-------

-------
                                                   EPA/630/R-92/001
                                                   February 1992
FRAMEWORK FOR ECOLOGICAL RISK ASSESSMENT
                       Risk Assessment Forum
                  U.S. Environmental Protection Agency
                       Washington, DC 20460
                                                Printed on Recycled Paper

-------
                                     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.
                                            11

-------
                                        CONTENTS


Acknowledgements	vi

Foreward	vii

Preface	  ix

Contributors and Reviewers	x

Executive Summary	  xiv


1. INTRODUCTION .			  1

       1.1.    Purpose and Scope of the Framework Report	  1
       1.2.    Intended Audience	  2
       1.3.    Definition and Applications of Ecological Risk Assessment	  2
       1.4.    Ecological Risk Assessment Framework  	  2
       1.5.    The Importance of Professional Judgment	  6
       1.6.    Organization	  6

2. PROBLEM FORMULATION	  9

       2.1.    Discussion Between the Risk Assessor and Risk Manager (Planning) 	  9
       2.2.    Stressor Characteristics, Ecosystem Potentially at Risk, and Ecological Effects ....  9

              2.2.1.  Stressor Characteristics	  11
              2.2.2.  Ecosystem Potentially at Risk	  11
              2.2.3.  Ecological Effects  	  12

       2.3.    Endpoint Selection  	  12
       2.4.    The Conceptual Model	  15

3. ANALYSIS PHASE   	  17

       3.1.    Characterization of Exposure  	  17

              3.1.1.  Stressor Characterization:  Distribution or Pattern of Change  	  17
              3.1.2.  Ecosystem Characterization	  19
              3.1.3.  Exposure Analyses	  20
              3.1.4.  Exposure Profile  	  21
                                             iii

-------
       3.2.    Characterization of Ecological Effects	  21

              3.2.1.  Evaluation of Relevant Effects Data	  21
              3.2.2.  Ecological Response Analyses	  22
              3.2.3.  Stressor-Response Profile 	  26

4. RISK CHARACTERIZATION  	   28

       4.1.    Risk Estimation  	  28

              4.1.1.  Integration of Stressor-Response and Exposure Profiles  	  28
              4.1.2.  Uncertainty			  30

       4.2.    Risk Description	  31

              4.2.1.  Ecological Risk Summary	  32
              4.2.2.  Interpretation of Ecological Significance	,	.  33

       4.3.    Discussion Between the Risk Assessor and
              Risk Manager (Results)	....	  34

5. KEY TERMS	 ..	  37

6. REFERENCES			  39
                                            iv

-------
                                       LIST OF BOXES





 Physical and Chemical Stressors as a Focus of the Framework		                        1




 Relationship of the Framework to a Paradigm for Human Health Risk Assessment	   3



 Use of the Term "Exposure"	                            5




 Characterization of Ecological Effects Used Instead of Hazard Assessment  	   6



 Additional Issues Related to the Framework   	               8



 Example Stressor Characteristicsr	                U



 Endpoint Terminology	                        12




 Considerations in Selecting Assessment Endpoints	            13



 Considerations in Selecting Measurement Endpoints 	             14



 Additional Issues in Problem Formulation	                     lg




 Extrapolations and Other Analyses Relating Measurement and Assessment Endpoints	   23



 Hill's Criteria for Evaluating Causal Associations (Hill, 1965) 	   25



 Additional Issues Related to the Analysis Phase	                  27



 Additional Issues Related to the Risk Characterization Phase  	     36






                                     LIST OF FIGURES






Figure 1.       Framework for Ecological Risk Assessment	   4



Figure 2.       Problem Formulation	_                    10



Figure 3.       Analysis	                  18




Figure 4.       Risk Characterization	            29

-------
                                  ACKNOWLEGEMENTS

       This U.S. Environmental Protection Agency (EPA) report has been developed under the
auspices of EPA's Risk Assessment Forum, a standing committee of EPA scientists charged with
developing risk assessment guidance for Agency-wide use.  An interoffice work group chaired by
Susan Norton (Office of Health and Environmental Assessment), Donald Rodier (Office of Toxic
Substances), and Suzanne Marcy (Office of Water) led this effort.  Other members of the work group
are Michael Brody, David Mauriello, Anne Sergeant, and Molly Whitworth.  William van der Schalie
and William Wood of the Risk Assessment Forum staff coordinated the project, which included peer
review by scientists from EPA, other Federal agencies, and the private sector.
                                              VI

-------
                                        FOREWARD

       Publication of this report, "Framework for Ecological Risk Assessment" (Framework Report),
is a first step in a long-term program to develop risk assessment guidelines for ecological effects.
EPA has been developing risk assessment guidelines primarily for human health effects for several
years.  In  1986, EPA issued five such guidelines, including cancer, developmental toxicity, and
exposure assessment (51 Federal Register 33992-34054, 24 September 1986). Although EPA had
issued guidance for cancer risk assessment 10 years earlier (41 Federal Register 21402. 1976), the
1986 guidelines substantially enlarged the scope of EPA's formal guidance by covering additional
health topics and by covering all areas in much greater depth.  Each of the guidelines was a product of
several years of discussion and review involving scientists and policymakers from EPA, other Federal
agencies, universities.,  industry, public interest groups,  and the general public.

       Preliminary work on comparable guidelines for ecological effects began in 1988.  As part of
this work, EPA studied existing assessments and identified issues to help develop a basis for
articulating guiding principles for the assessment of ecological risks (U.S. EPA, 1991).  At the same
time, EPA's Science Advisory Board urged EPA to expand its consideration of ecological risk issues
to include the broad array of chemical  and nonchemical stressors for which research and regulation are
authorized in the environmental laws administered by EPA (U.S. EPA, 1990b).  As a result, EPA has
embarked on a new program to develop guidelines for ecological risk  assessment. Like the program
for health effects guidance, this activity depends on the expertise of scientists and policymakers from a
broad spectrum and draws principles, information, and methods from many sources.

       In May 1991,  EPA invited experts in ecotoxicology and  ecological effects to Rockville,
Maryland, to attend a  peer review workshop on the draft Framework Report (56 Federal Register
20223, 2 May 1991).  The workshop draft proposed a  framework for ecological risk assessment
complemented by preliminary guidance on some of the ecological issues identified in the draft. On
the basis of the Rockville workshop recommendations  (U.S. EPA, 1991), the revised Framework
Report ii now limited to discussion of the basic framework (see  figure 1), complemented by second-
order diagrams that give structure and content to each  of the major elements in the Framework Report
(see figures 2 through 4).  Consistent with peer review recommendations, substantive risk assessment
guidance is being reserved for study and development  in future guidelines.

       The Framework Report is the product of a variety of activities that culminated in the Rockville
workshop.  Beginning early in 1990, EPA work groups and the National Academy of Sciences' (NAS)
Committee on Risk Assessment Methodology began to study the 1983 NAS risk assessment paradigm
(NRC, 1983), which provides the organizing principles for EPA's health risk guidelines, as a possible
foundation for ecological risk assessment. Early drafts of EPA's Framework Report received
preliminary peer comment late in 1990.

       In February 1991, NAS  sponsored a workshop in Warrenton, Virginia, to discuss whether any
single paradigm could accommodate all the diverse kinds of ecological risk assessments. There was a
consensus that a single paradigm is feasible but that the 1983 paradigm would require modification to
fulfill this role. In April 1991, EPA sponsored a strategic planning workshop in Miami, Florida. The
structure and elements of ecological risk assessment were further discussed.  Some participants in both
of these earlier meetings also attended  the Rockville workshop.  EPA  then integrated information,
concepts, and diagrams from these workshop reviews with EPA  practices and needs to propose a
                                              Vll

-------
working framework for interim use in EPA programs and for continued discussion as a basis for future
risk assessment guidelines.

       Use of the framework described in mis report is not a requirement within EPA, nor is it a
regulation of any kind. Rather, it is an interim product that is expected to evolve with use and
discussion.  EPA is publishing the Framework Report before proposing risk assessment guidelines for
public comment to generate discussion within EPA, among Government agencies, and with the public
to develop concepts, principles, and methods for use in future guidelines.  To facilitate such
discussion, EPA is presenting the framework at scientific meetings and inviting the public to submit
information relevant to use and development of the approaches outlined for ecological risk assessment
hi the report.
                                                                 Dorothy E. Patton, Ph.D.
                                                                 Chair
                                                                 Risk Assessment Forum
                                               viii

-------
                                          PREFACE

       Increased interest in ecological issues such as global climate change, habitat loss, acid
deposition, reduced biological diversity, and the ecological impacts of pesticides and toxic chemicals
prompts this Framework Report. This report describes basic elements, or a framework, for evaluating
scientific information on the adverse effects of physical and chemical stressors on the environment.
The framework offers starting principles and a simple structure as guidance for current ecological risk
assessments and as a foundation for future EPA proposals for risk assessment guidelines.

       The Framework Report is intended primarily for EPA risk assessors, EPA risk managers, and
persons who perform work under EPA contract or sponsorship. The terminology and concepts
described in the report may also assist other regulatory agencies, as well as members of the public
who are interested in ecological issues.
                                               IX

-------
                          CONTRIBUTORS AND REVIEWERS

       This report was prepared by members of the EPA technical panel listed below, with assistance
from the staff of EPA's Risk Assessment Forum.  Technical review was provided by numerous
individuals, including EPA scientists and participants in the May 1991 peer review workshop.
Editorial assistance was provided by R.O.W. Sciences, Inc.
Technical Panel

Co-Chairs

Suzanne Macy Marcy (through December 1990)
Office of Water

Susan Braen Norton
Office of Research and Development

Donald J. Rodier
Office of Toxic Substances


Members

Michael S. Brody
Office of Policy, Planning and Evaluation

David A. Mauriello
Office of Toxic Substances

Anne Sergeant
Office of Research and Development

Molly R. Whitworth
Office of Policy, Planning and Evaluation
Risk Assessment Forum Staff

William H. van der Schalie
Office of Research and Development

William P. Wood
Office of Research and Development

-------
                                          Reviewers
 M. Craig Barber
 U.S. Environmental Protection Agency
 Environmental Research Laboratory
 Athens, GA

 Richard S. Bennett, Jr.
 U.S. Environmental Protection Agency
 Environmental Research Laboratory
 Corvallis, OR

 Steven Bradbury
 U.S. Environmental Protection Agency
 Environmental Research Laboratory
 Duluth, MN

 Janet Burris
 U.S. Environmental Protection Agency
 Office of Emergency and Remedial Response
 Washington, DC

 David W. Charters
 U.S. Environmental Protection Agency
 Office of Solid Waste and Emergency
  Response
 Edison, NJ

 Patricia A. Cirone
 U.S. Environmental Protection Agency
 Region 10
 Seattle, WA

 James R. Clark
 U.S. Environmental Protection Agency
 Environmental Research Laboratory
 Gulf Breeze, FL

 Robert Davis
 U.S. Environmental Protection Agency
 Region 3
 Philadelphia, PA

 Anne Fairbrother
 U.S. Environmental Protection Agency
Environmental Research Laboratory
Corvallis, OR
 Jay Gamer
 U.S. Environmental Protection Agency
 Environmental Monitoring Systems Laboratory
 Las Vegas, NV

 Jack H. Gentile
 U.S. Environmental Protection Agency
 Environmental Research Laboratory
 Narragansett, RI

 Sarah Gerould
 U.S. Geological Survey
 Reston, VA

 George R.  Gibson, Jr.
 U.S. Environmental Protection Agency
 Office of Water
 Washington, DC

 Alden D. Hinckley
 U.S. Environmental Protection Agency
 Office of Policy, Planning and Evaluation
 Washington, DC

 Erich Hyatt
 U.S. Environmental Protection Agency
 Office of Research and Development
 Washington, DC

 Norman E. Kowal
 U.S. Environmental Protection Agency
 Systems Laboratory
 Cincinnati,  OH

