United States
Environmental Protection
1=1 m m Agency
EPA/690/R-12/020F
Final
11-20-2012
Provisional Peer-Reviewed Toxicity Values for
Methacrylonitrile
(CASRN 126-98-7)
Superfund Health Risk Technical Support Center
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
-------
AUTHORS, CONTRIBUTORS, AND REVIEWERS
CHEMICAL MANAGER
Jeff Swartout
National Center for Environmental Assessment, Cincinnati, OH
DRAFT DOCUMENT PREPARED BY
ICF International
9300 Lee Highway
Fairfax, VA 22031
PRIMARY INTERNAL REVIEWERS
Audrey Galizia, Dr PH
National Center for Environmental Assessment, Washington, DC
Paul G. Reinhart, PhD, DABT
National Center for Environmental Assessment, Research Triangle Park, NC
Q. Jay Zhao, PhD, MPH, DABT
National Center for Environmental Assessment, Cincinnati, OH
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).
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TABLE OF CONTENTS
COMMONLY USED ABBREVIATIONS iii
BACKGROUND 1
DISCLAIMERS 1
QUESTIONS REGARDING PPRTVs 1
INTRODUCTION 2
REVIEW OF POTENTIALLY RELEVANT DATA (CANCER AND NONCANCER) 4
HUMAN STUDIES 4
Oral Exposures 4
Inhalation Exposures 4
Short-term Studies 4
ANIMAL STUDIES 10
Oral Exposures 10
Short-term Studies 10
Subchronic Studies 10
Chronic Studies 14
Developmental Toxicity Studies 16
Reproductive Toxicity Studies 19
Other Studies 23
Inhalation Exposures 23
Short-term Studies 23
Subchronic Studies 24
Chronic Studies 25
Developmental Studies 25
Reproductive Studies 26
Other Studies 26
OTHER DATA (SHORT-TERM TESTS, OTHER EXAMINATIONS) 26
Tests Evaluating Carcinogenicity, Genotoxicity, and/or Mutagenicity 26
Other Toxicity Studies (Exposures Other Than Oral or Inhalation) 29
Metabolism/Toxicokinetic Studies 29
DERIVATION 01 PROVISIONAL VALUES 30
DERIVATION OI ORAL REFERENCE DOSES 31
Derivation of Subchronic Provisional RfD (Subchronic p-RfD) 31
Derivation of Provisional Chronic RfD (Chronic RfD) 34
DERIVATION OF INHALATION REFERENCE CONCENTRATIONS 35
Derivation of Subchronic Provisional RfC (Subchronic p-RfC) 35
Derivation of Chronic Provisional RfC (Chronic p-RfC) 36
CANCER WEIGHT-OF-EVIDENCE (WOE) DESCRIPTOR 38
DERIVATION OF PROVISIONAL CANCER POTENCY VALUES 38
Derivation of Provisional Oral Slope Factor (p-OSF) 38
Derivation of Provisional Inhalation Unit Risk (p-IUR) 38
APPENDIX A. PROVISIONAL SCREENING VALUES 40
APPENDIX B. DATA TABLES 41
APPENDIX C. BMD OUTPUTS 43
APPENDIX D. REFERENCES 51
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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 bound 95% confidence interval
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
NOAELrec
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 reference concentration (inhalation)
p-RfD
provisional reference dose (oral)
RfC
reference concentration (inhalation)
RfD
reference dose (oral)
UF
uncertainty factor
UFa
animal-to-human uncertainty factor
UFC
composite uncertainty factor
UFd
incomplete-to-complete database uncertainty factor
UFh
interhuman 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
METHACRYLONITRILE (CASRN 126-98-7)
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 (littp://www.epa.gov/iris). the respective PPRTVs are
removed from the database.
DISCLAIMERS
The PPRTV document provides toxicity values and information about the adverse effects
of the chemical and the evidence on which the value is based, including the strengths and
limitations of the data. All users are advised to review the information provided in this
document to ensure that the PPRTV used is appropriate for the types of exposures and
circumstances at the site in question and the risk management decision that would be supported
by the risk assessment.
Other U.S. Environmental Protection Agency (EPA) programs or external parties who
may choose to use PPRTVs are advised that Superfund resources will not generally be used to
respond to challenges, if any, of PPRTVs used in a context outside of the Superfund program.
QUESTIONS REGARDING PPRTVs
Questions regarding the contents and appropriate use of this PPRTV assessment should
be directed to the EPA Office of Research and Development's National Center for
Environmental Assessment, Superfund Health Risk Technical Support Center (513-569-7300).
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INTRODUCTION
Methacrylonitrile is an unsaturated aliphatic nitrile (NTP, 2000, 2001). Also known as
methylacrylonitrile or 2-cyanopropene, methacrylonitrile is commonly used in the preparation of
homopolymers and copolymers, elastomers, and plastics and as a chemical intermediate in the
preparation of acids, amides, amines, esters, and other nitriles (Budavari, 1996).
Methacrylonitrile is also used as a replacement for acrylonitrile in the manufacture of an
acrylonitrile/butadiene/styrene-like polymer (Considine, 1974). Methacrylonitrile has been
identified as a component in unfiltered cigarette smoke (Baker et al., 1984). Table 1 summarizes
physicochemical properties for methacrylonitrile. Figure 1 shows the chemical structure of
methacrylonitrile.
H3C
H2C
Figure 1. Methacrylonitrile Structure
Table 1. Physical Properties Table for Methacrylonitrile
(CASRN 126-98-7)"
Property (unit)
Value
Boiling point (°C)
90.3
Melting point (°C)
-35.8
Density (g/cm3)
0.8001
Vapor pressure (mm Hg at 25°C)
7.12
pH (unitless)
Data not available
Solubility in water (g/100 mL at 25°C)
2.54
Relative vapor density (air = 1)
2.31
Molecular weight (g/mol)
67.09
aChem ID Plus, 2010 and HSDB, 2009.
The IRIS database (U.S. EPA, 1987a) lists a Reference Dose (RfD) of
1 x 10 4 mg/kg-day for methacrylonitrile based on a subchronic inhalation study in dogs with
increased SGOT (serum glutamic oxaloacetic transaminase, also known as aspartate
aminotransferase [AST]) and SGPT (serum glutamic pyruvic transaminase, also known as
alanine aminotransferase [ALT]) levels where the lowest-observed-adverse-effect level
(LOAEL) was noted at 8.8 ppm, and the no-observed-adverse-effect level (NOAEL) was noted
at 3.2 ppm (Pozzani et al., 1968). The NOAEL was used as the point of departure to calculate
the RfD. Neither a Reference Concentration (RfC) nor a cancer assessment for methacrylonitrile
are listed in the IRIS database (U.S. EPA, 1987a). Methacrylonitrile is not included on the
Drinking Water Standards and Health Advisories List (U.S. EPA, 2006) or on the Chemical
Assessments and Related Activities (CARA) list (U.S. EPA, 1994). A subchronic RfD of
0.001 mg/kg-day is reported in the Health Effects Assessment Summary Tables (HEAST)
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(U.S. EPA, 2010) for increased SGPT based on the study by Pozzani et al. (1968). In addition,
both a subchronic RfC of 0.007 mg/m3 and a chronic RfC of 0.0007 mg/m3 for increased SGPT
levels based on Pozzani et al. (1968) are reported in the HEAST. HEAST also cites, for
methacrylonitrile, a Health and Environmental Effects Document (HEED) for selected nitriles
(U.S. EPA, 1987b). The toxicity of methacrylonitrile has not been reviewed by the Agency for
Toxic Substances and Disease Registry (ATSDR, 2010) or the World Health Organization
(WHO, 2010). The California Environmental Protection Agency (CalEPA, 2008) has not
derived toxicity values for exposure to methacrylonitrile. The American Conference of
Governmental Industrial Hygienists (ACGIH, 2005) has established a threshold limit value
(TLV) of 1 ppm for a time-weighted-average (TWA) with a "skin" notation (indicating possible
skin absorption). The National Institute of Occupational Safety and Health (NIOSH, 2010) has
also established a recommended exposure limit (REL) of 1-ppm (3 mg/m3) TWA for
methacrylonitrile, with a "skin" notation. No occupational exposure limit for methacrylonitrile
has been derived by the Occupational Safety and Health Administration (OSHA, 2010).
HEAST does not report any carcinogenicity values for methacrylonitrile (U.S. EPA,
2010). The International Agency for Research on Cancer (IARC, 2010) has not reviewed the
carcinogenic potential of methacrylonitrile. Methacrylonitrile is not included in the 12th Report
on Carcinogens (NTP, 2011). CalEPA (2008) has not derived a quantitative estimate of the
carcinogenic potential of methacrylonitrile. The National Toxicology Program (NTP) conducted
a 2-year carcinogenicity study of methacrylonitrile (gavage exposure) in rats and mice and
concluded that there was no evidence of carcinogenic activity in either sex of either species
(NTP, 2001).
Literature searches were conducted on sources published from 1900 through
March 7, 2012, for studies relevant to the derivation of provisional toxicity values for
methacrylonitrile, CASRN 126-98-7. 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 health
information: ACGIH, ATSDR, CalEPA, EPA IRIS, EPA HEAST, EPA HEEP, EPA OW, EPA
TSCATS/TSCATS2, NIOSH, NTP, OSHA, and RTECS.
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REVIEW OF POTENTIALLY RELEVANT DATA
(CANCER AND NONCANCER)
Table 2 provides an overview of the relevant database for methacrylonitrile and includes
all potentially relevant repeat-dose short-term-, subchronic-, and chronic-duration studies.
Principal studies are identified. Entries for the principal studies are bolded.
HUMAN STUDIES
Oral Exposures
No studies investigating the effects of oral exposure to methacrylonitrile in humans have
been identified.
Inhalation Exposures
The effects of inhalation exposure on humans to methacrylonitrile were evaluated in two
short-term studies (both identified as Pozzani et al., 1968). No other studies have been located
regarding the effects of inhalation exposure to methacrylonitrile in humans.
Short-term Studies
Pozzani et al. (1968) performed a peer-reviewed study involving 8-9 volunteers (ages
22-57, sex not specified) whereby subjects were exposed to methacrylonitrile vapor at
concentrations of 0, 2, 7, 14, or 24 ppm (equivalent to 0, 5.5, 19.2, 38.4, and 65.9 mg/m3).
Subjects were placed in a glass-lined room and exposed to a series of methacrylonitrile
concentrations in the following order: 24, 14, 0, 7, 14, 24, 7, 2, 0, and 2 ppm. Each of the
methacrylonitrile concentrations was administered for 1 minute, and after the series of
10 varying exposure concentrations, the study authors repeated the experiment with a minimum
time lapse of 45 minutes between experiments. The subjects were unaware of the order in which
they were exposed to the concentrations. Throughout the exposure, the subjects responded to
simple questions regarding odor detection and throat-, eye-, and nose irritation. At 24 and
14 ppm, most subjects could detect an odor initially, but only half the subjects could detect the
7-ppm concentration of methacrylonitrile. None of the subjects were able to distinguish 0 ppm
from 2 ppm. Subjects reported irritation of the throat (17% of subjects), eye (22% of subjects),
and nose (6% of subjects) after exposure to the 24-ppm concentration. No subjects reported
irritation at any other concentration. Based on the limited details in this study, the LOAEL is
identified as 24 ppm (65.9 mg/m3) with a NOAEL of 14 ppm (38.4 mg/m3) based on irritation of
mucous membranes.
Another experiment by Pozzani et al. (1968) exposed a group of nine volunteers (sex and
age not provided) to 2-ppm (equivalent to 5.5 mg/m3) methacrylonitrile vapor for 10 minutes. In
the same experiment, the study authors exposed another group of seven subjects (sex and age not
provided) to 14 ppm (equivalent to 38.4 mg/m3) for 10 minutes. Occurrence of throat-, eye-, and
nose irritation was recorded after each minute. Lacrimation as a result of exposure was also
measured after each minute, as well as the number of subjects able to detect an odor.
Lacrimation and nose-, throat-, and eye irritation were reported in at least 1-2 subjects over the
10-minute time interval at 2 ppm, and in at least one subject at 14 ppm. No other details were
provided. The details in this study were too limited to assign a NOAEL or LOAEL.
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Table 2. Summary of Potentially Relevant Data for Methacrylonitrile (CASRN 126-98-7)
Category
Number of
Male/Female,
Species, Study Type,
Study Duration
Dosimetry"
Critical Effects
NOAELa
BMDL/
BMCLa
LOAELa
Reference/Comments
Notesb
Human
1. Oral (mg/kg-d)a
None
2. Inhalation (mg/m3)a
Short-term
8-9 subjects (sex not
specified), case
report, 10 exposures
for 1 min, repeated
with 45 min or longer
intervals in between
0, 2, 7, 14,
24 ppm (0, 5.5,
19.2, 38.4, 65.9)
Nose- (6 %), throat- (17 %), or eye
irritation (22 %) experienced in the
high-dose group.
38.4
Not run
65.9
Pozzani et al. (1968)
16 subjects (sex and
age not specified),
case report, 10 min
2 ppm or 14 ppm
(5.5 [9 subjects]
or 38.4
[7 subjects])
Nose-, throat-, and eye irritation in at
least 1-2 subjects in both dose groups.
Not
determined
Not run
Not
determined
Pozzani et al. (1968)
Animal
1. Oral (mg/kg-d)a
Subchronic
10/10, F344/N rat,
gavage, 5 d/wk,
13 wk
0, 7.5,15, 30,
60,120 (0, 5.36,
10.7, 21.4,42.9,
85.7C)
Statistically significant increases
(>10%) in absolute and relative liver
and lung weights in males at
30 mg/kg-d. Statistically significant
increases in olfactory epithelium
metaplasia in males at 60 mg/kg-d
and females at 60 and 120 mg/kg-d.
10.7
5.06
21.4
NTP (2000)
PS
p-RfDs
12/12,
Sprague-Dawley rat,
daily gavage,
39-51d
0,7.5, 15, 30
Anemia in males at 21 mg/kg-d.
15
Not run
30
MHLW (2001)
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Table 2. Summary of Potentially Relevant Data for Methacrylonitrile (CASRN 126-98-7)
Category
Number of
Male/Female,
Species, Study Type,
Study Duration
Dosimetry"
Critical Effects
NOAELa
BMDL/
BMCLa
LOAEL'
Reference/Comments
Notesb
10-16/0,
Sprague-Dawley rat,
gavage, 5 d/wk,
12 wk
0, 50, 70, 90 (0,
36, 50, 64°)
Death of two rats at 50 mg/kg-d and
8 rats at 90 mg/kg-d. No changes in
electrophysiological parameters.
None
Not run
None
(FEL = 36)
Gagnaire et al. (1998)
10/10, B6C3Fi
mouse, gavage,
5 d/wk, 13 wk
0,0.75, 1.5,3,6,
12(0, 0.54, 1.1,
2.1,4.3, 8.6C)
No adverse treatment-related effects at
any dose. No effects on reproductive
organ weights or sperm motility
patterns.
8.6
Not run
None
NTP (2000)
Chronic
50/50, F344/N rat,
gavage, 5 d/wk, 2 yr
0, 3, 10, 30 (0,
2.14, 7.14, 21.4C)
Increased incidences of cytoplasmic
vacuolization in liver in males at
30 mg/kg-d and in females at
>3 mg/kg-d.
