EPA/635/R-03/013
www.epa.gov/iris
&EPA
TOXICOLOGICAL REVIEW
OF
1,1,1-TRICHLOROETHANE
(CAS No. 71-55-6)
In Support of Summary Information on the
Integrated Risk Information System (IRIS)
August 2007
U.S. Environmental Protection Agency
Washington, DC
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DISCLAIMER
This document has been reviewed in accordance with U.S. Environmental Protection
Agency (EPA) policy and approved for publication. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use.
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CONTENTS—TOXICOLOGICAL REVIEW OF 1,1,1-TRICHLOROETHANE
(CAS No. 71-55-6)
LIST OF TABLES v
LIST OF FIGURES vi
LIST OF ACRONYMS AND ABBREVIATIONS vii
FOREWORD ix
AUTHORS, CONTRIBUTORS, AND REVIEWERS x
1. INTRODUCTION 1
2. CHEMICAL AND PHYSICAL INFORMATION 3
3. TOXICOKINETICS 6
3.1. ABSORPTION 6
3.2. DISTRIBUTION 10
3.3. METABOLISM 14
3.4. ELIMINATION 19
3.5. PHYSIOLOGICALLY BASED PHARMACOKINETIC MODELS 20
3.5.1. Summary of Available Models 20
3.5.2. Model Selection 28
4. HAZARD IDENTIFICATION 30
4.1. STUDIES IN HUMANS—EPIDEMIOLOGY, CASE REPORTS, CLINICAL
CONTROLS 30
4.1.1. Oral Exposure 30
4.1.2. Inhalation Exposure 31
4.1.2.1. Experimental Human Exposure Studies 32
4.1.2.2. Epidemiological Studies 40
4.2. LESS-THAN-LIFETIME AND CHRONIC STUDIES AND CANCER
BIO AS SAYS IN ANIMALS—ORAL AND INHALATION 48
4.2.1. Oral Exposure 48
4.2.1.1. Acute Studies 48
4.2.1.2. Short-term Studies 49
4.2.1.3. Subchronic Studies 51
4.2.1.4. Chronic Studies 55
4.2.2. Inhalation Exposure 56
4.2.2.1. Acute Studies 56
4.2.2.2. Short-term Studies 61
4.2.2.3. Subchronic Studies 62
4.2.2.4. Chronic Studies 66
4.3. REPRODUCTIVE/DEVELOPMENTAL STUDIES—ORAL AND INHALATION... 68
4.3.1. Oral Exposure 68
4.3.2. Inhalation Exposure 72
11
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4.4. OTHER ENDPOINT-SPECIFIC STUDIES 77
4.4.1. Neurological Effects 77
4.4.1.1. Oral Exposure 77
4.4.1.2. Inhalation Exposure 77
4.4.2. Immunological Effects 85
4.4.3. Effects by Dermal Exposure 85
4.4.4. Effects by Parenteral Exposure 86
4.5. MECHANISTIC DATA AND OTHER STUDIES IN SUPPORT OF THE
MODE OF ACTION 87
4.5.1. Mechanistic Data from In Vitro Studies 87
4.5.2. Genotoxicity 88
4.6. SYNTHESIS OF MAJORNONCANCER EFFECTS 91
4.6.1. Oral 91
4.6.2. Inhalation 99
4.6.3. Mode-of-Action Information 112
4.7. EVALUATION OF CARCINOGENICITY 115
4.7.1. Summary of Overall Weight of Evidence 115
4.7.2. Synthesis of Human, Animal, and Other Supporting Evidence 115
4.8. SUSCEPTIBLE POPULATIONS AND LIFE STAGES 118
4.8.1. Possible Childhood Susceptibility 118
4.8.2. Possible Gender Differences 118
4.8.3. Other Potentially Susceptible Populations 118
5. DOSE-RESPONSE ASSESSMENTS 120
5.1. ORAL REFERENCE DOSE (RfD) 120
5.1.1. Acute Oral RfD 120
5.1.2. Short-term Oral RfD 120
5.1.3. Subchronic Oral RfD 121
5.1.3.1. Choice of Principal Study and Critical Effect—with
Rationale and Justification 121
5.1.3.2. Methods of Analysis 123
5.1.3.3. Subchronic RfD Derivation—Including Application of
Uncertainty Factors (UFs) 125
5.1.4. Chronic Oral RfD 126
5.1.4.1. Choice of Principal Study and Critical Effect—with
Rationale and Justification 126
5.1.4.2. Methods of Analysis 127
5.1.4.3. RfD Derivation—Including Application of Uncertainty
Factors (UFs) 127
5.1.4.4. Previous Oral Assessment 129
5.1.5. RfD Derivation Using Route-to-Route Extrapolation 129
5.1.5.1. Acute and Short-term Durations 129
5.1.5.2. Subchronic and Chronic Durations 130
5.2. INHALATION REFERENCE CONCENTRATION (RfC) 130
5.2.1. Acute Inhalation RfC 130
5.2.1.1. Choice of Principal Study and Critical Effect—with Rationale
and Justification 130
5.2.1.2. Methods of Analysis 137
iii
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5.2.1.3. Acute RfC Derivation—Including Application of Uncertainty
Factors (UFs) 138
5.2.2. Short-term Inhalation RfC 139
5.2.2.1. Choice of Principal Study and Critical Effect—with Rationale
and Justification 139
5.2.2.2. Methods of Analysis 142
5.2.2.3. Short-term RfC Derivation—Including Application of
Uncertainty Factors (UFs) 142
5.2.3. Subchronic Inhalation RfC 143
5.2.3.1. Choice of Principal Study and Critical Effect—with
Rationale and Justification 143
5.2.3.2. Methods of Analysis 146
5.2.3.3. Subchronic RfC Derivation—Including Application of
Uncertainty Factors (UFs) 147
5.2.4. Chronic Inhalation RfC 150
5.2.4.1. Choice of Principal Study and Critical Effect—with Rationale
and Justification 150
5.2.4.2. Methods of Analysis 151
5.2.4.3. Chronic RfC Derivation—Including Application of Uncertainty
Factors (UFs) 151
5.2.5. Previous Inhalation Assessment 155
5.3. CANCER ASSESSMENT 155
5.3.1. Oral Exposure 155
5.3.2. Inhalation Exposure 155
6. MAJOR CONCLUSIONS IN THE CHARACTERIZATION OF
HAZARD AND DOSE RESPONSE 156
6.1. HUMAN HAZARD POTENTIAL 156
6.2. DOSE RESPONSE 156
6.2.1. Noncancer/Oral 156
6.2.1.1. Acute and Short-term RfD 156
6.2.1.2. Subchronic and Chronic RfD 157
6.2.2. Noncancer/Inhalation 158
6.2.2.1. Acute Inhalation RfC 158
6.2.2.2. Short-term RfC 158
6.2.2.3. Subchronic and Chronic RfC 158
6.2.3. Cancer/Oral and Inhalation 160
7. REFERENCES 161
APPENDIX A: Summary of External Peer Review and Public Comments and Disposition .... A-1
APPENDIX B: Benchmark Dose Modeling Results and Output B-l
IV
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LIST OF TABLES
Table 2-1. Chemical identity of 1,1,1-trichloroethane 3
Table 2-2. Physicochemical properties of 1,1,1-trichloroethane 4
Table 3-1. Distribution and clearance of radioactivity in rat and mouse tissues following a
6-hour inhalation exposure to 150 or 1500 ppm [2-14C]-labeled
1,1,1-trichloroethane 11
Table 3-2. Tissue concentrations of radioactivity at several time periods
after 10-minute inhalation exposure of pregnant mice to [2-14C]-labeled
1,1,1-trichloroethane 13
Table 3-3. Summary of available models for 1,1,1-trichloroethane in rats and humans 20
Table 3-4. Parameters used in the Reitz PBPK models for 1,1,1-trichloroethane 23
Table 3-5. Parameter values in PBPK models for 1,1,1-trichloroethane 25
Table 3-6. Parameter values in the Poet et al. PBPK models for 1,1,1-trichloroethane 26
Table 4-1. Summary of human controlled-exposure studies and findings for
1,1,1-trichloroethane 33
Table 4-2. Summary of cancer epidemiology studies 45
Table 4-3. Effect of 1,1,1-trichloroethane on selected urinary parameters in male rats 51
Table 4-4. Terminal body weights of mice treated with 1,1,1 -trichloroethane for 90 days 54
Table 4-5. Incidence of anomalies in fetal rats after maternal exposure to
1,1,1-trichloroethane 73
Table 4-6. Summary noncancer results of major studies for oral exposure of humans to
1,1,1-trichloroethane 92
Table 4-7. Summary noncancer results of major studies for oral exposure of experimental
animals to 1,1,1-trichloroethane 93
Table 4-8. Summary noncancer results of major studies for inhalation exposure of
humans to 1,1,1-trichloroethane 100
Table 4-9. Summary noncancer results of major studies for inhalation exposure of
experimental animals to 1,1,1-trichloroethane 103
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Table 5-1. Comparison of survival in rats administered 1,1,1-trichloroethane by gavage
and in the diet 122
Table 5-2. Benchmark dose modeling results using terminal body weight data for mice 124
Table 5-3. Summary description of studies plotted in Figures 5-1 and 5-2 133
Table 5-4. Predicted exposure concentrations at different exposure durations for the target
internal dose 138
Table 5-5. Calculation of human equivalent concentrations using PBPK modeling
(using liver concentration as dose metric) 147
LIST OF FIGURES
Figure 3-1. Metabolic scheme for 1,1,1-trichloroethane 15
Figure 5-1. Exposure-response array for 1,1,1-trichloroethane 131
Figure 5-2. Exposure-response array for 1,1,1-trichloroethane 132
VI
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LIST OF ACRONYMS AND ABBREVIATIONS
ACGIH
ACL
ACTH
AEGL
AIC
ALA-D
ALL
ALT
AP
AST
ATSDR
AUC
BMD
BMDL
BMR
BRRC
BUN
cAMP
cGMP
CI
CNS
Ct
CV
CYP
ECso
EEG
EPA
ESRD
FEP
FOB
G-6-Pase
GD
GDH
GFAP
GGT
IARC
ICD
IL
IRIS
iv
LC50
LDH
LOAEL
American Conference of Governmental Industrial Hygienists
average lifetime concentration in the liver
adrenocorticotropic hormone
acute exposure guidelines
Akaike's Information Criterion
5-aminolevulinic acid dehydratase
acute lymphoblastic leukemia
alanine aminotransferase
alkaline phosphatase
aspartate aminotransferase
Agency for Toxic Substances Disease Registry
area under the curve
benchmark dose
95% lower bound on the benchmark dose
benchmark response
Bushy Run Research Center
blood urea nitrogen
cyclic adenosine monophosphate
cyclic guanosine monophosphate
confidence interval
central nervous system
concentration at the time of testing
concentration in venous blood
cytochrome P450
median effective concentration
electroencephalogram
U.S. Environmental Protection Agency
end-stage renal disease
exposure duration estimated to increase a toxicity endpoint in half of the animals
flash-evoked potential
functional observational battery
glucose-6-phosphatase
gestation day
glutamate dehydrogenase
glial fibrillary acidic protein
y-glutamyl transpeptidase
International Agency for Research on Cancer
isocitric dehydrogenase
interleukin
Integrated Risk Information System
intravenous
median lethal concentration
lactate dehydrogenase
lowest-observed-adverse-effect level
exposure duration estimated to kill half of the animals
vn
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MRI magnetic resonance imaging
MRL minimal risk level
MTD maximum tolerated dose
NAC National Advisory Committee (for AEGL)
NCI National Cancer Institute
NLM National Library of Medicine
NOAEL no-observed-adverse-effect level
NTP National Toxicology Program
OCT ornithine carbamoyl transferase
OR odds ratio
PBPK physiologically based pharmacokinetic
PD pharmacodynamics
PK pharmacokinetics
PND postnatal day
RBC red blood cell count
RD50 concentration producing a 50% decrease in respiratory rate
RfC reference concentration
RfD reference dose
RR relative risk
RTI Research Triangle Institute
SDH sorbitol dehydrogenase
SEP somatosensory-evoked potential
SIR standardized incidence ratio
SRI Stanford Research Institute
TCE trichloroethylene
TLV threshold limit value
TWA time-weighted average
UF uncertainty factor
UNEP United Nations Environment Programme
VEP visual evoked potential
VOC volatile organic solvent
WBC white blood cell count
Vlll
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FOREWORD
The purpose of this Toxicological Review is to provide scientific support and rationale
for the hazard and dose-response assessment in IRIS pertaining to exposure to
1,1,1-trichloroethane. It is not intended to be a comprehensive treatise on the chemical or
toxicological nature of 1,1,1-trichloroethane.
In Section 6, Major Conclusions in the Characterization of Hazard and Dose Response,
EPA has characterized its overall confidence in the quantitative and qualitative aspects of hazard
and dose response by addressing knowledge gaps, uncertainties, quality of data, and scientific
controversies. The discussion is intended to convey the limitations of the assessment and to aid
and guide the risk assessor in the ensuing steps of the risk assessment process.
For other general information about this assessment or other questions relating to IRIS,
the reader is referred to EPA's IRIS Hotline at (202) 566-1676 (phone), (202) 566-1749 (fax), or
hotline.iris@epa.gov (email address).
IX
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AUTHORS, CONTRIBUTORS, AND REVIEWERS
CHEMICAL MANAGER
Susan Rieth, MPH
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Washington, DC
AUTHORS
Susan Rieth, MPH
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Washington, DC
Joey Zhou, Ph.D.
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Washington, DC
Marc Odin, M.S., D.A.B.T.
Environmental Science Center
Syracuse Research Corporation
Syracuse, NY
Peter R. McClure, Ph.D., D.A.B.T.
Environmental Science Center
Syracuse Research Corporation
Syracuse, NY
REVIEWERS
This document and the accompanying IRIS Summary have been peer reviewed by EPA
scientists and independent scientists external to EPA. Comments from all peer reviewers were
evaluated carefully and considered by the Agency during the fmalization of this assessment.
During the fmalization process, the IRIS Program Director achieved common understanding of
the assessment among the Office of Research and Development; Office of Air and Radiation;
Office of Prevention, Pesticides, and Toxic Substances; Office of Solid Waste and Emergency
Response; Office of Water; Office of Policy, Economics, and Innovation; Office of Children's
Health Protection; Office of Environmental Information; and EPA's regional offices.
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INTERNAL EPA REVIEWERS
Robert Benson
Office of Partnerships and Regulatory Assistance, Region 8
Weihsueh Chiu
National Center for Environmental Assessment, Office of Research and Development
Robert Dewoskin
National Center for Environmental Assessment, Office of Research and Development
David Herr
National Health and Environmental Effects Research Laboratory, Office of Research and
Development
Charli Hiremath
National Center for Environmental Assessment, Office of Research and Development
Karl Jensen
National Health and Environmental Effects Research Laboratory, Office of Research and
Development
Gregory Miller
Office of Policy, Economics, and Innovation
Cheryl Siegel Scott
National Center for Environmental Assessment, Office of Research and Development
Dharm Singh
National Center for Environmental Assessment, Office of Research and Development
EXTERNAL PEER REVIEWERS
Jeffrey W. Fisher, PhD, Chair
University of Georgia
Scott E. Bowen, PhD
Wayne State University
Richard B. Mailman, PhD
University of North Carolina
XI
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Matthew D. Reed, PhD
Lovelace Respiratory Research Institute
D. Alan Warren, PhD
University of South Carolina
Summaries of the external peer reviewers' comments and public comments and the
disposition of their recommendations are provided in Appendix A.
xn
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1. INTRODUCTION
This document presents background information and justification for the Integrated Risk
Information System (IRIS) Summary of the hazard and dose-response assessment of
1,1,1-trichloroethane. IRIS Summaries may include oral reference dose (RfD) and inhalation
reference concentration (RfC) values for chronic and less-than-lifetime exposure durations, and a
carcinogenicity assessment.
The RfD and RfC provide quantitative information for use in risk assessments for health
effects known or assumed to be produced through a nonlinear (possibly threshold) mode of
action. The RfD (expressed in units of mg/kg-day) is defined as an estimate (with uncertainty
spanning perhaps an order of magnitude) of a daily exposure to the human population (including
sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a
lifetime. The inhalation RfC (expressed in units of mg/m3) is analogous to the oral RfD, but
provides a continuous inhalation exposure estimate. The inhalation RfC considers toxic effects
for both the respiratory system (portal-of-entry) and for effects peripheral to the respiratory
system (extrarespiratory or systemic effects). Reference values may also be derived for acute
(<24 hours), short-term (up to 30 days), and subchronic (up to 10% of average lifetime) exposure
durations, all of which are derived based on an assumption of continuous exposure throughout
the duration specified.
The carcinogenicity assessment provides information on the carcinogenic hazard
potential of the substance in question and quantitative estimates of risk from oral and inhalation
exposure. The information includes a weight-of-evidence judgment of the likelihood that the
agent is a human carcinogen and the conditions under which the carcinogenic effects may be
expressed. Quantitative risk estimates are derived from the application of a low-dose
extrapolation procedure, and are presented in two ways to better facilitate their use. First, route-
specific risk values are presented. The "oral slope factor" is an upper bound on the estimate of
risk per mg/kg-day of oral exposure. Similarly, a "unit risk" is an upper bound on the estimate
of risk per unit of concentration, either per ug/L drinking water or per ug/m3 air breathed.
Second, the estimated concentration of the chemical substance in drinking water or air when
associated with cancer risks of 1 in 10,000, 1 in 100,000, or 1 in 1,000,000 is also provided.
Development of these hazard identification and dose-response assessments for
1,1,1-trichloroethane has followed the general guidelines for risk assessment as set forth by the
National Research Council (1983). EPA guidelines and technical reports that may have been
used in the development of this assessment include the following: Guidelines for the Health Risk
Assessment of Chemical Mixtures (U.S. EPA, 1986a), Guidelines for Mutagenicity Risk
Assessment (U.S. EPA, 1986b), Guidelines for Developmental Toxicity Risk Assessment (U.S.
EPA, 199 la), Guidelines for Reproductive Toxicity Risk Assessment (U.S. EPA, 1996),
1
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Guidelines for Neurotoxicity Risk Assessment (U.S. EPA, 1998a), Guidelines for Carcinogen
Risk Assessment (U.S. EPA, 2005a), Supplemental Guidance for Assessing Susceptibility from
Early-Life Exposure to Carcinogens (U.S. EPA, 2005b), Recommendations for and
Documentation of Biological Values for Use in Risk Assessment (U.S. EPA, 1988a), (proposed)
Interim Policy for Particle Size and Limit Concentration Issues in Inhalation Toxicity (U.S.
EPA, 1994a), Methods for Derivation of Inhalation Reference Concentrations and Application of
Inhalation Dosimetry (U.S. EPA, 1994b), Use of the Benchmark Dose Approach in Health Risk
Assessment (U.S. EPA, 1995), Science Policy Council Handbook: Peer Review (U.S. EPA, 2006,
2000a, 1998b), Science Policy Council Handbook: Risk Characterization (U.S. EPA, 2000b),
Benchmark Dose Technical Guidance Document (U.S. EPA, 2000c), Supplementary Guidance
for Conducting Health Risk Assessment of Chemical Mixtures (U.S. EPA, 2000d), and^4 Review
of the Reference Dose and Reference Concentration Processes (U.S. EPA, 2002).
The literature search strategy employed for this compound was based on the CASRN and
at least one common name. Any pertinent scientific information submitted by the public to the
IRIS Submission Desk was also considered in the development of this document. The relevant
literature was reviewed through July 2007.
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2. CHEMICAL AND PHYSICAL INFORMATION
1,1,1-Trichloroethane is a colorless liquid with an odor resembling chloroform.
Information on chemical identity is presented in Table 2-1.
Table 2-1. Chemical identity of 1,14-trichloroethane
Characteristic
Chemical name
Synonyms
Trade names
Chemical formula
Chemical structure
CASa Registry
Shipping name/DOTa number
Standard Transportation Number
NIOSH RTECSa
EPA Hazardous Waste
OHM/TADSa
Value
1,1,1 -Trichloroethane
Methyl chloroform; alpha-Trichloroethane;
Methyltrichloromethane
Alpha-T; Aerothene MM; Aerothene TT; Algylen;
Baltana; CF 2; Chloroethane-NU; Chlorotene;
Chlorothane NU; Chlorothene NU; Chlorothene SM;
Chlorothene VG; Chlorylen; Dowclene LS; Gemalgene;
Genklene LB; ICI-CF 2; Inhibisol; Solvent 111; TCEA;
Trichloran; Trielene
C2H3C13
Cl
ci — — ci
CH3
71-55-6
UNa2831;IMOa6.1
4963375
KJ2975000
U226; F002
No data
Reference
Budavari, 2001
NLM, 2002
NLM, 2002
Budavari, 2001
Verschueren,
2001
Budavari, 2001
NLM, 2002
NLM, 2002
NLM, 2002
NLM, 2002
aCAS = Chemical Abstracts Service; DOT = Department of Transportation; UN = United Nations; IMO =
International Maritime Dangerous Goods Code; NIOSH = National Institute for Occupational Safety and Health;
RTECS = Registry of Toxic Effects of Chemical Substances; OHM/TADS = Oil and Hazardous
Materials/Technical Assistance Data System.
1,1,1-Trichloroethane is produced most commonly by reaction of hydrochloric acid with
vinyl chloride (from 1,2-dichloroethane) to obtain 1,1-dichloroethane, which can then undergo
thermal and photochemical chlorination (Agency for Toxic Substances Disease Registry
[ATSDR], 2006; National Library of Medicine [NLM], 2002; U.S. EPA, 1991b). Other methods
of production include the catalyzed addition of hydrogen chloride to 1,1-dichloroethylene and
the direct chlorination of ethane (ATSDR, 2006; NLM, 2002; U.S. EPA, 1991b). In order to
prevent reaction with aluminum and alloys, commercial grades of 1,1,1-trichloroethane contain
an inhibitor such as nitromethane, N-methylpyrrole, 1,4-dioxane, butylene oxide, 1,3-dioxolane,
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or a secondary butyl alcohol (ATSDR, 2006; Reid, 2001; U.S. EPA, 1991b). Physicochemical
properties for 1,1,1-trichloroethane are listed in Table 2-2.
Table 2-2. Physicochemical properties of 1,1,1-trichloroethane
Property
Molecular weight
Color
Physical state
Melting point
Boiling point
Density at 20°C
Odor
Odor threshold in air
Saturation concentration in air
Solubility:
Water
Organic solvents
Partition coefficients:
Log octanol/water
Log Koc
Vapor pressure
Vapor density
Critical temperature
Henry's law constant
Refractive index at 20°C
Heat of combustion
Heat of vaporization at 25°C
Autoignition temperature
Flash point
Flammability limits
Conversion factors
Value
133.40
Colorless
Liquid
-30.4°C
74.0°C
1.3390 g/ml
Mild, chloroform-like odor
100 ppm
726 g/m3 at 20°C; 1088 g/m3 at 30°C
1500mg/Lat25°C
Soluble in ethanol and chloroform; miscible in ether
2.49
2.02-2.03
100 mm Hg at 20°C; 155 mm Hg at 30°C
4.6
311.5°C
8 x 10~3 atm-m3/mol
1.4379
llOx 105J/kg
32.50 kJ/mol
500°C
None
7-16%
1 mg/m3 = 0.18 ppm; 1 ppm = 5.46 mg/m3
Reference
Lide, 2000
Lewis, 1997
Budavari, 2001
Lide, 2000
Lide, 2000
Lide, 2000
NIOSH, 1997
Weiss, 1986
Verschueren, 200 1
ATSDR, 2006
Lide, 2000
Hanschetal., 1995
ATSDR, 2006
Verschueren, 2001
Verschueren, 2001
NLM, 2002
NLM, 2002
Lide, 2000
NLM, 2002
NLM, 2002
Weiss, 1986
Lewis, 1997
Weiss, 1986
IARCa, 1999
aIARC = International Agency for Research on Cancer.
1,1,1-Trichloroethane was originally introduced as a replacement for other chlorinated
and flammable solvents like carbon tetrachloride (ATSDR, 2006; U.S. EPA, 1991b). Although
1,1,1-trichloroethane was formerly used extensively in a range of industrial applications and
consumer products, currently this chemical is used almost entirely as a precursor for
hydrofluorocarbons (ATSDR, 2006). According to ATSDR (2006), use of 1,1,1-trichloroethane
as of 1995 included as a hydrochlorofluorocarbon intermediate (60%), in vapor degreasing and
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cold cleaning (25%), as a solvent for adhesives (5%), in coatings and inks (3%), in textiles (2%),
and in electronics and miscellaneous (5%). 1,1,1-Trichloroethane was used extensively in
household products, including such products as adhesives and adhesive cleaners, lubricants,
general purpose liquid cleaners and spray degreasers, oven cleaners, spot removers, shoe polish,
and fabric finishes (ATSDR, 2006; NLM, 2002; Reid, 2001; IARC [International Agency for
Research on Cancer], 1999); however, it is no longer used in common household products
(ATSDR, 2006). This chemical was formerly used as a food and grain fumigant (ATSDR, 2006;
NLM, 2002).
1,1,1-Trichloroethane is one of the compounds addressed by the Montreal Protocol,
which stipulates that the production and consumption of these potentially ozone-depleting
substances in the stratosphere are to be phased out. Under the Montreal Protocol, the final
phase-out for developed countries for 1,1,1-trichloroethane was 1996, with selected exceptions
for existing stocks and essential uses; developing countries have until 2015 for their ban to take
effect (Krol et al., 2003; Doherty, 2000a,b; United Nations Environment Programme [UNEP],
2000).
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3. TOXICOKINETICS
3.1. ABSORPTION
In humans and experimental animals, 1,1,1-trichloroethane is well absorbed by all routes
of exposure. At least by inhalation, the rate of uptake is driven initially by tissue loading (i.e.,
accumulation in blood and tissues) and then by metabolism once steady state conditions have
been reached.
Studies in humans exposed to 1,1,1-trichloroethane demonstrate that it is rapidly and
efficiently absorbed by the respiratory tract. Expired alveolar air from a human subject who held
breaths of air containing 38Cl-labeled 1,1,1-trichloroethane for durations ranging from 15 to
40 seconds contained only 2-5% of the concentration of the inhaled compound (based on
activity of the radiolabel) (Morgan et al., 1972a,b, 1970). 1,1,1-Trichloroethane was detected in
arterial blood as soon as 10 seconds after the start of exposure in human subjects exposed to
approximately 250 ppm (1370 mg/m3) of 1,1,1-trichloroethane (Astrand et al., 1973).
Concentrations of 1,1,1-trichloroethane in blood and expired air increased rapidly in
human subjects (n = 6) exposed continuously to 35 or 350 ppm (190 or 1900 mg/m3)
1,1,1-trichloroethane for 6 hours; after only 1.5 hours, blood and expired air concentrations were
already about 90% of the concentrations later observed after 6 hours of exposure (Nolan et al.,
1984). Using a physiologically based pharmacokinetic (PBPK) model (developed from data for
concentrations of 1,1,1-trichloroethane and its principal metabolites, trichloroethanol and
trichloroacetic acid, in blood and urine collected from the six human subjects exposed to 35 or
350 ppm for 6 hours), it was predicted that the subjects absorbed respective averages of 101.6
and 1005 mg 1,1,1-trichloroethane during the 6 hours of exposure and that these amounts
represented about 25% of the 1,1,1-trichloroethane that was inhaled (Nolan et al., 1984).
Monster et al. (1979) exposed human subjects (n = 6) for 4 hours to 70 or 145 ppm (380 or
790 mg/m3) 1,1,1-trichloroethane while at rest or 142 ppm (780 mg/m3) while experiencing
alternating periods of rest and work (two 30-minute periods on a bicycle ergometer at 100W).
Minute volumes and concentration in exhaled air were measured at various times during and
after exposure. Estimated total uptake of 1,1,1-trichloroethane during the 4-hour exposure
period ranged from 140 to 240 mg for 70 ppm (380 mg/m3) at rest, 305 to 520 mg for 145 ppm
(790 mg/m3) at rest, and 435 to 610 mg for 142 ppm (780 mg/m3) with alternating periods of rest
and work; average total uptakes across subjects were 193, 429, and 538 mg, respectively.
Alveolar retention was calculated to be about 30% at the end of exposure (Monster et al., 1979).
Based on measurements of 1,1,1-trichloroethane in expired air and ventilation rates, estimates of
pulmonary retention ranged from 26.1 to 35.6% in human subjects (n = 3) exposed to 72 or
213 ppm (390 or 1160 mg/m3) 1,1,1-trichloroethane for 8 hours (Humbert and Fernandez, 1977).
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Studies in rats and mice provide supporting evidence that inhaled 1,1,1-trichloroethane is
rapidly and efficiently absorbed by the respiratory tract. Groups of male F344 rats (n = 16) and
male B6C3F1 mice (n = 16) were exposed to 150 or 1500 ppm (820 or 8190 mg/m3) of
[2-14C]-labeled 1,1,1-trichloroethane for 6 hours (Schumann et al., 1982a). Following exposure,
the urine, feces, and expired air were collected at regular intervals. Groups of four animals per
species were sacrificed at 0, 24, 48, and 72 hours postexposure for collection of tissues.
Amounts of radioactivity were measured in expired air (as unchanged 1,1,1-trichloroethane and
as CC>2), feces, urine, skin, liver, kidney, fat, and the remaining carcasses. Absorption of
1,1,1-trichloroethane was indicated by the detection of considerable radioactivity in the rat and
mouse liver, kidney, and fat tissues immediately after termination of exposure and by the
increased concentration of 1,1,1-trichloroethane equivalents in these tissues with increasing
exposure level (Table 3-1 in Section 3.2). In a companion experiment in which
1,1,1-trichloroethane was measured in blood samples collected at intervals during and after
6-hour exposure to 1,1,1-trichloroethane, blood concentrations of 1,1,1-trichloroethane were
about 2 and 20 ug/g blood in rats immediately after termination of exposure to 150 or 1500 ppm
(820 or 8190 mg/m3), respectively; in mice, blood concentrations were about 13 and 105 ug/g
blood immediately after termination of exposure to the same air concentrations (Schumann et al.,
1982a).
The percent uptake of inhaled 1,1,1-trichloroethane (i.e., pulmonary retention) has been
demonstrated to be time dependent. Monster et al. (1979) reported that percent uptake by
humans was approximately 95% at the onset of a 4-hour exposure to 70 or 145 ppm (380 or
790 mg/m3) 1,1,1-trichloroethane and decreased to approximately 30% at the end of exposure.
Similar results have been reported for male Sprague-Dawley rats exposed to 50 or 500 ppm
(270 or 2730 mg/m3) for 2 hours; percent uptake was about 80% at the onset of exposure and
declined to about 50% at the end of exposure (Dallas et al., 1989). Initial uptake of inhaled
1,1,1-trichloroethane is expected to be primarily influenced by tissue loading, but, once steady
state conditions are reached, uptake of 1,1,1-trichloroethane is expected to be driven primarily by
the decrease in the parent concentration in body fluids as a result of metabolism. Dallas et al.
(1989) noted that, once steady state is reached, percent uptake of 1,1,1-trichloroethane is
expected to be low, since 1,1,1-trichloroethane is slowly metabolized and readily excreted
predominately as unchanged compound in exhaled air (see Sections 3.2, 3.3, and 3.4).
No data on the extent or rate of absorption of 1,1,1-trichloroethane in the gastrointestinal
tract of humans are available, but results from animal studies indicate that absorption is rapid and
almost complete (>90%) (Reitz et al., 1988; Research Triangle Institute [RTI], 1988; Mitoma et
al., 1985).
In studies of male F344 rats (n = 3-4 per dose) given single gavage doses of 100, 300, or
1000 mg/kg of [2-14C]-labeled 1,1,1-trichloroethane in vegetable oil, radioactivity in exhaled air
7
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trapped in cold ethanol during a 24-hour postadministration period represented 96.7, 92.0, and
98.9% of the administered doses, respectively (RTI, 1988). In female B6C3F1 mice (n = 3)
given single doses of 100 or 300 mg/kg of the same material, radioactivity in trapped exhaled air
represented 96.7 and 92.0% of the administered doses, respectively. Rapid absorption was
indicated in both species by observations that radioactivity in air trapped in the first hour after
administration accounted for 7.8-11.2% of administered doses in rats and
10.6-18.5% of administered doses in mice (RTI, 1988).
Similar results indicating nearly complete gastrointestinal absorption were obtained in
another study in which groups of male Osborne-Mendel rats (n = 4) and male B6C3F1 mice
(n = 4) were given [l,2-14C]-labeled 1,1,1-trichloroethane (in corn oil) at dose levels of 3000 and
4000 mg/kg, respectively (Mitoma et al., 1985). In this study, animals were placed in
metabolism cages for 48 hours following dose administration to collect excreta (urine and feces)
and expired air (expired radioactivity was separated into volatile organic compounds, which was
assumed to be 1,1,1-trichloroethane, and expired CO2). In rats, the amounts of recovered
radioactivity (expressed as percentages of the administered dose) were 85.13% in trapped
expired organic compounds, 0.87% in trapped expired CC>2, 2.05% in excreta, and 1.20% in
carcasses; in mice, the respective percentages were 92.94%, 2.01%, 3.36%, and 0.72%.
In a study of male F344 rats (n = 4) with free access to drinking water containing [2-
14C]-labeled 1,1,1-trichloroethane for 8 hours, radioactivity in expired air, urine, and selected
tissues (liver, kidney, skin, and carcass homogenate) represented 95.2% of the average dose of
116 mg/kg (Reitz et al., 1988). Samples of expired air and urine were collected during exposure
and up to 48 hours after exposure, when rats were sacrificed.
Absorption of 1,1,1-trichloroethane by the skin has been demonstrated in human subjects
(Kezic et al., 2001, 2000; Riihimaki and Pfaffli, 1978; Fukabori et al., 1977; Stewart and Dodd,
1964). Immersing the thumb or hand in 1,1,1-trichloroethane for 30 minutes resulted in mean
peak alveolar air concentrations in human subjects of 1 or 22 ppm (5.5 or 120 mg/m3),
respectively (Stewart and Dodd, 1964). In another study, three subjects received two daily
1-hour occluded applications of 1,1,1-trichloroethane to forearm skin for five days (Fukabori et
al., 1977). Mean alveolar air concentrations of 1,1,1-trichloroethane after the second of two
daily concentrations ranged (across 5 consecutive days) from 1.9 to 4.8 ppm. Blood samples
collected immediately after the end of the last exposure on day 5 showed concentrations of
1,1,1-trichloroethane ranging (among the three subjects) from 1.1 to 8.8 ug/mL (average =
5.4 ug/mL). In another experiment with three subjects similarly exposed to 1,1,1-trichloroethane
for 1 hour only, average blood concentrations of 1,1,1-trichloroethane were 4.8, 3.4, and
3.4 ug/mL at 0, 30, and 60 minutes postexposure; average alveolar air concentrations at the same
intervals after exposure were 3.1, 1.8, and 1.2 ppm, respectively (Fukabori et al., 1977).
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Kezic et al. (2001) calculated an average dermal absorption flux of 56 nmol
1,1,1-trichloroethane/cm2-minute in human subjects (n = 3) exposed for 3 minutes to liquid
1,1,1-trichloroethane on a 3 cm2 area of forearm skin. Dermal permeation rates were calculated
from time courses of exhaled air concentration measured after dermal exposure and after a
reference inhalation exposure. Using the average dermal absorption flux, a daily intake of
0.5 mmol 1,1,1-trichloroethane was calculated for an exposure scenario that involved immersion
of a 360 cm2 area of skin for 3 minutes, eight times a day. This intake represented about 5% of
an estimated respiratory intake of 1,1,1-trichloroethane (9.6 mmol), resulting from an 8-hour
inhalation exposure to 1910 mg/m3, assuming an alveolar minute volume of 7 L/minute and a
respiratory retention percentage of 20%.
Riihimaki and Pfaffli (1978) estimated that absorption of airborne 1,1,1-trichloroethane
by the skin of human subjects represented 0.08% of the amount of 1,1,1-trichloroethane
absorbed by the respiratory tract. These investigators exposed two human subjects wearing thin
cloth pajamas, socks, and respiratory protection to 600 ppm of 1,1,1-trichloroethane for 3.5
hours. During exposure, the subjects cycled on a bicycle ergometer for 10 minutes of each full
hour of exposure. Expired air samples were collected at several intervals during and after
exposure. Based on 1,1,1-trichloroethane concentrations in expired air, the average amount of
1,1,1-trichloroethane absorbed by the skin was estimated to be 15.9 umol. It was calculated that,
in the absence of respiratory protection, 20,399 umol of 1,1,1-trichloroethane would have been
absorbed by the respiratory tract, assuming a ventilation rate of 10 L/minute and an average
pulmonary retention of 40%.
Dermal absorption of airborne 1,1,1-trichloroethane was also measured in five human
subjects exposed to a concentration of 1.57 mmol/L (about 38,380 ppm) (Kezic et al., 2000). In
this study, a forearm and hand (about 1000 cm2 area) were enclosed in a chamber with
1,1,1-trichloroethane vapor for 20 minutes, and exhaled alveolar air samples were collected at
intervals during and up to 6 hours after exposure. Concentrations of 1,1,1-trichloroethane in
exhaled air were determined by gas chromatography and flame ionization detection. From these
measurements (and measurements of exhaled air following a short-term inhalation exposure of
the subjects), the average absorption rate into the skin during the 20-minute exposure
(normalized to 1 nmol/L and 1000 cm2) was calculated to be 0.021 ± 0.003 cm/hour. Using this
absorption rate and assuming a whole-body skin area of 20,000 cm2, the amount of
1,1,1-trichloroethane absorbed into the skin from a 20-minute whole-body exposure to 1 nmol/L
of 1,1,1-trichloroethane was calculated to be 0.1% of the amount absorbed by the respiratory
tract during the same period.
Rapid dermal absorption has been demonstrated in male F344 rats exposed to pure
1,1,1-trichloroethane or one-third, two-thirds, or fully saturated aqueous solutions of
1,1,1-trichloroethane (Morgan et al., 1991). In these studies, 2 mL of test material were applied
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to an occluded 3.1 cm2 area of shaved dorsal skin for 24 hours. Blood samples were collected at
0, 0.5, 1, 2, 4, 8, 12, and 24 hours and concentrations of 1,1,1-trichloroethane were determined
by gas chromatography. With exposure to pure 1,1,1-trichloroethane, near maximum blood
levels of 1,1,1-trichloroethane (about 10 ug/mL blood) were attained within 0.5 hours and
remained essentially constant through 24 hours. With exposure to aqueous solutions, maximum
blood concentrations were attained between 4 and 8 hours of exposure and declined thereafter.
Maximum blood concentrations were about 20, 50, and 120 ng of 1,1,1-trichloroethane/mL
blood for one-third, two-thirds, and fully saturated solutions, respectively.
Skin:air partition coefficients for 1,1,1-trichloroethane and other volatile solvents have
been measured in vitro using strips of dorsal skin from 8- to 16-week-old F344 rats (Mattie et al.,
1994). These coefficients can be used in PBPK models describing the uptake of a chemical from
air or solutions into the skin (see Section 3.5). The coefficient for 1,1,1-trichloroethane
(10.8 ± 0.6) was near the lower end of the range of coefficients measured for 11 common
solvents. Hexane had the lowest coefficient (1.9 ± 0.1), and styrene had the highest (91.9 ± 6.8).
3.2. DISTRIBUTION
Results from studies of animals exposed by inhalation or gavage indicate that following
absorption, 1,1,1-trichloroethane is distributed to tissues throughout the body, with preferential
distribution to fat. Disposition in the body is similar in animals exposed once or repeatedly to
1,1,1 -trichloroethane. Studies in pregnant animals show that distribution to the placenta and
developing fetus is relatively low.
Immediately following 6-hour inhalation exposure of rats or mice to 150 or 1500 ppm
(820 or 8190 mg/m3) of [2-14C]-labeled 1,1,1-trichloroethane (Schumann et al., 1982a), the tissue
concentrations of 1,1,1-trichloroethane equivalents showed the order of fat > kidney > liver (see
Table 3-1).
Takahara (1986a) reported that, immediately following exposure of female mice to
1000 ppm (5460 mg/m3) of 1,1,1-trichloroethane for 2 hours, tissue concentrations showed the
following decreasing order: fat > liver > kidney > spleen ~ blood > lung ~ heart ~ brain. In male
hybrid dogs (n = 3) that were exposed (under continuous anesthesia) to 10,000 ppm
(54,600 mg/m3) of 1,1,1-trichloroethane for 3 minutes (four times at 4-hour intervals), wet
weight concentrations of 1,1,1-trichloroethane, 4 hours after the last exposure, showed the
following ranking order: abdominal fat > renal fat > brain ~ liver ~ kidney ~ lungs (Katagiri et
al., 1997). In mice, 2 hours after oral administration of 1000 mg/kg of [2-14C]-labeled
1,1,1-trichloroethane, amounts of radioactivity in tissues showed the following order: fat (53%
of body burden for those tissues analyzed) > muscle > stomach > liver > skin > blood > kidney >
lung (RTI, 1988). Similarly in rats, 1 hour after oral administration of 1000 mg/kg labeled
1,1,1-trichloroethane, amounts of radioactivity in tissues showed the following order: fat (62%
10
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of body burden) > muscle > liver > skin > blood ~ kidney ~ lung > thyroid (RTI, 1988). The
preferential accumulation of 1,1,1-trichloroethane in fatty tissues following a single exposure is
not persistent, as demonstrated by the rapid decline in rat and mouse tissue concentrations within
72 hours after exposure (Table 3-1).
Table 3-1. Distribution and clearance of radioactivity in rat and mouse
tissues following a 6-hour inhalation exposure to 150 or 1500 ppm
[2-14C]-labeled 1,1,1-trichloroethane
Species, exposure
level, tissue
Mouse, 150 ppm
Liver
Kidney
Fat
Mouse, 1500 ppm
Liver
Kidney
Fat
Rat, 150 ppm
Liver
Kidney
Fat
Rat, 1500 ppm
Liver
Kidney
Fat
1,1,1-Trichloroethane (nmol-equivalents/g of tissue)3
0 hour
76.0 ±7.5
74.6 ±6.7
1329 ±123
631 ±144
1103 ±579
16,198 ±1792
68.2 ±4.4
225 ±31
724 ± 236
504 ±33
994 ±261
8403 ± 1780
24 hour
5.0 ±0.8
7.0 ±2.0
10.2(1)
NDd
NDd
NDd
4.5 ±0.9
9.3 ±1.6
14.1 ±5.6
19.1 ±1.5
28.5 ±6.6
60.1 ±51.7
48 hour
2.8 ± 1.0
5.8 ±0.6
7.6(1)
NDd
NDd
NDd
4.2 ±0.4
7.5 ±0.6
ND
13.2 ±1.4
17.9 ±4.8
21.7 ± 10.6(2)
72 hour
4.4 ±0.7
3.0 ± 1.5(3)b
NDC
NDd
NDd
NDd
3.1 ±0.4
5.3 ±0.7
ND
9.8 ± 1.3
11.1±3.8
12.1(1)
aValues are means ± SD of data from four animals, unless otherwise noted.
bSome determinations were below the detection limit. When not all determinations were above the detection limit,
the number in parentheses represents the number of animals with values above the detection limit.
"Not detectable.
dThe authors stated that the inability to detect 14C-activity in the tissues of mice 24 hours after the 1500 ppm
exposure reflected the lower specific activity of [14C] 1,1,1-trichloroethane used relative to the other exposures.
Source: Schumann et al. (1982a).
Schumann et al. (1982b) compared the fate of inhaled 1,1,1-trichloroethane following
single or repeated exposure in male F344 rats and B6C3F1 mice. Rats and mice were exposed
by inhalation to 1500 ppm 1,1,1-trichloroethane for 6 hours/day, 5 days/week for approximately
16 months. On the last day of exposure, animals were exposed to 14C-labeled
1,1,1-trichloroethane. The fate of [14C]-1,1,1-trichloroethane in the repeat-exposure animals was
compared to a group of rats and mice that had been exposed concurrently to chamber air (i.e.,
age-matched controls) prior to receiving the single 6-hour exposure to 1500 ppm
[14C]-1,1,1-trichloroethane. Animals were followed for 72 hours after their final exposure.
14C-activity was measured in liver, kidney, and fat. Tissue concentrations of 14C-activity were
11
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similar between the singly and repeatedly exposed rats and mice. In mice, immediately after a
6-hour exposure to [14C]-l,l,l-trichloroethane, tissue concentrations in single and repeated
exposure animals, respectively, were (in nmol equivalent of 1,1,1-trichloroethane/g tissue):
liver—1794 ± 302 and 1489 ± 415; kidney—877 ± 186 and 817 ± 214; fat—10,603 ± 1528 and
8789 ± 2259. At 72 hours, postexposure, concentrations in mouse tissues were as follows:
liver—50.5 ± 9.8 and 45.9 ± 16.8; kidney—47.3 ± 14.4 and 36.5 ± 4.0; fat—both nondetectable.
Immediately after a 6-hour exposure, tissue concentrations in single and repeated exposure rats,
respectively, were as follows: liver—606 ± 75 and 641 ± 83; kidney—480 ± 146 and 490 ± 128;
fat—5685 ± 1424 and 4591 ± 1226. At 72 hours, postexposure concentrations were as follows:
liver—both nondetectable; kidney—30.0 and 76.5; fat—191 ± 113 and 144 ± 1.9. The authors
concluded that repeated exposure of rats and mice to 1500 ppm 1,1,1-trichloroethane did not
significantly alter the disposition of the chemical.
Schumann et al. (1982b) compared tissue concentrations of 14C activity in these older rats
and mice that received a single exposure to 1,1,1-trichloroethane (age 18 months) with those
from a single exposure study in younger (age 2.5-3.5 months) rats and mice (Schumann et al.,
1982a). This comparison revealed an age-related increased body burden (1.3-fold in rats and
two- to threefold in mice) and increased amount metabolized (1.6-fold in rats and five- to sixfold
in mice) in aged versus young animals. The authors suggested that the increased body burden
and extent of metabolism in the older animals may be a function of the greater fat content of the
older rodents.
Studies with pregnant C57BL mice indicate that distribution of radioactivity from
[2-14C]-labeled 1,1,1-trichloroethane to the placenta and developing fetus is low relative to other
tissues and organs (Danielsson et al., 1986). On gestation day (GD) 17, four groups of mice
were exposed by inhalation for 10 minutes in glass chambers into which volatilized
1,1,1-trichloroethane was introduced by heating corn oil solutions containing 100 uCi of
radiolabeled compound with a specific activity of 0.5 uCi/umol. Concentrations in the exposure
chambers were not determined. Groups of four mice were killed at 0, 0.5, 4, and 24 hours after
exposure, and concentrations of total and nonvolatile radioactivity in brain, lung, liver, kidney,
fetus, and placenta were determined. Immediately following exposure, concentrations of total
radioactivity in fetal and placental tissue samples were about 10-fold lower than concentrations
in other sampled tissues (Table 3-2). Concentrations in all tissues declined to very low levels at
the 24-hour sampling period (Table 3-2). At the 0-hour period, tissue concentrations of
nonvolatile radioactivity, taken as a measure of metabolized 1,1,1-trichloroethane, were only
small fractions (< about 10%) of the concentrations of total radioactivity, with the exceptions of
liver and lung, in which concentrations of nonvolatile radioactivity were about 31% and 23% of
total radioactivity concentrations, respectively (data not shown in Table 3-2).
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Table 3-2. Tissue concentrations of radioactivity at several time periods
after 10-minute inhalation exposure of pregnant mice to [2-14C]-labeled
1,1,1-trichloroethane
Tissue
Brain
Lung
Liver
Kidney
Fetus
Placenta
Tissue radioactivity (dpm/mg tissue)3
0 hour
123 ± 50
114 ±44
143 ± 74
97 ±4.2
9.3 ±1.7
14 ±2.7
0.5 hour
15 ±2
17 ±2.3
39 ±4.8
49 ±8.7
7.8 ±0.5
12 ±1.0
4 hour
1.4 ±0.2
6.6 ±0.7
13 ±1.5
7.2 ± 1.1
2.1 ±0.1
2.6 ±0.1
24 hour
0.3 ±0.03
2.0 ±0.3
5.3 ±1.0
1.4 ±0.3
0.7 ±0.1
0.9 ±0.2
aValues are means ± SE of tissue samples from four mice at each time interval; dpm = disintegrations per minute.
Tissues were sampled at low temperatures to prevent loss of volatile radioactivity. Separate sets of tissue samples
were heated to 50°C before determination of radioactivity to assess nonvolatile radioactivity (data not shown
above).
Source: Danielsson et al. (1986).
Several investigators have explored the effect of duration of exposure on the body burden
of 1,1,1 -trichloroethane. Using data from human volunteers exposed to 1,1,1 -trichloroethane,
Nolan et al. (1984) simulated repeated 8-hour daily exposures based on a three-compartment
pharmacokinetic model. The simulation indicated that, at the end of the fifth daily exposure, the
expired air and blood concentrations of 1,1,1-trichloroethane would be within 4 and 8%,
respectively, of the concentrations after a single 8-hour exposure and that the amount of
1,1,1-trichloroethane in the body would be 1.8 times that following a single exposure. This
simulation is in agreement with the results of a repeated exposure study in humans (Stewart et
al., 1969) in which the concentration of 1,1,1-trichloroethane in expired air increased very little
over 5 consecutive days of exposure to 507 ppm (2770 mg/m3) of 1,1,1-trichloroethane. The
simulation predicted that twelve daily exposures would be required to reach 95% of steady state
concentrations of 1,1,1-trichloroethane in the body (Nolan et al., 1984). At steady state, the
body would contain 3.6 times the amount of 1,1,1-trichloroethane as after a single 8-hour
exposure; about 70% of this would be in the fat. This percentage in fat is generally consistent
with the findings of RTI (1988), which reported a body burden in fat of 53 to 62% of the dose
retained in tissues 1 to 2 hours after gavage dosing. (Single-exposure inhalation studies in
animals generally presented tissue distribution data in terms of concentrations and not percent
total dose in a given tissue.) Thus, the available data suggest a possible increase in body burden
of 1,1,1-trichloroethane with repeated exposure; however, any increase in tissue concentrations
at steady state as compared with the concentration at the end of a single exposure is predicted to
be modest.
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3.3. METABOLISM
1,1,1-Trichloroethane is metabolized oxidatively, albeit to a limited extent, to
trichloroethanol and trichloroacetic acid by the cytochrome P450 (CYP) mixed function oxidase
system. These metabolites are excreted in the urine; other minor metabolites (carbon dioxide
[CC>2] and acetylene) are excreted in expired air. Studies in animals and humans demonstrate
that only a small fraction of absorbed 1,1,1-trichloroethane (<10%) is metabolized; a large
fraction of the absorbed dose is excreted unchanged in exhaled air. Some, but not all studies,
have found evidence of CYP enzyme induction by 1,1,1-trichloroethane.
1,1,1-Trichloroethane is metabolized at low rates to trichloroethanol (and its glucuronide
conjugate) and trichloroacetic acid; these metabolites are excreted in the urine in both humans
and experimental animals. A minor metabolite, CC>2, is eliminated in expired air (Johns et al.,
2006; Reitz et al., 1988; Mitoma et al., 1985; Nolan et al., 1984; Schumann et al., 1982a;
Monster et al., 1979; Hake et al., 1960). A general metabolic scheme for 1,1,1-trichloroethane is
presented in Figure 3-1.
14
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Cl H
I I
Cl—C—C-H
I I
Cl H
1,1,1 -trichloroethane
O,
H20
CYP2E1
CYP2B
CYP2C
CYP3A
Cl
Cl—C-CH2OH
Cl
trichloroethanol
O
glucuronic acid
trichloroethanol
glucuronide
OH
trichloroacetic acid
CO,
Figure 3-1. Metabolic scheme for l,l?l-trichloroethane.
The initial step in metabolism of 1,1,1-trichloroethane involves CYP monooxygenases,
with several CYP isozymes shown as contributing to metabolism. Evidence that the ethanol-
inducible CYP isozyme CYP2E1 contributes to the catalysis of the initial step comes from
studies in humans and animals. A group of volunteers was administered ethanol (0.35 mg/kg
body weight) daily for 7 days and was then exposed to 175 ppm (950 mg/m3)
1,1,1-trichloroethane for 2 hours (Johns et al., 2006). Prior ethanol consumption resulted in a
significant increase in metabolic clearance (mean increase = 25.4%). Ethanol pretreatment of
male Wistar rats (n = 5 per exposure group) increased the cumulative urinary excretion of
trichloroacetic acid and trichloroethanol following inhalation exposure to 50, 100, or 500 ppm
(270, 550, 2730 mg/m3) of 1,1,1-trichloroethane for 6 hours (Kaneko et al., 1994); mean in vitro
metabolic rates for 1,1,1-trichloroethane were 1.8 nmol per g liver and minute for liver
microsomes from ethanol-pretreated Wistar rats compared with 0.5 nmol per g liver and minute
15
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for microsomes from control Wistar rats (Sato et al., 1980); and antibody to purified human liver
CYP2E1 inhibited in vitro metabolism of 1,1,1-trichloroethane by human liver microsomes
(Guengerich et al., 1991). Phenobarbital-inducible CYP isozymes (CYP2B, 2C, or 3A) may also
be involved in the initial metabolic step. Rates of 1,1,1-trichloroethane metabolism by liver
microsomes from phenobarbital-treated rats were two- to fourfold greater than rates by
microsomes from control rats (Koizumi et al., 1983; Ivanetich and Van den Honert, 1981).
Conversion of trichloroethanol to trichloroacetic acid appears to involve the intermediate
formation of chloral hydrate and may involve alcohol and aldehyde dehydrogenases or CYP
mixed function oxidases (Casciola and Ivanetich, 1984; Ivanetich and Van den Honert, 1981).
Under conditions of hypoxia, evidence for reductive dechlorination of
1,1,1-trichloroethane via CYP to form acetylene has been reported in rats (Diirk et al., 1992;
Albano et al., 1985). This pathway is not expected to be biologically important except under
conditions of tissue hypoxia and is not presented in Figure 3-1.
Humans metabolize absorbed 1,1,1-trichloroethane to a limited extent (Nolan et al.,
1984; Monster et al., 1979). In humans (n = 6 per exposure scenario) exposed for 4 hours to 70
or 145 ppm (380 or 790 mg/m3) of 1,1,1-trichloroethane while at rest or 142 ppm (780 mg/m3)
while alternating periods of rest with intermittent workloads, about 60-80% of absorbed
compound was estimated to have been excreted unchanged in exhaled breath during a 163-hour
postexposure period (Monster et al., 1979). Excretion of the metabolites trichloroethanol and
trichloroacetic acid in urine collected for 70 hours after exposure accounted for about 2% and
0.5%, respectively, of the estimated amount of absorbed 1,1,1-trichloroethane. In humans
exposed to 35 or 350 ppm (190 or 1900 mg/m3) of 1,1,1-trichloroethane for 6 hours, it was
estimated that 91% of absorbed 1,1,1-trichloroethane was excreted unchanged by the lungs,
5-6% was metabolized and excreted in urine as the metabolites trichloroethanol or
trichloroacetic acid, and less than 1% remained in the body after 9 days (Nolan et al., 1984).
These estimates were made with a PBPK model that was developed with measurements of
1,1,1-trichloroethane in exhaled breath samples and of trichloroacetic acid and trichloroethanol
in urine samples collected from six human subjects at several intervals during a 9-day
postexposure period (Nolan et al., 1984).
Experiments with laboratory animals similarly indicate that ingested and inhaled
1,1,1-trichloroethane is slowly metabolized and predominantly excreted unmetabolized in
exhaled breath. In male Osborne-Mendel rats and male B6C3F1 mice treated by gavage with
1,1,1-trichloroethane in corn oil, 5 days/week for 4 weeks, followed by a single dose of
[l,2-14C]-labeled compound, recovery of the applied dose 48 hours after exposure (for rats and
mice, respectively) was as follows: 85.1 and 92.9% as unchanged compound in expired air;
0.9 and 2.0% as CC^in expired air; 2.1 and 3.4% as metabolites in urine; and 1.2 and 0.7% as
presumed metabolites remaining in the carcass (Mitoma et al., 1985). In male F344 rats supplied
16
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for 8 hours with drinking water containing [2-14C]-labeled 1,1,1-trichloroethane, 90.5% of the
dose was expired as unchanged 1,1,1-trichloroethane, 2.2% was expired as CC>2, and 2.2 and
1.3% were accounted for by metabolites in urine and carcasses, respectively (Reitz et al., 1985).
In male F344 rats (n = 4 per group) exposed by inhalation to 150 or 1500 ppm (820 or
8190 mg/m3) of [2-14C]-labeled 1,1,1-trichloroethane for 6 hours, 94.2 and 97.9% of recovered
radioactivity (during a 72-hour postexposure period) was accounted for by unchanged
1,1,1-trichloroethane in expired air, respectively (Schumann et al., 1982a). Similar results were
obtained for male B6C3F1 mice exposed according to the same exposure protocol, except that
average rates of metabolism in mice, calculated on a body weight basis, were two to three times
rates in rats (Schumann et al., 1982a). Following exposure to 150 ppm (820 mg/m3), average
metabolic rates were 8.87 ± 1.79 and 24.26 ± 10.28 umol/kg for rats and mice, respectively; after
exposure to 1500 ppm (8190 mg/m3), the rates were 24.64 ±1.15 and 42.06 ± 8.61 umol/kg,
respectively.
In vitro data provide supporting evidence that 1,1,1-trichloroethane is slowly metabolized
compared with several other small molecular weight chlorinated hydrocarbons. For example,
with rat liver microsomes, rates of metabolism were 0.5 nmol per g liver and minute for
1,1,1-trichloroethane compared with 21.0, 31.1, 19.1, and 18.9 nmol per g liver and minute for
1,1,2-trichloroethane, 1,1 -dichloroethylene, 1,1 -dichloroethane, and trichloroethylene,
respectively (Sato et al., 1980).
Studies by Shah and Lai (1976), Fuller et al. (1970), and Lai and Shah (1970)
demonstrated induction of drug metabolizing enzymes by acute inhalation of
1,1,1-trichloroethane in rats and mice; they showed (1) concentration- and duration-related
decreases in sleeping time induced by the parent-active, CYP-metabolized drugs hexobarbital,
meprobamate, and zoxazolamine, (2) increased microsomal metabolism of these drugs, (3) no
effect on sleeping time produced by barbital (not metabolized) or chloral hydrate (metabolized
by alcohol dehydrogenase), indicating that the effect on hexobarbital sleeping time was not due
to a general reduction in central nervous system (CNS) sensitivity to depressants, (4) increased
CYP and NADPH cytochrome c reductase (although not liver microsomal protein), (5) increased
absolute and relative liver weight, and (6) inhibition of these effects by the protein synthesis
inhibitors cycloheximide and actinomycin D, suggesting that 1,1,1-trichloroethane increases the
activity of drug metabolizing enzymes by inducing synthesis of new enzyme protein. With
24-hour exposure, the maximum inductive effect occurred at 3000 ppm; lower concentrations
were ineffective and higher concentrations were progressively less effective, possibly due to
toxicity. Bruckner et al. (2001) found significant dose-related increases in CYP2E1 and
CYP2B1/2 in male Sprague-Dawley rats given single oral doses >2500 mg/kg but no effect on
CYP1 Al or total CYP levels at doses up to 10,000 mg/kg. Peak activity for CYP2E1 and
CYP2B1/2 were reached at 6 and 12 hours after dosing, respectively; return to preexposure
17
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levels was fairly rapid (within 36-48 hours). With repeated oral exposure for 7 days, Platt and
Cockrill (1969) found significant increases in microsomal protein concentration and cell-sap
protein concentration in the liver of rats treated with 1650 mg/kg-day.
Other studies, however, failed to find evidence of enzyme induction by
1,1,1-trichloroethane. Wang et al. (1996) found that 6-hour exposure to 4000 ppm
(21,840 mg/m3) of 1,1,1-trichloroethane had no effect on microsomal protein, CYP (total or
specific isozymes), or specific monooxygenase activities in male Wistar rats. Subchronic
inhalation exposure (6 hours/day, 5 days/week for 4 weeks) to 820 ppm (4480 mg/m3) had no
effect on microsomal CYP in male Sprague-Dawley rats (Toftgard et al., 1981). Savolainen et
al. (1977) exposed groups of 10 adult male Sprague-Dawley rats to 0 or 500 ppm (2730 mg/m3)
of 1,1,1-trichloroethane vapor for 6 hours per day for 4 consecutive days. On the 5th day, 2 rats
from each group were sacrificed after 0, 2, 3, 4, or 6 hours of additional exposure. Liver
microsomal CYP was similar to that of controls in the rats sacrificed without exposure on the
5th day but was progressively decreased in rats with an additional 2-6 hours of exposure.
Significantly reduced hepatic CYP activity was also reported in male Wistar rats treated with a
single dose of 1375 mg/kg by gavage in olive oil and sacrificed 24 hours later (Vainio et al.,
1976). An explanation for the different findings regarding enzyme induction by
1,1,1-trichloroethane has not been postulated. It is possible, however, that the differences in
enzyme induction observed by different investigators may be a function of the differences in
dose level tested, number of hours after dosing CYP activity was measured, and whether the
activity of total CYP or specific CYP isozymes was measured.
It is unclear whether 1,1,1-trichloroethane may enhance its own biotransformation via
CYP induction. Koizumi et al. (1983) reported that exposing rats to 200, 400, or 800 ppm (1090,
2180, or 4370 mg/m3) 1,1,1-trichloroethane (24 hours/day for 10 days) increased the ability of
liver microsomes to metabolize 1,1,1-trichloroethane, compared to microsomes from fresh-air
controls. In contrast, repeated preexposure of rats and mice to 1500 ppm (8190 mg/m3)
1,1,1-trichloroethane for 16 months did not alter the routes of excretion, the extent of
metabolism, or the concentrations of radioactivity in tissues after a 6-hour inhalation exposure to
1500 ppm (8190 mg/m3) of [2-14C]-labeled 1,1,1-trichloroethane, compared with age-matched
rats given only a single 6-hour exposure (Schumann et al., 1982b).
