
Comments
"Carcinogenic to
Humans "
NS
NA
No human data has been identified.
"Likely to Be
Carcinogenic to
Humans"
Selected
Inhalation
NTP (1997) determined evidence of
carcinogenicity in female F344 rats and both
sexes of B6C3F, mice.
"Suggestive Evidence
of Carcinogenic
Potential"
NS
NA
Evidence points more towards likely to be
carcinogenic.
"Inadequate
Information to Assess
Carcinogenic
Potential"
Selected
Oral
No carcinogenicity studies via the oral route
of exposure have been identified.
"Not Likely to Be
Carcinogenic to
Humans "
NS
NA
Animal data indicate this is not true.
NS = not selected; NA = not applicable.
MODE-OF-ACTION DISCUSSION
There are insufficient data to clearly define a mutagenic mode of action. Therefore, a
linear approach is applied.
DERIVATION OF PROVISIONAL CANCER POTENCY VALUES
Derivation of Provisional Oral Slope Factor (p-OSF)
The lack of oral data on the carcinogenicity of nitromethane precludes the derivation of
quantitative estimates for oral (p-OSF) exposure.
Derivation of Provisional Inhalation Unit Risk (p-IUR)
The study in rats by NTP (1997) is selected as the principal study for derivation of the
p-IUR. The cancer endpoint is combined mammary gland fibroadenoma, adenoma, and
carcinoma in females. While the NTP study in mice provided similar data, the dose response
was clearer in rats. This study was peer reviewed, GLP compliant, and otherwise met the
standards of study design and performance. Details are provided in the "Review of Potentially
Relevant Data" section. Table 18 provides the data that have been applied to the BMDS model.
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Among the available, acceptable studies, this study represents the highest IUR from the relevant
studies in the database.
The following dosimetric adjustments have been made for inhalation treatment in
adjusting exposures for cancer analysis. Since the endpoint (mammary gland tumors) is outside
the respiratory tract, the HEC is calculated based upon extra-respiratory effects. Because the
rat/human blood gas partition coefficient ratio was not available, the default value of 1 was used
(U.S. EPA 1994b). The example shown is the for the low dose.
(EXPOSUREhec, exresp)ii = PPm x (ppm conversion) x (average daily dose) x
blood:gas partition coefficients
= ppm x (MW ^ 24.45) x ([hours exposed ^ 24] x
[days exposed ^ study duration]) x blood:gas partition
coefficient)
= 94 x (61.04 -h 24.45) x (6.2 - 24) x (5 - 7) x 1
= 43.3 mg/m3
Table 18. Incidence Data for Female Sprague-Dawley Rats Treated with
Nitromethane for 2 Years—Used for BMD Analysis"
(PPM)n
(EXPOSUREhec, exresp)ii
(mg/m3)
Number of Subjects
Response
0
0
50
21
94
43.3
50
25
188
86.6
50
34**
375
172.8
50
41**
aNTP (1997).
**Statistically significant difference from control (p < 0.01) using Fisher's exact test as performed by study
authors.
Table 19 shows the modeling results. Adequate model fit is obtained for the combined
mammary gland fibroadenoma, adenoma, and carcinoma data in female rats using the BMDS
version 2.1.2 multistage-cancer model (U.S. EPA, 2010). A BMCiohec exresp of 20.4 mg/m3
"3	'
and a BMCLiohec, exresp of 11.3 mg/m are calculated from BMD modeling with 10% extra risk
for combined mammary gland fibroadenoma, adenoma, and carcinoma (see Table 19). The
curve and BMDS output for the selected model only is provided in the BMD supplement (see
Appendix C); Table C. 1 provides the IURs for the various endpoints modeled.
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Table 19. Model Predictions for Combined Mammary Gland Fibroadenoma, Adenoma,

and Carcinoma in Females Rats
a


Goodness-of-Fit
AIC for Fitted
BMClOHEC, EXRESP
BMCLiOHEC, EXRESP

Model
p-V alueb
Model
(mg/m3)
(mg/m3)
Conclusions
Multistage-
0.49
253.652
20.4
11.3
Lowest BMCL
Cancer





aNTP (1997).
bValues <0.10 fail to meet conventional goodness-of-fit criteria.
AIC = Akaike's Information Criterion; BMC = benchmark concentration; BMCL = lower confidence limit (95%)
on the benchmark concentration; BMCio = BMC at a response rate of 10% incidence, extra risk. HEC = Human
Equivalent Concentration; EXRESP = HEC determined using the extra-respiratory method (U.S. EPA, 1994b)
p-IUR - 0.1a BMCLiOHEC, EXRESP
= 0.1 -h 11.3 m«/m3
= 8.8 x 10 3 (mg/m3)"1
aThe value 0.1 is the benchmark response/concentration (U.S. EPA 1994b, 2012).
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APPENDIX A. PROVISIONAL SCREENING VALUES
No screening values for nitromethane are derived.
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APPENDIX B. DATA TABLES
Table B.l. Mean Body Weights of Male and Female F344 Rats After Inhalation Exposure
to Nitromethane for 16 Days3
Parameter
Exposure Group, ppm (HEC, mg/m3)b
Male
0
94 (46)
188 (91)
375 (181)
750 (363)
1500 (726)
Sample size
5
5
5
5
5
5
Weight0
Initial
145 ±4
147 ±4 (101)
146 ±4 (101)
145 ± 3 (100)
144 ± 3 (99)
146 ±3 (101)
(g)
Final
182 ±4
189 ± 5 (104)
187 ±5 (103)
182 ±6 (100)
177 ± 4 (97)
171 ±4 (94)

Change
38 ±2
43 ±2 (113)
41 ±2 (108)
37 ± 3 (97)
34 ± 1 (89)
25 ±3** (66)
Female
0
94 (46)
188 (91)
375 (181)
750 (363)
1500 (726)
Sample size
5
5
5
5
5
5
Weight0
Initial
116 ± 2
116 ±2 (100)
116 ±2 (100)
116 ±2 (100)
117 ±2 (101)
117 ±2 (101)
(g)
Final
134 ±3
135 ±3 (101)
133 ±2 (99)
133 ±2 (99)
132 ± 1 (99)
128 ± 2 (96)

Change
17 ± 1
18 ±3 (106)
17 ± 1 (100)
18 ±2 (106)
15 ± 2 (88)
11 ± 1 (65)
"Source: NTP (1997).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
°Weights expressed as mean ± SE (% of control). Percent change from control in brackets.
**Significantly different from control (p < 0.01); Williams' or Dunnett's test performed by the study authors.
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Table B.2. Liver and Kidney Weights of Male and Female F344 Rats After Inhalation
Exposure to Nitromethane for 16 Days"
Parameter
Exposure Group, ppm (HEC, mg/m3)b
Male
0
94 (46)
188 (91)
375 (181)
750 (363)
1500 (726)
Sample size
5
5
5
5
5
5
Necropsy body
weight0 (g)
218 ±3
225 ± 5 (103)
223 ± 6 (102)
215 ±7 (99)
206 ± 4 (94)
192 ±4 (88)**
Liver
weight0
Absolute
(g)
8.922 ±
0.201
9.950 ±0.250
(112)
9.794 ±0.303
(110)
9.988 ±0.393
(112)
9.028 ±0.144
(101)
9.322 ±0.346
(104)
Relative
(mg/g)
40.98 ±
0.55
44.29 ±0.71
(108)**
43.87 ±0.66
(107)**
46.50 ±0.68
(113)**
43.84 ±0.63
(107)**
48.49 ±0.99
(118)**
Right
kidney
weight0
Absolute
(g)
0.852 ±
0.014
0.878 ±0.011
(103)
0.904 ± 0.029
(106)
0.870 ±0.037
(102)
0.854 ±0.016
(100)
0.880 ± 0.022
(103)
Relative
(mg/g)
3.91 ±
0.02
3.91 ±0.08
(100)
4.05 ±0.05
(104)
4.05 ±0.07
(104)
4.14 ±0.02
(106)*
4.58 ±0.08
(117)**
Female
0
94 (46)
188 (91)
375 (181)
750 (363)
1500 (726)
Sample size
5
5
5
5
5
5
Necropsy body
weight0 (g)
146 ±2
148 ±3 (101)
147 ±2 (101)
146 ± 2 (100)
143 ± 2 (98)
137 ± 3 (94)
Liver
weight0
Absolute
(g)
5.240 ±
0.182
5.472 ±0.193
(104)
5.578 ±0.187
(106)
5.750 ±0.160
(110)*
5.832 ±0.067
(111)*
6.204 ±0.118
(118)**
Relative
(mg/g)
35.95 ±
0.86
36.87 ±0.62
(103)
37.88 ±0.82
(105)
39.28 ± 1.09
(109)**
40.72 ± 0.22
(113)**
45.30 ±0.53
(126)**
Right
kidney
weight0
Absolute
(g)
0.612 ±
0.022
0.616 ±0.019
(101)
0.634 ±0.013
(104)
0.614 ±0.007
(100)
0.636 ±0.007
(104)
0.660 ± 0.009
(108)
Relative
(mg/g)
4.20 ±
0.13
4.15 ±0.05
(99)
4.31 ±0.08
(103)
4.19 ±0.04
(100)
4.44 ± 0.06
(106)
4.82 ±0.10
(115)**
"Source: NTP (1997).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
°Weights expressed as mean ± SE. Percent change from control in brackets.
* Significantly different from control (p < 0.05); Williams' or Dunnett's test performed by the study authors.
**Significantly different from control (p < 0.01); Williams' or Dunnett's test performed by the study authors.
45
Nitromethane

