EPA/625/3-91/022
February 1992
PEER REVIEW WORKSHOP REPORT
ON A
FRAMEWORK FOR ECOLOGICAL RISK ASSESSMENT
Risk Assessment Forum
U.S. Environmental Protection Agency
Washington, DC 20460
Printed on Recycled Paper
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DISCLAIMER
This document has been reviewed in accordance with U.S. Environmental Protection Agency
policy and approved for publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
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CONTENTS
Acknowledgements .:.... vi
Foreword yii
Preface viii
1. INTRODUCTION 1
1.1. Scope and Role of the Peer Review Panel 1
1.2. Peer Review Process 1
2. OVERALL COMMENTS AND RECOMMENDATIONS 4
2.1. Overall Recommendations 4
2.2. Specific Recommendations to Improve the Ecological
Risk Assessment Paradigm 4
2.3. Importance of Verification, Monitoring and Research 7
2.4. Issues Related to Overall Framework 8
3. COMMENTS ON THE PROBLEM DEFINITION COMPONENT 11
3.1. Issues Recommended for Discussion in the Framework
Document 11
3.2. Other Recommendations of the Panel 14
4. COMMENTS ON THE CHARACTERIZATION OF STRESS COMPONENT 15
4.1. Recommendations of the Panel 15
4.2. Other Recommendations 18
5. COMMENTS ON THE CHARACTERIZATION OF ECOLOGICAL EFFECTS
COMPONENT 19
6. COMMENTS ON THE RISK CHARACTERIZATION COMPONENT . 22
6.1. Adequacy of the Framework Document under Stated Definition 22
6.2. Need for Expansion of the Definition of Risk Characterization 24
6.3. Treatment of Expanded Definition in the Framework
Document 24
7. REFERENCES 27
in
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APPENDIX A MEETING MATERIALS
Agenda
List of Participants
List of Observers .
A-l
A-5
A-6
APPENDIX B PREMEETING MATERIALS
Draft Framework for Ecological Risk Assessment
Issues Papers
. B-l
B-57
IV
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LIST OF FIGURES
Figure 1. EPA's Draft Ecological Risk Assessment Paradigm 3
Figure 2. Ecological Risk Assessment Framework 6
Figure 3. Relationship Among Research, Monitoring and Verification,
and Improved Ecological Risk Assessment Tools . • • • 8
Figure 4. Problem Definition Component • 12
Figure 5. Characterization of Stress Component 16
Figure 6. Characterization of Ecological Effects Component 20
Figure 7. Risk Characterization Component 26
TABLES
List of Participants • 2
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ACKNOWLEGEMENTS
Many individuals contributed to this report. James Fava, Lawrence Barnthouse, Mark Harwell,
Kenneth Reckhow, and James Falco prepared the chairperson's summary and, prior to the workshop,
worked with the U.S. Environmental Protection Agency (EPA) staff to plan the meeting. William van
der Schalie, the Risk Assessment Forum coordinator for ecological effects, coordinated all workshop
and document development activities with the assistance of William Wood, associate staff director for
the Forum. Susan Brager of Eastern Research Group, Inc., an EPA contractor, worked with Dr. van
der Schalie, Dr. Wood, and Dr. Fava in all phases of this project, providing administrative and
logistical support.
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FOREWARD
In 1986, EPA issued five guidelines for health risk assessment (51 Federal Register 33992-
34054, September 24, 1986). Based on a 10-year effort, these guidelines set forth risk assessment
principles, concepts, and methods for cancer, developmental effects, mutagenic effects, exposure, and
chemical mixtures. Since then,-EPA has developed guidance in other health risk areas, for a total of
nine guidelines for health risk assessment in various phases of development. During this period,
individual EPA programs have generated program-specific guidance for ecological effects, but none
has been developed for EPA as a whole.
At the behest of the EPA Risk Assessment Council, EPA's Risk Assessment Forum has
sponsored three activities related to the development of Agency-wide ecological risk assessment
guidelines: (1) compilation of case studies to illustrate the state of the practice in ecological
assessments; (2) preparation of a long-term plan for developing ecological risk assessment guidelines;
and (3) development of a framework for ecological risk assessments that will offer a simple and
flexible structure for conducting and evaluating ecological risk assessments at EPA. The proposed
framework also is intended to contribute organizing principles for future ecological risk assessment
guidelines and is expected to evolve with experience.
A seven-person EPA workgroup, chaired by Susan Norton, Donald Rodier, and Suzanne
Marcy, prepared a draft EPA report entitled "Framework for Ecological Risk Assessment" (framework
draft), which incorporates comments from EPA reviewers on earlier drafts. The framework draft also
benefitted from insights gained at a February 1991 National Academy of Sciences (NAS) Conference
held at the Airlie House in Warrenton, Virginia, and from recommendations of EPA's Science
Advisory Board.
Ecologists and ecotoxicologists from academia, consulting firms, and Government (State and
Federal) brought expertise in a wide range of relevant disciplines to the Risk Assessment Forum's May
1991 peer review workshop for the framework draft. EPA did not expect to cover all of the many
principles, concepts, and methods that are important for ecological risk assessment in this one
workshop. Rather, EPA asked for expert opinion on the logic, scientific validity, and utility of the
principles proposed in the framework draft as general guidance for EPA risk assessors. EPA expected
the workshop participants to develop consensus on some parts of the document and useful
recommendations for change on others. Members of the public and EPA scientific staff attended the
workshop as observers.
The workshop was highly productive. Most significantly, the 20 peer reviewers, some of
whom had participated in the February 1991 NAS workshop and EPA's April 1991 ecological risk
strategic planning workshop, agreed during the discussion that the basic elements of the ecological risk
assessment process, rather than substantive guidance, should be the focus of the final framework
report. Accordingly, the peer reviewers developed information and identified issues to assist EPA in
this task.
Dorothy E. Patton, Ph.D.
Chair
Risk Assessment Forum
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PREFACE
On May 14,1991, EPA convened a 3-day workshop in Rockville, Maryland, for discussion
and peer review of the draft report "Framework for Ecological Risk Assessment" (56 Federal Register
20223; May 2, 1991). The framework draft and the workshop were part of a new EPA program for
developing risk assessment guidelines for ecological effects.
This workshop report highlights issues and recommendations developed at the Rockville
Workshop, which was chaired by Dr. James Fava of Roy F. Weston, Inc. The report features the
chairperson's summary of the workshop findings and includes a copy of the framework draft that was
the subject of the Rockville peer review. Based on the highly constructive and useful suggestions
presented in the chairperson's summary, EPA is simplifying and streamlining the framework draft for
publication in early 1992 as a step toward future development of EPA guidelines for ecological risk
assessment.
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1. INTRODUCTION
The U.S. Environmental Protection Agency (EPA) has established a program through its Risk
Assessment Forum to develop ecological risk assessment guidelines. As part of this effort, JEPA
developed a draft technical framework document for ecological risk assessment The technical
framework will provide general guidance and promote consistency within EPA on the basic principles
for conducting ecological risk assessments. The proposed framework also is intended to provide
organizing principles for future ecological risk assessment guidelines in specific subject areas.
1.1. SCOPE AND ROLE OF THE PEER REVIEW PANEL
In order to improve the technical basis for ecological risk assessment guidelines, EPA
requested an independent peer review of the draft "Framework for Ecological Risk Assessment," which
was prepared by the Risk Assessment Forum (EPA, 1991). A panel of 20 experts (see table 1)
participated in the peer review. These individuals represent expertise in a wide range of disciplines
and experience in ecological risk assessment.
1.2. PEER REVIEW PROCESS
The peer review of the draft framework involved three steps. First, the draft framework
document was mailed to each reviewer; each reviewer then prepared comments that were distributed to
all reviewers. Second, a peer review workshop was held to obtain an independent review of the logic,
scientific validity, and utility of the principles that were proposed in the framework document as
general guidance on ecological risk assessment Consensus was reached on some parts of the
document, and recommendations for change were made for other parts. Third, a written report was
prepared, summarizing the results of the workshop and presenting the panel's recommendations to
EPA. This report represents that third step.
EPA's draft "Framework for Ecological Risk Assessment" presents an ecological risk
assessment paradigm based on the National Academy of Sciences (NAS) human health risk assessment
paradigm, which was published in 1983 (NRG, 1983). The ecological risk assessment paradigm
presented in the draft framework consists of four components (figure 1): conceptual framework,
hazard assessment, exposure assessment and risk characterization. One of the panel's
recommendations is to use more ecologically relevant terms for three of these components: "problem
definition/scoping" replaces "conceptual framework," "characterization of ecological effects" replaces
"hazard assessment," and "characterization of stress" replaces "exposure assessment" These suggested
terms are used throughout this summary report.
Because the peer reviewers' charge was to conduct an independent review of the draft
framework and make suggestions to improve the framework, the panel's comments and
recommendations follow the draft framework's organization. The panel's overall recommendations are
presented hi section 2; comments on the conceptual framework (problem definition/scoping)
component are presented in section 3; suggestions on exposure assessment (characterization of stress)
and hazard assessment (characterization of ecological effects) are presented in sections 4 and 5; and,
finally, comments on the risk characterization component are discussed in section 6.
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Table 1. List of Participants
Workshop Chair
• James Fava, Roy F. Weston, Inc.
Workshop Topic Area Leaders
• Lawrence Bamthouse, Oak Ridge National Laboratory
• James Falco, Battelle Pacific Northwest Laboratory
• Mark Harwell, University of Miami
" Kenneth Reckhow, Duke University
Other Participants
William Adams, ABC Laboratories
John Bascietto, U.S. Department of Energy
Raymond Beaumier, Ohio Environmental Protection Agency
Harold Bergman, University of Wyoming
Nigel Blakeley, Washington Department of Ecology
Alyce Fritz, National Oceanic and Atmospheric Administration
James Gillett, Cornell University
Michael Harrass, U.S. Food and Drug Administration
Ronald Kendall, Clemson University
Wayne Landis, Western Washington University
Ralph Portier, Louisiana State University
John Rodgers, University of Mississippi
Peter Van Voris, Battelle Pacific Northwest Laboratory
James Weinberg, Woods Hole Oceanographic Institution
Randall Wentsel, U.S. Army Chemical Research, Development and Engineering Center
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Conceptual Framework
Stressor and Environmental Characterization
Endpoint Identification and Selection
Conceptual Model Formation
Hazard Assessment
Hazard Identification
Stressor Response
Exposure Assessment
Risk Characterization
Figure 1. EPA's Draft Ecological Risk Assessment Paradigm
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2. OVERALL COMMENTS AND RECOMMENDATIONS
The peer review panel would like to express appreciation for the opportunity to participate in
the peer review of the draft "Framework for Ecological Risk Assessment." The panel is pleased to
provide assistance in preparing a framework that EPA and the Risk Assessment Forum have indicated
will be the underlying foundation from which ecological risk assessment guidelines will be developed.
The individuals within EPA who prepared the draft framework should be commended for an excellent
job, and the panel would like to recognize the performance of those individuals at EPA who prepared
the draft document for review.
While the panel was mostly positive about the draft framework document, members were in
consensus that there are issues associated with ecological risk assessment that can only be addressed
more broadly throughout EPA. These issues and the panel's recommendations are presented below.
2.1. OVERALL RECOMMENDATIONS
EPA's management structure and approach to ecological risk assessment should be
examined. During the workshop, there was considerable discussion about the importance of
conducting ecological risk assessments in an integrated fashion. Because of the importance of
effectively using interdisciplinary teams to perform ecological risk assessments, the panel believes that
the current EPA organization should be critically examined to identify ways to foster and facilitate the
effective implementation of consistent and comprehensive ecological risk assessments. For example,
the current separation of the exposure and hazard assessment technical staffs in different branches,
which might inhibit such integration, should be carefully considered.
Ecological risk assessment terminology should be standardized throughout EPA. A
terminology workgroup should be formed to provide Agency-wide consistency. Once EPA produces
the framework, strategic plans, and guidelines documents, the terminology for ecological risk
assessment used by other agencies will probably follow EPA's lead.
2.2. SPECIFIC RECOMMENDATIONS TO IMPROVE THE ECOLOGICAL RISK
ASSESSMENT PARADIGM
One of the first and major areas of discussion by the panel was Ihe draft ecological risk
assessment paradigm developed by EPA. The panel agreed that, while using the National Academy of
Sciences (NAS) human health risk assessment paradigm as a basis was a good idea, that model should
not be adopted directly. There are many important differences between ecological and human health
risk assessment. For example, ecological risk assessment must include consideration of stressors other
than chemicals for evaluation. Also, ecological risk assessment concerns multiple species, populations,
communities, and ecosystem levels, while human health risk assessments focus on one species.
EPA should develop a paradigm for ecological risk assessment and then, if desired,
reference how the NAS human health risk assessment is similar to or is related to the ecological
risk assessment. Consistent with this recommendation, the panel strongly believes that the definitions
for the components of the ecological risk assessment paradigm should be ecologically based, not
human health based. Also, the panel recommends that EPA refer to the ecological risk assessment
paradigm as a framework. Throughout the remainder of this report, the panel will refer to the overall
ecological risk assessment paradigm as the ecological risk assessment framework.
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After much discussion, the panel developed a modified ecological risk assessment framework.
The modified framework is based on the one developed by EPA (see figure 1). Because the panel
recognizes EPA's desire to maintain similarity with the NAS human health risk assessment framework,
the modified framework presented here (figured) should be viewed as an evolution of the
NAS framework, recognizing distinct differences between human health and ecological risk
assessment The panel would like to emphasize that the modified framework is presented to EPA for
review and consideration. As EPA evaluates and develops the Technical Framework for Ecological
Risk Assessment, the panel's modified framework should be used as the basis for that development.
Several major distinctions were incorporated into the modified framework. For ecological risk
assessment, Hie framework must be able to incorporate both chemical and nonchemical stressors.
Thus, the panel suggests the term "characterization of stress" as a replacement for the term "exposure
assessment," which was used in the draft framework. (Exposure assessment is generally perceived as
referring to chemical exposure.) Second, ecological risk assessments must be able to incorporate
potential effects at various levels of biological organization (e.g., population, community, and
ecosystem). The panel recommends that EPA use the term "characterization of ecological effects
rather than "hazard assessment," as used in the draft framework. Using the suggested term will help
eliminate the inconsistent use of the term "hazard assessment," which has come to have several
different meanings.
Third, while ecological risk assessment must be considered a scientific and technical process,
the panel recognizes that policy influences ecological risk assessment. The reviewers believe that
policy input would be appropriate for the components of problem definition/scoping and risk
characterization. However, me analysis sections of Hie characterization of stress and ecological effects
must be allowed to proceed without policy influence. The panel agrees that risk assessors have the
responsibility to present scientific and technical recommendations as a key output of ecological risk
assessment. The panel also agrees that the final decision-making and risk management must take other
factors into account that are not addressed during the ecological risk assessment. Therefore, the panel
supports the need for a risk management component outside the ecological risk assessment framework.
Fourth, the draft framework describes two distinct components for hazard assessment and
exposure assessment. The panel believes strongly that these two components are not separate activities
that can proceed side by side, but are, in fact, interrelated. The modified framework indicates this
interrelationship as such, by including the two within one box with a dotted line between them. The
acceptance and recognition of this important element of ecological risk assessment have implications
for how the assessments are performed. Along with an understanding of this interrelationship, the
panel recommends that for ecological risk assessment to proceed, a team approach with qualified
individuals is required.
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Ecological Risk Assessment
Problem Definition/Scoping
Characterization
of
Stress
Characterization
of
Ecological
Effects
Decision-Making/
Risk Management
Verification
and
Monitoring
Figure 2. Ecological Risk Assessment Framework
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2.3. IMPORTANCE OF VERIFICATION, MONITORING, AND RESEARCH
EPA should adopt a long-term program to verify, monitor, and conduct research to improve
ecological risk assessment. The reviewers spent considerable time discussing the importance of using
verification, monitoring, and research to improve the framework and tools of ecological risk
assessment. The interrelationship among these components is shown hi figure 3.
The panel debated whether verification and monitoring should be included within the
ecological risk assessment framework. Reviewers strongly agreed that verification and monitoring are
essential to (1) determine the overall effectiveness of the ecological risk assessment framework; (2)
provide feedback to adjust and improve the framework in future years; (3) provide feedback to
evaluate the effectiveness and practicality of current policy and help adjust policy, as necessary; and
(4) provide feedback on scientific analysis of the framework to help identify requirements for new or
improved scientific tools. The foregoing interrelationships underscore the adaptive nature of ecological
risk assessment, which cannot be cast in concrete but, rather, must involve learning about and living
with natural systems.
Because overall verification is not included within the ecological risk assessment framework,
EPA must develop and perform the necessary verification within its other programs. Whether
current efforts for monitoring (e.g., the Environmental Monitoring and Assessment Program [EMAP])
are adequate is unknown. However, the panel believes that other forms of verification (e.g., quality
assurance/quality control (QA/QQ) are inadequate to meet the specified needs. Focused efforts are
needed to evaluate and verify the effectiveness of the ecological risk assessment framework as it is
being applied. For example, in the Superfund program or the Toxic Substances Program, sites and
decisions must be revisited and their effectiveness must be determined.
The framework document should discuss the dichotomy between the ideal ecological risk
assessment, as outlined in the developed framework, and the practicalities of present assessments by
EPA. Clearly the need to balance the framework between ideal and practical considerations is critical
to the successful use of the framework. Presenting ecological risk assessment too idealistically,
without clarification of what is currently practicable, will establish unrealistic expectations. On the
other hand, presenting ecological risk assessment only as it is practiced today will establish
expectations mat are too low, will reduce the likelihood of scientific advances, and will fail to meet
the anticipatory needs of EPA in addressing the priority ecological risks identified by the Science
Advisory, Board (SAB, 1990).
