EPA #PB 99-9635-8
OSWER #9285.7-31
August 2002
SHORT SHEET:
OVERVIEW OF THE IEUBK MODEL FOR
LEAD IN CHILDREN
Office of Solid Waste and Emergency Response
U.S. Environmental Protection Agency
Washington, DC 20460
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NOTICE
This document provides guidance to EPA staff. It also provides guidance to the public and to the
regulated community on how EPA intends to exercise its discretion in implementing the National
Contingency Plan. The guidance is designed to implement national policy on these issues. The document
does not, however, substitute for EPA's statutes or regulations, nor is it a regulation itself. Thus, it
cannot impose legally-binding requirements on EPA, States, or the regulated community, and may not
apply to a particular situation based upon the circumstances. EPA may change this guidance in the
future, as appropriate.
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U.S. ENVIRONMENTAL PROTECTION AGENCY
TECHNICAL REVIEW WORKGROUP FOR LEAD
The Technical Review Workgroup for Lead (TRW) is an interoffice workgroup convened by the U.S.
EPA Office of Solid Waste and Emergency Response/Office of Emergency and Remedial Response
(OSWER/OERR).
CO-CHAIRPERSONS
Region 4 NCEA/Washington
Kevin Koporec Paul White
Atlanta, GA
MEMBERS
Region 1 Region 10
Mary Ballew Marc Stifelman
Boston, MA Seattle, WA
Region 2 NCEA/Washington
Mark Maddaloni Karen Hogan
New York, NY
NCEA/Cincinnati
Region 3 Harlal Choudhury
Linda Watson
Philadelphia, PA NCEA/Research Triangle Park
Robert Elias
Region 5
Patricia VanLeeuwen OERR Mentor
Chicago, IL Larry Zaragoza
Office of Emergency and Remedial Response
Region 6 Washington, DC
Ghassan Khoury
Dallas, TX Executive Secretary
Richard Troast
Region 7 Office of Emergency and Remedial Response
Michael Beringer Washington, DC
Kansas City, KS
Associate
Region 8 Scott Everett
Jim Luey Department of Environmental Quality
Denver, CO Salt Lake City, UT
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Overview of the IEUBK Model for Lead in Children
What is the IEUBK Model for Lead (Pb) in Children?
The Integrated Exposure Uptake Biokinetic (IEUBK) Model for
Lead in Children is used to predict the risk of elevated blood
lead (PbB) levels in children (under the age of seven) that are
exposed to environmental lead (Pb) from many sources. The
model also predicts the risk (e.g., probability) that a typical
child, exposed to specified media Pb concentrations, will have
a PbB level greater or equal to the level associated with adverse
health effects (10 ^g/dL). Prior to the development of the
IEUBK model, a single slope factor constant had been used to
predict risk from exposure to lead, as is done for other
chemicals. The slope factor approach assumed a linear
relationship between environmental concentrations and risk
levels. Although, for Pb, the rate relationship is close to linear
at lower PbB levels, it is non-linear at higher levels, invalidating
the linear approach. Additionally, the linear approach did not
adequately address the site-specific variability and multi-media
nature of exposure to lead. The IEUBK model is the primary
tool used in determining risk-based cleanup levels at Pb
contaminated sites. The following modules are utilized in
predicting PbB concentrations, and risks in the IEUBK model:
Exposure, Uptake, Biokinetic, and Probability Distribution.
Exposure Module. This module uses Pb concentrations in the
environment and the rate at which a child breathes or ingests
contaminated mediate determine Pb exposure. Media that can
act as sources of Pb for a child include air (both indoor and
outdoor), which enters the body through the lungs, and water,
soil, dust (indoor), diet, and other sources (e.g., lead paint),
which enter the body through the gastrointestinal (GI) tract. The
Exposure Module estimates how much Pb enters a child's body
by calculating media-specific Pb intake rates using the following
equation:
Pb Intake Rate = Media Pb Concentration * Media Intake Rate
The values used for media Pb concentrations and media intake
rates are either derived from site-specific data or standard
default values established by EPA. The media intake rates are
age-specific. The Exposure Module calculates the intake of Pb
from each medium for use in the Uptake Module.
Uptake Module. This module modifies the Pb intake rates
calculated by the Exposure Module using absorption factors to
predict the uptake of Pb from the lungs and GI tract. Uptake is
defined as the fraction of the total Pb intake that crosses from
the lungs or GI tract to the bloodstream. Lead that enters the
body through the lungs is either absorbed through lung membranes
into the blood, transferred to the GI tract, or eliminated from the body
via exhaled air. Most Pb enters the body through the GI tract, by
either ingestion or movement from the nose, throat, and lungs. From
the GI tract, Pb is either absorbed into the blood or eliminated from
the gut via the feces. The Uptake Module calculates media-specific
Pb uptake rates using the following equation:
Pb Uptake Rate = Pb Intake Rate * Absorption Factor
The Pb intake rates are calculated by the Exposure Module, and the
absorption factors are typically standard default values establishedby
EPA. The Pb intake rates and absorption factors are both age- and
media-specific. Absorption factors reflect the percentage of Pb that
enters the bloodstream after intake from a specific medium. The
overall Pb uptake value can be obtained by summing the media-
specific Pb uptake values, up to a certain Pb intake concentration.
