EPA/630/R-92/002
February 1992
REPORT ON THE ECOLOGICAL RISK ASSESSMENT GUIDELINES
STRATEGIC PLANNING WORKSHOP
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 [[[ vii
Foreward ............................................... ............... viii
Preface [[[ ix
Authors and Contributors [[[ x
Executive Summary [[[ xi
1. BACKGROUND AND PURPOSE ............................................ 1
1.1. Background ................... . .................. . ............. 1
1.2. Purpose [[[ 1
1.3. Workshop Organization ...................................... ...... 2
2. OPENING PRESENTATION ____ . ........................................... 3
2.1. Ecological Risk Assessment: Organizing Principles
(Jack Gentile and Mark Harwell, Co-Chairs) ............................ 3
2.2. Background [[[ 3
2.3. Ecological Principles ...................... ....................... 3
2.4. Ecological Risk Assessment Variables ....................... , ......... 4
2.5. Ecological Risk Assessment Landscape - "The Cube" ...................... 5
3. WORKSHOP REPORTS ON ECOLOGICAL HIERARCHY .......................... 8
3.1. Introduction . . ................ ................................. 8
3.2. Organism-Population Work Group (Steve Bartell, Chair) .................... 8
3.2.1. Policy and Risk Analysis .................................... 8
3.2.2. Individuals and Populations ................................... 9
3.2.3. Alternatives and Innovations in Population Models .................. 9
3.2.4. Data ............. ..................................... 11
3.2.5. Extrapolation ............... ............ ................. 11
3.2.6. Miscellaneous ............................. . . ........ .- . . . 11
3.3. Community Work Group (Ann Bartuska, Chair) ......................... 12
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CONTENTS (cont.)
3.4. Ecosystem Work Group (David Weinstein, Chair) 15
3.4.1. Introduction 15
3.4.2. Criteria for Selecting Endpoints 15
3.4.3. Example Set of Criteria 15
3.4.4. Example List of Endpoints 16
3.4.5. Practical Considerations 18
3.4.6. Issues Requiring Further Consideration 18
4. SCIENTIFIC FEASIBILITY ISSUES 19
4.1. Introduction 19
4.2. Aquatic Ecosystems Work Group (Tom Duke, Chair) 19
4.2.1. Scientific Feasibility Issues 19
4.2.2. Research Needs 23
4.3. Terrestrial Ecosystems Work Group (William Smith, Chair) . 24
4.3.1. Introduction 24
4.3.2. Stress Characterization Research Needs . . .. 27
4.3.3. Ecological Characterization Research Needs 27
5. SPECIAL TOPICS 28
5.1. Introduction 28
5.2. Stress Characterization Work Group (Robert Huggett, Chair) 28
5.2.1. Introduction 28
5.2.2. Stress Characterization . . 28
5.2.3. Characteristics of Exposure Assessment '. 32
5.2.4. Measurement 32
5.2.5. Sources 33
5.2.6. Bioavailability 34
5.2.7. Models 35
5.2.8. Stress Research and Development Needs . . 35
5.2.9. _ Summary - 36
5.3. Ecosystems Classification Work Group (Richard Wiegert, Chair) 37
5.3.1. Scale-Independent/Qualitative Ecosystem Classification 37
IV
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CONTENTS (cont.)
6. ISSUES IN ECOLOGICAL RISK ASSESSMENT 39
6.1. Background 39
6.2. Characteristics of Ecological Risk Assessments 39
6.3. Road Map Work Group (Mark Harwell and Jack Gentile, Co-Chairs) 40
6.3.1. Problem Formulation 42
6.3.2. Response-Recovery Analysis 44
6.3.3. Environmental Decision-Making 46
6.3.4. Relationship to the Ecological Risk Framework 46
6.4. Proposed Future Ecological Risk Assessment Guidelines 47
6.4.1. Background 47
6.4.2. Ecological Risk Assessment Guidelines 49
6.4.3. Ecological Endpoints 49
6.4.4. Ecological Indicators 49
6.4.5. Stress Regime Characterization 50
6.4.6 Ecological Response Characterization . 50
6.4.7. Ecological Recovery 50
6.4.8. Environmental Decision-Making 50
6.4.9. Case-Specific Compendium 50
7. REFERENCES 51
APPENDIX A - AGENDA ' A-l
APPENDIX B - LIST OF PARTICIPANTS B-l
APPENDIX C ~ LIST OF OBSERVERS C-l
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LIST OF FIGURES
Figure 1. Three-Dimensional Matrix of Ecological Risk Organizing Principles 7
Figure 2. Current Strategy for Ecological Risk Assessment: Population Scale 25
Figure 3. Current Strategy for Ecological Risk Assessment: Ecosystem Scale 26
Figure 4. Example Categories of Stressors 30
Figure 5. Scientific Issues in Ecological Risk Assessment 41
Figure 6. Proposed Framework for Ecological Risk Assessment ^ 47
LIST OF TABLES
Table 1. Feasibility Matrix 21
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ACKNOWLEGEMENTS
The efforts of all the participants in the workshop that formed the basis for this report are
greatly appreciated. In particular, Dr. Mark Harwell and Dr. Jack Gentile provided overall leadership
for the workshop, and several other individuals acted as work group chairs, including Dr. Steven
Bartell (Organisms-Population), Dr. Ann Bartuska (Community), Dr. Tom Duke (Aquatic Ecosystems),
Dr. Robert Huggett (Stress Characterization), Dr. William Smith (Terrestrial Ecosystems), Dr. Richard
Weigert (Ecosystems Classification), and Dr. David Weinstein (Ecosystem). Dr. William van der
Schalie and Dr. William Wood of the Risk Assessment Forum Staff and Ms. Susan Brager of Eastern
Research Group also made significant contributions to the workshop and the workshop report.
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FOREWARD
In 1986, the U.S. Environmental Protection Agency (EPA) issued five guidelines for health
risk assessment (51 Federal Register 33992-34054, 24 Sept. 1986). Based on a ten-year-long effort,
these guidelines set forth risk assessment principles, concepts, and methods for cancer, developmental
effects, mutagenic effects, exposure assessment and chemical mixtures. Since then, EPA has
developed guidance in other health risk areas, with the result that a total of nine guidelines for health
risk assessment are available or under development. Despite controversies in some areas, each of the
guidelines has been well received and is widely used.
For several years, responding to requests from EPA scientists and from the public, EPA has
been weighing approaches to comparable guidance for ecological effects. In 1990, the Risk
Assessment Forum, which is responsible for EPA's Agency-wide risk assessment guidance, initiated
three ecological risk guidance projects: (1) a set of case studies to illustrate the "state-of-the-practice"
in ecological assessments; (2) a "framework" to describe the basic principles for ecological risk
assessment; and (3) a long-range plan for developing specific ecological risk guidelines, which was the
topic for a workshop held in Miami, Florida in April 1991.
The Miami Workshop was an important event for the Risk Assessment Forum. It was the first
step in a multi-year program to develop detailed guidelines for ecological risk assessment, hi essence,
EPA was seeking to identify and define the ecological effects counterparts to the existing EPA
guidelines for health risk assessment.
EPA did not expect to develop substantive guidance during this workshop; nor did EPA expect
to address or resolve all of the many issues that impact an activity of this kind. Rather, EPA asked
experts on ecology, ecotoxicology, and ecological risk to identify topical areas and define the general
scope for EPA's first ecological risk assessment guidelines through consideration of organizing
principles and scientific feasibility issues. This workshop report contributes to EPA's long-term plan
for the development of ecological risk assessment guidelines along with two other reports that discuss
a framework for conducting ecological risk assessments (U.S. EPA, in press-a; U.S. EPA in press-b).
Dorothy E. Patton, Ph.D.
Chair
Risk Assessment Forum
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PREFACE
On April 30, 1991, EPA convened a workshop to assist in developing guidelines for improving
ecological risk assessment (56 Federal Register 16333, 22 April 1991). Dr. Mark Harwell and Dr.
John Gentile chaired the three-day meeting, which was held at the University of Miami School of
Marine and Atmospheric Science. Participants included experts on ecology, ecotoxicology, and
ecological risk assessment from universities, EPA, other Federal agencies, and private organizations.
The Miami Workshop was the first of several workshops held during the spring of 1991 as
part of a new EPA program to develop guidelines for ecological risk assessment. Each workshop was
designed to open a dialogue among experts on issues pertaining to the development of such guidance.
This workshop report highlights issues and recommendations developed at the Miami Workshop.
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AUTHORS AND CONTRIBUTORS
EPA's Risk Assessment Forum sponsored a 3-day workshop on April 30 to May 2, 1991, at
the Rosenstiel School of Marine and Atmospheric Science at the University of Miami to examine the
technical basis for developing a strategic plan for future ecological risk assessment guidelines. Risk
Assessment Forum Staff provided overall guidance for this workshop. Appreciation is extended to the
University of Miami for hosting this workshop and to Christine Harwell and Melanie Bethel for onsite
support. Eastern Research Group, Inc. (EPA Contract No. 68-C1-0030) handled logistics for
participants and provided assistance for this report.
Authors
John H. Gentile (Co-Chair)
U.S. Environmental Protection Agency
Environmental Research Laboratory
Narragansett, RI
Mark A. Harwell (Co-Chair)
University of Miami
Miami, FL
Contributors
Steven Bartell (Chair, Population Work Group)
Oak Ridge National Laboratory
Oak Ridge, TN
Ann Bartuska (Chair, Community Work
Group)
USDA Forest Service
Washington, DC
Thomas Duke (Chair, Aquatic Work Group)
Technical Resources Institute
Gulf Breeze, FL
Robert Huggett (Chair, Stress Characterization
Work Group)
College of William and Mary
Gloucester Point, VA
William Smith (Chair, Terrestrial Work Group)
Yale University
New Haven, CT
David Weinstein (Chair, Ecosystem Work
Group)
Boyce Thompson Institute
Ithaca, NY
Richard Weigert (Chair, Ecosystem
Classification Work Group)
University of Georgia
Athens, GA
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EXECUTIVE SUMMARY
The U.S. Environmental Protection Agency (EPA) is developing guidelines for conducting
ecological risk assessments. This task is particularly challenging because ecological risks result from
exposure of populations, communities, and ecosystems to chemical and nonchemical stressors acting
individually or in combination over diverse spatial scales that can include multiple ecosystem types.
In view of the complex nature of this subject, and to provide a basis for planning ecological risk
assessment guidelines, EPA's Risk Assessment Forum convened a scientific workshop at the University
of Miami's Rosenstiel School of Marine and Atmospheric Science.
Scientists with expertise in ecology and ecological risk assessment from EPA, academia, and
other government agencies explored the technical bases for a strategic plan that could be used by EPA
for developing ecological risk assessment guidelines. Topics discussed included: (1) the optimal
scientific approach to organizing ecological risk assessments, (2) the scientific feasibility of
implementing ecological risk assessment guidelines for a wide range of stress categories and
ecosystems, (3) the scientific issues relative to the risk assessment process, and (4) the subject matter
and titles that will constitute the ecological risk assessment guidelines bookshelf. The major points
from these discussions are summarized below.
Organizing Variables. In a preworkshop paper, the following five variables were
proposed as the basis for organizing ecological risk assessments: ecosystem type,
stress type, spatial scale, temporal scale, and level of biological organization. These
five elements, which circumscribe the boundaries within which ecological risks occur,
represent the foundation for the ecological risk assessment process that will form the
basis for future guidelines. Each variable was discussed within the context of its
applicability to the risk assessment process. Scale, be it spatial, temporal, or level of
biological organization, is an important component of the ecological risk assessment
process to be addressed in future guidance. While current concepts of stress
characterization and exposure are most relevant to chemical stresses, future guidelines
must address the emerging importance of anthropogenic nonchemical stresses (e.g.,
global climate change, stratospheric ozone depletion, habitat destruction or alteration,
and species depletion) (U.S. EPA, 1990). The traditional structural classification of
ecosystems (e.g., deciduous forests, freshwater wetlands) should be supplemented with
functional properties (e.g., energy and nutrient cycling, decomposition) to facilitate the
coupling of stress modes of action to the nature of the ecological response and
recovery. Finally, guidance will be needed to ensure that the magnitude and extent of
the stress, the spatial and temporal scales, and the level of biological organization used
in the risk assessment are compatible.
Feasibility. The scientific feasibility of addressing ecological risk assessments was
examined from the perspective of both current knowledge and additional research that
will need to be conducted. Feasibility was based upon the adequacy of ecological
theory, models, and methods needed for making assessments at various levels of
biological organization. The following general observations emerged from the
discussions. Although an extensive body of ecological theory is available at all levels
of biological organization, its application to ecological risk is most well developed at
the organism and population levels of organization, primarily because of the historical
focus on chemical contamination. In general, the availability and applicability of
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ecological theory and models decreases when the scale of the risk assessment (i.e.,
temporal, spatial, and biological) increases and when there is more than one stress
operating simultaneously. Consequently, nonchemical and multiple stresses coupled
with regional or global spatial scales present serious challenges to our current scientific
understanding and capabilities and will require additional research before guidance can
be provided. r
Scientific Issues in Ecological Risk Assessments. The workshop examined a spectrum
of scientific issues associated with the ecological risk assessment process. This
included the full range and complexity of stress and ecological response issues, rather
than trying to adapt risk assessment approaches developed for non-ecological
problems. The result was a description of the process and associated scientific issues
that should" be addressed in ecological risk assessment guidelines. The following
issues were highlighted:
(1) it must be recognized that the stress-characterization process proceeds in
parallel with ecological-effects characterization, with inputs and feedbacks
occurring at several stages;
(2) guidance is needed for identifying the specific ecosystem(s) at risk and
selecting the appropriate ecological endpoints of concern;
(3) the actual characterization of ecological risks results from integrating the full
range of stress-response and recovery relationships, produced from both
qualitative and/or quantitative methodologies; and
(4) guidance and dialog on interfacing the risk assessment process with
"environmental decision-making" (risk management) are needed.
The Guidelines Bookshelf. Because of the complexity of the ecological risk
assessment process, a single guidance document is not feasible. Rather, workshop
participants proposed a Bookshelf that will contain both guidelines and supplemental
resource volumes. The foundation for future guidelines subject matter emerged from
the description of the ecological risk assessment process and related scientific issues.
The initial volume, the "Ecological Risk Assessment Guidelines", could provide
comprehensive guidance for conducting ecological risk assessments. This volume
would expand and provide greater detail on the risk assessment principles described in
EPA's "Framework for Ecological Risk Assessment" (U.S. EPA, in press-b), provide
criteria for selection of ecological endpoints, and provide scientific consensus on issues
critical to the conduct of ecological risk assessments. In addition, these guidelines
could include selected examples to illustrate the conduct of ecological risk assessments
for specific ecosystems and particular stresses. Simultaneously, other companion
volumes could be developed to provide detailed information on important components
of the risk assessment process. For example, volumes could be prepared for: (1)
selecting ecological endpoints and indicators, (2) stress characterization, (3) risk
characterization, (4) ecological effects and recovery, and (5) environmental decision-
making. These volumes would supplement the guidelines and-provide the detail
necessary for determining the risks for various stressors and ecosystems. The final
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volume on the bookshelf could be a compendium of case studies developed from the
application of the guidelines to a wide range of problem-oriented situations.
