Applied Wetlands Science - Chapter 4 pot

Kent, David J. et al “Ecological Risk Assessment of Wetlands” Applied Wetlands Science and Technology Editor Donald M. Kent Boca Raton: CRC Press LLC,2001 ©2001 CRC Press LLC CHAPTER 4 Ecological Risk Assessment of Wetlands David J. Kent, Kenneth D. Jenkins, and James F. Hobson CONTENTS The Human Health Risk Assessment Paradigm Ecological Risk Assessment The Ecological Risk Assessment Framework Problem Formulation Phase Choosing Biological Endpoints Spatial and Temporal Considerations Other Considerations Analysis Phase Exposure Characterization Ecological Effects Characterization Risk Characterization Phase Predictive Ecological Assessments Problem Formulation Exposure Characterization Ecological Effects Characterization Risk Characterization The Quotient Method for Risk Characterization Retrospective Ecological Assessments Problem Formulation Exposure Characterization Ecological Effects Characterization Risk Characterization Summary References ©2001 CRC Press LLC Until recently, the term risk assessment generally was applied to the estimate of risk to human health, typically from chemical exposure. For example, a cancer risk assessment is an estimate of the risk to humans from carcinogenic compounds. Recently, however, the term risk assessment has been applied to ecological systems. An ecological risk assessment is an estimate of the adverse effect to an ecosystem from chemical, physical, or biological stressors resulting from anthropogenic activ- ity. This recent interest in assessing ecological health is evidenced by several pub- lications (Bartell et al., 1992; Cairns et al., 1992; Suter, 1993; Newman and Strojan, 1998; Lewis et al., 1999) including two documents produced by the U.S. Environ- mental Protection Agency (USEPA, 1992, 1998). The first of these USEPA documents, Framework for Ecological Risk Assessment (1992), was intended as the first step in a long-term program to develop guidelines for the performance of ecological risk assessments. The second document, Guidelines for the Ecological Risk Assess- ment , provided more detailed information and is the current guidance on the subject. The principles of ecological risk assessment can be applied to any ecosystem, although they may be particularly relevant to wetlands. The extent and rate of wetland loss, as well as the biologic, economic, and social importance of wetlands, are well documented (Mitsch and Gosselink, 1986). Moreover, the transitional nature of wetlands may make them especially sensitive to stress. Despite the uniform application of assessment principles to ecological systems, individual wetlands are sufficiently different in their spatial, temporal, and physiochemical characters to warrant site-specific sampling and analysis (Figures 1 and 2). These differences will influence the design and interpretation of the ecological risk assessment. Figure 1 Risk assessment can be broadly applied to a variety of ecosystems. Nevertheless, individual wetlands are sufficiently different in their spatial, temporal, and physic- ochemical characters to warrant site-specific samping and analysis. A New England saltmarsh is shown here. ©2001 CRC Press LLC To understand the use of ecological risk assessment for wetland ecosystems, an introduction to the principles of risk assessment is necessary. The current basis for risk assessment is derived from the National Research Council Risk Assessment paradigm (1983). Following this, an in-depth discussion of the USEPA Ecological Risk Assessment Framework (USEPA, 1992) is presented as is a discussion of the challenges and strategies associated with carrying out assessments. Finally, examples of specific applications to wetland ecosystems are provided. THE HUMAN HEALTH RISK ASSESSMENT PARADIGM The risk assessment paradigm has been used for some time to evaluate the chronic impacts of environmental pollutants on human health. This strategy was initially conceptualized by the National Research Council Risk Assessment Panel (NRC, 1983) and formalized by the USEPA in its 1986 Guidelines (USEPA, 1986a–e). This risk assessment paradigm consists of several components: Figure 2 An Arkansas riverine system wetland. ©2001 CRC Press LLC • Hazard identification: does a chemical contaminant represent a specific threat to human health? Establishment of cause–effect relationships is central to this component. • Defining dose–response: what is the relationship between the magnitude of the exposure and the probability of an adverse health effect? • Exposure assessment: what is the potential for human exposure to the chemical of concern? • Risk characterization: what is the potential magnitude of risk to human health given the predicted exposure and dose–response data? What is the uncertainty associated with this risk estimate? Standard methodologies are employed to evaluate potential threats to human health. The methodologies usually involve determining all relevant effects and then summing those