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USE OF A PHYSIOLOGICALLY BASED TOXICOKINETIC MODEL TO SIMULATE CHRONIC DIETARY EXPOSURE IN FISH
Citation:
Nichols, J W., P N. Fitzsimmons, AND F W. Whiteman. USE OF A PHYSIOLOGICALLY BASED TOXICOKINETIC MODEL TO SIMULATE CHRONIC DIETARY EXPOSURE IN FISH. Presented at 2002 SETAC Annual Meeting, Salt Lake City, UT, November 16-20, 2002.
Description:
A physiologically based toxicokinetic (PBTK) model was developed to describe dietary uptake of hydrophobic organic chemicals by fish. The GI tract was modeled as four compartments corresponding to the stomach, pyloric ceca, upper intestine, and lower intestine. Partitioning coefficients were adjusted to account for changes in chemical affinity associated with uptake of dietary lipid, and the lumenal volume of each gut compartment was allowed to change in time to simulate nutrient uptake and bulk flow of digesta. The model was calibrated using data from rainbow trout that were fed a single meal of fathead minnows contaminated with TCB; log Kow of 6.1. The model was then used to simulate several chronic dosing scenarios. For TCB, the steady-state biomagnificatioon factor (BMF) predicted for a food-only exposure was 1.56, while in a combined food and water exposure the steady-state BMF was 2.46. Additional simulations were run for a set of hypothetical compounds with increasing log Kow values. These adjustments caused a decrease in predicted dietary assimilation efficiency, but the effect was highly non-linear. A model-based evaluation of competing assumptions regarding chemical flux in the upper GI tract suggested that similar results would be expected under either set of conditions. The results of this effort are consistent with data from experimental and field studies, and provide mechanistic support for the "digestion hypothesis" of chemical biomagnification in fish. This abstract does not necessarily reflect EPA policy.