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Siomara Gomez
Siomara Gomez

This document summarizes the IEUBK model, which predicts the risk of elevated blood lead levels in children exposed to environmental lead from multiple sources. The model consists of exposure, uptake, biokinetic, and probability distribution modules. It uses site-specific or default media concentrations and intake rates to estimate lead uptake and predict a typical child's blood lead level and risk of exceeding health standards. While generally accurate below 30 μg/dL, the model has limitations for short or irregular exposures and should not be used to predict an individual child's level. Site-specific data are recommended where available and representative.

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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
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.
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 M EMBERS 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
Overview of the IEUBK Model for Lead in Children What is the IEUBK Model for Lead (Pb) in Children? body through the lungs is either absorbed through lung membranes into the blood, transferred to the GI tract, or eliminated from the body The Integrated Exposure Uptake Biokinetic (IEUBK) Model for via exhaled air. Most Pb enters the body through the GI tract, by Lead in Children is used to predict the risk of elevated blood either ingestion or movement from the nose, throat, and lungs. From lead (PbB) levels in children (under the age of seven) that are the GI tract, Pb is either absorbed into the blood or eliminated from exposed to environmental lead (Pb) from many sources. The the gut via the feces. The Uptake Module calculates media-specific model also predicts the risk (e.g., probability) that a typical Pb uptake rates using the following equation: child, exposed to specified media Pb concentrations, will have a PbB level greater or equal to the level associated with adverse Pb Uptake Rate = Pb Intake Rate * Absorption Factor health effects (10 �g/dL). Prior to the development of the IEUBK model, a single slope factor constant had been used to The Pb intake rates are calculated by the Exposure Module, and the predict risk from exposure to lead, as is done for other absorption factorsare typically standard default values established by chemicals. The slope factor approach assumed a linear EPA. The Pb intake rates and absorption factors are both age- and relationship between environmental concentrations and risk media-specific. Absorption factors reflect the percentage of Pb that levels. Although, for Pb, the rate relationship is close to linear enters the bloodstream after intake from a specific medium. The at lower PbB levels, it is non-linear at higher levels, invalidating overall Pb uptake value can be obtained by summing the media- the linear approach. Additionally, the linear approach did not specific Pb uptake values, up to a certain Pb intake concentration. adequately address the site-specific variability and multi-media However, at high doses, the absorption factors must be modified to nature of exposure to lead. The IEUBK model is the primary account for saturation effects. The total rate of Pb uptake is tool used in determining risk-based cleanup levels at Pb calculated for use in the Biokinetic Module. contaminated sites. The following modules are utilized in predicting PbB concentrations, and risks in the IEUBK model: Biokinetic Module. This module addresses the transfer of absorbed Exposure, Uptake, Biokinetic, and Probability Distribution. 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 Exposure Module. This module uses Pb concentrations in the disposition of Pb in the extra-cellular fluid, red blood cells, liver, environment and the rate at which a child breathes or ingests kidney, spongy bone, compact bone (femur), and other soft tissue. contaminated media to determine Pb exposure. Media that can The total amount of Pb in each body compartment is age dependent act as sources of Pb for a child include air (both indoor and and calculated using total Pb uptake derived by the Uptake Module. outdoor), which enters the body through the lungs, and water, soil, dust (indoor), diet, and other sources (e.g., lead paint), The Biokinetic Module estimates transfer rates for Pb moving which enter the body through the gastrointestinal (GI) tract. The between compartments and through elimination pathways. A variety Exposure Module estimates how much Pb enters a child’s body of complex equations are used to calculate compartmental Pb transfer by calculating media-specific Pb intake rates using the following times. Based on site-specific environmental exposures input by the equation: user, a geometric mean PbB concentration is predicted. Pb Intake Rate = Media Pb Concentration * Media Intake Rate Probability Distribution Module. This module estimates a plausible distribution of PbB concentrations that is centered on the The values used for media Pb concentrations and media intake geometric mean PbB concentration calculated by the Biokinetic rates are either derived from site-specific data or standard Module. From this distribution, the model calculates the probability default values established by EPA. The media intake rates are or risk that a child’s PbB concentration will exceed a user-selected age-specific. The Exposure Module calculates the intake of Pb PbB level of concern (typically 10 �g/dL). In running this portion of from each medium for use in the Uptake Module. the model, the user specifies a PbB level of concern and a geometric standard deviation (GSD). For most sites EPA recommends use of Uptake Module. This module modifies the Pb intake rates the default values for both the GSD and PbB level of concern. 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 Media Concentrations for Input Soil Soil must be sampled. Site-specific data required. Refer to the IEUBKwin User’s Guide and 1994 Guidance Manual for additional information on this input parameter. Dust Site-specific data required or input value can be derived from soil Refer to the IEUBKwin User’s Guide and concentration using multiple source analysis. 1994 Guidance Manual for additional information on this input parameter. Air (default) 0.1 � g/m3 Ratio of indoor to outdoor air Pb conc. is 30%. Site-specific data may be substituted. Drinking Water (default) 4 � g/L Site-specific data may be substituted.
