Integrated exposure assessment of sewage workers to genotoxicants: an urinary biomarker approach and oxidative stress evaluation

Abstract

Background: Sewage workers are exposed to multiple chemicals among which many are suspected genotoxicants. Therefore, they might incur DNA damage and oxidative stress. We aimed to explore integrated urinary biomarkers, assessing the overall urine genotoxicity by in vitro comet and micronucleus assays and measuring urinary 8-oxo-2'-deoxyguanosine.

Methods: During three consecutive working days, polycyclic aromatic hydrocarbons and volatile organic compounds were sampled in workplace air of 34 sewage and 30 office workers, as indicators of airborne exposure. The last day, subjects collected their 24 hours urine. Genotoxicity of urinary extracts was assessed by comet and micronucleus assays on a HepG2 cell line. Using competitive enzymatic immunoassay we evaluated the 24 hours urinary 8-oxo-2'-deoxyguanosine excretion. Benzo(a)pyrene toxicity equivalent factors and inhalation unit risk for Benzo(a)pyrene and benzene were used to give an estimate of cancer risk levels.

Results: Workplace air concentrations of polycyclic aromatic hydrocarbons (e.g. 23.7 [range 2.4-104.6] ng.m-3 for fluoranthene) and volatile organic compounds (e.g. 19.1 ± 2.9 [standard error] μ.m-3 for benzene) were elevated in sewage compared to office workplaces (P < 0.01) and corresponded to an increased lifetime cancer risk. The urinary extracts of sewage workers showed higher genotoxicity (P < 0.001) than office workers.

Conclusions: The integrated and non-specific urinary biomarkers of exposure showed that sewage workers experience exposure to mixtures of genotoxicants in the workplace.

Figure 1

Volatile organic compounds (VOCs) concentration patterns in the workplaces air and from the nearest outdoor monitoring stations. Statistically significant higher means concentrations (P < 0.01) among sewage workers compared to all other groups for all substances. Comparison of workplace and ambient air concentrations is incomplete because some VOCs measured in the workplaces are not measured by traffic or background urban monitors (undecane, trichloroethylene, tetrachloroethylene, styrene, decane and 1,4-dichlorobenzene).

Figure 2

Effects of 24 h exposure to urine organic extract evaluated by comet and micronucleus assay performed on HepG2 cells. A) The bars are related to the means ± SD values of percent DNA tail obtained by comet assay. B) The bars are related to means ± SD values of MNi/1000 BNed obtained by Micronucleus assay. For comet assay, nine experiments were performed. For micronucleus assay, five experiments were performed. For both assays and in each experiment, B(a)P 40 μM and DMSO 1% final concentrations were the positive and negative controls; respectively. *Statistically significant (P < 0.001) compared to office workers. BNed, Binucleated cells MNi, micronuclei.

Figure 3

Box and whisker plot for the 24 hours urinary 8-oxodG level (pmole/kg 24 hours) in sewage and office workers, P = 0.28 for the mean differences. * Mean 8-oxodG, 8-oxo-2'-deoxyguanosine.