Understanding the contact between a stressor and a receptor is at the heart of exposure science—and the starting point for the committee’s expanded vision for exposure science in the 21st century. Federal, state, and municipal agency use of the concept of exposure to control environmental risks has contributed to major improvements in environmental protection in the United States and elsewhere. For example, the concept of exposure was instrumental in efforts to control secondhand tobacco smoke, a major source of exposure, but a minor contributor to emissions or ambient air pollution where measurement and regulation had focused previously.
New challenges and new scientific advances, documented in Chapters 4 and 5, impel us to an expanded vision of exposure science. Understanding aggregate or cumulative exposures in their full environmental context will require new approaches to exposure assessment—moving both inward and outward from the core point of contact.
We modify the exposome concept described in Chapter 1 in this broader vision of exposure science:
• Vision: exposure science extends from the point of contact between stressor and receptor inward into the organism and outward to the general environment, including the ecosphere.
We suggest the term “eco-exposome” to encapsulate the concept of this expanded vision.
In light of the new concept, we foresee, among other developments, the evolution of a universal exposure-tracking framework that allows the creation of an exposure narrative and the prediction of virtually all biologically relevant human and ecologic exposures with sensitivity, specificity, and wide coverage.
To retain its value, the principal goal of exposure science must continue to be the prevention and mitigation of adverse exposures to protect human and ecosystem health with a focus on the routes by which environmental stressors reach humans and ecosystems.
Given that vision, exposure science can maintain and augment its relevance to the everyday lives of citizens as they seek measures to protect their health and the health of the ecosystems on which they depend. Exposure science also will continue to contribute to understanding of exposures in numerous settings—outdoors, indoors, and in the occupational environment—and of how those exposures internalize in an organism.
Implicit in the eco-exposome concept is the recognition that humans live in and are part of an ecosphere and that human exposures are intimately linked to exposures flowing through ecosystems. Efforts to understand ecosystem exposures will improve our knowledge of how exposures affect human populations and individuals. Narrating the flow and pulse of exposures through the ecosphere, of which humans are part, also promotes a more thorough investigation of the potential sources of exposure and how these sources can be controlled to protect public and ecosystem health. Because the life courses of humans and ecosystems are dynamic, the eco-exposome will have to evolve scientifically to define what constitutes a biologically relevant exposure.
The committee’s vision is premised on scientific developments of the last decade. Advances in local sensor systems, remote sensing, analytic methods, molecular technologies, computational modeling systems, and bioinformatics have provided opportunities to develop systems approaches that can be integrated into exposure science. There is now an unprecedented opportunity to consider exposures from source to dose, on multiple levels of integration within the ecosphere (including time, space, and biologic scales), to multiple stressors, and scaled from molecular systems to individuals, populations, and ecosystems.
Many of the scientific innovations have been in fields outside traditional exposure science, and achieving the vision will require higher levels of transdisciplinary and interagency cooperation than have occurred in the field of exposure science in the past. In addition, collaborative approaches will be needed to engage communities and stakeholders from problem formulation through data collection to development of responsive solutions and to improve communication among and participation by stakeholders. Such engagement strategies in field studies can lead to more comprehensive application of exposure-science tools to health and environmental protection, including issues of environmental justice.
In this report, the committee presents a roadmap of how technologic innovations and strategic collaborations can advance exposure science in the 21st century. The committee believes that exposure science needs to deliver knowledge that is effective, timely, and relevant to current and future environmental-health challenges. To do so, exposure science needs to continue to build capacity to
• Assess and mitigate exposures quickly in the face of emerging environmental-health threats and natural and human-caused disasters.
• Predict and anticipate human and ecologic exposures related to existing and emerging threats.
• Customize solutions that are scaled to identified problems.
• Engage stakeholders associated with the development, review, and use of exposure-science information, including regulatory and health agencies and groups that might be disproportionately affected by exposures.
The committee recognizes the complex interdependence of human and ecologic systems and adopts an integrated definition of environmental health. In the context of the vision statement, exposure science addresses chemical, physical, and biologic stressors and associated behavioral and societal factors that affect human and ecologic health, including protection of vulnerable populations and susceptible individuals.
The following sections elaborate on core elements of the vision. Later chapters provide specific components of the roadmap for realizing the vision of exposure science in the 21st century.