However, at high doses, the absorption factors must be modified to
account for saturation effects. The total rate of Pb uptake is
calculated for use in the Biokinetic Module.
Biokinetic Module. This module addresses the transfer of absorbed
Pb between blood and other body tissues; the elimination of Pb from
the body via urine, feces, skin, hair, and nails; and the storage and/or
disposition of Pb in the extra-cellular fluid, red blood cells, liver,
kidney, spongy bone, compact bone (femur), and other soft tissue.
The total amount of Pb in each body compartment is age dependent
and calculated using total Pb uptake derived by the Uptake Module.
The Biokinetic Module estimates transfer rates for Pb moving
between compartments and through elimination pathways. A variety
of complex equations are used to calculate compartmentalPb transfer
times. Based on site-specific environmental exposures input by the
user, a geometric mean PbB concentration is predicted.
Probability Distribution Module. This module estimates a
plausible distribution of PbB concentrations that is centered on the
geometric mean PbB concentration calculated by the Biokinetic
Module. From this distribution, the model calculates the probability
or risk that a child's PbB concentration will exceed a user-selected
PbB level of concern (typically 10 ng/dL). In running this portion of
the model, the user specifies a PbB level of concern and a geometric
standard deviation (GSD). For most sites EPA recommends use of
the default values for both the GSD and PbB level of concern.
Media Concentrations for Input
Soil
Dust
Air (default)
Drinking Water (default)
Soil must be sampled. Site-specific data required.
Site-specific data required or input value can be derived from soil
concentration using multiple source analysis.
0.1 ng/m3
4^g/L
Refer to the lEUBKwin User's Guide and
1994 Guidance Manual for additional
information on this input parameter.
Refer to the lEUBKwin User's Guide and
1994 Guidance Manual for additional
information on this input parameter.
Ratio of indoor to outdoor air Pb cone, is
30%. Site-specific data may be substituted.
Site-specific data may be substituted.
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Media Intake Rates (Pb Intake Rate = Media Pb Concentration
Soil/Dust
Air
Drinking Water
Diet
Alternative Sources
0-1 yr 0.085 g/d
1-2 yrs 0.135 g/d
2-3 yrs 0.135 g/d
3-4 yrs 0.135 g/d
0-1 yr 2 nf/d
1-2 yrs 3 nf/d
0-1 yr 0.2 L/d
1-2 yrs 0.5 L/d
2-3 yrs 0.52 L/d
3-4 yrs 0.53 L/d
0-1 yr 5.53 ng Pb/d
1-2 yrs 5.78 ng Pb/d
2-3 yr 6.49 ng Pb/d
3-4 yr 6.24 ng Pb/d
4-5 yrs
5-6 yrs
6-7 yrs
2-5 yrs
5-7 yrs
4-5 yrs
5-6 yrs
6-7 yrs
4-5 yrs
5-6 yrs
6-7 yrs
* Media Intake Rate)
0.1 00 g/d
0.090 g/d
0.085 g/d
5 nf/d
7 nf/d
0.55 L/d
0.5 8 L/d
0.59 L/d
6.01 ngPb/d
6.34 ng Pb/d
7.00 ng Pb/d
Site-specific data may be used to account for intakes of Pb in
sources such as Pb paint.
Default intake values recommended. The
default intake value for total soil and dust
ingestion is a ratio of soil ingestion (45%) to
dust ingestion (5 5%).
Default values recommended.
Default values recommended.
Site-specific data may be used to augment the
default intake rates.
Refer to the lEUBKwin User's Guide and
1994 Guidance Manual for further discussion.
What are the module input and default values?
Exposure Module. Input values include media concentrations
and media intake rates. As shown in the table above, EPA has
established default concentrations for Pb in various media and
ingestion rates for air, drinking water, soil/dust, diet, and
alternative sources. The media intake default values are based
on data for children in most instances, with Pb exposures that
are characteristic of children in the U.S. since about 1980.
While these studies have not resolved all of the uncertainty in
childhood Pb exposure, they do provide a realistic basis for
quantitative modeling. The media intake default parameters
selected for use in the IEUBK model were selected from the
central portions of the ranges of values observed in the different
studies.
Use of the model defaults is recommended unless adequate, site-
specific monitoring data exist to define values that are higher or
lower in magnitude. For example, site-specific data for locally
caught fish or home-grown vegetables can be utilized to
augment the diet default values. This is especially significant
for sites where home-grown produce or local game represents a
large portion of dietary intake. Site-specific data are commonly
used in place of the model default values for Pb concentrations
in soil, dust, air, and water.
Site-specific soil data should be entered as an arithmetic mean
soil Pb concentration. In the absence of site-specific data on
other indoor sources of Pb, dust Pb concentrations may be
calculated from the arithmetic mean soil concentration according to
a default mass fraction ration of 0.7 (multiple source analysis).
