Reviewing USEPA Default Exposure Assumptions

a. Exposure Factors Handbook (USEPA 1989).

b. Exposure Factors Handbook (USEPA/ORD 1995).

c. Human-Health Evaluation Manual, Supplemental Guidance: Standard

Default Exposure Factors (USEPA/OSWER 1991a).

d. Guidance for Assessing Chemical Contaminant Data for use in Fish

Advisories. Volume I: Fish Sampling and Analysis (USEPA/OST 1993).

e. Guidance for Assessing Chemical Contaminant Data for use in Fish

Advisories. Volume II: Risk Assessment and Fish Consumption Limits

(USEPA/OST 1994).

Ingestion rate (IR). Fish consumption rates differ throughout the country, and for

specific subpopulations, the use of an "average" consumption rate for all

households may not accurately reflect the local consumption rate in a particular

subpopulation. It is recommended that the risk assessor review the consumption

values presented from key studies identified by the USEPA (e.g., USEPA/ORD

1995). From these data (or others in the literature), exposure factors should be

selected.

Absorption fraction (Abs). The absorption of the contaminants from the seafood

tissue through the gastrointestinal tract will depend upon the lipophilicity of the

compound, the degree to which the lipid soluble portion of the fish is absorbed, and

the contents of the human gastrointestinal (GI) tract at the time of ingestion of the

contaminated seafood, among other factors.

Exposure frequency (EF). The EF refers to the total number of seafood meals

consumed during the exposure duration. This frequency includes seafood harvested

from both the dredged material disposal site and elsewhere. This can range from up

to 10 meals per year for the recreational fishermen (USEPA/OERR 1992b) to once

or twice per week, or more, for those consuming fish harvested commercially or

caught by subsistence fishermen (USEPA/Office of Policy, Planning, and

Evaluation, and Research and Development 1991). The frequency of consumption

of one species can differ from another due to seasonality of catch.

Body weight (BWavg). The default value for average body weight over the

exposure period for adults is 70 kg. For children under the age of 6, the default

value is 15 kg (USEPA 1989), and for young adults or teens, it is appropriate to use

intermediate values.

Exposure duration (ED). The ED represents the length of time over which

exposure occurs. Typically, the default values represent upper-bound residential

durations of 30 years and median residential durations of 9 years at a single

residence. However, it is recommended that site-specific durations be used. If, for

example, the dredged material disposal site will be capped within 2 years of its use,

this should be reflected in the exposure duration.

Chapter 4 Human Health Risk Assessment