We compared the ability of the urinary excretion of trans,trans-muconic acid (t,t-MA), s-phenilmercapturic acid (s-PMA) and urinary benzene (U-Benz) to detect low level occupational and environmental exposure to benzene.

Methods We monitored airborne benzene by personal air sampling, and U-Benz, s-PMA, t,t-MA and cotinine (U-Cotinine) in spot urine samples, collected at 8 am and 8 pm, in 32 oil refinery workers and 65 subjects, randomly selected among the general population of urban and suburban Cagliari, Italy.

Results The median concentration of airborne benzene was 25.2 µg/m³ in oil refinery workers, and 8.5 µg/m³ in the general population subgroup. U-Benz in morning and evening samples was significantly more elevated among oil refinery workers than the general population subgroup (p = 0.012, and p = 7.4 x 10^-7, respectively) and among current smokers compared to non-smokers (p = 5.2 x 10^-8, and p = 5.2 x 10^-5 respectively). Benzene biomarkers and their readings in the two sampling phases were well correlated to each other. The Spearman’s correlation coefficient with airborne benzene was significant for U-Benz in the evening sample, but not for t,t-MA and s-PMA in either sampling. Morning U-Cotinine excretion showed a good correlation with U-Benz in the morning and in the evening sampling (p < 0.001), and with s-PMA in the evening sample (p < 0.001), but not with t,t-MA in either samplings. t,t-MA in the evening sample was the only biomarker showing a moderate inverse correlation with BMI (p < 0.05). The multiple regression analysis adjusting by BMI and number of cigarettes smoked during the day confirmed the results of the univariate analysis.

Discussion Our results suggest that unmetabolised U-Benz would allow a more reliable biomonitoring of low-level exposure to benzene than s-PMA and t,t-MA.