Concentrations of Pb in air and water are also measured at some sites.
If a representative number of samples is collected, arithmetic mean
concentrations should be calculated for use in the model. (See the
lEUBKwin User's Guide and 1994 Guidance Manual for technical
discussion of input parameters.)
Uptake Module. Input values include media-specific intake rates
and absorption factors, as explained above. The age-specific and
media-specific intake rates are calculated by the Exposure Module.
EPA has established standard default values for absorption factors
that are age- and media-specific. In cases of very high exposure to
Pb, absorption is characterized by saturable and non-saturable
components. The IEUBK model utilizes absorption factors which
reflects the relative bioavailability of Pb in specific media. The
model assumes that 50% of the Pb intake from drinking water and
food is absorbed and that 30% of the Pb intake from soil and dust is
absorbed. These absorption factors were estimated from the best
available studies of Pb uptake in children and adults. Some site-
specific conditions (e.g., the species of Pb present) may warrant
changing the absorption default values. However, detailed site-
specific studies are required to document the conditions that would
justify changing these values. (See TRW short sheet on
bioavailability: http://www.epa.gov/superfund/programs/lead/
products/sspbbioc.pdf.)
Biokinetic Module. There are no input values for this module.
The values utilized in this module have been incorporated into
the program code for the model and cannot be changed.
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Probability Distribution Module. Input values for this module
are the PbB level of concern and GSD. The recommended
default value for the PbB level of concern is 10 ^g/dL. This
level is based on health effects criteria. The GSD is a measure
of the relative variability in PbB concentrations for a child of
specified age or children from a hypothetical population whose
Pb exposures are known. It is intended to encompass the
variability resulting from biological and behavioral differences,
measurement variability from repeat sampling, sample location
variability, and analytical error. The recommended default
value for GSD is 1.6. This value is based on analyses of data
from neighborhoods with paired data sets for environmental
concentrations and PbB data. The GSD default value should be
appropriate for all sites, unless there are great differences in
child behavior and Pb biokinetics. Model users should not
substitute alternate values for the default GSD without detailed
site-specific studies designed to document the difference that
would justify changing the default value.
When should I use site-specific data instead of model
default values?
Site-specific data are recommended because there may be
potentially important differences among sites. Hence, use of
site-specific data would be expected to result in more accurate
predictions of PbB. However, such data should be evaluated for
merit prior to their use. Model defaults should only be replaced
when site-specific data are more representative than the default
values. Model default values should never by adjusted simply
to attainabettermatchbetweenmodel predictions and empirical
PbB data.
How similar are modeled and empirical blood lead
(PbB) concentrations?
The IEUBK model was calibrated against two different
community PbB and environmental Pb studies. Subsequent
comparisons involving well-conducted blood and environmental
Pb studies have demonstrated reasonably close agreement
between mean observed and predicted PbB concentrations, and
between observed and predicted exceedances of 10 ng/dL, for
children with adequate exposure characterizations. These
studies focused on communities with at least 15% of the
children having PbB concentrations greater than 10 ^g/dL.
Future comparisons will feature study groups that have less than
a 15% probability of exceeding 10
What are the limitations of the IEUBK model?
While the IEUBK model provides a fairly good estimate of risk from
exposure to Pb, as with all models, it has limitations to its use. First,
the model should not be relied upon to predict PbB accurately above
30 [ig/dL. Above this concentration, the relationship between
absorbed Pb and children's PbB concentrations has not been
characterized. However, this should not cause any difficulties for the
IEUBK model in risk assessment applications, as this value is well
above the level of concern of 10 ^g/dL. Additionally, the model
should not be used for exposure periods of less than three months, or
in which a higher exposure occurs less than one per week or varies
irregularly. Finally, it is not the goal of the IEUBK model to match
the measured PbB of a specific child. The model is designed to
predict an average PbB concentration for an entire population, or the
probability that a child with a specific exposure scenario would have
an elevated PbB.
Whom should I contact for more information?
More detailed information regarding the IEUBK Model can be
obtained through the following:
>• Guidance Manual for the Integrated Exposure Uptake
Biokinetic Model for Lead in Children (Publication 9285.7-15-
1).
>• Technical Support Document: Parameters and Equations Used
in the Integrated Exposure Uptake Biokinetic (IEUBK) Model
for lead in Children (Publication 9285.7-22).
>• User's Guide for the Integrated Exposure Uptake Biokinetic
Model for Lead in Children (IEUBK) Windows'* version
(Publication 9285.7-42).
* System Requirements and Design for the Integrated Exposure
Uptake Biokinetic Model for Lead in Children (IEUBK)
Windows* version (Publication 9285.7-43).
>• Reference Manual: Documentation of Updates for the
Integrated Exposure Uptake Biokinetic Model for Lead in
Children (IEUBK) Windows"3 version (Publication 9285.7-44).
>• Reviewing the Technical Review Workgroup for Lead (TRW)
home page (http://www.epa.gov/superfund/programs/lead).
Calling EPA's IEUBK Technical Support Center (1-866-282-
8622).
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