Urinary benzylmercapturic acid as a marker of occupational exposure to toluene

Objective: To examine if benzylmercapturic acid (or N-acetyl-S-benzyl cysteine) in urine can be used as a marker of occupational exposure to toluene. Methods: A factory survey was conducted in the latter half of a working week. A group of 46 men, who volunteered for the study, was engaged in ink preparation, surface coating or printing work. Diffusive samplers were used to measure average solvent exposure in an 8-h shift. End-of-shift urine samples were analyzed for benzylmercapturic acid (BMA) by a modification of an HPLC method originally developed for phenylmercapturic acid determination. Results: The workers were exposed primarily to toluene [TOL; 13 ppm as the geometric mean (GM) and 86 ppm at the maximum] together with isopropyl alcohol (< 1 and 4 ppm), ethyl acetate (2 and 127 ppm) and methyl ethyl ketone (2 and 142 ppm). BMA in urine correlated closely [correlation coefficient (r) = 0.7] with TOL in air, irrespective of correction for urine density. The lowest TOL concentration at which urinary BMA increased to a measurable level was approximately 10 ppm, and urinary BMA could separate the exposed from the non-exposed when TOL exposure was 15 ppm or higher. Conclusions: BMA in end-of-shift urine samples is a good marker of occupational TOL exposure. Urinalysis for BMA is sensitive enough to detect TOL exposure at 15 ppm, and therefore BMA appears to be more sensitive than hippuric acid and possibly o-cresol as a urinary marker of TOL exposure.