Media Intake Rates (Pb Intake Rate = Media Pb Concentration * Media Intake Rate) Soil/Dust 0-1 yr 0.085 g/d 4-5 yrs 0.100 g/d Default intake values recommended. The 1-2 yrs 0.135 g/d 5-6 yrs 0.090 g/d default intake value for total soil and dust 2-3 yrs 0.135 g/d 6-7 yrs 0.085 g/d ingestion is a ratio of soil ingestion (45%) to 3-4 yrs 0.135 g/d dust ingestion (55%). Air 0-1 yr 2 m3 /d 2-5 yrs 5 m3 /d Default values recommended. 1-2 yrs 3 m3 /d 5-7 yrs 7 m3 /d Drinking Water 0-1 yr 0.2 L/d 4-5 yrs 0.55 L/d Default values recommended. 1-2 yrs 0.5 L/d 5-6 yrs 0.58 L/d 2-3 yrs 0.52 L/d 6-7 yrs 0.59 L/d 3-4 yrs 0.53 L/d Diet 0-1 yr 5.53 � g Pb/d 4-5 yrs 6.01 � g Pb/d Site-specific data may be used to augment the 1-2 yrs 5.78 � g Pb/d 5-6 yrs 6.34 � g Pb/d default intake rates. 2-3 yr 6.49 � g Pb/d 6-7 yrs 7.00 � g Pb/d 3-4 yr 6.24 � g Pb/d Alternative Sources Site-specific data may be used to account for intakes of Pb in Refer to the IEUBKwin User’s Guide and sources such as Pb paint. 1994 Guidance Manual for further discussion. What are the module input and default values? calculated from the arithmetic mean soil concentration according to a default mass fraction ration of 0.7 (multiple source analysis). Exposure Module. Input values include media concentrations Concentrations of Pb in air and water are also measured at some sites. and media intake rates. As shown in the table above, EPA has If a representative number of samples is collected, arithmetic mean established default concentrations for Pb in various media and concentrations should be calculated for use in the model. (See the ingestion rates for air, drinking water, soil/dust, diet, and IEUBKwin User’s Guide and 1994 Guidance Manual for technical alternative sources. The media intake default values are based discussion of input parameters.) on data for children in most instances, with Pb exposures that are characteristic of children in the U.S. since about 1980. Uptake Module. Input values include media-specific intake rates While these studies have not resolved all of the uncertainty in and absorption factors, as explained above. The age-specific and childhood Pb exposure, they do provide a realistic basis for media-specific intake rates are calculated by the Exposure Module. quantitative modeling. The media intake default parameters EPA has established standard default values for absorption factors selected for use in the IEUBK model were selected from the that are age- and media-specific. In cases of very high exposure to central portions of the ranges of values observed in the different Pb, absorption is characterized by saturable and non-saturable studies. components. The IEUBK model utilizes absorption factors which reflects the relative bioavailability of Pb in specific media. The Use of the model defaults is recommended unless adequate, site- model assumes that 50% of the Pb intake from drinking water and specific monitoring data exist to define values that are higher or food is absorbed and that 30% of the Pb intake from soil and dust is lower in magnitude. For example, site-specific data for locally absorbed. These absorption factors were estimated from the best caught fish or home-grown vegetables can be utilized to available studies of Pb uptake in children and adults. Some site- augment the diet default values. This is especially significant specific conditions (e.g., the species of Pb present) may warrant for sites where home-grown produce or local game represents a changing the absorption default values. However, detailed site- large portion of dietary intake. Site-specific data are commonly specific studies are required to document the conditions that would used in place of the model default values for Pb concentrations justify changing these values. (See TRW short sheet on in soil, dust, air, and water. bioavailability: http://www.epa.gov/superfund/programs/lead/ products/sspbbioc.pdf.) Site-specific soil data should be entered as an arithmetic mean soil Pb concentration. In the absence of site-specific data on Biokinetic Module. There are no input values for this module. other indoor sources of Pb, dust Pb concentrations may be The values utilized in this module have been incorporated into the program code for the model and cannot be changed.
