Determination of specific mercapturic acids in human urine after experimental exposure to toluene or o-xylene

Volunteers were exposed to toluene and o-xylene for 4 h at 300 mg/m3 and 350 mg/m3, respectively, in an exposure chamber. Urine voided during and after the exposure was analysed for S-benzyl-N-acetylcysteine (toluene mercapturic acid) and S-(o-methylbenzyl)-N-acetylcysteine (o-xylene mercapturic acid). The amount of S-(o-methylbenzyl)-N-acetylcysteine found in urine after exposure corresponded to a metabolic yield of less than about 0.01% of the total uptake. No S-benzyl-N-acetylcysteine was found. Thus, determination of specific mercapturic acids after exposure to toluene or o-xylene can hardly be used for genotoxic monitoring.