Exposure refers to a measurable contact of an agent with a target or receptor for a specific duration of time. In the broadest terms, agents can be biological, physical, chemical, social, or psychological, and can produce both adverse and beneficial impacts to the target.
EPA has historically focused on minimizing negative impacts, but in a sustainability context assessing exposures that result in positive impacts is also relevant to evaluating tradeoffs. For human exposures, receptors can be individuals, populations, subpopulations, or life-stages of interest. For ecological systems, receptors can be individuals, populations, species communities, or ecosystems that include both wildlife and vegetation. For exposure to occur, the agent and the receptor must intersect in both space and time.
Exposure assessments characterize and predict this intersection by estimating the magnitude, frequency, and duration of exposure. Exposure assessments also describe the number and characteristics of the population exposed (e.g., vulnerable communities, ecosystems, or endangered species). They describe the sources, routes, pathways, and uncertainty in the assessment. Exposure assessments describe the environment as well as characterize and link the processes that impact the transport and transformation of agents from their source through contact with human or ecological receptors. These assessments are a central component in understanding environmental systems and how they change when intended or unintended perturbations occur.
How can Exposure Assessment Contribute to Sustainability?
Exposure assessments are often used as part of risk assessment. They describe the ways that humans and ecological receptors interact and provide the information needed to forecast and trace exposures, identify important future states of the system and the implications of those future system states (futures methods), describe the current state of the system, and evaluate the impact of decisions on both current and future system states.
Information generated through exposure assessments can be used to identify sustainability metrics that reflect the important processes in the system and that also serve as effective indicators of important changes in the system. Exposure assessments provide inputs to many of the other analytical tools in this document such as life-cycle assessment, health impact analysis, benefit-cost analysis, ecosystem service valuation, and environmental justice analysis.
What are the main steps in an Exposure Assessment?
Exposure assessments range from simple assessments (single agents/single receptor) to complex cumulative assessments that evaluate exposures involving multiple harmful and beneficial agents, (multiple pathways/multiple receptors). For complex ecosystem assessments, the dynamic nature of the natural environment must also be taken into account. The form and scope of an assessment will depend on the overall situation, the resulting exposure assessment question, the decision objectives, and in some cases, regulatory or statutory requirements; general steps in an exposure assessment are:
Step 1—formulate problem, including articulating the overall concern, the management or sustainability options, and the resources available to assess and manage the problem. Problem formulation should be done through stakeholder engagement and collaboration to ensure that the assessment is relevant to the specific problems being addressed. In a sustainability context, this step is crucial and may be more complex because each problem needs to be considered in the context of the overall system;
Step 2—define the target population and/or environment of concern;
Step 3—identify fall the agents of concern;
Step 4—identify relevant sources, fate and transport, routes and pathways of exposure for the target population and/or environment;
Step 5—quantify temporal and spatial distributions of agents in the environment and similar distributions for the target populations;
Step 6—quantify exposures or exposure distributions including the frequency and duration of exposure;
Step 7—estimate the contribution of each source and pathway;
Step 8—characterize results and their inherent uncertainty; and,
Step 9—communicate information from the assessment to decision-makers and all stakeholders. Again, in the context of sustainability this becomes a very important step given the various mitigation tradeoffs that should be considered.
Exposure assessments rely heavily on models to characterize the movement, transformation, removal, distribution, and interaction of agents and receptors within a system. Models enable the use of a systems approach covering a broad range of issues and allow for both prospective and retrospective assessments. Additionally, models provide the opportunity to evaluate the effectiveness of multiple management options, as well as unintended perturbations to the system.
What are the strengths and limits of Exposure Assessment in sustainability context?
Applying exposure assessment tools to sustainability will require the development and application of 21st century tools. This includes full development and evaluation of predictive environmental and exposure models for chemical, biological, physical, and geophysical data. These models must be capable of predicting exposures to agents for which little or no data exist. Also, these models must be interoperable such that multiple models can be seamlessly used within a larger systems context that integrates across the environmental, social and economic pillars.
Exposure assessment also requires the development of newer computational and sensing technologies that are sufficiently advanced to support the development of observational exposure networks, in order to more comprehensively describe the environment and populations in both time and space. Additionally, enhanced computational techniques to manage and analyze large complex data sets resulting from increased sensor networks need to be developed. Finally, methods for assessing exposures to multiple agents simultaneously must be improved.
How is Exposure Assessment used to support EPA decision-making?
Currently exposure assessments are used primarily as inputs for risk assessments when determining human or ecological risks and represent one of the four major steps in the risk assessment process. In this process, exposure assessments are used to estimate exposure or dose, which is combined with dose-response data to estimate risk.
Exposure assessments also provide information on the populations exposed as well as the sources, routes, and pathways for exposure. When used as part of an environmental justice analysis, exposure assessments can help identify vulnerable populations and evaluate environmental inequities. This information can be used to determine the most effective ways to reduce risk by minimizing exposure to harmful agents. By considering agents with positive impacts, exposure assessments can also be used to understand how to maximize benefits while minimizing risks. Exposure assessments could also be used to monitor status and trends by applying appropriate exposure indicators and monitoring changes in them over time. Using exposure assessments in this manner could help evaluate emerging risk concerns, identify unintended changes in the environment, and evaluate the impact of regulatory or societal decisions.