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Asbestiform Fibers
Nonoccupational Health Risks
Committee on Nonoccupational Health Risks
of Asbestiform Fibers
Board on Toxicology and Environmental Health Hazards
Commission on Life Sciences
National Research Council
NATIONAl ACADEMY pRESS
Washington, D.C. 1984
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National Academy Press 2101 Constitution Avenue, NW Washlugton, DC 20418
NOTICE: The project that is the subject of this report was approved by
the Gove ruing Board of the National Research Council, whose members are
drawn from the councils of the National Academy of Sciences, the National
Academy of Engineering, and the Institute of Medicine. The members of
the committee responsible for the report were chosen for their special
competences and with regard for appropriate balance.
This report has been reviewed by a group other than the authors
according to procedures approved by a Report Review Committee consisting
of members of the National Academy of Sciences, the National Academy of
Engineering, and the Institute of Medicine.
The National Research Council was established by the National Academy of
Sciences in 1916 to associate the broad community of science and
technology with the Academy's purposes of furthering knowledge and of
advising the federal government. The Council operates in accordance with
general policies determined by the Academy under the authority of its
congresaion~1 charter of IS63, which establishes the Academy as a
private, nonprofit, self-governing membership corporation. The Council
has become the principal operating agency of both the National Academy of
Sciences and the National Academy of Englneering in the conduct of their
services to the government, the public, and the scientific and
engineering communities. It is administered jointly by both Academies
and the Institute of Medicine. The National Academy of Engineering and
the Institute of Medicine were established in 1964 and 1970,
respectively, under the charter of the National Academy of Sciences.
The study reported here was supported by Contract EPA 68-01-4655
between the National Academy of Sciences and the Environmental Protection
Agency.
Library of Congress Catalog Card Number 84-60249
International Standard Book Number 0-309-03446-9
Printed in the United States of America
..
1
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t
.
l
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Commiltee on Nonoccupationa
of Asbestiform Fibers
Leater Brealow, Chairmsu
.
School of Public Health
University of California
Los Angeles, Calif.
Richard Bates
Health Effects Institute
Cambridge, Mass.
Henrik Bendixen
Department of Anesthesiology
Columbia University
College of Physicians
and Surgeons
New York, N.Y.
Strephen L. Brown
Independent Consultant
Portola Valley, Calif.
Patricia A. Buffler
University of Texas
Health Science Center
School of Public Health
University of Texas at Houston
Houston, Texas
Arthur M. Langer
Department of Com~,nity
Medicine
Environmental Sciences
Laboratory
Mt. Sinai School of Medicine
New York, N.Y.
Jeremiah Lynch
Exxon Chemical Company
East Millstone, N.J.
t
~ Health Risks
James A. Merchant
Department of Preventive
Medicine and Environmental
Health and the Department
of Internal Medicine
College of Medicine
University of Iowa
Iowa City, Ia.
Richard Monson
Department of Epidemiology
Harvard School of Public Health
Boston, Mass.
Brooke T. Mosaman
Department of Pathology
College of Medicine
University of Vermont
Burlington, Vt.
Jamen E. Troako
Department of Pediatrics
and Human Development
College of Human Medicine
Michigan State University
Eant Lansing, Mich.
John Van Ryzin
Division of Biostatistics
School of Public Health
Columbia University
New York, N.Y.
Tibor Zolta1
Department of Geology and
Geophysics
University of Minnesota
Minneapolis, Minn.
iii
..
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Consultant
Warren Heir
Department of Environmental
Health Sciences
School of }lygiene and
Public Health
The Johns Hopkins University
Baltimore, Md.
Hatior~al Research Council Staff
Barbara Mandula, Study Director
Frances M. Peter, Editor
Pamela Smith, Research Assistant
Waider~a Banks, A - inistrati~re
Secretary
Board on Toxicology and Environmental Health Hazards
Gerald N. Wogan, Chairman
Department of Nutrition and
Food Science
Massachusetts Institute of
Technology
Cambridge, Mass.
Philip Landrigan, Co-Vice-Chairman
National Institute for Occupational
Safety and Health
Robert Taft Iaboratories
Cincinn~ ti, Ohio
Donald Hornig, Co-llice-Chalrman
S choo] of Public Health
Ha rvard University
Boston, Hass.