effects to get a total effect value. ECOLOGICAL RISK ASSESSMENT Ecological risk assessments (ERA) examine the probability that undesirable ecological effects are occurring or may occur as a result of exposure to a stressor or a combination of stressors. The term stressors is used here to reflect the broad range of anthropogenic factors that can result in ecological perturbations. Stressors may include any chemical, physical, or biological factor resulting from anthropogenic activities that can cause an ecological disturbance. Most often, however, the term stressor refers to toxic chemicals. ERAs can be used to address a wide range of issues and are generally classified as predictive or retrospective. Predictive ERAs are designed to assess the risks associated with proposed actions, such as the introduction of new chemicals into the environment and the establishment of new sources of stressors or hypothetical accidents (USEPA, 1991). Predictive risk assessments have usually followed the NRC human health paradigm relatively closely while emphasizing the choice of biological endpoints and related stressor–response data. In contrast, retrospective ERAs address the risks associated with stressors released due to current or previous anthropogenic activities. Examples of retrospective assessments include evaluating the ecological impact of hazardous waste sites and previous releases or spills. The goal of this type of risk assessment is to establish and define the relationship between the pollution source, the distribution of stressors, the exposure of biological endpoints, and the level of effects of this exposure on the ecosystem. Retrospective assessments often take advantage of field data to define contaminant sources and measure adverse biological effect. Various levels of data collection or site-specific assessment may be necessary to provide the information required to design and conduct the retrospective ecological risk assessment, and to achieve a given level of confidence. The challenge here is to establish cause–effect relationships between the source of stressors and any observed ecological effects. Some ERAs, such as those used for wetlands, may involve both predictive and retrospective aspects. For example, in an assessment of a hazardous waste site, the ©2001 CRC Press LLC current status of the site may require a retrospective evaluation, but the long-term impact of various repetition scenarios would be addressed in a predictive fashion. As the type of risk assessment to be conducted is dependent upon the ultimate application of the results, a clear understanding of the objectives of the risk assessment is essential. The move to ERAs by the regulatory community is driven by a number of factors. From a legal standpoint, many of the underlying statutes require some form of evaluation of ecological risk. For example, the Superfund Amendment and Reautho- rization Act (1987) specifies that the actual and potential risk to public health and the environment must be assessed for each hazardous waste site. The use of a basic risk assessment paradigm would provide a structural framework for ecological assessment and a consistent strategy for managing various types of risk. This issue is particularly important when comparing the sensitivity of ecological endpoints relative to the human endpoint. In some cases, nonhuman endpoints may prove to be more sensitive than human endpoints, and would, thus, drive the overall risk assessment. This type of comparison is facilitated by consistency in the strategies used to carry out risk assessments for both types of endpoints. Although human health risk assessment strategies provide a useful model, assessing ecological risk has proven to be more complex. A number of factors contribute to this complexity. • Multiple biological endpoints: these could include multiple species, and various levels of biological organization (e.g., subcellular, individual, population, community, and ecosystem). • More complex exposure pathways: these are determined by the biological endpoints of concern. • Indirect effects: indirect effects such as habitat impairment or disruption of intertrophic relationships may be more important than direct exposure to chemicals. • Evaluating impacts on ecosystems: ecosystems are complex, their function is often not tightly coupled to stressor inputs, and they show resilience and recovery to varying degrees of stress. In spite of these complexities, there are some distinct advantages to estimating risk to ecological endpoints. Exposures and hazards can often be estimated directly on the species of concern or a closely related surrogate species. This may result in a more accurate estimate of risk, because there is no need for extrapolation from more distantly related species as is almost always the case in human risk assessment. This is particularly useful when multiple stressors or complex exposure matrices are involved. In ERAs, the biological endpoints of interest can often be