Age-Dependence in Radiation Dose and Risk Assessments. W. A. Chiu, N. Nelson, and L. Ralston, US Environmental Protection Agency, DC
A unique capability for in-depth age-dependent analyses exists in radiation risk assessment. While the general availability of age-specific behavioral parameters enables all human health risk assessments to at least account for age-dependent intake rates of potentially contaminated media, for radionuclides, the development of internationally accepted age-specific biokinetic and radiation risk models allows—in principle—for radiation risk assessments to be significantly more comprehensive in their treatment of age-dependence. With a few exceptions, though, radiation risk assessments have not considered age-dependence to the extent possible. This paper first reviews the general methodology for age-dependent radiation dose and risk calculations that couple fate and transport, intakes, biokinetics, and risk. It then presents calculations that compare dose/risk from intake of contaminated media beginning at different ages for two typical cases. One case considers media with a constant unit concentration of a radionuclide and its daughter products, corresponding to an equilibrium scenario. The other case considers media with an initial unit concentration that undergoes radioactive decay and daughter in-growth. As expected, the dose/risk is typically greater for exposure commencing as a child than as an adult. Quantitatively, however, even the relative effects of age depend significantly on media, exposure duration, and the time-evolution of radionuclide concentrations. Thus, generic correction factors for the effects of age are not possible. More generally, assessments of dose and risk that fully incorporate age-dependence require: (1) age-specific biokinetic and risk models, (2) age-specific behavioral parameters, (3) scenarios that specify the duration(s) of exposure and the media considered, and (4) fate and transport models that calculate concentrations as a function of time in each exposure medium. Disclaimer: This work has not been subjected to EPA’s peer and administrative review, and therefore may not necessarily reflect the views of EPA. No official endorsement should be inferred.
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