Development of An Air-to-Leaf Vapor Phase Transfer Factor for Dioxins and Furans
Results of an experiment in which grass was grown in a greenhouse and outdoors, and in soils of different concentration levels of dioxins and furans, were used in a modeling exercise to derive an air-to-leaf vapor phase transfer factor. The purpose of the experiment was to understand the pathways by which dioxins and furans enter the grass. A principal finding in the experiment was that dry gaseous deposition of these compounds, rather than particle deposition or soil-to-plant transfers, explained the concentrations found. A subset of the data from this experiment was used in a modeling framework in this paper. Specifically, the subset includes ambient air concentrations from the summer sampling for 1991 and the outdoor grass concentrations during the same period. The air-to-plant modeling framework is a simple empirical framework. Air-borne dioxin congeners are partitioned into a particle and a vapor phase. The particle phase dioxins settle onto plants and are weathered (washed off or blown off) from the plants using a simple first order weathering constant. Vapor phase dioxins "transfer" to plants using a simple air-to-leaf biotransfer factor. The experimental data was used to determine the air-to-leaf vapor phase biotransfer factor of this modeling framework.