*>EPA
EPA/690/R-23/007F | September 2023 | FINAL
United States
Environmental Protection
Agency
Provisional Peer-Reviewed Toxicity Values for
Methylcyclohexane
(CASRN 108-87-2)
PRO1*
SUPERFUND
U.S. EPA Office of Research and Development
Center for Public Health and Environmental Assessment
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A United $ta»s
Environmental Protection
%#UI r% Agency
EPA/690/R-23/007F
September 2023
https://www.epa.gov/pprtv
Provisional Peer-Reviewed Toxicity Values for
Methylcyclohexane
(CASRN 108-87-2)
Center for Public Health and Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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AUTHORS, CONTRIBUTORS, AND REVIEWERS
CHEMICAL MANAGER
James A. Weaver, PhD, DABT
Center for Public Health and Environmental Assessment, Research Triangle Park, NC
CONTRIBUTOR
Jay Zhao, MPH, PhD, DABT
Center for Public Health and Environmental Assessment, Cincinnati, OH
DRAFT DOCUMENT PREPARED BY
SRC, Inc.
7502 Round Pond Road
North Syracuse, NY 13212
PRIMARY INTERNAL REVIEWERS
Shana White, PhD
Center for Public Health and Environmental Assessment, Cincinnati, OH
John Stanek, PhD
Center for Public Health and Environmental Assessment, Research Triangle Park, NC
PRIMARY EXTERNAL REVIEWERS
Eastern Research Group, Inc.
110 Hartwell Avenue
Lexington, MA 02421-3136
PPRTV PROGRAM MANAGEMENT
Teresa L. Shannon
Center for Public Health and Environmental Assessment, Cincinnati, OH
Allison L. Phillips, PhD
Center for Public Health and Environmental Assessment, Cincinnati, OH
J. Phillip Kaiser, PhD, DABT
Center for Public Health and Environmental Assessment, Cincinnati, OH
Questions regarding the content of this PPRTV assessment should be directed to the U.S. EPA
Office of Research and Development (ORD) Center for Public Health and Environmental
Assessment (CPHEA) website at https://ecomments.epa.gov/pprtv.
li
Methylcyclohexane
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TABLE OF CONTENTS
COMMONLY USED ABBREVIATIONS AND ACRONYMS iv
BACKGROUND 1
QUALITY ASSURANCE 1
DISCLAIMERS 2
QUESTIONS REGARDING PPRTVs 2
1. INTRODUCTION 3
2. REVIEW OF POTENTIALLY RELEVANT DATA (NONCANCER AND CANCER) 7
2.1. HUMAN STUDIES 14
2.1.1. Oral Exposures 14
2.1.2. Inhalation Exposures 14
2.2. ANIMAL STUDIES 14
2.2.1. Oral Exposures 14
2.2.2. Inhalation Exposures 20
2.3. OTHER DATA (SHORT-TERM TESTS, OTHER EXAMINATIONS) 25
2.3.1. Genotoxi city 25
2.3.2. Supporting Human Studies 28
2.3.3. Supporting Animal Studies 38
2.3.4. Metabolism/Toxicokinetic Studies 38
2.3.5. Mode-of-Action/Mechanistic Studies 40
3. DERIVATION 01 PROVISIONAL VALUES 41
3.1. DERIVATION OF ORAL REFERENCE DOSES 41
3.2. DERIVATION OF INHALATION REFERENCE CONCENTRATIONS 41
3.3. SUMMARY OF NONCANCER PROVISIONAL REFERENCE VALUES 41
3.4. CANCER WEIGHT-OF-EVIDENCE DESCRIPTOR 42
3.5. DERIVATION OF PROVISIONAL CANCER RISK ESTIMATES 43
APPENDIX A. SCREENING PROVISIONAL VALUES 44
APPENDIX B. DATA TABLES 53
APPENDIX C. BENCHMARK DOSE MODELING RESULTS 65
APPENDIX D. REFERENCES 104
in
Methylcyclohexane
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COMMONLY USED ABBREVIATIONS AND ACRONYMS
a2u-g
alpha 2u-globulin
IVF
in vitro fertilization
ACGIH
American Conference of Governmental
LC50
median lethal concentration
Industrial Hygienists
LD50
median lethal dose
AIC
Akaike's information criterion
LOAEL
lowest-observed-adverse-effect level
ALD
approximate lethal dosage
MN
micronuclei
ALT
alanine aminotransferase
MNPCE
micronucleated polychromatic
AR
androgen receptor
erythrocyte
AST
aspartate aminotransferase
MOA
mode of action
atm
atmosphere
MTD
maximum tolerated dose
ATSDR
Agency for Toxic Substances and
NAG
7V-acetyl-P-D-glucosaminidase
Disease Registry
NCI
National Cancer Institute
BMC
benchmark concentration
NOAEL
no-observed-adverse-effect level
BMCL
benchmark concentration lower
NTP
National Toxicology Program
confidence limit
NZW
New Zealand White (rabbit breed)
BMD
benchmark dose
OCT
ornithine carbamoyl transferase
BMDL
benchmark dose lower confidence limit
ORD
Office of Research and Development
BMDS
Benchmark Dose Software
PBPK
physiologically based pharmacokinetic
BMR
benchmark response
PCNA
proliferating cell nuclear antigen
BUN
blood urea nitrogen
PND
postnatal day
BW
body weight
POD
point of departure
CA
chromosomal aberration
PODadj
duration-adjusted POD
CAS
Chemical Abstracts Service
QSAR
quantitative structure-activity
CASRN
Chemical Abstracts Service registry
relationship
number
RBC
red blood cell
CBI
covalent binding index
RDS
replicative DNA synthesis
CHO
Chinese hamster ovary (cell line cells)
RfC
inhalation reference concentration
CL
confidence limit
RfD
oral reference dose
CNS
central nervous system
RGDR
regional gas dose ratio
CPHEA
Center for Public Health and
RNA
ribonucleic acid
Environmental Assessment
SAR
structure-activity relationship
CPN
chronic progressive nephropathy
SCE
sister chromatid exchange
CYP450
cytochrome P450
SD
standard deviation
DAF
dosimetric adjustment factor
SDH
sorbitol dehydrogenase
DEN
diethylnitrosamine
SE
standard error
DMSO
dimethylsulfoxide
SGOT
serum glutamic oxaloacetic
DNA
deoxyribonucleic acid
transaminase, also known as AST
EPA
Environmental Protection Agency
SGPT
serum glutamic pyruvic transaminase,
ER
estrogen receptor
also known as ALT
FDA
Food and Drug Administration
SSD
systemic scleroderma
FEVi
forced expiratory volume of 1 second
TCA
trichloroacetic acid
GD
gestation day
TCE
trichloroethylene
GDH
glutamate dehydrogenase
TWA
time-weighted average
GGT
y-glutamyl transferase
UF
uncertainty factor
GSH
glutathione
UFa
interspecies uncertainty factor
GST
g 1 ut a t h i o nc - V-1 ra n s fc ra sc
UFC
composite uncertainty factor
Hb/g-A
animal blood-gas partition coefficient
UFd
database uncertainty factor
Hb/g-H
human blood-gas partition coefficient
UFh
intraspecies uncertainty factor
HEC
human equivalent concentration
UFl
LOAEL-to-NOAEL uncertainty factor
HED
human equivalent dose
UFS
subchronic-to-chronic uncertainty factor
i.p.
intraperitoneal
U.S.
United States of America
IRIS
Integrated Risk Information System
WBC
white blood cell
Abbreviations and acronyms not listed on this page are defined upon first use in the
PPRTV assessment.
iv
Methylcyclohexane
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DRAFT PROVISIONAL PEER-REVIEWED TOXICITY VALUES FOR
METHYLCYCLOHEXANE (CASRN 108-87-2)
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 U.S. Environmental Protection Agency (U.S. EPA)
guidance on human health toxicity value derivations.
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.
Currently available PPRTV assessments can be accessed on the U.S. EPA's PPRTV
website at https://www.epa.gov/pprtv. PPRTV assessments are eligible to be updated on a 5-year
cycle and revised as appropriate to incorporate new data or methodologies that might impact the
toxicity values or affect the characterization of the chemical's potential for causing
toxicologically relevant human-health effects. Questions regarding nomination of chemicals for
update can be sent to the appropriate U.S. EPA eComments Chemical Safety website at
https://ecomments.epa.gov/chemicalsafetv/.
QUALITY ASSURANCE
This work was conducted under the U.S. EPA Quality Assurance (QA) program to ensure
data are of known and acceptable quality to support their intended use. Surveillance of the work
by the assessment managers and programmatic scientific leads ensured adherence to QA
processes and criteria, as well as quick and effective resolution of any problems. The QA
manager, assessment managers, and programmatic scientific leads have determined under the
QA program that this work meets all U.S. EPA quality requirements. This PPRTV assessment
was written with guidance from the CPHEA Program Quality Assurance Project Plan (PQAPP),
the QAPP titled Program Quality Assurance Project Plan (PQAPP) for the Provisional Peer-
Reviewed Toxicity Values (PPRTVs) and Related Assessments/Documents
(L-CPAD-0032718-QP), and the PPRTV assessment development contractor QAPP titled
Quality Assurance Project Plan—Preparation of Provisional Toxicity Value (PTV) Documents
(L-CPAD-0031971-QP). As part of the QA system, a quality product review is done prior to
management clearance. A Technical Systems Audit may be performed at the discretion of the
QA staff.
All PPRTV assessments receive internal peer review by at least two CPHEA scientists
and an independent external peer review by at least three scientific experts. The reviews focus on
whether all studies have been correctly selected, interpreted, and adequately described for the
purposes of deriving a provisional reference value. The reviews also cover quantitative and
qualitative aspects of the provisional value development and address whether uncertainties
associated with the assessment have been adequately characterized.
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Methylcyclohexane
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DISCLAIMERS
The PPRTV document provides toxicity values and information about the toxicologically
relevant 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. 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.
This document has been reviewed in accordance with U.S. EPA policy and approved for
publication. Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
QUESTIONS REGARDING PPRTVS
Questions regarding the content of this PPRTV assessment should be directed to the
U.S. EPA ORD CPHEA website at https://ecomments.epa.gov/pprtv.
2
Methylcyclohexane
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EPA/690/R-23/007F
1. INTRODUCTION
Methylcyclohexane (CASRN 108-87-2) is a saturated cyclic hydrocarbon; its structure
consists of a six-membered ring substituted with one methyl group. Methylcyclohexane is used
as a solvent and as a raw material in synthetic processes for pharmaceuticals and dyes (QHCD.
2014). It is also used in jet fuel and in cleaning solutions. M et hy 1 cy cl oh ex a n e is listed on the
U.S. EPA's Toxic Substances Control Act (TSCA) public inventory (U.S. HP A. 202 Id) and is
registered with Europe's Registration, Evaluation, Authorisation and Restriction of Chemicals
(REACH) program (ECHA. 2021).
Methylcyclohexane is synthesized by catalytic hydrogenation of toluene (NCBL, 2021;
Campbell. 2011) or by reacting benzene with methane at elevated temperatures (Baxter. 2012).
Methylcyclohexane can also be distilled from crude petroleum oils via the acidic hydrocracking
of polycyclic aromatics (Baxter. 2012). The U.S. national aggregate production volume in 2015
ranged from 500,000 to <1,000,000 pounds (U.S. EPA. 202 la).
The empirical formula for methylcyclohexane is C7H14. The chemical structure is shown
in Figure 1. Table 1 summarizes the physicochemical properties of methylcyclohexane.
Methylcyclohexane is a clear, colorless liquid that is slightly soluble in water (14 mg/L at 25°C).
In the air, methylcyclohexane will exist in the vapor (gas) phase, based on a measured vapor
pressure of 46 mm Hg. Methylcyclohexane will be degraded in the atmosphere by reaction with
photochemically-produced hydroxyl radicals with a half-life of 1.1 days, calculated from an
estimated hydroxyl radical reaction rate constant of 1.02 x 10 " cm3/molecule-second at 25°C.
Volatilization from dry soil surfaces is expected, based upon its vapor pressure. Volatilization
from water or moist soil surfaces is expected based upon the Henry's law constant of
0.43 atm-m3/mole. The estimated soil adsorption coefficients for methylcyclohexane indicate
low to moderate potential for mobility in soil and low to moderate potential to adsorb to
suspended solids and sediment in aquatic environments. Methylcyclohexane does not contain
functional groups that are likely to hydrolyze under environmental conditions; therefore,
hydrolysis is not expected to be an important fate process.
ch3
Figure 1. Methylcyclohexane (CASRN 108-87-2) Structure
3
Methylcyclohexane
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EPA/690/R-23/007F
Table 1. Physicochemical Properties of Methylcyclohexane
(CASRN 108-87-2)
Property (unit)
Value3
Physical state
Liquidb
Boiling point (°C at 25 mm Hg)
101
Melting point (°C)
-127
Density (g/cm3 at 20°C)
0.798
Vapor pressure (mm Hg at 25°C)
46
pH (unitless)
NA
Acid dissociation constant (pKa) (unitless)
NA
Solubility in water (mg/L at 25°C)
14 (reported as 1.47 x 10 4 mol/L)
Octanol-water partition coefficient (log Kow)
3.61
Henry's law constant (atm-m3/mol at 25°C)
0.43
Soil adsorption coefficient (Koc) (L/kg)
302 (estimated)
Atmospheric OH rate constant (cm3/molecule-sec at 25°C)
1.02 x 10-11
Atmospheric half-life (d)
1.052 (calculated based on 1.5 x 106 OH/cm3 and a
12-h day)0
Relative vapor density (air =1)
3.39b
Molecular weight (g/mol)
98.189
Flash point (open cup in °C)
-4b
aU.S. EPA (2021b); data were extracted from the U.S. EPA CompTox Chemicals Dashboard (methylcyclohexane,
CASRN 108-87-2; https://comptox.epa.gov/dashboard/ehemical/details/DTXSID0047749; accessed February 16,
2022).
bNC6I (2021).
°U.S. EPA (2012b) (with user-entered inputs for boiling point = 101, melting point = -127. water
solubility = 14 mg/L, vapor pressure = 46 mm Hg, Henry's law constant = 0.43, log Kow = 3.61, and
SMILES = C(CCCC1)(C1)C).
NA = not applicable; SMILES = simplified molecular input line entry system.
A summary of available toxicity values for methylcyclohexane from the U.S. EPA and
other agencies/organizations is provided in Table 2.
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Methylcyclohexane
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Table 2. Summary of Available Toxicity Values for
Methylcyclohexane (CASRN 108-87-2)
Source (parameter)11 b
Value (applicability)
Notes
Reference0
Noncancer
IRIS
NV
NA
U.S. EPA (2021c)
HEAST (chronic and
subchronic RfCs)
3 mg/m3
Based on renal
mineralization and
papillary hyperplasia in
1-yr rat inhalation study
U.S. EPA (1997)
DWSHA
NV
NA
U.S. EPA (2018)
ATSDR
NV
NA
ATSDR (2021)
IPCS
NV
NA
IPCS (2021)
CalFPA
NV
NA
CalEPA (2021); CalEPA
(2020)
OSHA (PEL)
500 ppm (2,000 mg/m3)
8-h TWA (for general
industry, construction, and
shipyard employment)
OSHA (2021a): OSHA
(2021b): OSHA (2021c)
NIOSH (REL)
400 ppm (1,600 mg/m3)
10-h TWA
NIOSH (2019)
NIOSH (IDLH)
1,200 ppm
Based on 10% of the lower
explosive limit of 1.2%
NIOSH (1994)
ACGIH (TLV)
400 ppm
8-h TWA; based on upper
respiratory tract irritation,
CNS impairment, and liver
and kidney damage
ACGIH (2021)
Cancer
IRIS
NV
NA
U.S. EPA (2021c)
HEAST
NV
NA
U.S. EPA (2011)
DWSHA
NV
NA
U.S. EPA (2018)
NTP
NV
NA
NTP (2016)
IARC
NV
NA
IARC (2021)
CalEPA
NV
NA
CalEPA (2021); CalEPA
(2020)
ACGIH
NV
NA
ACGIH (2021)
aSources: ACGIH = American Conference of Governmental Industrial Hygienists; ATSDR = Agency for Toxic
Substances and Disease Registry; CalEPA = California Environmental Protection Agency; DWSHA = Drinking
Water Standards and Health Advisories; HEAST = Health Effects Assessment Summary Tables;
I ARC = International Agency for Research on Cancer; IPCS = International Programme on Chemical Safety;
IRIS = Integrated Risk Information System; NIOSH = National Institute for Occupational Safety and Health;
NTP = National Toxicology Program; OSHA = Occupational Safety and Health Administration.
Parameters: IDLH = immediately dangerous to life or health; PEL = permissible exposure limit;
REL = recommended exposure limit; RfC = reference concentration; TLV = threshold limit value.
°Reference date is the publication date for the database and not the date the source was accessed.
CNS = central nervous system; NA = not applicable; NV = not available; TWA = time-weighted average.
5
Methylcyclohexane
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EPA/690/R-23/007F
Non-date limited literature searches were conducted in July 2019 and updated in
June 2023 for studies relevant to the derivation of provisional toxicity values for
methylcyclohexane. Searches were conducted using the U.S. EPA's Health and Environmental
Research Online (HERO) database of scientific literature. HERO searches the following
databases: PubMed, TOXLINE1 (including TSCATS1), Scopus, and Web of Science. The
National Technical Reports Library (NTRL) was searched for government reports from 2018
through September 20202. The following resources were searched outside of HERO for
health-related values: American Conference of Governmental Industrial Hygienists (ACGIH),
Agency for Toxic Substances and Disease Registry (ATSDR), California Environmental
Protection Agency (CalEPA), Defense Technical Information Center (DTIC), European Centre
for Ecotoxicology and Toxicology of Chemicals (ECETOC), European Chemicals Agency
(ECHA), the U.S. EPA Chemical Data Access Tool (CDAT), the U.S. EPA ChemView, the
U.S. EPA Integrated Risk Information System (IRIS), the U.S. EPA Health Effects Assessment
Summary Tables (HEAST), the U.S. EPA Office of Water (OW), International Agency for
Research on Cancer (IARC), the U.S. EPA TSCATS2/TSCATS8e, the U.S. EPA High
Production Volume (HPV), Chemicals via IPCS INCHEM, Japan Existing Chemical Data Base
(JECDB), Organisation for Economic Co-operation and Development (OECD) Screening
Information Data Sets (SIDS), OECD International Uniform Chemical Information Database
(IUCLID), OECD HPV, National Institute for Occupational Safety and Health (NIOSH),
National Toxicology Program (NTP), Occupational Safety and Health Administration (OSHA),
and World Health Organization (WHO).
'Note that this version of TOXLINE is no longer updated
(https://www.nlm.nih.gov/databases/download/toxlinesubset.html'): therefore, it was not included in the literature
search update from June 2023.
2NTRL was a subset of TOXLINE until December 2019 when TOXLINE was discontinued. Searches of NTRL
were conducted starting in 2018 to ensure that references were not missed due to delays in importing items into the
database.
6 Methylcyclohexane
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2. REVIEW OF POTENTIALLY RELEVANT DATA
(NONCANCER AND CANCER)
Tables 3A and 3B provide overviews of the relevant noncancer and cancer evidence
bases, respectively, for methylcyclohexane and include all potentially relevant repeated-dose
short-term, subchronic, and chronic studies, as well as reproductive and developmental toxicity
studies. Principal studies used in the PPRTV assessment for derivation of provisional toxicity
values are identified in bold. The phrase "statistical significance" and term "significant," used
throughout the document, indicate ap-value of <0.05 unless otherwise specified.
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Table 3A. Summary of Potentially Relevant Noncancer Data for Methylcyclohexane (CASRN 108-87-2)
Category3
Number of Male/Female, Strain,
Species, Exposure Route,
Reported Doses, Study Duration
Dosimetryb
Critical Effects
NOAELb
LOAELb
Reference
(comments)
Notes0
Human
1. Oral (mg/kg-d)
ND
2. Inhalation (mg/m3)
ND
Animal
1. Oral (mg/kg-d)
Short-term
5-10 M/5-10 F, Crj:CD
0,100,300,1,000
Increased incidence of renal
100
300
EC H A (2001c)
PS,
(Sprague Dawley) rat, gavage
(corn oil), 28 d
tubule hyaline droplet
degeneration in males.
NPR
Reported doses: 0,100,300,
1,000 mg/kg-d
Short-term
12 M/5-12 F group, Crl:CD
(Sprague Dawley) rat, gavage
(corn oil), from 14 d prior to
mating, through mating and
gestation until LD 4 (mated
females), or for 28 d (males and
unmated females)
Reported doses: 0, 62.5, 250,
1,000 mg/kg-d
0, 62.5, 250, 1,000
Increased liver and kidney weights
in males and unmated females and
increased incidence of renal tubule
hyaline droplets in males.
250
1,000
JECDB (2013)
(This study is
published in
Japanese with
some tables and
figures in English,
or reported in
secondary
sources.): ECHA
(2011a): ECHA
(2011b)
NPR
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Table 3A. Summary of Potentially Relevant Noncancer Data for Methylcyclohexane (CASRN 108-87-2)
Category3
Number of Male/Female, Strain,
Species, Exposure Route,
Reported Doses, Study Duration
Dosimetryb
Critical Effects
NOAELb
LOAELb
Reference
(comments)
Notes0
Reproductive/
developmental
12 M/12 F group, Crl:CD
(Sprague Dawley) rat, gavage
(corn oil), from 14 d prior to
mating, through mating and
gestation until LD 4 (females), or
for 28 d (males)
Reported doses: 0, 62.5, 250,
1,000 mg/kg-d
0, 62.5, 250, 1,000
No reproductive or developmental
effects.
1,000
NDr
JECDB (2013)
(This study is
published in
Japanese with
some tables and
figures in English,
or reported in
secondary
sources.): ECHA
(2011a): ECHA
(2011b)
NPR
2. Inhalation (mg/m3)
Subchronic
10 M/10 F, Sprague Dawley rat,
whole-body vapor inhalation,
6 h/day, 5 d/wk for 13 wk
Reported analytical
concentrations: 0, 101.9, 339.4,
1,608 ppm
0, 73.07, 243.4, 1,153
None identified due to lack of details
in English on crucial endpoints.
NDr
NDr
Kim et al. (2006)
(This study is
published in
Korean with
English abstract,
tables, and
figures.)
PR
Chronic
65 M/65 F, CDF F344/CrlBR rat,
whole-body vapor inhalation,
6 h/d, 5 d/wk for 12 mo
Reported analytical
concentrations: 0, 400.2,
2,004 ppm
0, 287.0, 1,437
Increased incidences of renal
medullary mineralization and
papillary hyperplasia in males.
287.0
1,437
AFRL (1985): API
(1985)
PS,
NPR
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Methylcyclohexane
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Table 3A. Summary of Potentially Relevant Noncancer Data for Methylcyclohexane (CASRN 108-87-2)
Category3
Number of Male/Female, Strain,
Species, Exposure Route,
Reported Doses, Study Duration
Dosimetryb
Critical Effects
NOAELb
LOAELb
Reference
(comments)
Notes0
Chronic
0 M/200 F, C57BL/6J mouse,
whole-body vapor inhalation,
6 h/d, 5 d/wk for 12 mo
Reported analytical
concentrations: 0, 400.2,
2,004 ppm
0, 287.0, 1,437
No clear treatment-related,
toxicologically relevant effects
applicable to human health risk
assessment11.
1,437
NDr
AFRL (1985): API
(1985)
NPR
Chronic
100 M/0 F, Syrian golden
hamster, whole-body vapor
inhalation, 6 h/d, 5 d/wk for
12 mo
Reported analytical
concentrations: 0,400.2,
2,004 ppm
0, 287.0,1,437
Decreased body weight in males.
NDr
287
AFRL (1985): API
(1985)
PS,
NPR
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Methylcyclohexane
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Table 3A. Summary of Potentially Relevant Noncancer Data for Methylcyclohexane (CASRN 108-87-2)
Category3
Number of Male/Female, Strain,
Species, Exposure Route,
Reported Doses, Study Duration
Dosimetryb
Critical Effects
NOAELb
LOAELb
Reference
(comments)
Notes0
Chronic
4 M/4 F, beagle dog, whole-body
vapor inhalation, 6 h/d, 5 d/wk for
12 mo
Reported analytical
concentrations: 0, 400.2,
2,004 ppm
0, 287.0, 1,437
No clear treatment-related,
toxicologically relevant effects
applicable to human health risk
assessment11.
1,437
NDr
AFRL (1985): API
(1985)
NPR
aDuration categories are defined as follows: acute = exposure for <24 hours; short-term = repeated exposure for >24 hours to <30 days; subchronic = repeated exposure
for >30 days or <10% life span for humans (>30 days up to approximately 90 days in typically used laboratory animal species); and chronic = repeated exposure for
>10% life span for humans (>~90 days to 2 years in typically used laboratory animal species) (U.S. EPA. 2002).
bDosimetry: Doses are presented as ADDs (mg/kg-day) for oral noncancer effects and as HECs (in mg/m3) for inhalation noncancer effects. The HEC from animal
studies was calculated using the equation for ER effects from a Category 3 gas (U.S. EPA. 1994): HECer = continuous concentration in mg/m3 x ratio of animal:human
blood-gas partition coefficients using a default coefficient of 1 because the blood-air partition coefficients (logA'i,i(„i) for mice, hamsters, and dogs are unknown and the
rat logATbiood (0.79) is greater than the human logKbiood (0.61), as indicated by Abraham et at (2005).
°Notes: NPR = not peer reviewed; PR = peer reviewed; PS = principal study.
dLimited endpoints were evaluated. In addition, details on the collection of chamber concentrations and exposure to control animals were not provided.
ADD = adjusted daily dose; ER = extrarespiratory; F = female(s); HEC = human equivalent concentration; LD = lactation day;
LOAEL = lowest-observed-adverse-effect level; M = male(s); ND = no data; NDr = not determined; NOAEL = no-observed-adverse-effect level.
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Table 3B. Summary of Potentially Relevant Cancer Data for Methylcyclohexane (CASRN 108-87-2)
Number of Male/Female, Strain,
Species, Exposure Route,
Reference
Category
Reported Doses, Study Duration
Dosimetry3
Critical Effects
(comments)
Notesb
Human
1. Oral (mg/kg-d)
ND
2. Inhalation (mg/m3)
ND
Animal
1. Oral (mg/kg-d)
ND
2. Inhalation (mg/m3)
Carcinogenicity
65 M/65 F, CDF F344/CrlBR rat,
0, 287.0, 1,437
No evidence of carcinogenicity in a
AFRL (1985); API (1985)
NPR
whole-body vapor inhalation, 6 h/d,
limited study.
5 d/wk for 12 mo
Reported analytical concentrations:
0, 400.2, 2,004 ppm
Carcinogenicity
0 M/200 F, C57BL/6J mouse,
0, 287.0, 1,437
No evidence of carcinogenicity in a
AFRL (1985); API (1985)
NPR
whole-body vapor inhalation, 6 h/d,
limited study.
5 d/wk for 12 mo
Reported analytical concentrations:
0, 400.2, 2,004 ppm
Carcinogenicity
100 M/0 F, Syrian golden hamster,
0, 287.0, 1,437
No evidence of carcinogenicity in a
AFRL (1985); API (1985)
NPR
whole-body vapor inhalation, 6 h/d,
limited study.
5 d/wk for 12 mo
Reported analytical concentrations:
0, 400.2, 2,004 ppm
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Table 3B. Summary of Potentially Relevant Cancer Data for Methylcyclohexane (CASRN 108-87-2)
Category
Number of Male/Female, Strain,
Species, Exposure Route,
Reported Doses, Study Duration
Dosimetry3
Critical Effects
Reference
(comments)
Notesb
Carcinogenicity
4 M/4 F, beagle dog, whole-body
vapor inhalation, 6 h/d, 5 d/wk for
12 mo
Reported analytical concentrations:
0, 400.2, 2,004 ppm
0, 287.0, 1,437
No evidence of carcinogenicity in a
limited study.
AFRL (1985); API (1985)
NPR
aDosimetry: Inhalation exposure units are expressed as HECs (mg/m3). The HEC from animal studies was calculated using the equation for ER effects from a Category 3
gas (U.S. EPA. 19941: HECer = continuous concentration in mg/m3 x ratio of animal:humanblood-gas partition coefficients using a default coefficient of 1 because the
blood-air partition coefficients (logA'i,i„»i) for mice, hamsters, and dogs are unknown and the rat logA.'i,i„„i (0.79) is greater than the human logA.'i,i„„i (0.61), as indicated by
Abraham et al. (2005).
bNotes: NPR = not peer reviewed.
