Influence of non-occupational sources on the levels of biomarkers of internal dose for use in biological monitoring of occupational exposure to extremely low concentrations of benzene

To study how traditional (t,t-muconic acid--t,t-MA and S-phenylmercapturic--SPMA) and new (urinary benzene) urinary biomarkers of internal dose can contribute to exclude an occupational source of exposure to extremely low concentrations of benzene, also analyzing the influence that non-occupational sources of exposure, such as cigarette smoking and urban pollution, can have on the levels of these biomarkers.Assessment was made of 6 workers employed at a groundwater purification plant polluted by benzene (exposed) and 6 administrative clerks employed at the same plant (controls); both groups included smokers and non-smokers. Environmental monitoring (fixed and personal samplings lasting 8 hours) and biological monitoring (determinations of t,t-MA, SPMA, urinary benzene, and urinary creatinine so as to apply suitable adjustments) were performed in exposed workers on 10 successive days, including also rest days (background exposure), and in controls only once.Airborne benzene always resulted lower than the limit of detection of the analytical method in both fixed and personal samplings done on exposed workers and controls during working days, while personal samplings done on exposed workers during rest days showed benzene concentrations even higher than 5 microg/m3, that is the limit value for ambient air quality. Concentrations of t,t-MA, SPMA and urinary benzene did not show differences between exposed workers, regardless of whether they were studied on working or rest days, and controls and appeared to be largely within the reference value range for the Italian population. All biomarkers of internal dose examined in the study showed significantly higher values in smokers than non-smokers. In the latter, SPMA was always below the limit of detection, while urinary benzene resulted higher than the limit of detection in 60.0\% and 87.5\% of the determinations done on working and on rest days, respectively.In situations of occupational exposure to extremely low doses of benzene or of absence of exposure, the application of an integrated environmental--biological monitoring approach, involving the determination of SPMA and/or urinary benzene, together with a careful evaluation of those factors determining non-occupational exposure to the toxicant, seems indispensable in order to be able to exclude the presence of occupational exposure. In these particular situations of occupational exposure to benzene, the interpretation of the results of environmental and biological monitoring should not only consider the TLV or BEI, but also the limit value for ambient air quality and the reference value for the general population, since benzene is able to determine genotoxic carcinogenic effects even at exposure to extremely low concentrations of the toxicant.