 Ronald B. Landy
 U.S. Environmental Protection Agency
 Office of Technology Transfer and Regulatory
  Support
 Washington, DC

 Foster L. Mayer
 U.S. Environmental Protection Agency
Environmental Research Laboratory
Gulf Breeze, FL
                                            XI

-------
Melissa McCullough
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Washington, DC

J. Gareth Pearson
U.S. Environmental Protection Agency
Environmental Monitoring Systems Laboratory
Las Vegas, NV

Ronald Preston
U.S. Environmental Protection Agency
Region 3
Philadelphia, PA

John Schneider
U.S. Environmental Protection Agency
Region 5
Chicago, IL

Harvey Simon
U.S. Environmental Protection Agency
Region 2
New York, NY

Michael W. Slimak
U.S. Environmental Protection Agency
Office of Environmental Processes and Effects
  Research
Washington, DC

Q. Jerry  Stober
U.S. Environmental Protection Agency
Region 4
Atlanta, GA

Greg R.  Susanke
U.S. Environmental Protection Agency
Office of Pesticide Programs
Washington, DC

Leslie W. Touart
U.S. Environmental Protection Agency
Office of Pesticide Programs
Washington, DC
Michael E. Troyer
U.S. Environmental Protection Agency
Office of Technology Transfer and Regulatory
 Support
Washington, DC

Douglas J. Urban
U.S. Environmental Protection Agency
Office of Pesticide Programs
Washington, DC

Maurice G. Zeeman
U.S. Environmental Protection Agency
Office of Toxic Substances
Washington, DC
                                            Xll

-------
William J. Adams
ABC Laboratories
Columbia, MO

Lawrence W. Barnthouse
Oak Ridge National Laboratory
Oak Ridge, TN

John Bascietto
U.S. Department of Energy
Washington, DC

Raymond Beaumier
Ohio Environmental Protection Agency
Columbus, OH

Harold Bergman
University of Wyoming
Laramie, NY

Nigel Blakeley
Washington Department of Ecology
Olympia, WA

James Falco
Battelle Pacific Northwest Laboratory
Richland, WA

James A. Fava
Roy F. Weston,  Inc.
West Chester, PA

Alyce Fritz
National Oceanic and Atmospheric
  Administration
Seattle, WA

James W. Gillett
Cornell University
Ithaca, NY

Michael C. Harrass
Food and Drug Administration
Washington, DC
Peer Review Workshop Participants

                    Mark Harwell
                    University of Miami
                    Miami, FL

                    Ronald J. Kendall
                    Clemson University
                    Pendleton, SC
                    Wayne G. Landis
                    Western Washington University
                    Bellingham, WA

                    Ralph Portier
                    Louisiana State University
                    Baton Rouge, LA

                    Kenneth Reckhow
                    Duke University
                    Durham, NC

                    John H. Rodgers
                    University of Mississippi
                    University, MS

                    Peter Van Voris
                    Battelle Pacific Northwest Laboratory
                    Richland,  WA

                    James Weinberg
                    Woods Hole Oceanographic Institution
                    Woods Hole, MA

                    Randall S. Wentsel
                    U.S. Army Chemical Research, Development
                     and Engineering Center
                    Aberdeen  Proving Ground, MD
                                           xiii

-------
                                  EXECUTIVE SUMMARY

       This report, "Framework for Ecological Risk Assessment", is the first step in a long-term effort
to develop risk assessment guidelines for ecological effects. Its primary purpose is to offer a simple,
flexible structure for conducting and evaluating ecological risk assessment within EPA. Although the
Framework Report will serve as a foundation for development of future subject-specific guidelines, it
is neither a procedural guide nor a regulatory requirement within EPA and is expected to evolve with
experience.  The Framework Report is intended to foster consistent approaches to ecological risk
assessment within EPA, identify key issues, and define terms used in these assessments.

       Ecological risk assessments evaluate ecological effects caused by human activities such as
draining of wetlands or release of chemicals. The term "stressor" is used here to describe any
chemical, physical, or biological entity that can induce adverse effects on individuals, populations,
communities, or ecosystems. Thus, the ecological risk assessment process must be flexible while
providing a logical and scientific structure to accommodate a broad array of stressors.

       The framework is conceptually similar to  the approach used for human health risk  assessment,
but it is distinctive in its emphasis in three areas.  First, ecological risk assessment can consider effects
beyond those on individuals of a single species and may examine a population, community, or
ecosystem.  Second, there is no single set of ecological values to be protected that can be generally
applied.  Rather, these values are selected from a  number of possibilities based on both scientific and
policy considerations.  Finally, there is an increasing awareness of the need for ecological risk
assessments to consider nonchemical as well as chemical stressors.

       The framework consists of three major phases: (1) problem formulation, (2) analysis, and (3)
risk characterization. Problem formulation is a planning and scoping process that establishes the goals,
breadth, and focus of the risk assessment. Its end product is a conceptual model that identifies the
environmental values to be  protected (the assessment endpoints), the data needed, and the analyses to
be used.

       The analysis phase  develops profiles of environmental exposure and the  effects of the stressor.
The exposure profile characterizes the ecosystems in which the stressor may occur as well as the biota
that may be exposed.  It also describes the magnitude and spatial and temporal patterns of exposure.
The ecological effects profile summarizes data on the effects of the stressor and  relates them to the
assessment endpoints.

       Risk characterization integrates the exposure and effects profiles.  Risks  can be estimated using
a variety of techniques including comparing individual exposure and effects values, comparing me
distributions of exposure and effects, or using simulation models.  Risk can be expressed as a
qualitative or quantitative estimate, depending on available data.  In this step, the assessor also:

        "      describes the risks in terms of me assessment endpoint;

        »      discusses the ecological significance of the effects;

        •      summarizes overall confidence in the assessment; and

        »      discusses the results with the risk manager.
                                              xiv

-------
       The framework also recognizes several activities that are integral to, but separate from, the risk
assessment process as defined in this report.  For example, discussions between the risk assessor and
risk manager are important. At the initiation of the risk assessment, the risk manager can help ensure
that the risk assessment will ultimately provide information that is relevant to making decisions on the
issues under consideration, while the risk assessor can ensure that the risk assessment addresses all
relevant ecological concerns.  Similar discussions of the results of the risk assessment are important to
provide the risk manager with a full and complete understanding of the assessment's conclusions,
assumptions, and limitations.

       Other important companion activities to ecological risk assessment include data acquisition and
verification and monitoring studies.  New data are frequently required to conduct analyses that are
performed during the risk assessment  Data from verification studies can be used to validate the
predictions of a specific risk assessment as well as to evaluate the usefulness of the principles set forth
in the Framework.  Ecological effects or exposure monitoring can aid in the verification process and
suggest additional data, methods, or analyses that could improve future risk assessments.
                                              xv

-------

-------
1. INTRODUCTION

       Public, private, and government sectors of society are increasingly aware of ecological issues
including global climate change, habitat loss, acid deposition, a decrease in biological diversity, and
the ecological impacts of xenobiotic compounds such as pesticides and toxic chemicals.  To help
assess these and other ecological problems, the U.S. Environmental Protection Agency (EPA) has
developed this report, "Framework for Ecological Risk Assessment", which describes the basic
elements, or framework, of a process for evaluating scientific information on the adverse effects of
stressors on the environment  The term "stressor" is defined here as any physical, chemical,  or
biological entity that can induce an adverse effect (see box1).  Adverse ecological effects encompass a
wide range of disturbances ranging from mortality in an individual organism to a loss in
ecosystem function.
       This introductory section describes the
purpose, scope, and intended audience for this
report; discusses the definition and application of
ecological risk assessment; outlines the basic
elements of the proposed framework; and
describes the organization of this report.

1.1.  Purpose and Scope of the Framework
     Report

       An understanding of the finite purpose
and scope of this Framework Report is important.
EPA, other regulatory agencies, and other
organizations need detailed, comprehensive
guidance on methods for evaluating ecological
risk.  However, in discussing tentative plans for
developing such guidance with expert consultants
(U.S. EPA, 1991; U.S. EPA, in press-a), EPA
was  advised to first develop a simple framework as a foundation or blueprint for later comprehensive
guidance on ecological risk assessment

       With this background, the framework (see section 1.4) has two simple purposes, one
immediate and one longer term.  As a broad outline of the assessment process, the framework offers a
basic structure and starting principles for EPA's ecological risk assessments.  The process described by
the framework provides  wide latitude for planning and conducting individual risk assessments in many
diverse situations, each based on  the common principles discussed in the framework. The process also
will  help foster a consistent EPA approach for conducting and evaluating ecological risk assessments,
identify key issues, and provide operational definitions for terms used in ecological risk assessments.
  Physical and Chemical Stressors as a
        Focus of the Framework

This report does not discuss accidentally or
deliberately introduced species, genetically
engineered organisms, or organisms used to
control horticultural or agricultural pests.
While the general principles described in
the framework may be helpful in addressing
risks associated with these organisms, the
capacity of such organisms for reproduction
and biological interaction introduces
additional considerations that are not
addressed in this document
    1The boxes used throughout this document serve several purposes.  Some boxes provide additional
background and rationale for terms, whereas other boxes expand on concepts described in the text
The boxes at the end of each chapter highlight issues that are integral components of the risk
assessment process but require more research, analysis, and debate. Further discussion of these issues
is reserved for later guidelines.
                                              1

-------
       In addition, the framework offers basic principles around which long-term guidelines for
ecological risk assessment can be organized. With this in mind, this report does not provide
substantive guidance on factors that are integral to the risk assessment process such as analytical
methods, techniques for analyzing and interpreting data, or guidance on factors influencing policy.
Rather, on the basis of EPA experience and the recommendations of peer reviewers, EPA has reserved
discussion of these important aspects of any risk assessment for future guidelines, which will be based
on the process described in this report.

1.2.  Intended Audience

       The framework is primarily intended for EPA risk assessors, EPA risk managers, and other
persons who either perform work under EPA contract or sponsorship or are subject  to EPA
regulations.  The terminology and concepts described here also may be of assistance to other Federal,
State, and local agencies as well as to members of the general public who are interested in ecological
issues.

1.3.  Definition and Applications of Ecological Risk Assessment

       Ecological risk assessment is defined as a process that evaluates the likelihood that adverse
ecological effects may occur or are occurring as a result  of exposure to one or more stressors.  A risk
does not exist unless (1) the stressor has the inherent ability to cause one  or more adverse effects and
(2) it co-occurs with or contacts an ecological component (i.e., organisms, populations, communities,
or ecosystems) long enough and at a sufficient intensity to elicit the identified adverse effect
Ecological risk assessment may evaluate one or many stressors and ecological components.

       Ecological risk may be expressed in a variety of ways. While some ecological risk
assessments may provide true probabilistic estimates of both the adverse effect and  exposure elements,
others may be deterministic or even qualitative in nature. In these cases,  the likelihood of adverse
effects is expressed through a semiquantitative or qualitative comparison of effects and exposure.

       Ecological risk assessments can help identify environmental problems, establish priorities, and
provide a scientific basis for regulatory actions. The process can identify existing risks or forecast the
risks of stressors not yet present in the environment.  However, while ecological risk assessments can
play an important role in identifying and resolving environmental problems, risk assessments are not a
solution for addressing all environmental problems, nor are they always a prerequisite for
environmental management  Many environmental matters such as the  protection of habitats and
endangered species are compelling enough that there may not be enough time or data to do a risk
assessment.  In such cases, professional judgment and the mandates of a particular statute  will be the
driving forces in making decisions.

