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Ototoxicant Chemicals and Workplace Hearing Loss

Posted on by Thais C. Morata, PhD and Chuck Kardous, MS, PE

 

Image © OSHA

Since the 19th century, many therapeutic drugs have been known to affect hearing. Known as ototoxic drugs, many are used today in clinical situations despite these negative side effects because they are effective in treating serious, sometimes life-threatening conditions. Research has shown that exposure to certain chemicals in the workplace may also negatively affect how the ear functions, potentially causing hearing loss or balance problems, regardless of noise exposure. Substances containing ototoxicants include certain pesticides, solvents, metals and pharmaceuticals. The risk of hearing loss they pose can be increased when workers are exposed to these chemicals while working around elevated noise levels.  This combination often results in hearing loss that can be temporary or permanent, depending on the level of noise, the dose of the chemical, and the duration of the exposure. This hearing impairment affects many occupations and industries, from machinists to firefighters.

A new informational bulletin developed by OSHA and NIOSH raises awareness of this issue, provides examples of ototoxic chemicals, lists the industries and occupations at risk and provides prevention information. The hearing loss caused by chemicals can be very similar to a hearing loss caused by excessive noise. The fact that noise exposure is so common in modern societies might explain the delay in recognizing the risk to hearing that these chemicals can pose. Pure tone audiometry is a basic clinical test used to determine a person’s hearing sensitivity at specific frequencies, i.e., the softest sound that can be perceived in a quiet environment. It clearly identifies various hearing loss characteristics, but not its cause. Other hearing tests such as word recognition or otoacoustic emission tests examine other auditory functions. In some cases, these tests can help differentiate the effects of chemicals from the effects of noise, since chemicals might affect the more central portions of the auditory system (nerves or nuclei of the central nervous system, the pathways to the brain or in the brain itself). These hearing deficits may have a more pronounced impact on the worker’s life because not only are sounds be perceived as less loud, but also as distorted. Word recognition may be compromised, particularly in background noise, making it difficult, for instance, to hold a conversation in a busy restaurant or at a party.

The first step in preventing exposure to ototoxicants is to know if they are in the workplace. The publications cited in the bulletin identify known ototoxicants for example: toluene, styrene, carbon monoxide, acrylonitrile, and lead. When there is no information on a certain chemical’s ototoxicity, information on the chemical’s general toxicity, nephrotoxicity, and neurotoxicity may provide clues about the potential ototoxicity. Most chemicals that are known to affect the auditory system are also neurotoxic and/or nephrotoxic. One can review Safety Data Sheets (SDS) for ototoxic substances and/or chemicals, and ototoxic health hazards associated with ingredients in the product. For example, Figure 1 shows an SDS where ototoxicants may be in a product.

Figure 1

 

NIOSH continues its research on this subject, in collaboration with several partners, including France’s Research and Safety Institute (INRS) and other institutions in the U.S., Canada and China (Fuente et al., 2018). For more information, see the recent paper in the Journal of the Acoustical Society of America, “Use of the Kurtosis Statistic in an Evaluation of the Effects of Noise and Solvent Exposures on the Hearing Thresholds of Workers: An Exploratory Study

For more information on risk factors for hearing loss please visit the NIOSH Noise and Hearing Loss Prevention topic page.

Update:  Since this blog posted, a  new study was published (Dement 2018) which examined work history, health behavior, and hearing test results from more than 19,000 former construction workers to identify factors contributing to hearing loss. The researchers found that exposure to exposure to organic solvents along with exposure to loud noise on the job,  and smoking each increased a worker’s risk of hearing loss by 15-20%.  The prevalence of hearing impairment and risk ratios varied across sites and trade groups, which was accounted by the difference in exposure and other risk factors. Those who do not have access to the journal article can contact the author at john.dement@duke.edu.  Key findings were summarized by the CPWR – The Center for Construction Research and Training.

 

Thais C. Morata, PhD, is a research audiologist with the NIOSH Division of Applied Research and Technology and the Coordinator of the NORA Manufacturing Sector Council.

CAPT Chuck  Kardous, MS, PE, is a senior research engineer with the NIOSH Division of Applied Research and Technology.

