Assessing Uncertainty and Variability of Indirect Exposure to Dioxin Emission from Hazardous Waste Incinerator. S. H. Su and P. S. Price, ChemRisk - A Division of McLaren/Hart, 1685 Congress Street, Portland, ME 04102; J. R.. Harrington, Earth Technology, 12 Westbrook Common, Westbrook, ME 04098; and T. B. Abel and C. L. Curry, ChemRisk - A Division of McLaren/Hart, 1685 Congress Street, Portland, ME 04102
Risk from indirect exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) through the food chain from hazardous waste incinerator emissions is a major concern. In assessing the potential health risks from indirect exposure, uncertainties, such as contaminant deposition and biotransfer in the food chain, and variabilities, such as interpersonal variation in consumption rates and duration of exposure, are critical issues to address. To avoid serious propagation of conservatism resulting from the complex nature of indirect exposure risk assessment, proper treatment of uncertainty and variability variables is necessary. This analysis presents a two-dimensional Monte Carlo model of indirect exposure which separately characterizes uncertainty and variability. A case example is presented for exposure to TCDD from the consumption of beef from cattle raised on pasture downwind from a hypothetical incinerator located near the Gulf Coast of Texas. In this model, specific attention was given to uncertainties such as TCDD deposition on grass and soil, environmental fate and transport processes, consumption of grass and soil by beef cattle, regional agricultural practices, and variabilities in beef consumption in the general population and the cattle farmers living near the incinerator. The results of the analysis suggest that commonly used default values for indirect exposure overestimate the range of exposure that can be anticipated to occur at this site.