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1. BACKGROUND AND PURPOSE
1.1. Background,
EPA's risk assessment program historically has focused on developing guidelines for assessing
chemically induced risks to human health (U.S. EPA, 1986). EPA's extensive experience with specific
risk issues in human health has provided a sound basis for defining the scope, principles, and subject
matter for human health risk assessment guidelines. The subject, that is the endpoints for human
health risk assessment, resulted from extensive discussions during a period of several years prior to the
development of human health guidelines. In addition, the endpoints, such as carcinogenicity and
developmental toxicology, were of recognized public health and regulatory importance. Similar
discussions regarding the selection of endpoints for ecological risk assessment have begun only
recently and are confounded by the lack of specific legislative and regulatory guidance. Another
important factor in human health risk assessment is the focus on estimating the risks to a single
species, humans. Finally, human health assessments have traditionally assessed the risks from
radiological and chemical stresses.
Although there are similarities to human health risk assessments, ecological risk assessments
must consider exposure of populations, communities, and ecosystems to chemical and nonchemical
stresses acting individually or in combination over diverse spatial scales that can include multiple
ecosystem types (Barnthouse and Suter, 1986; U.S. EPA, 1988; Harwell et al., 1990). The scale and
complexity of ecological systems and their interactions with anthropogenic and natural stresses present
a challenge to preparing guidelines that can be used for assessing risks and recovery in these
ecosystems.
EPA, through its Risk Assessment Forum, is developing a set of guidelines for conducting
ecological risk assessments. It is anticipated that the guidelines will be used by EPA in conducting
ecological risk assessments and will likely be the basis for assessments conducted by other
organizations. Three activities are presently under way: (1) preparation of a framework document that
provides the basic philosophy and conceptual basis for ecological risk assessments; (2) preparation of a
case studies volume that illustrates how ecological risks are presently assessed;, and (3) preparation of
a long-range plan for developing future ecological risk assessment guidelines.
1.2. Purpose
The purpose of the strategic planning workshop was to provide EPA with recommendations on
the subject matter and feasibility of ecological risk assessment guidelines to be developed over the
next several years. A 3-day workshop was convened on April 30, 1991, at the Rosenstiel School of
Marine and Atmospheric Science (RSMAS) at the University of Miami to examine the technical basis
for developing a strategic plan for future ecological risk assessment guidelines (56 Federal Register
16333, 22 April 1991). Approximately 35 scientists from academia, EPA, and other Federal agencies
'participated in a series of work groups addressing various aspects of ecological risk assessment. The
goal of the workshop was first to identify the organizing variables that could be used to circumscribe
the spectrum of potential types of ecological risks for which guidance would be needed. Then,
through a review of scientific principles and feasibility, the workshop participants would aggregate
these potential options into a limited number of subject-specific candidate guidelines.
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1.3. Workshop Organization
The workshop opened with a presentation on ecological principles that described the major
elements in ecological risk assessment and was followed by a series of work group discussions that
expanded upon these principles in several different ways. This report reflects the discussions within
each work group and presents the scientific perspectives on ecological risk assessment and associated
guidelines that emerged from the discussions at the Miami workshop.
The first set of work groups reviewed the theoretical basis for ecological risk assessment,
addressing levels of ecological organization, types of ecosystems, categories of anthropogenic stresses,
and fundamentals of stress ecology. A second set of work groups examined pragmatic issues of
ecological risk assessment, i.e., what is feasible at present, what may be feasible after a few years of
research and development, and what is not feasible without considerable additional research and
improved understanding. These work groups examined different categories of ecosystems with respect
to the availability of laboratory and field data bases, availability of models and other analytical
methodologies, and knowledge of how ecosystems respond to stress. Finally, a third set of work
groups examined: (1) alternative ways to classify ecosystems; (2) issues of stress characterization; and
(3) processes for conducting ecological risk assessments, particularly as they relate to defining the
subject and content of future guidelines.
This workshop report begins with a discussion of organizing principles for ecological risk
assessment and describes how these principles are combined to delineate the boundaries within which
ecological risks occur and are assessed (section 2). This section is followed by three work group
reports, each examining a different level of ecological organization (section 3). Section 4 examines
the availability of analytical models and suitable data bases for aquatic and terrestrial systems and
addresses the feasibility of conducting ecological risk assessments. Section 5 addresses special topics
on stress and ecosystem classification. Section 6 provides a detailed description of the scientific
elements and issues pertinent to ecological risk assessment and illustrates the flow and integration of
information on stress and ecological effects required to evaluate risk. This section concludes with
recommendations on potential subject areas for future ecological risk assessment guidelines.
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2. OPENING PRESENTATION
2.1. Ecological Risk Assessment: Organizing Principles
(Jack Gentile and Mark Harwell, Co-Chairs)
2.2. Background
The first task of the workshop was to define the scope and subject matter of ecological risk
assessment guidelines. The ecological risk assessment guidelines should have the breadth and
flexibility to address a wide range of environmental risks resulting from individual and multiple
chemicals acting singly or in combination and from nonchemical stresses that occur over a wide range
of spatial, temporal, and biological scales. Consequently, the subject matter for the ecological risk
assessment guidelines was not predetermined. In contrast, the subject matter of the human health
guidelines was defined through extensive experience. The purpose of these initial workshop
discussions was to focus on the selection of organizing principles that have a strong scientific basis,
capture the essential features of the ecological risk assessment process, and that could be used to
delineate options for selecting the subject matter of future ecological risk assessment guidelines.
Three sources of information were used to identify the organizing principles: (1) knowledge
and understanding of the principles of stress ecology, (2) knowledge of the risk assessment process,
and (3) information on current and emerging environmental problems. For example, recent studies
suggest that the scale of environmental problems continues to increase from local to regional to global
and that nonchemical stresses are becoming increasingly important (U.S. EPA, 1990). This
information helps EPA decision-makers decide which problems are most important and where to focus
limited resources. This information also can be used to delineate the scope and relative importance of
scientific issues that need to be addressed in the guidelines development process.
2.3. Ecological Principles
Understanding the scope and factors that need to be considered in developing guidance for
ecological risk assessments requires knowledge of both the stress and the ecological system being
affected. Central to understanding the roles and interactions of a stress in ecological risk assessment is
knowledge of the stress regime experienced by various components of the ecosystems, how ecosystems
respond to stresses, and how ecosystems recover from or adapt to stress (Kelly and Harwell, 1989;
Kelly and Harwell, 1990).
Difficulties in predicting ecological responses and recovery from anthropogenic disturbances
derive from several factors. First, there are a wide array of types of ecosystems that are of concern to
humans. Second, unlike the human organism, which is tightly organized and highly homeostatic,
ecosystems are only loosely interconnected, with many different mechanisms for positive and negative
feedbacks and relatively low levels of homeostasis. Third, there is no universal, simple measure
(endpoint) of ecological health that is analogous to those measures used in human health risk
assessment.
Consequently, the workshop identified the need for criteria and guidance for selecting
endpoints for ecological risk assessments. Because of the complexity of ecosystems and their
interactions with natural and anthropogenic stresses, "ecological endpoints", that is those characteristics
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of ecosystems that are directly or indirectly important to the ecosystem and/or to humans, probably
will have to be identified on a stress- and ecosystem-specific basis.
Assessing the interactions of internally complex ecosystems of various types with individual
and multiple anthropogenic and natural stresses requires an understanding of the following important
issues:
the spatial and temporal scales of the stress;
differential intensity of stress across various components of the ecosystem;
interactions among anthropogenic stresses and between natural and human-induced
stresses;
natural variability and the problems of discriminating an anthropogenic stress from
background noise; and
" the different modes of action of the stress on the ecosystem.
Consequently, the possible stress-response relationships are quite diverse, are ecosystem- and
stress-specific, may involve a diverse set of ecological endpoints, and may include nonlinearities and
thresholds. Ecological recovery from mitigated or eliminated stress likewise involves multiple scales
of hierarchy, time, space, and is stress- and ecosystem-specific. Substantial uncertainties exist in
predicting stress-response and recovery relationships, some of which may be reduced through further
ecological research in the laboratory and the field or through improved model development. However,
because certain aspects of environmental uncertainty are intrinsically irreducible (e.g., natural
variability in weather or other physical conditions), environmental decision-making always must
proceed in the presence of uncertainties.
These principles illustrate the scope and diversity of issues that influence attempts to provide
specific predictions of an ecosystem's response to a stress. Recognizing that there are considerable
complexities and uncertainties should not preclude using expert scientific judgment to separate the
general relationships or principles useful for ecological risk assessment from the seemingly infinite
array of individual circumstances and uncertainties of ecosystems.
2.4. Ecological Risk Assessment Variables
The first step in the ecological risk assessment process is to identify the organizing variables
that circumscribe the potential landscape within which ecological risk assessments are defined and
conducted. It is clear from the foregoing discussion and other scientific evidence (U.S. EPA, 1990)
that stress, ecosystem type, level of ecological organization, spatial scale, and temporal scale are the
primary organizing variables in the ecological risk assessment process. Furthermore, "scale" (temporal,
spatial, and biological) is one of the factors distinguishing ecological risk from human health risk and
is a major source of uncertainty in ecological risk assessments.
Together, the following five variables can be used to bound the ecological risk assessment
landscape and capture the essential features of the risk assessment process. Each category can be
further subdivided, as desired, to reflect specific attributes of scale, organization, or stresses.
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Stress. The type, properties, temporal and spatial patterns, and interactions of the
stress are of fundamental importance in defining the temporal and spatial dimensions
and the potential types of ecological effects of the risk assessment.
Ecological Organization. Ecological organization reprsents the level of biological
complexity (for both ecological endpoints and indicators)" at which the ecological risk
assessment is conducted. In theory, the scale of ecological organization chosen for the
ecological risk assessment is dependent upon both the spatial and temporal scales of
the stress and the co-occurring ecosystem components affected by the stress.
Ecosystem Type. Ecological assessments are currently ecosystem-specific; that is,
assessments describe the risk of ecological effects for aquatic, terrestrial, or wetlands
categories of ecosystems and/or their respective subcategories. This type of
classification assumes that the stresses and the ecological effects do not interact and
that risks, therefore, can be segregated among ecosystem types.
Spatial Scale. Spatial scale delineates the area over which the stress is operative and
within which direct ecological effects may occur. Indirect ecological effects may
greatly expand the spatial scale required for the assessment.
Temporal Scale. Temporal scale defines the expected duration for the stress, the time-
scale for expression of direct and indirect ecological effects, and the time for the
ecosystem to recover once the stress is removed.
These variables represent explicitly or implicitly the primary categories of information that are
required for developing the "universe" of potential ecological risk assessment guidelines options.
2.5. Ecological Risk Assessment Landscape -- "The Cube"
Having proposed a suite of variables that are necessary for defining the subject matter and
content of ecological risk assessment guidelines, the next step was to examine various options for
combining variables. For example, the guidelines could be organized around stress and ecological
hierarchy, stress and ecosystem type, ecosystem type and ecological hierarchy, etc. The challenge was
to optimize the integration of the variables into one or more satisfactory configurations that capture the
scientific issues central to the risk assessment process.
The option presented and adopted at the workshop describes the scope of the ecological risk
assessment process as a three-dimensional matrix~"The Cube." This matrix recognizes the importance
of levels of ecological organization, stress type, and ecosystem type as the primary variables in the risk
assessment process (figure 1). The three-dimensional matrix illustrates the role of stress in defining
both the spatial dimensions of the problem and the ecosystem(s) at risk and the dependency among the
stress type, properties, mode of action, and the responses of ecological endpoints.
The scale and resolution of this matrix are particularly useful for ranking the relevancy and
importance of specific combinations of variables, for identifying scientific issues, and for determining
the state-of-the-science and feasibility of conducting risk assessments using each of these axes. One of
the goals of the Miami workshop was to evaluate the contribution of each of these organizing variables
to the risk assessment process. Since the biological response hierarchy axis is the source of the
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endpoints used in ecological risk assessments, the first task of the workshop was to evaluate both the
theory and feasibility of making assessments at the organism, population, community, and ecosystem
levels of ecological organization.
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3. WORKSHOP REPORTS ON ECOLOGICAL HIERARCHY
3.1. Introduction
Ecological hierarchy or level of ecological organization is one of the critical organizing
principles identified in the risk assessment process. Biological responses from one or more levels of
organization are used to assess ecological risks from both chemical and nonchemical stresses. To
examine this important principle, the workshop participants were divided into three work groups
representing the scales of ecological organization commonly used in ecological assessments:
organism-population, community, and ecosystem. The chairperson for each work group presented a
discussion initiation paper on the principles for each level of biological scale that are both generally
accepted within the scientific community and essential to the risk assessment process as conducted in
various ecosystem categories (e.g., aquatic, terrestrial).
Topics discussed in each work group included: (1) determining the scientific feasibility and
appropriateness of using each level of organization for assessing ecological risk as a function of spatial
and temporal scale, category of stress, and ecosystem type; (2) identifying scientific issues that are
critical to the risk assessment process but that exceed the current state-of-the-science; and (3)
determining the critical information gaps and research needs to be addressed.
While it is clear that resolution of these and other issues may have been beyond the scope of
this workshop, it was important that the critical issues be identified and accompanied with a statement
on the state-of-the-science. The perspective on feasibility that emerges can be used by EPA in
developing its ecological risk assessment guidelines strategy. The following section presents summary
reports from each work group chairperson.
3.2. Organism-Population Work Group (Steve Bartell, Chair)
3.2.1. Policy and Risk Analysis
Under the standard paradigm of risk assessment, regardless of the level of biological
organization, the process of risk assessment consists of several components: (1) the potentially
hazardous nature of the stress must be determined; (2) the degree of exposure to the stress must be
quantified (for toxic chemicals, the exposure must be translated into an estimate of dose to some
ecological target); and (3) dose must be translated into an estimate of risk for a corresponding
ecological endpoint.
The component processes of ecological risk closely parallel the process of human health risk
analysis. The development of credible methods for ecological risk analysis should not, however, be
constrained by the human health paradigm. Interestingly, the acceptable levels of risk for humans
appear to have been derived from social and economic reasons, not for the implications of human
survivorship or the population dynamics of humans. This contrasts with ecological risk analysis,
where levels of risk are assessed hi the context of overall population dynamics for the target
organisms.
The work group members were generally in agreement that methods for estimating ecological
risk to populations (and other hierarchical levels) cannot be developed independently of the policy
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objectives of regulation. Precisely formulated regulatory objectives are required to facilitate the design
of effective methods for estimating ecological risks in relation to EPA needs.
Currently, EPA uses ecological risk analysis to address different regulatory, policy, or
legislative demands. For example, the regulation of pesticides requires analysis of chemicals designed
to be toxic to specific populations. In contrast, under the Toxic Substances Control Act, risk analysis
is used to estimate the potential toxicity of new industrial chemicals. Within Superfund, ecological
risk analysis attempts to quantify the reductions in risk to populations in relation to alternative
remediation plans for hazardous waste sites.
To design useful and effective methods for population-level risk analysis, the technical
community should be involved with EPA policy- and decision-makers from the outset. This feedback
loop will help ensure that policy and regulatory needs are understood by the methods developers. In
turn, the methods developers can provide technical information in the most useful format and assist the
policymakers and regulators in understanding the ecological implications of their decisions. Policy,
regulations, and decisions are, after all, uncontrolled experiments. Monitoring the results of these
decisions can provide information for evaluating and refining methods and future decisions.
3.2.2. Individuals and Populations
The work group recognized the important point that population-level effects really reflect the
aggregate response of individual organisms. That is, exposure occurs at the level of the individual,
and individuals respond to stress. In this sense, it can be argued that the fundamental unit of
ecological risk analysis is the individual. Not all work group members, however, agreed; it also can
be argued that the population is the fundamental unit for risk analysis. One advantage is that
ecological risk methods aimed at the individual can take advantage of decades of detailed life-history
data, life tables/behavior information, etc. Summarizing individual responses at the level of the
population permits the development of risk methods in terms of classic demographic models, including
estimates of stress effects on natality, mortality, net reproductive potential, and other traditional
demographic descriptors.
