Carbon monoxide, noise tied to hearing loss

A new study says people who are exposed to consistently high levels of noise and carbon monoxide could suffer a hearing loss up to 50 per cent worse than if they were exposed to just the noise alone.

And that, say the researchers who conducted the study, should be of real concern to garage mechanics, welders, construction workers, servers in noisy, smoky bars and teenagers who listen to iPods while riding the bus.

Tony Leroux and Adriana Lacerda, both audiologists at the University of Montreal, will present their findings today to the annual meeting of the Acoustical Society of America at the Hyatt Regency Hotel.

Leroux says suffering a hearing loss of the kind he describes in his study could result in a person being unable to hear birdsong, the ring of cellphones, or conversation in a crowded, noisy place.

"If an affected couple has a one-to-one conversation in a living room, there's no problem," he said Tuesday in an interview. "But put that same couple in a restaurant with noise in the background and it's almost impossible for them to communicate."

Leroux and Lacerda made their conclusions after studying health reports of more than 8,600 Quebec workers who were exposed to both noise and carbon monoxide in the workplace, or just noise alone.

They found that workers who were exposed to carbon monoxide and noise levels over 90 decibels (comparable to the noise produced by a chainsaw) displayed significantly poorer hearing thresholds at high frequencies than workers who were exposed to noise levels alone.

The reason, Leroux said, is that the human ear needs oxygen to translate sounds into electrical impulses, which are then transmitted to the brain. Cells in the blood carry the oxygen to the ears, and the louder the noise, the more oxygen is required.

But the presence of carbon monoxide, he said, results in decreased levels of oxygen, which means blood cells carrying oxygen to the ear have to work that much harder if the person is going to hear properly.

"If you reduce the amount of oxygen available, you bring those cells to the edge of exhaustion -- metabolic exhaustion," Leroux said. Do it every day, year after year, he added, and your hearing is going to suffer.

"In our study we saw that it took at least 15 years to start showing this increase in hearing loss. The effect increases with the number of years of exposure."

To safeguard themselves, Leroux said, workers should wear effective hearing protectors and ensure here is proper ventilation at all times.

He and Leroux will now work with Quebec public health officials to make sure warnings about carbon monoxide and hearing loss are issued to all workers at risk. He reckons they number about 500,000 in that province alone.

Bill Lane, owner of the Ted Dash Car Clinic in Marpole, hadn't heard of the link between carbon monoxide and hearing loss until The Vancouver Sun phoned him Tuesday.

He said the clinic is always careful to ensure proper ventilation and hearing protection for its workers, but added that Leroux and Lacerda's findings were another "concern for anyone working in the trades."

Ran with fact box "Workers Most at Risk for Greater Loss ofHearing", which has been appended to the end of the story