Benzene is a recognized carcinogen. With the development of production technology and the improvement of labor protection facilities, the concentrations of benzene in the air of many workplaces have been far lower than the national occupational exposure limit. However, a large number of studies have found that low-concentration benzene still has an impact on the health of occupational populations.

This study is conducted to characterize the distributions of S-phenylmercapturic acid (S-PMA) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) in urine of workers exposed to lowconcentration benzene.

A cross-sectional survey was carried out to enroll 206 employees who took part in occupational health examination from a benzene-related automobile factory in Yangzhou from 2018 to 2019, including 120 workers in the automobile painting workstation as the exposure group and 86 office workers as the control group. The occupational exposure data, health examination data, and peripheral blood and urine samples were collected from the subjects. The blood samples were examined for routine blood test indicators. The urine samples were examined for the level of S-PMA by high-resolution quadrupole coupled with time-of-flight mass spectrometer, and the S-PMA level corrected by urine creatinine was taken as an internal exposure index. The contents of lipid peroxide malondialdehyde (MDA) in serum and 8-OHdG in urine were detected by colorimetry as indices of oxidative damage of lipid and DNA. After adjusting for sex, age, body mass index, smoking, and drinking, the effects of benzene exposure on peripheral blood and oxidative damage in workers and the correlations of S-PMA with 8-OHdG were analyzed. Multiple linear stepwise regression analysis was conducted with 8-OHdG as a dependent variable and S-PMA and possible influencing factors of 8-OHdG as independent variables.

Benzene release mainly occurred in the processes of paint mixing and painting in the automobile factory. Although the benzene concentration of each benzene exposure workstation did not exceed the national occupational exposure limit, the medians of urinary S-PMA, serum MDA, urinary 8-OHdG, and the abnormal rate of red blood cells of workers in the exposure group were 12.21μg·g^-1 (in terms of Cr, thereafter), 11.19μmol·L^-1, 169.18ng·g^-1, and 10.0%, respectively, higher than those in the control group (4.80 μg·g^-1, 9.08μmol·L^-1, 91.43 ng·g^-1, and 2.3%, respectively) (P < 0.001 or P < 0.05). After adjusting for smoking-related factors, the levels of S-PMA and 8-OHdG in the exposure group were higher than those in the control group for both smoking and non-smoking subjects (P < 0.05); only for the non-smoking participants, the MDA level in the exposure group was higher than that in the control group (P < 0.05); there was no significant difference in the abnormal rate of blood routine indicators between smokers and non-smokers. The results of Spearman correlation analysis showed that 8-OHdG was positively correlated with S-PMA (r=0.488, P < 0.05). The results of multiple regression analysis showed that the level of S-PMA in urine was positively correlated with the level of 8-OHdG in urineb (95% CI)=9.942 (9.337-10.547), P < 0.001.

Under occupational low-concentration benzene exposure, the level of S-PMA in urine of workers is still increased, there is a positive correlation between S-PMA (a benzene exposure marker) and 8-OHdG (a DNA injury marker), and oxidative damage is increased, indicating a relatively high health risk.