Excretion of radioactivity from rats and rabbits following cutaneous application of two 14C-labeled azo dyes.

A benzidine-derived azo dye, C.I. direct black 38 (DB38), and a p-phenylenediamine-derived dye, C.I. direct black 19 (DB19), labeled with carbon-14 in their aromatic amine moieties, were applied to the shaved dorsal skin of male Fischer-344 rats and New Zealand rabbits. Application sites were protected with nylon gauze and elastic bandage assemblies. Following application of measured amounts of radiolabeled dye in 0.1 M pH 10.2 carbonate buffer, serial urine and fecal samples were obtained from individual animals in metabolism cages at 24, 48, 72, 96, 120, and 144 h. Aliquots of urine and fecal homogenates were assayed for radioactivity by scintillation counting. Cumulative excretion of radioactivity from rats receiving DB38 was 0.05% of total dermal dose at 144 h in urine, and 0.16% of total dermal dose in feces. Cumulative excretion of radioactivity from DB38-treated rabbits at 144 h was 3.12% of total dermal dose in urine, and 5.12% in feces. From rats and rabbits receiving topical DB19, cumulative excretion of radioactivity at 144 h was less than that from DB38-treated animals. In rat urine, 0.04% of total dermal dose appeared; in rat feces, no radioactivity was recovered. In rabbit urine, 0.04% of dermal dose was found; 0.01% appeared in rabbit feces.