3.2.3. Alternatives and Innovations in Population Models
There are at least four population modeling approaches that could contribute to the
development of credible methods for ecological risk assessment. The following approaches are in
various stages of development:
Stable Population Theory. The theory of stable populations has produced the life-table
approaches and analyses employed traditionally to characterize population fluctuations.
Rates of increase, population structure (e.g., age, size, physiological condition),
reproductive value, and the sensitivities of these parameters have been thoroughly
examined and appear directly applicable to ecological risk assessment. The primary
drawback may be in the general availability of data. Nevertheless, the theory is
sufficiently advanced to the point of identifying the necessary measurements.
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* Equilibrium Population Theory. The theory of equilibrium populations has similarly
produced models that have been fairly well studied. These models formulate changes
in population structure and abundance that may be applicable to ecological risk
estimation.
" Stochastic Population Theory. The theory of stochastic populations can contribute
additional endpoints for risk analysis. Stochastic growth rates, population variability,
and probabilities of extinction are important components of stochastic theory. This
body of theory and the associated models, data collection methods, and analysis have
been less well developed. Stochastic population theory and methods may be
sufficiently developed for ecological risk assessment in 5 to 10 years.
Individual-Based Population Models. Individual-based population models that
explicitly represent individual organisms have been developed to describe population
dynamics. These models offer the advantage of integrating life-history information,.
demographics, behavior, and bioenergetics in algorithms that have been impossible or
extremely difficult to represent using traditional modeling approaches. These models
are largely in the exploratory stages; problems remain in terms of conceptualization,
parameter estimation, and computational demands. One work group member indicated
from experience with these kinds of models that the necessary detailed biological
information will seldom be available for species of interest. It is quite likely that the
computational constraints will relax before the data limitations decrease.
There remains much to be explored in the application of deterministic and stochastic
population models to ecological risk estimation. This also applies to continuous versus discrete
population models. For example, if organisms are modeled as discrete entities in continuous time, one
set of equations applies, and these equations are fairly well understood. If continuous rates are
expressed in discrete time, however, another set of equations describes the population, but these
equations are less well understood.
Accurate population forecasting based on process-level understanding will require a long-term
EPA investment. The three previously listed theories primarily project population change in relation to
current population structure. While it is possible to some degree to forecast from purely an empirical
approach (e.g., time-series analysis), true forecasting remains a challenging area for development, both
in theory and methods. Time-series methods remain limited by insufficient data for nearly all
populations of interest.
Between the aggregate demographic models and the detailed individual-based models lies an
intermediate level of population description. Special partial differential equations (e.g., von Foerster
equations) permit the simultaneous consideration of disparately scaled biological phenomena (e.g.,
feeding events over seconds or minutes, individual growth over days). The mathematical properties of
these equations are quite distinct from the classical demographic equations. The meaning of these
differences for ecological risk analysis should be explored.
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3.2.4. Data
The work group had several observations on the nature of data for use in estimating ecological
risks at the population level. One question that needs answering concerns the criteria for selecting
populations that are of interest in ecological risk analysis. Raptors, including the spotted owl and the
bald eagle, are easily justified choices in relation to concerns over habitat loss and pesticides. By
contrast, the tri-butyl tin (TBT) issue was decided in relation to a little-known population of mussels;
the case against TBT was simplified by a readily available, less toxic alternative. The "so-what"
question regarding population effects needs a consistent framework for assessment.
Concern was expressed that useful information produced by routine toxicity testing is not
commonly reported. The raw data and exposure-response curves for chemicals should be accessible in
addition to Hie routinely calculated toxicity benchmarks. More emphasis should be placed on chronic
testing. It also was noted that much information of potential value is simply not collected during
sample processing (e.g., length-weight data, histopathological data, condition). Data that might be
useful for extrapolating individual responses to populations or from laboratory to field are simply not
collected. Concern also was expressed that if individual organisms are collected and measured, a
sufficient sample of different ages, sizes, and sexes must be obtained in order to characterize
accurately the population, either in laboratory or field collections. Importantly, if population models
are to be implemented for estimating ecological risk, data and assays must be designed or modified to
provide the necessary input information. This information is particularly critical if the full potential of
individual-based models is to be realized. More detailed information at the individual level is needed.
3.2.5. Extrapolation
The work group recognized the need for extensive and continued efforts in addressing the
ability to extrapolate laboratory-measured toxicity to the field. There was consensus that resources
need to be committed to collection of additional field data. These data will be used to establish rules
for extrapolation, as well as for testing current population models, which the work group realized
represents a potential long-term EPA commitment. It was suggested that the EPA Environmental
Monitoring and Assessment Program (EMAP) might be involved in collecting some of the necessary
field data.
Interestingly, several work group members expressed the opinion that our ability to extrapolate
is better than generally believed and that accurate estimates of exposure concentrations are the key to
successful extrapolations. The distinction between exposure and dose is also important; one current
drawback of routine toxicity tests is that exposure is calculated, not measured, and dose is not
measured. As a result, no relationship between exposure and dose is established.
3.2.6. Miscellaneous
Experimental approaches to estimating ecological risk, even at the population level, remain
logistically prohibitive especially if a set of multiple stresses and potential target populations is
considered. The combinations and permutations escalate at a rate that removes experimental
approaches from serious consideration. The work group reserved some hope that the effects of
multiple stresses might be addressed through detailed study of the underlying mechanisms of exposure
and toxicity of individual stresses acting independently.
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Emphasis has been placed on structural entities for ecological risk analysis. Work group
members pointed out that it also is possible to emphasize processes. That is, populations represent an
integration of underlying birth, growth, and death processes, so why not focus directly on the
underlying dynamics as endpoints in risk analysis? It is possible to view populations in terms of
potential and to estimate the effects of stresses on the realization or altering of that potential. This
Shift in emphasis from structure to function might stimulate the development of new models and
assays for use in ecological risk assessment.
The issue of biomarkers was raised. There was consensus that these relatively new measures
might provide useful information regarding the exposure of individuals to stress. Much work remains
in understanding the implications of biomarkers for toxic effects at the level of the individual and the
population.
3.3. Community Work Group (Ann Bartuska, Chair)
3.3.1. Introduction
The charge for the Ecological Community-Level work group was to identify the endpoints, or
community characteristics of interest, when considering the risk of any ecosystem to any stress. The
work group was adamant and unanimous in its opinion that the "community" could not be separated
from either populations or ecosystems, because of the numerous interconnections and dependencies
across the levels. Rather, the work group recommends that "critical endpoints" be identified, and that
the nature of the endpoint (e.g., maintenance of species diversity) be determined at whichever level in
the biological hierarchy information is gathered and analyses are conducted.
A second overlying issue was generated by the questionhow is an endpoint selected? If
ultimately we want to provide some prediction of change from the intersection of stress "x" with
ecological endpoint "y," guidelines must be developed to determine the importance of change.
Importance in ecological terms is one approach, but equally important is the recognition of human
values and management goals in the decision-making process.
3.3.2. Selection of Stresses
In attempting to begin selection of endpoints, we kept coming back to the question, with
respect to which stress? The work group reviewed the proposed list of stresses and determined that
there are additional possible stresses that should be considered. The following list of stresses has been
stratified by spatial scale, although some factors are effective at more than one level. The list may not
be complete and can be modified based on the input from other groups.
1. Local Scale
organic additionsrelated to aquatic systems;
thermal pollutionspecifically effluent discharges;
electromagnetic (ionizing radiation);
habitat alterations and sedimentation;
eutrophication;
toxic effects; and
ozone additions (tropospheric).
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2. Regional Scale
acidic deposition;
ozone addition (tropospheric);
toxic effects;
species depletion or removal; and
management activities and habitat alteration.
3. Global Scale
ozone depletion (stratospheric); and
" global warming or cooling.
As a final comment, the work group indicated that in many cases stresses do not occur in
isolation. It is essential that stress co-occurrence and interactions be acknowledged and assessed
together.
3.3.3. Determination of Endpoints
Within the workshop guidelines, this work group focused on the community level of
organization, determining that communities will operationally be handled as the interaction of
populations. The overall or umbrella endpoint, therefore, became "sustainability of community
structure." The primary measurement endpoints are: number of species, abundance, and frequency.
No "value" was put on the number of species, that is, determining if endemic or introduced. This is
an issue that may need to be incorporated into the ecological risk assessment process. Some stresses
may create new habitats that can increase the number of species and presumably diversity. The value
of such a change across the landscape is important to consider. These measures should be evaluated
within the more complex endpoints of:
diversity;
competitionor more specifically, such issues as competitive release;
food-web analysis;
sensitivity of keystone species to the stress;
minimum number of species and their distribution to maintain a community (this
community endpoint also should be extended as a concept to the landscape, along with
number and distribution of species/communities to sustain an ecosystem); and
productivity.
While the relative importance of each of these ecological endpoints may vary depending on the
ecosystem of concern, the work group felt that all endpoints should be evaluated in an ecological risk
assessment.
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3.3.4. Information Needs
Within the ecological risk assessment process there will be a gathering of knowledge and,
perhaps more importantly, the identification of knowledge gaps. The information needs discussed
below reflect a hierarchy of short-term activities-things we can do now-and longer term research
efforts. The importance of the latter is in the refinement of a data base in order to reduce uncertainty.
(The following list does not necessarily reflect priorities, nor any particular sequence of events.)
Develop expert judgment/assessment on risk impact. This process would allow an a
priori description of what we know, and from this we could identify what we need to
know at the stress-endpoint intersection.
Develop model(s) to be used to assess impact of all stresses. These could be simple
models designed primarily for conceptualization and to identify information needs.
The models should be developed for a set of ecosystems selected for their value.
Monitor to characterize the way the community is structured now, using the selected
endpoints, and to identify changes at the community level.
Conduct exposure monitoring and characterization for each stress. It is especially
important that this information be linked to the field (i.e., "real-world" conditions) and
not theoretical conditions.
Perform fundamental work to describe the mechanisms of competition.
Develop a fundamental understanding of food-web structure.
« Conduct cause-and-effect experimentation, coupling laboratory/greenhouse results with
the field.
Several of the above-mentioned needs can be accomplished in reasonably short timeframes,
and actually may be only a focused compilation of readily available data. For others, some data can
be used in the risk assessment process now, but with a wide range of uncertainties. As new studies
are completed, the uncertainties may be reduced. Therefore, the ecological risk assessment process
should be able to adapt to the accumulation of new knowledge through continuous iterations.
In summary, the work group recommends that communities be viewed as the biological
structural component of ecosystems. For an expanded suite of possible stresses, the structural
endpoints (species number, abundance, shifting competitive state, etc.) remain constant in their
importance across stresses and across ecosystems. The information available to describe the endpoint
for a given stress-endpoint combination will vary, so the acquisition of new information and the
incorporation of this knowledge into the ecological risk assessment process must be ongoing, and the
ecological risk assessment process should remain fluid.
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3.4. Ecosystem Work Group (David Weinstein, Chair)
3.4.1. Introduction
Ecosystem-level considerations often have been insufficiently treated in ecological assessments
because of tiie complexity of interconnections within the ecosystem, the difficulty of identifying the
circumstances under which indirect pathways might cause effects, and the failure to recognize the
importance of these indirect pathways. However, since the ecosystem serves as a mediator of the
interactions within and among populations, within and between trophic levels in communities, and
between each population and its abiotic environment, the likelihood is high that ecosystem-level
processes influence the stress-response relationship between a stress and ecological characteristics or
endpoints of concern within the natural ecosystem. The consequences of such influences are high and
potentially of great magnitude, since ecosystem processes, such as nutrient regeneration and organic
matter transformation, are the means by which the suite of species within an ecosystem receive the
resources necessary for their sustenance. Consequently, the work group viewed the method by which
these ecosystem processes will be considered essential in risk assessment.
3.4.2. Criteria for Selecting Endpoints
A major phase in the ecological risk assessment process will be the identification of the critical
endpoints of relevance to ecosystem-level considerations. This work group attempted to define the
criteria that should be used to select these endpoints.
The first step is to recognize that the endpoints will have to be selected with reference to a
specific ecosystem and specific stress in'question. It is conceivable that each ecosystem will have a
separate list for each stress. However, it is anticipated that once these lists are constructed, similarities
across the lists for different stress-ecosystem combinations will permit aggregation, reducing the total
number of cases for which unique lists will be required. Development of the ecological risk
assessment guidelines should address this possibility.
3.4.3. Example Set of Criteria
There are two criteria that the work group initially determined to be important for selecting
endpoints of concern once the specific ecosystem and stress have been identified:
1. The endpoints must characterize the ability of the ecosystem to sustain its structure
(e.g., physical structure, diversity) and function (e.g., nutrient regeneration, carbon
flows). In other words, a change in the endpoint would indicate a change in the ability
of the ecosystem to sustain normal structure and normal function. A significant
change in the endpoint, therefore, would be inevitably followed by a change in the
capability of the ecosystem to continue to support its cast of species present at the time
. of the stress.
2. The endpoint must involve a characterization of the stocks and flows in the ecosystem.
The work group recognized that the quantities in standing stocks of material and in the
flows of energy, carbon material, and nutrients between these stocks are intimately
related to the ability to sustain normal processes and therefore are themselves key to
understanding the impacts of stresses.
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a) Examples of structural stocks and flows
diversity;
- traditional diversity,
- functional diversity, and
- diversity of economically important species;
physical habitat;
spatial heterogeneity; and
natural disturbance regime.
b) Examples of functional characteristics
regeneration of nutrients;
natural detoxification processes;
potential for increasing toxicity; and
major flows.
These criteria were constructed with specific aquatic ecosystems in mind, although they appear
to be sufficiently general to be used for any ecosystem. Nevertheless, the list may need to be
expanded as other ecosystems are given detailed consideration, a process that should be begun early in
the process of developing ecological risk assessment guidelines.
3.4.4. Example List of Endpoints
Using the above criteria of characterizing sustainability and/or stocks and flows, a list of
endpoints was created for the shallow-water marine ecosystem type, using an examination of the
important characteristics likely to be affected by nutrient addition. This list was considered to be
appropriate for freshwater lake and river ecosystems as well.
* Water turnover through the benthos. Under nutrient addition, maintenance of water
quality and clarity is dependent upon the rate of filtration by the benthos. The benthos
will remove particulates from water as it passes through the organisms, buffering the
rest of the ecosystem from changes in light availability associated with algal blooms
that otherwise would result from an influx of nutrients. Consequently, a measurement
of the amount of water that can be processed per unit time by the benthos will reflect
the relative degree to which an aquatic system can buffer nutrient addition.
* Change in composition within a trophic level. The ratios of key population guilds (or
functionally similar units) within a trophic level will be critical for the maintenance of
resource generation or regeneration rates upon which the rest of the ecosystem
depends. For example, shifts from the relative abundances of blue-green and green
taxa of algae will profoundly influence" species dependent upon one or the other of
these groups for fixation and generation of nutrients or carbon. Nutrient additions
have been demonstrated to cause a shift in this ratio.
Relative energy flow through the grazing food chain versus the detritus food chain.
Energy fixed through photosynthesis or entering the ecosystem through material influx
will be utilized by either grazing organisms or detritus decomposers. Depending on
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which of these pathways predominantly uses the carbon in an ecosystem, the response
to alteration in energy flow will be characteristically different. Since entire subsystems
; are developed to utilize the nutrients released by these processors, the response will
quickly be felt throughout the ecosystem. Therefore, a shift in the relative flow
through these two pathways will precede a significant change in the ecosystem.
