[Significance of urinary concentrations of S-benzyl-N-acetylcysteine (S-BMA) in subjects exposed to toluene].

Toluene is a widely diffuse solvent for oils, resins, rubber and paints, either alone or as a major component in a mixture; in the industrial environment it is currently present at concentrations of ppm. Toluene can be absorbed via the lungs or via the skin. The absorption of toluene via inhalation is related to the exposure level as well as the activities level of workers. Once absorbed into the body, toluene is metabolized in man to benzoic acid, followed by hepatic cytochrome P450 catalyzed glycine conjugation to form hippuric acid. Relatively small amounts appear in urine as o-cresol and p-cresol where they occur as glucoronide and sulfate derivate. Only a minor fraction of inhaled solvent is conjugated with glutathione with the production of S-benzyl-N-acetylcysteine (S-BMA). Several biological indicators have been proposed for evaluating toluene exposure in the workplace. These include urinary hippuric acid, toluene in blood, toluene in breath, o-cresol in urine and toluene in urine. We examined a group of 18 workers occupationally exposed to toluene, determining the concentrations of toluene in ambient air and S-BMA in urine. All urine samples were collected at the end of work shift. The renal excretion of S-BMA showed highly significant correlations with environmental data and with the other established parameters of biological monitoring of toluene. The median ambient air concentration was 15.7 ppm ranging from 2.9 to 70.3 ppm, the median concentration of S-BMA was 16.0 micrograms/g creatinine. S-BMA was detectable in urine samples of a control group of 87 subjects non occupationally exposed to toluene. Most of unexposed subjects showed S-BMA values lower than 10 micrograms/g creatinine both in smokers and in nonsmokers and no significant difference was found in samples (20) collected at three intervals during one day. Our finding further indicates that the metabolite S-BMA could be a marker of occupational toluene exposure.