Increase in Oxidative Stress Levels Following Welding Fume Inhalation: A Controlled Human Exposure Study

Background: Tungsten inert gas (TIG) welding represents one of the most widely used metal joining processes in industry. It has been shown to generate a large majority of particles at the nanoscale and to have low mass emission rates when compared to other types of welding. Despite evidence that TIG fume particles may produce reactive oxygen species (ROS), limited data is available for the time course changes of particle-associated oxidative stress in exposed TIG welders.

Methods: Twenty non-smoking male welding apprentices were exposed to TIG welding fumes for 60 minutes under controlled, well-ventilated settings. Exhaled breathe condensate (EBC), blood and urine were collected before exposure, immediately after exposure, 1hr and 3hrs post exposure. Volunteers participated in a control day to account for oxidative stress fluctuations due to circadian rhythm. Biological liquids were assessed for total reducing capacity, hydrogen peroxide (H2O2), malondialdehyde (MDA), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) concentrations at each time point. A linear mixed model was used to assess within day and between day differences.

Results: Significant increases in the measured biomarkers were found at 3hrs post exposure. At 3hrs post exposure, we found a 24% increase in plasma-H2O2 concentrations ([95%CI: 4% to 46%], p= 0.01); a 91% increase in urinary-H2O2 ([2% to 258%], p= 0.04); a 14% increase in plasma-8-OHdG ([0% to 31%], p= 0.049); and a 45% increase in urinary-8-OHdG ([ 3% to 105%], p= 0.03). Doubling particle number concentration (PNC) exposure was associated with a 22% increase of plasma-8-OHdG at 3hrs post exposure (p=0.01).

Conclusion : A 60-minute exposure to TIG welding fume in a controlled, well-ventilated setting induced acute oxidative stress at 3hrs post exposure in healthy, non-smoking apprentice welders not chronically exposed to welding fumes. As mass concentration of TIG fume particles is very low, it is recommended that additional exposure metrics such as PNC are considered for occupational risk assessments of TIG workplaces. Our findings highlight the importance of increasing awareness of TIG welding fume toxicity, especially given the realities of welding workplaces that may lack ventilation; and beliefs among interviewed welders that TIG represents a cleaner and safer welding process.