United State* Science Advisory EPA-SAB-IAQC-92-015
Environmental Board (A-101) January 1992
Protection Agency
v>EPA AN SAB REPORT: REVIEW
OF DRAFT FINAL EXPOSURE
ASSESSMENT GUIDELINES
REVIEW OF THE OFFICE OF
HEALTH AND ENVIRONMENTAL
ASSESSMENT AND THE RISK
ASSESSMENT FORUM'S DRAFT
FINAL GUIDELINES FOR EXPOSURE
ASSESSMENT (DATED MAY 8,
1991) BY THE INDOOR AIR
QUALITY AND TOTAL HUMAN
EXPOSURE COMMITTEE
U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Bouir." -', ' s ••'--:
Chicago, IL 60604-'; ,
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NOTICE
This report has been written as a part of the activities of the Science Advisory Board, a
public advisory group providing extramural scientific information and advice to the
Administrator and other officials of the Environmental Protection Agency. The Board is
structured to provide balanced, expert assessment of scientific matters related to problems
facing the Agency. This report has not been reviewed for approval by the Agency and,
hence, the contents of this report do not necessarily represent the views and policies of the
Environmental Protection Agency, nor of other agencies in the Executive Branch of the
Federal government, nor does mention of trade names or commercial products constitute a
recommendation for use.
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? UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON D.C. 20460
January 13, 1992
OFFICE OF
THE ADNONISTRATOR
SCIENCE ADVISORY BOARD
EPA-SAB-IAQC-92-015
Honorable William K. Reilly
Administrator
U.S. Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
Subject: Science Advisory Board's review of the Draft Final Exposure Assessment
Guidelines (SAB Final Review Draft dated August 8, 1991).
Dear Mr. Reilly:
On September 12-13, 1991, the Indoor Air Quality and Total Human Exposure
Committee of EPA's Science Advisory Board (SAB) reviewed the Agency's Draft Final
Exposure Assessment Guidelines. This is the latest revision of the Agency's exposure
guidelines, the SAB having reviewed and provided advice on earlier versions in 1986 and
1988. The Committee was asked by EPA's Risk Assessment Forum to provide advice on the
following issues: a) Is the document scientifically sound and does it represent current
thinking in exposure assessment? b) Are the concepts of exposure and dose presented in
Chapter 2 consistent and well characterized? c) What are the Committee's views on the
concepts and terms used in describing "high end exposure"? d) Is the presentation in
Chapter 6 concerning the role of uncertainty analysis in exposure assessment, the sources of
uncertainty, and approaches to characterizing uncertainty correct and scientifically adequate?
e) Are the approaches described in Chapter 7 relating to communicating the results of
exposure assessment well characterized and is the level of guidance presented sufficient?
The Committee found the draft document to be very well crafted and complete. It is
scientifically sound, and a major improvement over previous efforts. We were pleased to
observe that the- current draft document includes new developments in the exposure
assessment field since 1988, as well as providing satisfactory resolution of most of the
general and specific SAB concerns contained in our previous reviews. We were also pleased
to note the consistency of the approach and definitions with those in the 1991 National
Academy of Sciences exposure assessment report. We believe that the draft document is
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successful in setting out a broad theoretical framework for considering exposure
assessment. We found the presentation of uncertainty analysis to be
comprehensive, scientifically correct, and that it appropriately highlights the
importance of uncertainty assessment in exposure assessment.
While the document is a vast improvement over earlier drafts, it can be
further improved, especially with respect to the discussion of (high-end) exposures.
Thus, we offer a number of suggestions for improving the draft document. For
example, the discussion of exposure and dose that is presented in the draft
requires clarification and should be more consistent.
We suggest a specific alternative framework for characterizing the (high-
end) exposure. We believe that this will provide a firmer scientific basis for the
expression of the exposure estimators that result from the application of the
exposure assessment guidelines. The original figure (Figure 5.1) in the draft
document provides points of discussion consistent with current risk descriptors.
