| The current study characterizes the principal uncertainties surrounding the application of environmental models in the assessment of potential health risks related to dioxin emissions from a PCB incineration facility. The objectives of the current research involved: (1) the empirical characterization and preliminary validation of computer-based models used for exposure assessment and toxicological assessment; (2) characterization of the potential environmental consequences from ambient exposure to bioaccumulative chemicals; and (3) improved scientific support for risk management decisions concerning such industrial activities.; Based upon model specifications from the scientific literature, a physiologically-based pharmacokinetic (PBPK) model was adapted and revised to characterize the dispositional kinetics of the key polychlorinated dibenzo p-dioxin and dibenzofuran congeners (i.e., 2,3,7,8-tetrachlorodibenzo p-dioxin [TCDD], 2,3,7,8-tetrachlorodibenzofuran, 1,2,3,7,8-pentachlorodibenzofuran, and 2,3,4,7,8-pentachlorodibenzofuran) in the Sprague-Dawley rat (Rattus norvegicus) laboratory species and the Gapper's red-backed vole (Clethrionomys gapperi) sentinel species.; Results of the current application of the PBPK model developed for the vole sentinel species indicated that the revised model appears to provide a reasonably accurate estimation of chemical-specific disposition and elimination patterns. Furthermore, model results suggest that the internationally established methodology for Toxic Equivalency Factors (TEFs) may overestimate the apparent toxicity of the 2,3,4,7,8-PeCDF congener in relation to TCDD in the red-backed vole. Given that the 2,3,4,7,8-PeCDF congener represents the preponderance of the mass- and TEF-based concentration of dioxin/furan congeners measured in biota near incineration facilities, a systematic over-estimation of the TEF for this congener would have significant impacts on the outcome of an environmental risk assessment, based upon the red-backed vole as a sentinel species. |
