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Exposure Science in the 21st Century: A Vision and a Strategy (2012)

Chapter: Appendix C: Concepts and Terminology in Exposure Science

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Suggested Citation:"Appendix C: Concepts and Terminology in Exposure Science." National Research Council. 2012. Exposure Science in the 21st Century: A Vision and a Strategy. Washington, DC: The National Academies Press. doi: 10.17226/13507.
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Appendix C


Concepts and Terminology in Exposure Science

Exposure science and allied public-health disciplines have been challenged for more than 2 decades by inconsistent definitions and applications of the terms exposure and dose. From a strictly observational standpoint, three descriptors characterize the contact between a stressor and a receptor: amount (for example, concentration, mass, and energy), duration (for example, exposure period, duration, and frequency), and location within the system (for example, inhaled air, skin, or target tissue). In addition, some description of how endogenous factors may affect dose is important (for example, inhalation rate is affected by level of physical activity).

The terms external exposure and internal and target-site exposure are elements of the source-to-outcome continuum (see Figure C-1) used in the environmental-health field. The core concept is that the different levels of biologic or environmental organization are separated by barriers to transport or transport processes that need to be accounted for in understanding or describing the relationship between exposure measures on each side of a boundary or level of organization.

From Figure C-1 it is clear that the closer measures of exposure are to the target site for the outcome being examined, the greater is the utility of the data for assessing effects of specific stressors. Conversely, the closer measures of exposure are to environmental concentrations the greater the utility of the information for source emission assessment and control (Figure C-1). The choice of exposure measure is based on the goal of the study or intended use of the data but should always be selected according to what information best minimizes confounders and supports the study’s goal or hypothesis. Exposures at any level can be related conceptually and mathematically to exposures at any other level or to dose. On the basis of the above discussion, Figure C-2 (modified from Figure 1-2) provides a framework that more directly characterizes the theoretical and data-collection efforts of the field of exposure science. To accommodate recent advances in biologic monitoring, Figure C-2 contains the term Internal

Suggested Citation:"Appendix C: Concepts and Terminology in Exposure Science." National Research Council. 2012. Exposure Science in the 21st Century: A Vision and a Strategy. Washington, DC: The National Academies Press. doi: 10.17226/13507.
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Exposure instead of Dose in the “Exposure” box. This modification is intended to address the importance of measuring and quantifying exposure within the organism, but at least a level of organization away from the target site, for example, a specific tissue, or cell, in an organism or a specific compartment of an ecosystem.

The use of the term internal exposure1 is potentially a major shift for the field in that it can be used both in conceptual and theoretical discussions and in experimental design to characterize the processes associated with exposure biology. The quantitative definition of internal exposure is the same as originally discussed by Lioy (1990) and others, but it was described as an internal dose. As the field moves forward, the internal-exposure values can help to establish coherence in the quantitative units that are used to describe the exposure values associated with different routes of entry to the target (for example, mg/kg/day), whether human or ecologic. Therefore internal exposure links the internal-marker measurements of exposure (for example, blood and urine) directly to traditional external measures of exposure, and these in turn can be linked to a dose that is described for toxicologic sites of action or for clinical analyses.

p194.jpg

FIGURE C-1 Another view of the source-to-outcome continuum for exposure science. Exposure science can be applied at any level of biologic organization: the ecologic level, the community level, or the individual level—and within the individual at the level of external exposure, internal exposure, or target-site.

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1Internal exposure is defined as the contact between an agent or a receptor one level of physical or biologic organization past the external boundary toward the target site.

Suggested Citation:"Appendix C: Concepts and Terminology in Exposure Science." National Research Council. 2012. Exposure Science in the 21st Century: A Vision and a Strategy. Washington, DC: The National Academies Press. doi: 10.17226/13507.
×

p195.jpg

FIGURE C-2 Core elements of exposure science. This figure is modified from Figure 1-2, with Dose being replaced with Internal Exposure. The term environmental intensity is used, because some stressors, such as temperature excesses, cannot be easily measured as concentrations.

REFERENCE

Lioy, P.J. 1990. Assessing total human exposure to contaminants: A multidisciplinary approach. Environ. Sci. Technol. 24(7):938-945.

Suggested Citation:"Appendix C: Concepts and Terminology in Exposure Science." National Research Council. 2012. Exposure Science in the 21st Century: A Vision and a Strategy. Washington, DC: The National Academies Press. doi: 10.17226/13507.
×

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Suggested Citation:"Appendix C: Concepts and Terminology in Exposure Science." National Research Council. 2012. Exposure Science in the 21st Century: A Vision and a Strategy. Washington, DC: The National Academies Press. doi: 10.17226/13507.
×
Page 193
Suggested Citation:"Appendix C: Concepts and Terminology in Exposure Science." National Research Council. 2012. Exposure Science in the 21st Century: A Vision and a Strategy. Washington, DC: The National Academies Press. doi: 10.17226/13507.
×
Page 194
Suggested Citation:"Appendix C: Concepts and Terminology in Exposure Science." National Research Council. 2012. Exposure Science in the 21st Century: A Vision and a Strategy. Washington, DC: The National Academies Press. doi: 10.17226/13507.
×
Page 195
Suggested Citation:"Appendix C: Concepts and Terminology in Exposure Science." National Research Council. 2012. Exposure Science in the 21st Century: A Vision and a Strategy. Washington, DC: The National Academies Press. doi: 10.17226/13507.
×
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From the use of personal products to our consumption of food, water, and air, people are exposed to a wide array of agents each day--many with the potential to affect health. Exposure Science in the 21st Century: A Vision and A Strategy investigates the contact of humans or other organisms with those agents (that is, chemical, physical, and biologic stressors) and their fate in living systems. The concept of exposure science has been instrumental in helping us understand how stressors affect human and ecosystem health, and in efforts to prevent or reduce contact with harmful stressors. In this way exposure science has played an integral role in many areas of environmental health, and can help meet growing needs in environmental regulation, urban and ecosystem planning, and disaster management.

Exposure Science in the 21st Century: A Vision and A Strategy explains that there are increasing demands for exposure science information, for example to meet needs for data on the thousands of chemicals introduced into the market each year, and to better understand the health effects of prolonged low-level exposure to stressors. Recent advances in tools and technologies--including sensor systems, analytic methods, molecular technologies, computational tools, and bioinformatics--have provided the potential for more accurate and comprehensive exposure science data than ever before. This report also provides a roadmap to take advantage of the technologic innovations and strategic collaborations to move exposure science into the future.

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