Influencing factors of urinary 8-OHdG concentration in male workers exposed to low levels of benzene

Background Occupational health hazards of low-concentration benzene exposure have become a research focus as the benzene concentration in the workplace has been under control in various countries. DNA oxidative damage is considered to be the basis of benzene-induced cytotoxicity of bone marrow cells, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) is recognized as an indicator for evaluating oxidative damage of DNA, as well as an early effect indicator of benzene exposure. There needs more research to describe the concentration changes of 8-OHdG and relevant influencing factors in workers change under low-level benzene exposure.

Objective The current study investigates the influencing factors of urinary 8-OHdG concentration in male workers exposed to low levels of benzene, and analyze the relationship between urinary 8-OHdG concentration and cumulative exposure level of benzene based on the US Environmental Protection Agency (EPA) model of noncarcinogenic inhalation risk assessment.

Methods In four enterprises, 200 male exposure workers serving at 11 benzene exposed positions and 200 male control workers serving at administrative and logistic positions who underwent physical examinations during the same period were investigated through a cross-sectional study in July to August 2018. An occupational health field survey was carried out to detect the concentration of benzene exposure in workplace. A questionnaire survey was conducted to collected the general information of the study subjects, and their morning urine samples and blood samples were collected in health examination. US EPA noncarcinogenic inhalation risk assessment model was applied to obtained the cumulative benzene exposure concentration (EC) of workers. Urinary 8-OHdG concentrations were detected using high-performance liquid chromatography-tandem mass spectrometer (HPLC-MS-MS). Non-parametric test was used to compare the median concentration of 8-OHdG between two groups, and multiple logistic regression model was used to analyze the influencing factors of 8-OHdG concentration.

Results The concentration of 8 h time weighted average (C_TWA) of benzene of the benzene exposure workers was under current national occupational exposure limit. The cumulative benzene EC, based on the EPA noncarcinogenic inhalation risk assessment model, of the workers at different positions were 1.43-82.19 μg·m^-3. The two groups were comparable in age, body mass index, and alcohol consumption, except that the control group smoked more cigarettes than the exposure group (P=0.007). No differences were found between the two groups in the abnormal rates of white blood cells, neutrophils, and haemogloin. The median (P₂₅, P₇₅) concentration of urinary 8-OHdG in the exposure group7.29 (4.65, 11.82) μg·g^-1, in per gram of creatinine, thereafter was higher than that in the control group5.50 (3.80, 8.13) μg·g^-1 (P=0.016). The concentration of urinary 8-OHdG significantly increased when the concentration of cumulative benzene exposure was higher in the workers with cumulative benzene EC ≥ 10 μg·m^-3 versus those < 1.0 μg·m^-3 (OR=1.85, 95% CI:1.18-2.91), higher in the workers aged 45 years and above versus those aged below 35 years (OR=2.13, 95% CI:1.12-4.07), and higher in the workers with frequent hair dying (at least once a year) versus those without (OR=4.07, 95% CI:1.03-16.05).

Conclusion The increase of urinary 8-OHdG concentration in workers exposed to low concentrations of benzene occurs before the change of blood routine examination indicators. A cumulative benzene EC > 10μg·m^-3 would increase urinary 8-OHdG concentration.