Anoxia, or low levels of dissolved oxygen. The level of dissolved oxygen has been
well documented as a critical characteristic determining the ability of aquatic
ecosystems to sustain their structures and functions. Low levels of dissolved oxygen
often lead to noxious algae blooms.
Productivity in different trophic levels. Major fish production is probably the most
widely recognized marine ecosystem characteristic of concern. Because of the tight
coupling between fish productivity and productivity of other trophic levels, each is a
key endpoint and an endpoint demonstrated to be potentially affected by nutrient
addition.
» Physical structure. Most species in most ecosystems are dependent upon a specific
physical structuring of the system. They utilize this structure to acquire the quantities
of resources needed, or survive by the growth restrictions the structure places upon
their competitors. Consequently, changes in physical structure are likely to change the
pattern of resource availability and therefore the ability of species to compete and
survive.
» Ratio of recycled to new nutrient input. Organisms in ecosystems become adapted to
a characteristic pattern of nutrient availability. That pattern is vastly different if the
nutrient availability is recycled through biologically mediated (e.g., through
decomposition) versus physically mediated (e.g., through rainfall input). Shifts in the
ratio of recycled to new inputs will therefore result in shifts in the competitive ability
of species and, subsequently, the compositional mix that depends upon those relative
abilities.
Change in the disturbance regime. The work group considered the lists of endpoints
that would be generated for the shallow-water marine ecosystem type under different
types of stresses, namely pesticide input, species introductions, and changes in
hydrology. No new endpoints were identified, although after brief study several
endpoints did not appear to be appropriate for one or more of these additional stresses.
As the new stresses were considered, ways that each of the originally suggested
endpoints could reflect the ability of the marine ecosystem to sustain itself under the
stress were identified, leading to the suggestion that this list might be comprehensive
across different types of stresses. Since, as previously mentioned, the endpoint list
was also comprehensive for freshwater ecosystems, the work group.suspected that the
total number of lists needed might in practice not be large.
The next step in the process would be to consider a different ecosystem type, such as forests,
and compile the list of characteristics reflecting the ability of those ecosystems to sustain themselves
under different kinds of stresses. Following this task, it would be determined whether a change in the
criteria is necessary to cover the endpoints that should be identified in each new type of ecosystem.
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These steps are recommended to occur early in the process of developing ecological risk assessment
guidelines.
3.4.5. Practical Considerations
In practice the work group found it easier to select a particular stress-ecosystem combination
(such as pesticide addition to marine ecosystems), list the set of ecosystem characteristics of
importance (hereafter referred to as endpoints), and identify the criteria that were used to select items
for that list. This process was repeated for different stresses for a given ecosystem, with items added
to the list as warranted by consideration of the different stresses, and modification of the selection
criteria following if required. Presumably the same steps could be followed for each stress for a
different ecosystem type, yielding a separate list of endpoints for each stress-ecosystem combination,
but a single set of criteria applying to all endpoint lists.
3.4.6. Issues Requiring Further Consideration
« Should classification of ecosystems be based on functionality instead of the traditional
classification based on the physiognomy of the dominant organisms?
For the purposes of risk assessment, two ecosystems with similar rates of energy
and/or nutrient processing and similar pathways of material and energy flow might
have much more similar risks, and should therefore be treated as a single category,
than might two ecosystems classified together because they are both dominated by
large trees, for example.
Should classification be further subdivided by natural disturbance frequency?
Often the rate and frequency of natural disturbance have shaped the characteristic rates
of material and energy processing in ecosystems. Therefore, the risks of damage by
pollutants are likely to be more similar among ecosystems experiencing similar rates of
disturbances than among all forests, or among all lakes, or among all streams, etc.
Where do we put managed ecosystems, such as agricultural systems, in this
classification?
In determining endpoints:
- , Who determines what constitutes acceptable and unacceptable changes?
Do endpoints depend on spatial and temporal scale?
How do we deal with natural variability in determining a probabilistic dose
response?
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4. SCIENTIFIC FEASIBILITY ISSUES
4.1. Introduction
Having examined the state-of-the-science relative to the theories and principles available for
assessing risks at the various levels of ecological organization, two work groups were charged with
determining the feasibility of conducting ecological risk assessments in aquatic and terrestrial
ecosystems. These work groups focused on determining which methods and models are currently
available for assessing the risk from both chemical and nonchemical stresses and identifying additional
research that will be needed over the next decade. This latter information is important to EPA for
formulating a strategy for its ecological risk guidelines program.
4.2. Aquatic Ecosystems Work Group (Tom Duke, Chair)
4.2.1. Scientific Feasibility Issues
This work group addressed the feasibility of utilizing various ecological effects endpoints in an
ecological risk assessment procedure. Three feasibility categories were discussed: those endpoints
ready to be used immediately, those endpoints ready within 5 years, and those endpoints ready within
10 years. Research needed to develop new effects endpoints or improve present ones also was
discussed.
The work group defined feasibility, identified four aquatic ecosystem types, selected endpoints
for effects from lists provided by speakers earlier hi the workshop, and identified biological responses.
"Feasibility" was considered in terms of methods and interpretation, because many examples were
presented where methods to measure a specific endpoint are presently available (or soon will be
available), but the capacity, to interpret the results of the measurement will require another 5 or more
years of research. The group decided that a matrix approach is required to address the feasibility issue
and would involve various aquatic habitats, effects endpoints, and levels of biological responses. A
simple division of the aquatic environment into marine and freshwater ecosystems was considered to
be inadequate. A more habitat-oriented approach was recommended and resulted in selection of four
types of aquatic ecosystems: flowing water, shallow embayments, deep embayments, and wetlands.
Based on presentations made earlier in the workshop, endpoints were selected under the general
category of structure, function, and physical environment. Also, a biological response hierarchy of
individuals, populations, communities, and ecosystems was selected on the basis of previous
discussions at the plenary sessions.
The work group discussed a general approach to ecological risk assessment that would be from
the top (of biological hierarchy) down and from the bottom up. That is, one would assess the
particular ecosystem under question through literature, research, expert scientific judgment, etc., and
locate specific ecosystem structural and functional attributes that could be impacted by the stress or
stresses involved. Next, information would be developed at the individual organism level. This
information would be processed through models and other means to the population and possibly
community levels. The protocol at the population level would be:
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a) scientific assessment of the stress;
b) an individual viewed as a dynamic organism; it is a function of the stress (e.g.,
lipophilic chemicals require quantitative knowledge of lipid dynamics in the
individual);
c) exposure (this must be coupled with the individual--the receptor);
d) effector (e.g., the presence of the stress in the individual must be translated to
individual effects [QSARs]); and
e) population effects determination (the sum of individual effects is translated to
population-level endpoints).
The matrix for assessing the feasibility of using specific effects endpoints in ecosystem risk
assessment is presented in table 1. Feasibility of the methodology (designated "M") and interpretation
(designated "I") for each endpoint is rated numerically as follows:
» 0-indicates that the method is immediately available and utilized by EPA and other
agencies or agreed upon by the scientific community, and that a sufficient body of
knowledge and expertise exists presently to interpret the quantification of the endpoint;
» 5~indicates that the method or interpretative capacity is 5 years in the future; and
" 10indicates 10 years or more of work is required.
It was the opinion of the work group that the numerical designations should be viewed in a
relative, not absolute sense. The list of endpoints is obviously incomplete and should be viewed as an
example of how endpoints can be evaluated. A detailed listing of endpoints should be an early
component of the ecological risk assessment guidelines process.
The three categories of endpoints examined were based on measures of biological structure,
function, and physical environment (table 1). The extent and level of complexity to which these
structural and functional endpoints interact and could be measured and analyzed are nearly limitless.
The work group attempted to make the following rather simple "first-cut." Aquatic communities, for
example, can be classified as planktonic or benthic and within each of these categories can function
autotrophically or heterotrophically. Such an approach would be especially helpful in focusing food-
web measurements.
The physical environment endpoint was included to account for changes in abiotic components
of the ecosystem associated with impacts of a stress. Changes in the physical environment of an
ecological system could of course bring about changes in the biological structure (indirect effects).
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Table 1. Feasibility Matrix
Ecosystem-Level Endpoints
A. Biological Structure
Biomass Partitioning -
Quantify relative stocks
by meaningful groups
(e.g., plankton, benthos,
autotrophs, heterotrophs;
diatoms, flagellates,
blue-green algae)
Species Enumeration -
including diversity
Food Webs
B. Biological Funcation
Total System Metabolism -
Integrated holistic
measurement of entire
system metabolism
(e.g., upstream-
downstream, and diel
freshwater oxygen
concentrations)
Component Community
Metabolism - (e.g.,
light/dark bottles,
benthic chambers)
Carbon and Nitrogen
Flow - (e.g., internal
dynamics and external
sources and sinks)
C. Physical Environment
(i.e., substrate
characterization, flow
regime, depth, temperature,
light, turbidity)
0 0
Habitat
Flowing Sli allow Deep
Water Embayment Embayment Wetlands
Ma T MI MI MI
00-5 0 0-5 0 0-5 0 0-10
0 0-5 0 0-5 0 0-5 0 0-5
0-10 0-10 0-10 0-10 0-10 0-10 0-5 10
0 0-5 0-5 0-10 0-5 0-10 5
0 0-5 " 0 . 0
10
0 0-5 0 0-10 0 0-10 5 10
5 5-10 0 0-5 0 0-5 5 5-10
0 0-5
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Table 1 (cont.)
Population-Level Endpointsb
Biological Systems
Inverte-
Growth
Survival
Reproduction
Structure
age
size
physical variables
Fish
M
0
0-10
0-5-10
0
0
0-5
brates
I M
0-5 0-5
0-10 0-10
0-5-10 0-5
0-5
0-5 0-5
5-10
I
5-10
0-10
5-10
5-10
5-10
Plankton
M I
0-5 0-5
0-10 0-10
0 0-5
0-5
0-5
0-5
Other
Vertebrates
M
0-5
0-10
0-5
5-10
5-10
5-10
I
0-5
0-10
0-5
* M - Feasibility of methodology
I - Feasibility of interpretation
Numbers in the table reflect the estimated number of years until methodology is available or knowledge is
sufficient to interpret endpoint data. See text for additional explanation.
b Categories for the population matrix differ from the ecosystem matrix because the population-level endpoints
are more closely related to biological systems than to habitat.
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4.2.2. Research Needs
The work group identified the following general research needs:
» Develop information on the frequency and magnitude of natural disturbances. Effects
linked to anthropogenic stresses must be compared to underlying variability linked to
natural variation. A critical need exists to characterize natural variation and to address
signal-to-noise issues at the ecosystem level.
Develop a strong ecological theory concerning impact of stresses on structure and
function of ecosystems. In general, there is only a vague understanding of the linkage
between stresses and changes at the ecosystem level. There are notable exceptions; for
example, there is much evidence that may be used to predict ecosystem responses to
nutrient additions and organic additions. An understanding of the way these
ecosystem-level characteristics respond to stress and disturbance is needed. Except for
ecosystem-level (mesocosm) experiments, experimental approaches are not available.
Interpretation at the ecosystem level may not be generalizable for many stresses. There
is a need to develop protocols so as to avoid studying each stress. These protocols
may be similar to application of quantitative structure-activity relationships (QSARs) to
population-level studies.
Identify general exposure/effect responses for ecosystem endpoints from all available
sources (meta analysis).
Determine the interrelationships among local ecosystems that propagate effects to larger
(landscape or global) scales.
Improve the capacity of models to extrapolate from laboratory to field and from
individuals to populations and communities.
The following comments and research needs are related to the endpoints used in the feasibility
matrix at the population level of organization:
AbundanceMeasurements of abundance are feasible and routinely done. For fish,
relative abundance is usually easier to measure than absolute abundance. Populations
distributed over large areas can be difficult to estimate. Foreseeable research is
unlikely to lead to significant improvements.
Age/Size DistributionMeasurements of age/size distribution for fish are feasible and
routinely done. Precision is higher than for abundance estimates. This measurement is
sensitive to stress-it is often used to assess status of exploited populations. Some
improvements in aging techniques are possible from research on scale and otolith
analysis. Size/distribution is straightforward for invertebrates. For some mollusca, age
is estimated using techniques similar to those used for fish. For larger invertebrates,
age/size can be an indicator of stress. For smaller invertebrates, it is more an indicator
of predation intensity. Research is unlikely to lead to improvements.
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» Reproduction-Measurement of reproduction for fish is feasible and routinely done.
Reproductive status (mature or immature) is easy to determine. Fecundity is feasible,
but can be difficult to estimate in some species. Size-at-maturity is a commonly
viewed indicator of over-exploitation. For invertebrates, feasibility varies with taxon.
Utility as an indicator of stress is unclear.
Survival-Measurement of survival for fish is usually estimated indirectly from
abundance and age-distribution time series. Standard methods are available;
improvements are unlikely. For mammals, survival rates can be obtained directly from
radio-collared animals. Improvements in technology (e.g., size, cost of transmitters)
are likely in the near-term. Survival is an indicator of total stress level, but without
further information it does not reveal source of stress. For invertebrates, survival
usually is estimated indirectly from abundance and reproduction.
" Growth-For fish, past growth histories often can be estimated from scales or otoliths.
Growth can be used as an indicator of stress. Improvements are possible with further
research on otolith analysis.
* Physiological StatusFor fish, simple condition indices are widely used now. Some
physiological, histopathological, and biochemical .measures are now being used,
principally in research, as indicators of exposure and/or response to contaminants. In
general, most of these have proved difficult to interpret as indicators of effects. Some
indicators have been shown to be selective indicators of exposure to specific classes of
chemical stresses. This is an extremely important research area in which much
progress is possible. It provides a means of separating the effects of chemical stresses
from the effects of other natural and anthropogenic stresses.
4.3. Terrestrial Ecosystems Work Group (William Smith, Chair)
4.3.1. Introduction
In an effort to identify research required to improve ecological risk assessment methodology,
the Terrestrial Ecosystems work group identified "generic" strategies for risk assessments at the
population and ecosystem levels (figures 2 and 3). These figures suggest current state-of-the-science
capability and imply that additional data are required for more effective ecological risk assessments.
From this exercise, the work group developed specific suggestions for research needs that would
strengthen ecological risk assessment capabilities. These needs are presented under stress
characterization and ecological effects characterization categories.
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Figure 2. Current Strategy for Ecological Risk Assessment: Population Scale
RULE OF THUMB (e.gi, Quotient Method),
i
FRAGMENTS OF DEMOGRAPHIC DAT*
SIMPLEST DEMOGRAPHIC MODEL
; -Age at Maturity
-Survival to Maturity
'
-Fecundity
I
LIFE CYCLE DATA
-Laboratory
-Field
-Ecosystem Studies
-Keystone/Indicator
Species Appiication
Additional Research
ENVIRONMENTAL DETAIL
-Stochastieity
-Density Dependence
-Spatial Pattern/Subdivision
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Figure 3. Current Strategy for Ecological Risk Assessment: Ecosystem Scale
WATER, C, *l, P STATES
-Functional Groups
-Trophic Levels
i
WATER, C, H, P FLOW RATES
I
FLOW RATES AND
ENVIRONMENTAL VARIABLES
1
WATER, Cs N, P DYNAMICS
STANDING STOCKS
ELEMENTAL RATIOS
P/B RATIOS
TROPHIC EFRCIENCIES
FLOW DIVERSITY
TRAJECTORIES
- Dynamic Tendencies
- Change Prediction
Additional Research
COMPONENTS
-More System Detail
-Process Studies
'Field
* Microcosm
-Temporal Resolution
ENVIRONMENT
(Abiotic/Biotic)
-Spatiaf Elaboration
-Stochastic Drivers
-Feedback Effects
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4.3.2. Stress Characterization Research Needs
A primary research challenge in this area is the linkage between stress monitoring (exposure)
and dose (e.g., amount/duration of a chemical at a biological receptor site of action). For ecological
risk assessment, the need is especially great for improved understanding of dose at different ecological
hierarchies (i.e., individual, population, community, ecosystem, landscape); time scales; and spatial
scales. Additional research on dose kinetics also is required. Improved understanding of episodic
(peak) exposures versus chronic, longer term exposures is essential. Linkage of exposure data to
indirect as well as direct ecological effects also is needed.
