02 Dec 2022
30 Nov 2022
Petroleum refineries are major emitters of volatile organic compounds mainly benzene, toluene, ethyl benzene, and xylene (BTEX). Long term exposure to BTEX carries the risk of oxidative stress, through the production of ROS that may consume antioxidants including antioxidant enzymes and their cofactors like antioxidant trace metals. This study aimed to assess oxidative stress in petroleum workers exposed to BTEX. A cross sectional comparative approach was adopted. Forty workers exposed to BTEX together with an equal number of nonexposed workers were enrolled in this study after fulfilling inclusion and exclusion criteria and giving an informed written consent. Sociodemographic, occupational and medical data were collected from all workers, then BTEX exposure urinary biomarkers (S-phenyl mercapturic acid, hippuric acid, mandelic acid, methyl hippuric acid) and serum concentrations of antioxidant trace metals (Cu, Mn, Se, Zn, Fe) were measured, Activity of superoxide dismutase (SOD) and Glutathione peroxidase (GSH-Px) enzymes as biomarkers for oxidative stress were assessed. There was a significant increase in the median level of mandelic acid, hippuric acid, and S-phenyl mercapturic acid in BTEX exposed workers (219.72 mg/L, 129.20 mg/L and 43.33µg/L respectively) compared with unexposed workers (98.20 mg/L, 55.92 mg/L, and 27.95 µg/L respectively); p<0.001. No significant difference was detected between both groups on comparing levels of phenyl glyoxylic acid, and total methyl hippuric acid. Level of serum Cu, Se and Zn were significantly lower among BTEX exposed workers [74 ug/dL, 58.8 ng/ml and 69.43 ug/L respectively) compared with unexposed workers (98.0 ug/dL, and 96.3 ug/L, 107.70 ug/L respectively); (p<0.001). On the contrary, the mean level of serum Fe was significantly higher among BTEX exposed workers (100.13 ± 32.89 ug/dL) than in unexposed workers (86.76 ± 18.28 ug/dL), (p=0.028). Activity of serum SOD and GSH-Px enzymes were significantly lower among BTEX exposed workers 492.0 (520.0) U/ml; and 0.0 (127.0) mU/ml respectively] compared with unexposed workers (736.5 (793.2) U/ml; and 224.50 (41.0) mU/ml respectively); p<0.001. A significant direct correlation was found between level of mandelic acid in BTEX exposed workers and job duration (r=0.321, p=0.044). Levels of BTEX exposure biomarkers were inversely correlated with most antioxidant trace elements and oxidative stress biomarkers. Study results suggest that long term exposure to BTEX is linked to oxidative stress.