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Science and Judgment in Risk Assessment Committee on Risk Assessment of Hazardous Air Pollutants Board on Environmental Studies and Toxicology Commission on Life Sciences National Research Council NATIONAL ACADEMY PRESS Washington, D.C. 1994
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NATIONAL ACADEMY PRESS · 2101 Constitution Ave., N.W. · Washington, D.C. 20418
NOTICE: The project that is the subject of this report was approved by the Governing 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 competencies 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 project was supported by the U.S. Environmental Protection Agency under contract CR818293-01-0.
Library of Congress Cataloging-in-Publication Data
Science and judgment in risk assessment / Committee on Risk Assessment of Hazardous Air Pollutants, Board on Environmental Studies and Toxicology, Commission on Life Sciences., National Research Council. p. cm Includes bibliographal references and index. ISBN 0-309-04894-X 1. Air—Pollution—Toxicology—United States—Statistical methods. 2. Health risk assessment—Statistical methods. I. National Research Council (U.S.). Committee on Risk Assessment of Hazardous Air Pollutants. RA576.S365 1994 363.73'92'0973—dc20 94-17475 CIP
Copyright 1994 by the National Academy of Sciences. All rights reserved.
Printed in the United States of America
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Committee On Risk Assessment Of Hazardous Air Pollutants
KURT J. ISSELBACHER (Chairman), Massachusetts General Hospital, Charlestown, Mass.
ARTHUR C. UPTON (Vice-Chairman), New York University Medical Center (retired), N.Y.
JOHN C. BAILAR, McGill University School of Medicine, Montreal, Canada
KENNETH B. BISCHOFF, University of Delaware, Newark, Del.
KENNETH T. BOGEN, Lawrence Livermore National Laboratory, Livermore, Calif.
JOHN I. BRAUMAN, Stanford University, Calif.
DAVID D. DONIGER, Natural Resources Defense Council, Washington, D.C.*
JOHN DOULL, University of Kansas Medical Center, Kansas City, Kan.
ADAM M. FINKEL, Resources for the Future, Washington, D.C.
CURTIS C. HARRIS, National Cancer Institute, Bethesda, Md.
PHILIP K. HOPKE, Clarkson University, Potsdam, N.Y.
SHEILA S. JASANOFF, Cornell University, Ithaca, N.Y.
ROGER O. McCLELLAN, Chemical Industry Institute of Toxicology, Research Triangle Park, N.C.
LINCOLN E. MOSES, Stanford University, Calif.
D. WARNER NORTH, Decision Focus, Inc., Mountain View, Calif.
CRAIG N. OREN, Rutgers University School of Law, Camden, N.J.
REBECCA T. PARKIN, Beccam Services, Plainsboro, N.J.
EDO D. PELLIZZARI, Research Triangle Institute, N.C.
JOSEPH V. RODRICKS, Environ Corporation, Arlington, Va.
ARMISTEAD G. RUSSELL, Carnegie-Mellon University, Pittsburgh, Penn.
JAMES N. SEIBER, University of Nevada, Reno, Nev.
STEVEN N. SPAW, Law Environmental Incorporated, Austin, Tex.
JOHN D. SPENGLER, Harvard University, Boston, Mass.
BAILUS WALKER, University of Oklahoma, Oklahoma City, Okla.
HANSPETER WITSCHI, University of California, Davis, Calif.
Staff
RICHARD D. THOMAS, Program Director
DEBORAH D. STINE, Study Director
MARVIN A. SCHENIDERMAN, Senior Staff Scientist
GAIL CHARNELY, Senior Staff Officer
KATHLEEN STRATTON, Senior Staff Officer
RUTH E. CROSSGROVE, Information Specialist
ANNE M. SPRAGUE, Information Specialist
RUTH P. DANOFF, Project Assistant
SHELLEY A. NURSE, Senior Project Assistant
CATHERINE M. KUBIK, Senior Project Assistant
*Left committee in May 1993 upon becoming Deputy Director of the White House Office of Environmental Quality
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Board On Environmental Studies And Toxicology
PAUL G. RISSER (Chair), University of Miami, Oxford, Ohio
FREDERICK R. ANDERSON, Cadwalader, Wickersham & Taft, Washington, D.C.