1.4.  Ecological Risk Assessment Framework

       The distinctive nature of the framework results primarily from three differences in emphasis
relative to previous risk assessment approaches. First, ecological  risk assessment can consider effects
beyond those on individuals of a single species and may examine population, community, or
ecosystem impacts. Second, there is no one set of assessment endpoints (environmental values to be
protected) that can be generally applied. Rather, assessment endpoints are selected  from a very large
number of possibilities based on both scientific and policy considerations.  Finally,  a comprehensive

-------
approach to ecological risk assessment may go beyond the traditional emphasis on chemical effects to
consider the possible effects of nbnchemical stressors.
       The ecological risk assessment
framework is shown in figure 1. The risk
assessment process is based on two major
elements: characterization of exposure and
characterization of ecological effects.
Although these two elements are most
prominent during the analysis phase, aspects
of both exposure and effects also are
considered during problem formulation, as
illustrated by the arrows in the diagram.
The arrows also flow to  risk
characterization,  where the exposure and
effects elements are integrated to estimate
risk. The framework is conceptually similar
to the National Research Council (NRC)
paradigm for human health risk assessments
(NRC, 1983).

       The first phase of the framework is
problem formulation. Problem formulation
includes a preliminary characterization of
exposure and effects, as  well as examination
of scientific data and data needs, policy and
regulatory issues, and site-specific factors to
define  the feasibility, scope, and objectives
for the ecological risk assessment.  The level
of detail and  the information that will be
needed to complete the assessment also are
determined. This systematic planning phase
is proposed because ecological risk assessments often address the risks of stressors
to many species as well  as risks to communities and ecosystems.  In addition, there may be many
ways a stressor can elicit adverse effects  (e.g., direct effects on mortality and growth and indirect
effects such as decreased food supply). Problem formulation provides an early identification of key
factors to be  considered, which in  turn will produce a more scientifically sound risk assessment.
Relationship of the Framework to a Paradigm
     for Human Health Risk Assessment

In 1983, NRC published a paradigm that has
been used in the development of EPA's human
health risk assessment guidelines. The paradigm
has four phases:  hazard identification, dose-
response assessment, exposure assessment, and
risk characterization (NRC, 1983).  Although the
framework's problem formulation phase is not
explicitly identified in the NRC paradigm,
comparable planning issues are addressed in
practice at the beginning of all EPA risk
assessments.  In the framework's analysis phase,
characterization of exposure is analogous to
exposure assessment, while characterization of
ecological effects includes aspects of both
hazard identification and dose-response
assessment.  (The framework uses the term
"stressor response"  rather than "dose response"
because many Agency programs must address
stressors other than chemicals, and dose has
been used only for  chemicals.)  Risk
characterization is a similar process in both the
framework and the  NRC paradigm.

-------


Discussion
Between the
Risk Assessor
and
Risk Manager
(Planning)


























































Ecological Risk Assessment
PROBLEM FORMULATION

,",..„ ' , >- " "
f _,
-
j ff f

A I
A ,, Characterization ' Characterization
* ; of i of
h Exposure Ecological
i ^- ' Effects
i '
S 1
,

*" \r^^4?^ • ^
V "" "" <.•. -.s f f f , "••• *" f
"""'•", ' ,-.
'" \ *•""%,. t t" ^SS
"• *• \\ -.-.-.-. Jiff'
RISK CHARACTERIZATION
' ' • • , - ,


Discussion Between the
Risk Assessor and Risk Manager
(Results)
*
Rf«5lc Mananpmpni -^^ — —,















































§
0)
S
c_
w'
S!
o
3
Ml •
S.
rification
so
a
35
o
1
5"
(Q

I




1

Figure 1.  Framework for Ecological Risk Assessment




                      4

-------
       The second phase of the framework is termed analysis and consists of two activities,
characterization of exposure and characterization of ecological effects. The purpose of characterization
of exposure is to predict or measure the spatial and temporal distribution of a stressor and its co-
occurrence or contact with the ecological
components of concern, while the purpose of
characterization of ecological effects is to
identify and quantify the  adverse effects elicited
       Use of the Term "Exposure"
Some reviewers of earlier drafts of this
interim framework proposed that the term
"exposure",-which, as used in human health
risk assessment, generally refers to chemical
stressors,-not be used for the nonchemical
stressors that can affect a variety of
ecological components.  Other terms,
including "characterization of stress", have
been suggested. At this time, EPA prefers
exposure, partly because characterization of
stress does not convey the  important concept
of the co-occurrence and interaction of the
stressor with an ecological component  as
well as exposure does.
by a stressor and, to the extent possible, to
evaluate cause-and-effect relationships.

        The third phase of the framework is risk
characterization.  Risk characterization uses the
results of the exposure and ecological effects
analyses to evaluate the likelihood of adverse
ecological effects associated with exposure to a
stressor. It includes a summary of the
assumptions used, the scientific uncertainties,
and the strengths and  weaknesses of the
analyses.  In addition, the ecological significance
of the risks is discussed with consideration of
the types and magnitudes of the effects, their
spatial and temporal patterns, and the likelihood
of recovery.  The purpose is to provide a
complete picture of the analysis and results.

        In addition to showing the three phases
of the framework, figure  1  illustrates the need
for discussions between the risk assessor and
risk manager.  At the  initiation of the risk
assessment, the risk manager can help ensure
that the risk assessment will ultimately provide
information that is relevant to making decisions
on the issues under consideration, while the risk
assessor can ensure that the risk assessment
addresses all relevant  ecological concerns.
Similar discussions  of the results of the risk
assessment are important to provide the risk
manager with a full and complete understanding
of the assessment's conclusions, assumptions,
and limitations.

        Figure 1 also  indicates a role for
verification and monitoring in the framework.
Verification can include validation of the
ecological risk assessment process as well as confirmation of specific predictions made during a risk
assessment. Monitoring can aid in the verification process and may identify additional topics for risk
assessment. Verification and monitoring can help determine the overall effectiveness of the framework
approach, provide necessary feedback concerning the need for future modifications of the framework,
  Characterization of Ecological Effects
   Used Instead of Hazard Assessment

The framework'uses characterization of
ecological effects rather than hazard
assessment for two reasons. First, the term
"hazard" can be ambiguous, because it has
been used in the past to mean either
evaluating the intrinsic effects of a stressor
(U.S. EPA, 1979) or defining a margin of
safety or quotient by comparing a
lexicological endpoint of interest with an
estimate of exposure concentration (SETAC,
1987).   Second, many reviewers believed
that hazard is more relevant to chemical  than
to nonchemical stressors.

-------
help evaluate the effectiveness and practicality of policy decisions, and point out the need for new or
improved scientific techniques (U.S. EPA, in piess-a).

       The interaction between data acquisition and ecological risk assessment is also shown in figure
1. In this report, a distinction is made between data acquisition (which is outside of the risk
assessment process) and data analysis (which is an integral part of an ecological risk assessment). In
the problem formulation and analysis phases, the risk assessor may identify the need for additional
data to complete an analysis.  At this point, the risk assessment stops until me necessary data are
acquired.  When a need for additional data is recognized in risk characterization, new information
generally is used in the analysis or problem formulation phases. The distinction between data
acquisition and analysis generally is maintained in all of EPA's risk assessment guidelines; guidance
on data acquisition procedures are provided in documents prepared for specific EPA programs.

       The interactions between data acquisition and ecological risk assessment often result in an
iterative process.  For example,  data used during the analysis phase may be collected in tiers of
increasing complexity and cost.  A decision to advance from one tier to the next is based on decision
triggers set at certain levels of effect or exposure. Iterations of the entire risk assessment process also
may occur.  For example, a screening-level risk assessment may be performed using readily available
data and conservative assumptions; depending on the results, more data then may be collected to
support a more rigorous assessment.

1.5.  The Importance of Professional Judgment

       Ecological risk assessments, like human health risk assessments, are based on scientific data
that are frequently difficult and complex, conflicting or ambiguous, or incomplete.  Analyses of such
data for risk assessment purposes depends on professional judgment based on scientific expertise.
Professional judgment is necessary to:

       •      design and conceptualize the risk assessment;

       »      evaluate and select methods and models;

       »      determine the relevance of available data to me risk assessment;

       •      develop assumptions based on logic and scientific principles to fill data gaps; and

       •      interpret the ecological significance of predicted or observed effects.

       Because professional judgment is so important,  specialized knowledge and experience in the
various phases of ecological risk assessment is required. Thus, an interactive multidisciplinary team
that includes biologists and ecologists is a prerequisite for a successful ecological risk assessment.

1.6.  Organization

       The next three sections of this report are arranged to follow the framework sequentially.
Section 2 describes problem formulation; this section is particularly important for assessors to consider
when specific assessment endpoints are not determined  a priori by statute or other authority.  Sections
3 and 4 discuss analysis and risk characterization, respectively. Section 5 defines the terms used in

-------
this report, and section 6 provides literature references. The lists of ecological risk assessment issues
at the end of sections 1 through 4 highlight areas for further discussion and research. EPA believes
that these issues will require special attention in developing ecological risk assessment guidelines.

-------
o      Use
o      Use ofi
       nonchemical sfressbrs.
Related jte the Frame w»%

                   biological

                     forlxtth
                                                                         and
       Use of th& tenn ^aracterization of ecological effects rather than hazard assessment
           V:v^™;\ ;-,,-' ,!""    'l^9~-.

-------
2. PROBLEM FORMULATION

       Problem formulation is the first phase of ecological risk assessment and establishes the goals,
breadth, and focus of the assessment.  It is a systematic planning step that identifies the major factors
to be considered in a particular assessment, and it is linked to the regulatory and policy context of the
assessment.

       Entry into the ecological risk assessment process may be triggered by either an observed
ecological effect, such as visible damage to trees in a forest, or by the identification of a stressor or
activity of concern, such as the planned  filling of a marsh or the manufacture of a new chemical. The
problem formulation process (figure 2) then begins with the initial stages of characterizing exposure
and ecological effects, including evaluating the stressor characteristics, the ecosystem potentially at
risk, and the ecological effects expected or observed. Next, the assessment and measurement
endpoints are identified.  (Measurement  endpoints  are ecological characteristics that can be related to
the assessment endpoint.)  The outcome of problem formulation is a conceptual model that describes
how a given stressor might affect the ecological components in the environment. The conceptual
model also describes the relationships among the assessment and measurement endpoints, the data
required, and the methodologies  that will be  used to analyze the data. The conceptual model serves  as
input to the analysis  phase of the assessment.

2.1. Discussion Between the Risk  Assessor and  Risk Manager (Planning)

       To be meaningful and effective, ecological risk assessments must be relevant to regulatory
needs and public concerns as well as scientifically valid. Although  risk assessment and risk
management are distinct processes, establishing a two-way dialogue between risk assessors and risk
managers during the problem formulation phase can be a constructive means of achieving both societal
and scientific goals.  By bringing the management perspective to the discussion, risk managers charged
with protecting societal values can ensure that the  risk assessment will provide relevant information to
making decisions on the issue under consideration. By bringing scientific knowledge to the
discussion, the ecological risk assessor ensures that the assessment addresses all important ecological
concerns.  Both perspectives are necessary to appropriately utilize resources to produce scientifically
sound risk assessments that are  relevant to management decisions and public concerns.

2.2. Stressor Characteristics,  Ecosystem Potentially at Risk, and Ecological Effects

       The initial steps in problem formulation are the identification and preliminary characterization
of stressors, the ecosystem potentially at risk, and  ecological effects. Performing this analysis is an
interactive  process that contributes to both the selection of assessment and measurement endpoints and
the development, of a conceptual model.