Our suggested alternative (Figure 1 in our attached report) provides a more logical
basis for reporting the results of an exposure assessment to risk assessors, risk
managers and the scientific community. Its features are described in the attached
report.
The Science Advisory Board is pleased to have had the opportunity to review
this draft final document and to offer our advice. We would appreciate your
response to the advice we have provided in the attached report.
Sincerely,
Dr. Raymond Loehr, Chair
Executive Committee
Science Advisory Board
/}
'
Dr. Morton Lippmann, Chair
Indoor Air Quality and Total Human
Exposure Committee
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NOTICE
This report has been written as a part of the activities of the Science Advisory Board, a
public advisory group providing extramural scientific information and advice to the
Administrator and other officials of the Environmental Protection Agency. The Board is
structured to provide balanced, expert assessment of scientific matters related to problems
facing the Agency. This report has not been reviewed for approval by the Agency and,
hence, the contents of this report do not necessarily represent the views and policies of the
Environmental Protection Agency, nor of other agencies in the Executive Branch of the
Federal government, nor does mention of trade names or commercial products constitute a
recommendation for use.
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ABSTRACT
On September 12-13, 1991, the Indoor Air Quality and Total Human Exposure
Committee of EPA's Science Advisory Board (SAB) reviewed the Agency's Draft Final
Exposure Assessment Guidelines. This; is the latest revision of the Agency's exposure
guidelines, the SAB having reviewed and provided advice on earlier versions in 1986 and
1988. The Committee was asked by the Risk Assessment Forum to provide advice on the
following issues: a) Is the document scientifically sound and does it represent current
thinking in exposure assessment? b) Are the concepts of exposure and dose presented in
Chapter 2 consistent and well characterized? c) What are the Committee's views on the
concepts and terms used in describing "high end exposure"? d) [s the presentation in
Chapter 6 concerning the role of uncertainty analysis in exposure assessment, the sources of
uncertainty, and approaches to characterizing uncertainty correct and scientifically adequate?
e) Are the approaches described in Chapter 7 relating to communicating the results of
exposure assessment well characterized and is the level of guidance presented sufficient?
The Committee found the draft document to be well crafted and complete,
scientifically sound, and a major improvement over previous efforts. In addition, the
Committee noted that the draft document is consistent in approach and definitions with the
1991 National Academy of Sciences exposure assessment report. The Committee was
pleased that the current draft document included new developments in the exposure
assessment field that have taken place since 1988. The Committee was also pleased to
observe that it provided resolution of most of the general and specific SAB comments
provided during its previous reviews. The description and discussion of (high-end) exposure
was awkward and not as well done as the rest of the document, as; noted previously by the
Risk Assessment Forum. In this report, the Science Advisory Board offers an alternate
framework for considering (high-end) exposures, that the Committee believes is sounder
conceptually and analytically. The Committee also offers specific suggestions to improve the
clarity and usefulness of the guidelines.
KEY WORDS: Exposure; dose; high end exposure; exposure assessment; exposure
assessment guidelines.
