Noise is not the only cause of hearing loss

Noise exposure can cause hearing loss, but exposure to chemicals called ototoxicants may also cause hearing loss, even when noise levels are below OSHA’s action level. These chemicals can damage the inner ear, causing balance problems as well as hearing loss. Worse, some studies suggest that the combined effects of exposure to both noise and ototoxicants may increase hearing loss more dramatically.

According to OSHA, some ototoxicants include:

• Solvents such as carbon disulfide, n-hexane, toluene, p-xylene, ethylbenzene, n-propylbenzene, styrene and methylstyrene, and trichloroethylene;
• Asphyxiants such as carbon monoxide, hydrogen cyanide and its salts, and tobacco smoke;
• Nitriles such as 3-Butenenitrile, cis-2-pentenenitrile, acrylonitrile, cis-crotononitrile, and 3,3’-iminodipropionitrile; and
• Metals and compounds such as mercury compounds, germanium dioxide, organic tin compounds, and lead.

This is not a complete list, and limited evidence suggest ototoxicity of other chemicals including cadmium, arsenic, bromates, halogenated hydrocarbons, insecticides, alkylic compounds, and manganese.

Controlling exposure

Ototoxicants can reach the inner ear through the blood stream and cause injury to inner parts of the ear and connected neural pathways. Exposure may occur through inhalation, ingestion, or skin absorption. Health effects vary based on exposure frequency, intensity, duration, exposure to other hazards, and individual factors such as age.

The first step in preventing exposure is to know if ototoxicants are in the workplace. One way to identify them is by reviewing Safety Data Sheets (SDS) for ototoxic substances and/or chemicals, and ototoxic health hazards associated with ingredients in the product.

When ototoxicity information is not available, data on other toxicity may provide clues. Most chemicals that affect the auditory system are also neurotoxic and/or nephrotoxic. Information on whether a chemical produces reactive free radicals could also give clues about potential ototoxicity.

Once identified, prevention measures might include using a different chemical, adopting engineering or work practice controls, or evaluating personal protective equipment to limit exposures. Since many ototoxic substances can be absorbed through the skin, chemical-protective gloves, arm sleeves, aprons and other appropriate clothing can assist in reducing dermal exposure.