Probability Distribution Module. Input values for this module What are the limitations of the IEUBK model? are the PbB level of concern and GSD. The recommended default value for the PbB level of concern is 10 �g/dL. This While the IEUBK model provides a fairly good estimate of risk from level is based on health effects criteria. The GSD is a measure exposure to Pb, as with all models, it has limitations to its use. First, of the relative variability in PbB concentrations for a child of the model should not be relied upon to predict PbB accurately above specified age or children from a hypothetical population whose 30 �g/dL. Above this concentration, the relationship between Pb exposures are known. It is intended to encompass the absorbed Pb and children’s PbB concentrations has not been variability resulting from biological and behavioral differences, characterized. However, this should not cause any difficulties for the measurement variability from repeat sampling, sample location IEUBK model in risk assessment applications, as this value is well variability, and analytical error. The recommended default above the level of concern of 10 � g/dL. Additionally, the model value for GSD is 1.6. This value is based on analyses of data should not be used for exposure periods of less than three months, or from neighborhoods with paired data sets for environmental in which a higher exposure occurs less than one per week or varies concentrations and PbB data. The GSD default value should be irregularly. Finally, it is not the goal of the IEUBK model to match appropriate for all sites, unless there are great differences in the measured PbB of a specific child. The model is designed to child behavior and Pb biokinetics. Model users should not predict an average PbB concentration for an entire population, or the substitute alternate values for the default GSD without detailed probability that a child with a specific exposure scenario would have site-specific studies designed to document the difference that an elevated PbB. would justify changing the default value. Whom should I contact for more information? When should I use site-specific data instead of model default values? More detailed information regarding the IEUBK Model can be obtained through the following: � Guidance Manual for the Integrated Exposure Uptake Site-specific data are recommended because there may be Biokinetic Model for Lead in Children (Publication 9285.7-15- potentially important differences among sites. Hence, use of 1). site-specific data would be expected to result in more accurate � Technical Support Document: Parameters and Equations Used predictions of PbB. However, such data should be evaluated for in the Integrated Exposure Uptake Biokinetic (IEUBK) Model merit prior to their use. Model defaults should only be replaced for lead in Children (Publication 9285.7-22). when site-specific data are more representative than the default � User’s Guide for the Integrated Exposure Uptake Biokinetic values. Model default values should never by adjusted simply Model for Lead in Children (IEUBK) Windows® version to attain a better match between model predictions and empirical (Publication 9285.7-42). PbB data. � System Requirements and Design for the Integrated Exposure Uptake Biokinetic Model for Lead in Children (IEUBK) How similar are modeled and empirical blood lead Windows® version (Publication 9285.7-43). (PbB) concentrations? � Reference Manual: Documentation of Updates for the Integrated Exposure Uptake Biokinetic Model for Lead in The IEUBK model was calibrated against two different Children (IEUBK) Windows® version (Publication 9285.7-44). community PbB and environmental Pb studies. Subsequent � Reviewing the Technical Review Workgroup for Lead (TRW) comparisons involvingwell-conducted blood and environmental home page (http://www.epa.gov/superfund/programs/lead). Pb studies have demonstrated reasonably close agreement � Calling EPA’s IEUBK Technical Support Center (1-866-282- between mean observed and predicted PbB concentrations, and 8622). between observed and predicted exceedances of 10 � g/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 �g/dL.