4.3.3. Ecological Characterization Research Needs
Ecological understanding is improved by increased fundamental understanding of how
ecological .systems are structured and how they function. As a result, continued advancement of basic
ecological understanding is essential for improving ecological risk assessment strategies. A major
challenge is to partition anthropogenic stress effects from natural stress effects. Natural stresses are
varied, often recurrent, and have large associated variances. Research is needed on strategies to
partition subtle stress from dynamic system function. Understanding natural disturbance and
ecological responses (e.g., importance of functional redundancy, estimation of resilience and recovery
times) represents an opportunity to advance our ability to assess anthropogenic disturbances. Once a
site-specific problem has been selected for assessment, improved methodologies are needed to integrate
relevant existing information and data sets. Continued efforts to improve extrapolation of information
from laboratory to field, from species to species, and from one ecological scale to another are needed.
Multiple-stress interactions must be more adequately documented.
*
Factorial experiments and models provide experimental opportunities. Models developed or
applied in ecological risk assessments need to be standardized. For example, consensus must be
reached on the most important model parameters. How do stresses affect these parameters?
Sensitivity and formal uncertainty analyses must be performed. Further understanding of ecosystem
linkages is needed; the ability of a stressed forest to influence an associated stream or lake ecosystem
is one example. The significance of pattern for regional ecosystem and landscape scales must be
understood. We must account for the spatial heterogeneity of landscapes. Similarly, an understanding
of the significance of landscape pattern for habitats and species "source and sink" areas within
landscapes is needed. More effective tools must be developed to integrate geographic information
systems and remote sensing data.
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5. SPECIAL TOPICS
5.1. Introduction
During the first plenary session of the Miami workshop, stress characterization and ecosystem
classification were identified by the workshop participants as issues that warranted additional attention
in the workshop. Knowledge of the properties, distribution, behavior, and exposure patterns of stresses
was deemed to be as important as understanding ecological effects, both being inextricably interwoven
throughout the risk assessment process. Historically, ecological risks have focused on chemical
stresses. Recent reviews of current and future environmental problems, however, have emphasized the
increasing importance of nonchemical stresses (U.S. EPA, 1990), the interaction of multiple stresses,
and the abiotic modulation of stresses (U.S. EPA, 1991). Workshop participants considered
complementing the traditional structural classification of ecosystems with a classification system based
upon the functional characteristics of ecosystems. This type of classification would be process based,
have the advantage of not being linked to and limited by classic taxonomic classification, have
diagnostic value, and have a high degree of predictive value independent of ecosystem type. The
following section reports on the conclusions of the Stress Characterization and Ecosystem
Classification work groups.
5.2. Stress Characterization Work Group (Robert Huggett, Chair)
5.2.1. Introduction
The most widely used model for risk assessments was developed for human exposure to
hazardous chemicals (NRC, 1983). This report stated that risk characterization is a function of both
hazard and exposure. In this case, it is useful to define "hazard" as the inherent ability of some stress
to cause harm and "exposure" as the magnitude of stress on the system. In the case of a single
chemical and a single species, a dose-response relationship would relate the exposure to the hazard to
yield the risk estimate.
At the single-species/single-chemical level, tiiis model is straightforward and useable for
ecological risk assessments in either terrestrial or aquatic environments. It is at higher levels of
biological organization or when the exposure is to nonchemical and or multiple stresses that our basic
understanding of biochemistry, physiology, and ecological interactions, and our ignorance of the fate-
and-transport of chemicals, distribution of nonchemical stresses, etc., limit the accuracy of the risk
characterization. This section attempts to expand on some of the characteristics that link chemical,
physical, or biological stresses and exposure.
5.2.2. Stress Characterization
Consideration of exposure comes into play in at least two ways when performing an
ecological risk assessment. Exposure considerations are involved in the initial steps of the risk
assessment process, namely, in the conceptual problem definition phase, where exposure is utilized to
help define the scope of the problem. By considering the temporal scale of the exposure (i.e., acute,
episodic, or continuous) and the spatial scale over which exposure occurs (i.e., local, regional, or
global), this information can be used to identify populations, communities, and ecosystems potentially
at risk and, thereby, help define the scope and nature of the ecological risk assessment. After this
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initial scoping phase, stress characterization (exposure assessment) seeks to quantify the magnitude,
frequency, and duration of contact of the stress with the receptor.
The metric produced through the stress characterization assessment must be keyed to the
requirements of the stress-response assessment. For example, an exposure metric geared to individuals
in the population (e.g., mg-kg^-day"1) would be appropriate for population risk assessment. On the
other hand, when higher level (e.g., community and ecosystem) effects are the focus, the appropriate
stress or exposure metric should be keyed to the stress-response relationship available at these levels.
This stress/exposure metric may be expressed in units of flux (e.g., amount of stress per unit area per
unit time). Otherwise, the stress/exposure metric should be keyed to a lower level of biological
organization and the effects extrapolated through modeling to the higher levels.
Characterization of populations, communities, and ecosystems is an important and often
problematic aspect of ecological exposure assessment. Unlike the populations that are the focus of
human health risk assessments, generally there is much less information available about activity
patterns, abundance, demographics, and life histories of nonhuman populations. This information is
essential for constructing necessary scenarios of how populations come into contact with the stress.
Although this type of information may be available for populations of commercial interest, generally it
is not available or has not been combined into a useful form for ecological risk assessment purposes.
Another important consideration in ecological exposure assessment is how exposure to a stress
may alter natural behavior patterns, thereby affecting further exposure. In some cases, this may lead
to enhanced exposure (e.g., increased preening by birds after aerial spraying), while in other situations
initial exposure may lead to avoidance of contaminated locations or food sources. Little is currently
known about such behavioral modifications and how they may affect exposure by either enhancing or
mitigating it.
It is important to elaborate on the properties of stress relevant to ecological risk management.
The term "stress" has connotations that may be misleading under certain circumstances. The following
is an attempt to focus a future definition of stress on the factors that must be considered in ecological
risk assessment. First, a stress is characterized by its:
quality: chemical, physical, or biological;
intensity: concentration, magnitude, abundance/density;
duration: acute (short-term) versus chronic (long-term);
frequency: single event versus recurring or multiple exposures;
timing: time of occurrence relative to biological parameters such as spawning cycle;
and
scale: spatial extent and heterogeneity in intensity.
One approach for categorizing the quality of stress is illustrated in figure 4. In this figure, the
fate, transport, and exposure of organic versus inorganic chemicals are distinguished. This portion of
the scheme applies most directly to the introduction of chemicals to an ecosystem from an outside
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Figure 4. Example Categories of Stressors
CHEMICAL STRESSES
AQUATIC AND
TERRESTRIAL
FATE AND
TRANSPORT
PHYSICAL STRESSES
HABITAT ALTERATION
I
I I
Dredging Sedimentation
Impounding Turbitity
Withdrawal Radiation
Temperature etc.
I
I
TERRESTRIAL
I : I
Radiation
Erosion
Ground cover
etc.
BIOLOGICAL STRESSES
AQUATIC AND
TERRESTRIAL
Biological introduction
Species losses
Disease
etc.
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source. Other stresses that affect habitat quality may be classed as physical. The examples listed in
figure 4 each influence some physical property of an organism's habitat (e.g., temperature, light
penetration), or they may influence chemical properties of that habitat. For example, removal of
riparian vegetation in high-order streams may influence water temperature by increasing exposure to
sunlight. Discussion of biological stresses will follow.
The intensity of a stress is a measure of concentration (chemical), magnitude (physical), or
abundance/density (biological). The implication is that the intensity of a stress is related in some way
to its potential impacts. An example is a dose-response curve for some chemical additives. This
curve may be linear or curvilinear and may reflect certain threshold effects. Note also that the shape
of an "intensity-effect" curve may vary as a function of other stresses incurred by the system (i.e.,
multiple stresses) or by the duration, frequency, and timing of the stress.
The duration of a stress may be measured directly by change in its intensity through time. An
acute stress may be detected at some intensity for only a short period of time (e.g., a burst of ionizing
radiation) or may persist over longer periods because of fate-and-transport properties (e.g., solubility)
or source (e.g., constant supply, acid mine drainage). The frequency of occurrence of a stress is
particularly important if its effects are extreme or if its effects are cumulative. For example, release of
some chemical stresses may occur from some impoundments/lagoons whenever an extreme storm
event occurs that overflows the impoundment. The substance may cause acute effects or be
accumulated in tissues. Reoccurring exposure to ionizing radiation may cause harmful cumulative
effects. On the other hand, recurring exposure to some stresses below certain thresholds of impact
may allow a system to adapt to that agent.
The seasonality of a stress becomes important if it is a single-event or low-frequency stress.
For example, a single event/release/exposure for even an extreme stress may have minimal effects if it
occurs when the biota are dormant. The spatial scale and heterogeneity in the intensity of a stress also
must be considered in an ecological risk assessment. Airborne chemical stresses, for example, may be
chronic in nature, but their intensity may vary widely through space (and time) as a function of air-
mass dynamics and other conditions affecting deposition and exposure.
Biological stresses fall into a separate category, exemplified by species introductions, species
extinctions, or species extirpations (i.e., local extinctions). Species introductions may be deliberate, as
seen in biological control efforts using pest parasites or pathogens or in species reestablishment efforts,
but we are most familiar with species introductions that may be accidental (e.g., gypsy moth) or
simply unanticipated (e.g., successful establishment of ornamental species). Because of the nature of
biological stresses, these warrant special attention. For example, at the local scale (i.e., dealing with
stresses from a point source), point-source populations are directly involved, and it may not be useful
to quantify directly the effect of a stress. That is, for many of the stresses discussed thus far, impacts
may be extrapolated from dose-response information to population-level effects. In the case of
biological introductions, the mechanism of action is at the community level through disruption of
inter-specific interactions. Therefore, quantifying this kind of effect would best be done at the level of
the guild or functional group, where changes in competitive relationships would first be observable. In
the case of parasite or pathogen introductions, measurement of community-level phenomena is not
appropriate, since the level of action is at the individual level (i.e., the host organisms) and would have
patterns of effects similar to those deriving from toxicants and similar stresses acting on individuals.
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5.23. Characteristics of Exposure Assessment
Exposure to stresses generally occurs at the individual level; however, expression of that
exposure can be measured at the population or higher levels of organization. This characteristic
principle of exposure may hold true for direct effects only. The sensitivity to a stress may vary among
individuals of a population and among populations of a community. After direct effects occur,
remaining populations may not have the same genetic pool as before exposure. The population(s) may
then be more or less able to interact (e.g., competition, predation) in a community, thereby further
altering the potential for exposure at the community level.
For chemical stresses, the exposure of a population or community often is simplified by
assuming that all individuals in a population or community are exposed to the same concentration.
When the concentration varies spatially, another set of assumptions could be used to conduct the
exposure assessment more accurately. For example, for mobile organisms, the spatial arithmetic
average could be used to assess exposure of the population by assuming that each member of the
population is randomly moving in the averaged area. The spatial arithmetic average again could be
used to estimate risk to the population of sessile organisms by assuming that the organisms are
distributed randomly in the area. For a community of organisms, the spatial average could be used to
assess exposure by assuming that all individuals in the community are either moving randomly in the
area or are distributed randomly over the area.
Many of the same assumptions can be used when assessing physical alterations. For example,
exposure to stresses such as hydrologic changes, sedimentation, or dredging can be assessed by
assuming that all individuals in a population or community are exposed to the same amount of the
stress. When assessing physical alteration of habitat (e.g., decreased number of nesting or spawning
sites), exposure estimates can be simplified by assuming that all the individuals in a population will
randomly contact the altered habitat, or that the altered habitat is randomly distributed within Hie
spatial boundaries of the population. In both of these cases, the magnitude of altered habitat in the
population's range can be used to estimate the population's exposure.
5.2.4. Measurement
Exposure to hazardous, chemicals and other stresses can be approximated in one of two ways.
First it can be estimated by model predictions. The physical and chemical properties of the stress can
be combined with the biochemical and physiological properties of the organisms in question in such a
way as to yield predictions of the magnitude and duration of the stress. The other way to estimate
exposure is to measure it either directly or indirectly. Determination of tissue residue levels and
measuring body burdens of chemicals are examples of direct measurements. A major drawback to
tissue residue methods of estimating exposure to chemicals is that often the chemical is rapidly
metabolized and excreted. Therefore, only acute and/or perhaps high-magnitude exposures may be
noted.
Biomarkers often are used as indirect measurements of stress. In this context, biomarkers are
defined as biochemical, physiological, or histopathological manifestations of anthropogenic stress.
Among the assays that utilize biomarkers to measure exposure indirectly are:
» protein induction, such as cytochrome P450-induction to indicate exposure to petroleum
hydrocarbons or to some chlorinated organic compounds;
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immune system dysfunction resulting from exposure to polynuclear aromatic
hydrocarbons as well as some other chemical and physical stresses;
DNA alterations, such as covalent bonding of exogenous chemicals or strand breaks
indicating exposure to hazardous chemicals; and
bile metabolites, which measure the response of enzymatic activities on foreign
chemicals.
There are numerous other assays that offer Hie potential to indicate that the organism has been
exposed. A major drawback with biomarkers, however, is that our present understanding of the
linkages between biomarker response and effects is very rudimentary. It should not be assumed that a
biomarker response necessarily translates to an adverse effect. The recent research emphasis in this
field may rectify this situation.
5.2.5. Sources
Source identification and estimations of relative contributions by various sources becomes
critical when determining stress and exposure in the ecological risk assessment process. A significant
component of this is development of some understanding of the uncertainty surrounding source
identification.
Historical activity hi this field has dealt primarily with the introduction of chemicals into
aquatic environments via point sources. Conventional wisdom in this area would probably suggest that
the uncertainty about source estimation is lower for aquatic ecosystems than terrestrial ecosystems.
However, as we begin to consider a broader range of chemical introductions as well as nonchemical
stresses affecting both aquatic and terrestrial ecosystems via point and nonpoint sources, it may be that
this conventional wisdom breaks down. Atmospheric deposition of inorganic and organic compounds
onto both aquatic and terrestrial ecosystems is poorly understood or estimated at this point. Opinion
varies over our ability to measure or estimate both wet- and dry-deposition and resultant contributions
to aquatic and terrestrial ecosystems. For example, concern over deposition as an important source of
nitrogen to watersheds and associated aquatic resources such as the Chesapeake Bay has increased, but
is still poorly understood. Similarly, atmospheric deposition of toxic organic compounds to terrestrial
and aquatic ecosystems in the Arctic and upper Midwest is of apparent concern, but the uncertainty
associated with source estimations is quite large.
