Assessing RiskFeedback

In the Exposure Assessment, site data are evaluated to estimate chemical exposure point concentrations for COPCs in the various media and locations specified in the CSM. The combinations of exposure pathways and receptors for which risk will be quantified are specified. An exposure pathway describes the links between a chemical source or release and an exposure route (e.g., ingestion, inhalation, etc) via one or more environmental media and points of exposure. Chemical intake (aka, “dose”) is then calculated as a function of the concentration of a chemical in an environmental medium, the characteristics and behaviors of the potentially exposed individuals, and the nature of the health effects related to the chemical. “Dose” generally is conveyed as the body-weight-normalized mass of a chemical that enters the body during the period of exposure.

The EPA’s Exposure Factors Handbook provides a summary of the available statistical data on various factors used in assessing human exposure. This handbook is addressed to exposure assessors inside the agency as well as outside, who need to obtain data on standard factors to calculate human exposure to toxic chemicals. These factors include: drinking water consumption; soil ingestion; inhalation rates; dermal factors including skin area and soil adherence factors; consumption of fruits and vegetables, fish, meats, dairy products, and homegrown foods; breast milk intake; human activity factors; consumer product use; and residential characteristics. Recommended values are for the general population and also for various segments of the population who may have characteristics different from the general population. State Agencies may use different exposure factors for sites under their oversight. This is most often the case for sensitive populations, specific pollutants (for example, California uses a specific methodology for lead), or reuse that falls between "residential" and "industrial". Sites for recreational or open-space reuse may have less clearly defined frequency and duration of use/exposure factors. These factors should be agreed upon with the regulatory agencies and communicated to the public.

The National Center for Environmental Assessment (NCEA) has striven to include full discussions of the issues that assessors should consider in deciding how to use these data and recommendations. The document is in final form, but as new data become available updates will be posted on the NCEA Home Page.

NCEA has also produced a CD-ROM that contains an interactive version of the Exposure Factors Handbook. The CD-ROM has word search capabilities, downloadable tables, hypertext links to various chapters in the document, and key references. A two-part PDF version of the document can also be accessed through this NCEA web page.

A limited number of paper copies and CD-ROM version of the Handbook are available from the National Service Center for Environmental Publications (NSCEP) in Cincinnati, Ohio (phone 1-800-490-9198; 513-489-8190; FAX 513-489-8695). Please provide the title and EPA number when ordering from NSCEP. Documents may also be ordered on-line at www.epa.gov/ncepihom/ordering.htm.

EPA's National Exposure Research Laboratory (NERL) is comprised of several divisions with diversified research specialties. NERL conducts research and development that leads to improved methods, measurements and models to assess and predict exposures of humans and ecosystems to harmful pollutants and other conditions in air, water, soil, and food.

The Environmental Science Division has compiled a list of software applicable for site characterization. The software is listed at http://www.epa.gov/nerlesd1/databases/datahome.htm and can be obtained on a single CD; Site Characterization Library, Volume 1, Release 2" (EPA report number 600/C-98/001) through the EPA's National Service Center for Environmental Publications (800-490-9198) (http://www.epa.gov/ncepi).