EPA-Expo-Box (A Toolbox for Exposure Assessors)
Chapter 7 of EPA’s Exposure Factors Handbook: 2011 Edition (U.S. EPA, 2011) provides information on factors that affect dermal exposure, including skin surface area, dermal adherence of solids to the skin, film thickness of liquids on the skin, transfer of contaminant residues from surfaces to the skin, and other factors. Contaminant-specific factors related to dermal absorption and internal dose, however, are not provided in Chapter 7.
Skin surface area (SA) is an estimate of the amount of skin (cm2 or m2) that can be exposed to contaminants. The more skin exposed the greater potential for dermal absorption. Depending on the scenario, total body surface area or surface areas of specific body parts may be appropriate. Another dermal factor is the adherence factor (AF; mg/cm2), which represents the quantity of soil or solids that may adhere to the skin surface after contact, and this varies with activity. Recommended values for SA and AF are provided in the Handbook.
The film thickness of liquids on skin (cm) is a measure of the amount of material that remains on the skin after contact with a liquid (e.g., consumer product such as cleaning solution or soap). Residue transfer coefficients (cm2/hour) of contaminants to human skin will vary based on exposure conditions such as activity, contact surface, and age. Recommended values for these dermal factors are not provided in the Handbook because data are limited; however, data from relevant studies are described.
The Exposure Factors Tab of the Indirect Estimation Module provides links to data on dermal contact rates.
Other activity-specific factors that might be relevant for assessing exposures with contaminants via dermal contact are available in Chapter 16 of the Handbook, and this might include time spent indoors, time spent outdoors, event frequency (showers per week, swimming events per month), or time spent doing the specific activities (e.g., playing on dirt or grass, gardening, participating in outdoor recreation). Other exposure factors that might be needed for assessing dermal contact exposures include:
- Body weight (Chapter 8)
- Consumer product use information (Chapter 17)
- Life expectancy values, specifically when evaluating cancer risk (Chapter 18)
The Exposure Factors Tab of the Indirect Estimation Module provides links to data on other factors.
Dermal exposure factors should be selected to represent the age, gender (if appropriate), timeframe/activity level, and population group (e.g., resident, occupational worker) for the exposure scenario of interest. EPA’s Risk Assessment Guidance for Superfund (Part E, Supplemental Guidance for Dermal Risk Assessment) (U.S. EPA, 2004)) and Dermal Exposure Assessment: Principles and Applications (U.S. EPA, 1992a) provide additional guidance on the use of dermal contact parameters. Exposure factors related to dermal exposures are also described in the Soil and Dust, Water and Sediment, and Consumer Products Modules of the Media Tool Set in EPA-Expo-Box.