National Academies Press: OpenBook

Science and Judgment in Risk Assessment (1994)

Chapter: Front Matter

Suggested Citation:"Front Matter." National Research Council. 1994. Science and Judgment in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2125.
×

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

Suggested Citation:"Front Matter." National Research Council. 1994. Science and Judgment in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2125.
×

Page ii

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

Suggested Citation:"Front Matter." National Research Council. 1994. Science and Judgment in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2125.
×

Page iii

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

Suggested Citation:"Front Matter." National Research Council. 1994. Science and Judgment in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2125.
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Page iv

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

Suggested Citation:"Front Matter." National Research Council. 1994. Science and Judgment in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2125.
×

Page v

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

Suggested Citation:"Front Matter." National Research Council. 1994. Science and Judgment in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2125.
×

Page vi

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.

Suggested Citation:"Front Matter." National Research Council. 1994. Science and Judgment in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2125.
×

Page vii

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

Page viii Cite
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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.

Suggested Citation:"Front Matter." National Research Council. 1994. Science and Judgment in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2125.
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Page x

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

Suggested Citation:"Front Matter." National Research Council. 1994. Science and Judgment in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2125.
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Page xi

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

Suggested Citation:"Front Matter." National Research Council. 1994. Science and Judgment in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2125.
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Page xii

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

Page xiii Cite
Suggested Citation:"Front Matter." National Research Council. 1994. Science and Judgment in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2125.
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Page xiii

 

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

Suggested Citation:"Front Matter." National Research Council. 1994. Science and Judgment in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2125.
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Page xiv

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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The public depends on competent risk assessment from the federal government and the scientific community to grapple with the threat of pollution. When risk reports turn out to be overblown--or when risks are overlooked--public skepticism abounds.

This comprehensive and readable book explores how the U.S. Environmental Protection Agency (EPA) can improve its risk assessment practices, with a focus on implementation of the 1990 Clean Air Act Amendments.

With a wealth of detailed information, pertinent examples, and revealing analysis, the volume explores the "default option" and other basic concepts. It offers two views of EPA operations: The first examines how EPA currently assesses exposure to hazardous air pollutants, evaluates the toxicity of a substance, and characterizes the risk to the public.

The second, more holistic, view explores how EPA can improve in several critical areas of risk assessment by focusing on cross-cutting themes and incorporating more scientific judgment.

This comprehensive volume will be important to the EPA and other agencies, risk managers, environmental advocates, scientists, faculty, students, and concerned individuals.

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