2. A GUIDED TOUR THROUGH THE LEAD MODEL 

2.1 THE LEAD MODEL IS DRIVEN BY MENUS 

Environmental Protection Agency's Integrated Exposure, Uptake, and Biokinetic Model 

for Lead in Children (IEUBK Model) is a microcomputer program that performs many 

different functions related to estimating blood lead levels in children. The overall model 

functions are sketched in Figure 2-1. 

Figure 2-1. Schematic diagram of the overall functions of the lead model. Numbers in 

pentagons indicate sections in this document containing more detailed 

information. 

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The oval shapes are terminal steps (i.e., the beginning or end of a function or option). 

Rectangles show internal processes and rhomboids show user data entry operations or 

functions. Diamond-shaped figures are decision points where the user must choose one of the 

model options on a list. The "NO" branch usually follows the model's baseline or "default" 

parameters and functions. Horizontal and vertical arrows refer the user to another figure or 

page. 

The IEUBK model is menu-driven, with on-line help available in almost any menu. 

The main menu, where any use of the IEUBK model begins, is shown in Screen 2-1. There 

are five numbered options: 

1. Parameter Input Menu 

1: Air lead menu 

2: Dietary lead menu 

3: Drinking water lead menu 

4: Soil/Dust lead menu 

5: Alternative lead source menu 

6: Maternal lead menu 

L: Load pre-saved parameter input menu 

R: Return to Main Menu 

2. Computation Menu 

1: Run a single model simulation 

2: Multiple simulation runs with a range of values 

3: Blood lead versus media with a range of values 

4: Multiple simulation runs with batch input (input data file for each child 

or household) 

R: Return to Main Menu 

3. Output Processing Menu 

1: Save program parameters to file 

2: Plot graphs of blood lead distributions 

R: Return to Main Menu 

4. Help Menu 

1: General information 

2: Information about menus plus help in other menus 

R: Return to Main Menu 

5. Quit 

Q: Return to DOS prompt. 

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Screen 2-1. The main menu. 

We will briefly discuss the options in each of the input menus. Scientific justifications 

for the options and guidance values are provided in Section 2.3. 

2.2 DETAILED DESCRIPTION OF MENUS 

2.2.1 Help Menu (4) 

2.2.1.1 General Help (1) 

The General Help menu provides on-line information on the data or parameter entry 

menus, menu selections for running single or multiple model simulations, and use of 

keyboard keys. This information is shown in Screen 2-2. 

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Screen 2-2. The general help menu. 

2.2.1.2 Information Menu (2) 

The Information Menu provides on-line information on the parameter save and load file 

options, on multiple-run and output processing menus. The information is presented here in 

Screen 2-3. 

2.2.1.3 Other On-Line Help Menus 

Most menu screens contain additional information on the lower part of the screen. 

Additional information screens are available on specific menu options. 

2.2.2 Parameter Input Menus 

2.2.2.1 Air Lead (1) 

The Air Lead input parameter menu is shown in Screen 2-4 and schematically in Figure 

2-2. The air lead concentration is set initially to a typical 1993 urban value of 0.1 Fg/m3 

(U.S. Environmental Protection Agency, 1991c). It is assumed that the indoor air 

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Screen 2-3. The information menu. 

If you want t o vary air concent rati on for each year or view current 

variable dat a -----> Y for YES 

NO is displayed in this field if all yearly concent rati ons are equal. 

YES is displayed in this field if all yearly concent rati ons are NOT equal. 

NO MUST be select ed t o ent er a single conc. for Out door Air Lead Conc. 

HELP WI NDOW 

Esc: I N Menu F1: General HELP F5: RUN Model PgUp/ PgDn: ia Switch 

Vary Air Conc. By Year ??? <No/ Yes> : NO 

Out door Air Lead Concent rati on (μg/ m3) : 0.100 

Indoor Air Pb Conc. (Percent age of Outdoor) : 30.0 

View/ Change Time Spent Out doors / Yes> : Default 

View/ Change Ventilati on Rat es <No/ Yes> : Default 

View/ Change Lung Absorpti on % <No/ Yes> : Default 

Dat a Ent ry for AI R Press either: 

N for NO 

Y for YES 

Press 

MA Med

+ 

<No

Screen 2-4. The air lead menu. 

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Figure 2-2. Decision diagram for the air lead menu options. 

lead concentration is 30% of the outdoor concentration (i.e., 0.03 Fg/m3) initially. The time 

spent outdoors and ventilation rate are assumed to depend on the child's age. These 

parameters allow a time-weighted air lead intake to be calculated; 32% of that intake is 

absorbed through the lungs into the child's blood. All parameters except the indoor/outdoor 

air lead concentration ratio may be changed by entering YES in the first line. Some are 

age-specific values. 

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2.2.2.2 Dietary Lead (2) 

The Dietary Lead input parameter menu is shown in Screen 2-5 and schematically in 

Figure 2-3. The daily dietary lead intake values for each age apply to a typical U.S. child in 

a typical setting in the United States after 1990. These dietary lead values may be altered by 

entering YES to the query "View/Change Dietary Pb Intake?" During the period 1982-1989 

there was a distinct reduction in food lead generally attributed to the replacement of leadsoldered cans and the removal of lead from gasoline. Since 1990, food lead in U.S. 

supermarket food has remained relatively constant. Dietary lead ingestion for years prior to 

1990 are given in Section 2.3.2. 

Screen 2-5. The dietary lead main menu. 

If the dietary lead sources are non-standard, usually because of suspected contamination 

of fruits, vegetables, fish and meat raised locally or otherwise lead-contaminated, the user 

can enter specific values by responding YES to the query, "Use Alternate Diet values?" This 

invokes the alternative menu shown in Screen 2-6. 

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Figure 2-3. Decision diagram for the dietary lead menu options. 

2.2.2.3 Drinking Water Lead (3) 

The Water Lead input parameter menu is shown in Screen 2-7 and schematically in 

Figure 2-4. The water lead concentration is set initially to a typical 1990 urban value of 

4 Fg/L (Marcus and Holtzman, 1990). The age-specific ingestion of tap water is described in 

Section 2.3.3.2. Consumption may be modified by responding YES to "View/Change 

Drinking Water Intake?" and entering new values, as shown on Screen 2-8. 

Alternative information may be available in the form of measured lead concentration 

and percentage of tap water intake from water fountains or other outside sources, and water 

2-8
Screen 2-6. The alternative dietary source menu. 

Screen 2-7. The drinking water lead main menu. 

2-9
Figure 2-4. Decision diagram for the drinking water lead menu options. 

consumed at home in first-draw or flushed modes. This may be entered by responding YES 

to "Use Alternate Water Values?" 

2.2.2.4 Soil and Dust Lead (4) 

The Soil and Dust Lead input parameter menu is shown in Screen 2-9 and schematically 

in Figure 2-5. The soil and dust lead concentrations are set initially to a value of 200 Fg/g. 

The age-specific ingestion intake of soil and dust combined was estimated from the 

EPA/OAQPS staff paper on Exposure Assessment Methodology and Validation for the first 

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Screen 2-8. The age-specific drinking water consumption menu. 

Screen 2-9. The soil and dust main menu. 

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Figure 2-5. Decision diagram for the soil/dust lead menu options. 

version of the UBK model (U.S. Environmental Protection Agency, 1989a). Both 

concentration and intake may be modified by the user. 

As shown in Screen 2-9, both soil lead and dust lead concentrations may be changed on 

a yearly basis by user selection "2", allowing the user to construct reasonable site-specific 

scenarios. 

The multiple-source option ("3") on the dust entry line allows the user to use 

information about the contribution of soil lead, air lead, and other sources to household dust 

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lead. The Data Entry Screen for the Multiple Source Analysis (Screen 2-10) has three data 

entry lines. The first line is the fraction of the soil lead concentration that contributes to the 

concentration of lead in household dust. If there were no other sources, this would be the 

ratio of the dust lead concentration to the soil lead concentration. The current default value 

of 0.70 is appropriate to neighborhoods or residences in which loose particles of surface soil 

are readily transported into the house. The second data entry line is the contribution to 

household dust from the deposition of airborne lead, over and above the soil lead 

contribution. The current default value is an additive increment of 100 Fg/g lead in house 

dust for each Fg Pb/m3

 air. 