Edwa rd Bresnick
Eppley Institute for
Cancer Research
Dhi~reraity of Nebraska
Medical Center
Omaha, Nebraska
Herman N. Eisen
De pa rtment of Biology
Ma ssachusett6 Institute of
Technology
Cambridge, Mass.
Ronald Estabrook
Department of Biochemistry
University of Texas Medical
School
Della a, Ten ~
Emmanuel Farber
Department of Pathology
University of Toronto
Toronto, Ontario
Inlaid G. Hoel
Biometry and Risk Assessment
Program
National Institute of
Environmental Health Sciences
Resea rch Triangle Park, N . C .
Michael W. Lieberman
Department of Pa thology
Washington University School
of Medicine
St . Louis, Missouri
Abraham }1. Lilienfeld
School of Hygiene and
Public health
The Johns Hopkins University
Baltimore, Maryland
iv
.
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BOARD ON TOXICOLOGY AND ENVIRONMENTAL HEALTH HAZARDS (Continued)
Richard Merrill
School of Law
Unlversity of Virginia
Charlottesville, Virginia
1
Vaun A. Newill
Exxon Corporation
Medicine and Environmental
Health Department
New York, New York
John Peters
Department of Family and
Preventive Medicine
University of Southern California
School of Medicine
Los Angele a, California
Ex Of ficio Members
Gary P. Carlson
Purdue University
School of Pharmacy and
Pharmacal Science
Department of Pharmacology
and Toxicology
Lafayette, Indiana
Maureen Henderson
School of Public Health and
Community Medicine
Department of Epidemiology
University of Washington
Seattle, Washington
National Research Council Staff
Robert G. Tardiff, Executive Director,
until June 1983
Devra L. Davis, Executive Director,
September 1983 to present
Jacqueline K. Prince, Staff Assistant
v
Joseph V. Rodricks
Environ Corporation
Washington, D . C .
Liane B. Russell
Biology Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee
Ellen S ilbergeld
Toxic s Program
Environmental Defense Fund
Washington, D . C.
Roger O. McClellan
Lovelace Inhalation Toxicology
Research Institute
Albuquerque, New Mexico
Daniel B. Menzel
Department of Pharmacology
Duke University Medical Center
Durham, North Carolina
Norton Nelson
Institute of Environmental
Medicine
New York University Medical Center
New York, New York
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Preface
Industrial progress during the twentieth century has contributed to
our well-beirt8, but has also resulted in environmental changes that have
increased risks to human health. Not only are greater quantities and
varieties of hazardous materials being taken from the earth and used in
many ways, but the use of synthetic materials with similar physical and
chemical properties has also been growing.
Adverse health effects from many of these new exposures have been
receiving considerable attention. Radioactive substances, cigarette
smoke, petrochemicals, and asbestos, for example, are well known for
their potential to harm health.
The health risks from exposure to these and other materials are
provoking some alarm because of several characteristics that they have in
common. Relatively small, sometimes minute, amounts may cause severe
damage to health. People are often not aware of their exposure at the
time it occurs. Cancer, a particularly feared disease, can result.
Cancer and other adverse health effects typically occur many years after
exposure began. Evidence linking the particular substance to subsequent
disease may appear-ad be accepted--ouly decades after millions of
people have been exposed. Asbestiform fibers, which for purposes of this
report include both natural materials such as asbestos and synthetic
materials such as fibrous glass, typify the problem.
Although asbestos and some of its uses had been known for centuries,
twentieth century industry brought a vast increase in mining and
distribution of that material. Then, some years after hundreds of
thousands of workers had been exposed, it became apparent that
considerable damage to health, including cancer, Was occurring as a
result. Ascertaining the harm precisely was complicated because other
factors, especially cigarette smoking, often contributed to the same
effects. As the hazard became more widely known in recent years, annual
use of asbestos in the United States has dropped. However, asbestos had
already been widely distributed in schools and other buildings, in the
general outdoor air, and in some water supplies. Thus, tens of millions
of people are still being esposed-`lthough usually to very small amounts.
The usefulness of asbestos was so great that substitutes with some
similar physical properties were developed for commercial purposes. Do
these synthetic materials carry the same, or some, health risk because of
the characteristics they share with the naturally occurring asbestos?
