GHS Blog Post

Ototoxic Substances – Unexpected Causes of Hearing Loss in the Workplace

Photo: Wikimedia Commons/Klaus D. Peter

Noise exposures in the workplace can lead to hearing loss for workers down the road, and companies and regulatory agencies have focused for quite some time on limiting noise levels through the use of quieter equipment and appropriate protective measures.

Noise isn’t the only threat to your workers’ hearing, though. Certain substances used in the workplace, referred to generally as ototoxic substances, can impact the cochlea and nerves in the ear, leading to hearing loss over time. The impact on hearing is not only related to the detection of sound either, but also to the discrimination of sounds, making sounds distorted, according to Thais C. Morata, PhD, a researcher at NIOSH.

Research also suggests that when ototoxic exposures are combined with high noise levels, the negative effects on hearing can be even greater. Much of this research is ongoing, though, and it is difficult to draw clear, universal conclusions about ototoxic substances. Industrial workplaces are often loud and complex and they handle many substances daily, making it difficult to weed out exact causes of hearing loss.

Investigations do, however, suggest that hearing loss associated with ototoxic substances can impact hearing years before noise will, and these substances do pose threats to workers, especially those exposed to high levels of ototoxic substances or those exposed over long periods of time.

What Is an Ototoxic Substance?

An ototoxic substance damages the sense of hearing. These substances are often chemical solvents such as toluene or styrene, but can also be asphyxiants, nitriles, metals and pharmaceuticals, according to the European Agency for Safety and Health at Work (EU-OSHA).

Ear Diagram
The cochlea and nerves can be damaged by ototoxic substances. Image: Wikimedia Commons/Chittka L, Brockmann A

Below is a list of many substances that EU-OSHA describes as having good evidence in support of their ototoxicity:

Solvents (generally used for dissolving other substances):

  • Toluene – Used in the production of explosives and dyes, as a coating for fabrics and papers, and many other applications.
  • Styrene – Used in plastic, rubber and glass production.
  • Trichloroethylene – A cleaning and degreasing agent.
  • p-Xylene – Used in the manufacturing of many things including paints, varnishes, perfumes and insect repellents.
  • n-Hexane – A cleaning agent for furniture and textiles, among other uses.
  • Carbon Disulfide – Used in the manufacturing of soil disinfectants, rayon and other items.


  • Carbon Monoxide – Created when fuel is burned incompletely; produced by gas engines and other machinery.
  • Hydrogen Cyanide – Used in fumigation, mining and the production of plastics, dyes and pesticides.

Nitriles (generally used for making specific acids and resins; also used as solvents):


  • Lead – Used in some battery manufacturing; common in certain types of building renovations.
  • Mercury – Used in manufacturing, laboratory and pharmaceutical applications.
  • Tin – Used in manufacturing of electronics and as a fungicide in agriculture.
  • Germanium – A semi-conductor used in transistors, solar cells and other applications.

Additional ototoxic substances may include arsenic, tobacco smoke, manganese and some insecticides. Many pharmaceuticals including certain antibiotics and diuretics are also likely ototoxins, although these may be less likely to be a part of daily life in the workplace.

Many of these substances are present at industrial, construction or laboratory worksites, though, even if some of their names sound unfamiliar. Many of these workplaces also have significant noise levels, which can exacerbate hearing problems related to ototoxic substances.

EU-OSHA lists industries including painting, printing, construction, glue manufacture, ship building, metal products, petroleum, chemicals, leather products, agriculture, mining and furniture making as posing both noise and ototoxic chemical risks.

What Can Employers Do About Ototoxic Substances?

Ototoxic substances may sound intimidating to employers, but the bottom line is you need to prevent exposures to these hazardous substances. You can tackle this problem just as you would any other dangerous chemical or substance.

For chemicals, new GHS labels and safety data sheets should provide information about the health effects of the chemicals you’re dealing with. If you have ototoxic chemicals in your workplace, their labels should indicate they pose hearing hazards and provide information about how to handle the chemicals safely. Ototoxic chemicals don’t necessarily require any special treatment—you just need to follow your hazardous chemical handling guidelines—but you do need to be aware of the unique hazards these chemicals present.

For other substances such as metals or asphyxiants, consider what precautions you already take. If your workers encounter lead, which causes an array of health problems (not just hearing loss), they need proper respiratory protection. The same goes for asphyxiants; if carbon monoxide could be present, workers need safe air to breathe to prevent a disastrous situation.

Safety Label, Warning Label

Many ototoxic substances could also come into contact with skin, so be sure to provide appropriate gloves and other bodywear. Remember that the best way to keep employees safe is to eliminate hazardous substances from the workplace altogether whenever possible.

If you know ototoxic substances are present, you can also consider performing hearing tests for employees periodically to see if the hazards are being appropriately controlled.

Finally, employers can also create visual warnings in areas where ototoxic substances are used. Safety signs and labels in the actual work area can remind employees to wear PPE. Since high noise levels combined with ototoxic substances create a particularly dangerous situation, you could also make signs reminding workers about the importance of protecting themselves from loud noises.

Better Safe Than Sorry

Ototoxic substances are currently a subject of research, so guidelines for these hazards are less clear now than they might be in the future. Evidence shows that these substances are dangerous to human health, though. Pay attention to the specific substances your workplace uses, as hazard levels vary from one substance to another.

To learn more about hearing hazards in the workplace and how they can be prevented, read Buy Quiet Program Can Prevent Hearing Loss.

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