Screen 2-10. The multiple dust source menu. 

The third line asks whether the user wants to add other sources. If "Yes", then the 

Multiple Source Analysis Screen is replaced by the Alternative Indoor Dust Entry screen 

(Screen 2-11). The user may assign both the concentration and percentage of dust intake to 

baseline household dust, secondary occupational dust, dust at school, daycare, or second 

home, and the exposure to lead in dust from household paint measured as a percentage of 

total dust ingestion and its concentration. The default dust lead concentration in the 

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Screen 2-11. The alternative indoor dust menu. 

Alternative Indoor Dust Entry screen is 100% of household dust at 150 Fg/g. If the 

Alternative Source Analysis is not used, then the default dust contribution consists of 70% of 

the soil concentration plus 100 times the air lead concentration. For default conditions, the 

total dust lead concentration equals 150 Fg/g. 

If non-residential exposures to soil/dust are important, the user may access the multiple 

non-residential source menu. 

The combined soil/dust ingestion rate (grams total soil + dust per day) can be changed 

from the current default values in Screen 2-12. 

2.2.2.5 Alternate Source (5) 

The alternate exposure source menu is shown in Screen 2-13 and schematically in 

Figure 2-6. The default daily lead intake value for each age is set to 0 Fg Pb/day. The user 

has the option to input any source not otherwise covered by other menus. Examples might be 

the direct ingestion of lead-based paint, cosmetics or home remedies. In this case, the 

amount of lead per day needs to be calculated from the information available. If the 

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Screen 2-12. The soil/dust ingestion rate menu. 

Screen 2-13. The alternate lead source menu. 

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Figure 2-6. Decision diagram for the alternate lead source menu options. 

alternative source is lead-based paint (LBP), this exposure would be in addition to exposure 

to lead-based paint in house dust, which is Option 4 in the multiple source menu of soil and 

dust. See Section 4.7.1 for a discussion on issues in the use of the model for paint chips. 

Building an exposure scenario using this option should be done with care. The model 

assumes all entries represent chronic exposure. In the example above, the child would 

require immediate medical attention. Remember that the model output represents only those 

children defined by the exposure scenario. 

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2.2.2.6 Bioavailability of Lead in Food, Drinking Water, Soil, and Dust 

Bioavailability or absorption of intake from the gut or lung into the blood is a key 

element in relating external exposure to body burden. Lead intake from media with low 

bioavailability poses much less of a hazard than does the same intake from media with high 

bioavailability. The bioavailability of lead from normal infant diet is known to be very high 

(Alexander et al., 1974a,b; Ziegler et al., 1978; Ryu et al., 1983), with at least 40 to 50% of 

the dietary lead intake passing into the child's blood. See Section 4.1 for a discussion of 

bioavailability. 

The main functions of the bioavailability menu are shown in Figure 2-7. The model 

calculates lead absorption from the gut as a function of two components. The passive 

component does not depend on lead concentration in the gut and is not saturable. The 

facilitated or active component may become saturated when the total concentration of lead in 

the gut from total gut intake by all media is sufficiently large, which is a kinetically 

non-linear absorption mechanism. The data entry Screen 2-14 allows the user to specify the 

parameters for intake from soil, dust, drinking water, diet, and alternate sources. The total 

absorption percentage is the sum of the passive and facilitated absorption components. The 

default value of absorption for alternate sources is 0%, which requires that the user must 

enter the bioavailibilty of any specific alternative source, such as lead-based paint. 

The total absorption from any medium is then divided into two components, and the 

user specifies a small fraction of the total absorption percent for the passive or non-saturable 

(i.e., high-dose) component. The default is 20% of the total available for absorption. The 

percentage absorption in the larger saturable component is the remainder of the total available 

for absorption. For example, with a dietary lead intake of 50%, the absorption fraction for 

the passive component is 20% of 50%, or 10% of dietary lead intake, and the saturable 

component is 80% of 50%, or 40% of dietary lead intake. 

2.2.2.7 Maternal-Fetal Lead Exposure (6) 

The maternal lead exposure input parameter menu is shown in Screen 2-15. The lead is 

transferred from the mother to the fetus in utero. The lead that is stored in the tissues of the 

newborn child is calculated by entering the maternal blood lead value at birth (default = 2.5 

Fg/dL). The IEUBK model assumes that the infant's blood lead at birth is a fraction of the 

maternal blood lead level, and the amounts of lead in the blood and other tissues in the 

newborn infant are calculated so as to be consistent with concentration ratios observed in 

autopsies of newborn infants (Barry, 1981). 

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Figure 2-7. Decision diagram for the absorption/bioavailability menu options. 

2.2.2.8 Save and Load Options 

If the user wishes to use a certain set of model parameters as the starting point for 

another analysis, the parameter set created from use of Options 1 through 6 should be saved 

using the "S" option on the output menu accessed from the main menu, or the F6 option on 

any of the parameter input menus. The user may create an 8-character or shorter name for 

the file, which will be stored in the form [NAME].SV3. If a saved parameter set is needed 

later, it may be loaded from the "L" option on the Parameter Input Menu. 

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Screen 2-14. The absorption/bioavailability menu. 

Screen 2-15. The maternal/fetal lead exposure menu. 

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2.2.3 Computation Menu 

2.2.3.1 Run a Single Simulation of the Model (1) 

The menus for the Run command are shown in Screen 2-16. This option uses only the 

currently loaded parameter set. The user may view or change the time step for the 

numerical iteration. The default is four hours. We recommend setting the iteration time to 

the lowest convenient selection, and verifying all "important" solutions by rerunning the 

model with the shortest possible time step (currently 15 min). An output option (Option 2) 

allows plotting of results and calculation of probability of elevated blood lead. 

Screen 2-16. Single simulation using the program processing menu. 

2.2.3.2 Run Multiple Simulations of the Model for a Range of Media Lead (2) 

The menus for the Multiple Run command are shown in Screen 2-17 and schematically 

in Figure 2-8. More detailed menus for range selection and output are shown in Screens 2-18 

and 2-19. This option uses only the currently loaded parameter set, except that it repeats the 

run for each new value of a medium concentration (e.g., soil lead concentration) or intake 

(dietary lead as Fg Pb per day). The user may view or change the 

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Screen 2-17. Multiple simulation using the program processing menu. 

time step for the numerical iteration during the run step. We recommend verifying all of the 

"important" solutions by rerunning the model with the shortest possible time step (currently 

15 min). Since only one medium can be changed in each use of the "2" option, the user who 

wants to look at a range of soil lead values should use the Multiple Source Dust option "3" 

and a user-specified dust lead to soil lead concentration ratio. Output data for plotting, with 

overlays of results at each concentration in the range, may be saved when the user creates 

RANGE#.LAY files. 

2.2.3.3 Multiple Simulation Runs of a Medium To Find Concentration of Lead in the 

Medium That Produces a Specified Blood Lead (3) 

This option is similar to Option 2. The menus for the Multiple Run command are 

shown in Screen 2-20 and schematically in Figure 2-8. This option uses only the currently 

loaded parameter set, except that it repeats the run for each new value of a medium 

concentration (e.g., soil lead concentration) or intake (dietary lead as Fg Pb per day) until the 

specified age-dependent geometric mean blood lead level is achieved exactly by that 

concentration. 

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Figure 2-8. Decision diagram for the multiple simulation menu options. 

Since only one medium can be changed in each use of the Multiple Simulation Run "3" 

option, the user who wants to look at a range of soil lead values should use the Multiple 

Source Dust option "3" and a user-specified dust lead to soil lead concentration ratio. Output 

data for plotting may be saved when the user creates *.PBM files. 