None
Not run
2.14
NTP (2001)
50/50, B6C3Fi
mouse, gavage,
5 d/wk, 2 yr
0, 1.5, 3, 6 (0,
1.07, 2.14, 4.29c)
No nonneoplastic effects observed at
any dose.
4.29
Not run
None
NTP (2001)
Developmental
0/26,
Sprague-Dawley rat,
gavage, GDs 6-15
0, 5,25, 50
No effect on number of live fetuses,
fetal body weight, or morphological
development.
50
(develop-
mental),
50
(maternal)
Not run
None
(develop-
mental),
None
(maternal)
NTP (1993a); George
et al. (1996)
0/17-22, New
Zealand White rabbit,
gavage, GDs 6-19
0, 1,3,5
1 death at 3 mg/k-d, 1 death at
5 mg/kg-d in maternal rabbits
(unexplained). No adverse effect on
postimplantation loss or fetal body
weight. No effect on litter size or
malformations.
5 (develop-
mental),
5 (maternal)
Not run
None
(develop-
mental),
None
(maternal)
NTP (1993b); George
et al. (1996)
0/6 Sprague-Dawley
rat, gavage, 1st or
2nd wk of gestation
50 (1st wk of
gestation), 50,
100 (2nd wk of
gestation)
Ataxia, decreased body weights, edema
in fallopian tubes, effects on fertility.
None
Not run
50
Farooqui and Villarreal
(1992)
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Table 2. Summary of Potentially Relevant Data for Methacrylonitrile (CASRN 126-98-7)
Category
Number of
Male/Female,
Species, Study Type,
Study Duration
Dosimetry"
Critical Effects
NOAELa
BMDL/
BMCLa
LOAEL'
Reference/Comments
Notesb
Female
Sprague-Dawley rat
(number, not
provided), oral (no
further details
provided), 1st or
2nd wk of gestation
50 (1st wk of
gestation), 100
(2nd wk of
gestation)
Litters aborted at 50 mg/kg-d.
None
Not run
None
(FEL = 50)
Villarreal et al. (1988)
Reproductive
20/20,
Sprague-Dawley rat,
daily oral gavage,
Reproductive
Assessment by
Continuous Breeding
study, F0 exposed
from Day 1 for
approximately 15 wk,
F1 exposed from
weaning to
approximately 80 d
old.
F0: 0, 2, 7, 20
FLO, 20
In F1 rats, 19% decrease in epididymal
sperm density and organ weight
changes at 20 mg/kg-d but sperm
morphology not changed.
7 (F0)
9.7
20 (Fl)
NTP (1997)
12/12,
Sprague-Dawley rat,
daily gavage, 46 d
(m), 14 d before
mating to Day 4 of
lactation (f)
0,7.5, 15, 30
No effects on reproductive
performance such as mating, fertility,
delivery, and lactation in both sexes of
all treated rats.
30
Not run
None
MHLW (2001)
Carcinogenic
50/50, F344/N rat,
gavage, 5 d/wk, 2 yr
0, 3, 10, 30 (0, 2,
7, 21°)
No increase in neoplastic effects at any
dose.
None
Not run
None
NTP (2001)
50/50, B6C3Fi
mouse, 5 d/wk,
gavage, 2 yr
0, 1.5, 3,6(0, 1,
2, 4°)
No increase in neoplastic effects at any
dose.
None
Not run
None
NTP (2001)
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Table 2. Summary of Potentially Relevant Data for Methacrylonitrile (CASRN 126-98-7)
Category
Number of
Male/Female,
Species, Study Type,
Study Duration
Dosimetry"
Critical Effects
NOAELa
BMDL/
BMCLa
LOAEL'
Reference/Comments
Notesb
2. Inhalation (mg/m3)a
Short-term
6/6, Harlan-Wistar
rat, 0.47, 0.93, 1.88,
3.75,7.5, 14 min
234,270d
Death of 6/6 rats at 3.75-, 7.5-, and
14-min exposures.
None
Not run
None
(FEL =
234,270)
Pozzani et al. (1968)
6/6, Harlan-Wistar
rat, LC50, 4 h
Not provided
LC50 observed to be 899 mg/m3 (m),
and 1359 and 1918 mg/m3 (f).
None
Not run
None
Pozzani et al. (1968)
6/0, A/J strain mice,
LC50, 4 h
Not provided
LC50 observed to be 99 mg/m3.
None
Not run
None
Pozzani et al. (1968)
6/0, Albino guinea
pig, LC50, 4 h
Not provided
LC50 observed to be 241 mg/m3.
None
Not run
None
Pozzani et al. (1968)
4/0, Albino rabbit,
LC50, 4 h
Not provided
LC50 observed to be 100 mg/m3.
None
Not run
None
Pozzani et al. (1968)
0/3 dogs (2 mongrels
and 1 cocker spaniel),
LC50, 4 h
Not provided
LC50 not determined.
None
Not run
None
Pozzani et al. (1968)
Subchronic
12/12,
Harlan-Wistar rat,
7 h/d, 5 d/wk, 91 d
0,19.3, 52.6,
109.3 ppm
(0,11.0, 30.1,
62.5 mg/m3
HEC)e
At 62.5 mg/m3, statistically
significantly higher (>10%) relative
liver weights in males and females.
30.1
Not run
62.5
Pozzani et al. (1968)
PS
3/0, Beagle dog,
7 h/d, 5 d/wk, 90 d
0, 3.2, 8.8,
13.5 ppm
(0,1.8,4.9,
7.6 mg/m3)'
Transient increases in SGOT and
SGPT in 1/3 dogs at 4.9 mg/m3.
1.8
Not run
4.9
Pozzani et al. (1968).
IRIS (U.S. EPA,
1987a) derived an oral
RfD based on this
study, converting
from inhalation
exposure to oral
exposure (method no
longer used)
PS
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Table 2. Summary of Potentially Relevant Data for Methacrylonitrile (CASRN 126-98-7)
Category
Number of
Male/Female,
Species, Study Type,
Study Duration
Dosimetry"
Critical Effects
NOAEL3
BMDL/
BMCLa
LOAEL3
Reference/Comments
Notesb
Chronic
None
Developmental
0/20-23,
Sprague-Dawley rat,
6 h/d, GDs 6-20
0, 32.9, 68.5,
137, 274d
Statistically significantly reduced fetal
body weights at 274 mg/m3.
137
Not run
274
Saillenfait et al. (1993)
Reproductive
None
Carcinogenic
None
""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 effects. Values are converted to a human equivalent dose (HED in mg/kg-d) for oral carcinogenic effects. All
long-term exposure values (4 wk and longer) are converted from a discontinuous to a continuous (weekly) exposure. Values from animal developmental studies are not
adjusted to a continuous exposure.
bNotes: IRIS = Utilized by IRIS, date of last update; PS = Principal study, NPR = Not peer reviewed.
"Converted from a discontinuous (5 d/wk) to a continuous exposure (7 d/wk) by multiplying by 5^7.
dNot converted to HEC exposure because short-term study. Converted to mg/m3 equivalent concentrations as follows: ppm to mg/m3: mg/m3 = ppm x MW ^ 24.45; MW
methacrylonitrile = 67.09.
"Converted to HEC exposure as follows: dose x MW ^ 24.45 x (h/d ^ 24) x (d dosed ^ total d) x blood gas partition coefficient for extrarespiratory effect = ppm x
67.09 g/mole - 24.45 x (7 h- 24 h) x (65 d- 91 d) x 1 = ppm x 0.57166.
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ANIMAL STUDIES
Oral Exposures
The effects of oral exposure of animals to methacrylonitrile have been evaluated in
three subchronic (NTP, 2000; MHLW, 2001; Gagnaire et al., 1998), one chronic and
carcinogenic (NTP, 2001), two developmental (NTP, 1993a,b; George et al., 1996), and four
reproductive (NTP, 1997; MHLW, 2001; Farooqui and Villarreal, 1992; Villarreal et al., 1988)
studies.
Short-term Studies
No studies could be located regarding the effects of short-term oral exposure of animals
to methacrylonitrile.
Subchronic Studies
NTP, 2000; rat study
NTP (2000) is selected as the principal study for derivation of the subchronic p-RfD.
As part of a peer-reviewed subchronic study of methacrylonitrile, NTP (2000) performed gavage
studies in rats. This study was performed according to Good Laboratory Practice (GLP)
standards. Groups of 20 male and 20 female F344/N rats were administered doses of 0-, 7.5-,
15-, 30-, 60-, or 120-mg/kg-day methacrylonitrile (99.9% purity), for 5 days/week (calculated to
be equivalent to 0, 5.36, 10.7, 21.4, 42.9, and 85.7 mg/kg-day) by gavage in deionized, purified
water, for up to 13 weeks. Ten males and 10 females from each dose group were preselected for
interim evaluations at 32 days. The remaining 10 males and 10 females from each group were
dosed 5 days/week, for 13 weeks. At the end of the dosing period (either 32 days or 13 weeks),
the rats were euthanized and examined. All animals were necropsied, and the weight of the
heart, right kidney, liver, lung, stomach (without contents), right testis, and thymus were
recorded. Additionally, a clinical pathology evaluation, including hematology and clinical
chemistry analyses, was performed on interim evaluation rats on Day 4 (hematology and clinical
chemistry only) and on Day 32 on core study rats at the end of the 13-week study. A complete
histopathological examination was conducted on all control rats, male rats in the 60-mg/kg-day
dose group, female rats in the 120-mg/kg-day dose group, and all rats that died before scheduled
evaluations. Tissues that exhibited lesions at gross examination were also examined
microscopically in rats that received lower doses of methacrylonitrile. In addition, the nasal
cavity was identified as a target organ and examined in all lower dose groups. Statistical data
analysis was performed using the Fisher's Exact test, the parametric comparison procedures of
Williams and Dunnett, the nonparametric multiple comparison methods of Shirley and Dunn,
Jonckheere's test, and the Mann-Whitney U test.
At the 32-day interim evaluation, 9/10 male rats in the 120-mg/kg-day dose group died
during the first week of study, while all the female rats in the 120-mg/kg-day dose group
survived (NTP, 2000). Male rats administered 60 mg/kg-day in the 32-day interim evaluation
group showed statistically significantly lower mean body weights than the control group rats, but
the decrease was less than 10%.
In the 32-day interim evaluation, clinical toxicity effects were observed within minutes of
dosing and were dose dependent (NTP, 2000). The clinical toxicity effects observed were
lethargy, lacrimation, tremors, convulsions, ataxia, and abnormal breathing. The study authors
did not specify at which doses these effects were observed, or whether one sex was affected
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more than the other, but stated that the effects disappeared within several hours after dosing. In
addition, in this interim evaluation group, no effects were observed on hematology in males or
females when measured on Day 4, while on Day 32, there was a statistically significant decrease
in hemoglobin at the 60-mg/kg-day dose in males, and a statistically significant decrease in
hematocrit, hemoglobin, and erythrocytes at doses >30 mg/kg-day in females. Clinical
chemistry results (32-day interim evaluation group) on Day 4 showed statistically significant
decreases in males in urea nitrogen at doses >15 mg/kg-day, ALT at doses of 60 mg/kg-day, and
sorbitol dehydrogenase at doses >15 mg/kg-day. On Day 32, only ALT levels remained
statistically significantly decreased (at 60 mg/kg-day). In females, there was a statistically
significant decrease in ALT on Day 4 at doses >7.5 mg/kg-day. On Day 32 in females, urea
nitrogen was statistically significantly decreased at doses >60 mg/kg-day, and ALT was
statistically significantly decreased at doses >15 mg/kg-day.
In the 13-week evaluation (NTP, 2000), 2/10 male rats in the 60-mg/kg-day dose group
died during the first week. Only one male rat survived as long as 32 days. The remainder of the
male rats and one female rat in the 120-mg/kg-day dose group died before the end of the study.
When compared with the controls, male rats in the 60-mg/kg-day dose group had a slightly lower
(9.5%), but statistically significant, final mean body weight. Females in the 120-mg/kg-day dose
group also had lower (7.6%), but statistically significant, final mean body weights. Clinical
toxicity effects of the 13-week group were observed within minutes of dosing and included
lethargy, lacrimation, tremors, convulsions, ataxia, and abnormal breathing. These effects
disappeared within several hours of dosing. Minimal anemia, as indicated by decreased
hematocrit values, hemoglobin concentrations, and erythrocyte counts, was observed on Day 32
in males administered 60 or 120 mg/kg-day and females administered 30 mg/kg-day or greater.
At Week 13, the anemia had improved, as was revealed only by small (not statistically
significant) decreases in hemoglobin observed in males in the 60-mg/kg-day dose group and
females in the 120-mg/kg-day dose group. ALT was statistically significantly decreased in
females only at the highest dose (120 mg/kg-day).
A number of changes were observed in the relative and absolute organ weights at both
the 32-day interim evaluation and the 13-week evaluation (NTP, 2000). In the 32-day interim
evaluation at sacrifice, the absolute and relative liver weights of the female rats in the
120-mg/kg-day dose group were significantly greater (>10% difference in both absolute and
relative) than those of the controls. Female rats in the 60- and 120-mg/kg-day dose groups had
significantly greater stomach weights than the stomach weights of the control group. The
absolute weights of the right kidney and thymus of the male rats in the 60-mg/kg-day dose
group, and the absolute and relative thymus weights of female rats in the 120-mg/kg-day dose
group were significantly less than those of the control group. Relative heart, stomach, and right
testis weights were significantly greater in male rats in the 60-mg/kg-day dose group than the
control group.
In the 13-week evaluation, males in the 30- and 60-mg/kg-day dose groups had absolute
and relative liver weights that were statistically significantly greater than controls (at
30 mg/kg-day, absolute and relative liver weights >10% difference; at 60 mg/kg-day, absolute
liver weights <10% difference, relative liver weights >10% difference) (NTP, 2000). Males in
the 30- and 60-mg/kg-day dose groups also had relative lung weights that were statistically
significantly greater than controls (9.7% and 10.4%, respectively). Males in the 60-mg/kg-day
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dose group also had absolute stomach weights that were statistically significantly greater than
controls. The relative stomach weights of all dose groups of males were statistically
significantly greater than those in the control group. However, absolute stomach weights of
males were only statistically significantly increased in the 60-mg/kg-day dose group. Absolute
and relative stomach weights of females in the 60- or 120-mg/kg-day dose groups were
statistically significantly increased compared to the control group. Females that were
administered 60 or 120 mg/kg-day had absolute thymus weights that were statistically
significantly decreased compared to controls, and females in the 120-mg/kg-day dose group also
had statistically significantly decreased relative thymus weight when compared to the control
groups. Females in the 120-mg/kg-day dose group had relative heart, right kidney, and liver
weights that were statistically significantly greater (right kidney weights showed
<10% difference; liver weights >10% difference) than the control groups. No significant
differences were observed in reproductive organ weights or sperm motility parameters between
the males in any of the dose groups and the controls. In the 60- or 120-mg/kg-day dose groups,
females had significantly longer estrous cycles than the control group. Females administered the
60-mg/kg-day dose group spent more time in diestrus than those in the control group.
The study authors stated that no gross lesions observed at necropsy were attributed to
methacrylonitrile administration (NTP, 2000). The study authors identified the olfactory
epithelium of the nasal cavity as the primary target of methacrylonitrile toxicity in rats examined
microscopically. Treatment-related changes consisting of necrotic and metaplastic effects were
observed in the olfactory mucosa of the 60- and 120-mg/kg-day dose groups in both the 32-day
interim and 13-week evaluations in females. Necrosis of the olfactory epithelium was
characterized by the observation of cells undergoing different stages of necrosis.