-------
FINAL
7-26-2013
Table B.3. Histopathological Findings for Male and Female F344 Rats After Inhalation
Exposure to Nitromethane for 16 Days"
Parameter
Exposure Group, ppm (HEC, mg/m3)
Male
0
94 (5.7)b
188 (11.2)
375 (22.1)
750 (43.5)
1500 (86.1)
Nose/Turbinates,
degeneration, olfactory
epithelium0
0/5 (0)
0/5 (0)
0/ 5 (0)
5/5** (100;
1.0)
5/5** (100;
2.0)
5/5** (100;
2.0)
Male
0
94 (46)d
188 (91)
375 (181)
750 (363)
1500 (726)
Sciatic nerve degeneration0
0/4 (0)
0/5 (0)
0/5 (0)
5/5** (100;
1.0)
5/5** (100;
2.0)
5/5** (100;
3.0)
Female
0
94 (4.5)b
188 (8.9)
375 (17.7)
750 (35.3)
1500 (69.7)
Nose/Turbinates,
degeneration, olfactory
epithelium0
0/5 (0)
0/5 (0)
0/ 5 (0)
4/5* (80; 1.0)
5/5** (100;
1.8)
5/5** (100;
2.0)
Female
0
94 (46)d
188 (91)
375 (181)
750 (363)
1500 (726)
Sciatic nerve degeneration0
0/5 (0)
0/5 (0)
0/5 (0)
5/5** (100;
1.0)
5/5** (100;
2.0)
5/5** (100;
3.0)
"Source: NTP (1997).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day ^ 24) x (days dosed ^ total days) x RGDR; body weights used to determine the RGDR were
calculated as (initial body weight + final body weight) 2.
0 Values expressed as number observed with neoplasm/number examined for that neoplasm (% incidence; average
severity of lesions 1 = minimal, 2 = mild, 3 = moderate, 4 = marked).
dDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
* Significantly different from control (p < 0.05); Fischer exact test performed by the study authors.
**Significantly different from control (p < 0.01); Fischer exact test performed by the study authors.
46
Nitromethane

-------
FINAL
7-26-2013
Table B.4. Liver Weights of Male and Female B6C3Fi Mice After Inhalation
Exposure to Nitromethane for 16 Days"
Parameter
Exposure Group, ppm (HEC, mg/m3)b
Male
0
94 (46)
188 (91)
375 (181)
750 (363)
1500 (726)
Sample size
5
5
5
5
5
5
Necropsy body
weight0 (g)
27.4 ±0.6
29.0 ± 1.0
(106)
28.9 ±0.6
(105)
27.7 ±0.9
(101)
29.2 ±0.7
(107)
28.6 ±0.2
(104)
Liver
weight0
Absolute
(g)
1.376 ±
0.044
1.538 ±0.083
(112)
1.552 ±0.045
(113)
1.526 ±0.078
(HI)
1.752 ±0.081
(127)**
1.680 ±0.053
(122)**
Relative
(mg/g)
50.15 ±
0.67
52.99 ±2.14
(106)
53.63 ±0.53
(107)
54.96 ± 1.53
(110)*
59.93 ± 1.38
(120)**
58.72 ± 1.61
(117)**
Female
0
94 (46)
188 (91)
375 (181)
750 (363)
1500 (726)
Sample size
5
5
5
5
5
5
Necropsy body
weight0 (g)
23.3 ±0.2
23.7 ±0.3
(102)
23.6 ±0.3
(101)
23.8 ±0.4
(102)
24.7 ±0.4
(106)*
24.0 ±0.4
(103)
Liver
weight0
Absolute
(g)
1.146 ±
0.020
1.256 ±0.035
(110)*
1.338 ±0.037
(117)**
1.364 ±0.047
(119)**
1.442 ±0.020
(126)**
1.410 ±0.044
(123)**
Relative
(mg/g)
49.24 ±
0.96
53.00 ± 1.40
(108)*
56.77 ± 1.15
(115)**
57.28 ± 1.56
(116)**
58.44 ± 1.18
(119)**
58.70 ±0.90
(119)**
"Source: NTP (1997).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
°Weights expressed as mean ± SE (% of control).
* Significantly different from control (p < 0.05); Williams' or Dunnett's test performed by the study authors.
**Significantly different from control (p < 0.01); Williams' or Dunnett's test performed by the study authors.
47
Nitromethane

-------
FINAL
7-26-2013
Table B.5. Mean Body Weights of Male and Female F344 Rats After Inhalation
Exposure to Nitromethane for 13 Weeks"
Parameter
Exposure Group, ppm (HEC, mg/m3)b
Male
0
94 (43)
188 (87)
375 (173)
750 (346)
1500 (691)
Sample size
10
10
10
10
10
10
Weight0
(g)
Initial
107 ±3
105 ± 2 (98)
113 ±2 (106)
109 ±3 (102)
106 ± 2 (99)
109 ±2 (102)
Final
334 ±7
323 ± 7 (97)
345 ±4 (103)
336 ±5 (101)
327 ± 4 (98)
295 ± 10
(88)**
Change
228 ±6
218 ±7 (96)
232 ±3 (102)
227 ± 4 (100)
221 ±5 (97)
185 ±9 (81)**
Female
0
94 (43)
188 (87)
375 (173)
750 (346)
1500 (691)
Sample size
10
10
10
10
10
10
Weight0
(g)
Initial
95 ± 1
96 ±2 (101)
97 ± 2 (102)
95 ±2 (100)
96 ±2 (101)
94 ± 2 (99)
Final
185 ±5
197 ±3 (106)
197 ±3 (106)
198 ± 5 (107)
194 ±4 (105)
177 ± 4 (96)
Change
90 ±3
101 ±2 (112)
100 ±2 (111)
103 ±4
(114)**
97 ±2 (108)
84 ± 3 (93)
"Source: NTP (1997).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
°Weights expressed as mean ± SE (% of control).
**Significantly different from control (p < 0.01); Williams' or Dunnett's test performed by study authors.
48
Nitromethane