To fill the gap between the ideal and current risk assessments, EPA should establish a
research program that is focused to meet the ideal ecological risk assessment framework. The
relationship among research, monitoring and verification, and improved ecological risk assessment
tools is presented in figure 3. The panel strongly recommends that EPA use the developed framework
as the foundation not only for ecological risk assessment guidelines, but also for focused long-term
research, monitoring, and verification programs. Much of ecological risk assessment also requires a
more substantial commitment to basic research in both the biological and physical sciences. While
there are many documents that discuss the research needs of ecological risk assessment, one document
that might be useful to review is "Research Priorities in Environmental Risk Assessments" (SETAC,
1987).
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Monitoring
and
V Verification J'
Ecological
I Risk I
V Assessment/
Figure 3. Relationship Among Research, Monitoring and
Verification, and Improved Ecological Risk Assessment Tools
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2.4. ISSUES RELATED TO OVERALL FRAMEWORK
The framework document should be limited to the discussion of the first and second levels
of flowcharts (see figures included in this report). Because of Hie evolving science and application of
ecological risk assessment, more detailed presentations of methods should be included in the guidelines
to be developed. A more detailed discussion of the state of the practice also should be part of the
various guidelines and technical support documents proposed as part of the ecological risk assessment
strategic planning process.
The framework document should provide guidance in addressing ecological risk assessment
as a tiered approach. The panel also discussed the use of tiered approaches during the analysis phase
of ecological risk assessment. Ecological risk assessments differ in the breadth and depth of the
required data collection and analysis. A tiered approach would offer the opportunity to approach
ecological risk assessments from basic data sets (e.g., LD50 and LC50) or from requirements for more
complex data sets (e.g., field studies). Of critical concern are the triggers (or decision points) that
would move an ecological risk assessment from a lower case data requirement, to a more sophisticated
study, to full-scale field studies providing complex interactive data. Movement through the tiers
according to perceived data needs for evaluating certain ecological risks must be carefully considered.
Also, field validation using at least one appropriate model system (e.g., stream, lake, cropland,
rangeland) should be designed and implemented to test the ecological risk assessment process. In
other words, how confident (or how uncertain) are the predictions that a certain chemical or
nonchemical stressor might cause an aberration in the environment? Examples of some triggers to
more extensive data collection and analysis are the following:
• Specific regulatory requirements.
• Serious consequences associated with potential impacts.
• Lack of adequate data for extrapolations needed to proceed from the measurement
endpoints to the assessment endpoints.
• Potential for irreversible consequences.
The state of the practice of ecological risk assessment constitutes an expert judgment process
with a range of methodologies, including qualitative and quantitative tools. Another topic of
discussion was the use of the quotient method in ecological risk assessment. The panel was concerned
about the limitations of the quotient method and strongly recommended that EPA develop or expand
its research program to investigate innovative ways to integrate data for making risk characterizations.
The quotient method should be used in ecological risk assessment only in the context of wise use of
professional judgment and should not exceed professional judgment during decision-making. Another
suggestion was the addition of a range of values in the numerator and denominator used hi the
quotient method.
Given the importance of professional judgment in the final decision-making process, the panel
recommended that EPA incorporate language into the final framework document to express the need
for qualified environmental scientists and ecologists to participate in ecological risk assessments.
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The issues associated with uncertainty should be given much greater attention throughout
the framework document. There are many different components of uncertainty, ranging from
fundamental lack of understanding about ecological systems and anthropogenic stresses, to
measurement error and natural stochasticity. Some aspects are reducible with further research; others
are not. Consequently, environmental decision-making must proceed in the presence of uncertainties.
The presence of uncertainties must be recognized throughout the ecological risk assessment process,
and the types and magnitudes of the various components of uncertainty must be identified at each step
in the process.
These discussions should be carefully worded to convey the sense of uncertainties without
implying that little or nothing is known about ecological systems and their responses to anthropogenic
activities. Discussion of uncertainties should include such issues as the use of sensitivity analyses,
availability of qualitative and quantitative methods, precision versus accuracy, and QA/QC
requirements.
The framework document should be written to ensure that it will not be outdated quickly,
unless research illustrates that the basic framework needs revision. The panel emphasizes that the
ecological risk assessment framework document should be conceptually sound in order to be the basis
for future ecological risk assessment efforts, including guidelines. The panel strongly agrees that
ecological risk assessment performance will improve greatly over the next 5 to 10 years as research
enhances understanding of basic ecological processes and improves the tools. The scientific tools will
be improved and our basic understanding will be enhanced. Thus, the guidelines, not the framework,
will need to be revised.
The framework document should clearly state its objectives, the intended audience, and
where the framework fits into the overall ecological risk assessment strategy. The document should
be written so that it can be understood by decision-makers and risk assessors. It is recommended that
professional editing be used to highlight the important points and terms in the document. One
approach that should be considered is having sidebar information that could help communicate critical
definitions and concepts without disrupting the flow of the text. Good examples of this approach are
found in the policy-makers' summary document produced for the EPA Reports to Congress on global
climate change and in the summary document of the Science Advisory Board's "Reducing Risks"
report (SAB, 1990).
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3. COMMENTS ON THE PROBLEM DEFINITION COMPONENT
The peer review panel decided that the term "problem definition/scoping" better represents the
initial component of the framework than does the draft framework document's term "conceptual
framework." There is a clear need to examine the nature of the specific environmental problem at
hand initially and then to develop a conceptual model of the stress and its ecological response/recovery
relationships for affected ecological systems. This is the objective of the problem definition •
component as recommended by the panel.
The panel recommends adoption of the problem definition component illustrated in figure 4
and recommends that the framework report elaborate on this component in the context of the overall
revised ecological risk assessment framework discussed above. The following section suggests issues
and concepts for elaboration in the framework document.
3.1. ISSUES RECOMMENDED FOR DISCUSSION IN THE FRAMEWORK DOCUMENT
Ecological risk assessment, unlike human health risk assessment, must address a diverse set
of ecological systems, from tropical to arctic environments, deserts to lakes, and estuaries to alpine
systems. For each type of ecological system, there is a wide array of specific properties that may be
of concern with respect to human activities. These properties may cut across biological organizational
levels, from the reproductive viability of a particular population with special ecological or economic
importance, to community-level concerns for biodiversity, to ecosystem-level issues such as primary
productivity or nutrient processing, and landscape-level issues of maintaining the spatial heterogeneity
of a mosaic of ecosystems.
Human activities result in a plethora of environmental stresses, some of which are strictly
xenobiotic (e.g., releases of certain pesticides), while others consist of changes in the frequency or
intensity of natural physical conditions (e.g., global climate change or increased ultraviolet radiation
from stratospheric ozone depletion). Typically, multiple anthropogenic stresses occur simultaneously,
with potential interaction among stresses or in the response processes of biological systems.
Ecological risk assessment may occur over much wider temporal and spatial scales than those for
human health risk assessment.
Because of the great diversity of ecosystems, ecological components, and anthropogenic
stresses, ecological risk assessment must be flexible and adaptive, and the specific data needs,
analytical methodologies used, and interpretations made will vary considerably for different
environmental problems. The initial step in ecological risk assessment, therefore, must be detailed
problem definition, in which the characteristics of the ecological systems and anthropogenic stresses
are sufficiently specified to guide the particular ecological risk assessment.
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Problem Definition/Scoping Process for Ecological Risk Assessment
Policy Goals
Stressor
Characteristics
Endpoint Selection
1 - Assessment
2 - Measurement
Environmental
Characteristics
Conceptual
Model
Analysis
Figure 4. Problem Definition Component
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The problem definition/scoping phase of ecological risk assessment is closely linked to the
policy context of the environmental problem. The problem may be either stress-specific (such as the
risks of a new chemical or of global climate change) or effects-driven (such as when forest damage is
observed, and a risk assessment is conducted to explore possible causes). The policy connection
comes through identifying the environmental problem of concern and, in some cases, through
specification of the regulatory endpoints at issue. Here the term "regulatory endpoint" is defined as
the legislative, regulatory, or judicial norm for decision-making (e.g., the Clean Water Act regulatory
endpoints of "maintenance of a balanced indigenous population" and "unreasonable degradation of the
marine environment"). . . , . . . .,
The problem definition component should identify the particular ecological systems that are
at risk from a particular stress. The stress must be examined sufficiently to define its direct and
indirect target ecosystems, including consideration of such issues as the spatial extent of the stress, the
potential for transport across ecosystem boundaries, the transformations of the stress, and other factors
that relate to where in the environment the stress may occur. Using expert judgment with this and
similar stresses will identify those ecological systems and ecological components that might be
adversely affected by the stress.
Once the ecosystems of concern are specified, the problem definition component should
include selection of the appropriate endpoints for conducting the ecological risk assessment. Two
types of endpoints are required: assessment or ecological endpoints (i.e., the specific properties of
each ecosystem at risk that are used to evaluate the state or change in state of the ecological system);
and measurement endpoints or indicators (i.e., those aspects of the ecological system that are measured
to characterize the assessment endpoints). First the assessment endpoints must be identified, with
explicit attention to organizational hierarchy of the ecological system. A suite of assessment endpoints
is usually necessary, covering the species-, community-, ecosystem-, and landscape-level concerns for
the health of the at-risk ecosystem. The selection of assessment endpoints relates in part to the policy
interests (e.g., to specified regulatory endpoints or fo public concerns); thus, changes in assessment
endpoints must be related ultimately to changes in things about the ecosystem that humans care about
(anticipating the so what? question). But assessment endpoints are actually characteristics of the
ecological systems and, thus, must reflect ecological importance. Changes in the selected endpoints
would constitute changes in the health of the ecosystem. Moreover, the assessment endpoints selected
are in part a function of the specific stress of concern; for example, a chemical stress suspected of
causing avian eggshell thinning would logically have raptor population viability as one ecological
assessment endpoint.
Similarly, measurement endpoints or indicators should be specified in the problem definition
component. Each selected assessment endpoint should have one or more indicators that can be used to
characterize the state or change of state of the endpoint. These are the items that are actually
measured in a monitoring scheme or that represent data sought from a historical data base. The
indicators may be selected also for relevance to the policy concerns, although that is not necessary.
Indicators will be somewhat stress-specific, as is the case for endpoints. The ecological risk
assessment guidelines should specify criteria for selecting both assessment endpoints and associated
indicators.
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The problem definition component should include a conceptual model, in which initial
consideration of the stress-specific and ecosystem-specific situation is used to establish a working
concept of how the stress might be imposed on the environment (i.e,, a conceptual model of the
stress regime) and how the ecological systems might respond and recover when exposed to the stress
(Le., a conceptual model of the ecological response/recovery regime). The conceptual model, perhaps
comprising a set of testable hypotheses and assumptions, becomes the basis for entering the analysis
phase of the ecological risk assessment (see figure 2).
3.2. OTHER RECOMMENDATIONS OF THE PANEL
In addition to the above-described framework for the problem definition component, the panel
has several other recommendations for the framework development team. Many of the
recommendations apply to the overall framework paradigm, not just the problem definition component.
The problem definition component should include a discussion of uncertainties. As an
example, uncertainties about the ecosystems that might be at risk from a particular stress may, through
the expert judgment process, result in inclusion of ecosystems with less obvious risks. As experience
is gained for a particular stress type, the selection of ecosystems for examination in an ecological risk
assessment may eliminate some ecosystems from consideration. Similarly, uncertainties may suggest
that additional endpoints or indicators are required for evaluation of ecological risks. The initial
conceptual model itself is limited by the uncertainties, and as the ecological risk assessment proceeds,
or as experience is gained from similar ecological risk assessments, the conceptual model may be
refined and improved. The adaptive aspect of ecological risk assessment must be explicitly recognized
in the framework.
The framework document should specify an initial set of criteria for selecting ecological
assessment endpoints and measurement indicators for ecological risk assessment. Examples of the
criteria that should be specified for endpoints are ecological importance, relevance to regulatory
endpoints and/or public concerns, stress-specificity or susceptibility, predictability, and the purpose or
needs of the particular risk assessment. Examples of criteria that should be specified for indicators are
relevance to the assessment endpoint, signal-to-noise ratio, early-warning ability, stress-specificity, ease
or economy of measurement, availability of historical data, and predictability.
The framework document should include crisp examples of a few types of stresses, including
at least one xenobiotic chemical example and one nonchemical stress example, such as climate
cJiange or habitat alteration. The selected examples should be used throughout the framework
document to illustrate what is meant at each stage, from problem definition, endpoint and indicator
selection, through stress and recovery regime analyses, to risk characterization.
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4. COMMENTS ON THE CHARACTERIZATION OF STRESS COMPONENT
The peer review panel concluded that the term "characterization of stress" was preferred over
the term "exposure assessment," because it better incorporates both chemical and nonchemical
stressors. The panel developed a flowchart for the characterization of stress component (see figure 5).
Characterization of ecological stress requires consideration of a number of aspects. For
chemical stressors, source characterization, which usually results in defined distribution and rates of
release of chemical contaminants into the environment, must be considered. For other stressors,
biological, chemical, or physical changes that are the causes of ecosystem, stress are defined.
Modification of the stressor by ecosystems also should be evaluated. For chemical stressors, such
phenomena include transformation reactions that these chemicals may undergo and ecosystem
conditions such as pH, which may alter reaction rates.
For all stress, ecosystems stressors must be characterized. This must be done in conjunction
with ecological effects assessment because of the close relationship between these aspects of ecological,
risk assessment. Both abiotic and biotic features of ecosystems must be characterized.
Source and ecosystem characteristics are employed in model development, selection, and
verification. These models are used to characterize the behavior of chemical stressors in the
environment as well as to define the opportunity for exposures to ecosystems. For other stressors,
these models are used to predict the extent and severity of the stress and the ecosystem components
exposed to the stressors.
Finally, the results of modeling studies are evaluated and organized to establish a stressor
.profile that can be input to the risk characterization component (see figure 2). It should be
emphasized that stressor analysis requires the skills of a multidisciplinary team. Such assessments
should be carried out in conjunction with technical staff characterizing ecological effects to ensure that
all overlapping aspects are addressed and to minimize duplication of effort.
4.1. RECOMMENDATIONS OF THE PANEL
Stress characterization should include description of scaling phenomena and the definition
of heterogeneity of the ecosystem and ecosystem bounds. Both temporal and spatial aspects of
scaling should be included. Under scaling phenomena, it should be emphasized that spatial extent as
well as a temporal variation in stressor should be characterized. Time frames of interest include the
time required to complete a nutrient cycle, the life span of individual species, and the life span of the
ecosystem itself.
Characterizing the heterogeneity of the ecosystem should be emphasized. Heterogeneity in
ecosystems is a major confounding factor in characterizing the behavior of contaminants and other
stressors, and, in many cases, heterogeneity is a major factor in the maintenance or diminution of a
species in a particular ecosystem. When migratory species are of interest, characterization of all
occupied ecosystems and the role each ecosystem plays in the development of the species should be
specified.
15
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Problem Definition
Characterization of Stress
Source or
Biological/Chemical/
Physical Change
Characterization
K-\:
/ *
/ Modification \
( of Stress by )
\ Ecosystem /
Ecosystem
Characterization
i
Abiotic i Biotic
|
Characterization
of
Ecological
Effects
Analysis
Stress Model
Development/
Selection/
Verification
Stressor
Profile
(See Figure 6)
Risk Characterization
Figure 5. Characterization of Stress Component
16
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A synopsis from EPA's Exposure Guidelines should be included. Summaries of guidance
should be included in conjunction with describing the sources of uncertainty and methods for
describing these uncertainties, with descriptions of point-of-contact measurements, scenario evaluation,
and reconstructive assessment approaches. Given that the role of measurement and modeling of
ecosystem stressors is different from measurement and modeling of human exposures, these different
roles must be identified. •
The adaptation of these approaches to nonchemical stressors should be specified. The
meaning of a physical change that is analogous to a source should be described. The role of
approaches such as measurement, scenario evaluation, and reconstructive assessment should be
presented. The role of measurement techniques, as well as that of scenario evaluation, seems to be
straightforward. The role of reconstructive assessment techniques will require the discussion of field
studies and biomonitoring techniques.
• -
The framework should state that expert judgment is required to assess most stressors.
Expert judgment should be used to formulate assumptions in developing the scenario evaluation
approach and analogies from previous assessments when interpreting limited data using measurement
and retrospective assessment techniques. The use of simplified techniques, such as estimation of a
single exposure value in the quotient method, requires the maximum amount of expert judgment. The
framework should clearly state that when such methods are employed, the assessment should include
detailed descriptions of the logic and the assumptions made in describing an appropriate exposure
value.
The framework should state that gaps in stressor assessment technology exist and should
provide a brief description of a commitment to further guidelines development, implementation of
better methods, and research in the areas of source characterization, ecosystem characterization,
and stress model development and verification. It is clear that EPA has a variety of plans and
programs to address these issues. To provide a perspective for the framework, a summary statement
of these efforts and the direction that EPA intends to pursue would show how major gaps are expected
to be filled.
A stressor uncertainty characterization section should be added. This section should describe
the sources of uncertainty in source or physical change characteristics, ecosystem characteristic model
assumptions, and resultant stressor profile. The framework should specify that both qualitative and
quantitative methods can be used. It would be appropriate to note that when professional judgment is
used, qualitative descriptions of uncertainty may be crucially important. In most cases, including those
in which professional judgment is used, sensitivity analysis and/or simulation techniques should be
included as part of the assessment. For quantitative assessments, precision and accuracy of estimates
should be characterized.
The framework should indicate that every assessment should include QAJQC requirements.
This can be accomplished through the statement of data quality objectives required of studies
conducted within EPA. The framework should incorporate standard language about the scope and
intent of those objectives.
