What are they?
Ototoxic agents are substances or agents that can cause harmful effects on the auditory or vestibular system, such as hearing loss, tinnitus or balance disorders.
In the workplace, exposure to certain chemical agents may affect hearing directly or, particularly, interact with exposure to noise and increase the risk of hearing damage.
Spanish legislation establishes that, when assessing risks arising from exposure to noise, the health and safety effects resulting from the interaction between noise and work-related ototoxic substances must be taken into account, where technically feasible.
The available scientific evidence does not allow a universal and closed list of ototoxic substances to be established. Evidence concerning the effects of combined exposure to noise and chemical agents is uneven and, for many groups of substances, is still insufficient.
The Spanish Ministry of Health, in its Protocol for the specific health surveillance of workers exposed to noise and its Guide for the health surveillance of workers exposed to noise, indicates that there is evidence of a possible interaction between noise and certain chemical agents, including styrene, toluene and carbon monoxide.
For other solvents, metals and metalloids, nitriles, bromides, halogenated hydrocarbons and insecticides, the available evidence does not currently allow this hazard to be classified in the same way.
Therefore, considering a substance to be ototoxic should be based on the evidence available for each substance and on the specific conditions of exposure, avoiding closed lists that could give a false impression of certainty.
What should be done?
Prevention should primarily aim to eliminate or reduce exposure to the chemical agent and to noise.
In accordance with Royal Decree 374/2001, where there is a risk from hazardous chemical agents, priority must be given to eliminating the risk and, whenever possible, replacing the agent with one that is not hazardous or is less hazardous. If substitution is not possible, technical, organisational and collective protection measures must be applied and, where these are insufficient, personal protective equipment.
In workplaces where there is combined exposure to noise and substances that may affect hearing, the risk assessment must take this interaction into account. Royal Decree 286/2006 expressly establishes this obligation where technically feasible.
Preventive measures may include:
- eliminating or substituting hazardous substances whenever technically possible;
- using processes, equipment and working methods that reduce exposure;
- applying collective protection measures at the source of the risk;
- reducing the intensity and duration of exposure;
- avoiding, whenever possible, combined exposure to noise and substances that may interact with it;
- using appropriate hearing protection when the measures described above are insufficient;
- informing and training workers about the risks and preventive measures;
- carrying out health surveillance where required by legislation and the risk assessment.
Health surveillance should take into account both exposure to noise and possible exposure to chemical agents with effects on hearing. The Spanish Ministry of Health recommends closer monitoring of hearing effects where there is combined exposure to noise and certain chemical agents for which there is evidence of interaction.
Agents for which there is evidence of interaction with noise
According to the Spanish Ministry of Health's Protocol for the specific health surveillance of workers exposed to noise, the available evidence indicates:
Agent | Evidence concerning combined exposure with noise |
Styrene | Possible risk to hearing |
Toluene | Possible risk to hearing |
Carbon monoxide | Possible risk to hearing |
The official source itself states that the available evidence for other solvents and chemical agents does not currently allow them to be classified in the same way.
Regarding certain pharmacological treatments, the Spanish Ministry of Health indicates a possible interaction with noise for gentamicin, kanamycin, neomycin and cisplatin. This information is relevant to health surveillance, but these medicines should not be confused with chemical agents necessarily present in the workplace.
Classification
There is currently no specific regulatory classification of “ototoxic substances” under the CLP Regulation comparable to the categories for carcinogenicity, mutagenicity, reproductive toxicity or specific target organ toxicity.
Therefore, ototoxicity should not be used as if it were a CLP classification category.
The identification of possible ototoxic agents should be based on the toxicological information available for each substance and, in the occupational context, should particularly consider the possible interaction with noise.
In this respect, Royal Decree 286/2006 requires the effects resulting from interaction with work-related ototoxic substances to be taken into account when assessing noise-related risks, where technically feasible.
Guidance
- Spanish Ministry of Health. Protocol for the specific health surveillance of workers exposed to noise (2022). Includes a specific section on the hearing effects of combined exposure to noise and chemical, pharmacological and physical agents.
- Spanish Ministry of Health. Guide for the health surveillance of workers exposed to noise. Updates recommendations on health surveillance and combined exposure to noise and agents with possible ototoxic effects.
- INSST. Technical Guide for the assessment and prevention of risks related to chemical agents present in workplaces (2022).
- INSST. Technical Guide for the assessment and prevention of risks related to exposure to noise in workplaces (2022).
Legislation
- Law 31/1995 of 8 November on Occupational Risk Prevention.
- Royal Decree 374/2001 of 6 April, on the protection of the health and safety of workers against risks related to chemical agents at work.
- Royal Decree 286/2006 of 10 March, on the protection of the health and safety of workers against risks related to exposure to noise.
References
Spanish Ministry of Health
Protocol for the specific health surveillance of workers exposed to noise. 2nd edition, 2022.
The Public Health Commission of the Interterritorial Council of the National Health System approved the protocol in 2019. The document specifically includes an analysis of the effects on hearing of combined exposure to noise and chemical, pharmacological and physical agents.
Spanish Ministry of Health
Protocol for the specific health surveillance of workers exposed to noise
Guide for the health surveillance of workers exposed to noise
The guide updates recommendations on health surveillance and specifically addresses the effects of combined exposure to noise and physical, chemical or pharmacological agents with possible ototoxic effects.
INSST
INSST
Last updated
August 2026