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U.S. Environmental Protection Agency
Science Advisory Board
Indoor Air Quality and Total Human Exposure Committee
Chairman
Dr. Morton Lippmann, Institute of Environmental Medicine, New York University
Medical Center, Tuxedo, NY
Vice Chairman
Dr. Jan A. J. Stolwijk, School of Medicine, Department of Epidemiology and Public
Health, Yale University, New Haven, CT
Members
Dr. Joan M. Daisey, Indoor Environment Program, Lawrence Berkeley Laboratory,
Berkeley, CA '
Dr. Victor G. Laties, University of Rochester Medical Center, Rochester, NY
Dr. Paul J. Lioy, Department of Environmental and Community Medicine, Robert
Wood Johnson School of Medicine, Piscataway, NJ
Dr. Jonathan M. Samet, New Mexico Tumor Registry, Albuquerque, NM
Dr. Jerome J. Wesolowski, Air and Industrial Hygiene Laboratory, California
Department of Health, Berkeley, CA
Dr. James E. Woods, Jr., College of Architecture and Urban Studies, Virginia
Polytechnic Institute and State University, Blacksburg, VA
Science Advisory Board Staff
Mr. A. Robert Flaak, Assistant Staff Director and Designated Federal Official, Science
Advisory Board, U.S. EPA, Washington, DC
Ms. Carolyn Osborne, Program Assistant, Science Advisory Board, U.S. EPA,
Washington, DC
111
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TAELE OF CONTENTS
1. EXECUTIVE SUMMARY 1
2. INTRODUCTION 3
2.1 Background 3
2.2 Charge to the Committee 4
3. SPECIFIC FINDINGS 6
3.1 Concepts of Exposure and Dose 6
3.2 Discussion of "High End" Exposure 8
3.2.1 Definitions . . 8
3.2.2 High End Range 8
3.2.3 Highest Exposed Individual 9
3.2.4 Defining High End Exposure Graphically 9
3.3 Uncertainty Analysis 9
3.4 Communicating Exposure Assessment 11
Figure 1 - Estimators of levels of exposure within a known (or default)
distribution of exposures to a chemical agent 10
IV
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1. EXECUTIVE SUMMARY
On September 12-13, 1991, the Indoor Air Quality and Total Human Exposure
Committee of EPA's Science Advisory Board (SAB) reviewed the Agency's Draft Final
Exposure Assessment Guidelines. This is the latest revision of the Agency's exposure
guidelines, the SAB having reviewed and provided advice on earlier versions in 1986 and
1988. The Committee was asked by the Risk Assessment Forum to provide advice on the
following issues:
a) Is the document scientifically sound and does it represent current thinking in
exposure assessment?
b) Are the concepts of exposure and dose presented in Chapter 2 consistent and
well characterized?
c) What are the Committee's views on the concepts and terms used in describing
"high end exposure"?
d) Is the presentation in Chapter 6 concerning the role of uncertainty analysis in
exposure assessment, the sources of uncertainty, and approaches to
characterizing uncertainty correct and scientifically adequate?
e) Are the approaches described in Chapter 7 relating to communicating the
results of exposure assessment well characterized and is the level of guidance
presented sufficient?
The Committee found the draft document to be very well crafted and complete,
representing a scientifically sound and a major improvement over previous efforts. Not only
does the current draft document include new developments in the exposure assessment field
since 1988, the Committee was pleased to observe that it also provides resolution of most of
the general and specific SAB comments provided during its previous reviews.
The Committee provided a number of suggestions for improving the draft. The
discussion of exposure and dose that is presented in the draft requires clarification and should
be more consistent. The draft document emphasizes the need to derive dose from exposure
for the purpose of risk assessment. We believe that this argument is too exclusive; most
epidemiological studies provide information on exposure-response relation and not dose-
response relation. Using risk coefficients derived from epidemiological data, risk
characterization is possible without the intermediate step of estimating dose. Therefore, we
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suggest some modification of the general concepts of exposure and dose as presented in the
draft document.
We also offered an alternative framework for characterizing the (high-end) exposures.
The Committee felt that its version will provide a firmer scientific basis for the expression of
the exposure estimators that result from the application of the exposure assessment
guidelines. The original figure (Figure 5.1) in the draft document provides points of
discussion consistent with current risk descriptors. The Committee's revised figure (Figure 1
in this report) provides a more logical basis for reporting the results of an exposure
assessment to risk assessors, risk managers and the scientific community. Its features are
described in the attached report. And finally, the Committee found the presentation of
uncertainty analysis to be comprehensive and scientifically correct. The draft document
presents a strong statement of the importance of uncertainty assessment in exposure
assessment.
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2. INTRODUCTION
2.1 Background
In 1983, the National Academy of Sciences recommended that Federal regulatory
agencies establish guidelines which would promote consistency and technical quality in risk
assessment, and which would maintain the separation between risk assessment and risk
management. As a result of this recommendation, the U.S. EPA began work in 1984 on risk
assessment guidelines for carcinogenicity, mutagenicity, suspect developmental toxicants,
chemical mixtures, and exposure assessment. These guidelines were subjected to Science
Advisory Board (SAB) review prior to their September 1986 public release. The SAB
concluded "...that the 1986 Guidelines for Estimating Exposures provide the framework for
exposure assessment in a useful, diagrammatic way that aids overall understanding."1 It also
concluded that the guidelines were too limited in scope, and advised EPA to prepare
additional guidelines on the measurements of exposure.