17
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4.2. OTHER RECOMMENDATIONS
Because chemical stressors are not all equally available, bioavattabittty should be considered
as an aspect of chemical stressor assessment. For such stressors, this will require consideration of
transformations that the chemical undergoes and, for inorganic elements, the species of chemical
present. Consideration of bioavailability may require estimation of dosage in some assessments.
Chemical stressor exposure pathways from the source to the organism!system should be
defined. For nonchemical stressors, the relationship of a physical or other change should be related to
the occurrence of a stressor that affects an organism/system.
18
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5. COMMENTS ON THE CHARACTERIZATION OF ECOLOGICAL EFFECTS
COMPONENT
After much discussion, the panel agreed that the term "hazard assessment" in the draft
framework should be changed to the term "characterization of ecological effects." This would ;,
eliminate concerns about the inconsistent use of the term "hazard assessment," and could more
accurately reflect the broader levels of biological organization required in ecological risk assessment
The reviewers developed a proposed flowchart for the characterization of ecological effects component
(see figure 6).
Characterization of ecological effects refers to the determination of the relationship between.
the stressor and the endpoints identified during problem definition. Characterization will involve both
observation in the field (biotic/abiotic ecosystem characterization) and experimentation in controlled
settings. Both observation and experimentation contribute data and scientific understanding to the
development, selection, and verification of simulation models. The relationship between
observation/experimentation and model development/testing may be iterative; unsatisfactory model
verification may result in additional field or laboratory studies. Once the model is verified, it may be
used in stressor-response characterization, which concerns the relationship between the stressor and
assessment endpoints. The process of characterizing ecological effects probably also will involve
activities concerned with characterization of stress.
The workgroup on characterization of ecological effects developed a series of
recommendations that would improve the framework document. These recommendations are
summarized in the following paragraphs.
The risk characterization section of the framework document should present a more detailed
discussion of uncertainty. The importance of uncertainty analysis in ecological risk assessment was
discussed. Even though error calculations may occur in only one step, uncertainty is important hi all
components of risk assessment. As such, it should be discussed in all sections.
Statements should be added that identify (and reference) statistical issues and methods so
that specific guidance is provided in subsequent technical manuals. The discussion of statistical
methods, with frequent reference to regression analysis, ignores many difficult questions with regard to
selection and application of statistical methods when data are error-contaminated and models are non-
normal and/or nonlinear.
Technical guidance and detail should not appear in the framework document unless they
are necessary for identification of otherwise unfamiliar methods. Even in those cases, the discussion
should be brief. The dilemma concerning avoidance of technical details while maintaining clarity of
explanation could be solved by using "boxed-in" examples of statistical methods, applications, etc.
Field confirmation of an effect caused by a stressor should be assessed whenever possible,
since it is the field response of the assessment endpoint that is ultimately of consequence. In many
instances, experimentation provides strong support for causality, whereas field observation provides
evidence of correlation. Both are important, as noted in Hill's criteria. Still, it is important to
recognize the limited support for causality that correlation alone provides. The framework document
19
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Problem Definition
V *?;
Characterization
of
Stress
(See Rgure 5)
Characterization of Ecological Effects
Ecosystem
Characterization
i
Abiotic i Biotic
Data
Acquisition
Environmental
Effects
Characterization
Effects Model
Development/
Selection/
Verification
Stressor-Response
Characterization
Analysis
Risk Characterization
Figure 6. Characterization of Ecological Effects Component
20
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should include a brief discussion of the importance of field verification. A brief discussion also
should be added to address laboratory-to-field extrapolation and its role in ecological risk assessment.
Additional guidance and discussion on nonchemical stressors are needed.
It is important to build flexibility into the framework to allow for future methods
development. Flexibility in the framework would permit consideration of key unresolved issues, such
as how multiple stressors with interactions an4 synergisms should be addressed. The panel believes
that the framework should be flexible enough to allow new methods and approaches to be incorporated
in the various guidelines and technical documents without requiring alteration of the basic framework
itself.
21
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6. COMMENTS ON THE RISK CHARACTERIZATION COMPONENT
The 1983 NAS report, "Risk Assessment in the Federal Government," defines risk
characterization as
...the process of estimating the incidence of a [health] effect under the various conditions of
human exposure described in exposure assessment. It is performed by combining the exposure
and dose-response assessments. The summary effects of the uncertainties in the preceding
steps are described in this step.
The draft EPA framework document accepts the NAS definition but expands it to include ecological
effects and consequences. This definition implies the risk characterization section in the framework
document should discuss:
" Integration of exposure and stressor-response information.
» Summarization of uncertainties.
• The relationship between "consequences" and "effects."
In their premeeting comments, a significant number of reviewers suggested that risk
communication is Inadequately addressed in the draft framework document, and that communication
between scientists and managers is an important aspect of risk characterization. In light of these
comments, the discussion groups were asked to answer three questions:
• How adequately does the framework document address risk characterization under the
stated definition?
• Should the definition be expanded to explicitly include communication to decision-
makers or to the public at large?
• If an expanded definition is needed, how should the expansion be addressed in Hie
framework document?
6.1. ADEQUACY OF THE FRAMEWORK DOCUMENT UNDER STATED DEFINITION
Effects and Consequences
There was substantial confusion concerning the meanings of the terms "effect" and
"consequence" and the relationships of these terms to "assessment endpoints." The terms "effect" and
"consequence" are used nowhere else in the document, and their use in the risk characterization section
creates apparent conflicts between different sections.
22
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The conceptual framework development section defines assessment endpoints in terms of
immediate relevance to decision-making (e.g., acres of wetland lost, decline in biodiversity). Given
this definition, the consequences discussed in the risk characterization section should be synonymous
with assessment endpoints. However, the discussion of stressor-response assessment in the hazard '
assessment section appears to include extrapolation to assessment endpoints. This would imply that
effects, as defined in the risk characterization section, are synonymous with assessment endpoints and
that consequences are some new and previously undefined type of endpoint.
The discussion groups were unable to resolve this problem. One group suggested substituting
the term "occurrence" for "consequence," but later agreed that this change does not solve the problem.
The final consensus was that, if "consequence" is retained as the form in which risks are
communicated to managers, then consequences should be expressed in terms of assessment endpoints.
The hazard assessment and risk characterization sections, which both appear to discuss extrapolation to
assessment endpoints, must be reconciled. As stated above, this area was not resolved by the peer
review panel. However, we believe it is critical for EPA to reach a consensus on how best to proceed
in this area. The comments above are meant to be helpful as EPA proceeds with its considerations.
Uncertainty
The consensus among both risk characterization workgroups was that summarization of
uncertainties is a critical component of risk characterization. The value of scientific information in the
risk'assessment is conveyed in the uncertainty analysis. Scientific uncertainty is present in all risk
assessments. It does not prevent management and decision-making; rather, it provides a basis for
selecting among alternative actions and for deciding if (and what) additional information
(experimentation and/or observation) is needed.
The reviewers recommended recasting the uncertainty discussion in the risk characterization
section to include discussion of sources of uncertainty, methods of characterizing uncertainty, methods
of propagating uncertainty, and presentation of uncertainty.
Sources of uncertainty. The sources of scientific uncertainty in ecological risk assessment
include inadequate scientific knowledge, natural variability, measurement error, and sampling error
(e.g., standard error of an estimator). In actual practice, uncertainties that should be addressed
specifically include mis-specification of models used (e.g., excessive aggregation of variables and
inappropriate assumptions), error in parameter estimates, errors in the specification of initial
conditions, and errors in expert judgment
Methods of characterizing uncertainty. In some situations, uncertainty in an unknown quantity
(e.g., a model parameter or a measurement endpoint) may be estimated by means of standard measures
of statistical variability. Model errors can sometimes be estimated from a measure of goodness-of-fit
(predictions versus observations). In many situations, however, judgmental estimation of uncertainty is
the only option. This alternative is acceptable since methods of eliciting uncertainty estimates are
available from experts.
23
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Methods of propagating uncertainty. For model-based assessments, e.g., Monte Carlo or Latin
Hypercube simulation, first-order error analysis and response-surface analysis often are used to
estimate the influence of parameter errors on uncertainty concerning model predictions. Software for
performing these analyses is now widely available.
Presentation of uncertainty. The group noted the importance of properly communicating
uncertainty to decision-makers but did not offer specific comments on the adequacy of the framework
document's treatment of this topic.
Exposure-Response Integration
The consensus of the group was that the risk characterization section places far too much
emphasis on the "quotient method." The discussion of integration should be more general, and it
should be revised to eliminate the confusing distinctions among responses, effects, and consequences.
The material on the quotient method, if retained, should be condensed and put in a box as an example.
6.2. NEED FOR EXPANSION OF THE DEFINITION OF RISK CHARACTERIZATION
Workshop participants all recognized the need for communicating ecological risk information
to decision-makers and to the public at large. There was not, however, uniform agreement about the
role of risk analysts in this process. During the discussion, the group reached a consensus that
communication should be included in the definition of risk characterization, but in a carefully
circumscribed way. Risk characterization should include expression of risks in terms of assessment
endpoints of direct management relevance and communication to risk managers of the ecological
implications of alternative management actions. Communication to the public at large (magnitude and
significance of the risks and rationale for actions taken) is the responsibility of the risk manager.
6.3. TREATMENT OF EXPANDED DEFINITION IN THE FRAMEWORK DOCUMENT
Figure 7 is a flowchart for the risk characterization component of the framework. As
envisioned by the group, risk characterization includes several intervening steps between formal
exposure/effects integration (termed "Consequence Analysis" in the figure and taken to include
quantitative and qualitative uncertainty analysis) and communication to risk managers. These steps are
as follows:
1.
2.
3.
Expression of the quantitative results as a "consequence distribution," in which the
range of possible ecological responses is presented as a function of probability of
occurrence (quantitative or qualitative);
Interpretation of the ecological significance of the consequences (in narrative form);
and
Description of the ecological consequences (either quantitative or qualitative) of the
action alternatives available to the risk manager.
24
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As appropriate, all three steps would include discussion of uncertainty and weight-of-evidence
determinations. After the range of possible consequences and their relationship to both society's risk
goals and action alternatives are conveyed to tfie risk manager, the risk assessor's responsibility ends.
The risk manager must integrate relevant non-ecological considerations, make a decision, and then
communicate the decision to the public.
25
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Analysis
Risk
Characterization
Characterization
of
Stress
Characterization
of
Ecological
Effects
Integration
Uncertainty
Analysis
Consequence* Analysis
Consequence*
Frequency
Distribution
i
r
Interpretation
of
Ecological
Significance
i
r
Action
Alternatives
j, f
Decision-making/
Risk Management
^
r
•Other Inputs
Verification
and
V Monitoring /
'Consequence is used in this figure, even though the peer review panel did not reach
a consensus on its use.
Figure 7. Risk Characterization Component
26
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7. REFERENCES
National Research Council (NRG), 1983. Risk Assessment in the Federal Government: Managing the
Process. National Research Council, National Academy Press, Washington, DC.
Science Advisory Board (SAB), 1990. Reducing Risks: Setting Priorities and Strategies for
Environmental Protection. U.S. Environmental Protection Agency, Washington, DC.
Society of Environmental Toxicology and Chemistry (SETAC), 1987. Research Priorities in
Environmental Risk Assessment. Published by SETAC.
U.S. Environmental Protection Agency (EPA), 1991. Draft Framework for Ecological Risk
Assessment. Prepared by the Risk Assessment Forum.
27
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APPENDIX A
MEETING MATERIALS
-------
-------
AGENDA
U.S. Environmental Protection Agency
ECOLOGICAL RISK ASSESSMENT GUIDELINES:
WORKSHOP TO REVIEW FRAMEWORK DOCUMENT
TUESDAY. MAY 14.1991
8:30 a.m. -11:30 a.m. OPENING PLENARY SESSION
8:30 a.m. Welcome
Dorothy Patton, Chair, USEPA Risk Assessment Forum
8:45 a.m. Workshop Purpose and Objectives
James Fava, Roy F. Weston, Inc.
9:00 a.m. Ecorisk Activities of the NAS Committee on Risk Assessment Methodology
Lawrence Barnthouse, Oak Ridge National Laboratory
9:15 a.m. EPA's Strategic Planning Workshop for Ecorisk Assessment
Mark Harwell, University of Miami, Rosentiel School of Marine and Atmospheric
Science
9:30 a.m. Ecorisk Paradigm: Highlights
Susan Norton, USEPA
9:45 am. Ecorisk Paradigm: Issues Presentation
James Fava
10:00 a.m. BREAK
10:15 a.m. Ecorisk Paradigm: Discussion
James Fava
11:30 a.m. LUNCH
12:30 p.m. -1:30 pan.
PLENARY SESSION
12:30 p.m. Conceptual Framework Development: Highlights
David Mauriello, USEPA
12:45 p.m. Conceptual Framework Development: Issues Presentation
Mark Harwell
A-l
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TUESDAY. MAY 14.1991 (cont)
1:30 p.m. - 4:30 p.m.
WORKGROUP SESSIONS
1:30 p.m. Conceptual Framework Development: Discussion (Two Workgroups)
Mark Harwell and Lawrence Barnthouse
3:00 p.m. BREAK
3:15 p.m. Conceptual Framework Development: Discussion (cont.)
4:30 p.m. - 5:30 p.m. PLENARY SESSION
4:30 p.m. Conceptual Framework Development: Summary
Mark Harwell and Lawrence Barnthouse
5:30 p.m. ADJOURN
5:30 p.m. Reception - Pool Terrace
WEDNESDAY. MAY 15.1991
8:30 a.m. - 9:30 a.m. PLENARY SESSION
8:30 a,m. Hazard Assessment: Highlights
Donald Rodier, USEPA
8:45 a.m. Hazard Assessment Issues Presentation
Kenneth Reckhow, Duke University, School of Forestry and Environmental Studies
9:15 a.m. Exposure Assessment: Highlights
Anne Sergeant, USEPA
9:30 a.m. Exposure Assessment: Issues Presentation
James Falco, Battelle Pacific Northwest Laboratory
10:00 a.m. BREAK
10:15 a.m. - 12:15 p.m.
WORKGROUP SESSIONS
10:15 a.m. Hazard Assessment: Discussion
Kenneth Reckhow
Exposure Assessment: Discussion
James Falco
A-2
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WEDNESDAY. MAY 15,1991 (cont.)
12:15 p.m.
1:15 p.m. •
1:15 p.m.
1:45 p.m.
2:15 p.m.
2:30 p.m.
3:15 pjn.
3:30 p.m.
3:30 p.m.
LUNCH
3:15 p.m.
PLENARY SESSION
Hazard Assessment: Summary
Kenneth Reckhow
Exposure Assessment: Summary
James Falco
Risk Characterization: Highlights
Michael Brody, USEPA
Risk Characterization: Issues Presentation
Lawrence Barnthouse
BREAK
5:00 p.m.
WORKGROUP SESSIONS
Risk Characterization: Discussion (Two Workgroups)
Lawrence Barnthouse and Mark Harwell
5:00 p.m. - 5:30 p.m.
5:00 p.m.
PLENARY SESSION
5:30 p.m.
Risk Characterization: Summary
Lawrence Barnthouse and Mark Harwell
ADJOURN
THURSDAY. MAY 16.1991
8:30 a.m. -12:00 p.m. CLOSING PLENARY SESSION
8:30 a.m. OBSERVER COMMENTS
James Fava
9:30 a.m. FRAMEWORK FOR ECOLOGICAL RISK ASSESSMENT:
SUMMARY AND RECOMMENDATIONS
9:30 a.m.
Introduction
James Fava
A-3
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THURSDAY. MAY 16,1991 (cont)
9:35 a.m. Resolved Issues
Mark Harwell
10:15 a.m. BREAK
10:30 a.m. Unresolved Issues
Lawrence Barnthouse
11:15 a.m. Recommendations to EPA
James Fava
12:00 p.m. ADJOURN
A-4
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LIST OF PARTICIPANTS
U.S. Environmental Protection Agency
ECOLOGICAL RISK ASSESSMENT GUIDELINES:
WORKSHOP TO REVIEW FRAMEWORK DOCUMENT
William Adams
ABC Laboratories
Columbia, MO
Lawrence Barnthouse
Oak Ridge National Laboratory
Oak Ridge, TN
John Bascietto
U.S. Department of Energy
Washington, DC
Raymond Beaumier
Ohio Environmental Protection Agency
Columbus, OH
Harold Bergman
University of Wyoming
Laramie, WY
Nigel Blakely
Washington Department of Ecology
Olympia, WA
James Falco
Battelle Pacific Northwest Laboratory
Richland, WA
James Fava
Roy F. Weston, Inc.
West Chester, PA
Alyce Fritz
National Oceanic and
Atmospheric Administration
Seattle, WA
James Gillett
Cornell University
Ithaca, NY
Michael Harrass , ; .
U.S. Food and Drug Administration
Washington, DC
Mark Harwell
University of Miami
Miami, FL
Ronald Kendall
Clemson University
Pendleton, SC
Wayne Landis
Western Washington University
Bellingham, WA
Ralph Poitier
Louisiana State University
Baton Rouge, LA
Kenneth Reckhow
Duke University
Durham, NC
John Rodgers
University of Mississippi
University, MS
Peter Van Voris
Battelle Pacific Northwest Laboratory
Richland, WA
James Weinberg
Woods Hole Oceanographic Institution
Woods Hole, MA
Randall Wentsel
U.S. Army Chemical Research,
Development and Engineering Center
Aberdeen Proving Grounds, MD
A-5
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LIST OF OBSERVERS
U.S. Environmental Protection Agency
ECOLOGICAL RISK ASSESSMENT GUIDELINES:
WORKSHOP TO REVIEW FRAMEWORK DOCUMENT
Sidney Abel
Office of Pesticides and Toxic Substances
U.S. Environmental Protection Agency
Washington, DC
Larry Bowers
Law Environmental, Inc.
