Urinary excretion of unmetabolized benzene as an indicator of benzene exposure

Abstract

Benzene concentrations in urine samples (C_u, ng/L) from 110 workers exposed to benzene in chemical plants and gasoline pumps were determined by injecting urine supernate into a gas chromatograph. The urine was saturated with anhydrous N₂SO₄ to facilitate the passage of benzene in the air over the urine. The solvent was stripped from the urine surface and concentrated on an adsorbent substrate (Carbotrap tube) by means of a suction pump (flow rate 150 ml/m). Wash‐up of the head space was achieved by simultaneous intake of filtered air through charcoal. Benzene was thermi‐cally desorbed and injected in a column (thermal tube desorber, Supelco; 370°C thermal flash; borosilicate capillary glass column SPB‐1, 60 m length, 0.75 mm ID, 1 pm film thickness; GC Dani 8580‐FID). Benzene concentrations in the urine from 40 non‐exposed subjects (20 smokers > 20 cigarettes/d and 20 nonsmokers) were also determined [median value of 790 ng/L (10.17 nmol/L) and 131 ng/L (1.70 nmol/L), respectively]. The 8‐h time‐weighted exposure intensity (C_l, ng/m³) of individual workers was monitored by means of charcoal tubes. The median value for exposure to benzene was 736 ng/m³ (9.42 μmol/m³) [geometric standard deviation (CSD) ‐ 2.99; range 64 μg/m³ (0.82 μmol/m³) to 13,387 μg/m³) (171.30 μmol/m³)]. The following linear correlation was found between benzene concentrations in urine (C_u, ng/L) and benzene concentrations in the breathing zone (C_l, μg/m³):

log(C_u) = 0.645 × log(C_l) + 1.399 r ‐ .559, n = 110, p < .0007

With exclusion of workers who smoked from the study, the correlation between air benzene concentration and benzene measured in urine was:

log(C_u) = 0.872 × log(C_l) + 0.6 r = .763, n = 63, p < .0007

The study results indicate that the urinary level of benzene is an indicator of occupational exposure to benzene.