In December 1988 the Agency issued its Proposed Guidelines for Exposure Related
Measurements2. This document was reviewed by the Science Advisory Board's
Environmental Effects, Transport and Fate Committee (EETFC) December 1-2, 1988 in
Washington, DC. The Committee concluded that:
...the draft guidelines for exposure-related measurements provide a useful introduction
to the concepts that form the basis for techniques designed to measure and estimate
human exposure. The guidelines represent a logical complement to the Guidelines for
Estimating Exposures that were published and reviewed by the Board in 1986. It is
recommended that these guidelines be integrated into a single guideline document.
The integration will require careful attention to the linkages between measurements
and modeling3.
In 1991, the Agency completed its revised Guidelines for Exposure Assessment4.
This document combines, reformats and substantially updates the two earlier guideline
1 Evaluation of ihe Proposed Guidelines for Exposure-Related Measurements. Report of the Environmental Effects, Transport and Fate
Committee. US EPA Science Advisory Board. EPA-SAB-EETFC-89-020, May 1989, Section 3.1 - reference to earlier SAB review.
: Federal Register 53(232):48830-48853.
' Evaluation of the Proposed Guidelines for Exposure-Related Measurements. Report of the Environmental Effects, Transport and Fate
Committee. US EPA Science Advisory Board. EPA-SAB-EETFC-89-020, May 1989.
4 Science Advisory Board Review Draft, August 8, 1991. The Guidelines were prepared as part of an interoffice guideline development
program under the auspices of EPA's Risk Assessment Forum (RAF).
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documents. The 1991 document includes new developments in the exposure assessment field
since 1988, and offers resolution of general and specific SAB comments provided during its
previous review. The 1991 guidelines, which are consistent with the latest thinking in
exposure assessment (e.g., the recent National Academy of Sciences Report), were developed
by the Agency's Risk Assessment Forum (RAF) and the Office of Health and Environmental
Assessment (OHEA).
On September 12-13, 1991, the Indoor Air Quality and Total Human Exposure
Committee (IAQTHEC) of the SAB met to review the 1991 Draft-Final Guidelines for
Exposure Assessment. The meeting was held in Arlington, Virginia. This report was
reviewed by and received the final approval of the SAB's Executive Committee at its October
29-30, 1991 meeting held in Washington, DC. At that meeting, the Executive Committee
assigned the task of reviewing final edits and granting of final approval to two of its
members who served on behalf of the entire Executive Committee. Their final approval was
granted in early January 1992.
2.2 Charge to the Committee
Based upon a request from the Agency's Risk Assessment Forum, the Science
Advisory Board has been asked to review the Draft Final Exposure Assessment Guidelines
(SAB Review Draft dated August 8, 1991). The Committee has been asked to provide
advice on the following issues:
a. Is the draft document scientifically sound and does it represent current thinking
in exposure assessment?
b. Are the concepts of exposure and dose presented in Chapter 2 of the draft
consistent and well characterized?
c. What are the Committee's views on the concepts and terms used in describing
"high end exposure" (see Chapter 5 of the draft document)?
1) Does the Committee agree with the use and definitions of the terms
"reasonable worst case", "worst case" and "maximum exposure"?
2) Does the subdivision of the "high end" range in the circumstances
described in this section make sense? Will the subdivision of this
range, based on a target percentile, imply that the Agency has more
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faith in the detail it can provide than is warranted? Do the terms
"reasonable worst case" and "maximum exposure" represent good
choices to describe this subdivision? Should new terms be created?