Kennesaw, GA
Michael Brody
Office of Policy, Planning and Evaluation
U.S. Environmental Protection Agency
Washington, DC
Janet Burns
Office of Emergency, Remedial Response
U.S. Environmental Protection Agency
Washington, DC
Jeff Butuinik
Cleary, Gottlieb, Steen & Hamilton
Washington, DC
Chao Chen
Office of Health & Environmental Assessment
U.S. Environmental Protection Agency
Washington, DC
Damon Choppie
Bureau of National Affairs
Washington, DC
Charlotte Cogswell
Goldberg-Zoino &
Associates Geoenvironmental
Newton, MA
Thomas Dillon
U.S. Army Corps of Engineers
Vicksburg, MS
Donald Enye
FMC Corporation
Princeton, NJ
John Festa
American Paper Institute
Washington, DC
Jerry Frumkin
Government Institute
Rockville, MD
John Gentile
Environmental Research Laboratory
Office of Environmental Processes & Effects
Research
U.S. Environmental Protection Agency
Narragansett, RI
S. Ian Hartwell
Maryland Department of the Environment
Annapolis, MD
John Helm, HI
Office of Toxic Substances
U.S. Environmental Protection Agency
Washington, DC
Eliz Hirsch
ICI Americas, Inc.
Wilmington, DE
A-6
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D. Eric Hyatt
EMAP Integration and Assessment
U.S. Environmental Protection Agency
Research Triangle Park, NC
Paul Klauman
Lockheed Engineering and Science Company
Washington, DC
Norman Kowal
Environmental Criteria & Assessment Office
U.S. Environmental Protection Agency
Cincinnati, OH
Steven Kroner
Office of Solid Waste
U.S. Environmental Protection Agency
Washington, DC
Ronald Landy
Office of Technology Transfer and
Regulatory Support
U.S. Environmental Protection Agency
Washington, DC
Rick Linthurst
Office of Research & Development
U.S. Environmental Protection Agency
Washington, DC
David Mauriello
Office of Toxic Substances
U.S. Environmental Protection Agency
Washington, DC
Monte Mayes
The Dow Chemical Company
Midland, ML
Margaret McVey
ICF, Inc.
Fairfax, VA
John Meier
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH
Charles Menzie
Menzie-Cura and Associates, Inc.
Chehnsfbrd, MA
Eugene Mones
Unilever Research U.S., Inc.
Edgewater, NJ
Ralph Northrop
Office of Pesticides and
Toxic Substances
U.S. Environmental Protection Agency
Washington, DC
Susan Norton
Office of Health and Environmental
Assessment
U.S. Environmental Protection Agency
Washington, DC
Edward Odenkirchen
Environmental Impact Section
Food and Drug Administration
Washington, DC
Dorothy Patton
Risk Assessment Forum
U.S. Environmental Protection Agency
Washington, DC
Kevin Reinert
Science Management Corporation
Valley Forge, PA
Donald Rodier
Office of Toxic Substances
U.S. Environmental Protection Agency
Washington, DC
Philip Ross
Office of Federal Activities
U.S. Environmental Protection Agency
Washington, DC
Louis Scarano
Environ Corporation
Arlington, VA
A-7
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Anne Sergeant
Office of Health & Environmental Assessment
U.S. Environmental Protection Agency
Washington, DC
Bill Shade
Rohm & Haas Company
Spring House, PA
Michael Slimak
Office of Environmental Processes and
Effects
U.S. Environmental Protection Agency
Washington, DC
Rick Stevens
NOR-AM Chemical Company
Wilmington, DE
Jerry Stober
Office of Personnel Management
U.S. Environmental Protection Agency
Atlanta, GA
Greg Susanke
Office of Pesticides and Toxic Substances
U.S. Environmental Protection Agency
Washington, DC
Gregory Toth
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH
William van der Schalie
Risk Assessment Forum
U.S. Environmental Protection Agency
Washington, DC
Stephanie Weinstein
Jellinek, Schwartz, Connolly and Freshman
Washington, DC
Molly Whitworth
Office of Policy, Planning and Evaluation
U.S. Environmental Protection Agency
Washington, DC
Chris Wilkinson
Technical Services Group
Washington, DC
Keith Williams
U.S. Army
Environmental Hygiene Agency
Aberdeen Proving Ground, MD
William Wood
Risk Assessment Forum
U.S. Environmental Protection Agency
Washington, DC
Dick Worden
OPPE
U.S. Environmental Protection Agency
Washington, DC
I.E. Young
Union Carbide Chemicals &
Plastics Company, Inc.
Bound Brook, NJ
Maurice Zeeman
Office of Toxic Substances
U.S. Environmental Protection Agency
Washington, DC
A-8
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APPENDIX B
PREMEETING MATERIALS
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PEER REVIEW WORKSHOP DRAFT
FRAMEWORK FOR ECOLOGICAL RISK ASSESSMENT
Prepared for the
Risk Assessment Forum
U.S. Environmental Protection Agency
Washington, DC
March 1991
Co-Chairs
Susan Braen Norton
Donald J. Rodier
Suzanne Macy Marcy
Technical Panel
Michael Brody
Anne Sergeant
David Mauriello
Molly Whitworth
Staff
William van der Schalie
William P. Wood
DRAFT - DO NOT CITE OR QUOTE
B-l
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DRAFT: 00 NOT CITE, QUOTE, OR DISTRIBUTE
3/22/91
TABLE OF CONTENTS
1. INTRODUCTION . 1
1.1. Intended Audience 1
1.2. Definition of Ecological Risk Assessment 1
1.3. Applications of Ecological Risk Assessment. . . . '. 2
1.4. Document Background and Ancillary Activities ... 2
1.5. Purpose and Scope of the Framework Document .... 3
1.6. The Ecological Risk Paradigm 4
1.7. Ecological Risk Assessment Issues for Future
Consideration 8
1.8. Organization 11
2. CONCEPTUAL FRAMEWORK DEVELOPMENT 12
2.1. Stressor and Environmental Characterization ... 12
2.2. Endpoint Identification and Selection 13
2.2.1. Purpose and Needs, of the Assessment ... 15
2.2.2. Ecological Relevance 17
2.2.3. Susceptibility 18
2.2.4. Practical Constraints 19
2.3. Presentation of the Conceptual Model and Evaluation
Approach 20
3. HAZARD ASSESSMENT 23
3.1. Hazard Identification 23
3.2'. Stressor-Response Assessment 25
3.2.1. Types of Data and Analyses Used in
Stressor-Response Assessment 25
3.2.2. Extrapolation Methods for
Stressor-Response Assessments 26
4. EXPOSURE ASSESSMENT 29
4.1. Estimating Exposure 30
4.1.1. Exposure 'Scenario Evaluation 30
4.1.2. Reconstructive Exposure Assessment ... 31
5. ECOLOGICAL RISK CHARACTERIZATION 33
5.1. Assess the Likelihood of Adverse Effects
33
5.1.1,
5.1.2,
5.1.3
Basic Concepts 33
Quotient Method of Ecological Risk
Characterization 34
Additional Approaches 36
5.2. Describing the Consequences of Identified Risks
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5.2.2. Methods for Describing the Consequences
5.3. Uncertainty in Ecological Risk Characterization . .
5.3.2. Reducing Uncertainty in Ecological Risk
5.4. Communicating the Results of the Ecological Risk
PFF-PPENCES
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1.
FRAMEWORK FOR ECOLOGICAL RISK ASSESSMENT
INTRODUCTION
In 1984, the United States Environmental Protection Agency
(EPA) organized the Risk Assessment Guidelines program to ensure
scientific quality and technical consistency in the Agency's risk
assessments. The first group of five guidelines, issued in 1986,
focused on evaluating risks to human health. In addition to
concerns for human health, there has been an increased awareness in
the public, private, and governmental sectors of society regarding
ecological issues. These issues include global warming,, acid
deposition, a decrease in biological diversity, and the ecological
impacts of xenobiotic compounds such as pesticides and toxic
chemicals. This Framework for Ecological Risk Assessment is the
first agency-wide statement of general principles to guide
ecological risk assessment. It is intended to foster a consistent
Agency approach for conducting ecological risk assessments, help to
identify key issues and research needs, and provide operational
definitions for terminology. . In addition, it will serve as the
foundation for future subject-specific guidelines.
1.1. Intended Audience
This guidance is intended for risk assessors in the Agency,
and other persons who either perform work under Agency contract or
sponsorship or who are subject to Agency regulations1. Risk
managers in the Agency, other Federal agencies, and state and local
agencies may also benefit from this guidance since it clarifies the
terminology and methods used by assessors.
1.2. Definition of Ecological Risk Assessment
Ecological risk assessment evaluates the likelihood that
undesirable ecological effects may occur or are occurring as a
result of exposure-to one or more stressors. The term stressor is
defined here as any physical, chemical or biological entity that
can induce an adverse effect. Adverse ecological effects encompass
a wide range of disturbances, ranging from an increase in the
normal mortality rate in individual organisms to reductions or
deviations from normal ecosystem structure and function.
1 It is preferable that scientists with ecological training
perform and interpret ecological risk assessments. Those who do
not have this background may find the standard texts listed in the
references helpful (e.g., Odum, 1983; Krebs, 1985; Ricklefs, 1990;
and Pianka, 1988).
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Risk is a function of two major elements, hazard and exposure.
Hazard refers to the type and magnitude of effect caused by a
stressor. It is usually evaluated by identifying levels of a
stressor associated with effects observed in laboratory or field
studies. Exposure refers to the co-occurrence of a stressor with
an ecological component (e.g., individual, population, community,
or ecosystem). It is usually determined by measuring or estimating
the amount of the stressor in environmental compartments (e.g.,
air soil, water). An adverse effect is likely to occur in the
field only if exposure approaches or exceeds a levels associated
with the adverse effects identified in the hazard assessment. A
probabilistic statement about the likelihood of adverse effects can
be made when stochastic estimates of the two elements are provided.
The current state of the art in ecological risk assessment
permits only limited potential for developing stochastic estimates
of both the hazard and exposure elements. Thus, ecological risk
assessments often are deterministic in nature and likelihood is
expressed as a semi-quantitative comparison of exposure and hazard.
In some instances, such as evaluating current or past risks,
quantifying hazard and exposure may be difficult, and qualitative
risk estimates or opinions are often employed. Even though such
estimates may be qualitative, they are still considered to be risk
estimates in this document.
1.3. Applications of Ecological Risk Assessment.
Ecological risk assessments play a fundamental and often
pivotal role for addressing ecological effects. Ecological risk
assessments can be used to define problems, set priorities, and
serve as a basis for regulatory actions. The ecological risk
assessment process is flexible enough that it can be used to
predict future risks or assess adverse effects that are occurring
or have already occurred. An example of the former is an
evaluation of a new chemical not yet manufactured. Such
assessments are often referred to as predictive risk assessments.
Examples of the latter include evaluation of hazardous waste sites,
eu?r?phication of aquatic systems, and oil spills. These types of
assessments are commonly referred to as retrospective risk
assessments. Although the types of data and analyses may differ,
the elements of the risk assessment paradigm described in Section
1.6 are used in both types of assessments.
1.4. Document Background and Ancillary Activities
As part of the present effort in ecological risk assessment,
meeting were held in the spring and summer of 1990 tc. «»view
important scientific issues (Gentile et al., in press). Experts i,.
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ecology and ecological risk assessment met to discuss the
ecological risk assessment paradigm, uncertainty issues in hazard
and exposure assessment, and population modeling. Representatives
from state and federal agencies described how ecological risk
assessments are conducted in their organizations, and the EPA
Science Advisory Board provided an informal consultation on the
development of ecological risk assessment guidelines.
Based in part upon these meetings as well as extensive
discussions with EPA managers and scientists and outside experts,
EPA has initiated a three-part program to develop ecological risk
assessment guidelines. Two efforts are underway in addition to the
framework guidance document:
Compilation of Ecological Risk Assessment Case Studies. Peer-
reviewed case studies illustrating the "state-of-the-practice"
in ecological risk assessment are being compiled by six EPA
work groups chaired by personnel from the Regions,
Environmental Research Laboratories, and Headquarters.
Selected case studies represent a wide range of programmatic
tasks and ecosystem types. Individual case studies will be
compiled into an overall report that will include a
description of each study; a "tools" section that will contain
a cross-referenced listing of ecological risk methods, models,
and assessment schemes used in the case studies; and a
discussion of issues related to ecological risk assessment and
research needs. The report will provide interim assistance in
performing ecological risk assessments until additional
specific guidelines can be developed.
Plans for Future Guidelines. A work group has been formed to
create a work plan for long-term (1991-1998) development of
ecological risk guidelines. This group will coordinate with
other Agency ecological risk assessment activities, including
the core research program and the Ecological Monitoring and
Assessment Program (EMAP). Based on scientific feasibility
and EPA's program priorities, the work group will recommend
specific subject areas for future ecological risk assessment
guidelines.
1.5. Purpose and Scope of the Framework Document
This framework is intended to convey the general principles of
ecological risk assessment and provide a foundation for future
subject-specific guidelines. It will also foster a consistent
Agency approach for conducting ecological risk assessments, help to
identify key issues and research needs, and provide operational
definitions for terminology. It is not intended to serve as a
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detailed instructional guide or set of rules. The principles
discussed here apply to ecological risk assessments at the
individual, population, community, and ecosystem organizational
levels. The need for assessing risks at higher, organizational
levels (i.e., communities and ecosystems) has been highlighted
recently (U.S. EPA, 1990a,b). However, most operational methods
assess effects at lower levels of ecological organization (i.e.,
individuals and populations) and these methods provide most of the
examples discussed in this guidance. As methods for assessing
risks at higher organizational levels are developed, the Agency
will prepare more detailed guidelines.
Risks posed by introduced exotic species are not addressed
here because EPA does not have the authority to regulate these
organisms. EPA does have the authority to regulate genetically-
engineered organisms; although the risk assessment paradigm
described in Section 1.6 would conceptually apply to genetically-
engineered organisms, methods for evaluating the hazard of and
exposure to such organisms are still being investigated. As more
experience is gained, guidelines for evaluating the ecological
risks of genetically-engineered organisms will eventually be
developed.
1.6. The geological Risfe Paradigm
This guidance represents the first Agency-wide effort to
identify and discuss the elements of ecological risk assessment.
Figure 1 illustrates the elements of the ecological risk assessment
paradigm described in this framework. Figure 2 presents the
paradigm in the context of risk management and policy concerns.
The risk assessment paradigm published by the National Academy
of Sciences (NRC "red book," 1983) is used as a foundation for the
ecological risk assessment paradigm shown in Figure 1. The Academy
identified "four basic elements of risk assessment: 1) Hazard
Identification, 2) Dose-Response Assessment, 3) Exposure
Assessment,, and 4) Risk Characterization. For the purposes of
ecological risk, assessment, an additional step, Conceptual
Framework Development, is also shown. This is analogous to a
preliminary hazard identification that identifies adverse effects
associated with the stressor. It is proposed here since ecological
risk assessments, unlike human health assessments, must often
address the risks of stressors to many species as well as risks to
communities and ecosystems. In addition, there may be many ways a
stressor can elicit adverse effects (e.g., direct effects on
mortality and growth, or indirect effects such as decreased food
supply). A systematic planning element helps identify major
factors to be considered in a particular assessment in order to
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CONCEPTUAL FRAMEWORK
Stressor and Environmental Characterization
Endpoint identification and Selection
Conceptual Model Formulation
Hazard Assessment
Exposure Assessment
Hazard Identification
Stressor Response
RISK CHARACTERIZATION
Figure 1: Ecological Risk Assessment Paradigm
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CONCEPTUAL FRAMEWORK
Stressor and Environmental Characterization
Endpoint identification and Selection
Conceptual Model Formulation
Hazard Assessment
Hazard Identification
Stressor Response
Exposure Assessment
I
RISK CHARACTERIZATION
RISK MANAGEMENT
Figure 2: Activities Associated with Ecological Risk Assessment
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produce a scientifically-acceptable ecological risk assessment
relevant to risk management decisions.
There are three elements of Conceptual Framework Development.
Stressor and Environmental Characterization describes the
stressor's potential spatial and • temporal distribution and
identifies the ecological components that might be exposed to it.
Endpoint Identification describes the types of effects that may be
elicited by a certain stressor. Conceptual Model Formulation
summarizes plausible ways a stressor could cause adverse effects.
Section 2 describes these elements in more detail.
The four elements of the NAS paradigm complete the ecological
risk assessment paradigm. The term Hazard Identification is used
here in a manner similar to NAS (NRC, 1983) : "the process of
determining whether exposure to an agent can cause an increase in
the incidence of a health condition (cancer, birth defect, etc.)-
This element characterizes the nature and strength of the evidence
of causation." Dose-Response Assessment is "the process of
characterizing the relationship between the dose of an agent
administered or received and the incidence of an adverse health
effect in exposed populations and estimating the incidence of the
effect as a function of human exposure to the agent." The term
stressor-response. rather than dose-response, is used in this
guidance to include the great number of non-toxicological stressors
that impair ecological systems 1 Like the dose-response assessment
described by the NAS (NRC, 1983), stressor-response assessment
considers the intensity and pattern of exposure, and other
variables (e.g., gender, life-history stage) to evaluate the
responses elicited by a particular agent.
In many ecological risk assessments, the hazard identification
and stressor-response assessments may be conceptually close to one
another. In assessments that rely on laboratory data, the
information used for hazard identification (which effects are of
concern?) and stressor-response (what is the magnitude of the
effect?) may be obtained simultaneously. In other assessments,
information linking the stressor with the effect may be obtained
separately from the stressor-response assessment. To accommodate
both approaches, hazard identification and stressor-response are
retained but are treated as one element of the risk assessment
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paradigm, hazard assessment2. This information on hazard is
integrated with the exposure assessment to estimate risk.
