DEVELOPMENT AND VALIDATION OF AN AIR-TO-BEEF FOOD-CHAIN MODEL FOR DIOXIN-LIKE COMPOUNDS

A model for predicting concentrations of dioxin-like compounds in beef is developed and tested. The key premise of the model is that concent rations of these compounds in air are the source term, or starting poi nt, for estimating beef concentrations. Vapor-phase concentrations tra nsfer to vegetations that cattle consume, and particle-bound concentra tions deposit onto soils and these vegetations as well. Congener-speci fic bioconcentration parameters, coupled with assumptions on cattle di et, transform soil and vegetative concentrations into beef fat concent rations. The premise of the validation exercise is that a profile of t ypical air concentrations of dioxin-like compounds in a United States rural environment is an appropriate observed independent data set, and that a representative profile of United States beef concentrations of dioxin-like compounds is an appropriate observed dependent result. Th ese data were developed for the validation exercise. An observed conce ntration of dioxin toxic equivalents in whole beef of 0.48 ng/kg is co mpared with a predicted 0.36 ng/kg. Principal uncertainties in the app roach are identified and discussed. A major finding of this exercise w as that vapor phase transfers of dioxin-like compounds to vegetations that cattle consume dominate the estimation of final beef concentratio ns: over 80% of the modeled beef concentration was attributed to such transfers.