3) Does the Committee concur with the discussion of the difficulties
associated with characterizing the highest actual or potentially exposed
individual?
d. Is the presentation in Chapter 6 of the draft document concerning the role of
uncertainty analysis in exposure assessment, the sources of uncertainty, and
approaches to characterizing uncertainty correct and scientifically adequate?
e. Are the approaches described in Chapter 7 of the draft document relating to
communicating the results of exposure assessment well characterized and is the
level of guidance presented sufficient?
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3. SPECIFIC FINDINGS
3.1 Concepts of Exposure and Dose
EPA Question: Are the concepts of exposure and dose that are presented in Chapter
2 of the draft document consistent and well characterized?
The Committee considers the proposed guidelines for exposure assessment to be an
important advance over the previous versions, and an excellent documentation of progress
since the drafting of the previous guidelines. One significant improvement is the
development of definitions and concepts that are mutually consistent. This alone will bring
about a considerable simplification and sharpening of exposure assessments as well as the
communication of these exposure assessments to all clients, and especially to the risk
assessors.
There is still some confusion between concepts of dose and dose rate as well as that
of delivered dose and dose rate. These terms are being used in the document in a somewhat
interchangeable and not mutually exclusive way. The Committee feels that it may be
unnecessary and possibly counter-productive to try and account for all the terms that have
ever been used in different settings that may have overlapping definitions in different
disciplines. The "absorbed dose" has somewhat different meanings in dermatology, radiation
biology, and toxicology/pharmacology. The "delivered dose" is a concept that clearly
overlaps. It might be wiser to use one kind of terminology per concept and to add the
various dose alternatives to a glossary.
The draft document emphasizes the need to derive dose from exposure for the purpose
of risk assessment. We believe that this argument is too exclusive; most epidemiological
studies provide information on exposure-response relation and not dose-response relation.
Using risk coefficients derived from epidemiological data, risk characterization is possible
without the intermediate step of estimating dose. For example, the risk assessment for ETS
that was conducted by EPA used an empirically derived exposure-response relation. Radon
risks are also estimated without calculating dose. The exposure-response relation observed in
studies of underground miners is extrapolated to the indoor environment. Dose
characterizations have been carried out,, but primarily for the purpose of addressing
uncertainties in this extrapolation. Therefore, we suggest some modification of the general
concepts of exposure and dose, as they are laid out in the draft document. In a number of
locations the document indicates that it is limited to consideration of the exposure of humans
to chemical agents, and that some of the considerations and treatment may be of use in the
assessment of exposures to microbiological agents, and to exposures of non-human species.
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The Agency Staff may wish to consider giving the Guidelines a more appropriate title such as
"Guidelines for the Assessment of Human Exposures to Chemicals"?
There were a number of instances throughout the draft document where at the ends of
sections and chapters the Agency provided advice and cautions. We believe these should
have been placed in more prominent positions in the beginning of the section or chapter.
Some of these comments were cautions about the process that the exposure assessor should
observe, and about limitations to the power and applicability of assessment procedures.
Others dealt with the insights and training to develop judgments which often need to be made
before the design of the assessment process is accepted. For example, this could be
expressed in Figure 2-1 of the draft document where to the right of the "organ" symbol one
should see an arrow designating "elimination".
The Committee was advised at its meeting that these guidelines are aimed at exposure
assessors and the people requesting such assessments, those who will be using these exposure
assessments in carrying out risk assessments, and finally to those who will be making risk
management decisions. In general, many of these individuals will have different disciplinary
backgrounds. We were pleased at the recognition of this diversity in the draft document, and
in general urge that as much as possible be done to establish effective linkages between
exposure assessors and their clients before a protocol for an exposure assessment is
committed to or approved. The exposure assessor should be familiar with the ways an
exposure assessment is used later, and expend a serious effort in anticipating this use.
Careful design, which takes into account what is already known about the fate of the agent,
and the biological action of the agent in the human body will allow a much more useful
exposure assessment. As an example, the averaging time in an exposure assessment is very
likely to be affected by events inside the body. Similarly, peak exposure conditions are of
great importance in some risk assessments and immaterial in others. Our understanding of
the processes within the body are progressing rapidly and the exposure assessment guidelines
should anticipate that more such developments will occur.