Characterization of metaplasia was indicated by replacement of damaged olfactory epithelium
with respiratory epithelium and/or an undifferentiated type of epithelium. Due to the higher
survival rate of females in the 120-mg/kg-day dose group, olfactory toxicity was more apparent
in females than males, with statistically significant dose-related increases in the occurrence and
severity of olfactory lesions occurring in females at both the 32-day interim and 13-week
evaluations. In males, statistically significant increases in olfactory metaplasia were observed
only at 60 mg/kg-day, in both the 32-day interim and 13-week evaluations. The study authors
identified a NOAEL of 30 mg/kg-day for necrotic and metaplastic effects of the olfactory
epithelium in rats. However, based on the statistically significant increase in relative lung and
liver weights in male rats at 30 mg/kg-day, a LOAEL is identified at 30 mg/kg-day (adjusted for
dosing schedule), and a NOAEL is identified at 10.7 mg/kg-day (equivalent to 11 mg/kg-day).
NTP, 2000; mouse study
In the same peer-reviewed 13-week NTP gavage study in rats discussed above, groups of
20 male and 20 female B6C3Fi mice were administered 0-, 0.75-, 1.5-, 3-, 6-, or 12-mg/kg-day
methacrylonitrile (99.9% purity) (equivalent to 0, 0.54, 1.1, 2.1, 4.3, and 8.6 mg/kg-day) by
gavage in deionized, purified water, for 5 days/week, for 13 weeks (NTP, 2000). Ten animals of
each sex from each dose group were preselected for interim evaluations at 32 days then
sacrificed and examined. The remaining mice were sacrificed and examined at 13 weeks. All
animals were necropsied, and the weights of the heart, right kidney, liver, lung, stomach (without
contents), right testis, and thymus were recorded. A complete histopathological examination was
conducted on all control mice, male and female mice in the 12-mg/kg-day dose group, and all
mice that died before scheduled evaluations. Statistical data analyses were performed using the
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Fisher's Exact test, the parametric comparison procedures of Williams and Dunnett, the
nonparametric multiple comparison methods of Shirley and Dunn, Jonckheere's test, and the
Mann-Whitney U test.
In the 32-day interim evaluation, one male in the 12-mg/kg-day dose group died during
Week 3, and no reason was provided (NTP, 2000). Two females administered 1.5 mg/kg-day
died before the end of the study as a result of gavage dosing errors (as noted in the report). All
dosed groups had final mean body weights and mean body-weight gains that were similar to the
control groups. Clinical toxicity effects were dose dependent and included lethargy, tremors,
ataxia, convulsions, and abnormal breathing. All clinical toxicity effects were observed within
minutes of dosing and disappeared within 2 to 3 hours after dosing.
In the mice evaluated at the end of the 13-week evaluation, two females in the
12-mg/kg-day dose group died early; one death was the result of a gavage dosing error, and no
reason was provided for the other (NTP, 2000). All dosed mice had similar final mean body
weights and mean body-weight gains compared to the control groups. Clinical findings for the
13-week evaluation were similar to those observed at the 32-day interim evaluation: effects were
dose dependent and included lethargy, tremors, ataxia, convulsions, and abnormal breathing.
These toxic effects were observed within minutes of dosing and disappeared within 2 to 3 hours
after dosing.
Minimal differences were observed in organ weights at the 32-day interim evaluation and
the 13-week evaluation (NTP, 2000). In the 32-day interim evaluation, males in the
12-mg/kg-day dose group had absolute thymus weights that were significantly less than the
control groups. In the 32-day interim evaluation, the stomach weights of male mice that received
3 mg/kg-day or greater were significantly increased compared to the control group. At Week 13,
males in the two highest dose groups (6 and 12 mg/kg-day) had significantly increased relative
stomach weights (14% and 21% respectively), with increased (18%) absolute mean stomach
weight only at the highest dose. NTP stated that the toxicological significance of the
stomach-weight changes (without corresponding gross or microscopic pathologic changes) was
difficult to determine; EPA considers the increased stomach weights not to be of toxicological
significance. No significant differences in reproductive organ weights or sperm motility patterns
were observed between male dosed and control groups. In addition, there were no
biologically-significant differences observed in estrous cycle length or in the relative length of
time spent in estrous stages between female dosed and control groups.
No gross or microscopic treatment-related lesions were observed in any of the treated
groups (NTP, 2000). There were two unexplained deaths in the mice, one male at the 32-day
interim evaluation and one female at the end of the study, both in the 12-mg/kg-day dose group,
but they were not attributed to chemical treatment by the study authors, who stated that no
obvious chemical-related effects were observed in male or female mice administered doses up to
12 mg/kg-day in this study. After analyzing the study results and data EPA reached the same
conclusion and a NOAEL of 8.6 mg/kg-day (adjusted for dosing schedule) is established for this
study.
MHLW, 2001
A study performed by the Ministry of Health, Labour and Welfare of Japan (MHLW,
2001) examined the subchronic and reproductive effects of methacrylonitrile administration to
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Sprague-Dawley rats (see reproductive section below for a summary of the reproductive effects
from this study). The study report is available only in a secondary source (OECD, 2002) and is
not published in the peer-reviewed literature. OECD (2002) summarizes that MHLW (2001) met
the requirements of GLP, but peer-review status was not stated. Groups of 12 male and
12 female rats received doses of 0-, 7.5-, 15-, or 30-mg/kg-day methacrylonitrile (purity not
provided) by gavage daily. Males were dosed for 46 days from 14 days prior to mating; females
received treatment for 39-51 days from 14 days prior to mating, through mating and pregnancy,
to Day 4 of lactation. No clinical signs of toxicity were noted in the rats. No significant changes
were noted in body weight or feed consumption in males or females. Hematological analysis
(presumed at study termination) reported decreases in erythrocyte counts and hemoglobin
concentrations in males in the 30-mg/kg-day dose group. Analysis of blood chemistry showed a
decrease in potassium in males at 15 and 30 mg/kg-day, an increase in creatinine in males at
30-mg/kg-day, and increases in total bilirubin and glucose in females at 30-mg/kg-day.
Histopathological examination revealed slight extramedullar hematopoiesis in the spleen in
1/12, 0/12, 3/12, and 7/12 females at 0, 7.5, 15, and 30 mg/kg-day, respectively (Table B.2).
Only the response at 30 mg/kg-day was statistically significant. The study authors of the
summary (OECD, 2002) stated that, based on anemia at 30-mg/kg-day in males, the NOAEL for
repeated dose toxicity was considered to be 15 mg/kg-day. EPA considers the slight splenic
extramedullar hematopoiesis in females not to be of toxicological significance. A NOAEL of
15 mg/kg-day and a LOAEL of 30 mg/kg-day (adjusted for dosing schedule) are identified,
based on anemia in males.
Gagnaire etal., 1998
In a peer-reviewed study, Gagnaire et al. (1998) administered doses of 0-, 50-, 70-, and
90-mg/kg-day (calculated to be equivalent to 0, 36, 50, and 64 mg/kg-day) methacrylonitrile
(99% purity) by gavage to Sprague-Dawley rats, for 5 days/week, for 12 weeks. There were
10 rats in the control group, 12 rats in the 50-70-mg/kg-day dose groups, and 16 rats in the
90-mg/kg-day dose group. Two rats died in the 50-mg/kg-day dose group, and eight rats died in
the 90-mg/kg-day dose group. A 13% body-weight decrease was observed in the 90-mg/kg-day
dose group at the end of the 12th week of treatment. Electrophysiological parameters were
evaluated, consisting of the measurement of motor conduction velocity and sensory conduction
velocity of the tail nerve, and the amplitudes of the sensory action potential and of the muscular
action potential. No changes were noted in these parameters in the dosed groups as compared to
the control groups. No other effects were noted. Due to the high mortality in this study and
specialized design, neither a LOAEL nor a NOAEL is assigned.
Chronic Studies
Based on the above 13-week NTP (2000) study, a chronic study was performed by NTP
(2001) to study the effects of methacrylonitrile on F344/N rats. This peer-reviewed study was
performed in accordance with GLP standards. Groups of 50 male and 50 female F344/N rats
were administered methacrylonitrile (>99% purity) by gavage in deionized water. The animals
were administered doses of 0, 3, 10, or 30 mg/kg-day (calculated to be equivalent to 0, 2.14,
7.14, and 21.4 mg/kg-day), for 5 days/week, for 104 to 105 weeks. All animals were observed
twice daily and weighed at the beginning of the studies, every 4 weeks, and at necropsy. Clinical
findings were recorded on Days 8 and 29, every 4 weeks thereafter, and at necropsy. A complete
histopathological analysis was performed on all animals. In addition to gross lesions and tissue
masses, the study authors examined the following tissues: adrenal gland, bone with marrow,
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brain, clitoral gland, esophagus, heart and aorta, large intestine, small intestine, kidney, liver,
lung, lymph nodes, mammary gland, nose, ovary, pancreas, parathyroid gland, pituitary gland,
preputial gland, prostate gland, salivary gland, skin, spleen, stomach, testis with epididymis and
seminal vesicle, thymus, thyroid gland, trachea, urinary bladder, and uterus. Statistical analyses
were performed using the Kaplan and Meier method, Cox's method, the Poly-k test, Shirley and
Dunn's tests, Jonckheere's test, the Dixon and Massey test, and the Mann-Whitney test.
The survival of all the dosed groups was similar to the survival of the control groups
(NTP, 2001). In the 30-mg/kg-day dose group, mean body weights were less (not statistically
significantly less and <10% difference) than those of the control groups after Weeks 21 and 37
for males and females, respectively. No clinical effects related to methacrylonitrile
administration were observed.
Nonneoplastic effects were observed in the nose, liver, bone marrow, and pancreatic
exocrine gland (NTP, 2001). In the males and females administered 30 mg/kg-day, the
incidences of olfactory epithelial atrophy and metaplasia of the nose were significantly greater
than in the control groups. Study authors ranked average severity of the olfactory epithelial
atrophy as ranging from minimal to mild. Additionally, the study authors considered a diagnosis
of metaplasia of the olfactory epithelium to consist of complete loss of sensory and sustentacular
cells, which were replaced by thin pseudostratified, ciliate, nonciliated cuboidal, or columnar
epithelial cells (NTP, 2000). Histopathological evaluation of organs other than the nose showed
significantly greater incidences of diffuse cytoplasmic vacuolization in the liver in the group of
30-mg/kg-day males and in all dosed groups of females (>3 mg/kg-day) compared to control
groups. All male dosed groups experienced an increased incidence of pancreatic exocrine gland
hyperplasia; however, this incidence was comparable with the historical control range (NTP,
2001), and, therefore, was not considered by the study authors to be the result of
methacrylonitrile exposure. Bone marrow hyperplasia was increased in female rats receiving
30 mg/kg-day.
Regarding neoplastic effects, methacrylonitrile did not increase the incidence of
pancreatic exocrine gland neoplasms (NTP, 2001). Male rats exhibited a negative trend in the
incidence of mononuclear cell leukemia. In the 30-mg/kg-day dose group, male rats had
significantly fewer incidences of mononuclear cell leukemia than vehicle controls and had
incidences slightly lower than the historical range in controls (NTP, 2000). No increase in
neoplasms was observed. The study authors concluded that there was no evidence of
carcinogenic activity in male or female rats based on this study.
The study authors did not indicate a NOAEL or LOAEL for this study; however, they did
state that methacrylonitrile administration caused significant increases in the incidences of
nonneoplastic lesions of the nose and liver in rats (NTP, 2001). A LOAEL of 2.14 mg/kg-day
(adjusted for dosing schedule) is identified based on cytoplasmic vacuolization in the liver of
female rats. A NOAEL is not identified because this effect occurred at the lowest dose in female
rats.
In the same chronic NTP gavage study, groups of 50 male and 50 female B6C3Fi mice
were administered 0-, 1.5-, 3-, or 6-mg/kg-day (calculated to be equivalent to 0, 1.07, 2.14, and
4.29 mg/kg-day) methacrylonitrile (>99% purity) by gavage in deionized water, for 5 days/week,
for 2 years (NTP, 2001). All animals were observed twice daily and weighed at the beginning of
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the studies, every 4 weeks, and at necropsy. Clinical findings were recorded on Days 8 and 29,
every 4 weeks thereafter, and at necropsy. Following sacrifice, all animals were necropsied and
inspected for grossly and microscopically visible lesions on all organs and tissues. A complete
histopathological analysis was performed on all animals. In addition to gross lesions and tissues
masses, the following tissues were examined adrenal gland, bone with marrow, brain, clitoral
gland, esophagus, gallbladder, heart and aorta, large intestine, small intestine, kidney, liver, lung,
lymph nodes, mammary gland, nose, ovary, pancreas, parathyroid gland, pituitary gland,
preputial gland, prostate gland, salivary gland, skin, spleen, stomach, testis with epididymis and
seminal vesicle, thymus, thyroid gland, trachea, urinary bladder, and uterus. Statistical analyses
were performed using the Kaplan and Meier method, Cox's method, the Poly-k test, Shirley and
Dunn's tests, Jonckheere's test, the Dixon and Massey test, and the Mann-Whitney test.
All dosed groups had mean body weights that were not significantly different from the
body weights of the control groups (NTP, 2001). No increase in nonneoplastic or neoplastic
lesions was reported. The study authors concluded that there was no evidence of carcinogenic
activity in male or female mice based on this study (NTP, 2001).
The study authors did not indicate a NOAEL or LOAEL for this study (NTP, 2001).
Based on lack of increased incidences of nonneoplastic effects, a NOAEL of 4.29 mg/kg-day, the
highest dose administered, is identified. A LOAEL is not identified.
Developmental Toxicity Studies
NTP, 1993a; George etal., 1996; rat study
NTP performed a peer-reviewed study (NTP, 1993a; George et al., 1996) that measured
the effects of methacrylonitrile in distilled water administered by gavage to pregnant
Sprague-Dawley rats. This study was performed in accordance with GLP standards. Groups of
26 female rats received daily doses of 0-, 5-, 25-, or 50-mg/kg-day methacrylonitrile on
Gestational Days (GDs) 6 through 15. On GDs 0, 3, 6, 9, 12, 15, 18, and 20, the body weights of
the sperm-positive females, along with the food and water consumption weights, were recorded.
Clinical signs were recorded beginning on GD 6 through GD 20. On GD 20, approximately
25-26 females per group had confirmed pregnancies. At that time, all were sacrificed and
examined for clinical status and gestational outcome. Maternal body, liver, and uterine weights
were recorded, and external, visceral, and skeletal malformation inspections were carried out on
all live fetuses. Additionally, the number of implantation sites, resorptions, late fetal deaths, live
fetuses, and early resorptions were assessed. Statistical analyses were performed using analysis
of variance (ANOVA), William's multiple comparison test, and Dunnett's test.