-------
FINAL
7-26-2013
Table B.6. Select Hematology for Male and Female F344 Rats After Inhalation
Exposure to Nitromethane for 13 Weeks"
Parameter
Exposure Group, ppm (HEC, mg/m3)b
0
94 (43)
188 (87)
375 (173)
750 (346)
1500 (691)
Male
Sample size
10
10
10
10
10
10
Hematocrit0 (%)
Day 3
36.7 ±0.5
36.3 ±0.3 (99)
35.2 ±0.2
(96)*
33.1 ±0.3
(90)**
31.7 ±0.2
(86)**
32.3 ±0.2
(88)**
Day 23
40.7 ±
0.3d
43.2 ±0.9
(106)e
40.4 ±0.4
(99)f
37.6 ±0.4
(92)*
34.0 ±0.4
(84)**
30.3 ±0.4
(74)**
Week 13
46.3 ±0.1
46.6 ±0.4
(101)
46.1 ±0.4
(100)
44.6 ±0.3
(96)**
42.5 ±0.4
(92)**
39.2 ±0.4
(85)**
Hemoglobin0 (g/dL)
Day 3
13.9 ±0.2
13.5 ±0.1 (97)
13.3 ±0.1
(96)*
12.6 ±0.1
(91)**
12.2 ±0.1
(88)**
12.4 ±0.1
(89)**
Day 23
15.3 ±
0.2d
16.1 ±0.3
(105)e
15.0 ±0.1
(98)f
14.3 ±0.1
(93)*
13.2 ±0.1
(86)**
11.9 ± 0.1
(78)**
Week 13
15.3 ±0.1
15.4 ±0.1
(101)
15.2 ±0.1 (99)
14.8 ±0.1
(97)**
14.3 ±0.1
(93)**
13.4 ±0.2
(88)**
Erythrocytes0
(106/|iL)
Day 3
7.75 ±
0.10
7.58 ±0.08
(98)
7.38 ±0.08
(95)**
7.16 ±0.07
(92)**
6.97 ±0.04
(90)**
6.94 ±0.06
(90)**
Day 23
8.74 ±
0.06d
9.37 ±0.18
(107)*e
9.00 ± 0.07
(103)f
9.36 ±0.09
(107)*
9.10 ±0.09
(104)
7.77 ±0.11
(89)
Week 13
9.12 ±
0.03
9.43 ± 0.06
(103)**
9.53 ±0.08
(104)**
9.72 ±0.08
(107)**
10.10 ±0.09
(111)**
9.41 ±0.11
(103)**
Nucleated
erythrocytes
(103/hL)
Week 13
0.03 ±
0.02
0.04 ± 0.02
(133)
0.03 ± 0.03
(100)
0.11 ±0.03
(367)
0.08 ±0.03
(267)
0.27 ± 0.07
(900)**
MCV° (fL)
Day 3
47.2 ±0.3
47.9 ±0.3
(101)
47.7 ±0.4
(101)
46.2 ±0.1
(98)*
45.5 ±0.2
(96)**
46.3 ±0.2
(98)**
Day 23
46.5 ±
0.3d
46.0 ±0.2
(99)e
45.0 ±0.4
40.2 ±0.3
(86)**
37.5 ±0.2
(81)**
39.1 ±0.2
(84)**
Week 13
50.7 ±0.2
49.3 ±0.2
(97)**
48.4 ±0.2
(95)**
45.8 ±0.4
(90)**
42.0 ±0.6
(83)**
41.6 ±0.3
(82)**
MCH° (pg)
Day 3
17.9 ±0.1
17.8 ±0.1 (99)
18.1 ± 0.1
(101)
17.6 ±0.0
(98)*
17.5 ±0.1
(98)*
17.9 ±0.1
(100)
Day 23
17.5 ±
0.02d
17.2 ±0.1
(98)e
16.7 ±0.1
(95)**f
15.3 ±0.1
(87)**
14.5 ±0.0
(83)**
15.3 ±0.1
(87)**
Week 13
16.8 ±0.0
16.3 ±0.1
(97)**
16.0 ±0.0
(95)**
15.2 ±0.1
(90)**
14.1 ±0.2
(84)**
14.3 ±0.1
(85)**
MCHC0 (g/dL)
Day 3
37.8 ±0.2
37.3 ±0.1 (99)
37.8 ±0.1
(100)
38.1 ±0.1
(101)*
38.4 ±0.2
(103)*
38.6 ±0.1
(102)**
Day 23
37.5 ±
0.2d
37.3 ±0.1
(99)e
37.3 ±0.2
(99)f
38.2 ±0.3
(102)
38.8 ±0.2
(103)*
39.3 ±0.2
(105)**
Week 13
33.0 ±0.1
33.0 ±0.1
(100)
33.0 ±0.1
(100)
33.2 ±0.1
(101)
33.6 ±0.1
(102)**
34.3 ±0.3
(104)**
49
Nitromethane

-------
FINAL
7-26-2013
Table B.6. Select Hematology for Male and Female F344 Rats After Inhalation
Exposure to Nitromethane for 13 Weeks"
Parameter
Exposure Group, ppm (HEC, mg/m3)b
0
94 (43)
188 (87)
375 (173)
750 (346)
1500 (691)
Platelets0 (lo VjiL)
Day 3
663.6 ±
15.5
741.9 ± 13.8
(112)**
708.2 ± 13.5
(107)**
732.7 ± 17.8
(110)**
781.2 ± 10.5
(118)**
870.6 ± 16.3
(131)**
Day 23
643.8 ±
44. ld
663.4 ±8.8
(103)e
675.0 ± 16.0
(105)f
704.8 ± 19.2
(109)
878.4 ±22.5
(136)**
1325.2 ±24.0
(206)**
Week 13
538.3 ±
7.5
527.8 ± 16.7
(98)
539.2 ±5.7
(100)
578.7 ±6.1
(108)**
625.0 ±9.2
(116)**
817.4 ±32.9
(152)**
Methemoglobin0
(g/dL)
Day 3
0.16 ±
0.02f
0.14 ±0.02
(88)f
0.19 ±0.02
(119)e
0.34 ±0.02
(213)**
0.21 ±0.03
(13l)*8
0.22 ±0.02
(138)*e
Day 23
0.08 ±
0.01d
0.06 ±0.01
(75)e
0.08 ±0.01
(100)f
0.16 ±0.06
(200)
0.15 ±0.01
(188)*
0.28 ±0.02
(350)**
Week 13
0.15 ±
0.01
0.17 ±0.02
(113)
0.17 ±0.01
(113)*
0.17 ±0.01
(113)*
0.21 ±0.01
(140)**
0.41 ±0.09
(273)**
Female
Sample size
10
10
10
10
10
10
Hematocrit0 (%)
Day 3
38.9 ±0.6
38.7 ±0.3 (99)
38.1 ±0.4 (98)
36.7 ±0.3
(94)**
36.0 ±0.3
(93)**
36.6 ±0.4
(94)**
Day 23
42.6 ±0.3
40.5 ±0.9
(95)**
41.1 ±0.5
(96)*
37.9 ±0.4
(89)**
35.2 ±0.3
(83)**
31.7 ±0.2
(74)**e
Week 13
46.8 ±0.3
46.6 ±0.4
(100)
44.7 ±0.4
(96)**
44.4 ±0.5
(95)**
40.7 ±0.4
(87)**
37.8 ±0.4
(81)**
Hemoglobin0 (g/dL)
Day 3
14.9 ±0.2
14.9 ±0.1
(100)
14.6 ±0.2 (98)
14.0 ±0.1
(94)**
13.7 ±0.1
(92)**
14.1 ±0.2
(95)**
Day 23
16.2 ±0.1
15.4 ±0.3
(95)**
15.6 ±0.2
(96)*
14.5 ±0.1
(90)**
13.5 ±0.1
(83)**
12.5 ±0.1
(77)**e
Week 13
16.0 ±0.1
15.8 ±0.1 (99)
15.3 ±0.1
(96)**
15.3 ±0.1
(96)**
14.1 ±0.1
(88)**
13.4 ±0.2
(84)**
Erythrocytes0
(106/|iL)
Day 3
8.39 ±
0.15
8.42 ±0.07
(100)
8.34 ± 0.11
(99)
8.10 ±0.09
(97)
7.87 ±0.07
(94)**
8.14 ± 0.11
(97)*
Day 23
9.03 ±
0.06
8.86 ±0.18
(98)
9.35 ±0.09
(104)
9.32 ±0.09
(103)
9.14 ±0.09
(101)
8.16 ±0.06
(90)e
Week 13
8.71 ±
0.05
8.91 ±0.06
(102)
8.92 ±0.09
(102)
9.42 ±0.07
(108)**
9.24 ± 0.07
(106)**
8.51 ±0.10
(98)
Nucleated
erythrocytes0
Week 13
0.03 ±
0.01
0.07 ± 0.02
(233)
0.09 ±0.04
(300)
0.06 ± 0.04
(200)
0.22 ±0.09
(733)
0.30 ± 0.11
(1000)**
MCV0 (fL)
Day 3
46.5 ±0.2
45.8 ±0.2
(98)*
45.6 ±0.3
(98)*
45.3 ±0.2
(97)**
45.7 ±0.2
(98)**
45.0 ±0.2
(97)**
Day 23
47.0 ±0.0
45.8 ±0.2
(97)**
43.9 ±0.2
(93)**
40.6 ±0.2
(86)**
38.4 ±0.2
(82)**
38.8 ±0.2
(83)**e
Week 13
53.9 ±0.2
52.4 ±0.2
(97)**
50.1 ±0.3
(93)**
47.2 ±0.2
(88)**
44.2 ±0.5
(82)**
44.4 ±0.4
(82)**
50
Nitromethane

