EVALUATION OF BIOMARKERS FOR OCCUPATIONAL EXPOSURE TO BENZENE

Objective-To evaluate the relations between environmental benzene conc entrations and various biomarkers of exposure to benzene. Methods-Anal yses were carried out on environmental air, unmetabolised benzene in u rine, trans, trans-muconic acid (ttMA), and three major phenolic metab olites of benzene; catechol, hydroquinone, and phenol, in two field st udies on 64 workers exposed to benzene concentrations from 0.12 to 68 ppm, the time weighted average (TWA). Forty nonexposed subjects were a lso investigated. Results-Among the five urinary biomarkers studied, t tMA correlated best with environmental benzene concentration (correlat ion coefficient, r = 0.87). When urinary phenolic metabolites were com pared with environmental benzene, hydroquinone correlated best with be nzene in air. No correlation was found between unmetabolised benzene i n urine and environmental benzene concentrations. The correlation coef ficients for environmental benzene and end of shift catechol, hydroqui none, and phenol were 0.30, 0.70, and 0.66, respectively. Detailed ana lysis, however, suggests that urinary phenol was not a specific biomar ker for exposure below 5 ppm. In contrast, ttMA and hydroquinone seeme d to be specific and sensitive even at concentrations of below 1 ppm. Although unmetabolised benzene in urine showed good correlation with a tmospheric benzene (r = 0.50, P < 0.05), data were insufficient to sug gest that it is a useful biomarker for exposure to low concentrations of benzene. The results from the present study also showed that both t tMA and hydroquinone were able to differentiate the background level f ound in subjects not occupationally exposed and those exposed to less than 1 ppm of benzene. This suggests that these two biomarkers are use ful indices for monitoring low concentrations of benzene, Furthermore, these two metabolites are known to be involved in bone marrow leukaem ogenesis, their applications in biological monitoring could thus be im portant in risk assessment. Conclusions-The good correlations between ttMA, hydroquinone, and atmospheric benzene, even at concentrations of less than 1 ppm, suggest that they are sensitive and specific biomark ers for benzene exposure.