2.2.3.4 Batch Mode Multiple Simulation Runs Using Input Data Files (4) 

This option is similar to Option 2. The menus for the Batch Mode Run command are 

shown in Screen 2-21 and schematically in Figure 2-9. This option uses the currently loaded 

default parameter set, but repeats the run for using the new values for the five exposure 

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Screen 2-18. Selection of media for multiple range run. 

Screen 2-19. Range selection during multiple processing. 

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Screen 2-20. Using multiple simulation to find acceptable media concentrations for a 

predetermined blood lead concentration. 

Screen 2-21. Running the model in batch mode. 

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Figure 2-9. Decision diagram for the batch mode menu options. 

parameters (soil concentration, dust concentration, drinking water concentration, air 

concentration and alternate source consumption) for each child in the data set. The input data 

are entered one line at a time from a data set with a specified list of input variables. These 

must be created by the user in a special *.DAT file in the Lead Model directory. 

Each line of data may include: 

The child code or case; 

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The "family" identifier for individuals at the same living unit; 

An area, block, or neighborhood identifier; 

Each line of data must include: 

The child's age, in months, as of the end of the data collection period; 

The soil lead concentration, in Fg/g; 

The house dust lead concentration, in Fg/g; 

The drinking water lead concentration, in Fg/L; 

The air lead concentration, in Fg/m3; 

The alternate source intake rate, in Fg/day; 

The child's blood lead level at specified age, in Fg/dL. 

The child's age must be entered. Either a soil lead or a dust lead value is needed for the 

simulation, along with a stand-in value (imputation rule) if one of them is missing (for 

example, if the user does not fill in missing dust lead values, the current default is to replace 

a missing dust lead concentration by the soil lead concentration). The user may prefer to 

create an input data file with missing dust lead concentrations replaced by some fraction of 

the soil lead concentration. Missing values of air, water, and alternate lead are replaced by 

default values. If there is no actual child blood lead data, then Option 1 produces output data 

sets with *.ASC and *.TXT extensions that contain all of the input data, including imputed 

values, and predicted blood lead levels for each line of data. 

The batch mode option can be used to perform statistical analyses of simulated 

community blood lead distributions, even without observed blood lead levels (for example, if 

an investigator has carried out a multimedia environmental lead study at a site, without blood 

lead data being collected). However, this option will be even more useful if blood lead data 

from a well-conducted study are available for model comparisons using statistical tests in 

Option 5. Output data files may be reviewed using Option 2, as demonstrated in later 

sections. 

2.2.3.5 Statistical Analyses of Batch Mode Data Sets (4) 

A set of statistical procedures for analyzing batch mode data sets exists as a separate 

module in the IEUBK Lead Model. Although the Option 1 data sets can be edited and used 

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in any other statistical programs the user may have available, we have included in Option 5 

some of the most commonly used statistics, statistical hypothesis tests, and graphical data 

displays for comparing observed and modelled blood lead levels. We recommend using a 

variety of graphical and statistical techniques in evaluating the output of Batch Mode model 

runs. This will also be demonstrated in Section 5. 

2.3 BUILDING AN EXPOSURE SCENARIO 

2.3.1 Air Lead Menu 

2.3.1.1 Default Air Lead Exposure Parameters 

The default air lead concentration is 0.1 μg/m3, which is approximately the average 

1990 urban air lead concentration (U.S. Environmental Protection Agency, 1991b). During 

the period 1970-90, ambient air lead concentrations dropped drastically in the United States 

due to the phasedown of lead in gasoline (Figure 2-10). When adequate monitoring data exist 

to define concentrations higher or lower than the default outdoor lead concentrations, these 

should be used. Current air lead levels are low in most places in the United States, and do 

not require year-to-year specification. Elevated air lead levels have been reported around 

some point sources in the United States and Europe (Davis and Jamall, 1991) and lead 

modeling for changes in these sources requires year-by-year input data. 

A constant air lead value larger than 0.1 μg/m3 may be appropriate for assessment at 

locations in the vicinity of active point sources of lead emissions such as lead smelters or 

battery plants. In such cases, an appropriate estimate of annual average air lead concentration 

must be available. 

An example of a striking increase over time was the air lead levels in Kellogg/Silver 

Valley, Idaho, following a September 1973 baghouse fire. These levels remained elevated 

for a sufficiently long time such that the use of these values in predicting blood lead 

concentrations for 1974-1975 from the Lead Model was justified (Agency for Toxic 

Substances and Disease Registry, 1988). 

2.3.1.2 Ventilation Rate 

The intake of air increases from infancy to adulthood. The range of values for child 

ventilation rates was established by EPA (U.S. Environmental Protection Agency, 1989a) as 

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Figure 2-10. Historical relationship between lead in gasoline and lead in air in the

United States.

Source: 

2 to 3 m3/day at age 0 to 1 years, 3 to 5 m3/day at age 1, 4 to 5 m3/day at ages 2 and 3, 5 to

7 m3/day at ages 4 and 5, and 6 to 8 m3/day at age 6. 

of 2, 3, 5, and 7 m3

/day at ages 0+, 1, 2 to 4, and 5 to 7 respectively. 

exercise more than average will have a correspondingly greater intake, and those who are

very inactive will have a lower ventilation rate. 

modeling children who spend time at playgrounds or outdoor play areas near an air lead

source. 

neighborhood.

2.3.1.3 Indoor/Outdoor Activity Patterns

The range of values for outdoor time was established by EPA (U.S. Environmental

Protection Agency, 1989a) as 1 to 2 h/day in the first year of life, 1 to 3 h at age 1, 2 to 4 h

at age 2, and 2 to 5 h/day from ages 3 to 7. 

3, and 4 h/day at ages 0+, 1, 2, and 3+, respectively, roughly at the middle of these ranges. 

The outdoor air lead concentration provides a large part of the total air lead exposure,

because the indoor air lead concentration is typically only about 30% of the outdoor

U.S. Environmental Protection Agency (1986), with updating.

The Lead Model uses midrange values

Children who

The higher intakes may be useful in

Changes in activity pattern can change ventilation rate in a child or in a

The default values in the Lead Model are 1, 2,
concentration (U.S. Environmental Protection Agency, 1986). Site-to-site differences may 

exist due to natural ventilation, climate, season, family activity, and community access to 

outdoor play activities. 

2.3.1.4 Lung Absorption 

The range of values for child lung absorption was established by EPA (U.S. 

Environmntal Protection Agency, 1989a) as 25 to 45% for young children living in non-point 

source areas, and 42% for those living near point sources. The default value used in the 

Lead Model is 32%. Changes in the source of airborne particulates may also affect lung 

absorption. No quantitative recommendations can be made. 

EXAMPLE 2-1: Characterizing Effects of Air Lead Phasedown on Inhalation Intake 

If the Lead Model were to be used to estimate blood levels of children living in an 

urban area in previous decades, when the predominant sources of lead exposure for many 

U.S. children were air lead from combustion of leaded gasoline and dietary lead from leadsoldered food cans, it would necessary to use community air lead levels during that period of 

time. Representative values of air lead concentrations were presented in the EPA Air Quality 

Criteria Document for Lead (U.S. Environmental Protection Agency, 1986, Chapter 7, Table 

7-2) for urban center or suburban locations in nine metropolitan areas for 1970 through 1984. 

The reductions in air lead from 1977 through 1988 attributable to the phasedown of leaded 

gasoline are quite evident in both urban centers and suburban areas. For example, for a 

retrospective estimate of blood lead levels in children in 1981, one would need to start with 

1975 air lead levels to include prenatal exposure of children up to age 7 in 1981. Figure 2-10 

shows that air lead exposure in 1981 would be at 0.48 μg/m3

, and so on. For a 5-year old 

child in 1981, air lead exposure, at age 0+ in 1975 is 1.2 μg/m3

, and so on. This adjustment 

in air lead concentration does not estimate the indirect effects of air lead changes on blood 

lead through gradual changes in soil and dust lead. This example is generic, not site-specific, 

however. The air lead data entry screen for children born in 1975 is shown in Screen 2-22. 

