Low-dose benzene exposure monitoring of oil refinery workers: inhalation and biomarkers

Airborne benzene in workplaces has progressively decreased due to preventive actions and the redesigning of facility processes. Professionals who assess occupational exposure should select techniques to detect benzene levels comparable to ambient air exposure. Thus, sensitive biomarkers are needed to discriminate the effects of confounding factors, such as smoking or sorbic acid (SA). In order to identify sensitive biomarkers and to study their correlation with confounding factors, 23 oil refinery workers were enrolled in the study; their airborne benzene exposures and biomarkers were monitored. Urinary benzene (U-B), t,t-muconic acid (t,t-MA), and S-phenylmercapturic acid (SPMA) were quantified. Urinary cotinine (U-C) and t,t-sorbic acid (t,t-SA) were evaluated to flag smoking and SA intake, respectively. The benzene measured in personal inhalation sampling ranged from 0.6 to 83.5 (median 1.7) µg/m3. The concentration range of the biomarkers, U-B, t,t-MA, and SPMA, were 18–4893 ng/m3, <10–79.4 µg/g creatinine, and <0.5–3.96 µg/g creatinine, respectively. Pearson tests were carried out; the best correlations were between airborne benzene and U-B (µg/L r = 0.820, p < 0.001) and between benzene and SPMA (g/L r = 0.812, p < 0.001), followed by benzene and t,t-MA (mg/L r = 0.465, p = 0.039). From our study, U-B and SPMA result to be the most reliable biomarkers to assess the internal number of low doses of benzene exposure, thanks to their specificity and sensitivity.