Recommendations for Default Age Range in the IEUBK Model

OU:\I DIRECTIVE 9200.2-177

RECOMMENDATIONS FOR DEFAULT AGE RANGE IN THE IKUBK MODEL

Overview

Since 1994, the Office of Land and Emergency Management (OLEM), formerly known as
the Office of Solid Waste and Emergency Response (OSWER), has recommended the
Integrated Exposure Uptake Isokinetic Model for Lead in Children (IEUBK model) as a
risk assessment tool to support environmental cleanup decisions at current or future
anticipated residential sites (U.S. EPA, 1994a,b). The IEUBK model uses empirical data
from numerous scientific studies of lead uptake and biokinetics, contact rates of
children with contaminated media, and data on the presence and behavior of
environmental lead to predict a plausible distribution around the geometric mean (GM)
of blood lead (PbB) for a hypothetical child or population of children,1 The relative
variability of PbB concentrations around the GM is defined as the geometric standard
deviation (GSD). The GSD encompasses biological and behavioral differences,
measurement variability from repeat sampling, variability as a result of sample
locations, and analytical variability." From this distribution, the IEUBK model estimates
the risk (i.e.. probability) that a child's or a population of children's PbB concentration
will not exceed a certain PbB level (U.S. EPA, 1994a, 1998, White et al., 1998).

The IEUBK model is utilized for achieving a risk reduction goal of limiting exposure to
soil lead levels such that children (0-84 months old) would have no more than 5% risk
of exceeding a certain blood lead level (PbB) (U.S. EPA, 19943,!:)). In June 2012, Center
for Disease Control and Prevention (CDC) adopted the 97.5th percentile blood lead
concentration for children between 1-5 years old of the National Health and Nutrition
and Nutrition Survey (NHANES) as the reference value to target interv ention for
individual children and communities with blood lead levels at and above that
concentration (CDC, 2012). This reference value will be updated every 4 years based on

'Tlie GM represents the central tendency estimate (e.g., mean, 50"' percentile] of i'blJ concentration of children from
a hypothetical population (Hogan et al, 1998). If an arithmetic menu (or average) dietary' intake is used, the model
provides a centra! point estimate for risk of an ele\ated i'bli level. By definition, a central tendency estimate is
equally likely to over- or under-estimate the lead-intake at a contaminated site. Upper confidence limits (UCLs) can
he used in the IEUBK model; however, the 1EUBK model results could he interpreted as a more cousen ative
estimate of the risk of an elevated I'hB level. See U.S. K1JA (1994b) for further information.

•The IEUBK model uses a log-normal probability distribution to characterize this variability (U.S. EPA. 1994a). The
biokinetic component of the IEU K K model output provides a central estimate of PbB level, which is used to provide
the geometric standard deviation (GSD). The GSD encompasses biological and beha\ioral differences, measurement
variability from repeat sampling, \ ariability as a residt of sample locations, and analytical variability. In the IEUBK
model, the GS1) is intended to reflect only individual PhB variability, not variabilis in I'bB levels where different
individuals are exposed to substantially different media concentrations of lead. The recommended default value for
GSD (1.6) was derived from empirical studies with young children where both blood and environmental lead
concentrations were measured (White et a!., 1998).

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OLEM DIRECTIVE 9200.2-177

current PhB information from NHANKS. At this time, the 97.5th percentile for children
1-5 years old is equivalent to 5 ug/tiL (ACCLPP, 2012).

On December 22, 2016. KPA issued Directive 9200.2 167, Updated Scientific
Consideration for Lead in Soil Cleanups, which highlights the current science and risk
assessment tools that Regions may consider when implementing the 1QQ4 EPA
Directive, Revised Interim Soil Lead Guidance, for CERCLA Sites and RCRA
Corrective Action L'acilities. Today ">e recognize that the information provided in the
1994 Directive regarding blood lead levels may not be adequately protective for children
and adults, as it does not reflect current scientific consensus and national public health
recommendations regarding lead exposure and adverse health efieets. The directive
states:

The current scientific literature on lead toxicologu and epidemiology provides
evidence that ad verse h ealth effects are associated with blood lead levels (BLLs)
less than 10 ug/dL. For example. EPA s Office of Research and Development
reviewed the health effects evidence for lead in the 2()va Integrated Science
Assessment for Lead (ISA for I a: ad J and found that several studies have observed
"clear evidence of cognitive function decrements (as measured by Full Scale IQ
academic performance and executive function) m young children (4 to 11 11 ears
old) with mean or group blood lead levels between2 uq/dL and S ug/dL
(measured at various life stages and lime periods), "hi addition, the National
Toxicology Program's (2012} Monograph on Health Effects of Low- Level Lead
found sufficient evidence of delayed puberty, reduced post-natal growth, and
decreased hearing for children at BLLs below 10 ug/dL and adverse effects on
academic achievement, IQ other cognitive measures, attention-related behaviors,
and pn>blem behaviors at BLLs below 5 ug/dL.