Loizou et al. (1996) observed statistically significant and apparently dose-related
reductions in liver glutathione levels in male Wistar rats exposed to 4000 to 25,000 ppm
(21,840-136,500 mg/m3) of 1,1,1-trichloroethane for 3 hours; liver glutathione levels were
approximately 77% of the control level at 4000 ppm and 58% of the control level at 25,000 ppm.
Lung glutathione and liver and lung glutathione disulfide were unaffected. There was no
evidence of toxicity associated with the observed glutathione depletion. The mechanism by
which glutathione would be depleted by 1,1,1-trichloroethane is unclear, as the compound is
18
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little metabolized and binding of reactive intermediates by glutathione is not known for this
chemical. The researchers allowed that reductive dechlorination could lead to intermediates that
would react with glutathione but indicated this could not explain the observed glutathione
depletion, given the very low rate of reductive dechlorination of 1,1,1-trichloroethane. They
suggested that their finding may be related to uncoupling of the CYP system, leading to
hydrogen peroxide production, a phenomenon that has been associated with
1,1,1-trichloroethane in vitro (Takano et al., 1988; Ivanetich and Van den Honert, 1981).
3.4. ELIMINATION
Most 1,1,1-trichloroethane, whether received either by inhalation or oral exposure, is
excreted unchanged by the lungs in expired air. Only a small fraction is excreted in the urine as
trichloroacetic acid or trichloroethanol. Studies in animals and humans indicate that
1,1,1-trichloroethane is unlikely to accumulate to any significant extent with repeated exposure.
Results from human and animal studies indicate that most inhaled 1,1,1-trichloroethane is
rapidly excreted unchanged by the lungs in expired air (Nolan et al., 1984; Schumann et al.,
1982a; Monster et al., 1979); the same elimination path has been demonstrated to be important
following drinking water exposure in rats (Reitz et al., 1988) or gavage administration in rats and
mice (RTI, 1988; Mitoma et al., 1985). In rats and mice, urinary excretion of metabolites
accounted for only small fractions (1-2%) of orally administered doses (Reitz et al., 1988;
Mitoma etal., 1985).
In a study of exposed human volunteers, Nolan et al. (1984) found that the concentration
of 1,1,1-trichloroethane in blood rose rapidly during the initial portion of the exposure period
such that, by 1.5 hours, it was 90% of the mean concentration at 6 hours of exposure. (A similar
pattern of initial rapid increase followed by an apparent leveling off in blood concentration was
seen in 12 men exposed for 3 hours to 175 or 350 ppm [950 or 1900 mg/m3] of
1,1,1-trichloroethane [Mackay et al., 1987].) Based on blood and expired air concentrations,
elimination of 1,1,1-trichloroethane was described as triexponential, with estimated half lives of
44 minutes, 5.7 hours, and 53 hours for the initial, intermediate, and terminal phases,
respectively (Nolan et al., 1984). Measured blood concentrations at 1.5, 16, and 40 hours after
exposure were 59%, 7%, and 3%, respectively, of the concentration at the end of exposure.
In rats, elimination of 1,1,1-trichloroethane was rapid and diexponential, with estimated
half lives of 10.5-36 minutes for the initial and 139-258 for the terminal phase, and was
triexponential in mice, with estimated half lives of 2, 13, and 169-193 minutes for the initial,
intermediate, and terminal phases, respectively (Schumann et al., 1982a).
Several studies have described quantitative relationships between time-weighted average
(TWA) workplace air concentrations and urinary excretion of metabolites (Mizunuma et al.,
1995; Kawai et al., 1991; Seki et al., 1975) or 1,1,1-trichloroethane itself (Mizunuma et al.,
19
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1995). The American Conference of Governmental Industrial Hygienists (ACGIH) (2002)
recommends several biological exposure indices to monitor occupational exposure to
1,1,1-trichloroethane (methyl chloroform): (1) 40 ppm of 1,1,1-trichloroethane in end-exhaled
air, prior to the last shift of the workweek; (2) 10 mg/L of trichloroacetic acid in urine at the end
of the workweek; (3) 30 mg/L of total trichloroethanol in urine at the end of the shift at the end
of the workweek; and (4) 1 mg/L of total trichloroethanol in blood at the end of the shift at the
end of the workweek.
3.5. PHYSIOLOGICALLY BASED PHARMACOKINETIC MODELS
3.5.1. Summary of Available Models
Fourteen PBPK models for 1,1,1-trichloroethane in adult rodents or humans have been
published. These models were reviewed by Yang (2006) and are summarized in Table 3-3.
Selected models are more fully described below.
Table 3-3. Summary of available models for 1,1,1-trichloroethane in rats and
humans
Model
Caperosetal., 1982
Nolan etal., 1984
Gargasetal., 1986
Reitzetal., 1987, 1988
Bogen and Hall, 1989
Dallas etal., 1989
Leung, 1992
Yoshida, 1993
Lapare etal., 1995
Loizouetal., 1996
DeJongh et al., 1998
TardifandCharest-
Tardif, 1999
Poet et al., 2000
Dobrev etal., 2001,
2002
Structure
Fat, muscle, lung, and rapidly perfused tissues; clearance from rapidly perfused tissues
Fat, muscle, lung, and well perfused tissues; first-order metabolism in well perfused
tissues
Liver, viscera, muscle/skin, and fat; first-order metabolism in liver
Liver, fat, and slowly and rapidly perfused tissues; saturable metabolism in liver
Liver, fat, skin, and slowly and rapidly perfused tissues; saturable metabolism in liver
Blood, lung, liver, muscle, fat, and rapidly perfused tissues; first order metabolism in
liver
Fat, liver, and slowly and rapidly perfused tissues; saturable metabolism in liver
Fat, liver, and slowly and rapidly perfused tissues; saturable metabolism in liver
Lungs, liver, gastrointestinal tract, fat, muscle and skin, and rapidly and slowly
perfused tissues; saturable metabolism in liver
Fat, liver, and rapidly and slowly perfused tissues; first-order metabolism in liver
Fat, liver, brain, and rapidly and slowly perfused tissues; first-order metabolism in liver
Liver, fat, and slowly and rapidly perfused tissues; saturable metabolism in liver
Fat, skin, liver, and rapidly and slowly perfused tissues; saturable metabolism in liver
Fat, liver, and other tissues lumped into one or two compartments; saturable
metabolism in liver
Source: Yang (2006).
20
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Reitz et al. (1988) model
Reitz et al. (1988) developed a four-compartment (liver, rapidly perfused tissue, slowly
perfused tissue, and fat) perfusion limited PBPK model for 1,1,1-trichloroethane in rats, mice,
and humans. The model predicts 1,1,1-trichloroethane tissue concentrations following exposure
via inhalation, intravenous (iv) administration, gavage, or drinking water administration. The
model parameter values are shown in Table 3-4, and are updated numbers from previous
versions (Reitz et al., 1987). Tissue:blood partition coefficients (Table 3-4) were derived using a
vial-equilibration technique for rat blood, liver, fat, and muscle tissue. Blood:air partition
coefficients were determined with human and mouse blood (further details not reported).
Metabolism was restricted to the liver compartment, and was represented with standard terms for
Michaelis-Menten kinetics. Metabolic parameters Vmax and Km (Table 3-4) were optimized to fit
the parent blood concentration data for rats exposed to 150 or 1500 ppm (820 or 8190 mg/m3)
1,1,1-trichloroethane via inhalation for 6 hours (Schumann et al., 1982a).
The predictive capability of the model was evaluated by comparing various dose metrics
from the PBPK model simulations with the experimentally derived values from studies with 2- to
3-month-old rats and mice following drinking water (116 mg/kg-day) or inhalation exposures
(150 or 1500 ppm). Dose metrics evaluated included concentrations of parent
1,1,1-trichloroethane in blood, liver, and fat and total amount of metabolite in liver. Comparison
of simulations and data sets revealed the following:
• Rat inhalation study: Schumann et al. (1982a) determined the venous blood concentrations of
1,1,1-trichloroethane in male F344 rats during and after 6-hour exposure to 150 or 1500 ppm
1,1,1-trichloroethane in a head-only exposure system. The Reitz et al. (1988) model
simulated the postexposure data reasonably well, but the concentrations during exposure
were overpredicted by a factor of about 2.
• Rat intravenous study: The model predicted the shapes of the venous blood concentration
profiles (data obtained by Reitz et al., 1988) but somewhat underpredicted from about 1 hour
postexposure.
• Rat gavage study: The model simulation did not follow satisfactorily the shape of the time-
venous blood concentration curve (data collected by Reitz et al., 1988).
• Rat drinking water study: The model simulation of the rate of elimination of
14C-1,1,1-trichloroethane in exhaled air of the rats was comparable with the experimental
data by Reitz et al. (1988). In addition, the predicted amount metabolized (5.49 (imol, about
2% of ingested 1,1,1-trichloroethane) was also comparable with the experimental
measurement in urine and CC>2 (8.19 jimol, about 3% of ingested 1,1,1-trichloroethane).
• Mouse inhalation study: B6C3F1 mice had the same exposure scenario as the rats did in the
Schumann et al. (1982a) study. The model predicted well the venous blood concentrations of
21
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1,1,1-trichloroethane in mice (experimental data collected by Schumann et al. [1982a] under
the same experimental conditions as rats).
• Human volunteer inhalation study: The human inhalation data were collected by Nolan et al.
(1984) (exposed to 35 or 350 ppm for 6 hours). The model overpredicted the venous blood
concentrations during exposure by a factor of about 2 and predicted the postexposure
concentrations well. The predictions of 1,1,1-trichloroethane concentrations in expired air
agreed with the data.
Reitz et al. (1988) used their rat and mouse PBPK models to calculate average
concentrations of 1,1,1-trichloroethane in the liver over the lifetime of the animal (ACL) (i.e.,
the dose surrogate). The ACL for rats exposed by inhalation (6 hours/day, 5 days/week for 2
years) to 875 ppm (4780 mg/m3) was 28 umol/L and for mice exposed to 1500 ppm (8190
mg/m3) was 95 umol/L. These exposure levels were reported to have produced no effects on
liver histopathology in 1-year rat (Quast et al., 1978) and 2-year mouse bioassays (Quast et al.,
1988, 1984). This PBPK model was parameterized for humans and used to calculate the human
ACL from ingestion of 2 L of water per day with varying concentrations of
1,1,1-trichloroethane. The human ACL for a drinking water concentration of 300 ppb
1,1,1-trichloroethane (a concentration reported to have been the highest detected in some
finished drinking-water supplies) was predicted to be 0.01 umol/L (Reitz et al., 1988).
Comparison of this predicted human ACL (0.01 umol/L) with the ACLs derived from the PBPK
model runs at the rat drinking water no-observed-adverse-effect level (NOAEL) (28 umol/L) and
the mouse NOAEL (95 umol/L) yielded margins of exposure of 2800 and 9500, respectively.
The human PBPK model also predicted that the ACL for a person drinking water containing 10
ppb of 1,1,1-trichloroethane for 100 days would be 2.7 times higher than the ACL after one day
of drinking 10 ppb water, indicating only limited accumulation of 1,1,1-trichloroethane in the
liver after continuous long-term drinking water exposure.
22
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Table 3-4. Parameters used in the Reitz PBPK models for
l,l?l-trichloroethane
Parameter"
Weights
Body weight (kg)
Liver
Rapidly perfused
Slowly perfused
Fat
Flows (L/hour)
Alveolar ventilation
Cardiac output (COP)
Liver (% COP)
Rapidly perfused (% COP)
Slowly perfused (% COP)
Fat (% COP)
Partition coefficients
Blood:air
Liver: air
Rapidly perfused:air
Slowly perfused:air
Fat:air
Biochemical constants6
vmaxc
Km (mg/L)
Ka (hr"1) (lst-order rate constant for GI absorption)
Human
83.0b
3.1%
3.7%
61.1%
23.1%
348.0C
348.0C
24.0
49.0
18.0
9.0
2.53
8.6
8.6
3.15
263
0.419
5.75
-
Rat
0.215b
4.0%
5.0%
75.0%
7.0%
5.11C
5.11d
24.0
53.0
18.0
5.0
5.76
8.6
8.6
3.15
263
0.419
5.75
1.25
Mouse
0.029
4.0%
5.0%
78.0%
4.0%
1.26
1.26
24.0
56.0
18.0
2.0
10.8
8.6
8.6
3.15
263
0.419
5.75
-
""Parameter values in Reitz et al. (1988) were used in the current IRIS assessment except as noted in the footnotes to
this table.
bModeling performed in the current assessment used the following body weight values (rather than those in this table
from Reitz et al. [1988]): Human: actual weight of study subjects (if reported) or 70 kg if not reported. Animal:
actual reported body weights.
°In the current assessment, alveolar ventilation was scaled (rather than those in this table from Reitz et al.[1988]):
(alveolar ventilation rate constant =15 L/hour-kg) x BW0'74, where BW = body weight.
dln the current assessment, cardiac output rate was scaled (rather than those in this table from Reitz et al. [1988]):
(cardiac output rate = 15 L/hour-kg) x BW074.
eVmaxC and Km were obtained for the rat from the blood level data of Schumann et al. (1982a) by computer
optimization. VmaxC is an allometric measure of maximum velocity of metabolism, showing the following
relationship with maximum enzyme rate: Vmax = VmaxC x BW07.
Source: Reitz etal. (1988).
Gar gas et al. (1986) model
Gargas et al. (1986) developed a model for rats based on the styrene model by Ramsey
and Anderson (1984) comprised of four tissue compartments (liver, viscera, muscle/skin, and fat)
and a chemical exchange compartment (lung). Time-course concentrations and tissue and
blood:air partition coefficients (at 37°C) were obtained from close-chamber gas uptake studies.
Male F344 rats were exposed to 1,1,1-trichloroethane at initial chamber concentrations of 0.2,
1.0, 10, and 210 ppm. The model assumed equilibrium between the concentrations in blood
leaving the lung and in alveolar air, controlled by the blood:air partition coefficient, and that the
23
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tissue uptake of 1,1,1-trichloroethane was flow limited. The chemical was eliminated through
exhalation and first-order metabolism in the liver. Metabolic parameters used in the model were
obtained from optimization against gas uptake data by visual inspection. The model simulated
the chamber concentration data from the gas uptake pharmacokinetic studies (Gargas et al.
[1986]) in rats very well, but the PBPK model was not further verified with external data.
Bogen and Hall (1989) model
Bogen and Hall (1989) developed a PBPK model for 1,1,1-trichloroethane in gerbils by
scaling parameters of the Reitz et al. (1987) rat model with a gerbil:rat body weight ratio to the
0.7 power. A fifth compartment for skin was also added and parameterized for a reference
human weighing 70 kg. Parameter values for the gerbil and five compartment human models are
listed in Table 3-5. Parameter values for tissue-specific volumes and blood-perfusion rates, as
well as cardiac output, were taken from U.S. EPA (1988b) reference values, except that values
for skin were assumed to be 6% of the reference value for poorly perfused tissues. Blood:air and
tissue:blood partition coefficients, and the Km, were the same as those used in the Reitz et al.
(1987) human model. The human Vmax value from Reitz et al. (1987) of 5.84 mg/hour was
multiplied by a factor of 4(70/83)°'7 (= 3.55) to scale for body weight differences and an
hypothesized underestimation of the parameter of the total amount of 1,1,1-trichloroethane
metabolized. As the basis for the factor of 4, Bogen and Hall (1989) noted that the Reitz et al.
(1987) model underestimated urinary excretion of metabolites by a factor of 2 and that an
additional factor of 2 is needed to adjust for a proposed underestimation of the extent of
metabolism based only on urinary excretion due to metabolites not excreted and metabolites
exhaled as CC>2 that would not be detected in the urine.
Bogen and Hall (1989) used the mouse, rat, and gerbil PBPK models to estimate the
internal dose resulting from exposure to the no-effect levels for liver effects in mice,
neurological effects in gerbils, and developmental effects in rats from exposure to
1,1,1-trichloroethane. The dose metrics used were assumed to be directly applicable to humans
and were used in the human PBPK model to calculate corresponding applied time-weighted
doses for a reference 70 kg human. Three endpoints from three different studies were
considered, with a different dose metric used for each liver metabolite for liver effects (at steady
state) and parent compound in arterial blood for effects on the CNS and fetus (peak and average).
Bogen and Hall (1989) noted that drinking water concentrations predicted to be nontoxic to
humans by this PBPK approach were lower than drinking water concentrations predicted to be
nontoxic by the traditional "safety factor" approach without cross-species dosimetric adjustment.
24
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Table 3-5. Parameter values in PBPK models for 1,14-trichloroethane
Parameter
Weights
Body weight (kg)
Liver (% of body weight)
Rapidly perfused
Slowly perfused
Fat
Skin
Flows (L/hour)
Alveolar output
Cardiac output (COP)
Liver (% COP)
Rapidly perfused (% COP)
Slowly perfused (% COP)
Fat (% COP)
Skin (% COP)
Partition coefficients
Blood:air
Liver:blood
Rapidly perfused:blood
Slowly perfused:blood
Fat:blood
Skin:blood
Vmax (mg/hour)
Km (mg/L)
Gerbil
0.059
4%
5%
79%
4%
-
2.07
2.07
24
53
21
2
-
10.8
0.796
0.796
0.292
24.4
-
0.0356
6.43
Reference human
70.0
2.6%
5%
58.3%
19%
3.7%
378.0
372.0
26
44
23.5
5
1.5
2.53
3.4
3.4
1.25
104
53
20.7
6.43
Source: Bogen and Hall (1989).
Poet et al. (2000) model
In order to describe dermal uptake of 1,1,1-trichloroethane in rats and humans from soil
or water, Poet et al. (2000) modified the PBPK models developed by Reitz et al. (1988) to
include a separate skin compartment that was assumed to be a simple, "well-stirred" single
compartment. Equations to describe the rate of change of 1,1,1-trichloroethane across the skin
incorporated Pick's law and included parameters for surface area, blood flow to the skin,
skin:matrix (skin:soil or skin:water) partition coefficients, and permeability coefficient. Values
of model parameters are listed in Table 3-6. Skin:air partition coefficients were determined by
Mattie et al. (1994). Soil:air and waterair partition coefficients were determined by the vial-
equilibration technique.
Breath elimination data were obtained from rats exposed to 1,1,1-trichloroethane-
containing soil in a dermal exposure cell designed to capture volatilized 1,1,1-trichloroethane
and prevent contamination of exhaled breath. Breath elimination data for rats were also obtained
for 1,1,1-trichloroethane in an aqueous solution; the applied aqueous solution was occluded.
Humans were exposed by immersing one hand in 0.1% 1,1,1-trichloroethane aqueous solutions
or 0.75% 1,1,1-trichloroethane in soil. Rat and human skin permeability coefficients (Kps) were
optimized to fit the exhaled breath data. Resulting rat skin Kps were 0.25 and 0.15 cm/hour for
25
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the water and soil matrices, respectively. The estimated human Kp for water matrix exposures
(0.006 cm/hour) was about 40-fold lower than the corresponding rat Kp. This human value was
based on data from three subjects whose hands were not prehydrated: 0.0064, 0.0069, and
0.0057 cm/hour. The estimated water-matrix Kp for a fourth subject whose hand was
prehydrated by immersing his hand in water for 2 hours was much higher: 0.528 cm/hour. This
observation is consistent with the hypothesis that skin hydration results in an increased
permeability to many compounds. The optimized values of the human Kps for
1,1,1-trichloroethane in soil (0.002 ± 0.0005 cm/hour) were approximately one-third of the
water matrix Kps. Poet et al. (2000) used the PBPK models to simulate dermal exposures to
1,1,1-trichloroethane-contaminated water and soil in children and adults by using worst-case
EPA default assumptions. The simulation results indicated insignificant dermal absorption from
nonoccluded exposures (i.e., exposures not involving an impermeable covering over the test
material), independent of the length of exposure.
Table 3-6. Parameter values in the Poet et al. PBPK models for
1,1,1-trichloroethane
Parameter
Weights
Body weight (kg)
Liver (% of body weight)
Rapidly perfused
Slowly perfused
Fat
Skin
Flows (L/hour)
Alveolar output
Cardiac output (COP)
Liver (% COP)
Rapidly perfused (% COP)
Slowly perfused (% COP)
Fat (% COP)
Skin (% COP)
Partition coefficients
Blood:air
Liverair
Rapidly perfused:air
Slowly perfused: air
Fat: air
Skin: air
Waterair
Soil: air
Vmax (mg/kg-hour)
Km (mg/L)
Rat
0.189-0.219
4%
5%
75%
7%
10%
5.11
5.11
24
53
18
5
0.058
5.8
8.6
8.6
3.2
263
10.8
2.0
8.3
0.419
5.75
Human
68.4-95.3
3.1%
3.7%
61.1%
11.2-24.5%
3.5%
348
348
24
49
18
9
0.058
2.5
8.6
8.6
3.2
263
10.8
2.0
8.3
0.419
5.75
Source: Poet et al. (2000).
26
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Dobrevetal. (2002, 2001) interaction-based models for mixtures oftrichloroethylene,
tetrachloroethylene, and 1,1,1-trichloroethane
Dobrev et al. (2002, 2001) developed human and rat PBPK models to evaluate
interactions for mixed exposures to trichloroethylene, tetrachloroethylene, and
1,1,1-trichloroethane by incorporating terms for various types of competitive metabolism in the
liver. The Reitz et al. (1988) PBPK model was adapted for 1,1,1-trichloroethane. Metabolic
kinetic constants (K;s for competitive, uncompetitive, and noncompetitive mechanisms of
interaction) were estimated by optimizing parameter values to fit data from gas uptake
experiments in which rats were exposed to different initial concentrations of each mixture
component singly, or as mixtures, and air concentrations of the chemicals were measured in the
exposure chamber. Competitive inhibition was considered to be the most plausible interaction,
since competitive K; values for tetrachloroethylene and 1,1,1-trichloroethane (on
trichloroethylene metabolism) were much closer to the individual Michaelis-Menten affinity
constants (i.e., Km) than K; values for uncompetitive or noncompetitive inhibition. The
competitive inhibition model for the ternary mixture adequately described data from 12 gas
uptake experiments with F344 rats exposed to mixtures of all three chemicals at various
concentrations. The PBPK model predicted that concurrent exposure to occupational exposure
limits for each of the three chemicals (50 ppm for trichloroethylene; 350 ppm for
1,1,1-trichloroethane; 25 ppm for tetrachloroethylene) would produce a 22% and 15% increase
in trichloroethylene blood concentrations in rats and humans, respectively, compared with
exposure to 50 ppm trichloroethylene alone. Dobrev et al. (2002) speculated that these mixture-
induced changes would lead to higher bioavailability oftrichloroethylene with increased
amounts available to a glutathione-conjugation pathway that has been associated with kidney
damage.
Fisher et al. (1997) model for a lactating woman
A PBPK model for a lactating woman has been developed to estimate the amount of
common volatile solvents (including 1,1,1-trichloroethane) that a nursing infant may receive for
a given nursing schedule and maternal occupational exposure scenario (Fisher et al., 1997). To
develop the model, human blood:air and milk:air partition coefficients were determined in vitro
for 1,1,1-trichloroethane as 4.23 (SD = 1.61, n = 9) and 13.21 (SD = 4.80, n = 34), respectively.
Samples of blood and milk were collected from nine lactating women; partition coefficients were
determined by using a modification of the vial equilibrium method. The model predicted that
partitioning to milk (and excretion via the milk during nursing) was a minor physiological fate of
inhaled 1,1,1-trichloroethane in a lactating woman exposed under a plausible occupational
exposure scenario.
27
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3.5.2. Model Selection
A review by Yang (2006) reveals that a number of the models in Table 3-3 are variants of
the models by Gargas et al. (1986) and Reitz et al. (1988) (including Dobrev et al., 2002, 2001;
Poet et al., 2000; Tardif and Charest-Tardif, 1999; DeJongh et al., 1998; Yoshida, 1993; Leung,
1992; Bogen and Hall, 1989; Dallas et al., 1989). The models by Bogen and Hall (1989) and
Poet et al. (2000) added a skin compartment, a feature not relevant to the development of RfD
and RfC values. Dobrev et al. (2002, 2001) was developed specifically to examine interactions
among 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene. Caperos et al. (1982)
and Nolan et al. (1984) are earlier models that lump the liver compartment into the well perfused
tissue compartment; because 1,1,1-trichloroethane undergoes metabolism in the liver; this
lumping was not considered appropriate. The Lapare et al. (1995) model did not predict data
sets as well as Reitz et al. (1988), and the Loizou et al. (1996) model results could not be
successfully simulated by Yang (2006). Reitz et al. (1988) and Gargas et al. (1986) were
identified as the most appropriate PBPK models for 1,1,1-trichloroethane. These two models
were then further evaluated against 11 data sets.
The 11 data sets used for the further evaluation of the Reitz et al. (1988) and Gargas et al.
(1986) models were the following:
• Experimental rat pharmacokinetic data sets
- Schumann et al. (1982a)—inhalation data
- Gargas et al. (1986)—inhalation data
- Reitz et al. (1988)—intravenous, gavage, and inhalation data
- Loizou et al. (1996)—inhalation data
- You and Dallas (1998)—inhalation data
- Warren et al. (1998)—inhalation data
- Bruckner et al. (Yang [2006], personal communication)—gavage data
• Human pharmacokinetic data sets (all inhalation)
- Savolainen et al. (1981)
- Nolan etal. (1984)
- Mackay etal. (1987)
- Lapare etal. (1995)
Other data sets were available for model evaluation in addition to those listed above;
however, the above data sets met the following criteria: (1) essential experimental information,
such as strain, age, body weight, and dosing conditions were available, (2) preference given to
studies that used multiple exposure levels, (3) administration of the chemical by inhalation,
28
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intravenous, or oral administration, (4) provision of sufficient data points of the concentration-
time courses of the chemical in exposure chambers, blood, and/or organs, and (5) in the case of
human studies, conduct under appropriate ethical standards with written informed consent from
the participants.
Both models performed similarly on inhalation data sets (Yang, 2006). The Reitz et al.
(1988) model was designed to describe the disposition of 1,1,1-trichloroethane after multiple
routes of exposure (inhalation, oral, and iv injection), whereas the Gargas et al. (1986) model
described 1,1,1-trichloroethane disposition by the inhalation route only. Because it addressed
interspecies extrapolation as well as route-to-route extrapolation, the Reitz et al. (1988) model
was considered more versatile than Gargas et al. (1986). Therefore, Reitz et al. (1988) was used
in the current assessment for PBPK modeling applications. Parameter values for experimental
animal species and humans are those shown in Table 3-4. For the most part, parameter values
used in the current assessment are those from Reitz et al. (1988); other values used in the current
assessment are indicated in footnotes to Table 3-4.
29
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4. HAZARD IDENTIFICATION
4.1. STUDIES IN HUMANS—EPIDEMIOLOGY, CASE REPORTS, CLINICAL
CONTROLS
4.1.1. Oral Exposure
Stewart and Andrews (1966) reported the case of a man who accidentally ingested one
ounce (-600 mg/kg) of 1,1,1-trichloroethane and experienced an immediate burning sensation in
the mouth and throat, nausea after 30 minutes, severe vomiting and diarrhea after 1-6 hours, and
slightly elevated serum bilirubin levels after 48 hours (serum transaminase, blood urea nitrogen
[BUN], and other clinical pathology indices were normal). The subject showed no signs of CNS
depression (disorientation, incoordination, or drowsiness), and thorough neurological
examinations (details not reported) revealed no abnormalities.
Several epidemiological studies have investigated the potential relationship between
exposure to 1,1,1-trichloroethane in drinking water and pregnancy outcome. Bove et al. (1995)
studied birth outcomes over a 3-year period in 75 towns in northern New Jersey, where some
water supplies were contaminated with 1,1,1-trichloroethane and other chemicals. When the
data were analyzed on the basis of exposure specifically to 1,1,1-trichloroethane, odds ratios
(ORs) (ratio of risk of a defect in the population with the specified exposure to risk of the defect
in the portion of the study population without the specified exposure) exceeding one were found
for neural tube defects (OR =1.21; 50% confidence interval [CI]: 0.96-1.55) in the study
population exposed to >1 ppb of 1,1,1-trichloroethane and for oral cleft defects (OR = 1.39; 50%
CI: 0.97-1.93) in the study population exposed to >2 ppb of 1,1,1-trichloroethane. However, the
confidence intervals show that the odds ratios for neither of these defects differed significantly
from one (no association).
A series of studies was conducted to assess pregnancy outcomes over a 2-year period in a
portion of Santa Clara County, California, where one of the public drinking water wells was
contaminated with 1,1,1-trichloroethane (and smaller quantities of other chemicals) from a leak
in an underground storage tank (Shaw et al., 1990; Wrensch et al., 1990a,b; Deane et al., 1989;
Swan et al., 1989). There were statistically significant increases in relative risk (RR) for
spontaneous abortion (RR = 2.3; 95% CI: 1.3-4.2) and total congenital malformations (RR = 3.1;
95% CI: 1.1-10.4) in the initial study area during the 2-year exposure period. Follow-up studies
found a significant increase in relative risk for major congenital cardiac anomalies (RR = 2.2;
95% CI: 1.2-4.0) during the exposed period in the service area of the water company that
operated the contaminated well (a larger area than the initial study area) and that the risk of
congenital cardiac anomalies increased with increasing consumption of home tap water during
the exposed period. However, hydrogeological modeling and analysis of the spatial and
temporal distribution of cases showed that water from the contaminated well was unlikely to be
30
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responsible for any of the observed increases in adverse pregnancy outcomes (Wrensch et al.,
1990a). In addition, a second study area that received more of the contaminated well water than
the initial study area had no increase in any adverse pregnancy outcomes. Therefore, this series
of studies did not establish a causal association between 1,1,1-trichloroethane exposure in
drinking water and adverse pregnancy outcomes.
Isacson et al. (1985) found no association between the presence of detectable levels of
1,1,1-trichloroethane in the ground water drinking supply of Iowa towns (population 1000-
10,000) and the incidence of bladder, colon, rectum, prostate, lung, or breast cancer in town
residents over age 55 for the years 1969-1981. 1,1,1-Trichloroethane concentrations were
characterized only as <0.1 ug/L or >0.1 ug/L. Given the low doses that would result from a
0.1 ug/L concentration (e.g., a 70 kg adult who drank 2 L water/day would receive a
1,1,1-trichloroethane dose of 0.003 ug/kg-day), the study is unlikely to have been sufficiently
sensitive to pick up an association between chemical exposure and cancer.
4.1.2. Inhalation Exposure
CNS depressant effects are the predominant signs of acute inhalation exposure to
1,1,1-trichloroethane in humans. These effects become more severe as exposure duration and
concentration increase. Acute exposure to 500-1000 ppm (2730-5460 mg/m3) causes dizziness,
lightheadedness, and disturbances in equilibrium and coordination (Stewart et al., 1969, 1961;
Torkelson et al., 1958), and general anesthesia occurs at >10,000 ppm (54,600 mg/m3) (Dornette
and Jones, 1960). Aside from a transitory increase in urinary urobilinogen in two of four
subjects tested 6 hours after a 15-minute exposure to 2650 ppm (14,470 mg/m3) (Stewart et al.,
1961), these controlled exposure studies found no evidence that acute inhalation exposure to
1,1,1-trichloroethane produces hepatotoxicity or other systemic effects in humans, as determined
by liver function tests and serum chemistry, hematology, and urinalysis measurements (Stewart
et al., 1969, 1961; Dornette and Jones, 1960; Torkelson et al., 1958). Although effects on blood
pressure and electrocardiogram were not found at subanesthetic levels (Stewart et al., 1969,
1961; Torkelson et al., 1958), induction of anesthesia was accompanied by a slight decrease
(5-10 mm Hg) in systolic blood pressure in about half of the 50 patients tested and a large
decrease in 3 patients (60 mm Hg in one) (Dornette and Jones, 1960). Other observations in
patients under anesthesia that may have been related to 1,1,1-trichloroethane were premature
ventricular contractions in several patients and cardiac arrest (and subsequent death) in one
patient (Dornette and Jones, 1960).
Numerous case reports have documented the potentially lethal consequences of acute
overexposure to 1,1,1-trichloroethane vapor (Winek et al., 1997; del Amo et al., 1996; Sullivan,
1994; D'Costa and Gunasekera, 1990; Macdougall et al., 1987; Caplan et al., 1976; Travers,
1974; Stewart, 1971; Stahl et al., 1969). Simulations performed by some researchers estimated
31
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lethal levels in such cases to range from approximately 6000 ppm (32,760 mg/m3) to as high as
70,000 ppm (382,200 mg/m3) (Jones and Winter, 1983; Silverstein, 1983; Droz et al., 1982;
Northfield, 1981; Mercier, 1977 [cited in Northfield, 1981]; Hatfield andMaykoski, 1970).
Death due to 1,1,1-trichloroethane was usually attributed to respiratory arrest secondary to CNS
depression (Jones and Winter, 1983; Wise et al., 1983; Hall and Hine, 1966) or to cardiac
arrhythmias presumed to result from sensitization of the heart to epinephrine (Ranson and Berry,
1986; Garriott and Petty, 1980 [cited in Banathy and Chan, 1983]; Guberan et al., 1976; Bass,
1970).
Case reports have also produced suggestive evidence for persistent CNS effects (Gamier
et al., 1991; Gresham and Treip, 1983), persistent ventricular arrhythmias (McLeod et al., 1987;
Wright and Strobl, 1984), myocardial injury secondary to coronary spasm (Bailey et al., 1997;
Wodka and Jeong, 1991), distal sensory peripheral neuropathy (House et al., 1996, 1994; Howse
et al., 1989; Liss, 1988), hepatotoxicity (Gitelman and Dement, 1996; Cohen and Frank, 1994;
Hodgson et al., 1989; Thiele et al., 1982; Gerace, 1981; Halevy et al., 1980), renal toxicity
(Halevy et al., 1980), acute pulmonary eosinophilic pneumonia (Kelly and Ruffing, 1993), and
biliary-pancreatic cancer (Zarchy, 1996) associated with high-level 1,1,1-trichloroethane
exposure. Suggestive evidence from case reports, however, is inadequate to conclusively
establish any relationship between these effects and 1,1,1-trichloroethane exposure.
4.1.2.1. Experimental Human Exposure Studies
Controlled studies in humans exposed to 1,1,1-trichloroethane concentrations below
those causing gross CNS depression provide evidence of subtle neurological and nasal
inflammatory effects. The findings of these studies are summarized in Table 4-1.
32
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Table 4-1. Summary of human controlled-exposure studies and findings for l,l?l-trichloroethane
Reference
Exposure duration/
no., sex of subjects
Mackayetal., 1987
3.5 hours/12 M
Muttray et al., 2000
4 hours/12 M
Laineetal., 1996
5 hours/9 M
Experimental design/
NOAEL and LOAEL
0, 175, 350 ppm, 3.5 hours, continuous
exposure.
NBa testing @ 0, 20, 60, 120, &
180 min.
NOAEL: NDa
LOAEL3: 175 ppm
20, 200 ppm, 4 hours, continuous
exposure.
NB testing @ 0 and 3.7 hours.
NOAEL: ND
LOAEL: 200 ppm
Exposure day 1 : 200 ppm, 3 hours
exposure — > 40-min break — » 40 min
exposure. 10 min of exercise (bicycle
ergometer) at beginning of morning
and afternoon sessions.
Exposure day 2: 135 ppm (baseline
exposure) combined with transient
peak concentration (400 ppm).
Exposure day 3: control.
NB testing: EEG during 1st 20-minute
period (peak), body sway & reaction
times during 2nd 20-minute period (2nd
peak). Repeated after 120 minutes in
chamber and in afternoon session.
NOAEL: 200 ppm
LOAEL: ND
Measurement for
1,1,1-TCA
Blood @ 20, 60, 120, and
180 minutes
Venous blood @ 0 and
3.7 hours
Venous blood:
Morning session @ 7, 9, 11,
13, 15,20,40, 60, 120, and
180 minutes
Afternoon session @ 220, 227,
229,231,233,235,240,260,
and 290 minutes
Neurobehavioral test findings
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33
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Table 4-1. Summary of human controlled-exposure studies and findings for 1,1,1-trichloroethane
Reference
Exposure duration/
no., sex of subjects
Savolainen et al.,
1982a,b, 1981
4 hours/9 M
Salvini et al., 1971
8 hours/6 M
Gamberale &
Hultengren, 1973
0.5 hours/12 M
Experimental design/
NOAEL and LOAEL
200, 400 ppm, 4 hours, continuous.
NB testing: prior to exposure, between
2 minutes and 1% hours, and between
3 and 3% hours.
NOAEL: 400 ppm
LOAEL: ND
350, 450 ppm, 4 hours exposure — »
P/2 hours break — > 4 hours exposure
(8 hours total exposure time).
Alternating activities: 1 hour at rest,
then 20 minutes physical exercise.
NB testing: 0 and 8 hours (immediately
after entering exposure room and
before leaving exposure room).
NOAEL: 450 ppm
LOAEL: ND
250 ppm (30 minutes) — » 350 ppm
(30 minutes) — > 450 ppm (30 minutes)
— > 550 ppm (30 minutes).
NB testing: final 20 minutes of each
exposure period.
NOAEL: 250 ppm
LOAEL: 350 ppm
Measurement for
1,1,1-TCA
Venous blood @ preexposure,
1 hour, 2 hours, and 3% hours
-
Alveolar air @ every other
minute
Arterial blood (2 subjects):
37 measurements parallel to
alveolar air samples
Neurobehavioral test findings
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34
-------
Neurobehavioral performance was assessed in 12 adult male subjects (20-30-year-old
students or employees of the Department of Occupational Medicine at the Swedish National
Board of Occupational Safety and Health), who were exposed to progressively increasing
concentrations of 250, 350, 450, and 550 ppm (1370, 1900, 2450, and 3000 mg/m3) of
1,1,1-trichloroethane (purity not reported) in four successive 30-minute periods via respiratory
valve and mouthpiece (Gamberale and Hultengren, 1973). The taste and smell of the gas were
disguised by using menthol crystals. Review of the publication does not provide information on
the human subjects research ethics procedures undertaken in this study, but there is no evidence
that the conduct of the research was fundamentally unethical or significantly deficient relative to
the ethical standards prevailing at the time the research was conducted. The study was
conducted by the Swedish National Board of Occupational Safety and Health at exposure
concentrations below or only briefly (30 minutes) above the occupational limit for repeated
exposure (threshold limit value [TLV] of 350 ppm). Increases in concentration from 250 to 350
ppm and 450 to 550 ppm were performed without interruption in exposure, and the increase from
350 to 450 ppm was made after a 5-minute pause in exposure. Half of the subjects were exposed
to 1,1,1-trichloroethane on one day, followed by exposure to control conditions (pure air) 7 days
later; the remaining subjects were exposed similarly but in reverse order. Tests of manual
dexterity (wire spiral), perceptual speed (identical number and spokes tests), and simple and
choice reaction time were conducted in the final 20 minutes of each exposure period.
Performance was impaired in all five tests at >350 ppm (1900 mg/m3), with deficits that were
concentration related. Mean performance values in the wire spiral, identical number, spokes,
simple reaction time, and choice reaction time tests ranged from 6.4-9.8%, 6.8-10.9%, 14.5-
22.6%, 3.7-12.8%, and 1.7-6.8% lower than control values, respectively, at 350-550 ppm
(1900-3000 mg/m3). Statistical analysis revealed that at 350 ppm (1900 mg/m3) only
performance on the identical number test differed significantly from the control; at 450 ppm
(2450 mg/m3), performance differed significantly for four of the five tests and at 550 ppm
(3000 mg/m3) for all five of the tests. At 250 ppm (1370 mg/m3), mean performance values were
1.8%, 0.9%, 3.1%, 1.6%, and 1.7% lower than control values, respectively. Mean performance
at 250 ppm (1370 mg/m3) was not statistically significantly different from the control for any of
the tests. These findings suggest that the NOAEL and the lowest-observed-adverse-effect level
(LOAEL) for acute neurotoxic effects in this study were 250 ppm (1370 mg/m3) and 350 ppm
(1900 mg/m3), respectively.
In a study using similar endpoints, 12 adult male volunteers were chamber exposed to 0,
175, and 350 ppm (0, 950, and 1900 mg/m3) of 1,1,1-trichloroethane (purity not reported) for
3.5 hours (Mackay et al., 1987). Volunteers were recruited from the Health and Safety executive
staff of the Occupational Medicine and Hygiene Laboratories, UK. The exposure chamber
35
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program adhered to the protocol approved by the local Brent and Harrow Area Health Authority
Ethical Committee, and the study appears to have been conducted consistent with the ethical
standards prevailing at the time of the study. Each subject's three exposures were separated by
at least 14 days. Peppermint oil was introduced into the chamber to mask the odor of the
solvent. Neurobehavioral tests were performed 25 minutes before exposure and four times
during exposure starting at 20, 60, 120, and 180 minutes. Each test battery took 20-25 minutes
to complete. Testing included five psychomotor performance tests—simple reaction time, four-
choice reaction time, Stroop test (a test that measures susceptibility to distraction: subjects are
required to select the color of ink in which a color word was written and then choose the
appropriate color from four alternatives in the presence of highly distracting stimuli), syntactic
reasoning (via analysis of grammatical statements) and digital step-input tracking (a test that
measures eye-hand coordination), and a subjective measure of mood (stress-arousal checklist).
Measurements of 1,1,1-trichloroethane in blood, performed after 0, 20, 60, 120, and 180 minutes
of exposure, showed that levels rose rapidly during the first 20 minutes and began leveling off
after about 120 minutes. Blood levels were similar at 120 and 180 minutes; levels were
-12 umol/L blood at an exposure concentration of 950 mg/m3 and -24 umol/L blood at
1900 mg/m3 (as estimated from a graph). None of the subjects complained of headache,
discomfort, or nausea. Changes in neurobehavioral performance were observed at both exposure
levels, including increased simple reaction time, increased choice reaction time, impaired
performance in the tracking test, and improved performance in the Stroop test. The reaction time
tests appeared to be the most sensitive; however, only simple reaction time was adequately
quantified. The change in simple reaction time reportedly represented a 10-15% increase over
baseline performance; the magnitudes of change in the other tests are unclear due to a lack of
reported baseline performance values. For all tests, statistical analysis included analysis of
variance to determine the main effects of exposure and duration (and their interaction) but did
not include pair-wise tests to identify the specific exposure level at which a statistical difference
from controls was achieved. Differences among exposure levels for the various tests were
depicted graphically. When adjusted for both baseline (preexposure) and control (0 ppm)
exposures, performance changes in the more sensitive tests (e.g., simple reaction time) followed
the time course of 1,1,1-trichloroethane levels in blood and correlated with absolute blood levels.
Based on impaired psychomotor performance, particularly increased reaction time, the low dose
of 175 ppm (950 mg/m3) is a LOAEL for acute CNS effects.
Psychomotor effects were not reported in other acute studies conducted under similar
exposure conditions (Savolainen et al., 1982a,b, 1981; Salvini et al., 1971). In the Salvini et al.
(1971) study, six adult males (University of Pavia students, age 20-23 years) were exposed to
0 and 450 ppm (0 and 2450 mg/m3) of 1,1,1-trichloroethane (Chlorothene® NU) for 8 hours (two
36
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4-hour periods separated by a 1.5-hour interval with no exposure). Review of the publication
does not provide information on the human subjects research ethics procedures undertaken in
this study, but there is no evidence that the conduct of the research was fundamentally unethical
or significantly deficient relative to the ethical standards prevailing at the time the research was
conducted. The study was conducted by the Institute of Preventive Medicine for Workers and
Applied Psychology at the University of Pavia, Italy, using a single exposure at or just above the
TLV. In this study, each subject served as his own control by being exposed to control air 4
days following exposure to 1,1,1-trichloroethane. Three of the six subjects were first exposed to
1,1,1-trichloroethane and secondly to a control atmosphere. The remaining three subjects were
exposed in the reverse order The following were conducted immediately after the start of
exposure and again just prior to termination of exposure: a complex reaction time test, a manual
dexterity test, a perception test with tachistoscopic presentation, and Wechsler memory scale (to
evaluate instantaneous memory). The extent of impairment in performance in the
1,1,1-trichloroethane-exposed subjects was as follows: perception test—20% decrease;
immediate memory test—6% decrease; complex reaction time—2.5% decrease; and manual
ability and dexterity—no effect. None of the decrements in any of the tests were statistically
significant. There were, however, some transient complaints of dizziness and slight excitation
that were limited to the first 30 minutes of exposure, as well as some complaints of eye irritation
at the periods of peak exposure. The perception test revealed an interaction between
1,1,1-trichloroethane and mental stress. Based on eye irritation and slight dizziness, 450 ppm
(2450 mg/m3) was considered a LOAEL in this study.
In the Savolainen et al. (1982a,b, 1981) study, nine adult male volunteers (age 20-25
years) were exposed to 0, 200, and 400 ppm (0, 1090, and 2180 mg/m3) of 1,1,1-trichloroethane
(containing 0.5% dioxane stabilizer) for 4 hours with 1- or 2-week intervals between exposures;
each subject served as his own control. The nine subjects were divided into two groups; the
sequence of exposures was reversed for the two groups to minimize the effects of learning.
Peppermint oil vapor was used to mask the presence or absence of solvent odor. The study was
conducted in accordance with the ethical principles adopted by the World Medical Association
in the 1964 Declaration of Helsinki. The following tests were conducted before exposure, soon
after the start of exposure, and just before the end of exposure: simple reaction time, hand
tapping speed, critical flicker fusion threshold, gaze deviation nystagmus, and body sway. No
clear exposure-related effects on reaction time or other pyschomotor tests were found. Exposure
to 200 ppm (1090 mg/m3) 1,1,1-trichloroethane tended to improve performance, whereas
exposure to 400 ppm tended to have the opposite effect, although differences at 400 ppm
(2180 mg/m3), with the exception of one measurement for body sway (closed eyes only), were
37
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not statistically significantly different from control. Therefore, the high dose of 400 ppm
(2180 mg/m3) is considered a NOAEL for acute CNS effects in this study.
A subsequent study by these researchers investigated the neurological effects of
1,1,1-trichloroethane exposure combined with physical exercise (Laine et al., 1996). The study
was conducted in accordance with the ethical principles adopted by the World Medical
Association in the 1975 Declaration of Helsinki, and the protocol was approved by the Ethics
Committee of the Institute of Occupational Health in Helsinki, Finland. Nine healthy male
volunteers (university students, ages 21-24 years) were divided into three groups of three
subjects, with each group studied under three different exposure patterns on separate days. The
experiments were conducted over consecutive weeks so that the time interval between exposures
was at least 5 days. One exposure protocol consisted of exposure to a constant concentration of
200 ppm (1090 mg/m3) 1,1,1-trichloroethane for 3 hours (morning), followed by a 40-minute
lunch break and another 40-minute (afternoon) exposure period. A second protocol consisted of
exposure to a time-weighted average concentration of 200 ppm (1090 mg/m3) given as a baseline
of 135 ppm (740 mg/m3) with transient peaks up to 400 ppm (2180 mg/m3) for 20 minutes at the
start of the morning and afternoon exposure periods. The third exposure protocol comprised the
unexposed controls. The sequence of exposures was reversed to minimize the effects of
learning. Peppermint oil vapor was used to mask the presence or absence of solvent odor. In all
three groups, the subjects exercised on a stationary bicycle for 10 minutes at the start of the
morning and afternoon sessions. Electroencephalograms (EEGs) and body sway measurements
were recorded before, several times during, and 45 minutes after exposure. Visual evoked
potentials (VEPs) were measured before exposure and immediately after the morning and
afternoon exposure periods. Subjects reported no subjective symptoms, and no signs of
respiratory irritation were observed. No consistent, statistically significant effects on EEG,
VEPs, or equilibrium were found. Some deviations from control were observed but were not
considered by the investigators to be significant including short-lived (but statistically
significant) effects on EEG beta activity during the morning exposure session that was not
observed during the afternoon exposure session despite higher blood 1,1,1-trichloroethane
concentrations and sporadic changes in VEP values that were not statistically significant or
consistent. The 200 ppm (1090 mg/m3) level was therefore considered a NOAEL in this study.
EEG was also evaluated in 12 healthy male volunteers (nonsmokers, mean age
27.0 ± 1.9 years) exposed to 22 (control) and 200 ppm (120 and 1090 mg/m3)
1,1,1-trichloroethane (99.8%) in 4-hour exposure chamber sessions 1 week apart (Muttray et al.,
2000). Exposure to 22 ppm (odor detectable by humans), rather than 0 ppm, was used as the
control condition in an attempt to blind subjects and staff to the exposure conditions. The study
was performed in accordance with the ethical principles of the Declaration of Helsinki
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(1989 Hong Kong version), and the protocol was approved by the local ethics committee (Mainz,
Germany). EEG was recorded before (baseline) and during the last 15 minutes of exposure, with
eyes open and closed and during a choice reaction time test (color word stress test). EEG
spectral power was expressed as percentage absolute spectral power relative to baseline and was
calculated for each of 17 electrodes and each frequency band (5, 9, ai, 012, PI, P2). Subjective
symptoms were also recorded before, during, and after exposure. Scores for tiredness were
statistically significantly increased at the end of exposure to 200 ppm (1090 mg/m3), compared
with 22 ppm (120 mg/m3). No other symptoms were associated with 1,1,1-trichloroethane
exposure. EEG changes consistent with an increase in drowsiness (indicating a slight sedative
effect) were noted in the closed eye test at 200 ppm, in comparison to 22 ppm. In the closed eye
condition at 200 ppm compared to 22 ppm, the median percentage of spectral power increased at
all electrodes of the 5-band, statistically significantly at temporo-occipital leads. Percentage of
spectral power was elevated at most electrodes in the 9-band, was lower at the temporo-parietal-
occipital electrodes in the ai-band (statistically significant at one electrode), and was lower at all
electrodes in the a2-band (statistically significant at two electrodes). These differences were not
seen in the open eye or color word stress tests, but these tests are not as sensitive to changes in
vigilance. As part of the same experiment, nasal secretions were collected for determination of
inflammatory mediators, mean ciliary beat frequency of nasal respiratory cells was measured,
and mucociliary transport time was recorded (Muttray et al., 1999). The concentrations of
interleukins (IL-lp, IL-6, IL-8) in nasal secretions were statistically significantly increased after
exposure to 200 ppm, compared with 22 ppm. There were no changes in prostaglandin E2 levels
in nasal secretions, mucociliary transport time, ciliary beat frequency of nasal respiratory cells,
or subjective symptoms related to irritation. The increased levels of proinflammatory cytokines
in nasal secretions in the absence of related effects indicates a slight irritant response in the nasal
mucosa characterized by subclinical inflammation. This study identified a LOAEL of 200 ppm
(1090 mg/m3) for subtle neurological (tiredness and EEG changes) and nasal irritant (increased
levels of proinflammatory cytokines in nasal secretions) effects of 1,1,1-trichloroethane. A
NOAEL was not identified (the low concentration of 22 ppm (120 mg/m3) served as the control
for this study).
Muttray and coworkers also examined the acute effects of 1,1,1-trichloroethane on
human olfactory functioning (Muttray et al., 2004). Twelve healthy, nonsmoking students were
exposed to 20 (control) or 200 ppm (120 or 1090 mg/m3) 1,1,1-trichloroethane for 4 hours in an
exposure chamber using a crossover design. This study was performed in accordance with the
ethical principals of the Declaration of Helsinki (1989 Hong Kong version). Olfactory
functioning was investigated using Sniffm' Sticks and involved the determination of the odor
threshold for n-butanol and an odor identification test. An assessment of acute symptoms was
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also performed by using a questionnaire of the Swedish Performance Evaluation System
administered before, during, and after exposure (the questionnaire included 17 items related to
irritation of mucous membranes, difficulties in breathing, and symptoms related to the CNS).
Subjects did not report an increase in any acute symptoms, except for a slight increase in the
score for tiredness (p = 0.09). After 1 hour of exposure to 200 ppm 1,1,1-trichlororethane, the
investigators reported no effects on olfactory functioning, but after 4 hours they observed that
the olfactory threshold for n-butanol was slightly (p = 0.04) elevated. Odor identification was
not affected by exposure. The investigators speculated that the threshold shift could have been
caused by exposure-related inflammation of the olfactory mucosa or degeneration of receptor
cells but could not establish a basis for the observed effect without further testing. One
limitation of the study was ineffective blinding by using 20 ppm 1,1,1-trichloroethane as a
control.
4.1.2.2. Epidemiological Studies
Epidemiology studies of workers occupationally exposed to 1,1,1-trichloroethane have
also found neurological effects. Workers exposed to 1,1,1-trichloroethane at a factory in
Singapore reported neurological symptoms more frequently than matched controls from a factory
without 1,1,1-trichloroethane exposure (Tay and Pinnagoda, 1994). The study group comprised
50 workers exposed only to 1,1,1-trichloroethane at seven factories that used
1,1,1-trichloroethane in their cleaning and degreasing process. Controls were 50 workers from a
single factory without 1,1,1-trichloroethane exposure and were matched for age, sex, ethnic
group, and education. There were statistically significant increases in the prevalences of certain
symptoms, including tiredness, inability to concentrate, and memory impairment, in the exposed
group. This study is limited by reliance on subjective reporting of symptoms and possible
introduction of bias because the interviewer who collected the survey data was not blinded to
exposure status. Exposure was not quantified.
Kelafant et al. (1994) evaluated a group of 28 workers from a single employer, all of
whom had long-term exposure to "moderate to high" concentrations of 1,1,1-trichloroethane by
work history, for complaints of impaired short-term memory, inability to concentrate,
moodiness, irritability, and disequilibrium that had been occurring for an average of 3 years.
Other complaints were headaches, anxiety, fatigue, changed olfaction, and disturbed sleep.
Exposures occurred over a 10-year period. Work practices included use of 1,1,1-trichloroethane
in poorly ventilated areas, washing arms and hands in the concentrated solvent, and spraying
material to be cleaned with compressed air sprayers, all without respiratory protection.
Monitoring was not performed, but levels were high enough so that workers regularly reported
becoming light-headed, vertiginous, nauseated and fatigued and had on occasion observed
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coworkers become unconscious. Although few of the workers had been exposed to other
solvents, many had been exposed to asbestos, silica, and/or concentrated alkali cleaning agents.
The subjects averaged 42.0 years of age and 17.6 years of employment. Subjects received a
physical exam, chest radiograph, pulmonary function tests, electrocardiogram, hepatic function
tests, neuropsychological evaluation (questionnaire and test battery), magnetic resonance
imaging (MRI) of the brain, posture sway tests (posturography), and, if indicated, tests for
thyroid function, electroencephalogram, electromyogram/nerve conduction velocity, and
electronystagmography. No control group was included; subject data were compared to
published test normative data. Chest radiographs and pulmonary function tests were consistent
with early pneumoconiosis, presumably due to silica and/or asbestos exposure. Physical
examinations, electrocardiograms, hepatic function tests, and brain MRI were normal. Some
subjects displayed increased sway in the Romberg test and difficulty with tandem gait; almost all
were unable to maintain a monopedal stance for 5 seconds. In the posturography tests, posture
sway deficits were found in 24 of the 26 subjects tested; the number of subjects testing abnormal
increased with increasing difficulty of the postural task. Vestibular, somatosensory, and ocular
components of balance were all affected. Consistent, statistically significant deficits were found
for memory, intermediate memory, rhythm, and speed in the neuropsychological test battery.
This study suggests an association between neurobehavioral effects and prolonged exposure to
high concentrations of 1,1,1-trichloroethane in an occupational environment. However, NOAEL
and LOAEL values cannot be identified because exposures were not quantified.
Other studies did not find neurological effects in workers exposed to
1,1,1-trichloroethane. Maroni et al. (1977) investigated 22 female factory workers (mean age
32.4 years) who were exposed to 1,1,1-trichloroethane for a mean duration of 6.7 years via its
use as a lubricating and degreasing agent (other solvents had not been used). The workers were
divided into three groups of seven to eight, according to workplace levels of
1,1,1-trichloroethane, and compared with a reference group of seven females from the same
factory who had no past or present exposure to any solvent. Based on limited area monitoring
data, the exposure groups were 110, 140-160, and 200-990 ppm (600, 760-870, and 1090-
5400 mg/m3); seven of eight workers in the high concentration group were exposed to 200-
345 ppm (1090-1880 mg/m3). The investigation included a questionnaire on subjective
symptoms and work conditions, a general physical examination, neurological examinations
(signs of peripheral neuropathy, maximal conduction velocity, and slow fiber conduction
velocity in motor nerves), and a psychological test battery (23 variables, including intelligence,
psychomotor ability, and memory tests). Reaction time was not evaluated. No exposure-related
effects were found, indicating that the NOAEL is 200 ppm (1090 mg/m3). Confidence in this
neurotoxicity NOAEL is low because of the small study population (seven to eight per group),
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limited exposure data, and lack of data on some CNS endpoints known to be sensitive in acute
studies (e.g., reaction time).
Cherry et al. (1983) conducted neurological tests on workers engaged in paint
manufacture. Fifteen male workers (mean age 32.2 years) were studied over a 48-hour period
during which they were engaged in the manufacture of a special batch of paint. Air
measurements showed exposure to 1-46 ppm of 1,1,1-trichloroethane, as well as low
concentrations of toluene (1-4 ppm) and xylene (0-7 ppm). Neurological tests (visual analogue
scales to measure mood, digit symbol substitution test from the Wechsler Adult Intelligence
Scale, and simple reaction time) of each worker were administered for 20 minutes at the
beginning and end of a work shift. Referents comprised 36 workers without solvent exposure
from two other factories that followed the same shift pattern; the researchers noted that the
controls were poorly matched for age with the exposed workers. Of the measures of mood
examined, only physical tiredness showed statistically significantly greater deterioration in
exposed workers, compared with controls, on the morning shift; no differences reached statistical
significance for night-shift workers. No consistent association was found between blood
1,1,1-trichloroethane levels and mood changes. Performance test results (digit symbol
substitution test and simple reaction time test) showed no consistent evidence of an effect.
Morning shift workers (at beginning and end of shift) had slower reaction times than controls,
but no differences in performance were observed for afternoon or night shift workers. Overall,
the study did not demonstrate exposure-related effects. Because air concentrations in the plant
were identified as a broad range, a NOAEL could not be identified.
Kramer et al. (1978) studied primarily systemic endpoints in 151 matched pairs of
employees from two neighboring textile plants. One of the factories was reported to use large
quantities of 1,1,1-trichloroethane (Chlorothene NU, -94-96% 1,1,1-trichloroethane) as a
cleaning solvent. In the second plant, equipment cleaning was reported to be minimal and was
performed with unspecified nonchlorinated solvents (lack of exposure to 1,1,1-trichloroethane
was verified by industrial hygiene survey). Air samples were collected for 1,1,1-trichloroethane
analysis from various workstations within the "exposed" plant several times during a two-year
period preceding the health surveys and physical examinations. Physical examinations included
determination of blood pressure, heart rate, spirometric parameters, electrocardiogram, limited
neurological endpoints (Romberg test), urinalysis, and serum chemistry (alkaline phosphatase
[AP], alanine aminotransferase [ALT], aspartate aminotransferase [AST], y-glutamyl
transpeptidase [GOT], bilirubin, lactate dehydrogenase [LDH], BUN, protein) and hematology
indices. From the analysis of the air samples and the work histories of the subjects, exposed
workers were classified in one of five exposure groups: <15, 15-49, 50-99, 100-149, and 150-
249 ppm (<81, 81-269, 270-540, 550-810, and 820-1360 mg/m3). Exposed subjects were
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employed at the factory for <6 years. There were no significant exposure-related differences in
health histories or measured parameters between the exposed and unexposed workers. This
study showed no evidence of effects on cardiovascular, hepatic, or blood measures in workers
exposed to up to 150-249 ppm of 1,1,1-trichloroethane for up to 6 years, making this level
(150 ppm or 820 mg/m3) a NOAEL for the systemic effects evaluated in this study. The limited
neurological evaluation in this study was inadequate to identify a NOAEL or LOAEL for
neurological effects.
Garabrant et al. (2003) conducted a case-control study to examine the relationship
between solvent exposure (or jobs/hobbies with potential solvent exposure) and the development
of scleroderma among women diagnosed with scleroderma between 1980 and 1992 in Michigan
or Ohio. Six hundred sixty cases and 2227 controls matched for race, age, and geographic
region were interviewed by telephone; solvent exposure was self reported. The study found a
statistically significant increased odds ratio for "other chlorinated solvents" (OR = 2.0, 95% CI:
1.3-3.1) and "any solvent" (OR = 2.0, 95% CI: 1.5-2.5). This study found no significant
association between exposure to 1,1,1-trichloroethane (self-reported) and scleroderma (OR =
1.5; 95% CI: 0.7-3.2) or exposure verified by expert review (OR = 0.9; 95% CI: 0.3-2.8). The
number of cases exposed to 1,1,1-trichloroethane was small (nine self reported; four confirmed
by expert review).
Radican et al. (2006) conducted a retrospective occupational cohort study of end-stage
renal disease (ESRD) in aircraft workers exposed to 16 individual solvents and 2 solvent
mixtures. An occupational database was matched to the U.S. Renal Data System, a database that
captures the incidence of ESRD from 1973 onward. For the period 1973 to 2000, there was an
approximate twofold increased risk of ESRD among workers exposed to 1,1,1-trichloroethane
(as well as trichloroethylene and JP4 gasoline) (adjusted hazard ratio for 1,1,1-trichloroethane
= 2.31 [95% CI 1.04-5.10]; Cox regression model). When 2001-2002 data were included in the
analysis, the association was no longer significant (adjusted OR = 1.53 [95% CI 0.75-3.11];
logistic regression model). Investigators noted that uncertainty regarding the mechanism for
increased risk of ESRD, the observed attenuation in risk in 2001-2002, and the overlap of
exposures complicated the interpretation of the results.
