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

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there are many blood Pb studies reported in the literature, they are largely composed of
populations experiencing exposures from all pathways that are higher than current exposures.
No datasets were identified for specific subpopulations with exposures corresponding to current
exposures that would be appropriate for performance evaluation here. In the case of the general
urban case study, while it is not location-specific, we have not identified any contemporary
datasets for urban locations with ambient air Pb levels matching those modeled in the current
scenario that are not heavily influenced by Pb-paint. For the primary Pb smelter case study
location, the most generally available blood Pb monitoring study was completed in 2001 and
2002, and given the changes in exposures since that time and the use of a future (current NAAQS
attainment) scenario these older blood Pb surveys do not correspond to the exposures modeled
for this case study. In the case of the secondary Pb smelter, the blood Pb data available for the
county containing the secondary Pb smelter does not indicate residence location handicapping
efforts to consider blood Pb levels for children in the secondary Pb smelter case study location.
While blood Pb datasets were not identified for populations representative of those
modeled for the three case studies, we have compared the modeled blood Pb levels against
general national-scale blood Pb levels (for a child age group matching that modeled for the case
studies). While each of the case studies involves a population that is different than the national
population (reflecting the nature of the exposure scenario being considered), the background
exposures for the case studies and the national population are similar. Accordingly, the
relationship between the modeled blood Pb levels for each study area and the national
distribution are evaluated. For this evaluation, we have used measured values interpolated from
the NHANES IV dataset. Specifically, we have interpolated a series of percentile estimates for 7
yr olds based on summary data presented for NHANES IV (CDC, 2005). The process of
interpolating these values involved the following steps: (a) use summary statistics (GM and
associated confidence intervals) for 1-5 yr olds and 6-19 yr olds (for years 1999-2002) to
establish log-normal distributions for each age range, (b) identify population percentiles of
interest (e.g., median, 90 th , 95 th , 99.5 th percentiles) for each age group using these log-normal
distributions, and (c) interpolate a series of percentiles for a 7yr age cohort using the percentiles
for the two age ranges (the 1-5 yr old and 6-19 yr old). This interpolation procedure resulted in
the population percentile estimates for a 7 yr old cohort (for the years 1999-2002) presented in
Table 3-25.
July 2007 3-51 Draft – Do Not Quote or Cite