EPA-Expo-Box (A Toolbox for Exposure Assessors)
Dermal exposure assessment is a two-step process that considers the contact between contaminant and receptor as well as absorption of the contaminant into the body through the skin. The amount of contaminant absorbed represents what is available for interaction with target tissues or organs. The magnitude of exposure is a function of media-specific contaminant concentration, timeframe of exposure (e.g., acute, chronic), and other factors that affect dermal exposure such as skin surface area.
There are a few different ways to characterize dermal exposure and dose (U.S. EPA, 1992b):
- Potential dose is the amount of contaminant applied to skin, not all of which is actually absorbed.
- Applied dose is the amount of contaminant at the absorption barrier (e.g., skin) that can be absorbed by the body.
- Internal dose is the amount of contaminant absorbed and available for interaction with biological receptors (e.g., organs, tissues).
- Biologically effective dose is the amount of contaminant that interacts with the internal target tissue or organ.
An illustration of dermal exposure and dose is provided below.
The potential dose associated with dermal exposure involves the contaminant and the matrix in which it is suspended (e.g., soil) that could come into contact with the skin. It is unlikely that all of the potential dose will come into contact with the skin. The amount of contaminant contained in a medium, such as soil, that actually comes into contact with the skin is the applied dose. The internal dose is the amount of contaminant that gets past the exchange boundary (e.g., skin) and into the blood, or the amount of the contaminant that can interact with organs and tissues to cause biological effects (U.S. EPA, 1992b). The internal (or absorbed) dermal dose is determined by the rate at which the contaminant is absorbed, and this will be a function of contaminant properties.
Algorithms for specific dermal pathways are provided in the Calculations tab of this module.