Several case-control studies of spontaneous abortion and one longitudinal study of time
to pregnancy were conducted to examine the potential relationship between exposure to
1,1,1-trichloroethane (and other organic solvents) and adverse reproductive outcomes. The case-
control studies investigated the risk of spontaneous abortion in women exposed to
1,1,1-trichloroethane at work in Finland (Lindbohm et al., 1990) or through the use of household
products in Santa Clara County, California (Windham et al., 1991), or of the wives of male
workers occupationally exposed to 1,1,1-trichloroethane in Finland (Taskinen et al., 1989). The
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longitudinal study examined fertility (as measured by number of menstrual cycles required for
wife to become pregnant) in Finnish male workers with exposure to 1,1,1-trichloroethane
(Sallmen et al., 1998). All studies looked at multiple solvents, of which 1,1,1-trichloroethane
was only one. None of the studies found any statistically significant association between adverse
reproductive outcome and 1,1,1-trichloroethane exposure; however, small sample sizes
(4-15 cases in an exposure group) limited the power of these studies to find any association.
Further, exposure was not quantified in any of these studies.
Occupational exposure to 1,1,1-trichloroethane was not found to be associated with
cancer risk in case-control studies for astrocytic brain cancer in white males from three U.S.
states with prominent workforce representation in the petroleum refining and chemical
manufacturing industries (Heineman et al., 1994), renal cell carcinoma in Minnesota residents
(Dosemeci et al., 1999), pancreatic cancer in residents from 24 U.S. states (Kernan et al., 1999),
or esophageal or stomach cancer in workers at an industrial facility in Chula Vista, California
(Garland, 1987; Garabrant, 1986). A study of a cohort of Finnish workers found statistically
significantly increased standardized incidence ratios (SIRs) for cancer of the nervous system
(SIR = 6.05; 95% CI: 1.25-17.7) and multiple myeloma (SIR = 15.98; 95% CI: 1.93-57.7) in
male and female workers exposed to 1,1,1-trichloroethane (exposure assessed by blood
monitoring) (Anttila et al., 1995). However, these results are based on only three observed cases
for nervous system tumors and two cases (both females) for multiple myeloma. Because of the
small number of cases and the authors' acknowledgment that all or most of the solvent workers
were exposed to more than one solvent, the findings of this study are difficult to interpret. An
increased risk of multiple myeloma was also observed in workers exposed to
1,1,1-trichloroethane at an aircraft maintenance facility in Utah (SMR = 56.6; 95% CI: 6.85-
204.45), but again this result was based on only two observed cases, was seen only in females
(no observed cases in males), and was found in workers with multiple, overlapping exposures to
many chemicals (Spirtas et al., 1991). Spirtas et al. (1991) found no association between non-
Hodgkin's lymphoma and 1,1,1-trichloroethane exposure in these workers. An environmental
study found no significant correlation between release of 1,1,1-trichloroethane in 26 Florida
counties in 1987 (as recorded in the U.S. EPA Toxics Release Inventory) and age-adjusted
incidence of childhood brain tumors in these counties in 1992-1993 (Mulla, 1996). Infante-
Rivard et al. (2005) carried out a population-based case-control study to examine the association
between maternal exposure to occupational solvents, including 1,1,1-trichloroethane, and
childhood acute lymphoblastic leukemia (ALL). Exposure coding was conducted by a team of
chemists and industrial hygienists based on questionnaire responses. Increased risks for ALL
were observed for 1,1,1-trichloroethane, but the increases were not statistically significant.
Cancer epidemiological studies are summarized in Table 4-2.
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Table 4-2. Summary of cancer epidemiology studies
Study
Study design
Source/no, of subjects & referents
Pertinent findings
Comments
Garabrant, 1986
Cohort
Cohort: 14,067 employees at Rohr
plant; worked >4 years by Dec. 1982
Control: total U.S. white and nonwhite
populations and San Diego County
population.
No statistically significant increase in
risk was found for cancer of the
esophagus or other digestive tract
cancers.
Examination of the risk of
esophageal cancer.
Case-control
Cases: 14 decedents of esophageal
cancer and 8 decedents of stomach
cancer identified in Rohr plant cohort
Control: matched members of the
cohort who were alive at the age of
death of the case; 56 and 32 controls
for esophageal and stomach cancer,
respectively.
No statistically significantly elevated
OR found for cancer of the esophagus
or stomach.
OR (ever vs. never exposed):
OR j?-value
Esophageal cancer 1.67 0.56
Stomach cancer 3.15 0.26
Examination of risk of esophageal
and stomach cancer
Heinemanetal.,
1994
Case-control
Cases: 300 cases with diagnosed
astrocytic brain tumor (identified
through death certificates in LA, NJ, or
PA, 1978-1981).
Control: 320 matched controls
randomly selected from white male
residents who died of causes other than
brain tumor, cerebrovascular diseases,
epilepsy, suicide, homicide.
Exposure to 1,1,1-trichloroethane
showed little indication of an
association with brain cancer.
Brain cancer
OR
1.2
95% CI
0.9-1.8
Risk of astrocytic brain cancer was
examined for exposure to organic
solvents (as a general class) and six
individual chlorinated aliphatic
hydrocarbons. 1,1,1-Trichloroethane
exposure showed little indication of
an association; risk increases were
observed only among groups with
low exposure probability.
Dosemeci et al.,
1999
Case-control
Cases: 438 white patients newly
diagnosed with renal cell cancer
(RCC), identified through the MN
Cancer Surveillance System (1988-
1990).
Control: 687 population-based
controls.
The risk of RCC was not statistically
elevated in subjects exposed to
1,1,1 -trichloroethane.
OR 95% CI # cases
Men 0.88 0.6-1.3 53
Women 1.26 0.6-2.8 13
Total 0.94 0.7-1.3 66
Risk of RCC was examined for
exposure to all organic solvents
combined, all chlorinated aliphatic
hydrocarbons (CHC) combined, and
nine individual CHCs by using job
exposure matrices.
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Table 4-2. Summary of cancer epidemiology studies
Study
Study design
Source/no, of subjects & referents
Pertinent findings
Comments
KernanetaL
1999
Case-control
Cases: 63,097 persons who died from
pancreatic cancer (1984-93), using
National Cancer Institute, National
Center for Health Statistics (NCHS)
data.
Control: 252,386 persons who died
from causes other than cancer in same
time period, using NCHS data.
The risk of pancreatic cancer was not
statistically elevated in relation to
intensity of exposure to
1,1,1-trichloroethane and showed no
consistent pattern of elevation by
probability of exposure across race and
gender.
Relation between occupational
exposure and pancreatic cancer
mortality was examined.
Specifically, OR calculated for 36
occupations/industries and 11 solvent
exposures.
Spirtas etal.,
1991
Cohort
Cohort: workers at an aircraft
maintenance facility at Hill Air Force
Base, Utah (1952-1956);
27,223 person-years (men) and 1215
person-years (women) with
1,1,1-trichloroethane exposure.
Control: mortality experience for white
male and female population in U.S.
and Utah.
The risk of multiple myeloma was
statistically elevated in women only:
Obs person-years SMR (95% CD
2 1215 5660 (685-20445)
No cases were observed in men.
Relationship between 28 industrial
chemicals or chemical groups and
multiple myeloma or non-Hodgkin's
lymphoma was examined.
Anttilaetal.,
1995
Cohort
Cohort: 2050 men & 1924 women
biologically monitored for
occupational exposure to three
halogenated solvents at the Finnish
Institute of Occupational Health
(1967-1992); follow-up for cancer
through the Finnish Cancer Registry.
Control: Finnish Cancer Registry.
Overall cancer incidence was not
statistically elevated. Elevated SIR
was observed for two cancer sites only:
Cancer of the nervous system:
Obs SIR 95% CI
3 6.05 1.25-17.7
Multiple myeloma:
Obs SIR 95% CI
2 15.98 1.93-57.7
Relationship between exposure to
trichloroethylene,
tetrachloroethylene, and
1,1,1-trichloroethane and cancer
incidence (30 sites considered).
Investigators noted that it was not
possible to separate the effects of
other solvents from the monitored
ones and that 1,1,1-trichloroethane
contained 1,4-dioxane (
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Table 4-2. Summary of cancer epidemiology studies
Study
Study design
Source/no, of subjects & referents
Pertinent findings
Comments
Infante-Rivard et
al., 2005
Case-control
Cases: 790 parents of children
diagnosed with ALL between 1980
and 2000 in the province of Quebec,
Canada; recruited from tertiary cancer
centers.
Control: population-based controls
from two Canadian government
databases; children matched on sex
and age at time of diagnosis.
The ORs for childhood ALL were
elevated, but the increase was not
statistically significant.
OR 95% CI
Two years before 7.55 0.92-61.97
pregnancy up to
birth
During pregnancy 4.07 0.45-36.7
Analyses performed for 21 individual
solvents and 6 solvent mixtures.
Prevalence of exposure to individual
solvents was low. Investigators
considered power of the study to be
an issue.
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4.2. LESS-THAN-LIFETIME AND CHRONIC STUDIES AND CANCER BIOASSAYS
IN ANIMALS—ORAL AND INHALATION
4.2.1. Oral Exposure
4.2.1.1. Acute Studies
Lethality studies have reported single dose LD50 values for 1,1,1-trichloroethane of
9600-17,148 mg/kg in rats, 6000-11,240 mg/kg in mice, 9470 mg/kg in guinea pigs, and 5660
mg/kg in rabbits (Walum, 1998; Kinkead and Wolfe, 1992; Torkelson et al., 1958).
Acute studies of systemic toxicity of 1,1,1-trichloroethane have focused on the liver as a
potential target. Evidence of hepatotoxicity was reported by Xia and Yu (1992) and Tyson et al.
(1983). In the Xia and Yu (1992) study, unspecified numbers of adult female Wistar rats
(158± 14 g) were treated with single gavage doses of 0 or 5 mmol/kg (670 mg/kg) of
1,1,1-trichloroethane (purity not specified) in arachidonic oil. Rats were sacrificed after 6, 12,
24, 36, 48, or 72 hours for collection of blood (analyzed for enzyme markers of hepatotoxicity:
ALT, sorbitol dehydrogenase [SDH], and glutamate dehydrogenase [GDH]) and liver tissue
(analyzed for histopathology). There was a statistically significant 1.5-fold increase in serum
ALT in rats killed at 24 hours, although not before or after. Serum SDH and GDH were not
affected by treatment. No liver lesions were found by light microscopy. The
1,1,2-trichloroethane isomer was also tested in this study, producing much more obvious liver
toxicity (fourfold increase in ALT, large increases in SDH and GDH, microscopic lesions), with
maximal effect 24 hours after dosing. The similar time course of ALT changes for the two
isomers supports the position that the observed increase for 1,1,1-trichloroethane reflects a mild,
treatment-related effect on the liver and not a random event. The data suggest that serum ALT is
a sensitive indicator of hepatotoxicity for 1,1,1-trichloroethane and that the dose of 670 mg/kg
can be considered a LOAEL for this effect. Tyson et al. (1983) also reported evidence of
hepatotoxicity after acute oral exposure. Groups of three to five male Sprague-Dawley rats
weighing 140-230 g were given single gavage doses of approximately 0, 2, 9.5, or 19 mmol/kg
(0, 300, 1300, or 2500 mg/kg) of reagent grade 1,1,1-trichloroethane in corn oil. Blood was
collected 6 and 24 hours after dosing and analyzed for ALT and AST as indicators of
hepatotoxicity. Although there was no effect on serum ALT in this study, serum AST levels
were increased roughly twofold 6 hours after treatment with 2500 mg/kg-day. The increase was
no longer seen after 24 hours. This study, therefore, identified a NOAEL of 1300 mg/kg and a
LOAEL of 2500 mg/kg for mild hepatotoxicity.
In contrast to these studies, Bruckner et al. (2001) did not find evidence of hepatotoxicity
in rats at doses up to 4000 mg/kg. Male Sprague-Dawley rats (group size not specified)
weighing 200-220 g were given single doses of 0, 500, 1000, 2000, or 4000 mg/kg of
1,1,1-trichloroethane (>99% pure) by gavage in corn oil and sacrificed 24 hours later (Bruckner
et al., 2001). No mortality occurred, and there were no effects on liver weight or histopathology,
48
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serum enzyme indicators of hepatotoxicity (ALT, SDH, ornithine carbamoyl transferase [OCT]),
or hepatic nonprotein sulfhydryl levels or glucose-6-phosphatase (G-6-Pase) activity (data not
presented in the study report). The high dose of 4000 mg/kg was an apparent acute NOAEL for
liver endpoints in this study.
4.2.1.2. Short-term Studies
Liver and kidney effects were investigated in short-term oral studies (Bruckner et al.,
2001; National Toxicology Program [NTP], 1996). Bruckner et al. (2001) treated groups of
approximately 15 male Sprague-Dawley rats (230-260 g) with 0, 500, 5000, or 10,000 mg/kg of
1,1,1-trichloroethane (>99% pure) by gavage in corn oil nine times over 12 days (daily average
doses of 0, 375, 3750, or 7500 mg/kg-day). Groups of up to five rats were weighed and
sacrificed 1, 5, or 12 days after the start of dosing for clinical chemistry (ALT, SDH, OCT) and
biochemistry (hepatic nonprotein sulfhydryl and G-6-Pase) evaluations and examination of the
liver for histopathological changes. After each dosing, rats treated with 5000 or 10,000 mg/kg of
1,1,1-trichloroethane exhibited hyperexcitability for a brief period (20-30 minutes), followed by
an extended period of narcosis. Three rats in the 5000 mg/kg group died during the study (two
in the first 24 hours), while only one rat in the 10,000 mg/kg group survived to terminal sacrifice
(5/10 remaining after the day 1 sacrifice died before day 3 of the study). No clinical signs or
deaths were seen in the 500 mg/kg group. Body weight was significantly lower than in controls
in the 5000 and 10,000 mg/kg groups at 5 days (-15% reduction in both groups) and remained
lower at day 12 (-20% reduction in the 5000 mg/kg group and -37% reduction in the lone
survivor from the 10,000 mg/kg group). Body weight was similar to controls in the 500 mg/kg
group. No effect on the liver was found by serum chemistry, biochemistry, or histopathology
evaluations at any dose level (data not presented in the study report). Absolute liver weight was
about 20% lower than the control mean in the lone surviving rat at 10,000 mg/kg after 12 days.
This change does not necessarily indicate a target organ effect on the liver, however, given the
-37% reduction in body weight in this animal. Relative liver weights were not reported. This
study identified an apparent short-term NOAEL of 500 mg/kg (375 mg/kg-day), although only
the liver was investigated for target organ toxicity. The 5000 mg/kg (3750 mg/kg-day) dose
level is a LOAEL for gross CNS depression and associated mortality. The wide spacing between
the low dose (375 mg/kg-day) at which no effects were observed and the mid dose (3750 mg/kg-
day), which was associated with an increased incidence of mortality, limit the study's usefulness
in defining a NOAEL and LOAEL.
Consistent with the results of Bruckner et al. (2001), rats treated for 7 days with 0 or
1650 mg/kg-day of 1,1,1-trichloroethane by gavage in liquid paraffin had body and liver weights
similar to controls (Platt and Cockrill, 1969).
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NTP (1996) investigated renal and hepatic endpoints in a short-term study in which
groups of five male F344/N rats were administered 1,1,1-trichloroethane (purity 100%) by
gavage in corn oil at doses of 0, 0.62, or 1.24 mmol/kg-day (0, 83, or 165 mg/kg-day) for
21 days. Evaluations included survival, body weight gain, clinical signs, urinalysis (creatinine,
glucose, total protein, AST, GGT, N-acetyl-p-D-glucosaminidase, volume, specific gravity),
organ weights (liver, right kidney, right testis), and limited histological assessment (liver, right
kidney, gross lesions). The clinical and tissue pathology evaluations were limited in scope and
centered on renal endpoints because this study was part of an investigation of structure-activity
relationships involved in the induction of hyaline droplet nephropathy by halogenated ethanes.
One rat in the 165 mg/kg-day group died on the second day of the study; the cause of death was
not discussed. Otherwise, no clinical signs of toxicity were noted and body weights remained
similar to controls throughout the study. Urinalysis revealed large, statistically significant
increases in mean urinary protein (indicative of renal dysfunction and, possibly, tissue damage)
and AST (indicative of renal tissue damage) in the survivors in the 165 mg/kg-day group (see
Table 4-3). However, no histopathological lesions were found in the livers or kidneys of treated
rats, including renal hyaline droplet nephropathy, tubule regeneration, or granular casts.
Relative liver weight was significantly increased by ~11% in the 165 mg/kg-day rats, and,
although not statistically significant, absolute liver weight was also -9% higher than controls in
this group. There were no statistically significant changes in kidney or testis weight. NTP
considered the urinalysis results to be highly suggestive of renal injury at 165 mg/kg-day but
also noted the lack of supporting histopathology data. The small group size (four rats) in the 165
mg/kg-day group and the large standard errors for protein and AST concentrations in this group
suggest that the increases in the corresponding means could be due to high levels in a single
individual and, therefore, may not be related to treatment. Because of these questions about the
urinalysis results and the lack of supporting histopathology data, it is not clear whether the
observed urine changes indicate an adverse renal effect or whether any renal damage that did
occur was related to treatment. Therefore, NOAEL/LOAEL values were not assigned.
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Table 4-3. Effect of 1,14-trichloroethane on selected urinary parameters in
male rats
Parameter
Protein (ug/mg creatinine)
AST (mU/mg creatinine)
Dose (mg/kg-day)
0
1227 ± 78 (5)a
8 ± 1 (5)
83
1447 ± 130 (5)
16 ± 1 (5)
165
2198 ± 584 (4)b
466 ± 444 (4)b
"Mean ± standard error; number of animals in parentheses.
bSignificantly different from controls (p < 0.05).
Source: NTP (1996).
4.2.1.3. Subchronic Studies
Subchronic studies of 1,1,1-trichloroethane toxicity were conducted by gavage and
dietary exposure. In the gavage study, groups of 15-20 male Sprague-Dawley rats (200-260 g)
were treated with analytical grade 1,1,1-trichloroethane (>99% pure) at doses of 0, 500, 2500, or
5000 mg/kg by gavage in corn oil 5 days per week for up to 13 weeks (average daily doses of 0,
357, 1786, or 3571 mg/kg-day) (Bruckner et al., 2001). Blood for measurement of serum
enzyme level activities (ALT, SDH, OCT) was collected from five randomly selected rats from
each dose group on week 2 of the study. Subsequent collections of blood were performed on
alternating sets of rats every other week throughout the study. Moribund rats were sacrificed and
examined for gross pathology. On day 51 of the study, surviving rats in the 2500 and
5000 mg/kg groups were accidentally poisoned with 1,1-dichloroethene and all died within
24 hours from massive liver damage. Terminal sacrifice of the 0 and 500 mg/kg groups occurred
on day 92, except for five rats from each group that were allowed to recover for 1 week and then
sacrificed. At sacrifice, blood was collected for serum enzyme determination, and the livers
were weighed and processed for histopathological examination.
Clinical signs of toxicity and death were observed in the rats treated with 2500 or
5000 mg/kg of 1,1,1-trichloroethane (Bruckner et al., 2001). Rats in these groups showed
hyperexcitability followed by hours of narcosis immediately following each day's dose. By day
50 of the study, 33% of rats in the 2500 mg/kg group and 47% of rats in the 5000 mg/kg group
had died. The only finding in these animals upon gross necropsy was pulmonary congestion.
The deaths were attributed by the researchers to repeated, protracted CNS depression, although it
was noted that chronic murine pneumonia may also have contributed. According to the study
protocol, the 2500 and 5000 mg/kg-day groups were housed together in a different isolation
module than the 0 and 500 mg/kg-day groups. The study authors did not address whether
chronic murine pneumonia may have been present in all four exposure groups. There was one
death in the 500 mg/kg group that was due to gavage error. Body weights of the 2500 and 5000
mg/kg groups were significantly reduced for the time these animals were on study; the deficit on
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day 51 was about 22% in both groups. Body weight of the 500 mg/kg group was slightly lower
than in controls throughout the entire study, but the difference was never statistically significant.
Slight, twofold increases were seen in OCT activity in the 5000 mg/kg group throughout the 7
weeks these animals were on study; statistical significance was achieved on weeks 2 and 4. ALT
activity was also slightly and significantly increased in the 5000 mg/kg group on weeks 2 and 4
but after 6 weeks was similar to controls. SDH activity was significantly greater than controls in
all treated groups after 6 weeks, but comparisons to the values at 2 and 4 weeks and the lack of
any apparent dose-response suggest that this reflects a low level in the controls at 6 weeks rather
than a treatment-related effect. No significant changes in serum enzyme level activities were
seen in the 500 mg/kg group throughout the remainder of the study, and no effects on absolute or
relative liver weights or liver histopathology were found in this group after 13 weeks of exposure
or after the 1-week recovery period (data not presented in the study report). The 500 mg/kg
(357 mg/kg-day) dose is an apparent NOAEL in this study, although the liver was the only
potential target systematically investigated. The 2500 mg/kg (1786 mg/kg-day) dose level is a
LOAEL for gross CNS depression and associated mortality. The early accidental termination of
the 2500 and 5000 mg/kg-day groups and incomplete reporting of methods and results limit the
usefulness of this study.
A 13-week feeding study was conducted in rats and mice (NTP, 2000). Groups of
10 male and 10 female F344/N rats and B6C3F1 mice, 6-7 weeks old at the start of the study,
were fed diets containing 0 (untreated feed), 0 (placebo microcapsules), 5000, 10,000, 20,000,
40,000, or 80,000 ppm of microencapsulated 1,1,1-trichloroethane (>99% pure) 7 days/week for
13 weeks. Average daily doses calculated by the researchers were 290, 600, 1200, 2400, and
4800 mg/kg in male rats; 310, 650, 1250, 2500, and 5000 mg/kg in female rats; 850, 1770, 3500,
7370, and 15,000 mg/kg in male mice; and 1340, 2820, 5600, 11,125, and 23,000 mg/kg in
female mice. Clinical signs and body weight were recorded weekly. Feed consumption was
recorded every 3-4 days. Urine was collected for analysis and measurement of
1,1,1-trichloroethane metabolites from five randomly selected male rats in the vehicle control,
5000, 20,000 and 80,000 ppm groups on days 28 and 84. Blood for hematology and clinical
chemistry determinations was collected from all rats at the end of the study and from satellite
groups of 10 male and 10 female rats (exposed to the same concentrations as the main study
groups) on days 3 and 23. Vaginal cytology (over 12 days prior to sacrifice) and sperm motility
(at necropsy) evaluations were performed on all main study rats and mice in the vehicle control,
20,000, 40,000, and 80,000 ppm groups at the end of the study. All animals in the main study
were necropsied. Organs and tissues were examined for gross lesions, and the heart, lungs,
thymus, liver, right kidney, and right testis were weighed. Rats and mice in the untreated
control, vehicle control, and 80,000 ppm groups in the main study received complete
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histopathological examinations. Rats in the 5000, 10,000, 20,000, and 40,000 ppm main study
groups were examined for renal histopathology only.
All rats survived to study termination, and no clinical signs of toxicity were observed
(NTP, 2000). Body weight gain over the course of the study was significantly reduced in the
80,000 ppm male rats in comparison with both the untreated and vehicle controls. Final body
weight was 10% less than vehicle controls (statistically significant) but only 4% less than
untreated controls (not significant). Because of the nutritional content of the vehicle used (i.e.,
microcapsules composed of 80% food grade modified corn starch and 20% sucrose), the vehicle
control was considered the most appropriate comparison group. In the 80,000 ppm females,
body weight gain and final body weight were lower than vehicle and untreated controls, but only
the difference in final body weight versus vehicle controls (4.2%) was statistically significant.
Body weight changes in lower dose groups were unremarkable. Feed consumption was similar
to that of controls in all groups. Hematology analyses revealed minimal increases in red blood
cell count, hemoglobin, and hematocrit in male and female rats at 10,000 ppm and above. NTP
considered these changes to indicate a minimal hemoconcentration effect likely due to
physiological processes unrelated to 1,1,1-trichloroethane exposure. No lexicologically
meaningful changes were found in clinical chemistry or urine analyses. Absolute and relative
liver weights were significantly reduced in female rats treated with 80,000 ppm by about 15%
and 11%, respectively, in comparison with untreated and vehicle controls. In male rats treated
with 80,000 ppm, absolute liver weight was significantly reduced by about 13% compared with
vehicle controls but did not differ from untreated controls, and relative liver weight was
unaffected. Male rats treated with 20,000 ppm or above of 1,1,1-trichloroethane showed renal
lesions considered by study investigators to be consistent with a2u-globulin nephropathy, as
indicated by significant, dose-related increases in incidence and/or severity of renal tubule
hyaline degeneration, cast formation, and regeneration and chronic interstitial inflammation of
the kidney. Assays for the presence of a2U-globulin were not conducted. No lesions in other
tissues were observed in the males, and no lesions in any tissue were observed in the female rats.
Treatment with 1,1,1-trichloroethane had no effect on vaginal cytology parameters in female
rats. In males, epididymal spermatozoal concentration was significantly reduced by about 10% in
the 80,000 ppm group compared with vehicle controls (untreated controls not tested), but no
other associated changes were found. Renal changes associated with a2u-globulin nephropathy
in male rats are specific to this sex and species and are not considered to be predictive for effects
in humans (U.S. EPA, 1991c). Therefore, this study identified a LOAEL of 80,000 ppm
(4800 mg/kg-day in males and 5000 mg/kg-day in females) and a NOAEL of 40,000 ppm
(2400 mg/kg-day in males and 2500 mg/kg-day in females), based on reduced liver weights in
males and females and reduced epididymal spermatozoal concentration in males.
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Mice also showed no clinical signs of toxicity from 1,1,1-trichloroethane ingestion, and
suffered no mortality during the study (NTP, 2000). Significant, dose-related reductions in body
weight gain and terminal body weight were observed in male mice treated with 5000 ppm or
above and female mice treated with 10,000 ppm or above, in relation to both untreated and
vehicle controls. Terminal body weights for mice relative to controls are compiled in Table 4-4.
Feed consumption was generally greater in treated mice than in controls. Statistically
significant changes in absolute and/or relative organ weights were seen in the heart, liver, and
kidney in male mice and in the kidney in female mice. However, these changes were considered
by the researchers to be secondary to the changes in body weight and not lexicologically
significant. No gross or microscopic lesions due to 1,1,1-trichloroethane were seen in male or
female mice. Vaginal cytology parameters in treated female mice were similar to those in
controls. Male mice in the 80,000 ppm group had a significant 20% reduction in epididymal
spermatozoal concentration compared with vehicle controls (untreated controls not tested) but no
other associated changes. Effects on body weight were the most sensitive indicators of
1,1,1-trichloroethane toxicity in both male and female mice. NTP (2000) estimated the dose of
10,000 ppm (1770 mg/kg-day) in male and female mice to be a NOAEL and 20,000 ppm
(3500 mg/kg-day) to be a LOAEL based on decreases in terminal body weight greater than 10%
of the control values.
Table 4-4. Terminal body weights of mice treated with 1,1,1-trichloroethane
for 90 days
Group
Untreated control
Vehicle control
5,000 ppm
10,000 ppm
20,000 ppm
40,000 ppm
80,000 ppm
Male3
Final body
weight0 (g)
35.4 ±0.8
36.9 ±0.7
33.6±0.7e
33.7±0.6e
32.7 ± 0.5e'g
33.1±0.5e'g
31.3±0.4e'g
Mean weight
change0 (g)
12.8 ±0.5
13.7 ±0.5
11.2±0.5e'f
10.8 ± 0.5e'g
9.9 ± 0.4e'g
10.0 ± 0.3e'g
8.7 ± 0.3e'g
RBWd
(%)
91
91
88
90
85
Femaleb
Final body
weight0 (g)
28.8 ±0.9
29.3 ±0.8
28.4 ±0.6
27.2 ±0.8
26.0 ± 0.8e'g
25.8 ± 0.7e'g
24.5 ± 0.5e'g
Mean weight
change0 (g)
10.1 ±0.8
11.2 ±0.8
9.6 ±0.7
8.7±0.6e
7.5 ± 0.7e'g
7.2 ± 0.6e'g
6.2 ± 0.5e'g
RBWd
(%)
97
93
89
88
84
aCorresponding doses, in mg/kg-day, for male mice were: 850, 1770, 3500, 7370, and 15,000 mg/kg-day.
bCorresponding doses, in mg/kg-day, for female mice were: 1340, 2820, 5600, 11,125, and 23,000 mg/kg-day.
°Values are mean ± SE.
dRBW = body weight relative to vehicle control.
Significantly different (p < 0.01) from the vehicle control group.
Significantly different (p < 0.05) from the untreated control group.
8Significantly different (p < 0.01) from the untreated control group.
Source: NTP (2000).
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In a study designed to investigate the effect of 1,1,1-trichloroethane on water palatability,
groups of 32 male CD-I mice were given 1,1,1-trichloroethane (97% pure, stabilized with 3%
p-dioxane) in an Emulphor vehicle at concentrations of 0, 0.5, or 5.0 mg/mL (0, 103, or
1041 mg/kg-day, respectively, as estimated by the researchers) in the drinking water for 90 days
(Kallman and Kaempf, 1984). Neither body weight nor fluid intake, the only two variables
recorded, were influenced by exposure to 1,1,1-trichloroethane.
4.2.1.4. Chronic Studies
A chronic carcinogenesis bioassay was conducted in which technical grade
1,1,1-trichloroethane (-95% pure containing 3% dioxane stabilizer and 2% minor impurities)
was administered in corn oil by gavage to male and female Osborne-Mendel rats and B6C3F1
mice on 5 days/week for 78 weeks (National Cancer Institute [NCI], 1977). Control and treated
group sizes were 20/sex/species and 50/sex/species, respectively. Male and female rats were
treated with doses of 750 or 1500 mg/kg-day for 78 weeks and observed for the next 32 weeks;
untreated control rats were observed for 110 weeks. Low-dose male and female mice were
sequentially treated with 2000 mg/kg-day for 10 weeks, 2500 mg/kg-day for 10 weeks, and
3000 mg/kg-day for 58 weeks (TWA dose 2807 mg/kg-day), and observed for the following
12 weeks. High-dose male and female mice were sequentially treated with 4000 mg/kg-day for
10 weeks, 5000 mg/kg-day for 10 weeks, and 6000 mg/kg-day for 58 weeks (TWA dose
5615 mg/kg-day) and observed for the following 12 weeks. Untreated male and female control
mice were observed for 90 weeks. Study endpoints were limited to clinical observations, body
weight, food consumption, and histopathology. Effects in male and female rats included reduced
survival (-30-40% increased mortality compared to controls during the first year of the study),
decreased body weight (-10-15% in males, starting on week 20; up to -30% in females, starting
on week 75), and urine staining of abdominal fur in both the low and high dose groups. No
histopathological changes were observed. Effects occurred in mice in both dose groups,
including reduced survival in females (13 and 35% increase in low- and high-dose group
mortality during the first year) and -15-20% decreased body weight in both sexes. The reduced
survival in rats and mice was considered compound related by NCI (1977), although chronic
murine pneumonia was a prevalent spontaneous lesion in all control and treated groups of both
sexes and was a probable contributing factor in the early deaths. Based on reduced survival, the
lowest doses tested, 750 mg/kg-day (536 mg/kg-day after adjustment for 5 out of 7 days
exposure) in rats and 2807 mg/kg-day (2005 mg/kg-day after adjustment for 5 out of 7 days
exposure) in mice, are LOAELs for chronic exposure. The incidence and type of neoplasms
observed in treated rats and mice were similar to those observed in the untreated controls.
Because of the high rate of early mortality in treated animals, NCI did not consider this study to
be an adequate test of 1,1,1-trichloroethane carcinogenicity for either rats or mice.
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In a screening level chronic carcinogenesis bioassay, Sprague-Dawley rats were
administered 0 (50/sex) or 500 mg/kg (40/sex) 1,1,1-trichloroethane (technical grade containing
3.8% dioxane) by gavage in olive oil, 4-5 days/week for 104 weeks (Maltoni et al., 1986).
Adjusting for partial weekly exposure yields an estimated average daily dose of 321 mg/kg-day.
The experiment lasted 141 weeks, as animals that survived to the end of the treatment period
were allowed to live until spontaneous death. Body weight and survival were assessed
throughout the study, and complete necropsies, including histopathological examinations, were
performed on each animal. Survival of the treated and control animals over the course of the
study appeared to be comparable, although no statistical analysis was performed. Average body
weight was reduced in treated females after approximately 80 weeks of exposure; body weight in
exposed females was -12% and -25% lower than in controls at the end of the treatment and
observation periods, respectively. Tumor incidences were not analyzed statistically by the
researchers, but an apparent increase in the total incidence of leukemias occurred (13 in treated
rats, 4 in controls). This increase was mainly due to an apparent increase in immunoblastic
lymphosarcomas in the lungs of treated rats (seven in treated rats [five male, two female] and
one in controls [one male]). Increases for both total leukemias and pulmonary immunoblastic
lymphosarcomas in males and females combined were statistically significant (p < 0.05) by
Fisher's exact test, performed for the current evaluation; the increase in pulmonary
immunoblastic lymphosarcomas in males was of marginal significance (p = 0. 10). The study did
not include evaluation of nonneoplastic lesions. Based on reduction in body weight gain, this
study identifies a chronic LOAEL of 321 mg/kg-day. Tumor findings are considered
inconclusive because of inherent limitations of the experimental design (one dose, one species)
and incomplete analysis and reporting of results.
4.2.2. Inhalation Exposure
4.2.2.1. Acute Studies
Median lethal concentration (LCso) values ranged from 391 1 ppm (21,350 mg/m3) for a
2-hour exposure in mice (Horiguchi and Horiuchi, 1971) to 38,000 ppm (207,480 mg/m3) for a
15-minute exposure in rats (Clark and Tinston, 1982). However, most studies estimated
values between 10,000 and 30,000 ppm (54,600 and 163,800 mg/m3) (for durations ranging from
10 minutes to 7 hours) (Calhoun et al., 1988; Moser and Balster, 1985; Woolverton and Balster,
1981; Bonnet et al., 1980; Gradiski et al., 1978; Siegel et al., 1971; Adams et al., 1950). There
was a general trend for LC50 to decrease as the exposure duration increased. For example, Moser
and Balster (1985) estimated inhalation lethality in male CD-I mice after 10-, 30-, or 60-minute
exposures to 1,1,1-trichloroethane and found LCso values of 29,492, 20,616, and 18,358 ppm,
respectively (161,030, 1 12,560, and 100,230 mg/m3). There appears to be little difference in
susceptibility between rats and mice. Researchers in one laboratory that tested both species
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obtained a 6-hour LCso of 10,305 ppm (56,270 mg/m3) in male rats and 13,414 ppm
(73,240 mg/m3) in female mice exposed by the same protocol (Bonnet et al., 1980; Gradiski et
al., 1978).
1,1,1-Trichloroethane-associated lethality in these studies was generally preceded by
increasingly serious signs of CNS depression, including initial excitability, ataxia, loss of
righting reflex, loss of movement, narcosis, and irregular and shallow respiration (Calhoun et al.,
1988; Moser and Balster, 1985; Clark and Tinston, 1982; Woolverton and Balster, 1981; Bonnet
et al., 1980; Gehring, 1968; Adams et al., 1950; Lazarew, 1929). Clark and Tinston (1982)
estimated a median effective concentration (ECso) in rats for CNS depression of 5000 ppm
(27,300 mg/m3) for a 10-minute exposure. Studies designed specifically to investigate the
effects of 1,1,1-trichloroethane on the CNS are discussed in Section 4.4.
When performed, gross necropsy failed to find tissue lesions associated with mortality
(Calhoun et al., 1988; Bonnet et al., 1980). Death was generally attributed to cardiac or
respiratory depression (Clark and Tinston, 1982; Woolverton and Balster, 1981; Krantz et al.,
1959; Adams et al., 1950). Mechanistic studies have demonstrated that brief exposure to high
concentrations of 1,1,1-trichloroethane can produce direct depression of both the respiratory
center (Uchigasaki et al., 1998; Kobayashi et al., 1987a, 1986) and the heart (Uchigasaki et al.,
1998; Taylor et al., 1976; Belej et al., 1974; Herd et al. 1974). Depression of myocardial
function produces a concomitant reduction in blood pressure (Uchigasaki et al., 1998; Taylor et
al., 1976; Belej et al., 1974; Herd et al., 1974), which can result in death if blood pressure drops
too low (Herd et al., 1974; Krantz et al., 1959). Blood pressure is also reduced, to a lesser
extent, at lower exposure concentrations. At levels below which myocardial function is
depressed, the decrease in blood pressure appears to be due to a 1,1,1-trichloroethane-induced
increase in peripheral vasodilation (Aoki et al., 1997; Kobayashi et al., 1984, 1983; Herd et al.,
1974). The dose-response curve for effects on blood pressure was studied by Kobayashi et al.
(1983). These researchers observed a concentration-related decrease in systemic blood pressure,
with no effect at 3500 ppm (19,110 mg/m3), slight decreases at 4500-6200 ppm (24,570-
33,850 mg/m3), and larger decreases at 15,000-28,000 ppm (81,900-152,880 mg/m3) in
anesthetized mongrel dogs (7-14 kg) of both sexes exposed to various concentrations of
1,1,1-trichloroethane vapor by tracheal tube for 2 minutes. The slight decreases at around 5000
ppm (27,300 mg/m3) correspond to the threshold for decreased peripheral vascular resistance
observed in a follow-up study by the same researchers (Kobayashi et al., 1984). The larger
decreases at > 15,000 ppm (81,900 mg/m3) presumably correspond to decreases associated with
depressed myocardial function, which occurred at these concentrations in the study by Herd et al.
(1974). No gross or microscopic lesions in the heart were observed at any exposure level (Herd
et al., 1974). It has been proposed that depression of respiration, blood pressure and myocardial
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function by 1,1,1-trichloroethane may result, in part, from effects on the autonomic nervous
system (Kobayashi et al., 1988, 1987a,b, 1986).
Sensitization of the heart to epinephrine, resulting in the production of cardiac
arrhythmias, is another potential cause of death from high-level 1,1,1-trichloroethane exposure
(Rennick et al., 1949). Healthy male beagles were exposed by face mask to 2500, 5000, or
10,000 ppm (13,650, 27,300, or 54,600 mg/m3) of 1,1,1-trichloroethane for 10 minutes following
7 minutes exposure to house air and injected with epinephrine twice (a control dose after
2 minutes of the air exposure and a challenge dose after 5 minutes of chemical exposure).
Electrocardiographic signals were recorded. Arrhythmias were detected in 0/12 trials at
2500 ppm, 3/18 trials (17%) at 5000 ppm, and 12/12 trials (100%) at 10,000 ppm. Behavioral
changes (excitement and struggling) were observed in dogs exposed to 10,000 ppm (Reinhardt et
al., 1973). A similar study in which groups of 4-7 beagles were exposed by face mask to various
concentrations of 1,1,1-trichloroethane for 5-minute periods with challenge and control
adrenaline injections determined an EC50 of 7500 ppm (40,950 mg/m3) (95% CI: 4000-
11,000 ppm; 21,840-60,060 mg/m3) for cardiac sensitization by this chemical (Clark and
Tinston, 1973). Kobayashi et al. (1982) conducted a series of experiments in which anesthetized
dogs were given epinephrine by iv drip until bigeminy (extrasystole) occurred with and without
exposure to 1,1,1-trichloroethane vapor at concentrations of 1750 to 69,000 ppm (9560-
376,740 mg/m3) for periods ranging from 0.5 to 20 minutes. The ratio of epinephrine dose
needed to produce arrhythmia with and without 1,1,1-trichloroethane exposure was used to
measure the sensitizing effect of 1,1,1-trichloroethane. There were significant negative
correlations between this ratio and the product of exposure concentration and time (C x T) and
concentration alone when time was held constant, indicating that the sensitizing effect of
1,1,1-trichloroethane increased with exposure. For a 10-minute exposure, the threshold
concentration for cardiac sensitization was between 4900 and 8500 ppm (26,750 and
46,410 mg/m3).
Other studies of cardiac sensitization and arrhythmia in animals exposed to
1,1,1-trichloroethane found that (1) dogs with experimentally induced myocardial infarctions
were no more likely to show cardiac sensitization to 1,1,1-trichloroethane than healthy dogs
(Trochimowicz et al., 1976, 1974); (2) arrhythmias (premature ventricular contractions) occurred
in response to epinephrine challenge in anesthetized rabbits exposed to 5600 ppm
(30,580 mg/m3) of 1,1,1-trichloroethane for 7.5 minutes to 1 hour and were enhanced by
cotreatment with enzyme inhibitors (SKF-525A, Lilly 18947) that increased blood levels of
parent compound and slightly diminished by cotreatment with the enzyme inducer phenobarbital,
which slightly reduced the level of parent compound in the blood, suggesting that the cardiac
sensitizing property of 1,1,1-trichloroethane is due to the parent compound (Carlson, 1981); and
(3) 1,1,1-trichloroethane can produce arrhythmias without cotreatment with epinephrine at
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exceedingly high exposure levels (25,000-50,000 ppm [136,500-273,000 mg/m3] for 5 minutes
in anesthetized rhesus monkeys and 400,000 ppm [2,184,000 mg/m3] for 6 minutes in
anesthetized Swiss mice) (Aviado and Belej, 1974; Belej et al., 1974). Although cardiac
sensitization by 1,1,1-trichloroethane has been demonstrated repeatedly in a number of studies,
not all studies have reported positive results. Egle et al. (1976) found no evidence of cardiac
sensitization in anesthetized beagles exposed for 30 minutes to 5000 or 10,000 ppm (27,300 or
54,600 mg/m3) of 1,1,1-trichloroethane released from aerosols.
There is little evidence of damage to the liver or other tissues in acute inhalation studies
of 1,1,1-trichloroethane. Adams et al. (1950) exposed rats (10-84 per group, males and females
combined) to concentrations ranging from 5000 to 30,000 ppm (27,300 to 163,800 mg/m3) for
durations of 0.1-7 hours. Survivors generally recovered rapidly after the end of exposure and at
24 hours appeared normal and showed no effect on body weight. Internal examinations for
organ weight and histopathology (lung, heart, liver, kidneys, testes) were performed 24 hours
after exposure for groups of 3-5 rats exposed to 8000, 12,000, or 18,000 ppm (43,680, 65,520, or
98,280 mg/m3) for 0.1-7 hours and 17 unexposed control rats. Rats exposed to 8000 ppm for
7 hours had significantly increased relative liver weight (12%) and slight histopathology (fatty
change) in the liver. Rats exposed to 12,000 ppm for 7 hours had a larger increase in relative
liver weight (27%) and slight-to-moderate liver lesions, including more marked fatty changes
and, in some cases, congestion and hemorrhagic necrosis. A slight increase in relative kidney
weight (8%) at this dose was not accompanied by histopathology in this organ. Rats exposed to
18,000 ppm were only exposed for up to 2 hours, and the only significant effect in this group
was a small (11%) increase in relative kidney weight.
Studies with shorter exposure durations found no evidence of damage to the liver or other
tissues due to 1,1,1-trichloroethane. Carlson (1973) exposed groups of five adult male albino
rats to 11,600 or 13,070 ppm (63,340 or 71,360 mg/m3) 1,1,1-trichloroethane for 2 hours and
compared them with unexposed controls. No effects were observed on relative liver weight,
liver G-6-Pase activity, or serum levels of ALT and AST 22 hours after exposure termination,
although rats pretreated with phenobarbital (but not 3-methylcholanthrene) did have significantly
elevated enzyme levels (-four- to sevenfold). Cornish and Adefuin (1966) exposed male
Sprague-Dawley rats to 5000 ppm (27,300 mg/m3) for 6 hours, 10,000 ppm (54,600 mg/m3) for
2 or 4 hours, or 15,000 ppm (81,900 mg/m3) for 2 hours to reagent grade 1,1,1-trichloroethane.
No differences from unexposed controls were found 24 or 48 hours after exposure for serum
ALT, AST, or isocitric dehydrogenase (ICD) or for histopathology of the liver, kidney, adrenal,
spleen or lung. Two of 14 rats died after exposure to 15,000 ppm. Gehring (1968) found that in
female Swiss-Webster mice exposed to 13,500 ppm (73,710 mg/m3), the exposure duration
estimated to increase serum ALT (measured 24 hours after the start of exposure) in half of the
mice (ETso) could not be determined because it exceeded the estimate of time required to kill
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half of the mice (LTso ~ 10 hours). Loizou et al. (1996) observed no evidence of liver toxicity,
as assessed by serum SDH, LDH, and GDH, 2 hours postexposure in groups of four to six male
Wistar rats exposed to 1,1,1-trichloroethane for 3 hours at concentrations of 0, 2000, 4000, 8000,
15,000, or 25,000 ppm (0, 10,920, 21,840, 43,680, 81,900 or 136,500 mg/m3). There was no
effect on liver function (bromosulfalein retention test) in dogs anesthetized with
1,1,1-trichloroethane for 1 hour (Krantz et al., 1959). Takahara (1986b) measured serum ALT,
liver and plasma triglyceride, and liver ATP at 0, 3, 11, and 23 hours in female mice (five/group)
exposed to 800 ppm (4370 mg/m3) 1,1,1-trichloroethane for 3 hours. Although there appeared to
be some very mild changes over time, most notably an increase in liver triglyceride levels during
exposure, the study did not include a concurrent control group and there was no statistical
comparison of preexposure and postexposure groups.
The effects of acute inhalation exposure to 1,1,1-trichloroethane on hematological
parameters were studied in anesthetized dogs (Hobara et al., 1984, 1983). Groups of five
crossbred dogs (males and females, 2-5 years old) anesthetized with sodium pentobarbital were
exposed to 200, 500, 700, 1000, 1500, or 2000 ppm (1090, 2730, 3820, 5460, 8190, or
10,920 mg/m3) 1,1,1-trichloroethane for 1 hour or 700 ppm (3820 mg/m3) for 4 hours. A control
group of 15 dogs was sham exposed to fresh air only. Blood samples were collected before
exposure and 60 minutes after exposure in all groups and more frequently in the two 700 ppm
groups. No significant effect on erythrocyte count, hematocrit, or thrombocyte count was
observed. After the 1-hour exposure, leukocyte count was markedly and statistically
significantly reduced at 500 ppm and above (25-30% of control levels at 700 ppm and above).
Investigators observed a trend to recovery after the end of exposure. During the 4-hour
exposure, the minimum leukocyte count occurred in the first hour and the trend to recovery
started after 2 hours, even though exposure continued. Differential counts in the 700 ppm
studies showed marked decreases in neutrophils and increases in lymphocytes, with only slight
changes in eosinophils and monocytes. The changes in differential followed the same time
course as the overall decrease in leukocytes. The researchers suggested that these results could
reflect temporary trapping of neutrophils from peripheral blood in the capillary beds of other
tissues as 1,1,1-trichloroethane is taken up from the blood into the tissues. These findings,
therefore, appear to indicate a temporary physiological response to 1,1,1-trichloroethane, rather
than an adverse effect on the blood or hematopoietic tissues. Clotting time of blood from dogs
anesthetized with 1,1,1-trichloroethane for 1 hour was not different from unexposed controls
(Krantz et al., 1959).
Neuroendocrine effects were investigated in one study in rats. Groups of 8-12 male
Sprague-Dawley rats were exposed to 3500 or 5000 ppm (19,110 or 27,300 mg/m3)
1,1,1-trichloroethane (>99% pure) for 10 or 30 minutes or air exposed for 20 minutes (Pise et al.,
1998). Plasma corticosterone levels were statistically significantly decreased after 30 minutes at
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3500 ppm and 10 or 30 minutes at 5000 ppm. Plasma adrenocorticotropic hormone (ACTH)
levels were significantly reduced at 5000 ppm at both time points but not at 3500 ppm at either
time point. In the brain, no clear pattern of effect was seen on hypothalamic, hippocampal, or
cortical levels of ACTH or corticotropin-releasing factor.
The concentration producing a 50% decrease in respiratory rate (RDso), a measure of
respiratory irritation, was reported to be >1000 ppm (5460 mg/m3) for 1,1,1-trichloroethane in a
study in which pulmonary function was evaluated in male Swiss-Webster mice exposed to
1000 ppm of the chemical for 30 minutes (Stadler and Kennedy, 1996).
4.2.2.2. Short-term Studies
Groups of 10 male and 10 female rats (strain not specified) were exposed to 0 or
1000 ppm (0 or 5460 mg/m3) 1,1,1-trichloroethane from a stabilized commercial formulation
7 hours per day, 5 days per week for 4 weeks (22 exposures) (Dow Chemical Co., 1969). The
animals were monitored daily for clinical signs and body weight. Blood was collected for
hematological examination prior to exposure and on the 5th and 20th exposure days. Animals
were sacrificed at the end of the study and the major organs were examined for gross and
microscopic changes. The lung, liver, spleen, kidney, and gonad (males only) were weighed.
No deaths were observed in exposed rats, and no differences from controls were seen for clinical
signs, growth, hematology, relative organ weights, or gross or microscopic pathology. The study
defined a free-standing NOAEL of 1000 ppm (5460 mg/m3).
Other short-term inhalation studies were more restricted in the scope of endpoints
investigated. Groups of six adult male Wistar rats were exposed to 0, 200, 400, or 800 ppm (0,
1090, 2180, or 4370 mg/m3) 1,1,1-trichloroethane continuously for 10 days (Koizumi et al.,
1983). Limited hematology (red blood cell count, white blood cell count) and serum chemistry
(ALT) analyses were performed, and the liver was weighed and analyzed for enzyme activity.
There was no effect on hematology or serum ALT at any concentration. Relative liver weight
and liver mixed function oxidase activity were significantly increased in all treated groups. The
increase in liver weight appears to reflect enzyme induction, rather than toxicity, in this study,
making the high level of 800 ppm (4370 mg/m3) a NOAEL. A 48-hour study of similar design
found no effect of 1,1,1-trichloroethane on liver or red blood cell 5-aminolevulinic acid
dehydratase (ALA-D) activity, inhibition of which is an early indicator for disruption of heme
synthesis, at concentrations up to 800 ppm (4370 mg/m3) (Koizumi et al., 1984). NMRI mice
exposed to 625 ppm (3410 mg/m3) 1,1,1-trichloroethane continuously for 30 days showed slight
(8-12%), statistically significant increases in absolute liver and kidney weight in females and
decreased absolute spleen weight in males (Kjellstrand et al., 1985a). Neither body weights nor
relative organ weights were reported. These researchers also reported a slight significant
decrease in plasma butyrylcholine esterase activity in females, but no effect in males, suggesting
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that 1,1,1-trichloroethane did not affect testosterone activity in these animals. Slight increases
(15%) in absolute and relative liver weight were noted in male Sprague-Dawley rats exposed to
0 or 820 ppm (4480 mg/m3) 1,1,1-trichloroethane 6 hours/day, 5 days/week for 4 weeks
(Toftgard et al., 1981). Rats given repeated anesthesia with 1,1,1-trichloroethane, one hour per
day, for 3-9 days had no lesions in the kidney, brain, or spinal cord; 1/9 exposed animals had
midzonal necrosis of the hepatic parenchyma in the liver (Krantz et al., 1959).
4.2.2.3. Subchronic Studies
Groups of 20 male and 20 female CDF rats (4-6 weeks old) and B6C3F1 mice (5-
6 weeks old) were chamber exposed to 0, 150, 500, 1000, or 2000 ppm (820, 2730, 5460, or
10,920 mg/m3) of production grade 1,1,1-trichloroethane (-94% pure) for 6 hours/day,
5 days/week for up to 94 days (Calhoun et al., 1981). This study was conducted in preparation
for selecting exposure concentrations for the Quast et al. (1988, 1984) chronic study. An interim
sacrifice of 10 animals/sex/concentration was performed after 30 (rats) or 29 (mice) exposures,
and terminal sacrifice was conducted on the remaining 10 animals/sex/concentration after 62
(rats) or 63 (mice) exposures. Study endpoints included clinical signs, body weight, hematology,
clinical chemistry, urinalysis, liver triglyceride level, body and organ weights, gross pathology,
and histopathology. Gross pathology was evaluated in all animals following the interim and
terminal sacrifices. Histology was assessed as follows: liver and kidneys in all exposure groups
at interim sacrifice; possible target organs (liver, kidney, lung, nasal turbinates, esophagus,
trachea, thyroid, parathyroid, and/or gall bladder) in the 150, 500, and 1000 ppm (820, 2730, and
5460 mg/m3) groups at terminal sacrifice; and complete examinations in the 0 and 2000 ppm
(10,920 mg/m3) groups at terminal sacrifice. Histological changes were observed in the liver and
nasal turbinates of both species at 2000 ppm. Hepatic changes occurred in only a few animals at
2000 ppm and were generally minimal, including decreased hepatocyte size with altered staining
affinity suggestive of decreased glycogen content (3/10 female rats vs. 0/10 controls; 4/10 male
mice vs. 1/10 controls) and slight centrilobular hepatocellular swelling (2/10 male rats vs.
0/10 controls; 2/10 male mice vs. 0/10 controls). These histopathological changes more likely
represent an adaptive physiologic response (i.e., stimulation of the drug metabolizing enzyme
system) and as such are not considered adverse. The investigators considered remaining
microscopic findings not to be treatment related. The histopathology summary tables, however,
showed generalized hepatocellular atrophy in 2000 ppm male rats (3/10 vs. 0/10 controls and
lower-exposure groups) and focal necrosis in 2000 ppm female mice (2/10 vs. 0/10 in controls
and lower-exposure groups). These findings suggest adverse effects in the liver of 2000 ppm
rats and mice. Mild olfactory epithelium degeneration and other nasal alterations were found in
all male and female rats and approximately one-half of the male and female mice at 2000 ppm.
The turbinate changes were degenerate in type and confined to the olfactory epithelial region.
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Microscopically, they were characterized by loss of epithelial cytoplasmic processes and
flattening of the epithelium. These olfactory epithelial findings were not confirmed in
subsequent chronic studies by the same group of investigators (Quast et al., 1988, 1984).
Reduced mean body weight was also observed in 2000 ppm male rats after 82 and 88 days of
exposure (-7% lower than control values,/* < 0.05). No effects attributable to exposure were
found at 1000 ppm (5460 mg/m3) or less, indicating that this level is a NOAEL for both rats and
mice in this study. The LOAEL is 2000 ppm (10,920 mg/m3) in both species based on the
weight-of-evidence for mild liver effects and lesions of the nasal turbinates at this concentration.
MacEwen and Vernot (1974) exposed groups of 40 rats, 180 mice, 8 dogs, and
4 monkeys to 0, 250, or 1000 ppm (0, 1370, or 5460 mg/m3) 1,1,1-trichloroethane vapor
continuously for 100 days in Thomas domes. The findings of the mouse study were reported
separately by McNutt et al. (1975) and are described below. Rats, dogs, and monkeys were
weighed biweekly. Blood samples collected from dogs and monkeys at the time of weighing
were used for hematology (red blood cell count, white blood cell count, hemoglobin, hematocrit,
reticulocyte count) and serum chemistry (ALT, AST, AP, total bilirubin, triglycerides, BUN,
creatinine, protein, glucose, and electrolytes) determinations. Rats were sacrificed at the end of
the exposure period for organ weights, liver fat stains, and complete histopathology. No
exposure-related effects were seen in dogs or monkeys. The only treatment-related effect
reported in rats was a significant increase in relative liver weight at 1000 ppm (5460 mg/m3) (no
further information provided). Increased liver weight in the absence of pathology is not
generally considered to be an adverse effect. Although limited by incomplete reporting, the
1000 ppm (5460 mg/m3) level appears to have been a NOAEL in rats, dogs, and monkeys.
Mice were relatively more sensitive to 1,1,1-trichloroethane than rats, dogs, and
monkeys. Male CF-1 mice were chamber exposed to 0, 250, or 1000 ppm (0, 1370, or 5460
mg/m3) technical grade 1,1,1-trichloroethane (94-97% pure, 2.4-3.0% dioxane, 0.12-0.30%
butanol) continuously for up to 14 weeks (McNutt et al., 1975). Serial sacrifices were performed
on 10 mice/concentration at weekly intervals during the exposure period and at postexposure
weeks 2 and 4. Endpoints included clinical observations, food and water intake, liver weight,
liver fat content (determined by oil red O staining in three mice/concentration and triglyceride
analysis in remaining seven mice/concentration), liver ultrastructure (three mice/concentration),
and histology (liver, kidney, pancreas, intestine, heart, lung, and brain). Minimal changes,
consisting of occasional mild liver ultrastructural variations after 10 weeks of exposure, were
observed at 250 ppm (1370 mg/m3). At 1000 ppm (5460 mg/m3), hepatic ultrastructural changes
were more pronounced and accompanied by increases in relative liver weight, triglycerides, and
lesions visible by light microscopy. Relative liver weight and liver triglyceride values were 22%
(p < 0.01) and 237% (p < 0.01) higher at 1000 ppm compared to control values at exposure week
14. Histopathological changes included centrilobular hepatocyte swelling, vacuolation, lipid
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accumulation and, after 10 weeks, single-cell necrosis. By 12 weeks of exposure, necrosis of
individual hepatocytes (associated with acute inflammatory infiltrate and hypertrophy of Kupffer
cells) occurred in 40% of the mice exposed to 1000 ppm. Exposure-related effects in tissues
other than liver were not found. The minimal ultrastructural changes observed at 250 ppm do
not constitute clear evidence of an adverse effect. This study, therefore, identified aNOAEL of
250 ppm (1370 mg/m3) and LOAEL of 1000 ppm (5460 mg/m3) for liver effects in mice with
continuous exposure.
In another study, groups of 15 Long-Evans or Sprague-Dawley rats, 15 Hartley guinea
pigs, 3 New Zealand rabbits, 2 beagle dogs, and 3 squirrel monkeys were continuously or
intermittently exposed to commercial grade 1,1,1-trichloroethane vapor (Prendergast et al.,
1967). In the continuous exposure study, the animals were exposed to 0, 140, or 380 ppm (0,
760, or 2070 mg/m3) for 90 days. In the intermittent exposure study, the animals were exposed
to 2230 ppm (12,180 mg/m3) 8 hours/day, 5 days/week for 6 weeks. Endpoints in both studies
included clinical signs, body weight, and limited hematology (total and differential leukocyte
counts, hemoglobin, hematocrit) and histology (heart, lung, liver, spleen, and kidney). BUN was
determined in treated and control guinea pigs. The only notable finding was reduced body
weight gain in rabbits and dogs in the 380 ppm (2070 mg/m3) continuous exposure and
2230 ppm (12,180 mg/m3) intermittent exposure groups. Terminal body weights were not
reported, but it can be inferred from the data on initial body weight and growth that terminal
body weights were likely reduced by less than 5% in rabbits of both groups and intermittently
exposed dogs and by about 17% in dogs exposed continuously to 380 ppm. A NOAEL of
140 ppm (760 mg/m3) and LOAEL of 380 ppm (2070 mg/m3) are identified based on the
decreased body weight in dogs. Confidence in the LOAEL is low due to the small group sizes
(two dogs per group).
Torkelson et al. (1958) performed studies in which groups of four to five female guinea
pigs and four to five male rats were exposed to >1000 ppm (>5460 mg/m3) 1,1,1-trichloroethane
for <3 hours/day on 5 days/week for approximately 3 months. Toxicity endpoints were general
appearance and behavior, survival, hematology, body and organ weights, and gross and
histologic pathology of the major organs. The guinea pigs were exposed to 0 ppm (3 hours/day),
1000 ppm (5460 mg/m3) (0.3, 0.6, 1.2, or 3 hours/day) or 2000 ppm (10,920 mg/m3) (0.05, 0.1,
0.2, or 0.5 hours/day) for a total of 69 times in 98 days. Exposure to 1000 ppm for 3 hours/day
or 2000 ppm for 0.5 hours/day produced effects in the livers (fatty changes, increased organ
weight) and lungs (irritation, inflammation) of guinea pigs. The rats were exposed to 0 ppm (1
hour/day) or 10,000 ppm (54,600 mg/m3) (0.05, 0.1, 0.2, 0.5, or 1 hour/day) for a total of 70
times in 99 days. Effects were observed only in rats exposed for 1 hour/day; changes included
various degrees of anesthesia and slightly increased liver weight. The findings of this study
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indicate that guinea pigs were more sensitive than rats and that 1000 ppm (5460 mg/m3) is the
LOAEL in guinea pigs for this study.
Adams et al. (1950) also found guinea pigs to be more sensitive than other species.