-------
FINAL
7-26-2013
Table B.6. Select Hematology for Male and Female F344 Rats After Inhalation
Exposure to Nitromethane for 13 Weeks"
Parameter
Exposure Group, ppm (HEC, mg/m3)b
0
94 (43)
188 (87)
375 (173)
750 (346)
1500 (691)
mchc (pg)
Day 3
17.7 ±0.1
17.7 ±0.1
(100)
17.5 ±0.1 (99)
17.3 ±0.1
(98)**
17.4 ±0.1
(98)**
17.3 ±0.1
(98)**
Day 23
18.0 ±0.1
17.4 ±0.1
(97)**
16.7 ±0.1
(93)**
15.6 ±0.1
(87)**
14.8 ±0.1
(82)**
15.3 ±0.1
(85)**e
Week 13
18.3 ±0.1
17.7 ±0.1
(97)**
17.1 ±0.1
(93)**
16.2 ±0.1
(89)**
15.3 ±0.1
(84)**
15.7 ±0.1
(86)**
MCHC° (g/dL)
Day 3
38.1 ± 0.1
38.4 ±0.1
(101)
38.4 ±0.1
(101)
38.1 ±0.1
(100)
38.1 ±0.1
(100)
38.6 ±0.1
(101)**
Day 23
38.0 ±0.2
38.1 ±0.2
(100)
38.0 ±0.2
(100)
38.2 ±0.2
(101)
38.4 ±0.2
(101)
39.5 ±0.2
(104)**e
Week 13
34.1 ±0.2
33.9 ±0.2 (99)
34.2 ±0.2
(100)
34.4 ±0.2
(101)
34.7 ±0.2
(102)
35.4 ±0.2
(104)**
Platelets0 (10:V|iL)
Day 3
669.7 ±
26.8
586.2 ± 15.3
(88)*
609.0 ± 26.4
(91)
657.9 ± 17.9
(98)
668.0 ± 15.8
(100)
624.6 ± 17.6
(93)
Day 23
649.2 ±
12.7
628.9 ± 14.4
(97)
637.2 ± 12.6
(98)
698.7 ± 14.0
(108)
811.9 ± 14.4
(125)**
1179.0 ± 18.5
(182)**e
Week 13
534.2 ±
7.7
560.6 ± 10.8
(105)
528.4 ± 10.2
(99)
608.8 ± 11.7
(114)**
669.9 ± 10.8
(125)**
765.0 ±32.6
(143)**
Methemoglobin0
(g/dL)
Day 3
0.20 ±
0.03
0.27 ±0.10
(135)
0.17 ±0.04
(85)
0.10 ±0.02
(50)*
0.11 ±0.01
(55)
0.16 ±0.01
(80)
Day 23
0.09 ±
0.01
0.10 ±0.01
(Hl)f
0.12 ±0.01
(133)*
0.12 ±0.01
(133)**
0.19 ±0.01
(211)**
0.35 ±0.01
(389)**e
Week 13
0.20 ±
0.01
0.20 ±0.01
(100)
0.20 ±0.01
(100)
0.21 ±0.01
(105)
0.25 ±0.01
(125)**
0.40 ± 0.04
(200)**
"Source: NTP (1997).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x (hours
per day 24) x (days dosed total days) x blood:gas partition coefficient.
°Results expressed as mean ± SE (% of control).
dn = 6.
en = 8.
f« = 9.
sn = 7.
* Significantly different from control (p < 0.05); Williams' or Dunnett's test performed by study authors.
**Significantly different from control (p < 0.01); Williams' or Dunnett's test performed by study authors.
51
Nitromethane