MICHAEL J. BEAN, Environmental Defense Fund, Washington, D.C.
EULA BINGHAM, University of Cincinnati, Cincinnati, Ohio
EDWIN H. CLARK, Clean Sites, Inc., Alexandria, Va.
ALLAN H. CONNEY, Rutgers University, N.J.
JOHN L. EMMERSON, Eli Lilly & Company, Greenfield, Ind.
ROBERT C. FORNEY, Unionville, Pa.
ROBERT A. FROSCH, Harvard University, Cambridge, Mass.
KAI LEE, Williams College, Williamstown, Mass.
JANE LUBCHENCO, Oregon State University, Corvallis, Ore.
HAROLD A. MOONEY, Stanford University, Stanford, Calif.
GORDON ORIANS, University of Washington, Seattle, Wash.
FRANK L. PARKER, Vanderbilt University, Nashville, Tenn., and Clemson University, Anderson, S. C.
GEOFFREY PLACE, Hilton Head, S. C.
DAVID P. RALL, Washington, D.C.
LESLIE A. REAL, Indiana University, Bloomington, Ind.
KRISTIN SHRADER-FRECHETTE, University of South Florida, Tampa, Fla.
GERALD VAN BELLE, University of Washington, Seattle, Wash.
BAILUS WALKER, JR., University of Oklahoma, Oklahoma City, Okla.
Staff
JAMES J. REISA, Director
DAVID J. POLICANSKY, Associate Director and Program Director for Natural Resources and Applied Ecology
RICHARD D. THOMAS, Associate Director and Program Director for Human Toxicology and Risk Assessment
LEE R. PAULSON, Program Director for Information Systems and Statistics
RAYMOND A. WASSEL, Program Director for Environmental Sciences and Engineering
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Commission On Life Sciences
THOMAS D. POLLARD (Chair), Johns Hopkins Medical School, Baltimore, Md.
BRUCE N. AMES, University of California, Berkeley, Calif.
JOHN C. BAILAR, III, McGill University, Montreal, Canada
J. MICHAEL BISHOP, Hooper Research Foundation, University of California Medical Center, San Francisco, Calif.
JOHN E. BURRIS, Marine Biological Laboratory, Woods Hole, Mass.
MICHAEL T. CLEGG, University of California, Riverside, Calif.
GLENN A. CROSBY, Washington State University, Pullman, Wash.
LEROY E. HOOD, University of Washington, Seattle, Wash.
MARIAN E. KOSHLAND, University of California, Berkeley, Calif.
RICHARD E. LENSKI, Michigan State University, East Lansing, Mich.
EMIL A. PFITZER, Hoffmann-La Roche Inc., Nutley, N.J.
MALCOLM C. PIKE, University of Southern California School of Medicine, Los Angeles, Calif.
HENRY C. PITOT, III, University of Wisconsin, Madison, Wisc.
PAUL G. RISSER, Miami University, Oxford, Ohio
JOHNATHAN M. SAMET, University of New Mexico School of Medicine, Albuquerque, N.Mex.
HAROLD M. SCHMECK, JR., Armonk, N.Y.
CARLA J. SHATZ, University of California, Berkeley, Calif.
SUSAN S. TAYLOR, University of California at San Diego, La Jolla, Calif.
P. ROY VAGELOS, Merck & Company, Whitehouse Station, N.J.
JOHN L. VANDEBERG, Southwestern Foundation for Biomedical Research, San Antonio, Tex.
TORSTEN N. WIESEL, Rockefeller University, New York, N.Y.
PAUL GILMAN, Executive Director
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The National Academy of Sciences is a private, non-profit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences.
The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Robert M. White is president of the National Academy of Engineering.
The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine.
The National Research Council was organized 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 advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce Alberts and Dr. Robert M. White are chairman and vice chairman, respectively, of the National Research Council.
