Montréal, May 16th, 2005 – Researchers have gathered evidence which shows that combined chronic exposure to noise and carbon monoxide in the workplace induces hearing loss. Adriana Lacerda, researcher at the École d'orthophonie et d'audiologie of the Université de Montréal, presents her findings at the annual meeting of the Acoustical Society of America in Vancouver on Wednesday. Those findings are the result of a study conducted with over 8,600 workers exposed to both noise and carbon monoxide in the workplace. Among the riskier professions are welders, firefighters, garage mechanics, truckers, forklift operators and miners.
The correlation between carbon monoxide exposure and hearing loss had been established in previous animal studies but never in humans. Based on data gathered by the National Institute of Occupational Safety and Health, Lacerda compared the hearing of workers exposed to noise levels lower than 90 decibels for 8 hours to another group of workers exposed to noise levels above 90 decibels. In both groups, a sample of workers was also exposed to carbon monoxide.

The results revealed that the workers who were exposed to carbon monoxide and to noise levels above 90 decibels displayed significantly poorer hearing thresholds at high frequencies (from 3 to 6 kiloHertz). A larger shift was observed among workers with 25-29 years of noise exposure in the workplace.

"Based on these results, we recommend that such risks as chronic exposure to carbon monoxide be considered when assessing the risk of developing a noise-induced hearing loss," said Lacerda. One of several hypotheses to explain this phenomenon is that the reduction of oxygen in the blood stream accelerates the deterioration of the sensory cells of the inner ear.