-------
FINAL
7-26-2013
Table B.7. Histopathological Findings for Male and Female F344 Rats After
Inhalation Exposure to Nitromethane for 13 Weeks"
Parameter
Exposure Group, ppm (HEC, mg/m3)
Male
0
94 (6.6)b
188 (13.9)
375 (27.1)
750 (53.0)
1500 (100.1)
Nasal
turbinates0
Degeneration,
olfactory epithelium
0/10 (0)
d
0/ 10 (0)
9/10** (90;
1.0)
10/10**
(100; 1.0)
10/10**
(100; 1.0)
Hyaline droplets,
respiratory
epithelium
0/10 (0)
d
0/10 (0)
0/10 (0)
1/10(10; 1.0)
8/10 (80;
1.0)**
Hyperplasia, goblet
cell
0/10 (0)
d
0/10 (0)
0/10 (0)
1/10(10; 1.0)
10/10**
(100; 2.0)
Male
0
94 (43)e
188 (87)
375 (173)
750 (346)
1500 (691)
Sciatic nerve degeneration0
0/10 (0)
d
0/10 (0)
5/10* (50;
1.0)
10/10**
(100; 1.2)
10/10**
(100; 1.5)
Spinal cord degeneration0
0/10 (0)
d
0/10 (0)
9/10** (90;
1.0)
10/10**
(100; 1.4)
10/10**
(100; 2.0)
Bone marrow hyperplasia0
0/10 (0)
0/10 (0)
0/10 (0)
0/10 (0)
9/10** (90;
1.1)
10/10**
(100; 2.0)
Female
0
94 (4.8)b
188 (9.7)
375 (19.2)
750 (38.1)
1500 (72.1)
Nasal
turbinates0
Degeneration,
olfactory epithelium
0/10 (0)
0/10 (0)
1/10(10; 1.0)
10/10**
(100; 1.0)
10/10**
(100; 1.2)
10/10**
(100; 1.8)
Hyaline droplets,
respiratory
epithelium
0/10 (0)
0/10 (0)
0/10 (0)
0/10 (0)
4/10* (40;
1.0)
10/10**
(100; 1.0)
Hyperplasia, goblet
cell
0/10 (0)
0/10 (0)
0/10 (0)
0/10 (0)
2/10 (20; 1.5)
10/10**
(100; 1.7)
Female
0
94 (43)e
188 (87)
375 (173)
750 (346)
1500 (691)
Sciatic nerve degeneration0
0/10 (0)
d
0/10 (0)
8/10** (80;
1.0)
10/10**
(100; 1.1)
10/10**
(100; 1.8)
Spinal cord degeneration0
0/10 (0)
d
0/10 (0)
2/10 (20; 1.0)
10/10**
(100; 1.4)
10/10**
(100; 1.9)
Bone marrow hyperplasia0
0/10 (0)
0/10 (0)
1/10 (10; 2.0)
6/10** (60;
1.0)
7/10** (70;
1.1)
10/10**
(100; 1.7)
"Source: NTP (1997).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day ^ 24) x (days dosed ^ total days) x RGDR; body weights used to determine the RGDR were
calculated as (initial body weight + final body weight) 2.
°Values expressed as number observed with neoplasm/number examined for that neoplasm (% incidence; average
severity of lesions 1 = minimal, 2 = mild, 3 = moderate, 4 = marked).
dNot examined at this exposure concentration.
"Doses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
* Significantly different from control (p < 0.05); Fischer exact test performed by study authors.
**Significantly different from control (p < 0.01); Fischer exact test performed by study authors.
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Table B.8. Neurological Data for Male and Female F344 Rats After Inhalation
Exposure to Nitromethane for 13 Weeks"
Parameterb
Exposure Group, ppm (HEC, mg/m3)c
Male
0
94 (43)
188 (87)
375 (173)
750 (346)
1500 (691)
Sample size
10
10
10
10
10
10
Forelimb grip
strength (kg)
0.617 ±
0.025
0.554 ±0.015
(90)
0.583 ±0.037
(94)
0.592 ±0.021
(96)
0.568 ±0.029
(92)
0.471 ±0.024
(76)**
Hindlimb grip
strength (kg)
0.433 ±
0.020
0.399 ±0.026
(92)
0.407 ± 0.020
(94)
0.378 ±0.023
(87)
0.382 ±0.017
(88)
0.213 ±0.020
(49)**
Female
0
94 (43)
188 (87)
375 (173)
750 (346)
1500 (691)
Sample size
10
10
10
10
10
10
Forelimb grip
strength (kg)
0.598 ±
0.020
0.633 ±0.021
(106)
0.700 ±0.011
(117)**
0.619 ±0.029
(104)
0.585 ±0.019
(98)
0.632 ±0.018
(106)
Hindlimb grip
strength (kg)
0.403 ±
0.018
0.425 ±0.011
(105)
0.435 ±0.014
(108)
0.419 ±0.013
(104)
0.333 ±0.019
(83)**
0.209 ±0.015
(52)**
"Source: NTP (1997).
bResults expressed as mean ± SE (% of control).
Doses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
**Significantly different from control (p < 0.01); Williams' or Dunnett's test performed by study authors.
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Table B.9. Reproductive Tissue Data for Male F344 Rats After Inhalation
Exposure to Nitromethane for 13 Weeks"
Parameterb
Exposure Group, ppm (HEC, mg/m3)0
Male
0
375 (173)
750 (346)
1500 (691)
Sample size
10
10
10
10
Necropsy body weight
(g)
338 ±7
341 ±4 (101)
331 ±4 (98)
299 ±11 (88)**
Left cauda weight (g)
0.207 ± 0.004
0.210 ±0.004 (101)
0.204 ± 0.006 (99)
0.177 ±0.009 (86)**
Left epididymis
weight (g)
0.467 ± 0.009
0.468 ±0.006 (100)
0.444 ± 0.009 (95)
0.412 ±0.013 (88)**
Left testis weight (g)
1.39 ±0.03
1.36 ±0.01 (98)
1.34 ±0.02 (96)
1.29 ±0.02 (93)**
Sperm motility (%)
94.57 ± 1.30
92.16 ± 1.90 (97)
87.11 ± 1.88 (92)**
76.43 ±2.78 (81)**
Sperm concentration
(106/g cauda
epididymal tissue)
449 ± 45
483 ± 24 (108)
434 ± 35 (97)
380 ± 42 (85)
"Source: NTP (1997).
bResults expressed as mean ± SE (% of control).
Doses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
**Significantly different from control (p < 0.01); Williams' or Dunnett's test performed by study authors.
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Table B.10. Select Hematology Parameters for Male Sprague-Dawey Rats After
Inhalation Exposure to Nitromethane11
Parameter
Exposure Group, ppm (HEC, mg/m3)b
0
98 (51)
745 (388)
Sample size0
10
10
10
Hematocrit
(%o)
10 d
41.0 ±0.5
40.0 ±0.5 (98)*
39.0 ±0.9 (95)*
1 mo
44.0 ±0.3
43.0 ±0.4 (98)
42.0 ±0.4 (95)**
3 mo
44.0 ±0.7
44.0 ±0.7 (100)
41.0 ±0.3 (93)**
6 mo
43.0 ±0.5
43.0 ±0.7 (100)
40.0 ±0.8 (93)**
Hemoglobind
(%)
10 d
13.9 ±0.21
13.3 ±0.17 (96)*
12.9 ±0.25 (93)**
1 mo
14.6 ±0.13
14.9 ±0.16 (102)
13.7 ±0.17 (94)**
3 mo
14.8 ±0.23
14.6 ±0.26 (99)
13.0 ±0.22 (88)**
6 mo
14.0 ±0.23
14.6 ±0.23 (104)
12.3 ±0.22 (88)**
aSource: Lewis et al. (1979) and Huntingdon Research Center (1989).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
°Sample size was generally 9-10 animals per measurement, but the sample size was not always indicated.
Expressed as mean ± SE (% of control).
* Significantly different from control (p < 0.05); Student's /-test performed by study authors.
**Significantly different from control (p < 0.01); Student's /-test performed by study authors.
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Table B.ll. Liver and Kidney Weights of Male and Female B6C3Fi Mice After
Inhalation Exposure to Nitromethane for 13 Weeks"
Parameter
Exposure Group, ppm (HEC, mg/m3)b
Male
0
94 (43)
188 (87)
375 (173)
750 (346)
1500 (691)
Sample size
10
10
10
10
10
10
Necropsy body
weight0 (g)
36.1 ±0.5
35.9 ±0.5 (99)
35.5 ±0.8 (98)
36.3 ±0.6
(101)
35.2 ±0.4 (98)
34.7 ±0.5 (96)
Right
kidney
weight0
Absolute
(g)
0.294 ±
0.009
0.329 ±0.006
(112)**
0.322 ±0.005
(110)*
0.332 ±0.007
(113)**
0.339 ±0.007
(115)**
0.315 ±0.008
(107)
Relative
(mg/g)
8.15 ±
0.20
9.15 ± 0.11
(112)**
9.10 ± 0.15
(112)**
9.15 ±0.20
(112)**
9.63 ±0.20
(118)**
9.08 ±0.18
(111)**
Liver
weight0
Absolute
(g)
1.633 ±
0.040
1.700 ±0.023
(104)
1.678 ±0.031
(103)
1.731 ±0.027
(106)
1.789 ±0.029
(110)*
1.724 ±0.053
(106)
Relative
(mg/g)
45.27 ±
0.89
47.32 ±0.38
(105)
47.39 ±0.78
(105)
47.70 ± 0.60
(105)*
50.79 ±0.72
(112)**
49.62 ±0.99
(110)**
Female
0
94 (43)
188 (87)
375 (173)
750 (346)
1500 (691)
Sample size
10
10
10
10
10
10
Necropsy body
weight0 (g)
31.1 ± 0.7
31.5 ±0.7
(101)
32.8 ±0.7
(105)
34.2 ±0.8
(110)**
31.5 ± 0.5
(101)
30.4 ±0.5 (98)
Right
kidney
weight0
Absolute
(g)
0.210 ±
0.007
0.221 ±0.005
(105)
0.228 ± 0.005
(109)*
0.232 ±0.005
(110)*
0.231 ±0.006
(110)*
0.230 ± 0.006
(110)
Relative
(mg/g)
6.75 ±
0.18
7.03 ±0.15
(104)
6.97 ±0.15
(103)
6.80 ±0.17
(101)
7.33 ±0.21
(109)*
7.57 ±0.15
(112)**
Liver
weight0
Absolute
(g)
1.536 ±
0.033
1.590 ±0.030
(104)
1.604 ±0.044
(104)
1.639 ±0.037
(107)
1.563 ±0.041
(102)
1.575 ±0.050
(103)
Relative
(mg/g)
49.49 ±
0.99
50.64 ± 1.15
(102)
48.89 ±0.72
(99)
47.97 ±0.95
(97)
49.52 ±0.76
(100)
51.77 ± 1.25
(105)
"Source: NTP (1997).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
°Weights expressed as mean ± SE (% of control).
* Significantly different from control (p < 0.05); Williams' or Dunnett's test performed by study authors.
**Significantly different from control (p < 0.01); Williams' or Dunnett's test performed by study authors.
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Table B.12. Reproductive Tissue Data for Male and Female B6C3Fi Mice After
Inhalation Exposure to Nitromethane for 13 Weeks"
Parameter
Exposure Group, ppm (HEC, mg/m3)b
Male
0
375 (173)
750 (346)
1500 (691)
Sample size
10
10
10
10
Sperm motility (%)c
93.50 ±0.46
85.09 ± 1.21 (91)**
86.47 ± 1.17(92)**
82.41 ± 1.30 (88)**
Female
0
375 (173)
750 (346)
1500 (691)
Sample size
10
10
10
10
Estrous cycle length
(days) c'd
4.00 ± 0.00
4.33 ±0.14 (108)*
4.50 ±0.21 (113)*
4.71 ±0.26 (118)**
"Source: NTP (1997).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
°Results expressed as mean ± SE (% of control).
dEstrous cycle was longer than 12 days or was unclear for at least one mouse in all groups except the 750-ppm
group.
* Significantly different from control (p < 0.05); Shirley's test performed by study authors.
**Significantly different from control (p < 0.01); Shirley's test performed by study authors.
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Table B.13. Histopathological Findings for Male and Female B6C3Fi Mice
After Inhalation Exposure to Nitromethane for 13 Weeks3
Parameterb
Exposure Group, ppm (HEC, mg/m3)
Male
0
94 (7.1)c
188 (14.1)
375 (28.0)
750 (55.7)
1500
(112.7)
Nasal
turbinates
Degeneration,
olfactory epithelium
0/10 (0)
0/10 (0)
0/ 10 (0)
10/10**
(100; 1.0)
10/10**
(100; 1.3)
10/10**
(100; 2.0)
Hyaline droplets,
respiratory epithelium
0/10 (0)
0/10 (0)
1/10(10;
1.0)
10/10**
(100; 1.0)
10/10**
(100; 1.0)
10/10**
(100; 2.0)
Male
0
94 (43)d
188 (87)
375 (173)
750 (346)
1500 (691)
Spleen, extramedullary
hematopoiesis
0/10 (0)
1/10(10;
1.0)
0/10 (0)
1/10 (10;
1.0)
2/10 (20;
1.0)
10/10**
(100; 1.0)
Female
0
94 (5.9)c
188 (12.2)
375 (24.9)
750 (48.0)
1500 (93.9)
Nasal
turbinates
Degeneration,
olfactory epithelium
0/10 (0)
0/10 (0)
7/10** (70;
1.0)
10/10**
(100; 1.0)
10/10**
(100; 2.0)
10/10**
(100; 3.0)
Hyaline droplets,
respiratory epithelium
0/10 (0)
2/10 (20;
1.0)
9/10** (90;
1.0)
10/10**
(100; 2.0)
10/10**
(100; 2.0)
10/10**
(100; 3.0)
Female
0
94 (43)d
188 (87)
375 (173)
750 (346)
1500 (691)
Spleen, extramedullary
hematopoiesis
0/10 (0)
0/10 (0)
0/10 (0)
2/10 (20;
1.0)
3/10 (30;
1.0)
9/10** (90;
1.0)
"Source: NTP (1997).
bValues expressed as number observed with neoplasm/number examined for that neoplasm (% incidence; average
severity of lesions 1 = minimal, 2 = mild, 3 = moderate, 4 = marked).
Doses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day ^ 24) x (days dosed ^ total days) x RGDR; body weights used were for determining the RGDR were
calculated as (initial body weight + final body weight) 2.
dDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
**Significantly different from control (p < 0.01); Fischer exact test performed by study authors.
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Table B.14. Select Clinical Chemistry Parameters for Male New Zealand White Rabbits
After Inhalation Exposure to Nitromethane"