Assess and Mitigate
Assessing and mitigating exposures effectively require techniques for rapid measurement of single and multiple stressors on diverse geographic, temporal, and biologic scales and an enhanced infrastructure for rapid deployment of resources to address imminent threats, such as the Deepwater Horizon oil spill, Hurricane Katrina, and the tragedy of 9/11. In those three cases, there was a need to evaluate the status of the environment and the exposure of populations via a variety of pathways (such as air, water, soil, and food) while anticipating potential health effects. In the immediate aftermath of Hurricane Katrina, for example, there was an urgent need to evaluate drinking-water safety; a wide array of potential microbiologic and chemical contaminants in sediment, soil, and fish; and air-quality threats posed by mold, endotoxins, and other contaminants in indoor and outdoor environments. It is important that such assessments be handled quickly and effectively to inform and protect first responders, cleanup workers, and affected populations and to respond to stakeholder concerns about the potential for short-term and long-term health effects.
The use of more portable instruments and new techniques in biologic and environmental monitoring will enable faster identification of chemical, biologic, or physical stressors that are affecting humans or ecosystems. Testing of stressors of potential concern in targeted studies would allow rapid responses and deployment of exposure-mitigation measures.
Predict and Anticipate
Enhancing our predictive capabilities through the development of models or modeling systems will enable us to anticipate exposures and characterize exposures that had not been previously considered. For example, modeling will improve our ability to reconstruct external exposures on the basis of the increasing number of internal markers of exposures that are being collected. In addition, exposure models and controlled simulation studies will enable sustainable innovation in developing benign nanomaterials and less toxic chemical alternatives. Predictive tools will also allow us to develop exposure information on thousands of chemicals that are now in widespread use and will enable informed safety assessments of existing and new applications for these chemicals. Finally, predictive tools will allow us to forecast, prevent, and mitigate the potential effects of major societal problems, such as climate change, security threats, and urbanization. Innovative and expedient exposure-assessment approaches that strategically use diverse information such as structural properties of chemicals, nontargeted environmental surveillance, biomonitoring, and modeling and related data-integration tools are needed for the identification and quantification of relevant exposures that may pose a threat to ecosystems or human health.
Using such tools, especially in parallel with pathway-based toxicity screening, in the evaluation of new and emerging environmental stressors can help to ensure that substances in the marketplace are safer. The tools are likely to require broader access to data that now are commonly proprietary, including manufacturing, import, sales, and use data and chemical properties. New data-generation requirements also may be needed; for example, systematic toxicity screening and screening-level exposure assessments would provide a more robust basis for modeling. Exposure-based predictive screening could identify and predict introduction of chemicals that pose potentially serious environmental or health concerns. For example, thoughtful application of predictive tools would have prevented hasty promotion of methyl tertiary butyl ether as a replacement for lead in gasoline, which resulted in widespread contamination of groundwater, or universal application of polybrominated diphenyl ethers as flame retardants, which are now ubiquitous in trace amounts in human breast milk (Goldstein 2010; LaKind and Birnbaum 2010). Such prevention strategies could reduce the risk of disease in exposed populations, substantially reduce future mitigation costs occasioned by widespread environmental contamination, and encourage benign design and green-chemistry approaches to product development and waste disposal. Given that it will take many years to develop comprehensive toxicologic assessments for chemicals in commerce, exposure monitoring can help to ensure against unintended health and environmental consequences.
As stated in a 2009 National Research Council report (NRC 2009), the first step in a risk assessment should involve defining the scope of the assessment in the context of the decision that needs to be made. Adaptive exposure assessments could facilitate that approach by tailoring the level of detail to the problem that needs to be addressed. Such an assessment may take various forms, including very narrowly focused studies, assessments that evaluate exposures to multiple stressors to facilitate cumulative risk assessment, or assessments that focus on vulnerable or susceptible populations. Health-protective default values for exposure can be used in the absence of alternative information to expedite decision-making and to encourage generation of more chemical-specific data that are needed for risk assessment.
For example, a tiered approach that is customized according to expected future land uses and standardized health-protective default assumptions is incorporated into EPA’s supplemental soil screening guidance (SSG) (EPA 2002). The SSG is a tool used to standardize and speed the assessment and cleanup of contaminated soil at sites on the National Priorities List (Superfund). The original 1996 EPA SSG (EPA 1996) focused exclusively on residential land use and did not incorporate alternative scenarios, such as future commercial or industrial land use (which would require less thorough cleanup), risks to workers, dermal exposure pathways, or inhalation from indoor vapor intrusion. The 2002 revisions allowed greater customization of the solutions according to the populations that would probably be exposed (for example, children and workers), anticipated exposure pathways, and future use of the land. The SSG is designed to be used only as a first-tier approach to evaluating a site, and more detailed and fully customized exposure assessments should be done if the SSG indicates a potential concern. This example illustrates that it is possible for agencies to develop standardized approaches to exposure assessment that can allow rapid assessment and conservation of resources while incorporating an increasingly customized and site-specific approach where needed.
