Blog Post #314 – Chemicals Can Compound Potential For Hearing Loss

Excerpt from the OH&S Canada magazine

By: Trisha Richards

It’s not a stretch to say most people understand that exposure to excessive noise can damage hearing, but do they know chemicals can cause or exacerbate hearing loss?

Hearing loss from exposure to ototoxic chemicals occurs mainly through inhalation, where studies on experimental animals have shown that substances reach the inner ear through the bloodstream, causing damage to the nerves and other structures in the auditory system, explains Thais Morata, Ph. D., an audiologist at the National Institute for Occupational Safety and Health (NIOSH) in the United States. These chemicals can also be absorbed through the skin, Dr. Morata says.

Solvents are a common form of ototoxicant and can be found in paints, paint thinners, degreasers, adhesives, inks, glues, and enamels. And there’s no shortage of these.

For example, a variety of workers can be exposed to toluene, what Dr. Morata calls “one of the 50 most commonly produced industrial chemicals.” This can occur during the production, handling and use of toluene or toluene-containing products by chemical laboratory workers, gasoline blenders, lacquer workers, paint and paint thinner makers, petrochemical workers, painters and printers.

Styrene, a more potent but less common ototoxicant than toluene, for its part, is used in manufacturing synthetic rubber and fibreglass-reinforced polyester products, and can be found in floor waxes, polishes, paints, adhesives, metal cleaners and varnishes, Dr. Morata says.

She points out, though, that “environmental or occupational contaminants, the onset site, mechanism and extent of ototoxic damage of these toxicants vary according to risk factors that include type of chemical, interactions, exposure level and duration of administration.”

In some cases, a substance will not cause hearing loss on its own, but can exacerbate noise-related loss through a process called potentiation. This synergistic interaction between an ototoxic chemical and noise gives rise to a “combined biological effect of two hazards [which] is greater than the simple summation of the toxicity of each of the individual substances,” Dr. Morata explains.

At particular risk for this synergistic effect are welders, suggests Susan Ing, an occupational hygiene specialist with the Industrial Accident Prevention Association in Mississauga, Ontario. “They’re not only sucking in the welding fumes. They also have the high noise that is usually associated with welding,” Ing says.

But persistent warnings related to occupational hearing loss, at least in some cases, are falling on deaf ears. “You don’t find too many old tin bangers that can hear, but that just goes along with the trade,” says Mark Curtis, business manager and financial secretary for Local 276 of the Sheet Metal Workers in Victoria. “As far as the chemical portion of it, I would say awareness is limited,” Curtis says.

Ing concurs. “We’re dealing with chemical exposure that most people really don’t understand that much, and now we add on the synergistic effects of both chemical and noise.”

A best practice is to stay below 50 per cent of permissible exposure limits of the jurisdiction in question, says Ing. “But if you’re combining chemicals with a lot of noise, bring it down further. Knock off another 25 per cent.”

Noise is such an important risk factor “it probably has delayed the recognition of the risk to hearing that these chemicals can pose,” Dr. Morata says. Avoiding noise and chemical exposure remains the best preventive measure, she adds.

My opinion,

At present, I am studying for my CHSEP designation and the current course covers solvents. A previous course covered physical hazards such as noise so to see more and more of these type of articles the research helps me in my school work. I never realized the study of safety and how it deals with your day-to-day life.

By the way, the CHSEP (certification in health and safety environmental processes) is a relatively new program. MY understanding is that I qualify to write the CRSP (Canadian registers safety professional) exam. I hope to have both designations by the end of next year.

Wish me luck.

Remember — In Ontario, “ALL Accidents are Preventable”

HRS Group Inc. has a great team that can help you with all your health and safety needs including ‘Chemical Safety Awareness’ and ‘WHMIS’. Contact Deborah toll free at 1-877-907-7744 or locally at 705-749-1259.

We can also be reached at 

‘Work’ and ‘Play’ safe.

Daniel L. Beal
CHSEP – Foundation Level
VP & Senior Trainer
HRS Group Inc.