The 2016 Directive recommends that Regions consider the best science when selecting a
not to exceed blood iead level tor use in the IEUBK model,

RATIONALE AND RECOMMENDATION

NTP (2012) reported that children age 1-5 years consistently have higher blood Pb levels
than do older children. NTP hypothesized that this was likely due to hand-to-mouth
activity in voung children. Similarly, CDC (2007) reported that several studies show a
peak in children's blood Pb levels around 24 months of age. Neurological deficits have
been associated uith increased blood lead levels among children in this age range (NTP,
2012; see section 4.3.1) Thus, the focus of the JEUHK model on this age group is better
aligned with the most exposed population.

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OLKM DIRECTIVE 9200.2-177

To better align the CDC recommendation and the risk predictions for lead exposure at
Superfund sites, the TRW Lead Committee recommends that the default age range in
IEUBK model be modified to match the 1-5 year age range (12-72 months). See Figure 1.

IMPLEMENTATION

The default age range in the IEUBK model is a variable that may be changed by the user
to assess site-specific exposure conditions. In addition to the default, there are a number
of established age ranges and a user defined option that allows any interval of monthly
exposures and calculations. Risk assessments should derive preliminary remediation
goals (PRG) based on the age range that best represents the exposed population.

Aligning the default age range in the IEUBK model to match the age range used by CDC
to establish the reference value does not eliminate this flexibility in the IEUBK model.
Instead, it allows users to rapidly compare risk predictions from site exposures to the
public health goal that is recommended by CDC.

The 12-72 month age range generally results in a lower PRG than the 0-84 (or 6-84)
month age range because soil and dust ingestion rates are generally lower for children
aged 0-12 and 72-84 months (see Figure Screen 2-12 on page 2-15 of US EPA, 1994a).

User. Designated

User D esignated Age: OK.

Low Value 12 Cancel

High Value 72}

TRW Homepage:

http: //ww w. epa gov/superf und/heaIlh/contamiri3nts/teacl/indeK.htim

Figure 1. Recommended age range for human
health risk assessment at Superfund sites.

Rkfkkkncks

ACCLPP (Advisory Committee on Childhood Lead Poisoning Prevention). 2012. Low
Level Lead Exposure Harms Children: A Renewed Call for Primary Prevention:
Atlanta, GA. Centers for Disease Control and Prevention Available online at:

www.cde.gov/rieeh/1ead/ACCLPP/Final .Document o:-U)712.pdf,

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OLEM DIRECTIVE 9200.2-177

CDC (U.S. Centers for Disease Control and Prevention). 2007. Interpreting and
managing blood lead levels <10 pg/dl in children and reducing childhood
exposures to lead: recommendations of CDC's Advisory Committee on Childhood
Lead Poisoning Prevention. Morbidity and Mortality Weekly Report. Atlanta, GA:
Centers for Disease Control and Prevention (CDC). 1-15. Available online at:
http:/ / www.cde.Kov/nimwr/P D F / it/rr5608.pdf.

CDC (U.S. Centers for Disease Control and Prevention). 2012. Low level exposure harms
children: A renewed call for primary prevention. Report of the Advisory
Committee on Childhood Lead Poisoning Prevention. January 4. Available online
at: hUp://'www .cdc.goy /1 icch/' 1 o;ui/ACCLPP/ Final Hoe 1tnuMrl t) 3 () 712L[x ft .

NTP (National Toxicology Program). 2012. NTP Monograph: Health Effects of Low-
Level Lead. June 2012. OHAT/NIEHS/DIIHS. Available online at:
h11; 3: / /_n_t ] h n i c h s. n i h. gov/ N'T P / <1 h a 1 /1 A'ad/Final/MonographHoallhEtfcctsLowLe
ydLead NowjSSN soS.pdl

U.S. Environmental Protection Agency (U.S. EPA). 1994a. Guidance Manual for the
IEUBK Model for Lead in Children. Office of Solid Waste and Emergency
Response: Washington, DC. PB93-963510, OSWER #9285.7-15-1. February,
Available online at: hUp://w\\yyAipa..&o\ /supcrfu nd/lead/products. htir>.

U.S. EPA (U.S. Environmental Protection Agency). 1994b. OSWER Directive: Revised
Interim Soil Lead Guidance for CERCLA Sites and RCRA Corrective Action
Facilities. Office of Solid Waste and Emergency Response, U.S. Environmental
Protection Agency. Washington, DC. OSW?ER Directive #9355-4~i2. Available

online at:

www.epa.gov/snpcrfund/health / contaminants/lead/products/oswerdir. pdf

U.S. EPA (U.S. Environmental Protection Agency). 1998. Memorandum: OSWER

Directive: Clarification to the 1994 Revised Interim Soil Lead (Pb) Guidance for
CERCIJV Sites and RCRA Corrective Action Facilities. Office of Solid Waste and
Emergency Response: Washington, DC. EPA/54O/F-98/03O, PB98-963244,
OSWER #9285.7-52. March. Available from:

http://epa.gov/superfund/lcad/products/nhanes.pdf Directive #9200.4-27?.
August. Available online at:

http://www.cpa .gov/superfund/lead / productsZoswerQ8.pdf.

White, P.D.; Van Leeuwen, P.; Davis, B.D.; Maddaloni, M.; Hogan, K.A.; Marcus, A.IL;
Elias, R.W. 1998. The conceptual structure of the integrated exposure uptake
biokinetic model for lead in children. Environ Health Perspect 106 Suppl 6: 1513-
1530. Available online at: http://ehpneti.niehs.nih.gov

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