Exposure Group, ppm (HEC, mg/m3)b
Parameter
0
98 (51)
745 (388)
Sample size0
5
5
5
OCTd
1 mo
470 ± 147.9
788 ±65.7 (167)*
1790 ±310.0 (381)*
(Su/mL)
3 mo
840 ± 277.2
1363 ± 170.0 (162)
1970 ± 159.4 (235)*

6 mo
2940 ± 1591.5
1650 ±352.1 (56)
1110 ±259.0 (38)
Thyroxind
1 mo
3.4 ±0.42
2.8 ± 0.82 (82)
1.9 ±0.39 (56)*
(Hg/dL)
3 mo
2.2 ±0.38
0.8 ±0.43 (36)
1.4 ±0.31 (64)

6 mo
2.1 ±0.28
1.1 ±0.33 (52)*
1.0 ±0.23 (48)*
"Source: Lewis et al. (1979) and Huntingdon Research Center (1989).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
°Sample size per measurement was not specified, but five animals per treatment group were used.
Expressed as mean ± SE (% of control).
* Significantly different from control (p < 0.05); Mann-Whitney U test performed by the study authors.
Table B.15. Thyroid Weights of Male Sprague-Dawley Rats After Inhalation
Exposure to Nitromethane for 6 Months3
Parameter
Exposure Group, ppm (HEC, mg/m3)b
0
98 (51)
745 (388)
Thyroid
weight0
Sample size
10
10
10
Absolute (mg)
22.5 ± 1.3
26.7 ± 1.7(119)
28.3 ±0.8 (126)**
Relative (% x 1000)
3.9 ±0.2
4.4 ±0.2 (113)
5.3 ±0.2 (136)**
aSource: Lewis et al. (1979).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
°Values expressed as mean ± SE (% of control).
**Significantly different from control (p < 0.01); Student's t-test performed by the study authors.
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Table B.16. Nonneoplastic Lesions in Male and Female B6C3Fi Mice After
Inhalation Exposure to Nitromethane for 103 Weeks"
Parameterb
Exposure Group, ppm (HEC, mg/m3)
Males
0
188 (22.2)c
375 (44.9)
750 (91.6)
Nose
Nasolacrimal duct,
Inflammation
2/50 (4)
(1.5)
3/49 (6)
(1.3)
10/50 (20)*
(1.9)
10/50 (20)*
(1.9)

Olfactory epithelium, atrophy,
focal
3/50 (6)
(1.0)
8/49 (16)*
(1.1)
0/50 (0)
0/50 (0)

Olfactory epithelium,
degeneration
0/50 (0)
10/49 (20)**
(1.1)
50/50 (100)**
(2.5)
50/50 (100)**
(3.1)

Olfactory epithelium,
metaplasia
0/50 (0)
1/49 (2)
(2.0)
41/50 (82)**
(1.8)
49/50 (98)**
(2.0)

Respiratory epithelium,
degeneration, hyaline
5/50 (10)
(1.0)
5/49 (10)
(1.2)
50/50 (100)**
(1.9)
50/50 (100)**
(2.0)
Females
0
188 (87)d
375 (173)
750 (346)
Liver
Eosinophilic focus
4/50 (8)
7/49 (14)
11/49 (22)*
15/50 (30)*
Females
0
188 (21.9)c
375 (43.2)
750 (87.9)
Nose
Nasolacrimal duct,
Inflammation
1/50 (2)
(2.0)
0/49 (0)
3/50 (6)
(1.7)
3/50 (6)
(2.0)

Olfactory epithelium, atrophy,
focal
2/50 (4)
(1.0)
6/49 (12)
(1.0)
0/50 (0)
0/50 (0)

Olfactory epithelium,
degeneration
0/50 (0)
22/49 (45)**
(1.1)
50/50 (100)**
(2.7)
50/50 (100)**
(3.2)

Olfactory epithelium,
metaplasia
0/50 (0)
2/49 (4)
(1.0)
46/50 (92)**
(1.9)
48/50 (96)**
(2.2)

Respiratory epithelium,
degeneration, hyaline
16/50 (32)
(1.1)
39/49 (80)**
(1.5)
50/50 (100)**
(2.0)
50/50 (100)**
(2.5)
"Source: NTP (1997).
bValues expressed as number observed with neoplasm/number examined for that neoplasm (% incidence) (severity
when available).
Doses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x RGDR; average body weights from the study were used to
determine the RGDR.
dDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
* Significantly different from control (p < 0.05); Logistic regression test performed by the study authors.
**Significantly different from control (p < 0.01); Logistic regression test performed by the study authors.
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Table B.17. Thyroid Weights of Male New Zealand White Rabbits After Inhalation