-------
 Discussion
 Between the
Risk Assessor
    and
Risk Manager
  (Planning)
                                                        i PROBLEM FORMULATION
                                                         RISK CHARACTERIZATION
                         Stressor
                      Characteristics
Ecosystem
Potentially
  at Risk
Ecological
 Effects
 Endpoint
 Selection
Assessment
Measurement

                                             Conceptual
                                               Model
                                                                                         Q)
c:
55'
f¥
O
                                     «*-»•
                      O
                      3
                      0)
                      =}
                      CX.
                      g
                      O
                      :»

                      S1'
                      =!.
                                             ANALYSIS
                                Figure 2. Problem Formulation

                                            10

-------
2.2.1.  Stressor Characteristics

       The determination of stressor characteristics begins with the identification of potential chemical
or physical stressors.  Chemical stressors include a variety of inorganic and organic substances. Some
chemicals may result in secondary stressors, as in the case of stratospheric ozone depletion caused by
chlorofluorocarbons that could result in increased exposures to ultraviolet radiation. Physical stressors
include extremes of natural conditions (e.g., temperature and hydrologic changes) and habitat alteration
or destruction.  Stressors that may result from management practices, such as harvesting of fishery or
forest resources, also may be considered. Example stressor characteristics are summarized in the box
below. Gathering information on the characteristics of a stressor helps define the ecosystems
potentially at risk from the stressor as well  as the ecological effects that may result.
2.2.2.  Ecosystem Potentially at Risk

       The ecosystem within which effects
occur provides the ecological context for the
assessment. Knowledge of the ecosystem
potentially at risk can help identify ecological
components that may be affected and stressor-
ecosystem interactions relevant to developing
exposure scenarios.  The approach to identifying
the ecosystem potentially at risk from a stressor
depends in part on how the risk  assessment was
initiated.  If a stressor first was identified,
information on the spatial and temporal
distribution patterns  of the stressor can be
helpful in identifying ecosystems potentially at
risk.  Similarly, if the risk assessment is initiated
by observing effects, these effects  can directly
indicate ecosystems  or ecological components
that may be considered in the assessment.

       A wide range of ecosystem properties
may be considered during problem formulation.
These properties include aspects of the abiotic
environment (such as climatic conditions and
soil or sediment properties), ecosystem structure
(including the types  and abundances of different
species and their trophic level relationships), and
ecosystem function (such as the  ecosystem
energy source, pathways of energy utilization,
and nutrient processing) (U.S. EPA, in press-b).  hi
historical disturbances may be helpful in predicting
       Example Stressor Characteristics

   Type

   Chemical or physical

   Intensity

   Concentration or magnitude

   Duration

   Short or long term

   Frequency

   Single event,  episodic, or continuous

   Timing

   Occurrence relative to biological cycles

   Scale

   Spatial heterogeneity and extent
addition, knowledge of the types and patterns of
ecological responses to stressors.
        The need to evaluate spatial and temporal distribution and variation is inherent in many of
these example characteristics. Such information is especially useful for determining potential
exposure, that is, where there is co-occurrence of or contact between the stressor and ecological
components.
                                               11

-------
2.23.  Ecological Effects
        Ecological effects data may come from a variety of sources. Relevant sources of information
include field observations (e.g., fish or bird kills, changes in aquatic community structure), field tests
(e.g., microcosm or mesocosm tests), laboratory tests (e.g., single species or microcosm tests), and
chemical structure-activity relationships.  Available information on ecological effects can help focus
the assessment on specific stressors and on ecological components that should be evaluated.

        Many factors can influence the utility of available ecological effects data for problem
formulation.  For example, the applicability of laboratory-based tests may be affected by any
extrapolations required to specific field situations, while the interpretation of field observations may be
influenced by factors such as natural variability or the possible presence of stressors other than the
ones that are the primary focus of the risk assessment

2.3. Endpoint Selection
        Information compiled in the first stage
of problem formulation is used to help select
ecologically based endpoints that are relevant to
decisions made about protecting the
environment  An endpoint is a characteristic of
an ecological component (e.g., increased
mortality in fish) that may be affected by
exposure to a stressor (Suter, 1990a).  Two
types of endpoints are distinguished in this
report  Assessment endpoints are explicit
expressions of the actual environmental value
that is to be protected. Measurement endpoints
are measurable responses to a stressor that are
related to the valued characteristics chosen as
the assessment endpoints (Suter, 1990a).

        Assessment endpoints are the ultimate
focus in risk characterization and link the
measurement endpoints to the risk management
process (e.g., policy goals).  When an
assessment endpoint can be directly measured,
the measurement and assessment endpoints are the same.  In most cases, however, the assessment
endpoint cannot be directly measured, so a measurement endpoint (or a suite of measurement
endpoints) is selected that can be related, either qualitatively or quantitatively, to the assessment
endpoint For example, a decline in a sport fish population (the assessment endpoint) may be
evaluated using laboratory studies on the mortality of surrogate species, such as the fathead minnow
(the measurement endpoint). Sound professional judgment is necessary for proper assessment and
measurement endpoint selection, and it is important that both the selection rationale and the linkages
between measurement endpoints, assessment endpoints, and policy goals be clearly stated.
          Endpoint Terminology

Several reviewers have suggested using the
term "indicator" in place of "measurement
endpoint".  At this time, measurement
endpoint is preferred because it has a
specific meaning (a characteristic of an
ecological system that can be related to an
assessment endpoint), whereas  indicator can
have several different meanings.  For
example, indicator has been used at EPA to
mean (1) measures of administrative
accomplishments (e.g., number of permits
issued), (2) measures of exposure (e.g.,
chemical levels in sediments), or (3)
measures of ecosystem integrity.  These
indicators cannot always be related to an
assessment endpoint.
                                              12

-------
       Assessment and measurement endpoints may involve ecological components from any level of
biological organization, ranging from individual organisms to the ecosystem itself.  In general, the use
of a suite of assessment and measurement endpoints at different organizational levels can build greater
confidence in the conclusions of the risk assessment and ensure that all important endpoints are
evaluated.  In some situations, measurement endpoints at one level of organization may be related to
an assessment endpoint at a higher level.  For example, measurement endpoints at the individual level
(e.g., mortality, reproduction, and growth) could be used in a model to predict effects on an
assessment endpoint at the population level (e.g., viability of a trout population in a stream).

       General considerations for selecting assessment and measurement endpoints are detailed in the
following boxes.  More detailed discussions of endpoints and selection criteria can be found in Suter
(1989, 1990a), Kelly and Harwell (1990), U.S. Department of the Interior (1987), and U.S. EPA
(1990a).
                         Considerations in Selecting Assessment Endpoints

      Ecological Relevance

      Ecologically relevant endpoints reflect important characteristics of the system and are
      functionally related to other endpoints. Selection of ecologically relevant endpoints requires
      some understanding of the structure and function of the ecosystem potentially at risk. For
      example, an assessment endpoint could focus on changes in a species known to have a
      controlling  influence on the abundance and distribution of many other species in its
      community. Changes at higher levels of organization may be significant because of their
      potential for causing major effects at lower organizational levels.

      Policy Goals and Societal Values

      Good communication between the risk assessor and risk manager is important to ensure that
      ecologically relevant assessment endpoints reflect policy goals and societal values.  Societal
      concerns can range from protection of endangered or commercially or recreationally
      important species to preservation of ecosystem attributes for functional reasons (e.g., flood
      water retention by wetlands) or aesthetic reasons (e.g., visibility in the Grand Canyon).

      Susceptibility to the Stressor

      Ideally,  an  assessment endpoint would be likely to be both affected by exposure to a stressor
      and sensitive to the  specific type of effects caused by the stressor.  For example, if a
      chemical is known to bioaccumulate and is suspected of causing  eggshell thinning, an
      appropriate assessment endpoint might be raptor population viability.
                                               13

-------
                      Considerations in Selecting Measurement Endpoints

Relevance to an Assessment Endpoint

When an assessment endpoint cannot be directly measured, measurement endpoints are identified that
are correlated with or can be used to infer or predict changes in the assessment endpoint.

Consideration of Indirect Effects

Indirect effects occur when a stressor acts on elements of the ecosystem that are required by the
ecological component of concern.  For example, if the assessment endpoint is the population viability
of trout, measurement endpoints could evaluate possible stressor effects on trout prey species or habitat
requirements.

Sensitivity and Response Time

Rapidly responding measurement endpoints may be useful in providing early warnings of ecological
effects, and measurement endpoints also may be selected because they are sensitive surrogates of the
assessment endpoint In many cases, measurement endpoints at lower levels of biological organization
may be more sensitive than those at higher levels.  However, because of compensatory mechanisms
and other factors, a change in a measurement endpoint at a lower organizational level (e.g., a
biochemical alteration) may not necessarily be reflected in changes at a higher level (e.g., population
effects).

Signal-to-Noise Ratio

If a measurement endpoint is highly variable, the possibility of detecting stressor-related effects may be
greatly reduced even if the endpoint is sensitive to the stressor.

Consistency With Assessment Endpoint Exposure Scenarios

The ecological component of the measurement endpoint should be exposed by similar routes and at
similar or greater stressor levels as the ecological component of the assessment endpoint.

Diagnostic Ability

Measurement endpoints  that are unique or specific responses to a stressor may be very useful in
diagnosing the presence or effects of a stressor.  For example, measurement of acetylcholinesterase
inhibition may be useful for demonstrating responses to certain types of pesticides.   >  •

Practicality Issues

Ideal measurement endpoints are cost effective and easily measured.  The availability of a large
database for a measurement endpoint is* desirable to facilitate comparisons and develop models.
                                             14

-------
2.4.  The Conceptual Model

       The major focus of the conceptual model (figure 2) is the development of a series of working
hypotheses regarding how the stressor might affect ecological components of the natural environment
(NRC, 1986).  The conceptual model also includes descriptions of the ecosystem potentially at risk and
the relationship between measurement and assessment endpoints.

       During conceptual model development, a preliminary analysis of the ecosystem, stressor
characteristics, and ecological effects is used to define possible exposure scenarios. Exposure
scenarios consist of a qualitative description of how the various ecological components co-occur with
or contact the stressor.  Each scenario is defined in terms of the stressor, the type of biological system
and principal ecological components, how the stressor will contact or interact with the system, and the
spatial and temporal scales.

       For chemical stressors, the exposure scenario usually involves consideration of sources,
environmental transport, partitioning of the chemical among various environmental media,
chemical/biological transformation or speciation processes, and identification of potential routes of
exposure (e.g., ingestion). For nonchemical stressors such as water level or temperature changes or
physical  disturbance, the exposure scenario  describes the ecological components exposed and the
general temporal and spatial patterns of then- co-occurrence with the stressor. For example, for habitat
alterations, the exposure scenario may describe the extent and distributional pattern of disturbance, the
populations residing within or using the disturbed areas, and the spatial relationship of the disturbed
area to undisturbed areas.

       Although many hypotheses may be  generated during problem formulation, only those that are
considered most likely to contribute to risk  are selected for further evaluation in the analysis phase.
For these hypotheses, the conceptual model describes the approach that will be  used for the analysis
phase and the types of data and analytical tools that will be needed.  It is important that hypotheses
that are not carried forward in the assessment because of data gaps be acknowledged when uncertainty
is addressed in risk characterization.  Professional judgment is needed to select  the most appropriate
risk hypotheses, and it is important to document the selection rationale.
                                               15

-------
Role of risk management concerns in establishing assessment endpoints.
                           ''    '•'
Althougih it is important; to'wnslder ri$lyaktiageiae»t conceni$s'wlien
endpoints are selectedl there^is still unceitainly as to how these inputs should influence
the goals of the lisfc'assessment, the ecological components to be ptotected, and the
level of proteciiorfieqaire&        v'"     "                       -     '  '

Identifying specific assessment and^ineasurenient eadpolnts for different stressoms and
ecosystems.     s   %                                 ;
                                  16

-------
3. ANALYSIS PHASE

       The analysis phase of ecological risk assessment (figure 3) consists of the technical evaluation
of data on the potential effects and exposure of the stressor.  The analysis phase is based on the
conceptual model developed during problem formulation. Although this phase consists of
characterization of ecological effects and characterization of exposure, the dotted line in figure 3
illustrates that the two are performed interactively. An interaction between the two elements will
ensure that the ecological effects characterized are compatible with the biota and exposure pathways
identified in the exposure characterization.  The output of ecological effects characterization and
exposure characterization are summary profiles that are used in the risk characterization phase (section
4).  Discussion of uncertainty analysis, which is an important part of the analysis phase, may be found
in section 4.1.2.

