This study was performed to estimate the exposure to benzene, one of the most serious health hazards, in four phases of a turnaround in a petrochemical company, and to evaluate the suitability of trans,trans-muconic acid (tt-MA) to act as a biomarker of exposure to low benzene levels.

tt-MA was determined in 152 urine samples collected in 4 phases (‘before daily work’, ‘after daily work’, ‘purge’, and ‘inspection’ of turnaround work) from 19 exposed workers involved in turnaround work and 19 clerical workers. The ambient benzene levels were monitored simultaneously during the ‘purge’ process of turnaround work in the exposed group.

The median urinary tt-MA for the 4 phases was 0.046 mg/L, 0.082 mg/L, 0.507 mg/L, and 0.468 mg/L in the exposed group and 0.050 mg/L, 0.065 mg/L, 0.269 mg/L, and 0.331 mg/L in the clerical workers, respectively. The median urinary tt-MA for the exposed group was significantly higher than that of the clerical workers during the purge process (P<0.05). In the exposed group, median urinary tt-MA for the ‘before daily work’ phase was significantly lower than that of the other three phases (P<0.05). Even in the clerical workers, the urinary tt-MA level for the ‘before daily work’ phase was significantly lower than that of the turnaround (P<0.05). There was a very significant correlation between urinary tt-MA levels and ambient benzene levels (r(s) = 0.795, P<0.01).

The turnaround process increased the benzene exposure for all workers, even the clerical workers, in a petrochemical company handling benzene. Urinary tt-MA was found to be suitable as a biomarker for the exposure to low-level benzene.