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## Science and Judgment in Risk Assessment (1994) Board on Environmental Studies and Toxicology (BEST)

### Citation Manager

. "Appendix C: Calculation and Modeling of Exposure." Science and Judgment in Risk Assessment. Washington, DC: The National Academies Press, 1994.

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centration ¯Cj for the interval tj. A person's total exposure E to an airborne pollutant is the summation over all the microenvironments M in which the person is in contact with the pollutant:

The latter equation includes the totality of all locations and activities that the person can occupy and engage in.

To obtain the total exposure of a population Epop of N persons, it is necessary to sum the individual exposures Ei of all the persons in the population from i = 1 to N:

Generally, the amount of time spent in each microenvironment is averaged over the exposed population,

so that the average population exposure is given by

Thus, it is necessary to estimate the atmospheric concentration of the pollutant to which people are exposed to obtain Cj and their activity patterns to obtain tj.

#### Modeling Of Exposure

It is often impossible or impractical to measure the exposures of individuals or populations directly, and instead mathematical models are used to estimate exposures. Microenvironmental concentrations are estimated with concentration models, which are based on the physics and chemistry of the environment. The time spend by an individual in a microenvironment with a pollutant is another important input to an exposure model. Population-exposure models combine data representing the time-activity patterns of an entire population with pollutant concentrations.

##### Gaussian-Plume Models

Gaussian-plume models are used by the Environmental Protection Agency (EPA) to estimate the concentration of a pollutant at locations some distance from an emission source. The models have this name because they represent the

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 Front Matter (R1-R16) Executive Summary (1-15) 1 Introduction (16-22) Part I Current Approaches to Risk Assessment: 2 Risk Assessment and its Social and Regulatory Contexts (23-42) 3 Exposure Assessment (43-55) 4 Assessment of Toxicity (56-67) 5 Risk Characterization (68-78) Part II Strategies for Improving Risk Assessment: 6 Default Options (79-105) 7 Models, Methods, and Data (106-143) 8 Data Needs (144-159) 9 Uncertainty (160-187) 10 Variability (188-223) 11 Aggregation (224-242) Part III Implementation of Findings: 12 Implementation (243-268) References (269-286) Appendix A: Risk Assessment Methodologies: EPA (287-350) Appendix B: EPA Memorandum from Henry Habicht (351-374) Appendix C: Calculation and Modeling of Exposure (375-382) Appendix D: Working Paper for Considering Draft Revisions to the U.S. EPA Guidelines for Cancer Risk Assessment (383-448) Appendix E: Use of Pharmacokinetics to Extrapolate from Animal Data to Humans (449-452) Appendix F: Uncertainty Analysis of Health Risk Estimates (453-478) Appendix G: Improvement in Human Health Risk Assessment Utilizing Site- and Chemical-Specific Information: A Case Study (479-502) Appendix H-1: Some Definitional Concerns About Variability (503-504) Appendix H-2: Individual Susceptibility Factors (505-514) Appendix I: Aggregation (515-536) Appendix J: A Tiered Modeling Approach for Assessing the Risks Due to Sources of Hazardous Air Pollutants (537-582) Appendix K: Science Advisory Board Memorandum on the Integrated Risk Information System and EPA Response (583-590) Appendix L: Development of Data Used in Risk Assessment (591-598) Appendix M: Charge to the Committee (599-600) Appendix N-1: The Case for (601-628) Appendix N-2: Making Full Use of Scientific Information in Risk Assessment (629-640) Index (641-652)