Given the widespread occurrence of these materials, concerned federal
agencies commissioned studies to examine the potential health risk from
vii
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nonoccupational espo sure to asbestos. To one such study, the Safe
Drinking Water Committee of the National Research Council sought to
determine whether health damage was occurring because drinking water was
contaminated with asbestos fibers. The committee found that the
epidemioJogical studies of asbestos in drinking water had mayor
limitations in design, but that the committee's risk estimates were
compatible with the results of the epidemiological studies (National
Research Council, 1983~. Generally, the amount of asbestos in the
drinking waters studied would be likely to yield an increased risk too
small to detect.
The U.S. Consumer Product Safety Commission, in carrying out its
responsibility for protecting consumers, sought guidance from a Chronic
Hazard Advisory Panel on Asbestos. The latter body concluded that
"asbestos at all levels of exposure ...~should be regarded] ... as a
potential human carcinogen." Furthermore, the panel wrote, "It is
prudent to behave as if asbestos fibers may be carcinogenic at low
exposure levels and at small particle sizes" (U.S. Consumer Product
Safety Commission, 1983~. There has also been concern about asbestos in
schools, as evidenced by reports from the U.S. Environmental Protection
Agency (1980) and the U.S. General Accounting Office (1982~.
In a more general approach to the issue, broadening it beyond
asbestos, the Environmental Protection Agency asked the National Academy
of Sciences:
to evaluate the human health risks associated
with nonoccupational exposure to asbestiform
fibers, with emphasis on inhalation of outdoor
and indoor air, and
to determine the extent to which the physical-
chemical properties of the fibers may be
associated with the development of various human
diseases and the extent to which such information
may be incorporated into assessing health risks
resulting from exposure to the fibers.
To conduct that study, the National Research Council established the
Committee on Nonoccupational Health Risks of Asbestiform Fibers in August
1982. This is the report of that committee.
I personally would like to thank the committee members, who worked
extremely hard and persistently to bring the project to fruition. I
could not imagine a more thoughtful, energetic, and cooperative group for
approaching this comples problem. On behalf of the committee, I would
also like to thank the many persons from various groups and agencies who
viii
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provided the committee with unpublished draft documents, or who took the
time to answer questions and offer suggestions. Hey are too numerous to
mention individually. However, Dr. Dennis Kotchmar, EPA project officer,
deserves special mention, as do Mr. Colin Church, Dr. Robert Clifton,
Dr. Jon Konzen, Dr. James Leineweber, Dr. Marvin Schneiderman, ant
Mr. Paul White.
The committee is also grateful to the capable and devoted NRC project
staff, including Dr. Barbara Mandula, Ms. Pamela Smith, Ms. Dena Banks,
Me. Frances Peter, and the many others who assisted them at various
times, especially Me. Shirley Ash, Ms. LRslye Giese, Me. Jacqueline
Prince, Ms. Mary Ellen Scheckenbach, and ~8. Bernidean Williams.
Special thanks are also due Dr. Warren Muir, who was a consultant to
the committee. Finally, I wish to thank Dr. Robert Tardiff, who was
executive director of BOTEHH when the project began; Dr. Devra Davis,
present executive director of BOTEHH, who energetically shepherded the
project through its final stages; and Drs. Frederick Robbins and Alvin
Lazen of the Commission on Life Sciences for their continued interest and
support.
Lester Breelow
Chairman
Committee on Nonoccupational
Fibers
1X
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REFERENCES
Nations l Research Counci l . 1983. Drinking Water and Health. Vol . 5 .
A report of the Safe Drinking Water Committee, Commission on Life
Sciences. National Academy Press, Washington, D.C.
U.S. Consumer Product Safety Commission. 1983. Chronic Hazard Advisory
Panel on Asbestos. Consumer Product Safety Co~ission, Washington,
D.C.
U.S. Environmental Protection Agency. 1980. Asbestos-Containing
Materials in Schools. Health Effects and Magnitude of Exposure.
Support document for proposed rule 6 on friable asbe~tos-containing
materials in school buildings. Environmental Protection Agency,
Washington, D.C.
U.S. General Accounting Office. 1982. Asbestos in Schools: A Dilemma
General Account ing Of f ice, Wash ington, D . C .
.
x
.1
1
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Contents
EXECUTIVE SUMMARY . . . . . . . . . . .
Origin of the Study . . . . . . . .