Physical habitat alteration and biological stresses are relatively new areas to be considered in
the ecological risk assessment process. Estimation of the sources for these stresses may require a
somewhat different perspective than traditionally taken in source estimation in the chemical stress
field; in some instances, the concept of "source" may not even be particularly useful for these classes
of stresses.
The uncertainty of source identification and estimation may be greater in aquatic ecosystems
than terrestrial. This might be especially true for physical habitat alterations such as sedimentation,
water withdrawal, or thermal alterations in aquatic ecosystems. Classification of physical stresses
along the lines of point and nonpoint sources may lead to a useful analogy for considering the source
component. Dredging and impoundment as physical habitat stresses might be considered point
sources, while sedimentation may be more appropriately considered nonpoint.
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Biological stresses, such as species introductions, disease introduction, species removal,
harvesting, or stocking practices (e.g., clear-cutting, overstocking of fish in lakes), are increasingly
important stresses in ecological risk assessment. This class of stresses will often be.assessed by their
impact on biological interactions at the community level or perhaps changes in process rates at the
ecosystem level. Ability to identify the source of these stresses will vary substantially with individual
cases. In the case of management practices for biological components (e.g., overstocking), the source
is quite apparent. The introduction of biological stresses in the form of disease causing organisms or
exotic species often will be more difficult to trace as a source term and to develop any estimate of the
uncertainty associated with this. In these instances, uncertainty about source identification and source
contribution may be quite high.
The guidelines for ecological risk assessment should include specific recommendations for
addressing the uncertainty of source identification and partitioning of various sources to final exposure.
This uncertainty may well vary by stress class as well as ecosystem type. An integral component of
developing this uncertainty also will be the evaluation of partitioning of fate-and-transport as it varies
with source and system type (e.g., partitioning of organics in the sediment and water column).
5.2.6. Unavailability
Given a specific source of known magnitude, intensity, and duration, fate-and-transport models
can predict the distribution and persistence of chemical stresses in the environment. However, just
because a stress is present in the environment at high concentrations does not necessarily mean that it
is going to affect individuals in a dose-dependent manner. The actual bioavailability of the compound
will depend on chemical properties of the compound, physical and chemical properties of the matrix it
is in, and the distribution and life-history traits of the organism.
For example, in the case of hydrophobic organic contaminants in aquatic ecosystems,
bioavailability will be determined largely by the lipid partitioning behavior of the compound (as
indicated by its octanol/water partition coefficient, or KoJ. If it is in a sediment reservoir, the type of
the particles and organic carbon content also will figure prominently in the determination of the
bioavailability of the compound. If sufficient quantities of the compound are present in the water
column, the dissolved organic matter present will affect the bioavailable fractions.
For inorganic stresses such as metals, different factors influence bioavailability. Whether or
not the metal is free or in an organic form (e.g., mercury, selenium) will dramatically alter its
bioavailability. Of free metals, it is generally thought that the free ion is more bioavailable.
Determination of the free-ion activity requires detailed knowledge of all complexing agents present or
use of ion-specific electrodes. For metals in sediments, it has been proposed that the concentration of
acid-volatile sulfides controls the bioavailability of metals.
Once the bioavailable fraction of the stress in different components of the ecosystem is
determined, it is necessary to consider properties of the organism. Will it encounter the stress in its
diet, through diurnal exposure, and/or through respiratory surfaces? Does the organism possess
behavioral, structural, or biochemical defenses to avoid bioaccumulation of the compound at the site of
toxic action? How rapidly can the organism rid itself of the compound? All these parameters should
be considered when addressing the bioavailability of chemical stresses in the environment.
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5.2.7. Models
Mathematical models are increasingly being used to estimate fate, transport, and exposure.
Yet many of the models have not been adequately field-tested or validated or are not easy to use. The
input data are often very limited or of unknown quality. Available fate models typically look at only
single source, medium, stress, and exposure pathways, and, therefore, often look at only part of the
stress/exposure characterization spectrum.
At the present state-of-the-science, there are large uncertainties associated with model
predictions of certain components associated with exposure. Among these are:
sediment-water exchanges;
other intermedia exchanges/transfers;
bioavailability and biouptake;
metabolism;
extrapolations from lab to field;
multiple routes of exposure;
receptor behavior adjustment mechanisms; and
characterizing receptors at risk.
5.2.8. Stress Research and Development Needs
The Stress Characterization work group identified a number of specific recommendations and
needs for research (not necessarily listed in priority):
transfer efficiencies and rates from abiotic to biotic components (e.g., dermal exposure
from sediment, inhalation rates);
testing and validation of biomarkers of exposure;
better pharmacokinetic models, to enable better interpretation of tissue residue data;
better understanding of life history of organisms of interest;
" GIS or similar information system to overlay spatial and temporal scaling of stresses
with spatial and temporal aspects of species and life stages at risk;
» factors affecting toxicity (e.g., pH, salinity, hardness) which are, for the most part,
factors affecting exposure (research is needed to address this major area of uncertainty
in exposure estimates);
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how to extrapolate across the levels of biological organization relative to type of stress,
source of stress, magnitude of stress, etc. (e.g., given an exposure to a population, how
are other parts of a community exposed through predation?);
better methods to measure dry deposition;
better and more validation of mathematical models (e.g., spray drift, equilibrium
partitioning, bioaccumulation);
better methods for predicting/estimating/characterizing stresses other than chemicals;
more user-friendly analytical methods;
» quality-assured data bases for model inputs;
« methods to determine concentrations of polar organic contaminants in water, sediment,
soils, and tissues;
better understanding of feeding processes that affect bioavailability;
a better understanding of biotic and abiotic features that control remobilization and
release of contaminants in soils and sediments;
. the ability to model bed failure of cohesive sediments; and
" determination of the kinetics of sorption/desorption of hydrophobic chemicals.
5.2.9. Summary
Considerable progress has been made over the past decade in developing methodologies to
determine or approximate exposure. Mathematical models that combine and relate various biotic and
abiotic factors to yield estimates of exposure have or are being developed. The accuracy of exposure
predictions appears to be increasing; however, several factors, if better understood, could greatly
decrease the associated uncertainties. Among these is our present inability to model bed failure of
cohesive sediments. Since a substantial fraction of the hydrophobic chemicals in an aquatic ecosystem
are generally sorbed to fine-grained sediments, the deposition, resuspension, and transport of sediments
are major factors controlling the exposure of aquatic organisms to chemical stresses. Of a similar
nature is our ignorance of the variables controlling bioturbation and the resulting effects on the
physical distribution and biological availability of sediment-associated chemicals. These are just two
areas where research could provide answers that would benefit exposure predictions. Others include
the relative uptake of material from food versus solution via the gills, and the kinetics and magnitude
of uptake, storage, and depuration of hazardous chemicals in most of the noncommercially or
recreationally important species that inhabit aqueous ecosystems. For physical and biological stresses,
a better understanding of the interactions among biotic and abiotic components and biotic relationships
is needed.
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Even with these and other limitations, estimates of exposure can be made. The estimates will
have an associated uncertainty that will be difficult to assess without large-scale field validation
studies. However, more or less uncertainty may be acceptable depending on (1) the magnitude of the
hazard, (2) the dose/response relationship, (3) the resource at risk, (4) the recovery time, and (5) the
availability of alternatives.
5.3. Ecosystems Classification Work Group (Richard Wiegert, Chair)
5.3.1. Scale-Independent/Qualitative Ecosystem Classification
The traditional classification of ecosystems as lake, stream, forest, and grassland or freshwater,
marine, terrestrial, etc., offers little to the person concerned with evaluating the impact of a potential
stress. Here we propose a simple key that permits casting any ecological system into one of 64
distinct cells. Our criteria may be evaluated by a simple, subjective, ordinal system of measurement
(qualitative) or by somewhat more detailed ratio measures (quantitative), hi each scheme, the
measures are dimensionless, conferring the benefit of scale independence.
We begin our classification with the observation that any ecosystem must be impacted by
stresses delivered either through a gaseous (dry, terrestrial) phase or through an aqueous (wet, aquatic)
phase.1 "Thus our first decision divides ecosystems along a continuum from a totally aquatic (pelagic)
ecosystem to a totally terrestrial (upland) ecosystem.
As a second dichotomy, we have chosen to separate ecosystems according to the importance
of the source of energy, whether totally autochthonous (e.g., pelagic, open ocean) or totally
allochthonous (rare, such as the tops of high mountains). The rationale for this choice is the degree to
which an ecosystem will be sensitive to stresses affecting primary producers.
Third, we choose to divide ecosystems according to the degree to which the initially fixed
energy is degraded to heat through a series of biophagous (consumers of living resources) versus
saprophagous (consumers of nonliving resources) pathways. This criterion separates ecosystems into
those in which consumption is important in determining productivity in the previous trophic level
(biophages) from those in which consumers only indirectly affect the production of their resources
(saprophages). Those stresses affecting consumers in the first category can show "upstream" effects,
whereas stresses affecting saprophages will not show such effects.
Our fourth criterion for ecosystem classification evaluates the importance of the ecosystem as
an exporter of potential energy (i.e., is it a source or sink, degrading or storing more energy than it
receives?). Knowledge of this characteristic is relevant to decisions about what impacts the delivery of
a stress material to the system under consideration might have on coupled ecosystems. Storage of a
material could have very different consequences than passage of the material to an adjacent ecosystem.
lln the case of stresses such as UV-B radiation, the filter is either gaseous or aqueous. Stresses
delivered in precipitation are characterized by the medium into which the rain falls. Other exceptions are
physical manipulations such as dredging and clear-cutting.
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Our fifth criterion is the relative degree of nutrient recycling versus nutrient flux (recycling
plus export). Qualitatively, we express this as the importance of nutrient recycling; as a ratio, we
compute the rate of nutrient recycling versus the sum of recycling plus replacement. Stresses that
affect the organisms responsible for any aspect of recycling (including inputs such as N-fixation) will
obviously have different effects on ecosystems widely separated on this axis.
Lastly, we separate ecosystems on the basis of the frequency and duration/intensity of
disturbance. Ecosystems subjected to frequent and prolonged or intense physical (catastrophic)
disturbances are populated with organisms that have an evolutionary history significantly different than
those that have evolved hi a background of more moderate physical environmental variation. Clearly
the former ecosystems, because they are persistent, have the capacity of more rapid recolonization and
growth. We might expect that such ecosystems, everything else being equal, would recover more
rapidly from the Impact of a given stress.
This classification is clearly a very preliminary effort at devising a functional classification
scheme for ecosystems. This scheme will aid the effort to predict the effects of stresses by providing
a basis for identifying systems that may respond similarly to a given stress. We feel that it has the
virtues of ease of application and freedom from scale effects. In its simplest qualitative form, the
classification requires no more than a general, cursory knowledge of the ecosystem for implementation.
To achieve the ratio level of measurement requires only the simplest of ecosystem measurements. The
benefits to the environmental manager are that many redundant measurements can be avoided and the
necessary measurements more clearly delineated.
The proposed classification may be used without further analysis simply by comparing each of
the six criteria with the possible effect of the stress on that criterion. For example, a stress delivered
in water can be eliminated from consideration on the basis of criterion number 1 if the ecosystem is
entirely terrestrial.
A method (or methods) of representing the values statistically to obtain some weighted
assessment of sensitivity as a whole will be more generally useful. This approach calls for much
additional consideration about the ways hi which the criterion values can be graphically or statistically
displayed. This in turn requires some evaluation of how interdependent the criterion are, whether to
weigh them, and whether they should be nonlinear. We feel that this is a classification approach of
considerable potential value, but one that will require much more work. The work group recommends
that such activity be an early focus of the ecological risk assessment guidelines development process.
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6. ISSUES IN ECOLOGICAL RISK ASSESSMENT
6.1. Background
Recently, there has been considerable interest in ecological risk assessment within and outside
EPA. The National Academy of Sciences Committee on Risk Assessment Methodologies (CRAM)
conducted a workshop to examine the feasibility of using the human health paradigm for ecological
risk assessments. EPA's Risk Assessment Forum recently conducted a series of colloquia directed at
addressing issues in ecological risk assessment (U.S. EPA, 1991), one of which was devoted to me
question of an ecological risk paradigm. A Risk Assessment Forum work group is developing a
framework for ecological risk assessment. Several participants at the Miami workshop have been
participants and reviewers in both these activities and are aware of the philosophy, approaches, and
limitations of these activities. Because all these activities were occurring essentially concurrently, a
consensus statement of the ecological risk paradigm or even a detailed description of the risk
assessment process was not available at the time of the Miami workshop. The lack of a clearly
defined ecological risk paradigm was a limitation since one of the workshop goals was to recommend
possible titles, subject matter, and contents for future ecological risk assessment guidelines.
Recognizing this, workshop organizers convened a third special work group (the Road Map
work group) to examine and describe the risk assessment process at a level of detail necessary to:
understand how the three-dimensional matrix of stress, ecosystem type, and ecological
hierarchy could be aggregated to determine the ecosystem(s) at risk;
illustrate the importance of defining the endpoints in the ecological risk assessment
process;
» illustrate the interrelationships between stress and ecology;
identify the important scientific issues that would require in-depth technical support in
future guidelines; and
use the process and issues to recommend the subject matter and contents of future
ecological risk assessment guidelines.
6.2. Characteristics of Ecological Risk Assessments
Ecological risk assessment is the process of qualitatively or quantitatively estimating the
magnitude and probability (when feasible) of biological effects from exposure to individual or multiple
stresses. The process basically evaluates two fundamental types of scientific information: the
ecological effects resulting from co-occurrence with a stress, and the spatial and temporal intensity and
duration of the stress. To assess the interaction of one or more stresses (anthropogenic and/or natural)
and ecological effects (at one or more levels of biological organization) requires a descriptive model
that meets the following criteria:
sufficient flexibility to apply to the full range of ecosystems and anthropogenic
stresses;
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" adaptable, allowing improved ecological risk assessments as data and models develop
over time and as experience is gained following an initial environmental decision;
provides for a diversity of ecological endpoints upon which decisions are based and
progress is monitored;
explicitly considers the broad range of interactions between stress characterization and
ecological effects analyses, from defining the nature and scales of the problem initially,
to modifying the endpoints selected for evaluation, to affecting the stress-response and
recovery relationships; and
produces a synthesis output, derived from a suite of quantitative and qualitative
methodologies, that reflects probabilistically the range of stress-response relationships
for each endpoint and that can be used by the decision-maker along with analyses of
societal factors.
At the Miami workshop, it was decided that meeting these criteria in light of the ecological
realities discussed above would require the development of a "road map" that relied heavily upon
scientific judgment and expertise. Ideally, ecological risk assessment guidelines developed by EPA
should provide:
the necessary "guidance" and "landmarks" for selecting the appropriate course through
the three-dimensional ecological risk landscape ("The Cube"), which defines what is at
risk and how it will be assessed; and
the "appropriate technical support" in the form of a reference library for conducting
site- and stress-specific ecological risk assessments.
This approach is consistent with that taken in human health risk assessments where guidance
is preferable to a "cookbook" or protocol that attempts to anticipate and describe the specific steps to
be taken for every situation. The resultant descriptive model of the ecological risk assessment process
and the associated Guidelines Bookshelf are discussed below.
6.3. Road Map Work Group (Mark Harwell and Jack Gentile, Co-Chairs)
Beginning with the three-dimensional landscape or "Cube" as the framework within ecological
risks occur and are assessed, the Miami workshop's Road Map work group identified and described
the scientific issues associated with the process for conducting ecological risk assessments (figure 5).