2.3.2 Dietary Lead Menu 

2.3.2.1 Total Dietary Lead Exposure 

Data assembled from a variety of sources, including Market Basket Surveys 

(Pennington, 1983) and representing changes in consumer behavior over time, were used to 

construct dietary lead intake estimates as described in Chapter 7 of the EPA Air Quality 

Criteria Document for Lead (U.S. Environmental Protection Agency, 1986). The method is 

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Screen 2-22. Data entry for air. The user may input data from historical records of air 

lead concentrations on this screen. 

based on U.S. FDA Market Basket samples in 231 food categories and has been updated to 

1988 (U.S. Environmental Protection Agency, 1989a). Because two major sources of lead in 

food (lead-soldered cans and air deposition on food crops) have been greatly reduced or 

eliminated, dietary lead is believed to be relatively constant since 1990, especially for 

children under seven years. 

Table 2-1 shows how estimated mean dietary lead intake depends on the child's age, 

and that this intake has changed very drastically with the near-elimination of lead solder from 

food cans and other food packaging in the United States since the 1970s. Where site-specific 

dietary levels are not available, it is recommended that the values from Table 2-1 be used for 

the appropriate years and ages, and that the most recent values (1988) be assumed for all 

future years. Seasonal effects are omitted here since the Lead Model uses annual values for 

dietary exposure parameters. For alternate exposure scenarios with seasonal intakes, the user 

may need to calculate time-weighted annual averages from seasonal data. 

If the Lead Model is used in connection with historical exposures, for such purposes as 

model validation or retrospective dose reconstruction, the dietary intake data should be 

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TABLE 2-1. DIETARY LEAD INTAKE (Fg/day) FOR U.S. CHILDREN BY 

AGE, FOR EACH YEAR FROM 1978 TO PRESENT 

Age 

6-11 Mo 1 Year 2 Years 3 Years 4 Years 5 Years 6 Years 

19781 NE 45.8 52.9 52.7 52.7 55.6 NE 

19791 NE 41.2 48.0 47.8 47.8 50.3 NE 

19801 NE 31.4 36.9 36.9 36.9 38.7 NE 

19811 NE 28.3 33.8 33.7 36.8 35.8 NE 

19822 19.2 25.0 27.5 27.4 27.2 28.6 31.6 

19832 14.4 18.3 21.9 21.4 21.1 22.3 24.8 

19842 19.0 22.7 26.4 26.0 25.7 27.1 29.9 

19852 10.2 10.6 12.3 11.9 11.8 12.4 13.6 

7.9 8.2 9.4 9.1 8.9 9.4 10.3 * 1986

1987-Present3 5.5 5.8 6.5 6.2 6.0 6.3 7.0 

NOTES: NE = Not estimated. 

1 = Estimated by J. Cohen and D. Sledge, Table A-2 (U.S. Environmental Protection Agency, 

1989a). 

2 = U.S. Environmental Protection Agency (1986), updated with data from the FDA Market 

Basket Survey. 

3 = Average of 1986 Q4 through 1988 Q3. Further decreases in food lead concentrations since 

1987 are believed to be negligible. 

* = Linear extrapolation between 1985 and 1987. 

adjusted to the year when the data were collected. For prediction in future years, the most 

recent default value for each age may be used. 

2.3.2.2 Dietary Lead Exposure by Additional Pathways 

For some children, there are important dietary lead sources that are not characterized by 

the FDA Market Basket Survey data summarized in Table 2-1. Child-specific or site specific 

data will be needed to verify these alternative dietary lead sources. Local sources of fruit and 

vegetables are used in many small towns and in rural areas. Some individuals obtain much of 

their produce from their own gardens. If the local or home-grown produce is grown in soils 

with high concentrations of lead, or if the edible leafy portions are contaminated by airborne 

lead particles, then some fraction of the environmental lead may be added to the child's diet. 

The additional intake of lead in diet may become important if the environmental lead 

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concentrations are sufficiently high. This was important in evaluating the Bunker Hill 

Superfund site in Kellogg ID and was included in the Risk Assessment Data Evaluation 

Report (the "RADER") prepared by EPA (U.S. Environmental Protection Agency, 1990c). 

Additional pathways of dietary lead exposure are discussed in Example 2-2. 

Dietary lead exposure is the product of the amount of food consumed in each category 

and the concentration of lead in the food item. Normal intakes are reported by Pennington 

(1983). To adjust for home gardens, a fraction of this intake may be allocated by the 

Alternate Diet Entry Menu to local produce, and the rest to Market Basket produce that is not 

grown locally. 

Local game animals feeding on plants contaminated by lead in soil may also have 

elevated lead concentrations. Lead contamination of rivers and lakes by deposition and by 

erosion of leaded soils may also increase lead concentrations in local fish. Some rural 

families may use hunting and fishing as a significant supplement or even as their primary 

source of animal protein. See Baes et al. (1984) for a comprehensive approach to estimating 

pathways of trace elements in the food chain. A fraction of the meat and fish intake may be 

allocated by the Alternate Diet Entry Menu to local game and fish. 

Other consumer products may have nontrivial potential for dietary lead exposure. 

These include lead-glazed or soldered cooking and food preparation utensils, ethnic or 

regional preferences for food products with high lead content, and the use of oral ethnic 

medicines such as "empacho" or "azarcon" that have high concentrations of lead and are 

known to have caused cases of acute lead poisoning in children (Trotter, 1990; Sawyer et al., 

1985). No general recommendations about parameter values for these sources of lead can be 

made at this time. Approximate intake for oral medicines may be estimated from 

recommended or customary doses for young children. 

EXAMPLE 2-2: Characterizing Indirect Dietary Lead Intakes for an Old Lead Smelter 

Community 

Some data from the Human Health Risk Assessment (Jacobs Engineering, 1989) and the 

RADER for Kellogg ID may be useful (U.S. Environmental Protection Agency, 1990c). 

Table 2-2 shows that a large percentage of the population uses local produce, that the use of 

local produce increases toward the more rural Pinehurst area but the lead concentration 

decreases, and that the lead levels in local produce in 1983 were enormously higher than in 

2-32
TABLE 2-2. ESTIMATES OF LEAD INTAKE FROM CONSUMPTION OF LOCAL

PRODUCE BY CHILDREN, AGES 2 TO 6 YEARS, IN KELLOGG, IDAHO

Consumption (g/day) Concentration (Fg/g wet wt.) Intake (Fg/day) 

Percent Using Number of * * ** Area Local Produce Gardens Leafy Root Leafy Root In Summer 

Smelterville 16% 2 25 15 6.1 4.5 220 

Kellogg 36% 17 25 15 6.1+ 4.5+ 220+ 

Pinehurst 46% 20 25 15 3.5 2.2 121 

National 

Market -- -- 25 15 0.017 0.041 1 

Basket 

* NOTES: Leafy vegetables are lettuce and spinach. Root vegetables are carrots and beets. +Average of Kellogg and Smelterville. ** Annual average is 1/4 of this. 

Source: RADER Tables 5-8 and 5-4 (U.S. Environmental Protection Agency, 1990). 

Jacobs Engineering (1988) Table 7-16. 

the National Market Basket samples for the same period (1982 to 1984). The calculated 

increment of daily dietary lead intake during the summer months was 220 μg/day in the 

report. However, for the purposes of this example, we will assume that this total 

consumption occurs over the course of the year and includes fresh as well as frozen or canned 

produce to give an annual average increment of 55 μg/day. 

Table 2-3 shows that the lead concentration in fish in nearby Lake Coeur d'Alene in 

1985 was much higher than in the Columbia River and higher than fish at the average 

National Pesticide Monitoring Station lead concentration for 1976/1977. A moderate rate of 

consumption is two 2-oz fish portions per week, or 114 g/week = 16 g/day on average. The 

incremental intake from local fish is equal to the concentration difference, 0.80 to 0.34 = 

0.46 Fg/g times 16 g/day = 7.5 μg/day. 

Screen 2-23 shows dietary lead intakes for a typical child born in 1983, and Screen 2-24 

shows the extra exposure for intake from contaminated fish. 

