United States
Environmental Protection
Agency
Office of Health and
Environmental Assessment
Washington DC 20460
Research and Development
EPA/600/S8-89/043 Apr. 1990
&EPA Project Summary
Exposure Factors Handbook
John Schaum
This document provides a sum-
mary of the available data on various
factors used in assessing human
exposure including drinking water
consumption, consumption rates of
broad classes of food including
fruits, vegetables, beef, dairy pro-
ducts, and fish; soil ingestion; inhala-
tion rate; skin area; lifetime; activity
patterns; and body weight Addition-
ally, a number of specific exposure
scenarios are Identified with recom-
mendations for default values to use
when site-specific data are not avail-
able. The basic equations using
these parameters to calculate expo-
sure levels are also presented for
each scenario. Default values are
presented as rays from typical to
reasonable worst case and as fre-
quency distributions where approp-
riate data were available. Finally,
procedures for assessing the uncer-
tainties in exposure assessments are
also presented with Illustrative ex-
amples. These procedures Include
qualitative and quantitative methods
such as Monte Carlo and sensitivity
analysis.
This Project Summary was prepared
by £PA's Office of Health and
Environmental Assessment, Washing-
ton, DC, to announce key findings of
the research project that Is fully doc-
umented In a separate report of the
same title (See Project Report
information at back).
Introduction
The purpose of this handbook is to
provide a summary of the available data
on various factors used in assessing
exposure. Additionally, a number of
specific exposure scenarios are identified
with recommendations for default values
to use when site-specific data are not
available. The handbook will provide a
common data base which all Agency
programs can use to derive values for
exposure assessment factors. Thus, it
should help improve the consistency with
which exposure assessments are con-
ducted across the Agency, but still allow
different approaches as may be appro-
priate in consideration of policy, prece-
dent, or other factors. The document is
published in a 3-ring binder format to
allow convenient updates which we plan
to make as new data become available.
Background Information
The Exposure Factors Handbook is
intended to serve as a support document
to EPA's Guidelines for Estimating
Exposures (USEPA 1986) and Proposed
Guidelines for Exposure-Related Mea-
surements (USEPA 1988) by providing
data on standard factors that may be
needed to calculate human exposure to
toxic chemicals. The Guidelines were
developed to promote consistency
among the various exposure assessment
activities that are carried out by the
various EPA program offices. This
handbook should assist in this goal by
providing a consistent framework to
calculate exposure.
The handbook is organized by
grouping the factors into those needed
for each specific route of exposure (i.e.,
ingestion, inhalation, or dermal) or those
needed for more than one route. Stan-
dard exposure scenarios using these fac-
tors are included to facilitate the use of
the data. Finally, procedures for analyz-
ing uncertainty in exposure assessments
are presented.
The Exposure Factors Handbook is an
extension of earlier efforts towards
standardizing the Agency's exposure
assessment calculations sponsored by
the Exposure Assessment Group, Office
of Health and Environmental Assessment,
Office of Research and Development.
The EPA report, "Development of
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Statistical Distributions or Ranges of
Standard Factors Used in Exposure
Assessments" USEPA (1985), covered
body weight, body surface area, and
respiration rate. The results of this study
are incorporated into this handbook.
The Guidelines define exposure as the
contact with a chemical or physical
agent. The magnitude of the exposure is
the amount of the agent available at
human exchange boundaries (skin, lungs,
gut) during some specified time. Starting
with a general integral equation for
exposure (USEPA 1988), several expo-
sure equations can be derived depending
upon boundary assumptions. One of the
more useful of these derived equations
used for dealing with lifetime exposures
to agents with linear non- threshold
responses (i.e., our current assumptions
about many carcinogens) is the Lifetime
Average Daily Exposure (LADE) dis-
cussed below. Exposure assessments
are usually done to support risk assess-
ments; only exposure calculations used
to support cancer risk assessments and
repeated and prolonged (chronic) expo-
sures to noncarcinogens are covered in
this handbook.
For cancer risk assessments, expo-
sure is averaged over the body weight
and lifetime:
Lade Spoil =
Total Exposure
Bo4y Weight X Lifetime
The total exposure can be expanded as
follows:
Total _ Contain- x Contact x Exposure
Exposure ~ inant Con- Rate Duration
centration
Contaminant concentration is the
concentration of the contaminant in the
medium (air, food, soil, etc.) contacting
the body and has units of mass/volume
or mass/mass.
The contact rate refers to the rates of
inhalation, ingestion, and dermal contact
depending on the route of exposure. For
ingestion, the contact rate is simply the
amount of food containing the contam-
inant of interest that an individual ingests
during some specific time period (units of
mass/time). Much of this handbook is
devoted to standard rates of ingestion for
some broad classes of food.
