Ototoxicants are chemicals that have been identified by the Occupational Health and Safety Administration (OSHA) as causing hearing loss and balance issues when inhaled, absorbed through the skin, or ingested. They are found in some pesticides, solvents, medications, and other chemicals found workplaces. And, according to OSHA, their negative effect on a person’s hearing increases when workers are also exposed to elevated noise levels.

OSHA groups ototoxic chemicals into five categories:

• Pharmaceuticals (including analgesics and antibiotics)
• Solvents (including styrene, trichloroethylene, and toluene)
• Asphyxiants (including tobacco smoke and carbon monoxide)
• Nitriles (organic cyanide)
• Metals and Compounds (including mercury, lead, and trimethyltin chloride)

The National Institute for Occupational Safety and Health (NIOSH) estimates that there are about 10 million workers exposed to solvents, while an unknown number are being exposed to other ototoxicants. Examples of workplace activities where ototoxic chemicals and noise can combine to cause hearing loss include:

• Painting
• Printing
• Construction
• Boat building
• Furniture making
• Manufacturing of metal, fiberglass, leather and petroleum products
• Textile and apparel making
• Aircraft maintenance
• Assay laboratories
• Radiator repair
• Firefighting
• Pesticide spraying
• Fueling aircraft and motor vehicles
• Weapons firing

A NIOSH research study, done in collaboration with the Swedish Nordic Expert Group for Criteria Documentation of Health Risks from Chemicals (NEG), revealed that, over a 20-year period, a large proportion of workers (23 percent) in the chemical division of a paper mill showed hearing loss severe enough to be regarded as a work-related hearing loss.

In other NIOSH studies, the effects of styrene were investigated in male workers exposed to the chemical in factories producing bathtubs or plastic buttons. It was found that hearing loss was evident in workers exposed to styrene for five years or more. Also, a group of rotogravure printers, exposed to an average of 97 ppm toluene for 12 to 14 years, showed alterations of auditory-evoked brainstem responses. Among workers exposed to both toluene and noise in an adhesive material manufacturing plant, hearing loss was 6 times higher for the toluene-plus-noise group compared to a noise-only group.

OSHA notes that hearing tests do not distinguish between noise-induced or ototoxicant-induced hearing loss, and they recommend that employers explore whether ototoxic chemical exposure is playing a role in worker complaints of hearing loss and what can be done to reduce worker exposure. Recommended workplace control measures include the addition of more ventilation and further isolation of ototoxic chemicals to help reduce or eliminate worker exposure. Personal protective equipment (PPE) should be worn to prevent skin and respiratory absorption when other control methods prove to be insufficient.

As a hearing health professional, you should be aware of any ototoxic chemicals employees in your workplace are exposed to, and if they are complaining about any hearing difficulties. Their audiometric test results may be normal, but you may want to perform more comprehensive tests to evaluate whether the more central parts of their auditory system are being affected. They may not show evidence of hearing loss from ototoxic chemicals, but you can help them prevent future hearing loss by educating them about the potential hazards they face in the workplace daily and what needs to be done to reduce or eliminate the dangers.

Having the best industrial audiology equipment to test employee hearing always helps. e3 carries top-tier audiometers and sound booths from the world-leading manufacturers like Tremetrics and Interacoustics. Check out our occupational health product offerings today and get in touch with your local e3 office to learn more!

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