Presence in human urine of a new N-nitroso compound, N-nitrosothiazolidine 4-carboxylic acid

Urine samples collected in several countries from human subjects showed the presence of a number of N-nitroso compounds not previously identified. By several separative procedures and by comparison with authentic material, the major unknown N-nitroso compound was shown to be N-nitrosothiazolidine 4-carboxylic acid (NTCA). Although its origin in human urine is unknown, thiazolidine 4-carboxylic acid, the easily nitrosatable amine precursor, can be formed by reaction of formaldehyde with cysteine in vivo and in vitro. Thus measuring NTCA excreted in the urine may allow monitoring exposure of human subjects to precursors like formaldehyde and NO₃^- NO₂^-.