Guinea pigs, rats, rabbits, and a monkey were exposed to various concentrations of
1,1,1-trichloroethane (redistilled commercial product containing <1% dichloroethane) for
7 hours/day, 5 days/weeks for -1-3 months (Adams et al., 1950). Study endpoints included
general appearance, body weight, BUN, and weight and histology of selected major organs
(lungs, liver, kidneys, spleen, and testes). Groups of 9-20 guinea pigs, divided evenly between
the sexes, were exposed to 650, 1500, 3000, or 5000 ppm (3550, 8190, 16,380, or 27,300 mg/m3)
of 1,1,1-trichloroethane 5 days per week for 29 to 93 days. A concurrent control was run with
each group. Similarly constituted groups of rats were exposed to 3000 or 5000 ppm (16,380 or
27,300 mg/m3) for 44 to 67 days with concurrent controls by the same protocol. For rabbits,
groups of two females were exposed to 0 or 5000 ppm (0 or 27,300 mg/m3) 5 days/week for 44
days. A single female monkey was exposed to 3000 ppm (16,380 mg/m3) 5 days/week for
74 days (no control tested for this species). Guinea pigs had slight but significantly reduced
body weight gain at all exposure levels; at 650 ppm (3550 mg/m3), terminal body weights were
reduced to 86-94% of control values. Other effects in guinea pigs occurred at higher levels of
exposure, including slight fatty degeneration in liver at 3000 ppm (16,380 mg/m3) (incidence not
specified), slight to moderate fatty degeneration (not accompanied by necrosis) in liver at
5000 ppm (27,300 mg/m3) (10/10), and varying degrees of testicular degeneration at 5000 ppm
(incidence not specified). Effects in other species occurred at 5000 ppm and included signs of
anesthesia in rats and slightly decreased body weight gain in rabbits. Based on decreased body
weight gain in guinea pigs, the low concentration of 650 ppm (3550 mg/m3) is a LOAEL.
Truffert et al. (1977) exposed groups of 55 adult female Sprague-Dawley rats to 0 or
1100 mL/m3 of technical grade 1,1,1-trichloroethane 5 or 6 hours/day, 5 days/week for 15
weeks. Weight gain was monitored throughout the study. Periodic determinations were made
for hepatic DNA synthesis 4 hours after injection of radiolabeled thymidine. Sacrifices were
performed periodically during the study and at termination for hematology and pathological
examination of the lungs, liver, kidneys, adrenals, ovaries, and uterus. The only effect found in
treated rats was a 67% increase in hepatic DNA synthesis after 1 week of exposure that was not,
however, seen at later time periods. There was no corresponding effect on liver weight or
histopathology at any time. In light of the transitory nature of the observed change in DNA
synthesis and the failure to find corresponding tissue damage, the toxicological significance of
this finding is uncertain. The 1100 mL/m3 level is a NOAEL based on histopathology.
Groups of 20 male Wistar rats were exposed to 0 or 204 ppm (1110 mg/m3) of
1,1,1-trichloroethane vapor 8 hours per day, 5 days per week for 14 weeks (Eben and Kimmerle,
1974). Animals were weighed weekly. At study termination, analyses were performed for
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hematology (including red blood cell count, hemoglobin, hematocrit, and white blood cell count
and differential), blood glucose, and serum chemistry markers for hepatotoxicity (ALT, AST,
SDH, total bilirubin) and nephrotoxicity (urea, creatinine). Animals were examined by necropsy
for gross lesions, and the heart, lungs, liver, kidneys, adrenals, testes, and thyroid were weighed.
The same organs (except the thyroid) and the spleen were collected for histopathology in four
animals from each group. No treatment-related effects were seen. This study identified 204 ppm
(1110 mg/m3) as a free-standing NOAEL.
4.2.2.4. Chronic Studies
Quast et al. (1988, 1984, 1978) carried out two inhalation bioassays for
1,1,1-trichloroethane. In the first study, groups of 189, 94, and 92 Sprague-Dawley rats of each
sex were exposed to 0, 875, or 1750 ppm (0, 4780, or 9560 mg/m3) of 1,1,1-trichloroethane
6 hours/day, 5 days/week for 12 months (Quast et al., 1978; Rampy et al., 1977 [as cited in Quast
et al., 1988]). A commercial grade formulation was tested (-96% 1,1,1-trichloroethane by
weight; identity of the stabilizers and impurities was not provided). The animals were observed
for 19 months after the exposure period, making the total length of study 31 months (923 days).
Endpoints included clinical signs, body weight, hematology (7-10 rats/sex/group on study
months 12 and 24), urinalysis (10 rats/sex/group after 24 months), serum indices (BUN, ALT,
and AP activities prior to terminal necropsy), and pathology, including organ weights and
histology (all unscheduled deaths and moribund animals, 3 rats/sex/group at the end of the
exposure period, remaining rats at the end of the observation period). The only histopathologic
lesion considered by study investigators to be treatment related was an increased incidence of
focal hepatocellular alterations in females at 1750 ppm (9560 mg/m3) at the end of the
observation period (data not presented in the study report). Because these effects, observed
19 months after exposure to 1,1,1-trichloroethane, ceased and because other studies of
1,1,1-trichloroethane have generally not shown effects of 1,1,1-trichloroethane to progress even
while exposure is occurring, it is questionable whether the focal hepatocellular alterations in
high-exposure animals observed at 31 months can be considered as related to treatment.
Therefore, a NOAEL and LOAEL were not identified in this study. Exposure to
1,1,1-trichloroethane was not associated with an increased incidence of neoplastic lesions.
However, exposure was substantially less than lifetime and the maximum tolerated dose (MTD)
may not have been reached.
In the second study by Quast et al. (1988, 1984), groups of 80 male and 80 female F344
rats and B6C3F1 mice were exposed to 0, 150, 500, or 1500 ppm (0, 820, 2730, or 8190 mg/m3)
1,1,1-trichloroethane vapor for 6 hours/day, 5 days/week for 2 years (516 total exposure days).
A production grade 1,1,1-trichloroethane formulation was tested (-94% pure, with 5% stabilizers
[butylene oxide, t-amyl alcohol, methyl butynol, nitroethane, nitromethane] and <1% minor
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impurities). Ten rats and 10 mice of each sex from each exposure group were scheduled for
interim sacrifices after 6, 12, and 18 months of exposure, and the remaining 50 rats and
50 mice/sex/group were scheduled for sacrifice after 24 months of exposure. Clinical signs of
toxicity, mortality, hematology, serum chemistry, urinalysis endpoints (rats only), body weight,
organ weights (liver, kidneys, brain, heart, testes), gross pathology, and histopathology were
comprehensively assessed. In rats, histologic examinations were performed on all (53) tissues,
including the lung, trachea, larynx, and nasal turbinates (following exposure to 0 or 1500 ppm
[0 or 8190 mg/m3] for 6, 12, 18, or 24 months), liver (following exposure to 150 or 500 ppm for
6, 12, or 18 months), and selected (12) tissues (following exposure to 150 or 500 ppm for
24 months). In mice, histologic examinations included all tissues (following exposure to 0 or
1500 ppm for 6, 12, 18, or 24 months), selected tissues (following exposure to 150 or 500 ppm
for 6, 12, or 18 months), and all tissues (following exposure to 150 or 500 ppm for 24 months).
There was no statistically significant reduction in survival of treated rats or mice
compared with their respective controls, and survival at the end of the study ranged from 40-
70% (Quast et al., 1988, 1984). Female rats in both the 500 and 1500 ppm (2730 and
8190 mg/m3) groups showed slight, statistically significant deficits in body weight throughout
much of the study (-7% less than controls, estimated from growth curves); the researchers
considered the effect to be exposure related at 1500 ppm (8190 mg/m3). In rats, no exposure-
related histopathologic changes were observed with the exception of histopathologic changes in
the liver. Very slight microscopic hepatic changes ("accentuation of the normal hepatic lobular
pattern"; "altered cytoplasmic staining in the cells surrounding the central vein"; and
"hepatocytes in the portal region that appeared smaller in the exposed rats when compared with
their respective controls") were described in both male and female rats of the 1500 ppm exposure
group necropsied at 6 months (10/10 males and 10/10 females), 12 months (10/10 males and
10/10 females), and 18 months (7/10 males and 5/10 females); no difference from controls was
seen in the animals after 2 years of exposure because of confounding geriatric changes. These
histopathologic changes were not seen in any control or lower-dose animals at any time point.
The histopathologic findings at 1500 ppm are consistent with a minimal hepatocellular
hypertrophy, which is considered an adaptive physiologic response (i.e., stimulation of the drug
metabolizing enzyme system) and not a measure of toxicity. No effects were observed in mice.
In light of the adaptive physiologic nature of the liver findings in rats at the highest exposure
concentration, this study identified a NOAEL of 1500 ppm (8190 mg/m3) in rats and mice. A
LOAEL was not identified.
Tumor findings were unremarkable. In rats, there was a statistically significant trend for
increased incidence of bilateral benign testicular interstitial cell tumors in males (36/50, 30/50,
38/50, and 45/50 in the 0, 150, 500, and 1500 ppm groups, respectively) (Quast et al., 1988,
1984). There was no trend, however, for an increase in the overall (i.e., unilateral or bilateral)
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incidence of these tumors (43/50, 41/50, 41/50, and 49/50, respectively). In contrast to the oral
bioassay by Maltoni et al. (1986), there were no increases in leukemias or any lymphoreticular
proliferative processes. In mice, there was a statistically significant trend for increased adenoma
or cystadenoma of the lacrimal/Harderian gland in females (3/50, 1/50, 2/50, and 7/50,
respectively). The authors stated that the incidence was within the historical range of
spontaneous incidence for this strain of mouse; they did not consider the tumor to be treatment
related. This study found no clear evidence of a carcinogenic effect of 1,1,1-trichloroethane in
either rats or mice. However, the MTD was not reached in mice and may not have been reached
in rats, as the only toxic effects (described above) were a slight (<7%) reduction in body weight
gain in female rats and slight microscopic hepatic changes (suggestive of a physiologic response
only) in male and female rats exposed to the high concentration (1500 ppm or 8190 mg/m3).
The only other study of chronic duration was an older study reported by Torkelson et al.
(1958). Groups of 20 male and 20 female rats, 8 male and 8 female guinea pigs, 2 male and
2 female rabbits and 2 female monkeys were exposed 126-130 times to 0 or 500 ppm
(2730 mg/m3) of 1,1,1-trichloroethane (94-97% pure, 2.4-3.0% dioxane, 0.12%-0.3% butanol)
for 7 hours/day, 5 days/week for 6 months (Torkelson et al., 1958). Animal strains were not
reported. Assessment of general appearance and behavior, survival, hematology, body and organ
weights, gross pathology, and histopathology showed no exposure-related effects. The scope of
the histologic examinations was not specified but may be the same as the organs that were
weighed (lung, heart, liver, kidney, spleen, and testes). The lack of effects indicates that
500 ppm (2730 mg/m3) is a NOAEL for 6-month exposure in the rats, guinea pigs, and other
species.
4.3. REPRODUCTIVE/DEVELOPMENTAL STUDIES—ORAL AND INHALATION
4.3.1. Oral Exposure
Cardiac anomalies were associated with maternal exposure to 1,1,1-trichloroethane in an
exploratory study of 1,1,1-trichloroethane developmental toxicity (Hutcheon et al., 1985; Dapson
et al., 1984a,b). Groups of two to three male and seven to eight female Sprague-Dawley rats
(225-250 g) were given drinking water containing 0 or 10 ppm of 1,1,1-trichloroethane (97%
pure, stabilized with 3% 1,4-dioxane) in 0.05% Tween 80, starting before mating and continuing
through pregnancy and lactation. Based on the U.S. EPA (1988a) reference allometric equation
for water consumption and body weight data reported in the study, the dose is estimated to be
1.4 mg/kg-day. Rats in each group were mated until pregnant and then housed separately by sex.
Pregnant females were allowed to deliver naturally and nurse their pups. Pups and dams were
observed and weighed daily until weaning, when pups were sacrificed and necropsied. Hearts
were weighed and examined for gross structural abnormalities. Although not tested statistically,
length of exposure prior to successful mating appeared to be longer in treated rats (average =
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20.4 days; range = 7-27 days) than in controls (average = 14.7 days; range = 8-30 days). Given
the small number of males (two in the control group and three in the treated group) and the wide
range in time to successful mating (7-30 days), no biological significance is ascribed to this
finding. Gestation period, pup sex ratio, and litter size in treated rats were all similar to controls.
Five litters (52 pups) were weaned and sacrificed in the treated group, as were six litters
(70 pups) in the controls. Pup body weights at sacrifice were not affected by treatment. Pup
mean absolute heart weight was 9% higher in treated rats than controls, although the difference
was not statistically significant. The incidence of total gross cardiac anomalies (persistent
ductus arteriosus, remnant ductus arteriosus, right atrial hypoplasia, right atrial displacement,
other right atrial deformations [grooves, abnormal contour], left atrial hypoplasia, superior vena
cava abnormalities, and other abnormalities [excessive fat, large amount of pericardium]) was
increased in pups from the exposed group (32/52 = 62%) versus controls (3/70 = 4%). The most
prominent individual anomaly was persistent ductus arteriosus, which was seen in 15/52 or 29%
of treated group pups and 0/70 control pups. A comparison of cardiac anomalies based on
number of affected litters was not performed. No malformations were seen outside of the
cardiovascular system. Persistent ductus arteriosus was considered by the researchers to indicate
delay of cardiac development. Confidence in the results was limited, however, by use of only a
single dose level and incomplete analysis of the data (no litter-based comparisons of cardiac
abnormalities).
In a postnatal developmental study designed to assess the reproducibility of the
cardiovascular effects reported by Dapson et al. (1984a,b), Charles River CD rats were exposed
to drinking water containing 0 (water-only control), 0 (water containing stabilizer and
emulsifier), 3, 10, or 30 ppm of 1,1,1-trichloroethane (97% pure stabilized with 3% dioxane) in
0.05% Tween 80 emulsifying agent (George et al., 1989; NTP, 1987a). Groups of more than
30 males and 30 females (exact numbers not reported) were exposed for 14 days prior to
cohabitation for up to an additional 13 days. Male breeders and sperm-negative females were
killed after the cohabitation period was completed, and sperm-positive females (24-30 per
group) continued to be exposed through lactation (postnatal day [PND] 21). Reported average
compound consumption during the premating period was 0.3, 0.9, and 2.6 mg/kg-day for
exposed males and 0.3, 1.3, and 3.3 mg/kg-day for exposed females. Reported average maternal
intake was 0.3, 1.2, and 3.5 mg/kg-day from GD 0 to parturition and 0.6, 2.0, and 5.9 mg/kg-day
from PND 1 to PND 21. Evaluation of adult males and females included clinical signs, food and
water consumption, and body weight throughout the exposure period. Other endpoints included
number of implantation sites, gestation length, litter size and pup weight, and survival. Litters
containing >10 pups on PND 4 were culled to a litter size of 10 and the remaining pups were
evaluated until PND 21. The culled pups (PND 4) and surviving pups (PND 21) were sacrificed
and examined for visceral malformations with special attention given to the heart and
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surrounding vasculature. No treatment-related parental effects or changes in postnatal growth or
development of offspring were observed. Percent mortality from implantation to PND 1 was
significantly higher (224%, p < 0.05) in 30 ppm litters than in the vehicle control group, but this
increase appeared to be primarily due to high mortality (61%) in one litter on PND 1 and was not
accompanied by an effect on numbers of live pups/litter on PNDs 1 or 4. Of the pups found dead
on PND 1, patent ductus arteriosus occurred in 10/28 treated pups (six from four litters at 3 ppm,
one at 10 ppm, three from two litters at 30 ppm) (no occurrence in either control group). Patent
ductus arteriosus also occurred in one pup (3 ppm) culled on PND 4. Statistical analysis of
incidence by litter indicated no significant effect of treatment, and there was no evidence of
cardiac or other malformations in any dose group on PND 21, which was the time at which
Dapson et al. (1984a,b) reported effects. In the discussion of their results, NTP (1987a) noted
that functional closure of the ductus arteriosus (i.e., constriction of the smooth muscle wall) in
rats occurs in the first 1 to 3 hours after birth and that at this stage constriction is reversible. The
second stage of closure of the ductus arteriosus, which may take up to 5 days in the rat, involves
permanent sealing of the lumen vessel. NTP stated that the observation of ductus arteriosus in
animals found dead on PND 1 in the current study may have been a result of the absence of
chemical (prostaglandin or oxygen) control of constriction of the vessel; NTP did not consider
the finding an indication of abnormal development. Accordingly, 3.5 mg/kg-day (highest tested
dose) is considered a NOAEL for developmental toxicity.
A teratogenicity study of 1,1,1-trichloroethane (NTP, 1987b) was conducted in
conjunction with the postnatal developmental evaluation summarized above (NTP, 1987a).
Exposure and other aspects of the experimental design are essentially the same as in the
postnatal study except that dams were sacrificed on GD 20 and comprehensive teratological
examinations of fetuses were performed. Reported average compound consumption
corresponding to the 3, 10, and 30 ppm drinking water concentrations were 0.3, 0.6, and 2.0
mg/kg-day for males during the premating period and 0.3, 0.8, and 2.4 mg/kg-day for females
from premating to GD 20. No exposure-related maternal, embryotoxic, fetotoxic, or
developmental (external, visceral, skeletal, or cardiovascular) abnormalities were found,
indicating that 2.4 mg/kg-day (highest tested dose) is a developmental toxicity NOAEL.
An oral multigeneration reproduction study modified to include screening for teratogenic
and dominant lethal effects of 1,1,1-trichloroethane was conducted in mice (Lane et al., 1982).
Groups of 30 female and 10 male ICR Swiss mice (F0 generation) were provided drinking water
containing 1,1,1-trichloroethane (97% pure containing 3% p-dioxane stabilizer) in
concentrations of 0 (water-only control), 0 (vehicle control), 0.58, 1.75, or 5.83 mg/mL (reported
nominal calculated doses of 100, 300, or 1000 mg/kg-day) for 5 weeks prior to mating and
throughout gestation and lactation of the Fia litters. At 2 weeks postweaning of the Fia litters,
the FQ adults were remated to produce Fib litters. At 2 weeks postweaning of the Fib litters, the
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FO adults were remated for teratology and dominant lethal screening of female and male FIC pups,
respectively. The Fib litters were culled to 30 females and 10 males at weaning and placed on
test solutions until age 14 weeks when they were mated to produce the F2a litters. At 2 weeks
postweaning of the F2a pups, the Fib adults were remated for teratology and dominant lethal
screening of female and male F2b pups, respectively. Adult observations included body weight
and water consumption, reproductive performance (fertility index = [number females
pregnant/number females mated] x 100; gestation index = [number females with live
litters/number females pregnant] x 100), mortality, and gross pathology (necropsies performed
after week 24 or 25 of dosing). Offspring endpoints included litter size, body weight, viability
and lactation indices, and gross pathology (necropsies performed on Fia and Fib pups at age 21
days). The teratology screenings involved sacrificing females on GD 18 for assessment of
implantations, resorptions, fetal viability, gross malformations, visceral abnormalities (one-third
of fetuses), and skeletal abnormalities (remaining fetuses). Dominant lethal reproductive indices
were based on implantation, resorption, and fetal viability data in untreated females that were
mated with the exposed FIC and F2b males. No exposure-related effects on male or female
reproductive function (as evaluated by fertility and gestation indices) or offspring development
were found in this study, indicating that 1000 mg/kg-day, the highest dose tested, is a NOAEL
for reproductive and developmental toxicity.
Maurissen et al. (1994, 1993) conducted a study to investigate 1,1,1-trichloroethane for
neurodevelopmental effects. Groups of 50 (2 replicates of 25 each) mated sperm positive female
F344 rats were treated by gavage with 1,1,1-trichloroethane (>99.9% pure with <0.1% butylene
oxide stabilizer) in corn oil at doses of 0, 75, 250, or 750 mg/kg-day from GD 6 through PND
10. Dams were allowed to give birth naturally. From each replicate, 10 litters were selected for
testing and 1 other as an alternate for each dose (i.e., there were a total of 20 litters and 2
alternates selected for each dose). Preference was given to larger litters (eight or more pups)
with 4:4 or 5:3 sex ratios. Litters were culled to eight pups (four males and four females, if
possible) on PND 4. Dams were monitored for body weight and examined for neurobehavioral
signs throughout gestation and lactation. All pups were monitored for mortality and body weight
and examined for neurobehavioral signs throughout lactation. Subsets of pups from each litter
were evaluated periodically for physical maturation milestones (pinna detachment, incisor
eruption, eye opening, and testes descent/vaginal opening), motor activity, auditory brainstem
response, functional observational battery (handheld and open field observations and grip
performance test), learning and memory (delayed matching to position test), brain weight and
size (days 28 and 62), or neuropathology (days 28 and 62). No treatment-related effects were
seen in any parameter monitored in dams or pups, making 750 mg/kg-day a NOAEL for both
dams and pups in this study.
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4.3.2. Inhalation Exposure
Groups of 23 Sprague-Dawley rats and 13 Swiss Webster mice were exposed to 0 or
875 ppm (4780 mg/m3) 1,1,1-trichloroethane (94.52% pure) by inhalation for 7 hours/day on
GDs 6-15 (Schwetz et al., 1975). Maternal rats and mice were sacrificed on GDs 21 and 18,
respectively. Study parameters included maternal food consumption, body weight and liver
weight; numbers of live, dead, and resorbed fetuses and litters; fetal weight, length, and sex
ratio; and external (all fetuses), visceral (one half of fetuses), and skeletal (remaining fetuses)
anomalies. A slight (5%) increase in absolute, but not relative, liver weight was reported in
treated rat dams. No other effects were found in rat or mice dams or pups. The 875 ppm
(4780 mg/m3) level is a NOAEL for developmental effects.
York et al. (1982) exposed four groups of 30 Long-Evans hooded rats to 0 or 2100 ppm
(11,470 mg/m3) 1,1,1-trichloroethane (purity not reported) for 6 hours/day for 2 weeks prior to
mating (5 days/week) and throughout pregnancy (7 days/week) until GD 20 in a 2 x 2 factorial
design: (1) 1,1,1-trichloroethane before mating and during pregnancy, (2) 1,1,1-trichloroethane
before mating only, (3) 1,1,1-trichloroethane during pregnancy only, and (4) filtered air before
and during pregnancy. Half of the dams in each group were sacrificed on GD 21, and the
remaining dams were used for postnatal evaluations. Study parameters included maternal food
consumption, body weight, and liver weight; numbers of live, dead, and resorbed fetuses and
litters; fetal weight and sex ratio; external (all fetuses from sacrificed dams), visceral (four
fetuses/litter), and skeletal (four fetuses/litter) anomalies; postnatal body weights (litters at age
10 days and individual offspring at 20-day intervals from weaning to age 320 days) and gross
pathology (dams after weaning, offspring at age 12 months); and offspring neurobehavior (open-
field activity at age 21 days, running wheel activity at age 40-110 days, and amphetamine
challenge at age 110-120 days). No signs of maternal toxicity were observed in any group.
A very slight (<5%), but statistically significant, reversible decrease in fetal body weight was
found in groups 1 and 3, in comparison with groups 2 and 4 by ANOVA. There were no
significant differences in pup weight at birth (6.0, 5.8, 5.9, and 5.8 g for groups 1, 2, 3, and 4,
respectively). Overall incidences of skeletal and soft tissue anomalies were significantly
increased in group 1 (see Table 4-5), but specific types of anomalies were not increased and the
anomalies seen were considered indicative of reversible developmental delay (e.g., delayed
ossification). Postnatal evaluation revealed no effects on neurobehavioral development (as
measured by open-field activity, running wheel activity, and amphetamine challenge) or gross
lesions. The tested concentration of 2100 ppm (11,470 mg/m3) is considered a NOAEL for both
maternal and developmental toxicity in this study.
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Table 4-5. Incidence of anomalies in fetal rats after maternal exposure to
l,l?l-trichloroethane
Findings
Total skeletal anomalies
Total soft tissue anomalies
Number of affected fetuses (number of affected litters)3
Group 1
19 (8)b
6(6)c
Group 2
8(4)
2(2)
Group 3
1(1)
1(1)
Group 4
5(4)
0(0)
aGroup 1: exposure before mating and during pregnancy; Group 2: exposure before mating only; Group 3: exposure
during pregnancy only; Group 4: control.
bStatistically significant effect Group 1 >2,3,4.
Statistically significant effect Group 1 >4.
Source: York etal. (1982).
Subsequent studies found evidence of mild fetotoxicity at higher levels producing overt
effects in the dams. Groups of 30 timed-pregnant female Sprague-Dawley rats were exposed to
0, 1000, 3000, or 6000 ppm (0, 5460, 16,380, or 32,760 mg/m3) 1,1,1-trichloroethane
6 hours/day on GDs 6-15 (Bushy Run Research Center [BRRC], 1987a). The dams were
observed daily for clinical signs and weighed and monitored for food and water consumption
periodically during gestation. On GD 21, the dams were sacrificed for internal examination. All
live fetuses were examined for external and skeletal malformations, while half from each litter
were processed and examined for visceral malformations. No females died, delivered early,
aborted, or were removed from the study. The pregnancy rate was similar in all groups, so that
each group contained 22-25 litters. Maternal body weight gain over the entire gestation period
was significantly reduced in all treated groups, but maternal body weight was statistically less
than controls only in the 6000 ppm (32,760 mg/m3) group and only during the postexposure
phase of gestation. Food intake was significantly reduced in all groups during exposure and after
the end of exposure in the 3000 and 6000 ppm (16,380 and 32,760 mg/m3) groups. Water intake
was significantly increased during and after exposure in the 6000 ppm group. The only clinical
signs associated with treatment were perioral wetness and hypoactivity in the 6000 ppm
(32,760 mg/m3) dams. Necropsy revealed no treatment-related lesions in the dams. Gravid
uterine weight was significantly reduced in both the 3000 and 6000 ppm (16,380 and
32,760 mg/m3) groups. The decrease in gravid uterine weight in the 6000 ppm (32,760 mg/m3)
dams was apparently responsible for the decrease in body weight in this group, as the corrected
body weights (terminal body weight minus gravid uterine weight) did not differ from controls.
Absolute and relative liver weights were similar to controls in all groups. Gestational parameters
were unremarkable; slight decreases in corpora lutea/dam, total implants/litter, and viable
implants in the 6000 ppm (32,760 mg/m3) group were not considered treatment related since
ovulation occurred prior to the start of exposure and percent preimplantation loss, number of
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nonviable implants per litter (early or late resorptions or dead fetuses), and percent live fetuses
were all unaffected. Fetal body weight was significantly reduced by 6% for female fetuses in the
6000 ppm (32,760 mg/m3) group; decreases for male fetuses and all fetuses (about 4%) were not
statistically significant. No increases in fetal malformations were associated with treatment, but
significant increases (on a per litter basis) were seen for two fetal skeletal variations, nonossified
cervical centrum 6 and poorly ossified cervical centrum 7, in the 6000 ppm (32,760 mg/m3)
group, suggesting slight developmental delay at this concentration. This study identified a
NOAEL of 3000 ppm (16,380 mg/m3) and a LOAEL of 6000 ppm (32,760 mg/m3) for mild
fetotoxicity manifested by delayed cervical ossification and decreased body weights of female
fetuses. Maternal effects were also seen at the 6000 ppm level (32,760 mg/m3), including
hypoactivity and reductions in food consumption, body weight gain, body weight, and gravid
uterine weight.
In a companion study in rabbits, groups of 24 timed-pregnant New Zealand white rabbits
were exposed to 0, 1000, 3000, or 6000 ppm (0, 5460, 16,380, or 32,760 mg/m3) of
1,1,1-trichloroethane 6 hours per day on GDs 6-18 (BRRC, 1987b). Sacrifice for internal
examination occurred on GD 29. All live fetuses were examined for external and visceral
malformations; half from each litter were also processed and examined for skeletal
malformations. The pregnancy rate was high and not affected by treatment, so that 20-22 gravid
females were available in all groups. Several litters from multiple groups (including five from
the 1000 ppm [5460 mg/m3] group) were completely resorbed before scheduled sacrifice, leaving
16-21 litters in all groups. Does in the 3000 and 6000 ppm (16,380 and 32,760 mg/m3) groups
lost weight during the exposure period and had reduced body weight gain for the gestation
period as a whole, although body weights were not significantly affected at any time during the
study. Clinical signs were unremarkable. Necropsy revealed no treatment-related lesions, and
there were no treatment-related changes in gravid uterine weight or absolute or relative liver
weight. Gestational parameters were not altered by treatment. Slight, statistically significant
decreases in total implants per litter and viable implants in the 6000 ppm (32,760 mg/m3) group
were due to a nonsignificant decrease in corpora lutea per doe but were not accompanied by
increases in preimplantation loss or nonviable implants (early or late resorptions or dead fetuses)
or a decrease in percent live fetuses. Fetal body weights were similar in all groups. No increases
in fetal malformations were associated with treatment, but there was a statistically significant
increase (on a per litter basis) in the incidence of a supernumerary (13th) rib, a common skeletal
variation, in the 6000 ppm (32,760 mg/m3) group. This study identified a NOAEL of 3000 ppm
(16,380 mg/m3) and LOAEL of 6000 ppm (32,760 mg/m3) for mild fetotoxicity manifested by
increased incidence of a supernumerary (13th) rib. Reduced maternal weight gain was also
observed at the 6000 ppm (32,760 mg/m3) level.
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Jones et al. (1996) used two different exposure protocols to study the effects of late
gestational exposure to 1,1,1-trichloroethane. In the first experiment, groups of 10 timed-
pregnant CD-I mice were exposed to 0 (both sham-exposed to air and untreated groups) or
2000 ppm (10,920 mg/m3) 1,1,1-trichloroethane vapor, 17 hours/day, on GDs 12-17. In the
second experiment, groups of 12 timed-pregnant CD-I mice were exposed for 60 minutes,
3 times/day, to 0 (sham exposed) or 8000 ppm (43,680 mg/m3) 1,1,1-trichloroethane on GDs 12-
17. Dams in the second experiment only were semi quantitatively scored on a subset of tests
from a functional observational battery for neurobehavioral toxicity testing after the first
exposure each day. Dams in both experiments were allowed to give birth. After litter data were
collected, litters were culled to four of each sex (litters with less than seven pups were
discarded). Litters in the first experiment were fostered to surrogate mothers who had delivered
within 24 hours of the experimental dams. Fostering was not employed in the second
experiment. Pups in both experiments were observed for physical development and tested for
reflex development (righting and rooting reflexes), forelimb grip strength, motor coordination
(negative geotaxis and inverted screen tests), and spontaneous activity. Tests and observations
were conducted through PND 14 in the first experiment and PND 21 in the second experiment.
Some pups in the second experiment were retained until 85 days of age and tested for learning
and memory (one-trial passive avoidance conditioning).
Dams in the second experiment were nearly anesthetized during exposure, and the
observational battery revealed both gait abnormalities (splayed hindlimbs, severe sway, ataxia)
and clonic movements (mild tremors) that were not seen in controls (Jones et al., 1996). In
neither experiment was there any effect on maternal weight gain, number of litters, gestation
length, litter size, or number of live male or female pups per litter. Litter weight was about 15%
lower than in controls in both experiments, but the differences were not statistically significant.
Pup body weight was significantly reduced throughout most of the postnatal observation period
in both experiments, and, in both, significant delays were seen for attainment of all three
developmental landmarks monitored (pinnae detachment, incisor eruption, and eye opening).
Behavioral test results were similar in both experiments, with statistically significant impaired
performance in tests for righting reflex, rooting reflex (experiment 2 only), forelimb grip
strength, negative geotaxis, and inverted screen climbing (experiment 1 only). Spontaneous
motor activity was not altered by treatment, and there was no effect in the passive avoidance
conditioning test in experiment 2. This study found developmental delay and neurobehavioral
deficits in offspring exposed to 2000 ppm (10,920 mg/m3) for 17 hour/day, GDs 12-17, a
concentration that did not produce obvious maternal toxicity (although a systematic investigation
of behavioral effects in these dams was not conducted).
Coleman et al. (1999) reported the results of a similar study in rats. Mated female
Sprague-Dawley rats were exposed to 0 (sham air and untreated controls) or 7000 ppm
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(38,220 mg/m3) 1,1,1-trichloroethane for 60 minutes, three times per day, on GDs 13-19. There
were 9 pregnant dams in the treated group, 10 in the air-exposed controls, and 19 in the untreated
controls, which also served as foster dams for the treated pups. Dams were monitored for body
weight and food and water intake daily throughout gestation. After each exposure period, dams
were scored on an abbreviated functional observational battery. Dams were allowed to litter.
After litter data were collected (24 hours after birth), litters were culled to five of each sex. All
litters were fostered to surrogate mothers from the untreated control group, who had given birth
within 24 hours of the treated dams. The exposed dams were sacrificed and their uteri inspected
for implantation sites and resorptions. Pups were observed for physical development (body
weight and dates of pinnae detachment, incisor eruption, and eye opening) and tested for righting
reflex, coordination (negative geotaxis and inverted screen tests), muscle strength (vertical
screen and forelimb grip tests), and spontaneous motor activity through PND 21. Two pups from
each litter were sacrificed on PND 22 for determination of brain weights.
Maternal weight gain was significantly reduced during the exposure period in the treated
group, but the difference from controls over the whole gestation period was not statistically
significant (Coleman et al., 1999). There was also a trend for reduced food consumption in
treated rats, although the difference from controls was not statistically significant. Water
consumption was similar in the control and treated groups. The assessment of dam behavior
immediately after exposure revealed salivation, lacrimation, and abnormal gait (ataxia, body
dragging, splaying of hindlimbs) in the treated dams, none of which were observed in controls.
Of the nine treated dams, only seven produced offspring, as two completely resorbed their litters.
The treated group showed significant increases in gestation length, resorptions per litter (based
on either all litters or live litters), and mortality index ([number stillbirths + number
resorptions]/[number implantation sites]) and significant decreases in number of live pups per
litter (total and for each sex, based on either all litters or live litters) and litter weight. Pup birth
weight did not differ between the groups. Postnatal pup body weights were slightly reduced
compared to those of controls on PNDs 2-14 but not subsequently. Attainment of
developmental milestones was not delayed in the treated rats. In the behavioral tests, the treated
pups showed significant deficits in coordination (both negative geotaxis and inverted screen
tests) and muscle strength (both vertical screen and forelimb grip tests) and reduced spontaneous
ambulatory activity. Righting reflex was not affected. Body weight was significantly lower in
the treated rats used for brain weight measurements than in controls (13% deficit). Both absolute
(31% deficit) and relative (21% deficit) brain weight were significantly reduced in the treated
group, as was absolute cerebellar weight (25% deficit). This study found gross neurological
effects in dams, increased resorptions and decreased live pups per litter, and pup neurobehavioral
deficits in rats exposed to 7000 ppm (38,220 mg/m3) intermittently during the late gestational
period.
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4.4. OTHER ENDPOINT-SPECIFIC STUDIES
4.4.1. Neurological Effects
The acute neurological effects of 1,1,1-trichloroethane parallel those of the group of
volatile organic solvents (VOCs). As a group, VOCs produce depression of the CNS and are, in
general, capable of producing anesthesia. As the concentration of the VOC increases, the
relative concentration of oxygen in the inspired air may decrease, with the effect that the VOC
acts as an asphyxiant. A number of the more potent VOCs have been used to produce surgical
anesthesia. Sufficient neurological impairment can be observed at subanesthetic levels,
producing behavioral impairment such as unsteadiness, inability to concentrate, impaired motor
coordination, or decrements in motor or intellectual function. To a large extent, the time
necessary to produce anesthesia is directly related to the blood/gas partition coefficient, which
determines how readily the VOC will partition into the blood. The rapidity of development of
CNS effects almost ensures that the acute behavioral/narcotic effect of the solvent is due to the
solvent itself and not a metabolite, and the similarity of narcosis produced by solvents of diverse
structure suggests that the effects result from a physical interaction of the solvent with cells of
the CNS (Snyder and Andrews, 1996).
4.4.1.1. Oral Exposure
Limited information is available regarding neurological effects of 1,1,1-trichloroethane in
animals following oral exposure. Rats that were treated with 705 mg/kg-day of
1,1,1-trichloroethane by gavage for 2 days did not show any changes in behavior or appearance
that could be detected by a functional observational battery, although neurophysiological testing
performed after exposure for 4 days showed some alterations (Spencer et al., 1990).
Neurophysiological effects included marked flash-evoked potential (FEP) and EEG changes and
smaller alterations in somatosensory-evoked potential (SEP) and were similar to effects observed
after inhalation exposure to 2000 ppm for 4 days (see Section 4.4.1.2). No significant changes in
tissue levels of monoamine neurotransmitters and metabolites in the brain were found in rats
given a single oral dose of 3250 mg/kg of 1,1,1-trichloroethane and sacrificed 2 hours later
(Kanada et al., 1994).
4.4.1.2. Inhalation Exposure
The CNS-depressant effects of inhaled 1,1,1-trichloroethane are well known. The effects
range from subtle behavioral effects at relatively low concentrations to unconsciousness at very
high concentrations. Human data regarding neurological effects of 1,1,1-trichloroethane were
presented in Section 4.1. Animal studies support the results of the human studies.
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Increasingly serious signs of CNS depression preceded 1,1,1-trichloroethane-associated
lethality in acute animal inhalation studies. The progression of effects with increasing
concentration and duration of exposure in rats was described by Adams et al. (1950). At
5000 ppm (27,300 mg/m3), there was a decreased tendency to move about the chamber and a
reduced resistance to handling within an hour. At 10,000 ppm (54,600 mg/m3), effects
progressed from a markedly reduced tendency to move about the chamber after a few minutes, to
weakness and ataxia after 10 minutes, to irregular respiration and semiconsciousness after
3 hours, and, in some cases, to death. Similar effects occurred more rapidly at higher
concentrations. Clark and Tinston (1982) observed that death followed a progression from slight
ataxia to loss of righting reflex, loss of movement, narcosis, and shallow respiration in rats.
These researchers estimated an ECso in rats for CNS depression of 5000 ppm (27,300 mg/m3) for
a 10-minute exposure. Moser and Balster (1985) reported that signs of CNS depression in mice
exposed to high concentrations in lethality studies progressed from excitability and hyperactivity
to lethargy and complete cessation of activity, with shallow, rapid breathing indicating imminent
death. Effects indicative of CNS depression were also found in other lethality studies (Calhoun
et al., 1988; Woolverton and Balster, 1981; Bonnet et al., 1980; Gehring, 1968; Lazarew, 1929).
Studies designed specifically to investigate the effects of 1,1,1-trichloroethane on the CNS are
discussed below.
The neurobehavioral effects of 1,1,1-trichloroethane in laboratory animals have been
studied extensively following acute inhalation exposure. Observed effects include increased
motor activity (Wiley et al., 2002; Warren et al., 2000; Bowen and Balster, 1998, 1996; Albee et
al., 1990a; Kjellstrand et al., 1990, 1985b; Horiguchi and Horiuchi, 1971), reduced response rate
in operant behavior tests (Bowen and Balster, 1998; Bowen et al., 1998; Warren et al., 1998,
1997; You et al., 1994; Moser and Balster, 1986; Moser et al., 1985; Balster et al., 1982; Geller
et al., 1982; Mullin and Krivanek, 1982; Woolverton et al., 1982), impaired performance in
functional observational battery and similar tests (Paez-Martinez et al., 2001; Balster et al., 1997;
Bowen et al., 1996a,b; Moser and Balster, 1985; de Ceaurriz et al., 1983; Mullin and Krivanek,
1982; Woolverton and Balster, 1981), effect on anxiety-like actions (burying behavior) (Paez-
Martinez et al., 2003), and reduced response to induced seizures (Frantik et al., 1994; de
Ceaurriz et al., 1981).
Increases in motor activity were observed at concentrations as low as 1000 ppm
(5460 mg/m3) in acute animal studies. Horiguchi and Horiuchi (1971) found increased wheel-
turning activity in male mice exposed to 1000 ppm (5460 mg/m3) of 1,1,1-trichloroethane
2 hours/day, every other day, for nine exposures but did not test other concentrations. There was
no effect on open-field activity of male Sprague-Dawley rats exposed to 500 ppm (2730 mg/m3)
of 1,1,1-trichloroethane vapor 6 hours per day for 4 consecutive days (recorded 1 and 17 hours
after the 4-day exposure) (Savolainen et al., 1977). For a 1-hour exposure, Kjellstrand et al.
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(1985b) reported a slight increase in motor activity at 2000 ppm (10,920 mg/m3) and no effect at
1300 ppm (7100 mg/m3) in male mice. Bowen and Balster (1996) saw concentration-related
increases in motor activity in male mice (30-minute exposure) that were statistically significant
at 2500 ppm (13,650 mg/m3) (NOAEL = 1250 ppm [6830 mg/m3]) in a static exposure system
and 1250 ppm (6830 mg/m3) (NOAEL = 500 ppm [2730 mg/m3]) in a dynamic exposure system.
These researchers also found that motor activity decreased back towards or even under control
levels at very high concentrations (>10,000 ppm [54,600 mg/m3]). The biphasic nature of
1,1,1-trichloroethane's effect on motor activity was noted in other studies as well (Wiley et al.,
2002; Warren et al., 2000; Bowen and Balster, 1998). A study that directly compared sensitivity
of motor activity vs. operant behavior as an endpoint for 1,1,1-trichloroethane toxicity found
both endpoints to be equally sensitive in adult male mice exposed for 30 minutes (Bowen and
Balster, 1998). In male mice exposed to 1,1,1-trichloroethane at 2000, 6000, 10,000, or
13,300 ppm (10,920, 32,760, 54,600, or 72,620 mg/m3), 0.5 hours/day for 15 consecutive days
and tested using locomotor activity as well as functional observational battery (FOB), Bowen
and Balster (2006) found that both tolerance and sensitization occurred with repeated exposure,
with concentration primarily affecting the magnitude of the change and not whether tolerance or
sensitization occurred.
The most sensitive measure of effect on operant behavior was obtained in baboons. Four
juvenile male baboons trained in a match-to-sample discrimination task were exposed for 4 hours
to 0, 700, 1400, 1800, or 2100 ppm (0, 3820, 7640, 9830, or 11,470 mg/m3) of
1,1,1-trichloroethane (Geller et al., 1982). Although there was no effect on error rate at any
concentration, there was a marked significant decrease in number of trials attempted and a
significant increase in response time at > 1800 ppm (9830 mg/m3), with no difference from
controls at 700 or 1400 ppm (3820 or 7640 mg/m3). The same effects were seen at 1200 ppm
(6550 mg/m3) when the baboons were exposed at that concentration continuously for 7 days. No
other concentrations were tested in the 7-day study. In rodent studies, the lowest level reported
to produce decreases in operant task response rates was 2000 ppm (10,920 mg/m3) for exposure
durations ranging from 20-100 minutes (Bowen et al., 1998; Warren et al., 1998, 1997; Balster
et al., 1997, 1982). The no-effect level was 1000 ppm (5460 mg/m3) in all of these studies.
1,1,1-Trichloroethane impaired performance in various nonconditioned neurobehavioral
tests at concentrations as low as 2000 ppm (10,920 mg/m3). In the most sensitive of these, de
Ceaurriz et al. (1983) reported significant, concentration-related decreases in the duration of
immobility in male mice subjected to a 3-minute behavioral despair swimming test after 4 hour
exposure to 2064-3569 ppm (11,270-19,490 mg/m3). Lower concentrations were not tested.
Bowen et al. (1996b) demonstrated significant increases in open arm entries in an elevated plus-
maze by male mice exposed to >2500 ppm (13,650 mg/m3) for 30 minutes. At higher
concentrations, the time spent in open arms also increased. No lower concentrations were tested.
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Similar effects were reported by Paez-Martinez et al. (2001), although only concentrations
greater than 4000 ppm (21,840 mg/m3) were included in this study. Studies that included tests of
both conditioned behavior and FOB differed on the relative sensitivity of the assays. Mullin and
Krivanek (1982) found no effects in a general behavior screen (FOB) in male rats exposed to
1500 ppm (8190 mg/m3) for 4 hours but increasing failures at concentrations of 3000 to
12,000 ppm (16,380 to 65,520 mg/m3). This screen was more sensitive than the conditioned
avoidance test performed in the same study, which found effects only at >6000 ppm
(32,760 mg/m3). This is in contrast to the results of Balster et al. (1997), who found effects on
conditioned behavior at >2000 ppm (10,920 mg/m3) and effects on FOB only at >8000 ppm
(43,680 mg/m3).
The reduction in response to induced seizures may be more sensitive than other
behavioral measures of effect for 1,1,1-trichloroethane. Frantik et al. (1994) measured
neurophysiological response to electrical shock in male Wistar rats exposed for 4 hours and
female H strain mice exposed for 2 hours to air or 1,1,1-trichloroethane at various
concentrations. The concentrations estimated to produce a 30% depression in seizure discharge
(specifically, duration of tonic extension of hindlimb in rats and velocity of tonic extension in
mice) were 734 ppm (4000 mg/m3) in rats and 1810 ppm (9880 mg/m3) in mice. Effect on
seizure response was considerably less sensitive as a measure of 1,1,1-trichloroethane effect in
mice exposed to the chemical for 4 hours and given penetrazole to induce clonic convulsions
(de Ceaurriz et al., 1981). The concentration estimated to produce a 50% increase in seizure
threshold was 6644 ppm (36,280 mg/m3).
The CNS-depressant effects of 1,1,1-trichloroethane appear to be similar to those of
several other known CNS depressant chemicals, including ethanol and pentobarbital. Studies in
mice trained to lever press in response to exposure to pentobarbital, ethanol, diazepam, and
phencyclidine show that mice do not discriminate among the effects of 1,1,1-trichloroethane and
those of the former three chemicals but do discriminate between 1,1,1-trichloroethane and
phencyclidine. For example, Rees et al. (1987a,b) trained mice to press one lever in response to
ethanol (or pentobarbital) and another in response to a saline injection. Following a 20-minute
exposure to 1,1,1-trichloroethane, there was a concentration-dependent increase in the
percentage of time mice pressed the ethanol (or pentobarbital) lever, indicating that mice were
generalizing the effects of ethanol (or pentobarbital) to those of 1,1,1-trichloroethane. The EC50
was 850 ppm (4640 mg/m3) for mice to generalize from 1,1,1-trichloroethane to ethanol (1 g/kg)
and 2876 ppm (15,700 mg/m3) to generalize to pentobarbital (15 mg/kg) (Rees et al., 1987a,b).
1,1,1-Trichloroethane partially substituted for diazepam (67% at the maximum concentration of
16,000 ppm [87,360 mg/m3]) but did not substitute for phencyclidine at any concentration
(Bowen et al., 1999). In contrast to some other CNS depressants, there is little evidence of
animals developing tolerance to 1,1,1-trichloroethane with continued exposure. Moser et al.
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(1985) observed only slight attenuation of response suppression with repeated exposure to
1,1,1-trichloroethane (6000 ppm [32,760 mg/m3], 20 minutes/day, 4 days/week for 4 weeks) in
mice trained in an operant conditioning task. Kjellstrand et al. (1990) followed the time course
of motor activity during exposure and found that the increase in motor activity induced by
5000 ppm (27,300 mg/m3) 1,1,1-trichloroethane in mice remained relatively constant throughout
a 3-hour exposure period, in contrast to some other solvents that produced an initial increase that
subsequently returned to preexposure levels even while exposure continued. It has also been
shown that withdrawal symptoms occur in mice exposed to 1,1,1-trichloroethane for a period of
time and abruptly removed from exposure (Balster et al., 1997; Evans and Balster, 1993). Mice
exposed continuously for 4 days to concentrations of 500, 1000, 2000, or 4000 ppm (2730, 5460,
10,920, or 21,840 mg/m3) and then removed from exposure showed a concentration-related
increase in incidence and severity of handling-induced convulsions at all concentrations through
24 hours postexposure. No such convulsions were seen in controls at any time. The effects were
mitigated by reexposure to 1,1,1-trichloroethane or exposure to some other known depressants.
A few studies have investigated neurophysiological effects of 1,1,1-trichloroethane in
laboratory animals. EEG, FEP, and SEP were evaluated in F344 rats exposed to 0, 1000, or
2000 ppm (0, 5460, or 10,920 mg/m3) of 1,1,1-trichloroethane for 6 hours/day on 4 consecutive
days and tested before and immediately after exposure on the fourth day (Albee et al., 1990b).
Significant differences from control in EEG, FEP, and SEP were produced by
1,1,1-trichloroethane at both exposure conditions in a dose-related fashion. Hougaard et al.
(1984) also observed depression of EEG activity by 1,1,1-trichloroethane in anesthetized male
Wistar rats exposed to 7400 ppm (40,400 mg/m3) for 60 minutes. Other findings in these
animals were decreased blood pressure and increased cerebral blood flow throughout the brain.
These investigators also exposed unanesthetized rats to 0, 3500, 6000, or 7800 ppm (19,110,
32,760, or 42,590 mg/m3) for up to 2 hours. They found no effects at 3500 ppm (19,110 mg/m3);
noticeable intoxication, increased cerebral blood flow throughout the brain, and decreased local
glucose consumption in 10/24 brain regions at 6000 ppm (32,760 mg/m3); and ataxia and
decreased arterial blood pressure at 7800 ppm (42,590 mg/m3).
1,1,1-Trichloroethane has been observed to have neurochemical effects. The most
sensitive neurochemical change reported was decreased cyclic guanosine monophosphate
(cGMP) in the cerebellum of male mice exposed to 100 ppm (550 mg/m3) or more of
1,1,1-trichloroethane for 4 hours, with no effect at 70 ppm (380 mg/m3) (Nilsson, 1986a). cGMP
was also decreased in the cerebral cortex and brain stem at higher concentrations in this study.
Large (>50%) significant decreases in cGMP in cerebellum and medulla oblongata and smaller
decreases in cerebral cortex were seen in male CD-I mice exposed for 40 or 100 minutes to
5000 ppm (27,300 mg/m3) of 1,1,1-trichloroethane (You and Dallas, 2000). The same study also
showed significant decreases in cGMP in cerebellum, cortex, and hypothalamus (but not
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medulla) in male Sprague-Dawley rats exposed by the same protocol. In contrast to these
results, no effect on cortical cGMP was seen in anesthetized male Wistar rats exposed to
8000 ppm (43,680 mg/m3) of 1,1,1-trichloroethane for 5 or 60 minutes (Folbergrova et al.,
1984). However, cyclic adenosine monophosphate (cAMP) in the cerebral cortex was slightly
reduced at both time points in the Folbergrova et al. (1984) study. Nilsson (1986b) also
observed a slight reduction in cortical cAMP, with no effect on cAMP in cerebellum or
hippocampus, and a significant increase in cAMP in brain stem in male mice exposed to
1010 ppm (5500 mg/m3) or more for 4 hours. Cyclic nucleotides act as intracellular signal
transducers in nerve cells, and a change in levels of these molecules presents a potential
mechanism by which 1,1,1-trichloroethane could affect neurological function.
Other neurochemical changes were also noted in anesthetized male Wistar rats exposed
to 8000 ppm (43,680 mg/m3) of 1,1,1-trichloroethane for 5 or 60 minutes (Folbergrova et al.,
1984), including significant, reversible increases in lactate (-46% over control) and pyruvate
(20-40% over control) and citric acid cycle intermediates (all less than twofold increase over
control) in the cerebral cortex (without corresponding changes in the blood). The researchers
suggested these changes were consistent with stimulation of glycolysis (or possibly inhibition of
pyruvate oxidation) and moderate tissue hypoxia. Continuous exposure to 1200 ppm (6550
mg/m3) of 1,1,1-trichloroethane vapor in the air for 30 days had no effect on body or brain
weight or lipid class composition of the cerebral cortex in male Sprague-Dawley rats but did
produce slight, statistically significant changes in the fatty acid pattern of cerebral cortex
ethanolamine phosphoglyceride (Kyrklund and Haglid, 1991, 1990). The effect on fatty acid
pattern was not seen at 320 ppm (1750 mg/m3) (Kyrklund et al., 1988). The toxicological
significance of the observed change in fatty acid pattern is unclear; the researchers considered it
most likely to reflect an adaptive response to the altered local physiochemical environment
(Kyrklund and Haglid, 1991).
Several subchronic studies of 1,1,1-trichloroethane have specifically investigated
neurological endpoints in exposed animals (Mattsson et al., 1993; Karlsson et al., 1987;
Rosengren et al., 1985). In the Rosengren et al. (1985) study, groups of four male and four
female Mongolian gerbils were continuously exposed to 0, 70, 210, or 1000 ppm (0, 380, 1150,
or 5460 mg/m3) of 1,1,1-trichloroethane for 3 months. The control animals were sex-matched
littermates. All animals were sacrificed 4 months postexposure for assessment of brain weight
(total and cerebral cortex frontal, middle [sensorimotor], and dorsal [occipital] regions) and
regional biochemical alterations in the cerebral cortex. Brain histology and neurobehavioral
endpoints were not evaluated. The brain biochemical analyses consisted of determinations of
total protein and two astroglial protein (S-100 protein and glial fibrillary acidic protein [GFAP])
concentrations. No deaths occurred during the study, and no effects on body weight were found
at the end of the exposure or postexposure periods. Brain weight was significantly (p < 0.01)
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reduced in the 1000 ppm (5460 mg/m3) group, although the difference from controls was slight
(2.5% reduction). Significantly increased concentrations of GFAP were found in the
sensorimotor cerebral cortex following exposure to 210 ppm (1150 mg/m3) (-33%, estimated
from graph, p < 0.01) and 1000 ppm (5460 mg/m3) (~ 38%,/? < 0.01). GFAP levels were not
increased in the frontal cerebral cortex or the occipital cerebral cortex. Brain S-100 protein
concentrations were statistically significantly decreased (-9%) in the frontal cerebral cortex at
210 ppm but not in any other brain regions or at other exposure concentrations, and total protein
concentrations were statistically significantly decreased only in the sensorimotor cerebral cortex
(-8%) at 210 ppm (1150 mg/m3). GFAP is the main protein subunit of astroglial filaments and is
used by neurobiologists as a marker for demonstrating formation of astroglial fibrils in response
to brain injury. Increase in GFAP, therefore, is associated with astrogliosis and some insult to
the CNS, and the findings of this study indicate that the sensorimotor cerebral cortex was
affected by 1,1,1-trichloroethane. S-100 protein is also used as a marker for astroglial cell
increase in response to brain injury but is found in both protoplasmic and fibrillary astrocytes.
The authors speculated that the failure to observe an increase in S-100 could have been due to a
shift from protoplasmic to fibrillary astrocytes in response to 1,1,1-trichloroethane exposure,
although other studies have shown that similar compounds (trichloroethylene and
tetrachloroethylene) produced increases in S-100 as well as GFAP (Rosengren et al., 1985).
Based on increased GFAP, indicating brain astrogliosis, in gerbils following continuous
exposure, the NOAEL and LOAEL for CNS effects are 70 and 210 ppm (380 and 1150 mg/m3),
respectively.
A related study was conducted in which groups of six male and six female Mongolian
gerbils were continuously exposed to 0 or 70 ppm (380 mg/m3) commercial grade
1,1,1-trichloroethane (containing 5% dioxane-free stabilizers) for 3 months, followed by a
4-month exposure-free period, ending with sacrifice (Haglid et al., 1990; Karlsson et al., 1987).
Study endpoints included body weight and total and regional brain weight, brain protein, and
brain DNA concentrations; brain histology and neurobehavioral endpoints were not evaluated.
DNA concentration was used as a measure of cell density. Exposure to 70 ppm significantly
reduced DNA concentrations in three of nine brain areas investigated (posterior cerebellar
hemisphere, anterior cerebellar vermis, and hippocampus), although not the sensorimotor
cerebral cortex affected in the study by Rosengren et al. (1985). The reduction in DNA content
in these areas could reflect a decrease in cell density, possibly as a result of cell death and/or
inhibition of nonneuronal cell acquisition, although other interpretations are possible. Because
the toxicological significance of reduced DNA content and reliability of it as a biomarker are
unclear, the 70 ppm (380 mg/m3) level is not characterized as a NOAEL or LOAEL.
Neurobehavioral effects of 1,1,1-trichloroethane (99.9% pure, containing 0.1% butylene
oxide stabilizer) were evaluated in groups of 14 male and 14 female F344 rats (-16 weeks old)
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that were exposed to 0, 200, 630, or 2000 ppm (1090, 3440, and 10,920 mg/m3) for 6 hours/day,
5 days/week for 13 weeks (Mattsson et al., 1993). This study was conducted in response to
special neurotoxicity testing required by the U.S. EPA Interagency Testing Committee. Body
weight was measured weekly, clinical observations were performed twice daily, and detailed
physical examinations were performed weekly. FOB and hind- and forelimb grip performance
testing were conducted on all rats prior to the start of exposure, monthly during the study, and
65 or more hours after the end of the 13-week exposure period. Behavioral testing during the
study was conducted before the daily exposure period and, therefore, approximately 16 hours
after the end of the previous exposure. An electrophysiological test battery was conducted on
12 rats/sex/exposure level after 13 weeks of exposure (tests conducted 65 or more hours after the
end of exposure); this included FEP, cortical flicker response, auditory brainstem responses,
SEPs, and caudal nerve action potentials. Following the electrophysiological testing, animals
were necropsied for measurement of brain weight (five/sex/level) and neurohistopathology
assessment (five rats/sex in the 0 and 2000 ppm [10,920 mg/m3] groups). The neurohistological
examinations were comprehensive and included brain (10 areas), trigeminal ganglion and nerve,
eyes, spinal cord and nerve roots, dorsal root ganglia and peripheral nerves, and skeletal muscles.
Tissues from rats exposed to 200 or 630 ppm (1090 or 3440 mg/m3) were not examined due to
lack of treatment-related histological findings at 2000 ppm (10,920 mg/m3). The remaining rats
were held for 7 weeks postexposure, retested for grip performance, and examined for
histopathology of forelimb muscles and nerves.
The only notable findings were slight, statistically significant deficits in forelimb grip
performance in both sexes (-9% and -20% lower than controls in males and females,
respectively) of the 2000 ppm (10,920 mg/m3) group at exposure week 13 (but not before) in
comparison with concurrent controls at the same time point (Mattsson et al., 1993). The deficits
were not statistically significant in a more rigorous statistical treatment designed to take into
account the observed changes over time in the control and treated groups. Forelimb grip
performance in 2000 ppm rats was also significantly less than controls at postexposure week 7 in
comparison with concurrent controls, but this was due to an increase in control performance at
this time point in comparison to preexposure values. Forelimb grip performance in 2000 ppm
males and females at 7 weeks postexposure was improved in comparison to exposure week 13,
and roughly similar to preexposure performance levels. Hindlimb grip performance was not
affected at any time point, and the histopathological, electrophysiological, and FOB studies
found no supporting evidence consistent with a performance deficit in forelimb grip performance
(e.g., forelimb neuropathy). The investigators hypothesized that sedative properties of
1,1,1-trichloroethane may have been responsible for the effect on forelimb grip performance, but
this is unlikely since the sedative effects of 1,1,1-trichloroethane wear off quickly and the grip
tests were conducted well after the end of the previous exposure. This study, therefore, provides
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only weak evidence for a neurotoxic effect of 1,1,1-trichloroethane. Based on decreased
forelimb grip performance, 2000 ppm (10,920 mg/m3) is a LOAEL for CNS effects in rats; the
NOAEL is 630 ppm (3440 mg/m3).
4.4.2. Immunological Effects
There is no clear evidence for immunological effects produced by 1,1,1-trichloroethane
in animal studies. Aranyi et al. (1986) found that exposure of mice to 350 ppm (1900 mg/m3) of
1,1,1-trichloroethane for 3 hours per day on 1 or 5 days had no effect on mortality from
respiratory infection due to streptococcal pneumonia introduced simultaneously with chemical
exposure. These researchers found a slight significant increase in bactericidal activity of
alveolar macrophages against introduced 35S-Klebsiellapneumonia after single exposure but not
after repeated exposure, which the researchers did not consider to be treatment related.
Two studies from the Russian literature (Shmuter, 1977, 1973), available in English only
as an abstract, reported immunological effects (decreased summary liters of typhoid antibodies,
increased electrophoretic mobility of the antibodies towards P- and a-globulin fractions,
decreased response to sheep erythrocytes, increased spleen weight and cells in the spleen, and
decreased number of antibody producing cells) in rabbits and/or rats exposed by inhalation to
2 or 18 ppm (10 or 100 mg/m3) trichloroethane for an unspecified period, but the reliability of
this study could not be evaluated because of minimal reporting of study design and results.
Furthermore, it could not be ascertained whether exposure was to the 1,1,1- or 1,1,2-isomer of
trichloroethane. Therefore, these studies provide little useful information on the immunotoxic
potential of 1,1,1-trichloroethane.
4.4.3. Effects by Dermal Exposure
The toxicity of 1,1,1-trichloroethane by dermal exposure has been the subject of limited
investigation. Direct contact of the eyes and skin with 1,1,1-trichloroethane generally resulted in
mild to moderate irritation with single or repeated application (lyadomi et al., 2000; Wahlberg,
1984a,b; Kronevi et al., 1981; Duprat et al., 1976; Marzulli and Ruggles, 1973; Torkelson et al.,
1958). Lethality by the dermal route was low. No rabbit or guinea pig deaths resulted from
24-hour occlusive dermal exposure to <7000 mg/kg, and even a dose of 16,000 mg/kg killed
fewer than half the rabbits treated (Kinkead and Leahy, 1987; Wahlberg and Boman, 1979;
Torkelson et al., 1958). Guinea pigs treated with 2 mL (-7000 mg/kg) of 1,1,1-trichloroethane
had significantly lower body weights than controls throughout a 35-day observation period
following treatment (9% deficit at termination) (Wahlberg and Boman, 1979). Rabbits exposed
to 2 mL/kg (-2700 mg/kg) had body weights similar to controls over a 14-day observation
period after treatment (Kinkead and Leahy, 1987). Systemic effects from dermal exposure were
studied by Torkelson et al. (1958) and Viola et al. (1981). Torkelson et al. (1958) found no
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effect on mortality, clinical signs, body weight, food intake, hematology, or gross and
microscopic pathology and weights of the major organs in rabbits treated dermally with up to
500 mg/kg-day of 1,1,1-trichloroethane for 5 days/week for 90 days. In rats, however, Viola et
al. (1981) observed hepatocellular alterations (dark and granular cytoplasm, mitochondrial
swelling, fatty degeneration, inflammatory cell infiltration, disrupted mitochondria, and
cytoplasmic organelles in some hepatocytes) and serum enzyme changes indicative of
hepatotoxicity (increased AST, OCT, and GOT) in male Wistar rats treated dermally with 240-
320 mg/kg-day on 16 of 22 days. Body weight gain was also significantly reduced, leading to
about a 13% deficit in terminal body weight in the treated group. Renal and pancreatic histology
were normal.
