Metabolism of a dimethylbenzidine-based dye in rats and hamsters as determined by analysis of the urine for potentially carcinogenic aromatic amines.

Direct Red 2 was given as an aqueous solution to rats and hamsters to determine whether the dye is cleaved to potentially carcinogenic aromatic amines. Sensitive and specific assays of the urine from treated animals by EC/GC revealed appreciable levels of 3,3'-dimethylbenzidine, mono- and di-acetyldimethylbenzidine, and alkaline hydrolyzable conjugates. Peak concentrations of the metabolites in urine occurred 12 to 24 hours after administration to rats, and within 12 hours in hamsters. The levels of all metabolites and conjugates diminished rapidly in both species after peak concentrations were reached, with no residues detected after 96 hours. The results conclusively demonstrated in vivo cleavage of the dye in both species, and it is proposed that the analytical methods employed can be used for chemical monitoring of human urine.