EVALUATING THE MULTIMEDIA FATE OF ORGANIC-CHEMICALS - A LEVEL-III FUGACITY MODEL

A multimedia model is developed and applied to selected organic chemicals in evaluative and real regional environments. The model employs the fugacity concept and treats four bulk compartments: air, water, soil, and bottom sediment, which consist of subcompartments of varying proportions of air, water, and mineral and organic matter. Chemical equilibrium is assumed to apply within (but not between) each bulk compartment. Expressions are included for emissions, advective flows, degrading reactions, and interphase transport by diffusive and non-diffusive processes. Input to the model consists of a description of the environment, the physical-chemical and reaction properties of the chemical, and emission rates. For steady-state conditions the solution is a simple algebraic expression. The model is applied to six chemicals in the region of southern Ontario and the calculated fate and concentrations are compared with observations. The results suggest that the model may be used to determine the processes that control the environmental fate of chemicals in a region and provide approximate estimates of relative media concentrations.