Technical Overview of Ecological Risk Assessment
- Problem Formulation
- Analysis - Ecological Effects Characterization
- Analysis - Exposure Characterization
- Risk Characterization
About Problem Formulation
Before the ecological risk assessment is conducted, risk assessors and risk managers engage in a planning dialogue to ensure that the risk assessment will enable the risk managers to make informed environmental decisions. The characteristics of the risk assessment are determined by the agreements reached by the risk managers and risk assessors during the planning dialogue. As a first step, risk assessors and risk managers consider the value of conducting a risk assessment and the possible management options for mitigating or preventing the identified problems. If a decision is made to conduct a risk assessment, key participants are identified and involved in the ecological risk assessment process. During the planning process, risk assessors and risk managers are responsible for discussing and reaching agreement on the following items:
Risk managers should first define and communicate the nature of the regulatory action to the risk assessors. Regulatory actions can include new pesticide active ingredients, new uses of active ingredients, emergency exemptions, special local needs, and other actions. Along with defining the regulatory action, risk assessors and risk managers should also discuss any regulatory issues that can impact the risk assessment and risk management decision.
Management goals are statements about the desired condition or characteristics of ecological values that the public wants to protect. For example, management goals may include "preventing toxic levels of contamination in water, sediments, and biota" or "maintaining a sustainable aquatic community." Management goals drive the risk assessment and many times come from an enacted law, such as the Clean Water Act which has the goal to "protect and restore the chemical, physical, and biological integrity of the Nation's waters." Management goals can also be derived from interests expressed by the public.
Management options to achieve goals
Management options provide the framework for implementing the management goals. These options may include risk management decisions that establish consistent national policy across the country for a specific stressor (e.g., chemical) or a policy that is site-specific, or of management concern. When implemented, management decisions are designed to achieve a particular environmental goal. Management options may range from cancelling a particular use of a pesticide to label restrictions for limiting the application of a pesticide in certain areas of the country. Management options can provide a framework for defining the scope, focus, and conduct of a risk assessment.
Scope and complexity of the risk assessment
Risk assessments are constrained by the availability of valid data, expertise, time, and financial resources. The scope and complexity of the risk assessment is partly based on the uncertainty that can be tolerated in a decision supporting the risk assessment. Risk assessors and risk managers need to discuss how the uncertainty can be reduced through investment of resources. One approach for determining the complexity and resources for a risk assessment is to set up tiered evaluations that begin with simple decision criteria and proceed to more complex decision criteria that support complex management decisions. Risk assessments that are conducted for a large area involving multiple stressors and ecological values will require more resources and complexity than those based on a small localized area.
The planning summary includes agreements on the management goals, management options, and focus, scope and complexity of the risk assessment. These agreements can include the technical approach that will be taken in the risk assessment as well as the spatial and temporal scales of the risk assessment.
After planning agreements are reached, the problem formulation phase begins. This phase is critical as it provides the foundation for the risk assessment. In the problem formulation phase, risk hypotheses or assumptions are generated about why ecological effects have occurred or may occur as a result of human activities. Problem formulation is an interactive and iterative process where risk managers and risk assessors perform the following tasks:
Integrate available information
The quantity and quality of available information determine how the problem formulation can proceed. When key information of appropriate quality and quantity are available, problem formulation can proceed effectively. If data are limited, the risk assessment may either be suspended until sufficient data are collected or uncertainties may be clearly articulated in the risk characterization. Key information that is identified in the problem formulation includes stressor sources and characteristics, exposure, ecological effects, and characteristics of the ecosystem(s) to be protected. During this scoping process, available information is used to identify missing information and assessment endpoints and to develop a preliminary assessment of the problem. Information needs often increase as the complexity and scale of the risk assessment increases.
Evaluate the nature of the problem
In defining the nature of the stressor, risk assessors generally focus on the pesticide active ingredient although in some cases they may consider pesticide formulations, inert ingredients, or degradates based on available data. EPA does not routinely evaluate mixtures of active ingredients in its screening-level risk assessments. In accordance with the agency's risk assessment guidance, EPA documents the scope of the chemical stressors, the rationale for their consideration, the methods used to evaluate the risks, and their contribution to the overall conclusions of the risk assessment. Guidance for reporting on the environmental fate and transport of stressors of concern can be found at the following website: Guidance for Reporting on the Environmental Fate and Transport of the Stressors of Concern in Problem Formulations.
In characterizing pesticide use, risk assessors use the pesticide product labeling, which defines the nature of the pesticide use in the field. Use factors on the labeling also determine the input parameters for exposure models and the magnitude of exposure to non-target organisms. Characterization of pesticide use allows the risk assessors to focus the risk assessment on specific use patterns that are representative of a larger variety of use patterns. In this way, risk assessors can focus on use scenarios that reasonably represent the highest exposures.
Information on ecological effects or toxicity of pesticides to non-target organisms is obtained from acceptable toxicity tests conducted on a limited number of organisms that serve as surrogates for broad groups of animals and plants. For example the laboratory rat is the surrogate test species for mammals. Acute and chronic endpoints are selected from test data for the most sensitive species within these broad taxonomic groups. If acceptable toxicity data are available for other species that are not listed as surrogate species, they may be used in the risk assessment. In addition to registrant studies, alternate sources, including the scientific literature, can also be examined for toxicity data. Exposure data can be obtained from monitoring studies or estimated by computer simulation models. The exposure data describe the potential or actual contact of a pesticide with a plant, animal, or media.
Select assessment endpoints
Assessment endpoints are based on management goals identified in the planning dialogue and are critical in providing the direction and boundaries for the risk assessment. Assessment endpoints include two elements:
identification of the specific ecological entity that is to be protected, such as a species, a community, an ecosystem, or other entity of concern and
a characteristic about the entity of concern that is important to protect.
In a screening-level pesticide ecological risk assessment, typical assessment endpoints include reduced survival and growth, and reproductive impairments for individual animal species from direct acute and direct chronic exposures. For plants, the assessment endpoints are typically concerned with maintenance and growth of non-target species. Although these assessment endpoints are measured at the individual level, they indicate potential risk to populations.
Prepare a conceptual model
The conceptual model consists of two components:
a set of risk hypotheses that describe the predicted relationships among stressor, exposure, and assessment endpoint and
a diagram that illustrates the relationships in the risk hypotheses.
Typical conceptual models are flow diagrams that contain boxes and arrows illustrating these relationships. Developing a conceptual model allows the risk assessor to identify the available information regarding the pesticide, justify the model, identify data and information gaps, and rank model components in terms of uncertainty. Guidance for developing conceptual models for problem formulation can be found at the following site: Guidance for the Development of Conceptual Models for a Problem Formulation.
Develop an analysis plan
This is the final stage of problem formulation in which risk assessors develop a plan for analyzing data and characterizing risk. The analysis plan summarizes what has been done during problem formulation and targets those hypotheses that are likely to contribute to the risk. It also evaluates the risk hypotheses to determine how they will be assessed, develops the assessment design, identifies data gaps and uncertainties, determines which measures will be used to evaluate the risk hypotheses (e.g., LC50, NOAEC, EEC's), and ensures that the planned analyses will meet the risk managers' needs.
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