2.3.3 Drinking Water Lead Exposure Menu 

2.3.3.1 Drinking Water Lead Default Exposure Parameters 

Water sampling methods may be as first draw standing samples, partially flushed 

samples, or fully flushed samples. The highest lead concentrations at the tap are usually 

obtained for lead pipes, lead-alloy solder on copper pipes, or lead-alloy brass faucets and 

2-33
TABLE 2-3. ESTIMATES OF LEAD INTAKE FROM CONSUMPTION OF LOCAL

FISH BY CHILDREN, AGES 2 TO 6 YEARS, IN KELLOGG, IDAHO

* ** Fish Consumption Lead Intake 

Source 

Concentration 

(Fg/g wet wt.) (g/day) (Fg/day) 

Lake Coeur d'Alene 

(1985) 0.80 16 13.0 

Columbia River 

(1986) 0.34 16 5.5 

National Pesticide 

Monitoring Stations 

(1976-1977 August) 0.34 16 5.5 

NOTES: * Two-ounce portions, twice a week.

** For annual average, multiply by fraction of year when local fish are consumed. 

Source: RADER Tables 5-8 and 5-4 (U.S. Environmental Protection Agency, 1990). 

Jacobs Engineering (1989) Table 7-16. 

Screen 23. Using dietary lead intake for a child born in 1983 (see Example 2-2). 

2-34
Screen 24. Using dietary intake from local vegetables and fish in Kellogg (see 

Example 2-2). 

fittings in contact with corrosive water for several hours. The new EPA National Primary 

Drinking Water Regulation for Lead (NPDWR) requires public water systems to collect first 

draw samples, standing a minimum of 6 h, from a sample of homes targeted as potentially at 

risk. Water lead concentrations can be significantly different for different sampling 

protocols, depending on the sources of lead in water drawn through the tap. First draw 

samples generally have higher lead concentrations than flushed samples. The typical effects 

of different water sampling procedures are discussed in the Sampling Manual that is to 

accompany this model. 

Drinking water lead concentrations in the Lead Model are held constant during the 

entire seven years of the child's exposure. In the Case Studies below, household-specific 

water lead concentrations are used. If no household-specific or relevant community water 

lead data are available, we recommend using the default value of 4 μg/L. 

If a substantial fraction of the child's activity is spent outside the home, it may be useful 

to separate drinking water exposure into primary residence and secondary residence or 

daycare. A large number of U.S. children spend time during the weekday at daycare centers 

or secondary residences. If adults and older children in the household are either at work or at 

2-35
school during the day, there may be two stagnation periods for drinking water during the day 

—overnight, and midday. In this case, a larger fraction of the child's water lead exposure 

can occur at the higher "first-draw" concentrations. Some exposure scenarios are discussed 

by Marcus (1991) in evaluating the risk from lead leached out of newly installed brass 

faucets. The default scenario is defined by setting 50% of the child's water intake to 

household first-draw consumption. The remaining intake consists of partially flushed intake 

inside the home (35%) and water consumed outside the home (15%). The total intake of lead 

in drinking water would then be: 

PbW = 0.5 × PbW (first draw) + 0.35 × PbW (flushed) + 0.15 × PbW (fountain). 

There is no general rule for estimating the amount of water ingested from water coolers 

in day care centers or other non-home locations. Since the child's activities outside the home 

are likely to be different than inside the home, it is unlikely that the ratio of non-home to 

home water intake is proportional to the amount of time spent away from the home versus at 

home. Two drinks per day, each about 60 mL (2 oz) or 120 mL, is a reasonable upper limit 

for day care intake. The default is 15% of the daily tap water intake, which ranges from 75 

mL at age 1 year to 90 mL at age 6 years. 

2.3.3.2 Alternate Drinking Water Exposure by Age 

The default values in the IEUBK model (Table 2-4) are taken from the U.S. EPA 

Exposure Factors Handbook (U.S. Environmental Protection Agency, 1989c). A survey of 

drinking water consumption in U.S. children was reported by Ershow and Cantor (1989) in a 

study for the National Cancer Institute. These values have been smoothed and disaggregated 

into yearly values shown in Table 2-4. The range of values from the Ershow-Cantor data in 

Table 2-5 show that the default values for the IEUBK model are similar to but somewhat 

lower than the median values, but also contain information about the percentiles of the 

distribution of tap water intake, about gender differences in intake and other factors that you 

may find useful. A plausible scenario for elevated exposure to lead in drinking water would 

be to use larger tap water intakes, such as the 90th percentile values in Table 2-5. Note that 

for children receiving formula reconstituted with tap water, consumption of tap water would 

be much higher, perhaps closer to one liter per day. In an assessment addressing risks from 

lead in drinking water, the exposure to infants consuming reconstituted formula requires 

specific attention. 

2-36
TABLE 2-4. AVERAGE DAILY WATER INTAKE IN U.S. CHILDREN

* ** Ershow-Cantor Study IEUBK Model 

Total (L/day) Tap (L/day) Tap 

Age (Months) M F M F Age 

(Mo) 

Water Intake 

(L/day) 

0-5 0.992 1.035 0.250 0.293 0-5 0.20 

6-11 1.277 1.238 0.322 0.333 6-11 0.20 

12-23 0.50 

24-35 0.52 

12-47 1.409 1.300 0.683 0.606 36-47 0.53 

48-59 0.55 

60-71 0.58 

48-84 1.551 1.488 0.773 0.709 72-84 0.59 

* Ershow and Cantor (1989).

** U.S. Environmental Protection Agency Exposure Factors Handbook (1989c). 

TABLE 2-5. TAP WATER INTAKE (L/day) BY AGE CATEGORY 

Age Category Percentiles 

(Months) Mean 10 50 (Median) 90 

0 - 5 0.27 0 0.24 0.64 

6 - 11 0.33 0 0.27 0.69 

12 - 47 0.65 0.24 0.57 1.16 

48 - 84 0.74 0.30 0.66 1.30 

Source: Table 2-5, Ershow and Cantor (1989). 

2.3.4 Soil/Dust Lead Exposure Menu 

One of the most important uses of the IEUBK model is to compare risks among 

alternative soil lead and dust lead exposure scenarios. Many of these scenarios arise in 

assessing exposure reduction strategies. For example, in evaluating soil lead abatement at a 

particular residential yard, we might be interested in the following sequence of comparisons: 

(1) Calculate the risk of an elevated blood lead level for the present soil and 

dust lead levels; 

2-37
(2) Calculate the risk of an elevated blood lead level for the replacement of 

soil lead with soil having a lower lead concentration, along with cleaning 

up household dust; 

The first scenario describes risk to occupants with present exposure levels. The second 

scenario describes risk to occupants in the distant future after lower new lead levels have 

been achieved by abatement. The IEUBK model can accept input data describing both of 

these exposure scenarios. 

2.3.4.1 Soil and Dust Lead Default Exposure Parameters 

The natural concentration of lead in soil, from weathering of crustal materials, is 

estimated as about 10 to 25 μg/g. A plausible urban background is 75 to 200 μg/g (U.S. 

Environmental Protection Agency, 1989a; HUD, 1990). 

It is expected that lead concentrations in undisturbed soils may persist for many 

thousands of years. However, urban areas are hardly undisturbed environments and available 

data (von Lindern, 1991; Jacobs Engineering, 1990) suggest that near-surface soil lead 

concentrations may decrease by a few percent over a decade or so. It is usually adequate to 

assume a constant soil lead concentration unless soil abatement is included in the exposure 

scenario. 

It is also possible that the soil becomes recontaminated over time, for example if surface 

soil is abated and then is recontaminated by ongoing atmospheric lead deposition from nonabated sites near by or by contamination from deteriorating exterior lead-based paint. 

Changes in soil concentration can be incorporated on an annual basis in developing the 

exposure scenario. This is done with the Option "2" on the Soil/Dust Data Entry Menu. 

