URINARY-EXCRETION OF DIMETHYLHIPPURIC ACIDS IN HUMANS AFTER EXPOSURE TO TRIMETHYLBENZENES

The aim of this study was to determine the urinary excretion of dimeth ylhippuric acids (DMHAs) in humans after experimental chamber exposure to trimethylbenzene (TMB) vapor. The DMHAs have been put forward as s uitable biomarkers of exposure to products containing TMBs such as whi te spirit and petrol. Ten healthy male volunteers were exposed to TMB vapor in an exposure chamber for 2 h at a work load of 50 W. The subje cts were exposed on four occasions, to 25 ppm of 1,2,4-TMB, 1,2,3-TMB, and 1,3,5-TMB, respectively, and to 2 ppm of 1,2,4-TMB. Urine was col lected from the onset of exposure until the following morning. All six possible DMHA isomers were analyzed by high-performance liquid chroma tography. About 22% of the inhaled amount of 1,2,4-TMB was excreted as DMHAs within 24 h, mainly as 3,4-DMHA. The 24-h recovery of 1,2,3-TMB as DMHAs was 11%. Only 3% of the absorbed amount of 1,3,5-TMB was exc reted as 3,5-DMHA. The half-times of the different DMHA isomers ranged from 4 to 16 h. In addition to analysis of DMHAs, the excretion of un conjugated dimethylbenzoic acids in urine was estimated to account for approximately 3% of the dose of all TMBs. In conclusion, the urinary excretion of DMHA isomers may serve as a good indicator of TMR exposur e. In this controlled short-term-exposure study the sum of excretion r ate of several DMHA isomers reflected exposure more closely than did t he excretion rate of any single DMHA.