ER = extrarespiratory; F = female(s); HECer = human equivalent concentration; M = male(s).
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2.1. HUMAN STUDIES
2.1.1. Oral Exposures
No studies were identified.
2.1.2. Inhalation Exposures
No human studies adequate for determination of no-observed-adverse-effect level
(NOAEL) or lowest-observed-adverse-effect level (LOAEL) values were identified. Studies that
reported human data were confounded by co-exposures to other volatile organic compounds
(VOCs) and were not considered suitable for hazard identification or dose-response.
2.2. ANIMAL STUDIES
2.2.1. Oral Exposures
The effects of oral exposure to methylcyclohexane in animals have been evaluated in
short-term studies in rats (JHCDB. 2013; EC HA. 200 1c). one of which incorporated a screen for
reproductive and developmental effects (JECDB. 2013).
Short-Term Studies (Including Combined Reproductive and Developmental
Screening)
ECHA (2001c)
An unpublished, Good Laboratory Practice (GLP)-compliant OECD guideline 407
repeated-dose 28-day oral toxicity study in rats was summarized in secondary sources (ECHA.
2001c). which included select data tables for some endpoints that were adequate for review; the
primary report was not available.
Cij:CD (Sprague Dawley) rats (five/sex/group), aged 5 weeks at study initiation, were
administered methylcyclohexane (99.8% pure) doses of 0, 100, 300, or 1,000 mg/kg-day in corn
oil, via gavage, for 28 days. An additional five animals/sex were included in the control and
high-dose groups to evaluate reversal of effects following a 14-day recovery period. Analytical
measurements were taken at the first and last preparation of gavage solutions and were within
99.5 and 107.1%, respectively, of nominal concentrations. Doses were selected based on a
preliminary 14-day oral toxicity study that reported salivation in both sexes at 1,000 mg/kg-day.
Rats were checked 3 times/day during dosing for mortality and cage-side observations. Detailed
clinical observations and body-weight measurements were made once a week. Food consumption
was measured throughout the study. On the first and last day of dosing, neurobehavioral
endpoints (grip strength, motor activity, and hindlimb foot splay) were examined. Urine was
collected in the last week of dosing by placing the rats in metabolic cages and was tested for
volume, color, sediment, osmotic pressure, pH, occult blood, ketones, glucose [GLU], protein,
bilirubin, and urobilinogen. The day after the last dose, rats (five/sex/group) were euthanized and
examined. During the recovery period, the remaining rats in the control and high-dose groups
were checked twice a day for mortality and cage-side observations, body weights continued to be
recorded weekly, and urine was collected during the last week of recovery and examined as
above. Endpoints examined at the times of sacrifice included hematology (hematocrit [HCT],
hemoglobin [HGB], red blood cell [RBC] count, mean corpuscular volume [MCV], mean
corpuscular hemoglobin [MCH], mean corpuscular hemoglobin concentration [MCHC], platelets
[PLT], differential white blood cell [WBC] counts, reticulocytes, prothrombin time [PT],
activated partial thromboplastin time [APTT]), and fibrinogen) and clinical biochemistry
(alkaline phosphatase [ALP], aspartate aminotransferase [AST], GLU, total cholesterol [TC],
triglyceride [TG], blood urea nitrogen [BUN], creatinine [CRN], total bilirubin [TBIL], total
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protein [TP], albumin [ALB], albumin:globulin ratio [A/G], sodium [Na], potassium [K],
chloride [CI], calcium [Ca], and inorganic phosphorus [IP]). Organs that were weighed were not
specified (only data for absolute and relative liver and ovary weights and relative epididymis
weights were provided in the secondary sources). Animals were grossly examined, and
histopathology was performed on 29-30 tissues. Statistical tests included the Bartlett test,
Dunnett test, Steel test, Fisher's exact test, and Mann-Whitney U test.
No rats died during the study. The only clinical sign reported was salivation occurring
within 1 hour of dosing in males at >300 mg/kg-day and in females at 1,000 mg/kg-day. Data on
body weight were presented only as body-weight gain. Statistically significant increases in
body-weight gain during dosing (days 0-27) were observed in males at 300 mg/kg-day (26%
increase) and 1,000 mg/kg-day (20% increase) compared to controls (see Table B-l). Food
consumption was increased in the same dose groups. Treated females showed no increase in
body-weight gain. There were no functional neurobehavioral changes at any dose in either sex.
No treatment-related hematological effects were observed (data not shown). Serum
chemistry results were unremarkable (see Table B-2). Sporadic statistically significant changes
either showed no relationship to dose, fell within expected normal ranges for age-matched
CD (Sprague Dawley) rats (Giknis and Clifford. 2006). were not consistent with other findings,
occurred during the recovery period only, and/or were of unclear toxicological significance.
Statistically significantly increases in total protein (by 7%, relative to controls) and total
bilirubin (by 100% relative to controls) were in males at 1,000 and 300 mg/kg-day, respectively,
at the end of treatment. In addition, ALP was statistically significantly decreased (by 34%
relative to controls) in the high-dose males. In females treated with 1,000 mg/kg-day, total
cholesterol was statistically significantly increased (by 46% relative to controls) and AST was
statistically significantly decreased (by -11% relative to controls). In addition, the A/G ratio was
statistically significantly increased (by 14% relative to controls) at 100 mg/kg-day at the end of
treatment in females.
Absolute and relative liver weights were statistically significantly increased (by 22%,
relative to controls) in high-dose males at the end of treatment; increases persisted through the
recovery period (see Table B-3). An increase of 16% in absolute liver weight was seen in males
at 300 mg/kg-day, but the change in relative liver weight at this dose was only 6%. In females at
1,000 mg/kg-day, an increase in absolute weight of 10% and a significant 13% increase in
relative weight compared to controls were reported. After recovery, female liver weights were
increased <10% relative to controls. No changes in other organ weights at the end of treatment
were reported in either sex.
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Microscopic examination showed a significant increase in the incidence of hepatocellular
hypertrophy in 5/5 high-dose males and 1/5 high-dose females at the end of the treatment period
(see Table B-4); this lesion was not seen in animals euthanized after the recovery period. Male
rats also showed kidney hyaline droplet degeneration in 0/5, 1/5, 5/5, and 5/5 animals in the
control, 100, 300, and 1,000 mg/kg-day groups, respectively, at the end of treatment. This lesion
was observed in 1/5 high-dose males after recovery. In addition to "hyaline droplet
degeneration," which was observed only in males, the secondary source for this study also
reported "hyaline droplet formation" separately, an effect that was seen only in females. There is
no description in the secondary report of the two lesions or explanation for considering them
separately. Hyaline droplet formation was reported in 2/5 high-dose females at the end of dosing
and reached statistical significance in high-dose females (5/5) at the end of recovery. The study
authors of the secondary report considered the hyaline droplet degeneration in the kidneys of
male rats to be alpha 2u-globulin (a2u-g)-related and thus not relevant for humans, although it
was not specified whether the presence of a2u-g was actually assessed in this study. No increase
was reported in the incidence of other lesions that typically occur as part of the known
progression in a2u-g-associated nephrotoxicity (e.g., single cell necrosis in epithelium of
P2 segment of proximal tubule, accumulation of granular casts at junction of P3 segment and
loop of Henle, cell proliferation within the P2 segment, linear mineralization of tubules within
the renal papilla)(U.S. EPA. 1991). The study authors of the secondary report considered the
hyaline droplets in females to be of unclear etiology. U.S. EPA (1991) noted that hyaline
droplets may occur in female rats, albeit less frequently than in male rats, due to accumulation of
proteins other than a2u-g. As a result, the relationship to treatment and the toxicological
significance of the formation of these droplets in high-dose female rats are unclear.
A NOAEL of 100 mg/kg-day and a LOAEL of 300 mg/kg-day were identified from this
study based on increased incidence of renal hyaline droplet degeneration in male rats. Chemicals
inducing excessive accumulation of a2u-g in the hyaline droplets of male kidneys bind reversibly
to the a2u-g protein specifically produced in male rats, thus leading to hyaline droplet
accumulation and subsequent development of nephrotoxicity and possible renal tumor formation
(U.S. HP A. 1991). According to the U.S. EPA guidelines, the fulfillment of three criteria is
necessary to determine that renal toxicity is associated with a2u-g and therefore not relevant to
human health: (1) increased size and number of hyaline droplets; (2) identification of the
accumulating protein as a2u-g; and (3) the presence of other lesions associated with a2u-g
nephropathy (e.g., single cell necrosis, granular casts formation, and linear mineralization) (U.S.
HP A. 1991). Although the final step in the a2u-g pathway is the formation of kidney tumors, the
presence of kidney tumors is not always evident and should not invalidate other findings
characteristic of a2u-g toxicity. Other factors such as dose, other toxicities not related to a2u-g,
and length of exposure may complicate the ability to detect kidney tumors (U.S. HP A. 1991).
Details included in the secondary report did not indicate that a2u-g was measured in the study.
The secondary report also did not demonstrate a pathological sequence of other lesions
associated with a2u-g progression. Finally, hyaline droplet formation was observed in
2/5 high-dose females at the end of treatment and 5/5 females at the end of the recovery period,
suggesting that kidney effects not related to a2u-g may be occurring (HCHA. 2001c); together,
the data provide insufficient evidence to meet two of the three criteria outlined in U.S. HP A
(1991) to definitively attribute the observed hyaline droplet degeneration in male rats to a2u-g
nephropathy. Therefore, these effects are considered to be potentially relevant to human health.
At higher doses, biologically and statistically significant increases in absolute and relative liver
weights in male and female rats and significantly increased liver cell hypertrophy in male rats
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were observed. In this study, the administered doses of 100, 300, and 1,000 mg/kg-day
correspond to human equivalent doses (HEDs) of 24.9, 74.6, and 249 mg/kg-day for males and
23.2, 69.7, and 232 mg/kg-day in females3.
JECDB (2013); ECHA (201 la); ECHA (201 lb)
A GLP-compliant, unpublished OECD guideline 422 repeated-dose toxicity study with
an reproductive/developmental screening test is available as a report in Japanese (JECDB. 2013)
with some text, figures, and tables in English. The same study was described in detail in
secondary sources (ECHA. 201 1 a. b). The summary below was generated using the data from
the main study, along with additional methodological details provided in the secondary sources.
Ten-week-old Crl:CD (Sprague Dawley) rats (12 breeding pairs/group) were
administered methylcyclohexane (99.9% purity) in a corn oil vehicle, via gavage, at (nominal)
doses of 0, 62.5, 250, or 1,000 mg/kg-day. Males were dosed from 14 days prior to mating and
during the mating period for a total of 28 days. Females were dosed from 14 days prior to mating
and throughout mating and gestation until day 4 of lactation. A satellite set of unmated females
(10 per control and high-dose groups and 5 per low- and mid-dose groups) were dosed for a total
of 28 days. Half of the males from all groups (6/12 animals) and 5/10 unmated females from the
control and high-dose groups were allowed to recover for 14 days following the end of the
dosing period. Animals were euthanized either 1 day after the last administered dose or after
14 days of recovery, respectively.
Rats were checked twice a day during dosing for mortality and to make cage-side
observations. Detailed clinical signs (functional observational battery), including posture,
palpebral closure, excessive grooming, repetitive circling, biting behavior, clonic convulsions,
tonic convulsions, ease of removal from cage, ease of handling, muscle tone, fur condition,
mucous membranes condition, lacrimation, salivation, piloerection, pupil size, respiration, and
behavior in an open field test (frequency of urination, defecation, rearing and grooming, gait,
palpebral closure, consciousness, behavioral abnormalities, and righting reflex) were evaluated
in all groups before treatment and once a week during the dosing period. Sensory reactivity
(pupillary reflex, approaching behavior, response to touch, auditory reflex, and pain reflex), grip
strength, and spontaneous motor activity were measured at the end of dosing in males and
unmated females. Body weights were measured twice a week during dosing and on recovery
days 1, 4, 8, 11, 14, and 15. Food and water consumption were measured throughout the study.
Blood was drawn from males and unmated females at the end of dosing and after the recovery
period for hematology (RBC, HGB, HCT, MCV, MCH, MCHC, PLT, reticulocytes, PT, APTT,
fibrinogen, WBCs, lymphocytes, neutrophils, eosinophils, basophils, monocytes) and clinical
chemistry (AST, alanine aminotransferase [ALT], ALP, y-glutamyl transferase [GGT], TP, ALB,
A/G, TBIL, BUN, CRN, GLU, TC, TG, Na, K, CI, Ca, IP, and iron [Fe]) measurements. Thyroid
hormone (triiodothyronine [T3], thyroxin [T4], and thyroid stimulating hormone [TSH]) levels
were measured in both sexes at the end of dosing. Other endpoints included urinalysis (volume,
3The adjusted daily doses (ADDs) were converted to HEDs of 24.9, 74.6, and 249 mg/kg-day in low-, mid-, and
high-dose males and 23.2, 69.7, and 232 mg/kg-day in low-, mid-, and high-dose females using dosimetric
adjustment factors (DAFs) of 0.249 (males) and 0.232 (females), where HED = ADD x DAF. The DAFs were
calculated as follows: DAF = (BWa1/4 ^ BWh14), where DAF = dosimetric adjustment factor, BWa = animal body
weight, and BWh = human body weight. In the absence of body-weight data in the study, reference body weights of
0.267 kg for male and 0.204 kg for female Sprague Dawley rats in a subchronic study were used (U.S. EPA. 1988).
For humans, the reference body-weight value of 70 kg was used (U.S. EPA. 1988).
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color, pH, presence of protein, GLU, ketone bodies, bilirubin, occult blood, urobilinogen,
epithelial cells, RBC, WBC, casts, and crystals) and organ weights (brain, pituitary, salivary
glands, thyroids, thymus, heart, liver, spleen, kidneys, adrenals, testes, epididymides, ventral
prostate, seminal vesicles, ovaries, and uterus) in males and unmated females at the end of
dosing and after the recovery period. Gross necropsy was performed on males and unmated
females after dosing and after the recovery period and on mated females at the time of sacrifice.
With the exception of kidney tissues, which were examined in all male dose groups, histological
examinations after dosing were done on 44 tissues in 6/12 male and 5/10 unmated females in the
control and high-dose groups and in recovery animals. Histological examination of mated
females was performed on ovaries, uterus, vagina, and mammary gland tissues only.
Females in the mating groups were monitored for estrous cycle length and normality.
Reproductive indices (copulation index, fertility index, implantation index, gestation index,
delivery index, and birth index) were calculated. Female reproductive organ weights (ovaries and
uterus) were measured, and histopathological analysis included examinations of the mammary
gland, ovary, uterus, and vagina. Reproductive analysis in males was limited to organ weights
(testis, epididymis, ventral prostate, and seminal vesicles) and histopathology of those tissues;
sperm parameters were not evaluated. Litter observations included the number and sex of pups,
live and stillbirths, postnatal mortality, physical or behavioral abnormalities, pup body weights
and litter weights (lactation days [LDs] 0-4) and weight gain, and presence of gross anomalies.
Sex ratio at birth, live birth index, and viability indices were determined.
Details of statistical analyses were reported in Japanese in the primary study. Statistical
analysis, as described in the secondary sources (ECHA. 2011a. b), indicates the use of Bartletf s
test, Dunnett's test, Steel's test, F test, Student's Mest, Aspin-Welch /-test, Fisher's exact test,
and/or Cochran-Armitage test. Litter observations included the number and sex of pups,
stillbirths, live births, postnatal mortality, presence of gross anomalies, weight gain, and physical
or behavioral abnormalities.
No rats died during the study. Transient salivation was seen in some high-dose animals
immediately after dosing. Body weights of treated rats were comparable to controls throughout
the study. No treatment-related changes in food or water consumption were seen. There were no
changes in sensory reactivity, grip strength, or spontaneous motor activity in any group. At the
end of the treatment period, there were no significant hematological changes in males and only
small increases in reticulocyte and monocyte counts (within expected ranges) in the high-dose
unmated females; these changes were not seen in the treated recovery group females. Serum
chemistry changes are shown in Table B-5. Potential noteworthy findings were limited and
included statistically significant increases in ALT (74% increase), GGT (93% increase), and TC
(80%) increase) in high-dose males at the end of treatment; an increase in ALT (34% increase)
and TC (60% increase) was seen after the recovery period as well. These and all other observed
serum chemistry changes were, however, within the range expected for age- and sex-matched
rats of this strain (Giknis and Clifford. 2006). Thyroid hormone levels were comparable across
groups in both sexes. Urinalysis showed no treatment-related changes.
At the end of the treatment period, statistically and biologically (>10%) significant
increases in absolute and relative liver and kidney weights were found in the high-dose male rats
and in relative liver and kidney weights in unmated females relative to controls (see Table B-6).
Smaller changes that were not statistically significant were seen in the treated recovery group
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males. High-dose unmated females also showed statistically significant increases in absolute and
relative adrenal weights and relative uterus weights. Increased relative uterus weight was within
the historical normal range of the testing facility and was not considered treatment related. These
changes were not biologically significant or were not seen at all in the treated recovery group
females. Uterus weights were not increased in the mated females at any dose (evaluated on
LD 5).
No treatment-related gross findings were observed at necropsy. The only
treatment-related finding identified by histopathological examination was an increased incidence
of hyaline droplets in the kidneys of male rats at the end of the treatment period (observed in 0/6,
0/6, 4/6, and 6/6 males in the control, low-, mid-, and high-dose groups, respectively). The
pairwise increase in the high-dose group was statistically significant, as was the overall trend.
Lesion severity was reported to be slight in all cases. The lesion was not seen in the male rats
examined after the recovery period. The study authors of the secondary report of this study
(HCHA. 2011a) considered this lesion likely related to a2u-g accumulation, which is specific to
male rats and not relevant to humans. It is unclear, however, whether a2u-g was measured in this
study. There is no indication that such measurements were made in the English language
portions of the original Japanese study report. There is also no detailed discussion of this issue in
the secondary source (HCH A. 2011a). No increased incidences of other lesions typically
associated with progression of a2u-g nephrotoxicity were observed in any treatment group.
One animal in each of the control, 62.5 mg/kg-day, and 1,000 mg/kg-day groups did not
become pregnant. There were no significant maternal effects or differences in any of the
reproductive endpoints measured, including the copulation index, fertility index, length of
gestation, number of corpora lutea, implantation scars, and implantation index, between control
and treated animals. All the pups from one dam in the 250 mg/kg-day group died, presumably
due to hypothermia resulting from faulty nesting; this was likely accidental and not
treatment-related. Litter endpoints, including pups born, sex ratios, live birth, and viability
indices, were comparable across all groups. There were no statistically significant changes in pup
or litter body weights. No external abnormalities in pups were observed.
A systemic NOAEL of 250 mg/kg-day and LOAEL of 1,000 mg/kg-day were identified
from this study. Statistically and biologically (>10%) significant increases in liver and kidney
weights were seen in both male and female rats at 1,000 mg/kg-day. An effect on the liver was
also suggested by the small, but significant, increases in serum ALT and GGT found in the
1,000-mg/kg-day male rats. In the kidney, hyaline droplets were seen in male rats at
>250 mg/kg-day and were significantly increased at 1,000 mg/kg-day. Although considered by
the study authors of the secondary report to be associated with a2u-g accumulation (and
therefore not relevant to humans), it is not clear that a2u-g was measured in this study or that the
issue was considered in detail. No other lesions associated with a2u-g nephrotoxicity were
observed. Altogether, two of the three criteria (a2u-g protein verification and lesions associated
with a2u-g) required to demonstrate a2u-g nephrotoxicity due to methylcyclohexane exposure
were not satisfied based on the U.S. EPA's guidance (U.S. HP A. 1991). Because the available
data fail to provide sufficient evidence that the a2u-g process was operative, the hyaline droplets
are considered a human-relevant endpoint for this study. The high dose of 1,000 mg/kg-day is a
reproductive/developmental NOAEL, based on the absence of effects on these endpoints at any
dose. The administered doses of 62.5, 250, and 1,000 mg/kg-day correspond to HEDs of 17.1,
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68.6, and 273 mg/kg-day for males; 15.7, 63.0, and 251 mg/kg-day for unmated females; and
16.1, 64.2, and 255 mg/kg-day for mated females, respectively4.
Subchronic/Chronic Studies
No oral subchronic or chronic studies on methylcyclohexane in animals were identified.
2.2.2. Inhalation Exposures
Relevant studies on the effects of inhalation exposure of animals to methylcyclohexane
were limited to a subchronic study in rats (Kim et al.. 2006) and a chronic study in rats, mice,
hamsters, and dogs (AFRL. 1985; API. 1985).
Subchronic Studies
Kim et al. (2006)
A 13-week inhalation toxicity study published in Korean evaluated the effects of
methylcyclohexane inhalation exposure in rats. Due to the lack of available details in English on
crucial endpoints (e.g., organ weights and histopathology) and the poor quality of the available
translation, NOAEL and LOAEL values for this study were not determined.
Chronic/Carcinogenicity Studies
AFRL (1985); API (1985)
In an unpublished, non-peer-reviewed study with deficiencies in methods and data
reporting, AFRL (1985) exposed groups of 10-week-old CDF F344/CrlBR rats (65/sex/group),
8-week-old C57BL/6J mice (200 females/group), 12-week-old Syrian golden hamsters
(100 males/group), and 8-13-month-old purebred beagle dogs (4/sex/group), whole-body, to
nominal concentrations of 0, 400, or 2,000 ppm methylcyclohexane (-99% pure) vapors for
6 hours/day, 5 days/week for 1 year. Exposures were performed in two 840-cubic-foot exposure
chambers (two for each concentration). The measured methylcyclohexane mean concentrations
in each chamber were 401.5 and 398.9 ppm for the low-exposure group, respectively, and
1,998 and 2,009 ppm for the high-exposure group, respectively; the pair-averaged chamber
concentrations were 400.2 ppm (1,607 mg/m3) and 2,004 ppm (8,048 mg/m3), respectively5. At
the end of the exposure period, a small number of animals (10 rats/sex, 20 female mice, and
10 male hamsters) from each group were necropsied for histological analysis. The remaining
rodents were monitored for an additional year prior to sacrifice, and all dogs were held for
5 years postexposure. Overall, several deficiencies were identified in this study. For example,
three different lots of the test agent were used with purities ranging from 98.50 to 98.66%, with
the identified impurities being w-heptane (0.74-0.97%) and toluene (0.52-0.60%); details on the
4The ADDs were converted to HEDs of 17.1, 68.6, and 273 mg/kg-day in low-, mid-, and high-dose males; 15.7,
63.0, and 251 mg/kg-day in unmated low-, mid-, and high-dose females; and 16.1, 64.2, and 255.2 in mated low-,
mid-, and high-dose females using DAFs of 0.27 (males), 0.25 (unmated females), and 0.26 (mated females), where
HED = ADD x DAF. The DAFs were calculated as follows: DAF = (BWa1/4 ^ BWhI/4), where BWa = animal body
weight and BWh = human body weight. Individual animal body weights were provided in the study; group
time-weighted average (TWA) body weights determined for this review were 0.395, 0.398, and 0.391 kg (for low-,
mid-, and high-dose males, respectively); 0.282, 0.283, and 0.279 kg (for low-, mid-, and high-dose unmated
females, respectively); and 0.305, 0.305, and 0.297 kg (for mated low-, mid-, and high-dose females, respectively).
For humans, the reference value of 70 kg was used for body weight, as recommended by U.S. EPA (1988).
Analytical concentrations of 400.2 and 2,004 ppm were converted to mg/m3 using the following formula:
mg/m3 = (ppm x molecular weight [MW])/24.45, where MW = 98.186 g/mol (the molecular weight of
methylcyclohexane) and 24.45 is the volume occupied by 1 g/mol of any compound in a gaseous state at 25°C and
760 mm Hg.
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collection of chamber concentrations were not provided; details on the exposure to control
animals; and details on animal husbandry during exposures were omitted.
All animals were observed hourly during exposure and at least 6 times daily during
recovery. Body weights of rats, hamsters, and dogs were measured every 2 weeks during
exposure and biweekly (rats and hamsters) or biannually (dogs) during recovery. For the mice,
group weights were measured monthly (data not provided). Blood samples were collected from
the rats euthanized at the end of the 12-month exposure period and from dogs every 2 weeks
during the exposure period and every 6 months thereafter. Blood analyses included the
measurement of routine hematology (not further defined) and serum chemistry (electrolytes,
GLU, CRN, TBIL, TP, ALB, ALT, AST, and ALP) endpoints. At sacrifice (either after the
12-month exposure or the recovery period), organ weights were measured in rats and dogs
(organs not specified and data not shown). All animals were necropsied at death, and
histopathological examination of "approximately 33 tissues" was performed. The report provided
limited lesion incidence data for select tissues and excluded lesions of very low incidence
(AFRL. 1985).
The statistical methods used to evaluate data were not specified, but it was noted in the
study, for most endpoints, whether the values from the exposure groups were significantly
different from controls (i.e. ,p< 0 .05 orp < 0.01). Body weight, hematology, and clinical
chemistry values were reported as group means without measures of variance, precluding
performance of independent statistical analysis for these data. Some of the data presented in the
report that were not statistically analyzed by the study authors (e.g., early mouse deaths) were
analyzed by Fisher's exact test (two-tailed; p < 0.05) for this review. The results from each
species are reported separately below.
Rats
No differences in mortality across groups were discernable at the end of the 1-year
exposure period (based on the number of animals examined for histopathology, one male each
from the control and high-exposure groups and one control female died). Body-weight data were
graphically reported as means with no measures of variance. Based on the data, digitized using
the MATLAB tool, GRAB IT6, body weights of exposed males were slightly decreased compared
to controls throughout the exposure period and continuing to the end of the study; however, the
magnitudes of change were small (<10% in both the low- and high-exposure groups). Body
weights of exposed female rats were similar to controls throughout exposure and recovery.
Hematological and serum chemistry data were reported as means from 9 or 10 animals/sex group
with no measure of variance, although changes reaching statistical significance were indicated by
the study authors. Decreases in WBCs were observed in males (19 and 21% in the low- and
high-exposure groups, respectively) and in high-exposure females (33% decrease, compared with
controls) (see Table B-7), but the reported values fall within the normal range (Giknis and
Clifford. 2006). Differential counts were not reported. Statistically significant changes in HGB
and HCT in high- and low-exposure males, respectively, were not biologically relevant, and no
effect on RBCs was observed. Serum chemistry changes in males were unremarkable, and serum
chemistry data for end-of-exposure females were not reported due to hemolysis in most samples
' GRABIT (https://www.mathwoiks.com/matlabcentral/fileexchange/7173-grabit') is an application of MATLAB and
extracts data points from an image file using a graphical user interface.
21
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of female rat blood. The study authors did not consider any of these changes to be biologically
significant. No organ weight data were presented.
Histopathology data were available for a limited number of tissues from animals
euthanized at 12 months or that died earlier (see Table B-8). No statistically significant
non-neoplastic lesions were observed at 12 months in exposed rats, although renal tubular
dilatation in male rats (1/11, 2/10, and 4/11 in control, low-, and high-exposure rats,
respectively) was considered by the study authors to be biologically significant. In recovery
animals, insufficient data were provided to allow estimation of mortality incidence during the
recovery period. Histopathology findings were the only results reported at the end of the
recovery period (see Table B-8). At 24 months, high incidences of chronic progressive
nephropathy (CPN), a spontaneous age-related condition, were observed in all male (ranging
from 92 to 100%) and female (ranging from 14 to 29%) rat groups, including controls, regardless
of dose. Medullary mineralization and papillary hyperplasia, changes not typically associated
with CPN (U.S. EPA. 1991). were significantly increased in the high-exposure males, but not in
females, relative to controls. Unlike a2u-g nephropathy, CPN affects both sexes of rats and mice
but represents a different spectrum of lesions not limited to those associated with a2u-g
nephropathy (e.g., basement membrane thickening, nuclear crowding) and is more pronounced in
older animals (Hard et at.. 2009). In addition, renal tubular degeneration was seen in one control
and two exposed male rats. The study authors considered the renal lesions in males to be
consistent with a2u-g "hydrocarbon" nephropathy.