Both absolute and relative maternal feed consumption were significantly decreased
between GDs 6 through 9 in the 50-mg/kg-day dose group, while relative maternal feed
consumption was significantly increased between GDs 18 through 20 in the 50-mg/kg-day dose
group (NTP, 1993a; George et al., 1996). Between GDs 9 through 12, maternal feed
consumption was significantly greater than the controls at 25 mg/kg-day but significantly less
than the controls in the 50-mg/kg-day dose group. Maternal death, morbidity, or distinguishing
clinical signs were not detected. In addition, no significant adverse effect on maternal body
weights or weight changes was observed. No effect was observed on gravid uterine weights at
any dose level; however, maternal liver weight (absolute, relative, and adjusted) was statistically
significantly increased (but the liver-weight differences based on absolute liver-weight changes
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were <10%) in the 25- and 50-mg/kg-day dose groups. On GD 20, each pregnant animal had at
least one live fetus. Average number of implantation sites per litter, postimplantation deaths per
litter, live fetuses per litter, or mean fetal weight per litter did not differ between dosed and
control groups. The incidence of fetal morphological abnormalities was not affected by the
administration of methacrylonitrile. Therefore, a NOAEL of 50 mg/kg-day, the highest dose
administered, is identified for both maternal and developmental toxicity. A LOAEL is not
identified.
NIP, 1993b; George etal., 1996; rabbit study
The NTP performed another peer-reviewed experiment (NTP, 1993b; George et al.,
1996) that measured the effects of methacrylonitrile in distilled water administered by gavage to
pregnant New Zealand White rabbits. GLP standards were followed in this study. Animals
(17-22/dose group) received daily doses of 0-, 1-, 3-, or 5-mg/kg-day methacrylonitrile on
GDs 6-19. On GDs 0, 3, 6-19, 25, and 30, the maternal weights were recorded. Daily
observation for clinical signs occurred before, during, and after dosing. Approximately
17-22 females per group had confirmed pregnancies on GD 30; all animals were sacrificed and
examined for clinical status and gestational outcome. Maternal body, liver, and uterine weights
were recorded following sacrifice. External, visceral, and skeletal malformation inspections
were performed on all live fetuses. Additionally, the number of implantation sites, resorptions,
late fetal deaths, live fetuses, and early resorptions were measured. Statistical analyses were
performed using ANOVA, William's multiple comparison test, and Dunnett's test.
One animal in the 3-mg/kg-day dose group and another animal in the 5-mg/kg-day dose
group died on GD 20 (NTP, 1993b; George et al., 1996). The cause of death was not provided in
the study. Alopecia and resistance to dosing were observed more frequently in the dosed groups
than in the control groups; however, the study authors stated that these clinical signs were not
dose related and remained fairly constant throughout the study. Body weights and body-weight
changes were not affected by exposure to methacrylonitrile at any dose. Gravid uterine and liver
weights were unaffected by methacrylonitrile administration. Resorptions occurred in the
controls and in every dose group but were not dose related; five litters were resorbed in the
controls, four litters were resorbed in the 1-mg/kg-day dose group, four were resorbed in the
3-mg/kg-day dose group, and three were resorbed in the 5-mg/kg-day dose group. The number
of implantation sites per litter, percentage postimplantation loss per litter, live litter size, or mean
fetal body weight per litter were all unaffected by treatment. However, the percentage of male
pups per litter in the 5-mg/kg-day dose group was significantly decreased compared to the
number of male pups in the control group. Nevertheless, there was no effect on total live litter
size, and the study authors suggested that".. .the reduction in the ratio of live male fetuses in the
high-dose group was not biologically significant," and EPA agrees with this conclusion.
Administration of methacrylonitrile did not affect the occurrence of external, visceral, or skeletal
malformations or variations in fetuses at any dose level. A NOAEL at the highest dose tested of
5 mg/kg-day for developmental toxicity in rabbits is established in this study. A LOAEL is not
identified. Presuming that the two maternal deaths were unrelated to treatment, a NOAEL of
5 mg/kg-day is identified for maternal toxicity also.
Farooqui and Villarreal, 1992
Farooqui and Villarreal (1992) examined the maternal toxicity of methacrylonitrile in
Sprague-Dawley rats. This was a peer-reviewed study, but it was not stated whether the study
was conducted according to GLP standards. Animals were divided into three dose groups of six
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pregnant animals each, and each group was administered methacrylonitrile (purity not provided)
in safflower oil via gavage. Group I received 50 mg/kg-day during the first week of gestation,
Group II received 50 mg/kg-day during the second week of gestation, and Group III received
100 mg/kg-day, also during the second week of gestation. Physical signs of toxicity and their
severity were observed daily. All animals were weighed throughout the study. Litter size was
measured and recorded. At the end of the study, all animals were sacrificed and examined for
the occurrence and severity of morphological or physiological abnormalities.
Clinical signs of toxicity were observed within 1 hour following methacrylonitrile
administration. These signs were mild to severe and included ataxia, trembling, convulsions,
salivation, and irregular breathing; however, these signs disappeared at various times depending
on the dose of methacrylonitrile. Animals in Group I gained weight progressively more over the
first 15 days of gestation, yet never gained weight to the same extent as the controls. Following
this weight gain, the animals then started to lose weight, which was not observed in the control
group. Weight gain was observed in Group II, but at a much slower rate and to a lesser extent
than both the controls and Group I animals. Likewise, animals in Group III gained weight, but at
a much slower rate and to a lesser extent than the control group. Body-weight gain in all groups
was significantly less (p < 0.01) than the weight gain in the control group. Animals in Groups I
and III did not deliver litters, and only one animal in Group II delivered a litter. These results
differed significantly from the control group, which delivered normal size litters on GD 20. In a
number of the Group I animals, mild-to-severe edema in the fallopian tubes was observed, while
severe edema in the fallopian tubes was observed in the majority of rats in both Groups II and
III. One of the animals in Group III also presented with a globular structure in one of the
fallopian tubes. The control groups experienced edema; however, it was not to the extent of the
edema observed in Groups I through III. In fact, the treated groups experienced edema that was
significantly (statistical method not provided) greater than the controls. A LOAEL of
50 mg/kg-day is identified for this study based on reproductive effects, including effects on
fertility and edema in the fallopian tubes. A NOAEL is not identified because these effects were
noted at the lowest dose (50 mg/kg-day).
Villarreal et al. 1988
Villarreal et al. (1988) administered 50-mg/kg-day methacrylonitrile (purity not
provided) to pregnant Sprague-Dawley rats (number not provided) during the first week of
gestation and administered 100 mg/kg-day to pregnant Sprague-Dawley rats during the second
week of gestation. A dose-dependent significant (not stated whether statistically significant)
reduction in maternal body-weight gain was observed. Control rats delivered litters of a normal
size, and the rats administered methacrylonitrile failed to maintain their pregnancies and aborted
the fetuses. At the end of gestation, dose-dependent, mild-to-severe edema was observed in the
fallopian tubes of treated rats. No further details were provided on this study, including the
number of rats, whether there was a control group, and whether the route of administration was
via gavage, feed, or drinking water. GLP and peer-review status were not discussed, and the
study was published as part of conference proceedings results. A LOAEL and a NOAEL cannot
be identified from this study because litters were aborted at 50 mg/kg-day.
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Reproductive Toxicity Studies
NTP, 1997; range-finding study (Task 1)
NTP (1997) exposed Sprague-Dawley rats to methacrylonitrile by gavage according to
Reproductive Assessment by Continuous Breeding (RACB) protocols. This study was
performed according to GLP standards. During the dose range-finding phase (Task 1) of this
study, doses of 0-, 15-, 30-, 50-, and 70-mg/kg-day methacrylonitrile (99.97% purity) were
administered by gavage to groups of eight male and eight female animals for 28 days. The
animals were observed for clinical signs, and body weights and feed and water consumption
were recorded. The doses used in this task were used to determine the doses in the continuous
breeding phase (Task 2), which was the main part of this study. Throughout Task 1, the mean
body weights of males in the dosed groups decreased. Compared to controls, terminal body
weights were reduced by 1%, 9%, 13%, and 16% in males in the 15-, 30-, 50-, and 70-mg/kg-day
dose groups, respectively. Female terminal body weights were reduced by 1.5%, 3%, 7%, and
8%> in the 15-, 30-, 50-, and 70-mg/kg-day dose groups, respectively. Total body-weight gain,
compared to controls, was decreased in males by 11%, 34%, 63%, and 71% in the 15-, 30-, 50-,
and 70-mg/kg-day dose groups, respectively; all body-weight-gain decreases, except at
15 mg/kg-day, were statistically significant at the 0.05-level of significance; individual ^-values
were not reported. Female total body-weight gains decreased by 7%, 27%, 42%, and 51% in the
15-, 30-, 50-, and 70-mg/kg-day dose groups, respectively, reaching statistical significance
(p < 0.05) only at 50 mg/kg-day and above. Daily feed consumption was decreased in males by
3%>, 15%), 17%), and 23%, in the 15-, 30-, 50-, and 70-mg/kg-day dose groups, respectively.
Female feed consumption was reduced by 5%, 7%, 9%, and 12%, in the 15-, 30-, 50-, and
70-mg/kg-day dose groups, respectively. Water consumption was increased for males only at the
highest doses. Water consumption was increased for females as well, but only by 7% at the two
lowest dose levels. Two males in the 70-mg/kg-day dose group were found dead on Day 3, one
on Day 4, and one on Day 29. Gross necropsy on these animals revealed lesions in the liver and
gastrointestinal tract. Other lesions were observed, but the locations were not specified. A
mottled liver and pale kidneys, testes, and stomach, as well as foci on the liver and foci and dark
areas on the kidneys, were also reported in these male rats. Very few clinical signs were
observed during this task in either male or female rats, specified by the study authors only as
diarrhea and hunched and thin body presentation. A LOAEL of 30 mg/kg-day for decreased
body weight and body-weight gain in males and females is established for this study. The
NOAEL is 15 mg/kg-day.
NTP, 1997; continuous-breeding phase (Task 2)
Task 2 involved four groups of animals (F0) containing 20 pairs per group. One group
served as the control while the remaining three groups were administered doses of 0, 2, 7, and
20 mg/kg-day. Animals in the F0 generation were dosed via gavage every day from day 1 until
the day before necropsy. After 7 days of dosing, animals were paired and housed for 16 weeks.
Following this period, the pairs were separated, but dosing continued. Any litters produced
during the 16-week mating period were counted and weighed by sex on PND 1 and then
sacrificed. Litters born following the 16-week cohabitation period were assigned as the
F1 generation and remained with the dams until PND 21. Until approximately 80 days of age,
selected weanlings from the control and high-dose groups were reared in the same sex groups.
Animals from the F1 generation were dosed via gavage and were used for the second-generation
fertility assessment (Task 4 described below). Following weaning of the F1 generation,
hematology and clinical chemistry determinations were carried out on selected F0 animals that
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were then necropsied. In addition, terminal body weights and organ weights were recorded, and
sperm analysis was performed.
In Task 2, one control male, one control female, one male at 20 mg/kg-day, and two
females at 20 mg/kg-day died during Task 2 (NTP, 1997). For one control male and one
20 mg/kg-day female, the cause of death could not be determined. The remaining three animals
that died before scheduled evaluations died as a result of a gavage error. Clinical signs of
toxicity included abrasions, alopecia, swellings, discharge, thinness, lacrimation, tissue masses,
vaginal discharge, paleness, missing tip of tail, opacity, squinting, ulcers, rales, and salivation.
Less than 30% of animals per group (characterized by the study authors as a low-to-moderate
incidence) experienced these symptoms, and dose-related variation was not observed.
Exposure to methacrylonitrile during Task 2 did not affect fertility, as was indicated by
similar pregnancy indices (number delivering/number cohabitated) in the control and dosed
groups. As the number of litters increased for each pair, the pregnancy index decreased. When
compared to the controls, there were no differences in the mean average litters per pair, number
of live pups per litter, proportion of pups born alive, sex ratio, live pup weight, or adjusted live
pup weight in the dosed groups. The mean cumulative days to litter were similar among dose
groups. F0 male body weights were recorded on the day of their mate's delivery. The body
weights of males in the 20-mg/kg-day dose group were 3-6% less than the control group. This
observation continued throughout the study, as evidenced by reduced body weights on Weeks 6,
12, and 18. On Weeks 6, 12, and 18, mean body weights of females were similar among dose
groups. Average feed consumption of each dosed group, both male and female, was similar to
the average feed consumption of the control group.
No treatment-related hematology or clinical chemistry variations were observed in
Task 2, other than a decreased (4%) hemoglobin value in females in the 7-mg/kg-day dose group
and an increase (7%) in total protein in males in the 2-mg/kg-day dose group (NTP, 1997). The
study authors considered these changes not treatment related, because they were small and not
dose related. Body weights at the end of the study for the 20-mg/kg-day F0 males were 5% less
(not statistically significant) than the controls. Average body weights for females at the end of
the study were similar among all dose groups. In the 2-mg/kg-day F0 males, the mean absolute
adrenal weight was statistically significantly increased; however, no other absolute organ weight
differences were observed at the other doses. Many of the relative organ weights were increased
for males as compared to controls; the study authors stated that this was due to the slight
decrease in body weight. Both males and females in the 20-mg/kg-day dose group experienced
an increase in relative liver weights (13% increase in males, 12% increase in females) as
compared to the controls. There were statistically-significant increases in abnormal sperm
morphology observed in males dosed at 2 and 20 mg/kg-day, but only about 1% of sperm in
treated animals was reported as abnormal (Table B3). Additionally, the relative weights of the
right cauda epididymis (14% increase), right epididymis (12% increase), and stomach
(19%) increase) in males in the 20-mg/kg-day dose group were greater than those of the controls.
The number of spermatids per milligram testis, and the total number of spermatids per testis were
similar between all dose groups and the controls. The mean epididymal sperm density was
slightly increased (5.5%) in the high-dose group but not statistically significant. Males and
females of the F0 generation were free of treatment-related gross lesions. Cysts on the
epididymis and spleen, liver foci, small testis, and epididymis; torsion of the abdominal fat;
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nodule on the kidneys; and abscess on the skin were observed but considered incidental because
no dose-related response was observed. One F0 male in the 20-mg/kg-day dose group had cell
necrosis in the hepatocytes; however, the study authors did not consider this to be treatment
related.
Adult body weights of the F1 males in the 20-mg/kg-day dose group were decreased by
9-10% during Weeks 2-4 when compared to controls. Adult body weights of the F1 females in
the 20-mg/kg-day dose group were decreased by 6% on Week 2 but were comparable to controls
on Week 4. Mean feed consumption in the 20 mg/kg-day males in the F1 generation was
decreased by 8-11% during Weeks 2 and 4 compared to controls, while mean feed consumption
for the F1 females was similar between the control and the 20-mg/kg-day dose groups.
A LOAEL of 20 mg/kg-day is established for the continuous-breeding phase (Task 2) for
this study (NTP, 1997) based on increased epididymal weights (12-14%) and stomach weights
(19%) in F0 males and increased relative liver weights (12—13%) in F0 males and females. The
NOAEL is 7 mg/kg-day. Although increased mean adrenal weights were noted in the F0 males
at 2 mg/kg-day, adrenal organ weights were not increased at any other dose, so this effect does
not appear to be dose related. There were also unexplained deaths including one control male,
one male at 20 mg/kg-day, and two females at 20 mg/kg-day during Task 2. As these deaths
occurred in the controls as well as in the dosed animals, the deaths are judged not to be treatment
related.
NTP, 1997; fertility assessment (Task 4)
Due to lack of evidence of reproductive toxicity in the continuous breeding phase, the
crossover-mating task (Task 3) was omitted, and a fertility assessment (Task 4) was performed.
Twenty male and 20 female F1 weanlings were randomly selected from the control and
20-mg/kg-day dose groups for rearing to adulthood (only animals from the control and
20-mg/kg-day dose groups were used, due to the absence of reproductive toxicity in Task 2).