Major Findings and Recommendations
2
2
Evaluation al KINK ~ . . . . . . . . . . ~ ~ . . . . . .
Physicochemical Properties and Health Effects . . . . . .
Recommendations . . . . ~ . . . . . . . . . . . ~ . . . .
Summary of the Study ~ . . . . . . . . . . . . . . . . . . ~ .
Background . . . . ~ . . . . . . . . . ~ . . . . . . . ~ .
Materials of Concern . . . . . . . . . . ~ ~ . . . . . ~ .
Relationship of Fiber Characteristics
to Health Effects ...................
Measurement and Extent of Exposure . . . . . . . . . . . . 9
Health Effects Methodology . . . . . . . . . . . . . . . . 10
Health Effects of Asbestos 11
Health Effects of Nonasbestos
Asbestiform Fibers ~ 12
Evidence Associating Fiber Properties
with Adverse Health Effects 13
Risk Assessment 8 e ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ e 13
4
4
57
8
1 INTRODUCTION
. . . . . . . . . . 16
Concurrent National Research Council and
Government Activities Related to Asbestos . . . . . . . . . . 19
me Con mittee ' s Approach . . . . . . . . . 20
References . . . . . . . ~ . . . . . . . .
2
.
. . . . . . . . . .^
ASBESTIFORM FIBERS: HISTORICAL BACKGROUND, TERMaNOLOGY,
AND PHYSICOCHEMICAL PROPERTIES . . . . . . . . . . . . . . . 25
bestosin~story 25
MineralogicalTe~inology 26
~ ~ ~ in__ ~ . . . 31
Physical~ropercles OI ~ Den ~llo~-m r ~ v=` D . ~ . . ~ . . , . · . 31
Fiberlike Morphology . . . . . . . . . . . . . . . . . . . 32
Enhanced Strength and Flexibility 33
Diameter-Dependent Strength 33
Increased Physical and Chemical Durability 33
Defect-Free Surface Structure 34
Growth-Dependent Fiber Quality ......... 35
Sources on nluera' ram Lid . . . . . . .
~ . ~ _ _ ~ ~ _ ~ _ _ ~ ~ = _ _ ~ 4 ~ ~ _ ~
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CONTENTS
2 (cont.
3
4
Biologically Relevant Physicochemical Properties . . .
Re spirability . . . . . . . .
Size and Aspect Ratio (Length:Diameter) .........
Durability . . . . . . . . . . . . . . . . . . ~ . . . .
Flexibility and Tensile Strength ............
Chemical Composition e e · - e ·
Surface Area . . . . . ~ . . e · · · · · · · · · · · · ~
Surface Charge e ~ ~ ~ ~ ~ ~ ~ ~ 0
Standardized Asbestos Samples .
· · · -
S''mm ~ ry
Re commends tions . . . .
References . . . . . . . .
ASSESSING NONOCCUPATIONAL EXPOSURES TO
ASBESTIFORM FIBERS ..........
Definitions of Exposure ...................
Asbestiform Fibers and Weir Sources.. ...........
Exposure Potential for Asbestos ...............
Types of Exposure e · ~ - ~ ~ -
Quantitative Exposure Estimates ............
Exposure to Other Natural Mineral Fibers .
Attapulgite . . . . . . . . . . . .
Erionite . . . . . . . . . . .
Exposure to Man-Hade Fibers . . . . . . . . . . e e · · · ·
Man-Made Hineral Fibers . . . . . . . . . . e ~ ~ e e e e
Esposure to Other Man-Made Fih~re
e
36
36
36
37
38 t
38
39
39
39
40
42
43
48
i
48
52
55
55
61
68
69
70
71
71
75
76
e e e ~ e 77
e ~ ~ e ~ e e e a82
S''mmary and Recommendationse .