Tumor incidence data show no relationship between exposure to methylcyclohexane and
tumor formation under the conditions of the study (see Table B-9). The only statistically
significant finding was an increase in the incidence of unspecified testicular tumors in males
from the low-exposure group, but not the high-exposure group, at the 12-month sacrifice (0/11,
5/10, and 2/10 for the control, low-, and high-exposure groups, respectively). The study authors
noted that these were common spontaneous tumors in their rats; incidences of testicular
interstitial cell tumors were 89-96%) in the male rats (including controls) at 24 months. There
was no increase in renal tumors in the male rats, which is noteworthy relative to the study
author's contention that nonneoplastic renal lesions seen in male rats at 24 months may have
been related to a2u-g nephropathy, a condition associated with development of kidney tumors. In
females, there was only a nonsignificant increase in the incidence of mammary gland
fibroadenomas (0/47, 4/50, and 6/48 in the control, low-, and high-exposure groups,
respectively). The study authors indicated that all the neoplastic changes seen were those
expected in aging animals of this species.
A NOAEL of 1,607 mg/m3 and a LOAEL of 8,048 mg/m3 were identified based on
significantly increased incidences of medullary mineralization and papillary hyperplasia in male
rats at the end of the observation period at 24 months. The study authors considered these lesions
to be related to a2u-g nephropathy, and therefore not relevant to humans, but the extent to which
the data support that conclusion is unclear. There was no detailed discussion in the document.
Medullary mineralization and papillary hyperplasia are both known to occur in the later stages of
the progression in a2u-g-associated nephrotoxicity (U.S. EPA. 1991). Changes that typically
occur in the earlier stages of a2u-g-associated nephrotoxicity, such as increases in hyaline
droplets containing a2u-g, single cell necrosis, and granular casts, were not observed, but the
study did not include examination of rats before 12 months, when observation of these changes
(especially hyaline droplets and single cell necrosis) would have been more likely. Exacerbation
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of spontaneous CPN is another feature of a2u-g nephropathy that was not seen in this study
(possibly, however, because almost all male rats had the lesion, obscuring any potential
difference across groups, and lesion severity was not reported). The lack of renal tumors is
noteworthy, as a2u-g nephropathy is often associated with development of kidney tumors, but
not definitive, because tumor development depends on many factors (e.g., dose, exposure
duration, etc.). Altogether, two of the three criteria (increased hyaline droplet accumulation and
positive identification of the a2u-g protein) required by the U.S. EPA guidance (U.S. HP A. 1991)
to demonstrate a2u-g nephropathy due to methylcyclohexane exposure are not satisfied; thus, the
male rat kidney data are considered relevant for humans. The reported concentrations of 0, 1,607,
or 8,048 mg/m3 correspond to human equivalent concentration for extrarespiratory effects
(HECer) values of 0, 287.0, and 1,437 mg/m3, respectively7.
Mice
Limited results were reported for female mice. Based on the number of animals examined
for histopathology at or before the 1-year sacrifice, there appeared to be a slight increase in
mortality with exposure (9/200, 15/200, and 19/200 early deaths in the control, low-, and
high-exposure groups, respectively), but differences from control were not statistically
significant (p > 0.05 by two-tailed Fisher's exact test performed for this review). The study
authors did not report any effect on mortality. The timing and causes of death were not reported,
hindering any further analysis or interpretation of these results. For mice allowed to recover for
1 year after inhalation exposure to methylcyclohexane (161-171/group), insufficient data
precluded the estimation of the mortality incidence during the recovery period. Clinical signs and
body-weight results were not reported. Hematology and serum chemistry analyses were not
performed. No organ weights were reported. At 24 months, the incidences of multiple uterine
cysts were higher than controls at both exposure concentrations (10/164, 22/158, and 23/152 for
the control, low-, and high-exposure groups, respectively) and the incidences of malignant
lymphoma were higher than controls in the high-exposure group (45/171, 44/162, and 56/155 for
the control, low-, and high-exposure groups, respectively). However, the increases were within
the range of normal variation for these common lesions in aged mice (Ward, 2006). The study
authors did not consider any histopathological findings to be statistically or biologically
significant.
The high concentration of 8,048 mg/m3 is tentatively identified as a NOAEL based on the
lack of adverse effects seen in female mice. There is some uncertainty due to the limited
endpoints evaluated. The reported concentrations of 0, 1,607, or 8,048 mg/m3 correspond to
HECer values of 0, 287.0, and 1,437 mg/m3, respectively8.
7HEC values based on extrarespiratory effects were calculated by treating methylcyclohexane as a Category 3 gas
and using the following equation from U.S. EPA (1994) methodology: HECer = exposure concentration (mg/m3) x
(hours/day exposed 24 hours) x (days/week exposed 7 days) x ratio of blood-gas partition coefficient (logATbi00d)
(animal:human), using a default coefficient of 1 since the rat log/v'hiood (0.79) is greater than the log/M,i00d (0.61) as
indicated by Abraham et al. (2005).
8HEC values based on extrarespiratory effects were calculated by treating methylcyclohexane as a Category 3 gas
and using the following equation from U.S. EPA (1994) methodology: HECer = exposure concentration
(mg/m3) x (hours/day exposed 24 hours) x (days/week exposed 7 days) x ratio of blood-gas partition coefficient
(log/vhiood) (animakhuman), using a default coefficient of 1 since the mouse logATbi00d is unknown; the human
logATbbod is 0.61.
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Hamsters
No changes in the incidence of male hamster mortality during the 1-year exposure period
were discernable. Male hamsters exposed to either 1,607 or 8,048 mg/m3 methylcyclohexane for
1 year showed mean body-weight deficits exceeding 10% relative to controls, but not differing
between the two exposed groups. The data were not statistically analyzed, and no variance data
were provided. The decreases in mean body weight were evident within a month of the start of
exposure and continued to the end of the exposure period; however, body weight changes did not
persist following recovery. Hematology and serum chemistry endpoints were not measured in
hamsters. Histopathological examinations of tissues from male hamsters showed no
treatment-related findings at the end of exposure at 12 months or the end of observation at
24 months.
A LOAEL of 1,607 mg/m3 was determined for decreased body weight in male hamsters.
Deficits in mean values were seen in both dose groups and exceeded 10%, but did not differ
between dose groups. Statistical analysis could not be performed due to failure of the study
authors to provide any measure of variance. The reported concentrations of 0, 1,607, and
8,048 mg/m3 correspond to HECer values of 0, 287.0, and 1,437 mg/m3, respectively9.
Dogs
All beagle dogs (four/sex/group) exposed by inhalation to methylcyclohexane for 1 year
survived through another 5 years postexposure. Canine body-weight data were not provided. The
only biochemistry results provided in the study were serum ALT levels. The data were
graphically presented by study week with no measure of variance. Transient increases (Week 7
and Weeks 39-43) seen in the 8,048 mg/m3 group were attributed to one dog, and changes in the
1,607 mg/m3 group observed during Weeks 39-43 were attributed to two animals. No significant
differences in ALT levels were observed during the 5-year postexposure period. The study
authors noted that during the 5-year observation period, there were no indications of renal effects
(API, 1985). The study authors did not consider any of the observed lesions in the dogs to be
biologically or statistically significant. There were no treatment-related increased incidences of
neoplastic tumors in dogs.
A NOAEL of 8,048 mg/m3 was determined for the lack of clearly adverse effects in dogs
exposed to methylcyclohexane for 1 year. This determination is tentative due to the small
numbers of dogs used, the limited number of endpoints evaluated, and the long postexposure
observation period prior to their histopathologic examination. The reported concentrations of 0,
1,607, and 8,048 mg/m3 correspond to HECer values of 0, 287.0, and 1,437 mg/m3,
respectively10.
9HEC values based on extrarespiratory effects were calculated by treating methylcyclohexane as a Category 3 gas
and using the following equation from U.S. EPA (1994) methodology: HECer = exposure concentration
(mg/m3) x (hours/day exposed 24 hours) x (days/week exposed 7 days) x ratio of blood-gas partition coefficient
(log/v'hiood) (animal:human), using a default coefficient of 1 since the hamster logATbi00d is unknown; the human
logATbbod is 0.61.
10HEC values based on extrarespiratory effects were calculated by treating methylcyclohexane as a Category 3 gas
and using the following equation from U.S. EPA (1994) methodology: HECer = exposure concentration
(mg/m3) x (hours/day exposed 24 hours) x (days/week exposed 7 days) x ratio of blood-gas partition coefficient
(log/v'hiood) (animal:human), using a default coefficient of 1 since the hamster logATbi00d is unknown; the human
logATbbod is 0.61.
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2.3. OTHER DATA (SHORT-TERM TESTS, OTHER EXAMINATIONS)
2.3.1. Genotoxicity
Table 4 A provides an overview of genotoxicity studies of methylcyclohexane. The
limited data suggest that methylcyclohexane is not genotoxic. The chemical produced negative
results in two Ames tests with Salmonella typhimurium strains TA98, TA100, TA1535, and
TA1537 and Escherichia coli WP2uvrA both in the presence and absence of rat liver S9
metabolic activation (JKCDB. 2011a; EC HA. 2001a). M ethy 1 cy cl ohexane also did not induce
chromosomal aberrations in Chinese hamster lung cells in the presence or absence of rat liver S9
metabolic activation (JKCDB. 201 lb; ECHA. 2001b).
Methylcyclohexane coating on standard carbon black particles enhanced the effect of the
carbon black particles to reduce viability and increase oxidative deoxyribonucleic acid (DNA)
damage (fragment length analysis with restriction enzyme assay) in RAW 264.7 murine
macrophages (Rim et at.. 2011). but the relevance of these findings to genotoxicity of
methylcyclohexane is unclear.
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Table 4A. Summary of Methylcyclohexane Genotoxicity
Endpoint
Test System
Doses/Concentrations
Tested3
Results
Without
Activationb
Results
With
Activationb
Comments
References
Genotoxicity studies in prokaryotic organisms
Mutation
Salmonella typhimurium TA98,
TA100, TA1535, and TA1537
and Escherichia coli WPluvrA;
bacteria were tested with (0 or
0.781-200 ng/plate) and
without (0 or
0.097-25 ng/plate) metabolic
activation by S9 rat liver
fraction
Without activation: TA98
(25 ng/plate), TA100 and
TA1535 (3.13 ng/plate),
TA1537 (12.5 ng/plate),
WP2urvA (25 |ig/plate)
With activation: TA98,
TA100, and TA1535
(25 ng/plate), TA1537
(100 ng/plate), WP2urvA
(200 ng/plate)
Ames assay. No evidence of mutagenicity in
any of the strains tested with or without S9
activation.
Adequate study. Cytotoxicity was seen at
the highest one or two concentrations tested
in each strain, with and without activation,
as expected based on a preliminary study.
ECHA (2001a)
Mutation
S. typhimurium TA98, TA100,
TA1535, and TA1537 and
E. coli WP2mr. 1: bacteria were
tested with and without
metabolic activation by S9 rat
liver fraction (0 or
4.69-150 ng/plate for
S. typhimurium or
4.69-600 |ig/platc for coli)
With and without activation:
TA98, TA100, TA1535, and
TA1537 (150 ng/plate),
WPluvrA (600 |ig/plate)
Ames assay. No evidence of mutagenicity in
any of the strains tested with or without S9
activation.
Adequate study. Cytotoxicity was seen at
the highest one or two concentrations tested
in each strain, with and without activation,
as expected based on a preliminary study. It
was noted that no precipitates were seen at
any concentration.
JECDB (2011a)
Genotoxicity studies in mammalian cells—in vitro
CA
CHL/IU cells; tested for 6 h
with and without metabolic
activation by S9 rat liver
fraction and for 24 and 48 h
without metabolic activation (0
or 245-980 ng/mL)
980 iig/mL
No increase in CAs in any test condition.
Adequate study. No cytotoxicity was seen.
ECHA (2001b)
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Table 4A. Summary of Methylcyclohexane Genotoxicity
Endpoint
Test System
Doses/Concentrations
Tested3
Results
Without
Activationb
Results
With
Activationb
Comments
References
CA
CHL/IU cells; tested for 6 h
with and without metabolic
activation by S9 rat liver
fraction and for 24 h without
metabolic activation (0 or
40-160 ng/mL)
160 iig/mL
No increase in CAs in any test condition.
Adequate study. Cytotoxicity interfered with
detection of CAs only at the highest
concentrations tested (160 ng/mL in the 6-h
test and 120 ng/mL in the 24-h test). It was
noted that no precipitates were seen at any
concentration.
JECDB (20lib)
aLowest effective dose for positive results, highest dose tested for negative results.
b - = negative.
CA = chromosomal aberration; CHL = Chinese hamster lung.
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2.3.2. Supporting Human Studies
Table 4B summarizes epidemiological studies that investigated health effects in
populations with exposure to multiple VOCs that included methylcyclohexane. Due to the
confounding exposures to mixed VOCs in these studies, they are of limited use for
methylcyclohexane hazard identification and do not provide data for quantitative dose-response
analysis.
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Table 4B. Other Studies
Test
Materials and Methods
Results
Conclusions
References
Supporting evidence-noncancer effects in humans following inhalation exposure
Case-control
Within a group of elementary school students in Seoul, Korea,
asthma cases were identified based on a questionnaire and
confirmed by a physician (n = 33); controls matched for age
and sex were selected from the non-asthmatic students (n = 40).
Personal, indoor, and outdoor sampling for 10 VOCs, including
methylcyclohexane, was performed over 3 days. Levels of
VOCs were compared across groups.
Cases were exposed to significantly higher
levels of methylcyclohexane than controls in
outdoor air, but to similar levels in indoor air
and personal air samples, which contained
higher levels overall. Cases also had
significantly higher exposure than controls to
benzene, toluene, and o-xylene. After adjusting
for confounding factors in multiple regression
analysis, no significant relationship was seen
between VOC exposure and asthma.
The study found no
evidence of an
association between
childhood asthma and
exposure to
methylcyclohexane.
Hwang et al.
(2011)
Occupational
Liver function was assessed in a group of 42 workers who had
been exposed to a variety of solvents at a single U.K. factory
for an average of 11.4 yr and a group of 41 healthy U.K.
workers with no history of occupational solvent exposure and a
history of normal liver function test results in routine testing.
Urine and blood samples were collected from each subject at
the workplace. For solvent workers, personal exposure to
solvents was monitored on the day of biological monitoring by
using diffusive sampling tubes. Methylcyclohexane was among
the primary exposures of the solvent workers (6 ppm or
20 mg/m3). Other solvents detected at similar levels were
toluene, //-heptane, and xylene.
Serum levels of ALT, AST, ALP, GGT, and
bilirubin in the solvent-exposed workers did not
differ from controls. The only findings in
solvent-exposed workers relative to controls
were increased prevalence of abnormally high
urinary bile acid and increased mean urinary
levels of 6 p-hydroxycortisol (and ratio of
6 p-hydroxycortisol to urinary free Cortisol).
Within the solvent-exposed group, there was no
relationship between personal atmospheric
measurements of solvents or years of
employment and urinary bile acids or
6 p-hydroxycortisol levels.
The study found
limited evidence of
potential liver effects
in workers exposed to
multiple solvents but
no toxicologically
relevant effects
specifically attributed
to methylcyclohexane
exposure.
Mason et al.
(1994)
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Table 4B. Other Studies
Test
Materials and Methods
Results
Conclusions
References
Occupational
Test subjects were 21 workers at jobs with moderate-to-high
exposure to organic solvents employed for at least 2 years in
one of five military offset print shops in Belgium or Germany.
Personal air sampling conducted for each worker on a single
normal workday showed that workers in each plant were
exposed to an average of 10 organic solvents and the group as a
whole was exposed to over 25 different solvents
(methylcyclohexane was among the most common, along with
trichloroethane and //-heptane). Methylcyclohexane
concentrations in the exposed group ranged from not detected
to 9.5 mg/m3 in workplace air (<5% of the total concentration
of measured solvents). Controls were 21 military drivers
presumed to be without occupational solvent exposure matched
for age, sex, education level, and spoken language
(Dutch/French/German). Participants answered a general
questionnaire on age and lifestyle factors, reported
neurotoxicity symptoms, and provided medical history; were
given a physical exam; and underwent digital oximetry and
eight neurobehavioral tests.
Print shop workers had significantly more and
longer-lasting nocturnal oxygen desaturations
during sleep than controls; however, there was
no quantitative relationship between exposure
to solvents (estimated based on duration of
employment and hygienic practices) and
sleep-related events. In the questionnaire,
exposed workers had more complaints than
controls, particularly regarding mood. Hand-eye
coordination was reduced in print shop workers
compared to controls. There were no other
neuropsychiatric or neurobehavioral differences
between exposed workers and controls.
The study found some
evidence for more and
longer-lasting sleep
disturbances in
solvent-exposed print
shop workers than in
unexposed controls
but no toxicologically
relevant effects
specifically attributed
to methylcyclohexane
exposure.
Laire et al.
(1997)
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Table 4B. Other Studies
Test
Materials and Methods
Results
Conclusions
References
Case-control
Cases were 108 women clinically diagnosed with spontaneous
abortion at a single hospital in Italy (in a region where many
women work in the shoe industry, where solvents are widely
used) in 1987-1988. Controls were 108 women discharged
from the same hospital following normal delivery, matched
with cases for birth year, calendar year of hospital admission,
and city of residence. All participants were interviewed using a
standard questionnaire regarding pregnancy history, lifestyle
factors, medications taken during pregnancy, and jobs during
pregnancy (including details relating to use of solvents). Cases
and controls were categorized based on solvent exposure (none,
low, or high). Because solvent mixtures were generally used, no
attempt was made to specify any particular solvent in detail.
Out of 50 women exposed to solvents, 47 worked in
shoemaking and 3 worked in a leather goods factory. In
monitoring of 31 shoe factories from 1982 to 1992, 12 different
solvents were detected, including methylcyclohexane
(30-120 mg/m3).
Raw ORs for spontaneous abortion were
1.0 (based on 78 cases and 88 controls) in
women with no solvent exposure, 1.13 (based
on 12 cases and 12 controls) in women with low
solvent exposure, and 2.54 (based on 18 cases
and 8 controls) in women with high solvent
exposure. The elevated OR in women with high
solvent exposure was not statistically
significant. Significant increases in ORs were
found for smoking, coffee consumption,
previous abortions, and marital status as single.
After adjustment for confounding factors using
stepwise logistical regression, the RR for
spontaneous abortion was significantly
increased in women with high solvent exposure
(3.85 [95% CI 1.24-11.9]).
The study found
evidence that
exposure to solvents
may increase the risk
of spontaneous
abortion but no
toxicologically
relevant effects
specifically attributed
to methylcyclohexane
exposure.
Agnesi et al.
(1997)
Cross-sectional
study
Within a cohort of 976 neonates born in Leipzig, Germany
recruited between December 1997 and January 1999,
85 children (43 boys and 42 girls) in a randomly selected
subgroup were evaluated for immune status at birth (umbilical
cord blood taken at delivery and analyzed for T-cell function
using intracellular cytokine staining) and exposure to VOCs, as
assessed by passive sampling in the children's bedrooms for
4 wk after birth and questionnaires completed by the parents
about possible sources of VOC exposure during pregnancy
(e.g., painting, flooring, smoking, etc.). Methylcyclohexane was
among 28 VOCs measured in the children's bedrooms, with a
relatively low median concentration of 1.6 |ig/m3.
No significant association was found between
exposure to methylcyclohexane and
cytokine-producing cord blood T cells
(i.e., percentages of T cells producing IFN-y,
TNF-a, IL-2, or IL-4). Statistically significant
associations were found for several of the other
VOCs.
The study found some
evidence that
exposure to VOCs
may have an influence
on immune status of
the newborn child, but
no toxicologically
relevant effects
specifically attributed
to methylcyclohexane
exposure.
Lehmann et
al. (2002)
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Table 4B. Other Studies
Test
Materials and Methods
Results
Conclusions
References
Supporting evidence-cancer effects in human following inhalation exposure
Cancer cluster
After a professional football team moved to a new stadium in
New Jersey in 1976, four team members developed cancer
between 1980 and 1987: one each of non-Hodgkin's
lymphoma, glioblastoma, angiosarcoma, andHodgkin's
disease. Measurements for VOCs were taken in June-July 1988
from a practice field, a natural grass field outside of the
stadium, the new stadium, and a racetrack used by the athletes.
Methylcyclohexane was among 16 VOCs detected, at relatively
low levels ranging from 0.1 to 0.4 ppb (0.4-1.6 |ig/m3). A
cohort of 7,889 people who had worked at least 1 d at the
facility was constructed. A total of 146 cancer cases and
65 cancer deaths in the cohort occurring between January 1,
1978 and December 31, 1987 were analyzed in relation to New
Jersey cancer morbidity and mortality data.
No significant excess of cancer incidence or
mortality was observed for all tumors combined
or for tumors at any specific site, even with
consideration for latency, nor was there any
difference between indoor and non-indoor
workers.
The study found no
evidence that tumors
were increased in the
cohort studied and
was uninformative
regarding the
potential
carcinogenicity of
methylcyclohexane.
Kraut et al.
(1991)
Supporting evidence-noncancer effects in animals following oral exposure
Acute (oral)
Female rats (5/group, strain unknown) were administered single
doses of 0, 1,250, 2,500, or 5,000 mg/kg of methylcyclohexane
via gavage (vehicle appears to have been 0.2% carboxyl methyl
cellulose). Animals were observed for 14 d. Endpoints
evaluated included mortality, clinical findings, and body-weight
changes. Gross necropsies and histopathological examinations
were performed.
No deaths were observed. Clinical signs
(depression, soft feces, decreased locomotion,
solid perineal region, crouching position, and
anorexia) were reportedly observed in all
groups in a dose-related manner. Other effects,
observed only at 5,000 mg/kg, were decreased
body weight (<10%, NS), increased absolute
(10-13%, NS) and relative (19-25%, p < 0.05)
liver and kidney weights, and kidney lesions
(glomerular atrophy, congestion/hemorrhage,
and focal degeneration/necrosis each in
5/5 versus 0/5 in controls).
The rat LD0 was
>5,000 mg/kg.
Increased liver and
kidney weights and
kidney lesions were
seen at 5,000 mg/kg
in female rats.
Kim et al.
(2011c)
(This study is
published in
Korean, with
abstract and
data tables in
English.)
Acute (oral)
Rats (number, strain, and sex not specified) received a single
oral dose of technical-grade methylcyclohexane (70%
methylcyclohexane, 10% cyclohexane, 20%
dimethylcyclohexane) neat. No additional details were
provided.
ND
The rat LD5o was
>3,200 mg/kg.
Eastman
Kodak (1994)
32
Methylcyclohexane
-------
EPA/690/R-23/007F
Table 4B. Other Studies
Test
Materials and Methods
Results
Conclusions
References
Acute (oral)
Mice (number, sex, and strain not specified) were orally
administered methylcyclohexane (purity not reported). No
details were provided.
ND
The mouse LD5o was
2,250 mg/kg.
ECHA
(1982b)
Acute (oral)
Young white rabbits (one per dose) were administered single
doses of methylcyclohexane (97% pure, 3% toluene) at eight
dose levels ranging from 1,000 to 10,000 mg/kg via gavage
(use of vehicle not specified). Animals were observed for up to
14 d. Endpoints evaluated included mortality, clinical signs,
body weights, and gross necropsy. Blood was analyzed for
cellular elements.
Mortality occurred at >4,500 mg/kg; four
rabbits at these dose levels died within 84 hours
of dosing, while four rabbits at lower doses (up
to 4,000 mg/kg) survived. Severe diarrhea was
seen in the rabbits, including all that died,
within 3 hours of dosing. All animals lost
weight after dosing, but not in proportion to
dose. No hematological changes were found.
Necropsy of animals that died showed damage
to the heart, liver, and kidneys that may have
been due in part to intercurrent severe
pulmonary infection.
The rabbit LD0 and
LDLo were 4,000 and
4,500 mg/kg,
respectively.
Treon et al.
(1943b)
Short-term
(oral)
Male F344 rats (eight treated, six controls) were administered
water or methylcyclohexane neat at a dose of 800 mg/kg every
other day for 14 d. Kidneys were examined for histopathology
and specifically for lesions associated with a2u-g nephropathy.
Only "very slight traces of nephropathy" were
observed.
No increase in a2u-g
nephropathy was
found in male rats
treated with
400 mg/kg-d for 14 d.
Pamell et al.
(1988)
Short-term
(oral)
Male and female Cij:CD (Sprague Dawley) rats (number not
specified) were administered methylcyclohexane doses of 0,
100, 300, or 1,000 mg/kg-d via gavage in corn oil for 14 d.
No deaths occurred. Increased salivation was
seen in both sexes at 1,000 mg/kg-d.
No mortality occurred
in rats dosed by
gavage with
<1,000 mg/kg-d for
14 d.
ECHA
(2001c)
Preliminary
range-finding
study
Supporting evidence-noncancer effects in animals following inhalation exposure
Acute
(inhalation)
Rats (strain, sex, and number per group not reported) were
exposed to technical-grade methylcyclohexane (70% pure) at
concentrations of 11,000, 82,000, 184,000, or 260,000 mg/m3
for 0.22-6 h. Endpoints included mortality and clinical signs.
Mortality was observed at >82,000 mg/m3
within 14-70 min of exposure. Lethargy, ataxia,
and terminal convulsions were observed in
animals that died. At 11,000 mg/m3, no deaths
occurred, and lethargy was the only clinical
sign.
The rat LCo (6 h) and
LClo were
11,000 mg/m3 and
82,000 mg/m3,
respectively.
ECHA (1965)
33
Methylcyclohexane
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EPA/690/R-23/007F
Table 4B. Other Studies
Test
Materials and Methods
Results
Conclusions
References
Acute
(inhalation)
Rats (number, strain, and sex not reported) were exposed to a
cycloparaffinic solvent (90% methylcyclohexane) at a vapor
concentration of 7,700 ppm (30,920 mg/m3) for 4 h.
Sudden violent seizures were observed that
resulted in traumatic injury in one animal,
demonstrated by lesions to the spinal cord and
surrounding tissues and clinical presentation of
hindlimb paralysis.
Seizures occurred in
rats at 30,900 mg/m3.
Shell
Chemical
(1999)
Acute
(inhalation)
Rats (strain, number, and sex not reported in English) were
exposed to methylcyclohexane vapor concentrations of 0, 100,
500, 2,500, or 5,000 ppm (0, 402, 2,010, 10,040, or
20,100 mg/m3, respectively) for 4 h.
ND
The rat LC50 (4 h) was
15,054 mg/m3.
Kim et al.
(2006)
(This study is
published in
Korean, with
abstract and
data tables in
English.)
Acute
(inhalation)
Sprague Dawley rats (20 males/group) were exposed,
whole-body, to methylcyclohexane vapor concentrations of 0,
4,172, or 6,565 ppm (0, 16,750, or 26,360 mg/m3, respectively)
for 1 h. Half of the animals (10/group) were euthanized at the
end of the exposure period; the remaining animals were
necropsied after a 28-d observation period. Endpoints evaluated
included mortality, clinical signs, body weight, gross
pathology, and histopathological examinations.
No mortality was observed. An increase in
activity occurred at 16,700 mg/m3;
hyperactivity, slight loss of coordination, and
prostration were observed at 26,300 mg/m3. No
effects on body weight or gross or
histopathological lesions were observed.
The rat LCo (1 h) was
>26,300 mg/m3.
Clinical signs
indicative of CNS
effects were seen at
26,300 mg/m3.
Kinkead et al.
(1979)
Acute
(inhalation)
ICR mice (20 females/group) were exposed, whole-body, to
methylcyclohexane vapor concentrations of 0, 4,758, or
6,564 ppm (0, 19,110, or 26,360 mg/m3, respectively) for 1 h.
Half of the animals (10/group) were euthanized at the end of
the exposure period; the remaining animals were necropsied
after a 28-d observation period. Endpoints evaluated included
mortality, clinical signs, body weight, gross pathology, and
limited histopathological examinations (control and
low-exposure animals only).
No mortality was observed. At 19,100 mg/m3,
hyperactivity was observed during the exposure
period. At 26,300 mg/m3, hyperactivity
occurred along with coordination loss and
prostration. One mouse showed tono-clonic
spasms. Minimal-to-mild cytoplasmic changes
were found in the liver of 1/10 controls and
5/10 exposed animals. No other effects were
observed.
The mouse LCo (1 h)
was >26,300 mg/m3.
Clinical signs
indicative of CNS
effects and slight liver
changes were seen at
26,300 mg/m3.
Kinkead et al.
(1979)
Acute
(inhalation)
Mice (number, strain, and sex not available) were exposed to
methylcyclohexane vapors for 2 h.
