Mechanism of biomagnification in fish under laboratory and field conditions

While biomagnification of certain organic contaminants in food chains has b een observed in field studies, the mechanism of the biomagnification proces s is still unresolved. Knowledge of the mechanism by which contaminants are absorbed and biomagnified in food chains is important in environmental ris k assessment and studies of chemical bioavailability. In this study, we hyp othesize a fugacity based model of the gastrointestinal absorption of conta minants. We test the model in a 73 day laboratory, gastrointestinal magnifi cation study of 2,2',4,4',6,6'-hexachlorobiphenyl in adult rainbow trout (O ncorhynchus mykiss) and in a field study of the gastrointestinal magnificat ion of PCB congeners in rock bass (Ambloplites rupestris). Both studies sho w that the fugacity of the test chemicals in the gastrointestinal tract (GI T) can increase to levels up to 7-8-fold greater than those in the consumed food. The fugacity increase in the GIT is the result of a drop in the chym e's fugacity capacity for the test chemicals (i.e. approximately 4-fold in this study) and an increase in chemical concentration due to food absorptio n in the GIT (i.e. approximately 2-fold in this study). Food digestibility and absorption are found to be critical factors controlling biomagnificatio n factors and dietary uptake efficiencies under laboratory and field condit ions.