Estimating farfield organic chemical exposures, intake rates and intake fractions to human age classes

This study describes the development and application of the Farfield Human Exposure (FHX) model. This screening level model brings together information on chemical partitioning, degradation, environmental fate and transport, and food web bioaccumulation for assessing human age class-specific exposures from chemicals released to the environment. The Level III model calculates steady-state concentrations in multimedia compartments such as air, water, and soil, and various food groups including fruits, vegetables, milk, dairy, fish, and meats based on a unit emission rate. Human multimedia intake and ingestion rates determine unit emission based chemical exposures, intake rates and intake fractions for various age classes representing the general population. The FHX model is generally applicable to regional areas and is designed to use readily available chemical input data for screening level and priority setting evaluations. In the present study the model is parameterized for an evaluative regional area using Health Canada exposure factors to determine multimedia intake rates for seven selected age classes. The model outputs, human chemical intake rates and human intake fractions are described for four case study chemicals. Biotransformation and biomagnification processes in food webs are highlighted as key factors influencing human exposure. Future research needs to improve the model are discussed.