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Other Recent Reports Of The Board On Environmental Studies And Toxicology
Pesticides in the Diets of Infants and children (1993)
Issues in Risk Assessment (1993)
Setting Priorities for Land Conservation (1993)
Protecting Visibility in National Parks and Wilderness Areas (1993)
Biologic Markers in Immunotoxicology (1992)
Dolphins and the Tuna Industry (1992)
Environmental Neurotoxicology (1992)
Hazardous Materials on the Public Lands (1992)
Science and the National Parks (1992)
Animals as Sentinels of Environmental Health Hazards (1991)
Assessment of the U.S. Outer Continental Shelf Environmental Studies
Program, Volumes I-IV (1991-1993)
Human Exposure Assessment for Airborne Pollutants (1991)
Monitoring Human Tissues for Toxic Substances (1991)
Rethinking the Ozone Problem in Urban and Regional Air Pollution (1991)
Decline of the Sea Turtles (1990)
Tracking Toxic Substances at Industrial Facilities (1990)
Biologic Markers in Pulmonary Toxicology (1989)
Biologic Markers in Reproductive Toxicology (1989)
Copies of these reports may be ordered from the National Academy Press
(800) 624-6242
(202) 334-3313
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Page ix
Preface In the Clean Air Act Amendments of 1990, Congress directed the administrator of the Environmental Protection Agency (EPA) to engage the National Academy of Sciences (NAS) in a review of the methods that EPA uses to estimates toxicological risk. The resulting charge to the National Research Council (NRC) can be summarized in a short set of questions:
1.
Given that quantitative risk assessment is essential for EPA's implementation of the Clean Air Act, is EPA conducting risk assessments in the best possible manner?
2.
Has EPA developed mechanisms for keeping its risk-assessment procedures current in the face of new developments in science?
3.
Are adequate risk-related data being collected to permit EPA to carry out its mandates?
4.
What, if anything, should be done to improve EPA's development and use of risk assessments?
To meet the congressional mandate, and in response to the request from the administrator of EPA, the National Research Council established the Committee on Risk Assessment of Hazardous Air Pollutants under the the Board on Environmental Studies and Toxicology. The committee consisted of 25 members with expertise in medicine, epidemiology, chemistry, chemical engineering, environmental health, law, pharmacology and toxicology, risk assessment, risk management, occupational health, statistics, air monitoring, and public health. It included academics, industry scientists, public advocates, and state and local public-health officials.
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The first meeting of the committee was held on October 31, 1991. In the first several meetings, presentations were made to the committee by committee members and by individuals or representatives of groups with special concerns in the development and use of risk assessment. Among the latter were presenters on behalf of the American Industrial Health Council, the Chemical Manufacturers Association, the American Petroleum Institute, the American Iron and Steel Institute, the American Chemical Society, such official public-health groups as the Texas Air Control Board and the State and Territorial Air Pollution Program Administrators, and such public-interest groups as the Natural Resources Defense Council and the Environmental Defense Fund. Presentations were also made by the representative of a paint manufacturer and by a senior member of an environmental consulting company. The committee also was greatly aided by the previous reports and workshops of the NRC's Committee on Risk Assessment Methodology.
Early in the course of its deliberations the committee developed a set of issues for consideration and reply by EPA's Office of Air and Radiation and its Office of Research and Development. EPA's responses were presented to the committee during the committee's meetings in late March 1992.
James Powell, of the U.S. Senate staff, described to the committee both the legislative history of the Clean Air Act Amendments and the concerns of senators in the evolution of EPA's development of regulations. Greg Wetstone, of the U.S. House of Representatives staff, spoke to the committee about the need for accurate risk assessments and exposure measures. Henry Habicht, Michael Shapiro, Robert Kellum, and William Farland of EPA discussed where EPA was in risk assessment and how it got there. Their briefings enabled the committee to get off to a quick start in its work.
The committee was substantially helped in its activities by strong support from the NRC and BEST staff: Richard D. Thomas, the program director; Deborah D. Stine, the study director; Marvin A. Schneiderman, senior staff scientist; Norman Grossblatt, editor; Anne M. Sprague, information specialist; Ruth E. Crossgrove, information specialist; Ruth P. Danoff, project assistant; and Shelley A. Nurse and Catherine M. Kubik, senior project assistants.
Finally, we must express our thanks and appreciation to the hard-working members of the committee, who struggled through long meetings, read mountains of documents, listened with interest and concern to many presentations, and then prepared what we consider to be a thoughtful, comprehensive, and balanced report.
