Studies on the Metabolic Fate of [14C]2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) in the Mouse. KOSHAKJI, R. P., HARBISON, R. D., and BUSH, M. T. (1984). Toxicol. Appl. Pharmacol. 73, 69-77. After a single po dose (135 micrograms/kg; 62 microCi/kg) of 14C-labeled 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in male ICR/Ha Swiss mice, 67 to 76% of the administered dose was eliminated via the feces and 1 to 2% in the urine during the first 24 hr following treatment. It seems likely that most of this material was simply not absorbed. Much of the remaining chemical was then excreted slowly in the urine (2%) and feces (7%) during the next 10 days, partly as the unchanged compound and partly as metabolites. One of the metabolites (Fraction II) appears to be a single polar, acidic metabolite characterized in urine (0.4 +/- 0.1%) and feces (2.2 +/- 0.2%), and is also likely excreted as a glucuronide conjugate. The rest of the radioactivity was in the form of unchanged TCDD in the animal body (17 +/- 2%). Steady rates of decline in the concentrations of the 14C as well as of the unchanged TCDD were reached in the feces and urine after the fifth day following the administration of the chemical. Based on this steady rate, the half-life of the radioactivity in the body was approximately 20 days. Urine, feces, and whole body were analyzed by solvent extraction, 14C counting, thin-layer chromatography, and countercurrent distribution.