Urinary phenylmercapturic acid as a marker of occupational exposure to benzene

A hand-saving HPLC method to measure urinary phenylmercapturic acid (PMA) was developed which allows about 35 PMA determinations per day. The method involves conversion of pre-PMA to PMA by the addition of sulfuric acid to a urine sample, extraction into an ether-methanol mixture followed by condensation under a nitrogen stream. The condensate was introduced to a ODS-3 column in a HPLC system, and PMA in the column was eluted into a mobile phase of acetonitrile: methanol: perchloric acid: water. The elution of PMA was monitored at 205 nm. One determination will be completed in 40 min. The method was applied to analysis of end-of-shift urine samples from 152 workers exposed up to 210 ppm benzene, 66 workers exposed to a mixture of benzene (up to 116 ppm) and toluene + xylenes (up to 118 ppm), and 131 non-exposed controls of both sexes. A linear regression was established between time-weighted average intensity of exposure to benzene and urinary PMA. From the regression, it was calculated that urinary PMA level will be about 6.4 mg/l after 8-hour exposure to benzene at 100 ppm, and that PMA in urine accounted for about 0.1% of benzene absorbed. No effects of sex, age, and smoking habit of individuals were detected, and the effect of co-exposure to toluene + xylenes at the levels comparable to that of benzene was essentially nil, which indicates an advantage of PMA as a benzene exposure marker over monoto tri-phenolic metabolites or t,t-muconic acid.