Oral gavage dosing began on PND 22 and continued until 81 ± 11 days of age. Approximately
1 week before PND 81 ± 11, at least one male and female from each litter (avoiding sibling
mating) were selected to obtain 20 breeding pairs. All litters produced were evaluated on
PND 1. Selected F1 females were subjected to vaginal cytology sampling. Following sampling,
predetermined animals, both males and females, from the F1 generation were analyzed for
hematology and clinical chemistry determinations. Terminal body and organ weights were
obtained, and sperm analyses were performed. The data for number of pups from each litter,
number of live and dead pups, number of male and female pups, and total pup weight of each sex
were obtained. Statistical data analyses (for the entire study) were performed using ANOVA,
Dunnett's test, Dunn's test, Shirley's test, Jonckheere's test, Wilcoxon's test, and the
Cochran-Armitage test.
In Task 4, it was observed that the proportion of pups born alive in the final litter (to the
F1 generation) was similar between the control and 20-mg/kg-day dose group. Male pups born
to the 20-mg/kg-day dose group experienced a slight decrease in mean pup survival on PNDs 4,
7, 14, and 21; however, pup survival was similar to controls when both sexes were considered.
Average pup weights were similar among groups during the lactation phase of the last litter. On
PND 21, average body weights of the male and female pups born to the 20-mg/kg-day dose
group were similar to controls. On PND 81 ± 11, the mean body weights of the F1 females born
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to the 20-mg/kg-day dose group were 7% lower than controls, while the mean body weight of the
F1 males born to the 20-mg/kg-day dose group were not statistically significantly different from
the controls. On PND 1, no alteration in anogenital distance for the final litter was observed.
No differences were observed between the control and the 20-mg/kg-day dose group with
regard to reproductive performance in Task 4. This observation was supported by similar
pregnancy indices, number of pups per litter, pup weight, proportion of pups born alive, sex ratio
of pups, and gestation length between the 20-mg/kg-day and control groups. Immediately
following delivery, the mean dam weights were similar between the 20-mg/kg-day and control
groups. After dams delivered, their male partners were weighed, and the body weights of the
males in the 20-mg/kg-day dose group were 8% less (not statistically significant) than the
controls. The data for the amount of time spent in different estrous stages, cycle length, number
of cycles, number of cycling females, or number of females with regular cycles were not
different between the 20-mg/kg-day dose group and the control group.
During Weeks 2 and 4 of Task 4, a decrease in adult F1 male body weights at the
20-mg/kg-day dose group was observed when compared to controls. The females in the same
group experienced a mean body-weight decrease in Week 2 but not in Week 4. Feed
consumption of the 20-mg/kg-day dose group was unaffected by methacrylonitrile administration
when compared to controls, with the exception of males receiving 20 mg/kg-day during Weeks 2
and 4, when the mean feed consumption was decreased in males by 8-11%. Alopecia and
swelling at a low-to-moderate level of severity were the only clinical observations noted during
Task 4, and dose-related differences were not observed. Following unintentional removal from
the animal room, two animals were removed from the study. No animals died before scheduled
evaluation during Task 4.
In Task 4, changes noted in hematology or clinical chemistry parameters were an increase
(3%) in mean corpuscular hemoglobin in females in the 20-mg/kg-day dose group and a decrease
(33%) in mean serum ALT in females in this same dose group. These were not considered
biologically significant by the study authors because they were small and not associated with
other changes in liver or kidney parameters. Terminal body weights of the males (Fl) in the
20-mg/kg-day dose group were decreased by 9% compared to controls. No differences were
observed in body weights of Fl females. No differences were noted in the absolute organ
weights of either males or females. In Fl males at the 20-mg/kg-day dose group, increases were
observed in relative weights of the liver (13%), right epididymis (7%), ventral prostate (16%),
and stomach (11%) compared to controls. In Fl females in the 20-mg/kg-day dose group, the
relative liver weight was increased (13%) compared to controls (Table B.4). No differences
were noted in sperm analysis parameters, epididymal sperm morphology, or testicular head
counts. Epididymal sperm density was decreased by 19% in males at the 20-mg/kg-day dose
group. Cell necrosis of the hepatocytes, cytoplasmic vacuolization of the hepatocytes, renal
tubule degeneration, and renal tubule regeneration were observed by microscopic examination in
Fl males. In Fl females, microscopic examination revealed cell necrosis of the hepatocytes and
cytoplasmic vacuolization of the hepatocytes. The study authors (NTP, 1997) did not consider
any of the microscopic lesions to be treatment related because the incidence was similar between
the control and treated group; EPA agrees with the study authors' assessment.
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A LOAEL of 20 mg/kg-day for the fertility assessment (Task 4) of the NTP (1997) study
is identified based on decreased epididymal sperm density and increased organ weights (liver,
stomach, and ventral prostate) in F1 males. A NOAEL was not established in this phase of the
study, but a NOAEL of 7 mg/kg-day was determined in Task 2 for similar effects in F0 rats (see
discussion in subchronic p-RfD derivation section below).
MHLW, 2001
A study performed by the Ministry of Health, Labour and Welfare of Japan (MHLW,
2001) examined the reproductive effects of methacrylonitrile administration to Sprague-Dawley
rats. This study was summarized previously in the subchronic study section (page 19) and only
the reproductive toxicity outcomes are summarized here. Reproductive performance such as
mating, fertility, delivery, and lactation suffered no effects from methacrylonitrile administration.
Estrous cycles during the premating period were also not affected. A NOAEL for reproductive
toxicity for both males and females of 30 mg/kg-day, the highest dose tested, is identified for this
study. A LOAEL is not identified.
Other Studies
No additional studies could be located regarding the effects of oral exposure of animals to
methacrylonitrile.
Inhalation Exposures
The effects of inhalation exposure of animals to methacrylonitrile have been evaluated in
one short-term study on several species (Pozzani et al., 1968), in two subchronic studies in the
same study report (Pozzani et al., 1968), and in one developmental (Saillenfait et al., 1993)
study.
Short-term Studies
Pozzani et al. (1968) carried out a series of short-term studies on methacrylonitrile
inhalation in rats, mice, guinea pigs, rabbits, and dogs. In the first study, groups of 6 male and
female Harlan-Wistar rats were exposed to 85,500-ppm (calculated to be equivalent to
234,270 mg/m3) methacrylonitrile for 0.47, 0.93, 1.88, 3.75, 7.5, and 14 minutes. This exposure
resulted in mortality ratios of 0/6, 0/6, 1/6, 6/6, 6/6, and 6/6, respectively. In those animals that
died, prostration and loss of consciousness preceded death. The surviving rats gained weight
normally during a subsequent 14-day observation period. No other details were included in this
study (Pozzani et al., 1968).
In another short-term experiment by Pozzani et al. (1968), groups of six Harlan-Wistar
rats (male and female), six A/J strain mice (male), six albino guinea pigs (male), and four albino
rabbits (male) were exposed to various concentrations (not provided in study) for single 4-hour
periods in order to determine LC50 values. LC50 values were determined at 328 ppm (calculated
to be equivalent to 899 mg/m3) for male rats, 496 ppm (1359 mg/m3) and 700 ppm (1918 mg/m3)
for female rats, 36 ppm (99 mg/m3) for mice, 88 ppm (241 mg/m3) for guinea pigs, and 37 ppm
(100 mg/m3) for rabbits. Three female dogs (two mongrels and one cocker spaniel) were also
exposed to methacrylonitrile, but an LC50 was not determined. The study authors stated that the
dogs were considerably less resistant to methacrylonitrile vapor than the rat. The responses of all
the species were dose related and consisted of vomiting (dogs only), loss of consciousness,
tonic-clonic convulsions, and death. Most of the survivors gained weight normally during the
14-day observation period. No gross lesions attributable to exposure were found in any of the
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animals at autopsy. A NOAEL and LOAEL could not be identified because death—a frank
effect—was seen in all animal species tested.
Subchronic Studies
Pozzani et al. (1968); rat study
The rat study by Pozzani et al. (1968) is selected as the principal study for deriving
the subchronic and chronic p-RfCs. Pozzani et al. (1968) analyzed the effects of
methacrylonitrile inhalation exposure on Harlan-Wistar rats. Groups of 12 male and 12 female
rats were exposed to methacrylonitrile vapor (purity not provided) for an average of 7 hours/day,
5 days/week, for 91 days, at doses of 0, 19.3, 52.6, and 109.3 ppm (median measured
concentrations) (calculated to be equivalent to 0, 11.0, 30.1, and 62.5 mg/m3). This is a
published, peer-reviewed study; however, it was not stated whether GLP standards were
followed. Body-weight changes and liver and kidney weights were measured, and gross and
microscopic pathological evaluations were performed. Nineteen tissues (unspecified, but
excluding the brain) were sampled from each rat for microscopic examination.
Throughout the first day of exposure, seven male rats from the 109.3-ppm
methacrylonitrile group died, and another male from the 52.6-ppm group died on the second day.
No explanations were given for the deaths. Prior to death, loss of consciousness was observed;
however, convulsions were not reported. One male rat in the 109.3-ppm group appeared
prostrate on the 11th exposure day but recovered the next day. Upon autopsy, no other effects
were observed. No gross or microscopic lesions were observed in either the rats that died or the
survivors. Comparisons of body-weight gains of the dosed groups against the control groups
were performed on the 5th, 29th, 59th, and 91st days of exposure (absolute body weights were not
provided). Both males and females in the 109.3-ppm group and the females in the 52.6-ppm
group had weight gains that were significantly lower than the control groups after 5 days of
exposure. Significant body-weight losses were not observed in the treated rats compared to the
controls. Relative liver weights were increased for males by 9.7% (p < 0.05) at 52.6 ppm and
28% (p < 0.01) at 109.3 ppm relative to controls. Relative liver weights were increased for
females exposed to 52.6 ppm by 5.4% (NS) and 109.3 ppm by 27% (p < 0.001) relative to
controls. A NOAEL of 52.6 ppm (30.1 mg/m3) and a LOAEL of 109.3 ppm (62.5 mg/m3) are
identified from this study based on increased (>10%) relative liver weights in males and females.
Pozzani et al. (1968); dog study
In the same study report, Pozzani et al. (1968) performed a separate experiment in which
doses of 0-, 3.2-, 8.8-, and 13.5-ppm methacrylonitrile (equivalent to 0, 9, 24, and 37 mg/m3, as
calculated in IRIS (U.S. EPA, 1987a) were administered to groups of male beagles (3 dogs per
group). Pozzani et al. (1968) was selected as the principal study in IRIS (U.S. EPA, 1987a) to
calculate the oral chronic RfD. The values were converted from inhalation exposure to oral
exposure using an older method prior to current guidance on route-to-route conversion
methodology (U.S. EPA, 1994). The corresponding HEC exposure levels are 0, 1.8, 4.9, and
7.6 mg/m3, using the current inhalation dosimetry methods (U.S. EPA, 1994). There is no RfC
derived in IRIS, but this study was also used to calculate the subchronic and chronic inhalation
RfCs in HEAST (U.S. EPA, 2010). The animals were exposed for an average of 7 hours/day,
5 days/week, for 90 days. Body-weight changes and liver and kidney weights were measured.
Additionally, hematocrit, total white blood cell count, differential count, and blood urea nitrogen
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(BUN), serum glutamic oxalacetic transaminase (SGOT), serum glutamic pyruvic transaminase
(SGPT), and serum alkaline phosphatase (SAP) levels were measured.
In the 13.5-ppm dose group, one dog experienced tonic convulsions, trouble standing,
tachycardia, severely blocked optic discs, and loss of control over his hindquarters after 49 days
of exposure. However, all of these symptoms subsided within a day. Gross or microscopic
lesions were not observed. Another dog at the 13.5-ppm level also experienced loss of control
over his hindquarters, tonic convulsions, tachycardia, hurried and deep respiration, nystagmus,
and blocked optic discs after 39 days of exposure. These symptoms also subsided within a day.
This was the only animal in which microscopic lesions were observed, consisting of a marked
malacia of the floor of the third ventricle of the brain with massive accumulation of gitter cells
and some demyelinization of the corpus callosum. In one dog administered 8.8 ppm, noticeable
increases of SGOT and SGPT levels were observed, but these values decreased considerably
3 days later and were normal after the 41st, 61st, and 89th exposure days. A dog receiving the
3.2-ppm dose experienced a slight-but-transitory reversal in its neutrophil-lymphocyte ratio. No
other symptoms were observed. The study authors provided a "no-ill effect" range, or NOAEL,
of 3.2 to 8.8 ppm (9-24 mg/m3). The EPA (1987a) established a LOAEL of 24 mg/m3 and a
NOAEL of 9 mg/m3 based on transient increased SGOT and SGPT levels from this study.
Chronic Studies
No studies could be located regarding the effects of chronic inhalation exposure of
animals to methacrylonitrile.
Developmental Studies
In a developmental study, Saillenfait et al. (1993) exposed groups of 20-23 pregnant
Sprague-Dawley rats to methacrylonitrile for 6 hours/day on GDs 6-20. The study authors did
not state whether the study was performed in accordance with GLP standards. The
concentrations of methacrylonitrile (99% purity) were 0, 12, 25, 50, and 100 ppm (calculated to
be equivalent to 0, 32.9, 68.5, 137, and 274 mg/m3). Daily observations of rats were performed
throughout pregnancy. On GDs 0, 6, and 21, maternal body weights were recorded. Following
sacrifice, the uterus of each female was removed, weighed, dissected, and inspected for
implantation and resorption sites and live and dead fetuses. Weight, external irregularities, and
the sex of live fetuses were recorded. Live fetuses were then sacrificed and examined
microscopically for skeletal abnormalities. Statistical analyses using the Wilcoxon's and
Fisher's Exact tests were performed for the number of implantation sites, live fetuses, and body
weights.
During this study, maternal deaths were not observed (Saillenfait et al., 1993). Weight
gains among all dose groups did not differ from the control group after correction for uterus
weight. During GDs 6 through 21, a slight decrease in weight gain was observed; however, this
was a reflection of lower fetal body weights. Methacrylonitrile exposure did not affect
occurrence of pregnancy, average number of implantation sites, or average number of live
fetuses. In the 100-ppm dose group, one litter was completely resorbed. Additionally, the
100-ppm dose group exhibited an increase in the incidences of nonsurviving implants and
resorptions; however, this was not a statistically significant increase. The male-to-female sex
ratio was similar among all dose groups, with the exception of the 50-ppm dose group, where a
significant decrease in the number of males was observed. The study authors stated that this
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decrease appeared to be a random occurrence; however, no justification for this conclusion was
provided. Body-weight gain of both male and female pups was significantly (p < 0.01 male,
p < 0.05 female) reduced (>10%) at 100-ppm methacrylonitrile exposure. Gross malformations
in fetuses were not observed in any dose group. Occurrence of external, visceral, and skeletal
variants was similar between dose and control groups. The study authors concluded that a
NOAEL of 50 ppm (137 mg/m3) and a LOAEL of 100 ppm (274 mg/m3) could be established,
based on significantly reduced fetal body weights.
Reproductive Studies
No studies could be located regarding the reproductive effects of inhalation exposure of
animals to methacrylonitrile.
Other Studies
No additional studies could be located regarding the effects of inhalation exposure of
animals to methacrylonitrile.
