The Oxidative Stress of Mercaptan Odorant Due to Occupational Exposure: Adverse Effects on the Cholinergic System

Background: Tert-butyl mercaptan is one of the frequently used odorants derived from natural gases. It has been declared as a health hazard by the Occupational Safety and Health Administration (OSHA) in the USA. There is not much information available about the mercaptans long-term toxicity secondary to occupational exposure. This study was conducted to evaluate the oxidative stress caused by mercaptan odorant.  Methods: The inhalation exposure of 80 maintenance workers in a gas industry was evaluated, using NIOSH 2542 and samples analyzed by gas chromatography mass spectroscopy. Also, the administrative staff were selected as the unexposed workers with matching age and work experience compared to the exposed subjects. The lipid peroxidation and ferric reducing plasma ability (FRAP), was evaluated as oxidative stress biomarkers. The acetylcholinesterase activity was also assessed for the neurological risks. Results: The tert-butyl mercaptan exposure was evaluated at average 0.01 ppm (0.005 to 0.15 ppm). There was oxidative stress in maintenance workers along with a significant increase in the lipid peroxidation, and a decrease in FRAP level (P=0.0001). The acetyl cholinesterase activity was decreased in over half of the exposed subjects, and correlated significantly with the tert-butyl mercaptan level (r=-0.4, P=0.026). Conclusion: There was a correlation between the inhibition of acetyl cholinesterase activity and the induction of oxidative stress. Based on the findings, the chronic occupational exposure to tert-butyl mercaptan was identified as a health hazard. Therefore, specific health care strategies should be developed to minimize the toxic effect of this chemical.