ND
The mouse LC50 (2 h)
was 41,000 mg/m3
ECHA
(1982a)
34
Methylcyclohexane
-------
EPA/690/R-23/007F
Table 4B. Other Studies
Test
Materials and Methods
Results
Conclusions
References
Acute
(inhalation)
Mice (strain, sex, and number per group not reported) were
exposed to methylcyclohexane at concentrations ranging from
30,000 to 50,000 mg/m3 for up to 2 h. Animals were monitored
for mortality and clinical signs. The duration of observations
was not specified. Necropsies were performed.
Mortality occurred at 50,000 mg/m3 (number of
deaths not reported); some deaths occurred
within 1-2 min after the start of exposure.
Clinical signs in animals that died included
lethargy, narcosis, prostration, clonic
convulsions, and labored breathing. The
minimum narcotic concentration was
40,000 mg/m3.
The mouse LCo (2 h)
and LClo were
40,000 and
50,000 mg/m3,
respectively.
ECHA (1929)
Acute
(inhalation)
Rabbits (four per group; strain and sex not reported) were
exposed to a methylcyclohexane vapor concentration of
59,900 mg/m3 for 70 min.
There was 100% mortality in animals exposed
to 59,900 mg/m3. Severe convulsions, narcosis,
labored breathing, salivation, conjunctival
congestion with mucoid secretion and
lacrimation, and diarrhea were observed.
The rabbit
LCioo (70 min) was
59,900 mg/m3.
Treon et al.
(1943a)
Acute
(inhalation)
Beagle dogs (four per group, sex not specified) were exposed,
whole-body, to methylcyclohexane concentrations of 0 or
16,300 mg/m3 for 1 h. Animals were observed for 28 d.
Endpoints evaluated included mortality, clinical signs, and
body weights. Field trial evaluations were performed prior to
and after exposure. Neurological examinations (flexor reflex,
extensor thrust, tonic neck, tonic eye, righting, and placing
reflexes) were performed after exposure. Hematology and
clinical chemistry were done at 2 and 4 wk postexposure.
Necropsies and complete histology were performed after the
28-d observation period.
No mortality was observed. There were no
exposure-related effects on any of the endpoints
tested.
The dog LCo (1 h)
was >16,300 mg/m3.
There was no
evidence of CNS
effects.
Kinkead et al.
(1979)
Short-term
(inhalation)
Rabbits (four per group; strain and sex not reported) were
exposed 6 h/d, 5 d/wk to methylcyclohexane vapor
concentrations of 0, 28,750, or 39,550 mg/m3 for 2 wk,
11,350 mg/m3 for 3 wk, or 21,900 mg/m3 for 4 wk. Endpoints
included mortality, clinical sings, rectal temperature, body
weight, and hematology. Histology was performed following a
2-mo recovery period.
Effects were mortality (in four of four rabbits),
convulsions, light narcosis, labored breathing,
salivation, conjunctival congestion, and weight
loss at 39,600 mg/m3; mortality (in one of four
rabbits), lethargy, impaired coordination, and
decreased body weight at >28,750 mg/m3; only
slight lethargy at 21,900 mg/m3; and only
minimal liver and kidney lesions at
11,350 mg/m3.
The rabbit LCo and
LClo were 21,900 and
28,750 mg/m3,
respectively, with
repeated exposure.
Treon et al.
(1943a)
35
Methylcyclohexane
-------
EPA/690/R-23/007F
Table 4B. Other Studies
Test
Materials and Methods
Results
Conclusions
References
Subchronic
(inhalation)
Rabbits (four per group; strain and sex not reported) were
exposed to methylcyclohexane vapor for 6 h/d, 5 d/wk at
concentrations of 948 or 4,570 mg/m3 for 10 wk. Rabbits
exposed to clean air served as controls. Endpoints included
mortality, clinical sings, rectal temperature, body weight, and
hematology. Histology (limited details) was performed
following a 2-mo recovery period.
No effects were observed.
No effects were
observed in rabbits at
concentrations up to
4,570 mg/m3 for
10 wk.
Treon et al.
(1943a)
Subchronic
(inhalation)
A single Rhesus monkey (sex not specified) was exposed to
1,460 mg/m3 methylcyclohexane for 6 h/d, 5 d/wk for 10 wk.
Endpoints included mortality, clinical signs, rectal temperature,
body weight, and hematology. Histology was performed
following a 2-mo recovery period.
The monkey survived with no signs of
intoxication. There was a slight fall in the daily
rectal temperature during exposure. The
monkey gained weight during the exposure
period, but a control was not included for
comparison. No microscopic lesions were
observed.
No effects were
observed in a monkey
exposed to
1,460 mg/m3 for
10 wk in a limited
study (single animal
tested, no control).
Treon et al.
(1943a)
Supporting evidence-noncancer effects in animals following other routes of exposure
Acute (dermal)
A single white rabbit (sex, strain, age, and body weight not
provided) had 60 mL of methylcyclohexane applied for 1 h
(12;5-mL portions at 5-min intervals) to a clipped
24-square-inch area of skin (under a hood to prevent inhalation)
for 6 successive days. The corresponding dose provided by the
study authors was 86,700 mg/kg. Endpoints included mortality,
clinical signs, body weight, and gross observations at the site of
application.
The animal survived treatment. Skin irritation at
the site appeared on the 2nd day and increased
somewhat with successive treatments.
Hardening of the skin, thickening, and
ulceration appeared later, and the experiment
was terminated on the 6th day. In contrast to the
other chemicals tested, it was reported that there
was only slight hypothermia and weight loss
(weight was regained within 2 d).
The lethal dose was
>86,700 mg/kg.
There was evidence of
injury to the skin.
Treon et al.
(1943b)
36
Methylcyclohexane
-------
EPA/690/R-23/007F
Table 4B. Other Studies
Test
Materials and Methods
Results
Conclusions
References
Subchronic
(subcutaneous
injection)
Sprague Dawley rats (five/sex/group) were administered daily
subcutaneous injections of methylcyclohexane at 0, 10, 100, or
1,000 mg/kg-d in olive oil 5 d/wk for 13 wk. Endpoints
evaluated included mortality, clinical signs, FOB (including
motility, fall landing test, activity count, heart rate and blood
pressure, and serotonin levels), body weight, hematology,
serum chemistry, sperm counts, measurements of sex
hormones, estrous cyclicity, organ weights, and histopathology.
In the 1,000 mg/kg-d group, 4/5 males and
4/5 females died, all between the 5th and
60th day of the study. No deaths occurred at
<100 mg/kg-d. Body weights were significantly
decreased relative to controls in the
1,000-mg/kg-d males, starting on the 2nd week
of the study. Smaller, transitory body-weight
decreases were also seen in the 1,000-mg/kg-d
females. Body weights in the lower dose groups
did not differ from controls. Animals in the
1,000-mg/kg-d group showed a variety of
lesions in the liver (microgranuloma, bile-duct
proliferation), kidney (hyperemia, protein
casts), and heart (hyperemia, myocardial
necrosis). Incidences were not reported. Few
lesions were seen in the lower dose groups.
Testing results in the 10 and 100 mg/kg-d
groups for hematology, serum chemistry, organ
weights, neurobehavioral endpoints, blood
pressure, serotonin levels, estrous cyclicity in
females, testes and sperm in males, and
hormone levels in both sexes were generally
unremarkable, although some statistically
significant results were found.
The high dose of
1,000 mg/kg-d was a
FEL, based on high
mortality. The mid
dose of 100 mg/kg-d
was a NOAEL.
Kim et al.
(2011b): Kim
et al. (2011c)
This study is
published in
Korean, with
abstract and
data tables in
English.)
a2u-g = alpha 2u-globulin; ALP = alkaline phosphatase; ALT = alanine aminotransferase; AST = aspartate aminotransferase; CI = confidence interval; CNS = central
nervous system; FEL = frank-effect level; FOB = functional observation battery; GGT = y-glutamyl transferase; IFN-y = interferon-gamma; IL-2 = interleukin 2;
IL-4 = interleukin 4; LCo = highest concentration showing no mortality; LClo = lowest concentration that caused death; LC50 = median lethal concentration;
LC100 = lethal concentration causing 100% mortality; LD0 = highest dose showing no mortality; LDLo = lowest dose that caused death; LD50 = median lethal dose;
ND = no data; NOAEL = no-observed-adverse-effect level; NS = not statistically significant; OR = odds ratio; RR = relative risk; TNF-a = tumor necrosis factor-alpha;
U.K. = United Kingdom; VOC = volatile organic compound.
37
Methylcyclohexane
-------
EPA/690/R-23/007F
2.3.3. Supporting Animal Studies
The acute effects of oral and inhalation methylcyclohexane exposure are reported in
Table 4B along with short-term and subchronic studies that evaluated limited endpoints, were
inadequately reported, or were performed via alternate routes of exposure (e.g., dermal or
subcutaneous injection).
Acute lethality studies on methylcyclohexane indicate relatively low lethality via oral and
inhalation routes. In rats, a median lethal dose (LD50) of >3,200 mg/kg was reported in one study
(Eastman Kodak. 1994) and an LDo (highest dose showing no mortality) of >5,000 mg/kg was
reported in another (Kim et al.. 2011c). An LD50 of 2,250 mg/kg was reported in mice (ECHA.
1982b). In rabbits, no deaths occurred at doses up to 4,000 mg/kg, and the minimum lethal dose
was 4,500 mg/kg (Troon et al.. 1943b). In inhalation studies, rats survived exposures up to
26,300 mg/m3 for 1 hour (Kinkead et al.. 1979) and 11,000 mg/m3 for 6 hours (FX HA. 1965); a
4-hour median lethal concentration (LC50) of 15,054 mg/m3 was reported (Kim et al .. 2006).
Mice survived inhalation exposures up to 26,300 mg/m3 for 1 hour (Kinkead et al.. 1979) and
40,000 mg/m3 for 2 hours (ECHA. 1929). with a reported 2-hour LC50 of 41,000 mg/m3 (ECHA.
1982a). Mortality was 100% (4/4) in rabbits exposed to methylcyclohexane vapor concentrations
of 59,900 mg/m3 for 70 minutes (Troon et al.. 1943a). With repeated exposure for 2-10 weeks,
mortality in rabbits occurred at concentrations of 28,750 mg/m3, but not at concentrations
<21,900 mg/m3 (Troon et al.. 1943a). Sublethal effects in the available studies included clinical
signs indicative of central nervous system (CNS) effects, such as narcosis, ataxia, lethargy,
prostration, labored breathing, and convulsions (Shell Chemical. 1999; ECHA. 1965; Treon et
al.. 1943a). Effects on liver and kidney, including increases in organ weight and minimal-to-mild
lesions, were found in some studies (Kim et al.. 2011c; Kinkead et al.. 1979; Treon et al.. 1943a).
One study included specific histopathological examination for renal lesions characteristic of
a2u-g nephropathy in male rats treated with 400 mg/kg-day for 14 days but found only "very
slight traces of nephropathy" (Parnell et al .. 1988). In studies by other routes, dermal exposure
did not cause death in rabbits at a dose of 86,700 mg/kg (Treon et al.. 1943b). while repeated
subcutaneous injection was lethal at 1,000 mg/kg-day, but not at 100 mg/kg-day, in rats in a
13-week study (Kim et al.. 2011b; Kim et al.. 2011a).
2.3.4. Metabolism/Toxicokinetic Studies
Methylcyclohexane is absorbed following oral or inhalation exposure. Absorption
following oral exposure was >89% in rabbits administered single doses of 2.1-2.4 mmol/kg
(equivalent to 200-230 mg/kg) [U-14C]methylcyclohexane by gavage in water, based on total
and fecal radioactivity recoveries of 89.6-93.9 and 0.4-0.7%), respectively, through
approximately 60 hours postdosing (Elliott et al.. 1965). Methylcyclohexane is primarily
absorbed in the lung based on the blood-air partition coefficient (logwood). Based on indirect
assays in F344 rats measuring the rate of loss of methylcyclohexane in closed-battery jar
chambers, the maximum first-order rate constant for gas uptake in rats exposed to <50 ppm was
0.32 hour 1 kg 1 (Andersen. 1981). Rats exposed to 100 ppm (402 mg/m3) for 12 hours had
steady-state blood levels of 5.8 |imol/kg immediately following the end of exposure (Zahlsen et
al.. 1992). Based on these data, a logA'hi,KHi of 0.79 was calculated for rats (Abraham et al.. 2005).
A logKbiood of 0.61 was calculated separately for methylcyclohexane in humans (Abraham et al..
2005; Imbriani et al.. 1985).
Upon absorption, methylcyclohexane is distributed throughout the body.
Methylcyclohexane was found primarily in fat (356 |imol/kg), with lesser amounts in kidney
38
Methylcyclohexane
-------
EPA/690/R-23/007F
(94.7 |imol/kg), brain (45.7 |imol/kg), liver (30.1 |imol/kg), and blood (5.8 |imol/kg),
immediately following a 12-hour inhalation exposure to 100 ppm (402 mg/m3)
methylcyclohexane vapor (Zahisen et al.. 1992). Levels in tissues other than fat were similar
when the exposures were repeated on 2 additional days, suggesting that steady-state was
achieved within the daily 12-hour exposure period in these tissues. Levels in fat increased from
356 ± 41 |iinol/kg after Day 1 to 460 ± 79 |imol/kg after Day 2 and 550 ± 99 |imol/kg after
Day 3, suggesting some accumulation in fat. Twelve hours after the end of the last exposure
period, levels (of parent compound; metabolites were not monitored) had dropped close to
0 |imol/kg in all monitored tissues (2.9, 0.5, 0.5, and 0.1 |imol/kg left in kidney, liver, brain, and
blood, respectively) except fat, which still contained 231 |imol/kg. Based on these data, a
fat-blood partition coefficient (log Pm) of 1.95 was calculated for rats (Abraham and Ibrahim.
2006).
Methylcyclohexane is metabolized primarily via hydroxylation of the ring structure,
followed by conjugation with glucuronic acid (Parnell et al.. 1988; Frommer et al.. 1970; Elliott
et al.. 1965). In rabbits administered single doses of 2.1-2.4 mmol/kg (equivalent to
206-236 mg/kg) [U-14C]methylcyclohexane by gavage in water and monitored for
approximately 60 hours, most of the metabolites identified were glucuronide conjugates of the
following methylcyclohexanols in the urine: trans-4-, cis-3-, trans-3-, cis-4-, trans-2-, and cis-2-,
accounting for 14.7, 11.5, 10.5, 2.4, 1.3, and 0.6% of the administered radiolabel, respectively
(Elliott et al .. 1965). Small amounts of benzoic acid and cyclohexylmethanol were also observed
in the urine, which the study authors suggested may have resulted from hydroxylation of the
methyl group on the cyclohexane ring and subsequent aromatization. In male F344 rats orally
dosed once with 800 mg/kg methylcyclohexane, metabolites identified in urine collected over the
ensuing 48 hours were glucuronide conjugates of the following methylcyclohexanols:
/ra/7.s-2-hydroxy-6'/.s-4, 67.s-2-hydroxy-/ra/7.s-4, 67.s-2-hydroxy-67.s-4-, trans-3, trans-4, and
cyclohexylmethanol; relative abundances in the gas chromatograph tracing were 23.4, 15.7, <10,
<10, <10, and <10%, respectively (Parnell et al.. 1988)". Deichman and Thomas (1943) and
Treon et al. (1943b) also reported glucuronic acid conjugates in the urine of rabbits dosed orally
with methylcyclohexane. Using rat liver microsomes in vitro, Frommer et al. (1970)
demonstrated that hydroxylation of methylcyclohexane in the liver is mediated by cytochrome
P450 (CYP450) monooxygenases and that metabolism can be induced by using liver microsomes
from rats pretreated with phenobarbital.
The rapid loss from tissues (other than fat) of parent methylcyclohexane following
inhalation exposure in rats (Zahlsen et al.. 1992) suggests that metabolism and elimination of
methylcyclohexane are rapid (on the order of days). Data from Elliott et al. (1965) also support
rapid metabolism and elimination of methylcyclohexane, with elimination occurring primarily as
metabolites in the urine following oral dosing in rabbits. The percentages of administered
radioactivity recovered were 54.2-77.4%) in urine, 5.0-8.6%) in expired air as CO2, 4.4-15.9%) in
expired air as parent compound, 0.4-0.7%) in feces, and only 2.8-5.9%) remaining in body tissues
approximately 60 hours after dosing, meaning that the vast majority of administered radioactivity
was eliminated from the body within 60 hours, mostly as metabolites in the urine.
11 The study authors reported specific values for each of the metabolites, but the numbers for the less-abundant
metabolites differed between the text and Table 1 of Parnell et al. (1988). necessitating the presentation here of each
as <10%.
39
Methylcyclohexane
-------
EPA/690/R-23/007F
2.3.5. Mode-of-Action/Mechanistic Studies
The liver and kidney are primary target organs following methylcyclohexane exposures.
No mode-of-action or mechanistic studies on methylcyclohexane-induced effects on the liver
were identified. Methylcyclohexane effects on the kidney, seen in male rats in repeated-exposure
oral and inhalation studies (JKCDB. 2013; IX HA. 2011a. 2001c; AFRL. 1985). were attributed
by the study authors to a2u-g nephropathy, a male-rat-specific effect that is not relevant to
humans (U.S. EPA. 1991). However, none of these studies (nor any other in the database for
methylcyclohexane) provided a rigorous demonstration that the observed renal lesions were in
fact associated with accumulation of a2u-g, and not all findings in these studies were consistent
with this hypothesis. No specific mechanistic investigations of this endpoint were located for
methylcyclohexane.
40
Methylcyclohexane
-------
EPA/690/R-23/007F
3. DERIVATION OF PROVISIONAL VALUES
3.1. DERIVATION OF ORAL REFERENCE DOSES
The database of relevant studies for derivation of provisional reference doses (p-RfDs)
for methylcyclohexane is limited. No adequate human studies were identified. Animal studies
available via the oral route include an unpublished, non-peer-reviewed OECD 407 guideline
study as summarized in secondary sources (the primary study was not available for review) and
an unpublished, non-peer-reviewed OECD 422 guideline study published primarily in Japanese
(JKCDB. 2013). Due to the limitations of the available reports for these studies, p-RfDs cannot
be confidently derived. However, the available reports for the two studies provide sufficient data
to develop a screening subchronic p-RfD value for methylcyclohexane (see Appendix A).
3.2. DERIVATION OF INHALATION REFERENCE CONCENTRATIONS
Limited data are available for derivation of provisional reference concentrations (p-RfCs)
for methylcyclohexane. No adequate human studies were identified. Animal inhalation studies
include a study published primarily in Korean with data tables in English for a limited number of
endpoints (Kim et al.. 2006) and a study that was not published or peer-reviewed (AFRI.. 1985).
Due to the limitations of the available studies, p-RfCs cannot be confidently derived. However,
the 12-month AFRL (1985) study provides sufficient data to develop a screening chronic p-RfC
value for methylcyclohexane (see Appendix A).
3.3. SUMMARY OF NONCANCER PROVISIONAL REFERENCE VALUES
Table 5 presents a summary of noncancer provisional reference values.
41
Methylcyclohexane
-------
EPA/690/R-23/007F
Table 5. Summary of Noncancer Reference Values for
Methylcyclohexane (CASRN 108-87-2)
Toxicity Type
(units)
Species/Sex
Critical Effect
p-Reference
Value
POD
Method
POD
(HED/HEC)
UFc
Principal
Study
Screening
subchronic p-RfD
(mg/kg-d)
(see Appendix A)
Rat/M
Increased incidence of
renal tubule hyaline
droplet degeneration
1 X 10-2
BMDLio
3.37
300
ECHA
(2001c)
Chronic p-RfD
(mg/kg-d)
NDr
Subchronic p-RfC
(mg/m3)
NDr
Screening
chronic p-RfC
(mg/m3) (see
Appendix A)
Hamster/M
Decreased body
weight
9.5 x 10-2
LOAEL
287
AFRL
(1985)
BMD = benchmark dose; BMDL = 95% benchmark dose lower confidence limit on the BMD (subscripts denote
BMR: i.e., 10 = extra risk 10%); BMR = benchmark response; HEC = human equivalent concentration;
HED = human equivalent dose; LOAEL = lowest-observed-adverse-effect level; M = male(s); NDr = not
determined; POD = point of departure; p-RfC = provisional reference concentration; p-RfD = provisional reference
dose; UFC = composite uncertainty factor.
3.4. CANCER WEIGHT-OF-EVIDENCE DESCRIPTOR
Following the U.S. EPA (2005) Guidelines for Carcinogen Risk Assessment,
methylcyclohexane has inadequate information to assess carcinogenic potential by oral or
inhalation exposure (see Table 6). There are no human studies to indicate cancer risk. The
database of information regarding carcinogenicity of methylcyclohexane in animals is limited to
a single study in which CDF F344/CrlBR rats (65/sex/group), C57BL/6J mice (200 females/
group), Syrian golden hamsters (100 males/group), and purebred beagle dogs (4/sex/group) were
exposed to measured concentrations of 0, 1,607, or 8,048 mg/m3 methylcyclohexane (-99%
pure) vapors for 6 hours/day, 5 days/week for 1 year ( AFRL. 1985). Most rodents were held for
another year and all dogs were held for another 5 years prior to histopathological examination.
No exposure-related tumors were observed in any species, but there were serious limitations in
the design, conduct, and reporting of results of the study that may have impacted its ability to
detect an effect, including the short (1-year) exposure duration, small group sizes for dogs, and
insufficient exposure levels (the noncancer findings indicate that the maximum tolerated dose
[MTD] was not achieved in any species). Genotoxicity studies, including two Ames tests for
mutation in bacteria and two assays for chromosome aberrations in Chinese hamster lung cells,
were negative (JKCDB. 2011a. b; EC HA. 2001a. b).
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Table 6. Cancer WOE Descriptor for Methylcyclohexane (CASRN 108-87-2)
Possible WOE Descriptor
Designation
Route of Entry (oral,
inhalation, or both)
Comments
"Carcinogenic to Humans "
NS
NA
No human carcinogenicity data are
available.
"Likely to Be Carcinogenic to
Humans "
NS
NA
The available data do not support this
descriptor.
"Suggestive Evidence of
Carcinogenic Potential"
NS
NA
The available data do not support this
descriptor.
"Inadequate Information to
Assess Carcinogenic Potential"
Selected
Both
Selected based on lack of evidence for
carcinogenicity of methylcyclohexane
in a limited inhalation study and no
information by oral exposure.
"Not Likely to Be Carcinogenic
to Humans "
NS
NA
The available data do not support this
descriptor.
NA = not applicable; NS = not selected; WOE = weight-of-evidence.
3.5. DERIVATION OF PROVISIONAL CANCER RISK ESTIMATES
Due to a lack of carcinogenicity data, derivation of cancer risk estimates is precluded for
methylcyclohexane (see Table 7).
Table 7. Summary of Cancer Risk Estimates for
Methylcyclohexane (CASRN 108-87-2)
Toxicity Type
Species/Sex
Tumor Type
Cancer Value
Principal Study
p-OSF (mg/kg-d) 1
NDr
p-IUR (mg/m3) 1
NDr
NDr = not determined; p-IUR = provisional inhalation unit risk; p-OSF = provisional oral slope factor.
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APPENDIX A. SCREENING PROVISIONAL VALUES
Due to limitations of the studies described in the main Provisional Peer-Reviewed
Toxicity Value (PPRTV) assessment, it is inappropriate to derive provisional toxicity values for
methylcyclohexane. However, some information is available for this chemical, which although
insufficient to support derivation of a provisional toxicity value under current guidelines, may be
of limited use to risk assessors. In such cases, the Center for Public Health and Environmental
Assessment (CPHEA) summarizes available information in an appendix and develops a
"screening value." Appendices receive the same level of internal and external scientific peer
review as the provisional reference values to ensure their appropriateness within the limitations
detailed in the assessment. Users of screening toxicity values in an appendix to a PPRTV
assessment should understand that there could be more uncertainty associated with deriving an
appendix screening toxicity value than for a value presented in the body of the assessment.
Questions or concerns about the appropriate use of screening values should be directed to the
CPHEA.
A screening subchronic provisional reference dose (p-RfD) and a screening chronic
provisional reference concentration (p-RfC) were derived for methylcyclohexane. These
screening assessments are presented below.
DERIVATION OF SCREENING ORAL PROVISIONAL REFERENCE DOSES
As discussed in the main body of this assessment, the available reports of the
Organisation for Economic Co-operation and Development (OECD) guideline 407 repeated-dose
28-day gavage rat study (ECHA. 2001c) and the OECD guideline 422 combined repeated-dose
with reproductive/developmental screening study (JECDB. 2013) have limitations precluding
their use in deriving provisional toxicity values (unpublished, not peer-reviewed, available only
in a secondary source, and/or published primarily in a foreign language). While limited by these
shortcomings, the available reports for both studies provide sufficient information to suggest that
the studies were otherwise adequately designed and conducted and include dose-response
information on multiple endpoints suitable for quantitative toxicity assessment and derivation of
screening provisional toxicity values.
Treatment-related effects of methylcyclohexane in both studies were seen in the liver and
kidney, including lesions and organ weight increases. The renal effects were dismissed as being
largely consistent with alpha 2u-globulin (a2u-g) nephropathy by the study authors of the
secondary European Chemicals Agency (ECHA) reports in both studies (ECHA. 201 1 a. 2001c).
Although ECHA considered hyaline droplet formation related to a2u-g accumulation and
therefore not relevant to humans, the U.S. Environmental Protection Agency (U.S. EPA) has
specific guidance for the establishment of an a2u-g mode of action by which the default position
is to assume that renal effects in male rats are relevant to humans. According to the U.S. EPA
guidance, "a chemical can be described as inducing a2u-g accumulation with certainty only
when there is a positive identification of a2u-g in the hyaline droplets" (U.S. EPA. 1991).
Neither study (nor any other study in the database for methylcyclohexane) provided a rigorous
demonstration that the renal effects observed in male rats were, in fact, due to a2u-g
nephropathy, and both studies also reported limited renal changes in female rats. Because the
available data failed to provide sufficient evidence that the a2u-g process was operative, renal
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effects in the male rats are considered a human health-relevant endpoint for this assessment, as
outlined in the U.S. EPA a2u-g guidance (U.S. EPA. 1991) (see Section 2.2.1).
The data for increased absolute and relative liver and kidney weights and increased
incidence of hepatocellular hypertrophy and hyaline droplet lesions from the two available oral
short-term studies (JECDB. 2013; EC HA. 2001c) are shown in Tables A-1 and A-2. For the
organ weight data, relative weights were modeled preferentially over absolute weights. For
organs such as liver and kidney, whose weights are correlated with body weight, relative weights
provide the more reliable, inclusive measure of effect (Nirogi et at.. 2014; Bailev et at.. 2004).
Absolute weights were only modeled when modeling was unsuccessful for the relative weights
and the absolute weights showed a biologically significant change (>10%).
Table A-l. Data for Endpoints Considered for Derivation in Crj:CD
(Sprague Dawley) Rats Exposed to Methylcyclohexane via Gavage for
28 Days"
Endpoint
Males: ADD [HED] in mg/kg-db
0
100 [24.9]
300 [74.6]
1,000 [249]
Liver weightcd
Absolute (g)
Relative (%)
9.65 ±0.97
3.385 ±0.16
9.28 ± 1.89 (-4%)
3.225 ±0.339 (-5%)
11.22 ± 1.02 (+16%)
3.572 ±0.1 (+6%)
11.75 ±0.93 (+22%)*
4.13 ± 0.137 (+22%)**
Liver cell hypertrophy6
0/5 (0%)
0/5 (0%)
0/5 (0%)
5/5 (100%.)**
Kidney tubule hyaline
droplet degeneration6
0/5 (0%)
1/5 (20%)
5/5 (100%)**
5/5 (100%.)**
Endpoint
Females: ADD [HED] in mg/kg-d
0
100 [23.2]
300 [69.7]
1,000 [232]
Liver weightcd
Absolute (g)
Relative (%)
6.01 ±0.55
3.17 ±0.071
6.81 ±0.79 (+13%)
3.368 ±0.213 (+6%)
6.29 ± 0.49 (+5%)
3.231 ±0.09 (+2%)
6.6 ± 0.77 (+10%)
3.577 ±0.25 (+13%.)**
aECHA (2001c).
bThe ADDs were converted to HEDs [appearing in brackets] of 24.9, 74.6, and 249 mg/kg-day in low-, mid-, and
high-dose males, respectively, and 23.2, 69.7, and 232 mg/kg-day in low-, mid-, and high-dose females,
respectively, using DAFs of 0.249 (males) and 0.232 (females), where HED = ADD x DAF. The DAFs were
calculated as follows: DAF = (BWa1/4 + BWh14). In the absence of body-weight data in the study, reference body
weight of 0.267 kg for male and 0.204 kg for female Sprague Dawley rats in a subchronic study were used (U.S.