OTHER DATA (SHORT-TERM TESTS, OTHER EXAMINATIONS)
Tests Evaluating Carcinogenicity, Genotoxicity, and/or Mutagenicity
The genotoxicity and mutagenicity of methacrylonitrile has been tested in several in vitro
(Zeiger et al., 1987; MHLW, 2001; Zimmering et al., 1989; Knaap et al., 1985; Wu et al., 2009;
Vasanthakumari et al., 1997) and in vivo (Shelby et al., 1993; MacGregor et al., 1990) studies.
These genotoxicity tests are summarized in Table 3.
In several Ames mutagenicity tests, methacrylonitrile demonstrated negative results using
Salmonella typhimurium strains TA97, TA98, TA100, TA1535, and TA1537 in the presence and
absence of metabolic activation (Zeiger et al., 1987; MHLW, 2001; Knaap et al., 1985; Wu et al.,
2009). Another study by MHLW (2001) produced negative results in the Ames mutagenicity
test using Escherichia coli WP2 uvr A in the presence and absence of metabolic activation. In
male Drosophila melanogaster administered 6000-ppm methacrylonitrile, no sex-linked
recessive lethal mutations were observed in germ cells (Zimmering et al., 1989). In a brief
abstract, Knaap et al. (1985) reported that there was no evidence for mutagenicity in an Ames
assay in Salmonella typhimurium TA98 and TA100 (both with and without activation), in L5178
mouse lymphoma cells, or in a sex-linked recessive lethal test in Drosophila melanogaster. The
same abstract reported positive results observed in a fluctuation test in Klebsiella pneumoniae
(Knaap et al., 1985). In an assay for unscheduled DNA synthesis, results were inconclusive for
concentrations tested up to 40 r|M/plate in human HepG2 cells (Vasanthakumari et al., 1997). A
chromosomal aberration test in Chinese hamster lung cells found positive results with metabolic
activation but negative results without activation (MHLW, 2001). Wu et al. (2009) observed
DNA damage in an in vitro comet assay in human lymphocytes and Hep G2 cells.
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Table 3. Other Studies
Test
Materials and Methods
Results
Conclusions
References
Genotoxicity
Reverse mutation: Salmonella typhimurium strains TA97,TA98,
TA100, TA1535, TA1537 with and without activation (in vitro)
Negative
Doses tested up to
10,000 (ig/plate
Zeiger et al. (1987)
Reverse mutation: Salmonella typhimurium strains TA98,
TA100, TA1535, TA1537 with and without activation (in vitro)
Negative
Doses tested up to
5000 (ig/plate
MHLW (2001)
Reverse mutation: Salmonella typhimurium strains TA98,
TA100 with and without activation (in vitro)
Negative
No details reported in brief
abstract
Knaap et al. (1985)
Reverse mutation: Salmonella typhimurium strains TA98,
TA100
Negative
Doses tested up to
3000 (ig/plate
Wu et al. (2009)
Reverse mutation: Escherichia coli WP2 uvr with and without
activation (in vitro)
Negative
Doses tested up to
5000 (ig/plate
MHLW (2001)
Sex-linked recessive lethal mutations: Drosophila melanogaster
Negative
Doses tested up to 6000 ppm
Zimmering et al.
(1989)
Sex-linked recessive lethal mutations: Drosophila melanogaster
Negative
No details reported in brief
abstract
Knaap et al. (1985)
Gene mutation test: mouse lymphoma L5178Y cells (HPRT and
TK loci) (in vitro)
Negative
No details reported in brief
abstract
Knaap et al. (1985)
Fluctuation test: Klebsiella pneumoniae (in vitro)
Positive
No details reported in brief
abstract
Knaap et al. (1985)
Unscheduled DNA synthesis: human HepG2 cells (in vitro)
Inconclusive
Doses tested up to 40 r|m/plate
Vasanthakumari et
al. (1997)
Comet assay: DNA damage in human lymphocytes and Hep G2
cells
Positive
Positive doses tested at 250 (iM
or greater
Wu et al. (2009)
Micronucleus test: rat bone marrow (in vivo)
Negative
Doses tested up to 200 mg/kg
Shelby et al. (1993)
Chromosome aberration test: Chinese hamster lung cells with
and without activation (in vitro)
Equivocal
Negative (without activation),
Positive (with activation)
MHLW (2001)
Micronucleus test: mouse bone marrow (in vivo)
Negative
Doses tested up to 25 mg/kg
Shelby et al. (1993)
Micronucleus test: B6C3Fi mouse peripheral blood erythrocytes
(in vivo)
Negative
Doses tested up to 12 mg/kg
MacGregor et al.
(1990)
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Table 3. Other Studies
Test
Materials and Methods
Results
Conclusions
References
Other toxicity studies
(exposures other than
oral or inhalation)
Dermal LD50 in male albino New Zealand rabbits
LD50 value determined to
be 0.32 mL/kg
(0.19-0.51 mL/kg)
None
Pozzani et al. (1968)
Intragastric LD50 in rats
LD50 value determined to
be 0.24 g/kg
(0.16-0.36 g/kg)
None
Pozzani et al. (1968)
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Following administration of methacrylonitrile to male rats in vivo, significant induction
of micronuclei occurred in the 200 mg/kg dose group. However, no induction of micronucleated
polychromatic erythrocytes was observed in a second trial, and the study authors concluded that
the test was negative overall (Shelby et al., 1993). In male mice, no induction of micronucleated
polychromatic erythrocytes was observed following administration of methacrylonitrile
(Shelby et al., 1993). A third in vivo study found no induction of polychromatic erythrocytes in
the blood of male and female mice (MacGregor et al., 1990). Overall, in vitro and in vivo
genotoxicity assays suggest that methacrylonitrile is not mutagenic.
Other Toxicity Studies (Exposures Other Than Oral or Inhalation)
The effects of dermal and intragastric exposure of animals to methacrylonitrile have been
evaluated in two acute studies from the same study report (Pozzani et al., 1968). Table 3
summarizes these effects.
Pozzani et al. (1968) applied a single dose of methacrylonitrile to the shaved skin of male
albino New Zealand rabbits for 24 hours. Four rabbits received a dose of 0.5 mL/kg, while
another group of four rabbits received a dose of 0.25 mL/kg. Within 3 hours and 45 minutes, all
four rabbits receiving the highest dose experienced gasping and convulsions and then died. Only
one of the four rabbits at the lower dose (0.25 ml/kg) experienced gasping and convulsions
before death, which occurred within 2 hours and 40 minutes of methacrylonitrile application.
The study authors reported that the remaining three rabbits displayed no symptoms and gained
weight normally during the following 14-day recovery period. Based on this experiment, the
study authors determined a dermal LD50 value of 0.32 mL/kg (0.19-0.51 mL/kg).
In a separate experiment in the same study, Pozzani et al. (1968) determined an
intragastric LD50 value of 0.24 g/kg (0.16-0.36 g/kg) following a single intragastric dose
administered in rats. Groups of five rats (sex not provided) were administered 0.1, 0.2, or
0.4 g/kg. Four rats in the highest dose group died on the day of dosing; the surviving rat died on
the night of dosing. At both the 0.1- and 0.2-g/kg doses, one rat in each dose group died. All
animals that died following exposure experienced prostration and convulsion within 90 minutes
of administration. The same symptoms were experienced by some of the survivors, but to a
lesser extent. All survivors gained weight normally during the 14-day recovery period.
Metabolism/Toxicokinetic Studies
Absorption of methacrylonitrile occurs through the skin, respiratory tract, and
gastrointestinal tract and is distributed to all major tissues (Smyth et al, 1962; Pozzani et al.,
1968; Tanii and Hashimoto, 1984; Farooqui andMumtaz, 1991; Ghanayem etal., 1992).
Metabolism studies show that methacrylonitrile is metabolized via the cytochrome P-450 mixed
function oxidase system and through conjugation with reduced glutathione. This results in the
production of several metabolites possibly via an epoxide intermediate including cyanide and
acetone (Farooqui and Mumtaz, 1991; Ghanayem et al., 1992; Ghanayem and Burka, 1996).
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DERIVATION OF PROVISIONAL VALUES
Table 4 presents a summary of noncancer reference values. Table 5 presents a summary of cancer values for methacrylonitrile. IRIS
data are indicated in the table, if available.
Table 4. Summary of Noncancer Reference Values for Methacrylonitrile (CASRN 126-98-7)
Toxicity type (units)
Species/Sex
Critical Effect
p-Reference
Dose
POD Method
POD
UFC
Principal Study
Subchronic p-RfD (mg/kg-d)
Rat/M
Increased relative
lung weight in
males
5 x 1(T2
BMDL
5.06 mg/kg-d
100
NTP (2000)
Chronic RfD (mg/kg-d)
(IRIS; U.S. EPA, 1987a)
Dog/M
Increase in
SGOT, SGPT
levels
1 x 1(T4
NOAEL/LOAEL
(converted from
inhalation exposure)
0.34 mg/kg-d
3000
Pozzani et al. (1968)
Subchronic p-RfC (mg/m3)
Rat/M, F
liver weight
3 x KT1
NOAEL/LOAEL
30.1 mg/m3
100
Pozzani et al. (1968)
Chronic p-RfC (mg/m3)
Rat/M, F
liver weight
3 x 1(T2
NOAEL/LOAEL
30.1 mg/m3
1000
Pozzani et al. (1968)
Table 5. Summary of Cancer Reference Values for Methacrylonitrile
Toxicity Value
Reference Value
Tumor Type or Precursor Effect
Species/Sex
Principal Study
p-OSF
N/A
N/A
N/A
N/A
p-IUR
N/A
N/A
N/A
N/A
N/A = not available.
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A study by Farooqui et al. (1990) demonstrated the metabolism of methacrylonitrile to
cyanide by the cytochrome P-450 mixed function oxidase system. The study authors observed
localization of metabolic activity in the microsomal (rather than the nuclear, mitochondrial, or
cytosolic) fraction of the liver and noted the requirement for NADPH and oxygen during
metabolism. The study authors also reported that the rate of methacrylonitrile metabolism was
increased by treatments that enhanced hepatic cytochrome P-450 content, and similarly,
decreased when the hepatic cytochrome P-450 content was reduced. Acetone has also been
identified as a metabolite formed from methacrylonitrile metabolism, and it was suggested that
metabolism to acetone may further induce metabolism of methacrylonitrile and other cytochrome
P-450 substrates (Ghanayem et al., 1992). The elimination of methacrylonitrile (as unchanged
methacrylonitrile, acetone, and CO2) is primarily via expired air and urine (Ghanayem et al.,
1992; Ghanayem andBurka, 1996).
DERIVATION OF ORAL REFERENCE DOSES
Derivation of Subchronic Provisional RfD (Subchronic p-RfD)
There are no human studies examining the health effects from subchronic oral exposure
to methacrylonitrile. However, available animal subchronic and developmental/reproductive
studies could be used to derive a subchronic p-RfD (see Table 6). There are three available
subchronic oral animal studies for methacrylonitrile (NTP, 2000; MHLW, 2001; Gagnaire et al.,
1998). Of these three, NTP (2000) is selected for the purposes of deriving a subchronic p-RfD.
This is a peer-reviewed study, was performed according to GLP standards, and meets the
standards of study design and performance, with numbers of animals, examination of potential
toxicity information, and presentation of data included in the study report. MHLW (2001) was
summarized in OECD (2002), and the original study was not available for review. A NOAEL of
15 mg/kg-day and a LOAEL of 30 mg/kg-day are identified from this study, based on anemia in
males and extramedullary hematopoiesis in the spleen in females. Gagnaire et al. (1998)
exposed rats for 12 weeks to doses ranging up to 90 mg/kg-day; however, a NOAEL and a
LOAEL cannot be identified because of the high level of mortality in this study (2/12 rats died in
the lowest dose group). NTP (2000) exposed both rats and mice to methacrylonitrile for
13 weeks, with increased relative liver weights and relative lung weights in male rats at
21.4 mg/kg-day and increased relative stomach weight in male mice at 4.3 mg/kg-day. Increased
relative stomach weights at 6 and 9 mg/kg-day were reported for male mice in NTP (2000), but
no stomach lesions were observed. NTP stated that the toxicological significance of the
organ-weight changes (without corresponding gross or microscopic pathologic changes) was
difficult to determine. EPA considers the increased stomach weights not to be of toxicological
significance. A NOAEL of 10.7 mg/kg-day and a LOAEL of 21.4 mg/kg-day are identified for
rats, and a NOAEL of 2.1 mg/kg-day and a LOAEL of 4.3 mg/kg-day are identified for mice.
There are six reproductive/developmental studies for methacrylonitrile (NTP, 1993a,b,
1997; MHLW, 2001; Farooqui and Villarreal, 1992; Villarreal et al., 1988). In the NTP (1993a)
study, no developmental effects were noted at any dose in rats, resulting in a NOAEL of
50 mg/kg-day for developmental effects (with no LOAEL). A NOAEL of 50 mg/kg-day was
also noted by NTP (1993a) for maternal effects, because the only maternal effects noted were
increased liver weights, but the difference was less than 10%. In NTP (1993b), the only
reproductive effect noted in rabbits was a statistically-significant decrease in the percentage of
male fetuses, which was not considered biologically significant by the study authors. A NOAEL
at the highest dose of 5 mg/kg-day was established. Farooqui and Villarreal (1992) and
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Villarreal et al. (1988) only used two doses (50 and 100 mg/kg-day), with effects on fertility,
edema in fallopian tubes, and other effects noted at 50 mg/kg-day in Farooqui and Villarreal
(1992), and fetal deaths occurring at both doses in Villarreal et al. (1988). No reproductive
effects were noted in MHLW (2001) at doses up to 30 mg/kg-day. NTP (1997) reported a
decrease in epididymal sperm density in F1 males and organ-weight changes at 20 mg/kg-day.
Similar effects were reported for F0 animals at the same exposure level. Therefore, a LOAEL of
20 mg/kg-day is established for NTP (1997) based on increased epididymal weights (12-14%)
and stomach weights (19%) in F0 males, increased relative liver weights (12—13%) in F0 males
and females (Task 2), and decreased (19%) epididymal sperm density and increased organ
weights (liver, 13%; stomach, 11%; ventral prostate, 16%) in F1 males (Task 4). A NOAEL for
the F1 animals is not established.
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Table 6. Summary of Relevant Oral Subchronic or Developmental/Reproductive
Studies for Methacrylonitrile
Reference
#/Sex (M/F)
Exposure
(mg/kg-d)
Frequency/
duration
NOAEL3
(mg/kg-d)
LOAEL"
(mg/kg-d)
BMDLb
(mg/kg-d)
Critical
Endpoint
NTP
(2000)
10/10 rat
0,5, 11,21,
43, 85*
5 d/wk for
13 wk,
gavage
10.7
21.4
5.06
Increase in
absolute and
relative male lung
weights.
MHLW
(2001)
12/12 rat
0,5.4, 11,
21
39-51 d,
gavage
(frequency
not reported)
11
21
Not run
Anemia in males.
NTP
(1993a)
0/26 rat
0, 5, 25, 50
GDs 6-15
50 (dev.)
50
(maternal)
None (dev.)
None
(maternal)
Not run
No adverse
developmental or
maternal effects
NTP
(1997)
20/20 rat
0, 2, 7, 20
(F0)
0, 20 (Fl)
15 wk (F0)
Weaning to
80 d old (Fl)
7
20
9.7
Decrease in
epididymal sperm
density inFl
males;
organ-weight
changes.
