# Low-Dose Benzene Exposure Monitoring of Oil Refinery Workers: Inhalation and Biomarkers
## 3 Results and Discussion
This approach could be less representative that the one used in clinical practice, where 24 h of total urine collections are routine, and thus the measurement of creatinine is often used to adjust analyte concentrations for the effects of fluid balance. In the occupational settings, the ACGIH proposed acceptability criteria (range: 0.5-2.3 g/L) for urinary creatinine [32]. We found that all the urine samples were compliant with the ACGIH range. Three urine samples resulted in >10 ng/mL of U-C, probably due to passive smoking not reported in the questionnaire; thus, these subjects were not included in the study. The _t,t_-SA results ranged from <8.1 to 154 ug/L in the urine samples. Concerning the correlation between airborne benzene values and the biomarker concentrations, the combined results of personal air and biological monitoring are shown in Table 4. We can observe that when airborne benzene concentrations increase, higher values of U-B and SPMA were found in the biological samples (e.g., samples 7 and 16). This correlation was not so clear for _t,t_-MA; although some urine samples contained high values of this metabolite, the respective personal airborne monitoring showed low benzene concentration (e.g., samples 9 and 11). It is noticeable that high concentrations of toluene may lead to misjudging SPMA evaluation (e.g., samples 3 and 20), in line with the literature [33]. Inhalation exposure to benzene is generally low. It should be noted that operators involved in the study did not necessarily correspond to the ones performing tasks with higher benzene exposures, but the aim was to enroll exposed workers that likely were subject to a smaller number of confounding factors. In addition, we considered the contribution of the dermal route, whose potential influence had been indicated in a previous study [34]. However, none of the analyzed gloves showed traces of internal contamination that would have led to skin exposure. This finding is in line with the results of [PERSON] et al. [35]; in a similar study, they tested a charcoal pad sampler in a petrochemical setting, observing very low benzene concentration and estimating the contribution of the dermal route to internal benzene exposure as less than 0.06%. Therefore, only airborne benzene levels and biomarker concentrations in urine were compared. Our results show a considerable correlation between airborne benzene with U-B and SPMA (Pearson test = 0.820, \(p<\) 0.001 and 0.812, \(p<\) 0.001, respectively) (Table 5). Furthermore, U-B and SPMA have a better correlation than U-B and \(t\),\(t\)-MA (Pearson test = 0.795, \(p<\) 0.001 and 0.440, \(p=\) 0.052 respectively). In fact, most of the workers had been exposed to airborne benzene concentrations of less than 0.1 ppm, yet their _t,t_-MA level ranged from <10 ug/g creatinine to 79.4 ug/g creatinine. Moreover, workers with the highest amounts of _t,t_-MA did not correspond to those with the highest inhalation exposure. The weak correlation observed between _t,t_-MA and airborne benzene or the other metabolites analyzed might be due to the interference of dietary SA intake [36; 37]; therefore, only workers that declared no assumption of SA on the questionnaires were enlisted in this study. Nowadays, preservative additives are widely used in the food industry that they significantly affect urinary _t,t_-MA. Even if _t,t_-MA is a good biomarker for occupational exposure to airborne benzene in high concentration scenarios, it fails in low-dose exposure contexts due to its lack of specificity, e.g., for smoke and inter-individual metabolic variability [38]. Since preventative actions have generally lessened benzene exposure in the workplace, more sensitive biomarker exposures are now required. Hence, the growing interest in SPMA and U-B, which present high correlation rates with airborne benzene, is due to their specificity and not having interferences, such as SA for _t,t_-MA.