EPA #540-F-00-007
OSWER #9285.7-33
December 1999
SHORT SHEET:
IEUBK MODEL SOIL/DUST INGESTION RATES
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 8 NCEA/Washington
Jim Luey Paul White
Denver, CO
MEMBERS
Region 1 NCEA/Washington
Mary Ballew Karen Hogan
Boston, MA
NCEA/Cincinnati
Region 2 Harlal Choudhury
Mark Maddaloni
New York, NY NCEA/Research Triangle Park
Robert Elias
Region 4
Kevin Koporec OERR Mentor
Atlanta, GA Larry Zaragoza
Office of Emergency and Remedial Response
Region 5 Washington, DC
Patricia VanLeeuwen
Chicago, IL Executive Secretary
Richard Troast
Region 6 Office of Emergency and Remedial Response
Ghassan Khoury Washington, DC
Dallas, TX
Associate
Region 7 Scott Everett
Michael Beringer Department of Environmental Quality
Kansas City, KS Salt Lake City, UT
Region 10
Marc Stifelman
Seattle, WA
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IEUBK Model Soil/Dust Ingestion Rates
Purpose and Summary
This short sheet provides recommendations on substitution
of default soil/dust ingestion rates in the Integrated Exposure
Uptake Biokinetic Model for Lead in Children (IEUBK model).
In addition to reviewing basic information pertaining to this
parameter, the short sheet addresses questions on the adjust-
ment of default soil/dust ingestion values.
This short sheet reaffirms the provisions of the Administra-
tive Reform for Lead Risk Assessment that requires a review of
new data on soil ingestion before use in the IEUBK model by
the EPA's Office of Emergency and Remedial Response
(OERR). This review not only promotes better science but
also promotes sharing of information so that all EPA Regions
can benefit from improvements in soil/dust ingestion data.
Soil/Dust Ingestion Rates
One of the parameters that the IEUBK model uses to estimate
child blood lead concentrations is the ingestion of the mass of
soil and household dust. Young children are primarily exposed
to lead through fine particles of surface soil and household
dust that adhere to their fingers and are incidentally ingested
during normal hand-to-mouth activity. The rate at which soil/
dust is ingested depends on a number of factors including a
child's age, activity patterns, and total dust and soil accessible
in the environment. Soil and dust ingestion rates discussed in
this paper include both indoor and outdoor ingestion. The
contribution of outdoor soil to interior dust is discussed in the
MSD1 short sheet that was issued in 1998.
Age Dependent Default Soil/Dust Ingestion Rates
Used in the IEUBK Model
The age-specific default soil/dust ingestion rates recommended
foruse in the IEUBK model range from 0.085 to 0.135 g/day and
are illustrated in Table 1. These values are representative of
average daily intake rates; they do not incorporate variability
in consumption patterns, nor do they reflect pica behavior.
Clearly, there are children who will have soil and dust inges-
tion rates higher than the values reported in Table 1.
While there is uncertainty associated with the soil/dust inges-
tion rate values, a review conducted by the Technical Review
'MSD is a variable in the dust lead Multiple Source Analysis module of
the IEUBK model which represents the mass fraction of house dust
that is derived from outdoor soil.
TABLE 1- IEUBK Soil/Dust Ingestion Defaults by Age
Age Group (years)
0-1
1-2
2-3
3-4
4-5
5-6
6-7
IEUBK Model Defaults
(g/day)
0.085
0.135
0.135
0.135
0.100
0.090
0.085
Source: U.S. EPA, 1994
Workgroup (TRW) determined that these values are appropri-
ate and representative estimates of soil ingestion for U.S. chil-
dren. This is especially true for application in the IEUBK model
because the model has been calibrated and validated using
these default values.
Basis for Default Values
As indicated in the Guidance Manual for the IEUBK Model,
the development of default values for the rate of soil/dust
ingestion involved a literature review and relied upon an analy-
sis performed during a review of the National Ambient Air
Quality Standards (NAAQS) for lead. The calibration of the
IEUBK model employed these default values, and validation
study results performed to date show good agreement be-
tween model estimates using these intake values and empirical
blood lead measurements. For the purposes of the IEUBK
model it is recommended that the soil and dust ingestion rates
be defined on an age-specific basis as shown in Table 1. By
contrast, the Exposure Factors Handbook (U.S. EPA, 1997;
U.S. EPA, 1999) recommends the use of a mean of 0.10 g/day
for soil ingestion and reports a value of 0.20 g/day as a con-
servative estimate of the mean for soil ingestion. Given this
information from the Exposure Factors Handbook, the values
recommended for use in the IEUBK model represent central
values within the range of values observed in the soil and dust
ingestion studies. The default soil and dust ingestion values
are based on several observational studies of soil ingestion in
children. These studies were conducted in the U.S. by Binder
etal. (1986), Clausing etal. (1987), Calabresee/a/. (1989,1991),
vanWijnene/a/. (1990), and Davis et al. (1990), utilizing trace
elements to quantify soil ingestion rates. In general, this meth-
odology constitutes a reasonable basis for estimating the quan-
tity of soil ingested.
