Dietary bioaccumulation experiments with chlorobenzenes, PCBs, and mirex in guppies and goldfish are presented. The results demonstrate that, in the gastrointestinal tract of fish, the fugacity of very hydrophobic, nonmetabolizable chemicals (log Kow > 6) is elevated above the fugacity in the consumed food as a result of food digestion and absorption. Observed fugacities in fecal matter were up to 4.6-fold greater than the fugacity in the administered food. Fecal to food fugacity ratio ranged between 0.07 and 4.6 in guppies and between 0.014 and 4.5 in goldfish and increased with increasing Kow-Food digestion in the gastrointestinal tract was found to increase the chemical fugacity in the food 5-fold by altering the fugacity capacity of the food. An additional 2-3-fold increase in the chemical concentration and fugacity in the gastrointestinal tract is due to food absorption from the gastrointestinal tract. The findings support the "digestion" hypothesis as being the driving force of the biomagnification and food chain accumulation of hydrophobic organic chemicals. The study further illustrates the application of static head-space analysis to measure chemical fugacities in food and fecal samples.

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