       Characterization of exposure and ecological effects often requires the application of statistical
methods.  While the discussion of specific statistical methods is beyond the scope of this document,
selection of an appropriate statistical method involves both method assumptions  (e.g., independence of
errors, normality, equality of variances) and data set characteristics (e.g., distribution, presence of
outliers or influential data).  It should be noted that statistical significance does not always reflect
biological significance, and profound biological changes may not be detected by statistical tests.
Professional judgment often is required to evaluate the relationship between statistical and biological
significance.

3.1.  Characterization of Exposure

       Characterization of exposure (half of the analysis phase shown in figure  3) evaluates the
interaction of the stressor with the ecological component. Exposure can be expressed as co-occurrence
or contact depending on the stressor and the ecological component involved. An exposure profile is
developed that quantifies the magnitude and spatial and temporal distributions of exposure for the
scenarios developed during problem formulation and serves as input to the risk characterization.

3.1.1.  Stressor Characterization:  Distribution or Pattern of Change

       Stressor characterization involves determining the stressor's distribution or pattern of change.
Many techniques can be  applied to assist in this stressor characterization process. For chemical
stressors, a combination of modeling and monitoring data often is used. Available monitoring data
may include measures of releases into the environment and media concentrations over space and time.
Fate and transport models often are used that rely on physical and chemical characteristics of the
chemical coupled with the characteristics of the ecosystem.  For nonchemical stressors such as physical
alterations or harvesting, the pattern of change may depend on resource management or land-use
practices. Depending on the scale of the disturbance, the data for stressor characterization can be
provided by a variety of techniques, including  ground reconnaissance, aerial photographs, or satellite
imagery.
                                               17

-------
                PROBLEM FORMULATION
                RISK CHARACTERIZATION
PROBLEM FORMULATION
s
JJ,
N
X
S
V
N
Characterization of Exposure x Characterization of Ecological Effects
*'<»'<> f . . " , ,
-•• '-':. 	 *..:>* i 	 v ^ <

Stressor
Characterization:
Distribution or
Pattern of Change
Ecosystem
'^, Characterization

Abiotic
\V^ *r/ \\

/ * V
Exposure f t \
Analysis I t;
*

Exposure
Profile 1
c
EHHHiiiiii *•
\
Ifr

**
"
Evaluation
of Relevant
Effects Data

Ecological
Response
Analysis
t

Stressor-Response
Profile

f'





D
E
D)
1
C
S5'

ion; Verification and Monitoring
RISK CHARACTERIZATION
       Figure 3. Analysis




             18

-------
       During stressor characterization, one considers not only the primary stressor but also secondary
stressors that can arise as a result of various processes.  For example, removal of riparian (stream-side)
vegetation not only alters habitat structure directly, but can have additional ramifications such as
increased siltation and temperature rise. For chemicals, secondary stressors can be produced by a
range of environmental fate processes.

       The timing of the stressor's interaction with the biological system is another important
consideration. If the stressor is episodic in nature, different species and life stages may be affected.
In addition, the ultimate distribution of a stressor is rarely homogeneous; it is important to quantify
such heterogeneity whenever possible.

3.13.  Ecosystem Characterization

       During ecosystem characterization, the ecological context of the assessment is further analyzed.
In particular, the spatial and temporal distributions of the ecological component are characterized, and
the ecosystem attributes ttiat influence the distribution and nature of the stressor are considered.

       Characteristics of the ecosystem can greatly modify the ultimate nature and distribution of the
stressor.  Chemical stressors can be modified through biotransformation by microbial communities or
through other environmental fate processes, such as photolysis, hydrolysis, and sorption. The
bioavailability of chemical stressors also can be affected by the environment, which in turn influences
the exposure of ecological components.

       Physical stressors can be modified by the ecosystem as well. For example, siltation in streams
depends not only on sediment volume, but on flow regime and physical stream characteristics.
Similarly, nearby wetlands and levees influence water behavior during flood events.

       The spatial and temporal distributions of ecological components also are considered in
ecosystem characterization.  Characteristics of ecological components that influence their exposure to
the stressor are evaluated, including habitat needs, food preferences, reproductive cycles, and seasonal
activities such as migration and selective  use of resources. Spatial and temporal variations in the
distribution of the ecological component (e.g., sediment invertebrate distribution) may complicate
evaluations of exposure.  When available, species-specific information about activity patterns,
abundance, and life histories can be very  useful in evaluating spatial and temporal distributions.

        Another important consideration is how exposure to a stressor may alter natural behavior,
thereby affecting further exposure. In some cases, this may lead to enhanced exposure (e.g., increased
preening by birds after aerial pesticide spraying), while in other situations initial exposure may lead to
avoidance  of contaminated locations  or food sources (e.g., avoidance of certain waste effluents or
physically altered spawning beds by  some fish species).
                                               19

-------
 3.13. Exposure Analyses

        The next step is to combine the spatial and temporal distributions of both the ecological
 component and the stressor to evaluate exposure. In the case of physical alterations of communities
 and ecosystems, exposure can be expressed broadly as co-occurrence.  Exposure analyses of
 individuals often focus on actual contact with the stressor, because organisms may not contact all of
 the stressors present in an area.  For chemical stressors, the analyses may focus further on the amount
 of chemical that is bioavailable, that is, available for uptake by the organism.  Some chemical
 exposure analyses also follow the chemical within the organism's body and estimate the amount that
 reaches the target organ.  The focus of the analyses will depend on the stressors being evaluated  and
 the assessment and measurement endpoints.

        The temporal and spatial scales used to evaluate the stressor need to be compatible with the
 characteristics of the ecological component of interest. A temporal scale may encompass the lifespan
 of a species, a particular life stage, or a particular cycle, for example, the long-term succession of a
 forest community.  A spatial scale may encompass a forest, a lake, a watershed, or an entire regioa
 Stressor timing relative to organism life stage and activity patterns can greatly influence the occurrence
 of adverse effects.  Even short-term events may be significant if they coincide with critical life stages.
 Periods of reproductive activity may be especially important, because early life stages often are more
 sensitive to stressors, and adults also may be more vulnerable at this time.

        The most common approach to exposure analysis is to measure concentrations or amounts of a
 stressor and combine them with assumptions about co-occurrence, contact, or uptake. For example,
 exposure of aquatic organisms to chemicals often is expressed simply as concentration in the water
 column; aquatic organisms are assumed to contact the chemical.  Similarly,  exposures of organisms to
 habitat alteration often is expressed as hectares of habitat altered; organisms that utilize the habitat are
 assumed to co-occur with the alteration. Stressor measurements can also be combined with
 quantitative parameters describing the  frequency and magnitude of contact.  For example,
 concentrations of chemicals in food  items can be combined with ingestion rates to estimate dietary
 exposure of organisms.

        In some situations, the stressor can be measured at the actual point of contact while exposure
 occurs.   An example is the use of food collected from the mouths of nestling birds to evaluate
 exposure to pesticides through contaminated food (Kendall, 1991).  Although such point-of-contact
 measurements can be difficult to obtain, they reduce the need for assumptions about the frequency and
 magnitude  of contact.

       Patterns of exposure can be described using models that combine abiotic ecosystem attributes,
 stressor properties, and ecological component characteristics.  Model selection is based on the model's
 suitability for the ecosystem or component of interest, the availability of the requisite data, and the
 study objectives.  Model choices range from simple, screening-level procedures that require a
minimum of data to more sophisticated methods that describe processes in more detail but require a
considerable amount of data.

       Another approach to evaluating exposure uses chemical, biochemical, or physiological
evidence (e.g., biomarkers) of a previous exposure.  This approach has been used primarily for
assessing chemical exposures  and is  particularly useful when a residue or biomarker is diagnostic of
exposure to a particular chemical. These types of measurements are most useful for exposure

                                             20

-------
 characterization when they can be quantitatively linked to the amount of stressor originally contacted
 by the organism. Phaimacokinetic models are sometimes used to provide this linkage.

 3.1.4. Exposure Profile

        Using information obtained from the exposure analysis, the exposure profile quantifies the
 magnitude and spatial and temporal patterns of exposure for the scenarios developed during problem
 formulation and serves as input to risk characterization.  The exposure profile is only effective when
 its results are compatible with the stressor-response profile.  For example, appraisals of potential acute
 effects of chemical exposure may be averaged over short time periods to account for short-term pulsed
 stressor events.  It is important that characterizations for chronic stressors account for both long-term
 low-level exposure and possible shorter term higher level contact that may elicit similar adverse
 chronic effects.

        Exposure profiles can be expressed using a variety of units. For chemical stressors operating
 at the organism level, the usual metric is expressed in dose units (e.g., mg/kg body weight/day).  For
 higher levels of organization (e.g., an entire ecosystem), exposure may be expressed in units of
 concentration/unit area/time. For physical disturbance, the exposure profile may be expressed in other
 terms (e.g., percentage of habitat removed or the extent of flooding/year).

        An uncertainty assessment is an integral part of the characterization of exposure. In the
 majority of assessments, data will not be available for all aspects of the characterization of exposure,
 and those data that are available may be of questionable or unknown quality.  Typically, the assessor
 will have to rely on a number of assumptions with varying degrees of uncertainty associated with
 each. These assumptions will be based on a combination of professional judgment, inferences based
 on analogy with similar chemicals and conditions and estimation techniques, all of which contribute to
 the overall uncertainty. It is important that the assessor characterize each of the various sources of
 uncertainty and carry them  forward to the risk characterization so that they may be combined wifli a
 similar analysis conducted as part of the characterization of ecological effects.

 3.2. Characterization of Ecological Effects

       The relationship between the  stressor and the assessment and measurement endpoints identified
 during problem formulation is analyzed in characterization of ecological  effects (figure 3).  The
 evaluation begins with the evaluation of effects data that are relevant to the stressor. During
 ecological response analysis, the relationship between the stressor and the ecological effects elicited  is
 quantified, and cause-and-effect relationships are evaluated.  In addition,  extrapolations from
 measurement endpoints to assessment endpoints are conducted during this phase.  The product is a
 stressor-response profile that quantifies and summarizes the relationship of the stressor to the
 assessment endpoint. The stressor-response profile is then used as input  to risk characterization.

3.2.1. Evaluation of Relevant Effects Data

       The type of effects  data that are evaluated depends largely on the nature of the stressor and the
ecological component under evaluation.  Effects elicited by a stressor may range from mortality and
reproductive impairment in  individuals and populations to disruptions in community and ecosystem
function such as primary productivity. The evaluation process relies on professional judgment,
                                              21

-------
 especially when few data are available or when choices among several sources of data are required.  If
 available data are inadequate, new data may be needed before the assessment can be completed.

        Data are evaluated by considering their relevance to the measurement and assessment
 endpoints selected during problem formulation. The analysis techniques that will be used also are
 considered; data that minimize the need for extrapolation are desirable. Data quality (e.g., sufficiency
 of replications, adherence to good laboratory practices) is another important consideration. Finally,
 characteristics of the ecosystem potentially at risk will influence what data will be used. Ideally, the
 test system reflects the physical attributes of the ecosystem and will include the ecological components
 and life stages examined in the risk assessment

        Data from both field observations and experiments in controlled settings can be used to
 evaluate ecological effects. In some cases, such as for chemicals that have yet to be manufactured, test
 data for the specific stressor are not available. Quantitative structure-activity relationships (QSARs)
 are useful in these situations (Auer et al., 1990; Clements et al., 1988; McKim et al., 1987).

        Controlled laboratory and field tests (e.g., mesocosms) can provide strong causal evidence
 linking a stressor with a response and can also help discriminate between multiple stressors.  Data
 from laboratory studies tend to be less variable than those from field studies, but because
 environmental factors are controlled, responses may differ from those in the natural environment

        Observational field studies (e.g.,  comparison with reference sites) provide environmental
 realism that laboratory studies lack, although the presence of multiple stressors  and other confounding
 factors (e.g., habitat quality) in the natural environment can make it difficult to attribute observed
 effects to specific stressors. Confidence  in causal relationships can be improved by carefully selecting
 comparable reference sites or by evaluating changes along a stressor gradient where differences in
 other environmental factors are minimized. It is important to consider potential confounding factors
 during the analysis.