EPA. 1988). For humans, the reference body-weight value of 70 kg was used (U.S. EPA. 1988).
Data are mean ± SD from five animals.
dValue in parentheses is % change relative to control = ([treatment mean - control mean] + control mean) x 100.
"Values denote number of animals showing changes/total number of animals examined (% incidence).
* Significantly different from control (p < 0.05) as reported by the study authors.
**Significantly different from control (p < 0.01) as reported by the study authors.
ADD = adjusted daily dose; BWa = animal body weight; BWh = human body weight; DAF = dosimetric adjustment
factor; HED = human equivalent dose; SD = standard deviation.
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Table A-2. Data for Endpoints Considered for Derivation in Crl:CD
Sprague Dawley Rats Exposed to Methylcyclohexane via Gavage for
28 Days (Including Premating and Mating for Males)"
Endpoint
Males: ADD [HED] in mg/kg-db
0
62.5 [17.1]
250 [68.6]
1,000 [273]
Liver weightcd
Absolute (g)
Relative (g %)
11 ± 0.32
2.59 ±0.08
10.95 ± 0.98 (+0%)
2.64 ±0.18 (+2%)
11.65 ±0.57 (+6%)
2.81 ± 0.13 (+8%)*
15.18 ±0.94 (+38%)**
3.82 ± 0.13 (+47%)**
Kidney weightcd
Absolute (g)
Relative (g %)
2.75 ±0.16
0.65 ±0.03
2.99 ±0.31 (+9%)
0.72 ±0.07 (+11%)*
2.92 ±0.14 (+6%)
0.70 ± 0.03 (+8%)
3.14 ±0.20 (+14%)*
0.79 ± 0.04 (+22%)**
Kidney tubule hyaline
droplets6
0/6 (0%)
0/6 (0%)
4/6 (67%)
6/6 (100%)**
Endpoint
Unmated females: ADD [HED] in mg/kg-d
0
62.5 [15.7]
250 [63.0]
1,000 [251.3]
Liver weightcd
Absolute (g)
Relative (g %)
7.58 ±0.6
2.63 ±0.19
7.84 ± 0.47 (+3%)
2.75 ±0.14 (+5%)
7.77 ± 0.48 (+3%)
2.71 ±0.12 (+3%)
8.29 ± 0.88 (+9%)
3.02 ± 0.28 (+15%)*
Kidney weightcd
Absolute (g)
Relative (g %)
1.83 ±0.11
0.64 ± 0.04
1.87 ± 0.09 (+2%)
0.66 ± 0.03 (+3%)
1.95 ± 0.08 (+7%)
0.68 ± 0.03 (+6%)
2.04 ±0.25 (+11%)
0.74 ± 0.09 (+16%)*
aJECD6 (2013).
bThe ADDs were converted to HEDs [appearing in brackets] of 17.1, 68.6, and 273.4 mg/kg-day in low-, mid-, and
high-dose males, respectively, and 15.7, 63.0, and 251.3 mg/kg-day in low-, mid-, and high-dose females,
respectively, using DAFs of 0.27 (males) and 0.25 (females), where HED = ADD x DAF. The DAFs were
calculated as follows: DAF = (BWa1/4 + BWh1/4). Individual animal body weights were provided in the study; group
TWA body weights determined for this review were 0.395, 0.398, and 0.391 kg (for low-, mid-, and high-dose
males, respectively) and 0.282, 0.283, 0.279 kg (for low-, mid-, and high-dose unmated females, respectively). For
humans, the reference value of 70 kg was used for body weight, as recommended by U.S. EPA (1988).
°Values are expressed as mean ± SD from n = 6 (males), n = 5 (unmated females).
dValue in parentheses is % change relative to control = ([treatment mean - control mean] + control mean) x 100.
"Values denote the number of animals showing changes/total number of animals examined (% incidence).
* Significantly different from control (p < 0.05), as reported by the study authors (Dunnett's test).
**Significantly different from control (p < 0.01), as reported by the study authors (Dunnett's test).
ADD = adjusted daily dose; B Wa = animal body weight; BWh = human body weight; DAF = dosimetric adjustment
factor; HED = human equivalent dose; SD = standard deviation; TWA = time-weighted average.
Benchmark dose (BMD) modeling of these endpoints was performed using all available
continuous or dichotomous models in the U.S. EPA's Benchmark Dose Software (BMDS;
Version 3.2), as appropriate. Human equivalent dose (HED) values in mg/kg-day were used as
the dose metric. A benchmark response (BMR) of 10% relative deviation (O.IRD) was used for
the continuous liver and kidney weight data because a 10% change in these organ weights was
considered to be biologically significant. Dichotomous data were modeled using a BMR of 10%
extra risk.
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Tables A-3 and A-4 summarize the BMD modeling results and provide candidate points
of departure (PODs) for the modeled endpoints from the two studies. Details of model fit for
each data set are presented in Appendix C.
Table A-3. BMD and BMDL Values from Best Fitting Models in Crj:CD
(Sprague Dawley) Rats Exposed to Methylcyclohexane via Gavage for
28 Days"
Endpoints
Best Fitting Model
BMR
BMD (HED)
(mg/kg-d)
BMDL (HED)
(mg/kg-d)
Increased relative liver
weight (males)
No selected modelb
10% RD from control (0.1RD)
NA
NA
Increased absolute liver
weight (males)
Exponential 4
(constant variance)
10% RD from control (0.1RD)
39.86
13.47
Increased relative liver
weight (females)
No selected modelb
10% RD from control (0.1RD)
NA
NA
Increased liver cell
hypertrophy (males)
Log-logistic
10% extra risk
120.51
59.86
Increased kidney tubule
hyaline droplet
degeneration (males)
Multistage 2-degree
10% extra risk
13.35
3.37
aECHA (2001c).
bNo model provided adequate fit to the data.
BMD = benchmark dose; BMDL = benchmark dose lower confidence limit; BMR = benchmark response;
HED = human equivalent dose; NA = not applicable; RD = relative deviation.
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Table A-4. BMD and BMDL Values from Best Fitting Models for Endpoints
Considered for Derivation in Male and Female Crl:CD Sprague Dawley
Rats Exposed to Methylcyclohexane During Premating and Mating (Males
Only) or for 28 Days3
Endpoints
Best Fitting Model
BMR
BMD (HED)
(mg/kg-d)
BMDL (HED)
(mg/kg-d)
Increased relative liver
weight (males)
Exponential 2
(constant variance)
10% RD from control (0.1RD)
66.03
61.05
Increased relative liver
weight (females)
Polynomial 3-degree
(constant variance)
10% RD from control (0.1RD)
218.90
126.60
Increased relative kidney
weight (males)
No selected modelb
10% RD from control (0.1RD)
NA
NA
Increased relative kidney
weight (females)
Polynomial 3-degree
(nonconstant variance)
10% RD from control (0.1RD)
161.67
97.08
Increased kidney tubule
hyaline droplets (males)
Multistage 1-degree
10% extra risk
8.12
4.25
aJECD6 (2013).
bNo model provided adequate fit to the data.
BMD = benchmark dose; BMDL = benchmark dose lower confidence limit; BMR = benchmark response;
HED = human equivalent dose; NA = not applicable; RD = relative deviation.
Derivation of a Screening Subchronic Provisional Reference Dose
The 10% benchmark dose lower confidence limit (BMDLio) (HED) of 3.37 mg/kg-day
based on increased incidence of renal tubule hyaline droplet degeneration in male rats in the
ECHA (2001c) study is the most sensitive POD identified and is selected as the POD for
derivation of the screening subchronic p-RfD for methylcyclohexane.
The screening subchronic p-RfD of 1 x 10 2 mg/kg-day for methylcyclohexane is derived
by applying a composite uncertainty factor (UFc) of 300 (reflecting an interspecies uncertainty
factor [UFa] of 3, a database uncertainty factor [UFd] of 10,and an intraspecies uncertainty
factor [UFh] of 10) to the selected POD of 3.37 mg/kg-day, as follows:
Screening Subchronic p-RfD = POD (HED) UFc
= 3.37 mg/kg-day -^300
= 1 x 10"2 mg/kg-day
Table A-5 summarizes the uncertainty factors for the screening subchronic p-RfD for
methylcyclohexane.
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Table A-5. Uncertainty Factors for the Screening Subchronic p-RfD for
Methylcyclohexane (CASRN 108-97-2)
UF
Value
Justification
UFa
3
A UFa of 3 (10°5) is applied to account for uncertainty associated with extrapolating from animals to
humans when cross-species dosimetric adjustment (HED calculation) is performed.
UFd
10
A UFd of 10 is applied to account for deficiencies and uncertainties in the database. The
repeated-dose oral database for methylcyclohexane includes only two studies, both of which have
significant limitations. Reproductive/developmental endpoints were included in one study and no
effects were found, but only a limited screening-level assessment was performed.
UFh
10
A UFh of 10 is applied for interindividual variability in the absence of information to assess the
toxicokinetic and toxicodynamic variability of methylcyclohexane 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 the POD was derived from a study of suitable duration (28 days) for a
subchronic value.
UFC
300
Composite UF = UFA x UFD x UFH x UFL x UFS.
BMDL = benchmark dose lower confidence limit; HED = human equivalent dose;
LOAEL = lowest-observed-adverse-effect level; NOAEL = no-observed-adverse-effect level; POD = point of
departure; p-RfD = provisional reference dose; UF = uncertainty factor; UFA = interspecies uncertainty factor;
UFC = composite uncertainty factor; UFD = database uncertainty factor; UFH = intraspecies uncertainty factor;
UFl = LOAEL-to-NOAEL uncertainty factor; UFS = subchronic-to-chronic uncertainty factor.
Derivation of a Screening Chronic Provisional Reference Dose
The POD used for derivation of the screening subchronic p-RfD, the BMDLio (HED) for
increased incidence of renal tubule hyaline droplet degeneration in the 28-day study ( HCH A.
2001c) cannot be used directly for derivation of the screening chronic p-RfD, due to the short
duration of the critical study. Therefore, derivation of a screening chronic p-RfD is not supported
by the available database.
DERIVATION OF SCREENING INHALATION PROVISIONAL REFERENCE
CONCENTRATIONS
As discussed in the main body of this PPRTV assessment, the available inhalation studies
have limitations precluding their use in deriving provisional toxicity values (unpublished, not
peer-reviewed, written primarily in a foreign language). In order to account for the uncertainty
associated with deriving toxicity values from these limited study reports, the assessment is
considered a screening-level assessment.
AfRL (1985) exposed rats of both sexes, female mice, male hamsters, and dogs of both
sexes to methylcyclohexane vapor for 1 year and observed them for an additional 1 year
(rodents) or 5 years (dogs) prior to sacrifice. No effects clearly related to exposure were observed
in mice or dogs.
In rats, renal lesions (medullary mineralization and papillary hyperplasia) were increased
in the high-exposure males after the 1-year recovery at 24 months. The study authors considered
these lesions to be related to a2u-g nephropathy, but neither this study nor any other in the
database for methylcyclohexane provided a rigorous demonstration that the renal effects
observed in male rats were, in fact, due to a2u-g nephropathy. Based on the available data, only
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one of three criteria (the presence of lesions observed in the latter stages of a2u-g) were fulfilled
to satisfy the involvement of a2u-g as outlined by the U.S. EPA (1991) guidance. Because the
available data fail to provide sufficient evidence that the a2u-g process was operative, renal
effects in the male rats are considered a human health-relevant endpoint for this assessment. The
data for increased incidences of renal medullary mineralization and papillary hyperplasia in male
rats reported in AFRL (1985) are shown in Table A-6.
Table A-6. Renal Lesions in Male CDF F344/CrlBr Rats Exposed to
Methylcyclohexane Vapors for 6 Hours/Day, 5 Days/Week for 1 Year"
Endpoint
Time of Sacrifice
Exposure Concentration [HECer]1" in mg/m3
0
1,607 [287.0]
8,048 [1,437]
Medullary mineralization
24 months
1/53 (2%)°
2/55 (4%)
19/52 (37%)**
Papillary hyperplasia
24 months
1/53 (2%)
1/55 (2%)
23/52 (44%)**
aAFRL (1985).
' Reported concentrations; calculated HECer values appear in brackets. HEC values based on extrarespiratory
effects were calculated by treating methylcyclohexane as a Category 3 gas and using the following equation from
U.S. EPA (1994) methodology: HECer = exposure concentration (mg/m3) x (hours/day
exposed 24 hours) x (days/week exposed 7 days) x ratio of blood-gas partition coefficient (animakhuman),
using a default coefficient of 1 since the hamster blood-air partition coefficient (logA'i,i(„i) is unknown; the human
logATbbod is 0.61.
0Values denote number of animals showing changes/total number of animals examined (% incidence).
* Significantly different from control (p < 0.05) as reported by the study authors.
**Significantly different from control (p < 0.01) as reported by the study authors.
HECer = human equivalent concentration based on extrarespiratory effects.
BMD modeling of these endpoints was performed using all available dichotomous
models in the U.S. EPA's BMDS (Version 3.2). HEC values in mg/m3 were used as the dose
metric. The data were modeled using a BMR of 10% extra risk.
Table A-7 summarizes the BMD modeling results and provides candidate PODs for the
modeled endpoints. Details of model fit for each data set are presented in Appendix C.
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Table A-7. BMC and BMCL Values from Best Fitting Models for Increased
Renal Lesions in Male CDF F344/CrlBr Rats Exposed to Methylcyclohexane
Vapors for 6 Hours/Day, 5 Days/Week for 1 Year"
Endpoints
Best Fitting Model
BMR
BMC (HEC)
(mg/m3)
BMCL (HEC)
(mg/m3)
Medullary mineralization
Logistic
10% extra risk
816.3
660.1
Papillary hyperplasia
Logistic
10% extra risk
804.4
641.6
aAFRL (1985).
BMC = benchmark concentration; BMCL = benchmark concentration lower confidence limit; BMR = benchmark
response; HEC = human equivalent concentration.
In hamsters exposed to either 1,607 or 8,048 mg/m3 methylcyclohexane for 1 year, mean
body weight was decreased as early as 1 month and persisted throughout the exposure period.
Estimated data for decreased body weight in male hamsters are shown in Table A-8. The
LOAEL of 1,607 mg/m3 was selected as the POD for methylcyclohexane based on a biologically
significant decrease in body weight relative to control animals. In the absence of variance
reported by the study authors, these data were not amendable to BMD modeling with BMDS
(version 3.2). Instead, a LOAELhec of 297 mg/m3 was calculated based on body weight data
presented in Figure 3 of the study report (AFRL. 1985).
Table A-8. Body Weight in Male Syrian Golden Hamsters Exposed to
Methylcyclohexane Vapors for 6 Hours/Day, 5 Days/Week for 1 Year"
Endpoint
Time of Sacrifice
Exposure Concentration [HECer]11 in mg/m3
0
1,607 [287.0]
8,048 [1,437]
Body weight (g)°
12 mo
127
112 (-12%)
107 (-15%)
aAFRL (1985).
' Reported concentrations; calculated HECer values appear in brackets. HEC values based on extrarespiratory
effects were calculated by treating methylcyclohexane as a Category 3 gas and using the following equation from
U.S. EPA (1994) methodology: HECer = exposure concentration (mg/m3) x (hours/day
exposed 24 hours) x (days/week exposed 7 days) x ratio of blood-gas partition coefficient (animal:human),
using a default coefficient of 1 since the hamster blood-air partition coefficient (logA'i,i(„i) is unknown; the human
logATbbod is 0.61.
" Values denote estimated body weight based on Figure 3 of the study report (AFRL. 1985).
HECer = human equivalent concentration based on extrarespiratory effects.
Derivation of a Screening Subchronic Provisional Reference Concentration
There are no suitable human or animal data available to derive a subchronic provisional
reference concentration (p-RfC) for methylcyclohexane. (Kim et al.. 2006). an inhalation study
in rats study written in Korean with some data tables written in English, reported on a limited
number of endpoints that were not deemed suitable to identify and derive a POD. Therefore,
derivation of a screening chronic p-RfC is not supported by the available database.
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Derivation of a Screening Chronic Provisional RfC
The LOAELhec value of 287 mg/m3, based on decreased body weight >10% in male
Syrian golden hamsters exposed to methylcyclohexane for 1 year, is the most sensitive of the
three PODs identified from the AFRL (1985) study and is selected as the POD for derivation of
the screening chronic p-RfC.
The screening chronic p-RfC of 9.5 x 10 2 mg/m3 for methylcyclohexane is derived by
applying a UFc of 3,000 (reflecting a UFa of 3, a UFd of 10, a UFh of 10, and a UFl of 10) to
the selected POD of 287 mg/m3, as follows:
Screening Chronic p-RfC = POD (HEC) UFc
= 287 mg/m3 - 3,000
= 9.5 x 10"2 mg/m3
Table A-9 summarizes the uncertainty factors for the screening chronic p-RfC for
methylcyclohexane.
Table A-9. Uncertainty Factors for the Screening Chronic p-RfC for
Methylcyclohexane (CASRN 108-87-2)
UF
Value
Justification
UFa
3
A UFa of 3 (10°5) is applied to account for uncertainty associated with extrapolating from animals to
humans when cross-species dosimetric adjustment (HEC calculation) is performed.
UFd
10
A UFd of 10 is applied to account for deficiencies and uncertainties in the database. The
repeated-dose inhalation database for methylcyclohexane includes only two studies, both of which
have significant limitations. No inhalation studies evaluating reproductive or developmental
endpoints are available.
UFh
10
A UFh of 10 is applied for interindividual variability in the absence of information to assess the
toxicokinetic and toxicodynamic variability of methylcyclohexane in humans.
UFl
10
A UFl of 10 is applied for LOAEL to NOAEL extrapolation because the POD is a LOAEL.
UFS
1
A UFS of 1 is applied because the POD was derived from a study of suitable duration (1 yr) for a
chronic value.
UFC
3,000
Composite UF = UFA x UFD x UFH x UFL x UFS.
HEC = human equivalent concentration; LOAEL = lowest-observed-adverse-effect level;
NOAEL = no-observed-adverse-effect level; POD = point of departure; p-RfC = provisional reference
concentration; UF = uncertainty factor; UFA = interspecies uncertainty factor; UFC = composite uncertainty factor;
UFd = database uncertainty factor; UFH = intraspecies uncertainty factor; UFL = LOAEL-to-NOAEL uncertainty
factor; UFS = subchronic-to-chronic uncertainty factor.
52
Methylcyclohexane
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EPA/690/R-23/007F
APPENDIX B. DATA TABLES
Table B-l. Body Weight Gain and Food Consumption in Male and Female
Crj:CD (Sprague Dawley) Rats Treated with Methylcyclohexane via Gavage
for 28 Days"
Endpoint
Males: ADD [HED] in mg/kg-db
0
100 [24.9]
300 [74.6]
1,000 [249]
Body-weight gain (g)
(Days 0-27)
167 ± 32°
176 ± 33 (+5%)d
210 ± 24 (+26%)*
200 ± 26 (+20%)*
Total food consumption (g)
Males (Days 0-27)
Recovery males (Days 29-41)
515 ±31
294 ± 29
541 ± 60 (+5%)
ND
577 ± 36 (+12%)*
ND
598 ± 42(+16%)**
356 ± 35 (+21%)*
Endpoint
Females: ADD [HED] in mg/kg-db
0
100 [23.2]
300 [69.7]
1,000 [232]
Body-weight gain (g)
(Days 0-27)
87 ± 18
102 ± 24 (+17%)
91 ± 12 (+5%)
85 ± 13 (-2%)
aECHA (2001c).
bADD (mg/kg-day) values were reported in the secondary source; calculated HEDs appear in brackets.
Data are mean ± SD, from 10 animals (control and high-dose groups) or five animals (low- and mid-dose groups).
dValue in parentheses is % change relative to control = ([treatment mean - control mean] + control mean) x 100.
* Significantly different from control (p < 0.05) as reported by the study authors.
**Significantly different from control (p < 0.01) as reported by the study authors.
ADD = adjusted daily dose; HED = human equivalent dose; ND = not determined; SD = standard deviation.
53
Methylcyclohexane
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EPA/690/R-23/007F
Table B-2. Select Blood Biochemistry in Male and Female Crj:CD (Sprague
Dawley) Rats Treated with Methylcyclohexane via Gavage for 28 Days"
Endpoint
Males: ADD [HED] in mg/kg-db
0
100 [24.9]
300 [74.6]
1,000 [249]
After Dosing (Day 28)
ALP (U/L)
789 ± 101°
787 ±214 (+0%)d
672 ± 172 (-15%)
523 ± 90 (-34%)*
AST (U/L)
69 ±7
63 ± 6 (-9%)
69 ± 16 (+0%)
72 ± 17 (+4%)
TBIL (mg/dL)
0.02 ±0.01
0.02 ± 0.01 (+0%)
0.04 ± 0.01 (+100%)*
0.02 ± 0.01 (+0%)
TC (mg/dL)
53 ± 16
55 ± 7 (+4%)
62 ± 9 (+17%)
64 ± 5 (+21%)
TP (g/dL)
5.5 ±0.1
5.39 ±0.13 (-2%)
5.61 ±0.18 (+2%)
5.89 ± 0.16 (+7%)**
A/G
1.71 ±0.15
1.76 ±0.14 (+3%)
1.76 ±0.08 (+3%)
1.6 ± 0.07 (-6%)
After Recovery (Day 42)
ALP (U/L)
654 ± 93
NA
NA
520 ± 75 (-20%)*
TC (mg/dL)
46 ±5
NA
NA
72 ± 12 (+57%)**
TP (g/dL)
5.63 ±0.18
NA
NA
5.95 ± 0.14 (+6%)*
GLU (mg/dL)
165 ± 20
NA
NA
163 ± 15 (-1%)
A/G
1.7 ±0.07
NA
NA
1.52 ±0.12 (-11%)*
K (mmol/L)
4.97 ±0.06
NA
NA
4.54 ± 0.12 (-9%)**
Endpoint
Females: ADD [HED] in mg/kg-d
0
100 [23.2]
300 [69.7]
1,000 [232]
After Dosing (Day 28)
ALP (U/L)
450 ± 203
448 ± 97 (+0%)
548 ± 88 (+22%)
351 ± 109 (-22%)
AST (U/L)
79 ±7
70 ±9 (-11%)
70 ± 11 (-11%)
62 ± 8 (-22%)*
TBIL (mg/dL)
0.03 ±0.01
0.03 ±0.01 (+0%)
0.03 ±0.01 (+0%)
0.02 ±0.01 (-33%)
TC (mg/dL)
50 ±7
56 ± 7 (+12%)
59 ± 10 (+18%)
73 ± 13 (+46%)**
TP (g/dL)
5.78 ±0.23
5.71 ± 0.24 (-1%)
5.71 ±0.34 (-1%)
5.85 ± 0.19 (+1%)
A/G
1.85 ±0.04
2.11 ±0.07 (+14%)*
2 ±0.31 (+8%)
1.96 ± 0.2 (+6%)
54
Methylcyclohexane
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EPA/690/R-23/007F
Table B-2. Select Blood Biochemistry in Male and Female Crj:CD (Sprague
Dawley) Rats Treated with Methylcyclohexane via Gavage for 28 Days"
After Recovery (Day 42)
ALP (U/L)
295 ± 44
NA
NA
301 ± 56 (+2%)
TC (mg/dL)
67 ±7
NA
NA
64 ± 11 (-4%)
TP (g/dL)
6.09 ±0.43
NA
NA
6.01 ±0.23 (-1%)
GLU (mg/dL)
121 ± 11
NA
NA
139 ± 14 (+15%)*
A/G
1.84 ±0.12
NA
NA
1.87 ±0.19 (+2%)
K (mmol/L)
4.72 ±0.25
NA
NA
4.45 ± 0.44 (-6%)
aECHA (2001c).
bADD (mg/kg-day) values were reported in the secondary source; calculated HEDs appear in brackets.
Data are mean ± SD from five animals.
dValue in parentheses is % change relative to control = ([treatment mean - control mean] + control mean) x 100.
* Significantly different from control (p < 0.05) as reported by the study authors.
**Significantly different from control (p < 0.01) as reported by the study authors.
ADD = adjusted daily dose; A/G = albumin:globulin ratio; ALP = alkaline phosphatase; AST = aspartate
aminotransferase; GLU = glucose; HED = human equivalent dose; K = potassium NA = not applicable;
SD = standard deviation; TBIL = total bilirubin; TC = total cholesterol; TP = total protein.
55
Methylcyclohexane
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EPA/690/R-23/007F
Table B-3. Select Organ Weights in Male and Female Crj:CD (Sprague
Dawley) Rats Treated with Methylcyclohexane via Gavage for 28 Days"
Males: ADD [HED] in mg/kg-db
Endpoint
0
100 [24.9]
300 [74.6]
1,000 [249]
After Dosing (Day 28)
Liver weight
Absolute (g)
9.65 ± 0.97°
9.28 ± 1.89 (-4%)d
11.22 ± 1.02 (+16%)
11.75 ±0.93 (+22%)*
Relative (%)
3.385 ±0.16
3.225 ±0.339 (-5%)
3.572 ±0.1 (+6%)
4.13 ± 0.137 (+22%)**
After Recovery (Day 42)
Liver weight
Absolute (g)
9.99 ± 1.52
NA
NA
13.11 ± 1.20 (+31%)**
Relative (%)
3.119 ± 0.131
NA
NA
3.406 ± 0.169 (+9%)**
Females: ADD [HED] in mg/kg-d
Endpoint
0
100 [23.2]
300 [69.7]
1,000 [232]
After Dosing (Day 28)
Liver weight
Absolute (g)
6.01 ±0.55
6.81 ±0.79 (+13%)
6.29 ± 0.49 (+5%)
6.6 ± 0.77 (+10%)
Relative (%)
3.17 ±0.071
3.368 ±0.213 (+6%)
3.231 ±0.09 (+2%)
3.577 ±0.25 (+13%)**
After Recovery (Day 42)
Liver weight
Absolute (g)
6.11 ±0.71
NA
NA
6.61 ±0.54 (+8%)
Relative (%)
2.861 ±0.168
NA
NA
3.113 ±0.239 (+9%)
aECHA (2001c).
bADD (mg/kg-day) values were reported in the secondary source; calculated HEDs appear in brackets.
Data are mean ± SD from five animals.
dValue in parentheses is % change relative to control = ([treatment mean - control mean] + control mean) x 100.
* Significantly different from control (p < 0.05) as reported by the study authors.
**Significantly different from control (p < 0.01) as reported by the study authors.
ADD = adjusted daily dose; HED = human equivalent dose; NA = not applicable; SD = standard deviation.
56
Methylcyclohexane
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Table B-4. Select Histological Findings in Male and Female Crj:CD (Sprague
Dawley) Rats Treated with Methylcyclohexane via Gavage for 28 Days"
Males: ADD [HED] in mg/kg-db
Endpoint
0
100 [24.9]
300 [74.6]
1,000 [249]
After Dosing (Day 28)
Liver
Hypertrophy, hepatocytes
0/5 (0%)c
0/5 (0%)
0/5 (0%)
5/5 (100%)**
Kidney
Hyaline droplet formation
0/5 (0%)
0/5 (0%)
1/5 (20%)
0/5 (0%)
5/5 (100%)**
0/5 (0%)
5/5 (100%)**
0/5 (0%)
After Recovery (Day 42)
Kidney
Degeneration, hyaline droplet
Hyaline droplet formation
0/5 (0%)
0/5 (0%)
NA
NA
NA
NA
1/5 (20%)
0/5 (0%)
Females: ADD [HED] in mg/kg-d
Endpoint
0
100 [23.2]
300 [69.7]
1,000 [232]
After Dosing (Day 28)
Liver
Hypertrophy, hepatocytes
0/5 (0%)
0/5 (0%)
0/5 (0%)
1/5 (20%)
Kidney
Degeneration, hyaline droplet
Hyaline droplet formation
0/5 (0%)
0/5 (0%)
0/5 (0%)
0/5 (0%)
0/5 (0%)
0/5 (0%)
0/5 (0%)
2/5 (40%)
After Recovery (Day 42)
Kidney
Degeneration, hyaline droplet
Hyaline droplet formation
0/5 (0%)
0/5 (0%)
NA
NA
NA
NA
0/5 (0%)
5/5 (100%)**
aECHA (2001c).
bADD (mg/kg-day) values were reported in the secondary source; calculated HEDs appear in brackets.
0Values denote number of animals showing changes/total number of animals examined (% incidence).
