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

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Exposure Factors

Inhalation Risk—The Superfund Approach

As described in Chapter 6 of the Exposure Factors Handbook: 2011 Edition, the Superfund Program’s updated approach for determining inhalation risk eliminates use of inhalation rates when evaluating exposure to air contaminants [see RAGS, Part F (U.S. EPA, 2009)]. The updated methodology recommends using contaminant concentrations in air as the exposure metric (e.g., in mg/m3) instead of the intake of a contaminant in air based on inhalation rate and body weight (e.g., mg/kg-day).

Inhalation toxicity values like the IRIS and Superfund reference concentrations (RfCs) and inhalation unit risks (IURs) incorporate inhalation rate into their values.

To estimate human exposure to contaminants in ambient or indoor air, exposure factor information is needed. Exposure factors are human behaviors and characteristics that help determine an individual's exposure to an agent. When determining inhalation risk, inhalation rate and body weight might not be needed (see right).

When inhalation rates are needed, data are available in Chapter 6 of EPA’s Exposure Factors Handbook: 2011 Edition. Long-term inhalation rates are reported as daily rates in units of m3/day or m3/kg-day (adjusted for body weight). Short-term rates are described for various activities (e.g., walking, running, playing, housework, yard work) or activity levels (e.g., light, moderate, heavy) in units of m3/minute. Inhalation rates should be selected to represent the appropriate age/lifestage, gender (if appropriate), timeframe, and, if applicable, activity or activity level for the exposure scenario of interest.

Other activity-specific factors that may be relevant for assessing inhalation exposures associated with specific activity levels are available in Chapter 16 of the Handbook. These might include amount of time spent indoors, outdoors, or doing a specific activity (e.g., household work, physical leisure activities, passive leisure activities).

Other exposure factors that might be needed for assessing inhalation exposures include:

  • Body weight (Chapter 8)
  • Consumer product use (Chapter 17)
  • Life expectancy values, specifically when evaluating cancer risk (Chapter 18)
  • Building characteristics when assessing indoor air exposures (Chapter 19)

Exposure factor data may be accessed from the Exposure Factors Tab of the Indirect Estimation Module.

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