MHLW
(2001)
12/12 rat
0,5.4, 11,
21
39-51 d,
gavage
(frequency
not reported)
21
None
Not run
No reproductive
effects.
Farooqui
and
Villarreal
(1992)
0/6 rat
50 (1st wk
of
gestation),
50, 100
(2nd wk of
gestation)
1st or 2nd wk
of gestation
None
50
Not run
Ataxia, decreased
body weights,
edema in
fallopian tubes,
effects on fertility.
NTP
(1993b)
0/17-22 rabbit
0, 1, 3, 5
GD 6-19
5 (dev.)
5 (maternal)
None (dev.)
None
(maternal)
Not run
None
Principal study bolded.
*Doses adjusted for 5 d/wk dosing schedule.
hNOAELA|,[ = NOAEL x (gavage schedule).
bLOAELADJ = LOAEL x (gavage schedule).
Benchmark dose (BMD) modeling was conducted for the most sensitive
toxicologically-significant endpoints reported by NTP (2000) and NTP (1997, F0 and F1
animals); Tables B.l through B.3 present the data from the studies that were used in the BMD
modeling results. Tables C.l through C.4 present the corresponding results of the BMD
modeling. The focus of the BMD modeling was on endpoints that were defined as critical
effects in each of these studies, with a few other effects (manifesting at higher doses) included
that could inform the determination of the POD. A BMR of 10% relative deviation was used for
modeling liver weights, and a BMR of 1 standard deviation (1 SD) from the control mean was
used for all other continuous effects. Table C. 1 shows the BMD modeling results for the NTP
(2000) 13-week gavage study in mice and rats (data in Table B. 1). Tables C.2 and C.3 show the
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results for the F0 and F1 generations for the NTP (1997) two-generation reproduction study,
respectively (with corresponding data in Tables B.2 and B.3). Of all the endpoints modeled, the
lowest BMDL was obtained for increased relative lung weight in male rats in the subchronic
gavage study (NTP, 2000; Table C. 1). Therefore, the BMDLisd of 5.06 mg/kg-day for increased
relative lung weight in male rats in the NTP (2000) subchronic study is selected as the POD.
NTP (2000) is selected as the principal study to determine the subchronic p-RfD because
this study identified the lowest BMDL for potentially significant subchronic effects. The
BMDLisd of 5.06 mg/kg-day for increased relative lung weight in male mice (NTP, 2000) is
used to establish the POD for the subchronic p-RfD, which is derived as follows:
Subchronic p-RfD = BMDLisd UFc
= 5.06 mg/kg-day -M00
= 5 x 10~2 mg/kg-day
Tables 7 and 8, respectively, summarize the uncertainty factors and the confidence
descriptor for the subchronic p-RfD for methacrylonitrile.
Derivation of Provisional Chronic RfD (Chronic RfD)
No chronic p-RfD is developed. IRIS (U.S. EPA, 1987a) provides an RfD of
1 x 10 4 mg/kg-day, based on the Pozzani et al. (1968) subchronic dog inhalation study. The
critical effect (LOAEL) was increased SGOT and SGPT levels at 24 mg/m3. A NOAEL of
9 mg/m3 was used as the POD and converted to an oral exposure (0.34 mg/kg-day) based on a
dog inhalation rate of 4.3 rnVday, an absorption factor of 0.5, and an assumed dog body weight
of 12.7 kg. A total UF of 3000 was used, including a 10-fold factor for interspecies
extrapolation, a 10-fold factor for sensitive individuals, a 10-fold factor for the use of a
subchronic NOAEL, and a 3-fold factor because only inhalation studies were available,
neurotoxicity was not examined, and reproductive and chronic toxicity data were lacking
(U.S. EPA, 1987a). However, additional studies published after the IRIS assessment was
finalized were identified that may be relevant—particularly the chronic study by the National
Toxicology Program (NTP, 2001).
Table 7. Uncertainty Factors for Subchronic p-RfD of Methacrylonitrile
UF
Value
Justification
UFa
10
A UFa of 10 is applied for interspecies extrapolation to account for potential toxicokinetic and
toxicodynamic differences between rats and humans. There are no data to determine whether
humans are more or less sensitive than rats to the systemic toxicity of methacrylonitrile.
ufd
1
A UFd of 1 is applied because the database contains at least one acceptable two-generation
reproduction study in rats (NTP, 1997); at least one acceptable developmental study (NTP,
1993a,b).
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 in humans.
ufl
1
A UFl of 1 is applied because the POD is a BMDL.
UFS
1
A UFS of 1 is applied because a subchronic-duration study (NTP, 2000) was utilized as the
principal study.
UFC
100
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Table 8. Confidence Descriptor for
Subchronic p-RfD for Methacrylonitrile
Confidence Categories
Designation"
Discussion
Confidence in Study
H
Confidence in the principal study (NTP, 2000) is high because the
study was conducted according to GLP standards and meets the
standards of study design and performance, with numbers of animals,
examination of potential toxicity information, and presentation of
data.
Confidence in Database
H
Confidence in the database is high because data are available for a
variety of subchronic endpoints in rats and mice, and
reproductive/developmental studies are available for rats, mice, and
rabbits.
Confidence in Subchronic
p-RfD
H
The overall confidence in the subchronic p-RfD is high.
"L = Low, M = Medium, H = High.
DERIVATION OF INHALATION REFERENCE CONCENTRATIONS
Derivation of Subchronic Provisional RfC (Subchronic p-RfC)
There are no human subchronic studies available for methacrylonitrile. There is one
subchronic inhalation study available in rats and dogs (Pozzani et al., 1968) and one
developmental study in rats (Saillenfait et al., 1993). The Pozzani et al. (1968) study in dogs was
used as the principal study in the derivation of the IRIS RfD (the dose was converted from
inhalation to oral exposure in U.S. EPA, 1987a) and as the basis for the subchronic and chronic
inhalation RfC in HEAST (U.S. EPA, 2010). However, only three dogs per dose group were
used in Pozzani et al. (1968), and the critical endpoint used as the basis for the RfD and RfCs
(increases in SGOT and SGTP in one dog) was transitory. The Pozzani et al. (1968) study in rats
used 12 rats per group; higher relative liver weights were noted in males and females at
109.3 mg/m3 (equivalent to 62.5 mg/m3). Saillenfait et al. (1993) reported significantly reduced
fetal body weights at 274 mg/m3, resulting in the identification of a NOAEL of 137 mg/m3 and a
LOAEL of 274 mg/m3.
The Pozzani et al. (1968) study in rats is used as the principal study to determine the
subchronic p-RfC. This is a published, peer-reviewed study, but it was conducted prior to the
establishment of GLP standards. The critical effect (increased liver weight) is supported in the
oral-administration studies, having been observed in several rodent studies. A LOAEL of
62.5 mg/m3 for increased relative liver weight in males and females is identified in this study,
with a NOAEL of 30.1 mg/m3. BMD modeling cannot be conducted because variance measures
were not given for the reported endpoint means. The NOAELrec for extra-respiratory effects is
used to establish the POD as follows.
NOAEL hec — PPm x (MW 24.45) x (hours exposed 24) x (days exposed total days
of study) x (blood:air partition coefficient for extra-respiratory effects). The standard value of 1
is used for the blood:air partition coefficient because a measured value is not available.
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NOAELhec = 52.6ppmx(67.09-24.45)x(7hr-24hr)x(65-91)x(l)
= 30.1 mg/m3
The subchronic p-RfC is developed as follows:
Subchronic p-RfC = NOAEL hec, exresp ^ UFc
= 30.1 mg/m3 ^ 100
= 3 x 10-1 mg/m3
Tables 9 and 10, respectively, summarize the uncertainty factors and the confidence
descriptor for the subchronic p-RfC for methacrylonitrile.
Derivation of Chronic Provisional RfC (Chronic p-RfC)
There are no chronic studies available for inhalation exposure to methacrylonitrile.
Therefore, the subchronic rat study by Pozzani et al. (1968) will be used to derive the chronic
p-RfC, for the same reasons as discussed above for the subchronic p-RfC.
The chronic p-RfC is developed as follows:
Chronic p-RfC = NOAEL hec, exresp ^ UFc
= 30.1 mg/m3 - 1000
= 3 x 1 () 2 mg/m3
Tables 11 and 12, respectively, summarize the uncertainty factors and the confidence
descriptor for the chronic p-RfC for methacrylonitrile.
Table 9. Uncertainty Factors for Subchronic p-RfC of Methacrylonitrile
UF
Value
Justification
ufa
3
A UFa of 3 (10°5) 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. There are no data to determine whether humans are more or less sensitive than rats
to the systemic toxicity of methacrylonitrile.
ufd
3
A UFd of 3 (10°5) is applied because the database contains at least one acceptable developmental
inhalation study in rats (Saillenfait et al., 1993) but no two-generation inhalation reproduction
study. The oral two-generation reproduction study (NTP, 1997) does not satisfy the requirement
because of the indication that there could be significant metabolism in the liver, possibly leading
to first-pass effects. In addition, the sperm effects reported in that study occurred at exposure
levels similar to the critical effect for oral exposure and have the potential to be sensitive effects
by the inhalation route.
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 in humans.
ufl
1
A UFl of 1 is applied because the POD is a NOAEL.
UFS
1
A UFS of 1 is applied because a subchronic-duration study (Pozzani et al., 1968) was utilized as
the principal study.
UFC
100
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Table 10. Confidence Descriptors for Subchronic p-RfC for Methacrylonitrile
Confidence Categories
Designation"
Discussion
Confidence in study
L
Confidence in the principal study (Pozzani et al., 1968) is low
because details of the study, including the tissues examined, were
not provided. In addition, unexplained mortality occurred at the
higher exposure levels.
Confidence in database
L
Confidence in the database is low because data are not available for
a variety of subchronic endpoints, and data are not available on
reproductive effects.
Confidence in subchronic
p-RfC
L
The overall confidence in the subchronic p-RfC is low.
aL = Low, M = Medium, H = High.
Table 11. Uncertainty Factors for Chronic p-RfC of Methacrylonitrile
UF
Value
Justification
ufa
3
A UFa of 3 (10°5) 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. There are no data to determine whether humans are more or less sensitive than rats
to the systemic toxicity of methacrylonitrile.
ufd
3
A UFd of 3 (10°5) is applied because the database contains at least one acceptable developmental
inhalation study in rats (Saillenfait et al., 1993) but no acceptable inhalation two-generation
reproduction study. The oral two-generation reproduction study (NTP, 1997) does not satisfy the
requirement because of the indication that there could be significant metabolism in the liver,
possibly leading to first-pass effects. In addition, the sperm effects reported in that study
occurred at exposure levels similar to the critical effect for oral exposure and have the potential to
be sensitive effects by the inhalation route.
UFh
10
A UFh of 10 for 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 is a NOAEL.
UFS
10
A UFS of 10 is applied because a subchronic-duration study (Pozzani et al., 1968) was utilized as
the principal study.
UFC
1000
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Table 12. Confidence Descriptors for Chronic p-RfC for Methacrylonitrile
Confidence Categories
Designation"
Discussion
Confidence in study
L
Confidence in the principal study (Pozzani et al., 1968) is low
because details of the study, including the tissues examined, were not
provided. In addition, unexplained mortality occurred at the higher
exposure levels.
Confidence in database
L
Confidence in the database is low because data are not available for a
variety of subchronic endpoints, and data are not available on
reproductive effects.
Confidence in subchronic
p-RfC
L
The overall confidence in the subchronic p-RfC is low.
aL = Low, M = Medium, H = High.
CANCER WEIGHT-OF-EVIDENCE (WOE) DESCRIPTOR
No human data are available on the carcinogenicity of methacrylonitrile.
Methacrylonitrile has not been classified previously for carcinogenicity based on EPA's 1986
Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1986) or EPA's 2005 Guidelines for
Carcinogen Risk Assessment (U.S. EPA, 2005). The NTP (2001) conducted a 2-year cancer
study by gavage in rats and mice and concluded that".. .there was no evidence of carcinogenic
activity of methacrylonitrile in male or female F344/N rats administered 3, 10, or 30 mg/kg-day
and there was no evidence of carcinogenic activity of methacrylonitrile in male or female mice
administered 1.5, 3, or 6 mg/kg." Genotoxicity and mutagenicity studies have shown primarily
negative results. In in vitro studies, methacrylonitrile was negative for mutations in Salmonella
typhimurium (Zeiger et al., 1987; MHLW, 2001; Knaap et al., 1985; Wu et al., 2009) and did not
cause an increase in sex-linked recessive lethal mutations in Drosophila melanogaster
(Zimmering et al., 1989). Methacrylonitrile was positive in the fluctuation test in Klebsiella
pneumoniae (Knapp et al., 1985) and in a chromosome aberration test in Chinese hamster lung
cells with metabolic activation (but negative without metabolic activation) (MHLW, 2001). In
vivo, methacrylonitrile was negative for the induction of micronucleated polychromatic
erythrocytes in rats and mice (Shelby et al., 1993; MacGregor et al., 1990). A mutagenic mode
of carcinogenic action for methacrylonitrile is unlikely.
Therefore, given the negative mutagenicity data and negative data for carcinogenicity in
two species, the cancer WOE descriptor for methacrylonitrile is judged as "Not Likely to Be
Carcinogenic to Humans" by the oral route of exposure (Table 13).
DERIVATION OF PROVISIONAL CANCER POTENCY VALUES
Derivation of Provisional Oral Slope Factor (p-OSF)
No p-OFS can be derived due to inadequate carcinogenicity data.
Derivation of Provisional Inhalation Unit Risk (p-IUR)
No p-IUR can be derived due to inadequate carcinogenicity data.
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Table 13. Cancer WOE Descriptor for Methacrylonitrile
Possible WOE Descriptor
Designation
Route of Entry
(Oral, Inhalation,
or Both)
Comments
"Carcinogenic to Humans "
N/A
N/A
None
"Likely to Be Carcinogenic
to Humans "
N/A
N/A
None
"Suggestive Evidence of
Carcinogenic Potential"
N/A
N/A
None
"Inadequate Information to
Assess Carcinogenic
Potential"
N/A
Inhalation
Negative oral carcinogenicity data
are strong enough for a descriptor of
'Not likely to Be Carcinogenic to
HumansThere are inadequate
data to assess methacrylonitrile
carcinogenicity via the inhalation
route of exposure.
"Not Likely to Be
Carcinogenic to Humans"
Selected
Oral
A 2-year gavage study in rats and
mice showed no increase in cancer
incidence (NTP, 2001).
Mutagenicity studies have been
primarily negative.
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APPENDIX A. PROVISIONAL SCREENING VALUES
No provisional screening values were derived.
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APPENDIX B. DATA TABLES
Table B.l.
Relative Organ Weights in Mice and Rats in 13-Week Gavage Study of
Methacrylonitrilea'b
Rats
Vehicle
Control
5.4 mg/kg-d
11 mg/kg-d
21 mg/kg-d
43 mg/kg-d
85.7 mg/kg-d
Male rats
Animals examined
10
10
10
10
8
0
Liver
33.45 ±0.60
35.04 ±0.50
35.28 ±0.38
39.04 ±0.97"
40.09 ± 1.39"
-
Lung
4.43 ± 0.09
4.54 ±0.11
4.71 ±0.13
4.86 ±0.14*
4.89 ±0.09"
-
Female rats
Animals examined
10
10
10
10
10
9
Liver
32.89 ±0.75
32.43 ±0.54
33.22 ±0.53
34.06 ±0.60
33.25 ± 108
38.34 ± 113"
Thymus
1.26 ±0.06
1.29 ±0.08
1.24 ±0.05
1.24 ±0.05
1.10 ±0.09
0.87 ±0.03"
aNTP (2000).
bValues Given as Mean ± Std. Error (100 x Organ Weight [mg]/Body Weight [g]).