Kurt Isselbacher, M.D. Chairman
Arthur Upton, M.D. Vice Chairman
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Contents EXECUTIVE SUMMARY
1
1
INTRODUCTION
16
Charge to the Committee
17
Conceptual Framework of the Report
21
PART I CURRENT APPROACHES TO RISK ASSESSMENT
23
2
RISK ASSESSMENT AND ITS SOCIAL AND REGULATORY CONTEXTS
25
General Concepts
25
Historical Roots
29
NRC Study of Risk Assessment in the Federal Government
33
Events After Release of the 1983 NRC Report
34
Uses of Risk Assessment in the Regulation of Hazardous Air Pollutants
36
Noncancer Risk Associated with Hazardous Air Pollutants
39
Public Criticism of Conduct and Uses of Risk Assessment
40
3
EXPOSURE ASSESSMENT
43
Introduction
43
Emission Characterization
47
Modeling Used in Exposure Assessment
50
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4
ASSESSMENT OF TOXICITY
56
Introduction
56
Principles of Toxicity Assessment
56
New Trends in Toxicity Assessment
66
5
RISK CHARACTERIZATION
68
Introduction
68
Elements of Risk Characterization
69
PART II STRATEGIES FOR IMPROVING RISK ASSESSMENT
79
The Need for Risk-Assessment Principles
80
Reporting Risk Assessments
83
The Iterative Approach
84
6
DEFAULT OPTIONS
85
Adoption of Guidelines
85
Departures from Default Options
90
Current EPA Practice in Departing from Default Options
92
Findings and Recommendations
104
Process for Departures
105
7
MODELS, METHODS, AND DATA
106
Introduction
106
Emission Characterization
107
Exposure Assessment
112
Assessment of Toxicity
119
Findings and Recommendations
137
8
DATA NEEDS
144
Context of Data Needs
144
Implications for Priority-Setting
145
Data Needed for Risk Assessment
146
Data Management
156
Findings and Recommendations
157
9
UNCERTAINTY
160
Context of Uncertainty Analysis
160
Nature of Uncertainty
161
Problems with EPA's Current Approach to Uncertainty
166
Some Alternatives to EPA'S Approach
167
Specific Guidance on Uncertainty Analysis
175
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Risk Management and Uncertainty Analysis
179
Comparison, Ranking, and Harmonization of Risk Assessments
183
Findings and Recommendations
184
10
VARIABILITY
188
Introduction and Background
188
Exposure Variability
196
Variability in Human Susceptibility
200
Conclusions
203
Findings and Recommendations
217
11
AGGREGATION
224
Introduction
224
Exposure Routes
225
Risk-Inducing Agents
226
Types of Nonthreshold Risk
229
Measures and Characteristics of Risk
234
Findings and Recommendations
240
PART III IMPLEMENTATION OF FINDINGS
243
12
IMPLEMENTATION
245
Priority-Setting and Section 112
245
Iterative Risk Assessment
246
EPA Practices: Points to Consider
252
Institutional Issues in Risk Assessment and Management
256
Summary
263
Findings and Recommendations
264
REFERENCES
269
APPENDIXES
A
Risk Assessment Methodologies: EPA's Responses to Questions from the National Academy of Sciences
289
B
EPA Memorandum from Henry Habicht
351
C
Calculation and Modeling of Exposure
375
D
Working Paper for Considering Draft Revisions to the U.S. EPA Guidelines for Cancer Risk Assessment
383
E
Use of Pharmacokinetics to Extrapolate from Animal Data to Humans
449
F
Uncertainty Analysis of Health Risk Estimates
453
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G
Improvement in Human Health Risk Assessment Utilizing Site- and Chemical-Specific Information: A Case Study
479
H–1
Some Definitional Concerns About Variability
503
H–2
Individual Susceptibility Factors
505
I
Aggregation
515
J
A Tiered Modeling Approach for Assessing the Risks Due to Sources of Hazardous Air Pollutants
537
K
Science Advisory Board Memorandum on the Integrated Risk Information System and EPA Response
583
L
Development of Data Used in Risk Assessment
591
M
Charge to the Committee
599
N–1
The Case for ''Plausible Conservatism" in Choosing and Altering Defaults
601
N–2
Making Full Use of Scientific Information in Risk Assessment
629
INDEX
641
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SCIENCE
and
DGMENT
in Risk Assessment
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