2.3.4.2 Exposure to Soil and Dust 

The default value for total intake of soil and dust depends on age, and ranges from 85 to 

135 mg/day. These values are within the ranges identified in the OAQPS staff paper that 

supported the first UBK model and have been reviewed by the EPA Clean Air Science 

Advisory Committee. Recent investigations by Binder et al. (1986), Clausing et al. (1987), 

Calabrese et al. (1989, 1991b), van Wijnen et al. (1990), and Davis et al. (1990) apply the 

trace element approach to quantify ingestion rate. These investigations currently constitute 

the most appropriate basis for estimating the quantity of soil ingested. The results are 

summarized in Table 2-6. The van Wijnen et al. data are discussed in Section 2.3.4.4. It is 

likely that the intake rate depends on the child's age, activity pattern, and the total 

2-38
TABLE 2-6. DAILY INTAKE OF SOIL AND DUST ESTIMATED FROM

ELEMENTAL ABUNDANCES

Soil/Dust Intake, mg/day 

Study Element Median Mean Maximum 

Davis et al. (1991) 

Ages 2-7 years 

Calabrese et al. (1989) 

Ages 1-4 years 

Binder et al. (1986) 

Ages 1-3 years 

Clausing et al. (1987) 

Ages 2-4 years 

Al 25 39 904 

Si 59 82 535 

Ti 81 246 6,182 

Al 30 154 4,929 

Ti 30 170 3,597 

Y 11 65 5,269 

Zr 11 23 838 

Al 121 181 1,324 

Si 136 184 799 

Ti 618 1,834 17,076 

Al 92 232 979 

Ti 269 1,431 11,620 

AIR 106 124 302 

AIR = Acid Insoluble Residue. 

accessible dust and soil in the environment. It is recommended that soil and dust intake be 

defined by an age-dependent scenario shown in Table 2-7, as reviewed by the Clean Air 

Science Advisory Committee (U.S. Environmental Protection Agency, 1990b). 

Two of the studies, Davis et al. (1991) and Calabrese (1989), measured the dietary 

(including medication) intake of the trace elements and subtracted this quantity in estimating 

soil ingestion. These studies therefore provide the most complete quantitation of ingestion. 

Because Binder et al. (1986) did not measure dietary intake, the results for this study are 

likely to provide an upper bound on ingestion among those subjects. Van Wijnen et al. 

(1990) did not measure dietary intake but attempted to compensate for this approach by using 

the lowest observed tracer result for each child and subtracted out a value obtained for 

hospitalized children who were assumed not to ingest soil or dust. The combination of these 

two techniques may lead to a downward bias in ingestion estimates. 

2-39
TABLE 2-7. AGE-SPECIFIC SOIL AND DUST INTAKE

Adopted for 

Age (Years) Intake (g/day) Guidance Manual 

0 - <1 0 - 0.085 0.085 

1 - <2 0.080 - 0.135 0.135 

2 - <3 0.080 - 0.135 0.135 

3 - <4 0.080 - 0.135 0.135 

4 - <5 0.070 - 0.100 0.100 

5 - <6 0.060 - 0.090 0.090 

6 - <7 0.055 - 0.085 0.085 

Source: U.S. EPA (1989a). 

The reader should also note that there are statistical problems in interpreting an 

observed median value from these studies. For example, in a population of children who all 

ingested very small amounts of soil on most days but occasionally ingested larger quantities, 

the median from a short term measurement study will be below the average daily quantity 

ingested by any of the children. The mean value is not subject to this bias, and therefore is 

judged to be a more meaningful measure of ingestion. 

It should be noted that the 200 mg/d ingestion value presented in Superfund guidance 

can be supported as, roughly, an upper bound on mean ingestion considering the values seen 

in different ingestion studies. The values recommended for use in the model (85 to 

135 mg/d) represent a more central value within the range of values seen in different studies. 

The smaller study of Clausing et al. (1987) used methods similar to the later study of 

van Wijnen et al. The values shown for soil ingestion in Table 2-7 are uncorrected for 

dietary intake. The paper presents additional estimates using acid insoluble residue and tracer 

excretion by hospitalized children. 

2.3.4.3 Sources of Dust Exposure 

Contribution from Atmospheric Deposition and Soil 

We recommend collecting household dust data. If that has not been done, then Option 3 

may be used to estimate dust lead concentrations. The OAQPS Exposure Analysis and 

Methodology Validation (U.S. Environmental Protection Agency, 1989a), used for the earlier 

version of the model on which the current IEUBK Model is based, calculates the contribution 

2-40
of atmospheric deposition and soil to house dust by linear regression models between dust 

lead, soil lead, and air lead. There is a relationship between dust lead concentration in μg/g 

(denoted as PbD), soil lead concentration in μg/g (denoted as PbS), and air lead concentration 

in μg/m3

 (denoted as PbA). In a number of studies, statistically significant relationship of the 

form: 

PbD = $O + $S PbS + $A PbA 

This equation suggests that house dust lead concentration consists of three components: 

a soil component, which is the fraction $S of the soil concentration, an air component, 

consisting of a coefficient $A relating Fg/g lead in dust to Fg/m3 of lead in air, and a third 

component of $O coming from unidentified sources. 

As a default value in the model, we used $A = 100 μg/g per μg/m3 based on several 

analyses. We recommend a default soil-to-dust coefficient of 0.70, which represents some 

real sites where soil is a major contribution to household dust. The reader should be aware 

that other values have been identified for other site-specific exposure scenarios. 

Dust Lead Increment from School Dust 

Dust ingestion while at school may be significant, depending on the amount of exposure 

on the floor or playground. While the IEUBK model deals primarily with preschool 

children, some children may be in school and subject to a more structured regimen of hygiene 

and reduced dust exposure. The amount of dust ingested and its implicit fraction of total dust 

ingestion is not necessarily proportional to length of time at the facility. Hygiene and dust 

loading are additional predictive factors. Playground geometric mean dust lead levels of 170 

- 3,700 μg/g were reported by Duggan et al. (1985) in a sample of 11 British schools. 

Dust Lead Increment from Day Care 

Dust ingestion while at daycare (including nursery school and kindergarten) may be 

significant, depending on the amount of exposure on the floor or outside play area. Dutch 

children who spent a considerable amount of time at a daycare center were known to ingest a 

large quantity of dust and soil, although apparently much less in rainy weather than in good 

weather (van Wijnen et al., 1990). 

2-41
Dust Lead Increment from Second Home 

Children often spend several hours per day in the home of a relative or in an informal 

daycare setting. Dust exposure information can often be collected and used in the same 

manner as for the primary home. 

Dust Lead Increment Remaining from Primary Residence 

When the Multiple Source Analysis option is selected on the Soil/Dust Data Entry 

Menu, the IEUBK model offers the opportunity to change the soil and air parameters of the 

regression equation set at 0.70 and 100, respectively as default values. The selection of a 

default value for the soil-to-dust coefficient was based on empirical data. In sites where soilto-dust coefficients have been measured and where paint does not contribute greatly to dust, 

the range was from 0.09 to 0.85. Among the sites where soil-to-dust coefficients have been 

measured are the following: East Helena, 0.85 (0.81 and 0.89); Midvale, 0.70 (0.68, 0.72); 

Butte, 0.26; and Kellogg, 0.09. Recent data suggest the coefficient decreases over time at 

some sites where major sources of soil lead deposition are no longer active. The user is 

cautioned, however, that the contribution of soil to dust concentration varies greatly from site 

to site, and site-specific soil and dust data should be collected for use in the model. The user 

may choose to enter values for alternate sources of dust, including both an estimate of 

concentration (Fg/g) and relative contribution (%) for each source. Of the five alternate 

sources, two (secondary occupational dust and lead-based paint in home) represent 

contributions to house dust lead within the home, and three (dust at school, dust at daycare, 

and second home dust) represent exposure outside the primary home. If no selection is made 

from any of these five, the house dust concentration remains as calculated from the linear 

equation. If any of the five options are selected, this percentage is subtracted from the house 

dust component, the contribution from all sources is calculated, and the average is shown on 

the Multiple Source Average line of the Soil/Dust Data Entry Menu. This line appears only 

if the Multiple Source Option is selected. 