The exposure duration is the length of
time that contaminant contact lasts. The
time a person lives in an area, frequency
of bathing, time spent indoors vs. out-
doors, etc. all affect the exposure dura-
tion. The handbook gives some examples
of population behavior patterns, which
may be useful for exposure calculations.
When the above parameter levels
remain constant over time, they are
substituted directly into the exposure
equation. When they change with time, a
summation approach is needed to
calculate exposure. In either case, the
exposure duration is the length of time
exposure occurs at the concentration and
contact rate specified by the other
parameters in the equation.
The lifetime value used in the above
equation is the period of time over which
the administered dose is averaged. For
carcinogens, this should represent the
average life expectancy of the exposed
population. According to the 1986 edition
of the U.S. Bureau of the Census
Statistical Abstract of the United States,
the average life expectancy of men and
women is 74.7 years, and the figures
have shown a steady increase in life span
through time. Therefore, an average fig-
ure of 75 years is suggested for the life-
time of men and women. For exposure
estimates to be used for assessments
other than carcinogen risk, different aver-
aging periods are frequently used. For
acute exposures, the administered doses
are usually averaged over a day or single
event. For chronic noncancer effects, the
time period used is the actual period of
exposure. The objective in selecting the
averaging time is to express the expo-
sure in a way which makes it comparable
to the dose-response relationship used in
conjunction with the exposure estimate to
calculate risk.
The body weight used to calculate the
total exposure in the above equation
should reflect the average weight of the
exposed population during the time when
the exposure actually occurs. If the expo-
sure occurs continuously throughout an
individual's life or only during the adult
ages, using an adult average weight of 70
kg should provide sufficient accuracy.
However, when the exposure is limited to
childhood, the weight representing those
ages should be used.
Exposure Factors
The handbook summarizes the
available data on the following exposure
factors:
• drinking water consumption
• consumption of homegrown
fruits and vegetables
• consumption of homegrown beef
and dairy products
• consumption of recreationally
caught fish and shellfish
• soil ingestion
inhalation rates
body surface area |
lifetime
body weight
activity patterns
For each of these, the available literature
is summarized and historical precedents
discussed.
Exposure Scenarios
The handbook presents a series o
exposure scenarios to demonstrate how
to apply the exposure factor statistics
summarized earlier. The followinc
scenarios are currently included:
Ingestion of Drinking Water
Ingestion of Homegrown Fruits anc
Vegetables
Ingestion of Homegrown Meat anc
Dairy Products
Ingestion of Recreationally Caugh
Fish/Shellfish
Ingestion of Soil
Inhalation of Vapors Inside Residence
Inhalation of Vapors While Showering
Inhalation of Particulates Outside Res
idence
Inhalation of Particulates Inside Res
idence
For each scenario, the following informa
tion is provided:
• The basic equation for estimatini
exposure. This equation estimate;
exposure as the amount of con
taminant an individual contacts aver
aged over lifetime and body weighl
Expressed as a lifetime average, thi
exposure estimate is appropriate fo
computing cancer risk.
• Recommended default values for eac
parameter in the exposure equatior
These values are defaults in the sens
that they are intended to be used onl
when site-specific data are nc
available to make more accurat
estimates. Prior sections of this repo
provide data and procedures fc
estimating parameter values an
should be used in lieu of these defau
values if feasible. These default value
are presented in three ways: averag<
ranges, and distributions. The recorr
mended parameter values were dc
rived solely from our interpretation <
the available data. In many situation
different values may be appropriate 1
use in consideration of polio
precedent, strategy, or other factors.
• Justifications for each recommende
parameter value. To the extent poss
ble, these values were derived direct
from the preceding sections. In mar
cases, however, no appropriate da
were available and the recommend
tions were based on the be
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Table 1.
Ingestion of Drinking Water at Residence
SCENARIO: An individual ingests tap water and beverages made from tap
water at his residence. All tap water consumed at the residence is from one
contaminated source.
Lifetime Average Daily Exposure Spoil -
(CR) (C) (ED) (DF)
(BW) (LT) (365 days/yr)
CR
C
ED
DF1
BW
LT
Parameter
water consumption rate (L/day)
concentration of contaminant in water (mg/L)
exposure duration (day)
diet fraction
body weight (kg)
lifetime (yr)
Average
Range*
Distribution
CR
C
ED3
DF
BW
LT
1.4
Site Specific
3,285
0.75
70
75
1.4-2.0
3,285-10,950
0.75-1.0
70
75
p. 2-5
Not Available
Not Available
pp. 5-40 - 5-43
To Be Developed
1 Diet fraction refers to the proportion of drinking water an individual consumes at home from one
contaminated source.