Exposure assessment is defined -by NAS as "the process of
measuring or estimating the intensity, frequency, and duration of
human exposures to an agent currently present in the environment or
of estimating hypothetical exposures that might arise from the
release of new chemicals into the environment." Ecological
exposure assessment considers many of the same concerns; important
issues include exposure of multiple organisms, exposure to non-
chemical stresses, and the timing of the- exposure relative to
important life cycle attributes.
Risk characterization is defined by NAS as "the process of
estimating the incidence of a health effect under the various
conditions of human exposure described in exposure assessment."
This definition is applied here to ecological effects, but is
expanded to include a discussion, when applicable, of the
ecological consequences of observed or estimated adverse effects.
For example, a risk assessment demonstrating adverse effects on
aquatic invertebrates may also describe the ramifications of these
effects on other organisms such as fish. Risk characterization
includes a summary of the strengths, limitations and uncertainties
of the data and models used to form conclusions.
1.7. Ecological Risfc Assessment Issues for Future consideration
Incomplete information resulting from gaps in scientific
theory is common in both ecological and human health risk
assessments. The NAS emphasized the need to make necessary
judgements and proceed with risk assessments under these conditions
(NRC, 1983). At the same time, it is important to identify and
address critical scientific issues to fill information gaps and
advance the risk assessment process.
Table 1 presents a number of issues of special significance
for future ecological risk assessment guidelines. The orientation
of this document and the incomplete development of some subjects
2 The combination of hazard identification and stress-response
assessment is called "hazard assessment" here. Another definition
of hazard assessment is a quotient or margin of safety calculated
by comparing the toxicological endpoint of interest to an estimate
of exposure concentration. The latter definition refers to a
combination of stress-response assessment and exposure assessment.
This document uses only the former definition.
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Table 1: Issues in Ecological Risk Assessment
Conceptual Framework Development
How do endpoints identified for a risk assessment depend
on spatial and temporal scale and the type of stressor?
Are there endpoints that are most appropriate for
different types of assessment (e.g., priority-setting,
initial evaluations of risk, evaluation of remedial
alternatives)?
Hazard Assessment
How should different types of evidence be weighed?
What consideration should be given to data obtained from
tests conducted with nonstandard procedures or conducted
with surrogate species for which there is little
information on relative sensitivity?
How should the distribution of individual organism
responses to the stressor be taken into account?
What should be the basis for extrapolating among taxa,
organizational levels, and functional groups?
What should be the basis for extrapolating the effects of
physical perturbations?
What is the nature of the stressor-response function at higher
organizational levels (e.g., communities and ecosystems)?
Exposure Assessment
How should temporal and spatial variation in exposure
(e.g., transitory vs. resident populations, episodic
exposure) be considered?
How should multiple - stressors and multiple routes of
exposure be considered?
How is exposure influenced by physical, chemical, and
biological attributes of the environment?
What are the best attributes of physical disturbance for
assessing exposure (e.g., fragmentation, edge)?
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Table 1 (continued)
Risk Characterization
How is the potential for recovery factored into risk
characterization?
How can critical effects levels be incorporated into risk
characterization?
What role should assumptions play in reducing the
probability of a false negative (e.g., Type II error)?
How are the overall results of the risk assessment best
communicated?
What additional approaches are available for characterizing
uncertainty?
How can chemical and non-chemical stressors (e.g., habitat
alteration) be combined in the risk characterization process?
What alternatives to the quotient method are available for
risk characterization?
General Issues
What is the role of risk management and policy in the risk
assessment process?
What information, in addition to the points raised above, is
needed for conducting ecological risk assessments:
1. At regional and global scales?
2. At community and ecosystem levels?
3. For non-chemical stressors?
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reflect the lack of scientific knowledge in some areas. For
example, more methods are currently available for chemical
stressors and individual- or population-level effects than for
certain non-chemical stressors and community- or ecosystem-level
effects. However, risk assessment guideline development is an
evolutionary process, so new approaches or methods for dealing with.'
these issues may be incorporated into future guidelines as they
become available.
1.8. Organization
The remainder of this document is arranged sequentially.
Chapter 2 discusses conceptual framework development; this chapter
is particularly important for assessors to consider when endpoints
are not determined a priori by statute or other authority. Chapter
3 discusses hazard assessment, Chapter 4, exposure assessment and
Chapter 5, risk characterization. Chapter 6 contains the glossary.
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2.
CONCEPTUAL FRAMEWORK DEVELOPMENT
Conceptual framework development establishes the goals,
breadth, and focus of the ecological risk assessment. Its-product
is a conceptual' model that describes how a stressor might affect
organisms, populations, communities and ecosystems (i.e.,
ecological components) in the natural environment. This conceptual
model is evaluated further in the hazard identification, stressor-
response, and exposure assessments.
Conceptual framework development begins with the review of
available information on the characteristics of the stressor and
the receiving environment, including the organisms, populations,
communities, and ecosystems likely to be exposed. It also
describes the characteristics of the biological systems that might
be affected by exposure to the stressor'(i.e., endpoints). Some
endpoints are selected for further evaluation based on the purposes
of the assessment, ecological relevance, susceptibility, and
practical constraints. Selected endpoints and preliminary
information on the stressor are then integrated into the conceptual
model.
The extent and detail of the development process depend on the
purpose of the assessment and the amount of information available
on the situation under evaluation. One conceptual model may serve
a suite of similar risk assessments (e.g., for new individual
chemicals released to Water).
2.1. Stressor and Environmental Characterization
Conceptual framework development begins with the
identification of a stressor or group of stressors. In some cases,
an effect observed in the field or laboratory can be used to
identify stressors that can be evaluated further. In other cases,
the description of a source helps identify stressors. A
preliminary evaluation of the characteristics of the.'stressor and
the receiving environment helps evaluate the spatial and temporal
distribution of the stressor and identify the ecological components
that may be exposed to it.
The preliminary evaluation of the spatial and temporal
distribution of the stressor uses available information on its
source and the factors that influence its distribution and fate.
This includes information on release rates and patterns,
physicochemical properties such as water solubility and volatility,
and environmental characteristics such as soil type and climate.
The physical and chemical properties of the chemical stressors
provide important insight into fate and distribution, which in turn
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determines which ecological components might be exposed. The
components evaluated in ecological risk assessment are discussed
below and can include organisms, populations, communities, and
ecosystems.
The amount of information available to characterize the
temporal and spatial distribution of the stressor and identify
potentially exposed ecological components varies greatly among risk
assessments. In site-specific assessments (e.g., hazardous waste
sites), the physical characteristics are best described using data
obtained from site investigations and sampling. A general sense of
the expected physical environment and biological community can be
provided by using topographic maps, soil maps, remote sensing
techniques, and vegetative-cover or ecoregional maps. Expected
populations and organisms, can be identified by characterizing the
habitat at the site. Other stressors that may influence the
community should also be identified at this point.
When evaluating stressors released to particular habitats
(e.g., pesticides applied to agricultural lands), it is important
to consider- both exposed and adjacent areas. In addition, the
organisms using exposed and adjacent areas may vary in different
regions, even though the habitat may be similar.
In other assessments, very little is known about specific
potential exposure points, but fate-and-transpprt data and general
release locations can be used to describe generic or representative
exposure settings (e.g., aquatic habitats). In these cases, a
generic or surrogate community can be defined, and surrogate
organisms can be used to represent populations.
2.2. Endpoint Identification and Selection
The second major step in the planning process is the selection
of the characteristics of ecological components that can be
adversely affected by exposure to a stressor. For the purposes of
this document, these characteristics are called endpoints. An
endpoint describes the change in the characteristic (e.g.,
increased mortality), the ecological component that is affected
(e.g., trout) (Suter, 1990a), and often the spatial scale (e.g.,
long-terra population viability of.' a species within its current
range).
Assessment and measurement endpoints are often distinguished
in ecological risk assessments. Measurement endpoints are the
effects that can be measured. As used in this guidance, the
definition encompasses both the characteristic that is measured
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(mortality) and the quantitative summary of those measurements
(e.g. , an LC50)3.
Effects that are readily measured may not be directly useful
in risk management, because the significance of the response is not
always evident. Assessment endpoints are useful intermediaries
that describe the environmental value to be protected and thus link
measurement endpoints to the risk management process. They are the
ultimate focus of risk characterization. In the best case, the
assessment endpoint can be measured and then the measurement and
the assessment endpoint are the same. If an assessment endpoint
cannot be directly measured, measurement endpoints . are selected
that can be related, either qualitatively or quantitatively, to an
assessment endpoint.
Measurement and assessment endpoints are often categorized by
organizational levels. Organizational levels include individual
organisms, populations that include many individuals of the same
species, communities comprised of interacting multiple populations,
and ecosystems comprised of organisms and their abiotic
environment. Multiple units at one organizational level form the
next higher level, and changes at one level may, influence what
occurs at adjacent levels.
Each organizational level has both structural and functional
attributes that may serve as endpoints. Structural attributes of
ecological systems include, for example, the mass of individuals,
the age-class structure of populations, the number and distribution
of populations within a community, and the biomass of ecosystems.
Functional attributes involve the flow of mass and energy (e.g.,
respiration rate of individuals, intrinsic rate of increase of
populations, primary productivity of communities, and decomposition
and nutrient cycling rates of ecosystems) . The interaction between
structure and function is an area of active research. For example,
it is still -difficult to map functional attributes onto species
assemblages because organisms may perform more than one function,
and may perform different functions at different life stages.
3 Alternative terminology distinguishes between the
characteristic that is measured (called a response indicator) and
the quantitative summary of the results (called a measurement
endpoint) (U.S. EPA, 1990b).
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Table 2 presents example measurement and assessment endpoints;
in practice, an ecological component would also be specified4.
Endpoints at each organizational level have strengths and
limitations. Risk assessments are not confined to one
organizational level, and may use a suite of endpoints at multiple
levels for different aspects of the assessment* Measurement and
assessment endpoints are selected by considering the purpose of the
assessment, ecological relevance, susceptibility to the stressor,
and practical constraints. These criteria are discussed generally
below; more detailed discussions can be found in Suter (1990a),
Kelly and Harwell (1990), and U.S. EPA (1990b). Endpoint selection
relies on professional judgement; for this reason, the rationale
for selection should be clearly documented.
2.2.1.
Purpose and Needs of the Assessment
It is important to consider the purpose of the assessment when
selecting endpoints. Assessment endpoints. vary with program and
need within the program, for example, assessment endpoints selected
to support a decision under a specific regulation may differ
substantially from those used to support a request for further
testing. The assessor may wish to consult with the risk manager to
identify assessment endpoints for specific regulatory needs.
Measurement endpoints also vary with the purpose of the assessment.
For example^ a measurement endpoint diagnostic of a specific
stressor may be preferred when the assessment is based on field
observations and this causal evidence is particularly important to
the risk management decision.
Assessment endpoints may be selected because they are valued
by society (Clements, 1983). Examples include the maintenance of
commercially- or recreationally-important populations or the
viability of an endangered or threatened species. Other examples
are attributes of ecosystems that are valued for functional (e.g.,
.flood water retention by wetlands) or aesthetic reasons (e.g.,
visibility in the Grand Canyon). In some cases the adverse effect
is an increase in undesirable species; the risk assessment may then
focus on factors that favor these organisms.
4 Several areas of active research may provide useful
measurement endpoints in the future. These include bioraarkers,
which measure physiological and biochemical changes, and landscape-
level studies and models (e.g., Costanza et al., 1990), which
describe distribution patterns of communities and ecosystems. For
these measurements to be useful as endpoints, an established
relationship with endpoints like those shown in Table 2 is
necessary.
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Table 2: Recommended Endpoints at Each Level of Ecological
Organization^
LEVEL OF
ORGANIZATION
ASSESSMENT
ENDPOINTS
MEASUREMENT ENDPOINTS
Individual
Organism health
Death*
Growth* •
Reproduction*
Morbidity
Behavior
Population
Viability
Birth rate
Death rate
Immigration/Emigration
Age-Size-Class Structure*
Distribution*
Abundance*
Community
Deviation in
structure and
function from
unimpaired
community
Species shifts
Numbers of species*
Species dominance*
Trophic shifts
Ecosystem
Deviation in
structure and
function from
unimpaired system
Biomass*
Productivity (P/R ratio)*
Nutrient dynamics
Materials and energy flow*
# Generic examples are shown in this table; in practice, an
ecological component would also be specified (e.g., mortality in
trout; flood retention by wetlands). In addition, the spatial
scale of the endpoint is often specified.
* Depending on the goal of the assessment, these measurement
endpoints may also- serve as assessment endpoints.
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When evaluating populations that are valued, it is critical
that measurement endpoints include both direct and indirect
effects. Direct effects include changes in characteristics of the
valued population, such as increased mortality, reduced growth and
development, or impaired reproduction. Indirect effects include
similar effects on species upon which the valued population depends
for food or habitat (see the discussion on ecological relevance,
below).
When evaluating valued characteristics of communities and
ecosystems, it is important to recognize that measurement endpoints
at lower organizational levels may not adequately reflect adverse
effects on community structure and function. Endpoints at higher
organizational levels are difficult to quantitatively predict using
measurement endpoints at lower organizational levels because of
characteristics of ecological components that confer resiliency.
For example, individuals may be able to tolerate or compensate for
a stressor through some physiological mechanism. Communities and
ecosystems can continue to function despite changes in components
when many components provide similar functions5. For these
reasons, measurement endpoints at the same organizational level may
be the most useful, or, alternatively, a conservative approach may
select endpoints on the basis of susceptibility (see the discussion
on susceptibility below).
2.2.2.
Ecological Relevance
Ideal assessment and measurement endpoints are ecologically
relevant. Ecologically-relevant endpoints influence other
endpoints, both at the same organizational level and also at other
levels. Changes in endpoints at higher organizational levels or at
large spatial scales are often ecologically relevant because they
can involve large numbers of organisms, populations, communities,
and ecosystems.
Changes in endpoints at lower organizational levels can also
produce wide-ranging consequences. Changes in organisms and
populations that provide important functions in communities may
result in indirect effects on other community members. Keystone
5 While they enable a system to persist despite exposure to a
stressor, resistance mechanisms are not without costs.
Physiological tolerance mechanisms may require additional energy,
and may leave the organism less fit to compete or reproduce. Long-
term exposure to a stressor may decrease species or genetic
diversity; genotypes or species that compete well in the .face of
one stress may be more vulnerable to future, different stresses.
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species, for example, influence the abundance and distribution of
other community members; effects on them may induce changes
throughout the community. Community.interactions determine the
extent to which an effect will be manifested in more than one
organizational level. Food-web and trophic relationships are
primary characteristics to consider when evaluating indirect
effects. In addition, competition for key resources ('e.g., food,
nesting sites, mates) and important species-to-species interactions
(e.g., predator-prey relationships, mutualism, and commensalism)
should be considered. A complete risk assessment will account for
important ecological relationships during ehdpoint selection.
2.2.3.
Susceptibility
During early or minimal stages of exposure to a stressor, the
most susceptible individuals and processes are often the first to
be affected6. Because ecosystems consist of communities,
populations, and individual organisms, if shifts are observed at
the ecosystem level, it is likely that significant changes have
already occurred at lower organizational levels (Rapport et al.,
1985; Hermann, 1985; Kelly and Harwell, 1990; ESA, 1991). However,
because of differences in sensitivity within an organizational
level, adverse effects can be seen simultaneously at the
individual, population, community and ecosystem organizational
levels.
Information on relative susceptibility can be used to choose
endpoints that are among the first to be affected by exposure to a
stressor. Alternatively, this information can be used to select
the measurement endpoints that best represent response to a
stressor. Risk assessments based on endpoints that are not
susceptible will underestimate the risk to more susceptible
endpoints. For example, if an organism is tolerant of a stressor,
risk assessments based on responses of that organism will
underestimate risk to less-tolerant organisms, and may also
underestimate risk to a community of more-sensitive or more highly-
exposed populations.
Susceptibility to a stressor is a function of both exposure
and sensitivity. Relative sensitivity is often stressor-specific,
but can also vary with classes of stressors (e.g., narcotic
chemicals, pesticides). Data used to evaluate sensitivity can
6 Low inputs of some stresses (e.g., water, carbon dioxide)
can actually result in improvements in health or productivity under
some circumstances. This "subsidy effect" is not usually seen with
inputs of toxic chemicals (Odum et al., 1979).
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include chemical structure-activity relationships (SARs), effects
observed in the field, and laboratory stressor-response data.
Exposure to multiple stressors may make organisms more sensitive to
the particular stressor being assessed (e.g., in populations
exposed to habitat loss and harvesting, toxicological impacts may
have greater impact on population viability than toxicological
studies alone suggest). Although sensitivity directly influences
the outcome of the risk assessment, information on relative
sensitivity, particularly at higher organizational levels, is often
unavailable during the planning process.
The second aspect of susceptibility is exposure. When
evaluating endpoints at the individual and population level, it is
particularly important to consider life history attributes, since
life stage may influence both the sensitivity of the organism and
the magnitude of exposure. Organisms may not be present when a
stressor is introduced in the environment because they move into an
area for short periods to feed, breed, or mate, or they migrate on
a diurnal or seasonal basis. These organisms tend to be less
exposed than those living continually in the environment if the
rout© of exposure is similar. However, organism use of
environmental resources further influences the extent of exposure:
some species use resources where exposure will be greatest (e.g.,
predators at the top of the food web will incur greater exposure to
chemicals that bioaccumulate).