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  • 1. 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
  • 2. 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.
  • 3. 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 M EMBERS 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
  • 4. Overview of the IEUBK Model for Lead in Children What is the IEUBK Model for Lead (Pb) in Children? body through the lungs is either absorbed through lung membranes into the blood, transferred to the GI tract, or eliminated from the body The Integrated Exposure Uptake Biokinetic (IEUBK) Model for via exhaled air. Most Pb enters the body through the GI tract, by Lead in Children is used to predict the risk of elevated blood either ingestion or movement from the nose, throat, and lungs. From lead (PbB) levels in children (under the age of seven) that are the GI tract, Pb is either absorbed into the blood or eliminated from exposed to environmental lead (Pb) from many sources. The the gut via the feces. The Uptake Module calculates media-specific model also predicts the risk (e.g., probability) that a typical Pb uptake rates using the following equation: child, exposed to specified media Pb concentrations, will have a PbB level greater or equal to the level associated with adverse Pb Uptake Rate = Pb Intake Rate * Absorption Factor health effects (10 �g/dL). Prior to the development of the IEUBK model, a single slope factor constant had been used to The Pb intake rates are calculated by the Exposure Module, and the predict risk from exposure to lead, as is done for other absorption factorsare typically standard default values established by chemicals. The slope factor approach assumed a linear EPA. The Pb intake rates and absorption factors are both age- and relationship between environmental concentrations and risk media-specific. Absorption factors reflect the percentage of Pb that levels. Although, for Pb, the rate relationship is close to linear enters the bloodstream after intake from a specific medium. The at lower PbB levels, it is non-linear at higher levels, invalidating overall Pb uptake value can be obtained by summing the media- the linear approach. Additionally, the linear approach did not specific Pb uptake values, up to a certain Pb intake concentration. adequately address the site-specific variability and multi-media However, at high doses, the absorption factors must be modified to nature of exposure to lead. The IEUBK model is the primary account for saturation effects. The total rate of Pb uptake is tool used in determining risk-based cleanup levels at Pb calculated for use in the Biokinetic Module. contaminated sites. The following modules are utilized in predicting PbB concentrations, and risks in the IEUBK model: Biokinetic Module. This module addresses the transfer of absorbed Exposure, Uptake, Biokinetic, and Probability Distribution. 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 Exposure Module. This module uses Pb concentrations in the disposition of Pb in the extra-cellular fluid, red blood cells, liver, environment and the rate at which a child breathes or ingests kidney, spongy bone, compact bone (femur), and other soft tissue. contaminated media to determine Pb exposure. Media that can The total amount of Pb in each body compartment is age dependent act as sources of Pb for a child include air (both indoor and and calculated using total Pb uptake derived by the Uptake Module. outdoor), which enters the body through the lungs, and water, soil, dust (indoor), diet, and other sources (e.g., lead paint), The Biokinetic Module estimates transfer rates for Pb moving which enter the body through the gastrointestinal (GI) tract. The between compartments and through elimination pathways. A variety Exposure Module estimates how much Pb enters a child’s body of complex equations are used to calculate compartmental Pb transfer by calculating media-specific Pb intake rates using the following times. Based on site-specific environmental exposures input by the equation: user, a geometric mean PbB concentration is predicted. Pb Intake Rate = Media Pb Concentration * Media Intake Rate Probability Distribution Module. This module estimates a plausible distribution of PbB concentrations that is centered on the The values used for media Pb concentrations and media intake geometric mean PbB concentration calculated by the Biokinetic rates are either derived from site-specific data or standard Module. From this distribution, the model calculates the probability default values established by EPA. The media intake rates are or risk that a child’s PbB concentration will exceed a user-selected age-specific. The Exposure Module calculates the intake of Pb PbB level of concern (typically 10 �g/dL). In running this portion of from each medium for use in the Uptake Module. the model, the user specifies a PbB level of concern and a geometric standard deviation (GSD). For most sites EPA recommends use of Uptake Module. This module modifies the Pb intake rates the default values for both the GSD and PbB level of concern. 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 Media Concentrations for Input Soil Soil must be sampled. Site-specific data required. Refer to the IEUBKwin User’s Guide and 1994 Guidance Manual for additional information on this input parameter. Dust Site-specific data required or input value can be derived from soil Refer to the IEUBKwin User’s Guide and concentration using multiple source analysis. 1994 Guidance Manual for additional information on this input parameter. Air (default) 0.1 � g/m3 Ratio of indoor to outdoor air Pb conc. is 30%. Site-specific data may be substituted. Drinking Water (default) 4 � g/L Site-specific data may be substituted.