tested directly against the specific stressor or mixture of stressors of concern, thus eliminating the need to estimate such factors as stressor interactions, chemical form (speciation), and bioavailability. Despite the aforementioned advantages, the added complexity associated with ERAs results in a higher degree of uncertainty than is normally associated with human health-based risk assessments. This complexity requires more effort in the initial planning stages so that the final assessment is well focused. Furthermore, ©2001 CRC Press LLC some modifications of the basic NRC risk assessment paradigm are required. The Risk Assessment Forum within the USEPA has developed the framework (and now guidelines) for ecological risk assessment which addresses these issues, yet is con- ceptually consistent with human health risk assessment strategies. It is important to note that slight differences in terminology exist between the various ERA structures currently promoted. However, the elements are fairly analogous. For the sake of simplicity, the discussions in this chapter will utilize the USEPA framework terminology, although the concepts may be drawn from multiple sources. The Ecological Risk Assessment Framework Two major elements that form the basis of the ERA framework are the characterization of exposure and the characterization of ecological effects. Aspects of the two elements are considered in all phases of the framework process. While carrying this common thread throughout the paradigm, the framework is divided into three phases. The phases are problem evaluation, analysis, and risk characterization (Figure 3). Problem Formulation Phase The first step in this process requires defining the specific purpose of the ERA. Although this may seem trivial, many ERAs suffer from lack of clear focus and, as a result, may be ambiguous and misleading. Once the specific purpose of the assessment is defined, the specific goals that must be met to achieve this purpose are formulated. These goals provide a basis for establishing a precise conceptual study design. In undertaking the study design, a number of questions must first be addressed. • Is the ERA to be predictive or retrospective? • Is the ERA to be site-specific or generic? • What type of ecosystem(s) is at risk? • What types of stressors are involved? • What are the potential source(s) for a given stressor or set of stressors? Addressing these questions requires a rigorous review of available data. Where existing data are unavailable or incomplete, it may be necessary to carry out a preliminary study, particularly to establish the types of potential stressor. Most important, ecological risk assessment is often an iterative process. A given level of information is required for developing the design and objectives (i.e., the problem formulation). Additional data may be required for the complete ERA. Ultimately, the level of information needed and the extent of new data collection are dependent upon the objectives, such as the level of certainty desired. As well, the level of information is dependent upon the outcome of the previous iterations, for example, how much ecological impact has occurred at a given site or how hazardous a new chemical may be based on laboratory toxicity studies. ©2001 CRC Press LLC Choosing Biological Endpoints An important issue at this stage is determining the appropriate suite of biological endpoints to be used in the evaluation. Biological endpoints should be carefully chosen specifically to address the overall goals of the assessment. The parameters to be considered in choosing these endpoints should include the ecological relevance of the endpoint and the spatial and temporal occurrence of the endpoint relative to the distribution of the stressors and potential biological receptors. Figure 3 From the Framework for Ecological Risk Assessment (USEPA, 1992). ©2001 CRC Press LLC In ecological assessments the distinction is often made between assessment endpoints and measurement endpoints (Warren-Hicks et al., 1989; Suter, 1993). Assessment endpoints represent the ultimate resource(s) or final environmental val- ues that are to be protected. They should have social or biological relevance, be quantifiable, and provide useful information for resource management or regulatory decisions. For example, successful reproduction of a species in danger of extinction is an appropriate assessment endpoint. For populations that are valued for commer- cial or sport uses such as anadromous fish (e.g., salmon) or estuarine or marine shrimp, the important assessment endpoints could be growth, reproduction, or overall productivity. Other potential assessment endpoints include yield and productivity, market or sport value, recreational quality, and reproductive capability (see Warren- Hicks et al., 1989). In general, assessment endpoints focus on population and community parameters because ecological risk assessments are usually concerned with protecting these higher levels