Appendix E: Human Exposure Equations

Appendix E

Human Exposure Equations

This subsection calculates a separate dose of each contaminant for a receptor

based on:

Exposure Point Concentrations (EPC)

The EPCs are the measured or modeled chemical concentrations for each

pathway. The EPCs are unique to each scenario.

Exposure Assumptions

The exposure assumptions describe the receptor and the conditions under

which the receptor contacts the exposure point concentrations. Unless otherwise

indicated, these assumptions are standard U.S. Environmental Protection Agency

(USEPA) defaults (USEPA 1989, USEPA 1992c).1

Averaging Time (USEPA 1989)

The averaging time is the time over which the receptor is exposed for

noncarcinogenic risk and is a lifetime for carcinogenic risk. It will vary

depending upon the assumptions used.

For most exposure routes, the following equations assume that the absorption

of a COC into the bloodstream from the gastrointestinal tract and lungs is

100 percent. Therefore, these equations are not adjusted in any manner.

However, the dermal route of exposure will result in an absorption of a COC into

the bloodstream which is less than 100 percent. The equation describing the dose

from this exposure route is appropriately adjusted (USEPA 1992c).

The following equations are used to estimate doses. The inhalation route is

evaluated based on the concentration of contaminants in the air, not a dose

(USEPA 1989).

A complete list of references is located at the end of the main text.

Appendix E Human Exposure Equations