**Significantly different from control (p < 0.01) as reported by the study authors.
ADD = adjusted daily dose; HED = human equivalent dose; NA = not applicable.
57
Methylcyclohexane
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EPA/690/R-23/007F
Table B-5. Select Serum Biochemistry Results in Male and Female Crl:CD
Sprague Dawley Rats Treated with Methylcyclohexane via Gavage for
28 Days (Including Premating and Mating for Males)"
Endpoint
Males: ADD [HED] in mg/kg-db
0
62.5 [17.1]
250 [68.6]
1,000 [273.4]
After Dosing (Day 28)
ALT (IU/L)
25.5 ± l.lc
28.4 ±3.9 (+ll%)d
35.6 + 16.2 (+40%)
44.3 ± 17.6 (+74%)*
AST (IU/L)
85.4 ± 11.4
80.0 ± 8.4 (-6%)
94.7 + 37.8 (+11%)
90.8 + 25.1 (+6%)
ALP (IU/L)
426.4 ± 113.3
369.5 ± 92.3 (-13%)
359.7+ 43.8 (-16%)
364.2 + 137.7 (-15%)
GGT (IU/L)
0.61 ±0.08
0.51 ±0.11 (-16%)
0.65 + 0.17 (+7%)
1.18 ± 0.33 (+93%)*
TP (g/dL)
5.59 ±0.22
5.48 ±0.18 (-2%)
5.55 + 0.15 (-1%)
6.25 + 0.28 (+12%)**
TC (mg/dL)
45.1 ±5.9
60.8 ± 8.4 (+35%)*
60.5 ± 9.3 (+34%)*
81.2 ± 12.6 (+80%)**
TG (mg/dL)
39 ± 11
31.1 ±8.3 (-20%)
30.8 + 8.8 (-21%)
28.9+ 11.4 (-26%)
GLU (mg/dL)
107.9 ±7.5
112.1 ±9.2 (+4%)
103.2+ 6.7 (-4%)
97.9+ 10.1 (-9%)
CI (mEq/L)
108.6 ± 1
108.2 ± 1 (+0%)
107.2 ± 1.1 (-1%)*
105.7 ±0.5 (-3%)**
Ca (mg/dL)
9.6 ±0.2
9.5 ± 0.2 (-1%)
9.5 + 0.2 (-1%)
10 ± 0.2 (+4%)**
After Recovery (Day 42)
ALT (IU/L)
29.5 ±6.2
27.6 ± 2.9 (-6%)
30.7 + 6.4 (+4%)
39.6 ± 8.8 (+34%)*
AST (IU/L)
85.3 ± 16.4
85.5 ± 13 (+0%)
74.8 + 8.8 (-12%)
90.8 + 25 (+6%)
ALP (IU/L)
301.2 ±46.7
267 ± 17.1 (-11%)
308.3 + 39.3 (+2%)
326.4 + 40 (+8%)
GGT (IU/L)
0.44 ±0.11
0.41 ± 0.06 (-7%)
0.43 + 0.06 (-2%)
0.47+ 0.12 (+7%)
TP (g/dL)
5.64 ±0.13
5.65 ± 0.33 (+0%)
5.62 +0.19 (+0%)
5.87 + 0.47 (+4%)
TC (mg/dL)
45.3 ±6.3
51.6 ± 15.4 (+14%)
52.8 + 10.4 (+17%)
73.1 ± 13.5 (+61%)**
TG (mg/dL)
25.6 ± 11.4
31.6 ±7.1 (+23%)
37.4 + 22.1 (+46%)
33.7+ 12.6 (+32%)
GLU (mg/dL)
116.1 ±7.6
109.9 ± 8.2 (-5%)
103.3 + 8.8 (-11%)*
109.5 + 9.4 (-6%)
CI (mEq/L)
107.5 ± 1.1
108 ± 1.4 (+0%)
108.7 + 1.3 (+1%)
106.8+ 1.1 (-1%)
Ca (mg/dL)
9.5 ±0.4
9.4 ± 0.2 (-1%)
9.6 + 0.2 (+1%)
9.7 + 0.2 (+2%)
Endpoint
Unmated Females: ADD [HED] in mg/kg-d
0
62.5 [15.7]
250 [63.0]
1,000 [251.3]
After Dosing (Day 28)
ALT (IU/L)
21.8 ± 2
27.0 ± 7.5 (+24%)
25.0+ 1.8 (+15%)
25.0 + 6.6 (+15%)
AST (IU/L)
71.9 ± 12
76.5 ± 6.5 (+6%)
76.2 + 12.0 (+6%)
73.0+ 11.0 (+2%)
ALP (IU/L)
198.3 ±23.5
164 + 31.2 (-17%)
191.8 + 45.5 (-3%)
178.1 + 42 (-10%)
GGT (IU/L)
0.7 ±0.18
0.75 ±0.12 (+7%)
0.74+ 0.17 (+6%)
0.72+ 0.18 (+3%)
TP (g/dL)
6.04 ±0.4
5.94 + 0.37 (-2%)
6.04 + 0.07 (+0%)
6.35 + 0.48 (+5%)
TC (mg/dL)
63.5 ± 11.8
57+11.2 (-10%)
63.6+ 13.8 (+0%)
76.7+ 18.2 (+21%)
TG (mg/dL)
25.4 ± 14.3
23.9+12.1 (-6%)
18.7 + 4.8 (-26%)
27.4 + 16.9 (+8%)
GLU (mg/dL)
119.2 ± 10.6
110.1 + 2.7 (-8%)
110.2+ 9.0 (-8%)
105.9 ± 7.2 (-11%)*
CI (mEq/L)
108.4 ±0.9
107.1 + 1.8 (-1%)
108.3 + 1.2 (+0%)
108 + 2.4 (+0%)
58
Methylcyclohexane
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EPA/690/R-23/007F
Table B-5. Select Serum Biochemistry Results in Male and Female Crl:CD
Sprague Dawley Rats Treated with Methylcyclohexane via Gavage for
28 Days (Including Premating and Mating for Males)"
Ca (mg/dL)
9.7 ±0.3
9.8 ± 0.3 (+1%)
9.6 ±0.1 (-1%)
9.9 ± 0.5 (+2%)
After Recovery (Day 42)
ALT (IU/L)
25.2 ±3.8
NA
NA
39 ± 37.2 (+55%)
AST (IU/L)
65.4 ±4.1
NA
NA
92.7 ±69.1 (+42%)
ALP (IU/L)
134.3 ±30.4
NA
NA
137.2 ± 34 (+2%)
GGT (IU/L)
0.53 ±0.16
NA
NA
0.48 ± 0.07 (-9%)
TP (g/dL)
6.65 ±0.14
NA
NA
6.53 ± 0.25 (-2%)
TC (mg/dL)
78.8 ± 12.3
NA
NA
71.1 ± 16.7 (-10%)
TG (mg/dL)
25 ±3.4
NA
NA
24 ± 1.4 (-4%)
GLU (mg/dL)
118.3 ±9.2
NA
NA
120.5 ± 8.3 (+2%)
CI (mEq/L)
105.7 ±0.8
NA
NA
106.8 ± 1.3 (+1%)
Ca (mg/dL)
10.1 ±0.2
NA
NA
10.2 ± 0.3 (+1%)
aJECD6 (2013).
bADD (mg/kg-day) values were reported by the study authors; calculated HEDs appear in brackets.
°Values are expressed as mean ± SD from n = 6 (males), n = 5 (unmated females).
dValue in parentheses is % change relative to control = ([treatment mean - control mean] + control mean) x 100.
* Significantly different from control (p < 0.05), as reported by the study authors (Steel's test or Dunnett's test).
**Significantly different from control (p < 0.01), as reported by the study authors (Dunnett's test).
ADD = adjusted daily dose; ALT = alanine transaminase; AST = aspartate aminotransferase; ALP = alkaline
phosphatase; Ca = calcium; CI = chloride; GGT = y-glutamyl transferase; GLU = glucose; HED = human
equivalent dose; NA = not applicable; SD = standard deviation; TC = total cholesterol; TG = triglyceride;
TP = total protein.
59
Methylcyclohexane
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EPA/690/R-23/007F
Table B-6. Select Organ Weights of Male and Female Crl:CD Sprague
Dawley Rats Treated with Methylcyclohexane During Premating, Mating,
and Lactation or for 28 Days"
Males: ADD [HED] in mg/kg-db
Endpoint
0
62.5 [17.1]
250 [68.6]
1,000 [273.4]
After Dosing (Day 28)
Body weight (g)
425 ± 12°
415 ± 29 (-2%)d
416 + 9 (-2%)
398 + 29 (-6%)
Liver weight
Absolute (g)
11 ± 0.32
10.95 ± 0.98 (+0%)
11.65 + 0.57 (+6%)
15.18 ±0.94 (+38%)**
Relative (g %)
2.59 ±0.08
2.64 ±0.18 (+2%)
2.81 ± 0.13 (+8%)*
3.82 ± 0.13 (+47%)**
Kidney weight
Absolute (g)
2.75 ±0.16
2.99 ±0.31 (+9%)
2.92+ 0.14 (+6%)
3.14 + 0.20 (+14%)*
Relative (g %)
0.65 ±0.03
0.72 ±0.07 (+11%)*
0.70 + 0.03 (+8%)
0.79 ± 0.04 (+22%)**
Adrenal weight
Absolute (mg)
61.7 ±8.8
66.1 ± 6 (+7%)
55.9 + 6.8 (-9%)
68.9+11.9 (+12%)
Relative (mg %)
14.6 ±2.2
16 ± 2 (+10%)
13.4+1.5 (-8%)
17.3 + 2.8 (+18%)
After Recovery (Day 42)
Body weight (g)
446 ± 20
442 ± 13 (-1%)
448 + 30 (+0%)
433 + 41(—3%)
Liver weight
Absolute (g)
11.16 ± 1.42
10.97 ± 0.38 (-2%)
11.55 + 0.97 (+3%)
12.25 + 1.52 (+10%)
Relative (g %)
2.5 ±0.26
2.49 ± 0.07 (+0%)
2.57 + 0.1 (+3%)
2.83 + 0.17 (+13%)
Kidney weight
Absolute (g)
3.04 ±0.18
3.02 + 0.25 (-1%)
2.96 + 0.38 (-3%)
3.15 + 0.22 (+4%)
Relative (g %)
0.68 ±0.01
0.69 ± 0.05 (+1%)
0.66 + 0.08 (-3%)
0.73 + 0.05 (+7%)
Adrenal weight
Absolute (mg)
64.5 ±8.6
59.5 + 14.6 (-8%)
58.8+ 11 (-9%)
56.4 + 5.2 (-13%)
Relative (mg %)
14.5 ± 1.7
13.4 + 3 (-8%)
13.1 + 2.1 (-10%)
13.1 + 0.8 (-10%)
Unmated Females: ADD [HED] in mg/kg-d
Endpoint
0
62.5 [15.7]
250 [63.0]
1,000 [251.3]
After Dosing (Day 28)
Body weight (g)
289 ± 16
285 + 9 (-1%)
286 + 7 (-1%)
274 + 7 (-5%)
Liver weight
Absolute (g)
7.58 ±0.6
7.84 + 0.47 (+3%)
7.77 + 0.48 (+3%)
8.29 + 0.88 (+9%)
Relative (g %)
2.63 ±0.19
2.75+ 0.14 (+5%)
2.71 + 0.12 (+3%)
3.02 ± 0.28 (+15%)*
Kidney weight
Absolute (g)
1.83 ±0.11
1.87 + 0.09 (+2%)
1.95 + 0.08 (+7%)
2.04 + 0.25 (+11%)
Relative (g %)
0.64 ± 0.04
0.66 + 0.03 (+3%)
0.68 + 0.03 (+6%)
0.74 ± 0.09 (+16%)*
Adrenal weight
Absolute (mg)
65.3 ±5.6
75.3 + 8.7 (+15%)
74.7 + 6.5 (+14%)
84.1 + 8.5 (+29%)**
Relative (mg %)
22.7 ±2.6
26.5 + 3.5 (+17%)
26.1 + 2.7 (+15%)
30.6 ± 2.4 (+35%)**
60
Methylcyclohexane
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EPA/690/R-23/007F
Table B-6. Select Organ Weights of Male and Female Crl:CD Sprague
Dawley Rats Treated with Methylcyclohexane During Premating, Mating,
and Lactation or for 28 Days"
Uterus weight
Absolute (mg)
499 ± 69
542 ± 87 (+9%)
568 ± 148 (+14%)
665 ± 108 (+33%)
Relative (mg %)
173 ±23
190 ± 33 (+10%)
199 ± 54 (+15%)
243 ± 38 (+40%)*
After Recovery (Day 42)
Body weight (g)
295 ±5
NA
NA
293 ± 18 (-1%)
Liver weight
Absolute (g)
7.41 ±0.18
NA
NA
7.86 ± 0.37 (+6%)f
Relative (g %)
2.51 ±0.07
NA
NA
2.69 ± 0.23 (+7%)
Kidney weight
Absolute (g)
1.94 ±0.12
NA
NA
1.92 ± 0.18 (-1%)
Relative (g %)
0.66 ± 0.04
NA
NA
0.66 ± 0.06 (+0%)
Adrenal weight
Absolute (mg)
78.2 ±6.5
NA
NA
80.5 ± 10 (+3%)
Relative (mg %)
26.5 ±2.3
NA
NA
27.7 ± 4.5 (+5%)
Uterus weight
Absolute (mg)
581±165
NA
NA
595 ± 109 (+2%)
Relative (mg %)
196 ±56
NA
NA
203 ± 36 (+4%)
Mated Females: ADD [HED] in mg/kg-d
Endpoint
0
62.5 [16.0]
250 [63.9]
1,000 [253.9]
Day 5 of Lactation
Body weight (g)
309 ± 19
320 ±21
314 ± 18
297 ± 35
Uterus weight
Absolute (mg)
625 ± 92
647 ± 88 (+4%)
634 ± 95 (+1%)
657 ± 146 (+5%)
Relative (mg %)
202 ± 30
203 ± 29 (+0%)
202 ± 33 (+0%)
221 ± 39 (+9%)
aJECD6 (2013).
bADD (mg/kg-day) values were reported by the study authors; calculated HEDs appear in brackets.
°Values are expressed as mean ± SD from n = 6 (males), n = 5 (unmated females), and n = 11 (mated females).
dValue in parentheses is % change relative to control = ([treatment mean - control mean] + control mean) x 100.
* Significantly different from control (p < 0.05), as reported by the study authors (Dunnett's test).
**Significantly different from control (p < 0.01), as reported by the study authors (Dunnett's test).
tSignificantly different from control (p < 0.05), as reported by the study authors (Student's t-test).
ADD = adjusted daily dose; HED = human equivalent dose; NA = not applicable; SD = standard deviation.
61
Methylcyclohexane
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EPA/690/R-23/007F
Table B-7. Select Hematology in Male and Female CDF F344/CrlBr Rats
Exposed to Methylcyclohexane Vapors for 6 Hours/Day, 5 Days/Week for
1 Year"
Endpoint
Exposure Concentration [HECer]1" in mg/m3
0
1,607 [287.0]
8,048 [1,437]
Males
WBC (103)
6.7°
5.4 (-19%)d'*
5.3 (-21%)*
RBC (106)
9.7
9.8 (+1%)
9.7 (+0%)
HCT (%)
47.7
48.9 (+3%)*
47.0 (-1%)
HGB (g/dL)
15.2
15.4 (+1%)
14.7 (-3%)**
Females
WBC (103)
5.4
4.8 (-11%)
3.6 (-33%)*
RBC (106)
7.8
7.8 (+0%)
7.9 (+1%)
HCT (%)
44.1
43.1 (-2%)
44.0 (+0%)
HGB (g/dL)
14.5
14.4 (-1%)
14.3 (-1%)
aAFRL (1985).
' Reported concentrations; calculated HECer values appear in brackets.
Data are means from 9 or 10 animals; measures of variance were not provided.
dValue in parentheses is % change relative to control = ([treatment mean - control mean] control mean) x 100.
* Significantly different from control (p < 0.05) as reported by the study authors.
**Significantly different from control (p < 0.01) as reported by the study authors.
HCT = hematocrit; HGB = hemoglobin; HECer = human equivalent concentration based on extrarespiratory
effects; RBC = red blood cell; WBC = white blood cell.
62
Methylcyclohexane
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Table B-8. Renal Lesions in Male and Female CDF F344/CrlBr Rats
Exposed to Methylcyclohexane Vapors for 6 Hours/Day, 5 Days/Week
for 1 Year"
Endpoint
Time of Sacrifice
Exposure Concentration [HECer]1" in mg/m3
0
1,607 [287.0]
8,048 [1,437]
Males
Renal tubular dilatation
12 mo
1/11 (9%)°
2/10 (20%)
4/11 (36%)
CPN
Medullary mineralization
Papillary hyperplasia
Tubular degeneration
24 mo
49/53 (92%)
1/53 (2%)
1/53 (2%)
1/53 (2%)
52/55 (95%)
2/55 (4%)
1/55 (2%)
0/55 (0%)
52/52 (100%)
19/52 (37%)**
23/52 (44%)**
2/52 (4%)
Females
CPN
Medullary mineralization
24 mo
15/52 (29%)
4/52 (8%)
7/51 (14%)
0/51 (0%)
15/54 (28%)
1/54 (2%)
aAFRL (1985).
' Reported concentrations; calculated HECer values appear in brackets.
0Values denote number of animals showing changes/total number of animals examined (% incidence).
* Significantly different from control (p < 0.05) as reported by the study authors.
**Significantly different from control (p < 0.01) as reported by the study authors.
CPN = chronic progressive nephropathy; HECer = human equivalent concentration based on extrarespiratory
effects.
63
Methylcyclohexane
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EPA/690/R-23/007F
Table B-9. Select Neoplastic Lesions in Male and Female CDF F344/CrlBr
Rats Exposed to Methylcyclohexane Vapors for 6 Hours/Day, 5 Days/Week
for 1 Year"
Endpoint
Time of Sacrifice
Exposure Concentration [HECer]1" in mg/m3
0
1,607 [287.0]
8,048 [1,437]
Males
Testicular tumor (unspecified)
12 mo
0/11 (0%)c
5/10 (50%)*
2/10 (20%)
Testis (interstitial cell tumor)
24 mo
49/54 (91%)
49/55 (89%)
50/52 (96%)
Renal cell adenoma
Renal cell carcinoma
24 mo
0/54 (0%)
0/54 (0%)
0/55 (0%)
1/55 (2%)
1/52 (2%)
0/52 (0%)
Females
Mammary gland fibroadenoma
24 mo
0/47 (0%)
4/50 (8%)
6/48 (13%)
aAFRL (1985).
' Reported concentrations; calculated HECer values appear in brackets.
0Values denote number of animals showing changes/total number of animals examined (% incidence).
* Significantly different from control (p < 0.05) as reported by the study authors.
HECer = human equivalent concentration based on extrarespiratory effects.
64
Methylcyclohexane
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APPENDIX C. BENCHMARK DOSE MODELING RESULTS
MODELING PROCEDURE FOR DICHOTOMOUS DATA
Benchmark dose (BMD) modeling of dichotomous data was conducted with the
U.S. Environmental Protection Agency (U.S. EPA) Benchmark Dose Software (BMDS;
Version 3.2). For the dichotomous data, the Gamma, Logistic, Log-Logistic, Log-Probit,
Multistage, Probit, and Weibull dichotomous models available within the software were fit using
a benchmark response (BMR) of 10% extra risk. The Dichotomous Hill model was not
considered for the derivation of a point of departure (POD) because it has four parameters and
requires a data set with a minimum of five data points (including control). Alternative BMRs
may also be used where appropriate, as outlined in the Benchmark Dose Technical Guidance
(U.S. EPA. 2012a). In general, the BMR should be near the low end of the observable range of
increased risk in the study. BMRs that are too low can result in widely disparate benchmark dose
lower confidence limit (BMDL) estimates from different models (high model-dependence).
Adequacy of model fit was judged based on the %2 goodness-of-fitp-value {p > 0.1), magnitude
of scaled residuals for the dose group nearest to the BMD (absolute value <2.0), BMDL that is
not 10 times lower than the lowest nonzero dose, and visual inspection of the model fit. Among
all models providing adequate fit, the BMDL from the model with the lowest Akaike's
information criterion (AIC) was selected as a potential POD if the BMDLs were sufficiently
close (less than threefold); if the BMDLs were not sufficiently close (greater than threefold),
model-dependence was indicated, and the model with the lowest reliable BMDL was selected.
MODELING PROCEDURE FOR CONTINUOUS DATA
BMD modeling of continuous data was conducted with the U.S. EPA's BMDS
(Version 3.2). For the continuous data, the Exponential, Linear, Polynomial, and Power
continuous models were fit using a standard reporting BMR of 1 standard deviation (SD) relative
risk or 10% relative deviation as outlined in the Benchmark Dose Technical Guidance (U.S.
HP A. 2012a). The continuous Hill model was not considered for the derivation of a POD because
it has five parameters and requires a data set with a minimum of six data points (including
control). An adequate fit was judged based on the %2 goodness-of-fit p-v alue {p > 0.1), magnitude
of the scaled residuals for the dose group nearest to the BMD (absolute value <2.0), and visual
inspection of the model fit. In addition to these three criteria forjudging adequacy of model fit, a
determination was made as to whether the variance across dose groups was constant. If a
constant variance model was deemed appropriate based on the statistical test provided in BMDS
(i.e., Test 2; p-v alue >0.1), the final BMD results were estimated from a constant variance
model. If the test for homogeneity of variance was rejected (p-v alue <0.1), the model was run
again while modeling the variance as a power function of the mean to account for this
nonconstant variance. If this nonconstant variance model did not adequately fit the data
(i.e., Test 3; p-v alue <0.1), the data set was considered unsuitable for BMD modeling. Among all
models providing adequate fit, the lowest BMDL was selected if the BMDLs estimated from
different models varied by greater than threefold; otherwise, the BMDL from the model with the
lowest AIC was selected as a potential POD from which to derive the proposed reference value.
65
Methylcyclohexane
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EPA/690/R-23/007F
BMD MODELING TO IDENTIFY POTENTIAL PODS FOR DERIVATION OF A
SCREENING SUBCHRONIC PROVISIONAL REFERENCE DOSE (p-RfD)
Increased Relative Liver Weight in Male Crj:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days (ECUA. 2001c)
The procedure outlined above for continuous data was applied to the data for increased
relative liver weight in male Crj :CD (Sprague Dawley) rats orally exposed to methylcyclohexane
for 28 days (HCHA. 2001c). The constant variance model did not provide an adequate fit to the
variance data (Test 2; />value <0.01). The nonconstant variance model did provide an adequate
fit to the variance data (Test 3; />value >0.1); however, with the nonconstant variance model
applied, none of the models provided adequate fits to the means (Test 4; p-walue <0.1). The
results of the BMD modeling are summarized in Table C-l. Because none of the models
provided adequate fit to the data, this endpoint was not considered further.
Table C-l. BMD Modeling Results (Nonconstant Variance) for Increased
Relative Liver Weight in Male Crl:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days"
Model
Variance
/>-Valucb
Means
/>-Valucb
Scaled Residual
at Dose Nearest
BMD
AIC
BMDo.ird
(mg/kg-d)
HED
BMDLo.ird
(mg/kg-d)
HED
Exponential (model 2)°
0.11
0.06
0.55
-1.76
104.15
87.81
Exponential (model 3)°
0.11
0.02
0.67
0.20
112.39
87.92
Exponential (model 4)°
0.11
0.02
0.40
0.20
94.17
39.07
Exponential (model 5)°
0.11
NA
-0.25
-0.78
75.59
58.52
Polynomial (3-degree)d
0.11
0.06
0.43
-1.80
95.70
78.95
Polynomial (2-degree)d
0.11
0.06
0.43
-1.80
95.70
78.68
Power0
0.11
0.02
0.64
0.07
109.64
79.05
Linear"1
0.11
0.06
0.43
-1.80
95.70
78.68
aECHA (2001c).
bValues <0.10 fail to meet conventional goodness-of-fit criteria.
Tower restricted to be >1.
Coefficients restricted to be positive.
AIC = Akaike's information criterion; BMD = maximum likelihood estimate of the exposure concentration
associated with the selected BMR; BMDL = 95% benchmark dose lower confidence limit on the BMD (subscripts
denote BMR: i.e., 0.1RD = relative deviation of 10%); BMR = benchmark response; HED = human equivalent
dose; NA = not applicable (computation failed).
Increased Absolute Liver Weight in Male Crj:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days (ECUA. 2001c)
The procedure outlined above for continuous data was applied to the data for increased
absolute liver weight in male Crj :CD (Sprague Dawley) rats orally exposed to
methylcyclohexane for 28 days (FXHA. 2001c). The constant variance model provided adequate
fit to the variance data (Test 2p-walue >0.1). With the constant variance model applied, all
available models provided adequate fit to the means, except for the Exponential 5 model. Visual
66
Methylcyclohexane
-------
EPA/690/R-23/007F
inspection of the dose-response curves suggested adequate fit, BMDLs were not 10 times lower
than the lowest nonzero dose, and scaled residuals did not exceed ±2 units at the data point
closest to the BMD. BMDLs for models providing adequate fit were not sufficiently close
(differed by greater than threefold), so the model with the lowest BMDL was selected
(Exponential 4). The Exponential 4 model estimated human equivalent benchmark dose with
10% relative deviation (BMDo.ird) and benchmark dose lower confidence limit with 10%
relative deviation (BMDLo.ird) values of 39.9 and 13.5 mg/kg-day, respectively. The results of
the BMD modeling are summarized in Table C-2 and plotted in Figure C-l.
Table C-2. BMD Modeling Results (Constant Variance) for Increased
Absolute Liver Weight in Male Crl:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days"
Model
Variance
/>-Valucb
Means
/>-Valucb
Scaled Residual
at Dose Nearest
BMD
AIC
BMDo.ird
(mg/kg-d)
HED
BMDLo.ird
(mg/kg-d)
HED
Exponential (model 2)°
0.27
0.12
1.568173
72.04
115.74
75.78
Exponential (model 3)°
0.27
0.12
1.568171
72.04
115.74
76.54
Exponential (model 4)c *
0.27
0.10
-1.234229
72.44
39.9
13.5
Exponential (model 5)°
0.27
NA
-0.000001
72.02
70.41
25.65
Polynomial (3-degree)d
0.27
0.13
1.527652
71.86
106.43
65.78
Polynomial (2-degree)d
0.27
0.13
1.527652
71.86
106.43
65.78
Power0
0.27
0.13
1.527651
71.86
106.43
65.78
Linear"1
0.27
0.13
1.527651
71.86
106.43
65.78
aECHA (2001c).
bValues <0.10 fail to meet conventional goodness-of-fit criteria.
Tower restricted to be >1.
Coefficients restricted to be positive.
* Selected model. The constant variance model provided an adequate fit to the variance data. All models, except the
Exponential 5 model provided adequate fit to the means. BMDLs for models providing adequate fit were not
sufficiently close (differed by greater than threefold), so the model with the lowest BMDL was selected
(Exponential 4).
AIC = Akaike's information criterion; BMD = maximum likelihood estimate of the exposure concentration
associated with the selected BMR; BMDL = 95% benchmark dose lower confidence limit on the BMD (subscripts
denote BMR: i.e., 0.1RD = relative deviation of 10%); BMR = benchmark response; HED = human equivalent
dose; NA = not applicable (computation failed).
67
Methylcyclohexane
-------
EPA 690 R-23 00 7F
Frequentist Exponential Degree 4 Model with BMR of 0.1 Rel.
Dev. for the BMD and 0.95 Lower Confidence Limit for the BMDL
14
Estimated Probability
^^Response at BMD
O Data
BMD
BMDL
50
100
150
200
Dose
Figure C-l. Fit of Exponential 4-Degree Model to the Data for Increased Absolute Liver
Weight in Male Crl:CD (Sprague Dawley) Rats Exposed to Methylcyclohexane via Gavage
for 28 Days (ECHA. 2001c)
68
Methylcyclohexane
-------
EPA/690/R-23/00 7F
BMD Model Output of Exponential 4-Degree Model for Increased Absolute Liver Weight
in Male Crl:CD (Sprague Dawley) Rats Exposed to Methylcyclohexane via Gavage for
28 Days (IX HA, 2001c)
Frequentist Exponential Degree 4 Restricted
User Input
Info
Model
frequentist Exponential degree 4 vl.l
Dataset Name
Abs liv Wt M R
User notes
[Add user notes here]
Dose-Response Model
Mfdose] = a * [c-(c-l) * exp(-b * dose)]
Variance Model
Var[i] = alpha
Model Options
BMRType
Rel. Dev.
