Mediating effect of oxidative stress on blood pressure elevation in workers exposed to low concentrations of benzene, toluene, and xylene (BTX).

To investigate the mediating effect of oxidative stress on the relationships between low-concentration benzene, toluene, and xylene (BTX) exposure and blood pressure in workers. A cross-sectional study involving 841 workers from a petroleum refining enterprise in Hainan, China, was conducted. Among the workers, 615 workers were exposed to low-concentration BTX, and 216 workers were in the control group. S-phenylmercapturic acid (S-PMA), hippuric acid (HA), and methyl hippuric acid (MHA, including the three isomers 2-MHA, 3-MHA, and 4-MHA) were measured in the urine of workers via high-performance liquid chromatography‒tandem triple quadrupole mass spectrometry to assess the internal BTX burden. Oxidative stress markers, blood pressure, and their correlations were analysed in both the exposed and control groups of workers. Mediation analysis was used to investigate the potential role of oxidative stress in the relationship between BTX exposure and blood pressure. The concentrations of BTX at the sampling points in the enterprise were all below the limits stipulated in China's national occupational health criteria: occupational exposure limits for hazardous agents. With respect to the internal burden of BTX, the concentrations of the benzene metabolite S-PMA, the toluene metabolite HA, and the xylene metabolites 3-MHA and 4-MHA in the urine samples in the exposure group were greater than those in the control group (P < 0.05). The correlation analysis results revealed that the concentration of the benzene metabolite S-PMA in workers' urine was positively correlated with diastolic blood pressure (DBP) (r = 0.265, P < 0.05). Compared with those in the control group, DBP was greater (β = 1.363, 95% CI 0.088 -2.639), serum superoxide dismutase (SOD) activity was lower (β = - 0.037, 95% CI - 0.060 to - 0.013), and the serum malondialdehyde (MDA) concentration was greater (β = 0.066, 95% CI 0.022-0.110) in the exposure group. Partial correlation analysis revealed a positive correlation between DBP and MDA (r = 0.115, P < 0.01). The results of the mediation analysis indicated that MDA was a complete mediator between low BTX exposure and DBP (P < 0.05). Occupational exposure to low concentrations of BTX elevates blood pressure and oxidative stress among workers. A positive correlation between DBP and MDA was observed, with MDA acting as a complete mediator between low-concentration BTX exposure and DBP elevation.