Engaging broader audiences, including involving scientists in the concerns and needs of the public, will make the field more responsive and can improve problem formulation, monitoring and collection of data, access to data, and development of decision-making tools. Ultimately, the scientific results derived from the research will empower individuals, communities, and agencies in preventing and reducing exposures and in addressing environmental disparities. Engaging stakeholders will also mean moving beyond the science of inquiry to the science of engagement and the science of application (Boyer 1996). (Additional discussion on engaging the community to respond to health concerns is addressed in Chapter 6.)
Exposure science has played and will continue to play an important role in providing scientific data for use in assessing whether socially disadvantaged groups suffer disproportionate adverse exposures. Disadvantaged groups often have less access than other groups to beneficial or health-promoting exposures (such as access to parks and green spaces), an important consideration for population health (Sister et al. 2010; WHO 2010). And known interactions between psychosocial stressors and environmental exposures need to be considered and quantified for exposure science to be responsive (Shankardass et al. 2009).
Any effort to identify and quantify exposures in a way that fully addresses environmental disparities and that is capable of capturing the complex interactions between stressors in communities will need to use current measurement strategies and deploy new tools in exposure science broadly. Widespread implementation of biomonitoring of many chemicals in varied populations (on the basis of internal markers of exposure) will be useful in identifying exposure distributions and disparities. Key however is the need for exposure information to be accessible to community members and for them to have input in decisions involving exposure prevention or intervention. The committee maintains that it will be critically important to use such approaches as coupling of biomonitoring with collection of relevant environmental exposure data, source data, and health data to allow interpretation of the implications of exposures to facilitate prevention and intervention.
Participatory sensing techniques, which allow people to collect data on their own activities and on their communities, can be enabled for specific pollutants and exposure routes. However, people who are to be active in such programs need training, in both how to collect such data, and in its utility and limitations. Additionally the results need to be quality-assured and validated by trained professionals. For example, ubiquitous sensing technologies, such as those of smart cellular telephones, can facilitate collection of data on time—activity relationships that can provide information to support the need for measurements of pollutant exposures in many poorly characterized microenvironments. The development of user-friendly and less expensive monitoring equipment can allow trained people in communities to collect and upload their own data in partnership with researchers. Such partnerships would improve the value of the data collected and make more data available when setting priorities for exposure-control options. The collection and interpretation of such data raises many scientific questions and underscores the efforts needed to validate measurements and to determine how to integrate the information into models that support effective stakeholder engagement and decision-making.
Enhancing Exposure Science
Human and ecologic systems are inextricably linked. As part of the ecosystem, humans affect and are affected by interactions with the other organisms and nonliving components of the environment. At the most fundamental level,
human health and well-being depend on the goods (for example, clean air and water) and services (for example, groundwater recharge, carbon sequestration, pollination, and seed dispersal) that are provided by ecosystems. Ecosystem health protection will require an expansion of problem-solving approaches that recognize that humans are an integral part of complex ecosystems that operate on wide spatiotemporal scales and varying levels of biologic organization, with consideration of exposures occurring both outside and inside exposed organisms.
The better we understand the complex interactions and feedbacks among the various human and nonhuman components of ecosystems, the better we will understand the spatial and temporal variability in risk and magnitude of exposure. Incorporating ecologic information into exposure assessments will allow us to identify how ecosystems cause, buffer, or magnify exposures. By broadening the view of receptors to include both ecologic and human receptors through the eco-exposome concept, exposure science will be able to connect stressors to changes in ecosystem function and in the ecologic goods and services on which society depends. From an operational perspective, the first step toward that integration will occur during the problem-formulation stage, where the human—ecology linkages can be articulated explicitly. In broadening their view of receptors, researchers and regulators will consider not only human health outcomes but, when it is feasible, ecosystem attributes and their interdependences.
Major challenges in exposure science, combined with the opportunities presented by new technologies, suggest the need for a transformation in exposure science. Strategic investments in this transformation are crucial for development of health-protective strategies in the 21st century. The investments must address strategies for research, education and training, and outreach for the development of collaborative and responsive frameworks for implementing these strategies in a resource-constrained environment. Moving forward with such a vision will provide a strong scientific basis for policy decisions that are responsive to a broad array of stakeholders.
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