4.4.4. Effects by Parenteral Exposure
Parenteral studies are consistent with the characterization of 1,1,1-trichloroethane as a
weak hepatotoxicant. The chemical produced evidence of hepatotoxicity, including increases in
serum enzyme markers, altered liver function tests, and mild-to-moderate lesions, only at near-
lethal doses (Kukongviriyapan et al., 1995; Priestly and Plaa, 1976; Traiger and Plaa, 1974;
Cornish et al., 1973; Gehring, 1968; Klaassen and Plaa, 1967, 1966; Plaa et al., 1958), with little
or no effect at lower doses (Kukongviriyapan et al., 1995; Charbonneau et al., 1991; Honma,
1990; Stacey, 1989; Lundberg et al., 1986; Takahara, 1986b; Pollak and Harsas, 1982; Hanasono
et al., 1975; DiVincenzo and Krasavage, 1974; Traiger and Plaa, 1974; Cornish et al., 1973).
Even near-lethal doses failed to produce changes in liver triglyceride levels, G-6-Pase activity, or
lipid peroxides in rats (Klaassen and Plaa, 1969). The hepatotoxicity of 1,1,1-trichloroethane
was not affected by pretreatment with phenobarbital (Cornish et al., 1973), ethanol (Klaassen
and Plaa, 1967, 1966), isopropanol (Traiger and Plaa, 1974), acetone (Charbonneau et al., 1991;
Traiger and Plaa, 1974), alloxan (Hanasono et al., 1975), or nicotine (Priestly and Plaa, 1976).
There is little evidence from parenteral studies of a nephrotoxic effect of
1,1,1-trichloroethane. Studies in mice, dogs, and female rats found no effect of this compound
on renal function or the incidence of necrotic lesions, even at lethal doses (Bernard et al., 1989;
Klaassen and Plaa, 1967, 1966; Plaa and Larson, 1965; Plaa et al., 1958). The only kidney
effects observed were mild lesions at high doses: tubular swelling in mice (Plaa and Larson,
1965) and slight calcification of tubules in dogs (Klaassen and Plaa, 1967). Male rats were not
tested for nephrotoxicity in parenteral studies, so these studies do not address the potential of the
chemical to produce male rat specific a2U-globulin nephropathy, which has been reported
following oral exposure.
Intravenous injection of 1,1,1-trichloroethane resulted in a decrease in leukocyte count
and alterations in differential in dogs, which were similar to those seen after acute inhalation
exposure; there were no effects on erythrocyte count, hematocrit, or thrombocytes (Hobara et al.,
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1984, 1983). Intratesticular injection of 1,1,1-trichloroethane produced a significant decrease in
testicular DNA synthesis in male mice (Borzelleca and Carchman, 1982), but repeated
intraperitoneal injections had no effect on the incidence of sperm head abnormalities in mice
(Topham, 1981, 1980).
Neurological effects are well known following inhalation exposure to
1,1,1-trichloroethane but have not been widely studied by parenteral routes.
1,1,1-Trichloroethane was reported to have effects on electroretinogram and standing potential
of the eye in monkeys given low intravenous doses (Jarkman et al., 1985) and also to produce
vestibular disturbances, indicated by positional nystagmus (involuntary eye movements), but
without nystagmus response to rotary acceleration, in rabbits at low intravenous doses (Odkvist
et al., 1980, 1979; Larsby et al., 1978). In the brain, intraperitoneal injection of a sedating dose
of 1,1,1-trichloroethane (2400 mg/kg) in mice produced no effect on calcium flux into
synaptosomes (isolated nerve endings) from the cerebral cortex, while significantly decreasing
calcium flux into cerebellar synaptosomes and increasing calcium flux into brain stem
synaptosomes (Nilsson, 1987). The effect on voltage-dependent calcium channels could have
ramifications for neurotransmitter release and cyclic nucleotide metabolism and represents a
potential mechanism by which 1,1,1-trichloroethane might produce neurological effects.
4.5. MECHANISTIC DATA AND OTHER STUDIES IN SUPPORT OF THE MODE OF
ACTION
4.5.1. Mechanistic Data from In Vitro Studies
There is a body of evidence suggesting that the effects of 1,1,1-trichloroethane on the
heart (Herd and Martin, 1975; Krantz et al., 1959) and the liver (Kukongviriyapan et al., 1990)
may result, at least in part, from interference with energy generation within the cells. In isolated
hepatocytes, uptake of three chemicals with different active transport systems (taurocholate,
ouabain, 2-aminoisobutyric acid) was inhibited by subcytotoxic levels of 1,1,1-trichloroethane in
a dose-related fashion, while passive uptake of other substances (CdCb, 3-O-methyl-D-glucose)
was not affected (Kukongviriyapan et al., 1990). Cellular ATP and membrane ATPase activities
were reduced, suggesting that the effect on active transport systems may reflect an energy deficit
in the cells. Studies in isolated rat heart and liver mitochondria have demonstrated that
1,1,1-trichloroethane can uncouple oxidative phosphorylation, decreasing intracellular
respiration and production of ATP (Takano and Miyazaki, 1982; Ogata and Hasegawa, 1981;
Herd and Martin, 1975). The effect of 1,1,1-trichloroethane on energy generation is apparently
related to alterations in passive mitochondrial membrane permeability to calcium (Ca2+) and H+;
Ca2+-binding and sequestration mechanisms appeared unaffected (Herd and Martin, 1975).
Altered permeability of cell membranes to calcium has also been implicated in the
cardiac and nervous system effects of 1,1,1-trichloroethane. Reduced contractility of isolated
87
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cardiac myocytes exposed to 1,1,1-trichloroethane was shown to be due to an inhibitory action
on influx of extracellular calcium into the cell (Hoffmann et al., 1994, 1992; Toraason et al.,
1990). 1,1,1-Trichloroethane also changed calcium flux across cell membranes in isolated brain
synaptosomes (Robinson et al., 2001; Nilsson, 1987) and dorsal root ganglion neurons (Okuda et
al., 2001). Other studies found that 1,1,1-trichloroethane enhanced ligand-gated ion channel
activity: GABA-mediated synaptic currents in hippocampal neurons and ligand-evoked currents
of recombinant GABA and glycine receptors expressed in xenopus oocytes (Beckstead et al.,
2002, 2000). 1,1,1-Trichloroethane can produce effects on cell membranes by acting directly on
membrane-bound proteins; the chemical produced concentration-related inhibition of
acetylcholinesterase and ATPase in both isolated human red blood cells and rat synaptosomes
(Korpela, 1989; Korpela and Tahti, 1987, 1986; Tahti and Korpela, 1986). Incorporation into
the membrane, leading to modification of the immediate environment of gap junctions, was
hypothesized to explain the observed inhibition of gap junction intercellular communication in
cardiac myocytes by 1,1,1-trichloroethane (Toraason et al., 1992). Inhibition of intercellular
communication is thought to be related to the arrhythmogenic effects of 1,1,1-trichloroethane.
In studies using perfused rat liver and rat liver microsomes (Takano et al., 1988, 1985),
1,1,1-trichloroethane was also found to uncouple the CYP-dependent mixed function oxidase
system by binding to CYP (without undergoing significant metabolism—see Section 3.3),
leading to futile oxygen consumption and high hydrogen peroxide production, although not
peroxidation of membrane lipids. Although, 1,1,1-trichloroethane did not produce lipid
peroxidation in the liver in this study or others (Klaassen and Plaa, 1969), the compound did
produce evidence of lipid peroxidation in cultured arterial endothelial and aortic smooth muscle
cells when low levels of iron were also present (Tse et al., 1990). It was hypothesized by these
researchers that this interaction may explain toxic effects of 1,1,1-trichloroethane in tissues, such
as vascular cells, with little CYP or metabolic capacity.
Studies of direct injection of chick embryos found reduced survival and increased
malformations associated with injection of 1,1,1-trichloroethane (Gilani and Diaz, 1986;
Elovaara et al., 1979). 1,1,1-Trichloroethane had no effect on interferon induction in mouse
embryo fibroblasts (Sonnenfeld et al., 1983) or on the natural tumoricidal activity (natural killer,
natural cytotoxic, natural P815 killer) of human liver immune cells (Wright et al., 1994).
Inhibited induction of interferon and inhibition of natural immune function have been associated
with cancer produced by some chemicals.
4.5.2. Genotoxicity
The genotoxic effects of 1,1,1-trichloroethane have been studied extensively. The
chemical has shown little capacity to produce genotoxic effects in bacteria or fungi, regardless of
test system, use of metabolic activation, or measures to counter loss due to volatility. Results in
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mammalian test systems in vitro and in vivo were more mixed, although still predominantly
negative for assays other than cell transformation. The chemical has been shown to interact
weakly with DNA.
Results for the Ames salmonella assay have been mostly negative, both with and without
metabolic activation (Legault et al., 1994; Mersch-Sundermann, 1989; Milman et al., 1988;
Warner et al., 1988; Falck et al., 1985; Quillardet et al., 1985; Suovaniemi et al., 1985; Stanford
Research Institute [SRI], 1984; Dow Chemical Co., 1983, 1980; Baker and Bonin, 1981; Brooks
and Dean, 1981; Ichinotsubo et al., 1981; MacDonald, 1981; Martire et al., 1981; Nagao and
Takahashi, 1981; Richold and Jones, 1981; Rowland and Severn, 1981; Simmon and Shepherd,
1981; Trueman, 1981; Venitt and Crofton-Sleigh, 1981; Nestmann et al., 1980), although others
were positive with and without metabolic activation (Shimada et al., 1985; Nestmann et al.,
1984, 1980; IBM, 1982; Gocke et al., 1981; Simmon et al., 1977). The tests giving positive
results were carried out in a desiccator to maximize exposure, but so were several of those giving
negative results (Milman et al., 1988; Warner et al., 1988; SRI, 1984; Dow Chemical Co., 1983,
1980). Two studies have suggested that weakly positive results in the Ames salmonella assay
may be due to compounds included in commercial samples as stabilizers of
1,1,1-trichloroethane, rather than to 1,1,1-trichloroethane itself (Shimada et al., 1985; Nestmann
et al., 1984). Other tests of microbial mutagenicity in Salmonella typhimurium and Escherichia
coli were negative with or without metabolic activation (Legault et al., 1994; Roldan-Arjona et
al., 1991; Gatehouse, 1981; Hubbard et al., 1981; Matsushima et al., 1981; Skopek et al., 1981).
Tests for DNA damage in bacteria, assessed by SOS DNA repair induction (Legault et al., 1994;
Ono et al., 1991a,b; Nakamura et al., 1987; Quillardet et al., 1985; Thomson, 1981) or
differential killing (Green, 1981; Kada, 1981; Tweats, 1981), were negative, except for a weak
positive result with activation in a differential killing test in E. coli (Rosenkranz et al., 1981).
In the yeast Saccharomyces cerevisiae, 1,1,1-trichloroethane did not produce, with or
without metabolic activation, reverse mutation (Mehta and von Borstel, 1981), mitotic crossing
over (Kassinova et al., 1981), mitotic gene conversion (Jagannath et al., 1981; Sharp and Parry,
1981a; Zimmermann and Scheel, 1981), DNA damage (Sharp and Parry, 1981b), or chromosome
loss (Whittaker et al., 1990; Parry and Sharp, 1981) but did produce weak positive results in a
test for induction of deletions via intrachromosomal recombination (tested without activation
only) (Brennan and Schiestl, 1998). Results were negative for forward mutation in the yeast
Schizosaccharomycespombe, with or without activation (Loprieno, 1981).
1,1,1-Trichloroethane did not produce forward mutations, mitotic crossing over, or aneuploidy in
the mold Aspergillus nidulans, tested without activation (Crebelli et al., 1988; Crebelli and
Carere, 1987). In plants, 1,1,1-trichloroethane produced positive results for mutations in
tradescantia flowers (Schairer et al., 1983) and chromosomal aberrations in the onion Allium
cepa (Rank and Nielsen, 1994).
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Mixed results have been obtained for in vitro genotoxicity tests of mammalian cells. The
L5178Y mouse lymphoma cell mutagenesis assay has given both negative (Caspary et al., 1988;
Mitchell et al., 1988; Myhr and Caspary, 1988) and weakly positive results in different
laboratories (Caspary et al., 1988). 1,1,1-Trichloroethane did not cause unscheduled DNA
synthesis in HeLa cells (Martin and McDermid, 1981) or in rat hepatocytes (Williams et al.,
1989; Milman et al., 1988; Shimada et al., 1985; Dow Chemical Co., 1983; Naylor Dana
Institute, 1983; Althaus et al., 1982) but had a positive result in mouse hepatocytes (Milman et
al., 1988; Naylor Dana Institute, 1983). An assay for degranulation of endoplasmic reticulum
from rat hepatocytes was positive (Fey et al., 1981). 1,1,1-Trichloroethane has been both
positive (Galloway et al., 1987) and negative (Sofuni et al., 1985) in tests for chromosome
aberrations in cultured Chinese hamster cells. Assays for induction of micronuclei in
cytochalasin B-induced binucleate cells of human lymphoblastoid cell lines of varying metabolic
activity (AHH-1 with CYP1 Al activity, h2El with CYP2E1, and MCL-5 with multiple CYP
activities) were all positive (Doherty et al., 1996). Tests for sister chromatid exchange in
Chinese hamster ovary cells and human peripheral lymphocytes were negative (Lindahl-
Kiessling et al., 1989; Galloway et al., 1987; Perry and Thomson, 1981). Cell transformation
assays have been positive for BALBc/3T3 cells (Milman et al., 1988; Tu et al., 1985; Arthur D.
Little, 1983), rat embryo cells (Price et al., 1978), and hamster embryo cells (Hatch et al., 1983,
1982) but have given both positive (Daniel and Dehnel, 1981) and negative (Styles, 1981) results
with baby hamster kidney cells.
In vivo tests of 1,1,1-trichloroethane genotoxicity were predominantly negative. The
drosophila sex-linked recessive lethal assay has given negative results for injection (U.S. EPA,
1987; SRI, 1985; Gocke et al., 1981),, and both negative and weakly positive results for feeding
(U.S. EPA, 1987). An assay for interchromosomal mitotic recombination in drosophila
(white/white+ eye mosaic assay) was negative (Vogel and Nivard, 1993). The mouse
micronucleus assay has given negative results (ICI Central Toxicology Lab., 1990; Gocke et al.,
1981; Katz et al., 1981; Salamone et al., 1981; Tsuchimoto and Matter, 1981). A rat liver foci
assay for tumor-initiating and -promoting activity was negative for both (Milman et al., 1988;
Story et al., 1986). 1,1,1-Trichloroethane did not bind to calf thymus DNA in vitro (DiRenzo et
al., 1982), but in vivo binding of 1,1,1-trichloroethane to DNA, RNA, and protein was found to
be typical of very weak initiators (Prodi et al., 1988; Turina et al., 1986). Overall the highest
level of binding was to RNA. There was a small increase associated with both RNA and DNA
of the kidney compared to that of other organs, and binding was slightly higher in the mouse
than in the rat. Milman et al. (1988) reported similar findings, with greater binding of
1,1,1 -trichloroethane to mouse than to rat hepatic proteins. 1,1,1 -Trichloroethane did not cause
DNA damage (unwinding in fluorimetric assay) in mouse liver (Taningher et al., 1991).
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4.6. SYNTHESIS OF MAJOR NONCANCER EFFECTS
4.6.1. Oral
Tables 4-6 and 4-7 present summary noncancer results of the major studies for oral
exposure to 1,1,1-trichloroethane in humans and experimental animals, respectively. The human
oral toxicity literature is limited to a case report of accidental exposure and several
epidemiological investigations of the potential relationship between 1,1,1-trichloroethane
exposure in drinking water and pregnancy; no causal relationship was established.
The primary target of 1,1,1-trichloroethane at high oral doses is the CNS. Gross CNS
depression, as indicated by initial hyperexcitability followed by a period of prolonged narcosis
(often leading to death), was observed in rats given 1,1,1-trichloroethane by gavage in corn oil at
average doses of 3750 mg/kg-day or above for 12 days or 1786 mg/kg-day or above for 90 days
(Bruckner et al., 2001). No gross CNS effects were seen following gavage doses of 375 mg/kg-
day for 12 days or 357 mg/kg-day for 90 days (Bruckner et al., 2001). This study did not include
systematic investigation of neurological endpoints, however, making it uncertain whether
neurological effects more subtle than gross CNS depression may have gone undetected at these
doses. NCI (1977) found no evidence of gross CNS depression in rats treated by gavage in corn
oil at 536 or 1071 mg/kg-day for 78 weeks. Mice are apparently less susceptible than rats to
CNS effects from 1,1,1-trichloroethane, as even TWA gavage doses of 4011 mg/kg-day for
78 weeks failed to elicit clinically evident CNS effects. The potency of 1,1,1-trichloroethane to
induce CNS depression was clearly enhanced by bolus administration in the gavage studies. In
contrast to the LOAEL of 1786 mg/kg-day identified in the 13-week gavage study by Bruckner
et al. (2001), a 13-week feeding study in rats (NTP, 2000) reported no evidence of gross CNS
effects at doses up to 4800-5000 mg/kg-day. Tests for more subtle neurological effects detected
neurophysiological changes (EEG, FEP, SEP) in rats treated with 705 mg/kg-day of
1,1,1-trichloroethane by gavage for 4 days (Spencer et al., 1990). These investigators found no
neurobehavioral effects at this same gavage dose (705 mg/kg-day). Similarly, neurobehavioral
effects were not found in rats treated with 705 mg/kg-day by gavage for 2 days (Spencer et al.,
1990) or in rat dams or pups of dams treated with up to 750 mg/kg-day from GD 6 to PND 10
(Maurissen et al., 1994, 1993). The only available human data come from a case report of an
individual who swallowed a bolus dose of approximately 600 mg/kg of 1,1,1-trichloroethane on
a single occasion. No clinically evident CNS effects were reported, and thorough neurological
examinations designed to detect more subtle CNS effects revealed no abnormalities. The
neurological effects of 1,1,1-trichloroethane have been studied in more detail following
inhalation exposure.
91
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Table 4-6. Summary noncancer results of major studies for oral exposure of humans to l,l?l-trichloroethane
Study
population
Sex
Average
daily dose
(mg/kg-day)
Exposure
duration
NOAEL
(mg/kg-day)
LOAEL
(mg/kg-day)
Responses at LOAEL
Comments
Reference
Acute Exposure
One case
M
600
Once
NDa
600
Severe vomiting and
diarrhea, slightly elevated
serum bilirubin
No gross CNS effects and
no abnormalities in
neurological examination
Stewart and
Andrews, 1966
Short-term Exposure
No suitable short-term studies available
Subchronic Exposure
No suitable long-term studies available
Chronic Exposure
No suitable chronic studies available
aND = not determined.
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Table 4-7. Summary noncancer results of major studies for oral exposure of experimental animals to
1,1,1-trichloroethane
Species
Sex
Acute exposure
Rat
Rat
Rat
F
M
M
Short-term exposur
Rat
Rat
M
F
Average
daily dose"
Exposure
duration
NOAEL
(mg/kg-day)
LOAEL
(mg/kg-day)
Responses at LOAEL
Comments
Reference
0 or 670
(g)
0, 300, 1300,
or 2500
(g)
0, 500, 1000,
2000, or 4000
(g)
Once
Once
Once
NDb
1300
4000
670
2500
ND
Serum ALT increased
1.5-fold
Serum AST increased
twofold
None
No effect on serum SDH or
GDH and no liver lesions
detected. Study did not
investigate other endpoints.
Group sizes not specified.
No effect on serum ALT.
Study did not investigate
other endpoints. Small group
sizes (3-5 per dose).
No effect on serum ALT,
SDH, or OCT or liver weight
or histopathology. Study did
not investigate other
endpoints. Group sizes not
specified.
Xia and Yu,
1992
Tyson et al.,
1983
Bruckner et
al., 2001
e
0, 375, 3750,
or 7500
(g)
0 or 705
(g)
12 days
4 days
375
ND
3750
705
Death, narcosis,
reduced body weight
(20%)
Electrophysiological
changes (marked
changes in EEG and
FEP; smaller changes
in SEP)
No effect on serum ALT,
SDH, or OCT or liver weight
or histopathology. Study did
not investigate other
endpoints.
No neurobehavioral effects
(measured after 2 days of
exposure)
Bruckner et
al., 2001
Spencer et al.,
1990
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Table 4-7. Summary noncancer results of major studies for oral exposure of experimental animals to
1,1,1-trichloroethane
Species
Rat
Sex
F
Average
daily dose"
0, 75, 250, or
750
(g)
Exposure
duration
GD6-
PND 10
NOAEL
(mg/kg-day)
750
LOAEL
(mg/kg-day)
ND
Responses at LOAEL
None
Comments
No neurobehavioral effects in
dams or neurodevelopmental
effects in pups.
Reference
Maurissen et
al., 1993, 1994
Subchronic exposure
Rat
Rat
M
M,F
0, 357, 1786,
or 3571
(g)
M: 290, 600,
1200, 2400,
or 4800
F: 3 10, 650,
1250, 2500,
or 5000
(f)
13 weeks
13 weeks
357
2400-2500
1786
4800-5000
Death, narcosis,
reduced body weight
Reduced liver weights
(11-17%) in males and
females, and reduced
epididymal
spermatozoal
concentration (-10%)
in males
Early accidental termination
of the two high-dose groups.
No effect on serum ALT,
SDH, or OCT or liver weight
or histopathology in the low-
dose group. In the high-dose
group, slight increases in ALT
and OCT. Study did not
investigate other endpoints.
Hyaline droplet nephropathy
in male rats at 1200 mg/kg
and above (not considered
relevant to human health risk
assessment). Broad array of
endpoints assessed, including
complete histopathology at
high dose. Body weight
decreased but within 10% of
control.
Bruckner et
al., 2001
NTP, 2000
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Table 4-7. Summary noncancer results of major studies for oral exposure of experimental animals to
1,1,1-trichloroethane
Species
Mouse
Rat
Rat
Rat
Mouse
Sex
M, F
M, F
M,F
M,F
M,F
Average
daily dose"
M: 850, 1770,
3500, 7370,
or 15,000
F: 1340,
2820, 5600,
11,125, or
23,000
(f)
0 or 1.4
(dw)
0, 0.3, 1.2, or
3.5
(dw)
0, 0.3, 0.8, or
2.4
(dw)
0, 100, 300,
or 1000
(dw)
Exposure
duration
13 weeks
Before
mating
through
lactation
Before
mating
through
lactation
Before
mating
through
GD20
Before
mating
through
lactation;
multi-
generatio
n
NOAEL
(mg/kg-day)
1770-2820
ND
3.5
2.4
1000
LOAEL
(mg/kg-day)
3500-5600
1.4
ND
ND
ND
Responses at LOAEL
Decreased body weight
gain in males and
females (11-12%)
Increased cardiac
abnormalities,
especially persistent
ductus arteriosus, in
pups
None
None
None
Comments
Decreased body weight gain
at lower doses was within
10% of control values and
considered to be of marginal
biological significance. At
high dose (15,000 mg/kg-
day), epididymal
spermatozoal concentration
decreased in males (20%).
Complete histopathology at
high dose.
Small group sizes; few
endpoints examined;
incomplete analysis of data
(no litter-based comparison of
cardiac anomalies).
No increase in persistent
ductus arteriosus or other
cardiac anomalies in pups.
Large group sizes. Designed
to evaluate Dapson et al.
(1984a,b).
No maternal, embryotoxic,
fetotoxic, or developmental
(external, visceral, skeletal, or
cardiovascular) abnormalities
were found.
No effects on male or female
reproductive function or
offspring development.
Reference
NTP, 2000
Dapson et al.,
1984a,b
George etal.,
1989; NTP,
1987a
NTP, 1987b
Lane etal.,
1982
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Table 4-7. Summary noncancer results of major studies for oral exposure of experimental animals to
1,1,1-trichloroethane
Species
Sex
Chronic exposure
Rat
Mouse
Rat
M,F
M,F
M,F
Average
daily dose"
Exposure
duration
NOAEL
(mg/kg-day)
LOAEL
(mg/kg-day)
Responses at LOAEL
Comments
Reference
0, 536, or
1071
(g)
0, 2005, or
4011
(g)
0 or 321
(g)
78 weeks
78 weeks
104
weeks
ND
ND
ND
536
2005
321
Increased early
mortality and decreased
body weight
Increased early
mortality and decreased
body weight
Decreased body weight
in females (by ~12 and
25% at end of treatment
and observation
periods, respectively)
Cancer bioassay with limited
investigation of noncancer
endpoints.
Cancer bioassay with limited
investigation of noncancer
endpoints.
No effect on survival. Cancer
bioassay with limited
investigation of noncancer
endpoints.
NCI, 1977
NCI, 1977
Maltoni et al.,
1986
aDoses in mg/kg-day; route of administration in parentheses: dw = drinking water; f = feed; g = gavage.
bND = not determined.
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Evidence for the liver as a potential target of orally administered 1,1,1-trichloroethane is
equivocal. Some, but not all, studies suggest that 1,1,1-trichloroethane may produce mild
hepatotoxicity. An individual who swallowed one ounce of 1,1,1-trichloroethane (approximately
600 mg/kg), a dose that induced severe vomiting and diarrhea but no neurological effects, had
only a slight increase in serum bilirubin and no changes in serum ALT or AST (Stewart and
Andrews, 1966). In experimental animals, serum enzyme changes indicative of mild
hepatotoxicity were seen in two single dose gavage studies (at 670 mg/kg in one study and
2500 mg/kg with a NOAEL of 1300 mg/kg in the other) (Xia and Yu, 1992; Tyson et al., 1983)
and in a 13-week gavage study at a dose (3571 mg/kg-day) that was lethal to 50% of the rats
tested (Bruckner et al., 2001). In these studies, the observed changes were slight, occurred in
only one or two of multiple measures of hepatotoxicity examined, and were not accompanied by
gross or microscopic liver lesions. NTP (2000) reported decreases in relative and/or absolute
liver weight (12%) in female and male rats exposed to 4800-5000 mg/kg-day of
1,1,1-trichloroethane in the diet for 13 weeks (NOAEL = 2400-2500 mg/kg-day) (NTP, 2000).
No histopathologic changes in the liver were observed. Increases in liver weight, rather than
decreases, were found in most other studies that reported changes in liver weight, regardless of
exposure route. These increases in liver weight were generally associated with induction of
drug- metabolizing enzymes by 1,1,1-trichloroethane. Dermal, parenteral, and inhalation studies
support identification of 1,1,1-trichloroethane as a weak hepatotoxicant (e.g., Kukongviriyapan
et al., 1995; Quast et al., 1988, 1984; Viola et al., 1981; McNutt et al., 1975; Cornish et al., 1973;
Adams etal., 1950).
There is some evidence for the kidney as a target of 1,1,1-trichloroethane in male rats
following oral exposure. Male rats exposed to 1200 mg/kg-day or more in the diet for 13 weeks
showed renal lesions characteristic of a2U-globulin nephropathy, as indicated by significant,
dose-related increases in incidence and/or severity of renal tubule hyaline degeneration, cast
formation, and regeneration, and chronic interstitial inflammation of the kidney (NTP, 2000);
however, specific analysis for a,2u-globulin was not conducted by NTP. Renal changes
associated with a2U-globulin nephropathy in male rats are specific to this sex and species and are
not considered to be predictive for effects in humans (U.S. EPA, 1991c). In a 21-day gavage
study in rats, designed specifically to examine renal toxicity of halogenated ethanes (NTP,
1996), no renal lesions, including hyaline droplet nephropathy, tubule regeneration, or granular
casts, were seen at the high dose of 165 mg/kg-day. Increases in mean urine protein and AST
were reported in the high dose group in this study but may have been due to high levels in a
single individual, and, therefore, may not have been related to treatment. Male rats treated
dermally with 240-320 mg/kg-day for 3 weeks showed no evidence of renal lesions (Viola et al.,
1981). Parenteral studies found little evidence of nephrotoxicity even at lethal dose levels (e.g.,
Bernard et al., 1989; Klaassen and Plaa, 1967; Plaa et al., 1958) but were not conducted in male
97
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rats. The kidneys were not adequately evaluated as a potential endpoint of toxicity in other
subchronic or chronic oral studies. Inhalation studies, including studies of subchronic and
chronic durations, did not show renal effects in male rats or other species tested. The overall
weight of evidence does not show the kidney to be a sensitive target organ for
1,1,1 -trichloroethane.
Epididymal spermatozoal concentration was reduced in high-dose male rats (4800
mg/kg-day) and mice (15,000 mg/kg-day) in the 13-week feeding study (NTP, 2000). The
toxicological significance of these changes is uncertain, as the magnitude was relatively small
(10-20%) and no associated changes in sperm motility or the weight or histopathology of the
reproductive organs were seen in either species. The epididymis was not evaluated as a potential
endpoint of toxicity in other oral studies and was not identified as a target in inhalation studies.
Intratesticular injection of 1,1,1-trichloroethane produced a significant decrease in testicular
DNA synthesis in male mice (Borzelleca and Carchman, 1982), but repeated intraperitoneal
injections had no effect on the incidence of sperm head abnormalities in mice (Topham, 1981,
1980). No effect on male or female reproductive function was seen in mice tested in a
multigeneration oral study at doses up to 1000 mg/kg-day (Lane et al., 1982).
Significantly decreased body weight gain was the most sensitive effect in 13-week
feeding studies in rats and mice (NTP, 2000). In the 90-day gavage study (Bruckner et al.,
2001), low-dose rats had slightly nonsignificant reduced body weights (-95% of control) with no
other reported effects. Reduced body weight gain was observed in the 104-week study by
Maltoni et al. (1986) in the absence of effects on survival; nonneoplastic lesions were not further
examined in this study. Reduced body weight gain has also been observed in inhalation studies
in the absence of other toxicity (Prendergast et al., 1967; Adams et al., 1950) or at dose levels
causing minimal liver histopathologic changes (some reflective of an adaptive physiologic
response) (Quast et al., 1988, 1984; Calhoun et al., 1981).
One preliminary study reported cardiac abnormalities, especially persistent ductus
arteriosus, in rat pups of parents exposed to a low dose (1.4 mg/kg-day) of 1,1,1-trichloroethane
in drinking water (Dapson et al., 1984a,b). However, this study was limited by small group
sizes, use of only a single exposure level, examination of few endpoints, and incomplete analysis
of the data. Subsequent studies, designed to evaluate this observation and including large
numbers of animals, found no evidence of any developmental effects at dose levels up to 3.5
mg/kg-day (George et al., 1989; NTP, 1987a,b). The multigeneration study by Lane et al. (1982)
found no developmental effects in mice tested at doses up to 1000 mg/kg-day. A study designed
primarily to evaluate neurological endpoints in developing rat pups found no effects at doses up
to 750 mg/kg-day (Maurissen et al., 1994, 1993). Overall, the database shows no evidence of
developmental effects in rats or mice exposed to 1,1,1-trichloroethane by the oral route.
However, all of these studies were conducted at relatively low doses that failed to elicit maternal
98
-------
toxicity. Inhalation studies in rodents found evidence for developmental delay in fetuses and
delayed attainment of developmental milestones and neurodevelopmental effects in pups under
certain exposure regimens, including an exposure regimen that did not produce observable
effects in the dams (Coleman et al., 1999; Jones et al., 1996; BRRC, 1987a,b). Studies of direct
injection of chick embryos found reduced survival and increased malformations associated with
injection of 1,1,1-trichloroethane (Gilani and Diaz, 1986; Elovaara et al., 1979).
The available oral toxicity studies were not, in general, designed to examine whether the
effects associated with 1,1,1-trichloroethane were reversible upon cessation of exposure or
whether effects might manifest after some latency period. The CNS depressant effects of
1,1,1-trichloroethane, like those of other solvents, are generally considered to be readily
reversible (Evans and Balster, 1991). The effects are thought to be related to presence of the
parent compound in neural membranes and to resolve as the parent compound is rapidly
eliminated from the body following exposure. One 13-week oral toxicity study included a
1-week postexposure period; no effects were observed at either 13 weeks or 1 week
postexposure.
4.6.2. Inhalation
Tables 4-8 and 4-9 present summary noncancer results of the major studies for inhalation
exposure to 1,1,1-trichloroethane in humans and experimental animals, respectively.
99
-------
Table 4-8. Summary noncancer results of major studies for inhalation exposure of humans to 1,1,1-trichloroethane
Study
population
Sex
Exposure
concentration
(mg/m3)
Exposure
duration
NOAEL
(mg/m3)
LOAEL
(mg/m3)
Responses at LOAEL
Comments
Reference
Acute exposure
12 adult
volunteers
12 adult
volunteers
6 university
students
9 adult
volunteers
9 volunteers,
divided into
three groups of
three
M
M
M
M
M
0, 1370, 1900,
2450, and 3000
0, 950, and
1900
0 and 2450
0, 1090, and
2180
0, 1090
(steady), or
1090 (variable)
30
minutes
3.5 hours
8 hours
4 hours
3.67 hours
1370
NDb
ND
2180
1090
1900
950
2450
ND
ND
Impaired performance in
tests of manual dexterity
(wire spiral), perceptual
speed (identical number and
spokes tests), and simple and
choice reaction time.
Impaired performance in
tests of simple reaction time,
choice reaction time, and
tracking ability.
Transient eye irritation and
slight dizziness.
No effect in tests for simple
reaction time, hand tapping
speed, critical flicker fusion
threshold, gaze deviation
nystagmus, and body sway.
No significant effects on
subjective symptoms, EEG,
visual evoked potentials, or
equilibrium. No signs of
respiratory irritation.
All subjects progressively
exposed to all concentrations on
1 day and control conditions
another day. Tests conducted
during exposure.
All subjects exposed to each
concentration on a different
day. Tests conducted before and
during exposure.
All subjects exposed to both
exposure conditions on different
days. Tests conducted before
and during exposure. No effect
in tests for complex reaction
time, manual dexterity,
perception with tachistoscopic
presentation, and Wechsler
memory scale.
All subjects exposed to each
concentration on a different
day. Tests conducted before and
during exposure.
Subjects exercised on a
stationary bicycle for 10
minutes at the start of exposure.
Tests conducted before, during,
and after exposure.
Gamberale and
Hultengren,
1973
Mackay etal.,
1987
Salvini et al.,
1971
Savolainen et
al., 1982a,b,
1981
Laine et al.,
1996
100
-------
Table 4-8. Summary noncancer results of major studies for inhalation exposure of humans to 1,1,1-trichloroethane
Study
population
12 volunteers
Sex
M
Short-term exposure
Exposure
concentration
(mg/m3)
120 (control)
and 1090
Exposure
duration
4 hours
NOAEL
(mg/m3)
ND
LOAEL
(mg/m3)
1090
Responses at LOAEL
Subtle neurological effects
(tiredness and EEG changes)
and slight nasal irritant
response (increased levels of
proinflammatory cytokines
in nasal secretions).
Comments
All subjects exposed to both
exposure conditions on different
days. Tests conducted before
and during exposure.
Reference
Muttray etal.,
2000, 1999
No suitable short-term studies available
Subchronic exposure
No suitable subchronic studies available
Chronic exposure
28 workers
from a single
factory
Groups of 7-8
workers from
the same
factory
NSa
F
NS
0, 600, 760-
870, and 1090-
5400
10 years
6.7 years
average
ND
1090
ND
ND
Impaired performance in
tests of balance, memory,
intermediate memory,
rhythm, and speed.
No effect on subjective
symptoms, general physical
examination,
neurophysiological
examination, or
psychological test battery
(23 variables including
intelligence, psychomotor
ability, and memory tests).
Exposure levels unknown;
workers had been reporting
symptoms for an average of 3
years.
Reaction time, shown to be
sensitive in acute studies, was
not evaluated.
Kelafantetal.,
1994
Maroni et al.,
1977
101
-------
Table 4-8. Summary noncancer results of major studies for inhalation exposure of humans to 1,1,1-trichloroethane
Study
population
151 employees
in five groups
matched with
unexposed
workers from a
second factory
Sex
NS
Exposure
concentration
(mg/m3)
0, <81, 81-269,
270-540, 550-
810, and 820-
1360
Exposure
duration
<6 years
NOAEL
(mg/m3)
820
LOAEL
(mg/m3)
ND
Responses at LOAEL
No effect on health histories
or physical examinations
(blood pressure, heart rate,
spirometric parameters,
electrocardiogram,
urinalysis, hematology, and
serum chemistry).
Comments
Neurological investigation
limited to Romberg test.
Reference
Kramer et al.,
1978
aNS = not stated.
bND = not determined.
102
-------
Table 4-9. Summary noncancer results of major studies for inhalation exposure of experimental animals to
1,1,1-trichloroethane
Species
Sex
Acute exposure
Rat
Rat
Baboon
Rat
Mouse
Mouse
Mouse
M,F
M
M
M
F
M
M
Exposure
concentration
(mg/m3),
protocol1"
Exposure
duration
NOAELC
(mg/m3)
LOAELC
(mg/m3)
Responses at LOAEL
Comments
Reference
0, 43,680, or
65,520
0, 10,920, 21,840,
43,680, 81,900, or
136,500
0, 3820, 7640,
9830, or 11,470
NS
NS
11,270-19,490
0, 7100, or 10,920
7 hours
3 hours
4 hours
4 hours
2 hours
4 hours
1 hour
NDC
136,500
7640
ND
ND
ND
7100
43,680
ND
9830
4000
9880
11,270
10,920
Increased relative liver
weight (12%) and slight
histopathology (fatty
change) in the liver.
No effect on serum SDH,
LDH, or GDH.
Impaired performance in
match-to-sample
discrimination task.
30% depression in duration
of tonic extension of
hindlimb in response to
electrical shock.
30% depression in velocity
of tonic extension of
hindlimb in response to
electrical shock.
Decreased duration of
immobility in behavioral
despair swimming test.
Increased motor activity.
More severe changes,
including necrotic lesions
at the higher exposure
level. No liver effect after
2 hours exposure to
98,280.
Calculated EC30.
Calculated EC30.
Adams et al.,
1950
Loizouetal.,
1996
Gelleretal.,
1982
Frantiketal.,
1994
Frantiketal.,
1994
de Ceaurriz et
al., 1983
Kjellstrand et
al., 1985b
103
-------
Table 4-9. Summary noncancer results of major studies for inhalation exposure of experimental animals to
1,1,1-trichloroethane
Species
Mouse
Sex
M
Exposure
concentration
(mg/m3),
protocol1"
0, 2730, 6825,
13,650, 27,300,
40,950, or 54,600
Exposure
duration
30 minutes
NOAELC
(mg/m3)
2730
LOAELC
(mg/m3)
6830
Responses at LOAEL
Increased motor activity.
Comments
Results for dynamic
exposure system. Effects
at higher levels in static
exposure system.
Reference
Bowen and
Balster, 1996
Short-term exposure
Rat
Rat
Mouse
Rat
M,F
F
F
F
0 or 1140
(0 or 5460
7 hours/day,
5 days/week)
0 or 1390
(0 or 4780
7 hours/day)
0 or 1390
(0 or 4780
7 hours/day)
0, 1370, 4090, or
8190
(0, 5460, 16,380,
or 32,760
6 hours/day)
4 weeks
CDs 6-15
CDs 6-15
CDs 6-15
1140
(5460
7 hours/day,
5
days/week)
1390
(4780
7 hours/day)
1390
(4780
7 hours/day)
4090
(16,380
6 hours/day)
ND
ND
ND
8190
(32,760
6 hours/day)
None.
No maternal or
developmental effects.
No maternal or
developmental effects.
Mild fetotoxicity manifested
by delayed cervical
ossification and decreased
(-6%) body weights of
female fetuses.
Hypoactivity and reductions
in food consumption, body
weight gain, body weight,
and gravid uterine weight in
dams.
Wide array of endpoints
investigated, including
histopathology.
Sacrifice on GD 21.
Sacrifice on GD 18.
Sacrifice onGD 21.
Developmental effects
only at same level as overt
maternal effects.
Dow Chemical
Co., 1969
Schwetzetal.,
1975
Schwetzetal.,
1975
BRRC, 1987a
104
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Table 4-9. Summary noncancer results of major studies for inhalation exposure of experimental animals to
1,1,1-trichloroethane
Species
Rabbit
Mouse
Mouse
Rat
Baboon
Mouse
Sex
F
F
F
F
M
M
Exposure
concentration
(mg/m3),
protocol1"
0, 1370, 4090, or
8190
(0, 5460, 16,380,
or 32,760
6 hours/day)
0 or 7740
(0 or 10,920
17 hours/day)
0 or 5460
(0 or 43, 680
3 hours/day)
0 or 4780
(0 or 38,220
3 hours/day)
0 or 6550
(continuous)
0, 2730, 5460,
10,920, or 21,840
(continuous)
Exposure
duration
CDs 6-18
CDs 12-
17
CDs 12-
17
CDs 13-
19
7 days
4 days
NOAELC
(mg/m3)
4090
(16,380
6 hours/day)
ND
ND
ND
ND
ND
LOAELC
(mg/m3)
8190
(32,760
6 hours/day)
7740
(10,920
17 hours/day)
5460
(43,680
3 hours/day)
4780
(38,220
3 hours/day)
6550
2730
Responses at LOAEL
Mild fetotoxicity manifested
by increased incidence of
supernumerary rib.
Reduced maternal weight
gain in does.
No overt maternal effects.
Developmental delay and
neurobehavioral deficits in
offspring.
Anesthesia, gait
abnormalities (splayed hind-
limbs, severe sway, ataxia)
and clonic movements in
dams. Developmental delay
and neurobehavioral deficits
in offspring.
Gross neurological effects
in dams. Increased
resorptions and decreased
live pups per litter. Pup
neurobehavioral deficits.
Impaired performance in
match-to-sample
discrimination task.
Handling-induced
convulsions after exposure.
Comments
Sacrifice on GD 29.
Developmental effects
only at same level as overt
maternal effects.
Dams allowed to give
birth. Developmental
effects without maternal
effects.
Dams allowed to give
birth. Developmental
effects from an exposure
that also produced obvious
maternal toxicity.
Dams allowed to give
birth. Developmental
effects from an exposure
that also produced obvious
maternal toxicity.
Convulsions mitigated by
reexposure to
1,1,1 -trichloroethane or
other known depressants.
Interpreted by researchers
as symptom of withdrawal.
Reference
BRRC, 1987b
Jones et al.,
1996
Jones et al.,
1996
Coleman et
al., 1999
Gelleretal.,
1982
Balsteretal.,
1997; Evans
and Balster,
1993
105
-------
Table 4-9. Summary noncancer results of major studies for inhalation exposure of experimental animals to
1,1,1-trichloroethane
Species
Rat
Mouse
Sex
NSa
M
Exposure
concentration
(mg/m3),
protocol1"
0, 1360, or 2730
(0, 5460, or 10,920
6 hours/day)
0, 10,920, 32,760,
54,600, or 72,620
0.5 hours/day
Exposure
duration
4 days
15 days
NOAELC
(mg/m3)
ND
ND
LOAELC
(mg/m3)
1360
(5460
6 hours/day)
10,920
0.5 hours/day,
15 days
Responses at LOAEL
Significant differences from
control in EEG, FEP, and
SEP.
Tolerance or sensitization,
depending on the behavioral
measure tested.
Comments
Mice were tested using
locomotor activity and
FOB. Because exposures
represented repeated acute
exposures, exposures were
not adjusted to continuous
exposure.3
Reference
Albee et al.,
1990b
Bowen and
Balster, 2006
Subchronic exposure
Rat
Rat
Mouse
M
M,F
M,F
0 or 260
(0 or 1110
8 hours/day,
5 days/week)
0, 150, 490, 980,
or 1950
(0, 820, 2730,
5460, or 10,920
6 hours/day,
5 days/week)
0, 150, 490, 980,
or 1950
(0, 820, 2730,
5460, or 10,920
6 hours/day,
5 days/week)
14 weeks
94 days
94 days
260
(1110
8 hours/day,
5
days/week)
980
(5460
6 hours/day,
5
days/week)
980
(5460
6 hours/day,
5
days/week)
ND
1950
(10,920
6 hours/day,
5 days/week)
1950
(10,920
6 hours/day,
5 days/week)
None.
Decreased (7%) body
weight in males. Minimal
lesions in the liver and nasal
turbinates of males and
females.
Minimal lesions in the liver
and nasal turbinates of
males and females.
Wide array of endpoints
investigated, including
histopathology.
Wide array of endpoints
investigated, including
histopathology.
Wide array of endpoints
investigated, including
histopathology.
Eben and
Kimmerle,
1974
Calhounetal.,
1981
Calhounetal.,
1981
106
-------
Table 4-9. Summary noncancer results of major studies for inhalation exposure of experimental animals to
1,1,1-trichloroethane
Species
Mouse
Rat
Gerbil
Rat
Sex
M
F
M,F
M,F
Chronic exposure
Rat
M,F
Exposure
concentration
(mg/m3),
protocol1"
0, 1370, or 5460
(continuous)
0 or 2050-2870
(0 or 11, 470
6 hours/day,
5 days/week before
mating and
7 days/week
during gestation)
0,380, 1150, or
5460
(continuous)
0, 195, 610, or
1950
(0, 1090, 3440, or
10,920
6 hours/day,
5 days/week)
Exposure
duration
14 weeks
Before
mating
and/or GD
1-20
3 months
13 weeks
NOAELC
(mg/m3)
1370
2870
(11,470
6 hours/day,
5-7
days/week)
380
610
(3440
6 hours/day,
5
days/week)
LOAELC
(mg/m3)
5460
ND
1150
1950
(10,920
6 hours/day,
5 days/week)
Responses at LOAEL
Fatty change and necrosis in
hepatocytes.
No maternal or
developmental effects.
Increased GFAP, indicating
brain astrogliosis.
Impaired forelimb grip
performance after 13 weeks
but not earlier.
Comments
Minimal ultrastructural
liver changes in low-dose
group.
Half of the dams in each
group were sacrificed on
day 21, and the remaining
dams were used for
postnatal evaluations.
Animals examined 4
months after the end of
exposure.
Ambiguous evidence of
effect. No support from
tests of hind-limb grip
performance or other
behavioral,
electrophysiological, or
histopathological
evaluations.
Reference
McNutt et al.,
1975
York et al.,
1982
Rosengren et
al., 1985
Mattsson et
al., 1993
0 or 570
(0 or 2730
7 hours/day,
5 days/week)
6 months
570
(2730
7 hours/day,
5
days/week)
ND
None.
Wide array of endpoints
investigated, including
histopathology.
Torkelson et
al., 1958
107
-------
Table 4-9. Summary noncancer results of major studies for inhalation exposure of experimental animals to
1,1,1-trichloroethane
Species
Rat
Rat
Mouse
Sex
M,F
M,F
M,F
Exposure
concentration
(mg/m3),
protocol1"
0, 850, or 1710
(0, 4780, or 9560
6 hours/day,
5 days/week)
0, 150, 490, or
1460
(0, 820, 2730, or
8190
6 hours/day,
5 days/week)
0, 150, 490, or
1460
(0, 820, 2730, or
8190
6 hours/day,
5 days/week)
Exposure
duration
12 months
2 years
2 years
NOAELC
(mg/m3)
ND
1460
(8190
6 hours/day,
5
days/week)
1460
(8190
6 hours/day,
5
days/week)
LOAELC
(mg/m3)
ND
ND
ND
Responses at LOAEL
Focal hepatocellular
alterations in females after
19-month observation
period (i.e., study month
3 1). Questionable as to
whether effects could be
attributed to treatment.
Slight microscopic hepatic
changes in males and
females at 6-18 months
(confounding geriatric
changes at 24 months)
considered to be adaptive
physiologic changes and not
adverse. Slight (<7%)
decrease in body weight in
females.
None.
Comments
Wide array of endpoints
but few animals examined
for histopathology at end
of exposure period.
Comprehensive study.
Comprehensive study.
Reference
Quastetal.,
1978
Quast et al.,
1988, 1984
Quast et al.,
1988, 1984
aNS = not stated.
bActual exposure levels are presented for acute studies. For short-term, subchronic, and chronic studies, intermittent exposures (e.g., 6 hours/day, 5 days/week)
were adjusted to continuous (average daily) exposures. For example, intermittent exposure to 820 mg/m3 for 6 hours/day, 5 days/week yields an adjusted
(continuous) exposure concentration of 820 mg/m3 x 6/24 x 5/7 = 146 mg/m3. Actual (unadjusted) exposures are shown in parentheses.
°The dosimetric adjustment factor for 1,1,1-trichloroethane used to derive an HEC is 1 (see Table 5-3). Therefore, the NOAEL and LOAEL values presented in
this table are equivalent to HEC values. ND = not determined.
108
-------
CNS depressant effects are the predominant signs of acute inhalation exposure to
1,1,1-trichloroethane in humans and animals. Studies of subtle neurological effects in humans
provide the most sensitive indications of 1,1,1-trichloroethane toxicity. In male volunteers,
Gamberale and Hultengren (1973) found impaired performance in a number of neurobehavioral
performance tests at concentrations of 350 ppm (1900 mg/m3) and above (NOAEL = 250 ppm
[1370 mg/m3]) for a 30-minute exposure. Mackay et al. (1987) found similar effects at lower
levels (LOAEL =175 ppm [950 mg/m3], NOAEL not determined) in male volunteers receiving a
3.5-hour exposure. Tests for reaction time appeared to be the most sensitive. Muttray et al.
(2000) monitored the EEG of male volunteers with eyes closed, eyes open, and while performing
a choice reaction time test before and during 4-hour exposure to 200 ppm (1090 mg/m3)
1,1,1-trichloroethane and found changes consistent with increased drowsiness in the closed eye
test. Subjectively, the volunteers also reported increased tiredness. Animal studies have not
proved as sensitive as human studies for detection of neurological effects of acute
1,1,1-trichloroethane inhalation exposure. Neurological effects in animals were reported
following acute 1,1,1-trichloroethane exposure at concentrations of around 700 ppm
(4000 mg/m3) and above. Narcosis associated with acute exposure was shown to be reversible
(Adams et al., 1950). The most sensitive response reported in animal studies was depression of
seizure discharge (specifically, duration of tonic extension of hindlimb in rats) in response to
electrical shock. The concentration estimated to produce a 30% depression in seizure discharge
for a 4-hour exposure was 734 ppm (4000 mg/m3) (Frantik et al., 1994). Neurochemical changes
have been reported at lower concentrations, for example decreased cGMP in the cerebellum of
male mice exposed to 100 ppm (550 mg/m3) for 4 hours (Nilsson, 1986a). While changes in
levels of cyclic nucleotides, which act as secondary messengers in neural cells, could have
functional effects on the nervous system, there is no evidence that the chemical changes
observed in existing studies are indicative of such an effect.
Neurological effects have been observed at lower concentrations in animal studies with
repeated exposure. Continuous exposure to 500 ppm (2730 mg/m3) for 4 days resulted in a
concentration-related increase in incidence and severity of handling-induced convulsions in mice
through 24 hours postexposure (Evans and Balster, 1993; Balster et al., 1997). No such
convulsions were seen in controls at any time. The effects were mitigated by reexposure to
1,1,1-trichloroethane or exposure to other known depressants and were interpreted as symptoms
of withdrawal by the researchers. In a subchronic study designed to investigate persistent
neurotoxic effects, exposure to 2000 ppm (10,920 mg/m3) for 6 hours/day, 5 days/week (NOAEL
= 630 ppm or 3440 mg/m3) for 3 months (but not less) produced ambiguous evidence for a
deficit in forelimb grip performance in rats of both sexes (Mattsson et al., 1993); some indication
of a deficit was still present 7 weeks postexposure. Continuous exposure to 210 ppm
(1150 mg/m3) or above for 3 months produced increased concentrations of GFAP, a marker for
109
-------
formation of astroglial fibrils in response to brain injury, in the sensorimotor cerebral cortex of
exposed gerbils (evaluated 4 months after the end of exposure) (Rosengren et al., 1985). There
was no effect on GFAP at 70 ppm (380 mg/m3) and no dose-related effect on the concentrations
of S-100, another protein marker of astroglial cell increase, or total protein in regions of gerbil
brain. Another study from the same researchers (Karlsson et al., 1987) found decreased
concentration of DNA in three of nine brain areas examined in gerbils exposed to 70 ppm
(380 mg/m3) for 3 months (also evaluated 4 months after the end of exposure), although not in
the sensorimotor cerebral cortex affected in the study by Rosengren et al. (1985). Although
reduced DNA content in these areas could reflect a decrease in cell density, possibly as a result
of cell death and/or inhibition of nonneuronal cell acquisition, it is not clear that the observed
DNA changes constitute reliable evidence of an adverse effect. Chronic animal studies found no
evidence of gross CNS depression at exposures up to 1500 ppm (8190 mg/m3) for 6 hours/day,
5 days/week, but did not include investigation of more subtle neurological effects. A study of
workers with chronic occupational exposure to 1,1,1-trichloroethane provided evidence of
neurobehavioral effects in workers, but exposure levels were not determined (Kelafant et al.,
1994). Some other occupational studies did not find effects but included limited investigation of
neurological endpoints (Kramer et al., 1978) or included a battery of neurological tests but not
tests for reaction time, which was shown to be especially sensitive to 1,1,1-trichloroethane in
acute studies (Maroni et al., 1977).
Effects on respiration, blood pressure, and the heart have been associated with acute
exposure to high levels of 1,1,1-trichloroethane (approximately 5000 ppm [27,300 mg/m3] and
above) in both humans and animals (e.g., Dornette and Jones, 1960; Herd et al., 1974; Reinhardt
et al., 1973). These effects have not been observed at lower levels and do not constitute sensitive
measures of toxicity for 1,1,1-trichloroethane.
There is some evidence to suggest that nasal tissue is a sensitive target for
1,1,1-trichloroethane by inhalation exposure, although such effects have not been widely
reported. Muttray et al. (1999) found increased levels of proinflammatory cytokines in nasal
secretions from human volunteers exposed to 200 ppm (1090 mg/m3), indicating a slight irritant
response characterized by subclinical inflammation in the nasal mucosa. In animals, minimal
lesions of the nasal turbinates were observed in male and female rats and mice exposed to
2000 ppm (10,920 mg/m3), but not lower concentrations, for 6 hours/day, 5 days/week for
14 weeks (Calhoun et al., 1981). However, it is not clear that these lesions were related to
1,1,1-trichloroethane exposure, as subsequent chronic studies by the same group of investigators,
which included interim sacrifices at 6, 12, and 18 months in addition to terminal sacrifice at
24 months, did not find nasal lesions in rats and mice exposed on a similar schedule (1500 ppm
[8190 mg/m3] for up to 2 years) (Quast et al., 1988, 1984).
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The liver is not a sensitive target of 1,1,1-trichloroethane by acute inhalation exposure.
Aside from a transitory increase in urinary urobilinogen in two of four subjects given a 15-
minute exposure to 2650 ppm (14,470 mg/m3) (Stewart et al., 1961), controlled exposure studies
in humans found no evidence for hepatotoxicity, as determined by liver function tests and serum
chemistry, hematology, and urinalysis measurements (Stewart et al., 1969, 1961; Dornette and
Jones, 1960; Torkelson et al., 1958). In animals, Adams et al. (1950) reported increased relative
liver weight (12%) and slight histopathology (fatty change) in the liver of rats exposed to
8000 ppm (43,680 mg/m3) for 7 hours and a larger increase in relative liver weight (27%) and
slight to moderate liver lesions, including more marked fatty changes and, in some cases,
congestion and hemorrhagic necrosis, in rats exposed to 12,000 ppm (65,520 mg/m3) for 7 hours.
Exposure for shorter durations, even to much higher concentrations, produced little evidence of
hepatotoxicity in animal studies (Loizou et al., 1996; Carlson, 1973; Gehring, 1968; Cornish and
Adefuin, 1966; Krantz et al., 1959; Adams et al., 1950). In prolonged, repeated exposure animal
studies, however, the liver is a more sensitive target for 1,1,1-trichloroethane. Minimal liver
effects were observed in rats and mice following inhalation of 1,1,1-trichloroethane at 2000 ppm
(10,920 mg/m3) for 6 hours/day, 5 days/week for three months (NOAEL = 1000 ppm
[5460 mg/m3]) (Calhoun et al., 1981). More marked liver lesions were found in mice
continuously exposed to 1000 ppm (5460 mg/m3) for 14 weeks (McNutt et al., 1975).
Histopathologic changes in the liver suggestive of an adaptive physiologic response were
observed in rats exposed to 1500 ppm (8190 mg/m3) 6 hours/day, 5 days/week for 2 years (Quast
et al., 1988, 1984). Serum enzyme changes indicative of hepatotoxicity were not found,
however, in workers exposed to up to 150-249 ppm (820-1360 mg/m3) of 1,1,1-trichloroethane
for up to 6 years (Kramer et al., 1978).
Developmental effects have been reported following gestational exposure to
1,1,1-trichloroethane vapor in animals. Mild fetotoxic effects (skeletal variations, reduced fetal
weights) were observed at high concentrations (LOAEL = 6000 ppm [32,760 mg/m3] for
6 hours/day, NOAEL = 3000 ppm [16,380 mg/m3]) that also produced effects on maternal body
weight and behavior in both rats and rabbits (BRRC, 1987a,b). Similar studies using lower
concentrations found no developmental or maternal effects (Schwetz et al., 1975). Some
investigators have shown neurobehavioral deficits in the pups of mice and rats, following late
gestational exposure to 1,1,1-trichloroethane (Coleman et al., 1999; Jones et al., 1996). In mice,
achievement of developmental milestones was also delayed, and in rats there was also an
increase in the number of resorptions and decrease in the number of live pups per litter. While
these effects were produced at fairly high concentrations, they were not necessarily accompanied
by maternal effects. The mouse study (Jones et al., 1996) was performed using two exposure
protocols, both of which produced neurobehavioral performance deficits in the pups. In one, the
dams were exposed to 8000 ppm (43,680 mg/m3) 3 hours/day on GDs 12-17, for an average
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daily exposure of 5460 mg/m3. This protocol produced anesthesia, severe gait abnormalities and
clonic movements in dams. In the other, the dams were exposed to a lower concentration for a
longer period each day (2000 ppm [10,920 mg/m3] 17 hours/day on GDs 12-17), resulting in a
higher daily average concentration (7720 mg/m3) but no effects on the dams. These studies
demonstrated that maternal exposure to 1,1,1-trichloroethane can produce neurodevelopmental
effects in pups and that this can occur at exposures that do not produce observable effects in the
dams. Exposure of rats to a similar concentration (2100 ppm [11,470 mg/m3]) for a shorter daily
exposure period (6 hours) from before mating through gestation (average daily gestational
exposure of 2870 mg/m3) produced no effects on pup development or on the dams (York et al.,
1982). Case-control studies in humans found no evidence of an association between
spontaneous abortion and 1,1,1-trichloroethane exposure (Windham et al., 1991; Lindbohm et
al., 1990; Taskinen et al., 1989) but have little power to detect a relationship.
The available inhalation toxicity studies were not, in general, designed to examine
whether the effects of 1,1,1-trichloroethane were reversible upon cessation of exposure or
whether effects might manifest after some latency period. Investigations for neurochemical
changes in the brain conducted by Rosengren et al. (1985) were performed 4 months after the
exposure ended. It may be inferred, therefore, that changes observed in this study were not
readily reversible. It should be noted, however, that brain tissue was not examined at the end of
the exposure to which tissues at 4 months postexposure could be compared, and the toxicological
relevance of this finding is uncertain. The CNS depressant effects of 1,1,1-trichloroethane, like
those of other solvents, are generally considered to be readily reversible (Evans and Balster,
1991). The effects are thought to be related to presence of the parent compound in neural
membranes and to dissipate as the parent compound is rapidly eliminated from the body
following exposure.
4.6.3. Mode-of-Action Information
1,1,1-Trichloroethane is rapidly and extensively absorbed via oral or inhalation exposure.
Following absorption, the chemical is rapidly distributed throughout the body, with preferential
accumulation in fat. Most of the absorbed 1,1,1-trichloroethane is rapidly eliminated from the
body unchanged in the expired air. A small amount is metabolized in the liver. The initial step
of metabolism is oxidation to trichloroethanol by ethanol- and phenobarbital-inducible CYP
isozymes. The major urinary metabolites are trichloroethanol glucuronide and trichloroacetic
acid produced from further oxidation of trichloroethanol. Carbon dioxide, released by
metabolism of trichloroacetic acid and exhaled in the breath, is the other major metabolite.
Because 1,1,1-trichloroethane is not metabolized to a large extent, the parent compound
is suspected to be the proximal toxicant for depressive effects on the CNS, respiratory center,
and heart, which are evident almost immediately upon exposure under some conditions. Direct
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evidence for involvement specifically of the parent compound is limited. Studies in mice and
rats have demonstrated that 1,1,1-trichloroethane enters the brain and may reach concentrations
similar to those in blood and also that 1,1,1-trichloroethane is eliminated more slowly from the
brain than from blood. One rat study analyzed specifically for metabolites in the brain and did
not detect them (Westerberg and Larsson, 1982). No other comparable studies were located. It
is possible that the metabolite trichloroethanol may contribute to the neurological effects.
Trichloroethanol has been hypothesized to be the active agent responsible for the
pharmacological effects of the sedative/hypnotic drug chloral hydrate (U.S. EPA, 2000f). At the
clinically recommended dose of chloral hydrate (i.e., the dose causing clinical sedation), the
blood concentration of trichloroethanol is estimated to be ~5 mg/L (U.S. EPA, 2000f). Nolan et
al. (1984) found that a 6-hour exposure of humans to 350 ppm (1900 mg/m3)
1,1,1-trichloroethane resulted in a peak blood trichloroethanol concentration of approximately
0.4 mg/L, and Monster et al. (1979) found that exposure to 145 ppm (790 mg/m3)
1,1,1-trichloroethane for 4 hours resulted in a blood trichloroethanol concentration 2 hours after
exposure to 0.2 mg/L. The 1,1,1-trichloroethane exposure concentration used by Nolan et al.
