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

The disposition of [UL-C-14]2,2',5,5'-tetrachlorobiphenyl (TCB) in rainbow trout (Oncorhynchus mykiss) was studied in acute dietary exposures using TC B-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 w ith 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, a s did the lumenal contents/tissue ratio, Stomach content lipid declined bet ween 0 and 24 h, while the lipid content of chyme remained relatively const ant, These observations are consistent with liquid phase emptying of lipid and TCB to the upper intestine followed by rapid coassimilation. Tissue/blo od activity ratios for the stomach, lower intestine, muscle, liver, and kid ney were constant and probably represented near equilibrium conditions. The fat/blood activity ratio increased through 96 h, indicating that TCB was r edistributing to fat. The lower intestinal tissue/feces activity ratio incr eased between 6 and 24 h and then declined rapidly. Fecal lipid content als o increased between 6 and 24 h, but the amount of this increase was insuffi cient to explain observed changes in the distribution of TCB-derived activi ty. A small amount of 3-hydroxy TCB was detected in feces. Generally, howev er, metabolism had little or no impact on the uptake, distribution or elimi nation of TCB. Measured assimilation efficiencies exceeded 90% and are the highest ever reported in fish feeding studies with TCB.