of biological organization rather than individual organisms. However, when there is concern for endangered species, the assessment endpoints may indeed focus on the individual organism. In contrast, measurement endpoints represent the specific parameters that are to be measured in a given assessment. They are often chosen based upon practical considerations such as availability and ease of measurement. It is often impossible from a practical sense to measure some endpoints (e.g., endangered species) and other more obtainable measurement endpoints are chosen as surrogates for the actual assessment endpoints of interest. Such measurement endpoints should be well char- acterized and take into account exposure pathways and temporal factors. Ideally, measurement endpoints should be chosen so that the data from these endpoints can be linked directly or indirectly to appropriate assessment endpoints. This latter issue is often the most difficult to address in ERAs. At the level of the individual, measurement endpoints may include mortality, growth, and fecundity. Abundance and reproductive performance are measurement endpoints on a population level. Other measurement endpoints include species even- ness and diversity on a community level and biomass and productivity on an ecosystem level. Assessment of endangered species poses a special problem. Because exposure for an endangered species cannot usually be directly assessed, the residues of a contaminant in a principal food item can be a measurement endpoint. Alterna- tively, if exposure to a chemical and its potential impact on an endangered species is the assessment endpoint, then a co-existing species with similar life history habits might be used as a surrogate measurement endpoint. Spatial and Temporal Considerations Ultimately, the problem formulation phase should result in the establishment of the study design which will form the basis of the assessment. The design must take into account a number of environmental and ecological factors that may affect the stressors or their potential impact on biological systems. Many of these factors have spatial or temporal components that must be taken into account in the design. Spatial ©2001 CRC Press LLC factors include potential routes of exposure, other sources of stressors, location of sensitive biological resources, and factors that may modify contaminant mobility or availability. The changing composition of sediments is an example of the latter. Temporal factors may include seasonal changes in physical, chemical, or biological aspects of ecosystems that may influence the magnitude or form of the stressor or its potential to cause a biological effect. For example, increased surface water movement in the wet season in riparian habitats can dramatically affect contaminant migration and the potential for exposure. Also, seasonal variation in physical or chemical parameters such as temperature or pH can modify the bioavailability of contaminants, thus changing the nature of the exposure. The biological characteristics of the exposure matrix may also change temporally. Species may be present only seasonally as is typical of migratory waterfowl, anadromous fishes, or species that migrate seasonally within a local area. Exposure to a given species, population, or community may vary with seasonal changes in life history habits such as seasonal feeding patterns or reproductive cycles. Thus, temporal changes in the biological components of an ecosystem may influence the distribution of the stressor or the availability of the biological endpoint within the ecosystem. Temporal variation would affect the ultimate risk assessment. Therefore, these temporal patterns must be addressed in designing the sampling scheme and data collection for the risk assessment. Temporal considerations may also include long-term historical or predicted trends in stressor influence and potential seasonal variation in stressor impact. Historical or predicted trends are very important to understanding the overall impact of stress on an ecosystem and may be important to the application of risk information in risk management decisions such as remediation plans, wetland restoration, and registration of a new pesticide. Other Considerations Another factor to consider is the presence of biological resources that are either sensitive to stressor impact or may be of particular economic or social importance. Wetlands are nursery areas for many species that inhabit adjacent terrestrial and aquatic communities. Other resources may include populations of economically important species such as anadromous fish populations or endangered species which are protected by law. In completing the problem foundation phase of the ERA, these issues must be addressed in rigorous and systematic fashion. The ultimate goal is the development of a conceptual model that will serve as a basis for the ERA. The model should address the spatial and temporal distributions of potential stressors, appropriate biological endpoints, as well as probable routes and levels of exposure. Finally, the model should be precisely linked to the goals and purposes of the risk assessment. A well-conceived conceptual model is essential to the effective implementation of the subsequent component of the risk assessment. [...]