When little is known about susceptibility, a group of
endpoints is often evaluated in the hazard identification and
stressor-response assessment. For example, surrogate species are
often chosen to represent different trophic levels or taxonomic
groups. No single species is appropriate for every situation, but
surrogates can provide useful information with a reasonable
commitment of resources. The selection of surrogate species is
discussed in .U.S. EPA (1980, 1982, 1990c).
2.2.4.
Practical Constraints
A number of practical constraints further influence the
utility of measurement and assessment endpoints. Ideal assessment
endpoints have a clear, unambiguous definition and can be predicted
or measured. Ideal measurement endpoints have low natural
variability, are easy and inexpensive to measure, have standard
protocols, are supported by an existing data series, and produce
scientifically defensible results (U.S. DOI, 1987; Suter, 1989).
Endpoints at lower organizational levels are often the most
readily measured in controlled laboratory settings. However,
community and ecosystem endpoints may be the easiest way to detect
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effects in field studies. For example, microorganisms that break.
down organic matter may be adversely affected by a stressor, but
the effect 'may be difficult to recognize at the individual,
population, or community level. Inhibition of decomposition can be
evaluated at the ecosystem level by predicting or observing the
accumulation of leaf litter on a forest floor. In addition,rthe
natural variability in some endpoints at lower organizational
levels may be larger than those at higher levels. In these cases
it may be easier to detect stressor-related changes at higher
organizational levels.
2.3. Presentation of the Conceptual Model and Evaluation Approach
The information gathered on the stressor, the receiving
environment and endpoints is integrated into a conceptual model.
The conceptual model consists of a series of working hypotheses
regarding how the stressor might affect ecological components of
the natural environment7. The conceptual model summarizes the
hypotheses that will be evaluated in the hazard identification,
stressor-response, and exposure assessments, and provides a
foundation to determine whether the assessment will reflect all
logical ways a stressor could cause an adverse response and ensure
that important endpoints are considered.
The conceptual model can be presented in narrative or
schematic form. An example of a schematic diagram is shown in
Figure 3. In this example, decreased birth rate in a hypothetical
aquatic population was selected as an assessment; endpoint. The
diagram illustrates different measurement endpoints that can be
used to estimate decreased birth rate. The use of these diagrams
is also discussed in Barnthouse et al. (1982) and Rodier (1990).
Many hypotheses may be generated during conceptual framework
development; those that are most reasonable and quantifiable are
selected for further evaluation. Because of data gaps, some
hypotheses will not be carried further in the .assessment; it is
important that these hypotheses are noted when evaluating
uncertainty during Risk Characterization. Professional judgement
is needed to select the most appropriate risk hypotheses; the
selection rationale should be documented.
7 The term hypothesis, as used in this guidance, reflects this
preliminary thought process for relating and demonstrating
relationships between observed or predicted effects and the
stressor under evaluation. The NRC "green book" (1986) also
describes development and use of working hypotheses in ecological
assessments.
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egg
hatching
Population
Decline
Increased
death rate
Decreased
birth rate
Decreased
immigration
Increased
emigration
I
ised
ng
Changes
in mating
behavior
Reduced
production of
eggs or sperm
|
Avoidance
of spawnii
habitat
Insufficient
growth of
adults
Direct
reproductive
toxicity
Decrease
in food
supply
Increased
morbidity
Figure 3: Example flow diagram analysis of
decreased birth rate in a population
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Data are not always available to support the development of a
conceptual model. When data are insufficient for hypothesis
development, it cannot be concluded that there is no risk;
iterative evaluations are conducted to identify data gaps and
ensure that hypotheses are developed.
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3. HAZARD ASSESSMENT
Hazard assessment describes the relationship between the
stressor and the endpoints identified during conceptual framework
development. Hazard identification describes the causal
relationship between the stressor and the assessment and
measurement endpoints. Stressor-response assessment evaluates ±he
relationships between the stressor and measurement endpoints and
quantitatively extrapolates from these to assessment endpoints.
3.1. Hazard Identification
Hazard identification qualitatively evaluates the causal
relationship between a stressor and an adverse effect3. The
information gathered during hazard identification supports and
complements the stressor-response assessment. For example, when
the stressor-response relationship is based on laboratory studies,
the hazard identification might gather data on effects that occur
in the field. When stressor-response is based on observational
field data (e.g., biomonitoring), hazard identification might focus
on causal evidence.
Both controlled tests and observational studies may be used in
'hazard identification. Where test data are not available (e.g.,
for chemicals yet to be produced) , structure-activity relationships
may be helpful (Clements et al., 1988; Auer et al., 1990).
Evidence provided by these studies is evaluated by considering the
elements of statistical design and analysis, particularly with
respect to replication and variability. For example, statistical
methods are not very powerful (i.e., they cannot detect small
differences) when replication is low and variability is high, such
as in many observational studies. And statistical significance
does not always reflect biological significance; important
biological changes may not be detected by statistical tests.
Professional judgement and statistical consultation are both used
to evaluate statistical and biological significance.
Controlled laboratory and field tests can provide strong
causal evidence linking a stressor with a response, and can also be
used to discriminate between multiple stressors. Data from
laboratory studies tend to be less variable than those from field
studies because many environmental factors can be controlled in the
8 A causal relationship occurs when an event, condition or
characteristic plays an essential role in producing an adverse
response (Rothman, 1986).
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laboratory. However, because these factors are controlled,
responses may differ from those in the natural environment.
Observational field studies provide environmental realism that
laboratory' studies lack. However, the presence of multiple
stressors and other confounding factors (e.g., habitat quality) in
the natural environment can make it difficult to attribute observed
differences to specific stressors. Confidence in causal
relationships can be improved by carefully selecting comparable
reference sites, or by evaluating changes along a gradient of the
stressor where minimal differences in other environmental factors
are apparent. Potential confounding factors must be addressed
during the analysis.
Many of the concepts applied to evaluating causal
relationships in human epidemiology can be useful for evaluating
observational field studies. Hill (1965) suggested that nine
aspects of an association be considered when evaluating causality.
Rothman (1986) summarized these criteria as follows:
1) strength, a high magnitude of effect is associated with
exposure to the stressor;
2) consistency, the association is repeatedly observed under
different circumstances;
3) specificity, the effect is diagnostic of a stressor;
4) temporality, the stressor preceded the effect in time;
5) presence of a biological gradient, a positive correlation
between the stressor and response;
6) a plausible mechanism of action;
7) coherence, the hypothesis does not conflict with knowledge
of natural history and biology;
8) experimental evidence; and
9) analogy, similar stressors cause similar responses.
Not all of these criteria need to be satisfied, but each
incrementally reinforces the argument for causality. Addition
negative evidence does not rule out a causal association but may
indicate that knowledge of the association is incomplete.
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3.2. Stressor-Response Assessment
Stressor-response assessment quantifies the relationship
between .-the amount of the stressor and magnitude of response.
Ideally, it quantifies the relationship between the stressor and
the assessment endpoint identified during conceptual framework
development. When the assessment and measurement endpoint are the
same, this analysis is straightforward. When they are different,
the relationship between measurement and assessment endpoints is
quantified first, and then extrapolations are used to predict
changes in the assessment endpoint. In some cases, the
quantitative relationship between measurement and assessment
endpoints is not known, and qualitative inferences are made during
Risk Characterization (see Chapter 5).
3.2.1.
Types of Data and Analyses Used in Stressor-Response
Assessment
The specific experimental protocols and statistical analyses
used to assess stressor-response relationships depend on the
assessment objectives and available methods. Since methods change,
this discussion addresses the strengths and limitations of general
approaches.
Like hazard identification, stressor-response assessments can
be based gn controlled laboratory and field studies and
observational field studies. Stressor-response assessments often
progress from short-term, inexpensive tests that measure effects on
mortality to longer-term tests that evaluate sublethal effects such
as reduced growth, development, or reproduction. Similarly, the
test environment may progress from very uniform laboratory
conditions to more realistic mesocosm and field trials. The
decision for proceeding to a more detailed analysis can be based on
stressor-response information alone (e.g., the LC50 is at or below
a threshold value), or can be based on preliminary risk estimates.
Data from these studies can be used to test specific
hypotheses or conduct a regression analysis. Hypothesis testing is
most often used to identify a NOEL or LOEL (no-observed-effect and
lowest-observed-effect levels, respectively). Hypothesis testing
is a commonly-used and accepted approach, but has some important
limitations: 1) statistical significance may not correspond to
biological significance; and 2) a poor design or testing procedure
can reduce the apparent toxicity of the chemical (Barnthouse e.t
al.f 1986). When using hypothesis testing, the power of the test
to detect differences and the level of statistical significance
should both be reported.
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Regression analyses can generate stressor-response curves that
can evaluate risk at different exposure levels. Regression
analyses have been applied to both chemical and physical stressors
(for an example of the latter,.see Turner's [1977] analysis of the
relationship between wetland area and commercial shrimp harvest).
For practical reasons, the results of stressor-response curves are
often summarized as one reference point, for instance, an LC50 or
ECSO (lethal or effective concentration, respectively, in 50 percent
of a test population). Although useful, these values provide no
information about the slope or shape of the stressor-response
curve. When the entire curve is used, or when many reference
points are identified, the difference in magnitude of effect at
different .exposure levels can be reflected in the risk
characterization.
3.2.2.
Extrapolation Methods for Stressor-Rasponse Assessments
As discussed above, a stressor-response assessment ideally
quantifies the relationship between the amount of the stressor and
the/magnitude of change in the assessment endpoint. This section
describes quantitative methods used to extrapolate between
measurement and assessment endpoints. If quantitative methods are
not available, measurement and assessment endpoints may be linked
•qualitatively (see Chapter 5) . The rationale for any
extrapolations and- their associated uncertainty should be clearly
explained.
Most quantitative extrapolation methods assess response to
chemical exposure at the individual level. The discussion below
addresses species-to-species, endpoint-to-endpoint, and laboratory-
to-field extrapolations. Much less is known about extrapolating
among communities and ecosystems. Models to extrapolate between
levels of organization and evaluate indirect effects have rarely
been applied. Active research in these areas may provide
quantitative extrapolation methods in the future. Because these
models are most often used to provide a common framework to
describe and compare consequences of adverse effects rather than as
predictive extrapolation methods, they are discussed under Risk
Characterization (Chapter 5).
Species-to-Species Extrapolations
The difference in response between species is often estimated
based on relative differences in other attributes such as
physiology, morphology, or life history. The factors that
influence response vary from stressor to stressor. If a stressor's
mechanism of action is known, it may be easier to identify the
characteristics that influence response and perform more confident
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extrapolations. These general concepts can be applied to physical
as well as chemical stressors. For example, interspecies
extrapolations for habitat alteration can be qualitatively based on
life history characteristics such as resource utilization.
Statistical1 methods have great utility for species-to-species
extrapolations, although most of these focus on evaluating
responses of aquatic organisms to chemicals. One approach to
species-to-species extrapolations simply calculates concentrations
corresponding to a specific endpoint (e.g., an LC50) for a number
of species (see Sloof and Canton, 1983; Chapman, 1983; and Mayer et
al., 1986 for aquatic examples). Untested species are assumed to
fall within the same range (i.e., it is assumed that tested species
adequately represent the response of untested species) . The
response range can be very large, and increases as more species are
included in the study. However, the confidence that the response
of untested organisms falls within the range also increases with
the number of species.
Regression models can be used to reduce the confidence limits
and increase the utility of species-to-species extrapolations by
correlating taxonomic proximity with variation in response (Kenaga,
1978; Suter et al., 1983, 1986, 1987; Sloof, 1986; von Straalen and
Denneman, 1989) . These models indicate that taxonomic
extrapolations have narrower prediction limits for closely-related
species than for distantly-related species. In addition, the
prediction limits tend to be narrower for structurally-similar
chemicals (and chemicals with similar mechanisms of toxicity).
Exceptions may be expected when life-history characteristics or
biochemical and physiological processes are very different between
closely-related species.
An area of active research is toxicokinetic and toxicodynamic
modeling. These models evaluate inter- and intraspecies variation
in response to chemicals and may provide a basis for more
mechanistic extrapolations in the future.
Endpoint-to-Endpoint Extrapolations
Endpoint-to-endpoint extrapolations are used when short-term
endpoints are used to predict long-term or chronic effects (e.g.,
an LCSO used to predict a NOEL). These extrapolations often include
temporal and lifestage components and may combine several chronic
endpoints. All of these components are integrated in an analysis
of acute-to-chronic ratios or a regression analysis. The
relationships derived are then applied to other species for which
only acute data are available. The implicit assumption here is
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that the difference between acute and chronic toxicity remains
relatively constant between species.
Because of the many sources of uncertainty, this approach
often yields very large ranges of acute-to-chronic ratios and wide
prediction limits in regression analysis (see, for example,
Barnthouse et al., 1990 and Sloof et al., 1986). Endpoint-to-
endpoint extrapolations often vary because the'degree of response
differs between tests. For example, results from an acute test
will be expressed as an LD50, whereas results from a chronic.test
are often expressed as a NOEL or LOEL. One way to reduce the
confidence limits and increase the utility of these extrapolations
is to correlate endpoints separately ar standardize the degree of
response (Mayer, 1990; Mayer et al., 1 6; Suter et al., 1985).
Laboratory-to-Field Extrapolations
The responses of organisms exposed in the laboratory often
differ from those exposed under natural conditions; laboratory-to-
field extrapolations evaluate these differences. Laboratory
predictions may overestimate field response if they do not account
for compensatory or regulatory mechanisms, adaptation to stress, or
reduced bioavailability under field conditions (van Straalen and
Denneman, 1989; Suter et al., 1985). On the other hand, they may
underestimate field response if laboratory conditions do not
reflect actual field conditions, account for the ecological cost of
adaptation, or identify other interacting stressors.
When possible, factors that influence differences in response.
between the laboratory and field should be incorporated
quantitatively into the stressor-response assessment. For example,
some data are available that relate specific habitat
characteristics to changes in response to a stressor (e.g., water
hardness and metal toxicity). Similarly, some data are available
to help predict responses to complex mixtures that are composed of
chemicals having the same mechanism of action (see Broderius and
Kahl, 1985; McKim et al., 1987).
Laboratory-to-field extrapolations can greatly increase the
uncertainty of response estimates, but the direction of any bias is
often unclear. If the laboratory-to-field extrapolation appears to
be the major component of uncertainty in an assessment, field
studies may be warranted.
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4. EXPOSURE ASSESSMENT
For the purposes of this document, exposure assessment is
defined as the assessment of the spatial and temporal distribution
of a stressor and its co-occurrence with components .of ecological
systems. This definition is somewhat broader than that provided, in
the Guidelines for Exposure Assessment (U.S. EPA, 1991) which
focuses on human exposure to chemicals. The exposure guidelines
differentiate between exposure, the contact of a chemical with an
organism's outer boundary, and dose, the amount of chemical within
the outer boundary of the organism. While these definitions are
useful for chemical exposure to organisms, the broader definition
better represents exposure assessment for ecological components
(i.e., populations, communities, and ecosystems) where the boundary
of the system does not serve as a barrier.
Many of the other concepts presented in the Guidelines for
Exposure Assessment also apply to ecological exposure assessment.
Important aspects of ecological exposure assessment include the
following:
Many different ecological components within • a particular
environment may be exposed, including organisms, populations,
communities and ecosystems.
The timing of the exposure relative to the life stage and
seasonal activity patterns of exposed organisms can greatly
influence the occurrence of adverse effects. Even short-term
events may be significant if they coincide with critical life
stages.
The perception of, as well as direct contact with, a stressor
can cause adverse effects. For example, the perception of degraded
spawning habitat may cause animals to avoid spawning areas and
decrease reproductive success.
Exposure assessments are most effective when the results of
the exposure and stressor-response assessments are comparable. For
example, exposure estimates used to evaluate acute effects should
be averaged over .short periods of time to take into account
short-term, pulsed stressor events. Exposure assessments for
chronic stressors should account for both long-term, low-level
exposure and possible shorter-term, higher-level exposure that may
elicit similar adverse chronic effects. Other factors to consider
include cumulative effects from continuous or intermittent
exposures, the magnitude and frequency of exposure, and the life-
history stage of exposed organisms. Particular attention should be
given to exposure during periods of reproductive activity, since
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early life stages are often more sensitive to stressors, and adults
may also be more vulnerable during this time.
The description and analysis of uncertainty in exposure
assessments is combined with other uncertainty analyses in risk
characterization. Sources of uncertainty and methods .for
describing it are discussed in greater detail in Chapter 5 and in
the Guidelines for Exposure Assessment (U.S. EPA, 1991).
4.1. Estimating Exposure
Guidance on specific methodologies for conducting an exposure
assessment is beyond the scope of this document. However, the
overview of the basic philosophy and concepts of ecological
exposure assessment presented below provides a basis for method
selection.
There are three approaches used to quantify human exposure to
chemicals: point-of-contact measurements, scenario evaluation, and
reconstructive assessment (U.S. EPA, 1991). The point-of-contact
approach uses monitoring devices to measure the stressor at the
actual point of contact while exposure is occurring. Point-of-
contact measurements are rarely used in ecological risk assessment
because it is difficult to attach monitoring devices to free-
ranging organisms. The other two methods (scenario evaluation and
reconstructive) are discussed below.
4.1.1.
Exposure Scenario Evaluation
The scenario evaluation approach to exposure assessment
consists of two basic elements. First, the spatial and temporal
distribution of the stressor is measured or estimated. Second, the
distribution of the biological component and its characteristics
that influence exposure are evaluated. The two are combined to
evaluate the co-occurrence of the stressor and the ecological
component.
The first element of scenario evaluation measures or estimates
the stressor's spatial and temporal distribution. The initial fate
and transport evaluation conducted during conceptual framework
development should be used to focus measurement and modeling
activities. The measurement and modeling of chemical stressors are
discussed in detail in the Guidelines for Exposure Assessment (U.S.