The Agency noted in the draft document that there is a need to integrate the exposure
assessment with the other elements of the risk assessment and the risk management process.
In Chapter 5 of the draft there is considerable discussion of the connections between
exposure assessment and risk assessment. The Committee feels that the focus of Chapter 5
wavered between exposure assessment and risk assessment. Too much of the discussion and
the presentation is concerned with risk assessment, and therefore diverts from exposure
assessment.
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3.2 Discussion of "High End" Exposure
EPA Question: What are the Committee's views on the concepts and terms used in
describing "high end exposure" (see Chapter 5 of the Draft document)?
We are concerned about a definition of "high end exposure" as simply being above
about the 90th percentile, as well as the extension of this boundary to describe risk. When
applied to risk, this terminology has the potential to make it seem that all risks in the high
end are comparable, regardless of the nature and severity of the health effect. We do not
recommend replacing the existing terminology with potentially ambiguous terminology.
3.2.1 Definitions
EPA Question: Does the Committee agree with the use and definitions of the terms
"reasonable worst case", "worst case" and "maximum exposure"?
We recognize the historical significance of the terms "reasonable worst case", "worse
case", "maximum exposure";-and "maximally exposed individual (MEI)". We reviewed
these terms in the context of the Draft Final Exposure Assessment Guidelines, and found
them incongruent with the quantitative approach recommended in the text. We feel that these
terms have only qualitative value.
3.2.2 High End Range
EPA Question: Does the subdivision of the "high end" range in the circumstances
described in this section make uense? Will the subdivision of this range, based on a
target percentile, imply that the Agency has more faith in the detail it can provide
than is warranted? Do the terms "reasonable worst case" and " maximum exposure"
represent good choices to describe this subdivision? Should new terms be created?
The subdivision "high end" (> 90th percentile) is consistent with the risk descriptor
"high risk". In fact, it places similar weights and probably similar "uncertainties" on the
analysis and evaluation of population exposure. Other exposure estimators which parallel
specific risk descriptors are: a) the msan or median exposures; b) the definition or
estimation of an actual distribution of population exposures; c) a default exposure distribution
option; and d) a bounding estimate of exposure.
The targeted "high end" percentile is sufficiently broad to minimize over-reliance on a
single number. The confidence in any value or group of values will be achieved by
acquiring more data on background exposures, analogous exposures, and/or high exposure
8
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sub-groups that are not participating in highly unusual personal behavior (e.g. sniffing glue,
cleansing hands in gasoline). No new terms should be developed for estimators of exposure.
An exposure assessment should present the statistical features of a distribution with
interpretation, and any bounding estimates, and their inherent assumptions, to the risk
assessor.
The extent of protection in any given case should explicitly be stated in terms of the
percentile of the population considered at risk, i.e., if the intent is to protect 95 or 99% of
the population, the risk estimates or guidelines should be stated in those terms.
3.2.3 Highest Exposed Individual
EPA Question: Does the Committee concur with the discussion of the difficulties
associated with characterizing the highest actual or potentially exposed individual?
The Committee concurs with the discussion on the difficulties with characterization of
the highest actual or potentially exposed individuals.
3.2.4 Defining High End Exposure Graphically
Taking into account the above answers, and the discussion with EPA Staff at the
meeting, the Committee reached consensus on a recommended modification of Figure 5.1
(see page 76 of the draft document). The revised version provides a basis for the expression
of the exposure estimators that result from the application of the exposure assessment
guideline. Figure 5.1 provides points of discussion consistent with current risk descriptors.
Our revision of that figure (see Figure 1, below) provides a more logical quantitative basis
for reporting the results of an exposure assessment to risk assessors, risk managers and the
scientific community. We believe that these revisions to Figure 5.1 are an amalgamation and
simplification of the ideas expressed within Chapter 5.