 3.2.2.  Ecological Response Analyses

        The data used in characterization of ecological effects are analyzed to quantify the stressor-
 response relationship and to evaluate the evidence for causality. A variety of techniques may be used,
 including statistical methods and mathematical modeling. In some cases,  additional analyses to relate
 the measurement endpoint to the assessment endpoint may be necessary.

        Stressor-Response Analyses

        The stressor-response analysis describes the  relationship between the magnitude, frequency, or
 duration of the stressor in an observational or experimental setting and the magnitude of response.
The stressor-response analysis may focus on different aspects of the stressor-response relationship,
depending on the assessment objectives, the conceptual model, and the type of data used for the
 analysis.  Stressor-response analyses, such as those used for toxicity tests, often portray the magnitude
of the  stressor with respect to the magnitude of response. Other important aspects to consider include
the temporal (e.g., frequency, duration, and timing) and spatial distributions of the stressor in the
experimental or observational setting.  For physical stressors, specific attributes of the environment
after disturbance (e.g., reduced forest stand age) can be related to the response (e.g., decreased use by
spotted owls) (Thomas et al., 1990).
                                               22

-------
        Analyses Relating Measurement and Assessment Endpoints
        Ideally, the stressor-response
evaluation quantifies the relationship between
the stressor and the assessment endpoint.
When the assessment endpoint can be
measured, this analysis is straightforward.
When it cannot be measured, the relationship
between the stressor and measurement
endpoint is established first, then additional
extrapolations, analyses,  and assumptions are
used to predict or infer changes in the
assessment endpoint  The need for analyses
relating measurement and assessment endpoints
also may be identified during risk
characterization, after an initial evaluation of
risk.

        Measurement endpoints are related to
assessment endpoints using the logical
structure presented in the conceptual model.
In some cases, quantitative methods and
models are available, but often the relationship
can be described only qualitatively. Because
of the lack of standard methods for many of
these analyses, professional judgment is an
essential component of the evaluation. It is
important to clearly explain the rationale for
any analyses and assumptions.

        Extrapolations commonly used include
those between species, between responses,
from  laboratory to field,  and from field to
field. Differences in responses among taxa
depend on many  factors, including physiology,
metabolism, resource utilization, and life
history  strategy.  The relationship between
responses also depends on many factors,
including the mechanism of action and internal
distribution of the stressor within the  organism.
When extrapolating between different
laboratory and field settings, important
considerations include differences in the
physical environment and organism behavior
that will alter exposure, interactions with other
stressors, and interactions with other ecological
components.
  Extrapolations and Other Analyses Relating
    Measurement and Assessment Endpoints

Extrapolation Between Taxa

example: from bluegill sunfish mortality to
rainbow trout mortality

Extrapolation Between Responses

example: from bobwhite quail LC50 to bobwhite
quail NOEL (no observed effect level)

Extrapolation From Laboratory to Field

example: from mouse mortality under laboratory
conditions to mouse mortality in the field

Extrapolation From Field to Field

example: from reduced invertebrate community
diversity in one stream to  another stream

Analysis of Indirect Effects

example: relating removal of long-leaf pine to
reduced populations of red-cockaded woodpecker

Analysis of Higher Organizational Levels

example: relating reduced individual fecundity to
reduced population size

Analysis of Spatial and Temporal Scales

example: evaluation of the loss of a specific
wetland used by migratory birds in relation to the
larger scale habitat requirements of the species

Analysis of Recovery

example: relating short-term mortality to long-
term depauperation
                                               23

-------
        In addition to these extrapolations, an evaluation of indirect effects, other levels of
organization, other temporal and spatial scales, and recovery potential may be necessary. Whether
these analyses are required in a particular risk assessment will depend on the assessment endpoints
identified during problem formulation.

        Important factors to consider when evaluating indirect effects include interspecies interactions
(e.g., competition, disease), trophic-level relationships (e.g., predation), and resource utilizatioa
Effects on higher (or lower) organizational levels depend on the severity of the effect, the number and
life stage of organisms affected, the role of those organisms hi the community or ecosystem, and
ecological  compensatory mechanisms.

        The implications of adverse effects at spatial scales beyond the immediate area of concern may
be evaluated by considering ecological characteristics such as community structure and energy and
nutrient dynamics.  In addition, information from the characterization of exposure on the stressor's
spatial distribution may be useful.  Extrapolations between different temporal scales (e.g., from short-
term impacts to long-term effects) may consider the stressors' distribution through time (intensity,
duration, and frequency) relative to ecological dynamics (e.g., seasonal cycles, life cycle patterns).

        In  some cases, evaluation of long-term impacts will require consideration of ecological
recovery. Ecological recovery is difficult to predict and depends on the existence of a nearby source
of organisms, life history and dispersal strategies of the ecological components, and the chemical-
physical environmental quality following exposure to the stressor (Cairns, 1990; Poff and Ward, 1990;
Kelly and Harwell, 1990).  hi addition, there is some evidence to suggest that the types and frequency
of natural disturbances can influence the ability of communities to recover  (Schlosser, 1990).
                                              24

-------
       Evaluation of Causal Evidence

       Another important aspect of the ecological response analysis is to evaluate the strength of the
causal association between the stressor and the measurement and assessment endpoints. This
information supports and complements the stressor-response assessment and is of particular importance
when the stressor-response relationship is based on field observations.  Although proof of causality is
not a requirement for risk assessment, an evaluation of causal evidence augments the risk assessment
Many of the concepts applied in human epidemiology can be useful for evaluating causality in
observational field studies. For example, Hill (1965) suggested nine evaluation criteria for causal
associations.  An example of ecological causality analysis was provided by Woodman and Cowling
(1987), who evaluated the causal association between air pollutants and injury to forests.
                  Hill's Criteria for Evaluating Causal Associations (Hill, 1965)

  1. Strength: A high magnitude of effect is associated with exposure to the stressor.

  2. Consistency: The association is repeatedly observed under different circumstances.

  3. Specificity: The effect is diagnostic of a stressor.

  4. Temporality: The stressor precedes the effect in time.

  5. Presence of a biological gradient: A positive correlation between the stressor and response.

  6. A plausible mechanism of action.

  7. Coherence: The hypothesis does not conflict with knowledge of natural history and biology.

  8. Experimental evidence.

  9. Analogy: Similar stressors cause similar responses.

  Not all of these criteria must be satisfied, but each incrementally reinforces the argument for
  causality. Negative evidence does not rule out a causal association but may indicate incomplete
  knowledge of the relationship (Rothman, 1986).                            	
                                               25

-------
3.23. Stressor-Response Profile

        The results of the characterization of ecological effects are summarized in a stressor-response
profile that describes the stressor-response relationship, any extrapolations and additional analyses
conducted, and evidence of causality (e.g., field effects data).

        Ideally, the stressor-response relationship will relate the magnitude,  duration, frequency, and
timing of exposure in the study setting to the magnitude of effects.  For practical reasons, the results
of stressor-response curves are often summarized as one reference point, for instance, a 48-hour LC50.
Although useful, such values provide no information about the slope or shape of the stressor-response
curve. When the entire curve is used, or when points on the curve are identified, the difference in
magnitude  of effect at different exposure levels can be reflected in risk characterization.

        It is important to clearly describe and quantitatively estimate the assumptions and uncertainties
involved in the evaluation, where  possible.  Examples include  natural variability in ecological
characteristics and responses and uncertainties in the test system and extrapolations.  The description
and analysis of uncertainty in characterization of ecological effects are combined with uncertainty
analyses for the other ecological risk assessment elements during risk characterization.
                                             26

-------
o
o *
o
o
o
               Additional Issues Related to the Analysis Phase
                •v f           *•  .  . . f sf. . . JtJf. . -f  f      ...
_ - Quantifying cumulative impacts and sttess-fesponse
  '/-*'  lA'-~ _:„-. "";--7--" '"  ""-{-'  '  N
 , Improving |he pi^sdietion ol eoc^ysteai^cove^
  '                       "    ' '   ,   ":       -,".
                              of lodiieot ejects,
                                         for
' Improving Ifce
 Distiftguishtag ecosystem changes due to natural processes from Hiose caused by
 ,  ••  \, vc& -' '   '•   ''   ""   *           „',,	           "	
                                    27

-------
4.  RISK CHARACTERIZATION

       Risk characterization (figure 4) is the final phase of risk assessment.  During this phase, the
likelihood of adverse effects occurring as a result of exposure to a stressor are evaluated. Risk
characterization contains two major steps: risk estimation and risk description. The stressor-response
profile and the exposure profile from the analysis phase serve as input to risk estimation. The
uncertainties identified during all phases of the risk assessment also are analyzed and summarized.
The estimated risks are discussed by considering the types and magnitude of effects anticipated, the
spatial and temporal extent of the effects, and recovery potential. Supporting information in the form
of a weight-of-evidence discussion also is presented during this step.  The results of the risk
assessment, including the relevance of the identified risks to the original goals of the risk assessment,
then are discussed with the risk manager.

4.1. Risk Estimation

       Risk estimation consists of comparing the exposure and stressor-response profiles as well as
estimating and summarizing the associated uncertainties.

4.1.1.  Integration of Stressor-Response and Exposure Profiles

       Three  general approaches are discussed to illustrate the integration of the stressor-response and
exposure profiles:  (1) comparing single effect and exposure values; (2) comparing distributions of
effects and exposure; and (3) conducting simulation modeling. Because these are areas of active
research, particularly in the assessment of community- and landscape-level perturbations,  additional
integration approaches  are likely to be available in the future. The final choice as to which approach
will be selected depends on the original purpose of the assessment as well as time and data constraints.

       Comparing Single Effect and Exposure Values

       Many  risk assessments compare single effect values with predicted or measured levels of the
stressor.  The  effect values from the stressor-response profile may be used as is, or more commonly,
uncertainty or safety factors may be used to adjust the value.  The ratio or quotient of the exposure
value to the effect value provides the risk estimate.  If the quotient is one or more, an adverse effect is
considered likely to occur.  This approach, known as the Quotient Method (Barnthouse  et al.,  1986),
has been used extensively to evaluate the risks of chemical stressors (Nabholz  1991; Urban  and Cook,
1986). Although the Quotient Method is commonly used and accepted, it is the least probabilistic of
the approaches described here.   Also, correct usage of the Quotient Method is highly dependent on
professional judgment,  particularly in instances when the quotient approaches  one.  Greater  insight into
the magnitude of the effects expected at various levels of exposure can be obtained by evaluating the
full stressor-response curve instead of a single point and by considering the frequency, timing, and
duration of the exposure.
                                              28

-------
c
D
X S
xx »*=
X
X
X
X
X
^
s
- *

i!l




J PROBLEM FORMULATION
~| ANALYSIS
|| »RISK CHARACTERIZATION
N
X
X
X
X
X
X
ANALYSIS

/'



X-x
"

"


'
,
•.
:

-




Risk Estimation
Integration


'
Risk Description







Uncertainty
Analysis




Ecological

Risk

Summary

t

Interpretation

of

Ecological
Significance


,' '








.



































O
Pi
to

c
5|
o
3
«• •
•t
p"
a
0
0>
Q.
s
o
0
5'
(Q
t


1
Discussion Between the |
Risk Assessor and
Risk Manager i
(Results) j

Risk
t
1
1
Management -^— — — — — — — — J
Figure 4.  Risk Characterization




             29

-------
        Comparing Distributions of Effects and Exposure

        This approach uses distributions of effects and exposure (as opposed to single values) and thus
 makes probabilistic risk estimates easier to develop.  Risk is quantified by the degree of overlap
 between the two distributions; the more overlap, the greater the risk.  An example of this approach,
 Analysis of Extrapolation Error, is given in Barnthouse et al. (1986).  To construct valid distributions,
 it is important that sufficient data amenable to statistical treatment are available.