  • 5. Media Intake Rates (Pb Intake Rate = Media Pb Concentration * Media Intake Rate) Soil/Dust 0-1 yr 0.085 g/d 4-5 yrs 0.100 g/d Default intake values recommended. The 1-2 yrs 0.135 g/d 5-6 yrs 0.090 g/d default intake value for total soil and dust 2-3 yrs 0.135 g/d 6-7 yrs 0.085 g/d ingestion is a ratio of soil ingestion (45%) to 3-4 yrs 0.135 g/d dust ingestion (55%). Air 0-1 yr 2 m3 /d 2-5 yrs 5 m3 /d Default values recommended. 1-2 yrs 3 m3 /d 5-7 yrs 7 m3 /d Drinking Water 0-1 yr 0.2 L/d 4-5 yrs 0.55 L/d Default values recommended. 1-2 yrs 0.5 L/d 5-6 yrs 0.58 L/d 2-3 yrs 0.52 L/d 6-7 yrs 0.59 L/d 3-4 yrs 0.53 L/d Diet 0-1 yr 5.53 � g Pb/d 4-5 yrs 6.01 � g Pb/d Site-specific data may be used to augment the 1-2 yrs 5.78 � g Pb/d 5-6 yrs 6.34 � g Pb/d default intake rates. 2-3 yr 6.49 � g Pb/d 6-7 yrs 7.00 � g Pb/d 3-4 yr 6.24 � g Pb/d Alternative Sources Site-specific data may be used to account for intakes of Pb in Refer to the IEUBKwin User’s Guide and sources such as Pb paint. 1994 Guidance Manual for further discussion. What are the module input and default values? calculated from the arithmetic mean soil concentration according to a default mass fraction ration of 0.7 (multiple source analysis). Exposure Module. Input values include media concentrations Concentrations of Pb in air and water are also measured at some sites. and media intake rates. As shown in the table above, EPA has If a representative number of samples is collected, arithmetic mean established default concentrations for Pb in various media and concentrations should be calculated for use in the model. (See the ingestion rates for air, drinking water, soil/dust, diet, and IEUBKwin User’s Guide and 1994 Guidance Manual for technical alternative sources. The media intake default values are based discussion of input parameters.) on data for children in most instances, with Pb exposures that are characteristic of children in the U.S. since about 1980. Uptake Module. Input values include media-specific intake rates While these studies have not resolved all of the uncertainty in and absorption factors, as explained above. The age-specific and childhood Pb exposure, they do provide a realistic basis for media-specific intake rates are calculated by the Exposure Module. quantitative modeling. The media intake default parameters EPA has established standard default values for absorption factors selected for use in the IEUBK model were selected from the that are age- and media-specific. In cases of very high exposure to central portions of the ranges of values observed in the different Pb, absorption is characterized by saturable and non-saturable studies. components. The IEUBK model utilizes absorption factors which reflects the relative bioavailability of Pb in specific media. The Use of the model defaults is recommended unless adequate, site- model assumes that 50% of the Pb intake from drinking water and specific monitoring data exist to define values that are higher or food is absorbed and that 30% of the Pb intake from soil and dust is lower in magnitude. For example, site-specific data for locally absorbed. These absorption factors were estimated from the best caught fish or home-grown vegetables can be utilized to available studies of Pb uptake in children and adults. Some site- augment the diet default values. This is especially significant specific conditions (e.g., the species of Pb present) may warrant for sites where home-grown produce or local game represents a changing the absorption default values. However, detailed site- large portion of dietary intake. Site-specific data are commonly specific studies are required to document the conditions that would used in place of the model default values for Pb concentrations justify changing these values. (See TRW short sheet on in soil, dust, air, and water. bioavailability: http://www.epa.gov/superfund/programs/lead/ products/sspbbioc.pdf.) Site-specific soil data should be entered as an arithmetic mean soil Pb concentration. In the absence of site-specific data on Biokinetic Module. There are no input values for this module. other indoor sources of Pb, dust Pb concentrations may be The values utilized in this module have been incorporated into the program code for the model and cannot be changed.