Exposure to Nitromethane for 6 Months3



Exposure Group, ppm (HEC, mg/m3)b

Parameter
0
98 (51)
745 (388)
Thyroid
Sample size
5
5
5
weight0
Absolute (mg)
235 ±33
265 ±31 (113)
325 ±31 (138)

Relative (% x 1000)
6.0 ±0.6
7.0 ± 1.0(117)
8.0 ±0.7 (133)
"Source: Lewis et al. (1979d).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
°Values expressed as mean ± SE (% of control).
Table B.18. Mammary Tumors in Female F344 Rats After Inhalation Exposure to
Nitromethane for 103 Weeks3
Parameter0
Exposure Group, ppm (HEC, mg/m3)b
0
94 (43)
188 (87)
375 (173)
Fibroadenoma
19/50 (38)
21/50 (42)
33/50 (66)**
36/50 (72)**
Fibroadenoma or adenoma
20/50 (40)
21/50 (42)
33/50 (66)**
36/50 (72)**
Carcinoma
2/50 (4)
7/50 (14)
1/50 (2)
11/50 (22)**
Adenoma or carcinoma
4/50 (8)
7/50 (14)
1/50 (2)
13/50 (26)*
Fibroadenoma, adenoma, or carcinoma
21/50 (42)
25/50 (50)
34/50 (68)**
41/50 (82)**
"Source: NTP (1997).
bDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
°Values expressed as number observed with neoplasm/number examined for that neoplasm (% incidence).
* Significantly different from control (p < 0.05); Fischer exact test performed by the study authors.
**Significantly different from control (p < 0.01); Fischer exact test performed by the study authors.
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Table B.19. Neoplastic Lesions in Male and Female B6C3Fi Mice After Inhalation
Exposure to Nitromethane for 103 Weeks3
Parameterb
Exposure Group, ppm (HEC, mg/m3)
Males
0
188 (87)c
375 (173)
750 (346)
Harderian
gland
Adenoma
9/50 (18)
10/50 (20)
19/50 (38)*
32/50 (64)**
Carcinoma
1/50 (2)
1/50 (2)
6/50 (12)
5/50 (10)
Adenoma or carcinoma
10/50 (20)
11/50 (22)
25/50 (50)**
37/50 (74)**
Males
0
188 (359)d
375 (727)
750 (1484)
Lung
Alveolar/bronchiolar adenoma
11/50 (22)
10/50 (20)
9/50 (18)
12/50 (24)
Alveolar/bronchiolar carcinoma
2/50 (4)
3/50 (6)
3/50 (6)
11/50(22)**
Alveolar/bronchiolar adenoma
or carcinoma
13/50 (26)
13/50 (26)
12/50 (24)
20/50 (40)
Females
0
188 (87)b
375 (173)
750 (346)
Harderian
gland
Adenoma
5/50 (10)
7/50 (14)
16/50 (32)**
19/50 (38)**
Carcinoma
1/50 (2)
2/50 (4)
4/50 (8)
3/50 (6)
Adenoma or carcinoma
6/50 (12)
9/50 (18)
20/50 (40)**
21/50 (42)**
Liver
Hepatocellular adenoma
14/50 (28)
25/49 (51)*
17/49 (35)
35/50 (70)**
Hepatocellular adenoma,
multiple
3/50 (6)
13/49 (27)**
4/49 (8)
13/50 (26)**
Hepatocellular carcinoma
10/50 (20)
14/49 (29)
8/49 (16)
12/50 (24)
Hepatocellular adenoma or
carcinoma
19/50 (38)
34/49 (69)**
22/49 (45)
40/50 (80)**
Females
0
188 (355)d
375 (700)
750 (1423)
Lung
Alveolar/bronchiolar adenoma
3/50 (6)
3/50 (6)
2/49 (4)
9/50 (18)
Alveolar/bronchiolar carcinoma
0/50 (0)
3/50 (6)
5/49 (10)*
3/50 (6)
Alveolar/bronchiolar adenoma
or carcinoma
3/50 (6)
6/50 (12)
6/49 (12)
12/50 (24)*
"Source: NTP (1997).
bValues expressed as number observed with neoplasm/number examined for that neoplasm (% incidence).
Doses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x blood:gas partition coefficient.
dDoses are converted from ppm to mg/m3 using the following equation: HEC = ppm x (molecular weight ^ 24.45) x
(hours per day 24) x (days dosed total days) x RGDRtb+pu; average body weights from the study were used to
determine the RGDR.
* Significantly different from control (p < 0.05); Logistic regression test performed by the study authors.
**Significantly different from control (p < 0.01); Logistic regression test performed by the study authors.
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APPENDIX C. BMD OUTPUTS
Multistage Model with 0.95 Confidence Level
Multistage
1
0.8
0.6
0.4
0.2
0
BMDL
BMD
0
5
10
15
20
25
dose
10:13 03/10 2011
Figure C.l. Multistage BMD Model for Respiratory Epithelium Hyaline Droplets Data
(NTP, 1997)
Text Output for Multistage BMD Model for Respiratory Epithelium Hyaline Droplets Data
(NTP, 1997)
Multistage Model. (Version: 3.2; Date: 05/26/2010)
Input Data File:
C:/l/NTP97_13wk_RespEpiHyalDrop_F_mouse_HiDosDrop_Multi3_l.(d)
Gnuplot Plotting File:
C:/l/NTP97_13wk_RespEpiHyalDrop_F_mouse_HiDosDrop_Multi3_l.pit
Thu Mar 10 10:13:45 2011
[add_notes_here]
The form of the probability function is:
63
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P[response] = background + (1-background)*[1-EXP(
-betal*dose/sl-beta2*dose/s2-beta3* doseA3)]
The parameter betas are restricted to be positive
Dependent variable = DichEff
Independent variable = Dose
Total number of observations = 4
Total number of records with missing values = 0
Total number of parameters in model = 4
Total number of specified parameters = 0
Degree of polynomial = 3
Maximum number of iterations = 250
Relative Function Convergence has been set to: le-008
Parameter Convergence has been set to: le-008
Default Initial Parameter Values
Background =	0
Beta(l) =	0
Beta(2) =	0
Beta(3) = 6.66264e+015
Asymptotic Correlation Matrix of Parameter Estimates
( *** The model parameter(s) -Background -Beta(l) -Beta(2)
have been estimated at a boundary point, or have been specified by
the user,
and do not appear in the correlation matrix )
Beta(3)
Beta (3)	1
Parameter Estimates
95.0% Wald Confidence
Interval
Variable	Estimate	Std. Err.	Lower Conf. Limit Upper Conf.
Limit
Background
0
k
k
k
Beta(1)
0
k
k
k
Beta(2)
0
k
k
k
Beta(3)
0.00121122
-k
k
k
* - Indicates that this value is not calculated.
Analysis of Deviance Table
Model
Full model
Fitted model
Reduced model
Log(likelihood)
-8 .25485
-8 .27784
-27.6759
# Param's
4
1
1
Deviance Test d.f.
0.0459631
38.842
P-value
0.9974
<.0001
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0.0000
0.0000
0.000
0.000
10
0. 000
5.9362
0.2238
2 .238
2.000
10
-0.181
12.1994
0.8891
8.891
9.000
10
0.110
24.9367
1.0000
10.000
10.000
10
0. 000
Chi^2 =0.04	d.f. =3	P-value = 0.9975
Benchmark Dose Computation
Specified effect =	0.1
Risk Type =	Extra risk
Confidence level =	0.95
BMD =	4.43082
BMDL =	1.31366
BMDU =	5 .42422
Taken together, (1.31366, 5.42422) is a 90	% two-sided confidence
interval for the BMD
AIC:	18.5557
Goodness of Fit
Scaled
Dose	Est. Prob. Expected Observed	Size	Residual
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Multistage Model with 0.95 Confidence Level
Multistage
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
ESMDL
BMD
0
10
20
30
40
50
60
70
80
90
dose
10:32 03/10 2011
Figure C.2. Multistage BMD Model for Respiratory Epithelium Degeneration Data
(NTP, 1997)
Text Output for Multistage BMD Model for Respiratory Epithelium Degeneration Data
