Dietary uptake kinetics of 2,2',5,5'-tetrachlorobiphenyl in rainbow trout.

The disposition of [UL-(14)C]2,2',5,5'-tetrachlorobiphenyl (TCB) in rainbow trout (Oncorhynchus mykiss) was studied in acute dietary exposures using TCB-contaminated fathead minnows (Pimephales promelas). Trout were sampled at several postfeeding time points and TCB-derived radioactivity was measured in gut contents and selected tissues. Gastric evacuation was exponential with time and was 95% complete within 36 h of feeding. The ratio of activity in upper intestinal tissue to that in blood declined between 6 and 48 h, as did the lumenal contents/tissue ratio. Stomach content lipid declined between 0 and 24 h, while the lipid content of chyme remained relatively constant. These observations are consistent with liquid phase emptying of lipid and TCB to the upper intestine followed by rapid coassimilation. Tissue/blood activity ratios for the stomach, lower intestine, muscle, liver, and kidney were constant and probably represented near equilibrium conditions. The fat/blood activity ratio increased through 96 h, indicating that TCB was redistributing to fat. The lower intestinal tissue/feces activity ratio increased between 6 and 24 h and then declined rapidly. Fecal lipid content also increased between 6 and 24 h, but the amount of this increase was insufficient to explain observed changes in the distribution of TCB-derived activity. A small amount of 3-hydroxy TCB was detected in feces. Generally, however, metabolism had little or no impact on the uptake, distribution or elimination of TCB. Measured assimilation efficiencies exceeded 90% and are the highest ever reported in fish feeding studies with TCB.

A physiologically based toxicokinetic model for lake trout (Salvelinus namaycush).

A physiologically based toxicokinetic (PB-TK) model for fish, incorporating chemical exchange at the gill and accumulation in five tissue compartments, was parameterized and evaluated for lake trout (Salvelinus namaycush). Individual-based model parameterization was used to examine the effect of natural variability in physiological, morphological, and physico-chemical parameters on model predictions. The PB-TK model was used to predict uptake of organic chemicals across the gill and accumulation in blood and tissues in lake trout. To evaluate the accuracy of the model, a total of 13 adult lake trout were exposed to waterborne 1,1,2,2-tetrachloroethane (TCE), pentachloroethane (PCE), and hexachloroethane (HCE), concurrently, for periods of 6, 12, 24 or 48 h. The measured and predicted concentrations of TCE, PCE and HCE in expired water, dorsal aortic blood and tissues were generally within a factor of two, and in most instances much closer. Variability noted in model predictions, based on the individual-based model parameterization used in this study, reproduced variability observed in measured concentrations. The inference is made that parameters influencing variability in measured blood and tissue concentrations of xenobiotics are included and accurately represented in the model. This model contributes to a better understanding of the fundamental processes that regulate the uptake and disposition of xenobiotic chemicals in the lake trout. This information is crucial to developing a better understanding of the dynamic relationships between contaminant exposure and hazard to the lake trout.