  • 6. Probability Distribution Module. Input values for this module What are the limitations of the IEUBK model? are the PbB level of concern and GSD. The recommended default value for the PbB level of concern is 10 �g/dL. This While the IEUBK model provides a fairly good estimate of risk from level is based on health effects criteria. The GSD is a measure exposure to Pb, as with all models, it has limitations to its use. First, of the relative variability in PbB concentrations for a child of the model should not be relied upon to predict PbB accurately above specified age or children from a hypothetical population whose 30 �g/dL. Above this concentration, the relationship between Pb exposures are known. It is intended to encompass the absorbed Pb and children’s PbB concentrations has not been variability resulting from biological and behavioral differences, characterized. However, this should not cause any difficulties for the measurement variability from repeat sampling, sample location IEUBK model in risk assessment applications, as this value is well variability, and analytical error. The recommended default above the level of concern of 10 � g/dL. Additionally, the model value for GSD is 1.6. This value is based on analyses of data should not be used for exposure periods of less than three months, or from neighborhoods with paired data sets for environmental in which a higher exposure occurs less than one per week or varies concentrations and PbB data. The GSD default value should be irregularly. Finally, it is not the goal of the IEUBK model to match appropriate for all sites, unless there are great differences in the measured PbB of a specific child. The model is designed to child behavior and Pb biokinetics. Model users should not predict an average PbB concentration for an entire population, or the substitute alternate values for the default GSD without detailed probability that a child with a specific exposure scenario would have site-specific studies designed to document the difference that an elevated PbB. would justify changing the default value. Whom should I contact for more information? When should I use site-specific data instead of model default values? More detailed information regarding the IEUBK Model can be obtained through the following: � Guidance Manual for the Integrated Exposure Uptake Site-specific data are recommended because there may be Biokinetic Model for Lead in Children (Publication 9285.7-15- potentially important differences among sites. Hence, use of 1). site-specific data would be expected to result in more accurate � Technical Support Document: Parameters and Equations Used predictions of PbB. However, such data should be evaluated for in the Integrated Exposure Uptake Biokinetic (IEUBK) Model merit prior to their use. Model defaults should only be replaced for lead in Children (Publication 9285.7-22). when site-specific data are more representative than the default � User’s Guide for the Integrated Exposure Uptake Biokinetic values. Model default values should never by adjusted simply Model for Lead in Children (IEUBK) Windows® version to attain a better match between model predictions and empirical (Publication 9285.7-42). PbB data. � System Requirements and Design for the Integrated Exposure Uptake Biokinetic Model for Lead in Children (IEUBK) How similar are modeled and empirical blood lead Windows® version (Publication 9285.7-43). (PbB) concentrations? � Reference Manual: Documentation of Updates for the Integrated Exposure Uptake Biokinetic Model for Lead in The IEUBK model was calibrated against two different Children (IEUBK) Windows® version (Publication 9285.7-44). community PbB and environmental Pb studies. Subsequent � Reviewing the Technical Review Workgroup for Lead (TRW) comparisons involvingwell-conducted blood and environmental home page (http://www.epa.gov/superfund/programs/lead). Pb studies have demonstrated reasonably close agreement � Calling EPA’s IEUBK Technical Support Center (1-866-282- between mean observed and predicted PbB concentrations, and 8622). between observed and predicted exceedances of 10 � g/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 �g/dL.