3.3 Uncertainty Analysis
EPA Question: Is the presentation in Chapter 6 concerning the role of uncertainty
analysis in exposure assessment, the sources of uncertainty, and approaches to
characterizing uncertainty correct and scientifically adequate?
The Committee found the presentation of uncertainty analysis in Chapter 6 of the
document to be comprehensive and scientifically correct. The Chapter presents a strong
statement of the importance of uncertainty assessment in exposure assessment. The approach
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Figure 1
Recommended Alternative to Figure 5.1 of the Draft EPA Document
ESTIMATORS OF LEVELS OF EXPOSURE
WITHIN A KNOVW (OR DEFAULT*) DISTRIBUTION OF
EXPOSURE TO A CHEMICAL AGENT
3?
HIGH END OF EXPOSURE
Semi-Quantitative
Terminology
REASONABLE
WORST CASE
WORST CASE
[MAXIMUM EXPOSURE) i I ME!
Primary features of Figure 1 are the following:
a. Separation of the semi-quantitative measures of exposure from the quantitative estimators of
exposures depicted in the figure.
b. Emphasis on determining or estimating a distribution of population exposure (not concentration) and
selection of a default distribution when the actual distribution is not available or too little information can be
obtained to estimate the distribution.
c. Identification of several statistical ijstimators of exposure: 1) 50th percentile; 2) 90th percentile, the
"High End", 3) 95th percentile, 4) 98th percentile and a range for bounding estimates.
d. The Bounding Estimate is an estimate of individual exposure or dose where the estimate is
intentionally constructed to be higher than the individual in the distribution having the 99.9th percentile
exposure. A bounding estimate can be useful in constructing statements that the exposure is "not greater than
•
* Measured Distribution of Exposure.
** The Default Distribution - in the absence of sufficient data to establish the form of the distribution •
of exposure (not concentrations) for the population of interest, a default distribution using a log-normal format
should be employed. It should be defined on the basis of median and geometric standard deviation values
established using the best information available on the concentrations and the human activity patterns that lead to
exposure.
10
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presented in Chapter 6 correctly recognizes that uncertainty analysis cannot be done by
following a formula, that such a process can range from a very simple to a quite complex
process, and that the process requires scientific judgment. Both qualitative (choice of model
or measurement method, underlying assumptions, etc.) and quantitative aspects of uncertainty
are recognized and clearly presented. The types of uncertainties that must be considered
have been clearly identified and the various approaches which may be taken to evaluate
and/or estimate uncertainty are scientifically correct and adequate.
3.4 Communicating Exposure Assessment
EPA Question: Are the approaches described in Chapter 7 of the draft document
relating to communicating the results of exposure assessment well characterized and is
the level of guidance presented sufficient?
The Committee found the approaches described to be clear and orderly. However,
we believe that the chapter could use more emphasis on communicating and interpreting the
results. We discussed the possibility of a more standardized exposure assessment format, but
recognized that this might stifle creativity and result in formats that were "etched in stone".
As a result, we do not recommend such a course.
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t 4,
Distribution List
Administrator
Deputy Administrator
Assistant Administrators
Deputy Assistant Administrator for Research and Development
EPA Regional Administrators
EPA Laboratory Directors
Director, Risk Assessment Forum
Director, Office of Health and Environmental Assessment
Director, Exposure Assessment Group
EPA Headquarters Library
EPA Regional Libraries
EPA Laboratory Libraries
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United States Science Advisory EPA-SAB-IHEC-ADV-99-004 <
Environmental Board February 1999
Protection Agency Washington. DC www.9pa.gov/Sab
&EPA AN SAB ADVISORY: THE
NATIONAL HUMAN
EXPOSURE ASSESSMENT
SURVEY (NHEXAS) PILOT
STUDIES
PREPARED BY THE INTEGRATED
HUMAN EXPOSURE COMMITTEE
(IHEC) OF THE SCIENCE
ADVISORY BOARD (SAB)
U.S. Environmental Protection Agency
Region 5, Library (Pt-12J)
77 West Jackson Boulevard, 12th Ftooi
Chicago, It 60604-3590
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