EPA, 1991). Non-chemical stressors such as increased flooding can
be evaluated with techniques from geology, hydrology, engineering,
and other relevant fields. Physical alterations can be evaluated
by ground reconnaissance, aerial photographs, or:satellite imagery,
depending on the scale of the disturbance.,- Quantifying specific
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attributes of physical alteration (e.g., fragmentation, edge
effects) is an area of active research that may yield use.'ful
methods in the future.
The presence of one stressor may indicate that others are
present. For example, removal of riparian (streamside) vegetation
alters habitat structure directly. However, removal can also cause
siltation and increase water temperature. In this case the initial
stressor (vegetation removal) has additional ramifications
(siltation and temperature rise). Similarly, the discovery of one
chemical may provide good reason to test for others in the same
location.
The second element of scenario evaluation considers the
spatial and temporal distribution of the ecological 'components
under evaluation. It should also consider the characteristics of
these components that influence their co-occurrence with the
stressor, such as habitat, food preferences, and reproductive
cycles. Seasonal activities like migration and use of alternate
resources may substantially influence exposure and should also be
considered.
Exposure scenario evaluations use .information routinely
obtained by the Agency and are therefore cost-effective for
ecological exposure' assessments. The assessor should be aware that
scenario evaluation implicitly assumes that measured or estimated
stressor concentrations accurately represent those at the actual
point of contact. In addition, exposure scenario evaluations
commonly assess stressors individually, and may under- or
overestimate exposure to multiple stressors and mixtures. Scenario
evaluation can be performed with little or no data; consequently,
the underlying assumptions and uncertainties should be clearly
documented.
4.1.2.
Reconstructive Exposure Assessment
Reconstructive exposure assessments examine organisms to
determine the presence of, or previous exposure to, a stressor.
Biochemical or physiological evidence (e.g., biomarkers) may be
used to evaluate exposure. This form of exposure assessment is
most useful when a chemical or unique metabolite can be detected in
the exposed organisms. Changes in certain enzyme systems (such as
mixed-function oxidases) must be interpreted carefully because
other unrelated stressors may induce similar changes.
Retrospective exposure measurements (including biomarkers) are
most useful for risk assessment when 1) they can be quantitatively
linked to the.amount of stressor contacted by the organism; and 2)
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the relationship between the measurement and an adverse response
can be defined as part of the stressor-respbnse assessment.
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5. ECOLOGICAL RISK CHARACTERIZATION
Risk Characterization evaluates the likelihood that an adverse
ecological effect could occur as a- result of exposure to a
stressor, and may also address the significance or consequences of
identified risks. It integrates hazard identification, stressor-
response assessment, and exposure assessment to evaluate the
endpoints selected during conceptual framework development.
As discussed previously, the purpose of the risk
characterization determines its sophistication and depth. Before
proceeding, the assessor may wish to review the conceptual model
and the relationship between measurement and assessment endpoints
to evaluate how adequately the data meet the assessment's needs.
The strength of a risk assessment depends on its supporting
data. Because there are many interactions between organisms, their
environment, and introduced stressors, it may not be possible to
answer every question that arises in a particular assessment.
Thus, the assessor may need to supplement the analysis with
assumptions or models to bridge interpretational or data gaps that
arise during risk characterization. Any methods or assumptions
used, and the rationale for their application, should be explained.
Because ecological risk assessment is an area of current research,
methodologies and assumptions evolve and change. Future guidelines
may address developing technologies that might be used for
ecological risk assessments. In the interim, EPA encourages the
assessor to employ state-of-the-art methods and assumptions.
The four basic steps of ecological risk characterization are:
1. Evaluate the likelihood of adverse effects;
2. Describe the consequences of identified adverse effects;
3. Assess the uncertainty associated with the risk assessment and
the evidence that supports the conclusions; and
4. Communicate the results of the risk characterization.
These elements are discussed below.
5.1. Assess the Likelihood of Adverse Effects
5.1.1. Basic Concepts
Ecological risk assessment compares predicted or measured
environmental concentrations or levels of the stressor with the
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stressor-response data. Thus, the hazard posed by the stressor is
compared with the exposure to the stressor in'order to determine
the likelihood of effects resulting from a combination of the two.
The degree of quantification in the comparison or integration
step depends on the' available data. Most ecological risk
characterizations .for single-chemical stressors are easily
quantified because the endpoints used to determine hazard can be
measured in a field or laboratory setting, and exposure can be
measured or predicted. Characterizations for multiple-chemical
stressors are harder to develop because hazard and exposure data
are often unavailable and are difficult to determine empirically.
The quality and quantity of stressor-response and exposure
assessment data determine how the risk characterization can be
presented. When variation in the stressor-response and exposure
assessments is quantified, the results, can be presented
probabilistically (e.g., there is a 50 percent probability of a 10
percent"mortality). However, in most situations, data limitations
permit only qualitative risk expressions (e.g., the LCSO will
probably be exceeded).
Although desirable, a quantitative risk characterization is
not mandatory (nor may it be achievable) for a successful
ecological risk assessment. Qualitative judgements based on the
best available data can be very useful. If qualitative categories
of risk (e.g., high, medium, low) are used, it is important to
define the categories clearly.
. state-of-the-practice approaches, which are based on the
principle of comparing hazard with exposure, are presented in
subsequent sections.. Some methods use only a single measurement
endpoint such as an LCgo. If the results of an assessment are to
be used as decision criteria (e.g., determine the need _for
additional testing), a comparison of single measurement ertdpoints
may be appropriate. On the other hand, if the assessment compares
regulatory options for mitigation, it is desirable that -the risk
characterization compare several stressor levels to obtain-a range
of values. The latter approach provides better insight into the
magnitude or severity of hazard than a single measurement endpoint.
5.1.2.
Quotient Method of Ecological Risfc Characterization
A commonly-used method of ecological risk characterization is
called the Quotient Method (Barnthouse et al, 1986). It compares
hazard with exposure and has been used extensively for addressing
the risks of pesticides (U.S. EPA, 1986) and industrial chemicals
(U.S. EPA, 1990d). The algorithm is given below:
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Exposure Value
Stressor-Response Value
Quotient
Exposure estimates may be measured or estimated, and may need
to be adjusted to account for differences in bioavailability
between laboratory and field conditions. The frequency and
duration of the field exposure and the exposure used in the
stressor-response assessment should also be comparable. The
Quotient Method implicitly assumes that the predicted or measured
exposure duration equals or exceeds that of the toxicological tests
used to derive the stressor-response curves.
. Stressor-response values commonly used with the Quotient
Met hod. include LCsos, ECsos, LOELs, and maximum acceptable toxicant
concentrations (MATCs). When needed, stressor-response values
should include the extrapolation factors presented in Section
3.2.2. Often, the stressor-response values are adjusted to provide
some conservative measure of protection. As an example, one-tenth
of an MATC might be used as the stressor-response value (U.S. EPA,
1990d).
Interpretation of the Quotient Method is fairly
straightforward. The greater the expected exposure compared to
stressor-response values, the larger the quotient and greater the
risk (i.e., greater likelihood that the adverse effects described
by the stressor-response value will occur). The Quotient Method
works best when the ratio is either very low or very high. When
the ratio is near 1, the results cannot be interpreted with
certainty. Professional judgement should be used in such cases,
and additional hazard and exposure data might be sought. The
Quotient Method is most often applied by comparing one value from
the stressor-response curve to exposure levels. An extension of
this method that provides greater insight into the magnitude of
expected effects is to compare many stressor-response values.
The Quotient Method has several advantages: It is simple,
flexible, and amenable to the data obtained in standard
ecotoxicological tests and exposure assessments. Among the
disadvantages are that it cannot easily be applied to multiple
stressors or cumulative effects, and it cannot predict the
magnitude of any effect except that which corresponds to the
reference point used in the calculation.
The Quotient Method addresses risks of direct effects that can
be quantified; these may or may not be assessment endpoints. For
example, a stressor may not be directly toxic to a fish of
interest, but may be toxic to the invertebrates it feeds upon. The
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critical relationship between mortality in aquatic invertebrates
and reductions in a fish population may be difficult for a risk
manager to recognize unless the assessor links the two and
describes the consequences during risk characterization.
5.1.3.
Additional Approaches
The basic principle of integrating hazard and exposure can be
applied in many ways. For example, exposure assessment models have
been used to determine how often a particular stressor-response or
other reference value will be exceeded in rivers and streams during
a one-year season (U.S. EPA, 1988). Suter et al. (1983) .treat
reference values, such as an MATC, as probability distributions
that are matched against similar exposure distributions to
determine the probability of exceeding the reference. Models can
combine many different reference values with models of exposure:
For example, Pearlstine et al. (1985) combined hydrologic models
with stressor-response data relating water level to tree growth to
estimate the response of a bottomland hardwood community to
different water flow regimes.
5.2. Describing the Consequences of Identified Risks
5.2.1.
General Concepts
Many ecological risk assessments evaluate endpoints that can
be directly measured or estimated using a closely-related surrogate
or quantitative extrapolation methods. In these cases, the need
for an evaluation of the consequences is reduced. In other cases,
appropriate extrapolation methods relating measurement and
assessment endpoints are not available, and an evaluation of the
consequences of a measurement endpoints's occurrence is an integral
part of the risk characterization process.
Consequences include indirect effects, effects at multiple
organizational levels, and effects at greater spatial and temporal
scales. Indirect consequences of an adverse effect are evaluated
using the logical structure established during conceptual framework
development as well as professional judgement. Interspecies
relationships (e.g., predation) and resource utilization are
considered when evaluating indirect effects. Effects on higher
organizational levels depend on the severity of the effect, the
number of organisms affected, the role of those organisms in the
community or ecosystem, and characteristics that influence
resiliency (see Section 2.3.2).
The implications of adverse effects to greater spatial and
temporal scales are usually evaluated on a case-by-case basis and
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are influenced by the spatial and temporal distribution of the
stressor. The spatial extent of adverse effects can be compared to
the overall extent of the ecological resource. For example,
adverse effects to a resource that is small in scale (e.g., acidic
bogs) may have a small spatial effect, but represent a significant
degradation of the resource due to its overall scarcity.
Immigration and emigration patterns can be used to evaluate the
implications of a local loss (e.g., destruction of a local heron
rookery affects heron abundance over a much larger area). At the
ecosystem level, import and export functions are considered (e.g.,
destroying coastal wetlands can reduce nutrient export to adjoining
waterbodies).
The effects of short-term exposure may have long-term impacts.
The temporal extent of adverse affects depends in part on the
attributes of the exposed systems that influence resiliency and
recovery. Ecosystem recovery depends on physiological, life-
history, and genetic-adaptation mechanisms9, and is difficult to
predict. However, some useful generalizations can be drawn from
recent reviews (Cairns, 1990; Poff and Ward, 1990; Kelly and
Harwell, 1990). Recovery depends to a large extent on the
existence of a nearby source of organisms to immigrate to an
affected system. The source can be refugia within the affected
system, or a nearby unaffected area. If some individuals are in a
'latent or unsusceptible stage during exposure, these individuals
can provide-a source of immigrants. Organisms immigrating from
other areas must be able to reach the affected area," the distance
immigrating organisms can travel depends on their mode of transport
(e.g., by wind, water, self-propulsion) and the characteristics of
the habitat between the two areas. Finally, the success of the
immigrants depends on the chemical-physical environmental quality
following exposure to the stressor (e.g., presence of persistent
chemicals).
In summary, the evaluation of consequences may be critical for
certain risk assessments in which the relevance of measurement
endpoints is not clear to risk managers. However, not all
ecological risk assessments require an evaluation of consequences.
In cases where the stressor-response data indicate that direct
effects are the main concern and these endpoints can be measured or
estimated using quantitative extrapolation methods, further
evaluation of consequences may be unnecessary.
9 There is some evidence to suggest that these adaptive
mechanisms are influenced by historical patterns of temporal and
spatial heterogeneity.
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5.2.2. Methods for Describing the Consequences of Identified
Risks
There are twd basic methods for describing the consequences of
identified risks: 1) narrative statements and 2) mathematical
modeling.
Narrative statements describe the possible consequences if
adverse effects occur in the environment. This approach uses the
logical structure established during conceptual framework
development and supporting information to demonstrate the
consequences of concern.
When sufficiently supported, mathematical models can
quantitatively describe the consequences of identified risks. Most
often, they are used to provide a common framework for comparing
the consequences of adverse effects: For example, an assessor may
use laboratory data on the stressor's effect on the mortality and
reproduction of individual organisms to evaluate its effect on a
population. Mathematical models can extrapolate data for
individual organisms to effects at the population level.
The applications of mathematical models to ecological risk
assessment are not discussed here, but this topic may be addressed
in future guidelines. In general, models should be considered in
light of how well they make use of available data and support the
decision-making process.
No single model is suitable for all risk assessment, and the
assessor may want to apply more than one model to a system to
cross-check results. The most appropriate model is the one best
able to address the assessment endpoints selected during conceptual
framework development. Models used to project risks to natural
populations and communities can be divided into two main
categories:
a) Sinale-species population fdemographic) models can be used
to predict direct effects on a single population of concern.
These are basically bookkeeping models which balance natality
and mortality factors for the population in question.
b) Multispecies models can include both aquatic food web
models and terrestrial plant-succession or forest-gap models,
and may be used for risk assessments at the population,
community, or ecosystem level. Such models can assess both
direct and indirect effects of the stressor on the population
of interest and effects on the community or ecosystem as a
whole. Generally, these are large-scale mechanistic models
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comprised of a coupled system of difference or differential
equations. Both spatial and temporal dynamics can be modeled.
In summary, narrative explanations and mathematical models are
equally-valid approaches for describing and evaluating the
ecological consequences of an adverse effect. Either approach
should present the assumptions made and associated uncertainties.
5.3. Uncertainty in Ecological Risk Characterization
5.3.1.
Characterizing Uncertainty
In this step, the assessor describes the sources of
uncertainty in each step of the risk assessment and the impact of
each on the risk assessment's conclusions. Elements of uncertainty
include those associated with particular analyses, methods, and
techniques (e.g., fate-and-transport modeling, extrapolations). In
addition, the rationale behind any assumptions should be clearly
explained.
A useful approach to uncertainty characterization, suggested
by Holling (1978) , divides uncertainty into three major classes:
1) Events that can be predetermined, with known affects and known
probabilities of occurrence. This type of uncertainty has also
been described as quantitative uncertainty (Suter, 1990b).
Examples include natural variability (O'Neill, 1979) and
experimental, measurement, and sampling errors.
2) Events that are partially describabla, but hav« unknown outcomes
or probabilities. This type of uncertainty refers to incomplete
characterization of the system in question. In any assessment,
some variables are known but excluded by choice, and others are
unknown and therefore inadvertently excluded. This category deals
primarily with the hypotheses developed to explain the effects of
the stressor on the system. Insufficient data and. lack of
fundamental, understanding about ecological processes are- examples
of this type of uncertainty. Other sources are extrapolations from
reference systems, unpredictable perturbations, and indirect
effects (Harwell and Harwell, 1989).
3) Events for which we have no experience or knowledge, or that
involva unknown processes of unknown form. This category includes
"true" uncertainties, those for which we lack and cannot acquire
information. Such uncertainties may be manifested as inconsistent
results from alternative hypotheses or contradictory predictions
from alternative models.
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5.3.2.
Reducing Uncertainty in Ecological Risk Assessments
The approach used to reduce uncertainty in ecological risk
assessments varies with the source of the uncertainty and how it
influences the assessment.
Quantitative treatments of uncertainty deal primarily with the
first category of uncertainty (Finkel, 1990; Suter, 1990b). The
effects of this type of error on risk assessments have been
described by O'Neill and Gardner (1979). They can be quantified
using Monte-Carlo simulation or statistical uncertainty analysis
(O'Neill et al., 1982). Probability distributions for parameters
and processes enable the assessor to place statistical bounds on
the results of the assessment. Measurement errors can be minimized
by obtaining data in accordance with accepted methodologies
(published guidelines or other validated methods). Computational
errors should be minimized by adherence to good laboratory
practices and quality assurance procedures. Natural variability
can be acknowledged and described, but it normally cannot be
controlled or minimized. However, it may be described by
appropriate statistical distributions and the quantitative methods
described above.
Uncertainty due to data gaps (Category 2 above) is best
addressed by collecting additional information. Conceptual
uncertainty can be addressed during conceptual model formulation by
development of alternative risk hypotheses or alternative
predicative process models.
As noted by Suter (1990b) , one way to reduce uncertainty is to
use a combination of modeling, observation, and experimentation.
Where a strong causal relationship has been established,
observational or field studies may be the most appropriate for
reducing uncertainty, particularly conceptual uncertainty. For
example, effects observed in the laboratory can be verified by
outdoor studies, which reduce uncertainty about whether the
observed effects .will occur in the field. Where the cause of
observed effects is less certain, controlled laboratory experiments
or modeling may help reduce conceptual uncertainty. Once causality
is established, appropriate studies can be undertaken to reduce
quantitative uncertainty.
5.3.3.
Presenting Uncertainty
Quantitative approaches reduce but cannot eliminate the
effects of true uncertainty. At best, such approaches place bounds
on the risk assessment's conclusions. Differences between
predictions from alternative models or hypotheses may result in
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contradictory or ambiguous conclusions. While such differences may
be resolved by further analysis, decisions are often made in spite
of remaining uncertainties (Tversky and Kahneraan, 1974). Peterman
(1990a,b) suggested that risk assessments include an estimate of
the statistical power of the analysis, which can be used to
determine the probability of rejecting the null hypothesis
(concluding that the stressor causes no effect when an effect is
indeed present). This analysis is useful for evaluating the
results of several alternative models.