This process and associated issues are designed to integrate, through a sequence of logical steps, the
two fundamental types of information in the ecological risk assessment process: ecological effects
characterization and stress regime (exposure) characterization. The process is divided into two phases:
"problem formulation" and "analysis." The problem formulation phase describes the entry point into
the ecological risk landscape, identification of the ecosystems at risk, and the appropriate ecological
endpoints by which to assess the risks. In the analysis phase, stress-effects relationships are
40
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Figure 5. Scientific Issues in Ecological Risk Assessment
STRESS CHARACTERIZATION
ECO-EFFECTS CHARACTERIZATION
ENTERING
THE ECO-RISK
LANDSCAPE
IDENTIFYING THE
ECOLOGICAL .
SYSTEMS AT RISK
SELECTING THE
ECO-RESPONSES
AND INDICATORS
ANALYZING
THE RISKS
ESTMATING
RECOVERY
STRESS IDENTIFICATION
Stress type
- Stress properties
- Stress mode of action
- Stress amount
ECOLOGICAL EFFECTS
- Magnitude and extent of damage
- Relate ecosystem responses to
stress functions
ECOSYSTEM(S) AT RISK
- Define temporal, spatial, and
biological scales of effect
- Determine ecosystem structure
and functions co-ccurring with stress
STRESS CLASSIFICATION
- Stress classified by mode of
action and nature of ecological
effects
- Stress classified by space, time,
transport media
T
I
STRESS REGIME
Spatial and temporal patterns
Media transport
- Transformations
Bioavailability
Multiple stress interactions
ECOLOGICAL ENDPOINTS
- Selection criteria and "rules'
- Ecosystems affected
- Biologically scaled to time & space
- Structure and function
- Stress or damage appropriate
- Ecological significance
ECOLOGICAL INDICATORS
- Selection and interpretation criteria
- Integrated with eco-endpotnts
- Knowledge of natural variability
- Measures of statistical power
- Significance of observed changes
ECOLOGICAL RESPONSE
Experimental stress response data
Stress-response models
Probabilistic analyses
Uncertainty
ECOLOGICAL RECOVERY
Extent of damage
- Ecosystem redundancy
- Size and proximity of refugia
- Routes of emigration
WEIGHING
THE RISKS
ENVIRONMENTAL DECISION MAKING
ecotagkaiand aooetaJ factors '
P
f
o
b
f
e
m
r
m
a
t
&
1
i
9
t*
A
ft
y
$
i
s
D
&
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t
s
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tt
41
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determined and compared to actual stress scenarios co-occurring in the environment to estimate the
potential ecological risks. The ecological significance of the effects and the potential for recovery also
were discussed.2 The third phase of the process is environmental decision-making. This phase is
actually outside the scope of the actual risk assessment, but is identified and highlighted as being of
critical importance to the interpretation and use of the risk assessment results.
6.3.1. Problem Formulation
A fundamental difference between human health and ecological risk assessments is the
question of defining "what is at risk?" EPA's extensive experience with specific risk issues in human
health has provided a sound basis for defining the scope and subject matter for human health risk
assessment guidelines. The selection endpoints for human health risk assessments (e.g., cancer and
developmental toxicology) resulted from the recognized public health and regulatory importance and
extensive discussions over a period of several years. In contrast, discussions regarding the selection of
ecological endpoints for ecological risk assessment have begun only recently and are confounded by
the lack of specific legislative and regulatory guidance. The importance of defining the "subject" of
ecological risk assessments was emphasized at the recent CRAM workshop and has been a consistent
theme in several EPA-sponsored workshops.
The Miami workshop identified the need for an atlas or "road map" to direct the risk assessor
through the three-dimensional matrix of organizing variables ("The Cube") in order to determine "what
ecosystem(s) is at risk" and "how the risks will be measured." The atlas concept was chosen because
it is a readily understood metaphor that accurately describes the process of walking through the three-
dimensional matrix. The primary function of the atlas is to define the ecosystems at risk, make an
initial determination of the ecologically important characteristics and patterns of the stress, and
determine the most appropriate ecological endpoints for assessing the risks to the ecosystem. The atlas
provides the rationale and road map for integrating information on the three organizing principles
comprising the "Cube," which provides the foundation for the detailed risk analysis.
The purpose of the initial steps in the problem-formulation stage is to provide guidance to the
risk assessor on defining the spatial, temporal, and biological scope of the risk assessment. The initial
point-of-entry into the process is problem-determined, either dealing with a stress-specific problem
(e.g., decision to allow production of a new chemical or projecting the effects from global climate
change on ecosystems) or dealing with an observed ecological effect (e.g., visible damage to trees in a
forest, or large-scale die-off of seagrass). The former will require primarily prospective analyses
(inductive); the latter will require primarily retrospective (deductive) analyses.
The second step in problem formulation is identifying the range of ecosystems that are at risk
from the stress. If the problem is stress-driven, sufficient information about the stress will be needed
at this stage to help define the ecosystems at risk. This information includes knowledge of the nature
and properties of the stress, the spatial and temporal scale of the stress, and the intensity of the stress.
If the problem is ecological effects-driven, then observed damage will be used to determine the
2Although not treated explicitly by the Road Map work group, elements of "risk characterization,"
which is the integration of stress and ecosystem-response information and its ecological significance, are
implicit in both the analysis and decision-making phases.
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ecosystems at risk directly and, by extrapolation, the ecosystems for which no observed damage occurs
at present but which also may be at risk.
In addition to determining the different types of ecosystems mat are at risk, this second step of
problem formulation defines the spatial extent of the ecosystem(s) co-occurring with the stress; focuses
attention on the components of each at-risk ecosystem that may be directly or indirectly affected by
the stress; and determines the organizational scales that must be addressed (e.g., if consideration of
population-level effects will suffice or if ecosystem-level processes also must be evaluated). An
explicit part of this determination is to consider both structural and functional aspects of each at-risk
ecosystem in the context of potential direct or indirect effects from the stress.
The third step of the problem formulation provides criteria and guidance to the risk assessor
on selecting which ecological endpoints are most appropriate for evaluating the effects to the at-risk
ecosystems, where "ecological endpoint" is defined to be the specific ecological properties of concern.
This process is necessary because the potential number and variety of ecosystem properties that could
be affected by a human activity are virtually unlimited. Thus, for each ecosystem type at risk, the risk
assessor must consider the specific properties of the ecosystem that, if sufficiently altered, would
constitute a change in the ecosystem mat is of ecological or societal importance.
Ecological endpoints may be structural (e.g., community diversity) or functional (e.g., rates of
primary production). The endpoint should be relevant, having either ecological importance (e.g.,
keystone species, ecologically important processes) or societal (e.g., economically important,
endangered, or aesthetic species) importance. This relevance may be either direct (e.g., viability of a
marine mammal species) or indirect (e.g., the food base for that species). Selection of the ecological
endpoint in part is a function of the nature of the stress; i.e., some properties of the ecosystem may be
known to be vulnerable to one stress but not to another. Other criteria for selecting endpoints will be
developed in the ecological risk assessment guidelines, such as: natural variability of the endpoint;
comparability with other ecological risk assessments (e.g., using some endpoints in common with
different systems or different stresses); requirements-,of particular legislation or regulations; and
availability of data, models, and knowledge about the specific endpoint that can be used for
assessment. In any event, once the stress is known and the at-risk ecosystems are determined, there
must be a concerted effort to identify all aspects of those ecosystems that would be appropriate
properties upon which to evaluate the health of the ecosystem in the context of the stresses at hand.
Ideally, a suite of ecological endpoints .will be selected to ensure the full range of values about the
ecosystem are evaluated.
The fourth and final step in the problem formulation stage is selection of "ecological
indicators" defined to be the specific properties of ecosystems that are measured or monitored to
reflect on the state or the change of state of the ecological endpoints. Each selected endpoint should
have one or more associated indicators. These indicators may be the endpoint itself (e.g., numbers of
individuals in an endangered species population) or may relate to the endpoint directly (e.g., number of
eggs produced per nesting pair of birds) or indirectly (e.g., area of wetlands in a region available for
nesting habitat). Criteria proposed for selecting ecological indicators include:
- signal-to-noise ratio;
frequency of false-positive and false-negative indications of an ecological effect;
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« rapidity of indicator response (e.g., for early-warning indicator) versus degree of stress-
specificity (e.g., diagnostic indication of a particular stress);
statistical power (i.e., how much data would be required to demonstrate an effect);
ease or economy of measurement;
availability of historical data -bases; and
comparability across ecological systems or environmental problems.
As was the case with ecological endpoints, the selection of indicators also is stress-dependent.
The stress-classification process conducted to help identify the at-risk ecosystems and their ecological
endpoints will directly influence the selection of the suite of indicators.
6.3.2. Response-Recovery Analysis
The response-recovery analysis stage integrates both the stress-characterization components
and the ecological-effects characterization components to provide a qualitative or quantitative
characterization of the ecological risks. At this stage, the full set of stress characterization issues must
be addressed, including such issues as:
the nature of the stress (i.e., physical, chemical, or biological or xenobiotic versus
alterations in naturally occurring stresses);
the stress' spatial and temporal scales, including factors such as the spatial distribution
of stress-intensity levels, and the frequency and duration of the stress;
transformations of the stress in the environment (e.g., chemical modifications from
physicochemical or biological processes);
bioavailability of the stress (e.g., biouptake of chemicals, differential exposure of
different parts of an organism);
interactions with the physical environment (e.g., co-occurrence with periods of high
temperature and atmospheric inversions); and
interactions with other stresses (e.g., synergism between acid precipitation and ozone
exposure).
The analysis stage also includes detailed ecological stress-response assessments. This may
involve extrapolations among endpoints (e.g., extrapolations from laboratory data to the field) or
extrapolations across biological scales (e.g., from organisms to population, community, or higher levels
of organization). Such assessments may utilize:
» mathematical models of direct or indirect effects on ecological components;
the evaluation of analogs, such as paleoecological analogs of climate change;
44
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the experiences gained from different ecosystems of similar type for similar stresses;
structural activity relationships of chemicals;
new experiments to be conducted in the laboratory on physiological processes;
microcosms, mesocosms, or whole-ecosystem manipulations.
The interpretation of available data will fundamentally rely on expert judgment; initially expert
judgment may be the only methodology available. Assessments may be quantitative and probabilistic,
if adequate models and data are available. Whatever methodologies are available for quantitatively or
qualitatively evaluating the ecological endpoint responses for each at-risk ecosystem for the specific
stress regime(s) will be synthesized to assess the overall ecological effects from the stress. While the
goal is to have a predictive capability for stress-response relationships with low uncertainty, the
process allows for ecological risk assessments to proceed and to provide substantive guidance to the
decision-maker even in the presence of significant uncertainties. The uncertainties that exist in all
stages of the assessment must be made explicit and carried along (propagated) in the final analyses.
The scientific issues and process, as described in figure 5, explicitly consider the importance
of characterizing the stress regime as opposed to merely preparing a hazard assessment from
hypothetical levels of the stress. The final output from these stress-response analyses is a graphical
representation of how the ecological endpoints would respond to ranges of the stress. Since the
purpose of the stress-response analysis is to prepare a probabilistic evaluation of a range of stress-
response relationships, evaluations will be required for different intensities, durations, and frequencies
of the stress.
The methods used in the stress-response analyses are intended to be adaptive; that is, as new
methodologies are developed with improved predictive capabilities, they can be substituted into the
risk assessment process. Further, once a decision is made, monitoring of selected ecological indicators
can be instituted to determine the degree of coherence between the observed responses and those
predicted from the risk assessment. Review of this information may suggest the need to revise the
initial management decisions.
The ecological recovery characterization provides information on whether a stress-induced
effect on an ecosystem is reversible or is irreversible, which may be particularly important to both the
scientist and the decision-maker. Ecological recovery can be characterized in terms of:
the rate at which ecological endpoints recover once a stress is removed; \
how much recovery might ensue from reductions in the level or frequency of the stress;
and
the degree of recovery feasible or required for particular uses.
The recovery of ecological systems is related to:
the characteristics of the ecosystem;
45
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the nature of the stress;
previous ecosystem experience with the particular type of stress;
the intensity of the initial effect and its spatial extent;
the potential sources of propagules for replacing species;
how much the effects cut across functionally redundant components of the ecosystem;
intrinsic time-lags in the ecosystem; and
many other factors.
The methodologies applied to the recovery analyses range from sole reliance on expert
judgment to use of analogs, simple mathematical models, and detailed process-oriented simulation
models. The approach used to characterize ecological recovery, like stress-response analysis, is to be
adaptive and flexible, require the tracking of uncertainties, and, when possible, will produce
probabilistic outputs for the decision-maker. Finally, the output from the risk assessment becomes
input to the environmental decision-making process, which also incorporates factors such as
environmental policy, regulatory statutes, economics, and societal issues.
6.33. Environmental Decision-Making
The workshop participants recommended that guidance be developed for environmental
mangers on the use of ecological risk assessment information. Although the topic is outside the
purview of ecological risk assessment, environmental decision-making does interface with the risk
assessment process. Information applicable to environmental decision-making could be used to
develop guidance on interpreting information produced by the ecological risk assessment process; on
establishing levels of ecological significance (versus statistical significance) for changes in each type
of ecological endpoint; and on merging information on non-ecological issues, such as economic or
other societal considerations. This section also could include guidance to the risk assessor on
communicating the results of the risk assessment process.3 Thus, there appeared to be a need for
management guidelines for risk-based decision-making analogous to the guidelines being developed for
ecological risk assessment.
6.3.4. Relationship to the Ecological Risk Framework
The description of the ecological risk assessment process that emerged from the Road Map
work group was presented and discussed at the peer review of EPA's "Framework for Ecological Risk
Assessment" (May 14-16, 1991) (U.S. EPA, in press-b). It is clear that the framework for ecological
risk assessment recommended by the peer-review panel (figure 6) is philosophically and conceptually
similar to the process discussed above and illustrated in figure 5. In addition it was recognized that
concept and issues that constitute risk characterization, though not explicitly identified in figure
5, are covered in part in the analysis and environmental decision-making steps.
46
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Figure 6. Proposed Framework for Ecological Risk Assessment
Problem Definition and Scoping
,v
t ffff'&ff^fff. "
§
CharacterKatfon
of
Stress
ftfleds :*
Characterization
Decision-Making/
Risk Management
Verification
and
Monitoring
47
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additional detail would be needed for each of the framework components in order to provide
meaningful guidance. The scientific issues identified at the Miami workshop contributed substantively
to the development of the ecological risk framework and are embodied within the peer-review panel's
recommendations to EPA. One apparent difference between the ecological risk framework and the
ecological risk process described in this workshop report relates to the treatment of risk
characterization. Although these two workshops had different objectives, the philosophy, concepts,
and principles developed at both workshops are consistent, and only minor differences in terminology
remain to be resolved. The development of ecological risk guidelines is an evolving process, one that
will continually seek to incorporate new ideas and reflect the ever-changing state-of-the-science.
While this may result in modifications of terminology and specific details, the fundamental philosophy
and concepts are expected to remain unchanged.
