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EPA-Expo-Box (A Toolbox for Exposure Assessors)

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Air

Exposure Scenarios

Exposure to contaminants in ambient or indoor air can be estimated by first defining the exposure scenario of interest. Exposure scenarios typically include information on the sources and pathways of exposure, contaminants of concern, and receptor populations. They might also describe a receptor population’s activities that may affect exposure and the timeframe over which exposure occurs.

Inhalation Exposure—A Complicating Factor

The amount of chemical that is absorbed through the lung (i.e., the internal dose) may vary from the amount of the substance that is inhaled (i.e., the potential dose) based on the anatomy and physiology of the respiratory system and characteristics of the chemical. Assessors should be aware of how internal dose might vary from potential dose when evaluating potential risk.

For an inhalation exposure scenario, concentrations of the contaminants in air (modeled or measured) are needed to estimate exposure dose. Information about the receptor population(s) is also important. Adults and children could be exposed to contaminated air during a variety of activities in different environments, and exposures might occur over short durations (e.g., more than 24 hours, up to 30 days) or longer timeframes (e.g., more than 30 days).

After characterizing the exposed population and identifying exposure concentrations, it is important to define all appropriate exposure factor inputs for estimating potential exposures. Information on inhalation rates, timeframe of exposure, or other relevant patterns of behavior can be obtained from the Exposure Factors Handbook: 2011 Edition (see Exposure Factors tab in the Indirect Estimation Module of the Approaches Tool Set). Inhalation rates will vary between children and adults due to differences in size, physiology, behavior, and activity levels.

The table below provides some examples of scenarios involving air contaminants. The list of examples is not meant to be exhaustive; there are numerous other inhalation exposure scenarios that may be constructed based on the specific needs of the assessment. There are also numerous variations of the examples provided in the table. Additional information on exposure scenarios involving contaminated air may be found in the Indirect Estimation Module in the Approaches Tool Set of EPA-Expo-Box.

Examples of Exposure Scenarios Involving Air and Related
Exposure Factor Handbook: 2011 Edition Tables
Source/Pathway Population Activity/Timeframe Inhalation Rate Exposure Period
Ambient air General population; adults Routine activity; long-term; adjusted air concentration Not applicable Chronic
Ambient air; contaminated site School children Playing during time spent in elementary school; dose calculation
[Table 16-17]
Short-tem, activity-specific
[Table 6-2]
Sub-chronic
Ambient air; source-related contaminant Highly-exposed local population; adults and children Routine; long-term-dose calculation Daily
[Table 6-1]
Chronic or sub-chronic, depending on lifestage
Outdoor air; particulates from contaminated site Occupational; adults Site-specific construction; short-term; adjusted air concentration Not applicable Acute
Indoor air Infants or home-bound elderly adults Routine; less than lifetime; adjusted air concentration Not applicable Sub-chronic
Indoor air Occupational Working in contaminated office building; long-term occupational; adjusted air concentration
[Table 16-8]
Not applicable Chronic
Indoor air; consumer product use Consumers Cleaning with same consumer product over long timeframe
[Chapter 17]
Short-term, activity-specific
[Table 6-2]
Chronic
Indoor air; vapor intrusion from under-foundation source Residential adults and children Routine over lifetime; adjusted air concentration Not applicable Chronic
Indoor air; volatilization from water while showering Residential adults and children Showering daily
[Table 16-1]
Short-term, activity-specific
[Table 6-2]
Chronic or sub-chronic, depending on lifestage
Outdoor or indoor air; volatilization from swimming pool water Recreators Swimming over less than lifetime
[Table 16-1]
Short-term, activity-specific
[Table 6-2]
Sub-chronic
Indoor air; contamination in vehicle Commuters; adults Traveling in vehicle to and from work; less than lifetime
[Table 16-24]
Short-term, activity-specific
[Table 6-2]
Sub-chronic

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Several resources are available that illustrate inhalation exposure scenarios.

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