BMRF
0.1
Tail Probability
-
Confidence Level
0.95
Distribution Type
Normal
•
Variance Type
Constant
Model Data
Dependent Variable
HED
Independent Variable
Mean
Total # of Observations
4
Adverse Direction
Upward
69
Methylcyclohexane
-------
EPA/690/R-23/00 7F
Model Results
Benchmark Dose
BMD
39.85902309
BMDL
13.46632275
BMDU
173.0784801
AIC
72.44059703
Test4P-value
0.101059176
D.O.F.
1
Model Parameters
# of Parameters
4
Variable
Estimate
a
9.32129997
b
0.01061126
c
1.289946148
log-alpha
0.384152652
Goodness of Fit
Dose
Size
Estimated
Calc'd
Observed
Estimated
Calc'd SD
Observed
Scaled
Median
Median
Mean
SD
SD
Residual
0
5
9.32129997
9.65
9.65
1.211763
0.97
0.97
0.606550629
24.9
5
9.948849455
9.28
9.28
1.211763
1.89
1.89
-1.23422884
74.6
5
10.799341
11.22
11.22
1.211763
1.02
1.02
0.776242649
248.5
5
11.8305095
11.75
11.75
1.211763
0.93
0.93
-0.14B5643
Likelihoods of Interest
# of ^
Model
Log Likelihood*
Parameters
AIC
A1
-30.87592439
5
71.7518488
A2
-28.91408293
8
73.8281659
A3
-30.87592439
5
71.7518488
fitted
-32.22029852
4
72.440597
R
-36.94835965
2
77.8967193
' Includes additive constant of-18.37877. This constant was not included in the LL derivation prior to BMDS 3.0.
Tests of Interest
Test
2*Log(Likelihoo
d Ratio)
Test df
p-value
1
16.06855345
6
0.01339071
2
3.92368292
3
0.26982379
3
3.92368292
3
0.26982379
4
2.688748248
1
0.10105918
Increased Relative Liver Weight in Female Crj:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days (i'.CHA, 2001c)
The procedure outlined above for continuous data was applied to the data for increased
relative liver weight in female Crj :CD (Sprague Dawley) rats orally exposed to
methylcyclohexane for 28 days (ECHA, 2001c). The constant variance model did not provide an
adequate fit to the variance data (Test 2p-value <0.1). The nonconstant variance model did
provide an adequate fit to the variance data (Test 3 p-value >0.1); however, with the nonconstant
variance model applied, none of the models provided adequate fits to the means (Test 4
p-value <0.1). The results of the BMD modeling are summarized in Table C-3. Because none of
the models provided adequate fit to the data, this endpoint was not considered further.
70
Methylcyclohexane
-------
EPA/690/R-23/007F
Table C-3. BMD Modeling Results (Nonconstant Variance) for Increased
Relative Liver Weight in Female Crl:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days"
Model
Variance
/>-Valucb
Means
/>-Valucb
Scaled Residual
at Dose Nearest
BMD
AIC
BMDo.ird
(mg/kg-d)
HED
BMDLo.ird
(mg/kg-d)
HED
Exponential (model 2)°
0.64
0.0022
0.21
-6.42
222.34
142.28
Exponential (model 3)°
0.64
0.0022
0.21
-6.42
222.24
142.28
Exponential (model 4)°
0.64
0.0005
0.24
-4.38
223.94
0.00
Exponential (model 5)°
0.64
0.0005
0.23
-4.38
222.37
0.00
Polynomial (3-degree)d
0.64
0.0029
0.01
-7.01
232.02
145.96
Polynomial (2-degree)d
0.64
0.0005
0.07
-4.70
231.30
141.86
Power0
0.64
0.0021
0.23
-6.39
222.33
138.21
Linear"1
0.64
0.0021
0.23
-6.39
222.34
138.21
aECHA (2001c).
bValues <0.10 fail to meet conventional goodness-of-fit criteria.
Tower restricted to be >1.
Coefficients restricted to be positive.
AIC = Akaike's information criterion; BMD = maximum likelihood estimate of the exposure concentration
associated with the selected BMR; BMDL = 95% benchmark dose lower confidence limit on the BMD (subscripts
denote BMR: i.e., 0.1RD = relative deviation of 10%); BMR = benchmark response; HED = human equivalent
dose; NA = not applicable (computation failed).
Increased Incidence of Liver Cell Hypertrophy in Male Crj:CD (Sprague Dawley) Rats
Exposed to Methylcyclohexane via Gavage for 28 Days (ECUA. 2001c)
Incidences of liver cell hypertrophy in male Crj:CD (Sprague Dawley) rats exposed to
methylcyclohexane via gavage for 28 days were fit to the dichotomous models in the BMDS
(Version 3.2) using the procedure described above for dichotomous data. All the models
provided an adequate fit according to the %2 goodness-of-fit p-value (p >0,1) and scaled residuals
did not exceed ±2 units at the data point closest to the BMD (see Table C-4). The BMDL
computation failed when the Weibull model was applied to the data; therefore, this model was
not considered for selection. BMDLs for the remaining models were not sufficiently close
(differed by greater than threefold), so the model with the lowest BMDL (Multistage 1-degree)
was considered. However, fit of this model to the data was particularly poor. This is the least
flexible model applied, and visual inspection showed that the model shape was not representative
of the observed data at any point. For this reason, the Multistage 1-degree was rejected. Among
the remaining models, BMDLs were sufficiently close, so the model with the lowest AIC was
selected (Log-Logistic). Figure C-2 shows the fit of the Log-Logistic model to the data. Based on
HEDs, the 10% benchmark dose (BMDio) and 10% benchmark dose lower confidence limit
(BMDLio) values for increased incidence of liver hypertrophy in male Cij:CD (Sprague Dawley)
rats were 121 and 59.9 mg/kg-day, respectively.
71
Methylcyclohexane
-------
EPA/690/R-23/007F
Table C-4. BMD Modeling Results for Increased Incidence of Liver Cell
Hypertrophy in Male Crj:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days"
Model
X2 Goodness-
of-fit
/>-valucb
AIC
Scaled Residual at
Dose Nearest BMD
BMD io
(mg/kg-d)
HED
BMDLio
(mg/kg-d)
HED
Gamma0
0.996
2.12
-0.1908
102.96
55.69
Log-logisticd*
1.0
2.00
-0.0100
121
59.9
Multistage (degree = 3)e
0.88
3.29
-0.7153
76.57
33.51
Multistage (degree = 2)e
0.61
5.35
-1.0979
52.11
24.57
Multistage (degree = l)e
0.18
10.38
-0.8175
20.91
10.19
Weibull0
1.0
2.00
0.0002
186.52
0.00
Logistic
1.0
2.00
-0.0202
137.25
57.44
Log-probitd
1.0
4.00
-0.0003
133.84
59.91
Probit
1.0
4.00
0.0000
147.00
54.88
aECHA (2001c).
bValues <0.10 fail to meet conventional goodness-of-fit criteria.
Tower restricted to be >1.
dSlope restricted to be >1.
"Betas restricted to be >0.
* Selected model. All models provided adequate fit to the data, although the BMDL computation failed for the
Weibull model. BMDLs for the remaining models were not sufficiently close (differed by greater than threefold),
so the model with the lowest BMDL (Multistage 1-degree) was considered. However, fit of this model to the data
was particularly poor. This is the least flexible model applied, and visual inspection showed that the model shape
was not representative of the observed data at any point. Fortius reason, the Multistage 1-degree was rejected.
Among the remaining models, BMDLs were sufficiently close, so the model with the lowest AIC was selected
(Log-Logistic).
AIC = Akaike's information criterion; BMD = maximum likelihood estimate of the exposure concentration
associated with the selected BMR; BMDL = 95% benchmark dose lower confidence limit on the BMD (subscripts
denote BMR: i.e., 10 = exposure concentration associated with 10% extra risk); BMR = benchmark response;
HED = human equivalent dose; NA = not applicable (computation failed).
72
Methylcyclohexane
-------
EPA 690 R-23 00 7F
£ 0.6
o
a 0.4
cc
0.2
Frequentist Log-Logistic Model with BMR of 10% Extra Risk for
the BMD and 0.95 Lower Confidence Limit for the BMDL
9
o 0-
0
Estimated Probability
^^Response at BMD
O Data
BMD
BMDL
50
100
150
200
Dose
Figure C-2. Fit of Log-Logistic Model to the Data for Increased Incidence of Liver Cell
Hypertrophy in Male Cri:CD (Sprague Dawley) Rats Exposed to Methylcyclohexane via
Gavage for 28 Days (ECHA. 2001c)
73
Methylcyclohexane
-------
EPA 690 R-23 00 7F
BMD Model Output of Log-Logistic Model for Increased Incidence of Liver Cell
Hypertrophy in Male Cri:CD (Sprague Dawley) Rats Exposed to Methylcyclohexane via
Gavage for 28 Days (ECHA. 2001c)
User Input
Info
Model
frequentist Log-Logistic vl.l
Dataset Name
liv_hypertroph_M_R
User notes
[Add user notes here]
Dose-Response Model
P[dose] = g+(l-g)/[l+exp(-a-b*Log(dose))]
Model Options
Risk Type
Extra Risk
BMR
0.1
Confidence Level
0.95
Background
Estimated
Model Data
Dependent Variable
HED
Independent Variable
Incidence
Total # of Observations
4
74
Methylcyclohexane
-------
EPA 690 R-23 00 7F
Model Results
Benchmark Dose
BMD
120.5089082
BMDL
59.86096088
BMDU
206.1051687
AIC
2.000396496
P-value
0.999999258
D.O.F.
3
Chi2
0.00019825
Model Parameters
# of Parameters
3
Variable
Estimate
g
Bounded
a
-88.44825077
b
Bounded
Goodness of Fit
Dose
Estimated
Probability
Expected
Observed
Size
Scaled
Residual
0
1.523E-08
7.61499E-08
0
5
-0.000276
24.9
1.523E-08
7.61502E-08
D
5
-0.000276
74.6
1.9817E-05
9.90848 E-05
0
5
-0.0099542
248.5
0.999980198
4.999900991
5
5
0.0099504
Analysis of Deviance
Model
Log Likelihood
# of Parameters
Deviance
Test d.f.
P Value
Full Model
0
4
-
-
NA
Fitted Model
-0.000198248
1
0.0003965
3
0.9999979
Reduced Model
-11.24670289
1
22.4934058
3
<0.0001
Increased Incidence of Kidney Tubule Hyaline Droplet Degeneration in Male Crj:CD
(Sprague Dawley) Rats Exposed to Methylcyclohexane via Gavage for 28 Days (ECHA,
2001c)
Incidences of kidney tubule hyaline droplet degeneration in male Crj:CD (Sprague
Dawley) rats exposed to methylcyclohexane via gavage for 28 days were fit to the dichotomous
models in the BMDS (Version 3.2) using the procedure described above for dichotomous data.
All the models provided an adequate fit according to the %2 goodness-of-fit/rvalue (p > 0.1) and
scaled residuals did not exceed ±2 units at the data point closest to the BMD (see Table C-5).
The Multistage 1-degree model was considered questionable because the BMDL was more than
10 times lower than the lowest nonzero dose; therefore, this model was not considered for
selection. BMDLs for the remaining models were not sufficiently close (differed by greater than
threefold), so the model with the lowest BMDL (Multistage 2-degree) was selected. Figure C-3
shows the fit of the Multistage 2-degree model to the data. Based on HEDs, the BMDio and
BMDLio values for increased incidence of kidney tubule hyaline droplet degeneration in male
Cij:CD (Sprague Dawley) rats were 13.35 and 3.37 mg/kg-day, respectively.
75
Methylcyclohexane
-------
EPA/690/R-23/007F
Table C-5. BMD Modeling Results for Increased Incidence of Kidney
Tubule Hyaline Droplet Degeneration in Male Crj:CD (Sprague Dawley)
Rats Exposed to Methylcyclohexane via Gavage for 28 Days"
Model
X2 Goodness-
of-fit
/>-valucb
AIC
Scaled Residual at
Dose Nearest BMD
BMD io
(mg/kg-d)
HED
BMDLio
(mg/kg-d)
HED
Gamma0
1.00
7.01
-0.00186
21.73
5.70
Log-logisticd
1.00
9.01
-0.00113
22.61
9.35
Multistage (degree = 3)e
1.00
7.02
-0.05486
19.04
3.61
Multistage (degree = 2)e'*
0.93
7.67
-0.51755
13.4
3.4
Multistage (degree = l)e
0.31
12.22
-0.00028
4.21
2.10
Weibull0
0.99
7.15
-0.13495
17.71
16.71
Logistic
1.00
7.00
0.00006
22.89
9.05
Log-probitd
1.00
9.00
0.00000
23.38
9.26
Probit
1.00
7.07
0.00918
19.19
8.14
aECHA (2001c).
bValues <0.10 fail to meet conventional goodness-of-fit criteria.
Tower restricted to be >1.
dSlope restricted to be >1.
"Betas restricted to be >0.
* Selected model. All models provided adequate fit to the data. The Multistage 1-degree model was considered
questionable because the BMDL was more than ten times lower than the lowest nonzero dose; therefore, this model
was not considered for selection. BMDLs for the remaining models were not sufficiently close (differed by greater
than threefold), so the model with the lowest BMDL (Multistage 2-degree) was selected.
AIC = Akaike's information criterion; BMD = maximum likelihood estimate of the exposure concentration
associated with the selected BMR; BMDL = 95% benchmark dose lower confidence limit on the BMD (subscripts
denote BMR: i.e., 10 = exposure concentration associated with 10% extra risk); BMR = benchmark response;
HED = human equivalent dose; NA = not applicable (computation failed).
76
Methylcyclohexane
-------
EPA 690 R-23 00 7F
Frequentist Multistage Degree 2 Model with BMR of 10% Extra
Risk for the BMD and 0.95 Lower Confidence Limit for the BMDL
Q
Estimated Probability
^^Response at BMD
O Data
BMD
BMDL
100 150
Dose
200
Figure C-3. Fit of Multistage 2-Degree Model to the Data for Increased Incidence of
Kidney Tubule Hyaline Droplet Degeneration in Male Crj:CD (Sprague Dawley) Rats
Exposed to Methylcyclohexane via Gavage for 28 Days (ECHA, 2001c)
77
Methylcyclohexane
-------
EPA 690 R-23 00 7F
BMD Model Output of Multistage 2-Degree Model for Increased Incidence of Kidney
Tubule Hyaline Droplet Degeneration in Male Crj:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days (ECHA, 2001c)
Frequentist Multistage Degree 2 Restricted
User Input
Info
Model
frequentist Multistage degree 2vl.l
Dataset Name
Hy a 1 i n e_d ro p_d ege n_M_rat
User notes
Dose-Response Model
P[dose] =g + (l-g)*[l-exp(-bl*doseAl-b2*doseA2 -...)
Model Options
RiskType
Extra Risk
BMR
0.1
Confidence Level
0.95
Background
Estimated
Model Data
Dependent Variable
HED
Independent Variable
Incidence
Total # of Observations
4
78
Methylcyclohexane
-------
EPA 690 R-23 00 7F
Model Results
Benchmark Dose
BMD
13.35354628
BMDL
3.374676462
BMDU
21.29793115
AIC
7.674613074
P-value
0.92722381
D.O.F.
3
Chi2
0.461689187
Slope Factor
0.02963247
Model Parameters
# of Parameters
3
Variable
Estimate
g
Bounded
bl
Bounded
b2
0.00059086
Goodness of Fit
Dose
Estimated
Probability
Expected
Observed
Size
Scaled
Residual
0
1.523E-08
7.61499E-08
0
5
-0.000276
24.9
0.306732356
1.533661781
1
5
-0.5175482
74.6
0.962680177
4.813400883
5
5
0.44026461
248.5
1
5
5
5
3.7697E-08
Analysis of Deviance
Model
Log Likelihood
#of Parameters
Deviance
Test d.f.
P Value
Full Model
-2.502012118
4
-
-
NA
Fitted Model
-2.837306537
1
0.670588839
3
0.88009896
Reduced Model
-13.76277627
1
22.52152831
3
<0.0001
Increased Relative Liver Weights in Male Crl:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days During Premating and Mating (JECDB, 2013)
The procedure outlined above for continuous data was applied to the data for increased
relative liver weight in male Crl:CD (Sprague Dawley) rats orally exposed to methylcyclohexane
for 28 days during premating and mating (JECDB. 2013). The constant variance model provided
adequate fit to the variance data (Test 2/>-value >0.1). With the constant variance model applied,
all available models provided adequate fit to the means, except for the Exponential 5 model.
Visual inspection of the dose-response curves suggested adequate fit, BMDLs were not 10 times
lower than the lowest nonzero dose, and scaled residuals did not exceed ±2 units at the data point
closest to the BMD. BMDLs for models providing adequate fit were sufficiently close (differed
by less than threefold), so the model with the lowest AIC was selected (Exponential 2). The
Exponential 2 model estimated human equivalent BMDo.ird and BMDLo.ird values of 66.03 and
61.05 mg/kg-day, respectively. The results of the BMD modeling are summarized in Table C-6
and plotted in Figure C-4.
79
Methylcyclohexane
-------
EPA/690/R-23/007F
Table C-6. BMD Modeling Results (Constant Variance) for Increased
Relative Liver Weight in Male Crl:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days During Premating and Mating"
Model
Variance
/>-Valucb
Means
/>-Valucb
Scaled Residual
at Dose Nearest
BMD
AIC
BMDo.ird
(mg/kg-d)
HED
BMDLo.ird
(mg/kg-d)
HED
Exponential (model 2)c *
0.30
0.79
-0.562989
-26.00
66.0
61.1
Exponential (model 3)°
0.30
0.93
-0.028174
-24.48
79.09
61.50
Exponential (model 4)°
0.30
0.17
-1.123355
-22.59
55.70
45.23
Exponential (model 5)°
0.30
NA
-0.048939
-22.45
78.93
51.51
Polynomial (3-degree)d
0.30
1.00
0.000004
-24.48
79.26
52.76
Polynomial (2-degree)d
0.30
0.99
-0.002791
-24.48
79.18
52.76
Power0
0.30
0.86
-0.050385
-24.45
78.88
52.78
Linear"1
0.30
0.39
-1.111341
-24.60
55.77
50.42
aJECD6 (2013).
bValues <0.10 fail to meet conventional goodness-of-fit criteria.
Tower restricted to be >1.
Coefficients restricted to be positive.
* Selected model. The constant variance model provided an adequate fit to the variance data. All models, except the
Exponential 5 model, provided adequate fit to the means. BMDLs for models providing adequate fit were
sufficiently close (differed by less than threefold), so the model with the lowest AIC was selected (Exponential 2).
AIC = Akaike's information criterion; BMD = maximum likelihood estimate of the exposure concentration
associated with the selected BMR; BMDL = 95% benchmark dose lower confidence limit on the BMD (subscripts
denote BMR: i.e., 0.1RD = relative deviation of 10%); BMR = benchmark response; HED = human equivalent
dose; NA = not applicable (computation failed).
80
Methylcyclohexane
-------
EPA 690 R-23 00 7F
4.5
A
Frequentist Exponential Degree 2 Model with BMR of 0.1 Rel.
Dev. for the BMD and 0.95 Lower Confidence Limit for the BMDL
H
3.5
(D
tn
c
3
2.5
9
ft""""""" Estimated Probability
o
Q.
Response at BMD
-------
EPA 690 R-23 00 7F
BMD Model Output of Exponential 2-Degree Model for Increased Relative Liver Weight in
Male Crl:CD (Sprague Dawley) Rats Exposed to Methylcyclohexane via Gavage for
28 Days During Premating and Mating (JECDB, 2013)
Frequentist Exponential Degree 2 Restricted
User Input
Info
Model
frequentist Exponential degree 2 vl.l
Dataset Name
rel liv wt M R
User notes
JECB (2013) HERO 69S2772
Dose-Response Model
M[dose] = a * exp(±l * b * dose)
Variance Model
Var[i] = alpha
Model Options
BMR Type
Rel. Dev.
BMRF
0.1
Tail Probability
-
Confidence Level
0.95
Distribution Type
Normal
Variance Type
Constant
Model Data
Dependent Variable
HED
Independent Variable
Mean
Total # of Observations
4
Adverse Direction
Upward
82
Methylcyclohexane
-------
EPA 690 R-23 00 7F
Model Results
Benchmark Dose
BMD
66.03011427
BMDL
61.05298636
BMDU
71.92354647
AIC
-26.00262795
Te5t4P-value
0.7S5812921
D.O.F.
2
Model Parameters
# of Parameters
3
Variable
Estimate
a
2.570948485
b
0.001443434
log-alpha
-4.171223687
Goodness of Fit
Dose
Size
Estimated
Calc'd
Observed
Estimated
Calc'd SD
Observed
Scaled
Median
Median
Mean
SD
SD
Residual
0
6
2.570948485
2.59
2.59
0.12423109
0.08
0.08
0.375642618
17.1
6
2.635196141
2.64
2.64
0.12423109
0.18
0.18
0.09471868
68.6
6
2.838553175
2.81
2.81
0.12423109
0.13
0.13
-0.56298879
273.4
6
3.814882254
3.82
3.82
0.12423109
0.13
0.13
0.100907652
Likelihoods of Interest
# of
Model
Log Likelihood"
Parameters
AIC
A1
16.2423505
5
-22.484701
A2
18.05914626
8
-20.118293
A3
16.2423505
5
-22.484701
fitted
16.00131397
3
-26.002628
R
-18.13857944
2
40.2771589
* Includes additive constant of -22.05452. This constant was not included in the LL derivation prior to BMDS 3.0.
Tests of Interest
Test
2*Log(Likelihoo
d Ratio)
Test df
p-value
1
72.3954514
6
<0.0001
2
3.633591515
3
0.30384458
3
3.633591515
3
0.30384458
4
0.482073059
2
0.78581292
Increased Relative Liver Weights in Unmated Female Crl:CD (Sprague Dawley) Rats
Exposed to Methylcyclohexane via Gavage for 28 Days (JECDB, 2013)
The procedure outlined above for continuous data was applied to the data for increased
relative liver weight in unmated female Crl:CD (Sprague Dawley) rats orally exposed to
methylcyclohexane for 28 days (JECDB. 2013). The constant variance model provided adequate
fit to the variance data (Test 2/>-value >0.1). With the constant variance model applied, all
available models provided adequate fit to the means, except for the Exponential 5 model. Visual
inspection of the dose-response curves suggested adequate fit, BMDLs were not 10 times lower
than the lowest nonzero dose, and scaled residuals did not exceed ±2 units at the data point
closest to the BMD. BMDLs for models providing adequate fit were sufficiently close (differed
by less than threefold), so the model with the lowest AIC was selected (Polynomial 3-degree).
The Polynomial 3-degree model estimated human equivalent BMDo.ird and BMDLo.ird values
of 218.90 and 126.60 mg/kg-day, respectively. The results of the BMD modeling are
summarized in Table C-7 and plotted in Figure C-5.
83
Methylcyclohexane
-------
EPA/690/R-23/007F
Table C-7. BMD Modeling Results (Constant Variance) for Increased
Relative Liver Weight in Unmated Female Crl:CD (Sprague Dawley) Rats
Exposed to Methylcyclohexane via Gavage for 28 Days"
Model
Variance
/>-Valucb
Means
/>-Valucb
Scaled Residual at
Dose Nearest BMD
AIC
BMDo.ird
(mg/kg-d)
HED
BMDLo.ird
(mg/kg-d)
HED
Exponential (model 2)°
0.23
0.57
0.06169
-6.45
193.07
131.72
Exponential (model 3)°
0.23
0.29
0.02343
-4.47
207.50
131.88
Exponential (model 4)°
0.23
0.28
0.07442
-4.42
189.79
65.31
Exponential (model 5)°
0.23
NA
-0.00006
-2.36
243.00
64.73
Polynomial (3-degree)d*
0.23
0.60
0.00288
-6.55
219.0
126.60
Polynomial (2-degree)d
0.23
0.30
0.01260
-4.52
211.42
126.32
Power0
0.23
0.29
0.02201
-4.46
208.27
125.77
Linear"1
0.23
0.56
0.07489
-6.42
189.94
125.47
aJECD6 (2013).
bValues <0.10 fail to meet conventional goodness-of-fit criteria.
Tower restricted to be >1.
Coefficients restricted to be positive.
* Selected model. The constant variance model provided an adequate fit to the variance data. All models, except the
Exponential 5 model provided adequate fit to the means. BMDLs for models providing adequate fit were sufficiently
close (differed by less than threefold), so the model with the lowest AIC was selected (Polynomial 3 -degree).
AIC = Akaike's information criterion; BMD = maximum likelihood estimate of the exposure concentration
associated with the selected BMR; BMDL = 95% benchmark dose lower confidence limit on the BMD (subscripts
denote BMR: i.e., 0.1RD = relative deviation of 10%); BMR = benchmark response; HED = human equivalent dose;
NA = not applicable (computation failed).
84
Methylcyclohexane
-------
EPA 690 R-23 00 7F
Frequentist Polynomial Degree 3 Model with BMR of 0.1 Rel.
Dev. for the BMD and 0.95 Lower Confidence Limit for the BMDL
£
O
Q.
LO
CD
DC
4
3.5
3
2.5
2
1.5
1
0.5
0
6-® 9
L
Estimated Probability
^^Response at BMD
O Data
BMD
BMDL
50
100 150
Dose
200
250
Figure C-5. Fit of Polynomial 3-Degree Model to the Data for Increased Relative Liver
Weight in Unmated Female Crl:CD (Sprague Dawley) Rats Exposed to Methylcyclohexane
via Gavage for 28 Days (JECDB, 2013)
85
Methylcyclohexane
-------
EPA 690 R-23 00 7F
BMD Model Output of Polynomial 3-Degree Model for Increased Relative Liver Weight in
Unmated Female Crl:CD (Sprague Dawley) Rats Exposed to Methylcyclohexane via
Gavage for 28 Days (JECDB. 2013)
Frequentist Polynomial Degree 3 Restricted
User Input
Info
Model
frequentist Polynomial degree 3 vl.l
Dataset Name
rel liv wt unmated F R
User notes
JECB (2013) HERO 69S2772
Dose-Response Model
M[dose] =g + bl*dose + b2*doseA2 +...
Variance Model
Var[i] = alpha
Model Options
BMR Type
Rel. Dev.
BMRF
0.1
Tail Probability
-
Confidence Level
0.95
Distribution Type
Normal
Variance Type
Constant
Model Data
Dependent Variable
HED
Independent Variable
Mean
Total # of Observations
4
Adverse Direction
Upward
86
Methylcyclohexane
-------
EPA/690/R-23/00 7F
Model Results
Benchmark Dose
BMD
218.9001076
BMDL
126.5996693
BMDU
364.7746736
AIC
-6.552506626
Test 4 P-value
0.599860378
D.O.F.
2
Model Parameters
# of Parameters
5
Variable
Estimate
a
9
2.675879076
betal
0.000763083
beta 2
Bounded
beta 3
Bounded
alpha
0.031293475
Goodness of Fit
Dose
Size
Estimated
Median
Calc'd
Median
Observed
Mean
Estimated
5D
Calc'd SD
Observed
SD
Scaled
Residual
0
5
2.675879076
2.63
2.63
0.17689962
0.19
0.19
-0.57992624
15.7
5
2.687896573
2.75
2.75
0.17689962
0.14
0.14
0.785007254
63
5
2.726350255
2.71
2.71
0.17689962
0.12
0.12
-0.20667247
251.3
5
3.019772512
3.02
3.02
0.17689962
0.28
0.28
0,002875518
Likelihoods of Interest
# of
Model
Log Likelihood"
Parameters
AIC
A1
6.787311668
5
-3.5746233
A2
8.953031225
8
-1.9060624
A3
6.787311668
5
-3.5746233
fitted
6.276253313
3
-6.5525066
R
1.347492184
2
1.30501563
* Includes additive constant of -18.37877. This constant was not included in the LL derivation prior to BMDS 3.0.
Tests of Interest
Test
2*Log(Likeiihoo
d Ratio)
Test df
p-value
i
15.21107808
6
0.01867703
2
4.331439114
3
0.22782739
3
4.331439114
3
0.22782739
4
1.02211671
2
0.59986038
Increased Relative Kidney Weights in Male Crl:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days During Preinating and Mating (JECDB, 2013)
The procedure outlined above for continuous data was applied to the data for increased
relative kidney weight in male Crl:CD (Sprague Dawley) rats orally exposed to
methylcyclohexane for 28 days (JECDB. 2013). The constant variance model did not provide an
adequate fit to the variance data (Test 2 /rvalue <0.1). The nonconstant variance model also did
not provide an adequate fit to the variance data (Test 3 p-value <0.1). Because none of the
models provided adequate fit to the data, this endpoint was not considered further.