        Conducting Simulation Modeling

        Simulation models that can integrate both the stressor-response profile and exposure profile are
 useful for obtaining probabilistic estimates of risk. Two categories of simulation models are used for
 ecological risk assessment: single-species population models  are used to predict direct effects on a
 single population of concern using measurement endpoints at the individual level, while multi-species
 models include aquatic food web models and terrestrial plant succession models and are useful for
 evaluating both direct and indirect effects.

        When selecting a model, it is important to determine the appropriateness of the model for a
 particular application. For example, if indirect effects are of concern, a model of community-level
 interactions will be needed. Direct effects to a particular population of concern may  be better
 addressed with population models.  The validation status and use history of a model also are important
 considerations in model selection. Although simulation models are not commonly used for ecological
 risk assessment at the present time, this is an area of active research, and the use of simulation models
 is likely to increase.

        In addition to providing  estimates of risks, simulation models  also can be useful in discussing
 the results of the risk characterization to the risk manager.  This dialogue is particularly effective when
 the relationship between risks to certain measurement endpoints and the assessment endpoint are not
 readily apparent (e.g., certain indirect effects and large-scale ecosystem-level disturbances).

 4.1.2.  Uncertainty

        The uncertainty analysis identifies, and, to the extent possible, quantifies the uncertainty in
 problem formulation,  analysis, and risk characterization.  The uncertainties from each of these phases
 of the process are carried through as part of the total uncertainty in the risk assessment. The output
 from the uncertainty analysis is an evaluation of the impact of the uncertainties on the overall
 assessment and, when feasible, a description of the ways in which uncertainty could be reduced.

       A complete discussion of uncertainty is beyond the scope of this report, and the reader is
 referred to  the works of Finkel (1990), Rolling (1978), and Suter (1990b).  However,  a brief
 discussion of the  major sources  of uncertainty in ecological risk assessment is appropriate.  For
 illustrative purposes, four major areas of uncertainty are presented below.  These are not discrete
categories,  and  overlap does exist among them.  Any specific risk assessment may have uncertainties
in one or all of these categories.
                                              30

-------
       Conceptual Model Formulation

       As noted earlier, the conceptual model is the product of the problem formulation phase, which,
in turn, provides the foundation for the analysis phase and the development of the exposure and
stressor-response profiles.  If incorrect assumptions are made during conceptual model development
regarding the potential effects of a stressor, the environments impacted, or the species residing within
tiiose systems, then the final risk assessment will be flawed.  These types of uncertainties are perhaps
the most difficult to identify, quantify, and reduce.

       Information and Data

       Another important contributor of uncertainty is the incompleteness of the data or information
upon which the risk assessment is based.  In some instances, the risk assessment may be halted
temporarily until additional information is obtained. In other cases, certain basic information such as
life history data may be unobtainable with the resources available to the risk assessment  In yet other
cases,  fundamental understanding of some natural processes with an ecosystem may be lacking.  In
instances where additional information cannot be obtained, the role of professional judgment and
judicial use of assumptions are critical for the completion of the assessment

        Stochasticity (Natural Variability)

        Natural variability is a basic characteristic of stressors and ecological components as well as
the factors that influence their distribution (e.g., weather patterns, nutrient availability). As noted by
Suter (1990b), of all the contributions to uncertainty, Stochasticity is the only one that can be
acknowledged and described but not reduced. Natural variability is amenable to quantitative analyses,
including Monte Carlo simulation and statistical uncertainty analysis (O'Neill and Gardner, 1979;
O'Neill et al., 1982).

        Error

        Errors can be introduced through experimental design or the procedures used for measurement
 and sampling. Such errors can be  reduced by adherence to good laboratory practices and adherence to
 established experimental protocols.  Errors also can be introduced during simulation model
 development. Uncertainty in the development and use of models can be reduced through sensitivity
 analyses, comparison with similar models, and field validation.

        hi summary, uncertainty analyses provide the risk manager with an insight into the strengths
 and weaknesses of an assessment  The uncertainty analysis also can serve as a basis for making
 rational decisions regarding alternative actions as well as for  obtaining additional information to  reduce
 uncertainty in the risk estimates.

 4.2.  Risk Description

         Risk description has two primary elements.  The first is the ecological risk summary, which
 summarizes the results of the risk  estimation and uncertainty analysis and assesses confidence in the
 risk estimates through a discussion of the weight of evidence. The second element is interpretation of
 ecological significance, which describes the magnitude  of the identified risks to the assessment
 endpoint.

                                               31

-------
 4.2.1. Ecological Risk Summary

        The ecological risk summary summarizes the results of the risk estimation and discusses the
 uncertainties associated with problem formulation, analysis, and risk characterization. Next, the
 confidence in the risk estimates is expressed through a weight-of-evidence discussion.  The ecological
 risk summary may conclude  with an identification of additional analyses or data that might reduce the
 uncertainty in the risk estimates.  These three aspects of the ecological risk summary are discussed in
 the following sections.

        Summary of Risk Estimation and Uncertainty

        Ideally, the conclusions of the risk estimation are described as some type of quantitative
 statement (e.g., there is a 20  percent chance of 50 percent mortality).  However, in most instances,
 likelihood is expressed in a qualitative statement (e.g., there is a high likelihood of mortality
 occurring).  The uncertainties identified during the risk assessment are summarized either
 quantitatively or qualitatively, and the relative contribution of the various uncertainties to the risk
 estimates are discussed whenever possible.

        Weight of Evidence

        The weight-of-evidence discussion provides the risk manager with insight about the confidence
of the conclusions reached in the risk assessment by comparing the positive and negative aspects of
the data, including uncertainties identified throughout the process.  The considerations listed below are
useful in a weight-of-evidence discussion:

        •      The sufficiency and quality of the data. A risk assessment conducted with studies that
               completely characterize both the effects and exposure of the stressor has more
               credibility and support than an assessment that contains data gaps.  It is important to
               state if the data at hand were sufficient to support the findings of the assessment.  In
               addition, data validity (e.g., adherence to protocols, having sufficient replications) is an
               important facet of the weight-of-evidence analysis.

        •      Corroborative information.  Here the assessor incorporates supplementary information
               that is relevant to the conclusions reached in the assessment  Examples include
               reported incidences of effects elicited by the stressor (or similar stressor) and studies
               demonstrating agreement between model predictions and observed effects.

       •      Evidence of causality. The degree of correlation between the  presence of a stressor
               and some adverse effect is  an important consideration for many  ecological risk
               assessments.  This correlation is particularly true when an assessor is attempting to
               establish a link between certain observed field effects and the  cause of those effects.
               Further discussions of the evaluation of causal relationships may be found in the
               section on characterization of ecological effects (section 3.2.2.).
                                              32

-------
       Identification of Additional Analyses

       The need for certain analyses may not be identified until after the risk estimation step. For
example, the need to analyze the risks to a fish population (an assessment endpoint) due to an indirect
effect such as zooplankton mortality (a measurement endpoint) may not be established until after the
risk to zooplankton has been characterized. In such cases, another iteration through analysis or even
problem formulation may be necessary.

4.22.  Interpretation of Ecological Significance

       The interpretation of ecological significance places risk estimates in the context of the types
and extent of anticipated effects. It provides a critical link between the estimation of risks and the
communication of assessment results. The interpretation step relies on professional judgment and may
emphasize different aspects depending on the assessment Several aspects of ecological significance
that may be considered include the nature and magnitude of the effects, the spatial and temporal
patterns of the effects, and the potential for recovery once a stressor is removed.

       Nature and Magnitude of the Effects

       The relative significance of different effects may require further interpretation, especially when
changes in several assessment or measurement endpoints are observed or predicted.  For example, if a
risk assessment is concerned with the effects of stressors on several ecosystems in an area (such as a
forest, stream, and wetland), it is important to discuss the types of effects associated with each
ecosystem and where the greatest  impact is likely to occur.

       The magnitude of an effect will depend on its ecological context  For example, a reduction in
the reproductive rate may have little effect on a population that reproduces rapidly, but it may
dramatically reduce the numbers of a population that reproduces slowly.  Population-dependent and -
independent factors in the ecosystem also may influence the expression of the effect

       Finally, it is important to consider the effects in the context of both magnitude and the
likelihood of the effect occurring. In some cases, the likelihood of exposure to a stressor may be low,
but the effect resulting from the exposure would be devastating. For example, large oil spills may not
be common, but they can cause severe and extensive effects hi ecologically sensitive areas.

        Spatial and Temporal Patterns of the Effects

        The spatial and temporal distributions of the effect provide another perspective important to
interpreting ecological significance.  The extent of the area where the stressor is likely to occur is a
primary consideration when evaluating the spatial pattern of effects.  Clearly, a stressor distributed
over a larger area has a greater potential to affect more organisms than one confined to a small area.
However, a stressor that adversely affects small areas can have devastating effects if those areas
provide critical resources for certain species.  In addition, adverse effects to a resource that is small in
scale (e.g., acidic bogs) may have a small spatial effect but may represent a significant degradation of
the resource because of its overall scarcity.
                                              33

-------
         The duration of any effect is dependent on the persistence of the stressor as well as how often
 the stressor is likely to occur in the environment. It is important to remember that even short-term
 effects can be devastating if such exposure occurs during critical life stages of organisms.

         Recovery Potential

         A discussion of the recovery potential may be an integral part of risk description, although the
 need for such an evaluation will depend on the objective of the assessment and the assessment
 endpoints.  An evaluation of the recovery potential may require additional analyses, as discussed in
 section 3.1., and will depend on the nature, duration, and  extent of the stressor.

        Depending on the assessment objectives, all of the above factors may be used to place the
 risks into the broader ecological context. This discussion may consider the ramifications of the effects
 on other ecological components that were not specifically addressed in the assessment.  For example,
 an assessment that focused on the decline of alligator populations may include a discussion of the
 broader ecological role of the alligator, such as the construction of wallows that act as water reservoirs
 during droughts. In this way, the potential effects on the community that depends on the alligator
 wallows can be brought out hi risk characterization.

 43. Discussion Between the Risk Assessor and Risk Manager (Results)

        Risk characterization concludes the risk assessment process and provides the basis for
 discussions between the risk assessor and risk manager that pave the way for regulatory decision-
 making. The purpose of these discussions is to ensure that the results of the risk assessment are
 clearly and fully presented and to provide an opportunity for the  risk manager to ask for any necessary
 clarification.  Proper presentation of the risk assessment is essential to reduce the chance of over- or
 under-interpretation of the results. To permit the risk manager to evaluate the full  range of
 possibilities contained in the risk assessment, it is important that the risk assessor provide the
 following types of information:

        »      the goal of the risk assessment;

        •      the connection between the measurement and assessment endpoints;

        «      the magnitude and extent of the effect, including spatial and temporal considerations
               and,  if possible, recovery potential;

        •      the assumptions used and the uncertainties encountered during the risk assessment;

        »      a summary profile of the degrees  of risk as well as a weight-of-evidence analysis; and

        •      the incremental risk from stressors omer than those already under consideration (if
               possible).

