Lead Human Exposure and Health Risk Assessments for Selected ...

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three case studies were reasonable and supported by available empirical data. As
described in Section 3.5.2.2, the exceptions relate to use in those case studies of the
dust models predicting the greatest influence of air concentration on indoor dust Pb
among the set of dust models used. These were the general urban case study hybrid
dust model and the site-specific regression dust model used in the remediation zone
for the primary Pb smelter case study. In both cases, the ratios based on these models
were significantly higher than empirically derived ratios obtained from the literature.
However, the literature indicated a potential for higher ratios for locations with either
lower ambient air Pb levels or lower blood Pb levels, both conditions of which are
present at the two case studies. Therefore, the higher modeled ratios obtained using
the site-specific indoor dust models for the general urban and primary Pb smelter case
studies do not necessarily point to potential high bias in predicting blood Pb levels for
the study populations.
• Comparison of modeled blood Pb levels to nationally representative data: Our ability
to compare modeled blood Pb levels to empirical data was handicapped by a lack of
studies for populations of children directly comparable to those in the three case
studies (see Section 3.5.2.3). Therefore, we focused most of our evaluation of
modeled blood Pb levels on consideration of the national-level data obtained from
NHANES IV. Note that while higher-end population percentiles for the three case
studies might not be reflected in a national-level dataset, blood Pb levels associated
with background exposures for all three case studies are similar to blood Pb levels in
the national dataset. Thus, we considered a comparison of modeled blood Pb levels
for the three case studies against a national-scale dataset for central tendency
population percentiles appropriate. In this comparison, we included the highest and
lowest of the multiple sets of blood Pb estimates for the general urban case study
generated using the multiple modeling approaches employed used for this case study.
These two blood Pb distributions bracketed the NHANES IV based distribution,
which adds confidence to blood Pb modeling conducted for this case study. Results
for the primary Pb smelter were similar to the NHANES IV distribution across
population percentiles up to the 99th%, but then diverged with the case study
percentiles exceeding those for the national-level dataset. This result is not surprising
given the fact that exposure modeling for the primary Pb smelter did not fully
consider variability in background Pb exposure (e.g., paint, diet, drinking water). The
difference between the high-end population percentiles likely reflects primarily airrelated
exposures for the primary Pb smelter case study population and, had
background exposures been fully considered, the degree of divergence between the
July 2007 4-39 Draft – Do Not Quote or Cite