2.3.4.4 Fraction of Exposure as Soil or Dust 

We recommend using the default assumption that 45% of the total dust intake is derived 

from soil. The ratio of soil intake to dust intake is not simply proportional to the ratio of the 

number of waking hours that the child spends outdoors versus indoors. Children spend only 

15 to 30% of their waking hours playing outside but are more likely to be in contact with 

bare soil areas, in locations with large amounts of accessible loose particles, and are likely to 

wash their hands less often than when they are indoors. The default 45/55 ratio in the model 

represents our best judgement of a properly weighted ratio for this parameter. 

2-42
The issue of intake of soil and dust has not been properly resolved in the scientific 

literature. The distinction is important because there is some indication that even if soil lead 

is the principal source of dust lead, there may be chemical or physical differences between 

soil and dust that may affect bioavailability. Calabrese (1992) has found that most of the soil 

and dust intake in a soil pica child was in the soil component, but this is hardly representative 

of a larger population that may have large differences in relative exposure to soil and dust. 

Section 2.3.4.4 discusses the option to select the amount of dust and soil consumed by 

the child each day. The default values are age weighted from 85 to 135 mg/day, and this dust 

is ingested either during kitchen preparation of food or by hand-to-mouth activity during 

indoor and outdoor play activity. This section discusses the option to allocate a portion of the 

ingested dust to dust derived from soil that is ingested during outdoor play activity. This 

distinction is important when there are differences between the bioavailability of dust derived 

from soil and dust in the home, and when there are large differences in the concentration of 

dust from the two sources. When house dust is thought to be mostly of soil origin and each 

are expected to have similar bioavailability, the designation of this fraction is a moot point. 

It is in cases where house dust differs significantly from soil derived dust that the soil/dust 

ratio becomes important. One example might be the presence of interior lead-based paint. In 

this case the parameter can be effective in separating soil derived dust and paint derived dust 

into two components where both the amount ingested and percent absorbed can be correctly 

input into the model. 

There is some evidence that the soil intake is very responsive to exogenous factors, such 

as weather and location. Data reported by van Wijnen et al. (1990), summarized in Table 2-

8, show the lowest soil and dust intakes at daycare centers occurred in rainy weather, when 

the children had the least amount of outdoor activity. 

There is an implicit assumption that the exterior dust that a child ingests during outside 

play activity is derived completely from soil, and we use soil as a surrogate for exterior dust 

exposure. These intakes were measured during a 3 to 5 day sampling period, when soil and 

dust intake estimates ranged from 33 to 88 mg/day for children aged 1 to 2 years and from 12 

to 62 mg/day for children older than 3 years. The intake of soil and dust is describe in detail 

in Section 2.3.4.2. 

In the absence of any better data, we have reanalyzed and reinterpreted the van Wijnen 

et al. data based on the assumption that the rainy-weather intake is only interior dust, and 

2-43
TABLE 2-8. MINIMUM PERCENTAGE SOIL INTAKE AS A FUNCTION OF AGE 

IN DUTCH CHILDREN IN DAYCARE CENTERSa 

Estimated Geometric Mean LTM, mg/day 

Age (years) Good Rainy Difference (mg/d) 

<1 102 (4) 94 (3) 8 

1 - <2 229 (42) 103 (18) 126 

2 - <3 166 (65) 109 (33) 57 

4 - <5 132 (10) 124 (5) 8 

a

Minimum daily ingestion of acid insoluble residue or other tracers, denoted LTM (Limiting Tracer Method) 

from Table 4 in Van Wijnen et al. (1990). Number of children shown in parenthesis. 

that the good-weather intake is both interior and exterior dust although probably with a 

smaller amount of interior dust than in rainy weather. The authors also made the distinction 

between soil and dust in their discussion of the study. For our reanalysis, we took the rainyweather intake by age as dust and the good-weather intake as soil plus dust, to estimate an 

age-related difference of 8 to 126 mg/day soil (Table 2-8). The difference between LTM 

during good weather and LTM during mostly rainy weather is believed to be a lower bound 

on the soil intake. The combined intakes of soil and dust estimated by other authors are of a 

similar order of magnitude, such as the median soil and dust intake of 25 to 81 mg/day found 

by Davis et al. (1991) for children of ages 2 to 7 years in Richland-Pasco-Kennewick, 

Washington. We therefore assume that a substantial fraction of the combined soil and dust 

intake in U.S. children is in the form of soil, as suggested by the large difference in Table 

2-8 between good and rainy weather intakes, and a substantial fraction is in dust, as suggested 

by the large intake during rainy weather, in Table 2-8. The minimum intake, denoted LTM 

for Limiting Tracer Method, has not been corrected for food intake. However, it is likely 

that the differences between LTM intakes do not depend on food intake. 

2.3.4.5 Bioavailability of Lead in Soil and Dust 

The current assumption in the Lead Model is that 30% of dust and soil lead intake is 

absorbed into the blood. This is assumed to be partitioned into a nonsaturable component of 

6% and a saturable component of 24%. Some investigators (Steele et al., 1990) argue that 

the bioavailability of lead in soil from some old lead mining sites is much less than that of 

dissolved lead salts for several reasons: (1) large lead particles may not be completely 

dissolved in the GI tract; (2) the solubility of chemical species commonly found in mine 

wastes, particularly lead sulfide, is much lower than that of other lead salts. These 

2-44
hypotheses are based on studies in small laboratory animals such as rats (Barltrop and Khoo, 

1975; Barltrop and Meek, 1979), and while the results may be qualitatively relevant to 

humans, it is not clear how they should be extrapolated to humans or to other large animals 

with similar physiological properties such as baboons or swine. 

2.3.5 Alternate Source Exposure Menu 

One possible use of the Alternative Source Exposure Menu is the direct ingestion of 

chips of lead-based paint (LBP). The user might assume that a child with pica for paint 

ingests one paint chip per day. If this chip weighs 0.3 grams and contains lead at 10% 

(100,000 μg/g), then the calculated ingestion is 100,000 μg/g × 0.3 g/day, or 30,000 μg/day 

each day for a year. Note that this exposure would be in addition to exposure to lead-based 

paint in housedust, which is Option 4 in the Multiple Source Menu of Soil and Dust. The 

limited information available on the bioavailability of lead in paint chips suggests that at 

doses this high, absorption mechanisms may be largely saturated (Mallon, 1983), which 

would indicate appropriate adjustments in bioavailability. The user is referred to Section 4.7, 

and is encouraged to review the literature on this topic prior to making a risk assessment 

decision. Similar calculations can be made for the ingestion of soil or other non-food items. 

2.4 STARTING AND RUNNING THE MODEL 

2.4.1 Loading and Starting the Model 

The IEUBK Model is a stand alone software package that requires only an IBM 

compatible PC with DOS. The diskette accompanying this manual contains the following 

files: 

LEAD99d.EXE (the main program file) 

PBHELP99.HLP (a help file) 

PBSTAT.EXE (the statistical package) 

Several *.BGI files (for graphic output) 

One or more EXAMPLE*.DAT (sample data sets) 

2-45
Copy all files into a directory of your choice, then type LEAD99d at the DOS prompt 

to start the program. The initial screen gives the model name and version number. Several 

information screens with recent developments and other news items then follow. The Main 

Menu gives the user access to all of the menus described in this chapter. 

While the LEAD99d.EXE file occupies only about 160 KB on the hard drive, it will 

expand to a much larger size when loaded into RAM. Normally, a PC with 640 KB has 

enough RAM to run the program, but there may be some conflicts with TSR (Terminate and 

Stay Resident) programs. It may be necessary for the user to remove some TSR programs in 

order to run the IEUBK Model. 

The Model does not require a math co-processor, but calculations may take up to 20 

times longer without a co-processor. 

2.4.2 Running the Model 

The user should fill in the worksheet in Figure 2-11, which defines the exposure 

scenario, before proceeding with the parameter entries and the computations. 

2.4.2.1 Computation Options 

The computation menus present the user with a set of computation choices. One choice 

is the iteration time step, Selection "2". These choices range from 15 minutes to 30 days. 

