According to the fugacity approach (Mackay 1979), pollutant uptake by an organism is determined by the chemical fugacity differential between the organism and its environment. The Accumulation Factor (AF = (concentration of pollutant in animal tissue, C(sub t) (nanograms/g dry wt)/animal lipid (%/100))/(concentration of pollutant in sediment, C(sub s) (nanograms/g dry wt)/sediment total organic carbon, TOC (%/100))) is a simple, fugacity-based model which has been shown to be useful for predicting the bioaccumulation potential of hydrophobic neutral organic compounds in sediment-dwelling animals (Rubinstein et al. 1987; McElroy and Means 1988; Clarke et al. 1988; Ferraro et al. 1990). The theoretical basis for the AF model is discussed in Mackay (1979), Mackay and Paterson (1981, 1982), McFarland (1984), McFarland and Clarke (1986), and Lake et al. (1987). The model assumes chemical equilibrium or steady-state in the animals and the sediments to which they are exposed, no chemical transformation or phase transfer resistance, and chemical partitioning primarily between the organic pool in the sediment and the lipid pool in the animal.