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

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1 Table 3-23. Evaluation of model-predicted indoor dust Pb levels against empirical data 2 obtained from the literature. Case study Primary Pb smelter case study Secondary Pb smelter case study Modeled indoor dust Pb levels (ppm) Air quality scenario Median Current NAAQS Current conditions 5 th to 95 th Percentile (min-max) 122 50 - 2,318 (41 - 3,523) 63 60 – 73 (60 – 166) Indoor Dust Pb Observations reported in the literature - Residences near smelters: 1283-4140 ppm (CD, Table 3-8) - Jersey City, NJ housing (floor): 857 ppm (CD, Table 3-8) - Residences in the Midwest (windowsill): 954ppm (CD, Table 3-8) - Ottawa Canada housing (floor): 222 ppm (median), 406 ppm (mean) (Tang et al., 2004) - HUD survey of US housing: 87 ppm (median for newest houses, built 1960-1979), 406 ppm (median for oldest housing, build
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 3.5.2 Performance Evaluation Related to Blood Pb Modeling Performance evaluation completed in support of blood Pb modeling involved three steps: (a) evaluation of candidate blood Pb models for the analysis, (b) comparison of ambient outdoor air Pb-to-blood Pb ratios generated for the three case studies against ratios obtained from the literature and (c) comparison of modeled blood Pb levels for these three case studies against NHANES IV data. Each of these evaluation steps is discussed below. 3.5.2.1 Evaluation of Candidate Blood Pb Models Evaluation of candidate blood Pb models (IEUBK and Leggett) involved three separate stages: (a) application of the candidate models to three hypothetical individual-child exposure scenarios used previously by EPA and others in evaluations of blood Pb models, (b) comparison of candidate model predictions for a general U.S. childhood exposure scenario (using typical Pb exposures for key pathways) to NHANES IV empirical data, and (c) evaluation of candidate model performance in replicating measurements of urban child blood Pb levels obtained in Rochester. Detailed results of the evaluation of candidate blood Pb models are presented in Appendix J (and summarized in Section J.4). The first stage (focusing on reproducing results of previous performance evaluations) demonstrated that we were applying the candidate models correctly. Tests of the models against specific individual exposure scenarios (Section J.1.3) reproduced, to a high degree, the results of previous model comparison. The second stage of the model evaluation (focusing on reproducing general US child blood Pb levels presented in NHANES IV) demonstrated that, depending on assumptions regarding typical outdoor soil/dust and indoor dust Pb concentrations, the IEUBK model either moderately over-predicted child GM blood Pb levels (by two-fold or less) or generated predictions close to NHANES summary statistics (see Section J.3.1). By contrast, predictions from the Leggett model were more than three to six times higher than the age-specific NHANES IV GM values. The third stage of the model evaluation focused on evaluating the candidate models in predicting blood Pb levels for an urban child cohort (Appendix J, Section J.3.2). The dataset, which included matched Pb media concentrations (outdoor soil/dust and indoor dust levels) and blood Pb levels, was collected as part of an epidemiological study focusing on the effects of Pb exposure in children living in Rochester, NY (Lanphear et al., 1995; Lanphear and Roghmann, 1997). Blood Pb levels for each child sampled in the study were predicted using IEUBK and Leggett, with the measured media Pb levels collected as part of the study as inputs. These predicted blood Pb levels were then compared to the measured blood Pb levels for each child. The results of this stage of the model evaluation were similar to those from the NHANES July 2007 3-47 Draft – Do Not Quote or Cite
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Lead Human Exposure and Health Risk
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DISCLAIMER This document has been r
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comment. A final version of this do
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2.4 ANALYTICAL APPROACH ...........
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List of Figures Figure 1-1. Princip
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Table 4-17. Secondary Pb smelter ca
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1 concentrations in water, soil and
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1 showing impaired neurobehavioral
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1 assessment, summarized in Section
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1 Table 2-1. Key aspects of primary
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1 2.3 ASSESSMENT SCENARIOS 2 The de
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1 Table 2-3. Air quality scenarios
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1 southern California, where Pb has
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1 2 3 4 5 6 7 8 9 10 11 REFERENCES
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