Produced by the Technical Review Workgroup for Lead (TRW) "/\\
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It is necessary to make a distinction between the quantity of
soil ingested and the quantity of soil plus dust ingested. Logi-
cally, the latter quantity will be larger, and data from the soil
ingestion studies support this theory (Davis et al., 1990).
The experimental studies reporting estimates of soil ingestion
have generally relied upon mass balance studies employing
trace metals to estimate ingestion. While these studies have
been useful to derive estimates of soil ingestion, they are sub-
ject to considerable uncertainty, as reflected in the variation in
estimates for soil ingestion for the different trace metals. Many
factors that are believed to have influenced these uncertain-
ties. These factors include: lack of alignment in the measure-
ment of trace metals in food and waste; confounding influence
of trace metals from unknown sources; and loss of trace met-
als in urine (few studies examined trace metal loss in urine).
For these reasons and because the IEUBK model has been
calibrated and validated with the ingestion rate values in Table
1, the TRW strongly recommends these default estimates to
support lead risk assessment analyses performed with the
IEUBK model.
Substitution of Default Values of Ingestion Rates:
Technical Considerations
The IEUBK model default values for the rate of soil/dust inges-
tion do not reflect differences associated with variables that
may affect ingestion rates at different sites. Examples of such
variables include ground cover, climate, activity patterns, and
behavior. While inclusion of such information in a risk assess-
ment is desirable, often such data are not available to support
quantitative adjustment of ingestion rates in the IEUBK model.
Recognizing the technical difficulties of interpreting soil and
dust ingestion studies, the Administrative Reform for Lead
Risk Assessment specified that adjustments to the IEUBK
model default ingestion rates be performed only after OERR
recommends such a change. The process for obtaining a
recommendation is to submit all information pertaining to the
ingestion study to OERR for review by the TRW. The results
of the TRW review will be sent to the requestor, and, if any
improvement in the soil and dust ingestion estimate is war-
ranted, will be incorporated into guidance and shared among
other EPA Regions. This process promotes the sharing of data
and consistency in lead risk assessments.
References
Binder, S., Sokal, D., Maughan, D. 1986. Estimating soil inges-
tion: The use of tracer elements in estimating the amount of soil
ingested by young children. Arch. Environ. Health 41:341-345.
Calabrese, E., Barnes, R., Stanek, E. I, Pastides, H., Gilbert, C.,
Veneman, P., Wang, X., Lasztity, A., Kostecki, P. 1989. How
much soil do young children ingest: An epidemiological study.
Reg. Toxicol. Pharmacol. 10 (2): 123-137.
Calabrese, E., Stanek, E.J., Gilbert, C.E. 1991. Evidence of soil-
pica behavior and quantification of soil ingested. Human Experi.
Toxicol. 10:245-249.
Clausing, P., Brunekreef, B., van Wijnen. J.H. 1987. A method
for estimating soil ingestion by children. Int. Arch. Occup.
Environ. Health 59:73-82.
Davis, S., Waller, P., Buschbom, R., Ballou, I, White, P. 1990.
Quantitative estimates of soil ingestion in normal children be-
tween the ages of 2 and 7 years: population-based estimates
using aluminum, silicon, and Titanium as Soil Tracer Elements.
Arch. Environ. Health 45(2): 112-122.
U.S. Environmental Protection Agency. 1994. Guidance
Manual for the Integrated Exposure Uptake Biokinetic Model
for Lead in Children. Office of Emergency and Remedial Re-
sponse. EPA/540/R-93/081.
U.S. Environmental Protection Agency. 1996. Administrative
Reforms for Lead Risk Assessment. Memorandum to EPA Re-
gional Division Directors. Office of Emergency andRemedial
Response. Washington, DC 20460.
U.S. Environmental Protection Agency. 1997. Exposure Fac-
tors Handbook. Office of Research and Development, Volume
I-General Factors, EPA/600/P-95/002Fa, Office of Research and
Development, Washington, DC 20460.
U.S. Environmental Protection Agency. 1999. Exposure Fac-
tors Handbook. EPA/600/C-99/001 Office of Research and
Development, Washington, DC 20460.
Van Wijnen, J. H., Clausing, P. Brunekreef, B. 1990. Estimated
Soil Ingestionby Children Environ. Res. 51:147-162.
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