* Significantly different (p < 0.05) from the vehicle control group by William's or Dunnett's test.
** p < 0.01.
Table B.2. Sperm Morphology and Relative Organ Weights in F0 Rats in Two-Generation
Gavage Study of Methacrylonitrilea'b
Vehicle Control
2 mg/kg-d
7 mg/kg-d
20 mg/kg-d
Animals Examined
19
10
10
10
Males
Epididymal sperm morphology
(% abnormal)
0.29 ±0.08
0.95 ±0.22*
0.55 ±0.12
1.20 ±0.28*
Relative liver weight
36.52 ±0.86
36.42 ± 1.03
38.60 ±0.98
41.40 ±0.79*
Relative cauda epididymus weight
0.43 ±0.02
0.44 ± 0.02
0.45 ±0.02
0.49 ±0.01*
Females
Relative liver weight
36.87 ±0.86
38.53 ±0.82
36.33 ± 1.44
41.29 ±0.68*
aNTP (1997, Task 2).
bValues Given as Mean ± Std. Error (Organ Weight [mg]/Body Weight [g]).
* Significantly different (p < 0.05) from the vehicle control group by Shirley's or Dunn's test.
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Table B.3. Sperm Endpoints and Relative Organ Weights in F1 Rats in
Two-Generation Gavage Study of Methacrylonitrile3
Vehicle Control
20 mg/kg-d
Animals Examined
20
20b
Males
Cauda epididymal sperm density
(no. of sperm per mg cauda x 103)
357.31 ± 11.83
288.53 ±9.80
Epididymal sperm morphology
(% abnormal)
0.25 ±0.09
0.37 ±0.15
Relative liver weight (% BW)
3.772 ±0.3710
4.279 ± 0.4076
Relative ventral prostate weight (% BW)
0.198 ±0.0437
0.230 ±0.0380
Females
Relative liver weight (%)
3.374 ±0.3370
3.799 ±0.4092
aNTP (1997, Task 4).
b19 for sperm endpoints.
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APPENDIX C. BMD OUTPUTS
Table C.l. Benchmark Dose Modeling Results for 13-Week Gavage Study in Rats"
Model
BMRb
p-Value
AIC
BMD
BMDL
Notes
Male rats, relative lung weight
Exponential (M4)
1 SD
0.945
-47.12
14.2
5.06
Selected model. M4 not a better fit
than M2, statistically, but fits much
better in the BMR range
Exponential (M2)
1 SD
0.395
-46.47
33.4
21.9
BMDL > LOAEL
Linear (poly 1°)
1 SD
0.418
-44.61
32.4
20.8
4-degree polynomial allowed;
BMDL > LOAEL
Hill, unrestricted
1 SD
0.919
-45.44
13.4
4.85
Hill coefficient = 2.4
Power, unrestricted
1 SD
0.592
-46.40
18.3
2.61
Supralinear (power = 0.59)
Male rats, relative liver weight
Linear (poly 1°)
10% RD
0.123
129.41
17.8
13.9
Slightly better fit than exponential
Exponential (M4)
10% RD
0.102
130.19
14.9
9.76
Hill, unrestricted
10% RD
0.060
131.16
17.4
10.7
Relatively poor fit; Hill coefficient =
3.6
Power, unrestricted
10% RD
0.073
130.86
15.9
9.97
Relatively poor fit; supralinear
(power =0.84)
Female rats, relative liver weight
Polynomial (2°)
10% RD
0.585
169.50
49.1
25.6
4-degree polynomial allowed
Exponential (M4)
10% RD
0.413
170.43
63.3
42.7
Hill, unrestricted
10% RD
0.377
171.52
66.5
45.4
Hill coefficient =1.5
Power, unrestricted
10% RD
0.582
169.52
66.5
45.4
Power =1.5
Female rats, relative thymus weight
Modeled variance; variance model
did not fit (p = 0.076)
Polynomial (2°)
1 SD
0.871
-132.68
63.9
55.9
4-degree polynomial allowed
Exponential (M2)
1 SD
0.319
-129.22
39.8
28.0
Hill, unrestricted
1 SD
0.547
-128.72
66.5
failed
Hill coefficient =2.3
Power, unrestricted
1 SD
0.751
-130.71
66.5
39.6
Power = 2.3
aNTP (2000).
bRD = relative deviation; SD = standard deviation.
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Table C.2. Benchmark Dose Modeling Results for
F0 Generation in a Two-Generation Rat Study3
Model
BMRb
/7-Value
AIC
BMD
BMDL
Notes
F0 Males, relative liver weight
Linear (poly 1°)
10% RD
0.800
168.42
14.5
10.1
3-degree polynomial allowed
Exponential (M2)
10% RD
0.789
168.46
14.7
10.6
Hill
10% RD
NA
171.98
7.78
5.73
Saturated model0; Hill coefficient =
12.7
Hill, intercept
specified
10% RD
0.933
169.98
7.74
failed
Intercept = control mean;
Hill coefficient =13.5
Power, unrestricted
10% RD
0.508
170.42
14.1
6.80
Slightly supralinear (power =0.96)
F0 Males, relative cauda epididymus weight
Linear (poly 1°)
1 SD
0.579
-220.07
27.5
17.9
3-degree polynomial allowed
Exponential (M2)
1 SD
0.570
-220.03
26.9
18.2
Hill, restricted
1SD
0.304
-218.10
13.7
failed
Unrestricted model supralinear
Hill, unrestricted
1 SD
NA
-216.24
29.6
failed
Supralinear (power = 0.798);
saturated model
Power, unrestricted
1SD
0.339
-218.24
29.6
16.4
Supralinear (power = 0.792)
F0 Males, percent sperm abnormalities
No good model fits
Linear (poly 1°)
1 SD
0.0006
5.95
12.14
6.592
Best fit, but inadequate
F0 females, relative liver weight
No response near BMR, all fits
suboptimal
Polynomial (2°)
10% RD
0.446
172.38
17.1
13.7
4-degree polynomial allowed
Linear (poly 1°)
10% RD
0.069
176.10
14.1
10.2
Relatively poor fit
Exponential (M3)
10% RD
0.466
175.79
19.7
14.7
Hill
10% RD
0.466
173.30
19.6
7.79
Hill coefficient at upper bound
Power
10% RD
0.466
173.30
19.7
14.6
power = 17.9
aNTP (1997, Task 2).
bRD = relative deviation; SD = standard deviation.
°Residual degrees of freedom = 0.
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Table C.3. Benchmark Dose Modeling Results for
F1 Generation in a Two-Generation Rat Study3
Model
BMRb
p-Value
AIC
BMD
BMDL
Notes
F1 Males, cauda epididymus sperm density
Linear (poly 1°)
1 SD
C
-
13.7
9.71
Saturated modeld
F1 Males, relative liver weight
Linear (poly 1°)
10% RD
-
-
14.9
10.4
Saturated model
F1 Males, relative ventral prostate weight
Linear (poly 1°)
1 SD
-
-
25.0
14.9
Saturated model
F1 Males, relative stomach weight
Linear (poly 1°)
1 SD
-
-
17.7
11.8
Saturated model
F1 females, relative liver weight
Linear (poly 1°)
10% RD
-
-
15.9
10.6
Saturated model
aNTP (1997, Task 2).
bSD = standard deviation.
Saturated models; all /^-values = NA; AIC values not relevant.
dResidual degrees of freedom = 0.
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BMDS Output for Critical Effect: Increased Relative and Absolute Lung Weight in
Male Rats in 13-Week Gavage Study (NTP, 2000)
Exponential Model. (Version: 1.61; Date: 7/24/2009)
Input Data File:
C:\Usepa\BMDS21\Data\exp_Methacrylonitrile_NTP_2000_male_Setting.(d)
Gnuplot Plotting File:
Wed Jun 01 13:23:27 2011
BMDS Model Run
The form of the response function by Model:
Model 2
Model 3
Model 4
Model 5
Y[dose] = a * exp{sign * b * dose}
Y[dose] = a * exp{sign * (b * dose)Ad}
Y[dose] = a * [c-(c-l) * exp{-b * dose}]
Y[dose] = a * [c-(c-l) * exp{-(b * dose)Ad}]
Note: Y[dose] is the median response for exposure
sign = +1 for increasing trend in data;
sign = -1 for decreasing trend.
dose;
Model 2 is nested within Models 3 and 4.
Model 3 is nested within Model 5.
Model 4 is nested within Model 5.
Dependent variable = m_lung_rel
Independent variable = d
Data are assumed to be distributed: normally
Variance Model: exp(lnalpha +rho *ln(Y[dose]))
rho is set to 0.
A constant variance model is fit.
Total number of dose groups = 5
Total number of records with missing values = 0
Maximum number of iterations = 250
Relative Function Convergence has been set to: le-008
Parameter Convergence has been set to: le-008
MLE solution provided: Exact
Variable
lnalpha
2.15512
rho(S)
0
4 .2085
0.0384462
1.22003
1
(S) = Specified
b
d
Initial Parameter Values
Model 2 Model 3
-2.15512 -2.15512
0 0
4.51545 4.51545
0.00230953 0.00230953
Model 4
-2.15512
0
4.2085
0.0384462
1.22003
Model 5
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Parameter Estimates by Model
Variable
lnalpha
2.15503
rho
0
a
4.4289
b
0.0897299
c
1.1033
d
Model 2
-2.09311
0
4.52092
0.00224199
Model 3
-2.09311
0
4.52092
0. 00224199
Model 4
-2.14831
0
4.41104
0.0751941
1.11822
Model 5
1.70506
Table of Stats From Input Data
Dose
0
5.36
10.7
21.4
42.9
10
10
10
10
Obs Mean
4.43
4.54
4.71
4.86
4.89
Obs Std Dev
0.285
0.348
0.411
0.443
0.255
Estimated Values
of Interest
Model
Dose
Est Mean
Est Std
Scaled Residual
2
0
4.521
0.3511
-0.8188
5.36
4.576
0.3511
-0.3204
10.7
4 . 631
0.3511
0.7143
21.4
4 .743
0.3511
1.053
42.9
4.977
0.3511
-0.7036
3
0
4.521
0.3511
-0.8188
5.36
4.576
0.3511
-0.3204
10.7
4 . 631
0.3511
0.7143
21.4
4 .743
0.3511
1.053
42.9
4.977
0.3511
-0.7036
4
0
4.411
0.3416
0.1755
5.36
4.584
0.3416
-0.4076
10.7
4 . 699
0.3416
0.09925
21.4
4.828
0.3416
0.2944
42.9
4.912
0.3416
-0.1806
5
0
4.429
0.3404
0.01021
5.36
4 .543
0.3404
-0.02839
10.7
4.706
0.3404
0.03332
21.4
4.8 65
0.3404
-0.04217
42.9
4.886
0.3404
0.03022
Other models for which likelihoods are calculated:
Model A1: Yij = Mu(i) + e(ij)
Var{e(ij)} = SigmaA2
Model A2:
Yij = Mu (i) + e (i j )
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Var{e(ij)} = Sigma(i)^2
Model A3: Yij
Var{e(ij)}
Mu(i) + e(i j)
exp(lalpha + log(mean(i)) * rho)
Model R: Yij = Mu + e(i)
Var{e(ij)} = SigmaA2
Likelihoods of Interest
Model
A1
A2
A3
R
2
3
4
5
Log(likelihood) DF
27.72296 6
29.71493 10
27.72296 6
21.971 2
26.23462 3
26.23462 3
27.55938 4
27.72061 5
AIC
-43.44593
-39.42987
-43.44593
-39.94201
-46.46924
-46.46924
-47.11876
-45.44122
Additive constant for all log-likelihoods = -44.11. This constant added to the
above values gives the log-likelihood including the term that does not
depend on the model parameters.
Explanation of Tests
Does response and/or variances differ among Dose levels? (A2 vs. R)
Are Variances Homogeneous? (A2 vs. Al)
Are variances adeguately modeled? (A2 vs. A3)
Does Model 2 fit the data? (A3 vs. 2)
Test 5a: Does Model 3 fit the data? (A3 vs 3)
Test 5b: Is Model 3 better than Model 2? (3 vs. 2)
Test 6a: Does Model 4 fit the data? (A3 vs 4)
Test 6b: Is Model 4 better than Model 2? (4 vs. 2)
Test 7a: Does Model 5 fit the data? (A3 vs 5)
Test 7b: Is Model 5 better than Model 3? (5 vs. 3)
Test 7c: Is Model 5 better than Model 4? (5 vs. 4)
Test
Tests of Interest
-2*log(Likelihood Ratio)
D. F.
p-value
Test 1
15.49
8
0.05033
Test 2
3.984
4
0. 4082
Test 3
3.984
4
0. 4082
Test 4
2.977
3
0.3952
Test 5a
2.977
3
0.3952
Test 5b
-2 . 842e-013
0
N/A
Test 6a
0.3272
2
0.8491
Test 6b
2. 65
1
0.1036
Test 7a
0.004712
1
0.9453
Test 7b
2.972
2
0.2263
Test 7c
0.3225
1
0.5701
The p-value for Test 1 is greater than .05. There may not be a
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diffence between responses and/or variances among the dose levels
Modelling the data with a dose/response curve may not be appropriate.
The p-value for Test 2 is greater than .1. A homogeneous
variance model appears to be appropriate here.
The p-value for Test 3 is greater than .1. The modeled
variance appears to be appropriate here.
The p-value for Test 4 is greater than .1. Model 2 seems
to adeguately describe the data.
The p-value for Test 5a is greater than .1. Model 3 seems
to adeguately describe the data.
Degrees of freedom for Test 5b are less than or egual to 0.
The Chi-Sguare test for fit is not valid.
The p-value for Test 6a is greater than .1. Model 4 seems
to adeguately describe the data.
The p-value for Test 6b is greater than .05. Model 4 does
not seem to fit the data better than Model 2.
The p-value for Test 7a is greater than .1. Model 5 seems
to adeguately describe the data.
The p-value for Test 7b is greater than .05. Model 5 does
not seem to fit the data better than Model 3.
The p-value for Test 7c is greater than .05. Model 5 does
not seem to fit the data better than Model 4.
Benchmark Dose Computations:
Specified Effect = 1.000000
Risk Type = Estimated standard deviations from control
Confidence Level = 0.950000
BMD and BMDL by Model
Model
BMD
BMDL
2
3
4
5
33.3643
33.3643
14.1537
13.3654
21.8638
21.8638
5.06031
5.36922
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Exponential Model 2 with 0.95 Confidence Level
Exponential
5.2
5
4.8
4.6
4.4
4.2
BMDL
BMD
0
5
10
15
20
25
30
35
40
45
dose
13:29 06/01 2011
Exponential Model 4 with 0.95 Confidence Level
Exponential
5.2
5
4.8
4.6
4.4
4.2
BMDL
BMD
0
5
10
15
20
25
30
35
40
45
dose
13:29 06/01 2011
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Ghanayem BI; Sanchez IM; Burka LT. (1992) Effects of Dose, Strain and Dosing Vehicle on
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