The results of the risk assessment serve as input to the risk management process, where they are used
along with other inputs defined in EPA statutes, such as social and economic concerns, to evaluate risk
management options.
                                              34

-------
       In addition, based on the discussions between the risk assessor and risk manager, follow-on
activities to the risk assessment may be identified, including monitoring, studies to verify the
predictions of the risk assessment, or the collection of additional data to reduce the uncertainties in the
risk assessment. While a detailed discussion of the risk management process is beyond the scope of
this report, consideration of the basic principles of ecological risk assessment described here will
contribute to  a final product that is both credible  and germane to the needs of the risk manager.
                                               35

-------
0
a
o
a
o
         "*              s      '$'• -1              *•
       Additional Issues Related to the jRisJc Characterization Phase
              *%s.-- -" *      >*Vv\  "?.'-,'   ,4     %/
            .  . ,f  . „ ,ff  ^ :   •. ff£v,^ •-   ^     fr,^.    -. „  ^^ /„    ss,,^^  : f   f
         '"" \ " "'"""^ "* "*   XV"-"^^"  ^fv  ,r',41.,'   5f , "#,,^  '
Predicting ^etiase jrequired'fojf aa^eplogicd i»|>Dneot lo «:covey from a
            ""  % ^  -          /v-i- fffjj •>   r  '     f f s '     f s
Combining clje«tleal and uonchemicdt stressots in risk characterization,
          :.   ,.,.:..   >  '.'<•    -^,;        /     :  .   ,:^
              odltioal ^Teot levels iMo risk
                                                         in risk
                                          36

-------
5. KEY TERMS

assessment endooint-An explicit expression of the environmental value that is to be protected.

characterization of ecological effects-A portion of the analysis phase of ecological risk assessment that
       evaluates the ability of a stressor to cause adverse effects under a particular set of
       circumstances.

characterization of exposure-A portion of the analysis phase of ecological risk assessment that
       evaluates the interaction of the stressor with one or more ecological components.  Exposure
       can be expressed as co-occurrence, or contact depending on the stressor and ecological
       component involved.

communitv-An assemblage of populations of different species within a specified location in space and
       time.

conceptual model-The conceptual model describes a series of working hypotheses of how the stressor
       might affect ecological components.  The conceptual model also describes the ecosystem
        potentially at risk, the relationship between measurement and assessment endpoints, and
        exposure scenarios.

direct effect-An effect where the stressor acts on the ecological component of interest itself, not
        through effects on other components of the ecosystem (compare with definition for  indirect
        effect).

 ecological component-Any part of an ecological system, including individuals, populations,
        communities, and the ecosystem itself.

 ecological risk assessment-The process that evaluates the likelihood that adverse ecological effects
        may occur or are occurring as a result of exposure to one or more stressors.

 ecosystem-The biotic community and abiotic environment within a specified location in space and
        time.

 exposure-Co-occurrence of or contact between a stressor and an ecological component.

 exposure profile-The product of characterization of exposure in the analysis phase of ecological risk
         assessment. The exposure profile summarizes the magnitude  and spatial and temporal patterns
         of exposure for the scenarios described in the conceptual model.

 exposure scenario-A set of assumptions concerning how a exposure may take place, including
         assumptions about the exposure setting, stressor characteristics, and activities that may lead to
         exposure.

  indirect effect-An effect where the stressor acts on supporting components Of the ecosystem, which in
         turn have an effect on the ecological component of interest
                                               37

-------
 measurement endpoint—A measurable ecological characteristic that is related to the valued
        characteristic chosen as the assessment endpoint  Measurement endpoints are often expressed
        as the statistical or arithmetic summaries of the observations that comprise the measurement

 median lethal concentration (LCmV-A statistically  or graphically estimated concentration that is
        expected to be lethal to 50 percent of a group of organisms under specified conditions (ASTM,
        1990).

 no observed effect level (NOELV-The highest level of a stressor evaluated in a test that does not cause
        statistically significant differences from  the controls.

 population—An aggregate of individuals of a species within a specified location in space  and time.

 recovery—The partial or full return of a population or community to a condition that existed before the
        introduction of the stressor.

 risk characterization-A phase of ecological risk assessment that integrates the results of the exposure
        and ecological effects analyses to evaluate the likelihood of adverse ecological effects
        associated with  exposure to a stressor.  The ecological significance of the adverse effects is
        discussed, including consideration of the types  and magnitudes of the effects, their spatial and
        temporal patterns, and the likelihood of  recovery.

 stressor-Anv physical, chemical, or biological entity that can induce an adverse response.

 stressor-response prpfile-The product of characterization of ecological effects in the analysis phase of
        ecological risk assessment.  The stressor-response profile summarizes the data on the effects of
        a stressor and the relationship of the data to the assessment endpoint

trophic levels—A functional classification  of taxa within a community that is  based on feeding
        relationships (e.g., aquatic and terrestrial green plants comprise the first trophic level and
        herbivores comprise the second).

xenobiotic-A chemical or other stressor that does not occur naturally hi the environment.  Xenobiotics
        occur as a result of anthropogenic activities such as the application of pesticides and the
        discharge of industrial chemicals to air, land, or water.
                                              38

-------
6. REFERENCES

American Society for Testing and Materials.  (1990).  Standard terminology relating to biological
       effects and environmental fate.  E943-90. M:  ASTM: 1990 Annual Book of ASTM
       Standards. Section 11, Water and Environmental Technology,  ASTM, Philadelphia, PA.

ASTM, See American Society for Testing and Materials.

Auer, C.M.; Nabholz, J.V.; Baetcke, K.P. (1990). Mode of action and the assessment of chemical
       hazards in the presence of limiting data:  use of structure-activity relationships (SAR) under
       TSCA. Section 5. Environmental Health Perspectives (87):183-197.

Bamthouse, L.W.; Suter, G.W., II; Bartell, S.M.; Beauchamp, J.J.; Gardner, R.H.; Linder, E.; O'Neill,
       R.V.; Rosen, A.E.  (1986). User's Manual for Ecological Risk Assessment.  Publication No.
       2679, ORNL-6251.  Environmental Sciences Division, Oak Ridge National Laboratory, Oak
       Ridge, TN.

Cairns, J., Jr.  (1990). Lack of theoretical basis  for predicting rate and pathways of recovery. In:
       Yount, J.D.; Niemi, G.J., eds. Recovery of Lotic Communities and Ecosystems Following
       Disturbance: Theory and Application.   Environmental Management 14(5):517-526

Clements, R.G.; Johnson, D.W.; Lipnick, R.L.; Nabholz, J.V.; Newsome, L.D.  (1988).  Estimating
       toxicity of industrial chemicals to aquatic organisms using structure activity relationships.
       EPA-560-6-88-001. U.S. Environmental  Protection Agency, Washington, DC. (available from
       NTIS, Springfield, VA, PB89-117592.)

Finkel, A.M.  (1990). Confronting Uncertainty  in Risk Management: A Guide for Decision-Makers.
        Center for Risk Management, Resources for the Future, Washington, DC.

Hill, A.B.  (1965).  The environment and disease: association or causation? Proceedings of the Roval
        Society of Medicine.  58:295-300.

 Holling, C.S.  (1978). Adaptive Environmental  Assessment and Management.  John Wiley and Sons,
        New York, NY.

 Kelly, J.R.; Harwell, M.A.  (1990).  Indicators of ecosystem recovery.  In: Yount, J.D.; Niemi, G.J.,
        eds.  Recovery of Lotic Communities and Ecosystems Following Disturbance:  Theory and
        Application. Environmental Management 14(5):527-546

 Kendall, R.J.  (1991). Ecological risk assessment for terrestrial wildlife exposed to agrochemicals: a
        state-of-the-art review and recommendations for the future. Presented  at the Ecological Risk
        Assessment Workshop sponsored by the National Academy of Sciences Committee on Risk
        Assessment Methodology, 26 Feb -1 Mar 1991.

 McKim, J.M.; Bradbury, S.P.; Niemi, GJ. (1987). Fish acute toxicity syndromes and their use in the
        QSAR approach to hazard assessment.  Environmental Health Perspectives 71:171-186.
                                              39

-------
 Nabholz, J.V. (1991).  Environmental hazard and risk assessment under the United States Toxic
        Substances Control Act. Science of the Total Environment 109/110:649-665.

 National Research Council. (1983). Risk Assessment in the Federal Government: Managing the
        Process. National Research Council, National Academy Press, Washington, DC.

 National Research Council. (1986).  Ecological Knowledge and Environmental Problem-Solving:
        Concepts and Case Studies. National Research Council, National Academy Press, Washington,
        DC.

 NRG.  See National Research Council.

 O'Neill, R.V.  (1979).  Natural variability as a source of error in model predictions.  In: Systems
        Analysis of Ecosystems. G.S. Innis and R.V. O'Neill eds.  International Cooperative
        Publishing House. Burtonsville, Maryland, pp 23-32.

 O'Neill, R.V.; Gardner, R.H.;  (1979).. Sources of uncertainty in ecological models. In: Methodology
        in Systems Modeling and Simulation. B.P. Zeigler, M.S. Elzas, GJ. Klir, and T.I. Orens eds..
        North Holland Publishing Company, pp 447-463.

 Poff, NJU; Ward, J.V.  (1990). Physical habitat template of lotic systems:  recovery in the context of
        historical pattern of spatiotemporal heterogeneity. In:  Yount, J.D.;  Niemi, G.J., eds.
        Recovery of Lotic Communities and Ecosystems Following Disturbance: Theory and
        Application.  Environmental Management 14(5):629-646.

 Rothman, KJ. (1986). Modern Epidemiology. 1st ed. Little, Brown and Company, Boston, MA.

 Schlosser, I.J.  (1990).  Environmental variation, life history attributes, and community structure in
        stream fishes: implications for environmental management and assessment. Environmental
        Management 14(5):621-628.

 SETAC. See Society of Environmental Toxicology and Chemistry.

 Society of Environmental  Toxicology and Chemistry.  (1987).  Research Priorities in Environmental
        Risk Assessment.  Report of a workshop held in Breckenridge, CO,  August 16-21, 1987.
        Society of Environmental Toxicology and Chemistry, Washington, DC.

Suter n, G.W. (1989).  Ecological endpoints. In: U.S. EPA. Ecological Assessments of Hazardous
        Waste Sites: A field and laboratory reference document  Warren-Hicks, W.; Parkhurst, B.R.;
        S.S. Baker, Jr. eds. EPA 600/3-89/013. March 1989.

Suter II, G.W. (1990a). Endpoints for regional ecological risk assessments. Environmental
       Management  14(l):19-23.

Suter II, G.W. (1990b). Uncertainty in environmental risk assessment hi: von Furstenberg, G.M., ed.
       Acting Under Uncertainty: Multidisciplinary Conceptions. Kluwer Academic Publishers!
       Boston, MA.  pp 203-230.
                                            4C

-------
Thomas, J.W.; Foreman, E.D.; Lint, J.B.; Meslow, B.C.; Noon, B.R.; J. Verner.  (1990).  A
       Conservation Strategy for the Spotted Owl.  Interagency Scientific Committee to  Address the
       Conservation of the Northern Spotted Owl.  1990-791/20026.  U.S. Government Printing
       Office, Washington, DC.

Urban, D.J.; Cook, N.J. (1986). Standard Evaluation Procedure for Ecological Risk Assessment.
       EPA/540/09-86/167, Hazard Evaluation Division, Office of Pesticide Programs, U.S.
       Environmental Protection Agency,  Washington, DC%

U.S. Department of the Interior. (1987).  Injury to fish and wildlife species. Type B Technical
       information document.  CERCLA 301 Project.  Washington, DC.

U.S. EPA.  See U.S.  Environmental Protection Agency.

U.S. Environmental Protection Agency. (1979). Toxic Substances Control Act.  Discussion of
       premanufacture testing policies and technical issues; Request for comment. 44 Federal
       Register 16240-16292.

U.S. Environmental Protection Agency. (1990a). Environmental Monitoring and Assessment
       Program.  Ecological Indicators.  EPA/600/3-90/060, Office of Research and Development,
       Washington,  DC.

U.S. Environmental Protection Agency. (1990b). Reducing Risk: Setting Priorities and  Strategies for
       Environmental Protection.  Science Advisory Board SAB-EC-90-021, 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 prcss-b).  Ecological Risk Assessment Guidelines Strategic
       Planning Workshop.  EPA/630/R-92/(K)2, Risk Assessment Forum, Washington, DC.

Woodman, J.N.; Cowling, E.B. (1987).  Airborne chemicals and forest health.  Environmental
       Science and Technology 21(2): 120-126.
                                             41

-------

-------

-------

-------

-------

-------