Review of the Department of Defense Biokinetic Modeling Approach in Support of Establishing an Airborne Lead Exposure Limit (2020) / Chapter Skim
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to derive airborne concentrations of lead that correspond to BLLs for consideration by DoD management in establishing an updated OEL to replace the permissible exposure limit set by OSHA. DoD requested that the National Academies establish an expert committee to evaluate whether the DoD-O'Flaherty model used to derive airborne lead concentrations from BLLs was appropriate.
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1 Both models met criteria for having appropriate compartments or processes for describing lead biokinetics, addressing the essential exposure routes, handling background lead exposure and occupational lead exposure, and calculating the corresponding lead dose-metric. The committee found that both the O'Flaherty and Leggett+ models described available BLLs with similar accuracy.
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However a comprehensive error check of the model code is an important aspect of developing a biokinetic model for regulatory application. DoD should conduct and document an error check of the DoD-O'Flaherty model to assure there are no mathematical errors or errors in the code and equations, and that the model reasonably reproduces the analytic results published in the 2019 model support document.
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are required near sources of lead emissions that contribute, or are expected to contribute, to ambient air lead concentrations that exceed National Ambient Air Quality Standards. Therefore, measurements from source monitors may not reflect airborne lead concentrations experienced by DoD workers living and/or working at a distance from those sources.
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The data sources and general approach for developing the probability distributions of inhalation rates are reasonable. However, DoD should consider conducting additional Monte Carlo simulations at the candidate OELs using a distribution of inhalation rates (and cardiac outputs)
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The information topics included the DoD-O'Flaherty model structure, changes DoD made to the 2000 version of the O'Flaherty model, the basis for DoD's estimated average removal duration for DoD workers, who exhibited elevated BLLs; DoD job activities that have the potential to result in lead exposure; modeled exposure scenarios; and approaches for selecting model parameters for the Monte Carlo analyses.
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However, the committee observed that the results of the Monte Carlo analyses were not presented in a manner that gave the reader an appreciation for the prediction intervals or envelope. The results of Monte Carlo analysis would be more useful to the reader if they included mean values of measures with prediction intervals based on model uncertainty and variability/error in the data used for parameterization.
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