The default of 4 hours is adequate for most purposes. Setting this option on the RUN Menu 

also sets the iteration time for other computation modes, including the Batch Mode. 

2.4.2.2 Output Options 

At any time during the session, the program may be saved to a designated file. This 

gives the user the option of retrieving a set of parameters at some future session without 

reentering the parameters individually. After each model run, the user can select one of 

several plot options, which can be viewed on the screen, printed to file or sent to a printer. 

Most plots generated by the model can be printed by using the F10 key on the keyboard. The 

program presently interfaces with nine standard printer types or orientations. The Graphics 

Menu selection "7" allows user-specified scaling of the X-axis variable. Future versions of 

the model may have additional output options. 

2-46
IEUBK MODEL WORKSHEET 

SITE OR PROJECT: 

Model 

Version: Date: 

Model Run Control Number: Site Description: 

PARAMETER 

DEFAULT 

VALUE 

USER SELECTED 

OPTION UNITS 

AIR (constant) 

Outdoor air lead concentration 0.10 Fg/m3 

Ratio of indoor to outdoor air lead concentration 30 % 

AIR (by year) 

Air concentration 

Age = 0-1 year (0-11 mo), 

1-2 years (12-23 mo) 

2-3 years (24-35 mo) 

3-4 years (36-47 mo) 

4-5 years (48-59 mo) 

5-6 years (60-71 mo) 

6-7 years (72-84 mo) 

.10 

.10 

.10 

.10 

.10 

.10 

.10 

Fg/m3 

Time outdoors 

Age = 0-1 year (0-11 mo), 

1-2 years (12-23 mo) 

2-3 years (24-35 mo) 

3-7 years (36-83 mo) 

1 

2 

3 

4 

h/day 

Ventilation rate 

Age = 0-1 year (0-11 mo), 

1-2 years (12-23 mo) 

2-3 years (24-35 mo) 

3-4 years (36-47 mo) 

4-5 years (48-59 mo) 

5-6 years (60-71 mo) 

6-7 years (72-84 mo) 

2 

3 

5 

5 

5 

7 

7 

m 

2

/day 

Lung absorption 32 % 

DATA ENTRY FOR DIET (by year) 

Dietary lead intake 

Age = 0-1 year (0-11 mo), 

1-2 years (12-23 mo) 

2-3 years (24-35 mo) 

3-4 years (36-47 mo) 

4-5 years (48-59 mo) 

5-6 years (60-71 mo) 

6-7 years (72-84 mo) 

5.53 

5.78 

6.49 

6.24 

6.01 

6.34 

7.00 

Fg Pb /day 

Figure 2-11. Integrated exposure uptake biokinetic model sample worksheet. 

2-47
DATA ENTRY FOR ALTERNATE DIET SOURCES (by food class) 

Concentration: 

home-grown fruits 

home-grown vegetables 

fish from fishing 

game animals from hunting 

0 

0 

0 

0 

Fg Pb/g 

Percent of food class: 

home-grown fruits 

home-grown vegetables 

fish from fishing 

game animals from hunting 

0 

0 

0 

0 

% 

DATA ENTRY FOR DRINKING WATER 

Lead concentration in drinking water 4 Fg/L 

Ingestion rate 

Age = 0-1 year (0-11 mo), 

1-2 years (12-23 mo) 

2-3 years (24-35 mo) 

3-4 years (36-47 mo) 

4-5 years (48-59 mo) 

5-6 years (60-71 mo) 

6-7 years (72-84 mo) 

0.20 

0.50 

0.52 

0.53 

0.55 

0.58 

0.59 

liters/day 

DATA ENTRY FOR ALTERNATE DRINKING WATER SOURCES 

Concentration 

first-draw water 

flushed water 

fountain water 

4 

1 

10 

Fg/L 

Percentage of total intake 

first-draw water 

flushed water (not a user entry; calculated based 

on entries for first-draw and fountain 

percentages) 

fountain water 

50 

100 minus 

first draw and 

fountain 

15 

% 

DATA ENTRY FOR SOIL/DUST (constant) 

Concentration 

Soil 

Dust 

200 

200 

Fg/g 

Soil ingestion as percent of total soil and dust 

ingestion 

45 % 

Figure 2-11 (cont'd). Integrated exposure uptake biokinetic model sample worksheet. 

2-48
DATA ENTRY FOR SOIL/DUST INGESTION (by year) 

Soil/dust ingestion 

Age = 0-1 year (0-11 mo), 

1-2 years (12-23 mo) 

2-3 years (24-35 mo) 

3-4 years (36-47 mo) 

4-5 years (48-59 mo) 

5-6 years (60-71 mo) 

6-7 years (72-84 mo) 

0.085 

0.135 

0.135 

0.135 

0.100 

0.090 

0.085 

g/day 

DATA ENTRY FOR SOIL (by year) 

Soil lead concentration 

Age = 0-1 year (0-11 mo) 

1-2 years (12-23 mo) 

2-3 years (24-35 mo) 

3-4 years (36-47 mo) 

4-5 years (48-59 mo) 

5-6 years (60-71 mo) 

6-7 years (72-84 mo) 

0 

0 

0 

0 

0 

0 

0 

Fg/g 

DATA ENTRY FOR DUST (by year) 

Dust lead concentration 

Age = 0-1 year (0-11 mo) 

1-2 years (12-23 mo) 

2-3 years (24-35 mo) 

3-4 years (36-47 mo) 

4-5 years (48-59 mo) 

5-6 years (60-71 mo) 

6-7 years (72-84 mo) 

0 

0 

0 

0 

0 

0 

0 

Fg/g 

DATA ENTRY FOR SOIL/DUST MULTIPLE SOURCE ANALYSIS (constant) 

Ratio of dust lead concentration to soil lead 

concentration 

Ratio of dust lead concentration to outdoor air 

lead concentration 

0.70 

100 

unitless 

Fg Pb/g dust 

per Fg 

Pb/m3

 air 

DATA ENTRY FOR SOIL/DUST MULTIPLE SOURCE ANALYSIS WITH ALTERNATIVE 

HOUSEHOLD DUST LEAD SOURCES (constant) 

Concentration 

household dust (calculated) 

secondary occupational dust 

school dust 

daycare center dust 

second home 

interior lead-based paint 

150 

1,200 

200 

200 

200 

1,200 

Fg/g 

Figure 2-11 (cont'd). Integrated exposure uptake biokinetic model sample worksheet. 

2-49 
Percentage 

household dust (calculated) 

secondary occupational dust 

school dust 

daycare center dust 

second home 

interior lead-based paint 

100 minus all 

other 

0 

0 

0 

0 

0 

% 

BIOAVAILABILITY DATA ENTRY FOR ALL GUT ABSORPTION PATHWAYS 

Total lead absorption (at low intake) 

diet 

drinking water 

soil 

dust 

alternate source 

50 

50 

30 

30 

0 

% 

Fraction of lead absorbed passively at high intake 

diet 

drinking water 

soil 

dust 

alternate source 

0.2 

0.2 

0.2 

0.2 

0.2 

unitless 

DATA ENTRY FOR ALTERNATE SOURCES (by year) 

Total lead intake 

Age = 0-1 year (0-11 mo), 

1-2 years (12-23 mo) 

2-3 years (24-35 mo) 

3-4 years (36-47 mo) 

4-5 years (48-59 mo) 

5-6 years (60-71 mo) 

6-7 years (72-84 mo) 

0 

0 

0 

0 

0 

0 

0 

Fg/day 

DATA ENTRY MENU FOR MATERNAL-TO-NEWBORN LEAD EXPOSURE 

Mother's blood lead level at time of birth 2.5 Fg/dL 

DATA ENTRY MENU FOR PLOTTING AND RISK ESTIMATION 

Geometric standard deviation for blood lead, 

GSD 

1.6 unitless 

Blood lead level of concern, or cutoff 10 Fg/dL 

COMPUTATION OPTIONS 

Iteration time step for numerical integration 4 h 

Figure 2-11 (cont'd). Integrated exposure uptake biokinetic model sample worksheet. 

2-50