There is not always enough information to address all
questions that arise during a risk assessment, so the assessor
usually makes a number of assumptions based on data from the
stressor-response and exposure assessments. Because these
assumptions may introduce conceptual uncertainty, they should be
carefully explained in the risk characterization.
A weight-of-evidence approach is often used to present
information supporting the results and conclusions of the risk
characterization. Weight-of-evidence analysis evaluates data
quantity and quality as well as supplemental information (U.S. EPA,
19-90d) such as that described in Hazard Identification. This can
include data from field studies, observations of other adverse
effects caused by a particular stressor, and data on observed
effects for, similar types of stressors (e.g., those with similar
mode of action or belonging to the same chemical class).
The uncertainty analysis should present the strengths and
weaknesses of each risk assessment element and the impact of
associated uncertainties on the risk assessment's conclusions. A
clear presentation of how uncertainty could relate to final risk
management decisions can provide justification for obtaining or
requesting additional information to reduce uncertainty.
5.4. Communicating the Results of the Ecological Risk Assessment
The presentation of an ecological risk assessment is as
important as its scientific validity. Ecological risk assessments
may focus on endpoints not readily understood by managers
unfamiliar with biological or ecological concepts. Whether its
conclusion is a simple quotient or a sophisticated simulation, a
risk assessment may be misunderstood or misinterpreted if poorly
presented. Suggestions for communicating ecological risk
assessment results follow:
Clearly establish- the relationship between endnoints and
consequences.
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In many cases the assessment endpoint is not directly affected
by a stressor but will be severely impacted because of indirect
effects due to loss of essential supporting resources. The
assessor should explain the ecological relevance of such risks even
if only in a qualitative discussion.
Provide a summary profile of the degrees of risk.
Risk assessments that compare many stressor-response values to
exposure estimates provide greater insight into the magnitude of
effects. Summaries may be presented in tabular, graphic, or
narrative form. When more than one analytical method is employed,
all results should be discussed.
Restate the assumptions and uncertainties in the ecological risk
characterization.
Although assumptions and uncertainties are identified in each
element of ecological risk assessment, those that most influence
the conclusions should be repeated when communicating the results
of the ecological risk assessment. The weight of evidence
supporting the estimates should be clearly summarized.
Often, the data employed to conduct a risk assessment are
flawed or incomplete. Data deficiencies should be clearly
identified. The assessor should also describe the potential
contribution of more accurate or complete data to reducing the
uncertainty in the risk estimates.
Place risk in the context of severity, including temporal and
spatial attributes.
There is no universally-accepted scale that can be used to
compare ecological effects. However, the considerations outlined
in Section 2.2 can be used to guide discussion of direct and
indirect effects. Discussions of the spatial scale of effects
relative to the extent of the resource affected and the time frame
of the estimated effects add significantly to the value of a risk
assessment.
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6. GLOSSARY
Commensalism—A relationship between two species in which one
benefits from the association and the other is unaffected.
Community—An aggregate of multiple populations within a specified
location in space and time.
Direct Effect—Any adverse effect induced by a stressor that
directly affects an ecological component of concern (e.g.,
individual, population).
Ecological Risk Assessment—The characterization of effects of one
or more stressors on biotic components of ecosystems including
communities, populations, or individuals.
Ecosystem—The biotic community and abiotic environment within a
specified location in space and time.
Endpoint—A characteristic of an ecological system that can be
affected by exposure to a stressor.
Endpoint. Assessment—The characteristic of the ecological system
that is the focus of the risk assessment.
Endpoint. Measurement—An effect on an ecological component that
can be measured and described in some quantitative fashion.
Exposure—The co-occurrence of a stressor (including sensory
perception) with one or more ecological components.
Hazard—The intrinsic ability of a substance or other stressor to
cause adverse effects under a particular set of circumstances.
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Hazard Assessment10—The overall process of evaluating the type and
magnitude of adverse effects caused by a stressor. Hazard
Assessment consists of two steps -1) Hazard Identification and 2)
Stressor-Response Assessment. Hazard Identification--the
evaluation of the causal relationship between a stressor and an
adverse effect. .
Indirect Effect—An adverse effect elicited by a stressor to a
ecological component via a reduction or change its food supply or
•other trophic level disturbances such as predator/prey imbalances.
Keystone Species—A species whose function plays a critical role in
maintaining a particular community structure.
Lowest Observed Effect Level f LOEL1.--The lowest amount or
concentration of a stressor for which some effect is observed.
Maximum Acceptable Toxicant Concentration (MATC)—The maximum
concentration at which a stressor can be present and not be toxic
to the test organism. The MATC is normally calculated as the
geometric mean of the lowest: concentration for. which an adverse
effect was observed and the highest concentration that did not
yield any adverse effects.
Median Effective Concentration (EC501_—The concentration of a
stressor in water that is estimated to be effective in producing
some response, other than mortality, in 50 percent of the test
organisms over a specific time interval (e.g., a. 48-hour daphnid
ECSO) . '•"."•;•
Median Lethal Concentration (LC50)—The concentration of a stressor
in water that is estimated to be lethal to 50 percent of the test
organisms over a specific time interval (e.g., a 96-hour fish LC50) '-.
10 Hazard assessment currently has two commonly-used
definitions: The first is the evaluation of the intrinsic potential
of a stressor to cause adverse effects under a particular set of
circumstances. This definition refers to the combination of hazard
identification and stressor-response assessment. The second
definition is a quotient or margin of safety calculated by
comparing the toxicological endpoint of interest to an estimation
of exposure concentration. This definition refers to a combination
of stress response and exposure assessment. This document refers
only to the first definition, which confines hazard assessment to
hazard identification and stressor-response.
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Mutualism—A relationship between two species where both benefit
from the association and in fact cannot survive separately.
No Observed Effect Level (NOEL)—The amount or concentration of a
stressor that does not result in any adverse effect.
Null Hypothesis—-A hypothesis that states there is no difference
between parameters. The null hypothesis is usually designated as
V
Population—An aggregate of interbreeding individuals of a species
within a specified location in space and time.
Predictive Ecological Risk Assessment—The characterization of the
ecological effects of a stressor prior to its release or
occurrence.
Primary Productivity—The production of energy from sunlight by
green plants.
Recovery—The ability of a population or community to partially or
fully return to a level of equilibrium that existed prior to the
introduction of the stressor.
• Resiliency—The ability of a population or community to persist or
maintain itself in the presence of one or more stressors.
Retrospective Ecological Risk Assessment—The characterization of
the ecological effects of a stressor after or during its release or
occurrence.
Risk Characterization—The evaluation of the likelihood that
adverse ecological effects may occur as a result of exposure to a
stressor, including an evaluation of the consequences of these
effects.
Statistical Power—Defined as 1-B where B is th& .probability of
failing to reject the null hypothesis when in fact the null
hypothesis is false.
Stressor---Any physical, chemical, or biological entity that can
induce an adverse response.
Trophic Level—A functional classification of populations within a
community that is based upon feeding relationships (e.g., aquatic
and terrestrial green plants comprise the first trophic level and
herbivores comprise the second).
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Stressor-Resnonse Assessment—A quantifiable relationship between
the amount or concentration of stressor and the magnitude of
response observed in a test organism or other higher ecological
component (e.g., population).
Xenobiotic—A chemical or other stressor that does not occur
naturally in the environment. Xenobiotics occur as a result of
anthropogenic'activities such as the application of pesticides and
the discharge of industrial chemicals to air, land, or water.
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Framework Document Workshop
Pre-Meetinq Issues Papers
Ecorisk Paradigm
Conceptual Framework Development
* Hazard Identification and Stress-
Response Assessment
Exposure Assessment
Risk Characterization
B-57
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Pre-Meeting Issue Paper
WORKSHOP TOPIC: ECORISK PARADIGM
GENERAL ISSUE:
The proposed paradigm for ecorisk assessment is modeled
after the National Research Council paradigm for human
health risk (NRC, 1983). Is the modified paradigm presented
in the framework document appropriate for ecorisk
assessments/ or is another approach preferable?
FRAICEWORK APPROACH AND QUESTIONS:
1. The proposed ecorisk paradigm is quite similar to the NRC
health effects paradigm, but it also explicitly provides for an
initial planning process in ecorisk assessments.
la* Comment on whether the elements of the paradigm proposed in
the framework document are appropriate. In what situations,
if any/ would another paradigm be more appropriate?
Ib. It has been suggested that the conceptual framework
development step be included in an expanded hazard
identification section. Please comment on this suggestion.
Ic. Comment on the need to include a monitoring step (following
risk characterization) in the paradigm.
2. The framework document uses terms such as "risk assessment"
and "hazard"assessment" that either have no standard meaning or
are used inconsistently in the ecotoxicology literature.
2a. Comment on whether terminology related to the paradigm
(including "hazard assessment1* and "risk assessment") is
clearly defined and used consistently throughout the
document. Suggest alternate terms or definitions, if
appropriate.
2b. Comment on whether the definitions used in the glossary are
appropriate and recommend any additional terms that should
be added to the glossary.
3. The conceptual framework development section _(and the
framework document as a whole) emphasizes individual- or
population-level effects. While this may reflect the present
orientation of the Agency and the state of the science, some
scientists feel that there should be more emphasis on community-
and ecosystem-level measurements and effects.
3. What should be added or changed in the framework document to
place appropriate emphasis on community- and ecosystem-level
effects?
B-58
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4. The proposed ecorisk paradigm maintains a distinction
between the process of risk assessment (scientific analysis) and
risk management (which may include social, political, legal, and
economic/valuation factors) . This distinction is also .made in
human health risk assessments. However, there has been
considerable discussion as to the degree that policy or risk
management issues should influence the objectives that are
established at the outset of an ecorisk assessment. Thus, the
relationship between ecorisk assessment and management may need
additional clarification in the framework document.
4a. comment on the roles of risk management in the initial
stages of an ecorisk assessment (e.g. establishment of
assessment goals and endpoint selection) .
4b. What further explanations are needed, if any, of the role of
policy considerations in the ecorisk process?
4c. Comment on the role of valuation considerations, in any, in
ecorisk assessments. (Valuation concerns the assignment of
monetary or societal values to ecological resources).
5. The framework document distinguishes between those areas of
ecorisk assessment that are currently used and those areas that
are under development or show promise.
5. Comment on whether the distinctions between the present
s tat e-of- the- science and future research needs in ecorisk
assessment are clearly and appropriately made.
6. Some persons have commented that more examples should be
used throughout the document to illustrate points made.
6 . Where are additional examples needed?
examples that could be used?
Can, you suggest
7. In the introduction, issues for consideration and future
development are listed.
7. What issues, if any, should be added to the list?
B-59
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Pfe-Meeting Issue Paper
WORKSHOP TOPIC: CONCEPTUAL FRAMEWORK DEVELOPMENT
GENERAL ISSUE;
Conceptual framework development is proposed as the first
step in an ecorisk assessment. Does this section provide an
appropriate description of the process/ and are relevant
ecorisk issues adequately discussed?
FRAMEWORK APPROACH AND QUESTIONS;
8. The proposed criteria for endpoint selection are (1) purpose
and needs of the assessment, (2) ecological relevance, (3)
susceptiblity, and (4) practical constraints.
8. Which criteria, if any, should be added (such as type of
stressor) or deleted?
9. The framework document distinguishes between "assessment
endpoints" (the characteristics of an ecosystem that are the
focus of the risk assessment) and "measurement endpoints" (the
effects that are actually estimated or measured).
9a. What changes/ if any/ do you recommend in the terms
"measurement endpoint'* and "assessment endpoint"?
9b. What changes/ if any/ do you recommend in the examples shown
in Table 2?
10. The conceptual framework development section concludes with
the presentation of a conceptual model that is further evaluated
in the exposure and hazard assessment sections.
10, Comment on whether the development of a conceptual model is
a useful approach for focusing an ecorisk assessment. How
should a conceptual model be used?
11.The importance of spatial and temporal scaling factors is
mentioned briefly in the conceptual framework development section
(2.1.1 - Exposure Settings and Pathways).
11. What additional consideration, if any, should be given to
spatial and temporal scales?
12. Some decisions are based only upon preliminary information,
similar to that assembled during Conceptual Framework
Development. Examples include the decision to consult with the
U.S. Department of the Interior on endangered species and the
decision to implement an emergency removal.
12. Should the framework document acknowledge that Conceptual
Framework Development can be used in this fashion?
B-60
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Pr-e-Meeting Issue Paper
WORKSHOP TOPIC: HAZARD IDENTIFICATION AND
STRESS-RESPONSE ASSESSMENT
GENERAL ISSUE;
This section includes discussions,of the establishment of
the causal relationship between stressor and response
(hazard identification) and the quantification of that
relationship (stress-response). Are the emphasis and level
of detail provided for these topics appropriate?
FRAMEWORK APPROACH AND QUESTIONS;
13. The framework document distinguishes between hazard
identification and stress-response assessment, as is commonly
done in health risk assessments. Hazard identification, which
establishes a cause-effect relationship between a stressor and a
response, references Hill's criteria.
%13a. Comment on the necessity of distinguishing between hazard
identification and stress-response assessment.
13b. Discuss the usefulness of Hill's criteria for evaluating
cause-effect relationships in ecorisk assessments.
14. The stress-response section describes both extrapolation
techniques as well as the uncertainty associated with the
extrapolation process. Extrapolation may occur at several
levels: across endpoints at a given level of biological
organization, across levels of biological organization, from the
results of laboratory studies to the prediction of effects in the
field, and across temporal and spatial scales.
14a. Are there other currently accepted extrapolation methods
that should be added?
14b. Which portions of tha extrapolation or uncertainty
discussions should be condensed or expanded?
3,4c. Where should uncertainty be discussed, in this section or
under risk characterization? why?
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15. While the framework document recognizes the significance of
non-chemical stressors such as habitat alteration, sedimentation,
and nutrient loading, there is only minimal guidance provided on
these topics as compared with threats associated with toxic
chemicals. In addition, there is little information on how to
deal with multiple stressors (whether chemical or non-chemical)
or cumulative effects.
15a. How should the discussion of non-chemical stressors bo
expanded?
ISb. What additional guidance should be presented eoneeraiag the
risks of multiple stressors and cumulative effects?
B-62
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Pre-Meeting Issue Paper
WORKSHOP TOPIC: EXPOSURE ASSESSMENT
GENERAL ISSUSt
Does ts» discussion in this section adequately eov@r th®
major aspects of ecological exposure assessment?
FRAMEWORK APPROACH &ND QUESTIONS;
16. Exposure assessment is defined as the evaluation of the
temporal and spatial distribution of a stressor and its co-
•occurence with ecological components. The framework document
highlights several aspects of exposure assessment, including the
evaluation of multiple kinds of organisms, the importance of the
timing of exposure, and the perception of and direct contact with
a stress.
16. Are these considerations appropriate?
information should be highlighted?
What additional
17. Two methods of exposure assessment used in human health
assessment were applied to ecorisk exposure assessment.
17. Comment oa ta® usefulness ©f ta®s® two mataods. Waat other
methods, if any, should be added?
18. The framework document briefly discusses variables that may
modify or complicate exposure, assessments, such as the influence
of species-specific habitat and behavioral patterns,
bioavailability, multiple stressors, time-varying exposures, and
multiple exposure routes.
18. &r@ these topics adequately addressed ia view of the
objective* and scope of th@ framework documeat? If not,
what would you expand and now?
19. Methods for assessing uncertainty in exposure assessment are
deferred to chapter 5 of the framework document.
IS. What additional discussions of uncertainty ia exposure
assessment should be included ia this section or slsewhere,
if any?
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Pre-Meeting Issue Paper
WORKSHOP TOPIC: RISK CHARACTERIZATION
ISSUE;
The risJc characterization process is defined to include
determination of the likelihood of adverse effects,
evaluating the consequences of the adverse effects,
assessing uncertainties, and communicating the results of
the risk assessment. Does this provide a complete picture
of risk characterization as it is applied to ecorisk
assessment?
FRAMEWORK APPROACH AND QUESTIONS!
20. The primary approach proposed in the framework document for
evaluating the likelihood of adverse effects is the quotient
method, which provides a point estimate or a series of point
estimates of the ratio between exposure and effect levels. Other
methods may be available that provide a more complete picture of
risk by using a broader range, of the stress-response curve or by
considering a variety of different exposure scenarios.
20&.* Comment on the clarity and usefulness of the discussion of
the quotient and other methods.
2Qb. what are the alternatives to the quotient method of risk
characterization (particularly for higher levels of
ecological organization) , and how might they b« incorporated
into the framework document?
21. Risk assessments generally provide an estimate of the
probability of an adverse effect. The concept of ecorisk
assessment in the framework document has been broadened to
include more qualitative estimates of risk, such as might be used
for comparative risk assessments or risk ranking exercises.
21. Discuss whether ecorisk assessments should include
qualitative as well as quantitative evaluations of risk.
22. The section on uncertainty (5.3) describes general sources
of uncertainty and discusses reducing and presenting uncertainty.
22a. Is th» discussion of uncertainty clear?
should be changed?
What, if anything,
22b. What, if anything, should be added to the discussion of
weight of evidence?
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23. Ecosystem recovery is only mentioned briefly in the
framework document (section 5.4 - Describing the Consequences of
Identified Risks).
23a. Should more information on ecosystem recovery be included in
this document? If so, specifically what should be added?
23b. should ecosystem recovery b* discussed in any other
sections?
24. The consequences of effects (e.g. indirect effects/ erfacts
at higher levels of organization, and effects at other spatial
and temporal scales) are discussed in risk characterization.
24. Is the discussion of ecological consequences appropriately
located? Where else in the document should it be included?
B-65
*U.S. GOVERNMENT PRINTING OFFICE:! 992 .750-00^0077
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