(NTP, 1997)
Multistage Model. (Version: 3.2; Date: 05/26/2010)
Input Data File: C:/l/NTP97_103wk_RespEpiDegHyal_F_mouse_Multi3_l.(d)
Gnuplot Plotting File: C:/l/NTP97_103wk_RespEpiDegHyal_F_mouse_Multi3_l.pit
Thu Mar 10 10:32:54 2011
[add_notes_here]
The form of the probability function is:
P[response] = background + (1-background)*[1-EXP(
-betal*dose/sl-beta2*dose/s2-beta3* doseA3)]
The parameter betas are restricted to be positive
66
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Dependent variable = DichEff
Independent variable = Dose
Total number of observations = 4
Total number of records with missing values = 0
Total number of parameters in model = 4
Total number of specified parameters = 0
Degree of polynomial = 3
Maximum number of iterations = 250
Relative Function Convergence has been set to: le-008
Parameter Convergence has been set to: le-008
Default Initial Parameter Values
Background =	1
Beta(1) = 1.29371e+018
Beta(2) =	0
Beta(3) =	0
Asymptotic Correlation Matrix of Parameter Estimates
( *** The model parameter(s) -Beta(l) -Beta(2)
have been estimated at a boundary point, or have been specified by
the user,
and do not appear in the correlation matrix )
Background	Beta (3)
Background	1	-0.47
Beta (3)	-0.47	1
Parameter Estimates
Interval
Variable
Limit
Background
Beta(1)
Beta(2)
Beta(3)
Estimate
0.319859
0
0
0. 000114246
Std. Err.
95.0% Wald Confidence
Lower Conf. Limit Upper Conf.
Indicates that this value is not calculated.
Analysis of Deviance Table
Model
Full model
Fitted model
Reduced model
Log(likelihood)
-56.1379
-56.1413
-105.132
Param's
4
2
1
Deviance Test d.f.
0. 00669167
97.989
P-value
0.9967
<.0001
AIC:
116.283
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Goodness of Fit
Scaled
Dose	Est._Prob. Expected Observed	Size	Residual
0.0000
0.3199
15.993
16.000
50
0. 002
21.9354
0.7963
39.020
39.000
49
-0.007
43.2380
0.9999
49.997
50.000
50
0. 058
87.9212
1.0000
50.000
50.000
50
0. 000
Chi^2 = 0.00	d.f. = 2	P-value = 0.9983
Benchmark Dose Computation
Specified effect =	0.1
Risk Type =	Extra risk
Confidence level =	0.95
BMD =	9.73372
BMDL =	1.60241
BMDU =	11.3184
Taken together, (1.60241, 11.3184) is a 90	% two-sided confidence
interval for the BMD
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Multistage Cancer Model with 0.95 Confidence Level
Multistage Cancer
Linear extrapolation
0.9
0.8
0.7
0.6
0.5
0.4
0.3
BMDL
BMD
0
20
40
60
80
100
120
140
160
180
dose
10:55 03/10 2011
Figure C.3. Multistage Cancer BMD Model for Mammary Fibroadenoma,
Adenoma, or Carcinoma Data (NTP, 1997)
Text Output for Multistage-Cancer BMD Model for Mammary Fibroadenoma,
Adenoma, or Carcinoma Data (NTP, 1997)
Multistage Cancer Model. (Version: 1.9; Date: 05/26/2010)
Input Data File:
C:/l/NTP97_103wk_MamFibroadenoORAdenoORCarc_F_rat_MultiCanc3_l.(d)
Gnuplot Plotting File:
C:/l/NTP97_103wk_MamFibroadenoORAdenoORCarc_F_rat_MultiCanc3_l.pit
Thu Mar 10 10:55:56 2011
[add_notes_here]
The form of the probability function is:
P[response] = background + (1-background)*[1-EXP(
-betal*dose/sl-beta2*dose/s2-beta3* doseA3)]
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The parameter betas are restricted to be positive
Dependent variable = DichEff
Independent variable = Dose
Total number of observations = 4
Total number of records with missing values = 0
Total number of parameters in model = 4
Total number of specified parameters = 0
Degree of polynomial = 3
Maximum number of iterations = 250
Relative Function Convergence has been set to: le-008
Parameter Convergence has been set to: le-008
Default Initial Parameter Values
Background =	0.4 00 60 6
Beta(1) = 0.00594339
Beta(2) = 6.26236e-006
Beta(3) =	0
the user,
Background
Beta (1)
Beta (2)
Asymptotic Correlation Matrix of Parameter Estimates
( *** The model parameter(s) -Beta(3)
have been estimated at a boundary point, or have been specified by
and do not appear in the correlation matrix )
Background	Beta(l)	Beta(2)
1	-0.67	0.49
-0.67	1	-0.94
0.49	-0.94	1
Parameter Estimates
Interval
Variable
Limit
Background
Beta(1)
Beta(2)
Beta(3)
Estimate
0.410209
0.004892
1.2 6923e-005
0
Std. Err.
95.0% Wald Confidence
Lower Conf. Limit Upper Conf.
Indicates that this value is not calculated.
Analysis of Deviance Table
Model
Full model
Fitted model
Reduced model
Log(likelihood)
-123.585
-123.826
-134.186
# Param's
4
3
1
Deviance Test d.f.
0.481622
21.2027
P-value
0.4877
<.0001
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AIC:	253.652
Goodness of Fit
Scaled
Dose	Est._Prob. Expected Observed	Size	Residual
0.0000
0.4102
20.510
21.000
50
0.141
43.3000
0.5340
26.701
25.000
50
-0.482
86.6000
0.6489
32.447
34.000
50
0. 460
172.8000
0.8266
41.331
41.000
50
-0.124
Chi^2 = 0.48	d.f. = 1	P-value = 0.4887
Benchmark Dose Computation
Specified effect =	0.1
Risk Type =	Extra risk
Confidence level =	0.95
BMD =	20.452
BMDL =	11.2764
BMDU =	67.5516
Taken together, (11.2764, 67.5516) is a 90	% two-sided confidence
interval for the BMD
Multistage Cancer Slope Factor = 0.00886811
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Table C.l. Multistage Cancer Model Predictions for Tumor Data for Nitromethane"
Endpoint
Sex
Species
IURd
Goodness-of-Fit
p-V alueb
AICC
Mammary fibroadenoma, adenoma, or carcinoma
F
Rat
0.00886811
0.4887
253.65
Mammary fibroadenoma or adenoma
F
Rat
0.00717979
0.1631
263.41
Mammary fibroadenoma
F
Rat
0.00705667
0.3518
263.95
Hepatocellular adenoma or carcinoma
F
Mouse
0.00338166
0.0008
261.71
Harderian gland adenoma or carcinoma
M
Mouse
0.00283946
0.1674
237.29
Hepatocellular adenoma
F
Mouse
0.00254843
0.0121
263.79
Harderian gland adenoma
M
Mouse
0.00214776
0.4731
235.45
Harderian gland adenoma or carcinoma
F
Mouse
0.00194971
0.2630
225.79
Harderian gland adenoma
F
Mouse
0.00164856
0.4568
207.67
Mammary carcinoma
F
Rat
0.00126694
0.0245
131.45
Harderian gland carcinoma
M
Mouse
0.00055152
0.2574
95.47
Hepatocellular carcinoma
F
Mouse
0.00050530
0.3112
213.71
Harderian gland carcinoma
F
Mouse
0.00038784
0.5942
82.16
aNTP (1997).
bValues <0.10 fail to meet conventional goodness-of-fit criteria.
°AIC = Akaike's Information Criteria.
dAs calculated by BMDS.
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APPENDIX D. REFERENCES
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OSHA (Occupational Safety and Health Administration). (2006) Air contaminants:
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