References . . . . ~
MEASUREMENT OF EXPOSURE TO ASBESTIFORH FIBERS
Measurement Techniques e ~ e e e e ~ - -
Measuring Asbestos Dust in the Workolac
The Impinger Techaique e ~ ~ e e
The Membrane Pliter Techaique e e
l
Measuring Asbestos Dust in the Ambient Environment e e ~ e ~ e e86
Relationships Among Yarious Esposure Measurement
Methods . e e e ~ e e e e ~ e e e e e e ~ e e ~ e ~ e ~ e e e87
Exposure to Chrysotile in the Ambient Environment e ~ e e e e .90
Complicatirtg Factors in Enviror~mental Assays 91
Puture Measurement of Esposure to Asbestiform Fibers 91
Recommendations . . . . . . . . . . . . e ~ ~ ~ ~ e ~ ~ ~ 0 ~ e93
References . e ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ e ~ ~ e e e ~ ~ e ~ ~ ~ .93
xii
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r
1
CONTENTS
5 EFFECTS OF ASBESTIFORM FIBERS ON HUMAN HEALTH . ...... 97
Nature of Evidence eeeeeeeeeaeeee.
Biodisposition of Fibers eeeeea~eeeee.
Fiber Deposition eeeeeeeeeea~e.
r:1 ~nrance and Transport eeee.e
-~.e 97
---100
eeeeee103
eeee.eeeeee106
C1inical Aepects of Asbestos-Associated Diseases . . . . . . . 107
Neceseary Assumptione Ueed in Determining
Health Effects .................. 107
Sensitivity and Specificity of Clindcal
Evidence . . ee.~108
General Diagnostic Measures 109
Disease Associated with Nonoccupational TnhAlation
Exposures to Asbestiforn~ Fibers 114
Asbestos E~posure from Household Contacts 116
Neighborhood Exposure to Asbestos 116
Natural Sources of Asbestiform Fibers 117
Summary 119
Epidemiological Studies of Effects Resulting from the
Ingestior' of Asbestos in Drinking Water 119
Occupational Epidemiological Studies-~Methodological
Considerations .~123
Cancer Mortality in Occupational Cohorts Esposed
to Asbestos .~125
Mining and Milling e.~128
- 128
...... 131
.~131
MaDulaCl~uI:ll~5 ~ ~ e e ~
IDsulation e e e e e ~ ~ ~ ~ ~ ~ ~ ~ e
Shipyard 8 e ~ ~ ~ ~ ~ e e e e e ~
Relative Carcinogenicity of Different
Types of Asbestos ............
Effect 8 0 f Smoking . e e e e e e e ~ ~ e
Summary . e ~e ~
~ ~ e ~ e
- ~ ~ e ~ ~ e e
A`;bestosis and Asbestos-Associated Pleural Disease
in Occupatio~1 Cohorts .......
Mortality Studie 8 ~ ~ ~ ~ ~ e e ~ ~ ~ ~ e e e
Morbidity Studies . . e ~ ~ e e ~ ~ e
Sllmmary . e e ~ e ~ e e ~ ~ ~ e ~ e ~
Hdalth Effects of Occupational Exposure to
. . . . . 132
. . . . . . 133
. . . . . . 133
. . . . . . . . . 136
....... 140
Man-Made Mine ra1 rlDer ~..... , . 141
~--- . . . . . . . . . . . . . . . . . 141
e ~e 143
, e e ~145
e e ~e 146
~e e e ~e 146
e ~e ~e ~146
e ~e ~e e e ~}48
e e e 149
MO r D~u1 1- ~ ~ ~ ~ e ~ ,
Mortality e e e ~ ~ e · · ~ ~ e ~ e e e e
Summa ~ e e ~ ~ - - ~ ~ ~ ~ e e ~ ~ . =
AdditiorA 1 Occupatio~A1 Epidemiological Studies
Attapulgite e.~eee.~ee
~lceeeeeeeee.eee.
Recommendations eeee..eeeee
~fere~ce8 eeeeee
Xlil
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CONTENTS
6
IABORATORY STUDIES OF THE EFFECTS OF ASBESTIFORM FIBERS . . .
165
Studies in A~i~lal8 ~ ~ ~ ~ e ~ ~ e ~ e ~ e ~ ~ ~ e ~ ~ e e ~165
Lung Cancer . . e e e e e ~ e ~ e ~ ~ ~ ~ ~ e ~ ~ e ~ ~165
Mesothelioma . . e e e e e e e e ~ ~ ~ ~ ~ ~ e e e e e e 167
Fibrosis e e e e e e e e e e e e e e e e e ~ e e e ~ 0 e 168
Events in the Gastrointestinal Tract After
Exposure to Asbestos e e e e e e e ~ ~ ~ e ~ ~ e e e e
In Vitro Studies e e e e e e ~ e e e e e e e e ~ ~ e e e e e
Hemolytic A`;says . . e e e ~ e e ~ e e e e e e ~ ~ ~ e e
Cytotoxicity Studie8 e e ~ e e ~ e e ~ e ~ ~ e e ~ ~ e e
Alterations in Cells of the Immune System
After Exposure to Asbestiform Fibers . . . . . . O . .
