Ototoxic substances and noise at work


man with sound wave graphic superimposed on ear

An introduction for managers

Noise at work is a common hazard and is present to some extent in almost all workplaces. Its effects can lead to temporary or permanent hearing damage, and can impair workers’ efficiency. But exposure to excessive noise is not the only workplace hazard that can result in hearing impairment. Certain chemical agents, known as ototoxic substances, can also cause damage to people’s hearing.

What are ototoxic substances?

Ototoxic substances can damage the ear, resulting in hearing loss, ringing in the ear, or balance disorders. They are absorbed into the bloodstream and may affect the structures and/or the function of the inner ear, and the connected neurological pathways.

Whist it is thought that more than 700 separate groups of substances may be ototoxic in nature, only a limited number of these have been investigated for their association with hearing loss. The Institution of Occupational Safety and Health (IOSH) report that there are over 200 identified chemical agents that may affect hearing, either temporarily or permanently.

Clinical and epidemiological studies have found a link between exposure to certain solvents used at work, such as styrene, toluene, solvent mixtures, and jet fuels; and increased prevalence of hearing loss. Other substances containing ototoxic properties that workers may be exposed to include lead, trichloroethylene, mercury, carbon monoxide, carbon disulphide and tin.

Thinking about the simultaneous effect in your workplace

As we have mentioned already, work-related hearing loss isn’t just about exposure to noise. Simultaneous exposure to noise and ototoxic substances can increase the risk of hearing loss. So it’s important for employers to consider this, when identifying how their workers’ hearing may be affected.

There are many industries where workers may be exposed to ototoxic substances whilst carrying out noisy processes or working in noisy environments. Some of those industries may be obvious, such as those working in aircraft maintenance or aircraft refuelling, but other industries may not immediately stand out.

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Construction workers, for example, may be aware of exposure to noise from processes such as drilling and excavating, but may not consider whether the substances they use are ototoxic. Similarly, those who work in manufacturing may know about exposure to noise from machinery, but may not know that substances such as styrene are ototoxic, and may adversely affect hearing.

Can you manage the risk?

Considering exposure to ototoxic substances as a cause of work-related hearing loss is likely to be a new concept for many employers. In the UK, there is little official guidance on how to think about work-related hearing loss beyond exposure to noise.

Material Safety Data Sheets provide information on chemical products that help users of those chemicals to make a risk assessment. They describe the hazards the chemical presents, and give information on handling, storage and emergency measures in case of accident. But they generally do not indicate the ototoxicity of different substances, therefore making it difficult for employers to consider the impact that a substance may have on hearing.

Furthermore neither ‘The Control of Substances Hazardous to Health Regulations 2002 (as amended)’ nor ‘EH40/2005 Workplace exposure limits’ make reference to the ototoxic properties of substances.

As combined exposure to noise and ototoxic agents is not yet considered in establishing the workplace exposure levels for substances, employers must develop their own holistic approach to assessing and managing the risk.

Some simple steps to take include:

  1. Identifying ototoxic substances used at work and analysing how they are used, for example as part of noisy processes or tasks.
  2. Ensuring employees are made aware of the risks associated with ototoxic substances, and the measures in place to manage those risks.
  3. Including employees who are exposed to ototoxic substances in hearing conservation and health surveillance programmes.
  4. Reducing noise exposure limits for employees exposed to both noise and ototoxic agents.
  5. Labelling ototoxic substances and providing suitable information to employees who work with those substances.
  6. Seeking expert advice from health and safety and occupational hygiene specialists.

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