(1984) and Monster et al. (1979) is in the range associated with only minimal neurobehavioral
effects and produced blood trichloroethanol levels 10- to 25-fold lower than a blood level
associated with clinical sedation. It is plausible that higher 1,1,1-trichloroethane exposure
concentrations could produce blood trichloroethanol concentrations sufficient to cause sedation,
although data are not available to confirm this hypothesis.
The arrhythmogenic effects of 1,1,1-trichloroethane are also thought to be produced by
the parent compound. Animal studies have shown that the arrhythmias are not caused directly
by 1,1,1-trichloroethane but result from its sensitization of the heart to epinephrine. For this
effect, there is direct evidence that the parent compound, rather than metabolites, is responsible:
arrhythmias in response to epinephrine challenge in 1,1,1-trichloroethane-exposed rabbits were
enhanced by cotreatment with enzyme inhibitors (SKF-525A, Lilly 18947) that increased blood
levels of parent compound and were slightly diminished by cotreatment with the enzyme inducer
phenobarbital, which slightly reduced the level of parent compound in the blood (Carlson, 1981).
It is uncertain whether the hepatotoxic effects of 1,1,1-trichloroethane are due to the
parent compound or are mediated by metabolites (such as trichloroacetic acid and/or reactive
intermediates). For several other chlorinated hydrocarbons, it is well documented that liver
damage may be caused by reactive (free radical) intermediates generated during the oxidative
and/or reductive metabolism by microsomal CYP (Klaassen et al., 1996). However, there are
mechanisms by which the parent chlorinated hydrocarbon can produce liver effects as well. In
support of the involvement of metabolites in the hepatotoxicity of 1,1,1-trichloroethane, Carlson
(1973) found that rats pretreated with phenobarbital exhibited liver effects (increased serum
levels of ALT and AST) at an exposure concentration that did not produce such effects without
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phenobarbital pretreatment. Other studies, however, found that the hepatotoxicity of
1,1,1-trichloroethane was not affected by pretreatment with phenobarbital (Cornish et al., 1973)
or other inducers of CYP enzymes involved in metabolism of 1,1,1-trichloroethane: ethanol
(Klaassen and Plaa, 1967, 1966), isopropanol (Traiger and Plaa, 1974), or acetone (Charbonneau
et al., 1991; Traiger and Plaa, 1974).
The CNS depressant effects of 1,1,1-trichloroethane are thought to involve interactions of
the parent compound with lipids and/or proteins in neural membranes (Evans and Balster, 1991).
In general, the highly lipophilic nature of chlorinated hydrocarbons, such as
1,1,1-trichloroethane, allows them to cross the blood-brain barrier readily and partition into
lipids in neuronal membranes. This property allows them to interfere with neural membrane
function, bringing about CNS depression, behavioral changes, and anesthesia (Klaassen et al.,
1996). Effects of the 1,1,1-trichloroethane parent compound on the heart and liver also appear to
involve altered function of cellular and mitochondrial membranes. Supporting evidence that
1,1,1-trichloroethane can interact with proteinaceous components of membranes comes from
experiments showing that the chemical can inhibit the activity of membrane-bound integral
enzymes (acetylcholinesterase and magnesium-activated ATPase) in human red blood cells and
rat synaptosomes (Korpela, 1989; Korpela and Tahti, 1987, 1986; Tahti and Korpela, 1986).
Possibly as a result of interactions with membrane proteins, 1,1,1-trichloroethane can alter
membrane permeability to calcium. This ability has been demonstrated in brain synaptosomes
(Robinson et al., 2001; Nilsson, 1987) and dorsal root ganglion neurons (Okuda et al., 2001),
cardiac myocytes (Hoffmann et al., 1994, 1992; Toraason et al., 1990), and rat heart and liver
mitochondria (Herd and Martin, 1975). Demonstrated consequences of altered calcium
permeability include reduced contractility of cardiac myocytes (Hoffmann et al., 1994, 1992;
Toraason et al., 1990) and uncoupled oxidative phosphorylation leading to reduced cellular
respiration and ATP production in rat heart and liver mitochondria (Takano and Miyazaki, 1982;
Ogata and Hasegawa, 1981; Herd and Martin, 1975). Reduced cellular energy generation was
apparently responsible for inhibition of active transport systems in rat hepatocytes by
1,1,1-trichloroethane (Kukongviriyapan et al., 1990).
In addition to the depressive effect on the heart, membrane alterations are also thought to
play an important role in the occurrence of arrhythmogenic effects by 1,1,1-trichloroethane.
Incorporation of 1,1,1-trichloroethane into the membrane of cardiac myocytes in the region of
the gap junction has been hypothesized to explain the observed inhibition by
1,1,1-trichloroethane of gap junction intercellular communication in cardiac myocytes (Toraason
et al., 1992). Inhibition of intercellular communication is thought to be related to the
arrhythmogenic effects of 1,1,1-trichloroethane.
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4.7. EVALUATION OF CARCINOGENICITY
4.7.1. Summary of Overall Weight of Evidence
Under the Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005a), the database
for 1,1,1-trichloroethane provides inadequate information to assess carcinogenic potential.
Epidemiologic studies of humans chronically exposed to 1,1,1-trichloroethane are inconclusive.
A 2-year inhalation bioassay showed no treatment-related increase in tumors in rats and mice at
an exposure concentration below the maximum tolerated dose. The two available oral cancer
bioassays in rats and mice are considered inadequate for evaluation of carcinogenic potential.
1,1,1-Trichloroethane has been tested extensively for genotoxic potential. The chemical has
shown little capacity to produce genotoxic effects in bacteria or fungi. Results in mammalian
test systems in vitro and in vivo were more mixed, but still predominantly negative for assays
other than cell transformation. The chemical has been shown to interact weakly with DNA.
The previous IRIS assessment (1987) classified 1,1,1-trichloroethane as Group D (not
classifiable as to human carcinogenicity) under the 1986 Guidelines for Carcinogen Risk
Assessment (U.S. EPA, 1986c), based on a lack of data on the carcinogenicity of
1,1,1-trichloroethane in humans and inadequate evidence of carcinogenicity in animals.
4.7.2. Synthesis of Human, Animal, and Other Supporting Evidence
The potential carcinogenicity of 1,1,1-trichloroethane was examined in two occupational
cohort studies and several case-control and environmental studies. Finnish workers (male and
female combined) exposed to 1,1,1-trichloroethane had statistically significantly increased
standardized incidence ratios for cancer of the nervous system (SIR = 6.05; 95% CI: 1.25-17.7)
and multiple myeloma (SIR = 15.98; 95% CI: 1.93-57.7) (Anttila et al., 1995). The results are
based on only three cases of nervous system tumors and two cases (both females) of multiple
myeloma among 1,1,1-trichloroethane-exposed workers. The large confidence intervals reveal
the low statistical power of these findings. An increased risk of multiple myeloma was also
observed in female workers exposed to 1,1,1-trichloroethane at an aircraft maintenance facility
in Utah (SMR = 56.6; 95% CI: 6.85-204.45) (Spirtas et al., 1991). This result was also based on
only two observed cases. No cases of multiple myeloma were seen in men. In both studies,
workers were exposed to multiple solvents, and in neither case was it possible to isolate the
effects of 1,1,1-trichloroethane from those of other solvents. Case-control and environmental
studies did not find statistically significant associations between tumors of various types
(including astrocytic brain cancer) and 1,1,1-trichloroethane exposure (Infante-Rivard et al.,
2005; Dosemeci et al., 1999; Kernan et al., 1999; Mulla, 1996; Heineman et al., 1994; Garland,
1987; Garabrant, 1986; Isacson et al., 1985); however, the power of such studies to find an
association is low.
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1,1,1-Trichloroethane has been tested for carcinogenicity in rats and mice by the oral
route in two studies (Maltoni et al., 1986; NCI, 1977) and by the inhalation route in a 2-year
study (Quast et al., 1988, 1984) and a more limited 1-year study (Quast et al., 1978). Maltoni et
al. (1986) found a small increase in the incidence of leukemias, primarily pulmonary
immunoblastic lymphosarcomas, in Sprague-Dawley rats (male and female combined) treated
with 1,1,1-trichloroethane by gavage in oil for 104 weeks. These results were considered
inconclusive, however, because of the marginal nature of the findings, inherent limitations of the
experimental design (one dose level, one species), and incomplete analysis and reporting of
results (see discussion in Section 4.2.1.4). Oral studies by NCI (1977) in Osborne-Mendel rats
and B6C3F1 mice conducted at higher doses did not find tumor increases associated with
1,1,1-trichloroethane exposure but were not adequate tests due to high early mortality in all
groups of treated animals (due, at least in part, to intercurrent chronic murine pneumonia) that
left few animals at risk for development of late-appearing tumors. Inhalation studies by Quast et
al. (1988, 1984) found no evidence of a carcinogenic effect of 1,1,1-trichloroethane in either
F344 rats or B6C3F1 mice. In these studies, however, it appears that exposure levels were too
low. The MTD was not reached in mice (no adverse effects observed in either sex) and may not
have been reached in rats, as the only toxic effects noted were a slight reduction in body weight
gain in female rats and slight microscopic hepatic changes in male and female rats exposed to the
high concentration of 1500 ppm (8190 mg/m3). Therefore, the possibility of tumors occurring at
higher inhalation exposures cannot be ruled out. Quast et al. (1978) also exposed Sprague-
Dawley rats to 1,1,1-trichloroethane for 1 year, followed by a 19-month observation period. No
increase in neoplastic lesions was observed, although it should be noted that exposure was for
less than a lifetime and to a concentration that may not have reached the MTD.
Supporting studies provide mixed evidence regarding the carcinogenic potential of
1,1,1-trichloroethane. A rat liver foci assay for tumor-initiating and -promoting activity was
negative for both (Milman et al., 1988; Story et al., 1986). In vitro studies for effects associated
with carcinogens (inhibition of interferon induction in mouse embryo fibroblasts and inhibition
of the natural tumoricidal activity of human liver immune cells) were also negative (Wright et
al., 1994; Sonnenfeld et al., 1983). Although genotoxicity data were also primarily negative,
positive results were found in some tests, including six of seven reported cell transformation
assays (Milman et al., 1988; Tu et al., 1985; Arthur D. Little, 1983; Hatch et al., 1983, 1982;
Daniel and Dehnel, 1981; Styles, 1981; Price et al., 1978). It has also been shown that
1,1,1-trichloroethane has the ability to bind DNA, at least weakly, in vivo (Milman et al., 1988;
Prodi et al., 1988; Turina et al., 1986).
Loew et al. (1984) identified certain molecular properties of eight chloroethanes as
indicators of rank order of carcinogenic activity, specifically as indicators of the extent of
transformation to alcohols by CYP450 and subsequent formation of aldehydes (the latter
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assumed to be the active carcinogen, acting as electrophile in adduct formation with DNA
bases). Of the eight chloroethanes, 1,1,1-trichloroethane received the lowest rank order because
it does not form an aldehyde.
A potential complicating factor in interpreting the results of cancer bioassays of
1,1,1-trichloroethane is the frequent addition of stabilizing chemicals to commercial
formulations of this compound (Henschler et al., 1980). Several of these stabilizers have
produced positive responses in cancer bioassays with rats and mice (e.g., 1,4-dioxane, 1,2-
epoxybutane, and nitromethane). This is a potential confounding factor for many studies of
exposure to 1,1,1-trichloroethane but has been addressed in relatively few studies (Shimada et
al., 1985; Nestmann et al., 1984). The situation is complicated by the fact that not all
formulations of 1,1,1-trichloroethane contain the same stabilizers. For instance, the
1,1,1-trichloroethane formulations used in the three animal cancer bioassays described above
(Quast et al., 1988, 1984; Maltoni et al., 1986; NCI, 1977) contained different stabilizing
chemicals. Anttila et al. (1995) reported that small amounts of 1,4-dioxane (
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4.8. SUSCEPTIBLE POPULATIONS AND LIFE STAGES
4.8.1. Possible Childhood Susceptibility
Exposure of the fetus or neonate (via lactation) to 1,1,1-trichloroethane is possible;
however, pharmacokinetic data and the majority of developmental toxicity data indicate no
particular susceptibility of the fetus or neonate. Danielsson et al. (1986) exposed pregnant mice
(GD 17) to 14C-labeled 1,1,1-trichloroethane by inhalation and found concentrations in fetal and
placental tissues to be about 10-fold lower than concentrations in tissue samples from the dams
immediately after exposure. By 24 hours after exposure, maternal and fetal/piacental tissue
levels were all low. A PBPK model for a lactating woman (Fisher et al., 1997) predicted that
partitioning to milk (and excretion via the milk during nursing) was a minor physiological fate of
inhaled 1,1,1-trichloroethane in a lactating woman exposed under a plausible occupational
scenario (see also Section 3.5). Thus, pharmacokinetic data indicate no fetal/neonatal
susceptibility as a result of elevated exposure. In general, developmental toxicity has been
observed in developing animals only at exposure concentrations also toxic to the dam,
suggesting no particular susceptibility of the fetus to 1,1,1-trichloroethane. In only one
inhalation developmental study in mice (Jones et al., 1996) did exposure of the dams to 2000
ppm 1,1,1-trichloroethane produce developmental delays in offspring at a concentration that did
not produce obvious maternal toxicity. The relative sensitivity of dams and fetuses to
1,1,1-trichloroethane cannot be characterized with certainty based on this study, however,
because the study design did not include systematic investigation of behavioral effects in dams
and because the same exposure concentration has produced CNS effects in other rodent studies.
4.8.2. Possible Gender Differences
The NTP (2000) subchronic feeding study demonstrated the occurrence of renal lesions
in male, but not female, rats. The lesions included renal tubule hyaline degeneration, cast
formation, and regeneration and chronic interstitial inflammation of the kidney. The sex-specific
pattern of occurrence in rats, type of lesions observed, and absence of renal lesions in mice of
either sex in the same study are all consistent with the occurrence of a2U-globulin nephropathy in
the male rats, although a,2u-globulin was not specifically identified. This sex- and species-
specific condition is not considered to be predictive of effects in humans (U.S. EPA, 1991c).
4.8.3. Other Potentially Susceptible Populations
1,1,1-Trichloroethane can induce the activity of microsomal enzymes, particularly
CYP2E1 and CYP2B1/2 (Bruckner et al., 2001; Shah and Lai, 1976; Fuller et al., 1970; Lai and
Shah, 1970). As a result, 1,1,1-trichloroethane could potentially enhance the toxicity of other
chemicals, such as carbon tetrachloride and 1,1-dichloroethylene, that are metabolized by these
CYP isozymes to reactive intermediates. 1,1,1-Trichloroethane has also been shown to deplete
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liver glutathione (Loizou et al., 1996). Binding of reactive metabolites by glutathione is an
important detoxification pathway for many chemicals. Given the modest reduction in liver
glutathione (23 to 42%) even at relatively high exposure concentrations (4000 to 25,000 ppm
[21,840 to 136,500 mg/m3] 1,1,1-trichloroethane), it is not clear that depletion of glutathione
stores in the liver by 1,1,1-trichloroethane would likely enhance the toxicity of chemicals for
which the detoxification pathway includes conjugation with glutathione.
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5. DOSE-RESPONSE ASSESSMENTS
5.1. ORAL REFERENCE DOSE (RfD)
5.1.1. Acute Oral RfD
The acute oral data for 1,1,1-trichloroethane are inadequate to support derivation of an
acute oral RfD, a reference value intended for use with exposures up to 24 hours. Human data
are limited to the results of a single case report involving accidental ingestion of 1,1,1-
trichloroethane (Stewart and Andrews, 1966). In general, case reports are not useful as the basis
for a reference value. The minimal dose-response information and reporting of results provided
in this case report limit its utility for dose-response analysis.
Acute animal studies are limited to the following:
(1) A handful of studies that investigated only hepatic endpoints and found conflicting results as
to the potency of 1,1,1-trichloroethane by acute oral exposure in rats (Bruckner et al., 2001; Xia
and Yu, 1992; Tyson et al., 1983). Xia and Yu (1992) reported only a transient 1.5-fold increase
in ALT and no histopathological changes of the liver following a single 670 mg/kg dose of
1,1,1-trichloroethane. Tyson et al. (1983) found no change in ALT in rats given a single
2500 mg/kg dose of 1,1,1-trichloroethane and only a transient increase in AST (twofold).
Bruckner et al. (2001), in contrast, found no evidence of hepatotoxicity following a single oral
gavage dose of 4000 mg/kg.
(2) A study that found no significant changes in levels of neurotransmitters in the brains of rats
dosed with 3250 mg/kg of 1,1,1-trichloroethane by gavage (Kanada et al., 1994).
(3) LDso determinations.
These studies failed to clearly establish sensitive targets of toxicity or dose-response
relationships for acute oral exposure to 1,1,1-trichloroethane. Accordingly, an acute RfD was
not derived.
5.1.2. Short-term Oral RfD
The short-term oral data for 1,1,1-trichloroethane are inadequate to support derivation of
a short-term oral RfD, a reference value intended for use with exposures for more than 24 hours,
up to 30 days. No short-term human data are available. Short-term animal studies identified
dose levels associated with gross CNS depression and death by gavage exposure (Bruckner et al.,
2001) but failed to conclusively identify targets or effect levels not associated with frank toxicity
(Bruckner et al., 2001; NTP, 1996; Maurissen et al., 1994, 1993; Spencer et al., 1990; Platt and
Cockrill, 1969). Spencer et al. (1990) observed neurophysiological changes at a relatively low
dose level (705 mg/kg-day), but a threshold for these changes was not identified (only one dose
level was tested) and the toxicological significance of these changes is uncertain, as other
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neurotoxicological endpoints were unaffected at similar doses (Maurissen et al., 1994, 1993;
Spencer et al., 1990).
Because the available short-term oral toxicity studies failed to identify effects of
biological significance other than frank toxicity (i.e., gross CNS depression or death), a short-
term RfD was not derived.
5.1.3. Subchronic Oral RfD
The subchronic oral RfD is intended for use with exposures for more than 30 days, up to
approximately 10% of the lifespan in humans (or up to approximately 90 days in typically used
laboratory animal species).
5.1.3.1. Choice of Principal Study and Critical Effect—with Rationale and Justification
No human data involving exposures of subchronic duration are available. Subchronic
animal studies include studies of developmental and reproductive toxicity, which did not
conclusively demonstrate the occurrence of effects due to 1,1,1-trichloroethane (George et al.,
1989; NTP, 1987a,b; Dapson et al., 1984a,b; Lane et al., 1982), and studies of systemic toxicity
by gavage (Bruckner et al., 2001) and dietary (NTP, 2000) exposure.
Bruckner et al. (2001) reported a LOAEL of 2500 mg/kg (1786 mg/kg-day when adjusted
for exposure 5 days per week) for gross CNS depression and death in rats exposed by gavage.
Investigation of systemic endpoints was limited to the liver; only mild hepatic changes were
found and only at lethal doses. Sensitive neurological endpoints were not monitored. In the
feeding study, NTP (2000) observed no gross CNS effects or deaths at doses up to about
5000 mg/kg-day in rats or 23,000 mg/kg-day in mice. Dose-related decreases in body weight
gain and terminal body weight were observed; terminal body weights were 10% lower than the
vehicle control at a dose of-4800 mg/kg-day in the male rat and 11-12% lower than the vehicle
control at 3500 or 5600 mg/kg-day in the male and female mouse, respectively. Target organ
effects found in this study were of uncertain toxicological significance. Renal lesions were
reported in male rats at >1200 mg/kg-day. NTP (2000) considered the types of lesions observed
and their occurrence only in male rats to be consistent with development of a,2u-globulin
nephropathy, a nephropathy specific to male rats and not considered relevant to human health
risk assessment (NTP, 2000; U.S. EPA, 1991c). Assays to confirm the presence of a2u-globulin
itself, however, were not conducted. Similar renal effects have not been reported in any other
studies in the 1,1,1-trichloroethane database, including a short-term NTP (1996) study designed
specifically to look for this effect. NTP (2000) also reported slight (10-20%) reductions in
epididymal spermatozoal concentrations in high-dose male rats and mice at dose levels
accompanied by reduced body weight gain (4800 mg/kg-day in rats and 15,000 mg/kg-day in
mice). NTP (2000) considered this slight reduction in epididymal sperm count to be treatment
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related, probably affecting the epididymis. There were, however, no weight or histopathologic
changes in this organ, and the absence of reproductive effects in other studies does not support
effects on reproductive tissues as a sensitive target. The NTP (2000) study did not include
investigation of sensitive neurological endpoints in either rats or mice. There were no clinical
findings or histopathologic changes in the brain related to chemical exposure.
The differences in the findings of the Bruckner et al. (2001) and NTP (2000) studies can
be attributed to the bolus dosing employed by Bruckner et al. (2001). In comparison to relatively
steady intake throughout the day via dietary administration, bolus dosing will produce much
higher peak blood levels, as the entire daily dose is rapidly absorbed all at once. The gross CNS
effects and mortality observed by Bruckner et al. (2001) are likely a reflection of the high peak
blood levels by this mode of administration. This is particularly apparent by comparing survival
in the male rats in the 13-week rat studies involving gavage administration (Bruckner et al.,
2001) and dietary administration (NTP, 2000) (see Table 5-1).
Table 5-1. Comparison of survival in rats administered 1,14-trichloroethane
by gavage and in the diet
Study
(method of administration)
NTP, 2000 (diet)
Bruckner et al., 2001 (gavage)
Dose (mg/kg-day)
290
357
600
1200
1790
2400
3570
4800
Survival (%)
100
-
-
93
100
-
100
-
-
67
100
-
-
53
100
-
The findings from bolus exposure to 1,1,1-trichloroethane are considered less relevant to
subchronic or chronic exposure conditions in humans. Accordingly, the 90-day dietary study in
rats and mice (NTP, 2000) was selected as the basis for the subchronic oral RfD, and treatment-
related decrements in body weight gain in mice as the critical effect.
Decreased body weight appears to be a sensitive effect in other subchronic and chronic
studies by oral or inhalation routes of exposure, either in the absence of other toxicity (Bruckner
et al., 2001; Prendergast et al., 1967; Adams et al., 1950) or at doses causing minimal liver
changes (possibly physiologic changes) (Quast et al., 1988, 1984; Calhoun et al., 1981).
Reduced body weight has also been observed at levels causing reduced survival without clear
indication of any target organ toxicity (Bruckner et al., 2001; NCI, 1977).
While decreased body weight in the absence of specific measures of target organ toxicity
is not preferred for use as a critical effect, other organizations have considered effects on body
weight to be a functional effect. EPA's Office of Pesticide Programs (U.S. EPA, 2003)
identified the following considerations in interpreting body weight data for pesticides: (1) body
weight changes may be related to food intake, and analysis of one without the other is of limited
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value; (2) changes in food consumption and body weight gains can influence, or be influenced
by, many aspects of animal responses, including metabolic, hormonal, and homeostatic
mechanisms, disease processes, and maturation; (3) reduced body weight gain related to diet
palatability is often evidenced in the first 2 or 3 weeks of the study and may dissipate as animals
develop a tolerance or adapt to test article modification of the diet; and (4) an evaluation of body
weight should be integrated with other study data in a weight-of-evidence approach and should
be considered with respect to both statistical and biological significance. The International
Program on Chemical Safety (IPCS, 1999, 1987) considers weight loss to be a functional
manifestation, noting that reduced weight gain has played a major role as an endpoint in
toxicological studies in various ways; a generalized decrement in weight gain has been used to
define an effect level in the absence of other toxic manifestations, provided reduced food intake
is not the obvious cause.
The body weight findings for 1,1,1-trichloroethane were considered in light of the
considerations identified by U.S. EPA (2003) and IPCS (1999, 1987). The finding of decreased
body weight gain in animals exposed to 1,1,1-trichloroethane was observed across studies. In
the NTP toxicity study, the reductions in body weight gain were not transient nor were they
accompanied by reduced food intake, and there was no indication that body weight recovered
with time on study (i.e., nothing that suggested the development of a tolerance). Further, the
differences in body weight were statistically significant and were dose related for male and
female mice. For these reasons, reduced body weight gain in mice was considered to be a
biologically relevant basis for the RfD.
5.1.3.2. Methods of Analysis
The subchronic RfD was derived using benchmark dose analysis of body weight data
from male and female mice exposed to 1,1,1-trichloroethane for 90 days (NTP, 2000). These
data were presented previously in Section 4.2.1.3 (Table 4-4).
Continuous data models (linear, polynomial, power, and Hill) with a constant variance
were fit to the data by using U.S. EPA Benchmark Dose Software (BMDS) (version 1.4). The
software was used to calculate potential points of departure for deriving the subchronic RfD by
estimating the effective dose at a specified level of response (BMDX) and its 95% lower bound
(BMDLX). A 10% change in mean terminal body weight relative to the control mean was
selected as the benchmark response (BMR) level for this continuous data set. A 10% change in
body weight is the minimal level of change generally considered to be biologically significant
(U.S. EPA, 2000c).
The BMDS outputs for mouse body weight data are summarized in Table 5-2. All
models provided an adequate fit of the female body weight data based on the goodness-of-fit
statistic (p-value > 0.1). The Hill model provided the best fit of the data for the female mouse
123
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(based on the lowest Akaike's Information Criterion [AIC]); the detailed BMD modeling output
for the Hill model is presented in Appendix B.
Table 5-2. Benchmark dose modeling results using terminal body weight
data for mice
Model
Female mouse
Linear
Polynomial
Power
Hill
Male mouse
Hill
GOFPa
0.1428
0.1428
0.1428
0.6893
0.1417
AIC
159.4
159.4
159.4
157.2
139.2
BMD10b
(mg/kg-day)
15,024.6
15,024.6
15,024.6
5064.4
1943.1
BMDL10C
(mg/kg-day)
11,256.5
11,256.5
11,256.5
2155.2
594.3
aGOFP = goodness-of-fit/>-value for chi-square.
bBMD10 = benchmark dose calculated by BMDS associated with a 10% decrease in mean body weight relative to the
control mean.
°BMDL10 = 95% lower confidence limit on the BMD10 as calculated by BMDS.
Source: NTP (2000).
With the exception of the Hill model, the continuous data models did not provide an
adequate fit of the body weight data for the male mouse (i.e., goodness-of-fit/>-value < 0.1). The
Hill model provided an adequate fit of the male mouse data (see Table 5-2); the detailed BMD
modeling output is presented in Appendix B.
Visual inspection of plots of body weight data for the male and female mouse (Appendix
B) reveals that the female data set provides a much better relationship of dose and response than
does the male data set. In the case of the male data set, the first four dose groups show a flat
dose-response relationship; in the dose range between 850 and 7370 mg/kg-day, the body weight
decrease (relative to controls) approaches 10%, but male mouse body weight appears to be
relatively insensitive to increasing doses of 1,1,1-trichloroethane. A decrease in body weight
relative to the control appears to exceed 10% only in the high-dose (15,000 mg/kg-day) male
mice. Although the Hill model provided an adequate fit of the male mouse data, the resulting
BMDLio of 594 mg/kg-day is not consistent with the data that show no relationship between
dose and reduction in body weight gain at a dose as high as 7370 mg/kg-day. NTP (2000) noted
that feed consumption and estimates of average daily dose were determined by the disappearance
of feed from the feeder and may not accurately represent intake. It is possible that imprecision in
dose estimates may have contributed to the observed dose-response relationship in male mice.
Because male and female mice generally responded similarly to 1,1,1-trichloroethane in
the diet (i.e., the decrease in body weight was similar, with terminal body weights in high-dose
124
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male and female mice 84-85% of controls) and because the female body weight data showed a
clearer relationship between dose and response, the female mouse data were used as the basis for
the subchronic RfD. The BMDLio for female body weight data based on the Hill model of
2155 mg/kg-day was selected as the point of departure for the subchronic RfD.
5.1.3.3. Subchronic RfD Derivation—Including Application of Uncertainty Factors (UFs)
The BMDLio of 2155 mg/kg-day was used as the point of departure for calculating the
subchronic RfD. This point of departure is associated with a 10% change in the mean terminal
body weight relative to the control mean. A composite uncertainty factor (UF) of 300 was
applied to this point of departure: 10 for extrapolation from animals to humans, 10 for
intraspecies variation (human variability), and 3 for database deficiencies.
• A 10-fold UF was used to account for laboratory animal-to-human interspecies differences.
This default UF accounts for differences in the toxicokinetics and toxicodynamics between
the model species and humans.
• A default 10-fold UF for intraspecies differences was used to account for potentially
susceptible individuals in the absence of information on the variability of response to
1,1,1-trichloroethane in the human population.
• A UF to extrapolate from a LOAEL to a NOAEL was not necessary because BMD modeling
was used to determine the point of departure.
• A UF to extrapolate from a shorter to a longer duration was not necessary because the
subchronic RfD was derived from a study of subchronic duration.
• A threefold UF was used to account for deficiencies in the available 1,1,1-trichloroethane
database. Oral reproductive and developmental toxicity studies include a multigeneration
study in mice, drinking water developmental toxicity studies in rats, and a study of
developmental neurotoxicity in rats, none of which clearly demonstrated any effects. The
principal study, a 13-week NTP (2000) toxicity study, was conducted under an interagency
agreement with the ATSDR to address data needs identified by ATSDR. Specifically,
ATSDR identified the need for data from intermediate-duration oral exposure studies to
provide information that would help determine the NOAELs and LOAELs for systemic,
neurological, reproductive, and developmental effects. NTP (2000) was a well-conducted
repeat-dose oral study but did not examine the potential for subtle neurotoxicity. Acute
neurotoxicity was observed by the oral route following bolus dosing (e.g., hyperexcitability
and narcosis reported by Bruckner et al. [2001]) and by the inhalation route, where signs of
CNS depression have been extensively documented. As discussed more thoroughly in the
justification of the database uncertainty factor used in the derivation of the subchronic RfC,
some uncertainty exists with respect to the neurotoxicity database for 1,1,1-trichloroethane,
125
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notably associated with findings from the epidemiological literature and from the Rosengren
et al. (1985) study in gerbils. Thus, lack of endpoints for subtle neurotoxic potential
following repeated exposure is considered a deficiency in the oral database for this chemical
in light of evidence of its acute neurotoxicity and uncertainties in the inhalation neurotoxicity
database.
The subchronic RfD for 1,1,1-trichloroethane was calculated as follows:
Subchronic RfD = BMDLio-UF
= 2155 mg/kg-day -300
= 7 mg/kg-day
5.1.4. Chronic Oral RfD
The chronic oral RfD is intended for use with exposures for more than approximately
10% of the lifespan in humans (or more than approximately 90 days to 2 years in typically used
laboratory animal species).
5.1.4.1. Choice of Principal Study and Critical Effect—with Rationale and Justification
No chronic human data for 1,1,1-trichloroethane are available. Chronic oral animal
studies consist of two cancer bioassays (Maltoni et al., 1986; NCI, 1977). NCI (1977) exposed
male and female rats and mice to 1,1,1-trichloroethane by gavage for 78 weeks. In rats, effects
included reduced survival and decreased body weight but no clinical observations or
histopathological changes. Effects in mice consisted of reduced survival and decreased body
weight. Chronic murine pneumonia was a probable contributing factor in the early deaths.
Because of the high rate of early mortality, NCI did not consider this to be an adequate test of
1,1,1-trichloroethane carcinogenicity (and by extension, noncancer toxicity). Body weight data
from the study were provided in graphical format only without error bars, and a consistent dose-
response relationship was not apparent.
Maltoni et al. (1986) administered 1,1,1-trichloroethane to rats by gavage at a single dose
level for 104 weeks in a screening level carcinogenicity bioassay. The study did not include an
evaluation of nonneoplastic lesions. A treatment-related reduction in body weight was observed
in female rats but not males. Body weight data were reported graphically only and without error
bars.
Both NCI (1977) and Maltoni et al. (1986) were designed as cancer bioassays and
included only limited investigation of noncancer endpoints. Decreased body weight gain was the
only noncancer effect reported and in the case of NCI (1977) was confounded by poor survival.
In both studies, body weight data were provided graphically only. Finally, both NCI (1977) and
126
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Maltoni et al. (1986) used gavage administration. As discussed in Section 5.1.3.1, gavage
administration produces toxicity that likely reflects the high peak blood levels associated with
bolus dosing and is considered less relevant than the toxicity associated with dietary
administration. Therefore, these studies did not provide data suitable for reference value
derivation.
In the absence of adequate chronic toxicity data, the 90-day toxicity study conducted by
NTP (2000) was used as a basis for deriving the chronic oral RfD.
5.1.4.2. Methods of Analysis
The point of departure of 2155 mg/kg-day was derived from decreased terminal body
weight in female mice relative to the control from NTP (2000) and application of BMD
modeling methods as described in Section 5.1.3.2 for the subchronic oral RfD. This point of
departure represents a 10% change in mean terminal body weight relative to the control mean.
5.1.4.3. RfD Derivation—Including Application of Uncertainty Factors (UFs)
A composite UF of 1000 was applied to the point of departure of 2155 mg/kg-day: 10 for
extrapolation from animals to humans, 10 for intraspecies variation (human variability), 3 for
extrapolation from subchronic to chronic exposure duration, and 3 for database deficiencies.
• A 10-fold UF was used to account for laboratory animal-to-human interspecies differences.
This default UF accounts for differences in the toxicokinetics and toxicodynamics between
the model species and humans.
• A default 10-fold UF for intraspecies differences was used to account for potentially
susceptible individuals in the absence of information on the variability of response to
1,1,1-trichloroethane in the human population.
• A UF to extrapolate from a LOAEL to a NOAEL was not necessary because BMD modeling
was used to determine the point of departure.
• A threefold UF was used to extrapolate from subchronic to chronic exposure duration. The
available body weight data from chronic toxicity studies suggest that body weight effects did
not become more pronounced with duration of exposure. In the NCI (1976) cancer bioassay,
body weight data are presented in graphic format only. Visual inspection of these graphs for
rats shows reduction in mean body weight in treated animals in year 1 (beginning between
weeks 10 and 20) to be similar to the weight reduction in year 2 (with the exception of low-
dose females, where elevated mortality confounded body weight results). Similarly for mice,
the treatment-related mean body weight reduction in year 1 (beginning between weeks 10
and 20) was similar to that in year 2 for male mice; for females, the differences in mean body
weight were slightly higher in year two.
127
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The inhalation study by Quast et al. (1988, 1984) similarly revealed no progression in
any 1,1,1-trichloroethane-associated effects with length of exposure. Mean body weight
reduction in female rats vs. controls was similar in year 1 and 2 (1,1,1-trichloroethane did not
produce statistically significant effects on body weight in male rats or male and female
mice). Histopathologic changes of the liver in rats, the only other exposure-related effect in
this study, showed no progression in incidence or severity from the first interim sacrifice
(6 months) to study termination (2 years). For these reasons, a partial UF of 3 is used for
extrapolation from subchronic to chronic exposure duration.
Removing the UF for subchronic to chronic extrapolation was not considered appropriate
because lifetime oral data are not available to fully characterize the potential chronic toxicity
of 1,1,1 trichloroethane. The Maltoni et al. (1986) study was designed as a cancer bioassay
only and did not include evaluation of nonneoplastic lesions. In the NCI (1977) bioassay,
high early mortality was observed in rats and mice, probably due to murine pneumonia, and
thus NCI (1977) considered the study to be inadequate.
A threefold UF was used to account for deficiencies in the available 1,1,1 trichloroethane
database. Oral reproductive and developmental toxicity studies include a multigeneration
study in mice, drinking water developmental toxicity studies in rats, and a study of
developmental neurotoxicity in rats, none of which clearly demonstrated any effects. Neither
the available chronic studies nor the 13-week NTP study included investigation of sensitive
neurological endpoints. As noted in the discussion of the subchronic database UF, the
principal study, a 13-week NTP (2000) toxicity study, was conducted under an interagency
agreement with the ATSDR to address data needs identified by ATSDR. Specifically,
ATSDR identified the need for data from intermediate-duration oral exposure studies to
provide information that would help determine the NOAELs and LOAELs for systemic,
neurological, reproductive, and developmental effects. NTP (2000) was a well-conducted
repeat-dose oral study but did not examine the potential for subtle neurotoxicity. Acute
neurotoxicity was observed by the oral route following bolus dosing (e.g., hyperexcitability
and narcosis reported by Bruckner et al. [2001]) and by the inhalation route, where signs of
CNS depression have been extensively documented. As discussed more thoroughly in the
justification of the database uncertainty factor used in the derivation of the chronic RfC,
some uncertainty exists with respect to the neurotoxicity database for 1,1,1-trichloroethane,
notably associated with findings from the epidemiological literature and from the Rosengren
et al. (1985) study in gerbils. Lack of endpoints for subtle neurotoxic potential following
repeated exposure is considered a deficiency in the oral database for this chemical in light of
evidence for acute neurotoxicity and uncertainty in the inhalation database.
128
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The chronic RfD for 1,1,1-trichloroethane was calculated as follows:
Chronic RfD = BMDLio + UF
= 2155mg/kg-day-1000
= 2 mg/kg-day
5.1.4.4. Previous Oral Assessment
A chronic oral assessment for 1,1,1-trichloroethane had been previously included on the
IRIS database but was withdrawn in 1991.
5.1.5. RfD Derivation Using Route-to-Route Extrapolation
Consideration was also given to the derivation of oral RfDs for 1,1,1-trichloroethane
using relevant inhalation data and route-to-route extrapolation with the aid of a PBPK model.
Several factors support the use of route-to-route extrapolation for 1,1,1-trichloroethane.
1,1,1-Trichloroethane is well absorbed by all pathways of exposure and is largely excreted
unchanged by the lungs in the expired air, whether administration is by oral or inhalation
exposure. Evidence suggests that the metabolism of 1,1,1-trichloroethane following oral and
inhalation exposure is similar (see Section 3).
PBPK modeling was conducted for the U.S. EPA by Yang (2006) using the Reitz et al.
(1988) model (see Section 3.5). Application of the model is more fully described in Yang
(2006).
5.1.5.1. Acute and Short-term Durations
Yang (2006) explored the use of available PBPK models and, in particular, the Reitz et
al. (1988) model to carry out route-to-route extrapolation of findings from acute inhalation
studies to the oral route. Reitz et al. (1988) reported that their model did not provide an adequate
simulation of experimentally derived gavage rat data from their own laboratory. The Reitz et al.
(1988) model also did not simulate well the oral gavage data of Bruckner, which included time
course concentrations of 1,1,1-trichloroethane in venous blood, liver, fat, and kidney for time
intervals up to approximately 3 hours (Yang, 2006; personal communication). In particular, the
PBPK model did not fit the absorption phase well. Varying the absorption rate constant (Ka)
failed to improve the fit.
Because the available PBPK model for 1,1,1-trichloroethane did not adequately simulate
the pharmacokinetic behavior of 1,1,1-trichloroethane from two acute oral data sets and because
the model could not be evaluated using short-term oral data sets, the use of a PBPK model to
extrapolate from acute and short-term inhalation data to the oral route was not supported.
129
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5.1.5.2. Subchronic and Chronic Durations
Consideration was given to the derivation of subchronic and chronic oral RfDs by
extrapolation of the inhalation RfC. As described more fully in Sections 5.2.3.1 and 5.2.4.1, the
repeat-dose studies used for the evaluation of subchronic and chronic inhalation exposure were
the 2-year bioassay in rats by Quast et al. (1988, 1984) and the 14-week study in mice by
McNutt et al. (1975), where the target organ for 1,1,1-trichloroethane was the liver. As
discussed in Section 4.6.1, evidence for the liver as a potential target following oral
administration of 1,1,1-trichloroethane is equivocal; some, but not all, studies suggest that
1,1,1-trichloroethane may produce mild hepatotoxicity following oral exposure. The most
comprehensive study of 1,1,1-trichloroethane oral toxicity, the subchronic toxicity study by NTP
(2000), reported no changes in liver histopathology or clinical chemistry that would suggest the
liver to be a sensitive target organ in rats or mice. Similarly, Bruckner et al. (2001) found only
small and transient elevations in liver enzymes at gavage doses of 1,1,1-trichloroethane high
enough to cause increased mortality. Thus, given the apparent differences in relative
hepatotoxicity of 1,1,1-trichloroethane by the oral and inhalation routes, a route-to-route
extrapolation approach to derive the subchronic or chronic oral RfD was not considered
appropriate.
5.2. INHALATION REFERENCE CONCENTRATION (RfC)
5.2.1. Acute Inhalation RfC
The acute inhalation RfC is intended for use with exposures up to 24 hours.
5.2.1.1. Choice of Principal Study and Critical Effect—with Rationale and Justification
The acute inhalation toxicity database for 1,1,1-trichloroethane is extensive. The most
sensitive target following acute inhalation exposure has been shown to be the CNS. Selected
studies that examined CNS effects after acute inhalation exposure, some considered candidates
for RfC derivation, are presented in Figures 5-1 and 5-2 (exposure-response array) and Table 5-
3. Figure 5-1 presents an array of inhalation studies over a range of HEC concentrations up to
22,000 mg/m3. To provide better resolution of study information in the low end of the exposure
range, Figure 5-2 presents the same array of studies but over a more narrow range of exposure
concentrations (up to 5000 mg/m3).
130
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20000
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Figure 5-1. Exposure-response array for 1,14-trichloroethane.
131
-------
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Figure 5-2. Exposure-response array for 1,14-trichloroethane.
(Range on the y axis restricted to 5000 mg/m3 to improve resolution at the low exposure region.)
132
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Table 5-3. Summary description of studies plotted in Figures 5-1 and 5-2
Reference
value category
Acute
Short-term
Subchronic
Reference
Gamberale and Hultengren, 1973
Mackay et al., 1987
Muttray et al., 2000
Salvini et al., 1971
Bowen and Balster, 1996
Kjellstrand et al., 1985b
Frantik et al., 1994
Frantik et al., 1994
de Ceaurriz et al., 1983
Gelleretal., 1982
Jones etal., 1996
Colemanetal., 1999
BRRC, 1987a
BRRC, 1987b
Balster et al., 1997; Evans and
Balster, 1993
Albeeetal., 1990b
Gelleretal., 1982
Calhoun et al., 1981
Calhoun et al., 1981
McNuttetal., 1975
Mattssonetal., 1993
Figure 5-1 &
5-2 identifier
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Exposure duration
0.5 hour
3.5 hours
4 hours
8 hours
0.5 hour
1 hour
2 hours
4 hours
4 hours
4 hours
CDs 12-17, 3 hours/day
CDs 13-19, 3 hours/day
GDs 6-15, 6 hours/day
CDs 6-18, 6 hours/day
4 days, continuous
4 days, 6 hours/day
7 days, continuous
94 days, 5 days/week,
6 hours/day
94 days, 5 days/week,
6 hours/day
14 weeks
90 days, 5 days/week,
6 hours/day
HECa
(mg/m3)
1370 N°
950 Lc
1090 Lc
2450 Lc
2730 Nc
7 100 1ST
9880 Lc
4000 Lc
1 1,270 L°
7640 Nc
5460 L
4780 L
4090 N
4090 N
2730 L
1360 L
6550 L
980 N
980 N
1370 N
610 N
Species
Human
Human
Human
Human
Mouse
Mouse
Mouse
Rat
Mouse
Baboon
Mouse
Rat
Rat
Rabbit
Mouse
Rat
Baboon
Rat
Mouse
Mouse
Rat
Type of effectb
NB
NB
NB
NB
NB
NB
NB
NB
NB
NB
ND
ND
D
D
NB
NP
ND
HP
HP
HP
D
133
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Reference
value category
Chronic
Reference
Quastetal., 1988, 1984
Figure 5-1 &
5-2 identifier
22
Exposure duration
2 years, 5 days/week,
6 hours/day
HECa
(mg/m3)
1460 N
Species
Rat
Type of effectb
HP
aHECs calculated assuming extrarespiratory effects for a category 3 gas (U.S. EPA, 1994b; U.S. EPA, 2000e). The default procedure for category 3 gases
involves adjustment of the experimental exposure concentration by a dosimetric adjustment factor (DAF), which is calculated as the ratio of the blood:gas (air)
partition coefficient (Hb/g) for the laboratory species to the Hb/g for humans. According to Table 3-4, the Hb/g for the rat and mouse is 5.76 and 10.8, respectively,
and for humans is 2.53. The RfC methodology stipulates that, where the animal coefficient is greater than the human coefficient or where Hb/g values are
unknown, a value of 1 is used for the ratio (U.S. EPA, 1994b). The RfC methodology (U.S. EPA, 1994b) was developed specifically for deriving chronic
reference values (i.e., for use with long-term repeated exposures under which steady-state conditions are likely to be attained). Because 1,1,1-trichloroethane
reaches steady state relatively quickly (see Section 3), EPA's RfC methodology is considered applicable to short-term and subchronic RfC values as well as
chronic values. For developing acute inhalation RfCs for category 3 gases, EPA's draft acute reference exposure methodology (U.S. EPA, 2000e) recommends
that the ratio of animal/human Hb/g also be used as the default for HEC derivation. Therefore, the DAF applied to the duration adjusted concentrations for
studies involving all exposure durations is 1 (see Table 4-9). Unless flagged (with a superscript c), the exposure concentration was adjusted to a continuous
exposure (e.g., a 6 hours/day exposure concentration was adjusted to 6/24). NOAELs or LOAELs were used as the point of departure for all of the data sets
presented in this table. BMD methods were considered. The data sets were not amenable to BMD methods, however, for one or more of the following reasons:
use of only one exposure concentration, presentation of results in graphical format only or as a mean without standard deviations or standard errors, elevated
incidence in the high-dose group only, or a measured response not amenable to BMD methods (e.g., biphasic response, response presented as a numerical
score).
bD = developmental; HP = hepatic; NB = neurobehavioral; ND = neurodevelopmental; NP = neurophysiological.
0 The HEC was not extrapolated to an equivalent 24-hour concentration for data sets where the exposure duration was less than 24 hours. In these cases, the HEC
represents the actual exposure concentration. N = NOAEL; L = LOAEL.
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As Figures 5-1 and 5-2 show, studies of controlled exposure to 1,1,1-trichloroethane in
humans provide the most sensitive measure of effect for this chemical. In particular, the studies
of neurobehavioral performance by Mackay et al. (1987), Gamberale and Hultengren (1973), and
Muttray et al. (2000, 1999) identified the lowest effect levels among the available human studies.
Mackay et al. (1987) reported exposure-related impaired performance in tests of simple reaction
time, choice reaction time, and digital step-input tracking at 175 and 350 ppm (950 and
1900 mg/m3). Exposures in this study were conducted for 3.5 hours with neurobehavioral
performance evaluated at four time periods during the exposure. Gamberale and Hultengren
(1973) observed performance deficits in tests of simple and choice reaction time, manual
dexterity, and perceptual speed at 350 ppm (1900 mg/m3) following a 30-minute exposure.
These researchers found no effect at 250 ppm (1370 mg/m3). Muttray et al. (2000, 1999) found
EEG changes consistent with increased drowsiness, as well as subjectively reported tiredness, in
volunteers performing a choice reaction time test with eyes closed during a 4-hour exposure to
200 ppm (1090 mg/m3) 1,1,1-trichloroethane. The lower exposure level of 22 ppm (120 mg/m3)
served as the control in this study. Overall, these studies suggest a slight effect on
neurobehavioral performance at exposure concentrations in the range of-200 to 400 ppm
(-1000-2000 mg/m3) for up to 4 hours of exposure.
Collectively, the human intentional dosing studies provide some insight into the duration
of exposure to 1,1,1-trichloroethane before adverse effects on neurobehavioral performance are
observed. Mackay et al. (1987) measured psychomotor performance deficits beginning 20, 60,
120, and 180 minutes after exposure began. Changes in test performance were observed at an
exposure concentration of 950 mg/m3 as early as 20 minutes in some tests (e.g., tracking time on
target, tracking room mean square error, and simple reaction time), but in other tests impaired
performance at 20 minutes was minimal and increased with exposure duration (e.g., tracking
time outside target, four-choice reaction time, and Stroop test). It is unclear to what extent the
changes observed at the earliest testing interval were biologically significant. Other
investigators did not similarly observe deficits in performance after only 20 minutes of exposure.
As shown in Table 4-1, simple and choice reaction times were assessed by Mackay et al. (1987),
Savolainen et al. (1982a,b, 1981), and Gamberale and Hultengren (1973). After 4 hours of
continuous exposure to a concentration of 400 ppm (2180 mg/m3), Savolainen et al. (1982a,b,
1981) found no significant changes in simple reaction time in exposed volunteers. Gamberale
and Hultengren (1973) reported no significant changes in tests of simple and choice reaction
time following 30 minutes of exposure to 250 ppm (1370 mg/m3) 1,1,1-trichloroethane but did
see changes after 1 hour to a TWA concentration of 300 ppm ([1640 mg/m3]; 250 ppm for 30
minutes followed by 350 ppm for 30 minutes). Thus, the Savolainen et al. (1982a,b, 1981) and
Gamberale and Hultengren (1973) studies do not confirm a finding of neurobehavioral effects
following 20 minutes of exposure; however, the Gamberale and Hultengren (1973) findings
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suggest that changes in neurobehavioral performance may occur after 60 minutes of exposure to
an exposure concentration of 300 ppm, generally consistent with the findings for Mackay et al.
(1987) also at 60 minutes of exposure. Therefore, based on evidence from human intentional
dosing studies as a whole, it appears that exposure to 950 mg/m3 1,1,1-trichloroethane for 60
minutes represents a LOAEL.
There is extensive supporting evidence from the experimental animal literature that the
CNS is a sensitive target for 1,1,1-trichloroethane. Neurological effects have been widely
demonstrated in acute animal studies and have been shown to be by far the most sensitive
endpoints in these studies. In comparison with the human data, however, neurological effects in
animals have been reported only at considerably higher concentrations (>700 ppm [>4000
mg/m3] for effects of toxicological significance in acute studies).
Developmental effects have been reported in experimental animals following gestational
exposure to 1,1,1-trichloroethane, including neurobehavioral deficits in pups (mice and rats)
following late gestational exposure of the dams (Coleman et al., 1999; Jones et al., 1996).
Although the developmental toxicity studies for 1,1,1-trichloroethane involved repeated
(6- to7-day) exposures during gestation, it is a plausible assumption for developmental toxic
effects that "a single exposure at a critical time in development may produce an adverse
developmental effect, i.e., repeated exposure is not a necessary prerequisite for developmental
toxicity to be manifested" as discussed in EPA's Guidelines for Development Toxicity Risk
Assessment (U.S. EPA, 199 la). To that end, the results of these studies are considered relevant
to an acute exposure.
Reported neurodevelopmental effects occurred, however, at average daily exposure
concentrations considerably higher than the levels at which neurobehavioral effects have been
observed in human controlled exposure studies. For example, BRRC (1987a,b) reported an
effect level for fetotoxicity in the rat and rabbit of 32,760 mg/m3, 6 hours/day, on GDs 6-15 or
6-18, respectively. Three other developmental toxicity studies (Coleman et al., 1999; Jones et
al., 1996; Schwetz et al., 1975) reported either no developmental toxicity or effect levels well
above the levels at which neurobehavioral effects were observed in human controlled exposure
studies; further, because these three studies included only a single exposure concentration, they
were not considered an appropriate basis for acute RfC development.
Human and experimental animal data on the neurological effects of 1,1,1-trichloroethane
in humans are considered to be the most sensitive and appropriate basis for derivation of the
acute inhalation RfC. Mackay et al. (1987) was selected as the principal study for derivation of
the acute RfC, with Gamberale and Hultengren (1973) and Muttray et al. (2000, 1999) providing
support for effects on neurobehavioral performance.
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5.2.1.2. Methods of Analysis
The use of benchmark dose methods was considered in analyzing the data set from
Mackay et al. (1987). This study included two exposure levels and controls and found
statistically significant concentration-related effects on several variables; however, only mean
changes were presented, without standard deviations or standard errors. Further, the finding of
performance deficits associated with 1,1,1-trichloroethane exposure in this study is based on the
pattern of performance changes in a battery of behavioral tests, rather than on the results of a
single test. For these reasons, the data were not considered amenable to BMD analysis.
Therefore, the LOAEL of 950 mg/m3 following 1 hour of exposure was used as the point of
departure for derivation of the acute RfC.
Because acute exposure durations are defined as 24 hours or less, there is interest in
deriving RfCs for durations of 1, 4, 8, and 24 hours. The Reitz et al. (1988) PBPK model was
used with data from Mackay et al. (1987) to predict effect levels at other acute exposure
durations between 1 and 24 hours (Yang, 2006). As discussed in Section 3.5.2, the Reitz et al.
(1988) model was evaluated using three human pharmacokinetic data sets (all involving
inhalation exposure) and acceptably predicted the experimental data sets. Data points (blood
1,1,1-trichloroethane concentration vs. time) from the graphic presentation of results in Mackay
et al. (1987) were extracted using DigiMatic software (Yang et al., 2006).
Consideration was given to whether the area under the concentration vs. time curve
(AUC) or the momentary concentration in the blood at the time of testing (Ct) constitutes the
better internal dose metric in the case of the Mackay et al. (1987) study. Because Mackay et al.
(1987) had actual measurements of blood concentration at the time of neurobehavioral testing
(20, 60, 120, and 180 minutes), Ct was already available. Ct was determined to be the more
appropriate dose metric as supported by the following:
• Several laboratory animal studies of 1,1,1-trichloroethane have shown a correlation between
blood and brain 1,1,1-trichloroethane concentration and certain neurological deficits.
Warren et al. (2000, 1998) found that blood and brain concentrations at the time of testing, as
well as blood and brain Cmax and AUC values, were strongly correlated with operant
performance in the rat receiving acute inhalation exposures to 1,1,1 trichloroethane for up to
100 minutes and with locomotor activity in the mouse at acute inhalation exposures up to 30
minutes in duration. In both studies, the investigators noted that all three values were
suitable for predicting 1,1,1-trichloroethane-induced response rate changes. These
investigators also reported that the assumption that all equivalent products of concentration
and time (C * T) result in the same degree of toxicity (Haber's rule) was not valid under the
given exposure conditions.
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• Studies of related solvents show momentary blood concentration to be the more appropriate
dose metric. Specifically, studies of trichloroethylene (TCE) have shown that acute
neurological deficits in rats (as measured by changes in performance of a behavioral signal
detection task or changes in visual evoked potentials) are related to the momentary
concentrations of TCE in blood or brain at the time of the neurobehavioral assessment and
not to the total amount of TCE exposure expressed as AUG. Preliminary evidence suggests a
similar relationship exists for toluene (Boyes et al., 2005, 2003; Bushnell et al., 2005).
Boyes et al. (2005, 2000) reported that Haber's rule did not accurately predict outcome for
different combinations of C x T for TCE.
• While the brain is the target of toxicity following acute inhalation exposure, brain
concentrations of 1,1,1-trichloroethane cannot be collected in human subjects. Animal
studies show that blood and brain concentrations are strongly correlated (Warren et al., 2000,
1998) and, therefore, that blood concentrations are an effective surrogate for target tissue
(brain) concentrations.
Based on data from Mackay et al. (1987), Yang (2006) estimated the internal dose
(concentration in venous blood [CV]) in humans exposed to 950 mg/m3 1,1,1-trichloroethane for
1 hour (1.33 mg/L). The model was then used to predict the exposure concentration required to
achieve the same target internal dose (1.33 mg/L) after 4, 8, and 24 hours of exposure using
continuous exposure assumptions. These exposure concentrations are provided in column 2 of
Table 5-4 below.
Table 5-4. Predicted exposure concentrations at different exposure durations
for the target internal dose
Exposure duration
(hours)
1
4
8
24
1,14-Trichloroethane exposure concentration
(mg/m3) for CV = 1.33 mg/La
950
715.3
693.4
649.8
UF
100
100
100
100
Acute RfC (mg/m3)
9
7
7
6
a Target internal dose CV = 1.33 mg/L (or 9.97 uM).
Source: Yang (2006).
5.2.1.3. Acute RfC Derivation—Including Application of Uncertainty Factors (UFs)
The acute human LOAEL for 1 hour and predicted LOAELs for 4, 8, and 24 hours served
as the points of departure for the acute RfC values at different durations. A composite UF of 100
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was applied to these points of departure: 10 to extrapolate from a LOAEL to aNOAEL and 10
for intraspecies variation (human variability).
• A default 10-fold UF for intraspecies differences was used to account for potentially
susceptible individuals in the absence of information on the variability of response to
1,1,1-trichloroethane in the human population.
• An interspecies UF was not necessary because the critical effect is based on human data.
• A default 10-fold UF for extrapolation from a LOAEL to a NOAEL was used because the
lowest exposure concentration examined in the principal study was associated with a
measurable deficit in a neurobehavioral test.
• A UF to extrapolate from a shorter to a longer exposure duration was not necessary because
the acute RfC was derived from a study using an acute exposure protocol; a PBPK model
was used to extrapolate to other acute exposure durations.
• A database UF was not applied because the database for this chemical was considered
relatively complete. The inhalation database includes extensive testing for acute toxicity and
inhalation developmental toxicity studies in three species. The neurobehavioral effects of
1,1,1-trichloroethane, the most sensitive effect following acute inhalation exposure, has been
investigated in both animals and humans.
The acute RfC values for 1,1,1-trichloroethane were calculated as follows:
Acute RfC = LOAEL/UF
and are presented in column 4 of Table 5-4 above.
5.2.2. Short-term Inhalation RfC
The short-term inhalation RfC is intended for use with exposures for more than 24 hours,
up to 30 days.
5.2.2.1. Choice of Principal Study and Critical Effect—with Rationale and Justification
No useful short-term inhalation studies in humans were located. Short-term studies in
animals include investigations of neurological and developmental effects. The most sensitive
effects in the animal studies were neurological: (1) development of withdrawal symptoms
(handling-induced convulsions mitigated by reexposure to 1,1,1-trichloroethane or exposure to
some other known depressants) in mice exposed to 500 ppm (2730 mg/m3) or more of
1,1,1-trichloroethane continuously for 4 days and abruptly removed from exposure (Balster et
al., 1997; Evans and Balster, 1993) and (2) neurophysiological changes in rats following
exposure to 1000 ppm (5460 mg/m3) 6 hours/day for 4 days (adjusted concentration of 250 ppm
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[1360 mg/m3]) (Albee et al., 1990b). Developmental effects were found only at higher
concentrations (adjusted concentrations 875 ppm [>4780 mg/m3]).
The LOAEL of 175 ppm (950 mg/m3) for neurobehavioral effects in humans with acute
exposure to 1,1,1-trichloroethane (Mackay et al., 1987) is below the effect level from any of the
available short-term animal studies. This would suggest that protecting against acute
neurobehavioral effects observed in human controlled-exposure studies will protect against the
effects reported in short-term, repeat-exposure studies in animals. Consideration of the
protectiveness of acute exposure data for repeat exposure situations requires consideration of the
influence of exposure duration on neurobehavioral toxicity and the duration extrapolation.
Influence of exposure duration on neurobehavioral toxicity. Short-term human data are
not available to directly establish whether 1,1,1-trichloroethane would produce neurobehavioral
effects at lower levels with repeated exposure than with acute exposure. Human subject data
from Mackay et al. (1987) suggest that neurobehavioral effects are correlated with momentary
blood levels of 1,1,1-trichloroethane for time points up to 3.5 hours but not longer exposure
durations. Available toxicokinetic data, in combination with toxicity data from animals, inform
the relationship between exposure duration and expression of neurobehavioral toxicity.
Toxicokinetic data from humans and animals suggest that 1,1,1-trichloroethane will
preferentially partition to fat but is unlikely to accumulate in body tissues. Following single
inhalation exposure, 1,1,1-trichloroethane is rapidly cleared from fat, with 1,1,1-trichloroethane
partitioning back into blood and then being exhaled from the body (Schumann et al., 1982a). As
discussed in Section 3.4, Schumann et al. (1982b) compared disposition and elimination of
1,1,1-trichloroethane in rats and mice exposed to 1500 ppm 1,1,1-trichloroethane for 6
hours/day, 5 days/week for 16 months (with the last day of exposure to radiolabeled compound)
to age-matched controls exposed once to radiolabeled compound. Concentrations of radiolabel
in fat and other tissues at 0 and 72 hours after exposure to the radiolabeled compound were
comparable in animals receiving a single 6-hour exposure and in animals that had been exposed
for 16 months. The results showed no significant effect of repeated exposure to
1,1,1-trichloroethane on the disposition of radiolabeled compound compared to single exposure.
Nolan et al. (1984) simulated repeated 8-hour daily exposure of humans based on a three-
compartment pharmacokinetic model and predicted that 12 daily exposures would be required to
reach 95% of steady-state concentrations of 1,1,1-trichloroethane in the body. At steady state,
Nolan et al. (1984) predicted that the body would contain 3.6 times the amount of
1,1,1-trichloroethane as after a single 8-hour exposure and that -70% of this would be in the fat.
Rats and mice receiving a single oral exposure (1000 mg/kg) of radiolabeled
1,1,1-trichloroethane had 53-62% of the 1,1,1-trichloroethane deposited in tissues present in the
fat 1 to 2 hours after exposure, a range similar to that predicted by Nolan et al. (1984) at steady
state. On balance, the available data suggest that 1,1,1-trichloroethane preferentially distributes
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to fat following both acute and repeated exposure to a similar extent, that partitioning to fat is at
equilibrium with blood concentration, and that, once exposure ceases, 1,1,1-trichloroethane is
cleared from the fat.