87
Methylcyclohexane
-------
EPA/690/R-23/007F
Increased Relative Kidney Weights in Unmated Female Crl:CD (Sprague Dawley) Rats
Exposed to Methylcyclohexane via Gavage for 28 Days (JECP6, 2013)
The procedure outlined above for continuous data was applied to the data for increased
relative kidney weight in unmated female Crl:CD (Sprague Dawley) rats orally exposed to
methylcyclohexane for 28 days (JHCDB. 2013). The constant variance model did not provide
adequate fit to the variance data (Test 2p-walue <0.1), but the nonconstant variance model did.
With the nonconstant variance model applied, all available models provided adequate fit to the
means. Visual inspection of the dose-response curves suggested adequate fit, BMDLs were not
10 times lower than the lowest nonzero dose, and scaled residuals did not exceed ±2 units at the
data point closest to the BMD. BMDLs for models providing adequate fit were sufficiently close
(differed by less than threefold), so the model with the lowest AIC was selected (Polynomial
3-degree). The Polynomial 3-degree model estimated human equivalent BMDo.ird and
BMDLo.ird values of 161.67 and 97.08 mg/kg-day, respectively. The results of the BMD
modeling are summarized in Table C-8 and plotted in Figure C-6.
Table C-8. BMD Modeling Results (Nonconstant Variance) for Increased
Relative Kidney Weight in Unmated Female Crl:CD (Sprague Dawley) Rats
Exposed to Methylcyclohexane via Gavage for 28 Days"
Model
Variance
/>-Valucb
Means
/>-Valucb
Scaled Residual
at Dose Nearest
BMD
AIC
BMDo.ird
(mg/kg-d)
HED
BMDLo.ird
(mg/kg-d)
HED
Exponential (model 2)°
0.32
0.94
-0.26
-63.68
166.13
103.26
Exponential (model 3)°
0.32
0.94
-0.26
-63.68
166.15
103.26
Exponential (model 4)°
0.32
0.77
0.33
-61.72
156.02
58.33
Exponential (model 5)°
0.32
0.76
-0.24
-61.72
157.40
58.41
Polynomial (3-degree)d*
0.32
0.95
-0.25
-63.70
162.0
97.1
Polynomial (2-degree)d
0.32
0.95
-0.25
-63.70
161.67
97.03
Power0
0.32
0.95
-0.25
-63.70
161.67
97.08
Linear"1
0.32
0.95
-0.25
-63.70
161.67
97.03
•'JHCDB (21)13).
bValues <0.10 fail to meet conventional goodness-of-fit criteria.
Tower restricted to be >1.
Coefficients restricted to be positive.
* Selected model. The constant variance model did not provide an adequate fit to the variance data, but the
nonconstant variance model did. With the nonconstant variance model applied, all models provided adequate fit to
the means. BMDLs for models providing adequate fit were sufficiently close (differed by less than threefold), so the
model with the lowest AIC was selected (Polynomial 3-degree).
AIC = Akaike's information criterion; BMD = maximum likelihood estimate of the exposure concentration
associated with the selected BMR; BMDL = 95% benchmark dose lower confidence limit on the BMD (subscripts
denote BMR: i.e., 0.1RD = relative deviation of 10%); BMR = benchmark response; HED = human equivalent dose.
88
Methylcyclohexane
-------
EPA 690 R-23 00 7F
Frequentist Polynomial Degree 3 Model with BMR of 0.1 Rel.
Dev. for the BMD and 0.95 Lower Confidence Limit for the BMDL
0.9
0.8
0.7
§ °-5
a °-4
^ 0.3
0.2
0.1
0
-U
50
100
150
200
250
Estimated Probability
^^Response at BMD
O Data
BMD
BMDL
Dose
Figure C-6. Fit of Polynomial 3-Degree Model to the Data for Increased Relative Kidney
Weight in Unmated Female Crl:CD (Sprague Dawley) Rats Exposed to Methylcyclohexane
via Gavage for 28 Days (JECDB, 2013)
89
Methylcyclohexane
-------
EPA 690 R-23 00 7F
BMD Model Output of Polynomial 3-Degree Model for Increased Relative Kidney Weight
in Unmated Female Crl:CD (Sprague Dawley) Rats Exposed to Methylcyclohexane via
Gavage for 28 Days (JECDB. 2013)
Frequentist Polynomial Degree 3 Restricted
User Input
Info
Model
frequentist Polynomial degree 3 vl.l
Dataset Name
rel kid wt unmated F R
User notes
JECB (2013) HERO 69S2772
Dose-Response Model
M[dose] =g + bl*dose + b2*doseA2 + ...
Variance Model
Var[i] = alpha * mean[i] Arho
Model Options
BMR Type
Rel. Dev.
BMRF
0.1
Tail Probability
-
Confidence Level
0.95
Distribution Type
Normal
Variance Type
Non-Constant
Model Data
Dependent Variable
HED
Independent Variable
Mean
Total # of Observations
4
Adverse Direction
Upward
90
Methylcyclohexane
-------
EPA 690 R-23 00 7F
Model Results
Benchmark Dose
BMD
161.6889733
BMDL
37.07765358
BMDU
337.3418582
AIC
-63.70461833
Test4P-value 1
0.343135135
D.O.F.
2
Model Parameters
# of Parameters
6
Variable
Estimate
9
0.647330031
betal
0.000400776
beta2
Bounded
beta3
Bounded
rho
13.1378527
alpha
-1.353486086
Goodness of Fit
Dose
Size
Estimated
Calc'd
Observed
Estimated
Calc'd
Observe
Scaled
Median
Median
Mean
SD
SD
d SD
Residual
0
c
0.647930091
0.64
0.64
0.029379
0.04
0.04
-0.6035666
15.7
5
0.654222273
0.66
0.66
0.031305
0.03
0.03
0.4127001
bJ
b
U.tlrfTI ('tiyrt
U.bu
U.btf
U.U3 { fbb
U.U3
U. U J
U.4U3Ht:b9
251.3
5
0.746645079
0.74
0.74
0.075897
0.09
0.09
-0.2547016
Likelihoods of Interest
#of
Model
Log Likelihood'
F'arameters
AIC
A1
32.3696909
5
-54.73938
A2
37.05235099
8
-58.1047
A3
35.90445037
6
-59.8089
fitted
35.65230949
4
-63.70462
R
27.61545393
2
-51.23091
" Includes additive constant of -18.37877. This constant was not included in the LL derivation prior to BMDS 3.0.
Tests of Interest
Test
2'Log[Likelihoo
d Ratio)
Test df
p-ualue
1
18.87379412
6
0.U04382
2
9.365320186
3
0.024808
3
2.295801233
2
0.317302
4
0.104281759
2
0.949195
Increased Incidence of Kidney Tubule Hyaline Droplets in Male Crl:CD (Sprague Dawley)
Rats Exposed to Methylcyclohexane via Gavage for 28 Days During Premating and Mating
(JECDB. 2013)
Incidences of kidney tubule hyaline droplets in male Crl:CD (Sprague Dawley) rats
exposed to methylcyclohexane via gavage for 28 days during premating and mating were fit to
the dichotomous models in the BMDS (Version 3.2) using the procedure described above for
dichotomous data. All the models provided an adequate fit according to the %2 goodness-of-fit
/rvalue (p > 0.1) and scaled residuals did not exceed ±2 units at the data point closest to the
BMD (see Table C-9). BMDLs for the models were not sufficiently close (differed by greater
than threefold), so the model with the lowest BMDL (Multistage 1-degree) was selected.
Figure C-7 shows the fit of the Multistage 1-degree model to the data. Based on HEDs, the
BMDio and BMDLio values for increased incidence of hyaline droplets in male Crl:CD (Sprague
Dawley) rats were 8.12 and 4.25 mg/kg-day, respectively.
91
Methylcyclohexane
-------
EPA/690/R-23/007F
Table C-9. BMD Modeling Results for Increased Incidence of Kidney
Tubule Hyaline Droplets in Male Crl:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days During Premating and Mating"
Model
X2 Goodness-
of-fit />-valucb
AIC
Scaled Residual
at Dose Nearest
BMD
BMD io
(mg/kg-d)
HED
BMDLio
(mg/kg-d)
HED
Gamma0
1.00
13.64
6.8 x 10-5
45.02
9.26
Log-logisticd
1.00
9.64
5.8 x 10-7
54.46
12.09
Multistage (degree = 3)e
0.99
9.84
-0.32
31.69
7.49
Multistage (degree = 2)e
0.81
12.41
-0.62
22.40
6.40
Multistage (degree = 1 )'•'
0.40
14.80
-0.00031
8.12
4.25
Weibull0
1.00
9.77
-0.26
34.02
8.47
Logistic
1.00
11.64
8.5 x 10-6
57.99
18.96
Log-probitd
1.00
11.64
3.0 x 10-10
50.32
12.05
Probit
1.00
9.66
-0.095
42.72
17.21
aJECD6 (2013).
bValues <0.10 fail to meet conventional goodness-of-fit criteria.
Tower restricted to be >1.
dSlope restricted to be >1.
"Betas restricted to be >0.
* Selected model. All models provided adequate fit to the data. BMDLs were not sufficiently close (differed by
greater than threefold), so the model with the lowest BMDL (Multistage 1-degree) was selected.
AIC = Akaike's information criterion; BMD = maximum likelihood estimate of the exposure concentration
associated with the selected BMR; BMDL = 95% benchmark dose lower confidence limit on the BMD (subscripts
denote BMR: i.e., 10 = exposure concentration associated with 10% extra risk); BMR = benchmark response;
HED = human equivalent dose; NA = not applicable (computation failed).
92
Methylcyclohexane
-------
EPA 690 R-23 00 7F
Frequentist Multistage Degree 1 Model with BMR of 10% Extra
Risk for the BMD and 0.95 Lower Confidence Limit for the BMDL
Estimated Probability
Response at BMD
— — Linear Extrapolation
O Data
BMD
BMDL
Figure C-7. Fit of Multistage 1-Degree Model to the Data for Increased Incidence of
Kidney Tubule Hyaline Droplets in Male Crl:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days During Premating and Mating (JECDB, 2013)
93
Methylcyclohexane
-------
EPA 690 R-23 00 7F
BMD Model Output of Multistage 1-Degree Model for Increased Incidence of Kidney
Tubule Hyaline Droplets in Male Crl:CD (Sprague Dawley) Rats Exposed to
Methylcyclohexane via Gavage for 28 Days During Premating and Mating (JECDB, 2013)
Frequentist Multistage 1 Degree Restricted
User Input
Info
Model
frequentist Multistage degree lvl.l
Dataset Name
Hyaline_Droplet_M_rat
User notes
Dose-Response Model
P[dose] =g + (l-g)*[l-exp(-bl*dose/vl-b2*doseA2-...)]
Model Options
Risk Type
Extra Risk
BMR
0.1
Confidence Level
0.95
Background
Estimated
Model Data
Dependent Variable
HED
Independent Variable
Incidence
Total # of Observations
4
94
Methylcyclohexane
-------
EPA 690 R-23 00 7F
Model Results
Benchmark Dose
BMD
3.119923939
BMDL
4.253517746
BMDU
16.18663929
AIC
14.8029746
P-value
0.403233628
D.O.F.
2
Chi2
1.816478324
Slope Factor
0.023509952
Model Parameters
# of Parameters
2
Variable
Estimate
g
1.5S233E-0S
bl
0.012975553
Goodness of Fit
Dose
Estimated
Probability
Expected
Observed
Size
Scaled
Residual
0
1.58233E-08
9.49395E-08
0
6
-0.0003081
17.1
0.198990104
1.193940622
0
6
-1.2208784
68.6
0.589394743
3.536368459
4
6
0.38475296
273.4
0.971203928
5.827223567
6
6
0.42178102
Analysis of Deviance
Model
Log Likelihood
# of Parameters
Deviance
Test d.f.
P Value
Full Model
-3.81908501
4
-
-
NA
Fitted Model
-5.401437293
2
3.164804576
2
0.20548088
Reduced Model
-16.30063333
1
24.96310675
3
<0.0001
BMD MODELING TO IDENTIFY POTENTIAL PODS FOR DERIVATION OF A
SCREENING CHRONIC PROVISIONAL REFERENCE CONCENTRATION (p-RfC)
Increased Incidence of Renal Medullary Mineralization in Male CDF F344/CrlBr Rats
Exposed to Methylcyclohexane Vapors for 6 Hours/Day, 5 Days/Week for 1 Year (AFRL,
1985)
Incidences of renal medullary mineralization in male CDF F344/CrlBr rats exposed to
methylcyclohexane vapors for 6 hours/day, 5 days/week for 1 year were fit to the dichotomous
models in the BMDS (Version 3.2) using the procedure described above for dichotomous data.
Three models (Multistage 1-degree, Logistic, and Probit) provided an adequate fit according to
the x2 goodness-of-fit/rvalue (p > 0.1) and had scaled residuals that did not exceed ±2 units at
the data point closest to the benchmark concentration (BMC) (see Table C-10). The
X2 goodness-of-fit /^-values could not be calculated for the other models because they were
saturated (i.e., degrees of freedom \df\ = 0); therefore, these models were not considered for
selection. Among the models that provided adequate fit, benchmark concentration lower
confidence limits (BMCLs) were sufficiently close (differed by less than threefold), so the model
with the lowest AIC (Logistic) was selected. Figure C-8 shows the fit of the Logistic model to
95
Methylcyclohexane
-------
EPA/690/R-23/007F
the data. Based on human equivalent concentrations (HECs), the 10% benchmark concentration
(BMCio) and 10% benchmark concentration lower confidence limit (BMCLio) values for
increased incidence of renal medullary mineralization in male CDF F344/CrlBr rats were
816.27 and 660.05 mg/m3, respectively.
Table C-10. BMD Modeling Results for Increased Incidence of Renal
Medullary Mineralization in Male CDF F344/CrlBr Rats Exposed to
Methylcyclohexane Vapors for 6 Hours/Day, 5 Days/Week for 1 Year"
Model
X2 Goodness-
of-fit
/>-valucb
AIC
Scaled Residual at
Dose Nearest BMC
BMCio
(mg/m3)
HECer
BMCLio
(mg/m3)
HECer
Gamma0
NA
101.38
-6.40 x 10-7
671.80
358.35
Log-logisticd
NA
101.38
-0.000249
676.34
353.97
Multistage (degree = 2)e
NA
101.38
-1.29 x 10-5
703.43
360.73
Multistage (degree = l)e
0.14
101.98
-1.30
396.82
277.61
Weibull0
NA
101.38
-0.000296
701.05
358.72
Logistic*
1.00
99.38
-0.00293
816.27
660.05
Log-probitd
NA
101.38
4.47 x 10-5
617.03
346.46
Probit
0.89
99.40
-0.0938
745.92
600.58
aAFRL (1985).
bValues <0.10 fail to meet conventional goodness-of-fit criteria.
Tower restricted to be >1.
dSlope restricted to be >1.
"Betas restricted to be >0.
* Selected model. The Multistage 1-degree, Logistic, and Probit models provided an adequate fit to the data. The
X2 goodness-of-fit ^-values could not be calculated for the other models. Among the models providing adequate fit,
BMCLs were sufficiently close (differed by less than threefold), so the model with the lowest AIC was selected
(Logistic).
AIC = Akaike's information criterion; BMC = maximum likelihood estimate of the concentration associated with
the selected BMR; BMCL = 95% benchmark concentration lower confidence limit on the BMC (subscripts denote
BMR: i.e., 10 = exposure concentration associated with 10% extra risk); BMR = benchmark response;
HEC = human equivalent concentration; NA = not applicable (computation failed).
96
Methylcyclohexane
-------
EPA 690 R-23 00 7F
Frequentist Logistic Model with BMR of 10% Extra Risk for the
BMC and 0.95 Lower Confidence Limit for the BMCL
0.8
£ 0.6
o
a! 0.4
en
0.2
0
5
200
400
600 800
Dose
1000
1200
1400
Estimated Probability
^^Response at BMD
O Data
BMD
BMDL
Figure C-8. Fit of Logistic Model to the Data for Increased Incidence of Renal Medullary
Mineralization in Male CDF F344/CrlBr Rats Exposed to Methylcyclohexane Vapors for
6 Hours/Day, 5 Days/Week for 1 Year (AFRL, 1985)
97
Methylcyclohexane
-------
EPA 690 R-23 00 7F
BMD Model Output of Logistic Model for Increased Incidence of Renal Medullary
Mineralization in Male CDF F344/CrlBr Rats Exposed to Methylcyclohexane Vapors for
6 Hours/Day, 5 Days/Week for 1 Year (AFRL, 1985)
User Input
Info
Model
frequentist Logistic vl.l
Dataset Name
med min kid M rat
User notes
Dose-Response Model
P[dose] = l/[l+exp{-a-b*dose)]
Model Options
Risk Type
Extra Risk
BMR
0.1
Confidence Level
0.95
Background
Estimated
Model Data
Dependent Variable
HECER
Independent Variable
Incidence
Total # of Observations
3
98
Methylcyclohexane
-------
EPA 690 R-23 00 7F
Model Results
Benchmark Dose
BMD
S16.2660672
BMDL
660.0483152
BMDU
9S4.6848764
AIC
99.37590091
P-value
0.996474229
D.O.F.
1
Chi2
1.9526SE-05
Model Parameters
# of Parameters
2
Variable
Estimate
a
-3.954572712
b
0.002367736
Goodness of Fit
Dose
Estimated
Probability
Expected
Observed
Size
Scaled
Residual
0
0.018806397
0.996739043
1
53
0.00329744
287
0.036437726
2.004074919
2
55
-0.0029324
1437
0.36536899
18.99918748
19
52
0.00023399
Analysis of Deviance
Model
Log Likelihood
# of Parameters
Deviance
Test d.f.
P Value
Full Model
-47.68794069
3
-
-
NA
Fitted Model
-47.68795045
2
1.95196E-05
1
0.99647487
Reduced Model
-64.06386791
1
32.75185443
2
<0.0001
Increased Incidence of Renal Papillary Hyperplasia in Male CDF F344/CrlBr Rats
Exposed to Methylcyclohexane Vapors for 6 Hours/Day, 5 Days/Week for 1 Year (AFRL,
1985)
Incidences of renal papillary hyperplasia in male CDF F344/CrlBr rats exposed to
methylcyclohexane vapors for 6 hours/day, 5 days/week for 1 year were fit to the dichotomous
models in the BMDS (Version 3.2) using the procedure described above for dichotomous data.
Three models (Multistage 2-degree, Logistic, and Probit) provided an adequate fit according to
the x2 goodness-of-fit/rvalue (p > 0.1) and had scaled residuals that did not exceed ±2 units at
the data point closest to the BMC (see Table C-l 1). The Multistage 1-degree model did not
provide adequate fit. The %2 goodness-of-fit /^-values could not be calculated for the other models
because they were saturated (i.e., df= 0); therefore, these models were not considered for
selection. Among the models that provided adequate fit, BMCLs were sufficiently close (differed
by less than threefold), so the model with the lowest AIC (Logistic) was selected. Figure C-9
shows the fit of the Logistic model to the data. Based on HECs, the BMCio and BMCLio values
for increased incidence of renal papillary hyperplasia in male CDF F344/CrlBr rats were
804.35 and 641.61 mg/m3, respectively.
99
Methylcyclohexane
-------
EPA/690/R-23/007F
Table C-ll. BMD Modeling Results for Increased Incidence of Renal
Papillary Hyperplasia in Male CDF F344/CrlBr Rats Exposed to
Methylcyclohexane Vapors for 6 Hours/Day, 5 Days/Week for 1 Year"
Model
X2 Goodness-
of-fit
/>-valucb
AIC
Scaled Residual at
Dose Nearest BMC
BMC 10
(mg/m3)
HECer
BMCLio
(mg/m3)
HECer
Gamma0
NA
97.31
0.00051
1,030.29
447.22
Log-logisticd
NA
97.31
-1.7 x 10-5
1,291.40
441.65
Multistage (degree = 2)e
0.44
95.99
-0.66
625.74
440.87
Multistage (degree = l)e
0.02
102.29
-2.0
327.43
235.26
Weibull0
NA
97.31
-1.3 x 10-5
1,308.92
456.47
Logistic*
0.53
95.68
-0.39
804.35
642.0
Log-probitd
NA
97.31
4.9 x 10-6
1,278.74
419.05
Probit
0.42
95.92
-0.51
720.86
575.77
aAFRL (1985).
bValues <0.10 fail to meet conventional goodness-of-fit criteria.
Tower restricted to be >1.
dSlope restricted to be >1.
"Betas restricted to be >0.
*Selected model. The Multistage 2-degree, Logistic, and Probit models provided an adequate fit to the data. The
Multistage 1-degree model did not provide adequate fit. The x2 goodness-of-fit ^-values could not be calculated for
the other models. Among the models providing adequate fit, BMCLs were sufficiently close (differed by less than
threefold), so the model with the lowest AIC was selected (Logistic).
AIC = Akaike's information criterion; BMC = maximum likelihood estimate of the concentration associated with
the selected BMR; BMCL = 95% benchmark concentration lower confidence limit on the BMC (subscripts denote
BMR: i.e., 10 = exposure concentration associated with 10% extra risk); BMR = benchmark response;
HEC = human equivalent concentration; NA = not applicable (computation failed).
100
Methylcyclohexane
-------
EPA 690 R-23 00 7F
Frequentist Logistic Model with BMR of 10% Extra Risk for the
BMC and 0.95 Lower Confidence Limit for the BMCL
0.8
£ 0.6
o
a! 0.4
en
0.2
0 (£
200
400
600 800
Dose
1000
1200
1400
Estimated Probability
^^Response at BMD
O Data
BMD
BMDL
Figure C-9. Fit of Logistic Model to the Data for Increased Incidence of Renal Papillary
Hyperplasia in Male CDF F344/CrlBr Rats Exposed to Methylcyclohexane Vapors for
6 Hours/Day, 5 Days/Week for 1 Year (AFRL, 1985)
101
Methylcyclohexane
-------
EPA 690 R-23 00 7F
BMD Model Output of Logistic Model for Increased Incidence of Renal Papillary
Hyperplasia in Male CDF F344/CrlBr Rats Exposed to Methylcyclohexane Vapors for
6 Hours/Day, 5 Days/Week for 1 Year (AFRL, 1985)
Frequentist Logistic Restricted
User Input
Info
Model
frequentist Logistic vl.l
Dataset Name
pappilary_hyperplas_kid_M_rat
User notes
Dose-Response Model
P[dose] = l/[H-exp(-a-b*dose)]
Model Options
RiskType
Extra Risk
BMR
0.1
Confidence Level
0.95
Background
Estimated
Model Data
Dependent Variable
HECER
Independent Variable
Incidence
Total # of Observations
3
102
Methylcyclohexane
-------
EPA/690/R-23/00 7F
Model Results
Benchmark Dose
BMD
804.3477117
BMDL
641.6145639
BMDU
976.5547886
AIC
95.68144797
P-value
0.534235207
D.O.F.
1
Chi2
0.386329316
Model Parameters
# of Parameters
2
Variable
Estimate
a
-4.431318473
b
0.002917294
Goodness of Fit
Dose
Estimated
Probability
Expected
Observed
Size
Scaled
Residual
0
0.011758875
0.623220359
1
53
0.48010381
287
0.026751337
1.471323508
1
55
-0.3938702
1437
0.44049154
22.90556007
23
52
0.02638043
Analysis of Deviance
Model
Log Likelihood
# of Parameters
Deviance
Test d.f.
P Value
Full Model
-45.65571206
3
-
-
IMA
Fitted Model
-45.84072398
2
0.370023856
1
0.54299126
Reduced Model
-69.34381973
1
47.37621534
2
<0.0001
103
Methylcyclohexane
-------
EPA/690/R-23/007F
APPENDIX D. REFERENCES
Abraham. MH; Ibrahim. A. (2006). Air to fat and blood to fat distribution of volatile organic
compounds and drugs: Linear free energy analyses. Eur J Med Chem 41: 1430-1438.
http://dx.doi.Org/10.1016/i.eimech.2006.07.012
Abraham. MH; Ibrahim. A; Acree. WE. Jr. (2005). Air to blood distribution of volatile organic
compounds: A linear free energy analysis. Chem Res Toxicol 18: 904-911.
http://dx.doi.org/10.1021/txQ50066d
ACGIH. (2021). 2021 TLVs and BEls: Based on the documentation of the threshold limit values
for chemical substances and physical agents & biological exposure indices. Cincinnati,
OH. https://portal.acgih.Org/s/store#/store/browse/detail/al54W00000BOag7OAD
AFRL. (1985). Chronic inhalation exposure of experimental animals to methylcyclohexane with
cover letter dated 082686 [TSCA Submission], (OTS0511483. 40-8589005. 42084 B2-4.
TSCATS/207410). American Petroleum Institute.
https://ntrl.ntis. gov/NTRL/dashboard/searchResults.xhtml?searchQuerv=OTSQ511483
Agnesi. R; Valentini. F; Mastrangelo. G. (1997). Risk of spontaneous abortion and maternal
exposure to organic solvents in the shoe industry. Int Arch Occup Environ Health 69:
311-316. http://dx.doi.org/10.1007/s00420005Q153
Andersen. ME. (1981). A physiologically based toxicokinetic description of the metabolism of
inhaled gases and vapors: Analysis at steady state. Toxicol Appl Pharmacol 60: 509-526.
http://dx.doi.org/10.1016/0041-008X(81)90338-0
API (1985). Twelve-month chronic inhalation exposures to methylcyclohexane with cover letter
[TSCA Submission], (OTS0206798. 878216027. TSCATS/031389).
ATSDR. (2021). Toxic substances portal: Toxicological profiles [Database], Atlanta, GA.
Retrieved from https://www.atsdr.cdc.gov/toxprofiledocs/index.html
Bailey. SA; Zidett. RH; Perry. RW. (2004). Relationships between organ weight and body/brain
weight in the rat: What is the best analytical endpoint? Toxicol Pathol 32: 448-466.
http://dx.doi.org/10.1080/0192623049Q465874
Baxter. CS. (2012). Alicyclic hydrocarbons. In E Bingham; B Cohrssen (Eds.), Patty's
toxicology: Volume 2 (6th ed., pp. 103-152). Hoboken, NJ: John Wiley & Sons.
http://dx.doi.org/10.1002/0471435139.toxQ50.pub2
CalEPA. (2020). Consolidated table of OEHHA/CARB approved risk assessment health values.
Sacramento, California, https://ww2.arb.ca.gov/resources/documents/consolidated-table-
oehha-carb-approved-risk-assessment-hcal th-values
CalEPA. (2021). OEHHA chemical database [Database], Sacramento, CA: Office of
Environmental Health Hazard Assessment. Retrieved from
http s://oehha.ca. gov/chemicals
Campbell. ML. (2011). Cyclohexane [Encyclopedia], In Ulltnann's encyclopedia of industrial
chemistry (7th ed.). Hoboken, NJ: John Wiley & Sons.
http://dx.doi.org/10.1002/143560Q7.a08 209.pub2
Deichman. W; Thomas. G. (1943). Glucuronic acid in the urine as a measure of the absorption of
certain organic compounds. J Ind Hyg Toxicol 25: 286-292.
Eastman Kodak. (1994). Toxicity and health hazard summary of methyl cyclohexane with cover
letter dated 021594 [TSCA Submission], (OTS0556685. 86940000089).
ECHA. (1929). M ethyl cy cl ohexane: Acute toxicity: inhalation: 005 weight of evidence |
experimental result, https://echa.europa.eu/lt/registration-dossier- registered-
dossier/ 15991 7 3 3 MocumentUUID02eeb 10f-2722-4e6e-9793-9e852701 e 100
104
Methylcyclohexane
-------
EPA/690/R-23/007F
ECHA. (1965). M ethyl cy cl ohexane: Acute toxicity: inhalation: 006 weight of evidence |
experimental result. https://echa.europa.eu/registration-dossier/-/registered-
dossier/15991/7/3/3/?documentUUID=30687d06-fa6b-4f7d-bc8d-fb8395a713fc
ECHA. (1982a). M ethy 1 cy cl ohexane: Acute toxicity: inhalation: 007 weight of evidence |
experimental result, https://echa.europa.eu/registration-dossier/-/registered-
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