PHYSIOLOGICALLY-BASED TOXICOKINETIC MODEL FOR MATERNAL TRANSFER OF 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN IN BROOK TROUT (SALVELINUS-FONTINALIS)

A physiologically based toxicokinetic (PB-TK) model was developed to d escribe the uptake, distribution, and elimination of 2,3,7,8-tetrachlo rodibenzo-p-dioxin (TCDD) in female brook trout during a B-month feedi ng and depuration study. Dietary uptake was modeled under two assumpti ons, uptake proceeds to equilibrium between blood exiting the intestin al tract and the contents of the intestinal tract, and uptake is limit ed by desorption of TCDD from gut contents and/or diffusion from the l umen into tissues. Model outputs were evaluated by comparison with mea sured TCDD residues. The best model fit to the data was obtained by im posing a moderate diffusion limitation on gut uptake. Of the parameter s that comprise the gut submodel, whole body residue predictions were most sensitive to changes in the diffusion rate constant and fecal ege stion rate. Chemical residues in fat were indicative of an internal di sequilibrium with other tissues during the loading phase of the study. Accurate simulations of this behavior were obtained using a diffusion -limited tissue description. Chemical residues in liver, muscle, and o varies were adequately described by assuming that uptake and eliminati on were blood flow limited. Spawning probably resulted in a small incr ease in whole body TCDD concentration and did not appear to represent an important route of chemical elimination. These results suggest that field-derived whole body TCDD residues could be used to estimate resi dues in developing ovaries of brook trout to within a factor of two, p rovided that whole body and ovary lipid content were known.