Toxicity data in animals provide limited information related to the potential for effects to
occur at lower concentrations with repeated vs. acute exposure. For the most part, the specific
neurological endpoints examined in acute studies differ from those examined in repeat-dose
studies. In addition, dose spacing in acute and repeat dose studies differs so that the proximity of
NOAELs or LOAELs from acute and repeat dose studies to their respective thresholds is
uncertain. Therefore, a comparison of the lowest acute effect level in Table 5-3 (4000 mg/m3)
with the lowest short-term effect level (2730 mg/m3 for continuous exposure) provides only
limited insights into whether duration of exposure influences the exposure concentration at
which neurological effects occur.
Some data from animal studies allow a direct comparison of the same endpoint for acute
and short-term exposure durations. Baboons displayed impaired performance in a match-to-
sample discrimination task at a concentration of 1200 ppm (6550 mg/m3) with continuous
exposure for 7 days, while the NOAEL and LOAEL for this effect were 1400 and 1800 ppm
(7640 and 9830 mg/m3), respectively, with 4-hour exposure (Geller et al., 1982). This result
suggests a reduction of the threshold for a behavioral effect from 7640 mg/m3 to <6550 mg/m3 as
the exposure duration increased from 4 hours to 7 days. The magnitude of the change is
unknown because only a single concentration was tested in the 7-day experiment, precluding
identification of a threshold for this duration.
On the other hand, mice exposed repeatedly to 6000 ppm (32,760 mg/m3)
1,1,1-trichloroethane for 20 minutes per day, 4 days per week, over a 4-week period all
maintained baseline performance in a fixed-ratio responding task during initial air exposures of
each daily session and all recovered each day after solvent exposure, indicating no residual effect
of the chemical with repeated exposures (Moser et al., 1985). Furthermore, suppression of
responding by 1,1,1-trichloroethane changed only slightly over the course of the study (slight
statistically significant increase in responding over the first 2 weeks of the study and significant
decrease in latency for recovery of responding after the daily exposure terminated). These
investigators also exposed mice to increasing concentrations of 1,1,1-trichloroethane (1000,
2000, 4000, and 8000 ppm [5460, 10,920, 21,840, and 43,680 mg/m3]) in consecutive 8-minute
sessions once per week over the 4 weeks of the study. Comparison of the resulting exposure-
response curves and ECso values showed no significant shifts in either direction with increasing
number of exposure sessions. These results show no evidence for a reduced threshold for
neurobehavioral effects with repeated vs. acute exposure. They also show development of only
minimal tolerance to 1,1,1-trichloroethane with repeated exposure.
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Concentration x time adjustment of exposure concentration. As discussed previously,
results from studies of 1,1,1-trichloroethane and related solvents in animal models demonstrate
that Haber's rule is not an accurate predictor of acute CNS toxicity (e.g., Boyes et al., 2005,
2000; Warren et al., 2000, 1998). Accordingly, acute neurobehavioral data from Mackay et al.
(1987) were not adjusted for an exposure duration less than 24 hours. For exposures of longer
duration and for endpoints other than CNS, exposures were adjusted to continuous exposure (i.e.,
Haber's rule was assumed to apply) as a conservative estimate of exposure.
Selection of the point of departure. The comparison of points of departure from studies
of short-term duration (1360 mg/m3 and above; see Figures 5-1 and 5-2 and Table 5-3) with the
acute LOAEL from the controlled human study report by Mackay et al. (1987) (950 mg/m3)
suggests that results from short-term animal studies are not necessarily protective of acute
neurobehavioral effects seen in human intentional dosing studies. Accordingly, the results from
Mackay et al. (1987) were further analyzed as the basis for a more health protective point of
departure for the short-term RfC.
5.2.2.2. Methods of Analysis
PBPK modeling was used with data from Mackay et al. (1987) to predict effect levels at
short-term exposure durations as described in Section 5.2.1.2. As described in Section 5.2.1.2
(for the acute RfC), Yang (2006) identified the internal dose of 1,1,1-trichloroethane (i.e., CV) in
humans associated with exposure to 950 mg/m3 for 1 hour (i.e., the exposure considered to be
associated with biologically significant changes in neurobehavioral performance). Yang (2006)
used the Reitz et al. (1988) model to predict the exposure concentration required to achieve the
same target internal dose once steady state had been reached at 336 hours (14 days). This
exposure concentration was predicted to be 526 mg/m3. (Near steady-state CVs were achieved
considerably sooner than 336 hours. 1,1,1-Trichloroethane concentrations were at 87% of steady
state at 48 hours, at 94% at 96 hours, and 98% of steady state at 168 hours.)
5.2.2.3. Short-term RfC Derivation—Including Application of Uncertainty Factors (UFs)
The short-term inhalation RfC was estimated from the point of departure of 526 mg/m3
derived from Mackay et al. (1987) and with use of PBPK modeling to predict steady state
conditions. This point of departure was divided by a composite UF of 100: 10 for intraspecies
variation (human variability) and 10 to extrapolate from a LOAEL to a NOAEL.
• A default 10-fold UF for intraspecies differences was used to account for potentially
susceptible individuals in the absence of information on the variability of response to
1,1,1-trichloroethane in the human population.
• An interspecies UF was not necessary because the critical effect is based on human data.
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• A default 10-fold UF for extrapolation from a LOAEL to a NOAEL was used because the
lowest exposure concentration examined in the principal study was associated with a
measurable deficit in a neurobehavioral test. A PBPK model was used to predict the
exposure concentration that would produce 1,1,1-trichloroethane levels associated with
biologically significant changes in neurobehavioral performance when steady state had been
achieved (14 days). Therefore, a UF for duration extrapolation was not considered
necessary.
• A database UF was not applied because the short-term inhalation database was considered
relatively complete. The database includes inhalation developmental toxicity studies in three
species as well as several studies that investigated neurobehavioral effects of
1,1,1-trichloroethane following short-term exposure. The short-term RfC is based on a study
of human neuropsychomotor performance (Mackay et al., 1987) extrapolated to short-term
steady-state conditions. The acute literature suggests that the human model is more sensitive
to neurobehavioral toxicity of 1,1,1-trichloroethane than the animal models tested, and thus
Mackay et al. (1987) is an appropriate and sensitive data set for derivation of the short-term
RfC. Further, the available data suggest that repeated exposure to 1,1,1-trichloroethane
should not result in an appreciable reduction in the threshold for neurobehavioral effects.
This is supported by chronic animal studies, in which no overt neurobehavioral effects were
observed even after 2 years of exposure of rats and mice to concentrations as high as
8190 mg/m3 for 6 hours/day, 5 days/week.
The short-term RfC was calculated as follows:
Short-term RfC = point of departure + UF
= 526 mg/m3 + 100
= 5 mg/m3
5.2.3. Subchronic Inhalation RfC
The subchronic inhalation RfC is intended for use with exposures for more than 30 days,
up to approximately 10% of the lifespan in humans (or up to approximately 90 days in typically
used laboratory animal species).
5.2.3.1. Choice of Principal Study and Critical Effect—with Rationale and Justification
No useful subchronic studies in humans were located. The lowest effect level identified
in animals in subchronic studies was increased GFAP, potentially indicating formation of
astroglial fibrils in response to brain injury, in the sensorimotor cerebral cortex of gerbils
exposed continuously to 210 ppm (1150 mg/m3) for 3 months and evaluated 4 months after the
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end of exposure (Rosengren et al., 1985). There is some uncertainty, however, regarding the
toxicological significance of this finding. Acute responses to severe chemical-induced injury to
localized regions of the brain have been associated with several-fold increases in GFAP. In
addition to neuronal injury, however, other nonpathological conditions, such as intense
stimulation, can also be associated with detectable increases in GFAP, although such increases
are typically of a much smaller magnitude.
The increases observed by Rosengren et al. (1985), estimated from graphs, are -33%
above control values for 210 ppm (1150 mg/m3) and -40% for 1000 ppm (5460 mg/m3). This
effect appears to be treatment related but not dose dependent. Changes were observed in protein
concentration and S-100 in other brain regions only in the group exposed to 210 ppm and not in
the 1000-ppm group. These latter changes are therefore not considered treatment related.
S-100 protein, another marker for astrogliosis, was not increased in this study; studies of other
compounds (ethanol, trichloroethylene, and tetrachloroethylene) by the same researchers found
increases in both GFAP and S-100 protein. Overall, the data do not provide compelling
evidence for a dose-related effect on neurochemical parameters.
The reliable measurement of GFAP in specific brain regions requires consistent
dissection, since different brain regions normally have significantly different levels of GFAP.
For example, the concentration of GFAP in the hippocampus is dramatically greater than that in
overlying sensorimotor cortex. Retention of fragments of hippocampus with the overlying
cortex during dissection or inclusion of varying amounts of white matter could result in
anomalous values. The description of the sample collection by Rosengren et al. (1985) is not
adequate to determine if safeguards were undertaken to avoid the possibility of systematic errors
of this type.
The increased GFAP levels observed in the 210- and 1000-ppm groups could reflect
subtle but persistent alterations in 1,1,1-trichloroethane-exposed animals or other treatment-
related alterations in other aspects of brain homeostasis; however, the neurochemical findings
reported by Rosengren et al. (1985) are equivocal. Furthermore, there are no other findings from
pathological, physiological, or neurochemical studies that provide additional support for a
biological basis for the significance of a region-specific, treatment-related effect on the
sensorimotor cortex. Specifically, comprehensive neurohistopathology assessment found no
evidence of brain injury in rats exposed to 2000 ppm (10,920 mg/m3) 1,1,1-trichloroethane
intermittently for 3 months (duration adjusted concentration of 1950 mg/m3) (Mattsson et al.,
1993). Studies using standard techniques also failed to detect histological evidence of brain
damage in rats or mice, most notably following intermittent exposure to 1500 ppm (8190 mg/m3)
(duration adjusted concentration of 1440 mg/m3) for 2 years (Quast et al., 1988, 1984).
Consequently, the GFAP findings of Rosengren et al. (1985) were not considered to be adequate
to establish a critical effect for subchronic exposure to 1,1,1-trichloroethane.
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Other subchronic studies in animals found ambiguous evidence for impaired forelimb
grip strength and minimal lesions of the nasal turbinates with exposure to 2000 ppm
(10,900 mg/m3) (duration adjusted concentration of 1939 mg/m3) for 13 weeks (Mattsson et al.,
1993; Calhoun et al., 1981). The deficits in forelimb grip strength reported in Mattsson et al.
(1993) were not statistically significant, using a statistical treatment designed to take into
account the observed changes over time in the control and treated group, and were not confirmed
by histopathological, electrophysiological, or FOB tests in the same study (see Section 4.4.1.2).
Lesions of the nasal turbinates observed by Calhoun et al. (1981) were not confirmed in
subsequent chronic studies by the same group of investigators (Quast et al., 1988, 1984).
Therefore, neither effect was considered appropriate as the basis for an inhalation reference
value.
More consistent is the finding of histopathologic changes in the liver associated with
1,1,1-trichloroethane exposure. Quast et al. (1988, 1984) exposed rats and mice to
1,1,1-trichloroethane for up to 2 years, with interim sacrifices at 6, 12, and 18 months, and found
minor histopathological changes in the liver in rats exposed to 1500 ppm (8190 mg/m3),
6 hours/day, 5 days/week (duration adjusted concentration = 1460 mg/m3). Hepatic changes
were not seen in control or lower-exposure animals. Hepatic changes in the 1500-ppm rats
(including altered staining around the central vein and smaller appearance of hepatocytes in the
portal region) suggest a physiologic response of centrilobular hepatocytes (i.e., hypertrophy = an
increase in the size of liver parenchymal cells that may represent a response to xenobiotic
exposure by increasing metabolic capacity, resulting in induction of metabolic enzymes). No
other histopathological changes of the liver were observed, and clinical chemistry values and
organ weights were unaffected by treatment. Together, these findings suggest that the
histopathological changes in rats do not reflect an adverse effect. In evaluating whether or not
the observed changes should be considered adverse, consideration was given to Lewis et al.
(2002), who noted "[n]onadverse effects are usually adaptive or compensatory responses or
findings that are below a threshold level or do not fulfill the criteria that define their biological
significance. However, often the distinction between adverse and nonadverse effects is not
clearly defined and interpretation needs scientific judgment on a case-by-case basis." No
differences in histopathology from controls were discernible after 2 years of exposure because of
confounding geriatric changes. Because interim sacrifices were performed at 6, 12, and 18
months, the study provides information relevant to both subchronic and chronic exposure
durations.
In a 13-week range-finding study, Calhoun et al. (1981) reported effects in rats and mice
exposed to 2000 ppm 6 hours/day, 5 days/week (duration adjusted concentration = 1950 mg/m3)
similar to those observed in rats by Quast et al. (1988, 1984) (i.e., decreased hepatocyte size with
altered staining affinity and slight centrilobular hepatocellular swelling) but also reported low
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incidences of generalized hepatocellular atrophy in male rats and focal necrosis in female mice at
this concentration. Treatment-related effects were not reported at the lower concentrations.
More substantial liver lesions, including fatty change and necrosis, were reported in mice
exposed continuously to 1000 ppm (5460 mg/m3) for 14 weeks (McNutt et al., 1975). In mice
exposed to the lower exposure concentration (250 ppm [1360 mg/m3]) continuously for 14
weeks, minimal ultrastructural changes were observed that were generally consistent with those
reported by Quast et al. (1988, 1984) and not considered adverse.
Thus, the experimental literature suggests that subchronic exposure to
1,1,1-trichloroethane induces hepatocellular hypertrophy at concentrations (adjusted for
continuous exposure) of 1370 to 1460 mg/m3 (Quast et al, 1988, 1984; McNutt et al., 1975);
these effects do not appear to progress in severity or incidence with exposure duration (Quast et
al., 1988, 1984) and are considered a physiologic rather than adverse response. At a duration-
adjusted exposure concentration of 1950 mg/m3, the histopathologic findings from a 13-week
range-finding study indicated liver toxicity in rats and mice (Calhoun et al., 1981). Because the
study was designed as a range-finding study, however, the findings cannot be considered
definitive. At an exposure concentration of 5460 mg/m3 (about fourfold higher than the
NOAELs from McNutt et al. [1975] and Quast et al. [1988, 1984]), clear hepatotoxicity was
observed (McNutt et al., 1975), with effects including increased relative liver weight and
triglyceride levels, increased lipid content, and necrosis.
Quast et al. (1988, 1984) and McNutt et al. (1975) together can be used to establish a
NOAEL and LOAEL for effects on the liver in rodents. The highest tested concentration in
Quast et al. of 1460 mg/m3 (duration adjusted) is considered a NOAEL, and the concentration in
the McNutt et al. (1975) study associated with clear hepatotoxic effects (5460 mg/m3) is a
LOAEL. The data from these studies were used for dose-response analysis. Quast et al. (1988,
1984) was selected as a coprincipal study because it is the most comprehensive repeat-dose
inhalation study of 1,1,1-trichloroethane, and McNutt et al. (1975) was selected because it
establishes a clear adverse effect level, whereas the treatment-related effects in Quast et al.
(1988, 1984) are not considered adverse.
5.2.3.2. Methods of Analysis
The use of BMD methods was considered in analyzing the data sets from Quast et al.
(1988, 1984) and McNutt et al. (1975). Because the treatment-related response at the highest
concentration tested in Quast et al. (1988, 1984) was not considered adverse and because McNutt
et al. (1975) did not provide incidence data, neither data set was considered amenable to BMD
methods. The NOAEL (8190 mg/m3, 6 hours/day, 5 days/week [duration adjusted =
1460 mg/m3]) was used as the point of departure.
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Yang (2006) used the Reitz et al. (1988) PBPK model to extrapolate from the animal
NOAEL from Quast et al. (1988, 1984) to humans. The model was run for 6 months of exposure
(time to first sacrifice). (The TWA AUC did not change with exposures longer than 6 months,
indicating steady state had been achieved.)
Yang (2006) estimated the TWA liver 1,1,1-trichloroethane AUC resulting from
inhalation exposure at various values for the NOAEL. Both liver and venous blood AUCs were
considered as possible dose metrics; however, the TWA AUC for liver was considered the more
appropriate dose metric because the liver is the target organ of 1,1,1-trichloroethane toxicity.
The predicted TWA AUC for liver at steady state derived from the PBPK analysis of Yang
(2006) is shown in Table 5-5. The calculated human inhalation exposure concentration
(assuming continuous exposure) corresponding to the TWA AUC is also shown in Table 5-5.
Table 5-5. Calculation of human equivalent concentrations using PBPK
modeling (using liver concentration as dose metric)
Rat exposure concentration — NOAEL from Quast et al. (1988, 1984)
Predicted AUCa
Predicted TWA AUCa
Calculated human inhalation exposure concentration13
8190 mg/m3, 6 hours/day, 5 days/week
57,826 mg x hours/L
317 mg-hours/L-day [13 mg/L]
1553 mg/m3
a At t = 4380 hours (6 months). The TWA AUC did not change with exposures longer than 6 months, indicating
steady state had been achieved.
b Calculated based on TWA AUC for liver in humans equivalent to the rat internal dose under continuous infusion
conditions up to 4380 hours. Yang (2006) examined the relationship between exposure concentration and internal
dose for exposure concentrations ranging over 5 orders of magnitude. The human exposure concentration (for
continuous exposure) was calculated based on the TWA AUC in humans equivalent to the respective rat internal
dose under inhalation exposure concentrations ranging from 27.3 to 273,000 mg/m3. The relation (on a log scale)
was shown to be linear over this range of concentrations. Using liver as the dose metric, the calculated human
exposure concentration was lower than the rat exposure concentration, yielding the same internal dose by a factor
of 5.27. The values in this table are interpolated using the relationship presented in Yang (2006).
Source: Based on Yang (2006).
5.2.3.3. Subchronic RfC Derivation—Including Application of Uncertainty Factors (UFs)
The calculated human inhalation exposure of 1553 mg/m3 corresponding to the NOAEL
from Quast et al. (1988, 1984) was used as the point of departure for calculating a subchronic
RfC. A composite UF of 100 was applied to the point of departure (3 for extrapolation from
animals to humans, 10 for intraspecies variation (human variability), and 3 for database
deficiencies), as follows:
A threefold UF was used to account for pharmacodynamic uncertainty in extrapolating from
laboratory animals to humans. Use of a PBPK model accounts for differences in the
toxicokinetics between rats and humans.
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A default 10-fold UF for intraspecies differences was used to account for potentially
susceptible individuals in the absence of information on the variability of response to
1,1,1-trichloroethane in the human population.
A UF to extrapolate from a LOAEL to a NOAEL was not necessary because a NOAEL was
used to determine the point of departure.
A UF to extrapolate from a shorter to a longer duration was not necessary because the
NOAEL came from a 2-year chronic study with interim sacrifices at 6, 12, and 18 months; no
progression in liver histopathological findings was observed after 6 months.
A database UF of 3 was applied to account for deficiencies in the subchronic database for
1,1,1 -trichloroethane. Although the database for 1,1,1 -trichloroethane following subchronic
durations is relatively complete, there exists some uncertainty related to the potential
neurotoxicity of 1,1,1-trichloroethane following repeated exposure. The inhalation database
includes several multidose studies that examined a range of endpoints, inhalation
developmental toxicity studies in three species, and a single-generation
reproductive/developmental toxicity study that included exposure prior to mating. Although
an inhalation multigeneration study has not been conducted, a multigeneration reproductive
study of 1,1,1-trichloroethane by the oral route (Lane et al., 1982), that found no evidence of
reproductive toxicity, is available. In addition, an oral developmental neurotoxicity study
(Maurissen et al., 1994, 1993), sponsored by the Halogenated Solvents Industry Alliance
under a 1,1,1-trichloroethane Testing Consent Order with EPA, is available. Because
pharmacokinetic data for 1,1,1-trichloroethane do not suggest route-specific differences in
target organs, the findings from these oral studies can inform an evaluation of reproductive
and neurodevelopmental toxicity following inhalation exposures. Limited information exists
regarding the immunotoxicity of 1,1,1-trichloroethane by any route of exposure, although the
limited information provides no clear evidence of immunotoxic potential. Aranyi et al.
(1986) found no evidence of immunotoxicity in an in vivo study in mice involving acute
inhalation exposure to 1,1,1-trichloroethane, and in repeat dose studies no effects were
reported on spleen weight or histopathology (Calhoun et al., 1981; Prendergast et al., 1967;
Torkelson et al., 1958; Adams et al., 1950) or spleen or thymus histopathology (Quast et al.,
1988, 1984).
The neurotoxicity of 1,1,1-trichloroethane in humans and animals following acute
exposure has been extensively documented; in animal models, acute 1,1,1-trichloroethane
exposure has caused CNS depression and effects on motor activity and cognitive function.
On balance, the available animal data suggest that repeated exposure to 1,1,1-trichloroethane
does not cause overt effects on the CNS. Concern about the potential for
1,1,1-trichloroethane to affect the nervous system following prolonged exposure is raised by
epidemiological findings and the findings of Rosengren et al. (1985) in gerbils. In a study of
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28 workers exposed occupationally to 1,1,1-trichloroethane, Kelafant et al. (1994) reported
increased sway in the Romberg test and statistically significant deficits for memory,
intermediate memory, rhythm, and speed in a neuropsychological test battery. Workplace
exposures were not measured, the number of workers in the study was small, and Kelafant et
al. (1994) findings were not confirmed in other limited studies of worker populations (Cherry
et al., 1983; Maroni et al., 1977). Nevertheless, the qualitative findings from Kelafant et al.
(1994) raise some concern about potential neurotoxic outcomes following prolonged
1,1,1-trichloroethane exposure. A limited number of experimental animal studies examined
neurotoxic endpoints following repeated exposure. In a test of schedule-controlled operant
behavior (fixed-ratio responding task), Moser et al. (1985) found that mice exposed
repeatedly to high levels of 1,1,1-trichloroethane for 20 minutes per day, 4 days per week,
over a 4-week period recovered each day after solvent exposure, indicating no residual effect
of the chemical with repeated exposures; however, no similar study involving subchronic
exposure is available. Mattsson et al. (1993) reported slight but statistically significant
deficits in forelimb grip performance in rats exposed for 13 weeks; investigators considered
the deficit possibly attributable to the sedative properties of 1,1,1-trichloroethane. No other
deficits indicative of neurotoxicity were observed (the study included an FOB, evaluations of
visual, auditory, somatosensory, and caudal nerve-evoked potentials, and histopathologic
examination), although evaluation for cognitive deficits was not performed. In light of the
qualitative findings from the epidemiological literature, additional evaluation of cognitive
endpoints for subchronic durations would reduce uncertainty in the database.
Rosengren et al. (1985) reported a small but statistically significant increase in regional
brain levels of GFAP, a biomarker of glial hypertrophy in response to neuronal injury, in
gerbils exposed to 1,1,1-trichloroethane for 3 months. Questions were raised about the
reliability of these findings, and they were not supported by pathological, physiological, or
neurochemical findings from other studies (see Section 5.2.3.1); however, the findings raise a
potential concern for effects on the CNS in the absence of an adequately conducted
confirmatory study. On balance, issues raised by neurotoxicity findings for
1,1,1-trichloroethane support a database UF of 3 for the subchronic RfC.
The subchronic RfC for 1,1,1-trichloroethane of 16 mg/m3 based on data from Quast et
al. (1988, 1984) was calculated as follows:
Subchronic RfC = point of departure + UF
= 1553 mg/m3-100
= 16 mg/m3
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Comparison to Shorter Duration RfCs and Final Subchronic RfC Derivation. The
value of the subchronic RfC of 16 mg/m3 derived from Quast et al. (1988, 1984) turns out to be
larger than the acute and short-term RfCs for 1,1,1-trichloroethane, which range from 5 to
9 mg/m3. It is generally anticipated, however, that acute (or short-term) RfCs would be higher in
absolute value than the subchronic or chronic RfC for that chemical since the acute (or short-
term) exposure durations are greatly reduced compared with exposures of subchronic or chronic
duration. In the case of 1,1,1-trichloroethane, the effect levels for acute/short-term and
subchronic inhalation exposures might not necessarily be expected to follow a continuum from
higher to lower for a number of reasons as follows:
• The point of departure for the acute (and short-term) exposure duration is based on CNS
effects in humans, whereas the point of departure for subchronic and chronic exposure
durations is based on liver effects in rats and mice. Thus, the target organ for acute/short-
term exposure durations differs from that for sub chronic/chronic exposure durations.
Although the modes of action for the CNS and liver effects of 1,1,1-trichloroethane have not
been established, it is likely that the modes of action at the two sites of toxicity are different.
• The endpoints examined following acute exposure to 1,1,1-trichloroethane differ from those
examined following subchronic or chronic exposure. In particular, sensitive neurobehavioral
testing in humans is available for evaluating 1,1,1-trichloroethane acute toxicity. In fact,
human test batteries proved to be more sensitive than animal models of acute
neurobehavioral toxicity. Sensitive testing for neurobehavioral effects in either humans or
animals is unavailable following repeated exposure.
• The acute/short-term RfCs are based on analysis of peak exposure, whereas
sub chronic/chronic RfCs are based on AUC exposure.
For 1,1,1-trichloroethane, the short-term RfC of 5 mg/m3 is clearly protective of health
effects associated with subchronic exposure. Accordingly, the subchronic RfC is set at 5 mg/m3
so as not to exceed the limiting reference value derived for short-term exposure.
5.2.4. Chronic Inhalation RfC
The chronic inhalation RfC is intended for use with exposures for more than
approximately 10% of the lifespan in humans (or more than approximately 90 days to 2 years in
typically used laboratory animal species).
5.2.4.1. Choice of Principal Study and Critical Effect—-with Rationale and Justification
Studies of workers with chronic occupational exposure to 1,1,1-trichloroethane provide
only limited data for use in dose-response assessment. Kelafant et al. (1994) found evidence of
neurobehavioral effects in a group of workers exposed to high concentrations of
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1,1,1-trichloroethane over a 10-year period, but exposures were not quantified. Maroni et al.
(1977) did not find neurological effects in another group of workers, but exposures (110-
345 ppm [600-1880 mg/m3] for most workers) were estimated based on very limited data, group
sizes were small (seven to eight per group), and the neurological tests did not include reaction
time, which was found to be the most sensitive endpoint in the controlled exposure studies.
Kramer et al. (1978) conducted a larger study but included only limited investigation of
neurological endpoints (Romberg test).
Animal studies of chronic duration were limited to studies by Quast et al. (1988, 1984) in
rats and mice. As discussed in Section 5.2.3.1, Quast et al. (1988, 1984) found only minor
histopathological changes in the liver in rats at interim sacrifice at a concentration of 1500 ppm
(8190 mg/m3) (duration adjusted concentrations = 1460 mg/m3). These findings appeared to
reflect a physiologic response of centrilobular hepatocytes and were not considered adverse.
Further, because of confounding geriatric changes, no treatment-related effects were discernible
at the final 2-year sacrifice. As discussed in Section 5.2.3.1 for the subchronic RfC, a LOAEL
for liver effects can be estimated from the McNutt et al. (1975) study, where clearly adverse
effects on the liver were reported in mice following continuous exposure to 1000 ppm
(5460 mg/m3) for 14 weeks. Quast et al. (1988, 1984) and McNutt et al. (1975) are used as
coprincipal studies to define the NOAEL and LOAEL. Although McNutt et al. (1975) was a
subchronic study, the findings from Quast et al. (1988, 1984) suggest a lack of progression of
effects, at least at the NOAEL, from subchronic to chronic exposure durations.
5.2.4.2. Methods of Analysis
The methods used to derive the chronic RfC for 1,1,1-trichloroethane are the same as
those used to derive the subchronic RfC. As described in Section 5.2.3.2, the NOAEL from the
Quast et al. (1988, 1984) study (8190 mg/m3, 6 hours/day, 5 days/week) was used as the point of
departure. PBPK modeling was performed to predict the human exposure concentration
(assuming continuous inhalation exposure) of 1553 mg/m3 (using the TWA AUC for liver as the
dose metric) (see Table 5-5).
5.2.4.3. Chronic RfC Derivation—Including Application of Uncertainty Factors (UFs)
The calculated human inhalation exposure of 1553 mg/m3 corresponding to the NOAEL
from Quast et al. (1988, 1984) was used as the point of departure for calculating a chronic RfD.
A TWA AUC for liver was used as the dose metric because the liver is the target organ of
1,1,1-trichloroethane toxicity. A composite UF of 100 was applied to the point of departure (3
for extrapolation from animals to humans, 10 for intraspecies variation (human variability), and
3 for database deficiencies), as follows:
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• A threefold UF was used to account for pharmacodynamic uncertainty in extrapolating from
laboratory animals to humans. Use of a PBPK model accounts for differences in the
toxicokinetics between rats and humans.
• A default 10-fold UF for intraspecies differences was used to account for potentially
susceptible individuals in the absence of information on the variability of response to
1,1,1-trichloroethane in the human population.
• A UF to extrapolate from a LOAEL to a NOAEL was not necessary because a NOAEL was
used to determine the point of departure.
• A UF to extrapolate from a shorter to a longer duration was not necessary because the
NOAEL came from a 2-year chronic study with interim sacrifices at 6, 12, and 18 months; no
progression in liver histopathological findings was observed after 6 months.
• A database UF of 3 was applied to account for deficiencies in the chronic database for
1,1,1 -trichloroethane. Although the database for 1,1,1 -trichloroethane is relatively complete,
there exists some uncertainty related to the potential neurotoxicity of 1,1,1-trichloroethane
following repeated exposure. The inhalation database includes 2-year chronic inhalation
bioassays in rats and mice, inhalation developmental toxicity studies in three species, and a
single generation reproductive/developmental toxicity study that included exposure prior to
mating. Although an inhalation multigeneration study has not been conducted, a
multigeneration reproductive study of 1,1,1-trichloroethane by the oral route (Lane et al.,
1982), that found no evidence of reproductive toxicity, is available. In addition, an oral
developmental neurotoxicity study (Maurissen et al., 1994, 1993), sponsored by the
Halogenated Solvents Industry Alliance under a 1,1,1-trichloroethane Testing Consent Order
with EPA, is available. Because pharmacokinetic data for 1,1,1-trichloroethane do not
suggest route-specific differences in target organs, the findings from these oral studies can
inform an evaluation of reproductive and neurodevelopmental toxicity following inhalation
exposures. Limited information exists regarding the immunotoxicity of 1,1,1-trichloroethane
by any route of exposure, although the limited information provides no clear evidence of
immunotoxic potential. Aranyi et al. (1986) found no evidence of immunotoxicity in an in
vivo study in mice involving acute inhalation exposure to 1,1,1-trichloroethane, and in repeat
dose studies no effects were reported on spleen weight or histopathology (Calhoun et al.,
1981; Prendergast et al., 1967; Torkelson et al., 1958; Adams et al., 1950) or spleen or
thymus histopathology (Quast et al., 1988, 1984).
The neurotoxicity of 1,1,1-trichloroethane in humans and animals following acute
exposure has been extensively documented; in animal models, acute 1,1,1-trichloroethane
exposure has caused CNS depression and effects on motor activity and cognitive function.
On balance, the available animal data suggest that repeated exposure to 1,1,1-trichloroethane
does not cause overt effects on the CNS. Concern about the potential for
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1,1,1-trichloroethane to affect the nervous system following prolonged exposure is raised by
epidemiological findings and the subchronic findings of Rosengren et al. (1985) in gerbils.
In a study of 28 workers exposed occupationally to 1,1,1-trichloroethane, Kelafant et al.
(1994) reported increased sway in the Romberg test and statistically significant deficits for
memory, intermediate memory, rhythm, and speed in a neuropsychological test battery.
Workplace exposures were not measured, the number of workers in the study was small, and
Kelafant et al. (1994) findings were not confirmed in other limited studies of worker
populations (Cherry et al., 1983; Maroni et al., 1977). Nevertheless, the qualitative findings
from Kelafant et al. (1994) raise some concern about potential neurotoxic outcomes
following prolonged 1,1,1 -trichloroethane exposure. A limited number of experimental
animal studies examined neurotoxic endpoints following repeated exposure. In a test of
schedule-controlled operant behavior (fixed-ratio responding task), Moser et al. (1985) found
that mice exposed repeatedly to high levels of 1,1,1-trichloroethane for 20 minutes per day, 4
days per week, over a 4-week period recovered each day after solvent exposure, indicating
no residual effect of the chemical with repeated exposures; however, no similar study
involving subchronic or chronic exposure is available. Mattsson et al. (1993) reported slight
but statistically significant deficits in forelimb grip performance in rats exposed for 13
weeks; investigators considered the deficit possibly attributable to the sedative properties of
1,1,1-trichloroethane. No other deficits indicative of neurotoxicity were observed (the study
included an FOB, evaluations of visual, auditory, somatosensory, and caudal nerve-evoked
potentials, and histopathologic examination), although evaluation for cognitive deficits was
not performed. In light of the qualitative findings from the epidemiological literature,
additional evaluation of cognitive endpoints for subchronic or chronic durations would
reduce uncertainty in the database.
Rosengren et al. (1985) reported a small but statistically significant increase in regional
brain levels of GFAP, a biomarker of glial hypertrophy in response to neuronal injury, in
gerbils exposed to 1,1,1-trichloroethane for 3 months. Questions were raised about the
reliability of these findings, and they were not supported by pathological, physiological, or
neurochemical findings from other studies (see Section 5.2.3.1); however, the findings raise a
potential concern for effects on the CNS in the absence of an adequately conducted
confirmatory study. On balance, issues raised by neurotoxicity findings for
1,1,1-trichloroethane support a database UF of 3 for the chronic RfC.
The chronic RfC for 1,1,1-trichloroethane of 16 mg/m3 based on data from Quast et al.
(1988, 1984) was calculated as follows:
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Chronic RfC = point of departure + UF
= 1553 mg/m3-100
= 16 mg/m3
Comparison to Shorter Duration RfCs and Final Chronic RfC Derivation. The value of the
chronic RfC of 16 mg/m3 derived from Quast et al. (1988, 1984) turns out to be larger than the
acute and short-term RfCs for 1,1,1-trichloroethane, which range from 5 to 9 mg/m3. It is
generally anticipated, however, that acute (or short-term) RfCs would be higher in absolute value
than the subchronic or chronic RfC for that chemical since the acute (or short-term) exposure
durations are greatly reduced compared to exposures of subchronic or chronic duration. In the
case of 1,1,1-trichloroethane, the effect levels for acute/short-term and chronic inhalation
exposures might not necessarily be expected to follow a continuum from higher to lower for a
number of reasons.
• The point of departure for the acute (and short-term) exposure duration is based on CNS
effects in humans, whereas the point of departure for subchronic and chronic exposure
durations is based on liver effects in rats and mice. Thus, the target organ for acute/short-
term exposure durations differs from that for sub chronic/chronic exposure durations.
Although the modes of action for the CNS and liver effects of 1,1,1-trichloroethane have not
been established, it is likely that the modes of action at the two sites of toxicity are different.
• The endpoints examined following acute exposure to 1,1,1-trichloroethane differ from those
examined following subchronic or chronic exposure. In particular, sensitive neurobehavioral
testing in humans is available for evaluating 1,1,1-trichloroethane acute toxicity. In fact,
human test batteries proved to be more sensitive than animal models of acute
neurobehavioral toxicity. Sensitive testing for neurobehavioral effects in either humans or
animals is unavailable following repeated exposure.
• The acute/short-term RfCs are based on analysis of peak exposure, whereas
sub chronic/chronic RfCs are based on AUC exposure.
For 1,1,1-trichloroethane, the short-term RfC of 5 mg/m3 is clearly protective of health
effects associated with chronic exposure. Accordingly, the chronic RfC is set at 5 mg/m3 so as
not to exceed the limiting reference value derived for short-term exposure.
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5.2.5. Previous Inhalation Assessment
No inhalation assessment for 1,1,1-trichloroethane was previously included in the IRIS
database.
5.3. CANCER ASSESSMENT
As discussed in Section 4.7, some human epidemiological studies of
1,1,1-trichloroethane have found statistically increased incidences of cancer, but these studies
are limited by the number of subjects in the cohort, the low number of cases reported, and
confounding exposures to other solvents. 1,1,1 -Trichloroethane has been tested for
carcinogenicity in rats and mice by the oral route in two studies (Maltoni et al., 1986; NCI, 1977)
and by the inhalation route in one study (Quast et al., 1988, 1984). These bioassays either
showed no treatment-related increase in tumors or are considered inadequate for evaluation of
carcinogenic potential. 1,1,1-Trichloroethane has been tested extensively for genotoxic
potential; results are predominantly negative. The chemical has been shown to interact weakly
with DNA.
Under the Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005a), the database
for 1,1,1-trichloroethane provides inadequate information to assess carcinogenic potential. This
characterization is based on inadequate evidence of carcinogenicity in humans and animals.
Accordingly, the development of quantitative assessments of the carcinogenicity of
1,1,1-trichloroethane is not supported.
5.3.1. Oral Exposure
Not applicable.
5.3.2. Inhalation Exposure
Not applicable.
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6. MAJOR CONCLUSIONS IN THE CHARACTERIZATION OF
HAZARD AND DOSE RESPONSE
6.1. HUMAN HAZARD POTENTIAL
1,1,1-Trichloroethane is a widely used industrial solvent. The chemical is well absorbed
following oral, inhalation, and dermal exposure. Blood levels approach steady state after
approximately 2 hours of inhalation exposure. 1,1,1-Trichloroethane is rapidly distributed
throughout the body. The highest concentrations are found in fatty tissues. Most of the absorbed
1,1,1-trichloroethane is rapidly eliminated from the body unchanged in the expired air. A small
amount is metabolized in the liver to trichloroethanol and trichloroacetic acid, which are
excreted in the urine. 1,1,1 -Trichloroethane and its metabolites have been shown not to
accumulate to a large extent with repeated exposure.
The CNS is the most sensitive target for 1,1,1-trichloroethane following inhalation
exposure. Deficits in neurobehavioral performance tests have been widely reported in humans
and animals with acute exposure. Neurodevelopmental effects and neurochemical evidence of
gliosis have been reported in inhalation animal studies of longer duration. Gross CNS
depression is seen after exposure (by inhalation or gavage) to high levels. High levels have also
been found to produce depression of respiration and blood pressure and to produce cardiac
arrhythmia by sensitizing the heart to endogenous epinephrine. Animal studies have also shown
1,1,1-trichloroethane to be a weak hepatotoxicant, producing mild effects on the liver at
relatively high levels.
Most of the effects of 1,1,1-trichloroethane are thought to be produced by the parent
compound, primarily by interfering with the function of mitochondrial and cellular membranes.
Although produced only in low quantities, the metabolites trichloroethanol and trichloroacetic
acid are known to have effects on the nervous system and liver, respectively, and may contribute
to the observed effects on these targets.
Under the Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005a), the database
for 1,1,1-trichloroethane provides inadequate information to assess carcinogenic potential. This
characterization is based on inadequate evidence of carcinogenicity in humans and animals.
6.2. DOSE RESPONSE
6.2.1. Noncancer/Oral
6.2.1.1. Acute and Short-term RfD
Oral data for 1,1,1-trichloroethane are inadequate to support dose-response assessment
for acute and short-term exposure durations.
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6.2.1.2. Subchronic and Chronic RfD
The NTP (2000) subchronic study was used as the basis for the RfD. Decreased body
weight gain was observed in male and female exposed mice relative to the control, which was
not due to reduced feed consumption. The data were analyzed with BMD methods to derive a
point of departure of 2155 mg/kg-day (associated with a 10% change in mean terminal body
weight in female mice relative to the control mean). The subchronic oral RfD of 7 mg/kg-day
was derived from this point of departure and application of a composite UF of 300 (10 for
extrapolation from animals to humans, 10 for extrapolation to the most susceptible humans, and
3 for database deficiencies). The chronic oral RfD of 2 mg/kg-day was derived from the same
point of departure and application of a composite UF of 1000 (10 for extrapolation from animals
to humans, 10 for extrapolation to the most susceptible humans, 3 for extrapolation from
subchronic to chronic exposure duration, and 3 for database deficiencies).
Overall confidence in both the subchronic and chronic RfDs is low-medium. Confidence
in the principal study, NTP (2000), is considered high. The principal study (NTP, 2000), a 90-
day feeding study in rats and mice, is a recently conducted, peer-reviewed study performed with
standard protocols for NTP toxicity studies. 1,1,1 -Trichloroethane was microencapsulated and
administered in the diet to avoid chemical loss due to volatilization and to avoid toxicity that can
occur when administered in a bolus dose. Although the principal study is considered of high
confidence, the interpretation of the critical effect from this study, reduced mean terminal body
weight, merits discussion. Reduction in body weight gain was a consistent finding in studies of
1,1,1-trichloroethane toxicity across studies, species, and routes of exposure, though effects on
body weight were not associated with other target organ toxicity. External peer reviewers
expressed various opinions about the use of reduced body weight as the critical effect. See
Appendix A, Section B (question 3) for a more thorough summary of the comments from
external peer reviewers on endpoint selection. Confidence in the oral database is low-medium.
Chronic oral animal studies were designed as cancer bioassays with only limited investigation of
noncancer endpoints. Oral reproductive and developmental toxicity studies include a
multigeneration study in mice, drinking water developmental toxicity studies in rats, and a study
of developmental neurotoxicity in rats. Repeat-dose studies, including NTP (2000), did not
include investigation of sensitive neurological endpoints; the neurological endpoints in repeat-
dose oral studies were limited to clinical observations and brain histopathology. Considering the
confidence in the principal study, the endpoint selection, and the database, the overall confidence
in the RfD is low-medium.
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6.2.2. Noncancer/Inhalation
6.2.2.1. Acute Inhalation RfC
The most sensitive endpoint for dose-response assessment is the effect of acute exposure
on performance in neurobehavioral tests conducted by Mackay et al. (1987) in human
volunteers. The data in this study were not presented in a manner amenable to BMD modeling,
so the LOAEL of 950 mg/m3 following exposure for 1 hour was used as the point of departure
for the dose-response assessment (a NOAEL was not identified). PBPK modeling was used for
duration extrapolation (i.e., to derive acute RfC values for other exposure durations between 1
and 24 hours). Based on the assumption that CNS effects are correlated with blood
1,1,1-trichloroethane levels, the 1,1,1-trichloroethane level in blood associated with a 1-hour
exposure to 950 mg/m3 was determined. A PBPK model (Reitz et al., 1988) was used to
estimate the ambient (external) exposure concentration required to achieve the same blood
(internal) concentration following exposures of 4, 8, and 24 hours. The external concentrations
were 715, 693, and 650 mg/m3, respectively. Acute RfC values of 9, 7, 7, and 6 mg/m3 for 1, 4,
8, and 24 hours, respectively, were derived by applying a composite UF of 100 (10 for use of a
LOAEL and 10 for extrapolation to the most susceptible humans).
6.2.2.2. Short-term RfC
The acute neurobehavioral LOAEL of 950 mg/m3 (following a 1-hour exposure) from the
Mackay et al. (1987) study was observed to be lower than the LOAEL for any endpoint in
studies of short-term duration. A PBPK model (Reitz et al., 1988) was used to estimate the
external exposure concentration (526 mg/m3) required to achieve the same blood (internal)
concentration once steady state was reached at 14 days. Use of the acute inhalation data for
longer exposures is supported by toxicokinetic evidence that 1,1,1-trichloroethane and its
metabolites do not accumulate in blood to any appreciable extent, if at all, with repeated
exposure. The weight of evidence of the animal toxicity data suggests there is no lowering of the
threshold for neurobehavioral effects with repeated vs. acute exposure, although such evidence is
limited. The short-term RfC of 5 mg/m3 was derived by applying a UF of 100 (10 for
extrapolation to the most susceptible humans and 10 for extrapolation from a LOAEL to a
NOAEL) to the point of departure of 526 mg/m3.
6.2.2.3. Subchronic and Chronic RfC
The most appropriate repeat-dose studies for derivation of the subchronic and chronic
RfCs are the 2-year inhalation bioassay in rats and mice by Quast et al. (1988, 1984) and the
14-week inhalation study in mice by McNutt et al. (1975). The highest concentration tested in
Quast et al. (1988, 1984) caused treatment-related effects in the liver of rats considered to be
adaptive physiological changes and not adverse (designated as a NOAEL); the highest
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concentration tested in the McNutt et al. (1975) study, which was 3.7-folder higher than the
NOAEL in Quast et al. (1988, 1984) (when both concentrations were adjusted for continuous
exposure), caused clearly adverse effects on the liver in the mouse. PBPK modeling was used to
estimate the HEC at the NOAEL (1553 mg/m3, based on a TWA AUC concentration in liver as
the dose metric). A composite UF of 100 (3 for extrapolation from animals to humans, 10 for
extrapolation to the most susceptible humans, and 3 for database deficiencies) was applied to
obtain an RfC of 16 mg/m3. Because the histopathologic findings in Quast et al. (1988, 1984)
were observed at the 6-month sacrifice and did not progress in incidence or severity at later
interim sacrifices, the RfC could apply to both subchronic and chronic durations. This value of
the subchronic RfC (16 mg/m3) derived from a repeat-dose inhalation study turns out to be larger
than the acute and short-term RfCs for 1,1,1-trichloroethane, which range from 5 to 9 mg/m3. It
is generally anticipated that acute (or short-term) RfCs would be higher in absolute value than
the subchronic or chronic RfC for that chemical since the acute (or short-term) exposure
durations are greatly reduced compared to exposures of subchronic or chronic duration. In the
case of 1,1,1-trichloroethane, clearly the short-term RfC of 5 mg/m3 is protective of health
effects associated with subchronic and chronic exposure. Accordingly, the subchronic and
chronic RfCs are set at 5 mg/m3 so as not to exceed the limiting reference value derived for
short-term exposure.
Overall confidence in the acute inhalation RfC is medium. Confidence in the principal
study (Mackay et al., 1987) is medium. The study included a battery of neurobehavioral tests
and correlated test outcomes with blood 1,1,1-trichloroethane levels. The number of volunteers
was relatively small (12), and standard deviation/standard errors were not reported. Confidence
in the acute inhalation database is high. The acute inhalation database is extensive, including
both human and animal studies focused on the most sensitive endpoint, neurotoxicity. The
inhalation database also includes inhalation developmental toxicity studies in three species.
Overall confidence in the short-term inhalation RfC is medium. Confidence in the
principal study, Mackay et al. (1987) and in the short-term database is medium. Several animal
studies of short-term exposure duration are available. Although most are limited in the scope of
the endpoints investigated, these studies focused on endpoints expected to be the most sensitive
following acute/short-term exposure.
Overall confidence in the subchronic and chronic RfCs is medium. Confidence in Quast
et al. (1988, 1984), one of the coprincipal studies, is high. This study was well conducted, using
two species, adequate numbers of animals, and interim sacrifices. Failure to use an exposure
concentration high enough to produce treatment-related effects in this study was offset by the
McNutt et al. (1975) study, which included an exposure concentration that resulted in clearly
adverse hepatotoxic effects. Confidence in the database is medium. The database includes a
2-year chronic inhalation bioassay in rats and mice, inhalation developmental toxicity studies in
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three species, and a single generation reproductive/developmental toxicity study that included
exposure prior to mating. Although an inhalation multigeneration study has not been conducted,
a multigeneration reproductive study by the oral route is available. While the available repeat-
dose studies do not provide evidence of overt neurobehavioral effects, most repeat-dose studies
did not include examination of subtle CNS toxicity.
6.2.3. Cancer/Oral and Inhalation
Under the Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005a), the database
for 1,1,1-trichloroethane is inadequate to assess human carcinogenic potential. Accordingly, a
quantitative assessment of carcinogenic potential was not performed.
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Assessment, Office of Research and Development, U.S. Environmental Protection Agency, Washington, DC under
ORISE Subcontract 5-10329. [unpublished report].
York, RG; Sowrey, BM; Hastings, L. (1982) Evaluation of teratogenicity and neurotoxicity with maternal inhalation
exposure to methyl chloroform. J Toxicol Environ Health 9:251-266.
Yoshida, K. (1993) Preliminary exposure assessment of volatile chlorinated hydrocarbons in Japan. Chemosphere
27:621-630.
You, L; Dallas, CE. (2000) Effects of inhaled 1,1,1-trichloroethane on the regional brain cyclic GMP levels in mice
and rats. J Toxicol Environ Health A 60(5):331-341.
You, L; Muralidhara, S; Dallas, CE. (1994) Comparisons between operant response and 1,1,1-trichloroethane
toxicokinetics in mouse blood and brain. Toxicology 93(2-3): 151-163.
Zarchy, TM. (1996) Chlorinated hydrocarbon solvents and biliary-pancreatic cancer: report of three cases. Am J Ind
Med30(3):341-342.
Zimmermann, FK; Scheel, I. (1981) Induction of mitotic gene conversion in strain D7 of Saccharomyces cerevisiae
by 42 coded chemicals. In: de Serres, FJ; Ashby, J; eds. Evaluation of short-term tests for carcinogens: report of the
International Collaborative Program. New York, NY: Elsevier/North Holland. Prog Mutat Res 1:481-490.
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APPENDIX A
Summary of External Peer Review and Public Comments and Disposition
The support document and IRIS summary for 1,1,1-trichloroethane have undergone both
Agency review performed by scientists within EPA and a more formal external peer review
performed by scientists in accordance with EPA guidance on peer review (U.S. EPA, 2006).
Comments made by the Agency reviewers were addressed prior to submitting the documents for
external peer review and are not part of this appendix. The five external peer reviewers were
tasked with providing written answers to general questions on the overall assessment and on
chemical-specific questions in areas of scientific controversy or uncertainty. A summary of
significant comments made by the external reviewers and the public and EPA's responses to
these comments follows.
EXTERNAL PEER REVIEW PANEL COMMENTS
The reviewers made several editorial suggestions to clarify specific portions of the text.
These changes were incorporated in the document as appropriate and are not discussed further.
A. General Comments
1. Is the ToxicologicalReview logical, clear, and concise? Has EPA objectively and
transparently represented and synthesized the scientific evidence for noncancer and cancer
hazard?
Comments: All reviewers found the document to be logical and clear. One reviewer did
not consider the Toxicological Review to be concise and suggested that those studies clearly not
having any decisive relevance to RfD or RfC derivation or qualitative cancer evaluation be
excluded. Another reviewer questioned whether the classical definition of RfD and RfC applies
to less-than-lifetime exposures and asked whether a new definition was needed. One reviewer
suggested that a brief review be provided on the behavioral toxicity of chemical anesthetics that
are either structurally or functionally similar to 1,1,1-trichloroethane that would provide context
for the non-neurotoxicologist on the activity of 1,1,1-trichloroethane.
Response: The content of the Toxicological Review was consistent with the outline for
IRIS toxicological reviews; an attempt had been made to limit the discussion of studies that did
not bear directly on the reference values. The definitions used for reference values for less-than-
lifetime exposure durations are those in the IRIS Glossary at www.epa.gov/iris. A brief
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discussion of the behavioral toxicity of chemical anesthetics was added to Section 4.4.1,
Neurological Effects.
2. Are you aware of additional studies that should be considered in the assessment of the
noncancer and cancer health effects of 1,1,1-trichloroethane?
Comments: One reviewer identified the following additional literature:
Loew, GH; Rebagliati, M; Poulsen, M. (1984) Metabolism and relative carcinogenic potency of
chloroethanes: a quantum chemical structure-activity study. Cancer Biochem Biophys 7:109-132.
Lynge, E; Anttila, A; Hemminki, K. (1997) Organic solvents and cancer. Cancer Causes Control 8:406-
419.
Stewart, PA; Lee, JS; Marano, DE; et al. (1991) Retrospective cohort mortality study of workers at an
aircraft maintenance facility. II. Exposures and their assessment. Br J Ind Med 48:531-537.
Dickerson, CL; Biesemeier, JA. (1982) Aspiration of methyl chloroform. Vet Hum Toxicol 24:167-168.
Muttray, A; Moll, B; Faas, M; et al. (2004) Acute effects of 1,1,1-trichloroethane on human olfactory
functioning. American J Rhinology 18:113-117.
Troutman, WG. (1988) Additional deaths associated with the intentional inhalation of typewriter correction
fluid. Vet Human Toxicol 30:130-132.
Verschuuren, HG; de Rooij, CG. (1990) Health risk assessment of environmental exposure to
1,1,1-trichloroethane. Regul Toxicol Pharmacol 11:90-99.
Yost, MG; Rose, MA; Morgan, MS. (2003) An evaluation of Fourier transform infrared (FTIR)
spectroscopy for detecting organic solvents in expired breath. Applied Occup Environ Hygiene 18:160-
169.
One reviewer considered the unpublished inhalation study of 1,1,1-trichloroethane in
Sprague-Dawley rats by Quast et al. (1978) (also Rampy et al., 1977) to be relevant as a chronic
(1-year) bioassay in a second rat species.
Response: Additional study summaries were added where relevant. Those citations to
studies that were reviews, studies of analytical methods or exposure only, or involved multiple
chemical exposures were not included in the Toxicological Review. Discussion of the 1-year
Quast et al. (1978) inhalation bioassay was added to the synthesis of evidence for
carcinogenicity in Section 4.7.2 of the Toxicological Review.
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B. Oral Reference Dose (RfD) Values
1. The conclusion was reached that the available oral toxicity information was inadequate to
support derivation of oral RfD values for acute and short-term exposure durations. Do you agree
with this conclusion? Is the rationale for not developing an acute or short-term oral RfD
transparent and objective? If you disagree, what study should be used to derive an oral RfD?
Comments: All five reviewers agreed with the conclusion that the available oral toxicity
information was insufficient to support derivation of oral RfD values for acute and short-term
exposure durations. One of these reviewers considered the rationale for not providing acute or
short-term RfDs to be too terse and suggested that a better summary of the weaknesses of each
study be given, leading to the conclusion that an oral RfD could not be developed. A second
reviewer stated that the rationale "could be somewhat expanded." One reviewer also
recommended that justification for not doing route-to-route extrapolation be articulated.
Response: A rationale for not developing oral RfDs for acute and short-term exposure
durations is provided in Sections 5.1.1 and 5.1.2 of the Toxicological Review, and justification
for not performing route-to-route extrapolation for these exposure durations was provided in
Section 5.1.5.1. The rationale for not developing acute and short-term oral RfDs was expanded.
2. The 90-day dietary study by the National Toxicology Program (NTP, 2000) was selected as
the basis for the subchronic and chronic oral RfDs. Is the selection of NTP (2000) as the
principal study scientifically justified? Is the rationale for selecting this transparent and
objective? Are there any other studies that you believe would be justified scientifically as the
bases for the subchronic and chronic RfDs?
Comments: Four reviewers agreed with the selection of the NTP (2000) study as the
principal study and considered the rationale for this selection to be transparent and objective.
One reviewer considered the selection of NTP (2000) to be transparent and more relevant for
subchronic and chronic oral RfD derivation than the Bruckner et al. (2001) study. Nevertheless,
this reviewer questioned the selection of the NTP (2000) study because he believed the critical
effect (reduced body weight) could be considered adaptive rather than adverse. This reviewer
suggested that the Agency reconsider route-to-route extrapolation (using mild hepatotoxicity or
astrogliosis [Rosengren et al., 1985] as critical effects) in place of oral data from the NTP study.
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Response: Based on feedback from the majority of the peer reviewers, the NTP (2000)
bioassay was retained as the principal study. The issues raised by one reviewer that largely
relate to the selection of the critical effect are addressed more thoroughly under charge questions
3 and 6 below.
3. A 10% decrease in mean terminal body weight of the mouse relative to the control mean
served as the basis for the subchronic and chronic oral RfDs. Is the selection of decreased body
weight gain as the critical effect scientifically justified? Has the rationale for selection of this
critical effect been transparently and objectively described? Is a 10% decrease in mean terminal
body weight the most scientifically justified response to use given the findings of NTP (2000) of
a statistically significant decrease in mean terminal body weight (compared to the control mean)
at a dose lower than the BMDLio? Would presenting a BMD analysis of the 1% and 5%
responses be helpful to the reader? If you disagree with the choice of body weight as the critical
effect is there a preferable alternative?
Comments: All reviewers expressed some reservations concerning the use of body weight
as the critical effect. Two reviewers considered the selection of decreased body weight to be
adequately justified; two reviewers suggested that the rationale be expanded. Of these
reviewers, one questioned the possible relevance at lower doses; he considered the endpoint
weak, but a toxic response. A second reviewer suggested that support for decreased body weight
could be improved further by including more descriptions from the pharmacology/toxicology
literature clarifying the use of body weight as a critical effect. A third reviewer considered the
choice to be the best available, if suboptimal. A fourth reviewer noted that the lack of associated
daily observations, gross necropsy observations, or general histopathology associated with the
decreased body weight make defending this selection difficult; nevertheless, this reviewer
considered the selection of body weight as the critical effect to set the RfD to be reasonable.
None of these four reviewers could identify a more appropriate alternative endpoint for the RfD,
and none of the five reviewers indicated that the data were not appropriate for use in deriving an
RfD. The fifth reviewer noted that reduced body weight could be considered adaptive rather
than adverse, and expressed preference for deriving an RfD using route-to-route extrapolation,
with a focus on those inhalation studies reporting mild hepatotoxicity or, alternatively, the
subchronic inhalation study of Rosengren et al. (1985) reporting astrogliosis in the cerebral
sensorimotor cortex.
One reviewer stated that he would support, but not necessarily recommend, presentation
of the BMD analysis of the 1% and 5% responses. A second reviewer stated that he saw little to
no benefit from presenting benchmark dose analyses of the 1 and 5% responses.
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Response: Use of reduced body weight as the critical effect was retained. Additional
support for body weight as a potential adverse effect was provided in Section 5.1.3.1. For the
reasons discussed in Section 5.1.5.2, route-to-route extrapolation was not considered
scientifically supported in the case of 1,1,1-trichloroethane. The empirical data does not support
the liver as a sensitive target organ following oral exposure; even the recent NTP (2000) study
found no evidence of liver toxicity in mice or rats at a dietary concentration as high as
80,000 ppm. For reasons discussed in Section 5.2.3.1 and in response to question C.10 below,
the Rosengren et al. (1985) study was not considered to be sufficiently reliable to be used as the
basis for a reference value by any route of exposure.
In light of the lack of support for providing a BMD analysis using alternative BMR
values, only the BMD and BMDL for a BMR of 10% was provided.
4. Are the uncertainty factors applied to the point of departure for the derivation of the
subchronic and chronic RfD values scientifically justified and transparently and objectively
described?
Comments: All five reviewers generally agreed that the uncertainty factors (UFs) applied
in the derivation of the subchronic and chronic RfD were appropriate and objectively described.
One reviewer observed that there are experimental data that may stimulate conversation as to the
need for a UF for subchronic to chronic extrapolation in the derivation of the chronic oral RfD.
Response: In light of the general agreement with the UF values used to derive the
subchronic and chronic RfDs, the UFs used in the draft assessment were retained.
5. A database uncertainty factor of 3 was applied in deriving the subchronic and chronic RfDs
principally because the available oral studies did not specifically examine the potential for subtle
neurotoxicity following repeated exposures. Has the rationale and justification for this
uncertainty factor been transparently and objectively described? Is the application of this
uncertainty factor scientifically justified? Please consider the appropriateness of this UF in light
of the full database for 1,1,1-trichloroethane and, in particular, whether consideration of
uncertainties in the inhalation database with respect to neurotoxicity should be reflected in the
database uncertainty factor for the oral reference values.
Comments: Four reviews believed the rationale and justification for the database UF of 3
was justified and transparently and objectively described. One of these reviewers considered the
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choice of the UF to be conservative but acceptable and clearly rationalized. One reviewer found
"it interesting that EPA embraces the inhalation study of Rosengren et al. to justify the database
UF for oral RfD derivation, but considers the study inadequate to establish inhalation RfCs.
With that said, like EPA, I feel as though the inhalation database for 1,1,1-trichloroethane is
relevant to the oral route (and visa versa), especially considering that the chemical's
toxicokinetic profile suggests many of its toxicities should be the same regardless of the pathway
by which it is absorbed."
Response: In light of the general agreement with the database UF value used to derive the
subchronic and chronic RfDs, a database UF of 3 was retained. The comment related to the
Rosengren et al. (1985) study is addressed in response to comments on charge question 10 on the
inhalation RfC.
6. As an alternative to the subchronic and chronic oral RfDs derived using data from the NTP
(2000) dietary study, consideration was given to use of physiologically based pharmacokinetic
(PBPK) modeling to extrapolate findings from a 2-year inhalation bioassay (Quast et al., 1988,
1984) to the oral route (i.e., route extrapolation). Is the decision not to use route extrapolation to
derive oral RfD values (as discussed in Section 5.1.1. of the Toxicological Review) transparently
and objectively described?
Comments: Three reviewers considered the rationale and justification for not using route-
to-route extrapolation to have been transparently and objectively described, with one noting that
the apparent differences in comparative hepatotoxicity following oral exposure (mild
hepatotoxicity) and inhalation exposure (pronounced hepatotoxicity) preclude route-to-route
extrapolation at this time. A fourth reviewer did not support the decision to forego route-to-route
extrapolation. This reviewer could think of no reason why 1,1,1 -trichloroethane via the oral
route would be less effective at targeting the liver than when administered via inhalation (e.g.,
hepatic first-pass elimination is essentially a non-issue with 1,1,1-trichloroethane) and might
have predicted the opposite. For this reason, he recommended that the Agency perhaps
reconsider inhalation-to-oral extrapolation, whether it be based on the hepatotoxicity NOAEL of
Quast et al. (1988, 1984) or the LOAEL of McNutt et al. (1975) (or a combination of the two), or
a study examining another critical effect altogether. A fifth reviewer stated that the PBPK
modeling (route-to-route) could inform selection of the UF, even if the Agency did not
extrapolate both route (inhalation to oral) and response (neurotoxicity from inhalation to oral
ingestion). He noted that gavage doses give transient high peak concentrations, which may skew
the interpretation somewhat. This reviewer thought that the authors of the PBPK modeling effort
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should have used other approaches for describing the unpublished Bruckner kinetic data (cited in
Yang, 2006) using two compartments for oral absorption and that presentation of error bars
would be useful.
