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ToxSci Advance Access published online on December 2, 2003
Toxicological Sciences, doi:10.1093/toxsci/kfh032
Toxicological Sciences © Society of Toxicology 2003; all rights reserved
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Received June 4, 2003; accepted October 23, 2003
© 2003 Society of Toxicology

Biotransformation and Toxicokinetics

A Physiologically Based Toxicokinetic Model for Dietary Uptake of Hydrophobic Organic Compounds by Fish II. Simulation of Chronic Exposure Scenarios

John W. Nichols 1*, Patrick N. Fitzsimmons 1, and Frank W. Whiteman 1

1 U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201 Congdon Boulevard, Duluth, Minnesota, 55804

* To whom correspondence should be addressed. E-mail: nichols.john{at}epa.gov.


  Abstract

A physiologically based toxicokinetic (PBTK) model for dietary uptake of hydrophobic organic compounds by fish was used to simulate dosing scenarios commonly encountered in experimental and field studies. Simulations were initially generated for a model compound, [UL-14C] 2,2',5,5'-tetrachlorobiphenyl ([14C] PCB 52). Steady-state exposures were simulated by calculating chemical concentrations in tissues of the predator corresponding to an equilibrium distribution between the fish and water (termed the bioconcentration, or BCF residue data set). This residue data set was then varied in a proportional manner until whole-body chemical concentrations exhibited no net change for each set of exposure conditions. For [14C] PCB 52, the proportional increase in BCF residues (termed the biomagnification factor, or BMF) required to achieve steady-state in a food-only exposure was 2.24, while in a combined food and water exposure the BMF was 3.11. Additional simulations for the food and water exposure scenario were obtained for a set of hypothetical organic compounds with increasing log KOW values. Using gut permeability coefficients determined for [14C] PCB 52, predicted BMFs increased with chemical log KOW, achieving levels much higher than those reported in field-sampling efforts. BMFs comparable to measured values were obtained by reducing permeability coefficients within each gut segment in a log KOW-dependent manner. This predicted decrease in chemical permeability is consistent with earlier work suggesting that dietary absorption of hydrophobic compounds by fish is controlled in part by factors that vary with chemical log KOW. Relatively low rates of metabolism or growth were shown to have a substantial impact on steady-state biomagnification of chemical residues.


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J. W. Nichols, P. N. Fitzsimmons, F. W. Whiteman, T. D. Dawson, L. Babeu, and J. Juenemann
A Physiologically Based Toxicokinetic Model for Dietary Uptake of Hydrophobic Organic Compounds by Fish: I. Feeding Studies with 2,2',5,5'-Tetrachlorobiphenyl
Toxicol. Sci., February 1, 2004; 77(2): 206 - 218.
[Abstract] [Full Text] [PDF]


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