2 Range represents the assumed typical value and the assumed reasonable worst-case value.
3 Exposure duration refers to the actual number of days exposed at a given residence.
judgments of the authors in conjunc-
tions with EPA. Users are encouraged
to modify these assumptions based on
site-specific information.
An example of the exposure scenario
presentation for home water consumption
is shown in Table 1.
Rationale for Recommended
Values for Consumption of
Drinking Water at Residence
Consumption Rate
The water consumption rate of 2 L/day
is a historical figure set by the U.S. Army
90th
Average Range percentile
(L/day) (Uday) (L/day) Reference
1.63 - - NAS1977
(calcu-
lated)
1.39 0.80-1.96 2.0 Cantor et al.
1987
1.25 0.08-2.80 1.90 Gillies and
Paulm 1983
1.20 - - Pennington
1983
Ave. 1.4
and used extensively throughout the EPA
and other agencies. As discussed in
Section 2.2, Part I, the scientific literature
suggests an average adult drinking water
consumption rate of 1.4 L/day. These
data can be summarized as follows:
For reasonable worst-case value, the
90th percentile rate reported by Gillies
and Paulin (1983), 1.90 L/day, suggests
that a rate of 2.0 L/day may be a
reasonable approximation. The 90th
percentile value suggested by Cantor et
al. (1987) is also approximately 2.0 L/day.
This value is recommended as the
reasonable worst-case consumption rate.
Exposure Duration
It is assumed that an individual is
exposed every day at the same con-
sumption rate. Assuming that an
individual spends an average of 9 years
at each residence, total exposure would
be for 3,285 days. Using a reasonable
worst-case assumption of 30 years at any
one residence, total exposure would be
10,950 days. These 9- and 30-year
values represent a judgment of how long
a person will live in one area (See Section
5.3.5).
Diet Fraction
Based on survey data on time spent at
home see Section 5.3.3), the average
individual would consume 75 percent of
the total amount of water consumed per
day at home and 25 percent would be
consumed away from home. For the
reasonable worst-case value, it was
assumed that the individual would
consume 100 percent of the total amount
at home.
Body Weight
The average body weight for an adult
(men and women combined was
calculated to be 71.8 kg (USEPA 1985).
Since this approximates the consensus
value of 70 kg traditionally used for
exposure/risk assessments, the value of
70 kg should be used to represent
average body weight
Lifetime
According to the Bureau of the Census
Statistical Abstract of the United States
(Bureau of Census, 1986), the average
life expectancy of men and women is
74.6 years, and the figures have shown a
steady increase in life span through time.
Therefore, an average figure of 75 years
was used for the lifetime of men and
women.
References
Bureau of the Census. 1986. Statistical
Abstract of the United States. 107th
Edition. Washington, DC. U.S.
Governmental Printing Office.
Cantor, K.P., Hoover, R., Hartge, P., et
al. 1987. Bladder cancer, drinking water
source, and tap water consumption: A
case-control study. J. National Cancer
Institute 7Q(Q):1269-1279
Gillies, M.E., Paulin, H.V. 1983.
Variability of mineral intakes from
drinking water: A possible explanation for
the controversy over the relationship of
water quality to cardiovascular disease.
InternationalJ. Epidemiology 12(1):45-50.
National Academy of Sciences-
National Research Council. 1977.
Drinking Water and Health. Vol. 1.
Washington, DC.
Pennington JAT. 1983. Revision of the
total diet study food list and diets. J. Am.
Dietetic Assoc. 82:166-173.
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U.S. EPA. 1985. Development of
statistical distributions or ranges of
standard factors used in exposure
assessment. Washington, DC. Office of
Health and Environmental Assessment.
EPA/600/8-85/010. Available from NTIS,
Springfield, VA. PB85-242667.
U.S. EPA. 1986. U.S. Environ-
mental Protection Agency. Methods for
assessing exposure to chemical sub-
stances. Vol. 8. Methods for assessing
environmental pathways of food
contamination. EPA/560/5-85-008.
U.S. EPA. 1988. U.S. Environ-
mental Protection Agency. Proposed'
guidelines for exposure-related mea-
surements and request for comments;
notice. Federal Register 53(FR)48830-
4885.
John Schaum (also the Project Officer) is with the Office of Health and
Environmental Assessment, Washington, DC, 20460.
The complete report, entitled "Exposure Factors Handbook," (Order No. PB 90-
106 7741 AS; Cost: $31.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be conti
Office of Health and EnvironWHRal Assessment
U.S. Environmental Protection Agency
Washington. DC, 20460
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
U.S.OFFICIAL MAIL
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