 

Reference

Fuente A, Qiu W, Zhang M, Xie H, Kardous CA, Campo P, Morata TC. Use of the kurtosis statistic in an evaluation of the effects of noise and solvent exposures on the hearing thresholds of workers: An exploratory study. J Acoust Soc Am. 2018 Mar; 143(3):1704. https://doi.org/10.1121/1.5028368

Dement J, Welch L, Ringen K, Cranford K, Quinn P.  Hearing loss among older construction workers: Updated analyses. AJIM. 2018 April:61(4): 326. https://doi.org/10.1002/ajim.22827

 

 

Posted on by Thais C. Morata, PhD and Chuck Kardous, MS, PE

11 comments on “Ototoxicant Chemicals and Workplace Hearing Loss”

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    Hello,
    My name Is Erica M. Bluff-Hopp,
    I work as an Animal Control Officer for the city of Rialto,. I have been a ACO for 14 yrs.’ and I work with very loud barking dogs, screaming, meowing cats, metal truck doors slamming and chemicals to clean the animal control trucks from diseases. I have lost two decimals of hearing loss and I have a hard time hearing anyone talking over white noise. Is there anyway I can prove that all of this is due to my work? I understand this might not be the right forum, but Workman’s Comp does not believe my hearing lose is due to work and Animal Control is forgotten about as a whole when it comes to dangers, chemicals, noise at the job.

    Thank you,
    Sincerely,
    Erica

    Hello Erica and thanks for sharing your concerns with us. NIOSH is a research organization and is not an enforcement agency. We also do not get involved in individual workers compensation cases. We do conduct research to prevent illnesses and injuries for workers. Part of our research program involves responding to requests from employers, unions, or groups of workers to conduct health hazard evaluations (HHE) upon request. The completed HHEs form the basis to recommend risk reduction strategies.

    NIOSH researchers have evaluated noise exposure and hearing loss of employees of kennels, animal hospitals, and animal shelters. We have several HHEs that you can find on this page (scroll down to noise): https://www.cdc.gov/niosh/topics/veterinary/physical.html. In all of the HHE’s conducted at kennels and animal shelters, NIOSH reported cases of hearing loss among employees. In all of these cases NIOSH recommended: (1) enroll employees in a hearing loss prevention program; (2) require the use of ear plugs or ear muffs in the kennel area; and (3) maintain ear muffs by making sure they are clean and by replacing the cushions every 6 months or sooner if necessary.

    Erica,
    Guessing your in CA, CA has an OSHA State Plan so public sector employees should be covered by the hearing conservation standard. It’s not guaranteed but Cal OSHA may determine that your employer should have enrolled you in a hearing conservation program and provided u an initial audiogram and subsequent annual audiograms. However workers comp is it’s own thing and does not always match up with OSHA hearing loss definitions and etc.

    Hello Thais C. Morata,
    You wrote an informative article about hearing loss because many people are aware of this. I have some knowledge about hearing loss but this article adds some hidden awareness about hearing loss.
    thank you for this article!!

    Hi everyone –

    NIOSH and OSHA are not the only organizations increasingly focused on ototoxins and noise.

    The American Conference of Governmental Industrial Hygienists (ACGIH), in its Threshold Limited Values and Biological Exposure Indices (TLVs® and BEIs®) booklet includes a note which was expanded and updated in 2018:

    “The designation OTO for hearing disorders in the “Notations” column highlights the potential for a chemical to cause hearing impairment alone or in combination with noise, even below 85 dBA. The OTO notation is reserved for chemicals that have been shown, through animal studies or human experience, to adversely affect auditory capacity, usually manifested as a permanent audiometric threshold shift (difficulty in detecting sounds) as well as difficulties in processing sounds. Certain solvents, predominantly aromatic hydrocarbons, but also some halogenated solvents, metals and chemicals that cause anoxia, have been shown to cause hearing disorders. Some solvents appear to act synergistically with noise, whereas carbon monoxide potentiates noise effects. The OTO notation is intended to focus attention, not only on engineering controls, administrative controls and personal protective equipment needed to reduce airborne concentrations, but also on other means of preventing excessive combined exposures with noise to prevent hearing disorders. Specifically, affected employees may need to be enrolled in hearing conservation and medical surveillance programs to more closely monitor auditory capacity. Please refer to the TLV for Physical Agents Documentation on Audible Sound section on Ototoxicity.”

    The reference for this is: American Conference of Governmental Industrial Hygienists. 2018 TLVs(R) and BEIs(R): Notice of Intended Change. American Conference of Governmental Industrial Hygienists, Cincinnati, OH. 2018. p 74.

    Rick

    Thank you for your comment and for bringing up ACGIH’s updated information on noise. More information on approaches to address the risk from combined exposures to noise and chemicals, including a similar proposal of a “noise” notation to call attention to the increased risk to hearing is available in this review document from the Nordic Expert Group for Criteria Documentation of Health Risks from Chemicals Occupational exposure to chemicals and hearing impairment

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