Low air levels of benzene: Correlation between biomarkers of exposure and genotoxic effects

Abstract This study was aimed to identify useful biomarkers of exposure and effect in workers exposed to low levels of benzene, and to evaluate any correlations existing between these parameters. Benzene exposure was measured in 33 petrochemical industry operators (PIO), 28 service station attendants (SSA), 21 gasoline pump maintenance workers (GPMW) and 51 non-exposed controls by GC-FID analysis. Samples were collected with personal passive samplers (Radiello). End-shift urine samples were collected for t,t-muconic acid (t,t-MA) determination by HPLC and for S-phenylmercapturic acid (S-PMA) measurement by HPLC-MS/MS. The alkaline version of the comet assay and, in a subgroup of 19 SSA and 16 control subjects, chromosomal aberrations (CA) and glutathione (GSH) levels were measured in peripheral blood lymphocytes. Personal benzene exposure was significantly higher in PIO, SSA and GPMW as compared to controls. The urinary excretion of the two metabolites showed a significant increase in SSA (p=0.0258 and p=0.0001, for t,t-MA and S-PMA, respectively) and in PIO (p=0.0013 and p=0.0001, for t,t-MA and S-PMA, respectively) as compared with the control group, while no such increase was observed for GPMW, for whom occupational exposure was not continuous and occurred on specific working days only. Significant increases of DNA damage were found by the comet assay for tail moment (TM) and tail length (TL) in SSA (p<0.0001 and p=0.008, for TM and TL, respectively) and PIO (p<0.0001 and p<0.0001, for TM and TL, respectively) when compared with controls. The PIO group also displayed a significant increase in the number of cells with comet (p<0.0001). Smoking habits did not appear to interfere with these results in any of the groups. No difference was found in percentage of CA between exposed workers and controls. Significant correlations were found, in all groups, between benzene exposure and the more representative comet parameter TM (r=0.509, p=0.007; r=0.525, p=0.017 and r=0.420, p=0.046 in SSA, GPMW, and PIO, respectively). A trend of negative correlation was observed between DNA damage and either GSH or urine S-PMA for exposed workers. In summary, in present study urinary S-PMA and DNA damage by the comet assay were both sensitive to exposure to low levels of benzene, and GSH seems to play an important defence role against benzene-dependent DNA damage.