6.4. Proposed Future Ecological Risk Assessment Guidelines
6.4.1. Background
The Guidelines Bookshelf is a proposed set of guidance volumes to be produced by EPA in its
ecological risk assessment guidelines development process.4 The guidance volumes in the series
should not consist of "cookbooks," i.e., case-specific guidelines written for particular types of
environmental problems or for particular types of ecological systems. Rather, the volumes should
constitute a reference library that the risk assessor can use in conducting a particular ecological risk
assessment. The recommendations from the Road Map work group are that the subject matter of the
guidelines Bookshelf reflect the scientific issues and the process for ecological risk assessment
described hi figure 5. Focusing the contents of the proposed guidelines on the risk assessment process
will produce generic, broadly applicable guidance that can be easily adapted and tailored to specific
ecosystem problems. Based upon this rationale, the Guidelines Bookshelf recommended by the Road
Map work group includes:
I. Ecological Risk Assessment Guidelines
II. Ecological Endpoints
in. Ecological Indicators
IV. Stress Regime Characterization
V. Ecological Response Characterization
VI. Ecological Recovery
VII. Environmental Decision-Making
VIII. Compendium of Case-Specific Examples
*The first volume on the bookshelf will be the "Framework for Ecological Risk Assessment" which
describes the ecological risk assessment principles and concepts. It was not included in this listing
because it does not provide the level of detail necessary for guidance.
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6.4.2. Ecological Risk Assessment Guidelines
The Ecological Risk Assessment Guidelines volume, which will evolve from an expansion of
EPA's "Framework for Ecological Risk Assessment", will be the primary guidance volume on the
bookshelf and will describe in detail the full spectrum of scientific issues associated with the
ecological risk assessment process. This volume will describe the principles and criteria for each
phase, explain the process for conducting ecological risk assessments, and, through selected
hypothetical analogs, demonstrate the specific steps and processes that would be pursued for assessing
the risks to specific ecosystems from particular stresses. The problem formulation phase of the
Ecological Risk Assessment Guidelines will function as an "atlas" in the sense that it will describe and
integrate the full landscape of organizing principles in which ecological risks occur and consequently
risk assessments should be conducted. A primary function of the problem formulation phase will be to
define the ecosystems at risk, make an initial determination on the ecologically important
characteristics of the stress, determine the most appropriate ecological endpoints for assessing the risks
to the ecosystem, and provide the foundation for the detailed risk analysis phase.
The Ecological Risk Assessment Guidelines will be generic and will focus on scientific issues
and the ecological risk process, rather than on details of specific applications. However, the Miami
and other workshops have stressed the importance of having case studies or hypothetical analogs to
illustrate how the guidelines are to be applied and how they will function. It is recommended,
therefore, that this initial volume have a sufficient number of examples to illustrate the scope and
variety of applications.
However, providing sufficient level of detail on all the important scientific issues for a subject
as complex as ecological risk may not be feasible in a single volume. The following volumes will
provide the level of detail necessary for ecological risk guidance and should be developed in parallel
with the generic guidance described above.
6.4.3. Ecological Endpoints
The Ecological Endpoints volume will detail the principles and issues associated with
ecological endpoints, including the specific criteria that should be applied to selecting the suite of
ecological endpoints germane to a particular environmental problem and for a particular ecological
system type. The endpoints volume will identify criteria for selecting endpoints that might be used,
given the diversity of ecosystems and stresses of concern to EPA, and the bases for selecting the
particular subset of endpoints appropriate to the problem at hand.
6.4.4. Ecological Indicators
Similarly, the Ecological Indicators volume will detail the principles, issues, and criteria for
selecting the specific indicators to be measured for each ecological endpoint used in the ecological risk
assessment. Perhaps these latter two volumes, (endpoints and indicators) could be combined into a
single volume. Also, within these two volumes will be a discussion of how to evaluate the ecological
significance of changes in endpoints (and indicators) as the initial examination of statistical power,
uncertainties, and natural variability issues.
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6.4.5. Stress Regime Characterization
The Stress Regime Characterization guidance will discuss the complete set of issues associated
with understanding the characteristics of the stress in its entirety (i.e., the nature of the stress, its
spatial extent, intensity, duration, frequency, interactions). In a sense, this volume is analogous to an
exposure assessment volume, but will be much broader in that nonchemical stresses will be equally
important and will require different kinds of attention from the stress characterization (exposure) issues
for chemicals in the environment
6.4.6. Ecological Response Characterization
The Ecological Response Characterization volume will describe the various methodologies for
evaluating stress-ecological response relationships, including: expert judgment; various methods for
qualitative evaluations; extrapolations from laboratory, microcosm, or field data; and various types of
quantitative, predictive models of components of ecosystems. The applicability, availability, and
uncertainties for each approach, as well as guidance on when to use a particular method, will be
detailed. This volume will be a key methodology document that will be updated routinely as new
methods become available.
6.4.7. Ecological Recovery
The Ecological Recovery volume will likewise detail the principles, issues, and methods for
addressing issues of ecological recovery upon elimination or mitigation of stress. Again,
methodologies for evaluating recovery (expert judgment through predictive models) will be discussed,
as will all germane issues of uncertainty. This volume also will be updated periodically as
methodologies and understanding of recovery issues improve.
6.4.8. Environmental Decision-Making
Originally, the environmental decision-making volume was conceived as a separate volume
that was not a part of the ecological risk assessment process per se. Instead, this volume would
provide specific guidance to the decision-maker on how to interpret the information produced by the
ecological risk assessment process and how to merge this information with information on economics
or societal values. However, a need still remains for guidance on environmental decision-making that
is specifically tailored to and developed by risk managers on how to effectively incorporate the results
of risk assessments into a risk-based decision-making framework.
6.4.9. Case-Specific Compendium
Finally, a compendium of actual case-specific studies that have been conducted using the
Ecological Risk Assessment Guidelines should be included as part of the bookshelf. This volume will
be a "living document," frequently revised and updated with new examples of actual ecological risk
assessments. Eventually, this volume will contain a sufficient number of examples so that the full
range of types of ecological risk assessments that might be encountered by a risk assessor will be
represented by at least one case example in this compendium. While not supplanting the overall
generic approach, the case-specific compendium will illustrate, in detail, the application of the
Ecological Risk Assessment Guidelines to specific ecosystems, regulatory statutes, and problem-
oriented studies.
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7. REFERENCES
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R.V.; Rosen, A.E. (1986). User's Manual for Ecological Risk Assessment. Publication No.
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Harwell, M. A.; Harwell, C.C.; Weinstein, D.A.; Kelly, J.R. (1990). Characterizing ecosystem
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Auerbach, S.I.; Bartuska, A.M.; Harwell, M.A., eds. Ecological Risks: Perspectives from
Poland and the United States. National Academy of Sciences Press, pp 91-115.
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Harwell, M.A.; Kelly, J.R.; Kimball, K., eds. Ecotoxicology: Problems and Approaches.
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G.J., eds. Recovery of Lotic Communities and Ecosystems Following Disturbance: Theory and
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NRC. See National Research Council.
National Research Council. (1983). Risk Assessment in the Federal Government: Managing
the Process. National Research Council, National Academy Press, Washington, DC.
U.S. EPA. See U.S. Environmental Protection Agency.
U.S. Environmental Protection Agency. (1986). The Risk Assessment Guidelines of 1986.
EPA/600/8-87/045, Washington, DC.
U.S. Environmental Protection Agency. (1988). Review of Ecological Risk Assessment
Methods. EPA/230/10-88/041, Washington, DC.
U.S. Environmental Protection Agency. (1990). The Report of the Ecology and Welfare
Subcommittee, Relative Risk Reduction Project. In: Reducing Risks: Setting Priorities and
...-. Strategies for Environmental Protection. EPA SAB-EC-90-021A, Science Advisory Board,
Washington, DC.
U.S. Environmental Protection Agency. (1991). Summary Report on Issues in Ecological Risk
Assessment EPA/625/3-91/018, Risk Assessment Forum, Washington, DC.
U.S. Environmental Protection Agency, (in press-a). Peer Review Workshop Report on a Framework
for Ecological Risk Assessment. EPA/625/3-91/022, Risk Assessment Forum, Washington,
DC.
U.S. Environmental Protection Agency, (in press-b). Framework for Ecological Risk Assessment.
EPA/630/R-92/001. Risk Assessment Forum, Washington, DC.
51
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APPENDIX A
AGENDA
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AGENDA
U.S. Environmental Protection Agency
ECOLOGICAL RISK ASSESSMENT GUIDELINES
STRATEGIC PLANNING WORKSHOP
TUESDAY. APRIL 30. 1991
8:30 a.m. - 12:15 p.m. Opening Plenary Session: Issues and Objectives
8:30 a.m.
8:50 a.mj
9:15 a.m.
10:00 a.m.
Welcome and Workshop Objectives
Dorothy Patton
Ecorisk Framework
William van der Schalie
Scientific Principles for Ecorisk
John Gentile
BREAK
10:15 a.m. -12:15 p.m.
Ecological Hierarchy Presentation
10:15 a.m. Organisms/Population
Steven Bartell
ll:00a.m. Communities
Ann Bartuska
ll:30a.m. Ecosystems
David Weinstein
12:00 p.m. Wrap-up/Charge to Ecological Hierarchy Work Groups
Mark Harwell
12:15 p.m. LUNCH
1:30 p.m. - 5:00 p.m. Ecological Hierarchy Work Groups
1:30 p.m.
Work Group Sessions
Steven Bartell, Ann Bartuska, and David Weinstein
A-l
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TUESDAY, APRIL 30,1991 (cont.)
3:10 p.m. BREAK
3:30 p.m. Work Group Sessions (cont.)
5:00 p.m. ADJOURN
5:00 p.m. RSMAS Reception - Smith Commons
WEDNESDAY. MAY 1,1991
8:30 a.m. -10:00 a.m. Plenary: Reports and Discussion
8:30 a.m. Welcome to RSMAS
Otis Brown, Associate Dean for Research
8:40 a.m. Organisms/Population
Steven Bartell
9:00 a.m. Communities
Ann Bartuska
9:30 a.m. Ecosystems
David Weinstein
10:00 a.m. Wrap-up/Charge to Ecosystem Work Groups
Mark Harwell
10:10 a.m. BREAK
10:30 a.m. - 5:00 p.m. Scientific Feasibility Work Groups
10:30 a.m. Work Group Sessions by Ecosystems Type
Robert Hugget and William Smith
12:15 p.m. LUNCH
1:30 p.m. Work Group Sessions (cont.)
Evaluate Scientific Feasibility
3:30 pjn. BREAK
A-2
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WEDNESDAY, MAY 1, 1991 (cont)
4:00 p.m.
4:30 p.m.
Work Group Sessions (cont.)
Prioritize Guidelines and Prepare Recommendations
ADJOURN
THURSDAY, MAY 2.1991
8:00 a.m. - 9:45 a.m. Scientific Feasibility Work Groups
8:00 a.m.
Work Group Sessions (cont.)
Prioritize Guidelines and Prepare Recommendations
9:45 a.m. BREAK
10:00 a.m. -12:00 p.m. Closing Plenary: Candidate Guidelines
10:00 a.m. Aquatic Guidance
Robert Huggett
10:15 a.m. Wrap-up
10:30 a.m. Terrestrial Guidance
William Smith
10:45 a.m. Wrap-up
11:00 a.m. Workshop Recommendations
Mark Harwell
12:00rp.m. ADJOURN
A-3
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APPENDIX B
LIST OF PARTICIPANTS
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LIST OF PARTICIPANTS
U.S. Environmental Protection Agency
ECOLOGICAL RISK ASSESSMENT GUIDELINES
STRATEGIC PLANNING WORKSHOP
Lawrence Barnthouse
Oak Ridge National Laboratory
Oak Ridge, TN
Steven Bartell
Oak Ridge National Laboratory
Oak Ridge, TN
Ann Bartuska
U.S. Department of Agriculture
Forest Service
Ashville, NC
Steven Bradbury
U.S. Environmental Protection Agency
Environmental Research Laboratory - Duluth
Duluth, MN
Hal Caswell
Woods Hole Oceanographic Institute
Woods Hole, MA
David Charters
U.S. Environmental Protection Agency
Emergency Response Team
Edison, NJ
William Cooper
Michigan State University
East Lansing, MI
Michael Coughenour
Colorado State University
Fort Collins, CO
Wendell Cropper
University of Florida
Gainesville, FL
Thomas Duke
Technical Resources Institute
Gulf Breeze, FL
Anne Fairbrother
U.S. Environmental Protection Agency
Corvallis, OR
Jeffrey Frithsen
Versar, Inc.
Columbia, MD
Jack Gentile
U.S. Environmental Protection Agency
Environmental Research Laboratory
Narragansett, RI
Herbert Grover
Environmental Scientist
Sandia Park, NM
Thomas Hallam
University of Tennessee
Department of Mathematics
Knoxville, TN
Mark Harwell
University of Miami
Rosenstiel School of Marine &
Atmospheric Science
Miami, FL
Robert Huggett
Virginia Institute of Marine Sciences
School of Marine Sciences
College of William and Mary
Gloucester Point, VA
B-l
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Erich Hyatt
U.S. Environmental Protection Agency
EMAP Integration & Assessment
Research Triangle Park, NC
John Kelly
Battelle Ocean Science
Duxbury, MA
James Kremer
University of Southern California
Department of Biological Sciences
Los Angeles, CA
David Mauriello
U.S. Environmental Protection Agency
Office of Toxic Substances
Washington, DC
Foster Mayer
U.S. Environmental Protection Agency
Environmental Research Laboratory
Gulf Breeze, PL
Anne McElroy
University of Massachusetts
Environmental Science Program
Boston, MA
Steven Paulsen
University of Nevada
Northrop Facility
c/o U.S. Environmental Protection Agency
Corvallis, OR
Eric Preston
U.S. Environmental Protection Agency
Corvallis, OR
John Schalles
Creighton University
Department of Biology
Omaha, NE
Michael Slimak
U.S. Environmental Protection Agency
Office of Environmental Processes &
Effects Research
Washington, DC
William Smith
Yale University
School of Forestry &
Environmental Studies
New Haven, CT
Samuel Snedaker
University of Miami
Rosenstiel School of Marine &
Atmospheric Science
Miami, FL
Kent Thornton
FTN Associates, Ltd.
Little Rock, AR
Thomas Waddell
U.S. Environmental Protection Agency
Athens, GA
Richard Weigert
University of Georgia
Department of Zoology
Athens, GA
David Weinstein
Boyce Thompson Institute
Ithaca, NY
B-2
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APPENDIX C
LIST OF OBSERVERS
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U.S. Environmental Protection Agency
ECOLOGICAL RISK ASSESSMENT GUIDELINES:
STRATEGIC PLANNING REPORT WORKSHOP
University of Miami
Miami, FL
April 30-May 2,1991
LIST OF OBSERVERS
Janet Bums
Biologist
U.S. Environmental Protection Agency
Washington, DC
William Easton
Miami, FL
John Festa
American Paper Institute
Washington, DC
Chris Harwell
University of Miami
Rosenstiel School of Marine &
Atmospheric Science
Miami, FL
Normal Kowal
U.S. Environmental Protection Agency
ECAO
Cincinnati, OH
Ronald Landy
U.S. Environmental Protection Agency
Office of Research and Development
Washington, DC
Steve Light
Policy Director
South Florida Water Management District
West Palm Beach, FL
Charles Menzie
Menzie Cura & Associates, Inc.
Chelmsford, MA
Dorothy Patton
U.S. Environmental Protection Agency
Risk Assessment Forum
Washington, DC
J. Brad Peebles
Principal Specialist
Florida Power & Light
West Palm Beach, FL
Susan Norton
U.S. Environmental Protection Agency
Office of Health & Environmental
Assessment
Washington, DC
Denice Shaw
U.S. Environmental Protection Agency
Environmental Scientist
Las Vegas, NV
William van der Schalie
U.S. Environmental Protection Agency
Risk Assessment Forum
Washington, DC
William Wood
U.S. Environmental Protection Agency
Risk Assessment Forum
Washington, DC
C-l
U.S. GOVERNMENT PRINTING OFFICE: 1992-648-003/60075
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