... September 24, 1986d U.S Environmental Protection Agency, Guidelines for exposure assessment, Fed Regist., 51, 340 42, September 24, 1986e U.S Environmental Protection Agency, Review of Ecological Risk Assessment Methods, EPW23O-1 0-8 8-O41, 1988 U.S Environmental Protection Agency, Rapid Bioassessment Protocols for Use in Streams and Rivers: Benthic Macroinvertebrates and Fish, EPA /44 4/ 4- 8 9-0 01, 1989a... Evaluation Procedure, Ecological Risk Assessment, EPA 540 / 9-8 5-0 01, 1986 U.S Environmental Protection Agency, Pesticide Assessment Guidelines, Subdivision E, Hazard Evaluation: Wildlife and Aquatic Organisms, EPA 540 / 9-8 2-0 24, 1982a U.S Environmental Protection Agency, Pesticide Assessment Guidelines, Subdivision N, Chemistry: Environmental Fate, EPA 540 / 9-8 2-0 21, 1982b U.S Environmental Protection Agency,... Part A, EPA/ 540 /l-89/002, 1989b ©2001 CRC Press LLC U.S Environmental Protection Agency, Risk Assessment Guidance for Superfund Vol 11, Environmental Evaluation Manual, 1989c U.S Environmental Protection Agency, Water Quality Standards for Wetlands: National Guidance, EPA 44 0/S-9 0-0 11, 1990 U.S Environmental Protection Agency, Summary Report on Issues in Ecological Risk Assessment, EPA/625/ 3-9 1/018, 1991... 24, 1986a U.S Environmental Protection Agency, Guidelines for mutagenicity risk assessment, Fed Regist., 51, 340 06, September 24, 1986b U.S Environmental Protection Agency, Guidelines for health risk assessment of chemical mixtures, Fed Regist., 51, 340 14, September 24, 1986c U.S Environmental Protection Agency, Guidelines for health assessment of suspect developmental toxicants, Fed Regist., 51, 340 28,... Emergent and riverine wetlands are associated ©2001 CRC Press LLC with the bayou Approximately 40 0 ha of rice drainage enter into the bayou above and below our hypothetical field For this example, let us assume that the herbicide has a maximum application rate of 2.7 kg (5 lb) active ingredient per hectare and is applied only once a year, just prior to the permanent flood Figure 4 The typical rice field... Number 2679, ORNL-6251, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 1986 Bartell, S M., Gardner, R H., and O’Neill, R V., Ecological Risk Estimation, Lewis Publishers, Chelsea, MI, 1992 Burmaster, D E and Anderson, P D., Principles of good practice for the use of Monte Carlo techniques in human health and ecological risk assessments, Risk Anal., 14, 47 7, 19 94 Burns, L A.,... evaluating the broad scale effects of the site on the adjacent wetlands A second approach for evaluating the impact of the site on the adjacent tidal wetlands can be used in parallel with the random sampling approach described above In this approach, the sampling focus is on the potential route by which onsite stressors may be transported off-site and into the tidal wetland In this nonrandom sampling... on the site and in the adjacent wetlands The exposure characterization discussion thus far has been limited to determining the nature and distribution of stressors on the site and neighboring wetlands An equally important component of this phase of the ERA is to evaluate the potential routes by which organisms may be exposed to the stressor In the example, routes of potential exposure include direct... recurrent exposures, or high potential for bioaccumulation or reproductive effects Tier II studies are automatically required for any aquatic use of herbicides Tier II avian reproduction studies may also be triggered if Tier I avian tests indicate toxicity Tier III full life-cycle tests with fish may be required if the EEC is more than 0.1 of the NOEC from the Tier II fish early-life-stage study, or if data... Exposure Analysis Modeling System (EXAMS): User Manual and System Documention, EPA/600/ 3-8 2-0 23, 1982 Cairns, Jr., J., Niederlehner, B R., and Orvos, D R., Eds., Predicting Ecosystem Risk, Princeton Scientific, Princeton, NJ, 1992 Durda, J L., Ecological risk assessments under Superfund, Water Environ Technol., 45 , 42 , 1993 ECOFRAM, Aquatic draft report, The Ecological Committee on FIFRA Risk Assessment . Assessment of Wetlands Applied Wetlands Science and Technology Editor Donald M. Kent Boca Raton: CRC Press LLC,2001 ©2001 CRC Press LLC CHAPTER 4 Ecological Risk Assessment of Wetlands . transitional nature of wetlands may make them especially sensitive to stress. Despite the uniform application of assessment principles to ecological systems, individual wetlands are sufficiently different. be broadly applied to a variety of ecosystems. Nevertheless, individual wetlands are sufficiently different in their spatial, temporal, and physic- ochemical characters to warrant site-specific samping