Effects on Fibroblasts in Vitro . . . . . . . . . . . .
Initiation-Promotion Model of Carcinogenesis . . . O . . . .
Interaction of Asbestiform Fibers with DNA . . . . . . .
Tumor Promotion ~ . . . . . . . . . . . O . . . . . . .
In Vitro Studies with Mesothelial Cells O . . . . . . .
Toteractions Between Fibers and Polycyclic
Aromatic Hydrocarbons (PAHs) . . . . . . . . . . . . .
Conclusions . . . . . O . . . . . . O . . . . . e e ~ ~ ~ ~ e
Asbestiform Fibers: Initiators and/or
Promoters of Lung Tumors?. . . . . e ~ ~ ~ e e e e ~ e
Asbestiform Fibers: Initiators and/or
Promoters of Malignant Mesothelioma? . . . . e
Asbestiform Fibers: Possible HechaDisme
- of Fibrosis . . ~ . . ~ . . . . . . . e e ~ ~ ~ ~ e
Su~lm~ ry ~ ~ ~ ~ ~ ~ e ~ ~ ~ ~ ~ ~ ~ ~ e
Recommendations . . e ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ e e e
References . . . ~ ~ O O . . . . . ~ . e ~ e
7 RISK AS SESSMENT . . . . . . . . . . . . e ~ e e ~ e e
The Process of Risk Assessment . . e e e e e e e e e e e ~ ~
Quantitative Risk Assessment e e e e e e e e e e e e e e e e
Mathematical Model for Carcinogenic
Risk Estimate e e e e e e e e e e e e e e e e e e
Published Risk A8sessments e e e ~ ~ ~ ~ e ~ ~ e e e e e ~ e
Lung Cancer Risk From Nonoccupational
Enviro~mental Exposures . . e e e ~
Mesothelioma Risk From Nonoccupational
Environmental Exposures . . e e e e
169
170
170
171
ll
-
172
173
173
175
176
177
177
177
177
179
180
180
183
184
200
200
205
206
208
208
209
Quantitative Risk Assesament for Nonoccupational
Eavironmental E2posures ~ e e e e a e ~ e e e e e e e e e e
Lifetime Risk Estimates for Lung Cancer
and Mesothelioma e ~ e e e e e e e e e e e e e e e e ~ 211
Risk Assessments for Special Subpopulations e e e e e e 221
xiv
1
211
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CONTENTS
7 (cont.)
Comparative Risk Assessment . .
Methods e ~ e ~ ~ ~ ~ ~ ~ ~ e ~
General Methodological Considerations
Scoring Considerations e ~ e ~ ~ ~ e
Discussion of Comparative Risks. . e
Summary and Recommendations
References
.222
.222
. .223
. .226
. .228
. .230
. .232
APPENDIX A: Asbestos Exposure and Human Disease. Hallmark
Observations and Studies from 1898-1979 . . . . .237
APPENDIX B:
APPENDIX C:
Natural and Synthetic Fibrous Substances
and Some of their Known Biological Effects O
Fiber-Quality Parameters of Selected
Asbestos, Whisker, and Glass Fibers . .
· -
.244
APPENDIX D: Conceptual Model of Fiber Exposure . . . . . . . .261
APPENDIX E: Epidemiological Studies Among Cohorts
Exposed to Asbestos . . . . . . . . . e ~ e ~ ~ ~ ~ 267
APPENDIX F: Effects of Administering Asbestiform
Fibers to Animals. . . . . . . . . . e ~ ~ ~ ~ ~ ~ 300
APPENDIX G: Development of Some Equat ions Used for
Quant itat ive Risk As se s sment . . . . . . . . . . . 311
APPENDIX H: Comparative Risk Assessment Score Sheet s . . . . . 314
APPENDIX I: Background Information on Members of the
Committee on Nonoccupational Health Risks
of Asbestiform Fibers . . . . . . . . . . . . . .332
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9