Response: For the reasons provided in Section 5.1.5.2 (i.e., the apparent differences in
relative hepatotoxicity of 1,1,1-trichloroethane by the oral and inhalation routes), a route-to-
route extrapolation approach to derive the subchronic or chronic oral RfD was not considered
appropriate. All but one reviewer considered the rationale and justification for not using route-
to-route extrapolation to have been transparently and objectively described. As noted by one of
the peer reviewers, a biological reason for the difference in liver toxicity by oral and inhalation
exposure could not be provided; nevertheless, the empirical data show a marked difference in
hepatotoxicity by route of exposure. For these reasons, the decision not to apply route-to-route
extrapolation was retained.
It is not clear that the lack of comparability of dose-response by the oral and inhalation
routes is a function of transient high peak concentrations following oral administration. The oral
RfD was based on an NTP study (2000) involving dietary administration that did not produce the
same effects (e.g., gross CNS effects and mortality) as observed in a similar gavage study
(Bruckner etal., 2001).
The objective of the PBPK modeling for 1,1,1-trichloroethane was to apply existing
models published in the peer-reviewed literature. While the modeling effort by Yang (2006)
made it clear that the existing models did not adequately simulate unpublished gavage data
provided by Bruckner (see Yang, 2006), revision of existing models to include two
compartments for oral absorption in order to better describe the Bruckner kinetic data was
beyond the scope of the current assessment. The addition of error bars on the data points would
not change the conclusions from the Yang (2006) analysis.
C. Inhalation Reference Concentration (RfC) Values
1. The acute inhalation study by Mackay et al. (1987) involving the examination of
neurobehavioral effects in humans was selected as the basis for the acute inhalation RfC. Is the
selection of Mackay et al. (1987) as the principal study scientifically justified? Is the rationale
for selecting this study transparent and objective? Are there any other studies that you believe
would be justified scientifically as the basis for the acute RfC?
Comments: All five reviewers supported the selection of Mackay et al. (1987) as the
basis for the acute inhalation RfC. These reviewers generally considered this to be a well-
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conducted study that examined the effect of several concentrations of 1,1,1-trichloroethane on a
battery of psychomotor tests and believed that the rationale and justification for not using other
studies was transparently and objectively described. One reviewer noted that neurobehavioral
effects appear to be a sensitive endpoint for inhaled 1,1,1-trichloroethane and can often can pick
up changes at lower concentrations in humans than in laboratory animals. A second reviewer
noted that the study lacks pair-wise comparisons that preclude one from determining the
exposure levels at which statistically significant changes in specific psychomotor tests occurred
but did not suffer from the fatal flaws that often accompany psychomotor evaluations of solvent-
exposed human subjects.
Response: Based on the comments of the peer reviewers, no revision of the Toxicological
Review was considered necessary.
2. PBPK modeling was used to extrapolate from the LOAEL (950 mg/m3 exposure for one hour)
to 4-, 8-, and 24-hour exposure durations. Is this duration extrapolation scientifically supported?
Was duration extrapolation correctly performed? Please provide any other comments concerning
EPA's conduct of this extrapolation. Is the PBPK approach transparently and objectively
described?
Comments: All five reviewers considered duration extrapolation to be scientifically
supported and transparently and objectively described. One reviewer noted that the observation
in the Toxicological Review that the C x T relationship did not do a good job predicting
outcomes should be extended to how the acute exposure guidelines (AEGL) process uses a
modified form of Haber's rule to describe C x T but further noted that, if PBPK models are
available, the use of PBPK modeling is preferred over the modified Haber's rule approach (ten
Berge).
Response: Based on the comments of the peer reviewers, PBPK modeling was retained as
the approach for accomplishing duration extrapolation. As noted by one of the reviewers, the
use of PBPK modeling is preferred over the ten Berge modification of Haber's rule (Cn x t = k).
Therefore, it does not appear necessary to describe this alternative duration extrapolation
approach in the Toxicological Review. It should be noted that neither Haber's rule nor the ten
Berge modification of Haber's rule was applied by the National Advisory Committee for Acute
Exposure Guideline Levels for Hazardous Substances (NAC/AEGL) in developing the AEGL-1
(predicted to be associated with nondisabling, transient, reversible effects) for
1,1,1-trichloroethane (NAC/AEGL report available at
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http://www.epa.gov/oppt/aegl/pubs/tsd203.pdf); the AEGL-1 derived using 4-hour exposure data
was used for all time points (10 minutes to 8 hours) based on the observation that severity of
effects did not increase with duration of exposure (at least for exposures up to 8 hours).
Extrapolation using C" x t = k was applied only in deriving the 1,1,1-trichloroethane AEGL-2
(predicted to be associated with irreversible or other serious, long-lasting adverse health effects
or an impaired ability to escape) and AEGL-3 (predicted to be associated with life-threatening
health effects or death) values, for which there are no corresponding IRIS reference values.
3. The study results of Mackay et al. (1987) were used to derive the short-term RfC, with PBPK
modeling used to extrapolate to steady-state conditions. Is the Mackay et al. (1987) study the
most appropriate as the basis for the short-term RfC? If so, is this extrapolation scientifically
justified? Are the model assumptions, parameter values, and selection of dose metrics clearly
presented and supported? Are there any other studies that you believe would be justified
scientifically as the basis for the short-term RfC?
Comments: All five reviewers supported the choice the Mackay et al. (1987) study as the
basis for the derivation of the short-term RfC and considered the extrapolation approach to be
sound and the model assumption, parameter values, and selection of dose metrics clearly
presented and supported. Reviewers could not identify another study that would be a better basis
for the short-term RfC.
Response: Based on the comments of the peer reviewers, no revision of the Toxicological
Review was considered necessary.
4. The Quast et al. (1988, 1984) 2-year inhalation bioassay and the McNutt et al. (1975) 14-week
inhalation study were jointly used as the basis for the subchronic and chronic RfCs. Is the
selection of these as coprincipal studies (see Sections 5.2.3.1 and 5.2.4.1) appropriate? Is the
rationale for selecting these studies transparent and objective? Are there any other studies that
you believe would be justified scientifically as the basis for the subchronic and chronic RfCs?
Comments: Three reviewers considered the decision to use the Quast (1988, 1984) and
McNutt et al. (1975) studies together as the basis for the subchronic and chronic RfC values to
be appropriate and transparent. These reviewers were not aware of any other relevant studies
that could be a basis for determining subchronic and chronic RfCs. A fourth reviewer
considered the data sets to be adequate.
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One reviewer did not consider EPA's rationale for dismissing Rosengren et al. (1985)
from consideration as the principal study to be convincing. This reviewer believed that the
Rosengren et al. (1985) study demonstrated quite possibly the most sensitive effect and
warranted further consideration (or at least further explanation as to why it was not selected as
the principal study). This position was based on the following: (1) other studies, many nearly
identical in design to that of Rosengren et al. (1985), have reported GFAP increases following
toluene, styrene, xylene, and dichloromethane exposures (references provided below); (2) some
studies that show that S-100 and GFAPs are frequently expressed differentially in various brain
regions following chemical insult; and (3) GFAP has been validated as an indicator of
neurotoxicity under conditions where traditional histopathology has failed to reveal the damage.
Finally, this reviewer noted that the database UF of 3, driven largely by questions surrounding
1,1,1-trichloroethane's neurotoxicity that stem from Rosengren et al. (1985), makes EPA's
choice of the hepatotoxicity studies more palatable.
Rosengren, LE; Haglid, KG. (1989) Long term neurotoxicity of styrene. A quantitative study of glial
fibrillary acidic protein (GFA) and S-100. Br J Ind Med 46(5):316-320.
Rosengren, LE; Kjellstrand, P; Aurell, A; et al. (1986) Irreversible effects of dichloromethane on the brain
after long term exposure: a quantitative study of DNA and the glial cell marker proteins S-100 and GFA.
Br J Ind Med 43(5):291-299.
Rosengren, LE; Kjellstrand, P; Aurell, A; et al. (1986) Irreversible effects of xylene on the brain after long
term exposure: a quantitative study of DNA and the glial cell marker proteins S-100 and GFA.
Neurotoxicology 7(3):121-135.
Gotohda, T; Tokunaga, I; Kubo, S; et al. (2000) Effect of toluene inhalation on astrocytes and neurotrophic
factor in rat brain. Forensic Sci Int 113(l-3):233-238.
Little, AR Jr; Gong, Z; Singh, U; et al. (1998) Decreases in brain glial fibrillary acidic protein (GFAP) are
associated with increased serum corticosterone following inhalation exposure to toluene. Neurotoxicology
19(4-5):739-747.
Wang, S; Karlsson, JE; Kyrklund, T; et al. (1993) Perchloroethylene-induced reduction in glial and
neuronal cell marker proteins in rat brain. Pharmacol Toxicol 72(4-5):273-278.
Response: Based on the majority of comments from the peer reviewers, findings from the
Quast et al. (1988, 1984) and McNutt et al. (1975) studies were retained as the basis for the
subchronic and chronic RfC values. For the reasons discussed in comment/response C.10 below,
the Rosengren et al. (1985) study was rejected as the basis for the RfC.
5. The minimal histopathological findings in the liver observed in the Quast et al. (1988, 1984)
rat study were judged to reflect an adaptive physiological response and not an adverse effect. Is
this judgment scientifically appropriate and objectively supported?
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Comments: All five reviewers agreed with EPA's interpretation of the histopathological
findings. One of these reviewers recommended that EPA provide a discussion of what
constitutes adaptive and adverse and a very brief mechanistic explanation as to why certain cell
populations in the liver undergo morphological change in their adaptive response to
1,1,1-trichloroethane to enable the reader to better understand EPA's justification for classifying
effects as NOAELs or LOAELs.
Response: Consistent with the comments of the peer reviewers, the characterization of
liver histopathology findings from the Quast et al. (1988, 1984) rat study were retained.
As stated by Lewis et al. (2002), "Nonadverse effects are usually adaptive or
compensatory responses or findings that are below a threshold level or do not fulfill the criteria
that define their biological significance. However, often the distinction between adverse and
nonadverse effects is not clearly defined and interpretation needs scientific judgment on a case-
by-case basis." U.S. EPA (2002) has offered similar guidance on distinguishing between
adaptive and adverse effects:
"Professional judgment is required to decide, on the basis of a thorough review of
all available data and studies, whether any observed effect is adverse and how the
results fit with what is known about the underlying mode of action. These
judgments require the input of experts trained in toxicology, statistics, and
epidemiology and, often, of specialists in the structure and function of the target
organ systems. Both the biological and the statistical significance of the effects
are considered when making these judgments.
Decisions about the amount of change to consider adverse must always be
made using professional judgment and must be viewed in light of all the data
available on the endpoint of concern. All toxicological data on a chemical must be
reviewed before deciding whether an effect is biologically significant and
adverse."
Lewis, RW; Billington, R; Debryune, E; et al. (2002) Recognition of adverse and nonadverse effects in
toxicity studies. Toxicol Pathol 30:66-74.
U.S. EPA. (2002) A Review of the Reference Dose and Reference Concentration Processes. EPA/630/P-
02/002F.
As suggested by the above authors, the decision to characterize the histopathologic
changes observed in the Quast et al. (1988, 1984) rat study was reached on a case-by-case basis,
considering all the available data on that endpoint and input from pathologists and experts in
rodent liver toxicity. The discussion of the liver findings from Quast et al. (1988, 1984) in
Section 5.2.3.1 of the Toxicological Review was expanded to provide better support for the
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histopathologic changes as not adverse, and a brief discussion cellular changes corresponding to
liver hypertrophy was provided.
6. PBPK modeling was used to extrapolate the point of departure from Quast et al. (1988, 1984)
to humans. Is the PBPK modeling for interspecies extrapolation scientifically justified and
transparently and objectively described? Are the model assumptions, parameter values, and
selection of dose metrics clearly presented and supported?
Comments: Four reviewers considered the PBPK model for interspecies extrapolation
(rat-to-human) to be scientifically justified and transparently and objectively described. One of
these reviewers noted that aspects of the PBPK modeling suggested that the models in some
cases are not totally adequate in describing the actual kinetics. A fifth reviewer evaluated the
information using steady-state assumptions and noted that different results would likely be
obtained if blood AUC was used instead of liver AUC as the dosimetric and if peak
concentration was used instead of AUC. This reviewer recommended that the Agency evaluate
the modeling portion of this document with reference to the Agency guidance document for
using PBPK models in regulatory decisions.
Response: The peer reviewers generally supported the PBPK modeling conducted for
1,1,1-trichloroethane for use in interspecies extrapolation. As noted in a previous response, the
objective of the PBPK modeling for 1,1,1-trichloroethane was to apply existing models
published in the peer-reviewed literature. While the modeling effort by Yang (2006)
demonstrated that the existing models did not adequately simulate all data sets (e.g., the
unpublished gavage data from Bruckner), revision of existing models in order to better describe
these data sets was beyond the scope of the current assessment.
Based on the PBPK modeling effort of Yang (2006), EPA concurs that different
outcomes will be obtained by use of blood AUC versus liver AUC as the dose metric, and in the
case of the acute inhalation RfC, peak concentration versus AUC. In the case of the
sub chronic/chronic RfC, the TWA AUC for liver was considered to be the more appropriate dose
metric (versus AUC for blood) because the liver is the target of 1,1,1-trichloroethane toxicity. In
the case of the acute RfC, consideration was given to AUC versus momentary concentration in
the blood at the time of testing (Ct) (see Section 5.2.1.2). Experimental data for
1,1,1-trichloroethane and related solvents suggest that Ct is related to neurological deficits and is
therefore the more appropriate dose metric. The modeling was conducted in a manner generally
consistent with EPA's August 2006 "Approaches for the Application of Physiologically Based
Pharmacokinetic (PBPK) Models and Supporting Data in Risk Assessment" (EPA/600/R-
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05/043F); however, it should be noted that this EPA document was not available at the time that
the modeling effort for 1,1,1-trichloroethane was performed.
7. Are the uncertainty factors applied to the point of departure for the derivation of the acute,
short-term, subchronic, and chronic RfC values scientifically justified and transparently and
objectively described?
Comments: All five reviewers considered the UFs used in the derivation of the four RfC
values to be scientifically justified and adequately described. With respect to the acute RfC
based on the Mackay et al. (1987) study, one reviewer observed that usually a UF of 3 (not 10) is
used when PBPK was used to predict toxicokinetics, leaving a UF of 3 (101/2) for
toxicodynamics. He suggested that perhaps a UF of 3, rather than 10, should be used for
susceptible populations because this was presented as a pharmacodynamic issue.
Response: Consistent with the majority of comments from the peer reviewers, the values
of the UFs were not changed. One reviewer suggested that consideration be given to an
intraspecies UF of 3 (rather than 10) for the acute RfC. Information on the intraindividual
variability in response to 1,1,1-trichloroethane (resulting from both differences in
pharmacokinetics and pharmacodynamics), however, is limited and was not considered sufficient
to depart from the default UF of 10.
8. Database uncertainty factors were not applied in deriving the acute and short-term RfCs. A
database uncertainty factor of 3 was used in deriving subchronic and chronic RfCs. Has the
rationale and justification for the application of the database uncertainty factor been
transparently and objectively described? Is the application of this uncertainty factor
scientifically justified, particularly with respect to the existing literature (both human and
animal) on 1,1,1-trichloroethane neurotoxicity?
Comments: Four reviewers supported the database UF of 3. One of these reviewers felt
that the Rosengren et al. (1985) study alone was sufficient to generate some degree of
uncertainty over the risk for neurotoxicity posed by repetitive exposures over a prolonged period
(e.g., the LOAEL from Rosengren et al. [1985] is 210 ppm [continuous exposure for 12 weeks]
while that from McNutt et al. [1975] is 1000 ppm [continuous exposure for 14 weeks]). A fifth
reviewer expressed discomfort with use of the Rosengren et al. (1985) study to support the UF of
O
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Response: Based on the feedback from the majority of the peer reviewers (four out of
five) that concurred with the use of a database UF of 3, the database UF of 3 was retained.
9. Because the value of the subchronic and chronic RfC exceeded the values of the acute and
short-term RfCs, the subchronic and chronic RfC was set at 5 mg/m3 so as not to exceed the
limiting reference value derived for short-term exposure. Is this decision scientifically justified
and transparently and objectively described? Please comment on whether you believe there
might be more appropriate explanations than those discussed in Sections 5.2.3.3 and 5.2.4.3 for
why the acute and short-term inhalation RfC values were smaller than the subchronic and
chronic RfC values.
Comments: All five reviewers agreed that the decision to set the subchronic and chronic
RfC at 5 mg/m3 was scientifically justified and transparently and objectively described. These
reviewers were not able to offer additional explanations beyond those discussed in the
Toxicological Review for why the acute and short-term inhalation RfC values were smaller than
the subchronic and chronic RfC values. A fifth reviewer generally agreed with EPA's approach
but observed that "reducing the RfCs merely because they 'don't make sense' when examined
relative to one another belittles EPA's process of hazard and dose-response evaluation... given
the obvious time, financial resources, and effort expended at applying state-of-the-science
methods to RfD and RfC derivation in the present case." Although this reviewer did not believe
that EPA's approach was scientifically justified "if good science is so readily dismissed," he
considered EPA's decision to be transparently and objectively described.
Response: Consistent with the input from four of the five peer reviewers, the values for
the subchronic and chronic RfC and the rationale for the derivation of those values were
retained. In response to one reviewer's concern regarding the decision to limit the value of the
subchronic and chronic RfC to 5 mg/m3, EPA points to the rationale for this decision in Sections
5.2.3.3 and 5.2.4.3 of the Toxicological Review; the Agency continues to believe that the
approach and resulting reference values have merit.
10. Rosengren et al. (1985) reported increased glial fibrillary acidic protein (GFAP), a marker
for formation of astroglial fibrils in response to brain injury, in the sensorimotor cerebral cortex
of 1,1,1-trichloroethane-exposed gerbils. The EPA did not consider these findings to be
sufficiently reliable or of sufficient toxicological significance to use as the basis for the
subchronic RfC. Is this decision scientifically justified, particularly in light of observed
neurobehavioral effects associated with acute exposure to 1,1,1-trichloroethane? Is this decision
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transparently and objectively described? The Rosengren et al. (1985) study was used to inform
the value of the database uncertainty factor used in deriving the subchronic and chronic RfDs
and RfCs. Was consideration of this study appropriate in the context of the database uncertainty
factor?
Comments: Four reviewers agreed with EPA's position that the Rosengren et al. (1985)
study was unreliable as the basis for the subchronic RfC. One of these reviewers observed that
use more information is needed to link the protein changes in the brain with pathology of the
brain and alterations in behavior, combined with a hypothesis about mode of action. A second of
these reviewers identified specific reservations beyond those cited in the EPA review.
Specifically, this reviewer noted that the conclusion in the Rosengren et al. (1985) study of
significant decrease in brain weight is not supported by the data based on an independent
statistical analysis. Using an unpaired t-test without correcting for multiple comparisons, he
found that the high concentration of 1,1,1-trichloroethane did not cause a significant decrease in
brain weight, and further questioned Rosengren's use of a non-parametric analysis method for
parametric data. This reviewer also expressed concern about the extremely small SEMs (15-
25%) reported in this work based on personal laboratory experience. This reviewer believed this
SEM to be unexpectedly precise since it needed to account for normal inter-animal variability,
inter-animal differences in response to 1,1,1-trichloroethane, the fact that only a small portion of
the extractable cellular GFAP is sampled, and an assay method that is indirect and itself would
be expected to have a relatively large (>10%) coefficient of variation.
One reviewer stated that EPA did not adequately justify the dismissal of Rosengren et al.
(1985) from consideration as its principal study, noting that the LOAEL of 210 ppm from this
study suggests that what is quite possibly the most sensitive effect of 1,1,1-trichloroethane
warrants further consideration. This reviewer pointed to several studies, many nearly identical in
design to that of Rosengren et al. (1985), that report GFAP increases following toluene, styrene,
xylene, and dichloromethane exposures and noted that studies show that S-100 and GFA proteins
are frequently expressed differentially in various brain regions following chemical insult. This
reviewer also noted that GFAP has been validated as an indicator of neurotoxicity under
conditions where traditional histopathology has failed to reveal the damage. While this peer
reviewer was not necessarily advocating that the Quast et al. (1988, 1984) and McNutt et al.
(1975) studies be shelved in favor of Rosengren et al. (1985), neither was he convinced that
EPA's subchronic RfC is based on the "best available" study.
Three reviewers believed that the Rosengren et al. (1985) study raised potential concern
for the effects of 1,1,1-trichloroethane on the central nervous system (CNS), so consideration of
this study was appropriate in the context of the database UF. Because of the unreliability of
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Rosengren et al. (1985), a fourth reviewer did not feel the study should be used to support the
RfC calculations (e.g., in determination of a UF in the RfC).
Response: Based on the comments from the majority of the peer reviewers (four out of
five) that considered the Rosengren et al. (1985) study to be sufficiently unreliable, EPA's
decision not to use this study as the basis for the subchronic and chronic RfCs was retained.
This decision was strengthened by the additional brain weight analysis performed by one of the
peer reviewers and by this reviewer's observations related to variability of the GFAP findings.
EPA agrees with the fifth reviewer who pointed out that GFAP has been validated as an
indicator of neurotoxicity. As noted in EPA's 1998 Guidelines for Neurotoxicity Risk
Assessment, "[mjeasures of GFAP are now included as an optional test in the Neurotoxicity
Screening Battery." These guidelines also state that "[t]he interpretation of a chemical-induced
change in GFAP is facilitated by corroborative data from the neuropathology or neuroanatomy
evaluation." This reviewer cited O'Callaghan (former EPA scientist) and colleagues as stating
that elevations in GFAP are widely accepted as indicators of brain damage. O'Callaghan,
Jensen, and Miller (1995) also stated that "we do not advocate the use of this or any other
approach to neurotoxicity assessment as a stand-alone method. This is because every approach
has its drawbacks and GFAP assays are no exception." Disadvantages identified by O'Callaghan
et al. (1995) included the fact that both detection and characterization require a time-course
analysis, and that there are a few conditions under which GFAP levels may increase that do not
appear to result from localized damage, e.g., increased or decreased neuronal activity. Thus,
EPA agrees that GFAP is an appropriate indicator of neuronal damage; however, in the case of
the current study, corroborative neuropathology or neuroanatomoy evaluation data were not
available, nor was GFAP time-course data collected.
Dr. Karl Jensen, an EPA scientist and co-author of the paper with Dr. O'Callaghan,
conducted a critical review of the paper by Rosengren et al. (1985) on behalf of EPA's National
Center for Environmental Assessment (NCEA), and identified the issues with the study that are
summarized in Section 5.2.3.1 of the Toxicological Review.
Finally, this peer reviewer pointed to several studies nearly identical in design to that of
Rosengren et al. (1985) that reported GFAP increases following toluene, styrene, xylene, and
dichloromethane exposures. These studies were all performed by Rosengren and colleagues, and
appear to share some of the same issues as their study of 1,1,1-trichloroethane. Notable among
these issues is the use of a study protocol that did not include time-course data. In fact,
Rosengren and colleagues measured GFAP only after a postexposure period of 4 months, which
complicated interpretation of results.
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O'Callaghan, JP; Jensen, KF; Miller, DB. (1995) Quantitative aspects of drag and toxicant-induced
astrogliosis. Neurochemmt 26:115-124.
U.S. EPA (1998). Guidelines for neurotoxicity risk assessment. Federal Register 63(93):26926-26954.
EPA/630/R-95/001F.
Also consistent with the input from the majority of the peer reviewers, the database UF of
3 was retained as partly supported by the uncertainty introduced by the unconfirmed findings of
the Rosengren et al. (1985) study.
D. Cancer Assessment
1. Do the available data support the conclusion that the database for 1,1,1-trichloroethane
provides inadequate information to assess carcinogenic potential based on the weight-of-
evidence categories in the EPA 2005 Guidelines for Carcinogen Risk Assessment! Please
describe the basis for your view.
Comments: All five reviewers supported the conclusion that the available database for
assessment of the carcinogenic potential of 1,1,1-trichloroethane is inadequate. Two reviewers
indicated that more discussion is needed about the Maltoni et al. (1986) study, which suggests
some positive sporadic findings. One reviewer felt that the sum total of the available data might
have led to a conclusion that was a bit more definitive (e.g., the genotoxicity data are suggestive
of a very low risk of carcinogenicity); it would seem that the carcinogenic potential of
1,1,1-trichloroethane was likely to be very low as regards potential exposure levels. Another
reviewer recommended that the carcinogenicity discussion consider the chronic inhalation study
of 1,1,1-trichloroethane in Sprague-Dawley rats (Quast et al., 1978; Rampy et al., 1977). In this
particular study, rats were exposed to 0, 875, or 1750 ppm for 6 hours/day, 5 days/week, for
12 months and allowed to survive until 31 months. While similar to the inhalation bioassay of
Quast et al. (1988, 1984) in that there was no evidence of a carcinogenic response, the study
differs with respect to the strain of rat utilized (i.e., Sprague-Dawley versus F344) and serves as
the only other chronic bioassay to that of Maltoni et al. (1986) to use the Sprague-Dawley rat.
Response: Text was added to Section 4.7.2, Synthesis of Human, Animal, and Other
Supporting Evidence, referring the reader to Section 4.2.1.4 for a more complete discussion of
the Maltoni et al. (1986) study and its limitations. A discussion of the 1-year inhalation study by
Quast et al. (1978) was added to Section 4.7.2, with consideration given to the extent to which
the study informed the potential human carcinogenicity of 1,1,1-trichloroethane. Although the
available data do not show 1,1,1-trichloroethane to be carcinogenic, EPA maintains that the data
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are insufficient to characterize the potential for carcinogenicity at all doses. One- and 2-year
inhalation studies were both negative, but the two available oral studies were both inadequate to
assess carcinogenicity, and one of the metabolites of 1,1,1-trichloroethane (trichloroacetic acid)
has been reported to produce liver tumors in mice. Therefore, the available data does not appear
to support a more definitive conclusion about human carcinogenic potential.
PUBLIC COMMENTS
Ten submissions from the public were received, five of which offered substantive
comments on the assessment for 1,1,1-trichloroethane. Those submissions received during the
official public comment period were distributed to the external peer review panel prior to the
public meeting and discussion of the assessment. Submissions offered some editorial comments
and suggestions for clarification of specific portions of the text. Changes were incorporated in
the Toxicological Review as appropriate and are not discussed further in this appendix.
A. Oral Reference Dose (RfD) Values
1. Selection of the Principal Study/Critical Effect
Comment: One commenter stated that the extensive toxicological database for
1,1,1-trichloroethane indicates that this compound has little potential for toxicity at any
environmentally relevant dose level and that the endpoint of a 10% decrease in body weight
following extremely high doses of 1,1,1-trichloroethane is not lexicologically relevant to
extrapolation to low environmental exposures. The commenter also observed that the effects
observed from the vehicle alone in this study make it difficult to fully appreciate what effects the
chemical actually had. Accordingly, the commenter believed that consideration should be given
to choosing not to derive an RfD for this compound. However, if an RfD is to be derived, the
level should be chosen based on route-to-route extrapolation, using a chronic infusion dose level
that would result in blood concentrations equivalent to those associated with exposure at the
chronicRfC.
Response: As noted in Question B.3 above, the external peer reviewers expressed some
reservations with the use of body weight as the critical effect; however, four of the five
reviewers considered the selection of decreased body weight to be reasonable. These reviewers
could not identify a more appropriate alternative endpoint and considered the rationale for
selection of decreased body weight as the critical effect to have been transparently and
objectively described.
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For the reasons discussed in Section 5.1.5.1, route-to-route extrapolation was not
considered scientifically supported in the case of 1,1,1-trichloroethane. The empirical data does
not support the liver as a sensitive target organ following oral exposure; even the recent NTP
(2000) study found no evidence of liver toxicity in mice or rats at a dietary concentration as high
as 80,000 ppm.
2. Selection of Uncertainty Factors
Comments: Two commenters stated that from a scientific point of view, there is some
redundancy (or "double counting") in the UF of 3 for duration and another UF of 3 for database
deficiencies, as these are likely addressing the same data gap. Another commenter stated that the
data used by EPA as support for a "partial UF of 3" for extrapolation from subchronic-to-chronic
exposure duration provide sufficient justification for a UF of 1.
One commenter observed that there does not appear to be a 10-fold difference in
sensitivity between humans and rodents based on a comparison with available human data so
that a 10-fold UF for animal-to-human extrapolation is likely overly conservative.
Two commenters did not find support for use of a database UF. These commenters noted
that the epidemiology literature for occupational workers is not very supportive of neurological
toxicity being a concern in humans, including workers exposed to air concentrations as high as
350 ppm, and that it is unlikely that environmental exposures to humans would ever approach
those associated with these adverse affects. One of these commenters noted that epidemiological
data are frequently lacking in assessments, but this lack is not typically deemed indicative of a
need for a database uncertainty factor and further that the findings of the available studies for
1,1,1-trichloroethane are conflicting and limited (i.e., Kelafant et al. [1994] report evidence of a
neurobehavioral effect, while Maroni et al. [1977] and Kramer et al. [1978] did not). Regarding
the uncertainty associated with the Rosengren et al. (1985) findings, one reviewer stated that
(1) support was lacking for a direct association between GFAP elevation and the subtle effects of
concern to EPA, (2) a relationship between astrogliosis and the subtle effects of concern to EPA
has not been demonstrated, and (3) the potential for 1,1,1-TCE to produce astrogliosis
(irrespective of the relevance of astrogliosis to neurobehavioral effects) was adequately
evaluated in subchronic or chronic animal studies (e.g., Quast et al., 1988).
Response: In the absence of a chronic study, a default UF of 10 is typically applied for
extrapolation of subchronic to chronic exposure data. With 1,1,1-trichloroethane, evidence of
nonprogression of body weight effects supports reduction of the UF from 10 to 3. The database
UF is not intended to account for lack of a chronic study. Rather, a partial database UF of 3 was
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applied in deriving the subchronic and chronic RfD to account for uncertainty with respect to
neurotoxicity. EPA does not believe that the use of these two factors represents double counting.
EPA considered alternative values for the subchronic to chronic UF. EPA believes that
evidence from available oral studies suggests that effects on body weight do not become more
severe with increasing exposure duration and that inhalation data demonstrate that liver toxicity
similarly does not progress with increasing exposure duration. Lifetime oral studies of
1,1,1-trichloroethane are, however, inadequate to fully characterize chronic toxicity. The
Maltoni et al. (1986) study was designed as a cancer bioassay only and did not include
evaluation of nonneoplastic lesions. In the NCI (1977) bioassay, high early mortality was
observed in rats and mice, probably due to murine pneumonia, and thus NCI (1977) considered
the study to be inadequate. Thus, in light of the incomplete understanding of potential oral
chronic toxicity for 1,1,1-trichloroethane, a subchronic to chronic UF of one was not considered
appropriate.
EPA does not consider the available data for the oral route to be sufficient to characterize
differences in 1,1,1-trichloroethane pharmacokinetics (PK) and pharmacodynamics (PD)
between humans and animals. All available PK data in humans come from inhalation exposure
studies; no PK data are available for oral exposures. The default UF of 10 for interspecies
extrapolation is therefore considered appropriate.
The external peer reviewers generally agreed with the partial database UF of 3. EPA
agrees that epidemiology data is not a requirement for a complete database but is taken into
consideration when it raises a "red flag," as does the Kelafant et al. (1994) study. EPA agrees
that the Rosengren et al. (1985) study, because of questions of reliability, does not establish a
relationship between 1,1,1-trichloroethane exposure and CNS toxicity. The findings do,
however, raise some degree of uncertainty. Together, these findings contributed to the decision
to apply a database UF of 3.
3. Use of PBPK Modeling for Route-to-route Extrapolation
Comments: One reviewer noted that chronic continuous infusion exposure at the RfD
would be estimated to result in a blood level over 1000 times less than those reported to result in
subtle neurological symptoms in human experimental studies, suggesting that the RfD is overly
conservative.
Response: The subchronic and chronic RfDs were derived using standard risk assessment
practices (i.e., selection of a critical effect that was scientifically supported, use of benchmark
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dose modeling to identify the point of departure for the RfD, and application of standard
uncertainty factors).
B. Inhalation Reference Concentration (RfC) Values
1. Selection of the Principal Study (Mackay et al., 1987) for the Acute RfC
Comments: One commenter considered the Mackay et al. (1987) study to be an
appropriate and conservative basis for the acute RfC derivation, noting that other experimental
human exposure studies generally provide results within a factor of about 3. This commenter,
however, stated that EPA's selection of the point of departure for the estimation of the RfC from
this study, suggesting that the blood concentrations at 1 hour be considered a minimal LOAEL
and the blood concentration at 20 minutes the NOAEL.
Two other comm enters questioned the selection of the Mackay et al. (1987) study as the
principal study, noting (1) the lack of reproducibility of simple reaction time (the most sensitive
endpoint in this study) as a concern (e.g., no clear effects on simple reaction time were found by
Savolainen et al. [1982a,b, 1981]) and (2) the difficulty discerning whether these results are
biologically significant or a function of the natural variability of the endpoint. One of the two
reviewers also noted that the Mackay et al. (1987) study was considered by other groups, such as
the National Advisory Committee (NAC) Acute Exposure Guideline Levels (AEGL) for
Hazardous Substances and the ACGIH in the development of exposure guidelines for
1,1,1-trichloroethane, but was not selected as the basis for the AEGL exposure guideline level
for short-term exposure periods or the ACGIH threshold limit value (TLV). Rather, these groups
used a weight-of-evidence approach from several human studies in determining airborne
guidelines levels.
Response: The Mackay et al. (1987) study results were not reproduced in the studies by
Savolainen et al. (1982a,b, 1981); however, effects on neurobehavioral performance were
reported in test batteries conducted by Muttray et al. (2000) and Gamberale and Hultengren
(1973) at concentrations similar to those administered in the Mackay et al. (1987) study.
Collectively, these studies supported a CNS effect of 1,1,1-trichloroethane in humans following
acute exposure. Thus, EPA used a weight-of-evidence analysis to determine the critical effect,
the Mackay study specifically, to derive the point of departure. External peer reviewers
generally supported the selection of Mackay et al. (1987) as the principal study, considering the
study to be well conducted. The ATSDR also selected the Mackay et al. (1987) study as the
basis for the acute minimal risk level (MRL) for 1,1,1-trichloroethane (ATSDR Toxicological
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Profile available at http://www.atsdr.cdc.gov/toxprofiles/tp70.html). Thus, the Mackay et al.
(1987) study was retained as the basis for the acute RfC.
EPA did not intend to characterize the 20-minute blood concentration from Mackay et al.
(1987) as aNOAEL. As noted in Section 5.2.1.1:
"Changes in test performance were observed at an exposure concentration of
950 mg/m3 as early as 20 minutes in some tests (e.g., tracking time on target,
tracking room mean square (RMS) error, and simple reaction time), but in other
tests impaired performance at 20 minutes was minimal and increased with
exposure duration (e.g., tracking time outside target, four-choice reaction time,
and Stroop test). It is unclear to what extent the changes observed at the earliest
testing interval were biologically significant. Other investigators did not similarly
observe deficits in performance after only 20 minutes of exposure... [HJowever,
the Gamberale and Hultengren (1973) findings suggest that changes in
neurobehavioral performance may occur after 60 minutes of exposure to an
exposure concentration of 300 ppm, generally consistent with the findings for
Mackay et al. (1987) also at 60 minutes of exposure."
Therefore, EPA found adequate support for the characterization of the
1,1,1-trichloroethane blood concentration at 60 minutes as a LOAEL, whereas support for
characterization of a NOAEL or LOAEL at shorter exposure durations was not considered
adequate.
2. Selection of the Principal Study (Quast et al., 1988, 1984; McNutt et al., 1975) for the
Sub chronic and Chronic RfCs
Comments: One commenter observed that the Quast et al. (1988, 1984) data regarding
hepatic changes following subchronic and chronic inhalation are informative for consideration as
a point of departure for the subchronic and chronic RfC values; however, the air concentration
required to achieve the long-term liver concentration at the Quast et al. (1988, 1984) NOAEL is
approximately 3 times higher than the air concentration associated with steady-state blood
concentrations at the LOAEL in the Mackay et al. (1987) study of human neurobehavioral
effects. Therefore, this commenter suggested an integrated assessment of four studies (three in
animals, one in humans) as the basis for selection of a subchronic and chronic RfC value. These
four studies were: (1) the inhalation studies of Quast et al. (1988, 1984), in conjunction with the
study by McNutt et al. (1975); (2) the subchronic neurotoxicity study by Mattsson et al. (1993);
(3) the study by Rosengren et al. (1985) of alterations in protein expression in the brains of
gerbils exposed sub chronically; and (4) the blood concentration-response data from Mackay et
al. (1987). The commenter noted that two of the approaches result in RfC values of 5 mg/m3,
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while two result in RfC values of 50 mg/m3, which bracket the short-term RfC values and
confirm the general impression based on the toxicological database that 1,1,1-TCA has little
potential for chronic toxicity at exposure levels below those that result in acute neurobehavioral
responses.
Response: EPA believes that the approach used to derive the subchronic and chronic
RfCs presented in the 1,1,1-trichloroethane Toxicological Review is consistent with the
integrated, multistudy approach suggested by the commenter. The inhalation studies of Quast et
al. (1988, 1984), McNutt et al. (1975), and Mackay et al. (1987) were specifically taken into
consideration in deriving the RfC. As discussed in response to comment C. 10, the Rosengren et
al. (1985) study was not considered sufficiently reliable to use in deriving a reference value. The
results of Mattsson et al. (1983) were also considered as the basis for the sub chronic/chronic RfC
(see Section 5.2.3.3 and Figures 5-1 and 5-2); however, the deficits in forelimb grip strength
reported in Mattsson et al. (1983) were not statistically significant using a statistical treatment
designed to take into account the observed changes over time in the control and treated group
and were not confirmed by histopathological, electrophysiological, or FOB tests in the same
study (see Section 4.4.1.2).
3. Use of PBPK Modeling for Interspecies Extrapolation
Comments: Two commenters endorsed the use of PBPK modeling to account for
interspecies differences in pharmacokinetic behavior. A third commenter observed that the
model was not fully tested against the available data. The commenter noted that, according to
the Toxicological Review, the Gargas et al. (1986) and Reitz et al. (1988) studies were evaluated
against 11 data sets by Yang (2006). The commenter stated that it should be acknowledged by
EPA that the test data were a subset of the available data and that additional model testing could
have been conducted; the commenter identified the following specific data that do not appear to
have deficiencies that should preclude their use in model evaluation:
Johns, DO; Daniell, WE; Shen, DD; et al. (2006) Ethanol-induced increase in the metabolic clearance of
1,1,1-trichloroethane in human volunteers. Toxicol Sci 92:61-70. (Human inhalation exposure) Note
provided by commenter: Appeared in print in June 2006, shortly before completion of Yang, 30 July 2006.
Dobrev, ID; Andersen, ME; Yang, RH. (2001) Assessing interaction thresholds for trichloroethylene in
combination with tetrachloroethylene and 1,1,1-trichloroethane using gas uptake studies and PBPK
modeling. Arch Toxicol 75:134-144. Note provided by commenter: The model had minimal modification
compared to Reitz and Gargas models, and presumably the fit was good. While it may essentially be
duplicative of fits to similar data sets, it should have been included for completeness.
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Dallas, CE; Bruckner, JV; Maedgen, JL; et al. (1986) A method for direct measurement of systemic uptake
and elimination of volatile organics in small animals. J Pharmacol Meth 16:239-250.
Filser, JG. (1992) The closed chamber technique-uptake, endogenous production, excretion, steady-state
kinetics and rates of metabolism of gases and vapors. Arch Toxicol 66:1-10 (Closed chamber data)
Kaneko, T; Wang, PY; Sato, A. (1994) Enzymes induced by ethanol differently affect the pharmacokinetics
of trichloroethylene and 1,1,1-trichloroethane. Occup EnvironMed 51:113-119 (Inhalation exposure)
Mitoma, C; Steeger, T; Jackson, SE; et al. (1985) Metabolic disposition study of chlorinated hydrocarbons
in rats and mice. Drug Chem Toxicol 8:183-194 (Oral dosing)
Savolainen, H; Pfaffli, P; Tengen, M; et al. (1977) Trichloroethylene and 1,1,1-trichloroethane: Effects on
brain and liver after five days intermittent inhalation. Arch Toxicol 38:229-237 (Inhalation exposure)
Tardif and Charest-Tardif. (1999) The importance of measured end-points in demonstrating the occurrence
of interactions: a case study with methylchloroform and m-xylene. Toxicol Sci 49:312-317. (Inhalation
exposure; 400 ppm, 4 hours). Note provided by commenter: this paper uses a reconstruction of the Reitz
model. While the model does a pretty good job predicting concentrations during exposure, it appears to
underpredict post exposure concentrations (c.f. Figures 1 and 4).
Warren, DA; Reigle, TG; Muralidhara, S; etal. (1998) Schedule-controlled operant behavior of rats during
1,1,1-trichloroethane inhalation: relationship to blood and brain solvent concentrations. Neurotoxicol
Teratol 20:143-153. (Inhalationexposure)
Yoshida T, AndohK, FukuharaM. (1998) Estimation of absorption of environmental contaminants in low-
level exposure by pharmacokinetic analysis. J Toxicol Environ Health A 54:145-158. (Closed chamber
uptake studies)
Response: It is acknowledged that other data sets were available that could have been
used to evaluate the model; however, the studies used by Yang (2006) were considered to
provide some of the best data sets for model evaluation and met the criteria discussed in Yang
(2006). Text was added to Section 3.5.2 to indicate that other data sets were available for model
evaluation but were not used.
4. Selection of Uncertainty Factors (UF)
Comments:
Acute RfC—LOAEL to NOAEL UF. Five commenters offered feedback on the LOAEL to
NOAEL UF used to derive the acute RfC, suggesting that the UF should be reduced from 10 to
3. Commenters noted that the use of a full factor of 10 for LOAEL to NOAEL extrapolation was
excessive in light of the lack of neurobehavioral findings in other studies of human volunteers
involving various neurobehavioral measures or the minimal effects observed by other
investigators examining neurobehavioral effects in human volunteers at similar or higher
exposure concentrations and times.
One commenter considered a LOAEL to NOAEL UF of 10 to be excessive in light of
documentation of the ACGIH TLV (quotation provided by commenter): "Short-term inhalation
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of methyl chloroform at 350 ppm for 2 hours (Gamberale and Hultengren, 1973) or two 4-hour
periods at 450 ppm (Salvini et al., 1971) is very near the acute lowest-observed-adverse effect
level or the no-observed-adverse effect level in that some measures of dexterity and mental
alertness were either reduced or were unaffected, respectively."
Acute RfC—Intraspecies UF. Three commenters stated that a full default UF of 10 for
intraspecies extrapolation was not necessary. One of these commenters noted that the use of 10
for human variability is appropriate but substantially conservative due to the pharmacokinetic
characteristics of 1,1,1-trichloroethane. This reviewer noted that for a volatile organic compound
such as 1,1,1-trichloroethane with limited metabolism and elimination occurring primarily via
exhalation, Pelekis et al. (2001) found that variations in physiological parameters among adults
or between adults and children would account for generally less than a factor of 2 differences in
attained blood concentrations following inhalation exposures. Thus, the implicit pharmacokinetic
factor of 3.2 included in the UF of 10 is conservative. A second commenter suggested that
consideration be given to a lower intraspecies UF for pharmacokinetic variability because blood
1,1,1-trichloroethane concentrations should not vary substantially among similarly exposed
individuals due to a generally low rate of metabolism, and the fact that blood:air PCs are not
anticipated to have significant interindividual variability. A third commenter recommended an
intraspecies UF of 2 to 3 based on (1) the NAC/AEGL committee's use of a factor of 2 for
intraspecies variability (supported by the observation that the threshold for mild CNS effects for
humans does not seem to vary by more than two- to threefold) and (2) susceptibility of
individuals to 1,1,1-trichloroethane as a volatile anesthetic in the range of two- to threefold.
Subchronic/chronic: Database UF. Three commenters offered input on the database UF
used in deriving the subchronic and chronic RfCs. Two of these reviewers considered the
database to be fairly complete and did not believe any significant data gaps needed to be filled.
One of the reviewers considered the uncertainty regarding the potential for long-term
neurotoxicity following repeated exposures to be a duration UF issue, not a database uncertainty
factor issue. The third reviewer noted that epidemiological data are frequently lacking in
assessments, but this lack is not typically deemed indicative of a need for a database uncertainty
factor and further that the findings of the available studies for 1,1,1-trichloroethane are
conflicting and limited (i.e., Kelafant et al. [1994] report evidence of a neurobehavioral effect,
while Maroni et al. [1977] and Kramer et al. [1978] do not). Regarding the uncertainty
associated with the Rosengren et al. (1985) findings, this reviewer stated that (1) support was
lacking for a direct association between GFAP elevation and the subtle effects of concern to
EPA, (2) a relationship between astrogliosis and the subtle effects of concern to EPA has not
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been demonstrated, and (3) the potential for 1,1,1-TCE to produce astrogliosis (irrespective of
the relevance of astrogliosis to neurobehavioral effects) was adequately evaluated in subchronic
or chronic animal studies (e.g., Quast et al., 1988).
Response:
Acute RfC—LOAEL to NOAEL UF. Although the findings from the Mackay et al. (1987)
study were not reproduced in all human volunteer studies, the finding of neurobehavioral deficits
was reported by Muttray et al. (2000) and Gamberale and Hultengren (1973) at similar exposure
concentrations and durations. ATSDR similarly used a LOAEL to NOAEL UF of 10 in deriving
their acute MRL (available at http://www.atsdr.cdc.gov/toxprofiles/tp70.html).
Acute RfC—Intraspecies UF. As noted by one commenter, Pelekis et al. (2001) reported
that the magnitude of the pharmacokinetic (PK) component of the human intraspecies UF for
volatile organic compounds (VOCs) varies between 0.033 and 2.85. The pharmacodynamic
(PD) component of the intraspecies UF for 1,1,1-trichloroethane is unknown; however, assuming
a value of 3.2 for the PD component of intraspecies variability and the upper end of the range for
the PK component based on Pelekis et al. (2001), the overall intraspecies UF is close to 10.
Support for the NAC/AEGL committee's use of an intraspecies UF of 3 comes in part from a
study of experimental use of 1,1,1-trichloroethane as an anesthetic (Dornette and Jones, 1960).
1,1,1-Trichloroethane was administered with nitrous oxide; the authors stated that at least one-
fourth the total narcosis could be attributed to the nitrous oxide and that no attempt was made to
assess the effect of 1,1,1-trichloroethane alone. Of the 50 patients included in this study, only
two were less than 10 years old, and two were more than 70 years old. While informative, the
study does not provide data on response to 1,1,1-trichloroethane alone for a representative
sample of the general population. Overall, the available data were not considered sufficient to
reduce the intraspecies UF from a default of 10.
Subchronic/chronic: Database UF. As noted in a related response on the database UF
for the RfD, the external peer reviewers generally agreed with the partial database UF of 3. EPA
agrees that epidemiology data are not a requirement for a complete database but are taken into
consideration when they raise a "red flag," as does the Kelafant et al. (1994) study. EPA agrees
that the Rosengren et al. (1985) study, because of questions of reliability, does not establish a
relationship between 1,1,1-trichloroethane exposure and CNS toxicity. The findings do,
however, raise some degree of uncertainty. Together, these findings contributed to the decision
to apply a database UF of 3.
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5. Setting the Value of the Subchronic and Chronic RfC So as Not to Exceed the Values of the
Acute and Short-term RfCs
Comments: Two commenters provided observations on EPA's decision to limit the
subchronic and chronic RfC values to be no greater than the short-term RfC. One of these
commenters considered the inconsistency among short- and long-term RfCs to be an artifact
resulting from the selection of an insensitive endpoint for the subchronic and chronic RfC
derivation. A second commenter observed that given the care with which the subchronic and
chronic values were derived from the data, adoption of the acute and short-term RfCs of 5 mg/m3
as protective for subchronic and chronic exposures seemed to be an odd practice; in effect, the
single Mackay data set becomes the basis for all four RfCs, which this commenter found
especially worrisome given the amount of data on this compound.
Response: The five external peer reviewers agreed that the decision to set the subchronic
and chronic RfC at 5 mg/m3 was scientifically justified and transparently and objectively
described. Sections 5.2.3.3 and 5.2.4.3 offer the following reasons as to why the effect levels for
acute/short-term and sub chronic/chronic inhalation exposures might not necessarily be expected
to follow a continuum from higher to lower (i.e., the inconsistency is not necessarily an artifact).
The point of departure for the acute/short-term exposure duration is based on central
nervous system (CNS) effects in humans, whereas the point of departure for subchronic and
chronic exposure durations is based on liver effects in rats and mice. Thus, the target organ for
acute/short-term exposure durations differs from that for sub chronic/chronic exposure durations.
Although the modes of action for the CNS and liver effects of 1,1,1 -trichloroethane have not
been established, it is likely that the modes of action at the two sites of toxicity are different.
The endpoints examined following acute exposure to 1,1,1-trichloroethane differ from
those examined following subchronic or chronic exposure. In particular, sensitive
neurobehavioral testing in humans is available for evaluating 1,1,1-trichloroethane acute
toxicity. In fact, human test batteries proved to be more sensitive than animal models of acute
neurobehavioral toxicity. Sensitive testing for neurobehavioral effects in either humans or
animals is unavailable following repeated exposure.
The acute/short-term RfCs are based on analysis of peak exposure, whereas
subchronic/chronic RfCs are based on area-under-the-curve (AUC) exposure.
While the Mackay et al. (1987) data set was, in fact, used to derive the acute and short-
term RfCs, the entire database for 1,1,1-trichloroethane was considered in identifying the
principal study and critical effect, and a number of other studies in humans and animals were
considered supporting.
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6. Issue of the Reliability of the Rosengren et al. (1985) Study and Use of GFAP Findings as the
Basis for the Subchronic and Chronic RfDs and RfCs
Comments: The California Environmental Protection Agency (Cal EPA) disagreed with
EPA's decision not to use the Rosengren et al. (1985) study as the basis for reference values,
noting that other scientific reviewers (including ATSDR, the World Health Organization
(WHO), Cal EPA's Office of Environmental Health and Hazard Assessment Toxic Air
Contaminant group, and the University of California peer reviewers of the Public Health Goal
document) evaluated Rosengren et al. (1985) and concluded that it is a relevant study and
endpoint for risk assessment. In addition, Cal EPA noted that this study is a standard
neurotoxicity study type, used in the biodiesel testing program. While failure to replicate this
toxicological observation is a concern, Cal EPA noted that it is not unusual to find a critical
study on a chemical for which a replication study has not been attempted or is lacking in some
other fashion. Therefore, Cal EPA concluded that the Rosengren et al. (1985) study deserves to
be utilized in a calculation of a health-protective level for 1,1,1-trichloroethane. Cal EPA noted
that the EPA RfD of 2 mg/kg-day is equivalent to 140 mg/day for a 70-kg human and that the
Cal EPA risk assessment provides an equivalent health-protective value of 5.3 mg/day, making
the Cal EPA assessment about 25 times more health protective.
Another commenter concurred with EPA's assessment of the Rosengren et al. (1985) data
as providing inconsistent and weak evidence of long-term neurological effects and did not
consider the data from this study sufficient to suggest the potential for chronic effects. This
commenter also believed that the uncertainty posed by interpretation of this study is better
represented as a duration UF rather than database UF, as studies on all endpoints of concern are
present in the database.
Response: EPA maintains that the Rosengren et al. (1985) study is not sufficiently
reliable to serve as the basis for the RfC; the issues with this study are presented in Section
5.2.3.1 of the Toxicological Review. Further, one of the external peer reviewers identified
specific reservations with this study beyond those cited in the EPA review. Specifically, this
reviewer noted that (1) the conclusion in the Rosengren et al. (1985) study of significant
decrease in brain weight is not supported by the data based on an independent statistical analysis
and (2) he had concerns about the extremely small SEMs reported in this work based on his
personal laboratory experience. Regarding point (2), he observed that the coefficient of variation
(CV) for GFAP data of 15-25% estimated by this peer reviewer (based on Figures 1 and 2 from
Rosengren et al. [1985]), which includes all sources of biological and toxicant-induced
variability on top of the variance from the analytical endpoint (considered by this review to be a
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relatively imprecise technique), seemed to be unexpectedly precise. Specifically, this CV would
have to account for (1) normal interanimal variability, (2) interanimal differences in response to
1,1,1-trichloroethane, (3) the fact that only of a small portion of the extractable cellular GFAP is
sampled (another source of variability), and (4) an assay method that is indirect and itself would
be expected to have a relatively large CV (greater than 10%).
Thus, based on the comments from the majority of the external peer reviewers (four out
of five) that considered the Rosengren et al. (1985) study to be unreliable and the additional
issues raised by one of the external peer reviewers, EPA retained the decision not to use this
study as the basis for the subchronic and chronic RfCs. As an acknowledgement of the
uncertainty introduced by the unconfirmed findings of the Rosengren et al. (1985) study,
however, a database UF of 3 was used to derive the RfC.
7. Comparison of the Proposed Acute RfC with Other Standards and Guidelines
Comment: One commenter compared the proposed acute RfC values with other acute
standards and guidelines, including AEGL-1, ERPG-1, NIOSH ceiling, OSHA PEL, ACGffl
TLV-TWA, ACGffl-STEL, MAK (German), and MAC (Dutch). This commenter described the
AEGL-1 and ERPG-1 as airborne concentrations of a substance above which it is predicted that
the general population, including susceptible individuals, could experience notable discomfort,
irritation, or certain asymptomatic, nonsensory effects, and further described airborne
concentrations below the AEGL-1 as levels that would not result in any adverse effect to the
general population. While acknowledging that AEGLs and ERPGs are somewhat different than
the acute RfC values, this commenter stated that all of these values would be expected to be in
the same general range; however, the RfC values (1-2 ppm) are significantly lower than the
other regulatory values (100 ppm for the MAC to 450 ppm for the 15-minute ACGIH STEL).
This commenter stated that the enormous differences in these values needed to be reconciled.
Response: EPA disagrees with the commenter's conclusion that the acute RfC would be
expected to be in the same range as emergency or occupational standards. The RfC is intended
to be an estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous
inhalation exposure to the human population (including sensitive subgroups) that is likely to be
without an appreciable risk of deleterious effects; acute RfC values have been developed for
durations ranging from 1 to 24 hours. In contrast, the AEGL-1 and ERPG-1 are community
emergency standards at which effects are expected. As noted in the 2000 technical support
document for the interim AEGLs for 1,1,1-trichloroethane (available at
http://www.epa.gov/oppt/aegl/pubs/tsd203.pdf), the statement is made that "Airborne
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concentrations below the AEGL-1 represent exposure levels that could produce mild and
progressively increasing odor, taste, and sensory irritation, or certain nonsymptomatic,
nonsensory effects. ... Although the AEGL values represent threshold levels for the general
public, including sensitive subpopulations, it is recognized that certain individuals, subject to
unique or idiosyncratic responses, could experience the effects described at concentrations below
the corresponding AEGL level." For 1,1,1-trichloroethane, AEGL-1 values have been
developed for exposure durations ranging from 10 minutes to 8 hours. The ERPG-1 is similar to
the AEGL-1 but applies to exposures up to 1 hour only.
Similarly, occupational standards, which are generally developed for a healthy worker
population, are not considered comparable to the acute RfC intended to protect the general
population.
A more appropriate comparison would be to acute exposure limits intended to provide
general public health protection. In particular, the acute MRL for 1,1,1-trichloroethane derived
by the ATSDR is 2 ppm (10.9 mg/m3) (available at
http://www.atsdr.cdc.gov/toxprofiles/tp70.html), which is similar to the acute RfC values of
1-2 ppm for exposures ranging from 1 to 24 hours. The ATSDR acute MRL is also based on the
study by Mackay et al. (1987).
C. Cancer Assessment
1. Selection of a Cancer Weight-of-Evidence Category
Comments: One commenter believed the agency should rethink the cancer classification
applied to 1,1,1-trichloroethane (inadequate information to assess carcinogenic potential).,
noting that neither the Quast et al. (1978) study, in which rats were exposed for 12 months at
doses as high as 1750 ppm (with 19 month postexposure period) nor the Quast et al. (1988)
study, in which animals were exposed for 2 years with doses as high as 1500 ppm, found
evidence of carcinogenicity. This commenter believed the scientific evidence supports the
position that 1,1,1-trichloroethane is not carcinogenic in mice or rats, even lacking data from an
unrealistically high MTD.
Response: Although the available data do not show 1,1,1-trichloroethane to be
carcinogenic, EPA maintains that the data are insufficient to characterize 1,1,1-trichloroethane as
not carcinogenic in mice or rats. One- and two-year inhalation studies were both negative;
however, the two available oral studies were both inadequate to assess carcinogenicity, and one
of the metabolites of 1,1,1-trichloroethane (trichloroacetic acid) has been reported to produce
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liver tumors in mice. Therefore, the available data does not appear to support a more definitive
conclusion about animal or human carcinogenic potential.
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APPENDIX B
Benchmark Dose Modeling Results and Output
Terminal Body Weight in Female Mice (NTP, 2000)—Hill Model
Hill Model with 0.95 Confidence Level
31
30
29
o 28
8-
27
26
25
24
23
Hill
BMDL
BMD
5000
10000
15000
20000
dose
08:52 03/09 2006
Dependent variable = MEAN
Independent variable = DoseMg-Kg-D
rho is set to 0
Power parameter restricted to be greater than 1
A constant variance model is fit
Total number of dose groups = 6
Total number of records with missing values = 0
Maximum number of iterations = 250
Relative Function Convergence has been set to: le
Parameter Convergence has been set to: le-008
Default Initial Parameter Values
alpha = 4.75395
rho = 0 Specified
intercept = 29.3
n = 1.30346
k = 3515
B-l
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Parameter Estimates
95.0% Wald Confidence Interval
Variable Estimate Std. Err. Lower Conf. Limit Upper Conf. Limit
alpha 4.65846 1.156 2.39274 6.92417
intercept 29.3467 0 29.3467 29.3467
-12.1202 1.7114
-2.64078 4.98353
4061.89 4071.87
alpha
intercept
v
n
K
alpha
1
-1. 9e-007
-1 . 9e-007
-1 . 4e-007
2.7e-007
intercept
-1. 9e-007
1
-0.37
-0.25
-0.13
k
2.7e-007
-0.13
-0. 84
-0. 81
1
Table of Data and Estimated Values of Interest
Est Mean Obs Std Dev Est Std Dev Scaled Res.
Model Al: Yij = Mu(i) + e(ij
Var{e(ij)} = Sigma~2
Model
Al
A2
A3
fitted
R
Explanation of Tests
Test 1: Do responses and/or variances differ among Dose levels? (A2 vs. R)
Test 2: Are Variances Homogeneous? (Al vs A2)
Test 3: Are variances adeguately modeled? (A2 vs. A3)
Test 4: Does the Model for the Mean Fit? (A3 vs. fitted)
B-2
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Tests of Interest
Test -2*log(Likelihood Ratio) Test df
10
The p-value for Test 3 is greater than .1. The modeled variance appears to be appropriate here
Benchmark Dose Computation
Specified effect = 0.1
Risk Type = Relative risk
Confidence level = 0.95
BMD = 5064.36
BMDL = 2155.2
B-3
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Terminal Body Weight in Male Mice (NTP, 2000)—Hill Model
Hill Model with 0.95 Confidence Level
39
38
37
8 36
c
§35
0
°L 34
ro
0
2 33
32
31
30
- Hill
- <
\
\
- \1
\
'BiyiPL
--
\
\
-j
\
j
^x—- :
;
BMD , , , , , , ]
2000 4000
6000 8000 10000 12000 14000
dose
08:53 03/09 2006
Dependent variable = MEAN
Independent variable = DoseMg-Kg-D
rho is set to 0
Power parameter restricted to be greater than 1
A constant variance model is fit
Total number of dose groups = 6
Total number of records with missing values = 0
Maximum number of iterations = 250
Relative Function Convergence has been set to: le
Parameter Convergence has been set to: le-008
alpha =
rho =
intercept =
B-4
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Parameter Estimates
Variable
alpha
intercept
95.0% Wald Confidence Interval
Lower Conf. Limit Upper Conf. Limit
0.00389591 6.55291
36.8476 36.8476
-13.3203 3.44932
Asymptotic Correlation Matrix of Parameter Estimates
alpha
intercept
Table of Data and Estimated Values of Interest
Est Mean
Obs Std Dev Est Std Dev
1.81
1.81
1.81
1. 81
1. 81
1. 81
Model R: Yi = Mu + e(i)
Var{e (i ) } = Sigma~2
Model
Al
A2
A3
fitted
R
Log(likelihood)
-62.896204
-60.577188
-62.896204
-65.620708
-83.580886
# Param's
12
Explanation of Tests
Test 1: Do responses and/or variances differ among Dose levels? (A2 vs. R)
Test 2: Are Variances Homogeneous? (Al vs A2)
Test 3: Are variances adequately modeled? (A2 vs. A3)
Test 4: Does the Model for the Mean Fit? (A3 vs. fitted)
B-5
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Tests of Interest
Test -2*log(Likelihood Ratio) Test df
Test 1 46.0074 10
Test 2 4.63803 5
Test 3 4.63803 5
Test 4 5.44901 3
The p-value for Test 3 is greater than .1. The modeled variance appears to be appropriate here
Benchmark Dose Computation
Specified effect = 0.1
Risk Type = Relative risk
Confidence level = 0.95
BMD = 1943.08
BMDL = 594.296
B-6
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