Noise and Carbon Monoxide Increase Hearing Loss

June 2005

Editor: Researchers at the University of Montreal have discovered that the presence of carbon monoxide causes increased hearing loss to people exposed to loud noises. The following article from the Canadian Broadcasting Corporation (cbc.ca) is reproduced with their kind permission.

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Cocktail of noise and carbon monoxide increases hearing loss: study

MONTREAL - Garage mechanics, firefighters and truckers, listen up: a new study shows chronic exposure to noise plus carbon monoxide increases hearing loss.

The Université de Montréal study of 8,600 workers between 1983 and 1996 is the first to link carbon monoxide and hearing loss in humans. It is to be published in the Journal of the Acoustical Society of America by early next year.

Lead researcher Adriana Lacerda is to present the study on Wednesday in Vancouver at the society's annual meeting.

The results revealed that workers who were exposed to carbon monoxide and noise levels above 90 decibels - the sound of a chainsaw - had trouble hearing high frequencies (from three to six kilohertz). A larger shift was observed among workers with 25-29 years of noise exposure in the workplace.

These workers would not be able to hear birds singing or telephones ringing, study supervisor Tony Leroux told CBC News Online.

"They are not deaf but they have a larger hearing loss than we would expect if they were just exposed to noise," Leroux said.

The hearing loss took place over decades. Most workers did not show significant hearing loss until after 20 years in the work place.

The study suggested hearing loss was caused by lower levels of oxygen in the blood stream, which accelerates the deterioration of the sensory cells of the inner ear.

"The inner ear that contains the sensory cells needs a lot of oxygen to operate," Leroux said. "They are suffering from anoxia, a lack of oxygen."

Another theory is that both noise and carbon monoxide produce free radicals - atoms that attack the bonds of chemical reactions - which damage cells.

The U.S. National Institute of Occupational Safety and Health estimates that nearly one million workers are exposed to significant levels of carbon monoxide. Those at risk include welders, fork lift operators, foundry workers, industrial mechanics, diesel engine operators and miners.

Leroux said rock musicians in smoky bars would appear to be candidates for increased hearing loss, but were not studied because carbon monoxide is just one component of cigarette smoke.

Wearing earplugs is not enough to stop the damage, Leroux said. Alternative energy sources should be found for many of these workers who work with motors, he said.

And he said a growing pastime in Quebec, indoor go-cart racing, is ripe for hearing loss. Part of the solution could be powerful ventilation systems and mufflers. "But carts have to make noise to be fun," he noted.

Copyright (c) CBC 2005